Fly ash-based geopolymer concrete and preparation method thereof

Abstract

The invention provides normal-temperature cured fly ash-based geopolymer concrete which comprises coarse aggregate, fine aggregate and a cementing material, and the cementing material is mainly composed of fly ash and is doped with a small amount of cement. The geopolymer cementing material is characterized in that the geopolymer cementing material is prepared from a small amount of cement, fly ash and an alkali activator, and the alkali activator is formed by mixing water glass and sodium hydroxide with the industrial analytic purity larger than or equal to 96%. Under the normal-temperature curing condition, the geopolymer concrete is good in fluidity, high in later strength, high in sulfate corrosion resistance, high in water permeation resistance and suitable for being used in a sewage treatment plant.

Description

Technical Field

[0001] The invention belongs to the technical field of construction engineering, and in particular relates to a fly ash-based geopolymer concrete and a preparation method thereof. Background Art

[0002] With the rapid development of engineering construction, the amount of concrete used has increased significantly, and the demand for silicate cement has also risen simultaneously. In addition to emitting a large amount of CO2, traditional cement production is also accompanied by a large amount of NO2, SO2, dust particles and other harmful substances. Cement production not only consumes a lot of energy, but also has certain pollution, which is inconsistent with the "dual carbon" goal.

[0003] Geopolymer is an inorganic polymer generated by the chemical reaction of an alkali activator and active silicon-aluminum. It has excellent mechanical properties, acid and alkali resistance, high temperature resistance, and metal ion fixation properties. It is a feasible material to replace cement. However, geopolymer concrete also has some disadvantages: 1. The preparation process requires a high amount of each material, and each component must be accurately measured and fully mixed to ensure good performance. 2. The performance of geopolymer concrete is greatly affected by the curing conditions. 3. The production cost is high, and its cost is 8-10 times that of ordinary concrete.

[0004] The main function of a sewage treatment plant is to purify sewage, so ensuring the corrosion resistance and impermeability of water storage structures is the minimum requirement for geopolymer concrete to be used in sewage treatment plants. A fly ash-based polymer concrete mix suitable for the SO42- ion environment of sewage treatment plants has been developed to fully or partially replace cement concrete, and its feasibility in sewage treatment plants has been verified through slump tests, strength tests, impermeability tests, and corrosion tests, realizing solid waste resource utilization and energy conservation and emission reduction, providing a new path for future green municipal construction. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies in the above-mentioned prior art and to provide a fly ash-based geopolymer concrete, which has high strength, strong sulfate corrosion resistance, and strong water penetration resistance, and is suitable for use in sewage treatment plants.

[0006] Another object of the present invention is to provide a method for preparing the above fly ash-based geopolymer concrete.

[0007] As conceived above, the technical solution of the present invention is: a fly ash-based geopolymer concrete, comprising coarse aggregate, fine aggregate and cementitious material, wherein the cementitious material comprises fly ash and cement. The characteristic is that the geopolymer cementitious material is made of a small amount of cement, fly ash and an alkali activator, wherein the alkali activator is a mixture of water glass and industrial analytically pure sodium hydroxide ≥96%.

[0008] The above-mentioned method for preparing fly ash-based geopolymer concrete comprises the following steps:

[0009] (1) firstly prepare a 12 mol / L sodium hydroxide solution using sodium hydroxide powder (industrial analytical grade ≥ 96%), and then add the solution to water glass with a modulus of 3.3 in a ratio of 1:2.5 to obtain an alkaline activator I;

[0010] (2) mixing fly ash, cement, coarse aggregate and fine aggregate to obtain mixture II;

[0011] (3) The alkali activator obtained in step (1) and the mixture obtained in step (2) are further stirred and mixed to obtain fly ash-based geopolymer concrete III.

[0012] Preferably, the mixing process I comprises: after the sodium hydroxide, water glass and water are evenly mixed, they need to be left to stand for 12-24 hours according to actual conditions to dissipate heat to room temperature (20-30° C.) before use.

[0013] Preferably, the conditions of mixing II in step (2) at least meet the following conditions: stirring rate of 200 rpm and time of 120 s.

[0014] Preferably, the conditions of mixing III in step (3) at least meet: a stirring rate of 200 rpm and a stirring time of 240 s.

[0015] Preferably, the weight ratio of the raw materials is: coarse aggregate: fine aggregate: cement: fly ash: alkali activator = (49-51): (21-24): (3-5): (14-16): (9-11).

[0016] Preferably, the water glass is a light yellow transparent viscous liquid with the following parameters: SiO2=26.98%, Na2O=8.53%, water content of 64.49%, Baume degree of 38.5, modulus M=3.3; sodium hydroxide is white flakes with industrial analytical purity of ≥96%.

