Mechanical Bond Strength Research Articles

Quantifying cation-π interactions in marine adhesive proteins using single-molecule force spectroscopy

In marine adhesives, cation-π interactions play an important role in their liquid-liquid phase separation process and underlying their strong interfacial bonding. However, it remains challenging to study the strength of cation-π interactions at the single-molecule level. Here, we engineer a recombinant chimeric polyprotein containing the mussel foot proteins-5 (MFP5) and a finger print domain GB1 to unambiguiously quantify the strength of cation-π interactions using atomic force microscopy (AFM)-based single-molecule force spectroscopy. Our results show that the formation of intermolecular cation-π interactions can be triggered at elevated salt concentrations, consistent with previous ensemble studies. Individual cation-π interaction ruptures at about 70 pN at a pulling speed of 1.6 μm s−1, comparable to the strength of other non-covalent interactions. The strength of cation-π interactions is weakly dependent on pH, which is in stark contrast with the hydrogen bonding and charge-charge interactions. Moreover, we find that the position of the cation-π bonds are formed randomly along the polyprotein chains. The propensity of forming long range cation-π interactions increases considerably when increasing the pH from 4 to 8, presumably due to the neutralization of the positive changes of MFP5. Our study directly quantifies the mechanical strength of cation-π bonds in the biological relavent settings and reveals key design parameters that may inspire the design of biomimetic strong underwater adhesives.

Mechanical properties, impact resistance and bond strength of green concrete incorporating waste glass powder and waste fine plastic aggregate

Mechanical properties, impact resistance and bond strength of green concrete incorporating waste glass powder and waste fine plastic aggregate

Influence of photodynamic therapy and intracanal medication on Martens hardness, elastic modulus and bond strength of glass-fiber posts to endodontically treated root dentin

BackgroundThe purpose of this in vitro study was to evaluate the influence of photodynamic therapy (PDT) with methylene blue photosensitizer (PS) and calcium hydroxide intracanal medication on Martens hardness (MH), elastic modulus (Eit) and adhesive bond strength of glass-fiber posts in different thirds of intraradicular dentin. MethodsNinety-six bovine teeth were distributed into the following 6 experimental groups: a negative control irrigated with deionized water; a positive control irrigated with deionized water and filled with calcium hydroxide intracanal medication (Ca[OH]2); Ca[OH]2 + methylene blue 50 mg/L without activation; Ca[OH]2 + methylene blue 100 mg/L without activation; Ca[OH]2 + methylene blue 50 mg/L activated by red laser; and Ca[OH]2 + methylene blue 100 mg/L activated by red laser (n = 16). MH and Eit were measured using an ultramicrodurometer under load action of 3 mN (n = 8). Adhesive bond strength was measured using the push-out test in a universal testing machine (n = 8), and representative samples underwent scanning electron microscopy. Data on MH, Eit, and bond strength were subjected to normality tests and analyzed by ANOVA and Tukey's test (α = 0.05). ResultsMethylene blue PS, activated or not by red laser, associated with calcium hydroxide medication did not promote significant difference as compared to the control groups irrigated with deionized water, associated or not with the use of intracanal medication, regarding mechanical properties and bond strength (p > 0.05). Experimental groups showed no difference between the thirds regarding root canal depth (p > 0.05), except for the positive control group, in which the apical third showed higher Eit values than the middle third (p = 0.0324). There was a predominance of mixed failure in all experimental groups, excepted the red laser-activated group treated with the highest concentration of methylene blue, which showed predominance of adhesive failure. ConclusionsPDT with methylene blue PS at 50 mg/L, associated with intracanal calcium hydroxide medication is a satisfactory alternative for endodontic treatment as there is no interference in the mechanical properties and bond strength among glass-fiber posts to intraradicular dentin at any depth of the root canal.

Relationships between Flexural and Bonding Properties, Marginal Adaptation, and Polymerization Shrinkage in Flowable Composite Restorations for Dental Application

To evaluate the flexural and bonding properties, marginal adaptation, and polymerization shrinkage in flowable composite restorations and their relationships, four new generation flowable composites, one conventional, and one bulk-fill flowable composite were used in this study. Flexural properties of the composites and shear bond strength to enamel and dentin for flowable restorations were measured immediately and 24 h after polymerization. Marginal adaptation, polymerization shrinkage, and stress were also investigated immediately after polymerization. The flexural properties, and bond strength of the flowable composites to enamel and dentin were much lower immediately after polymerization than at 24 h, regardless of the type of the composite. Polymerization shrinkage and stress varied depending on the material, and bulk-fill flowable composite showed much lower values than the others. The marginal adaptation and polymerization shrinkage of the composites appeared to have a much stronger correlation with a shear bond strength to dentin than to enamel. The weak mechanical properties and bond strengths of flowable composites in the early stage after polymerization must be taken into account when using them in the clinic. In addition, clinicians should be aware that polymerization shrinkage of flowable composites can still lead to the formation of gaps and failure of adaptation to the cavity regardless of the type of composite.

