3:1 sand/cement with about 6:1 PVA/water, prime the surface with the PVA mix and allow to dry first. 1" minimum and cover with 500 gauge polythene for a week or so to retain water.
Better to install a couple of screeds (wooden rails) on stakes either side. Pour in the mix, and use a third piece of timber across them to shuffle along the job to get your flat surface As it is a driveway the slightly rough surface will be a boon on frosty mornings. You may of course finish the surface with a float.
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