Effect of Sulfate Attack on Reinforced Concrete Columns Confined with CFRP Sheets under Axial Compression
Publication: Journal of Composites for Construction
Volume 25, Issue 6
Abstract
Sulfate ions in saltwater can considerably deteriorate the strength and durability of reinforced concrete (RC). To date, there has been no study that systematically investigates the effects of a sulfate attack on the capacity of mid-/large-scale RC columns confined with carbon fiber–reinforced polymer (CFRP). The capacity of CFRP-confined concrete columns subjected to sulfate attacks with various schemes and durations (up to 210 days) was examined in this study. The primary objectives of this study were to (1) examine the effect of a sulfate attack on the structural properties of midscale RC columns confined with CFRP; (2) quantify the contribution of the sulfate-damaged concrete core and CFRP confinement to the load-carrying capacity of the columns; and (3) propose a new formula to estimate the compressive strength of FRP-confined sulfate-damaged concrete considering the exposing time, number of FRP layers, and concrete strength. The experimental results showed that the sulfate attack significantly reduced the initial axial stiffness of the column up to 36% and increased its ultimate axial displacement up to about 40%. These influences in the CFRP-strengthened columns were slightly lower than those of unstrengthened ones. The sulfate attack considerably reduced the strength of the unstrengthened columns (up to 29.4%), but it only slightly affected the capacity of the strengthened columns with a 3.7% reduction. The strength reduction increased with the number of wet–dry cycles. CFRP confinement effectively mitigated the penetration of sulfate ions into the concrete core and, thus, slowed the degradation of the strength up to 90%. An empirical formula was proposed to estimate the strength of the CFRP-confined concrete subjected to a sulfate attack with close predictions regarding the experimental results.
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Acknowledgments
This research was funded by the Vietnam National University Ho Chi Minh City (VNU-HCM) under Grant No. B2020-20-02. The authors also acknowledge the support from Ho Chi Minh City University of Technology (HCMUT) and VNU-HCM for using their facility.
Notation
The following symbols are used in this paper:
- Ac
- cross-sectional area of concrete, mm2;
- Ae
- effective cross-sectional area of concrete, mm2;
- Ag
- cross-sectional area of columns, mm2;
- Ast
- cross-sectional area of longitudinal reinforcements, mm2;
- Ctlc
- experimental factor accounting for immersion time in sulfate solution, the number of FRP layers, and properties of concrete;
- D
- equivalent diameter of rectangular section, mm;
- EA0
- axial initial stiffness, kN/mm;
- Eadhesive
- elastic modulus of adhesive, GPa;
- Ef
- elastic modulus of CFRP sheets, GPa;
- Es
- elastic modulus of steel, GPa;
- compressive strength of confined concrete, MPa;
- compressive strength of unconfined concrete cylinders, MPa;
- fc,cube
- compressive strength of unconfined concrete cubes, MPa;
- fadhesive,u
- tensile strength of adhesive, MPa;
- fffu
- ultimate strength of CFRP sheets, MPa;
- fl
- lateral confinement stress, MPa;
- fsp,cube
- spliting tensile strength of concrete from concrete cubes, MPa;
- fu
- ultimate strength of longitudinal reinforcements, MPa;
- fuw
- ultimate strength of stirrups, MPa;
- fy
- yield strength of longitudinal reinforcements, MPa;
- fyw
- yield strength of stirrups, MPa;
- IEPCFRP
- sulfate prevention efficiency index;
- k1
- confinement calibration factor for confined concrete = 3.3 (Lam and Teng 2003);
- ks1
- shape factor;
- My
- index for concrete strength;
- n
- number of CFRP layers;
- Pcore
- contribution of concrete core to the axial load–carrying capacity, kN;
- PFRP
- contribution of CFRP to the axial load–carrying capacity, kN;
- Pu
- failure load, kN;
- Pu,0
- failure load of unconfined columns, kN;
- Pu,60
- failure load of columns in Group B, kN;
- Pu,Lam-Teng,pred
- predicted load-carrying capacity of the columns using Lam and Teng’s (2003) model, kN;
- Pu,mode,pred
- predicted load-carrying capacity of the columns using the proposed model, kN;
- Pu,exp
- experimental load-carrying capacity of the columns, kN;
- Py
- yielding load, kN;
- Rc
- radius of rounded corners, mm;
- t
- number of wet–dry cycles;
- tf
- nominal thickness of CFRP sheets, mm;
- x
- group index, = C (150 cycles) or = D (210 cycles);
- δy
- axial displacement at yielding load, mm;
- δhu
- lateral displacement at the failure load, mm;
- δvu
- axial displacement at the failure load, mm;
- ɛcu
- ultimate compressive strain of concrete, ‰;
- ɛf
- CFRP strain, ‰;
- ɛfu
- rupture strain of CFRP sheets, ‰;
- ɛj
- Nominal rupture strain of CFRP sheets, ‰;
- ɛst
- longitudinal-reinforcement strain, ‰;
- ɛstu
- longitudinal-reinforcement strain at the failure load, ‰;
- ɛsw
- stirrup strain, ‰;
- ɛswu
- stirrup strain at the failure load, ‰; and
- ρsc
- longitudinal-reinforcement ratio.
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Received: Dec 23, 2020
Accepted: Jun 5, 2021
Published online: Aug 30, 2021
Published in print: Dec 1, 2021
Discussion open until: Jan 30, 2022
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