Autoclaved aerated concrete using MSWI bottom ash as an aerating agent

Abstract

Various examples are provided related to autoclaved aerated concrete using MSWI bottom ash as an aerating agent. In one example, a method for production of autoclaved aerated concrete (AAC) includes forming a bottom ash (BA) sand mixture by combining municipal solid waste incineration (MSWI) BA with quartz silica sand, the MSWI BA having a particle size of about 1.2 mm or less; generating an AAC slurry by mixing the BA sand mixture with at least cement, lime and water; filling a mold with the AAC slurry; and autoclaving the molded AAC slurry in the mold. The MSWI BA can be pulverized and filtered through a sieve stack prior to combining with the quartz silica sand. The MSWI BA have a particle size of about 170 µm or less. about 30 µm or less, or about 15 µm or less.

Description

AUTOCLAVED AERATED CONCRETE USING MSWI BOTTOM ASH AS AN AERATING AGENTCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to, and the benefit of, U.S. provisional application entitled “Autoclaved Aerated Concrete Using MSWI Bottom Ash as an Aerating Agent” having serial no. 63 / 601 ,304, filed November 21 , 2023, which is hereby incorporated by reference in its entirety.BACKGROUND

[0002] With Municipal solid waste (MSW) generation in the United States (US) increased to over 230 million Mg in 2015, reducing the volume of the waste that must be disposed of in landfills is becoming an increasingly important. Municipal solid waste incineration (MSWI) for energy and material recovery has become an outlet to achieve this goal. However, MSWI ash is a remnant borne from the combustion process and must be managed appropriately. Byproducts in MSWI ash comprise fine fly ash, often laden with heavy metals, chlorides, and alkalis, which is captured by the air pollution control equipment, and bottom ash (BA) which is typically coarser material remaining in the boiler after combustion. In the US, facility operators typically commingle MSWI BA and fly ash for disposal in a lined landfill.SUMMARY

[0003] Aspects of the present disclosure are related to autoclaved aerated concrete using MSWI bottom ash as an aerating agent. In one aspect, among others, a method for production of autoclaved aerated concrete (AAC) comprises forming a bottom ash (BA) sand mixture by combining municipal solid waste incineration (MSWI) BA with quartz silica sand, the MSWI BA having a particle size of about 1 .2 mm or less; generating an AAC slurry by mixing the BA sand mixture with at least cement, lime and water; filling a mold with the AAC slurry; and autoclaving the molded AAC slurry in the mold. In one or more aspects, the MSWI BA can have a particle size of about 170 pm or less, about 30 pm or less, or about 15 pm or less. The method can comprise pulverizing the MSWI BA and filtering the pulverized MSWI BA through a sieve stack prior to combining with the quartz silica sand. The MSWI BA can be pulverized by hammer milling or disc pulverizing. In various aspects, the MSWI BA can be about 15%wt of a total dry component mass of the AAC slurry or can be about 10%wt of a total dry component mass of the AAC slurry. The method can comprise preppingthe mold for casting and steam curing. The mold can be covered in high-temperature epoxy demolding tape.

[0004] Other systems, methods, features, and advantages of the present disclosure will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims. In addition, all optional and preferred features and modifications of the described embodiments are usable in all aspects of the disclosure taught herein. Furthermore, the individual features of the dependent claims, as well as all optional and preferred features and modifications of the described embodiments are combinable and interchangeable with one another.BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

[0006] FIG. 1 is a table illustrating a summary of different size groups used for material characterization of “less than” bottom ash (BA), in accordance with various embodiments of the present disclosure.

[0007] FIG. 2A illustrates an example of a water displacement method to measure volume of hydrogen gas production via chemical reaction, in accordance with various embodiments of the present disclosure.

[0008] FIG. 2B is an image showing an experimental setup for hydrogen gas production rate measurements, in accordance with various embodiments of the present disclosure.

[0009] FIG. 3 includes images illustrating examples of hammer milling, in accordance with various embodiments of the present disclosure.

[0010] FIGS. 4A and 4B include a plot and table illustrating particle size distribution and characteristics for metallic aluminum powder (Al), hammer milled PBulk (PBulkJHM), pulverized PBulk (PBulk_Pulv), and pulverized SBulk (SBulk_Pulv), in accordance with various embodiments of the present disclosure.

[0011] FIG. 5 includes images showing molds, demolded and wire-cut AAC, and autoclaves at an industrial AAC facility, in accordance with various embodiments of the present disclosure.

[0012] FIGS. 6A and 6B include images showing molds and an autoclave for laboratoryscale AAC production and a table illustrating mixture design proportions for laboratory-made AAC, in accordance with various embodiments of the present disclosure.

[0013] FIG. 7 includes a plot illustrating particle size distribution of metallic aluminum powder (Al), fine silica sand (UF Sand), finely ground sand from an AAC industrial producer (AS), pulverized PBulk, and pulverized SBulk, in accordance with various embodiments of the present disclosure.

[0014] FIG. 8 includes images illustrating examples of elemental map of metallic aluminum powder (left) and pulverized PBulk (right) via scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), in accordance with various embodiments of the present disclosure.

[0015] FIG. 9 includes images showing mixing, vibrating, and casting for AAC specimens made in the laboratory, in accordance with various embodiments of the present disclosure.

[0016] FIGS. 10A and 10B illustrate an example of a thermal insulation test setup, in accordance with various embodiments of the present disclosure.

[0017] FIG. 11 A illustrates an example of measured heat flux and temperatures at the cold and hot sides of the specimens for a reference calcium silicate rigid board insulation from thermal insulation testing, in accordance with various embodiments of the present disclosure.

[0018] FIG. 11B illustrates an example of calculated R-value based upon measured heat flux and temperature difference of FIG. 11A, in accordance with various embodiments of the present disclosure.

[0019] FIG. 12 is a schematic diagram illustrating an example of the proposed production of AAC using “less than” BA as the sole aerating agent and a partial silica source, in accordance with various embodiments of the present disclosure.

[0020] FIGS. 13A and 13B illustrate examples of economic scenarios to determine the cost versus benefit of using “less than” BA as an aerating component for AAC, in accordance with various embodiments of the present disclosure.

[0021] FIGS. 14A and 14B illustrate examples of gradation characteristics and particle gradation curves (% cumulative passing) for “less than” BA from Facility S and Facility P, in accordance with various embodiments of the present disclosure.

[0022] FIG. 15 is a table illustrating examples of apparent specific gravities of the different size fraction groups of “less than” BA from Facility S and P, in accordance with various embodiments of the present disclosure.

[0023] FIG. 16 is a table illustrating an example of mineralogical composition of “less than” BA by quantitative XRD, in accordance with various embodiments of the present disclosure.

[0024] FIGS. 17A-17D illustrate examples of environmentally available total elemental concentration of aluminum, calcium, copper, and iron in the bulk and sieve group samples for “less than” BA from Facility S and Facility P, respectively, in accordance with various embodiments of the present disclosure.

[0025] FIG. 18 is a table illustrating an example of chemical oxide composition of “less than” BA by XRF, in accordance with various embodiments of the present disclosure.

[0026] FIGS. 19A and 19B illustrate examples of hydrogen gas production for 0.50 and 0.75 grams of aluminum powder in lime-saturated solutions with varying concentrations of NaOH, in accordance with various embodiments of the present disclosure.

[0027] FIGS. 20A and 20B illustrate examples of hydrogen gas production for 25 grams of hammer-milled MSWI BA from Facility P in lime-saturated solutions with varying concentrations of NaOH, in accordance with various embodiments of the present disclosure.

[0028] FIGS. 21 A and 21 B illustrate examples of hydrogen gas production for 25 grams of pulverized MSWI BA from Facility P and Facility S in lime-saturated solutions with varying concentrations of NaOH, in accordance with various embodiments of the present disclosure.

[0029] FIG. 22 is a table illustrating an example of AAC classification criteria based on compressive strength and dry density for laboratory-scale 50-mm cube specimens, in accordance with various embodiments of the present disclosure.

[0030] FIG. 23 is a table illustrating a summary of dry density and compressive stress for AAC mixtures, in accordance with various embodiments of the present disclosure.

[0031] FIG. 24 illustrates a comparison of strength-to-density ratios of laboratory- and industrial-scale AACs, in accordance with various embodiments of the present disclosure.

[0032] FIG. 25 illustrates a relationship between compressive strength and dry density of laboratory- and industrial-scale AAC differentiated by AAC type, in accordance with various embodiments of the present disclosure.

[0033] FIG. 26 is a table illustrating an example of leaching results for select AAC specimens, in accordance with various embodiments of the present disclosure.

[0034] FIG. 27 is a table illustrating a summary of R-Values for selected specimens, in accordance with various embodiments of the present disclosure.DETAILED DESCRIPTION

[0035] Disclosed herein are various examples related to autoclaved aerated concrete using MSWI bottom ash as an aerating agent. Autoclaved aerated concrete (AAC) is alightweight cellular cement-based precast building material that offers excellent thermal insulation, fire resistance, resistance to mold and insects, soundproofing, durability, and structural integrity. When used as building envelopes, AAC also enhances indoor air quality while reducing the energy required to maintain optimal living conditions. Furthermore, AAC contains less portland cement per unit volume than typical concrete due to its low density, making it a more sustainable alternative for wall, floor, and roof construction. Reference will now be made in detail to the description of the embodiments as illustrated in the drawings, wherein like reference numbers indicate like parts throughout the several views.

[0036] Municipal Solid Waste Incineration (MSWI) is an effective waste management strategy that can reduce landfill occupancy and generate recoverable energy. Incineration can reduce waste volume by 90%, leaving behind non-combustible residuals that predominantly occur as granular bottom ash (BA). BA constitutes approximately 80-90% of the residual waste generated by MSWI facilities, most of which is co-disposed with FA in landfills due to issues with regulatory definitions of hazardous wastes. This practice has limited the market for recycling MSWI BA in other industries such as construction in the US. However, the growing cost of landfilling and the emphasis on a circular economy have led to research on alternative end-of-life management scenarios for the less hazardous BA. The purpose of this research is to assess the utility of reusing the finer BA fraction, or “less than” BA (<3 / 8 inches) in the AAC industry.

[0037] Given the regulatory burdens, costs, and unsustainable practice of landfilling, organizations such as the Hinkley Center have supported research into alternative residual management strategies in line with sustainable materials management. Laboratory and pilotscale research has been conducted on the use of MSWI BA as raw portland cement clinker feedstock, supplementary cementitious materials (SCMs), and aggregates in road bases, portland cement concrete (PCC), and asphalt concrete. This disclosure expands the recycling options for BA to include raw material in AAC that benefits producers, end-users, and taxpayers.

[0038] Specific to PCC construction, the coarser BA fraction (> 3 / 8 inches) has shown promise as an aggregate in as well as a road base when blended with conventional aggregates such as limestone. The “less than” BA, though, degrades the strength and durability of concrete and thus has limited application in conventional PCC construction. This is largely because metallic aluminum tends to concentrate in the finer fraction of BA. Previous studies have observed uncontrolled expansion of concrete specimens that have incorporated “less than” BA.

[0039] Metallic aluminum impedes the reuse of “less than” BA in construction. Costly and complex processes typically used for waste separation and metals recovery may be applied to reduce aluminum content in BA. However, the majority of the aluminum isconcentrated in the “less than” BA fraction, making it impossible to recover using standard eddy current separation technology commonly used to remove non-ferrous metals from MSWI Ash. Moreover, an important consequence of incineration at temperatures above 850 °C is that aluminum metal can melt and reform as alloys or bound to structures containing silicon, iron, and calcium during cooling.

[0040] Metallic aluminum reacts in alkaline systems such as concrete pore solution, releasing hydrogen gas in a reaction called water splitting. In MSWI BA-amended PCC, this gas can increase porosity when generated during setting and can exert localized expansive stress after setting, leading to microcracking or popouts. When sufficient gas is generated, the strength and durability of PCC are adversely affected.

[0041] In AAC, metallic aluminum powder or paste is used to entrain a uniform set of air bubbles and cause expansion while fresh AAC slurries remain fluid. As the fresh AAC slurries harden via hydration, air voids generated by hydrogen gas stabilize and result in a porous cellular structure characterized by small spherical voids approximately 1 to 5 mm in diameter. When air voids are uniformly distributed, the cellular structure is responsible for AAC properties such as low density, high thermal and acoustic insulation, fire resistance, durability to freeze-thaw damage, and ease of machining post-autoclaving.

[0042] MSWI BA has the potential to substitute conventional metallic aluminum aerating agents in AAC production. The “less than” BA, despite having higher aluminum content, is a low-value commodity that is less costly than metallic aluminum powder or paste and has high availability. The use of MSWI BA for AAC is particularly relevant to Florida as one of the largest producers of AAC is the AERCON Company, located in Haines City. AERCON refers to both the company and the comprehensive building system that employs AAC panels and blocks, which are ideal for a variety of projects ranging from commercial to residential, as well as industrial, educational, and public undertakings. AERCON's cutting-edge manufacturing plant spans over 100,000 square feet and is configured to produce block and engineered panels that can be transported by truck or rail throughout the United States in a cost-effective manner. The facility is located less than 100 miles from 5 MSWI facilities in the Orlando and Tampa Bay area. As a result, there is a high likelihood of a successful partnership between AERCON and one or more MSWI facilities.

