Towards optimization of mechanical and microstructural performances of Fe-rich laterite geopolymer binders cured at room temperature by varying the activating solution

Abstract

In the present study, the performances of the end products prepared using calcined iron-rich laterite at 600 °C (LAT600) with different alkaline solution (AS) to calcined laterite (AS/LAT600) mass ratio (0.45–0.65) were investigated. The effect of AS/LAT600 mass ratio on microstructural and mechanical properties of consolidated geopolymer samples, such as compressive strength, porosity, bulk density, water absorption, mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) analysis were determined. Geopolymer made with AS/LAT600 ratio of 0.55 yields the highest compressive strength (54 ± 0.38 MPa) and compact structure. Increasing the AS/LAT600 mass ratio (0.45–0.65) increased the setting time, flowability and decreased the SiO₂/Fe₂O₃ and Al₂O₃/Fe₂O₃ molar ratios and compressive strength leading to a weak structure. Both cumulative volume intrusion and cumulative pore area increased from 0.11 to 0.20 mL g⁻¹ and 65.20 to 90.93 m² g⁻¹, respectively. Such enhancement is linked to changes that occur into the geopolymer network when high alkaline activator/laterite is used. Therefore, further increase of AS/LAT600 mass ratio improved the workability, delaying the polycondensation rate of dissolved calcined laterite and not positively affecting the mechanical strength development. Nevertheless, the performance of the end products could be found application in building engineering.