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| Flexible membrane materials |
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Pages in this section include:
The range of flexible membrane liners is extremely wide with new
products appearing regularly on the market. A range of common materials
and those identified during the seepage remediation project are described
below, although this list is by no means exhaustive:
- PVC - Polyvinyl chloride (PVC) contains
plasticisers that enable it to become a soft flexible structure
suitable to be used to line channels. However, PVC is susceptible
to contact with various chemicals and exposure to UV radiation,
which causes the material to become brittle. Its susceptibility
to UV radiation means that some form of cover is usually required.
This is the most widely used material.
- HDPE - High-density polyethylene
(HDPE) is similar to the material used in black polyethylene
pipes. It has a broad chemical resistance and excellent UV resistance,
but has a lack of flexibility and can develop brittle stress
cracking if not properly formulated. Since HDPE is a very stiff
material, it cannot be prefabricated into panels. Instead it
is delivered to the site in rolls up to 6m wide (9m in the United
States) and all the seaming is done on-site.
- VLDPE and LLDPE -
Very low-density polyethylene (VLDPE) and linear low-density
polyethylene (LLDPE) were introduced to address the shortcomings
of HDPE in terms of flexibility. These are less crystalline forms
of polyethylene which result in increased flexibility and a membrane
less conducive to brittle stress cracking. However, some degree
of chemical and UV exposure resistance is sacrificed as a result,
and these materials are generally not recommended for exposed
applications, although UV-stabilised products are available.
While more flexible than HDPE, these LDPE materials are still
not as flexible as PVC for ease in handling during installation.
- FPP - Flexible polypropylene (FPP)
is produced in both unreinforced (PPU) and reinforced (PPR) form
to provide a choice in terms of tensile behaviour. The unreinforced
membrane is typically very flexible with excellent elongation
capabilities, but the reinforced membrane has low thermal expansion
properties. FPP has quite a good resistance to common chemical
exposures, excellent mechanical properties and excellent UV performance
when the polymer is properly stabilised. This is sometimes referred
to as FPA (flexible polypropylene alloy).
- CSPE - Chlorosulfonated polyethylene
(CSPE) or Hypalon is based on the use of chlorine and sulfur
to modify and soften the polyethylene structure in order to make
the material more flexible to facilitate seaming. CSPE membranes
are scrim-reinforced for strength and dimensional stability.
CSPE provides very good chemical resistance, excellent UV exposure
performance and is not subject to cracking and embrittlement
with long-term exposure.
- CPER - Reinforced chlorinated polyethylene
(CPER) is a product similar to CSPE
- EIA - Ethylene interpolymer alloy
(EIA) is an alloy of PVC resin with a special ethylene interpolymer
that results in a flexible plastic-free material. EIA geomembranes
maintain the advantages of PVC but have a high degree of durability
and chemical resistance, especially in relation to hydrocarbons
and extreme temperatures. Membranes are typically fabricated
with a high-strength reinforcing scrim. This product is typically
used for speciality applications and is quite expensive.
- EPDM and butyl
rubber - Butyl rubber is a weather resistant, flexible,
high-elongation and durable membrane. EPDM (ethylene propylene
diene monomer) was developed from butyl rubber and is installed
as liners, caps and covers in environmental containment applications
worldwide, but is relatively new to the channel remediation
industry. It exhibits excellent elongation characteristics
and does not require a soil cover. It exhibits high tensile
strength and excellent resistance to punctures, UV radiation,
weathering and microbial attack.
- DamSeal - The DamSeal concept involves
the in-situ application of a mineral-filled, rubberised bitumen
emulsion to a geotextile fabric liner. The DamSeal emulsion impregnates
the geotextile and forms a waterproof lining for channel floors
and batters. Liquid Boot is a similar product.
- Asphalt - Asphalt is used in several
different lining methods. Thinner asphalt layers are generally
regarded as a flexible membrane liner. Types of flexible membrane
asphalt liners include sprayed-in-place asphalt, and hot-rolled
asphalt, and polymer-modified asphalt roll membranes.
