The control of thermal and shrinkage cracking in reinforced concrete

© 1977 Dr. Martin H. MurrayWide, randomly spaced cracks in lightly reinforced concrete members result from restrained reductions in the volume of the member. Extensive research in the past has identified the causes of these volume changes (e.g. thermal contraction, creep and drying shrinkage) but comparatively little research effort has been directed specifically towards controlling the cracks induced by these movements. This thesis examines the control of thermal and shrinkage cracking in reinforced concrete members. A survey of the literature discusses the causes of this type of cracking and identifies the critically important role played by the bond of reinforcing to the surrounding concrete; the majority of current crack width prediction formulae are shown to be unsatisfactory. A review follows of recent structures in which thermal and shrinkage cracks were causing concern, and indicates that present design recommendations and criteria are inadequate. Simple and comprehensive theoretical models of restrained concrete members are developed and equations are derived enabling the prediction of the behaviour of cracks. Experimental work determined the mechanisms by which different types of reinforcing act to control the width and shape of cracks in reinforced concrete walls. Amounts of conventional reinforcing up to four times greater than presently recommended values are shown to be necessary to achieve a controlled pattern of cracks, and fundamental differences identified between the control exercised by deformed bar and fabric reinforcement