Search

The durability of concrete structures is often reduced owing to the corrosion of reinforcement in an aggressive environment. Ordinary reinforcement methods, such as wrapping section steel or steel plate, are also vulnerable to corrosion. Using 6061-T6 aluminium alloy as near-surface reinforcement of the concrete structure is a feasible method. In this study, the corrosion resistance of 6061-T6 aluminium alloy bars was studied by simulating the coastal environment, atmospheric environment, and concrete internal environment with chloride solution, simulated acid rain solution, and saturated Ca(OH)2 solution. The corrosion rate of the 6061-T6 aluminium alloy in the above environments was tested using a weight loss method, and its corrosion resistance was evaluated using the metal corrosion resistance classification standard. Based on the electrochemical reaction mechanism, the polarisation properties and AC impedance spectra of steel and 6061-T6 aluminium alloy were compared, and the corrosion resistance mechanisms of steel and the 6061-T6 aluminium alloy in the above corrosive environments were obtained. The results show that the 6061-T6 aluminium alloy has better corrosion resistance than steel bars in chloride and atmospheric environments, with corrosion currents of 0.012 and 0.037 µA·cm−2, and 8-day corrosion rates of 0.051 and 0.031 mm·a−1, respectively. However, owing to the activity of the aluminium alloy, its corrosion resistance in an alkaline environment inside concrete is poor; the corrosion current is 0.22 µA·cm−2 and the 8-day corrosion rate is 16.166 mm·a−1. The research results can provide a reference for applying aluminium alloy bars as external prestressed concrete bars and near-surface steel bars.

The reasonable inclusion of hybrid fibers can leverage the advantages of each kind of fiber and enhance the frost resistance and flexural toughness of concrete. Previous studies on hybrid steel-polypropylene fiber reinforced concrete (HSPFRC) focused primarily on its mechanics instead of its frost resistance. In this work, the compressive strength, splitting tensile strength, mass loss rate, relative dynamic elastic modulus (RDEM), and flexural toughness of HSPFRC after freezing-thawing (F-T) are studied, and the relative importance of each factor affecting the frost resistance of HSPFRC is quantified by using fuzzy rough set theory. The results show that the inclusion of hybrid fibers has a noticeable effect on the frost resistance of HSPFRC after hundreds of F-T cycles and that the effect on the splitting tensile strength is greater than that on the compressive strength. After 500 F-T cycles, as the steel fiber (SF) content increases, the compressive strength and splitting tensile strength increase by factors of approximately 5 and 4, respectively, the flexural toughness is strengthened, and the mass loss rate is reduced by more than 90%. The addition of polypropylene fibers (PFs) has a relatively small effect on the strength of HSPFRC but reduces the mass loss of HSPFRC by almost 80%. However, the suitability of the RDEM for evaluating the frost resistance of HSPFRC remains uncertain. Quantified by fuzzy rough set theory, the weights of the factors affecting the frost resistance of HSPFRC are 0.50 (number of F-T cycles) > 0.35 (SF content) > 0.15 (PF content), verifying the experimental results.

Chloride attack is the severe problem that coral aggregate concrete (CAC) structure must face to in the application. Chloride ion distribution brings by coral aggregates is hence an important concern. This laboratory study explored the effects of silica fume (SF) and granulated blast furnace slag (GBFS) on the mechanical properties and chloride ion distribution brought by coral aggregates in CAC. Three types of CAC were designed including fly ash (FA), SF, and GBFS CAC, FA CAC was used as a reference sample. Apart from the compressive strength of CAC, the splitting tensile strength, total chloride content (Ct), free chloride content (Cf), and chloride binding capacity (R) were measured. The hydration products, theoretical total pore volume (P), and interfacial transition zone (ITZ) of CAC were characterized by X-ray powder diffraction, Thermogravimetric analysis, and Scanning Electron Microscopy. The result indicated that SF and GBFS had a negative effect on the compressive strength, splitting tensile strength and R of CAC at the early ages. The long-term Cf of CAC decreased by the addition of SF, while, this value rises with the GBFS content. The long-term R of CAC became stronger with SF content, but it became weaker with GBFS content. In addition, the large content of SF or GBFS decreased the P of CAC. The ITZs of CAC became denser and homogeneous due to the pozzolanic activity of SF and GBFS as well as “internal curing” of coral aggregate.

