基于紧密堆积理论的混凝土弹性模量与徐变控制

Concrete Elastic Modulus and Creep Control Based on Dense Packing Theory

为降低连续刚构桥跨中下挠幅度,针对弹性模量与徐变2种影响因素,提出一种基于骨料紧密堆积理论的配合比优化控制方法,并对比原配合比研究了优化控制方法对不同龄期与环境下的弹性模量与徐变的影响;结合SEM(scanning electron microscope)与MIP(mercury intrusion porosimetry)试验,从混凝土微观层面分析优化机理,以CEB-FIP(1990)模型为基础,提出考虑弹性模量成熟度的修正模型.结果表明:优化控制方法对早龄期混凝土弹性模量具有明显的控制效果,但界面过渡区面积的增加限制了后期弹性模量的发展;相同条件下,优化后混凝土徐变系数较原配合比降低了12%~23%;环境对混凝土徐变影响与优化控制方法相比占主导作用,不同环境下混凝土徐变变化幅度在45%~60%;混凝土徐变随加载龄期延长而减小,且优化后混凝土在较小加载龄期时,徐变仍比较大加载龄期的原配合比混凝土徐变降低3%~13%;优化后混凝土早龄期内部孔隙与微裂缝数量减少,改善了混凝土内部结构;修正后的CEB-FIP(1990)模型对徐变预测精度更高.

In order to reduce the deflection amplitude of the continuous rigid frame bridge span,an optimized control method of mix proportion based on the dense packing theory of aggregates was proposed for the two influencing factors of elastic modulus and creep.In addition,the original mix proportion was studied to analyze the influence of the optimized control method on the elastic modulus and creep under different ages and environments.At the same time,the optimization mechanism was analyzed from the microscopic level of concrete in combination with scanning electron microscope(SEM)and mercury intrusion porosimetry(MIP)experiments.Based on the CEB-FIP(1990)model,a modified model considering the maturity of elastic modulus was proposed.The results show that the optimized control method can effectively control the elastic modulus of concrete at an early age,but the increase in the area of the interface transition zone limits the later development of the elastic modulus.Under the same conditions,the creep coefficient of the optimized concrete is reduced by 12%–23%compared with the original mix proportion.Moreover,the influence of the environment on the concrete creep is dominant compared with the optimized control method.The variation range of concrete creep under different environments is between 45%and 60%.Concrete creep decreases with the loading age,and the creep of optimized concrete at a small loading age is still 3%–13%lower than the original mix proportion of the concrete at a large loading age.After optimization,the number of internal pores and micro-cracks in the concrete at an early age is reduced.Therefore,the internal structure of the concrete is improved.The modified CEB-FIP(1990)model has higher accuracy in predicting creep.