Composite additive improving self-contraction of concrete

Abstract

The invention relates to a compound admixture for improving the self-contraction property of concrete, and belongs to the technical field of the admixture. The prior materials used for improving the self-contraction of the concrete mainly comprise expansion agent, shrinkage reducing agent and fiber, but the materials are not effective when the materials are used solely. The invention is characterized in that the compound admixture is formed by evenly mixing I-class fly ash, milled limestone powder, dihydrate gypsum, raw alum clay and dimethyl siloxane, wherein, the weight percent of each component is showed as follows: 20 to 40 percent of the I-class fly ash, 30 to 60 percent of the milled limestone powder, 5 to 10 percent of the dihydrate gypsum, 10 to 20 percent of the raw alum clay and 3 to 5 percent of the dimethyl siloxane; the finenesses of the milled limestone powder, the dihydrate gypsum and the raw alum clay are larger than 350m2 / kg. When the invention is mixed into the concrete with high strength and large area and the self-compacting concrete, and the relative ambient humidity is less than 50 percent, the invention can obviously reduce the self contraction rate of the concrete by more than 30 percent and improve the strength, the mobility and the durability of the concrete.

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...

AI Technical Summary

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