In recent years, skin cancer has become one of the most common cancers. Among all types of skin cancers, melanoma is the most fatal one and many people die of this disease every year. Early detection can greatly reduce the death rate and save more lives. Skin lesions are one of the early symptoms of melanoma and other types of skin cancer. So accurately recognizing various skin lesions in early stage is of great significance. There have been lots of existing works based on convolutional neural networks (CNN) to solve skin lesion classification but seldom do they involve the similarity among different lesions. For example, we find that some lesions like melanoma and nevi look similar in appearance which is hard for neural network to distinguish categories of skin lesions. Inspired by fine-grained image classification, we propose a novel network to distinguish each category accurately. In our paper, we design an effective module, distinct region proposal module (DRPM), to extract the distinct regions from each image. Spatial attention and channel-wise attention are both utilized to enrich feature maps and guide the network to focus on the highlighted areas in a weakly-supervised way. In addition, two preprocessing steps are added to ensure the network to get better results. We demonstrate the potential of the proposed method on ISIC 2017 dataset. Experiments show that our approach is effective and efficient.

Diabetic Retinopathy (DR) is a leading cause of blindness. It often happens to people who suffer from diabetes and seldom has early warning signs. Automatically DR detection and severity grading are helpful for clinicians by providing a second opinion. An automatic classification system classifies fundus images into 5 degrees of severity. In this paper, we propose a DR grading model based on lesion correlation graph using Graph Convolution Network (GCN) and Convolution Neural Network (CNN). We extract the irregular lesion region by calculating SURF descriptors in the fundus image. We then clusters descriptors into a number of cluster centroids which is regarded as node representation. With the assistance of GCN, we learn lesion correlation. After fusing correlation information and fundus image feature, which is derived from CNN model, we obtain the final classification result. Furthermore, we provide two evaluation measures: accuracy and Cohen's Kappa value for comparison on different experiments. So far, our model achieves good result in several DR datasets. Contribution- We introduce the idea of utilizing correlations among lesions learned by GCN to improve the grading result.

Coal gangue, a by-product produced during the process of coal mining and washing, has a serious impact on the environment. Using coal gangue as a concrete aggregate has been proven helpful in potentially improving its value and reducing its environmental impact to a certain extent. However, the high water absorption and low strength of coal gangue aggregate cause a poor frost resistance of coal gangue aggregate concrete (CGAC), and thus limits its application in cold areas. This study attempted to modify the CGAC with steel fibers (including hooked-end, undulated, and copper-plated steel fiber) and slag powder, and investigated its frost resistance. Moreover, the impact that steel fiber and slag powder had on air-void characteristics of CGAC was also analyzed. The results show that when steel fibers were incorporated into CGAC, the compressive strength and splitting tensile strength of CGAC reduced significantly after freezing/thawing and that they experienced the smallest reduction when the content of the steel fiber was 1 vol.% and the undulated steel fibers worked best. However, the effect of slag powder on frost resistance of CGAC at an early age was not obvious, which may be related to the slower pozzolanic reaction of slag powder. Incorporating steel fiber or slag powder into CGAC can optimize its mesostructure and make the air-voids of concrete smaller, which is beneficial to its frost resistance. The results provide a good way to improve the performance of CGAC, expand its application in cold regions, and reduce the pollution caused by coal gangue.

The volume expansion of reinforcement corrosion products resulting from the corrosion of steel reinforcement embedded into concrete causes the concrete&rsquo, s protective layer to crack or spall, reducing the durability of the concrete structure. Thus, it is necessary to analyze concrete cracking caused by reinforcement corrosion. This study focused on the occurrence of non-uniform reinforcement corrosion in a natural environment. The characteristics of the rust layer were used to deduce the unequal radial displacement distribution function of concrete around both angular and non-angular bars. Additionally, the relationship between the corrosion ratio and the radial displacement of the concrete around the bar was established quantitatively. Concrete cracking due to the non-uniform corrosion of reinforcements was simulated using steel bars embedded in concrete that were of uneven displacement because of rust expansion. The distribution of the principal tensile stress around the bar was examined. A formula for calculating the critical radial displacement at the point when cracking began was obtained and used to predict the corrosion ratio of the concrete cover. The determined analytical corrosion ratio agreed well with the test result. The effect factor analysis based on the finite element method indicated that increasing the concrete strength and concrete cover thickness delays concrete cracking and that the adjacent rebar causes the stress superposition phenomenon.

