vt report on foundation

7/29/2019 vt report on foundation

1/47

1

ACKNOWLEDGMENT

Before we get to more important things, we would like to thank numerous people,

without whom our summer training would have been very difficult.

We would like to thank National Building Construction Corporation Limited for

providing us with the necessary, whole-hearted guidance and valuable suggestions

throughout our training period, without which this endeavor would not have been

possible.

We are very grateful to Mr. M. Manna, Regional Manager & Mr. P.Saha, Project In-

charge, for their continuous support. We thank Mr Sagar Sahoo & Mr. Rajiv Rao,

Planning, for guiding us right from the start.

We profoundly express our gratitude to Mr. Kamal Bhattacharya, for being kind &

helpful in getting us the summer training.

Finally, We acknowledge each and every member of staff at the construction site , for

their wholehearted co-operation, which made our summer training comfortable and

successful.


2/47

2

NATIONAL BUILDING CONSTRUCTION

CORPORATION PROFILE

YEAR OF INCORPORATION

NBCC was incorporated in November 1960 as a wholly owned Government of India

undertakingunder the erstwhile Ministry of Works, Housing & Supply ("MoWHS"), which is

now known as the Ministry of Urban Development ("MoUD").

AN ISO COMPANY

ISO 9001:2008 Certification has been awarded to NBCC for its Project Management and

Consultancy Divisions. ISO 9001:2008 certification issued by Bureau of Indian Standards is

valid up to March 2014.

AUTHORISED CAPITAL

The authorized, issued and paid-up equity share capital is Rs. 120 crore. This includes Rs.

30 crore of fully paid-up bonus shares to the existing share holder s as on 30-09-2011.

PERFORMANCE RECOGNITION

On October 14, 2008, the Government granted NBCCSchedule "A" PSU status. NBCC has

also been awarded ISO 9001:2008 from the Bureau of Indian Standards in respect of our

consultancy and project management division. NBCC has also received "Excellent" rating

from MoUD for each of the Fiscal years from 2004 to 2010 and Ministry of Heavy Industries

& Public Enterprises has awarded us with an "Excellence Award". MoUD grants us

"Excellent" rating if all the targets set out in the MoU with MoUD for the respective Fiscal

year are acheived. Further, in 2011, for one of our PMC projects, we were awarded an

"Appreciation Shield" for quality and timely completion of NSEZ Noida Project by the

Ministry of Commerce & Industry and the Development Commissioner, NSEZ.


3/47

3

AREAS OF OPERATION

NBCC is one of the few public sector companies engaged in the business of

(i) project management consultancy services for civil construction projects ("PMC")

(ii) civil infrastructure for power sector and real estate development.

NBCC is headquartered in New Delhi and in addition has 10 regional / zonal offices across

India. The projects undertaken by our Company are spread across 23 states and 1 union

territory in India. In addition, NBCC has also have also undertaken projects overseas.

NBCC's PMC business segment includes providing management and consultancy services

for a range of civil construction projects including residential and commercial complexes,

redevelopment of buildings and colonies, hospitals, educational institutions; infrastructure

works for security personnel, border fencing as well as infrastructure projects such asroads, water supply systems, storm water systems and water storage solutions.

NBCC's civil Infrastructure for power sector segment includes providing engineering and

construction services for power projects, including design and execution of (i) civil and

structural works for power projects (ii) Cooling towers (iii) Chimneys.

NBCC's real estate development segment focuses on principally two types of projects,

namely, (i) residential projects, such as apartments and townships and (ii) commercial

projects, such as corporate office buildings and shopping malls.

COMPUTERIZATION AND TRANSPARENCY

NBCC makes extensive use of information and communication technologies for the

execution and management of its projects. NBCC has implemented Enterprise Resource

Planning ("ERP") system in some business processes related to accounting, salaries, HRM

system and e-Bidding system. In addition, NBCC's team has access to domain controller and

additional domain controller, cluster servers, IT security management, network

management etc. IT security management is also utilized for the continuous upkeep of

security products , solutions, products, tools. The online computer maintenance services

ensures accurate management of the organizations hardware and software complaints

electronically, including hardware management, complaint tracking, minimum problem

rectification time, better reports management and optimal performance. NBCC also

hascentralised its database and has begun digitising its records and has business continuity

servers to protect the electronic data and ensure maximum uptime.


4/47

4

PROJECT MANAGEMENT CONSULTANCYFOR CIVIL

CONSTRUCTION PROJECTS ("PMC")

Our PMC business segment includes providing management and consultancy services for a

range of civil construction projects including residential and commercial complexes,

redevelopment of buildings and colonies, hospitals, educational institutions; infrastructure

works for security personnel, border fencing as well as infrastructure projects such as

roads, water supply systems, storm water systems and water storage solutions. Some of

our clients in this segment are or have been, ESIC, Ministry of Defence, Ministry of Home

Affairs (including Security forces like CRPF, CISF, NSG, BSF), Ministry of External Affairs,

MoUD, Ministry of Commerce and Industry, Ministry of Corporate Affairs, Ministry of

Finance, Haryana Urban Infrastructure Development Board, IIT Roorkee, IIT Kharagpur, IITPatna, SVNIT, amongst others.

Our key completed projects during the period April 01, 2006 tillSeptember 30, 2011, based

on the total contract value, include road works at Agartala, construction of defence campus

at Jaipur, Jodhpur, Ahemdabad, Ambala, Sulur, CBI headquarters at New Delhi, Extension of

campus of MDU university and IIT Roorkee. Our key domestic PMC Ongoing Projects based

on the total outstanding contract value, include Indo Bangladesh Border Fencing Works at

Meghalaya, ESIC Hospital, Parel (Mumbai). We presently have one overseas PMC Ongoing

Project at Male, Maldives for construction of India - Maldives Friendship Faculty of

Hospitality & Tourism Studies.

