CEMENT - THE BINDER

CEMENT

       Cement is used as a binding material in the construction. The cement is obtained by burning a mixture of calcium and clay material at a very high temperature and then grinding the clinker so produced to a fine powder. In the year 1924, The Portland cement was first produced by a mason Joseph Aspdin in England.

Types of Cement

In addition to ordinary portland cement there are many varieties of cement. Important varieties are

briefly explained below:

(i) White Cement: 

       The cement when made free from colouring oxides of iron, manganese and chlorium results into white cement. In the manufacture of this cement, the oil fuel is used instead of coal for burning. White cement is used for the floor finishes, plastering, ornamental works etc. In swimming

pools white cement is used to replace glazed tiles. It is used for fixing marbles and glazed tiles.

(ii) Coloured Cement: 

      The cements of desired colours are produced by intimately mixing pigments with ordinary cement. The chlorium oxide gives green colour. Cobalt produce blue colour. Iron oxide with different proportion produce brown, red or yellow colour. Addition of manganese dioxide gives black or brown coloured cement. These cements are used for giving finishing touches to floors, walls, window sills, roofs etc.

(iii) Quick Setting Cement: 

       Quick setting cement is produced by reducing the percentage of gypsum and adding a small amount of aluminium sulphate during the manufacture of cement. Finer grinding also adds to quick setting property. This cement starts setting within 5 minutes after adding water and becomes hard mass within 30 minutes. This cement is used to lay concrete under static or slowly running water.

(iv) Rapid Hardening Cement: 

    This cement can be produced by increasing lime content and burning at high temperature while manufacturing cement. Grinding to very fine is also necessary. Though the initial and final setting time of this cement is the same as that of portland cement, it gains strength in early days. This property helps in earlier removal of formworks and speed in construction activity.

(v) Low Heat Cement: 

      In mass concrete works like construction of dams, heat produced due to hydration of cement will not get dispersed easily. This may give rise to cracks. Hence in such constructions it is preferable to use low heat cement. This cement contains low percentage (5%) of tricalcium aluminate (C3A) and higher percentage (46%) of dicalcium silicate (C2S).

(vi) Pozzolana Cement:

     Pozzolana is a volcanic power found in Italy. It can be processed from shales and certain types of clay also. In this cement pozzolana material is 10 to 30 per cent. It can resist action of sulphate. It releases less heat during setting. It imparts higher degree of water tightness. Its tensile strength is high but compressive strength is low. It is used for mass concrete works. It is also used in sewage line works.

(vii) Expanding Cement: 

       This cement expands as it sets. This property is achieved by adding expanding medium like sulphoaluminate and a stabilizing agent to ordinary cement. This is used for filling the cracks in concrete structures.

(viii) High Alumina Cement:

      It is manufactured by calcining a mixture of lime and bauxite. It is more resistant to sulphate and acid attack. It develops almost full strength within 24 hours of adding water. It is used for under water works.

(ix) Blast Furnace Cement:

     In the manufacture of pig iron, slag comes out as a waste product. By grinding clinkers of cement with about 60 to 65 percent of slag, this cement is produced. The properties of this cement are more or less same as ordinary cement, but it is cheap, since it utilise waste product. This cement is durable but it gains the strength slowly and hence needs longer period of curing.

(x) Acid Resistant Cement: 

     This cement is produced by adding acid resistant aggregated such

as quartz, quartzite, sodium silicate or soluble glass. This cement has good resistance to action of acid

and water. It is commonly used in the construction of chemical factories.

(xi) Sulphate Resistant Cement:

      By keeping the percentage of tricalcium aluminate C3A below five per cent in ordinary cement this cement is produced. It is used in the construction of structures which are likely to be damaged by alkaline conditions. Examples of such structures are canals, culverts etc.

(xii) Fly Ash Blended Cement: 

     Fly ash is a byproduct in thermal stations. The particles of fly ash are very minute and they fly in the air, creating air pollution problems. Thermal power stations have to spend lot of money to arrest fly ash and dispose safely. It is found that one of the best way to dispose fly ash is to mix it with cement in controlled condition and derive some of the beneficiary effects on cement. Nowadays cement factories produce the fly ash in their own thermal stations or borrow it from other thermal stations and further process it to make it suitable to blend with cement. 20 to 30% fly

ash is used for blending.

