Flexicore - Construction


Flexicore is a type of precast, prestressed concrete floor slab. Often used in construction of multi story buildings.

It has advantages over poured concrete floor:

lighter in weight and often cheaper.

Wet concrete does not need to be pumped or carried up to higher floors.

The slabs which are manufactured off site are simply lifted with a crane and set in place.

Prestressed flexicore offers a long-span, lightweight deck:

Camber is an inherent feature of prestressed concrete.

Prestressed Concrete

A method for overcoming concrete's natural weakness in tension. It can be used to produce beams, floors or bridges with a longer span than is practical with ordinary reinforced concrete. Prestressing tendons (generally of high tensile steel cable or rods) are used to provide a clamping load which produces a compressive stress that offsets the tensile stress that the concrete compression member would otherwise experience due to a bending load.

Prestressing can be accomplished by:

Pre-tensioned concrete
Cast around already tensioned tendons. This method produces a good bond between the tendon and concrete, which both protects the tendon from corrosion and allows for direct transfer of tension. When cured the concrete adheres and bonds to the bars and when the tension is released it is transferred to concrete as compression by static friction. It requires stout anchoring points between which the tendon is to be stretched and the tendons are usually in a straight line. Thus, most pretensioned concrete elements are prefabricated in a factory and must be transported to the construction site, which limits their size. Pre-tensioned elements may be balcony elements, lintels, floor slabs, beams or foundation piles.

Bonded post-tensioned concrete
Bonded post-tensioned concrete is the descriptive term for a method of applying compression after pouring concrete and the curing process. The concrete is cast around a plastic, steel or aluminium curved duct, to follow the area where otherwise tension would occur in the concrete element. A set of tendons is fished through the duct and the concrete is poured. Once the concrete has hardened, the tendons are tensioned by hydraulic jacks that react against the concrete member itself. When the tendons have stretched sufficiently, according to the design specifications, they are wedged in position and maintain tension after the jacks are removed, transferring pressure to the concrete. The duct is then grouted to protect the tendons from corrosion. This method is commonly used to create monolithic slabs for house construction in locations where expansive soils create problems for the typical perimeter foundation. All stresses from seasonal expansion and contraction of the underlying soil are taken into the entire tensioned slab, which supports the building without significant flexure. Post-stressing is also used in the construction of various bridges, both after concrete is cured after support by falsework and by the assembly of prefabricated sections, as in the segmental bridge.The advantages of this system over unbonded post-tensioning are:

Unbonded post-tensioned concrete
Unbonded post tensioned concrete differs from bonded post-tensioning by providing each individual cable permanent freedom of movement relative to the concrete. To achieve this, each individual tendon is coated with a grease and covered by a plastic sheathing formed in an extrusion process. The transfer of tension to the concrete is achieved by the steel cable acting against steel anchors embedded in the perimeter of the slab. The main disadvantage over bonded post tensioning is the fact a cable can destress itself and burst out of the slab if damaged. The advantages of this system over bonded post tensioning are:
The ability to individually adjust cables based on field conditions
The procedure of post-stress grouting is eliminated.
The ability to de-stress the tendons before attempting repair work.

pre cast - Flexicore - concrete - prestressed and precast