Estimation of ultimate tension load of methylmethacrylate bonded steel rods into concrete

This paper introduces an alternative method of predicting ultimate tension load of methylmethacrylate (MMA) bonded steel rods into concrete. In general, the elastic model is found to predict many of the major experimentally observed characteristics of adhesively bonded steel rods. This theory gives quite reasonable results when applied to epoxy adhesives, but does not agree with data of MMA adhesives. It is necessary, therefore, to modify the analysis in order to bring the elastic model into agreement with test data. This is done by assuming that c, which is a parameter in the analysis, is a function of the shear strain. The solution based on this concept leads to a more general equation which includes as a special case the elastic model previously used to represent the dependence of ultimate tension load on the bond length. Experimental evidence appears to indicate that the ultimate tension load of a MMA bonded steel rod can be predicted, to a good approximation, using this model.     

Comparison study of dicyandiamide-cured epoxy bonded steel joints and polyamidoamine-cured epoxy bonded steel joints

There are instances where efficiency and safety may be compromised as a result of deteriorating fluid transport systems. Thus, it is worth evaluating other methods that can repair the damage for a temporary period without shutting down the operation. The objective was to evaluate the durability of an epoxy-bonded steel in aqueous environments that would represent such a repair. EPON^® 828 was chosen as the epoxy resin, and dicyandiamide and polyamidoamine were two types of curing agents evaluated in this study. The epoxy-bonded steel joints were exposed in either distilled water or 3.4% NaCl solution for various times. The mechanical strength of the bonded joints was evaluated using a three-point flexure test. The interfacial shear strength of unaged samples ranged from 0.93 to 0.32 MPa. It was found that the interfacial shear strength decreased with aging time for both epoxy-bonded systems. Scanning electron microscopy (SEM), optical microscopy, and X-ray photoelectron spectroscopy (XPS) were used to determine the locus of failure of the bonded joints. It was concluded that failure occurred cohesively within the oxide layer if oxides were present on the substrate surface prior to the bonding procedure.     

The transfer of stress through a steel to concrete adhesive bond

This paper describes part of a programme of research aimed at investigating the potential for strengthening reinforced concrete beams in shear by means of externally bonded steel plates. This may be a useful strengthening technique following the assessment of older bridge and building structures designed to outdated codes of practice. In order to produce a design guide for such shear plate bonding, a method for determining the anchorage length needs to be devised. By measuring the strain distribution in a steel plate adhesively bonded to a concrete block, the shear stress distribution within the adhesive and the effective anchorage length can be determined. A series of 15 experimental tests have been conducted to investigate the transfer of stress through a steel-concrete adhesive bond. The experimental programme was supported by theoretical and finite element analysis. The shear stress in a steel-concrete adhesive bond was found to be distributed exponentially, peaking at the loaded end of the specimen. For the specimens used, the stress distribution was distributed over a length of up to 155 mm for serviceability loads.     

An experimental study on the dependence of the strength of adhesively bonded joints with thickness and mechanical properties of the adhesives

Adhesive bonding joints are widely applied in many engineering fields. Their overall strength is much dependent on the thickness of adhesive layers. Many previous experimental studies have found that the ultimate failure strength of the bonding structure increases with the decrease of the adhesive thickness. However, few of them consider the effect of adhesive intrinsic material parameters on the relation between the overall strength and adhesive thickness. In the present investigation, the effect of the adhesive thickness on the overall strength of the lightweight metallic adhesive bonding joints was experimentally studied, considering the effect of the adhesive toughness. The results show that the variations of overall strength resulting from the adhesive thicknesses have remarkable discrepancy due to the toughness of the adhesive, which is in agreement with the previous model prediction.     

Evaluation of parameters affecting adhesive strength of high build epoxy coatings on textured and plasma treated metallic substrates

Epoxy coating systems have been used throughout the years for protecting critical industrial assets. To ensure superior coating adhesion and longevity, abrasive blasting has been traditionally employed to texture metallic surfaces. Though a large variety of abrasives are available in the industry, coal slag (aluminium silicate) and garnet (mineral abrasive) have remained popular choices until now owing to their easy availability. However, depleting reserves of coal slag owing to stricter environmental regulations and shortage of good quality garnet have fueled the need to identify substitutes. This work is focused on evaluating the effect of surface texturing on adhesive strength of epoxy coatings using two novel abrasive types – olivine (obtained from dunite rock) and calcium silicate (iron furnace slag) which are available in abundance and present an excellent alternative. The surface textures of various blast cleaned mild steel (A36) and stainless steel (316L) substrates were evaluated using a combination of techniques namely, optical profilometry (spatial parameters), replica tape method as per ASTM D 4417 (Method C) (height parameter) and scanning electron microscopy (Secondary electron imaging/energy dispersive X-ray spectroscopy analyses) for embedded particle composition analysis. Correlations were drawn to the wettability of metallic substrates textured using the selected abrasives. Adhesive strength tests on high build epoxy coatings, performed in accordance with ASTM D4541 revealed exceptional performance using various grades of both olivine and calcium silicate abrasives. The effect of air plasma treatment on adhesive strength of epoxy coatings applied on mild steel substrates were also studied.     

