Mechanical Properties, Microstructure and Thermal Conductivity of Concrete Block Containing Fly Ash

Abstract

This paper presents the results on the mechanical properties, microstructure and thermal conductivity of concrete block containing fly ash at a ratio of binder : sand : stone dust of 1:2:8 by weight. Portland cement type I was replaced by fly ash at 10%, 20% and 30% by weight of binder, while the water-to-binder ratios of 0.70, 0.80, and 0.90 were used. Measurement of unit weight, water absorption, porosity, compressive strength, thermal conductivity and scanning electron microscopy were  conducted. The results showed that the compressive strength of air-cured concrete block containing 30% fly ash was lower than that of a control concrete block. Nevertheless, when air cured for 7 days, the compressive strength was noted to be higher than that specified by the Thai Industrial Standard 58-1990, which is no less
than 2.5 MPa at 28 days. The unit weight of concrete block containing fly ash decreased with a decrease in the fly ash content, whereas its porosity and water absorption increased with the increased fly ash content. Concrete block with partial replacement of cement by fly ash exhibited lower thermal conductivity than the control concrete block. In addition, the thermal conductivity decreased with the increased water-tobinder ratio.