Bar Surface Research Articles

Physicochemical, Nutritional, Microstructural, Surface and Sensory Properties of a Model High-Protein Bars Intended for Athletes Depending on the Type of Protein and Syrup Used.

The main objective of this study was to investigate the possibility of using a combination of vegetable proteins from soybean (SOY), rice (RPC), and pea (PEA) with liquid syrups: tapioca fiber (TF), oligofructose (OF), and maltitol (ML) in the application of high-protein bars to determine the ability of these ingredients to modify the textural, physicochemical, nutritional, surface properties, microstructure, sensory parameters, and technological suitability. Ten variants of the samples were made, including the control sample made of whey protein concentrate (WPC) in combination with glucose syrup (GS). All combinations used had a positive effect on the hardness reduction of the bars after the storage period. Microstructure and the contact angle showed a large influence on the proteins and syrups used on the features of the manufactured products, primarily on the increased hydrophobicity of the surface of samples made of RPC + ML, SOY + OF, and RPC + TF. The combination of proteins and syrups used significantly reduced the sugar content of the product. Water activity (<0.7), dynamic viscosity (<27 mPas∙g/cm3), and sensory analysis (the highest final ratings) showed that bars made of RPC + OF, SOY + OF, and SOY + ML are characterized by a high potential for use in this type of products.

Conventional and Microcellular Injection Molding of a Highly Filled Polycarbonate Composite with Glass Fibers and Carbon Black.

Conventional solid injection molding (CIM) and microcellular injection molding (MIM) of a highly filled polycarbonate (PC) composite with glass fibers and carbon black were performed for molding ASTM tensile test bars and a box-shape part with variable wall thickness. A scanning electron microscope (SEM) was used to examine the microstructure at the fractured surface of the tensile test bar samples. The fine and uniform cellular structure suggests that the PC composite is a suitable material for foaming applications. Standard tensile tests showed that, while the ultimate strength and elongation at break were lower for the foamed test bars at 4.0–11.4% weight reduction, their specific Young’s modulus was comparable to that of their solid counterparts. A melt flow and transition model was proposed to explain the unique, irregular “tiger-stripes” exhibited on the surface of solid test bars. Increasing the supercritical fluid (SCF) dosage and weight reduction of foamed samples resulted in swirl marks on the part surface, making the tiger-stripes less noticeable. Finally, it was found that an injection pressure reduction of 25.8% could be achieved with MIM for molding a complex box-shaped part in a consistent and reliable fashion.

Synthesis, characterization of SnO2 three-dimensional microbars decorated with nanostructures and electrical properties of PMMA-SnO2 nanocomposites

Novel Tin Oxide (SnO2) three-dimensional microbars (3D: L≈10 µm × B≈1 µm × T≈1 µm) decorated with nanostructures (<100 nm) on the surface were synthesized using a template and surfactant free simple reaction method. Effect of calcination temperature on SnO2 structures were investigated. At non-calcinated condition, dense aggregated particles covers the surface of micro bars. The aggregated surface particles disintegrate to form random networks of nanoparticles at 200 ºC and at 400 ºC individual clusters of nanoparticles were formed. A rutile cassiterite tetragonal crystal structure of SnO2 was observed using X-ray diffraction (XRD). The SnO2 micro-nano structures were analysed by UV-Visible (UV-Vis) spectroscopy and was found to have an average energy band gap of 3.07 eV. Fourier Transform Infra-Red (FTIR) spectroscopy was used to identify the presence of functional groups. Micro-nanostructures were identified using Field Emission-Scanning Electron Microscopy (FE-SEM) with elemental analysis obtained from Energy Dispersive X-ray Analysis (EDX) spectroscopy. Electrically conducting polymer nanocomposites were fabricated using Poly Methyl Methacrylate (PMMA) as matrix and SnO2 micro-nano structures as the conducting fillers. Alternating current (AC) electrical properties of PMMA-SnO2 nanocomposite films were investigated using Impedance Spectroscopy. Effect of SnO2 loading and effect of frequency on the electrical properties were studied. Percolation threshold of the composites was found to be at 1 wt% of SnO2 and exhibited a conductivity of 2.3×10−8 S/cm with 2 wt% SnO2 loading.