[0043] However, research is limited to the use of the “less than” BA fraction in AAC production. There are gaps in the literature regarding practical beneficiation processes that can economically scale for industrial production. Moreover, there is limited information on AAC mixture design guidance to enhance the performance of “less than” BA as an aerating agent.Materials Characterization

[0044] MSWI BA Sampling and Processing. Fresh MSWI BA samples were acquired from two different MSWI facilities in Florida, USA. One sample was collected from a mass burn facility (Facility P) while the other was acquired from a refuse-derived fuel facility (Facility S). The Facility P BA was sub-sampled from a pile of fresh BA screened to pass 3 / 8 inches by plant personnel and shipped to the processing facility in sealed 5-gallon buckets. Since the Facility P BA was screened to pass 3 / 8 inches, the material did not undergo further screening. The fresh BA was sampled from Facility S that was stockpiled by plant personnel and transported in sealed 5-gallon buckets. The Facility S sample was collected before undergoing further metal recovery processes to preserve metallic aluminum content. Moreover, since Facility S BA was acquired in bulk, the ash was screened at the processing facility to pass the 3 / 8-inch sieve (9.51-mm sieve). Fresh samples were collected to eliminate aging as a potential variable during the assessment of “less than” BA in AAC production. The BA used during material characterization, aeration efficiency, and performance evaluation were screened to below 3 / 8 inches (9.51 mm). Any material greater than 3 / 8 inches (9.51 mm) was not considered for analysis. Since the BA from both facilities used for further assessment were “less than” 3 / 8 inches (9.51 mm), they were referenced as “’less than’ BA” throughout the disclosure.

[0045] Material Characterization of “less than” BA. Properties of the raw AAC materials such as density, chemistry, and mineralogy can play important roles throughout the AAC production chain, from aeration of the fresh slurry to strength of the final AAC product. A suite of material characterization tests was performed on the “less than” BA samples with an emphasis on understanding how aluminum and silica partition across different-size fractions. Aluminum and silica partitioning was used to determine effective and practical processes to enhance the performance of “less than” BA as a raw AAC mixture component. A secondary objective was to identify chemical impurities that may degrade AAC performance and pose risks to human health and the environment.

[0046] Before analysis, “less than” BA samples were oven-dried to 110 °C overnight until constant mass. After drying, representative subsamples were collected using the cone and quarter method prescribed in ASTM C702. Two diagonal quarters were selected for further analysis while the remaining two quarters were stored in sealed 5-gallon buckets as reserves.

[0047] The gradation characteristics of the “less than” BA were determined using sieve analysis. Gradation characteristics provide insight into appropriate beneficiation strategies for “less than” BA when coupled with elemental partitioning. Sieve analysis was performed on dried “less than” BA sub-samples, from Facility S and Facility P, following ASTM C136. Approximately 1200 grams were used for assessment to ensure results were representative of the bulk “less than” BA and sufficient material was retained on individual sieves within thesieve stack for further material characterization. An automated Ro-Tap mechanical sieve shaker and 10-inch diameter sieves were used for analysis to accommodate 1200 grams of material. The sieve stack included the following sieve sizes: 3 / 8 inches (9.51 mm), No. 4 (4.75 mm), No. 8 (2.36 mm), No. 16 (1.19 mm), No. 30 (0.595 mm), No. 50 (0.297 mm), No. 100 (0.149 mm), No. 200 (0.074 mm), and pan (< 0.074 mm). Sieves were cleaned using isopropanol and dried with compressed air before loading samples. After the sieves were cleaned, dried, weighed, and restacked, 1200 grams of “less than” BA from the sub-samples were weighed and carefully loaded into the stack. After a 10-minute run period, the agitated sieves were carefully removed from the stack and weighed. The cumulative percent passing and the fineness moduli of the less than BA from Facilities S and P were calculated.

[0048] Further materials characterization included tests for specific gravity (SG), totally environmentally available elemental concentration, bulk chemical oxide composition, and mineralogy. These tests were conducted on bulk less than BA (unsieved) and across different size fractions (sieved). Different size fractions of the less than BA were subdivided into size groups as shown in the table of FIG. 1 . Descriptions for each size group are provided in the “Description” column of the table of FIG. 1 . Four classes of size groups were selected: Bulk, 4-16, 30-50, and 100-P. As an example, the “S4-16” sample refers to “less than” BA from Facility S passing the 3 / 8-inch (9.51 -mm) sieve and retained on the No. 4, No. 8, and No. 16 sieves. The “SBulk” size group refers to unsieved “less than” BA from Facility S, with particle sizes ranging from 0 to 9.51 mm. In cases of material retained on the No. 100 sieve through the pan, further sieving was needed to gather sufficient materials for characterization. Depending on the test, the properties of material retained on individual sieves from the sieve stack described earlier were used to calculate the expected property or composition for a specific size group. Before further analysis, the material was finely ground into a powder.

[0049] Since AAC strength class requirements are based on strength and density, the relationship between the SG of “less than” BA and the density of AAC may affect classification and, thus, use in building construction. The SG of finely ground samples from the different size groups and individual sieves was assessed using a QUANTACHROME ULTRAPYC 1200e helium pycnometer. The SG of size groups Bulk, 4-16, and 30-50 were measured directly while the SG of the size group 100-P was calculated based on the SG measurements and proportions of material retained on the individual sieves within the size group. Samples from different size groups and sieve sizes were added to the 10 cm3sample cell until approximately 3 / 4thof the cell volume was filled. The sample mass was measured, and the sample cell was loaded into the cell holder within the pycnometer. The cell holder was then sealed using an airtight lid. The sample mass was inputted into the pycnometer settings and testing was started. The pycnometer meters helium gas into the sample cellwhile measuring pressure using a pressure transducer. After the pressure reading stabilizes, the coupling valve connecting the sample cell chamber to a reference cell chamber with a fixed volume opens and allows the helium gas to expand into the reference cell. The pressure is again measured after the pressure is stabilized. Sample volume is calculated using Boyle’s law relating the change in pressure and volume under isothermal conditions. The instrument completes this process five times for each sample and reports an average of five SG readings.

[0050] Mineralogy of raw materials may play an important role in the performance of AAC. Past research suggests that the use of silica sources with high amorphous content as partial or complete quartz silica sand replacements can alter crystalline phase formation during autoclaving and improve autoclaving efficiency. The amorphous content of MSWI BA is reported to range from approximately 30 to 80% wt. Given the potential to change phase development in AAC, the crystalline and amorphous content of the “less than” BA was determined using powder x-ray diffraction (XRD). Phase composition and amorphous content were determined using Rietveld refinement on powder samples using the internal standard method. Powdered samples from each size group were spiked with corundum, as the internal standard, at a sample mass fraction of 20% and backfilled onto an aluminum bracket holder. A Panalytical X’Pert Powder diffractometer was used to collect XRD data from spiked specimens. An open-source software, PROFEX, was used to process diffraction data via Rietveld refinement.

[0051] Concentrations of total environmentally available elements were determined using inductively coupled plasma-atomic emissions spectroscopy (ICP-AES) following the digestion process outlined in EPA method 3050B (1996). The digestion process outlined in EPA method 3050B is not sufficient to solubilize chemicals bound to silicate structures, according to the method. Measurement of elements bound in silicate frameworks requires more aggressive digestion methods involving the use of microwave digestion or hydrofluoric acid. However, it is assumed that elements not measured by the EPA 3050B are unlikely to react or pose a substantial hazard within AAC mixtures before autoclaving. Thus, the results of the ICP-AES analysis will give insight into the distribution of aluminum and other metals that will have practical effects on the aerating performance and safety of “less than” BA. Samples were dried, finely ground, and weighed out to 1 to 2 grams. The samples were digested using successive additions of concentrated hydrochloric acid, nitric acid, and ultrapure water (> 18 MQ). The digestion solution was then filtered, diluted, and analyzed using a Thermofisher ICAP 6200 ICP-AES instrument using argon as the working gas. Analysis was conducted on material retained on individual sieves within the sieve stack used for sieve analysis. The “less than” BA retained on individual sieves were assessed for total element concentrations using ICP-AES to determine elemental partitioning across the bulkash and different size fractions. Three replicate samples retained on each sieve were digested and analyzed. The average elemental concentrations in material retained on each sieve were used to calculate the expected concentrations within the different size groups. The calculation of elemental concentration for the bulk ash and size fractions accounted for the proportion of material retained on each sieve from sieve analysis.

[0052] The elemental oxide composition of finely ground samples from the different size groups was assessed using X-ray fluorescence (XRF) by a third-party laboratory at a major industrial cement plant in Florida, USA. The fusion bead method was used to process samples for analysis. During sample preparation, the loss on ignition (LOI) of each sample group was measured. The assessment was conducted on true samples within each size group. The XRF elemental composition allows for the analysis of silica and potentially silicate-bound elements, unlike the ICP-AES method on EPA 3050B digested samples.Aeration Efficiency

[0053] Conventional aluminum aerating agents like aluminum powder or paste quickly react to form hydrogen gas within fresh autoclaved aerated concrete (AAC) mixtures. Hydrogen formed during the very early stages of AAC hydration, while the mixture is still fluid, entrains a well-distributed and relatively homogenous mixture of small air bubbles (diameters ~ 1-5 mm). This process results in low density and improved thermal and acoustic insulation. The efficiency of aeration, though, decreases as AAC slurries harden due to hydration. Hydrogen generated during the later stages of AAC setting will nonuniformly entrap large air voids, causing poor expansion and weak points, which will lower overall AAC performance. Thus, the hydrogen production rate of aerating agents should be a design factor for AAC mixtures, especially when considering the use of novel aerating sources like municipal solid waste incineration (MSWI) bottom ash. Although MSWI bottom ash is a significant source of aluminum, the size-, facility- and age-dependent variability in composition and mineralogy can affect the aeration of AAC. Thus, the rate of hydrogen gas production of MSWI bottom ash should be evaluated to determine the most effective ways of processing and incorporating MSWI-based aerating agents into AAC mixtures.

[0054] Experimental Setup. Industrial-scale AAC producers commonly use metallic aluminum powder or paste to aerate fresh AAC slurries. The chemical reaction between metallic aluminum and the alkaline aqueous AAC slurry releases hydrogen gas to uniformly entrain air bubbles while the slurry is still fluid. Improper aeration can degrade the performance of the final AAC product. As the slurry hardens and builds viscosity through the process of hydration, the production of gas can lead to air entrapment, cracking, and degraded overall performance. Most of the expansion and aeration of the AAC slurry occurs within the first hour after the start of mixing. Given the timeframe for aeration, the potentialrate of hydrogen gas production, or aeration efficiency, of novel aerating agents such as MSWI BA should be assessed.

[0055] A method for measuring time-dependent hydrogen gas production was developed and used to select appropriate MSWI BA beneficiation processes to enhance performance as AAC aerating agents. The method used in this study was based on a modified version of the method described in “A Simple, Low-cost, and Robust System to Measure the Volume of Hydrogen Evolved by Chemical Reactions with Aqueous Solutions” by P. Brack et al. (J. Vis. Exp., 2016). The intended application of the method was to assess water-splitting chemicals (i.e., chemicals that react with water to produce hydrogen gas and hydroxyl ions) for use in powering portable hydrogen fuel cell devices with high accuracy and precise timekeeping. To accomplish this, a method was designed to measure the timedependent evolution of hydrogen gas generated during the reaction of water-splitting chemicals in heated aqueous sodium hydroxide solutions by combining a common water displacement-based gas volume measurement technique with automated data-logging.

[0056] Water displacement is a common technique for measuring the volume of waterinsoluble gas generated during a chemical reaction. The concept involved the reaction of the water-splitting chemical occurring in an aqueous solution, that can be adjusted for pH using an alkali hydroxide, within an airtight reaction vessel. The hydrogen gas produced in the reaction vessel was channeled into a filled water reservoir, which is usually an inverted graduated cylinder or an open-air container that allows gas to enter and water to exit. A water-filled inverted cylinder was used within an open-air water bath that was filled. As gas entered the water reservoir, water in the reservoir was displaced. Depending on the type of reservoir used, the decrease in the volume of water in the reservoir was recorded or the displaced water was channeled into another container in which the increase in water volume or mass was recorded. Corrections to the final volume or mass readings were applied to account for the effects of partial pressures of water vapor and the displacing gas based on Dalton’s Law.

[0057] The mass or volume of displaced water and time from the start of the reaction are often recorded by hand, which can be cumbersome and have high operator-induced variability. To achieve more accurate readings and better temporal resolution, the use of a data-logging mass balance was proposed to automatically record mass displacement with time. For the method, as the gas displaced water in the inverted cylinder, the water in the at- capacity water bath overflowed. The overflow from the water bath was channeled into an empty container that sat atop a data-logging mass balance. The measured mass of the water was equivalent to the hydrogen gas produced during the reaction after correcting for the partial pressure of water vapor and hydrogen gas via Dalton’s law.

[0058] The methodology used in builds upon the method by using an airtight water reservoir with inlet and outlet channels allowing for the inflow of gas and outflow of displaced water. The displaced water is channeled into a collection vessel, through semi-rigid tubing. The mass of water fed into the collection vessel is measured using a data logging mass balance. The data from the mass balance is logged in real-time to a computer text file using an RS232 connection at a rate of three data points per second. The conceptual basis of the method used in this study is shown in FIG. 2A while an image of the actual experimental setup for hydrogen gas production rate measurements is shown in FIG. 2B.

[0059] The components of the experimental setup in FIG. 2B include the reaction vessel (A), a magnetic stir plate set to 600 RPM (B), piping (C) connecting the reaction vessel to the water reservoir (D), a pressure gauge (E) installed to monitor pressure buildup in the water reservoir, the collection / measurement vessel (F), the datalogging mass balance (G) with a 0.01 -gram readout, an RS232 cable (H) used to connect the computer (I) to the mass balance, rubber stoppers (J) on the reaction vessel and water reservoir to ensure airtightness with machined undersized holes in the stoppers to firmly seat channel and pressure gauge piping, and pipe values (K) for refilling the water reservoir without removing airtight rubber stoppers, and a rubber stopper (L) installed on the collection / measurement vessel (F) to firmly seat piping and reduce noise in data from the movement of the pipe. The rubber stopper (L) has two machined holes, one to seat piping and one to ensure the air in the measurement / collection vessel (F) can escape during the inflow of displaced water from the reservoir (D).

