Hayato OTANI

Study on the Specifications and Performance of a Bridge Pavement Base Course Constructed with a Milled Residual Layer and a New Leveling Layer

Osamu TAKAHASHI

The deterioration of concrete bridge decks in highway bridges is primarily caused by fatigue due to repeated vehicular loading. The presence of water on the deck surface during fatigue progression significantly accelerates crack propagation, deck deterioration, and pavement damage. To prevent the intrusion of rainwater and chloride ions into the deck, a waterproofing layer is installed between the bridge pavement and the concrete deck.
Recently, high-durability waterproofing systems have been widely adopted. Although these systems have a longer service life than the pavement, they are often removed and reconstructed during pavement replacement, even before reaching the end of their service life. This practice increases construction costs and extends construction periods. Moreover, conventional removal using backhoes can damage the concrete cover of the bridge deck.
Previous research proposed leaving approximately 20 mm of the asphalt concrete (AC) layer above the waterproofing membrane during milling and reusing it as an intermediate waterproofing layer by impregnating it with a high-concentration polymer-modified asphalt emulsion. Experimental results demonstrated that this treatment restored impermeability and mechanical performance. However, the intermediate layer alone showed slightly inferior impermeability and resistance to plastic flow compared with newly constructed AC.
To address this limitation, this study proposes a composite base course consisting of the emulsion-treated residual layer and an additional leveling layer placed on top. Based on literature review and mixture-level comparative tests, a stone mastic asphalt mixture with a maximum aggregate size of 5 mm was selected for the leveling layer. Experimental evaluation confirmed that the composite system provides impermeability and mechanical performance equivalent to those of a newly constructed AC base course.