Influence of chemical activation on the strength and durability of lime–corn cob ash cement

Abstract

The slow rate of strength gain and the relatively poor durability of lime–pozzolana binders limit their broader use in sustainable construction applications. This study examined how chemical activation influences the physicochemical characteristics, compressive strength, porosity, and sulfuric acid resistance of lime–corn cob ash (CCA) mortars. CCA was analyzed using X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and electrical conductivity tests to evaluate its pozzolanic behavior. Mortars containing a 50:50 lime–CCA ratio were prepared using water, 0.5 M NaOH, and 0.5 M Na₂SO₄ as mixing media. The results indicated that CCA is rich in silica (61.61% SiO₂), with a combined SiO₂ + Al₂O₃ + Fe₂O₃ content of 72.19%, confirming its suitability as a pozzolanic material. The reduction in electrical conductivity of about 28.1% after 240 min suggests moderate pozzolanic reactivity of CCA. Chemical activation markedly enhanced performance. Compressive strength increased from 2.91 MPa in the non-activated system to 5.92 MPa and 7.77 MPa for Na₂SO₄ and NaOH-activated mortars, respectively. Porosity showed a decreasing trend from L100–H₂O to LCCA50–0.5 M NaOH. Under sulfuric acid exposure, activated mortars experienced lower mass and strength losses than non-activated ones, with NaOH activation providing the best resistance. In contrast, pure lime mortar fully disintegrated under acidic conditions. The results confirm that chemical activation significantly improves the mechanical performance and durability of lime–CCA binders. The study demonstrates the viability of corn cob ash as a sustainable pozzolanic material for low-carbon, non-structural construction applications and highlights the effectiveness of different chemical activators in enhancing lime-based systems.