Mechanical and Microstructural Properties of Meta-Halloysite-Based Geopolymer Mortars Cured at Room Temperature

Abstract

Abstract In this study, meta-halloysite (MH) mixed with an alkaline solution(8, 10, and 12 M) was used as a binder phase to produce geopolymer mortars with alkaline solution/MH ratios of 0.6, 0.7, and 0.8. The flow slump behaviour, setting time, and mechanical properties of the end products were studied at room temperature. The microstructural properties of the geopolymer mortars were evaluated using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. The results indicated that the cohesion between the geopolymer binder and quartz sand aggregates improved with an increase in the molarity and alkaline solution/meta-halloysite ratio from 0.6 to 0.8. The corresponding slump and flow values increased from 25 to 118 mm, 14 to 115 mm, and 12 to 102 mm, whereas the setting time increased from 77 to 163 min, 54 to 140 min, and 35to 121 min,respectively, with an increase in the alkaline solution concentration. Increasing the alkaline solution/MH ratio (from 0.6 to 0.8) improved the dissolution of the solid precursor and produced a sufficient amount of geopolymer,ensuring the formation of a dense and compact structure with few accessible voids, thus justifying the reduction in water absorption and porosity. A similar trend was observed in the compressive, flexural, and tensile strengths, which increased with the alkaline activator/solid precursor and curing time (7 and 28 days). The geopolymer mortar samples prepared using 0.8 and 12 M NaOH developed high compressive strength (65 MPa), lower porosity, and lower water absorption.