How to Protect Concrete and Steel Infrastructure with High-performance Spray-applied Waterproofing Technologies
A recent “60 Minutes” TV broadcast called “Falling Apart” explains that “America’s roads, bridges, airports and rail lines are outdated and need to be fixed” due to decades of neglect. The broadcast goes on to state that “nearly 70,000 bridges in America – one out of every nine – is now considered to be structurally deficient” and that according to the American Society of Civil Engineers (ASCE), “32 percent of the major roads in America are now in poor condition and in need of major repairs.”
The problem with much of America’s infrastructure is that it has outlived its intended service life, and a failure of traditional waterproofing coatings has led to a significant corrosion of structural elements, including corroded rebar and crumbling concrete.
Fortunately, new high-performance waterproofing alternatives are replacing more traditional materials such as sheet goods and sacrificial short-term liquid sealants to help civil and structural engineers cost-effectively protect and maintain critical infrastructure ranging from rail, highway and pedestrian bridges to tunnels, parking decks, airport terminals and DOT entrance/exit ramps.
This new category of spray-applied waterproofing products are seamless, rugged, fast-curing, impervious to water, able to bridge cracks, and capable of lasting decades without extensive maintenance.
“Spray-applied waterproofing now accounts for over 50% of the membranes applied to our bridges,” says Alexander Bardow, P.E., Massachusetts DOT’s State Bridge Engineer, member of American Association of State Highway and Transportation Officials’ (AASHTO’s) Subcommittee on Bridges and Structures representing Massachusetts, and past President of Boston Society of Civil Engineers Section of ASCE.
“What drove us to spray-applied waterproofing is its enhanced durability, bonding to concrete, and crack bridging ability,” says Bardow, who oversees and helps to prioritize work on 5,000 bridges that receive federal funds for MassDOT.
Bardow explains, “If cracks form due to deck deterioration or traffic loading, then water gets into those cracks and the concrete matrix. The [underlying] membrane must be pliable enough to accommodate these cracks without failing.”
Renovating Boston’s Callahan Tunnel
The Callahan Tunnel, originally opened in 1961, recently underwent a renovation project and took advantage of the new waterproofing materials. The tunnel was closed shortly after Christmas 2013 for a multi-million dollar renovation project. The floor had badly deteriorated and after a wall panel fell in 2012, many more were soon discovered to be defective. Because this main throughway to East Boston and Logan International Airport carries 30,000 cars a day, many drivers and area businesses were concerned a three-month closure would cause massive traffic problems and delays.
With the help of Bridge Preservation’s state-of-the-art, high-performance, spray-applied tunnel waterproofing membrane, as well as the highly trained staff of approved applicator Island Pavement Cutting Co. Inc., the Callahan Tunnel project was completed two days ahead of schedule with nearly one mile of new waterproofed roadway and two miles of waterproofed curbs.
Specializing in the rail and highway markets, Bridge Preservation, based in Kansas City, Kan., manufactures high-performance, spray-applied waterproofing membrane systems designed to permanently protect rail and highway structures. These rapid-setting, high-build elastomeric spray-applied waterproofing systems are impervious to deicing chemicals, water, ballast, stray current and other factors that contribute to accelerated deterioration and wear of elevated structures.
The high-performance, spray-applied tunnel waterproofing installation began by preparing the concrete roadway and precast concrete curbs with steel bumpers. The roadway was prepared using a shot blaster and the curbs were abrasive blasted. Compressed air was then used to remove any excess dust and debris from the surface, which could interfere with the bond between the waterproofing membrane and the substrates. The prepared surfaces were then primed using Bridge Preservation Primers, specially formulated primer systems designed for use on concrete and metal substrates.
The temperature in the tunnel was approximately 40°F, which is cold enough to halt the curing process of some primer systems. However, the fast curing BD Concrete Primer is capable of curing at extremely low temperatures, even down to 0°F. This fast-curing primer system allowed the roadway to be waterproofed less than one hour after the primer application.
Bridge Deck Membrane (BDM), the base spray-applied tunnel waterproofing membrane, was then installed using two high-tech spray robots, which allowed for a fast, consistent application of 80 mils, the thickness required to meet the ASTM C1305 Crack Bridging Test.
Immediately following the application of the base membrane, a 40 mil coat of aggregated BD Top Coat was applied. This slower setting topping membrane allows aggregate to be broadcast into it, resulting in a highly durable non-skid coating that can accept temporary high speed vehicular traffic (<65 mph). This Aggregated Top Coat also provides additional shear resistance for the asphalt overlay, greatly enhancing the bond between these two layers.
The precast concrete curbs with steel bumpers were primed using BD Multi-Use Primer, a special primer system designed specifically for use on multiple types of substrates. The curbs were then coated using BD Aliphatic Coating, which is a highly durable, UV and color stable coating system. The horizontal portions of the curbs received an aggregate broadcast following the coating application, which provided a non-skid pedestrian walkway.
Island Pavement Cutting Co. Inc. was able to install 102,000 sq ft of BDM and BD Top Coat, as well as 10,500 sq ft of BD Aliphatic Coating in only five days. During the final two days, the highly trained installation crews of Island Pavement managed to install 60,000 sq ft of roadway membrane in only 16 hours (two 8-hour shifts). A 2-in. asphalt overlay was installed over the membrane, resulting in a long-lasting and highly durable waterproofed roadway.
Due in part to the innovative, high-performance, spray-applied tunnel waterproofing products from Bridge Preservation LLC, and the extremely fast installation by Island Pavement Cutting Co. Inc., Massachusetts DOT was able to open the Callahan Tunnel two full days ahead of schedule.