Biochar modified super sulfate cement-based material and preparation method thereof

Abstract

The invention discloses a biochar modified super sulfate cement-based material and a preparation method thereof. The cement-based material comprises 20%-25% of a super sulfate cement mixture, 60%-65% of sand, 0.02%-0.05% of a water reducing agent and the balance of water, the super sulfate cement mixture comprises 65%-80% of slag, 15%-20% of desulfurized gypsum, 2%-5% of cement and 3%-10% of charcoal. The preparation method comprises the following steps: carrying out high-temperature anaerobic cracking on waste biomass, and grinding to obtain biochar; stirring and mixing the desulfurized gypsum, the slag, the cement and the biochar to obtain a mixture; and mixing the water reducing agent with water, adding the mixture, stirring, adding the sand, and stirring to obtain the concrete. According to the anti-freezing super sulfate cement mortar, the anti-freezing and thawing performance is remarkably improved, the mass loss rate is reduced to 0.61% after 25 times of freezing and thawing cycles at the 3d age, and the compressive strength loss rate is reduced to 37.90%.

Description

Technical Field

[0001] The present invention relates to a cement-based material and a preparation method thereof, and particularly to a biochar-modified supersulfate cement-based material and a preparation method thereof. Background Art

[0002] In recent years, supersulfate cement has received extensive attention due to its extremely low carbon emissions and the ability to absorb solid waste. However, supersulfate cement will be significantly damaged in a severe cold environment, severely restricting its wide application in cold regions or extreme weather conditions. The preparation method of an antifreeze supersulfate concrete proposed in the invention patent CN 114394813 B improves the antifreeze performance of supersulfate cement by adding a composite additive. However, adding lactic acid will significantly reduce the early hydration degree and mechanical properties of supersulfate cement, and it is necessary to carry out long-term curing to achieve the improvement of antifreeze performance. While the chemical additives and curing costs are high, it does not match the construction requirements in actual projects. The antifreeze supersulfate cement mortar needs to maintain the early strength and improve its freeze-thaw resistance at all ages. It is necessary to use a preparation process of supersulfate cement mortar with low cost, no need for long-term curing, and capable of improving the antifreeze performance. Summary of the Invention

[0003] Object of the Invention: The object of the present invention is to provide a biochar-modified supersulfate cement-based material with significantly improved freeze-thaw resistance; the second object of the present invention is to provide a preparation method of the above biochar-modified supersulfate cement-based material.

[0004] Technical Solution: The biochar-modified supersulfate cement-based material described in the present invention includes the following components in mass percentage: 20% - 25% of supersulfate cement mixture, 60% - 65% of sand, 0.2‰ - 0.5‰ of water reducer, and the balance of water;

[0005] The supersulfate cement mixture includes the following components in mass percentage: 65% - 80% of slag, 15% - 20% of desulfurized gypsum, 2% - 5% of cement, and 3 - 10% of biochar.

[0006] Among them, the water reducer is a polycarboxylate-based water reducer with a solid content of 40 - 50%.

[0007] Among them, the biochar is bamboo biochar or corn straw biochar.

[0008] The preparation method of the above biochar-modified supersulfate cement-based material includes the following steps:

[0009] (1) Subject the waste biomass to high-temperature anaerobic pyrolysis and grinding to obtain the required biochar;

[0010] (2) Mix the desulfurized gypsum, slag, cement, and biochar to obtain a supersulfate cement mixture;

[0011] (3) Mix the water reducer with water, add the supersulfate cement mixture, and stir;

[0012] (4) Add sand to the mixed cement paste and stir to prepare a biochar-modified supersulfate cement-based material.

[0013] Among them, in step (1), the waste biomass is bamboo or corn straw.

[0014] Among them, in step (1), the temperature of the anaerobic pyrolysis is 650 - 750 °C, and the calcination duration is 4 - 5 h; the protective gas during anaerobic pyrolysis is nitrogen or argon.

[0015] Among them, in step (2), the desulfurized gypsum used is CaSO4·1 / 2H2O or CaSO4·2H2O.

[0016] Among them, in step (3), the stirring is low-speed stirring at 65 rpm for 30 - 35 s.

