Exploration of mechanical performance, porous structure, and self-cleaning behavior for hydrothermally cured sustainable cementitious composites containing de-aluminated metakaolin waste and TiO2 nanoparticles

Abstract

The main goal behind this research is to produce antimicrobial cementitious composites with acceptable mechanical characteristics based on de-aluminated metakaolin waste (DAK) and commercial titania. Two cementitious blends have been prepared: OPC containing 50%DAK and OPC containing 45%DAK +5% TiO2 NPs. Regarding curing time and cost, these blends were treated under two different curing regimes: normal curing under tap water for up to 28-days at room temperature and hydrothermal curing at various steam pressures of up to 12 bars. Compared with the reference paste (OPC/28days), compressive strength test, phases identification, morphology, textural characteristics, and microbial resistivity test were conducted. It was found that the normal cured cementitious composite containing titania NPs possessed the highest strength (88 MPa) compared with reference (80 MPa) and OPC+50%DAK (58 MPa). On the other hand, the strength value for cementitious composite modified with TiO2 NPs reached 96 MPa under autoclave curing at 4 bars for 8 h and became 61.6 MPa for OPC+50%DAK. XRD and TGA/DTG techniques confirmed the formation of binding hydrates (C-S-Hs, C-A-S-Hs and C-A-Hs) under different curing conditions. SEM/EDX indicated stacked plates, fibers, and rods of C-S-Hs under hydrothermal treatment. N2-adsorption/desorption technique revealed that autoclaving conditions significantly reduced the pore diameter of the prepared blends. Two fungi strains (Mucor-circinelloide and Aspergillus-terreus) and two bacteria strains (Gram Positive-Bacillus subtilis-ATCC6633, Gram negative-K. pneumonia-ATCC13883) were used to conduct a self-cleaning test. According to the agar diffusion test, high inhibition zones were observed for normally cured OPC-50%DAK and OPC-45%DAK-5%TiO2 pastes.