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Concrete is a composite material consisting of a binder, gravel, and aggregate, mixed with water (Li 3). The history of concrete dates back to ancient Egypt, where builders used straw and clay make building blocks. Their goal was to produce a durable construction material as the basis for building larger structures.
Currently, concrete is the most widely used construction material in the world. The creation of concrete revolutionized the practice of design and architecture because it gave builders new possibilities. This paper traces the history of concrete, and examines the current application of concrete in construction projects.
The paper starts by examining the history of concrete since the time of the Egyptians to the present. It then surveys the types of concrete used in the world today. The paper then explores the concrete framing systems followed by a discussion of the unique attributes of concrete. The final section of the paper deals with modern uses of concrete in architecture and design, and the environmental impacts of concrete production and usage.
Historical Methods of Making Concrete
The Egyptians were the first people to make a composite material designed to improve its structural qualities as a building material. They mixed straw and clay to make bricks. The Egyptian straw bricks could withstand cracking. This meant that buildings made with straw bricks lasted longer than buildings made from clay bricks. Egyptian straw bricks date back to 3000 BC (Brookes 34).
The Romans were the first people to develop durable concrete. Many concrete structures constructed during the Roman era that still stand today. The Romans discovered that a mixture of volcanic ash, quick lime, and pumice dried into a hard substrate suitable for construction (Li 6).
They went ahead to use this mixture in the construction of their structures. Many structures from the Roman era that still stand today came up between 300 BC and 400 AD. After the collapse of the Roman Empire, concrete technology disappeared until early in the nineteenth century.
During the nineteenth century, a British researcher named James Parker rediscovered hydraulic concrete after conducting research into Roman methods of concrete making. The Industrial Revolution led to resurgence in the use of concrete for construction. In the same period, a British mason named Joseph Aspdin patented Portland cement after inventing a procedure for producing cement from baked lime. Cement became a primary ingredient in the preparation of concrete.
After the rediscovery of concrete, architects and engineers continued to experiment with different ratios of the materials used in the production of concrete. The result was a plethora of concrete types available for different uses today. Part of the ideas that came up from these experiments was the reinforcement of concrete. This gave rise to new possibilities in the building and construction industry.
Types of Concrete
The third classification of concrete types is according to additives. Three examples of concrete based on their additives are Fiber reinforced concrete, macro-defect-free (MDF) concrete and DSP concrete (Li 17). DSP is the acronym for concrete whose density has been increased using small particles (Li 17). There are many other types of additives used to make different types of concrete for various applications.
In practice, concrete users use specific names to refer to specific concrete types depending on their composition and their uses. This system yields a long list of concrete types. It is important to sample a few of these concrete types to illustrate this point.
When construction technologists need to add a layer of concrete to line a rock face or to hold back soil, they sometimes choose to shoot concrete using compressed air. This saves time and it eliminates the need for formwork. Concrete applied in this manner is called “shotcrete” (Fling 3).
Shotcrete is useful for lining tunnels to reduce or eliminate seepage during construction. The actual mixture of concrete used as shotcrete depends on the need. Hydraulic concrete mixtures can help to stop leaks, while lightweight concrete can be used for aesthetic purposes.
The ease of making concrete has led to the development of many kinds of concrete. The differences in concrete types arise from the ratio of materials used in their production and the type aggregate used. The classification of concrete depends on the unit weight, compressive strength, and the additives in it (Li 16).
The classification of concrete according to unit weight gives four main types of concrete. These are “ultra-lightweight concrete (<1200 Kg/m3), lightweight concrete (1200-1800 Kg/m3), normal-weight concrete (1800-2400 Kg/m3), and heavyweight concrete (>3200 Kg/m3) (Li 17).
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The unit weight of the concrete determines its applicability for various uses. For instance, lightweight concrete is not ideal for load bearing structures. On the other extreme, heavyweight concrete can withstand heavy loads and is an ideal nuclear shield. This means that heavyweight concrete is ideal for the construction of nuclear plants and is ideal for the construction of high radiation installations.
Compressive strength refers to the ability of concrete to withstand pressure from compressive forces. Classification of concrete by compressive strength yields four main classes. These are, “low-strength concrete (<20 MPa), moderate-strength concrete (20-50 MPa), high-strength concrete (50-150 MPa), and ultra high-strength concrete (>150 MPa)” (Li 17). The pressure that some structures need to withstand is very high.