As of September 30, 2011PMC Projects

Ongoing Projects Forthcoming Projects

Number of Projects 130 59

Contract Value (in million) 162,764.24 23,786.40*

Outstanding Contract Value/ Order Book (in million)

79,240.52 23,786.40*


5/47

5

REAL ESTATE DEVELOPMENT

Our real estate development segment focuses on principally two types of projects,

namely, (i) residential projects, such as apartments and townships and (ii)

commercial projects, such as corporate office buildings and shopping malls. OurCompany has undertaken real estate projects which are spread across 10 states in

India. As ofJanuary 15, 2012, our Land Reserves aggregate approximately 127.918

Acre. Our Land Reserves are located in Delhi, Uttar Pradesh, Patna, Gurgaon,

Kolkata, Kochi, Alwar and Lucknow.

As on January 15, 2012, our completed commercial projects include commercial

complex at Vadodara, Cuttack, Agartala, Ghaziabad (Uttar Pradesh) and at

BhikajiCama Place, PragatiVihar and PushpVihar in New Delhi. Further, some of our

key real estate development Ongoing Projects include residential complex at "NBCC

Heights" at Sector-89, Gurgaon, Haryana; Khekra (Phase-I), Baghpat, Uttar Pradesh;residential-cum-commercial complex at Bahadurpur, Phase-I, Patna; New

Delhi,Sukias Lane at Kolkata and Hemanta Basu Sarani Complex. The following table

represents details for types of real estate projects, as of January 15, 2012:

Type ofReal

EstateDevelopm

ent

CompletedProjects

Ongoing Projects Forthcoming Projects

No. ofProjec

ts

Developable

Area

No. ofProjec

ts

Developable Area

Saleable Area

Leasable Area

No. ofProjec

ts

Developable Area

Saleable Area

Leasable Area

Residential

Nil - 4 3,732,0533,410,4

030 6 5,555,821

4,878,882

147,585

Commercial

8 1,076,65 3 407,633 239,560 66,624 6 2,323,9081,724,1

01290,78

6

Total 8 1,076,65 7 4,139,6863,649,9

6366,624 12 7,879,729

6,602,983

438,353


6/47

6

CIVIL INFRASTRUCTURE FOR POWER SECTOR

Our civil Infrastructure for power sector segment includes providing engineering

and construction services for power projects, including design and execution of (i)

civil and structural works for power projects (ii) Cooling towers (iii) Chimneys.Some of our clients in this segment include NTPC Limited, BHEL, APGENCO Limited,

Uttar Pradesh RajyaVidyutUtpadan Nigam Limited, MAHAGENCO Limited and

Karnataka Power Corporation Limited.

Our completed key projects, during the period April 01, 2006 till September 30,

2011based on the total contract value, include construction of civil, structural and

architectural works for 2x250 MW at Korba, Chattisgarh;Rihand Main Plant , Civil

Works in Uttar Pradesh our key On-going PMC Projects, based on the total

outstanding contract value, include cooling tower, chimney at Farakka Super

Thermal Power Project, West Bengal, ,Koderma Thermal Power Project atJharkhand, Durgapur, Thermal Power Project at West Bengal, Rihand Super Thermal

Power Project, Uttar Pradesh, Barh Super Thermal Power Project, Patna, Mauda and

Vindhyachal Super Thermal Projectat Maharashtra & Madhya Pradesh respectively.

As of September 30, 2011 Civil Infrastructure for power projects(Ongoing Projects)

Number of projects 14

Contract Value(` in million) 7,875.43

Outstanding Contract Value / Order Book(`in million)

3,199.49


7/47

7

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


8/47

8

PROBLEMS FACED AT SITE

There were numerous problems which were faced at site. Some of these were

purely due to the human errors and poor workmanship but some were due to

unseen factors.

1. There was a problem in providing beams at one location as per the standarddrawings so the drawings were changed by consulting the structural designersand architect

2. There was problem pouring concrete in one beam due to small area availablefor pouring and compacting. The solution to this problem was that the size ofsteel was increased but the number of steel bars was decreased so as toprovide the total area same.

3. No window was there in staircases which lead to complete darkness, so it wasdecided to change the drawing by consulting the concerned authorities.

4. The depth if beam above the door was 35 earlier but to keep the size of the

door as per the standard it was changed to 3.

5.Frequent power cuts lead to increase in the cost of construction as generatorswere used to meet the power requirements

6.Laying of foundations was postponed by 1 month due to the rainy season.


9/47

9

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 toidentify 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 (JCBs) were used for excavating the soil. Adequate precautions are taken to see thatthe excavation operations do not damage the adjoining structures. Excavation is carried outproviding 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 54 from

Ground Level.


10/47

10

PCCPlain 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 fullcompaction. 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 aperiod 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 differentialsettlements 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 tocome. So a slightest error can cause huge problems and therefore all this is checked and passed


11/47

11

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.


12/47

12

ADVANTAGES OF USING PORTLAND POZZOLANA CEMENT OVEROPC

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 thermalstrain 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 thequality 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 mayeven 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 deleteriouseffects. 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 andthese 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 ifinadvertently 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 ofloss in the quality. Following are the dont that should be followed -

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

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


13/47

13

(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, dont 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.


14/47

14

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 properlyscreened 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 aggregatesshould be free from coagulated lumps.

Grading of natural sand or crushed stone i.e. fine aggregates shall be such that not more than 5percent 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.


