Low-carbon permeable concrete based on modified recycled aggregate and preparation method thereof

Abstract

The present invention discloses permeable concrete based on modified recycled aggregate, which comprises the following components by weight: 260-500 parts of low-carbon cementitious material, 900-1600 parts of modified recycled coarse aggregate, 50-200 parts of fine aggregate, 90-180 parts of water, and 9-30 parts of a water reducer. The modified recycled aggregate preparation method comprises the following steps: mechanically crushing building demolition materials to remove impurities to obtain 5-10 mm recycled coarse aggregate; soaking or spraying the recycled coarse aggregate with an acetic acid aqueous solution to moisten it; sequentially impregnating it with a calcium source solution and a nutrient solution under vacuum conditions; and finally impregnating it with a microbial suspension. In view of the problem that a large difference in carbonization degree exists during the carbonization curing process of permeable concrete prepared from low-carbon cementitious material, the present invention provides permeable concrete based on modified recycled aggregate and a preparation method thereof. By modifying the recycled aggregate, not only can the defects of the recycled aggregate itself be improved, but the carbonization homogeneity of the low-carbon permeable concrete can also be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of building materials, and particularly relates to permeable concrete and a preparation method thereof. Background Art

[0002] Low-carbon concrete not only uses low-carbon cement with lower carbon emissions, but also fixes a portion of carbon dioxide during the carbonation curing process. This has a significant impact on carbon reduction and emission reduction in the building materials industry, and research on low-carbon concrete has become a hot topic. At present, how to deepen the depth of carbonation is the focus and difficulty of low-carbon concrete research. Researchers mainly study the carbonation curing system, mix design, and carbonation enhancers, but there is less research on the carbonation situation inside low-carbon concrete. There is a large amount of construction and demolition waste worldwide, which pollutes the environment; the consumption and mining of natural sand and gravel on the ecological environment is also an urgent problem to be solved. Therefore, the use of construction waste as recycled aggregate is also one of the research hotspots; however, recycled aggregates have disadvantages such as high porosity, high water absorption, and low strength.

[0003] Carbonation curing is inevitable when using low-carbon cementitious materials to prepare permeable concrete. Although permeable concrete has certain air permeability due to its own characteristics, there is still a problem of large difference in carbonization degree between the surface and the interior during the actual preparation process, resulting in inconsistent internal and external strength, which seriously affects the service life. Summary of the Invention

[0004] In response to the problem that there are large differences in the degree of carbonization during the carbonization curing process of permeable concrete prepared from low-carbon cementitious materials, the present invention provides a permeable concrete based on modified recycled aggregate and a preparation method thereof. By modifying the recycled aggregate, not only the defects of the recycled aggregate itself can be improved, but also the carbonization homogeneity of the low-carbon permeable concrete can be improved.

[0005] In order to achieve the above purpose, the technical solutions adopted are as follows:

[0006] Pervious concrete based on modified recycled aggregate, the composition in parts by weight is as follows:

[0007] 260-500 parts of low-carbon cementitious material, 900-1600 parts of modified recycled coarse aggregate, 50-200 parts of fine aggregate, 90-180 parts of water, and 9-30 parts of water reducer;

[0008] The modified recycled aggregate preparation method comprises the following steps:

[0009] (1) Mechanically crush the demolished building materials to remove impurities and obtain 5-10mm recycled coarse aggregate;

[0010] (2) The recycled coarse aggregate is soaked or sprayed with an acetic acid aqueous solution;

[0011] (3) Under vacuum conditions, soak with calcium source solution and nutrient solution in turn; finally, soak with microbial suspension.

[0012] According to the above scheme, the concentration of the acetic acid aqueous solution in step 2 is 1% to 3%, and the treatment time is 12h to 24h.

[0013] According to the above scheme, the calcium source solution in step 3 is a calcium lactate solution, or a mixed solution of calcium lactate and calcium formate, with a concentration of 60-80 g / l.

[0014] According to the above scheme, the nutrient solution in step 3 is a yeast extract solution or a glucose solution with a concentration of 1 to 3 g / l.

