Pre-Wetted Lightweight Coarse Aggregate Reduces Long-Term Deformations of High Performance Lightweight Concrete

Abstract

By using high-strength/high performance lightweight concrete in prestressed bridge girders, lengths of bridge girders can be extended by 15-20%. To understand the implications of the use of lightweight aggregate on prestressing losses, long-term creep and shrinkage deformations are of special interest. Long-term deformation of three high performance concrete mixtures was measured. The concretes were developed using Type III portland cement, silica fume, Class F fly ash, natural sand, and 12.7-mm MSA coarse aggregates. In each concrete, the coarse aggregate was varied, among normal weight gneissic granite, pre-wetted lightweight expanded slate, or air-dried lightweight expanded slate. Concrete compressive strengths greater than 75.9 MPa at 24 hours were obtained. Loading and drying (at 23oC and 50% relative humidity) for creep and shrinkage specimens started at 24 hours of age to best replicate conditions at a precast concrete manufacturing yard. When loaded at 24 hours, the long-term deformation of the pre-wetted lightweight aggregate concrete was less than that of the normal weight aggregate mix. The lightweight concrete with the initially dry aggregate exhibited the largest long-term deformation. These results agree with observations in the literature that the water initially stored in the aggregate is released over time and is able to reduce the long-term deformation of the high performance lightweight concrete.