Investigation the Moisture Susceptibility of Warm-Mix Asphalt Modified with Nano-TiO2 and Waste Rubber Granules

Moisture damage is one of the disadvantages of warm mix asphalt. Recently, researchers use appropriate additives such as waste materials to address this issue. This study aims to overcome the moisture sensitivity of warm-mix asphalt (WMA) using additives such as nanomaterials as well as waste rubber granules. Bitumen (60/70) with a total weight of 1, 3, and 5% of Nano-TiO2 as well as 0, 10, and 20% of rubber granules by total weight of granite aggregate. The mixing and compaction temperature of bitumens were determined using a rotational viscosity test (RV). The optimal bitumen percentage was determined using the Marshall method. The results showed that the Nano-TiO2 has a small effect on this value, but the use of rubber granules has changed this percentage. To assess the moisture susceptibility of mixtures, indirect tensile strength test and resilient modulus test were used, and two criteria of indirect tensile strength ratio (TSR) and resilient modulus ratio (RMR) were calculated to compare the performance of the mixtures through the different freeze-thaw cycles. The results of experiments show that the addition of Nano-TiO2 to bitumen alone improves moisture resistance, but the use of rubber granules reduces this resistance. According to the results of this study, to improve the efficiency of the mixture containing rubber granules from the perspective of the TSR index, Nano-TiO2 should be used. For this purpose, the minimum required percentage of Nano-TiO2, to replace 10% of rubber granules, is 3%. From the RMR index point of view, all mixtures modified with Nano-TiO2, as well as the design containing 10% rubber granules, will pass the limit of Iranian regulation and will be acceptable in terms of moisture susceptibility.