ABSTRACT
Over 300 million tones of industrial wastes are being produced per annum by chemical and agricultural process in India. These materials pose problems of disposal and health hazards. The wastes like phosphogypsum, fluorogypsum and red mud contain obnoxious impurities which adversely affect the strength and other properties of building materials based on them. Out of several wastes being produced at present, the use of phosphogypsum, flurogypsum, lime sludge, hypo sludge, red mud, and mine tailing is of paramount significance to protect the environment.

Paper making generally produces a large amount of solid waste. Paper fibers can be recycled only a limited number of times before they become too short or weak to make high quality paper. It means that the broken, low- quality paper fibers are separated out to become waste sludge. All the inks, dyes, coatings, pigments, staples and “stickies” (tape, plastic films, etc.) are also washed off the recycled fibers to join the waste solids. The shiny finish on glossy magazine-type paper is produced using a fine kaolin clay coating, which also becomes solid waste during recycling. This paper mill sludge consumes a large percentage of local landfill space for each and every year. Worse yet, some of the wastes are land spread on cropland as a disposal technique, raising concerns about trace contaminants building up in soil or running off into area lakes and streams. Some companies burn their sludge in incinerators, contributing to our serious air pollution problems. To reduce disposal and pollution problems emanating from these industrial wastes, it is most essential to develop profitable building materials from them. Keeping this in view, investigations were undertaken to produce low cast concrete by blending various ratios of cement with hypo sludge.

This project is concerned with experimental investigation on strength of concrete and optimum percentage of the partial replacement by replacing cement via 10%, 20%, 30%, 40%, 50%, 60% and 70% of Hypo Sludge.

Keywords: Hypo Sludge, Pozzolanic Property, supplementary cementitious materials.

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Introduction to Pre Engineered Buildings

Technological improvement over the year has contributed immensely to the enhancement of quality of life through various new products and services. One such revolution was the pre engineered buildings. Through its origin can be traced back to 1960’s its potential has been felt only during the recent years. This was mainly due to the development in technology, which helped in computerizing the design and design.

Though initially only off the shelf products were available in these configurations aided by the technological development tailor made solutions are also made using this technology in very short durations. A recent survey by the Metal Building Associations (MBMA) shows that about 60% of the non residential low rises building in USA are pre engineered buildings.

Although PEB systems are extensively used in industrial and many other non residential constructions world wide, it is relatively a new concept in India. These concepts were introduced to the Indian markets lately in the late 1990’s with the opening up of the economy and a number of multi nationals setting up their projects.The market potential of PEB’s is 1.2 million tones per annum. The current pre engineered steel building manufacturing capacity is 0.35 million tones per annum. The industry is growing at the compound rate of 25 to 30 %.

With respect to design of the structure and aesthetic appearance India is way behind. Indian manufacturers are trying to catch up; comparatively PEB’s is a new concept in India. Beside, in fabrication and other areas of PEB India is very good. As compared to other countries Indian codes for building design are stringent but safer. IS standards are upgraded continuously. In India, American codes are also followed. Continue Reading »

Here is the project report of a civil engineering student who has spent 6 months on a training site.Due to security reasons,the project details, estimation, some portion of design and quantity calculations have been omitted.But to help the civil engineering students we had shown all the necessary works..

Sequence of Structure Work

1) Site Clearance

2) Demarcation of Site

3) Positioning of Central coordinate ie (0,0,0) as per grid plan

4) Surveying and layout

5) Excavation

6) Laying of PCC

7) Bar Binding and placement of foundation steel

8 ) Shuttering and Scaffolding

9) Concreting

10) Electrical and Plumbing

11) Deshuttering

12) Brickwork

13) Doors and windows frames along with lintels

14) Wiring for electrical purposes

15) Plastering

16) Flooring and tiling work

17) Painting

18) Final Completion and handing over the project

Construction Process And Materials Used

Site Clearance- The very first step is site clearance which involves removal of grass and vegetation along with any other objections which might be there in the site location.

Demarcation of Site- The whole area on which construction is to be done is marked so as to identify the construction zone. In our project, a plot of 450*350 sq ft was chosen and the respective marking was done.

