The Construction Civil

Irrigation Engineering

2010-02-26T21:42:00.000-08:00

Irrigation is defined as the means of artificial supply of water to the soil for raising crops. It is a science of planning and designing an efficient, low-cost, economic irrigation system to fit natural conditions. It is the engineering of controlling and harnessing the various natural sources of water, by the construction of dams and reservoirs, canals and finally distributing the water to the agricultural fields. Irrigation engineering includes the study and design of works in connection with river control, drainage of water-logged areas, and generation of hydroelectric power.

Necessity of Irrigation:
India is basically an agricultural country, and all its resources depend on the agricultural output. Water is evidently the most vital element in the plant life. Water is normally supplied to the plants by nature through rains. However, the total rainfall in a particular area may be either insufficient, or ill-timed. inorder to get the maximum yield, it is essential to supply the optimum quantity of water, and to maintain correct timing of water. This is possible only through a systematic irrigation system-by collecting water during the periods of excess rainfall and releasing it to the crop as and when it is needed. Thus the necessity of irrigation can be summarised below,

1. Less Rainfall:
When the total rainfall is less than needed for the crop, artificial supply is necessary. In such a case, irrigation work may be constructed at a place where more water is available, and then to convey the water to the area where there is deficiency of water.

2. Non-Uniform Rainfall:
The rainfall in a particular area may not be uniform over the crop period. During the early periods of the crop, rain may be there, but no water may be available at the end, with the result that either the yield may be less, or the crop may die altogether.

3. Commercial crops with additional water:
The rainfall in a particular area may be sufficient to raise the usual crops, but more water may be necessary for raising commercial and cash crops.

4. Controlled water supply:
By the construction of proper distribution system, the yield of the crop may be increased.

Concrete Bleeding

2010-02-25T06:33:00.000-08:00

Water being the lightest ingredient of all the other materials in concrete, bleeding, i.e., the upward movement of water when concrete settle downwards, is natural in concrete. The bleeding water, in certain situations emerge at the surface and in some other situations may not come up to the surface. But bleeding does take place.

The bleeding water gets trapped by flat or flaky pieces of aggregates and also by reinforcement and gets accumulated below such aggregates and reinforcement. This is known as internal bleeding. In addition to internal bleeding, the water may further emerge out and accumulate on the top surface of concrete.

Firstly the internal bleeding water trapped below flat pieces of aggregate and reinforcement affect the bond between hardened cement paste, (hcp) and aggregate or reinforcement on account of local higher W/C ratio. The interface is easily prone to microcracking due to shrinkage stresses caused on dissipation of heat of hydration and drying shrinkage. The interface becomes a weak link in concrete. On loading, the micro cracks propagate further, making the concrete susceptible to degradation by environmental agencies.

The bleeding water, emerged at the top surface of concrete, when evaporates make the top surface porous, having very little abrasion resistances. Often, masons float the concrete when bleeding water is still standing on the surface. Too much working of the top surface presses the coarse aggregate down and brings up fine particles of cement and water. Such top surface made up of too fine materials with excess water develops cracks and craziness, affecting durability of concrete.

Types and Causes of Cracks in Concrete

2010-02-25T06:08:00.000-08:00

Types and Causes of Cracks in Concrete

There are many causes why cracks occur in concrete. The crack may occur in concrete due to one of the following cases which is illustrated in the below figure. There are two stages in which the crack occur in concrete, they are before hardening stage and after hardening stage.

(Click on the image for better view)

Materials for Self Compacting Concrete

2010-02-19T18:17:00.000-08:00

Some of the materials used for preparing self compacting concrete are,

Cement : Ordinary Portland Cement.

Aggregates : The maximum size of aggregate is generally limited to 20 mm. Aggregate of size 10 to 12mm is desirable for structures having congested reinforcement. Wherever possible size of aggregate higher than 20mm could aslo be used. Well graded cubical or rounded aggregates are desirable. Aggregates should be of uniform quality with respect to shape and grading.

Fine aggregates can be natural or manufactured. The grading must be uniform throughout the work. The moisture content or absorption characteristics must be closely monitored as quality of Self Compacting Concrete will be sensitive to such changes. Particles smaller than 0.125 mm i.e. 125 micron size are considered as FINES which contribute to the powder content.

Mixing Water : Water quality must be established on the same line as that for using reinforced
concrete or prestressed concrete.

Chemical Admixtures : Superplaseizers are an essential component of Self Compacting Concrete to provide necessary workability. The new generation superplasticizers termed poly-carboxylated ethers (PCE) is particularly useful for Self Compacting Concrete.

