Coal-derived materials for soil stabilization and methods of making the same

Abstract

Embodiments of the present disclosure relate to pyrolysis char stabilized soils (PCSSs). The PCSS includes a composition having a pyrolysis char (PC), cement, water, and soil. The composition is about 0.1% to about 50% of PC and about 1% to about 50% cement by weight. The method includes mixing a pyrolysis char (PC) and soil to form a dry mixture. Water and cement are mixed to form a cement mixture. The dry mixture and the cement mixture to form a wet mixture. The wet mixture is transferred to a mold to form a pyrolysis char stabilized soil (PCSS). The PCSS is cured. The PCSS is demolded and sealed.

Description

BACKGROUND Field

[0001] Embodiments of the present disclosure generally relate to soil stabilization materials. In particular, the disclosure relates to pyrolysis char stabilized soil (PCSSs) and methods of fabricating PCSSs. Description of the Related Art

[0002] Coal currently serves an important role as an energy source. However, an increasing demand for renewable energy has reduced the production and consumption of coal in the United States of America (USA). Coal is carbon-rich, and its use in energy generation may affect atmospheric CO2 levels. The air pollution and global environmental issues associated with the combustion of coal have limited the continuous application of coal in energy production. Specifically, according to the Bureau of Safety and Environmental Enforcement (BSEE), global warming results from a various greenhouse gas emissions is partly due to fossil fuel burning, such as the combustion of coal. Therefore, several studies are being conducted to create new nonenergy and fuel opportunities for Wyoming coal.

[0003] Wyoming is rated as one or the major producers of coal in the USA. The Wyoming Powder River Basin (PRB) coal plays an important role in the Wyoming energy industry. However, renewable energy is slowly replacing the coal industry, causing the market price of coal to drop. Thus, to attract new investment through technological innovation and support coal mine operations, environmentally friendly methods to create new diversified coal products are needed. One concern is characterizing the eco-efficiency of char products, which includes life-cycle metrics.

[0004] Fine-grain soil materials, such as silt and clay, are weak soils that exhibit low strength, high deformation, and less load bearing capacity. Fine grained soils have the capacity to attract and store water, due to the presence of negative charges on clay minerals that create a diffuse double layer between clay particles. The increase in water content reduces the strength of the soil. These characteristics lead the challenges for fine-grained soils. Soil stabilization is commonly used mitigation technique to improve the engineering properties of weak soils that create a soft ground.

[0005] Therefore, there is a need for improved soil stabilization products derived from coal and methods of fabrication thereof. SUMMARY

[0006] In one embodiment, a composition is disclosed. The composition includes pyrolysis char (PC), cement, water, and soil. The composition is about 0.1% to about 50% of PC and about 1% to about 50% cement by weight.

[0007] In another embodiment, a method is disclosed. The method includes mixing a pyrolysis char (PC) and soil to form a dry mixture. Water and cement are mixed to form a cement mixture. The dry mixture and the cement mixture to form a wet mixture. The wet mixture is transferred to a mold to form a pyrolysis char stabilized soil (PCSS). The PCSS is cured. The PCSS is demolded and sealed. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments and are therefore not to be considered limiting of its scope, and may admit to other equally effective embodiments.

[0009] Figure 1 illustrates a flow diagram of a method of forming a composition, according to embodiments of the disclosure.

[0010] Figure 2 A illustrates a micrograph of the SEM of the PC at 5 pm, according to embodiments of the disclosure.

[0011] Figure 2B illustrates a micrograph of the SEM of the PC at 50 pm, according to embodiments of the disclosure.

[0012] Figure 2C illustrates a micrograph of the SEM of the PC at 500 pm, according to embodiments of the disclosure.

[0013] Figure 3 illustrates a graph of the particle size distribution of soil, according to embodiments of the disclosure.

[0014] Figure 4 illustrates a graph of the water content percentage of the soil, according to embodiments of the disclosure.

[0015] Figure 5 illustrates a graph of the x-ray diffraction (XRD) analysis of PC, according to embodiments of the disclosure.

[0016] Figure 6 illustrates a graph of the Fourier-Transform Infrared Spectroscopy (FTIR) analysis of PC at varying pyrolysis temperatures, according to embodiments of the disclosure.

[0017] Figure 7 illustrates a graph of the FTIR analysis of PC pyrolyzed at 850°C, according to embodiments of the disclosure.

[0018] Figure 8 illustrates a graph of the density of the cement stabilized soil, according to embodiments of the disclosure.

[0019] Figure 9 illustrates a graph of the compressive strength of cement stabilized soil, according to embodiments of the disclosure.

[0020] Figure 10 illustrates a graph of the thermal conductivity of cement stabilized soil, according to embodiments of the disclosure.

[0021] Figure 11A illustrates a graph of an X-ray diffraction (XRD) pattern for untreated soil, according to embodiments of the disclosure.

[0022] Figure 11B illustrates a graph of an XRD pattern for stabilized soils, according to embodiments of the disclosure.

[0023] Figure 12A illustrates a graph of the thermogravimetric analysis and differential thermal analysis (TGA-DTA) of untreated soil, according to embodiments of the disclosure.

[0024] Figure 12B illustrates a graph of the TGA-DTA of stabilized soils, according to embodiments of the disclosure.

[0025] Figure 13 A illustrates a graph of the density of stabilized soils with 5% cement, according to embodiments of the disclosure.

[0026] Figure 13B illustrates a graph of the density of stabilized soils with 10% cement, according to embodiments of the disclosure.

[0027] Figure 13C illustrates a graph of the density of stabilized soils with 15% cement, according to embodiments of the disclosure.

[0028] Figure 14 illustrates a graph of the water content of stabilized soils with varying PC and cement material contents, according to embodiments of the disclosure.

[0029] Figure 15A illustrates a graph of the thermal conductivity of the stabilized soils at a cement content of 5%, according to embodiments of the disclosure.

[0030] Figure 15B illustrates a graph of the thermal conductivity of the stabilized soils at a cement content of 10%, according to embodiments of the disclosure.

[0031] Figure 15C illustrates a graph of the thermal conductivity of the stabilized soils at a cement content of 20%, according to embodiments of the disclosure.

[0032] Figure 16A illustrates a graph of the compressive strength of stabilized soils at 5% cement content, according to embodiments of the disclosure.

[0033] Figure 16B illustrates a graph of the compressive strength of stabilized soils at 10% cement content, according to embodiments of the disclosure.

[0034] Figure 16C illustrates a graph of the compressive strength of stabilized soils at 20% cement content, according to embodiments of the disclosure.

[0035] Figure 17A illustrates a graph of the axial strain versus axial stress of the pure-cement stabilized soil, according to embodiments of the disclosure.

[0036] Figure 17B illustrates a graph of the axial strain versus axial stress of the PCSS having 10% cement content, according to embodiments of the disclosure.

[0037] Figure 17C illustrates a graph of the axial strain versus axial stress of the PCSS having 20% cement content, according to embodiments of the disclosure.

[0038] Figure 17D illustrates a graph of the axial strain versus axial stress of the PCSS having 30% cement content, according to embodiments of the disclosure.

[0039] Figure 18A illustrates a graph of the shear strength of the stabilized soils, according to embodiments of the disclosure.

[0040] Figure 18B illustrates a graph of the axial strain at failure of the stabilized soils, according to embodiments of the disclosure.

[0041] Figure 18C illustrates a graph of the elastic modulus of the stabilized soils, according to embodiments of the disclosure.

[0042] Figure 18D illustrates a graph of the cohesion and angle of internal friction values of stabilized soils, according to embodiments of the disclosure.

[0043] Figure 19 illustrates a graph of the particle size distribution of PC and cement, according to embodiments of the disclosure.

[0044] Figure 20 illustrates the XRD analysis of the raw soil, according to embodiments of the disclosure.

[0045] Figure 21A illustrates a graph of the x-ray diffraction (XRD) analysis of pure-cement stabilized soil, according to embodiments of the disclosure.

[0046] Figure 2 IB illustrates a graph of XRD of PCSS with 30% PC, according to embodiments of the disclosure.

[0047] Figure 22A illustrates the thermogravimetric analysis (TGA) of pure-cement stabilized soil, according to embodiments of the disclosure.

[0048] Figure 22B illustrates the differential thermal analysis (DTA) of the pure-cement stabilized soil, according to embodiments of the disclosure.

[0049] Figure 22C illustrates the differential thermal analysis (DTA) of the PCSS with 30% PC, according to embodiments of the disclosure.

[0050] Figure 22D illustrates the differential thermal analysis (DTA) of the PCSS with 30% PC, according to embodiments of the disclosure.

[0051] Figure 23A illustrates a micrograph of the SEM images and a graph of the EDS results for the PCSS after curing 28 days, according to embodiments of the disclosure.

[0052] Figure 23B illustrates a micrograph of the SEM images and a graph of the EDS results for the PCSS after 28 days curing and 12 F-T cycles, according to embodiments of the disclosure.

[0053] Figure 23C illustrates a micrograph of the SEM images and a graph of the EDS results for the PCSS after 28 days curing and 12 W-D cycles, according to embodiments of the disclosure.

[0054] Figure 23D illustrates a micrograph of the SEM images and a graph of the EDS results for the PCSS after 28 days curing and 28 days of SA, according to embodiments of the disclosure.

[0055] Figure 24A illustrates a micrograph of PC of a PCSS after 28 days of curing and 12 F-T cycles, according to embodiments of the disclosure.

[0056] Figure 24B illustrates a micrograph of PC of a PCSS after 28 days of curing and 12 W-D cycles, according to embodiments of the disclosure.

[0057] Figure 24A illustrates a micrograph of PC of a PCSS after 28 days of curing and 28 days of SA, according to embodiments of the disclosure.

[0058] Figure 25A illustrates a graph of the weight change of stabilized soils with 5% cement content after 28 days curing and 12 F-T cycles, according to embodiments of the disclosure.

[0059] Figure 25B illustrates a graph of the volume change of stabilized soils with 5% cement content after 28 days curing and 12 F-T cycles, according to embodiments of the disclosure.

[0060] Figure 25C illustrates a graph of the weight change of stabilized soils with 10% cement content after 28 days curing and 12 F-T cycles, according to embodiments of the disclosure.

[0061] Figure 25D illustrates a graph of the volume change of stabilized soils with 10% cement content after 28 days curing and 12 F-T cycles, according to embodiments of the disclosure.

[0062] Figure 25E illustrates a graph of the weight change of stabilized soils with 20% cement content after 28 days curing and 12 F-T cycles, according to embodiments of the disclosure.

