Loss Of Bond Strength Research Articles

Bond of steel bars in S-PVA-HF concrete with different cooling methods after high-temperature exposure

This experimental study compared the effect of natural cooling and water spray cooling on the bond properties of steel and steel-PVA hybrid fiber (S-PVA-HF) concrete after being exposed to high temperatures. Twenty-seven plain concrete specimens and fifty-four S-PVA-HF concrete specimens were designed for pullout tests using different cooling methods from high temperatures. This paper explored the bond strength and slip of steel bars and S-PVA-HF concrete with different temperatures and fiber admixtures after cooling from a high temperature. The differences and characteristics of the loss of bond properties of steel bars and S-PVA-HF concrete after natural cooling and water spray cooling were revealed. Phenomena during the heating process and changes in the apparent characteristics and mass burn-off rate after high-temperature exposure were analyzed The results showed that the bond strength and ductility of the specimens mixed with fibers were higher after high-temperature exposure compared with the normal concrete specimens. The bond strength of the specimens decreased upon increasing the temperature. Water spray cooling resulted in a greater loss in bond strength than natural cooling, but it improved the ultimate slip value of reinforced concrete. The ultimate slip value for normal concrete, P1S8 (mixed fiber concrete with 0.1 % PVA fiber + 0.8 % steel fiber), and P1S14 (mixed fiber concrete with 0.1 % PVA fiber + 0.8 % steel fiber) concrete specimens were improved by 8.54 %, 5.36 %, and 8.19 %, respectively.This shows that water spray cooling improved the ductility of concrete. The relationship between ultimate bond strength and ultimate slip value of steel bars and S-PVA-HF concrete after different cooling methods from high temperatures was developed.

Localization patterns emerging in CPTu tests in a saturated natural clay soil

In this work, the mechanics of cone penetration during CPTu tests in Osaka clay, a natural structured silty clay, was investigated with the Particle Finite Element Method (PFEM). To describe the behavior of the soil, the FD_MILAN model, recently proposed by the Authors, was adopted. The model, based on the multiplicative decomposition of the deformation gradient, incorporates a scalar internal variable, the bond strength Pt, to quantify the effects of structure. The macroscopic description of mechanical destructuration effects is provided by the hardening law of Pt, according to which the bond strength decreases monotonically with accumulated plastic deformations. The brittle behavior resulting from the softening process associated to destructuration make the soil quite susceptible to the spontaneous development of strain localization in the form of shear bands. In order to deal with strain localization phenomena, the model is equipped with a non-local version of the hardening laws, incorporating a material constant – the characteristic length ℓc – which provides the material with an internal length scale. The objective of this work was to get some insight on the effects of the characteristic length and of the initial degree of structure on: the kinematics of the soil deformation around the advancing cone tip; the evolution of soil structure with accumulated plastic deformations; the excess pore pressure field generated in the soil as a result of the hydro-mechanical coupling between the solid skeleton and the pore water, and the net cone resistance measured at the base of the cone. The results of the PFEM simulations show that the deformations around the piezocone are strongly affected by the characteristic length. For heavily structured soils, when ℓc is relatively small with respect to cone radius, the accumulated plastic deviatoric deformation field is characterized by clearly visible shear bands while, as ℓc increases, the detection of localized deformation regions becomes more difficult, if not impossible. This depends on the fact that, for large values of ℓc, the shear band width may be of comparable size to the cone radius. In all cases, the soil around the advancing piezocone is subjected to a very strong destructuration process, which leads to the complete loss of bond strength in a large region around the cone tip and shaft. As a consequence, the use of conventional Nc values from the literature in the interpretation of the CPTu test performed in heavily structured soils could provide undrained strength values closer to the ultimate undrained shear strength. At the same time, the use of empirical correlation to estimate the yield stress in oedometric conditions would lead to a significant underestimation of the overconsolidation ratio.

