Harovel G. Wheat

Effect of Chlorides on Reinforcing Steel Exposed to Simulated Concrete Solutions

Abstract The behavior of steel in chloride-free and chloride-contaminated simulated concrete solutions was studied to observe the degradation of steel as a result of addition of chlorides. One of t...

Using polymers to minimize corrosion of steel in concrete

Efforts to restrict chloride transport can lead to changes in the corrosion rate of steel in cement-based materials, such as concrete. Two potential methods have been examined for several years. They include: the addition of polymer fibers to the concrete at the time of mixing; and the encapsulation of previously contaminated concrete using polymer resin or polymer composites. It has been reported that the first method could minimize initial chloride intrusion and that the latter method could prevent additional chloride intrusion if concrete is already salt-contaminated. The effectiveness of these methods in minimizing corrosion was evaluated based on changes in corrosion rates determined using polarization resistance measurements. The results, which have been observed over a period of several years, will be reported. Limitations of polarization resistance measurements to evaluate the effectiveness of these methods as means of minimizing corrosion will also be discussed.

Corrosion behavior of steel in concrete made with Pyrament® blended cement

Abstract The corrosion behavior of steel in reinforced concrete made using Pyrament® blended cement and having water-cement ratios of 0.25, 0.27, and 0.29 has been determined by means of electrochemical techniques such as polarization resistance. Based on tests conducted on samples continuously immersed in a 3.5% NaCl solution as well as those subjected to alternating wetting and drying conditions for three years, the concrete has provided remarkable corrosion protection to the embedded steel.

CORROSION OF REINFORCED STEEL BARS EMBEDDED IN CONCRETE: A STUDY OF ELECTROCHEMICAL AND SURFACE ANALYSIS

We present a study of corrosion of reinforced steel bars embedded in concrete. We carried out both electrochemical analysis / £ c o p o l a r i z a t i o n resistance (Rp), and electrochemical impedance spectroscopy (EIS)/ and surface analysis by AES, XPS, SEM, and ED AX. We found that 1/RP >28 μ8/αη 2 , which gives /C0IT > 0.73 μΑ/cm, indicating that severe corrosion was occurring. After a 20-week exposure, the Nyquist plot of the electrochemical impedance Ζ (/ω) showed two capacitive arcs and rests of a third one, the corresponding time constants RC being related to the double layer, the interfacial thin film, and the concrete matrix, respectively. The interfacial thin film resistance (Rf) and the double-layer resistance (Rc,) are found to be about 220 Ω and 320 Ω, respectively. Departure from the capacitive semi-circles is observed, indicating the presence of diffusion-driven corrosion. Analysis of AES allowed us to determine the concentration of corrosion products on the surface and in the near surface region. Migration of S, C, and Ca to the surface was observed. From the XPS spectra we conclude, at room temperature, the existence of the following iron compounds: Fe203, and FeCl2, as well as the formation of CaC0 3 ; these compounds appear before an 2 Also with: CICATA-IPN * In postdoctoral stay in CCMC-UNAM

Repair and rehabilitation of corrosiondamaged concrete elements using FRP composite wraps

Reinforced concrete structures have been wrapped to provide strength and confinement in the presence of seismic loads. The wrapping of structures as a means of mitigating corrosion is relatively recent. The objective of the work to be described is to investigate the long-term effectiveness of fiber-reinforced polymer (FRP) composite wraps in mitigating corrosion in reinforced concrete elements in severe environments.

Monitoring corrosion protection provided by fibre reinforced composites

A laboratory research programme was initiated to complement a field investigation in which composite materials were being used to wrap 12 corrosion damaged bridges in Texas. The programme, which started in 1997 and was sponsored by the Texas Department of Transportation, included more than 60 laboratory specimens that were designed to simulate bridge bents and columns. The primary objective was to determine whether composite wrapping could be used as a means of rehabilitating corrosion damaged structures. Since that time, the laboratory specimens have been subjected to intermittent exposure to saltwater conditions. They have been monitored using corrosion (half-cell) potential measurements that indicate the probability of corrosion activity. In addition, corrosion rate measurements have been determined on some of the specimens after exposure. Selected specimens have been removed from testing and subjected to thorough post exposure examination on a regular basis. The focus has been on the difference in the behaviour of the wrapped and unwrapped specimens. The composite systems used included a vinyl ester resin and two epoxy resins in combination with a selected fabric containing glass fibres. The laboratory specimens have been exposed to saltwater for more than four years. This paper represents a summary of some of the most significant findings during that time, as well as a comparison of those results with some of the results obtained in the field investigation.

Corrosion damage in composite-wrapped structures

Composite wrapping is a means of rehabilitating corrosion-damaged reinforced concrete structures. Concern has been raised about this method and the potential for accelerating the problem unless provisions are made for arresting the existing corrosion. Parallel field and lab studies have been initiated to address factors influencing the effectiveness of such procedures. In particular, use of corrosion inhibitors as a pretreatment prior to wrapping is being studied. Other considerations are the types of fibers and polymer resins that are most appropriate, the severity of damage that can be accommodated, and peculiarities associated with different geometries. Preliminary results indicate that wrapping may aid in retarding the ingress of additional chlorides, but may also trap moisture.

Comparison of corrosion behavior of different prestressing strand types

In order to complement a large-scale long-term investigation of prestressing strand types for post-tensionsing of bridges, passive and active electrochemical tests were carried out on bare and grouted specimens exposed to salt water conditions as a function of time. The materials tested included seven-wire strands made of hot dip galvanized or zinc coated steel, stainless steel, stainless clad steel, copper clad steel, flow-filled epoxy coated steel and conventional steel as control. Based on corrosion potentials, polarization resistance tests, potentiodynamic tests, weight loss, and visual observations, epoxy coated strands, stainless and stainless clad strands were identified as possible alternatives to conventional steel that might help to minimize corrosion.