The Influence Of Drying Conditions On Performance Of Internally Cured Concrete Containing Pre-wetted Lightweight Fine Aggregate

Early age cracking caused by shrinkageis common problems in concrete and will hazarded the safety and durability of concrete infrastructure. As the effect of traditional external-curing is not effective and the working conditions of shrinkage-reduce agent and swelling agent are complicated, internal curing has emerged as a new technology for producing concrete with increasing resistance and enhanced durability, which attracted widespread attention of scholars. The point is reducing autogenous shrinkage via pre-wetted lightweight aggregates that readily release water as needed for hydration. In the past few decades, internal curing technology research has achieved initial results,butthere is scope to go much further on concrete shrinkage, strength and the potential of cracking under different curing conditions.By comprehensive researchof shrinkage, strength and the cracking risk of internal concrete with fine lightweight aggregate, it is found that the fine lightweight aggregate(LWFA)is porous and the poreswith diameter of 1-10 um are in large proportion by total pore volume. It is a highly efficient internal curing material with great absorption and water releasing nature.But its strength is only 9.8MPa, lower than the normal-weight aggregate.The particle size is between 2mm-10 mm, which can be uniform distribution in concrete and effectively promoting the hydration of the concrete;In sealed curing condition, autogenous shrinkage of concretewith internal curing technology can be significantly even completely reduced. But in drying condition, the shrinkage-reduced effect decreased.Concrete mass loss is related to the drying shrinkage and relative humility, which decreased in two stages.Thestrengthdevelopment of internal curing concrete in standard curing condition depends not only on the water cement ratio, but also on the strength of LWFA. In general, the 28 d compressive strength and flexural strength of internal curing concrete is lower than the normal aggeregate concrete of the same water cement ratio. The strength of both kinds of concrete is sensitive to curing conditions, which influenced internal curing concrete more in later period, and the longer sealed curing time the higher of the strength. Both compressive strength and flexural strength in sealed curing condition are lower than in standard curing condition, the longersealing thesmaller strength losing.Flexural strength is more sensitive to the curing condition, in order to lower the potential of early cracking, it should avoid premature of early drying curing.Even in sealed curing condition, normal aggregate concrete still cracked because of high autogenous shrinkage. The effect of prolong sealed curing condition is not obviously to improve cracking potential. The cracking risk of internal concrete is reduced in sealed curing condition, however, once exposed to drying environment, the rapid growth of drying shrinkage may lead internal curing concrete to crack.