[0060] In contrast to the previously outlined method that conducted tests at elevated temperatures, this study conducted tests at ambient laboratory temperatures to ensure isothermal conditions were met across the experimental setup. Reactions occurring at elevated temperatures, although would accelerate gas production, would also require monitoring the temperatures of the reservoir water and the displaced water in the collection vessel to ensure that Dalton’s law and the ideal gas law are properly applied to convert the mass of displaced water to the volume of hydrogen gas. Although the generated gas is likely to be sufficiently cooled by the time it reaches the reservoir, in-situ temperature monitoring would be difficult to implement given the need for air-tight seals.

[0061] As shown in FIG. 2B, the reaction vessel (A) used in this study was a 1000 mL Buchner flask centered on a magnetic stir plate (B) set to 600 RPM. During testing, the flask is filled with 500 mL of lime-saturated deionized (DI) aqueous solution with varying quantities of sodium hydroxide and a magnetic stir bar spinning at 600 RPM. All testing occurred under ambient conditions in the laboratory (73 ± 5 °F (23 ± 3 °C)). The start of the reaction occurs when a water-splitting compound (MSWI BA or metallic aluminum powder) is quickly and carefully added to the solution in the flask. After the addition of the water-splitting compoundinto the solution, a rubber stopper (J) is quickly and firmly placed into the opening of the reaction vessel to ensure airtightness, and then taped down using strong, reinforced duct tape as an insurance measure. Gas produced during the reaction flows out of the reaction vessel through a flexible tube (C) firmly seated on the short stem of the reaction vessel. Again, strong duct tape is used to fix the flexible tube onto the short stem of the flask to ensure the stability of the tube connection since the flow of hydrogen gas can be intense in certain instances.

[0062] The flexible tube is connected to a semi-rigid tube that channels hydrogen gas into the water reservoir (D) through an undersized hole machined through the permanent rubber stopper (K). The hole was undersized concerning the outer diameter of the semi-rigid rube to ensure the tube was firmly seated and prevented gas leakage. The water reservoir used in this study was a 2000 mL Buchner flask. The volume of the water in the reservoir is important for measuring large volumes of gas produced during the reaction. The reservoir was firmly fitted with a permanent rubber stopper machined to have three undersized holes to seat semi-rigid tubing while ensuring airtightness. The short stem of the 2000 mL Buchner flask was sealed shut using super glue and a small rubber stopper from the inside to prevent gas leakage. The stability of the stopper on the reservoir was found to be important in producing accurate results. During early trial testing, when hydrogen gas production was particularly intense, the stopper would sometimes become unsealed. This allowed hydrogen gas to escape into the environment. Thus, the rubber stopper on the reservoir was tied down using a series of zip ties. Duct tape with sufficiently rough scrim backing is placed on the underside of the reservoir, where the zip ties contact the reservoir, to prevent slippage. The reservoir stopper has three undersized holes for tubing: one for a gas inlet, one to channel displaced water to the collection vessel (F) and allow refilling, and one to connect a pressure gauge (E) with a measurement range of up to 15 PSIG. Since the rubber stopper has the potential to unseal under intense gas production, the pressure gauge was added to ensure that testing conditions were under isobaric conditions. Testing occurred at isothermal and isobaric conditions to ensure that the ideal gas law can be simply applied to convert the measured mass of displaced water to the volume of gas produced during the reaction. Any observed increase in pressure within the reaction vessel would thus invalidate results. Adjustments such as using less of the water-splitting reactants can be made to prevent substantial gas buildup in the reservoir and a blowout of the stopper.

[0063] The tubing which channels displaced water from the reservoir to the collection vessel is split into two separate tubes that are reconnected using a valve (K). The valve on this tube is installed to allow the reservoir to be refilled without needing to remove the zip- tied stopper. Before refilling the reservoir, the tubes leading to the reaction vessel and the collection vessel need to be disconnected from both values (K) such that the valves remainfirmly connected to the tubes leading to the reservoir. During refilling, both values remain open, and the water outlet tube is used to channel water into the reservoir. If both valves are closed, water will not flow into the reservoir. If the valve connected to the water outlet tube from the reservoir remains open while the gas inlet valve is closed, pressure will build up in the reservoir during refilling which may unseal the stopper, break the pressure gauge, or unseat the closed valve. If the gas inlet valve is used during refilling and the water outlet valve is open, the water in the reservoir will be channeled out through the water outlet tube and the reservoir water level will not rise.

[0064] Water displaced by gas is channeled from the reservoir to the collection vessel through tubing that has one end seated at the bottom of the water reservoir and one end seated at the bottom of the collection vessel. Both ends of the tube are seated at the bottom of the respective vessels to ensure continuous water flow during testing. The tube was stabilized within the collection vessel using a stopper with a machined undersized hole. This is important because the movement of the tube within the collection vessel can lead to erroneous mass readings. To prevent pressure buildup and ensure the collection vessel remains under atmospheric pressure, a second hole is machined into the stopper so that displaced air can escape as water fills the vessel.

[0065] Before the start of the test, which is when the water-splitting compound is added to the aqueous solution in the reaction vessel, the collection vessel needs to be emptied and placed onto the zeroed data logging mass balance. Once the collection vessel is placed on top of the mass balance, data logging software on the computer is turned on and data from the mass balance is logged in real-time. For this study, the mass balance is connected to a computer using an RS232-to-usb connection to allow real-time data logging. It was important, in this study, to not zero the scale after placing the empty collection vessel on top. Before the start of the reaction, non-zero mass readings are logged. This is because the open-source data logging software used in this study was limited to only logging mass readings from the balance at a rate of three data points per second without time stamps. While data logging, the mass balance should only be fared to zero after the water-splitting chemical is added to the aqueous solution in the reaction vessel and the reaction vessel is sealed. By zeroing the mass balance when the water-splitting compound is added to the solution, an artificial marker is created in the logged data that indicates the start of the reaction. The first zero value in the logged data is the start of the reaction. Time stamps can be added to logged data after testing has ended given that the sampling rate is known. In this study, it was determined that mass data was being logged at a sampling rate of three data points per second. Unless the logging software can appropriately timestamp each data point with sufficient time resolution, this should be the proper method of recording the start ofthe reaction and timestamping logged data to avoid significant operator error. After a certain duration, the test can be stopped, and the logged data can be saved.

[0066] The mass of water collected over time is equivalent to the volume of the displacing gas due to isothermal and isobaric testing conditions. However, the displacing gas contains some amount of water vapor along with the gas produced during the reaction. Dalton’s law of partial pressures can used to calculate the volume of the gas generated by the reaction. Dalton’s law states that the pressure within a container is equivalent to the sum of the partial pressures of each type of gas within the container as shown by Eqn. (1).PTis the total pressure within a container and P, is the partial pressure of gas i, with n referring to the different individual gases present. For this study, only hydrogen gas and water vapor are considered. Other gases may be produced during the reaction of MSWI residuals in alkaline solutions such as NH3, however, the production of these gases is likely minor in MSWI BA and was not considered during analysis. Thus, Dalton’s law boils down to the sum of the partial pressure of water vapor and that of hydrogen gas as shown in Eqn. (2), which illustrates the application of Dalton’s law of partial pressure to the measurement of hydrogen gas produced during the reaction between an aqueous solution and a waterspitting compound.PT — PH2O + PH2

[0067] The partial pressure of water vapor is well characterized across different temperatures. At the laboratory temperature of 73 ± 5 °F (23 ± 3 °C), the partial pressure of water vapor is calculated to be approximately 2.8 kPa (2.3 to 3.4 kPa). Given that the reaction occurred under ambient conditions, the total pressure in the reaction vessel is equal to the atmospheric pressure, or 101 .3 kPa. Thus, under ambient laboratory conditions, hydrogen gas has a partial pressure of 98.5 kPa (97.9 to 99 kPa). Using the ideal gas law, the volume of hydrogen gas accounts for approximately 97.2% (96.6 to 97.7%) of the volume of the measured displacing gas. A 2 to 4% variation in the proportion of hydrogen gas in the measured gas volume was not considered significant for this study. Thus, hydrogen gas volume was calculated by scaling the measured gas volume by 97.2%. Although this is true under controlled laboratory conditions, it should be noted that the vapor pressure of water varies non-linearly with temperature and, thus, temperature should be measured during testing for the most accurate results when this method is used in the field.

[0068] Aeration Efficiency Assessment. Research was carried out to determine effective beneficiation strategies to enhance the aeration efficiency of “less than” BA for practical, industrial applications. Key factors that affect the hydrogen production rate include particle size of metallic aluminum and solution alkalinity. Past research has shown that hydrogen gasproduction is strongly dependent on the particle size of the hydrogen-producing reactants and alkalinity of the aqueous solutions. Specific to MSWI BA, increasing the fineness of MSWI BA leads to higher rates and yields of hydrogen gas production. This is largely because hydrogen gas production occurs at the surface of aluminum particles, with a higher surface area leading to a higher hydrogen gas production rate and yields. The alkalinity of the solution in which the reaction occurs also affects the hydrogen production rate. This is because aluminum metal reacts readily with oxygen and water vapor in the air to form a thin oxide layer which inhibits contact with water under ambient conditions. However, the oxide layer is readily dissolvable in solutions with high pH. High pH environments remove the oxide layer and prevent the formation of additional oxide layers from reaction products, allowing hydrogen gas production to continue unimpeded.

[0069] Thus, the effects of particle size and solution alkalinity on the aeration efficiency of “less than” BA were examined. Fine metallic aluminum powder (200 Mesh, Pure, Spectrum Chemical) was used as the control to compare performance of MSWI BA and as a reference to assess the validity of the hydrogen gas test method. Based on material characterization results, aluminum mostly resided in the coarser fractions of “less than” BA from both facilities. Thus, the “less than” BA samples were crushed in bulk since sieving out finer fractions would reduce the mass fraction of aluminum. It is possible to sieve out the coarser fractions, however, this would need additional effort and therefore increase the cost of beneficiation of MSWI BA at the industrial scale. Two types of size reduction techniques were used: hammer milling and pulverization. Hammer milling was done by hand using a thick, heavy steel rod as shown while a belt-driven disc pulverizer manufactured by Bico was used to pulverize the BA samples as shown in FIG. 3. Hammer milling using a heavy steel rebar is shown on the left and the pulverizer is shown on the right.

[0070] Laser particle size analysis (LPA) was used to characterize the particle size distribution of the hammer milled and pulverized samples. The LPA results are shown in FIG. 4A and the cumulative passing curve parameters are summarized in the table in FIG. 4B. The plot of FIG. 4A illustrates particle size distribution for metallic aluminum powder (Al), hammer milled PBulk (PBulkJHM), pulverized PBulk (PBulk_Pulv), and pulverized SBulk (SBulk_Pulv). Hammer milling led to a coarser particle size distribution than pulverization. The pulverized “less than” BA also had similar median particle sizes as the metallic aluminum powder. However, the pulverized “less than” BA samples had more coarse and fine particles at the extremes of the particle size distributions than the metallic aluminum powder. This can be attributed to the highly heterogeneous nature of the “less than” BA. The median particle size of the metallic aluminum powder was within range of what is typically used in industrial production.Production and Performance Assessment of AAC with “less than” BA

[0071] Material properties and the aeration efficiency of “less than’’ BA were assessed in previous sections. Results indicated that bulk pulverization was a practical and efficient method of enhancing the aeration efficiency of “less than” BA. Aluminum largely resided in the coarse fractions while the coarsest size group constituted the majority of the “less than” BA gradation. Screening to isolate the fine fraction may reduce energy input for grinding but would also lead to lower gas production and higher rates of BA disposal. Moreover, hydrogen gas production rates of pulverized bulk “less than” BA were similar to that of metallic aluminum powder and had low sensitivity to solution alkalinity. In line with the circular economy concept, the incorporation of pulverized bulk “less than” BA would divert more BA from landfilling while needing minor adjustments to typical AAC mixture designs with minimal to no need for boosting alkalinity.

[0072] Next, the production and testing of laboratory-scale AAC made with conventional metallic aluminum powder (control specimens) and bulk pulverized “less than” BA as aerating agents is detailed. Metallic aluminum powder was used to make control AAC specimens to establish baseline performance. Pulverized PBulk and SBulk were used as both aerating agents and partial silica sand replacements in AAC. An iterative approach was used to select AAC mixture components, mixture designs, mixing processes, precuring duration and temperature, and autoclaving duration for test specimens. The mixture design, mixing, curing, and autoclaving parameters were first determined for control AAC specimens made with metallic aluminum powder and then optimized for specimens made with pulverized PBulk and SBulk. This was to ensure that the production of laboratory-scale AAC mixtures made with metallic aluminum powder and the “less than” BA followed the same process for mixing, casting, curing, and autoclaving and that mixture designs were not substantially different. The performance of AAC amended with bulk “less than” BA was assessed using dry density, compressive strength, thermal insulation, and bulk leaching and compared to the performance of control AAC specimens. Moreover, two industrial AAC blocks were acquired from an industrial AAC producer in Florida and tested for dry density, compressive strength, and thermal insulation. This was primarily to show that AAC made with bulk “less than” BA could perform as well as manufactured AAC used in construction.

