Sweeping the dirt debris over the existing concrete slab will allow the joint to occur. The simple answer is YES, you can pour new concrete over existing concrete. New concrete will likely shrink at a different rate than existing concrete if mix designs are not carefully combined. If you simply pour new concrete on it and don't fix the problem, the same thing will most likely happen with new concrete.
Your path can gain a new life by adding a new layer of concrete on top, without the need to excavate the existing road and start from scratch. Yes, you can place new concrete over old concrete as long as there are no problems such as significant cracks or frost with your existing concrete. The new concrete will fill the pothole completely when it is fresh, but will quickly shrink from the edges as it sets. When the existing concrete has the right quality, you can pour a new, thin slab on top of the old concrete, provided that the new layer contains wire mesh or fiber reinforcement.
Make sure the braces are level and place a wire mesh barrier over the existing concrete inside the barrier. Alternatively, do some research on concrete-safe chemicals that will help lift paint so you can scrape it off. As I mentioned before, anything, such as a door or a staircase, would justify getting rid of old concrete and starting from scratch. Check if adding a few inches of new concrete would prevent you from closing a door or obstructing a walkway before starting work.
The slab poured onto an existing concrete slab is more prone to frost and crack damage due to the joint between the two layers of concrete. When the existing concrete is severely damaged, with large cracks passing through the structure, you need to completely tear it off and replace it. Every time new concrete is to be joined to old concrete, cracks are likely to form and the sections will begin to separate. Concrete slabs, especially older ones, usually do not meet this standard and therefore require a screed.
It is essential to properly prepare and clean the existing slab before placing the new concrete on top. If you pour something thinner than 1.5 inches, you won't have enough cement paste on and around the aggregate to get strong concrete.