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Brick Masonry Construction, Lab Tests , Classes of brick, defects in brick

brick masonry construction

This chapter is about Brick masonry, Classification of bricks, specifications of different types  of  bricks, testing of bricks different shapes of bricks         

Classes of brick

a) First class Brick:

   These bricks are roughly burnt, have uniform color, water absorption less than 15% and minimum compressive strength of 10.5  N/mm2. They have plane, rectangular faces with parallel sides and right angled edges.

b) Second class Brick:

  They have distorted round edges slightly rough surface with water absorption below 20 % and minimum compressive strength of 7 N/mm2 .

c)   Third class Brick:

They are not uniform in shape and are slightly under burnt or over burnt shouldn’t have water absorption more than 25%. 

d)   Over burnt (Jhama) bricks:

They are over-burnt, irregular in shape, hard and strong. These bricks are used in foundation, road material and flooring.

Requirements of good brick

a)   It should be well burnt and have uniform red color.

b)   It should give clear ringing sound when struck against another brick.

c)   When a brick is let to fall freely from 1 m. height on a hard floor, it should not break.

d)  It should not be scrached by finger nail.

e)   It should have unifonn structure throughout its body without any distortions.

Specification of different types of bricks

a)   Machine made bricks

Bricks shall be of uniform deep red or copper color, thoroughly burnt without being vitrified, regular in shape and size and shall have sharp and  suare sides and edges and parallel faces for uniformity in the thickness of the courses of brickwork. Bricks  shall  be  first  class  machine  made bricks of quality approved by the engineer and free from grit and other impurities such  as  lime, iron and other deleterious salts. They shall be uniform shaped, well-burnt, sound and hard with sharp edges and shall emit ringing sound when struck with a mallet. The size of the brick shall be 24cm X l l.2cm X 5.7cm unless otherwise specified, with a tolerance of ± 3mm  in each direction. The compressive strength shall be more than 3.5 N/mm2

b)   Chimney made bricks

Bricks  shall  be  first  class  chimney  made  bricks  of quality approved by the engineer and free from grit and other impurities such as lime, iron and other deleterious salts. They shall be uniform  shaped,  well-burnt, sound and hard with sharp edges and shall emit ringing sound when struck with a mallet. The size of the brick shall be 22.9cm X 1 l .2cm X 5.5cm unless otherwise specified  with  a  tolerance  of ± 3mm  in  each direction.  The compressive strength shall be more than 3.5 N/mm.  The bricks

shall be provided with frogs.

c)   Dachi bricks

Bricks shall be machine pressed chimney made traditional bricks of first class quality approved by the engineer and free from grit and other impurities  such as lime, iron and other deleterious salts. They shall be uniform shaped, well-burnt, sound and hard with sharp edges and shall emit ringing sound when struck with a mallet. The size of the brick shall be 21.Scm X 10cm X 5.6ctn unless otherwise specified,  with a tolerance of ± 2mm in each direction.  The compressive  strength shall be more than 3 N/mm2 . All bricks shall be built in stretcher bond.  Each brick shall  be set with bed and vertical joints filled thoroughly with mortar finished in Surkhi pointing.

Tests for brick

a)   Compressive strength test

Apparatus:

• Compression testing machine

Procedure:

The minimum number of specimen required for compressive strength is five. The specimen brick is immersed in water for 24 hours. The frog of the brick is filed is filled flush with 1:3 mortar and brick is stored under damp jute bags for 24 hours followed by immersion in clean water for three days. The specimen is then placed between the plates of compression testing machine. Load is applied axially at a uniform rate 14 N/mm2 and the maximum load at which the specimen fails is noted for determination of compressive strength of brick given by

Compressive strength =  Maximum load at failure / Loaded area of brick 

b)   Water absorption test

Apparatus:

•   Balance

.   Ventilated oven

Preconditioning:

Dry the specimen in a ventilated oven at a temperature of 105 to 115 0C  till it  attains substantially  constant mass. Cool the specimen to room temperature and the  weight  is (M1).

