State of Technology Report for Force Main Rehabilitation, Final ...

3.4.2.2 Reinforced Mortar Linings. A modification of cement mortar lining is to incorporate some
steel reinforcement in the mix to accommodate structural needs. One such modification, ferrocement,
uses fine wire mesh to reinforce the mortar mix, enhancing its tensile strength and crack resistance.
Figure 3-8 illustrates the typical stress-strain performance of a ferrocement composite. The crack
resistance of the composite is dependent on the relative volume of mesh reinforcement to mix.
Figure 3-8. Typical Stress Strain Curve for Ferrocement (Newman, 2000)
This concept was used for the design of a 50-inch (1,250-mm) diameter asbestos cement sewer force main
in Tel Aviv, Israel (Thomson et al., 2006). The 50-inch (1,250-mm) force main experienced a
catastrophic failure. Investigation found that a groove had been eroded down the invert of the main.
Stress concentrations caused by the groove placed the main in danger of future failure. The main
operated under high pressure (150 psi [10.3 bar]) and could not be sliplined. The only feasible method of
rehabilitation was to build a fully structural liner inside the existing main. A thin hybrid liner, less than
2.36 inches (60 mm) thick, was designed incorporating reinforced concrete covered by a two-mesh
ferrocement layer. Polymer fibers were also incorporated into the mortar mix to enhance crack resistance.
An epoxy liner was specified for further corrosion protection, but was not deemed necessary.
3.4.2.3 Epoxy Spray-on Linings. Potable water in the UK comes predominantly from surface water,
could be characterized as soft water, and is aggressive to cement mortar linings. Consequently, back in
the 1970s and 1980s, water main lining contractors in the UK began to research for alternative materials.
The WRc (formerly known as the Water Research Center), in conjunction with one epoxy vendor (E.
Wood Ltd.), developed an epoxy material and delivery system that could meet the strict UK water quality
standards. Within a very short time period, epoxy lining completely replaced cement mortar lining. With
a much shorter cure period of 16 hours, water mains can be returned to service within 36 hours. The
following epoxy coating systems are approved by the Drinking Water Inspectorate (DWI) in the UK:
• 3M E. Wood Ltd – Scotchkote 162 PWX and Geopox GX 014
• Leighs Paints – Pipegard P300
• Subterra – ELC 173/90
The first field trial of epoxy lining in the US, co-sponsored by the American Water Works Research
Foundation (AWWARF, now known as Water Research Foundation), WRc, and the epoxy contractor,
was in 1993 in Chester, PA. Epoxy lining usage has not taken off in the US as it did in the UK. There
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