Steel corrosion is major reason of the deterioration of reinforced concrete structures. Decreasing the transportation of erosion ions in concrete is one of effective methods to protect the steel from corrosion. In the present work, a novel nano-hydrophobic admixture is introduced to improve the ion-diffusion properties and the corrosion resistance of reinforced steel. Compared with unmodified concrete, the nano-hydrophobic admixture effectively decreases the water adsorption, water evaporation, and chloride ions transport in a concrete structure, and then improved the concrete’s durability. The concrete’s water adsorption decreased more than 78%, and the initial corrosion time of reinforced steel is prolonged more than one time by treatment with the nano-hydrophobic admixture. The inhibition penetration of the medium in concrete modified by hydrophobic nanoparticles is the key to provide the protective properties of steel reinforcement from chloride erosion.

As a kind of coating material, the inorganic coating of alkali-activated metakaolin geopolymer cured at high temperature has been studied a lot for special applications. To our best knowledge, however, not much attention has been given to investigate the influence of SiO₂/Na₂O molar ratio on property of the geopolymer coating. This paper is, thus, dedicated to investigate the role of SiO₂/Na₂O molar ratio on property and microstructure of metakaolin-based geopolymer coating at ambient temperature. The effects on setting behavior, adhesive strength, shrinkage deformation and permeability are discussed. Multiple experiments were used to reveal microstructure changes of the geopolymer coating with different ratios of SiO₂/Na₂O, including Mercury Intrusion Porosimetry (MIP), Scanning Electron Microscope (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). The results indicated that the optimal ratio of SiO₂/Na₂O was 1.0 for good properties of adhesive strength, shrinkage and impermeability. In addition, it has been found that the setting time of geopolymer coating increased with SiO₂/Na₂O ratio which increased from 0.8 to 1.5. That agrees well with the other property and results of exothermal rate of alkali-activated metakaolin. As for the microstructural changes, the SiO₂/Na₂O ratio of 1.0 reduced pore size and porosity of the geopolymer coating and particularly increased volume percentage of pores with a size lower than 20 nm. Besides, FTIR results suggested that geopolymer prepared by the ratio of 1.0 was likely to produce more heterogeneous geopolymer due to a greater silicate structural reorganization.

The damage development trend of concrete with cracks in salt‐freezing environment is systematically studied. The cracks are also tested in intact concrete for comparison, and crack characterization is introduced. The mass loss, the relative dynamic elastic modulus, and the change of crack width are analyzed. Results show that the crack width increases as the salt‐freezing cycle progresses. Following the development trend of the cracks, concrete cracks can be divided into three categories: 0–40, 40–100, and 100–150 μm. The mass loss increases significantly, and the change of relative dynamic elastic modulus decreases in concrete with an initial crack compared with the intact concrete. When the crack width is 80 μm, a maximum mass loss rate of 0.19% and a minimum relative dynamic elastic modulus of 75.81% can be obtained. These test results prove that crack and freeze‐thaw coupling can influence each other and accelerate the failure of concrete. Overall, this study can serve as a basis for the durability design and life improvement of concrete structures.

Integral hydrophobic treatment is the most effective method to prolong the service life of the concrete by resisting the transport of water containing aggressive ions. The hydrophobicity phenomenon of cementitious materials with carboxylic acid type admixture has been presented, and experimental studies, including water adsorption, amount of hydration products, and pore system, are conducted to reveal the hydrophobicity mechanism. It is reported that cementitious materials containing hydrophobic admixture present excellent water resistance ability, and the experimental results of nitrogen adsorption isotherm show that carboxylic acid type admixture addition increases pore volume and surface area of cement pastes. In addition, the fractal geometry theory is applied to reveal the relation between the pore structure and the permeability coefficient of cement pastes with a hydrophobic agent. In conclusion, the high tortuosity fractal dimension and the hydrophobicity of the pore surface result in water resistance when the cementitious system is mixed with a new type of hydrophobic admixture.

Physical salt attack (PSA) is one of the dominant durability issues of cement-based materials, where salt crystallization pressure is the driving force inducing damage. However, research on the temperature-related deterioration behavior of cement-based materials is limited. In this study, salt-contaminated cement mortars were rewetted at different temperatures. The assessment criteria were based on the visual appearance, weight evolution and size distribution of scaled materials, and the alterations in the microstructure were investigated by microscopy, thermal and mineralogical analyses. The results indicated that more severe damage developed at 5 °C than that at 20 °C due to the greater crystallization pressure caused by the conversion from thenardite (Na₂SO₄) to mirabilite (Na₂SO₄·10H₂O) at the lower temperature. No damage was observed at 35 °C, since the repeated dissolution and re-crystallization of thenardite were harmless for the specimens. In addition, two distinct damage patterns were observed for PSA performed at 5 °C and 20 °C, namely, granular disintegration and contour scaling.