Optimisation of Sustainable Rubberized Concrete Modified with Metakaolin and Liquid Polymer: A Performance Review using Response Surface Methodology

The study looks at how to improve rubberized concrete with metakaolin and SBR latex using response surface methodology, aiming to support more sustainable building. The study tackles two problems: how to dispose old tires and how to cut cement’s carbon emissions. It swaps some sand for crumb rubber (0–10%) and replaces part of the cement with metakaolin (0–20%). The recycled coarse aggregate turned out to have a specific gravity of 2.71, a bulk density of 1875 kg/m³, and water absorption of 1.51%. Natural river sand showed a specific gravity of 2.64, a bulk density of 1825 kg/m³, and a high water absorption rate of 2.3%. In comparison, the crumb rubber had a small specific gravity of 1.14, a low bulk density of 445 kg/m³, and very little water absorption, just 0.2%. Chemical tests showed the metakaolin reacts strongly, with high amounts of silica, alumina, and iron. With a central composite design using 20 tests, we carefully studied how these materials interact with liquid polymer (0–10%) and then checked both fresh and hardened properties. The tests showed that crumb rubber and metakaolin usually make the mix stiffer, but adding the liquid polymer made it much easier to work with, raising the slump to 10 mm. At 28 days, the concrete reached compressive strengths from 21.5 to 34 N/mm². Using ANOVA, the study found a very strong result (p < 0.0001) and the best mix was 15% metakaolin, 8% crumb rubber, and 8% liquid polymer, giving a predicted compressive strength of 32.45 N/mm². EDX and XRF tests showed a big change: the calcium-rich control shifted to a silica-heavy matrix, proving the pozzolanic reaction worked better and formed tighter transition zones between layers. The experiments confirmed the model was very accurate, with errors under 5%. In short, using metakaolin together with a liquid polymer helps create strong, eco-friendly rubberized concrete that works well for structural uses.