Why are separation membranes used between concrete pavement slab and sub-base?

(i) It prevents the loss of water from cement paste which affects the strength of concrete slab.(ii) It enhances the movement of concrete slab relative to sub-base layer and reduces the frictional forces developed at their interface.(iii) It avoids the possibility of active aggressive agents from soil water being attached to the concrete slab.(iv) It prevents the intermixing of freshly placed concrete with loose materials on the surface of sub-base.

* To reduce the friction forces between Concrete Slab and the Sub Base. * It helps in the movement of Concrete Slab when level changes occurs due to moisture and temperature change. * It segregates the Concrete Slab and freshly poured Concrete. * It also reduce the water and cement loss in shape of immature concrete which ultimately effects the compressive strength and its durability.

The separation membrane reduces the frictional forces between the concrete slabs and the sub-base. The membrane aids the movement of the concrete slab in reference to the sub-base when changes in the level of the moisture and  temperature occurs.

 It aids in the segregation of sub-base materials from freshly placed concrete.

The separation membrane also helps in the reduction of cement and water loss in the form of immature concrete. Immature concrete greatly affects the strength of the concrete. It also affects the durability of it.

 

 A good example of a separation  membranes is polythene sheeting which is commonly used.

Separation membrane arrests the flow of cement concrete slurry from Concrete pavement slab to Sub-base. Therefore, any loss of slurry will imbalance the Water-Cement ratio of Concrete and it may result in loss of compressive strength, workability, shrinkage cracks will appear on surface after setting of concrete, etc.

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 The purpose of separation membrane between the concrete pavement slab and the sub-base are as follows: > The separation membrane reduces the frictional forces between the concrete slabs and the sub-base.

To help not to soil absorption of mortar concrete when casting