Reduction In Bond Strength Research Articles

Modeling Bond Between Corrosion-Cracked Concrete and Composite Sheets

A new empirical model for the prediction of bond strength between corrosion-cracked concrete and FRP sheets is proposed in this work. The model considers the impact of concrete-cracking level as well as the geometric characteristics of FRP sheets. Experimental data (from tests on reinforced concrete blocks underwent varying corrosion levels before attached to carbon FRP (CFRP) sheets at variable bond lengths and widths) is employed in the empirical modeling. Corrosion-induced cracks at widths of about 0.2–0.9 mm lead to reductions in bond strength and slippage at failure at ranges of 25–44% and 18–68%, respectively. The developed statistical model captures the correct trend for bond stress–slip relationship and precisely predicts bond characteristics between corroding concrete and CFRP sheets in terms of key parameters. The degradation parameters (incorporated in this model) confirmed those provided by the ACI committee 440 at ranges of 0.66–0.86 for bond strength and 0.63–0.89 for slip at ultimate bond stress. The prediction accuracy of the present model of published data shows the highest when compared with that of well-known published models.

Effect of fly ash and corrosion on bond behavior in reinforced concrete

AbstractReinforcing steel bar can exert its strength and ductility by bonding to concrete. However, corrosion of steel bars reduces the bonding effect. This study mainly investigated the coupling effects of fly ash (FA) and corrosion on bond behavior. The impressed current method was utilized to achieve the target corrosion degrees. Three crucial factors that have impact on bond behavior was considered, which were FA content, corrosion degree and stirrups. The bond behavior was discussed using the bond‐slip curves. The results showed that the slight corrosion (less than 2.1%) can improve the bond behavior, the supplement of 15% FA can result in a higher ultimate bond strength and to a substantial extent offset the reduction in bond strength owing to the severe corrosion of rebar. The effects of stirrups on bond strength mainly focused on fly ash concrete (FAC) and had an almost negligible impact on ordinary concrete. The results and discussions can be of great significance to establish the bond‐slip constitutive model under multi‐factor coupling conditions and also can give some important advices to the design of engineering structures.

ASSESSMENT THE IMPACT OF MORINGA OLEIFERA EXTRACTS AND ASCORBIC ACID SOLUTION AS ANTIOXIDANTS ON MICROSHEAR BOND STRENGTH OF RESIN COMPOSITE TO BLEACHED BOVINE ENAMEL (IN VITRO STUDY)

Objective: The study was conducted to assess the impact of Moringa Oleifera and ascorbic acid on microshear bond strength of composite resin to bleached Enamel. Methods: Twenty-five bovine incisors were divided into five groups of 5 teeth each; Group I : Where no bleaching was done and no antioxidants were used , Group II: Where bleaching was done, but no antioxidants were used, Group III (Positive control group): Bleaching followed by treatment with 10 % Ascorbic acid solution for 10 minutes, Group IV : Bleaching followed by treatment with 80 % ethanol extract of Moringa Oleifera for 10 minutes, Group V: Bleaching followed by treatment with 80 % methanol extract of Moringa Oleifera for 10 minutes. Resin composite was applied on enamel surfaces of all groups. The microshear bond strength were evaluated for all groups. Results: The results revealed statistically significant difference between the five groups where the highest mean value (17.34 Mpa) was recorded for (Group I; No bleaching) followed by (9.22 Mpa) was recorded for (Group III; Ascorbic Acid treatment after bleaching). The least mean value (4.41 Mpa) was recorded for (group II; No antioxidant after bleaching). No statistically significant difference was found between (Group III) and (Group IV). Conclusion: Using 10 % Ascorbic acid solution could reverse the reduced bond strength after bleaching and Ethanol extract of Moringa Oleifera can be a future candidate to be used as antioxidant solution after bleaching. KEYWORDS: Antioxidants, Microshear bond test, Ascorbic acid , Moringa Oleifera , At office bleaching.

