Construction material aggregates

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Construction Material Fine & Coarse aggregates


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Aggregates are inert granular materials such as sand, gravel, or crushed stone that, along with water and portland cement, are an essential ingredient in concrete. For a good concrete mix, aggregates need to be clean, hard, strong particles free of absorbed chemicals or coatings of clay and other fine materials that could cause the deterioration of concrete. Aggregates, which account for 60 to 75 percent of the total volume of concrete, are divided into two distinct categories--fine and coarse. Fine aggregates generally consist of natural sand or crushed stone with most particles passing through a 3/8-inch sieve. Coarse aggregates are any particles greater than 0.19 inch, but generally range between 3/8 and 1.5 inches in diameter. Gravels constitute the majority of coarse aggregate used in concrete with crushed stone making up most of the remainder.

characteristics of aggregates that are considered include: grading durability particle shape and surface texture abrasion and skid resistance unit weights and voids absorption and surface moisture


THE AGGREGATES

0.150 to 4.75 mm

Fine Aggregate = Sand = Bazri Sand between 4.75 mm to 0.150mm in size is called Fine aggregate

4.75 to 63 mm

Coarse Aggregate = Rodi Material in form of broken stone or rounded stone between 4.7mm to 63 mm size is called coarse aggregate


Classification of Fine Aggregate (Sand ) ( IS 383-1970) IS SIEVE NO

7

Zone - I

Coarse Zone - II

Fine Zone - III

Very Fine Zone - IV

Zone - V

25

Millimeter

I.S. SIEVE SIZE

Very Coarse

14

10

4.75

2.36

52 100 Microns

1.18 600

300

150

100 90-100 60-95 30-70 15-34 5-20

0-10

100 90-100 75-100 55-90 35-59 8-30

0-10

100 90-100 85-100 75-100 60-79 12-40 0-10

100 95-100 95-100 90-100 80-100 15-50 0-15 -

-

100 100

85-100 65-95 0-60


Grading ď Ž Grading is the distribution of particles of

angular materials among various sizes. Grading is usually expressed in terms of cumulative percentage passing each sieve.


Grading Different standards and specifications specify grading limits for both fine and coarse aggregates. There are several reasons for specifying grading limits and maximum aggregate size, they affect relative:

 Relative aggregate proportions  Cement and water requirement  Workability  Pump ability  Economy  Shrinkage and durability of concrete


Grading : wire-mesh sieves  Aggregates that do not have deficiency or excess of

any size and give smooth grading curve will produce the most satisfactory results.  The aggregate particle size is determined by using wire-mesh sieves with square openings:  7 standard sieves ranging from 150 μm to 10 mm for fine aggregates fine aggregates 10mm 4.75mm 2.36mm 1.18mm 600 μm 300 μm 150 μm

 8 standard sieves ranging from 4.75 mm to 80 mm

for coarse aggregates 80mm 63mm 40mm 20mm 16mm 12.5 mm 10mm 4.75mm coarse aggregates


Grading : Selection of aggregates ď Ž Proper selection of various sizes will be very effective

in reducing the total volume of voids between aggregates . The cement paste requirement is related the void content of the combined aggregates.

Production of satisfactory; economical concrete requires aggregates of low void content, but not the lowest


Fine Aggregate Grading ď Ž Wide range in fine aggregate gradation is

permitted by IS 383-1970. The most desirable fine-aggregate gradation depends on the type of work, the richness of the mixture, and the maximum size of coarse aggregate. ď Ž For example, in leaner mixtures, or when small-size coarse aggregates are used, a grading that approaches the maximum recommended percentage passing each sieve is desirable for workability.


The following table shows the limits of masonry mortar ( IS 2116 -1980 ) with respect to fine aggregates IS Sieve size

Percentage passing by mass IS 2116 -1980

4.75 mm

(No. 4)

100%

2.36 mm

(No.7)

90 to 100%

1.18 mm

(No. 14)

70 to 100%

600 μm

(No. 25)

40 to 100%

300 μm

(No. 52)

5 to 70%

150 μm

(No. 100)

0 to 15%


Fineness Modulus

ď Ž The fineness modulus (FM) for both fine and coarse

aggregates is obtained by adding the cumulative percentages by mass retained on each of a specified series of sieves and dividing the sum by 100. ď Ž The FM is an index of the fineness of the aggregate. The higher the FM, the coarser the aggregate. FM of fine aggregate is useful in estimating proportions of fine and coarse aggregate in concrete mixtures.


