Stability of Cement Mortar Lining in Drinking Water Supply Pipelines under Different Hardness and Alkalinity Conditions

Cement mortar lined iron pipes are widely used in drinking water distributions systems (DWDS), but the quantitative evaluation of chemical stability of the cement mortar lining (CML) under different drinking water conditions is still scarce. Here, we established pipe reactors using DN100 cement mortar lined ductile iron pipe to investigate the pipe material leaching into water and the corresponding changes in surface properties under a wide range of hardnesses (0-330 mg/L as CaCO3) and alkalinities (0-250 mg/L as CaCO3). Results showed that drinking water with hardness and alkalinity of higher than 30 mg/L can markedly decrease CML material release via the formation of a calcium carbonate layer. The thickness of the calcium carbonate precipitation layer and the corrosion affected depth of CML were dependent on the concentration levels of water hardness and alkalinity. CML contacted with low alkalinity and low hardness water (A30H30) was affected to a depth of about 71 mu m and a precipitation layer thickness of about 11 mu m formed on the surface, while the CML contacted with high alkalinity and moderate hardness water (A250H160) was affected to a depth of 37 mu m and a precipitation layer thickness of 41 mu m. More importantly, the formation of the calcium carbonate layer by Ca2+ migration from both sides of the CML- water interface could occur even if the initial water CCPP (calcium carbonate precipitation potential) was negative, which expanded the range of water quality suitable for CML pipe application.

Automated summary

The quantitative evaluation of the chemical stability of cement mortar lining (CML) in cement mortar lined iron pipes under different drinking water conditions is still lacking. This study investigated the leaching of pipe material into water and changes in surface properties using pipe reactors. Results showed that water with hardness and alkalinity higher than 30 mg/L can significantly decrease the release of CML material by forming a calcium carbonate layer. The formation of the calcium carbonate layer can occur even if the initial water calcium carbonate precipitation potential (CCPP) is negative.