Durability Design of Concrete Structures

4Leaching

This chapter presents the leaching process of structural concretes by soft water in the environment. Leaching refers to the dissolution of solid phases of porous materials through pore solution transport. For cement‐based materials, leaching is usually related to the dissolution of calcium in the solid matrix. The stability of cement hydrates is affected by the leaching process and the properties of structural concrete are compromised. Leaching is a long‐term process for concrete, and contact with soft water, water with low salinity, is an indispensable condition. This chapter begins with the engineering cases of leaching deterioration by flowing water and then introduces the mechanisms and the influential factors of the process. On the basis of state‐of‐the‐art knowledge, two models are given for calcium leaching of concrete. Some useful indicators, especially the leaching depth of portlandite (CH), are identified for engineering use. Finally, considerations for durability design are developed.

4.1 Phenomena and Observations

Concrete consists of a solid matrix, including hydrates and aggregates, and porosity, which is the void space not occupied by the solid phases. The pores of concrete are more or less occupied by a liquid solution. In the hardened state, the solid phases are in dissolution equilibrium with the liquid phase in pores. The solid phases, especially the hydrates from cements and mineral admixtures, are stable at this chemical equilibrium. This solid–liquid ...