it appears the stain's shallow because of the scaling - see the white cpot ? we own rotary deckcrawlers w/carbide teeth so we'd use 1 of those ( aurand ) to remove the scaling,,, IF the surface of the d/w's totally s***, we'd run a walk-behind scarifier ( edco ) over it then overlay the d/w.
tools - bosch bulldog w/1" or 2" brick chisel to remove scaling,,, ' CLR ' for the rust stain,,, acid-wash the d/w w/muriatic 1:8 wtr pickling solution, rinse, then neutralize remaining acid w/1:8 wtr solution out of the std plastic garden watering thingie,,, 3,500psi p/w will clean well - better if you can find a turbo nozzle for it ( faster & more complete cleaning ),,, apron store ' cement-all ' for an overlay product ( we used it for bdge deck jnt reprs 25 yrs ago for va dot & i still drive over them on the way back to upstate ny
we use elitecrete but there are other good materials,,, i'd advise to avoid mtls which have the installer add polymer on-site,,, the just add wtr mtls are MUCH easier to use + they offer less opportunity to f up,,, other'n that, grab a stiff push broom - some use a squeegee to lay down the stuff but i like the broom as 1 can texture in the broom finish while installing the polymer-modified o'lay,,, its a technique we fancy we developed but some other guy out there's done the same & probably wants the credit for himself
so be it
ooops, color - they use white cement in these mixes so you'll need to experiment to find YOUR color- sher-wms sells wtr-bas'd pigments & will even put it in a NEW can for you,,, find the color grey you want & buy a pint,,, add pigment to mix wtr FIRST then add bagg'd mix,,, you might f up a bog or 2 @ 1st but you'll soon get the idea + its only for the base coat which will be cover'd up,,, sealing conc o'lays is optional as w/any conc work -euclid, meadows, basf, & prosoco are 4 good sources
i'd feel much more optimistic re the op's success IF he stays OUT of the apron store as those jabonies don't know dick about conc ( apologies to concretemasonry who is a valued contributor to this forum )
probably should incl a disclaimer - my monitor's horrible & all we've got for info is what the h/o sez [ oy ! ] nevertheless, good luck !
neal, leave bdge alone & GET OFF MY A**,,, you aren't the boss of me ;-) MY boss is still upstairs in bed - sleeping,,, have a nice day !