SLIP FORMWORK USE FOR SLIP FORMWORK USE FOR CONSTRUCTIONSCONSTRUCTIONS

PRESENTED BY :

SHUBHANGI GAJBHIYE (701019)

SACHIN KHEDEKAR (701028)

PARIKSHEETA KORE (701030)

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Topics to be covered in todays session

• Introduction to formworkTypesImportance• Slip formworkHorizontal constructionVertical constructionMaterial useSafety

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Introduction

• Formwork :

Temporary boarding or sheeting erected to contain freshly placed and compacted concrete until it has gained sufficient strength to be self-supporting.

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Importance of formwork

• Formwork system is the key factor determining the success of a construction project in terms of

-speed-quality-cost-safety of works

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• Formwork greatly affects the final appearance of the finished structure

• Formwork is a large proportion of the total cost of a structure

• The ultimate economical success of formwork lies in the ease with which it can be stripped

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Importance of formwork

Classification of Formwork

• Sizes• Materials of construction• Nature of operation

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Classification according to sizes

• Small-sized formwork -operation by workers manually -timber and aluminium• Large-sized formwork -crane facilities are required in the operation-reduce the number of jointing and to minimize the

number of lift. -stiffening components -studs and soldier.

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Classification according to materials of construction

• Timber-most popular formwork material -low initial cost -high adaptability to complicated shape-labour intensive and environmental unfriendly

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Classification according to materials of construction

• Steel -hot-rolled or cold-formed sections-heavy weight -suitable for large-sized panels• Aluminium-stiff and light weight-higher material and labour cost-excellent finish

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Classification according to nature of operation

-Manually operated formwork-Self-lifted formwork -Crane-lifted formwork-Gantry, traveling and tunnel type formwork

system

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Innovations in concrete formwork

Glass reinforced plastic formwork Flying formworkJump formworkSlip formwork

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Slip formwork

• Slipforming is a construction technique which has been used for decades for production of concrete structures

• Use for vertical structures and horizontal structures such as towers, bridge columns reinforced concrete pavement.

• Used where geometry of structure and wall thickness changes

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Slip formwork

• Method of vertically extruding a reinforced concrete section and is suitable for construction of core walls in high-rise structures – lift shafts, stair shafts, towers.

• The formwork rises continuously, at a rate of about 300 mm per hour, supporting itself on the core and not relying on support or access from other parts of the building or permanent works.

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Types of construction

• Horizontal construction• Vertical construction

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Horizontal construction

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Slipform Paving Technique

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Slipform Paving Technique

• It is process used to consolidate, form into geometric shape finish a Plain Cement Concrete (PCC) mass by pulling the forms continuously through and surrounding plastic concrete mass.

• Appropriate for larger jobs that require high production rates.

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The key components of slipform paving

• Charging conveyor • Spreading plough / Spreading auger• Paving mould• Concrete vibrators• Finishing beam and super smoother• Machine frame• Crawler tracks

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Charging conveyor

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Charging conveyor

• It conveyed the concrete to a hopper • Different hydraulically driven systems are available to

carry out this job• Mixes the concrete thoroughly during transport • Capable of conveying the concrete at an incline of up

to 45°. • Its large diameter offers ample capacity to ensure that

the paving mould is supplied with concrete continuously also during truck changes.

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Charging conveyor

• Subject to extremely low wear and tear • Conveying speed can be adjusted • Depending on the location of access roads and

the position of the conveying system and paving mould, a transverse conveyor may be required

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Spreading plough / Spreading auger

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Spreading plough / Spreading auger

• Small slipform paver models are equipped with a spreading auger. It spreads the concrete ahead of the front metering screed behind which the concrete profile is formed.

• Larger machine models are equipped with a spreading plough which moves back and forth in front of the paving mould, distributing the concrete across the entire working width.

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Paving mould

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Paving mould

• Can be changed quickly and easily, and can have almost any given shape

• offset application: The paving mould is mounted at the side of the paver eg. traffic parapets.

• Inset application: The paving mould is mounted between the paver's crawler tracks eg. paving of concrete slabs.

