Understanding how pore-system geometry governs mechanical performance remains essential for designing slag-blended cementitious materials. This study investigates the time-dependent coupling between porosity P and fractal dimension D and its implications for strength development and brittleness evolution in cementitious materials with slag dosage variation (0–40%). Compressive strength (fc), flexural strength (ff), the compressive-to-flexural strength ratio (fc/ff, used as a practical brittleness proxy), porosity (%), fractal dimension, and low-field nuclear magnetic resonance (LF-NMR) permeability (k, mD) were evaluated at 3, 7, and 28 days. Results reveal a pronounced age dependence in microstructure–property relationships. At 28 days, increasing slag dosage led to monotonic pore refinement and geometric reorganization, evidenced by reduced porosity (4. 84% → 3. 88%), increased fractal dimension (2. 754 → 2. 820), and decreased permeability (0. 00025 → 0. 00011 mD), accompanied by enhanced mechanical performance (47. 73 → 49. 33 MPa in fc; 6. 34 → 7. 11 MPa in ff) and reduced brittleness (fc/ff: 7. 53 → 6. 94). In contrast, a critical 7-day decoupling was observed: slag mixtures exhibited substantially lower porosity (≈5. 42–5. 69% vs. 7. 07% for the reference) yet lower compressive strength (≈34. 81–35. 29 MPa vs. 38. 65 MPa), indicating that porosity alone is insufficient to interpret early-age compressive capacity. Across ages, permeability and fractal trends highlight the role of pore-network connectivity and geometric complexity in governing transport resistance and fracture-related behavior. Overall, the findings demonstrate that a time-dependent porosity–fractal coupling framework provides a coherent pathway “from pore geometry to strength, ” particularly for brittleness-relevant indices where geometric effects are amplified.
Huang et al. (Thu,) studied this question.