Fatigue resistance of hydraulically bound mixtures with synthetic fibers and crumb rubber for semi-rigid pavements

Semi-rigid pavements with hydraulically bound mixture (HBM) base courses exhibit high bearing capacity and durability. However, their main drawback lies in reflective cracking, which limits their service life. This article presents the results of fatigue tests that were designed to evaluate the influence of synthetic fibers and crumb rubber on their mechanical properties and durability. The study included a reference mixture of C8/10 and mixtures modified with synthetic microfibers, synthetic macrofibers, fine crumb rubber (0/0.8mm), and coarse crumb rubber (0.5/1.5mm). Compressive strength, frost resistance, and flexural strength were evaluated. In addition, non-standardized tests procedures, such as fatigue resistance, elastic modulus, and residual strength, were applied. The results showed that the addition of synthetic macrofibers significantly increased fatigue resistance by 20% and tripled total fracture energy compared to the unmodified mixture. Fine crumb rubber also contributed to improved fatigue resistance, although with a simultaneous reduction in resistance to water and frost damage. Synthetic microfibers improved the total fracture energy by 78%. The addition of coarse crumb rubber resulted in a significant reduction in compressive strength, flexural strength, frost resistance, and elastic modulus. Statistical analysis did not reveal significant correlations between fatigue resistance and other mechanical parameters, indicating the need to assess this property separately when designing HBM. The study confirmed that the use of appropriate additives, particularly synthetic macrofibers, can effectively reduce cracking and enhance the fatigue durability of HBM used as base course in semi-rigid pavements.