Preparation method of low-carbon shrinkage and high-strength alkali-activated foam concrete with sand tailing mud

Abstract

The application discloses a preparation method of low-carbon shrinkage-resistant high-strength alkali-activated foam concrete of sand washing tailing mud, which comprises the following steps: firstly, mixing, stirring, and blending slag, an additive, and treated sand washing tailing mud; then, adding glass fiber and pretreated waste coffee residue and mixing; continuously adding water glass solution and stirring; finally, adding a pretreated foaming agent to prepare the alkali-activated foam concrete of sand washing tailing mud, and uniformly stirring the foam to obtain the alkali-activated foam concrete of sand washing tailing mud. In one aspect, the stability of the foam is optimized by means of microwave treatment of the foaming agent, control of the concentration of the foaming liquid, and incorporation of the additive; in another aspect, the strength of the foam concrete is improved by incorporation of the composite fiber, so that the low-carbon shrinkage-resistant high-strength alkali-activated foam concrete of sand washing tailing mud is prepared. The green and excellent performance of the foam concrete makes it have a wide popularization prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical fields of solid waste utilization and foam concrete preparation, and specifically discloses a preparation method of low-carbon shrinkage-inhibiting high-strength alkali-activated sand washing tailing mud foam concrete. BACKGROUND

[0002] With the restriction of natural sand and gravel resource mining in China, the production quantity of machine-made sand and gravel shows an upward trend in China. The process of quarrying machine-made sand and gravel mainly includes three steps of crushing, washing and selection, and a large amount of sand washing tailing mud is often generated in the washing process. At present, the main treatment method for the sand washing tailing mud is mainly stacking, which often causes a series of problems. For example, the stacking of sand washing tailing mud occupies a large amount of land resources, causes land desertification and resource waste; in addition, the sand washing tailing mud itself contains a large amount of fine particles, which on the one hand is washed and flows into rivers with rainwater to pollute the environment, and on the other hand causes dust when it is dry, which is easy to cause respiratory diseases when inhaled by human body. Therefore, it is urgent to use a more reasonable way to dispose of the increasing amount of stacked sand washing tailing mud.

[0003] Foam concrete is a kind of light thermal insulation material containing a large amount of closed pores, which can be used as a thermal insulation material for walls, roofs, floors, pipes and other parts, and at the same time, it can also be used as a filling material for ecological islands, artificial wetlands, sponge cities and other projects, to increase the green area, improve water quality and air quality, and improve the sustainability of the ecological environment. From the above analysis, it can be seen that the application range of foam concrete is very wide, and if the sand washing tailing mud can be applied to foam concrete, the large amount of sand washing tailing mud can be quickly disposed of. SUMMARY

[0004] The main purpose of the present application is to apply the sand washing tailing mud waste to the foam concrete, to reduce the harm caused by a large amount of stacked sand washing tailing mud, and to realize the high value-added utilization of the sand washing tailing mud.

[0005] To achieve the above purpose, the present application provides the following technical solutions:

[0006] A preparation method of low-carbon shrinkage-inhibiting high-strength alkali-activated sand washing tailing mud foam concrete, characterized in that it comprises the following steps:

[0007] 1) The sand washing tailing mud is mainly composed of stone powder and mud, wherein the amount of stone powder is ≤50%, and the amount of mud is ≥50%, the sand washing tailing mud is baked at 100 DEG C for 12 hours and ball milled for 20-60 minutes, and the particles with a particle size ≥3mm in the sand washing tailing mud after ball milling are removed for use;

[0008] 2) The activator is dissolved in clean water, and the activator mixed solution is cooled to room temperature for standby;

[0009] 3) The pre-treatment cement foaming agent is diluted with water to obtain a foaming liquid, and the dilution ratio is 30-60 times (the product is mixed with 30-60 times mass of water evenly).

[0010] 4) The materials are measured according to the mass ratio: the sand washing tail mud, slag and additive are put into the mortar mixing pot, and the mixed powder is prepared by stirring at a speed of 62±5 r / min for 1 min, the slag is S95 slag, and the additive is one or more of sodium chloride, sodium hydroxide, sodium carbonate and calcium hydroxide; the fibers are uniformly dispersed into the mixed powder, and the mixed dry material is prepared by stirring at a speed of 62±5 r / min for 2 min; the activator mixed solution is poured into the mixed dry material, and the mixed slurry is prepared by stirring at a speed of 62±5 r / min for 2 min; the prepared foaming liquid is made into uniform foam by a foaming machine, and the foam is added to the mixed slurry, and the stirring is carried out at a speed of 62±5 r / min for 1 min, then the stirring pot is taken out and the materials remaining on the pot wall and the pot bottom are scraped with tools; the stirring pot is put back and continues to stir at a speed of 62±5 r / min for 1-2 min to ensure that the foam is uniformly dispersed in the mixed slurry, and finally the mixture presents a creamy state, and the fluid consistency is easy to pour, thus the alkali-activated sand washing tail mud foam concrete slurry is obtained;