Positioning of Central coordinate and layout- The centre point was marked with the help of a thread and plumb bob as per the grid drawing. With respect to this center point, all the other points of columns were to be decided so its exact position is very critical.

Excavation

Excavation was carried out both manually as well as mechanically. Normally 1-2 earth excavators (JCB’s) were used for excavating the soil. Adequate precautions are taken to see that the excavation operations do not damage the adjoining structures. Excavation is carried out providing adequate side slopes and dressing of excavation bottom. The soil present beneath the surface was too clayey so it was dumped and was not used for back filling. The filling is done in layer not exceeding 20 cm layer and than its compacted. Depth of excavation was 5’4” from Ground Level.

PCC – Plain Cement Concrete

After the process of excavation, laying of plain cement concrete that is PCC is done. A layer of 4 inches was made in such a manner that it was not mixed with the soil. It provides a solid bas for the raft foundation and a mix of 1:5:10 that is, 1 part of cement to 5 parts of fine aggregates and 10 parts of coarse aggregates by volume were used in it. Plain concrete is vibrated to achieve full compaction. Concrete placed below ground should be protected from falling earth during and after placing. Concrete placed in ground containing deleterious substances should be kept free from contact with such a ground and with water draining there from during placing and for a period of seven days. When joint in a layer of concrete are unavoidable, and end is sloped at an angle of 30 and junctions of different layers break joint in laying upper layer of concrete. The lower surface is made rough and clean watered before upper layer is laid.

Laying of Foundation

At our site, Raft foundations are used to spread the load from a structure over a large area, normally the entire area of the structure. Normally raft foundation is used when large load is to be distributed and it is not possible to provide individual footings due to space constraints that is they would overlap on each other. Raft foundations have the advantage of reducing differential settlements as the concrete slab resists differential movements between loading positions. They are often needed on soft or loose soils with low bearing capacity as they can spread the loads over a larger area.

In laying of raft foundation, special care is taken in the reinforcement and construction of plinth beams and columns. It is the main portion on which ultimately whole of the structure load is to come. So a slightest error can cause huge problems and therefore all this is checked and passed by the engineer in charge of the site.

Apart from raft foundation, individual footings were used in the mess area which was extended beyond the C and D blocks.

Cement

Portland cement is composed of calcium silicates and aluminate and aluminoferrite It is obtained by blending predetermined proportions limestone clay and other minerals in small quantities which is pulverized and heated at high temperature – around 1500 deg centigrade to produce ‘clinker’. The clinker is then ground with small quantities of gypsum to produce a fine powder called Ordinary Portland Cement (OPC). When mixed with water, sand and stone, it combines slowly with the water to form a hard mass called concrete. Cement is a hygroscopic material meaning that it absorbs moisture In presence of moisture it undergoes chemical reaction termed as hydration. Therefore cement remains in good condition as long as it does not come in contact with moisture. If cement is more than three months old then it should be tested for its strength before being taken into use.

The Bureau of Indian Standards (BIS) has classified OPC in three different grades The classification is mainly based on the compressive strength of cement-sand mortar cubes of face area 50 cm2 composed of 1 part of cement to 3 parts of standard sand by weight with a water-cement ratio arrived at by a specified procedure. The grades are

(i) 33 grade

(ii) 43 grade

(iii) 53 grade

The grade number indicates the minimum compressive strength of cement sand mortar in N/mm2 at 28 days, as tested by above mentioned procedure.

Portland Pozzolana Cement (PPC) is obtained by either intergrinding a pozzolanic material with clinker and gypsum, or by blending ground pozzolana with Portland cement. Nowadays good quality fly ash is available from Thermal Power Plants, which are processed and used in manufacturing of PPC.

Advantages of using Portland pozzolana cement over OPC

Pozzolana combines with lime and alkali in cement when water is added and forms compounds which contribute to strength, impermeability and sulphate resistance. It also contributes to workability, reduced bleeding and controls destructive expansion from alkali-aggregate reaction. It reduces heat of hydration thereby controlling temperature differentials, which causes thermal strain and resultant cracking n mass concrete structures like dams. The colour of PPC comes from the colour of the pozzolanic material used. PPC containing fly ash as a pozzolana will invariably be slightly different colour than the OPC.One thing should be kept in mind that is the quality of cement depends upon the raw materials used and the quality control measures adopted during its manufacture, and not on the shade of the cement. The cement gets its colour from the nature and colour of raw materials used, which will be different from factory to factory, and may even differ in the different batches of cement produced in a factory. Further, the colour of the finished concrete is affected also by the colour of the aggregates, and to a lesser extent by the colour of the cement. Preference for any cement on the basis of colour alone is technically misplaced.

