Bond strength of eco-friendly class C fly ash-based thermally cured alkali-activated concrete to portland cement concrete

Abstract

Sixty percent of existing USA bridges were constructed using conventional concrete (CC), i.e., ordinary Portland cement (OPC)-based concrete. Due to aging and changes in standards, many of these bridges require structural repair. To develop engineering-sound repairs, the bond strength between the repair material and existing structure needs to be investigated. This study investigated the bond strength between CC and alkali-activated concrete (AAC) as a repair material using slant shear and pull-off tests. The AACs were synthesized using five different class C fly ashes with different chemical compositions and physical properties. The AAC was cured at an elevated temperature of 158 °F for 24 h. The bond interface surface is subjected to different types of stresses during the service life of the repaired structure. Therefore, slant shear and pull-off tests were performed to assess the bond strength between CC and AAC bond surfaces subjected to compression-shear and direct tension, respectively. For the slant shear, three inclination interface angles of 45°, 33.75̊, and 22.5° were investigated. For the pull-off test, a bonding agent and sandblasting were investigated. The slant shear results displayed that the adhesion coefficient and the internal friction angle of the AAC repair ranged from 4.96 to 6.94 psi and 24° to 35°, respectively. Furthermore, while the sandblasting surface treatment improved the bond strength, the bonding agent did not.