Other types may be incorporated as necessary, such as Viscosity Modifying Agents (VMA) for stability, air entraining agents (AEA) to improve freeze-thaw resistance, and retarders for Control of Setting.

Inspection and Testing of Structures

2010-02-19T05:26:00.000-08:00

Concrete is a very faithful construction material. If care is taken with respect to various constituent materials and workmanship, it, generally, does not fail to give the required results. In case the test results show unacceptable values, the compressive strength can be established from core test and load test.

Core Test
The points from which the cores to be taken can be established from cube testing register. If not possible it can be at the descretion of inspecting authority. The number of test cores will be not less than three which should represent the whole of the doubtful concrete.

The core strength should be converted to equivalent cube strength. If the equivalent cube strength gives at least 85 per cent of characteristic strength of the grade of concrete, and no individual core has a strength less than 75 per cent, the strength of the concrete can be considered adequate.

In case the core test results do not satisfy the requirements or where such core tests have not been done, load test may be resorted to.

Load Tests for Flexural Member
The structure should be subjected to a load equal to full load plus 1.25 times the live load for a period of 24 hours and then the imposed load is removed.

The deflection due to imposed load only is recorded. If within 24 hours of removal of the imposed load, the structure does not recover at least 75 per cent of the deflection under super imposed load, the test may be repeated after a lapse of 72 hours. If the recovery is less than 80 percent, the structure is deemed to be unacceptable.

If the maximum deflection in mm, shown during 24 hour under load is less than 40 L2 / d, where l is the effective span in metre and D, is the overall depth of the section in mm, it is not necessary for the recovery to be measured and the recovery provision mentioned above does not apply.

Concrete Shrinkage

2010-02-11T05:29:00.000-08:00

The concrete is subjected to changes in volume either autogenous or induced. Volume change is one of the most detrimental properties of concrete, which affects the long-term strength and durability. To the practical engineer, the aspect of volume change in concrete is important from the point of view that it causes unsightly cracks in concrete. The effect of volume change due to thermal properties of aggregate and concrete, due to alkali/aggregate reaction, due to sulphate action etc. Presently we shall discuss the volume change on account of inherenet properties of concrete “shrinkage”.

One of the most objectionable defects in concrete is the presence of cracks, particularly in floors and pavements. One of the important factors that contribute to the cracks in floors and pavements is that due to shrinkage. It is difficult to make concrete which does not shrink and crack. It is only a question of magnitude. Now the question is how to reduce the shrinkage and shrinkage cracks in concrete structures. As shrinkage is an inherent property of concrete it demands greater understanding of the various properties of concrete, which influence its shrinkage characteristics. It is only when the mechanism of all kinds of shrinkage and the factors affecting the shrinkage are understood, an engineer will be in a better position to control and limit the shrinkage in the body of concrete.

The term shrinkage is loosely used to describe the various aspects of volume changes in concrete due to loss of moisture at different stages due to different reasons. To understand this aspect more closely, shrinkage can be classified in the following ways,

1. Plastic Shrinkage
2. Drying Shrinkage
3. Autogeneous Shrinkage
4. Carbonation Shrinkage.

1. Plastic shrinkage :
Shrinkage of this type manifests itself soon after the concrete is placed in the forms while the concrete is still in the plastic state. Loss of water by evaporation from the surface of concrete or by the absorption by aggregate or subgrade, is believed to be the reasons of plastic shrinkage. The loss of water results in the reduction of volume. The aggregate particles or the reinforcement comes in the way of subsidence due to which cracks may appear at the surface or internally around the aggregate or reinforcement.

In case of floors and pavements where the surface area exposed to drying is large as compared to depth, when this large surface is exposed to hot sun and drying wind, the surface of concrete dries very fast which results in plastic shrinkage.

Sometimes even if the concrete is not subjected to severe drying, but poorly made with a high water/ cement ratio, large quantity of water bleeds and accumulates at the surface. When this water at the surface dries out, the surface concrete collapses causing cracks.

Plastic concrete is sometimes subjected to unintended vibration or yielding of formwork support which again causes plastic shrinkage cracks as the concrete at this stage has not developed enough strength. From the above it can be inferred that high water/ cement ratio, badly proportioned concrete, rapid drying, greater bleeding, unintended vibration etc., are some of the reasons for plastic shrinkage. It can also be further added that richer concrete undergoes greater plastic shrinkage.

