C4 - SIEVE ANALYSIS (AGGREGATE GRADING) FOR FINE AND
COARSE AGGREGATE
INTRODUCTION
Aggregate is one of the basic constituents of concrete. Aggregates are natural or artificial mineral particles that act as a filler, usually constituting about 75 per cent of the volume of the concrete. Although they are essentially inert, aggregates have definite effects on the properties of concrete and their selection is important to the effective use of concrete. 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 <5mm) and coarse (size >5mm) aggregates are generally required to be within the limits specified in BS 882: 1992.
THEORY
Gradation or particle-size distribution refers to the proportions by mass of aggregate particle distributed in specified particle size ranges. It is important properties that will affect several characteristics of concrete such as mix proportioning, workability, economy, porosity, durability, and shrinkage. Gradation of aggregates is determined from sieve analysis, in which a representative sample of the aggregate is passed through a series of sieves, and the weight retained in each sieve (expressed as a percentage of the sample weight) is compared with the grading limits specified. The results of a sieve analysis are often plotted on graph with sieve sizes on the horizontal axis and percentage of fine and coarse passing aggregate on the vertical axis. Size, range, and gradation can be identified on a graph. Limit is usually specified for the percentage of material passing each sieve, the limits being indicated in Figure C4-1. A plot of the upper and lower specified limits is called an envelope, which shows them for type M fine aggregate and one designated size 20 mm of coarse aggregate. Notice that most of the fine aggregate pass through a No.4 (4.75mm) sieve, but a very large percentage of the coarse aggregates are retained on a No. 4 (4.75mm) sieve. Aggregate size and gradation are often specified by listing sieve sizes and a range of “percent passing” for each size. The sample being tested sieved with the specified sieves and is acceptable if, for each sieve, the sample’s percentage falls within the limit specified ranges.
OBJECTIVES
The objective of this experiment is to obtain the grading curve for both fine and coarse aggregate.
APPARATUS
1. Balance – balance or scale used in testing fine and coarse aggregates shall have readability and accuracy as follow:
For fine aggregate, readable to 0.1g and accurate to 0.1g or 0.1% of the test load For coarse aggregate or mixtures of fine and coarse aggregate, readable and accurate to 0.5g 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 fine aggregate, standard sieve size of 10 mm, 5.00 mm, 2.36 mm, 1.18 mm, 600µm, 300µm, and 150µm.
For coarse aggregate, standard sieve size of 28 mm, 19 mm, 13.2 mm, 9.5 mm, 4.75 mm, and 2.36 mm.
3. Mechanical Sieve Shaker – a mechanical sieving device, used to create vibration of the sieve to cause all particles to bounce.
4. Oven – an oven of appropriate size capable of maintaining a uniform temperature of 105 ± 5°C.
PROCEDURES Fine Aggregate
1. A representative sample was chosen by quartering (according to BS 812: Part 102: 1984) or by using a sample splitter (Fig. C4-3). The sample to be tested should be the approximate weight desired when dry. For this experiment, about 500g of fine aggregate was weighted.
2. The samples were dried to a constant weight in the furnace at a temperature of 105 ± 5°C.
3. The samples were cooled down. The desired sieves were nested to decrease aperture size from top to bottom.
4. The sample was placed on the top sieve and was agitated by mechanical sieve shaker for 2 minutes for a sufficient period so that not more than 1 percent by weight of the residue on any individual sieve will pass that sieve after completion. 5. The weight of each size increment was determined by weighing the residue
contained on each sieve. This may 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 were added into the same pan and the cumulative weight was determined.
Coarse Aggregate
1. A representative sample was choosing by quartering (according to BS 812: Part 102: 1984) or by use of a sample splitter (Fig. C4-3). The sample to be tested should be the approximate weight desired when dry. For this experiment, 2 kg of coarse aggregate was weighted.