Effect of mono-dopants (Mg2+) and co-dopants (Mg2+, Zr4+) on the dielectric, ferroelectric and optical properties of BaTiO3 ceramics

In this work, BaTiO3, Ba(Mg0.01Ti0.99)O3, Ba(Mg0.015Ti0.985)O3, Ba(Mg0.02Ti0.98)O3 and Ba(Mg0.01Zr0.15Ti0.84)O3 ceramics have been prepared through conventional solid-state route to investigate the effects of Mg2+ and Zr4+ dopants as mono-substitution (only Mg2+) and co-substitution (Mg2+ and Zr4+) of B-site on the structural, electrical and optical properties of BaTiO3 ceramics. Exhibiting perovskite structure, Ba(MgxTi1−x)O3 ceramics revealed a decrement pattern of tetragonality with the increment of the concentration of MgO which was confirmed through Rietveld analysis. Morphological analysis of the sintered samples by scanning electron microscope showed a grain growth retardation phenomenon with Mg2+ addition. Releasing from this retardation process, Ba(Mg0.01Zr0.15Ti0.84)O3 showed a maximum dielectric constant of ∼1269.94 due to the enhanced domain wall motion and the confinement within the solubility limit of Mg2+. The ferroelectric characteristic of Ba(MgxTi1−x)O3 was sluggish due to the effects of grain size and its boundary. The optical band gap for BaTiO3 was found to be decreased from 3.55 eV to 3.06 eV with the addition Mg2+ content but for Ba(Mg0.01Zr0.15Ti0.84)O3, the value increased due to the Burstein-Moss effect. Again the FTIR analysis proved that no impurity phases were formed during the doping phenomenon, but in Ba(MgxTi1-x)O3 ceramics, a significant reduction of Ti-O bond strength was observed. However, BaTiO3, Ba(Mg0.01Ti0.99)O3, Ba(Mg0.015Ti0.985)O3 and Ba(Mg0.02Ti0.98)O3 ceramics had manifested P-E loop having lower remanent polarization and coercive field compared to Ba(Mg0.01Zr0.15Ti0.84)O3 ceramics with moderate electrical and optical properties. So, co-doping with Mg2+ and Zr4+ evidenced a favorable accession for the increment of the properties of BaTiO3 ceramics.

Effect of Incorporation of Silver Nanoparticles on the Tensile Bond Strength of a Long term Soft Denture Liner.

Objectives This study aimed at assessing the effect of the addition of silver nanoparticles (SNPs) to a silicone soft liner on its tensile bond strength to denture base resin. Materials and Methods SNPs were added to Mucopren cold cure soft liner in 0 (control), 0.5, 1, 2, and 3 wt% concentrations and bonded in 120 stainless steel molds with processed heat cure acrylic resin blocks. Liner/resin combination samples were divided into two groups. The first half was stored for 2 days in distilled water at 37°C and then subjected to tensile bond strength, while the other half were thermocycled 3000 times before testing. Mean bond strength, expressed in mega pascals (MPa), was determined in the tensile test with the use of a universal testing machine at a crosshead speed of 5 mm/min. Statistical Analysis Data were analyzed using SPSS via one-way analysis of variance test, t -test, and Tukey’s posthoc, at a 95% confidence level ( p < 0.05). Results Addition of SNPs and thermocycling both caused a significant reduction in the tensile bond strength of Mucopren to acrylic resin; however, in the thermocycled group, the bond strength increased with the increase in the concentration of SNPs ( p < 0.001). Conclusion Addition of SNPs to Mucopren soft silicone liner reduces its tensile bond strength to denture acrylic resin.

