![]() The mass measurement only includes the aggregate particle. Apparent Specific Gravity, G sa. The volume measurement only includes the volume of the aggregate particle it does not include the volume of any water permeable voids.Several different types of specific gravity are commonly used depending upon how the volume of water permeable voids (or pores) within the aggregate are addressed (Figure 3): 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. 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. It is generally desirable to avoid highly absorptive aggregate in HMA. Absorption can indicate the amount of asphalt binder the aggregate will absorb.High values can indicate non-durable aggregate.Aggregate absorption is a useful quality because: Aggregate Absorption UseĪggregate absorption is the increase in mass due to water in the pores of the material. 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. A change in aggregate mineral or physical properties can result in a change in specific gravity. Material Change Indicatorįinally, specific gravity differences can be used to indicate a possible material change. Water absorption can also be an indicator of asphalt absorption. 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.ĭifferences in specific gravity can also be used to separate deleterious, or bad, particles from aggregate particles using a heavy media liquid. ![]() Specific gravity can also indicate possible material contamination. Material Contamination Indicator and Separator An incorrect specific gravity value will result in incorrectly calculated volumes and ultimately result in an incorrect mix design. Correct and accurate material specific gravity determinations are vital to proper mix design. ![]() 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. Superpave mix design is a volumetric process it relies on mixing constituent materials on the basis of their volume. Specific Gravity UseĪggregate specific gravity is used in a number of applications including Superpave mix design, deleterious particle indentification and separation, and material property change identification. Pores that absorb water are also referred to as “water permeable voids”. Therefore, by definition, water at a temperature of 73.4☏ (23☌) has a specific gravity of 1.Ībsorption, 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. Specific gravity is a measure of a material’s density (mass per unit volume) as compared to the density of water at 73.4☏ (23☌). ![]() AASHTO T 84 and ASTM C 128: Specific Gravity and Absorption of Fine Aggregate.The standard fine aggregate specific gravity and absorption test is: Absorption can be used as an indicator of aggregate durability as well as the volume of asphalt binder it is likely to absorb. 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.Īggregate 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). Saturated surface dry (water fills the aggregate pores).The fine aggregate specific gravity test measures fine aggregate weight under three different sample conditions: Figure 1: Fine aggregate specific gravity sample and pycnometer. It is similar in nature to the coarse aggregate specific gravity test. The 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.
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