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CURRENT PRACTICE SHEET
on Bridge Deck Waterproofing

CORROSION

Reinforced concrete is one of the most versatile of structural materials and is extremely durable if properly constructed.

It is recognised however that a degree of porosity will always occur and this, allied to surface wear and hairline cracking, will allow water and corrosive materials, especially carbon dioxide from the air and chlorides from de-icing salts, to penetrate the concrete and attack the steel reinforcement bar. Concrete is naturally alkaline and therefore protects the steel, but the effect of contact with these materials is to reduce the alkaline environment and allow an electrolytic process to start, corroding the steel. The concrete effectively becomes a battery.

The result of the corrosion and rusting is to expand the steel which then damages, and eventually destroys, the surrounding concrete.

The primary defence against these destructive agents is good, dense concrete allied to a proven waterproofing membrane installed by a qualified and responsible contractor.

DECK WATERPROOFING SYSTEMS

The bridge deck waterproofing industry has developed beyond recognition and is continually producing new products and advanced techniques to comply with the latest standards and levels of competence demanded by bridge owners.

The products currently available can be divided into two main categories:

Sheet Systems

These basically consist of pre formed sheets based mainly on bituminous polymeric and elastomeric materials. They are bonded to the bridge deck, to form a continuous membrane, using bitumen adhesive (or they are self adhesive).

Originated from simple roofing membranes, manufacturers have endeavoured to develop systems that would satisfy the specific and enhanced requirements of the bridge deck waterproofing market. Generally, however, they have now been superseded by the more modem liquid sprayed systems.

Liquid (Sprayed) Systems

These systems represent a new generation of deck waterproofing applications developed over the last 25 years to meet the higher technological demands and standards imposed on the industry. Technology has also been developed to allow the application of most preferred systems by spray which offers consistency and continuity. They largely fall into two categories, acrylics and polyurethanes.

The systems normally consist of three elements:

i) Primer

Used to penetrate and seal the concrete substrate, enhancing the bond of the subsequent membrane

ii) Membrane

The waterproofing element of the system. Applied in one or two coats

iii) Tack/Bond Coat

Specially developed tack coats to enhance the bond of the membrane to the wide variety of surfacing mixes encountered around the globe.

These systems offer rapid cure and application and form a tough flexible seamless coating with no vulnerable joints. They also offer ease of detailing and can cope with the uneven surfaces usually encountered on bridge decks.

Systems based on methyl methacrylate and polyurethane resins have proved successful and can offer a world wide track record of success.
 

PERFORMANCE REQUIREMENTS

Irrespective of the system used, it is essential that the following performance criteria must apply in order to negate potential concerns surrounding leakage, poor bonding and embrittlement or softening of the membrane.

• Impermeable to water
• Good adhesion to the deck
• Good adhesion to surfacing
• Capable of bridging shrinkage cracks in concrete
• Tolerant of deck texture and detail
• Tough to withstand site damage including paving equipment
• Safe to apply
• Able to withstand elevated surfacing temperatures
• Applied over a wide range of ambient conditions
• Non degradable

SITE PRACTICE AND APPLICATION

The success of the bridge deck waterproofing operation is often reliant on site procedures, workmanship and the prevailing weather condition. Good, professional preparation is as important as the properties of the product, or system, to be used.

The following represents the major issues to be addressed before work commences on site:

• the availability of design, detailing, construction and material records from the employer's site engineer
• the availability of an approved and properly trained workforce and experienced, qualified supervision
• facilities for adequate and protected storage of materials to be used
• suitable, safe access to the bridge deck for equipment, materials and personnel
• agreement and discussion by all parties to establish an acceptable method statement and programme
• the condition and preparation of the concrete deck which should be sound, even, uncontaminated, dry and dust free and be laid to provide a U4 finish, thereby offering optimum opportunity for a strong and durable bond to the waterproofing membrane
• review of the weather conditions likely to affect the waterproofing operation
• the use of an appropriate primer
• the choice and application of an appropriate, approved and certificated waterproofing system in compliance with current Highways Agency standards
• proper time allowance for the curing process
• adequate protection of the membrane at all times prior to the application of the asphalt road surface
• the use of an appropriate tack coat where necessary
• the application of an approved asphaltic road surface in compliance with current UK Standards, utilising low void content mix designs.

REFERENCES AND FURTHER READING

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Bridge Deck Waterproofing Association
PO Box 4174, Crowthorne, RG42 9LE
Tel: 01344 775576, Fax: 01344 775576, E-mail: secretary.bdwa@sky.com