FR0231

Sept 1991

SUMMARY

I OBJECTIVES

To review critically the current state of U.K. knowledge on water quality problems associated with the use of cement mortar linings for the internal corrosion protection of ferrous water mains.

Cement mortar lining activity has increased significantly to meet 'levels of service' regulatory requirements in a cost effective manner. However, under certain conditions the use of cement mortar linings can lead to pH, aluminium and lead levels in excess of limits defined in the Water Supply (Water Quality) Regulations 1989. Guidance on the use of cement mortar lining is therefore required to help ensure compliance with regulations.

Lime leaching from all types of cement mortar lining currently used in the U.K. can potentially result in pH levels of the conveyed water in excess of the maximum admissible value (MAV) of 9.5 (as defined in the Water Supply (Water Quality) Regulations 1989). Factory applied cement linings appear to cause lower pH levels relative to in situ linings, when tested under equivalent conditions. Of the two commonly used in situ cement mortar linings, the blast furnace slag (BFS) modified mortar results in lower pH levels compared with Ordinary Portland Cement (OPC) mortar. In all cases pH levels increase as retention time of the supply water in the pipe length increases. pH levels decrease as pipe diameter and supply water alkalinity increase. pH levels can be controlled by flushing, bicarbonate dosing and in the case of factory linings by the use of bitumen seal coatings; however, flushing and dosing are only short term solutions and the long term behaviour of seal coatings is uncertain.

1. In situ applied OPC mortar linings should not be used if the supply water alkalinity is less than 55mg CaCO₃/l.
2. In situ applied BFS modified mortar linings should not be used if the supply water alkalinity is less than 35mg CaCO₃/l.
3. Factory applied PFA modified mortar linings should not be used if the supply water alkalinity is less than
   25 mg CaCO₃/l.
4. If retention times of the supply water in a system are likely to be significantly greater than eight hours, pH levels in excess of 9.5 may occur even if the supply water alkalinity is higher than the recommended minimum; consequently, caution should be exercised when considering the use of cement mortar linings where cumulative maximum retention times may be relatively high.
5. In situations where water quality problems may occur, the use of approved alternatives to cement mortar lining, e.g. epoxy resin, is strongly recommended.

An introduction to the water quality problems associated with the use of cement mortar linings in contact with potable water is presented. U.K. experiences and data for both factory and in situ applied linings are critically reviewed and recommendations for use of the materials are given with regard to potential effects on water quality.

Copies of the Report are available from FWR, price £15.00 less 20% to FWR Members