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Importance of Specific Gravity of Aggregates in Concrete Mix Design

Specific Gravity is defined as the ratio of Weight of Aggregate to the Weight of equal Volume of water. The specific gravity of an aggregate is considered to be a measure of strength or quality of the material. Aggregates having low specific gravity are generally weaker than those with high specific gravity. This property helps in a general identification of aggregates.

The specific gravity of aggregates normally used in construction ranges from about 2.5 to 3.0 with an average value of about 2.68.

Specific gravity influences the concrete mix in the following ways:

1. Specific Gravity of Aggregates Affects Concrete Volume

Specific gravity of aggregates that are planned to be used in concrete mix design is determined to study the absolute volume of aggregates that will occupy in the concrete mixture. Absolute volume of aggregates refers to the space occupied by the aggregate particles i.e. the volume of solid matter and internal aggregate pores, which excludes the voids between particle

When, aggregate of one specific gravity in concrete mixture is combined with aggregates of another specific gravity, the concrete volume yields or changes. 

Concrete is always sold by volume. The volume change in concrete means, the purchaser is either receiving less concrete than ordered or the producer is supplying more concrete than purchased.

2. Determination of Deleterious Materials in Concrete

Some deleterious materials are lighter than good aggregates. Hence, tracking the specific gravity can sometime indicate a change of material or possible contamination. 

The difference in specific gravity can be used during the production to separate the deleterious material from the good using a heavy media liquid. 

3. Determination of Percentage voids and Solid Volume of Aggregates

γd = Dry unit weight of aggregates

γw = Unit weight of water

w = water content

na = Percentage voids;

G=Specific gravity of aggregates

4. Specific Gravity Affects Density of Concrete

Aggregates with higher specific gravity implies higher strength. Higher dense concrete implies higher strength concrete.

Also Read:

Determination of Specific Gravity/Relative density of Coarse Aggregates- ASTM Standards 


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