[0017] Preferably, the modulus of the alkali activator is 1.45, the mass ratio of the sum of sodium oxide and silicon dioxide in water glass to the cementitious material, that is, the alkali content is 15% to 19%, and the replacement rate of cement for fly ash is 20%.

[0018] Preferably, the coarse aggregate is crushed stone with a particle size range of 4.75 mm to 26.5 mm, and its screening and grading has the following characteristics on the basis of meeting the upper and lower limit requirements of "Pebbles and Crushed Stones for Construction" (GB / T 14685-2011):

[0019] Coarse aggregate screening test requirements

[0020]

[0021] Preferably, the particle size of the fine aggregate is in the range of 0.15 mm to 4.75 mm, and its screening and grading has the following characteristics on the basis of meeting the upper and lower limit requirements of "Pebbles and Crushed Stones for Construction" (GB / T 14685-2011):

[0022] Fine Aggregate Screening Test Requirements

[0023]

[0024] Preferably, the cement is PO 42.5 ordinary Portland cement, which meets the requirements of "General Portland Cement" (GB175-2007), and its performance meets the following requirements:

[0025]

[0026] Preferably, the fly ash is low-calcium fly ash, and its composition is:

[0027] The main components of fly ash

[0028]

[0029] The present invention has the following advantages and positive effects:

[0030] 1. Referring to the "Test Method for Cement Mortar Strength (ISO Method)" (GB / T 17671-2021), the 28d flexural strength of the mortar specimen configured by the cementitious material in the formula of the present invention can reach 14.8MPa, and the compressive strength can reach 49.2MPa. The strength of the mortar specimen meets the requirements of the "General Portland Cement" specification;

[0031] 2. With reference to the Standard Test Methods for Physical and Mechanical Properties of Concrete (GB / T 50081-2019) and the Standard Test Methods for Long-term Performance and Durability of Ordinary Concrete (GB / T50082-2009), the concrete made of cementitious materials, coarse aggregate, fine aggregate and composite alkali activator in the present invention has been subjected to strength tests, permeability tests and corrosion tests. The test results show that its 28d compressive strength can reach 48.8MPa, 90d compressive strength can reach 54.1MPa, 28d splitting strength can reach 3.66MPa, and the compressive corrosion resistance coefficient K after 60 times of 5% sodium sulfate solution dry-wet cycle is f It is 1.34 and the water-resistance grade is P11.

[0032] 3. The present invention has been verified through the above-mentioned test to be a fly ash-based polymer concrete suitable for the SO42- ion environment of a sewage treatment plant, which can fully or partially replace cement concrete, thereby realizing solid waste resource utilization and energy conservation and emission reduction.

[0033] 4. The present invention has low production cost. DETAILED DESCRIPTION

[0034] The invention provides a fly ash-based geopolymer concrete, comprising coarse aggregate, fine aggregate, cementitious material and composite alkali activator, wherein the cementitious material comprises fly ash and cement, and the mass ratio of the above raw materials is: coarse aggregate: fine aggregate: cement: fly ash: composite alkali activator = (49-51): (21-24): (3-5): (14-16): (9-11).

[0035] The coarse aggregate is crushed stone with a particle size range of 4.75 mm to 26.5 mm, and its screening and grading distribution has the following characteristics on the basis of meeting the upper and lower limit requirements of "Pebbles and Crushed Stones for Construction" (GB / T 14685-2011):

[0036] Coarse aggregate screening test requirements

[0037]

[0038] The particle size range of the fine aggregate is 0.15 mm to 4.75 mm, and its screening and grading has the following characteristics on the basis of meeting the upper and lower limit requirements of "Pebbles and Crushed Stones for Construction" (GB / T 14685-2011):

[0039] Fine Aggregate Screening Test Requirements

[0040]

[0041] The cement is PO 42.5 ordinary Portland cement, which meets the requirements of "General Portland Cement" (GB175-2007), and its performance meets the following requirements:

[0042]

[0043]

[0044] Preferably, the fly ash is low-calcium fly ash, the main components of which are:

[0045] The main components of fly ash

[0046]

[0047] The present invention provides a method for preparing fly ash-based geopolymer concrete, comprising the following steps:

[0048] 1. First, sodium hydroxide powder (industrial analytical grade ≥96%) is used to prepare a 12 mol / L sodium hydroxide solution, and then added to water glass with a modulus of 3.3, the ratio of the two being 1:2.5, to obtain an alkaline activator I;

[0049] 2. Stir and mix low-calcium fly ash, PO 42.5 ordinary Portland cement, coarse aggregate and fine aggregate to obtain mixture II;

[0050] 3. The alkali activator obtained in step (1) and the mixture obtained in step (2) are further stirred and mixed to obtain fly ash-based geopolymer concrete III.

