Study of recycled concrete for paving blocks to reduce the carbon footprint of concrete

Abstract

This research studied the use of recycled concrete as a component of paving block products by forming paving blocks mixed with concrete waste at 20, 40 and 60 percent by weight and testing the physical and mechanical properties of the materials. The experimental results showed that the compressive strength, density and water absorption values were inversely proportional to the ratio of concrete waste, i.e., the compressive strength, density and water absorption values were highest when concrete waste was mixed at 20 percent and gradually decreased as the amount of concrete waste was increased. This was consistent with the results of the analysis using a Scanning Electron Microscope (SEM) that created images from electrons reflected from the surface of the sample, which showed cracks on the surface of the specimen. Therefore, the mechanical properties were deteriorated. In addition, when analyzing the influence of the type of concrete waste, the composite materials of the concrete had the poorest mechanical and physical properties. The study of the recycling process of separating the concrete waste from the concrete mixing plant into rocks, sand and mortar waste found that the carbon footprint of greenhouse gases was 1.11 kg CO₂e/m², which was separated into values from the activities of raw material acquisition (recycling process), production process and the transportation process was equal to 0.0688 kg CO₂e/m², 0.9964 kg CO₂e/m² and 0.0356 kg CO₂e/m², respectively. The process with the highest carbon footprint of greenhouse gases was the recycling process, with a value of 65 percent, followed by the transportation process, with a value of 35 percent. When compared to the disposal by dumping in bulk (the original method), making paving blocks from recycled concrete can reduce greenhouse gas emissions by up to 95.62 percent. Mixing concrete waste for reuse instead of landfilling or other forms of disposal is a method that helps reduce environmental problems and creates the highest benefit.