Man Made Mountains

Concrete

In a world where the ground can spontaneously and violently shake, the wind can gust at hundreds of kilometres an hour, and waves can crash over the land with the power to destroy everything in their path, concrete can make the construction – and endurance – of record breaking skyscrapers, bridges, towers and statues possible.

Concrete is a mixture of several different ingredients which include an aggregate – a hard, earthy material such as gravel, sand, crushed stone, recycled concrete or another synthetic substance. These aggregates are actually among the most world’s most mined materials, because they form a very important part of a good concrete mixture. In addition to building materials, aggregates are also used on road shoulders, beneath foundations, in railroads and for irrigation, among many other uses.

The resulting ‘miracle mixture’, concrete, is the most used material in the world, utilised in the construction of myriad items which can even include pipes and boats. Many of the world’s tallest buildings are made of reinforced concrete. The technology involved with creating the substance was used by the ancient Romans where it was used to build the Colosseum and the dome of the Pantheon. After the Empire fell, the technology was essentially lost until the mid 18th century.

An early form of concrete (investigated in the 1960s and 70s) actually occurred naturally about 12 million years ago when some oil shale combusted near a bed of limestone. In human history, lime mortars were used around 800BC through Greece, Crete and Cyprus, and the Romans made extensive use of it from approximately 300BC to 476AD. In ancient Rome, the mixture was quicklime, pozzolana and pumice for an aggregate.

Modern tests illustrate that the concrete that was used by the ancient Romans had as much compressive strength as that which we use today, however its tensile strength was far lower than modern reinforced concrete because of the former’s lack of steel. Ancient concrete was so durable that many of the structures that were built still remain today – for example, the Pont Du Gard and the Baths of Carcalla.

In addition to the aggregate, another component of concrete is the binder; in modern concrete this is typically Portland cement and other cementitious materials such as fly ash or slag cement. Portland cement was patented by Joseph Aspdin in 1824, so named because of its colour, which is very similar to the limestone found on the English Isle of Portland. This type of cement is made by heating limestone with clay to produce a product called clinker, which is then ground with a source of sulfate such as gypsum.

Unfortunately, heating limestone and clay to produce the clinker needed for cement produces more carbon dioxide emissions than just about anything else on the planet. Though obviously important to modern building techniques, the manufacture of cement produces negative environmental impacts at all stages of the process. As for concrete itself, there is a reason why the “concrete jungle” is considered environmentally problematic. Large concrete areas can cause surface water runoff, responsible for soil erosion, water pollution, and flooding. Another effect that is produced by concrete as well as asphalt is the urban heat island effect, whereby concrete will absorb, gather and hold the heat energy from the sun and then radiate it into the atmosphere, even well into the night, making dense urban areas typically much hotter than their rural surroundings. The demolition of concrete structures, whether by man or natural disaster, releases dust that is highly alkaline and contributes greatly to local air pollution.

Concrete can, however, be recycled by collecting and removing all foreign contaminants such as metal rebar, wood, plastic, etc. The remaining material is then stockpiled and used as gravel or aggregate for new concrete structures. The benefits of this were realised when concrete debris started to fill up landfills; in fact a national study was conducted in 1983 which approximated that 17 per cent of worldwide landfill was actually concrete based waste. This is mainly because concrete structures are generally very large; if the Burj Khalifa (the tallest building in the world at present) was to meet the demolition crew tomorrow, it would fill several landfills on its own with over 55,000 tonnes of concrete rubble.

Concrete can seen as a form of artificial sedimentary rock, with extremely stable components. Many structures that are built with concrete have a life expectancy of 100 years but it has been suggested by researchers that adding silica fume could extend the life of a concrete structure to an astonishing 16,000 years. There are also forms of ‘self healing’ concrete that will last longer than traditional concrete. Structures such as the Hoover Dam in the USA are intended to last, essentially, forever.

Watertight, airtight and solid, concrete increases heating and cooling efficiency because it will not leak air as much as a building product such as wood or metal (it also boasts far superior fire resistance). Year round, concrete will maintain a certain average temperature and store that energy, thus keeping the room temperature steady rather than constantly fluctuating. It can usually be manufactured fairly close to its final destination which reduces the energy inputs needed to transport it. Although the production of cement produces a high level of emissions, the remainder of the concrete production process takes a relatively low amount of energy.

Although weak in tension, concrete is very strong in compression. Because structures that are made of concrete experience very high tensile and compressional loads during events such as earthquakes, they can be prone to shearing or cracking. Although reinforced concrete is made to flex when the earth moves, un-reinforced concrete structures are the most dangerous structures that one can inhabit during such a catastrophe because they can quickly turn into rubble.

In fact, heating and cooling alone can cause concrete to crack because it will expand and contract. A team of Dutch scientists is testing a new form of concrete that contains special bacteria that when exposed to water will form limestone which will fill cracks – self-healing concrete.

After being poured, concrete can take a very long time to reach 100 per cent of its intended strength; within four weeks of being poured, however, it will reach up to 90 per cent of its strength. The most important factor that affects the strength of the finished material is how it is cured. The main problem with concrete that can cause it to have less strength is when the water evaporates too quickly, causing the concrete to dry too fast and shrink too quickly. The best way to prevent this from happening is to keep the surface damp while the concrete is curing.

Concrete can be mixed in different forms depending on what kind of strength it needs, how workable it needs to be and how pretty it needs to look. It can be shaped and moulded into just about anything that can be dreamed up. It can last for hundreds of years; it can even be mixed as a fluid so that it can be pumped through hoses to the top of a building. Concrete is so very common and yet there is nothing else on the planet like it – not that we need a substitute because it is such a versatile material just the way it is.

Home Automation

Call it ‘domotics,’ and you are likely to receive a blank stare, but refer to it as ‘smart home’ or ‘home automation,’ and you will get a nod of acknowledgement. For the past few years, consumers have heard the word ‘smart’ attached to countless products and services, from food and drink to snacks like popcorn and mobile phones, which no one seems to refer to as a ‘cellphone’ anymore. Yet what, exactly, constitutes ‘smart’?

June 2, 2020, 3:41 PM AEST