This document presents an experimental study on the mechanical behavior of crumb rubber in high strength concrete. Several laboratory tests were conducted to evaluate the effect of partially replacing fine aggregates in concrete with discarded tire rubber (crumb rubber) ranging from 0-25% on the mechanical properties of high strength concrete. The properties tested included compressive strength, split tensile strength, and flexural strength at 7 and 28 days. The results showed that the strengths generally decreased with increasing rubber content, with up to a 68% reduction in compressive strength and 49% reduction in split tensile strength observed. However, concretes with 5% crumb rubber replacement showed only minor strength reductions of around 5-10% compared to normal concrete.