Concrete Delamination Research Articles

Fracture characterization of concrete/epoxy interface affected by moisture

Knowledge on durability of concrete/epoxy bonded systems is becoming essential as the use of these systems in applications such as fiber-reinforced polymer (FRP) in strengthening of concrete structures is becoming increasingly popular. Prior research studies in this area indicate that moisture plays an important role on durability of these systems. Premature failures of the bonded system may occur regardless of the durability of the individual constituent materials forming the material system, and that the durability of the overall FRP-bonded system may be governed by the interface integrity. In this study, fracture toughness of concrete/epoxy interfaces as affected by combinations of various degrees of moisture ingress and temperature levels is quantified. For this purpose, sandwiched beam specimens containing concrete/epoxy interfaces were tested and analyzed using the concepts of fracture mechanics. Mechanical properties of individual materials constituting the interface (concrete and epoxy) were also characterized for the evaluation of the corresponding interface fracture toughness. Experimental results have shown a significant decrease, up to about 50%, in the interface fracture toughness of concrete/epoxy bond with selected levels of moisture and temperature conditioning of the specimens for both mode I and mixed mode conditions, and that moisture affected debonding may occur in the interface region involving a distinctive dry-to-wet debonding mode shift from material decohesion (concrete delamination) to interface separation. The mechanistic knowledge and the experimental data presented in this paper will serve as a basis for the use in the design improvement of material systems containing such interfaces for better system durability.

Thermographic Imaging of Subsurface Deterioration in Concrete Bridges

The deterioration of concrete bridge components due to corrosion presents a significant challenge for bridge owners worldwide. Deterioration commonly develops at the level of embedded reinforcing steel because of the expansion of corrosion products and resulting stresses in the concrete. As a result, deterioration cannot be detected with visual inspection until it has progressed sufficiently to be manifest in spalling or advanced deterioration of the concrete. This paper presents the results of a study to develop thermal imaging (infrared imaging) for detection of subsurface deterioration. This nondestructive evaluation technique detects delamination on the basis of resulting perturbations in the heat transfer characteristics of the concrete, which are manifest as variations in surface temperature. The technique has the advantage of being applied from a distance and thus reduces access and traffic control requirements. However, it depends on certain environmental conditions to achieve thermal gradients in the concrete needed to detect subsurface deterioration. This study explored the effects of environmental parameters on the detectability of delamination in concrete. Specifically, the effects of diurnal temperature changes on the detection of damage in the soffit area of bridges are reported. Experimental studies and field testing were conducted. This paper focuses on guideline requirements developed through the research for the effective application of the technology in the field and describes experience with application of the technology for the detection of deterioration in a typical highway bridge.

Concrete Delamination Caused by Steel Reinforcement Corrosion

Practical experience and laboratory observations indicate that corrosion affected reinforced concrete structures are prone more to cracking and delamination of the concrete than to the loss of structural strength. A review of research literature suggests that insufficient theoretical work on corrosion induced concrete delamination has been undertaken. This paper proposes a theoretical method to predict the time to concrete delamination caused by steel reinforcement corrosion. The method is based on fracture mechanics and uses crack opening in concrete as the criterion for its delamination. An analytical model is derived to determine the crack width in concrete. A numerical example is given to illustrate the proposed method and a comparison with both test results and an empirical model indicates a good agreement. It is found in the paper that the corrosion rate is the most significant single factor that affects the time to concrete delamination. The proposed method can be used for the prediction of time to concrete delamination for reinforced concrete structures located in chloride-laden environments. In principle, this provides a means for judging timely intervention and as such has the potential to prolong the service life of corrosion affected concrete structures.

An experimental study on delamination of FRP plates bonded to concrete

Results of an experimental campaign on FRP–concrete delamination are presented. Specimens with different bonded lengths and plate widths have been tested. Strain gauges along the FRP plate have been used to measure longitudinal strains. For long bonded lengths, progressive debonding along the specimens has been followed. Starting from experimental data, average shear stress–slips data have been computed. By post-processing these data, non-linear interface laws for two different plate widths have been calibrated. Increase of maximum shear stress with decreasing plate width has been observed, whereas no significant plate width effect on fracture energy and delamination force has been found. Experimental tests have been simulated by adopting a numerical bond-slip model and the above mentioned non-linear law for the FRP–concrete interface. Numerical results in good agreement with experimental results have been obtained, both at low and very high loading levels.

Peel and Shear Fracture Characterization of Debonding in FRP Plated Concrete Affected by Moisture

The objective of this paper is to develop a new mechanistic understanding of moisture affected debonding failures in carbon fiber reinforced polymer (CFRP) plated concrete systems by mechanically testing accelerated moisture conditioned mesoscale peel and shear interface fracture specimens. Central to the investigation is the use of interface fracture toughness as the quantification parameter of the CFRP-epoxy-concrete trilayer system, which is considered a bond property, to analyze, compare, and correlate physical observations. Results have shown that fracture toughness of the CFRP bonded concrete systems significantly degrades, and its value becomes asymptotic with increasing moisture ingress. This asymptotic behavior is associated with certain moisture concentration levels as predicted by a three-dimensional moisture diffusion simulation. The generally observed debonding mode by concrete delamination for the dry specimens changes to an epoxy/concrete interface separation mode for the wet specimens. Finite element fracture computation, mixed-mode characterization, and kink criterion implementation synergistically suggest that the interface separation mode is attributed to an interfacial material toughening and an interface weakening mechanism as a consequence of moisture diffusion.

