Environment-friendly light jet mortar material produced from municipal waste incineration bottom ash

Abstract

The invention belongs to the technical field of mortar materials, and particularly discloses an environment-friendly light jet mortar material produced from municipal waste incineration bottom ash, which comprises the municipal waste incineration bottom ash, a cementing material, a water reducing agent, an accelerator and water, the cementing material comprises cement, silica fume and fly ash, the addition amount of the municipal waste incineration bottom ash accounts for 40-50% of the total mass, and the addition amount of the water reducing agent accounts for 10-20% of the total mass. The addition amount of the coal ash accounts for 0-18% of the total mass, the addition amount of the silica fume accounts for 0-12% of the total mass, the addition amount of the accelerator accounts for 6-9% of the total mass, and the use amount of the water reducing agent accounts for 1.5 wt% of the use amount of the cementing material. According to the environment-friendly light jet mortar material produced by adopting the municipal waste incineration bottom ash, in order to reduce the influence of the municipal waste incineration bottom ash on the environment and find a substitute of natural sand, the potential application of the municipal waste incineration bottom ash as a fine aggregate is discussed; meanwhile, the influence of the auxiliary cementing material on improvement of the performance of the jet mortar prepared from the municipal waste incineration bottom ash is investigated.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and more particularly to an environmentally friendly lightweight shotcrete mortar material produced from municipal solid waste incineration bottom ash. Background Art

[0002] Shotcrete or shot mortar is a new type of building material that is transported through a pipeline by a spraying machine using compressed air or other power and applied to the sprayed surface. Due to its fast construction speed, simple process, and flexible construction operation mode, shotcrete is widely used in projects such as slope and tunnel excavation surface stabilization, structural repair, and reinforcement. It should be noted that shotcrete is a special pouring process rather than a new material. Shot mortar is composed of coarse and fine aggregates, cementitious materials, and admixtures in accordance with the design ratio. The traditional shotcrete developed from shot mortar at the earliest has the disadvantages of high self-weight, poor bonding performance, and short service life. Developing high-performance shotcrete by improving the workability and strength of the mortar is a promising method.

[0003] In the preparation process of shotcrete / mortar, a large amount of aggregate is often required because they can not only play a "skeleton" role but also effectively fill into the matrix to improve the density, which directly affects the long-term mechanical or durability performance of shot mortar / concrete. Therefore, great attention should be paid to the quality of aggregate when designing high-performance shot mortar. Although some scholars have investigated the feasibility of replacing natural fine sand with manufactured sand, natural sand is still the main source of fine aggregate in the construction industry. However, with the rapid growth of sand demand and the resource depletion and environmental pollution caused by over-exploitation of river sand, finding substitutes for natural raw materials has always been the focus of research in the construction field. The quality of aggregate directly affects the self-weight of shotcrete / mortar, thus affecting the construction quality, such as the problems of more rebound of shotcrete, difficult adhesion, and falling off. Therefore, it is very important to explore a lightweight green aggregate to replace natural fine sand. Among them, fine recycled concrete aggregate (<4mm) has been widely studied as a substitute for natural sand in mortar. Municipal solid waste incineration bottom ash (MSWIBA) is a waste generated during the incineration of municipal solid waste and is a solid particle with a wide particle size distribution. According to this characteristic, the application of MSWIBA as an auxiliary cementitious material or replacing aggregate in the construction field has received great attention. Therefore, it is promising to try to use MSWIBA as fine aggregate to design environmentally friendly building materials.

[0004] Except for a small part of municipal solid waste being recycled or treated in waste incinerators, most of the waste is landfilled, and the leaching of soluble toxins in MSWIBA poses a potential threat to soil and groundwater. Previous studies have shown that applying MSWIBA solidified or stabilized (S / S) with a gelling agent in the construction industry is a relatively effective method, and using MSWIBA to replace natural aggregates to prepare the mortar matrix of shotcrete can be an extension of this exploration. This method can provide effective performance data for new environmentally friendly mortars and also provide a new application approach for exploring the resource recycling and reuse of MSWIBA. Summary of the Invention

[0005] The object of the present invention is to provide an environmentally friendly lightweight shotcrete mortar material produced from municipal solid waste incineration bottom ash. In order to reduce the environmental impact of municipal solid waste incineration bottom ash and find a substitute for natural sand, the potential use of municipal solid waste incineration bottom ash as fine aggregate is explored, and at the same time, the influence of supplementary cementitious materials on improving the performance of shotcrete mortar prepared from municipal solid waste incineration bottom ash is investigated. It provides new insights for opening up new application ways for large-scale recycling of municipal solid waste incineration bottom ash and also provides effective test data for designing new environmentally friendly lightweight shotcrete mortar.

