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JADAGURU DATTATRAY COLLEGE OF TECHNOLOGY
INDORE
INDUSTRIAL TRAINING
AT
DREAM INFRASTRUCTURE
(RAJKOT)
GUIDED BY:- SUBMITTED BY:-
Kishor kalavadiya CHETAN SOLANKI(Training incharge) 0833CE093D05
(CE 7thSEM)
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ACKNOWLEDGEMENT
I am highly obliged and thankful to my
guide Mr. Kishor Kalavadiya (training incharge) forvaluable suggestion, guidance and inspiration time totime.
I am also very grateful to Mr.Rajubhai
Sonigra and Mr.Pareshbhai Dabhi who hasencouraged & issued me to provide all help from company
to complete this training.
I am also thankful to staff of company for
their kind suggestion & co-operation.
Lastly I express sincere thanks to my
colleagues who directly or indirectly helped me incompleting my task.
Date:././ CHETAN SOLANKI0833CE093D05
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DECLEARATION
I CHETAN SOLANKI student of civilengineering , Jagadaguru Dattatray college of
techonology-INDORE. here by declare that thework presented in the training report, entitledIndustrial Training at DREAM
INFRASTRUCTURE is outcome of my own work,it bona-fied, correct to the best of my knowledgeand this work has been carried out taking care of
Engineering Ethics. The work presented does not
infringe any patented work and has not beensubmitted to any University for the award of any
degree or any professional Diploma.
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CONTENT
1. INTRODUCTION
2. SEQUANCE OF STRUCTURE WORK
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SEQUENCEOF 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
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Definition of Damp-proof course
A course of some impermeable material laid in the
foundation walls of building near the ground to preventdampness from rising into the building.
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Background
Rising damp can occur for various reasons - the failure of anexisting damp proof course, bridging due to the raising of
external ground or internal floor levels, or in older
buildings, the complete absence of a damp proof course.
Brick, stone and mortar are porous allowing damp fromthe ground to rise by capillary action, carrying with it groundsalts including chlorides and nitrates. These salts from
the ground can absorb moisture from the atmosphere
leading to wall dampness in conditions of high relativehumidity. Also they can ruin decorations and break downinternal plaster.
Building standards in many countries require most newbuildings to incorporate a DPC/DPM at the time of
construction. This may consist of a thin strip of plastic, acourse of engineering brick or slate, or a layer ofbitumen.
Materials
Materials widely used for damp proofing include
Flexible materials like hot bitumen, plastic sheets,bituminous felts, sheets of lead, copper, etc.
Semi-rigid materials like mastic asphalt
Rigid materials like impervious bricks, stones, slates,cement mortar or cement concrete painted withbitumen, etc.
http://en.wikipedia.org/wiki/Rising_damp_(structural)http://en.wikipedia.org/wiki/Capillary_actionhttp://en.wikipedia.org/wiki/Atmospherehttp://en.wikipedia.org/wiki/Wallhttp://en.wikipedia.org/wiki/Brickhttp://en.wikipedia.org/wiki/Slatehttp://en.wikipedia.org/wiki/Bitumenhttp://en.wikipedia.org/wiki/Mastic_asphalthttp://en.wikipedia.org/wiki/Rising_damp_(structural)http://en.wikipedia.org/wiki/Capillary_actionhttp://en.wikipedia.org/wiki/Atmospherehttp://en.wikipedia.org/wiki/Wallhttp://en.wikipedia.org/wiki/Brickhttp://en.wikipedia.org/wiki/Slatehttp://en.wikipedia.org/wiki/Bitumenhttp://en.wikipedia.org/wiki/Mastic_asphalt8/3/2019 Training Report on Constuction Megment
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Stones
Mortar with waterproofing compounds
Coarse sand layers under floors
Continuous plastic sheets under floors
Construction
A DPC is usually a thick plastic strip bedded into the
mortar between two courses of bricks or blocks. It canoften be seen as a thin plastic line in the mortar near
ground level.
A DPM is usually a thick polythene sheet laid under thefloor slab, to allow the slab to dry out and keep outgroundwater. It is often laid on a bed of sand, to preventthe sharp edges of the hardcore damaging it.
To create a continuous barrier, pieces of DPC or DPM are
welded together. In addition, the DPC is welded to theDPM around the outside edges of the ground floor,
completely sealing the inside of the building from thedamp ground under it.
In a cavity wall, there is usually a DPC in both the outerand inner wall. In the outer wall it is normally 150-200mm above ground level (the height of 2-3 brickcourses). This allows rain to form puddles and splash up
off the ground, without saturating the wall above DPC
level. The wall below the DPC may become saturated inrainy weather. The DPC in the inner wall is usually belowfloor level, (under a suspended timber floor structure),or, with a solid concrete floor, it is usually foundimmediately above the floor slab so that it can be linked
to the DPM under the floor slab. This enables installation
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of skirting boards above floor level without fear of
puncturing it. Alternatively, instead of fitting separateinner and outer DPCs, it is common in commercialhousebuilding to use a one-piece length of rigid plastic,(albeit an angled section), which fits neatly across the
cavity and slots into both walls (a cavity tray). This
method requires the need for weep vents to enablerainwater ingress to drain from the cavities otherwiserising dampness could occur from above the DPC.