15/47

15

Unit Weight of Materials Used at ConstructionSite

Following table shows unit weight of materials used at construction site. Please note

this is for reference purpose only and may vary from place and type of material.

We are thankful to Engineer Prince Saha for submitting this very useful information

to us.

S.No Material Theoretical

Weight

in(KG/M)

Approx Weight at Site

in

Remarks

Kg Per

1 Cement 1440 50 Bag

2 Steel 7850 d/162 d -dia in mm

3 Sand-

Dry 1600 50 to 55 farma 1 farma=1.25cft

River 1840 57 to 63 farma 1 farma=1.25cft

4 Stone(basalt) 2850 to 2960 48 to 52 farma metal 12mm to 20mm

5 Water 1000 1 liter

6 PCC 2240 8.24 to 8.5 Cubemould

cube mouldsize=15x15x15cm

7 RCC 2% Steel 2420

8 Bricks 1600 to 1920 1.9 to 2 no 9x4x2 3/4

4.8 to 4.9 no 9x6x3 3/4

9 Brick Masonry 1920

10 Soil(damp) 1760 50 to 55 cft Black cotton

11 Cement concrete

block(solid)

1800 18 to 20 cft 30x15x20 cm

10 to 11 no 30x10x20 cm

12 Cement Mortar 2080 57 to 62 cft

13 Lime Mortar 1760 48 to 52 cft14 Lime 640 30 bag

15 Glass 2530 0.9 to 0.95 sft 4mm tk plain

16 Teak Wood 670 to 830 18 to 20 cft

17 Sal Wood 990 22 to 24 cft

18 Marble mosaic tile 2.8 to 3.2 no 25x25x22mm

4.8 to 5.2 no 30x30x25mm


16/47

16

19 Chequered tile 2.5 to 2.8 no 25x25x22mm

20 Glazed tile15x15cm 0.20 to 0.25 no 5mm tk

21 Marble Stone 2620 5.1 sft 3/4tk

22 Granite Stone 2460-2800 5.35 sft 3/4tk

23 Coddappa 2720 6.4 sft 1 1/4tk

24 A.C.sheet corrugated 16 1.2 sft

25 Bitumen 1040 220 Drum 200liter drum

26 Window frame (simpledesign)

1.9 to2.1 sft

27 Door Frame

a)30070 25 to 27 no section 4x2 1/2

b)26x70 24 to 26 no section 4x2 1/2

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 ofbricks. 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 properlyanchored 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.

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 toregion ,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.

There are many checks that can be applied to see the quality of bricks used on the site.Normally

the bricks are tested for Compressive strength, water absorption, dimensional tolerances and


17/47

17

efflorescence. However at small construction sites the quality of bricks can be assessed based on

following, which is prevalent in many sites.

Visual check Bricks should be well burnt and of uniform size and color.

Striking of two bricks together should produce a metallic ringing sound.

It should have surface so hard that cant be scratched by the fingernails.

A good brick should not break if dropped in standing position from one metre above ground

level.

A good brick shouldnt absorb moisture of more than 15-20% by weight, when soaked in water

For example; a good brick of 2 kg shouldnt weigh more than 2.3 to 2.4 kg if immersed inwater for 24 hours.

PRECAUTIONS TO BE TAKEN IN BRICK MASONRY WORK

Bricks should be soaked in water for adequate period so that the water penetrates

to its full thickness. Normally 6 to 8 hours of wetting is sufficient.

A systematic bond must be maintained throughout the b rickwork. Vertical joints

shouldnt be continuous but staggered.

The joint thickness shouldnt exceed 1 cm. It should be thoroughly filled with the


18/47

18

cement mortar 1:4 to 1:6 (Cement: Sand by volume)

All bricks should be placed on their bed with frogs on top (depression on top of the

brick for providing bond with mortar).

Thread, plumb bob and spirit level should be used for alignment, verticality and

horizontality of construction.

Joints should be raked and properly finished with trowel or float, toprovide good bond.

A maximum of one metre wall height should be constructed in a day.

Brickwork should be properly cured for at least 10 days

REINFORCEMENT

Steel reinforcements are used, generally, in the form of bars of circular cross section in concrete

structure. They are like a skeleton in human body. Plain concrete without steel or any otherreinforcement is strong in compression but weak in tension. Steel is one of the best forms of

reinforcements, to take care of those stresses and to strengthen concrete to bear all kinds of loads

Mild steel bars conforming to IS: 432 (Part I) and Cold-worked steel high strength deformed bars

conforming to IS: 1786 (grade Fe 415 and grade Fe 500, where 415 and 500 indicate yield

stresses 415 N/mm2 and 500 N/mm2 respectively) are commonly used. Grade Fe 415 is beingused most commonly nowadays. This has limited the use of plain mild steel bars because of

higher yield stress and bond strength resulting in saving of steel quantity. Some companies havebrought thermo mechanically treated (TMT) and corrosion resistant steel (CRS) bars with added

features.

Bars range in diameter from 6 to 50 mm. Cold-worked steel high strength deformed bars start

from 8 mm diameter. For general house constructions, bars of diameter 6 to 20 mm are used

Transverse reinforcements are very important. They not only take care of structural requirementsbut also help main reinforcements to remain in desired position. They play a very significant role

while abrupt changes or reversal of stresses like earthquake etc.

They should be closely spaced as per the drawing and properly tied to the main/longitudinalreinforcement

TERMS USED IN REINFORCEMENT

BAR-BENDING-SCHEDULE

Bar-bending-schedule is the schedule of reinforcement bars prepared in advance before cutting


19/47

19

and bending of rebars. This schedule contains all details of size, shape and dimension of rebars to

be cut.