[0015] According to the above scheme, the microorganism in step 3 is aerobic Bacillus pseudofirmus or Bacillus cohnii.

[0016] According to the above scheme, each immersion time in step 3 is 5 to 8 hours, and drying is required after each immersion.

[0017] According to the above scheme, the low-carbon cementitious material is a mixture of low-carbon clinker and mineral powder, and the ratio of low-carbon clinker to mineral powder is 1:0.25-0.6; the content of CS, C2S, and C3S2 in the low-carbon clinker is ≥80%.

[0018] According to the above scheme, the fineness modulus of the fine aggregate is 2.1~3.2, the stone powder content is ≤17%, and the crushing value is ≤20%.

[0019] The method for preparing the permeable concrete based on modified recycled aggregate comprises the following steps:

[0020] 1) Mixing the above raw materials in a mixer to obtain a permeable concrete mixture;

[0021] 2) The obtained permeable concrete mixture is vibrated and pressed into shape, and then placed in a CO2 curing environment for carbonization curing to obtain a permeable concrete product.

[0022] According to the above plan, the carbonization curing system is: CO2 volume concentration 20~80%, O2 volume concentration 20~80%, curing temperature 20~55℃, curing pressure 0.1~1.0MPa, and curing time 12~48h.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] Recycled aggregates have the characteristics of high water absorption and porosity. Under a vacuum environment, they can absorb more microorganisms and calcium source substrates, which helps microorganisms decompose to produce more CO2 and CaCO3, making the internal structure of concrete more compact.

[0025] During the modified process of the recycled aggregate of the present invention, calcium lactate and calcium formate are adsorbed, wherein calcium lactate reacts with O2 to generate CaCO3 and CO2; calcium formate reacts with Ca(OH)2 and O2 to generate CaCO3; carbonization active components in the low-carbon cementitious material and unhydrated cement minerals on the surface of the recycled aggregate further react with the generated CO2 to obtain more CaCO3 precipitation, the degree of carbonization inside the concrete is more sufficient, and the carbonization homogeneity of the concrete is improved; at the same time, the carbonization effect reduces the voids in the recycled aggregate and improves the firmness.

[0026] During the modification process of the recycled aggregate of the present invention, microorganisms are adsorbed. After activation, the microbial strains synthesize acid anhydrase by themselves, using the calcium source substrate attached to the surface of the modified recycled coarse aggregate as a deposition precursor to react with substrates such as calcium lactate or calcium formate to produce CaCO3. The reaction mechanism is as follows:

[0027] CaC6H 10 O6+6O2→CaCO3↓+5CO2↑+5H2O;

[0028] Ca(CHO2)2+Ca(OH)2+O2→2CaCO3↓ + 2H2O.

[0029] The present invention requires that the CO2 concentration during carbonization curing be 20-80% VOL, and the flue gas concentration at the kiln tail can meet the requirement, thereby reducing the CO2 purification process in production and lowering industrial energy consumption.

[0030] Low-carbon cementitious materials and recycled aggregates pretreated with acetic acid are suitable for the survival of microorganisms and can improve the survival rate of microorganisms without the need for biological sequestration; low-carbon cementitious materials are composed of low-carbon clinker and mineral powder, and the carbon emission factors of both are smaller than those of ordinary silicate clinker. Using low-carbon cementitious materials to replace traditional silicate cement can promote the green and healthy development of the cement industry. DETAILED DESCRIPTION

[0031] The following examples further illustrate the technical solutions of the present invention but are not intended to limit the scope of protection of the present invention.

[0032] The specific embodiments provide two types of low-carbon cementitious materials. In the first-grade low-carbon cementitious material, the ratio of low-carbon cement to mineral powder is 1:0.3, and the mineral components CS, C2S, and C3S2 each contain 91%. In the second-grade low-carbon cementitious material, the ratio of low-carbon cement to mineral powder is 1:0.5, and the mineral components CS, C2S, and C3S2 contain 86%. The ordinary Portland cement used is PO42.5 cement.

[0033] The recycled coarse aggregate used was obtained by crushing construction waste concrete with a jaw crusher. The recycled coarse aggregate was soaked in acetic acid for 12 hours and four types of modified recycled aggregates were obtained after different modification processes.

