Effect of geothermal waste on strength and microstructure of alkali-activated slag cement mortars

Mortars of blast furnace slag replaced with 10% of a geothermal silica waste were cured for 90 days. The binder was activated by 6 wt.% Na2O equivalent of NaOH and water glass. The presence of the silica enhanced the formation of hydration products as shown by nonevaporable water (NEW) results. Backscattered electron images indicated that the microstructures of blended slag had less porosity than those of neat slag mortars and the interfacial zone between aggregate and hydration products was dense and of homogeneous composition similar to the matrix of hydration products. The main hydration products were C-S-H and for NaOH a hydrotalcite type phase was found as finely intermixed with the C-S-H. (C) 2003 Elsevier Ltd. All rights reserved.