SPECIFIC GRAVITY & ABSORPTION CAPACITY OF AGGREGATES EA102 SPECIFIC GRAVITY & ABSORPTION CAPACITY OF AGGREGATES

The density, ρ of any material is the mass per unit of volume: EA102 Density The density, ρ of any material is the mass per unit of volume: i.e., For example, how many kilograms in 1 cubic metre of the material? 1 m3 or, how many grams in 1 cubic centimetre of the material? 1 cm3

EA102 At 4˚ C, water has a density, ρw of exactly 1000 kilograms per cubic metre 1 m3 At 4˚ C, water has a density, ρw of exactly 1 gram per cubic centimetre 1 cm3 At 20˚ C (standard), water has a density, ρw of 0.99823 gram per cubic centimetre

EA102 To find the density of any material, a sample of the material is weighed in air, Mair and then in water, Mwater. The difference between the mass in air and water is the mass of the water displaced by the material when placed in the water:

EA102 , Since, Since the volume of the material weighed is the same as the volume of water it displaces…

EA102 Specific Gravity The specific gravity, G of a material is just its density relative to the density of water:

Moisture States in Aggregates EA102 Moisture States in Aggregates There are 4 distinct moisture states for aggregates: Saturated Surface Dried, SSD Free Moisture Oven Dried Air Dried (Water between particles) (Hygroscopic Moisture) (No Moisture) Voids Filled with Water Water Permeable Voids Moisture from Air Particle coated with water Aggregate Particle

EA102 Moisture Content The moisture content of a soil or aggregate is the mass of water per unit mass of dry material. Moisture content is often expressed as a percentage, i.e., the mass of water in grams per 100 grams of dry material.

EA102 Absorption Capacity The absorption capacity, %ABS is the moisture content of the material when it is in the saturated surface dried state. We need to know the %ABS of the sand and stone used to make concrete because if they are drier than SSD then they will absorb some of the mixing water. On the other hand, if there is free moisture in the aggregate then there will be too much water in the mix.

EA102 Example The %ABS of stock sand is 1.5% and we need 8 kg of sand in the SSD condition to make concrete. A 499.6 gram sample of the stock sand was dried over a bunsen burner to a constant mass of 486.4 grams. How much of the sand should be used? First find the moisture content: This means that if we weighed out 8 kg of the sand, we’d get less than 8 kg of sand at SSD and extra (free) water. We therefore must weigh out extra sand in order to get 8 kg at SSD.

APPROXIMATELY, an extra 2.71-1.5 = 1.21% of the required SSD mass. EA102 How much? APPROXIMATELY, an extra 2.71-1.5 = 1.21% of the required SSD mass. ( ) The mathematically correct version of this % correction is: This translates to 0.0121 x 8.000 = an extra 0.0968 or 0.097 kg of sand. This means an extra 0.097 kg of water will be brought into the mix, so the mixing water should be reduced by 0.097 kg to compensate.

EA102 BULK SPECIFIC GRAVITY In order to calculate volumes of the concrete mix components, we need to know the Bulk SSD Specific Gravities of the sand and stone, the specific gravity of Portland Cement and the density of water. Bulk SSD Density is calculated by dividing the mass of the material at SSD by the bulk volume of the material. For sand (Lab 2 part A), a pycnometer is used to find the bulk volume of a 500.0 gram sample of sand at SSD.

Fill to calibration mark with water and weigh: B EA102 A pycnometer is a glass vessel used to determine the volume of small-grained loose material. Fill to calibration mark with water and weigh: B neck Place entire 500.0 g sample into pyc., cover with water, vacuum, fill to calibration mark and weigh: C calibration mark Empty contents of pyc., into oven container of known mass; after 18 h at 110°C find mass of container and sample and then dried sample: A bulb scale

EA102 Oven Tags Any material placed in the oven MUST be properly identified…hence the oven tag: 1NV12 4 2006-01-26 156.2 624.3 For these to work, you must fill them out accurately and completely. When you have finished, file them in the box with your class code in the drawer at WS 8 (208). Use the paper clip to keep all 3 of your tags together.

EA102 Specific Gravities There are 3 different specific gravities calculated for the sand and stone: ASTM Bulk Specific Gravity: SSD Bulk Specific Gravity: Apparent Specific Gravity: