Abstract
The moisture sensitivity of asphalt concrete is one of the most important failures that roads face during their service life. In recent years, many efforts have been made to reduce this failure in asphalt concrete. Anti-stripping additives are one of the most widely used methods to mitigate this failure, but the effect of these additives on the main mechanisms of moisture sensitivity has received less attention. This study examined the impact of using dodecyl amide, nano-calcium carbonate, and dry resin additives to decrease moisture sensitivity and its mechanisms in asphalt concrete. The materials used were granite, limestone, and PG 64 - 16 bitumen. Nano-calcium carbonate (0.5% and 1%), dry resin (2% and 4%), and dodecyl amide (0.5% and 1% by the weight of bitumen) were used as the bitumen modifiers. The modified Lottman in 1, 2, and 3 freeze-thaw cycles and Pull Off test in cohesion and adhesion failure states were used to assess the moisture sensitivity of asphalt concrete samples. All three additives increased the indirect tensile strength ratio in multiple freeze-thaw cycles and, thus, improved these samples' performance against moisture. The greatest indirect tensile strength improvements ranged from 37 to 80% for nano-calcium carbonate and 32-79% for dry resin, while dodecyl amide caused increases from 11 to 40%. The samples' tensile strength ratio increased by 20-60%, with the highest results for 1% NCC and 4% dry resin. Pull Off test results demonstrated that changing the aggregate did not affect the cohesion Pull Off, but changing the aggregate and bitumen affected the adhesion Pull Off resistance. The Pull Off test results indicated that nano-calcium carbonate provided better performance in cohesion states with increases of 1.2 to 3.2 kPa for limestone and 1.3 to 3.3 kPa for granite. Dry resin excelled in adhesion states with increases of 1.5 to 3.6 kPa for limestone and 1.8 to 3.8 kPa for granite. These results highlight the need for further attention to the mechanisms of cohesion in identifying moisture damage in asphalt mixtures.