EXPERIMENTAL STUDY ON HIGH-CALCIUM ALKALI-ACTIVATED MATERIALS: SLAG, PALM KERNEL SHELL ASH, AND CLASS C FLY ASH-BASED MORTAR

Abstract

This study investigates the development of sustainable high-calcium alkali-activated mortar incorporating Ground Granulated Blast Furnace Slag (GGBS), Palm Kernel Shell Ash (PKSA), and Class C Fly Ash (CFA) as hybrid binders, using locally available Bholari brown sand as the sole fine aggregate. Mortar mixes were activated using sodium hydroxide (NaOH) solutions with molarities ranging from 8 M to 16 M, while the sand-to-binder (S/B) ratio was maintained at 2.0 to evaluate its influence on fresh and mechanical properties. Cylindrical specimens (100 mm diameter × 200 mm height) were initially cured at room temperature or in an oven at 60 °C for 5 hours and then stored under ambient laboratory conditions until testing. Experimental results indicate that compressive strength increased significantly with NaOH molarity up to an optimum range (12–14 M), after which slight reductions occurred at higher molarity levels due to rapid gel precipitation and microstructural defects. Oven curing enhanced early-age strength and densified the matrix. The 28-day compressive strength of 50% Slag + 50% CFA mixes reached up to 55 MPa, while PKSA-rich mixes achieved approximately 35–40 MPa. The study concludes that hybrid high-calcium binders, combined with locally available Bholari sand, can produce high-performance, eco-friendly mortar suitable for sustainable construction