[0006] To achieve the above object, the present invention provides an environmentally friendly lightweight shotcrete mortar material produced from municipal solid waste incineration bottom ash, including municipal solid waste incineration bottom ash, cementitious material, water reducer, accelerator, and water. The cementitious material includes cement, silica fume, and fly ash. The addition amount of municipal solid waste incineration bottom ash accounts for 40 - 50% of the total mass, the addition amount of fly ash accounts for 0 - 18% of the total mass, the addition amount of silica fume accounts for 0 - 12% of the total mass, the addition amount of accelerator accounts for 6 - 9% of the total mass, and the dosage of water reducer is 1.5wt% of the dosage of cementitious material.

[0007] Preferably, the addition amount of fly ash accounts for 6% of the total mass, the addition amount of silica fume accounts for 12% of the total mass, and the addition amount of accelerator accounts for 9% of the total mass.

[0008] Preferably, the cement is P·O42.5 ordinary Portland cement.

[0009] Preferably, the mass ratio of water to cementitious material is 0.38 - 0.47.

[0010] Preferably, the mass ratio of water to cementitious material is 0.38.

[0011] Preferably, the fly ash is Class F, Grade Ⅰ.

[0012] Preferably, the municipal solid waste incineration bottom ash is the municipal solid waste incineration bottom ash after removing impurities and drying, with particle sizes of 0.15, 0.3, 0.6, 1.18, 2.36, 4.75mm, and fineness modulus of 3.05.

[0013] Preferably, the main chemical component of the bottom ash from municipal solid waste incineration is silica, and its content is greater than 70%.

[0014] Preferably, the water reducing agent is a polycarboxylate-based high-performance water reducing agent.

[0015] Preferably, the accelerating agent is a liquid alkali-free accelerating agent of aluminum sulfate.

[0016] The advantages and beneficial effects of the environmentally friendly lightweight shotcrete mortar material produced by the present invention using the above-mentioned bottom ash from municipal solid waste incineration are as follows:

[0017] 1. In order to reduce the environmental impact of the bottom ash from municipal solid waste incineration and find a substitute for natural sand, the present invention explores the potential use of the bottom ash from municipal solid waste incineration as fine aggregate, and at the same time investigates the influence of supplementary cementitious materials on improving the performance of shotcrete mortar prepared from the bottom ash from municipal solid waste incineration. It provides new insights for opening up new application ways for large-scale recycling of the bottom ash from municipal solid waste incineration, and at the same time provides effective test data for designing new environmentally friendly lightweight shotcrete mortar.

[0018] 2. The proper substitution of the bottom ash from municipal solid waste incineration for natural sand in the present invention has little effect on the mechanical strength, and the proper incorporation of cementitious materials and admixtures can effectively improve the performance. Using the bottom ash from municipal solid waste incineration as fine aggregate in shotcrete mortar as an environmentally friendly building material, it is very promising to apply it to the repair of concrete pipes and the repair of reinforced concrete pipe column structures.

[0019] The technical solutions of the present invention will be further described in detail below through the drawings and embodiments. Description of the Drawings

[0020] Figure 1 It is a diagram of the mechanical strength results of the verification example of the present invention, where (a) is the compressive strength of groups S1 - S8, (b) is the compressive strength of groups S9 - S16, (c) is the flexural strength of groups S1 - S8, and (d) is the flexural strength of groups S9 - S16;

[0021] Figure 2 It is a diagram of the orthogonal test results of the setting time of the cement paste in the verification example of the present invention;

[0022] Figure 3 It is a diagram of the orthogonal test results of the workability of the mortar in the verification example of the present invention;

[0023] Figure 4 It is a diagram of the hydration heat flow curves of the composite cementitious material paste from 0 to 0.5 h and from 0 to 48 h in the verification example of the present invention, where (a) is for groups S1, S2, S3, S4, and (b) is for groups S1, S5, S9, S13;

[0024] Figure 5XRD patterns of different curing ages in the verification examples of the present invention, where (a) represents groups S1, S2, S3, and S4, and (b) represents groups S1, S5, S9, and S13;

[0025] Figure 6 Microstructural diagrams of mortar studied by scanning electron microscopy technology in the verification examples of the present invention, where (a) is for 1-day hydration, (b) is for 28-day hydration, (c) is the fracture surface of sand, (d) is the Mswib fracture surface, (e) is the hydrate filled in micropores, and (f) is the interweaving of different hydrates;

[0026] Figure 7 MIP result diagrams in the verification examples of the present invention, where (a) is the cumulative pore content, (b) is the pore distribution, and (c) is the pore volume and total porosity;

[0027] Figure 8 Comparison diagram of the leaching amounts of harmful elements in the verification examples of the present invention. Detailed implementation manners

[0028] The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0029] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the field to which the present invention belongs.

[0030] Unless otherwise defined, the materials and equipment used in the present invention can be obtained through regular commercial channels.

