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.

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.

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。

如何对混凝土进行寿命预测及评估是一个至今尚未解决的国际重大科技问题，实现混凝土的寿命设计必将有力地推动混凝土科技的发展。针对混凝土的耐久未失效过程实质是一个内部损伤演变的逐步劣化过程这一事实，本工作结合了可靠度与损伤理论，首次提出了能适用于不同边界条件以及包括单因素和多因素复合作用下的更加符合实际的有关混凝土寿命预测方面的普适多元Weibull分布模型；并为了该模型的具体应用，采用网格部分的手段，提出了相应的算法和编制了对应的计算程序；最后对该模型作了进一步的补充说明，从而为混凝土的寿合设计提供了一个新民路和新方法，其对于混凝土的寿命设计具有一定的启发指导意义。

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。