Lightweight aggregate batched at a high degree of saturation may be substituted for normalweight aggregates to provide internal curing in concrete containing a high volume of cementitious materials. High cementitious concretes are vulnerable to self-desiccation and early-age cracking, and benefit significantly from the slowly released internal moisture. Field experience has shown that High Strength Concrete is not necessarily High Performance Concrete and that High Performance Concrete need not necessarily be high strength. A frequent, unintended consequence of high strength concrete is early-age cracking. This application is significantly helpful for vertical members and concretes containing high volumes of pozzolans that are sensitive to curing procedures. In this application, density reduction is a bonus.
Photo courtesy of P. Lura, O.M. Jensen, S.I. Igarashi. Experimental Observation of Internal Water Curing of Concrete. Materials and Structures, 2007, 40, 211-220.
Time dependent improvement in the quality of concrete containing pre-wet lightweight aggregate is greater than that with normalweight. The reason is better hydration of the cementitious fraction provided by moisture available from the slowly released reservoir of absorbed water within the pores of the lightweight aggregate. The fact that absorbed moisture in the lightweight was available for internal curing has been known for more than four decades. The first documentation of improved long term strength gains made possible by the use of saturated normalweight aggregates, was reported in 1957 by Paul Klieger, who, in addition, commented in detail on the role of absorbed water in lightweight aggregates for extended internal curing.