Reinforced concrete pipe (RCP) is the strongest pipe material for storm sewers and culverts. Flexible pipe doesn’t come close.
RCP provides the primary structure for storm sewer and culvert installations. Flexible pipelines, on the other hand, get most of their strength from compacted granular embedment materials.
RCP lasts a long time.
We know this because concrete culverts and storm sewers have been around for well over 100 years. RCP’s factory-made and tested primary structure gives design engineers confidence it will last a long time.
Despite unsubstantiated longevity claims, plastic pipe simply hasn’t been around long enough to know for certain how long it will last. Plastic pipe’s field-made primary aggregate-soil structure is affected by the realities of challenging construction conditions and inconsistent adherence to deflection testing specifications.
RCP’s built-in strength means it’s the only pipe material able to withstand heavy vehicle traffic in shallow storm sewer and culvert installations.
For example, Minnesota DOT specifications stipulate that RCP can be safely installed under mainline pavements with as little as 1.5 feet of cover. Conversely, for plastic pipe under mainline roads, MnDOT acknowledges its structural limitations by requiring a minimum of 3 feet of cover for polypropylene and HDPE.
Professional civil engineers know that designer liability is a big deal, so selecting pipe materials best suited for storm sewers and culverts will help to minimize engineer liability.
Concrete pipe’s built-in, plant-tested primary structure reduces the design engineer’s professional liability because concrete pipe is much less prone to structural failure/collapse than flexible pipe. It’s one of the main reasons why concrete pipe is the number 1 choice for liability-weary engineers.
Some claim that concrete pipe is more difficult to install because it’s heavy. The reality: concrete pipe’s inherently large mass is, ironically, the reason concrete pipe is easier to install properly:
Plastic pipe is not easier to install properly. While it’s true plastic pipe’s inherent light weight allows construction workers to move small diameter plastic pipe by hand, plastic pipe’s light weight is, ironically, detrimental to proper installation. That’s because plastic’s light weight makes it difficult for contractors to maintain line and grade as the critical structural granular embedment is compacted in thin lifts around the pipe.
Plastic pipe is prone to movement while embedment materials are compacted around the pipe. This often makes maintaining line and grade ore difficult with plastic pipe.
Government agencies and business are increasingly considering the environmental benefits of infrastructure products – including storm sewer and culvert pipe materials.
When designing infrastructure, civil engineers should specify materials and products that are the safest and highest quality, perform as intended for the design life of the project, and have the best overall value. Sustainable and resilient concrete pipe satisfies these criteria.
Don’t be fooled by misinformation: despite its substantial mass, concrete pipe is not difficult to install.
In fact, concrete’s large mass makes it easier to install properly. Once the utility contractor installs a concrete pipe section in the bedding, it stays put while haunch and backfill materials are compacted around it. This means concrete pipe gives you better line and grade control compared to lighter weight flexible pipe products.
Concrete pipe doesn’t burn.
High Density Polyethylene Pipe (HDPE) is flammable. This makes it unsuitable for culverts and storm sewers where the possibility of fire exists. Road culverts and routine burning of rural ditches come to mind. Plastic culverts can, and do, burn throughout their entire length when exposed to flame from a burning ditch, with road collapse a common result.
According to MnDOT’s plastic pipe tech memo:
“Plastic pipe should not be used where there is a likelihood of exposure to fire without fire mitigation. Fire mitigation alternatives include concrete slope paving, concrete headwall, and concrete aprons. Use of fire mitigation alternatives requires a design detail in the plan and a special provision indicating additional cost of fire mitigation is included in the contract unit price of the pipe pay item.“
Concrete pipe joints are easy to install in the field. Whether it’s a gasketed joint (MnDOT 3006 spec) or a tied tongue and groove joint (MnDOT 3000 spec) traditional used for rural culverts, utility contractors routinely install these joints with minimal fuss.
Plastic pipe joints are prone to leakage when the pipes deflect beyond commonly acceptable deflection limits.
Concrete pipe’s inherent mass means flotation is a non-issue.
Plastic pipe, on the other hand, is susceptible to flotation when the water table gets too high, and numerous examples exist where buoyancy forces have pushed plastic culverts and storm sewers to the surface, sometimes ruining expensive pavements and shutting down roads for expensive repairs.
MnDOT’s Plastic Pipe Tech Memo includes a table listing minimum cover requirements, with cover minimums increasing with diameter. Design engineers should follow this guidance to help minimize plastic pipe buoyancy risk.
Minnesota’s concrete pipe manufacturing industry employees nearly 1,000 people in good paying factory jobs and professional salaried positions. Hundreds of employees in supporting industries also benefit.
The flexible pipe industry employees far fewer Minnesota workers due to most of its manufacturing located outside of Minnesota.
By specifying concrete pipe, you support Minnesota’s economy.