What material properties need to be specified in modeling concrete with reinforcements in Abaqus?

Use the concrete model available with rebar to model the reinforcements. 
Section 1.1.5 of the ABAQUS Example's manual gives an example of the collapse analysis of a concrete slab subjected to a central point load. 
The data file for that example is collapse example. 
The complete set of ABAQUS input files can be obtained by using the following command :

   abaqus fetch j=collapseconcslab*

*CONCRETE
  3000., 0.      abs. value of compressive stress, abs. value of plastic strain.
  5500., 0.0015                "                              "

*FAILURE RATIOS
  1.16, 0.0836

This is used to define the shape of the failure surface (see section 11.5.1 of the ABAQUS USER's manual Vol. II). 
The first parameter is the ratio of the ultimate biaxial compression stress, to theuniaxial compressive stress. Default is 1.16. 
The second parameter is the absolute value of the ratio of uniaxial tensile stressat failure to the uniaxial compressive stress at failure. Default is 0.09. 

Tension Stiffening

*TENSION STIFFENING  
  1., 0.
  0., 2.E-3

First parameter is the fraction of remaining stress to stress at cracking. The second parameter is the absolute value of the direct strain minus the direct strain at cracking. 
This defines the retained tensile stress normal to the crack as a function of the deformation in the direction of the normal to the crack. 

Shear Retention

*SHEAR RETENTION

Not used for this example. 

Reinforcement modelling

*REBAR is used to model the reinforcement. 

*REBAR,ELEMENT=SHELL,MATERIAL=SLABMT,GEOMETRY=ISOPARAMETRIC,NAME=YY
SLAB, 0.014875, 1., -0.435, 4
*REBAR,ELEMENT=SHELL,MATERIAL=SLABMT,GEOMETRY=ISOPARAMETRIC,NAME=XX
SLAB, 0.014875, 1., -0.435, 1

Here SLAB is the element name or name of the element set that contains these rebars. The geometry is ISOPARAMETRIC. Other choice is SKEW. ELEMENT can be BEAM, SHELL, AXISHELL or CONTINUUM type. The following are the other parameters specified :

• cross-sectional area of the rebar.
• spacing of the rebars in the plane of the shell
• position of the rebar. Distance from the reference surface. Here the mid-surface is the reference surface and the minus sign indicates that the distance is measured in the opposite direction to the direction of positive normal. The positive normal is defined by the right hand rule as the nodes are considered in an anti-clockwise sequence.
• edge number to which rebars are similar.

Alternate Method of modelling REBAR Reinforcements

Alternatively REBAR can be modelled as follows :

*NODE 
....
....
**-------------------END NODES FOR REBAR BEAM ELEMENTS
     501,         0.0,        0.15,       -0.02
     541,         1.5,        0.15,       -0.02
     601,         0.0,        0.15,       -0.07
     641,         1.5,        0.15,       -0.07 
     701,         0.0,        0.60,       -0.02
     741,         1.5,        0.60,       -0.02
     801,         0.0,        0.60,       -0.07
     841,         1.5,        0.60,       -0.07 
....
....
**---------------------GENERATE INTERMEDIATE NODES
*NGEN, NSET=BAR10TF
 701, 741, 2
*NGEN, NSET=BAR10TB
 801, 841, 2
...
...
**--------------------GENERATE THE BEAM ELEMENTS
*ELEMENT, TYPE=B31
701, 701, 703
801, 801, 803
*ELGEN, ELSET=BAR10TF
701, 20, 2, 1, 1, 1, 1
*ELGEN, ELSET=BAR10TB
801, 20, 2, 1, 1, 1, 1
...
...
**---------------------DEFINE THE MATERIAL PROPERTIES
*MATERIAL, NAME=BAR8
**
**  8 mm dia bar
**
*ELASTIC, TYPE=ISO
197.E6, 0.3
*PLASTIC
 354.E3, 0.
 364.E3, 0.0018
**
**---------------------DEFINE THE SECTION PROPERTIES
...
...
*BEAM SECTION, SECTION=CIRC, MATERIAL=BAR10, ELSET=BAR10TF
  0.005
*BEAM SECTION, SECTION=CIRC, MATERIAL=BAR10, ELSET=BAR10TB
  0.005
...
**--------------------DEFINE AN ELEMENT SET WHICH CONTAINS
**--------------------THE ELEMENTS THROUGH WHICH THE REBAR
**--------------------ELEMENTS PASSES.
....
*ELSET, ELSET=TOP, GENERATE
 5, 80, 5
**
**--------------------
*EMBEDDED ELEMENT,HOST ELSET=TOP
BAR10TF,BAR10TB
**