[0063] Figure 25F illustrates a graph of the volume change of stabilized soils with 20% cement content after 28 days curing and 12 F-T cycles, according to embodiments of the disclosure.

[0064] Figure 26A illustrates a graph of the weight change of stabilized soils with 5% cement content after 28 days curing and 12 W-D cycles, according to embodiments of the disclosure.

[0065] Figure 26B illustrates a graph of the volume change of stabilized soils with 5% cement content after 28 days curing and 12 W-D cycles, according to embodiments of the disclosure.

[0066] Figure 26C illustrates a graph of the weight change of stabilized soils with 10% cement content after 28 days curing and 12 W-D cycles, according to embodiments of the disclosure.

[0067] Figure 26D illustrates a graph of the volume change of stabilized soils with 10% cement content after 28 days curing and 12 W-D cycles, according to embodiments of the disclosure.

[0068] Figure 26E illustrates a graph of the weight change of stabilized soils with 20% cement content after 28 days curing and 12 W-D cycles, according to embodiments of the disclosure.

[0069] Figure 26F illustrates a graph of the volume change of stabilized soils with 20% cement content after 28 days curing and 12 W-D cycles, according to embodiments of the disclosure.

[0070] Figure 27A illustrates a graph of the weight change of stabilized soils with 5% cement content after 28 days curing and under 28 days of sulfate attack, according to embodiments of the disclosure.

[0071] Figure 27B illustrates a graph of the volume change of stabilized soils with 5% cement content after 28 days curing and under 28 days of sulfate attack, according to embodiments of the disclosure.

[0072] Figure 27C illustrates a graph of the weight change of stabilized soils with 10% cement content after 28 days curing and under 28 days of sulfate attack, according to embodiments of the disclosure.

[0073] Figure 27D illustrates a graph of the volume change of stabilized soils with 10% cement content after 28 days curing and under 28 days of sulfate attack, according to embodiments of the disclosure.

[0074] Figure 27E illustrates a graph of the weight change of stabilized soils with 20% cement content after 28 days curing and under 28 days of sulfate attack, according to embodiments of the disclosure.

[0075] Figure 27F illustrates a graph of the volume change of stabilized soils with 20% cement content after 28 days curing and under 28 days of sulfate attack, according to embodiments of the disclosure.

[0076] Figure 28A illustrates a graph of the compressive strength of the stabilized soils at a cement content of 5%, according to embodiments of the disclosure.

[0077] Figure 28B illustrates a graph of the compressive strength of the stabilized soils at a cement content of 10%, according to embodiments of the disclosure.

[0078] Figure 28C illustrates a graph of the compressive strength of the stabilized soils at a cement content of 20%, according to embodiments of the disclosure.

[0079] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. DETAILED DESCRIPTION

[0080] Embodiments of the present disclosure generally relate to soil stabilization materials. In particular, the disclosure relates to pyrolysis char stabilized soil (PCSSs) and methods of fabricating PCSSs. In one embodiment, pyrolysis char stabilized soil (PCSSs) are disclosed. In yet another embodiment, a method of forming PCSSs is disclosed.

[0081] The inventors have found new and improved methods of fabricating PCSSs and compositions for PCSSs from raw coal by mixing pyrolysis char (PC) with cement and soil to improve physical properties. Briefly, raw coal is thermo-chemically converted to produce PC, and the resulting PC is then converted to PC stabilized soil (PCSSs).

[0082] The desire for environmentally-friendly materials, energy savings, and reduced energy consumption in soil stabilization materials can be addressed by the materials described herein. Soil stabilization materials made with PC result in stabilized soil having increased density, increased strength and stiffness, decreased permeability, increased load bearing capacity, and reduced soil settlement when compared to conventional materials, such as pure-cement stabilized soil. Further, the stabilized soil have increased thermal conductivity and durability (e.g., wet-dry durability, freeze-thaw durability, and sulfate attack durability). Further still, the addition of PC facilitates the formation of physically and chemically bound water by consuming more free water. These materials, through recycling / reuse and decreasing the amount of energy usage in fabrication, further lessens the environmental impact of the PCSSs.

[0083] The use of headings is for the purposes of convenience and does not limit the scope of the present disclosure. Embodiments described herein can be combined with other embodiments.

[0084] As used herein, a “composition” can include component(s) of the composition, reaction product(s) of two or more components of the composition, a remainder balance of remaining starting component(s), or combinations thereof. Compositions of the present disclosure can be prepared by any suitable mixing process. COMPOSITIONS

[0085] Embodiments of the present disclosure generally relate to soil stabilization materials. In particular, the disclosure relates to pyrolysis char stabilized soils (PCSSs) and methods of fabricating PCSSs.

[0086] A composition (e.g., a PCSS) includes PC, cement, water, and soil. The PCSSs may include about 0.1% to about 50% of PC, such as about 5% to about 30% PC. The PCSSs may include about 1% to about 50% cement, such as about 5% to about 30% cement. The cement mixture may have a water to cement (w / c) ratio of about 0.5 to about 1.5, such as about 1.0.

[0087] The cement may include ordinary Portland Cement Type I, ordinary Portland Cement Type II are defined using ASTM C150 / C150M (ASTM 2022). Standard sand is defined using ASTM C33 / C33M (ASTM 2018).

[0088] The PC may include about 75% to about 85% fixed carbon, about 10% to about 20 % ash, about 1% to about 3% moisture, and about 0.5% to about 1.5% volatile matter. The PC may be pyrolyzed at between about 800°C and about 900°C, such as about 850°C.

[0089] The PCSSs have a compressive strength from about 1 MPa to about 5 MPa, such as about 3 MPA to about 4 MPa. The density of the PCSSs is from about 1.6 g / cm3 to about 1.9 g / cm3. The compressive strength of the PCSSs is greater than that of a pure-cement stabilized soil. The PCSSs have a thermal conductivity of about 0.2 W / mK to about 0.8 W / mK. The PCSSs have a shear strength of about 0.5 MPa to about 1.5 MPa. The PCSSs have an axial strain at failure of about 1.5% to about 4 %. The PCSSs have an elastic modulus of about 50 MPa to about 150 MPa. The PCSSs have a cohesion of about 300 kPa to about 400 kPa.

[0090] Figure 1 illustrates a flow diagram of a method 100 of forming a composition (e.g., pyrolysis char stabilized soils (PCSSs)). At operation 101, soil and PC are mixed to form a dry mixture. The PC and soil may be sieved. The soil was oven-dried at about 100°C to about 125°C, such as about 110°C for about 12 hours to about 26 hours, such as about 24 hours, before being sieved. The sieved PC and soil are weighed and mixed for 1 minute to about 5 minutes, such as about 3 minutes using a laboratory mixer to form the dry mixture. The soil was disturbed and collected at a shallow depth (less than about 0.5 m). The measured plastic limit of the soil was used as the initial water content of the soil at the depth.

[0091] At operation 102, water and cement are mixed to form a cement mixture. The water was weighed according to the w / c ratio in cement grout and soil’s plastic limit. The w / c ratio is about 0.5 to about 1.5, such as about 1.0.

[0092] At operation 103, the cement mixture and the dry mixture are mixed to form a wet mixture. The cement mixture and dry mixture are mixed for about 1 minute to about 5 minutes, such as about 3 minutes.

[0093] At operation 104, the wet mixture is transferred to cylindrical molds to form PCSSs. The molds are 100 mm of height by 50 mm of diameter. The wet mixture is transferred in three equal layers with each layer being struck 50 times to remove air bubbles and compact the wet mixture.

[0094] At operation 106, the PCSSs are cured. The PCSSs are cured for about hours to about 108 hours, such as about 72 hours. The molds may be covered with a plastic membrane to prevent moisture loss.

[0095] At operation 108, the PCSSs are demolded and sealed in an airtight container (e.g., a plastic bag). The airtight containers are stored in a laboratory environment with a relative humidity of -40% and a temperature of about 22°C. The PCSSs are cured for 7, 13, 28, and 60 days. USES

[0096] Embodiments of the present disclosure generally relate to soil stabilization materials. In particular, the disclosure relates to pyrolysis char stabilized soil (PCSSs) and methods of fabricating PCSSs. Compositions described herein can also be used for various applications.

[0097] Illustrative, but non-limiting, applications include soil-stabilizers, road construction material stabilizers, landfill stabilizers, and ground improvement materials.

[0098] The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to make and use embodiments of the present disclosure, and are not intended to limit the scope of embodiments of the present disclosure. Efforts have been made to ensure accuracy with respect to numbers used by some experimental errors and deviations should be accounted for. EXAMPLES Test Methods

[0099] The PC is sieved using ASTM No. 50 sieve (300 pm). Raw soil was sieved using ASTM No. 10 sieve (2 mm).

[0100] Thermal conductivity of PCSSs was measured using a thermal constant analyzer (e.g., a Hot Disk TPS 1500) with a sensor (Hot Disk Kapton-insulated) according to ISO 22007-2.

[0101] The triaxial compression test of the PCSSs is measured using GeoJac Digital Load Actuators at four different confining pressures of 25 kPA, 50 kPa, and 200 kPA and a constant strain control of about 0.5% / min.

[0102] Freeze-thaw durability tests for Experiment 1 are performed in accordance with ASTM C67 (2021). Freeze-thaw durability tests for Experiment 2 are performed in accordance with ASTM standard Cl645. Freeze-thaw durability tests for Experiment 3 are performed in accordance with ASTM standard C666. Freeze-thaw durability tests for Experiment 2 are performed in accordance with ASTM standard D560 (ASTM 2016). A total of 12 freeze-thaw (F-T) cycles were conducted for PCSSs. One F-T cycle was constituted of 24 hours freezing section at -23 °C (using a chest freezer with temperature control) and 24 hours thawing section at ambient temperature (23 ± 2 °C). The dimensions (including height and diameter) and weight of samples were measured at every freezing / thawing section (i.e., 24 hours) using a digital Vernier caliper and laboratory scale, respectively.

[0103] The water content of the PCSSs was measured according to ASTM D2216.

[0104] Wet-dry cycles were performed according to ASTM standard D559 (ASTM 2015b).

[0105] X-ray diffraction (XRD) of PCSSs is performed using a Rigaku SmartLab diffractometer, with a CuKa radiation source. The equipment was operated at 40 kV and 40 mA, and the angle of reflection (29) varied between 5° and 60°.

[0106] The scanning electron microscope (SEM) micrographs were made using FEI Quanta 250 SEM machine.