- Geosynthetic clay liner - Geosynthetic
clay liners (GCL) consist of clay material, usually bentonite,
woven into the middle of two geotextile layers. This lining mechanism
uses the beneficial properties of bentonite, and the material
to which it is bonded holds the bentonite in place. GCLs require
at least 300m cover of soil ballast over the GCL to provide sufficient
force to confine the expansion of the bentonite core layer.
- Polyurethane coated geotextile -
Similar to the DamSeal concept, but with the application of a
UV-resistant 1.5mm thick polyurethane cover over a geotextile
fabric.
- On-site fabricated plastic - On-site
fabricated plastic is an emerging technology that is not yet
commercially available. The technology will enable production
of a continuous plastic film, without the need for seams. The
manufacturer anticipates that the product will be of appropriate
strength, competitively priced compared to 0.75mm HDPE, and require
less subgrade preparation than standard flexible plastic sheeting.
As a guide, attribute ratings of some of the more common membranes
are provided in Table 1 Geomembrane attribute ratings below.
Further product information including advantages, disadvantages,
application
issues
and properties of some materials
is detailed in Table 2 Geomembrane options below.
Table 1 Geomembrane attribute
ratings
|
| Attribute |
PVC |
HDPE |
VLDPE |
CSPE |
FPP |
Sprayed bitumen |
GCL |
|
|
General chemical exposure
|
Excellent
|
Excellent
|
Good
|
Excellent - when cured
|
Excellent
|
Fair
|
Fair
|
|
Hydrocarbon exposure
|
Fair
|
Good
|
Good
|
Good - when cured
|
Good
|
Poor
|
Poor
|
|
Weathering (UV exposure)
|
Fair
|
Excellent
|
Fair
|
Excellent - when cured
|
Good
|
Fair
|
Poor
|
|
Thermal stability
|
Good
|
High coeff. of thermal expansion
|
High coeff. of thermal expansion
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Excellent - when reinforced
|
Good-excellent when reinforced
|
Poor
|
Good
|
|
Tensile performance
|
Good
|
Good
|
Good
|
Good
|
Good
|
Poor
|
Good
|
|
Uni-axial elongation performance
|
Excellent
|
Excellent
|
Excellent
|
Excellent
|
Excellent
|
Poor
|
Fair
|
|
Multi-axial elongation performance
|
Excellent
|
Poor
|
Excellent
|
Excellent
|
Excellent
|
Fair
|
Fair
|
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Puncture performance
|
Excellent
|
Fair
|
Excellent
|
Good
|
Good
|
Fair
|
Good
|
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Abrasion resistance
|
Excellent
|
Fair
|
Fair
|
Fair
|
Good
|
Fair
|
Good
|
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Seaming methods
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Heat or solvent bonding - good
|
Heat - Excellent
|
Heat - Excellent
|
Heat or solvent bonding - good
|
Heat - Excellent
|
Sprayed Laps
|
Laps only
|
|
Repair in service
|
Good
|
Good
|
Good
|
Poor - requires adhesives
|
Good
|
Good
|
NA
|
|
Stress cracking
|
Does not occur
|
Fair
|
Good
|
Good
|
Does not occur
|
NA
|
Does not occur
|
|
Flexibility in Detailing
|
Excellent
|
Fair
|
Good
|
Good
|
Good
|
Good
|
NA
|
|
Roll cost
|
Medium
|
Low
|
Low -Medium
|
High
|
Medium
|
Low
|
Medium
|
|
Table 2 Geomembrane options
|
| Material |
Advantages |
Disadvantages |
Application |
Properties |
|
|
PVC
|
Resists acids and bases
Flexible
Most workable of all geomembranes
Offers superior puncture resistance
|
Susceptible to damage from burrowing freshwater life
Susceptible to stiffness with aging
Becomes brittle at 0¬C, making it difficult to handle
in cold seasons
Not UV resistant, susceptible to damage from the sun
|
Where off site fabrication is possible.
