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Classification of Bricks

This article is on the Classification of Bricks Based on Quality. In this article, you will learn about the different classes of bricks with important characteristics/properties.

This article will be helpful and informative for civil engineers and civil engineering students.

You may also love to read: 10 quality of bricks used in building construction

Classification of Bricks

1. First Class brick

First-class brick is mainly used for load-bearing walls for multi-story buildings.

Characteristics of first-class brick are as follows:

  1. Color: Uniform dark red color
  2. Size and Shape: Should have a standard size and have a smooth surface free from
    cracks and should have sharp edges
  3. Soundness: When two bricks stuck together, they should give metallic sound.
  4. Hardness: It should be hard that it could not be scratched by fingernails.
  5. Porosity: It should not absorb water more than 15 % of its dry weight when immerse-
    in water for 24 hrs
  6. Strength: Minimum crossing strength should not be less than 140 kg/cm2
  7. Water absorption should be less than 15 % of its dry weight.
  8. Durability: Should be able to resist the effects of weathering agencies like temperature variations, rain, frost action, etc.
  9. Efflorescence: Should not contain alkaline salts which may cause efflorescence
    on its surface and decay the bricks.

2. Second Class Brick

Second class bricks are not suitable for the load-bearing walls for more than two-story buildings.

Characteristics of second class brick are as follows:

  1. It should not absorb water more than 20% to 22% of its dry weight when immersed in water for 24 hrs.
  2. The compressive strength of second class bricks is between 70 to 140 kg/cm2.
  3. Medium red in color.
  4. The shape and size are good.
  5. These bricks are burnt well.

3. Third Class Brick

The third class of bricks is generally used for temporary works.

Characteristics of third class brick are as follows:

  1. It should not absorb water more than 22% to 25% of its dry weight when immersed in water for 24 hrs.
  2. The compressive strength of third class bricks is between 35 to 70 kg/cm2.
  3. Light red in color.
  4. The shape and size are poor
  5. These bricks are not burnt well and weak.

You may also searching for: Properties of Bricks

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Composition of Brick

Bricks may define as a structural unit of rectangular shape and convenient site that is made from suitable types of clays by different processes involving molding, drying, and burning. In this article, you will learn about the materials used to make brick and its properties.

Even at present, brick is the most basic and favored material for common constructions though out the world.

The popularity of brick as a material of constructions is because of their local and cheap availability, strength, durability, reliability and insulating property against heat and sound.

Composition of brick or materials used in making brick

In general, it is observed that any soil that contains one-fourth part of clay and three by fourth parts of sand and silt is suitable for making bricks.

Good brick earth should be such that when prepared with water it can be easily molded dried and burnt without cracking or warping. It should contain a small quality at finely divided lime to help in binding the particles of brick together by melting the particles of sand.

A little oxide of iron should also be present which would give the brick its peculiar red color and act as a flux in the same manner as lime.

However, suitable brick earth should have various constituents in the following proportion.

i) Alumina or clay (20% – 30%)

  1. It shows the plastic character to the clay in wet conditions and is capable of being molded to any shape.
  2. When alumina is greater than 30% brick will become more plastic and also shrink more and develop cracks on drying.
  3. If less than 20%, it may be difficult to mold to proper shapes and develop cracks on a molding. So it provides plasticity resistance against shrinkage and makes the brick hard.

ii) Silica or sand (50% to 60%)

  1. Silica is present in much clay in two forms as a constituent of clay minerals and also as free. It is in the form of sand or quartz.
  2. Silica is infusible except at very high temperature but in the presence of alumina is nearly equal proportions and the oxide of iron it fuses at low temperature.
  3. Unlike the silicate of Alumina, its presence in clay produces hardness, resistance to heat, durability and prevents shrinkage and warping.
  4. Excess of it makes the bricks brittle.

iii) Lime (4% to 6%)

  1. When present in small quantities in the finely divided state it reduces shrinkage of brick, helps silica to melt at lower temperature and binds the particles of the brick together resulting in greater strength of brick.
  2. Excess of lime causes the brick to melt and lose its shape.

