Optimisation of the mechanical properties of structural concrete incorporating recycled glass aggregates

​The exponential increase in the use of concrete has placed significant strain on the environment due to the demand for natural resources needed for its production, including cement, aggregates, and water. This strain is particularly pronounced in the United Kingdom and many other countries, where substantial amounts of waste glass are generated. Recycling procedures produce glass that can be utilized as aggregate material. Therefore, the production of local and eco-friendly materials to replace traditional ones and prevent their disposal in landfills is crucial for alleviating both economic and environmental pressures.

​The study addresses the theme of partially replacing natural aggregates with recycled glass to produce sustainable and structurally sound concrete with mechanical properties comparable to or better than conventional concrete. Various replacement rates of natural aggregates with glass aggregates were investigated. Additionally, the experimental program was designed to ‘optimise the mechanical properties of structural concrete incorporating recycled glass aggregates’ The initial phase of the experiment focused on determining the impact of glass particles on the fresh properties of concrete. The objective of the latter part of the experimental program was to identify the level of substitution of natural aggregates with glass aggregates at which the characteristics of hardened concrete are affected. Natural aggregate (NA) was replaced with glass aggregate at percentages of 10%, 20%, 30%, 40%, 50%, 75%, and 100% in a concrete mix design with a target strength of 30 MPa.

​The general trends observed indicated that concrete mixes containing more than 20% glass aggregate (GA) exhibited superior performance in both fresh and hardened states compared to other mixes. Workability of concrete and slump loss over time were not adversely affected for mixes containing over 20% glass. Additionally, glass concrete demonstrated a lower density compared to control concrete. Compressive strength testing results revealed higher compressive strength for all mixes except the 75% glass mix, which exhibited a slight reduction. Similarly, pulse velocity testing showed a peak at 34.36 Km/s for 20% glass concrete, followed by a decrease with increasing glass-to-natural aggregate ratios in the concrete.

​However, the inclusion of glass triggered Alkali-silica reaction (ASR), significantly reducing the durability of the concrete. ASR data indicated that 10-20% recycled glass aggregate (RGA) had no adverse effects, and no harmful expansion due to ASR occurred during testing.

​However, samples containing 20% or more glass aggregate exhibited deleterious effects of ASR, a conclusion supported by scanning electron microscope study findings.