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The combination of realkalisation and migrating corrosion inhibitor (MCI) was proposed as a protective technique for structures subjected to carbonation-induced corrosion; the effects on passivated steel bars in partly carbonated concrete were investigated. The corrosion behaviours of treated steel bars under three exposure conditions (natural indoor environment, accelerated carbonation and simulated carbonated concrete pore solution) were examined and the effects of amino-alcohol-based and amino-carboxylate-based MCIs were compared. The surface morphology of steel bars was observed by scanning electron microscopy, which indicated that MCIs could be adsorbed on the bar surfaces. Moreover, potentiodynamic polarisation curves were obtained and electrochemical impedance spectroscopy was performed. Results corresponding to a natural indoor environment and accelerated carbonation showed that current would destabilise the passivated steel bars but that the corrosion resistance of treated steel bars was significantly enhanced. According to the results in simulated carbonated concrete pore solution, the corrosion behaviour of steel bar was related to the type of MCI and the treatment parameters. Compared with amino-carboxylate-based MCI, the adsorption of amino-alcohol-based MCI was more stable although it was weakened with a decrease in pH. In general, treatment by realkalisation and MCI is more effective than simple application of realkalisation or MCI. [ABSTRACT FROM AUTHOR]

Through direct shear tests, this paper aimed to research the effect of fine marble aggregate on the shear strength and fractal dimension of the interface between soil and concrete corroded by sulfuric acid. More realistic concrete rough surfaces than the artificially roughened surfaces were formed by immersing four concrete plates in plastic buckets filled with sulfuric acid for different periods of time. The sand was adopted to imitate the soil. 3D laser scanner was employed to obtain the digital shapes of concrete plates subjected to sulfuric acid, and the rough surfaces were evaluated by fractal dimension. Large direct shear experiments were performed to obtain the curves of the interface shear stress and shear displacement between sand and corroded concrete plate. The method of data fitting was adopted to calculate the parameters of shear strength (i.e., friction angle and the cohesive) and the parameters of the Clough–Duncan hyperbolic model. The results indicated that as the corrosion days increased, the surface of the concrete plate became rougher, the surface fractal dimensions of the concrete corroded by sulfuric acid became bigger, and the interface friction angle became greater. The friction angle of the interface and the fractal dimensions of the surface of the concrete plate containing crushed gravel and marble sand were smaller than that of the concrete plate containing crushed gravel and river sand. [ABSTRACT FROM AUTHOR]

When exposed to sulfuric acid environments, the service life of concrete structures would be reduced due to the high alkalinity of concrete. The influence of three factors including water/cement ratio, the pH value of the solution, and the chemical composition of the aggregate on the resistance of concrete subjected to sulfuric acid has been widely investigated by previous researchers. This paper aims to investigate the influence of these three factors on the durability evaluation indicators including mass loss and surface fractal dimension through orthogonal experiments, which has been reported rarely in previous research. Four combinations of coarse and fine aggregate including gravel and river sand, gravel and crushed marble sand, crushed marble stone and river sand, and crushed marble stone and marble sand were adopted, and three water/cement ratios including 0.35, 0.45, and 0.55 were selected, and the sulfuric acid solution pH values 0.95, 2, and 4 were chosen in this paper. The results showed that the larger the water/cement ratio, the smaller the mass loss and the surface fractal dimension of the specimens, and with the decrease of the pH value of the sulfuric acid solution, the mass loss and the surface fractal dimension of the specimens would be increased. The concrete specimen containing gravel and river sand had the greatest surface fractal dimension and greatest mass loss, while the concrete specimen containing crushed marble sand had a smaller surface fractal dimension and a smaller mass loss. The dominant and secondary order of three factors on mass loss and surface fractal dimension of concrete subjected to sulfuric acid was the pH value of the solution > the chemical composition of the aggregate > the water/cement ratio. [ABSTRACT FROM AUTHOR]

• Relevance and applicability of migration test and diffusion test for GRPC studied. • Both test showed that GRPC has excellent chloride penetration resistance. • Chloride ingress resistance improved at later age due to pozzolanic activity of RP. • Pore structure was refined due to pozzolanic activity of RP. • Appropriate test age in migration test should be selected for GRPC. Green reactive powder concrete (GRPC) with recycled powder (RP) from construction waste has been developed. To determine chloride ingress, the relevance and applicability of two test methods, migration test and diffusion test, for GRPC were investigated. GRPC with different RP replacement was tested by both methods. The chloride penetration resistance is reduced at early age and improved at later age due to the pozzolanic activity of RP, which can produce C-S-H and refine the pore structure, as proved by MIP results. The migration test was recommended for RPC without RP, while for RPC with pozzolanic materials, appropriate test age should be selected. [ABSTRACT FROM AUTHOR]

