Abstract
The combination of low clinker high-performance concrete (LCHPC) and ultra-high modulus (UHM) carbon fibre reinforced polymer (CFRP) tendons was recently proposed for prestressed structural elements. The 70% reduction in cement content resulting in limited creep and shrinkage of the LCHPC in comparison to a conventional high-performance concrete (HPC) and the very high UHM-CFRP tendon stiffness (> 509 GPa) were expected to impact the mechanical behaviour of such structures. This study focuses on the behaviour of 3 m-long beam specimens during prestressing, concrete hardening and in 4 point-bending experiments. Fibre optic sensors were implemented inside the CFRP tendons to measure strain during those stages and a digital image correlation system was employed to monitor the 4-point-bending tests. After 28 days, the LCHPC recipe, despite a 70% cement reduction and much smaller environmental footprint, did not show measurable differences in the prestress loss behaviour in comparison to a conventional HPC. The UHM-CFRP prestressing tendons, because of their stiffness, showed both higher prestress losses of around 40% and on average a nearly doubled prestress transfer length. However, they increased the beam`s maximum load-bearing capacity by 21% and showed 47% less deflection at failure in comparison to beams prestressed with the standard modulus (UTS)-CFRP tendons.
Highlights
Sustainable and innovative designs in construction can make a significant contribution for improving the carbon footprint of structures in the future
This study identifies the amounts of each individual contributor to the total prestress loss, precisely measures the prestress transfer length of the carbon fibre reinforced polymer (CFRP) tendons and discusses approaches for improving the ultimate load bearing capacity of CFRPprestressed beam elements
A high performance self-compacting concrete (HPSCC) was selected to investigate the influence of the CFRP prestressing tendon‘s stiffness on the structural performance of prestressed concrete beams. This concrete recipe with a water to binder ratio (w/b) of 0.35, named C1, contained 443.0 kg/m3 of ordinary Portland cement CEM I 52.5 R, 120.0 kg/m3 fly ash, 20.0 kg/m3 silica fume, 1107 kg/m3 sand 0/4, 487 kg/ m3 gravel 4/8 and 5.2 kg/m3 superplasticizer (SP). This is the same recipe that was recently employed as a reference mix during the development of low clinker high performance concretes (LCHPC) [6], based on a high-performance concrete (HPC) used by the Swiss precast industry in CFRP prestressed structural elements [36]
Summary
Sustainable and innovative designs in construction can make a significant contribution for improving the carbon footprint of structures in the future. Already in the 1990s, one first step for improving the structural design of building facades was the development of slender carbon fibre reinforced polymer (CFRP) prestressed elements [1, 2]. New guidelines [4, 5] are allowing the development of novel low clinker high performance concretes (LCHPC) with clinker replacement levels of up to 70% [6]. The combination of both materials results in a very promising composite system that satisfies both the sustainability aspects and the technical improvement objectives
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