Zr/ZrO2 sensors for in situ measurement of pH in high-temperature and -pressure aqueous solutions

The aim of this study is to develop new pH sensors that can be used to test and monitor hydrogen ion activity in hydrothermal conditions. A Zr/ZrO2 oxidation electrode is fabricated for in situ pH measurement of high-temperature aqueous solutions. This sensor responds rapidly and precisely to pH over a wide range of temperature and pressure. The Zr/ZrO2 electrode was made by oxidizing zirconium metal wire with Na2CO3 melt, which produced a thin film of ZrO2 on its surface. Thus, an oxidation-reduction electrode was produced. The Zr/ZrO2 electrode has a good electrochemical stability over a wide range of pH in high-temperature aqueous solutions when used with a Ag/AgCl reference electrode. Measurements of the Zr/ZrO2 sensor potential against a Ag/AgCl reference electrode is shown to vary linearly with pH between temperatures 20 and 200 degrees C. The slope of the potential versus pH at high temperature is slightly below the theoretical value indicated by the Nernst equation; such deviation is attributed to the fact that the sensor is not strictly at equilibrium with the solution to be tested in a short period of time. The Zr/ZrO2 sensor can be calibrated over the conditions that exist in the natural deep-seawater. Our studies showed that the Zr/ZrO2 electrode is a suitable pH sensor for the hydrothermal systems at midocean ridge or other geothermal systems with the high-temperature environment. Yttria-stabilized zirconia sensors have also been used to investigate the pH of hydrothermal fluids in hot springs vents at midocean ridge. These sensors, however, are not sensitive below 200 degrees C. Zr/ZrO2 sensors have wider temperature range and can be severed as good alternative sensors for measuring the pH of hydrothermal fluids.     

模拟混凝土孔隙液中钢筋电化学腐蚀行为及pH值的影响作用

应用极化曲线法和电化学阻抗技术,结合扫描电子显微镜方法,测试钢筋在模拟混凝土孔隙液中的钝化与去钝化行为,以及溶液pH值对钢筋电化学腐蚀行为的影响作用.结果表明,钢筋在pH值为12.50的模拟液中处于钝态,随着溶液pH值的降低,钢筋的耐蚀性下降.钢筋表面去钝化发生腐蚀的临界PH值在11.12-11.05范围内.     

钢纤维增韧微膨胀钢管混凝土界面粘结性能研究

进行了30根钢纤维微膨胀钢管混凝土试件推出试验,系统研究了核心混凝土与管壁的界面粘结性能,阐述了推出试验过程中试件界面粘结破坏特征,并对界面粘结性能的影响因素进行了分析。结果表明,钢纤维微膨胀钢管混凝土界面粘结强度较普通钢管混凝土明显提高。径厚比和含钢率是钢纤维微膨胀钢管混凝土界面粘结强度的主要影响因素。钢纤维的掺加导致微膨胀钢管混凝土界面粘结性能降低,其体积掺量建议不宜超过0.75%。含钢率达到22%时,钢纤维掺量与界面长度对界面粘结性能影响不明显。     

Potentiometric thick-film sensors for measuring the pH of concrete

Concrete carbonation is one of the main triggers of the corrosion process and hence of the premature deterioration of concrete reinforcements. In order to monitor and control the carbonation process, a potentiometric sensor using thick-film technology was developed. This paper includes the results of the research carried out to characterise the pH sensor, including the materials, response time, sensitivity, detection limit, reproducibility, reversibility and the study of chloride interference. The sensors have been studied in pore solutions and concrete specimens. The study shows that the thick-film sensor has a potentiometric response to variations in pH and is capable of providing continuous, real-time information on the progress of the carbonation front.     