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Concrete vibrators

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Concrete vibrators

• vibrate at high frequency .• causes the air bubbles to dissipate, enabling

them to escape from the concrete.• mounted so as to prevent vibrations from being

transmitted to the paver .• available as straight or elbow-type vibrators and

are driven electrically or hydraulically.

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Finishing beam and super smoother

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• finishing beam : - move back and forth perpendicular to the

machine's direction of travel- remove all irregularities in the concrete surface- used mostly when inserting dowel bars in single-

layer concrete pavements but is equally suitable for other concrete paving applications

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• super smoother :- a combined longitudinal and transverse

movement- levels out all remaining irregularities in the upper

area of the concrete slurry- surface produced offers excellent riding qualities.

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Machine frame

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Machine frame

• The basic module of all slipform pavers is a telescoping main frame which can be extended to the desired paving width by means of extension elements.

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Crawler tracks

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Crawler tracks

• Depending on the machine model, 2, 3 or 4 crawler tracks can be mounted either directly on the machine frame or on bolster beams

• Suspended on lifting cylinders which are hydraulically height-adjustable individually

• This design offers maximum flexibility for positioning the crawler tracks

• Enable extremely high, wide or cantilevering concrete slabs or profiles to be paved.

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Slipform Paving Operations

• Transporting and Spreading :- Concrete is deposited in front of the paver within

45 minutes from the time cement has been charged into the mixing drum

- Non - agitating equipment are used only when haul time less than 15 minutes

- No equipment is allowed to operate on the prepared and compacted underlying material in front of the paver-finisher

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- Additional water is added to truck mixers to bring slump within specified range provided the mixture water-cement ratio is not exceeded

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• Placing Reinforcing Steel :- positioned on suitable chairs securely fastened to

the sub-grade prior to concrete placement- may be placed on an initial layer of consolidated

concrete, with the subsequent layer placed within 30 minutes of the first layer placement

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operating principle of slipform paving

• Inset application• Offset application

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Inset application

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Inset application- The paving mould is mounted between the paver's

crawler tracks eg. paving of concrete slabs.- the concrete is delivered by trucks and dumped

ahead of the slipform paver.- spread by an excavator when working at large

paving widths - vibrators emitting high-frequency vibrations

ensure optimum compaction of the concrete during the slipforming process

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Inset application

- Tie bars and dowel bars are inserted into the freshly paved concrete automatically

- finishing beam and super smoother put the finishing touches to the new pavement.

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Offset application

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offset application

- The paving mould is mounted at the side of the paver eg. traffic parapets.

- Concrete mixers used for delivering concrete into the slipform paver’s receiving hopper

- concrete is transported to the offset mould in a continuous operation either via a slewable charging conveyor

- vibrators are installed in the mould in accordance with customer specifications.

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offset application

- The paving mould produces a concrete structure of uniform, superior quality and excellent finish with monolithic profile .

- Before concrete hardens, the surface of the pavement is given a texture

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Moist or Membrane Curing

- prevents moisture loss but does not supply any additional water is called the Membrane Curing

- It involve placing a waterproof covering over a slab- Curing compounds are typically formed using

resins, waxes or synthetic rubbers with a dissolved volatile solvent

- Once the solvent evaporates, the curing compound forms a near impermeable membrane over the PCC

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Precautions

Concrete is continuously protected against loss of moisture and rapid temperature changes for at least 7 days

Unhardened concrete is protected from rain and flowing water

Prevent plastic shrinkagePlastic shrinkage cracks that occur are filled by

injection of epoxy resin after the concrete hardens.

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Advantages of slipform paving

• Uses Low-Slump :- slump of the order of 0-75 mm - higher compression and flexural strengths than

comparable high slump mixes.

• High Productivity :- Slipform paving production rates are in the range of 65

- 100 m3/hr for mainline paving which translates into between 70 - 90 m/hr of 3.66 m wide, 250 mm thick PCC surface course.

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• Smooth Riding Surface :- Automation and computer control allow slipform

pavers to produce very smooth riding surfaces (IRI on the order of 0.90 m/km or less).

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Vertical slipform

Components of vertical slip form:

Components of vertical construction

• Yokelegs :- used to lift the slipform structure as one

integral unit- transfer lifting reactions to jacks- acts as the main connecting member for

walkway platforms, masons’ scaffold, yoke beams, top platforms, etc.

