Building Materials, Third Edition

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One of the serious limitation of reinforced cement concrete is the cracking which is a natural
phenomenon for concrete constructions. Once cracks occur they do not disappear even after
removal of load. If the width of these cracks is to be kept within permissible limits, the steel
stress has to be kept low. Presence of cracks lowers the capacity of structure to bear reversal of
stresses, impact vibration and shocks. Also, the reinforcing bars may get corroded in due
course of time and the concrete deteriorates. Besides these disadvantages, the presence of
cracks makes theory of reinforced concrete quite irrational. Efforts were made to eliminate the
cracking of concrete by artificially introducing in it either before or simultaneously with the
application of external loads, a compressive force of permanent nature. This force is so applied
that it causes compressive stresses in that zone of the member where tensile stress will be
caused by external loads. The tensile stress in concrete will thus be neutralized and it will not
crack.