Procedure:

The specimen is completely dried as in preconditioning then Immerse  in clean water at a temperature of 27 ± 2°C for24 hours. Then remove the specimen and clean  out any traces of water with  a damp cloth and weight  the specimen.  Complete  the  weighing  3 minutes  after the specimen has been removed  from water and record the weight (M2).

Result:  

Water  absorption = (M1-M2)/M1 X 100%

c)    Efflorescence test

Apparatus:

• Glass  or porcelain dish  180mm X 180mm X 40mm depth for square and  200mm  diameter  X  40 mm  depth for cylindrical shape

Related: Types of cement their properties and Uses

Procedure:

First of all the end of the bricks is placed in the dish, the depth of immersion in water being  25mm. The whole arrangement is placed in warm well ventilated room upto the time of  all the water in the dish is absorbed by the specimens and the surplus water evaporates.  The dish containing  the   brick  is covered with   suitable glass cylinder to prevent excessive   evaporation from  the  dish  may  not  occur. After water absorving is completed  and  bricks  appear  to be dry, place  a similar  quantity  of water  in the dish and allow it to evaporate  same as above.  Examine  the  bricks   for eflorescence  after the second evaporation and report  the results.

Results:

From the above test examination  efflorescence  shall be reported  as  ‘nil’, ‘slight’, ‘moderate’, heavy’  or ‘serious’  in accordance  with the following definitions.

•    Nil – When there is no any percentage  deposit of efflorescence.

•   Slight – when there is less than 10 percent of the exposed area of the brick is covered with a thin deposit of salts.

•   Moderate  – When there  is  a heavier  deposit  than under ‘slight’ and covering up to 50 percent of the exposed aarea of the  brick surface  but  unaccompanied  by  poWdering of flaking of the surfaces.

•   Heavy – If the deposit of salts covering 50 percent or more of the exposed area of the brick  surface but unaccompanied by powdering  or flaking  of the surfaces the this is heavy efflorescent.

•  Serious   –  At the serious condition  there   is   a   heavy  deposit of  salts in the form of  powdering and / or flaking of the exposed surfaces.

Defects in brick masonry

a)   Corrosion of embedded fixtures

Such a defect is induced by dampness  in brick walls . The iron or steel fixtures like pipes, frames or holdfasts embedded in the brick masonry get correded due to dampness and hence expand with the formation of rust. This defect is countered by using dense mortar cover of 15 to 25 mm thick while embedding the fixtures.

b)  Efflorescence

It is a phenomenon in which white patches of soluble salts form in the surface of the brick when such bricks come in contact with water. This defect is developed in bricks containing excessive soluble salts. Regular washing and brushing of the effected surface is remedial to such defect.

c)   Shrinkage cracks

The alternate swlling and shrinking of bricks due to absorption and evaporation of water respectively, causes cracks near the joints. Such defect can be minimized by using good quality bricks and protecting brick from getting damp.

d)   Sulphate attack   

This  defect  is  prominent  in places where the brickwork is exposed to moisture influence like in boundary wall unplastered external walls, parapet walls, manholes, retaining walls etc.

Sulphate attack relies upon a number of conditions occurring simultaneouly;  it requires water saturation over a relatively long period, a source of sulphates and reasonable amount of tricalcium aluminate.

Even where these factors exist simultaneously, the attack will take a relatively long time to develop. In case of brickwork, the sulphate salts present in brick react with alumina of cement in case of cement mortar and with hydraulic lime  in case of lime mortar provided that there is sufficient contact with water.

This reaction increases the volume of mortar and leads to chipping and spalling of bricks. Sulphate attack can be checked by any technique that limits the entry of water in the body of brickwork.

