Uptake swelling and thermal expansion of CFRP tendons

Abstract

Carbon-fibre-reinforced polymer (CFRP) tendons can be used as a corrosion-resistant alternative to steel for reinforcing or prestressing concrete in aggressive marine environments. The design lives of many civil marine structures often span decades and so the long-term durability of the internal reinforcement is important. One significant, yet overlooked, aspect of CFRP tendon durability is its susceptibility to swell on absorption of aqueous solutions including water and salt water. This paper reviews uptake-induced swelling in CFRP materials and draws comparisons with studies of swelling caused by thermal effects. The diffusion of aqueous solutions and their interaction with the polymer matrix are identified as the primary mechanisms responsible for the swelling. Experimental details are presented that correlate the uptake of water and salt water to swelling observed in CFRP tendons. The results are contrasted with both uptake-and thermal-driven behaviour cited in the literature. Lamé 's equations are used to estimate the magnitude of the resulting stresses induced in the surrounding concrete. The practical significance of the findings is discussed, including the potential for cracking in the surrounding concrete cover and the implications for the tendon-concrete bond.

Analytical predictive model for the long-term bond performance of CFRP tendons in concrete

“…Swelling expansion in CFRPs seems to be related with the environmental RH. Cairns and Adams [45] reported much lower dimensional changes than Scott and Lees [20] for CFRP composite systems exposed at RH=98% and T=65.5°C and the relationship between the swelling expansion strain (x10 -3 ) and moisture uptake (%) was linearly related with a coefficient α1=3.65×10 -3 . Compressive stresses have been found to reduce the rate of moisture uptake in FRPs so the restrained expansion of a tendon in concrete could affect the mass uptake and hence the expected swelling [46].…”

“…Bare CFRP tendons have been found to swell in diameter when subjected to water [20] but the moisture availability at the bond interfaces is affected by the concrete permeability or cracking. The effects of swelling expansion of FRP bars exposed in a concrete humid environment on the bond strength and bond failure modes are difficult to isolate.…”

“…Once the mass uptake is known, a relationship between the swelling expansion strain in CFRP tendons and the moisture uptake can be applied. Based on experimental data derived for bare CFRP tendons immersed in deionised water at 20°C, Scott and Lees [20] proposed that:…”

How to Strengthen Flat Slabs on Punching Shear – Traditionally With Steel or Innovative, by Using Fiber Composite Materials?

“…In case of composites containing carbon fibres (CFRP) this difference is not as clearly marked and stands at approximately 10%. Experimental research (Scott & Lees, 2009;Sivanendran & Lees, 2015) has emphasized one more property that should take into consideration when using CFRP materials -it has…”

Editorial

“…This first issue contains papers on strengthening wrought iron 1 (until recently a problem area because of the unique laminar structure of wrought iron), adhesive bonding of FRP to steel structures 2,3 (which requires excellent surface preparation and produces a variety of stress concentrations that must be carefully considered at the design stage), the behaviour of carbon fibre and aramid tendons 4,5 (a very promising area for new build) and long-term environmental effects on FRP joints 6 . The authors are all prominent in the area of FRP research.…”