The use of Fiber-reinforced polymer (FRP) composite materials in new construction and repair of concrete structures has been growing rapidly in recent years. FRP provides options and benefits not available using traditional materials. The promise of FRP materials lies in their high-strength, lightweight, noncorrosive, nonconducting, and nonmagnetic properties. ACI Committee 440 has published several guides providing recommendations for the use of FRP materials based on available test data, technical reports, and field applications. The aim of these document is to help practitioners implement FRP technology while providing testimony that design and construction with FRP materials systems is rapidly moving from emerging to mainstream technology.

This paper introduces a rectangular concrete-filled fiber reinforced polymer (FRP) tube (CFFT) hybrid beam with an inner voided tube. The beam contains an outer rectangular filament-wound glass fiber reinforced polymer (GFRP) tube, and an inner voided circular filament-wound GFRP tube shifted toward the tension zone. The space between the tubes is filled with concrete. Steel bars, at the tension side, were provided to enhance both stiffness and serviceability of the beam. The flexural behavior of this voided CFFT beam was compared with a fully CFFT beam and another conventional steel reinforced concrete (RC) beam having identical dimensions. The results showed that the new hybrid composite beam behaves positively in terms of strength, ductility, and failure propagation, in addition to its high durability. The results also showed that, while the weight of the voided CFFT beam is 30% lighter than the weight of the conventional RC beam or the fully CFFT beam, its flexural capacity is 141% and 6% higher than their flexural capacities, respectively.

Coarse recycled concrete aggregate (RCA) has been studied as a replacement for natural aggregate (NA) in concrete for decades. RCA is still predominantly used in non-structural applications such as filler, road sub-base, drainage material, and low quality concrete. However, there is increased interest in using RCA in new structural concrete due to restrictions on landfilling of construction and demolition (C&D) waste and on the scarcity of natural aggregates, especially in urban megacities. The compressive strength of concrete with coarse RCA is typically 15–30% less than that with NA. This feasibility study was conducted to evaluate the effect of FRP strengthening on RCA beams as compared with NA beams also strengthened with FRP. Four RCA and four NA beams were strengthened in flexure and in shear using hand laid-up carbon-epoxy FRP materials. A combination of longitudinal strips on the beam soffit and intermittent closed hoop wraps along the length were used. The FRP-strengthened beams were designed to yield and then fail in compression with the FRP still attached. The results of the testing are described. The ability of FRP strengthening to, (1) change the failure mode of RCA beams, and, (2) to improve the reliability of RCA concrete beams constructed or repaired with FRP materials is discussed. It was found, surprisingly, that the FRP-strengthening was effective in increasing the capacity of the RCA beams. This is attributed to a different failure mechanism of the RCA beams from that of the NA beams tested.

Steel prestressed cored slab superstructures are a common structural system for multi-span bridges in coastal North Carolina. However, due to the aggressive marine environment several such bridges are in need of major repairs or replacement after being in service for little more than 40 years. To address this issue two research projects were undertaken in parallel. The first project involved a critical assessment of non-destructive evaluation techniques in an attempt to predict the extent of corrosion deterioration and hence, the residual strength of cored slabs from existing bridges. Twelve cored slabs taken from two in-service bridges scheduled for superstructure replacement were tested to failure in the laboratory to validate residual strength predictions. The second project involved the design, manufacture and testing of a full-scale CFRP prestressed cored slab reinforced with GFRP stirrups, and a typical steel prestressed cored slab control specimen. The results of the destructive laboratory testing enabled validation of the prediction of the flexural performance and strength of CFRP prestressed cored slabs relative to existing design recommendations. Direct comparison to the new steel prestressed control cored slab and similar existing cored slabs with varying degrees of deterioration from the first the research project was also undertaken.

An experimental study was conducted to determine the transfer length of prestressed Glass Fiber Reinforced Polymer bars. This paper is a part of a broad program that studies the long-term behaviour of GFRP prestressed concrete beams. 16 GFRP prestressed concrete beams were cast in this study. The parameters included were; prestressing level; 300 MPa (44 ksi) and 500 MPa (73 ksi), concrete compressive strength; 30 MPa (4440 psi) and 70 MPa (10000 psi), and the GFRP bar diameter;12Φ (No. 4) and 16Φ (No.5). Accurate estimation of the transfer length is necessary for elastic stress calculations at the service limit state and for the shear design of prestressed members. Strain gauges were used to measure strains on the GFRP bars and DEMEC gauges were used to measure the concrete surface strains at the level of the prestressed GFRP bar to determine the transfer length. The transfer length of 16Φ (No.5) GFRP bars in concrete with compressive strength of 30 MPa (4440 psi) was found to be about 17 db, and 14 db for prestressing levels of 500 MPa (73 ksi) and 300 MPa (44 ksi), respectively. The measured transfer length values were used to improve the transfer length estimates provided by the ACI 440.4 R-04 equation by calibrating the material coefficient factor (αt) used in the ACI equation.