A comparison of bending strength between adhesive and steel reinforced concrete with steel only reinforced concrete

Cracking of brittle cementitious composites subjected to excessive loading causes a potential reduction in material performance. Steel bars or metal fibers typically act as tensile reinforcing in concrete composites to increase the material's structural capacity in bending and to delay or prevent matrix cracking.The goal of this research is to determine whether the performance in bending strength and material integrity of a typically reinforced cementitious composite may be improved through the release of “healing” chemicals, such as adhesives, from hollow fibers into cracks induced by loading in addition to the metal reinforcing. Adhesive-filled repair fibers are intended to break immediately upon cracking in the concrete thereby activating the healing process with the release of a sealing or adhering substance. This self-repair occurs whenever and wherever cracks are generated.     

Experimental investigation into the effect of DC glow discharge pretreatment of HDPE on tensile lap shear strength

The present investigation aims to optimise the process parameters of DC glow discharge treatment through air in terms of discharge power and time of exposure for attaining best adhesive joint of high-density polyethylene (HDPE) to mild steel. The as- received and DC glow discharge exposed HDPE surfaces have been characterised by energy dispersive spectra (EDS). It is observed that with increasing power level up to 13 W, tensile lap shear strength of adhesive (Araldite AY 105) joint of HDPE to mild steel increases and then decreases. At 13 W power level, joint strength increases up to 120 s of exposure and then decreases. At the optimised condition for the surface modification, the effect of two different adhesives Araldite AY 105 and Araldite 2011 on the strength of polymer to mild steel, polymer to polymer and mild steel to mild steel joints have been examined. It is observed that tensile lap shear strength of HDPE–HDPE joint and HDPE–mild steel joint does not change with the change of adhesive and this could be possible as initiation of fracture takes place from subsurface layer of the polymer. This is confirmed by studies under optical microscopy and EDS, which shows when the polymer has been modified by exposure under glow discharge the failure is observed to initiate from subsurface layer of the HDPE, then within the adhesive cohesively and thereafter in the mild steel to adhesive interface.     

The shear strength of composite secondary bonded single-lap joints with different fabrication methods

Abstract

The shear strength of composite secondary bonded single-lap joints was studied in this article. To optimize the adhesive thickness and ensure stable mechanical properties, an improved mold was applied. Based on this mold, a total of 15 specimens (180 samples) were examined and they were fabricated with various overlap lengths, curing pressures, adhesive thicknesses, ply angles, and surface treatment methods. The experimental results indicated that the improved mold not only significantly increased the uniformity of the adhesive thickness but also enhanced the shear strength of the joints and the shear strength was improved by approximately 13% compared to that of conventional methods. Moreover, the shear strength was decreased in specimens with increased overlap lengths and increased in samples with an increased curing pressure. Furthermore, the shear strength of the specimens was also affected by the adhesive thicknesses, ply angles, and surface treatment methods. The mechanisms can be ascribed to the effect of the fabrication method on the failure mode. A facile platform for optimizing these parameters is provided in this article. Based on this platform, the shear strength of the joints was enhanced to 33.5?MPa.     

外加磁场对粘接接头剪切强度的影响

采用自制的装置研究了磁场对由环氧胶层连接的钢制单搭接接头剪切强度的影响，结果表明．在所采取的试验条件下．试样叠合后立即施加的磁场可显著影响接头的强度；垂直于胶层的磁场提高接头的剪切强度效果高于平行磁场，磁场处理的时间以4h左右为宜。     

Effect of moisture content in uncured adhesive on static strength of bonded galvanized DP600 steel joints

Experiments to characterize the effect of moisture content in uncured adhesive on static strength of bonded galvanized DP600 steel joints were conducted. Prior to adhesive curing, the adhesive and galvanized steel coupons were pre-exposed to 96% relative humidity at 40 °C (i.e., open-faced exposure). It was found that the exposure of adhesive and steel sheets in hot humid environment decreases the quasi-static strength of adhesive-bonded galvanized DP600 steel joints by as much as 96% after 1008 h of exposure. Optical microscopy and scanning electron microscopy of quasi-static tensile tested specimens and moisture absorption testing of bulk adhesive revealed that static strength degradation is mainly due to the plasticization and micro-cracking of adhesive and zinc oxidation by the water vapor.     

