Concrete contractors are among the most important stakeholders in most construction works. While some sustainable structures are made from pure wood and glass, most commercial and industrial buildings are still made from cement. Today, we will look into the basics, importance and advantages of different cement types used in the construction industry.
What is Concrete?
Concrete is a vital element and a vitally important thing that is used in several individual and commercial buildings. It solidifies and hardens after mixing with water and placement due to a chemical process known as hydration. It binds other building materials together. It is a material extensively used in the construction process and is made by mixing aggregate, cement, small stones, sand, gravel, and water. All the components bond together to create a stone-like material.
The Romans invented hydraulic cement-based concrete. The British improved upon it and popularized it in the modern world. The Pantheon in Rome is one of the finest examples of Roman architecture that has survived to this day and has a 42-meter-diameter dome made of poured concrete.
Uses of Cement in Construction
Cement is probably the most used man-made material. Concrete is used to make:
- architectural structures
- roads and bridges
- parking structures
- walls and footings for gates
- fences and poles
How Cement Works
The material grows together from a moldable liquid into a hard, rigid solid. In the world today, concrete has become a fact of modern life. Six billion tons of concrete are used around the world each year. The addition of sand, fine aggregates and coarse aggregates of up to a few centimeters makes concrete. It is a porous material whose properties depend on its different kinds of pore space. Air voids are entrapped in the mixing process, the capillary pores, which are spaces occupied by water from mixing.
Concrete has compressible strength related to the overall porosity of the cement paste and the amount and form of the aggregates.
Cement in Today’s Construction
Concrete in the present infrastructure has been deteriorating at a fast pace due to the corrosion of reinforcing steel coming from the including chloride and other ions from road salts, marine areas and ground soils.
Nowadays, the focus is on the transport aspect of concrete which includes diffusivity, permeability, and absorption. Concrete is a complex composite, which needs improvement, monitoring, and control.
The amount of water in the mix is compared with the cement amount called the water/cement ratio. The lower the water-cement ratio, the stronger the concrete is. It has higher strength and less permeability. The qualities expected of it are resistant to freezing and thawing and deicing chemicals, water-tightness, low permeability, wear resistance, and formidable strength.
Admixtures are additions to the mix which are used to achieve certain goals. When Accelerating admixture-accelerators are added to concrete, they reduce the setting time of the concrete and accelerate strength. The amount of reduction in setting time varies. Retarding admixtures are often used in hot weather conditions to delay setting time. The use of Fly ash reduces the heat generated by the concrete.
Advantages of Using Concrete in Construction
Advantages of concrete. Among all the construction materials used in the world, concrete is most widely used due to its unique benefits compared to other materials. Ten significant advantages of concrete are explained below.
Concrete is Economical
Compared to engineered cementitious materials used for construction, the production cost of cement concrete is very low. Again, it is inexpensive and widely available around the globe when compared to steel, polymers and other construction materials. Major ingredients of concrete are cement, water, and aggregates. All of these are readily available in local markets at a low cost.
Concrete Hardens at Ambient Temperature
Concrete sets, hardens, and gains its strength at regular room temperature or ambient temperature. This is because cement is a low-temperature bonded inorganic material. Thus concrete can be used irrespective of ambient weather conditions and optimized with admixtures if required.
Ability to be Cast into Shape
Fresh concrete is flowable and is in a liquid state. Hence, concrete can be poured into various form-works or shuttering configurations to form desired shapes and sizes at the construction site. Concrete can be cast into complex shapes and configurations by adjusting the mix.
Energy Efficiency in Production
The amount of energy required for the production of concrete is low compared with steel. For plain cement concrete, only 450–750 kWh/ton energy is required and that of reinforced concrete is 800–3200 kWh/ton. Production of structural steel demands 8000 kWh/ton or more to make, which is almost 3-10 times the energy consumption.
Excellent Water Resistance Characteristics
Though chemicals in water can induce corrosion in concrete and reinforced concrete, concrete can withstand water without serious deterioration compared to wood and steel. Due to this property, concrete is ideal for underwater and submerged applications like for building structures, pipelines, dams, canals, linings and waterfront structures Pure water is not deleterious to concrete and not even to reinforced concrete, chemicals dissolved in water such as sulfates, chlorides, and carbon dioxide causes corrosion.
