Sustainable Waste Tyre Rubber Fibre-Reinforced Mortar: CO2 Curing Versus Water Curing for 28-Day Test

CO ₂ accelerated curing improves concrete strength by fostering carbonation and reducing the carbon footprint through CO ₂ sequestration, supporting sustainability. In contrast, end-of-life vehicle tyres harm the environment by leaching toxins, releasing pollutants, and contributing to landfill overcrowding. The properties of mortars with combined tyre fibre and CO ₂ curing, as well as the data-based modelling in mortar production, are not well understood. To address this gap, this study explored using 0.5 and 1% shredded waste tyre rubber fibre (WTRF) as a fibre in mortar prisms (40 × 40 × 160 mm) and beams (100 × 100 × 500 mm), and tested for flexural strength and load-deflection responses after 28 days of water and CO ₂ accelerated curing (20% CO ₂ at 20 °C and 60% relative humidity). In addition, the mathematical data-based models were developed for all the beams and compared with the experimentally measured load deflection of the beams. Results showed that CO ₂ curing significantly increased flexural strength for the prisms (42% for 0.5% and 21% for 1% WTRF) and enhanced load capacity for the beams (9% for 0.5% and 2% for 1% WTRF) compared to water curing. Data-driven models mirrored accurately the experimental results (coefficient of determination, R ² ≈ 0.999 in most cases), including a very non-linear region after the formation of the major crack. These outcomes indicate that CO ₂ curing is a promising approach for creating stronger, sustainable concrete, where CO ₂ is permanently converted to CaCO ₃, and tyres can be used as fibre, both combining to promote sustainability.