You want a dry ice, soda or sand blast for that...dry ice is best.I sold my gas pressure washer after 5 years for 90% of what I paid for it, and I bought a electric 3000 psi ryobi (1.1gpm) and it did the job just fine.... but.. big learning curve with electric, it will remove the dirt, but it doesn't wash it away, so I did like 2 squares at a time, then I would use 40 degree wand and push all the dirt to the next few sections, and continue.
this took me a couple hours.
however I only paid 260 bucks for this 3000 psi ryobi, and it did an exceptional job, just I have to do rinses between sections to remove the dirt that it breaks free from the surface cleaner. can't complain otherwise. it is more convenient though, the gasser gave me issues every 2 years with carb despite using stabilizer.