Control of Plastic Shrinkage Cracking of Concrete with Fibers

控制混凝土的塑性收缩裂缝与密歇根大学Antoine E.Naaman，Ann Arbora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裂缝，塑性收缩裂缝发生在龄期的头24小时内，主要发生在板和类似的约束结构中，而混凝土仍然是塑料或半塑性的，在达到任何显著强度之前。虽然许多研究涉及纤维增强混凝土的拉伸、弯曲和断裂性能的预测模型，但到目前为止还没有“理论”解释为什么少量(0.1%至0.3%体积分数)的细纤维有助于控制混凝土中的塑性收缩裂缝。这项研究提供了一个合理的答案。提出了一个广泛的实验方案和一个有限的分析方案。其主要目标是：1)评估多种纤维对混凝土塑性收缩裂缝特性的影响；2)了解纤维控制塑性收缩裂缝的基本机理；3)开发解释这些机理的分析模型；4)对各种纤维的有效性和纤维参数进行参数评估；5)就最理想的纤维性能提供一些建议；以及6)对于给定的纤维，建议在最不利的条件下有效控制塑性收缩裂缝所需的最小纤维体积分数。这些结果将有助于比较对控制塑性收缩开裂很重要的纤维性能和参数，以及对提高复合材料的力学性能很重要的那些性能。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.