盐冻循环下粉煤灰再生混凝土性能劣化规律及寿命预测

Performance deterioration law and life prediction of fly ash recycled concrete under salt-freezing cycle

为研究粉煤灰再生混凝土在高寒、盐渍土地区的耐久性问题,以质量分数为3%的NaCl和5%的Na_(2)SO_(4)混合溶液为冻融介质,采用快冻法对不同粉煤灰掺量的再生混凝土进行冻融循环试验,测定各组试件的质量损失、抗压强度以及相对动弹性模量的数据,研究粉煤灰再生混凝土在盐冻耦合作用下的性能劣化规律,并通过抛物线损伤模型预测再生混凝土的耐久性寿命。研究结果表明:在盐冻侵蚀作用下,不同掺量粉煤灰再生混凝土的相对动弹性模量和抗压强度变化均呈现前期平缓下降,后期快速下降的趋势,而质量损失率则前期缓慢增长,后期快速增加;抛物线模型能较好表征粉煤灰再生混凝土在复合盐环境下的冻融损伤,其模型拟合曲线与试验结果符合较好,具有较高的精度;当粉煤灰掺量为20%时,再生混凝土的抗冻耐久性寿命最长。

In order to study the durability of fly ash recycled concrete in alpine and saline soil areas,using the mixed solution of 3%NaCl and 5%Na_(2)SO_(4)by mass fraction as the freeze-thaw medium,the freeze-thaw cycle test was carried out on recycled concrete with different fly ash contents by the quick freezing method.The mass loss,compressive strength and relative dynamic elastic modulus of each group of recycled concrete specimens are measured,and the performance degradation law of fly ash recycled concrete under the coupling action of freeze-thaw and compound salt erosion is studied,and durability life of recycled concrete is predicted by parabolic damage model.The research results show that under the action of salt freezing erosion,the relative dynamic elastic modulus and compressive strength of recycled concrete with different contents of fly ash show a trend of gentle decline in the early stage and rapid decline in the later stage,while the mass loss rate increases slowly in the early stage,and increased rapidly in the later period;the parabolic model can better characterize the freeze-thaw damage of fly ash recycled concrete in the compound salt environment,and the model fitting curve is in good agreement with the test results and has high accuracy;When it is 20%,recycled concrete has the longest durability life in the salt-freezing environment.