Experimental Monitoring of Long-Term Structural Behaviour and Prestress Losses of BFRP Pretensioned Beams Under Sustained Loading

Abstract

The recent interest in expanding the scope of application of Fibre Reinforced Polymers (FRP) in the construction industry has been a driver of copious research. The favourable mechanical properties of FRP make them suitable for internal reinforcement of concrete elements with specific service conditions. Nonetheless, the low Young modulus of glass fibre reinforced polymers (GFRP) and basalt fibre reinforced polymers (BFRP) has been a concern, as it negatively affects the serviceability performance of flexural composite reinforced concrete elements. Prestressing has emerged as a possible method for limiting the deflections and cracking and has been shown as effective in numerous papers. However, long-term behaviour of such structural members has not yet been investigated extensively; therefore, this paper aims to give information on long-term behaviour and losses of prestress of pretensions BFRP beams.

The experiment was conducted on six BFRP pretensioned concrete beams. The samples were of equal dimensions and reinforcement, with pairs of different prestress levels: two beams prestressed to 20%, two to 30% and two prestressed to 40% of the ultimate tensile capacity of the BFRP bars. The beams were then subjected to long-term sustained loading, equal to approximate working permanent loads. Strain level in the BFRP bars was electronically recorded, as well as deflections, surface strain and cracking of the elements. The paper presents the results of six months of continuous monitoring, as well as results of final destructive four-point bending testing.