Settling Of Cement

When water is mixed with cement, the paste so formed remains pliable and plastic for a short time. During this period it is possible to disturb the paste and remit it without any deleterious effects. As the reaction between water and cement continues, the paste loses its plasticity. This early period in the hardening of cement is referred to as ‘setting’ of cement.

Initial and final setting time of cement

Initial set is when the cement paste loses its plasticity and stiffens considerably. Final set is the point when the paste hardens and can sustain some minor load. Both are arbitrary points and these are determined by Vicat needle penetration resistance

Slow or fast setting normally depends on the nature of cement. It could also be due to extraneous factors not related to the cement. The ambient conditions play an important role. In hot weather, the setting is faster, in cold weather, setting is delayed Some types of salts, chemicals, clay, etc if inadvertently get mixed with the sand, aggregate and water could accelerate or delay the setting of concrete.

Storage of Cement

It needs extra care or else can lead to loss not only in terms of financial loss but also in terms of loss in the quality. Following are the don’t that should be followed -

(i) Do not store bags in a building or a godown in which the walls, roof and floor are not completely weatherproof.

(ii) Do not store bags in a new warehouse until the interior has thoroughly dried out.

(iii) Do not be content with badly fitting windows and doors, make sure they fit properly and ensure that they are kept shut.

(iv) Do not stack bags against the wall. Similarly, don’t pile them on the floor unless it is a dry concrete floor. If not, bags should be stacked on wooden planks or sleepers.

(v) Do not forget to pile the bags close together

(vi) Do not pile more than 15 bags high and arrange the bags in a header-and-stretcher fashion.

(vii) Do not disturb the stored cement until it is to be taken out for use.

(viii) Do not take out bags from one tier only. Step back two or three tiers.

(ix) Do not keep dead storage. The principle of first-in first-out should be followed in removing bags.

(x) Do not stack bags on the ground for temporary storage at work site. Pile them on a raised, dry platform and cover with tarpaulin or polythene sheet.

Coarse Aggregate

Coarse aggregate for the works should be river gravel or crushed stone .It should be hard, strong, dense, durable, clean, and free from clay or loamy admixtures or quarry refuse or vegetable matter. The pieces of aggregates should be cubical, or rounded shaped and should have granular or crystalline or smooth (but not glossy) non-powdery surfaces.Aggregates should be properly screened and if necessary washed clean before use.

Coarse aggregates containing flat, elongated or flaky pieces or mica should be rejected. The grading of coarse aggregates should be as per specifications of IS-383.

After 24-hrs immersion in water, a previously dried sample of the coarse aggregate should not gain in weight more than 5%.

Aggregates should be stored in such a way as to prevent segregation of sizes and avoid contamination with fines.

Depending upon the coarse aggregate color, there quality can be determined as:

Black => very good quality

Blue => good

Whitish =>bad quality

 

Fine Aggregate

Aggregate which is passed through 4.75 IS Sieve is termed as fine aggregate. Fine aggregate is added to concrete to assist workability and to bring uniformity in mixture. Usually, the natural river sand is used as fine aggregate. Important thing to be considered is that fine aggregates should be free from coagulated lumps.

Grading of natural sand or crushed stone i.e. fine aggregates shall be such that not more than 5 percent shall exceed 5 mm in size, not more than 10% shall IS sieve No. 150 not less than 45% or more than 85% shall pass IS sieve No. 1.18 mm and not less than 25% or more than 60% shall pass IS sieve No. 600 micron.

BRICKWORK

Brickwork is masonry done with bricks and mortar and is generally used to build partition walls. In our site, all the external walls were of concrete and most of the internal walls were made of bricks. English bond was used and a ration of 1:4 (1 cement: 4 coarse sand) and 1:6 were used depending upon whether the wall is 4.5 inches or 9 inches. The reinforcement shall be 2 nos. M.S. round bars or as indicated. The diameter of bars was 8mm. The first layer of reinforcement was used at second course and then at every fourth course of brick work. The bars were properly anchored at their ends where the portions and or where these walls join with other walls. The in laid steel reinforcement was completely embedded in mortar.

