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Fine agg

he fine aggregate specific gravity test (Figure 1) is used to calculate the specific gravity of a fine

aggregate sample by determining the ratio of the weight of a given volume of aggregate to the weight of

an equal volume of water. It is similar in nature to the coarse aggregate specific gravity test.

Figure 1: Fine aggregate specific gravity sample and pychnometer.

The fine aggregate specific gravity test measures fine aggregate weight under three different sample

conditions:

Oven-dry (no water in sample). Saturated surface dry (water fills the aggregate pores). Submerged in water (underwater).Using these three weights and their relationships, a sample's apparent specific gravity, bulk specific

gravity and bulk SSD specific gravity as well as absorption can be calculated.

Aggregate specific gravity is needed to determine weight-to-volume relationships and to calculate

various volume-related quantities such as voids in mineral aggregate (VMA), and voids filled by asphalt

(VFA). Absorption can be used as an indicator of aggregate durability as well as the volume of asphalt

binder it is likely to absorb.

The standard fine aggregate specific gravity and absorption test is:

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AASHTO T 84 and ASTM C 128: Specific Gravity and Absorption of Fine Aggregate[edit]

Background

Specific gravity is a measure of a material's density (mass per unit volume) as compared to the density

of water at 73.4F (23C). Therefore, by definition, water at a temperature of 73.4F (23C) has a

specific gravity of 1.

Absorption, which is also determined by the same test procefure, is a measure of the amount of water

that an aggregate can absorb into its pore structure. Pores that absorb water are also referred to as

"water permeable voids".

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Specific Gravity Use

Aggregate specific gravity is used in a number of applications including Superpave mix design,

deleterious particle indentification and separation, and material property change identification.

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Superpave Mix Design

Superpave mix design is a volumetric process; it relies on mixing constituent materials on the basis of

their volume. However, aggregate and asphalt binder volumes are diffucult to measure directly,

therefore a material's weight is typically measured and then converted to a volume based on its specific

gravity. Correct and accurate material specific gravity determinations are vital to proper mix design. An

incorrect specific gravity value will result in incorrectly calculated volumes and ultimately result in an

incorrect mix design.

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Material Contamination Indicator and Separator

Specific gravity can also indicate possible material contamination. For instance, deleterious particles

(Figure 2) are often lighter than aggregate particles and therefore, a large amount of deleterious

material in an aggregate sample may result in an abnormally low specific gravity.

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Differences in specific gravity can also be used to separate deleterious, or bad, particles from aggregate

particles using a heavy media liquid. Water absorption can also be an indicator of asphalt absorption.

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Material Change Indicator

Finally, specific gravity differences can be used to indicate a possible material change. A change in

aggregate mineral or physical properties can result in a change in specific gravity. For instance, if a

quarry operation constantly monitors the specific gravity of its output aggregate, a change in specific

gravity beyond that normally expected could indicate the quarrying has moved into a new rock

formation with significantly different mineral or physical properties.

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Aggregate Absorption Use

Aggregate absorption is the increase in mass due to water in the pores of the material. Aggregate

absorption is a useful quality because:

1. High values can indicate non-durable aggregate.2. Absorption can indicate the amount of asphalt binder the aggregate will absorb.

It is generally desirable to avoid highly absorptive aggregate in HMA. This is because asphalt binder that

is absorbed by the aggregate is not available to coat the aggregate particle surface and is therefore not

available for bonding. Therefore, highly absorptive aggregates (often specified as over 5 percent

absorption) require more asphalt binder to develop the same film thickness as less absorptive

aggregates making the resulting HMA more expensive.

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