Pull‐off capacity of FRP–concrete composite bonded with epoxy/geopolymer at elevated temperature

AbstractExternally bonded strengthening technique to the concrete has been widely used with epoxy adhesive. However, the adhesive is considerably weak against high temperatures, which has been regarded as the critical point in the loss of integrity of the strengthened system. Alternatively, geopolymer materials have shown an excellent performance at high temperatures, thus, their potential to be used as adhesive material has been investigated in this work. In experimentation, the composite specimens were developed using both types of adhesives, epoxy and geopolymer, and their performance was evaluated at three temperature levels (20, 60, and 120°C) by conducting pull‐off strength tests and classifying their failure modes. It was observed that the strength of concrete and epoxy was reduced with temperature. In contrast, the strength of geopolymer‐based adhesives strength was increased due to the reactivity of the precursor at high temperatures. Also, bond strength was reduced for both composite specimens at elevated temperatures. The highest bond strength was observed for the epoxy‐based adhesive system at 20°C, and about 70% loss in bond strength was observed when exposed to 120°C. The failure mode was also shifted from concrete to adhesive interface failure, that is, failure between the adhesive and the fiber fabric layer. The geopolymer‐based adhesive system has lower strength than its counterpart at all temperature levels, and the failure mode was adhesive interface failure. To enhance the bonding capacity at high temperatures, efforts are being made by adding different minerals has been employed. From the experimental results, it was found that there were some improvements, however, it was still less than that of epoxy‐based system. Further optimization of the geopolymer adhesive using minerals is required and then high‐thermal resistance geopolymer adhesive can be established.

Residual Bond Strength of Highly Corroded Reinforced Concrete

Corrosion of reinforcement due to chloride attacks in the marine environment is a natural phenomenon. Corrosion of reinforcement produces corrosion products of high volume, which deteriorates the structural integrity of reinforced concrete structures due to loss of bond, cracking, and spalling of the concrete. Existing literature has documented tests investigating the bond behavior of uncorroded and corroded specimens, but there is a dearth of data pertaining to a more advanced stage (higher mass loss) of corrosion. In the current study, an accelerated corrosion test was conducted on cylindrical (lollypop) specimens, which involved utilizing an impressed current laboratory technique to induce three distinct levels of corrosion (10%, 20%, and 40% mass loss). Moreover, to assess bond strength, the pull-out tests were performed on both corroded and uncorroded specimens. The present study deals with the residual bond strength at three different corrosion levels, as a function of different parameters such as clear cover (CC), water-cement (W/C) ratio, and two different reinforcement diameters. Experimental data reveals that the mass loss achieved is lesser than the target mass loss for all specimens. It is observed that at higher corrosion levels, where the mass loss exceeds 10% or cracks appear on the surface of the reinforced structure, both an increase in mass loss and a decrease in residual bond strength is consistently observed. These effects remain consistent regardless of whether the parameters such as bar diameter, W/C ratio, and CC are increased or decreased. The statistical analysis was performed on the experimental data to develop predictive models for estimating the residual bond strength and mass loss. For higher mass loss of 30% to 35%, the corresponding bond strength for all of the specimens falls within the range of 4 Mpa to 6 MPa.

Interface adhesion of fresh-on-fresh cast ultra-high performance concrete–normal concrete: Effect and mechanism of pour delay and ambient humidity

The Ultra-high performance concrete (UHPC)-normal concrete (NC) composite element in this study was created using the fresh-on-fresh casting process with NC placed over UHPC. The impact of the pour delay of 0, 25 min, 1 h, 3 h, 7 h, 10 h, and 24 h as well as the placement environment of standard curing and dry indoors conditions on the interface bond strength were investigated. The findings demonstrate that, under standard curing conditions, a suitable pour delay can not only guarantee the interface bond strength but also decrease the dispersion; While when the pour delay exceeds a certain limit, the interface bond strength decreases linearly until the final setting of UHPC. However, in the dry condition, only a short exposure time will lead to a significant decline in the interface bond strength. From the combination result of computerized tomography (CT) and backscattered electron (BSE) test, it is found that the interface bonding is due to the synergistic effect of aggregate interlocking, fiber anchoring and staggered growth of hydration products. While in a dry condition, the evaporation of water led to the formation of a thin hardening layer on the surface of UHPC, which hindered the interaction between UHPC and NC, and finally led to the rapid loss of interface bond strength.