Efficiency of ECE Applied on RC Slab using Locally Available Un-Galvanized Steel with Conductive Cement Paste Anode

Electro-chemical Chloride Extraction (ECE) is considered one of the most effective technique used to extract chloride ions from reinforced concrete structures. Effectiveness of using ECE depends on some important factors such as anode type, current intensity, extraction duration, type of rebar and chemical properties of concrete. On the other hand, ECE may cause some detrimental effects on some mechanical properties of concrete and steel such as a reduction in bond and compressive strengths of concrete, and embrittlement (i.e. reduction in ductility) ductility of reinforcing steel. The major aim of this research work was to investigate the effectiveness of ECE using locally available un-galvanized steel mesh with conductive cement paste anode as a new type of anode on a reinforced concrete slab as a structural element. The slab behavior before and after ECE was studied by determining compressive strength, water absorption rate, concrete chloride content and steel corrosion potential. The slab behavior was studied taken into consideration the established steel arrangement with spacing 20 cm between re-bars. Another aim of this research work was to investigate the effect of initial chloride content on chloride extraction efficiency by applying optimum current intensity and duration (3 A/m2 and 6 weeks) on cylinders with pure chloride content 0.4% and 0.8% (by weight of cement). Effectiveness of ECE with small initial chloride content 0.4% and 0.8% was compared with that of high initial chloride content (2.5%) in order to know if the initial chloride content is an important factor on ECE effectiveness or not.

Interface bond strength of lightweight low-cement functionally layered concrete elements

Production of cement accounts for around 5% of human-made carbon emissions. When the selection of a cement-intensive mix with low porosity is driven by durability requirements, the resulting low permeability of the material is only fully exploited in peripheral regions of the element where the material acts as a physical barrier against the penetration of aggressive substances. This paper explores the potential of casting layered prismatic elements composed of an external durability layer and a lightweight core section as a means to achieve cement and weight savings. Layered elements are traditionally obtained by casting new concrete layers onto already hardened older concrete layers. A major problem with this technique is that planes of weakness are obtained at the interfaces between the layers. The bond between the layers can be improved by casting the materials at approximately the same time. However, research to date has not yet demonstrated the viability of producing elements with wet cast external layers. Furthermore, the effects of delays between successive pours on the mechanical tensile performance of the interfaces in layered elements have not been quantified. An original method is presented to form prismatic elements composed of an external durability layer and a lightweight core section by casting two concrete mixes at approximately the same time. The approach is validated by realising a proof-of-concept prototype layered element. A set of additional layered elements are cast with various pour delays and cored across the interface between their layers to characterize the interlayer bond strength by direct tension. To interpret the mechanisms affecting the bond, the variation of tensile bond strength with the location of the sample and the impact of roughness are also investigated. When the pour delay was minimal, failure did not occur at the interlayer. The relationship between pour delay and bond strength is markedly nonlinear, with bond strength reductions of more than 30% for pour delays of only three hours. It was also found that the bond strength of the interface varies significantly with the considered location and that up to 40% of the bond strength reduction due to a delay between the castings can be recovered by roughening the surface of the older concrete prior to casting the newer mix. The successful realisation of wet cast prismatic elements with an external durability layer is an important step towards the realisation of light-weight layered concrete elements with low embodied energy.

Bond characteristics of corroded pullout specimens exposed to elevated temperatures

This paper presents an experimental study carried out to examine the extent of deterioration of bond properties of super ductile (SD) TMT reinforcing steel bars with normal strength concrete on account of exposure to multiple combinations of corrosion-induced damage in terms of mass loss and exposure to elevated temperatures. The study involved an experimental evaluation of bond properties and behavior of corroded pullout specimens exposed to elevated temperatures. RILEM specified Pullout specimens with centrally placed rebars of various sizes were exposed to impressed current accelerated corrosion to achieve desired levels of corrosion in terms of percent mass loss of (2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, and 18%, etc.). and then to temperatures targeted at (200 °C, 400 °C, 500 °C, 600 °C, 700 °C & 800 °C). The corroded and subsequently heated pull out bond specimens were tested to failure in pull-out mode using displacement controlled UTM to investigate the residual bond strength and bond-slip behavior. The slip of the rebar, at the loaded as well as the unloaded end, was recorded through a set of linear variable displacement transducers (LVDT) arrangement mounted to the projected reinforcing bar on each side of the specimen. The study presents unique bond-slip response curves depicting the overall behavior of the bond mechanism. The results indicate a notable reduction in bond strength as well as the bond-slip response of pullout specimens on account of the superimposition of the two phenomena. A detailed account of the test results, analysis and discussion has been presented. The findings of this study have direct implications on procedures used for predicting the ultimate behavior of aged or corroded structural elements exposed to an accidental fire. A trend of deteriorations has been established for all research variables and a model best fitting the experimental data has been proposed in terms of a regression correlation.

