Concrete slab is one of the main elements for the construction industry. During the curing process, concrete slab panels tend to curl up at joints and around its perimeter. Curled up slabs are unsafe and can cause the concrete panels to endure high levels of stress, which leads to cracks and maintenance issues down the road.
Differential shrinkage is the basic cause of curling. This occurs as the exposed top surface of the slab shrinks and the core of the slab does not. Concrete slabs, like many other construction materials, are not dimensionally stable when subjected to changes in the moisture content. The factors that affect the amount of curling in a concrete slab are the subbase material, concrete mix characteristics such as water/cement (w/c) ratio, cement type, aggregate type, admixture types, cement content and mix temperature.
Forming a series of saw-cut joints in a slab is one method to reduce stress due to shrinkage. Saw-cut joints are spaced according to guidelines from the cement association, and should have a depth of at least one-quarter of the slab thickness. By having a saw-cut in a concrete slab, the propagation of cracks in the slab is controlled and the weakened planes where the concrete can crack in a straight line forms. This produces an aesthetically pleasing appearance since the crack takes place below the finished concrete surface. The concrete has still cracked which is normal behaviour, but the absence of random cracks at the concrete surface gives the appearance of an un-cracked section.
Also for reducing curling in the concrete slab, the prior arts suggest to use different additives such as synthetic macro fibres, steel fibres to be added to ready-mix concrete. The cost of adding chemical additives to the concrete slab is high and it raises the construction cost. Another way to reduce curl is to reinforce the slab with large amounts of steel rebar which also increases the construction cost.