[0034] 1# Recycled coarse aggregate: Soak the recycled coarse aggregate in 1% acetic acid for 16 hours, then impregnate twice with a 70g / L calcium lactate and 1g / L yeast extract solution under vacuum conditions, followed by a final impregnation with a Bacillus pseudofirmus spore suspension; each impregnation lasts 5 hours. After impregnation, dry in a drying oven at 35°C for 1 day.

[0035] 2# Recycled coarse aggregate: Soak the recycled coarse aggregate in 2% acetic acid for 12 hours, then impregnate twice with a 60g / L calcium lactate and 2g / L yeast extract solution under vacuum conditions, followed by a final impregnation with a Bacillus pseudofirmus spore suspension. Each impregnation lasts 5 hours, and after impregnation, dry in a drying oven at 35°C for 1 day.

[0036] 3# Recycled coarse aggregate: Soak the recycled coarse aggregate in 2% acetic acid for 12 hours, then impregnate twice with a 70g / L calcium lactate and 1g / L yeast extract solution under vacuum conditions, followed by a final impregnation with an aerobic Bacillus pseudofirmus spore suspension. Each impregnation lasts for 6 hours. After impregnation, dry in a drying oven at 35°C for 2 days.

[0037] 4# recycled coarse aggregate: soak the recycled coarse aggregate in 1% acetic acid for 16 hours, impregnate it twice with 70g / L calcium lactate and 2g / L yeast extract solution under vacuum conditions, and then perform the final impregnation with Bacillus cohnii spore suspension; each impregnation time is 5 hours, and after impregnation, place it in a drying oven at 35℃ and dry it for 1 day.

[0038] There are two types of microorganisms: Bacillus pseudofirmus and Bacillus cohnii.

[0039] The fine aggregate used was dolomite machine-made sand with a fineness modulus of 3.0, a stone powder content of 4.4%, an MB value of 0.25, a crushing value of 22%, and a moisture content of 1%. A naphthalene-based water-reducing agent with a water-reducing rate of 20% was used as the admixture. Unless otherwise specified, all raw materials used in the specific embodiment were commercially available.

[0040] The specific embodiment also provides a modified natural coarse aggregate, comprising dolomite and limestone, with a particle size of 5-10 mm, continuous grading, a needle- and flake-shaped particle content (mass percentage) of 1.8%, a crushing value of 10%, and a saturated surface dry water absorption of 0.9%. The modification process is as follows: the recycled coarse aggregate is soaked in 1% acetic acid for 16 hours, then impregnated twice under vacuum with a 70g / L calcium lactate and 1g / L yeast extract solution, followed by a final impregnation with a suspension of Bacillus pseudofirmus spores; each impregnation lasts 5 hours, and the aggregate is dried in a drying oven at 35°C for 1 day.

[0041] Example 1

[0042] A permeable concrete based on modified recycled aggregate and a preparation method thereof, wherein the preparation steps are as follows:

[0043] 1) Weigh all raw materials and mix them evenly in a horizontal mixer to prepare a concrete mixture, wherein the mass proportions of the raw materials are as follows: 360 parts of 1# low-carbon cementitious material, 1600 parts of 1# modified recycled coarse aggregate, 200 parts of fine aggregate, 110 parts of water, and 18 parts of water reducer;

[0044] 2) The obtained permeable concrete mixture is vibrated and pressed into shape, and then placed in a CO2 curing environment for carbonization curing to obtain a permeable concrete product, wherein the carbonization system is: curing temperature 35°C, curing pressure 0.4 MPa, curing time 24 h, CO2 volume concentration 60%, and O2 volume concentration 40%.

[0045] Example 2

[0046] A permeable concrete based on modified recycled aggregate and a preparation method thereof are carried out according to the method in Example 1, except that 2# low-carbon cementitious material is used.

[0047] Example 3

[0048] A permeable concrete based on modified recycled aggregate and a preparation method thereof are carried out according to the method in Example 1, except that the coarse aggregate is 2# modified recycled aggregate.

