PSI - Issue 64

André Weber et al. / Procedia Structural Integrity 64 (2024) 1959–1966 A. Weber/ Structural Integrity Procedia 00 (2019) 000 – 000

1960

2

1. Introduction Most FRPs are known as durable and non corrosive materials. For the use in alkaline concrete standard test protocols have been established [ISO, ACI, CSA]. In special applications where further chemical attack cannot be excluded, additional tests have been performed. A special view on the behaviour of FRPs under sustained loads is needed for rebars and tendons containing glass and basalt fibres as these fibres themselves are not stable in alkaline environment without a good protection. In addition, these fibres are susceptible to so called creep rupture. For the chemical durability chapter 3 in the fib Bulletin 40 gives a good overview, which can be concluded here in a short form. All FRP reinforcing materials manufactured with high quality from known vinylester or alkaline resistant epoxy resins can withstand even severe environmental conditions for a service life. Generally, the values for important properties like the tensile strength or the stiffness degrade only by a low percentage in accelerated tests. The same can be stated for freeze thaw cycles. For products with low manufacturing quality no statement can be made for the durability or generalized to other products, even if made from good ingredients. Only Products manufactured under controlled conditions are handled here. A special attention shall be paid to the maximum sustained stress in the reinforcement as generally a greater part of the load can be dead load.

Nomenclature FRP

fibre reinforced polymer

ISO ACI CSA Fib EC2

International Organization for Stsndardization

American Concrete Institute

Canadian Standards Association, CSA group

féderation international de béton

Eurocode 2: EN 1992-1 Design of concrete structures glass transition temperature (of the resin)

T g

2. Different Test Approachs for Sustained Loads The known durability for most FRPs in alkaline concrete led to a broad interest in different rebar systems. Generally the values for important properties like the tensile strength or the stiffness degrade only by a low percentage in accelerated tests. The same can be stated for freeze thaw cycles. Under sustained loads rebars and tendons containing glass and basalt fibres a deeper look is needed especially for the so called creep rupture. This led to established standard test protocols [ISO, ACI, CSA]. Especially for these topics appropriate choice of raw material as well as manufacturing quality is important, so no statement can be made for the durability or generalized to other products, even if made from good ingredients. A special attention shall be paid to the maximum sustained stress in the reinforcement as generally a greater part of the load can be dead load. In the following paragraphs different testing and evaluation concepts being representative for a lifetime with different levels of sustained load and different evaluations are discussed. 2.1. Creep and Creep Rupture Creep is the steady increase of strain under a certain sustained load. For polymers this phenomenon is well known and described by different approaches. For solid materials like glass, basalt, carbon or aramid fibres the creep is much lower (although glass as well as basalt is a subcooled liquid and aramid is a melt oriented highly crystalline polymer).