Effect of gamma radiation on the strength development of metakaolin-based geopolymer

Geopolymer has gained growing interest as an alternative cementitious material to ordinary Portland cement for the immobilization of radioactive wastes. This paper presents a study that examined the effect of gamma irradiation on the geopolymerization kinetics and strength development of metakaolinbased geopolymer as a potential matrix for immobilizing radioactive waste. The geopolymer samples, prepared with a water to binder ratio of 0.55 and aged for 1 hour, 24 hours, 7 days and 28 days, were exposed to 12.6 kGy gamma radiation at a dose rate of 25 Gy/h and 70 Gy/h. The results showed that gamma radiation exerted a negative effect on the geopolymerization kinetics and strength development. The compressive strength for hardening MK-based geopolymer (1 hour, 24 hours of age before irradiation) was lower than that of non-irradiated ones, whereas that of hardened samples (7 days and 28 days of age before irradiation) increased upon irradiation. Despite this, the compressive strength for all irradiated specimens ranged between 33 and 67 MPa, exceeding the minimum of 8 MPa required by the Belgian waste acceptance criteria for radioactive waste forms. Fourier Transform Infrared spectroscopy results showed that no new bonds were formed upon irradiation, implying that gamma radiation induced no change in the phase assemblage of the geopolymer. Based on these findings, the MK-based geopolymer shows great promise as a potential matrix for radioactive waste immobilization.