2. Procedure no 2-5 was repeated using appropriate sieve size.
DATA & CALCULATION
Sample Calculation:
For Fine Aggregate with BS Sieve Size No.7 (1.18 mm):
Passed Weight = total retained weight – cumulative retained weight = 500 – ( 5 + 31 + 73 )
= 391 g
Retained Percentage = retained weight x 100 % total retained weight
= 100% 500
73
x
= 14.6 %
Passed Percentage = passed weight x 100 % total passed weight
= 100% 500
391
x
For Coarse Aggregate with BS Sieve Size 14.0 mm:
Passed Weight = total retained weight – cumulative retained weight = 2000 – ( 0 + 282 + 844 )
= 874 g
Retained Percentage = retained weight x 100 % total retained weight
= 100%
2000 844
x
= 42.20 %
Passed Percentage = passed weight x 100 % total passed weight
= 100% 2000 874 x = 43.70 % DISCUSSION
Aggregate is a rock like material of various sizes and shapes that is used in concrete mix. According to ASTM, it can be defines as a granular material such as sand, gravel, crushed stone, or iron-blast slag used with cementing medium to form mortar or concrete. Aggregates contribute 65 to 85 per cent of a concrete mix, accounting for more than 30 per cent of the total cost. According to 3.3.2, MS 523: PART 1: 1993, for most work; 20 mm aggregates are suitable to be used. If there is no restriction to the flow of concrete into section, 40 mm or larger size of aggregates should be permitted.
For fine aggregate:
From the gradation curve that plotted, almost all the passed percentage of sample of fine aggregate falls within the specified range for type M fine aggregate except for the BS Sieve Size No.52. Therefore, the fine aggregate being tested can be considered as well-graded aggregate.
From the data and calculation, the total weight of fine aggregate calculated was 493g which was less than the actual weight 500g with 7g loss. There are some factors that might affect the accuracy of the experiment:
i. The sample was not dried to a constant weight in the furnace at a temperature of 105 ± 5oC.
ii. Some particles that left in sieve apparatus for previous experiment may drop into our sample during shaking.
iii. The aggregate that used is not really pure and may contain others material such as dried leave or dust.
iv. Some dust or other material that contained in aggregate had lost when the sieves were shaken and hence affect the accuracy of the experiment.
For coarse aggregate:
From the gradation curve we plotted, the passed percentage of sample of 20 mm coarse aggregate falls out of the specified range.
From the shape of the curve, a line nearly horizontal line at the bottom of the graph shows that there was some small change in passed percentage through several successive sieves. Therefore, very little material was passed through these sieves. This indicates that there was a gap in the gradation. Thus, the sample of coarse aggregate did not give a well-graded aggregate.
From our analysis, there are some factors that might affect the accuracy and quality of the experiment:
i. The sample was not dried to constant weight in the furnace at a temperature of 105 ± 5oC.
ii. The sample of coarse aggregate was too coarse and errors will occur when producing concrete.
COMMENTS
In order to minimize the possible errors and hence improve the quality and accuracy of the experiment, we strongly suggested that:
i. The sample has to be dried to constant weight in the furnace at a temperature of 105 ± 5oC.
ii. The sample has to be cooled down after drying.
iii. The sample must be make sure free from any other materials such as dried leave or dust.
iv. The sieves have to be taken out one by one very cautiously using strip before weighing to avoid losing aggregate weight.
CONCLUSION
By conducting this experiment, the grading curve for both fine and coarse aggregate had been obtained and the aggregate that we tested can be graded.
By referring to the grading curve for fine aggregate, the grading curve was almost plotted inside the typical grading envelope. Therefore, the fine aggregate in the experiment can be considered as well-graded aggregate.
While base on the grading curve for coarse aggregate, the properties of the coarse aggregate, the graph plotted was out of the range of the typical grading envelope. Therefore, the sample for coarse aggregate cannot be considered as poor-graded aggregate. The sample cannot provide a desired quality, so it is not recommended to be used in concrete mixes.
The aggregates particles should retain their strength, shape, and texture when used with materials such as cement. The combination of fine and course aggregates of proper or acceptable shape will have effect on the workability, cement -water ratio, and characteristic strength to meet the quality of cement needed and economy of concrete or other products.
REFERENCES
1. SAM 4062 CIVIL ENGINEERING LABORATORY II , Faculty of Civil Engineering, Universiti Teknologi Malaysia.
2. CIVIL ENGINEERING MATERIALS Second Edition , Shan Somayaji, Prentice-Hall Inc, 2001, New Jersey.
3. CIVIL ENGINEERING MATERIALS , Dr. Abdul Rahman Mohd Sam, Fakulti Kejuruteraan Awam, Universiti Teknologi Malaysia.
