Plastic shrinkage cracks

Plastic Shrinkage Cracks Properties & Preventions

1. PLASTIC SHRINKAGE CRACKS - Himanshu Pooniya

2. Causes of floor & surface cracks…! Cracks occurs in a material when the tensile stress applied is more then its tensile strength. Concrete has a low tensile strength & undergo large volume change – swells in wet & shrinks as it dries Volume of Hydrated Cement Paste – sensitive to its moisture content, controlled by RH of environment. Shrinkage Component in concrete is cement paste. Degree of Shrinkage – W/C, Age & Environmental Condition.

3. CRACKS Cracks Non Structural Environmental Conditiions Design Materials Construction Practices Structural Detailing

4. CRACKS Plastic Shrinkage Cracks FRESH CONCRETE Plastic Settlement Cracks HARDEND CONCRETE Drying Shrinkage Cracks

5. Plastic shrinkage cracks Plastic Shrinkage Cracks are caused by a rapid loss of water from the surface of concrete before it has set. The critical condition exists when the rate of evaporation of surface moisture exceeds the rate at which rising bleed water can replace it. Surface Water evaporation faster then bleed water-surface shrink more than the interior concrete. As the interior concrete restrains shrinkage of the surface concrete, stresses that exceed the concrete’s tensile strength development, resulting in surface cracks.

6. Plastic shrinkage cracks

7. Effect of Bleed Water in plastic shrinkage cracks In order to insure Plastic Shrinkage Cracking, make sure there is no bleed water. Bleed Water is a direct function of total surface area in the mix: Most Surface Area  Less Bleed Water Less Surface Area  More Bleed Water

8. Concrete in practice “If Plastic Shrinkage Cracks appear during final finishing, the finisher may be able to close with striking each side of the crack with a float refinishing, can close the crack”

9. PREVENTIONS OF surface cracks…! Protect from direct sunlight & wind, by plastic cover or start early Curing. Do not use sand which lack fines. Keep Low Slump. Uses of Water Retarders Agents However, when this occurs, precautions as described below, should be taken to avoid further cracking:-

10. CURING: (2 ND Stage of PREVENTIONS OF surface cracks) A good curing system makes sure that the evaporation potential of the surface of the concrete is 0.0

11. Thank you