The Impact of Recycled Glass and Demolition Sand on Delayed Ettringite Formation and Mechanical Performance of Sustainable Concrete

Concrete poses many environmental and economic problems due to its heavy reliance on natural resources. The objective of this study was to explore the potential of utilizing recycled materials, specifically waste glass powder and demolition sand, to assess their effectiveness in reducing the formation of delayed ettringite and consequently enhancing the strength of sustainable concrete. This study assesses the combined effects of waste glass powder and demolition sand on stable, sustainable concrete under sulfate exposure. A comprehensive experimental program included 23 mixes using different types of fine aggregate in concrete: standard sand, demolition sand, and mixes with 10–30% ground glass fines replacing Portland cement (PC). Also, the effects of added sodium sulfate and gypsum (1%, 3%, and 5%) on compressive, tensile, and flexural strengths were analyzed by conducting mechanical tests at 7, 28, and 56 days. Finally, SEM, EDS, and XRD were conducted to analyze the microstructures of the concrete mixes. Using gypsum and sodium sulfate provides sulfate ions to study their effects on Delayed Ettringite Formation and mechanical performance. The results of the present work showed that the optimal mix (20% glass powder with 1–3% gypsum) achieved a 21% increase in 28-day compressive strength and a denser microstructure with reduced microcracking. Gypsum showed more stable behavior under the tested conditions compared with sodium sulfate. The microstructure studies supported this conclusion and further demonstrate that optimal amounts of glass result in a denser concrete matrix with less cracking, which is used much more effectively.