          Fly ash blended cements have superior quality of resistance to weathering action. The ultimate

strength gained is the same as that with ordinary portland cement. However strength gained in the initial stage is slow. 

 Properties of Ordinary Portland Cement

(i) Chemical properties: 

     Portland cement consists of the following chemical compounds:

        (a) Tricalcium silicate 3 CaO.SiO2 (C3S) 40%

        (b) Dicalcium silicate 2CaO.SiO2 (C2S) 30%

        (c) Tricalcium aluminate 3CaO.Al2O3 (C3A) 11%

        (d) Tetracalcium aluminate 4CaO.Al2O3.Fe2O3 (C3AF) 11%

                     There may be small quantities of impurities present such as calcium oxide (CaO) and magnesium oxide (MgO).

          When water is added to cement, C3A is the first to react and cause initial set. It generates great

amount of heat. C3S hydrates early and develops strength in the first 28 days. It also generates heat. C2S is the next to hydrate. It hydrates slowly and is responsible for increase in ultimate strength. C4AF is comparatively inactive compound.

(ii) Physical properties: 

       The following physical properties should be checked before selecting a portland cement for the civil engineering works. IS 269–1967 specifies the method of testing and prescribes the limits:

     (a) Fineness 

     (b) Setting time

     (c) Soundness 

     (d) Crushing strength.

(a) Fineness:

        It is measured in terms of percentage of weight retained after sieving the cement

through 90 micron sieve or by surface area of cement in square centimeters per gramme of cement.

According to IS code specification weight retained on the sieve should not be more than 10 per cent. In terms of specific surface should not be less than 2250 cm2/gm. 

(b) Setting time:

         A period of 30 minutes as minimum setting time for initial setting and a maximum

period of 600 minutes as maximum setting time is specified by IS code, provided the tests are conducted as per the procedure prescribed by IS 269-1967.

(c) Soundness:

     Once the concrete has hardened it is necessary to ensure that no volumetric

changes takes place. The cement is said to be unsound, if it exhibits volumetric instability after hardening. IS code recommends test with Le Chatelier mould for testing this property. At the end of the test, the indicator of Le Chatelier mould should not expand by more than 10 mm.

(d) Crushing strength:

      For this mortar cubes are made with standard sand and tested in compression testing machine as per the specification of IS code. The minimum strength specified is 16 N/mm2 after 3 days and 22 N/mm2 after 7 days of curing.

Uses of Cement

Cement is used widely for the construction of various structures. Some of them are listed below:

    (i) Cement slurry is used for filling cracks in concrete structures.

    (ii) Cement mortar is used for masonry work, plastering and pointing.

    (iii) Cement concrete is used for the construction of various structures like buildings, bridges.

        water tanks, tunnels, docks, harhours etc.

   (iv) Cement is used to manufacture lamp posts, telephone posts, railway sleepers, piles etc.

   (v) For manufacturing cement pipes, garden seats, dust bins, flower pots etc. cement is commonly

        used.

   (vi) It is useful for the construction of roads, footpaths, courts for various sports etc.

BRICKS

STONES- THE TRADITIONAL BUILDING MATERIAL

STONES

        Stone is a ‘naturally available building material’ which has been used from the early age of civilization. It is available in the form of rocks, which is cut to required size and shape and used as building block.

Type of Stones

          Stones used for civil engineering works may be classified in the following three ways:

• Geological
• Physical
• Chemical

Geological Classification

           Based on their origin of formation stones are classified into three main groups—

• Igneous, 
• sedimentary and 
• metamorphic rocks.

1.Igneous Rocks: 

         These rocks are formed by cooling and solidifying of the rock masses from

their molten magmatic condition of the material of the earth. Generally igneous rocks are strong and

durable. Granite, trap and basalt are the rocks belonging to this category, Granites are formed by slow

cooling of the lava under thick cover on the top. 

2.Sedimentary Rocks: 

         Due to weathering action of water, wind and frost existing rocks disintegrates. The disintegrated material is carried by wind and water; the water being most powerful medium. Flowing water deposits its suspended materials at some points of obstacles to its flow. These deposited layers of materials get consolidated under pressure and by heat. Chemical agents also contribute to the cementing of the deposits. The rocks thus formed are more uniform, fine grained and compact in

their nature. They represent a bedded or stratified structure in general. Sand stones, lime stones, mud

stones etc. belong to this class of rock.

