Lightweight Aggregates as an Internal Curing Agent for Low-Cracking High-Performance Concrete

Abstract

The use of lightweight aggregates to supply a source of internal curing for Low Cracking, High Performance Concrete (LC-HPC) is evaluated. Prior research is used as a basis to estimate the amount of with lightweight aggregate replacement needed to optimize the amount of moisture available in the mix for internal curing. An aggregate optimization program (KU Mix) is revised to include modifications for the addition of aggregate with different specific gravities, such as lightweight aggregate, for the purposes of internal curing. Fourteen concrete mixes are designed to evaluate the free shrinkage and strength properties of LC-HPC mixes with lightweight aggregate for the purposes of internal curing. Six mixes in Program I are used to evaluate different replacement levels of lightweight aggregate. Eight mixes in Program II are used to evaluate the use of lightweight aggregate with Grade 100 slag. All mixes have a water/cement ratio of 0.44, 24.7% paste content (equivalent to a cement content of 540 lb/yd3) and an air content of 8%. Both 7-day and 14-day curing periods are evaluated for the free shrinkage specimens. Cylinders are cast for every batch and tested for the 28-day strength. The effect of adding lightweight aggregate does not significantly decrease the strength of any one mix. The addition of the lightweight aggregate increases the amount of internal curing water available and reduces shrinkage. The recommended mixes to reduce free shrinkage from Programs I and II were the 14-day cured lightweight aggregate mix with the highest level of replacement and the 14-day cured lightweight aggregate mix with a 30% cement replacement of slag, respectively.