[0073] Laboratory-scale AAC production. Production of AAC at the laboratory scale was iterative and focused primarily on optimizing mixture designs as well as the mixing, casting, precuring, demolding, and autoclaving process. This process was adopted so that laboratory-scale AAC specimens could be demolded and autoclaved without disintegrating. The main constraint in the laboratory, which is not typically an issue during industrial-scale production, was the size of the laboratory-scale autoclave limited the size of the specimens. For industrial production, AAC specimens are made in large molds that can be wire cut foruniform, parallel faces as shown in the images of FIG. 5. The molds are shown on the left, the demolded and wire-cut AAC is shown in the center, and the autoclaves are shown on the right at an industrial AAC facility. The molds and cement autoclave, shown in the images of FIG. 6A, used for laboratory-scale AAC production are much smaller and allow for less error during demolding. The 2x2x12 inch (51x51x305 mm) molds are shown on the left and the cement autoclave used for laboratory-scale AAC production is shown on the right. For accurate compressive strength testing of laboratory-scale specimens, load must be applied to two parallel opposite faces. Since laboratory specimens were size-constrained, the formfinished faces were kept intact to ensure the two opposite faces are smooth and uniform for testing. Thus, a series of trial tests were conducted to determine the best mixture design parameters, mixing methods, and precuring conditions that enabled demolding specimens with intact surfaces.

[0074] The final mixture designs for the control and “less than” BA-based AAC specimens are shown in the table of FIG. 6B. The dry AAC mixture components included an ASTM C150 type l / ll ordinary portland cement (OPC), a fine pure quartz silica sand (UF Sand), calcium hydroxide (C), sodium hydroxide (N), and metallic aluminum powder (Al), and pulverized “less than” BA from either facility (PBA) as the aerating agent. A finely ground quartz silica sand was also acquired from an industrial AAC producer. The abbreviation used for the industrial sand is “AS”. The “solids” are OPC, UF Sand, AS, C, N, and PBA. The metallic aluminum powder was considered an additive and included in mixtures at an addition rate by mass of the solids fraction. The water-to-solids mass ratio, or W / S, selected for the control specimens was 0.8 and 0.7 while the W / S selected for the “less than” BAbased specimens were 0.7 and 0.6. The lower W / S for the “less than” BA-based specimens was needed to ensure the specimens did not disintegrate during demolding. At higher W / S, the “less than” BA-based specimens were not able to be demolded without severe damage. A water-reducing admixture, polycarboxylate ether (PCE) was used to enhance the fluidity of the fresh AAC slurry. Due to the difference in W / S and the fact that “less than” BA reduced fresh fluidity, the PCE content used for the control specimens was fixed at 0.50% wt. OPC while used for the “less than” BA-based mixtures was fixed at 0.85%wt. OPC. The hydrated lime, or calcium hydroxide (C), content used in all mixtures was 24.19%wt. solids and the sodium hydroxide (N) content was 0.81 %wt. solids for all mixtures to ensure that mixtures were sufficiently hardened before demolding. Lower calcium hydroxide and sodium hydroxide content led to AAC specimens that were too weak for demolding, especially for AAC specimens made with “less than” BA. Finally, an air-entraining agent (AEA) was used at various doses in the mixtures to enhance and stabilize the air-void distribution.

[0075] The specimen IDs shown in the table of FIG. 6B indicate the most significant parts of the mixture design. For instance, “AI_0.07AI_0.7W_0.5E” refers to a control AACmixture made with the UF sand, metallic aluminum powder with an addition rate of 0.07%wt. solids, a W / S of 0.7, and an AEA dosage of 0.5 fl. oz / cwt of solids. A specimen ID of “P10_0.6W_1 E_AS” indicates an AAC mixture made with pulverized PBulk at an incorporation rate of 10%wt. solids, AS instead of UF sand, a W / S of 0.60, and an AEA dosage of 1 fl. oz / cwt. of solids.

[0076] The particle size distributions of the metallic aluminum powder (Al), fine silica sand (UF Sand), finely ground sand from an AAC industrial producer (AS), pulverized PBulk, and pulverized SBulk are shown in FIG. 7. The UF sand was acquired from a supplier of finely ground and very pure quartz silica sands while the AS quartz silica sand was acquired from an industrial AAC producer that grinds construction sand onsite using a large ball mill. The high-purity metallic aluminum powder (Al) was acquired from Spectrum Chemical. The UF sand was slightly finer than the industrial sand (AS). Moreover, the pulverized PBulk was finer than the pulverized SBulk and metallic aluminum powder.

[0077] FIG. 8 shows the scanning electron microscope (SEM) / backscatter electron (BSE) pictogram of the metallic aluminum powder (on the left) and pulverized PBulk (on the right). Elemental mapping was acquired by energy dispersive spectroscopy (EDS). The images show that the particles of the metallic aluminum particles were generally smooth and almost entirely aluminum. The EDS map of the PBulk shows a large variation in elements, elemental distributions, and particle shapes. Aluminum was found in locations with silicon, iron, and calcium with few particles that were pure aluminum.

[0078] A beneficial step before mixing was to ensure that the molds were prepped for casting and steam curing. For each specimen, two-gang 2x2x12-inch (51x51x305- mm) molds, shown in FIG. 6A, were used. The molds were set up following the procedure outlined in ASTM C157 (2024), with petroleum jelly used to ensure water tightness. After setup, the molds were carefully covered in high-temperature epoxy demolding tape, while ensuring that any air bubbles and gaps were removed. Thin layers of petroleum jelly and motor oil were placed on top of the tape for additional lubrication. This step ensured that the hardened AAC specimens could be demolded without damaging the form-finished sides. The molds were then placed into a rigid plastic container that could be sealed. Water was poured into the container, ensuring that water did not get into the inside of the molds. The container along with the molds and water were sealed and then placed into a 60 °C oven.

[0079] The mixing, casting, and precuring processes occurred at elevated temperatures of 60 °C. Precuring refers to the treatment of specimens immediately after casting and before autoclaving. FIG. 9 shows images of the mixing on the left, vibrating in the center, and casting process on the right. Before mixing, potable tap water was heated to 60 °C. Then, the heated water was added to a 6x12-inch cylinder along with AEA. After, calcium hydroxide and sodium hydroxide were slowly added to water and homogenized for threeminutes at 600 RPM using an overhead mixer seen in FIG. 9. The sides of the cylinder were scrapped, while the mixer was running, using a rubber spatula to ensure the calcium and sodium hydroxide powders were thoroughly mixed in the slurry. The mixer was stopped after three minutes; half the cement, silica sand, and PCE were added to the slurry and the sides were scraped with the spatula. The slurry was again mixed for three minutes at approximately 600 RPM to ensure homogenization while continuously scraping the inside walls of the cylinder. After the second three-minute mix period, the mixer was stopped, and the aerating agent was added. The mixer was set to 800 RPM and the aerating agent was thoroughly mixed into the slurry for 40 seconds. After the final 40-second mixing period, the slurry was vibrated using a concrete vibrator and then poured into the heated molds in the water-filled containers within the ovens set to 60 °C. After pouring, a large trowel was used to scrap off excess slurry from the molds. Moreover, every two to five minutes, the expanding slurry was also scrapped off from the top of the molds. Scrapping the excess expanding slurry would continue for up to 15 minutes or until the slurry was no longer sufficiently fluid to be finished. This step prevented, especially for the “less than” BA-based samples, the collapse of the cellular structure during precuring.

[0080] After scrapping, the containers were sealed to ensure water did not escape during steam curing. The specimens were steam-cured at 60 °C for 48 hours before demolding and autoclaving. Again, this precuring step (steam curing at 60 °C for 48 hours before demolding and autoclaving) was necessary so that both the control and “less than” BA-amended specimens would be demolded without damage.

[0081] After the 48-hour steam cure, the specimens were removed from the ovens and allowed to cool before troweling and demolding. Once cooled to room temperature, the portions of the specimens that expanded above the top edge of the molds were removed using a trowel. After troweling, the specimens were carefully demolded. Care was taken to ensure the integrity of the edges and the form-finished faces. After demolding, the specimens were cut to 9 inches in length and then placed into the cement autoclave at 175 PSIG and slightly more than 190 °C for 24 hours as shown in FIG. 6A. After autoclaving, the specimens were cut into 2-inch (51 mm) cubes and 1x2x2-inch (25x51x51-mm) plate sections using a scroll saw. Three cube specimens were used for dry density and compressive strength measurements, two cube specimens were used for bulk monolith leaching tests, and two plate sections were used for thermal insulation testing. All specimens were oven-dried at 110 °C for at least 24 hours before testing.

[0082] Compressive Strength and Dry Density Testing. Compression tests were performed following a modified ASTM C1693 (2017) procedure. Testing was conducted on oven-dried 2-inch (51-mm) cubes. After drying, the weight and length dimensions of the specimens were recorded. The volumes of the specimens were calculated using thedimensional measurements of the cube. Dry density was calculated as the ratio of the recorded weight to the calculated volume. After taking dimensional measurements, the specimens were prepped for compression testing. Two opposite form-finished faces were used as the loading surfaces. During compression testing, the specimens were loaded at 0.05 inches / min (1 .27 mm / min) until failure and the peak load was recorded as the breaking load. The compressive strength was calculated as the ratio of the peak load to the area of the cube’s transverse to the direction of loading.

[0083] Bulk Monolith Tank Leaching Test. Bulk monolith leaching tests were conducted on 2-inch (51-mm) cube AAC specimens in deionized water, as the leaching solution, following a modified version of EPA Method 1315 (2017). The primary issue with using AAC specimens was that they tended to float if moisture content was low. Thus, the specimens were vacuum-saturated with deionized water for 24 hours before placing them into leaching containers. After vacuum saturation, the specimens were submerged in deionized water in the leaching containers. To ensure all six faces were exposed to the leaching solution, the specimens were suspended in the leaching tanks using fish wire. The volume of deionized water used for all specimens was 1400 mL for all specimens. This was per EPA 1315, which requires the solution volume to the exposed surface area (L / SA) of the monolith to be 9 ± 1 mL / cm2.

[0084] Thermal Insulation Testing. Thermal insulation properties were tested using a single-sided guarded hot plate assembly following a modified version of ASTM C177 (2023). The concept of the design is shown in the schematic diagram of FIG. 10A and the actual setup is shown in the images of FIG. 10B. A digital hotplate was used to meter the temperature on the hot side from 45 °C to 50 °C. Specimens (and aluminum blocks) were cut into 1x2x2 inch (25x51x51 mm) plates for analysis. Two replicates were assessed per specimen. The 1 -inch (25-mm) thick AAC specimens could only be made with a max width and length of 2 inches (51 mm) due to the limitations of autoclave dimensions. However, to accurately measure the thermal insulation of plate specimens, area to thickness ratio is kept large. The setup used in this study had a low area-to-thickness ratio of 4, which increases the potential for edge heat loss and inaccurate results. Rather than use the results as an absolute measure of thermal insulation, the results were used to draw a comparison between the control AAC made with metallic aluminum powder and AAC made with “less than” BA. The results were also compared to those of a rigid calcium silicate insulation board, used as the reference of known R-Value, and AAC produced through industrial processes.

[0085] Since the hot plate area was larger than that of the specimens, an aluminum block with the same area and thickness as the specimens was placed in between the specimens and the hot plate. The aluminum block was able to reach the meteredtemperature quickly due to its high thermal conductivity and thus was used as the hot side of the assembly. Ceramic fiber insulation was used as the guards, surrounding both the aluminum block and the specimen on edges transverse to the direction of heat flow. This minimized heat flow into the specimens from the edges not in contact with the aluminum block. A water-cooled cold plate was used to ensure the cold side of the specimen remained at a constant temperature. The cold plate was connected to a temperature-controlled water bath set to 20 °C. Weights were used to ensure the cold plate was secured to the cold side of the specimen. A thermocouple was placed in between the specimen and aluminum block (the hot side) and a calibrated heat flux sensor (PHFS-01e, FluxTeq) with an integrated thermocouple was placed on the cold side, in between the cold plate and the specimen. Data was recorded from the thermocouples and the integrated heatflux sensor using a data acquisition device until stable temperature and heat flux readings were established.

[0086] The setup was assessed using an insulating material of known R-value. The insulating material was a 1 -inch (25-mm) thick rigid calcium silicate insulation board with a density of 40 lbs / ft3(640 kg / m3) and an R-Value of 1.3 ft2-°F-h / BTU acquired from McMaster Carr. FIG. 11 A shows the output of thermocouples on the hot and cold sides of the reference material as well as the heat flux readings on the cold side. The figure shows that heat flux readings were stable in regions where the hot side was at a constant temperature and increased in response to an increase in the temperature of the hot side. Regions, where the thermocouple and heat flux sensor readings were stable, are highlighted in the figure. An R- Value was calculated based on measured heat flux and temperature difference between hot and cold side from thermal insulation testing of reference calcium silicate rigid board insulation. FIG. 11 B shows the calculated R-value based on the temperature difference at the cold and hot sides along with the heat flux readings. The highlighted regions in FIGS. 11 A and 11 B show areas where the system reached a steady state at the two different temperature regimes. The expected R-value for the reference is also shown in the figure. Although calculated R-Values were significantly different than expected the R-Values of the reference in the highlighted regions of stability were similar despite the different hot side temperatures indicating good repeatability. For assessment of the AAC specimens, R- Values were calculated and graphed similarly to what is shown in the figures below. Regions of steady-state heat flow were determined and the average R-Values within those regions were determined for the references and specimens.Economic Feasibility of Incorporating “less than” BA into Industrial AAC Production

[0087] A pressing hurdle for the reuse of “less than” BA in industrial AAC production is economic viability. Past research conducted a thorough economic cost analysis on processing MSWI BA for use as a road base as an alternative to landfilling from theperspective of the MSWI facility. Two potential scenarios were assessed, with both focusing on the beneficiation of MSWI BA at the site of generation. The first scenario included processing MSWI BA using conventional screening methods to meet gradation requirements for road bases and shipment to an aggregate stockyard. The second scenario incorporated an advanced metals recovery process in addition to screening and shipment to a stockyard. In the second scenario, the costs of processing MSWI BA for metals recovery and screening would be partially recovered by the sale of the recovered metals. Considering fixed capital costs, labor, operations, and maintenance, both scenarios were found to be economically competitive when throughput was sufficiently high.

