IS Codes for Cement and Concrete

IS 269:1989 – Specification for ordinary Portland cement, 33 grade

IS 383:1970 – Specification for coarse and fine aggregates from natural sources for concrete

IS 455:1989 Specification for Portland slag cement

IS 456:2000 Code of practice for plain and reinforced concrete

IS 457:1957 Code of practice for general construction of plain and reinforced concrete for dams and other massive structures

IS 516:1959 Method of test for strength of concrete

IS 650:1991 Specification for standard sand for testing of cement

IS 1199:1959 Methods of sampling and analysis of concrete

IS 1343:1980 Code of practice for prestressed concrete

IS 1344:1981 Specification for calcined clay pozzolana

IS 1489(Part 1):1991 Specification for Portland pozzolana cement Part 1 Flyash based

IS 1489(Part 2):1991 Specification for Portland-pozzolana cement: Part 2 Calcined clay based

IS 1727:1967 Methods of test for pozzolanic materials

IS 2386(Part 1):1963 Methods of test for aggregates for concrete: Part 1 Particle size and shape

IS 2386(Part 2):1963 Methods of test for aggreegates for concrete: Part 2 Estimation of deleterious materials and organic impurities

IS 2386(Part 3):1963 Methods of test for aggregates for concrete: Part 3 Specific gravity, density, voids, absorption and bulking

IS 2386(Part 4):1963 Methods of test for aggregates for concrete: Part 4 Mechanical properties

IS 2386(Part 5):1963 Methods of test for aggregates for concrete : Part 5 Soundness

IS 2386(Part 6):1963 Methods of test for aggregates for concrete : Part 6 Measuring mortar making properties of fine aggregates

IS 2386(Part 7):1963 Methods of test for aggregates for concrete : Part 7 Alkali aggregate reactivity

IS 2386(Part 8):1963 Methods of test for aggregates for concrete: Part 8 Petrographic examination

IS 2430:1986 Methods for sampling of aggregates for concrete

IS 2502:1963 Code of practice for bending and fixing of bars for concrete reinforcement

IS 2645:2003 Integral waterproofing compounds for cement mortar and concrete – Specification

IS 2770(Part 1):1967 Methods of testing bond in reinforced concrete: Part 1 Pull-out test

IS 3085:1965 Method of test for permeability of cement mortar and concrete

IS 3370(Part 1):2009 Code of practice for concrete structures for storage of liquids: Part 1 General requirements

IS 3370(Part 2):2009 Code of practice for concrete structures for storage of liquids: Part 2 Reinforced concrete structures

IS 3370(Part 3):1967 Code of practice for concrete structures for the storage of liquids: Part 3 Prestressed concrete

IS 3370(Part 4):1967 Code of practice for concrete structures for the storage of liquids: Part 4 Design tables

IS 3466:1988 Specification for masonry cement

IS 3535:1986 Methods of sampling hydraulic cement

IS 3558:1983 Code of practice for use of immersion vibrators

IS 3812(Part 1):2003 Specification for pulverized fuel ash Part 1 For use as pozzolana in cement, cement
mortar and concrete

IS 3812(Part 2):2003 Specification for pulverized fuel ash Part 2 For use as admixture in cement mortar and
concrete

IS 4031(Part 1):1996 Methods of physical tests for hydraulic cement: Part 1 Determination of fineness by dry sieving

IS 4031(Part 2):1999 Methods of physical tests for hydraulic cement: Part 2 Determination of fineness by specific surface by Blaine air permeability method

IS 4031(Part 3):1988 Methods of physical tests for hydraulic cement: Part 3 Determination of soundness

IS 4031(Part 4):1988 Methods of physical tests for hydraulic cement: Part 4 Determination of consistency of standard cement paste

IS 4031(Part 5):1988 Methods of physical tests for hydraulic cement: Part 5 Determination of initial and final setting times

IS 4031(Part 6):1988 Methods of physical tests for hydraulic cement: Part 6 Determination of compressive strength of hydraulic cement (other than masonry cement)

IS 4031(Part 7):1988 Methods of physical tests for hydraulic cement: Part 7 Determination of compressive strength of masonry cement

IS 4031(Part 8):1988 Methods of physical tests for hydraulic cement: Part 8 Determination of transverse and compressive strength of plastic mortar using prism

IS 4031(Part 9):1988 Methods of physical tests for hydraulic cement: Part 9 Determination of heat of hydration

IS 4031(Part 10):1988 Methods of physical tests for hydraulic cement: Part 10 Determination of drying shrinkage

IS 4031(Part 11):1988 Methods of physical tests for hydraulic cement: Part 11 Determination of density

IS 4031(Part 12):1988 Methods of physical tests for hydraulic cement: Part 12 Determination of air content of hydraulic cement mortar

IS 4031(Part 13):1988 Methods of physical tests for hydraulic cement: Part 13 Measurement of water retentivity of masonry cement

IS 4031(Part 14):1989 Methods of physical tests for hydraulic cement: Part 14 Determination of false set

IS 4031(Part 15):1991 Methods of physical test for hydraulic cement: Part 15 Determination of fineness by wet sieving

IS 4032:1985 Method of chemical analysis of hydraulic cement

IS 4305:1967 Glossary of terms relating to pozzolana

IS 4634:1991 Methods for testing performance of batch-type concrete mixers

IS 4845:1968 Definitions and terminology relating to hydraulic

IS 4926:2003 Ready mixed concrete – Code of practice

IS 5512:1983 Specification for flow table for use in tests of hydraulic cements and pozzolanic materials

IS 5513:1996 Specification for vicat apparatus

IS 5514:1996 Specification for apparatus used in Le-Chatelier test

IS 5515:1983 Specification for compaction factor apparatus

IS 5516:1996 Specification for variable flow type air-permeability apparatus (Blaine type)

IS 5525:1969 Recommendations for detailing of reinforcement in reinforced concrete works

IS 5536:1969 Specification for constant flow type air- permeability apparatus (Lea and Nurse type)

IS 5816:1999 Method of test for splitting tensile strength of concrete

IS 6452:1989 Specification for high alumina cement for structural use

IS 6461(Part 1):1972 Glossary of terms relating to cement concrete: Part 1 Concrete aggregates

IS 6461(Part 2):1972 Glossary of terms relating to cement concrete: Part 2 Materials (other than cement and aggregate)

IS 6461(Part 3):1972 Glossary of terms relating to cement concrete: Part 3 Concrete reinforcement

IS 6461(Part 4):1972 Glossary of terms relating to cement concrete: Part 4 Types of concrete

IS 6461(Part 5):1972 Glossary of terms relating to cement concrete: Part 5 Formwork for concrete

IS 6461(Part 6):1972 Glossary of terms relating to cement concrete: Part 6 Equipment, tools and plant

IS 6461(Part 7):1973 Glossary of terms relating to cement concrete: Part 7 Mixing, laying, compaction, curing and other construction aspects

