Preparation method of silica-calcium slag-phosphogypsum-based shrinkage reducing agent for ultra-high performance concrete

Abstract

The application discloses a preparation method of a silica-calcium slag-phosphogypsum-based shrinkage reducing agent for ultra-high performance concrete, and the method comprises the following steps: mixing, wet grinding, aging, washing, filtering and drying raw silica-calcium slag, raw phosphogypsum and a dispersion stabilizer to obtain a mixture A; mixing the raw silica-calcium slag and the raw phosphogypsum at a mass ratio of (1.8-2.5):1, wherein the water-material ratio of the wet grinding process is 2-3, and the ball-material ratio is 6-8; autoclave curing the mixture A, and then low-temperature drying and crushing the mixture A after the autoclave curing is completed to obtain a mixture B; uniformly mixing attapulgite into the mixture B to obtain the silica-calcium slag-phosphogypsum-based shrinkage reducing agent for the ultra-high performance concrete; the application can greatly reduce the shrinkage of the ultra-high performance concrete (UHPC), has no adverse effect on the fluidity and setting time of the UHPC, and is beneficial to improving the early mechanical properties of the UHPC; meanwhile, the preparation process is simple, the silica-calcium slag and the phosphogypsum are effectively utilized, and a new direction is provided for the resource utilization of the silica-calcium slag and the phosphogypsum.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of building materials, and particularly relates to a preparation method of a silicon-calcium slag-phosphogypsum-based shrinkage reducing agent. BACKGROUND

[0002] Ultra-high performance concrete (UHPC) is usually designed and prepared according to the closest packing theory, and its high density makes it a kind of fiber reinforced cement-based composite material with ultra-high mechanical properties, durability and toughness, which is widely used in the preparation of large-span pedestrian bridges, highway and railway bridges, thin-walled silos, nuclear waste tanks, cable anchorage reinforcement plates, ATM protective shells and the like.

[0003] The amount of UHPC glue is much higher than that of ordinary concrete, and in order to reduce the interface transition zone and improve the toughness, the coarse aggregate is usually removed, so that the shrinkage of UHPC is larger and the cracking risk is higher. At present, there are three kinds of technical methods for UHPC shrinkage reduction: mixing with expansion agent to produce volume expansion to compensate for shrinkage; mixing with internal curing agent to improve the internal relative humidity of concrete to reduce shrinkage; and using shrinkage reducing agent to reduce the surface tension of capillary pores to reduce shrinkage.

[0004] The above method or combination of several methods can reduce the shrinkage of UHPC to a certain extent, but the internal curing agent is usually a porous material, which increases the pores of UHPC and easily causes the decrease of the overall mechanical properties of UHPC; the expansion reaction of the expansion agent usually needs sufficient water, but the water-binder ratio of UHPC is low (0.12-0.18), so the expansion agent is difficult to fully react, resulting in insufficient expansion, and the unreacted expansion agent in UHPC is easy to react violently when meeting water in the later stage, leading to cracking and even pulverization of UHPC construction; the shrinkage reducing agent will delay the cement hydration and prolong the cement setting time, which is not conducive to the development of the early strength of UHPC.

[0005] Therefore, it is an urgent technical problem to develop a shrinkage reducing agent which can effectively reduce the shrinkage of UHPC without adversely affecting the strength of UHPC. SUMMARY

[0006] The application aims to provide a preparation method of a silicon-calcium slag-phosphogypsum-based shrinkage reducing agent for ultra-high performance concrete, which can effectively reduce the shrinkage of UHPC without adversely affecting the fluidity and setting time, and is beneficial to improve the early mechanical properties of UHPC.

[0007] In order to achieve the above-mentioned purpose, the technical scheme is as follows:

[0008] A preparation method of a silicon-calcium slag-phosphogypsum-based shrinkage reducing agent for ultra-high performance concrete, comprising the following steps:

[0009] 1) mixing raw calcium silicate slag, raw phosphogypsum, and a dispersion stabilizer, wet-grinding, aging, washing, filtering, and drying to obtain a mixture A;

[0010] 2) curing the mixture A by autoclaving, drying at low temperature, and pulverizing to obtain the mixture B;

[0011] 3) Add attapulgite to mixture B and mix evenly to obtain a calcium silicate slag-phosphogypsum based shrinkage reducing agent for ultra-high performance concrete.

