Using generated textures with the Displacement Modifier in blender is kind of outdated, because it relies on the old blender internal textures. You can't mix these textures using Cycles nodes and therefore also won't be able to bake them using Cycles. While there probably is a way of achieving this switching over to blender internal i would recommend you not to use Texture Displacement Modifier but rather to do it the native Cycles way:
Cycles "Displacement" output socket
By default it affects the normals and the angle based shading math and (not the geometry itself like the Displacement Modifier). So it's an efficient way to fake roughness/displacement similar to using a normal map.
Because the floor is very flat and even you probably won't see great difference to real geometry displacement like in your screenshot.
Experimental: Cycles Microdisplacements + Adaptive Subdivision Modifier
If real geometry displacement is needed Cycles offers a new (still experimental) technique introducing real geometry (micro-)displacement. It is very handy and memory/performance efficient because the actual subdivision and displacement only happens in the renderengine while the object stays lowpoly while editing. This video by Andrew Price gives a good overview.
Here is how to enable it in three steps:
Enable Experimental Cycles in the Render-Tab:
Switch to Geometry Displacement in the objects material:
Add Subdivision Modifier "Simple" and "Adaptive": A dicing scale of 1 means the mesh gets subdivided pixeldense - there will be at least one "sub-vertex" per rendered pixel.
Option 1: Using one object/material
So this is how you could setup one cycles material for both concrete and puddles:
Option 2: Two separate objects/materials
The setup above has the disadvantage that if the water is semitransparent the concrete shining through doesn't have displacement.
Another solution would be to add a second plane below the concrete that serves as the water level and use the puddles mask to dig holes in the concrete material. This requires micro-displacement. In this screen I have exaggerated the effect for demonstration purpose:
Also check out the other cycles procedural texture nodes. As an alternative you could also create the holes using sculpt mode...