<p>The significance of this research is to determination the effect of rubber waste (RW) on the characteristics of high strength concrete (HSC). In addition, decreasing of HSC spalls, the elimination of the cement content needed in concrete, the quantities of harmful gases like CO and CO₂ released from specimens containing RW exposed to high temperatures were also investigated. In this study, RW granules were used to replace 0.5% of the fine aggregate weight, while fly ash (FA) replaced 25%, 30%, and 35% of the cement weight. To compensate for the expected strength reduction after utilizing FA and RW, 10% of the cement weight was replaced with silica fume (SF). Part of the specimens was exposed to temperatures of 400&#xa0;°C and 800&#xa0;°C to evaluate the influence of high temperatures on compressive strength, flexural strength, porosity, heated specimens spalling, and CO and CO₂ gases emissions. The results showed that combined SF and FA improved compressive and flexural strength but reduced it when specimens were exposed to 800°C. Spalls appeared in SF-containing specimens subjected to 800&#xa0;°C but not in RW-containing specimens combined with SF and FA. The porosity of control specimens increased as temperature increased, whereas the presence of SF and FA in HSC specimens refined the pores by 42%. According to the results from this study the incorporating fly ash improves the porous structure of concrete, increases concrete’s resistance to high temperature, and reduces the negative effect of fine rubber aggregate produced from tire waste and reduced the risk of spalling. However, it produced CO gas at levels higher than what humans can breathe in a confined environment.</p>