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Precast Makes World Better Place to Live

Precast technology is becoming the most viable construction option that can contribute to achieve sustainable development. In view of this, to acquaint our readers with several precast advantages, we have taken excerpts from the book "The Little Green Book of Concrete-Sustainable construction with precast concrete."

It is vital that we invest in infrastructure which is long-lasting and robust - but we must also consider the overall quality of the environment so that it is a healthy world for people to live and sustain. The onset of the effects of climate change putting pressure on future civil engineering structures could be much greater than today. Precast concrete as one of the innovative products of technology allows constructing buildings sustainably in the face of such adversity.

Even before moving on to the precast technology and its products, the sustainability factor is well achieved in the precast manufacturing industry itself. Steps to encourage resource efficiency and to design out waste throughout the manufacturing and construction process are well maintained by the manufactures. End-of-life destinies such as recycling for concrete aggregates or deconstruction for re-use in buildings or structures are increasingly being considered.

Uses natural raw materials

All the materials that go into precast concrete products come from natural and recycled sources, mainly inorganic. This means they are subject to minimal processing or chemical treatments to render them suitable for use, which results in concrete having a relatively low embodied energy value, unlike highly processed materials, such as plastics.

The precast industry works hard to improve the efficiency of cement use by maximising hydration and by optimising cement content to reduce embodied CO2. The use of other cementitious materials such as ground granulated blast furnace slag and pulverised fuel ash is also growing. Both these additions have much lower embodied CO2 than Portland cement.

Cement v/s Precast

Making cement in a kiln requires a great deal of heat energy, but the amount of non-renewable fossil fuels used to produce this heat is being reduced. The great majority of precast concrete mixes is made up of low carbon footprint sand, gravel or crushed rock meaning that the carbon content of cement is diluted many times over. The confusion between cement and concrete carbon footprints is the major source of misinformation about the real beneficial sustainability characteristics of concrete.

All the materials that go into precast concrete products come from natural and recycled sources, mainly inorganic. This means they are subject to minimal processing or chemical treatments to render them suitable for use, which results in concrete having a relatively low embodied energy value, unlike highly processed materials, such as plastics.

Efficiency and recycling

Precast is produced in factories under strictly controlled conditions which means excellent resource efficiency for materials, labour, energy and processes. Today"s precast factories are clean and productive, and many use computer-controlled processes for batching, mixing and casting. Major efficiency programmes are also helping reduce factories" energy consumption.

The highly effective recycling systems used in precast factories enable virtually all process water, slurry, aggregates or cement to be safely re-captured and put back into production. This means that a closed-loop system is in operation - one which minimises any outgoing waste materials. Total precast factory waste to landfill averages under 0.2% of a product"s weight.

Why choose Precast

Before moving on to the crux of the advantages of choosing precast, is saving on the time aspect. This can be achieved with either on- or off-site construction providing the design team with a clear, well-organised production schedule for every project. Effective panelisation can also reduce material waste and save time. Also, the production of precast concrete off-site, in a factory, means that construction sites are cleaner, quieter and safer. The installation of precast units is usually fast and efficient. Such efficiency helps to reduce the impact that construction has on surrounding areas. This social aspect of sustainability in precast is therefore a major benefit - helping to improve construction"s reputation with the public.

Rapid erection on site and minimum waste

Fast construction on site means a shorter period of disturbance for surrounding properties. Precast units arrive ready for installation and can be scheduled to be on site "just-in-time" so they can be lifted directly into place. This prevents unnecessary handling and so reduces the diesel or electricity used by mobile plant and cranes.

Using precast is a highly effective strategy to reduce waste from wet concrete, formwork and other sources. Even if all does not go to plan on site due to changing designs, precast products can always be used elsewhere. Scrap created at the building site can be segregated, collected and broken up to create aggregate.

Offers safety and instant work platform

The usage of codes of practice for safe delivery and erection and innovations has made the use of precast concrete even safer. Precast structures and in particular floors and staircases provide an early, secure and broad platform from which subsequent site activities can be undertaken. Thus, it helps in speeding up of construction. No vibration, no other noise-generating processes are needed to install most precast concrete products, whatever their size.

Precast is produced in factories under strictly controlled conditions which means excellent resource efficiency for materials, labour, energy and processes.

Built to a precise specification, easy to clean and repair

Precast companies work with specialist fixing teams to install their products. This guarantees precise, reliable workmanship ensuring that the quality of service from precast is maintained long after the products leave the factory. Any minor damage or dents during construction may lead to compromise on the appearance. However, the excellent surface finishes of precast makes cleaning and repairs easier.

