Exploration of fungal resistivity and mechanical performance of Zn-phases-doped geopolymers: ZnO and Zn/Al-LDH nanoparticles

Abstract

Generation of green geopolymer pastes that are based on a 1:1 slag/fly ash ratio (Geo) is the main objective of this study owing to the limited production of cementitious slag in Egypt. Different doses of ZnO and Zn-Al-CO₃ layered double hydroxide (LDH) were individually incorporated in geopolymer pastes to attain our aim and are coded Geo, Geo-0.5 %ZnO, Geo-1 %ZnO, Geo-0.5 %LDH, and Geo-1 %LDH. Setting times of fresh pastes and compressive strength of hardened pastes up to 28-days of conventional alkali-activation have been measured. Setting times of fresh pastes and compressive strength of hardened pastes up to 28-days of conventional alkali-activation have been measured. The results confirmed that adding ZnO and LDH NPs to the neat geopolymeric paste (Geo) significantly accelerated the setting process within 7–23 mins, especially for samples Geo-1 %ZnO and Geo-1 %LDH with 7/17 and 8.4/17.5 min., respectively. On the other hand, mechanical results indicated that pastes containing zinc oxide had poor compressive strength, especially in the early stages while 0.5 % LDH nanoparticles had a positive role as the strength values reached 8.9, 40, 60 MPa at 1, 7, and 28 days of curing, respectively. This behaviour is attributed to creating different types of zinc/silicon-containing phases like zinc-alumino-silicate-hydrates (Z-A-S-H, Zn₆Al₁₂Si₁₂O₄₈.29H₂O), zinc-silicate-hydroxide-hydrate (Z-S-H, Zn₄Si₂O₇(OH)₂·H₂O) and calcium-zinc-silicate (CaZnSi₂O₆) which detected by XRD. Moreover, TGA and SEM techniques affirmed the catalytic performance of LDH nanoparticles inside the geopolymeric structure as extra quantities of CSH, CASH, and C₃AH₆ have been generated. Anti-fungal activity test for some selected geopolymeric pastes was conducted via agar diffusion test (ASTMD4300–1). Geo-0.5 % ZnO and Geo-0.5 %LDH samples possessed the highest recorded inhibition zones against Aspergillus Niger and Mucor Circinelloid -AUMMC 11656, especially against Penicillium Glabrum-OP69417 with 51±1, and 67±2, respectively.