[0031] Example 1

[0032] An environment-friendly lightweight shotcrete mortar material produced from municipal solid waste incineration bottom ash, including municipal solid waste incineration bottom ash, cementitious materials (SCMs), water reducer, accelerator, and water. The cementitious materials include cement, silica fume (SF), and fly ash (FA). The addition amount of municipal solid waste incineration bottom ash (MSWIBA) accounts for 40% of the total mass, the addition amount of fly ash (FA) accounts for 10% of the total mass, the addition amount of silica fume (SF) accounts for 5% of the total mass, the addition amount of the accelerator accounts for 6% of the total mass, and the dosage of the water reducer is 1.5 wt% of the dosage of the cementitious materials.

[0033] The cement is P.O42.5 ordinary Portland cement (OPC).

[0034] The mass ratio of water to cementitious materials (water-cement ratio) is 0.38.

[0035] The fly ash (FA) is Class F, Grade I.

[0036] The municipal solid waste incineration bottom ash (MSWIBA) is the bottom ash of municipal solid waste incineration after impurity removal and drying, with particle sizes of 0.15, 0.3, 0.6, 1.18, 2.36, and 4.75 mm, and a fineness modulus of 3.05.

[0037] The main chemical component of the municipal solid waste incineration bottom ash (MSWIBA) is silicon dioxide, and its content is greater than 70%.

[0038] The water reducing agent is a polycarboxylate-based high-performance water reducing agent.

[0039] The accelerating agent is a liquid alkali-free accelerating agent of aluminum sulfate.

[0040] Example 2

[0041] The difference from Example 1 is that the addition amount of the municipal solid waste incineration bottom ash accounts for 50% of the total mass, the addition amount of fly ash accounts for 5% of the total mass, the addition amount of silica fume accounts for 10% of the total mass, the addition amount of the accelerating agent accounts for 8% of the total mass, and the mass ratio of water to cementitious material is 0.41. The rest is the same as in Example 1.

[0042] Verification Example

[0043] The orthogonal design theory is applied to the research of the environmentally friendly sprayed mortar with municipal solid waste incineration bottom ash. Combining the existing test results, four control factors are determined: the content of fly ash (FA), the content of silica fume (SF), the ratio of water to cementitious material (water-cement ratio) (W / B), and the content of the accelerating agent, which are denoted as factor A, factor B, factor C, and factor D respectively. Each factor considers four control levels, and a total of 16 groups of tests are carried out. At the same time, a four-factor - four-level L16(4 4 ) orthogonal test table is designed, as shown in Table 1, and the orthogonal experimental mix proportion combination design table is shown in Table 2.

[0044] Table 1 Orthogonal test factor and level design table

[0045]

[0046] Table 2 Orthogonal experimental mix proportion combination design table

[0047]

[0048] 1. Specimen preparation.

[0049] After weighing the gelling materials and putting them into a mortar mixer to stir evenly, add the corresponding water and water reducer, stir at low speed for 30 s, and then stir at high speed for 30 s. Stop stirring and scrape the slurry on the edge and bottom of the mixing pot. Add municipal solid waste incineration bottom ash (MSWIBA) and standard sand, stir at low speed for 30 s and then at high speed for 30 s. After stopping stirring, add the accelerating agent, stir at low speed for 5 s and then at high speed for 15 s, and fill the mortar into a test mold of 40 mm×40 mm×160 mm within 50 s, with 3 specimens in each group. All samples in the mold are covered with plastic film to reduce water loss, and demold after curing for 1 d under environmental conditions (23±2℃). The curing environment is standard curing (relative humidity greater than 90%, temperature 20±2℃). The curing times are 1 d, 7 d, and 28 d.

[0050] 2. Test items.

[0051] (1) Test the setting time of the neat cement of S1-S13 according to the mix ratio in Table 2.

[0052] (2) Analyze the initial hydration kinetics of the composite gelling materials in MSWIBA mortar by isothermal calorimetry.

[0053] (3) Prepare the fresh mortar according to the requirements in specimen preparation, and then test the fluidity and consistency of the fresh mortar, measure the fluidity of MSWIBA environmental protection mortar, and take the maximum diameters in two mutually perpendicular directions as the test results during the test. The mortar consistency can be tested with reference to the "Standard Test Method for Basic Properties of Building Mortar" (JGJ / T 70-2009) to obtain the results.

[0054] (4) Take out the specimens for testing after reaching the curing age. Calculate the compressive strength and flexural strength according to the "Test Method for Strength of Cement Mortar" (GB / T 17671-2021).

[0055] (5) Analyze the mortar specimens cured for 1 d and 28 d respectively by a high-resolution X-ray analyzer. The specimens are dried to a constant weight in a vacuum drying oven at 45℃ and ground into powder passing through a 75μm sieve. During the test, the scanning angle is designed in the 2θ range of 5°-65°, and the scanning time for each point is 0.2 s.

