Average Bond Strength Research Articles

EXPERIMENTAL STUDY ON STEEL AND POLYPROPYLENE FIBERS MORTAR BOND STRENGTH UNDER UNIAXIAL TENSION

The present study aims to investigate the bond behavior between fibers and mortar matrix in fiber-reinforced concrete, which was explored through a uniaxial tension test. The bond behavior was studied for different types of embedded fibers: steel fibers, polypropylene fibers, and hybridizations of steel and polypropylene fibers. The mixture proportion was determined based on the absolute volume method with a water-to-binder ratio (w/b) of 0.29 to achieve high-strength mortar. The high-strength mortar was cast by utilizing an industrial waste by-product of both silica fume and fly ash as a partial cement replacement. The compressive strength and uniaxial tension tests on high-strength mortar were conducted at the ages of 28 and 140 days. The long-term bond-strength behavior was investigated at the age of 140 days. The results showed that the average compressive strengths of hardened mortar on 28 and 140 days were 54.82 MPa and 69.37 MPa, respectively. Whereas, the average fiber-mortar bond strengths with steel, polypropylene, and hybridized fibers were 8.62 MPa, 8.37 MPa, and 7.30 MPa, respectively, at 28 days and 11.22 MPa, 10.21 MPa, and 11.82 MPa, respectively, at 140 days. Compared to the equivalent bond strength of the steel fiber, the polypropylene fiber had an equivalent bond strength of 2.90% and 9.00% lower at the ages of 28 and 140 days. Meanwhile, the equivalent bond strength of hybridized fiber was 15.31% lower than that of steel fiber; however, the long-term behavior of the hybridized fiber showed its performance was about 5,35% higher than that of steel fiber at 140 days.

Bond behavior between bundled composite bars and concrete using beam-end pullout tests

Bundled reinforcement can improve construction efficiency by reducing the number of connectors required. The steel-fiber reinforced polymer (FRP) composite bar (SFCB) is a novel reinforcement with high strength, moderate modulus of elasticity and good durability. Four groups of pullout tests were carried out, with parameters including the number of bars within each bundle, bonded length, and rebar type (steel bar, BFRP bar, SFCB). The failure modes of bar pullout without or after yielding, rebar fracture, and concrete splitting were observed. Compared to the single-bar specimen, the two-bar and three-bar bundled specimens resulted in approximately 30% and 40% decrease in average bond strength. The yielding slip sy of the three-bar bundled SFCB specimen is 3.8 times that of the single-bar specimen, indicating that bundled reinforcement can effectively control sy. A simplified bond strength prediction method and a bond stress-slip constitutive model based on the equivalent effective area approach are proposed. Finite element (FE) models were established and verified, and the failure modes of bar fracture are obtained by varying the bonded lengths for different bundled reinforcements, the ultimate slip of four-bar bundled BFRP bars increased by 127%. Recommendations for the development length of bundled SFCBs are proposed based on the FE results, which provide enough safety redundancy.

Effect of the Nd:YAG laser on the micro-tensile bond strength of composite resin to dentin with hypersensitivity using different universal adhesives.

This study aimed to evaluate the effect of the Nd: YAG laser on the tensile bond strength of composite resin to dentin with hypersensitivity using different universal bonding systems. After cutting the crown of 252 molars, buccal cervical enamel was removed at a thickness of approximately 2 mm, and 252 smooth dentin surfaces were exposed. Then they were etched with 0.5 M ethylenediaminetetraacetic acid (pH = 7.4) to stimulate hypersensitivity. The specimens were then randomly divided into 12 groups (n= 21) according to the surface treatments performed. After etching and bonding according to the manufacturer's recommendations in each group, the entire dentin surface was restored with Valux Plus composite resin. The samples were thermocycled and a universal test machine was used to measure the microtensile bond strength. The failure mode for each sample was observed under a stereomicroscope. For data analysis, the Bonferroni test, the independent t-test and the three-way anova test were used. The average microtensile bond strength in non-laser samples was higher than the average in laser samples (P<0.001). In comparison with the bonding agent type in both cases with and without laser, the highest average microtensile bond strength was related to ALL-BOND (P<0.001), meanwhile the lowest average tensile strength in samples without laser was related to G-Premio universal adhesive (P<0.001), and the lowest average microtensile strength in samples with laser belonged to Prime and Bond Elect group (P<0.001). Nd: YAG laser irradiation of the dentin surface before applying the adhesive significantly decreased the microtensile bond strength of the composite resin to the dentin surface. Key words:Nd:YAG laser, Bond strength, Dentin, hypersensitivity, Universal adhesives.

