Module 5. Building construction materials and type of building construction

Lesson 27

27.1 Introduction

Selection of building materials mainly stones, wood, metal and glass are very important for dairy plants, because each and every section has its specific requirements. There are different types of stones used for flooring and skirting and it should have desirable properties to with stand to prevailing conditions of different sections. Similarly requirement of type of wood depends on its position in a windows, doors and other applications, soft woods requires seasoning treatment and application varnish and oil paints to prevent yeast and mould growth. Selection of metal depends on type of vessels used for processing, particularly to with stand high pressure and to meet sanitary standards. The glasses used in the dairy are specifically designed with wire mesh inside, so that no glass pieces will fall in the product. In certain sections like, butter, ghee and cheese manufacturing, glasses are used to control sun light particularly UV light to prevent oxidation of fat and related defects in the product.

27.2 Stones

Stones are obtained from rock, a portion of the earth’s crust having no definite shape or chemical composition. Stones are used as the construction material for the following.

  • Material for foundations and walls of buildings, dams, bridges
  • Material for road and concrete making in the form of either broken or crushed stones called aggregates/ gravels/ peebles.
  • Used as thin slabs for paving/flooring.
  • Used as roofing tiles
  • Lime stones are used as a flux material in the blast furnaces
  • In view of several artificial materials developed recently for flooring and roof, the use of natural stone in many applications has become limited.

27.3 Requirements of Good Structural Stones

When stone is used as structural material, the following considerations are to be considered.

(i) Strength: It should be sufficiently strong against crushing. The stones having more compact grains with higher density are stronger. A dense and compact stone has very few or no pores and thus does not absorb water. A stone of igneous origin is stronger than one of sedimentary formation. A crystalline stone is superior to a non-crystalline one and the finer the crystalline structure, the stronger it is. The specific gravity of good stone should not be less than 2.7. It is desirable to have crushing strength of building stone more than 100 N/mm2. The crushing strength of some commonly used stone is given below.

• Granite: 75-127 N/mm2
• Sand stone: 64 N/mm2
• Lime stone: 54 N/mm2
• Durability: It depends on (a) chemical composition (b) physical structure (c) weathering effects and (d) place or position in the structure. It depends on type of stone and working conditions.
• Appearance: The appearance of a stone in relation to the design is of great importance from an architectural point of view. Appearance depends on the colour and the ease with which stone can be dressed, rubbed or polished, for which slightly softer stone is selected. It is desirable that the colour of stone is uniform, no weathering effect, and free from clay holes.
• Dressing properties: The ability of stone for cutting, carved etc is important for building material. In order to perform dressing operations with ease, it should be relatively soft with compact grains. Stone should be homogeneous in texture rather than crystalline. The development of many machines and advancement of technology, the dressing of even hard stone has become quite easy for many applications of stones.
• Hardness: It is expressed in terms of co-efficient of hardness. The common accepted norms for various categories of hardness are greater than 17 considered as high, between 14 to 17 as medium hardness and less than 14 as poor hardness.
• Wear percentage: If the value of wear is more than 3 percent, then the stone is regarded as unsatisfactory.
• Seasoning and Weathering: After quarrying stone should be seasoned for 6-12 months and there should not be any change in various properties. A good quality of stone should not show remarkable weathering effect.
• Texture: Stone should be free from cavities, cracks etc.
• Toughness: It is expressed in terms of toughness index. The common accepted norms for various categories of toughness are greater than 19 considered as high, between 13 to 19 as moderate toughness and less than 13 as poor toughness.
• Water absorption: The absorption of water should not exceed 0.6 % of weight.

27.4 Basis of Classification of Stones

There are 4 basis of classification of stones as under.

1) Geological (based on mode of formation)

2) Physical (depending upon structure)

3) Chemical (depending on composition)

4) Practical (based on use)

27.5 Use of Stone

Use of natural stone is various purposes is given below.

(i) Structure (ii) Face work

(iii) Paving (iv) Basic material

27.6 Stone Quarrying

The process of taking out stone from natural rock is knows as quarrying.

27.7 Artificial Stones

  • Cement concrete blocks
  • Mosaic tiles
  • Terrazo

27.8 Wood

Wood is of two types – hard wood and soft wood. Hard wood is used for building construction and soft wood is mostly used for packaging material and boxes. Plywood is obtained from inferior quality wood after some processing, and it is used for making furniture. Hardwood is seasoned to reduce moisture content and is also treated with creosote oil. Hard woods are used in the room where moist conditions prevail and it is properly seasoned to prevent any kind of mould growth and contamination. Soft woods are used in the dairy for cold store doors and covered with stainless steel sheet.

Soft wood is obtained from trees of Deodar, Kali, Chir, Pine, Walnut and Spruce etc. Soft woods are resinous and light in colour. It is general characteristics that trees having needle like leaves give soft wood.

Sal, Teak, Shisham, Pyngado, Oak, Beach and Ash are some of the examples of hard wood obtained from broad leaf trees. Hard woods are relatively darker in colour, heavy, close grained and strong. They are non-resinous.

27.8.1 Timber wood

Timber wood is suitable for building or engineering purposes. When in living tree, the timber is called ‘standing timber’. When trees are cut down, it is called ‘rough timber’ and when it is sawn into various market sizes, such as beams, battens, posts, planks etc., it is called ‘convert timber’

27.8.2 Seasoning of wood

The growing tree contains a large amount of moisture which may be 150% of the dry weight of the timber. The process of removal by drying the excess moisture from the wood in a controlled manner to prevent the shrinkage which occurs, causing cracks and other defects is called seasoning. Seasoning may be natural or artificial. Natural seasoning is best but it takes long time. Artificial seasoning may be water seasoning, boiling or kiln seasoning.