Bond durability performance of sand-coated BFRP bars in high-strength fiber reinforced concrete

The ever-increasing utilization of fiber-reinforced polymer (FRP) bars has led to a surge in research regarding their bonding properties with concrete. In this study, the bond durability behavior between high-strength fiber-reinforced concrete (FRC) and sand-coated basalt FRP (BFRP) bars was examined under three different environmental conditions including immersion in seawater solution at 50 °C for 3, 6, and 9 months, immersion in the sulfuric acid solution for 3, 6, and 9 months with an ambient temperature range of 20 to 30 °C, and exposure to 270 freeze–thaw cycles. A total of 60 pull-out samples were prepared using either basalt (B) fibers or polypropylene (PP) fibers. Plain concrete pull-out samples were served as controls. Test results revealed that all exposures have degraded the bond, leading to pull-out failure in all of the specimens. Exposure to 50 °C seawater was found to cause the most significant degradation. However, the use of basalt fibers helped to mitigate the loss of bond strength in the specimens when compared to plain concrete specimens. For example, after 3, 6, and 9 months of exposure to 50 °C seawater, bond strength retentions of 73.58%, 56.04%, and 34.47% were observed for basalt FRC (BFRC) specimens, compared to 39.64%, 49.37%, and 29.61% for plain concrete specimens. On the other hand, a lower retention in bond strength of 16.28% was recorded for polypropylene FRC (PPFRC) specimens at 9 months of exposure to 50 °C seawater. The bond stress-slip relationship of the tested bars was accurately predicted using two calibrated analytical models: the Eligehausen, Popov, and Bertero (BPE) model and the Cosenza, Manfredi, and Realfonzo (CMR) model. Notably, both models showed a strong correlation with the observed bond stress-slip relationships in the experiments.

Effect of bacterial resistant zwitterionic derivative incorporation on the physical properties of resin-modified glass ionomer luting cement

Biofilms induce microbial-mediated surface roughening and deterioration of cement. In this study, zwitterionic derivatives (ZD) of sulfobetaine methacrylate (SBMA) and 2-methacryloyloxyethyl phosphorylcholine, were added in concentrations of 0, 1, and 3% to three different types of commercially available resin-modified glass ionomer cement (RMGIC) (RMC-I: RelyX Luting 2, RMC-II: Nexus RMGI, and RMC-III: GC FujiCEM 2). The unmodified RMGICs served as the control group for comparison. The resistance of Streptococcus mutans to ZD-modified RMGIC was evaluated with a monoculture biofilm assay. The following physical properties of the ZD-modified RMGIC were assessed: wettability, film thickness, flexural strength, elastic modulus, shear bond strength, and failure mode. The ZD-modified RMGIC significantly inhibited biofilm formation, with at least a 30% reduction compared to the control group. The addition of ZD improved the wettability of RMGIC; however, only 3% of the SBMA group was statistically different (P < 0.05). The film thickness increased in proportion to the increasing ZD concentrations; there was no statistical difference within the RMC-I (P > 0.05). The experimental groups' flexural strength, elastic modulus, and shear bond strength showed an insignificant decrease from the control group; there was no statistical difference within the RMC-I (P > 0.05). The mode of failure differed slightly in each group, but all groups showed dominance in the adhesive and mixed failure. Thus, the addition of 1 wt.% ZD in RMGIC favorably enhanced the resistance to Streptococcus mutans without any tangible loss in flexural and shear bond strength.

Understanding the moisture sensitivity of warm-mix asphalt binders based on bond strength

Moisture damage in asphalt mixtures is typically attributed to the loss of bond strength at the interface of the asphalt binder and aggregate matrix. Selecting an appropriate combination of materials that resist moisture-induced damage is therefore critical. This concern is of utmost importance when asphalt mixtures are prepared at lower temperatures (i.e. warm-mix asphalt (WMA) mixtures). An attempt was thus made to quantify the impact of moisture on asphalt mixtures prepared using four different WMA additives and two aggregates through bond strength tests. The results showed that WMA binders imparted similar or even higher bond strength than the base asphalt binder, regardless of the aggregate source and moisture exposure (wet or dry). The use of WMA additives improved the moisture sensitivity (evaluated through the bond strength ratio), despite lower production temperatures, compared with the base asphalt binder (VG30). Statistical analysis showed that the asphalt binder type significantly affected the bonding mechanism and moisture sensitivity. Based on the ranking protocol used in this study, use of the chemical-based WMA additive Rediset showed the best performance compared with other WMA additives in VG30.

