Report No DWI0786

CEMENTITIOUS LININGS AND WATER QUALITY PART 2 SOLUTIONS TO THE PROBLEMS CAUSED BY ORDINARY PORTLAND CEMENT

DWI0786

Oct 1988

SUMMARY

I OBJECT

To develop methods to overcome the water quality problems observed when small diameter water mains are relined with ordinary Portland cement (OPC).

II REASON

Previous work has shown that following the lining of small diameter water mains with OPC, in areas with a very low alkalinity supply water, pH and aluminium levels can be elevated above EC directive limits for prolonged periods.

III CONCLUSIONS

Three methods were developed which reduced pH and aluminium levels following cementitious relining. These were: (a) to use a blast furnace slag (BFS) cement containing 65% BFS and 35% OPC, (b) to dose sodium bicarbonate at 50mg/l to the supply water, and (c) to reduce the contact time between the water and cement mortar.

The most practical of these to implement is the BPS cement mortar which reduces pH levels to within EC directive limits within a few days in water with an alkalinity of 35mg/l and above. In waters with very low alkalinities (< 10mg/l) this cement produces pH levels between 0.5 and 1 unit lower than the pH levels observed following lining with OPC.

The sodium bicarbonate dosing is effective at reducing pH levels in very low alkalinity waters but would be more costly and difficult to implement.

Reducing contact times or increasing the flow through the main also reduces pH levels following lining. The reduction in contact time could be achieved by inducing a low flow at dead ends or linking dead ends together. These methods may be undesirable and costly to implement.

IV RESUME

A series of laboratory studies and field trials were carried out in order to find potential solutions to the problem of high pH levels following cement mortar lining. These resulted in the development of a new type of cement for relining, a method of dosing sodium bicarbonate to the supply water to increase it's alkalinity and methods to reduce the contact time in the main.

Copies of this report may be available as an Acrobat pdf download under the 'Pre 2000 Reports' heading on the DWI website.