Sieve analysis of fine and coarse aggregate for concrete

Definitions

1. Maximum Size (of aggregate) - in specifications for, or description of aggregate, the smallest sieve opening through which the entire amount of aggregate is required to pass.
2. Nominal Maximum Size (of aggregate) - in specifications for, or description of aggregate, the smallest sieve opening through which the entire amount of the aggregate is permitted to pass.

Objectives

1. Determine the Nominal maximum size of aggregate.
2. Calculate the "Fine Modules" of the aggregate which defined as the sum of the cumulative percentage retained on the sieves.
3. Determine the grading or size distribution of the aggregate.

Theory

The process of dividing a sample of aggregate into fraction of the same particles size is known as sieve analysis and its purpose is to determine the grading or size distribution of the aggregate by using air-dried aggregate.
concrete and asphalt mixes require a grain size distribution that will provide a dense, strong mixture. This is accomplished by ensuring that the shape of the grain size distribution curve is similar to the standard. This shape assures maximum density and strength. The voids between the larger aggregates are filled with medium aggregates. The remaining voids are filled with still finer and smaller particles.

 

Equipments

1. Sieve for coarse aggregate: 19mm, 12.5mm, 9.5mm, 6.3mm and 4.75mm. and pan
2. Sieve for fine aggregate: 6.3mm, 5.0mm, 2.0mm, 1.6mm, 0.500mm, 0.200mm, 0.160mm and pan
3. Mechanical sieve shaker which use to create vibrated the sieves to cause segregation of the particles according the sieves.
4. Balance.

Methodology

Coarse aggregate:

- Determine the weight of the sample of the aggregate which we have

1. Nest the sieves in order of decreasing size of opening from top to the bottom, on plate over mechanical sieve shaker.

2. Drop the all sample (1461.0gm) on the highest sieve and switch on mechanical sieve shaker for short period.

3. Separate the sieves and determine the weight of each aggregate retained in each sieve and also the pan.

Fine aggregate:

1. The same procedure obtained in coarse aggregate test but we use different sieves :-

(6.3, 5.0, 2.0, 1.6, 0.500, 0.200, 0.160) mm & pan.

- Note: If the total mass retained in the sieves less than the original weight of the sample, this shortage (error) distributes for all the sieves proportion to each weight in each sieve .

 

Data and Calculation

Coarse aggregate

Total weight : 1461 g

- Table 1 : Gradation on course aggregate

Finer modulus = ( ∑ cumulative percent retained ) / 100
= (1.711+40.903+74.476+96.078+97.433+100)/100 = 4.106

Maximum Aggregates Size= 25 mm
Nominal Size = 19 mm

 

Fine aggregate

total weight : 200 g ( before washing)
149.5 ( after washing)

- Table 2 : Gradation on fine aggregate

 

Source of errors:

Personal: Spread some dust during sieving which led to reduce the mass of the sample, we can notice that in the fine aggregate, we had some errors, but in the coarse aggregate the error was 0 .
Inaccuracies in taking readings.
Non-completion of the time period needed by the mechanical shaker.

Mechanical: 

Inequality openings of sieves. 

Inaccuracy of the balance used in weighing the sample.

 

Engineering use

Sieve analysis test results in gradation of aggregates in coarse and fine on the basis of their particle sizes.

Gradation is usually specified for each engineering application it is used for. For example, foundations might only call for coarse aggregates, and therefore an open gradation is needed.

Gradation is primarily a concern in pavement mix design. Concrete could call for both coarse and fine particles and a dense graded aggregate would be needed. Asphalt design also calls for a dense graded aggregate. Gradation also applies to sub-grades in paving, which is the material that a road is paved on. Gradation, in this case, depends on the type of road (i.e. highway, rural, suburban) that is being paved.