Salt frost scaling depths in cement-based materials: A surface structure analysis of drying effects and aggregate grading

The durability of concrete in cold climates is substantially degraded by freeze-thaw cycles and de-icing salts, yet standard laboratory tests often fail to predict field performance due to unrealistic continuous saturation conditions. This study investigates the effect of more realistic environmental conditioning, specifically preconditioning and intermittent drying periods, on the salt frost scaling of concrete. Utilizing high-resolution 3D laser scanning, this work, for the first time, conducts a spatially resolved surface structure analysis of scaling depths on mortars and concretes made with various cement types, including Portland, limestone, composite, and blast furnace slag cements. A primary finding is that intermittent drying induces an additional weakened near-surface layer due to drying shrinkage-induced micro-cracks and carbonation. This layer causes an initial acceleration of scaling immediately after the drying period. However, the corresponding reduction in the material’s degree of saturation leads to a decreased scaling rate in subsequent freeze-thaw cycles. The extent of this behavior is primarily dependent on the cement type. Blast furnace slag cement, in particular, showed increased susceptibility to scaling when exposed to CO 2 during drying. Furthermore, the spatially resolved analysis revealed that concrete experienced more severe scaling than mortar, with damage initiating in a crater-like pattern around larger aggregates, highlighting the vulnerability of the interfacial transition zone. These results demonstrate that incorporating drying cycles is essential for realistic laboratory assessment and provide a deeper mechanical understanding of how moisture dynamics and material composition govern salt frost scaling, helping to bridge the gap between laboratory results and real-world performance. • Evaluation of salt frost scaling depth utilizing 3D laser scanning data. • Dry preconditioning reduces surface scaling due to decreased moisture content. • Intermittent drying increases early scaling but induces long term reduction. • Near-surface ITZ of aggregates increases surface scaling depths depending on size.