Effect of corrosion on bond in reinforced concrete under cyclic loading

Cyclic loading can result in severe deterioration in the bond between reinforcing steel bar and the surrounding concrete, especially when the reinforcement is corroded. In this study, tests were carried out for bond stress-slip response of corroded reinforcement with concrete under cyclic loading. Parameters investigated include: corrosion level, confinement, bar type, and loading history. The results revealed that bond behaviour was significantly reduced under cyclic loading. Degradation in bond was significantly less for deformed bars than for smooth bars at the initial loading cycle, but the difference was diminished with loading. The bond reduction was more substantial for unconfined steel bars than for confined bars. The relatively high level of corrosion caused degradation primarily in the initial five cycles, the effect of corrosion being decreased with loading. It was also demonstrated that the cyclic bond stress-slip curves depended on loading history.     

Bond behaviour of corroded reinforcing steel bars in concrete

The effect of steel corrosion on bond between steel bars and the surrounding concrete was investigated for different corrosion levels. Both pullout tests and finite element analysis were used and the results from the two were compared. An electrolyte corrosion technique was used to accelerate steel corrosion. For confined deformed bars, a medium level (around 4%) of corrosion had no substantial influence on the bond strength, but substantial reduction in bond took place when corrosion increased thereafter to a higher level of around 6%. It is demonstrated that the confinement supplied an effective way to counteract bond loss for corroded steel bars of a medium (around 4% to 6%) corrosion level. The results of finite element analyses, where it was assumed that rust behaved like a granular material, showed a reasonably good agreement with the experiments regarding bond strength and bond stiffness.     

Comparison of methods for evaluating bond strength between concrete substrate and repair materials

This investigation was aimed at studying the effect of test methods on bond strength between concrete substrate and repair material. Four test methods with cementitious or modified-cementitious repair materials, and two surface roughnesses were studied. The methods used were pull-off, slant shear, splitting prism and a new direct shear named Bi-Surface shear test. While the coefficient of variation (COV) for each type of test was acceptable, the bond strengths from some tests were up to eight times larger than those obtained from others. It is imperative that the bond tests be selected such that they represent the state of stress the structure is subjected to in the field. The new test method was easy to carry out and had reasonable results and can be developed by further investigations.     

A strain-softening model for steel-concrete bond

A new analytical model is proposed to describe the bond strength between a ribbed reinforcement bar and concrete. The model is based on the partly cracked solution of a thick-walled cylinder exposed to radial internal pressure. Instead of considering the minimum crack number in previous solutions, smeared cracking and average stress-strain of concrete in tension are used in radial direction to describe the softening behavior of concrete. The results are compared with Tepfers' classic solutions and other previous solutions.     

Corrosion influence on bond in reinforced concrete

The bond between reinforcing steel and the surrounding concrete can be deteriorated by corrosion. Pullout tests were carried out to evaluate the effects of corrosion on bond and bond-slip behavior, for a series of specimens with varying reinforcement corrosion levels between 0% and 9%, and for specimens with and without stirrups that provide confinement. Specimens with both smooth and deformed bars were tested. The tests were designed to provide the data required to assess the bond properties, including the ultimate bond strength and free-end slip for various degrees of corrosion under pullout loads. The specimens were tested in an MTS testing machine on which loads, slips and displacements were recorded. Some conclusions have been reached based on the test results.     

Behavior of high strength concrete with and without steel fiber reinforcement in triaxial compression

Based on an extensive experimental program, this paper studies the behavior of high strength concrete and steel fiber reinforced high strength concrete under uniaxial and triaxial compression. Triaxial stress-strain relations and failure criteria are used to evaluate the effect of steel fiber reinforcement on the mechanical properties of high strength concrete in triaxial compression, which is found to be insignificant.     

Time-temperature analysis of bond strength of a rebar after fire exposure

The extent of damage to a steel-reinforced concrete structure due to fire exposure must be evaluated before deciding whether to reuse, reinforce, or abandon the structure. Understanding the long-term effects of high temperature on steel-reinforced concrete structures is also important for predicting the service life of a structure in a high-temperature environment. These effects include changes in strength, stiffness, toughness, bond strength of the rebar, and so on. The change in the bond strength of rebars is studied herein. The experimental results of postfiring pullout tests show a substantial decrease in bond strength if the exposure temperature reaches 200 °C or higher. The current investigation proposes a procedure, based on a single function, to calculate changes in bond strength for predicting residual bond strength of a rebar due to exposure to constant or fluctuating high temperatures. This forecasting method is termed temperature-time analysis and offers excellent agreement with the experimental results.     

