Bond Strength Development Research Articles

Optical and mechanical factors in the temporal development of tooth–composite bond

ObjectivesTo obtain an accurate picture of the temporal development of bond strength between resin composites and tooth structures during cure for assessing debonding at the tooth–composite interface. MethodsAn assembly of uncured composite sandwiched between a glass block and a dentin slab with a layer of pre-cured adhesive was used in this study. A conventional composite was compared against a bulk-fill composite. The rate of bond formation was determined by measuring the tensile bond strength of specimens of different thicknesses at different time points during cure. The changing light irradiance exiting the composite as it cured was also recorded. Mode of fracture was analyzed by examining the fracture surfaces. ResultsPhoto-bleaching occurred in both resin composites. The development of the dentin–composite bond strength was initially dictated by the developing cohesive strength of the resin composite, and its final value was capped by the strength of the preformed dentin–adhesive bond. The higher interfacial irradiance in the bulk-fill composite did not lead to faster development of the overall bond strength. This was caused by its slower rate of cohesive strength development as reflected in the longer time for its interfacial irradiance to plateau and the greater proportion of cohesive failure seen in the initial stage of polymerization. The law of reciprocity did not hold for the development of dentin bond strength. SignificanceThe results from this study, when compared with the development of shrinkage stress, can be used as a basis for ensuring the integrity of the dentin–composite interface during cure.

Bond strength between concrete layers of three-layer concrete structures

Development of the methods for the calculating reinforced concrete structures covers a wide range of issues, including the expansion of the application of new innovative materials such as concrete and reinforcement. In practice, modern construction of multilayer structures is made of concrete with different strengths and it is compulsory to conduct numerical and experimental studies of the bond strength between concrete layers with different strengths. In this study, the influence of some physical-mechanical factors and temporal manufacturing parameters on the monolithic bond of concrete layers of three-layer structures made of concrete with different densities according depending on the sample is considered. An experiment was conducted to evaluate the development of the shear bond strength between two concrete layers of three-layers sandwich concrete. Three-layer samples consist of normal concrete (NC) in the external layers and lightweight concrete (LWC) in the inner layer. The results of the study show that these factors directly affect the monolithic bond of concrete layers in three-layer structures, which are made by concrete of different strengths. The obtained scientific results allow the determination of reasonable parameters to ensure the monolithic bond of concrete layers with different strengths of the 3-layers structure in design and production.

Bond Behaviour of Steel and Concrete with Pull-Out Test

This experimental investigation presents the influence of rebar’s which has protecting coating, rested rebar and fresh rebar and there bond strength development between the steel and concrete. Pull-out experiment was conducted Universal Testing Machine (UTM) which has a capacity of 400 KN as per IS code procedure. The tested rebar includes rusty rebar, acid preserved rebar and cement chemical compound anticorrosive coated rebar. The Concrete mix design for M25 grade of concrete were used and therefore 18 concrete cube specimens with external projection of steel rod were tested. The various load slip behaviour was studied at the free end finish and loaded end victimization dial gauges. The last word bond stress just like the lowest load worth of 0.025 mm metal slip and 0.25 mm slip was thought of as a result of the usable bond strength of steel rebar’s and concrete. The check results blatant correlation exists between Load at 0.025 mm free finish slip and 0.25 mm loaded finish slip. It had been found that presence of rust and cement compound anticorrosive coating among the steel concrete interface appreciably can increase the bond strength of the order of 20 % and 27 % severally for 16mm diameter bars as compared to rust free rebar. For 20mm dia. Bars has totally different bond strength for rusty rebar’s and therefore the increase in bond strength for coated bars are compared with 2 differing kinds of uncoated bars and rusted rebar’s were determined. It’s over that presence of rust influences in reduction / increase in bond strength hoping on the character of rust at the interface among the initial ages. Application of cement compound coating has been improves the bond strength of the order of 31% – 37 % to satisfies the necessities of Burse Indian Standards code (IS)

