Mitigating alkali silica reaction using waste glass powder

Abstract

Alkali silica reaction (ASR), the most widespread alkali-aggregate reaction (AAR), is a significant durability problem affecting concrete. A deleterious gel is formed due to the reaction between alkali oxides and reactive aggregates containing silica. This gel causes expansion, which in turn causes small cracks that affect the durability and mechanical properties of the concrete later. Although ASR causes cracks in concrete, the fundamental issue with ASR is the prevalence of additional durability concerns, such as corrosion in steel, that could ultimately lead to extreme results. Much research has been done to keep ASR expansion within the safe limits mentioned in related standards. Chemical and mineral additives, such as lithium and different supplementary cementitious materials (SCMs), can mitigate the expansion of ASR. Recently, some studies introduced waste glass in powder form as a mineral additive to mitigate ASR, and they found promising results with some problems in mechanical properties. However, more research is needed to understand how waste glass mitigates ASR and how we can solve its negative effect on mechanical properties. Environmental problems are considered one of the most significant problems in scientific society. Waste glass is an important environmental problem due to its large volume and slow decomposition rate. Glass is non-biodegradable and can take thousands of years to decompose in landfills. Improperly disposed of waste glass can contribute to environmental problems such as pollution, climate change, and habitat destruction. Therefore, using waste glass to produce cement-based materials can contribute to sustainability by reducing environmental issues. This experimental study proposes using waste glass powder (WGP) and nano silica (NS) as mineral additives to mitigate ASR. Different percentages of (WGP): 10%, 15%, 20%, and 25%, with 1%, 1.5%, and 2% of nano silica as cementitious replacement were examined. Nano-silica accelerates the early-age hydration reactions in mortar, while waste glass powder mitigates. Waste glass powder and cement used for the production were tested using an X-ray fluorescence test (XRF) to learn the elemental composition of both materials. The average particle size of WGP was 60µm before production to increase the effectiveness in mitigating ASR. Different tests were conducted to investigate the effect of WGP-NS combinations on mortar properties. A flowability test determined the workability of mortars with glass powder and Nano silica. Air content for mortars containing different amounts of WGP and NS was calculated during the production phase. An accelerated mortar bar test was conducted for different combinations to measure the expansion in each mortar. Flexural and compressive strength tests were conducted on prismatic specimens at 7 and 28 days. First, three flexural strength tests were conducted on samples to divide each specimen into two pieces (6). Three of the six pieces were tested in a compression machine, and the other three were used for a capillary water absorption test to see the influence of WGP and NS on the permeability of mortar. The results showed a positive effect of WGP-NS on mitigating ASR and limiting the reduction in the mechanical properties of mortars, especially at an early age. Scanning Electronic Microscope (SEM) and Thermo Gravimetric Analysis (TGA) tests were performed to examine the pozzolanic reaction of glass powder and see the cracks and different hydration products in the specimens. Also, X-ray diffraction analysis was performed to investigate the effect of WGP and NS on CH consumption C-S-H formation and quartz formation. SEM showed the ability of WGP to reduce the cracks that resulted from alkali-silica gel formation. Also, results showed a denser microstructure in mortars produced with WGP and NS. XRD and TGA tests presented the pozzolanic activity of WGP. The fine particles of glass powder, which contain high levels of Si+4 and Ca2+, conduct a pozzolanic reaction, and they dissolve completely in the hydration process to form C-S-H. This pozzolanic reaction causes insufficient presence of SiO2 to form the ASR gel. In addition to the improvements in the properties of mortars, replacing the cement with these mineral additives (WGP and NS) can be considered a recycling process and contribute to sustainability principles.