Improvement of adhesive bonding of grit-blasted steel substrates by using diluted resin as a primer

This study reveals the micro-structural details on the metal substrate surface prepared by grit blasting, and then proposes a simple resin pre-coating method aiming at full wetting of the substrate surface for stronger adhesive bonding. The resin pre-coating solution consisting of around 90% acetone and around 10% resin without hardener is used as a primer, which can be sprayed or blushed onto the grit-blasted metal substrate. The acetone solution can carry resin deep into micro-cavities created by grit blasting and effectively coat and wet micro-debris so that micro-voids or gaps between the adhesive joint and metal substrate can be removed. Since the resin pre-coating does not contain hardener and remains wet, the wettability of the substrate is also improved. The normal epoxy adhesive with hardener can then be applied onto the substrate surface. Despite having the primer-like function, the proposed resin pre-coating method still maintains the simplicity of one epoxy resin system. Based on the current study, a resin and acetone solution without hardener does not seem to have adverse effects on the final bonding strengths of adhesive joints, although acetone is known to have detrimental effects on resin and hardener adhesive systems. Four different surface conditions are examined, each having 14 specimens: (1) Grit-Blasted (GB) surface, (2) GB-surface with ultrasonic cleaning, (3) GB-surface with resin Pre-Coating (PC) only, and (4) GB-surface with both ultrasonic cleaning and PC. 25% improvement in the shear strength has been achieved by the resin pre-coating method, even without ultrasonic cleaning, in comparison with 8% improvement after ultrasonic cleaning. These results show GB-surface with PC is beneficial to adhesive bonding, which can be adopted for structural applications even if thorough substrate surface cleaning on site is not possible. The improved wettability of metal substrates after resin pre-coating contributes to the maximum possible utilization of the contact areas over the roughened substrate surfaces and thus leads to the enhanced adhesive bond strength.     

Effect of steel fiber on the deicer-scaling resistance of concrete

Effects of steel fibers on the deicer-scaling resistance of concrete were investigated in this paper. Results show that the deicer-scaling resistance of concrete is reduced by the addition of steel fibers at the same air content, especially for the air-entrained concrete, even though the flexural strength of concrete is significantly improved by the addition of fibers. The reason is that the average air-void spacing factor of concrete becomes larger due to the addition of steel fibers. The variations in the deicer-scaling resistance among the different concrete qualities can be fully explained by the spacing factor values.     

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

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

Modelization of the joint formation stage in a concrete structure reinforced by carbon fiber plastic plates

One reinforcement technique for concrete structures consists of using a tension-resistant material (carbon fibers in an epoxy matrix), tightly linked to the concrete support by means of an adhesive through which stresses are transmitted. Reported failures in actual applications are usually due to a poor-quality adhesive/concrete joint. Current research is aimed at studying the joint formation phase. We have focused on the adhesive penetration process that precedes polymer curing. A solvent-based type of adhesive has been selected for this study since its higher fluidity should enable producing a higher-quality joint. We have used numerical techniques in order to solve differential equations describing the major physical phenomena involved in the adhesive penetration process. The numerical results obtained allow us to highlight those physical parameters that actually influence adhesive penetration and to roughly estimate the mechanical strengthening of the adhesive joint.     

Effect of pressing parameters on the shear strength of beech specimens bonded with low solvent liquefied wood

Liquefied wood (LW) is a naturally based product which has the potential to be used as an adhesive. It can be used as a part of a polymer formulation, as a part of an adhesive mixture with commercial adhesives, or as an independent material for wood bonding. In this study, wood was liquefied at 180?°C using ethylene glycol as the solvent and sulphuric acid as a catalyst. In the first part of research, LW with different pH values was used for the bonding of solid wood at 200?°C for 15?min. In the second part, LW with an optimal pH value was used for bonding at different press temperatures for 15?min. In the third part, the minimum pressing time at the optimal pH value and at the optimal press temperature was determined. Unmodified LW with a negative pH value, a press temperature of 180?°C, and a pressing time of 12?min was determined to be optimal (based on highest shear strength) for the bonding of 5?mm thick wood lamellas with the LW used in this study. At these conditions bonds exhibited shear strength of around 7?N/mm² which was too low to attain standard requirements. Despite this, high wood failure (100%) was observed as a consequence of low pH value and high press temperature which caused damage of the part of beech lamellas where LW was applied.     