As a new type of cement-matrix composite material, coral aggregate concrete exhibits excellent properties, such as local material availability and enhanced efficiency, while being cost-effective. Coral aggregate concrete can be viable for construction on islands and reefs. Reinforced concrete structures generally exhibit low durability in marine environments, owing to long-term corrosion by chloride salts. Therefore, resistance to chloride ion attacks plays a significant role in improving the durability of concrete structures. As a non-destructive testing technique, resistivity is used for characterising the resistance of concrete to chloride ion penetration. In this study, the resistivity of coral aggregate concrete is measured using an improved alternating-current test method, and the improved method overcomes the limitations that is prone to polarization reaction and heating of the solution under exposure to voltage for an extended period. Porosity was used to analyze the reasons for the different resistivity values of coral concrete from micro-aspects. The resistivity model at 365 days was established considering the effects of temperature, humidity, admixture, and water-binder ratio on coral aggregate concrete. The hydration characteristics of cement and admixture were used to establish a time-varying model for predicting the resistivity of coral aggregate concrete.

This study investigates the chloride transport performance of coral aggregate concrete (CAC) in a marine environment. The effects of the aggregate type, strength grade, and fly ash (FA) content on the chloride concentration distribution, surface chloride concentration (Cs), chloride diffusion coefficient (Da), and porosity are discussed. The results show that the higher the strength grade of CAC is, the lower the Cs and Da will be. The Cs and Da of CAC initially decrease and then increase with increasing FA content. The compressive strength of CAC has a negative correlation with the Da, whereas the porosity is positively correlated with Da. The Da of CAC is higher than that of ordinary aggregate concrete (OAC) at the same exposure time. The Cs of CAC increases exponentially with the erosion time. In addition, the attenuation law of Da with the exposure time can be expressed as a power function. The decay rate of CAC is relatively slow, and the age reduction factor (m) of OAC is 11.95% higher than that of CAC. Furthermore, the age reduction factor is positively correlated with the strength grade and FA content. The content of Friedel's salt decreases gradually with increasing CAC strength grade at the same exposure time; with increasing erosion time, the content of Friedel's salt also increases, but the magnitude of increase is reduced.

The stress relaxation behavior of cement and asphalt mortar (CA mortar) under different initial strain levels was investigated. Results show that the stress relaxation of CA mortar can be divided into two parts: the attenuation stress relaxation stage and stable stress relaxation stage. With the increasing strain levels, the relaxed stress, stress relaxation rate, stress relaxation modulus and specific stress relaxation of CA mortar increase gradually. Under the same initial strain level, the relaxed stress of type I CA mortar and type II CA mortar are little different, whereas the specific stress relaxation of type I CA mortar is much greater than that of type II CA mortar. In the strain range of 0.32–0.80%, the isochronous stress-strain relation of type I CA mortar is linear. When the strain is greater than 0.80%, the isochronous stress-strain relationship concaves to the strain axis gradually. The isochronous stress-strain relationship of type II CA mortar show linear increase in the strain range of 0.47–1.42%. A stress relaxation model based on thermodynamic theory was established, which agrees very well with the experimental results.

The pore characteristics of hybrid basalt–polypropylene fibre-reinforced concrete (HBPRC) are investigated using mercury intrusion porosimetry. The research results indicate that the cumulative pore volume of concrete increases with fibre addition. The pore surface fractal dimension (DS) of HBPRC in gel, capillary, and large pore regions decreases sequentially although it has no physical characteristics in a transition pore region. The incorporation of fibres has an insignificant effect on DS in gel and capillary pore regions; however, it has a reducing effect on DS in the large pore region. Furthermore, the greater the concrete strength, the larger DS becomes and the greater the reducing effect of fibres on DS in the large pore region. Through microscopic and mesoscopic analyses, it has been suggested that bubbles introduced by fibres and the weak dispersion of such fibres are the main reasons for the deterioration of the large pore structure of HBPRC.

