引气混凝土在冻融循环过程中的氯离子渗透与孔结构

C30和C50引气混凝土在3.5%NaCl溶液中自然浸泡或快速冻融循环,测试盐冻过程中混凝土表面和内部的超声声时,混凝土中的氯离子浓度分布及孔结构演变。研究结果表明:超声声时较好反映了混凝土在盐冻过程中的损伤演化,其表面和内部超声声时均先下降,后保持稳定,当混凝土剥落严重时迅速上升;冻融循环过程中的低温环境降低了混凝土表面氯离子浓度和氯离子扩散速度,但冻融损伤程度的增加将导致混凝土中氯离子扩散速度的提高;盐冻循环50,150和400次时,C50混凝土中孔径大于100 nm毛细孔数量由31.85%提高到42.70%和56.60%,孔径大于0.1 mm的微裂纹数量由12.80%降低为8.37%,并最终提高到25.29%。此外,混凝土经过150次冻融循环,相比于C30混凝土,C50混凝土中孔径大于100 nm的毛细孔数量降低20.10%,微裂纹数量降低43.44%。

Chloride penetration and pore structure of air entrained concrete subjected to freeze-thaw cycles

The deterioration,chloride ion distribution and pore structure of concrete under the influence of salt frost are systematically investigated.The compressive strength grade of air entrainment concrete is C30 and C50.The corrosion regimes are employed: freeze-thaw cycles in 3.5% NaCl solution,and naturally immersion(stored in 3.5% NaCl solution with the same time of freeze-thaw cycles).The experimental results show that the ultrasonic time passes through the interior and surface of concrete attacked by salt frost decrease firstly,then keep steady,and lastly decrease to failure due to mass loss and deterioration of concrete.The low temperature in salt frost environment reduces surface chloride concentration of concrete and retards chloride ion penetration into concrete.The increasing micro-crack in concrete due to salt frost damage accelerates chloride ion penetration into concrete.The capillary pore(≥100 nm) amount increases from 31.80% to 42.70%,then to 56.60%,when the salt frost rises from 50 cycles to 150 cycles and to 400 cycles.And the microcrack(hole diameter ≥0.1 mm) amount of concrete decreases from 12.80% to 8.37%,and then increases to 25.29% as salt frost cycles change from 50 times to 150,and to 400 times.In comparison with C30 concrete after 150 times of salt frost,the capillary pore of C50 concrete decreases by 20.10% and the correspondingly microcrack decreases by 43.44%.