Modelling a comprehensive relation between water quality and cement degradation in the drinking water distribution network

Abstract

[EN] Over a quarter of the Dutch drinking water distribution network consists of cementitious pipe materials (e.g. asbestos cement, concrete and cement-coated cast iron). Leaching of cement components into the drinking water may lead to changes in water quality and to a reduction of a pipe’s structural integrity. Many utilities worldwide condition their drinking water to prevent leaching. Several indices can be derived from a given water composition to estimate how well the water composition will protect against leaching. While water utilities have so far achieved good results using for instance the Langlier Saturation Index (LSI) and the Calcium Carbonate Precipitation Potential (CCPP) as an indicators, scientific authors have already posed in the past that the protection against leaching depends on a complex interplay between many chemical components in both the drinking water and the cement, and that no single index is sufficient to guarantee protection. In the presented work, a comprehensive model of the chemical and physical interactions between a cement pipe and drinking water is constructed. The model takes any given drinking water composition for input and returns a description of the chemical and microstructural changes that develop in the pipe wall over time as leaching progresses. The model shows reasonable agreement with leaching experiments described in literature. Using such a model, one can evaluate the protective capabilities of a given water quality based on all its aspects rather than just the aspects captured by derived indices. The model can be a powerful research tool for studying the interactions between drinking water and pipe materials, but this approach should also already prove to be a valuable aid for process engineers to optimize their conditioning strategies in practice, and for asset managers to translate historical water quality data to an estimation of the structural integrity of their cementitious pipes.