Wire mesh is commonly placed in concrete slabs for two primary reasons:
-to resist breaking apart and deteriorating when the slab eventually does crack
-to increase flexural strength of the slab .
Also, another situation where wire mesh can offer benefits is when a poor or weak subgrade exists and may be expected to move or settle. Wire mesh in a slab can offer tensile/flexural strength to the concrete, spreading loads over more area.
A common thought process is that steel wire mesh keeps the slab from cracking. The accuracy of this theory depends on where the wire mesh is placed and how well the subgrade is designed and compacted:
When wire mesh is installed in the lower 1/3 of the slab, it will have increased flexural (and in turn tensile) strength when one point load bends the slab downward.
When placed in the top 1/3 of the slab, it will have increased flexural strength in between two point loads which bend either side of the slab downward.
This is why it is common for some engineers to specify mesh in the upper and lower 1/3 of the slab both. Many engineers simply feel placement in the center of the slab is a logical compromise, offering some flexural strength increases in both bending applications mentioned above. Wire mesh can come epoxy coated (to resist o resist corrosion and rust) or ‘black’ steel which is uncoated.
Sometimes the engineer will require the mesh be placed on bolsters or chairs to assure the mesh will rest in the correct portion of the slab section. There are many kinds of wire mesh bolsters available; There are plastic standalone supports which support the mesh at intersecting wire. More commonly there are continuous steel bolsters which are laid parallel to each other as often as is required to support the mesh and any traffic on top.
This presents a challenge during concrete placement as the workers have to walk on or maneuver around the elevated wire mesh. Also if the concrete truck needs to drive up within the proposed slab area during placement this is near impossible with elevated mesh in place on bolsters. Because of this, sometimes the workers will pull the mesh up to the proper elevation with a specialized tool as the concrete is placed.
The most common welded wire mesh sizes are as follows:
6×6 W1.4/W1.4 10/10 (20lbs/100SF)
6×6 W2.1/W2.1 8/8 (30lbs/100SF)
6×6 W2.9/W2.9 6/6 (41lbs/100SF)
6×6 W4.0/W4.0 4/4 (56lbs/100SF)
4×4 W1.4/W1.4 10/10 (20lbs/100SF)
4×4 W2.1/W2.1 8/8 (30lbs/100SF)
4×4 W2.9/W2.9 6/6 (41lbs/100SF)
4×4 W4.0/W4.0 4/4 (56lbs/100SF)
The meaning behind the above designation are as follows :
6×6 (6″ by 6″ openings) W1.4/W1.4 (area in sq. inch of the wire cross section .014sq in) 10/10 (wire gauge of 10)
The above mesh sizes most commonly come in 8’ x 12.5’ or 8’ x 15’ sheets. Concrete pavement road mesh comes in different sizes than the above standard sheet mesh and is typically more heavy duty.