The Modification Effect Of Hydrophobic And Air-entraining For Concrete

For the cold area traffic engineering, in the deicing salt environment, the addition of air-entraining agent can improve the frost resistance of concrete in traffic engineering, but it does not improve the permeability of the concrete, the destruction of concrete structures in traffic engineering is often due to chloride of environment penetration into the pore of concrete by capillary action, lead to rebar corrosion causes the destruction of concrete structure occurred. This paper studied on the double modification effect of concrete mixed hydrophobic and air-entraining admixture in traffic engineering in cold area. Combined with ASTM C1202 test measures and SEM microscopic methods, found that mixing hydrophobic and air-entraining admixture, the addition of hydrophobic admixture can significantly improved the ability of the concrete anti-chloride, which is caused decreased by excessive air content, at the same time within the mixed hydrophobic admixture can significantly improve the surface characteristics of concrete micro-pores, reduce the capillary action of concrete micro-pores. Show that the mixed hydrophobic and air-entraining admixtures have significantly improved effect of concrete in the cold area engineering.Usually resistant to salt water corrosion of concrete prepared with fly ash and slag grinding fine admixture, however, such mixed concrete frost resistance is bad, resistant to seawater freeze-thaw performance is worse, usually with higher air-entraining, can overcome the defects. In the project, even if the liquidity of concrete is very good, the difference in bubble size and its distribution is very complicated. In order to prepare the concrete with high resistant to seawater freezing-thawing and corrosion, this paper studied on the relationship of the high air content of concrete with high resistance to sea water freezing-thawing and chloride ion diffusion coefficient. It was found that concrete air content, bubble fractal dimension and electric flux has good correlation, concrete anti-chloride ion diffusion ability can introduce bubbles cluster fractal dimension and bubbles distribution fractal dimension to characterization. With the increase of fractal dimension, the concrete resistance to chloride ion diffusion capacity enhanced. the complexity of the bubble was reflected from the bubble distribution fractal dimension, which objectively describes the gradation of bubbles, bubbles gradation improved greatly improve the concrete anti-chloride ion diffusion capacity.For further research on durability of concrete material under salt frozen conditions in cold area, the non air-entraining concrete with water-binder ratio of 0.4 and 0.28, air-entraining concrete with water-binder ratio 0.28 and the air content 7.0% are studied respectively. The fractal dimension of three kinds of concrete pore at different pore diameter range were determined by MIP(mereury intrusion porosimetry) before and after salt freezing and were studied in a comparative way. The research shows that the fractal dimension of pore diameter at range of 50nm ~ 550nm after salt freezing changed remarkably, namely salt frozen process has greater influence on pore within this range. Objectively the pore within this range in concrete suffered supercooled water osmotic pressure is the greatest. In addition, the total porosity reduced after salt freezing injury while fractal dimension changed more obviously. The fractal dimension of concrete pore could be a good reflection of concrete structure after salt freezing injury, showing that the diameter at 50nm ~ 550nm after salt frozen injury coarsening is obvious. Thus the fractal dimension of diameter within this range can be used as a key parameters after salt freezing injury.