Control of Plastic Shrinkage Cracking of Concrete with Fibers

用纤维控制混凝土的塑性收缩开裂项目摘要：合成纤维在混凝土中最大的单一应用是控制塑性收缩开裂，这种开裂发生在楼板和类似的约束结构的前24小时内，而混凝土仍然是塑性或半塑性的，在它达到任何显著的强度之前。虽然许多研究都涉及纤维增强混凝土的拉伸、弯曲和断裂性能的预测模型，但迄今为止还没有“理论”解释为什么少量的细纤维（体积的0.1%至0.3%）有助于控制混凝土的塑性收缩开裂。这项研究提供了一个理性的答案。提出了一个广泛的实验方案和一个有限的分析方案。主要目的是：1)评价多种纤维对混凝土塑性收缩开裂特性的影响，这些纤维涵盖了广泛的性能；2)了解纤维控制塑性收缩开裂的基本机理；3)为这些机制建立一个分析模型；4)对各种纤维和纤维参数的有效性进行参数化评价；5)对最理想的纤维性能提出一些建议；6)对于给定的纤维，推荐在大多数不利条件下有效控制塑性收缩开裂所需的纤维的最小体积分数。研究结果将有助于比较纤维的性能和参数，这些性能对控制塑性收缩开裂很重要，而这些性能对改善复合材料的机械性能很重要。这项研究预计将对未来纤维，特别是合成纤维在混凝土中的使用产生重大的经济影响。

CONTROL OF PLASTIC SHRINKAGE CRACKING OF CONCRETEWITH FIBERSAntoine E. NaamanUniversity of Michigan, Ann ArborProject Summary:The largest single application of synthetic fibers in concrete is in the~control of plastic shrinkage cracking which occurs during the first twenty four hours of age, mostly in slabs and similar restrained structures, while the concrete is still plastic or semi-plastic and before it has attained any significant strength. While numerous studies have dealt with prediction models for the tensile, bending, and fracture properties of fiber reinforced concrete, there is so far no "theoretical" explanation on why a small amount (0.1% to 0.3% by volume) of fine fibers helps control plastic shrinkage cracking in concrete. This study offers to provide a rational answer. An extensive experimental program is proposed and a limited analytical program suggested. The main objectives are: 1) to evaluate the effect of a number of fibers, covering a wide range of properties, on the plastic shrinkage cracking characteristics of concrete; 2) to understand the basic mechanisms by which fibers control plastic shrinkage cracking; 3) to develop an analytical model accounting for such mechanisms; 4) to carry out a parametric evaluation of the effectiveness of various fibers and fiber parameters; 5) to provide some recommendations on the most desirable fiber properties; and, 6) to recommend, for a given fiber, the minimum volume fraction of fibers needed to effectively control plastic shrinkage cracking under most adverse conditions. The results will help compare fiber properties and parameters that are important for control of plastic shrinkage cracking with those properties that are important for improving the mechanical properties of the composite. This study is expected to have a significant economic impact on the future use of fibers, particularly synthetic types, in concrete.