Concrete can withstand high temperatures better than wood and steel. Calcium silicate hydrate, C-S-H, which is the main binder in concrete, can withstand until 910 deg C. Concrete is a bad conductor of heat; it can store a considerable amount of heat from the environment. Concrete can withstand heat for 2–6 hours, enabling sufficient time for rescue operations in case of fire. It is used to fireproof steel and used in high temperature and blast applications.
Ability to Consume and Recycle Waste
Many industrial wastes can be recycled as a substitute for cement or aggregate. This includes fly ash, slag, also known as GGBFS or ground granulated blast-furnaces slag, waste glass, and even ground vehicle tires in concrete. Thus concrete production can significantly reduce environmental impacts due to industrial waste. Using these wastes improves the properties of concrete as well; therefore, the quality of the structure is not compromised.
Application in Reinforced Concrete
Concrete has a comparable coefficient of thermal expansion to steel. “steel 1.2 × 10−5 and concrete 1.0–1.5 × 10−5”. Concrete imparts protection to steel in corrosive environments due to the existence of CH and other alkalies. Moreover, concrete contributes to the compressive strength of reinforced concrete members and structures.
Low or Zero Maintenance Required
Concrete structures do not require coating or painting for regular applications to protect weathering compared to steel or wooden structures where it is inevitable. The coating is to be replaced and redone on a routine basis making the maintenance cost for concrete much lower than that for steel or wood.
One of the major advantages of concrete is its ability to be used in different application methodologies. Concrete is hand applied, poured, pumped, sprayed, grouted and also used for advanced applications like shotcreting in tunnels.
Types of Concrete
In concrete technology, a variety of type-names has been used for different types of concrete. This classification is based on three factors:
- Type of material used in its making.
- Nature of stress conditions.
- And it’s density.
Now, here is a brief account of the different types of concrete:
Plain or Ordinary Concrete
It is one of the most commonly used types of concrete. In this type of concrete, the essential constituents are cement, sand and coarse aggregates designed and mixed with a specified quantity of water.
The ratio of essential constituents may be varied within wide limits. A very commonly used mix design, widely known as Nominal Mix Design, is 1:2:4.
Plain concrete is mostly used to construct pavements and buildings, where very high tensile strength is not required. It is also used in the construction of Dams.
Any type of concrete having a density of less than 1920 Kg/m3 is classed as lightweight concrete.
Various types of aggregates that are used in the manufacturing of lightweight concrete include natural materials like pumice and scoria, artificial materials like expanded shales and clays and processed materials like perlite and vermiculite.
The single important property of lightweight concrete is its very low thermal conductivity.
For example, Thermal conductivity – the k value for plain concrete may be as high as 10-12. But the thermal conductivity of Lightweight concrete is about 0.3.
Lightweight Concretes are used, depending upon their composition, for thermal insulation, for protecting steel structures, they are also used in long-span bridge decks, and even as building blocks.
This type of concrete is also called heavyweight concrete. In this concrete type, the density varies between 3000-4000 Kg/m3.
These types of concrete are prepared by using high density crushed rocks as coarse aggregates. Among such materials, Barytes is the most commonly used material, which has a specific gravity of 4.5.
It is mostly used in atomic power plants and other similar structures because it protects all types of radiation.
It is also called RCC (Reinforced Cement Concrete). In this concrete type, steel in various forms is used as reinforcement to give very high tensile strength.
In fact, it is because of the combined action of plain concrete (having high compressive strength) and steel (having high tensile strength).
The steel reinforcement is cast in rods, bars, meshes, and all conceivable shapes.
Every care is taken to ensure the maximum bond between the reinforcement and the concrete during the setting and hardening process.
Thus, the resulting material (RCC) is capable of bearing all types of stress in any construction. RCC is the most crucial concrete type.
This term refers to numerous types of concrete shapes that are cast into molds either in a factory or at the site.
However, they are not used in construction until they are completely set and hardened in a controlled condition. Some of the examples of Precast Concrete are; precast poles, fence posts, concrete lintels, staircase units, concrete blocks, and cast stones, etc.
These structural and decorative members are prepared in a well-equipped place where all arrangements are made for:
- Perfect proportioning of the ingredients of concrete.
