Extrusion welding HDPE liner with LLDPE

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Welding HDPE with LLDPE? Woven geopipe?

Questions and answers from the GMA Techline

I have a project where the contractor is insisting that welding a 2mm single-side textured HDPE geomembrane to a concrete structure (HDPE polylock embedded) with LLDPE rods is not a compromise in the quality of the weld and therefore no different from welding with HDPE rods.

I disagree. I also have a concern about the bond strength because the temperature needed to weld the HDPE is higher than the LLDPE, so the integrity of the materials during the welding process will be compromised. Ipso facto, I am recommending that the contractor and project owner not accept this practice.

Am I right or am I off my rocker?

Ray | USA

Ray,

I agree with you that welding HDPE to HDPE should not be done with LLDPE rod. That said, the HDPE imbedded in the concrete is indeed HDPE at a formulated density of about 0.943–0.946 g/cc whereas the HDPE geomembrane is about 0.941 to 0.943 g/cc. (The HDPE geomembrane is actually made from MDPE resin and only with the additives does its density go over 0.941g/cc, which ASTM then designates as HDPE.) This slight mismatch in density means that selection of the welding rod’s density is important and the target value should be as close as possible to 0.943 g/cc.

Bob Koerner | GMA Techline