With few exceptions, concrete slabs must be reinforced with steel bars or steel mesh. Concrete has excellent compressive strength. However, the tensile strength of concrete is weak relative to its compressive strength. That being said, concrete is hard to crush concrete. Instead, it is much easier to rip it off. 

compressive strength

Concrete Strength: The sand and gravel in concrete give it its compressive strength. Sand and rocks in concrete can support enormous weights. The harder the rock and the more rock in the mix, the higher the compressive strength of the concrete. Although the standard mix ratio is four parts—two to four parts crushed stone, two parts sand, and one part cement—this ratio can be adjusted to give the concrete higher compressive strength. 

Tensile strength

Tensile strength is the first thing to fail in slabs: reinforced concrete slabs are needed because it is not the compressive integrity of the slab that fails in first place. Yield is tensile strength. The reason why floor tiles crack and break is the tensile strength of the concrete. While the rock and sand in concrete give it its compressive strength, all of concrete's tensile strength comes from cement, which has a much lower tensile strength than rock and sand in compression. 

The tensile strength of concrete is ten times less than the compressive strength.

Tensile strength is the bonding strength of a material: Cement is an adhesive that keeps all three components of concrete intact after curing. But, like glue, cement can crack. The bending and twisting of concrete for tensile strength. Like a broken stick, when the ground under the concrete slab settles or expands, the concrete cracks at the point of impact.

Rebar and Reinforcing Mesh: The solution to low tensile strength concrete without rebar and reinforcing mesh. Intuitively, steel bars and steel mesh do not appear to improve the tensile strength of concrete. The reinforcement bar bends and bends when it is lifted. The mixture is even risen. However, when embedded in concrete, they significantly increase the tensile strength of the concrete because the compressive force of the tensile weight is distributed throughout the reinforcement. Also, when the steel bars are tied in a lattice, the tensile strength of the steel bars is greatly improved by overlapping them vertically.

Rebar and cage dimensions: Single-layer rebar tiles generally provide a concrete slab with sufficient strength tensile to resist soil movement and expansion that occurs. as follows. However, for situations where additional force is required, there are two options. The first is to increase the size of the rebar used. For every 1/4-inch increase in rebar diameter, the total load resistance will more than double. For example, the absolute load strength of #4 rebar (5/8-inch rebar) is 13,564 psi. 7/8-inch bars - 6 gauge bars - have a pure load strength of 30,148 psi. #11 rebar is an inch and a half of rebar that is seven times stronger than #4 rebar.

Another way to increase the tensile strength of the slab is to double the curtains with cages.

A reinforced concrete slab with an internal cage is more than four times stronger than a slab with a single horizontal curtain. While costing more than twice as much, the caged reinforced concrete slab is strong enough to hang and support the top weight thanks to the addition of rebar. An example of a reinforced concrete slab with an internal cage is the suspended terrace on both sides of apartment buildings.

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