There is an urgent demand for durability data in the field of FRP composites. This project focuses on evaluating certain durability characteristic of FRP reinforcing bars in terms of strength and elastic modulus reduction at different loading and environmental conditions. Specially, this project is to identify the degradation mechanisms of FRP rods under harsh environments, sustained stress and thermal conditions; to develop strength and stiffness reduction factors using accelerated test for the evaluation of alkaline effects on durability of GFRP rods; to develop a model from accelerated laboratory tests for prediction of service life of FRP bars in concrete corresponding to observed experimental behaviour. Additionally, various micro-structural analysis tests are being conducted to identify the degradation mechanisms of the GFRP bars. The test program consists of experimental tests and theoretical analyses. The test specimens will be tested under the combination conditions of environmental exposure, temperature and application of a constant load for different exposed periods. The following parameters were used in this research, which are: 1. Sustained tensile stress. Axial tension was applied on all bars during the entire duration of the test to mimic field conditions. The sustained stress is a major factor in this durability study as it gives way to the external media to migrate through the micro-cracks on the matrix around the fibres, increasing the attack level. The stress level was kept at 20-40% of the guaranteed tensile stress, corresponding to strains of 2400- 4000µe. These levels of strains are about 1-2 times the values recommended by current codes, this was done to explore the potentials of the material and evaluate how conservative the current codes are. 2. Surrounding media: Two different media were used to simulate the most common state of the bars in the field; de-ionized water and alkaline solution. The alkaline solution (pH = 12.7-13.1) simulates the cement paste and was kept constant throughout the test. 3. Temperature: Both ambient and elevated temperatures were used. The elevated temperatures were used to expedite the absorption of the medium solution by the GFRP bars . Ambient temperature is defined by 20oC and elevated temperature was 45 to 75oC. 4. Diameters of GFRP ISOROD bars. Three types of more used diameters (9,12.7 and 15.9 mm) are used to evaluate the scale effect. 5. Types of testing . An accelerated exposure in high temperature for 1, 2 and 3 months. For verification , some tests have been done for long-term duration (8 and 14 months).
The experimental program has been completed in May 2004 and the writing of the thesis is in progress.
The residual mechanical properties of GFRP bars are investigated under combined effects of temperature and alkaline or water medium, in addition to constant sustained tension. The data obtained are focused on the residual strength and stiffness as affected by these parameters. The research proves the almost no change in the elastic modulus of the GFRP bars will take place, an acceptable drop in the ultimate strength and failure strain were observed. The environmental reduction factors recommended by many codes for the allowable strength of FRP bars are thought to be very conservative . The findings suggest the need to adopt less conservative design limits than currently used. The elevated temperature used is believed to simulate the site conditions over 75 years. The findings suggest the need to adopt less conservative design limits than currently used.
G., Nkurunziza (2004). "Performance of glass FRP bars as reinforcement for concrete structures under the effect of sustained loads and elevated temperature in humid and alkaline environment". Ph.D. Thesis (in French), Department of Civil Engineering, Université de Sherbrooke, Sherbrooke, Québec, August, 248 p.
G., Nkurunziza, R. Masmoudi, and B. Benmokrane, "Effect of Sustained Tensile Stress and Temperature on Residual Strength of GFRP Composite Bars", CDCC-02, Montréal 29-31 mai, 2002.
Masmoudi, R., Nkurunziza, G., Benmokrane, B. and Cousin, P. "Durability of Glass FRP Composite Bars for Concrete Structures under Tensile Sustained Load in Wet and Alkaline Environments", CSCE Annual Conference, Moncton, Nouveau-Brunswick, Canada, 4-7 June 2003.
G. Nkurunziza, P. Cousin, R. Masmoudi, and B. Benmokrane, "Effect of Sustained Stress and Temperature on GFRP Composite Bars Properties: Preliminary Experiment in De-ionized Water and Alkaline Solution", (accepted for publication in the International Journal of Material and Product Technology.
G. Nkurunziza, A. S. Debaiky, B. Benmokrane, and R. Masmoudi, Effect of Creep and Environment on Long-term Tensile Properties of Glass FRP Reinforcing Bars, 4th International Conference on Advanced Composite Materials in Bridges and Structures, Calgary, Alberta, 20-23, 2004.
G. Nkurunziza, B. Benmokrane, and A. Debaiky, "Residual Tensile Properties of GFRP Bars under Loading in Severe Environments", ACI Journal (to be submitted)
Poster presentation during Radio Canada visit to the Department of Civil Engineering, University of Sherbrooke, Sherbrooke, May 2003.
Poster presentation at the 7th Annual ISIS Canada Conference, Halifax NS, 28-30 April 2004.