Ding Yongfa, Li Hongbo, Zhang Hubiao, Li Sheng, Zhang Xuanshuo, Hua Shudong, Zhao Jing, Tong Yufei
College of Civil and Hydraulic Engineering, Ningxia University, Yinchuan 750021, China.
Engineering Research Center for Efficient Utilization of Water Resources in Modern Agriculture in Arid Regions, Yinchuan 750021, China.
Materials (Basel). 2022 May 20;15(10):3684. doi: 10.3390/ma15103684.
To study the shrinkage and freeze-thaw durability of cement-fly-ash-stabilized brick and concrete reclaimed gravel mixture (CFRBCA), recycled gravel was used to replace 100% of the natural gravel in cement-and-fly-ash-stabilized gravel (CFRCA). Five different mixture ratios of recycled brick and recycled concrete were designed. Dry shrinkage tests, temperature shrinkage tests, freeze-thaw cycle tests, ultrasonic tests, and microscopic analyses were then conducted. The test results showed that the water loss rate, dry shrinkage strain, and dry shrinkage coefficient of CFRBCA increased as the age and brick content increased and tended to be stable by approximately the 40th day of age. The reclaimed gravel content had a great influence on the temperature shrinkage of CFRBCA: the temperature shrinkage coefficient first increased and then decreased as the temperature decreased and reached a peak at -10 to 0 °C. The microstructure analysis showed that as the number of freeze-thaw cycles increases, cracks appear and extend in the CFRBCA, hydration products gradually change from dense to loose, and the Ca/Si ratio increases. Through these experiments, the logarithmic relationship model between ultrasonic wave velocity and CFRBCA strength damage, which can better predict the strength loss caused by CFRBCA variation with freeze-thaw cycles, was established. The brick content is the key parameter affecting the durability of the freeze-thawed CFRBCA, and thus the brick slag content should be properly controlled in engineering applications.
为研究水泥-粉煤灰-稳定砖与混凝土再生砾石混合料（CFRBCA）的收缩及冻融耐久性，采用再生砾石完全替代水泥-粉煤灰-稳定砾石（CFRCA）中的天然砾石。设计了五种不同的再生砖与再生混凝土混合比例。随后进行了干缩试验、温缩试验、冻融循环试验、超声波试验及微观分析。试验结果表明，CFRBCA的失水率、干缩应变和干缩系数随龄期和砖含量的增加而增大，在龄期约40天时趋于稳定。再生砾石含量对CFRBCA的温缩影响较大：温缩系数随温度降低先增大后减小，在-10至0℃时达到峰值。微观结构分析表明，随着冻融循环次数的增加，CFRBCA中出现裂纹并扩展，水化产物逐渐由致密变为疏松，Ca/Si比增大。通过这些试验，建立了超声波声速与CFRBCA强度损伤之间的对数关系模型，该模型能更好地预测CFRBCA随冻融循环变化引起的强度损失。砖含量是影响冻融后CFRBCA耐久性的关键参数，因此在工程应用中应适当控制砖渣含量。
