need the plastic propertis of concrete

Meisam,

Unless the concrete is highly confined (i.e., under a state of triaxial compression) an elastic model with damage is good enough.  That is true if the blast is away from the surface and if the concrete is not too thick or constrained in all directions by, say, a mountain.  See for example http://math.nist.gov/mcsd/savg/parallel/epc/index.html.  Also, the properties may vary considerably depending on the microstructure and constituents of the concrete.

You can get a feel for what's involved by looking at Chapter 14. Plasticity Aspects of Reinforced Concrete in Inelastic Analysis of Structures by Milan Jirasek and Zdenek Bazant. 

-- Biswajit