Seismic Retrofitting of Corroded Reinforced Concrete Columns Using Carbon Composites

ACI Structural Journal, May/Jun 2007 by Aquino, Wilkins, Hawkins, Neil M

This laboratory study concerns the use of carbon composites to restore the seismic effectiveness of corrosion-damaged reinforced concrete bridge columns with inadequate length lap-spliced reinforcement at their base and subjected to severe environmental conditions. Large-diameter reinforced concrete columns were corroded using external currents, repaired with different layouts of carbon composite material, and then tested to failure under lateral cyclic loading. Bond degradation due to corrosion dictated the losses in ductility and load capacities for the corroded columns. Columns retrofitted with carbon composites, and having well-consolidated repair concrete had maximum load and ductility capacities exceeding those of a control column, which simulated the original as-built condition.

Keywords: bridge; column; corrosion; reinforced concrete; seismic.

(ProQuest-CSA LLC: ... denotes formulae omitted.)

INTRODUCTION

Corrosion of reinforcing steel in concrete structures is a significant durability problem for bridges and parking garages located in chloride-bearing environments.1-5 Maintenance of corrosion-damaged structures costs the government and private sectors millions of dollars every year. In addition, if the structure is located in a region of high seismic risk, the adequacy of the deteriorated structure to withstand the seismic loadings for which it was originally designed is highly questionable, raising additional safety concerns.

This research project was undertaken by the University of Illinois at Urbana-Champaign to address concerns related to the long-term structural behavior of columns deteriorated by corrosion and retrofitted with carbon fiber-reinforced polymeric composites (CFRP). The project involved a laboratory study of the effect of freezing environments and seismic actions on corrosion-damaged CFRP retrofitted columns. The laboratory study complemented an ongoing field study of the performance of 12 columns retrofitted with CFRP. In the laboratory, accelerated corrosion damage was induced using external currents and then the effectiveness of using CFRP to enhance the seismic capacity of repaired columns was examined. This paper investigates the effectiveness of using CFRP to enhance the seismic capacity of corrosion-damaged bridge columns. The work related to freezing-and-thawing durability of the repaired columns is reported in Reference 1.

RESEARCH SIGNIFICANCE

Corrosion represents one of the most serious threats to civil infrastructure. The behavior of reinforced concrete elements affected by corrosion and subjected to earthquake loading is still not well understood. In addition, the feasibility of retrofitting corroded reinforced concrete elements using carbon composites has been limited to small-scale laboratory experiments. This paper presents an experimental study on the behavior of large-scale corroded reinforced concrete columns and the feasibility of using carbon composites to restore their structural capacity.

BACKGROUND

Advanced composite materials (ACMs) have considerable potential for the repair of reinforced concrete structures damaged by corrosion1.6-11 Although ACMs have been widely accepted for the seismic retrofit of reinforced concrete structures, their use in repairing corroded structures has received less attention. ACMs can be a viable alternative to steel jackets for the repair of corrosion-damaged reinforced concrete structures. Lee et al.7 studied the response of reinforced concrete axially-loaded columns with corroded reinforcement that were repaired using carbon fiber-reinforced composite (CFRP) wraps. Corroded columns without wraps showed moderate decreases in ultimate axial loads and marked reductions in ultimate axial displacements compared with non-corroded control samples. Columns corroded and repaired with CFRP showed significant increases in ultimate load and ductility compared with control specimens. Pantazopoulou et al.10 used small-scale specimens to study the effectiveness of ACMs in upgrading the response of corrosion-damaged axially loaded columns. Columns repaired without removing damaged concrete before the application of the ACMs performed better than the columns where damaged concrete was first replaced with a repair grout. Tastani and Pantazopoulou11 used half-scale specimens to examine the structural behavior of corrosion-damaged columns with reinforcement details representative of pre-1980 codes. Columns were upgraded using glass and CFRP wraps after being conditioned using accelerated electrochemical corrosion. After upgrading, specimens were tested to failure under axial compression. The best performance was seen for specimens with the concrete cover replaced by high strength grout prior to wrapping. Columns repaired with CFRP showed brittle failures.

Masoud and Soudki8 tested reinforced concrete beams deteriorated by corrosion, repaired with CFRP, and subjected to monotonic and fatigue loading. CFRP significantly improved the mechanical response of beams deteriorated by corrosion. Soudki and Sherwood9 investigated the effect of corrosion on reinforced concrete beams already strengthened with CFRP. They found that ultimate strength, yield strength, and stiffness decreased with increasing levels of corrosion in all their specimens. The reduction in load and deformation capacity, however, was less pronounced in members strengthened using CFRP. Chung et al.4 electrochemically corroded the reinforcement in slabs to between 85 and 99% of its original cross-sectional area and then tested the slabs to failure under four point bending. Starting from the 2% corrosion level, there was an increasing effect of corrosion level on bond strength and development length.