دانلود رایگان مقاله انگلیسی بررسی تجربی بر رفتار پیوند بین خوردگی-شکسته بتن مسلح و ورق CFRP - تیلور و فرانسیس 2017

ABSTRACT

Bond behavior between corrosion damaged reinforced concrete and carbon fiber reinforced concrete polymer (CFRP) sheets was experimentally investigated. Forty ordinary strength concrete blocks (150 × 150 × 200 mm) were reinforced at one side across the 200-mmdimension using three conventional ϕ12 mm steel bars at a spacing of (30, 40, and 50  mm) at a concrete clear cover of 15  mm. Thirty blocks were subjected to a cyclic treatment in 3% chloride solution until corrosion initiated and resulted in three different global cracking widths of up to 0.90 mm. Both control and corrosion damaged blocks were attached to CFRP sheets over their steel reinforced zone at bond lengths and widths ranging from (90 to 150 mm) and (50 to 150 mm), respectively, with CFRP bond length-to-bar spacing ratio kept constant at 1/3. Near-end pull-off tests were carried out using a special setup, mounted on a Universal Testing machine. Corrosion cracking caused significant reductions in bond strength, and slippage at ultimate stress at (41 and 68%), respectively. Other bond characteristics such as stress at first slippage, and bond stiffness and toughness were reduced, as well, by as high as (83, 44 and 67%) of those of control specimens, respectively. Corrosion cracks were more detrimental for smaller bond length and width values; especially after first and second corrosion stages, where bond failure was categorized by concrete skin peelingoff.

6. Conclusions

The following points highlight the main outcomes and conclusions extracted from the test results:

(1) The cracks observed on the surface of concrete blocks were parallel to the reinforcement bars and varied from two to three cracks depending upon the spacing between the reinforcing bars, and the corrosion level. The width of cracks increased with corrosion stages reaching a maximum of 1.1 mm after the last stage.

(2) The global mass loss of steel reinforcement due to corrosion increased from 2.4% at first to 5.6% at the final stage.

(3) The bond stress-slip relationship of various pull-off specimens maintained the same curve shape, regardless of the CFRP sheets’ geometric characteristics or corrosion cracking extent. It showed linear behavior after imitation of slippage until a point representing about 50% of ultimate bond stress before became nonlinear until failure.

(4) The reinforcement corrosion reduced bond characterizes, namely, bond strength, bond stress at slippage, ultimate slippage, bond stiffness and bond toughness between CFRP sheets and concrete with corroding steel by as much as 41, 83, 68, 44, and 67%, respectively.

(5) The impact of corrosion cracks was more detrimental as bond length and width was decreased; especially at first and second corrosion stages. After the third stage, the magnitude of reduction in bond characteristics was either unaffected or slightly affected by CFRP sheet’s geometric properties.

(6) The failure mode for pull-off specimens, having reinforcing steel bars spacing of 30–40 mm (corresponding sheets’ bond length of 90 and 120 mm), changed from skin peeling-off to concrete cover detachment at the last stage.