27.8.3 Preservation of wood

Timber is liable to attack by dry rot and other fungi. The function of a preservative is to poison the food matter in the timber. But this poison should not be dangerous to carpenter and must not wash out in rain. The best time to apply preservatives is the early summer. The usual methods of preservation are tarring, charring, painting, creosoting, solignum paints and Ascu treatment.

Tarring consists of coating the timber with hot coal tar. Tarring is adopted only for work of rough character such as timber fences, ends of doors and window frames built into walls.

Charring is adapted to the portions which are embedded in the ground. The ends of posts are charred over a wood fire to a depth of about ½” and then quenched with water. Painting consists of applying 3 or 4 coats of an oil paint. Solignum paints are effective preservatives against attack by white ants. The process of Ascu treatment for the preservation of wood has been developed at the Forest Research Institute at Dehradun. The powder developed for the purpose is dissolved in water. Six parts of powder are dissolved in 100 parts of water and then applied or sprayed on timber.

27.8.4 Fire proofing

Wood can catch fire very easily and it is difficult to make it fireproof. However, chemicals such as 2 coats of 2% solution of Borax or sodium arsenate are effective in retarding the action of fire.

27.9 Metals

Metals are used in the dairy for different purposes. Mild steel is used for fabrication of sheds, grills, foundations, pipelines, and as structural steel. Cast iron is used for drainage of effluent as well as for the fabrication of various components of machines. Stainless steel is used for fabrication of dairy equipment and milk pipelines.

27.9.1 Stainless steels (SS)

Stainless steels were invented to overcome the problem of corrosion which is a major concern of food and many other industries. The alloy of steel containing iron-chromium-nickel is known as stainless steels which do not rust in sea water and are resistant to acids and several other chemicals. Stainless steels typically contain between 9 and 30 percent chromium and varying amounts of nickel, molybdenum, copper, sulfur, titanium, niobium, etc., may be added to obtain the desired mechanical properties and service life. Having all these properties, SS are widely used in dairy and food industry. Stainless steel is considered noble metal for use in dairy industry. Stainless steels are classified based on the chemical composition and it provides information to overcome many types of corrosion. Some of the limitations of SS employed in food and dairy industry are attack by lactic and malic acids at elevated temperature and poor thermal conductivity. However, these limitations may be overcome by carefully selection & fabrication, optimized operating condition, care and maintenance of the equipment. Classification of SS

Stainless steels are basically classified as austenitic, ferritic, martensitic, duplex and super-austenitic grades. Each of these main groups contains a number of alloys that are defined according to the chemical composition and specified in European and American international standards. Apart from chromium, the alloy constituents molybdenum, nickel and nitrogen are of great importance to the corrosion resistance. Carbon will always be present to a certain degree, and it is important for the welding properties. In addition, copper, manganese, sulphur, titanium and niobium are used as alloy constituents to impart certain properties. Stainless steel is typical wrought alloy AISI (American Iron and Steel Institution) series designations, includes: 200 (high manganese austenitic), 300 (austenitic), and 400 & 500 (ferritic & martensitic). Martensitic and ferritic steels are magnetic and martensitic steels are typically hardened by heat treatment and are not easily formable. Austenitic steels harden when cold worked. Duplex grades (austenitic/ferritic) are more resistant to stress corrosion cracking than austenitic and are tougher than ferritic grades. Desirable properties of SS

The properties of stainless steel play an important role in the design of various equipments. The use of high quality SS in fabrication of processing equipments helps not only to prevent corrosion but also ensures purity of food product handled in those equipments. In addition to this, stainless steels are easy to clean and maintain and a number of different products can be manufactured in the same equipment. If properly utilized, equipment made of stainless steel can be expected to last for many years. In selecting austenitic stainless steels, a number of factors other than corrosion performance should be considered. Among these are their usually attractive appearance, good mechanical properties, and excellent fabrication characteristics. On a life-cycle basis, the alloys are often the most cost-effective. Important characteristic to be considered in selecting the proper type of stainless steel for a specific application are listed below.

• Corrosion resistance
• Resistance to oxidation and sulfidation
• Strength and ductility at ambient and service temperatures
• Suitability for intended fabrication techniques
• Suitability for intended cleaning procedures
• Stability of properties in service
• Toughness
• Resistance to abrasion, erosion, galling, and seizing
• Surface finish and/or reflectivity
• Physical property characteristics such as magnetic properties, thermal conductivity and electrical resistivity
• Total cost, including initial cost, installed cost, and the effective life expectancy of the finished product

27.10 Steel

Steel is an intermediate stage between cast iron and wrought iron. The cast iron contains 2-4 % carbon while wrought iron has carbon content less than 0.15%. In steel, the carbon content varies between 0.25 to 1.5 %. There is no graphite in the steel. The steel becomes harder and tougher as its carbon content increases. Steel is used for various applications in dairy industry.

27.11 Aluminium

Aluminum is used as frame work for doors and windows in dairy and food processing plants. The desirable properties of aluminum which makes it suitable are light weight, softness, and appearance. Its use is limited by the fact that it is tarnished and corroded by ordinary alkaline dairy cleaners and sterilizers.

Last modified: Thursday, 4 October 2012, 9:12 AM