Bond Behaviour between Carbon Fibre Strand and Mortar under Marine Environment

Abstract

Owing to the steel corrosion in traditional steel reinforced concrete structures exposed to marine environment, the present study explores carbon fibre textile reinforced mortar (TRM) as the alternative construction material. Moreover, sea sand and seawater can be used in casting mortar in this study, because carbon fibre is non-corrosive. Focusing on the long-term bond degradation at the interface between the carbon fibre strand (CFS) and mortar in carbon fibre TRM under marine environments, experimental and numerical investigations have been carried out by using single CFS-reinforced mortar (CFSRM) specimens.

Interfacial debonding is one of the key failure modes in TRM, due to the poor bonding between CFS and mortar compared with traditional steel rebar to mortar. Since the pull-out performance is selected to assess the interfacial durability of TRM, this thesis derived an analytical solution of interfacial bond-slip behaviour during the pull-out process. The moisture-induced degradation has also been discussed in this research, with a particular focus on the effects of hygroscopic expansion and interfacial ageing.

Considering that there exists a scientific challenge of understanding CFSRM durability before it can be applied to practice extensively, this study focuses on the real working condition in the offshore area and thus investigates its durability problems by coupling two different degradation mechanisms altogether, namely hygroscopic expansion and interfacial ageing. Although each of them has been individually studied in literature so far, this study innovatively takes them into account simultaneously to investigate the coupling effect. At last, a long-term prediction model based on multiphysics is proposed to estimate its interfacial degradation behaviour under marine environment.

The present study includes both experimental work and numerical testing. A total of 125 samples are tested in experiments. Mortar samples are used for strength, flowability and diffusion tests, containing 24 cubes (100 mm), 24 cylinders (200×100 mm height/diameter), three prisms (40×40×160 mm), fresh mortar and eight small cylinders (50×20 mm height/diameter). 28 CFS samples are used for mechanical and physical tests. 32 CFSRM cylinders (50×20 mm height/diameter) are used for pull-out tests. All above-mentioned tests are carried out in University of Plymouth. According to material parameters acquired from experiments, COMSOL Multiphysics software is used to build the multi-field numerical model which simulates the coupling effects of water diffusion, hygroscopic expansion, and immersion temperature on the bond degradation of CFSRM. As the present thesis proposes a three-parameter durability (TPD) model based on Arrhenius Law to predict the interfacial ageing over time, TPD model is further used in the numerical testing and then validated by the experimental records. Finally, the present thesis proposes a hand calculation method of pull-out force retention under long-term conditioning, based on above-mentioned experimental and numerical analyses altogether.