Pavlovic, Ana (2022) Long-term structural and environmental performance of pretensioned BFRP reinforced concrete beams. (PhD thesis), Kingston University, .
Abstract
Anthropogenic influence on climate change and biodiversity loss have been highlighted as some of the greatest challenges of modern age. Within this context, it is more important than ever that the construction industry, as one of the main contributors to the global emissions, re-examine the traditionally used materials, approaches, and technologies. Finding optimal engineering solutions for each application and focus on life cycle thinking is necessary to meet the net-zero carbon targets and prevent further damage to the environment. With this in mind, one line of research is looking at the utilisation of basalt fibre reinforced polymers (BFRP) for reinforcement of concrete structures. It is an economically competitive, low embodied carbon material, produced from a widely available volcanic rock, with an excellent strength-to-weight-ratio and corrosion resistance. To prevent inefficient use of the material, which is caused by its low longitudinal elastic modulus, prestressing was proven to be an effective method, ensuring a significant increase of serviceability limit states governed capacity, even at prestress levels as low as 30%. However, due to the novelty of material, there is much to be learned about its performance over time. With the aim of contributing to the identified knowledge gap, this PhD research project combines an experimental, numerical and life cycle assessment (LCA) approach, to gain a multi-faceted understanding of the potential of this alternative reinforcement. Initially, tensile and creep tests of BFRP bars were conducted to gain understanding of the mechanical properties of the material. The main experimental programme incorporated 20 beam samples, with varying level of prestress, and concrete strength. The beams were subjected to long-term monitoring in unloaded conditions and under sustained loading, as well as destructive four-point bending tests. The behaviour of the beams was modelled using a Finite Element Analysis (FEA) software, as well as a numerical moment-area method (MAM) approach. Lastly, a comprehensive LCA study was developed, comparing BFRP with other reinforcing materials, and examining the benefit that can be achieved with its utilisation based on the outcomes of the structural testing of beams. Through the testing programme, it was demonstrated that the mechanical properties retention of BFRP is appropriate for long-term prestressing. The structural performance of the beams under sustained loading remained stable, and the measured changes of the strain level in the bars corresponded to the calculated ones. Additionally, it was shown that the flexural behaviour could be predicted with sufficient accuracy using both the FEA and the MAM approach. Finally, it was demonstrated that the environmental performance of BFRP bars is superior to all other reinforcing bar options considered. The combined evidence gives further reassurance to the suitability of BFRP for developing sustainable and durable concrete elements.
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