- Thorough mixing of the cement, aggregates, and water to obtain the mix of the desired design and consistency.
- Careful handling during transport and placement in the perfect design molds.
- Perfect curing, under the controlled conditions of temperature and humidity. Even steam curing is used to obtain precast products having high strength in much less time.
- The construction industry’s latest trend is to shift more and more to prefabricated concrete units in building construction.
It is a special type of reinforced concrete in which the reinforcement bars are tensioned before being embedded in the concrete.
Such tensioned wires are held firm at each end while the concrete mix is placed. The result is that when the concrete sets and hardens, the whole concrete members, so the cast is put into compression.
This arrangement makes the lower section of the reinforced concrete stronger against tension, which is the principal cause of the development of tension cracks in un-tensioned reinforced concrete.
Since pre-stressing involves jacks and tensioning equipment, the pre-stressed concrete is also cast in the factories.
Some of its advantages are the following.
- The potential compressive strength of concrete gets considerably increased.
- The risk of the development of tension cracks in the lower sections of beams is considerably reduced.
- The shear resistance is greatly reduced. This eliminates the necessity of stirrups to a great extent.
- Lighter members can be used than the un-tensioned (normal) reinforced-concrete.
- The prestressed concrete is greatly favored in constructing bridges, long-span roofs, and most structures with a heavy dead load.
Air Entrained Concrete
It is a specially prepared plain concrete in which air is entrained in the form of thousands of uniformly distributed particles.
The Volume of air thus, entrained may range between 3-6 percent of the concrete. The air entrainment is achieved by adding a small quantity of foaming or gas-forming agents at the mixing stage.
Fatty acids, fatty alcohols, and resins are some common air-entraining agents. Air entrained concrete is more resistant to Scaling, Deterioration due to freezing and thawing, and Abrasion.
When the recycled glass is used as an aggregate in the concrete, this type of concrete is known as Glass Concrete.
They provide better thermal insulation and also have a great appealing look as compared to other types.
Rapid Hardening Concrete
This type of concrete is mostly used in underwater construction and in repairing roads. Because its hardening time is significantly less, it can be hardened in just a few hours.
They are also used in building construction, where the work should be done fast.
Asphalt concrete is a combination of aggregates and asphalt. It is also known as Asphalt. They are vastly used in the highways, airports, as well as in the embankments.
They can be hardened in just an hour. That is the reason for its vast usage inroads.
In this type of concrete, lime is used as a binding material with the aggregates. Before the invention of cement, the most used concrete was lime concrete.
In today’s age, Lime concrete is also used in floors, domes, and so on.
Roller Compacted Concrete
This concrete is mostly used as a filling material. They don’t have a better strength value. They are lean concrete and are compacted with the help of heavy means, like rollers.
A significantly less amount of cement is used in this type of concrete.
They are ordinary concrete with some little differences and are mostly used for architectural purposes.
A stamp of different shape and design placed on the concrete structures when they are in their plastic state to acquire an appealing look design.
Pigments are used for color purposes of different types to give it a more realistic and appealing look.
Pumped concrete is used for high rise buildings where concrete conveyance other than the pump is not an easy task.
They are made workable enough for an easy conveyance. Fines materials are used for a better supply. The finer the material is, the easier the discharge will be.
The pump used for conveyance purposes is made from rigid or flexible materials to discharge the concrete easily.
In this type, more quantity of water is added to the concrete mix, and then the mixture is poured into the form-work.
The excess water is then removed from the concrete with the help of a vacuum pump. That is why it is called vacuum concrete.
This technique is used to attain the strength of concrete early. It will attain the compressive strength within 10 days compared to 28 days of ordinary concrete.
Permeable concrete is prepared in such a manner that the water can be passed in it. They have about 15 to 20% voids so that the water can pass in it.
They are used in those areas where stormwater issues persist.
Shotcrete is concrete prepared in the same manner as ordinary, but the difference is that they are placed differently.
They are placed with the help of higher air pressure through nozzles. The benefit of this technique is that the compaction and placing of concrete will be done simultaneously.
This concrete type is prepared in concrete plants and or transported with the help of truck-mounted transit mixtures.
Once they are reached at the site then, there is no further treatment necessary.