Study on the bond properties between steel bar and fiber reinforced concrete after high temperatures

The bond-slip performance between steel bar and normal concrete (NC) and steel fiber reinforced concrete (SFRC) after high temperature were investigated in this paper. The central pull-out test was performed on 40 specimens with specific parameters including the fraction of steel fiber by volume (Vf = 0 %, 0.5 %, 1.0 %, and 1.5 %) and temperature (T = 20 °C, 200 °C, 400 °C, 600 °C, and 800 °C). The results demonstrate that the bond strength increased with the increase of Vf. The increase in bond strength of SFRC specimens compared to NC specimens is more than 66.9 % after 600 °C. As the temperature increases, the bond strength decreases. The bond strength loss after 600 °C compared to room temperature was more than 46.6 % for SFRC and NC specimens. The synergistic effect of steel fibers and aggregates formed a rigid skeleton for bridging cracks, improving the bond strength between steel bar and SFRC. The cumulative initial damage (interface and thermal cracks) generated by temperature reduced the bond strength. An empirical formula for predicting the bond strength was proposed. The bond stiffness decreased with the increase of temperature and increased with the increase of Vf. SFRC specimens with Vf = 1.5 % exhibited insignificant changes in bond toughness after high temperature compared to those with Vf = 1.0 %. The steel fibers significantly improved the bond toughness of SFRC specimens at room temperature. Empirical formulas for predicting bond stiffness and bond toughness were proposed. A prediction model for the bond-slip relationship between steel bar and SFRC after high temperature considering Vf and temperature was proposed. It is found that the established model of the bond-slip relationship agreed well with the experimental results.

Performance evaluation of temperature-regulating asphalt mixture with thermochromic materials and low freezing point materials

Asphalt pavement absorbs a lot of heat in the summer because of its dark surface, which makes it susceptible to high-temperature. By altering the asphalt pavement’s ability to reflect solar radiation, thermochromic materials can regulate the temperature of the road. However, the thermochromic modified asphalt’s ability to regulate temperature is weak during the winter, when the road surface is covered in snow and ice or when there is no direct sunlight. Materials with low freezing points can lower the pavement’s freezing temperature and produce the snow melting and deicing effects. A type of temperature-regulating road asphalt material can be created by mixing low freezing point material and thermochromic material in a certain ratio with road asphalt. The blue thermochromic materials of 3%, 5% and 7% by weight were applied to the matrix asphalt to prepare thermochromic asphalt binders, respectively. The low freezing point materials replaced 25%, 50% and 75% of the mineral filler volume.The pavement performance, deicing performance and cooling performance of the tempering asphalt mixture were evaluated by orthogonal test design. According to the findings, the temperature-regulating asphalt combination performs substantially better at cooling and deicing than the unmodified asphalt mixture. When the replacement rate of low freezing point materials changes from 25 % to 75 %, the bond strength loss of modified asphalt mixture increases from 46 % to 75 %. The pavement surface temperature can be reduced by a maximum of 4–9 °C during the day by using a temperature-regulating asphalt composition. In this study, it is advised to use 5 % thermochromic dosage and 50 % replacement rate of low freezing point materials, taking into account the overall balance of performance enhancement.