Bamboo Bonding in Concrete: A Critical Research

Housing needs across developing countries are at its peak especially due to increasing population growth rate. This has caused a great demand for conventional building materials leading to over-exploitation of natural resources required for their production along with their detrimental effects on the environment. Sustainable construction practices are thus required which involves the application of materials such as bamboo, fly ash, kenaf, etc. Bamboo is a lightweight, costeffective, environment-friendly material with more than six times the strength by weight ratio compared to steel. This paper reviews the application of bamboo in the form of reinforcement in concrete with detailed aspects focussed on its bond strength development in concrete. Different bamboo reinforcement treatment processes developed in literature combined with their applications and limitations are presented. It was observed that with Sikadur 32 Gel epoxy coating method and with the application of G.I. rolled wires method, 3.25MPa and 9.71MPa of bond strength could be achieved respectively. This highlights that with proper surface treatment processes, bamboo as reinforcement in concrete can develop significant bond strength compared to steel reinforcement. However, issues such as lack of codal guidelines, non-standardized pull out testing mechanism to incorporate density variation of fibers, combined with wide variation in its properties requires further standardization before its mass application.

Development of Bond Strength of Reinforcement Steel in New Generation Concretes

The paper presents an experimental investigation of the steel-to-concrete bond using a pull-out test. Namely, the development of bond strength of reinforcement steel in new generation concretes was investigated. In the tests high-performance self-compacting (HPSCC) and vibrationally consolidated concretes (HPC), with the same water-to-binder ratio and made of components with the same properties, were used. For comparison purposes, the normal concrete was also used. For each concrete used in the experiment, a compressive strength development test was performed. To assess the development of bond strength in the tests, cubic specimens with the dimensions 160x160x160 mm were used. In each test element, ribbed reinforcing bar with a diameter of 16 mm was embedded in. Two variants of orientation of reinforcing bars with respect to the direction of concreting were considered - perpendicular and parallel. Test results showed that the development of bond strength between steel rebars and concrete increases with the increasing age. Additionally, the bond strength between steel rebars and concrete escalated with the increasing concrete strength. However, the development of bond stress with age was faster than the development of compressive strength, especially at early test ages. No significant difference was noticed between HPC and HPSCC mixes in terms of bond or compressive strength development with age. The conducted studies showed that in new generation concretes as well as in normal concretes the rebars placed parallel to the direction of concreting obtained higher values of the bond strength in comparison to rebars placed perpendicularly. This behaviour was observed in all stages of bond development.

Evaluation of bonding between reclaimed asphalt aggregate and bitumen emulsion composites

The bond strength between bituminous binder and aggregate is fundamental to evaluate the performance and durability of cold bitumen emulsion mixtures (CBEM). The interaction developed at binder-aggregate interface is strongly dependent on the properties of aggregate, residual bitumen and emulsifiers, as well as on the environmental conditions affecting emulsion breaking. When reclaimed asphalt (RA) aggregate is used in the production of CBEM, the adhesion issue becomes more complex because the residual bitumen interacts with the aged bitumen film coating the RA aggregate surface. In this research, the binder bond strength (BBS) test was performed to evaluate the bonding between a bitumen emulsion, a cold mastic prepared using limestone filler and artificial RA substrates produced using two aggregate sources. The moisture sensitivity along with the effect of curing temperature and time on the bond strength development were also evaluated. The results showed good affinity between both cold bitumen emulsion composites and the aged bitumen film coating the RA substrate, also highlighting a reduced moisture sensitivity for most of the tested systems. Moreover, the BBS results allowed to properly discriminate the effect of curing temperature and time on bond strength between the artificial RA aggregate and the cold bitumen emulsion composites.

Bond behavior of epoxy-coated rebar in ultra-high performance concrete

The bond behavior of epoxy-coated rebar embedded in two different ultra-high performance concrete (UHPC) mixtures is experimentally investigated by a uniaxial pullout test, and the effect of embedment length, side cover, and mixture type on the bond stress-slip relationship is predicted using a double-phase analytical model. The bond mechanism and failure modes of rebar in UHPC are similar to those observed in normal concrete. The embedment length and side cover have significant influence on the bond behavior of epoxy-coated rebar in UHPC, and more drastic bond stress hardening and softening are observed for the case of larger embedment length and side cover. Two UHPC mixtures exhibit comparable bond strength and critical development length because they have close mechanical properties gained at test age. The adopted analytical model matches well with the experimental bond-slip response of epoxy-coated rebar in UHPC, and both the characteristic parameters in the model show an increasing trend when more dramatic hardening and softening of bond stress exhibit.

