Prestressing low clinker structural concrete elements by ultra-high modulus carbon fibre reinforced polymer tendons

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.

An Analysis of the Transfer Lengths of Different Types of Prestressed Fiber-Reinforced Polymer Reinforcement

“…The transfer length is a function of several factors that depend on the properties of both the prestressing reinforcement and the concrete. Therefore, many studies were performed to investigate the influence of concrete compressive strength [ 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ], prestress level [ 29 , 30 , 31 , 32 , 33 , 36 , 37 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 ], reinforcement diameter [ 24 , 26 , 29 , 30 , 31 , 32 , 35 , 36 , 37 , 38 , 48 ], concrete cover [ 26 , 29 , 30 , 31 , 32 , 35 , 48 , 49 , 50 ], reinforcement surface conditions [ 24 , 35 , 36 , 37 , 38 , 47 ...…”

Untersuchung des Verbundverhaltens von CFK‐Spannlitzen in Beton mit faseroptischen Sensoren

“…Zur Erfassung der Bewehrungsdehnungen können Dehnungsmessstreifen (DMS) direkt auf die Spannglieder aufgebracht werden, was allerdings zu einer Unterbrechung des Verbunds und zur Beschädigung der DMS führen kann. Sofern fertigungstechnisch möglich, können faseroptische Sensoren in die Bewehrung integriert werden (Smart Strand) [17,18]. Hierfür wird bei der Herstellung des Kerndrahts der CFK-Litzen ein FOS in den CFK-Draht eingebettet.…”