Novel bioactive adhesive containing dimethylaminohexadecyl methacrylate and calcium phosphate nanoparticles to inhibit metalloproteinases and nanoleakage with three months of aging in artificial saliva

ObjectivesThe objectives of this study were to: (1) develop a multifunctional adhesive via dimethylaminohexadecyl methacrylate (DMAHDM) and nanoparticles of amorphous calcium phosphate (NACP); and (2) investigate its ability to provide metalloproteinases (MMPs) deactivation and remineralization for long-term dentin bonding durability. MethodsDMAHDM and NACP were incorporated into Adper™ Single Bond 2 Adhesive (SB2) at mass fractions of 5% and 20%, respectively. Degree of conversion and contact angle were measured. Endogenous MMP activity of the demineralized dentin beams, Masson’s trichrome staining, nano-indentation, microtensile bond strength and interfacial nanoleakage analyses were investigated after 24 h and 3 months of storage aging in artificial saliva. ResultsAdding DMAHDM and NACP did not compromise the degree of conversion and contact angle of SB2 (p > 0.05). DMAHDM and NACP incorporation reduced the endogenous MMP activity by 53 %, facilitated remineralization, and increased the Young’s modulus of hybrid layer by 49 % after 3 months of aging in artificial saliva, compared to control. For SB2 Control, the dentin bond strength decreased by 38 %, with greater nanoleakage expression, after 3 months of aging (p < 0.05). However, DMAHDM+NACP group showed no loss in bond strength, with much less nanoleakage, after 3 months of aging (p > 0.05). SignificanceDMAHDM+NACP adhesive greatly reduced MMP-degradation activity in demineralized dentin, induced remineralization at adhesive-dentin interface, and maintained the dentin bond strength after aging, without adversely affecting polymerization and dentin wettability. This new adhesive has great potential to help eliminate secondary caries, prevent hybrid layer degradation, and increase the resin-dentin bond longevity.

Experimental and numerical investigations of interfacial bond in self-compacting concrete-filled steel tubes made with waste steel slag aggregates

New self-compacting concrete (SCC) mixtures were designed to improve the interfacial bond strength in concrete-filled steel tubes (CFST) at 30 days and one year. The proposed SCC mixtures involved the strengthening of bond strength by using waste steel slag aggregates (SSA). A total of thirty-six circular and squared tube specimens with different ratios (0%, 25% and 50%) of SSA as a replacement by weight of coarse and fine aggregates in SCC were initially prepared. The results revealed that the using of SSA in SCC enhanced the specimens' bond strength for both shapes of steel tubes and the bond strength was reduced with an increase of concrete's age. Additionally, the incorporating of SSA did not decrease the loss in bond strength at one year. A three-dimensional non-linear finite element (FE) analysis was further conducted to simulate the interfacial bond-slip mechanism between two surfaces of the infill concrete and inner steel tubes.

Correlation between dental enamel chemical composition and bracket debonding, comparing adhesive systems through a scanning electron microscope.

Literature reports indicate that during bracket removal there can be enamel damage. We compare the shear bond strength (SBS) and tooth enamel loss of four adhesive systems and identify the Ca/P ratio. Then a total of 20 premolars were divided into four groups of five each. After prophylaxis, photographs were taken at 35× with a scanning electron microscope (SEM) and analyzed with X-ray spectroscopy (EDS) at 250×. Brackets were bonded with Transbond™ MIP(G1), Transbond™ PLUS SEP(G2), Enlight(G3) and Stylus®(G4) adhesives, 24 h after were debonded with a Instron universal testing machine at 1 mm/min. All the brackets were photographed with the SEM. The amount of lost enamel was measured with AutoCad. All the results were measured with a significance level p < .05. The SBS general average at debonding was 7.94 ± 2.26 MPa, meanwhile the SBS for G1, G2, G3 and G4 was 9.38 ± 1.46, 6.28 ± 0.69, 9.08 ± 2.45 and 7.04 ± 2.64 MPa respectively. 90% of the samples had no enamel loss, 10% had enamel loss. Only two samples in G1 presented an enamel loss area of 0.34mm2 and 0.80mm2 respectively. From EDS analysis, the Ca/P ratio was 1.6 ± 0.05, 1.61 ± 0.03, 1.64 ± 0.83 and 1.59 ± 0.07 for G1, G2, G3 and G4 respectively; no statistically significant differences were found. We conclude that no association was found between the Ca/P ratio and enamel damage when brackets are removed. HIGHLIGHTS: Where enamel is lost, we observe fractures, steps, horizontal and vertical enamel loss. There is a loss of tooth enamel from 0.34 to 0.80 mm2 with Transbond PLUS SEP. Structural loss of enamel is almost inevitable during the separation of the bracket.

