Cracking of fresh and hardened concrete

In general, concrete cracking may be distinguished into two cracking that developed when the concrete is fresh (plastic stage) and cracking that developed when the concrete is hardened. 

Cracking that developed in fresh concrete can be further distinguished into the following  

Early thermal contraction cracking or thermal stress cracking 

Drying shrinkage cracking or long-term drying shrinkage cracks 

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Successful repair of cracking is often very difficult to attain. Cracking in fresh or hardened concrete is a type of failure that is far easier to prevent and almost impossible to repair efficiently and successfully. 

The strength of Portland cement concrete may be increased by additional reinforcement. This is usually accomplished by means of steel rods, wires, bars (rebar), or mesh, which are embedded into the fresh and uncured concrete. Thus, the reinforcement renders the hardened structure capable of supporting greater tensile, compressive, and shear stresses. Even if cracks develop in the concrete, considerable reinforcement is maintained. 

Concrete in the fresh state should have good workability in order to be properly placed and compacted in the mould so that it can reach the expected properties after hardening. The most relevant properties of hardened concrete are strength, deformation due to loading or thermal and moisture variations, resistance to cracking, and durability. 

Chloride ions may be introduced to the fresh mix from mixing water, marine aggregate, or admixtures with chloride components. The chloride ions also penetrate to the hardened concrete materials from the air through pores, bleed-water channels, entrapped-air voids and cracks. The density of the material and its impermeability is decisive to improving the durability in the case of possible chloride ions attack under service conditions. The intensity of penetration of chlorides is considered as proportional to the value... 

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