Experimental and numerical investigation of splicing of concrete-filled fiber-reinforced polymer tubes

The structural performance of spliced, concrete-filled FRP tubes was evaluated. The splices consisted of an internal FRP collar adhesively bonded to the tube segments and a concrete reinforcing cage of carbon fiber composite cable (CFCC). Spliced beams were tested to determine the splice flexural capacity. Adhesive bond strength and CFCC development lengths were experimentally determined. Splice behavior was investigated with 3D finite-element models employing a modified concrete damage plasticity model and cohesive interfaces. Model predictions were in good agreement with the experiments; the predicted capacity was 13.8% greater than the 113.1 kN average failure load of the splice.

Study of Tensile Bond Strength for Structural Silicone Sealants after Artificial Accelerated Aging

Tensile bond strength is one of the most significant properties for structural silicone sealants used in the glass curtain walls. During the service process, aging of the silicone sealants shall be involved in comprehensive actions of environment factors, e.g. temperature, humidity, and ultraviolet light etc. In this study, artificial accelerated aging test was conducted to make clear the development of tensile bond strength, Shore hardness and elongation. The test results show that: (i) the specimens under damp-heat test have more degeneration than specimens under humidity-freeze test; (ii) the environment of high temperature and high humidity leads to the change of tensile bond, Shore hardness, elongation, and results in interfacial failure of samples.

Correlation of Adhesive Performance between Automated Bond Evaluation System Tests and Plywood Tests: A Case Study of Lignin-Phenol-Formaldehyde Adhesives*

Abstract The automated bond evaluation system (ABES), which recently became ASTM D7998-15 standard test method, is an effective tool for screen testing of different water-based wood adhesive formulations. This method enables rapid evaluations of mechanical responsiveness of different adhesive formulations to various press temperatures and/or press times, providing an efficient and realistic comparison of bondability and reactivity among the adhesive formulations. Based on extensive testing work, this article provides experimental findings and evidence for the use of this method to evaluate bonding performance of lignin as a major ingredient in the phenolic adhesive system. The relationship between bond strength development and press temperature can be established for a particular adhesive formulation using this method, which can then help the formulation and optimization of a wood adhesive containing lignin. Softwood plywood experiments demonstrated that there is a strong correlation between ABES test results and adhesive performance in the panel products.

Ligneous resole adhesives for exterior-grade plywood

The performance of lignin–phenol–formaldehyde (LPF) resole adhesives was investigated for exterior-grade plywood manufacture using commercial pine kraft lignin to replace 40 wt% of phenol. Furthermore, the implementation of a lignin methylolation step prior to resole cooking was tested aiming to activate lignin towards the electrophilic aromatic addition of formaldehyde and to improve thus the performance of the respective adhesive. Comprehensive monitoring of the resole cooking process and characterization of the obtained resins confirmed a significant network expanding effect of lignin. This is evident from the fast increase of viscosity which occurs, however, at the expense of cross-link density, as reflected by the somewhat longer B-time measured for both types of ligneous PF resins. Evaluation of bonding strength development using a bond strength development test confirmed that the less dense network of LPF resins translates into delayed bond formation compared to the PF reference resin. Methylolation of lignin prior to resole cooking had no significant impact on bond formation as evident from the very similar behaviour during the bond strength development test. However, both the studied LPF resins turned out to be suitable adhesives for the manufacture of plywood panels for outdoor usage. Specimen prepared from beech veneers fulfilled the respective standards as determined by shear strength and bending strength tests.

Evaluation of the Development of Bond Strength between Two Concrete Layers

This paper provides an analysis of the development of bond strength in composite members of the concrete-to-concrete type. The experimental study was performed to evaluate the development of the bond strength between two concrete layers. In the study, two different types of concrete were used – normal concrete (NC) and high-performance concrete (HPC). Composite specimens of the substrate and overlay were of the NC-HPC and HPC-HPC types and reference NC-NC specimens were also made. The analysis of the bond strength was performed on composite cubes of size 150x150x150 mm which were subjected to splitting tension tests after 3, 7, 14 and 28 days of curing of the concrete overlay. The results of the study show that the basic phenomenon which affects bond strength is adhesion between concrete layers which develops with curing of the concrete overlay. The highest increase in the value of tensile bond strength was observed in the first 3 days of curing of the composite specimens. In this period the NC-NC composite reaches 53% of its 28-day tensile bond strength, the NC-HPC specimen – 67% and the HPC-HPC – 74%. The experiments showed different modes of interface failure depending on the configuration type of concrete in composite specimens. In the case of composite specimens NC-NC and HPC-HPC the observed dominant interface failure mode occurred within the overlay transition zone. For the NC-HPC specimens, the interface failure mode was observed both in the overlay transition zone and in substrate made of NC. No changes in the modes of bond mechanism failure were observed during curing of the composite specimens. The results obtained were compared with the existing studies in the literature on bond strength in composite concrete members.