[0017] Among them, in step (4), the stirring is low-speed stirring at 65 rpm for 30 - 35 s and then high-speed stirring at 130 rpm for 30 - 35 s.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following remarkable effects:

[0019] (1) For the frost-resistant supersulfate cement mortar of the present invention, the frost resistance performance is significantly improved. After 25 freeze-thaw cycles at the 3d age, the mass loss rate is reduced to 0.61%, and the compressive strength loss rate is reduced to 37.90%. After 25 freeze-thaw cycles at the 28d age, the mass loss rate is reduced to 0.09%, and the compressive strength loss rate is reduced to 9.91%.

[0020] (2) For the frost-resistant supersulfate cement mortar of the present invention, the early hydration and later strength are significantly enhanced. The 3d flexural strength is increased by about 36%, and the 28d compressive strength is increased by about 22%. Biochar can promote the hydration process of supersulfate cement at all ages; the preparation of biochar and its raw materials are simple and easy to obtain, and at the same time, it can consume a large amount of agricultural waste, with low cost, low carbon, and green. Description of the Drawings

[0021] Figure 1 Pore structure of bamboo biochar measured by nitrogen adsorption method;

[0022] Figure 2 Pore structure of corn straw biochar measured by nitrogen adsorption method;

[0023] Figure 3Water absorption rate of bamboo biochar at different times;

[0024] Figure 4 Water absorption rate of corn straw biochar at different times. Detailed implementation manners

[0025] The present invention will be further described in detail below.

[0026] Example 1

[0027] (1) Prepare bamboo biochar: Put the waste bamboo after preliminary crushing into a tubular furnace, introduce nitrogen as a protective gas, heat it to 700 °C at a heating rate of 25 °C / min, and continuously calcine for 4 h to obtain 1 kg of bamboo biochar. Use a crusher to crush it and pass through a 60-mesh sieve, with a particle size of 0.25 mm;

[0028] (2) Degas the bamboo biochar sample at 120 °C for 12 hours, and perform adsorption and desorption in an N2 atmosphere using a Quantachrome AutosorbIQ MP full-automatic specific surface and porosity analyzer. The obtained pore characteristics are as Figure 1 shown;

[0029] (3) Pass the bamboo biochar through sieves with pore sizes of 0.3 mm and 0.15 mm respectively, divide the biochar particles into three grades of r>0.3 mm, 0.3 mm>r>0.15 mm, and r<0.15 mm. After soaking in water for 3, 5, 8, 15, 25, and 45 minutes respectively, centrifuge at a speed of 10,000 rpm for 5 minutes, and then dry at 60 °C for 12 h. Calculate the different water absorption rates of the two biochars through the mass difference before and after, and the obtained results are as Figure 3 shown;

[0030] (4) Prepare 500 g of supersulfate cement mixture: Take 370 g of slag, 100 g of desulfurized gypsum, 10 g of cement, and 20 g of bamboo biochar, stir and mix them to obtain;

[0031] (5) Mix 500 g of supersulfate cement mixture, 1 g of water reducer and 250 g of water, stir slowly for 30 s, and then add 1350 g of sand to prepare a biochar-modified frost-resistant supersulfate cement-based material.

[0032] After the stirring is completed, carry out mortar forming. Remove the formwork at the age of 1 d and transfer it to a standard curing room. After curing to the ages of 3 d, 7 d, and 28 d, carry out strength tests and freeze-thaw cycle experiments of the cement-based material, etc. The experimental results are shown in Tables 1-5.

[0033] Example 2

[0034] (1) Preparation of bamboo biochar: The waste bamboo was preliminarily crushed and then placed in a tubular furnace. Nitrogen was introduced as a protective gas, and the temperature was raised to 700 °C at a heating rate of 25 °C / min and calcined for 4 h to obtain 1 kg of bamboo biochar. It was crushed using a crusher and passed through a 60-mesh sieve, with a particle size of 0.25 mm;

[0035] (2) Pore structure analysis of the bamboo biochar was carried out, and the experimental process was the same as that in Example 1;

[0036] (3) Water absorption analysis of the bamboo biochar was carried out, and the experimental process was the same as that in Example 1;

[0037] (4) Preparation of 500 g of supersulfate cement mixture: 350 g of slag, 100 g of desulfurized gypsum, 10 g of cement, and 40 g of bamboo biochar were taken and stirred and mixed to obtain it;

[0038] (5) 500 g of the supersulfate cement mixture, 1 g of water reducer, and 250 g of water were mixed and slowly stirred for 30 s, and then 1350 g of sand was added to prepare the biochar-modified frost-resistant supersulfate cement-based material.