3.Metamorphic Rocks: 

       Previously formed igneous and sedimentary rocks undergo changes due to metamorphic action of pressure and internal heat. For example due to metamorphic action limestone changes to marble, sandstone becomes quartzite.

Physical Classification

          Based on the structure, the rocks may be classified as:

                   • Stratified rocks

                   • Unstratified rocks

1.Stratified Rocks: 

         These rocks are having layered structure. They possess planes of stratification or cleavage. They can be easily split along these planes. Sand stones, lime stones etc. are the examples of this class of stones.

2.Unstratified Rocks: 

        These rocks are not stratified. They possess crystalline and compact grains. They cannot be split in to thin slab. Granite, marble etc. are the examples of this type of rocks.

3.Foliated Rocks: 

        These rocks have a tendency to split along a definite direction only. The direction need not be parallel to each other as in case of stratified rocks. This type of structure is very

common in case of metamorphic rocks.

Chemical Classification

                   On the basis of their chemical composition engineers prefer to classify rocks as:

                       • Silicious rocks

                       • Argillaceous rocks and

                       • Calcareous rocks

1.Siliceous rocks: 

             The main content of these rocks is silica. They are hard and durable. Examples of such rocks are granite, trap, sand stones etc.

2.Argillaceous rocks: 

               The main constituent of these rocks is argil i.e., clay. These stones are hard and durable but they are brittle. They cannot withstand shock. Slates and laterites are examples of this type of rocks.

3.Calcareous rocks: 

           The main constituent of these rocks is calcium carbonate. Limestone is a

calcareous rock of sedimentary origin while marble is a calcareous rock of metamorphic origin.

Uses of Stones

         Stones are used in the following civil engineering constructions:

• Stone masonry is used for the construction of foundations, walls, columns and arches.
• Stones are used for flooring.
• Stone slabs are used as damp proof courses, lintels and even as roofing materials.
• Stones with good appearance are used for the face works of buildings. Polished marbles and
• granite are commonly used for face works.
• Stones are used for paving of roads, footpaths and open spaces round the buildings.
• Stones are also used in the constructions of piers and abutments of bridges, dams and retaining
• walls.
• Crushed stones with graved are used to provide base course for roads. When mixed with tar
• they form finishing coat.
• Crushed stones are used in the following works also:

1. As a basic inert material in concrete
2. For making artificial stones and building blocks
3. As railway ballast.

COLUMNS

   A column can be defined as a vertical structural member designed to transmit a compressive load. A Column transmits the load from ceiling/roof slab and beam, including its own weight to the foundation.

Types of Columns

Columns can be classified bases on its Shape, Slenderness ratio, type of loading and Pattern of lateral reinforcement.

 Classification based on Slenderness ratio

Long Column or Slender:

 The length is greater than the critical buckling length and it fails by buckling.

• Short Column : :The length is less than the critical buckling length and it fails by shearing.
• Intermediate Column

 Based on shape

•  Rectangle
• Square
• Circular
• Polygon

 Based on type of loading

• Axially loaded column
• Axial load and non-axial bending column
• Axial load and biaxial bending column

 Based on pattern of lateral reinforcement

• Tied columns
• Spiral columns

RCC Columns (Reinforced Concrete Columns)

A reinforced concrete column can be defined as a structural member with a steel frame (reinforcement bars) composed of concrete that is been designed to carry compressive loads.

Structural Members

Structural Members

Those members that are interconnected in such a way so as to constitute a structure are called structural members.

Beam

Beam is a flexure member of the structure. It is subjected to transverse loading such as vertical loads, and gravity loads. These loads create shear and bending within the beam.

Columns

A long vertical member mostly subjected to compressive loads is called column

Strut

A compressive member of a structure is called strut.

Beam-Column

A structural member subjected to compression as well as flexure is called beam column

Grid

A network of beam intersecting each other at right angles and subjected to vertical loads is called grid.

Cables and Arches

Cables are usually suspended at their ends and are allowed to sag. The forces are then pure tension and are directed along the axis of the cable. Arches are similar to cables except hath they are inverted. They carry compressive loads that are directed along the axis of the arch.

Plates and Slabs

Plates are three dimensional flat structural components usually made of metal that are often found in floors and roofs of structures. Slabs are similar to plates except that they are usually made of concrete.