Preliminary study on interfacial bond strength due to successive casting lifts of self-consolidating concrete – Effect of thixotropy

Vibration is prohibited during placement of freshly mixed self-consolidating concrete (SCC), making it particularly sensitive to delays or stoppages during multi-layers casting. This paper seeks to propose suitable testing methods that can be used to assess the effect of delays between successive lifts on interfacial bond strength of hardened material, including the proposal of time limits necessary to ensure proper mixing of cast layers. Two methods for testing bond by slant shear and pull-off are tested and compared. The SCC mixtures were proportioned to exhibit low to high thixotropic levels, while the relative delay between cast layers was set to 30, 60, and 120min after initial mixing. Test results have shown that the lowest drop in interfacial bond strength occurred for moderately thixotropic mixtures, given the moderate bleeding rate that prevented dryness of the first cast layer while, at the same time, avoided excessive increase in water that reduces bond strength development along the interfaces.

Lignin Phenol Formaldehyde Resoles: The Impact of Lignin Type on Adhesive Properties

Lignin-phenol-formaldehyde (LPF) resoles were prepared using different types of lignin at various levels of phenol replacement by lignin (0 to 40 wt.%). Adhesive properties including thermal behavior as determined by differential scanning calorimetry (DSC), time-dependent development of bond strength during hot pressing as determined by automated bonding evaluation system (ABES), tensile shear strength of solid beech wood lap-joints, and free formaldehyde content of the adhesives were investigated. Preparation of phenol-formaldehyde (PF) resole was accomplished using molar ratios of formaldehyde/phenol and NaOH/phenol of 2.5 and 0.3, respectively. Four different types of technical lignins were studied: Sarkanda grass soda lignin, wheat straw soda lignin, pine kraft lignin, and beech organosolv lignin. The synthesis of the resoles was optimized for 20 and 40 wt.% phenol replacement by lignin. Increasing substitution of phenol resulted in faster gain of LPF viscosity for all studied lignins. The best curing performances of the LPF resoles were observed for pine kraft lignin at both 20 and 40% phenol replacement. The amount of formaldehyde not consumed during cooking increased with increasing level of phenol replacement. However, no differences in free formaldehyde content were observed between the different lignin samples at comparable levels of phenol replacement.

Determining the temporal development of dentin-composite bond strength during curing

ObjectivesAs composite restorations cure a competition develops between bond formation and shrinkage stress at the composite-dentin interface. Thus, understanding the temporal development of tooth-composite bond strength should enable better assessment of tooth-composite debonding. MethodsIn this study, bond strengths of composite-dentin specimens obtained from tensile test at different curing times were used to determine the bond formation rate. By varying the composite thickness and output from the curing light, their effects on the rate of bond formation for two different materials (a conventional and a bulk-fill composite) were also investigated. The proportions of cohesive and adhesive failure were determined by analysis of electron micrographs of the fractured surfaces. ResultsThe development of dentin-composite bond strength (S) with time (t) can be described by the equation: S=Smax(1−exp(−αt)), where Smax is the final bond strength (∼12MPa for both composites) and α the rate of bond formation. Using bulk-fill and thinner specimens gave faster bond formation. In fact, the higher the irradiance at the interface, the higher the rate of bond formation. However, α had a maximum value of ∼0.6s−1 and the rule of reciprocity did not hold. A minimum dose of ∼2J/cm2 was required to achieve adequate bond strength. The predominant failure mode changed from cohesive in the composite and adhesive to interfacial at the adhesive-dentin interface, indicating the latter to be the weakest link in the cured dentin-composite assemblies considered. SignificanceWhen combined with the temporal development of shrinkage stress, the current results will help determine the likelihood of tooth-composite debonding.

