Local Bond Strength of Vitreous Enamel Coated Rebar to Concrete

In this paper, the bond strength between vitreous enamel coated rebar and concrete is characterized through testing of 96 pullout cylinder specimens. Key parameters investigated include rebar diameter, coating condition, confinement condition, concrete cover-to-rebar diameter ratio, and concrete strength. The unconfined and confined cylinders fail in concrete splitting with crushing zones distributed at rib fronts and concrete splitting plus shearing off, respectively. The enamel coating reduces the crushing angle and increases the crushing length of concrete. within the test ranges of various parameters, the overall increase in bond strength of the enamel coated rebar in normal concrete is approximately 15%. Confinement or reduction of rebar size can increase the effect of enamel coating on the bond strength by 2-4%

Monoenergetic energy doubling in a hybrid laser-plasma wakefield accelerator

An ultracompact laser-plasma-generated, fs-scale electron double bunch system can be injected into a high-density driver/witness-type plasma wakefield accelerator afterburner stage to boost the witness electrons monoenergetically to energies far beyond twice their initial energy on the GeV scale. The combination of conservation of monoenergetic phase-space structure and fs duration with radial electric plasma fields E(r) similar to 100 GV/m leads to dramatic transversal witness compression and unprecedented charge densities. It seems feasible to upscale and implement the scheme to future accelerator systems

Global Bond Behavior of Enamel-Coated Rebar in Concrete Beams with Spliced Reinforcement

This paper presents an experimental study of vitreous enamel coating effects on the bond strength between deformed rebar and normal strength concrete. A total of 24 beam splice beam specimens were tested under 4-point loading with four parameters investigated: rebar size, lap splice length, coating and confinement conditions. As the splice length increases, the ratio of bond strength between coated rebar and black rebar was found to increase from 1.0 to a maximum value of 1.44 and decrease to 1.0. The maximum bond strength ratio corresponds to a splice length over rebar diameter ratio of 20-35 when the maximum elastic stress is developed in enamel-coated rebar. For a splice length over rebar diameter ratio of less than 20, an average of 10% bond strength increase was observed due to confinement provided by transverse stirrups. The concrete beams reinforced with enamel-coated rebar have a greater number of smaller flexural cracks than those containing black rebar since the enamel coated rebar can more effectively receives stress from the concrete

Chemically Reactive Enamel: A Steel Rebar Coating for Enhanced Durability of Concrete Structures

Since 2007, the research group at Missouri University of Science and Technology has initiated and sustained a series of systematic studies on steel rebar and plates coated with vitreous enamels for enhanced corrosion resistance and for rebar bond strength in concrete. This paper presents a summary review on the corrosion performance and performance consistence of various enamel-coated steel rebar and plates in two corrosion environments. Specifically, three types of enamel coating (pure, mixed, and double enamel) were investigated with four types of specimens (steel plates, smooth steel rebar, deformed steel rebar, and smooth steel rebar embedded in mortar cylinder) in 3.5wt.% NaCl solution and saturated Ca(OH)2 solution. Their corrosion resistances and mechanisms are compared with fusion-bonded epoxy coating. Electrochemical impedance spectroscope and linear polarization resistance tests were respectively performed for short-term and long-term corrosion performances of coated rebar over a period of 173 days. An emphasis is placed on the effects of coating thickness, thickness variation, potential damage, mortar protection, and corrosion environment on the corrosion behavior of uncoated and coated steel. Due to the isolated nature of air bubbles trapped inside them during high temperature firing, the pure and double enamel coatings are more corrosion resistant and more sensitive to the coating thickness and potential damage than the mixed enamel coating. This general conclusion is independent of the test solution. Mortar cover further increases the corrosion resistance of tested specimens. For deformed steel rebar, coating damage and thickness variation due to the presence of rebar ribs are the two main causes for low corrosion resistance. The double enamel coating provides the most consistent corrosion performances for various specimen applications and is thus recommended for the design of reinforced concrete structures in corrosive environments

Corrosion Behavior of Enamel Coated Steel Rebar by EIS

In this study, the corrosion process of enamel-coated deformed rebar completely immersed in 3.5 wt.% NaCl solution was evaluated over a period of 84 days by EIS testing. Three types of enamel coating were investigated: pure enamel, 50/50 enamel coating, and double enamel. Surface condition of the enamel coatings that were intentionally damaged prior to corrosion tests was visually examined at different immersion times. After 84 days of testing, the damaged coating areas were characterized by SEM, and the corrosion products on and adjacent to the damaged areas were collected and analyzed by XRD. Corrosion initiated at the damaged locations with no undercutting of the coating observed. The 50/50 enamel coating had the least corrosion resistance, due to its interconnected pore structure, and prior damage drastically reduced the corrosion resistance of pure and double enamel coated rebar. © (2012) Trans Tech Publications, Switzerland