IS 6461(Part 8):1973 Glossary of terms relating to cement concrete

IS 6461(Part 9):1972 Glossary of terms relating of cement concrete:Part 9 Structural aspects

IS 6461(Part 10):1973 Glossary of terms relating to cement concrete:Part 10 Tests and testing apparatus

IS 6461(Part 11):1973 Glossary of terms relating to cement concrete: Part 11 Prestressed concrete

IS 6461(Part 12):1973 Glossary of terms relating to cement concrete: Part 12 Miscellaneous

IS 6491:1972 Method of sampling fly ash

IS 6909:1990 Specification for supersulphated cement

IS 6925:1973 Methods of test for determination of water soluble chlorides in concrete admixtures

IS 7246:1974 Recommendations for use of table vibrators for consolidating concrete

IS 7320:1974 Specification for concrete slump test apparatus

IS 7325:1974 Specification for apparatus for determining constituents of fresh concrete

IS 7861(Part 1):1975 Code of practice for extreme weather concreting: Part 1 Recommended practice for hot weather

IS 7861(Part 2):1981 Code of practice for extreme weather concreting:Part 2 Recommended practice for cold weather concreting

IS 8041:1990 Specification for rapid hardening Portland cement

IS 8042:1989 Specification for white Portland cement

IS 8043:1991 Specification for hydrophobic Portland cement

IS 8112:1989 Specification for 43 grade ordinary Portland

IS 8125:1976 Dimensions and materials of cement rotary kilns, components and auxiliaries (dry process with
suspension preheater)

IS 8142:1976 Method of test for determining setting time of concrete by penetration resistance

IS 8229:1986 Specification for oil-well cement

IS 8425:1977 Code of practice for determination of specific surface area of powders by air permeability

IS 9012:1978 Recommended practice for shotcreting

IS 9013:1978 Method of making, curing and determining compressive strength of accelerated cured
concrete test specimens

IS 9103:1999 Specification for admixtures for concrete

IS 9142:1979 Specification for artificial light weight aggregates for concrete masonry units

IS 9284:1979 Method of test for abrasion resistance of concrete

IS 9376:1979 Specification for apparatus for measuring aggregate crushing value and ten percent fines

IS 9377:1979 Specification for apparatus for aggregate impact

IS 9399:1979 Specification for apparatus for flexural testing of concrete

IS 9459:1980 Specification for apparatus for use in measurement of length change of hardened cement paste, mortar and concrete

IS 9799:1981 Specification for pressure meter for determination of air content of freshly mixed concrete

IS 10070:1982 Specification for machine for abrasion testing of coarse aggregates

IS 10078 :1982 Specification for jolting apparatus for testing

IS 10079:1982 Specification for cylindrical metal measures for use in tests of aggregates and concrete

IS 10080:1982 Specification for vibration machine for casting Oct standard cement mortar cubes

IS 10086:1982 Specification for moulds for use in tests of cement and concrete

IS 10262:2009 Guidelines for concrete mix proportioning

IS 10510:1983 Specification for vee-bee consistometer

IS 10850:1984 Specification for apparatus for measurement of water retentivity of masonry cement

IS 10890:1984 Specification for planetary mixer used in tests of cement and pozzolana

IS 11262:1985 Specification for calorimeter for determination of heat of hydration of hydraulic cement

IS 11263:1985 Specification for cylinder measures for determination of air content of hydraulic cement

IS 11578:1986 Method for determination of specific surface area of powder and porous particle using low
temperature gas absorption techniques

IS 11993:1987 Code of practice for use of screed board concrete vibrators

IS 12089:1987 Specification for granulated slag for manufacture of Portland slag cement

IS 12119:1987 General requirements for pan mixers for concrete

IS 12269:1987 Specification for 53 grade ordinary Portland

IS 12303:1987 Criteria for design of RCC hinges Dec

IS 12330:1988 Specification for sulphate resisting Portland

IS 12423:1988 Method for colorimetric analysis of hydraulic

IS 12600:1989 Specification for low heat Portland cement

IS 12803:1989 Methods of analysis of hydraulic cement by X-ray fluorescence spectrometer

IS 12813:1989 Method of analysis of hydraulic cement by atomic absorption spectrophotometer

IS 12870:1989 Methods of sampling calcined clay pozzolana

IS 13311(Part 1):1992 Methods of non-destructive testing of concrete: Part 1 Ultrasonic pulse velocity

IS 13311(Part 2):1992 Methods of non-destructive testing of concrete: Part 2 Rebound hammer

IS 14345:1996 Specification for autoclave apparatus

IS 14687:1999 Guidelines for falsework for concrete structures

IS 14858:2000 Requirements for compression testing machine used for testing of concrete and mortar

IS 14959(Part 1):2001 Method of test for determination of water soluble and acid soluble chlorides in mortar and concrete:Part 1 Fresh mortar and concrete

IS 14959(Part 2):2001 Method of test for determination of water soluble and acid soluble chlorides in mortar and concrete:Part 2 Hardened mortar and concrete

IS 15388:2003 Silica fume – Specification

Top 10 Job Interview Mistakes

When you finally do sit down to interview with a prospective employer and you are really, sincerely interested in working for them, then it is important for you to be prepared to handle every facet of the job interview. If you can focus yourself on the most important facets of the initial employment interview with a company that you are serious about working for, then you should be able to relax yourself, as well as to be more in control of the message that you are trying to send to the prospective employer.

By now you should have a pretty basic idea of the biggest and most critical
mistakes that need to be avoided in your initial job interview if you want to be successful in proving to the interviewer that you are the best candidate for the job. There is an art to job interviews, and by taking the tips and information in this report seriously, you have already taken positive steps to mastering this excellent art. Once you learn how to master job interviews, you will not have trouble securing any job or position that you want. By avoiding these ten critical mistakes, you can launch yourself forward, proving that you are the right candidate for the job rather than making a fatal mistake that will cost you the job of your dreams. It may be surprising how easily a handful of small mistakes could affect your job interview success in some pretty serious ways. If you are serious about the job that you are applying for, and you really want to stand out as a positive and memorable candidate, then it is absolutely vital that you avoid these ten critical mistakes.

There are ten critical mistakes that need to be avoided if you want to be successful in the job interview process.

01 – Inadequate Preparation for the Interview – Show up to your interview with the right preparation. Research the company and the job that you are applying for long before you leave for your interview.
02 – Arriving Too Early or Too Late – The best way to arrive to your interview is to show up ten to fifteen minutes early. Arriving too early or too late can seriously hurt your chances of job interview success.
03 – Having the Wrong Attitude – Your attitude says a lot about how serious you are about the job and the job interview. Have the right attitude and avoid verbal and non-verbal cues that you are distracted or that your heart is not truly in the interview.
04 – Being Unprepared for Interview Questions – Most interviewers ask very similar questions which means that you can prepare yourself a great deal before you walk in to your interview. Practice your answers to the tougher interview questions and you will have better luck answering them in the interview.
05 – Not Asking the Right Questions – At the end of most interviews, the person who is interviewing you will ask “Do you have any questions for me?” You need to be prepared to ask questions that are relevant to the job in question.