LAP LENGTH

Lap length is the length overlap of bars tied to extend the reinforcement length.. Lap length about50 times the diameter of the bar is considered safe. Laps of neighboring bar lengths should be

staggered and should not be provided at one level/line. At one cross section, a maximum of 50%

bars should be lapped. In case, required lap length is not available at junction because of spaceand other constraints, bars can be joined with couplers or welded (with correct choice of method

of welding).

ANCHORAGE LENGTH

This is the additional length of steel of one structure required to be inserted in other at thejunction. For example, main bars of beam in column at beam column junction, column bars infooting etc. The length requirement is similar to the lap length mentioned in previous question or

as per the design instructions

COVER BLOCK

Cover blocks are placed to prevent the steel rods from touching the shuttering plates and there by

providing a minimum cover and fix the reinforcements as per the design drawings. Sometimes it

is commonly seen that the cover gets misplaced during the concreting activity. To prevent this,tying of cover with steel bars using thin steel wires called binding wires (projected from cover

surface and placed during making or casting of cover blocks) is recommended. Covers should bemade of cement sand mortar (1:3). Ideally, cover should have strength similar to the surroundingconcrete, with the least perimeter so that chances of water to penetrate through periphery will be

minimized. Provision of minimum covers as per the Indian standards for durability of the whole

structure should be ensured.

Shape of the cover blocks could be cubical or cylindrical. However, cover indicates thickness of

the cover block. Normally, cubical cover blocks are used. As a thumb rule, minimum cover of 2in footings, 1.5 in columns and 1 for other structures may be ensured.

Structural element Cover to reinforcement (mm)

Footings 40Columns 40

Slabs 15

Beams 25

Retaining wall 25 for earth face

20 for other face


20/47

20

THINGS TO NOTE

Reinforcement should be free from loose rust, oil paints, mud etc. it should be cut, bent and fixedproperly. The reinforcement shall be placed and maintained in position by providing proper

cover blocks, spacers, supporting bars, laps etc. Reinforcements shall be placed and tied such

that concrete placement is possible without segregation, and compaction possible by animmersion vibrator.

Three types of bars were used in reinforcement of a slab. These include straight bars, crank barand an extra bar. The main steel is placed in which the straight steel is binded first, then the

crank steel is placed and extra steel is placed in the end. The extra steel comes over the support

while crank is encountered at distance of (1-distance between the supports) from thesurroundings supports.

For providing nominal cover to the steel in beam, cover blocks were used which were made ofconcrete and were casted with a thin steel wire in the center which projects outward. These keep

the reinforcement at a distance from bottom of shuttering. For maintaining the gap between themain steel and the distribution steel, steel chairs are placed between them

SHUTTERING AND SCAFFOLDING

DEFINITION

The term SHUTTERING or FORMWORK includes all forms, moulds, sheeting, shuttering

planks, walrus, poles, posts, standards, leizers, V-Heads, struts, and structure, ties, prights,

walling steel rods, bolts, wedges, and all other temporary supports to the concrete during theprocess of sheeting.


21/47

21

FORM WORK

Forms or moulds or shutters are the receptacles in which concrete is placed, so that it will have

the desired shape or outline when hardened. Once the concrete develops adequate strength, the

forms are removed. Forms are generally made of the materials like timber, plywood, steel, etc.

Generally camber is provided in the formwork for horizontal members to counteract the effect ofdeflection caused due to the weight of reinforcement and concrete placed over that. A proper

lubrication of shuttering plates is also done before the placement of reinforcement. The oil film

sandwiched between concrete and formwork surface not only helps in easy removal of shutteringbut also prevents loss of moisture from the concrete through absorption and evaporation.

The steel form work was designed and constructed to the shapes, lines and dimensions shown on

the drawings. All forms were sufficiently water tight to prevent leakage of mortar. Forms wereso constructed as to be removable in sections. One side of the column forms were left open and

the open side filled in board by board successively as the concrete is placed and compacted

except when vibrators are used. A key was made at the end of each casting in concrete columnsof appropriate size to give proper bondings to columns and walls as per relevant IS.

CLEANING AND TREATMENT OF FORMS

All rubbish, particularly chippings, shavings and saw dust, was removed from the interior of theforms (steel) before the concrete is placed. The form work in contact with the concrete was

cleaned and thoroughly wetted or treated with an approved composition to prevent adhesion

between form work and concrete. Care was taken that such approved composition is kept out ofcontact with the reinforcement.


22/47

22

DESIGN

The form-work should be designed and constructed such that the concrete can be properly placedand thoroughly compacted to obtain the required shape, position, and levels subject

ERECTION OF FORMWORK

The following applies to all formwork:

a) Care should be taken that all formwork is set to plumb and true to line and level.

b) When reinforcement passes through the formwork care should be taken to ensure close

fitting joints against the steel bars so as to avoid loss of fines during the compaction of

concrete.

c) If formwork is held together by bolts or wires, these should be so fixed that no iron is

exposed on surface against which concrete is to be laid.

d) Provision is made in the shuttering for beams, columns and walls for a port hole of

convenient size so that all extraneous materials that may be collected could be

removed just prior to concreting.

e) Formwork is so arranged as to permit removal of forms without jarring the concrete.

Wedges, clamps, and bolts should be used where practicable instead of nails.

f) Surfaces of forms in contact with concrete are oiled with a mould oil of approved

quality. The use of oil, which darkens the surface of the concrete, is not allowed. Oiling

is done before reinforcement is placed and care taken that no oil comes in contact with

the reinforcement while it is placed in position. The formwork is kept thoroughly wet

during concreting and the whole time that it is left in place.

Immediately before concreting is commenced, the formwork is carefully examined to

ensure the following:

a) Removal of all dirt, shavings, sawdust and other refuse by brushing and washing.


