Effects of hydrophobic expanded silicate aggregates on properties of structural lightweight aggregate concrete

This article addresses the performance of structural lightweight aggregate concretes and the relation of their performance to density class. Natural expanded silicate materials treated with a hydrophobic agent were used and their effects were systematically investigated. Three lightweight concretes with densities of about 1,000, 1,150, and 1,400 kg/m3 (classes D1.0, D1.2, and D1.4) were designed by applying an optimized particle packing theory. The microstructure, mechanical properties, and durability of the developed concretes were determined and the relations of these properties with density were evaluated. The lightweight concretes showed excellent structural efficiency, with 28-day compressive strengths of about 23, 28, and 42 MPa, respectively. Microstructural analyses showed that the developed concretes had a rather compact microstructure, contributing to enhanced strength. Existing codes for calculating concrete E-modulus were compared, and the best predicting formula is proposed. Mix D1.4 showed relatively low drying shrinkage, which can be attributed to relatively low initial water use and the internal curing effect brought about by the applied lightweight aggregate. The developed mixes showed excellent durability, as indicated by very low water penetration after 72 h of exposure under a pressure of 0.5 MPa (5 bars) and very small mass loss after 56 cycles of a freeze-thaw test under both deionized water and NaCl conditions.