06 – Dressing Inappropriately – While most people think they have a good idea of what interview dress is like, many are wrong. It would be advisable for you to scope out the work place beforehand so that you can dress appropriately before you arrive.
07 – Asking about Salary or Benefits – There are a number of questions that you should absolutely refuse to bring up during the interview process, one of which relates to salary and benefits which should not be brought up until a job offer is on the table.
08 – Not Arriving with the Right Documents – Preparing yourself with the right documents, including work samples, references, referrals, recommendations and copies of your curriculum vitae or resume is vital to being ready for an interview and showing your interviewer that you are serious about the job.
09 – Being Dishonest or Impolite – Attitude is everything. Be honest, be polite, and give your prospective employer a good impression of who you are. After all, your interviewer may very well be your future boss!
10 – Marketing Yourself Incorrectly – Job interviews are all about marketing yourself right. Sell your skills, talents and hobbies and make yourself memorable and you will go far. The more memorable you are, the more you will stand out from other candidates who are trying to get the same job that you are interested in. Stand out from the crowd in your interview, and you truly will go far.

You truly are on your way to mastering the art of the successful job interview! The more you practice in front of a mirror, the more you will be able to fine tune your ability to answer questions properly, to ask questions well, to eliminate negative habits or negative attitudes, and to create an appearance that is visually appealing to your prospective employer while giving them the impression that you are an excellent candidate for whatever job you are applying for. By avoiding these ten critical mistakes in your initial job interview, you will have much greater success in your interviews, it’s that simple. Good luck!

The Girder: A Support Beam used in construction

A girder is a support beam used in construction. Girders often have an I-beam cross section for strength, but may also have a box shape, Z shape or other forms. Girder is the term used to denote the main horizontal support of a structure which supports smaller beams. A girder is commonly used many times in the building of bridges, and planes.

The Warren type girder combines strength with economy of materials and can therefore be relatively light. Patented in 1848 by its designers James Warren and Willoughby Theobald Monzani, its structure consists of longitudinal members joined only by angled cross-members, forming alternately inverted equilateral triangle-shaped spaces along its length, ensuring that no individual strut, beam, or tie is subject to bending or torsional straining forces, but only to tension or compression. It is an improvement over the Neville truss which uses a spacing configuration of isosceles triangles.

Five Steps to check the quality of cement at Site?

1) insert your hand in cement it should give cool feeling
not warm(moisture content).

2)it should not content any lumps or dust

3)it should be green color

4)take pinch of cement rubbed between fingers it should
give smooth finish(feeling).

5)take handful of cement and throw it into bucket full of
water it should float on the surface of water for some time.

What is the allowable Silt Percentage in Sand?

The excessive presence of silt in the sand reduces the bonding between cement and aggregates. It increases water demand for concrete. This reduces the strength of the concrete.

 

It also modifies the setting times of concrete. It can cause cracks in hardened concrete. Hence, silt content is undesirable in the sand. Here is a simple method to find out the silt content in sand.

 

The permissible limit of silt content

The silt content should be less than 8 % by volume.

 

What to do if silt content is more than the allowable limit?

The sand having silt content more than 8 %, should not be used in concrete. However, the sand can be used after washing. It brings the sand content below the permissible limit.

 

Frequency of Testing of silt content

The silt content should be tested daily and once for each truck at the time of unloading at sites.

What is Retaining wall in Construction?

A Retaining Wall is a structure designed and constructed to resist the lateral pressure of soil when there is a desired change in ground elevation that exceeds the angle of repose of the soil. The basement wall is thus one form of retaining wall.

However, the term is most often used to refer to a cantilever retaining wall, which is a freestanding structure without lateral support at its top

Typically retaining walls are cantilevered from a footing extending up beyond the grade on one side and retaining a higher level grade on the opposite side. The walls must resist the lateral pressures generated by loose soils or, in some cases, water pressures.

The most important consideration in proper design and installation of retaining walls is to recognize and counteract the fact that the retained material is attempting to move forward and downslope due to gravity. This creates lateral earth pressure behind the wall which depends on the angle of internal friction (phi) and the cohesive strength (c) of the retained material, as well as the direction and magnitude of movement the retaining structure undergoes.

Lateral earth pressures are zero at the top of the wall and - in homogenous ground - increase proportionally to a maximum value at the lowest depth. Earth pressures will push the wall forward or overturn it if not properly addressed. Also, any groundwater behind the wall that is not dissipated by a drainage system causes hydrostatic pressure on the wall. The total pressure or thrust may be assumed to act at one-third from the lowest depth for lengthwise stretches of uniform height.

Unless the wall is designed to retain water, It is important to have proper drainage behind the wall in order to limit the pressure to the wall's design value. Drainage materials will reduce or eliminate the hydrostatic pressure and improve the stability of the material behind the wall. Drystone retaining walls are normally self-draining.

As an example, the International Building Code requires retaining walls to be designed to ensure stability against overturning, sliding, excessive foundation pressure and water uplift; and that they be designed for a safety factor of 1.5 against lateral sliding and overturning

What is Theodolite? and its Usage?

A theodolite is a precision instrument for measuring angles in the horizontal and vertical planes. Theodolites are mainly used for surveying applications, and have been adapted for specialized purposes in fields like meteorology and rocket launch technology. A modern theodolite consists of a movable telescope mounted within two perpendicular axes — the horizontal or trunnion axis, and the vertical axis. When the telescope is pointed at a target object, the angle of each of these axes can be measured with great precision, typically to seconds of arc.
Transit refers to a specialized type of theodolite developed in the early 19th century. It featured a telescope that could "flip over" ("transit the scope") to allow easy back-sighting and doubling of angles for error reduction. Some transit instruments were capable of reading angles directly to thirty seconds. In the middle of the 20th century, "transit" came to refer to a simple form of theodolite with less precision, lacking features such as scale magnification and micrometers. Although precise electronic theodolites have become widespread tools, the transit still finds use as a lightweight tool on construction sites. Furthermore, the Brunton Pocket Transit, commonly employed for field measurements by geologists and archaeologists, has been in continuous use since 1894. Some types of transits do not measure vertical angles.

The Burj Khalifa, tallest Skyscrapper.

Burj Khalifa known as Burj Dubai prior to its inauguration, is a skyscraper in Dubai, United Arab Emirates, and is currently the tallest man-made structure ever built, at 828 m (2,717 ft). Construction began on 21 September 2004, with the exterior of the structure completed on 1 October 2009. The building officially opened on 4 January 2010, and is part of the new 2 km2 (490-acre) flagship development called Downtown Dubai at the 'First Interchange' along Sheikh Zayed Road, near Dubai's main business district.

What is Contour Line's?

