As a guess I would say:
1/ carry out tensile and compressive (cube) tests on the material and then depending on whether or not you need to model cracking and crushing and plasticity...
2a/ use a concrete constitutive model and plug this information (elastic-plastic properties) into your FE package (to include tension softening) or...
2b/ for a linear analysis use the concrete constitutive model and use linear props
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