Coarse Aggregate Grading  IS 383-1970 permits a wide range in

grading and variety of grading sizes  Usually more water and cement is required for small-size aggregate than for large sizes, due to an increase in total aggregate surface area.  The optimum maximum size of coarse aggregate for higher strength depends on:   

Relative strength of the cement paste Cement-aggregate bond Strength of the aggregate particles


Coarse Aggregate Grading ď Ž Maximum size of aggregate: the smallest

sieve that all of a particular aggregate must pass through. ď Ž Nominal maximum size of an aggregate: the smallest sieve size through which the major portion of the aggregate must pass (90%100%). ď Ž Example: 40 mm nominal size has 100% passing a sieve size of 63 mm and 85 to100% passing 40mm sieve


Single Size Aggregates (ungraded) Percentage passing for nominal size of aggregates in mm IS SIEVE SIZE (MM)

63mm (2 in)

80

100

63

85 to100

100

40

0 to 30

85 to100

100

20

0 to 5

0 to 20

85 to100

100

16

-

-

85 to100

100

12.5

-

-

-

85 to100

100

10

0 to 5

0 to 20

0 to 30

0 to 45

85 to100

0 to 5

0 to 10

0 to 20

4.75

40 mm (1 ½ in)

20 mm (3/4 in)

16 mm (5/8 in)

12.5 mm (1/2 in)

10mm (3/8 in)


Maximum Nominal Size of Aggregate for Various Works IS SIEVE SIZE (MM)

80 63 40 20 16 12.5 10 4.75

63mm (2 in)

40 mm (1 ½ in)

Non Reinforced R.C work foundation work

20 mm (3/4 in)

R.C work (beam , column, slabs )

16 mm (5/8 in)

12.5 mm (1/2 in)

10mm (3/8 in)

Shell roof and thin members

In R.C. Works The maximum Size of aggregate is governed by the rule that it should not exceed “ minimum spacing – 5mm”


Maximum Size of Aggregates (Nominal)  The maximum size of aggregate that must be

used generally depends on the following:  

Size and shape of the concrete member The amount and distribution of reinforcing steel

 In general the maximum size of aggregate

particles should not exceed:   

1/5 of the narrowest dimension of a concrete member 3/4 the clear spacing between reinforcing bars and between the reinforcing bars and forms 1/3 the depth of slabs



Gap-Graded aggregates ď Ž When certain particle sizes are

intentionally omitted. Example, for an aggregate of 19 mm maximum size, the 4.75 mm to 9.5 mm particles can be omitted without making the concrete harsh subject to segregation. Gap-graded mixes are used in architectural concrete to obtain uniform textures in exposed – aggregate finishes.


Particle Shape and Surface Texture  The shape and surface texture affect the properties of fresh

concrete more than the properties of hardened concrete.

 Rough-texture, and angular particles require more water to

produce workable concrete than do smooth, rounded and compact particles. For both crushed or noncrushed aggregate, proper gradation gives the same strength for the same cement factor.

 Bond between cement paste and a given aggregate generally

increases the particles surfaces change from smooth and rounded to rough and angular. The increase in bond is important for selecting aggregates for concrete where strength at early age is important.

 Aggregate should be free of flat or elongated particles.

Because they require an increase in mixing water and thus may affect the strength of concrete particularly in flexure.


TESTS OF AGGREGATES Fine Aggregates

Coarse Aggregates

1. Test for grading (particle size)

1. Test for Particle size

2. Test for bulking of sand

2. Test for shape

3. Test for organic impurities

3. Test for flakiness

4. Test for clay and silt content

4. Test for organic impurities 5. Test for moisture content 6. Test for Load for 10% Fineness value. 7. Aggregate crushing value 8. Test for water absorption and specific gravity 9. Test for aggregate impact 10. Attrition Test 11. Bulk Density and void ratio


PARTICLE SIZE (IS 2386-1963 PART-1) This test is made by sieve analysis using sieves given in table below: IS SIEVES FOR SIEVE ANALYSIS OF AGGREGATES FOR CONCRETE

TYPE

SIEVE DESIGNATIONS

Square hole, perforated plate

80-mm, 63-mm, 50-mm, 40-mm, 31.5-mm, 25-mm, 20-mm, 16-mm, 12.5-mm, l0-mm, 6.3-mm, 4.75-mm

