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, maganese 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 form works 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) Pozzulana Cement:

 Pozzulana is a volcanic power found in Italy. It can be processed from shales and certain types of clay also. In this cement pozzulana 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 sulpho aluminate 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 per cent 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. Now-a-days 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.

Types of Bridges

Bridges by Structure

• Arch bridges – These bridges uses arch as a main structural component (arch is always located below the bridge, never above it). They are made with one or more hinges, depending of what kind of load and stress forces they must endure. Examples of arch bridge are “Old Bridge” in Mostar, Bosnia and Herzegovina and The Hell Gate Bridge in New York.
• Beam bridges – Very basic type of bridges that are supported by several beams of various shapes and sizes. They can be inclined or V shaped. Example of beam bridge is Lake Pontchartrain Causeway in southern Louisiana.
• Truss bridges – Very popular bridge designs that uses diagonal mesh of posts above the bridge. The two most common designs are the king posts (two diagonal posts supported by single vertical post in the center) and queen posts (two diagonal posts, two vertical pots and horizontal post that connect two vertical posts at the top).
• Cantilever bridges – Similar in appearance to arch bridges, but they support their load not trough vertical bracing but trough diagonal bracing. They often use truss formation both below and above the bridge. Example of cantilever bridge is Queensboro Bridge in New York City.
• Tied arch bridges – Similar to arch bridges, but they transfer weight of the bridge and traffic load to the top chord that is connected to the bottom cords in bridge foundation. They are often called bowstring arches or bowstring bridges.
• Suspension bridges – Bridges that use ropes or cables from the vertical suspender to hold the weight of bridge deck and traffic. Example of suspension bridge is Golden Gate Bridge in San Francisco.
• Cable-stayed bridges – Bridge that uses deck cables that are directly connected to one or more vertical columns. Cables are usually connected to columns in two ways – harp design (each cable is attached to the different point of the column, creating harp like design of “strings” and fan design (all cables connect to one point at the top of the column).

Fixed or moveable bridges

• Fixed – Majority of bridges are fixed, with no moveable parts to provide higher clearance for river/sea transport that is flowing below them. They are designed to stay where they are made to the point they are deemed unusable or demolished.
• Temporary bridges – Bridges made from modular basic components that can be moved by medium or light machinery. They are usually used in military engineering or in circumstances when fixed bridges are repaired.
• Moveable – They have moveable decks, most often powered by electricity.

Types by use

• Car Traffic – The most common type of bridge, with two or more lanes designed to carry car and truck traffic of various intensities.
• Pedestrian – Usually made in urban environments, or in terrain where car transport is inaccessible (rough mountainous terrain, forests, etc.).
• Double-decked – Built to provide best possible flow of traffic across bodies of water or rough terrain. Most offen they have large amount of car lanes, and sometimes have dedicated area for train tracks.
• Train bridges – Bridges made specifically to carry one or multiple lane of train tracks.
• Pipelines – Bridges made to carry pipelines across water or inaccessible terrains. Pipelines can carry water, air, gas and communication cables.
• Viaducts – Ancient structures created to carry water from water rich areas to dry cities.
• Commercial bridges – Modern bridges that host commercial buildings such as restaurants and shops.

Types by materials

• Natural materials
• Wood
• Stone
• Concrete and Steel
• Advanced materials

Classification of Surveying

Surveying may be classified on the basis of nature of the survey field, object of survey, instruments used and the methods employed.

1. Classification Based on Nature of Survey Field

This basis survey may be classified as land survey, marine or hydraulic survey and astronomical survey.

Land Survey

It involves measurement of various objects on land. This type of survey may be further classified as given below:

(a) Topographic Survey:

It is meant for plotting natural features like rivers, lakes, forests and hills as well as man made features like roads, railways, towns, villages and canals.

(b) Cadestal Survey:

 It is for marking the boundaries of municipalities, villages, talukas, districts, states etc. The survey made to mark properties of individuals also come under this category.

(c) City Survey:

 The survey made in connection with the construction of streets, water supply and sewage lines fall under this category.

Marine or Hydrographic Survey

Survey conducted to find depth of water at various points in bodies of water like sea, river and lakes fall under this category. Finding depth of water at specified points is known as sounding.

Astronomical Survey

Observations made to heavenly bodies like sun, stars etc., to locate absolute positions of points on the earth and for the purpose of calculating local time is known as astronomical survey.

