James Giancaspro

Flexural response of inorganic hybrid composites with E-glass and carbon fibers

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.

FRP composites for reinforced and prestressed concrete structures : a guide to fundamentals and design for repair and retrofit

Chapter 1: Introduction Chapter 2: Constituent Materials Chapter 3: Fabrication Techniques Chapter 4: Common Repair Systems Chapter 5: Flexure: Reinforced Concrete Chapter 6: Flexure: Prestressed Concrete Chapter 7: Shear in beams Chapter 8: Columns Chapter 9: Load Testing

Expansive Grout-Based Gripping Systems for Tensile Testing of Large-Diameter Composite Bars

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 grouts 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. DOI: 10.1061/(ASCE)MT.1943-5533 .0000807.

Environmental Evaluation of Abrasive Blasting with Sand, Water, and Dry Ice

The objective of this case study was to perform an evaluation of the environmental eects 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 (CO2) emissions, fuel consumption, energy consumption, and project duration. The results indicated that for sand blasting and water jetting, CO2 emissions stemming from vehicular trac near the construction site was the primary fac- tor contributing to environmental detriment. However, the CO2 contribution from sublimation of the dry ice translated into 80% and 64% more CO2 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.

High Strength Fiber Composites for fabricating fire-resistant wood with improved mechanical properties

This paper deals with one of the new research areas of Professor Hans Wolf Reinhardt, namely textile-reinforced structural members. Typically, wood is a light, versatile construction material well known for its ease of installation. The major drawbacks are its relatively low strength and stiffness, poor visco-elastic long-term deformation, and insufficient fire resistance. The results presented in this paper deal with the use of high modulus carbon / inorganic polymer composite skins to fabricate a sandwich plate that can be engineered to obtain high strength, high stiffness, and excellent fire resistance. The inorganic polymer is fire-resistant, can withstand 800°C indefinitely, and provides protection for both carbon fibers and the wood substrate. Sandwich plates were fabricated using balsa wood for applications that are weight-critical such as those in aerospace and naval structures. For applications in buildings, beams cut from typical woods such as oak were strengthened to improve their flexural strength and long-term deflection stability. The modulus of carbon fiber was 600 GPa and high stiffness values can be obtained with a very low reinforcement ratio. The strengthened beams were tested in flexure; while the fire resistance was evaluated, using the standard OSU (Ohio State University) heat release and NBS (National Bureau of Standards) smoke burner tests. The strengthened composite satisfied the high temperature (fire) requirements of the Federal Aviation Administration of the United States of America. This paper presents the flexural and high temperature response of the strengthened beams.

Concrete Surface Topography as a Function of Freeze-Thaw Exposure and Abrasive Blasting

This study investigated the topography of plain concrete during freeze-thaw exposure and following abrasive blasting. The independent variables included the water-cementitious material ratio (w/cm) (0.42, 0.50, or 0.56); the number of freeze-thaw cycles (100, 200, or 300); and the blasting method (dry ice or sand). Using the three-dimensional (3D) surface roughness as the response parameter, the analysis of variance (ANOVA) results indicated that the number of freeze-thaw cycles is most influential in governing the measured roughness due to both freezing and thawing and abrasive blasting. The statistical data indicate that the roughnesses created by the blasting methods are not significantly different, which suggests that both dry ice and sand produced equivalent surface topography. However, qualitative examinations revealed that sand blasting generated a relatively uniform surface, whereas dry ice blasting created localized damage in the form of pitting. This effect may stem from differences in the flow behavior and size of the particles prior to impact with the substrate.

A Novel Bearing Swivel Joint and a Universal Joint for Concrete Pull-Off Testing Using a Material Testing Machine

The overall goal of this short study was to integrate two pull-off coupling devices for concrete: a bearing swivel joint and a universal joint, into an existing material testing machine. Their performance was evaluated in terms of efficiency using setup duration and compared to that of a commercially available portable testing device. Fifty-three pull-off tests were conducted on concrete prisms in accordance with ASTM C1583-04. Our results indicate that the portable tester was most efficient (6 min/test), followed by the universal joint (16 min/test), and then the bearing swivel joint (22 min/test). An online movie, as referenced in the text, demonstrates the modified test procedure, and recommendations for improvements to the test method are briefly discussed. Future testing will evaluate the variability among test results from the three devices.

Analysis and Design Recommendations of FRP-Strengthened Prestressed Concrete Beams

This paper describes how there are a limited number of experimental results available on the retrofit of prestressed concrete structural elements. In addition, there is a lack of analytical models that deal with the flexural performance of such elements. This paper addresses the latter problem by presenting a methodology for analysis and design of prestressed concrete flexural elements strengthened with externally bonded, fiber reinforced composites. The method provides systematic suggestions on the analysis and design of strengthened prestressed concrete beams with both bonded and unbonded tendons. The method can be used to determine the flexural capacity and to compute stresses and strains in concrete, tendons, and externally bonded fiber reinforcement. Compared to existing experimental data on carbon strengthened beams, the model provides very good prediction of the flexural performance of strengthened prestressed beams. The equations are also applicable to other fiber types including glass, steel, and aramid.