Onthelist do you have any idea what type of cockroaches these are. Are they the great big Australian/American roaches, or one of the smaller varieties?
There are lots of different species of cockroaches and in general the ones outside aren’t problematic, unless someone has a serious phobia. They probably won’t come inside if it’s a species that is currently living fulltime outside. You’re far better of treating the house to kill the occasionally invader than trying to nuke your yard. There’s just no point I can see in killing off the local insect life
But if you have no environmental sensitivity at all….
You’re going to need some sort of powder. Concrete is just too porous and to alkaline for any commonly available liquid insecticide to be effective. Get down to your local hardware store and see what they have in the way of either granules, dusts or wettable powders. You will generally find that dusts and granules will be sold primarily as ant dusts, but they work just fine on roaches as well. Of course you will need some fine weather for powders to work.
Borax itself is fairly useless as a contact poison, especially outside where it absorbs moisture so readily. If you wish to you can try making a bait by mixing it 1:10 with sugar, but in general food baiting is ineffective against cockroaches when the have that much food available.
There are a range of pheromone baits available, but availability to the general public varies from location to location and they end to be expensive, but they are astoundingly effective. If you have the money and can find any these are the way to go.