Metakaolin-based geopolymer concretes for nuclear protection: On the perspective of physicochemical, durability, and microstructure

As a striking contribution of metakaolin to geopolymer concretes, the varying contents of metakaolin with quartz powder are included the mixtures with ground granulated blast furnace slag, and quartz sand to observe the mechanical, physical, transport, microstructure, and nuclear protection parameters of the samples, within this study. The geopolymer concrete samples are tested for the mechanical transport and physical properties depending on the curing time, curing temperature, and the raw/by-product material type. The results show that the samples containing the most metakaolin performed well with a 24-h compressive strength of 131.78 MPa. Increasing the curing temperature and curing time affected both mechanical, physical and transport properties. In addition, the microstructure of the samples was analyzed by scanning electron microscopy, x-ray diffraction, and Fourier transform infrared spectroscopy. Moreover, the effect of increasing metakaolin reinforcement on the nuclear protection capacity of the produced geopolymer concretes with experimental gamma transmission and neutron dose measurements was investigated. The M3 sample with high content of both metakaolin and granulated blast-furnace slag showed the highest resistance to gamma photons in the energy range of 0.081-0.383 MeV. The produced geopolymer samples absorbed almost 40% of the fast neutrons with 4.5 MeV energy. Neutron removal cross sections of the produced geopolymer concretes are in the range of 0.0952-0.0949 cm(-1) and are larger than those of B4C, graphite, and boric acid. The findings of this study revealed that the addition of metakaolin improved the mechanical, nuclear shielding and structural properties of geopolymer concretes.