The Cement Mortar Lining Solution
Unlined cast-iron pipe was the material choice for water distribution systems from the beginning of this century to the mid-1960s. Although alternative products are increasingly being used, cast iron water mains account for the majority of pipe in most distribution systems in municipalities in Ontario and across Canada. If their structural integrity is adequate, breaks should not occur, but their carrying capacity can be severely reduced due to a variety of factors.
One major factor is the corrosion of steel, which is caused by the electrochemical process that requires the flow of an electric current as well as one or more chemical processes. As the corrosion process occurs, the interior wall of the pipe will develop pits as material is lost, resulting in the formation of tubercules. This corroded material, in combination with mineral deposits, is known as encrustation and tuberculation. Pipe deterioration will vary due to existing factors (in some cases necessitating complete replacement) but aggressive encrustation will force the issue of infrastructure renewal.
Replacing the iron piping system is not financially realistic. Thus, rehabilitation to improve water quality with the use of various trenchless technology techniques has become a cost-effective alternative.
Common Issues Arising from Aging Water Distribution Systems
Based on the fact that the structural integrity of the existing pipe is adequate, problems that can be corrected include:
- a severe reduction in pipe hydraulic carrying capacity,
- aggressive corrosive build up resulting in encrustation and tuberculation,
- increased pumping and maintenance costs,
- reduction in water quality,
- increased bacteriological growth within the distribution system,
- leakage water loss and infiltration,
- existence of high lead content due to old joint corrosion,
- a chlorine residual deficiency,
- decline in pipe material performance resulting in: unpleasant taste, offensive odour, turbidity and poor colour.
The Cement Mortar Lining Solution
The method that has been developed to counteract a number of problems is cement mortar lining. The water mains are cleaned by removing all turbercules and then a cement mortar lining is applied to the interior pipe walls to prevent the formation of new tubercules. This method has salvaged existing pipe by internally rehabilitating unlined cast-iron pipe in older, in-place pipelines.
The chemical nature of the cement itself maintains a zone of alkalinity at the mortar/metal interface. This prevents corrosion of the pipe wall since the moisture contained within the pores of the cement mortar has been raised in pH to a level well beyond that which will permit corrosion in ferrous metals.
Cement mortar also has the ability to self heal and seal cracks, which may occur during initial setting shrinkage. This process is known as “autogenous healing”. It is generally considered to be a carbonation process in which the free lime on the cement hydrates with the cement grains.
In practice these processes have been shown to effectively protect water mains from subsequent corrosion and leakage for many decades.
Advantages of Cleaning and Cement Mortar Lining
Advantages of this method compared to traditional “open cut” replacement are:
- the cement mortar lining creates a zone of high pH, a chemical shield that permanently prevents rust from forming between the lining and the pipe,
- a cement mortar lining offers high compression strength, creating an “arch action” which holds the lining in tight contact with the pipe wall,
- it can be applied to pipeline materials such as cast iron, steel or ductile iron,
- the pipeline can be rehabilitated while in place,
- the rehabilitated areas are supplied with water and fire protection via a temporary by-pass system. Disruption of water service to residents is minimal,
- a minimal disruption of services and traffic because small excavation pits are used to access the pipe,
- individual water services do not have to be excavated,
- the method facilitates an overall cleanliness of the project, as opposed to the excavation of entire road sections,
substantial economic savings for the municipality can be realized.
The Proven Protection
Benefits After Cleaning and Cement Mortar Lining:
- increased hydraulic carrying capacity in rehabilitated system,
- improved fire flow from hydrants, which can reduce insurance rates,
- reduced pumping costs,
- savings in the cost of energy to pump water,
- elimination of red (rusty) water,
- extension of water main life,
- curtailing of coliform bacteria regrowth,
- savings in the cost of chemical treatment,
- stabilization of chlorine residuals,
- clean, clear water free of odour, poor colour, unpleasant taste and turbidity,
- clean better tasting water,
- makes previously lost water available for sale,
- reduction in danger of undermined pavement,
- resistance to chemical attack,
- encasement of lead joints to reduce threat to water safety.