Classification of Aggregates & Properties of Aggregates

Classification of Aggregates & Properties of Aggregates

Classification of Aggregates & Properties of Aggregates in our comprehensive blog post. Delving deep into the world of construction materials, this article unpacks the varied types of aggregates, their distinct classifications, and the crucial properties that define their utility in infrastructure. Explore the significance of aggregate classification and understand how their unique properties influence their applications in diverse construction projects. Dive into this informative piece to gain a profound understanding of these foundational materials shaping the construction industry.

Classification of Aggregates

Based on geological origin

natural aggregate:

Crushing from quarries of existing rocks. Such as igneous, sedimentary or metamorphic rocks.

artificial aggregates:

Crushing of bricks, blast furnace slag and synthetic aggregates

based on size

coarse aggregates:

The size of aggregates is between 4.75 mm to 80 mm.

fine aggregates:

Size of aggregates is between 0.06 ( 60 μm ) to 4.75 mm.

based on shape

Round:

Surface area ↓, Cement paste required ↓, minimum void (32%).

irregular:

Voids around 36%, required more cement paste than rounded.

angular:

Maximum voids around 40%, cement paste required is more.

NOTES:

As per IS 383 : 1970, the fine aggregate is divided into 4 zones

% Passing through a 600 μm sieve	15 - 34 %	35 - 59 %	60 - 79 %	80 - 100 %
Zone	I	II	III	IV

Zone I > Zone II > Zone III> Zone IV

--------------→

Fineness increases.

--------------→

Size decreases.

properties of aggregates

• Properties of the aggregate govern the property of the mixture (concrete) in which it is used.
• Property under consideration is the strength & workability of the mixture.

Strength:

• It represents the resistance of a material against gradual loading.
• It depends on the interparticle locking between aggregates & bond strength (which is the function of contact area & roughness).

Workability:

• It is the ease with which we can work (mixing, transporting, placing and finishing) with the mixture.
• This ease of work depends upon the friction between the particles, which can be reduced by the lubricating action of the paste of binding materials.

Properties:

Shape

• The shape of aggregates governs both the workability & strength of the mixture.
• Rounded aggregates lead to the formation of a workable mix having low strength, as lesser is the area to be lubricated in this case & poorer is the interparticle locking and bond strength.
• Angular aggregates lead to the formation of a strong mix, having less workability as better is the interparticle locking and bond strength but more is the area to be lubricated in this case.
• Flaky and elongated aggregates lead to the formation of a poor mix, which has low strength & low workability, as poor is the interparticle locking and higher is the area to be lubricated in this case.

Note: Excellent concrete is made by using crushed stone, but the particles should be roughly cubical in shape.

angular / rounded aggregate:

• Angularity/Roundness of aggregates is measured in terms of the parameter "Angularity Number" (AN), which represents the volume of voids in the sample.
• AN varies in the range of 0 - 11. If % voids in the sample are 33%, AN = 0 and % voids in the sample are 44%, it is taken to be 11.

Important Question

Q: If the weight of coarse aggregate has a specific gravity of 2.65, which is filled into a cylinder of volume 0.003 m³ is 5247 gm. What is the angularity number & comment upon the shape of aggregates?

Sol:

Volume of cylinder = 0.003 m³
Weight of solid = 5247 gm
Density of water = 1000 kg/m³
Specific Gravity (G) = ρ_s / ρ_w = M_s/V_sρ_w

V_s = Volume of solid
M_s = Mass of solid
G = Specific gravity
ρ_w = Density of water
ρ_s = Density of solid

V_s = 0.00198 m³

Volume of sample = V_s + V_v

V_v = V - V_s

V_V = 0.003 - 0.00198 = 0.00102 m³

% V_v = V_v/V * 100 = 0.00102/ 0.003 * 100

Angularity number = 34 - 33 = 1
Shape - More rounded less angular.

Flaky aggreegate:

• Flakiness of aggregates is measured in terms of the parameter flakiness index.
• This test is not applicable for aggregates having a size smaller than
  6.3 mm.
• Flaky particles are those with the least lateral dimension, which is smaller than 0.6 (3/5) times its mean dimension.
• Flakiness is defined as % of flaky particles in the sample and is determined using the flakiness index test.
• In order to perform this test, a sufficient quantity of aggregates must be considered, such that 200 pieces of each fraction can be gauged.
• Particles of each fraction are passed turn by turn through the respective opening over the "THICKNESS GAUGE" and the weight of aggregates passing through these openings is noted and when expressed in terms of the original weight of aggregates, it is termed as flakiness index.
• Flaky aggregates must not be more than 15%, in general, to be used for the preparation of concrete.

elongated aggreegate:

• Elongated aggregates are those, the greatest size of which is greater than 1.8 times its mean size.
• Elongation of the aggregate is measured in terms of the parameter elongation index, which represents the % of elongated particles in the sample.
• This test is not applicable for aggregates having a size smaller than 6.3 mm.
• To perform this test, a sufficient quantity of aggregates must be taken, such that 200 pieces of each fraction can be gauged.
• Particles are then passed through the respective opening over the length gauge & aggregates retained over these openings are weighted.

