TESTING OF CONSTRUCTION MATERIALS ON SITE :

Many types of materials are used in civil engineering constructions for various activities. Therefore, before starting the work at site we need to check all the materials used in construction work i.e., Cement, Bricks, Concrete, Sand, Aggrigate etc.

v Cement:

Cement is the most important material used in construction. It is used in almost every item of construction. The function of cement is to strengthen it by adding sand and gravel.

There are two main types of testing, for cement quality.

Field testing
Laboratory testing

Field testing:

Field testing is sufficient when cement is to be used for a small construction or for less important construction. There is no special need for laboratory testing

How to check quality of cement on a field.

The bag of cement should be machine sewn.
It should weigh 50 kg.
The color of the cement should be uniformly greenish gray or brown.
The cement should feel cold when you put your hand in the cement bag.
Cement bag should not have lumps.
The cement should feel smooth to the touch. Sandy or clayey cement looks gritty.
A handful of cement should be floated in water for a while.
Make a water-thick paste in about 100 gm of cement. Make a sharp-edged cake out of it. Place the cake on a glass plate, gently place the plate in a bucket filled with water. The shape of the cake should not change while taking the plate down into the water. After 24 hours, the cake should retain its original shape as well as gain a little strength.

Laboratory testing:

When cement is to be used in an important construction or in a large space, the quality of cement cannot be determined on the basis of field testing alone. In such a case, it is very important for the cement user to undergo laboratory testing of the cement.

Cement is subjected to laboratory testing for its following properties:

1. Fineness

2. Consistency

3. Setting time

4. Compressive strength

5. Soundness

6. Heat of hydration

7. Chemical composition

Fineness:

The fineness of cement is a measure of cement particle size and is denoted as terms of the specific surface area of cement. The Test is done by sieving cement samples through a standard IS sieve.

Consistency:

The standard consistency of cement paste is defined as the percentage of water added In 300gm weights of cement which will permit a Vicat plunger having 50 mm length and 10 mm diameter to penetrate in cement paste to a depth of 33-35 mm from the top of the mold

Setting time:

Initial Setting Time of Cement: It is the time elapsed between the moments that the water is added to the cement, to the time that the paste starts losing its plasticity.

Final Setting Time of Cement: It is the time elapsed between the moment the water is added to the cement and the time when cement paste loses its plasticity completely and has attained sufficient firmness to resist certain definite pressure.

Compressive strength:

The Tensile Strength of Cement is the maximum load that cement in its hardened state can withstand without fracture when tension is applied.

It is necessary to test the tensile strength of cement or concrete because concrete structures are highly prone to tensile cracking due to various kinds of load applied. As compared to Compressive Strength Tensile strength is very low.

Soundness:

The soundness of cement indicates the stability of any cement during the volume change in the process of setting and hardening.

In case the volume change in cement is unstable after setting and hardening, the concrete element will crack, which can affect the quality of the structure or even cause serious accidents, known as poor dimensional stability.

Heat of hydration:

During the Curing of Concrete, Hydro-thermal Reaction takes place, resulting in the production of heat because of chemical reactions. The rise of heat in concrete could be as high as 50^oC.

Hence in order to reduce such heat, low heat cement is used. The test is carried out using a calorimeter using the principle of heat gain.

Chemical composition:

The components present in cement for forming cement as the complete products are lime or limestone, silica (SiO2), alumina (Al2O2), magnesia (MgO), etc. Among which most important raw materials required for making cement are limestone, clay, and marl.

Points to keep in mind while storing cement:

Store rooms floor, walls, roof etc. should be waterproof.
Windows and the number of doors should be kept minimum.
The level of plinth should be higher than the ground level.
Cement bags should be kept 30 cm away from the wall.
Kept 14 bags in one column of cement row. That Means the height of cement bags row should not exceed 14 bags,
Cement bags should be placed on the floor in a damp area with wooden planks.
Old bags should be used first.
To reduce air circulation between the cement bags, space should not be kept between the column of cement bags.
Cement should not be stored for a long time.

v Bricks:

Brick is also an important building material. Bricks are usually made from clay or by mixing Fly ash with clay. It is commonly used in the following items of construction.

