Investigation of surface scaling and internal damage in concrete using the slab test

Concrete structures in cold climates are particularly vulnerable to deterioration from F-T cycles, especially in the presence of deicing salts. Such exposure can cause both surface scaling and internal microstructural damage, threatening long-term durability and service life. While surface scaling is readily observable, internal deterioration often develops unnoticed, highlighting the importance of combined evaluation methods. This study investigates the influence of binder type, water-to-binder ratio and air content on the salt F-T resistance of concrete. Fourteen mix designs were prepared and tested according to the slab test method (CEN/TS 12390-9), with three key focuses including quantification of surface scaling over both early (0–14 days) and extended (14–56 days) F-T phases, evaluation of internal damage using ultrasonic pulse velocity (UPV), and measurement of liquid uptake and hardened porosity to analyse their effects on the damage. Compressive strength tests were also performed for complementary analysis. The collected data allows correlations to be drawn between surface scaling, internal cracking, and liquid transport properties, providing insights into how material parameters and preconditioning processes govern F-T performance. The findings also indicate which combinations of binder type, water to binder ratio, and air content most effectively improve resistance to salt scaling and internal damage, thereby contributing to guidelines for designing durable concrete in cold and saline environments. Results show that the presence of an adequate air-void system and lower water to binder ratio is the governing parameter for salt-frost durability. Non-air-entrained mixtures experienced catastrophic failure, characterized by simultaneous high surface scaling and severe internal microcracking (up to 28% loss in RDM). In contrast, air-entrained mixtures maintained excellent structural integrity and low mass loss in general. Active liquid uptake during the freeze-thaw cycles exhibited a strong positive correlation with both scaling and internal damage, serving as a more reliable predictor of failure than static capillary porosity. Additionally, anal-ysis of the scaling process revealed that evaluating the scaling rate at 14 cycles onward effectively separates intrinsic material durability from initial surface vulnerabilities. While slag-blended cements (CEM III/A) exhibited slightly higher early-age scaling, their steady-state deterioration rates remained highly stable when adequately air-entrained.