Comprehension of demoulding mechanisms at the formwork/oil/concrete interface

The implementation of concrete and its association with a release agent influence the aesthetics of the concrete facings. The mineral oils tend to be replaced by vegetable formulations, to reduce the impact of the substances spilled in the environment. From a technical point of view, it is important to characterize the action of these new formulations at the interface concrete/oil/formwork. Two performing techniques have been used to study the physico-chemical processes, the tribometry and electrochemical impedance spectroscopy. The correlation of the results obtained allowed to improve the understanding of the mechanisms involved at the interface mould/oil, in connection with the use of an acidifier in the formulation.      

Meso-scale numerical investigation on cracking of cover concrete induced by corrosion of reinforcing steel

Concrete cover cracking induced by corrosion of steel reinforcement is a major influencing factor for durability and serviceability of reinforced concrete structures. Here in this study, the influence of concrete meso-structure on the failure pattern of concrete cover is accounted for. The concrete is assumed to be a three-phase composite composed of aggregate, mortar matrix and the interfacial transition zone (ITZ). And a concrete random aggregate structure is established for the study on the mechanical behavior of radial corrosion expansion. In the present simulations, the plasticity damaged model is used to describe the mechanical behavior of the mortar matrix and the ITZ, and it is assumed that the corrosion of steel reinforcement is uniform. The cracking of concrete cover due to steel reinforcement corrosion is numerically simulated. The simulation results have a good agreement with the available test data and they are between the two analytical results. The failure patterns obtained from the macro-scale homogeneous model and the meso-scale heterogeneous model are compared. Furthermore, the influences of ratio of cover thickness and reinforcement diameter (i.e. c/d), the location of the steel reinforcement (i.e., placed at the middle and corner zones) and the concrete tensile strength on the steel corrosion rate when the concrete cover cracks are investigated. Finally, some useful conclusions are drawn.     

In situ measurements of aggregation and disaggregation of Cu(II) complex at liquid/liquid interface

Aggregation of Cu(II)-5-(octadecyloxy)-2-(2-thiazolylazo)phenol (TARC18) complex at the heptane/water interface was measured directly by a centrifugal liquid membrane spectrometry and a two-phase microflow API-MS method. When the pH of an aqueous phase was increased from 4 to 6, the 1:1 complex of Cu(II)-TARC18, which was formed as a positively charged complex at the interface, formed further an aggregate, accompanied by the change of spectra suggesting its aggregation. The MS spectra of the interfacial species indicated the formation of 2:3 complex for Cu(II) and TARC18 under the conditions that the aggregate was formed. This observation allowed us to analyze the interfacial aggregation stoichiometrically: the aggregate of the 2:3 complex was formed from a 1:1 complex at the interface. The addition of purine base of adenine or guanine into the system resulted in the disruption of the aggregate by the formation of a new three-element complex of 1:1:1 for Cu(II), TARC18, and the base, showing a bathochromic shift in the spectra. Thus, the disaggregation experiment showed an interfacial molecular recognition ability of the Cu(II)-TARC18 aggregate for hydrophobic bases.     

Evaluation of bond quality at the interface between steel bar and concrete using the small-dimension break-off test

This paper investigates the feasibility of using the small-dimension break-off test for evaluation of the bond quality at the interface between steel bar and concrete. Experimental studies were performed on bar-type concrete specimens and reinforced concrete beams. Twelve bar-type concrete specimens containing plain and deformed steel bars with different diameters were used to develop the relationship between the break-off moment and the adhesive strength at the steel bar/concrete interface. Subsequently, three reinforced concrete beams containing normal reinforcing bars, epoxy-coated reinforcing bars, and bars smeared with oil to simulate various adhesive conditions at the bar/concrete interface were used to study how the break-off moment and the bond strength were affected by the different adhesive conditions. In addition, two beam specimens containing normal reinforcing bars were vibrated severely on a self-made shaking table shortly after initial setting of concrete to simulate the bond damage in fresh reinforced concrete beams due to unexpected vibration or impact. Experimental results show that the effective break-off moment has a good correlation with the adhesive strength at the interface between steel bar and concrete. The break-off moment increases with an increase in bond strength. It is demonstrated that the small-dimension break-off test is capable of evaluating damage at the steel bar/concrete interface.     