Bricks can be of two types. These are:

1) Traditional Bricks-The dimension if traditional bricks vary from 21 cm to 25cm in length,10 to 13 cm in width and 7.5 cm in height in different parts of country .The commonly adopted normal size of traditional brick is 23 * 11.5*7.5 cm with a view to achieve uniformity in size of bricks all over country.

2) Modular Bricks- Indian standard institution has established a standard size of bricks such a brick is known as a modular brick. The normal size of brick is taken as 20*10*10 cm whereas its actual dimensions are 19*9*9 cm masonry with modular bricks workout to be cheaper there is saving in the consumption of bricks, mortar and labour as compared with masonry with traditional bricks.

Strength of brick masonry

The permissible compressive stress in brick masonry depends upon the following factors:

1. Type and strength of brick.

2. Mix of motor.

3. Size and shape of masonry construction.

The strength of brick masonry depends upon the strength of bricks used in the masonry construction. The strength of bricks depends upon the nature of soil used for making and the method adopted for molding and burning of bricks .since the nature of soil varies from region to region ,the average strength of bricks varies from as low as 30kg/sq cm to 150 kg /sq cm the basic compressive stress are different crushing strength.

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Concreting

Concrete is a mixture of cement, sand, stone aggregates and water. A cage of steel rods used together with the concrete mix leads to the formation of Reinforced Cement Concrete popularly known as RCC.

Concrete has two main stages

1) Fresh Concrete

2) Hardened Concrete

Fresh Concrete should be stable and should not segregate or bleed during transportation and placing when it is subjected to forces during handling operations of limited nature. The mix should be cohesive and mobile enough to be placed in the form around the reinforcement and should be able to cast into the required shape without loosing continuity or homogeneity under the available techniques of placing the concrete at a particular job. The mix should be amenable to proper and through compaction into a dense, compact concrete with minimum voids under the existing facilities of compaction at the site. A best mix from the point of view of campactibility should achieve a 99 percent elimination of the original voids present.

Segregation

The stability of a concrete mix requires that it should not segregate and bleed during the transportation and placing. Segregation can be defined as separating out of the ingredients of a concrete mix, so that the mix is no longer in a homogeneous condition. Only the stable homogeneous mix can be fully compacted

The segregation depends upon the handling and placing operations. The tendency to segregate, amount of coarse aggregate, and with the increased slump. The tendency to segregate can be minimized by:

a. Reducing the height of drop by concrete.

b. Not using the vibration as a means of spreading a heap of of concrete into a level mass over a large area.

c. Reducing the continued vibration over a longer time, as the coarse aggregate tends to settle to the bottom and the scum would rise to the surface.

d. Adding small quantity of water which improves cohesion of the mix.

Bleeding

Bleeding is due to the rise of water in the mix to the surface because of the inability of the solid particles in the mix to hold all the mixing water during settling of particles under the effect of compaction. The bleeding causes formation of a porous, weak and non durable concrete layer at the top of placed concrete. In case of lean mixes bleeding may create capillary channels increasing the permeability of the concrete. When the concrete is placed in different layers and each layer is compacted after allowing certain time to lapse before the next layer is laid, the bleeding may cause a plane of weakness between two layers. Any laitance formed should be removed by brushing and washing before a new layer is added. Over compacting the surface should be avoided.

Hardened Concrete

One of the most important properties of the hardened concrete is its strength which represents the ability if concrete to resist forces. If the nature of the force is to produce compression, the strength is termed compressive strength. The compressive strength of hardened concrete is generally considered to be the most important property and is often taken as the index of the overall quality of concrete. The strength can indirectly give an idea of the most of the other properties of concrete which are related directly to the structure of hardened cement paste. A stronger concrete is dense, compact, impermeable and resistant to weathering and to some chemicals. However, a stronger concrete may exhibit higher drying shrinkage with consequent cracking, due to the presence of higher cement content.

