Rubber

Properties and Uses of Rubber:

Rubber is not only elastic, but is also waterproof and is a good electrical insulator. Natural rubber is resilient and is resistant to tearing. Some types of rubber are resistant to oils, solvents, and other chemicals.
In a raw state, natural and synthetic rubber become sticky when hot and brittle when cold. The vulcanization process modifies rubber so that these changes will not occur. In the typical vulcanization process, sulfur and certain other substances are added to raw rubber and the mixture is then heated. The process tends to increase rubber's elasticity and its resistance to heat, cold, abrasion, and oxidation. It also makes rubber relatively airtight and resistant to deterioration by sunlight.
The molecules that make up rubber are long, coiled, and twisted. They are elongated by a stretching force and tend to resume their original shape when the force is removed, giving rubber the property of elasticity. Vulcanization sets up chemical linkages between the molecules, improving rubber's ability to return to its original shape after it is stretched.

Uses:

Rubber is made into articles as diverse as raincoats and sponges, bowling balls and pillows, electrical insulation and erasers. People ride on rubber tires and walk on rubber heels. Rubber is also used in toys, balls, rafts, elastic bandages, adhesives, paints, hoses, and a multitude of other products.
The single most important use of rubber is for tires. Most tires contain several kinds of rubber, both natural and synthetic. Radial automobile tires contain a greater percentage of natural rubber than other types of automobile tires because radial tires have flexible sidewalls that tend to produce a buildup of heat, to which natural rubber has a superior resistance. Either natural or synthetic rubber is suitable for most uses, and price determines which is used.

Elasticity

Linear elasticity:

As noted above, for small deformations, most elastic materials such as springs exhibit linear elasticity and can be described by a linear relation between the stress and strain. This relationship is known as Hooke's law. A geometry-dependent version of the idea^[4] was first formulated by Robert Hooke in 1675 as a Latin anagram, "ceiiinosssttuv". He published the answer in 1678: "Ut tensio, sic vis" meaning "As the extension, so the force", a linear relationship commonly referred to as Hooke's law. This law can be stated as a relationship between force F and displacement x,                     
  where k is a constant known as the rate or spring constant. It can also be stated as a relationship between stress σ and strain :
  where E Is known as the elastic modulus or Young's modulus.Although the general proportionality constant between stress and strain in three dimensions is a 4th order tensor, systems that exhibit symmetry, such as a one-dimensional rod, can often be reduced to applications of Hooke's law.

Crystal

Crystal structure:

In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms, ions or molecules in a crystalline liquid or solid. It describes a highly ordered structure, occurring due to the intrinsic nature of its constituents to form symmetric patterns.
The crystal lattice can be thought of as an array of 'small boxes' infinitely repeating in all three spatial directions. Such a unit cell is the smallest unit of volume that contains all of the structural and symmetry information to build-up the macroscopic structure of the lattice by translation.
Patterns are located upon the points of a lattice, which is an array of points repeating periodically in three dimensions. The lengths of the edges of a unit cell and the angles between them are called the lattice parameters. The symmetry properties of the crystal are embodied in its space group.^[1]
A crystal's structure and symmetry play a role in determining many of its physical properties, such as cleavage, electronic band structure, and optical transparency.

Material with Ferro cement

Ferro cement:

Ferro cement, also referred to as Ferro concrete or reinforced concrete, a mixture of Portland cement and sand applied over layers of woven or expanded steel mesh and closely spaced small-diameter steel rods rebar. It can be used to form relatively thin, compound-curved sheets of concrete ideal for such applications as hulls for boats, shell roofs, and water tanks. It has a wide range of other uses including sculpture and prefabricated building components. The term "Ferro cement" has been applied by extension to other composite materials, including some containing no cement and no ferrous material.
The original inventor of the material, Frenchman Joseph Monier, dubbed it "cement armé," but after another French inventor, Joseph-Louis Lambot, constructed a small ferrocement boat and exhibited the vessel at the Exposition Universally in 1855, the name "ferciment" (in accordance with Lambot's 1855 patent) stuck instead. The patent was granted in Belgium and only applied to that country. At the time of Monier's first patent, July 1867, he planned to use his material to create urns, planters, and cisterns. These implements were traditionally made from ceramics, but large-scale, kiln-fired projects were expensive and prone to failure. In 1875, he expanded his patents to include bridges and designed his first steel-and-concrete bridge. The outer layer was sculpted to mimic rustic logs and timbers, thereby also ushering Faux Bois concrete into common practice.
Recent trends have "ferrocement" being referred to as ferro concrete or reinforced concrete to better describe the end product instead of its components. By understanding that aggregates mixed with Portland cement form concrete, but many things can be called cement, it is hoped this may avoid the confusion of many compounds or techniques that are not Ferro concrete.
Ferro concrete has relatively good strength and resistance to impact. When used in house construction in developing countries, it can provide better resistance to fire, earthquake, and corrosion than traditional materials, such as wood, adobe and stone masonry. It has been popular in developed countries for yacht building because the technique can be learned relatively quickly, allowing people to cut costs by supplying their own labor. In the 1930s through 1950's, it became popular in the United States as a construction and sculpting method for novelty architecture, examples of which created "dinosaurs in the desert".

Curing of Concrete Structure

Curing

In all but the least critical applications, care must be taken to properly cure concrete, to achieve best strength and hardness. This happens after the concrete has been placed. Cement requires a moist, controlled environment to gain strength and harden fully. The cement paste hardens over time, initially setting and becoming rigid though very weak and gaining in strength in the weeks following. In around 4 weeks, typically over 90% of the final strength is reached, though strengthening may continue for decades.^[46] The conversion of calcium hydroxide in the concrete into calcium carbonate from absorption of CO₂ over several decades further strengthens the concrete and makes it more resistant to damage. However, this reaction, called carbonation, lowers the pH of the cement pore solution and can cause the reinforcement bars to corrode.

Hydration and hardening of concrete during the first three days is critical. Abnormally fast drying and shrinkage due to factors such as evaporation from wind during placement may lead to increased tensile stresses at a time when it has not yet gained sufficient strength, resulting in greater shrinkage cracking. The early strength of the concrete can be increased if it is kept damp during the curing process. Minimizing stress prior to curing minimizes cracking. High-early-strength concrete is designed to hydrate faster, often by increased use of cement that increases shrinkage and cracking. The strength of concrete changes (increases) for up to three years. It depends on cross-section dimension of elements and conditions of structure exploitation.^[47]

During this period concrete must be kept under controlled temperature and humid atmosphere. In practice, this is achieved by spraying or ponding the concrete surface with water, thereby protecting the concrete mass from ill effects of ambient conditions. The picture to the right shows one of many ways to achieve this, ponding – submerging setting concrete in water and wrapping in plastic to contain the water in the mix. Additional common curing methods include wet burlap and/or plastic sheeting covering the fresh concrete, or by spraying on a water-impermeable temporary curing membrane.

Properly curing concrete leads to increased strength and lower permeability and avoids cracking where the surface dries out prematurely. Care must also be taken to avoid freezing or overheating due to the exothermic setting of cement. Improper curing can cause scaling, reduced strength, poor abrasion resistance and cracking.