Optimization of Cementitious Concrete Mix Design Containing Various Percentages of Recycled Tire Rubber Granules and Reclaimed Asphalt Pavement (RAP)

Concrete is one of the most widely used construction materials, with large quantities consumed globally each year. Incorporating recycled and industrial waste materials into concrete mixtures is an economical and sustainable approach to producing green concrete, helping to reduce environmental issues related to waste disposal and storage. Recycled tire rubber granules and reclaimed asphalt pavement (RAP) are among the waste materials produced in large volumes. Replacing natural aggregates with these materials can contribute to the development of cost-effective and sustainable concrete. However, ensuring the strength and mechanical properties of such concrete is essential for maintaining its performance. A key indicator of the durability and service life of concrete structures is their resistance to cracking, which is measured by fracture toughness. This study investigates the crack growth behavior of concrete mixtures containing different percentages of tire rubber granules and RAP. To achieve this, the Taguchi experimental design method was employed, with rubber granule content ranging from 0% to 9% by volume and RAP content varying from 0% to 40%. In total, 16 different concrete mixtures were evaluated. Fracture toughness tests were conducted using pre-notched flexural disk specimens. The results demonstrated that the type and percentage of additives significantly influence the crack resistance of concrete. For statistical analysis, analysis of variance (ANOVA) was first applied to assess the effects of factors, followed by a Pareto chart to illustrate their impact. According to these analyses, both additives had a significant effect on concrete fracture behavior, with RAP having a greater influence than tire rubber granules. Additionally, the optimal mix design, consisting of 30% RAP, 70% limestone aggregate, and no tire rubber granules, exhibited the highest fracture toughness.