Luke Tebb: October 2014

Concrete

How is it Made?

Concrete in its simplest form is created from aggregates, sand and water. The aggregates are used to form the paste, the sand is used for texture and the water holds it all together. In ancient times, hay or straw was used for the aggregate. Modern concrete is more complex.
Concrete today is composed of a variety of dry materials such as cement, fly ash and sand. These are then mixed with water to form a hardened paste mixture which is used to form a variety of shapes and forms.
Cement, which is the main component of modern concrete, is made up of materials such as limestone, clay, gypsum, chemical additives and gravel. The sand used in concrete is course sand made from ground glass.

The mixture of modern concrete, as stated above, contains aggregate material. This material is often various sizes depending on the future use of the concrete. The aggregate material can use many types of stone, as listed above, but can also use recycled material such as oyster shell or waste material from coal-fired power generating plants.
Concrete consists of two essential parts, the filler and the binding. The filler is either a fine or coarse mixture such as sand while the binding is the cement and water. The binder forms a glue to hold the filler together. To make concrete, the correct amounts of both dry material and water must be added. Like baking a cake, concrete requires proper measures and methods to ensure a thorough blend and strong setting to hold together. This mixture is usually along the line of one part cement, two parts sand and three parts stone with enough water to form a paste.

How Long will it Last?

The life expectancy of concrete (maintained) is well over 100 years. However concrete that has been effected by a natural disaster eg: flooding or Hurricane will decay very fast.

Degradation

Concrete degradation may have various causes. Concrete can be damaged by fire, aggregate expansion, sea water effects, bacterial corrosion, calcium leaching, physical damage and chemical damage (from carbonatation, chlorides, sulfates and distilled water). This process adversely affects concrete exposed to these damaging stimuli.

The expansion of the corrosion products (iron oxides) of carbon steel reinforcement structures may induce mechanical stress that can cause the formation of cracks and disrupt the concrete structure. If the rebars have been poorly installed and are located too close to the concrete surface in contact with the air, spalling can easily occur: flat fragments of concrete are detached from the concrete mass by the rebars corrosion and may fall down.

Damage can occur during the casting and de-shuttering processes. For instance, the corners of beams can be damaged during the removal of shuttering because they are less effectively compacted by means of vibration (improved by using form-vibrators). Other physical damage can be caused by the use of steel shuttering without base plates. The steel shuttering pinches the top surface of a concrete slab due to the weight of the next slab being constructed.

What are the pros and cons of concrete?

A concrete home can cost more to build than a wood home, but it could make up for that by keeping cooler than a wood-framed house when it’s hot outside.

Concrete, because it is solid and is not food source for termites, could cause you fewer worries over pests. Some insurance companies like that so much that they give discounts to homeowners whose houses are made from concrete block.

Concrete also is a good sound-proofing material; in fact, it can repel sound waves. And the homes are so sturdy that they can last for hundreds of years.

Still, a concrete block can be prone to settlement cracks and to efflorescence, those white marks that appear when concrete gets wet and then dries quickly. And building a masonry house can be more labor-intensive that putting up a frame home.

Steel

How is it Made?

When iron is smelted from its ore, it contains more carbon than is desirable. To become steel, it must be reprocessed to reduce the carbon to the correct amount, at which point other elements can be added. In modern facilities, this liquid is then continuously cast into long slabs or cast into ingots. Approximately 96% of steel is continuously cast, while only 4% is produced as ingots.
The ingots are then heated in a soaking pit and hot rolled into slabs, blooms, or billets. Slabs are hot or cold rolled into sheet metal or plates. Billets are hot or cold rolled into bars, rods, and wire. Blooms are hot or cold rolled into structural steel, such as I-beams and rails. In modern steel mills these processes often occur in one assembly line, with ore coming in and finished steel coming out. Sometimes after a steel's final rolling it is heat treated for strength, however this is relatively rare.

How Long will it Last?

Thanks to exceptional resistance to fire, corrosion and pests, steel framed buildings are the first choice for extreme environmental conditions. Because steel doesn’t need treating with pesticides, preservatives or glues, it’s also safer for people handling and living or working around it.

Degradation

Iron and steel, the most commonly used metals, corrode in many media including most outdoor atmospheres. Usually they are selected not for their corrosion resistance but for such properties as strength, ease of fabrication, and cost. These differences show up in the rate of metal lost due to rusting. All steels and low-alloy steels rust in moist atmospheres. In some circumstances, the addition of 0.3% copper to carbon steel can reduce the rate of rusting by one quarter or even by one half.

What are the pros and cons of Steel?

Steel buildings are the most cost-effective and structurally-sound structures in architecture today. To date, it is hard to find an example, besides the World Trade Centre Towers, of a steel building that has collapsed. Not only are steel metal buildings cheap to build, but they are also resilient, resisting the elements, termites and even natural disasters like earthquakes. Reinforcing with additions or heating/cooling upgrades is easier than with wood structures too, experts say.