Effect of polymerization on free water in polyacrylamide hydrogels observed with Brillouin spectroscopy.

Brillouin spectroscopy is used to determine the effects of polymer concentration, crosslinking density, and polymerization on the longitudinal storage and loss moduli of polyacrylamide hydrogels. The model established by Chiarelli et al. is implemented to calculate the speed of sound in the free water [Chiarelli et al., The Journal of the Acoustical Society of America, 2010, 127(3), 1197-1207]. The polymer concentration has the greatest effect on the moduli of the polymer matrix. We determined that the crosslink density has no measurable effect on the logitudinal storage or loss modulus of polyacrylamide hydrogels when measurements are made at GHz frequencies, in contrast to measurements made at kHz frequencies as documented by other studies. However, the moduli are independent of monomer concentration if the acrylamide is not polymerized. We show at the GHz frequency that the incorporation of acrylamide polymer chains affects the mechanical properties of the free water. The speed of sound in the free water is reduced by the introduction of polymerized acrylamide. The long polymer chains and their interactions with the bounded water disrupt the bonding organization of the unbound water, causing a reduction of the average hydrogen bond strength between free water molecules. This results in a decreased speed of sound in the free water and an increase in the longitudinal storage modulus of the hydrogel.

Comparison of shear bond strength of different types of intracanal posts in restoring extensively damaged primary anterior teeth.

Severe caries in early childhood is a concern for both children receiving dental treatment and their parents. This dental disease progresses rapidly and quickly damages the coronal part of the tooth. When there is insufficient coronal structure to support a coronal restoration, using intracanal components following root canal treatment increases tooth resistance and helps provide retention for the coronal restoration. This study compared the shear bond strength of three types of intracanal posts (composite resin post, reverse metal post, and fiber post) in severely damaged primary anterior teeth. This in vitro study was conducted on 30 extracted anterior primary teeth with at least two-thirds of healthy roots and no prior pulp treatment. The teeth were randomly divided into three groups of 10: group 1: composite resin post with 8th generation universal bonding, group 2: reverse metal post with GC restorative glass cement, and group 3: fiber post with GC restorative glass cement. After placing the post, the samples were restored with a height of 3 mm from cementoenamel junction (CEJ) using an Anterior GC Gradia Packable composite resin. All the samples underwent 500 cycles of thermocycling in a hot water bath at 55±2 °C and a cold water bath at 5±2 °C. The shear strength of the samples was then evaluated using an electromechanical universal testing machine at a rate of 1 mm/min and at a location 2 mm coronal to the CEJ in terms of megapascals. The average shear bond strength of composite resin posts with 8th generation bonding application was 8.02220 MPa, reverse metal posts with glass ionomer application was 13.8600 MPa, and fiber posts with glass ionomer application was 9.7400 MPa. Based on these findings, it can be concluded that the highest shear bond strength in this study was related to the reverse metal post, and the lowest shear bond strength was related to the composite resin post. According to the results, reverse metal posts demonstrated better shear bond strength than composite resin posts and fiber posts (P<0.05).

Dispersion, ionic bonding and vibrational shifts in phospho-aluminosilicate glasses.

Understanding the relationships between structure and properties of aluminosilicate glasses is of interest in magmatic studies as well as for glass applications as mechanical or optical components. Glass properties may be tailored by the incorporation of additional elements, and here we studied the effect of phosphate incorporation on refractive index and the degree of ionic bonding in aluminosilicate glasses. The studied glasses in the system SiO2-Al2O3-Na2O-P2O5 had a metaluminous composition (Al:Na = 1) with the content of SiO2 ranging from 50 to 70 mol% and of P2O5 from 0 to 7.5 mol%. Refractive index was measured at four wavelengths from visible to near-infrared and found to decrease both with increasing P2O5 content (at the expense of NaAlO2) and with increasing SiO2 content (by substitution of SiO4 for AlO4 groups). This trend correlated with a decrease in density while, additionally, the formation of Al-O-P bonds with an SiO2-like structure may account for this change. The degree of ionic bonding, assessed via optical basicity and oxygen polarisability, decreased with increasing P2O5 and SiO2 content. Despite the complexity of the studied glasses, oxygen polarisability and optical basicity were found to follow Duffy's empirical equation for simple oxide glasses. In the high frequency infrared and Raman spectra, band shifts were observed with increasing P2O5 and SiO2 content. They indicated changing average bond strength of the glass network and showed a linear correlation with optical basicity.