[0049] Example 4

[0050] A permeable concrete based on modified recycled aggregate and a preparation method thereof are carried out according to the method in Example 1, except that the coarse aggregate is 3# modified recycled aggregate.

[0051] Example 5

[0052] A permeable concrete based on modified recycled aggregate is prepared according to the method in Example 1, except that the coarse aggregate is 4# modified recycled aggregate.

[0053] Example 6

[0054] Example 1 was repeated, except that the concrete mix ratio used was different. The mix ratio of this example was: 410 parts of 1# low-carbon cementitious material, 1400 parts of 1# modified recycled coarse aggregate, 200 parts of fine aggregate, 130 parts of water, and 26 parts of water reducer.

[0055] Example 7

[0056] A permeable concrete based on modified recycled aggregate is prepared according to the method of Example 1, except that the carbonation curing CO2 volume concentration is 30% and the O2 volume concentration is 70%.

[0057] Comparative Example 1

[0058] A permeable concrete with modified recycled aggregate and a preparation method thereof are prepared according to the method in Example 1, except that the low-carbon cementitious material in the raw materials is replaced with PO42.5 cement, and there is no carbonization curing process.

[0059] Comparative Example 2

[0060] A permeable concrete of modified recycled aggregate and a preparation method thereof are prepared according to the method in Example 1, except that the recycled aggregate used is not treated with acetic acid.

[0061] Comparative Example 3

[0062] A permeable concrete of modified recycled aggregate and a preparation method thereof are carried out according to the method in Example 1, except that the recycled aggregate used is free of calcium lactate and is not subjected to yeast extraction or microbial modification process.

[0063] Comparative Example 4

[0064] A permeable concrete of modified recycled aggregate and a preparation method thereof are carried out according to the method in Example 1, except that the prepared concrete is placed in an environment with a carbon dioxide concentration of 100% VOL for curing.

[0065] Comparative Example 5

[0066] A permeable concrete with modified recycled aggregate and a preparation method thereof are carried out according to the method in Example 1, except that the microorganism used is Bacillus pasteurianus.

[0067] Comparative Example 6

[0068] A permeable concrete with modified recycled aggregate and a preparation method thereof are carried out according to the method in Example 1, except that the coarse aggregate used is natural coarse aggregate modified by microorganisms.

[0069] Performance testing methods

[0070] The recycled aggregate permeable concrete prepared in Examples 1 to 6 and Comparative Examples 1 to 6 was subjected to performance tests in accordance with CJJ / T135-2009 "Technical Specification for Permeable Cement Concrete Pavement" and JTG 3420-2020 "Test Procedure for Cement and Cement Concrete in Highway Engineering". The volume of the specimen used for the internal carbonization depth test was 100 mm × 100 mm × 100 mm. The results are shown in Table 1.

[0071] Table 1 Performance test results of permeable concrete obtained from Examples 1 to 6 and Comparative Examples 1 to 6

[0072]

[0073] As can be seen from Table 1:

[0074] In Comparative Example 1, ordinary silicate PO42.5 cement is used as the cementitious material. The concrete system is strongly alkaline, which is not conducive to the survival of microorganisms. In addition, there are fewer carbonized active minerals involved, which is not conducive to the formation of CaCO3. Therefore, the overall performance of the permeable concrete is weaker than that of Examples 1-7.

[0075] Since the recycled aggregate in Comparative Example 2 has not been acidified, its surface is alkaline, which is not conducive to the survival of loaded microorganisms, and the precipitation of CO2 and CaCO3 inside the concrete is reduced. Therefore, the performance of the obtained permeable concrete is weaker than that of Examples 1-7.

[0076] Since the recycled aggregate in Comparative Example 3 has not undergone a microbial modification process, the strength of the permeable concrete comes from the hydration of the mineral components of the low-carbon cementitious material. The surface strength of the recycled aggregate is poor and the bonding with the cement mineral is weak. Therefore, the performance of the obtained permeable concrete is weaker than that of Examples 1-7.

