Development of sustainable high performance self compacting concrete using construction & demolition waste and steel slag

A significant quantity of energy is utilized in the construction industry with the highest energy being used in producing Ordinary Portland Cement (OPC) and crushing aggregates. This high energy consumption is highly correlated to high CO2 emissions, and other greenhouse gases. To achieve desired outcomes, the following methods can be implemented. Firstly, Construction & Demolition Waste (C&D waste) and steel slag can be incorporated. In the present study, six different concrete mixes were designed by replacing 30% of the cement with Fly Ash (FA) and Ground Granulated Blast Furnace Slag (GGBS). Additionally fine aggregate was replaced with Manufactured Sand (M-sand), C&D waste, and steel slag in varying proportions of 0, 33, 50, and 100%. Effectively enhancing concrete density and durability, steel slag replacement level does not lead to excessive weight, while losing no structural integrity. This research examines the workability and mechanical properties of high-strength, self-compacting concrete containing sustainable materials, including sustainable materials such as steel slag and C&D waste. Workability is assessed using slump flow, V-funnel, and L-box tests, while mechanical properties are evaluated through compressive strength, split tensile strength, and flexural strength tests. Durability is analysed by using half-cell potential, ultrasonic pulse velocity, acid attack resistance, and Rapid Chloride Permeability tests, with results compared to those of conventional concrete. Incorporating C&D waste and steel slag in concrete promotes sustainability by reducing waste, conserving resources, and improving concrete strength and durability. It was also noted that the test result of all the mixes met the flow, passing, and filling ability as stipulated by the European Federation Dedicated to Specialist Construction Chemicals and Concrete (EFNARC) guidelines. The findings suggested that SCC strength was reduced up to 26% by increasing C&D waste and steel slag, with greatest loss at full replacement by slag sand and partial replacements up to 33% giving favourable results. Based on microstructural analysis, poor interface bonds, increased porosity, and uneven Ca/Si ratio in the microstructure were identified as key factors that lead to the strength reduction. By using C&D waste and steel slag, SCC becomes more sustainable, less emissions, and more resource conservation. It also points out how the strength, durability, and cost effectiveness of recycled materials can be optimized.