Fineness Modulus Calculation

The Fineness Modulus (FM) is an empirical figure obtained by adding the total percentage of the sample of an aggregate retained on each of a specified series of sieves, and dividing the sum by 100.

Example

A sieve analysis was performed on a 500g sample of fine aggregate. The mass retained on the standard sieves is as follows: No. 4 (10g), No. 8 (55g), No. 16 (110g), No. 30 (100g), No. 50 (120g), No. 100 (85g), and the Pan (20g). Calculate the Fineness Modulus and interpret the result.

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Specific Gravity and Absorption of Coarse Aggregate

Determining the specific gravity and absorption of aggregates is crucial for concrete mix design, as it dictates the volume the aggregate will occupy and how much mix water it will absorb.

Example

A sample of coarse aggregate is tested according to ASTM C127. The following weights are recorded: Weight of oven-dry sample in air (AA) = 3250 g Weight of saturated-surface-dry (SSD) sample in air (BB) = 3300 g Weight of saturated sample in water (CC) = 2080 g
Calculate the Bulk Specific Gravity (dry basis), Bulk Specific Gravity (SSD basis), Apparent Specific Gravity, and Absorption Capacity.

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Blending of Aggregates

Often, a single aggregate source will not meet the required gradation specifications. In such cases, two or more aggregates must be blended together in specific proportions to achieve a combined gradation that falls within the acceptable limits.

Example

A concrete mix requires a combined aggregate gradation. You have two available aggregates: Aggregate A (Coarse) and Aggregate B (Fine). The target specification for the percentage passing the 9.5 mm (3/8 in.) sieve is 55%.
Sieve analysis shows that:
  • Aggregate A has 15% passing the 9.5 mm sieve.
  • Aggregate B has 95% passing the 9.5 mm sieve.
Determine the exact proportions (percentages) of Aggregate A and Aggregate B that must be blended to meet the target of exactly 55% passing the 9.5 mm sieve.

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