Effect of Water Content on the Properties of Lightweight Alkali-Activated Slag Concrete

Abstract

The water content and lightweight aggregate proportions in lightweight alkali-activated (AA) concrete need to be carefully managed to control the quick slump loss of fresh concrete and to meet the mechanical properties that are required for structural concrete. This study tested 10 lightweight AA slag concrete specimens to evaluate the effect of the water content on the workability and various mechanical properties of the concrete. The source material, ground granulated blast furnace slag, was activated by using sodium silicate and calcium hydroxide powders to produce a cementless binder. The rate of development of the compressive strength and the shrinkage strain measured from the concrete specimens were compared with empirical models proposed by American Concrete Institute (ACI) 209 for normal-weight portland cement concrete. To examine the practical applicability of the lightweight AA slag concrete, the splitting tensile strength and the moduli of elasticity and rupture recorded from the concrete specimens were compared with empirical equations and a database for lightweight ordinary portland cement (OPC) concrete, whenever possible. The test results showed that an increase of water content alleviated the quick slump loss of the fresh concrete and slightly increased the compressive strength of the hardened lightweight AA slag concrete. Additionally, the rate of development of the compressive strength of lightweight AA slag concrete cured under room temperature was comparable with that of steam-cured early strength portland cement concrete. The splitting tensile strength and the moduli of rupture and elasticity of lightweight AA slag concrete were comparatively better than those of lightweight OPC concrete. As a result, they can be conservatively evaluated by using the empirical models that are recommended for lightweight OPC concrete. Moreover, the extent of shrinkage strain of lightweight AA slag concrete was larger than that predicted from the empirical model specified in ACI 209 at an early age and after 40 days, regardless of the water content.