The anchor design for Low-Carbon Concretes still lacks parameters that link microchemistry to structural performance. This work introduces a microstructural coefficient \(\eta\) , defined from gel density and interfacial porosity of the N-A - S-H / C - A - S-H networks, to extend the classical Tepfers. The analytical derivation shows that \(\eta\) multiplies the circumferential stress solution without altering its geometric scale, predicting a linear increase in initial stiffness and anchor energy. Three-dimensional bar–matrix contact simulations (FEniCS) for \(\eta =1.0-1.6\) and two cover ratios \(\lambda = d/c = 0.20,\;0.14\) confirmed this prediction within 3 % for peak hoop stress and 2 % for secant stiffness. A \(2\times 3\) factorial pull-out program on fly-ash concretes (two covers, three Si / Al ratios) experimentally validated the proportionality \(K_{\text {exp}} = \eta K_{0}\) experimentally; two-way ANOVA ranked gel chemistry as the dominant factor, explaining up to 93 % of stiffness variance at 28 days, while residual errors remained negligible. The metric sweeps of the fracture number \(\kappa\) and the friction number \(\textrm{Re}_{\mu }\) confirmed that \(\eta\) governs the stiffness, \(\kappa\) controls the post-peak toughness and \(\textrm{Re}_{\mu }\) scales the residual plateau, delineating a domain of validity of \(\eta \le 1.6\) , \(\kappa \ge 0.004\) , \(0.12\le \lambda \le 0.25\) . These convergent results demonstrate that a single parameter captures the chemomechanical enhancement of alkali-activated concretes, providing a direct calibration rule that can be incorporated into future revisions of the ACI 323 Low-Carbon Concrete code.