[0088] However, throughput largely depends on demand from the end-user. Because the economics of diverting MSWI BA from landfills were favorable to MSWI facilities when demand was sufficiently high, the economic analysis presented in this study largely focused on the benefits and costs associated with processing and incorporating “less than’’ BA into AAC from the perspective of the end-user, the AAC producer, “less than” BA, particularly PBulk from Facility P, was demonstrated to be an effective substitute for conventional metallic aluminum aerating agents based on performance. The PBulk-amended AAC specimens were able to develop the necessary strength and density to meet standardized strength class specifications for use in construction. For “less than” BA-amended AAC to meet specifications, slight adjustments to mixture designs were needed relative to the designs of the controls. The adjustments, including lower W / S and the use of admixtures, were not considered to substantial for large AAC producers to implement.

[0089] There are a few drivers of cost that should be considered when using “less than” BA in AAC production: screening MSWI BA to below 3 / 8 inches, transportation to the AAC production facility, finely grinding “less than” BA to sufficient fineness, and admixture costs. Facility P implements a large-scale screening process that separates MSWI BA particles greater than 3 / 8 inches from those passing 3 / 8 inches. Thus, it was assumed that screening would occur at the MSWI facility using existing equipment at no cost to either the MSWI facility or AAC producer. Furthermore, most advanced industrial AAC producers grind quartz silica sand down a median particle size of approximately 20 pm onsite using large ball mills. Although “less than” BA is more heterogeneous than quartz silica sand, the hardest component in the BA is likely to be glass which has similar hardness to quartz. Furthermore, since “less than” BA would partially replace the quartz silica sand fraction and constitute up to 10%wt. of the dry solids mass in an AAC mix, it was assumed that a comparatively small amount of “less than” BA could be interground with quartz silica sand with no loss in grinding efficiency. Furthermore, since “less than” BA is expected to be the sole aerating agent, onsite storage of the finely ground “less than” BA and sand slurry can occur in the silo / bunker previously occupied by metallic aluminum powder or paste. The bunker isdesigned to reduce the risks of explosions inherent to the storage of large quantities of metallic aluminum powder or paste. Although finely ground “less than” BA is likely to be less explosive than metallic aluminum, there is potential for hydrogen gas to build up in a contained storage system and cause an explosion. Thus, the “less than” BA and sand slurry would need to be stored in areas that can properly contain such explosions.

[0090] FIG. 12 shows an example of the proposed process to produce “less than” BA- amended AAC based on the assumptions that “less than” BA will be interground and costored with the silica sand in the ball mill and bunker previously occupied by metallic aluminum powder or paste.

[0091] Economic assessment for using “less than” BA as an alternative to conventional aerating agents and partial quartz silica sand replacement was conducted by comparing the costs of producing a cubic meter of conventional AAC to the cost of producing a cubic meter of “less than” BA-amended AAC. The primary assumptions used for analysis are as follows:• “less than” BA is generated by MSWI BA using existing screening methods at no additional cost to AAC producer• Cost of transporting “less than” BA to the AAC producer is negligible• “less than” BA will be inter-ground and co-stored with sand slurry which does not increase the cost of production

[0092] The systems and system boundary used for economic assessment are schematically illustrated in FIG. 13A. The economic scenarios to determine the cost versus benefit of using “less than” BA as an aerating for conventional AAC and the proposed mixture design (systems 1 and 2, respectively). For analysis, the mixture design for system 1 , the conventional AAC, was acquired from an industrial AAC producer is shown in the upper table of FIG. 13B. When ““less than”” BA is used, only the sand and the recycled sand will be substituted. The proposed mixture design using ““less than”” BA as an aerating agent and partial silica replacement is shown in lower table of FIG. 13B.Results - Materials Characterization

[0093] Ash Gradation Results (Sieve Analysis). Results from sieve analysis indicated that most of the particles in Facility S and Facility P “less than” BA were in the coarsest size group, with comparatively minor quantities in the finer groups. The table of FIG. 14A summarizes the gradation characteristics of the “less than” BA from Facility S and P while FIG. 14B displays the gradation curves from sieve analysis. The plot shows the particle gradation curves (% cumulative passing) for “less than" BA from Facility S and Facility P. The median particle sizes (D5o) and fineness moduli (FM) of the two “less than” BA samples were similar despite being sourced from MSWI facilities from different parts of Florida and using different incineration processes. Results indicated that the “less than” BA sampleswere slightly coarser than ASTM C33 fine aggregates used in concrete. Both “less than’’ BA samples exceeded the FM upper limit of 3.1 and failed to meet lower and upper cumulative percent passing limits for some of the larger-sized sieves as prescribed in ASTM C33 for fine aggregates.

[0094] Although the “less than” BA samples did not qualify as ASTM C33 fine aggregate, research has shown that including intermediate-sized aggregates along with fine and coarse aggregates can enhance concrete workability and strength through more efficient particle packing. However, “less than” BA would need some form of pretreatment to completely remove or oxidize metallic aluminum before use as a concrete aggregate. Research has shown that MSWI BA pretreatment such as soaking in highly alkaline solutions can oxidize and render aluminum inert, improving performance in cementitious systems. However, further research is needed to determine the effects on strength and durability as well as to optimize alkaline pretreatments to reduce the need to use alkali hydroxides such as sodium and potassium hydroxides.

[0095] In terms of AAC, MSWI BA is generally coarser than construction silica sand used to supply silica for AAC production. The most significant source of silica in MSWI BA stems from waste glass, which has similar hardness and grindability as quartz in silica sand commonly used in AAC production. Since silica sand is finely ground to a median size of approximately 20 to 30 pm before use in AAC to enhance autoclaving efficiency, the use of MSWI BA may require slightly more grinding energy.

[0096] Apparent Specific Gravity Results (Helium Pycnometry). The specific gravities (SGs) of the finely ground samples from different size groups are summarized in the table of FIG. 15. Samples from size groups “Bulk”, “4-16”, and “30-50” were measured directly using helium pycnometry. The SGs of the samples retained on each sieve within the “100-P” group were measured separately and used to estimate the SG of the samples within the “100-P” size group. The proportion of material retained on individual sieves was used in estimating the SG of the “100-P” group.

[0097] Results indicated that the SGs of the “less than” BA size groups were on the higher end of SGs reported in the literature (1.5 to 2.8) and within the range of SGs for silica sand commonly used in concrete construction. Since the SGs of the Facility S and P size groups were similar to those of typical silica sand, the SGs of “less than” BA are unlikely to influence the strength and density relationship of AAC when used as a partial silica sand replacement.

[0098] The SG of the PBulk sample was approximately 5.3% higher than that of the SBulk sample. Although the difference in SG of bulk ash between facilities was minor, it may be explained by the differences in incineration processes. The mass burn facility, Facility P does not process MSW to remove ferrous and non-ferrous metallic materials from the wastestream before incineration. Thus, dense incombustible materials would be retained in the incinerated residuals. In contrast, Facility S (an RDF facility) shreds and removes incombustible, inorganic MSW fraction before combustion to increase the quantity of combustible, organic materials fed into the incinerator. This includes the removal of relatively large appliances, ferrous and non-ferrous objects, sand, and glass using overhead magnets, eddy current separators, and rotating trommel screens. The reduction in denser incombustible materials in favor of less dense organic materials will translate into a less dense incineration residual. However, eddy current separation is generally ineffective at removing non-ferrous metals such as aluminum when particle sizes are small. Since the “less than” BA consists of the finer fraction of BA, it is unlikely that the lower specific gravity of SBulk is due to having less aluminum metal than PBulk. Thus, the lower SG of the Facility S BA samples could partially be explained by other factors such as processing effects on ferrous metals, regional differences in the MSW stream, or a higher quantity of unburnt organic materials.

[0099] Moreover, SG generally decreased as the particle size of the “less than” BA decreased. Since “less than” BA samples from both facilities were generally coarse according to sieve analysis, the SGs of the bulk samples were more like SGs of the coarsest sieve group than the finer groups. Though differences in SGs between size groups were noticeable, the differences were not substantial. For “less than” BA from Facility S, the difference in SGs between the coarsest and finest sieve groups was approximately 4.2% while the difference was about 7.0% for “less than” BA from Facility P.

[0100] Mineralogical Composition Results (XRD). Quantitative XRD results, summarized in the table of FIG. 16, showed that “less than” BA samples from different size groups were mostly amorphous. The amorphous content of PBulk (76.3%) and SBulk (78.8%) was similar and fell within the range reported in the literature. The most dominant phases found in the crystalline component of PBulk and SBulk were calcite, ettringite, and quartz. Secondary phases included calcium aluminum nitrate hydroxide, muscovite, and gypsum. Ettringite and quartz were found in higher quantities in Facility P “less than” BA compared to the Facility S ash.

[0101] Total Elemental Concentrations Results (ICP-AES). The partitioning of aluminum and chemicals that may pose risks to human health and the environments within “less than” BA size groups were evaluated using ICP-AES following the EPA 3050B (1996) digestion process. Elemental partitioning can provide stakeholders guidance on the management, processing, and safe handling of “less than” BA in AAC production. Given some of the limitations of the EPA 3050b digestion process in mobilizing species bound within silicate structures, the elemental concentrations found during testing are considered to represent what may become “environmentally available”. Despite the highly alkaline environment of thefresh AAC slurry, silicate-bound elemental species are unlikely to mobilize and react during the aeration and precuring process. Thus, for guidance on the most appropriate ways to incorporate the “less than” BA as an AAC aerating agent, the environmentally available concentration of aluminum may be sufficient. However, it should be noted that silicate minerals dissolve and react during autoclaving, regardless of stability under ambient conditions. Autoclaving may change the mobility of silicate-bound chemical species, leading to changes in phase formation during autoclaving as well as the overall performance of AAC post-autoclaving. Given the innately complex and heterogeneous composition of MSWI BA, it would be difficult to differentiate the effects of trace chemicals on performance. For practical purposes, however, the data can provide an estimate of potentially mobile species that can affect AAC performance.

[0102] It should be noted that ICP-AES analysis following EPA 3050B digestion does not differentiate between aluminum from metallic aluminum, aluminum alloys, or aluminum oxides. The data, though, can be used to inform beneficiation strategies to optimize the performance of “less than” BA as an aerating agent. Results indicated that aluminum, calcium, iron, and copper had the highest total environmentally available concentrations, shown in FIGS. 17A and 17B, in the bulk “less than” BA samples. The concentrations of all elements analyzed are summarized in the tables of FIGS. 17C and 17D for “less than” BA from Facility S and P, respectively. Elements in the tables of FIGS. 17C and 17D are presented in descending order of concentration within SBulk and PBulk. Since most of the “less than” BA from Facility S and P were retained on the larger sieves, the elemental compositions of the bulk “less than” BA samples were largely influenced by the coarsest sieve group.

[0103] Given that metallic aluminum concentration is important to the production of AAC, a deeper analysis of aluminum distribution is warranted. Concentrations of aluminum were greatest in the coarsest size groups of “less than” BA from both facilities, consistent with past research on elemental partitioning across the finer MSWI BA size fractions. The S4-16 size group had an aluminum content of 14.4% wt. compared to 4.1% wt. in the S100-P group. Like Facility S, the coarsest size group sample from Facility P (P4-16) had an aluminum content of 4.2% wt. while the content in P100-P was 1.0% wt. Thus, using the finest size group for AAC production may not be an effective strategy despite the potential for reducing the energy needed for grinding. This is because the finer fraction has relatively low aluminum content, necessitating the use of much larger quantities for AAC production to achieve similar aeration as the bulk “less than” BA or coarser sieve groups. Furthermore, the fraction of “less than” BA retained on the finest sieve group was “less than” that retained on the coarser fractions according to sieve analysis. Large quantities of “less than” BA would have to be processed to obtain enough aluminous fines for aeration. The unused “less than”BA would then have to be managed primarily through landfilling, increasing overall production costs due to tipping fees.

[0104] PBulk had an aluminum concentration of approximately 3.1 % while the concentration was 9.0% in SBulk. The difference can be attributed to differences in processing. The metallic aluminum components of the MSW incineration stream in Facility S are shredded and treated using eddy current separators before combustion. Given the inefficiency of the eddy current separator in removing smaller aluminum particles, the shredded aluminum fragments were likely retained in the “less than” BA produced by Facility S. Facility P combusts MSW “as-is” which would lead to much of the total aluminum content to be retained in the coarse fraction of incineration residuals. The aluminum content in the Facility P and Facility S bulk samples were generally consistent with, or slightly higher than, values reported in the literature for MSWI BA, especially in the finer fractions. Differences from past studies may attributed to the innate heterogeneity of BA as well as the preprocessing technologies used for metals recovery. Given the higher aluminum content, Facility S “less than” BA would seem to be a more ideal aerating agent than “less than” BA from Facility P. However, when considering the notion of a circular economy, the lower aluminum content of PBulk would lead to higher landfill diversion rates and thus should not be ignored in favor of BA with higher aluminum content. This is because more of the “less than” BA with lower aluminum content would have to be used in AAC production to achieve similar aeration than BA with higher aluminum content. Also noteworthy is the high variability of aluminum content in the Facility S samples compared to that in the Facility P samples. The higher variability in aluminum content would need more frequent testing to ensure an appropriate quantity is being used for aeration.

[0105] Copper followed the same trend as aluminum in “less than” BA from both facilities and reflects what has been reported in the literature. The distribution of iron was generally uniform across each of the “less than” BA size groups for Facility S and across PBulk, P4- 16, and P30-50, a trend which is also consistent with the literature. However, the concentration of iron in the P100-P was anomalously lower than in the finest size groups of Facility P. Moreover, iron content was higher in Facility P “less than” BA compared to BA from Facility S. This is likely because Facility S removes ferrous metals from the incineration stream using magnets before combustion while Facility P combusts MSW without preprocessing. The calcium content in Facility S increased as particle sizes decreased. For Facility P, calcium content was lowest in the coarsest size group but similar across size groups P30-50 and P100-P. More calcium content in the finer fraction may indicate that a large fraction of calcium originated from more friable materials than aluminum, iron, and copper.

