Enhancing the Mechanical Properties of Crumb Rubber Concrete through Polypropylene Mixing via a Pre-Mixing Technique

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The utilization of waste tires as aggregates in sustainable concrete production has undergone extensive research over the past several years. However, incorporating crumb tires has been discovered to lead to a reduction in the compressive strength of concrete. This paper introduces a novel technique aimed at enhancing bonding conditions and mechanical properties of rubberized concrete (RuC). The approach involves blending a thermoplastic material (such as polypropylene), tire crumb, and cement as a mineral additive, followed by heat treatment of the mixture. This new method for creating a mixture of plastic rubber particles before adding rubber to concrete is called the pre-mixing technique. By adjusting the plastic component, additive composition, or their mixing ratios, the recuperation of strength in RuC can be enhanced. Compression and stress-strain tests demonstrated that the incorporation of these new synthetic compounds improved compressive strength. Furthermore, properties such as toughness index, ultimate strain, and flexural strength were also elevated. Scanning electron microscope (SEM) results depicted an improved bonding condition in the interfacial transition zone (ITZ) between cement paste and the amalgamated rubber-plastic particles, as opposed to non-modified rubber particles. A strength recovery factor was introduced in which a better evaluation of using rubber and modified rubber on the related strength could be done. The study also proposes a mechanical model for the evaluated rubber concretes, exhibiting minimal error. The investigation revealed that replacing 25% of fine aggregate with pre-mixed rubber particles resulted in a significant 60.4% increase in compressive strength. The highest compressive strength recovery, at 52%, was observed when 10% of fine aggregate was replaced with pre-mixed rubber. Furthermore, the toughness index exhibited a notable improvement of 68% and 33% for 15% and 25% replacement of fine aggregate with pre-mixed rubber, respectively.