Henry E. Cardenas

Corrosion Mitigation in Mature Reinforced Concrete Using Nanoscale Pozzolan Deposition

Electrokinetic nanoparticle (EN) treatments were employed to mitigate corrosion in reinforced concrete. In this approach an electric field was used to drive pozzolanic nanoparticles through the capillary pores of concrete and directly to the reinforcement. The intent was to use the nanoparticles as pore-blocking agents to prevent the ingress of chlorides. Treatment effectiveness was examined for both freshly batched and relatively mature concrete. Cylindrical reinforced concrete specimens were subjected to EN treatment immediately after batching and then exposed to chlorides for a period of two years. The EN-treated specimens exhibited a reduction in corrosion rates by a factor of 74 as compared to the untreated controls. Another set of specimens was subjected to chlorides for a period of two years prior to EN treatment application. Electrochemical chloride extraction and EN treatments were performed on these mature specimens for one week. These specimens were placed back into saltwater exposure for an ad...

Corrosion Mitigation in Reinforced Concrete Beams via Nanoparticle Treatment

Reinforcement corrosion in concrete is a major cause of damage in the civil infrastructure. This study evaluates the corrosion behavior of reinforced concrete beams when subjected to electrokinetic nanoparticle (EN) treatment. The EN treatment used an electric field to transport 24 nm nanoparticles directly to the steel reinforcement via capillary pores. Each beam was subjected to saltwater exposure followed by electrochemical chloride extraction (ECE) in concurrence with EN treatment. The specimens were re-exposed to saltwater following treatment. The results from this test indicate significantly lower corrosion current density among the EN-treated specimens (0.014 mA/cm2 [0.09 mA/in.2]) compared to the untreated control specimens (2.12 mA/cm2 [13.67 mA/in.2]). Mercury intrusion porosimetry (MIP) was used to examine the microstructural impact of the treatment process. A reduction in the porosity (adjacent to the steel) of as much as 74% was observed due to EN treatment. During treatment application, the electric field also caused chlorides to be drawn away from the reinforcement and extracted from the concrete beam. After the chloride was extracted, the nanoparticles appeared to form a physical barrier against chloride repenetration.

Diffusion Analysis of Chloride in Concrete Following Electrokinetic Nanoparticle Treatment

Concrete is a highly porous material which is susceptible to the migration of highly deleterious species such as chlorides and sulfates. Various external sources including sea salt spray, direct sea water wetting, deicing salts and brine tanks harbor chlorides that can enter reinforced concrete. Chlorides diffuse into the capillary pores of concrete and come into contact with the rebar. When chloride concentration at the rebar exceeds a threshold level it breaks down the passive layer of oxide, leading to chloride induced corrosion. Application of electrokinetics using positively charged nanoparticles for corrosion protection in reinforced concrete structures is an emerging technology. This technique involves the principle of electrophoretic migration of nanoparticles to hinder chloride diffusion in the concrete. The re-entry of the chlorides is inhibited by the electrodeposited assembly of the nanoparticles at the rebar interface. In this work electrochemical impedance spectroscopy (EIS) combined with equivalent circuit analysis was used to predict chloride diffusion coefficients as influenced by nanoparticle treatments. Untreated controls exhibited a diffusion coefficient of 3.59 × 10−12 m2 /s which is slightly higher than the corrosion initiation benchmark value of 1.63 × 10−12 m2 /s that is noted in the literature for mature concrete with a 0.5 water/cement mass ratio. The electrokinetic nanoparticle (EN) treated specimens exhibited a diffusion coefficient of 1.41 × 10−13 m2 /s which was 25 times lower than the untreated controls. Following an exposure period of three years the mature EN treated specimens exhibited lower chloride content by a factor of 27. These findings indicate that the EN treatment can significantly lower diffusion coefficients thereby delaying the initiation of corrosion.Copyright

Galvanically assisted crevicing of electroplated chrome press cylinders

Abstract Printing press cylinders release ink that is stored in a surface pattern of micro-indentations. The cylinder consists of a steel substrate electroplated with a layer of copper. A micro-indentation pattern is applied followed by a 10 μm top layer of electroplated chrome. This layer generally contains microcracks at a rate if 1000 cracks/2·5 cm. Chrome flaking was common during the warm summer months, leading to costly shutdowns. Corroded cylinders were examined using optical and scanning electron microscopy, energy dispersive spectroscopy, corrosion potential measurement and chemical analysis. It was found that rapid crevicing was taking place in the microcracks. At the chrome/copper interface, galvanically assisted crevicing further accelerated the flaking process. It was also found that the percentage of micro-indentations found to exhibit corrosion spots correlated well with measured corrosion potentials. Polymeric storage covers were recommended to limit atmospheric sources of moisture, oxygen, chlorides and sulphates.