Plaster
Lime plaster
Lime plaster is a mixture of calcium hydroxide and sand
(or other inert fillers). Carbon dioxide in the atmosphere
causes the plaster to set by transforming the calciumhydroxide into calcium carbonate (limestone). Whitewash isbased on the same chemistry.
To make lime plaster, limestone (calcium carbonate) isheated to produce quicklime (calcium oxide). Water is then
added to produce slaked lime (calcium hydroxide), which issold as a white powder. Additional water is added to form
a paste prior to use. The paste may be stored in air-tightcontainers. Once exposed to the atmosphere, the calciumhydroxide turns back into limestone, causing the plasterto set.
Lime plaster was a common building material for wallsurfaces in a process known as lath and plaster, whereby a
http://en.wikipedia.org/wiki/Limestonehttp://en.wikipedia.org/wiki/Whitewashhttp://en.wikipedia.org/wiki/Limestonehttp://en.wikipedia.org/wiki/Quicklimehttp://en.wikipedia.org/wiki/Slaked_limehttp://en.wikipedia.org/wiki/Lath_and_plasterhttp://en.wikipedia.org/wiki/Limestonehttp://en.wikipedia.org/wiki/Whitewashhttp://en.wikipedia.org/wiki/Limestonehttp://en.wikipedia.org/wiki/Quicklimehttp://en.wikipedia.org/wiki/Slaked_limehttp://en.wikipedia.org/wiki/Lath_and_plaster8/3/2019 Training Report on Constuction Megment
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series of wooden strips on a studwork frame was covered
with a semi-dry plaster that hardened into a surface. Theplaster used in most lath and plaster construction wasmainly lime plaster, with a cure time of about a month. Tostabilize the lime plaster during curing, small amounts of
Plaster of Paris were incorporated into the mix. Because
Plaster of Paris sets quickly, "retardants" were used toslow setting time enough to allow workers to mix largeworking quantities of lime putty plaster. A modern formof this method uses expanded metal mesh over wood ormetal structures, which allows a great freedom of design
as it is adaptable to both simple and compound curves.Today this building method has been partly replaced with
drywall, also composed mostly of gypsum plaster. In both
these methods a primary advantage of the material isthat it is resistant to a fire within a room and so canassist in reducing or eliminating structural damage or
destruction provided the fire is promptly extinguished.
Lime plaster is used for true frescoes. Pigments, diluted in
water, are applied to the still wet plaster.
Cement plaster
Cement plaster is a mixture of suitable plaster, sand,
portland cement and water which is normally applied to
masonry interiors and exteriors to achieve a smoothsurface. Interior surfaces sometimes receive a final layer
of gypsum plaster. Walls constructed with stock bricks arenormally plastered while face brick walls are not plastered.Various cement-based plasters are also used asproprietary spray fireproofing products. These usually use
vermiculite as lightweight aggregate. Heavy versions ofsuch plasters are also in use for exterior fireproofing, to
protect LPG vessels, pipe bridges and vessel skirts.
http://en.wikipedia.org/wiki/Wall_studhttp://en.wikipedia.org/wiki/Lime_plasterhttp://en.wikipedia.org/wiki/Drywallhttp://en.wikipedia.org/wiki/Frescohttp://en.wikipedia.org/wiki/Pigmenthttp://en.wikipedia.org/wiki/Portland_cementhttp://en.wikipedia.org/wiki/London_stock_brickhttp://en.wikipedia.org/wiki/Brickworkhttp://en.wikipedia.org/wiki/Fireproofinghttp://en.wikipedia.org/wiki/Vermiculitehttp://en.wikipedia.org/wiki/Wall_studhttp://en.wikipedia.org/wiki/Lime_plasterhttp://en.wikipedia.org/wiki/Drywallhttp://en.wikipedia.org/wiki/Frescohttp://en.wikipedia.org/wiki/Pigmenthttp://en.wikipedia.org/wiki/Portland_cementhttp://en.wikipedia.org/wiki/London_stock_brickhttp://en.wikipedia.org/wiki/Brickworkhttp://en.wikipedia.org/wiki/Fireproofinghttp://en.wikipedia.org/wiki/Vermiculite8/3/2019 Training Report on Constuction Megment
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Gypsum plaster
Plaster of Paris is a type of building material based on
calcium sulphatehemihydrate, nominally CaSO41/2H2O. It iscreated by heating gypsum to about 300F (150 C).
2 CaSO42H2O 2 CaSO40.5H2O + 3 H2O (released
as steam).
A large gypsum deposit at Montmartre in Paris is the sourceof the name. When the dry plaster powder is mixed withwater, it re-forms into gypsum.
One of the skills used in movie and theatrical sets is thatof "plasterer", gypsum plaster often being used to simulatethe appearance of surfaces of wood, stone, or metal.