A contour line (also isoline or isarithm) of a function of two variables is a curve along which the function has a constant value. In cartography, a contour line (often just called a "contour") joins points of equal elevation (height) above a given level, such as mean sea level. A contour map is a map illustrated with contour lines, for example a topographic map, which thus shows valleys and hills, and the steepness of slopes. The contour interval of a contour map is the difference in elevation between successive contour lines.

Tips on e-mailing resumes

Tips on e-mailing - from my Experience

an HR who receives thousands of resumes daily

Today sending resumes through e-mails is the most effective & fastest way
of job hunting. If you notice your resume getting rejected frequently and
inadequate responses to your emails, go through the following ten tips to
increase the effectiveness of your resume.

1. While applying for a job, as far as possible try to put the company's
mailID in the 'TO' column instead of keeping it in the 'CC' or
'BCC' column.

2. Do not keep any other company's mailID in the 'CC' of the same
mail.

3. If necessary you can keep your own mailID in the 'CC' of the same
mail.

4. While sending resumes to many E-mail Ids at the same time, keep all the
addresses in the 'BCC' of the mail which will not be visible for the
recipients. Also put your own mailID in the 'TO' column.

5. You can paste your resume in the mail Text or can be attached as a document
unless it is specifically mentioned.

6. While applying for any company's notifications, do follow the
instructions word by word.

7. When you are asked to write any particular 'subject line', write
exactly what is being asked to do. This is Very very important because today all
the mail boxes are attacked by spam & virus mails and the recipient will be
filtering your mails automatically/manually based on the mail subject only.

For eg. When you are asked to write the subject 'Software
Engineer-Bangalore", write exactly that and do not write "I am
applying for the post of Software Engineer - Bangalore"

8. Also try to write the important part of your subject at the beginning
because in the recipient's mail box the longest subjects will be truncated
and only the first part will be displayed.

For eg. Instead of writing 'My Freshersworld.com registration no. is
cse12345' try writing 'cse12345 - Freshersworld.com Registration
no.'. Please note here that the company will be looking only for your
registration no. and it is better if you write just " cse12345 ".

9. Pls note that all your casual mails with the subject ' Freshers
Resume' or 'Registration details' will be summarily deleted and do
not spend time on sending such mails where the notification asks you to put
specific 'subject'.

10. Do not send the mail 3 or 4 times in order to make sure it reaches
correctly which may irritate the recipient. Instead, in the first mail itself
put your own mailID in the 'BCC' and check if the mail is received
properly.

What is Construction Estimating?

The preparation of estimates represents one of the most important functions performed in any business enterprise. In the construction industry, the quality of performance of this function is paramount to the success of the parties engaged in the overall management of capital expenditures for construction projects.

The estimating process, in some form, is used as soon as the idea for a project is conceived. Estimates are prepared and updated continually as the project scope and definition develops and, in many cases, throughout construction of the project or facility.

The parties engaged in delivering the project continually ask themselves “What will it cost?” To answer this question, some type of estimate must be developed. Obviously, the precise answer to this question cannot be determined until the project is completed. Posing this type of question elicits a finite answer from the estimator. This answer, or estimate, represents only an approximation or expected value for the cost. The eventual accuracy of this approximation depends on how closely the actual conditions and specific details of the project match the expectations of the estimator.

Extreme care must be exercised by the estimator in the preparation of the estimate to subjectively

weigh the potential variations in future conditions. The estimate should convey an assessment of the

accuracy and risks.

 

Estimating Defined

Estimating is a complex process involving collection of available and pertinent information relating to the scope of a project, expected resource consumption, and future changes in resource costs. The process involves synthesis of this information through a mental process of visualization of the constructing process for the project. This visualization is mentally translated into an approximation of the final cost.

Estimating at any stage of the project cycle involves considerable effort to gather information. The estimator must collect and review all of the detailed plans, specifications, available site data, available resource data (labor, materials, and equipment), contract documents, resource cost information, pertinent government regulations, and applicable owner requirements. Information gathering is a continual process by estimators due to the uniqueness of each project and constant changes in the industry environment. Unlike the production from a manufacturing facility, each product of a construction firm represents a prototype. Considerable effort in planning is required before a cost estimate can be established. Most of the effort in establishing the estimate revolves around determining the approximation of the cost to produce the one-time product.

The estimator must systematically convert information into a forecast of the component and collective costs that will be incurred in delivering the project or facility. This synthesis of information is accomplished by mentally building the project from the ground up. Each step of the building process should be accounted for along with the necessary support activities and embedded temporary work items required for completion.

The estimator must have some form of systematic approach to ensure that all cost items have been

incorporated and that none have been duplicated. Later in this chapter is a discussion of alternate

systematic approaches that are used.

The quality of an estimate depends on the qualifications and abilities of the estimator. In general, an

estimator must demonstrate the following capabilities and qualifications:

• Extensive knowledge of construction

• Knowledge of construction materials and methods

• Knowledge of construction practices and contracts

• Ability to read and write construction documents

• Ability to sketch construction details

• Ability to communicate graphically and verbally

• Strong background in business and economics

• Ability to visualize work items

• Broad background in design and code requirements

What is Form Work Technology? What are the advantages of Form Work Technology?

We know about the traditional ways of construction and we should start the construction work of the next slab after completing the previous one. We can construct the slabs, pillars and other things at a time in the form work construction. We can construct the slabs every week and there is no need to wait for the completion of the curing. This is mostly popular in Korea.

The quality and finishing of the slabs, pillars and walls will be good as the shuttering works are done with the aluminum plates. As the rendering is done, the surface will be formed very nicely.
It is very easy to take the shuttering items from one floor to another floor.
The wiring and the plumbing works are done after the concrete works but they are started earlier.
There won’t be mistakes in the construction works and there is no need of the plastering works or the walls. There is no need of more number of workers and the scrap is less.

Design and Construction of Concrete Formwork

Design and Construction of Concrete Formwork

Concrete formwork serves as a mold to produce concrete elements having a desired size and configuration. It is usually erected for this purpose and then removed after the concrete has cured to a satisfactory strength. In some cases, concrete forms may be left in place to become part of the permanent structure. For satisfactory performance, formwork must be adequately strong and stiff to carry the loads produced by the concrete, the workers placing and finishing the concrete, and any equipment or materials supported by the forms. For many concrete structures, the largest single component of the cost is the formwork. To control this cost, it is important to select and use concrete forms that are well suited for the job. In addition to being economical, formwork must also be constructed with sufficient quality to produce a finished concrete element that meets job specifications for size, position, and finish. The forms must also be designed, constructed, and used so that all safety regulations are met.

Formwork costs can exceed 50% of the total cost of the concrete structure, and formwork cost savings should ideally begin with the architect and engineer. They should choose the sizes and shapes of the elements of the structure, after considering the forming requirements and formwork costs, in addition
to the usual design requirements of appearance and strength. Keeping constant dimensions from floor to floor, using dimensions that match standard material sizes, and avoiding complex shapes for elements in order to save concrete are some examples of how the architect and structural engineer can reduce forming costs.

