CONSTRUCTION TECHNIQUES FOR CRACK CONTROL OF CAST-IN-PLACE CONCRETE SLABS AND WALLS

Abstract

The paper presents recommended construction techniques for crack control of cast-inplace concrete slabs and walls. The crack control in this paper refers to controlling or preventing crack formation during the placing, stiffening and shrinking of fresh concrete. These cracks are influenced by means and methods of construction as opposed to structural cracks due to imposed loads. The techniques affecting construction crack formation involve details regarding volume and length of concrete pour, casting sequence, concrete curing and mix design. These strategies are related directly to concrete joints. Various joint types: saw cut, contraction, expansion and construction joints are discussed. The paper emphasizes that saw cut joint is a dummy or fake joint and has no use for crack control. The suggested techniques recommend the use of full-face construction joints to limit the length of each pour segment to 5m to 10m maximum, followed by water curing of concrete for a minimum elapsed time before placing the adjacent pour. For large projects, several alternate slab panels may be poured simultaneously. The closure pours between the first pour panels can then be cast after the minimum elapsed time. It is noted that continuous wet water curing of concrete is recommended over membrane curing method for better quality control. Lastly, concrete mix which includes 15% to 20% of fly ash is recommended for lower heat of hydration and concrete shrinkage. Several proven examples of successful projects using the recommended techniques, within the past 50 years, are given to confirm the effectiveness of the methods.