Nowadays, plasterers are just as likely to use expandedpolystyrene, although the job title remains unchanged.
TypeStart of
setting inSetting
timeVolumechange
1.A-fastsetting 2 min 15 min +1%
2.B-regularsetting
6min 30min +1%
3.C-slowsetting 20min 90min +2%
Masonry
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Masonry is the building of structures from individual
units laid in and bound together by mortar; the termmasonrycan also refer to the units themselves. Thecommon materials of masonry construction are brick, stonesuch as marble, granite, travertine, limestone; concrete block, glassblock, stucco, and tile. Masonry is generally a highly
durable form of construction. However, the materialsused, the quality of the mortar and workmanship, andthe pattern in which the units are assembled cansignificantly affect the durability of the overall masonryconstruction.
Applications
Masonry is commonly used for the walls of buildings,retaining walls and monuments. Brick and concrete block
are the most common types of masonry in use inindustrialized nations and may be either weight-bearingor a veneer. Concrete blocks, especially those with hollowcores, offer various possibilities in masonry construction.
They generally provide great compressive strength, andare best suited to structures with light transverse loading
when the cores remain unfilled. Filling some or all of thecores with concrete or concrete with steelreinforcement(typically rebar) offers much greater tensileand lateral strength to structures.
Advantages
The use of materials such as brick and stone canincrease the thermal mass of a building, giving
increased comfort in the heat of summer and thecold of winter, and can be ideal for passive solarapplications.
http://en.wikipedia.org/wiki/Mortar_(masonry)http://en.wikipedia.org/wiki/Brickhttp://en.wikipedia.org/wiki/Rock_(geology)http://en.wikipedia.org/wiki/Marblehttp://en.wikipedia.org/wiki/Granitehttp://en.wikipedia.org/wiki/Travertinehttp://en.wikipedia.org/wiki/Limestonehttp://en.wikipedia.org/wiki/Concrete_blockhttp://en.wikipedia.org/wiki/Glasshttp://en.wikipedia.org/wiki/Tilehttp://en.wikipedia.org/wiki/Masonry#Veneer_masonryhttp://en.wikipedia.org/wiki/Rebarhttp://en.wikipedia.org/wiki/Thermal_masshttp://en.wikipedia.org/wiki/Passive_solarhttp://en.wikipedia.org/wiki/Mortar_(masonry)http://en.wikipedia.org/wiki/Brickhttp://en.wikipedia.org/wiki/Rock_(geology)http://en.wikipedia.org/wiki/Marblehttp://en.wikipedia.org/wiki/Granitehttp://en.wikipedia.org/wiki/Travertinehttp://en.wikipedia.org/wiki/Limestonehttp://en.wikipedia.org/wiki/Concrete_blockhttp://en.wikipedia.org/wiki/Glasshttp://en.wikipedia.org/wiki/Tilehttp://en.wikipedia.org/wiki/Masonry#Veneer_masonryhttp://en.wikipedia.org/wiki/Rebarhttp://en.wikipedia.org/wiki/Thermal_masshttp://en.wikipedia.org/wiki/Passive_solar8/3/2019 Training Report on Constuction Megment
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Brick typically will not require painting and so can
provide a structure with reduced life-cycle costs,although sealing appropriately will reduce potential
spalling due to frost damage. Non-decorative concreteblock generally is painted or stuccoed if exposed.
The appearance, especially when well crafted, can
impart an impression of solidity and permanence. Masonry is very heat resistant and thus provides
good fire protection.
Masonry walls are more resistant to projectiles, suchas debris from hurricanes or tornadoes than walls of wood
or other softer, less dense materials.
Unreinforced Masonry structure built in compression
with (Preferably in lime mortar) has the life of more
than 500 years as compared to 30 to 100 for steel orRCC structure.
Disadvantages
Extreme weather causes degradation of masonrywall surfaces due to frost damage. This type ofdamage is common with certain types of brick,though rare with concrete blocks. If non-concrete
(clay-based) brick is to be used, care should betaken to select bricks suitable for the climate in
question.
Masonry tends to be heavy and must be built upon a
strong foundation (usually reinforced concrete) to avoidsettling and cracking. If expansive soils (such as
adobe clay) are present, this foundation needs to bequite elaborate and the services of a qualified
structural engineer may be required, particularly inearthquake prone regions.
http://en.wikipedia.org/wiki/Spallhttp://en.wikipedia.org/wiki/Frosthttp://en.wikipedia.org/wiki/Stuccohttp://en.wikipedia.org/wiki/Hurricaneshttp://en.wikipedia.org/wiki/Tornadohttp://en.wikipedia.org/wiki/Reinforced_concretehttp://en.wikipedia.org/wiki/Adobe_clayhttp://en.wikipedia.org/wiki/Earthquakehttp://en.wikipedia.org/wiki/Spallhttp://en.wikipedia.org/wiki/Frosthttp://en.wikipedia.org/wiki/Stuccohttp://en.wikipedia.org/wiki/Hurricaneshttp://en.wikipedia.org/wiki/Tornadohttp://en.wikipedia.org/wiki/Reinforced_concretehttp://en.wikipedia.org/wiki/Adobe_clayhttp://en.wikipedia.org/wiki/Earthquake8/3/2019 Training Report on Constuction Megment
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Structural limitations
Masonry boasts an impressive compressive strength(vertical loads) but is much lower in tensile strength
(twisting or stretching) unless reinforced. The tensilestrength of masonry walls can be strengthened by
thickening the wall, or by building masonrypiers (verticalcolumns or ribs) at intervals. Where practical, steelreinforcements can be added.
