Concrete is the composite material that is composed of a mixture of fine and coarse aggregates bonded together with biding material which hardens over time. The binding material mostly includes fluid cement paste, lime putty, lime etc.
In other words, when water is added to a mixture of cement, fine and coarse aggregates, a workable paste is formed which hardens with time. Such paste is known as concrete.
The binding material such as cement reacts with the water and other constituents to form a hard matrix that binds the materials together into a durable stone-like material that has many uses. Concrete is a type of construction material used all over the world. It is often said that the present age is a concrete age.
Concrete is extensively used for the construction of columns, beams, foundations, slabs and other load-bearing elements of buildings, roads, dams, bridges etc.
The growing popularity of the concrete in civil engineering works is due to its distinctive characteristics like strength, durability, low-maintenance, energy-efficiency and sustainability.
The major application areas of concrete include the following:
b. Residential and Commercial Buildings
c. Roads and Driveways
e. Culverts and Sewers
g. Concrete Bridges
h. Marine Constructions
2. Types of Concrete
The classification of concrete is done based on various factors such as types of material used in the preparation of concrete, the density of concrete, nature of the stress conditions etc. The different types of concrete have been further discussed below:
a. Plain Concrete / Ordinary Concrete
Plain concrete is also commonly referred to as ordinary concrete.
It is one of the most extensively used concrete all over the world.
The plain concrete essentially constitutes of cement, sand, and coarse aggregates mixed with a definite proportion of water.
The proportion of the different constitutes may vary depending upon the application of the concrete. The most commonly adopted proportion of plain concrete is 1:2:4.
Plain concrete is widely used for the construction of buildings, pavements, dams and other structures where high tensile strength is generally not required.
Some of the important properties of plain concrete can be listed as follows:
a. The density of plain concrete varies from 2200 kg/m³ to 2500 kg/m³.
b. The compressive strength of plain concrete varies from 200 kg/cm² to 500 kg/cm².
c. The degree of durability of plan concrete is satisfactory.
Some of the uses of Plain Concrete can be listed as follows:
a. It can be used as bed concrete below the wall footings, column footings as well as on the walls below the beams.
b. It can be used as sill concrete to achieve an even and hard surface at the window sills and the ventilator sills.
c. It can be used for the coping works over the parapet walls and the compound walls.
d. It can be used for the construction of buildings, retaining walls and pavements that do not require high tensile strength.
e. It can be used for the dam construction and lining of storage tanks and reservoirs.
f. It can also be used for the plinth protection works.
However, a major limitation of Plain Concrete is that it is not suitable for construction of the structures that are likely to be subjected to wind loads, seismic loads etc.
b. Lightweight Concrete
Lightweight concrete can be defined as the type of concrete that has a density of less than 1920kg/m³.
The lightweight concrete is also commonly referred to as the cellular concrete.
This type of concrete contains a mixture of lightweight coarse aggregates, fine aggregates, binding material and water in a definite proportion.
The lightweight aggregates that are commonly used include expanded shale, clay and other similar materials that have been burned in a rotary kiln and thus have developed a porous structure.
Sometimes, blast furnace slag is also used as aggregate for the lightweight concrete.
Mostly, the density of the lightweight concrete may vary between 1440kg/m³ to 1840kg/m³.
Some of the uses of lightweight concrete can be listed as follows:
a. It is extensively used for the screeds and thickening purposes such as thickening of roofs, floors etc.
b. It can be used for the casting of structural steel to prevent it from fire hazards, corrosion etc.
c. It can be used for the heat insulation on roofs as well as for the insulation of water pipes and walls.
d. It can be used for the construction of general partition walls and panel walls in the frame structures.
e. It can be used for the surface rendering of external walls in residential buildings.
f. The possibility of spalling is relatively lower in lightweight concrete.
Some of the advantages of lightweight concrete can be listed as follows:
a. The lightweight concrete greatly reduces the dead load and thus allows longer span.
b. The decreased dead load also ensures lower haulage and handling costs and thus a faster construction rate can be achieved.
c. The use of lightweight concrete in the construction of floors, partition walls, external cladding and other structural members of the frame structures can offer greater flexibility in design and also save the time and cost of construction.
d. Due to the low thermal conductivity of the lightweight concrete, it can be used for the insulation works.
However, a major disadvantage of the lightweight concrete is that the depth within which corrosion can occur is nearly twice than that of normal concrete.
c. High-Density Concrete
As the name itself implies, it has a relatively higher density than other types of concrete.
This type of concrete is also commonly referred to as the heavyweight concrete.
The high-density concrete is manufactured from the high density crushed rocks and similar coarse aggregates such as barites, magnetites etc.
Mostly, the density of such concrete ranges from 3000 kg/m³ to 4000 kg/m³.