Effect of grape seed extract on the bond strength and adhesion durability of universal adhesive to dentin

The effects of grape seed extract (GSE) on the microtensile bond strength (µTBS) and resin-dentin bond durability of universal adhesive to dentin were investigated, while the resin-dentin interface was evaluated using a scanning electron microscope (SEM). Flat occlusal dentin surfaces of 80 sound human molars assigned to, control and GSE-pretreated groups & further divided into etch-and-rinse (E&R) and self-etch (SE) adhesion subgroups. In each subgroup, molars tested immediately (t0; n = 10) & after 6 months (t6; n = 10). In GSE-pretreated group, 10% GSE was prepared in hot water & then used for 1 min pretreatment after etching (15s) in the E&R subgroup or before application of adhesion in the SE subgroup. Composite build-ups made incrementally, and dentin beams sectioned and tested for µTBS at the baseline (24 h) and 6 months. Sections were obtained for SEM analysis. In the 6-month treatment, beams stored in artificial saliva, subjected to thermal cycling, and then tested. The failure modes of fracture surfaces were identified with a stereomicroscope. Comparing the t0 and t6 timepoints, significant reduction in µTBS in all groups compared with their respective controls after aging, but the percentage of bond loss due to aging in the GSE-pretreated groups was less than controls. Most failure modes were mixed. GSE (10%) pretreatment for 1 min before adhesion enhanced the durability of the resin-dentin bond but did not completely eliminate loss of bond strength.

Structural Performance Degradation of Corrosion-Damaged Reinforced Concrete Beams Based on Finite Element Analysis

The impact of the seismic performance of corrosion-damaged reinforced concrete (RC) members on the overall seismic performance of the entire RC structure must be investigated. Related research results provide important guidance for a more accurate seismic performance evaluation of RC structures with corroded members including beams and columns. However, currently available technologies for the seismic evaluation of existing RC structures do not consider the impact of reinforcement corrosion-induced deterioration on the seismic performance of RC members. The main focus of this study is on proposing a practical methodology to evaluate the seismic performance of such buildings. More specifically, the proposed methodology enables a direct quantitative evaluation of seismic performance by estimating the structural performance based on the strength and deformation capacity of corroded members. In pursuit of this research background and the objectives, our research team first performed an experimental study to estimate the impact of reinforcement corrosion on the structural behavior of RC shear beams and flexural beams and determine the factors associated with structural performance deterioration. A high correlation between the half-cell potential (HCP) before and after reinforcement corrosion of RC beams and the structural performance degradation factor based on the energy absorption capacity has been seen previously. In this study, a finite element analysis (FEA) was conducted, in which bond strength loss between rebar and concrete due to reinforcement corrosion of beam members was considered as one of the aging-related degradation factors, and the correlation between structural performance degradation before and after corrosion in beam members was studied. In addition, we compared and analyzed the results of the previous experimental research and FEA conducted in this study and proposed a structural performance degradation factor as a function of corrosion of shear and flexural beams. The research results indicate that the FEA-derived bonding factor (β) and performance degradation factor (ϕ) of flexural beam can be approximated with the equation ϕ=(0.36−β)−1+101 (R2 = 0.94), together with β–mV (average potential difference in voltage) correlation mV =(1.36−β)/(0.018−0.05β). In the case of shear beams, FEA resulted in ϕ=37.3β+63, which enables regression approximation, showing a high correlation (R2 = 0.98), together with β–mV correlation (mV =932.5β−1075). Using the mV–β–ϕ correlation curves, the bonding factor (β) depending on the degree of corrosion of RC beam members and the performance degradation factor (ϕ) based on the consequent strength-deformation capacity can be evaluated.