Brick
Solid brickwork is made of two or more layers of bricks with
the units running horizontally (called stretcherbricks)bound together with bricks running transverse to the wall
(called "header" bricks). Each row of bricks is known as acourse. The pattern of headers and stretchers employed
gives rise to different bonds such as the common bond
(with every sixth course composed of headers), theEnglish bond, and the Flemish bond (with alternatingstretcher and header bricks present on every course).
Bonds can differ in strength and in insulating ability.Vertically staggered bonds tend to be somewhat stronger
and less prone to major cracking than a non-staggeredbond.
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Portland cement mortar
Portland cement mortar (often known simply as cement
mortar) is created by mixing Ordinary Portland cement (OPC)with sand and water.
It was invented in 1794 by Joseph Aspdin and patentedon 18 December 1824, largely as a result of variousscientific efforts to develop stronger mortars than existed
at the time. It was popularized during the late nineteenthcentury, and owing to the First World War, by 1930 it had
superseded lime mortar for new construction. The mainreasons for this were that Portland cement sets hard andquickly, allowing a faster pace of construction, andrequires less skilled workers. However, as a general rule,
Portland cement should not be used for the repair ofolder buildings constructed in lime mortar, which require
the flexibility, softness and breathability of lime if theyare to function correctly.
http://en.wikipedia.org/wiki/Portland_cementhttp://en.wikipedia.org/wiki/Sandhttp://en.wikipedia.org/wiki/Portland_cementhttp://en.wikipedia.org/wiki/Sand8/3/2019 Training Report on Constuction Megment
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Brickwork bonds
Flemish bond
Flemish bond, also known as Dutch bond, has
historically always been considered the most decorativebond, and for this reason was used extensively for
dwellings until the adoption of the cavity wall. It iscreated by alternately laying headers and stretchers in a
single course. The next course is laid so that a headerlies in the middle of the stretcher in the course below.
This bond is one brick thick. It is quite difficult to layFlemish bond properly, since for best effect all theperpendiculars (vertical mortar joints) need to be verticallyaligned. If only oneface of a Flemish bond wall is
exposed, one third of the bricks are not visible, andhence may be of low visual quality. This is a better ratio
than for English bond, Flemish bond's main rival for load-bearing walls.
http://en.wikipedia.org/wiki/Mortar_(masonry)http://en.wikipedia.org/wiki/File:Billbeee-flemishb.pnghttp://en.wikipedia.org/wiki/Mortar_(masonry)8/3/2019 Training Report on Constuction Megment
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A common variation often found in early 18th century
buildings is Glazed-headed Flemish Bond, in which theexposed headers are burned until they vitrify with a blackglassy surface. Monk bond' is a variant of Flemishbond, with two stretchers between the headers in
each row, and the headers centred over the join
between the two stretchers in the row below. Acommon variant isWessex Bondwith three stretchersbetween each header. This is easier to lay than fullFlemish Bond and produces a less intense, butnevertheless "pretty" brickwork face.
English bond
This bond has two alternating courses of stretchers and
headers, with the headers centered on the stretchers,and each alternate row vertically aligned. There is avariant in which the second course of stretchers is half
offset from the first, giving rise to English cross bondor Dutch bond.
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REINFORCE CEMENT CONCRETE
Use in construction
Concrete is reinforced to give it extra tensile strength;
without reinforcement, many concrete buildings wouldnot have been possible.
Reinforced concrete can encompass many types ofstructures and components, including slabs, walls, beams,
columns, foundations, frames and more.
Reinforced concrete can be classified as precast or cast in-situconcrete.
Much of the focus on reinforcing concrete is placed on floorsystems. Designing and implementing the most efficientfloor system is key to creating optimal buildingstructures. Small changes in the design of a floor systemcan have significant impact on material costs,
construction schedule, ultimate strength, operating costs,occupancy levels and end use of a building.
