High-strength geopolymer recycled aggregate concrete load-bearing structural material
Technical Field
The invention belongs to the field of novel building environment-friendly materials, and particularly relates to a high-strength geopolymer recycled aggregate concrete load-bearing structural material and a preparation method thereof.
Background
Carbon emissions from the construction industry account for 29% of the total carbon emissions from human activities, most of which are generated during cement manufacturing. Meanwhile, a large amount of industrial waste materials are produced in industrial production and accumulated everywhere, and great pressure is also caused to environmental protection. Therefore, the utilization of industrial waste materials instead of cement in building materials is becoming a big trend of energy saving and environmental protection, and therefore geopolymer concrete is produced. The geopolymer concrete adopts industrial waste residues such as fly ash, slag and the like to replace cement, and the activity of the industrial waste is excited by the alkali activator, so that the problem of environmental pollution in the cement production process can be effectively solved, and the carbon emission in the building industry is obviously reduced.
At present, the waste concrete produced by demolishing old buildings in China each year exceeds 3 hundred million tons and accounts for 40 percent of all construction wastes, and most of the waste concrete is treated in a landfill and natural stacking mode, so that the environment is badly influenced, and the resource waste is also caused. The waste concrete is recycled, crushed and graded to prepare recycled aggregate, and industrial waste such as fly ash is used for partially replacing cement, so that the recycled concrete prepared by mixing can remarkably reduce huge energy consumption generated in natural aggregate mining and cement manufacturing, and has the effects of reducing carbon emission and protecting the environment.
Therefore, the green and environment-friendly geopolymer recycled concrete formed by combining the geopolymer and the recycled aggregate can realize great ecological benefit and remarkable economic benefit. However, recycled aggregate concrete has the disadvantages of low strength, low elastic modulus and the like, and geopolymer concrete not only has low strength but also has high viscosity and poor working performance such as slump, water spreading and the like, so that the recycled aggregate concrete is difficult to be used as a load-bearing structural material. In view of the above, the innovation of the invention is to provide a preparation method of high-strength geopolymer recycled aggregate concrete, the 28d compressive strength of the concrete can reach 80MPa or above, and the concrete has better working performance, can be filled in a steel pipe to form steel pipe geopolymer recycled coarse aggregate concrete, achieves the effects of high bearing capacity and good working performance through the combined effect of the concrete and the concrete, and can be widely used for vertical bearing structures of important buildings.
Disclosure of Invention
The invention aims to provide a high-strength geopolymer recycled aggregate concrete load-bearing structural material and a preparation method thereof, wherein the 28d compressive strength of the material can reach C90, and the material has better slump and fluidity and can be used for load-bearing structural members in buildings.
In order to achieve the purpose, the invention adopts the technical scheme that:
the high-strength geopolymer recycled aggregate concrete load-bearing structural material comprises the following raw materials of fly ash, slag, sand, natural aggregate, recycled aggregate, an alkali activator and a water reducing agent.
Each cubic meter of high-strength polymer recycled aggregate concrete load-bearing structural material comprises 216.6-346.7 kg/m of pulverized fuel ash, 86.7-216.6 kg/m of slag, 698.7 kg/m of sand, 321-1283.9 kg/m of natural aggregate, 321-962.9 kg/m of recycled aggregate, 0.1-8.7 kg/m of water reducing agent and 208.2 kg/m of alkali-activator.
The fly ash is F-grade low-calcium fly ash, is mainly generated by burning bituminous coal or anthracite, has CaO content lower than 10 percent and is formed by 57.95 percent of SiO2And 21.86% of Al2O3The composition, particle size is 160-315 μm.
The slag is S95 grade granulated slag, and the main component of the slag is CaCO3And mCaO. nAl2O3The melt of (2).
The grain diameter of the sand is 0.16-1.25mm, and the fineness modulus is 1.9.
The natural aggregate is granite macadam with the particle size of 5-20 mm.
The recycled aggregate is an artificially crushed C50 test block, and the particle size is 2.36-16.0 mm.
The alkali activator is prepared from 100g of water glass solution with the density of 1660kg/m through high-speed flowering, 14.8g of sodium hydroxide solid and 28.5g of water.
The water reducing agent is a polycarboxylic acid high-performance water reducing agent, the chemical components of the water reducing agent are various high-molecular organic compounds taking polycarboxylate as a main body, and the water reducing agent is generated by graft copolymerization and has the water reducing rate of more than 25%.
