lecture 01 - introduction to the properties of building materials

8/12/2019 LECTURE 01 - Introduction to the Properties of Building Materials

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1 POLYTECHNIC OF NAMIBIA D.A.S.P CMT 501Y- CONSTRUCTION MATERIALS AND TECHNOLOGY

POLYTECHNIC OF NAMIBIA

DEPARTMENT OF ARCHITECTURE& SPACIAL PLANNING

CMT 501Y Const ruc t ion Mater ial s & Techno logy 1LECTURE # 1 In t roduc t ion to the proper t ies of Cons t ruc t ion Mater ial s

Lecturer InformationLecturers name: Mr. Jens WiedowEmail: [email protected] phone: (061) 207 2926Office location: Department of Architecture OfficesOffice hours: 08:00 17:00Consultation hours: Consultation times can befound on the doors of lecturers offices.


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TheCharacteristic of materials can be divided into the following categories:

1. Chemical2. Physical3. Mechanical4. Dimension

1. Chemical characteristics:

Chemical characteristics of a material are those that relateto the molecular structure or composition of a materialThese characteristics are:

- Chemical composition : Oxide or Compound- Acidity or Alkalinity- Weathering- Corrosion, measured as the weight of Corrosion (R)

The important characteristic of the chemical characteristic ofbuilding materials i s its durability .Durability is the ability of a material to resist the following:

- physical abrasion or wear- the elements: sun, rain and wind- corrosion caused by moisture of chemical action

These characteristics are important as they will indicate the appropriate material to be used for a specific purpose, and the correct combination ofmaterials to be used together.e.g. Timber has a poor durability in the sun, and has to be treated appropriately.oruntreated Steel should not be used at the coast as it is not durable when faced with sea-water and corrodes.


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2. Physical characteristics:

Physical characteristics of a material are those that relateto the interaction of a material with various forms of energy.These characteristics are:

- Density: measured in force per unit area (kg/m, also Megapascals or Mpa)- Conductivity

- Thermal: measured in Watts per metre Kelvin (W/m x K)- Electric: measured in Siemens per meter (S/m)

- Acoustic (sound transmission/absorption), the Sound Reduction Index measured in decibels (db)- Optical (translucent/opaque)- Combustibility (ability to ignite or resist ignition)- Weight: measure in Kg.

3. Mechanical characteristics:

Mechanical characteristics of a material are those that areDisplayed with the application of forces on them.These characteristics are:

- Strengthcompressive strengthtensile strengthshear strength

- Toughness- Stiffness, or resistance to deformation, measured as k in newtons per meter.- Elasticity , measured as Youngs Modulus, or the Modulus of Elasticity - Plasticity- Ductility- Brittleness- Hardness


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The most effective structural materials are those which combine elasticity and stiffness.Elasticity is the ability of a material to deform under stress (bend, stretch, or compress)and return to its original shape.Every material has an elastic limit beyond which it will permanently deform or break.Those materials that have low elastic limits are termed brittle.The stiffness of a material is a measure of the force required to pull or push a material to itselastic limit.

4. Dimensional characteristics:

Dimensionalcharacteristics of a material are those that aredetermined by size, shape and finish.

These relate to the visual properties of a material:

- color- pattern- texture

Most Materials are manufactured in standard sizes. These stock sizes may vary slightly between manufacturers and should be verified duringthe design and planning phase of the building to avoid unnecessary cutting and waste of material during construction.For the same reason, the modular characteristics of building materials such as masonry units and plywood should be considered in determininga buildings dimensions.


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Reasons for choice of a building material.

These characteristics of materials determine their applicability and appropriateness in construction.Hence brick is commonly used in construction as it conforms to the following characteristics:

1. Chemical - Brick is a durable material and can withstand the effects of the elements and physical abrasion.2. Physical - Brick is a relatively dense material that has:low thermal conductivity (thus reduces the amount of heat gain),

good fire resistance (it cannot burn),good acoustic resistance ( you cannot hear very well through a brick wall)relatively low weight (their sizes can be easily handled on site)

3. Mechanical Brick is a Hard material with high strength, low elasticity and brittleness.4. Dimensional- Brick comes in standard sizes and can thus be easily combined into a wall. It furthermore has a pleasing visual appearance.

Materials are generally tested for their suitability for a particular purpose in a testing facility or materials laboratory that provide information oftheir characteristics.

Examples of the laboratories is the SABS (South African Bureau of Standards) and the NSI (Namibian Standards Institute).

Building regulations often prescribe that certain materials are tested on a regular basis to confirm their characteristics. e.g. concrete is usuallytested to determine its strength on every large construction site.


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Application of Materials & components in construction

Certain Materials are appropriate when used in certain areas, and in certain building components.The most common construction materials are:

Concrete

Concrete has a wide application in the construction industry because it combinesmany of the advantages of wood, steel, and masonry (bricks).It is inherently strong in compression and tension; it can encase and bond with steelreinforcement. It is capable of being formed into almost any shape with a variety ofsurface finishes, textures and patterns. It provides fireproof construction.Concrete is commonly used for building foundations, walls, and concrete structures(columns and beams).

MasonryMasonry refers to man-made units which are formed and hardened into modular units.This modular aspect (i.e. uniform size and proportional relationship) distinguishesmasonry form most of the other construction materials.Masonry is commonly used to build walls and the building enclosure.

Wood

As a construction material, wood offers in addition to its strength, durability and lightweight, and easy workability, natural beauty and warmth to sight an touch. Althoughit has become necessary to employ conservation measures to ensure a continuedsupply, wood is still used in construction in a variety of forms. Generally Wood is usedin the manufacture of furniture, joinery and roof trusses.


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StoneStone is an aggregate of combination of materials, each of which is composed ofinorganic chemical substances. Almost all stone is affected by sudden changes intemperature and should not be used where fire-resistance is required.

As a structural load-bearing wall material, stone is similar to modular unit masonry.

Stone is commonly used as an aesthetic material in wall cladding, and infrequentlyas a material to construct foundations.

Steel

Steel is used for heavy and light structural framing as well as a wide range ofbuilding products such as windows, doors, hardwear, and fastenings. As astructural material, steel combines high strength and stiffness with elasticity.Measure in terms of weight to volume, it is probably the strongest low-costmaterial available. Steel is available as a construction material in certain shapes,commonly called steel sections.

Glass

Glass is a chemically inert, transparent, hard, brittle material. It is used in buildingconstruction in various forms. Foamed or cellular glass is used as thermal insulation.Glass fibers form glass wool used for acoustic and thermal insulation. Glass is commonlyused to glaze a buildings windows.


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lecture 01 - introduction to the properties of building materials

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