Important Question

Q: The dimension of aggregate are shown in figure

For the given aggregate, the correct option is:

a) Elongated but not flaky
b) Flaky but not elongated
c) Both elongated and flaky

texture of aggregate:

TERM - Surface texture: The surface texture of aggregate represents the relative percentage of the area of aggregates that is smooth or rough.

• Smooth textured aggregates lead to the formation of workable concrete but have low strength, as lesser is the area to be lubricated in this case and lower is the bond strength and interparticle locking.

Important question

Q: How do rough aggregates lead to the formation of strong concrete having low workability?

Sol: In rough aggregates, the area to be lubricated is more thus workability is low, but the interparticle locking and bond strength is better than smooth aggregates thus it leads to the formation of strong concrete with low workability.

Grading of aggregate:

• Grading of aggregates directly governs the workability and strength of concrete in which it is used for construction.
• A well-graded sample of aggregate results in both workable and strong concrete, as more is the availability of free cement paste in this case for lubrication and better is the interparticle locking and bond strength.
• Grading of aggregates is done by "particle size distribution analysis (sieve analysis)".
• The result of gradation is expressed in terms of parameters Cu and Cc (coefficient of uniformity and coefficient of curvature, respectively).

size of aggregate:

• In sieve analysis, a parameter referred to as fineness modulus is also determined, which is used to indicate the fineness and coarseness of aggregates in absolute terms.
• Fineness modulus is defined as the cumulative% of aggregates retained over different sieves, ranging from 80 mm - 150 microns divided by a constant (generally taken to be 100).
• Higher is the value of fineness modulus, coarser are the aggregates and vice-versa.

important question:

Q: Amongst coarse or fine aggregates, which type of aggregate gives high workability?

Sol: Coarse aggregate. The surface area of coarse aggregate is less as compared to fine aggregate, thus less lubrication is required which results in high workability.

Fine aggregate → Surface area ↑ → Workability ↓
→ Contact area ↑ → Bond strength ↑

Sieve Size	Weight Retained	% Weight Retained	Cumulative % Weight Retained
80 mm	20	10	10
40 mm	40	20	30
20 mm	15	7.5	37.5
10 mm	5	2.5	40
4.75 mm	5	2.5	42.5
2.36 mm	15	7.5	50
1.18 mm	20	10	60
600 µm	40	20	80
300 µm	25	12.5	92.5
150 µm	15	7.5	100
	Σ = 200		542.5

Let the constant = 100
FM = 542.5 / 100

FM = 5.425
The value of FM indicates the size of sieves mentioned above, starting from the lowest size as the mean size of aggregate in a sample.
If FM = 1 [Refer to table above]
(Starting from lowest)
The average size of the particle is 150 µm
If FM = 2, the avg. size of the particle is 300 µm
If FM = 3, the avg. size of the particle is 600 µm
If FM = 5.425, the avg. size of the particle is between 2.36 mm and 4.75 mm.

NOTE : a)

Sand	FM
fine sand	2.2 - 2.6
Medium sand	2.6 - 2.9
Coarse Sand	2.9 - 3.2

b) Sand having FM > 3.2 is not suitable for the preparation of concrete.

important question:

Q: If FM is less, the strength of concrete will be more/less?

Sol: If FM is less, the particles will be finer, the contact area will be more, the bond strength will be more; thus, the strength will be more.

FM ↓ Finer ↑ Contact area ↑ Bond strength ↑
FM ↑ Coarse ↑ Surface area ↓  Workability ↑

Q: If 20 kg of coarse aggregate is sieved through 80 mm, 40 mm, 20 mm, 10 mm, 4.75 mm, 2.36 mm, 1.18 mm, 600 um, 300 um, 150 um sieves and weight retained is 0 kg, 0 kg, 6 kg, 6 kg, 8 kg, respectively, then the FM of the aggregate is:

a) 7.30
b) 7.35
c) 6.90
d) 9.20

Sol:

Sieve Size	Weight Retained	% Weight Retained	Cumulative % Weight Retained
80 mm	0	0	0
40 mm	0	0	0
20 mm	6	30	30
10 mm	6	30	60
4.75 mm	8	40	100
2.36 mm	0	0	100
1.18 mm	0	0	100
600 µm	0	0	100
300 µm	0	0	100
150 µm	0	0	100
	Σ = 20 kg		Σ = 690

FM = 690 / 100 = 6.9

So, the correct answer is C).

previous year's important question:

Q: If the fineness modulus of a sample of fine aggregates is 4.3, the mean size of the particles in the sample is between:

a) 2.36 mm to 4.75 mm
b) 1.18 mm and 2.36 mm
c) 300 µm and 600 µm
d) 150 µm and 300 µm

Sol: b)
(GATE-2019, SET-II)

strength of aggregate:

• The strength of aggregate directly governs the strength of concrete, which is used for construction.
  It is defined as the ability of aggregates to resist gradual loading.
• It is determined in terms of parameters "aggregate crushing value", which is found using the "aggregate crushing value test".
• In this test sample of aggregate passing through a 12.5 mm sieve and retained over a 10 mm sieve is subjected to gradual loading with the help of a 40 tonnes plunger for 10 minutes.
• The sample is then passed through a 2.36 mm sieve, and the weight of particles passing through the sieve is noted, which when expressed in terms of the original weight of aggregates is termed as aggregate crushing value.
  For aggregate to be used for pavement construction. It must not exceed 30%, and for general construction, it must not exceed 45%.

