Durability of cement mortar-covered BFRP bars in simulated seawater environment

Abstract

To assess the durability of basalt fibre-reinforced polymer (BFRP) bars used to reinforce concrete structures in ocean engineering, the evolution of the thermomechanical properties of cement mortar-covered BFRP bars immersed in simulated seawater environments was studied. The cover thicknesses were set as 10 mm and 20 mm, the immersion temperatures were room temperature (≈28 °C), 40 °C, and 60 °C, and the immersion media were an alkaline solution and distilled water. A set of bare glass fibre-reinforced polymer (GFRP) bars was used for comparison. After one year, the mechanical properties of the bare BFRP bars immersed in a 60 °C alkaline solution deteriorated the most, and the tensile strength decreased from 954.2 MPa to 762.3, 594.7, and 515.5 MPa for the bare BFRP bars and the 10 mm and 20 mm cement mortar-covered specimens immersed in distilled water at room temperature, respectively. The results indicated that alkalinity is a key factor causing the degradation of BFRP and that deterioration is more evident in large-sized cement mortar. In addition, an alkali–aggregate reaction (AAR) of SiO2 in the basalt fibre was evidenced by the presence of a white gel at the interface between the BFRP bars and cement mortar. Thus, AAR is detrimental to the mechanical properties of the cement mortar-covered BFRP specimens in the initial stage. With an increase in immersion time, the cement mortar layer exhibited a protective effect, particularly for the small-sized cement mortar-covered specimens. The BFRP bars are more durable than the GFRP bars owing to the higher fibre volume fraction of GFRP.