COMPOSITE
MANHOLE
COVERS
The Next Step in Manhole Protection
By Eric Dupré
I
f you’ve spent any time working
in the infrastructure industry, material names such as PVC, HDPE,
resins, CIPP, epoxy and fiberglass
are common. So why has just about
every structure in our sewer system
been re-engineered and designed using these types of materials except
for the manhole cover?
I would assume the old cliché “If it
ain’t broke, don’t fix it” would be one
of the first reasons, but our manholes
are broke and we do need to fix them.
In fact, in 2008, an article in Trenchless Technology reported that the
United States had nearly 20 million manholes, with approximately half installed before
1960 and are nearing or
exceeding their design
life, according to the
U.S. Environmental
Protection Agency.
Another contributing factor slowing the use of new
materials in the
manhole market
is a lack of a viable, commercialized product available in the United
States. Today, however, there are alternatives — notably
composite, non-metallic manhole covers.
Background
The first U.S. patent for a
manhole cover was issued to
Henry Smith Jr. in 1870 — almost
150 years ago —and that old technol38
TRENCHLESS TECHNOLOGY
August 2015
ogy is still what we most commonly
use today. If you thought about scope
of the advancements that have been
made since 1870, you would conclude
that there would be more options
Corrosion is a major cause of
failure of metal products used
in sewer systems, so material
selection becomes extremely
critical when designing
systems that can withstand
such harsh environments.
available. Oftentimes, it’s the simplest
things that are overlooked. However,
the moment we stop improving, is the
moment we stop moving forward.
So, what are the issues with the manhole covers that have been in use for the
last century and a half? Here’s a brief list:
• Corrosion/ Seizing
• Theft
• Weight/Injury
• Inflow leaks
• Lower quality
• High Carbon Foot Print
• Limited Options
Addressing Concerns
Corrosion is a major cause of
failure of metal products used
in sewer systems, so material selection becomes
extremely critical when
designing systems that
can withstand such
harsh environments.
The majority of all
manhole covers are
made from cast-iron
and when exposed
to corrosive sewer
environments that
contain H2S gases,
the cast-iron will
deteriorate rapidly.
This can cause the
ring and cover to seize,
making difficult — if not
impossible — to open
the cover without breaking
it open with a sledge hammer.This can destroy the cover,
which then requires replacement
of the same cast-iron again — somewhat of a vicious cycle.
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The world is facing one of the largest pandemics of metal theft in our
history due to the demand for metal
and recycled metals. By using materials that do not have a scrap metal
value would deter millions of dollars
of theft. Often the replacement cost
isn’t the biggest or costliest liability,
it’s the safety risk of having an exposed open manhole to the public.
The weight of the typical cast-iron
manhole cover can be from 175 to 300
lbs. This far exceeds the 50-lb OSHA
limits on lifting for lower back injuries.
As larger openings are needed to come
up to OSHA codes for confined space
entry, the weight will only increase,
making it harder to handle these covers, which will also increase safety risk
factors.
Most existing cast-iron manhole
cover units do not have built-in means
to prevent inflow leaks. When you
talk about millions of manholes, all of
those small leaks add up to billions of
gallons of extraneous water entering
our sewer systems annually, resulting
in unnecessary treatment expenses.
This item alone could very well justify
replacement or an upgrade in manhole
covers — not to mention it’s likely beyond its design life.
Lower quality metals are and will
be an issue we have to deal with
from here on out due to the world’s
demand on reusing scrap metal and
recycling governmental initiatives/
policies. While reusing old, un-used
metal may sound like a great idea, it
has some unintended consequences.
Old metals have rust, oxides and various other containments in them. Once
metaled back into new products, those
containments accelerate the deterioration of the product, which accelerates
the replacement of the product. This
may lower the initial cost of the product, but it just doesn’t last as long and
actually results in a diminished longterm return on investment and essentially creates the opposite effect of the
“green” purpose.
Lessening our carbon footprint — or
becoming more “green” — is a growing trend and something that we have
to accept in the construction market.
Recognizing that, the use of cast-iron
products is very “un-green.” To create
cast-iron, tons and tons of earth must
be mined, refined and processed before casting process can even begin.
Once in process, heating and handling places a large demand on enwww.trenchlessonline.com
ergy through the metaling stage. The
transporting of mass volumes of raw
materials and finished product is also
a huge carbon impact due to the sheer
weight that requires larger industrial
and commercial vehicles.
Cast-iron products have limited options vs. composite materials that can
be made of many configurations, material combinations, colors and customization, due to the unique properties
of thermal plastic technologies available today.
Moving Forward
When you combine all these advantages of what composite manholes
can be, you have just engineered a solution product that has removed the
majority of all the negative aspects
of the traditionally used product.
This is truly a technological advancement that benefits the end users, as
intended. Many accessory products
have been created over the years to
enhance and deal with the issues of
cast-iron manhole covers, but now we
August 2015
TRENCHLESS TECHNOLOGY
39
have a complete packaged unit with
all these built-in options.
What is the future of this type of composite manhole? The raw materials
that composite manholes are made
of have already proven to be
highly durable, lighter, stronger
and corrosion resistant. The
fact that this is a new type
of product means that more
in-ground, long-term case
studies are needed to garner
more credibility, which just
takes time. In side-by-side
testing, these composites
have shown to be just as or
stronger than cast-iron products using accepted design
criteria such as AASHTO’s M-306
load testing for traffic rating. Educating the engineering community
and decision-makers on this new type
of product is essential, in addition to
product evaluations by system owners
by conducting pilot projects to prove the
product’s merit.
I firmly believe and envision composite manhole covers will become
a standard construction product just
like PVC pipe and high-density plas-
tic water meter boxes have become
standard across the industry due to
the overwhelming benefits of the
composite material properties. Like
any product, there are expectation and limitations. Composite
manhole covers will have their
proper place and over time
they will find their way onto
the jobsite. In fact, NASSCO,
in conjunction with industry manufactures, will
have standard specs shortly.
The fact that this is a new type
of product means that more inground, long-term case studies
are needed to garner more
credibility, which just takes time.
Eric Dupré is president of
BlueGreen Municipal Solutions, a division of Southern
Trenchless Solutions. He is
a NACE member and committee chair, an SSPC Certified Concrete Coating Inspector,
and a member of the Trenchless
Technology Industry Advisory Board
(IAB).
SOURCES:
1. http://www.sewerhistory.org/grfx/
components/mhcvrhist1.htm
2. http://docslide.us/documents/
2008-manhole-guide.html
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solutions
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