The production process of high-performance concrete is inseparable from water-reducing agents, because adding a sufficient amount of water-reducing agents can not only save a lot of production costs, but also improve production quality.
Compared with naphthalene and melamine admixtures, the new type of water reducing agent has a different mechanism of action. It has a comb-shaped molecular structure with multiple active groups on the main chain, and Strongly polar, with hydrophilic active groups on the side chain. The main chain is adsorbed on the surface of cement particles and separates the cement particles from water through charge repulsion; the side chains spatially block the cement particles and water to achieve a very high water reduction rate, increase the cohesion of concrete, and improve the uniformity of concrete. sex. The longer the main chain and the shorter the side chain, the better the retention performance of the admixture; the shorter the main chain, the longer the side chain, the higher the water reduction rate; during production, the length of the main chain and side chain can be adjusted to meet different requirements. Concrete workability, retention performance and concrete viscosity requirements. Since the main chain does not completely cover the surface of the cement particles, the uncovered part can be hydrated. As the alkalinity increases, the charge repulsion and spatial barrier are destroyed, and the cement can be quickly hydrated, so this type of admixture can be It has long workability retention performance and does not affect the normal setting of concrete. It is precisely because of its special mechanism of action that it can greatly improve and effectively control the workability of concrete at a lower dosage. The plasticization of concrete can be maintained for a longer time. The concrete mixture is as soft as a liquid. The concrete It has strong cohesion (no segregation, dispersion or bleeding), and the coagulation time and gas content can be adjusted as needed. The hardened concrete has high strength, low shrinkage, low permeability, good resistance to carbonization and chemical attack, and a uniform concrete surface.
This article mainly uses water reducing agent, fly ash, slag and silica fume as admixtures to prepare C80 high performance concrete, and discusses the effects of admixture dosage and sand rate changes on concrete and easy sex and intensity.
Application of JH water-reducing agent in the production of C80 high-performance concrete
JH water-reducing agent has been used in many key projects such as rail transit. The Taikoo Hui project uses a large number of C60 pumped concrete, which is mixed with fly ash and slag. The concrete prepared with JHJS has low viscosity and good workability. There is basically no loss of fluidity within two hours. The concrete is easy to pump and has stable strength development. The lowest intensity in 28 days was greater than 70 MPa, and the average intensity was greater than 72 MPa. The Zhujiang City and Zhongshan International Financial Center projects have extensively used C70, C80 and C90 large flow pumped concrete. The JHJS content in C70 concrete is 1.3% to 1.5%, and the C80 content is 1.8% to 2.0%; C70, C80 Both are added with 10-30 kg/cubic meter of silica fume and 20%-30% ground slag; the concrete prepared with JHJS has low viscosity and good workability. There is basically no loss of fluidity in 2.5 hours, and the concrete is easy to pump. , the strength development is stable, the minimum strength of C70 concrete in 28 days is greater than 80 MPa, and the average strength is greater than 84 MPa; the minimum strength of C80 concrete in 28 days is greater than 92 MPa, and the average strength is greater than 96 MPa; the concrete appearance is uniform and dense, without harmful cracks , won unanimous praise from the construction and all parties.
Using materials such as JH water-reducing agent, grade II or above high-quality fly ash, S95 grade ground slag and silica fume, C80 high-performance concrete with high strength guarantee rate and excellent performance can be formulated. The prepared concrete has good workability, small loss of fluidity over time, and is easy to pump for construction. After the concrete is poured, it has a uniform and dense appearance without harmful cracks. The incorporation of fly ash and silica fume can significantly improve the workability of C80 concrete.
With the increase in fly ash content, the workability of C80 concrete is improved, while the increase in slag content reduces the workability of concrete, and the incorporation of fly ash and slag is more obvious. The early strength of concrete is greatly reduced, and with the increase in dosage, the 3-day strength continues to decrease. However, the increase in the total amount of cement substituted by slag and fly ash has no obvious effect on the 28-day strength of concrete.
The increase in sand rate can reduce the viscosity of C80 concrete, improve the workability of concrete, and increase the fluidity of concrete; while ensuring consistent workability of concrete, river sand with different fineness modulus It has little effect on the strength of C80 concrete.
The incorporation of silica fume significantly reduces the viscosity of C80 concrete, and the workability of the concrete is significantly better than that of C80 concrete mixed with fly ash alone or double mixed with fly ash and slag. However, with the addition of silica fume With the addition of water, the water demand also increases, and the amount of admixture increases significantly while keeping the water-cement ratio unchanged. Comprehensive consideration, the amount of silica fume should not exceed 8%. </p
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