BRICKS, TYPES AND ITS TEST

BRICKS

 Bricks are blocks of tampered clay molded to suitable shapes and sizes while it is still in plastic condition, dried in the sun and burnt. Classification Bricks are broadly classified Into Two 

Categories 

 1) Sun Dried Bricks Or Kacha bricks

2) Burnt bricks or Pucca bricks 

1) Sun dried bricks 

 These bricks after moulding have been dried in the sun and are used in the construction of temporary and cheap structures.

These types of bricks should not be used at places of heavy rains.

 2) Burnt bricks or Pucca  

These are of the following four types  

a)  First class bricks

 These are well burned bricks of uniform color.

 These are free from cracks.

Scratch with finger nails leaves no mark

 These do not absorb more than 15% of their weight of water    

When struck with each other give a sharp metallic ringing sound

These are free from nodules of free lime Uses: used in face work of structures not to be plastered Used in flooring and reinforced brickwork. 

b) Second Class Brickwork

These are as hard and well burnt bricks as the first class but may be somewhat irregular in shape or size and may have slight rough surface.

Uses:

used in unimportant situations or in places where the masonry is to be plastered.

Used as brick ballast in RCC work and in lime concrete.

c) Third Class Bricks:

 These are under burnt bricks,

These are soft These have lighter color These emit a dull sound when struck against each other Uses:

 these are used in temporary constructions not subjected to heavy loads or too heavy rains

d) Over Burnt Bricks:

These are over burnt bricks that are being near the fire in the kiln get fused and lose their shap

Uses:

Used in the foundations of structures Used as aggregate for concrete Used as road metal

Classification of bricks based on compressive strength

Bricks shall be classified based on their compressive strength as given in table below:

CLASS DESIGNATION	AVG. COMPRESSIVE STRENGTH NOT LESS THAN (Kg/cm2)
350	350
300	300
250	250
200	200
175	175
150	150
125	125
100	100
75	75
50	50
35	35

Standard Tests of Bricks

Burnt clay bricks are subjected to the following tests

a) Test for compressive strength (crushing strength)

 b) Test for water absorption

c) Test for efflorescence

a) Test for compressive strength (crushing strength)

The brick specimen is immersed in water for 24 hours. The frog of the brick is filled flush with 1:3 cement mortars and the specimen is stored in damp jute bag for 24 hours and then immersed in clean water for 24 hours. The specimen is placed in compression testing machine with 6 mm plywood on top and bottom of it to get uniform load on the specimen. Then load is applied axially at a uniform rate of 14 N/mm2. The crushing load is noted. Then the crushing strength is the ratio of crushing load to the area of brick loaded. Average of five specimens is taken as the crushing strength

b) Test for water absorption

Brick specimen is weighed dry. Then they are immersed in water for a period of 24 hours. The specimen are taken out and wiped with cloth. The weight of each specimen in wet condition is determined. The difference in weight indicates the water absorbed. Then the percentage absorption is the ratio of water absorbed to dry weight multiplied by 100. The average of five specimens is taken.  

 Water absorption=w2-w1/w1 *100  

Where w1=weight of dry brick           

W2=weight of wet brick after 24 hours immersion in water

c) Test for efflorescence

Place the brick specimen in a glass dish containing water to a depth of 25 mm in a well-ventilated room. After all the water is absorbed or evaporated again add water for a depth of 25 mm. After second evaporation observe the bricks for white/grey patches.

 The observation is reported as ‘nil’, ‘slight’, ‘moderate’, ‘heavy’ or serious to mean

(a) Nil: No patches

 (b) Slight: 10% of area covered with deposits

(c) Moderate: 10 to 50% area covered with deposit but unaccompanied by flaking of the surface.

(d) Heavy: More than 50 per cent area covered with deposits but unaccompanied by flaking of the surface.

 (e) Serious: Heavy deposits of salt accompanied by flaking of the surface

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BRIDGES AND ITS TYPES

:DIFFERENT TYPES OF BRIDGES AND ITS SUITABILITY:

Definition:-

 A bridge is a structure providing passage over an obstacle without closing the way beneath. The required passage may be for a road, a railway, pedestrians, a canal or a pipeline. The obstacle to be crossed may be a river, a road, railway or a valley. In other words, bridge is a structure for carrying the road traffic or other moving loads over a depression or obstruction such as channel, road or railway. A bridge is an arrangement made to cross an obstacle in the form of a low ground or a stream or a river without closing the way beneath.

Components of bridge

The bridge structure comprises of the following parts.   Superstructure or Decking This includes slab, girder, truss, etc. This bears the load passing over it and transmits the forces caused by the same to the substructures.   Bearings The bearings transmit the load received from the decking on to the substructure and are provided for distribution of the load evenly over the substructure material which may not have sufficient bearing strength to bear the superstructure load directly.

Substructure

This comprises piers and abutments, wing walls or returns and their foundation.

 • Piers and Abutments These are vertical structures supporting deck/bearing provided for transmitting the load down to the bed/earth through foundation.

 • Wing walls and Returns These are provided as extension of the abutments to retain the earth of approach bank which otherwise has a natural angle of repose.

• Foundation  This is provided to transmit the load from the piers or abutments and wings or returns to and evenly distribute the load on to the strata. This is to be provided sufficiently deep so that it is not affected by the scour caused by the flow in the river and does not get undermined. While the above mentioned are structurally operational parts, for safety hand rails or parapets, guard rails or curbs are provided over the decking in order to prevent vehicle or user from falling into the stream or for the separation of traffic streams.

Classification

Bridges may be classified in many ways, as below. 

 According to the flexibility of superstructure as fixed span bridges or movable bridges.

 • Fixed span superstructure

 In case of fixed span superstructure, the superstructure remains in a fixed position and most of the bridges are of this category. 

• Movable span bridges

 In case of movable span superstructure, the superstructure is lifted or moved with the help of some suitable arrangement.

  According to the position of bridge floor relative to the formation level and the highest flood discharge as deck bridges, through bridges or semi- through bridges.

• Deck bridges

Deck-type bridges refer to those in which the road deck is carried on the top flange or on top of the supporting girders. The deck slab or sleeper may cantilever out to some extent beyond the extreme longitudinal girder 

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