[0012] The present invention grinds the original calcium silicate slag and the original phosphogypsum to a certain fineness through a wet grinding process, utilizes an acid-base neutralization reaction to fully react alkaline substances such as sodium hydroxide in the calcium silicate slag and acidic substances such as phosphoric acid in the phosphogypsum to generate sodium salt, thereby adjusting the pH value of the mixture, and then removes the sodium salt generated by the acid-base reaction through aging, washing, filtering and other means, and pre-treats the soluble phosphorus, soluble fluorine, organic matter and the like in the phosphogypsum, and then, through pressure steam curing, pre-hydrates the β-C2S in the calcium silicate slag to generate calcium hydroxide and CSH gel, thereby generating Calcium hydroxide reacts with residual soluble fluorine in phosphogypsum to form calcium fluoride, which reacts with eutectic phosphorus and residual soluble phosphorus to form calcium phosphate, thereby solidifying soluble fluorine, soluble phosphorus, and eutectic phosphorus, effectively reducing the adverse effects of impurities in calcium silicate slag and phosphogypsum on the workability, hydration process, and mechanical properties of cement concrete. Simultaneously, the CSH gel generated by the prehydration reaction of calcium silicate slag can serve as a hydration nucleation inducer for cement concrete, improving its early strength, while the insoluble calcium fluoride and calcium phosphate generated can serve as nucleation and dispersion reinforcement phases, improving its overall mechanical properties. Furthermore, in order to effectively control the rate at which dihydrate gypsum in phosphogypsum reacts with cement to form expansive ettringite, thereby preventing the ettringite from reacting too quickly and forming a large number of internal defects within the cement concrete, which would result in a decrease in the mechanical properties of the component, the present invention incorporates attapulgite with a layered chain structure to adsorb the shrinkage-reducing agent of the present invention, thereby reducing the release rate of its effective components during the cement hydration reaction.

[0013] Optionally, in step 1, the pH value of the original calcium silicate slag is 11-13, and the moisture content is 15-30 wt%; the pH value of the original phosphogypsum is 1.5-4.5, and the moisture content is 10-20 wt%.

[0014] Optionally, the original calcium silicate slag and original phosphogypsum in step 1 are mixed in a mass ratio of (1.8-2.5):1, the water-to-material ratio of the wet grinding process is 2-3, and the ball-to-material ratio is 6-8.

[0015] Optionally, step 1 further includes respectively measuring the moisture content of the original calcium silicate slag and the original phosphogypsum, and determining the amount of water added for wet grinding based on the moisture content of the original calcium silicate slag and the original phosphogypsum.

[0016] The present invention controls the amount of water used for wet grinding by jointly controlling the moisture content and the water-to-material ratio, thereby preventing the influence of the moisture content of the original calcium-silicon slag and original phosphogypsum on the dispersion effect of the materials during the wet grinding process, thereby facilitating improved grinding efficiency of the original calcium-silicon slag and original phosphogypsum, as well as improved separation of impurities in the original calcium-silicon slag and original phosphogypsum. Furthermore, in the present invention, the original calcium-silicon slag and original phosphogypsum are mixed at a mass ratio of (1.8-2.5):1, ensuring that the acid-base neutralization reaction of the original calcium-silicon slag and original phosphogypsum is fully carried out. Furthermore, by controlling the number of washing and filtration times, the pH value of the mixture A can be adjusted to within a range of 9-11, facilitating a high degree of reaction of the calcium-silicon slag hydration reaction during the subsequent autoclave curing process, and promoting the solidification of soluble fluorine, soluble phosphorus, and eutectic phosphorus in the phosphogypsum.