[0011] 5) The obtained creamy alkali-activated sand washing tail mud foam concrete slurry is molded and covered with a film, and placed in an environment with a temperature of 23±2 ℃ and a relative humidity of 65±15% for 1 d, and then hardened and demolded, and placed in an environment with a temperature of 20±2 ℃ and a relative humidity of more than 95% for 28 d, thus the low-carbon shrinkage high-strength alkali-activated sand washing tail mud foam concrete is prepared.

[0012] Specifically, the activator in step 2) is solid water glass with a solid content of 100% and a modulus of 1-1.5 mol.

[0013] Specifically, in step 3), the cement foaming agent is LG-2258 produced by Shandong Yousuo Chemical Technology Co., Ltd., and the pre-treatment cement foaming agent is obtained by placing the original solution of the cement foaming agent in a microwave oven, setting the microwave power to 500 W, and heating for 30-40 seconds.

[0014] Specifically, in step 4), the fiber is a fiber mixed in a ratio of 2:1 of glass fiber and modified waste coffee grounds. Further, the modified waste coffee grounds are obtained by soaking the waste coffee grounds in a 3 mol / L sodium hydroxide solution for 1 h, and then drying the soaked waste coffee grounds in an oven at 100 ℃ until the weight is constant.

[0015] The alkali-activated sand washing tail mud foam concrete prepared by the present application has the following advantages:

[0016] 1) The present application is mainly based on the preparation of foamed concrete of sand washing tailings and alkali activated cementitious materials, the sand washing tailings are partially replaced by slag and mixed into foamed concrete, which not only solves the environmental pollution caused by the accumulation of sand washing tailings to a certain extent, but also realizes the transformation of waste into treasure. Using alkali activated cementitious materials instead of traditional cement is very consistent with the current "double carbon policy", which is green and environmentally friendly.

[0017] 2) The present application uses treated sand washing tailings as raw material, the prepared foamed concrete has small shrinkage and high strength, and the utilization rate of sand washing tailings is as high as 30%. The performance of the prepared alkali activated foamed concrete meets the corresponding requirements of the national standard "JGT266-2011 Foamed Concrete", and its mechanical properties are more excellent than those of traditional cement foamed concrete.

[0018] 3) The fibers used in the present application, namely, glass fiber and waste coffee grounds, can inhibit shrinkage and improve the mechanical properties of alkali activated foamed concrete. For waste coffee grounds, as a material containing pores, it has a large specific surface area, so it can play an internal curing effect in foamed concrete to inhibit shrinkage. In addition, its porous structure can also act as a nucleation site to promote the growth of hydration products and thus improve the strength of foamed concrete. For glass fiber, on the one hand, it also has the ability to retain water and delay evaporation, thereby playing a role in inhibiting shrinkage. On the other hand, glass fiber has very strong compressive strength, which can form a random support system when uniformly dispersed in foamed concrete, dispersing the directional stress of foamed concrete, preventing the occurrence and development of primary cracks in foamed concrete, eliminating or reducing the number and size of primary microcracks, greatly improving the crack resistance and impermeability of concrete, thereby inhibiting the shrinkage of foamed concrete and optimizing its mechanical properties.

[0019] 4) The mechanical properties or durability of foamed concrete depend largely on the quality of the foam. The present application improves the foam density, foam stability and viscosity in foamed concrete by microwave treatment of foaming agent, control of foaming liquid concentration and addition of admixtures, thereby ultimately improving the performance of foamed concrete. DETAILED DESCRIPTION

[0020] Example 1: The strength of traditional foamed concrete is relatively low, and alkali activated cementitious materials often have the advantage of high strength. Therefore, in this embodiment, sand washing tailings are applied to alkali activated foamed concrete to avoid the application of sand washing tailings leading to significant deterioration of the strength of foamed concrete. However, alkali activated foamed concrete often has problems such as large shrinkage and easy cracking, which is mainly caused by the fast alkali activation reaction. In this embodiment, low-activity sand washing tailings are used to replace high-activity slag in alkali activated foamed concrete, which can reduce the degree of alkali activation reaction and thus improve the shrinkage and cracking problems.