TRANSPORTATION ENGINEERING – II Question Paper- Sample

B.E. / B.Tech. DEGREE EXAMINATION, APRIL / MAY 2004
Sixth Semester
Civil Engineering
CE338 – TRANSPORTATION ENGINEERING – II
(Model Question Paper)

Time : Three hours Maximum : 100 Marks

Answer ALL questions
Part – A (10 x 2 = 20 Marks)

1. State the role of railways in economic development of the nation.
2. What are the components of permanent way?
3. What do you understand by creep in rails? State any two of its impact.
4. What do you mean by Track-circuiting?
5. List the different types of airport parking systems.
6. Write different systems of aircraft parking adjacent to terminal building.
7. State any two factors which necessitate the navigational aids in water transport.
8. Compare the warehouse and transit sheds in terms of their purpose and location.
9. What is meant by BOT concept?
10. How net present value (NPV) is defined?

Part – B (5 x 16 = 80 Marks)

11. (a) Define the two measures of benefit cost ratio and evaluate the Benefit Cost Ratio
criteria. (6)

(b) The cash flow stream of a project is given below.
Year Cash flow in Rs.
0 -8000
1 +2000
2 –1000
3 +10,000
4 +2000

Calculate the internal rate of return. (10)

12. (a) (i) Describe in detail the different types of surveys to be carried out in case of new
railway project. (10)

(ii) What are the factors on which the speed of the trains on curves depend? Write the
formulae that are generally employed in Indian Railways to find the speed of trains
on broad gauge, metre gauge and narrow gauge. (6)

(OR)

(b) Explain the following of any four, with sketches if necessary. (4x4=16)

(i) Gradient
(ii) Super elevation
(iii) Widening of gauges in curves
(iv) Grade compensation
(v) Transition curves
(vi) Coning of wheels


13. (a) Draw a neat diagram of a simple right-hand turn out and show its various components. Explain the working principles of the turnout. (16)

(OR)

(b) Define interlocking and explain the principles if interlocking. Describe the various mechanical devices used for interlocking. (16)


14. (a) (i) Describe the factors that influence the selection of site of an airport. (10)
(ii) What are the functions of ICAO and its structure? (6)

(OR)



(b) Following are the average wind data for an airport site, for the wind intensity is above 6Kmph. Draw a wind rose diagram and determine the best orientation of runway. Determine the percentage of time in a year during which the runway can be used for flights. (16)

Wind Direction % time Wind Direction % time Wind Direction % time Wind Direction % time
N 6.6 E 1.8 S 7.7 W 3.9
NNE 10.3 ESE 0.9 SSW 14.3 WNW 0.5
NE 8.1 SE 0.4 SW 10.6 NW 0.3
ENE 3.1 SSE 4.1 WSW 5.7 NNW 4.2


15. (a) (i) What are the requirements of good ports? Briefly describe the classification and the
components of harbours. (10)
(ii) Describe the following: (2 x 3 = 6)
1. Mooring and Mooring accessories 2. Navigational aids
(OR)
(b) Explain with neat sketches, the functions and working principles of the following.
(4 x 4 = 16)
(i) Jetties (ii) Landing stages (iii) Spring fenders (iv) Dolphins.

STRUCTURAL DESIGN Question Paper- Sample

B.E / B.Tech. DEGREE EXAMINATION, APRIL / MAY 2004
Sixth Semester
Civil Engineering
CE337 – STRUCTURAL DESIGN – II
(Model Question Paper)

Time : Three hours Maximum : 100 Marks

Answer ALL questions
Use M20 concrete and Fe 415 steel for all problems
Part – A (10 x 2 = 20 marks)

1. Define moment of resistance.
2. What are the three factors must be considered while designing a water retaining structure?
3. Distinguish between characteristic strength and design strength.
4. What are the magnitudes of crack width allowed in concrete structures for various environments?
5. What are the effects of shear in RC beams?
6. Distinguish between flexural bond and anchorage bond.
7. Define Slenderness ratio of column. How columns are classified based on this ratio?
8. Distinguish between braced and unbraced column.
9. Under what circumstances is a trapezoidal shape preferred to a rectangular shape for a two column combined footing?
10. Define cavity wall and shear wall.

Part – B (5 x 16 = 80 marks)

11. (i) What are the advantages of limit state method over other methods? (4)
(ii) Design a RC rectangular beam by working stress method for a simply supported span of 5m and carrying a superimposed load of 20 kN/m inclusive of its self weight. Take width of beam as 300 mm. (12)

12. (a) (i) What are the assumptions made in analysis and design of flexural members for Limit state of collapse? (4)
(ii) Design a T-beam by Limit state approach for a span of 6m simply supported a their ends by 300mm. The beams are spaced at 3.5m centre to centre. The live load on the slab is 3 kN/m2. (12)

(OR)

(b) (i) Write the design procedure for deflection control of beams. (4)
(ii) Design a two way slab of 2m x 3m by Limit state method, simply supported on all four sides. The thickness of wall is 200mm. The corners of the slab are not held down. It has to carry a characteristic live load of 10 kN/m2. (12)

13. (a) (i) What is mean by development length? In what places development length of bars in tension should be checked? (4)
(ii) A T-beam of flange size 700 mm x 120 mm and web size 350 mm x 680 mm is subjected to factored bending moment of 215 kN-m, factored shear of 150 kN and factored torsion of 105 kN-m. Design the reinforcements by using Limit state method. Take cover to centre of steel as 50mm. (12)
(OR)
(b) (i) What is mean by anchorage of steel bars? What are the IS provisions for providing anchorages for shear reinforcement? (4)
(ii) A doubly reinforced simply supported rectangular beam of 250 mm x 450 mm effective size carries a characteristic imposed load of 8 kN/m. The clear span of the beam is 7 m. It is reinforced with 4 numbers of 16mm dia bars in the tension zone and 3 numbers of 16mm dia bars in compression zone throughout its length. Taking partial safety factor as 1.5, design the shear reinforcement. (12)

14. (a) (i) Draw and explain the interaction diagram of columns. (4)
(ii) Design a column of 400 mm x 600 mm size carrying factored load = 1600 kN, factored moment (major axis) = 120 kN-m and factored moment (minor axis) = 90 kN-m. Take d’=60mm. (12)
(OR)
(b) (i) Explain the behaviour of tied column and spiral column subject to axial loading. (4)
(ii) Design a biaxially eccentrically loaded braced rectangular column of size 300 mm x 480 mm subjected to factored axial load of 1000 kN and factored moments of 80 kN-m and 30 kN-m with respect to major and minor axis respectively at the top end. Assume the column is bent in single curvature. Take factored moments with respect to major and minor axis as 110 kN-m and 40 kN-m at the bottom end. The unsupported length of column is 5.8 m and effective length in long and short directions are 5.4m and 4.2m. (12)