[0077] In Comparative Example 4, the concentration of carbonized CO2 is 100%, and the microorganisms are aerobic bacterial spores that require oxygen to decompose the substrate to generate CO2 and CaCO3 precipitation. Therefore, the performance of the permeable concrete prepared in Comparative Example 4 is weaker than that of Examples 1-7.

[0078] The microorganisms used in Comparative Example 5 do not have the function of decomposing nutrients to generate CO2 and CaCO3 precipitation, so the performance of the permeable concrete prepared in Comparative Example 5 is weaker than that of Examples 1-7.

[0079] The coarse aggregate used in Comparative Example 6 is modified natural coarse aggregate, which has few surface pores and few carbonizable minerals, and can absorb less loaded microorganisms and nutrient substrates, which is not conducive to the generation of CO2 and CaCO3 precipitation. The internal aggregate and carbonization product have weak meshing force, so the performance of the permeable concrete prepared in Comparative Example 6 is weaker than that of Examples 1-7.

[0080] The above results show that the recycled aggregate permeable concrete prepared in Examples 1 to 7 has high compressive strength, good carbonization degree and freeze-thaw resistance; the carbonization curing CO2 concentration is low, and the low-carbon cementitious material has low carbon emissions, which has important environmental and economic benefits.

[0081] The above embodiments are merely examples for illustrative purposes only and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications may be made based on the above descriptions. It is not necessary and impossible to enumerate all implementation methods here. Therefore, any obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. Permeable concrete based on modified recycled aggregate, characterized by The composition is calculated by weight as follows: 260-500 parts of low-carbon cementitious material, 900-1600 parts of modified recycled coarse aggregate, 50-200 parts of fine aggregate, 90-180 parts of water, and 9-30 parts of water reducer; The modified recycled coarse aggregate preparation method comprises the following steps: (1) Mechanically crush the demolished building materials to remove impurities and obtain 5-10mm recycled coarse aggregate; (2) The recycled coarse aggregate is soaked or sprayed with an acetic acid aqueous solution; (3) Impregnating with calcium source solution and nutrient solution in sequence under vacuum conditions; and finally impregnating with microbial suspension; the calcium source solution is calcium lactate solution, or a mixed solution of calcium lactate and calcium formate; the microorganism is aerobic Bacillus pseudofirmus or Bacillus cohnii.

2. The permeable concrete based on modified recycled aggregate according to claim 1, characterized in that The concentration of the acetic acid aqueous solution in step 2 is 1% to 3%, and the treatment time is 12h to 24h.

3. The permeable concrete based on modified recycled aggregate according to claim 1, characterized in that The concentration of the calcium source solution in step 3 is 60-80 g / l.

4. The permeable concrete based on modified recycled aggregate according to claim 1, characterized in that The nutrient solution in step 3 is a yeast extract solution or a glucose solution with a concentration of 1 to 3 g / l.

5. The permeable concrete based on modified recycled aggregate according to claim 1, characterized in that In step 3, each immersion time is 5 to 8 hours, and drying is required after each immersion.

6. The permeable concrete based on modified recycled aggregate according to claim 1, characterized in that The low-carbon cementitious material is a mixture of low-carbon clinker and mineral powder, with the ratio of low-carbon clinker to mineral powder being 1:0.25-0.6; the contents of CS, C2S and C3S2 in the low-carbon clinker being ≥80%.

7. The permeable concrete based on modified recycled aggregate according to claim 1, characterized in that The fineness modulus of the fine aggregate is 2.1-3.2, the stone powder content is ≤17%, and the crushing value is ≤20%.

8. The method for preparing permeable concrete based on modified recycled aggregate according to claim 1, characterized in that The following steps are involved: 1) Mixing the above raw materials uniformly to obtain a permeable concrete mixture; 2) The obtained permeable concrete mixture is vibrated and pressed into shape, and then placed in a CO2 curing environment for carbonization curing to obtain a permeable concrete product.

9. The method for preparing permeable concrete based on modified recycled aggregate according to claim 8, characterized in that The carbonization curing system is: CO2 volume concentration 20~80%, O2 volume concentration 20~80%, curing temperature 20~55℃, curing pressure 0.1~1.0MPa, and curing time 12~48h.

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