Response Surfaces for Fresh and Hardened Properties of Concrete with E-Waste (HIPS)

The fresh and hardened properties of concrete with E-waste plastic, that is, high impact polystyrene (HIPS), as a partial replacement for coarse aggregate were analyzed using response surface methodology (RSM). Face-centred central composite response surface design was used in this study. The statistical models were developed between the factors (HIPS and water cement ratio) and their response variables (slump, fresh density, dry density, compressive strength, spilt tensile strength, and flexural strength). The Design-Expert 9.0.3 software package was used to analyze the experimental values. The relationships were established and final mathematical models in terms of coded factors from predicted responses were developed. The effects of factors on properties for all variables were seen visually from the response surface and contour plot. Validation of experiments has shown that the experimental value closely agreed with the predicted value, which validates the calculated response surface models with desirability？=？1. The HIPS replacement influenced all the properties of concrete than water cement ratio. Even though all properties show the decline trend, the experimented values and predicted values give a hope that the E-waste plastic (HIPS) can be used as coarse aggregate up to certain percentage of replacement in concrete which successively reduces the hazardous solid waste problem and conserves the natural resources from exhaustion. 1. Introduction Generation of solid waste and its safe disposal have become a challenging task for developing and developed countries. Among the solid waste, electronic waste (E-waste) shows an alarming growth. For the past few decades, the developed and developing countries totally ignored this waste. The major reasons are complexity of waste, lack of recycling infrastructure, recycling in informal sector, lack of awareness among people, and so forth. Now, the E-waste generation receives the attention of the developed countries but their way of recycling the E-waste is different; that is, they have started exporting this harm to developing countries as shown in Figure 1 [1, 2]. E-waste comprises many toxic substances like mercury, lead, cadmium, brominated flame-retardants, beryllium, polyvinyl chloride, printed circuit boards, plastic casings, cathode ray tubes, batteries, and cable sheathing, and so forth, which are harmful to human health and environment if not handled properly [3–5]. In developing countries, after recovering the precious metals and useful materials from the E-waste in informal manner, the waste is