Civil Engineering Materials.

 

Introduction

Civil Engineering Materials (Building / Construction materials) are those materials that are used in various civil engineering works like construction and repair of buildings, bridges, tunnels, roads, dams, etc.

Civil engineering materials have an important role to play in this modern age of technology. They have been used since the dawn of time and human civilization. Although their most important use is in construction activities, no field of engineering is conceivable without their use.

 

Scope of Civil Engineering Materials

The Scope of civil engineering materials includes new works and repair and maintenance of the following: civil engineering structures, dams, buildings, tunnels, bridges, highway pavement, sewers, water containment structures, roofing, etc. Civil engineering materials have an important contribution to our national economy as its output governs both the quality and rate of construction works.

 

Types of Civil Engineering Materials

There are generally two types of civil engineering materials. They are as follows:

1. Natural
2. Wood
3. Clay/ Soil
4. Rock
5. Gravel

 

2. Artificial
3. Cement
4. Brick
5. Ceramics
6. Glass
7. Paints And Varnishes
8. Plastics
9. Tiles, Marbles, Granites

 

Metals:-

It is a material that is typically hard, opaque, shiny and has good electrical and thermal conductivity. Generally, they can be hammered or pressed permanently out of shape without breaking or cracking. Eg. Iron, copper, zinc, etc. Metals are further divided into :

Ferrous Metals: Cast iron, steel etc

Non-ferrous metal: Zinc, aluminum etc.

 

Timber:

It is one of the oldest material of construction. From the prehistoric times till date, timbers have been used in a variety of ways in building construction, bridge construction, in tunnel and many other engineering activities. It is obtained from trees. It is a natural material.

 

Ceramics:

Ceramics is an inorganic, non-metallic, solid-material, comprising metal, non-metal and metalloid atoms primarily held in ionic and covalent bond. Ceramics are generally made by taking mixture of earthen materials, clay, powder and water, and shaping them into desired forms. Eg. Plates, porcelain, tiles, toilets etc.

 

Polymers:

Polymers are made up of many molecules all stung together to from long chains. Polymers are of two types :-

1. Natural Polymers :- wood, natural rubber, cellulose, silk, etc
2. Synthetic Polymers: – PVC, Nylon, synthetic rubber etc. Synthetic polymers have many engineering applications like piping.

 

Composites:

Composite is a material made from two or more constituent materials with significantly different physical and chemical properties, that when combined, produces a material with characteristics different form the individual components. Eg. Concrete, Cement, fiberglass, etc.

 

Properties of Civil Engineering Materials

 

1. Physical Properties:

Physical properties are those properties that are determined by nature i.e. under the condition in which external forces are not considered.

 

1. Density:

It is the mass of a unit volume of homogeneous material.

i.e. Density = Mass / Volume = M / V

unit : gram / cm3

 

Bulk density :

It is the mass of a unit volume of material in its natural state (with pores and voids) calculated as

i.e bulk density = M / V (kg/ m3)

Properties like strength and heat conductivity are greatly affected by their bulk density.

Material                                                    Bulk density(kg/m3)

brick                                                           1600-1800

granite                                                       2500-2700

sand                                                           1450-1650

steel                                                           7800

 

Density Index:

It is the ratio of bulk density to density.

 

1. Specific gravity:

It is the ratio of mass/weight of a given volume of material to the weight/mass of equal volume of water at 4˚C.

 

True/absolute specific gravity:

If both the permeable and impermeable voids are excluded to determine the true volume of solids, the specific gravity is called true or absolute specific gravity.

 

Apparent or mass specific gravity:

If both the permeable and impermeable voids are included to determine the true volume of solids, the specific gravity is called apparent or mass specific gravity.

 

1. Opacity:

It is the degree to which light is not allowed to travel through the body.

 

1. Porosity:

It is the degree to which volume of the material is interspersed with pores. It is expressed as the ratio of the volume of pores to that of the materials.

 

1. Water absorption capacity:

It denotes the ability of the material to absorb and retain water. It is defined as the ratio of absorbed water to the dry weight of same material in the specific time period.

i.e Mw = ( m1-m/M ) * 100

where, m1 = mass of saturated material (g)

M = mass of dry material (g)

It is expressed in percentage.

 

1. Fire resistivity:

It is the ability of the material to resist the action of high temperature without any appreciable deformation and sustainable loss of strength. In other words, it is the resistance against fire.