There are many pros to erecting steel buildings, versus traditional wooden edifices. For starters, steel is lighter than wood, concrete and brick. It can't warp, expand, contract, absorb water, feed termites, rust, catch fire or become a breeding ground for fungus. Since most steel is flame-retardant, many insurance companies reduce rates for home owners who choose steel building products. The government also recognizes steel as an energy-efficient, eco-friendly choice, so they reward citizens with tax credits.

As with anything, there are a few cons to steel buildings too. First, not all builders are familiar with building metal structures, let alone constructing to the latest standards, using the most up-to-date computer software. Special tools are required to work with this material, which not every builder will have. They will need to employ very specific designs to brace the steel correctly. Additionally, some metals are coated in oil, which may cause a toxic odour while working with it. The biggest disadvantage of working with steel is that it is an excellent conductor of heat, so in colder areas, the heat can be absorbed into the structure and quickly lost. Mould also has a tendency of growing around steel studs in the winter. To combat the energy issue, home owners can use a double wall system or high efficiency insulation to prevent heat transfer.

Timber

How is it Made?

selected
harvested
trimmed
transported to mill
rough cut
mill cut
cured and dried
the by-products are sent for other uses (particle board / plywood)
transported to fill orders

How Long will it Last?

20 years lucky ....15 maximum for treated wood, now when you retreat it over and over you keep weakening it further and further because all wood preservatives soften the fibres and naturally the result is crumbly wood but all wood preserved not exposed to the environment could outlive you, in other words the fence posts you put into the ground will rot above ground and 50 years later the part under the ground will likely still be as fresh and new as when you put them into the ground ...even a treated wood foundation for a playhouse or shed will still be like new

Degradation

Wood is subject to degradation by bacteria, fungi, insects, marine borers, and climatic, mechanical, chemical, and thermal factors. Degradation can affect wood of living trees, logs, or products, causing changes in appearance, structure, or chemical composition; these changes range from simple discoloration to alterations that render wood completely useless. It should be noted that wood can last for hundreds or thousands of years, as demonstrated, for example, by furniture and other wooden items found in excellent condition in the tombs of ancient Egyptian pharaohs (see Egyptian art). Wood is degraded or destroyed not with the passage of time but only under the action of external factors.

What are the pros and cons of Timber?

Pine is an inexpensive, lightweight wood that can be yellowish or whitish with brown knots. It's often used for rustic pieces, like farmhouse-style tables.

Pros: It's low-cost, and it takes paint well, so it's great for kids' furniture. (The same holds true for birch and poplar.) Pine develops a nice, rustic patina from age and use, and it resists shrinking and swelling.

Cons: It's a softwood, so it's prone to scratches and dents.

A thatched roof constitutes a very hostile environment for micro-organisms to grow; in the past hot dry summers and frosty snowy winters controlled the speed of decay, by keeping thatch relatively dry and controlling fungal growth. Periods of prolonged heavy rain in the recent past have encouraged the growth of moss and algae, not just on thatch but on tiled roofs, trees and garden furniture, with warmer winters further contributing to expanding colonisation on thatch. The present climatic conditions will shorten the life expectancy of many thatched roofs. Research carried out by Kirby and Rayner (1989) suggested that under normal conditions 2cm of a thatch surface is worn away annual by weathering It can be expected that a thatch wearing normally will be wet after rain at the surface to a depth of 2cm, but even after continuous heavy rain the moisture content below the surface will be less than17% deeper inside the thatch. It is believed that many of the current problems associated with early degradation are either inherent in the raw material or are associated with changing climatic conditions.

Long Straw

Physical wear on a straw thatch. Algae formed a biofilm on the thatch in the winter and a dry summer has caused the film to contract. This has caused tearing and breakage of the butt ends of the straw

Reports of early failure in water reed thatch, within 4-10 years, were first recorded in 1970, and by 1983 had given rise to considerable cause for concern. At that time the majority of affected reed was home produced; researchers from the Universities of Bath and East Anglia investigated both the potential for infection of freshly harvested reed during storage and also studied the degradation process within thatch. Then as now complaints are associated with soft, weak reed, colonisation of the surface by clumps of organisms that dry out in sunny conditions and cause the surface to physically degrade in windy conditions. This surface colonisation and physical Prolonged periods of rain encourage the colonisation of the straw thatch surface with algae and mosses. These hold moisture and prevent the thatch from drying out interaction with the thatch allows the ingress of water into underlying thatch layers providing conditions suitable for further degradation of the reed by fungi and a subsequent reduced life expectancy for the roof. The main body of research on decay of lignin rich materials has been carried out on wood and wood products. However, there are only a limited number of organisms that form symbiotic functions in the decay process many of these organisms appear to naturally colonise both wood and other decaying vegetation such as thatch. In this particular form of attack, decay is not homogenous across the whole surface of the coat work, but can be seen as “bleached” areas in either zones or patches; this type of decay is not necessarily associated with high wear areas of a roof such as the junctions of dormers, valleys or gullies. Stems taken from within these patches have often lost both tensile and compression strength causing them to collapse and fragment.