Plastic shrinkage can be reduced mainly by preventing the rapid loss of water from surface. This can be done by covering the surface with polyethylene sheeting immediately on finishing operation; by monomolecular coatings by fog spray that keeps the surface moist; or by working at night. An effective method of removing plastic shrinkage cracks is to revibrate the concrete in a controlled manner. Use of small quantity of aluminium power is also suggested to offset the effect of plastic shrinkage. Similarly, expansive cement or shrinkage compensating cement also can be used for controlling the shrinkage during the setting o f concrete. The principal property of such cement is that the expansion induced in the plastic concrete will almost offset the normal shrinkage due to lo ss o f mo isture. Under correct usage, the distance between the joints can sometimes be tripled without increasing the level of shrinkage cracking. Further, use of unneeded high slump concrete, over sanded mix, higher air entraining should be discouraged in order to reduce the higher plastic shrinkage.

2. Drying Shrinkage:
Just as the hydration of cement is an ever lasting process, the drying shrinkage is also an ever lasting process when concrete is subjected to drying conditions. The drying shrinkage of concrete is analogous to the mechanism of drying of timber specimen. The loss of free water contained in hardened concrete, does not result in any appreciable dimension change. It is the loss of water held in gel pores that causes the change in the volume. Under drying conditions, the gel water is lost progressively over a long time, as long as the concrete is kept in drying conditions. It is theoretically estimated that the total linear change due to long time drying shrinkage could be of the order of 10,000 microns. But values upto 4,000 microns have been actually observed.

Cement paste shrinks more than mortar and mortar shrinks more than concrete. Concrete made with smaller size aggregate shrinks more than concrete made with bigger size aggregate. The magnitude of drying shrinkage is also a function of the fineness of gel. The finer the gel the more is the shrinkage. It has been pointed out earlier that the high pressure steam cured concrete with low specific surface of gel, shrinks much less than that of normally cured cement gel.

3. Autogeneous Shrinkage:
In a conservative system i.e. where no moisture movement to or from the paste is permitted, when temperature is constant some shrinkage may occur. The shrinkage of such a conservative system is known as a autogeneous shrinkage.

Autogeneous shrinkage is of minor importance and is not applicable in practice to many situations except that of mass of concrete in the interior of a concrete dam. The magnitude of autogeneous shrinkage is in the order of about 100 microns.

4. Carbonation Shrinkage:
Carbonation shrinkage is a phenomenon very recently recognised. Carbon dioxide present in the atmoshphere reacts in the presence of water with hydrated cement. Calcium hydroxide gets converted to calcium carbonate and also some other cement compounds are decomposed. Such a complete decomposition of calcium compound in hydrated cement is chemically possible even at the low pressure of carbon dioxide in normal atmoshphere. Carbonation penetrates beyond the exposed surface of concrete only very slowly.

The rate of penetration of carbon dioxide depends also on the moisture content of the concrete and the relative humidity of the ambient medium. Carbonation is accompanied by an increase in weight of the concrete and by shrinkage. Carbonation shrinkage is probably caused by the dissolution of crystals of calcium hydroxide and deposition of calcium carbonate in its place. As the new product is less in volume than the product replaced, shrinkage takes place.

Carbonation of concrete also results in increased strength and reduced permeability, possibly because water released by carbonation promotes the process of hydration and also calcium carbonate reduces the voids within the cement paste. As the magnitude of carbonation shrinkage is very small when compared to long term drying shrinkage, this aspect is not of much significance. But carbonation reduces the alkalinity of concrete which gives a protective coating to the reinforcement against rusting. If depth of carbonation reaches up to steel reinforcements, the steel becomes liable for corrosion.

Brick Masonry

2010-02-10T04:56:00.000-08:00

BrickMasonry is unified mass obtained by sytematic bonding arrangement of laying bricks and bonding them together with mortar. Brick is a building unit of hard inorganic clay material of a size which canbe conveniently handled. They can be easily arranged in to various shapes for most of the structure, some of the examples are foundations, walls, columns, buttresses, retaining structures, window sills, jambs, corbels, copings, ornamental brickwork, circular brickwork, fire places, flumes, tall chimneys, cavity walls, thresholds, culverts, steps, floors, arches, etc., The strength of brick masonry work depends upon the quality of bricks and type of mortar used.

Mortar is a pasty material formed by the addition of water to a mixture composed of an aggregate (sand) and a binding material (cement or lime) which may be handled with a trowel. The mortar units the individual bricks together. Generally, following types of mortar are in use,

Mud mortar
Cement mortar
Lime mortar
Cement lime mortar

Mud mortar is used for the temporary construction. Cement mortar is used for permanent structures. In order to select a suitable type of mortar for a given construction, we must know the type of desired finish, the magnitude and nature of super-imposed load, the effect of weathering agencies and the importance of structure.

