Aggregate is one of the basic constituents of concrete. Its quality is of considerable importance because about three-quarter of the volume of concrete is occupied by aggregates. One of the physical properties of aggregate that influence the property of concrete is the grading of aggregate. The grading of aggregate defines the proportions of particles of different size in the aggregate. The grading of fine (size < 5 mm) and coarse (size > 5 mm) aggregates are generally required to be within the limits specified in BS 882: 1992.
The objective of this experiment is to obtain the grading curve for both fine and coarse aggregate.
1. Balance - balance or scale used in testing fine and coarse aggregates shall have readability and accuracy as follows: For fine aggregate, readable to 0.1 g and accurate to 0.1 g or 0.1 % of the test load. For coarse aggregate, or mixtures of fine and coarse aggregate, readable and accurate to 0.5 g or 0.1 % of the test load. 2. Sieves – the sizes and apertures appropriate to the specification of the material being tested, complying with BS 410: For coarse aggregate, standard sieve size of 50.0 mm, 37.5 mm, 20.0 mm, 14.0 mm, 10.0 mm, 5.0 mm and 2.36 mm (Fig. 2C1-1). For fine aggregate, standard sieve size of 10 mm, 5.00 mm, 2.36 mm, 1.18 mm, 600m, 300 m and 150 m (Fig. 2C1-2). 3. Mechanical Sieve Shaker -a mechanical sieving device, used to create vibration of the sieve to cause the particles to bounce. 4. Oven - an oven of appropriate size capable of maintaining a uniform temperature of 105°±5°C.
1. Representative sample was chosen by quartering (according to BS 812: Part 102: 1984) or by use of a sample splitter (Fig. 2C1-3). The sample to be tested should be the approximate weight desired when dry. For this experiment, about 500 grams of fine aggregate was weighed. 2. The samples was dried to constant weight in the furnace at a temperature of 105° ±5° C. 3. The samples was cooled down. The desired sieves was nested in order of decreasing aperture size from top to bottom. 4. The sample was placed on the top sieve and the sieves was agitated by mechanical sieve shaker for a sufficient period so that after completion, not more than one percent by weight of the residue on any individual sieve will pass that sieve. 5. The weight of each size increment was determined by weighing the residue contained on each sieve. This has be done in a cumulative fashion by starting with the smallest, particles in the bottom pan. After this weight has been determined, the next larger particles was added into the same pan and the cumulative weight was determined. Coarse Aggregate
1. A representative sample was chosen by quartering (according to BS 812: Part 102: 1984) or by use of a sample splitter (Fig. 2C1-3). The sample to be tested should be the approximate weight desired when dry. For this experiment, about 3 kilograms of coarse aggregate was weighed. 2. The procedure no. 2 to 5 was repeated as stated for fine aggregate using appropriate sieve size.
DATA AND ANALYSIS
A. Fine aggregate sample weight : 500g
BS sievesize| Weightof seive(gm)| Weight of Sieve + Sample (gm)| Retained Weight(gm)| Passed Weight(gm)| Retained Percentage(%)| Passed Percentage(%)| 5mm| 760| 770| 10| 490| 2| 98|
No.7(2.36mm)| 736| 814| 78| 412| 15.6| 82.4|
No.14(1.18mm)| 653| 791| 138| 274| 27.6| 54.8|
No.25(600m)| 633| 753| 120| 154| 24.0| 30.8|
No.52(300m)| 574| 657| 83| 71| 16.6| 14.2|
No.100(150m)| 553| 600| 47| 24| 9.4| 4.8|
Pan| 541| 565| 24| 0| 4.8| 0.0|
For 5mm BS sieve size of fine aggregate,
Retained weight (gm) = (weight of sieve + sample) – (weight of sieve) = 770 g – 760 g
= 10 g
Passed weight (gm) = (actual weight) – (retained weight)...