Some of the important uses of high-density concrete can be listed as follows:
a. It is extensively used in nuclear power plants and similar structures.
b. It is also used for high-density radiation shielding purposes.
Some of the advantages offered by high-density concrete can be listed as follows:
a. It offers high gamma-ray and neutron attenuation.
b. This type of concrete has good mechanical properties and is suitable for a wide range of structural constructions.
However, the major disadvantage of the high-density concrete is that it has an extremely heavyweight and thus the handling of such concrete may be troublesome.
d. Reinforced Concrete
The reinforced concrete is very commonly referred to as RCC i.e. reinforced cement concrete.
It is obtained from the conventional cement concrete after the addition of reinforcement in it. The reinforcement includes the steel bars, rods and meshes.
The primary objective of using the reinforced concrete is to ensure that the concrete has considerable compressive as well as tensile strength.
It is made such that the reinforcements withstand the tensile forces while the concrete withstands the compressive forces.
Some of the advantages of reinforced concrete can be listed as follows:
a. It imparts high compressive and tensile strength.
b. It offers good durability with low maintenance costs.
c. It offers considerable resistance to fire hazard and weathering.
d. The construction using this type of concrete requires less skilled manpower.
Some of the disadvantages of reinforced concrete can be listed as follows:
a. It does not have certainty of final strength i.e. the final strength of the reinforced concrete depends upon mixing, casting and curing of the concrete.
b. This type of concrete is prone to the development of shrinkage cracks.
c. The tensile strength of reinforced concrete is only about one-tenth of the compressive strength.
e. Precast Concrete
Precast concrete is a construction product produced by casting the concrete in the steel or timber mould which is then cured and transported to the site for assembling.
This type of concrete is used in the beams, columns, panels, floors, tunnels, concrete lintels, staircase units, fence and precast poles etc.
The major applications of the precast concrete can be listed as follows:
a. It is extensively used in the structural components such as beams, columns, panel walls, floors etc.
b. It is also used for making various forms of pre-stressed precast building elements.
c. It is used for the various utilities such as water tanks, drainage chambers, septic tanks, tunnels etc.
d. It can be easily moulded into any desired shape and thus are used in various architectural monuments, sculptures etc.
The major disadvantage of precast concrete is that it is extremely heavy and large. Thus, the handling and assembling of the precast concrete can pose significant difficulties.
f. Pre-stressed Concrete
It essentially consists of reinforcement bars that have been tensioned beforehand.
In other words, it is the type of concrete that permits the inclusion of predetermined engineering stresses on it to counteract the stresses induced due to loading.
The pre-stressed concrete not only have considerable compressive strength but also have considerable tensile strength. This is ensured by utilizing the high compressive strength of the concrete along with the high tensile strength of the reinforcement bars.
It is the strongest and most reliable type of concrete. It is extensively used for the massive structures constructions and various structural components such as columns, floor beams and utilities such as railway sleepers, roofing etc.
Some of the main advantages offered by the pre-stressed concrete can be listed as follows:
a. It offers a very high degree of durability and reliability.
b. It has higher strength and thus can withstand massive loads.
c. It requires fewer joints and lesser construction materials.
Some of the disadvantages of prestressed concrete can be listed as follows:
a. Pre-tensioning of the reinforcement bars must be done before they are embedded in the concrete.
b. The installation of the pre-stressed concrete requires special equipment and tools such as anchorage, jacks etc as well as highly skilled manpower.
c. The cost of prestressed concrete is relatively higher.
g. Air-Entrained Concrete
Air-entrained concrete consists of microscopic air bubbles that comprise about 4 to 7 % of the total concrete volume.
In this regard, the air-entrained concrete is manufactured using certain air-entraining agents such as air-entraining admixtures and similar cement.
The most common types of air-entraining agents used include fatty acids, resins and fatty alcohols.
The air bubbles in the concrete are microscopic with varying sizes.
The main purpose of adding the air bubbles in the concrete is to remove or minimize the internal pressure by allowing space for the water to extend during the freezing of water.
Some of the advantages of air-entrained concrete can be listed as follows:
a. It offers a high degree of resistance to alternate freezing and thawing actions.
b. It is less susceptible to deterioration by abrasion, shrinkage crack and scaling.
c. It offers a greater degree of workability.
However, the major drawback of the air-entrained concrete is that the addition of the air-entraining agent significantly increases the porosity of the concrete thereby increasing the total unit weight of the concrete.
h. Lime Concrete
As the name itself implies, lime is used as binding material.
It is a mixture of coarse aggregates, fine aggregates and lime in a suitable proportion of water.
Lime concrete was used extensively in ancient times.
