Evaluation of Mechanical Performance, Porous Structure and Self-Cleaning Behavior for Hydrothermally Cured Cementitious Composites Containing De-Aluminated Metakaolin Waste and Tio2 Nanoparticles

Abstract

The main objective behind this research is to recycle the largest possible amount of industrial wastes as de-aluminated metakaolin (DAK), to produce self-cleaning cementitious products with different categories in terms of mechanical efficacy. Hence, TiO 2 NPs and hydrothermal treatment played vital roles in achieving this target. Three pastes were prepared in this investigation; OPC paste was prepared under normal curing conditions (tap water for 28-days at 25 o C in high humidity) while the other two pastes (OPC-50%DAK and OPC-45%DAK-5%TiO 2 ) were treated in different curing regimes; normal and hydrothermal at various steam pressures up to 12 bars, Compressive strength results, at normal curing, confirmed that composite containing titania NPs possessed the highest strength (88MPa) comparing with OPC (80MPa) and OPC-50%DAK (58MPa). In autoclave at 4bars for 8hrs, the maximum strength values were 61.6 and 96MPa for OPC-50%DAK and OPC-45%DAK-5%TiO 2 , respectively. To minimize the consumed energy, 4 bars for 4hrs was the selected time to conduct the remained part of the work. SEM/EDX, XRD and TGA/DTG techniques were utilized to identify the morphology/shape of the formed hydrates (C-S-Hs, C-A-S-Hs and C-A-Hs) under different curing conditions. N 2 -adsorption/desorption test confirmed meso-porosity rearrangement. Four pathogenic microorganisms were used to conduct self-cleaning test for the selected composites; two fungi strains (Mucor-circinelloide and Aspergillus- terreus) and two bacteria strains (Gram positive-Bacillus subtilis-ATCC6633, Gram negative-K. pneumonia-ATCC13883). According to the agar diffusion test, the results indicated high microbial resistance for OPC-50%DAK and OPC-45%DAK-5%TiO2 pastes, especially treated under normal conditions.

Keywords: Hydrothermal treatment, Self-cleaning, Antimicrobial activity, De-aluminated metakaolin, TiO2 nanoparticles.