LIGHTWEIGHT AGGREGATE PARTICLE SHAPE EFFECT ON STRUCTURAL CONCRETE

An exploratory investigation of six lightweight fine aggregates was conducted in an effort to extend the concept, developed with normal weight fine aggregates or sands, that one of the most important properties of fine aggregates is their particle shape features--angularity and texture as measured by loose void content. They affect mixing water requirements, water-cement ratio and, consequently, most of the strength characteristics of mortar having a constant cement-aggragate ratio. For a range of 10 percent in loose void content, compressive strength varied about 2000 psi (150 kgf/cm2). The lightweight fine aggregates were generally found to have high void contents and mortar mixing water requirements; therefore, they had lower strengths when compared to natural sand mortars. Further extending the results of this exploratory work, each of the lightweight fine aggregates, as well as that from a seventh source, and their coarse companions, were combined with the same natural quartzite, sand and gravel. Concrete was designed to contain 517 lb (234 kg) of cement, to have a 3 to 4 in. (8 to 10 cm) slump and no entrained air. Both compressive and flexural strength responded to these changes in mixing water content as a function of water-cement ratio. This concept leads to a more accurate design of structural lightweight concrete according to normal weight procedures.