Aggregates

Nilanjan Mitra

Aggregates

• Natural sand/gravel deposits : deposited glacial formations, river deposits, or along beaches of lakes and seas. E.g. : limestone, granite, sandstone, etc.

• Crushed rock : Igneous rocks e.g. : basalt, granite. Sedimentary rocks e.g. : limestone, gypsum, shale, dolomite, sandstone Metamorphous rocks e.g. : slate, marble, quartzite, gneiss.

• Slag and mine refuse : Blast furnace slag, Industrial materials such as certain types of light volcanic rock, plastics used to produce lightweight concrete.

• Pulverized concrete and bituminous pavements substitute for natural aggregates which are costly; bituminous layers can be recycled and used in pavements.

• Other recycled and waste material : Crushed glass, rubber pellets, bricks, building rubble…

• Fine aggregates-4.75 mm (sieve No.4) to 75 microns (Sieve No.200)

• Coarse aggregate-Greater than 4.75 mm (no.4)

• Fines-Less than 75 microns (no.200)

Classification

Grading of Aggregates(Sieve analysis - ASTM C 136)

- Variation in grading can seriously affect the properties of concrete.- The cement required for concrete is proportional to void content of combined agg.- ASTM C33 grading for Fine-Aggregates (refer table in pg. 34)

- Fine agg. must not be more than 45% retained between any two consecutivestandard sieves

- Fineness modulus 2.3 to 3.1 (do not vary between 0.2 from agg. source)(higher FM --- coarser aggregate)

Sieve #Sieve Size

(mm)

Weight Retained

(g)Percent Retained

(%)

Percent Finer (cumulative

percent passing)

(%)

Percent Coarser (cumulative %

retained)(%)

3/8" 9.5 0 0 100 0

#4 4.75 60 2.84 97.16 2.84

#8 2.26 150 7.11 90.05 9.95

#16 1.18 400 18.96 71.09 28.91

#30 0.60 500 23.70 47.39 52.61

#50 0.30 510 24.17 23.22 76.78

#100 0.15 488 23.13 0.09 99.91

Pan - 2 0.09 0 100.00

Total 2110

Fineness Modulus = 2.71

Average sieve size= No 30

Particle size distribution graph of fine aggregates

0

10

20

30

40

50

60

70

80

90

100

0.1 1 10

Sieve Opening (mm) logarithmic scale

Perc

ent F

iner

(%)

Min. value

Max value

Sample

• Absorption, Porosity and Permeability Absorption relates to the particle’s ability to absorb a liquid. Porosity is a ratio of the volume of the pores to the total volume of the

particle. Permeability refers to the particle’s ability to allow liquids to pass through.

• Surface TextureThe pattern and the relative roughness or smoothness of the aggregate

particle. Plays a big role in developing the bond between an aggregate and a cementing material. A rough surface texture gives the cementing material something to grip, producing a stronger bond, and thus creating a stronger hot mix asphalt or Portland cement concrete.

• Strength and ElasticityStrength is the measure of ability of an aggregate particle to stand up to pulling or crushing forces. Elasticity measures the “stretch” in a particle. High strength and elasticity are desirable in aggregate Base and surface courses. These qualities minimize the rate of disintegration and maximize the stability of the compacted material.

• Density and Specific GravityDensity is the weight per unit volume of a substance. Specific gravity is the ratio of the density of the substance to the density of water. Helps in determining the amount of asphalt needed in the hot mix asphalt.

• Aggregate voidsThere are aggregate particle voids and voids between aggregate particles. Most aggregate particles have voids, which are natural pores that are filled with air or water. It influence the specific gravity and absorption of the aggregate materials.

• Specific gravity and water absorption• Abrasion Resistance• Soundness • Impact Value Test • Particle size and shape• Aggregate voids

Physical tests of Aggregates

Specific gravity (Relative density)- ratio of the weight of the aggregate to the weight of an equal absolute volume

of water (water displaced on immersion).- These specific gravity of aggregates can be determined both at oven-dry state

and at SSD state.- Specific gravity at oven dry state --- Apparent SG- Specific gravity at SSD state --- Bulk SG- typically values range from 2.4-2.9 for natural aggregates

Absorption capacity & Moisture content

- AC = (SSD weight – OD weight) * 100 / (OD weight)- MC = (Sample weight – OD weight) * 100 / (OD weight) - If MC of sample > AC WET else DRY- If WET then Surface Moisture = MC – AC- Fine agg have higher surface moisture (surface tension) (2-6%)

compared to Coarse agg (0.5-2%)- Typically coarse agg. AC = 0.2-4% fine agg = 0.2-2%- Bulking is increase in total volume of moist fine agg over same dry weight

(due to surface tension). Finer the sand – higher bulking.

BRICK and Masonry

- Nilanjan Mitra

nilanjan@civil.iitkgp.ernet.in

Clay heated @ < 640 deg C -- only Physical change@ 700 -1100 deg C --- chemical change, alumina & silica fuse together

resulting in compound which is strong & stable Brick@ > 1300 deg C -- above materials get vitrified (bricks lose shape)

Brick size = 20 X 10 X 10 cm. – Nominal, Actual = 19 x 9 x 9 cm.