Effect of Log Soaking and the Temperature of Peeling on the Properties of Rotary-Cut Birch (Betula pendula Roth) Veneer Bonded with Phenol-Formaldehyde Adhesive

Heating logs prior to peeling positively affects the surface properties of veneer as well as the wood-adhesive bond strength. However, the mechanism behind this increase in strength is not fully understood. The aim of the present study was to separate the influence of soaking temperature and peeling temperature on the physical surface properties and bonding quality. Rotary-cut birch (Betula pendula Roth) logs were soaked at 70 °C, and half of them were subsequently cooled to 20 °C prior to peeling. Surface roughness measurements, scanning electron microscopy (SEM), surface integrity testing, color measurements, and wood-adhesive bond testing were conducted with an automated bonding evaluation system. The results showed that logs soaked at 70 °C and peeled at 20 °C had roughness, color, integrity, bond strength, and wetting properties more similar to logs soaked and peeled at 70 °C than those soaked and peeled at 20 °C. In every test conducted, the effect of soaking temperature was greater than the effect of peeling temperature. High-temperature soaking not only caused softening of the material during the peeling process, but it also caused irreversible changes in the wood material, which affected the veneer surface characteristics and bond strength development.

Laboratory and field evaluation of several types of soil nails for different geological conditions

For steep slopes with difficult access or slopes in a corrosive environment, there are various problems associated with the use of conventional steel reinforcement bars as soil nails. For loose-fill slopes or clay slopes, the development of adequate nail bond strength is another practical issue that should be considered. Carbon fiber–reinforced polymer (CFRP) and glass fiber–reinforced polymer (GFRP) in several forms and installation methods have been studied as the alternatives to the classical steel bar. Extensive laboratory tests on the materials and field tests on different types of soil nails with various methods of installation have been carried out in Hong Kong, Korea, and Australia. Test results support the use of these materials with an innovative installation method as soil nails under different geological conditions, and the suitability and performance of these materials under different conditions are assessed in the present study.

A New Methodology to Evaluate the Cure of Resin-Impregnated Paper for HPL

This paper presents a study on the curing conditions of several resin-impregnated papers and its impact on the performance of HPL (high-pressure decorative laminate). A new methodology for evaluating the bond strength development between the different layers of a HPL(overlay, decorative, and kraft papers) was developed using ABES (Automated Bonding Evaluation System) equipment. The proposed method can be applied to the study of the curing step of the different impregnated paper and the development of bonds between them (overlay paper on decorative paper, decorative paper on kraft paper, and kraft paper on kraft paper) trying to simulate the hot-pressing of an industrial HPL. This will permit to establish a more adapted temperature gradient in hot-press in order to achieve the same curing rate for all layers and provide a good final overall product quality.

Finite Element Implementation of a Bonding Model and Application to Roll Bonding of Aluminum Sheets of Largely Different Yield Strength

Roll bonding is a joining-by-forming operation, in which two or more metallic strips or plates are bonded permanently through the pressure and plastic deformation in the roll gap. Although roll bonding has been successfully used in industrial production over many years, difficulties occur especially when materials of largely different yield strength are roll-bonded, e.g. when hard aluminum alloys are clad with soft commercially pure aluminum. Examples are AA2024 sheets used in wing and fuselage structures of aircrafts, which are clad with AA1050 to improve the corrosion resistance. Likewise, aluminum sheets for heat exchangers consist of a hard base material that is clad with a soft solderable aluminum alloy. In these cases, the strength difference may influence the bonding behavior since the softer face sheet has to transmit the deformation to the harder core material. To analyze and optimize such cases, a bonding model integrated into a numerical framework for the simulation of the roll bonding process is required. In this paper, a finite element model is presented, in which the development of bond strength is simulated using a cohesive contact formulation. The model is used to study the bonding behavior of laboratory-scale roll bonding trials of two aluminum alloys with a large difference in yield strength. It is found that shear stresses are generated towards the end of the roll gap that may exceed the shear bond strength created earlier in the roll gap such that no firm bond is obtained. The conditions under which bonding is successful are analyzed using a finite element simulation study with varying yield stress differences and pass reductions and summarized in a map.

Energy and bond strength development during ultrasonic consolidation

A process model was developed that couples the effects of the three adjustable ultrasonic consolidation (UC) process parameters (amplitude, force and speed) into a single term – thermal weld energy due to frictional and volumetric heat generation. Infrared thermography was used to evaluate weld energy during UC and a relationship was established between weld energy and the peel strength of ultrasonically consolidated aluminum. An optimum processing widow was identified for bonding Al 1100-0 and Al 3003-H14 based on UC processing temperature and weld time. Bonding occurred well below the material melting temperatures, confirming that thermal softening in the bulk of the material or melting are not the bonding mechanisms and that bonding takes place in the solid-state.