High recycled content with lowest energy values

During its lifetime precast concrete will effectively re-absorb much of the carbon dioxide that was used to create it in the first place. Precast units, will ultimately re-absorb the CO2 used to create them, a process called carbonation that accelerates when products are crushed for recycling at end of life. Most standard aggregate concrete blocks are 100% recyclable and some use up to 97% reclaimed material in their manufacture. The large precast retaining wall units shown here are made mainly from recycled materials and are relocatable.

Many precast products now contain by-products or recycled waste materials, such as pulverised fuel ash from coal-fired power stations and granulated slag from blast furnaces. The demand from buyers for products with a higher recycled content is growing steadily. Precast concrete products such as blocks have some of the lowest (and best) embodied energy values of all commonly used construction products.

Minimises reliance on fossil fuels

On a large scale, precast concrete is used to construct the towers for wind turbines, but even on a domestic scale precast products support the drive to use renewable technologies. An innovative roof tile has been developed that incorporates photovoltaic cells - these harness the energy from daylight to create electricity, every day, even if the sun is not shining.

In addition, concrete is not as vulnerable as plastics and asphalt to increases in oil and gas prices and is well-positioned for the post-oil age, especially considering the growing diversion of wood as biofuel for heating and power systems, a trend that will significantly raise global timber prices.

Can be re-used

At the end of a structure"s life, precast units can be re-used in their entirety, for example floor slabs can be reclaimed as whole elements. These could be re-installed in the same building or even transported a short distance and used in a comparable structure elsewhere. Now, with a greater number of products incorporating technical information on a bar code or microchip, designers can be more confident about re-using precast products, such as piles and frame elements.

Tailored to requirements and thermally versatile

Concrete is tremendously versatile as a material. It can be dense or lightweight and this allows a choice when designing a structure"s thermal behaviour. Dense precast concrete can act as a thermal sink and lightweight as an insulator. Where insulation is needed, lightweight concrete blocks have an insulation value three times better than dense concrete, but of course dense concrete has better thermal mass. This important characteristic of precast concrete can be seen in its application as a medium for heating or cooling, whether this is via air or fluids. The hollow cores in precast floors can be used or pipes can be cast into slabs, to form cooling systems that use up to 50% less energy than air conditioning. Precast piles are also available with built-in ground source heat exchange systems.

Recent studies show that lightweight homes in the UK will suffer significant overheating if summer temperatures rise as predicted. By contrast, masonry and concrete houses with solar shading will be more comfortable to live in and less likely to become reliant on air conditioning systems to maintain habitable temperatures inside because they make best use of concrete"s thermal mass properties.

According to research by Arup, compared with an equivalent lightweight house, a masonry or concrete house will pay back its CO2 "investment" within 11 years, and then continue to provide savings over its life.

Precast is good for life

Quality of life is a clear priority in sustainability as is ensuring that we are constructing a built environment that will last for successive generations, not just for today. Precast concrete offers significant sustainable benefits in these areas. The choice of precast concrete in a building or structure means that you are building-in resilience. The inherent properties of the material help it to withstand all manner of weather conditions, infestations and other less common threats such as explosions. Precast concrete goes on increasing its strength for hundreds of years after it is cast. It won"t shrink, warp, move or creep excessively, so can be relied upon to perform consistently year after year.

Precast concrete is resistant to rain penetration and wind-blown debris - only concrete and masonry walls can provide this protection. Precast concrete and masonry products offer better protection against the possible effects of climate change because of its robustness, durability and have structural integrity.

Resistant to rust and chemical attacks

Precast concrete is corrosion-resistant and can therefore be used even in very aggressive environments. For example, precast concrete piers are resistant to the inter-tidal anaerobic attack experienced in some marine environments. For vehicle hard-standing, aircraft standing aprons and other paved areas, concrete paving blocks are an ideal choice because they are resistant to fuel and oil spills. Their use makes sense economically and environmentally because pavement repairs are localised, using less materials and causing less disruption.

Everyday resilience

On a domestic scale, precast and masonry are also used for basements where below ground living needs robust and waterproof construction. Precast concrete is resilient in the face of intense pressure. For example, when used for underground pipes, precast are resistant to up to 5,000 psi water jetting pressure. Precast concrete is an inert family of products, so it does not leach out any harmful chemicals. This means it is safe to use in applications like distribution of drinking water through tunnels. It also means that when precast concrete is used to store or transport potentially harmful fluids, these will be contained securely although specialist advice is always recommended.

Rot proof, fungus proof and mildew resistant

Precast is dense, tough and does not shrink or warp and hence will not fall prey to enemies of organic materials. It is also inedible to termites and rodents. Organic building materials make the best food for these pests. Precast concrete is resistant to attack from termites and other infestations such as rats and mice, so buildings made with concrete and masonry will be less susceptible to such damage.