[0056] (6) In order to better observe the distribution of hydration products and the change of microtopography inside the shotcrete MSWIBA mortar, scanning electron microscopy (SEM) tests are carried out on the specimens. The apparent morphology of the reaction products is observed by using a scanning electron microscope.

[0057] (7) MIP tests were carried out on mortar specimens cured for 28 days. The specimens were prepared into cube samples of about 10 mm, placed in a vacuum drying oven at 45 °C for 48 h, and then the pore size and pore size distribution of the samples were measured using a Micromeritics Autopore IV 9510 mercury porosimeter.

[0058] (8) The leaching of soluble heavy metals is a major problem in the treatment and recycling of MSWIBA. Heavy metal leaching tests were carried out on MSWIBA and sprayed mortar specimens. Particles with a particle size of 0.125 - 0.25 mm were collected as test samples, mixed with 0.1 mol acetic acid solution in a container, and the ratio of the solution to the test sample was 10:1 (L / kg). The solid-liquid mixture of the sample and acetic acid was shaken for 16 h, the filtrate was collected, and the heavy metal concentration in the leachate was determined by inductively coupled plasma emission spectrometry.

[0059] 3. Test results.

[0060] From Figure 1 in (a) and Figure 1 in (b), it can be seen that the compressive strength of the test group at 1 day was less than that of the S1 group. The 1-day compressive strength of the S13 group was the smallest among all groups, which decreased by approximately 40.9% relative to the S1 group. Combining with "Accelerators for Shotcrete" (GB / T 35159-2017), the 1-day compressive strength of the S13 group in the orthogonal test was 18.5 MPa, which met the requirement for the 1-day compressive strength of mortar containing accelerators (greater than 7 MPa). Compared with the S1 group (47.5 MPa), the S6 group, S11 group, S12 group, and S16 group increased by approximately 12.63%, 8.42%, 4.84%, and 12.21% respectively. Generally speaking, the compressive strength of these groups was relatively excellent. This was mainly because the MSWIBA aggregate belonged to a porous structure and could absorb more water, and MSWIBA contained a certain amount of minerals similar to OPC, which led to some activity on the surface of MSWIBA. When the water-binder ratio was low (0.38), a part of the water was stored in MSWIBA, enabling it to play the role of internal curing. Therefore, there were more hydration products at the contact surface between MSWIBA particles and OPC or SCMs. The lower water-binder ratio would reduce the water system pores in the matrix, thereby improving the matrix density of the sprayed mortar.

[0061] Figure 1 in (c) and Figure 1Figure (d) shows the flexural strength development of each group of mortar at different ages. At the curing ages of 1 d and 7 d, the flexural strengths of Group S1 were 5.7 MPa and 6.9 MPa respectively. Under the early hydration conditions, the use of FA and SF to replace OPC significantly affected the strength development of the mortar specimens, and the flexural strengths of other test groups were generally lower than that of Group S1. At the 28th day of hydration, the flexural strengths of Group S11 and Group S12 exceeded that of Group S1 without adding SCMs, and were increased by approximately 12% and 8% respectively compared with the flexural strength of Group S1 (7.5 MPa). The effect of SCMs on improving flexural strength is smaller than that on improving compressive strength, which may be related to the internal porous structure of MSWIBA. Such a high-porosity material will significantly affect the cement-based matrix, such as increasing harmful pores or reducing compactness, etc.

[0062] Although there are certain fluctuations in the strengths of MSWIBA mortars with different material ratios, generally speaking, the strength of the shotcrete mortar is basically higher than that of the mortar with a single and large dosage of SCM. According to Table 2, Groups S1, S2, S3, S4 and Groups S1, S5, S9, S13 are the test groups with single addition of SF and single addition of FA respectively. It can be seen from Figure 1 that when adding one kind of SCMs to the sprayed MSWIBA mortar, with the increase of the SCM dosage, the compressive strength and flexural strength of the specimens at each age decreased. This may be because the particle size of SF is small, the specific surface area is large, and the hydration reaction rate is fast, which significantly shortens the setting time of the sprayed MSWIBA mortar and helps to improve the early strength of the mortar specimens. Reasonably compounding and adding FA and SF into the mortar can give full play to the advantages of SCMs and help to improve the influence of MSWIBA on weakening the mechanical properties of the mortar specimens. The environmentally friendly mortar in the present invention has the characteristics of early strength and fast hardening while containing a large dosage of MSWIBA, which is very helpful for the application of this lightweight shotcrete mortar in engineering.

[0063] The setting time of the neat cement paste changes with the levels of each factor as Figure 2 shown. In the "Technical Specification for Application of Shotcrete" (JGJ / T 372 - 2016), it is stipulated that the setting time of the neat cement paste with accelerator should meet the requirements of initial setting time ≤ 5 min and final setting time ≤ 12 min. It can be seen from Figure 2 that Groups S2, S3, S4, S5, S6, S9, S11, S12, S15 and S16 all meet the requirements of initial setting and final setting times. Observing the 6 test groups (Groups S1, S7, S8, S10, S13, S14) that do not meet the specification requirements, it is found that the influence of water-binder ratio and accelerator dosage on the setting time is generally greater than that of SCMs dosage.

