TOPIC 1: INTRODUCTION TO CONSTRUCTION MATERIALS.

TOPIC 1: INTRODUCTION TO CONSTRUCTION MATERIALS. There are certain factors which affect the choice of materials for a particular scheme. The most important of these is the climatic background. Another factor is the ec ...

TOPIC 1: INTRODUCTION TO CONSTRUCTION MATERIALS. There are certain factors which affect the choice of materials for a particular scheme. The most important of these is the climatic background. Another factor is the economic aspect of the choice of materials. The rapid advance of construction methods, the increasing introduction of mechanical tools and plants and changes in the organisation of the building industry may greatly influence the choice of materials. The principal properties of building materials predetermine their applications. To develop products of greater economic efficiency, its important to compare the performance of similar kinds of materials under specific service conditions. Expenditures for running an installation can be minimised by improving the quality of building materials and products. PHYSICAL PROPERTIES. 1. DENSITY-It’s the mass of a unit volume of a homogeneous material. 2. POROSITY-it’s the degree to which volume of the material is intercepted with pores. Its expressed as the ratio of the volume of pores to that of the specimen. Dense materials which have low porosity are used for constructions requiring high mechanical strength. 3. HYGROSCOPICITY-It’s the property of a material to absorb water vapour from air. Its influenced by air-temperature and relative humidity, pores-their types, number and size and by the nature of substance involved. 4. WATER ABSORPTION- denotes the ability of a material to absorb and retain water. Its expressed as a percentage in weight or of the volume of dry material. 5. WEATHERING RESISTANCE- it’s the ability of a material to endure wet and dry conditions for a long period without considerable deformation and loss of mechanical strength. 6. WATER PERMEABILITY-it’s the capacity of a material to allow water to penetrate under pressure. Materials like glass, steel and bitumen are impervious. 7. FROST RESISTANCE- It’s the ability of a water saturated material to endure repeated freezing and thawing with considerable decrease of mechanical strength. 8. HEAT CONDUCTIVITY-it’s the ability of a material to conduct heat. Materials with large size pores have high heat conductivity because the air inside the pores enhances heat transfer. 9. THERMAL CAPACITY-it’s the property of a material to absorb heat described by its specific heat. Thermal capacity is of concern in the calculation of thermal capacity of walls. 10. FIRE RESISTANCE- it’s the ability of a material to resist the action of high temperature without any appreciable deformation and substantial loss of strength. Fire resistant materials are those which char, smoulder and ignite with difficulty when subjected to fire or high temperatures for long period but continue to burn or smoulder only in the presence of flame eg wood impregnated with fire proofing chemicals. Non combustive materials neither crack nor lose shape such as clay bricks, whereas others like steel suffer considerable deformation under the action of high temperature. 11. REFRACTORINESS- ability of a material to withstand prolonged action of high temperature without melting or losing shape. 12. CHEMICAL RESISTANCE- ability of a material to withstand the action of acids, alkalis, sea water and gases. Natural stone materials eg limestone, marble and dolomite are eroded even by weak acids. Wood has low resistance to acids and alkalis. Bitumen disintegrates under the action of alkali liquors. 13. DURABILITY-ability of a material to resist the combined effects of atmospheric and other factors