Investigating the effect of cationic emulsified bitumen as an admixture of roller-compacted concrete pavement on the progress of alkali-silica reaction

Alkali silica reaction (ASR) is one of the mechanisms that can reduce the durability of concrete. ASR causes concrete to swell, thereby creating internal stresses, which result in micro-cracking. This study investigated the impact of using rapid setting cationic bitumen emulsion (CRS) as an additive in roller-compacted concrete (RCC) on the progress of Alkali silica reaction (ASR). For this purpose, RCC specimens with different bitumen contents by weight of cement were prepared and subjected to ASR simulation conditions for one year. Length change, ultrasonic pulse velocity, and compressive strength tests were performed at the different ages (3, 7, 28, 90, 180, and 360 days). In addition, water absorption (WA) test, and Semi-circular bending (SCB) test at notch depths 19, 25 and 32 mm in loading mode I were performed, and thereby, the ASR-induced damage in terms of change in critical strain energy release rate (Delta JC) and water absorption (Delta WA) were also assessed. The results showed that as the bitumen content increased, the intensity of ASR progression decreased. In the control specimen (EAC0), a 0.1% increase in length, a 50% decrease in fracture toughness, and a 25% increase in water absorption due to ASR progress were observed, while for the specimen with 8% bitumen (EAC8), the results of 0.05% increase in length and 11% decrease in fracture toughness and 8% increase in water absorption were revealed. Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometry (EDS) were performed to examine the microstructure of the specimens, as well. These examinations exhibited the fast progress of ASR and the extensive production of alkali-silica gel in the specimens without bitumen. However, in the mixture EAC8, aggregates near the bitumen-containing area revealed no trace of gel production, indicating that bitumen protects aggregates against ASR. One- and two-way analyzes of variance (ANOVA) performed at a 95% confidence level also confirmed the effectiveness of bitumen in preventing or reducing the intensity of ASR-induced damage in rollercompacted concrete.