Glass has been a fascinating material to humankind since it was first made in about 500 BC. At first, thought to possess magical properties, glass has come a long way. It is one of the most versatile and oldest materials in the building industry. From its humble beginnings as a windowpane in luxury houses of Pompeii to sophisticated structural members in new age buildings, its role in architecture has evolved over the years.
A BRIEF HISTORY OF GLASS IN THE BUILDING INDUSTRY
In prehistoric times, Obsidian (Naturally occurring glass found near volcanic regions) and fulgurite (glass formed naturally after lightning strikes sand) were used to make weapons. The manmade glass was used as a luxury material was used in decorations, jewelry, vessels, and crockery.
Glass blowing was discovered in the 1st century in Europe, this revolutionized the glass-making industry. The technique spread throughout the Roman Empire. Production of Clear glass, by the introduction of manganese dioxide, saw glass being used for architectural purposes. Cast glass windows began to appear in the most important buildings and villas in Rome and Pompeii. Over the next 1,000 years, glass making spread through all of Europe and the Middle East. In the 7th century, Anglo Saxon glass was used in churches and cathedrals
By the 11th-century sheet, glass was made by the crown glass process. In this process, the glassblower would spin molten glass at the end of a rod until it flattened into a disk. The disk would then be cut into panes. By the 13th century, this technique was perfected in Venice. Stain glass windows were used in gothic renaissance and baroque architecture from the 11th to the 18th century. The examples of stunning patterns created by using colorful glass are immortalized by great artists all over the world. The Crown glass process was used up to the mid-19th century. in the 19th century, flat / sheet glass windows were used in making windows. These were completely flat and did not have any optical distortions.
But glass was still an item of luxury as it took large resources, brilliant skill, and immense energy to be produced. In 1958 Pilkington and Bickerstaff introduced the revolutionary float glass process to the world. This method gave the sheet uniform thickness and very flat surfaces. Modern windows are made from float glass.
HOW GLASS IS USED IN CONSTRUCTION
From the beginning of the 20th-century modern architecture has been instrumental in the mass production of concrete, glass, and steel buildings in the factories we call cities. This ideology helped accommodate the housing needs of the burgeoning middle class. Glass and steel construction have become the symbol of development in many countries, where people tend to see these buildings as symbols of affluence and luxury.
PRODUCTION OF GLASS
Production of glass:
Making glass is a very ancient process, with archaeological evidence of glass making dating back to before 2500 BC. Once a rare and prized art, manufacturing glass has become a common industry thanks to the Pilkington process.
Traditionally glass was made by blowing liquid glass derived by melting sand calcium oxide and sodium carbonate to extremely high temperatures and then cooling the liquid to the desired shape. For a few thousand years the recipe to make glass has been the same. It’s just that its properties can be enhanced by adding certain admixtures to the raw materials or by providing a suitable coating to meet different needs.
Pilkington process:
Large quantities of raw materials (clear sand, calcium oxide, and sodium carbonate)are brought to the glass production plant. They are then weighed and mixed in the right proportion. Certain admixtures are added to the batch to give the glass appropriate proprieties or color.
The mixture is then heated in a gas-fired furnace or electric smelter, pot furnace or kiln. Quartz sand without additives becomes glass at a temperature of 2,300 degrees Celsius Adding sodium carbonate (soda) reduces the temperature needed to make glass to 1,500 degrees Celsius.
A homogeneous mixture of molten glass is then formed. This mixture is then floated on molten tin to form glass of desired thickness. After the hot end of the process is over, the glass is set to cool. The way in which the glass is cooled determines its strength. It has to be cooled after maintaining a suitable temperature i.e. it has to be annealed. If it cooled over an extremely short duration of time the glass can become too brittle to handle. Annealing glass is critical to its durability
Glass making is an energy extensive process. One tonne of glass production requires 4 gigajoules of energy. That is as much energy as a wind mill produces in a day! This much energy can also be used to light over 200 homes. (Albeit they are not constructed with glass)
PROPERTIES OF GLASS
Transparency: This property allows visual connection with the outside world. Its transparency can be permanently altered by adding admixtures to the initial batch mix. By the advent of technology clear glass panels used in buildings can be made opaque. (Electro chromatic glazing)
U value: The U-value is the measure of how much heat is transferred through the window. The lower the U-value the better the insulation properties of the glass– the better it is at keeping the heat or cold out.
Strength: Glass is a brittle material but with the advent of science and technology, certain laminates and admixtures can increase its modulus of rupture( ability to resist deformation under load).
Greenhouse effect: The greenhouse effect refers to circumstances where the short wavelengths of visible light from the sun pass through glass and are absorbed, but the longer infrared re-radiation from the heated objects are unable to pass through the glass. This trapping leads to more heating and a higher resultant temperature.
Workability: It is capable of being worked in many ways. It can be blown, drawn or pressed. It is possible to obtain glass with diversified properties- clear, colorless, diffused and stained. Glass can also bewelded by fusion.
Recyclable: Glass is 100% recyclable, cullets (Scraps of broken or waste glass gathered for re-melting) are used as raw materials in glass manufacture, as aggregates in concrete construction etc.
Solar heat gain coefficient: It is the fraction of incident solar radiation that actually enters a building through the entire window assembly as heat gain.
Visible transmittance: Visible transmittance is the fraction of visible light that comes through the glass.
Energy efficiency and acoustic control: Energy-efficient glazing is the term used to describe double glazing or triple glazing use in modern windows in homes. Unlike the original single glazing or old double glazing, energy-efficient glazing incorporates coated (low-emissivity) glass to prevent heat from escaping through the windows. The air barrier also enhances acoustic control.
TYPES OF GLASS
Float Glass: Float glass is also called soda-lime glass or clear glass. This is produced by annealing the molten glass and is clear and flat. Its modulus of rupture is 5000-6000 psi. Stronger than Rocky Balboa taking punches from 2000 psi punches man Ivan Drago. It is available in standard thickness ranging from 2mm to 20mm. and has a weight range of 6-26kg/m2. It has too much transparency and can cause glare. It is used in making canopies, shop fronts, glass blocks, railing partitions, etc.
Tinted Glass: Certain additions to the glass batch mix can add color to the clear glass without compromising its strength. Iron oxide is added to give the glass a green tint; sulfur in different concentrations can make the glass yellow, red or black. Copper sulfate can turn it blue. Etc.
Toughened Glass This type of glass is tempered, may have distortions and low visibility but it breaks into small dice-like pieces at modulus of rupture of 3600 psi. Hence it is used in making fire-resistant doors etc. They are available in the same weight and thickness range as float glass.
Laminated Glass: This type of glass is made by sandwiching glass panels within a protective layer. It is heavier than normal glass and may cause optical distortions as well. It is tough and protects from UV radiation (99%) and insulates sound by 50%. Used in glass facades, aquariums, bridges, staircases, floor slabs, etc.
Shatterproof glass: By adding a polyvinyl butyral layer, shatterproof glass is made. This type of glass does not form sharp-edged pieces even when broken. Used in skylight, window, flooring, etc
Extra clean glass: This type of glass is hydrophilic i.e. The water moves over them without leaving any marks and photocatylitic i.e. they are covered with Nanoparticles that attack and break dirt making it easier to clean and maintain.
Double Glazed Units: These are made by providing air gap between two glass panes in order to reduce the heat loss and gain. Normal glass can cause immense amount of heat gain and upto 30%of loss of heat of air conditioning energy. Green, energy efficient glass can reduce this impact.
Chromatic glass: This type of glass can control daylight and transparency effectively. These glass are available in three forms- photochromatic (light sensitive lamination on glass), thermochromatic (heat sensitive lamination on glass) and electrochromatic (light sensitive glass the transparency of which can be controlled by electricity switch.) It can be used in meeting rooms and ICUs
Glass wool: Glass wool is a thermal insulation that consists of intertwined and flexible glass fibers, which causes it to "package" air, and consequently make good insulating materials. Glass wool can be used as filler or insulators in buildings, also for soundproofing.
Glass blocks: Hollow glass wall blocks are manufactured as two separate halves and, while the glass is still molten, the two pieces are pressed together and annealed. The resulting glass blocks will have a partial vacuum at the hollow center. Glass bricks provide visual obscuration while admitting light
PROPERTIES OF GLASS
Polycarbonate: This elastic is 300 times stronger than glass, is resistant to most chemicals, is twice as lighter than class, has high abrasion and impact resistance. It can transmit as much light as glass without many distortions. Applications include window, green house glazing etc.
Acrylic: Acrylic is made of thermo plasticsis weather resistant, is 5 times stronger than glass but is prone to scratches. It has excellent optics, is softer than glass but can accumulate a lot of dust. This is extensively used in to make playhouses, green house etc.
GRP panels: GRP is manufactured by combining hundreds of glass strands together using a pigmented thermosetting UV resin.Glass-reinforced plastics are also used to produce house building components such as roofing laminate, canopies etc. The material is light and easy to handle. It is used in the construction of composite housing and insulation to reduce heat loss.
ETFE: Ethylene tetrafluoroethylene is a plastic with high strength and corrosion resistance. It has high energy radiation resistance properties, it is strong, self cleaning and recyclable.
The versatility of glass keeps on increasing as scientists find new applications to this wonder material. Glass is now being used in the building industry as insulation material, structural component, external glazing material, cladding material; it is used to make delicate looking fenestrations on facades as well as conventional windows. With the advent of green technology in construction, glass is constantly undergoing transformation. Solar power glass, switchable glass projection screens are a few of the newer uses. This is one material to look out for!
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