Some of the other desirable properties like shear and tensile strengths, modulus of elasticity, bond, impact and durability etc. are generally related to compressive strength. As the compressive strength can be measured easily on standard sized cube or cylindrical specimens, it can be specified as a criterion for studying the effect of any variable on the quality of concrete. However, the concrete gives different values of any property under different testing conditions. Hence method of testing, size of specimen and the rate of loading etc. are stipulated while testing the concrete to minimize the variations in test results. The statistical methods are commonly used for specifying the quantitative value of any particular property of hardened concrete.

Compressive Strength

The compressive strength of concrete is defined as the load which causes the failure of specimen, per unit area of cross-section in uniaxial compression under given rate of loading. The strength of concrete is expressed as N/mm². The compressive strength at 28 days after casting is taken as a criterion for specifying the quality of concrete. This is termed as grade of concrete. IS 456 – 2000 stipulates the use of 150 mm cubes.

Tensile Strength

The concrete has low tensile strength; it ranges from 8-12 per cent of its compressive strength. An average value of 10 per cent is generally adopted.

Shear Strength

The concrete subjected to bending and shear stress is accompanied by tensile and compressive stresses. The shear failures are due to resulting diagonal tension. The shear strength is generally 12-13 per cent of its compressive strength.

Bond Strength

The resistance of concrete to the slipping of reinforcing bars embedded in concrete is called bond strength. The bond strength is provided by adhesion of hardened cement paste, and by the friction of concrete and steel. It is also affected by shrinkage of concrete relative to steel. On an average bond strength is taken as 10 per cent of its compressive strength.

Facts about Cement and Concrete

1) Water required by 1 bag of cement is something in the range of 25-28 litres

2) Quality of concrete has nothing to do with its color.

3) The mortar / concrete should be consumed as early as possible after addition of water to it. The hydration of cement starts the moment water is added to it. As the hydration progresses the cement paste starts stiffening and loses its plasticity. The concrete should not be disturbed after this. Normally, this is about 45 – 50 minutes.

4) MPa is abbreviated form of mega Pascal, which is a unit of pressure. 1 MPa is equivalent to a pressure of 10Kg /cm2. The strength of concrete & cement is expressed in terms of pressure a standard cube can withstand. The Ordinary Portland Cement, commonly called OPC is available in three grades namely 33, 43 & 53 grades. Thus, for 43 grade cement standard cement & sand mortar cube would give a minimum strength of 43 MPa or 430 Kg /cm2 when tested under standard curing conditions for 28 days.

Compressive Strength of Concrete depends on following factors

(i) w/c ratio

(ii) Characteristics of cement

(iii) Characteristics of aggregates

(iv) Time of mixing

(v) Degree of compaction

(vi) Temperature and period of curing

(vii) Age of concrete

(viii)Air entertainment

(ix) Conditions of testing

Precautions for water to be used in concrete

* It is good to use potable quality of water.

It should be free from impurities and harmful ingredients.

Seawater isn’t recommended.

The water fit for mixing is fit for curing too

Use of minimum quantity of mixing water, consistent with the degree of workability required to enable easy placing and compaction of concrete, is advisable.

Ensure that water is measured and added.

Low water to cement ratio is essential for good performance of the structure in the long run.

Common Reasons for lack of quality in concrete work

Use of too much or too little water for mixing, or water carelessly added during mixing

Incomplete mixing of aggregate with cement

Improper grading of aggregates resulting in segregation or bleeding of concrete.

Inadequate compaction of concrete

Using concrete which has already begun to set.

Placing of concrete on a dry foundation without properly wetting it with water.

Use of dirty aggregate or water containing earthy matter, clay or lime.

Too much troweling of the concrete surface.

Leaving the finished concrete surface exposed to sun and wind during the first ten days after placing without protecting it and keeping it damp by proper methods of curing.

Construction joints are the joints provided between successive pours of concrete that have been carried out after a time lag. As far as possible the construction joints should be avoided and every care should be taken to keep their numbers minimal. Since, presence of these joints creates a plane of weakness within the concrete body, these joints should be preplanned and their location should be such that they are at places where they are subjected to minimum bending moment and minimum shear force.

