Developing green slag/bentonite-based geopolymers modified with meso-porous tungsten oxide: Zeolitic phases, mechanical performance and gamma-radiation mitigation

In an attempt to maintain the sustainable development goals in the construction sector via reducing the raw-materials/energy consumption and greenhouse-gas emissions related to cement production, a green nano-modified slag/bentonite-based alkali-activated material was developed. Firstly, the green composites were prepared by mixing slag and bentonite with a ratio of 2:1. Several factors like NaOH-concentration (6, 8, 10 wt%); thermal treatment of bentonite (as-received “RB” and thermally treated at 650 °C “TB”); curing conditions (normal-curing for 3 and 28-days as well as hydrothermal-curing at 3, 6, 9, 15 bar for 4 h) and meso-porous tungsten oxide nano-particles “WO₃-NPs” inclusion (0.25, 0.5 and 1 wt%) were studied to assign the optimum conditions for fabricating composites with adequate mechanical properties and radiation-shielding ability. The mechanical performance and radiation shielding were evaluated by measuring the compressive-strengths and linear attenuation coefficient “μ”/ half value layer “HVL” using ¹³⁷Cs, respectively. The results reveal the feasibility of using 8 wt% NaOH, TB, hydrothermal-curing at 3 bar/4 h and 0.5 wt% WO₃-NPs in fabricating low-cost/pre-cast/environmentally friendly building material with superior compressive-strength (53.6 MPa). Also, the radiation shielding results substantiate that this developed composite achieved adequate μ and HVL values, referring to its efficiency as a radiation-blocker. The synergistic impact of alkali-hydrothermal-activation, the high pozzolanicity of TB and the nucleation-site/potential-seeds effect of WO₃-NPs are the main reasons behind forming strength-giving-phases from stratlingite, hydrogarnet, analcime and pentasil zeolitic phase (ZSM-5), as proved by X-ray diffraction (XRD), thermogravimetric analysis (TGA/DTG) and scanning electron microscopy (SEM). The presence of such phases reinforced the microstructure, thus improving the mechanical performance and radiation shielding capability.