You may also love to read: 10 quality of bricks used in building construction

iv) Iron oxide (4% to 6%)

  1. Iron oxide acts as a flux, it lowers down the softening temperature of silica and other clay components during firing.
  2. The iron oxide imparts the very characteristic red color to the burnt brick.
  3. The excess of iron oxide makes the brick too soft during the burning stage, they suffer deformation in shape and make the dark blue color.
  4. A deficiency of iron oxide in the clay may make their burning difficult and also give then a yellowish appearance.

v) Magnesia: (1% to 2%)

  1. Small qualities at magnesia in brick earth make the brick of yellowish color and reduce shrinkage.
  2. But excess of magnesia leads to the delay of bricks.

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Heat treatment of steel

Heat treatment (heat treating) is a process in which the desire mechanical properties of steel are achieved by heating it to a different temperature. There are many types of heat treatment processes for steel.

Types of Heat Treatment

A) Annealing

Annealing is a process of heating steel in which temperature generally above the critical temperature, holding it for a definite period of time and cooling it at a slow rate. While cooling the steel embed inside the ash, lime or sand-like non-conducting materials.

Types of Annealing:

  1. Full annealing:- In this process, the metal is first heated up to 500 degrees Celcius above the critical temperature and hold it for one to two hours. Then the steel is cooled slowly to obtain the desired micro-structure.
  2. Isothermal annealing:- In isothermal annealing process steel is heated as in full annealing and allowed to rapid cool up to the temperature at which the transformation is desired. Then the steel is held at the temperature necessary to complete the transformation.
  3. Sub critical annealing:- This type of annealing first steel is heated below the critical temperature and allowing it to cool after holding it for 2 to 4 hours. This is also called the process annealing.
  4. Spheroidization:- Steel is heated at or just below the lower critical temperature and holds for a sufficient period of time to form small spheroids, then cooling very slowly.

Importance or uses of Annealing

  1. To improve machine ability.
  2. To soften the steel by re-crystallization and refine the grain size.
  3. For the improve ductility and malleability.
  4. To relieve the internal stresses produced during forging, pressing, etc.
  5. To improve the electrical and magnetic properties of steel.
  6. For removing the entrapped air, blow holes, pipes, etc. formed during casting.
  7. To overcome other imperfection produced during plastic deformation.

B) Normalizing

Normalizing is the process of heat treatment in which steel is heated up to 50-degree temperature above the critical temperature and allowed to cool in still air. This process is used to improve the quality of cast, welded or forged steel. It is also used to improve the quality of over heated or non-uniformity heated steel.

Importance or Use of Normalizing:

  1. To end the coarse-grained structure obtained during forging, rolling, extrusion, etc.
  2. For the improvement of the strength of medium carbon steel.
  3. To improve the machinability of steel.
  4. To reduce the internal stresses etc.

Read this: Detail about steel bar and its composition

Hardening of steel

C) Quenching/hardening of steel

In Quenching or hardening of steel, the steel is heated above its critical temperature and then allowed to cool rapidly by plunging it into the liquid bath. This form the extremely hard needle-like structure known as martensite. Clearwater, salty water or oil is used as quenching media to obtain desired hardness. It not only increases the hardness and resistance against wearing but also decreases the toughness and increases brittleness.

D) Tempering

Tempering is the process of heating quenched steel to some predetermined temperature between room temperature and critical temperature, holding it for the time sufficient to transformation and then cooling it at a slow rate in air.

Steel, when allowed for quenching produces a highly hard structure known as martensite. Martensite is not only hard but also brittle and thus decreases toughness.

Importance or uses of tempering

  1. To increase the toughness and ductility.
  2. To decrease the hardness.
  3. To relieve the stress produced during quenching.

Read this: Differences between cast iron, wrought iron, mild steel, and hard steel

E) Surface hardening

Surface hardening is the process in which the outer surface of the steel is hardened and the core of the steel is only refined.

