Reinforced concrete or plastic pipe–it seems like a simple question, but in fact is not. The two materials have proponents and detractors in approximately equal numbers and there is little correlation of material to specific use, and size, by itself, is rarely a consideration.
Specifying reinforced concrete pipe over plastic for sanitary sewers, storm drains, culverts and irrigation is contingent on availability, personal preference, geographic location, tradition, logistics, traffic, ease of installation, reliability, conformance to existing standards, longevity and of course the bottom line–cost.
Both of the options—concrete and plastic—represent, in effect, the new generation of materials designed to fulfill the requirements of moving or diverting liquid substance, including sewage, from one location to another. The need for replacement of aging pipes and diversion channels is a reality; Modern improvements and standards will alleviate some shortcomings associated with older systems.
Current standards for environmental protection, engineered strength and manufacturing compliance dictate that a longer life span and increased reliability will become the new norm, regardless of material. Repair, compatibility issues and initial cost in some cases dictate one material over the other. But the more important considerations are durability, value, efficiency and performance.
In general terms, the candidates are both “qualified.”
Basis of Comparison
To be fair in comparing reinforced concrete pipe to plastic, some basis for comparison must be established. The following areas have merit:
Relative cost- Ease of installation
- Availability
- Adaptability to Conditions
- Conformance to Standards
- Expected Longevity
- Probability/Possibility of Failure
- Repair Options
- Environmental Factors
Debate concerning relative merits of each material sometimes reaches epic proportions, reflecting the perceptions and regulations in different regions. Multiple studies confirm that there are no easy answers, and governing agencies in various jurisdictions enact diverse requirements.
Does Use Determine Choice?
A recent study commissioned by the National Precast Concrete Association (NPCA) offers a fair comparison of the pros and cons of RCP (reinforced concrete pipe) and HDPE (high density polyethylene) in storm water drainage situations. It provides an interesting glimpse into the rationale and references for selection of a specific material in a specific application.
Various state highway department specifiers are cited in this specific application, including soil condition, depth of installation, volume of traffic (ADT) of the road above in cross drain installations, possible reactive or corrosive site and soil conditions, ground water, and pipe diameter.
The primary takeaway from the study is that each material possesses strengths and weaknesses in certain measure, and each must be properly installed in order to perform to its potential. Beyond that, it is emphasized that, while concrete has been used for a very long time and has proven characteristics as well as recognized deficiencies, plastic pipe is a relatively recent material and data is still being collected on its long-term performance.
RCP, it is pointed out, arrives on site at its full structural strength. It is a known quantity and installation is generally straightforward. Plastic pipe, on the other hand, must be site-assembled. Installation procedures are more demanding, structural integrity must be tested, and total costs may include a requirement for engineered backfill, on-site inspection and post-installation laser testing. In truth, the long-term durability of each material demands installation expertise. The fact remains that total cost includes more than the initial price of materials.
It is evident that a myriad conclusions can be reached, and many different requirements are imposed based on the same raw data, i.e., test results for two very different materials.
Know the Past, Look to the Future
Industry leaders point out that making judgments based on limited criteria can lead to skewed results. The perception that older concrete systems invariably have poor joints is misleading. History confirms that some of these joints were never intended to prevent soil or water infiltration, but rather to simply keep the pipe in line. In some cases, water infiltration was a desired characteristic, and it was only in the mid-twentieth century that water-tightness became a design criteria that facilitated use of high-pressure water mains.
With continuing development, the prospect exists that reinforced concrete will be used in certain instances while in other places and for other uses, plastic becomes the material of choice. While concrete is still the most prevalent construction material in use on the planet, other materials will continue to be developed to challenge that position. Specifying architects and engineers cannot afford to make judgments based on limited criteria and making informed decisions may become increasingly difficult.
One thing is certain: The future will continue to unfold. And construction materials will continue to be improved. That is a given.
Download our Concrete vs Plastic Infographic! With our infographic, you can quickly evaluate when, where and which pipe should be used on your projects.