Some of the important properties of lime concrete can be listed as follows:
a. It is capable of withstanding considerable magnitude of loads.
b. It offers a high degree of plasticity as well as workability.
c. It has good resistance to weathering actions.
d. It also possesses significant waterproofing property and volumetric stability.
e. The setting time of lime concrete is relatively longer.
f. It consumes less energy during production and the carbon dioxide emitted is also lower.
Some of the advantages offered by lime concrete can be listed as follows:
a. It is cheap and readily available.
b. It is suitable for almost all type of load-bearing constructions such as beams, columns, walls etc.
c. Due to its waterproofing property, lime concrete can be used to prevent the dampness in floors and walls.
Some of the disadvantages of lime concrete can be listed as follows:
a. It takes a considerably longer time to set.
b.The curing period of lime concrete is also longer.
c. The time taken by the lime concrete to gain strength is longer.
i. Rapid Hardening Concrete
As the name itself implies, it hardens within a very short period.
The hardening time of such concrete is only about 30 mins.
Due to the quick hardening property, it is extensively used in the construction works that have to be completed within a short period.
Some of the major uses of rapid hardening concrete can be listed as follows:
a. It is widely used for the repair of road pavements.
b. It is also used for underwater construction works.
j. Asphalt Concrete
Asphalt Concrete is made up of a mixture of aggregates and asphalt cement.
Asphalt concrete is also commonly known as asphalt or blacktop.
Generally, the composition of asphalt concrete consists of 90-95% of aggregates and 5-10% of asphalt cement.
This type of concrete also hardens within a relatively short period.
Some of the uses of asphalt concrete can be listed as follows:
a. It is widely used for the surfacing as well as repairing of the highway pavements, runways in airports and parking lots.
b. It is also used for the construction of the core of embankment dams.
k. Glass Concrete
Glass concrete essentially consists of a mixture of binding materials and recycled glass as the aggregates. It is a modern type of concrete.
The addition of recycled glass in the concrete enhances the thermal insulation properties.
Glass concrete is used for the architecturally important structures due to its pleasing aesthetic properties.
l. Roller Compacted Concrete
Roller compacted concrete is the lean concrete that is placed and duly compacted utilizing heavy earth moving equipment.
The most commonly used earthmoving equipment for this purpose is the heavy roller.
Roller compacted concrete consists of a very little amount of the binding material i.e. cement. Due to this reason, the roller compacted concrete is mostly used for the filling and excavation works.
Once the concrete is placed, compaction is done to ensure the concrete gains high density and forms a hard monolithic block.
m. Stamped Concrete
Stamped Concrete consists of a mixture of aggregates, binding materials and stamped materials.
Usually, the stamps of various design and pigments of different colours are added during the plastic state to the concrete to increase the aesthetic appearance of the concrete.
The commonly used stamps are replicate stones, slate, flagstone, tile, brick etc.
Stamped concrete is widely employed for the architectural purpose such as for patios, pool decks, driveways etc.
Some of the advantages of the stamped concrete can be listed as follows:
a. It greatly increases the aesthetic value of the constructions where it is used.
b. It is cheaper than pavers, bricks and tiles.
c. The stamped concrete offers great flexibility in terms of design and colour.
d. It is quite durable with a long life span.
Some of the disadvantages of stamped concrete can be listed as follows:
a. It is more susceptible to develop cracks.
b. It requires relatively more maintenance and repair.
c. It is also prone to damage by the alternate freezing and thawing action.
n. Pumped Concrete
Pumped concrete is transported utilizing rigid pipes or flexible hoes at suitable pressure and directly discharged to the desired area.
Mostly, such pumping of the concrete is done when there is a limitation of space.
The common types of the pumping equipment used includes piston-type concrete pump, pneumatic type concrete pump and squeeze pressure type concrete pump and the conveying equipment includes rigid pipes, flexible hose, couplings etc.
The concrete must be mixed into a very workable mix so that it can easily be pumped.
For the ease of conveyance and discharge, a sufficient amount of the fines are added to the mix.
Pumped concrete is extensively used for high rise buildings where other means of concrete transportation is difficult.
o. Vacuum Concrete
In the vacuum concrete, a significant amount of water is first added to the concrete mix then the mixture is duly poured in the formwork and finally the excess water is removed utilizing the vacuum pump or vacuum mats. Thus, the name vacuum concrete is given to this type of concrete.
The main purpose of dewatering the excess water from the concrete is to ensure early gain of strength of concrete.
Usually, the vacuum concrete gains its strength within 10 days.
Some of the advantages of vacuum concrete can be listed as follows:
a. The curing period of vacuum concrete is very short.
b. The bond strength of vacuum concrete is about 20% higher than that of ordinary concrete.
c, The final strength of the vacuum concrete is also 25% higher than that of the ordinary concrete.
d. Vacuum concrete has a relatively higher density.
e. This concrete also hardens rapidly and the formworks can be removed within thirty minutes of pouring the concrete.
