INTRODUCTION TO CONSTRUCTION MATERIAL

AND TECHNOLOGY

BY

RAHUL SINHA

•PHYSICAL AND MECHANICAL PROPERTIES •SAND •BRICKS

PHYSICAL & MECHANICAL PROPERTIES OF

CONSTRUCTION MATERIALS

Physical properties

Density : mass/unit volume of homogeneous material

Bulk density : mass/unit volume of material in its natural state

Density index = bulk density/density

Porosity = volume of voids or pores/ total volume

Porosity is indicative of bulk density, heat conductivity, durability, etc.

Hygroscopicity: Ability of the material to absorb water vapour from air

Depends on: air temp., relative humidity, pores- their types, number and size.

Water Absorption: Ability of the material to absorb and retain water.

Coefficient of softening = compressive strength in saturated condition / compressive strength in dry state.

Material with coefficient of softening less than 0.8 should not be recommended in the situations exposed to action of moisture

Weathering Resistance: Ability to overcome the alternate wet and dry conditions for a long period without considerable deformation and loss of mechanical strength.

Water Permeability: Capacity to allow water to penetrate under pressure.

Frost Resistance: Ability of a water saturated material to endure repeated freezing and thawing without considerable decrease of mechanical strength.

Heat conductivity: Ability of a material to conduct heat. Depends on nature of material, its structure, porosity and mean temperature at which heat exchange takes place.

Fire resistance: The ability of a material to resist the

action of high temperature without any appreciable

deformation and substantial loss of strength.

Refractoriness: Ability to withstand prolonged action

of high temperature without melting or losing shape.

Materials resisting prolonged temperatures of 1580оC

or more are known as refractory.

Chemical Resistance: Ability of material to withstand

the action of acids, alkalies, sea water and gases.

Durability: ability to resist the combined effects of

atmospheric and other factors.

MECHANICAL PROPERTIES

Strength: The ability of the material to resist failure under the action of stresses caused by loads, the most common being compression, tension, bending and impact.

Hardness: Ability of a material to resist any deformation cause by external forces. Mohr’s scale (1-10) is used to find the hardness of materials.

Elasticity: ability of the material to restore its initial form and dimensions after the load is removed.

Plasticity: Ability of material to change its shape under load without cracking and to retain the shape to some extent after the load is removed.

Ductility: ability of the material to be brought

into wires. It is quantified by the value of strain

at the fracture point of the stress-strain curve.

Toughness: it is the ability of the material to

absorb energy. It is measured in two ways:

1.integration of stress-strain curve

2.charpy test

TEST FOR STONES(FIELD AND LABORATORY

TEST)

FIELD TEST

1.Absorption test

2.Smith’s test

3.Toughness test

4.Moh’s scale of hardness test

5.Acid test

6.Crystallization test

FIELD TESTS

Absorption test:

1.A 50g sample of the rock or stone is taken and

immersed in distilled water.

2.Water absorbed in 24 hours is obtained.

It should not exceed 0.6%

Smith’s test: To determine the deterioration

of stones when immersed in water.

1.A sample of stone is placed in distilled water in a

glass vessel and vigorously stirred. It is kept in

water for at least 24 hours. If the water turns

muddy, then the stone contains earthy

substances.

Toughness test: Hit the stone with a hammer and find how tough it is to break it with the hammer.

Moh’s scale of hardness test: Scratch the surface of stone with a penknife (as per Moh’s scale of hardness).

Acid test: to test the presence of calcium carbonate in the stone.

1.A cube of stone weighing about 50 to 100g is immersed in 1% of HCl for 7days.

2.If the sample contains powder on its surface and broken sharp edges, then there is a presence of calcium carbonate.

Crystallization test: It is performed to test the durability of the stone.

1.A 40mm cube of stone is immersed in 14% sodium sulphate solution for 2 hours.

2.It is dried in oven at 100O C.

3. This process is repeated at least 5 times.

4.The loss of weight and presence of cracking are noted.

5. The stone is durable if the loss in weight and cracks are minimum

LABORATORY TEST

Attrition test

Crushing Test

Freezing and thawing test

Hardness test

Aggregate Impact test

Microscopic test

Attrition test:

1.This test is used for stone aggregates used in road construction.

We use Deval’s abrasion testing machine.

2.The results of test indicate that the resisting power of stones

against the grinding action under traffic. Following procedure is

adopted.

3.Sample of stone pieces (specified grading of around 60 mm size),

weighing 5kg, are put in both the cylinders of Deval’s attrition

test machine containing steel spheres. Diameter and length of

cylinders are 20 and 34 cm respectively.

4.The Cylinders are closed. Their axes make an angle of 30о with

horizontal. The cylinders are rotated about its axis for 5 hours at

the rate of 30 rpm.

5.After rotation, the contents are taken out from the cylinders and

they are passed through a sieve of 1.5 mm mesh size.

