Mechanical Performance and Durability of Mortar Based on Slag Cement and NaOH-Activated Slag

Abstract

This paper investigates the valorization of slag in cement production in order to obtain a sustainable mortar and participate in protecting the environment. The study evaluated the setting time, hydration heat, mechanical strengths, drying shrinkage, sulfuric acid and sulfate attack of mortars. These mortars are based on Portland cement (PC), slag cements containing 10%, 30% and 50% slag and alkali-activated slag (AAS) using 6% and 9% of sodium hydroxide (NaOH). The results show that the increase in slag replacement rate increases the setting time accompanied by a drop in initial mechanical strength such that the compressive strength decreased by 30% at two days for a 50% slag substitution; also, it considerably reduces the shrinkage and hydration heat. The resistance to sulfate and sulfuric acid attack increases with the slag replacement rate. NaOH-activated slag mortar is the most resistant binder to sulfate attack and sulfuric acid, but it develops a lower mechanical strength and a more significant shrinkage than PC mortar. X-ray diffraction (XRD) analysis carried out on binder paste shows the formation of the same main hydration products in PC and slag cement with a small amount of portlandite in the last binder. Calcium silicate hydrate (CSH) and Hydrotalcite are the main hydration products of AAS.