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

CO2 accelerated curing improves concrete strength by fostering carbonation and reducing the carbon footprint through CO2 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 CO2 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 CO2 accelerated curing (20% CO2 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 CO2 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, R2 ≈ 0.999 in most cases), including a very non-linear region after the formation of the major crack. These outcomes indicate that CO2 curing is a promising approach for creating stronger, sustainable concrete, where CO2 is permanently converted to CaCO3, and tyres can be used as fibre, both combining to promote sustainability.