Novel bulking technologies for cellulose fibres

Abstract This paper deals with the details of preparation of three principal routes for bulking of cellulose fibres. One route is dry cross-linking/hornification using aluminium ions and other salts followed by drying/curing. The mechanisms of these reactions still remain unknown. A second route is physical grafting of fibres using carboxymethylcellulose and bringing the acidic groups into their aluminium form before forming a sheet of paper/board. Hence, curing is not necessary, and this constitutes a unique wet bulking methodology. The mechanism behind this method is believed to be an increase in the surface friction of fibres, when the electrostatic double layer is shielded together with electrostatic cross-linking with aluminium ions. The higher friction between fibres partly prevents the sheet consolidation during drying. A third route is physical grafting of fibres using carboxymethyl cellulose and ion-exchanging the acidic groups with aluminium salts before drying and curing of the fibres. A most interesting factor is that all the thermal treatment methods do not form fibre nodules due to interfibre crosslinking during the heat treatment, a commonly observed phenomena when dealing with chemical crosslinking of fibres. All routes investigated are water-based and should be fairly simple to implement in commercial operations. An inherent advantage is that the bulking is associated with lower water retention values, which should be advantageous for a higher solids content after pressing and, hence, beneficial for paper machine productivity. Bulking is, however, also associated with a loss in bond strength, which in most cases must be alleviated using various additives such as starches and microfibrillated cellulose and it has also been demonstrated in the project how the strength properties (such as z-strength) could be restored at a higher bulk.

Numerical Study of the Bond Strength Evolution of Corroded Reinforcement in Concrete in Pull-Out Tests

The corrosion of rebars in reinforced concrete structures impacts their geometry (diameter and ribs) and mass, damages the concrete at the interface between the two materials, deteriorates the bond strength, and causes the cracking of the concrete cover. In the following study, a 2D numerical model of the pull-out test is presented in order to study the impact of corrosion on the bond strength. Several parameters are investigated: the embedment depth, the rebar’s diameter, and the width of the concrete cover. The model reproduces the slip of the rebar and the failure through the splitting of concrete. It integrates an interface between the two materials and a concrete damage model that simulate the deterioration of concrete in compression and tension. The results obtained are validated with experimental data from the literature. Moreover, a parametric study is carried out to determine the impact of the embedment depth, the diameter of the rebar, and the concrete cover on the bond strength. The present study confirms that a greater embedment depth increases the pulling load. The study also confirms that the rebar’s diameter impacts highly the loss of bond between the rebar and the concrete cover. Lastly, the final main result of this paper is that the width of the concrete cover slows the loss of bond strength between the two materials.

Effect of sodium nitrite on chloride-induced corrosion of steel in concrete

Corrosion attack on reinforcement steel in concrete causes cracking, loss of bond strength, reduction in steel cross-section, and decrement of serviceability. Among the various measures applied to protect corrosion of steel, the use of inhibitors is one of them. The present work evaluates the effectiveness of sodium nitrite as corrosion inhibitor in inhibiting chloride induced corrosion attack on reinforcement steel in concrete. Electrochemical tests included half-cell potential and linear polarization resistance were carried out on steel in concrete specimens. For electrochemical tests, reinforced concrete prisms with a steel bar placed centrally were made from concrete mixes using 53 grade Portland cement at w/c ratio of 0.50 and admixed with different dosages of sodium chloride and sodium nitrite. The dosages of sodium chloride used were 3% and 6% (by cement mass) and the dosages of sodium nitrite were 0%, 1.5%, 3%, and 4.5% (by cement mass). At the end of 28 days of curing, the prisms were dried for 10 days in laboratory exposure condition and then exposed to chloride solution containing 3% sodium chloride with alternating wet-dry process. The electrochemical tests were conducted on the prisms at different intervals. At the end of exposure period to chloride environment, free chlorides of the prisms at different depth intervals were determined. In addition, concrete cubes were also prepared from the same concrete mixes to obtain the 28-day compressive strength. The obtained results indicated that addition of nitrite in concrete admixed with chloride reduces the compressive strength of concrete. Further, corrosion of steel in concrete increased with increment in the dosage of admixed chloride salts. The addition of nitrite minimized the corrosion attack on steel bar in concrete and its effectiveness against corrosion was enhanced at higher dosages. With an increment in dosages of admixed sodium chloride, the free chlorides increased at all depth intervals from concrete surface. However, there was no noticeable variation in free chlorides with admixed sodium nitrite dosages at different depth intervals from the concrete surface.

