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In 2009, Kurimoto Plastics Co. won a JEC Asia Innovation Award (Building & Construction category) for an innovative fibreglass-reinforced plastic mortar (FRPM) pipe for sewage systems. The pipe was developed jointly with its partner, the National Institute for Rural Engineering (Japan).
(Published on February-March 2010 – JEC Magazine #55)
In recent years, Japan has experienced major problems with concrete sewage pipes corroded by the highly acid environment in sewage systems. As a result, the Japanese authorities are pressing for sewage system pipes with strong corrosion resistance and improved durability. Moreover, a demand for earthquakeresistant sewage systems emerged after the Great Hanshin Earthquake. Here is Kurimoto’s solution within this context.
Structure of FRPM pipes
FRPM pipes are made of a layer of resin mortar sandwiched between interior and exterior FRP layers. The whole system is formed and hardened into one body. The FRP layers consist of high-strength glass fibres circumferentially and axially wound using the filament winding process and hardened with thermosetting unsaturated polyester resin. The resin mortar is a polyester concrete made from selected fine sand hardened with unsaturated polyester resin. Its compressive strength is several times as high as an ordinary cement concrete. The interior and exterior FRP layers bear the bending stress of pipes, while the middle resin mortar layer keeps each FRP layer at a certain interval and transmits shearing force. Dynamically, this structure is ideal, offering excellent resistance to external pressures such as soil and truck loads, and to various internal pressures as well.
FRPM pipes have excellent corrosionresistance and durability properties, while concrete sewage pipes are corroded by the highly acid environment found in sewage systems. FRPM pipes have excellent earthquake-proof properties, and they do not crack even in case of a strong earthquake. These flexible pipes can adjust to ground displacement due to the flexibility and elasticity of joints. FRPM pipes are strong enough to withstand internal and external pressures. Due to their flexibility, the stress occurring in the ground is lower than for non-flexible pipes. Therefore, they don’t require any special foundation, regardless of ground depth. Superior dimensional precision at joints and an original rubber ring design guarantee outstanding water tightness, with no risk of leakage or external injuries. FRPM pipes also have a smooth inner surface with a velocity coefficient c=150 (Hazen-Williams formula) and a roughness coefficient n=0.010 (Manning formula). They exhibit excellent hydraulic characteristics. As compared with steel and concrete pipes, the smaller diameter of FRPM pipes can be used at the same flow volume and inclination.
FRPM pipes are specified in such standards as JSWAS K-2, JSWAS K-16 (Japan Sewage Works Association) and JIS A 5350 (Japanese Industrial Standards). Kurimoto developed rehabilitation methods for over-aged pipelines and tunnels as part of a joint research project with the National Institute for Rural Engineering.
These include the SIL method, which uses thin-walled FRPM pipes to rehabilitate over-aged pipelines, and the horseshoe-type pipe-in-tunnel construction method for the rehabilitation of over-aged tunnels. These methods allow fast rehabilitation while reducing costs.
FRPM pipe applications
FRPM pipes can replace steel and concrete pipes to lower costs and prolong the system’s life. They are used in the following applications:
Sewage: 200-3,000 mm in diameter; Jacking pipes : 150-1,650 mm in diameter
Water irrigation systems : 200-3,000 mm in diameter
Tube well casing and screen : 150-600 mm in diameter
Power and communication cable protection : 100-300 mm in diameter