The durability of concrete structures is influenced by various factors, and the durability damage mechanism is different when the structure is in different environmental conditions. This will have implications for improving the durability of concrete structures and extending its service life if the special environmental condition is taken into account in the durability design. Aimed at the environmental zonation for concrete durability, this paper investigated the durability factors influencing concrete structures in Shaanxi Province, China, including atmospheric temperature, precipitation, corrosive gas, and acid rain. The variations of the above-mentioned factors were analyzed and the indexes of environmental zonation were proposed. According to the zoning principle, the weights of zoning indexes calculated using fuzzy rough sets were used to divide Shaanxi Province into three first-level zones, namely the Freeze-Thaw Cycle Zone, the Neutralization&ndash, Freeze-Thaw Interaction Zone, and the Neutralization Zone. These three zones were then subdivided into nine second-level zones. The main mechanism of concrete deterioration and the environmental characteristics of all zones were then analyzed. The method proposed in this paper puts forward clear zoning indexes and quantifies them, which can improve the quality and accuracy of the zoning results. Moreover, the research achievements are helpful for engineers to reduce the impact of the environment on structure and the maintenance cost during the structural service life to a certain extent.

With the development of marine technology, the potential of coral aggregate concrete (CAC) for use in the construction of reefs has been identified. However, the shape, surface structure, high porosity, and chloride-ion-carrying properties of coral aggregates yield special microstructures and affect the mechanical properties and durability of CAC. This study investigates the effect of basalt fiber (BF) on the mechanical properties, chloride content carried in coral aggregates, and water absorption of CAC. The results indicate that with the increase in fiber content, the mechanical properties and water absorption resistance of basalt fiber reinforced coral aggregate concrete present an increasing trend then followed decreasing trend. Furthermore, 0.05% BF yields the highest improving effect on the mechanical properties and water absorption resistance at 28 days. Compared with the reference concrete, the compressive strength and splitting tensile strength of CAC with 0.05% BF increase by 9.87% and 1.36% at 28 days, respectively. When the fiber content continues to increase, the strengthening effect decreases, and cause adverse effects. The dissolution of chloride in coral aggregates was accelerated by 0.05% BF, while the chloride dissolution was inhibited by 0.1%–0.2% BF. Moreover, the microstructure of CAC is investigated to elucidate the enhancement mechanism of BF in terms of thermogravimetric analysis, theoretical total pore volume, fiber bonding performance, and fiber-matrix interfacial characteristics.

As a new type of cement-based composite material, coral aggregate concrete exhibits excellent performance in terms of using local materials, high efficiency and economy, and broad application prospects in the construction of ocean-going island reef projects. In this study, based on the corrosion mechanism of steel bars, the critical chloride concentration in coral aggregate concrete was obtained, and the model of the rebar corrosion initiation conditions was established. Combined with electrochemical test and power loading device, the stainless steel bar replaces an electrode in energized devices and it is the counter electrode in electrochemical test. A rapid determination method was proposed for chloride ions accelerated by the electric field by improving the anode energization acceleration method. The linear polarization resistance method and electrochemical impedance spectroscopy were used to analyze the time-dependent denaturation of the corrosion potential and corrosion current in the coral aggregate concrete. The corroded layer on the steel reinforcement surface was observed using scanning electron microscopy. The rebar corrosion rate in the coral aggregate concrete was 0.25 µA/cm2 at the beginning of steel corrosion, and the corrosion rate ratio in the coral aggregate concrete and common aggregate concrete was 1.67. Based on the similarity theory of life test, an accelerated life test was used to predict the durability life of the coral aggregate concrete structures.

