Soran University

Faculty of Engineering

Civil Engineering Department

Absorption of Coarse Aggregate

Student: Sarchia KhursheedGroup: 2Experiment NO.: 2Date: 18.11.2015Supervisor: Arianfar Haji

Introduction

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Absorption is the increase in the mass of aggregate due to water being absorbed into the pores of the material, but not including water adhering to the outside surface of the particles, expressed as a percentage of the dry mass. The aggregate is considered “dry” when it has been maintained at a temperature of 110 ±5°C for sufficient time to remove all uncombined waterThe laboratory standard for absorption is that obtained after submerging dry aggregate for approximately 15 hours in water. Aggregates mined from below the water table may have a higher absorption, when used, if not allowed to dry. Conversely, some aggregates, when used, may contain an amount of absorbed moisture less than the 15 hours soaked condition. For an aggregate that has been in contact with water and that has free moisture on the particle surfaces, the percentage of free moisture can be determined by deducting the absorption from the total moisture content.The pores in lightweight aggregates may or may not become filled with water after immersion for 15 hours. In fact, many such aggregates can remain immersed in water for several days without satisfying most of the aggregates’ absorption potential. Therefore, this method is not intended for use with lightweight aggregate.

ObjectiveTo determine the absorption of given sample of coarse aggregates.

Apparatus A balance or scale of capacity not less than 3 kg, readable and

accurate to 0.5 g and of such a type and shape as to permit the basket containing the sample to be suspended from the beam and the weighed in water.

A well ventilated oven thermostatically controlled to maintain a temperature of 100°C to 110°C.

A wire basket of not more than 6.3 mm mesh or a perforated container of convenient size.

A stout water tight container of convenient size. A glass container Two dry soft absorbent cloths each not less than 75×45 cm A shallow tray of area no less than 650 cm2

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Materials Coarse aggregate Distilled water

ProcedureI. The sample should be thoroughly washed to remove finer

particles and dust, drained and then placed in the wire basket and immersed in distilled water at a temperature between 22 and 32oC.

II. After immersion, the entrapped air should be removed by lifting the basket and allowing it to drop 25 times in 25 seconds. The basket and sample should remain immersed for a period of 24 + ½ hrs afterwards.

III. The basket and aggregates should then be removed from the water, allowed to drain for a few minutes, after which the aggregates should be gently emptied from the basket on to one of the dry clothes and gently surface-dried with the cloth, transferring it to a second dry cloth when the first would remove no further moisture. The aggregates should be spread on the second cloth and exposed to the atmosphere away from direct sunlight till it appears to be completely surface-dry. The aggregates should be weighed (Weight ‘A’).

IV. The aggregates should then be placed in an oven at a temperature of 100 to 110oC for 24hrs. It should then be removed from the oven, cooled and weighed (Weight ‘B’).

Data and Calculations

WeightsGroups A B

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1 306 g 305 g

2 351 g 352 g

3 325 g 325 g

A = Weight of aggregate in SSD condition.B = Weight of the oven dry aggregate in air (100 – 110°C)

Absorption (%) = A−BB

×100

Group 1: 306g−305 g305g×100 = 0.328 %

Group 2: 351g−352g352g×100 = -0.284 %

Group 3: 325g−325g325g×100 = 0 %

DiscussionFrom the weight of aggregate in SSD condition (A) and weight of oven dry aggregate (B) we can obtain the absorption of coarse aggregate by this equation (A−B

B×100), after obtaining the weights of coarse

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aggregate in SSD condition and oven dry condition we use it in the equation, weight of (A) must be greater than (B) because of absorption of water, and the rate of absorption must be greater than 0 and less than 2.In this experiment our result (Group 2) it seems a bad result because the result is less than 0 and sign is minus, about another two groups, the result of Group 1 between 0 and 2 may it better than two groups, about the result of Group 3 it is 0, these results clear that maybe there are some problems in measuring and process of this test, it be better to reply this experiments to obtain some probable results.

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