Mechanical performance of a bond-type anchorage system for CFRP cable exposed to elevated temperature

Both high-temperature pullout tests without and with pre-tension load were conducted on the bond-type anchorage system specimens with bonding medium of UHPC (Ultra-high Performance Concrete) for Carbon fiber reinforced polymer (CFRP) cable in order to fully understand the bonding behavior of CFRP cable-UHPC interface under high temperature. The variation laws of ultimate pullout load, average bond strength of CFRP cable-UHPC interface and slippage corresponding to ultimate pullout load were uncovered in two types of high-temperature pullout tests. Then, the bond performances of CFRP cable-UHPC interface in high-temperature pullout tests with pre-tension load ratio from 0.2 to 0.6 and target temperature in the range of 100–210 ℃ were compared to these in high-temperature pullout tests without pre-tension load in order to identify the effect of temperature-load path. Finally, theoretical models for determining average bond strength of CFRP cable-UHPC interface and critical bond length of CFRP cable for the bond-type anchorage system under high temperature were developed by incorporating effects of high temperature and pre-tension load ratio. The obtained results demonstrate that the dominant failure mode of the bond-type anchorage system in high-temperature pullout tests is slip failure of CFRP cable-UHPC interface, and shear failure morphologies of embossed rid for CFRP tendon are closely correlated with target temperature. In high-temperature pullout tests without pre-tension load, the average bond strength of CFRP tendon-UHPC interface gradually decreased as the increasing target temperature, the corresponding attenuation ratios in temperature ranges of 25–300 ℃ and 300–400 ℃ are 84% and 47%, respectively. In high-temperature pullout tests with pre-tension load, the average bond strength of CFRP tendon-UHPC interface approximately linearly decreased as the increasing target temperature or pre-tension load ratio. The presence of pre-tension load results in acceleration of damage of CFRP cable-UHPC interface, and the damage degree is proportional to pre-tension load. The developed theoretical models of mechanical properties for the bond-type anchorage system exposed to high temperature can accurately predict average bond strength of CFRP cable-UHPC interface and critical bond length of CFRP cable.

Effect of initial pretension on dynamic bond behavior of an ultra-high performance concrete-filled anchorage for carbon fiber-reinforced polymer tendons

This paper is focused on the effect of initial pretension on the dynamic bond performance of the anchorage under impact loads. Drop-weight impact tests were conducted on 15 groups of specimens with four embedded lengths and various pretension ratios; the effects of pretension and embedded length on the bond strength and slip of the anchorage are discussed in the paper. The test results show that a higher pretension ratio led to severer surface damage on the CFRP tendons. With the increase of the pretension ratio, the mechanical interlocking between CFRP ribs and UHPC was improved, leading to an increased average bond strength. By contrast, the relatively large shear deformation and severe damage of CFRP ribs induced by pretension formed “initial defects”, which resulted in a lower residual bond performance during impact loading. Based on the test results, a pretension ratio-dependent strength retention function was proposed to quantify the shear damage effect of CFRP ribs caused by pretension; by incorporating this function, accurate formulas were developed for determining the dynamic bond strength of a pretensioned anchorage.

Fabrication of a new bamboo composite with large-size high-quality flattened surface

Bamboo is a highly lignified grass with a thin wall and hollow interior. Recombination technology is commonly used to realize its scaling utilization. In this study, a high-quality flattened bamboo recombination panel (BRP) was fabricated based on the full utilization of bamboo. The BRP was designed with sandwich structure and a core layer composed of a mixture of bamboo skin strips and bamboo pith particles upon hot pressing, resembling a reinforced bar-concrete structure. The surface layer was made from densified bamboo slices through thermal-flattening (TF) to achieve stress relief and realize deformation resistant, surface modified resulted in decreased hydrophilicity. The performance of the flattened bamboo slices and BRP was analyzed, the results showed that the TF treatment was successfully modified the bamboo mid-slices, which were compressed and densified during the process. The TF treatment realized stress relief and increased surface hardness and hydrophobicity, because of a reduction in the number of free hydroxyl groups in hemicellulose. The vascular bundles and parenchyma cells of the bamboo mid-slices underwent different extents of contraction. Further, the initial moisture content was negatively correlated with the compression rate. Dynamic mechanical analysis results showed that through the TF treatment conducted at an initial moisture content (MC) of 30%, temperature of 160 ℃ and time of 4 min (30%−160 ℃−4 min) the storage elastic modulus of bamboo mid-slices increased from 5133 to 8867 MPa. The average internal bond strength, surface bond strength, and thickness swelling of the BRP bonded by phenol formaldehyde (PF) and urea-formaldehyde (UF) resins were 0.71, 0.6 MPa; 0.89, 0.82 MPa; and 9.1%, 14.7%, respectively, which meet national standards. The BRP had a high-quality flattening effect, and the flattened width could reach 2–5 times the circumference of the bamboo culm, and the performance matched that of oriented strand boards, confirming to be an upgraded product of bamboo-flattening boards and bamboo- oriented strand boards.

