IIRC--the petrobond was made by mixing sand with a cut-back asphalt,
then allowed to cure-(evaporate the solvent) then ready for use---
today they would probably use a waterbased emulsion (solvent much cheaper)

back when I wuz building county roads, there was a large area in the
county that had just the "right" sand for asphalt stabilizing. We'd cut
the sand up about 6" deep, windrow it on one side, drive a 5000gal
tanker down the road with a 3" valve open, dumping out a cut back
asphalt-about 60/40% with grader following and covering the "oil"
withabout 2 " of sand---usually took 5 or 6 truckloads of asphalt per
mile--Then it was bladed back & forth across the road until it was well
mixed and the solvent had evaporated...you could test it by grabbing a
handful , squeezing real hard , seeing how well it held its shape. You
could toss it into the windrow without it breaking.--Then if you dusted
off your hands & nothing stuck to them, it was ready to compact---made
an excellent base, which was then oiled & chipped a couple of times.

The reason for the Asphalt was that when dried back out--it was quite
rigid, .---some cheeapskates would sell a rural farmer a product called
tank bottoms- which was a parrafin like substance with some petroleum
left in it...this contimued to stay soft & lubricate the sand particles
so that they would never stiffen up--Same thing with used motor
oil--it's a lubricant, not a cement.

"course this was back when oil was $3 to $4 a BARREL---10¢ a gallon.