6.Quantity of material which is retained on the sieve is weighed.

7.Percentage wear = loss in weight x 100/ Initial weight.

8.Los Angeles machine is used to overcome defects in Deval’s

abrasion machine.

9.If Los Angeles abrasion machine is used, percentage wear should

not be more 16% for a good road aggregate.

Crushing Test: This test is used for concrete aggregates and aim is to determine the crushing or compressive strength.

Sample of stone is cut into cubes of size 40mm. Sides of cubes are finely dressed and finished. Minimum number of specimens to be tested is 3.

Such specimens to be placed in water for about 72 hours prior to test and thereafter tested in saturated condition.

Load bearing surface is then covered with plaster of Paris or 5 mm thick plywood. Load is applied axially on the cube in a crushing test machine.

Rate of loading is 140 kg/cm2/min.

Crushing strength of the stone per unit area = Max. load at which sample fails per unit Area of bearing face.

Hardness Test:

A cylindrical stone of diameter 25 mm and height 25 mm is taken from the sample stone.

It is weighed.

It is placed in Dorry’s testing machine and pressed with a pressure of 1.25 kg.

Annular steel disc of machine is then rotated at a speed of 28 rpm.

During the rotation of disc, course sand of standard specification is sprinkled on the top of disc.

After 1000 revolutions, specimen is taken out and weighed.

Coefficient of Hardness = [20- (loss in weight in g)]/3

Freezing and thawing test:

1.Specimen of stone is kept immersed in water for

24 hours.

2.It is then placed in a freezing mixture at -12о C

for 24 hours.

3.It is then thawed or warmed at atmospheric

temperature. This should be done in a shade to

prevent any effect due to wind, sunrays, rain etc.

4.Above procedure is repeated several times ( at

least 7 times) and after which the specimen are

carefully examined for any damage.

Aggregate Impact test:

This test is for aggregates in concrete that undergoes impact as in runways in airports. Materials passing through 12.5 mm and retained on 10 mm are filled in the standard layers, each layer tamped with 25 strokes of iron rod. A hammer weighing 14 kg is dropped from a height of 380 mm 15 times and the resulting material is sieved through a 2.36 mm I.S sieve. The percentage fine is the aggregate impact test value. It should not be more than 45% for aggregates for concrete for ordinary use and not more than 30% for aggregates for concrete for runways and pavements. For Indian aggregates, it ranges from 15 to 30%.

Microscopic test:

In this test, thin sections of the stone are taken and placed under the microscope to study the grain size, mineral constituents and presence of harmful materials.

SAND

SAND

Sand is essentially quartz (SiO2) and formed by

the disintegration of sand stone due to

weathering effects.

Sand between 4.75 mm (about 5 mm) and 0.15

mm size is called fine aggregate. It is used for

making concrete, mortars and plastering. It is

also used for filling under floor, basements.

Impurities in sand: Clay, silt, salts, mica and

organic matter, shells, wood particles etc. are the

main impurities in sand. It is better to use

impurities free sand and sum of impurities

should not exceed 5%.

PROPERTIES OF GOOD SAND

It should be chemically inert

It should be clean and coarse. It should be free

from any organic or vegetable matter.

It should contain sharp, angular and durable

grains

It should not contain salts which attract moisture

from the atmosphere

It should be well graded, i.e., should contain

particles of various sizes in suitable proportions

BULKING OF SAND

The presence of moisture in sand increases the volume of sand.

This is due to the fact that moisture causes a film of water around sand particles (capillary action) and that does not allow the particles to come closer to each other.

The above phenomenon results in increase in volume of sand and is known as bulking of sand.

For a moisture content of about 5 to 8 %, the increase in volume may be as much as 20 to 40 %, depending up on the grading of sand.

The finer the material, the more will be increase in volume for a given moisture content.

TEST OF BULKING OF SAND

Bulking that can take place for given sand can be

easily determined by rehandling it.

Pour enough rehandled sand in a 250 cc

measuring cylinder. By consolidating it by simple

shaking only, make it come to a level.

Let the height be ‘h1’. Pour water to the sand and

stir it well to saturate the sand till the level of

water is above the sand.

The decrease in volume of sand is noted by

measuring its new height (h2).

Now the percentage bulking of sand can be

calculated as 100x (h1-h2)/h2).

TEST FOR ORGANIC IMPURITIES

This is an important test for dirty sands.

A 350 mL graduated glass bottle is filled to 75 mL with 3% solution of sodium hydroxide.

Sand is added to this solution till 125 mL mark is reached, and then it is made up to 200 mL by adding more caustic solution. The bottle is stoppered, shaken vigorously to enable the organic matter to be digested and allowed to stand for 24 hours.

A dark colour of the liquid above sand indicates the presence of objectionable amount of organic substances in sand. In such cases, the sand should be washed before it is used and a retest is done to test the organic impurities.

