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Towards Low Impact and Innovative New Concrete Structures: Exploitation of FRP Fabric Reinforcement

Periodic Reporting for period 1 - TLIINCSEFFR (Towards Low Impact and Innovative New Concrete Structures: Exploitation of FRP Fabric Reinforcement)

Reporting period: 2018-10-01 to 2020-09-30

This study offers a novel and low-impact solution aiming to reduce over 50% embodied energy in building construction. The reduction is achieved by 1) an optimal design of concrete elements upon internal force distribution, 2) an effective usage of 3D FRP consisting of both flexural and shear reinforcements to fit in the complex geometry due to the optimal design, and 3) the novel application of the 3D FRP reinforcement as a stay-in-place formwork for casting concrete. A successful acceptance of this study in construction section will help to achieve the urgent UK goal of 80-90% reduction in carbon emissions by 2050.
A MATLAB-based code has been developed to determine the behaviour of 3D CFRP reinforced concrete beams. The code includes the impact of 3D CFRP geometries and aggregate coating on concrete cracking and the post-peak behaviours. Then, experimental results have been applied to validate the proposed design code. The main findings of the study are the following:

1. The proposed 3D CFRP reinforcements (i.e. U-channel (UC), U-channel with an aggregate coating (UCA), U-channel with intermittent closed loops (UCL), and U-channel with an aggregate coating and intermittent closed loops (UCAL)) are able to improve the tensile contribution of cracked concrete. After cracking, cracked concrete is expected to be bounded within the 3D CFRP reinforcements contributing to additional tensile strength and stiffness, which might allow 3D CFRP reinforce concrete to develop comparable capacity and load-deflection stiffness to steel reinforced equivalence. Unlike conventional assumptions of ignoring the tensile contribution of cracked concrete in reinforced concrete elements, the tensile strength of the cracked concrete in the 3D CFRP reinforced concrete is suggested to be 0.3ft.
2. Alternatively, the load-deflection stiffness can be improved by coating aggregate on the surface of UC reinforcements, i.e. UCA reinforcements. Experimental results indicates that the aggregate coating technique is able to double the apparent stiffness of CFRP material and allow the ultimate failure to be occurred at a favorable compressive strain of 0.003 or larger. In this research, the stiffness improvement can be presented as a double CFRP modulus (i.e. 2Ef) for the design purpose. On the other hand, the usage of close loops (i.e. UCL) tends to prevent a premature failure at a compressive strain less than 0.003 while this improvement prevents fresh concrete from well contacting with CFRPs during the casting. This unfavorably contacting issue would result in a premature CFRP-concrete slip, compromising the apparent stiffness of CFRPs. The compromised stiffness can be presented as 0.9Ef. The incorporation of aggregate coating and close-loop techniques is expected to deliver a load-deflection stiffness between that of UCA and UCL. Therefore, UCA reinforcements are recommended as a promising steel replacement for reinforced concrete.
3. The pre-peak behaviors of 3D CFRP reinforced concrete (i.e. B1 and B3) have been well described by the equations developed in literature [1]. The peak has been defined as the compressive strain of concrete reaches the observed equivalence at the maximum load. After the peak, the failure of anchorages resulted in a sudden drop of the applied load, and then a plateau up to the ultimate failure [1-2]. This observation suggests a debonding propagation of CFRPs after the peak. Then, the post-peak capacity can be determined by the transferred force in the bottom CFRP, i.e. the bond strength. Additional rotations resulted from CFRP-concrete slip and the elongation of debonded CFRP contribute to the post-peak deflections, which can be determined by the equation in literature [1-2].
4. Based on the calibrated models and equations, low-impact concrete elements having optimal non-prismatic geometries could be developed to achieve comparable capacity and ductility to that of steel reinforced equivalence. Moreover, the proposed 3D CFRP materials can be applied as stay-in-place formworks for realizing complex geometries and further saving constructional energy.
Enhanced the career prospectus of the researcher.
During this fellowship, the Researcher Dr Sun had significantly expanded his knowledge in the use of CFRP composites in construction industry by conducting a highly promising, emerging and inter-disciplinary research field in developing CFRP reinforcement systems for non-prismatic concrete beams. This will propel him to be one of the world leading experts in the innovative applications of FRPs in construction industry. The experimental, theoretical and numerical research skills and the ability to transform research results into developing designs that the Researcher has gained in this fellowship that is transferable helping him to reach professional maturity as an independent researcher. In addition to providing him the excellent research experience, the leadership and management abilities (e.g. project management, self and time management, scientific communication, teaching/supervision, mentoring junior colleagues, proposal writing, professional development training courses, etc.) as well as networking opportunities have enhanced his profile and his future career prospectus.

Quality of the proposed measures to exploit and disseminate the actions results.
Journal papers and conference presentations. It has resulted in two papers submitting in highly reputed international journals/conference to present the research results. Academic collaborations. The study has been gaining attention from academic peers. The light-weight and flexible reinforcements are considered as a perfect for 3D printed concrete which has built collaborations with Prof. Cavalaro, Prof. Buswell and Prof. Austin at Loughborough University. The project outcome have also been disseminated to research groups at a number of reputed Chinese Universities; namely Lanzhou University (invited by Prof. Zhang), Changan University (invited by Prof. Xing) and Quaqiao University (invited by Prof. Guo) taking the advantage of the Researcher’s contacts with them. Moreover, the research outcomes have been introduced to relative research groups at University of Leeds, University of Sheffield, Cardiff University, Queen’s University Belfast, and University of Nottingham during the researcher’s interview for a lecturer position. Dissemination to industry. The research outcomes have also been introduced to industrial firms and government agency, e.g. Arup, Ensoft and Fujian Province. Upon the outcomes, the researcher has developed an industrial proposal for an up to 3 million RMB Fujian-Province grants.

Potential impacts.
The outcome of the project has great potential to initiate a new paradigm in the EU construction industry that moves towards less material intensive and more sustainable industry within 10-15 year time scale. This will resolve a major existing barrier to achieving the long-term EU goal of reducing carbon footprint. The considerably less use of concrete will also help to reduce self-weight of the structures, and this will enable the use of thinner (smaller) structural elements providing further savings of the materials. The overall economic benefits of the proposed research to the construction industry is significant where in EU 2012, the construction industry contributed to ~€1500 billion in economic output, ~13 million jobs were in the construction industry.