Mechanical properties and microstructure of lightweight aggregate concrete with and without fibers

Abstract

The effects of several factors such as dry apparent density, water-to-binder ratio, properties of expanded shale aggregates, and fiber volume fraction, on the mechanical properties of lightweight aggregate concrete (LWAC) were experimentally investigated. Performance of LWAC were characterized through compressive strength, splitting tensile strength and flexural strength. This paper characterizes the morphology and microstructure of lightweight aggregate and two types of interfacial transition zone (ITZ) by using scanning electron microscopy (SEM). More than 40 different LWAC mixtures included five different expanded shale aggregates and two types of fiber were designed and fabricated, exhibited 28-day compressive strength from 47 to 86 MPa for dry apparent density of 1720–1940 kg/m3, respectively. The test results shown that both water-to-binder ratio and lightweight aggregate properties have significant effects on the LWAC. Crushed shale aggregate with dense shell and low absorption was recommended. The addition of fiber had a slight impact on compressive strength but resulted in significant increases in splitting tensile strength and flexural strength. The maximum increase in strength was achieved at a volume fraction of carbon fibers of 0.9%. Furthermore, microstructure investigation revealed that a slight wall effect occurred in the ITZ of lightweight aggregate with a dense shell and low water absorption.