[0051] 8. The method according to claim 7, characterized in that the process of mixing I in step (1) comprises: uniformly mixing sodium hydroxide, water glass and water and then standing for more than 24 hours to fully dissipate heat before use;

[0052] Preferably, the conditions of mixing II in step (2) at least meet the following conditions: stirring rate of 200 rpm, time of 120 s;

[0053] Preferably, the conditions of mixing III in step (3) at least meet: a stirring rate of 200 rpm and a stirring time of 240 s.

[0054] The mortar test block made of geopolymer cementitious material in the present invention can achieve a maximum compressive strength of 49.23 MPa at 28 days when the alkali activator modulus is 1.2, the alkali content is 15%, and the replacement rate of cement for fly ash is 20%.

[0055] The mechanical properties test research process and results of concrete made by adding coarse aggregate, fine aggregate and cementitious materials to the geopolymer cementitious material are as follows:

[0056] Taking the mass ratio of alkali activator solution to cementitious material (Al / B=0.48, 0.54, 0.60) and the molar concentration of NaOH (M=10M, 12M, 14M) as independent variables, the mix proportion of fly ash-based polymer concrete was designed and cubic specimens were made. The compressive strength at 28 days and 90 days and the splitting tensile strength at 28 days were measured. The effects of the mass ratio of alkali activator solution to cementitious material and the molar concentration of NaOH on the strength of fly ash-based polymer concrete were studied.

[0057] 1) Although the fly ash-based polymer concrete mixture is viscous, it has good workability and the slump ranges from 150 mm to 200 mm. In general, the slump increases with the increase of NaOH concentration and Al / B.

[0058] 2) Except for the Al / B0.54-14M test block, the 28-day cubic compressive strength of the other test blocks is greater than 30MPa, meeting the C30 strength requirement. The 28-day compressive strength of the test block Al / B0.54-12M is the highest (48.80MPa), followed by the test block Al / B0.60-10M (38.53MPa); the 90-day compressive strength of the test block Al / B0.48-10M is the highest (54.09MPa), followed by the test block Al / B0.48-12M (52.79MPa).

[0059] 3) The compressive strength of fly ash-based polymer concrete generally increases with age, and the 90-day compressive strength increases by -4%% to 65% compared with 28 days, with an average increase of 30%. When Al / B = 0.48 and the NaOH molar concentration is 10M, the 90-day compressive strength increases the most. When the NaOH molar concentration is 10M, the increase in compressive strength with age increases with the decrease of Al / B.

[0060] 4) Under different conditions, the 28-day compressive strength of fly ash-based polymer concrete varies with the test factors (Al / B, NaOH molar concentration) in different ways. As the reaction continues, the 90-day compressive strength of fly ash-based polymer concrete tends to be consistent with the test factors. When the NaOH molar concentration is 10-14M, the 90-day compressive strength of fly ash-based polymer concrete decreases with the increase of Al / B; when Al / B = 0.48-0.60, the 90-day compressive strength of fly ash-based polymer concrete also decreases with the increase of NaOH molar concentration.

[0061] 5) When the molar concentration of NaOH is 10M and 12M, the 28-day splitting tensile strength of fly ash-based polymer concrete decreases with the increase of Al / B; when the molar concentration of NaOH is 14M, the splitting tensile strength of geopolymer concrete first increases and then decreases with the increase of Al / B. When Al / B is 0.48 and 0.6, the 28-day splitting tensile strength of fly ash-based polymer concrete first increases and then decreases with the increase of NaOH molar concentration, while when Al / B is 0.54, the splitting tensile strength gradually increases with the increase of NaOH molar concentration. The 28-day splitting tensile strength of geopolymer concrete prepared when Al / B is 0.48 and NaOH molar concentration is 12M is the highest (3.66MPa), followed by the specimen Al / B0.48-10M (3.28MPa).

[0062] The process and results of the durability test are as follows: 6 groups of mix ratios (Al / B = 0.48, 0.60, NaOH concentration = 10M, 12M, 14M) that meet the C30 strength grade were selected to prepare fly ash-based polymer concrete test blocks, and 60 dry-wet cycle tests of 5% sodium sulfate solution were carried out after 28 days of natural curing in the laboratory. According to the results of the sulfate erosion test, a group of mix ratios with the smallest corrosion resistance coefficient (Al / B = 0.48, NaOH concentration = 12M) was selected to prepare fly ash-based polymer concrete anti-permeability test pieces, and the step-by-step pressurization method was used to evaluate its anti-permeability grade to ensure that the selected geopolymer concrete formula meets both the construction requirements of the sewage treatment plant structure and the strength, sulfate corrosion and water seepage requirements. The main conclusions are as follows:

[0063] 1) After 60 dry-wet cycles, the test block turned white as a whole, and some test blocks had a little white powder on the surface. Sulfate corrosion caused the concrete surface to be easily powdered, but the appearance did not change significantly. Except for the test block Al / B0.48-12M, which had a 13% decrease in compressive strength after 60 dry-wet cycles in sodium sulfate solution, the compressive strength of the remaining test blocks was higher than that of the control group, and the corrosion resistance coefficient K f The values ​​are 108% to 134%, indicating that these test blocks did not suffer internal damage after 60 cycles of 5% sodium sulfate solution and have good resistance to sodium sulfate corrosion.

