Reference: Cement and Concrete Composites, Vol. 26 (6), 677-685, 2004.


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MITIGATION STRATEGIES FOR AUTOGENOUS SHRINKAGE CRACKING



D.P. Bentza 1 and O.M. Jensenb

aBuilding and Fire Research Laboratory
100 Bureau Drive Stop 8621
National Institute of Standards and Technology
Gaithersburg, MD 20899-8621 USA
bAalborg University
DK-9000 Aalborg
DENMARK


ABSTRACT

As the use of high-performance concrete has increased, problems with early-age cracking have become prominent. The reduction in water-to-cement ratio, the incorporation of silica fume, and the increase in binder content of high-performance concretes all contribute to this problem. In this paper, the fundamental parameters contributing to the autogenous shrinkage and resultant early-age cracking of concrete are presented. Basic characteristics of the cement paste that contribute to or control the autogenous shrinkage response include the surface tension of the pore solution, the geometry of the pore network, the visco-elastic response of the developing solid framework, and the kinetics of the cementitious reactions. While the complexity of this phenomenon may hinder a quantitative interpretation of a specific cement-based system, it also offers a wide variety of possible solutions to the problem of early-age cracking due to autogenous shrinkage. Mitigation strategies discussed in this paper include: the addition of shrinkage-reducing admixtures more commonly used to control drying shrinkage, control of the cement particle size distribution, modification of the mineralogical composition of the cement, the addition of saturated lightweight fine aggregates, the use of controlled permeability formwork, and the new concept of "water-entrained" concrete. As with any remedy, new problems may be created by the application of each of these strategies. But, with careful attention to detail in the field, it should be possible to minimize cracking due to autogenous shrinkage via some combination of the presented approaches.



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