why do concrete surface flake and spall?

Concrete surface flake and spall for one or more of the followings reasons :

• In areas of the country that are subjected to freezing and thawing the concrete should be air-entrained to resist flaking and scaling of the surface . If air entrained concrete is not used , there will be subsequent damange to the surface
• The water /cement ratio should be as low as possible to improve durability of the surface . Too much water in the mix will produce a weaker , less durable concrete that will contribute to early flaking and spalling of the surface
• THe finishing opereations hould not begin until the water sheen on the surface is gone and excess bledd water on the surface has had a chance to evaporate . IF this excess water is worked into the concrete because the finishiong operation are begun too soon , the concrete , on the surface will have to high a water content and will be weaker and less durable .