23/47

23

b) The tightness of joint between panels of sheathing and between these and any hardened core.

c) The correct location of tie bars bracing and spacers, and especially connections of

bracing.

d) That all wedges are secured and firm in position.

e) That provision is made for traffic on formwork not to bear directly on reinforcement

steel.

VERTICALITY OF THE STUCTURE

All the outer columns of the frame were checked for plumb by plumb-bob as the work proceeds

to upper floors. Internal columns were checked by taking measurements from outer row of

columns for their exact position. Jack were used to lift the supporting rods called props

STRIPPING TIME OR REMOVAL OF FORMWORK

Forms were not struck until the concrete has attained a strength at least twice the stress to whichthe concrete may be subjected at the time of removal of form work. The strength referred is that

of concrete using the same cement and aggregates with the same proportions and cured under

conditions of temperature and moisture similar to those existing on the work. Where so required,

form work was left longer in normal circumstances

Form work was removed in such a manner as would not cause any shock or vibration that would

damage the concrete. Before removal of props, concrete surface was exposed to ascertain that theconcrete has sufficiently hardened. Where the shape of element is such that form work has re-

entrant angles, the form work was removed as soon as possible after the concrete has set, to

avoid shrinkage cracking occurring due to the restraint imposed. As a guideline, withtemperature above 20 degree following time limits should be followed:

Structural Component Age

Footings 1 day

Sides of beams, columns, lintels, wall 2 days

Underside of beams spanning less than 6m 14 days

Underside of beams spanning over 6m 21 days

Underside of slabs spanning less than 4m 7 daysUnderside of slabs spanning more than 4m 14 days

Flat slab bottom 21 days


24/47

24

CONCRETE MAKING

Just mix cement, aggregates and water, cast this mix in a mould, open the mould next

day. A uniform hard mass will be found, which is known as concrete, any body can makeit. The simplecity in making concrete make this material to be look like very simple in its

production, yet it as not so simple. Due to ignorance about concrete no other building

materials ever mis-used as concrete in the construction. In India concrete is being used

in the construction since the last 70 years. Yet 80% of the builders have no proper

understanding of this materials. Go to any construction site (except big construction

sites) you will find that sand and aggregates are being taken in iron tasla or cane baskets

to charge the mixer without the consideration of site aggregates actual grindings,

moisture content and bulking of sand. The water is poured in the mixer without any

measured quantity. It could be well imagine what sort of concrete structure will be

made with the concrete being produced in this crude method.

Most of the contractors, builders, masons etc. still follow 1:2:4 or 1:1.5:3 mixes they are

not aware of Design Mixes and Concrete Admixtures. This paper described how Design

Mixes can be converted into volume with 1 Bag Cement, 2 Boxes of sand and 4 Boxes of

Aggregate. The site practical problem is the dispersion of water and liquid admixtures

into the mixer. For this the site should fabricate a plastic circular graduated measuring

container of 30 lit capacity with a tap fitted at its bottom. This container is to be fitted

on top of the mixer. From this container water and liquid admixtures can conveniently

poured direct into the mixer in a measured quantity.

EXAMPLE OF MIX DESIGN

1. For a construction site M-25 Grade of concrete is required to be designed as per IS:

456-2000. The mix will be taken by volume. Workability required is 50 mm slump.

Normal Superplasticizer will be used in the mix. The materials will be mixed at site in atilting drum mixer of one cement bag capacity.

2. For durability consideration, maximum free W/C ration = 0.50 minimum cement

content 300 kg/m3

including Fly ash.

3. Test datas of aggregates are as given in table-1.


25/47

25

4. Cement will be used PPC, having 7 days average compressive strength of 37.5 N/mm2

5. Mean design target strength:

25 + 1.65 x 5 = 33.3 N/mm2 at 28 days age

Table-1 Test Data of Dehradun Aggregates:

I.S. Sieve Size Percentage Passing

River Sand 20 mm Crushed Aggregate

40 mm 100 100

20 mm 100 86

10 mm 95 3

4.75 mm 79 0

2.36 mm 72

1.18 mm 56

600 micron 47

300 micron 27

150 micron 6

Specific Gravity 2.65 2.65

Water absorption % 0.80 0.50

Bulk density kg/lit 1.78 1.40

Note : The sand is not falling to any grading Zone of IS : 383-1970. The aggregate grading

is 20 mm single sized as per IS: 383-1970.

If 95% this sand passes on 4.75 mm sieve, then the sand will become of Zone-II as per IS

: 383-1970. The following mix is worked out as per Zone-II sand. For detail calculations

refer reference of No. 1.

a) For the target strength and given cement and Aggregate W/C ration found to be =


26/47

26

0.49

b) Water for OPC 190 kg/m3. For PCC 5/100 x 190 = 9.5 , Say 10

190 10 = 180 kg/m3

to give 50 mm of Slump with the given aggregates. Normal

Superplasticizer at a dosages of

7 ml/kg cement will give 15% water reduction without loss of workability.

Water = 180 27 = 153 kg/m3

c) Cement = 153/0.49 = 312 kg/m3

d) Density of OPC concrete = 2405 kg/m3

Density for PPC Concrete = 2405 24 = Say 2380 kg/m3

e) Aggregates = 2380 -153 312 = 1915 kg/m3

f) Sand (Zone-II) = 1915 x 0.36 = 689 kg/m3

g) 20 mm aggregate = 1915 689 = 1226 kg/m

3

Mix. No. 1 On the basis of saturated and surface dry aggregates-

Water =153 kg/m3

PCC=312 kg/m3

Sand=689 kg/m3

20 mm Aggregate=1226 ml/m3

Mix No. 2

95-79 = 16% oversized particles in the sand is to be adjusted in the above mix. The

modified mix on the basis of saturated and surface dry aggregates is given below:

Water=153 kg/m3

PCC=312 kg/m3

Sand=820 kg/m3

20 mm Aggregate =1095 kg/m3

Normal Superplasticizer=2184 kg/m3

Accordingly mix ratio by weight on the basis of saturated and surface dry aggregates is

given below:

Cement : Sand : 20 mm Agg.

