Structural Lightweight Concrete for Composite Design

ASTM Designation C330 defines lightweight aggregates for structural concrete in a number of ways: it names most available materials; it lists maximum permissible unit weights of coarse and fine fractions; it describes limiting aggregate tests; and it specifies tests for concrete-making ability. The ACI Building Code defines structural concrete as having a compressive strength of 2,500 psi or more. ACI 613A-59, a standard for Mix Proportioning Lightweight Concrete, establishes a top unit weight for the concrete at 115 1bs per cu ft. Three other major factors work toward limiting which aggregates are considered truly structural lightweight aggregates—availability, cost, and proven performance. The concrete-making properties of most lightweight aggregates are shown in a spectrum of concrete unit weights (Fig. 1). Vermiculite and perlite are extremely light materials used in insulating fill concrete ranging in density from 15 to 50 pcf and in strength from 300 to as high as 1,000 psi. Pumice and scoria are natural lightweight aggregates found in volcanic deposits; hence, they have limited availability. Concrete made with these aggregates is in an intermediate range as far as weight and strength are concerned.