Welded wire fabric is a series of parallel longitudinal wires welded to cross wires by electric fusion method with accurate spacing. The welding work is done by machinery which ensures the precise dimensions and results in considerable savings in time, labour and money.
In this article, we will study the general specification, advantages, uses and comparison of welded wire fibre concrete.
General Specification of Welded Wire Fibre Concrete
The material used in manufacturing the wires for welded fibre is either stainless steel rebar rods or galvanized steel rods that have excellent resistance to corrosion and can be used in wet conditions.
The wires conform to IS:432-Pt II/1982 which specifies an ultimate tensile strength of 570 N/mm2 and a characteristic strength of 480 N/mm2.
2. Shape and Size
The commonly available shapes of the welded wire fibre are rectangle and square. The fabric can be manufactured for widths up to 3000mm with lengths limited by transportation considerations. When supplied in ready-to-lay flat sheet form the standard length is 5500mm. Otherwise, the fabric can be supplied in the rolled form in standard lengths of 15m,30m or 45m.
Wires used for the manufacture of fabric are generally manufactured in the range of 2mm to 12mm diameter. It is manufactured conforming to 1566-1982 with long and cross-wire spacings varying from 25mm to 400mm.
3. Cutting and Forming
Welded wire fabric can be easily cut with the help of wire cutters. If the mesh is to be laid in a staircase, it can be easily bent into the required size and laid down.
4. Lapping and Clearance
As the wire fibres are available in any sizes required, lapping is not usually required, but in the case, if lapping is required, a minimum of 6 inches of lapping is recommended.
As a standard practice, 1 to 3 inches of clearance is given between the wire fabric and formwork.
Vibrating plastic concrete reinforced with welded fibre mesh is recommended in order to ensure the mix is distributed completely and the fabric is properly embedded all around to the cracking.
Comparison between Welded Wire Fibre and Conventional Reinforcement
|Welded Wire Fabric||Conventional Reinforcement|
|Increased permeability.||Reduction of permeability|
|Bond can deteriorate over time||Bonds effectively with concrete permanently|
|No surface protection provided||Improves surface durability|
|Minor resistance provided if properly placed||Improves impact, shatter and abrasion resistance|
|Difficult to install and expensive - high labor costs||Easy to use and cost effective - no labor costs|
|Difficult to place, especially if rolls - 1" minimum cover required||Easy to place in concrete mix - No minimum cover|
|No effect on finish, but difficult to maintain placement in slab||Easy to finish with minor effect on workability of mix|
|Will deteriorate if not properly placed and protected||Alkali resistant|
|Will deteriorate if not properly placed and protected||Acid resistant|
|Corrodes when exposed to water and chemicals||Corrosion resistant|
|Increases tensile strength if properly placed||Increases tensile strength of plain non-reinforced concrete|
|Provides reinforcement in one plane||Provides three dimensional reinforcement|
|Increases ductility if properly placed||Increases ductility|
|Permanent if visible with little remedy possible||No lasting aesthetics and can be easily remedied if necessary|
|Meets ASTM specifications if placed properly||Meets or exceeds ASTM specifications|
|Storage difficult and detrimental if stored outside||Can be stored for long periods of time|
Advantages of Welded Wire Fabric in Concrete
1. Higher Design Strength
The structural behaviour of welded wire fabric is the same as that of HYSD bars or plain mild steel bars. The higher strength is due to the strength of welded wires.
2. Better Bonding
The main factor responsible for the bonding of concrete is the peripheral surface area. The rigid mechanical interconnections by means of welds to cross-wires are primarily responsible for stress transfer from concrete to steel and vice-versa in the case of welded wire fabric.
Each of the rigid welds capable of resisting up to 210 N/mm2 ensure quick and complete stress transfer within 2 welded joints from the critical section.
3. Effective Crack Resistance
The two major properties of welded wire fibre which help in reduction of cracks in the concrete are the strong mechanical anchorage of the welds at each intersection and the close spacing of thinner wires.
The close spacing of wires serves as most effective in countering the non-load phenomena or strain induced stresses due to shrinkage and temperature changes. This property of the welded wire fibre preserves the structural integrity of the slab.
The most obvious and clinching advantage in the use of welded wire fabric is the immediate and positive savings in labour and time. There is no cutting of bars, no marking and spacing them out, and above all no laborious tying of wires.
5. Flexible in Handing and Placing
The usage of thinner wires lends the fabric as extremely flexible in handling. Coupled with the availability in long lengths in roll form, welded wire fabric provides the ideal and convenient solution for all kinds of repair work by Re-plastering or Guniting.
Uses of Welded Wire Fabric in Concrete
- Structural flat slabs or in slabs with beam slab construction.
- Large area floor slabs on ground, pavements, airport runways, aprons etc to achieve crack-free joint fewer surfaces.
- Concrete elements of curved or difficult shapes such as arches, domes, lotus petals etc. where the flexibility of welded wire fabric and its ready to use nature aids all the way.
- Precast elements which are thin or are difficult to reinforce such as curved arch flat members, Hyperbolic Paraboloid Shells, folded plate roof girders, fins, thin pardis or chajja drops.
- Standard mass production precast R.C.C and prestressed elements like slab panels, wall panels.
- As a bonding fabric during guniting or during re-plastering required for Repairs and rehabilitation of structures.
- Unstressed shaping or form reinforcement used in Prestressed Concrete Girders of Box, I, T or Double T-section.
- Ferrocement or Ferrocrete works where welded wire fabric is the only solution for forming the reinforcing matrix for precast elements such as water tanks, fins, shelves etc.