Experimental and Numerical Study on Interface Bond Strength and Anchorage Performance of Steel Bars within Prefabricated Concrete.

This study investigates the interface bond strength and anchorage performance of steel bars within prefabricated concrete. Twenty-two specimens were designed and manufactured to study the interface bond behavior of deformed and plain steel bars under a larger cover thickness. Diameter of steel bars, strength grade of concrete, and anchorage length were considered influential factors. The finite element method (ABAQUS) was used for the validation of experimental results. The interface bond’s failure mechanism and the anchorage length in the prefabricated concrete under different concrete strength levels were explored and compared to national and international codes. A suitable value of the basic anchoring length for the prefabricated structure was recommended. The results show that the interface bond strength of prefabricated bridge members is directly proportional to the strength grade of the concrete, inversely proportional to the reinforcement diameter, and less related to anchorage length. The effect of the cover thickness of the surrounding concrete is negligible. Conversely, the bearing capacity of prefabricated bridge members depends on the strength of the concrete, the diameter of the steel bar, and the anchorage length. Furthermore, it is concluded that the mechanical bond strength accounts for 88% of the bond strength within prefabricated concrete.

Experimental study on the mechanical properties of grouted sleeve joint with the fiber-reinforced grouting material

In recent years, more and more attention has been paid to the grouting material and technology of sleeve connection due to the wide application of prefabricated construction. The performance of sleeve connection, normally determined by the grouting material and technology of sleeves, has a significant influence on the seismic performance of prefabricated concrete structures. This paper presented an experimental study on the mechanical properties of the fiber-reinforced grouting materials and grouted sleeve joints, and the experimental parameters included the fiber type, fiber volume fraction, and fiber length. The main properties of the grouting materials were investigated, including fluidity, compressive strength, and flexural strength. The test results showed that the incorporation of fibers with different types, volume fractions, and lengths had different effects on the mechanical properties of the grouting material. Based on the grouting material tests, the sleeve splice test was conducted to investigate the influence of different anchorage lengths on the sleeve splice under the uniaxial loading, which indicated that substantial improvement could be observed for the mechanical properties and residual bond strength of the splices with fiber-reinforced grouting materials.

Alternative stabilised rammed earth materials incorporating recycled waste and industrial by-products: A study of mechanical properties, flexure and bond strength

Developing low-embodied energy building materials can significantly contribute to reducing global greenhouse gas emissions. However, these new building materials must be properly understood before they can or will be adopted by the construction industry. Rammed earth materials with low greenhouse gas emissions have been developed based on the principles of alkali-activated stabilisation as replacements for conventional construction materials.In previous work by the authors, the strength development, durability and sustainability, via life cycle assessment, of these new materials have already been studied. However, how these materials interact with and affect embedded reinforcement is poorly understood, as are methods to test these properties. Their applicability in modern construction is therefore currently limited. This paper extends the understanding of these materials through flexural and push-out testing of specimens reinforced with steel and glass-fibre reinforced polymer bars. We determine mechanical properties of the alternatively-stabilised rammed earth materials and study the composite behaviour of the reinforced materials. The suitability of current testing standards for elastic modulus, Poisson’s ratio, and indirect tensile, bond, shear and flexural strengths, originally designed for concrete specimens, were evaluated for RE materials. These were compared with design rules and predictions made using concrete standard AS 3600 and rammed earth standards (NZS 4297-4299), handbook (HB 195) and rammed earth and concrete literature.Results showed that existing testing procedures specified for concrete specimens were appropriate for estimating Poisson’s ratio and shear modulus as well as for determining flexural and shear strengths for rammed earth. Existing rammed earth recommendations given in NZS 4297 for estimating elastic modulus should continue to be followed. An alternative compressive reinforcement bond test, similar to RILEM AAC 8.2 push-out standard for autoclaved aerated concrete, was proposed; however, more work is required to establish a better prediction model for bond strength. Results indicated that current expressions to relate indirect tensile to unconfined compressive strength are suitable for compressive strengths up to 20 MPa.

