A Capacitive Electrode Approach for Real-Time Monitoring of Geopolymer Concrete

Monitoring the setting behaviour of geopolymer concrete (GPC) remains challenging due to the lack of reliable, non-destructive techniques capable of capturing its rapid and chemistry-dependent evolution. Existing methods provide limited insight into the dielectric response associated with geopolymerisation, creating a gap in real-time assessment of setting and reaction kinetics. This study proposes the use of a capacitive electrode method as a non-destructive tool to monitor and predict the setting and evolution of GPC. Several GPC mixtures were prepared by varying the alkaline solution–to–fly ash ratio (0.45–0.65) and the sodium silicate–to–alkaline solution ratio (0.65–0.85). Setting time was determined using penetration resistance, while dielectric constant (ε′) and loss factor (ε′′) were measured using a developed capacitive electrode cell. The results show that geopolymer evolution is most effectively monitored within the frequency range of 15–25 MHz, with ε′ and ε′′ providing a high-accuracy estimation of setting time. The dielectric constant (ε′) effectively captures overall geopolymer evolution, whereas the loss factor (ε′′) sensitively distinguishes reaction rates associated with different activator compositions. These findings demonstrate that the capacitive electrode method offers a rapid, accurate, and non-destructive approach for real-time monitoring of geopolymer concrete, supporting improved quality control and optimization of sustainable construction materials.