Utilization of red ceramic waste in the production of binary eco-friendly alkali-activated binder: Fresh and hardened state investigation

The utilization of waste and by-products as precursors in alkali-activated materials has great importance in the reduction of environmental pollution on slopes, landfills, and highways. Properties studies of alkali-activated mixtures using red ceramic waste (RCW) and blast furnace slag (BFS) have been scarcely investigated in the literature. This paper aims to evaluate the properties and behavior of alkali-activated pastes based on RCW and BFS. The influence of the following parameters was evaluated: silica modulus (Ms) between 1.0 and 1.3 and RCW content (25, 50, and 75 %). The compressive strength, workability, and reaction kinetics were analyzed. In addition, embodied environmental impacts and FTIR microstructural analyses were performed. Flow diameters in the range of 147.3 mm to 163 mm (Ms = 1.3) and 142.4 mm to 154.1 mm (Ms = 1.0) were observed and the RCW incorporation slightly reduced mixtures workability. An optimum RCW content in the range of 25 %-50 % was identified, which provided excellent mechanical and microstructural properties reaching values up to 68.68 MPa for the best mixture and values above 50 MPa for systems with 50 % RCW. Higher RCW contents also led to reaction delays according to the isothermal calorimetry test. The increase in Ms generated higher band intensities of the Si-O-T chemical bonds. The mixtures evaluated had significantly lower CO2 emissions and equivalent energy consumption than OPC-based binders, with reductions of up to 65.6 % (CO2 emission) and 75.2 % (energy consumption), indicating the environmental benefit provided by this type of mixture.