What each method actually does
Sweeping, whether by machine or manually, lifts loose material: dust, grit, film fragments, timber splinters and granular spill. It is quick, it needs no water, and it can be done in a lane that is briefly quiet. What it does not do is remove the thin adhered film of rubber, oil and fine dust that builds on a sealed surface under wheel traffic, and no increase in sweeping frequency will change that.
Scrubbing applies water, chemistry and mechanical action, then recovers the solution. It removes the adhered layer and restores the appearance of a sealed slab in a way sweeping cannot approach. The cost is water, drying time, a released area and a machine that needs somewhere to fill and dump. Those requirements are why it belongs on a cycle rather than in a nightly routine. It also produces waste water that has to go somewhere the site has agreed to.