[0021] The preparation method of the low-carbon shrinkage-inhibiting high-strength alkali-activated foam concrete from sand washing tailings mud comprises the following steps:

[0022] 1) Obtain sand washing tailings mud from a machine-made sand production line, wherein the sand washing tailings mud mainly consists of stone powder and mud, and the content of the stone powder is 26% and the content of the mud is 71% after crushing. The crushed sand washing tailings mud is baked at 100°C for 12 hours and ball milled for 30 minutes, and the particles with a particle size of ≥3 mm in the ball-milled sand washing tailings mud are removed.

[0023] 2) Dissolve solid water glass with a modulus of 1 mol in clean water, and the mass ratio of the two is 1:5 (1 mol of solid water glass: clean water). Let the mixed solution of the activator cool to room temperature and stand for use;

[0024] 3) Put the stock solution of the cement foaming agent into a microwave oven, set the microwave power to 500W, and heat for 30 seconds. Then dilute the foaming agent with 30 times the mass of clean water, mix uniformly to obtain a foaming solution;

[0025] 4) Measure the mass ratio of each group of materials, i.e. 25 parts of sand washing tailings mud, 50 parts of slag, 8.2 parts of foaming solution, 36 parts of mixed solution of activator, 2.1 parts of fiber, and 0.045 parts of additive. First, put the sand washing tailings mud, slag and additive into the mortar mixing pot, stir at a speed of 62±5 r / min for 1 min to obtain a mixed powder, wherein the slag is S95 slag and the additive is sodium chloride and calcium hydroxide; secondly, put the fiber into the mixed powder and stir at a speed of 62±5 r / min for 2 min to obtain a mixed dry material; then, pour the mixed solution of the activator into the mixed dry material and stir at a speed of 62±5 r / min for 2 min to obtain a mixed slurry; then, prepare uniform foam through a foaming machine on site, and add the foam to the mixed slurry and stir at a speed of 62±5 r / min for 1 min, then take out the mixing pot and scrape the materials remaining on the pot wall and bottom with tools; finally, put it back into the mixing pot and continue to stir at a speed of 62±5 r / min for 1.5 min to ensure that the foam is uniformly dispersed in the mixed slurry. When the final mixture presents a creamy consistency and is easy to pour, the alkali-activated foam concrete slurry from sand washing tailings mud is obtained;

[0026] 5) Pour the obtained creamy alkali-activated foam concrete slurry from sand washing tailings mud into a mold, cover it with a film and place it in a laboratory environment (temperature 23±2 ℃, relative humidity 65±15%) for 1 day, then harden it and remove it from the mold. After removing the mold, place it in a standard curing room environment (temperature 20±2 ℃, relative humidity above 95%) for 28 days to prepare low-carbon shrinkage-inhibiting high-strength alkali-activated foam concrete from sand washing tailings mud.

[0027] It should be noted that the application of low-activity sand washing tailings can also cause the problem of significant reduction in the strength of alkali-activated foam concrete. Therefore, the performance of foam concrete depends largely on the quality of the foaming agent. In order to prove that the alkali-activated sand washing tailings foam concrete of this example has the characteristics of low shrinkage and high strength, the following control examples are designed.

[0028] Control Example 1: The alkali-activated sand washing tailings foam concrete of this scheme does not use a pretreated cement foaming agent and does not mix fibers and admixtures. The mass ratio of other materials and the mixing process are the same as in Example 1.

[0029] Control Example 2: The alkali-activated sand washing tailings foam concrete of this scheme does not use a pretreated cement foaming agent and the foaming agent is diluted with 80 times water to obtain a foaming liquid. Similarly, no fibers and admixtures are mixed. The mass ratio of other materials and the mixing process are the same as in Example 1.

[0030] Control Example 3: The foam concrete of this scheme is a cement-based foam concrete with the same water-binder ratio as Example 1.

[0031] Control Example 4: The alkali-activated foam concrete of this scheme does not use sand washing tailings instead of slag. In addition, the cement foaming agent is not pretreated and does not mix fibers and admixtures. The mass ratio of other materials and the mixing process are the same as in Example 1.

[0032] After 28 days of curing of the alkali-activated sand washing tailings foam concrete and the cement-based foam concrete, the dry density and compressive strength were tested according to the standard JGT 266-2011 "Foam Concrete". The 48h dry shrinkage was tested according to the standard GB / T 11969-2020 "Autoclaved Aerated Concrete Performance Test" test method. The performance test results of the sand washing tailings foam concrete obtained in the examples and control examples are shown in the table below.