The bond of near-surface mounted reinforcement to low-strength concrete

This paper focuses on the bond between near-surface mounted (NSM) reinforcement and low-strength concrete. In order to investigate this, eight beams made of low-strength concrete were made. The compressive strength of this concrete varied from 14.22?MPa to 16.83?MPa. These beams were then tensioned under monotonic loading until failure. The test setups differed in terms of their groove size and the type of reinforcement (a rod and plate of carbon fiber reinforced polymer, prestressing steel). Based on the achieved results and analysis, it was found that the NSM method can be applied to low-strength concrete. Furthermore, the application of a NSM reinforcement rod and plate, made of the carbon fiber reinforced polymer, and prestressing steel showed a satisfactory bond strength when compared to low-strength concrete. However, the carbon plates performed better in terms of failure load and rate use than the rods made of carbon and the prestressing steel. Moreover, the results showed that the increase of groove size for the near-surface mounted reinforcement made of prestressing steel did not have an effect on the failure mode. In addition, a significant increase of the failure load was observed for the prestressing steel. Finally, the effect of concrete strength was analyzed and compared with the results found in literature.     

几种高炉喷补料粘结强度及耐磨性的研究

本文研究了市售喷补料ＢＦＳ、ＭＳ３与华东冶金学院研制的高炉喷补料ＨＧＳ０１和ＨＧＳ０２的粘结强度和耐磨性。结果表明．粘结强度与耐磨性主要取决于喷补料本身的性质，而对某一给定的喷补料而言，受补面的性状对粘结强度有重要影响。     

The effect of recycled concrete aggregate properties on the bond strength between RCA concrete and steel reinforcement

The purpose of this study was to investigate the influence that replacing natural coarse aggregate with recycled concrete aggregate (RCA) has on concrete bond strength with reinforcing steel. Two sources of RCA were used along with one natural aggregate source. Numerous aggregate properties were measured for all aggregate sources. Two types of concrete mixture proportions were developed replacing 100% of the natural aggregate with RCA. The first type maintained the same water–cement ratios while the second type was designed to achieve the same compressive strengths. Beam-end specimens were tested to determine the relative bond strength of RCA and natural aggregate concrete. On average, natural aggregate concrete specimens had bond strengths that were 9 to 19% higher than the equivalent RCA specimens. Bond strength and the aggregate crushing value seemed to correlate well for all concrete types.     

Influence of the roughness of aggregate surface on the interface bond strength

An experimental investigation on the bond strength of the interface between mortar and aggregate is reported. Composite compact specimens were used for applying Mode I and Mode II loading effects. The influence of the type of mortar and type of aggregate and its roughness on the bond strength of the interface has been studied. It has been observed that the bond strength of the interface in tension is significantly low, though the mortars exhibited higher strength. The highest tensile bond strength values have been observed with rough concrete surface with M-13 mortar. The bond strength of the interface in Mode I load depends on the type of aggregate surface and its roughness, and the type of mortar. The bond strength of the interface between mortar M-13 cast against rough concrete in direct tension seems to be about one third of the strength of the mortar. However, it is about 1/20th to 1/10th with the mortar M-12 in sandwiched composite specimens. The bond strength of the interface in shear (Mode II) significantly increases as the roughness and the phase angle of the aggregate surface increase. The strength of mortar on the interface bond strength has been very significant. The sandwiched composite specimens show relatively low bond strength in Mode I loading. The behavior of the interface in both Mode I and Mode II loading effects has been brittle, indicating catastrophic failure.     

Shrinkage stress,long-term adaptation and bond strength of low-shrinkage composite resins

PurposeTo evaluate the internal adaptation, bond strength, and polymerization stress of silorane- and methacrylate-based composite resins.Material and methodsThree methacrylate-based composite resins (Heliomolar; Tetric N-Ceram and Aelite LS) and one silorane-based composite resin (Filtek Silorane) were tested. Polymerization stress (n=5) was determined by the insertion of the composite resin between rods of polymethyl methacrylate. The ratio of the maximum force of contraction was recorded and the cross-sectional area of the rod was used to calculate the nominal stress. Bond strength was evaluated by microtensile bond test. Dentin surfaces of human third molars were bonded, sectioned, and stored for 24 h or 1 year in distilled water before the bond strength test. The ratio of maximum force and the adhered area was used for the bond strength calculation. For internal adaptation analysis, third molars received Class II cavities and were restored according to either an incremental oblique or bulk-filling technique. After being sectioned perpendicularly, impressions were taken and epoxy resin replicas were obtained of the internal surfaces of the restorations (after 24 h and 1 year of storage) to analyze gap formation using scanning electron microscopy.ResultsFiltek Silorane showed the highest​ bond strength after one year of storage, the lowest formation of gaps, and polymerization stress similar to methacrylate-based materials.ConclusionSilorane restorative material presented polymerization stress comparable to that of methacrylate-based composite resins, stable dentin bond strength after one year and better internal adaptation to the cavity walls, showing good alternative to traditional composite resins and promising longevity.     