Influence of CFRP confinement on bond behavior of steel deformed bar embedded in concrete exposed to high temperature

The effectiveness of retrofitting with carbon-fiber-reinforced polymer (CFRP) wrapping for maintaining and improving the bond between steel rebars and heat-damaged concrete was extensively studied. Here, the effect of temperature (room temperature as the reference, 200, 400, 600, and 800 °C), concrete cover (25 mm and 35 mm), concrete compressive strength (30 and 40 MPa), and CFRP wrapping had on the concrete-rebar bond were investigated by conducting experiments. The results show that retrofitting with CFRP can not only significantly increase the bond strength of the specimens subjected to elevated temperatures, but also change the failure mode from brittle to a more ductile one, i.e., rebar pull-out failure. Moreover, the mechanical properties degraded as temperature increased, especially after 400 °C, such that at 800 °C, the compressive strength was reduced by about 80%. Exposure to heat reduced the concrete-rebar bond strength in the pull-out test specimens, and the level to bond strength reduction was less pronounced in the specimens with greater compressive strength and concrete cover. However, confinement with CFRP sheets significantly improved the bond strength, which was more considerable for the specimens exposed to higher temperatures. The effectiveness of CFRP wrapping was more significant for the specimens with a lower compressive strength and thinner concrete cover.

Improving water-splitting efficiency of water electrolysis process via highly conductive nanomaterials at lower voltages

The present study explores the opportunity to enhance the hydrogen production rate (HPR) at lower voltage in water electrolysis process by introducing conductive nanoparticles into electrolyte. The development of sustainable, cost-effective, reliable, clean, efficient, and renewable resources of energy systems is crucial for meeting the increasing energy demand. Among the various technologies developed to produce hydrogen, water electrolysis is the simplest, easy to operate, and ready to use in many industries, but it is still not cost-effective. Three different conductive nanomaterials: graphene nanoflakes, multi-wall carbon nanotubes (MWCNTs), and indium tin oxide, were incorporated into acidic electrolyte solutions of the water-splitting process. Experimental results reveal that among these nanomaterials, the incorporation of MWCNTs and graphene nanoflakes into electrolyte solutions considerably improved HPR. The highest HPR was observed at MWCNTs concentration of between 0.25 and 0.5 wt%. At 0.5 wt% MWCNTs and applied voltage of 4 V, about 170% improvement in the HPR was achieved when compared to base case (without nanoparticles into the electrolyte). An applied voltage of 10 V with the same MWCNTs concentration produced the maximum HPR of 2.7 ml/min. At the same concentration and voltage, the introduction of graphene into the electrolyte produced HPR of 2.5 ml/min. The effects of acid concentration and temperature on the HPR were also investigated. The HPR gradually increased with increasing acid concentrations in the dispersion due to the concentrations of ionic activators, which weakens the strength between oxygen and hydrogen bonds. Higher temperature also ameliorates the HPR because of the reduced bond strength. This approach of using nanomaterials in the electrolysis process could save up to 30% of energy input during this procedure.

