The effect of sodium chloride solution, freeze-thaw cycling and externally applied load on the performance of concrete was experimentally investigated. The results show that the concrete specimens subjected to freeze-thaw cycling scaled more severely in chloride sah solution than those in water, and weight losses oftbe specimens tested in chloride salt solution were twice as much as those tested in water, However. dynamic modulus of elasticity of the concrete specimens deceased more slowly in chloride salt solution than in water due to the decline in the freezing point of the chloride salt solution compared with water, tt is also shown that the performance deterioration in the concrete suhjected to muhidamaging processes was significantly accelerated. The larger the stress ratios, the fewer freeze-thaw cycles the concrete contd bear. When steel fiber is incorporated, performance degradation in the steel fiber-reinforced concrete exposed to the mubidamaging processes could be considerably retarded.

A research program was carried out to investigate the residual compressive strength of high-porformance concrete (HPC) and normal strength concrete (NSC) after they were exposed to high temperatures, 8O0℃ and 1100℃, and two cooling regimes, Test results obtained showed that eompared with the strength at room temperature, the residual strength of both HPC and NSC dropped sharply after exposure to high temperatures. Water cooling, which resulted in a significant thermal shock. caused a bit more severn deterioration in strength compared to furnace cooling. Thermal shock was not necessarily the primary cause for spalling in HPC. Mereury intrusion porosimetry tests were carried out to measure variation in the pore structure of concrete. Sigaifieant changes in the cumulative pore volume curves before and after high lemperatures in both NSC and HPC were observed. The cumulative pore votume of HPC increased more remarkably than thai of NSC. The difference between the effects of the two cooling regimes on mechanical property as well as the microstmeture decreased at 1100℃ when compared 800℃.

通过综合分析提出，钢纤维与水泥基体、集料与水泥浆的界面层不仅可以改善和强化，而且经过有效地调整界同区的组成和结构，界面层及其薄弱特征完全能够消失，并且还有再强化的可能，再强化程度则与界面区组成结构密切相关，这是扩大纤维效应范围、强化空间随机叠加、配制高性能水泥基复合材料的理论基础，本工作还研究了界面效应与高强混凝土、钢纤维高强水泥基复合材料在反复荷载作用下疲劳特性的关系。实验结果表明，因钢纤维与硅灰的复合效应及界面区的再强化，钢纤维水泥基复合材料的疲劳次数可提高一个数量级或疲劳强度提高两倍以上。

The addition of ufitratine powder (UFP)to concrete can improve the fluidity of concrete, showing a water-reducing effect The aim of this article was to analyze the water-reducing mechanism of UFP both experimentally and theoretically. Three UFPs-fine ground slag. highcalcium fly ash, and low-calcium fly ash--weN chosen for the study. The contrastive experiments were done to investigate the fluidity of mortars with 30%, 45%, 60%. and 75% equivalent cement replaced by fine ground slag. high-calcium fly ash. and low-calcium fly ash. respectively. The results showed the physical and chemical characteristic of the powder, such as their grain morphology, glass phase activities, densities, specific areas, and their groin eumuhdng conditions, can strongly affect their water-reducing effect.

作为混凝土寿命预测普适模型的应用篇，介绍了模型在冻融作用下的具体应用，根据该模型，提出了适用于冻融条件（包括复合其它因素）作用下的混凝土的多元Weibull冻融的损伤模型；同时，展开了快速冻融以及硫酸铵侵蚀与冻融复合作用下的耐久性实验，并根据实验结果对冻融模型进了验证，并与神经元计算方法进行了比较，结果表明，该模型在冻融条件下的应用是成功的。另外，为了实现模型由实验室条件向实际工程应用的跨越，本文提出了模型的实际应用方法并根据该方法对北京十三陵抽水蓄能电站这一现场环境下混凝土的寿命进行了数值模信，从而为实际复杂环境下的混凝土寿合评估提供了一个新思路和新方法，具有一定的应用推广价值。