Researches On Resistance To Chloride Ion Penetration And Microstructures Of Air-entraining HPC

Air-entrained concrete (AEC) has long been used in engineering practice because of advantages like low permeability, good freezing resistance and erosion resistance. Due to the addition of air-entraining agent (AEA), a large number of stable small air bubbles are produced in concrete with a uniform distribution and closed shape. Therefore, the structure of AEC is more complicated than conventional concrete. At present, research has indicated that air-entraining can depress the rate of chloride permeability in concrete by 15%-20%. Nowadays, high performance concrete (HPC) has been used widely in engineering practice, so it is important to study the effect of entrained air on the rate of chloride penetration in HPCIn this paper, the resistance of air-entrained HPC to chloride ion penetration and its microstructures such as pore structures and ITZ are studied with different amounts of air-entraining agent (AEA), different vibrating time and different w/b ratios in order to clarify the mechanism of it. The following conclusions are drawn:1. With the increasing amounts of AEA, the resistance of air-entrained HPC to chloride ion penetration is increased as well till the optimum amount, followed by a obvious decline of it The trend of changes agrees well with the pore structures of air-entrained HPC. The research results indicate that resistance chloride penetration is controlled by pores with diameters less than 0.1μm in the range of optimum amounts of AEA, and it would be strengthened with more of these pores. On the contrary, if the amounts of AEA are more than the optimum amount, it is controlled by pores larger than 0.1μm and it would be weakened with more of these pores.2. With different vibration time, the resistance of air-entrained HPC to chloride ion penetration shows an upper parabolic curve trend with increasing vibration time, and the vibration time has an optimum point. Meanwhile, resistance chloride penetration has a better corresponding relationship with the pore structures of air-entrained HPC. The research results indicate that resistance chloride penetration is controlled by pores with diameter more than 0.1μm within the optimum vibration time, and it would be strengthened with less of these pores. On the contrary, it is controlled by pores with diameters less than 0.1μm if the vibration time is longer than the optimum value, and it would be strengthened with less of these pores.3. With different w/b ratios, the resistance of air-entrained HPC to chloride ion penetration is weakened gradually with increasing w/b ratios, and it is weakened greatly when the amount of water is increased a lot. The research results indicate that both the pore structures and ITZ of air-ehtrained HPC are weakened greatly if the w/b ratios are high, so the deterioration of resistance chloride penetration could be regarded as the effects of both the deterioration of ITZ and connectivity of pores.