For instance, the pillars of a skyscraper must withstand the stresses resulting from the weight of the entire building. In this case, only high strength concrete is appropriate. However, structures that carry minimal loads such as small footbridges can operate normally with moderate strength concrete. Low strength concrete is ideal for partitions and sub grades of roads (Li 18).
In some situations, design considerations favor the use of concrete with air spaces to allow water to seep. The concrete mixture used for this purpose is called pervious concrete. The use of pervious concrete reduces the need for artificial drainage. It also makes it easy to put up concrete structures that do not interfere with water flow to underground water systems.
The third type of concrete is glass concrete. This type of concrete uses recycled glass as the aggregate. The use of glass in this manner improves the appearance of the cured concrete. In addition, glass concrete has better thermal properties and is more durable than many concrete types.
As indicated previously, there are very many concrete types. The examples above are illustrative of the concrete types available for use in building and construction. More types of concrete will be available in the future based on current research efforts that are seeking to improve the quality of concrete.
Concrete Framing Systems
The choice of concrete framing systems is one of the important decisions every designer must make. Framing systems have direct cost implications for all design projects. Poor choice of a concrete framing system can also compromise the stability of the building after construction. It is important for a designer to be aware of the options available and the impact of using each alternative. Fling gave three reasons why the choice of a framing system matters during preliminary design (1).
First, it leads to the generation of important information about the structural design of the building for use by all stakeholders (Fling 1). Secondly, it increases the efficiency of the project manager because the preliminary design helps in the identification of problems early in the project (Fling 2). Thirdly, it enables designers to optimize their designs before construction begins (Fling 2). The options designers have when choosing concrete framing systems are as follows.
First, designers can use the flat plate framing system. The flat plate is very simple and economical to construct because it requires little formwork. It gives designers the flexibility to decide on the location of the supporting columns. Its main disadvantage is that it is susceptible to deflection. Secondly, it has a very low capacity to absorb sheer stress. The ideal application of the flat plate framing system is in buildings with low loads such as hotels and hospitals.
The second framing system to choose from is the flat slab. Flat slabs require more formwork because of the need to increase the area of contact between the columns and the base of the slab. This framing system can withstand more weight, and can handle longer spans compared to the flat plate framing system.
Thirdly, a designer can use the banded slab framing system. The main difference between this framing system and the previous two is that the beams supporting the slab are flatter but wider. This reduces problems associated with low beams. It is costlier that the flat plate and the flat slab because of more formwork requirements. It is ideal for tall buildings.
The fourth framing system is the hoist slab. In this option, several beams run across the bottom of the slab with two beams supporting the resulting framework. The hoist slab is lightweight because it uses small quantities of construction materials. However, the formwork needed to construct this slab is more expensive than the flat plate framing system.
The fifth framing system is the waffle slab. Waffle slabs get their name from the waffle-like appearance of the ceiling. This framing system is ideal for creating longer slabs because the additional span dimensions do not result in additional dead weight.
This framing system limits the construction of partitions because the partitions must match the waffles to achieve a clean finish. The formwork for this framing system is expensive and its construction requires experience. This framing system is ideal for covering large spaces since it can support larger spans without requiring additional columns.
Unique Attributes of Concrete
Concrete has several unique attributes that contribute towards its wide acceptance as a construction material. It is also possible to reduce or eliminate its weaknesses by adding various compounds and structural support systems during its production.
First, concrete has very high compressive strength. This explains its wide usage in the construction of load bearing parts in various construction projects. The actual tensile strength of concrete varies depending on concrete type. Usually changing the ratios of the materials used in its production leads to changes in tensile strength. This means that adjusting the mixing ratios of concrete can help to achieve desired tensile qualities.
Secondly, concrete has very low tensile strength. The actual values vary depending on the type of concrete. This means that concrete is not ideal for the construction of structures that experience tensile forces. This is what led to the development of reinforced concrete. The steel in the reinforced concrete increases its tensile strength significantly.
Concrete has low elasticity. This means that it cannot recover once it is deformed. Elastic forces acting on concrete can lead to the formation of cracks during the process of destructive deformation. These cracks damage the structural qualities of concrete and compromise its ability to withstand tensile and compressive forces.
The fourth important quality of concrete is that it has a very low coefficient of thermal expansion. Concrete does not expand or contract appreciably based on temperature changes. This quality makes concrete ideal for the construction of large structures because temperature changes have little effect on its mechanical properties.
Finally, concrete is prone to creep under constant load. This mechanism relives the stress experienced under constant load. Creep helps concrete structures to set and can contribute to their stability. However, too much creep can lead to weaknesses in concrete structures.