[0107] The thermogravimetric analysis and differential thermal analysis (TGA-DTA) was performed using ASTM Cl872. The thermogravimetric analysis was performed using TA Instruments Q500. The temperature was incrementally increased from room temperature to 950 °C at a rate of 10 °C / min, all within an argon gas environment flowing at 50 mL / min.

[0108] The particle size distribution (PSD) of PC and cement were quantified based on the laser diffraction method using Malvern Mastersizer 2000 particle size analyzer.

[0109] Sulfate attack testing was performed in accordance with ASTM standard C1012 (ASTM 2018) (for cement mortars).

[0110] Microstructural and morphological properties of PCSS were examined based on scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) using the Hitachi 3700N scanning electron microscope (in secondary electron mode). Prior to the SEM and EDS analysis, the PCSS were coated with a gold layer to improve image clarity. EXPERIMENTAL Characterization of PC

[0111] Figure 2 illustrates a micrograph of the scanning electron microscopy (SEM) of the PC. Figure 2A illustrates a micrograph of the SEM of the PC at 5 pm. Figure 2B illustrates a micrograph of the SEM of the PC at 50 pm. Figure 2C illustrates a micrograph of the SEM of the PC at 500 pm. PC is a light and porous coal byproduct with conchoidal fractures and bubbles. The SEM micrographs show surface roughness and the porous structures of the PC.

[0112] Table 1 shows a summary of the chemical composition of a pyrolysis char (PC). The PC in is fabricated from PC produced using Powder River Basin (PRB) coal in Wyoming. The coal is pyrolyzed at a temperature of about 850 °C. The predominant chemical components of PC include fixed carbon (about 81.3%), ash (about 16%), moisture (about 2.8%), and volatile matter (about 2.4%). The majority material is fixed carbon, while the amount of volatile contents contained in the PC are low (e.g., less than 3%). Table 1. Summary of the Chemical Composition of a Pyrolysis Char (PC). Material Ultimate Analysis Proximate Analysis N C O H S H2O Ash Volatile PC 1.05 81.31 14.77 2.07 2.8 2.77 15.93 2.4

[0113] Table 2 shows a summary of the material properties of the PC. The nitrogen adsorption isotherm measurements measured the average pore size and pore volume of the PC. The average pore size was about 1.4 nm. The pore volume was about 0.09 cm3 / g. The high BET surface area may promote the hydration of cement in soil. Table 2. Summary of the Material Properties of the PC. Property PC Heating Value 850°C Pore Volume 0.09 cm3 / g Average Pore Size 1.4 nm BET Specific Surface Area 262 m2 / g Elemental Composition C, Mg, Al, S, and Fe

[0114] Table 3 shows the results of the Brunauer, Emmett, and Teller (BET) specific surface area analysis of the PC. The BET analysis of the PC was about 262 m2 / g. Table 3. Summary of the BET Specific Surface Area Analysis of PC. BET surface area: 262.1657 ±2.1273 m2 / g Slope: 0.37219 ±0.00301 g / mmol Y-intercept: -0.00006   ±   0.00020 g / mmol C: -5,988.074414 Qm: 2.68725 mmol / g Correlation coefficient: 0.9999017 Molecular cross-sectional area: 0.1620 nm2 Relative Pressure (p / p°) Quantity       Adsorbed (mmol / g) l / [Q(p° / p-l)] 0.010368 2.64902 0.003955 0.031986 2.808293 0.011766 0.06736 2.911681 0.024805 0.079894 2.937881 0.029556 0.099875 2.97075 0.03735 0.031986 2.64902 0.003955 9.931986 2.898293 9.911766 9.96736 2.911681 9.924895 9.979894 2.937881 9.929556

[0115] Figure 3 illustrates a graph of the particle size distribution of soil. Table 4 shows a summary of the particle size distribution of the PC. The soil is coarse-grained, as shown by the high percentage of large-sized particles in Figure 3. Table 4. Summary of the Particle Size Distribution of the PC. PC Particle Size (pm) Composition (%) Average Composition (%) >499 5-6 5.6 499 12-19 14.7 399 21-25 23.9 75 42-59 46.1 <75 7-12 19.8

[0116] Figure 4 illustrates a graph of the water content percentage of the soil. Figure 5 illustrates a graph of the x-ray diffraction (XRD) analysis of PC. The XRD analysis indicates a peak at a 29 of about 26.55°. The peak may correspond with the presence of graphite and silicon. Other materials detected by the XRD analysis include carbon at a 29 of about 50°, sulphur at a 29 of about 23°, silicon at a 29 of about 69°, and nitrogen at a 29 of about 44°.

[0117] Figure 6 illustrates a graph of the Fourier-Transform Infrared Spectroscopy (FTIR) analysis of PC at varying pyrolysis temperatures. Figure 7 illustrates a graph of the Fourier-Transform Infrared Spectroscopy (FTIR) analysis of PC pyrolyzed at 850°C. The FTIR analysis may be used to determine the functional groups in the PC. FTIR identifies the characteristic fundamental vibrations of molecules to determine the molecular structure of a material. The PC is pyrolyzed at temperatures of 600°C, 700°C, 800°C, 850°C, and 900°C. The decomposition and evaporation of the organic matter during the pyrolysis of coal may cause the disappearance of vibrational bonds and a reduction in the intensity of the bands. The PC at all pyrolysis temperatures had a peak 691 at a wavenumber of 2919 cm'1 and a peak 692 at wavenumber 1439 cm'1. The peak 601 may indicate a stretching aliphatic C-H bond. The peak 602 may indicate an aliphatic C-H bond. An additional peak 603 for all PCs is observed at a wavenumber of about 1050 cm'1. The peak 603 may indicate stretching C-0 groups. A peak 604 is shown for the 600°C PC at a wavenumber of about 1600'1. The peak 604 may indicate bending ring C-H bonds. The intensity of the peaks generally decline as the pyrolysis temperature increases. This may be due to the decomposition of the organic matter, which turns carbon materials in graphitic-like materials.

[0118] At a wavenumber of about 882 cm'1, a peak 701 is observed which may indicate C-0 functional groups, such as cyclic anhydrides. The anhydride includes two carbonyls due to two carbons attaching to an oxygen atom. Between the wavenumbers of about 910 cm'1 and 1085 cm'1, a peak is observed, which may indicate a bending CH double bond of an alkene group. A vinylidene, cis and trans, may be observed at a wavenumber of about 890 cm'1, about 690 cm'1, and about 965 cm'1. The bands may be due to the C-H bond bending in the plane of a benzene ring. Benzene may exhibit a peak 702 at a wavenumber of about 1035 cm'1.

[0119] Between the wavenumbers of 1370 cm'1 and 1430 cm -1, a peak is observed which may indicate asymmetric methyl bending of CH3 or CH2. Aromatic rings may include a series of weak bands in the 2000 cm'1 to 1700 cm'1 range, which may arise from overtones and combinations of lower wavenumber vibrations. Benzene may exhibit bands in the 1959 cm'1 to 1814 cm'1 range. These bands may be used to determine a substitution pattern on a benzene ring.

[0120] A peak 704 between the wavenumbers 1620 cm'1 and 1899 cm'1 is observed, which may indicate a double bond of an alkene group. Therefore, the peak may be attributed to ring modes of an aromatic spectra. Further, a decreasing slope is observed from 1900 cm'1 to 4000 cm'1.

[0121] Figure 8 illustrates a graph of the density of the cement stabilized soil. Figure 9 illustrates a graph of the compressive strength of cement stabilized soil. Figure 10 illustrates a graph of the thermal conductivity of cement stabilized soil. Experiment 1

[0122] Table 5 shows a summary of the soil characteristics. Soil collected from the area around Laramie, Wyoming, has a plastic limit of about 23% and liquid limit of about 32%. The soil is classified as clayey sand (SC) according to the Unified Soil Classification System (USCS). Table 5. Summary of Soil Characteristics. Location Plastic limit (%) Liquid limit (%) Specific gravity Particle size distribution Soil type No. 4 (%) No. 8 (%) No. 40 (%) No. 100 (%) No. 200 (%) Laramie, WY 23 32 2.71 80.4 76.1 51.8 30.6 17.7 Clayey sand

[0123] A cement grout (CG or slurry), used in wet deep mixing or jet grouting for soft ground improvement, has water / cement (w / c) ratios of about 0.8 to about 1.2. To stabilize clayey sand (or clayey soil), a cement material content (defined as cement / dry soil weight ratio) ranges from about 2% to about 10%. For soft clay or soil with high clay content, the cement material content ranges from about 10% to about 40%. The addition of PC may reduce the bleeding of the cement grout and may lead to an increase in viscosity of PC cement grouts (PCCG) with a PC content (defined as PC / cement material weight ratio) from about 0.1% to about 50%. The pyrolysis char stabilized soil (PCSS) samples were prepared with three cement material contents (5, 10, and 20%), three PC contents (0, 10, 20, and 30%), and a w / c ratio of about 1.0.

[0124] The PC and raw soil are sieved. The raw soil was oven-dried at about 110°C for about 24 hours and sieved. The sieved PC and soil are weighed and mixed for 3 minutes using a laboratory mixer to form a dry mixture. The soil was disturbed and collected at a shallow depth (less than about 0.5 m). The measured plastic limit of the soil was used as the initial water content of the soil at the depth. Fresh water and cement material is mixed to make a cement mixture. The water was weighed according to the w / c ratio in cement grout and soil’s plastic limit. The cement mixture and the dry mixture are mixed to make a wet mixture. The cement mixture and dry mixture are mixed for about 3 min. The wet mixture is transferred to cylindrical molds to form PCSSs. The molds are 100 mm of height by 50 mm of diameter. The wet mixture is transferred in three equal layers with each layer being struck 50 times to remove air bubbles and compact the wet mixture. The molds are cured for about 72 hours while covered with a plastic membrane to prevent moisture loss. The PCSSs are demolded and sealed in an airtight container (e.g., a plastic bag). The airtight containers are stored in a laboratory environment with a relative humidity of -40% and a temperature of about 22°C. The PCSSs are cured for 7, 13, 28, and 60 days.

[0125] Figure 11A illustrates a graph of an X-ray diffraction (XRD) pattern for untreated soil. Figure 1 IB illustrates a graph of an XRD pattern for stabilized soils. The stabilized soils include pure-cement stabilized soils and PCSS. For untreated soil, minerals including gypsum (29 = 11.6°), calcite (29 = 29.4°), quartz (29 = 26.6°), and dolomite (29 = 31.0°) are observed. The PCSSs were cured for 28 days. The peaks for gypsum at 29 = 11.6° and 29 = 23.4° are not observed in the PCSSs. This may be due to the consumption of gypsum during cement hydration to form ettringite with a peak at 29= 15.8°.