Cement Types

2010-02-06T06:59:00.000-08:00

Some of the different cement types are listed below,

Self Compacting Concrete

2010-02-06T06:31:00.000-08:00

Self compacting concrete is a concrete which compacts itself, there is no further compaction required for self compacting concrete. Making concrete structures without vibration, have been done in the past. For examples, placement of concrete under water is done by the use of tremie without vibration. Mass concrete, and shaft concrete can be successfully placed without vibration. But the above examples of concrete are generally of lower strength and difficult to obtain consistent quality. Modern application of self-compacting concrete (SCC) is focussed on high performance, better and more reliable and uniform quality.

Recognising the lack of uniformity and complete compaction of concrete by vibration, researchers at the University of Tokyo, Japan, started in late 1980’s to develop Self compacting concrete. By the early 1990’s, Japan has developed and used SCC that does not require vibration to achieve full compaction. By the year 2000, the SCC has become popular in Japan for prefabricated products and ready mixed concrete. The utilisation of self compacting concrete started growing rapidly.

Self compacting concrete has been described as “the most revolutionary development in concrete construction for several decades”. Originally developed in Japan to offset a growing shortage of skilled labour, it has proved to be beneficial from the following points,

1. Faster construction,
2. Improved durability,
3. Reduction in site manpower,
4. Better surface finish,
5. Easier placing,
6. Safer working environment.

Concrete Carbonation

2010-02-05T23:57:00.000-08:00

Carbonation of concrete is a process by which carbon dioxide from the air penetrates into concrete and reacts with calcium hydroxide to form calcium carbonates. The conversion of Ca(OH)2 into CaCO3 by the action of CO2 results in a small shrinkage.

CO2 by itself is not reactive. In the presence of moisture, CO2 changes into dilute carbonic acid which attacks the concrete and also reduces alkalinity of concrete.

Air contains CO2. The concentration of CO2 in rural air may be about 0.03 per cent by volume. In large cities the content may go up to 0.3 per cent or exceptionally it may go up to even 1.0 per cent. In the tunnel, if not well ventilated the intensity may be much higher.

The pH value of pore water in the hardened concrete is generally between 12.5 to 13.5 depending upon the alkali content of cement. The high alkalinity forms a thin passivating layer around steel reinforcement and protect it from action of oxygen and water. As long as steel is placed in a highly alkaline condition, it is not going to corrode. Such condition is known as passivation.

In actual practice CO2 present in atmosphere in smaller or greater concentration, permeates into concrete and carbonates the concrete and reduces the alkalinity of concrete. The pH value of pore water in the hardened cement paste which was around 13 will be reduced to around 9.0. When all the Ca(OH)2 has become carbonated, the pH value will reduce upto about 8.3 In such a low pH value, the protective layer gets destroyed and the steel is exposed to corrosion.

The carbonation of concrete is one of the main reasons for corrosion of reinforcement. Of course, oxygen and moisture are the other components required for corrosion of embedded steel.

The carbonation of concrete is one of the main reasons for corrosion of reinforcement. Of course, oxygen and moisture are the other components required for corrosion of embedded steel.

Rate of Carbonation:

The rate of carbonation depends on the following factors.

1. The level of pore water i.e., relative humidity.
2. Grade of concrete
3. Permeability of concrete
4. Whether the concrete is protected or not
5. depth of cover
6. Time

It is interesting to know that if pore is filled with water the diffusion of CO2 is very slow. But whatever CO2 is diffused into the concrete, is readily formed into dilute carbonic acid reduces the alkalinity. On the other hand if the pores are rather dry, that is at low relative humidity the CO2 remains in gaseous form and does not react with hydrated cement. The moisture penetration from external source is necessary to carbonate the concrete.

The highest rate of carbonation occurs at a relative humidity of between 50 and 70 percent.The rate of carbonation depth will be slower in case of stronger concrete for the obvious reason that stronger concrete is much denser with lower W/C ratio. It again indicates that the permeability of the concrete, particularly that of skin concrete is much less at lower W/C and as such the diffusion of CO2 does not take place faster, as in the case of more permeable concrete with higher W/C ratio. Depth of cover plays an important role in protecting the steel from carbonation.

Measurement of depth of carbonation:

A common and simple method for establishing the extent of carbonation is to treat the freshly broken surface of concrete with a solution of phenophthalein in diluted alcohol. If the Ca(OH) is unaffected by CO2 the colour turns out to be pink. If the concrete is carbonated it will remain uncloured. It should be noted that the pink colour indicates that enough Ca(OH)2 is present but it may have been carbonated to a lesser extent. The colour pink will show even up to a pH value of about 9.5.