Behavior of reinforced concrete
Materials
Concrete is a mixture of cement (usually Portland cement)and stone aggregate. When mixed with a small amount ofwater, the cement hydrates form microscopic opaquecrystal lattices encapsulating and locking the aggregateinto a rigid structure. Typical concrete mixes have high
resistance to compressivestresses (about 4,000 psi (28
http://en.wikipedia.org/wiki/Slabhttp://en.wikipedia.org/wiki/Wallhttp://en.wikipedia.org/wiki/Beam_(structure)http://en.wikipedia.org/wiki/Columnhttp://en.wikipedia.org/wiki/Foundation_(architecture)http://en.wikipedia.org/wiki/Framing_(construction)http://en.wikipedia.org/wiki/Precasthttp://en.wikipedia.org/wiki/Cast_in-situ_concretehttp://en.wikipedia.org/wiki/Cast_in-situ_concretehttp://en.wikipedia.org/wiki/Floorhttp://en.wikipedia.org/wiki/Portland_cementhttp://en.wikipedia.org/wiki/Construction_aggregatehttp://en.wikipedia.org/wiki/Hydrateshttp://en.wikipedia.org/wiki/Physical_compressionhttp://en.wikipedia.org/wiki/Stress_(physics)http://en.wikipedia.org/wiki/Slabhttp://en.wikipedia.org/wiki/Wallhttp://en.wikipedia.org/wiki/Beam_(structure)http://en.wikipedia.org/wiki/Columnhttp://en.wikipedia.org/wiki/Foundation_(architecture)http://en.wikipedia.org/wiki/Framing_(construction)http://en.wikipedia.org/wiki/Precasthttp://en.wikipedia.org/wiki/Cast_in-situ_concretehttp://en.wikipedia.org/wiki/Cast_in-situ_concretehttp://en.wikipedia.org/wiki/Floorhttp://en.wikipedia.org/wiki/Portland_cementhttp://en.wikipedia.org/wiki/Construction_aggregatehttp://en.wikipedia.org/wiki/Hydrateshttp://en.wikipedia.org/wiki/Physical_compressionhttp://en.wikipedia.org/wiki/Stress_(physics)8/3/2019 Training Report on Constuction Megment
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MPa)); however, any appreciable tension (e.g., due to
bending) will break the microscopic rigid lattice, resulting incracking and separation of the concrete. For this reason,typical non-reinforced concrete must be well supported toprevent the development of tension.
If a material with high strength in tension, such as steel, isplaced in concrete, then the composite material,
reinforced concrete, resists not only compression butalso bending and other direct tensile actions. A reinforcedconcrete section where the concrete resists thecompression and steel resists the tension can be made
into almost any shape and size for the constructionindustry.
Key characteristics
Three physical characteristics give reinforced concrete itsspecial properties.
First, the coefficient of thermal expansion of concrete is similar to
that of steel, eliminating large internal stresses due todifferences in thermal expansion or contraction.
Second, when the cement paste within the concrete
hardens this conforms to the surface details of the steel,permitting any stress to be transmitted efficientlybetween the different materials. Usually steel bars areroughened or corrugated to further improve the bond or
cohesion between the concrete and steel.Third, the alkaline chemical environment provided by the
alkali reserve (KOH, NaOH) and the portlandite (calciumhydroxide) contained in the hardened cement paste causesa passivating film to form on the surface of the steel,making it much more resistant to corrosion than it would be
http://en.wikipedia.org/wiki/Tension_(mechanics)http://en.wikipedia.org/wiki/Bendinghttp://en.wikipedia.org/wiki/Steelhttp://en.wikipedia.org/wiki/Coefficient_of_thermal_expansionhttp://en.wikipedia.org/wiki/Heathttp://en.wikipedia.org/wiki/Chemical_bondhttp://en.wikipedia.org/wiki/PHhttp://en.wikipedia.org/wiki/Alkalihttp://en.wikipedia.org/wiki/Portlanditehttp://en.wikipedia.org/wiki/Calcium_hydroxidehttp://en.wikipedia.org/wiki/Calcium_hydroxidehttp://en.wikipedia.org/wiki/Passivationhttp://en.wikipedia.org/wiki/Corrosionhttp://en.wikipedia.org/wiki/Tension_(mechanics)http://en.wikipedia.org/wiki/Bendinghttp://en.wikipedia.org/wiki/Steelhttp://en.wikipedia.org/wiki/Coefficient_of_thermal_expansionhttp://en.wikipedia.org/wiki/Heathttp://en.wikipedia.org/wiki/Chemical_bondhttp://en.wikipedia.org/wiki/PHhttp://en.wikipedia.org/wiki/Alkalihttp://en.wikipedia.org/wiki/Portlanditehttp://en.wikipedia.org/wiki/Calcium_hydroxidehttp://en.wikipedia.org/wiki/Calcium_hydroxidehttp://en.wikipedia.org/wiki/Passivationhttp://en.wikipedia.org/wiki/Corrosion8/3/2019 Training Report on Constuction Megment
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in neutral or acidic conditions. When the cement paste
exposed to the air and meteoric water reacts with theatmospheric CO2, portlandite and the Calcium Silicate Hydrate(CSH) of the hardened cement paste becomeprogressively carbonated and the high pH gradually
decreases from 13.5 12.5 to 8.5, the pH of water in
equilibrium with calcite (calcium carbonate) and the steel is nolonger passivated.
