The Use of Aramid Fibre Reinforced Plastics as Prestressing Tendons for Concrete

C.J. Burgoyne and J.M. Lees

Engineering Department, University of Cambridge, Cambridge, UK

The term continuous fibre reinforcing material (CFRM) includes both fibre ropes and fibre reinforced plastics (FRPs). Fibre ropes are made up of continuous strands which can be either twisted, braided or parallel lay. In the case of parallel lay ropes, the fibres arc usually protected by an outer polythene sheath. Although the ropes are well suited as either external post-tensioning or internal unbonded tendons, they cannot be used as bonded concrete reinforcernent since the fibres are free to move relative to each other, In fibre reinforced plastics (FRPs), the continuous fibres are embedded in a resin matrix. The matrix transfers the load between the outer and inner fibres and hence where it is necessary to bond the CFRM to concrete, fibre reinforced plastics (FRPs) are appropriate. The current work considers the use of fibre reinforced plastics (FRPs) as concrete reinforcement.

In the construction industry, the most commonly used fibre reinforced plastics (FRPs) are carbon fibre reinforced plastics (CFRPs), glass fibre reinforced plastics (GFRPs) and aramid fibre reinforced plastics (AFRPs). Unlike steel, fibre reinforced plastics (FRPs) are purely elastic materials. They do not yield and hence failure of fibre reinforced plastic (FRP) materials is brittle and sudden. This property has important repercussions on the structural behaviour of concrete structures reinforced or prestressed with fibre reinforced plastics (FRPs).

One problem with using fibre reinforced plastics (FRPs) as prestressing tendons is the difficulty in finding suitable permanent anchorage systems. The transverse strength of fibre reinforced plastics (FRPs) is low and stress concentrations generated in the anchors can lead to the premature failure of a tendon. However, this is not prohibitive since pre-tensioned applications eliminate the need for long-term anchoring systems; the development of term anchorages for post-tensioning systems is an active field of study.

The use of continuous fibre reinforcing materials (CFRMs) as concrete reinforcement is a potential solution to the current problems associated with the corrosion of steel reinforcement. In addition, the high strength of these materials means that CFRM tendons are particularly well suited to prestressed concrete applications. The current study investigates the flexural behaviour of concrete prestressed with aramid fibre reinforced plastics (AFRPs). A particular focus was the influence of the bond between the aramid fibre reinforced plastic (AFRP) and concrete on the flexural response of a beam.