Plateau Climate Environment Factors Influence On Concrete Durability And Its Mechanism

The typical climates of the Qinghai-Tibet Plateau area are characterized by large temperature difference,drying and low air pressure compared with the plain areas.The concrete exposed to the harsh environment of the plateau for a long time will bring great challenges to its service performance and adverse effects to the later durability of the structure.Therefore,it has great practical significance to study the changes of the internal structure and durability of concrete in the plateau climate environment and establish the relationship between its internal structure and macro-durability,and improve the durability in the plateau area in order to optimize the internal structure of concrete.In this paper,the preparation and curing procedure of concrete in the plateau and plain area were completed simultaneously,the internal structure of the concrete in the plateau climate environment is revealed from multiple angles,and the link between meso structure,microstructure and macro durability of the concrete are established by comparison.By cutting the block and surface treatment of the hardened concrete test block,the mesopore structure change of the concrete is measured by the porosity analyzer of the hardened concrete,and the microscopic morphology of the transition area of the concrete interface is observed by scanning electron microscope(SEM)and atomic force microscope(AFM).The mechanical properties of the transition zone of the concrete interface were tested using a microhardness tester.The results show that the mesopore structure level is blocked by the hydration process of the cement and the bubble stability is reduced,resulting in changes in the characteristics of the hardened concrete pores under the plateau climate environment.The air content increases,the pore spacing factor decreases,the average pore size becomes larger.The content of pores in the range of 200～2000μm increased significantly;From the level of ITZ microstructure,it can be found that a large number of cracks appeared in the transition zone of the interface of hardened concrete,the microhardness decreased,and the roughness Rq increased,resulting in the decline of the overall macroscopic properties of the concrete.The air-entraining effect of the airentraining agent in the plateau environment is weakened,and the number of bubbles that can be used to buffer the frost heaving pressure generated in the early low-temperature environment is greatly reduced,so that the structure of the concrete was destroyed early.Through scanning electron microscopy and atomic force microscopy,it can be found that a large number of obvious cracks and ravines appear in the transition area of the concrete interface in the plateau environment,and a large number of connected pores are formed in the interface transition area,resulting in a decrease in its durability.The mesopore structure and the deterioration of the microstructure of the interface transition area lead to the reduction of the macro-durability of concrete.