[0126] Peaks associated with dolomite are observed in the PCSSs. At the ambient temperature, only a small amount of dolomite may be involved in the cement hydration reaction for forming the monocarbonate and hemicarbonate. The addition of carbonate ions from dolomite increases the CO2 / AI2O3 ratio, thus enhancing the formation of carbonate-AFm phases. Peak intensities in PCSSs are lower than cement stabilized soils. Higher peak intensities may be correlated with increased formation of crystalline phase. XRD patterns of cement stabilized soils show peak intensities of hydration products (e.g., ettringite and portlandite) that increase with curing time. Therefore, the addition of PC to stabilized soil may have less crystalline phases of soil minerals (e.g., quartz and dolomite) and hydration products (calcium silicate hydrate, CSH). This may be due to the addition of PC leading to acceleration of cement hydration, which facilitates formation of the amorphous CSH gel by consuming crystalline phases (e.g., alite and belite) in unhydrated cement. In addition, the participation of fine quartz particles in the pozzolanic reaction may reduce the intensities of characteristic peaks of quartz, e.g., more pre-existed fine quartz particles in soils are consumed in char-cement stabilized soil. Further still, compared to physically bound water, free water reacts with unhydrated cement particles. Compared to cement stabilized soil, the free water content of PCSSs would be reduced due to the PC with high specific surface area (262 m2 / g) may convert free water to physically bound water that is tightly attached to the PC. The crystalline phases of hydration products tend to be formed in an environment with more free water, contributing higher intensities of peaks in cement stabilized soils compared to that of PCSSs.

[0127] Figure 12A illustrates a graph of the thermogravimetric analysis and differential thermal analysis (TGA-DTA) of untreated soil. The cement content of the untreated soil is about 20% and is cured for 28 days. A peak for the minerals in untreated soil, including gypsum and carbonate minerals, is observed at from a dehydration temperature range of about 40°C to about 350°C (for physically bound water and gypsum). A peak is observed at a decarbonation temperature range from about 600°C to about 950°C for calcite and dolomite. The largest peak is observed at a temperature of about 128°C. This peak may be attributed to the dehydration of gypsum. The main dehydration temperature range for gypsum is between about 95°C to about 170°C. A narrow dehydration temperature range of about 100°C to about 130°C is consistent with the peak of the DTA curve at the same range for the untreated soil. Two peaks are observed at a range from about 753°C to about 798°C and a range of about 850°C to about 950°C. These peaks may be attributed to the decarbonation temperatures for dolomite and other forms of calcium carbonate (e.g., a chemical reagent, natural calcite, and natural limestone). Dolomite is a double salt consisting of calcium carbonate (CaCOs) and magnesium carbonate MgCCh. The decarbonation temperature for magnesium carbonate is about 680°C to about 850°C, while the decarbonation temperature of calcium carbonate is about 850°C to about 950°C. Thus, in the decarbonation range of untreated soil, the first peak from about 753°C to about 798°C may be attributed to both calcite and magnesium carbonate, while the second peak may be attributed to calcium carbonate in dolomite.

[0128] Figure 12B illustrates a graph of the TGA-DTA of stabilized soils. The graph illustrates a pure-cement stabilized soil and a PGSS. The dominant peak attributed to gypsum in the untreated soil is reduced in the PCSS. This may be due to a portion of the gypsum being consumed during the cement hydration reaction in the PCSS. Compared to the pure cement stabilized soil, higher peaks are observed in the PCSS for the dehydration of ettringite and CSH. This may be due to PC facilitating the cement hydration in the PCSS. Mild peaks which may be attributed to gypsum are observed in the pure cement stabilized soil when compared to the PCSS. This may be due to the nucleation and filler effects of adding porous PC in PCSS, which may facilitate the formation of the cementitious matrix and ettringite with consuming more gypsum. When compared to untreated soil, a decrease is observed in the peaks in the range of the dehydration and decarbonation temperatures. However, peaks around 400°C to about 550°C are observed, which may be attributed to the dehydroxylation of portlandite. In the decarbonation temperature range, the addition of PC may cause the peak associated with calcium carbonate in dolomite to shift to a lower temperature, when compared to the pure cement stabilized soil. The addition of PC may change the concentration of ions (e.g., Na+ and Mg2+) in the pore solution of PCSS. The main peaks for magnesium carbonate and calcium carbonate decomposition in dolomite may have shifted to lower temperatures due to addition NaCl and MgCl2.

[0129] Figure 13 A illustrates a graph of the density of stabilized soils with 5% cement. Figure 13B illustrates a graph of the density of stabilized soils with 10% cement. Figure 13C illustrates a graph of the density of stabilized soils with 15% cement. The stabilized soils include pure-cement stabilized soils and PCSSs. The density of the stabilized soils ranges from about 1.65 g / cm3 to about 1.88 g / cm3. At the same cement and PC content, the density increases as curing time increases from 7 days to 60 days. The PCSSs were kept in sealed conditions with constant room temperature. The volumetric expansion of the PCSSs may contribute to a decrease in the density of the PCSSs. For PCSSs with sulfate provided by gypsum, the volumetric expansion may be attributed to the formation of ettringite, the absorption of water by the formed ettringite, and osmosis-induced swelling of clay minerals.

[0130] A change in the PC content does not significantly affect the density of PCSSs. For example, at a fixed cement content, the density of PCSSs with a PC content of 30% is about 3.5% lower than that of pure cement stabilized soil. The density of the PCSSs decreases as the curing time increases. This may be due to the fact that, when compared to cement hydration products, such as CSH (1.9-2.0 g / cm3), portlandite (2.24 g / cm3), and ettringite (1.7-1.8 g / cm3), the porous PC has a low density (less than 1 g / cm3). In samples with low or no PC content, limited or no change was observed in the density of the stabilized soil.

[0131] Figure 14 illustrates a graph of the water content of stabilized soils with varying PC and cement material contents. The PCSS was cured for 28 days. For pure cement stabilized soils, the water content increased with increasing cement content. The higher amount of water may be due to the water incorporated during the wet mixture, since the w / c ratio in the cement mixture is fixed at 1:1. For samples with 10% PC, the water content of the PCSS decreased about 3.4%, 10.4%, and 20.3% compared to the pure cement stabilized soil at the same cement content. This may be due to 1) the physically bound water attaching to the porous PC that are not removed during at an oven-drying temperature of 110°C, which may cause a lower water content in the PCSS, or 2) the addition of PC facilitating the formation of CSH. The chemically bound water in CSH may be difficult to remove, and the dehydration temperature of CSH ranges from about 100°C to about 300°C. Therefore, compared to pure cement stabilized soils, more CSH formed with a higher content of chemically bound water may lead to a water content in PCSS.

[0132] At a fixed cement content, increasing the PC content may lead to an increase in the water content. Air-dried PC may have a water content of up to 7%, leading to a higher water content in the PCSS as more PC is added. Further, the exothermic reaction of cement hydration cannot be fully prevente4d by during in a sealed condition. Therefore, the high water holding capacity (170%) in PC may cause the free water to be held in the PCSS, increasing the water content as the PC increases. The increasing water content may lead to improved long-term strength performance for PCSSs, as the water held by the PC can be gradually released to promote further cement hydration.

[0133] Figure 15A illustrates a graph of the thermal conductivity of the stabilized soils at a cement content of 5%. Figure 15B illustrates a graph of the thermal conductivity of the stabilized soils at a cement content of 10%. Figure 15C illustrates a graph of the thermal conductivity of the stabilized soils at a cement content of 20%. Regardless of PC content, the thermal conductivity decreased as the cement curing time increased. This may be due to the formed hydration products and change in microstructural phases. The thermal conductivity of clinker phases in unhydrated cement (e.g., alite (3.35 W / mK) and belite (3.45 W / mK)) is higher than that of the main hydration products (e.g., CSH (0.5-1.25) W / mK and CH (1.32 W / mK)). As the curing time increased, the unhydrated cement products are consumed, resulting in a reduction in the thermal conductivity of the PCSS. Further, the porosity of the PCSS may increase as curing time increases. Due to the low thermal conductivity of air (0.026 W / mK), the porosity increase in the PCSS may cause more open space in capillary and gel pores filled with air, which may contribute to the reduction in thermal conductivity as the curing time increases.

[0134] The reduction in the thermal conductivity of PCSS may be beneficial for applications such as underground liquefied natural gas (LNG) constructions, where stabilized soil with low thermal conductivity may reduce the potential damages in adjacent facilities due to the temperature changes during the operation. For buildings with cement stabilized earth materials, the low thermal conductivity may reduce energy consumption within the household. At cement contents of 5% and 10%, regardless of various curing times, increasing the PC content in PCSS may lead to a decrease in thermal conductivity. For example, the thermal conductivity of PCSS with a PC content of 30% and a cement content of 5% and 10%, on average, were 18.7% and 9.9% lower than the corresponding pure cement stabilized soils. The promotion of more hydration products, such as CSH, and the porous structures of the PC may be the main factors contributing to the reduction in thermal conductivity.

[0135] At a cement content of 20%, in the early curing period, PC addition causes a decrease in thermal conductivity. As the curing time increased to 60 days, the thermal conductivity of PCSS with a PC content of 20% or 30%, were about 12.1% and about 28.5% higher than that of pure cement stabilized soils. This may be due to the high water content of the PC.

[0136] Figure 16A illustrates a graph of the compressive strength of stabilized soils at 5% cement content. Figure 16B illustrates a graph of the compressive strength of stabilized soils at 10% cement content. Figure 16C illustrates a graph of the compressive strength of stabilized soils at 20% cement content. Compared to pure cement stabilizers, PCSSs have an increased compressive strength. For example, at a cement content of 5%, regardless of the curing time, the compressive strength of the PCSS at 10% PC, 20% PC, and 30% PC is, one average, 16.1%, 8.6%, and 2% higher than the pure cement stabilized soil. This may be due to the fact that PC facilitates cement hydration and the formation of CSH and ettringite. Further, the pre-existing soil minerals, such as fine quartz and gypsum, may be more actively involved in the hydration reaction due to the addition of PC. The porous PC, with a high water holding capacity, may gradually release the held water to the coil cementitious matrix to promote the secondary cement hydration and further improve strength. As the cement content increases to 10% and 20%, the compressive strength of PCSS with a PC content of 30% is, on average, 15.6% to 23% higher than that of the corresponding pure-cement stabilized soil. At low cement contents of 5%, the compressive strength of the PCSS with a PC content of 30% is only 2% greater than the corresponding pure-cement stabilized soil. This may be due to the low cement content in the PCSS which, as PC content is increased, has a negative dilution effect of PC on the cement, leading to a decrease in compressive strength. The positive effects of promoting hydration of unhydrated cement through the water released by the PC is reduced due to the limited amount of cement, leading to minimal strength improvement.

