The filler slab is based on the principle that for roofs which are simply supported, the upper part of the slab is subjected to compressive forces and the lower part of the slab experience tensile forces. Concrete is very good in withstanding compressive forces and steel bears the load due to tensile forces. Thus the lower tensile region of the slab does not need any concrete except for holding the steel reinforcements together.
Therefore in a conventional RCC slab lot of concrete is wasted and it needs extra reinforcement due to added load of the concrete which can otherwise be replaced by low-cost and light weight filler materials, which will reduce the dead weight as well as the cost of the slab to 25% (as 40% less steel is used and 30% less concrete).
The simplest filler is to use two fifth grade Mangalore tiles, that is what is used in our projects,they do not have any structural value- they are mere ‘fillers’. The different materials that can alternatively be used are waste and cheap like Country tile, Earthen pots, Hollow blocks, Coconut shells, Thermocol, etc. Besides the roof this technique can also be used for the window sun-shades.
Thus the filler slab as the roof has the following advantages :
· Due to the reduction of concrete volume, the overall cost of slab is lower than solid slab even after considering additional cost of Mangalore tiles.
· The consumption of steel is lesser than that of the solid slab.