Bond behavior of spirally confined bar splices in grout

Despite various studies on the bond behavior of Glass-Fiber Reinforced Polymer (GFRP), an available literature on the bond behavior of GFRP bars in grouted confined by spiral is limited. In the present study, the bond behaviour of deformed steel and GFRP reinforcing bars connected by a grouted spiral connection was investigated. Flexural pull-out test was performed on 24 beam specimens to evaluate the bar bond strength. The test parameters were the spiral diameter and pitch distance. The test results showed that the spiral confinement significantly improved the bond performance of GFRP bars and deformed steel main bars. The bond strength of GFRP was decreased by damage of the outer layer of GFRP bars due to detachment of sand grains on the GFRP bar surface. As the spiral diameter decreased from 45 to 25 mm, the bond strength increased by 9.7 ∼ 14.5% due to higher confinement stress. In the deformed steel reinforcing bars, the reduced spiral diameter increased the bond strength by 40%.

Effect of creep on corrosion-induced cracking

Corrosion-induced cracking is the most widely encountered and studied long-term deterioration process in reinforced concrete. Naturally occurring corrosion rates are so low that rust accumulates often over tens of years near the surface of the reinforcement bars before sufficient pressure in the surrounding concrete is generated to induce cracking in the concrete cover. To speed up the process in laboratory tests, corrosion setups with impressed currents have been developed in which the corrosion rate is controlled to be so high that cracking of the concrete cover occurs within a few days. Extrapolating the results of these accelerated tests to those of naturally occurring corrosion requires an understanding of the influence of long-term creep deformations of concrete on the corrosion-induced cracking process. In mathematical models in the literature, creep deformations are often ignored for accelerated but considered for natural corrosion rates in the form of an effective modulus.In this work, three numerical models of increasing complexity are proposed with the aim to investigate the effect of creep on corrosion-induced cracking. The simplest approach is based on an uncracked axis-symmetric thick-walled cylinder combined with a plastic limit on the radial pressure-induced by the accumulation of rust. The model with intermediate complexity comprises a thick-walled cylinder model divided into an inner cracked and an outer uncracked layer. The most comprehensive model consists of a thick-walled cylinder discretised by a three-dimensional lattice approach. Basic creep is predicted in all three approaches by means of the B3 model developed by Bažant and co-workers. Time dependence of strength of concrete is modelled using fib Model Code expressions. It is shown that for the comprehensive lattice model, creep has limited influence on critical corrosion penetration, which indicates that the dependence of the critical corrosion penetration on corrosion rate must have other sources.

Finite Boundary Conditions Due to the Bar Presence in the Model of Chloride Penetration.

The chloride penetration is usually modelled through the application of a solution of Fick’s second law of diffusion, based on the assumption of semi-infinite boundary conditions. However, the presence of the bars, on whose surface the chlorides accumulate, makes this assumption incorrect. As the time progresses, the chlorides in the steel/concrete interface increase in concentration more than the chlorides overpassing the bar position without obstacles. This circumstance, although previously studied, has not been introduced in common practice, in spite of it supposes early reaching of the chloride threshold. The study in this paper shows a deterministic analysis of the chloride diffusion process by the finite element method (FEM) which numerically solves Fick’s second law, taking into account the accumulation of the chlorides on the bar surface. Several examples are calculated and factors between the finite/semi-infinite solutions are given. These factors depend on the cover depth and the diffusion coefficient, and with less importance, on the diameter of the bar, which make it unfeasible to propose a general trend.

