By far, carbon and glass fibers are the most popular fiber reinforcements for composites. Traditional carbon composites are relatively expensive since the manufacturing process requires significant heat and pressure, while the carbon fibers themselves are inherently expensive to produce. In addition, they are often flammable and their use is restricted when fire is a critical design parameter. Glass fabrics are approximately one order of magnitude less expensive than similar carbon fabrics. However, they lack the stiffness and the durability needed for many high performance applications. By combining these two types of fibers, hybrid composites can be fabricated that are strong, yet relatively inexpensive to produce. The primary objective of this study was to experimentally investigate the effects of bonding high strength carbon fibers to E-glass composite cores using a high temperature, inorganic matrix known as geopolymer. Carbon fibers were bonded to E-glass cores (i) on only the tension face, (ii) on both the tension and compression faces, or (iii) dispersed throughout the core in alternating layers to obtain a strong, yet economical, hybrid composite laminate. For each response measured (flexural capacity, stiffness, and ductility), at least one hybrid configuration displayed mechanical properties comparable to all carbon composite laminates. The results indicate that hybrid composite plates manufactured using 3k unidirectional carbon tape exhibit increases in flexural capacity of approximately 700% over those manufactured using E-glass fibers alone. In general, as the relative amount of carbon fibers increased, the likelihood of precipitating a compression failure also increased. For 92% of the specimens tested, the threshold for obtaining a compression failure was utilizing 30% carbon fibers. The results presented herein can dictate future studies to optimize hybrid performance and to achieve economical configurations for a given set of design requirements.

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The objective of this case study was to perform an evaluation of the environmental effects of three surface preparation methods used in civil infrastructure: sand blasting, water jetting, and dry ice blasting. The study was based upon a bridge rehabilitation project in which surface preparation of the reinforced concrete pier caps was undertaken. The assessment considered four response variables: carbon dioxide (CO 2) emissions, fuel consumption, energy consumption, and project duration. The results indicated that for sand blasting and water jetting, CO 2 emissions stemming from vehicular traffic near the construction site was the primary factor contributing to environmental detriment. However, the CO 2 contribution from sublimation of the dry ice translated into 80% and 64% more CO 2 than sand blasting and water jetting, respectively. Compared to sand blasting and water jetting, dry ice blasting yielded the shortest project duration and reduced fuel consumption by 7.6% and 13%, respectively.

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Tensile and shear testing to final fracture of large-diameter, fiber-reinforced polymer (FRP) composite round bars is often challenging because local stress triaxiality near the gripping ends can precipitate premature failure at these locations, instead of in the desired test gauge section. A method using expansive grout materials has been used, though its design is impaired by the lack of understanding of the gripping pressure developed by the confined expansive grout material. In this paper, an analytical solution has been derived to correlate the hoop strain on the outer surface of the confining steel pipe (caused by grout expansion in the steel pipe) to the grout’s elastic modulus and coefficient of linear expansion. By experimentally measuring the exterior surface hoop strains of two different steel pipes, the elastic modulus and coefficient of linear expansion were determined. This solution has been generalized to include the composite bar and predict the gripping pressure at the bar-grout interface for any given pipe and composite bar combination. Based on the analytical results, expressions for key design parameters for improved expansive grout-based gripping systems, including the minimum grip length, optimum dimensions of the confinement pipes, and minimum volume of the grout material, have been provided. Based on the improved design, glass FRP bars of diameters 19.0 to 38.0 mm (0.75 to 1.5 in.) were tested without gripping problems and with failure loads up to 534 kN (126 kip), which significantly exceeds 400 kN (90 kip), the load level identified as a threshold of concern

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