Geomembrane specifications from various sources are presented as they are obtained
- by the regulating agency in each country, by national institutes, by
trade association, and any other nationally recognized group. We also present
specifications generated by industry-recognized leaders familiar with field
problems and construction quality assurance practices, with brief explanations
of the differences compared to the conventional specifications. It must
be recognized that these latter specifications are likely more advanced
and may not be accepted by regulating agencies.
We
acknowledge the fact that all materials are not yet represented, but
we are working to make the list complete. (Items underlined are linked.)
|
HDPE
high density polyethylene |
|
CSPE |
PVC
polyvinyl chloride |
|
LLDPE
linear low density polyethylene |
mPE |
|
PP
polypropylene |
HDPE
HDPE
resins are made by many manufacturers using different manufacturing
processes. Each adds different comonomers to the HDPE to modify its
molecular structure, and different additive packages to protect against
oxidation and UV radiation, thus there are many HDPEs. However, all
their conventional mechanical and physical properties are very similar.
They differ only in one respect - their resistance to stress cracking.
And this difference can be a factor of 500 to 1000. Therefore, this
is the single-most important parameter that must be specified. The AO
and UV additives are consumed during service, but they are present in
sufficient quantities so that, without abuse, the geomembranes will
last far longer than is practically required.
Properly
designed, manufactured, specified, installed, CQA'd, tested, and operated,
an HDPE geomembrane should have a lifetime of a few hundred years. Four
sets of HDPE specifications are presented:
Geosynthetic
Research Institute, GRI GM13, Index
Revision 2, generated in 1997.
- Smooth
sheet, English units
- Smooth
sheet, SI units
- Textured
sheet, English units
- Textured
sheet, SI units
GRI
GM13
Note
that this standard was developed strictly for quality control purposes,
and was not intended to be a material specification, although it
undoubtedly serves as one. Note especially the frequency of QC testing
- it depends on the parameter being measured - there is no requirement
to test all properties at the same frequency. The same consideration
should be extended to CQA conformance testing specifications. There
are no seam specifications in this standard.
International
Association of Geosynthetics Installers (2000) (USA).
- Smooth
sheet
- Seams
IAGI
This specification was first published in April 2000. They
use GRI GM13 specifications for the material. However, it has
its own specifications for seams.
Bundesanstalt
fur Materialforschung und - prufung (BAM) (1992/English - 1999/German).
I-CORP
INTERNATIONAL, Inc. (2000) (USA)
- Smooth
sheet
- Textured
sheet
- Seams
I-CORP
This specification was developed after years of failure analysis and on-site
CQA. Its major differences are in requirements for stress cracking resistance
in both geomembrane and seams. Strength parameters are not required for seams
since the low cross sectional area of the geomembrane tab prevents adequate
challenge to seam bond strength if bond efficiency exceeds only 10 to 25%
depending on geomembrane thickness. The geomembrane will always fail first.
Note
that the conventionally used NSF 54 specification is no longer applicable
since it was withdrawn in July 1997.

TEXTURED
HDPE GEOMEMBRANE
Increased
friction on HDPE geomembrane is generated in two ways - by random texturing
and by specifically designed surface profiles.
The
random texturing is created in one of two ways - integrally with
the geomembrane manufacturing or as a secondary process. In the former,
nitrogen gas is pumped into the PE in the outside layer extruders
of a three layer coextrusion system. As the geomembrane exits the
extruder and the external pressure is reduced the gas explodes to
the surface thereby roughening it like a turbulent ocean. The minimum
thickness of the resulting sheet is essentially controlled by the
thickness of the core extruded layer. In the secondary process, pulverized
PE (usually LDPE) is dropped onto the hot surface of just-extruded
or reheated geomembrane. The lower melting point of the LDPE results
in it melting and welding to the surface of the HDPE as a small blob.
Alternatively, small droplets of molten PE can be "sprayed" on
to the surface of the HDPE. The minimum thickness of these geomembranes
remains the same as if the material were smooth sheet.
With
secondary process texturing, a balance between sufficient bonding
to minimize the ability to scrape off the texturing and over-welding
that might induce residual stresses and susceptibility to stress
cracking adjacent to the weld is required. In primary process texturing,
the potential for stress cracking is reduced. The texture cannot
be removed, but minimum thickness is much less predictable.
In
structured surfaces the hot extruded geomembrane is squeezed between
calendering rolls, one or both of which are profiled to produce the
surface geometry as the geomembrane thickness is also established.
Such profiles cannot be scraped off, there is no welding associated
with them, residual stresses can be eliminated by careful design,
texturing is consistent over the surface of the geomembrane, and
structures can be designed for optimum interaction with different
adjacent materials. Thus, all textures/structures are not equal.
Velcro-type hairs will interact better with a nonwoven geotextile
than will a smoother structure, for instance. Some will stick better
to clay, others to geotextile. Some are designed as a compromise
for every possible mating surface - geotextile, clay, sand.
Some
are textured on one side, some on both sides. However, in the finished
lining system they should be "stickier" on the bottom than
on the top in order to keep a permanent stress out of the geomembrane.
If sliding on a slope is going to occur, it is generally better that
sliding occur on top of the liner so the liner remains intact. The
required veneer stability in the soil above a smooth liner can be
obtained with a woven geotextile or a geogrid.