Numerical modeling of the rebar/concrete interface: case of the flat steel rebars

This paper presents the methodology used to identify the mechanical behaviour of a steel-concrete interface in the case of a particular steel reinforcement (flat steel). The methodology consists in simulating the statistical mechanical behaviour of reinforced concrete tie-beams, subjected to tension, using a probabilistic discrete approach for the mechanical behaviour of the concrete under axial tension and a deterministic model for the steel-concrete interface. The model proposed for the interface is in the frame of damage mechanics taking into account physical phenomena related to the interface (cohesion and slip). The tie-beams are reinforced by a flat steel rebar with a rectangular cross section of 25 × 3.5 mm. Results of this numerical simulation have been compared to some experimental tests results. These comparisons are performed in terms of global responses (load-displacement curves) and of local responses (crack openings, number of cracks and cracks’ spacing).     

Simultaneous measurement of shrinkage and temperature of reactive powder concrete at early-age using fibre Bragg grating sensors

The physical properties of reactive powder concrete (RPC) at early-age, i.e., the first 24 h from casting, and up to an age of 7 days is investigated experimentally using fibre Bragg gratings (FBGs), a type of fibre-optic sensors. A number of FBG sensors are multiplexed together and embedded directly into the RPC specimens, and the shrinkage and temperature change are measured directly and simultaneously. The final setting time and specimen size effect were also investigated. Results showed that there is an interplay between the shrinkage and temperature. The overall shrinkage for 7 days is 488 με, with the early-age shrinkage contributing about 77% of this. The temperature curve exhibits a double peak behaviour, with the first peak appears at about 7 h, which is the final setting time. There is a size effect in that smaller prisms have a higher overall shrinkage and lower temperature change than larger prisms.     

Influence of corrosion rate on the mechanical interaction of reinforcing steel,oxide and concrete

This study offers an experimental and numerical analysis of the influence of the current density on oxide formation and the resulting cracking of reinforced concrete subjected to accelerated corrosion. The specimens were idealized reinforced concrete prisms in which a calibrated steel tube replaced the standard ribbed bar reported in most published works. This allowed the evolution of the inner diameter and volume of the tube to be recorded, providing relevant information on the mechanical interactions of the steel–oxide–concrete system. In addition, the information recorded during the tests also included the evolution of the corrosion depth and width of the main crack that grew across the concrete cover. Furthermore, the crack pattern after the corrosion process was analyzed by using slices of the specimens impregnated with fluorescent resin. Experiments were conducted for several current densities. The results show that decreasing the corrosion current density results in an increase in the corrosion depth necessary for crack initiation, a smaller effective volumetric expansion and a more irregular crack pattern. When combined with finite-element simulations carried out by using a model that reproduces the expansive behavior of the oxide and the cohesive fracture of concrete, the results show that the effective expansion factor of the oxide becomes smaller as the density of current is reduced. This would suggest that the corrosion rate affects both the pressure build-up in the growing oxide layer and, closely linked to this, the diffusion of oxide within the pores and cracks in the surrounding concrete.     

Effects of reinforcement configuration and sustained load on the behaviour of reinforced concrete beams affected by reinforcing steel corrosion

Corrosion of reinforcing steel bars in concrete is one of the main causes of early deterioration and reduction of service life of reinforced concrete (RC) structures. This paper reports on the results of an experimental programme that was carried out to study the effect of reinforcement corrosion on the serviceability behaviour of RC beams under load. The main parameters investigated were the effects of reinforcement arrangement and the magnitude of the sustained load. Four series of scaled beams were tested, each series containing six beams, three of which were subjected to reinforcement corrosion while the other three were used as un-corroded control beams. All these beams carried the same sustained load during the process of reinforcement corrosion. The reinforcement arrangement for the fourth test series was identical to the first series but these beams carried a higher sustained test load. All the beams were subjected to a four-point bending load arrangement. Corrosion of the tension reinforcement was accelerated using an impressed current while the soffits of the beams were immersed in a 3% sodium chloride solution. The evolution of reinforcement corrosion and central deflection under simultaneous load and corrosion is given. The deflections of the beams increase with progressive corrosion of the reinforcement especially during the early stages of corrosion as a result of propagation of transverse cracks and the expansive stresses induced by the corrosion products. The importance of the arrangement of the steel in the section of concrete on the performance in terms of deflection was also clarified.     

