Opportunities and Risks Arising from the Properties of FRP Materials Used for Structural Strengthening

Abstract

Modern composite materials, made on the basis of non-metallic continuous fibers are increasingly used in civil engineering, in particular to strengthen building structures. In strengthening of RC structures the utilization of externally bonded FRP composites is only up to 35% because of the pilling-off failure mechanism. This problem can be solved by the use of pretensioned composite laminates. Due to more complex behavior, the strengthening of structures using prestressing technology needs a careful design approach and a full understanding of the behavior of both the materials and elements. The advantages and risks of the presented technology, which may determinate the success of the entire project, are highlighted in the article.

Possibilities of Increasing Effectiveness of RC Structure Strengthening with FRP Materials

“…This is also extremely important in conditions where it is necessary to consider the accidental loading, e.g., in structures that exist in seismic areas or those subjected to impact loads. When CFRP strips with an initial elongation of 0.9% (which could be equivalent to force 220 kN; this is the same as in monostrand steel tendon) are used, the prestressing system acts such as ‘a rubber band’ and each change in strain is within the elastic range of the material behaviour [ 55 ]. Thus, even with large cyclic strain changes on the composite tendon, the structure can still safely handle the load.…”

Performances, challenges and opportunities in strengthening reinforced concrete structures by using FRPs – A state-of-the-art review

“…Different types of acidic media may be produced as a result of the moisture content and gases and liquids present in the surroundings, which may attack the adjacent structures. It was reported that carbon fibres showed excellent resistance to acid attack, but other fibres are considered weak against acid attacks [110]; glass fibres display very low resistance to alkaline environments compared to other fibres [7]. Besides, upon exposure to an acidic or alkaline solution, polymeric resins are most degraded and their T g may be reduced [93,111].…”

“…Extreme brittleness and successive micro-cracking may arise in polymer composites after the reaction with UV photons. Aramid fibres lose their strength and change colour, but carbon and glass fibres display sufficiently stable properties, when exposed to UV light [6,7,9]. This radiation has reduced effect on the properties when fibres are combined with a polymeric matrix to form composites of FRPs [7].…”

“…Aramid fibres lose their strength and change colour, but carbon and glass fibres display sufficiently stable properties, when exposed to UV light [6,7,9]. This radiation has reduced effect on the properties when fibres are combined with a polymeric matrix to form composites of FRPs [7]. The polymeric coating on FRP laminates does not directly inhibit the degradation of the FRP, but acts as a self-sacrificing layer which prevents direct attack of the fibres by the UV radiation [99].…”

“…1. FRPs may consist of carbon, glass, aramid and basalt fibres that are bonded together by the matrix of a polymer such as epoxy, vinyl ester or polyester to form CFRP, GFRP, AFRP and BFRP, respectively [5][6][7][8][9][10]. FRP materials are being used in the forms of laminates, rods, dry fibres or sheets in concrete structures.…”