Abstract

Concrete is sensitive to environmental changes, especially during the first few days after casting. Volumetric changes due to drying, temperature, plastic and autogenous shrinkage are often experienced. These changes are critical during early ages when the concrete is most vulnerable to cracking. Reinforcement and joints are used to control shrinkage and leads to cracking. Bad cracking leaves the reinforcement exposed to air and moisture, which may cause it to rust and weaken concrete. Plastic shrinkage is the result of a very rapid loss of moisture from freshly laid concrete within a few hours of placement, while the concrete is still plastic and before it gains any significant strength. This loss is generally caused by various material parameters such as cement content, aggregate content, water-cement ratio and the admixtures. In addition to these environmental factors such as air and concrete temperature, relative humidity (RH) and wind velocity also cater to shrinkage. When the moisture from the surface of freshly placed concrete evaporates faster than the moisture which is replaced by bleed water, the surface concrete shrinks. Plastic shrinkage cracking of concrete is a widespread problem in concrete construction, particularly in thin applications such as highway pavements, slabs cast on grade, surface repairs, overlays, patching, and shotcrete tunnel linings. If premature surface cracks occur, they may accelerate the ingress of aggressive agents, salts and moisture and reduce long-term durability. The current research is motivated to study the influence of various material parameters on the degree of plastic shrinkage cracking in concrete and to quantify more reliable crack estimation.

Key words: Plastic shrinkage, concrete, cracks.