The corrosion problem of steel bars is the greatest factor in limiting the life expectancy of reinforced concrete structures. In North America, this phenomenon has been exacerbated in parking garages and bridge decks by the use of de-icing salts and significant fluctuations of temperature. Canada's roads and bridges are subject to some of the harshest conditions due to freeze thaw cycles and the heavy applications of de-icing salts. The use of non-corrosive (FRP) reinforcing bars for concrete bridge decks provides a potential for increased service life, economic, and environmental benefits. Since GFRP rebar is more economical than the other available types (carbon and aramid FRP rebars), it is more attractive for infrastructure applications and to the construction industry. This innovative structural material has also the potential to reduce construction costs by eliminating the use of large concrete cover, membrane and pavement items (typical Canadian concrete bridge deck slabs consists of two mats of steel bars with an increased concrete cover (up to 65 mm in the top), a membrane and pavement as added protection against corrosion), as well as to reduce the burden of repair and maintenance life cycle costs. The mechanical and physical properties of FRP reinforcing bar are very different from those of steel reinforcement. The design formulas and construction details that are well established for steel-reinforced concrete structures can not be used for FRP-reinforced ones. Thus, it is required to define new and suitable design methods for concrete structures reinforced with FRP’s to take into account this type of behaviour. Also, the coefficient of thermal expansion of FRP reinforcement in the transverse direction is very different from that of concrete (2 to 4 times that of concrete for glass FRP). While this coefficient for steel is very close to that of concrete. When temperature changes up and down (Bridge decks in Canada in general are subjected to a variation of temperature from – 40 C0 to +35 C0), this difference in coefficient of thermal expansion affects the bond and cracking behaviour of FRP-reinforced concrete elements. As well, GFRP has relatively low modulus of elasticity (40 GPa) compared to steel (200 GPa). This relatively low modulus of GFRP reduces the serviceability performance of the flexural members.
The design of reinforced concrete deck slabs is usually governed by the serviceability and durability concerns, represented in cracking, deflections, fatigue limits as well as punching shear capacity under concentrated loads. Recently, there have been concerns regarding the long-term and fatigue behaviour of FRP reinforced concrete slabs. Limited experimental and analytical data is available on the behaviour of concrete deck slabs reinforced with FRP bars. Even less research on the fatigue response of concrete deck slabs reinforced with FRP bars was carried out. Virtually no work has been done on the effects of cold temperature or freeze-thaw action on deck slabs reinforced with FRP bars. More research is needed to investigate the effect of different parameters (such as concrete cover, type of FRP reinforcement, reinforcement ratio, bar size and spacing) that affect the behaviour of deck slabs under sever environment (e.g., freeze-thaw and wet-dry cycles) and loading conditions.
The concrete bridge deck slabs is the most bridge component exposed to corrosion, due to direct exposure to freeze/thaw cycles, de-icing salts, and to ever increasing traffic. Furthermore, in the amendment to Chapter 16 of CHBDC- dealing with FRP as reinforcement for concrete bridges, new design provisions including new equations to calculate crack width, deflection, and stress limits are introduced. These new design equations need to be improved/validated through experiments. The main objectives of this research activity are:  to quantify the effect of the different design parameters such as the concrete cover, GFRP reinforcement ratio (size of bar and spacing), and concrete compressive strength on their behaviour;  to define acceptable ranges (or design factors) for glass FRP bars based on durability investigations (ex. fatigue limits, environmental reduction factors taking into account the effect of freeze/thaw and thermal cycling, humidity, etc,);  to develop/validate/improve design guidelines and design formulas for predicting long-term deflections and crack widths of concrete deck slabs reinforced with FRP bars.
This research activity consists of three phases, which investigate the following parameters: (1) Type of FRP bars (carbon or glass) (2) Spacing between girders, (3) Deck slab thickness, (4) Overhang length, (5) Concrete strength, (6) Type of loading, (7) FRP reinforcement ratio for longitudinal and transverse directions, (8) Composite versus non-composite design. Phase 1 includes the laboratory testing of two types of bridge deck slabs: one-way simply supported slabs and isolated edge-restrained bridge deck slabs reinforced with FRP bars. The span and the thickness of the slabs will range from 1.8 to 3.8 m and 175 to 240 mm, respectively. These spans and thicknesses of the slabs represent the common size of the girder type bridges as indicated in the CHBDC. The one-way slabs will be designed and tested in four-point bending to evaluate the flexural behaviour according to the Section 8.8 of the CHBDC (flexural design method). The isolated edge-restrained slabs will be designed and tested under a single concentrated load representing the footprint of a truckload according to the Section 8.18 and 16.8.7 of the CHBDC (empirical design method). This is to simulate the real conditions taking into account the influence of the membrane forces and the arching action on the behaviour and capacity of the bridge decks. For both types of slabs, the loads will be applied in both monotonic and cyclic modes.
Phase 2 includes laboratory testing of full-scale continuous bridge deck prototypes using the same spans and thicknesses of the slab as in phase I with an overall dimensions ranging between 4.008.00 and 6.0012.00 m. The bridge deck prototypes will consist of slabs continuous over two spans with an overhang (0.75 - 1.50 m) at each side. The slabs will be cast-in-place and supported on three main girders. Two types of girders will be used: steel and prestressed concrete (including the NETB concrete girders prestressed with FRP tendons developed in activity 1b-phase 2 of this research proposal). These girders will be supported laterally using steel frames similar to those used in Phase I. Based on the test results of Phase 1, different FRP reinforcement configurations will be used in the top and bottom layers. A single or multiple concentrated loads similar to that used in Phase 1 will be used. Different modes (monotonic and cyclic) and combinations of loading will be applied. This load will be applied, up to failure to evaluate and make direct comparison between the different reinforcement configurations. These bridge deck prototypes will be constructed and tested in the new testing facility provided by CFI Laboratory (see activity 8a of this research proposal).
In phase 3, an analytical modelling will be carried out using the
commercially available computer software (e.g. ANACAP, ADINA, ABAQUS, and ANSYS)
through non-linear finite element analysis (FEA) to predict the behaviour of
concrete slabs. Non-linear FEA will be conducted to investigate the stresses
arising from the thermal incompatibility of FRP and concrete. The experimental
results will be used to calibrate the analytical results. Using the computer
program, parametric studies to investigate different factors such as ratio of
concrete cover to bar diameter, reinforcement ratios, temperature gradients, and
cyclic loading can be carried out.
During the first five-year term of the chair, some of the work described in phase 1 and 3 has already been completed (FRP reinforcement type, ratio, and configuration under monotonic loading conditions have investigated experimentally and analytically).