A Detailed Investigation of the Bond Performance of Basalt Fiber-Reinforced Polymer Bars in Geopolymer Concrete

This comprehensive experimental study aimed to determine the bond performance of basalt fiber reinforced polymer (BFRP) bars in geopolymer concrete (GC). The study examined the bond performance of BFRP bars and GC by considering several parameters, including bar diameters of 8, 10, and 12 mm, embedment lengths of 4, 8, and 12 db mm (where db is the diameter of the bar), concrete covers of 20, 40, and 70 mm and compressive strengths of 21.7 and 34.4 MPa. The study also compared the effect of the bar surface and bar type on GC bond performance. Eventually, the results were compared with ordinary concrete (OC). The obtained results indicated that an increase in the BFRP bar diameter results in a decrease in the average bond stress. Similarly, an increase in the length of the bond leads to a reduction in the bond stress. The specimen possessing a short embedment length failed due to bar pullout, while the specimens with a longer embedment length failed as a result of concrete splitting. The outcomes also showed that the strength of bond increases with an increase in compressive strength and cover thickness. Furthermore, the results also indicated that BFRP-reinforced GC has comparable bond performance to steel-reinforced GC and BFRP-reinforced OC and performed better than OC. Last, Comparisons between the existing bond-slip models were offered to demonstrate the best bond stress-slip model for FRP bars and GC for ascending branch up to ultimate bond stress of the bond slip curves and for whole curves.

Study on the bond behavior between steel bar with different derusting methods and concrete

In this paper, three different derusting methods: angle grinder, rust remover and shot blasting machine were selected to remove the corrosion products on the surface of steel bars with different corrosion ratios. The bond behavior between steel bars and concrete after different derusting methods was experimentally studied. To carry out this study, deformed steel bars with diameters of 14 mm, 18 mm, 22 mm and 25 mm were selected to conduct corrosion in the natural environment and 36 center-pulled specimens were cast. The following contents were studied during the test: (1) the weakening of the surface rib height of steel bar after various derusting methods; (2) the effects of derusting methods, corrosion ratio and steel bar diameter on the bond strength and peak slip were studied, the influence mechanism of various factors on the bond performance of specimens was revealed, and the influence law of various factors on the bond performance of specimens was summarized; (3) the bond-slip constitutive relation between steel bar and concrete with different diameters after different derusting methods were studied.

A numerical study of chloride migration in concrete under electrochemical repair

Electrochemical repair (ECR) is one of the most effective methods of removing chloride from offshore engineering structures to improve their durability. The diffusion of chloride and electrochemical migration are key stages in this process. In this work, a new numerical chloride migration–diffusion model was established using the Nernst–Planck equation. The distributions of free chloride ions in concrete in the stages of free chloride diffusion and ECR were simulated and the effects of the external potential and cathode position on ECR efficiency were analysed. The results showed that ECR can effectively remove chloride ions from concrete. After 12 weeks of ECR, the chloride removal efficiency was more than 66%. With an increase in the repair time, the ECR efficiency decreased gradually. In the initial stage of ECR, the chloride concentration on the rebar surface decreased rapidly. After 4 weeks of ECR, the chloride concentration tended to stabilise. The ECR efficiency also improved with an increase in external potential increases, with the chloride concentration on the reinforcing bar surface decreasing rapidly. When cathodes are set on both sides of the concrete, the ECR time should be extended and the external potential should be increased to achieve a better repair effect.

Chloride diffusion models for plain and blended cement concretes exposed to laboratory and atmospheric marine conditions

Chloride-induced corrosion of steel in a reinforced concrete structure compromises its safety and may decrease the designed service-life. The initiation and the rate of reinforcement corrosion mainly depends on the diffusion of chloride ions to the surface of the steel bars. As such, it is important to determine the coefficient of apparent chloride diffusion (Da) for the type of concrete to be used in a structure, which is time-consuming. Therefore, the development of a short-term and simple procedure to predict Da is highly desirable. This study was conducted to develop a correlation between the short-term chloride migration coefficient (Dnssm) and long-term Da for Type I, Type V and pozzolanic cement concretes. Two groups of concrete specimens, each consisting of five concrete mixtures designed with a w/b ratio of 0.4, were prepared. The first group was exposed to a marine exposure site for 10 years and Da was evaluated after 1, 2, 5 and 10 years. The second group was tested according to NT BUILD 492 under laboratory conditions to determine the short-term Dnssm. Correlation models between the field and laboratory results were developed and statistically validated by comparing the predicted values with the measured ones. The predicted Da values are within ±7% of the measured values. Further, the Dnssm of pozzolanic cement concretes is 2.20–4.40 and 3.55 to 7.30 times less than that of Type I and Type V cement concretes, respectively. The developed models can be utilized to assess the long-term Da by determining the short-term Dnssm.

