The adhesion strength of fibre-reinforced repair concrete under hot coastal conditions

Harmful environmental conditions in coastal regions, such as high temperatures and wet–dry cycles, may cause extensive damages to concrete structures. One of the prevalent repair methods for such structures is the placement of repair concrete on damaged concrete layers. In this work, the adhesion of high-strength repair concrete reinforced with steel fibre (SF) and polypropylene fibre (PPF) to bed concrete layers was examined under this environment. Environmental conditions were simulated using different numbers of wet–dry cycles at ambient temperature and at 40°C. Splitting tensile tests were used to evaluate the adhesion between the repair and bed concrete layers. After 180 days of wet–dry cycles 40°C, the high-strength concrete (HSC) mixes with hybrid fibres (HS-St+PP), PPF (HS-PP) and SF (HS-St) provided greater adhesion strength than the HSC without fibre (increases of 39.52, 25.74 and 11.97%, respectively). The combined conditions of wet–dry cycles and high temperatures were far more destructive than wet–dry cycles at ambient temperature. Compared with the ambient-temperature condition, the HS (HSC without fibre), HS-St, HS-PP and HS-St+PP specimens exposed to 40°C showed an average decrease in adhesion strength of 15.48, 15.30, 29.30 and 32.82%, respectively. The lowest shrinkage rates and the highest adhesion strengths were achieved in the mix with hybrid fibres.