Enhancement of mechanical properties of high−volume fly ash concrete using glass nano powder and effective microorganisms

Abstract

The low strength at early ages poses a major challenge to cement replacement with high volume fly ash of concrete (HVFA). The attempts to address strength reduction of HVFA concrete have not yet framed as radical solutions, considering the engineering solutions and the economic cost. So, this study aimed to investigate strategies to use local waste materials, which are more abundant and less expensive, to compensate for the strength loss associated with using HVFA as cement replacement. Both glass bottle waste nano-powder (GBWNP), and effective microorganisms (EMs) may offer a promising material for increasing strength at early ages due to their availability and minimal cost. In addition, GBWNP has sufficient pozzolanic properties to assist the pozzolanic reaction that can compensate for the early age strength reduction associated with HVFA concrete. To achieve the study goals, a series of modified concrete were prepared with 50% fly ash (FA), as cement replacement, 10% EMs as mixing water replacement, and 2%, 4%, 6%, 8%, and 10% of GBWNP as nano additives. The fresh properties of the new synthesized mixes were tested in terms of slump value and fresh-state density. The hardened properties examined are mechanical strength including compressive, flexural, and split strengths at 3, 7, 28, 56, and 90 days. The modulus of elasticity and water absorption were evaluated at 28 days. To generate more knowledge about the microstructures of the new modified specimens, various technical tests, including scanning electronic microscope (SEM), the energy dispersive X-ray spectra (EDS), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) at ages of 7 and 28 days. Results of the examined specimens show that the integrated addition of GBWNP and EMs significantly improves strength indexes at all the tested ages. The specimens with 10% EMs as mixing water replacement and 4% GBWNP demonstrate mechanical performance comparable with that of the control samples at almost all curing ages, whilst the mix prepared with 6% GBWNP outperformed the control mix of normal concrete at all curing ages. The microstructural analysis showed that hydration products increase, and the microstructure compactness and homogeneity enhance by inclusion both GBWNP and EMs, especially in case of the inclusion of 10% EMs and 6% GBWNP. Furthermore, a decreasing trend of calcium to silicon ratio (Ca:Si) and calcium to aluminium ratio (Ca:Al) due to the inclusion of GBWNP while an increasing trend of silicon to aluminium ratio (Si:Al) was observed, which confirm the role of GBWNP to boost FA to react faster, hence, improving strength properties. By employing fly ash and glass bottle waste, this study also seeks to contribute to the improvement of the environment by encouraging the recycling of waste in concrete sectors, providing efficient solutions to the landfill problems.