[0064] When the dosage of the accelerating agent is 6%, the setting times of groups S1, S7, and S14 exceed the specification requirements. Under the same accelerating agent dosage, comparing group S1 with group S12 that meets the specification requirements, it is found that when the water-binder ratio of group S12 is higher than that of group S1, its setting time (final setting time and initial setting time) is significantly shorter than that of group S1. Under the same accelerating agent dosage, adding SCMs to replace a part of OPC can accelerate the setting of the sprayed MSWIBA mortar. This is because compared with group S1 (fresh mortar prepared with 100% OPC), 12% of SF is incorporated into group S12, greatly shortening the setting time. In addition, this shorter setting time can minimize the shedding of the sprayed MSWIBA mortar when it is applied to infrastructure in the future, and thus adhere and solidify with the old concrete or steel mesh very quickly. When the accelerating agent dosages are 7% and 8%, the number of test groups with unqualified setting times is 2 groups (groups S8 and S13) and 1 group (group S10) respectively, and the water-binder ratios of these three groups are at a relatively high level at this time. When the accelerating agent dosage is increased to 9%, the setting times of the 4 test groups (groups S4, S6, S9, and S15) at this level all meet the specification. Too low water-binder ratio will affect the molding quality of the specimens and the fluidity of the fresh mortar, and ultimately bring negative impacts to the on-site construction of the sprayed MSWIBA mortar, such as the blockage of the spraying and grouting pipes, etc., while excessive use of the accelerating agent may delay the strength development and the hydration of the cementitious materials, thus affecting the matrix density of the mortar and ultimately reducing its durability.

[0065] Figure 3 The results are for the workability of the mortar mixture. The consistencies of each test group are distributed between 21 mm and 84 mm, and the flow diameters are distributed in the range of 141 mm to 259 mm, indicating that the fresh mortar has good workability. It shows that the changes in the parameters of the mix proportion have a great influence on the workability of the mortar mixture. At the same time, when the mix proportion of the mortar in the present invention is relatively low, it can still maintain good workability, which is helpful for the on-site construction of the sprayed mortar (such as not being easily blocked during pumping, etc.) and also convenient for the transportation of long-distance mixer trucks.

[0066] Figure 4 They are the heat flow curves of the composite cementitious material pastes of groups S1, S2, S3, S4 and groups S1, S5, S9, S13 respectively. In order to analyze the influence of different mixing components on the hydration of the paste, the parameters for analyzing the heat of hydration curves are determined, as shown in Tables 3 and 4.

[0067] Table 3 Parameters of the heat flow curves of the composite pastes

[0068]

[0069] When studying the influence of adding different dosages of SF on the hydration reaction of composite cementitious material paste in orthogonal experiments, in order to reduce the interference of FA dosage, groups S1, S2, S3, and S4 were selected as the analysis objects. It can be seen from Table 3 that regardless of the changes in the water-binder ratio W / B and the dosage of accelerator, adding SF increased the maximum heat flow of the acceleration peak and the energy release in the first 60 minutes of hydration. And with the increase of SF dosage, the time for the paste to reach the maximum heat flow of the hydration main peak shortened. Without adding SF, the time for the paste to reach the maximum heat flow of the main peak was delayed by about 1.12 h compared with the paste with an SF dosage of 12%. The incorporation of fine-particle-size SF provided additional surface area for the nucleation and precipitation of hydration products, and the heat released by the hydration of OPC increased the temperature environment in the matrix, thus accelerating the early hydration of the paste.

[0070] Table 4 Parameters of the heat flow curve of the composite paste

[0071]

[0072] Groups S1, S5, S9, and S13 were pastes with different FA dosages and without adding SF. By analyzing the heat flow curve and its characteristic parameters. It can be seen from Table 4 that when adding FA to the mortar, the maximum heat flow of the acceleration peak and the energy release in the first 60 minutes increased.