1 : 2.63 : 3.51 W/C Ratio = 0.49

Mix ratio by volume on the basis of room dry aggregates is given below:

Cement : Sand : 20 mm Agg.


27/47

27

1 : 2.14 : 3.63 Free W/C Ratio = 0.49

MIX RATIO BY VOLUME FOR ONE BAG OF CEMENT

1. Cement = One bag = 50 kg = 35 lit = 35000 cc

2. Sand (room dry) = 2.14 x 35 = 74.9 lit = 74900 cc

3. 20 mm Aggregate (room dry) = 3.63 x 35 = 127.05 lit = 127050 cc

4. Free Water = 24.5 lit

5. Normal Superplasticizer = 350 ml

MEASURING BOXES TO BE MADE AT SITE

1. Cement = One bag = 50 kg

2. Sand (room dry) = 33 x 33 x 34.4 cm two boxes

3. 20 mm Aggregate (room dry) = 33 x 33 x 29.2 cm .. four boxes

4. Free Water = 24.5 lit5. Normal Superplasticizer = 350 ml

In the above example M-25 Design mix is converted to the familiar 1 bag cement : 2

boxes of sand and 4 boxes of aggregate. While making concrete at site the moisture

content of site sand and aggregate must be taken into account in the mixing water and

bulking of sand. In the field trial mixes are to be carried out to finalize the mix.


28/47

28

FOUNDATION

The building foundation or sub structure is that part of a structure which is placed below the surface of

the ground and which transmits the superstructure load to the underlying soil ultimately. It is the part of

a structural system that supports and anchors the superstructure of a building. Foundation is the most

important part of a building. Building activity starts with the formation of foundation. Main activities of

building foundation are:-

To distribute building load to soil beneath

To distribute the load uniformly

To grapnel the structure to the ground to resist movement due to lateral force

To prevent sinking of the structure.

Any part of a structure that serves to transmit the load to the earth or rock can be called foundation.

The higher and heavier the building is to be, the wider and deeper the supports of footings for the

foundation have to be.

PURPOSE OF FOUNDATION

To pass out building weight to the soil beneath evenly;

To prevent differential settlement of building;

To provide a plane surface for the convenience of construction;

To make building substantial and durable by continuing the structure in the soil.

TYPES OF FOUNDATION:

Depending on tthhee ddeepptthh oofftthhee llooaadd--ttrraannssffeerr mmeemmbbeerr bbeellooww tthhee ssuuppeerr--ssttrruuccttuurree and tthhee

ttyyppee ooffttrraannssffeerr llooaadd mmeecchhaanniissmm foundation can be classified into two types:

a) Shallow Foundation

b) Deep Foundation.


29/47

29

The classification on foundation has been provided in flow chart as follows:

Classification of Foundation

a) SSHHAALLLLOOWWFFOOUUNNDDAATTIIOONN:A shallow foundation is a type of foundation which transfers building loads to the earth

very near the surface. The objective of shallow foundation is to distribute the structural

concentrated load over a wide horizontal area at a little depth rather than a range of

depths.

Shallow foundation is often selected when the soil has a good bearing capacity and the

structural load will not cause excessive settlement of the underlying soil layers. In

general, shallow foundations are more simple and cost effective to construct than deep

foundations because little soil is removed or disturbed.Shallow foundation construction

is typically utilized for most residential and light commercial raised floor buildings.

Foundation

Shallow

SpreadFootings

WallFootings

IsolatedColumnFootings

GrillageFoundation

CombinedFootings

MatFoundation

EccentrcallyLoaded

Footings

Deep

PileFoundation

Pre-castPiles

Cast-in -situ Piles

Cofferdams Caisson


30/47

30

SPREAD FOOTINGS:

Spread footing is a common term used to

refer shallow foundations which transfers

concentrated loads to a wide range area. Itincludes reinforced concrete footings, wall

footings, isolated column footings. Spread

footing provides a stable base or platform at a

low depth and it prevents the structure from

settling into the ground.

Spread Footing

ISOLATED COLUMN FOOTINGS:

Isolated column footings are used to support single columns. Each individual isolated

footing provides support for each individual column, pier, post or other single

concentrated load. So, they act as a base for a column. They transfer the superimposed

structural load to a wide range of soil. They are the most economical types of footings

and are used when columns are spaced at relatively long distances. They can be square,

rectangular or even circular in plan view.

Isolated footings can be of brick masonry, stone masonry or of Reinforced Cement

Concrete (R.C.C.) depending on amount of load, project expanses and materials

available. The base of the footing depends on the load bearing capacity of soil and the

superimposed load. They are also known as pad footing or individual column footing.

Generally isolated footings are used in case of reinforced concrete structure buildings.

WALL FOOTINGS:

This type of shallow footing supports a wall by providing footing beneath the entire wall

structure. This type of footing is used when columns are made of bricks.


31/47

31

GRILLAGEFOOTINGS:In case of low bearing capacity of soil and avoiding deep excavation grillage

foundation can be used. Grillage foundation can reduce the superimposed load

of column within the safe bearing capacity of the soil. The grillage can be made

of steel or timber.