[0106] Based on the exceedance of residential and industrial Florida Soil Cleanup Targets (FSCTs), several elements were identified as constituents of potential concern (COPC) from a health hazard perspective (FDEP, 2017). For the size groups from Facility S, the COPC were aluminum, copper, lead, barium, antimony, and arsenic as highlighted in the table of FIG. 17C. The COPC for Facility P samples were copper, lead, barium, antimony, arsenic, and cadmium as highlighted in the table of FIG. 17D. Although concentrations of these COPC exceeded residential (highlighted in darker grey) or commercial (highlighted in lighter grey) FSCTs in at least one of the size groups for a given facility, focus should be placed on COPC in SBulk and PBulk exceeding FSCTs for commercial applications. During AAC production, the bulk “less than’’ BA is expected to be handled solely by AAC facility personnel. The only element surpassing industrial cleanup targets was lead in the PBulk sample. Residential exposure will occur only after the “less than” BA has been solidified within an AAC matrix. Past research has shown autoclaving to effectively immobilize heavy metals present in MSWI BA, suggesting COPC exposure risk to the general public is likely low when “less than” BA is used in AAC products. However, further research is recommended to determine the effects of “less than” BA-amended AAC on indoor air quality to confirm the low risk of exposure.

[0107] Chemical Oxide Composition Results (XRF). Bulk chemical oxide composition and LOI on different size groups of “less than” BA were determined through XRF analysis. Results for chemical oxide composition were conducted on “less than” BA sieved to meet the conditions of each size group. FIG. 18 shows the chemical oxide composition of “less than” BA by XRF. Like ICP-AES results discussed in the previous section, XRF results suggest that the compositions of PBulk and SBulk were mostly influenced by the coarsest fraction.

[0108] The major oxides present in the “less than” BA size groups from both facilities were silica, calcium oxide, alumina, and iron oxide, consistent with past research. Moreover, the mass fractions of minor constituents fell within the range of values found in the literature. Alumina and silica contents were broadly similar in the PBulk and SBulk samples, while calcium oxide was higher in the Facility S samples. The iron oxide content was 90% higher in PBulk than in SBulk. The difference in iron oxide content between SBulk and PBulk is consistent with the results of ICP-AES and is most likely because Facility S removes iron from the incineration stream with magnets before combustion, unlike Facility P. This would increase the iron content in the incineration residuals from Facility P.

[0109] Based on XRF data, alumina is largely concentrated in the coarsest fractions of the “less than” BA, similar to ICP-AES results. However, the alumina content in the PBulk sample was found to be slightly higher than in the SBulk sample which contrasts with the aluminum concentration results from ICP-AES analysis. This may suggest that some of the aluminum in the PBulk sample was bound to chemical structures that did not solubilizeduring the digestion process for ICP-AES. XRF can detect elemental species regardless of chemical environment while detection via ICP-AES strongly depends on the preparation and digestion method. The difference between XRF and ICP-AES is further highlighted by differences in sodium content. A large proportion of sodium in MSWI BA stems from the waste silica glass, which constitutes a major component of BA. Sodium bound to the silicate structure of glass would not be expected to mobilize during the EPA 3050B digestion process, resulting in lower concentration during ICP-AES analysis compared to XRF analysis. For example, sodium, as indicated by XRF data, constituted approximately 2.6% of the PBulk mass while ICP-AES data suggested that the mass fraction of sodium in PBulk was 0.64%.

[0110] Although the ICP-AES and XRF methods can result in different concentrations for certain elements of interest, both methods can be applied to assess the quality of BA for use in AAC. Aluminum is important for proper aeration of fresh AAC slurry. Aeration predominately occurs immediately after mixing under ambient conditions or slightly elevated temperatures. Thus, analysis should focus on aluminum that will be available to react and aerate during the mixing and curing stage of AAC production, before autoclaving. The most effective analytical method, in the case of aluminum, would be ICP-AES analysis following the EPA 3050B digestion process. Aside from aluminum content, the silica content needs to be determined. This is because silica, along with burnt or hydrated lime, is the main reactant during autoclaving. For silica, which is unlikely to sufficiently solubilize during the EPA 3050B digestion process, the most effective analytical method would be XRF.

[0111] Another important tool for assessing the quality of “less than” BA for use in AAC may be LOI. Past research indicates that approximately 1 to 2% of organic carbon can remain unburnt in MSWI BA due to innate incineration inefficiencies. Unburnt organic carbon, especially in fly ash from coal combustion, can lower the effectiveness of surfactantbased air-entraining agents and increase water needs in cementitious systems. A common test to determine organic carbon in fly ash is LOI. However, LOI can overestimate unburnt carbon due to the presence of other compounds that experience mass loss at temperatures typically used during LOI testing such as calcium carbonate, calcium hydroxide, and calcium sulfates. The LOI value in the table of FIG. 18 represents the mass loss of “less than” BA during preparation for the fusion bead method for XRF. The materials were oven-dried until constant mass and weighed before creating the fusion bead. To make a fusion bead, the target sample is mixed with a known quantity of a lithium borate fluxing agent and heated to approximately 1000 °C. After heating and cooling, the bead is weighed. The LOI from this process is determined to be the difference between the mass of the bead and the mass of the sample and fluxing agent.

[0112] The “less than” BA from both facilities were found to have elevated LOIs from XRF; the LOIs of PBulk and SBulk ere 5.4% and 10.9%, respectively. Calcium carbonate, which was found in both “less than” BA samples as calcite during quantitative XRD analysis, can decompose within the temperature range of the XRF fused bead preparation. When heated to temperatures above approximately 700 °C, calcium carbonate decomposes into carbon dioxide gas and calcium oxide, losing approximately 44% of its original mass. Based on quantitative XRD results, the mass fraction of calcite was 4.5% in PBulk and 4.2% in SBulk. Thus, about 2.0% and 1 .8% of the LOI in the PBulk and SBulk, respectively, can be explained by the decomposition of calcite. The remainder potentially consists of unburnt organic carbon stemming from incomplete incineration. The SBulk sample had a much higher LOI than the PBulk sample, which likely reflects the different incineration processes used by Facility S and P. The incineration feedstock for Facility S is preprocessed to increase the quantity of organic materials. Thus, the higher LOI of SBulk may indicate relatively higher unburnt organic carbon than in PBulk. Further assessment using test methods that specifically measure organic carbon content should be used to assess the quality of “less than” BA for use in AAC since there is potential that unburnt carbon content can lead to inefficient aeration and poor performance.Results - Aeration Efficiency

[0113] Aeration Efficiency of Metallic Aluminum Powder. Hydrogen gas production due to the water-splitting reaction of metallic aluminum powder in lime-saturated aqueous solutions with 2N and 4N sodium hydroxide was measured over time. The 2N and 4N sodium hydroxide lime-saturated aqueous solutions are, respectively, referred to as the 2N and 4N solutions for brevity. Tests were conducted on 0.50 grams of metallic aluminum powder in 2N and 4N solutions as well as on 0.75 grams in the 2N solution. For brevity, the specimens were assigned IDs based on the mass of metallic aluminum powder and solution alkalinity. As an example, “AI_0.50 g_2N” refers to the specimen with 0.50 g of metallic aluminum powder in the 2N solution.

[0114] The gas volume measured during testing was corrected using Dalton’s law to account for water vapor under ambient laboratory temperature. The corrected results, presented in FIG. 19A, shows that the reaction of metallic aluminum powder in alkaline solutions occurred rapidly. Hydrogen gas production is shown for 0.50 and 0.75 grams of aluminum powder in lime-saturated solutions with varying concentrations of NaOH. The specimen label, “AI_0.50 g_2N”, indicates metallic aluminum powder at 0.50 grams in 2N NaOH lime-saturated solution. Moreover, solution alkalinity had a negligible impact on the yield and rate of hydrogen gas production from metallic aluminum powder. Results also indicated that the test for hydrogen gas production, from water-splitting chemical reactions, developed for this study was reasonably accurate and reliable. The solid and dashed“expected” lines are, respectively, used to depict the expected total volume of hydrogen gas generated by the complete reaction of 0.50 and 0.75 grams of pure metallic aluminum powder in alkaline aqueous solutions. To calculate the expected quantity of hydrogen gas that can be produced by the reaction of a certain mass of pure metallic aluminum in alkaline solutions, the chemical equations shown by Eqn. (1) and the density of hydrogen gas under the ambient laboratory temperature were used. Despite small variations in gas volume measurements, the expected and measured volumes of hydrogen gas are nearly similar. The difference between the measured and expected hydrogen gas volume generated by the reaction of the metallic aluminum powders in an alkaline solution varied by 3 to 5% after the measured hydrogen gas evolution curves stabilized. Eqns. (3a) and (3b) illustrate the watersplitting chemical reactions between aluminum, sodium hydroxide, and water.

[0115] Disregarding minor variations in the measured gas volume over the test duration, the gas generation curves in FIG. 19A indicate that the maximum volume of hydrogen gas occurred rapidly after the start of the reaction. For reference, the “start of reaction” occurs when aerating agents are added to the alkaline solutions in the reaction vessel. After maximums were reached, the hydrogen gas generation curves for the metallic aluminum powder specimens quickly stabilized and remained nearly constant during the remainder of the test duration. The sharp increase in hydrogen gas production during the early stages of hydration can be attributed to the fine particle size of the metallic aluminum powder. The reaction between water and metallic aluminum occurs on the surface of the metallic aluminum particles. The very fine metallic aluminum powder would have a high surface area available for reaction, resulting in a fast rate of hydrogen gas production. In contrast, the total yield, or volume, of hydrogen gas produced during the reaction is largely controlled by the mass of metallic aluminum available for reaction. This indicates that metallic aluminum content in the aluminum powders was likely exhausted when the gas generation curves reached their peak and became constant.

[0116] Key factors determining the effectiveness of aerating agents include the yield and rate of hydrogen gas production after the addition of fresh AAC slurries. Many variables can impact the yield and rate of hydrogen gas produced during the water-splitting reaction between metallic aluminum and aqueous solutions. For novel aerating agents with complex compositions such as “less than” BA, AAC producers need a way to accurately and quickly evaluate different beneficiation strategies to efficiently enhance aerating performance. This not only requires an accurate, fast, and reliable test method but also a practical evaluation framework. In conventional AAC production, metallic aluminum is expected to react rapidly,releasing nearly all the potential hydrogen gas within the first hour after addition to the fresh AAC slurry. This is because AAC slurries stiffen over time due to cementitious hydration reactions. Hydrogen gas produced before stiffening will effectively aerate the slurry. After a certain stiffness is achieved, hydrogen gas production will exert expansive stress and induce cracking in the surrounding cementitious matrix.

[0117] A framework for evaluating the aeration efficiency of “less than’’ BA for use in AAC production for this study was developed based on the maximum hydrogen gas generated within a certain time after the start of the reaction. The goal of this framework is to determine whether the beneficiation processes selected for this study (hammer milling and pulverization) can sufficiently enhance the potential aeration efficiency of “less than” BA for industrial applications. The results will be compared to those of metallic aluminum powder since it is the conventional aerating agent used in the field. However, caution should be used when developing a framework to assess aerating agents in practice. The 2N and 4N solution chemistries used in this study do not necessarily approximate the complex solution chemistries of typical AAC mixture designs. The alkalinities of the 2N and 4N solutions are likely to be much higher than what aeration agents will experience during use in AAC production. The alkalinities selected for testing were to assess the pH-sensitivity of the “less than” BA. Furthermore, chemicals present in fresh AAC slurries such as slurries and early- age cement hydrate products were not represented in the alkaline solutions used during testing. Although it was deemed appropriate for this study, the evaluation framework used in practice should consider the chemistries of the AAC mixture designs in which novel aerating agents will be used to ensure that the hydrogen gas production test results reflect in-situ performance. Developing solution chemistries and evaluation criteria that truly approximate the performance of novel aerating agents in AAC production will require further assessment.

[0118] The table of FIG. 19B summarizes the maximum volume of hydrogen gas produced within the first hour, the first two hours, and the entire 12-hour measurement period for metallic aluminum powder specimens. The table also highlights the percent ratio of the maximum volume of hydrogen gas produced within the first hour to the maximum measured across the 12-hour test period. Expectedly, nearly all the hydrogen gas that could be produced by a given mass of metallic aluminum powder was generated within the first hour after the reaction. This evaluation system was used to determine the practical applicability of “less than” BA as an aerating agent. In cases where “less than” 100% of the total hydrogen gas was generated within the first hour, engineering judgment was used to determine whether cost-effective adjustments to AAC mixture designs could be made or whether further processing was needed.

[0119] Given that a known quantity of metallic aluminum powder was used in each of the three aeration efficiency tests shown in the table of 19B, the average volume of hydrogengas per gram of metallic aluminum powder was calculated. This value can be used to determine the approximate metallic aluminum content in the SBulk and PBulk, based on aeration efficiency results across a test duration of 12 hours.

