纤维再生混凝土早期收缩与开裂机理及其控制研究

Fiber reinforced recycled aggregate concrete (FRAC) has a huge application prospect due to it can be recycled and environment-friend. In order to improving the defects of FRAC that cause by recycle aggregate, such as big deformation and internal cracks, the research of this project is focused on the early age shrinkage and cracking performance of FRAC and the method to improve the defects. Effects of replacement ratio of recycled aggregate, fiber type, fiber content and compressive strength on the setting time, relative humidity and temperature, early deformation and stress, crack distribution, crack number, crack width, crack developing tendency and fracture toughness were conducted through ultrasonic nondestructive testing, humidity and temperature sensor, optical fiber Bragg grating, Digital image correlation (DIC), the plate cracking and Notch beam experiment. Based on the test results, the calculation model of setting time, relative humidity and temperature, early shrinkage and stress, concrete strength, crack performance of FRAC were established considering the effects of recycled aggregate and fiber through the theoretical analysis. Crack criterion FRAC was put forward and control methods of shrinkage and cracking of FRAC were establish based on the optimal mixture design.

纤维再生混凝土作为一种可循环利用的绿色建筑材料具有巨大的应用前景。为了改善纤维再生混凝土变形大、内部裂纹多等由再生骨料引起的缺陷，本项目针对纤维再生混凝土早期变形及开裂性能展开研究，探讨其改善方法。应用超声波无损检测、温湿度传感器、光纤布拉格光栅、数字图像处理技术，结合平板开裂和切口梁试验，研究粗骨料取代率、纤维类型、纤维掺量和混凝土强度对纤维再生混凝土凝结时间、内部相对湿度和温度分布、早期变形和应力、早期裂缝分布面积、裂缝根数、裂缝宽度、断裂韧度及裂缝发展趋势等的影响。结合理论分析，分别建立纤维再生混凝土初凝和终凝时间、内部温度和湿度分布、收缩变形和应力、强度发展和开裂性能与再生骨料和纤维之间的关系模型，提出其早期开裂判据以及基于配合比优化设计的早期收缩和开裂的控制方法。

纤维再生混凝土材料作为一种绿色、可循环利用的建筑材料，能够消耗大量的建筑垃圾，同时减少对天然砂石资源的开采和利用，对降低建材行业的碳足迹、保护自然资源和环境有着重要的意义。再生骨料表面包裹水泥砂浆、内部裂纹多，其收缩变形远大于天然混凝土，早期开裂更加严重。本项目针对纤维再生混凝土的早期收缩和开裂性能展开试验和理论研究。采用非接触收缩仪测定纤维再生混凝土从浇筑至28天龄期的干燥收缩和自收缩变形，采用平板开裂试验测试纤维再生混凝土的早期开裂及裂缝发展规律，采用切口梁的三点弯曲试验测定其在荷载作用下的裂纹扩展规律。纤维再生混凝土的收缩变形、早期开裂随着再生骨料取代率的增加而增大，随着聚丙烯纤维掺量的增加而降低，随着钢纤维掺量的增大呈现先增加后减小的趋势。纤维再生混凝土荷载作用下裂纹发展规律与普通混凝土相似，随着再生骨料取代率的增加，初裂荷载减小，起裂韧度和断裂韧度都有所降低，随着聚丙烯纤维以及钢纤维的掺入，起裂荷载变化不大，但起裂韧度和断裂韧度均随着纤维掺量的增加而增大，尤其是钢纤维对再生混凝土的增韧效果明显。通过试验数据回归分析，建立了纤维再生混凝土早期干燥收缩变形、自收缩变形、裂缝增大系数、裂缝降低系数与再生骨料取代率以及纤维掺量之间的计算模型。同时建立了基于目前强度和目标工作性能的纤维再生混凝土配合比优化设计方法。对纤维再生混凝土的工程应用奠定了理论基础。