2. Classification Based on Object of Survey

On the basis of object of survey the classification can be as engineering survey, military survey, mines survey, geological survey and archeological survey.
(a) Engineering Survey: The objective of this type of survey is to collect data for designing civil engineering projects like roads, railways, irrigation, water supply and sewage disposals. These surveys are further sub-divided into: Reconnaissance Survey for determining feasibility and estimation of the scheme. Preliminary Survey for collecting more information to estimate the cost of the project, and Location Survey to set the work on the ground.

(b) Military Survey: This survey is meant for working out plans of strategic importance.

(c) Mines Survey: This is used for exploring mineral wealth.

(d) Geological Survey: This survey is for finding different strata in the earth’s crust.

(e) Archeological Survey: This survey is for unearthing relics of antiquity.

3.  Classification Based on Instruments Used

Based on the instruments used, surveying may be classified as:

(i) Chain survey
(ii) Compass survey
(iii) Plane table survey
(iv) Theodolite survey
(v) Tacheometric survey
(vi) Modern survey using electronic distance meters and total station
(vii) Photographic and Aerial survey

The survey is taught to civil engineering students mainly based on this classification.

4. Classification Based on Methods Employed

On this basis surveying is classified as triangulation and traversing.

(i) Triangulation: In this method control points are established through a network of triangles.
(ii) Traversing: In this scheme of establishing control points consists of a series of connected points established through linear and angular measurements. If the last line meets the starting point it is called as closed traverse. If it does not meet, it is known as open traverse.

                               AFATECOL         "Engineering your dreams with us"

What is Subcontractor

A subcontractor is a person or a company hired by a general contractor to perform part of the work of a construction job. For example, a contractor might be building a house, but might hire a firm or a person specializing in electrical engineering to install the electrical systems needed in the house. Generally the subcontractor will either relieve the main contractor of part of the building work, or will be able to perform work at lower expense or at a greater skill level than the general contractor could.

Often, a subcontractor, whether an individual or a business, forms relationships with several general contractors. The general contractor working with a subcontractor does not employ the subcontractor as a regular employee in most cases. Instead the subcontractor is either an independent contractor, or is a company that provides its employees with required benefits like health insurance coverage.

Not having to extend benefits to a subcontractor is one way that the general contractor saves money on a job. However, if problems occur because of faulty work on the part of the subcontractor, usually the general contractor is held liable for such problems. The general contractor may attempt to seek redress with the subcontractor, or have defined terms in the contract with a subcontractor stipulating that the liability would be more evenly shared.

Frequently, though, hiring a subcontractor, or several, is a way to avoid problems in construction. Specialized workers like plumbers, electricians, or people who install heating and cooling devices, often called HVAC workers, tend to have more knowledge and training in their given field. While simply building something requires training and knowledge, people who are specialists better perform certain types of work.

The subcontractor and the general contractor are served well by being able to form good working relationships with each other. For the general contractor, access to a reliable subcontractor can mean finishing jobs on time and on budget. For the subcontractor, a good reputation among contractors means greater opportunities for consistent work.

A subcontractor often holds licenses in his or her specialty field. He or she might hold a general license to conduct work in a state, and also hold advanced licensing. Such licensing implies a certain amount of hours practicing his or her trade and knowledge regarding state building codes.

In some cases, one may also refer to a person hired for a few days of work, without a specialized field as a subcontractor. Really the more accurate term is independent contractor. The person is usually a temporary employee of the contractor, hired to finish work on time, or to temporarily replace another worker who is ill. This type of subcontractor may not have a general contractor’s license but may be hired for his or her carpentry skills.

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BASIC REQUIREMENT OF A BUILDING

The planning and construction of a building should be aimed at fulfilling the following 12 requirements:

1. Strength and Stability:

Building should be capable of transferring the expected loads in its life period safely to the ground. Design of various structural components like slabs, beams, walls, columns and footing should ensure safety. None of the structural components should buckle, overturn and collapse.

2. Dimensional Stability:

Excessive deformation of structural components give a sense of instability and result into crack in walls, flooring etc. All structural components, should be so designed that deflections do not exceed the permissible values specified in the codes.

3. Resistance to Dampness:

Dampness in a building is a great nuisance and it may reduce the life of the building. Great care should be taken in planning and in the construction of the building to avoid dampness.

4. Resistance to Fire:

Regarding achieving resistance to fire, the basic requirements laid down in the codes are:
(a) the structure should not ignite easily.
(b) building orientation should be such that spread of fire is slow.
(c) In case of fire, there should be means of easy access to vacate building quickly.