[0073] To explore the influence of the changes in the dosages of SF and FA on the hydration products of the specimens, the XRD patterns of the mortar in groups S1, S2, S3, S4 and groups S1, S5, S9, S13 cured for 1 d and 28 d are as Figure 5 shown. The main crystalline phase products generated are AFt, calcite, and tobermorite (C-S-H). C3S comes from unreacted OPC, and SiO2 comes from MSWIBA during the preparation of the mortar. From Figure 5 it can be observed that in the case of adding an accelerator, obvious AFt characteristic peaks can also be observed in the mortar specimens cured for 1 d. The reticular structure formed by the interlaced growth of these AFt contributed to the excellent early strength of the mortar specimens. The characteristic peaks of calcite can also be clearly observed in Figure 4 it. On the one hand, it is generated by the reaction of part of the cementitious material with carbon dioxide, and on the other hand, it may be related to some impurities contained in MSWIBA. From Figure 5 it can be observed that in the case of adding an accelerator, obvious AFt characteristic peaks can also be observed in the mortar specimens cured for 1 d. Research shows that the Al 3+ , SO4 2- ionized by the alkali-free liquid accelerator and the Ca 2+The reaction generates crystalline AFt. The interlaced growth of these AFt forms a network structure that contributes to the excellent early strength of the mortar specimens. At the same time, the formation of AFt consumes a large amount of calcium hydroxide, further accelerating the hydration of C3S. CSH (tobermorite) produced by C3S hydration is the main product of the hydration reaction inside the mortar, which is reflected in the characteristic peak of about 29.4° in the XRD spectrum. This mineral phase is a compound that can directly determine the sandblasting MSWIBA mortar. Compared with Figure 5 In (a), the specimens with different SF contents were only detected with obvious C3S in the early stage. Figure 5 In the middle (b) S13 group, incompletely hydrated C3S was still detected at 28 days, which may be related to the lower volcanic ash reaction activity of FA.

[0074] From the XRD analysis, it can be seen that although the mortar prepared by partially replacing sand with different amounts of SCMs and MSWIBA caused a certain degree of delay in hydration time, the addition of accelerators appropriately compensated for the disadvantage of low mechanical strength caused by insufficient reactivity of SCMs in the early stage. This shows that environmentally friendly sprayed MSWIBA mortar can develop good mechanical strength under appropriate proportions.

[0075] In order to understand the microscopic morphology of the hydration products, the microscopic morphology and compound products of the samples cured for 28 days were observed using SEM technology. In the MSWIBA mortar paste using alkali-free liquid accelerator, needle-shaped AFt can be observed to be generated and attached to the cement matrix at the initial stage of the hydration reaction, such as Figure 6 As shown in (a). While accelerating the hydration reaction, the ionization of the accelerator produces SO4 2- The rich sulfate content in MSWIBA leads to the formation and aggregation of AFt. Figure 6 In (b), it can be observed that AFt provides nucleation sites for the generation of CSH in the form of nucleation seeds in the voids, filling the voids and making the structure dense.

[0076] Figure 6 (cd) are SEM images of the bonding between the fracture surface of standard sand and MSWIBA and the matrix. Figure 6 It can be seen in (c) that there are obvious microcracks between the interface transition zone of standard sand and matrix, the fracture interface is smooth, and there is no hydration product to fill and connect between natural fine aggregate and matrix. Unlike standard sand, the irregular shape and rough surface of MSWIBA are conducive to the attachment of hydration products, and MSWIBA particles are well embedded in the matrix, such as Figure 6As shown in Fig. (d). However, due to the loose structure and high porosity of MSWIBA particles, incorporating them as a substitute for standard sand into mortar will increase the matrix porosity and the water absorption of the mortar. Therefore, SCMs are added to maximize the mechanical properties and minimize the adverse effects of MSWIBA on the mortar properties.

[0077] When MSWIBA is used as fine aggregate in mortar, metallic Al or Al / Zn alloy in MSWIBA reacts in the alkaline environment of cement hydration to generate H2, inducing the formation of internal expansion or cracks in the mortar, which has an adverse effect on the mortar properties. Incorporating SCMs as partial substitutes for OPC can enhance the densification of the paste and improve the porosity, which has been widely recognized. On the one hand, finer FA and SF particles can fill the voids between OPC particles. On the other hand, the pores caused by the chemical reaction of metal and alkali in MSWIBA to produce hydrogen or the initial defects in the preparation process can be filled by SCMs and the hydration products generated by their pozzolanic reaction, playing a role in reducing the risk of potential crack opening and improving the mechanical properties, as Figure 6 shown in Fig. (e - f).

[0078] The pores of the sprayed MSWIBA mortar were investigated by MIP test, mainly including cumulative pore content, pore size distribution and total porosity, and the test results are as Figure 7 shown.

[0079] From Figure 7 Fig. (a), it can be observed that the S13 group has the largest cumulative pore content of 0.1507 mL / g, followed by the S4 group with 0.1327 mL / g. The cumulative pore contents of the S6 group and the S11 group are significantly lower than those of the S4 group and the S13 group, being 0.1015 mL / g and 0.1071 mL / g respectively, which are close to 0.1049 mL / g of the control group S1. The pore size distribution of the MSWIBA mortar is as Figure 7 shown in Fig. (b). Compared with the S1 group, the transition pores of other mortars are significantly reduced, while the capillary pores and large pores increase. Figure 7In (c), the percentage of pore volume of each type and the total porosity are shown. The total porosity of the S13 group is the largest, at 25.6%, followed by the S4 group at 23.7%. The total porosities of the S6 group and the S11 group are the smallest, at 19.1% and 19.5% respectively. The changing trend of the porosity is negatively correlated with the mechanical strength. The incorporation of SCMs changes the pore structure of the mortar. The proportion of macropores in the matrix increases significantly, while the proportion of transitional pores decreases. This phenomenon is particularly obvious in the S4 group and the S13 group with single addition of FA and SF respectively. It should be noted that although the total porosity and capillary porosity of the S4 group and the S13 group are higher, their average pore diameters of 40.45 nm and 45.93 nm are lower than 46.39 nm of the S1 group. The average pore diameters of the S6 group and the S11 group are 37.90 nm and 37.79 nm, further indicating that reasonable compound addition of SCMs can refine pores and play a role in improving the mechanical properties of the mortar.

