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yeah you are right...if it is simply supported then theoretically! no moment at top and no required reinforcement at top! but in reality we have some ethics for structures...and the CODE defines these ethics....so in reality we require bottom bars to be extended into supports....where practically there is no moment...(positve) similarly the top bars are extended upto a length equal to developement length plus d after the inflection point these minimum precautions are required to avoid failure in case of moment reversal and to provide structural integrity... generally at the discontinous ends you need one third of positive reinforcement in case of simply supported slabs but due to curling of slab edges, torsion, and temperature shirnkage and due to relative stiffness of of the beams or supports there is a need to provide top reinforcement at discontinous ends... thats y may be you have seen at some places that every other bar is bent up to give negative reinforcement area over masonry walls supports in our typical house construction in pakistan. means half of the positive moment reinforcement area is provided on discontinous egdes.. This is just a simply supported case of slabs resting on masonry walls... In case of continous slabs resting on concrete beams the negative moment is some times more than positive...

crush is a rock! and concrete is a composite material made up of different materials. Many factors are involved for example as umar quoted w/c ratio...distribution of crush and their sizes...quality of cement...there is air too in the concrete mixtures then the curing and setting temperatures...if only crush or rock is to be used alone they how they will stick together...so we add cement and water and fine crush to make it a mixture...whose properties are different that the original elements used to make that mixture...

by both sides i mean in one direction...bt the top reinf is on all four sides..... @waqar this is normal! the moment at middle span is high because of 1 span (simply supported)...so if an alternate bar is provided at top...this is perfectly normal..yeah it will take stresses as far as you have provided enough reinforcement and with proper splice and development lengths...