Influence of the coarse aggregates size on the frost resistance in normal and polycarboxylate mixed concrete

Abstract

The durability and safety of concrete structures depend heavily on their frost resistance. Previous studies indicated that the addition of coarse aggregates (CAs) and water reducing admixtures (WRA) can significantly improve the mechanical properties of concrete. However, the role of CAs size proportion on the frost resistance of normal (NC) and WRA mixed concrete (WRC) has not been well understood. In this study, the small (5∼10 mm) and large (10∼20 mm) grading CAs were mixed as the low (small: large = 90 : 10), medium (small: large = 40 : 60) and high (small: large = 10 : 90) mix proportion in NC and WRC. The mass test, ultrasonic measurement, compressive and splitting tests, mercury intrusion porosimetry (MIP) analysis were applied to investigate the variations of mass weight, elastic modulus, compressive and splitting strength, and porosity characteristics of NC and WRC under freezing and thawing (F-T) cycles. Additionally, a damage model was established to analyze the correlation between the macroscopic and microscopic damage of NC and WRC. The results showed that: i) The concrete with medium CAs mix proportion owned the best workability and mechanical properties before F-T cycles, and exhibited the least mechanical loss and porosity evolution after F-T cycles; ii) The incorporation of WRA improved the workability and mechanical properties of concrete, and mitigated the mechanical loss and porosity evolution after F-T cycles, but did not change the influence of CAs mix proportion; iii) The macroscopic changes in the mechanical properties of concrete were found to be related to the microscopic damage on porosity characteristics, which was minimum with the medium CAs mix proportion. Overall, our study emphasized the importance of CAs size proportion in enhancing the mechanical properties and frost resistance of NC and WRC. These findings can serve as valuable reference for field applications.