[0039] After the stirring was completed, mortar forming was carried out. After demolding at the age of 1 d, it was moved into a standard curing room. After curing to the ages of 3 d, 7 d, and 28 d, strength tests and freeze-thaw cycle experiments of the cement-based material were carried out. The experimental results are shown in Tables 1 to 5.

[0040] Example 3

[0041] (1) Preparation of corn straw biochar: The corn straw was preliminarily crushed and then placed in a tubular furnace. Nitrogen was introduced as a protective gas, and the temperature was raised to 700 °C at a heating rate of 25 °C / min and calcined for 4 h to obtain 1 kg of corn straw biochar. It was crushed using a crusher and passed through a 60-mesh sieve, with a particle size of 0.25 mm;

[0042] (2) The corn straw biochar sample was degassed at 120 °C for 12 hours, and adsorption and desorption were carried out in an N2 atmosphere using a Quantachrome Autosorb IQ MP fully automatic specific surface area and porosity analyzer. The obtained pore characteristics are as Figure 2 shown;

[0043] (3) The corn straw biochar was passed through sieves with pore diameters of 0.3 mm and 0.15 mm respectively. The biochar particles were divided into three grades: r > 0.3 mm, 0.3 mm > r > 0.15 mm, and r < 0.15 mm. After soaking in water for 3, 5, 8, 15, 25, and 45 minutes respectively, centrifugation was carried out at a speed of 10000 rpm for 5 minutes, and then dried at 60 °C for 12 h. The different water absorption rates of the two biochars were calculated through the mass difference before and after, and the obtained results are as Figure 4 shown;

[0044] (4) Prepare 500 g of supersulphate cement mixture: Take 370 g of slag, 100 g of desulphurized gypsum, 10 g of cement, and 20 g of corn straw biochar, stir and mix them to obtain it;

[0045] (5) Mix 500 g of supersulphate cement mixture, 1 g of water reducing agent and 250 g of water, stir slowly for 30 s, and then add 1350 g of sand to prepare biochar-modified frost-resistant supersulphate cement-based material.

[0046] After the stirring is completed, mortar forming is carried out. Demoulding is carried out at the age of 1 d and then moved into the standard curing room. After curing to the ages of 3 d, 7 d and 28 d, strength tests and freeze-thaw cycle experiments of the cement-based material are carried out. The experimental results are shown in Tables 1 - 5.

[0047] Example 4

[0048] (1) Prepare bamboo biochar: Put the waste bamboo after preliminary crushing into a tubular furnace, introduce nitrogen as a protective gas, heat it up to 700 °C at a heating rate of 25 °C / min, and continuously calcine for 4 h to prepare 1 kg of corn straw biochar. Use a crusher to crush it and pass through a 60-mesh sieve, with a particle size of 0.25 mm;

[0049] (2) Conduct pore structure analysis on the corn straw biochar. The experimental process is the same as that in Example 3;

[0050] (3) Conduct water absorption analysis on the corn straw biochar. The experimental process is the same as that in Example 3;

[0051] (4) Prepare 500 g of supersulphate cement mixture: Take 350 g of slag, 100 g of desulphurized gypsum, 10 g of cement, and 40 g of corn straw biochar, stir and mix them to obtain it;

[0052] (5) Mix 500 g of supersulphate cement mixture, 1 g of water reducing agent and 250 g of water, stir slowly for 30 s, and then add 1350 g of sand to prepare biochar-modified frost-resistant supersulphate cement-based material.

[0053] After the stirring is completed, mortar forming is carried out. Demoulding is carried out at the age of 1 d and then moved into the standard curing room. After curing to the ages of 3 d, 7 d and 28 d, strength tests and freeze-thaw cycle experiments of the cement-based material are carried out. The experimental results are shown in Tables 1 - 5.

[0054] Comparative Example 1

[0055] (1) Mix 500 g of ordinary Portland cement, 1 g of water reducing agent and 250 g of water, stir slowly for 30 s, and then add 1350 g of sand to prepare ordinary Portland cement mortar;

[0056] After the stirring is completed, mortar forming is carried out. The formwork is removed at the age of 1 day and transferred to a standard curing room. After curing to the ages of 3 days, 7 days and 28 days, tests such as the strength test of cement mortar and freeze-thaw cycle experiment are carried out, and the experimental results are shown in Tables 1 to 5.

