氯盐冻融循环与侵蚀作用下活性粉末混凝土的耐久性研究
发布时间：2018-08-23 19:40
【摘要】：多因素耦合作用下混凝土结构耐久性失效问题越来越严重,活性粉末混凝土作为一种水泥基复合材料,具有超高的力学性能和优异的耐久性能,适用于恶劣环境下混凝土结构的主体或防护材料。本文针对氯盐冻融循环与侵蚀耦合作用下活性粉末混凝土的耐久性展开了研究,分别通过氯离子侵蚀单因素作用试验、氯盐冻融循环与侵蚀耦合作用(以下简称耦合作用)试验、毛细吸入试验、氯离子含量测定试验、水中再水化试验等,测定了耦合作用下活性粉末混凝土性能指标变化规律,进行了耦合作用下寿命预测,分析了耦合作用下活性粉末混凝土劣化机理。论文首先研究了活性粉末混凝土在氯离子侵蚀以及耦合作用下物理和力学性能的变化规律。耦合循环过程中,质量损失率随着耦合循环次数的增加略微增大,相对动弹性模量几乎不变,抗压强度的变化分为三个阶段:初始快速下降段-稳定段-加速下降段;自然浸泡过程中,抗压强度随着自然浸泡时间的增加呈现降低的趋势,可能是再水化的影响。采用质量损失率来评价耦合作用下活性粉末混凝土的耐久性是不科学的,且相对动弹性模量不宜单独用作评价活性粉末混凝土耐久性的指标。基于自然浸泡以及耦合循环后试样内氯离子含量测定结果,提出考虑冻融损伤影响的氯离子扩散系数计算方法,氯离子扩散系数随着耦合循环次数的增加先减小后增大;分别考虑冻融损伤破坏、氯离子侵蚀破坏、耦合作用破坏三种情况建立寿命预测模型。在此基础上,基于元胞自动机模型对自然浸泡、冻融循环条件下氯离子扩散进行模拟,可为复杂环境下侵蚀介质扩散模拟提供参考。通过活性粉末混凝土毛细吸入试验,考虑钢纤维掺量、溶液浓度等因素对溶液吸入量和毛细吸液系数的影响,分析了自然浸泡和耦合作用后活性粉末混凝土的毛细吸入特性变化。结果表明:活性粉末混凝土的溶液吸入量随着时间的增加前期增长较快,后期增长缓慢,溶液吸入量在15～180 min和180-540 min两阶段均与t1/2成正比;浸泡720d溶液吸入量略大于未浸泡试件,耦合作用后溶液吸入量显著降低,可能是再水化的影响。通过水中再水化试验,分析再水化作用对活性粉末混凝土性能的影响,自然浸泡以及耦合作用过程中发生了再水化反应,有絮状、片状、针棒状、无定型产物以及钙矾石类侵蚀产物生成;再水化作用可以对致密的混凝土结构造成损伤,也会在一定程度上修复损伤。在水泥基水化模型的基础上提出新的再水化模型,模型模拟值与试验值吻合良好,可以为后续再水化模型的研究提供参考。在此基础上,根据Gibbs-Thomson方程,分析孔径以及NaCl浓度对孔隙结冰温度的影响;测定NaCl浓度和温度对体积结冰膨胀率的影响。根据上述结果,分析耦合作用下活性粉末混凝土性能变化的原因。活性粉末混凝土内部结构致密是其在氯盐冻融循环与侵蚀耦合作用下具有良好耐久性的主要原因。
[Abstract]:Durability failure of concrete structures under multi-factor coupling is becoming more and more serious. Reactive powder concrete (RPC), as a kind of cement-based composite material, has super-high mechanical properties and excellent durability. It is suitable for the main body or protective materials of concrete structures in harsh environments. The durability of reactive powder concrete (RPC) was studied. The performance index of RPC was determined by chloride ion corrosion single factor test, chloride salt freeze-thaw cycle and corrosion coupling test, capillary inhalation test, chloride ion content determination test and water rehydration test. The degradation mechanism of RPC under coupling action is analyzed. Firstly, the physical and mechanical properties of RPC under chloride ion erosion and coupling action are studied. With a slight increase in the relative dynamic elastic modulus, the change of compressive strength can be divided into three stages: the initial rapid descent stage - stable stage - Accelerated descent stage; the compressive strength decreases with the increase of natural soaking time, which may be the effect of rehydration. The durability of RPC is unscientific and the relative dynamic modulus of elasticity is not suitable to be used solely as an index to evaluate the durability of RPC.Based on the results of chloride ion content in samples after natural immersion and coupling cycling, a calculation method of chloride ion diffusion coefficient considering the effect of freeze-thaw damage and chloride ion diffusion system is proposed. The number decreases first and then increases with the increase of coupling cycles; life prediction models are established for three cases: freeze-thaw damage, chloride ion erosion and coupling damage. On this basis, chloride diffusion under natural immersion and freeze-thaw cycles is simulated based on cellular automata model, which can be used for erosion in complex environments. Based on the capillary inhalation test of reactive powder concrete (RPC), considering the influence of steel fiber content and solution concentration on the capillary inhalation capacity and capillary absorption coefficient, the capillary inhalation characteristics of RPC after natural immersion and coupling action were analyzed. The amount of liquid inhalation increased rapidly in the early stage and slowly in the later stage with the increase of time. The amount of liquid inhalation was proportional to t1/2 in the 15-180 min and 180-540 min stages. The amount of liquid inhalation in 720 days was slightly larger than that in the unsoaked sample, and the amount of liquid inhalation decreased significantly after coupling action, which may be the effect of rehydration. The influence of rehydration on the properties of RPC is that rehydration reactions occur during natural immersion and coupling, such as flocculent, flaky, needle-bar, amorphous products and Ettringite corrosion products; rehydration can damage the compact concrete structure and repair the damage to a certain extent. Based on the cement-based hydration model, a new rehydration model is proposed. The simulated values are in good agreement with the experimental values, which can be used as a reference for the subsequent study of the rehydration model. Based on the above results, the reason for the performance change of RPC under the coupling action is analyzed. The internal structure of RPC is dense, which is the main reason for its good durability under the coupling action of chloride freeze-thaw cycle and erosion.
