A physically based constitutive model for the behavior of concrete dis
continuities is proposed. To consider a detailed mechanism that expres
ses the microscopic features of concrete discontinuities, the crack su
rface is idealized with both sawtooth and circular asperities. The saw
tooth asperities represent the contact between mortar and mortar, whil
e the circular asperities are used to simulate the phenomenon of aggre
gate interlock (i.e., contact between aggregate and mortar). The behav
ior of the two types of contact is investigated. To simulate all possi
ble kinds of nonlinearities, two independent hyperbolic surfaces with
a Mohr-Coulomb surface as an asymptotic surface for both the plastic p
otential and yield function are defined in stress space. Basic materia
l parameters such as cohesion, internal friction angle, dilatancy angl
e, and tensile strength are varied according to the accumulated damage
at the crack interface. Finally, several paths are considered to eval
uate the capability of the proposed model. The model is amenable to im
plementation in such numerical procedures as finite element computer p
rogramming.