[0017] Optionally, the dispersion stabilizer is composed of polyethylene glycol and wollastonite fiber; the amount of the polyethylene glycol is 0.05-0.08% of the total mass of the original calcium silicate slag and the original phosphogypsum; the amount of the wollastonite fiber is 1-2% of the total mass of the original calcium silicate slag and the original phosphogypsum.

[0018] Optionally, the wollastonite fiber has an aspect ratio of 15-20, a length of 400-500 μm, and a width of 20-30 μm.

[0019] Optionally, the polyethylene glycol is one of PEG400 and PEG600.

[0020] The present invention uses polyethylene glycol and wollastonite fibers as dispersing stabilizers during the wet grinding process. Polyethylene glycol can reduce the surface tension of the liquid, promoting better dispersion of solid particles in the liquid. The micro-nano needle-like structure of the wollastonite fibers can, on the one hand, be interspersed between the solid particles during the wet grinding process to prevent solid particle agglomeration. On the other hand, the micro-nanoscale size enables a certain adsorption effect on the solid particles, thereby preventing slurry stratification during the wet grinding process, which affects the grinding efficiency of the calcium silicate slag and phosphogypsum. At the same time, after the wet grinding is completed, the slurry is washed, filtered, and dried. The wollastonite fibers, together with the calcium silicate slag and the calcium silicate slag, form a mixed material A, which can serve as a nucleating agent for the hydration reaction of the calcium silicate slag during the subsequent autoclave curing process, promoting the reverse of the hydration reaction.

[0021] Optionally, the grinding speed of the wet grinding process in step 1) is 100-200 rpm, and the grinding time is 35-45 min.

[0022] Optionally, the specific surface area of ​​the mixture A obtained in step 1) is not less than 300m 2 / kg; moisture content is 20-25wt%.

[0023] Optionally, the steam pressure of the autoclave curing in step 2) is 1.1-1.3 MPa, and the steam temperature is 185-200°C.

[0024] The present invention can provide suitable humidity for the reaction between the calcium silicate slag and the phosphogypsum by controlling the fineness and moisture content of the mixture A and the curing conditions of the autoclave curing, and ensure an effective contact area between the particles, thereby promoting a higher reaction rate and reaction degree between the calcium silicate slag and the phosphogypsum.

[0025] Optionally, the low-temperature drying in step 2) is performed at a temperature of 40-45°C.

[0026] Optionally, in step 3), the mass ratio of the mixture B to the attapulgite is 1:(0.05-0.1); the fineness of the attapulgite is 200 mesh-325 mesh.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The present invention is based on an acid-base neutralization reaction and uses a wet grinding process to pretreat impurities and adjust the pH of original calcium silicate slag and original phosphogypsum. Then, the hydration reaction of the calcium silicate slag is used to solidify the soluble fluorine, soluble phosphorus, and eutectic phosphorus in the phosphogypsum. Finally, the ion release rate is controlled by attapulgite with a layered chain structure, thereby obtaining a calcium silicate slag-phosphogypsum-based shrinkage-reducing agent with good shrinkage-reducing effect. When the calcium silicate slag-phosphogypsum-based shrinkage-reducing agent prepared by the present invention is used in UHPC, it can significantly reduce the shrinkage of UHPC, while having no adverse effects on the fluidity and setting time of UHPC, and is conducive to improving the early mechanical properties of UHPC.

[0029] 2. The preparation process of the present invention is simple, and the effective utilization of calcium silicate slag and phosphogypsum is achieved, providing a new direction for the resource utilization of calcium silicate slag and phosphogypsum. DETAILED DESCRIPTION

[0030] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with specific examples, but the content of the present invention is not limited to the following examples.