【学位授予单位】：北京交通大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TU528
[Abstract]:Durability failure of concrete structures under multi-factor coupling is becoming more and more serious. Reactive powder concrete (RPC), as a kind of cement-based composite material, has super-high mechanical properties and excellent durability. It is suitable for the main body or protective materials of concrete structures in harsh environments. The durability of reactive powder concrete (RPC) was studied. The performance index of RPC was determined by chloride ion corrosion single factor test, chloride salt freeze-thaw cycle and corrosion coupling test, capillary inhalation test, chloride ion content determination test and water rehydration test. The degradation mechanism of RPC under coupling action is analyzed. Firstly, the physical and mechanical properties of RPC under chloride ion erosion and coupling action are studied. With a slight increase in the relative dynamic elastic modulus, the change of compressive strength can be divided into three stages: the initial rapid descent stage - stable stage - Accelerated descent stage; the compressive strength decreases with the increase of natural soaking time, which may be the effect of rehydration. The durability of RPC is unscientific and the relative dynamic modulus of elasticity is not suitable to be used solely as an index to evaluate the durability of RPC.Based on the results of chloride ion content in samples after natural immersion and coupling cycling, a calculation method of chloride ion diffusion coefficient considering the effect of freeze-thaw damage and chloride ion diffusion system is proposed. The number decreases first and then increases with the increase of coupling cycles; life prediction models are established for three cases: freeze-thaw damage, chloride ion erosion and coupling damage. On this basis, chloride diffusion under natural immersion and freeze-thaw cycles is simulated based on cellular automata model, which can be used for erosion in complex environments. Based on the capillary inhalation test of reactive powder concrete (RPC), considering the influence of steel fiber content and solution concentration on the capillary inhalation capacity and capillary absorption coefficient, the capillary inhalation characteristics of RPC after natural immersion and coupling action were analyzed. The amount of liquid inhalation increased rapidly in the early stage and slowly in the later stage with the increase of time. The amount of liquid inhalation was proportional to t1/2 in the 15-180 min and 180-540 min stages. The amount of liquid inhalation in 720 days was slightly larger than that in the unsoaked sample, and the amount of liquid inhalation decreased significantly after coupling action, which may be the effect of rehydration. The influence of rehydration on the properties of RPC is that rehydration reactions occur during natural immersion and coupling, such as flocculent, flaky, needle-bar, amorphous products and Ettringite corrosion products; rehydration can damage the compact concrete structure and repair the damage to a certain extent. Based on the cement-based hydration model, a new rehydration model is proposed. The simulated values are in good agreement with the experimental values, which can be used as a reference for the subsequent study of the rehydration model. Based on the above results, the reason for the performance change of RPC under the coupling action is analyzed. The internal structure of RPC is dense, which is the main reason for its good durability under the coupling action of chloride freeze-thaw cycle and erosion.
【学位授予单位】：北京交通大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TU528
【参考文献】
相关期刊论文 前10条
1 姜作杰;;冻融循环作用下混凝土毛细孔结构的劣化机制[J];华侨大学学报(自然科学版);2015年06期
2 王立成;鲍玖文;李淑红;;损伤混凝土毛细吸水性能试验研究和水分分布预测分析[J];大连理工大学学报;2015年06期
3 赵军;李洪杰;高丹盈;;锈蚀后钢纤维和钢纤维混凝土的力学性能[J];建筑材料学报;2015年03期
4 韩松;涂亚秋;安明U，
本文编号：2199713
本文链接：https://www.wllwen.com/kejilunwen/huaxuehuagong/2199713.html
