inquiry on concrete covers

huangyhg

inquiry on concrete covers
here is a basic question that i would like to find an answer. i am searching for farther explaination on concrete covers.
1.) minimum concrete cover for slab is 20mm while that of a beam is 40mm. why the difference considering that they have the same exposures?
2.) considering that the slab and beam is monolithically poured, the top concrete cover will have a variance (40mm for beam, 20mm for slab ). usually, what is done is that the top bars for slabs is placed on top of the main beam bars. this increases the slab concrete cover but reduces the effectivity of the slab considering it is designed for 20mm cover. is this the reason why cracks appear along the beam ( top portion )?
3.) what other effects can come from when the concrete cover of slab is increased to 40mm ( item 2 situation )?
4.) any suggestions to maintain the 20mm cover when monolithically poured with the beam?
thanks in advance.
just re-posted