As a rule of thumb, only to give an idea on orders ofmagnitude, steel is protected at pH above ~11 but startsto corrode below ~10 depending on
steel characteristics and local physico-chemical conditionswhen concrete becomes carbonated. Carbonation ofconcrete along with chloride ingress are amongst the chief
reasons for the failure ofreinforcement bars in concrete.
The relative cross-sectional area of steel required fortypical reinforced concrete is usually quite small andvaries from 1% for most beams and slabs to 6% for
some columns. Reinforcing bars are normally round in cross-section and vary in diameter. Reinforced concrete
structures sometimes have provisions such as ventilatedhollow cores to control their moisture & humidity.
Distribution of concrete (in spite of reinforcement)strength characteristics along the cross-section of verticalreinforced concrete elements is inhomogeneous.
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 bethere in the site location.
http://en.wikipedia.org/wiki/Calcium_Silicate_Hydratehttp://en.wikipedia.org/wiki/CSHhttp://en.wikipedia.org/wiki/Calcitehttp://en.wikipedia.org/wiki/Calcium_carbonatehttp://en.wikipedia.org/wiki/Carbonationhttp://en.wikipedia.org/wiki/Chloridehttp://en.wikipedia.org/wiki/Reinforcement_barhttp://en.wikipedia.org/wiki/Areahttp://en.wikipedia.org/wiki/Rebarhttp://en.wikipedia.org/wiki/Calcium_Silicate_Hydratehttp://en.wikipedia.org/wiki/CSHhttp://en.wikipedia.org/wiki/Calcitehttp://en.wikipedia.org/wiki/Calcium_carbonatehttp://en.wikipedia.org/wiki/Carbonationhttp://en.wikipedia.org/wiki/Chloridehttp://en.wikipedia.org/wiki/Reinforcement_barhttp://en.wikipedia.org/wiki/Areahttp://en.wikipedia.org/wiki/Rebar8/3/2019 Training Report on Constuction Megment
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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 of450*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. Adequateprecautions 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 thesurface 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 itscompacted. Depth of excavation was 54 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 notmixed 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 toachieve full compaction. Concrete placed below ground should be protected
from falling earth during and after placing. Concrete placed in groundcontaining deleterious substances should be kept free from contact with such
a ground and with water draining there from during placing and for a periodof 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 layingupper layer of concrete. The lower surface is made rough and clean watered
before upper layer is laid.
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LAYINGOF 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 raftfoundation 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 wouldoverlap on each other. Raft foundations have the advantage of reducing
differential settlements as the concrete slab resists differential movementsbetween 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 andconstruction 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 theengineer in charge of the site.
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Apart from raft foundation, individual footings were used in the mess areawhich was extended beyond the C and D blocks.
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CEMENT
Portland cement is composed of calcium silicates and aluminate and
aluminoferrite It is obtained by blending predetermined proportionslimestone 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 mixedwith 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 reactiontermed as hydration. Therefore cement remains in good condition as long as
it does not come in contact with moisture. If cement is more than threemonths 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 differentgrades 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 ratioarrived 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 apozzolanic material with clinker and gypsum, or by blending ground
pozzolana with Portland cement. Nowadays good quality fly ash is availablefrom Thermal Power Plants, which are processed and used in manufacturing
of PPC.
ADVANTAGESOFUSING PORTLANDPOZZOLANACEMENTOVEROPC
Pozzolana combines with lime and alkali in cement when water is added and
forms compounds which contribute to strength, impermeability and sulphateresistance. It also contributes to workability, reduced bleeding and controls
destructive expansion from alkali-aggregate reaction. It reduces heat of
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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 differentcolour 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 thecement. The cement gets its colour from the nature and colour of raw
materials used, which will be different from factory to factory, and may evendiffer 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. Preferencefor 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 pasteand remit it without any deleterious effects. As the reaction between waterand cement continues, the paste loses its plasticity. This early period in the
hardening of cement is referred to as setting of cement.
INITIALANDFINALSETTINGTIMEOFCEMENT
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 ambientconditions 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.
STORAGEOF CEMENT
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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 dont that should befollowed -
(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 theyfit 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 onwooden 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.
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(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.
Damp-proof course
A course of some impermeable material laid in the foundation walls ofbuilding near the ground to prevent dampness from rising into the building.
Rising damp can occur for various reasons - the failure of an existing damp
proof course, bridging due to the raising of external ground or internal floorlevels, or in older buildings, the complete absence of a damp proof course.
Brick, stone and mortar are porous allowing damp from the ground to rise by
capillary action, carrying with it ground salts including chlorides and nitrates.These salts from the ground can absorb moisture from the atmosphere
leading to wall dampness in conditions of high relative humidity. Also theycan ruin decorations and break down internal plaster.
Building standards in many countries require most new buildings to
incorporate a DPC/DPM at the time of construction. This may consist of athin strip of plastic, a course of engineering brick or slate, or a layer of
bitumen.
Materials
Materials widely used for damp proofing include
Flexible materials like hot bitumen, plastic sheets, bituminous felts,sheets of lead, copper, etc.
