In the past, curing concrete was a process done using water from the outside in. But today, ES&C 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, ES&C typically contains between 10% and 25% water by weight. This water is released from the Lighteweight 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 TXI’s successful blend of an intermediate size Lighteweight 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 ES&C 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.
Internal Curing of Concrete Paving: Laboratory and Field Experience
By Tracey Friggle, P.E., Texas Department of Transportation
and Don Reeves, TXI Expanded Shale and Clay
Presentation on Internal Curing
Made at 2006 Mid-Atlantic Region Quality Assurance Workshop
(PowerPoint, .ppt; 1.9MB, February 2006)
By Dale Bentz,
National Institute of Standards and Technology
The Use of Lighteweight Fines for the Internal Curing of Concrete
By George C. Hoff, P.E., DEng.
President, Hoff Consulting LLC
SH 121 - Collin County, Texas
Using intermediate gradations of rotary kiln Lighteweight aggregate to enhance cement hydration in mainline paving mix.