Some of the disadvantages of vacuum concrete can be listed as follows:
a. Vacuum concrete is more prone to damage by seepage and joint breakage.
p. Permeable Concrete
As the name itself implies, it permits a certain amount of water to pass through it.
Permeable concrete is designed such that it has high porosity.
The void content in the permeable concrete is about 15 to 20% to ensure the passage of water.
This type of concrete is highly suitable for areas where the passing of runoff and stormwater exists.
It is used extensively in the sustainable construction techniques in the parking areas, greenhouses, side lots etc.
Shortcrete consists of the mixture of water, aggregates and binding materials like the ordinary concrete but is sprayed pneumatically utilizing a nozzle.
The spraying of the shortcrete is done at a high velocity to ensure a homogenous mass of concrete.
Apart from the regular constituents, the shortcrete also includes some additives such as silica fumes to improve its characteristics.
Shortcrete if mixed and applied properly, develops high strength and is highly durable.
r. Ready-mix Concrete
Ready-mix concrete is already mixed and can be directly transported to the site.
Such type of concrete is prepared in the concrete plants and transported utilizing transit mounted trucks.
It is highly suitable when the works have to be completed within a short period.
Some of the advantages offered by the ready-mix concrete can be listed as follows:
a. It reduces the total time required for the completion of works thereby ensuring the speed of construction.
b. The use of ready-mix concrete reduces the overhead costs of labour.
c. It reduces the possible wastage of materials and has less impact on the environment.
s. Self Consolidated Concrete
Self consolidated concrete is also commonly referred to as self-compacting concrete (SCC).
Self consolidated concrete essentially consists of an extremely flowable mix that can easily flow through the formwork.
Thus it does not require any form of mechanical consolidation.
This type of concrete is non-segregating in nature and offers a high degree of workability.
t. Fibre Reinforced Concrete
Fibre Reinforced Concrete consists of a mixture of aggregates, binding materials and uniformly dispersed fibres.
Mostly, the fibre used includes steel fibres having a diameter ranging from 10 to 20 microns and having a length of 10 to 50mm.
However, fibres made up of polymers, glass carbon etc may also be used.
The primary objective of adding such fibre is to increase the tensile strength, resilience and flexibility of the concrete.
Fibre-reinforced concrete is extensively used as the overlays for road pavements, bridges, runways etc.
u. Fly Ash Concrete
Fly ash concrete essentially consists of fly ash.
The fly ash may be used in place of the fine aggregates or cement or even both in some cases.
The most widely used replacement proportion is 30 % of fine aggregates and 20 % of cement.
The most commonly used fly ash is the one obtained from coals that is finer than cement particles.
The primary objective of adding fly ash is to enhance the workability and durability of the concrete.
v. High-Strength Concrete
High-strength concrete is also commonly referred to as high-performance concrete (HPC).
The concrete having a strength greater than 40N/mm² is known as high-strength concrete.
In general, the strength of such concrete ranges from 60N/mm² to 80N/mm².
The general composition of the high strength concrete consists of aggregates, binding materials, water and additives such as fly ash silica fumes, superplasticizers etc.
Some of the important properties of high-strength concrete can be listed as follows:
a. It consists of very high strength and has good resistance to heavy loadings.
b. It also offers a high degree of resistance to fire hazards and shrinkage.
c. It has fair self-compacting property.
w. Silica Fume Concrete
Silica Fume Concrete consists of silica fumes added to it.
The silica fume is a finely divided particle mostly obtained as the by-product of silica.
The silica fumes are in actual six times finer than the cement particles.
The primary objective of adding the silica fumes is to reduce the pore spaces in the concrete thereby ensuring that the concrete gains high strength.
x. Polymer concrete
Polymer concrete consists of additional substances known as polymers.
The primary objective of this concrete is same as that of the silica fume concrete i.e. to increase the strength of the concrete by reducing the pore spaces present in the concrete.
The polymer concrete can be further classified into the following types:
d. Partially Impregnated and Surface Coated Polymer Concrete
y. Ferro Cement Concrete
The Ferro cement concrete is a mixture of water, aggregates, binding materials (cement) and wire meshes.
The wire meshes are impregnated into the cement concrete in a closely spaced manner.
Mostly, the steel wires of diameter ranging from 0.5to 1mm are used to form such meshes.
The primary objective of adding such wire meshes is to increase the tensile strength and ductility of the concrete.
z. Pre-Packed Concrete
Pre-packed concrete is the type of concrete in which the coarse aggregate is first packed into the formwork followed by the pouring of cement-sand grout.
The addition of the cement-sand grout ensures that all the pores of the pre-packed aggregates are filled thereby eliminating the shrinkage.
Such type of concrete is extensively used for large constructions with construction joints.
|Read More: Grades of Concrete|
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