The plant location will be at an adjustable location so that the concrete can be supplied before the setting time can be started.
These types of concrete are compacted by their weight, mean by the process of consolidation. There is no need to use a vibrator or doing manual compaction.
The workability of concrete is always high in this type. That is the reason it is also known as flowing concrete.
Fiber Reinforced Concrete
The type of concrete in which steel fibers 10 to 20 microns in diameter and 10 to 50 mm in length is used.
Fiber increases resilience, tensile strength, flexibility, and other qualities.
The fibers may be of different materials like steel, polymer, glass, carbon, or even natural fibers like coconut fiber.
Some types of fibers react with the cement; special care should be taken while using them. It has been used mostly as overlays for pavements in bridges, airports, and industrial floors.
Fiber reinforced concrete can also be used in places where increased resistance to cracking is required.
Fly Ash Concrete
Concrete using fly ash is called fly ash concrete. Fly ash is obtained from coals. Fly ash can be used to replace fine aggregates or cement or to replace partially both.
Up to 30 percent replacement of fine aggregates and 20 percent replacement of cement have been reported.
Fly ash improves workability in the fresh concrete and durability and strength in hardened concrete.
The particles of fly ash should be finer than cement particles.
High Strength Concrete
High-strength concrete is concrete with a strength over 40 N/mm2. It is also known as High-performance concrete (HPC).
High-performance concrete is used to achieve some special concrete properties like high strength, low shrinkage, self-compaction, high fire resistance, etc.
Normally, such concrete’s strength should be over 60 N/mm2 (Strengths up to 80 N/mm2 have been reported).
The materials used in the HPC are the following:
- Coarse and fine aggregates of the required quality
- Supplementary cementing materials like silica fume, fly ash, blast furnace slag, etc.
- Superplasticizers (high water reducing agents)
- Air entraining agents (optional)
Silica Fume Concrete
Silica fume is a byproduct of silica, which is very finely divided in the industry. Concrete in which silica fume is used is called “silica fume concrete.”
The typical concrete with a normal water-cement ratio always has micro-pores, which limits the strength of regular concrete.
Silica fumes consist of very fine particles (actually, six times finer than cement particles).
Hence, if it is added to the concrete mix, the minute pore spaces can be reduced, resulting in high-strength concrete.
Polymerization is a process of conversion of monomers into polymers. In typical concrete, you should have seen that micro-pores cannot be avoided.
The impregnation of monomer into these pores and subsequent polymerization is the technique that has been developed recently to reduce the porosity of the concrete and to improve its strength and other properties.
The following are the four types of polymer concrete materials available at present:
- Polymer impregnated concrete (PIC)
- Polymer Portland cement concrete (PPCC)
- Polymer concrete (PC)
- Partially-impregnated and surface-coated polymer concrete
Ferro Cement Concrete
Ferro cement concrete should not be confused with fiber concrete. Ferro cement consists of closely spaced wire-meshes which are impregnated with a rich mix of cement mortar.
Usually, 0.5 to 1.0 mm diameter steel wires are formed into meshes.
Mortar 1:2 to 1:3 with a water-cement ratio of 0.4 to 0.45 is poured into the form-work with fabricated steel by using layers of the wire mesh.
The steel content of this concrete will be as high as 300 to 500 kg/m3 of mortar. As the material consists of a large percentage of steel, it has high ductility and tensile strength.
The material was developed in 1940 by the Italian architect P. L. Nervi to build a large number of pleasing structural forms.
Generally, concrete is prepared by mixing different ingredients.
However, it is also possible to pack some of the ingredients (coarse aggregate) in the form-work and then fill the pores with specially prepared cement-sand grout so that it will fill all the pores and form a concrete mass.
Pre-packed concrete is used in special situations, such as where a large volume of concrete (like a large machine block foundation) has to be concreted without construction joints.
One of the advantages of pre-packed concrete is that it has very little shrinkage.
Concrete is an essential part of any construction project. But you don’t even need a professional to tell you that concrete forms a crucial part of any building or structure. Just take a look at the buildings surrounding you, the pavements you walk on, and other various structures around. Concrete is everywhere.
To make the most of its properties, you just need to realize which concrete type is best for a particular project.