Bridging early-age particle packing parameters and later surface electrical resistivity: mechanistic insights into silica fume cementitious systems

Electrical resistivity (ER) is a well-established property of cementitious materials, widely used as a durability parameter in the quality control and inspection of concrete structures. However, the relationship between ER and particle packing parameters remains unclear. This study investigates how the water-to-binder ratio, solid particle packing parameters, and the water film thickness (WFT), a spatial parameter that defines interparticle spacing, correlate with surface electrical resistivity (SER) in cementitious pastes with silica fume (SF) replacement at ratios of 0%, 5%, 10%, 15%, and 20% (by weight). The SER measurements were carried out from 7 to 180 days. In addition, the study investigates compressive strength, thermogravimetric analysis (TGA), and eco-efficiency indexes. The results show a strong correlation among SER, particle packing parameters, WFT, and SF cement replacement. At 180 days, SER increases were approximately 480% (5% SF), 653% (10% SF), 438% (15% SF), and 877% (20% SF) compared with the control mixture. This non-linear trend, specifically the lower relative increase in SER observed for the 15% SF mixture compared to the 10% and 20% SF mixtures, is directly linked to a lower WFT, which spatially restricts the progression of the pozzolanic reaction, as evidenced by TGA. These findings provide novel mechanistic insights into the link between microstructural packing parameters and the electromechanical behaviour of cementitious materials. Regarding mechanical behaviour, initial clinker dilution reduced early-age strength for replacements exceeding 10%, but pozzolanic activity compensated at 28 days. SF improved the ecoefficiency of cementitious pastes by reducing cement consumption and the contributions of pozzolanic reactions.