Evaluation of the bond behavior of steel reinforcing bars in recycled fine aggregate concrete

This paper describes pullout test results on deformed reinforcing bars in natural and recycled fine aggregate (RFA) concrete. The effects of bar location and RFA grade on bond strength between reinforcing bar and recycled aggregate concrete (RAC) were evaluated through the experimental program. A total of 150 pullout specimens were fabricated for the experiment. Two reinforcing bar orientations were considered with respect to the casting direction; vertical bars and horizontal bars, the latter of which was prepared to evaluate top-bar effect. Considered variables included four RFA replacement ratios (RFArs), two water-absorption grades (RFA-A: 5.83%, RFA-B: 7.95%) of RFA and three reinforcing bar locations (75, 225 and 375 mm height from the bottom of the casting mold). In addition, to evaluate the thermal and aging effect on bond behavior between the reinforcing bar and RFA concrete, some parts of pullout specimens had exposed to rapid freeze–thaw environment or been cured at air during 28 or 730 days. Test results demonstrated that bond strength does not seem to be affected by the RFAr for higher RFA grades (RFA-A), at least up to 60% RFAr. In contrast, the RAC including lower RFA grade (RFA-B) showed clear decreases in bond strength with increasing RFAr, similar to the trend observed for compressive strength. For horizontal pullout specimens, RFA concrete specimens showed higher bond strength gap between top and bottom bars than natural aggregate concrete (NAC) specimens. Bond strengths of the horizontally cast pullout specimens were affected by the flowability of concrete rather than the RFAr or RFA grade. No noticeable degradation occurred during freeze–thaw cycling of the RAC specimens, indicating that the RFA used in this study is appropriate for use in freeze–thaw environments.     

Effects of reinforcement configuration and sustained load on the behaviour of reinforced concrete beams affected by reinforcing steel corrosion

Corrosion of reinforcing steel bars in concrete is one of the main causes of early deterioration and reduction of service life of reinforced concrete (RC) structures. This paper reports on the results of an experimental programme that was carried out to study the effect of reinforcement corrosion on the serviceability behaviour of RC beams under load. The main parameters investigated were the effects of reinforcement arrangement and the magnitude of the sustained load. Four series of scaled beams were tested, each series containing six beams, three of which were subjected to reinforcement corrosion while the other three were used as un-corroded control beams. All these beams carried the same sustained load during the process of reinforcement corrosion. The reinforcement arrangement for the fourth test series was identical to the first series but these beams carried a higher sustained test load. All the beams were subjected to a four-point bending load arrangement. Corrosion of the tension reinforcement was accelerated using an impressed current while the soffits of the beams were immersed in a 3% sodium chloride solution. The evolution of reinforcement corrosion and central deflection under simultaneous load and corrosion is given. The deflections of the beams increase with progressive corrosion of the reinforcement especially during the early stages of corrosion as a result of propagation of transverse cracks and the expansive stresses induced by the corrosion products. The importance of the arrangement of the steel in the section of concrete on the performance in terms of deflection was also clarified.     

Stress-strain behavior of reinforcing steel and concrete under seismic strain rates and low temperatures

This study investigates experimentally the uniaxial stress-strain behavior of reinforcing steel bars and concrete cylinders under various combinations of earth-quake-type strain rate (quasi-static to 0.1 /s) and temperature typical of summer and winter conditions in cold urban regions (+20°C to −40°C). The main objective of these tests was to give an indication of the combined effects of these two parameters on the uniaxial, monotonic, stress-strain curves of these materials. The results of the tensile tests indicate that the yield strength and the tensile strength of reinforcing steel increase moderately as both the strain rate increases and the temperature drops. The results of the compressive tests indicate that the compressive strength and Young’s modulus of concrete increase significantly as the strain rate increases and the temperature decreases.