[0120] Aeration Efficiency of “less than” BA: Effects of Hammer Milling. Hydrogen gas generation was much slower in the hammer-milled PBulk specimens than in the metallic aluminum specimens. FIG. 20A shows hydrogen gas production for 25 grams of hammer- milled MSWI BA from Facility P in lime-saturated solutions with varying concentrations of NaOH. The specimen label, “PBulk_25 g_2N_HM”, indicates 25 grams of hammer milled PBulk in a lime-saturated 2N sodium hydroxide aqueous solution. As shown in the table of FIG. 20B, approximately 61% of the total volume of hydrogen gas produced during measurement was generated within the first hour by the hammer-milled PBulk specimen in the 4N solution. In the 2N solution, approximately 41% of the gas generation occurred within the first hour after the start of the reaction. Two observations can be made from the results: hammer-milled specimens are far more sensitive to solution alkalinity than metallic aluminum powder and the use of hammer-milled PBulk in AAC would require substantial adjustments to mixture designs. Potential adjustments include using alkali hydroxides such as sodium or potassium hydroxide to increase the alkalinity of fresh AAC slurries or ensuring fresh AAC mixtures remain fluid for longer periods by adding hydration retarders. While both approaches will increase material costs, the use of alkali hydroxides in high dosages can lower AAC strength while hydration delaying agents will increase production time since producers will have to wait longer for AAC specimens to stiffen before demolding, cutting, and autoclaving. Thus, it is unlikely that hammer-milled PBulk will have practical application as an aerating agent.

[0121] Aeration Efficiency of “less than” BA: Effects of Pulverization. Pulverization significantly enhanced the hydrogen gas production rate of “less than” BA compared to hammer milling. FIG. 21 A shows hydrogen gas production for 25 grams of pulverized MSWI BA from Facility P and Facility S in lime-saturated solutions with varying concentrations of NaOH. The specimen label, “PBulk_25 g_2N_Pulv”, indicates 25 grams of pulverized PBulk in a lime-saturated 2N sodium hydroxide aqueous solution. Furthermore, the pulverized ash was far less sensitive to solution alkalinity. Test results suggest that higher fineness and mechanical agitation through pulverization most likely contributed to the higher reactivity of pulverized “less than” BA compared to hammer milled “less than” BA. As discussed earlier, the rate of hydrogen gas production from water splitting reaction is largely attributable to the surface area available for reaction. The higher fineness of the pulverized “less than” BA, compared to the hammer-milled ashes, likely increased the surface area of metallic aluminum exposed to the alkaline aqueous solution. Moreover, past research has shown that the oxide layer inhibiting the water-splitting reaction of metallic aluminum under ambientconditions not only dissolves in high alkalinity but can also disintegrate during mechanical agitation, exposing more metal surface area for reaction with water. Mechanical pulverization exerted far more agitation and impact energy than hammer milling by hand, which may have disintegrated more of the reaction-impeding oxide layer. Overall, mechanically milling “less than” BA to sufficient fineness is an effective beneficiation strategy for use as an aerating agent in AAC. Mixture designs incorporating sufficiently fine and mechanically milled “less than” BA as aerating agents would likely not require adjustments to boost alkalinity.

[0122] The rate of gas generation during early periods of reaction was approximately similar to that of metallic aluminum powder. However, a key difference was that the timedependent hydrogen gas volume curves of the pulverized PBulk and SBulk specimens did not stabilize as quickly as they did for the metallic aluminum powders. This indicates the pulverized PBulk and SBulk specimens still had the potential to produce a slight amount of hydrogen gas after the first hour of reaction. This is seen in the table of FIG. 21 B which tabulates the percentages of hydrogen gas volume generated within the first hour of reaction relative to the maximum volume of gas generated during measurement for the pulverized “less than” BA specimens. In the 2N solutions, the pulverized SBulk and PBulk, respectively, generated about 98% and 95% of the maximum measured gas volume. In the 4N solutions, the values were 93% and 99%, respectively, for pulverized SBulk and PBulk. Although “less than” 100% of the reaction occurred within the first hour, the benefit from milling the “less than” BA to higher fineness for faster reactivity would likely be outweighed by the additional cost. Moreover, the metallic aluminum in “less than” BA is not necessarily pure since aluminum can undergo alloying and aggregation during incineration, resulting in different hydrogen gas production rates. Thus, the results were deemed sufficient for the use of “less than” PBulk and Sbulk for AAC production.

[0123] For both SBulk and PBulk, the maximum hydrogen gas generated during the entire 12-hour measurement period was similar across different solution alkalinities. Furthermore, the hydrogen gas generation curves in FIG. 21 A were approximately horizontal, with some variation across time. This may indicate that most of the reactive metallic aluminum in the different “less than” BA had reacted by the end of the 12-hour test duration. Using the pure metallic aluminum powder as a reference, the results of this test can be used to determine the approximate mass fraction of metallic aluminum in the PBulk and SBulk samples. Determining the metallic aluminum metal content can help AAC producers decide the most appropriate dosage of “less than” BA when used as an aerating agent. From tests conducted on metallic aluminum powder, the table of FIG. 19B shows that the average volume of hydrogen gas produced per gram of aluminum was 1282.3 ml_ H2 / g Al. Based on the average volume of hydrogen gas produced per gram of the pulverized “less than” BA samples during measurement, as shown in the table of FIG. 21 B, PBulk had anapproximate metallic aluminum content of 2.5%wt. while SBulk had a metallic aluminum content of about 2.9%wt.

[0124] It is important to use a cost-benefit analysis approach when evaluating new sources of aerating agents and potential beneficiation processes. If all the hydrogen gas needs to be generated within the first hour, then slightly more milling can be applied. Although the median particle sizes for the SBulk and PBulk were similar to that of the metallic aluminum power as shown in the table of FIG. 4B, the pulverized BAs had more particles in the coarser size fractions. Some of these coarser particles may have had metallic aluminum which contributed to hydrogen gas released after the first hour. Further milling, though, would increase the cost of production due to the higher energy input and may not yield substantially better results given that more than 93% of the maximum measured hydrogen gas volume occurred within the first hour. The composition of MSWI BA is heterogeneous due to the variability in the MSW incineration feedstock and thermal transformations that occur during incineration. Incineration at MSWI facilities occurs at temperatures of 850 °C and above, higher than the melting point of metallic aluminum (660 °C). This can lead to the formation of aluminum droplets or alloys with other metals during cooling

[0125] The results suggest that the hydrogen gas volume test method and a suitable evaluation framework can be valuable resources for AAC producers in assessing the quality of sampling “less than” BA and size reduction processes. For a better approximation of performance in situ, solution chemistries should be adjusted (pH and chemical compositions) to capture the fresh AAC environment. Moreover, for more effective framework development, the following should be considered during analysis: the proportion of hydrogen gas produced within the first hour relative to the total amount of hydrogen gas produced during a reasonable period (12 hours or more), improvements to the proportion of gas generated in the first hour due to different beneficiation processes, and cost-benefit analysis of different beneficiation processes.Results - Production and Performance Testing of Autoclaved Aerated Concrete

[0126] Compressive Strength and Dry Density Results. Strength and density are two of the most important parameters used in AAC construction. The Florida Building Code requires AAC masonry units to comply with ASTM C1693 strength classes, which subdivides AAC into classes based on dry density and compression strength. These strength classes provide uniform guidance on selecting the most appropriate type of manufactured AAC for a given construction application. The table of FIG. 22 provides a generalized summary of dry density limits and minimum compressive strength for strength classes, as defined in ASTM C1693. These were adopted to assess whether laboratory-scale specimens have sufficient performance for use in construction.

[0127] Results of compressive strength and dry density testing for laboratory- and industrial-scale specimens are summarized in the table of FIG. 23. Data is presented as the average of three replicates along with associated coefficients of variance (COVs). Testing was conducted on 50-mm cube specimens. Specimens were made with the fine UF sand except for specimens “AI_0.07AI_0.7W_1 E_AS” and “P10_0.6W_1E_AS” which were made with finely ground sand acquired from the industrial AAC producer in Florida, USA. Three AAC types were assessed: Al-Control, PBulk, SBulk, and Indust. The Al-Control, PBulk, and SBulk refer to laboratory-made specimens, based on the type of aerating agent used, while the Indust, type AAC specimens were acquired from an industrial AAC producer in Florida and produced using high-purity metallic aluminum paste.

[0128] In general, results indicate that pulverized PBulk and SBulk can be used as aerating agents in the production of code-compliant AAC. All laboratory-scale AAC controls made using metallic aluminum powder and most of the specimens made with pulverized “less than” BA were able to meet the strength and density requirements for at least one strength class defined in the table of FIG. 22. AAC specimens acquired from the industrial producer were able to meet requirements for strength classes 4 and 5. Most of the control specimens met the strength and density requirements for AAC 6, the strength class defining performance of the strongest and densest code-compliant AAC. Five of the nine specimens made using pulverized PBulk met requirements for AAC 5 and AAC 6, one PBulk-based AAC specimen met requirements for AAC 4, and one met those for AAC 3. The “P15_0.7W_0.1 E” did not meet the required minimum compressive strength for any strength class, despite having a dry density of at least 476.7 kg / m3. For AAC made with pulverized SBulk, one specimen met the requirements for AAC 4, one for AAC 2, and two did not meet the requirements for any strength class. Lower W / S, higher AEA dosage, and lower pulverized “less than” BA content increased the likelihood that AAC specimens made with PBulk and SBulk will meet requirements for at least one strength class.

[0129] Although the AAC specimens made with “less than” BA from either facility met conditions for AAC classification, the PBulk specimens were generally stronger and denser than those of the SBulk specimens. The most likely mechanism as to why PBulk produced stronger and denser AACs than SBulk was that the SBulk had a higher metallic aluminum content than PBulk. For example, the dry density and compressive strength of “S10_0.7W_0.1 E” were, respectively, 21% and 49% lower than those of “P10_0.7W_0.1 E”. Similarly, the density and strength of the “S10_0.6W_1 E” were, respectively, 15% and 38% lower than those of the “P10_0.6W_1 E”. The only difference between the SBulk and PBulk- based AAC specimens, in these cases, was the source of pulverized “less than” BA. The mass fraction of the SBulk and PBulk relative to the dry component mass of the AAC specimens was the same. This is consistent with ICP-AES data on environmentally availableconcentrations of aluminum, which indicated that SBulk had higher aluminum than PBulk. In terms of XRF data, the oxide concentrations of aluminum were similar in PBulk and SBulk.

[0130] According to results in the table of FIG. 23, key factors that influenced both strength and density for each AAC type were the W / S, aerating agent content (metallic aluminum powder, pulverized SBulk, and pulverized PBulk), silica sand fineness, and AEA dosage. A decrease in W / S increased both the strength and density of AAC mixtures. Change in the W / S ratio had a stronger effect on the density and strength of the “less than” BA based AAC specimens than in the control specimens. This effect may be due to the absorptive nature of the “less than” BA, even after pulverization. Moreover, lower metallic aluminum powder in the control specimens and lower PBulk and SBulk content in the “less than” BA-based AACs led to higher densities and lower strengths.

[0131] The use of the coarser sand (AS) decreased compressive strength in both the control and PBulk-based AACs but had differing effects on densities. For the PBulk sample, replacing the very fine sand (P10_0.6W_1 E) with the coarser sand (P10_0.6W_1 E_AS) decreased strength by 24% with negligible change in density. In the control AAC specimens, swapping out the fine UF sand (AI_0.07AI_0.7W_1 E) for the coarser industrial AS sand (AI_0.07AI_0.7W_1 E_AS) decreased strength by 46% and decreased density by 15%. Although there was a decrease in density, the percent decrease in density was not as substantial as it was for strength. Results indicated that strength loss in the control and PBulk-based AAC specimens when using coarser sand may be due to mechanisms other than just density loss. Past research suggests that finer sand can reduce the autoclaving time needed to generate tobermorite, which enhances the mechanical properties of AAC. During autoclaving, the greater reaction between silica and calcium hydroxide strengthens AAC partly by shifting the distribution of small pores towards finer sizes without affecting total pore volume. However, studies have also shown that finer sand can reduce strength by lowering the fluidity of the fresh AAC mixture and increasing air void content. In this study, both the control and “less than” BA-based AAC mixtures were mixed with PCE to improve fresh fluidity. This may have enhanced workability sufficiently to offset the effects of higher sand fineness on fresh properties and, thus, the overall strength after autoclaving.

[0132] Furthermore, the AEA dosage was found to strongly affect the performance of AAC made with SBulk and PBulk. Results indicated the strength and density of the PBulk and SBulk specimens increased substantially as AEA dosed increased up to an optimum. AEA doses greater than the optimum resulted in lower strength and density. Strength-to- density ratio can be used to more clearly show the effects of AEA dosage as well as other different mixture design parameters on the strength and density relationship of different AAC types. FIG. 24 displays the strength-to-density ratios of different laboratory and industrialscale AAC specimens. Ratios were calculated by dividing compressive strength by density.For a given AAC type, the specimens are ordered by decreasing strength-to-density ratios. Different colors are used to highlight ratios for different AAC types; the control metallic aluminum powder-based specimens are shown in black, the PBulk specimens in green, SBulk specimens in purple, and industrial-scale specimens in red. For the control, PBulk, and SBulk specimens, increasing the AEA dosage from 0.1 to 1 fl. oz (29.6 mL) per cwt, enhanced the strength-to-density ratio while increasing it to 1 fl. oz per cwt reduced the ratio. Moreover, higher AEA dosages were needed for the PBulk specimens to achieve similar strength-to-density ratios as the control specimen.

[0133] For practical applications, results suggested that some adjustments to AAC mixture designs may be needed when using “less than’’ BA as aerating agents. Among these adjustments, lower W / S and higher AEA dosages were the most effective in producing specimens with similar or better performance compared to the controls. However, these adjustments are not considered economically or logistically significant for industrial production.

