Impact of electron-beam and gamma-ray on the compressive strength, surface features and phase composition of β-Ni(OH)2-impregnating-geopolymer pastes

In the sol-gel method, nano-materials are obtained by the calcination of the produced hydroxide, which represents several drawbacks, such as high toxicity, high cost and high energy consumption. Therefore, for the first time, β-Ni(OH)2 was used instead of nano-NiO to develop green geopolymeric composites with high-dose radiation tolerance. The mix-design was formulated using slag and fly ash (1:1) activated with 5 wt.% NaOH and modified with 0.5, 1 and 2 wt.% β-Ni(OH)2. The fresh properties were investigated. It was found that increasing the β-Ni(OH)2 dose reduces workability (mini-slump test) with a slight increase in density. A compressive strength test was performed for all specimens before (cured for 28-days) and after exposure to different radiation doses (100, 200 and 300 KGy). Electron-beam and gamma-ray were used as various sources of radiation. The results demonstrated that incorporating β-Ni(OH)2 in the non-irradiated and irradiated composites enhanced their performance at all additional levels. The irradiation process by electron-beam and gamma-ray positively impacts the compressive strength at all radiation doses, especially at 200 KGy. The highest compressive strength was achieved by the specimen containing 0.5 wt.% β-Ni(OH)2 (67.3 MPa at 28-days, 88 MPa at 200KGy/electron-beam and 76.5 MPa at 200KGy/gamma-ray). The XRD, TGA/DTG and SEM analysis techniques proved that the synergistic impact of β-Ni(OH)2 (high reactivity and filling/catalytic impact) and irradiation process (activation unreacted precursors) motivate the formation of new binding phases such as NiAl2O4, CaNiSi2O6 and analcime as well as ordering zeolitic phases in cross-linked structure, causing improvement in the performance.