Investigating Damage Evolution of Concrete with Silica Fume Under Freeze–Thaw Conditions Using DIC Technology and Gray Model Approach

Silica fume (SF) is extensively utilized for enhancing concrete properties. This study examines the impact of SF dosage on concrete frost resistance. Specimens were produced by replacing cement with SF at 5%, 10%, 20%, and 30% ratios. Mechanical testing and microscopic characterization measured variations in mass loss, relative dynamic elastic modulus, flexural strength, hydration products, and pore structure. Digital image correlation tracked failure development during flexural tests. Results indicated that SF-modified concrete showed lower mass loss, better elastic modulus retention, and improved flexural strength maintenance compared to plain concrete after identical freeze–thaw (F-T) cycles. Additionally, SF-modified concrete demonstrated reduced crack widths and slower crack expansion during bending. The 10% SF mixture, after 300 cycles, achieved optimal results characterized by 2.83% mass loss, 88.1% relative dynamic modulus, and only a 17% flexural strength reduction. Microscopic studies confirm that SF addition increases calcium silicate hydrate formation, decreases calcium hydroxide levels, and refines pore structure with higher density. These modifications enhance frost resistance. A service-life prediction model using gray model approach methodology projected that 10% SF concrete would last 2.01 times longer than unmodified concrete under F-T exposure.