Underground ant nests are typically made of soil and rubble mixed with dead plant bodies, ant secretions, and other organic substances. The clay content is high, and the natural clay materials show pozzolanic activity after calcination. In this study, the underground ant nest materials of Iridomyrmex anceps, which is a common ant in the Shanghai area, are calcined and ground, and the material properties of calcined ant nest clay powder (CANCP) are characterized from six aspects: chemical composition, particle morphology, specific gravity, specific surface area, particle size distribution and pozzolanic activity index. The pozzolanic activity of CANCP is evaluated by the strength contribution rate of pozzolanic activity, revealing that CANCP is beneficial to the strength of the mortar system from an early age. The influence of CANCP on the compressive strength of concrete is analyzed using three aspects, namely, content, curing age and calcination temperature, and it is found that the three aspects of CANCP have a strong influence on the compressive strength of concrete. [ABSTRACT FROM AUTHOR]

• Laser scanning technology could be applicate to digitize the concrete surface corroded by sulfuric acid. • The corrosion depth of concrete subjected to sulfuric acid could be expressed as a Gaussian random process. • As the corrosion time increased, the mean of the corrosion depth became larger and the distribution of the corrosion depth became more non-uniform. • Concrete corrosion depth predicted by the Gaussian random process model established by laser scanning method was considered to possess higher credibility and better security. Accurate prediction of corrosion depth degradation law can provide a basis for the determination of the sacrificial layer thickness and the cover thickness of the concrete structural members in a corrosive environment. This study aims to explore a more accurate and safe method to predict corrosion depth. Six sets of concrete cylinder concrete specimens were adopted to perform an accelerated corrosion test in sulfuric acid solution with pH ≈ 0.95 for six different scheduled durations. 3D coordinates of a large number of points on the corroded cylindrical surface were obtained with the help of the 3D laser scanning technology. Then, a comparative study was carried out for the corrosion depth measured with the laser scanning method and vernier caliper method. The results prove that concrete corrosion depth predicted by the Gaussian random process model established by the laser scanning method was considered to possess higher credibility and better security. [ABSTRACT FROM AUTHOR]

• The irregular cross-sectional area of concrete were measured by laser scanners. • The stress–strain curves were obtained for concrete corroded by sulfuric acid. • The relationship between the mechanical propertiesand mass loss was explored. This study aims to provide some references on understanding the uniaxial compression behaviors of concrete corroded by sulfuric acid. Six groups of concrete cylinder specimens were immersed in sulfuric acid solution with pH≈0.95 for different days. 3D laser scanning technology was applicated to obtain 3D coordinates of the points on the corroded cylindrical surface. The irregular cross sectional areas of each specimen were calculated at intervals of 1 mm along the longitudinal axis by MATLAB. The elastic modulus, peak strain, ultimate strain and peak stress were calculated through the experimental complete stress–strain curves. It showed that as the corrosion time increased, the elastic modulus, peak strain and peak stress gradually decreased. The ultimate strain decreased first and then increased over time. The parameters of the stress–strain model including the ascending and descending stages were obtained by fitting the experimental data. The relationship between the mechanical properties and mass loss was explored. [ABSTRACT FROM AUTHOR]

This study investigates the influence of volume content of aggregates, maximum size and type of coarse aggregates, water-to-cement ratio and curing temperature on mechanical properties, i.e. prismatic compressive strength ( f c ), static modulus of elasticity ( E c ) and dynamic modulus of elasticity ( E d ) of concrete at early age. A new equation is proposed to correlate prismatic compressive strength and elastic moduli of concrete. Based on the experimental data and the analysis results, the E c – E d relationship is also proposed. It is found that the relationship between E c and E d is linear, and the coefficients of linear relationship are analyzed by multiple regression analysis, considering aggregate content, maximum size of the coarse aggregate, water-to-cement ratio and curing temperature. It is found that the volume content of aggregates is the most significant factor that influences the E c – E d relationship. [ABSTRACT FROM AUTHOR]