Fine mesh, wire cloth

3.35-mm, 2.36-mm, l.l8mm, 600.micron, 300-micron, 150-micron, 75-micron


PARTICLE SIZE (IS 2386-1963 PART-1)

Mechanical Shaker

Manual Shaker


AGGREGATE SIZE (IS 383-1970)


BULKING OF SAND The capillary action between sand particle does not allow the particle to come closer to each other this is called bulking of sand. Experiment: To test for bulking of sand. Equipment: flat bottomed cylindrical glass container, water, rod, damp sand, tray. Method 1. Place the damp sand into the container and measure the volume. (D) 2. Pour the sand onto the tray. 3. Half fill the container with water. 4. Put the sand into the container and mix using the rod until fully saturated. 5. Measure the height. (d) Result [Calculate as] D – d x 100 d 1


TEST FOR ORGANIC IMPURITIES This is an important test for dirty sands. A sample of sand is digested at ordinary temperature in a solution of sodium hydroxide (NaOH). If the sand contains certain organic materials, thought to be largely of a humus nature, the filtered solution resulting from this treatment will found to be of a color ranging from light yellow up through the reds to that which appears almost black. The depth of color has been found to furnish a measure of the effect of the impurities on the strength of mortars made from such sands. The depth of color may be measured by comparison with proper color standards.


Test For Clay & Silt Content Amount of silt in a single batch of sand Experiment: To show the amount of silt in a single batch of sand Equipment: sand, 1000ml measuring cylinder, salt, water. Method 1. Pour 150ml of salt water into the cylinder. 2. Add sand until the water level reaches the 300ml mark. 3. More salt is added to bring the level up to the 500ml mark. 4. Cover the top and shake vigorously. 5. Leave to settle for three hours. 6. Measure volume of silt and volume of sand.

% SILT =

Height of silt Height of sand

X 100

Conclusion Silt in the concrete prevents cement and aggregates bonding together, resulting in weak concrete. 8% or less of silt is acceptable, anything higher than this and the cement will not bond fully with the aggregate.


Test For Shape (IS 2386-1963 PART-1) Aggregates which happen to fall in a particular size range may have rounded, cubical, angular, flaky or elongated particles. It is evident that the flaky and elongated particles will have less strength and durability when compared with cubical, angular or rounded particles of the same aggregate. Hence too flaky and too much elongated aggregates should be avoided as far as possible.


Test For Flakiness The particle shape of the aggregate mass is determined by the percentage of flaky and elongated particles in it. Aggregates which are flaky or elongated are detrimental to higher workability and stability of mixes. The flakiness index is defined as the percentage by weight of aggregate particles whose least dimension is less than 0.6 times their mean size. Test procedure had been standardized in India (IS:2386 part-I)

Flakiness Guage


Test For Elongation Index The elongation index of an aggregate is defined as the percentage by weight of particles whose greatest dimension (length) is 1.8 times their mean dimension. This test is applicable to aggregates larger than 6.3 mm. This test is also specified in (IS:2386 Part-I). However there are no recognized limits for the elongation index.

Elongation Guage


Test For Moisture Content The easy test is the drying method in an oven or heating in an open pan in the field. It can also be carried out by pouring an inflammable liquid like methylated spirit and igniting it to evaporate water. Since aggregates are porous (to some extent) they can absorb moisture. This is a concern for PCC because aggregate is generally not dried and therefore the aggregate moisture content will affect the water content (and thus the water-cement ratio also) of the produced PCC and the water content also affects aggregate proportioning (because it contributes to aggregate weight).

where:

MC = moisture content expressed as a percentage Wstock = weight of aggregate in stockpile condition WSSD = weight of aggregate in SSD condition


Test For Moisture Content In general, there are four aggregate moisture conditions:

Oven-dry (OD).

All moisture is removed by heating the aggregate in an oven at 105째C (221째F) to constant weight (this usually constitutes heating it overnight). All pores connected to the surface are empty and the aggregate is fully absorbent.

Airdry (AD).

All moisture is removed from the surface, but pores connected to the surface are partially filled with water. The aggregate is somewhat absorbent.

Saturated surface dry (SSD).

All pores connected to the surface are filled with water, but the surface is dry. The aggregate is neither absorbent nor does it contribute water to the concrete mixture.

Wet.

All pores connected to the surface are filled with water and there is excess moisture on the surface. The aggregate contributes water to the concrete mixture.