Effect of scan strategy and heat input on the shear strength of laser cladded Stellite 21 layers on AISI H13 tool steel in as-deposited and heat treated conditions

Coating of hard-facing, wear and corrosion resistant materials on working surfaces of engineering parts made of relatively lower grade materials plays an important role in their service life as this is dictated by the coating material rather than the substrate material. However, the quality of coating in terms of pores- and crack- free deposition, low dilution and good bond strength is vital for the working life of coatings. In this work, bond strength of laser cladded Stellite 21 layers deposited on AISI H13 tool steel with different scanning strategies and line energy is investigated by subjecting the clad-substrate interface to shear force. As Stellite 21 is deposited to improve surface property of high-temperature dies and also for refurbishing worn out dies, bond strength of cladded specimens subjected to a high thermal cycle was also measured. Three sets of shear test specimens of rectangular clad build-up were made with different deposition strategies. First two sets have same laser line energy, but interfacial layers have overlapped clad tracks deposited in two orthogonal directions to study the effect of track orientation on the bond strength. In the third set line energy was doubled by reducing the scan speed. Bond strength was more for shear force applied along the direction of clad tracks. Higher interfacial bond strength of clad tracks parallel to shear stress direction compared to transverse tracks could be resulting by the similar effect that the orientation of fibers in a composite have on its strength. Deposition with higher line energy also had higher bond strength because of more uniform overlapped clad interface. However, specimens subjected to heating up to 1000 °C followed by furnace cooling had much reduced bond strength due to grain coarsening. Results are supported by the micro-structure, micro-hardness, dilution and elemental analyses of cladding and fractured surfaces.

Weakening the bond strength of luting agents could be a goal in implant retained prosthetics

Aim of the study: The current study was conducted to provide a simple practical technique to relatively weaken the bond strength of E.max Press copings retained to zirconia implant abutment models. This technique should facilitate crown retrieval from onto implant abutments without affecting the integrity of the ceramic crowns, abutment or the implant’s integration, yet, the crown is still well retained during service.Materials and methods: Twenty four zirconia implant abutment models were specially fabricated for the current study, to which 24 e.max press copings were cemented. According to the cementation technique, the samples were divided into four groups, 6 samples each. In Gp A, copings were cemented with a temporary resin luting cement without any surface treatment to the abutment models or the intaglio surfaces of the copings. In Gp B, abutments’ surfaces as well as intaglio surfaces of the copings were treated according to manufacturers’ instructions before cementation with permanent resin luting cement. In Gp C, abutments’ surfaces were coated with a single coat of fresh whole saliva before cementing copings with the permanent resin luting cement. In Gp D, same as in Gp C with replacement of saliva with single coat of glycerin. All assemblies were then subjected to aging through thermocycling for 5000 cycles.All assemblies were then tested for retention of coping cemented to the zirconia implant abutment models and failure surfaces were then examined by stereomicroscope to detect the mode of failure.Results: All samples in Gp A failed before any mechanical testing. Gp C reviled insignificant bond strength results compared to Gps B and D. However, Gp D showed significant reduction in bond strength compared to Gp B.Conclusions: Glycerin coating of zirconia implant abutments before use of permanent resin luting cement would be a good technique to retain crown in place for longer time, yet still liable to easy retrieval.

The effect of chlorhexidine application on the microtensile bond strength and durability of a total-etch adhesive

Abstract Aim: The aim of this study was to evaluate the effect of chlorhexidine (CHX) on resin–dentin microtensile bond strength (μTBS) after 6-month aging and to compare with sodium hypochlorite. Materials and Methods: A total of 40 extracted human third molar teeth were mounted in the acrylic resin. Flat occlusal surfaces of dentin were exposed, and after acid etching, the samples were divided randomly into four groups as follows: (a) Control group: Single Bond adhesive resin was applied. (b) The dentin surfaces were exposed to 2% CHX, and then, Single Bond was applied. (c) Dentin surfaces were treated by 5.25% sodium hypochlorite; after rinsing and drying, Single Bond was applied. (d) At first, 5.25% sodium hypochlorite was applied for 30 s, and then, 2% CHX and Single Bond adhesive were applied. Finally, Filtek P60 composite was bonded on the dentin surface. The samples of each group were divided into two subgroups of 24 h and 6 months. μTBS tests were performed using universal testing machine. Afterward, modes of failures were investigated. The statistical analyses were carried out using ANOVA, t-test, and Dunnett’s test. Results: The mean of μTBS for the 24-h and 6-month groups was 15.19 and 10.99 MPa, respectively. Bond strength of all groups except Group D decreased after 6 months, and this bond strength reduction in Group C was more than other groups. Most failure modes were in adhesive type. Conclusions: The use of CHX did not have better preservation of μTBS when compared to control group. Use of hypochlorite is not recommended.