Review and synthesis of stress intensity factor (SIF) solutions for circular inner cracks in round bars under tension loading

In this paper, stress intensity factor (SIF) is calculated in a bar subjected to tensile loading, considering a circular inner crack that exhibits certain eccentricity in relation to the cylinder axis. The computation is made by means of the finite element method (FEM) using a three dimensional (3D) model and the J-integral, the analyzed variables being the diameter and the eccentricity of the circular inner crack. Results show how the SIF is higher at the point of the crack front closest to the bar surface and that an increase of crack eccentricity or of crack diameter raises the difference between the SIF values at the opposite crack points located at minimum and maximum distance from the bar surface.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ ГЕОМЕТРИЧЕСКИХ ПАРАМЕТРОВ АБРАЗИВНЫХ ЗЕРЕН ХОНИНГОВАЛЬНЫХ БРУСКОВ НА МИКРОГЕОМЕТРИЮ ПОВЕРХНОСТИ ДЕТАЛЕЙ

The static theory of honing has not been sufficiently developed, since the process of mass cutting with abrasive grains is random by its nature. This fact complicates the mathematical description of this phenomenon. The research aim was to develop a technique for modeling honing to calculate the process parameters, taking into account the elastic deformations of the abrasive tool. To solve the problems of statistical theory (analyzing the microgeometry of a machine part, metal removal and cutting forces), the studies involved probabilistic analysis and Monte Carlo simulation. Based on the distribution probability of abrasive grains over the cutting layer of the tool and the process kinematics, the law of distribution of the heights of part microroughnesses was determined. Using the distribution law, the authors found the parameters of the surface roughness of the part and the cutting process characteristics: the area of cuts, the number of contact grains, etc. A mathematical relationship has been established between the distribution of abrasive grains along the height and the distribution of the depth of scratches left by the tool on a polished sample. The geometric parameters of the cutting surface of diamond bars were determined taking into account their discrete model. Comparison of the calculated and experimental values of the bar parameters proved the correctness of the proposed methodology. Analytical dependences were obtained in general form for determining the parameters of the surface roughness of the machine part, the metal removal rate, cutting forces, cut areas, the number of contact grains, etc. The developed honing modeling technique helps determine the process parameters taking into account elastic deformations of the abrasive tool. Taking into account the characteristics of the bars, the average profile of the grains and the density of their distribution along the height, we can determine all the parameters of the machine part microgeometry. The results of the conducted probabilistic research are also applicable to other types of abrasive processing.

Local bond strength prediction of deformed reinforcing bars in concrete considering heterogeneity at interface regions

An analytical model is proposed to predict local bond strength (τf) by incorporating heterogeneity at interface regions for deformed reinforcing bars centrally anchored in concrete. The rib width on the bar surface is introduced as an interfacial characteristic parameter G in the proposed model; this accounts for the heterogeneity. Both τf and the local interfacial fracture energy (GIIf) of each specimen were found to be linked to G and can be determined analytically from the maximum pull-out loads (Fmax) from tests. It was found that the predicted τf was larger than the maximum average bond stress (τavg-max); the discrepancy between the two values reduced with an increase in L/G. Moreover, with an increase in L/G, the predicted τf showed a certain decrease, with the reduction decreasing with stronger interfacial homogeneity. The predicted GIIf was found to be significantly increased because of the weaker boundary effect. The validity of the proposed model was verified using comparisons of predicted Fmax (using the determined values of τf and GIIf) and the experimental Fmax, with the only failure mode being bar pull-out. Moreover, the model can be applied to steel or fibre-reinforced polymer bars and the concrete refers to all types of cementitious materials.

