The practical solution to concrete shrinkage: Trinity Lightweight intraCure™ is the internal curing process used for portland cement based products to reduce early age cracking utilizing rotary kiln lightweight aggregate with a minimum absorption of 18%.
In the past, curing concrete was a process done using water from the outside in. But today, expanded shale and clay is used as a substitute for normal-weight aggregates to provide a source of moisture for internal curing that promotes more complete hydration of various cementitious materials.
Due to the inherently low permeability of the surrounding environment, internal curing is particularly beneficial in concrete with a low-water-cementitious material ratio (w/cm) where external curing has little effect on hydration in the internal portion of the concrete. With an emphasis on durability, and with the trend to high performance concrete, internal curing is needed to reduce both autogenous shrinkage and cracking.
With regard to high performance concrete, it is difficult to provide curing water from the top surface at the rate that is required to satisfy the ongoing chemical shrinkage, as the capillary passageways often become clogged with the products of cement hydration. However, expanded shale and clay typically contains between 18% and 25% water by weight. This water is released from the lightweight aggregate pores as the concrete cures and replaces a portion of the original mixture water that is consumed by the hydration process.
One example of Trinity’s successful blend of an intermediate size lightweight aggregate into concrete mixture took place for use in residential applications in which a 3/8 in. to No. 8 (9.5) to 2.36mm lightweight aggregate met all the requirements of ASTM C 330 and replaced a portion of both the coarse and fine aggregates. This aggregate size not only enhanced the hydration of the cementitious materials, but also complemented the total aggregate grading in the concrete.