Low strength of concrete and chloride attack introduced by coral aggregate limit the application of coral aggregate concrete (CAC) on the island far from the mainland. This investigation explores the effects of different amounts of basalt fiber (BF) on the Cl− distribution brought by coral aggregates, splitting tensile strength, and compressive strength in BF-reinforced CAC (BFRCAC). The CAC samples were fabricated incorporating four volume fractions of BF (0.05, 0.1, 0.15, and 0.2 vol%) and without BF which used as the contrast group. The theoretical total pore volume of BFRCAC was calculated on the basis of thermogravimetric (TG) and the hydration products of BFRCAC was analyzed by X-ray powder diffraction (XRD). Furthermore, the surface topography and role of BF in CAC was analyzed using scanning electron microscopy (SEM). The results indicated the compressive strength and splitting tensile strength of CAC were enhanced by incorporating BF, and the addition of 1.5 vol% or 2.0 vol% BF has a better impact. The inclusion of 0.05% BF accelerates the exudation of chloride ions from the coral aggregate. In contrast, a dosage of BF above 0.05% can suppress the exudation of chloride ions. The results of XRD and TG demonstrated the Cl− in CAC from coral aggregate combined in the shape of Friedel’s salt. SEM can observe the BF tightly bonded to the CAC and the microcracks were controlled by BF, which is contribute to reduce the exudation of chloride ions in the aggregate.

In view of the abnormal phenomena in the movement of the 4-stage hydraulic cylinder, this paper establishes the basic motion model of the multi-stage hydraulic cylinder by melting point nodal cavity method, and analyses the variation law of its external load. On this basis, the erection process of the multi-stage hydraulic cylinder is simulated and analyzed by AMESim, and it is found that the sudden change of pressure at the change of the stage will cause the vibration of the multi-stage. Found that the abnormal vibration of the third piston occurs during the retraction process of the hydraulic cylinder, which is caused by the insufficient guide distance of the 3 stage piston of the multi-stage hydraulic cylinder. The sealing conditions of the piston and the guide sleeve are improved by increasing the guide length of the piston appropriately, and the correctness of the improved scheme is verified by the way of simulation, that is, it can effectively suppress the vibration of the third piston. Vibration occurs during retraction. Some improvement suggestions are provided for vibration reduction of multi-stage hydraulic cylinder.

Given the different hydration processes of ordinary concrete, shotcrete with low-alkali accelerator not only has short final setting time and high early age mechanical properties but also different hydration products. Shotcrete microstructure was studied at different curing ages by X-ray diffraction, thermogravimetry–differential scanning calorimetry, and scanning electron microscopy to investigate its hydration process. The pore structure and permeability of shotcrete were also tested. The mechanical properties of shotcrete were then studied. Results showed that under the effect of accelerator, the retarded action of gypsum disappeared in the cement–accelerator–water system. C 3 A hydrated quickly to form calcium aluminate hydrate (CAH) crystals, and a mesh structure was formed by ettringite, albite, and CAH. A large amount of hydration heat improved the hydration rate of the cement clinker mineral and the density, thus leading to high mechanical properties at the early curing age. The setting time of pastes increased with increasing water–binder ratio and fly ash (FA) dosage. Thus, the hydration process and the microstructure and morphology of the hydration products changed. Excessive water and FA increased the percentage of pores in shotcrete, which directly caused poor permeability. The permeability and compressive strength were poor when the FA dosage was 30% compared with that of 20%. Based on the investigation, a simple 0.5 power relationship between compressive strength and splitting tensile strength of mixture S2, meanwhile, there was an exponential relationship between mechanical performance and permeability or porosity, respectively.

Proper chemical treatment of recycled carbon fiber composites (RCFC) has been demonstrated to potentially add value to them, by improving the performance of cementitious materials incorporating them. This laboratory investigation mainly explored the use of saturated (simulated concrete) pore solution (SPS) to treat RCFC that contains cured epoxy resin, before its use in cementitious mortar. A total of seven mortar mixtures were fabricated, incorporating untreated RCFC, RCFC treated by SPS for different time periods followed by triisopropanolamine (TIPA), or RCFC treated by montmorillonite nanoclay emulsion (mNCE, at the nanoclay dosage of 0.75% by weight of cementitious binder). The water-to-binder (w/b) ratio of all mortar mixtures was 0.50 and the RCFC was admixed at 1% by volume. The compressive strength and splitting tensile strength of RCFC reinforced mortar were evaluated. The chemical characterization (by FTIR), thermogravimetric analysis, and microscopic investigation (by SEM) helped explain the observed engineering performance data. The residue epoxy resin on the surface of the RCFC was removed by the immersion in SPS, but a long-time treatment may result in damage of the fiber surface. The chemical treatment of RCFC showed both mechanical and chemical benefits to its adhesion with the cementitious mortar. Admixing mNCE achieved outstanding strengths of the mortar similar to those of mortars treated by SPS for 0.5 h and then TIPA.

