Sulfate Attack on Concrete - Chapter 7

Modeling of deterioration processes - Hệ thống xi măng ngậm nước được sử dụng trong xây dựng một loạt các cấu trúc. Trong suốt cuộc đời dịch vụ của họ, nhiều của các cấu trúc tiếp xúc với các loại hóa chất xâm lược liên quan đến các ion sulfate. Trong hầu hết trường hợp, các cơ chế suy giảm liên quan đến việc vận chuyển chất lỏng và / hoặc các loài hóa học hòa tan bên trong cấu trúc lỗ rỗng của vật liệu. Vận chuyển vật chất này (trong các phương tiện truyền thông bão hòa. | 7 Modeling of deterioration processes INTRODUCTION Hydrated cement systems are used in the construction of a wide range of structures. During their service life many of these structures are exposed to various types of chemical aggression involving sulfate ions. In most cases the deterioration mechanisms involve the transport of fluids and or dissolved chemical species within the pore structure of the material. This transport of matter in saturated or unsaturated media can either be due to a concentration gradient diffusion a pressure gradient permeation or capillary suction. In many cases the durability of the material is controlled by its ability to act as a tight barrier that can effectively impede or at least slow down the transport process. Given their direct influence on durability mass transport processes have been the objects of a great deal of interest by researchers. Although the existing knowledge of the parameters affecting the mass transport properties of cement-based materials is far from being complete the research done on the subject has greatly contributed to improve the understanding of these phenomena. A survey of the numerous technical and scientific reports published on the subject over the past decades is beyond the scope of this report and comprehensive reviews can be found elsewhere Nilsson et al. 1996 Marchand et al. 1999 . As will be discussed in the last chapter of this book the assessment of the resistance of concrete to sulfate attack by laboratory or in situ tests is often difficult and generally time-consuming Harboe 1982 Clifton et al. 1999 Figg 1999 . For this reason a great deal of effort has been made towards developing microstructure-based models that can reliably predict the behavior of hydrated cement systems subjected to sulfate attack. A critical review of the most pertinent models proposed in the literature is presented in this chapter. Some of these models have been previously reviewed by other authors Clifton 1991 .