Semi-rigid materials like mastic asphalt
Rigid materials like impervious bricks, stones, slates, cement mortar or
cement concrete painted with bitumen, etc.
Stones
Mortar with waterproofing compounds
Coarse sand layers under floors Continuous plastic sheets under floors
Construction
http://en.wikipedia.org/wiki/Rising_damp_(structural)http://en.wikipedia.org/wiki/Capillary_actionhttp://en.wikipedia.org/wiki/Atmospherehttp://en.wikipedia.org/wiki/Wallhttp://en.wikipedia.org/wiki/Brickhttp://en.wikipedia.org/wiki/Slatehttp://en.wikipedia.org/wiki/Bitumenhttp://en.wikipedia.org/wiki/Mastic_asphalthttp://en.wikipedia.org/wiki/Rising_damp_(structural)http://en.wikipedia.org/wiki/Capillary_actionhttp://en.wikipedia.org/wiki/Atmospherehttp://en.wikipedia.org/wiki/Wallhttp://en.wikipedia.org/wiki/Brickhttp://en.wikipedia.org/wiki/Slatehttp://en.wikipedia.org/wiki/Bitumenhttp://en.wikipedia.org/wiki/Mastic_asphalt8/3/2019 Training Report on Constuction Megment
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A DPC is usually a thick plastic strip bedded into the mortar between two
courses of bricks or blocks. It can often be seen as a thin plastic line in themortar near ground level.
A DPM is usually a thick polythene sheet laid under the floor slab, to allow
the slab to dry out and keep out groundwater. It is often laid on a bed ofsand, to prevent the sharp edges of the hardcore damaging it.
To create a continuous barrier, pieces of DPC or DPM are welded together. Inaddition, the DPC is welded to the DPM around the outside edges of theground floor, completely sealing the inside of the building from the damp
ground under it.
In a cavity wall, there is usually a DPC in both the outer and inner wall. In
the outer wall it is normally 150-200mm above ground level (the height of
2-3 brick courses). This allows rain to form puddles and splash up off theground, without saturating the wall above DPC level. The wall below the DPC
may become saturated in rainy weather. The DPC in the inner wall is usuallybelow floor level, (under a suspended timber floor structure), or, with a solid
concrete floor, it is usually found immediately above the floor slab so that itcan be linked to the DPM under the floor slab. This enables installation ofskirting boards above floor level without fear of puncturing it. Alternatively,
instead of fitting separate inner and outer DPCs, it is common in commercialhousebuilding to use a one-piece length of rigid plastic, (albeit an angled
section), which fits neatly across the cavity and slots into both walls (a
cavity tray). This method requires the need for weep vents to enablerainwater ingress to drain from the cavities otherwise rising dampness could
occur from above the DPC.
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 loamyadmixtures 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-powderysurfaces.Aggregates should be properly screened and if necessary washedclean before use.
Coarse aggregates containing flat, elongated or flaky pieces or mica should
be rejected. The grading of coarse aggregates should be as perspecifications of IS-383.
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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 ofsizes 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 tobring uniformity in mixture. Usually, the natural river sand is used as fine
aggregate. Important thing to be considered is that fine aggregates shouldbe 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 ISsieve 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 andmost 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 uponwhether 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 firstlayer 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 steelreinforcement was completely embedded in mortar.
Bricks can be of two types. These are:
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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 partsof 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 overcountry.
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 cmmasonry with modular bricks workout to be cheaper there is saving in the
consumption of bricks, mortar and labour as compared with masonry withtraditional bricks.
STRENGTHOFBRICKMASONRY
The permissible compressive stress in brick masonry depends upon thefollowing 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 ofsoil 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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There are many checks that can be applied to see the quality of bricks usedon the site.Normally the bricks are tested for Compressive strength, water
absorption, dimensional tolerances and 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 in water 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 brickwork. Vertical
joints
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shouldnt be continuous but staggered.
The joint thickness shouldnt exceed 1 cm. It should be thoroughly filledwith the
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, to provide
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 crosssection in concrete structure. They are like a skeleton in human body. Plain
concrete without steel or any other reinforcement is strong in compressionbut 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 highstrength 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 being used mostcommonly 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 have brought 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 strengthdeformed bars start from 8 mm diameter. For general house constructions,
bars of diameter 6 to 20 mm are used
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Transverse reinforcements are very important. They not only take care of
structural requirements but also help main reinforcements to remain indesired 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 themain/longitudinal reinforcement
TERMSUSEDIN REINFORCEMENT
BAR-BENDING-SCHEDULE
Bar-bending-schedule is the schedule of reinforcement bars prepared in
advance before cutting and bending of rebars. This schedule contains alldetails of size, shape and dimension of rebars to be cut.
