Fresh Plastic Shrinkage Cracks and analysis

1. Plastic Shrinkage Cracks
• Usually associated with hot weather concreting or any time
when ambient conditions produce rapid evaporation
• Occurs when water is lost from concrete during plastic state
(water evaporation > bleeding water)
• by evaporation (bleeding, humidity, wind, T°C)
• by suction of underlying dry concrete or soil

2. Fresh Concrete – Plastic Shrinkage
Plastic shrinkage
• Result of improper curing
• Surface layer shrinks; inside concrete is plastic

3. Interaction Between Bleeding & Evaporation
Evaporation
Bleed water
surface water
Bleed water = evaporation

4. Plastic Settlement Cracks

5. Time of Occurrence

6. Plastic Shrinkage cracks
Special precautions in hot weather concreting
1. Moisten concrete aggregate that are dry and absorptive
2. Keep concrete temperature low by cooling aggregate and
mixing water
3. Dampen the subgrade and fog forms prior to placing
concrete
4. Erect temporary windbreaks to reduce wind velocity over the
concrete surface
5. Erect temporary sunshades to reduce concrete surface
temperatures
6. Protect the concrete with temporary coverings such as
polyethylene during delay between placing and finishing
7. Fog the slag immediately after placing and before finishing
8. Add plastic fibres