ACV = ( weight of fraction passing through appropriate sieve / weight of surface dry sample ) / 100

ACV ∝ 1/ Strength

toughness of aggregate:

• Toughness of aggregate directly governs the toughness of concrete in which it is used for construction.
• It is defined as the ability of aggregates to resist impact loading.
• It is represented in terms of the parameter "aggregate impact value" and is determined by performing the "aggregate impact value test".
• In this test sample of aggregate passing through 12.5 mm sieve and retained over a 10 mm sieve is subjected to impact loading with the help of 14 kg hammer, that is allowed to fall freely from the height of 38 cm over the sample, 15 times.
• The sample is then passed through a 2.36 mm sieve, and the weight of aggregates passing through this sieve is noted and when expressed in terms of the original weight of the aggregate is termed as aggregate impact value.
• For aggregate to be used in pavement construction, it must not exceed 30% & for general construction, it must not exceed 45%.

AIV = (B/A) * 100

where B = weight of fraction passing through 2.36 mm sieve

A = Weight of oven dry sample

AIV ∝ 1/ Toughness

hardness of aggregate:

What is Hardness?

Hardness of aggregate is defined as the resistance against wear and tear or abrasion.

• The hardness of aggregate directly governs the hardness of concrete in which it is used for construction.
• It is referred to in terms of a parameter termed "aggregate abrasion value" and is found using the following test:
  a) Deval abrasion test
  b) Dorry abrasion test
  c) Los Angeles abrasion test
• In these tests, the sample of aggregate is subjected to wear and tear in rotating cylinder, having steel balls in it.
• The sample is then passed through 1.7 mm sieve and the weight of aggregates passing through this sieve is noted, which when expressed in terms of the original weight of aggregates is termed as aggregate abrasion value.
• For pavement construction, it must not exceed 30%, and for general construction, it must not exceed 50%

Important Facts

Soundness test of aggregate is performed as per IS-2386 PART V. This test is performed to study the resistance of coarse and fine aggregates to weathering action.

previous year's questions

Q: The Los Angeles test for stone aggregate is used to examine:

a) Abrasion resistance
b) Crushing strength
c) Soundness
d) Specific gravity

Sol: a)
(GATE-2020, SET-I)

Q: Match the following:

The correct match of test methods under Group-I to properties under Group-ll is:
a) P - 4, Q - 1, R- 2, S- 3
b) P - 2, Q-1, R- 4, - 3
c) P - 3, - 4, R- 1, S- 2
d) P - 2, Q - 4, R - 3, S - 1
Sol: b)
(GATE-2020, SET-II)

alkali aggregate reaction

• Alkalis undergo an expansive reaction with aggregates causing its disintegration, which is also termed as cancer of concrete.
• The alkali-silica - gel imparts osmatic pressure over the set concrete gel, which is mainly responsible for the formation of cracks; however, its exact mechanism is still not known.

Factors affecting alkali-aggregate reaction:

• I Reactive type of aggregate
• ii) High alkali content cement
• iii) Availability of moisture
• iv) Temperature conditions: Favourable temperature for the reaction is 10 - 38°C.

Control of alkali-aggregate reaction:

It can be controlled by the following considerations:

• i) By selecting non-reactive aggregate
• ii) By using low alkali cement
• iii) By using pozzolanic material (fly ash, surkhi, crushed stone dust)
• iv) Air-entraining agents: They prevent the development of osmotic pressure.

bulking of sand:

• The increase in the volume of a given mass of fine aggregate caused by the presence of water.
• Water forms a film over the fine aggregate particles & exerts surface tension and pushes them apart, which increases the volume.
• The extent of bulking depends upon the percentage of moisture present in sand and its fineness.
• Bulking of sand is more for finer particles and less for coarser particles.
  Fine sand > Medium sand > Coarse sand
• Bulking of sand is maximum at 5% moisture content.

Important FACTS

If dry sand is used, then no correction is applied. But if the moist sand is used, then correction is applied.
Example: If the bulking of sand is 20% and if mix ratio is 1: 2: 4 (dry sand), then the actual volume of sand used will be 1.20 × 2 = 2.4 instead of 2 per volume of cement. And mix ratio will be 1: 2.4 : 4 (moist sand).

As per IS 650, Indian Standard Sand - ENNORE Sand is used, which is obtained from Tamil Nadu.

Particle Size	Gradation
1 - 2 mm	33.33 %
500 µm - 1 mm	33.33 %
90 µm - 500 µm	33.33 %

Important Keywords

To understand all the fundamental regarding STONE & AGGREGATES do visit the following category.

To understand all about the fundamental concept of Rocks Mining And The Characteristic Of Quality Building Stones do visit the following article

To understand all about the fundamental concept of Testing And Preservation Of Stone And Artificial Stones do visit the following article

To understand all about the Building Material do visit the following category.