Efficacy of Composite-Strengthening on Axial Capacity of Concrete Subjected to Sulfate-Induced Damage
Yongcheng Ji and Yail J. Kim
Appears on pages(s):
Carbon fiber reinforced polymer (CFRP), Composite, Durability, Fourier transform infrared spectroscopy (FTIR), Strengthening, Sulfuric acid, Thermogravimetric analysis (TGA)
This paper presents the potential of carbon fiber reinforced polymer (CFRP) composite sheets for protecting concrete members subjected to sulfate-induced damage. Two types of concrete cylinders with and without CFRP-strengthening are immersed in a 5% sulfuric acid solution for 6 weeks, and their physical and chemical responses are comparatively studied. Also examined is the behavior of the strengthening system consisting of carbon fibers and an epoxy resin in such an environment. Test methods include Fourier transform infrared spectroscopy, thermogravimetric analysis, and destructive mechanical loading in compression. The pH values measured at 0- and 6-week exposure periods indicate that the plain concrete cylinders have actively interacted with sulfuric acid, whereas those specimens with CFRP have not. The damage induced by sulfuric acid appears to be localized at the surface level of the plain concrete, according to the qualitative examinations done by a digital microscope. The chemical responses of the epoxy and CFRP are similar in terms of functional groups, in spite of different absorbance peaks (the carbon fibers retard chemical reactions between the CFRP and sulfuric acid). The thermogravimetric analysis clarifies that the core concrete of the strengthened cylinders is protected by the CFRP, including a gradual decrease in mass with temperature that is contrary to the case of the unstrengthened concrete showing an abrupt
change in mass drop. The load-bearing capacity of the plain and strengthened concrete cylinders is reduced by 57% and 23%, respectively, because of the sulfuric acid exposure. A visual assessment on the failed cylinders supports that the concrete core is effectively protected by CFRP-strengthening, although the permeation of sulfuric acid through the CFRP-wrap occurs.