Influence of silica-fume’s addition technique and curing conditions on microstructure, physical and mechanical properties of geopolymer

Geopolymer as ecofriendly and energy saving material is estimated as excellent building material in construction sector. The current study focuses on studying the influence of silica fume mixing technique, its contents (2.3, 4.6, 6.9%) and curing conditions on microstructure, physical and mechanical properties of metakaolin-based geopolymers. Two mixing methods and two various curing conditions (air and 100% relative humidity) were utilized for production of geopolymers. The prepared geopolymers were investigated by various techniques such as x-ray diffraction (XRD), Fourier transforms Infrared spectroscopy (FTIR) and Scanning electron microscope (SEM). The bulk density, apparent porosity and compressive strength were also examined. The results revealed that the aforementioned parameters were significantly affected the properties of the produced geopolymers. The physico-mechanical properties were improved when the geopolymers prepared by the proposed method (Dissolving silica fume in 12 M NaOH before mixing with metakaolin), as compared to that prepared by other method (mixing of silica fume with metakaolin before addition of NaOH). The properties of geopolymers cured in air were better than that cured in 100% relative humidity. The optimum percentage of silica fume that gave the best properties was 2.3%, after which the properties were reduced. The geopolymers that contained 2.3% silica fume, exhibited the highest compressive strength (45.13 and 39.97 MPa), while the geopolymers that contained 6.9% silica fume displayed the lowest compressive strength (17.11 and 15.5 MPa), when cured in air or 100% RH, respectively.