If that rock was collected south of Orlando, its known as 'Miami Oolitic.' The same rock that is found in Florida's reef, save for a couple thousand years of have sand smashed in, which has caused some of the various pores and such to fill in. There are some rocks that are better then others in regards of porosity, look for those. Some which mirror traditional aquarium rock. Pressure washing is what I did as well, wear your swim trunks.
I have a quite a bit of these rocks in my 125. There is really no difference from this rock then dried base rock in terms of 'life.' Everything in dead in both. I would never recommend completely filling a tank with this stuff. My personal guideline is to stay under 40% (either for collected rock, dry base rock, or both) of total pounds of rock in the tank and have at least the other 60% live rock.
There are real risks, as mentioned, that they have absorded chemicals and/other nastys that could wipe out a tank. If you found this rock along side the road, dump it. The rock I have collected was from freshly cleared construction sites out west in Broward (Parkland specifically). Areas where it's unlikely any human set foot before.
The pH on those rocks is also initially a little low. If you decide to use that one or some others, after you power clean, you'll need to soak the rocks in a hyper-pH tub (rubbermaid, with a fair bit of pH+ buffer dumped in) for about month before adding to your tank. All you need is saltwater, a rubbermiad or bin large enough to fill with water to completely cover the rock, and a powerhead.
Forgot to add, since these rocks are dead, just like base rock, you will cycle them as well. Add in another month for thes guys in the rubbermaid to cycle if you adding them to an established tank. If you're setting up a tank you can skip this step (as the tank's cycle will cured these rocks).
Also, don't bleach, bleach won't really do any sorts of 'cleaning' but it is very hard to get out of the rock.