Kovler Konstantin
National Building Research Institute, Faculty of Civil and Environmental Engineering, Technion-Israel Institute of Technology, Technion City, Haifa 32000, Israel.
J Environ Radioact. 2006;86(3):354-66. doi: 10.1016/j.jenvrad.2005.10.005. Epub 2005 Dec 13.
The unique properties of radon as a noble gas are used for monitoring cement hydration and microstructural transformations in cementitious system. It is found that the radon concentration curve for hydrating cement paste enclosed in the chamber increases from zero (more accurately - background) concentrations, similar to unhydrated cement. However, radon concentrations developed within 3 days in the test chamber containing cement paste were approximately 20 times higher than those of unhydrated cement. This fact proves the importance of microstructural transformations taking place in the process of cement hydration, in comparison with cement grain, which is a time-stable material. It is concluded that monitoring cement hydration by means of radon exhalation method makes it possible to distinguish between three main stages, which are readily seen in the time dependence of radon concentration: stage I (dormant period), stage II (setting and intensive microstructural transformations) and stage III (densification of the structure and drying). The information presented improves our understanding of the main physical mechanisms resulting in the characteristic behavior of radon exhalation in the course of cement hydration. The maximum value of radon exhalation rate observed, when cement sets, can reach 0.6 mBq kg(-1) s(-1) and sometimes exceeds 1.0 mBq kg(-1) s(-1). These values exceed significantly to those known before for cementitious materials. At the same time, the minimum ventilation rate accepted in the design practice (0.5 h(-1)), guarantees that the concentrations in most of the cases will not exceed the action level and that they are not of any radiological concern for construction workers employed in concreting in closed spaces.
氡作为一种惰性气体的独特性质被用于监测水泥水化过程以及胶凝体系中的微观结构转变。研究发现，封闭在室内的水化水泥浆体的氡浓度曲线从零（更准确地说是背景值）浓度开始上升，这与未水化的水泥类似。然而，在装有水泥浆体的试验室内，3天内产生的氡浓度比未水化水泥的氡浓度高出约20倍。这一事实证明了与作为时间稳定材料的水泥颗粒相比，水泥水化过程中发生的微观结构转变的重要性。研究得出结论，通过氡析出法监测水泥水化能够区分出三个主要阶段，这在氡浓度的时间依赖性中很容易看出：第一阶段（静止期）、第二阶段（凝结和剧烈的微观结构转变）和第三阶段（结构致密化和干燥）。所提供的信息增进了我们对导致水泥水化过程中氡析出特征行为的主要物理机制的理解。观察到的水泥凝结时氡析出率的最大值可达0.6 mBq kg⁻¹ s⁻¹，有时超过1.0 mBq kg⁻¹ s⁻¹。这些值显著高于此前已知的胶凝材料的值。同时，设计实践中接受的最小通风率（0.5 h⁻¹）确保在大多数情况下浓度不会超过行动水平，并且对于在封闭空间内进行混凝土浇筑作业的建筑工人来说不存在任何放射性问题。
