| Better Bridges
New York Stretches Bridge Deck Life
A water-proofing membrane stopped rot on Fire Island Inlet Bridge.
by Frank Constantino
New York’s Robert Moses Causeway carries approximately 30,000
vehicles each day. It is a route which sees a marked increase in traffic
levels during the summer months as New Yorkers strive to escape the
oppressive heat of the city and the surrounding suburbs by visiting the
resorts of Jones and Fire Island Beaches.
The Fire Island Inlet Bridge, which is an integral part of the
Causeway, is a two-lane, steel arch span and causeway with a concrete deck
that carries Route 908 over Fire Island Inlet.
Construction of the Bridge was completed in 1964 and although a
relatively young structure, less than 40-years old, its concrete deck has
suffered from severe chloride ingress resulting in cracks, spalling, and
the formation of potholes.
Studies carried out on the substrate and the rate of corrosion
indicated that no protective waterproofing system was used on the deck
when the bridge was built. The extent of the deterioration is such that
the New York State Department of Transportation, which took over
responsibility for the maintenance of the structure in 1977, is soon to
begin design studies to replace the bridge, highlighting the importance
and cost-effectiveness of installing a water-proofing system during the
initial construction.
Any new structure built as a result of these design studies, in the
longer term, will give the opportunity to alleviate some of the congestion
at this well known choke point as the increasing recreational activity on
Fire Island generates more traffic. However, in the meantime, the NYSDOT
wished to extend the life of the current structure by preventing further
chloride ingress and slowing the rate of corrosion.
To achieve these goals a complete refurbishment of the deck was vital.
Taking action
The design engineers on the project, Hardesty & Hanover, to meet
the client’s brief, specified the use of an effective, proven
spray-applied waterproofing membrane used in conjunction with a 0.75-inch
micro-surfacing overlay.
This combination would not only achieve the client’s goal of
extending the life of the structure, but milling 0.75-inch of the concrete
surfacing and replacing it with the same depth of micro-surfacing would
ensure matching with existing joint elevations. More importantly the
specified system would be lightweight — reducing dead load, could be
applied rapidly minimizing disruption to traffic, and would be very cost
effective. The waterproofing system also needed to provide an excellent
bond to the concrete deck. Specs called for the system to follow the
contours of the milled deck and have no vulnerable seams or joints.
Hardesty & Hanover specified the use of Stirling Lloyd’s
Eliminator system. The system is a rapid-curing, seamless, spray-applied
waterproofing membrane based on methyl-methacrylate resins.
The system was selected at least partially for its past performance in
similar circumstances. The shear forces exerted on the
waterproofing/wearing course interface when using micro-surfacing are far
greater than those associated with normal surfacing depths. The Eliminator
system has proved that its bond to micro-surfacing can withstand these
forces.
For example, the system had already been very successfully used in
conjunction with micro-surfacing on the Manhattan and Queensboro Bridges
in New York City, which are subjected to much heavier loads and much
higher traffic densities.
Spraying
The system, being liquid applied, could cope with the contours of the
rough, milled-concrete deck and its rapid spray application. Its fast cure
ensured that the maintenance work would cause minimum possible disruption,
a major consideration.
The contract to apply the system was awarded to Venture Construction of
Pembroke, New Hampshire. Once the deck had been correctly prepared,
Venture Construction crews spray applied Stirling Lloyd’s PAR1 methyl-methacrylate
primer to the substrate. This sealed the deck and enhanced the adhesion of
the subsequent membrane to the deck.
Once the primer had cured, typically in under an hour, the Eliminator
membrane was spray applied in two color-contrasting coats to aid quality
control and ensure the integrity of the membrane.
As part of the unique on-site quality assurance program, adhesion tests
were carried out to confirm that the adhesion to the concrete was greater
than the 100 psi required by the specification. Wet film thickness checks
were used to constantly monitor the thickness of the membrane to ensure
that the required thickness was achieved.
The first coat, pigmented yellow, was applied to give a thickness of 80
mils. Once this had cured, the application of the second coat began.
Pigmented grey, this was applied to give a thickness of 40 mils.
While still in its liquid state, aggregate was broadcast into the
membrane to provide a mechanical shear key, enhancing the bond to the
subsequently applied micro-surfacing.
The contractor was able, despite the work restrictions imposed by the
traffic management system and the work schedule of the micro-surfacing
operation, to apply the complete system to the 111,000 square feet of deck
in just 12 days.
Once application had taken place, the system could be trafficked in
under an hour.
Frank Constantino represents Stirling
Lloyd.
Reprinted from Better Roads Magazine
February 2004 |
