Question

Relate aggregates, concrete, asphalt, cement materials individually, and relate each material to the other materials. For example, how do they relate to a concrete or asphalt mixture? The goal is to demonstrate a thorough understanding of each material and their relationships to each other. Focus on a discussion and the significance of individual material groupings (aggregates, concrete (including Modulus Of Elasticity), asphalt, and cement), and explain in detail their importance to quality concrete and asphalt mixtures. Talk about “What, How, and Why.” Demonstrate a thorough understanding of each material.

Answer 1

Asphalt mixture - An asphalt mixture is composed of

• Aggregates - Gravel , Sand and Stone.
• Bitumen

1) Aggregates

• Gravel - These are loose aggregates that contribute to the toughness and soundness properties of the asphalt mix .These are the largest particles in an asphalt mix and have voids between them ,which needs to be filled by crushed stone and sand , bound by bitumen .
• Sand - These are the finest loose particles which contribute to properties like surface texture, soundness and absorbtion of the asphalt .They fill the voids between the larger aggregates and help them bond with each other.
• Crushed Stone - These are also the loose particles in an asphalt mix and contribute to toughness , soundness and texture .They are smoother than gravel and also fill the voids between the larger gravel particles .

2) Bitumen - It is a by-product of refined crude oil and is an excellent binder .It binds the gravel , sand and crushed stone together .It fills the voids between the aggregates and provides a smooth surface on the roads . It's elastic properties make the asphalt stiff as a whole.

Concrete Mixture - A concrete mixture is composed of

• Cement - It is an excellent binding material which ,after mixing with water forms a solid substance meaning that it makes the materials mixed with it solid as a whole .It is composed of lime , silica , iron , alumina , magnesia and alkalis.

1) Lime - Cement is mostly composed of lime , it forms most of the calcium silicate and calcium aluminate from lime .

2)Silica - The second largest component in cement is Silica which is important for the strength of cement as it formd Di-Calcium Silicate and Tri- Calcium silicate.

3)Iron oxide - It imparts colour to the cement and also is responsible for hardness and strength of cement.

4)Alumina - It is responsible for quick setting property of cement .

5)Magnesia - It imparts colour and hardness to the cement

6)Alkalis - It helps in the setting time of concrete.

• Sand - It is a fine aggregate which adds to the volume of the concrete and also adds to the density of the concrete .It also imparts strength to the concrete , adds to workability of concrete.
• Water - Water is also an important composition in concrete as without water ,the hydration of cement cannot occur which leads to the cement being a binder to hold all the aggregates together to form concrete.
• Admixture - Admixture are substances which imparts concrete with the desirable properties like strength , setting time , resistance etc.

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