During renovations, the new curb can be cast directly on top of the old one, so expensive excavation and disposal is avoided. Alternatively, the old curb can be milled away, and then a new one is cast.
When new curbs are established, concrete is laid directly on top of the asphalt. It has several benefits. Time-consuming digging and setting can be completely avoided. At the same time, the concrete is cast all the way down to the asphalt without the typical joint, where water and weeds usually collect.