15. (a) (i) Explain briefly the load transfer mechanism in two column combined footing. (4)
(ii) Design an isolated footing for a column 300mm x 500 mm reinforced with 6 numbers of 25 mm dia bars subject to a factored axial load of 1000 kN and a factored uniaxial moment of 120 kN-m at the column base. Assume that the moment is reversible. The safe bearing capacity of soil may be taken as 200 kN/m2 at a depth of 1.25 m. (12)
(OR)
(b) (i) Define effective thickness of a wall. How the effective thickness can be taken for solid
walls, cavity walls and cross walls. (4)
(ii) Design an interior brick masonry cross wall of a storey building to carry 100 mm thick RCC slab with 3m ceiling height. The wall is unstiffened and it supports 2.65 m wide slab. Take Live load on roof = 1.5 kN/m2. Live load on floor = 2.0 kN/m2. (12)

ENVIRONMENTAL ENGINEERING Question Paper- Sample

B.E / B. Tech. DEGREE EXAMINATION, APRIL / MAY 2004
Sixth Semester
Civil Engineering
CE 339 – ENVIRONMENTAL ENGINEERING – II
(INCLUDING DRAWING)
(Model Question Paper)
Time : Four hours Maximum : 100 Marks

Answer ALL questions
Part – A (10 x 2 = 20 marks)

1. State the purpose of aeration process.
2. What do you mean by “Terminal velocity gradient (G)”?
3. Define microstraining.
4. State the method of disposal of screenings.
5. What is sutro weir?
6. How do you distinguish between plug flow and completely mixed flow?
7. What do you mean by epilimnion zone in lakes?
8. State the difference between sewage forming and effluent irrigation.
9. State the causes for bulking of sludge in activated sludge process.
10. What do you mean by two stage digestion of sludge?

Part – B (5 x 16 = 80 Marks)

11. (i) Explain the theory of filtration in water purification.
(ii) Distinguish between slow sand rapid sand filters with reference to
a. Rate of filtration
b. Filter media of sand
c. Loss of head
d. Effective size of sand (16)

12. (a) Explain the difference between grit chamber and Detritus tank and describe the
principles involved in the design of grit chamber. (16)

(OR)

(b) How are the stabilization ponds classified? Explain briefly the process of stabilization in
each case. (16)


13. (a) (i) Explain the self purification of streams and indicate how sunlight helps in such
purification? (10)

(ii) Write a brief note on minimum DO content in polluted stream for survival of aquatic
life. (6)
(OR)

(b) What are different stages of sludge digestion. Explain briefly about each stage in the
process of sludge digestion. (16)


14. (a) (i) Design the water depth for a mixing basin having round end baffles in order to
treat 48 million litres/day of water. The tank may be divided into two identical compartments by providing a longitudinal partition wall with each half having clear width of 8m. Assume suitable detention period and flow velocity through the basin. The clear distance between the baffles may be kept as equal to the minimum permissible. Mention the number of channels in the tank and also the overall inside length of the tank. (16)

(OR)

(b) (i) Design a sedimentation tank for a water tank works, which supplies 1.4 x 106 litre/day
to the town. The sedimentation period is 5 hours, the velocity of flow is 12 cm/min,
depth of water in the tank is 4.0 m assuming an allowance for sludge is to be made as
80 cm. (16)


15. (a) Design an activated sludge digester for secondary treatment of 10,000 m3 /day of
municipal wastewater. After primary clarification, the BOD is 150 mg/L, and it is desired to have not more than 5 mg/L of BOD in the effluent. A completely mixed reactor is to be used, and pilot plant analysis has established the following kinetic values; y=0.5kg/kg, kd = 0.05d-1 assuming an MLSS concentration of 3000 mg/L and an up flow concentration of 10,000 mg/L from the secondary clarifier, determine:
(i) The volume of the reactor
(ii) The mass and volume of solids that must be waster each day and
(iii) The recycle ratio. (16)
(OR)

(b) (i) Design the dimensions, required for sludge drying bed for the sludge obtained from
the digestion tank for 40,000 population. (8)
(ii) Design a septic tank for the following data:
No. of people = 100
Sewage / capital / day = 120 litres
Desludging period = 1 year
Length to width ratio = 4:1 (8)

Foundation Eng. Question Paper- Sample

B.E. / B.Tech. DEGREE EXAMINATIONS, APRIL / MAY 2004
Sixth Semester
Civil Engineering
CE340 – FOUNDATION ENGINEERING

(Model Question Paper)

Time : Three hours Maximum : 100 Marks
Answer ALL questions
Part A (10 x 2 = 20 marks)

1. Give the important parameter to fix the significant depth of exploration.
2. Mention the factors that affect the sample disturbance.
3. What are the different types of shear failures? Draw the sketches.
4. Mention the components of settlement of foundation.
5. Differentiate between cantilever footing and raft foundation.
6. List out the methods for design of mat foundation.
7. Under what circumstances the negative skin friction will develop.
8. List out the necessities of pile foundation.
9. State the assumptions made in Rankine’s earth pressure theory.
10. What is the critical height of unsupported vertical cut in case of cohesive soils?

Part B (5 x 16 = 80)

11. Design a strap footing for the two columns. The allowable soil pressure is 100 kN/m2. Load on left column = 600 kN. Load on right column = 1000 kN, size of left column = 0.3m x 0.3m, size of right column = 0.4m x 0.4m, centre to centre distance between columns = 6m. Eccentricity of footing of left column = 1m. Take the allowable soil pressure as 100 kN/m2. Draw BMD and SFD. Find the thickness of footings for the design B.M. (16)

12. (a) Explain the factors governing the spacing, number and depth of bore holes for a
multi-storey building project. (4)
(b) Explain the SPT test with neat sketch and give the correlation between SPT – N values and relative density. (8)

(c) What are the corrections required for SPT-N value? (4)

(OR)

(a) What are the commonly used methods of soil exploration? Explain any one method in detail. (8)
(b) What are the basic requirements of good foundation? (4)
(c) What are the necessary data required for plotting the bore log for any soil investigation project. (4)

13. Calculate the ultimate bearing capacity per unit area of (i) Strip footing 2.5m wide (ii) Square footing 4.75 x 4.75 m (iii) Circular footing 5.25m diameter. The footing is supported on a soil for which the following data is available.  = 19.5 kN/m3 ; C=17.0 kN/m2, =200, depth=1.75 m.
Use Terzhaghi’s equation. Take Nc = 17.7, Nq = 7.5, and Nr = 5.0. (16)

(OR)

A building 10m x 20m in plan is built on a raft foundation resting on the surface. The soil profile consists of 4m dense sand over 3m thick silty clay layer resting on rock. The water table is at 2m below ground level. Consolidation test conducted on UDS of clay layer gave the results as follows.
Initial and final void ratios and corresponding stresses are,
e0 = 1.1; 0’ = 2000 kN/m2; ef = 1.0; f’ = 1000 kN/m2; (16)

14. (a) Classify the pile based on functions, mode of transfer of load and method of
installation with neat sketches. (8)
(b) Explain how do you determine pile load capacity from pile load test. (8)

(OR)

A pile group consists of 9 piles of 30 cm diameter and 10 m length driven in clay. Unconfined compressive strength of soil is 200 kN/m2 and insitu density of soil is 20 kN/m3. Determine the safe load for the pile group.  = 0.6 and F.S. = 3. (16)


15. Determine the active pressure on the retaining wall shown in figure by Culmann’s method. (16)










(OR)

A retaining wall 4m height with smooth backfill and horizontal surface subjected to a surcharge of 36 kN/m2 uniformly. Saturated density of backfill is 18 kN/m3,  = 300, C=0, find the active earth pressure and the point of application of the resultant pressure. (16)

Top Construction Companies

Here is the list of top construction companies in India on the basis of their tie-ups with their international counterparts, technological advancements, generating money from the market to trigger their expansion plans and for establishing an entire township in the wastelands and making it the hottest commercial destination.