[0134] Given the interdependence of AAC strength and density, their relationship can be used to compare the overall quality of AAC specimens made using different aerating agents and methods. FIG. 25 shows the relationship between compressive strength and dry density of laboratory- and industrial-scale AAC differentiated by AAC type displays the relationship of strength and density of different types of AAC studies in this research project. The relationships for AAC specimens are highlighted by different AAC types: control AAC specimens are shown in black circles, AAC made with PBulk are shown in green diamonds, specimens made with SBulk are shown in purple triangles, and the specimens manufactured by a large industrial producer are shown in red squares. The data indicated that the AAC made using conventional aerating agents was generally stronger than specimens made with “less than” BA with similar densities. The instances where PBulk and SBulk AAC specimens had similar or better strengths than the control specimens, with similar densities included specimens with the optimal dose of AEA and a W / S of 0.60. The general trend, though, may have resulted from the effects of “less than” BA on the fresh properties of the AAC slurries. During production, it was noted that fresh AAC slurries containing “less than” BA were less fluid than the control AACs, which may have resulted in lower aeration efficiency, poorer air void distribution, and lower strength. Although slightly more PCE was used in the AAC specimens with less than BA than in the controls, the use of PBulk and SBulk may require higher doses of PCE than used in this study. Moreover, the complex chemical and physical composition of MSWI BA is known to alter the reaction kinetics of conventional cementitious systems. There is potential that the reaction kinetics of AAC were impacted by the trace chemistry of “less than” BA during autoclaving.

[0135] Leaching Results. Monolith leaching results for a select set of AAC specimens made with metallic aluminum powder (Al) and PBulk are shown in the table of FIG. 26. Overall, the results indicate that monolith leaching risk from AACs does not increase substantially when PBulk is used as an aerating agent in this study. Of the assessed elements, leached elemental concentrations were generally similar across the measurement durations between the control and PBulk specimens. Aluminum and antimony, which were listed as COPCs in past work, were generally below detection limits across all specimens. Lead, a potential COPC for industrial applications, was found in elevated concentrations compared to other analyzed elements in the leaching solutions for the control and PBulk specimens. The specimen order, from greatest to lowest 28-day leached lead concentrations, was “P15_0.7W_0.1E” > “P10_0.7W_0.5E” > “P10_0.6W_1 E” = “AI_0.07AI_0.7W_1 E (Control)”. From the total environmentally available results, lead was found to be in elevated concentrations in the PBulk sample. Furthermore, the environmentally available elemental concentrations results indicated that PBulk had significantly higher lead concentrations than the UF sand that was partially replaced. This would suggest that some of the lead in the PBulk had leached out, but not in significant quantities. Cadmium was also found in elevated concentrations relative to the analyzed elements in the leached solutions. However, 28-day concentrations of leached cadmium in the PBulk specimens were similar or lower than that of the control, indicating that the leached cadmium was unlikely due to the PBulk.

[0136] Thermal Conductivity and Insulation. The results of thermal insulation testing are shown in the table of FIG. 27. Thermal insulation tests were conducted on specimens with a width and length of 2 inches (51 mm) and a thickness of 1 inch (25 mm) using a modified version of the single-sided guarded hotplate design with a single cold plate and a heat flux meter (ASTM C177). A 1 -inch (25-mm) thick rigid calcium silicate (CaSi) insulation board with a density of 40 lbs / ft3(640 kg / m3) and an R-Value of 1 .3 °F-ft2-hr / Btu was used as a reference. The width and thickness of the reference was cut to 2 inches (51 mm). The measured R-Values of the reference at 45 °C and 50 °C were respectively about 36% and 37% lower than the expected R-value of about 1 .3 as per the manufacturer. The error expected is largely due to the relatively high thickness-to-width ratio used in this study. A more accurate test would use specimens that had larger area-to-thickness ratios to minimize heat loss from the edges. However, the width and lengths of specimens used for thermal insulation testing were selected based on the maximum allowable size by the cement autoclave. However, the repeatability of the tests across different temperatures indicates that the results can be used to assess relative thermal insulation properties.

[0137] Results indicate that the thermal insulation properties of the PBulk AAC specimens were generally similar to the control AAC and AAC acquired from an industrialproducer. The laboratory-scale AAC specimens made with PBulk had similar R-Values as the control and the industrial AAC specimens. Moreover, the “P15_0.7W_0.5E” had the highest R-value amongst the AAC specimens, similar to that of the reference insulation board across both of the assessed temperatures.Results - Economic Feasibility of Incorporating “less than” BA into Industrial AAC Production

[0138] Economic Cost Analysis Results. Economic assessment indicated that the use of “less than” BA would reduce the cost of industrial AAC production, marginally, by approximately 7.3%, even under favorable assumptions. The price for each component, except for metallic aluminum powder, was obtained from USGS (2024). The price for metallic aluminum powder was obtained from past literature. Although the price of metallic aluminum powder is significantly higher than other AAC components, it is used in small quantities and thus constitutes a small fraction of the cost of a unit volume of AAC. The cost of industrial silica sand, cement, and lime constitutes the bulk of the cost of AAC per cubic meter. Since “less than” BA replaces the silica sand fraction, most of the reduction in cost in system 2 is due to the use of less sand.

[0139] Although favorable economics are important for end-users to adopt “less than” BA as a raw material, there are still gaps in the research regarding the performance of “less than” BA in AAC production. Elevated chlorides, heavy metals, and loss on ignition values, as observed in this work, have implications for the durability, environmental and health impacts, and fresh performance of AAC systems. Furthermore, current regulatory constraints hamper the reusability of “less than” BA in construction, especially those in residential areas where AAC is primarily used.

[0140] The feasibility of the fine fraction (“less than”) of MSWI BA as an aerating agent in AAC production was examined and shown. The dry components of AAC have a relatively small particle size which needs the determination of the most effective size reduction methods for “less than” BA which utilizes a combination of materials characterization and assessment of aeration efficiency. The determination of the technical feasibility includes an assessment the partitioned aluminum across particle size which was used to determine the optimal beneficiation processes to enhance the performance of “less than” BA as an aerating agent.

[0141] The materials characterization provided results which included that aluminum largely presided in the coarsest fractions of “less than” BA. This is likely indicative of the behavior of aluminum during incineration where the aluminum melts, forms fine droplets, and recombine with other metals alloys, or other sintered products or a process which can be defined as “uncontrolled alloying”. Although the aluminum fragments are small, the material they are bound is likely large. However, the fact that aluminum was mostly found in thecoarsest fractions precludes sieving as a less energetic method of size reducing the “less than” BA for use in AAC. Size reduction was needed for processing “less than” BA before use in AAC production. Two crushing methods were used: one that led to a coarse powder (hammer milled) and one that led to a fine powder (pulverized). The aeration efficiency of “less than” BA was assessed using hydrogen gas production rates. The finer portion of the “less than” BA achieved similar aeration efficiency, metallic aluminum powder which is the as a conventional aerating agent with the AAC industry. The reactivity of the finer “less than” BA was less sensitive to solution alkalinity and therefore, conventional AAC mixture designs can feasibly accommodate “less than” BA as an aerating agent without needing to adjust for alkalinity. Conversely, the coarser fraction of the “less than” BA utilizes a high quantity of alkali hydroxides to induce rapid dissolution to achieve sufficient aeration during the mixing and curing phase. The use of a higher pH solution would increase the costs of production and is not scalable to industry. Accordingly, the pulverized “less than” BA was used in the production of AAC.

[0142] The pulverized “less than” BA was incorporated into AAC as an aerating agent and was assessed for effects on density, strength, thermal insulation, and leaching. Control AAC was cast using metallic aluminum powder as the sole aerating agent. Additionally, two different types of AAC were acquired from an industrial producer and assessed for density, strength, and thermal insulation. Although the strength of the less than BA amended AACs was generally lower than those of the controls and the industrially produced AACs for a given density, the less than BA-amended AACs were able to meet strength class requirements for strength and density when incorporation rates were 10%wt. dry AAC materials. This would suggest that BA-amended AAC have potential for use in structural construction applications. Moreover, the use of a slightly coarser quartz silica sand, although reduced strength and the “less than” BA-amended AAC achieves similar strength-to-density ratio as the control when optimal doses of air-entraining agents (AEA) were used. This suggests that the “less than” BA negatively affects air void formation within AAC.

[0143] The potential of leaching was assessed using bulk monolith tests on AAC specimens made with “less than” BA and the control. With the exception of lead, the leaching of heavy metals leaching the “less than” BA-amended AAC was not of concern. The heavy metal concentrations were comparatively low in the leached solutions, while cadmium concentrations were found to be similar in the control and “less than” BA-amended specimens.

[0144] High thermal insulation is one of the many benefits offered by AAC over other masonry materials and cementitious systems. Based on the results of thermal insulation testing, AACs made with “less than” BA were able to develop similar or slightly better thermal insulation properties than control and AAC produced using industry standards.

[0145] Under economically favorable assumptions, the use of “less than” BA would decrease the cost of AAC production. This was largely because the inclusion rate of “less than” BA for effective AAC production was limited to 10%wt. of dry AAC components. Allowing higher addition rates would lead to more significant reductions in AAC production costs.

[0146] Municipal solid waste incineration (MSWI) is a sustainable waste management practice used to reduce landfill volume and recover energy. Incineration residuals, bottom ash (BA), and fly ash (FA) are often co-disposed in landfills to comply with hazardous waste regulations. There has been recent interest in finding sustainable and cost-effective ways of recycling BA in high-value markets such as construction. Past research demonstrates BA to be an effective construction material but also highlights limiting factors such as the presence of metallic aluminum, particularly in the “less than BA” fraction (MSWI BA < 3 / 8 inches (9.51 mm)). This research project examines the utility of “less than” BA as a raw material in autoclaved aerated concrete (AAC) production. Metallic aluminum powder or paste is extensively used as an AAC aerating agent; aluminum metal generates hydrogen gas in fresh AAC slurries to uniformly disperse air voids, leading to low density and a cellular matrix. Silica, in the form of finely ground quartz sand, is also required to develop sufficient strength in AAC for load-bearing construction applications. Given the high silica content and presence of metallic aluminum in “less than” BA, reuse as an aerating agent and partial silica source can be a cost-effective and sustainable alternative to landfilling. Research has shown that MSWI BA can be an effective raw AAC material but often, as a supplement to conventional aerating agents or with limited variations in mixture designs. The research presented in this study examined the use of “less than” BA, specifically, as a sole aerating agent and partial silica source with a focus on beneficiation (size-reduction processes) and practical mixture designs leading to AAC being useable in building construction. Laboratory assessment of two different sources of “less than” BA indicated that aluminum largely concentrated in the coarser fraction (> 1.18 mm), precluding the use of screening to isolate the fine fraction as an effective size-reduction technique. This necessitated crushing “less than” BA into a powder. Finer “less than” BA, although needing more grinding energy to produce, had similar aeration efficiency as conventional metallic aluminum powder. Unlike the coarser “less than” BA powder, using the finer “less than” BA did not require boosting alkalinity when used in AAC. Thus, finer “less than” BA was used to produce AAC specimens while metallic aluminum was used to produce control AAC specimens. Although strength was slightly lower compared to controls with similar density, AAC made with fine “less than” BA was able to adequately meet strength and density requirements for a range of standardized strength classes. This work demonstrated that “less than” BA can be used for load-bearing applications with slight adjustments to mixture designs. Moreover, thermalinsulation and bulk monolith leaching results for “less than” BA-amended AAC were similar to those of the controls. When considering current market values and proportions of typical materials used in industrial AAC production, economic cost analysis showed that “less than” BA can lower, albeit marginally, AAC production costs when inter-ground and co-stored with silica sand. Throughout this research, several areas for future research were identified. These include the fate and mobility of “less than” BA-borne chlorides in reinforced AAC systems, assessing methods of reducing organic carbon in “less than” BA, effects of organics removal on the fresh and hardened performance of AAC, fate, and transport of heavy metals in “less than” BA-amended AAC.

[0147] It should be emphasized that the above-described embodiments of the present disclosure are merely possible examples of implementations set forth for a clear understanding of the principles of the disclosure. Many variations and modifications may be made to the above-described embodiment(s) without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.

[0148] The term "substantially" is meant to permit deviations from the descriptive term that don't negatively impact the intended purpose. Descriptive terms are implicitly understood to be modified by the word substantially, even if the term is not explicitly modified by the word substantially.

[0149] It should be noted that ratios, concentrations, amounts, and other numerical data may be expressed herein in a range format. It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a concentration range of “about 0.1% to about 5%” should be interpreted to include not only the explicitly recited concentration of about 0.1 wt% to about 5 wt%, but also include individual concentrations (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.5%, 1.1%, 2.2%, 3.3%, and 4.4%) within the indicated range. The term “about” can include traditional rounding according to significant figures of numerical values. In addition, the phrase “about ‘x’ to ‘y’” includes “about x’ to about ‘y’”.

Claims

CLAIMSTherefore, at least the following is claimed:

1. A method for production of autoclaved aerated concrete (AAC), comprising: forming a bottom ash (BA) sand mixture by combining municipal solid waste incineration (MSWI) BA with quartz silica sand, the MSWI BA having a particle size of about 1.2 mm or less; generating an AAC slurry by mixing the BA sand mixture with at least cement, lime and water; filling a mold with the AAC slurry; and autoclaving the molded AAC slurry in the mold.

2. The method of claim 1 , wherein the MSWI BA have a particle size of about 170 pm or less.

3. The method of claim 2, wherein the MSWI BA have a particle size of about 30 pm or less.

4. The method of claim 3, wherein the MSWI BA have a particle size of about 15 pm or less.

5. The method of claim 1 , comprising pulverizing the MSWI BA and filtering the pulverized MSWI BA through a sieve stack prior to combining with the quartz silica sand.

6. The method of claim 5, wherein the MSWI BA is pulverized by hammer milling or disc pulverizing.

7. The method of claim 1 , wherein the MSWI BA is about 15%wt of a total dry component mass of the AAC slurry.

8. The method of claim 8, wherein the MSWI BA is about 10%wt of a total dry component mass of the AAC slurry.

9. The method of claim 1 , comprising prepping the mold for casting and steam curing.

10. The method of claim 9, wherein the mold is covered in high-temperature epoxy demolding tape.

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