POURING AND CONSOLIDATION

Concrete (M20) was used for all works in column, beams and slabs. It was well consolidated by vibrating using portable mechanical vibrators. Care was taken to ensure that concrete is not over vibrated so as to cause segregation. The layers of concrete are so placed that the bottom layer does not finally set before the top layer is placed. The vibrators maintain the whole of concrete under treatment in an adequate state of agitation, such that deaeration and effective compaction is attained at a state commensurate with the supply of concrete from the mixers. The vibrator continue during the whole period occupied by placing of concrete, the vibrators being adjusted so that the centre vibrations approximate to the centre of the mass being compacted at the time of placing. Shaking of reinforcement for the purpose of compaction should be avoided. Compaction shall be completed before initial setting starts i.e. within thirty minute of addition of water to the dry mixture.

The concrete was deposited in its final position in a manner to preclude segregation of ingredients. In case of column and walls, the shuttering was so adjusted that the vertical drop of concrete is not more than 1.5 m at a time. In case of concreting of slabs and beams, the pipe from the batching plant was directly taken to the closest point.

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Concrete Mix Design

Introduction

The process of selecting suitable ingredients of concrete and determining their relative amounts with the objective of producing a concrete of the required, strength, durability, and workability as economically as possible, is termed the concrete mix design. The proportioning of ingredient of concrete is governed by the required performance of concrete in 2 states, namely the plastic and the hardened states. If the plastic concrete is not workable, it cannot be properly placed and compacted. The property of workability, therefore, becomes of vital importance.

The compressive strength of hardened concrete which is generally considered to be an index of its other properties, depends upon many factors, e.g. quality and quantity of cement, water and aggregates; batching and mixing; placing, compaction and curing. The cost of concrete is made up of the cost of materials, plant and labour. The variations in the cost of materials arise from the fact that the cement is several times costly than the aggregate, thus the aim is to produce as lean a mix as possible. From technical point of view the rich mixes may lead to high shrinkage and cracking in the structural concrete, and to evolution of high heat of hydration in mass concrete which may cause cracking.

The actual cost of concrete is related to the cost of materials required for producing a minimum mean strength called characteristic strength that is specified by the designer of the structure. This depends on the quality control measures, but there is no doubt that the quality control adds to the cost of concrete. The extent of quality control is often an economic compromise, and depends on the size and type of job. The cost of labour depends on the workability of mix, e.g., a concrete mix of inadequate workability may result in a high cost of labour to obtain a degree of compaction with available equipment.

Requirements of concrete mix design

The requirements which form the basis of selection and proportioning of mix ingredients are :

a ) The minimum compressive strength required from structural consideration

b) The adequate workability necessary for full compaction with the compacting equipment available.

c) Maximum water-cement ratio and/or maximum cement content to give adequate durability for the particular site conditions

d) Maximum cement content to avoid shrinkage cracking due to temperature cycle in mass concrete.

Types of Mixes

1. Nominal Mixes

In the past the specifications for concrete prescribed the proportions of cement, fine and coarse aggregates. These mixes of fixed cement-aggregate ratio which ensures adequate strength are termed nominal mixes. These offer simplicity and under normal circumstances, have a margin of strength above that specified. However, due to the variability of mix ingredients the nominal concrete for a given workability varies widely in strength.

2. Standard mixes

The nominal mixes of fixed cement-aggregate ratio (by volume) vary widely in strength and may result in under- or over-rich mixes. For this reason, the minimum compressive strength has been included in many specifications. These mixes are termed standard mixes.

IS 456-2000 has designated the concrete mixes into a number of grades as M10, M15, M20, M25, M30, M35 and M40. In this designation the letter M refers to the mix and the number to the specified 28 day cube strength of mix in N/mm². The mixes of grades M10, M15, M20 and M25 correspond approximately to the mix proportions (1:3:6), (1:2:4), (1:1.5:3) and (1:1:2) respectively.

3. Designed Mixes

In these mixes the performance of the concrete is specified by the designer but the mix proportions are determined by the producer of concrete, except that the minimum cement content can be laid down. This is most rational approach to the selection of mix proportions with specific materials in mind possessing more or less unique characteristics. The approach results in the production of concrete with the appropriate properties most economically. However, the designed mix does not serve as a guide since this does not guarantee the correct mix proportions for the prescribed performance.

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