there is an autocad fill that i find typically comes in with consultant DWGs that has a reasonably good concrete symbol fill. search for it in the attributes of a DWG file and transfer it across to your own project/template. i think it's called something like "CONC...." followed by lots of numbers and letters. there is no bitmap preview for it either - it appears as though it's a blank square.
if you still can't find it, send me a PM and when i next get my laptop online i'll email you a PLA . . .
or are you actually talking about visualisation rather than drawing 'fills'? if so, use the lightworks rendering engine and make your own 'procedural' concrete surface - take a look in the manual for the process and play to your heart's content!
HTH
~/archiben
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