Bond strength and durability of universal adhesive agents with lithium disilicate ceramics: A shear bond strength study

The aim was to assess the shear bond strength (SBS) of lithium disilicate (LD) ceramic to resin composite with different universal adhesives, duration of ageing and silane. One hundred and twenty LD ceramic discs were processed, fired and etched (HF acid 5%) for 20 s (sec). All specimens were divided into 12 groups (n = 10), based on different combinations of, 3 different universal adhesives [Scotchbond (SB) Universal Adhesive, All-Bond (AB) Universal, and Futurabond U (FU)], silane and different duration of ageing [24 h and 3 months]. Composite resin cylinders (Tetric ceram) (3mm × 2 mm) were formed using bonding jig on ceramic and were light-cured. The specimens in groups 1–6 and 7–12 were stored in distilled water (37 °C) for 24 h and 3 months (thermocycling -5000 cycles 5–55 °C/30 s dwell time) before being subjected to bond strength testing respectively. Using universal testing machine shear bond test was performed at a crosshead speed of 1 mm/min. Failure modes and fracture patterns were assessed using stereomicroscope and scanning electron microscope. Analysis of variance was performed to analyze data. SBS was significantly higher with silane than without silane (p < 0.01), regardless of the type of adhesive or storage duration. Specimens tested at 24 h storage showed significantly higher (p < 0.01) SBS than specimens tested after 3-months. A comparison among different universal adhesives showed significantly distinct bond strength (p < 0.01). Optimal bonds to LD were achieved by application of silane. While ageing through storage had a negative impact on the SBS, it varied among different adhesives.     

A new model for the estimation of compressive strength of Portland cement concrete

In this article, on the basis of the existing experimental data, an empirical equation for calculating the compressive strength of Portland cement concrete is developed. The determination of the compressive strengths by the equation described here relies on accurate determination of the water to cement ratio which gives maximum compressive strength and the analysis of its variation with the curing time. The results obtained for the plain (without admixture) and latex modified concretes at the age of 28 days show that this ratio ranges from 0.18 to 0.23. These values are reasonably close to the non-evaporable water content reported for the Portland cement. On the other hand, this range as determined by the above procedure limits the usefulness of the proposed equation for predicting the compressive strength of silica fume blended Portland cement concretes. However, a general method of solving problems of this type allows the determination of upper and lower bounds of this range. This method requires the measurement of at least two compressive strengths corresponding to two different water to cement ratios.     

Studies on the evaluation of the performance of organic coatings used for the prevention of corrosion of steel rebars in concrete structures

Corrosion of steel rebars in reinforced concrete constructions, particularly those located in marine environments and industrially polluted areas is one of the major problems baffling the construction industry all over the world including India. A suitable protective coating to rebar is found to improve the durability of such structures under aggressive exposures. The performance of a few polymeric coatings based on different resins such as acrylic polyol-aromatic isocyanate, polyester polyol-aromatic isocyanate, acrylic resin and epoxy–silicone–polyamide containing ordinary Portland cement or flyash as extenders and titanium dioxide and zinc phosphate as main pigments on rebar in concrete has been evaluated using mechanical strength tests and accelerated corrosion tests. It is observed that, of the 16 coating formulations, four have been found to perform well as effective and durable coatings.     

Influence of silica fume on the tensile strength of concrete

The present paper is directed towards developing a better understanding on the isolated contribution of silica fume on the tensile strengths of high-performance concrete (HPC). Extensive experimentation was carried out over water-binder ratios ranging from 0.26 to 0.42 and silica fume-binder ratios from 0.0 to 0.3. For all the mixes, compressive, flexural and split tensile strengths were determined at 28 days. The compressive, as well as the tensile, strengths increased with silica fume incorporation, and the results indicate that the optimum replacement percentage is not a constant one but depends on the water-cementitious material (w/cm) ratio of the mix. Compared with split tensile strengths, flexural strengths have exhibited greater improvements. Based on the test results, relationships between the 28-day flexural and split tensile strengths with the compressive strength of silica fume concrete have been developed using statistical methods.     

Evaluation of mechanical and laser surface pre-treatments on the strength of adhesive bonded steel joints for the automotive industry

Recent research efforts in the automotive industry have been focused on the integration of high-strength steels within lightweight vehicles by using improved joining techniques. The present work falls in this subject area and is focused on the analysis of adhesive bonded dual-phase steel/epoxy joints for the automotive industry. Two quasi-static loadcases were considered, i.e. single-lap and T-peel tests, and various surface preparation strategies were evaluated. In particular, the mating surfaces were pre-treated by using pulsed laser irradiation with a fiber laser (1064 nm) and comparisons were made with degreasing and sand blasting. Moreover, the effects of bondline thickness and adhesive type were also assessed. To this aim, two epoxy adhesives with fairly different mechanical behavior (i.e. strain hardening versus elasto-plastic) were deployed for joints fabrication. Finally, T-peel tests were also carried out after sample cycling under controlled high humidity and temperature (i.e. accelerated aging). The obtained results highlighted the beneficial effect of laser irradiation on the joints’ mechanical behavior under both static and hydrothermal loadings.