The Relationship between Roller Compacted Concrete Durability and Air Void Parameters using X-Ray Computed Tomography

This study aims to investigate the relationship between the durability parameters of roller-compacted concrete pavement (RCCP) exposed to freeze-thaw conditions and the characteristics of the air void obtained by X-ray computed tomography (CT). For this purpose, eight RCCP designs with four water to cement ratios of 0.35, 0.4, 0.45, and 0.5 were prepared using two compaction methods including a vibrating table and vibrating hammer. Properties such as air void content, mass changes, ultrasonic pulse velocity, and relative dynamic modulus were investigated. In addition, CT scan and image processing techniques were used to estimate the air void content in designed RCCPs. To identify the air void, the volumetric-based global thresholding algorithm method was used. The results showed that with the increase of the water to cement ratio, the percentage of air void increases until the optimal value is reached and then decreases. The difference between the results of durability indicators in the two compaction methods increased with the decrease of the water to cement ratio. RCCPs made with a water to cement ratio of 0.35 in the vibrating hammer method and water to cement ratios of 0.35 and 0.4 in the vibrating table method suffered the most damage after freeze-thaw cycles. The increase in capillary pores has a negative effect on the structure of roller-compacted concrete and the presence of fine pores has a positive effect on freeze-thaw durability. In both compaction methods, the optimal amount of water to cement ratio was 0.45 showing appropriate durability indicators.