[0137] Figure 17A illustrates a graph of the axial strain versus axial stress of the pure-cement stabilized soil. Figure 17B illustrates a graph of the axial strain versus axial stress of the PCSS having 10% cement content. Figure 17C illustrates a graph of the axial strain versus axial stress of the PCSS having 20% cement content. Figure 17D illustrates a graph of the axial strain versus axial stress of the PCSS having 30% cement content. The PCSSs and pure-cement stabilized soil have confining pressures of 25 kPa, 50 kPa, and 200kPa. As the confining pressure increases, brittle to ductile transition behaviors and an increase in the max shear strength may be observed in all PCSSs and the pure-cement stabilized soil. This may be due to a decrease in the degree of saturation and increase in the void ratio as cement hydration consumes water with increasing curing times. Further, as the confining pressure increases, the void ratio is decreased in the PCSS, which may lead to increased shear strength and ductile behavior. The initial stress-strain curves exhibit increasing slopes (i.e., a concave shape) in all PCSS samples. This may be due to the closure of cracks and compliant pores during the deviatoric loading. For the PCSSs under a confining pressure of 25 kPa, the corresponding axial strain at cracks closure (sCc) is higher than that of the corresponding pure-cement stabilized soil. This may be due to the addition of PC with porous structures.

[0138] Figure 18A illustrates a graph of the shear strength of the stabilized soils. Similar to the compressive strength, the shear strength of the PCSS is, on average, 35.7% higher than that of pure-cement stabilized soil at different confining pressures. This may be due to the PC facilitates cement hydration and a reaction between soil minerals, such as ettringite, and cement, which may lead to more ettringite and CSH formation.

[0139] Figure 18B illustrates a graph of the axial strain at failure of the stabilized soils. Figure 18C illustrates a graph of the elastic modulus of the stabilized soils. The axial strain and elastic modulus of PCSS are, on average, 26.7% higher and 15.8% lower, respectively, than that of pure-cement stabilized soil. This may be due to PC increasing the void ratio, leading to ductile behavior.

[0140] Figure 18D illustrates a graph of the cohesion and angle of internal friction values of stabilized soils. The graph is based on the Mohr-Coulomb criterion. Compared to pure-cement stabilized soil, the addition of PC lead to 17.7% higher cohesion and 16.7% higher angle of internal friction. This may enhance the stability and bearing capacity of soils and may be beneficial for multiple engineering applications, such as excavation, trenching, retaining walls and slope stability, embankments and roadway constructions, etc.

[0141] In summation, PCSSs utilizing PC gives the desired mechanical properties of a soil stabilizers. Compared to pure-cement stabilized soils, PCSSs have less crystalline phases of soil minerals and hydration products, which may be due to an acceleration of cement hydration and pozzolanic reaction and reduction of free water. At low PC contents, the water content of the PC is lower than that of pure-cement stabilized soil. This may be due to the addition of PC, which facilitates the formation of physically and chemically bound water by consuming more free water. As the PC content increases, the water content may increase in the PCSS. This may be due to preexisting water and higher water holding capacity in PC particles. Compared to pure-cement stabilized soil, regardless of different curing times, thermal conductivity and compressive strength of PCSS are 0-9%lower and 8-16% higher, respectively. Under triaxial compression, the addition of PC may further enhance the stability and bearing capacity with 35.7% higher max shear strength, 17.7% higher cohesion, and 16.7% higher angle of internal friction. Experiment 2:

[0142] Figure 19 illustrates a graph of the particle size distribution of PC and cement. The PC was produced from Powder River Basin coal in Wyoming at a pyrolysis temperature of 850°C. Based on the proximate analysis, the main chemical component of the coal char has been quantified as 80.05% fixed carbon by weight. Portland cement type I & II was used in this study. The Brunauer-Emmett-Teller (BET) specific surface areas of PC and cement were measured as 262 and 1.2 m2 / g, respectively. Table 6 shows a summary of the D10 / D50 / D90 particle sizes and span of PSD of PC and cement. Table 6. Summary of the Particle Sizes and Particle Size Distribution. Material Dio (pm) D50 (pm) D90 (pm) Span of PSD, (D90-D10) / D50 Coal char 4.99 53.38 180.55 3.29 Cement 2.60 13.07 34.83 2.46

[0143] The PCSS has a water / cement ratio of 1.0, cement content of 5%, 10%, and 20%, as defined as cement / dried soil weight ratio, and four PC contents of 0%, 10%, 20%, and 30%, as defined by char / cement weight ratio. The raw soil is collected from Laramie, Wyoming. The plastic limit (PL) and liquid limit (LL) of soil were measured as 23% and 32%, respectively. The particle size distribution of soil was obtained as 80.4% passing No.4 sieve (4.75 mm), 76.1% passing No. 8 sieve (2.36 mm), 51.8% passingNo. 40 sieve (0.425 mm), 30.6% passing No. 100 sieve (0.150 mm), and 17.7% passing No. 200 sieve (0.075 mm) by weight.

[0144] Figure 20 illustrates the XRD analysis of the raw soil. The soil was classified as clayey sand (SC) according to USCS. The XRD analysis identified minerals in crystalline phases, including calcite, dolomite, gypsum, and quartz. The raw soil underwent an oven-drying process set as 110°C and 24 hours, followed by sieving through a No. 10 sieve (2 mm). The weighted cement, PC, and dried soil were homogenously mixed for 3 minutes using a laboratory mixer. The raw soil samples were highly disturbed and extracted from a superficial layer at a depth of less than 0.5 m. The initial water content of raw soil was measured as only 5.1%. The PL of 23% was used as the designed water content of soil because PL is an important geotechnical property that can affect the strength performance of soil and in situ water content of natural soil is generally lower than the corresponding LL, except for some soft clays collected near the waterways. The total amount of water added to the dry mixture should be constituted by two parts: 1) water in a cement grout quantified based on w / c ratio of 1.0 and cement contents from about 0% to about 30%, and 2) water in the soil quantified based on the measured PL (23%). The water was added to the dry mixture for mixing another 3 minutes. Subsequently, the wet mixture was transferred to cylindrical molds (height = 100 mm and diameter = 50 mm) and tapped against the table for 50 blows per layer and three equal layers to remove the trapped air bubbles. Molds filled with wet mixtures were covered with plastic membranes and initially cured before demolding. After 72 hours, all samples were demolded, sealed using airtight plastic bags, and stored in an ambient environment (relative humidity = 40-45% and temperature = 23 ± 2 °C) until reaching 28 days. Nine replicate samples were prepared for each mixture proportion.

[0145] After completing the curing process (i.e., 28 days), the PCSSs were divided into three groups for conducting durability tests, including freeze-thaw (F-T) cycles, wet-dry (W-D) cycles, and sulfate attack (SA).

[0146] Total of 12 wet-dry (W-D) cycles were performed for PCSS. For each W-D cycle, the PCSS was submerged in water at ambient temperature for 6 hours. Subsequently, the PCSS were transferred to an oven at 70°C for 42 hours for drying. The dimensions and weight of PCSS were also measured after finishing each wetting / drying section.

[0147] A sulfate solution was prepared by mixing 50 g of sodium sulfate (Na2SO4) and 900 g of deionized water. PCSS was fully submerged in sulfate solution for soaking up to 28 days. The dimension and weight of samples were measured at 3, 7, 14, and 28 days. The volume change (or weight change) of the PCSS due to each freezing / thawing section, wetting / drying section, and designed soaking times at sulfate solution was determined with respect to the initial volume (or weight) of the PCSS cured for 28 days.

[0148] After completing respective F-T, W-D, and SA tests, the unconfined compressive strength tests were conducted with a constant displacement rate of 1 mm / min until failure. The small particles from the crushed PCSS were reserved for material characterization tests. For XRD and thermogravimetric analysis-thermal differential analysis (TGA-DTA), small particles were sieved through a 75 pm sieve and then oven-dried at 60°C for 24 hours.

[0149] Figure 21A illustrates a graph of the x-ray diffraction (XRD) analysis of pure-cement stabilized soil. Figure 2IB illustrates a graph of XRD of PCSS with 30% PC. The pure-cement stabilized soil and PCSS are tested after 12 F-T cycles, 12 W-D cycles, and 28 days of SA. For pure-cement stabilized soil, the clear peaks associated with ettringite (29 = 16°) are observed after 12 F-T cycles and 28 days of SA. By comparison, the peak for ettringite is not observed in the pure-cement stabilized soil that was cured for 28 days, tested prior to conducting any durability tests, and after 12 W-D cycles. This may be due to the fact that the cement hydration reaction continues with forming more hydrated products (including ettringite) in pure-cement stabilized soils during the F-T cycles and SA, which may contributes to higher intensities of ettringite observed in those pure-cement stabilized soils, as compared to the pure- cement stabilized soils cured for 28 days without undergoing the durability testing. In addition, no significant peak associated with ettringite is observed in the sample with W-D cycles. This may be due to the high drying temperature of 70°C. Compared to other common hydration products, the ettringite is thermally unstable and may start to decompose at a temperature of 60°C. Further, the sulfate-rich environment (i.e., the sample under 28 days of SA in this study) may promote the formation of ettringite in cement-stabilized soil.