Corrosion behavior of HRB400 and HRB400M steel bars in concrete under DC interference

The influence of direct current interference on the corrosion behavior of HRB400 and HRB400M steel bars in simulated concrete solution was studied using methods such as weight loss experiment, electrochemical experiment, surface technology and product analysis. The research results showed that with the increase of DC interference voltage, the corrosion rates of HRB400 and HRB400M steel bars would increase. The corrosion resistance of HRB400M steel bars was better than HRB400 steel bars under the experimental conditions. In addition, direct current interference could cause damage to the corrosion product layer on the surface of HRB400 steel bars and HRB400M steel bars. And the corrosion form and corrosion product types of HRB400 and HRB400M steel bars would be affected by direct current interference. The main corrosion products of HRB400 steel bars included γ-FeOOH and Fe2O3 when it was not interfered by DC. When DC interference was applied, the main corrosion products included Fe3O4 and Fe2O3. The corrosion products on the surface of HRB400M steel bars were mainly Fe3O4 and Fe2O3, and the types of products increased to form Cr2O3 and MnFe2O4.

Bond performance of tensile lap-spliced basalt-FRP reinforcement in high-strength concrete beams

This paper investigates the bond between high-strength concrete (HSC) and tensile lap-spliced basalt fiber-reinforced polymer (BFRP) bars. Ten large-scale BFRP-reinforced concrete beams (300 × 450 × 3900 mm) were fabricated and tested under four-point loading until failure. The parameters investigated included the BFRP bar diameter (10, 12, and 16 mm), the splice length (400–1200 mm range), and the bar surface texture (sand-coated (SC) and helically wrapped (HW)). Test results demonstrated that the flexural capacity of the beams reinforced with SC-BFRP bars was almost similar to that of beams reinforced with HW-BFRP bars. However, SC-BFRP bars showed a slightly higher bond with concrete compared to that of helically wrapped counterparts. The bond strength of spliced BFRP bars was inversely related to the splice length. Also, BFRP bars with larger diameter bars require longer splice lengths to reach their maximum capacity. Finally, the experimentally estimated critical splice lengths were compared to those calculated by existing models and code-based equations. Both ACI 440.1R-15 and CSA S806-12 provisions were conservative in predicting splice length for BFRP bars. However, the CSA-S6-14 design code was more accurate in estimating the splice length for BFRP with bigger diameters. Though, it was not conservative with smaller diameters.

Experimental study on multi-component corrosion inhibitor for steel bar in chloride environment

This paper investigates one type of multi-component corrosion inhibitor for steel bars in chloride environment. Triethanolamine (TEA), tri-isopropanolamine (TIPA), sodium monofluorophos-phate (MFP) and sodium molybdate (T-4) were proportioned to prepare this multi-component corrosion inhibitor. Corrosion behavior of steel bar was evaluated using the polarization curve, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The polarization curves were fitted using the adsorption isotherm models. Experimental results indicated that the steel bar corrosion in chloride solution can be reduced by the addition of either organic or inorganic corrosion inhibitors. This is attributed to the fact that organic corrosion inhibitor can form an adsorption film on the steel bar surface and inorganic corrosion inhibitor abates electrochemical reaction of steel bars. Compared to single component corrosion inhibitors, the corrosion rate of steel bars in simulated pore solution was significantly restrained by the multi-component corrosion inhibitor. The adsorption of multi-component corrosion inhibitor on the surface of steel bar can significantly reinforce the passive film by means of physical (organic) or chemical (inorganic) process. For all the investigated corrosion inhibitors, the adsorption isotherms were in good agreement with experimental results. The EIS result and equivalent electrochemical circuit confirmed the chemical reaction and physical adsorption process of the multi-component corrosion inhibitor. Therefore, the chloride induced corrosion of steel bars can be effectively controlled by the multi-component corrosion inhibitor.

Local bond strength prediction of deformed reinforcing bars in concrete by considering heterogeneity at interface regions

An analytical model is proposed in this paper to predict the local bond strength τf by incorporating the heterogeneity at interface regions for deformed reinforcing bars centrally anchored in concrete. The rib width on bar surface is introduced as an interfacial characteristic parameter G in the proposed model accounting for the heterogeneity. Both the τf and local interfacial fracture energy GIIf from each specimen are linked to the G and determined analytically if the maximum pull-out loads Fmax are given from the test. It is found that the predicted τf is larger than the maximum average bond stress τavg-max. The discrepancy between the two values is reduced with the increasing of L/G. Moreover, as the L/G increases, the predicted τf shows a certain decrease and the reduction becomes smaller with stronger interfacial homogeneity. The predicted GIIf is significantly increased because of the weaker boundary effect. The validity of the proposed model is verified upon the comparisons between the predicted Fmax using the determined τf and GIIf and the experimental ones with the only failure mode of bar pull-out. Moreover, the bars here can be steel or FRP (fiber-reinforced polymer) bars, and the concrete refers to all types of cementitious materials.

