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In order to prolong the service life of cement-based materials subjected to external chloride ion attacks, two kinds of methods, a surface treatment and chloride immobilization, were combined by fabricating a nanosilica-modified cement paste and coating it on mortar samples as a surface treatment material (HSM). The protective effect of the HSM was evaluated according to its surface hardness, and an RCM test was carried out, which indicated that the attached layer could both increase the surface hardness and decrease the chloride diffusion coefficient. Then, the chloride immobilization mechanisms were illustrated in terms of chloride blocking resistance, chemical binding and physical binding X-ray diffraction (XRD), and thermogravimetric/derivative thermogravimetric (TG/DTG) and thermodynamic modeling. The results showed that the hybrid nanomaterials that modified the cementitious surface treatment materials may effectively improve the chloride-resistant property of a matrix with content of no more than 1%. This research outcome could provide evidence that hybrid nanosilica can be applied in surface treatment technology. [ABSTRACT FROM AUTHOR]

This research investigated the impact of substituting sand with graphite tailings (GT) on the chloride ion erosion resistance of recycled aggregate concrete (RAC). The role of GT is to significantly inhibit the penetration of chloride ions into the interior and slow down the corrosion process. However, the durability of graphite tailings recycled aggregate concrete (GTRAC) still depends on the replacement rate of recycled aggregate. At the same time, a multi-scale dynamic model of physical adsorption-chemical binding-free transport and erosion of chloride ions in GTRAC were established based on unsteady viscous fluid force and molecular dynamics. • The purpose of improve the sulfate attack performance of concrete by GT was proved. • The Proportioning design was optimized for improving the performance. • The mechanism of action of GT was discussed. • A multi-scale dynamic model was established in this paper. [ABSTRACT FROM AUTHOR]

Carbonation durability is an important subject for recycled coarse aggregate concrete (RAC) applied to structural concrete. Extensive studies were carried out on the carbonation resistance of RAC under general environmental conditions, but limited researches investigated carbonation resistance when exposed to chloride ion corrosion, which is an essential aspect for reinforced concrete materials to be adopted in real-world applications. This paper presents a study on the carbonation durability of two generations of 100% RAC with the effect of chloride ion corrosion. The quality evolution of recycled concrete coarse aggregate (RCA) with the increasing recycling cycles was analyzed, and carbonation depth, compressive strength and the porosity of RAC were measured before and after chloride ion corrosion. The results show that the effect of chloride ion corrosion negatively affected the carbonation resistance of RAC, and the negative effect was more severe with the increasing recycling cycles of RCA. Chloride ion corrosion led to a decrease in compressive strength, while an increase in carbonation depth and the porosity of RAC. The equation of concrete total porosity and carbonation depth was established, which could effectively judge the deterioration of carbonation resistance of RAC. [ABSTRACT FROM AUTHOR]