Abstract
Self-desiccation and autogenous shrinkage of high-strength concretes is one of their drawbacks which cannot be readily accommodated by conventional curing. The concept of internal curing using lightweight soaked aggregates, to provide internal reservoirs of water which enable uniform curing of the whole cross-section, has been advanced by several groups. The present study is intended to develop this approach further, by optimizing the porosity and size of the aggregates to enable successful internal curing with only a small amount of aggregates, which could be viewed as additives rather than bulk replacement of conventional aggregates. The approach taken was to increase the porosity of the aggregates and reduce their size, to obtain a system with numerous internal reservoirs of sufficiently small spacing to allow water to be readily discharged from the aggregate and transported over the whole range of the matrix. It was shown that aggregates with porosities of about 50% by volume, a size of a few millimeters, and contents of less than 50 kg/m3 could provide full elimination of autogenous shrinkage in concretes having w/cm as low as 0.25, with only a small affect on strength. The parameters controlling the efficiency of the aggregates were assessed, indicating that their pore structure is the most important one, and that water from within the aggregates can be readily transported into the matrix to a distance of few millimeters.