Uses of Concrete in Design and Architecture
Concrete has various uses in design and architecture. Its widespread use in the construction industry arises from its unique qualities. The following are some of the uses of concrete in design and architecture.
First concrete is the main material used in the construction of columns and slabs in buildings. While it is possible to construct low-level buildings with wood and other materials, it is impossible to construct high-rise buildings without concrete. Concrete makes it possible for planners to build skyscrapers that make the most use of small land areas.
The second widespread use of concrete around the world is the construction of bridges. Before the development of concrete technology, bridge designers used steel and wood as the main materials for bridge construction. These materials could not withstand severe weather. Concrete replaced them as the material of choice because of its resilience in extreme weather conditions.
Concrete is also a very important material in road design. Technically speaking, tarmac is a type of concrete that uses bitumen in the place of cement. Apart from this, conventional concrete forms the sub grades of roads during road construction. In areas with extreme weather, concrete roads are more resilient compared to bitumen roads.
Concrete is ideal for making working surfaces in kitchens and industries. Its strength makes it ideal for molding large sinks and tubs for industrial use. Its ability to withstand shock and corrosion makes it a perfect choice for the construction of platforms for heavy machines.
Exposed-aggregate concrete is a popular material for making driveways. This type of concrete is strong enough to withstand wear. In addition, exposed-aggregate concrete is ideal for use in areas with high human traffic. It can withstand the wear arising from heavy use.
Glass concrete is becoming popular because of its beauty. Glass concrete is also very strong and can withstand wear and tear. In addition, it has impressive corrosion resistant qualities.
Concrete is also gaining ground as an ideal substitute for metallic and wooden poles used in the distribution of electricity. The use of concrete poles is reducing the demand for trees previously used to make poles. Since concrete does not need chemical treatment to withstand corrosion, the use of concrete poles will eliminate the demand for the chemicals used to treat wooden poles. Architects and designers can use concrete poles as part of sustainable design.
Many storm drains and sewerage lines are made using concrete pipes. Concrete is resistant to corrosion, and it does not leak. In addition, the ease of molding concrete pipes makes it possible to plan for custom systems during architectural design.
High-density concrete can block radiation. This is why shields made from concrete blocks are important in the design and construction of nuclear facilities. In addition, high-density concrete is ideal for making bomb shelters and for erecting security barriers. In this regard, architects and designers can use concrete as the material of choice to design maximum-security facilities.
Concrete has both positive and negative impacts on the environment. The positive impacts of the production and use of concrete are as follows. First, the production of concrete encourages the recycling of materials from other industries. This reduces environmental pollution. For instance, the production of glass concrete uses recycled glass from other industries. This type of concrete is durable and ensures that waste glass becomes useful as part of a concrete structure (Li 23).
The second positive impact of concrete production is that it helps to reduce the damage to the environment caused by the use of wood in construction. The use of concrete posts for fencing helps to reduce the number of trees needed to build fences. In addition, designers currently prefer concrete to wood in the construction of structures such as bridges. This means that concrete can help to reduce the damage to the environment resulting from the use of wood in construction projects.
The negative impacts of concrete usage to the environment are as follows. First, an analysis of the life cycle of concrete shows that it the largest contributor to global greenhouse gas emissions. Estimates place the contribution of concrete production to global greenhouse gas emissions at ten to fifteen percent (Harris 44).
Secondly, concrete requires aggregates as well as cement for its production. Many of the aggregates used to produce concrete come from mines around the world. Therefore, the production of concrete contributes to the destruction of landforms and the pollution of the environment because of mining activities.
The third impact of concrete use to the environment is that it leads to the generation of waste that is difficult to dispose. In the past, concrete waste ended up in landfills in different parts of the world. New efforts to recycle concrete from collapsed structures still do not salvage all the concrete waste available in the world. In this respect, the continued use of concrete will pose a challenge to the conservation of the environment especially after existing concrete structures outlive their useful lives.
In conclusion, concrete is a very interesting material for designers and architects. Its appeal will remain for a long time to come because of its outstanding qualities. However, more thought must go into how best to use concrete in order to conserve the environment.
Brookes, Alan. Innovation in Architecture: A Path to the Future. New York, NY: Taylor & Francis, 2003. Print.
Fling, Russel S. How to Choose a Concrete Framing System. Aberdeen: The Aberdeen Group, 1988. Print.
Harris, Frances. Global Environmental Issues. Chichester: John Wiley & Sons, 2004. Print.
Li, Zongjin. Advanced Concrete Technology. New York: John Wiley and Sons, 2011. Print.