Alkali-activated mortars: Workability and rheological behaviour

Workability and rheology in alkali-activated materials (AAMs) have been scarcely studied and differ substantially from ordinary Portland cement (OPC) systems. This study aims to explore the workability and rheology of alkali-activated slag (MS) and fly ash (AAFA) mortars, ascertaining the effect of the precursor, the nature and concentration of the alkaline activators and the aggregate content. Mortars were prepared varying the aggregate/binder and liquid/binder ratios. OPC mortars were used as a reference. Mortar workability was determined by flow table measurements. The rheological tests included the stress growth test and torque at constant shear rate. Mortars were tested for 7 day compressive strength. AAS and AAFA mortar workability was more sensitive to changes in the liquid/solid ratio than OPC mortars. In MM mortars, fluidity was found to be proportional to the liquid/solid ratio and dependent upon aggregate content. When in a plastic state, MS and AAFA mortars activated with waterglass solutions exhibited larger spreads and greater workability than OPC mortars, confirming the fluidising effect of waterglass. Rheology of AAS mortars was more influenced by the nature and concentration of the alkaline activator than that of AAFA mortars. Rheological behaviour of AAS and AAFA mortars fits the Bingham model. (C) 2017 Elsevier Ltd. All rights reserved.