Fiber Reinforced Polymer (FRP) Composites for Infrastructure Applications

The effect of environmental and loading conditions on the degradation of Interlaminar Shear Strength (ILSS) of the carbon-epoxy composite specimens was studied. The hygrothermal conditions capture the synergistic effects of field exposure and extreme temperatures. A short beam shear test (SBST) was performed to determine the Interlaminar Shear Strength (ILSS) of environmentally aged composite specimens in accordance with ASTM D2344-84. Initially, a standard two-dimensional cohesive layer constitutive model was employed in order to simulate the experiment using an in-house FEA code (NOVA-3D). Numerical instabilities, encountered using the standard cohesive layer model, were overcome by incorporating viscoelastic regularization in the constitutive equations of the cohesive layer. This modification also enabled the analysis to continue beyond the point of peak failure load. The model was able to accurately simulate the load vs. displacement behavior of most of the SBST samples aged under various hygrothermal and synergistically applied stress conditions. Further, the effect of displacement rate on the ILSS of specimens was studied using NOVA-3D. The model indicated a strong dependence of viscoelastic cohesive strength on the displacement rate. Regrettably, the predicted rate dependence could not be verified experimentally.

Advanced fiber reinforced polymer (FRP) composite materials have been increasingly used in many applications relevant to the Army’s transformation. Many of these applications require the FRP composites to perform over long periods in harsh environments with extremes of temperature, humidity, water, and exposure to ultraviolet radiation and chemicals. It is important to understand the long term durability of FRP composites to environmental stimuli. This paper presents results of the hygrothermal degradation of E-glass/epoxy composites in accelerated tests and compares these results to predictions made using a modeling methodology based on Arrhenius-type reaction laws. To investigate the hygrothermal degradation behavior, E-glass/epoxy composites were subjected to accelerated tests at controlled temperatures and relative humidities. The specimens were exposed in an unloaded state and with a static tensile load of 2% of the ultimate transverse tensile strength. In the model predictions, three degradation mechanisms were considered: (1) post-curing, (2) thermal degradation, and (3) hygrothermal degradation.

Increased use of fiber reinforced polymeric composites in an outdoor environment has led to questions concerning their environmental durability, particularly as related to ultraviolet (UV) radiation, moisture, and temperature exposure. This chapter describes the effects of UV and UV radiation + condensation (UC) on the static and dynamic compressive properties of unidirectional glass/epoxy composites. The samples were manufactured using an infusion process with and without nanophased epoxy and exposed to UV radiation and UC conditioning for 5, 10, and 15 days respectively. Nanophased epoxy was prepared with 1 wt%and 2 wt% nanoclay. Static compression tests were carried out using MTS test system under displacement control mode at a crosshead speed of 1.27 mm/min. Dynamic compression tests were carried out using modified Split Hopkinson Pressure Bar (SHPB) at different strain rates. The compressive strength and stiffness were evaluated as functions of strain rate. Results of the study showed that samples lost weight when exposed to UV radiation, whereas they gained weight when exposed to UC conditioning. Weight gain or loss was lower for nanophased composites when compared to neat samples. Static and high strain compressive properties reduced for all the nanophased samples when compared with room temperature samples. However, the loss in compressive properties was lowest in nanophased composites with 2 wt% nanoclay.

There is overwhelming consensus among researchers that the bond strength between concrete and fiber reinforced polymer composite materials would be the first to yield when the composite is exposed to high temperatures. In this chapter, a semi-empirical model is developed that accounts for molecular bond breakup and viscosity conversion degree rate values to predict the normalized bond strength at elevated temperatures. The model is assessed with limited experimental data from available literature. Our results show that the proposed approach correlates well with the available experimental results. This formulation can be used for design of FRP reinforced concrete members at elevated temperatures, particularly in identifying critical bond strength and comparison of alternative proposed FRP reinforcing systems.

Fiber reinforced polymer (FRP) panels may be used in deployable ­structures such as those required for the protection and mobility of armed forces. In this study, FRP panels were fabricated by hand in the laboratory and subjected to impact loading to investigate the resistance against impact actions. A striker with a hemispherical head having a diameter of 100 mm and weight of 43 kg, was allowed to drop freely along a frictionless guide from a height of 4 m onto the panels. Both carbon and glass FRP panels with up to ten plies of fiber sheets were investigated. The panels were subjected to a maximum of ten successive impacts. The impact characteristics, including the impact force and impulse, strains and displacements, and energy absorption capacity, are reported and compared. Test results showed that carbon FRP panels were likely to fail by punching shear with a small amount of fiber reinforcement. Otherwise, the energy absorption capacity of FRP panels increased with the amount of fiber reinforcement. Also, carbon FRP panels exhibited higher energy absorption capacity compared to glass FRP panels.