Bond responses and anchorage length of GFRP bar in precast recycled aggregate concrete

Precast recycled aggregate concrete (PRAC) employs precast reject-derived recycled aggregates (PRAs) and exhibits mechanical properties on par with or superior to those of natural aggregate concrete (NAC). Nevertheless, the durability of PRAC is hampered by aged mortar. To address this issue, integrating high durability glass fiber reinforced polymer (GFRP) bars into PRAC emerges as a potential solution for constructing enduring structures. Building upon this context, the study focuses on the bond responses between PRAC and GFRP bars, an area with limited existing research. Three main tasks were conducted: Firstly, a comprehensive test program involving 108 pullout samples was conducted to investigate the key variables' effects on bond failure mode and stress-slip relationship. Subsequently, an equation was developed to determine the peak bond strength of recycled aggregate concrete (RAC) based on available test data. Additionally, reliability analyses were performed to discuss the anchorage length of GFRP bar embedded in RAC. The findings are as follows: (a) The PRAC's bond capacity initially increased then decreased with rising PRA content. At full replacement, PRAC's bond strength was 28.3% lower than NAC. However, a two stage mixing approach restored PRAC's bond capacity to NAC levels. (b) Helical wrapping of the GFRP bar consistently exhibited the highest bond capacity, with an average bond strength 51% greater than a sand coated GFRP bar and 21% higher than a GFRP bar treated with both helical wrapping and sand coating. (c) Current codes specifying the critical anchorage length for FRP bar in NAC were often unsafe for RAC. Hence, a new expression, factoring in RA content, type and RAC mixing method, was proposed to determine the suitable anchorage length.

Effect of Plasma Radiation and Other Surface Preparation Methods on Microtensile Bond Strength of Repaired Aged Resin Composite.

Objectives: The purpose of this study was to compare the effect of plasma irradiation and other surface preparation methods on the microtensile bond strength of repaired resin composites. Materials and Methods: Twenty molds of a universal nanohybrid composite were prepared, aged and subjected to thermocycling. The specimens were divided into 5 groups for surface preparations including, C (Control): application of GC G-Premio Bond (GP) only; SB: sandblasting with alumina and GP; SI: application of phosphoric acid etching, silane, and unfilled resin; RB: roughening by diamond bur, phosphoric acid etching and GP; PL: application of argon and atmosphere plasma and then GP. The specimens were repaired with the new resin composite, cut to 1mm2 beam, and then subjected to thermocycling. The microtensile bond strengths were measured using a universal testing machine. The failure modes were assessed with a stereomicroscope. Data were analyzed using two-way ANOVA and Tukey's test. The level of significance was α=0.05. Results: The highest mean bond strength was found for the application of universal bonding GC GP in controls (26.62MPa) and the lowest average bond strength belonged to the SI groups (9.06MPa). The difference in the mean bond strength between the SI group and other groups was significant (P<0.05). The failure mode of specimens in all groups was predominantly adhesive. Conclusion: The application of GP as an intermediate universal adhesive established a proper bond between the old and new resin composite. In addition, the plasma application and other surface preparation methods did not significantly improve the bond strength.