Effect of Non-Thermal Atmospheric Pressure Plasma (NTP) and Zirconia Primer Treatment on Shear Bond Strength between Y-TZP and Resin Cement

The purpose of this study was to investigate the effect of non-thermal atmospheric pressure plasma (NTP) treatment on the sandblasting of mechanical method and zirconia primer of chemical method used to increase the bond strength between zirconia and resin cement. In this study, Y-TZP was divided into 4 groups according to the surface treatment methods as follows: Zirconia primer (Pr), NTP + Zirconia primer (NTP + Pr), Sandblasting + Zirconia primer (Sb + Pr), Sandblasting + NTP + Zirconia primer (Sb + NTP + Pr). Then, two types of resin cement (G-CEM LinkAce and Rely X-U200) were used to measure the shear bond strength (SBS) and they were divided into non-thermal cycling group and thermal cycling group for aging effect. Statistical analyses were performed using the Kruskal-Wallis test and Mann-Whitney U test. The result of the surface energy (SE), there was no significant difference among the groups (p > 0.05). As a result of the SBS test, the Sb + Pr group had a significantly higher SBS value than the other groups regardless of the resin cement type (p < 0.05), and the decrease rate after thermal cycling treatment was the lowest. On the other hand, the NTP + Pr group showed significantly lower SBS values than the other groups except for the case of using Rely X-U200 (p < 0.05), and the reduction rate after thermal cycling was the highest. The Sb + NTP + Pr group did not differ significantly from the Pr group (p > 0.05). Within the limitations of two successive studies, treatment with NTP after sandblasting used for mechanical bond strength showed a positive effect on initial SBS. However, when NTP was treated before the zirconia primer used for the chemical bond strength, it showed a negative effect on SBS compared to other treatment methods, which was noticeable after the thermal cycling treatment.

Cell Interconnections in Battery Packs Using Laser-assisted Ultrasonic Wire Bonding

Abstract This paper presents the results of a series of bonding tests using a laser-assisted ultrasonic wire bonding process. Aluminium and copper wire, both 500 μm (20 mil) thick, were bonded to nickel-coated steel caps of type 21700 battery cells. Mechanical bond strength tests prove that laser-assisted wire bonding has significant advantages over room temperature wire bonding. For example, it can be used to reduce the process time with aluminium wire or to increase the bondability of copper wire on nickel-coated steel. The results show a direct relation between tool tip temperature and measured bond strength. The quality of the joints was effectively improved by heating the tool tip up to 430 °C. These advantages are the same as in classic thermosonic wire bonding, but without the major disadvantage of having to heat to whole package. The cell temperature was shown to remain safely below the critical 60 °C in any application.

Optimal constant-stress ADDT plan with one main effect and one interaction effect

PurposeDegradation measurement of some products requires destructive inspection; that is, the degradation of each unit can be observed only once. For example, observation on the mechanical strength of interconnection bonds or on the dielectric strength of insulators requires destruction of the unit. Testing high-reliability items under normal operating conditions yields a small amount of degradation in a reasonable length of time. To overcome this problem, the items are tested at higher than normal stress level – an approach called an accelerated destructive degradation test (ADDT). The present paper deals with formulation of constant-stress ADDT (CSADDT) plan with the test specimens subject to stress induced by temperature and voltage.Design/methodology/approachThe stress–life relationship between temperature and voltage is described using Zhurkov–Arrhenius model. The fractional factorial experiment has been used to determine optimal number of stress combinations. The product's degradation path follows Wiener process. The model parameters are estimated using method of maximum likelihood. The optimum plan consists in finding out optimum allocations at each inspection time corresponding to each stress combination by using variance optimality criterion.FindingsThe method developed has been explained using a numerical example wherein point estimates and confidence intervals for the model parameters have been obtained and likelihood ratio test has been used to test for the presence of interaction effect. It has been found that both the temperature and the interaction between temperature and voltage influence the quantile lifetime of the product. Sensitivity analysis is also carried out.Originality/valueMost of the work in the literature on the design of ADDT plans focusses on only a single stress factor. An interaction exists among two or more stress factors if the effect of one factor on a response depends on the levels of other factors. In this paper, an optimal CSADDT plan is studied with one main effect and one interaction effect. The method developed can help engineers study the effect of elevated temperature and its interaction with another stress factor, say, voltage on quantile lifetime of a high-reliability unit likely to last for several years.

