Search

This paper assessed the electromigration behavior of ethanolamine and its efficiency as a corrosion inhibitor of rebar during the realkalization. Cylindrical concrete specimen (diameter 45 mm, height 20 mm) with steel rebar (6 mm in diameter, 35 mm in length) were artificially carbonated and corroded in an accelerated manner with impressed anodic current. The specimens were realkalized in the electrolyte solution containing ethanolamine, while the steel rebars were connected to the cathodic current (200 mA·h, 1 A/m2). After 25 days of monitoring the repair process, experimental data revealed notable changes in electrochemical parameters. The corrosion potential increased from −627 mV to −236 mV, signifying a reduction in corrosion activity. The cathodic exchange current density decreased from 4.9 μA/cm2 to 2.3 μA/cm2, showing a decrease in the corrosion rate. Also, the pH value of the solution dropped to a comparatively lower level, the ethanolamine and potassium ion concentrations decreased from 22 to 30.54 g/L to 3.22 and 10.23 g/L, respectively. Moreover, nitrogen detection on the steel surface and varied levels of ethanolamine concentration at different depths in the concrete were also measured, both indicating a clear migration of inhibitor to the steel surface to form a passive film.

The durability of concrete is determined by its pore structure and permeability. The present work examines the effect of pore structure and porosity on the permeability of concrete after nearly a century natural carbonation. The samples were cored from a concrete building built in 1931. X-ray diffraction analysis, phenolphthalein dye test, Mercury Intrusion Porosimetry (MIP) were conducted to ascertain the composition, the carbonation depth, the permeability, the porosity and pore size distribution of samples. The experimental results revealed that the front of core samples was completely carbonated. The fractal dimension was calculated using the Mandelbrot model to characterize the pore structure. The combined harmless and less harmless pore proportions exhibited a linear correlation with the fractal dimension. A relationship between permeability and fractal dimension is established. The increase in the fractal dimension resulted in a gradual decrease in the oxygen diffusion coefficient. The diffusion coefficient tends to plateau when the fractal dimension exceeds a critical value of the combined pore proportion. While the pore proportion of concrete was higher than 14.64%, there was no significant effect on the permeability. The results of this study can serve for future assessments of concrete durability.

This paper reports the corrosion inhibition effect of the realkalization and corrosion inhibitors combination treatment on steel rebars. First, the corrosion was studied in simulated carbonated concrete and simulated realkalized concrete environments and then compared with the corrosion, while realkalization-corrosion inhibitor treatment was applied. The corrosion inhibitors studied are monoethanolamine (MEA), dimethylethanolamine (DEMA) and triethylenetetramine (TETA). Through the electrochemical measurement; the potential of steel rebars in realkalized environment containing MEA and DMEA shifted in positive direction by 84 mV and 66 mV; the current destiny of each group decreased by 3.76 and 2.33 μA/cm2, respectively. Unlike the addition of TETA shifted the potential in negative direction by 281 mV and increased the current density by 27.72 μA/cm2. Comparing steel rebars surfaces, the realkalization-corrosion inhibitors groups showed a better inhibition effect than the two control groups (simulated carbonated concrete and simulated realkalized environments). Among the corrosion inhibitors used, MEA has the best corrosion inhibition effect in the electrochemical realkalized concrete environment, it can form a protective film on the steel rebars through physical and chemical adsorption, which can effectively inhibit the corrosion of steel rebars. The result confirms that, by the combination of MEA and electrochemical realkalization, the corrosion inhibition in carbonated reinforced concrete can improve significantly.

This paper reports on the utilization of recycled moso bamboo sawdust (BS) as a substitute in a new bio-based cementitious material. In order to improve the incompatibility between biomass and cement matrix, the study firstly investigated the effect of pretreatment methods on the BS. Cold water, hot water, and alkaline solution were used. The SEM images and mechanical results showed that alkali-treated BS presented a more favorable bonding interface in the cementitious matrix, while both compressive and flexural strength were higher than for the other two treatments. Hence, the alkaline treatment method was adopted for additional studies on the effect of BS content on the microstructural, physical, rheological, and mechanical properties of composite mortar. Cement was replaced by alkali-treated BS at 1%, 3%, 5%, and 7% by mass in the mortar mixture. An increased proportion of BS led to a delayed cement setting and a reduction in workability, but a lighter and more porous structure compared to the conventional mortar. Meanwhile, the mechanical performance of composite decreased with BS content, while the compressive and flexural strength ranged between 14.1 and 37.8 MPa and 2.4 and 4.5 MPa, respectively, but still met the minimum strength requirements of masonry construction. The cement matrix incorporated 3% and 5% BS can be classified as load-bearing lightweight concrete. This result confirms that recycled BS can be a sustainable component to produce a lightweight and structural bio-based cementitious material.

The cracks in concrete are a fast transport path for chlorides and influence the service life of concrete structures in chloride environments. This study aimed to reveal the effect of crack geometry on chloride diffusion in cracked concrete. The chloride diffusion process in cracked concrete was simulated with the finite difference method by solving Fick’s law. The results showed that the apparent chloride diffusivity was lower in more tortuous cracks, and the cracks with more narrow points also showed lower apparent chloride diffusivity. For tortuous cracks, a higher crack width meant relatively more straight cracks, and consequently, higher apparent chloride diffusivity, while a lower crack width resulted in more tortuous cracks and lower apparent chloride diffusivity. The crack depth showed a more significant influence on the chloride penetration depth in cracked concrete than crack geometry did. Compared with rectangular and V-shaped cracks, the chloride diffusion process in cracked concrete with a tortuous crack was slower at the early immersion age. At the same crack depth, the crack geometry showed a marginal influence on the chloride penetration depth in cracked concrete during long-term immersion.

Permeability of concrete is regarded as a basic indicator of its durability. This paper proposed a simple model to predict the permeability of engineered cementitious composites (ECC), which are fiber reinforced cementitious composites with extremely high ductility and toughness. The permeability of cement paste in ECC was firstly determined based on the general effective media theory. The needed microstructure information of cement paste was obtained from a simulated microstructure. Porosity of the interfacial transition zone (ITZ) was obtained with an ITZ porosity model, and then used to calculate the permeability of ITZ. The permeability of the matrix was determined according to the general self-consistent scheme, and the influence of fiber was simplified with its volume fraction. The calculated permeability of ECC was verified with results from water permeability tests and the accuracy of the model was acceptable for cement-based materials.