Aggregates

Aggregate plays an important role in concrete, the purpose of the aggregates within this mixture is to provide a rigid skeletal structure and to reduce the space occupied by the cement paste. Usually it is supplied in one of two main forms: precast (blocks, tiles, pipes, bridge beams, flooring systems, etc) or ready-mixed (as a liquid paste ready for pouring). It is used for the foundations, walls, floors, roofs and partitions of buildings, as well as bridges, dams, power stations and many other kinds of physical structures.

Aggregates are the materials in the inert granular form and these include the crushed stone, gravel and sand. When mixed with the Portland cement and water, these become the essential ingredients when it comes to the making of concrete. If one wants the mix of good concrete, the aggregates have to be clean and hard. The particles have to be strong and there has to be the absence of clay coatings and the absorbed chemicals. There should also be the absence of fine materials that are responsible for causing the deterioration of the concrete.

There is a strong influence of the aggregates on the recent mixed as well as hardened properties of the concrete. Another influence is on the proportion of the mixture as well as the economy. The fact is aggregate selection is process of importance. There is expectation in slight variation in the aggregate properties and there are certain important characteristics as mentioned below:

• Grading
• Durability
• Surface texture and shape of the particle
• Skid resistance and abrasion
• Voids and unit weights
• Surface moisture and absorption

The reference of grading is with respect to determining the particle size distribution as far as the aggregate is concerned. The limits of grading and the maximum size of aggregate are specified because these properties have an impact the aggregate amount used apart from the water and cement requirements, pump-ability, durability and workability of concrete. In the general cases, in case, there is the correct selection of the water cement ratio, there is use of wide range of grading without the major impact on strength.