When post tension is done usually the top surface is getting uneven (curved) due to small deflections. How to achieve an even surface in that case?
I there any standard methods to achieve this?
In post tensioning, cables are draped with no tension. After the concrete has set, the strands are placed in tension, which pulls the lower face into compression and places the upper face into tension. In other words the slab is bowed into a concave downward shaped curve. This is preparatory for a structure or load to be placed on the slab. When the load is added, the additional downward forces pushes the bowed surface back down, adding compression in the top face and tension in the bottom face. The slab tends to a balanced force in both surfaces. If this were not the case the load would tend to place the top face into compression and the bottom in tension, leading to cracking up from the bottom as concrete is weak in tension and strong in compression.
Hope this helps
If the PT slab is correctly designed, the balancing load should be about 50% to 66% of the dead load ( approx. equals to the own wight of slab ). in this case the long term deflection of slab will be downward, hence if you want to reduce this deflection, you can use the traditional camber technique.
an even surface will be difficult to obtain if you consider long term deflections
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