5. Heat Insulation:

A building should be so oriented and designed that it insulates interior from heat.

6. Sound Insulation:

Buildings should be planned against outdoor and indoor noises.

7. Protection from Termite:

Buildings should be protected from termites.

8. Durability:

Each and every component of the building should be durable.

9. Security against Burglary:

This is the basic need the owner of the building expects.

10. Lighting and Ventilation:

For healthy and happy living natural light and ventilations are required. Diffused light and good cross ventilation should be available inside the building.

11. Comforts and Conveniences:

Various units in the building should be properly grouped and integrated keeping in mind the comfort and convenience of the user.

12. Economy:

Economy without sacrificing comfort, convenience and durability is another basic requirement of the building.

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TYPES OF CONSTRUCTION ESTIMATES

There are several kinds of estimating techniques; these can be grouped into two main categories:

1. Approximate Estimates
An approximate estimate is an approximate or rough estimate prepared to obtain an approximate cost in a short time. For certain purposes the use of such methods is justified.

2. Detailed Estimate
A detailed estimate of the cost of a project is prepared by determining the quantities and costs of every thing that a contractor is required to provide and do for the satisfactory completion of the work. It is the best and most reliable form of estimate. A detailed estimate may be prepared in the following two ways

(a) Unit Quantity Method
In the unit quantity method, the work is divided into as many operations or items as are required. A unit of measurement is decided. The total quantity of work under each item is taken out in the proper unit of measurement. The total cost per unit quantity of each item is analyzed and worked out. Then the total cost for the item is found by multiplying the cost per unit quantity by the number of units.

For example, while estimating the cost of a building work, the quantity of brickwork in the building would be measured in cubic meters. The total cost (which includes cost of materials. labor, plant, overheads and profit) per cubic meter of brickwork would be found and then this unit cost multiplied by the number of cubic meters of brickwork in the building would give the estimated cost of brickwork. This method has the advantage that the unit costs on various jobs can be readily compared and that the total estimate can easily be corrected for variations in quantities.

(b) Total Quantity Method
In the total quantity method, an item of work is divided into the following five subdivisions:

(I) Materials
(II) Labor
(III) Plant
(IV) Overheads
(V) Profit

The total quantities of each kind or class of material or labor are found and multiplied by their individual unit cost. Similarly, the cost of plant, overhead expenses and profit are determined.

How to Start a Construction Company?

Starting a construction company can be a profitable venture under the right circumstances. Construction is an industry that will always be in demand and will not yield easily to automation. If you have experience in construction and want to start your own company, be sure to research requirements, laws, and business basics before taking the plunge.

One of the first things to consider before starting your own construction company is financing. If you do not have available funds to purchase materials, tools, and labor, you will need to arrange financing for the start up of your company. You also need to make sure you have a contractor’s license and bonding insurance to protect you.

The amount of financing you need will vary greatly depending on the size of the construction projects you intend to start out with. If you are performing small jobs such as remodels, additions, or decks, you might be able to purchase materials and tools on credit. Remember that interest eats away at profit, so be sure that you can meet a completion date and collect your fees from your clients in a timely manner.

It is extremely important to have an understanding of cost estimation when you bid a project. Underbidding yourself to get jobs will soon eat away at your profits and eventually doom your success. However, if you bid too high, your more established competitors will beat you out. If you do not know how to bid competitively, you should either develop the skill or hire someone who is knowledgeable about construction estimation.

With funds available for purchasing materials, insurance to cover potential accidents, and clients, you will have to turn your attention to your craft force. If you plan to be on site at all times overseeing the construction process, you can easily manage your craft force. If you intend to work hands off, you’ll need to hire someone experienced at leading a crew of workers to make sure the job is done right and according to schedule.

Start with small jobs and advertise by word of mouth. Do a good job for your initial clients, and they will spread the word. Ask to place temporary signs at a completed site for advertising purposes as well. Make sure you have someone available to provide estimates for potential clients without holding up current construction projects. As your company grows, you can hire additional personnel to assist with certain jobs.

Be sure to develop a good relationship with building inspectors in your area and to have both a business attorney and an accountant at your disposal should you need their services. Careful planning and attention to detail will ensure that your construction company stays afloat during the roughest first two years of operation. With a qualified craft force and a desire to succeed, you can grow a solid small to mid-sized construction company within five years.