Related Posts:
1. Concrete Shrinkage
2. Action of sewage on concrete
3. Concrete Compaction
4. Joints in Concrete
5. Concrete curing

Stone Masonry

2010-02-03T21:16:00.000-08:00

Stone Masonry is the art of building the structures in stones. In some parts of the country, building stones are abundantly available in nature. These stones when cut and dressed to the proper shapes, provide an economical material for the construction of various parts of a building which are located in hilly areas.

Uses of Stone Masonry:

Stone masonry construction is used in,
1. Building foundations, dams, monumental structures.
2. Building walls, piers, columns, pillars, light houses, and architectural works.
3. Arches, domes, lintels and beams
4. Roofs, floors, pavings.
5. Railway ballast, blackboards and electrical switchboards.
6. In the construction of retaining walls.
7. It is used in the construction of integrated living homes and integrated design construction.

Selection of stone for stone masonry:

Selection of stone depends on,
1. Availability,
2. Ease of working,
3. Appearance,
4. Strength and stability,
5. Polishing characteristics,
6. Economy,
7. Durability.

Mosaic Flooring or China Mosaic Tile Floor

2010-02-01T23:12:00.000-08:00

The mosaic flooring consists of tiles available in variety of patter and colours, is commonly used in operation theatres, temples, bath-rooms and superior type of building floors.

For construction of mosaic flooring, first of all, a hard concrete base is laid. Over this concrete base, while it is still wet, a 2 cm layer of cement mortar (1:2) is evenly laid. sometimes, instead of cement mortar using monolithically, a lime surkhi mortar is first spread to a depth of about 6 cm and levelled; over which a layer of paste or cementing material is laid in thickness not exceeding 3 mm. Upon the bed of the cement mortar (cementing material) small pieces of broken tiles are arranged in definite patterns. After this, cement or coloured cement is sprinkled at the top and surface is rolled by light stone roller till the even surface is attained. this surface is left for 24 hours to dry and then it is rubbed with pumice stone to get a smooth and polished surface. The polished surface is finally allowed to dry for about two weeks before use.

Related Posts:

1. Cork Flooring
2. Rubber Flooring
3. Glass Flooring
4. Timber Flooring
5. Brick Flooring
6. Terrazzo Flooring
7. Hardwood flooring
8. Laminate flooring

Terrazzo Flooring

2010-02-01T21:58:00.000-08:00

Terrazzo flooring is a special type of concrete flooring in which marble chips are used as aggregates, and this concrete on polishing with carborundum stone presents a smooth surface. Any desired colour can be obtained by using marble chips of different shades and sizes and also by using different coloured cement. The aggregate shades are exposed by grinding the surface. Normally, terrazzo mix having proportions 1:2 to 3 (1 cement : 2 to 3 marble chips) depending upon the size of marble chips, is used.

The terrazzo flooring is becoming very popular these days for providing floor finishes in banks, hostels, office buildings and other public or social buildings, on account of its excellent wear-resisting properties and decorative effects.

Terrazzo finish is atleast 10 mm thick and comprises a mixture of desired cement (i.e, coloured cement), marble powder and coarse aggregate, such as chippings of marble, quartzite, pearl, glass, etc., of selected colours and of sizes graded from 2 mm to 8 mm. Sometimes, larger particles up to 10 mm are used. This terrazzo finish is installed over the concrete base course in following two ways or methods,

In one method, the cement concrete base is covered uniformly by a 6 mm sand cushion, over which a tar paper is placed. On this paper, a layer of rich mortar (1:3) about 30 mm thick is deposited.

In another method, terrazzo finish is applied monolithically. First of all, a thin coat of cement is spread over the wet concrete base. This layer is then swept with a broom and a layer of cement mortar (1 cement : 2 sand) 12 mm thick is evenly spread immediately over it.

The metal dividing stirrups, about 30 mm in width and 1.3 mm in thickness, are inserted on edge in the mortar bed in desired patterns before it hardens.

When the mortar bed has sufficiently hardened, a terrazzo mixture (1 cement : 3 marble chips), 6 to 12 mm thick, depending upon the size of chips, with water just sufficient to make a workable mix for the mosaic finish, is applied. This terrazzo layer is then rolled lengthwise as well as cross wise. About 85% of the marble or aggregate should be exposed over the finished surface and to achieve this, it may be necessary to add additional chips during the rolling process.

After curing for several days, the surface is carefully polished by means of a grinding machine fitted with carborundum grinding stone disc. During the process of grinding, the surface is kept wet. Holes or pores, if any, are filled with a thin grout of cement paste, having same tint as the terrazzo finish. After this, the surface is again cured for few days and finally ground by grinding machine fitted with a finer carborundum stone disc. Finally, the whole surface is washed with a weak solution of soft soap in warm water. The surface, so produced, is pleasing in apperance and sanitary in nature.