EMAT-Based Inspection of Concrete-Filled Steel Pipes for Internal Voids and Inclusions

Concrete-filled steel pipes have been used as piles for supporting civil and marine structures. These piles provide good bending resistance, and can be easily spliced for long depth installation. However, these piles are usually exposed in hostile environments such as seawater and deicing materials. Thus, the outside corrosion of the steel pipe can reduce the wall thickness and the corrosion-induced delamination of internal concrete can increase internal volume or pressure. In addition, the void that can possibly exist in the pipe reduces the bending resistance. To avoid structural failure due to this type of deterioration, appropriate inspection and repair techniques are to be developed. The acoustic method is attractive for this inspection since it is relatively simple and versatile. Especially, guided wave techniques have strong potentials for this inspection because of long-distance inspection capability. There are different transducer-coupling mechanisms available for the guided wave inspection techniques. Electro-magnetic acoustic transducers (EMATs) give relatively consistent results in comparison to piezoelectric transducers since they do not need any couplant. EMATs are used for transmitting and receiving cylindrical guided waves through concrete-filled steel pipes. It is shown that EMAT-generated cylindrical guided wave techniques have good potential for the interface inspection of concrete-filled steel pipes.

Underwater inspection of concrete-filled steel pipes using guided waves

Concrete-filled steel pipes have been widely used as piles for supporting marine and civil structures. They provide good bending resistance and can be easily spliced for long depth installations. In addition, they have high strength and ductility and are an economical solution for bridges. However, these piles are usually exposed in water, particularly seawater, and thus the outside corrosion of the steel pipe can reduce the wall thickness and the corrosion-induced delamination of internal concrete can increase internal volume or pressure. To avoid this type of deterioration, appropriate inspection and repair techniques are required. The acoustic method is an attractive method for the interface delamination detection since it is relatively simple and versatile. Guided wave techniques have particularly strong potential for this type of inspection and the feasibility of the guided wave techniques for detecting the interface inspection is investigated in this paper. A special coupling mechanism for transmitting the guided waves is introduced for the experimental study. An analytical study is also carried out to identify the cylindrical guided wave modes that are sensitive to the interface separation. This study shows the feasibility of using guided waves for underwater inspection of concrete-filled steel pipes.

Significance of Midspan Debonding Failure in FRP-Plated Concrete Beams

Reinforced concrete beams enhanced in flexure with adhesively-bonded fibre reinforced polymer plates are susceptible to a brittle form of failure, defined by delamination of the cover concrete attached to the adhesive that causes the plates to debond from the beam. This paper demonstrates that, while previous research has focused almost singularly on one debond mode in which concrete delamination progresses from the ends of the plates inwards, there exists another critical debond mode that initiates near flexural cracks in the midspan region of the plated beam and propagates out to the ends of the plates. Data from large-scale experimental work are presented to show that midspan debond action is triggered by high shear stresses transmitted from the plates through the adhesive to the cover concrete. These stresses arise initially from tension stiffening in the cracked concrete and corrosion of the embedded steel. It is shown that strain gauge data are required from both the bonded and exposed surfaces of t...

Application of FRP laminates for strengthening of a reinforced-concrete T-beam bridge structure

This paper describes application of fiber-reinforced polymer (FRP) composite laminates to strengthen an aging reinforced-concrete T-beam bridge in South Troy, Rensselaer County, New York. Leakage at the end joints of this single-span structure led to substantial moisture and salt infiltration in the bridge superstructure. Presence of efflorescence was observed, and freeze-thaw cracking and concrete delamination at some locations on the beams were noted. Concerns about integrity of the steel reinforcing and overall safety of the bridge were raised. These concerns were heightened by the absence of any documents pertaining to the bridge design, such as rebar size, steel type, concrete strength, and design loads. Thus, a decision was made to strengthen the bridge using bonded FRP-laminates. Load tests were conducted to evaluate effectiveness of the strengthening system and investigate its effect on structural behavior, and tests results were compared with those obtained using classical analysis.

Versalzung und Korrosion von Spritzbeton (Sicherheitsstollen des Gotthard-Strassentunnels)

The corrosion behavior of shotcrete in the safety gallery of the motorway tunnel Gotthard was investigated. The tunnel was built in 1972/73, sections with waterleading rocks show various signs of concrete degradation. Samples of corroded concrete were investigated in the laboratory for their chemical and mineralogical compositions. X-ray diffraction (XRD), X-ray fluorescence (XRF), and methods to determine acid-soluble silicon compounds and insoluble contents were used to characterize the samples.Comparisons of original concrete with corroded samples show the existence of discrete interaction mechanisms. These mechanisms lead either to harmless efflorescence, to detachments of concrete from the rock or to more or less complete degradation of the cement paste. Delamination or deterioration of concrete are related to the amount and kind of transformation products formed due to action of specific ionic species of the interacting water. Special attention is drawn to the formation of thaumasite, which may be formed under special conditions, even when sulfate-resistant cements have been used.Physical and chemical properties of the cement paste as well as the composition of interacting water are important for the service life of a concrete structure. The potential of concrete degradation due to interaction with aggressive water may be lowered by preventing its contact or by draining the water not to force it to penetrate the concrete structure.

A Random Field Excursion Model of Salt Induced Concrete Delamination.

Salt induced concrete delamination is a problem often encountered in parking garage slabs in northern climates where deicing salts are heavily used. A random field model of the delamination process is investigated and compared against some field data. Delaminated regions of the slab are modeled as excursions of a random field above a prescribed threshold and the growth of these regions with time is obtained by allowing the threshold to fall as a function of time. Simulation based excursion statistics are used to obtain the mean and variability of various aspects of the delamination process using this model.