[0031] The specific embodiment provides

[0032] Example 1

[0033] A method for preparing a calcium silicate slag-phosphogypsum-based shrinkage reducing agent for ultra-high performance concrete, comprising the following steps:

[0034] 1) The moisture content of the original calcium silicate slag and the original phosphogypsum was measured respectively. The pH value of the original calcium silicate slag was 11.53, the moisture content was 25.4%, and the pH value of the original phosphogypsum was 2.55, the moisture content was 15.8%;

[0035] 2) Weighing raw calcium silicate slag and raw phosphogypsum in a mass ratio of 1.8:1;

[0036] 3) The amount of water added for wet grinding is determined according to the mass, moisture content, and water-to-material ratio of the original calcium-silicon slag and original phosphogypsum in the wet grinding process. The amount of water added for wet grinding W satisfies the following conditions: W=Wr×(m1+m2)-m1×W1 / (1+W1)-m2×W2 / (1+W2). In this embodiment, the water-to-material ratio is set to 2.

[0037] 4) The weighed raw calcium silicate slag, raw phosphogypsum, and water were placed in a wet grinder with a ball-to-material ratio of 6, and a dispersion stabilizer consisting of polyethylene glycol and wollastonite fiber was added. The mixture was ground at a grinding speed of 100 rpm for 45 minutes, then aged for 6 hours, washed and filtered until the pH value of the supernatant was within the range of 9-11, and then dried at 105°C to obtain a wet grinder with a moisture content of 20% and a specific surface area of ​​320 m 2 / kg of mixture A, wherein the grinding media consists of steel balls with diameters of 5 mm, 10 mm, and 20 mm, and the mass ratio of the steel balls of different diameters is 5 mm:10 mm:20 mm=1:2:1; the amount of polyethylene glycol (PEG600) in the dispersion stabilizer is 0.05% of the total mass of the original calcium silicate slag and the original phosphogypsum; the amount of wollastonite fiber in the dispersion stabilizer is 1% of the total mass of the original calcium silicate slag and the original phosphogypsum, and the wollastonite fiber has a length of 450 μm, a width of 25 μm, and an aspect ratio of 18;

[0038] 5) Mixture A was autoclaved and cured for 8 h at a steam pressure of 1.1 MPa and a steam temperature of 185°C. After autoclaving, the mixture was dried at 45°C and then ball-milled for 2 min to obtain mixture B.

[0039] 6) Add a certain amount of attapulgite with a fineness of 325 mesh to mixture B and mix evenly to obtain a silica-calcium slag-phosphogypsum based shrinkage reducing agent for ultra-high performance concrete, wherein the mass ratio of mixture B to attapulgite is 1:0.05.

[0040] Example 2

[0041] A method for preparing a calcium silicate slag-phosphogypsum-based shrinkage reducing agent for ultra-high performance concrete, comprising the following steps:

[0042] 1) The moisture content of the original calcium silicate slag and the original phosphogypsum was measured respectively. The pH value of the original calcium silicate slag was 11.53, the moisture content was 25.4%, and the pH value of the original phosphogypsum was 2.55, the moisture content was 15.8%;

[0043] 2) Weighing raw calcium silicate slag and raw phosphogypsum in a mass ratio of 2.5:1;

[0044] 3) The amount of water added for wet grinding is determined according to the mass, moisture content, and water-to-material ratio of the original calcium-silicon slag and original phosphogypsum in the wet grinding process. The amount of water added for wet grinding W satisfies the following conditions: W=Wr×(m1+m2)-m1×W1 / (1+W1)-m2×W2 / (1+W2) for the moisture content W1 of the original calcium-silicon slag, the mass m1 of the original calcium-silicon slag, the moisture content W2 of the original phosphogypsum, the mass m2 of the original phosphogypsum, and the water-to-material ratio Wr of the wet grinding process. In this embodiment, the water-to-material ratio is set to 3.