Larsen & Toubro:

It is India's biggest construction organization. Supported by its equally proficient allied sectors, the Engineering, Construction and Contracts Division of L&T provides EPC solutions on concept and expenses which could be incurred while performing engineering and infrastructure projects on large scale. L&T's ECC department carry out large scale projects entailing ground-breaking design and wide-ranging construction services ranging from procurement, furnishing, fitting, testing and commissioning. L&T is known for its excellence and timely deliverance. With an annual turnover of Rs 25,000 crore, L&T has more 12,000 skilled professional working for it.

DLF:

DLF's chief business is to develop housing, marketable and retail properties. Currently it has undertaken the development of 70 million sq ft of housing projects which it intends to finish in the next three years. DLF has joined hands with Delhi Development Authority to develop townships in Amritsar, Pune, Gurgaon, Mumbai, Chennai and Goa. DLF has been the construction company behind different malls in Hyderabad, Delhi, Bangalore, Mumbai, Amritsar, Ludhiana, Kochi and Chennai. The company is also developing 50-75 hotels along with Hilton Hotels and infrastructure and SEZ in India in collaboration with Laing O'Rourke (UK).

Tata Projects:

Tata Projects registered an annual turnover of Rs 2,300 crore on July 1, 2007. With more than 1,500 professionals the company has emerged as one of the chief player in EPC projects. Over the last four years, it has attained a CAGR of 50 per cent which quadrupled its annual turnover of 2006-07. Tata Projects functions in concentrated divisions like broadcast and distribution, steel, power production, oil, gas and hydrocarbons and industrial infrastructure through its five strategic business units (SBU)

Gammon India:

With an annual turnover of more than Rs 7,010 crore, Gammon India is famously known as 'Builders to the Nation'. It is the one and only construction firm in India to get an ISO 9001 authorization for its operational sectors in civil engineering and has successfully carried out diverse civil engineering operations some of which include constructing one of the longest river bridge in Asia at Patna across the Ganges and the longest bridge in India across river Jadukata.

Hindustan Construction Company:

The Company has a reputation of performing large-scale infrastructure projects besides developing hi-tech construction equipments. It has carried out a number of challenging and expensive projects in sectors like oil and gas pipeline, power, urban infrastructure, transportation, irrigation and water supply, etc. HCC has also acquired projects in countries like Iraq, Tanzania, Saudi Arabia, Bhutan and Sri Lanka. It was the first Indian firm to execute and sustain an integrated quality administration structure and has an annual turnover of more than Rs 2,394.50 crore.

Sobha Developers Ltd:

With an annual turnover of Rs 1,189 crore, Sobha Developers Ltd was initiated by the now chairman PNC Menon in the year 1995. On June 30, 2007, the company has 3,706 skilled professionals working for it. At present it owns Rs 3,500-acre land in eight Indian cities namely Coimbatore, Bangalore, Mysore, Chennai, Thrissur, Kochi, Pune and Hosur. The company's clientele include some of the top players in IT, hotel and construction sector such as Hewlett Packard, Mico, Infosys, Ramaraju Developers, Dell, Timken, etc.

Shapoorji Pallonji & Co:

The Company has more than 3,500 professionals working for it and is largely driven by its loyalty to consumer satisfaction. Some of the major projects undertaken by Shapoorji Pallonji & Co are World Trade Centre, Mumbai; TELCO industrial complex, Pune; Bhabha Atomic Research Centre, Kalpakkam; HSBC Bank, Mumbai; Hotel Taj Intercontinental, Mumbai; Bank of India, Mumbai; Indira Gandhi International Airport, New Delhi, etc. the company has created magnum opus of construction and has been a consistent executer of challenging projects.

Unitech:

Recently Ramesh Chandra, Unitech's Chairman has declared the investment of $ 720 million by his company in the coming four years to develop 28 hotels along with Marriott International. Its chief activities include construction, expansion of real-estate, consultancy in associated sectors, hotels, electrical broadcast and information technology.

Nagarjuna Construction Company:

The Company has a track record of more than 28 years and is structured in nine business categories including housing, water and environment, irrigation, transportation, oil and gas, electrical, metals, real estate and power. It has an annual turnover of Rs 7,300 crore and plays an active role in developing BOT road projects, seaports, BOOT hydropower projects, etc.

Punj Lloyd:

Crowned as 'all-terrain specialists', Punj Lloyd is one of the biggest Indian engineering construction firms. The company performs its operations in Asia Pacific, China, Middle East, Europe, Africa, South Asia and Caspian. It provides services ranging from engineering to project administration, innovative designs to construction, to eminent clients like Petroleum Development Oman, British Petroleum, Pertamina, Shell, ADNOC, Cairn Energy, etc.

What is Ready-mix concrete? Advantages and Disadvantages?

Ready-mix concrete is a type of concrete that is manufactured in a factory or batching plant, according to a set recipe, and then delivered to a work site, by truck mounted transit mixers . This results in a precise mixture, allowing specialty concrete mixtures to be developed and implemented on construction sites. The first ready-mix factory was built in the 1930s, but the industry did not begin to expand significantly until the 1960s, and it has continued to grow since then.

Ready-mix concrete is sometimes preferred over on-site concrete mixing because of the precision of the mixture and reduced work site confusion. However, using a pre-determined concrete mixture reduces flexibility, both in the supply chain and in the actual components of the concrete.

The leading ready-mix concrete supplier worldwide is the Mexican concrete company Cemex; its main competitor is France-based Lafarge

Ready Mixed Concrete is also referred as the customized concrete products for commercial purpose. the Ready-mix Concrete Company offer different concrete according to user's mix design or industrial standard.

The Ready mixed concrete company is required to equip themselves with up-to-date equipment’, such as transit mixer, concrete pump, and Concrete Batching Plant, which needs visualized production management software and also PLC controller.

