SITE INVESTIGATION OF CHANGES IN CONVEYED WATER QUALITY AFTER LINING
WATER MAINS WITH BLAST FURNACE SLAG CEMENT MORTAR - KIRK MERRINGTON
Report No DWI0284
To investigate the effect on water quality of lining a dead end main
with blast furnace slag cement mortar (BFS) in a moderately low
alkalinity water and to compare the findings with those from a
parallel trial using ordinary Portland cement (OPC).
Cement mortar is widely used to internally renovate corroded iron
water mains throughout the UK. In some cases the pH levels of the
water passing through newly lined mains can be elevated above the EC
directive maximum advisable limits. To alleviate this, WRc has
developed a modified mortar replacing 65% of the OPC with BFS. The
new BFS mortar, during laboratory and field trials has been found to
reduce the pH in the conveyed water by up to one pH unit in
comparison to OPC. The trial in Kirk Merrington has been conducted
as part of a series of field trials to investigate the effect on pH
of using BFS mortar in waters of varying alkalinity. This site was
chosen as the alkalinity of the water was approximately 22 mg/l as
CaCO3, a level not previously examined.
- The pH of the conveyed water in contact with the blast furnace
slag mortar and the ordinary Portland cement mortar linings remained
above the EC directive MAV of 9.5 for a period of 10 to 11 weeks
after return to service.
- The BFS mortar lined length produced conveyed water pH values
approximately 0.4 units less than the comparable OPC length during
the period of 1 to 6 weeks.
- The concentrations of aluminium, calcium, potassium and sodium
within the conveyed water was initially high, but all metal
concentrations for both linings were below their EC MAV's by the
- The concentration values obtained for metals, and the alkalinity
and conductivity throughout the duration of the trial were not
significantly different between the BFS and OPC lined lengths.
Copies of this report may be available as an Acrobat pdf download under the 'Pre 2000 Reports' heading on the DWI website.
- Although the use of blast furnace slag mortar shows little medium
or long term benefit, BFS cement 'Mainline' should be used in waters
with alkalinity of around 22 mg/l as CaCO3, as reductions in pH of
the conveyed water are seen in the short term.
- Due to the high levels of pH and metals occurring within the
conveyed water within the first few days after lining for both
cement mortar types, a flushing programme should be initiated to
alleviate any water quality problems during this period.
- Where dead end mains or-long rural lengths with low flows are
lined, the flow on the main should be increased. This could be
achieved by joining up dead ends to form a through main or by a
controlled wastage at the dead end.
- WRc should further investigate the use of blast furnace slag
cements by carrying further field trials in softer waters with an
alkalinity of around 12-18 mg/l as CaCO3 as no information yet
exists at this level.
- Further field measurements should be taken at Kirk Merrington, at
6 months and 1 year intervals after lining.