The reaction mechanism of water glass-slag-fly ash is used to explain the high strength property of the material, and the process can be described as follows: when the fly ash is mixed with the alkali solution, the Al-O bonds (-Al-O-) in the glass body are first exposed to OH-The charge distribution is deviated, Al-O bonds are broken, and the chemical reaction equation is as follows:
meanwhile, the silicon-oxygen bond (-Si-O-) in the glass body is changed similarly, the aluminosilicate structure in the fly ash glass body is decomposed to form a random network structure similar to the glass body, and the chemical reaction equation is as follows:
along with the bond breaking depolymerization process, silicate, aluminate and aluminosilicate in different polymerization states are polymerized and crystallized again to form the aluminosilicate gel polymer, and the chemical reaction equation is as follows:
the synthesis reaction of fly ash/slag-based geopolymer is similar to the above process, and is also a solid-liquid two-phase reaction between solid-phase slag particles and fly ash particles with a liquid-phase water glass excitant. When the mixture of the fly ash and the slag is mixed with an excitant solution, wherein the activity of the slag is higher, under the action of alkali, firstly, covalent bonds of Si-O-Si, Si-O-Al, Al-O-Al and the like in the slag glass body are broken, so that the structure of the alumino-silica glass body is strongly destroyed, and the chemical reaction equation is as follows:
to decompose it to produce SiO
4 4-、AlO
5 4-Plasma and Ca
2+、Ca(OH)
+Or Ca (H2O) (OH)
+Plasma, and then, the glass body (aluminosilicate) in the fly ash is promoted to be continuously disintegrated to generate SiO due to the alkalinity enhancement in the liquid phase
4 4-、AlO
5 4-And (3) plasma. In one aspect, SiO
4 4-And AlO
5 4-Further polymerization of ions under the action of alkali and final formation of natural ore similar to that in earth crustThe alkali aluminosilicate network structure of the product.
On the other hand, the lower the degree of polymerization of the silicon-oxygen tetrahedron, the stronger the reactivity. The oxygen ions are replaced by hydroxide ions, which cause the surface of the siliceous raw material particles to be OH-substituted-Covered, or even the degree of freedom of the tetrahedron increases, to H3SiO4 -Into solution. And the slag is disintegrated to produce Ca2+、Ca(OH)+Or Ca (H)2O)(OH)+Plasma and H3SiO4 -The reaction produced a C-S-H gel, namely:
the preparation method of the high-strength geopolymer recycled aggregate concrete load-bearing structural material comprises the following steps:
(1) 100g of a water glass solution, 14.8g of a sodium hydroxide solid and 28.5g of an alkali activator solution having a modulus of 1.4 were prepared before water extraction.
(2) Mixing slag, fly ash and sand according to the proportion of 1: adding the mixture into a cement mortar stirrer according to the proportion of 1.6, uniformly mixing, and slowly stirring for 30 s.
(3) Adding stone and recycled aggregate with the mixing amount of 0.65 into a concrete stirring pot, slowly stirring for 30s, slowly adding the prepared alkaline activator and 2% of water reducing agent, generally uniformly adding the alkaline activator and the water reducing agent for 3 times, and stirring for 5-7 min (determined according to the fluidity of geopolymer concrete).
(4) Pouring the mixture into a cube test mold with the side length of 100mm, respectively placing the cube test mold into a blast drying oven at room temperature and 60 ℃ for curing for 2d, and then demolding.
(5) A layer of plastic bag is sleeved outside the test block to simulate the steel pipe closed environment, and the test block is placed in a standard curing box for curing to the required age, wherein the temperature of the standard curing box is usually controlled to be 20 +/-2 ℃, and the humidity is controlled to be about 95%.
The invention has the beneficial effects that: according to the invention, through strict experiments, the proportioning parameters of the high-strength polymer recycled aggregate concrete are selected and determined, and the fracture tensile property, the elastic modulus and the microstructure of the concrete are analyzed, so that the prepared concrete has the highest compressive strength of 90MPa, the fracture tensile strength of 6.0MPa and the elastic modulus of about 30-40 GPa under normal-temperature curing, and the concrete also keeps good slump and fluidity under better compressive strength. Overcomes the defects of poor working performance of geopolymer, low strength and low elastic modulus of recycled aggregate concrete, and can apply the green environment-friendly building material to a load-bearing structure.
Drawings
FIG. 1 is a flow chart of a manufacturing process of an embodiment of the present invention.
FIG. 2 is a comparison of 28d compressive strengths under different slag mixing amounts and different curing conditions when the liquid-solid ratio of the first embodiment of the invention is 0.4.
