Effects of Curing Conditions on the Self-Healing of Geopolymer Paste

Abstract

Geopolymers are inorganic polymers produced by the reaction of aluminosilicates and alkaline solutions and show good mechanical and thermal features with a huge potential for use in the construction industry. Furthermore, geopolymers with self-healing properties can considerably decrease repair or maintenance costs and support economic and environmental sustainability. This study aimed to observe the self-healing capability of sodium silicate-containing agents in geopolymer pastes. Polyethylene glycol (PEG) and epoxy resin were used to encapsulate sodium silicate. The prepared healing agent was introduced into fly ash and metakaolin-based geopolymer samples. After curing for 28 days under room conditions, the samples were subjected to compressive loading to introduce cracks. The cracked samples were stored under three conditions: at 60°C under 100% relative humidity (RH), at room temperature under 100% RH, and at room temperature in water. After various durations, optical images were captured using a light microscope to determine the closure of the cracks. X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) were used to identify healing products. Additionally, the change in compressive strength was used as an indicator of self-healing. The results showed that the sodium silicate agents could heal the cracks with narrow widths (<15μm) under all conditions and supported strength recovery. XRD and FT-IR results indicated that the main healing materials were aluminosilicate phases.