WHY USE REINFORCEMENT?

As a forced is applied to concrete there will be compressive, tensile and shear forces acting on the concrete. Concrete naturally resist compression (squashing), very well, but is relatively weak in tension (stretching).

Horizontal and/or vertical reinforcement is used in all type of concrete structure where tensile or shear forces may crack or break the concrete. HORIZONTAL reinforcement helps resist tension forces. VERTICAL reinforcemet helps resist shear forces.

Below are some examples of reinforcement use :

In a SUSPENDED (of the ground) concrete slab, horizontal reinforcement resist tension and vertical reinforcement (in say supporting beams) resist shear forces.

In a SLAB ON GROUND, reinforcement increase the tensile strength and helps control the wicth of shrinkage cracks.

Uses of reinforcement include : increasing the spacing of control.
: odd shaped slab
: slabs with re-entrant corners.

REINFORCEMENT POSITION

The position of reinforcement will be shown in the plans. Reinforcement must be fixed in the right position to best resist compressive, tensile and shear forces and help control cracking.

The reinforcement in trenches and slab rest on BAR CHAIRS and must be securely fixed to the bar chairs so it wont move mhen conrete is placed around it.

Concrete cover the reinforcement must be placed so there is enough concrete covering it to protect it from rusting.Typical covers are shown in the diagram.

Cracking and reinforcement alone will not stop cracking, but helps control cracking. It is used to control the width of shringkage cracks.

Conrete reinforcement bond to help control the width of cracks, or their location
(at joints). There must be a strong bond between concrete and reinforcement. This allows the tensile forces (which the concrete has a very low ability to resist) to be transferred to the reinforcement.

To help achieve a strong bond :

The reinforcement should be CLEAN (free from flakely rust, dirt or grease).

The concrete should be PROPERLY COMPACTED around the reinforcement bars.

Reinforcement bars and mesh should be located so that there is enough room between the bars to place and compact the concrete.


Types of reinforcement two types of steel reinforcement used are mesh sheets or loose bars. Loose bars are normally deformed, while mesh may be made from either smooth or deformed barss. Typical bars diammetres are 12, 16, 20 and 24 mm.typical mesh size are SL42, 52, 62, 72, and 82. The SL stands for Square mesh Low Ducity and the numbers represent meanings as well. For examples, for SL42 the 4 is the nominal bar size and the 2 refers to the wire spacing (200mm).

Fibre reinforcement synthetic fibre can be added to concrete to aid in minimizing early age plastic shrinkage and can reduce the presence of excessive bleedwater. However, synthetic fibres are not a replacement for fabric or steel reinforcement. In slab on ground construction the control joint spacing is the same as plain concrete.

Steel fibres are used for the above and to improve the toughness of conrete. However they can be used to control drying shrinkage cracking over limited spacings and oddshaped slabs. They also increase the flexural, or bending, strength of the conrete.