[0057] Comparative Example 2

[0058] (1) Prepare 500 g of supersulfate cement mixture: Take 390 g of slag, 100 g of desulfurized gypsum, and 10 g of cement, stir and mix them to obtain it.

[0059] (2) Mix 500 g of supersulfate cement mixture, 1 g of water reducer and 250 g of water, stir slowly for 30 s, and then add 1350 g of sand to prepare supersulfate cement mortar.

[0060] After the stirring is completed, mortar forming is carried out. The formwork is removed at the age of 1 day and transferred to a standard curing room. After curing to the ages of 3 days, 7 days and 28 days, tests such as the strength test of cement mortar and freeze-thaw cycle experiment are carried out, and the experimental results are shown in Tables 1 to 5.

[0061] Table 1 Mass loss rate (%) of cement-based materials after freeze-thaw cycles at different ages

[0062] Age Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 3d 18.20 13.45 15.67 8.55 1.16 31.29 7d 13.28 9.87 11.94 5.78 0.99 23.91 28d 8.44 5.72 6.22 3.10 0.72 11.07

[0063] Table 2 Flexural strength loss rate (%) of cement-based materials after freeze-thaw cycles at different ages

[0064] Age Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 3d 58.13 50.00 66.10 59.18 25.35 78.05 7d 51.16 43.47 55.79 48.72 18.42 75.00 28d 30.59 15.41 28.71 11.11 4.65 50.00

[0065] Table 3 Compressive strength loss rate (%) of cement-based materials after freeze-thaw cycles at different ages

[0066] Age Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 3d 59.24 46.11 56.74 37.90 11.72 68.58 7d 27.66 20.62 25.47 16.41 8.20 37.12 28d 22.87 11.34 18.51 9.91 3.00 26.83

[0067] Table 4 Flexural strength (MPa) of cement-based materials at different ages

[0068] Age Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 3d 5.3 5.7 5 5.2 6.0 4.2 7d 7.7 8.1 7.6 8.3 10.5 6.6 28d 9.4 10.4 9.4 11.0 12.5 8.2

[0069] Table 5 Compressive strength (MPa) of cement-based materials at different ages

[0070] Age Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 3d 15.90 16.50 16.35 17.40 29.05 14.05 7d 32.90 35.65 34.25 37.85 42.80 28.65 28d 55.25 56.80 55.95 57.55 53.85 46.80

[0071] The reference group of supersulfate cement mortar at 3d age, i.e., Comparative Example 2, after 25 freeze-thaw cycles, the mass loss rate reached 31.29%, and the flexural and compressive strength loss rates were 78.05% and 68.58%; these data were 11.07%, 50.00% and 26.83% at 28d age; the freeze-thaw performance indexes of ordinary Portland cement were better than those of the reference supersulfate cement at all ages; after adding bamboo biochar and corn straw biochar, i.e., the mass loss rate, flexural and compressive strength loss rates of Examples 1 and 3 at 3d age were 18.20%, 58.13%, 59.24% and 15.67%, 66.10%, 56.74%; the mass loss rate, flexural and compressive strength loss rates at 28d age were 8.44%, 30.59%, 22.87% and 6.22%, 28.17%, 18.51%, the mass loss rate decreased, and the strength loss rates after freeze-thaw all decreased; after adjusting the dosage of biochar in the components, such as Examples 2 and 4, the mass loss rate, flexural and compressive strength loss rates at 3d age were 13.45%, 50.00%, 46.11% and 8.55%, 59.18%, 37.90%; the mass loss rate, flexural and compressive strength loss rates at 28d age were 5.72%, 15.41%, 11.34% and 3.10%, 11.11%, 9.91%, the mass and strength loss rates were lower, and were slightly lower than the level of ordinary Portland cement.

[0072] Figure 1 The nanoscale pore structure of the biochar measured by the nitrogen adsorption method is shown in the figure. Bamboo biochar has more nanopores around 5nm, while corn straw biochar has more nanopores around 2nm. The small pores of both can prevent water from entering through surface tension in the thawed state and can serve as the growth space for ice crystals during the freezing process, thereby reducing the crystallization pressure of water during the freeze-thaw process and reducing the degree of freeze-thaw damage.

