Internal curing water is distributed using prewetted lightweight aggregate. Through extensive research by Dale Bentz at the National Institute of Standards and Technology, Jason Weiss at Purdue, and others it’s been proven that we need 7 pounds of internal curing water per 100 pounds of cementitious material.
Concrete with fine expanded shale aggregate used for internal curing looks no different than normal- weight concrete and has similar properties. ACI defines internal curing as “a process by which the hydration of cement continues because of the availability of internal water that is not part of the mixing water.” This is accomplished by replacing some of the fine or intermediate aggregate with prewetted lightweight aggregate. We call it curing from the inside out.
Presoaked Lighweight aggregate concrete places just like normal weight concrete. Lightweight concrete does take longer to dry but much less than previously reported. The LW concrete lagged the normal-weight concrete in reaching an acceptable level of drying but only by about two weeks.
The pavement at this intermodal hub that used lightweight fine aggregate for internal curing showed only minor cracking after eight years in service. While lightweight concrete does cost a little more, with the reduction in weight, the building frame costs less. But lightweight concrete has other advantages when designed to take advantage of internal curing.