TEST FOR SILT AND CLAY

A sample of sand to be tested is placed without drying in a 200 mL measuring cylinder, to 100 mL mark. Add clean water up to 150 mL mark. A pinch of salt is added to it.

The mixture is then shaken vigorously, the last few shakes being in sidewise direction. Allow the solids to settle down for a period of 3 hours.

First the sand settles and then silt and clay over it. The height of silt and clay over sand should not be more than 8 % of sand below it to classify the sand as good.

Sand is taken from a heap and rubbed against the fingers. If fingers are stained, it indicates that sand contains earthy matter.

BRICKS

PROPERTIES OF BRICKS

Bricks are made from specially selected and

matured brick-earth consisting chiefly of Silica

(35 – 70 %) and alumina (10 to 20 %).

Too much silica tends to make the brick brittle

and too much alumina makes the brick wrap and

crack on drying and burning.

Color:

The agents like lime, magnesia, oxide of iron

which act as a colouring agent and flux to assist

fusion during burning of the brick earth.

Shape

Bricks are made in traditional size and also in

metric size prescribed by BIS.

The actual size of bricks is 19x9x9 and its

nominal size is 20x10x10.

The bricks of thickness lesser than normal are

called tile bricks. (19x9x4).

Frog: Depression made at the top of a brick is

called the frog. Brickwork is constructed with the

frog laid facing upwards. It serves to place the

name of the manufacturer and also as a key to

the mortar to bond bricks together.

CLASSIFICATION OF BRICKS

According to general physical requirements: Class I, Class II and Class III.

I.S. classification of bricks according to strength (10 to 3.5 N/mm2)

According to use: common bricks, engineering brick (for carrying heavy loads), facing bricks, Fire bricks, special (special shape)

SAMPLING AND TESTING OF BRICKS FOR ITS

PROPERTIES

Sampling

The sampling size should be 20 bricks from a lot of 50,000 (10 N/mm2) and the same number from a lot of 100,000 (7.5 to 3.5 N/mm2).

Test for bricks:

Compressive strength

Water absorption

Efflorescence

Dimensional tolerance

Hardness

Soundness

Structure

COMPRESSIVE STRENGTH

Five bricks are taken at random and their dimensions are noted to 1 mm accuracy.

Bricks are then immersed in water of 25 to 29оC for 24 hours. The surplus moisture is drained and frogs are filled with cement mortar (1:3).

Bricks kept under jut bag for another 24 hours and after which it is immersed in clean water for 3 days.

Then bricks are removed and wiped dry and placed with the flat surface horizontal and mortar filled face up between 3 plywood sheets each of 3 mm thickness.

The load is applied at the rate of 140 kg/cm2/min. till the failure of specimen takes place as indicated by the needle of the testing machine turning back.

Average of 5 value are reported as compressive strength.

Average value should not be less than specified value.

WATER ABSORPTION

Five bricks are taken for test

Bricks are dried in an oven at 110 to 115о C (48 hours) and then cooled to room temperature and noted its initial weight as W1.

Bricks are then kept in clean water at 27 ± 2 о C for 24 hours and then wiped dry with a damp cloth and weight W2 is measured.

The percentage water absorption = (W2-W1)*100/W1

The average percentage water absorption of Class I bricks should not be more than 20%, class II should not be more than 22% and of Class III bricks should not be more than 25%.

EFFLORESCENCE

This test should be conducted in a well-ventilated room at 18-30о C. Average value on 5 samples taken at random is reported.

The brick is placed vertically in a dish 30 cm X 20 cm approximately in size with 2.5 cm immersed in distilled water.

The whole water is allowed to be absorbed by the brick and evaporated through it. After the bricks appear dry, same quantity of water is placed in the dish and allowed to evaporate.

The brick is to be examined after the second evaporation and reported as follows:

1.nil: when there is no precipitate deposit of salt.

2.slight:when not more than 10% of the area is covered by the salt.

3.moderate:when heavy deposit covers 50% of the area but unaccompanied by powdering of the surface.

4.heavy:when heavy deposit covers more than 50% of the area and accompanied with powdering of the surface.

5.serious:when there is heavy deposit of salts accompanied with powdering of the surface and the deposition tends to increase in the repeated wetting of the specimen.

Generally bricks are slight to moderate efflorescent.

Dimensional tolerance

The whole 20 bricks of the sample are selected at random to check measurement of length, width & height. These dimensions are to be measured in one or two lots of ten each. Variations in dimensions are allowed only within narrow limits, ± 3 % for class I and ± 8 % for other classes.

hardness

A scratch is made on the surface of the brick with the finger nail. In a good brick, no impression will be left on the surface.

Soundness

Two bricks are taken, one in each hand, and they are struck with each other lightly. A clear metallic ringing sound should be produced and the bricks should not get break.

Structure

The brick is broken and structure is examined. It should be homogeneous free from defects such as holes and lumps.

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