LAPLENGTH
Lap length is the length overlap of bars tied to extend the reinforcementlength.. Lap length about 50 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% barsshould be lapped. In case, required lap length is not available at junction
because of space and other constraints, bars can be joined with couplers orwelded (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 the junction. For example, main bars of beam in column at beamcolumn junction, column bars in
footing etc. The length requirement is similar to the lap length mentioned in
previous question or as per the design instructions
COVERBLOCK
Cover blocks are placed to prevent the steel rods from touching the
shuttering plates and there by providing a minimum cover and fix thereinforcements 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 be made of cement sand mortar
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(1:3). Ideally, cover should have strength similar to the surrounding
concrete, with the least perimeter so that chances of water to penetratethrough 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, coverindicates thickness of the cover block. Normally, cubical cover blocks are
used. As a thumb rule, minimum cover of 2 in footings, 1.5 in columns and
1 for other structures may be ensured.
Structural element Cover to reinforcement (mm)
Footings 40
Columns 40
Slabs 15
Beams 25
Retaining wall 25 for earth face
20 for other face
THINGSTO NOTE
Reinforcement should be free from loose rust, oil paints, mud etc. it should
be cut, bent and fixed properly. The reinforcement shall be placed andmaintained in position by providing proper cover blocks, spacers, supporting
bars, laps etc. Reinforcements shall be placed and tied such that concreteplacement is possible without segregation, and compaction possible by an
immersion vibrator.
For any steel reinforcement bar, weight per running meter is equal to
d*d/162 Kg, where d is diameter of the bar in mm. For example, 10 mmdiameter bar will weigh 1010/162 = 0.617 Kg/m
Three types of bars were used in reinforcement of a slab. These includestraight bars, crank bar and an extra bar. The main steel is placed in which
the straight steel is binded first, then the crank steel is placed and extrasteel 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 the surroundings supports.
For providing nominal cover to the steel in beam, cover blocks were usedwhich were made of concrete and were casted with a thin steel wire in the
center which projects outward. These keep the reinforcement at a distance
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from bottom of shuttering. For maintaining the gap between the main 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 the process ofsheeting.
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 of deflection caused due to the weight of reinforcement
and concrete placed over that. A proper lubrication of shuttering plates isalso done before the placement of reinforcement. The oil film
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sandwiched between concrete and formwork surface not only helps in easy
removal of shuttering but also prevents loss of moisture from the concretethrough 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 toprevent leakage of mortar. Forms were so 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 andcompacted except when vibrators are used. A key was made at the end of
each casting in concrete columns of appropriate size to give proper bondingsto 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 the forms (steel) before the concrete is placed. The formwork 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 of contact with the reinforcement.
DESIGN
The form-work should be designed and constructed such that the concretecan be properly placed and thoroughly compacted to obtain the required
shape, position, and levels subject
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ERECTION OF FORMWORK
The following applies to all formwork:
a) Care should be taken that all formwork is set to plumb and true to lineand 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 thecompaction of
concrete.
c) If formwork is held together by bolts or wires, these should be so fixedthat 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 ofapproved
quality. The use of oil, which darkens the surface of the concrete, is notallowed. 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 keptthoroughly wet
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during concreting and the whole time that it is left in place.
Immediately before concreting is commenced, the formwork iscarefully examined to ensure the following:
a) Removal of all dirt, shavings, sawdust and other refuse by brushing and
washing.
b) The tightness of joint between panels of sheathing and between theseand any hardened core.
c) The correct location of tie bars bracing and spacers, and especiallyconnections 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 wereused 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 leasttwice the stress to which the 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 underconditions 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 the concrete has sufficientlyhardened. 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 concretehas set, to avoid shrinkage cracking occurring due to the restraint imposed.
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As a guideline, with temperature 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 days
Underside of slabs spanning more than 4m 14 days
Flat slab bottom 21 days
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 powdercalled 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 withmoisture. If cement is more than three months old then it should
be tested for its strength before being taken into use.
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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.
ADVANTAGESOFUSING PORTLANDPOZZOLANACEMENTOVEROPC:
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
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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 ispossible 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.
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INITIALANDFINALSETTINGTIMEOFCEMENT:
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.
LIST OF TOOLS & EQUIPMENT
1) Shovel2) Pan M.S. 35 cms diameter 128
3) Forma wooden for measuring aggregate4) Bucket C.I. 35 cms diameter5) Masons Plumb Rule with Spirit level
6) Masons Square 30 cms x 30 cms7) Sieve for Sand 1/16 inches, 100 x 60 cms.8) Sieve for Sand 1/8 inches, 100 x 60 cms.
9) Trowel 10 x 3 10) Tool Cutting Set of 611) Brick Hammer with Handle
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12) Rule 4 folds wooden 60 cms.
13) 6 Painting Trowel14) Line Pins Corner Block15) Motor Board16) Wire Board
17) Wooden Float
18) Steel Float19) Spirit Level 1220) Chisel hammer headed21) Bolster22) Claw Hammer
23) Spade24) Measuring tape 100 (Steel)
25) Ladder aluminium 10 feet height
26) Pick Axe27) Rammer Axe28) Crow bar 1 diameter 5 feet long
29)Hand Hammer 2 lbs.
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