The strength and resilience of precast structures means that extra safety is always built in, often over and above what is required by design codes. In some cases, this benefit could be a life-saver. Precast concrete can resist massive impacts. There is a growing need for built structures to be more resilient to threats from flood and fire.

Induces healthy indoor environments

The simple lines and smart edges of precast concrete are easy to keep clean. It provides a less friendly environment for dust mites that may trigger asthma and other respiratory conditions. Precast is also a very poor host for mould and mildew. In its daily use, precast concrete is an inert substance, so it doesn"t emit or give off any gases, toxic compounds or volatile organic compounds.

Built for generations

By adhering to the principles of "lifetime homes", successive generations of people can be accommodated in the same properties without recourse to major changes or even relocation.

The usage of codes of practice for safe delivery and erection and innovations has made the use of precast concrete even safer. Precast structures and in particular floors and staircases provide an early, secure and broad platform from which subsequent site activities can be undertaken.

Precast concrete responds well to this important aspect of social sustainability in its use for basements, which provide easily adaptable extra space for playrooms, utility rooms or even home offices -removing the need for commuting. Basements can save up to 27% of land required to build the same volume of living space in a house with two storeys above ground. The fact that precast elements can be dismantled means that it is easy to add extensions or new wings to precast structures. Where precast panels were used it is simple to remove them and continue building -they can be re-installed on completion

Protects against fire

Precast is fireproof. It does not catch fire or burn. It protects against the spread of fire between rooms or properties. In fire tests, concrete performs consistently well, typically needing very little remedial treatment following exposure to the high temperatures of a fire. In most cases, some minor patching and a new coat of paint may be all that is required to make good. Studies in Sweden have indicated that a major fire is more than 10 times less likely to develop in houses built from concrete or masonry. Furthermore, Professor Ulrich Schneider of Vienna University of Technology has also found a clear link between construction materials and fire safety - there are about three times fewer fire victims in countries which build mainly in concrete, masonry and stone.

Precast concrete flood mats and barriers can protect river banks and livelihoods - and with the onset of climate change, such flooding could
become more frequent and widespread.

Just like many other concrete and masonry materials, precast concrete does not melt in high temperatures. This means that there is no need for protective paints or special insulation. Concrete will not drip molten particles in a fire, and this helps protect human life by providing safe escape routes and preventing fire spread.

Essential for sustainable transport systems

Clean, greener options for travelling to work, school or home are being built throughout the UK, and precast concrete is at the heart of many schemes. Guided bus lanes and track beds, and bridges for light rail or tram systems commonly include precast elements because they are long-lasting, durable and robust that can also have a very attractive surface finish.

Clean energy from wind turbines

Precast concrete is often used for wind turbines - its high levels of weather resistance and inherent stiffness help provide a stable and resilient structure. Precast concrete rings create wind turbine towers that generate electricity which is a renewable resource. However, the best locations to place wind turbines are also often the harshest environments, so it is important to use a structural material that does not rust or decay.

Saves energy in the city

On a hot day, pale coloured concrete finishes, including paving and roofs, reflect more sunlight and heat than dark surfaces, so keeping buildings cooler and mitigating the "urban heat island" effect. This reduces urban energy use because people are less likely to use air conditioning.

Well-suited to water containment

The strength and resilient properties of precast makes it an excellent material for containment, whether this is for water storage, domestic rainwater or grey water collection. Concrete pipeline systems play a key role in taking sewerage flows for treatment. Rigid pipes mean no leakage and centuries of performance.

Precast concrete flood mats and barriers can protect river banks and livelihoods - and with the onset of climate change, such flooding could become more frequent and widespread. The use of similar precast elements can also be used to create breakwaters and artificial reefs out to sea.

Mouldability of Precast

The "mouldability" of precast allows it to replicate classical designs. The same techniques of casting-in textures of precast can be used to increase the skid resistance of the surface of a precast concrete unit. This can be particularly useful in busy paved areas, steps and ramps where, for example in winter, icy patches could cause slips and falls. Everywhere you look you will see innovations in precast concrete hard landscaping and street furniture. For example, large planters, planted bridge abutments and living walls help to make places greener and more pleasant. This also has the effect of increasing biodiversity -the plants support insect life and wild birds too.

The optional inclusion of titanium dioxide in cement does not only produce white precast concrete but also helps to keep the finished product clean. It does this by capturing dirt particles which are then washed away by rainfall. Clean buildings look more attractive and are less likely to be subjected to vandalism, damage and graffiti.

Reference

In view of this, to acquaint our readers with several precast advantages, we have taken excerpts from the book "The Little Green Book of Concrete-Sustainable construction with precast concrete."


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