• Walkway Bracket :- Inside and outside brackets are connected with

the respective yoke legs with the help of a pin for easy erection and dismantling along with a pipe strut to support cantilever portion to facilitate placing of concrete.

• Shutters and Walers :- It maintain correct profile of structure to be slip

formed and resist concreting pressure.

• Lifting Jacks :- facilitate lifting of Slipform assembly- located preferably at equal intervals to enable to

lift slipform as one integral unit- Capacity is decided depending upon the reactions

at point of lifting.

• Hydraulic Pump :- provided to circulate required quantity of

hydraulic oil at desired pressure for lifting jacks

• Jacking/Climbing Rods :- located centrally in the wall to be cast or at equal distance

in yoke beams depending upon the number of jacks- It is generally of 48mm, 32mm, or 25mm in diameter

based upon the capacity of jacks.- entire load of the Slipform assembly is transferred to

jacking rods when jacks are energized.

• Tapered Sleeve: - Tapered sleeve tubes are provided to prevent fresh

concrete coming in contact with jack rods

yoke beam:

• Connecting member between inside and outside yoke legs.•Jacks are mounted over yoke beams.•Yoke beam transfers lifting forces of jacks to yoke legs.

Slip-formed 200m chimney at West Burton power station, Nottinghamshire (courtesy Bierrrum)

Vertical construction

• Concrete is continuously placed, compacted, and formwork is pulled up.

• Rate of slipping of formwork is depends upon temperature and strength development of concrete .

• It withstand without the support of the formwork.

• This method is suitable for uniform shapped structures.

• The formwork rises continuously, at a rate of about 300 mm per hour.

• The formwork system has three platforms. 1) upper 2) middle 3) lower • Typically, the concrete stays in a vertical slip

form for 1.5 - 6 hours.• The form is not deep and it moves so that

concrete is not in the form for long.• Jointless concrete structure is constructed.

• The height of a vertical slip form can range from about 1 m to 2 m with the most common size being 1.2 m tall.

Slip form structural detail

Relation between concrete setting time and slipform rate:

• It is calculated by using the following equation: VS = (h1- h2) / (ts - tt)

Where

VS = Slipform rate [mm / h]h1 = The distance from the top of the slipform panel to the average curing front [mm]h2 = The distance from top of the slipform panel to the average freeboard [mm] ts = Setting time [h]tt = Time from mixing of the concrete to placing[h]

BASIC CONSTRUCTION SEQUENCE• The formwork and the access platform are

assembled on the ground.• The assembly is raised using hydraulic jacks.• As the formwork rises continuously,

continuous concrete and rebar supply are needed until the operation is finished.

• At the end of the operation the formwork is removed using a crane.

• The entire process is thoroughly inspected and highly controlled.

PROCESS EFFICIENCY:• Careful planning of construction can achieve

high rates of production.• The slip form does not require a crane to

move upwards so the need for crane time is reduced.

• As this formwork operates independently, formation of the core in advance of the rest of the structure, This can help to provide stability to the main structure during its construction.

• Slip form systems require a small but highly skilled workforce on site.

Why choose slip forming?

• Slip forming is best used when there is little need to change the formwork.

• The costs are higher in setup but reduced overall due to the speed of completion.

• There is a minimum height of construction of about four floors, above which the cost of slip forming becomes economical.

Before choosing slip forming some of the things to consider:

• The concreting will take place in a very short time.

• The initial setting up time insitu will be longer than for conventional forms but can be reduced by construction of the forms in large slabs off site.

• The cost per square meter of the equipment will be more than for conventional forms.

• Labour costs will be higher due to shift work but productivity will be good.

• There are no construction joints.• Standby plant and workers are needed.• It is easy to obtain a good key for subsequent

finishes.• The final tolerance for the completed work is

about same as that for other methods.• Economizing on the design of the slip form

may lead to major and expensive problems.

DESIGN OF SLIP FORMWORK:• The structure consists basically of five parts:1)form face and its supports2)yokes and cross members3)jacking equipment which keeps the form moving4)work platform at the top level of the form5) hanging work platform, below the form face

where the workers finish the surface as it exits the form.