Different methods of surface hardening are

  1. Case hardening: It is the process at which steel is heated in presence of solid, liquid or gas which is rich in carbon content in order to enable the surface to be hardened while retaining a tough ductile core.
    • Different types or methods of Case hardening
      1. Pack hardening: In this process steel is kept inside a box and surrounded by carbon-rich compound and heated to a temperature of 9000C to 9200C, depending upon the composition of the steel. Then the steel is allowed to cool and removed from the box. Now, it is quenched in water or other suitable media.
      2. Liquid carburizing: In this process, the steel is plunged to molten salt containing carbon such as sodium cyanide. This produces a thin layer of hardened steel. Then the steel is quenched as in the case of pack hardening.
      3. Gas carburizing: This process is carried out by heating the steel in a furnace into which the gas which is rich in carbon such as methane, propane, etc are introduced. There should be a continuous flow of carburizing gas.
  2. Nitriding: This process of surface hardening is used for only special alloy steel and not for plain carbon steel. In this process, no carbon is used for hardening, but nitrogen gas is used. Nitrogen is introduced to the steel by passing ammonia gas through the furnace containing steel and heated to a temperature between 4800C to 5400C.
  3. Cyaniding: In this process, steel is heated in molten cyanide salt at about 8500C followed by quenching. Both carbon and nitrogen are absorbed in this process.
  4. Flame hardening: In this process, the part of the surface to be hardened is heated above the critical temperature by flame and quenched rapidly. It is used to harden the more wearing parts of the machine such as gear teeth.

In this way, the heat treatment of steel is done.

You may be searching for this: Detail about the formation of Cast iron

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Steel – Composition, Properties & Types

Steel is the alloy of iron and carbon. Nowadays, steel has become the backbone of civil engineering construction. Steel may be plain carbon steel or alloy steel. Plain carbon steel is the steel at which carbon only forms an alloy with iron.

About 92% of steel is produced as plain carbon steel. Alloy steel is that at which iron is alloyed with other metals and carbon. About 85% of steel is found as alloy steel.
An increase in the carbon content increases the tensile and compressive strength of the steel. But the brittleness of the steel increases and thus the malleability and ductility decreases.

(A) Composition of steel

Steel is composed of iron, carbon and other alloying metals. Steel containing only iron and carbon is known as plain carbon steel.

Depending upon the carbon content, steel is classified as low carbon steel, medium carbon steel, and high carbon steel.

  • Steel containing less than 0.25% of carbon is known as low carbon steel.
  • If the carbon content lies between 0.25% to 0.7% then the steel is known as medium carbon steel.
  • In this, the carbon content is greater than 0.7% it is referred to as high carbon steel.

If the steel contains other metal also in the form of alloy with iron, steel is known as alloy steel. Stainless steel, nickel steel, vanadium steel, tungsten steel, etc. are examples of alloy steel.

(B) Properties of steel

Mechanical properties of the steel is determined by the carbon content in the steel. In general following are the properties of steel:

  1. Steel possesses high strength than other forms of iron such as cast iron or wrought iron.
  2. It can absorb shock and is elastic.
  3. It is malleable and ductile.
  4. Heat treatment can be done in the steel to improve the grain distribution and the quality of steel.
  5. Some alloy steel has corrosion resistance, but plain carbon steel is affected by corrosion.
  6. It can be welded to plain carbon steel easily.

(C) Types of steels

Depending upon various modes classification of steels can be of various types. However, the classification on the basis of their Chemical Composition is very commonly adopted.

Two major groups of steels recognized on this basis are-
A) Plain carbon steels and
B) Alloy steels

(I) Carbon steel or Plain Carbon Steel

This is the first major group of steels. In them, carbon is the only controlling component besides iron.

They are further sub-divided into three sub-types.

Low carbon steels(C= 0.05 to 0.35%) – These are also termed as soft steels or very commonly as mild steel (MS). The mild steels are tough and ductile. These can be easily welded. These steels are used for making nuts, bolts, rivets, sheets and other parts of common utility.

Medium carbon steels (C=0.35 to 0.55%) – These are also termed as medium steels. These are hard and strong comparatively. Are resistant to wear. They are used commonly for construction purposes as structural members and reinforcement.