The Effect of Remineralizing Agents With/Without CO2 Laser Irradiation on Structural and Mechanical Properties of Enamel and its Shear Bond Strength to Orthodontic Brackets.

Introduction: Remineralizing agents may be used for the treatment of white spot lesions (WSLs) prior to bracket bonding. However, some concerns exist regarding their possible interference with the etching and bonding process, negatively affecting the bond strength. This study aimed to assess the effect of two remineralizing agents with/without CO2 laser irradiation on the mechanical properties and shear bond strength (SBS) of demineralized enamel to the orthodontic bracket. Methods: This study evaluated 60 premolar teeth in 6 groups (n=10) as follows: (I) sound enamel, (II) demineralized enamel, (III) Nupro remineralizing agent (N), (IV) Nupro and CO2 laser (N/L), (V) Teethmate remineralizing agent (T), and (VI) Teethmate and CO2 laser (T/L). The remineralizing agents were applied to the enamel surfaces after their immersion in a demineralizing solution for 5 days. In groups IV and VI, the CO2 laser with a 10.6 μm wavelength, 10 ms pulse duration, a 50 Hz repetition rate, 0.3 mm beam diameter and 0.7 W power was irradiated after applying the remineralizing agents. Brackets were bonded to the enamel surfaces and SBS was measured by a universal testing machine. For the assessment of enamel microhardness, 20 sections of molar teeth were divided into 4 groups (n=5; N, N/L, T, T/L) and their microhardness was measured before demineralization, after demineralization and after remineralization. X-ray diffraction (XRD) analysis, field-emission scanning electron microscopy (FESEM) and energy-dispersive spectrometry (EDS) were carried out to assess the formation of hydroxyapatite. The atomic percentages of the C, O, P, Ca, Na, Si, F and Ca/P ratio were determined by EDS analysis. Results: The SBS significantly decreased in group II (P<0.001). There was no significant difference among the groups I, III, IV, V and VI (P<0.05). This finding was similar to the microhardness results, which showed an increase in microhardness after remineralization (P<0.05), with no difference among the remineralizing agents. The Ca/P ratio was the highest in the Nupro group and the lowest in the demineralized group. Conclusion: Remineralizing agents can significantly improve the microhardness and structural properties of demineralized enamel to a level similar to that of sound enamel with no adverse effect on SBS to orthodontic brackets.

Experimental verification and simulation of fracture behavior of CFRP reinforced self-consolidating concrete beams with initial notch

The current study presents numerical and experimental approaches in the assessment of fracture behavior of self-consolidating concrete beams strengthened with carbon fiber-reinforced polymer (CFRP) lamina. The failure modes, mid-span displacement, and the load-bearing capacity of specimens with initial notches at mid-span are analyzed by varying the notch length and the beam height. Furthermore, the effects of variations in CFRP and concrete mechanical properties, bond strength, and notch location are examined by using the non-linear finite element analysis. Findings reveal that stress concentration in concrete and CFRP, in the vicinity of initial notch, as well as the failure of specimens occur as a result of CFRP debonding and crack extension. Moreover, it is observed that load- mid-span displacement curves are characterized by two peak load points strength. At the first stage, the applied load increases up to one peak value and then at the second stage there is a drop in the load-caring capacity. The applied load is then improved to another peak value due to the relatively high cohesive effect of the CFRP sheet at the third stage. Among different variables, the second peak load shows higher sensitivity to variations of the elastic modulus of CFRP, and bond strength at interface. As the notch approaches the beam support, and hence the relative distance from mid-span changes from 0 to 2/3, the two peak loads are respectively escalated by 116 and 58%, and thus the inclined crack propagates toward mid-span.

Performance of lightweight cementitious composite incorporating carbon nanofibers

Cellular concrete is a type of lightweight concrete traditionally applied in building industry for its thermal and acoustic insulation properties. However, in recent years, there is a surge in interest in potential applications of cellular concrete as a structural component due to its low self-weight, saving in raw materials and sustainability. Cellular concrete can be broadly divided into aerated concrete and foam concrete based on the pore-formation approaches. However, foam concrete is preferred to aerated concrete for structural applications due to better bubble size distribution, non-autoclaved curing process and no limitations in the dimensions of components. The main challenge for foam concrete is to have high-performance pore walls to provide required mechanical properties, shrinkage resistance, and durability under reduced density. In this paper, an ultrahigh performance concrete (UHPC) produced by a low water/cement ratio, optimum particle grading and incorporating carbon nanofibers (CNFs) was used as a base mix. It was then blended with homogeneous micro-foam bubbles to produce a lightweight cementitious composite (CNF-LCC) with 1500 ± 50 kg/m3 density for structural use. The novelty of CNF-LCC is that it has excellent mechanical properties and bond strength with steel reinforcement compared with traditional foam concrete, which is promising for structural applications. In addition, other engineering properties including early-age shrinkage resistance and durability of CNF-LCC are superior to normal weight concrete and lightweight aggregate concrete. Furthermore, CNFs can produce varying degrees of improvement on these engineering properties due to modification of its microstructure.