Microtensile Bond Strength of Bulk-fill Resin Composite Restorations in High C-factor Cavities

To evaluate the microtensile bond strength (μTBS) and the fracture modes of four bulk-fill resin composites (Tetric EvoCeram Bulk Fill/Ivoclar Vivadent, Filtek Bulk Fill/3M ESPE, Venus Bulk Fill/Heraus Kulzer, and Filtek Bulk Fill Flow/3M ESPE) and one conventional incrementally filled resin composite (Filtek Z250/3M ESPE) inserted in class I cavities, after 24 hours and 6 months of water storage. In all, 30 sound human extracted molars were divided into five restorative groups. Standardized class I cavities were prepared and restored following the manufacturer's instructions. The restored teeth were then assigned into one of the storage times (24 hours or 6 months). The molars were then cut into 1 mm2 sticks and submitted to μTBS. All fractured specimens were analyzed under a stereomicroscope (40×). Data were submitted to analysis of variance (ANOVA) and the Tukey post hoc test was applied for comparison between groups; and paired t test for comparison within storage times (p = 0.05). After 24 hours of storage, statistically significant differences were observed between Filtek Z250 and Filtek Bulk Fill Flow groups. However, after 6 months, no statistical differences were observed between groups. Additionally, no differences were observed for the μTBS between the storage times. Adhesive failures were the most frequent fracture mode after 24 hours (54%) and 6 months (43%), the resin cohesive fracture mode showed 16% for 24 hours and 14% for 6 months, the dentin cohesive fracture mode showed 14% for 24 hours and 26% for 6 months, and the mixed fracture mode showed 16% for 24 hours and 17% for 6 months. Bulk-fill resin composites obtained similar μTBS in high C-factor cavities as conventional incrementally filled resin composites. No bond strength reduction was observed after 6 months of storage. Single increment restorations in high C-factor cavities with bulk-fill resin composites did not reduce μTBS after 24 hours or 6 months of storage. The comparable results to the conventional incrementally filled resin composites and the reduction in the operative time, make the bulk-fill resin composites a restorative option for posterior teeth restorations.

Clinical efficacy of universal adhesives for the restoration of noncarious cervical lesions: A randomized clinical trial.

Introduction:The efficacy of an adhesive agent is an important aspect in restoring noncarious cervical lesion (NCCL) as studies have proved that compromise in adhesive agent results in reduced bond strength. The purpose of this prospective randomized double-blind clinical trial was to evaluate the efficacy of the newly formulated “universal” dental adhesive in the restoration of NCCLs in permanent dentition using either a self-etch or a selective-etch approach.Materials and Methods:The study was done following the consolidated standards of reporting trials. 100 NCCLs randomly divided into 2 groups were restored using G-Premio Bond adhesive and Genial flowable composite in selective etch mode and self-etch mode. Restorations were evaluated at 1 week, 6 months, and 12 months using modified US Public Health Service criteria for marginal staining, fracture, and postoperative sensitivity. Statistical analysis was performed using appropriate tests.Results:Recall rates were 100%, 98%, and 78% at the evaluation time. The result showed that neither the self-etch nor the selective etch mode had significant difference in ALPHA/BRAVO/CHARLIE scores (P > 0.05). Percentage-wise comparison showed less changes reported in the selective etch group compared to self-etch group.Conclusion:It was concluded that there was no statistical significance between the groups for the parameters evaluated, but selective etch performed better than self-etch group.

Improving shear bond strength of metallic brackets after whitening.

