Feasibility of Alkali-Activated Slag Paste as Injection Material for Rehabilitation of Concrete Structures

Alkali-activated materials (AAMs) have recently been used as a suitable replacement for conventional ordinary portland cement (OPC) mixtures. This study evaluates rheological, injectability, and mechanical properties of alkali-activated slag (AAS) mixes to assess the possibility of using AAS pastes as coating mortars for the rehabilitation of concrete structures. Mixtures are produced with the incorporation of silica fume (SF) up to 15% of total binder weight in AAS pastes. A combination of sodium hydroxide (NaOH) and sodium silicate (water glass) is used to activate aluminosilicate sources. Water glass:NaOH ratios of 0.4 and 0.5 and activator solution:pozzolan ratios of 0.55 and 0.65 are selected after initial attempts to evaluate the effect of activator solution characteristics on the rheology properties of AAS mixtures. Samples are prepared in two moisture conditions (dry and damp) in order to assess the effect of moisture presence on the performance of AAS injection pastes. Setting time, fluidity, injectability, tensile strength, capillary absorption, and slant shear tests are conducted on AAS pastes. Microstructure analysis is performed on the selected mixtures. According to results obtained from limited experimental work conducted in this study, 5% SF addition results in higher setting time and injectability of AAS pastes. In addition, it is found that an increase in water glass content in AAS pastes results in lower setting time and fluidity, which in turn results in a low level of injectability. The results of tests conducted on damp and dry samples show a high level of compatibility of AAS paste with moisture presence.