Composite additive for improving self-contraction of concrete

Abstract

A composite admixture for improving concrete self-shrinkage belongs to the technical field of concrete admixtures. At present, the materials for improving the self-shrinkage of concrete mainly include: expansion agent, shrinkage reducing agent and fiber. But the effect of above-mentioned material used alone is not ideal, the present invention is characterized in that: adopt I class fly ash, ground limestone powder, dihydrate gypsum, raw alum, dimethyl siloxane to mix uniformly to make, each component The weight percentages are: Class I fly ash accounts for 20-40%, ground limestone powder accounts for 30-60%, dihydrate gypsum accounts for 5-10%, raw alum clay accounts for 10-20%, dimethylsiloxane Alkanes account for 3-5%; the fineness of the ground limestone powder, dihydrate gypsum and raw alum is greater than 350m2 / kg. When the composite admixture of the present invention is added to high-strength concrete, mass concrete and self-compacting concrete, it can significantly reduce the self-shrinkage rate of concrete by more than 30% under the condition that the relative humidity of the environment is lower than 50%, and has a significant impact on concrete strength and fluidity. and durability are improved.

Description

technical field [0001] The invention belongs to the technical field of concrete admixtures. Specifically, it is an organic-inorganic composite admixture that can significantly reduce the autogenous shrinkage of high-strength concrete, but does not affect the workability, strength and durability of concrete. Background technique [0002] Concrete self-shrinkage is the reduction of macroscopic volume of cement-based cementitious materials under the condition of constant temperature and constant weight with the progress of hydration after initial setting. Autogenous shrinkage does not include volume changes caused by drying, sedimentation, temperature changes, and external forces. The reason for autogenous shrinkage is that as the cement hydration proceeds, a large number of microscopic pores are formed in the hardened cement stone, and the free water in the pores gradually decreases, that is, the relative humidity inside the cement stone decreases, but at the same time, there...

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Problems solved by technology

However, the effect of using the above materials alone is not ideal. For example, although the expansion agent can compensate for shrinkage or produce micro-expansion in the early stage, it requires a large amount of water due to its own hydration, and the heat of hydration is relatively high, while the water consumption of high-strength concrete itself is very low. , so it is difficult to maintain the expansion due to lack of water inside the concrete in the later stage, but it will increase the self-shrinkage and cold shrinkage

Although the general shrinkage reducing agent can reduce the self-shrinkage, it will reduce the strength and fluidity of the concrete at the same time, and it is expensive and difficult to apply in engineering

Fiber can not actively reduce autogenous shrinkage, but can passively limit the further development of autogenous shrinkage, and the fiber is expensive, and it is difficult to apply ordinary concrete

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