摘要
采用快冻法,将再生骨料取代率为30%的混凝土分别置于3%Na_(2)SO_(4)、5%Na_(2)SO_(4)、10%Na_(2)SO_(4)(均为质量分数)溶液以及水中进行冻融循环试验,测试再生混凝土质量损失率、相对动弹性模量变化、抗压强度损失率,并利用电子显微镜、能谱仪和X射线衍射等方法分析再生混凝土损伤层的微观结构,以超声波平测法确定损伤层厚度,引入侵蚀系数对以损伤层厚度为评价指标的损伤度进行优化。结果表明,当冻融循环为0~200次、Na_(2)SO_(4)溶液浓度大于5%时,抗压强度侵蚀系数始终小于1,即Na_(2)SO_(4)溶液对再生混凝土宏观力学性能损伤的促进作用明显,而对微观结构损伤的抑制作用明显。在再生混凝土冻融循环初期,以冻融侵蚀为主;冻融循环后期,以硫酸盐化学侵蚀为主,再生混凝土经化学侵蚀后生成钙矾石和石膏等膨胀产物,并出现膨胀裂缝,在冻融循环作用下裂缝迅速扩展,损伤层厚度增加。以损伤层厚度为评价指标的损伤度经优化后准确性至少提高了26.33%。
The concretes with recycled aggregate mass replacement rate of 30%were placed in 3%Na_(2)SO_(4),5%Na_(2)SO_(4),10%Na_(2)SO_(4)(3%,5%,10%,mass fraction)solution and water for freeze-thaw cycles test by quick freezing method.The mass loss rate,relative dynamic elastic modulus change and compressive strength loss rate of recycled aggregate concrete were tested.The microstructure of the damaged layer of recycled aggregate concrete was analyzed by electron microscope,energy spectrometer and X-ray diffraction.The thickness of the damaged layer was determined by ultrasonic flat measurement method,and the erosion coefficient was introduced to optimize the damage degree with the thickness of the damaged layer as the evaluation index.The results show that:when freeze-thaw cycles is 0~200 times and the concentration of Na_(2)SO_(4) solution is greater than 5%,the erosion coefficient of compressive strength is always less than 1,in other ways,Na_(2)SO_(4) solution has obvious promoting effect on the macroscopic mechanical performance damage of recycled aggregate concrete,but has obvious inhibitory effect on the microstructure damage.In the early stage of freeze-thaw cycles of recycled aggregate concrete,freeze-thaw erosion is the main factor.In the later stage of freeze-thaw cycles,sulfate chemical erosion is the main factor.After chemical erosion,expansion products such as ettringite and gypsum are formed in recycled aggregate concrete,and they lead to expansion cracks.The cracks expand rapidly under the action of freeze-thaw cycles,and the thickness of the damaged layer increases.The accuracy of the damage degree based on the thickness of the damage layer as the evaluation index is improved by at least 26.33%after optimization.
作者
齐晓
肖前慧
邱继生
刘书林
QI Xiao;XIAO Qianhui;QIU Jisheng;LIU Shulin(School of Architecture and Civil Engineering,Xi’an University of Science and Technology,Xi’an 710054,China)
出处
《硅酸盐通报》
CAS
北大核心
2023年第4期1194-1204,共11页
Bulletin of the Chinese Ceramic Society
基金
国家自然科学基金面上项目(42071100)
陕西省自然科学基础项目研究(2018JQ5215)。
关键词
再生混凝土
冻融循环
硫酸盐侵蚀
微观结构
损伤度
recycled aggregate concrete
freeze-thaw cycle
sulfate attack
microstructure
damage degree
