TAILIEUCHUNG - Shrinkage characteristics of concrete blocks

Shrinkage strain data from tests of blocks from twenty-four block plants in Ontario shows that the majority of shrinkage occurs during later stages of drying. From a fully saturated state, it is generally necessary to remove much more than half of the water before significant shrinkage begins. From this data, it appears that water content as an absolute rather than a relative value may be a better indicator of the benefits of predrying as a measure to preshrink the block and limit the potential for shrinkage in situ. Questions are raised regarding the benefits of current specifications for moisturecontrolled block. | a 1 01 MSeventh Canadian Masonry Symposium MB MlMcMaster University H ỀMĩĩamỉlton Ontario June 4-7 1995 SHRINKAGE CHARACTERISTICS OF CONCRETE BLOCKS Robert G. Drysdale1 and Magdy M. Khattab2 ABSTRACT Shrinkage strain data from tests of blocks from twenty-four block plants in Ontario shows that the majority of shrinkage occurs during later stages of drying. From a fully saturated state it is generally necessary to remove much more than half of the water before significant shrinkage begins. From this data it appears that water content as an absolute rather than a relative value may be a better indicator of the benefits of predrying as a measure to preshrink the block and limit the potential for shrinkage in situ. Questions are raised regarding the benefits of current specifications for moisture-controlled block. INTRODUCTION Background Concrete is known to expand when it absorbs water and to shrink when it dries. For concrete block construction particularly when it is unreinforced significant shrinkage will cause unsightly cracks in the tension-weak masonry. Besides being unsightly these cracks can negatively affect rain penetration and strength characteristics. Although use of movement joints at relatively close spacing is an effective way of reducing the stresses caused by shrinkage and thereby minimizing cracking it is logical to reduce the problem itself by limiting the amount of shrinkage that can occur. In this way standardized 1 Professor Department of Civil Engineering McMaster University Hamilton Ontario L8S 4L7 2 Post-doctoral Fellow McMaster University and Assistant Professor on leave from Faculty of Engineering Ain Shams University Cairo Egypt. Drysdale et al. 950 spacings for movement joints can be worked out and designer and owner satisfaction with concrete block construction can be protected. The factors affecting the shrinkage of concrete as we know them are well explained in books on concrete technology. However most shrinkage research has been done

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• Shrinkage characteristics of concrete blocks
• Concrete blocks
• Blocks from twenty four block plants
• Water before significant shrinkage begins
• Current specifications