FIG. 3 is a comparison of 28d compressive strengths under different curing conditions and different slag mixing amounts when the liquid-solid ratio of the second embodiment of the invention is 0.45.
FIG. 4 shows the development trend of the concrete tensile strength at split of the recycled polymer aggregate with different slag contents in example two of the present invention.
FIG. 5 shows scanning results of an electron microscope according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be noted that the following examples should not be construed as limiting the scope of the present invention.
The high-strength geopolymer recycled aggregate concrete load-bearing structural material comprises fly ash, slag, sand, natural aggregate, recycled aggregate, an alkali activator and a water reducing agent.
In a specific embodiment, 216.6-346.7 kg/m of fly ash is added into high-strength polymer recycled aggregate concrete per cubic meter for carrying out double-row harvest, and the main component is Al2O3And SiO2The F-grade low-calcium fly ash.
In a specific embodiment, the fine aggregate is clear water fine river sand, and 0-698.7 kg/m of high-strength polymer recycled aggregate concrete is added per cubic meter for carrying out heavy planting, the grain diameter is 0.16-1.25mm, and the preferred glue-sand ratio is 1.6-2.0.
In a specific embodiment, 321-962.9 kg/m of recycled aggregate is added into high-strength polymer recycled aggregate concrete per cubic meter, the recycled aggregate is obtained from a test block reserved in the teaching of the department, the strength of the test block is C50, the recycled aggregate is manually crushed, then crushed by an XPC-125X 100 crusher and mechanically screened in a laboratory, the particle size is approximately 4.75-16.0mm, and the water absorption is 4.1%.
In one embodiment, 0-208.2 kg/m weight of alkali-activator is loaded into each cubic meter of high-strength recycled polymer aggregate concrete, and the main components are water glass solution with the mass of 100g and the density of 1660kg/m weight of harvested water glass, 14.8g of sodium hydroxide solid and 28.5g of water.
In a specific embodiment, the water reducing agent is added into the high-strength polymer recycled aggregate concrete per cubic meter at a ratio of 0.1-8.7 kg/m for carrying out the high-performance polycarboxylic acid water reducing agent.
The preparation method of the high-strength geopolymer recycled aggregate concrete comprises the following steps: the preparation is mainly prepared by taking fly ash and sand as experimental materials and mixing sodium silicate aqueous solution and sodium hydroxide as alkaline activator solution, and the alkaline activator is firstly prepared to the required modulus 1d ahead of time. In the stirring process, a concrete stirring pot is used, firstly slag, fly ash and sand are put into the concrete stirring pot, the mixture is slowly stirred for 30s to be uniformly mixed, then stones are added into the mixture and slowly stirred for 30s, and an alkaline activator and a water reducing agent are slowly added into the mixture, wherein the alkaline activator and the water reducing agent are usually uniformly added for 3 times, the mixture needs to be stirred for 5-7 min (determined according to the fluidity of the concrete), and finally the high-strength geopolymer recycled aggregate concrete is prepared, is convenient and quick, and is suitable for load-bearing structural members.
The geopolymer recycled aggregate concrete prepared by the material is tested for 28d compressive strength, splitting tensile strength and elastic modulus under different liquid-solid ratios and different slag mixing amounts, and the influence rule of the liquid-solid ratio and the slag mixing amount of the material on the working performance of the geopolymer recycled aggregate concrete is determined, so that the geopolymer recycled aggregate concrete with high performance is prepared.
The first embodiment is as follows:
(1) in the present example, the first and second substrates were,the cementing material adopts F-grade fly ash and S95-grade blast furnace granulated slag, the fine aggregate is clear water river sand, the grain size is 0-5mm, the fineness modulus is 2.2, and the sand rate is 0.35. The natural aggregate is stone with 5-20mm continuous gradation, the regenerated aggregate is a teaching C50 test block of the subject after manual and mechanical crushing, the grain size is 5-16mm continuous gradation, and the substitution rate of the regenerated aggregate is 25%. The alkali activator is prepared by carrying out chemical reaction on 100g of water glass solution with the density of 1660kg/m, 14.8g of sodium hydroxide solid and 28.5g of water through SiO2+2NaOH+8H2O==Na2SiO3·9H2O was formulated one day in advance with a water glass modulus of 1.4. The water reducing agent is a polycarboxylic acid high-efficiency water reducing agent, and the mixing proportion is shown in table 1.
(2) The above materials were mixed to prepare a high strength recycled polymer aggregate concrete, and the compressive strength of the concrete was measured for 28 days under different conditions of normal temperature and high temperature, and the results are shown in fig. 2.
Example two:
(1) in this example, the material parameters were in accordance with those in the above example, and the compounding ratio is shown in Table 2.
(2) The materials are stirred to prepare high-strength recycled polymer aggregate concrete, and the compression strength and the splitting tensile strength of the concrete under different conditions of normal temperature and high temperature for 28 days are detected, and the results are shown in fig. 3 and 4.
Example three:
(1) in this example, the material parameters were in accordance with those in the above example, and the compounding ratio is shown in Table 3.
(2) The above materials were mixed to prepare a high strength recycled polymer aggregate concrete, and the compressive strength, elastic modulus and fluidity at 28 days under different conditions of normal temperature and high temperature were measured, and the results are shown in table 4.
Example four:
(1) in this example, the material parameters were in accordance with those in the above example, and the compounding ratio is shown in Table 5.
(2) The above materials were mixed to prepare a high strength recycled polymer aggregate concrete, and the compressive strength, elastic modulus and fluidity at 28 days under different conditions of normal temperature and high temperature were measured, and the results are shown in table 6.
Example five:
(1) in this example, the material parameters were in accordance with those in the above example, and the compounding ratio is shown in Table 7.
(2) The above materials were mixed to prepare a high strength recycled polymer aggregate concrete, and the compressive strength, elastic modulus and fluidity at 28 days under different conditions of normal temperature and high temperature were measured, and the results are shown in table 8.
The performance test of the high-strength polymer recycled aggregate concrete in the above embodiment is as follows:
FIG. 2 is a 28d compressive strength line graph of the high-strength polymer recycled aggregate concrete under different slag mixing amounts and different curing conditions when the liquid-solid ratio is 0.4, and it can be seen from the graph that the 28d compressive strength of the concrete cured at high temperature and normal temperature can reach the maximum values of 94.6 and 87.8MPa respectively when the slag mixing amount is 40%.
FIG. 3 is a 28d compressive strength line graph of the high-strength recycled polymer aggregate concrete under different slag contents and different curing conditions at a liquid-solid ratio of 0.45, and it can be seen from the graph that the 28d compressive strength of the concrete cured at high temperature and normal temperature can reach the maximum values of 86.8 and 87.6MPa respectively at a slag content of 40%. The mixing proportion of 0.45 is selected because the difference of the 28d compressive strength of the concrete under the normal-temperature curing condition with 40 percent of slag mixing amount is not large when the liquid-solid ratio is 0.4 and 0.45, and the fluidity problem of the material is comprehensively considered.
FIG. 4 shows the development trend of the cleavage tensile strength of the concrete with different slag contents and high strength recycled polymer aggregate. According to the optimum proportion GCS determined in the past, the splitting tensile strength under the high-temperature and normal-temperature curing conditions respectively reaches 7.1MPa and 6.0MPa, and the splitting tensile strength is superior to that of the fly ash geopolymer concrete.
Table 4 shows the material characteristics of the recycled aggregate concrete of the high strength polymer at different blending amounts of recycled aggregate when the blending amount of slag is 20%. The results show that: compared with 50 percent and 75 percent of the mixing amount of the recycled aggregate, when the mixing amount of the recycled aggregate is 25 percent, the 28d compressive strength of the concrete can reach 53.67MPa at most, the elastic modulus is 31.1GPa, and the slump is 225 mm.
Table 6 shows the material characteristics of the recycled aggregate concrete of high strength polymer at different blending amounts of recycled aggregate when the slag blending amount is 50%. The results show that: compared with 50 percent and 75 percent of the mixing amount of the recycled aggregate, when the mixing amount of the recycled aggregate is 25 percent, the 28d compressive strength of the concrete can reach 81.91MPa at most, the elastic modulus is 34.3GPa, and the slump is 185 mm. Compared with 20% of slag, the compressive strength is improved by 52%, the elastic modulus is improved by 11%, but the slump is reduced by 40 mm.
Table 8 shows the modulus of elasticity of the high strength polymer recycled aggregate concrete in various strength grades. The elastic modulus of the geopolymer concrete with the parameters is small as a whole and is approximately between 20GPa and 40 GPa. The elastic modulus shows a tendency to increase with increasing strength. Compared with ordinary portland cement concrete, the concrete has the advantages of slightly higher brittleness, smaller early deformation and higher rigidity.
Fig. 5 shows the result of electron microscope scanning. Through microstructure analysis, the fly ash glass beads react completely, and the structure after reaction is compact, which is the main reason for higher strength of the slag-fly ash geopolymer concrete.
The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.