They can expose reinforcing steel to oxygen and moisture and make the steel more susceptible to corrosion. While the specific causes of cracking are manifold, cracks are normally caused by stresses that develop in concrete due to the restraint of volumetric change or to loads which are applied to the structure. Within each of these categories there are a number of factors at work. A successful crack control program must recognize these factors and deal with each of them, in turn. This report presents the principal causes of crack- ing and a detailed discussion of crack control pro- cedures.
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They conclude that this procedure is useful for monitoring crack growth in concrete due to fatigue. Based on the appearance of the fracture surface, which shows a combination of both aggregate fracture and bond failure, they feel that fracture toughness is not a pertinent material property. However, they state that an effective fracture toughness might be a significant material property if related to specific material and specimen variables such as aggregate size and gradation, and proportions of the mix, and if the calculation considers the nonlinear material re- sponse of concrete.
A number of investigators do not feel that the Griffith theory of linear fracture mechanics is di- rectly applicable to all concrete 2. Some like Swartz, et a1. Clearly, specimen size requirements must be given more attention.
Of key interest in future work are the observations by Walsh2. References 2. Hsu, Thomas T. Hsu, Thomas, T. Slate, Floyd O. Evans, R. Brooks, J. Meyers, Bernard L. Shah, Surendra P. Sturman, Gerald M. Griffith, A. Kaplan, M. Romualdi, James P. Huang, T. Lott, James L. Naus, Dan J. Brown, J. Evans, A. July , pp. Mindess, Sidney, and Nadeau, John S. Walsh, P. Gjorv, O. Swartz, Stuart E. Testa, Rene B.
Spooner, D. Louis, Aug. III, pp. Karsan, I. Demir, and Jirsa, James Neville, A. Darwin, David, and Slate, F. Perry, C. Carino, Nicholas J. Tasuju, M. Ebrahim; Slate, Floyd 0. Hillemeier, B. It is one of the most serious problems encountered in concrete construction. Good design and construction practice can minimize the amount of cracking and eliminate the visible large cracks by the use of adequate re- inforcement and contraction joints.
Although drying shrinkage is one of the principal causes of cracking, temperature stresses, chemical reactions, frost action, as well as excessive tensile stresses due to loads on the structure, are fre- quently responsible for cracking of hardened con- crete. Cracking may also develop in the concrete prior to hardening due to plastic shrinkage. Information presented in this chapter concerns only the subjects of cracking of hardened concrete due to drying shrinkage; factors influencing shrink- age; control of cracking; and the use of expansive ce- ments to minimize cracking.
The subject of construction practices and specifica- tions to minimize drying shrinkage is covered in Chapter 8 Sections 8. If the shrinkage of concrete caused by drying could take place without any restraint, the concrete would not crack. However, in a structure the concrete is al- ways subject to some degree of restraint by either the foundation or another part of the structure or by the reinforcing steel embedded in the concrete.
This combination of shrinkage and restraint develops ten- sile stresses. When this tensile stress reaches the tensile strength, the concrete will crack.
This is illus- trated in Fig. Another type of restraint is developed by the dif- ference in shrinkage at the surface and in the inte- rior of a concrete member, especially at early ages. Since the drying shrinkage is always larger at the exposed surface, the interior portion of the member restrains the shrinkage of the surface concrete, thus developing tensile stresses.
This may cause surface cracking, which are cracks that do not penetrate deep into the concrete. These surface cracks may with time penetrate deeper into the concrete mem- ber as the interior portion of the concrete is subject to additional drying.
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The scatter is considerable. Due to the inherent low because of moisture gradients. The actions that tend to make a mixture tions. Precast panels made of low- progresses upward.
ACI 224R_90 Control of Cracking in Concrete