[0080] Combined with the above analysis, the MSWIBA sprayed mortar has a dense and uniform microstructure and sufficient hydration products after full hydration. From a microscopic perspective, it is demonstrated that the synergistic effect of FA and SF with MSWIBA will not have a negative impact on the mortar performance to a certain extent, confirming the possibility of using MSWIBA as fine aggregate to prepare the matrix of sprayed concrete mortar.

[0081] The workability and mechanical properties of MSWIBA mortar were tested by orthogonal experiment, and the obtained data were analyzed by range analysis, variance analysis and grey relational analysis. The importance ranking of the influence of each factor on different evaluation indexes and the optimal level combination in the orthogonal experiment are shown in Table 5. It can be seen from Table 5 that the influence of factor C (water-binder ratio) on the mechanical properties of the mortar is always the largest, while for factors A (FA content), B (SF content) and D (accelerator content), the primary and secondary influence orders on different evaluation indexes need to be considered to determine the optimal level. Combining range analysis and grey relational analysis, the optimal level combinations of water-binder ratio and accelerator content are C1D2 and C1D4, and the optimal levels of FA content are A1, A2 and A3. For factor B, its influence is second only to factor C under the evaluation index of 28-day compressive strength, and the optimal level B4 at this time is selected as the mix ratio combination for the verification experiment. The mix ratio combination design of the verification experiment is shown in Table 6.

[0082] Table 5 Results of factor influence ranking and optimal level combination

[0083]

[0084] Table 6 Mix ratio combination design table of verification experiment

[0085]

[0086]

[0087] The performance of groups S2412, S2414, S3412, and S3414 was compared through verification tests, and the test results are shown in Table 7. Compared with the orthogonal test combinations, the maximum compressive strength of S2414 at 28 days increased from 53.5 MPa in group S6 to 53.7 MPa, the maximum flexural strength was the same as 8.4 MPa in group S11, the maximum mechanical strength appeared in the same mix ratio, the setting time also met the requirements of JGJ / T 372 - 2016, and the workability was also better than the original parameter combinations of the orthogonal tests (groups S1, S6, and S11), and various performances were improved.

[0088] Table 7 Verification Test Results

[0089]

[0090] Meanwhile, considering the impact of harmful elements in MSWIBA and the mortar prepared therefrom on the natural environment, the test measured the leaching amounts of heavy metal elements in MSWIBA and groups S1 and S2414, and evaluated the potential environmental impact of MSWIBA mortar. The toxicity leaching contents in the sprayed MSWIBA mortar and MSWIBA particles are as Figure 8 shown. It can be seen from Figure 8 that after using MSWIBA as fine aggregate to produce mortar, the leaching concentrations of toxic components decreased significantly and all met the standards of GB5085.7 - 2019, which also indicates that it is feasible to apply the sprayed MSWIBA mortar as a large - scale recycling and reuse approach for MSWIBA particles in actual infrastructure projects.

[0091] In summary, through verification tests, an optimal mix ratio of MSWIBA mortar was selected, where the FA content is 6%, the SF content is 12%, the water - binder ratio is 0.38, and the accelerator content is 9%. This mix ratio is suitable for future large - scale production of sprayed mortar or commercial sprayed concrete.

[0092] (1) In the present invention, well - graded MSWIBA is used to replace standard sand as fine aggregate to prepare mortar, which can have good mechanical strength under appropriate mix ratios. Compared with group S1 without adding SCMs, the compressive and flexural strengths of the mortar specimens with single or compound addition of SCMs decreased to varying degrees at 1 day, but the compressive strength began to increase after 1 day. At 28 days, the compressive strengths of groups S6, S11, S12, and S16 increased by 4.84% - 12.63% compared with group S1, and the flexural strength ratios of groups S11 and S12 increased by 12% and 8% respectively compared with group S1. Compared with the flexural strength, compound addition of SCMs is more beneficial to the development of compressive strength.