Bond behavior of CFRP-concrete with surface groove subjected to chloride wet-dry cycles: Experimental, strength model and design method

To investigate the effect of chloride wet-dry exposure on the bond behavior of CFRP-concrete with surface groove, firstly, four groups of single-lap tensile specimens with different groove width-to-depth ratios were designed and conducted. After the four groups of specimens were subjected to accelerated corrosion, failure modes and bond behavior were investigated. Secondly, based on two categories of failure modes, models were proposed to calculate the bond strength for fracture failure (model I) and debonding failure (model II) of the specimens, respectively. Finally, a bond design method has been proposed for CFRP-concrete with surface groove that was specifically developed for coastal environments. The results show that the failure mode of the surface groove method changes from the CFRP fracture without erosion to the CFRP sheet mixed failure and debonding failure. The bond strength of grooving method decreases along with the wet-dry cycles. The width-to-depth ratio is positively related to the average bond strength and there is an optimum value. Compared with the experimental values, the values of calculation model I are slightly higher, and the values predicted by calculation model II are within acceptable limits. These indicate that the grooving method has better bond behavior under chloride salt solution wet-dry cycles, and the proposed design method is applicable to guiding the bond design of the interface in coastal environments.

Mechanical behavior and constitutive relationship of bond interface in steel plate-reinforced shield tunnels

In order to explore the mechanical properties and failure mechanism of the bond interface of steel plate reinforced shield tunnels, a series of uniaxial tensile and uniaxial shear experiments were conducted in this study. The impact of bond interface parameters on the mechanical properties of the reinforced interface was mainly analyzed, including the failure mode, ultimate bearing capacity, average bond strength, and stress-strain relationship of the bond interface. To enable numerical simulation of the mechanical behavior at the bond interface, a stress-strain constitutive relationship equation for the bond interface is established using the least squares method. The main conclusions are as follows: For steel plate-concrete interface bonded with epoxy resin, the shear resistance of the bond interface generally surpasses the tensile resistance under the same interface parameters. Tensile load predominate leads to the cohesive failure of the concrete while the interface layer remains undamaged. In contrast, shear load mainly results in the detachment between the steel plate and the interface layer. The ultimate bearing capacity and bond strength of the interface can be enhanced by decreasing the interface thickness or increasing the interface roughness. Moreover, an expansion bolt can further increase the mechanical property of the bond interface, and the improvement effect intensifies with higher expansion bolt grades. The stress–strain curve of the bond interface can be divided into three stages with elastic stage, softening stage and debond stage. The main difference of stress–strain curve under different bond interface parameters lies in the stage before the softening of the bond interface. The interface stress-strain curve is primarily influenced by the thickness of the bond interface and the grade of expansion bolts, whereas the roughness of the concrete surface has minimal effect.

Test and analysis of the interfacial bond behaviour of circular concrete-filled wire-arc additively manufactured steel tubes

Interfacial bond behaviour of the circular concrete-filled wire-arc directed energy deposition (DED) steel tubes was investigated experimentally, in which wire-arc DED, commonly referred to as wire-arc additive manufacturing (WAAM), represents a metal 3D printing method. Firstly, a 3D laser scanning was employed to generate the 3D models of the WAAM steel components to obtain the geometric features. A parameter relating to the surface undulation was proposed to evaluate the roughness of the WAAM steel tubes. The results of tensile testing undertaken to obtain the mechanical properties of the WAAM material were summarised. Twelve push-out specimens were tested to obtain the load-slip response and bond strength, while the influence of surface undulation, diameter-to-thickness ratio and interface length was also assessed, respectively. The test results demonstrated that: 1) after reaching the peak load, a slowly descending region appeared until a relatively stable residual load was achieved; 2) the average bond stresses of the push-out specimens were greater than those of the push-out specimens fabricated by conventional steel tubes and even checkered steel tube. Comparisons of the bond strength of the push-out specimens against existing structural design standards indicated the design guidelines of various codes were quite conservative. There needs to consider the influence of the surface undulation of the WAAM steel tube. Finally, based on the nonlinear regression of the test data generated in the present study, an empirical equation was proposed for the prediction of the average bond strength for concrete-filled WAAM steel tubes.

On the Factors That Determine the Bond Behaviour of GFRP Bars to Concrete: An Experimental Investigation

It is becoming accepted that glass-fibre-reinforced polymer (GFRP) is a credible and effective replacement for steel in reinforced concrete (RC) to meet structural requirements whilst addressing durability concerns posed by steel over the long term. A better understanding of the bond behaviour between GFRP and concrete is essential for reliably and efficiently designing concrete structures with reinforced GFRP bars. This paper presents a parametric study of the bond behaviour of GFRP bars to concrete where the effects of the length, diameter, concrete strength, concrete cover thickness and rebar surface morphology of GFRP bars were investigated via a series of pull-out tests. The test results indicate that the bond strength of GFRP bars is predominantly influenced by their surface morphology, embedment length and diameter. On the other hand, the effects of concrete strength and cover thickness appear to have a limited impact on the bond strengths of GFRP rebars to concrete. It is shown that ribbed GFRP bars exhibit the highest bond energy of 89.4 Nmm and an average bond strength of 11.9 MPa. Moreover, the analysis of failure modes indicated the unique effect of GFRP surface morphology on failure mode. It is shown that 100% of ribbed GFRP failed due to concrete split, while 85% of sand-coated bars experienced failure due to bar slip. This examination of failure modes and their corresponding bond strengths provides a unique perspective on the bond behaviour between GFRP bars and concrete.

