Elements of a Bridge-Deck System

The primary aim of waterproofing layers under a bridge-deck pavement is to protect the structural concrete from penetrating water and de-icing chemicals. As shown in Fig. 1, such a waterproofing system often consists of a polymer – modified bitumen membrane (PBM) that is glued to the concrete surface by an adhesive-bonding agent or by welding with a torch. Generally, the bridge-deck pavement consists of two layers of mastic asphalt (MA), composed of aggregate with a maximum aggregate size of 8 mm, 11mm, or 16 mm and a 6.5% by weight binder of 20/30 penetration grade to survive extreme traffic conditions [1]. In addition to this, epoxy sealing, acrylate, or polyurethane is used as a waterproofing layer on concrete bridge decks. MA has virtually no air voids. Therefore, it contributes to the waterproofing properties of the system. In gen­eral, bituminous waterproofing membranes on bridges have a thickness of 5 mm. They are typically made of styrene-butadiene-styrene polymer-modified bitumen that is carried by glass fiber and polyester fabrics in the center of the sheet. Usually, the upper surface is treated with talcum, sand, and granules for ultraviolet radiation protection. High-quality waterproofing membranes have good thermal stability, flexibility at low temperature, and good adhesion to the concrete surface.

FIG. 1—Scheme of a concrete bridge-deck waterproofing system [2].

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Failure of the adhesive bond between a concrete surface and a waterproof­ing membrane PBM can occur because of the lack of strength of the concrete or insufficient adhesion and cohesion of the bituminous membrane layer. In addi­tion to this, the welding process can affect the strength of the concrete. Heating can lead to tension in the upper surface followed by cracking or detachment. Various techniques can be used to improve the adhesion, such as sandblasting and water jetting, etc. Possible use of low-viscosity epoxy resin as bonding agent and seal against humidity may be helpful [3].