Crushing Test One of the model in which pavement material can fail is by crushing under compressive stress. A test is standardized by IS:2386 part-IV and used to determine the crushing strength of aggregates. The aggregate crushing value provides a relative measure of resistance to crushing under gradually applied crushing load. The test consists of subjecting the specimen of aggregate in standard mould to a compression test under standard load conditions. Dry aggregates passing through 12.5 mm sieves and retained 10 mm sieves are filled in a cylindrical measure of 11.5 mm diameter and 18 cm height in three layers. Each layer is tampered 25 times with at standard tamping rod. The test sample is weighed and placed in the test cylinder in three layers each layer being tampered again. The specimen is subjected to a compressive load of 40 tonnes gradually applied at the rate of 4 tonnes per minute. Then crushed aggregates are then sieved through 2.36 mm sieve and weight of passing material (W 2) is expressed as percentage of the weight of the total sample (W 1) which is the aggregate crushing value.


Crushing Test

A value less than 10 signifies an exceptionally strong aggregate while above 35 would normally be regarded as weak aggregates.

Crushing test setup


Test For Water Absorption & Specific Gravity The specific gravity and water absorption of aggregates are important properties that are required for the design of concrete and bituminous mixes. The specific gravity of a solid is the ratio of its mass to that of an equal volume of distilled water at a specified temperature. A sample of aggregates not less than 2kg is washed and immersed in water for 24 hours and its immersed weight in water is found (A). It is taken out of the water and the saturated surface dry sample is weighed in air (B). It is then overdried and weighed (c).

C Specific Gravity =

Percent Water Absorption =

B-A

B-C

X 100

C Dry Aggregate

Wet Aggregate


Aggregate Impact Test The aggregate impact test is carried out to evaluate the esistance to impact of aggregates. Aggregates passing 12.5 mm sieve and retained on 10 mm sieve is filled in a cylindrical steel cup of internal dia 10.2 mm and depth 5 cm which is attached to a metal base of impact testing machine. The material is filled in 3 layers where each layer is tamped for 25 number of blows. Metal hammer of weight 13.5 to 14 Kg is arranged to drop with a free fall of 38.0 cm by vertical guides and the test specimen is subjected to 15 number of blows. The crushed aggregate is allowed to pass through 2.36 mm IS sieve. The impact value is measured as percentage of aggregates passing sieve (W2) to the total weight of the sample (W 1)


Aggregate Impact Test

Impact test setup

IMPACT Test Video

Aggregates to be used for wearing course, the impact value shouldn't exceed 30 percent. For bituminous macadam the maximum permissible value is 35 percent. For Water bound macadam base courses the maximum permissible value defined by IRC is 40 percent


Aggregate Abrasion Value (Attrition Test) Abrasion test is carried out to test the hardness property of aggregates and to decide whether they are suitable for different pavement construction works. Los Angeles abrasion test is a preferred one for carrying out the hardness property and has been standardized in India (IS:2386 part-IV). The principle of Los Angeles abrasion test is to find the percentage wear due to relative rubbing action between the aggregate and steel balls used as abrasive charge. Los Angeles machine consists of circular drum of internal diameter 700 mm and length 520 mm mounted on horizontal axis enabling it to be rotated (see Figure 2). An abrasive charge consisting of cast iron spherical balls of 48 mm diameters and weight 340-445 g is placed in the cylinder along with the aggregates. The number of the abrasive spheres varies according to the grading of the sample. The quantity of aggregates to be used depends upon the gradation and usually ranges from 5-10 kg. The cylinder is then locked and rotated at the speed of 3033 rpm for a total of 500 -1000 revolutions depending upon the gradation of aggregates.


Aggregate Abrasion Value (Attrition Test) After specified revolutions(500 to 1000 ) , the material is sieved through 1.7 mm sieve and passed fraction is expressed as percentage total weight of the sample. This value is called Los Angeles abrasion value. It should not be more then 16% for a good aggregates

Los Angeles abrasion test setup


Bulk Density And Void Ratio Bulk density is determined bypacking the aggregate into a specified container of known volume and determining the weight of the aggregates packed. Weight

Bulk Density = γ =

Volume Void Ratio =

Gs - γ γ

Where Gs = Specific gravity of aggregate Specific Gravity : the ratio of the mass of a unit volume of a material at a stated temperature to the mass of the same volume of gas-free distilled water at a stated temperature( i.e. 23° C)


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