Concrete must be placed carefully to prevent bleeding. Bleeding is the formation of a layer of water on the surface of freshly placed concrete when the aggregates and cement separate from the water. Bleeding reduces the concrete strength.
Vibration is used to consolidate stiff concrete by increasing its fluidity. Too much vibration, especially in wet and highly workable concrete mixtures, can cause segregation and a weakening of the concrete.
Hydration is the chemical reaction between cement and water. As the hydrating cement paste hardens it forms a bond with itself and the aggregate. A strong concrete is formed by cement paste with few pores and low water content because it has more cement to bond with the aggregate. High heat of hydration can protect concrete from freezing when it is placed during winter. Too much heat of hydration can put excessive stress on on large concrete structures such as dams.
Materials In Concrete.
2.Concrete Aggregates - Concrete Slump.
3.Concrete Placement - Vibration - Hydration.
4.Types of Portland Cement - Concrete Moisture & Cracking.
5.Watertight Concrete - Supplementary Cementing Materials.
6.Supplementary Cementing Materials.
7.Chemicals That Damage Concrete.
8.Concrete Aggregate Properties.
9.Angular & Smooth Aggregate Properties.
12.Air Entraining Admixtures.
13.Air Entraining Admixtures Continued.
14.Conditions Affecting Concrete Air Volume.
15.Superplasticizers & Other Admixtures.
16.Ordering & Mixing Concrete.
17.Concrete Mixing - Subgrade Preparation.
18.Subbase Preparation - Concrete Placement.
22.Hot Weather Concreting.
23.Cold Weather Concreting.
24.Concrete Slump Test.