Mortars of alkali-activated blast furnace slag with high aggregate:binder ratios

• Mortars of high aggregate:binder ratios with alkali activated blast furnace slag were investigated.
• Previous reports on similar mortar composition were not found.
• Conditions included low alkali concentration to reduce cost and problems associated to alkalis.
• Low water/binder ratios were used in mortars of semi-dry consistency for precast products.
• The implications of the above are related to strength development and reactivity of the slag.

Mortars with high aggregate:binder ratios of 10:1 and 8:1 were investigated with binders of blast furnace slag activated with 2.5%, 3.4%, 4.5%, and 6.5% Na2O relative to the mass of slag and using sodium silicate solutions with moduli SiO2/Na2O of 1.3, 1.5, 1.7, 2.0 and 2.2. The mortars were formulated at low water/binder ratio in semi-dry mixes to produce bricks. The modulus of 1.7 was chosen as most adequate and the effects of the % Na2O and temperature, on strength development, were then investigated. Various formulations showed compressive strength useful for construction, where mortars with aggregate:binder of 8:1, activated with 3.5% Na2O and cured at 60 °C registered 20 MPa at 28 days, while mortars with 8:1 and 10:1 with 6% Na2O cured at 20 °C reached 20 and 13.3 MPa, respectively.