荷载和环境共同作用下混凝土中氯离子传输的试验研究

Experimental study on chloride transport in concrete under environmental and loading coupling conditions

荷载和环境作用影响着混凝土中的氯盐传输过程和混凝土结构的服役寿命。采用弹簧加载系统对8根钢筋混凝土梁施加极限抗弯承载力28%、22%、16%和10%的持续弯曲荷载,并测定混凝土梁跨中部位的局部应变;氯盐侵蚀试验在多功能人工模拟环境试验箱中进行,4根混凝土梁置于5%的Na Cl溶液并在环境温度为50℃下进行浸泡试验,其余4根钢筋混凝土梁在全自动干湿循环试验箱中进行干湿循环试验,干燥过程中环境相对湿度为60%。氯盐侵蚀60 d后对混凝土梁受拉区和受压区取粉分析氯离子浓度。结果表明:与未承受荷载混凝土试件的氯离子传输速率相比,拉应变达到526με时氯离子扩散系数达到未承受荷载时的2.4倍,压应变达到90με时氯离子扩散系数无明显改变,而当压应变达到175με时氯离子扩散系数降低为无荷载作用时的0.4倍,拉应力加速了氯离子的传输速率,而压应力在一定范围内能够抑制氯离子的传输;且干湿循环条件下混凝土的氯离子传输速率明显高于浸泡条件的混凝土。"拉应力+干湿循环"条件对氯离子的传输影响最大;混凝土局部应变与氯离子扩散系数的相关性较好,能够反映荷载作用对氯盐传输的影响。在一定应变范围内,氯离子扩散系数随拉应变的增大而提高,随压应变增大而降低。

Chloride transport process and service life of concrete structures are affected by surrounding envi-ronment and loading conditions. Sustained bending load of 28%, 22%, 16% and 10% of ultimate bendingload was applied on 8 reinforced concrete beams by a spring loading system, respectively. Meanwhile, thelocal strains on the mid-span height of RC beams were measured. Immersion tests were conducted on 4beams while drying-wetting tests were on the other 4 beams in an artificial climate chamber under the con-dition of chloride solution of 5%, environment temperature of 50℃ and RH of 60%. An automatic dry-ing-wetting device was used to simulate the ocean tide. After 60 days,to determine the chloride ions con-centration, the concrete specimens were drilled at tension zone and compression zone in the mid-span ofthe RC beam. Compared with the chloride transport process in unstressed concrete, chloride transport pro-cess was accelerated by tensile stress and suppressed by compression stress. The chloride diffusivity in con-crete with tension strain of 526με is about 2.4 times faster than that in unstressed concrete,and the chloride diffusivity of concrete with compression strain of 90με is the same as the unstressed concrete,but the chloride diffusivity of concrete with the compression strain of 175με is 0.4 times slower than the unstressed concrete. And the chloride transport in RC beams under drying-wetting condition is faster than the ones un-der immersion condition. Among the different loading and environmental condition couplings, tension stressand drying-wetting coupling is the most serious condition for chloride transport. It can be found that the lo-cal strain of concrete is in good correlation with chloride ion diffusion coefficient,which can reflect the ef-fect of loading on chloride transport. Within a range of strain in concrete,chloride diffusion coefficient in-creases with the increasing ensile strain,and decreases with the increasing compressive strain.