[0093] (2) Microscopic analyses such as hydration heat, XRD, SEM, and MIP indicate that the synergistic effect of SCMs and MSWIBA does not negatively affect the mortar properties to a certain extent. When the matrix undergoes a hydration reaction, the incorporated FA and SF increase the maximum heat flow of the acceleration peak and the energy release of the composite cementitious system, promoting the formation and aggregation of more hydration products in the matrix, thereby accelerating the early hydration of the paste. The incorporation of fine particles of SCMs provides additional nucleation sites for the hydration products, optimizes the pore structure, and enables better attachment of MSWIBA particles to the matrix. The well-graded MSWIBA improves the compactness of the mortar, thereby improving the physical and microscopic properties of the mortar.

[0094] (3) The optimal mix proportion of MSWIBA mortar is 6% FA content, 12% SF content, 0.38 water-binder ratio, and 9% accelerator content. The final mortar consistency is 49 mm, the fluidity is 184 mm, and the 28-day compressive strength and flexural strength are 53.7 MPa and 8.4 MPa, respectively, with good performance.

[0095] However, since shotcrete / mortar is often used in tunnels and mines where sulfate attack is likely to occur, the porous structure of MSWIBA itself is not conducive to durability. Therefore, it is necessary to understand the effects of accelerators and SCMs on the sulfate resistance of MSWIBA-LWSM. In addition, conducting a life cycle assessment (LCA) of materials containing MSWIBA has a positive effect on enhancing public acceptance. These considerations will be further studied in the next stage when preparing lightweight aggregate shotcrete using MSWIBA-LWSM and cold-bonded artificial aggregates of MSWIBA.

[0096] Therefore, for the environmentally friendly lightweight shotcrete mortar material produced by the present invention using the above-mentioned municipal solid waste incineration bottom ash, in order to reduce the environmental impact of municipal solid waste incineration bottom ash and find a substitute for natural sand, the potential use of municipal solid waste incineration bottom ash as fine aggregate is explored, and at the same time, the influence of supplementary cementitious materials on improving the properties of shotcrete mortar prepared from municipal solid waste incineration bottom ash is investigated. It provides new insights for opening up new application ways for large-scale recycling of municipal solid waste incineration bottom ash, and at the same time provides effective experimental data for designing new environmentally friendly lightweight shotcrete mortar.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements do not make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. Environmentally friendly lightweight spraying mortar material produced from bottom ash from municipal waste incineration, characterized by: The invention comprises bottom ash from incineration of urban waste, cementitious materials, water reducing agent, accelerating setting agent and water. The cementitious materials comprise cement, silica fume and fly ash. The amount of bottom ash from incineration of urban waste accounts for 40-50% of the total mass, the amount of fly ash accounts for 0-18% of the total mass, the amount of silica fume accounts for 0-12% of the total mass, the amount of accelerating setting agent accounts for 6-9% of the total mass, and the amount of water reducing agent is 1.5wt% of the amount of cementitious materials.

2. The environmentally friendly lightweight spraying mortar material produced from the bottom ash of municipal waste incineration according to claim 1 is characterized in that: The added amount of fly ash accounts for 6% of the total mass, the added amount of silica fume accounts for 12% of the total mass, and the added amount of accelerating setting agent accounts for 9% of the total mass.

3. The environmentally friendly lightweight spraying mortar material produced from the bottom ash of municipal waste incineration according to claim 1 is characterized in that: The cement is P.O42.5 ordinary Portland cement.

4. The environmentally friendly lightweight spraying mortar material produced from the bottom ash of municipal waste incineration according to claim 1, characterized in that: The mass ratio of water to cementitious material is 0.38-0.

47.

5. The environmentally friendly lightweight sprayed mortar material produced from the bottom ash of municipal waste incineration according to claim 4, characterized in that: The mass ratio of water to cementitious material is 0.

38.

6. The environmentally friendly lightweight spraying mortar material produced from the bottom ash of municipal waste incineration according to claim 1, characterized in that: Fly ash is Class F, Class Ⅰ.

7. The environmentally friendly lightweight sprayed mortar material produced from the bottom ash of municipal waste incineration according to claim 1, characterized in that: The municipal waste incineration bottom ash is the municipal waste incineration bottom ash that has been removed of impurities and dried, with particle sizes of 0.15, 0.3, 0.6, 1.18, 2.36, and 4.75 mm and a fineness modulus of 3.

05.

8. The environmentally friendly lightweight sprayed mortar material produced from the bottom ash of municipal waste incineration according to claim 1, characterized in that: The main chemical component of municipal waste incineration bottom ash is silicon dioxide, and its content is greater than 70%.

9. The environmentally friendly lightweight spraying mortar material produced from the bottom ash of municipal waste incineration according to claim 1, characterized in that: The water reducing agent is a polycarboxylic acid-based high-performance water reducing agent.

10. The environmentally friendly lightweight sprayed mortar material produced from the bottom ash of municipal waste incineration according to claim 1, characterized in that: The quick-setting agent is aluminum sulfate liquid alkali-free quick-setting agent.

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