Plastic shrinkage cracking in concrete

Abstract

Cracks in concrete structures are a normal phenomenon and can have many causes. In most cases a certain degree of cracking can be accepted. though freedom from cracks is required for certain types of construction. By and large all cracking is due to external conditions which impose upon the concrete a tensile stress and accompanying strain which exceeds its ultimate strain. However. it is often difficult to identify the direct external cause when the damage first occurs because data and measurement results regarding important parameters are seldom available. Cracks do not generally become a problem until the crack width has reached a certain size. Analyses of cases of cracking show that such cracks normally occur in the transition phase between the fresh and solid states of the concrete. It is probable that cracks which in practice are usually called 'shrinkage cracks', i.e. cracks due to the drying out of more or less hardened concrete, have rather occurred at earlier stages when the concrete's shrinkage reinforcement is of little or no importance in the formation of cracks.