[0150] As the PC is added to the cement-soil system, the intensities reduction and broadening peaks for most crystalline minerals in PCSS are observed, as compared to those peak characteristics in pure-cement stabilized soils. The addition of PC may facilitate a high degree of cement hydration with more calcium silicate hydrates (C-S-H) gel formed. This may be due to the favorable properties of PC in cement-based materials, which may include the filler effect of fine PC, nucleation effect caused by electrostatic force between negatively charged PC and positively charged parts in cement particles, and high water holding capacity cause by capillary force of porous structures in PC. As a higher amount of C-S-H is formed in PCSS, more soil minerals with crystalline phases (e.g., quartz and calcite) tend to be covered with C-S-H gel, which may lead to the reduction of the intensities of peaks due to the coating and shielding effects of amorphous C-S-H. The PC may also enhance the pozzolanic reactions and the involvement of fine quartz particles in the pozzolanic reaction. This may lead to a decrease of intensities of quartz peaks, as the pre-existed fine quartz particles from the raw soil are consumed with increasing the degree of structural disorder (i.e., transition from crystalline phase to amorphous phase). This may also contribute to the peak broadening and intensity weakening. It is worth noting that for PCSS, intensities of peaks associated with calcite and C-S-H (at 29 = 29-31°) in PCSS subjected to W-D cycles and SA are higher than that of PCSS subjected to F-T cycles. During cement hydration, crystalline phases of minerals may be formed in the environment with sufficient moisture. The PCSS subjected to W-D cycles and SA are fully submerged in the water and sulfate solution, respectively, which may lead to the formation of more minerals with crystalline phases (e.g., calcite and crystalline C-S-H) and hence the increase of intensities.

[0151] Figure 22A illustrates the thermogravimetric analysis (TGA) of pure-cement stabilized soil. Figure 22B illustrates the differential thermal analysis (DTA) of the pure-cement stabilized soil. Figure 22C illustrates the differential thermal analysis (DTA) of the PCSS with 30% PC. Figure 22D illustrates the differential thermal analysis (DTA) of the PCSS with 30% PC. The TGA-DTA analysis is performed after 12 F-T cycles, 12 W-D cycles, and 28 days of SA. In the DTA curves, peaks for the dehydration of hydrated products and bound water at a temperature range of about 60°C to about 350°C, dehydroxylation of portlandite and CH at a temperature range of about 400°C to about 500°C, and decarbonization of carbonate minerals, i.e., calcite and dolomite, at a temperature range of about 600°C to about 850°C, are observed for pure-cement stabilized soils and PCSS, respectively. Regardless of different conditions of F-T, W-D, and sulfate attack, the main weight loss (-20%) is observed at temperature > 600°C due to the decarbonation of minerals in both pure-cement stabilized soil and PCSS. The amount of cement (e.g., < 20% with respect to the weight of soil) and PC (< 6% with respect to the weight of soil) added to the stabilized soil system may have a limited effect on the TGA. The high content of preexisting calcite and dolomite in raw soil may more significantly affects the TGA and may lead to the high weight loss in the decarbonization temperature range.

[0152] In the dehydration temperature range, for pure-cement stabilized soils, three DTA subpeaks are observed which may correspond to ettringite, C-S-H, and gypsum. The first subpeak, associated with ettringite, of the pure-cement stabilized soil cured for 28 days is slightly lower than that of pure-cement stabilized soil after F-T and slightly higher than pure-cement stabilized soil after W-D. This may be due to the internal curing continuing at the thawing sections the pure-cement stabilized soil after F-T, which may increase ettringite formation. During drying sections, some ettringite loses crystalline water (i.e., chemically bound water), leading to the lower DTA peak in the pure-cement stabilized soil after W-D. The second subpeak, associated with C-S-H, of both pure-cement stabilized soil after F-T and W-D is higher than that of the pure-cement stabilized soil cured for 28 days. This may be due to the hydration reaction continuing during the durability tests, thus forming more hydration products (e.g., ettringite and C-S-H). The thermal stability of C-S-H is better than that of ettringite, which may lead to a higher second subpeak in the pure-cement stabilized soil after W-D. The third subpeaks, associated with gypsum, are observed in the pure-cement stabilized soil cured for 28 days and after SA. This may be the fact that, when compared to pure-cement stabilized soil cured for 28 days, the continued hydration causes more gypsum to be consumed by unhydrated cement, which may contribute to the disappearance of the DTA peak at the gypsum dehydration temperature for pure-cement stabilized soil after F-T and W-D. Further, the SA can crack in cement-based materials due to the excessively formed ettringite. The additional gypsum may be formed due to the reaction between sulfate ions and CH. In the dehydroxylation temperature range, the CH peak of the pure-cement stabilized soil after SA is noticeably lower than the other three pure-cement stabilized soil due to reacting with the sulfate ions and forming of gypsum.

[0153] ForPCSS, at the same curing condition (28 days), compared to pure-cement stabilized soil, the increment of ettringite and C-S-H peaks and disappearance of gypsum peak are found in PCSS. This may indicate that the addition of PC can facilitate the cement hydration by forming more ettringite and C-S-H, while consuming preexisted gypsum in raw soil. The C-S-H subpeak of PCSS after F-T is higher than that of PCSS cured for 28 days. However, the C-S-H subpeaks of PCSS after SA and W-D are higher and lower, respectively, than that of the PCSS cured for 28 days. This may be due to the fact that, compared to the other two durability tests (F-T and SA), PCSS subjected to 28 days of SA may absorb more bound water due to the high water holding capacity of PC. The bound water that is tightly attached to porous structures of PC may not be effectively removed at a lower temperature corresponding to the first subpeak of ettringite. A DTA peak at ~900°C may be observed due to the decomposition of Na2SO4 in an argon gas environment only in PCSS after SA. This may be due to the fact that PC absorbs the sulfate solution, causing the higher peaks associated with C-S-H (including bound water) and Na2SO4. Further, for PCSS during W-D cycles, the wet and dry sections provide sufficient water for the formation of hydration products and atmospheric CO2 for the formation of carbonate phases. Hence, the subpeak of C-S-H in PCSS after W-D is lower than that of PCSSs cured for 28 days, F-T, and SA mainly due to the carbonation of C-S-H and CH. This may be observed in the low DTA peak associated with CH and high DTA peak associated with carbonate mineral (calcite) in PCSS after W-D.

[0154] Table 7 shows a summary of the estimated bound water and CH contents in pure-cement cement stabilized soil and PCSS under various durability tests. Regardless of PC content, the bound water and CH contents of pure-cement stabilized soils and PCSSs after W-D and SA are lower than those cured 28 days and after F-T. This may be due to a loss of crystalline water in ettringite during W-D cycles and consumption of sulfate ions and CH to form gypsum. Table 7. Summary of the Estimated Bound Water and CH Content. Composition (%) T (°C) Cement stabilized soils Char-cement stabilized soils 28D 28D + 12F-T 28D+ 12W-D 28D+ SA 28D 28D+ 12F-T 28D+ 12W-D 28D+ SA Bound water 60 350 5.5 5.5 5.1 4.1 5.7 6.3 4.9 5.5 Portlandite (CH) 400 500 8.3 8.9 7.8 7.0 9.8 9.3 8.2 6.4

[0155] In the decarbonation temperature range, the total TGA weight loss for both pure-cement stabilized soil and PCSS cured for 28 days are about 20.56% and about 20.81%, respectively. Two stages of significant decreasing trend in TGA curves, corresponding to the decarbonation of calcite and dolomite, are observed. The weight loss associated with dolomite in PCSS (about 8.83%) is higher than that of pure-cement stabilized soil (about 7.99%). Calcite and dolomite have function as inert fillers and active participants during the cement hydration process, which may be affected by temperature, pH of pore solution, calcite-dolomite ratio, etc. The addition of PC may affect the chemical environment, e.g., ion dissolutions and pH values, in cement-soil systems with carbonate minerals and hinder dedolomitization. The stiffness of dolomite is higher than that of calcite. More inert dolomite serving as filler may be beneficial for strength development of PCSS.

[0156] Figure 23A illustrates a micrograph of the SEM images and a graph of the EDS results for the PCSS after curing 28 days. Figure 23B illustrates a micrograph of the SEM images and a graph of the EDS results for the PCSS after 28 days curing and 12 F-T cycles. Figure 23C illustrates a micrograph of the SEM images and a graph of the EDS results for the PCSS after 28 days curing and 12 W-D cycles. Figure 23D illustrates a micrograph of the SEM images and a graph of the EDS results for the PCSS after 28 days curing and 28 days of SA. The PCSS has a cement content of 20% and a PC content of 30%. After curing for 28 days, typical hydration products (including C-S-H gel and ettringite), calcite, and porous PC are observed in PCSS when compared to the surface morphology of cement pastes cured in a humidity chamber (relative humidity > 99%) and pore solution (to simulate similar concentrations of ions in cement paste) using the supercritical drying method. As curing time increases, the surface morphology of PCSS cured in a humidity chamber and pore solution are different, which exhibit sintered characteristics and reticular network structure of C-S-H gel with embedding ettringite. Although the PCSS is cured at a sealed condition and room temperature, a similar reticular structure of C-S-H gel with embedding ettringite is observed in PCSS. This may indicate that, due to addition of PC, the hydration process in PCSS is similar to the cement samples cured at pore solution, since sufficient water absorbed in PC can be gradually released to promote the cement hydration. Quartz is covered with C-S-H gel and the degree of crystallinity decreases. The intensity of peaks associated with quartz reduces due to shielding and coating effects of the formed C-S-H gel at a favorable curing condition because of the addition of PC in the cement-soil system.

[0157] After 12 F-T cycles, the morphology of C-S-H in PCSS is similar to that of PCSS cured for 28 days. Although some crystalline gypsum is observed based on SEM and EDS results, the amount of gypsum in amorphous phases found in the PCSS after F-T cycles indicates that the hydration reaction continues by consuming gypsum in soil during the F-T cycles. For PCSS after 12 W-D cycles, compared to PCSS cured for 28 days and 12 F-T cycles, the minerals have amorphous phases and / or are covered by C-S-H gel. The SEM and EDS results (with high peaks of aluminum and sulfate) indicate the existence of short needle-shaped ettringite. This may be due to the fact that during the oven drying sections, the rapid evaporation of pore solution through the large capillary pores (due to the addition of PC) in the porous reticular network structure accelerates the growth of C-S-H. Meanwhile, the W-D cycles may negatively impact the morphology of needle (or rod) like crystalline minerals (e.g., ettringite and gypsum) and the corresponding interlocking effect. For example, although the dehydrated ettringite may retain an intrinsic needle shape at the temperature up to 546°C, under the oven-drying condition, the length of ettringite needles decreases. This may be due to the loss of bound water and the weakening of the interlocking effect among the long ettringite needles that may be beneficial for strength development for PCSS. For PCSS after 28 days of SA, a large amount of crystalline gypsum is observed. This may be due to the reaction between CH and sulfate ions from the external solution. Due to the addition of PC, more sulfate solution may be transported to the internal soil samples because of capillary force of porous PC, which may lead to the formation of more needle / rod shaped crystalline minerals, which may enhance the interlocking effect and increase porosity on the strength performance of PCSS.

