Mechanical Property Prediction in Silica Fume and Crumb Rubber–Modified Concrete: Soft Computing and Experimental Approach

To address the environmental impact of greenhouse gases in cement production, incorporating cement substitute materials is crucial. However, the slow degradation of discarded tires poses environmental challenges, making burial or incineration unsustainable. This study explores the integration of discarded tires as crumb rubber in concrete and the use of silica fume as a cement substitute. Experimental methods, coupled with neurofuzzy systems, were employed to predict the mechanical properties of the resulting modified concretes. In the experimental approach, silica fume replaced cement at weight percentages of 0%, 10%, 12%, and 15%, while crumb rubber substituted sand at volume percentages of 0%, 10%, and 25%. Compressive and flexural strengths were evaluated at seven, 28, and 90 days, with tensile strength assessed at 28 days. The neurofuzzy system utilized six inputs—cement, gravel, sand, silica fume, water–cement ratio, and sample age—to forecast tensile and compressive strength in silica fume-containing concrete. Similarly, six inputs—cement, gravel, sand, crumb rubber, water–cement ratio, and sample age—were used to predict flexural and compressive strength in rubber-containing concrete. The findings reveal that the inclusion of silica fume enhances the mechanical properties of concrete, while the introduction of crumb rubber diminishes these properties. Specifically, a quantitative analysis demonstrates the positive impact of silica fume on the strength and contrasting effect of crumb rubber. The neurofuzzy system exhibits remarkable accuracy in predicting tensile and compressive strength for silica fume-containing concrete and flexural and compressive strength for rubber-containing concrete.