COMBINED FOOTINGS:A combined footing is nothing but a combination of pad footings having a

common base. A combined footing is constructed when (i) a column lies very

close to the property line and (ii) to prevent overlapping of footings when

columns are very adjacent. They can be rectangular or trapezoidal in plan.

Combined footing proves to be more cost effective than a single column footing.

MATFOUNDATION:

A mat is a slab that supports multiple columns. It is typically used when thebearing capacity of soil is very low. When required footings will cover more than

half the area beneath a structure, it is often desirable to enlarge and combine

the footings to cover the entire area. A mat foundation may be cheaper than

individual footings because of reduced forming costs and simpler excavation

procedures. Although mat foundations are more difficult and more costly to

design but they prove to be more effective.

ECCENTRICALLYLOADED FOOTINGS:

It is a spread or wall footing that must resist a moment in addition to the axial

column load.

b) DDEEEEPPFFOOUUNNDDAATTIIOONN:A deep foundation is used when the bearing capacity of soil is low near ground. When a

building structure transmits excessive loads to a soil with low bearing capacity near

ground, settlement of the foundation takes place which endangers the stability of the

structure. In that case deep foundation is used to ensure good bearing capacity of soil at

a considerable amount of depth. A deep foundation requires considerable amount of

materials and earthwork resulting increased cost and effort. Piles, cofferdams and

caissons are some the familiar forms of deep foundations.


32/47

32

IISSOOLLAATTEEDDCCOOLLUUMMNNFFOOOOTTIINNGG

Dependingon structural load and soil isolated footing can be of following types:

BBRRIICCKKPPIILLLLAARRFFOOOOTTIINNGG: When the structural columns are made of bricks this type ofisolated footing is often used. This is the most economic type of isolated columnfooting. The width and the depth of the footing depend on load to be carried and

bearing capacity of the soil. The width is found by offsets running symmetrical round

the column.

SSttoonnee PPiillllaarr FFoooottiinngg: Stone pillar footings are stronger than brick pillars.Construction of this type of footing is similar to brick pillar footing. The width and the

depth of this footing is a bit bigger because of the stone sizes. This type of footing is

weak in resisting bending. So they are not used against long heavy structural loads.

RR..CC..CC.. CCoolluummnn FFoooottiinngg: In case of column subjected to heavy loading and bendingthis type of column footing provides a superior solution in shallow foundation. Made

with reinforcement and concrete this type of footing is high on strength and bending.

The footing is reinforced cross ways by re-bar placed at right angles to one another.

This type footing is capable of transmitting massive loads with a reduced footing

depth. This type is used as a most effective form of isolated footing. Due to its strong

structure this footing is used against high building structures provided that the soil

has sufficient bearing capacity.

INDEPENDENT COLUMN FOOTING REQUIREMENTS:The main requirements of an independent footing are as follows:

i. Must distribute loads evenly to the soil;

ii. Must be well drained to prevent wash-out;

iii. Must bear on engineered soil.


33/47

33

Foundation Alternatives and Cost Evaluation

As noted earlier, the two major alternate foundation types are the shallow and

deep foundations. Shallow foundations are discussed in this chapter. Deep

foundation alternatives including piles and drilled shafts are discussed in the next

chapter. Proprietary foundation systems should not be excluded as they may be the

most economical alternative in a given set of conditions. Cost analyses ofall feasible

alternatives may lead to the elimination of some foundations that were otherwise

qualified under the engineering study.

Other factors that must be considered in the final foundation selection are the

availability of materials and equipment, the qualifications and experience of local

contractors and construction companies, as well as environmental

limitations/considerations on construction access or activities. Whether it is for

shallow or deep foundations, it is recommended that foundation support cost be

defined as the total cost of the foundation system divided by the load the foundation

supports in tons. Thus, the cost of the foundation system should be expressed in

terms of dollars per ton loadthat will be supported. For anequitable comparison, the

total foundation cost should include all costs associated with a given foundation

system including the need for excavation or retention systems,environmental

restrictions on construction activities, e.g., vibrations, noise, disposal of

contaminated excavated spoils, pile caps and cap size, etc. For major projects, if the

estimated costs of alternative foundation systems during the design stage are within

15 percent of each other, then alternate foundation designs should be considered

for inclusion in contract documents. If alternate designs are included in the contract

documents, both designs should be adequately detailed. For example, if two pile

foundation alternatives are detailed, the bid quantity pile lengths should reflect the

estimated pile lengths for each alternative. Otherwise,material costs and not the

installed foundation cost will likely determine the low bid. Use of alternate

foundation designs will generally provide the most cost effective foundation system.

A conventional design alternate should generally be included with a proprietary

design alternate in the final project documents to stimulate competition and to

anticipate value engineered proposals from contractors.


34/47

34

STEPS OF ISOLATED FOOTING

SOIL EXCAVATION

LEVELLING & DRESSING OF SOIL SURFACE

PLACEMENT OF BRICK FLAT SOLING LAYER

GIVING A CEMENT CONCRETE LAYER ON IT

PLACEMENT OF CEMENT CONCRETE BLOCK

PLACING OF REINFORCEMENT

SHUTTERING

CONCRETE CASTING

REMOVAL OF FORMWORK

CURING

BACKFILLING OF EXCAVATED AREA


35/47

35

SOIL EXCAVATION

To set a footing, the first step is to excavate the soil of respective area. At first the area should

be located. The depth of excavation depends on the desired strength as strength increases with

depth. We see the tools that are used in excavation below,

PICS

In most cases, baskets & spades are used for excavation. Deep excavation damages adjacent

constructions. In this phase, shore piles or other preventive means are used. Soil sloping can also

reduce this damage. The picture below shows how workers dig soil during excavation,

Fig: Excavation


36/47

36

The area of footings are chosen according to design. First the C.G of footings is located.