Frog in a brick.

Types of bricks (based on manufacturing process) : Wire-cut & Pressed brick

Brick classification General physical requirements Class I, II, III (color, burnt, shape,

water absorption 24 hrs in cold water by weight [20, 22, 25]), Efflorescence.I.S. Classification based on strength 10, 7.5, 5, 3.5.

Test for bricks compressive strength, water absorption [sat. coeff., IRA], Efflorescence,

Advantage of brick construction:

• Initial cost as well as cost of maintenance• Thermal mass• Sustainability and recyclable

The world's highest brick tower of St. Martins Church in Landshut,Germany completed in 1500

MACHU PICHU

A closer view of the structure shows the brick used.

Bricks

Clay bricks

Variety

Quality

Type

Calcium silicate bricks Seven grades

Detailed brick classification

Common Brick: suitable for general building work as a minor load bearing structure, no special finish to the brick with regards to texture and color.Facing Brick: attractive appearance – color red, orange, yellow, grey and whiteEngineering bricks : Suitable for engineering purpose, divided into two divisions:

Class Average compressive strength(in N/mm2)

Average absorption boiling(%wt)

A 69.0 4.5

B 48.5 7.0

Variety

Common

Facing

Engineering

Types

Solid

Perforated

Hollow

Cellular

Special

Standard special

Solid: The bricks in which the holes passing through it do not exceed 25% of its volume or frogs (depression in the bed face of a brick) do not exceed 20% of its volume

Perforated

Hollow & Cellular

Special

Calcium Silicate bricks:made from a lean mixture of slaked lime and fine silicious sand, molded under mechanical pressure and hardened under steam pressure

class Compressive strength(MN/m^2)

1 7.02A 14.02B 14.03A 20.53B 20.54 27.55 34.57 48.5

Process of brick making:

This kiln in Uganda relies on a massive fire but there is some insulation on top. The walls are coated with mud to reduce convection. This kiln contains about 3,000 bricks.

This kiln in El Salvador, while using a massive amount of wood, would probably not be successful without the grass insulation. In addition to adding fuel to the fire, the grass turns to fine ash and retains the heat. About 300 bricks came from this burn.

This coal fired kiln in India relies on its volume to retain heat. The larger the kiln, the less heat is lost in relation to the volume since the surface area increases only on the square ofthe size while the volume increases on the cube of its size.This kiln is firing only 150,000 bricks but they like to fire up to 1,000,000 bricks at once.

About fifteen families are involved in making and firing the bricks in this kiln.

Air goes under, and coal is placed in strategically located layers (where the bricks are on edge). Tradition and years of experience undoubtedly contribute to this success.

Even so, errors and melt downs occur and most brick makers expect to lose a certainproportion of their efforts. These bricks are melted together due to excessive heat near thecenter of the kiln

These kilns near Torreon, Mexico fire about 25,000 bricks at once. Since all of the trees and biomass have already been cut down, they now rely on garbage and trash for fuel.

This kiln in Honduras is representative of many kilns in the world. It might have foursemi-permanent walls, no roof, wood is placed underneath.

The inside wall of the kiln has becomeself fired.Bricks are stacked in certain patterns to allow heat circulation.

The Bull's trench kiln

• It was invented in 19th

century by a British engineer, W. Bull.

• Its greatest advantage is its low cost of construction and comparatively low energy consumption.

• It is widely used in Pakistan, India, Bangladesh and Myanmar

• The kiln can be made circular or elliptical in shape.

• It is constructed on dry land, by digging a trench, 6 - 9 m wide, 2 -2.5 m deep, and 100 - 150 m long.

• The firing in a Bull's trench kiln is continuous, day and night. • Green bricks are loaded and finished bricks are drawn all the time.

• The fuel saving is achieved by reusing part of the energy that is otherwise lost in periodic kilns.

• Daily output is 15 - 25,000 bricks.

• Chimneys, 6 - 10 m high, made of sheet metal, are placed on top of the brick setting.• They are moved around as the firing progresses.• There are two main drawbacks with moveable chimneys;

-The metal sheets are eaten up by corrosion within 1.5 - 2 months, and

-during the time it takes to move the chimneys, the temperature drops.

-The loss of temperature increases, fuel consumption by about 5 - 10%.

• Bull's trench kiln with a fixed central chimney is now widely used

• More fuel efficiency compared to periodic kilns.• Low initial investment.• High capacity.

Advantages of the Bull's trench kiln

• The kiln is fired continuously and has to be loaded with a constant number of bricks every day.

• This demands a good organization of the brick production, and the production cannot easily be adjusted to fluctuations in the brick market.• The firing crew needs long time experience.• Its moveable chimneys have a short working life.

Disadvantages of the Bull's trench kiln

Overview of a modern brick factory

A robot handles bricks in a modern plant

Properties of bricks

Test for bricks compressive strength, water absorption, Efflorescence,

Different Type of cut bricks

Different terminologies in brick laying

Different types of masonry bonds

ADOBE Bricks

Mixing mud and straw in brick frames

The citadel of Arg-é Bam: The world's largest adobe structure, dating to at least 500 BC.