[0045] 4) The weighed raw calcium silicate slag, raw phosphogypsum, and water were put into a wet grinder with a ball-to-material ratio of 8, and a dispersion stabilizer consisting of polyethylene glycol and wollastonite fiber was added. The mixture was ground at a grinding speed of 200 rpm for 35 minutes, then aged for 6 hours, washed and filtered until the pH value of the supernatant was within the range of 9-11, and dried at 105°C to obtain a product with a moisture content of 20% and a specific surface area of ​​350 m 2 / kg of mixture A, wherein the grinding media consists of steel balls with diameters of 5 mm, 10 mm, and 20 mm, and the mass ratio of the steel balls with different diameters is 5 mm:10 mm:20 mm=1:2:1; the dispersion stabilizer consists of polyethylene glycol (PEG400) and wollastonite fiber, and the amount of polyethylene glycol is 0.08% of the total mass of the original calcium silicate slag and the original phosphogypsum; the amount of wollastonite fiber is 2% of the total mass of the original calcium silicate slag and the original phosphogypsum, and the wollastonite fiber has a length of 450 μm, a width of 25 μm, and an aspect ratio of 18;

[0046] 5) Mixture A was autoclaved and cured for 6 h at a steam pressure of 1.3 MPa and a steam temperature of 200°C. After the autoclave curing, the mixture was dried at 45°C and then ball-milled for 2 min to obtain mixture B.

[0047] 6) Add a certain amount of attapulgite with a fineness of 200 mesh to mixture B and mix evenly to obtain a calcium silicate slag-phosphogypsum based shrinkage reducing agent for ultra-high performance concrete, wherein the mass ratio of mixture B to attapulgite is 1:0.1.

[0048] Comparative Example 1

[0049] Example 1 was repeated, and the amount of dispersion stabilizer added during the wet grinding process was 0. The specific surface area of ​​the mixture A obtained in this comparative example was 260 m 2 / kg.

[0050] Comparative Example 2

[0051] Example 1 was repeated, but polyethylene glycol was used as the dispersion stabilizer in the wet grinding process, and the amount used was 0.05% of the total mass of the original calcium silicate slag and the original phosphogypsum. The specific surface area of ​​the mixture A obtained in this comparative example was 300m2 / kg.

[0052] Comparative Example 3

[0053] Example 1 was repeated, and the dispersing stabilizer was used alone in the wet grinding process, and the amount of wollastonite fiber was 1% of the total mass of the raw silicium calcium slag and raw phosphogypsum. The specific surface area of the mixture A obtained in this comparative example was 280 m 2 / kg.

[0054] Comparative Example 4

[0055] Example 1 was repeated, and the amount of attapulgite added was 0.

[0056] The suitable amount of the silicium calcium slag-phosphogypsum-based shrinkage-reducing agent for ultra-high performance concrete obtained by the present application is 10-20% of the total amount of cementitious materials (internal addition). The silicium calcium slag-phosphogypsum-based shrinkage-reducing agent for ultra-high performance concrete obtained by Examples 1-2 and Comparative Examples 1-4 of the present application was used in ultra-high performance concrete, and the samples were standard cured to the specified age, and their performance was tested, wherein the amount of the shrinkage-reducing agent was 15% of the total amount of cementitious materials (internal addition), and the blank sample was an ultra-high performance concrete sample without the shrinkage-reducing agent of the present application. The mixture ratio (kg / m 3 ) of the blank sample and the ultra-high performance concrete sample with the shrinkage-reducing agent obtained by the examples and comparative examples is shown in Table 1, and the test results are shown in Table 2.

[0057] Table 1

[0058] cement silica fume microbeads Shrinkage reducing agent water Polycarboxylate water reducer quartz sand Steel Fiber 726 145 166 0 176 8.3 1037 156 618 123 141 155 176 8.3 1037 156

[0059] Table 2

[0060]

