An initial trial mixture proportioning procedure for structural lightweight aggregate concrete

In this study, a straightforward mixture-proportioning procedure for structural lightweight-aggregate concrete (LWAC) was developed to determine the unit content of each ingredient to achieve the target values for slump, compressive strength, dry density, and air content of the concrete. To develop this approach, the design equations to determine the water-to-cement ratio and the unit water content were empirically formulated by performing a regression analysis over 347 data points. These data points were compiled from ordinary Portland cement concrete mixtures with expanded fly ash or clay lightweight aggregates. To determine the volumetric ratio of coarse aggregate per unit weight, a mathematical solution was established under two boundary conditions: the absolute volume and the dry density of concrete. The reliability of the proposed procedure was verified by testing five ready-mixed concrete batches at different replacement levels of lightweight fine aggregates for natural sand. In the concrete batches, expanded clay particles that were manufactured in a rotary kiln were used as the lightweight aggregates. The required values of the target parameters and the experimental values were compared. The results demonstrated that the proposed procedure provided a reasonable guide to obtain the first trial mixture of LWAC that varied with the requirements of the concrete and the properties of lightweight aggregates.