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Tabatabaei Z.S.,Missouri University of Science and Technology | Volz J.S.,Missouri University of Science and Technology | Gliha B.P.,U.S. Army | Keener D.I.,Pro Perma Engineered Coatings
Journal of Materials in Civil Engineering | Year: 2013

This paper discusses the development and testing of long carbon fibers-fibers 75 mm long or longer-to improve the resistance of reinforced concrete to dynamic loading, such as blasts and impact. In the past, attempts to use long fibers in concrete have failed as a result of both balling (agglomeration) and poor dispersion of the fibers. In the present study, two types of long carbon fibers were developed and optimized for their use in reinforced concrete. The resulting long carbon fiber-reinforced concrete (LCFRC) was subsequently evaluated through impact and blast testing. Full-scale blast testing revealed that these fibers significantly increased the resistance of concrete spalling. In terms of the amount of material lost during the blast, LCFRC panels outperformed nonfiber concrete panels by nearly a factor of 10. This significant reduction in weight loss for the LCFRC panels translates into a substantial decrease in harmful, flying debris in a blast event, and a corresponding reduction in blast lethality. © 2013 American Society of Civil Engineers. Source


Tabatabaei Z.S.,Missouri University of Science and Technology | Volz J.S.,Missouri University of Science and Technology | Keener D.I.,Pro Perma Engineered Coatings | Gliha B.P.,Missouri University of Science and Technology
Materials and Design | Year: 2014

The addition of long carbon fibers (fibers more than 10. mm in length) to traditional reinforced concrete is proposed as a method to improve the impact spalling resistance of concrete. A series of experimental tests were conducted to compare the impact resistance of plain concrete (PC), steel reinforced concrete, and four different types of long carbon fiber reinforced concrete (LCFRC) panels. The plain and conventional steel reinforced concrete panels served as control specimens. Of the four types of long carbon fibers tested in this study, the first fiber type consisted of an epoxy-impregnated, bidirectional weave (Type A), while the remaining types consisted of fiber tow with three different variations of a polypropylene support system (Type B). To determine the properties and performance of the LCFRC, experimental testing included a drop weight impact test of the panels as well as a standard ASTM test method for flexural performance of fiber-reinforced concrete. The results from each test in terms of impact energy, time histories of impact load and deflection, strain energy, failure crack pattern, and flexural properties were then compared to one another. This comparison indicated that adding long carbon fibers to concrete increases the post-cracking behavior of the concrete and decreases fragmentation during an impact test. Of the four fibers tested, Fiber Type B3 exhibited the highest performance, absorbing more energy during impact. This result is most likely related to the unique shape of this type of fiber in comparison to the others, which allowed more extensive wetting of the fiber with cement paste and thus improved bond to the cementitious matrix. © 2013 Elsevier Ltd. Source


Tang F.,Missouri University of Science and Technology | Cheng X.,Missouri University of Science and Technology | Chen G.,Missouri University of Science and Technology | Brow R.K.,Missouri University of Science and Technology | And 2 more authors.
Electrochimica Acta | Year: 2013

The electrochemical behavior of enamel coated carbon steel in simulated concrete pore water solution with various chloride concentrations was investigated by open circuit potential, linear polarization resistance, and electrochemical impedance spectroscopy tests. The phase composition, microstructure, and tensile strength of enamels were characterized by X-ray diffraction, scanning electron microscopy, and pull-off tests. Three types of coatings with pure, mixed, and double enamels were studied and compared for their corrosion behavior. Test results indicated that all three types of enamel coatings can reduce the corrosion current density of carbon steel in an alkaline environment with chloride; the pure and double coatings are superior to the mixed enamel coating. Cohesive failures were observed within the three coatings while their interface with the steel substrate remained intact. In comparison with the pure enamel, the mixed enamel was stronger with smaller open channels formed due to the addition of calcium silicate and the double enamel was weaker with larger air bubbles trapped in the inner pure enamel layer by the outer mixed enamel layer. © 2013 Elsevier Ltd. Source


Tang F.,Missouri University of Science and Technology | Chen G.,Missouri University of Science and Technology | Volz J.S.,Missouri University of Science and Technology | Brow R.K.,Missouri University of Science and Technology | Koenigstein M.,Pro Perma Engineered Coatings
Construction and Building Materials | Year: 2012

Corrosion behavior of enamel-coated reinforcing steel bars in 3.5 wt.% NaCl solution is evaluated by open-circuit potential, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization testing. Three types of enamel coating are investigated: a pure enamel coating, a mixed enamel coating that consists of 50% pure enamel and 50% calcium silicate by weight, and a double enamel coating that has an inner pure enamel layer and an outer 50/50 enamel layer. The coatings are characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS) techniques. SEM images reveal that all three enamel coatings have a porous structure. The pores in the pure and double enamel are disconnected, while those in the mixed enamel are interconnected. Electrochemical tests demonstrate that both pure and double enamel coatings can significantly improve corrosion resistance, while the mixed enamel coating offers very little protection. © 2012 Elsevier Ltd. All rights reserved. Source


Wu C.,Missouri University of Science and Technology | Chen G.,Missouri University of Science and Technology | Volz J.S.,Missouri University of Science and Technology | Brow R.K.,Missouri University of Science and Technology | Koenigstein M.L.,Pro Perma Engineered Coatings
Construction and Building Materials | Year: 2012

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%. © 2012 Elsevier Ltd. All rights reserved. Source

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