Bricks are usually used to withstand compressive loads.

Tests for quality of bricks :

Bricks should be well baked. Its color should be a uniform dark night.
The Edges of bricks should be uniformly sharp.
Bricks should not be broken from a height of approximately 1.2 m.
A metallic ringing sound should be produced when two bricks collide with each other.
Brick surfaces should be hard enough. Scratching brick surface with the Help of finger nails scratch impression not left on brick surface.
When breaking a brick, its texture should be uniform and compact.
There should be a “frog” on the top surface of the brick, so that the grip is maintained between the upper and lower two layers of masonry.

Size of brick:

The standard size of a brick should be as follows.

Standard size:19 cm x 9 cm x 9 cm
Modular Size: 20cm x10cm x10cm.
bricks should weigh 2.7 to 3.1 kg. According to I.S. another standard size of brick is 19 cm x 9 cm x 4 cm which is not very Popular.
After cleaning the sides of the brick, the length of the 20 bricks Should be according to Below.

	1^st class brick	2^nd class brick
Length	368 to 392cm	350 to 410cm
Width	174 to 186cm	165 to 195cm
Heigh	174 to 186cm	165 to195cm

Length of 20 Brick (I.S : 1077-1976)

Water absorption of Bricks: (IS ; 1077 -1976)

After immersed Brick in water for 24 hours,

Water absorption of first class bricks should not absorb more than 20% water.
Water absorption of second class bricks should not absorb more than 22% water.
Water absorption of third class brick should not absorb more than 25% water.

Compressive strength of Brick:

Compressive strength of First class brick :7.0 N/mm2 to 14 N/mm2
Compressive strength of Second class brick: 7.0 N/mm2 to 3.5 N/mm2
Compressive strength of third class brick: less than 3.5 N/mm2

Efflorescence test for brick:

This test is done to find out the alkali content in bricks.
Arrange 5 bricks in a dish so that they stand on top of each other.
Fill this dish with distilled water to a depth of 2.5 cm.
Leave the dish open in the air at a temperature of 20 to 30.
When all the water has evaporated again fill the dish to a depth of 2.5 cm.
Observe the bricks when all the water has evaporated.

v Aggregate :

Important Point to Check Quality of Aggregate:

There are two main types of aggregate. Fine aggregate and coarse aggregate
Aggregates are smaller than 4.75 mm is known as Fine aggregate.
Aggregates are larger than 4.75 mm is known as Coarse aggregate.
According to I.S : 383 -1970 Natural aggregates should be the first choice.
Grading limits of Fine Aggregate according to I.S : 383 -1970, table – 4 years
The amount of flaky and elongated particles should be less in Coarse Aggregate.
The fineness modulus (F.M.) for Fine aggregate should be between 2 to 3.2.
The fineness modulus (F.M.) for Coarse aggregate should be between.5.5 to 8.0.

v Sand:

Quality of Sand on Site:-

Sand is one of the most important constituents of concrete. The main purpose of mixing sand (fine aggregate) in concrete is to fill the voids between Coarse aggregate. And the voids between fine aggregate is filled with cement. Sand bulks the concrete and helps to increase the workability of concrete.

Sand is formed by the weathering of rocks. Well, different regions use the variety of sands (Pit sand, River sand, Sea Sand) in construction according to the availability. A good fine aggregate used in construction should be well graded (all particles that have almost same size).

The fine aggregate used for construction should pass 4.75mm sieve and retain on 150 microns sieve.

QUALITY TESTING OF CONSTRUCTION MATERIALS ON SITE

v Cement:

Field testing:

How to check quality of cement on a field.

Laboratory testing: