Geosynthetics February/March 2021 - 12

THE

GMA TECHLINE

answers all
Moderated by George R. Koerner

THE GEOSYNTHETIC
INSTITUTE ANSWERS
YOUR QUESTIONS
gmatechline@ifai.com
View past questions and answers at
https://tinyurl.com/GMATechline. Email
gmatechline@ifai.com anytime for fast,
free, direct technical answers.

LINER FOR CONCRETE WASHOUTS

TESTING PEC MATERIALS

Q: I am a specifications engineer for the
Roadway Design Division at the Oklahoma
Department of Transportation. I am in the
process of updating some of our stormwater
control standards. One of these is the
concrete washout system. In all or most of the
standards and specifications I've read online
from other state DOTs, not one seems to go
into detail as to the specification or minimum
criteria needed for the " plastic liner. " There
are phrases such as " minimum of 10 mil thick "
and " impermeable and leak-proof, " etc., but
I don't see anything that would refer to a
specification or other federal agency's (EPA,
ASTM, AASHTO, etc.) document.

Q: I have a question regarding product
testing. We have a product called PEC that
is a combination of nonwoven as a backing
sheet and knitted with polyester yarn in both
directions. To capture the true movement,
we remove the yarn of other direction when
conducting the test. You may find more details
from the attached file.

Can you help me with criteria you think DOTs
should follow when using a liner for concrete
washouts in their transportation projects?
A: Nice to hear from you, and I hope this
email finds you well. 10-mil " plastic sheet " is
covered under federal specifications by the
Defense Logistics Agency. The Commercial
Item Description is A-A-3174 Plastic Sheet,
Polyolefin, and different Type, Class, Grade and
Finishes are defined in the spec. In addition,
these materials are also covered by the
following ASTM specifications:
ASTM C171, Standard Specification for Sheet
Materials Used for Curing Concrete, and
ASTM D2103, Specification for Polyethylene
Film and Sheeting.
I hope this information helps.
P.S. Given the choice between clear and
black, the black generally lasts longer (i.e.,
more durable).

10

Geosynthetics | February March 2021

FYI, the yarn is having higher strength
compared to the nonwoven. The strength
and elongation are mainly contributed from
polyester yarn where their elongation of raw
yarn is less than 10%. So, we remove the yarn
of other direction when testing, as the effect
is negligible.
We would appreciate it if you could provide
your opinion and guidance about this practice
used during testing.
A: This is not so simple. By cutting the principal
yarns free of the confining cross machine
webbing, one stops a very nasty artifact of
the wide width tensile (WWT) test, which
is unique to testing PEC materials. Namely,
the webbing knifing through the principal
direction yarns and prematurely breaking the
PEC material is far lower than the anticipated
ultimate tensile strength (from single yarn
testing and Pearce equation extrapolation).
Unfortunately, this phenomenon is real, and I
have seen it happen in the field. I do not think
you have the liberty to remove the webbing
during setup of the WWT test without express
written consent of the engineer-owner.
WWT are performance tests for design, not
index tests for saturated process control or
conformance use.
https://www.tinyurl.com/GMATechline
Geosynthetics February/March 2021

Table of Contents for the Digital Edition of Geosynthetics February/March 2021
