Durability Study on Concrete Bridge Decks With Pultruded FRP Stay-in-Place Structural Forms
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This study consists of three phases examining the durability of concrete bridge decks with stay-in-place GFRP structural forms that completely replace the bottom reinforcing bars. Phase I examines the effect of aggressive freeze-thaw (FT) cycles on strength of small scale decks. The concern has been whether entrapped moisture may cause ‘frost-jacking’ of the form. Eleven specimens were built, each using two spliced flat GFRP plates with T-shape ribs, spanning the gap between girders. The study simulated various surface treatments of the form as well as unbonded and bonded lap splices. The decks were cracked before being saturated and subjected to up to 300 FT cycles at +5°C to -18°C core temperatures. Some specimens were thawed without being submerged and one specimen had perforated forms for drainage. Subsequent testing to failure showed no reduction in ultimate capacity or stiffness, despite the 23% reduction in tensile strength of GFRP coupons from the same form, because failure was governed by punching shear. Phase II compares the GFRP form tested in Phase I to another corrugated form, using short one way slabs to trigger a shear-bond failure. Nine slabs with different surface treatments were fabricated and some were exposed to the same FT cycles. It was clearly shown that flat-ribbed forms are superior to corrugated ones, as no loss in strength occurred after FT exposure, whereas corrugated form-specimens lost 18-21%. This is attributed to the anchorage advantage provided by the T-shape rib embedment in concrete. In Phase III accelerated aging of the two GFRP forms is studied in 3% salt solution at 23, 40 and 55oC for up to 224 days, using 170 coupons to establish tensile strength retentions. Data were assessed using Analysis of Variance (ANOVA). It was shown that the tensile strength retentions of both forms were similar and reduced from 77 to 63% as the temperature increased from 23 to 55°C. Results also showed that the polymer matrix is not fully degraded by the hydrolysis as no significant changes occurred in glass transition temperature. When data was fitted in the Arrhenius service life model, it showed that after 100 years, the ribbed form will suffer more deterioration than the corrugated one as the strength retentions at a location with annual mean temperatures of 10oC were 42 and 61%, respectively.