Internal Curing Efficiency of Prewetted LWFAs on Concrete Humidity and Autogenous Shrinkage Development

Internal curing (IC) technology using prewetted lightweight fine aggregates (LWFAs) as additives has been proved an effective means for mitigating both autogenous shrinkage and early-age cracking under the sealed-cured conditions. However, complete elimination of autogenous shrinkage may not be necessary, as negative effects, such as the durability problems, might be induced by an excessive amount of LWFAs introduced. To better utilize internal curing technology for durable concretes, this study investigates the microstructure and the desorption properties of sintered fly ash and expanded shale LWFAs. The influences of these two types of LWFAs on autogenous shrinkage and internal RH development were experimentally evaluated in concrete with w/c of 0.3 and 0.4. The internal curing efficiency, defined as the relative volume ratio of LWFAs in paste matrix as compared to that used for completely mitigating autogenous shrinkage, is a function of particle size and spacing of LWFAs. The results show that 100% internal curing efficiency (no autogenous shrinkage at the age of 28 days) can be achieved if the ratio of the LWFA particle/paste proximity and the particle size (2L=hRi) approach 1.1. DOI: 10.1061/(ASCE)MT.1943- 5533.0000883. © 2014 American Society of Civil Engineers.