Related Posts:

1. Cork Flooring
2. Rubber Flooring
3. Glass Flooring
4. Timber Flooring
5. Brick Flooring

Brick Flooring

2010-02-01T21:13:00.000-08:00

Brick flooring is suitable for cheap construction, and for places where heavy articles are to be stored as in case of ware houses, stores and godowns. Brick flooring is commonly used in alluvial places, where stone is scarce and well burnt bricks of good quality are readily available. The brick flooring may be laid with bricks laid flat, or on edge arranged in hearing-bone pattern, or set at right angles to the walls.

The bricks, whether laid flat or on edge, are set in ordinary mortar and pointed with cement, or set in hydraulic mortar. Brick-on edge is preferred to bricks laid flat, because the former being less liable to crack under pressure than the latter and also having the higher depth gives a greater thickness in the former case to resist the moisture penetration.

The method of brick flooring is as follows,

First of all, an excavation is made about 40 cm or so below the intended surface or level of the floor depending upon the nature of soil and the type of structure. The earth is then levelled, watered and well rammed, until it becomesdry and hard. On the bed so prepared, the sub-grade should be made with a 25 cm layer of rubble or brick bats, and covered with 10 to 15 cm thick layer of lime concrete or lean cement concrete (1 cement : 3 sand : 6 C.A.). Upon the prepared subgrade, the bricks are laid in desired shape (may be in parallel rows or herring-bone pattern) and set in cement or lime mortar. The joints should be preferably be 1.5 mm in thickness. The joints, sometimes may be required to be pointed to have better appearance. For Pointing purposes, the mortar is first raked out from the joints to a depth of about 2 cm and then pointed with cement mortar. For brick flooring outside the building, the bricks joints are grouted with dry sand and the process is termed as sand grouting.
Merits of brick flooring:

It offers a durable and sufficiently hard floor surface.
It provides a non-slippery and fire-resistant surface.
It is cheaper in initial cost as compared to cement concrete, mosaic, terrazzo flooring, etc.,
It is easy in maintenance.

Demerits:

The only drawback of this flooring is that it is water absorbent.

Timber Flooring

2010-01-31T23:32:00.000-08:00

The timber flooring is best suited for buildings on hill stations or in localities where the climate is damp. However timber flooring is used carpentry halls, dancing halls, auditoriums, etc., The timber flooring is not much used for ground floors in India. In this type of flooring, the prevention of dampness is most important and hence all possible measures should be taken to check the dampness from rising above.

The entire area of the building below the ground floor of timber is covered with an impervious material in order to prevent dampness. This material may be either cement concrete or asphalt. Generally, a 15 cm layer of concrete known as oversite concrete, is placed all over the bed, and DPC (Damp proofing courses) are inserted throughout the width of the wall immediately below the wall plate.

Timber flooring essentially consists of boarding supported on timber joists called bridging joists or floor joists, which are nailed to the wall plates at their ends. In case of large rooms, where the distance between the wall is considerable, intermediate walls, called sleeper or dwarf walls, are constructed to support the joiss along their length. Longitudinal timber members called 'sleeper plates', are fixed on the top of sleeper walls and the timber joists are secured to the sleeper walls by nailing to the sleeper wall plates.

The hollow space between the flooring and the oversite concrete is kept dry and fully ventilatedby keeping openings in the main walls above the ground level.

Glass Floor

2010-01-31T22:59:00.000-08:00

The glass flooring can be used for special purposes where it is desired to transmit light from an upper floor to a lower floor such as from a ground floor to a basement. this floor is not commonly used for floors, in general.

In the construction of glass flooring, the structural glass in the form of tiles, blocks, etc., is fitted within frames of various types. The structural glass is available in different forms of varying thicknesses, usually from 10 to 30 mm. The frame-work containing structural glass blocks should be closely spaced that the glass flooring can safely sustain the anticipated loads.

Rubber Flooring

2010-01-31T22:15:00.000-08:00

Rubber flooring are being used to a large extent in public and industrial buildings because of their good wearing qualities, resiliency (i.e., elasticity) and noise insulation. The flooring material is made up of pure rubber mixed with fillers, such as cotton fibre, granulated cork or asbestos fibre and the desired colouring pigments. Rubber flooring is manufactured in the form of sheets or tiles, in a variety of patterns and colours. The thickness of tiles or sheets ranges between 3 to 10 mm.