 

Forms of brick

a)  Full brick: It is the undisturbed brick having original shape and size.

b)  Queen-closer:  When a brick is cut into two  portions along its length, it forms queen-closer.

c)  Queen-closer quarter:  When a queen-closer is broken into two identical pieces, it is known as queen-closer quarter.

d)   King closer: When a triani’JJU piece of the brick lying between the center of one end and the center of its adjacent side, is removed, it forms a king closer.

e)   Beveled  Closer:  When the stretcher face of the brick is beveled in such a way that half width is maintained at one end and full width at the other end, it is known as beveled closer.

f)   Mitred  closer:  When a header of the brick is  cut splayed or mitred at an angle  of 45° to 60° for full width, it is known as mitred closer.   

g)  Half bat: Bat is the portion of the brick cut along the width. If the bat length is half the original brick length, it is called half bat.

h)   Three  quarter bat: When the length of the bat is equal to three quarters of the length of a full brick, it is called three quarter bat.

i)   Beveled  bat:  Any bat  which has  its  width beveled is called beveled bat.

Types of Brick bonds in brick masonry

a)   English bond

 It consists of alternate  courses  of header  and  stretcher. Each header is placed centralfy above each stretcher.

b)  Flemish bond

     Alternate bricks  are placed  as header and stretcher  in every course.

Flemish bond
Flemish bond

c)   Stretcher bond

All bricks are laid with stretchers on the face of the wall.

Stretcher bond

d)   Header bond

All bricks are laid with headers on the face of the wall.

e)   Raking bond

Bricks are laid at an inclination to the direction of the wall.

f)  Diagonal bond

Bricks are inclined at 45° in the same direction and the extreme comers of the series remain in contact with the external line of stretcher.

g)  Herring-bone bond

Bricks are inclined at, 45°  in opposite direction from the center of the wall thickness.

Rat trap bond and its advantages

A rat-trap bond is a type of wall brick masonry bond in which edge is used to leading the brick, not in the center. (i.e. the height of each course in case of a brick size 230x110x75 mm, this is 110 mm plus mortar thickness) such that the shinner and rowlock are visible on the face of masonry as shown in the figure.

This gives the wall an internal cavity which is the major reason that makes it possible to considerably save the bricks, sand, and cement. This cavity adds a Green building  feature  that helps to  maintain improved thermal comfort.

A serious care must be taken while  designing  the wall lengths   and  heights  for  a  structure. The openings  and   wall dimensions  must be in multiples  of the module.  Also, the course below sill and lintel must be a solid course by placing bricks on edge and the masonry on the sides of the openings should be solid as it will help in fixing of the opening frame.

The advantages of using rat trap bond are:

a)   By adopting this method of masonry, approx. 20-35%  less bricks and 30-50% less mortar  are required;  also this reduces the cost of a 9-inch wall by 20-30 % and productivity of work enhances.

b)  For 1 m3 of rat trap bond, 470 bricks are required compared to conventional brick wall wherea total of 550 bricks are required.

c)  Rat trap  bond wall is a cavity wall construction with added advantage of thermal comfort. The advantages of this is that interiors remain cooler in summer and warmer in winter.

d)   Rat trap bond when kept exposed, creates aesthetically pleasing wall surface and cost of plastering and painting also may be avoided.

e)   Rat trap bond can be  used  for  load-bearing wall as well as thick partition walls.

f)   All works such as pillars, sill bands, window, and tie beams can be concealed.

g)    The walls have approximately 20% less dead weight and hence the foundations and other supporting structural members can suitably be designed,  this gives an added advantage of cost-saving for the foundation.

h)    In this process reinforcement bars can be easily inserted through the cavity till the foundation for the purpose of more structural safety in sophisticated system.

Shapes of brick

a)         Plinth header

b)         Plinth stretcher

c)         External plinth return

d)         Cant brick

e)         Squint brick

t)         Radial stretcher

g)        Radial header

h)        Single bullnose

i)          Double bullnose

j)          Double cant

k)        Saddleback

l)       Internal plinth return  

m)       Internal plinth

 n)         External plinth

o)         Birdsmouth

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