High carbon steels(C=0.55 to 1.5%) – These are also termed as hard steels. It posses very great hardness and high compressive strength values. They are resistant to wear. They are used commonly for the manufacturing of ball bearing roller, saw, crushers, and locomotive tyres.

Functions of carbon in steels

Carbon in steel plays a very vital role in controlling their properties, Thus, the tensile strength of steel increases with an increase in the carbon content until its proportion reaches 0.83%. Any increase in carbon content beyond this limit will affect the tensile strength of steel adversely.
The ductility of steels decreases with an increase in carbon content. Also, the hardness of steels increases with the increase in carbon content. The compressive strength is also found to increase with the increase in carbon content.

Usual impurities in steel and their effects

  1. Manganese (0.2 to 1%- has positive influence like increases tensile strength and hardness of steel. But beyond this limit, it increases the brittleness of steel)
  2. Silicon (Kept below 0.4%, since this acts as a deoxidizer. Beyond this limit this increases the brittleness.)
  3. Phosphorus (Kept below 0.05%. This shows a cold-short effect if exceeds this limit.)\
  4. Sulphur (Kept below 0.05%. This shows a red short effect if exceeds this
    limit.)

(II) Alloys Steel (Steel Alloys)

Besides carbon other elements that impart distinctive characteristics to steel are add in iron to produce steel alloy. Formation of steel alloy is made to increase strength, hardness, toughness, resistance against corrosion, etc.

Important steel alloys and function of alloying elements are discussed below.

1. Stainless steel

Stainless Steel is the alloy steel containing more than 12 of the chromium alloyed with the iron Chromium forms a dense and tough layer of oxide around the metal surface and is highly resistive to corrosion.

It is basically sub-categorized into three groups

  1. The first group of stainless steel consists of less than 14% of Chromium and is known as Plan Chromium stainless steel. It contains sass than 0.4 % of carbon with traces of copper, tungsten, Nickel, etc, This Group of stainless steel can be hardened, Welded, machined and are satisfactory corrosion resistant, They are used to prepare steam valves turbine besides surgical instrument scissors knifes gears shafts ball bearing spring, etc.
  2. The second group of stainless steel consists of 14-20% of chromium and o.45 of carbon. They are more brittle and difficult to heat treatment. Also can be forget welded machined and rolled. They are used to prepare wire pipes. They are also used in chemical and food plants.
  3. When the steel contains at least 24 of combined Chromium and Nickel, then it goes under the third category of steel Generally 188 stainless steel –18chromium and nickel alloyed with Iron_ is very common in use. This steel has excellent resistance against corrosion and improved tensile strength. This steel is very tough. It can be welded, forged and rolled. Machining of this steel is difficult. These steels are used in chemical plants, tanks, cooking utensils, preparing pump shaft, screw, nut bolt, etc.

2. Nickel steel

Nickel steel contains about 3.5% of nickel alloyed with iron. It contains 0.5% to 1% of carbon. The presence of nickel imparts hardness, toughness, improves strength and corrosion resistance. This type of alloy steel is used in automatic parts, airplanes, cables, and shafts. Inver, widely used to prepare to measure tape is the alloy of nickel and steel. It consists of 30-40 % of nickel and has a very coefficient of thermal expansion.

3. Tungsten steel

Tungsten steel is known as high-speed steel as it is used in the high-speed cutting tools and drilling machines. It contains 14-20% of tungsten and 3-8% of chromium. It also contains carbon, vanadium, and molybdenum.

4. Vanadium steel

Vanadium steel possesses a high value of elasticity and is capable of resisting shocks. It is very strong and more ductile. Also, it improves fatigue resistance. It is used for making tools. It contains 0.1 to 2% of vanadium.

5. Manganese steel

Manganese steel contains different amounts of manganese ranging from 1-14% depending upon the purpose of the resulting product. Very hard, tough and strong in nature. It improves the plasticity of metal. It is used in preparing machine parts, rails, etc. manganese steel is non-magnetic.

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