[0061] As can be seen from Table 2, in the preparation of ultra-high performance concrete, the addition of the silicium calcium slag-phosphogypsum-based shrinkage-reducing agent of the present application can greatly reduce the shrinkage of the test piece, and also can improve the early strength of the test piece, although the late strength is reduced, but the reduction is not significant, and the shrinkage-reducing agent of the present application has no obvious adverse effect on the working performance of the paste. Compared with Example 1, in the wet grinding process, the dispersing stabilizer was removed (Comparative Example 1), or only polyethylene glycol and wollastonite fiber were used as the dispersing stabilizer (Comparative Examples 2 and 3), and the grinding efficiency of the mixture was reduced, resulting in a reduction in the specific surface area of the mixture and the reaction activity, and further resulting in a reduction in the early strength of the prepared UHPC, and the late strength was also reduced due to the reduction in the reaction activity, and also resulting in an increase in the 28d shrinkage. Compared with Example 1, the attapulgite was removed (Comparative Example 4), and the 1d strength of the test piece was greatly improved, but the SO4 2-The release rate is too fast, resulting in a higher rate of reaction with cement hydration products to form ettringite, which increases the number of defects inside the paste and increases the strength reduction of the specimen after 3 days.

[0062] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a calcium silicate slag-phosphogypsum-based shrinkage reducing agent for ultra-high performance concrete, characterized in that The following steps are involved: 1) Wet-grinding raw calcium silicate slag, raw phosphogypsum, and a dispersion stabilizer, aging, washing, filtering, and drying to obtain a mixture A; the raw calcium silicate slag and raw phosphogypsum are mixed in a mass ratio of (1.8-2.5):1; the dispersion stabilizer comprises polyethylene glycol and wollastonite fiber; the amount of the polyethylene glycol is 0.05-0.08% of the total mass of the raw calcium silicate slag and the raw phosphogypsum; the amount of the wollastonite fiber is 1-2% of the total mass of the raw calcium silicate slag and the raw phosphogypsum; 2) Mixture A is autoclaved and cured, and then low-temperature dried and crushed to obtain mixture B; 3) Adding attapulgite to mixture B and mixing evenly to obtain a calcium silicate slag-phosphogypsum based shrinkage reducing agent for ultra-high performance concrete; the mass ratio of the mixture B to the attapulgite is 1:(0.05-0.1).

2. The method for preparing the calcium silicate slag-phosphogypsum based shrinkage reducing agent according to claim 1, wherein In step 1), the pH value of the original calcium silicate slag is 11-13, and the moisture content is 15-30wt%; the pH value of the original phosphogypsum is 1.5-4.5, and the moisture content is 10-20wt%.

3. The method for preparing the calcium silicate slag-phosphogypsum based shrinkage reducing agent according to claim 1, wherein In step 1), the water-to-material ratio of the wet grinding process is 2-3, and the ball-to-material ratio is 6-8.

4. The method for preparing the calcium silicate slag-phosphogypsum based shrinkage reducing agent according to claim 1, wherein Step 1) further includes measuring the moisture content of the original calcium silicate slag and the original phosphogypsum, respectively, and determining the amount of water added for wet grinding based on the moisture content of the original calcium silicate slag and the original phosphogypsum.

5. The method for preparing the calcium silicate slag-phosphogypsum based shrinkage reducing agent according to claim 1, wherein The wollastonite fiber has an aspect ratio of 15-20, a length of 400-500 μm, and a width of 20-30 μm; and the polyethylene glycol is one of PEG400 and PEG600.

6. The method for preparing the calcium silicate slag-phosphogypsum based shrinkage reducing agent according to claim 1, characterized in that Step 1) The wet grinding process has a grinding speed of 100-200 rpm and a grinding time of 35-45 min.

7. The method for preparing the calcium silicate slag-phosphogypsum based shrinkage reducing agent according to claim 1, characterized in that Step 1) The specific surface area of ​​the mixture A obtained is not less than 300 m 2 / kg; moisture content is 20-25wt%.

8. The method for preparing the calcium silicate slag-phosphogypsum based shrinkage reducing agent according to claim 1, characterized in that The steam pressure of the pressure steam curing in step 2) is 1.1-1.3 MPa, and the steam temperature is 185-200°C; the drying temperature of the low-temperature drying is 40-45°C.

9. The method for preparing the calcium silicate slag-phosphogypsum based shrinkage reducing agent according to claim 1, characterized in that The fineness of the attapulgite in step 3) is 200-325 mesh.

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