Use of expanded clay and silica fume for the improvement of mechanical, physical and thermal performances of structural lightweight concretes

ABSTRACT In this study an investigation was carried out for the execution of concretes with high strength, low density and excellent thermal properties, in order to execute energy-efficient constructions. Structural Lightweight Concretes were studied using two different granulometries of expanded clay (C05 and C15), where the coarse aggregate was replaced by 0, 25, 50, 75 and 100%. To promote the maintenance of consistency and resistance, superplasticizer and silica fume were used in the mixtures. Based on the methodology used, the concretes were physically and mechanically characterized, in accordance with current national and international standards. The density of the concretes, in the hardened state, ranged from 1,787 to 2,400 kg/m³ and, for compressive strength, ranged from 26 to 53 MPa at 7 days of age. The thermal conductivity test, using the protected hot plate method, was performed according to EN 12667, where was observed a variation of 0.61 to 1.00 W/mK. Microstructural information of the interfacial transition zone between aggregate and cement matrix were obtained with the purpose of analyzing the relationship with mechanical resistance. The investigation revealed that, with the addition of expanded clay (C05 and C15) and silica fume in the concretes, there was reduction of the density and the mechanical resistance, while the thermal characteristics improved.