Investigations of portland limestone cement and waste glass powder for sustainable ultra-high performance concrete

This study investigated sustainable binder alternatives for ultra-high performance concrete (UHPC), addressing environmental concerns associated with the high cement content commonly used in UHPC mixtures. Specifically, the research focused on the potential of portland limestone cement (PLC) and waste glass powder, as affordable and available alternative materials. Six UHPC mixtures were examined, including three mixtures with ordinary portland cement (OPC) and three with PLC. Binder compositions were varied, with one set using 15% silica fume, the second set using a 7.5%‐7.5% combination of silica fume and waste glass powder, and a third set using 15% waste glass powder in each cement group. A comprehensive testing program was devised to assess key properties, such as flow, heat of hydration, compressive strength, shrinkage, surface resistivity, and water absorption, leading to original insights into workability, hydration kinetics, mechanical performance, and durability. A set of microstructural analyses using scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) resulted in additional details, explaining the contributions of PLC and waste glass powder to UHPC properties. SEM images revealed uniform binder distributions without clustering, while XRD confirmed stable hydration phases, with the waste glass powder providing a source of amorphous silica that effectively reacted with calcium hydroxide to form additional calcium silicate hydrate gels. TGA results showed the thermal stability of the mixtures, demonstrating that PLC and waste glass powder can be proper replacements for OPC and silica fume, meeting performance benchmarks while enhancing sustainability.