In the present study, the chemo-thermal modeling of time-dependent hydration phenomenon of the recycled-aggregate-based mortar and natural-aggregate-based mortar has been achieved via the modified Arrhenius' law and 3D finite element analyses. The experimental measurements about the heat release rate and total hydration heat have been taken into account for the numerical experiments later on. The numerical results confirm that hydration gradient across the cement paste matrix is disturbed by the existence of aggregates during the hydration process for both mortars. The gap spaces between cement paste and aggregates at Interfacial Transition Zone (ITZ) have been studied via Replica Method. However, the comparison among the numerical and experimental findings reveals that the numerical solutions provide different outcomes at ITZ for recycling mortar specimens. This matter substantiates that the modified Arrhenius' law cannot be applied to the recycling mortar hydration modeling and needs to be revised to take into account the additional considerations pertaining to the thermo-chemically activated reactions through the recycled aggregates including cement pastes at very early age. Some fresh routes in the analytical and numerical modeling of the recycled-sand-based mortars are discussed. (C) 2016 Elsevier B.V. All rights reserved.