冻融循环条件下混凝土中的水分迁移(英文)

MOISTURE MIGRATION IN CONCRETE EXPOSED TO FREEZE-THAW CYCLES

分析了混凝土冻融循环劣化新的原因和机理。冻融循环过程中,混凝土孔隙中的水有些冻结而另一些没有冻结。由于渗透压以及冰和水之间化学能差的作用,每次冻融循环未冻结孔中的水分向冻结孔隙迁移。这种迁移是从小孔向大孔的单向流动,原因在于大孔具有较高的冰点,在冻融循环降温阶段先于小孔中的水冻结,而在升温阶段迟于小孔融解。接近表面的孔隙在融解阶段可从外部吸水,原因在于冰融解后体积减小,在孔隙中形成负压。经过一定次数的冻融循环以后,部分孔隙尤其是靠近表面的大孔高度饱和,在后续的冻融循环中孔隙中的压力很大。孔隙中的压力所导致的周围孔壁中的拉应力可能引起基体开裂。接近表面的孔由于很容易从外部吸水饱和,表面层开裂严重,从而导致表面剥落。内部大孔也可能饱和而引起内部开裂,导致相对动弹性模量下降。

A new interpretation of freeze-thaw deterioration of concrete is proposed.In the progress of freeze-thaw cycling,the water in some pores in concrete may be frozen,while others are unfrozen.Moisture flow from the unfrozen pores to the frozen pores occurs in each cycle driven by osmotic pressure and the difference in chemical energy between the ice and water.The moisture flow is a one-way process from smaller pores to larger pores because the water in larger pores has higher freezing point and freeze earlier than that in smaller pores.The pores near surface may suck up water from outside in the heating stage of freeze-thaw cycles owing to the vacuum caused by the decrease in volume of water when melted.After a number of freeze-thaw cycles,some larger pores become highly saturated,especially for larger pores near surface,and the pressure induced in the pores is very high in the later freeze-thaw cycles.The resultant tensile stress in the matrix around the larger pores may induce the cracking of the pore wall.Due to easily taking up water from outside,the pores in the surface layer of concrete specimens are much easier to be saturated than that in the interior,which leads to the severe cracking in surface layers and hence the surface scaling.The larger pores in the interior of specimens may be saturated and lead to cracking,which result in the decrease of relative dynamic elasticity modulus.