Standard Method of Test for Specific Gravity and Absorption of Coarse Aggregates-Civil-ZESHTECH
Standard Method of Test for Specific Gravity and Absorption of Coarse Aggregates.
Scope:
This test method covers the determination of bulk specific gravity and water Absorption of coarse aggregates.
Aim:
• To measure the strength or quality of the material
• To determine the water absorption of aggregates
Introduction:
There are four determinations that may be made from this procedure. They are as follows:
• Bulk dry specific gravity (Gsb)
• Bulk SSD specific gravity (Gsb SSD)
• Apparent specific gravity (Gsa)
• Absorption (% Abs)
Definitions:
• Absorption: The increase in weight due to water contained in the pores of the material.
• Bulk Dry Specific Gravity: The ratio of the weight in air of a unit volume of aggregate at a stated temperature to the weight in air of an equal volume of gas-free distilled water at the stated temperature.
• Bulk SSD Specific Gravity: The ratio of the weight in air of a unit volume of aggregate, including the weight of water within the voids filled to the extent achieved by submerging in water for approximately 15 hours, to the weight in air of an equal volume of gas-free distilled water at the stated temperature.
• Apparent Specific Gravity: The ratio of the weight in air of a unit volume of the impermeable portion of aggregate (does not include the permeable pores in aggregate) to the weight in air of an equal volume of gas-free distilled water at the stated temperature.
• SSD – (Saturated, Surface Dry): The condition in which the aggregate has been soaked in water and has absorbed water into its pore spaces. The excess, free surface moisture has been removed so that the particles are still saturated, but the surface of the particle is essentially dry.
Apparatus: Sample container, Balance, Suspended Apparatus, Sieve No#4 , Water tank
Procedure:
• Dry the test sample to constant mass at a temperature of 110 + 5°C, cool in air at room temperature for 1 to 3 h for test samples of 37.5-mm (1 1⁄2-in.) nominal maximum size, or longer for larger
sizes until the aggregate has cooled to a temperature that is comfortable to handle.
• Subsequently immerse the aggregate in water at room temperature for a period of 24 + 4h.
• Remove the test sample from the water and roll it in a large absorbent cloth until all visible films of water are removed. Wipe the larger particles individually. A moving stream of air is permitted to assist in the drying operation. Take care to avoid evaporation of water from aggregate pores during the surface drying operation.
• Determine the mass of the test sample in the saturated surface dry condition. After determining the
mass in air, immediately place the saturated surface dry test sample in the sample container and determine its apparent mass in water at 23 + 2.0°C.
• Take care to remove all entrapped air before determining its mass by shaking the container while immersed.
• Dry the test sample to constant mass at a temperature of 110 + 5°C, cool in air at room temperature1 to 3h, or until the aggregate has cooled to a temperature that is comfortable to handle, and determine the mass.
Calculations/ Results:
A = Oven dry weight =1000g B = SSD weight =1003.9g C = Weight in water =562g
Bulk Specific Gravity (Gsb) Gsb = A / (B-C) =2.26
Bulk SSD Specific Gravity (Gsb SSD) Gsb SSD = B / (B-C) =2.27
Apparent Specific Gravity (Gsa) Gsa = A / (A-C) =2.28
Absorption (% Abs) % Abs. = [(B-A) / A] x 100=.39%
Recommendations:
The specific gravity of aggregates normally used in road construction ranges from about 2.5 to 3.0 with an average of about 2.68.
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