Does photodynamic therapy with methylene blue affect the mechanical properties and bond strength of glass-fiber posts in different thirds of intraradicular dentin?

There are few studies on the influence of methylene blue as a photosensitiser on the mechanical properties and adhesion of glass-fiber posts to intraradicular dentin. Thus, this in vitro study aimed to evaluate the influence of photodynamic therapy with a methylene blue photosensitizer on the Martens hardness, elastic modulus, and bond strength of glass-fiber posts in different thirds of intraradicular dentin. Eighty bovine teeth were divided into the following five groups: a control using deionized water, and four other groups according to the methylene blue concentration (50 mg/L or 100 mg/L) and substrate treatment (with or without red laser action). Ultramicrohardness test was used to evaluate the mechanical properties in different regions of the root dentin (n = 8). Push-out analysis was evaluated using a universal testing machine (n = 8). Data were subjected to the Kruskal-Wallis test, followed by Dunn's test for comparing groups, and the Friedman test for comparing thirds (α = 0.05). Representative scanning electron microscopy images were obtained. In general, methylene blue in distinct concentrations, with or without laser action, did not cause differences in the mechanical properties or bond strength in different regions of root dentin (P > 0.05). Methylene blue at a higher concentration, activated with laser, produced lower bond strength values in the middle third of the root canal (P < 0.05). Methylene blue at 50 mg/L had no influence on the mechanical properties of the bovine tooth and the bond strength of the glass-fiber posts to intraradicular dentin.

Influence of artificial aggregate on mechanical properties, fracture parameters and bond strength of concretes

The paper presented herein investigates the mechanical performance of concrete involving lightweight and normal weight aggregates with similar compressive strength. For this, two compressive strength values, 25 and 45 MPa, were considered for the concretes produced by normal and lightweight aggregates. Therefore, four concrete mixtures were designed at different water-to-cement ratios and cement contents. The lightweight aggregate utilized in this study was produced through cold bonding pelletization of fly ash and cement at ambient temperature in a specially designed tilted pan. The artificial lightweight aggregate used as a substitution of natural aggregate had similar particle size distribution to that of natural aggregate. The same mixing procedure was adopted to produce concrete and the testing specimens attained from each mixture were cured at the same circumstances. After the 28-day curing period, the specimens were tested for compressive strength and modulus of elasticity, splitting tensile and flexural strengths. Moreover, advanced mechanical properties such as fracture parameters, bond strength between embedded reinforcement and the concrete were also investigated. The test results indicated that it is possible to produce the lightweight aggregate concrete having similar compressive strength with the natural aggregate concrete, however, the utilization of artificial lightweight aggregates significantly influenced the investigated mechanical and fracture properties of the concretes despite having the similar compressive strengths. But, it was also observed that the utilization of lightweight aggregate made the concrete more ductile.

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.

Influence of Lime Solution on the Bonding Strength of a Mortar Coating Base

Mortar bond covering systems are multilayered and applied to a base, composed of render mortars (stucco, plaster) followed by some decorative element for a finishing touches (paint, ceramic plate, ornamental stones, etc.). In order to homogenize the characteristics of the base material and to increase the bond with the render mortar, it is a common practice to apply some type of preparation, either an even, smooth solution such as wetting the walls, or roughened solution utilizing roughcast. Studies have shown that the presence of calcium ions in ceramic bases results in the formation of a more dense crystalline structure at the interface, which culminates with higher mechanical bond strength. In this light, the present study presents an experimental investigation, the purpose of which is to evaluate, in a comparative way, the direct tensile strength of bond of a mortar coating applied to the same base, preceded in its application by five different preparation techniques. It can be concluded from this study that the preparation of the mortar base is of fundamental importance for bonding strength and, therefore, the addition of a lime solution to the roughcast is economically feasible and a satisfactory alternative in order to obtain positive results in environments where bond strength is critical.

