What is Concrete?
Concrete is a composite building material consist of aggregate bonded together with a fluidic cement which gets harden over time. Most use of the term "concrete" refers to Portland cement concrete or to concretes made with other hydraulic cements, such as ciment fondu. However, road surfaces are also a type of concrete, known as "asphaltic concrete", where the cement material is bitumen.
Types of Concrete:-
1. Normal concrete
2. High Strength Concrete
3. High Performance Concrete
4. Air Entrained Concrete
5. Light Weight Concrete
6. Self Compacting Concrete
7. Shotcrete
8. Pervious Concrete
9. Roller Compacted Concrete
Composition of Concrete:-
• Cement - Ordinary Portland Cement , Portland
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a) Used as structural concrete-Used to construct structural members such as Reinforced Cement Concrete ( RCC) and Pre-Stressed Concrete (PSC) members and
b) Used as a protection material to structural steel against fire – Primarily Plain Cement Concrete (PCC)
Material properties:-
1. Thermal Expansion:- Thermal expansion is the characteristics of matter to change in shape, area, and volume in relation to a change in temperature, through heat transfer.
There are four properties which play a vital role in thermal expansion of concrete:-
• The type of cement content in the concrete
• The type of aggregate, i.e Coarse, fine, carbonecious, silicious,etc.
• Water content in the concrete when there is change or deviation in temperature
• Age of concrete
Concrete has a positive coefficient of thermal expansion.
Which is an indication that when there is a rise in temperature, the thermal expansion of concrete increases.
However the rate of increase in thermal expansion is not linear.
2. Thermal Conductivity:- Thermal conductivity is defined as the quantity of heat that flows in one second through a cube of unit size and when the opposite faces of the cubes is maintained at a temperature difference of 1
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• The thermal diffusivity decreases with increase in temperature.
5. Compressive Strength of Concrete:-
Compressive strength of concrete depends on the relative proportion of individual materials present in the concrete.
Influence of temperature on the strength of concrete depends on the strength behaviour of various materials present in concrete as well.
Concrete loses strength with increase in temperature.
It is interesting to note that up to about 200 C, the reduction in the strength of concrete is nominal.
On the other hand, when temperature reaches at 500 C and above, concrete starts deteriorating its strength rapidly.
With the development of temperature in concrete, the ferric oxide present in aggregate becomes dehydrated or get reacted with lime present in cement paste.
This results a color change in the concrete and the process is irreversible.
The colour change occurs at a fairly well defined temperature as indicated below.
up to about 300 C - There is no change in the colour of the concrete( normal colour is gray )
at 300 C - Colour changes to Pink, Red or Reddish
Most people may not realise but concrete plays a vital part in our lives daily. It shapes and creates the built environment in which we are surrounded by, such as schools, bridges, roads, housing, hospitals, dams and so much mores. Concrete is the most used man made material in the world, averaging around 3 tonnes annually for each person. In comparison with other building materials such as wood, steel, plastic and aluminium, over twice as much concrete is used globally than any of these materials. It is the material choice of most purposes due to its strength, durability, thermal mass and its cost.
In this paper we have studied compressive strength of concrete by replacing natural aggregate with recycled aggregate by 25%, 50% and 75%.This mixture formed in the sample of cubes of dimension 150x150x150mm3.
Aitcin P.C, “Cements of yesterday and today Concrete of tomorrow”, Cement and Concrete Research, Vol. 30, (2000), pp 1349 - 1359.
2) While many High Performance Concretes exhibits rapid stiffening and early strength gain, other’s may have long set times and low early strengths.
[20] BS Part 116: 1983. Testing Concrete and determination of compressive strength. British Standards Institution ;
Concrete is one of the world’s most popular construction materials. Some six billion tonnes of concrete is produced each year in the world, making it approximately one ton of concrete for every human being per year (Fardis, 2012, p.116). However, the lifecycle of concrete does not make it the most sustainable building material at the moment. Because of limited natural resources, concerns over green house gases, and landfill problems, concrete production is being cut-back, or at least cannot be increased to keep up with population increase. In this essay, I will look at what makes concrete an unsustainable material and possible solutions to make concrete a more sustainable material.
Aggregate: in cement concrete to gain good quality aggregates are used in two groups. Sand and coarse
In this report, we will introduce and illustrate on precast concrete, pre-stressed concrete, ready-mix concrete, reinforced concrete, terrazzo and Urbanite in details.
Through investigating the various properties of Cement/Concrete/Mortar, Glass, and Ceramics/Porcelain I have come to understand the chemical composition, type of bond, structure, and the daily use of each of the substances. Cement is composed of calcium which usually is acquired from limestone and silicon which is usually from sand, shale or clay (aluminosilicates). The structure of cement is in between the two extremes of an ionic and a covalent model. It is between an ionic oxide lattice and a tetrahedral covalent network. Cement when wet or when dry has both cohesive and adhesive properties. Concrete is created through the mixture of cement (filler), fine and coarse aggregate (binder), and water. With the characteristics of these materials, concrete’s type of bond attributes to its high thermal insulation properties and the strength of the material itself. Concrete is used for building materials and due to its thermal insulation properties as insulators. Mortar is a mixture of cementitious materials, water, and aggregate. For commercial use in buildings and constructions, it is useful by having water retentivity and its strength after stiffening and hardening. In addition, the content in the mortar of cement as well as air content affects the strength of the tensile bond between the mortar and the masonry. Due to the materials that compose mortar, it developed a chemical structure that is similar to its components. Also, in daily use, mortar is used for construction for buildings to attach segments together.
Ordinary Portland cement (C 53 grade) conforming to the requirements of IS 12269 (ASTM C 150-85A) was used in the study. Natural river sand was used as fine aggregate and crushed angular granite stone was used as coarse aggregate. Coarse aggregate with combined grading of 50% passing through 20mm sieve and retained on 12.5mm and 50% passing through 12.5mm and retained on 4.75mm sieve conforming to IRC 44 was adopted.
The increased cohesiveness of concrete makes it more liable for surface scaling in frosty weather.
...nd Calderwood 1978; Suaris and Shah 1984), because it requires higher energy to split the fibers from the concrete.
They reduce the cost of construction, modify the properties of concrete and improve the quality of concrete during mixing, transportation, placing and curing.
The two properties were usually used to estimate the tensile strength of concrete; however, they didn’t usually yield the same results. Taguchi's optimization technique was employed to reduce the number of trials needed to get the results. The results showed that the splitting tensile strength ranged between 60-80% of the modulus of rupture which was also known as the flexural strength.
Okamura, H., and Ouchi, M. (2003). Self-compacting concrete. Journal of Advanced Concrete Technology, 1 (1), 5-15. Retrieved 28 November, 2011 from http://www.eng-forum.com/articles/articles/selfconcrete.pdf