Experimental Investigation on Recycled Glass Powder as a Pozzolanic Cement

Abstract

Cement is the main ingredient in concrete, and the production of cement is a costly and energy absorbing process. In addition, production of cement ominously contributes to environmental pollution, as 1 ton of cement releases about 0.9 ton of CO2 in the atmosphere. Since cement is the material which is primarily responsible for the cost and the pollution, there is a critical need to develop materials which exhibit cementitious property and could be used as a substitute of cement. Supplementary Cementitious Materials (SCM), are substances which possess cementitious properties, hence they can be used as a partial/total replacement of cement. Recently, use of recycled material, such as waste glass powder (WGP), has received augmented attention in the concrete industry. At first, waste glass was used as an aggregate replacement in concrete and it was observed that the mechanical and durability properties of the modified concrete were degraded due to the increased potential of Alkali-Silica Reaction (ASR). Later, literature studies have shown that ASR occurrence in concrete is dependent on the particle size distribution of the glass used. As the particle size decreases the ASR probability reduces. These results motivated the use of recycled glass powder (RGP) with microscopic particle size distribution as cement replacement. There are multiple benefits of using RGP as cement replacement: firstly, using a waste material would reduce the load on the landfills, secondly, the total cost would be less as recycled WGP is replacing the costly cement; and finally, the use of RGP would lead to sustainable construction as a consequence of a decrease in cement manufacturing. The present study deals with the experimental investigation on RGP as a pozzolanic cement. The Glass Powder (GP) used in this experiment was provided by the Australian company, Enviro Sand who supplied samples with two particle sizes of 75 μm and 150 μm for the purpose of this research. The main aim of this research project is to study the pozzolanic performance of GP having a particle size smaller than 150 μm. The current study involves an extensive experimental program which includes: density, compressive strength, tensile strength, pozzolanic activity, water absorption, chloride resistance, heat of hydration and drying shrinkage. Extensive concrete specimens of standard cube, cylinder and rectangular prism of standard dimensions are prepared to investigate the various material, strength and durability properties by varying the GP content. In addition, present experimental work consists of enhancing the pozzolanic performance of the GP by varying the curing conditions and modifying the mix design. In total, about 700 specimens were tested in three stages in this experimental research work The optimisations resulted in Strength Activity Index (SAI) of coarse GP which was comparable to the SAI values of much fine GP reported by the earlier published research works. Since a considerable amount of energy would be consumed in grinding the glass from coarse to fine, the grinding energy would in turn lead to increment in the cost and rise in harmful carbon di oxide emissions. The current research is significant owing to the multiple benefits mentioned in the previous paragraph, furthermore, locally, according to a recent report from Australian National Waste, Australia generates around 1.1 million tonnes of glass waste which is equivalent to about 45 kg glass per capita and approximately 44% of it is landfilled. This practice of dumping the glass waste in landfills is environmentally unsustainable, since glass is non bio-degradable in nature. The last stage mix design alteration resulted in a maximum SAI of 117%. In addition, it resulted in higher resistance to chloride ion penetration of 17% and about 23% lower heat of hydration than the control mix at 30% replacement of the coarse GP.