Autogenous volume changes at early ages

Concrete shrinkage is of increasing concern when making durable structures. Over time, the shrinkage induces cracking can severely decrease the concrete life expectancy. These volume changes are often attributed to drying of the concrete, in which the particles are drawn closer together with the moisture loss to the surrounding environment. It is generally expected to occur over a long time period, though recent observations have focused on early age or plastic drying problems. In this phase the concrete is still moist after mixing. Difficulties in measuring have prevented extensive understanding of the influences on plastic shrinkage. The most common solution is to avoid drying by proper curing methods occurring soon after placement of the concrete. A supplementary problem to the drying shrinkage at early ages is the changes that occur when no moisture transfer is permitted with the environment. This volume reduction is called autogenous shrinkage, which is attributed to chemistry and internal structural changes. At 100% RH, a specimen will still undergo a horizontal and vertical shrinkage. The vertical shrinkage is settlement occurring as a result of excess bleed water migrating to the concrete surface and the aggregates settling. The horizontal autogenous shrinkage is of concern and interest, as it can result in unpreventable cracks. It is this problem which needs further investigation in order to improve the durability of concrete.