Building Materials, Third Edition

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because of its versatility. The simple reason for its extensive use in the construction of almost
all civil engineering works is that the properties can be controlled within a wide range by using
appropriate ingredients and by special mechanical, physical and chemical processing techniques.
Buildings—from single storey to multistorey, bridges, piers, dams, weirs, retaining walls,
liquid retaining structures, reservoirs chimneys, bins, silos, runways, pavements, shells, arches,
railway sleepers are but a few examples of cement concrete applications.

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—X Concretes are classified as lime concrete, gypsum concrete and
cement concrete.

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X The cement concrete is specified by proportions of
different ingredients, e.g., 1 (cement) : 1.5 (fine aggregate) : 3 (coarse aggregate). It is presumed
that by adhering to such perspective specifications satisfactory performance may be achieved.
The usual mix proportions of cement concrete are given in Table 10.1. Here, M refers to the mix.
This type of concrete mix is also known as nominal mix. Conventional nominal mix proportions
have limited significance, since the quantity of fine aggregate is fixed irrespective of the cement
content, water-cement ratio and the maximum size of aggregate to be used. The proportions of
materials of nominal mix concrete as given in Table 10.1 are prevalent in field. However, IS: 456
restricts its use only up to M-20 grade.

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XWhen the concrete properties such as strength,
water-cement ratio, compaction factor, slump, etc., are specified the concrete may be classified
as designed-mix concrete.
For a design mix concrete the mix is designed to produce the grade of concrete having the
required workability and a characteristic strength not less than the appropriate values as
specified in Table 10.2.

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X Depending upon the strength (N/mm^2 ) of concrete
cubes (150 mm side) at 28 days, concrete is classified as given in Table 10.2.

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It is further classified as low strength concrete (< 20 N/mm^2 ), medium strength concrete
(20–40 N/mm^2 ) and high strength concrete (>40 N/mm^2 ).

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X On the basis of density, concrete is classified as super heavy (over 2500
kg/m^3 ), dense (1800-2500 kg/m^3 ), light weight (500–1800 kg/m^3 ) and extra light weight concrete
(below 500 kg/m^3 ).