BEst thing to clean concrete is oxalic acid. Works well - can be bought at any hardware store as crystals, which you dissolve in water.
I have had a Karcher for 10+ years, Replaced the main capacitor once, and the hose once, and no other issues. Blasts crap off driveways easily - it's got some testicular grunt
I stupidly used it on a mates car one - good bye silver trim... and some other paint