Influence of Surface Treatment of Recycled Aggregates on Mechanical Properties and Bond Strength of Self-Compacting Concrete

In the last decade there has been a massive growth for development of concrete infrastructures all around the world. Take into account environmental concerns, concrete technology should direct efforts toward assuring development and fabrication of sustainable and resilient concrete. For this purpose, incorporation of recycled concrete aggregate in concrete products particularly self-compacting concrete (SCC) for structural and non-structural application would be significant achievement. In this study the fresh and hardened properties of SCC prepared by substituting natural aggregates (NA) with recycled coarse aggregates (RCA). In addition, bonding behaviour of reinforced RCA-SCC for structural application was investigated. Moreover, surface treatment of RCA using lithium silicate solution was proposed to investigate its feasibility to improve the fresh and hardened properties of SCC as well as its bonding strength. The mechanical properties including compressive strength, tensile strength and elastic modulus of SCC mixes using untreated RCA and treated RCA (TRCA) were investigated. The results showed an improvement in performance of SCC mixes made with TRCA in compare with the untreated samples. The bond behaviour between SCC made with RCA and steel reinforcement was studied and the relationship between the brittleness and bonding of SCC mixes using untreated RCA and TRCA determined. The effect of surface treatment on the interfacial transition zone (ITZ) between adhered mortar and RCA studied using scanning electron microscope (SEM). It was determined that the treatment of RCA improved the bond at the ITZ through densification. The results gave experimental evidence of the suitability of RCA-SCC for structural use and application in reinforced concrete.

Incorporation of EGCG into an etch-and-rinse adhesive system: mechanical properties and bond strength to caries affected dentin

This study evaluated how a matrix metalloproteinase (MMP) inhibitor (EGCG) incorporated into an etch-and-rinse adhesive system (AS) affects the long-term microtensile bond strength (MTBS) to caries affected dentin (CAD) and flexural strength (FS) of AS. Forty CAD surfaces received acid conditioning and were randomly divided into four groups (n = 10): EGCG-PRE – dentin treatment with 200 μg/mL EGCG solution; EGCG-INC – 200 μg/mL EGCG solution incorporated into SA; CHX-PRE – dentin treatment with 2% digluconate solution; NT – no treatment. The AS (Adper Single Bond 2, 3M ESPE) was applied and resin composite blocks were built on the dentin. Beam-shaped specimens (0.8 mm2) were obtained submitted to MTBS testing following 24 h, 6 months or 1 year of water storage (WS). Adhesive interface was analyzed by SEM. FS testing was performed by preparing specimens with the adhesive system, with or without the EGCG solution (200 μg/mL) (n = 10). Tests were carried out in a universal machine (0.5 mm/min). MTBS data were submitted to two-way ANOVA and Tukey’s test, whereas FS data, to the Student’s t-test (α = 0.05). MTBS values were not affected by EGCG application, either incorporated or used as a dentin treatment agent, regardless of the WS period; however, CHX negatively affected MTBS to CAD (p < 0.001). WS significantly reduced MTBS values (p < 0.001) from the 6-months time point. FS was not affected by EGCG incorporation into the SA (p = 0.2527). EGCG incorporation into AS was unable to maintain bond stability to CAD over time, whereas it did not compromise adhesive’s property.

Bond-slip behaviour between FRP tubes and seawater sea sand concrete

In the present study the bond-slip behavior between FRP tubes and seawater sea sand concrete is studied using push-out tests. Pultruded and filament winding FRP tubes with different fibre orientations and diameter-to-thickness ratios (D/t) were constructed to investigate the effect of confinement pressure on the bond behaviour. Moreover, to study the effect of fibre type, three types of FRP (i.e.; GFRP, CFRP and BFRP) were used. In addition, the mechanical and chemical bond strength of concrete filled FRP tubes were quantified and compared. CFRP and BFRP tubes showed the highest and the lowest bond strengths, respectively. Furthermore, it was concluded that the real confinement pressure of the tubes has a significant effect on the bond strength: the greater the real confinement pressure, the larger the bond strength (i.e. the tubes with smaller D/t ratio and fibres orientated in 89° showed greater bond strength compared to the tubes with larger D/t and different fibres orientations). Repeating the push-out test for four times, for each sample, showed that the slip starts earlier by increasing the number of repetition, while the bond strength remained almost the same. This shows that the bond strength of tubes is mostly governed by the friction (confinement pressure) rather than the adhesion (chemical bond).