Slag-modified metakaolin-based 3D printed geopolymer: Mechanical characterisation, microstructural properties, and nitrogen physisorption pore analysis

This study aims to enhance metakaolin (MK)-based binders with slag up to 30% at 10% intervals and increase the aggregate-to-binder ratio (a/b) from 1.6 in a previous study to 2 for extrusion-based 3D printed geopolymer concrete (3DPGPC). Sodium phosphate (3% by mass of binders) was used to tailor the fresh properties of the slag-modified MK-based 3DPGPC mixtures to achieve sufficient open time for constructability. After 28 days of curing age, cylindrical 3DPGPC specimens cored perpendicular to the printing direction (D1) exhibit an average compressive strength of 23.7–31.52 MPa and the specimens cored parallel to the printing direction (D3) exhibit an average compressive strength of 25.25–33.13 MPa. Also, an increase in a/b from 1.6 to 2 increases the average compressive strength by 18% in D1 and 25% in D3. The average flexural strength of specimens in D1 attained 5.48–7.29 MPa, while the average interlayer bond strength of 3DPGPC beam specimens attained 5.40–6.90 MPa. An increase in a/b from 1.6 to 2 enhanced average flexural strength by 6%. Furthermore, the 28-day splitting tensile strength of cored cylindrical 3DPGPC specimens attained 1.79–2.16 MPa in D1 and 2.04–2.43 MPa in D3. Microstructural characterisation revealed the formation of C-S-H, N-A-S-H and C-A-S-H gel with increasing slag inclusion due to the presence of Ca2+ion. Nitrogen physisorption analysis shows that the adsorption and desorption isotherm curves and hysteresis loops were not altered but more nitrogen by volume was absorbed due to the formation of a significant quantity of C-S-H, N-A-S-H and C-A-S-H gel. The adsorption and desorption isotherms fall under the mesopores structure of 2–50 nm using the IUPAC technical report classification. The Brunauer-Emmett-Teller (BET) surface area increases by 67, 69, and 78% as slag content increases by 10, 20 and 30% due to the polymerisation of the reactive phases, which densify the matrices. The enhanced mechanical performance, microstructural properties, and pore structure system of slag-modified MK-based 3DPGPC ascertained that it is suitable for construction applications.

Optimization of surface roughness, phase transformation and shear bond strength in sandblasting process of YTZP using statistical machine learning

Sandblasting process is often applied to roughen the intaglio of yttria tetragonal zirconia polycrystals (YTZP) surfaces for easy and quality adhesion and micro-shear retention with dentine/resin cements. Sandblasting process parameters have shown to influence, at different scales, surface roughness, phase transformation and shear bond strength, all of which are referred, herein, as performance characteristics. This study aimed to find the parametric settings of sandblasting parameters that could simultaneously optimize these performance characteristics, hypothetically testing the probability. YTZP surfaces were sandblasted at different levels of incidence angle (IA), abrasive particle size (AP), pressure(P) and sandblasting time (ST) following the Taguchi method based on the two-level parametric process settings (L8(27)). Surface morphologies, roughness (SR), monoclinic content (MC), and shear bond strength (SS) were characterized by the SEM, average surface roughness, XRD, and shear bond strength tests, respectively. Rough surfaces containing scratches, plastic deformation streaks, micro cracks and pitting were observed. According to the Taguchi method, the same optimum sandblasting parametric setting maximized SR and MC but failed to maximize SS. Subsequently, the principal component analysis embedded in statistical machine learning was applied to find the optimum sandblasting parametric setting that maximized all the performance characteristics. The optimum sandblasting setting of IA = 45°, AP = 110 μm, ST = 20 s and P = 400 kPa predicted the maximum values of SR = 0.773 μm, MC = 36% and SS = 16.6 MPa. Analysis of variance confirmed AP and P as the most influencing parameters affecting all performance characteristics. Finally, these results provide a systematic and comprehensive route for optimizing sandblasting roughening of YTZP surfaces which can be adopted in adhesive dental and orthodontic industry.

