Abstract

The main objective of the present research was to develop a general proportioning methodology for structural sand-lightweight concrete (SLC). The study considers lightweight aggregate concrete as a two-phase material. The first phase, composed of cement, water and siliceous natural sand, is called the resistant phase, and contributes to the structural strength. The second phase is the lightweight phase, constituted by coarse lightweight aggregate, and is meant to decrease the concrete density. The application of this approach appears to be feasible because the transition zone would be a limiting factor for the strength development on these types of concrete. An extensive experiment program was carried out, including 47 trial mixtures, in which the type and proportion of each one of the phases were varied to analyze the principal factors directly affecting the SLC properties. Cubic and cylindrical compressive strength tests at 3, 7, and 28 days. Density, compressive strength, and modulus of elasticity tests in air-dry conditions were preformed. Workability (slump), freshly mixed density, and air content tests were also performed. The obtained results allow for the proposition of relationships between the proportioning variables and the objective or design variables: slump, compressive strength, and density of concrete. An SLC mixture proportioning methodology that allows the use of a wide range of lightweight aggregates and applications is presented. In the proposed methodology the lightweight aggregate content is determined by density requirements: the water dosage by the specified slump; the freshly mixed density; and the grading of the total aggregate. The strength and proportions of the phases and the specified compressive strength control the cement content. Finally, the siliceous natural sand content is determined by the condition that the absolute volume of the mixture must be 1 m(3). An easy measured index representing the structural capacity of the lightweight aggregate is also proposed.