For over 40 years the U.K. Highways Agency has used waterproofing products to protect bridges and reduce the need for costly structural repair and maintenance. Many other world government agencies are now following in their footsteps.
In brief, concrete or steel structures situated in any climate, be it hot or cold, wet or dry, are subject to some form of structural corrosion. Aggressive environmental influences such as acidic rain, winter salts, extreme temperatures and microbial attack can exacerbate cracks and holes in concrete structures and expose steel reinforcements to corrosion which causes untimely decay of the bridge and high repair and maintenance costs for the client.
An effective waterproofing layer will help protect the bridge from premature degradation. The U.K. Highways Agency recognized the importance of waterproofing back in the 1960s and since then it has been mandatory to waterproof all bridge structures in England, Ireland, Scotland and Wales.
Prior to the 1990s a number of waterproofing products were installed on U.K. bridges and later failed due to a variety of problems including poor substrate bond, large areas of pin holing, blistering and cracking. To stop the use of ineffective products the U.K. DOT implemented a strict test standard for waterproofing products (BD47). Today one of the most effective forms of waterproofing available is the spray applied systems. These systems are watertight, spray seamlessly and provide excellent adhesion to concrete and steel surfaces. Spray applied products also are highly flexible and can seal cracks permanently unlike sheet and epoxy waterproofing systems.
Pitchmastic PmB Ltd. installs the PmB waterproofing system. PmB membrane, which is formulated using Bayer’s Baytec elastomers, is a polyurethane membrane with no fillers or solvents. It provides a strong and durable waterproofing layer even under extreme conditions of loading, temperature, microbial, chloride and chemical attack. Over 43 million sq ft of PmB has been applied to structures worldwide.
In 1996 Pitchmastic completed waterproofing works on the Second Severn Crossing. This 3-mile-long bridge, built over the Severn Estuary, connects England and Wales. The new bridge was built to take pressure off the first Severn Crossing which was slowly disintegrating due to increased traffic rates and the high winds and salts found in the surrounding harsh coastal environment. By completion Pitchmastic had applied PmB to 2 million sq ft making this project the largest waterproofing contract to be awarded in the U.K. in the last 20 years.
Installation of the PmB waterproofing system began with the application of a polyurethane primer to prepare the surface for the PmB membrane. The membrane itself was applied using Pitchmastic’s spray machinery which is capable of spraying up to 21,500 sq ft per day. On this particular contract large areas required waterproofing in short time periods, therefore Pitchmastic elected to use multiple spray machines and several teams of spray operatives on site to maximize output. The final part of the PmB waterproofing system was to apply a PmB bituminous tack coat to accept the hot asphalt overlay materials. Use of the mobile spray machinery along with the ease of application of the PmB waterproofing system meant that even this inflexible program could be met.
The Boyne Bridge, an asymmetric 56 cable stay bridge with a main span of 170 meters in Ireland, carries the M1 northern motorway over the Boyne River and is southern Ireland’s largest cable-stayed bridge.
The project specification called for a waterproofing system which held a BBA certificate, the construction industry’s certificate of approval. The PmB waterproofing system holds BBA certification in roads and bridges and tanking.
Pitchmastic PmB Ltd. uses a network of licensed applicators to apply the PmB system outside the U.K. The waterproofing works on the Boyne Bridge were sublet to Pitchmastic’s Irish applicator; however, due to the large scale of the project, Pitchmastic also directly supplied labor and additional spray machinery. The specially constructed articulated spray unit was used to achieve outputs up to 2,000 sq ft per hour from each of the two spray heads.
In addition to applying a waterproofing layer to the carriageway the client required a non-slip coating on the footways on either side of the bridge. For these areas Pitchmastic offered the client a combined waterproofing and antiskid system to provide a slip-free surface for pedestrian and maintenance personnel.
As with all PmB applications, waterproofing on the Boyne Bridge was subject to extensive on-site quality checks including electronic leak detection and tensile bond strength. Samples from each batch of applied materials also were sent away for independent testing to check membrane properties.