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Résumé Cette étude a pour but d’évaluer expérimentalement le comportement uniaxial d’éprouvettes d’acier d’armature et de cylindres de béton. Des essais furent réalisés pour différentes combinaisons de températures (+20°C à −40°C) et de taux de déformation typiques d’événements sismiques (quasi-statique à 0.1 /s). L’objectif principal de ces essais était de donner une indication sur les effects combinés de ces deux paramètres sur les courbes contrainte-déformation, uniaxiales et monotones de ces matériaux. Les résultats de ces essais en traction indiquent que la limite élastique et la résistance à la traction de l’acier d’armatures s’accroissent légèrement lorsque que l’on observe à la fois une hausse du taux de déformation et une baisse de la température. Les résultats des essais de compression indiquent que la résistance à la compression et le module d’Young du béton augmentent de manière significantive quand le taux de déformation augmente et que la température baisse.

     

In situ imaging of multiphase bio-interfaces at the micro-/nanoscale

The multiphase bio-interfacial system constituted by biological surfaces and their surrounding environment is usually considered to be an essential clue for exploring the mysterious relationship between surface architecture and function. As a visualizing method to understand these systems, in situ imaging of multiphase interfaces (e.g., air/liquid/solid and oil/water/solid systems) at the micro-/nanoscale, still remains a huge challenge, as a result of their heterogeneity and complexity. Here, recent progress on real-space micro-/nanoscale imaging of multiphase bio-interfacial systems is reviewed; this includes several techniques and imaging results on bio-interfaces, such as the lotus leaf, fish scale, living cell's surface, and fresh tissue surface. The results evidently show that interfacial structures have a significant impact on the state of the microscopic multiphase interface, further influencing specific functions. Based on this research, technical innovations, some more complicated multiphase interface systems, and structure-function coupling mechanism are proposed.     

电场辅助原位合成TiB2-TiC-Ni/TiAl/Ti功能梯度材料及界面结构

采用电场激活压力辅助合成技术（FAPAS）并结合原位反应的方法制备TiB2-TiC-Ni/TiAl/Ti功能梯度材料,研究了TiB2-TiC-Ni/TiAl/Ti功能梯度材料的界面微结构特征及其结合强度,分析了梯度材料界面的微观组织和元素分布,并分析了试样的抗剪切强度和显微硬度。研究表明：制备的TiB2-TiC-Ni/...     

D-葡萄糖酸钠对模拟混凝土孔隙液中钢筋的缓蚀作用

应用电化学阻抗谱研究D-葡萄糖酸钠对含有氯离子的模拟混凝土孔隙液中钢筋的缓蚀作用,并对其缓蚀机理进行探索.结果表明,0.01mol/L D-葡萄糖酸钠对钢筋具有良好的缓蚀效果,其缓蚀作用主要是通过在钢筋表面和氯离子竞争吸附,最终形成一层吸附膜对钢筋起到保护作用.     

In situ observation and measurement of the SAW thin-film acoustoelectric effect

The thin-film acoustoelectric effect in SAW devices describes the interaction of electrical energy between a SAW in a piezoelectric medium and a thin film in the wave's propagation path. The real-time observation of the thin-film acoustoelectric interaction is useful in the design and characterization of SAW sensors (i.e., temperature, humidity, viscosity, voltage, current, Hall effects, etc.). An in situ test fixture was designed to be mechanically, thermally, and electrically stable. Data acquisition software and an electron beam evaporation system were configured for real-time thin-film characterization during film growth. Data have been observed for more than 20 SAW devices and over a wide range of frequencies (i.e., 62 MHz to 1 GHz). The results suggest that the use of the in situ procedure yielded good agreement between theoretical predictions and the measured data, which demonstrates a method for the characterization of a SAW H(2)-gas sensor in real-time.