A new way to increase the long-term bond strength of new-to-old concrete by the use of fly ash

The short-term and long-term bond strengths of new-to-old concrete were experimentally investigated with an emphasis on the influence of new concretes and binders. These new concretes included ordinary Portland cement concrete, expansive concrete and high-volume fly ash concrete, while the binders included pure cement paste (C-binder), expansive binder (E-binder) and fly ash mortar (F-binder). The results showed that the short-term bond strength of all specimens with fly ash concrete was lower than that with ordinary Portland cement concrete, which in turn was lower than that with expansive concrete. The bond strength of the specimens with F-binder was the lowest at the age of 7 days. However, the long-term bond strength of all specimens with added fly ash was the highest and strength losses were observed in the specimens repaired with expansive concrete or E-binder at the age of 3 years. The microstructure of the transition zone with F-binder was also studied by using both scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) at the ages of 28 days and 1 year, respectively.     

The effect of combined use of chitosan and PIPS on push-out bond strength of root canal filling materials

Adhesion of root canal filling materials to root dentin is important for the long-term success of the treatment. Push-out bond strength test is used to evaluate the adhesion capacity of root canal filling materials to root canal walls. The aim of the present study is to compare the bond strength of root canal filling materials to root dentin after irrigation with EDTA, chitosan and the combination of chitosan and PIPS irridation using push-out bond strength test. Forty-eight extracted teeth were resected until 13-mm long roots were obtained. Root canals were prepared with a size-25 OneShape instrument. Samples were divided into three groups each including 15 roots. Group 1: Canals were rinsed with 0.2% chitosan and subjected to laser irridation with PIPS at the same time. Group 2: Canals were rinsed with 0.2% chitosan. Group 3: Canals were rinsed with EDTA. All canals were filled with .06 tapered gutta-percha and AH-plus sealer. One-mm thick slices were taken from coronal, middle and apical one-thirds of the roots. Push-out bond strength was determined using a Universal Testing Machine. One root from each group was observed under SEM to evaluate the degree of smear removal. Statistical analysis was performed with Kruskall-Wallis test. Results showed that bond strength values were statistically similar in overall evaluation for all groups (p > .05). In segmental evaluation, group 1 revealed the highest bond strength in apical one-third compared to other groups (p < .05).     

Er,Cr:YSGG laser irradiation influence on Y-TZP bond strength to resin cement

The aim of this study was to evaluate Y-TZP surface pretreatment with different protocols on microshear bond strength (μSBS) ceramic-cement interface. One hundred and sixty pre-sintered IPS e-max ZirCAD (Ivoclar-Vivadent) blocks were randomly divided into sixteen groups according to surface treatment (n=20): G1- no treatment (control); G2- ceramic primer; G3- tribochemical silica coating; G4- tribochemical silica coating+primer; G5- airborne particle abrasion (Al₂O₃); G6- airborne particle abrasion (Al₂O₃)+primer; G7- Er,Cr:YSGG laser; G8- Er,Cr:YSGG laser+primer. All specimens were sintered before surface treatment, except lasers groups, which were sintered after laser irradiation. Ceramic blocks were bonded with Panavia F resin cement (Kuraray, Okayama, Japan) (n=10) or RelyX ARC (3M ESPE, St. Paul, MN, USA) (n=10). The μSBS tests were carried out in a universal testing machine at a speed of 1mm/min after 24 h (n=5) or 6 months storage (n=5). Differences were found for both resin cements and storage conditions in relation to μSBS values (p<0.05). However, no significant difference for interaction between factors was observed in cemented blocks with RelyX ARC. Panavia F resin cement showed significant differences for interaction between factors (p<0.05). Laser treatment was not sufficient to increase μSBS values between Y-TZP and resin cements. Tribochemical silica coating followed by primer achieved the highest immediate μSBS values. The storage did not affect negatively μSBS values to both evaluated cements.     

Influence of fibers on bond strength of concrete exposed to elevated temperature

Concrete is a building material having good fire resistance and the resistance depend on many factors including the properties of its constituent materials. Fiber Reinforced Concrete (FRC) apart from improving mechanical properties has better fire resistance than conventional concrete. Bond strength of concrete is one of the important properties to be considered by structural engineers while designing reinforced concrete cements. In this research, an experimental investigation has been carried out to determine the effect of fibers on the bond strength of different grades (M20, M30, M40 and M50) of concrete subjected to elevated temperature. Different types of fibers such as Aramid, Basalt, Carbon, Glass and Polypropylene were used in the concrete with a volume proportion of 0.25% to determine the bond strength by pull-out test. Prior to the pull-out test, the specimens were kept in a furnace and subjected to elevated temperatures following standard fire curve as per ISO 834. Based on the test results of the investigations, type of fiber, grade of concrete and duration of heating were found to be the key parameters that affect the bond strength of concrete. The contribution of carbon fiber in enhancing the bond strength was found to be more significant compared to other fibers. An empirical relationship has been developed to predict the bond strength of FRC at a slip of 0.25?mm. This empirical relationship is validated with experimental results.     