 

1. Mechanical Properties:

Mechanical Properties are the characteristics of a material that are displaced under the account of an external force applied to the materials.

1. Strength

It is defined as the ability of a material to resist the failure under the action of stresses caused by loads.

1. Compressive Strength :

Capacity to withstand axially directed pushing forces.

 

1. Tensile Strength:

Maximum stress while being stretched or pulled before necking.

 

• Shear Strength:

It is the ability to withstand shearing.

 

1. Flexural Strength ( Modulus of rupture/ bend strength/ fracture strength)

It is defined as the stress in a material just before it yields in a flexural test.

 

1. Impact Strength:

It is the ability of the material to absorb shock and impact energy without breaking.

 

1. Hardness:

It is the ability of the material to resist abrasion (friction), scratches, cutting and penetration.

 

1. Ductility:

Capacity of a material to go large plastic deformation under the tensile load without rupture is called ductility. Steel, copper are ductile materials.

 

1. Elasticity:

It is the ability of a material to gain its initial shape and size after the load is removed. It is measured by young’s modulus of elasticity. Young’s modulus of elasticity is defined as the ratio of stress to strain.

i.e. E = Stress / Strain

 

1. Resilience:

It is the ability of a material to absorb energy when it is deformed elastically and release that energy upon unloading, to resist impact or shock.

 

1. Toughness:

It is the ability of the material to absorb energy and deform plastically without fracturing.

 

1. Stiffness:

The stiffness of a body is a measure of resistance offered by an elastic body to deformation. Force required to produce unit deformation in a material is called stiffness. It is denoted by ‘K’.

 

1. Abrasive resistance:

It is the property of a material to resist the wearing of the surface of material due to friction between one another. This property is important for road construction material.

 

1. Fatigue:

It is the weakening of material caused by repeatedly applied loads.

 

1. Creep:

It can be defined as the slow and progressive deformation (permanent) of a material with time under constant stress.

 

1. Thermal Properties:

The characteristics of a material which are governed by the temperature are known as thermal properties.

1. Specific heat/ specific heat capacity:

It is defined as the amount of heat required to raise the temperature of the unit mass of the material by 1˚C. The specific heat of water is 1 Calorie/ gram˚C.

 

1. Thermal Conductivity:

It is the ability of a material to conduct heat. The rate at which heat can flow through a material under the influence of given temperature gradient is determined by thermal conductivity (K).

 

1. Thermal Expansion:

When thermal energy is added to a material, it changes its dimension. Such phenomenon is called thermal expansion. It is the tendency of a material to change in shape, area and volume in response to change in temperature.

 

1. Electrical Properties:
2. Conductivity:

It is the measure of a material’s ability to conduct an electrical current. Its SI unit is Siemens per meter.

 

1. Electric Permittivity:

It is the measure of resistance that is encountered when forming an electric field in a medium. In SI unit, permittivity is measured in farad per meter (F/m).

 

1. Dielectric Strength:

It is a measure of the electric strength of a material as an insulator. It can be defined as the maximum voltage that can be applied to a given material without causing it to breakdown. Its SI unit is volt/meter (V/m).

 

1. Magnetic Properties:

2. Magnetic Permeability:

It is the measure of the ability of the material to support the formation of a magnetic field within itself. It is represented by “miu”. Its SI unit is henry per meter (H/m).

 

1. Magnetic Retentivity:

The ability of a material to retain magnetism after a external magnetic field is removed is called magnetic retentivity.

 

Material-Environment (Temperature, humidity, rain and fire ) interaction :-

There is no use of materials without interaction with the environment. Environmental factors greatly affects the choice of material for a particular scheme. The important factors is the climatic background.

Different materials in forms of construction have developed in different parts of world as a result of climatic differences.

Most of the construction materials are exposed to the open natural environment. Construction materials should be selected in such a way that they can overcome the environmental attacks like heating and thawing effects, wind, rain etc.

In areas having high and low temperature proper insulating materials like roof tiles ( mostly in Terai region), hollow bricks, mud, etc. should be provided.

In humid areas, materials which are strong enough to resist the moisture attack like inert materials such as plastics, stone masonry, etc. are provided.

In rainy areas, water proofing materials are used to prevent water leakage like dense concreting. Generally, timbers are not used in exposed area.

In the area having high risk of fire, fire resistant materials are used like concrete, stone, brick, etc. Metallic objects and timbers should not be used in such places.