中文摘要：

为了更好地预测混凝土抗开裂性能，研究了混凝土特征拉应变随时间的变化规律。通过弯拉试验方法，研究水泥强度等级与掺加纤维对混凝土1～180d各龄期的初裂拉应变和极限拉应变的影响，分析初裂拉应变与弯拉强度和静力受压弹性模量比值的关系，建立了极限拉应变随龄期发展的关系式，提出最终极限拉应变与特征龄期的概念。试验结果表明，混凝土的初裂拉应变与混凝土弯拉强度和静力受压弹性模量的比值具有良好的线性关系，混凝土极限拉应变随时间成负指数增长，提高水泥强度等级与掺加纤维均可以提高混凝土最终极限拉应变，但提高幅度并不显著，相对而言，以特征龄期来评价混凝土抗裂性能更加重要。

英文摘要：

The development of tensile strain capacity of concrete with curing age was studied to predict the risk of concrete cracking. The influences of cement strength grade and fiber addition on the critical tensile strain and ultimate tensile strain of the Concrete from 1 d to 180 d were investigated in flexural tests. The relationship between the critical tensile strain and the ratio of flexural strength to static modulus of elasticity was analyzed, and a formula of ultimate tensile strain and age was established, which led to the concepts of final ultimate tensile strain and characteristic age. The experimental results show that there is a good linear relation between the critical tensile strain and the ratio of flexural strength to static modulus of elasticity. The ultimate tensile strain exhibits a negative exponential increase with age. The final ultimate tensile strain increases within a narrow rang with the increase of cement strength and fiber addition. It is more effective tO evaluate the concrete cracking resistance by the characteristic age.