硫酸盐干湿循环作用下废水混凝土寿命预测模型

Service Life Prediction Model for Wastewater Concrete Under Sulfate Dry-wet Cycle

为解决中国西北高寒盐渍土地区混凝土的耐久性问题,采用不同掺量搅拌站废水拌制混凝土,以研究其在抗硫酸盐-干湿循环双重作用下的影响。以0%,25%,50%,75%,100%比例混凝土搅拌站废水取代等质量饮用水混合拌制C40混凝土,以20%比例粉煤灰等质量取代水泥。混凝土试件为40 mm×40 mm×160 mm,采用5%浓度的硫酸镁溶液进行全浸泡干湿循环试验,测试混凝土的抗压强度、抗折强度、相对动弹性模量、质量及吸水率。以相对动弹性模量为评价指标,利用灰色预测GM(1,1)模型及损伤二次函数衰减模型进行寿命预测。结果表明:随着废水替代率的增加,混凝土抗压强度损失率先减小后增大,干湿循环下的混凝土质量损失率由高到低依次为C40-75,C40-100,C40-50,C40-25;搅拌站废水的主要氧化物与水泥类似,微观形貌多为多孔状不规则颗粒,可以延缓C40混凝土在硫酸盐干湿循环环境中的劣化速度,使混凝土提高抵抗SO_(4)^(2-)侵入的能力,其中废水替代率为50%时混凝土抗SO_(4)^(2-)侵蚀能力最好;GM(1,1)寿命预测显示废水替代率为50%时混凝土耐久性年限最长,其耐久年限提高了2.3倍,可抵抗74次硫酸盐-干湿循环,且衰减模型相关系数R^(2)大于0.94,具有较高精度。

To solve the durability problem of concrete in salty soil environment in the alpine region of Northwest China,the influence of different mixing plant wastewater on the durability of concrete against sulfate dry-wet cycle was investigated.To study the influence of different dosage of mixing plant wastewater on concrete resistance to sulfate under dry-wet cycle,the concrete mixing plant wastewater was mixed with C40 concrete by replacing potable water with 0%,25%,50%,75%,and 100%proportion of equal mass.The fly ash replaced cement with 20%proportion of equal mass.The specimens of 40 mm×40 mm×160 mm were tested by using 5%concentration of magnesium sulfate solution for full immersion dry-wet cycle test.The compressive strength,flexural strength,relative dynamic elastic modulus,mass and water absorption of concrete were tested.The relative dynamic elastic modulus was also used as the evaluation index,and the life prediction was carried out by using the gray prediction GM(1,1)model and damage quadratic decay model.The result indicates that with the increase of wastewater substitution rate,the concrete compressive strength loss firstly decreases and then increases.The rate of concrete mass loss under dry-wet cycle is C40-75,C40-100,C40-50,and C40-25 in descending order.The main oxides of mixing plant wastewater are similar to cement,and the microscopic morphology is mostly porous irregular particles,which can delay the deterioration rate of C40 concrete in sulfate dry-wet cycle.The degradation rate of C40 concrete in sulfate dry-wet cycle environment can slow down the deterioration rate of C40 concrete in cycle environment,so that the concrete improves the resistance to the invasion of SO_(4)^(2-),of which the concrete has the best resistance to SO_(4)^(2-) erosion when the wastewater substitution rate is 50%.The GM(1,1)life prediction shows that the concrete has the longest durability life when the wastewater substitution rate is 50%.The durability life increases by 2.3 times.The concrete can resist 74 times sulfate dry-wet cycle.The decay model correlation coefficient R^(2) is greater than 0.94,which has high accuracy.