1. Cement and Concrete
Concrete is an artificial conglomerate,with the following constituents:
Cement
Aggregate
Water
Cement replacements and admixtures

2. Properties
Fluid when wet
Initial setting in approx 12 hours
Strength increases with time
Strong in compression, weak in tension
Fire resistance
Durability
Chemical resistance

3. Standards
There are a bewildering number of British and European standards covering the design, specification, use and testing of concrete.
Two key standards are:
BS 5328 (Parts 1 to 4) and
BS EN 206 which will ultimately replace it.

4. Reacts with water to harden and bind the other constituents.
Cement
Reacts with water to harden and bind the other constituents.
May be replaced in part by other pozzolanic materials.
The cement content has a significant bearing on the strength of the final product.
A pozzolan is a material which, when combined with calcium hydroxide, exhibits cementitious properties. Pozzolans are commonly used as an addition (the technical term is "admixture") to Portland cement concrete mixtures to increase the long-term strength and other material properties of Portland cement concrete. Pozzolans are primarily vitreous siliceous materials which react with calcium hydroxide to form calcium silicates; other cementitious materials may also be formed depending on the constituents of the pozzolan.

5. Types of Cement
Ordinary Portland Cement OPC
Rapid Hardening Portland Cement RHPC
Sulphate Resisting Portland Cement SRPC
White Portland Cement
Low Heat Portland Cement
Masonry Cement
Portland Pulverised Fuel Ash Cement

6. Aggregates
The major bulk of the concrete
Usually separate coarse and fine aggregate used
Large bearing on final concrete properties.
Lightweight aggregates may be used to produce low-density concrete.

7. Water
Should be clean and free from impurities
Water content will affect workability
Too much water – weak concrete
Lightweight aggregates may be used to produce low-density concrete.

8. Admixtures
Accelerators
Retarders
Water reducers (Plasticisers)
Air entrainers
Superplasticisers

9. Testing (BS 1881)
The Slump Test:
A site test to determine the workability of the fresh concrete.
The Concrete Cube Test:
A laboratory test to determine the compressive strength of hardened concrete.
BS 1881 will be superseded by BS EN by December 2003.

10. Specification
BS 5328 describes four ways of specifying
Designed Mix
Prescribed Mix
Standard Mix
Designated Mix
BS EN 206 has just three ways.