Micro-structure and Macro-performance: Surface Layer Evolution of Concrete under Long-term Exposure in Harsh Plateau Climate

We conducted a series tests on surface layers of plateau concrete at the ages of 180 and 540 days, including the most superficial cement paste, the 5 mm thick surface mortar, and the 50 mm thick surface concrete. Thermogravimetry and nitrogen absorption porosimetry on cement past, mercury intrusion porosimetry on mortar, and microhardness test on interface transition zone between mortar and coarse aggregate were conducted to evaluate the hydration degree and characterize the micro-structure. Whilst, tests for the rebound strength, abrasion resistance, and chloride ion impenetrability of concrete were conducted to assess the macroperformance. The experimental results show that, affected by the harsh plateau climate, outward surfaces have lower hydration degrees and worse pore structure than inward surfaces. As the hydration of concrete surface is ongoing after the age of 180 days, both the micro-structure and the macro-performance are continuously improved. In the long-term, either the orientation or the depth towards surface does not significantly affect concrete performance. Surface carbonation brings positive effects on mechanical properties but negative effects on the durability. Additionally, standard test result of chloride ion impenetrability is found significantly affected by the atmospheric pressure. For a same batch of concrete, charge passed in plateau regions is obviously lower than that in common regions.