[0064] 2) When the molar concentration of NaOH is 12M and 14M, the corrosion resistance coefficient K f As Al / B increases, K f As Al / B increases, K f The maximum value is 134%, which occurs at Al / B0.60-14M. When Al / B is 0.6, K f As the molar concentration of NaOH increases, K f As the molar concentration of NaOH increases, K f The minimum value of 87% occurs at Al / B0.48-12M.

[0065] 3) The impermeability grade of the fly ash-based polymer concrete prepared with Al / B=0.48 and NaOH concentration=12M is 11, which is greater than the requirement of impermeability grade 8.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A fly ash-based geopolymer concrete, comprising coarse aggregate, fine aggregate and cementitious material, wherein the cementitious material comprises fly ash and cement. The characteristics are: The geopolymer cementitious material is made of a small amount of cement, fly ash and an alkali activator, wherein the alkali activator is a mixture of water glass and industrial analytically pure sodium hydroxide of ≥96%.

2. A process for preparing fly ash-based geopolymer concrete according to claim 1, characterized in that: The following steps are involved: (1) firstly prepare a 12 mol / L sodium hydroxide solution using sodium hydroxide powder (industrial analytical grade ≥ 96%), and then add the solution to water glass with a modulus of 3.3 in a ratio of 1:2.5 to obtain an alkaline activator I; (2) mixing fly ash, cement, coarse aggregate and fine aggregate to obtain mixture II; (3) The alkali activator obtained in step (1) and the mixture obtained in step (2) are further stirred and mixed to obtain fly ash-based geopolymer concrete III.

3. The method for preparing an alkali activator for preparing fly ash-based geopolymer concrete according to claim 2, characterized in that: The process of step (1) comprises: mixing sodium hydroxide, water glass and water evenly, leaving the mixture to stand for 12-24 hours according to the amount of materials used, and using the alkali-activated solution after the solution cools down to room temperature.

4. The method for preparing fly ash-based geopolymer concrete according to claim 2, characterized in that: The conditions of mixing II in step (2) at least meet the following requirements: stirring rate of 200 rpm and time of 120 s.

5. The method for preparing fly ash-based geopolymer concrete according to claim 2, characterized in that: The conditions of mixing III in step (3) at least meet the following requirements: stirring rate of 200 rpm and time of 240 s.

6. The method for preparing fly ash-based geopolymer concrete according to claim 1, characterized in that: The mass ratio of the raw materials is: coarse aggregate: fine aggregate: cement: fly ash: alkali activator = (49-51): (21-24): (3-5): (14-16): (9-11).

7. The method for preparing fly ash-based geopolymer concrete according to claim 1, characterized in that: The water glass is a light yellow transparent viscous liquid with the following parameters: SiO2=26.98%, Na2O=8.53%, water content of 64.49%, Baume degree of 38.5, modulus M=3.3; the sodium hydroxide is white flake, and the industrial analytical purity is ≥96%.

8. The method for preparing fly ash-based geopolymer concrete according to claim 1, characterized in that: The modulus of the alkali activator is 1.2, the mass ratio of the sum of sodium oxide and silicon dioxide in water glass to the cementitious material, that is, the alkali content is 15%, and the replacement rate of cement for fly ash is 20%.

9. The method for preparing fly ash-based geopolymer concrete according to claim 1, characterized in that: The coarse aggregate is crushed stone with a particle size range of 4.75 mm to 26.5 mm, and its screening and grading has the following characteristics on the basis of meeting the upper and lower limit requirements of "Pebbles and Crushed Stones for Construction" (GB / T14685-2011): Coarse aggregate screening test requirements 10. The method for preparing fly ash-based geopolymer concrete according to claim 1, characterized in that: The particle size range of the fine aggregate is 0.15 mm to 4.75 mm, and its screening and grading has the following characteristics on the basis of meeting the upper and lower limit requirements of "Pebbles and Crushed Stones for Construction" (GB / T 14685-2011): Fine Aggregate Screening Test Requirements 11. The method for preparing fly ash-based geopolymer concrete according to claim 1, characterized in that: The cement is PO 42.5 ordinary Portland cement, which meets the requirements of "General Portland Cement" (GB175-2007), and its performance meets the following requirements:

12. The method for preparing fly ash-based geopolymer concrete according to claim 1, characterized in that: The fly ash is low-calcium fly ash, and its composition is: The main components of fly ash

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