This paper describes an experimental study of the seismic performance of steel-reinforced recycled concrete (SRRC) columns. Based on low cyclic loading tests of seven 1:2.5-scaled column specimens, the failure modes, hysteresis loops, skeleton curves, ductility, energy dissipation capacity, and stiffness degradation of SRRC columns were analyzed. The influence of recycled coarse aggregate (RCA) replacement percentages, axial compression ratios, and stirrup ratios on the seismic performance of SRRC columns was investigated in detail. The test results show that the seismic performance of SRRC columns decreases slightly as the RCA replacement percentage increases. The results also indicate that appropriate design of the axial compression ratio and stirrup ratio can improve the seismic performance of SRRC columns. The average values of the ductility factor and the equivalent viscous damping coefficient with respect to the loop of ultimate load of the columns were 3.47 and 0.217, respectively, which reflect the SRRC columns’ good performance in terms of earthquake resistance.

Environment is the external factor that affects the durability of concrete structures. Buildings in different regions with different climates will respond to durability deterioration in different ways. For macroenvironmental regionalization, the dominant factor analysis method of the climatic zonation was applied into the environmental regionalization in this paper. Based on the environmental characteristics in China and the effect of environmental factor on the durability of concrete structure, the proper regionalization indexes are chosen, and the environmental regionalization is made. For microenvironmental regionalization, fuzzy set and rough set theories were used in date mining on discrete measured data, and the weight determination of various factors affecting durability was transformed into evaluation of the significance of attributes among rough sets. The method of durability environmental regionalization is established by analyzing the degree of influence that various factors have on the durability of concrete structures. The result of durability environmental regionalization for concrete structures in Shenzhen city shows that the proposed approach is reasonable.

Concrete carbonation is one of the most significant causes of deterioration of reinforced concrete structures in atmospheric environment. However, current models based on the laboratory tests cannot predict carbonation depth accurately. In this paper, the BP neural network is optimized by the particle swarm optimization (PSO) algorithm to establish the model of the length of the partial carbonation zone for concrete. After simulation training, the improved model is applied to a concrete bridge for carbonation depth prediction. The results show that the improved model, which has faster a convergence rate, has a good ability in predicting the length of the partial carbonation zone of the reinforced concrete, and the predicted value matches the field-measured value very well, which provides scientific guidance to durability design, assessment, and life prediction for concrete structures.

The service life of many concrete structures depends upon their resistance to chloride ingress. Service life models estimate the time required for chloride ions to reach the reinforcing steel, to build up a critical concentration, and to initiate corrosion. Fick’s second law and the Nernst–Planck equation are two of the more popular methods that are used to estimate chloride ingress. While chloride ions are usually the primary consideration, in general they are not present by themselves. The co-present cations and anions can influence the rate of chloride ingress. This paper discusses how the apparent chloride diffusion coefficient, based on Fick’s second law, is dependent on the chemical composition and concentration of the ponding solutions. This study examines the influence of the chemical composition and concentration of solutions on the chloride binding capacity, on the consequential microstructural changes as determined with scanning electron microscopy using energy dispersive X-ray spectra (SEM-EDS), on the surface charges of the pore walls, and on the overall chloride ingress of the concrete materials. Chloride ingress predictions based on the Nernst–Planck equation were also compared with the experimental chloride profiles. The Nernst–Planck approach provided good predictions at low salt concentrations (less than 1.0 mol/L NaCl) using a single porosity, tortuosity, and binding approach. At higher concentrations, the binding and change of microstructure was under-predicted, and thus the chloride ingress was over-estimated.