Interfacial Bond Properties of Underwater Concrete Coated with Bisphenol A Epoxy Resins.

This study investigated changes in the interfacial properties of epoxy-coated concrete exposed to various conditions, regarding the epoxy type, coating equipment, and exposure environment and period. The measured coating thickness and pull-off bond strength exhibited diverse trends, depending on the exposure period and conditions. In the real sea (RS) environment, the average bond strengths for bisphenol A (BPA) (E1), BPA with zinc powder (E2), and BPA with cresyl glycidyl ether (E3) were 1.26, 1.93, and 1.92 MPa, respectively. The coating method did not significantly affect the measured coating thickness and strength values. The conventional roller (D1) exhibited the highest thickness variation, with a value of 214.45 μm. The RS condition significantly increased the coating thickness (34% to 158%) compared to the tap water (TW) condition. The exposure conditions had little impact on bond strength except for E3, which showed an increased strength (2.71 MPa) over 7-91 days, especially under RS conditions, while E2 remained constant at approximately 1.82 MPa. This study offers insights into factors influencing marine concrete coating performance and discusses limitations and future work.

Bond stress-slip behavior of ultrahigh-strength steel bars with spiral grooves embedded in plain and steel fiber high-strength recycled aggregate concrete

This study investigated the bond behavior of ultrahigh-strength steel bars with spiral grooves (UHSSBs) embedded in high-strength recycled aggregate concrete (RAC). Forty-five pullout specimens under monotonic loadings were designed to evaluate the effect of several parameters on the bond strength. The variables included concrete strength (50 MPa–60 MPa); recycled concrete aggregate (RCA) replacement ratio (0 %, 50 %, and 100 %); embedment length (5db, 10db, and 20db); concrete cover (25 mm, 45 mm, and 68.7 mm); surface treatment; volume fraction of steel fibers in RAC and stirrup ratio. The failure modes of these tests mainly concentrated on two types, pullout-type bond failure and splitting-type bond failure. According to the typical bond stress-slip curves and trendlines of plotted values, the bond strength increased with increasing of concrete compressive strength. For specimens with splitting-type bond failure, the higher normalized bond strength was observed in higher RCA replacement ratio and concrete cover thickness. The factors of embedment length and surface treatment were also proven to be effective for bond strength. For specimens with pullout-type bond failure, the presence of steel fibers and stirrups substantially restricted the splitting crack growth and improved the bond failure modes. Combined with previous experimental results, simple empirical equations for the average bond strength and bond stress-slip relationship between UHSSBs and RAC under different types of bond failure were developed by regression analysis, which can capture the experimental data with high accuracy.

Impact of Heating Exposure on the Micro-Push-Out Bond Strength of Bioceramic Sealers

Introduction. The aim of this study was to evaluate the effect of heating of bioceramic and epoxy resin-based sealers on their micro-push-out bond strength (BS) to root canal dentin. Methods. After criterial selection, 30 human teeth were decoronated and 1-mm thick slices (n = 60) were obtained perpendicularly along tooth axis, from cervical and middle root thirds, with a diamond disc attached to a cutting machine. In each slice, three 1.0-mm diameter orifices were made. After rinsing with 17% EDTA and 2.5% NaOCl, each orifice was filled with Bio-C Sealer or BioRoot RCS or AH Plus, according to the manufacturers’ instructions. After filling, half of the slices (n = 30) were heated at 100°C for 1 min, and the other half were kept at room temperature. After 7 days-controlled storage, micro-push-out test was performed in a Universal Testing Machine. Failures were analyzed using a stereomicroscope. Statistical analysis was performed with One-Way ANOVA and post hoc Tukey (α = 5%) tests. Results. AH Plus demonstrated higher BS values after heating ( p = 0.001 ) when compared to nonheated. The other sealers did not show a statistically significant difference ( p &gt; 0.05 ). When heated, the average BS values for AH Plus were higher than for BioRoot RCS and Bio-C Sealer ( p &lt; 0.001 ). Cohesive failure mode was the most frequent, followed by adhesive and mixed ones. Conclusion. Heating provided a higher push-out BS to root dentin for AH Plus and did not influence BioRoot RCS or Bio-C sealer.