LLDPE
Linear
low density polyethylene (LLDPE) is a linear microstructure version
of the LDPE commonly used for packaging and in construction as a
vapor barrier. LDPE is
amorphous (noncrystalline) while LLDPE is about 5% crystalline. In comparison,
HDPE geomembranes are about 50% crystalline. LLDPE's do not quite have the
chemical resistance of HDPE, nor do they have the tensile strength, but they
do have better elongation performance and stress cracking resistance. Hence
their preferred use in landfill caps, for instance, where they may be subjected
to deformation due to differential settlement of the waste - they will conform
to the new profile without a significant influence as the long term performance
of the geomembrane.
Two
standards for LLDPE are the new (2000) GRI
GM17 specification, and
a manufacturer's typical specification. Also included is specification
for mPE, a new high strength, high
ductility LLDPE made using a manufactures metallocene catalyst technology.
Note
that LLDPE geomembranes are made with resins with a fairly wide range
of density - higher density products have properties approaching
those of MDPE/HDPE,
while lower density products have properties more approaching those of the
old VLDPE. The major difference is in the multiaxial strain at burst. But also
associated with
these differences are differences in the method of applying the pressure and
measuring the strain in the multiaxial burst test. Whether the pressure is
increased and the strain
is measured continuously or incrementally can significantly affect the results.
After much initial discussion GRI GM17 was written to encompass the full range
of LLDPEs.

PP
At
present PP geomembrane resin is made by only one manufacturer, Montell,
although others are now looking at it. There are only two or three
slightly different modifications to the basic resin that produce
geomembranes with slightly different properties, predominantly in
the melting point. PP geomembranes contain similar AO and UV additives
to HDPE.
When
PP is reinforced, the properties become a function of the type of
reinforcement. Typical specifications for a reinforced material are
presented. However, we recommend
that you discuss actual properties with the different manufacturers.
BASELL
SPECIFICATIONS (UNREINFORCED)
|
Property |
Test
Method |
40
mil |
60
mil |
|
|
|
|
|
|
Minimum
Thickness (mil) |
|
36 |
54 |
|
Carbon
Black Content (%) |
|
2.75 ± 0.5 |
2.75 ± 0.5 |
|
Tensile
Properties: (Avg. MD & TD) |
ASTM
D638 Type IV, 20 ipm NSF 54 modified |
|
|
|
|
Strength
at Break (lb./in) |
|
65 |
95 |
|
|
Elongation
at Break (%) |
(2.5" gauge
length) |
>500 |
>500 |
|
Tear
Resistance (lb.) |
|
12 |
18 |
|
Puncture
Resistance (lb.) |
FTMS
101, Method 2065 or D4833 |
38 |
45 |
|
Dimensional
Stability (% change) |
ASTM
D1204 (1 hr. at 100° C) |
± 2 |
± 2 |
TYPICAL
SPECIFICATIONS
(SINGLE
PLY) REINFORCED PP GEOMEMBRANE 1 SPECIFICATIONS (TYPICAL)
| PARAMETER |
TEST
MODE |
VALUE |
| Thickness |
ASTM
D5199 |
± 10% |
| Density |
ASTM
D1505 |
< 0.090
g/cm3 |
| Carbon
content (1.) |
ASTM
D1603 |
2.5-3.0% |
| Carbon
dispersion |
ASTM
D5596 |
Category
1 or 2 |
| Tensile
stress at break (2.) |
ASTM
D638 (IV) |
> 18
MPa |
| Tensile
elongation at break (2.) |
ASTM
D638 (IV) |
> 600% |
| Puncture
resistance |
FTMS
101C (2065) |
> 150
N/mm |
| Tear
resistance |
ASTM
D1204 |
|
| Dimensional
stability |
ASTM
D1204 |
± 2% |
1.
black material only
2. gage length 50 mm, tested at 50 mm/min
PVC
PVC
resins are made by several manufacturers, but the performance of
a geomembrane is controlled more by the plasticizer (approx 30%)
that is added than the resin itself. The plasticizer gives the geomembrane
its flexibility. Liquid plasticizers can be volatilized or extracted
out of the geomembrane, hence the requirement that they be covered.
However, the PVC can be plasticized or alloyed with another polymer
(KEE, ketone ethylene ester) to form ethylene interpolymer alloy,
known by several different trade names. Such geomembranes have good
weathering performance.
See
PVC Geomembrane Institute's (PGI) 1104
specification for conventional PVC geomembrane.