Surface preparation is less than ideal
To increase the service life and reduce installation
problems a thicker liner of 0.51mm (0.25mm originally)
Doubling the thickness increases construction cost
by 15%.
|
Tensile strength 140 kg/cm2
Ultimate elongation 300%
Available gauges 0.2-0.85mm
Available widths 1.2-19m
Joining by heat, solvent or adhesive
Density 1.25
|
|
HDPE
|
Cost-effective over large areas
|
Inflexible
Requires specialist welding equipment
Requires well-prepared surfaces
Low resistance to vertical stress
|
Cost-effective over large areas
Industry standards for the installation of HDPE liners
have been released by the International Association of
Geosynthetic Installers (IAGI)
Most common material used
|
Excellent UV damage resistance
Wide range of chemical resistance
Joining by welding
Available gauges 0.4mm to >2mm
Available widths <6m
|
|
FPP
|
Flexible
|
Some problems with fuel immersion
Requires specialist welding equipment
|
Where long life in harsh conditions is required
Especially suited to situations where soil movement
is expected
|
Good UV damage resistance
Wide range of chemical resistance
|
|
VLDPE and LLDPE
|
Puncture resistance has improved
Resistant to biological deterioration and chemical
attack
Resistant to root penetration
Becomes brittle at 15¬C rather than zero, allowing
installation in cold season
|
Very susceptible to sun damage
|
Short-term applications < 2years if not covered
Long-term application if covered and installed correctly >50years,
general expectation of 20-30 years.
Has been applied in Australia as woven polyethylene
at 0.2mm thickness generally.
|
Tensile strength 126 kg/cm2
Ultimate elongation 500%, minimised for woven PE.
Available gauges 0.15-0.5mm
Available widths 5.0-12m
Joining by heat, tape or adhesive
Density 1.25
|
|
GCL
|
High puncture resistance
High friction capabilities with adjacent soils
Reduce or replaces clay liner component of a composite
liners
|
Generally more expensive
Requires protection from exposure damage
|
Bentonite is placed in between two geomembranes which
are then stitched together to from a geotextile
Applied the same as other geomembranes
|
Refer to Geosynthetic clay liners
|
|
Butyl
and EPDM
|
Suitable for relining old concrete channels
Good weathering properties
Flexibility, toughness and good ageing properties
Resistance to most chemicals and abrasion
Can withstand extreme temperature changes
Resistant to sun damage
EPDM has better properties than butyl rubber
|
Requires protection from mechanical damage and vandalism
if exposed
Relatively high cost
Can suffer from ozone depletion and poor shrinkage
Service life dependent on careful and consistent fabrication
which is difficult for large projects
|
Special attention required to ensure adequate bonding
and anchoring
Has been in service for 10 years both covered and uncovered
with essentially no change
Can be reinforced with nylon
Can be used to meet specific service requirements that
are not possible with less costly membrane materials
|
Tensile strength 84 kg/cm2
Ultimate elongation 300%
Available gauges 0.8-3.0mm
Available widths 8.5-14m
Joining by adhesive
Density 1.25
|
|
References: Hickey (1971), Morrison and Starbuck
(1984), Kraatz (1977), Sally (1965), Sinclair Knight Merz (1998),
pers comm Alan Liebeck (2000)
| Related
pages |
 |
Flexible membrane
lining techniques
Covered liners
High-density
polyethylene (0.75mm)
Geosynthetic
clay liners
Exposed liners
High-density
polyethylene (2mm exposed)
High-density
polyethylene (1.5mm exposed)
Linear
low-density PE and very low-density PE
(1.5mm)
DamSeal
Unreinforced
polypropylene (1mm)
Unreinforced
polypropylene (0.75mm)
Reinforced
polypropylene (1.1mm)
Butyl
rubber
Asphalt |
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