Effects of Kinetic Parameters on Initial Setting Time, Microstructure and Mechanical Strength of Volcanic Ash-based Phosphate Inorganic Polymers

Abstract

This study assesses the effects of curing temperatures (28 and 60 °C) and P2O5 / H2O molar ratio percentages (4 to 12 %) on initial setting time, microstructure and mechanical strength of volcanic ash-based phosphate inorganic polymers. The inorganic polymers along with the raw materials were characterized by X Ray Fluorescence (XRF), X Ray Diffraction (XRD), Fourier Transform Infra Red (FTIR) spectroscopy and Scanning Electron Microscopy (SEM). In addition, initial setting time of pastes was determined along with compressive strength and water absorption on specimens aged 28 days. The results showed that initial setting time decreases with the increase of P2O5 / H2O molar ratio percentage in the range of 126 − 20 Min (28 °C) and 20 − 10 Min (60 °C). Conversely, either at 28 or 60 °C curing, compressive strength increases with the increase of P2O5 / H2O molar ratio percentage. FTIR spectra show the presence of Ca-O and Fe-O and Al-O-P-O bonds. Dependent on curing temperature, new crystalline phases including hydroxyl apatite, brushite, sigloite, aluminium phosphate hydrate, potassium magnesium phosphate hydrate and silicon hydrogen phosphate were formed. Hence, initial setting time, microstructure and mechanical strength of volcanic ash-based phosphate inorganic polymers are P2O5 / H2O molar ratio percentage, curing temperature and chemical composition dependent.