ABSTRACTObjective: To evaluate a protocol for bonding metallic brackets after bleaching with hydrogen peroxide (HP). Methods: 60 extracted maxillary premolar were randomly divided into an unbleached control group and two groups bleached with a solution of 35% hydrogen peroxide prior to bonding. The teeth in one of the treated groups were bonded immediately after bleaching; while the other group was treated with 10% sodium ascorbate immediately after bleaching and before bonding. The teeth in all groups were stored in an artificial saliva solution for 7 days after bonding. The shear bond strength data was measured in megapascals (MPa) and the fail attempts were verified. The significance level was established at p< 0.05. Results: The unbleached group, in which brackets were bonded to untreated enamel, had the highest bond strength values (11.0 ± 5.7MPa) in comparison to the bleached group (7.14 ± 40MPa), in which brackets were bonded to recently bleached enamel. Slightly improved bond strength was observed in the antioxidant group (8.13 ± 5.4MPa), in which the teeth were bleached and then the antioxidant was applied to the teeth before bonding. Unbleached and bleached groups showed statistically significant difference for shear bond strength (p=0.03) and load strength (p=0.03); no significant differences were noted between unbleached and antioxidant groups (p=0.52).Conclusion: The antioxidant treatment applied immediately after bleaching was effective in reversing the reduction in shear bond strength of brackets after tooth bleaching.

Effect of Elevated Temperature on Bond Strength of Concrete

In the case of exposure of reinforced concrete structure to accidental fire, an assessment of its residual capacity is needed. Bond strength of concrete was observed under elevated temperatures (150°, 250°, 350° and 500°C) in this study. Cylindrical specimens were prepared for pull-out tests to find out the bond behavior and to observe the mechanical properties of concrete. All the specimens were 100 mm diameter and 200 mm height. The pull-out specimens contain a 10 mm steel bar at its center. The specimens were tested at 52 days age following a 28 days water curing. Samples were preheated for 3 hours at 100°C temperature and then put into the furnace for 1 hour at the target temperature. Samples were tested before preheating as controlled specimens. In case of mechanical properties and the bond strength of concrete, there were no remarkable changes due to elevated temperature up to 150°C. However, the mechanical properties and bond strength were decreased gradually after 150°C temperature. Maximum reduction of bond strength observed was 52.13% and 49.8% at 500°C for testing within 1 hour and after 24 hours of heating respectively when compared to the controlled specimens. Bond strength was found to reduce at a greater rate than compressive strength due to the elevated temperature.

Assessment of microcracks and shear bond strength after debonding orthodontic ceramic brackets on enamel priorly etched by different Er,Cr:YSGG and Er:YAG laser settings without acid application: An in vitro study

Enamel microcrack formation has a high incidence after mechanical debonding of ceramic brackets. This may be due to high delivered shear bond strength values when enamel is priorly etched by phosphoric acid. It is still not well elucidated in the literature if laser etching affects enamel the same way. The aim of the research was to analyze different Er,Cr:YSGG and Er:YAG laser etching settings as an alternative to phosphoric acid, in an attempt to prevent enamel microcrack formation during laser etching and mechanical debonding, while reducing the shear bond strength to the minimal clinical acceptable value. One hundred and thirty-three teeth were randomly divided into 7 experimental groups according to their etching modalities. Settings used for enamel etching were in Er,Cr:YSGG groups: Er,Cr:YSGG (1.5Watt, W/20Hertz, Hz); Er,Cr:YSGG (1.5W/15Hz) and Er,Cr:YSGG (2W/20Hz) and settings used for enamel etching in Er:YAG groups were: Er:YAG (60 millijoules, mJ), Er:YAG (80mJ) and Er:YAG (100mJ). Group C etched with 37% phosphoric acid served as control. Microscopic analysis was performed to assess presence of enamel microcracks. Shear bond strength was evaluated after thermocycling using Weibull survival analysis. All groups showed a reduction in additional microcracks after debonding when compared to control, but only group Er:YAG (60mJ) exhibited a statistically significant difference. Groups Er:YAG (80mJ), control and Er:YAG (100mJ) showed respectively the highest probability of survival at various stress levels followed by groups Er:YAG (60mJ); Er,Cr:YSGG (1.5W/15Hz); Er,Cr:YSGG (2W/20Hz) and Er,Cr:YSGG (1.5W/20Hz) that presented a relatively considerable risk of failure, even at low stress levels. When considering reduction of enamel microcrack formation and clinical acceptable shear bond strength, none of the groups succeeded both. Etching by Er:YAG (60mJ) and Er,Cr:YSGG (1.5W/15Hz), showed the least overall microcrack incidence between groups, but Er:YAG (60mJ) displayed significant reduction compared to phosphoric acid. However, etching by Er:YAG (80mJ) had the most predictable results in term of shear bond strength.

