Abstract

The disposal of scrapped off-the-road (OTR) tires is a growing challenge for the mining industry. Currently, most scrapped OTR tires are abandoned in stockpiles or buried at mine sites, occupying substantial amounts of land, and posing ecological threats. As a result, it is important to recycle scrapped OTR tires in an eco-friendly way. Pyrolysis has been recognized as a green way to dispose of waste tires as it generates neither emissions nor remnant wastes, where recycled carbon black (RCB) is a major by-product recovered from scrapped OTR tires. Reutilizing these recycling by-products can not only reduce their environmental impacts but also bring potential benefits. To this end, this study appraised the capacity of RCB derived from scrapped OTR tires, denoted as RCB-OTR, as aggregates to develop thermal insulation mortars. Sand in Ordinary Portland cement (OPC)-based mortars was replaced by RCB-OTR in volumetric proportions of 0, 30, 60, and 100%. Experimental investigations were performed to characterize the properties of developed thermal insulation mortars, including thermal properties, density, ultrasonic pulse velocity tests, and unconfined compressive strength (UCS). Thermalgravimetric analysis and scanning electron microscope tests were used to demonstrate the hydration reaction and the microstructure of the samples. The results revealed that the developed thermal insulation mortars had oven-dry densities between 1058 ± 1 and 2045 ± 5 kg/m³ and a 28-day UCS between 8.6 ± 0.74 and 37.3 ± 0.76 MPa. Mortars at RCB-OTR replacement ratios below 30% can be employed as load-bearing units. Replacing all sand with RCB-OTR resulted in a considerable decrease in thermal conductivity from 1.800 ± 0.071 to 0.272 ± 0.021 W/mK, the volumetric heat capacity from 1.438 ± 0.063 to 1.044 ± 0.079 MJ/m³K, and thermal diffusivity from 1.255 ± 0.089 to 0.263 ± 0.034 mm²/s. Overall, mortars mixed with RCB-OTR exhibited good thermal insulation performance and satisfactory mechanical properties, demonstrating that RCB-OTR is a promising lightweight aggregate for thermal insulation building materials. This is the first study to incorporate RCB-OTR into cement-based materials and evaluate the thermal properties. Using the developed thermal insulation building materials could help reduce a building’s energy consumption, promoting energy efficiency. More importantly, this study is of great interest and significance to the mining industry because proper recycling and utilization of scrapped OTR tires will bring potential revenue, reduce the size of stockpiles, and mitigate the influence on the environment, moving the mining industry closer to its goal of net-zero operational emissions.