The impact of wurtzite and mesoporous Zn-Al-CO3 LDH on the performance of alkali-activated-slag: Setting times, compressive strength, and radiation attenuation

Although including wurtzite (ZnO) in cementitious materials significantly enhances gamma-radiation mitigation, its use is not recommended as it excessively prolongs the setting time and negatively affects the early strength. Hence, this study attempts to address these issues while enhancing radiation-shielding by including Zn-Al-CO3 layered double hydroxide (LDH) as an alternative for ZnO. Wurtzite and LDH nanoparticles were laboratory-prepared via the co-precipitation method; their specific surface areas were found to be 2290 and 65483 cm2/g, respectively, referring to the high reactivity of LDH. Five pastes were prepared; alkali-activated slag was used as a control specimen (0 wt% nanoparticles), while the others contained 0.5 and 1 wt% ZnO or LDH. The comparative study showed that incorporating Zn-phase as LDH solved the abovementioned problems. The setting time of LDH-modified specimens fits in the standard limit (50–375 mins), while others contain ZnO exceed this limit. The inclusion of 0.5 wt%LDH showed a remarkable enhancement in mechanical performance; compressive-strength values increased by 36.2 and 31.1 % concerning the control specimen after 1 and 28-days, respectively. In contrast, the same dose of ZnO reduced strength by 26.3 and 13 %. Moreover, the LDH-modified specimens displayed the highest linear-attenuation coefficient and lowest half-value layer when exposed to two gamma-ray sources (Co-60 and Cs-137). The X-ray diffraction, thermogravimetric analysis and scanning electron microscope proved that the formation of Zn(OH)2 in the ZnO-modified specimens is the main reason behind high retardation and reduction in compressive-strength. The filling/active-seeds/chemical-reactivity actions of LDH resulted from its high surface area, forming a high amount from different strength-giving-phases (compact structure) in the LDH-modified specimens. •The inclusion of Zn/Al-CO3 LDH to AAS fresh pastes did not exceed the standard limit of initial/final setting times.•The incorporation of 0.5 %LDH developed the compressive strength of AAS pastes.•Zinc oxide nanorod acted as a retarder during alkali-activation process.•Alkali-activated pastes modified with 0.5 %LDH paste exhibited the highest values of linear attenuation coefficients.