The excavated soil is kept near the footing as later it can be used for backfilling.

PIC: excavated soil nearby the footing

LEVELLING & DRESSING OF SOIL SURFACE

After excavation, the most important step is to level the soil surface. The load of the construction

should be vertical & for this, leveling & dressing is must. Otherwise the construction might be

subjected to tilting to one side. Sand layer & brick chips are often used for leveling & dressing.

In our site LEVELLING & DRESSING were done by sand layer.


37/47

37

PLACEMENT OF BRICK FLAT SOLING LAYER

Now a hard & plane surface is needed. For this purpose we place a brick layer on previous layer.

It is called BRICK FLAT SOLLING. In this layer bricks are arranged in a regular combination.

The upper surface of the layer should be uniformly planed. Below we see a brick flat soling.

CEMENT CONCRETE LAYER

Generally a C.C (cement concrete) layer having 3 height is kept on the brick layer. It is named

as CEMENT CONCRETE LAYER. It provides a smooth, uniform & strong surface for

reinforcement frame. The mix ratio for C.C layer is cement:sand:aggregate=1:3:6.

But sometimes it is avoided to reduce expenses.

PLACING OF CEMENT CONCRETE BLOCK

Usually some CC blocks are kept on the CC layer to maintain the clear cover between CC layer

& reinforcement. It is also very important to prevent the reinforcement from corrosion. There is

no standard size of blocks. It varies with size of footing & clear cover.

Sometimes brick or half brick can be used instead of CC block. But bricks are not uniformly

smooth plane. Its strength is also less than CC block. So, it is better to use CC blocs as clear

cover. Generally its size is 3x3x3.


38/47

38

PLACING OF REINFORCEMENT

Now it is a very important step to place reinforcements. First we should maintain available clear

cover by using CC blocks. We must tie rebars with G.I wires or welding. It is done so that

rebars remains intact in all the time even during the casting. First a single frame of horizontal

reinforcement is kept upon the CC block. The number & diameter of reinforcements depends

upon the strength of construction. And it is determined by design engineer.

The rebars are tied by hand at the outer place if the case is respectively small. But for large case,it is done on the brick flat soling. Because it is difficult to move & place a large case.

Fig: Formation of a case Fig: Tied by G.I wire


39/47

39

Fig: Preparing column

The case must remain horizontal. It is done by plumb bob. The figure below we see how a case is

being horizontal by plumb bob.

Fig: Making horizontal

After placing the case, the centre of case is marked as the column can be placed.


40/47

40

Fig: Fixing the column position

Now the column is placed upon the marking space. It must be vertical. Then it is also tied with

case. After making vertical the column is supported to remain fixed.

Fig: Placing of column


41/47

41

Fig: making it vertical

SHUTTERING

Shuttering means the solid boundary around the concrete. It resists water flow. It also bears the

load of concrete. So a shuttering should be enough water tight & strong. The amount of water

should remain constant in order to get a proper hydration. There are two kinds of shuttering,

1. Wooden shuttering &

2. Steel shuttering

Wooden shuttering is more chip than steel shuttering. But it is less water proof & less strong. It

also lasts a short time. On the other hand steel shuttering is strong enough. It also can be used


42/47

42

more times. But it is costly. Side shuttering can be removed after 3 days as after this time

concrete get required strength.

Fig: Wood shuttering

The minimum requirements of a shuttering:

*It should be enough strong to bear the load

*It should be water tight

*It should be economical

*Its inner surface should be plane

*Its joints should be made carefully

*It should retain the concrete shape from all types of distortions.


43/47

43

Problems in isolated footing

1. Segregation: Separationof constituents of a heterogeneous mixture so that their distribution

is no longer uniform is termed as segregation. In case of concrete casting when it is thrown

from a large height

Figure: segregation.

Segregation occurs due to the difference in particles size (sometimes in the specific gravity of

the mix ingredients) .There are two types of segregation. In the first, the coarser particles tend

to separate out since travel further long distance. In the second, segregation is occurred by

separation of grout (water &cement). Here in our project aggregates were thrown from a

remarkable height. As a result the ingredients were separated as they hit the lower rebar layer.This segregation will ultimately decrease the strength of the concrete. So proper arrange should

be taken to prevent segregation.

Concrete is being thrown fro about 10 h


44/47

44

2. Compaction: In our observed site, for compacting concrete they used both rodding &

vibration procedure.

In case of using vibrator, it should kept in mind that vibrator must be vertical. But in our project

vibrator was used aligned.

Roding

withbamboo


45/47

45

Figure:

Aligned vibrating.

3.Improper clear cover maintainance: Clear cover is a very important fact in structure. For the

structure under the ground clear should be maintained at least 3. If clear cover is not

maintained properly then the moisture content around the structure will penetrate into the

structure & cause corrosion to the reinforcement . Finally collapse the structure.

Figure: Improper clear cover maintainance

Aligned

vibrating

Improperclear cover


46/47

46

4. Water logging during casting: Mix proportion is very much important for the design strength.

In our site during casting, water logged continuously. The source of water may be rain water or

leakage from nearby pipes or drains.

Figure: Water logging during casting

5. Brick as C.C block & no C.C layer: In isolated footing we normally use BFS & C.C layer to

provide a flat surface. But in our project BFS was used with no mortar. Here they also did not

use C.C layer as well as C.C block. For maintenance of the clear cover between the BFS bricks

were directly used as C.C block that is shown in the following figure.

Loggedwater


47/47

Figure: Brick as C.C block & no C.C layer

Bricks as

C.C

vt report on foundation

Documents