Influence of glass fiber post translucency on microhardness and dentin bond strength of resin cement at different root levels

The aims of this study were (a) to evaluate the influence of glass fiber post translucency on the hardness of a light-cure resin cement within the root canal; (b) to assess dentin bond strength at different root levels. Fifty human canine roots were randomly divided into five groups. Translucent posts (Exacto, Angelus; White Post DC, FGM; FRC Postec Plus, Ivoclar Vivadent) were used in three groups, opaque posts (Exacto Opaco, Angelus) were used in one group and no posts were used in the last group. The posts were cemented using a light-cure resin cement (Variolink N Base, Ivoclar Vivadent). The roots were cross-sectioned into slices (two from the cervical, two from the middle, and two from the apical thirds) which were then submitted to microhardness and push-out tests. Two-way analysis of variance and Tukey test were performed. Cement microhardness was significantly higher in the translucent post groups when compared to opaque posts and no post. At the apical third, the White Post DC and FRC Postec groups showed higher microhardness values than those in the Exacto Translucido group. The type of glass fiber post did not significantly influence bond strength values. White Post DC and FRC Postec Plus provided higher resin cement microhardness values, especially at the most apical thirds. Bond strength was not dependent on the type of post used. Failure mode analysis suggested superior cement curing when the translucent posts were used.     

Effects of mixing techniques and dentin moisture conditions on push-out bond strength of ProRoot MTA and Biodentine

Objective: To evaluate the influence of manual and mechanical mixing techniques as well as the effects of moisture on the push-out bond strength of ProRoot MTA (Dentsply Tulsa Dental, Tulsa, OK, USA) and Biodentine (Septodont, Saint Maur des Fosses, France) to radicular dentin.

Material and methods: Two hundred and forty dentin discs were assigned into three groups with respect to the moisture condition tested: (1) dry, (2) paper points, (3) wet. The discs were further divided into four subgroups according to the calcium silicate cements (CSCs) and mixing techniques used: (1) ProRoot MTA mixed manually, (2) ProRoot MTA mixed mechanically, (3) Biodentine mixed manually, and (4) Biodentine mixed mechanically. Bond strengths of the cements to root canal dentin were measured using a push-out test setup. The data were statistically analyzed using three-way ANOVA and Bonferroni post hoc test p = 0.05.

Results: The data indicated that the push-out bond strength values were significantly affected by CSCs, mixing techniques, and moisture conditions (p < 0.001). Dry conditions caused a significant decrease in bond strength values for both CSCs (p < 0.001). The mean bond strength of Biodentine was significantly higher than that of ProRoot MTA, regardless of the mixing techniques and moisture conditions (p < 0.001). Mechanical mixing favored bond strength values statistically compared to manual mixing (p < .001).

Conclusion: The mixing techniques and moisture conditions have an effect on the push-out bond strengths of ProRoot MTA and Biodentine. Dry samples and manual mixing of cements deteriorate the push-out bond strengths values.     

Rupture probability of coarse aggregate on fracture surface of concrete

In this work, the fracture surface of concrete was analyzed by the digital image analysis (DIA) technique, and the rupture probability of the coarse aggregate (RPCA) was used to represent the failure mode of the aggregate at the fracture surface. The relationships between the RPCA, the water-binder ratio (W/B), and the size and type of coarse aggregate were investigated. Preliminary results showed that: (1) RPCA increases with decreasing W/B of concrete. (2) RPCA of concrete with coarse aggregates having a maximum size of 16 mm is higher than that with other sizes of coarse aggregate. The influence of the size of coarse aggregate on the RPCA is more significant in high strength concrete than in normal strength concrete. (3) With reduction of W/B, the interfacial bond of concrete with crushed gravel improves more significantly than with round gravel according to their RPCA. (4) RPCA depends not only on the intrinsic strength, size, and shape but also on the reactivity of the coarse aggregate.     

Performance of seawater-mixed concrete in the tidal environment

Compressive strength, mineralogy, chloride ingress, and corrosion of steel bars embedded in concrete made with seawater and tap water are summarized here based on the several long-term exposure investigations under tidal environment. Seawater-mixed concrete shows earlier strength gain. After 20 years of exposure, no significant difference in the compressive strength of concrete is observed for concrete mixed with seawater and tap water. The initial amount of chloride (due to the use of seawater) may cause the initiation of corrosion at the locations of the steel bars having voids/gaps at the steel-concrete interface immediately after casting concrete. The use of seawater results in the formation of deeper corrosion pits compared to the same with tap water.