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DURABILITY ISSUES AND CHALLENGES FOR MATERIAL ADVANCEMENT IN FRP EMPLOYED…
DURABILITY ISSUES AND CHALLENGES FOR MATERIAL ADVANCEMENT IN FRP EMPLOYED IN THE CONSTRUCTION INDUSTRY
COMPONENTS FOR FPR
FRP : Composed of continuous fibers (carbon, glass, aramid) embedded in a thermosetting resin matrix (epoxy, vinylester or polyester resins) that holds together the fiber and transfers the load between them.
Thermosetting resin :
- act as adhesive between FRP and substrate
- chemical nature of adhesive will have a decisive influence on the performance and behavior of the FRP and on the effectiveness of the whole intervention
Behavior of FRP depends on :
- Properties of the individual materials
- Performance of the FRP-adhesive and adhesive-substrate interface bond
- Bond between the reinforcement and substrate
- The ability to transfers stresses at the interface
Techniques to apply FRP :
- The precured FRP pregress are adhesively bonded as prefabricated elements to the concrete substrate
- The composite is applied through a "wet lay-up" of fabrics directly onto the substrate
*Both techniques has weakest link which represented by cold-cured thermosetting resin or epoxy used as adhesive in 1st case and as matrix/adhesive in 2nd.
- Resin : responsible for the overall integrity of the rehabilitated structure as it must assure an effective stress transfer among structure and FRP reinforcement (it can undergo chemical and physical degradation by environmental actions and mechanical stresses)
The properties and durability of FRP-substrate bond can be enhanced by surface modification through mechanical treatments or functionalization with coupling agents.
The main consequences of a cure at ambient temperatures of epoxy adhesives for cold cured thermosetting (epoxy) resins are :
- long curing times to achieve sufficient mechanical properties
- the curing reactions often not completed because of the kinetic restraints
- moderate glass transition temperature (Tg) which is > 65-70C is attainable if curing happened in low winter temperature
- Absorption of external water (atmospheric moisture / rain) produce decrease of initial Tg but negative of mechanical and adhesive properties
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