[0073] Combined with Figure 2 the water absorption rate results, corn straw biochar and bamboo biochar can absorb water to reach full saturation within 3 minutes, and biochar with a larger particle size can absorb more water. The maximum 3-minute water absorption rate of bamboo biochar is 191%, and the maximum 3-minute water absorption rate of corn straw is 206%. During the freeze-thaw process, biochar can quickly absorb some of the water in the system, thereby reducing the volume expansion caused by water crystallization. The higher water absorption rate of corn straw can bring better freeze-thaw resistance.

[0074] Combined with the test results in Table 4 and Table 5, the introduction of biochar improved the flexural strength and compressive strength of the cement mortar at all ages. The flexural strength at 28 days was improved compared with that of the reference supersulfate cement mortar, and the compressive strength exceeded that of the ordinary Portland cement mortar at the same age. This indicates that it not only improved the freeze-thaw resistance of the supersulfate cement mortar but also had the effect of improving the mechanical properties.

[0075] The data of the comparative examples and the examples show that the incorporation of bamboo biochar and corn straw biochar can promote the hydration process and improve the strength of the supersulfate cement mortar at all ages, and basically meet or even exceed the strength standard of the ordinary Portland cement at the age of 28 days. At the same time, bamboo biochar and corn straw biochar, through their own water absorption properties, absorb or release the water in the pores during the freeze-thaw process, reducing the volume expansion caused by water crystallization in the system. The introduction of the two biochars can reduce the mass and strength loss rates of the supersulfate cement mortar after freeze-thaw, without affecting the workability, and significantly improve the mechanical properties, making all aspects of its performance indicators reach a level slightly lower than or close to that of the ordinary Portland cement mortar.

Claims

1. A biochar-modified supersulfate cement-based material, characterized in that: The invention comprises the following components in percentage by weight: 20% to 25% of supersulfate cement mixture, 60% to 65% of sand, 0.2‰ to 0.5‰ of water reducing agent and the balance of water; The super sulfate cement mixture comprises the following components in percentage by mass: 65% to 80% of slag, 15% to 20% of desulfurized gypsum, 2% to 5% of cement and 3% to 10% of biochar.

2. The biochar-modified supersulfate cement-based material according to claim 1, characterized in that: The water reducing agent is a polycarboxylic acid water reducing agent with a solid content of 40 to 50%.

3. The biochar-modified supersulfate cement-based material according to claim 1, characterized in that: The biochar is bamboo biochar or corn straw biochar.

4. A method for preparing the biochar-modified supersulfate cement-based material according to claim 1, characterized in that: The following steps are involved: (1) subjecting the waste biomass to high-temperature anaerobic pyrolysis and grinding to obtain the desired biochar; (2) mixing desulfurized gypsum, slag, cement and biochar to obtain a supersulfate cement mixture; (3) mixing the water reducer with water, adding the super sulfate cement mixture and stirring; (4) Adding sand to the mixed cement paste and stirring to obtain a biochar-modified supersulfate cement-based material.

5. The method for preparing the biochar-modified supersulfate cement-based material according to claim 4, characterized in that: In step (1), the waste biomass is bamboo or corn stalks.

6. The method for preparing the biochar-modified supersulfate cement-based material according to claim 4, characterized in that: In step (1), the temperature of the anaerobic pyrolysis is 650-750° C., and the calcination time is 4-5 hours.

7. The method for preparing the biochar-modified supersulfate cement-based material according to claim 4, characterized in that: In step (1), the protective gas during anaerobic pyrolysis is nitrogen or argon.

8. The method for preparing the biochar-modified supersulfate cement-based material according to claim 4, characterized in that: In step (2), the desulfurized gypsum used is CaSO4·1 / 2H2O or CaSO4·2H2O.

9. The method for preparing the biochar-modified supersulfate cement-based material according to claim 4, characterized in that: In step (3), the stirring is low-speed stirring, and the duration is 30 to 35 seconds.

10. The method for preparing the biochar-modified supersulfate cement-based material according to claim 4, characterized in that: In step (4), the mixture is first stirred at a low speed for 30 to 35 seconds and then stirred at a high speed for 30 to 35 seconds.

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