Bond GFRP-Concrete under environmental exposure

ACI Structural Journal, 2013

Reinforced concrete (RC) beams externally strengthened with glass fi ber-reinforced polymer (GFRP) strips bonded to the soffi t may see their load-carrying capacity reduced due to environmental conditions-especially due to the deterioration of bond between the adhesively bonded laminates and concrete, causing premature failure. More research has been published on the detachment of the laminate progressing from the anchorage zone than on failure induced by the formation of fl exural or shear-fl exural cracks in the midspan followed by fi ber-reinforced polymer (FRP) separation and failure designated as intermediate crack (IC) debonding. An experimental program to study degradation of the GFRP laminate beam specimens after accelerated temperature cycles, namely: 1) freezing-and-thawing type; and 2) cycles of the same amplitude (40°C [104°F]) and an upper limit approximately 70% of the glass vitreous transition temperature of the resin, T g , is described. Effects on the bond stress and ultimate capacity are reported. Substantial differences between shear and bending-induced failure and a decrease of bond stresses and engagement of the laminates on the structural response are analyzed.

This study presents an experimental investigation on the bond durability of GFRP bars in concrete when subjected to harsh environments. The pullout specimens having different concrete covers were designed based on a created database to demonstrate the generality of the current experimental program. The freeze-thaw (FT) cycles, alkaline-saline (AS) solution, and both coupled effects were used to simulate environmental conditions in cold regions. The durability performance in terms of the failure mode, weight loss, relative dynamic modulus of elasticity, durability factor, as well as the bond strength, were measured and investigated accordingly. The test results revealed that the concrete cover with three times of the bar diameter was not sufficient to resist the environmental agents when exposed to weathering, including FT cycles, in which all the pullout specimens failed by concrete splitting. The coupled scenario of FT cycles and AS solution was observed to be the worst case among all the environmental conditions. Moreover, the analytical models: modified Bertero-Eligehausen-Popov (mBPE) model and Cosenza-Manfredi-Realfonzo (CMR) model, were calibrated by considering the environmental influences based on the experimental data to better demonstrate the degradation of GFRP-concrete bond.

Use of Fibre Reinforced Polymers in new and existing structures is increasing at a rapid pace. The effectiveness of structural upgrade in the short-term tests has been demonstrated repeatedly in the laboratory tests and field applications. However, the longterm durability of the FRP and FRP-reinforced concrete has not been investigated to a point that a designer can suggest the application of FRP with the same confidence as the traditional materials. In this paper, selected results from an extensive test program are presented in which the durability of FRP materials and FRP-reinforced concrete was investigated. The environmental parameters to which the specimens were subjected included freeze-thaw cycling (50, 100, 200, and 300 cycles), UV radiation (1200, 2400, and 4800 hours), temperature variation (28, 56, 112, and 336 cycles), NaOH solutions with pH 10 and pH 12 concentrations (7, 14, 28, and 84 days), and moisture (7, 14, 28, and 84 days). Specimens comprised FRP coupons and FRP-FRP single lap bond specimens. The tests carried out on the specimens examined the influence of various environmental conditions on their mechanical properties such as stress-strain characteristics and bond between FRP and FRP. Results to-date indicate that the exposure to most of the environmental conditions has minimal effects on the properties tested during this experimental program. Freeze-thaw cycles and moisture exposure seemed to be the two environmental conditions with noticeable effects on the bond properties of single lap bonded specimens.

2007

Carbon and glass Fibre Reinforced Polymers (CFRP and GFRP) have proved very effective in restoring and upgrading the performance of concrete structures. However, concerns about the durability of FRP’s have been a major obstruction to a rapid growth in their application in concrete structures. For a designer to suggest the application of FRP with the same confidence as the traditional materials, it is vital to know how these new materials perform when exposed to severe environments. In this paper, selected results from an extensive test program are presented in which the durability of FRP-reinforced concrete was investigated. The environmental parameters to which the specimens were subjected included freeze-thaw cycling, temperature variation, and NaOH solutions with pH 10, pH 12 and pH 13.7 concentrations. Specimens comprised FRP wrapped concrete cylinders and FRP bonded concrete prisms. The tests carried out on the specimens examined the influence of various environmental condition...

SP-230: 7th International Symposium on Fiber-Reinforced (FRP) Polymer Reinforcement for Concrete Structures, 2005

Synopsis: Externally bonded GFRP fabrics are being increasingly used for seismic retrofit and rehabilitation of concrete structures, due to their high strength to weight ratio and low cost in comparison to carbon and aramid fibers. However, glass fibers are vulnerable to attack caused by harsh environmental weathering conditions such as freezing-thawing, wetting-drying, and exposure to alkaline and acidic environments. Concerned with durability, this study is based on fracture mechanics to evaluate the interface durability of GFRP bonded to Normal Concrete (NC) and High-Performance Concrete (HPC). Three types of specimens are evaluated: (1) newly bonded unconditioned specimens, (2) environmentally conditioned specimens, and (3) correspondingly base-line companion specimens. Two types of environmental ageing protocols are defined: (1) freeze-thaw cycling under in calcium chloride, used to simulate the deleterious effect of the deicing salts; and (2) alternate wetting and drying in so...

