Temperature field distribution and microstructure of cement-based materials under cryogenic freeze-thaw cycles

Cryogenic temperature is one of the most severe conditions for the application of cement-based materials. In this paper, the effects of different factors on the temperature field distribution in cement paste and mortar under cryogenic freeze-thaw cycles were investigated. Based on the analysis of internal pore structure and micro-morphology, the main influencing factors were determined, and the failure mechanism of cement-based materials was analyzed. The results indicated that under the condition of unsteady multi-dimensional heat conduction, the temperature field in the cement-based materials presented gradient distribution and the temperature variation in the specimen lagged, the temperature in the center of the specimen lagged most because the heat transfer in the specimen had energy consumption. Several factors such as adding fine aggregate, reducing water-to-cement ratio and low water content could improve the freeze-thaw cycles resistance of cement-based materials to a certain extent. The cryogenic freeze-thaw damage was highly related to the freezing and migration of pore water due to the cryopump effect. The pore structure was destroyed and many micro-cracks below 20 nm were produced. Under the further crystallization pressure, the larger pores were formed by destroying, expanding and connecting, thus affecting the mechanical properties and durability of cement-based materials. (C) 2020 Elsevier Ltd. All rights reserved.