采用中子照相观测无裂缝和带裂缝混凝土的水分侵入(英文)

Observation of Water Penetration into Uncracked and Cracked Steel Reinforced Concrete Elements by Means of Neutron Radiography

钢筋混凝土结构的使用寿命在很大程度上取决于混凝土材料本身的质量、保护层厚度、侵蚀环境等.水和溶解于水中的有害离子能够通过混凝土孔隙的毛细吸附、扩散或两者的复合作用侵入到混凝土内部.两者复合作用的机理非常复杂,无法通过简单的模型进行描述,因此,目前对侵蚀环境下钢筋混凝土结构的使用寿命预测方法还不完全成熟.成功采用了一种有力的检测方法———中子照相,来观测水分在多孔混凝土中的运动过程,试验结果为今后建立可靠的寿命预测模型提供了坚实的试验基础.在介绍中子照相基本原理的基础上,对无裂缝和带裂缝混凝土的毛细吸水过程进行了实时中子成像.水分在钢筋与混凝土的界面处以及在裂缝前方的断裂区内部的运动过程尤为特殊.首次就水分的侵入过程进行了详细的可视化研究,试验结果有助于进一步更好地理解钢筋混凝土的劣化机理,寻求提高混凝土耐久性的措施.

Service life of reinforced concrete structures depends on the quality of concrete, the cover thickness, and the aggressiveness of the environment. Water and harmful compounds dissolved in water are taken up into the porous structure of concrete by capillary action and diffusion or a combination thereof. The combined process is very complex and cannot be described by simple models. Therefore prediction of service life of reinforced concrete structures in aggressive environment remains unreliable. In this contribution it will be shown that neutron radiography is a very powerful method to study moisture uptake and movement in porous materials such as concrete. Results will provide us with a solid basis for reliable predictive models. app the the First fundamentals of the test method will be briefly described. It will be shown how this method can be lied to follow the time dependent process of capillary suction quantitatively. In addition uptake of water in vicinity of cracks has been studied in some detail. It is of particular interest that movement of water into interface between steel reinforcement and concrete and into the fracture process zone ahead of a crack tip can be visualized and determined quantitatively by means of neutron radiography. It is the first time that these decisive processes with respect to durability can be studied in detail. The obtained results will be discussed and the potential of the test method for future investigations will be outlined. Results presented in this contribution will help us to understand better deteriorating processes in reinforced concrete structures and to find ways to improve durability.