Bond Strength of Fusion Bonded Epoxy-Coated Reinforcement in Concrete

Fusion-bonded epoxy-coated steel is expected to extend the service life of the reinforced concrete structure in chloride-laden environments. However, the effect of coating on the bond-strength between rebar and concrete is not well understood yet. This research, therefore, studied the effect of epoxy-coating on the bond characteristics of reinforcing bars in concrete. The bond characteristics were assessed through pullout test considering variables viz. concrete strength, embedded length and bar diameter. The load was applied to reinforcing bars embedded in concrete until bond strength between the bar and concrete exceeded. Bond strength of epoxy-coated bars was compared with that of the uncoated bars. It was found that epoxy-coating reduced the bond strength approximately 25% for Ø20mm bar and 12% for Ø16mm and Ø12mm bar. As with uncoated bar, bond strength of coated bars were also increased with concrete strength. However, the bond strength ratio between coated and uncoated bars was found almost independent of concrete strength. Based on the test results, a development length modification factor of 1.33 is proposed for Ø20mm bar and 1.15 for Ø12mm and Ø16mm bar to compensate the bond strength reduction due to the epoxy coating.

Ultrashort-pulse laser as a surface treatment for bonding between zirconia and resin cement

ObjectivesTo evaluate ultrashort-pulse laser (UPL) as a surface treatment for improved bond strength to Yttria-tetragonal zirconia polycrystalline (Y-TZP). MethodsFully-sintered Y-TZP samples received either no treatment (CTL), or were treated by alumina blasting (ALB), tribochemical silica coating (SIL), or one of two UPL patterns: multiple pulses laser surface dots with 2.5μm spacing (8mJ, 10kHz)(LSD); or single pulse laser surface lines with 2.5μm spacing (4mJ, 6.7kHz)(LSL). Surface roughness, wettability (contact angle), and quantification of crystalline phases were evaluated for each group (n=3/group). Y-TZP treated slabs were cemented to resin composite slabs using silane and 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-containing adhesive. Beams from the Y-TZP/resin blocks were microtensile tested (n=5/group) after 48h water incubation (37°C) with or without subsequent thermocycling (5–55°C, 5000 cycles). ResultsAll surface treatments increased surface roughness values versus control (P<0.001). Contact angles were lowest for SIL (6.57±2.37°) and highest for control (50.97±6.30°). LSL and LSD were the only treatments that did not increase the relative monoclinic phase. All surface treatments significantly increased microtensile bond strengths (μTBS) compared with the control group (P<0.001), with highest values for UPL (LSD: 35.40±4.53MPa>LSL: 31.84±8.46MPa>SIL: 19.95±3.99MPa=ALB: 19.51±2.55MPa>CTL: 14.51±2.23MPa). Thermocycling significantly reduced bond strength for all treatments in a surface treatment-dependent manner. SignificanceThe ability of UPL to alter Y-TZP surface morphology, increase wettability and μTBS without increasing the monoclinic content suggests its potential to improve bonding to the underlying resin cement and tooth without compromising the strength of the restoration.