Early-Age Strength of Alkali-Activated Slag Mortar Based on Burned Oyster Shell and Other Chemical Activators

An alkaline-activated, ground-granulated blast furnace slag (BFS) was used as a binder for mortar prepared using river sand. Sixteen mortar mixes with four different BFS:sand ratios (4%, 8%, 12%, and 16% dry weight) were investigated. The BFS hydration of these mortar mixes was activated using four different activator solutions (1 mol): burned oyster shell (OS), calcium hydroxide (CH), sodium hydroxide (SH), and potassium hydroxide (PH). After curing for 3 and 7 days, the unconfined compressive strength (UCS) of the mortar increases with an increasing BFS:sand ratio, regardless of the activator type. The UCS of the mortar increased with increasing pH value of the activator. The mortar activated with OS had similar but slightly lower mechanical properties (60%-90% UCS, 70%-97% peak load strain, 0.78%-100% maximum strain, 40%-114% elastic modulus, 55%-100% toughness) relative to the mortar activated by CH, while the mortars activated by SH had mechanical properties similar to those of the mortar activated by PH. In all mortar samples, activated by different activators, CSH, C4AH13, and C4AC over bar H11 were found. The mechanical properties (strength, peak load strain, maximum strain, elastic modulus, and toughness) of the mortar samples were analyzed.