Q.
a) Define concrete. State the functions of each material used in concrete mix. (10 marks)
b) Clarify workability of concrete. Explain the factors influencing the workability of concrete. (15 marks)
(25 marks, 2019 Q6)
A.
a) Define concrete and function of each material used in concrete mix.
Concrete, an artificial stone-like mass, is the composite material that is created by mixing binding material (cement or lime) along with the aggregate (sand, gravel, stone, brick chips, etc.), water, admixtures, etc in specific proportions. The strength and quality are dependent on the mixing proportions.
The formula for producing concrete from its ingredients can be presented in the following equation:
Concrete =
Binding Material + Fine & Coarse aggregate + Water + Admixture (optional)
Concrete is a very necessary and useful material for construction work. Once all the ingredients -cement, aggregate, and water unit of measurement mixed inside the required proportions, the cement and water begin a reaction with one another to bind themselves into a hardened mass. This hardens rock-like mass is the concrete.
Ref:
https://civiltoday.com/civil-engineering-materials/concrete/270-concrete-definition-components-types
Contrary to popular belief, concrete and cement are not the same thing; cement is actually just a component of concrete. Concrete is made up of three basic components: water, aggregate (rock, sand, or gravel) and Portland cement. Cement, usually in powder form, acts as a binding agent when mixed with water and aggregates. This combination, or concrete mix, will be poured and harden into the durable material with which we are all familiar.
Components of a basic concrete mix
There are three basic ingredients in the concrete mix:
- Portland Cement
- Water
- Aggregates (rock and sand)
Portland Cement - The cement and water form a paste that coats the aggregate and sand in the mix. The paste hardens and binds the aggregates and sand together.
Water- Water is needed to chemically react with the cement (hydration) and too provide workability with the concrete. The amount of water in the mix in pounds compared with the amount of cement is called the water/cement ratio. The lower the w/c ratio, the stronger the concrete. (higher strength, less permeability)
Aggregates- Sand is the fine aggregate. Gravel or crushed stone is the coarse aggregate in most mixes.
Desired properties of concrete
1. The concrete mix is workable. It can be placed and consolidated properly by yourself or your workmen.
2. Desired qualities of the hardened concrete are met: for example, resistance to freezing and thawing and deicing chemicals, watertightness (low permeability) , wear resistance, and strength. Know what you are trying to achieve with the concrete.
3. Economy. Since the quality depends mainly on the water to cement ratio, the water requirement should be minimized to reduce the cement requirement (and thus reduce the cost).
Take these steps to reduce the water and cement requirements:
- use the stiffest mix possible
- use the largest size aggregate practical for the job.
- Use the optimum ratio of fine to coarse aggregate.
Ref:
https://www.concretenetwork.com/concrete.html
b) Workability of concrete. Factors influencing.
Further on
Ref:
Earlier posts.