For the construction of rubber flooring, a base of concrete R.C.C. or wood is prepared, with a caution that concrete slab has been water-proofed properly. The rubber tiles are then cemented to the smooth and dry base of concrete or wood by means of a special adhesive.

Though rubber flooring is expensive in its initial cost, yet it provides a durable wearing surface. However, oil , grease and gasoline make the floor slippery and difficult to restore it in good condition.

Rubber sheets are supplied usually in sizes 500 x 90 cm, 350 x 90 cm, and 250 x 90 cm.
Rubber tiles are supplied usually, in sizes, 20 x 20 cm, 30 x 30 cm, and 45 x 45 cm.
For the above mentioned three sizes, the corresponding thicknesses are specified as 3.2 mm, 4.8 mm, and 6.4 mm respectively.

Merits of Rubber flooring:

It provides an attractive, resilient, durable and cheap surface.
It offers surface which can be easily washed and cleaned.
Being moderately warm with cushioning effect, it gives comfortable living and working conditions.
It offers adequate insulation against noise and heat.

Demerits:

It is subjected to rotting when kept wet for sufficient time and its use is not recommended for basements.
Rubber Flooring does not offer resistance against fire, being combustible in nature.
This covering when applied over wooden base may get torn, under excessive sub-floor movements.

Cork Flooring

2010-01-31T21:37:00.000-08:00

Cork flooring, natural cork is nothing but the outer bark of the cork oak tree which is used in the flooring after manufacturing it in the form of tiles and carpets like linoleum flooring, also provides a warm, noiseless, non-slippery and resilient flooring, and possesses good heat insulation qualities. The cork flooring is generally used to obtain a noiseless floor as in case of libraries, churches, radio-broadcasting studios, theatres, hospitals, art galleries, schools, etc., This type of flooring should not be used in basements or such other floors which are constantly subjected to dampness.

For construction of cork flooring, first of all a sub-floor or base made of 3:1 or 4:1 sand cement screed finished with a wood float or any other dry level floor (concrete or wooden) is prepared for receiving cork flooring. Over this base, cork tiles or cork carpet are laid in a similar manner as a linoleum covering.

Regarding cork flooring, the following salient features should be noted:

Cork tiles are manufactured from high grade cork bar and are available in standard sizes (from 10 cm x 10 cm to 30 cm x 90 cm) with varying shades in different thicknesses (from 5 mm to 15 mm).
Cork tiles are usually made in two qualities, ordinary and heavy density. The heavy density tiles are used when heavy wear is expected, like floors of theatres, schools, art galleries, etc., Tile joints are either tongue and groove type or butt types.
Cork carpet is prepared by heating granules of cork with linseed oil, etc., and then compressing it by rolling on canvass. The cork carpet, being more absorbent, is difficult to maintain it clean.

Merits of Cork Flooring:

It provides an attractive, resilient, durable and cheap surface.
Being moderately warm with cushioning effect, it gives comfortable living and working conditions.
It offers adequate insulation against noise and heat.

Demerits:

It is subjected to rotting when kept wet for sufficient time and its use is not recommended for basements.
Cork Flooring does not offer resistance against fire, being combustible in nature.
This covering when applied over wooden base may get torn, under excessive sub-floor movements.

Ferrocement

2010-01-20T06:19:00.000-08:00

Ferrocement is a special type of reinforced concrete composed of closely spaced layers of continuous relatively thin metallic or nonmetallic mesh or wire embedded in mortar. It is constructed by hand plastering, shotcrete, laminating (forcing the mesh into fresh mortar), or a combination of these methods.

The mortar mixture generally has a sand-cement ratio of 1.5 to 2.5 and a water-cement ratio of 0.35 to 0.50. Reinforcement makes up about 5% to 6% of the ferrocement volume. Fibers and admixtures may also be used to modify the mortar properties. Polymers or cement-based coatings are often applied to the finished surface to reduce porosity.

Ferrocement is considered easy to produce in a variety of shapes and sizes; however, it is labor intensive. Ferrocement is used to construct thin shell roofs, swimming pools, tunnel linings, silos, tanks, prefabricated houses, barges, boats, sculptures, and thin panels or sections usually less than 25 mm thick.

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Action of Sewage on Concrete

2010-01-17T05:30:00.000-08:00

Domestic sewage has not got detrimental effect on good concrete. As such, concrete pipes are used for conveying sewage; also concrete is used for constructing sewage treatment plants. Hydrogen sulphide gas which may be evolved from septic sewage in sewer or sludge digestion tank, though by itself is not harmful, may promote the formation of sulphuric acid which can attack the concrete surface above the liquid level. Concrete sewers running full are not attacked.