Ready Mixed Concrete, or RMC as it is popularly called, refers to concrete that is specifically manufactured for delivery to the customer's construction site in a freshly mixed and plastic or unhardened state. Concrete itself is a mixture of Portland cement, water and aggregates comprising sand and gravel or crushed stone. In traditional work sites, each of these materials is procured separately and mixed in specified proportions at site to make concrete. Ready Mixed Concrete is bought and sold by volume - usually expressed in cubic meters. RMC can be custom-made to suit different applications.

Ready Mixed Concrete is manufactured under computer-controlled operations and transported and placed at site using sophisticated equipment and methods. RMC assures its customers numerous benefits.

Advantages of Ready mix Concrete over Site mix Concrete

§  A centralized concrete batching plant can serve a wide area.

§  The plants are located in areas zoned for industrial use, and yet the delivery trucks can service residential districts or inner cities.

§  Better quality concrete is produced.

§  Elimination of storage space for basic materials at site.

§  Elimination of procurement / hiring of plant and machinery

§  Wastage of basic materials is avoided.

§  Labor associated with production of concrete is eliminated.

§  Time required is greatly reduced.

§  Noise and dust pollution at site is reduced.

§  Reduce cost.

§   

Disadvantages of Ready-Mix Concrete

§  The materials are batched at a central plant, and the mixing begins at that plant, so the traveling time from the plant to the site is critical over longer distances. Some sites are just too far away, though this is usually a commercial rather than technical issue.

§  Generation of additional road traffic; furthermore, access roads, and site access have to be able to carry the weight of the truck and load. Concrete is approx. 2.5tonne per m³. This problem can be overcome by utilizing so-called 'minimix' companies, using smaller 4m³ capacity mixers able to access more restricted sites.

§  Concrete's limited timespan between mixing and going-off means that ready-mix should be placed within 90 minutes of batching at the plant.

 

Aggregate

Aggregate is the component of a composite material that resists compressive stress and provides bulk to the composite material. For efficient filling, aggregate should be much smaller than the finished item, but have a wide variety of sizes. For example, the particles of stone used to make concrete typically include both sand and gravel.

Comparison to fiber composites

Aggregate composites tend to be much easier to fabricate, and much more predictable in their finished properties, than fiber composites. This is because fiber orientation and continuity can have an overwhelming effect, but can be difficult to control and assess. Fabrication aside, aggregate materials themselves also tend to be less expensive; the most common aggregates (mentioned above) are found in nature and can often be used with only minimal processing.

Not all composite materials include aggregate in their design. This is because aggregate particles tend to have about the same dimensions in every direction (that is, an aspect ratio of about one), so that aggregate composites do not display the level of synergy that fiber composites often do. A strong aggregate held together by a weak matrix will be weak in tension, whereas fibers can be less sensitive to matrix properties, especially if they are properly oriented and run the entire length of the part (i.e., a continuous filament).

Most composites are filled with particles whose aspect ratio lies somewhere between oriented filaments and spherical aggregates. A good compromise is chopped fiber, where the performance of filament or cloth is traded off in favor of more aggregate-like processing techniques. Ellipsoid and plate-shaped aggregates are also usededit] Aggregate properties

In most cases, the ideal finished piece would be 100% aggregate. A given application's most desirable quality (be it high strength, low cost, high dielectric constant, or low density) is usually most prominent in the aggregate itself; all the aggregate lacks is the ability to flow on a small scale, and form attachments between particles. The matrix is specifically chosen to serve this role, but its abilities should not be abused.

Aggregate size

Experiments and mathematical models show that more of a given volume can be filled with hard spheres if it is first filled with large spheres, then the spaces between (interstices) are filled with smaller spheres, and the new interstices filled with still smaller spheres as many times as possible. For this reason, control of particle size distribution can be quite important in the choice of aggregate; appropriate simulations or experiments are necessary to determine the optimal proportions of different-sized particles.

The upper limit to particle size depends on the amount of flow required before the composite sets (the gravel in paving concrete can be fairly coarse, but fine sand must be used for tile mortar), whereas the lower limit is due to the thickness of matrix material at which its properties change (clay is not included in concrete because it would "absorb" the matrix, preventing a strong bond to other aggregate particles). Particle size distribution is also the subject of much study in the fields of ceramics and powder metallurgy.

Some exceptions to this rule include:

Toughened composites

Toughness is a compromise between the (often contradictory) requirements of strength and plasticity. In many cases, the aggregate will have one of these properties, and will benefit if the matrix can add what it lacks. Perhaps the most accessible examples of this are composites with an organic matrix and ceramic aggregate, such as asphalt concrete ("tarmac") and filled plastic (i.e., Nylon mixed with powdered glass), although most metal matrix composites also benefit from this effect. In this case, the correct balance of hard and soft components is necessary or the material will become either too weak or too brittle.

Nanocomposites

Many materials properties change radically at small length scales (see nanotechnology). In the case where this change is desirable, a certain range of aggregate size is necessary to ensure good performance. This naturally sets a lower limit to the amount of matrix material used.

Unless some practical method is implemented to orient the particles in micro- or nano-composites, their small size and (usually) high strength relative to the particle-matrix bond allows any macroscopic object made from them to be treated as an aggregate composite in many respects.

While bulk synthesis of such nanoparticles as carbon nanotubes is currently too expensive for widespread use, some less extreme nanostructured materials can be synthesized by traditional methods, including electrospinning and spray pyrolysis. One important aggregate made by spray pyrolysis is glass microspheres. Often called microballoons, they consist of a hollow shell several tens of nanometers thick and approximately one micrometer in diameter. Casting them in a polymer matrix yields syntactic foam, with extremely high compressive strength for its low density.

Many traditional nanocomposites escape the problem of aggregate synthesis in one of two ways:

Natural aggregates: By far the most widely-used aggregates for nano-composites are naturally occurring. Usually these are ceramic materials whose crystalline structure is extremely directional, allowing it to be easily separated into flakes or fibers. The nanotechnology touted by General Motors for automotive use is in the former category: a fine-grained clay with a laminar structure suspended in a thermoplastic olefin (a class which includes many common plastics like polyethylene and polypropylene). The latter category includes fibrous asbestos composites (popular in the mid-20th century), often with matrix materials such as linoleum and Portland cement.

In-situ aggregate formation: Many micro-composites form their aggregate particles by a process of self-assembly. For example, in high impact polystyrene, two immiscible phases of polymer (including brittle polystyrene and rubbery polybutadiene) are mixed together. Special molecules (graft copolymers) include separate portions which are soluble in each phase, and so are only stable at the interface between them, in the manner of a detergent. Since the number of this type of molecule determines the interfacial area, and since spheres naturally form to minimize surface tension, synthetic chemists can control the size of polybutediene droplets in the molten mix, which harden to form rubbery aggregates in a hard matrix. Dispersion strengthening is a similar example from the field of metallurgy. In glass-ceramics, the aggregate is often chosen to have a negative coefficient of thermal expansion, and the proportion of aggregate to matrix adjusted so that the overall expansion is very near zero. Aggregate size can be reduced so that the material is transparent to infrared light.