Bond behaviour between basalt fibre reinforced polymer sheets and concrete with or without coconut fibre for pounding mitigation

Abstract

Fibre reinforced polymer (FRP) sheets have been used as restrainers for unseating and pounding mitigations between bridge decks. It has been experimentally found that FRP sheets reduce the relative movement between the involved members. Similarly, FRP sheets can be used as a pounding mitigation method between adjacent structures by connecting the involved members to act as a single unit. Increasing structural stiffness is also a means of pounding mitigation and FRP sheet – coconut fibre reinforced concrete (CFRC) forms a composite with increased structural stiffness when compared with normal concrete. While FRP sheets made of synthetic fibres are of high strength, they have the disadvantages of being expensive and non- eco-friendly. Basalt fibres, obtained from basalt rocks, can withstand high temperatures. Recently, the use of basalt FRP sheets has increased in both the construction industry and in research. This study was focused on the bond behaviour between concrete (with and without coconut fibre) and BFRP sheets, as the bond is the first factor to be studied when BFRP - CFRC is used as a mitigation method for pounding. First, the bond behaviour between concrete (with and without coconut fibres) and BFRP sheets adhered externally was studied when a monotonic tensile load is applied on the BFRP sheets. The failure mode, load capacity of BFRP sheet and concrete system, and the strain distribution along the bonded length of the sheet on the concrete surface were analysed. The factors considered while analysing the bond between concrete and BFRP sheets were coconut fibre content in concrete, length of BFRP sheets bonded to the concrete surface and thickness of bonded BFRP sheets. The experimentally obtained results were compared with that obtained using existing models in literature. While samples with 2 layers of BFRP sheet experienced BFRP rupture, debonding of the sheets from the concrete surface was observed as the common failure mode in other samples. While debonding load increased with the number of BFRP sheet layers, the strain in the sheet, and the displacement at the initial point of contact between the sheet and concrete surface near the loaded end were reduced. To show the variation in strength capacity due to debonding, a set of bending tests was done on plain concrete (PC) beams and CFRC beams with BFRP sheets at the tension side. Then, the bond between concrete and BFRP sheet was experimentally observed when two concrete prisms samples were used as a substitute for adjacent buildings prone to pounding during earthquakes, and BFRP sheets bonded or adhered to on the prisms surface were used as a mitigation method (connecting the two concrete prisms to act as a single unit). The samples underwent a rocking mechanism during cyclic loading, and the strain in the sheet was concentrated at the separation of the prisms. The strain in BFRP sheet at the separation reduced with an increase in the number of layers of the sheets.