[0158] Figure 24A illustrates a micrograph of PC of a PCSS after 28 days of curing and 12 F-T cycles. Figure 24B illustrates a micrograph of PC of a PCSS after 28 days of curing and 12 W-D cycles. Figure 24A illustrates a micrograph of PC of a PCSS after 28 days of curing and 28 days of SA. For PCSS after 28 days of curing and 12 FT cycles and PCSS after 28 days of cuing and W-D cycles, the pore spaces of the PC are filled with hydration products. The hydrophobicity of surface of PC increases with increasing pyrolysis temperature due to the reduction of oxygen-containing functional groups (e.g., carboxyl and hydroxyl groups). The hydroxyl groups increase on the surface of PC treated in an alkaline environment (e.g., during the cement hydration in stabilized soils). This may enable the formation of hydration products in the pore spaces of the PC and increase the strength of PCSS. For PCSS after SA, hydration products are observed on the surface of the PC, which may contribute to the relatively low strength of the PCSS. This may be due to the hydrophobicity of PC, pH value of pore solution, Ca / Si ratio, etc.

[0159] Figure 25A illustrates a graph of the weight change of stabilized soils with 5% cement content after 28 days curing and 12 F-T cycles. Figure 25B illustrates a graph of the volume change of stabilized soils with 5% cement content after 28 days curing and 12 F-T cycles. Figure 25C illustrates a graph of the weight change of stabilized soils with 10% cement content after 28 days curing and 12 F-T cycles. Figure 25D illustrates a graph of the volume change of stabilized soils with 10% cement content after 28 days curing and 12 F-T cycles. Figure 25E illustrates a graph of the weight change of stabilized soils with 20% cement content after 28 days curing and 12 F-T cycles. Figure 25F illustrates a graph of the volume change of stabilized soils with 20% cement content after 28 days curing and 12 F-T cycles. Generally, regardless of different PC contents and F-T cycles, the average weight loss increases from 2.9% to 4.8% as cement content increases from 5% to 20%. As the cement content increases, a higher amount of water is added to the stabilized soils due to the fixed w / c ratio of 1.0. The weight loss of soil samples during the F-T cycles may be attributed to both water evaporation and ice sublimation. The increasing initial water content increases the water loss in stabilized soils. Although the hydration products serving as coating materials help prevent water evaporation and ice sublimation, reducing weight loss, the water content is still a factor affecting the weight change behavior of stabilized soil during F-T cycles. At the cement content of 5%, considering that the total amount of PC added is also limited (0.5-1.5% of the weight of soil), weight changes of all stabilized soil are similar. At the cement content of 10%, the weight loss of PCSS is lower after the 6th F-T cycle because PC addition promotes the cement hydration and hydration products with increased bound water content, which assists in a decrease of the free water loss during F-T cycles. As cement content increases to 20%, a relatively high weight loss is only found in PCSS with PC content of 30% after the 7th F-T cycle, indicating that increasing PC content may cause a negative impact on weight change due to the intrinsic hydrophobic surface of PC particles.

[0160] The average volume changes (including shrinkage and expansion) of pure-cement stabilized soils at cement contents of 5%, 10%, and 20% are -0.75%, -0.37%, and -0.31%, respectively. By comparison, the PCSS at cement contents of 5%, 10%, and 20% show lower volume changes, i.e., -0.49%, -0.15%, and -0.13%, respectively. This may be due to that fact that, in the freezing section, the transportation of free water from the internal to surface of soil samples (i.e., frost heaving) and free water to ice transition starting from the surface by gradually forming thin ice layer and closing preexisted microcracks due to volumetric expansion of ice contribute to the freezing shrinkage behavior of soil. PC addition leads to the decrease of free water content (by transforming into bound water) in the cement-soil system, which reduces the effect of frost heaving as less ice is formed on the surface, and causes a decreased volume change in PCSS. For untreated soil, both volumetric expansion and shrinkage after freezing depend on the degree of saturation of soil and soil particle realignment due to frozen pore water. The rigid structure in stabilized soil is formed due to hydration reaction and soil particle realignment. The formation of ice crystals within the stabilized soil during freezing may cause plastic deformation, which made lead to an enlargement of the inter-aggregate pores. The volume may exhibit expansion due to the persistence of the larger pore sizes after the thawing section. PC addition in the PCSS reduces plastic deformation by forming less ice, which contributes to decreased volumetric expansion. Compared to pure-cement stabilized soil, incorporation of PC facilitates hydration reaction with additional hydration products formed and reduced minerals in crystalline phases. This may enable formation of a more rigid structure with less volume change under F-T cycles.

[0161] Figure 26A illustrates a graph of the weight change of stabilized soils with 5% cement content after 28 days curing and 12 W-D cycles. Figure 26B illustrates a graph of the volume change of stabilized soils with 5% cement content after 28 days curing and 12 W-D cycles. Figure 26C illustrates a graph of the weight change of stabilized soils with 10% cement content after 28 days curing and 12 W-D cycles. Figure 26D illustrates a graph of the volume change of stabilized soils with 10% cement content after 28 days curing and 12 W-D cycles. Figure 26E illustrates a graph of the weight change of stabilized soils with 20% cement content after 28 days curing and 12 W-D cycles. Figure 26F illustrates a graph of the volume change of stabilized soils with 20% cement content after 28 days curing and 12 W-D cycles. The weight and volume changes of pure-cement stabilized soils at the cement contents of 5%, 10%, and 20% are about -10.5%, -10.8%, and -9.9%, respectively. The PCSSs exhibit similar weight changes, i.e., -10.2%, -10.5%, and -10.2%, respectively. This may indicate that the W-D testing conditions (e.g., oven temperature, soaking, and drying time) are a more dominant factor when compared to chemical compositions (e.g., different cement and PC contents) for determining the weight change behaviors of stabilized soils. At relatively low cement content (e.g., 5-10%), the average weight change of PCSS is slightly (2.8%) lower than that of pure-cement stabilized soil, as PC addition promotes cement hydration, thus forming additional hydration products and reducing the weight loss during the drying process due to the free water-to-bound water (in hydrates and PC particles) transition and wetting process. This may be due to micropores in stabilized soil structure and PC being filled and coated with more hydration products. As cement content increases to 30%, a minimal increment (3%) of average weight change is observed in the PCSS. This is due to the fact that, as cement content increases, the PC content also increases. Although the PC addition may still lower the weight change, more PC with high water holding capacity cause higher water absorption during the wetting process and a higher tendency to lose the water on PC particles due to capillary force during the drying process. Compared to cement stabilized soil, the volume change of stabilized soil subjected to W-D cycles of PCSSs show reduced volumetric shrinkages. This may indicate that PC addition improves the resistance of volume change under W-D cycles primarily due to increase of hydration products formed with rigid structure and enhanced coating and filling effects. A similar volumetric shrinkage is observed of pure-cement stabilized soil (raw soil = low plasticity clay (CL) and cement content < 20%) at the initial W-D cycles. However, after an average of 6-7 W-D cycles, volumetric expansion of pure-cement stabilized soil is obtained as the disintegration process dominates by creating large voids. By comparison, after achieving all 12 F-T cycles, no volumetric expansion is observed for the stabilized soils, which may be attributed to the raw soil having less expansive clay contents.

[0162] Figure 27A illustrates a graph of the weight change of stabilized soils with 5% cement content after 28 days curing and under 28 days of sulfate attack. Figure 27B illustrates a graph of the volume change of stabilized soils with 5% cement content after 28 days curing and under 28 days of sulfate attack. Figure 27C illustrates a graph of the weight change of stabilized soils with 10% cement content after 28 days curing and under 28 days of sulfate attack. Figure 27D illustrates a graph of the volume change of stabilized soils with 10% cement content after 28 days curing and under 28 days of sulfate attack. Figure 27E illustrates a graph of the weight change of stabilized soils with 20% cement content after 28 days curing and under 28 days of sulfate attack. Figure 27F illustrates a graph of the volume change of stabilized soils with 20% cement content after 28 days curing and under 28 days of sulfate attack. The high water holding capacity of PC enables a higher tendency of weight gain in PCSSs, especially for PCSSs with high char content (e.g., 30%) and / or at an early period of soaking time due to insufficient hydration products filled or coated on porous PC. As soaking time for SA increases, a higher weight in PCSSs may be attributed to absorption of sulfate solution. At cement content of 10%, the weight gain of stabilized soil with 20% PC content is higher than that with 30% PC content. However, the weight gain also does not always increase with increasing soaking time. For example, the weight gain of PCSSs with 30% PC content decreases as soaking time increases from 14 to 28 days. Other factors, including microstructures, contents and morphological properties of hydration products (e.g. weight reduction during SA is only observed in char-cement stabilized soil with a higher cement content of 10-20%), and ionic transportation and precipitation, may also affect weight change behaviors in PCSSs.

[0163] At cement contents of 5% and 10%, compared to pure-cement stabilized soil at 28 days of SA, the volume change (volumetric expansion) of PCSSs with PC contents of 20% and 30% is higher, while the volume change (slight volumetric expansion or shrinkage) of PCSSs with 10% PC content is lower. As the cement content increases to 20%, the volume change of all PCSSs tends to remain constant, which is lower than that of pure-cement stabilized soils. This may be attributed to the promotion of gypsum formation, suppression of ettringite formation, and changes in pore spaces in soil structures and PC particles. For cement-based materials subjected to SA, the volumetric expansion and subsequent cracks developed can be attributed to the formation of both ettringite and gypsum (Tian and Cohen 2000). Ettringite favors a relatively high pH (> 10.7) environment of pore solution. As pH decreases below 10, only gypsum remains the stable phase. PC addition facilitates the sulfate solution (pH = 7) absorption in stabilized soils and hence suppresses the ettringite formation by reducing the pH value of the pore solution. The pH value is also affected by the dissolved CH and consumption of CH by reacting with sulfate ions. Promoting gypsum formation leads to the decrease of pH value. At a lower cement content (5-10%), as more PC is added to the stabilized soil, the promotion of gypsum formation contributes to the volumetric expansion. As cement content increases to 20%, more hydration products are formed, developing a rigid structure. The newly formed gypsum tends to fill the pre-existed void spaces and cause the closure of cracks / pores in soil structures / PC, contributing to the limited volume change at the macroscopic level.