Successful utilization of advanced polymer composite materials in civil infrastructures have long been recognized in bridge deck applications. The concept of ‘steel-free’ in concrete bridge decks can be achieved by replacing the conventional steel reinforcement with fiber reinforced polymer (FRP) based reinforcing materials. Reviewed in this chapter are steel-free bridge decks reinforced with these composite reinforcement in forms of round or square rods, 2-D or 3-D grids or gratings, flat or curved FRP plate, sandwich panel with foam/balsa/steel inserts, stiffened or corrugated stay-in-place formwork, and polymer decks.

Fiber-Reinforced Polymer (FRP) strengthening of structural systems has increased in applications over recent years. The many benefits that the technology offers are significant. Field validation of FRP-strengthened bridges through load testing provides a means of measuring the performance of a bridge over time. Non-contact optical surveying equipment is one such method that can measure the deflection of bridges subjected to a static load. Since 1999, more than 25 FRP bridges in Missouri have either been repaired or constructed using FRP products to serve as demonstration and case study projects. A remaining question related to this technology is their long-term field performance. This work presents the load testing results of four bridges located in Morgan County, Crawford County, Iron County, and Dallas County, Missouri. These bridges were originally strengthened in 2003 with different FRP technologies and subsequently load tested biennially. The investigation focused primarily on determining if the bridges had undergone any degradation in the FRP material properties based upon the structures’ response to loading. Deflection and load distribution between girders was monitored. Pre- and post-load testing results were compared to better understand the performance over time and study structural degradation. Finally, the visual inspection results of these bridges by the researchers are presented. FRP is slowly making strides within the Civil Engineering community. The widespread acceptance of these materials is hampered by their unproven long-term reliability. Monitoring deflections of bridges constructed with FRP technologies under static load testing can help validate the long term performance of these materials.

Long-term performance and extended service life are issues of vital importance to the Department of Defense (DoD). The DoD seeks alternative construction materials to replace more traditional materials, such as wood and steel, for heavily loaded infrastructure to combat this expensive corrosion and bio-degradation problem. Recently, two military bridge installations were completed, composed entirely of a reinforced thermoplastic composite lumber (RTCL) material that is capable of supporting the load of an M1 Abrams tank at approximately 64,410 kg (71 tons). The RTCL material selected for these applications is polypropylene (PP) coated fiberglass blended with high-density polyethylene (HDPE). Advantages of using RTCL include the following qualities: corrosion, insect, and rot resistance; no toxic chemical treatments required to increase service life; environmentally friendly; diversion of waste plastics from landfills; reduction of deforestation, green house gases, and global warming. RTCL has many advantages but does behave differently than traditional materials and certain properties must be addressed during the design stage. Both bridges are continually monitored, have performed well over the first year and a half, and are more cost-effective than any other construction material. Details of the material, design considerations, and construction are reviewed.

Two severely deteriorated long-span, precast, prestressed, box-girder bridges, located in Defiance, Ohio, were selected by the Federal Highway Administration’s (FHWA’s) Innovative Bridge Research and Construction Program for rehabilitation using advanced carbon fiber polymer (CFRP) composite materials, full-scale live-load testing, and long-term structural health monitoring. The root cause of deterioration was an improper deck drainage scheme, which had enabled the de-icing salts and water to corrode the prestressing strands and spall the concrete. Sika’s CFRP stress-head system, a post-tensioned and bonded external strengthening technique, was utilized to restore the original load carrying capacity of the deteriorated beams. An integral component of the rehabilitation plan was a long-term, structural health monitoring system (SHM), installed to monitor the performance of selected beams on the bridges. The structural health monitoring system consisted of vibrating wire strain gages with integrated thermistors to monitor changes in strain and temperature on 11 beams on the bridges. The data compiled reveal that compression is induced in the bottom of the deteriorated beams, thereby improving the load-carrying capacity. The use of the external Stress Head post-tensioning system proved to be a viable and effective means to strengthen a deficient box girder bridge. In addition, a series of full-scale live load tests were conducted prior to and following the completion of bridge rehabilitations. Strain transducers were employed to monitor the structural response under the multiple passes of truck loads. An overview of the compilation of the short-term live load test results and long-term structural health monitoring data is presented in this manuscript. The behavior of both bridges in terms of strain response history is summarized.

The main goal of this work is to determine the economic feasibility of Fiber Reinforced Polymer (FRP) as the primary material for construction of short span bridge decks. The analysis is based on a comparison of the lifecycle costs for a cast-in-place steel reinforced concrete bridge and FRP bridge deck over a 60-year time horizon; both have dimensions of 8.0 m (26.3 ft) long by 8.3 m (27.2 ft) wide. The total cost estimate using the FRP material ranges from $82 to $182 per square foot ($882–$1958 per sq meter) with a range average of $132 per square foot ($1,420 per sq meter). It is also shown that the breakeven construction cost of the FRP deck is $113 per square foot ($1216 per sq meter) for a discount rate of 2%. The main factors affecting the analysis are costs of material, traffic delays, and discount rate.