Mineralization strategy on dentin bond stability: a systematic review of in vitro studies and meta-analysis

Objectives This study aimed to systematically review the literature on laboratory researches and statistically determine the influence of mineralizing strategy on the dentin bond stability. Methods The search was conducted in PubMed/MEDLINE, Web of Science, EMBASE, and SCOPUS according to the PRISM guidelines. From 2200 possible eligible articles, 50 were selected for full-text analysis, and 15 were included in the systematic review. Two authors independently selected the studies, extracted the data, and assessed the risk of bias. Bond strength analysis was conducted by RevMan5.3 with random effects model (α = 0.05), comparing control (without mineralizing strategy) and experimental groups (mineralizing strategy). Results Fifteen included trials concerned 46 comparisons between experimental groups adopting mineralizing strategy and control groups. Mineralization strategy reduced the dentin bond strength loss after aging. Although non-significant, the aging bond strength was higher than traditional bond methods (p = 0.07), the improvement was significant in pretreat (p = 0.01) and etch and rinse subgroup (p = 0.04). A significant reduction was found in immediate bond strength was associated with the use of mineralization strategy (p = 0.003). The majority of included studies were scored high risk of bias, high heterogeneity was presented in the meta-analyses. Conclusion Mineralization strategy reduced the dentin bond strength loss after aging. Bond strength after aging tends to be increased by mineralization strategy when used as a pretreat procedure, and in etch and rinse adhesive system. However, the mineralization strategy reduced the immediate dentin bond strength and didn’t influence aging bond strength in total.

Bond behavior of lightweight concrete-filled steel tubes containing rock wool waste after exposure to high temperatures

Evaluating the concrete-steel composite action and bond behavior in structures with concrete-filled steel tube (CFT) members is an essential part of the design phase of these structures, especially for exposure to fire as a potential risk in the service life of any structure. In this research, the natural bond strength and bond stress-slip behavior of lightweight concrete-filled steel tubes (LCFTs) containing rock wool waste following thermal loading at elevated temperatures were investigated. For this purpose, 40 CFT specimens consisting of circular steel sections filled with lightweight concrete containing several volume contents of rock wool waste (0, 2.5, 5, 7.5, and 10%) were made and thermally loaded at 20, 200, 400, and 600 °C. Afterward, all the lightweight concrete-filled steel tube (LCFT) specimens were subjected to up to four loading cycles in the load-reversed push-out test. The first loading cycle was conducted to investigate the heat-induced bond strength loss of the LCFT specimens and the impact of rock wool waste on this parameter, while the remaining cycles were conducted to assess the macrolocking component (after the loss of chemical adhesion and microlocking components). The findings demonstrated that raising the temperature to 600 °C decreased the bond strength of the LCFT specimens by up to 97% relative to that at the room temperature, while the presence of rock wool relatively compensated for this severe loss. The incorporation of rock wool into the lightweight concrete mix increased the bond strength values of the LCFT specimens after thermal loading at 200, 400, and 600 °C by up to 20.2, 18.2, and 7.2%, respectively, relative to that of the reference specimen (lacking rock wool). In the macrolocking assessment, the first cycle was compared with the third one, and the second cycle was compared with the fourth one. It was observed that at the room temperature, the bond strength of the LCFT specimens in the third cycle decreased by 40–52% relative to that in the first cycle (with the average macrolocking contribution of 53%), while this reduction reached 21–27% in the fourth cycle relative to the second one. Furthermore, by increasing the temperature to 200 °C, the bond strength values in the second to fourth cycles increased by up to 71.2% relative to the corresponding values at the room temperature, while for the target temperatures of 400 and 600 °C, the corresponding bond strength values dropped by up to 96.6 and 98.9%, respectively. In the end, a prediction model for the bond strength of LCFT specimens containing rock wool waste was proposed as a function of temperature.