Materials

Fiber-reinforced polymer (FRP) composites have gained increasing recognition and application in the field of civil engineering in recent decades due to their notable mechanical properties and chemical resistance. However, FRP composites may also be affected by harsh environmental conditions (e.g., water, alkaline solutions, saline solutions, elevated temperature) and exhibit mechanical phenomena (e.g., creep rupture, fatigue, shrinkage) that could affect the performance of the FRP reinforced/strengthened concrete (FRP-RSC) elements. This paper presents the current state-of-the-art on the key environmental and mechanical conditions affecting the durability and mechanical properties of the main FRP composites used in reinforced concrete (RC) structures (i.e., Glass/vinyl-ester FRP bars and Carbon/epoxy FRP fabrics for internal and external application, respectively). The most likely sources and their effects on the physical/mechanical properties of FRP composites are highlighted herei...

Advances in FRP Composites in Civil Engineering, 2011

In reinforced concrete structures, temperature-induced stresses can be a major concern in regions of drastic temperature changes. FRP reinforced concrete elements are specially susceptible to more damage due to temperature changes because of the mismatching thermal properties between FRP bars and concrete. Furthermore, sustained loads may also damage the bond between FRP bars and concrete and can lead to an unexpected increase of the required anchoring length. Therefore, this research program is designed to investigate experimentally the durability of FRP bond to concrete elements subjected to the effects of freeze-thaw cycles and sustained loads. A FRP-reinforced concrete specimen was developed to apply axialtension sustained loads to GFRP bars eccentrically located within the concrete environment. Test specimens were subjected simultaneously to the dual effects of 250 freeze-thaw cycles along with sustained load. A total of six test specimens were constructed and tested. The test parameters included bar diameter and concrete cover. After conditioning, each test specimen was sectioned to two replicates (halves) for pull-out test. Another series of twelve unconditioned standard pull-out specimens were constructed and tested as control. Test results are presents in terms of bond-slip relationships and ultimate pull-out strength. Test results showed that freeze-thaw cycles along with sustained load resulted in increase in the bond strength of GFRP bars to concrete.

A study on the bond capacity of fibre reinforced polymer (FRP) bars in concrete at elevated temperature is presented. By understanding the effects of temperature on the polymer resin matrix and on the FRPs' tensile and bond properties, and by rationally optimising the placement and anchorage of the bars, FRP reinforcements may be designed as fire-safe alternatives to steel reinforcement for concrete. However, this requires an understanding of the critical issues for FRP that could cause structural collapse under service loads during fire. The investigation presented in this paper includes determination of the glass transition temperature (T g) of two commercially available, FRP reinforcing bars using dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). Reductions in bond strength of these FRP bars at elevated temperature are also presented using steady-state bond pullout tests. It is shown that bond strength reduces at elevated temperature in the region of the lowest T g value, determined using various possible test methods and definitions. The presented data are useful in making rational assessments of the likely structural fire resistance of FRP reinforced concrete elements, and will be used in analysis and interpretation of upcoming large-scale fire tests on FRP reinforced concrete slabs.

Construction and Building Materials, 2020

Drawing on information obtained via double lap shear tests, this paper discusses FRP-concrete bond behavior following five weeks of exposure to several accelerated hygrothermal conditions. Material tests were also carried out for both dry carbon fibers and the epoxy used in the bond study under similar hygrothermal conditions. The bond-slip relationship for the hygrothermal conditions were developed, and fracture energy calculated for the FRP-concrete bond. The use of degraded material properties obtained from material test coupons under the same exposure conditions prevented overestimation of the FRP-concrete bond fracture energy. Testing revealed that the FRP-concrete bond strength increased as temperature increased at low humidity (dry heat) — a potential consequence of alteration in the epoxy glass transition temperature. The bond strength of concrete with steel slag incorporated was superior at all temperatures and low humidity. In response to continuous or periodic submergence in water, specimen failure mode transitioned from substrate failure to adhesive-concrete interface failure. Alternating two-day wet/dry cycles resulted in a 12% drop of FRP-concrete bond strength. Under low humidity, the FRP dry fiber tensile stress increased as temperature increased (dry heat), while the opposite dynamic was observed in the epoxy coupons.

Cement & Concrete Composites, 1997

were obtained in order to evaluate their maximum capacity, stiffness, and ductility. The pe$ormance of the wet/dry exposed specimens was compared with those kept at room temperature.