[0033]

[0034] From the dry density data, among the five groups of foam concrete, Control Example 2 could not be formed. The dry densities of the other four groups of foam concrete were between 570 and 633 kg / m 3 The alkali-activated sand washing tailings foam concrete of Control Example 2 could not be formed, mainly because the poor quality of the foaming agent caused the bubbles produced by the foaming agent to be unstable. The foaming agent was not pretreated, the foaming liquid concentration was too low, and no admixtures were added, all of which caused the foam to be largely destroyed during the mixing process.

[0035] From the compressive strength data, it can be seen that the compressive strength of the formed foam concrete of Example 1 is obviously superior to that of the traditional cement slurry foam concrete (Comparative Example 3), which shows that it has the characteristics of high strength. Compared with Comparative Example 1, the mechanical properties of Example 1 are also obviously improved, which shows that the pretreated cement foaming agent and the incorporation of fibers and admixtures can improve the mechanical properties of the alkali-activated sand washing tailing mud foam concrete.

[0036] From the drying shrinkage data, it can be seen that the drying shrinkage of the formed foam concrete of Example 1 is obviously lower than that of Comparative Examples 1 and 4, which shows that the incorporation of sand washing tailing mud, pretreated cement foaming agent, fibers and admixtures can inhibit the drying shrinkage of the alkali-activated sand washing tailing mud foam concrete.

[0037] The above only describes the preferred embodiments of the present application, and any equivalent changes and modifications made within the scope of the patent application of the present application shall be included in the scope of the present application.

Claims

1. A method for preparing low-carbon, shrinkage-inhibited, high-strength alkali-activated sand washing tailings foam concrete, characterized in that The following steps are involved: 1) The sand washing tailings are mainly composed of stone powder and mud, wherein the stone powder content is ≤50% and the mud content is ≥50%. The sand washing tailings are dried at 100°C for 12 hours and ball milled for 20-60 minutes. The particles with a particle size of ≥3mm in the sand washing tailings after ball milling are removed for later use; 2) Dissolve the stimulator in clean water and let the mixed solution stand until it cools to room temperature before use; 3) Dilute the pretreated cement foaming agent with clean water to obtain a foaming liquid with a dilution ratio of 30 to 60 times. Place the original solution of the cement foaming agent in a microwave oven, set the microwave power to 500W, and heat for 30 to 40 seconds; 4) Measure each group of materials according to the mass ratio for use, including: 25 parts of sand washing tailings, 50 parts of slag, 8.2 parts of foaming liquid, 36 parts of activator mixed solution, 2.1 parts of fiber, and 0.045 parts of admixture. The fiber is a mixture of glass fiber and modified waste coffee grounds in a ratio of 2:

1. The modified waste coffee grounds are obtained by soaking the waste coffee grounds in a 3 mol / L sodium hydroxide solution for 1 hour, and then drying the soaked waste coffee grounds in a 100°C oven to constant weight; the sand washing tailings, slag, and admixture are added to a mortar stirring pot and stirred at a speed of 62±5 r / min for 1 minute to obtain a mixed powder. The slag is S95 slag, and the admixture is one or more of sodium chloride, sodium hydroxide, sodium carbonate, and calcium hydroxide. ; Disperse the fibers evenly into the mixed powder, and stir at a speed of 62±5r / min for 2 minutes to obtain a mixed dry material; pour the activator mixed solution into the mixed dry material, and stir at a speed of 62±5r / min for 2 minutes to obtain a mixed slurry; use the prepared foaming liquid to make uniform foam through a foaming machine, and add the foam to the mixed slurry, and stir at a speed of 62±5r / min for 1 minute, then remove the stirring pot and use a tool to scrape the material remaining on the pot wall and bottom; return the stirring pot and continue stirring at a speed of 62±5r / min for 1~2 minutes to ensure that the foam is evenly dispersed in the mixed slurry. When the final mixture presents a creamy, fluid consistency that is easy to pour, the alkali-activated washed sand tailings foam concrete slurry is obtained; 5) The resulting creamy alkali-activated sand-washing tailings foam concrete slurry was injection molded, covered with a film, and placed in an environment at a temperature of 23±2°C and a relative humidity of 65±15% for 1 day. After hardening, the mold was removed. After removal of the mold, the slurry was placed in an environment at a temperature of 20±2°C and a relative humidity of greater than 95% and cured for 28 days to prepare low-carbon, shrinkage-inhibited, and high-strength alkali-activated sand-washing tailings foam concrete.

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