Inflence of curing and loading conditions on stress-strain relationship of super high strength concrete.

本课题的目的是为阐明400 ~ 1000 kgf/cm^2高强度结构混凝土的应力-应变曲线特性，特别是抗压强度后的落枝特性，获取基础数据。在第一年，由于加载火焰的刚度和加载控制技术严重影响了针对该特性的加载试验结果，提出了一种由高刚度加载火焰和由计算机系统控制的执行器组成的实验系统。第二年，采用加载系统和直径为100mm、高度为200mm的混凝土柱试件，对影响性能的诸多因素进行了试验研究。结果表明：(1)水中养护混凝土的初始刚度最大，达到极限强度后的强度折减幅度在水中养护、密封养护和空气养护三种条件中最大。(2)当固化条件由密封状态变为空气状态时，密封状态固化天数越多，(1)所述行为越显著。(3)正常和高早强硅酸盐水泥的应力应变关系差异不大。(4)与混凝土抗压强度成正比，初始刚度和极限强度时的应变变大，极限强度后的强度折减更严重。(5)在4种应力-应变曲线方程中，Shirai方程最适合混凝土在水中养护的试验结果，而对其他养护条件的拟合效果较差。

The object of this project is to obtain fundamental data in order to clarify behavior of stress-strain curve of structural concrete with high strength ranged from 400 to 1000 kgf/cm^2, and especially the behaivor of falling branch after compresivve strength.In the first year, since stiffness of a loading flame and a control technique of loading influence severely the results of loading test focused on such behaviors, an experiment system was proposed, which consisted of a loading flame with high stiffness and an actuator controled by a computer system.In the second year, experimental study on many influence factors on the behavior carried out by using the loading system and concrete sylinder specimens with a diameter of 100mm and a hight of 200mm. The results are summarized as the follows :(1)The concrete curing in water has the largest initial stiffness and severest strength reduction after the ultimate strength among three conditions of curing in water, sealing and air. (2)In case of curing condition changed from in sealing to in air, the more curing days in sealing is, the more remarkable the behavior mentioned in (1) is. (3)The difference of stress-strain relationship is little between normal and high-early-strength Portland cements. (4)The initial stiffness and the strain at ultimate strength become larger and the strength reduction after ultimate strength becomes severer proportional to compressive strength of concrete. (5)Among the four previous equations expressing the stress-strain curves, Shirai's equation is the best fit to the experimental resurt of concrete curing in water but not good to the other curing conditions.