If the sewage contains more than 150 ppm of soluble sulphate salts (as SO4), sulphate attack may take place. Domestic sewage rarely contains this amount of sulphate salts but discharge of certain industrial wastes into sewer could increase the concentration of sulphate salts.

Concrete pipes to carry sewage should be of low permeability to minimise penetration of liquid. This could be done by rich concrete, low water cement ratio and good compaction to increase the durability of the sewer. It should be seen that formation of sulphuric acid is avoided by keeping sufficient quantity of flow, proper ventilation of sewer and by avoiding the stagnation or septicity of sewage.

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IS Design

2010-01-06T06:05:00.000-08:00

IS Design - Indian Standards.

For the design of buildings or for the design of bridges and other structural members IS code books are required.

A Civil Engineer must follow the guidelines provided in the IS Design.

Some of the IS codes available in India in the field of construction are,

IS 456 : 2000 Code of practice for plain and reinforced concrete
IS 516 : 1959 Method of test for strength of concrete
IS 650 : 1991 Specification for standard sand for testing of cement
IS 1343: 1980 Code of practice for prestressed concrete
IS 2430: 1986 Methods for sampling of aggregates for concrete
IS 2505: 1980 General requirements for concrete vibrators
IS 3466: 1988 Specification for masonry cement
IS 4032: 1985 Method of chemical analysis of hydraulic cement
IS 5816: 1999 Method of test for splitting tensile strength of concrete.

Vibrating Platform

2010-01-05T00:26:00.000-08:00

Platform vibrator is nothing but a table vibrator, but it is larger in size. This is used in the manufacture of large prefabricated concrete elements such as electric poles, railway sleepers, prefabricated roofing elements etc. Sometimes, the platform vibrator is also coupled with jerking or shock giving arrangements such that a thorugh compaction is given to the concrete.

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Vibrating Table

Vibrating Table

2010-01-05T00:20:00.000-08:00

This is the special case of formwork vibrator, where the vibrator is clamped to the table. or table is mounted on springs which are vibrated transferring the vibration to the table. They are commonly used for vibrating concrete cubes. Any article kept on the table gets vibrated. This is adopted mostly in the laboratories and in making small but precise prefabricated R.C.C. members.

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Vibrating Platform

Concrete Fence Posts

2010-01-04T23:16:00.000-08:00

The concrete fence posts are very useful for laying fences around the building, or garden, or in an empty land. Many of them prefer concrete fence posts rather than steel fence posts because of the following advantages,

Concrete fence posts does not corrode easily as steel corrodes rapidly when exposed to alternate temperatures.
Concrete fence posts have high durability and hence it has long service life.
Installation is easy as it does not require much tools as in that of steel posts.
Highly resistance to exposure conditions.
Cheap when compared to steel of same thickness.

Transit Mixer

2010-01-04T22:59:00.000-08:00

Transit mixer is one of the most popular equipments for transporting concrete over a long distance particularly in Ready Mixed Concrete plant (RMC). In India, today (2000 AD) there are about 35 RMC plants and a number of central batching plants are working. It is a fair estimate that there are over 600 transit mixer in operation in India. They are truck mounted having a capacity of 4 to 7 m3. There are two variations. In one, mixed concrete is transported to the site by keeping it agitated all along at a speed varying between 2 to 6 revolutions per minute. In the other category, the concrete is batched at the central batching plant and mixing is done in the truck mixer either in transit or immediately prior to discharging the concrete at site. Transit mixer permits longer haul and is less vulnerable in case of delay. The truck mixer the speed of rotating of drum is between 4–16 revolution per minute. A limit of 300 revolutions for both agitating and mixing is laid down by ASTM C 94 or alternatively, the concretes must be placed within 1.5 of mixing. In case of transit mixer, water need not be added till such time the mixing is commenced. BS 5328 – 1991, restrict the time of 2 hours during which, cement and moist sand are allowed to remain in contact. But the above restrictions are to be on the safe side. Exceeding these limit is not going to be harmful if the mix remains sufficiently workable for full compaction.

With the development of twin fin process mixer, the transit mixer have become more efficient in mixing. In these mixers, in addition to the outer spirals, have two opposed inner spirals. The outer spirals convey the mix materials towards the bottom of the drum, while the opposed mixing spirals push the mix towards the feed opening. The repeated counter current mixing process is taking place within the mixer drum. Sometimes a small concrete pump is also mounted on the truck carrying transit mixer. This pump, pumps the concrete discharged from transit mixer. Currently we have placer boom also as part of the truck carrying transit mixer and concrete pump and with their help concrete is transported, pumped and placed into the formwork of a structure easily.