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AIM OF THE EXPERIMENT: To determine the gradation of coarse aggregate by sieve analysis.
CODE OF REFERENCE:
Fig 1: Sieve Shaker motor operated
Coarse aggregate is the one retained on 4.75 mm IS Sieve. When the aggregate contains sizes differently in suitable proportions, it is called graded aggregate. The workability of concrete is also improved with well graded aggregate. Single size aggregates make the concrete harsh and does not work well with trowel and between the cables, strands or sheathing. The coarse aggregate may be of the following types –
The graded coarse aggregate is defined by its nominal size i.e., 40 mm, 20 mm, 16 mm, 12.5 mm, etc. For example, a graded aggregate of nominal size 12.5 mm means an aggregate most of which passes the 12.5 mm IS Sieve. Because the aggregates are formed due to natural disintegration of rocks or by the artificial crushing of rock or gravel, they derive their many of the properties from the parent rocks. These properties are chemical, mineral composition, petrographic description, hardness, strength, pore structure, colour, etc. Other properties which are not possessed by parent rock or gravel are shape, size, texture, absorption, etc. Furthermore, sub-classifications are there like in shape, round, angular varieties are there, in unit weight classification normal weight, lightweight is there and many more. All these properties may have a considerable effect on the quality in fresh and hardened states.
Within these limits, the nominal maximum size of coarse aggregate may be as large as possible for low to moderately high strength concrete. The bigger the size of aggregate, lesser is the surface area and hence less amount of water is required for wetting the surface and less matrix or paste is required that lubricates the surface so as to reduce internal friction. For a given quantity of water and paste, bigger size of aggregate will give higher workability.Coarse aggregates are used in various tests like slump test, vee bee test, etc. in order to ascertain the suitability of coarse aggregate in making better quality of concrete.
RELEVANCE OF THE EXPERIMENT:
OBSERVATIONS AND RESULTS
The coarse aggregate both graded and single sized shall be supplied in nominal sizes as per specifications given as under:
Weight of sample taken = __________ kg.
|Sl No.||IS Sieve No||Weight retained in kg||% weight retained||Cumulative % weight retained||% passing||As per IS 383-1970||Remarks|
The minimum weight for different nominal sizes of aggregates may be taken as below:
|Maximum size present in substantial proportions in mm||Maximum suggested weight of sample to be taken for sieving in kg||Minimum weight of sample to be taken for sieving as per IS 2386 (Part-1)-1963 in kg|
The sample of aggregates does/does not conform to IS 383-1970.
• The hand gloves should be worn during the experiment so as to avoid any injury.
• Safety shoes and aprons at the time of test must be worn for protection.
• Cleaning and drying before the commencement of test is recommended.
• Careful sieving should be adopted.
• The electric balance should be checked before weighing.
• Sieves should be arranged in correct order.
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