Effect of slaked lime on the geopolymers synthesis of natural pozzolan from Moroccan Middle Atlas

This study presents the effect of slaked lime (Ca(OH)2) on the physical and microstructural properties of geopolymers based on natural Moroccan pozzolan. The slaked lime was incorporated at 4, 8, and 12% replacement by weight of pozzolan. Aqueous solutions of sodium hydroxide (NaOH) with different molarities (4, 6, 8, 10, and 12 M) and sodium silicate (Na2SiO3) were used as alkali activators. The molarity of 8 M NaOH was selected as the optimal concentration. The effect of slaked lime was evaluated by measuring the compressive strength (Rc), P wave propagation velocity (Vp), bulk density (D), porosity (P), and water absorption (A). Complementary studies using X-ray diffraction (XRD) and scanning electron microscopy (SEM) were also performed. The results revealed that the incorporation of 8% of slaked lime catalyzed the geopolymerization reaction and promoted the dissolution of the crystalline phases as well as the amorphous phase of pozzolan. These improvements in the geopolymerization reaction resulted in the formation of new phases such as phillipsite-type calcium zeolite and calcium aluminosilicate hydrate, producing the best-performing geopolymer from a physico-mechanical point of view (Rc = 23.05 MPa, Vp = 2.21 km/s, D = 2.05 g/cm3, P = 5.13%, and A = 2.49%).