Volume 14 (2016) Issue 7 Pages 324-334
In this paper, the effect of internal curing with pre-soaked lightweight aggregate (PSLWA) on shrinkage and interior relative humidity of four series concretes with compressive strength at 28 days around 30MPa, 60MP, 90MPa and 100MPa is investigated. The shrinkage induced cracking performance of concretes is evaluated with concrete-steel composite ring tests. The results show that the development of the internal relative humidity of concrete since casting exhibits first a vapor saturated stage (RH=100%, stage I), followed by gradually reducing stage (RH<100%, stage II). Under sealing, internal relative humidity at the center of the specimen for a given age is obviously decreased with increase of concrete strength. Under drying, similar internal relative humidity value is observed at 28 days for all concretes without internal curing. As PSLWA was added, the reduction rate on interior humidity in stage II is significantly decreased. But the efficiency on internal humidity rising is greatly influenced by concrete strength. The autogenous shrinkage is in-creased with increase of concrete strength. The drying shrinkage is decreased with increase of concrete strength. The total shrinkage of concrete is increased with increase of concrete strength. As PSLWA was added, the shrinkage reduction in both autogenous and drying shrinkages is obviously in high strength concretes, such as 90MPa and 100MPa concretes. The shrinkage reduction of internal curing on relatively low strength concrete, such 30MPa and 60MPa concrete is not obvious. Internal curing with PSLWA can greatly improve the shrinkage induced cracking performance. All concrete rings without internal curing are cracked under drying. The compressive strain in the steel ring at the concrete ring cracking is about 75 to 101μm/m. By contrast, the stable compressive strain at the inner steel ring for the concretes with internal curing becomes 10 to 40μm/m and no visible cracks were found on the specimens.