You might be surprised to hear AmeriTex Pipe & Products LLC says “yes”. Why? Because the new documented requirements of SS 4216 are a safety win for the traveling public.
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Prior to 2022, plastic pipe (polyethylene or PP) was not formally approved for use in TXDoT projects and thus avoided the rigorous standards required by TXDoT. With the adoption of the Special Specification for Thermoplastic Pipe Culverts and Drains, it is no longer acceptable to simply substitute plastic pipe for reinforced concrete on a project. Now, a time-consuming design and installation process is required and includes a mandated, post-installation deflection test with the engineer present.
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Plastic pipe itself does not have load-bearing strength required for a storm drainage system to function both as a conduit AND a structure. Thus, it requires an “engineered installation” to meet the load-bearing requirements for a TxDOT project. The new spec, Special Specification 4216, provides a very detailed installation requirement for plastic pipe.
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Once the structural fill is completed, the contractor must wait 30 days prior to conducting a deflection test. This test must be completed in the presence of the design engineer. Only the engineer can authorize a deflection test prior to 30 days and would place the responsibility for the integrity of the installation on the engineer.
In addition to the deflection test in SS4216, what other responsibilities are given to the engineer? In ASTM D2321, the standard for installation of thermoplastic pipe, the design engineer has 25 responsibilities related to a proper installation. Under the TxDOT standard, the designer is tasked with specifying the structural and final backfill, ensuring the filter fabric is adequate if needed, specifying maximum fill depths, and is responsible for design of the trench protection system.
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After the pipe is installed, TxDOT requires that concrete, non-flammable, end treatments and wingwalls be used to protect the exposed end of the pipe. This is to protect the plastic pipe from both damage caused by potential impact to the flexible pipe, and to prevent possible fire damage due to the flammable nature of petroleum based products such as plastic.
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Understanding what is required in specifying and using plastic pipe is beneficial to us all. Mandating that the engineer be present when inspecting the final installation is a strong statement as to the absolute necessity for a proper plastic pipe installation. Plastic pipe is a conduit with very little strength. The load-bearing ability of a plastic pipe installation is up to 90% dependent on the installation. Proper design of the installation by the engineer, competent construction of the pipe system by the contractor, and accurate inspection of the installation are the three critical steps in infrastructure construction. TxDOT has recognized this, and we will all benefit from these safety measures.
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The plastic pipe producers claim in their press releases that the approval came about in part because TxDOT can lower costs using plastic pipe; however, when the costs of a proper plastic pipe installation are factored in, the total installation costs of RCP and PP are comparable.
When choosing the pipe for a TxDOT project, you are choosing between an engineered product Reinforced Concrete Pipe (RCP) & an engineered installation Polypropylene Pipe (PP).
Not only is reinforced concrete pipe a superior product for strength and durability and low lifecycle cost, the industry is a major factor in the prosperity of Texas with over $635.8 million in sales in 2018. The reinforced concrete pipe industry also contributes significantly to the broader state economy with these macroeconomic impacts:
