Construction Materials and Their Properties
Construction Materials
Construction is a material-intensive activity consuming vast quantities of resources like glass, metal, and PVC. Concrete is a preferred choice for building and infrastructure projects. It’s a composite of inert materials (sand and gravel) and a binder, cement. A chemical reaction with water (hydration) hardens the mixture, increasing its strength and rigidity. Additives can enhance color, setting time, and properties like waterproofing. Concrete’s initial pasty form allows it to be molded into various shapes.
Early concrete use dates back to ancient Egyptian builders who utilized mud and plaster as binding agents. Romans improved concrete by adding volcanic ash, increasing its durability and enabling underwater setting. This innovation proved crucial for constructing bridge foundations, many of which remain standing today. A significant advancement was the invention of Portland cement in the 19th century, produced by calcining and grinding limestone and clay, then mixing with gypsum.
Reinforced concrete, incorporating iron bars within the mix before hardening, addresses concrete’s weakness in tension. Prestressed concrete further revolutionized construction by enhancing flexural strength.
Corrosion of Metals
Metals are abundant, hard, malleable, and excellent conductors of heat and electricity. Alloys combine metals to create enhanced properties. However, most metals are susceptible to corrosion, often interpreted as their reversion to their natural oxidized state. Metallurgical techniques separate oxygen from pure metal, but exposure to water and air over time causes them to oxidize. Modern alloys and treatments retard corrosion, but their effectiveness is limited and often requires maintenance.
Risks Associated with Material Production
Some materials pose environmental or health risks, arising from raw material extraction, processing, or inherent toxicity. Certain materials exhibit toxicity under specific conditions, while others are used despite known risks (e.g., mercury). Some materials are used until discovered to be toxic (e.g., certain thermal insulations). International agencies compile lists of hazardous substances. The Montreal Protocol successfully promoted the replacement of CFCs.
Technology for the Kitchen
- Stainless steel pans replaced aluminum and ceramic cookware. Stainless steel is hygienic, durable, and easy to clean, but not a good heat conductor.
- Ceramic cooktops are popular for easy cleaning but can scratch easily.
- Glass is widely used for its cleanability and aesthetic appeal.
- Plastic is used as a glass substitute (containers).
- Microfiber cloths retain water better than conventional fabrics.
- Composite countertops are more durable and acid-resistant than marble, though less aesthetically pleasing.
Polymers
While often associated with plastic, many substances fall under the polymer category.
Types of Polymers
- Natural: Derived from animal or plant sources.
- Transformed: Examples include vulcanized rubber and celluloid.
- Synthetic: Most polymers are synthetic and classified into:
- Thermoplastics: Become liquid when heated without chemical change, allowing for repeated melting and reshaping (e.g., polypropylene).
- Thermosetting plastics: Initially fluid when heated, but upon cooling, form a rigid, brittle, three-dimensional network that cannot be remolded. While more challenging to work with and non-recyclable, they offer superior corrosion and temperature resistance.