Numerical Simulation of Non-Uniformly Distributed Corrosion in Reinforced Concrete Cross-Section.

Reinforced concrete structures can be strongly damaged by chloride corrosion of reinforcement. Rust accumulated around rebars involves a volumetric expansion, causing cracking of the surrounding concrete. To simulate the corrosion progress, the initiation phase of the corrosion process is first examined, taking into account the phenomena of oxygen and chloride transport as well as the corrosion current flow. This makes it possible to estimate the mass of produced rust, whereby a corrosion level is defined. A combination of three numerical methods is used to solve the coupled problem. The example object of the research is a beam cross-section with four reinforcement bars. The proposed methodology allows one to predict evolving chloride concentration and time to reinforcement depassivation, depending on the reinforcement position and on the location of a point on the bar surface. Moreover, the dependence of the corrosion initiation time on the chloride diffusion coefficient, chloride threshold, and reinforcement cover thickness is examined.

Experimental investigation of crack width variation along the concrete cover depth in reinforced concrete specimens with ribbed bars and smooth bars

Crack width variation along the concrete cover depth has been studied from the past for better understanding of the cracking phenomenon in reinforced concrete (RC) structures. Previous studies have highlighted important cracking behaviors like internal cracks. The behavior of ‘slip’ between the reinforcement and concrete and the formation of a nonuniform crack face along the concrete cover depth are still not very clearly understood. An experimental program has been conducted to study the crack width variation along the cover depth in concrete prisms reinforced with a central ribbed bar and smooth bar, by varying the concrete cover depths. Both in specimens with smooth bars (SS) and specimens with ribbed bars (SR), crack width is larger on the concrete surface than at the steel bar surface. The crack width at the reinforcement is considerably larger in the SS than in the SR. In the SR, the crack width increases from the reinforcement along the cover depth bi-linearly, while, in the SS, it increases linearly. For the SR, the aforementioned behavior is due to the occurrence of internal cracks. In the SS, significant slip has been identified at the reinforcement and concrete interface, whereas negligible slip has been observed in the SR. A surface crack width calculation model has been developed, considering both the strain difference and the effect of the nonuniform crack face along the concrete cover depth. Its predictions showed good agreement with the experimental surface crack widths from the conducted study and with the results from the experiments in literature.

Restriction of Cl- and SO4 2- Ions Transport in Alkali Activated Slag Cement Concrete in Seawater

The relevance of alkali activated slag cement (AASC) concretes for structures operated in seawater is due to their enhanced resistance in aggressive environments. The application of high consistency fresh concretes is accompanied by negative changes in their structure with higher penetration of aggressive environments. Thus, the methods to prevent corrosion of steel reinforcement in plasticized AASC concrete are actual for investigations. It is shown, that modification of plasticized AASC concrete (consistency class S4) by the complex «alumina cement - portland cement - clinoptilolite - trisodium phosphate (Na3PO4·12H2O)» restrict the transport of aggressive Cl- and SO4 2- ions. The results of DTA, XRD, electron microscopy, microzond analysis show that mentioned complex limits transport of the mentioned aggressive ions due to their binding by AFm phases in hydration products, exchange with OH- ions in the structure of clinoptilolite, formation of hydrated products of apatite group Ca5(PO4)3(OH, Cl). This was confirmed by qualitative reaction on Cl- and SO4 2- ions in concrete structure, as well as by assessing of surface and mass loss of steel bars embedded in AASC concrete after 9 months in seawater. It was ensured the advanced crystallization with densification of microstructure, which increases corrosion resistance of artificial stone.