Set out, construct and assemble formwork for slip form methods of construction:

• Forming Concrete Nibs• Prefabricating Jump and Slip Formwork• Locating and Strengthening Formwork Lift Points• Placement of Block outs and Penetrations• Positioning Reinforcement Steel• Positioning Work Platforms and Safety Screens• Installing Yokes and Jacking Systems and

Connecting them to the MasterControl Unit

General structure of slipform:

REMOVAL OF FORMWORK:

• Determination must be based on compliance with one of the following:

1)The plans and specifications stipulate conditions for removal of forms and shores, such conditions have been followed.

2)The concrete has been properly tested with an appropriate American Society for Testing and Materials (ASTM)

THEORETICAL DETAILS OF CONCRETE HARDENING IN THE SLIP FORM:

SLIP FORM WORKS BY CONCRETE PUMP:• Concrete pump has accelerated the rate of

concreting.• By this method we can reduce the manpower.• As pouring time is less and uniform layer well

before the initial setting time of concrete.• And this gives smooth surface wall.

Sketch diagram for Slipform Works at Clinker Silo:

MATERIAL FOR CONSTRUCTION

SELF CONSOLIDATING CONCRETE• Self Consolidating Concrete is an emerging

class of concrete materials that offers great potential, because of:

1. improved ease of placement. 2. increased rate of construction. 3. reduced cost through reduced time and

labor.

SELF CONSOLIDATING CONCRETE

• The SCC for slip-form paving will not be as fluid as the conventional SCC, but it will be workable enough for machine placement

• Allows self-compaction with minimum segregation.

• Has property of robustness.

CHEMICAL ADMIXTURE

• The two principle chemical admixtures in SCC are:

1)synthetic high-range water reducer (superplasticizer)

2)viscosity modifying admixture (VMA).

SCC OVER ORDINARY CONCRETE:

• The need for vibration required by conventional concrete during slip-form paving is eliminated.

• Concrete quality is improved due to elimination of vibrator trails and a more uniform air void system.

• Elimination of vibration succeeds in reducing problems such as segregation and air loss

SCC OVER ORDINARY CONCRETE

• Smoothness of pavement is improved by minimizing hand surface-finishing requirements.

• SCC for slip-form paving boosts production efficiency by increasing construction speed and decreasing costs for labor and machine energy consumption.

• The noise disturbance generated by vibrators is avoided.

SCC OVER ORDINARY CONCRETE:

• Mix design is more complex as it contains more ingredients that each of them might affect the rheological properties differently.

• The requirements from SCC are far more demanding, thus what might be acceptable for ordinary concrete, might not meet SCC requirements.

Test on SCC

• Flowability : slump flow test using the traditional slump cone.

• Resistance to Surface segregation of SCC in the field :

1) Settlement test 2) Penetration test

BENEFITS

• Careful planning of construction process can achieve high production rates.

• Does not require crane to move upwards, Minimize crane use.

• Availability of the different working platforms in the formwork system allows the exposed concrete at the bottom of the rising formwork to be finished, making it an integral part of the construction process.

BENEFITS

• Certain formwork systems permit construction of tapered cores and towers.

• Slip form systems require a small but highly skilled workforce on site.

SUSTAINABILITY FEATURES

• The repetitive uniform nature of the work leads to reduced concrete wastage.

• The formwork system is reusable with little waste generated compared to traditional formwork.

• Slip form systems can offer safe and cost effective solutions for certain high-rise building structures.

SAFETY

• Working platforms, guard rails, ladders and wind shields are normally built into the completed system.

• Strength of concrete in the wall below must be closely controlled to achieve stability during operation.

OTHER CONSIDERATIONS

• This formwork is more economical for buildings more than seven storeys high.

• Little flexibility for change once continuous concreting has begun therefore extensive planning and special detailing are needed.

• Setting rate of the concrete had to be constantly monitored to ensure that it is matched with the speed at which the forms are raised.

OTHER CONSIDERATIONS

• The structure being slipformed should have significant dimensions in both major axes to ensure stability of the system.

• Standby plant and equipment should be available though cold jointing may occasionally be necessary.