[0164] Figure 28A illustrates a graph of the compressive strength of the stabilized soils at a cement content of 5%. Figure 28B illustrates a graph of the compressive strength of the stabilized soils at a cement content of 10%. Figure 28C illustrates a graph of the compressive strength of the stabilized soils at a cement content of 20%. The stabilized soils are cured for 60 days, cured for 28 days and 12 F-T cycles, cured for 28 days and 12 W-D cycles, and cured for 28 days and under 28 days of SA. Regardless of durability test conditions, the compressive strength of PCSS is consistently better than that of pure-cement stabilized soil at the same cement content. For cement contents of 5%, 10%, and 20%, the optimum PC contents (with the highest compressive strength) of PCSS are found at 10%, 30%, and 30%, respectively. The comprehensive strength improvement in PCSS due to PC addition may be attributed to the promotion of cement hydration and formation of amorphous hydrates (e.g., C-S-H gel) or crystalline products (e.g., gypsum in samples after SA) with covering soil minerals and filling voids. The compressive strength of PCSS with cement content of 5% and PC contents of 20% and 30% after SA is lower than the corresponding pure-cement stabilized soil. This may be due to the fact that the pure-cement stabilized soil has a less rigid structure formed, and the promotion of gypsum formation due to PC addition may cause a reduction in strength by creating additional cracks. At the same cement and PC contents, the compressive strength of stabilized soil after SA is consistently lower than that of stabilized soil after F-T and W-D. This may be due to the decalcification of C-S-H and microcracks caused by the formation of ettringite and gypsum.

[0165] In summation, the PCSS cured for 28 days and after various durability test conditions have reduced intensities and broadening peaks for most crystalline minerals due to an increase in the formation of hydration products. This may be due to PC additions leading to more soil minerals with crystalline phases (e.g., quartz and calcite), which tend to be covered with amorphous C-S-H gel.

[0166] Upon 28 days of curing, PCSSs, in comparison to pure-cement stabilized soil, demonstrate an increase in DTA peaks associated with ettringite and C-S-H and a disappearance of DTA peak associated with gypsum. This may be due to PC facilitating cement hydration, forming more ettringite and C-S-H, and concurrently consuming preexisting gypsum in the raw soil.

[0167] The reticular structure of C-S-H gel with embedding ettringite is observed in PCSS cured for 28 days and after F-T cycles and W-D cycles. This may be due to sufficient water being absorbed in PC, which can be gradually released to promote cement hydration. A large amount of crystalline gypsum (with less ettringite formed) is found in the SEM image of PCSS after SA, which may be due to the promotion of gypsum formation and suppression of ettringite formation, as PC can more effectively absorb external sulfate solution and hence reduce pH value of pore solution.

[0168] Subjected to 12 F-T cycles and 12 W-D cycles, most PCSSs exhibit better volumetric stability (i.e., less volume change) compared to pure-cement stabilized soil. For stabilized soils after 28 days of SA, the volume changes of PCSSs with a low char content (10%) and / or high cement content (30%) tend to remain constant.

[0169] The compressive strength improvement in most PCSSs subjected to F-T cycles, W-D cycles, and SA is achieved due to PC addition, which may promote cement hydration and form more amorphous hydration products by filling voids or covering soil minerals. EMBODIMENTS LISTING

[0170] Clause 1. composition, including: pyrolysis char (PC); cement; water; and soil, wherein the composition is about 0.1% to about 50% of PC and about 1% to about 50% cement by weight.

[0171] Clause 2. The composition of clause 1, wherein the composition has a water to cement ratio (w / c) of about 0.5 to about 1.5.

[0172] Clause 3. The composition of clause 1, wherein the cement may include ordinary Portland Cement Type I or ordinary Portland Cement Type II.

[0173] Clause 4. The composition of clause 1, wherein the PC may include about 75% to about 85% fixed carbon, about 10% to about 20 % ash, about 1% to about 3% moisture, and about 0.5% to about 1.5% volatile matter.

[0174] Clause 5. The composition of clause 1, wherein the PC may be pyrolyzed at between about 800°C and about 900°C, such as about 850°C.

[0175] Clause 6. The composition of clause 1, wherein the composition has a compressive strength from about 1 MPa to about 5 MPa.

[0176] Clause 7. The composition of clause 1, wherein the composition has a compressive strength from about 3 MPA to about 4 MPa.

[0177] Clause 8. The composition of clause 1, wherein the composition has a density from about 1.6 g / cm3 to about 1.9 g / cm3.

[0178] Clause 9. The PCSS of clause 1, wherein the PCSS has a thermal conductivity of about 0.2 W / mK to about 0.8 W / mK.

[0179] Clause 10. The composition of clause 1, wherein composition has a shear strength of about 0.5 MPa to about 1.5 MPa.

[0180] Clause 11. The composition of clause 1, wherein the composition has an axial strain at failure of about 1.5% to about 4 %.

[0181] Clause 12. The composition of clause 1, wherein the composition has an elastic modulus of about 50 MPa to about 150 MPa.

[0182] Clause 13. The composition of clause 1, wherein the composition has a cohesion of about 300 kPa to about 400 kPa.

[0183] Clause 14. A method of forming a composition, the method comprising: mixing a pyrolysis char (PC) and soil to form a dry mixture; mixing water and cement to form a cement mixture; mixing the dry mixture and the cement mixture to form a wet mixture; transferring the wet mixture to a mold to form a pyrolysis char stabilized soil (PCSS); curing the PCSS; and demolding and sealing the PCSS.

[0184] Clause 15. The method of clause 14, wherein the PC and the soil are sieved before mixing the PC and soil.

[0185] Clause 16. The method of clause 15, wherein the PC is sieved using an ASTMNo. 50 sieve (300 pm).

[0186] Clause 17. The method of clause 15, wherein the raw soil was sieved using ASTM No. 10 sieve (2 mm).

[0187] Clause 18. The method of clause 15, wherein the soil is oven-dried at about 100°C to about 125°C for about 12 hours to about 26 hours before being sieved.

[0188] Clause 19. The method of clause 14, wherein the PC and soil are mixed for 1 minute to about 5 minutes.

[0189] Clause 20. The method of clause 14, the water and cement are mixed at a ratio of about 0.5 to about 1.5.

[0190] Clause 21. The method of clause 14, wherein the cement mixture and dry mixture are mixed for about 1 minute to about 5 minutes.

[0191] Clause 22. The method of clause 14, wherein the molds are 100 mm of height by 50 mm of diameter.

[0192] Clause 23. The method of clause 14, wherein the PCSSs are cured for about hours to about 108 hours.

[0193] Clause 24. The method of clause 14, wherein the molds are covered with a plastic membrane.

[0194] Clause 25. The method of clause 14, wherein the PCSSs are sealed in an airtight container.

[0195] Clause 20. The method of clause 25, wherein the airtight containers are stored in a relative humidity of-40% and a temperature of about 22°C.

[0196] Clause 20. The method of clause 14, wherein the PCSSs are cured for about 7 to about 60 days.

[0197] As is apparent from the foregoing general description and the specific aspects, while forms of the aspects have been illustrated and described, various modifications can be made without departing from the spirit and scope of the present disclosure. Accordingly, it is not intended that the present disclosure be limited thereby. Likewise, the term “comprising” is considered synonymous with the term “including.” Likewise whenever a composition, process operation, process operations, an element or a group of elements is preceded with the transitional phrase “comprising,” it is understood that we also contemplate the same composition or group of elements with transitional phrases “consisting essentially of,” “consisting of,” “selected from the group of consisting of,” or “Is” preceding the recitation of the composition, process operation, process operations, element, or elements and vice versa, such as the terms “comprising,” “consisting essentially of,” “consisting of’ also include the product of the combinations of elements listed after the term.

[0198] For purposes of this present disclosure, and unless otherwise specified, all numerical values within the detailed description and the claims herein are modified by “about” or “approximately” the indicated value, and consider experimental error and variations that would be expected by a person having ordinary skill in the art. For the sake of brevity, only certain ranges are explicitly disclosed herein. However, ranges from any lower limit may be combined with any upper limit to recite a range not explicitly recited, as well as, ranges from any lower limit may be combined with any other lower limit to recite a range not explicitly recited, in the same way, ranges from any upper limit may be combined with any other upper limit to recite a range not explicitly recited. For example, the recitation of the numerical range 1 to 5 includes the subranges 1 to 4, 1.5 to 4.5, 1 to 2, among other subranges. As another example, the recitation of the numerical ranges 1 to 5, such as 2 to 4, includes the subranges 1 to 4 and 2 to 5, among other subranges. Additionally, within a range includes every point or individual value between its end points even though not explicitly recited. For example, the recitation of the numerical range 1 to 5 includes the numbers 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, among other numbers. Thus, every point or individual value may serve as its own lower or upper limit combined with any other point or individual value or any other lower or upper limit, to recite a range not explicitly recited.

[0199] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof.

Claims

1. A composition, comprising:pyrolysis char (PC);cement;water; andsoil, wherein the composition is about 0.1% to about 50% of PC and about 1% to about 50% cement by weight.

2. The composition of claim 1, wherein the composition has a water to cement ratio (w / c) of about 0.5 to about 1.5.

3. The composition of claim 1, wherein the PC may be pyrolyzed at between about 800°C and about 900°C, such as about 850°C.

4. The composition of claim 1, wherein the composition has a compressive strength from about 1 MPa to about 5 MPa.

5. The composition of claim 1, wherein the composition has a compressive strength from about 3 MPA to about 4 MPa.

6. The composition of claim 1, wherein the composition has a density from about 1.6 g / cm3 to about 1.9 g / cm3.

7. The composition of claim 1, wherein the composition has a thermalconductivity of about 0.2 W / mK to about 0.8 W / mK.

8. The composition of claim 1, wherein composition has a shear strength of about 0.5 MPa to about 1.5 MPa.

9. The composition of claim 1, wherein the composition has an elastic modulus of about 50 MPa to about 150 MPa.

10. The composition of claim 1, wherein the composition has an axial strain at failure of about 1.5% to about 4 %.

11. A method of forming a composition, the method comprising:mixing a pyrolysis char (PC) and soil to form a dry mixture;mixing water and cement to form a cement mixture;mixing the dry mixture and the cement mixture to form a wet mixture;transferring the wet mixture to a mold to form a pyrolysis char stabilized soil (PCSS);curing the PCSS; anddemolding and sealing the PCSS.

12. The method of claim 11, wherein the PC and soil are mixed for 1 minute to about 5 minutes.

13. The method of claim 11, the water and cement are mixed at a ratio of about 0.5 to about 1.5.

14. The method of claim 11, wherein the cement mixture and dry mixture are mixed for about 1 minute to about 5 minutes.

15. The method of claim 11, wherein the PC and the soil are sieved before mixing the PC and soil.

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