Construction of post tension slab

Post-Tensioned concrete slab was originally developed during the 1930's by a Frenchman, Eugene Freyssinet, who realized that placing concrete under compression greatly increased its strength

1. Department of Civil Engineering
Indian Institute of Technology Kanpur
Arvind Vishavkarma
TextbooksorReferenceMaterials
[1]https://www.youtube.com/watch?v=jeHI92RYr5Q
[2]http://www.fdot.gov/structures/structuresresearchcenter/Final%20Reports/B
C354_73.pdf
[3]http://www.buildersshow.com/Documents/course_handouts/Post
Tensioned%20Concrete%20in%20Residential%20Construction.pdf
[4]http://www.cclint.com/uploads/PDFs/Post-tensioned-Slabs.pdf
CONSTRUCTION OF
POST-TENSION SLAB

2. Department of Civil Engineering
Indian Institute of Technology Kanpur
PRESENTATION FOR CE647A –CONSTRUCTION METHODS
Overview
▪History
▪Definition
▪Application
▪Construction Process
▪Advantage

3. History
▪Post-Tensionedconcreteslabwasoriginallydevelopedduring
the1930'sbyaFrenchman,EugeneFreyssinet,whorealized
thatplacingconcreteundercompressiongreatlyincreasedits
strength.
▪AfterWorldWarII,post-tensionedconcreteslabbecamea
popularbuildingmethodbecauseofthesteelshortageandthe
needtoreplacedamagedandbombed-outbridges.
▪Thedesignanduseofthismethodwaneduntilthemid-1960's,
whenmuchofitsutilizationwasintheareaofground-
supportedslabsforwarehouse,apartment,andresidential
floors.
▪In1976,thePost-TensioningInstitute,whichrecognizedthe
expandinginterestinthefield,wasformed.
3

4. Post Tension slab
▪ThetermPosttensioningisusedtodescribe
theprocessofintroducinginternalforces(or
stress)intotheconcreteormasonryelement
duringtheconstructionprocessinorderto
counteracttheexternalloadappliedwhenthe
structureisputintouseknownasserviceload.
4

5. Post Tension slab
▪PostTensionslabisareinforcedconcreteslab
supporteddirectlybyconcretecolumnswithout
theuseofbeams.
▪Post-tensioningslabcablesplacedinsideplastic
ductsorsleeves,arepositionedintheforms
beforetheconcreteisplaced.
▪Constructionofpost-tensionslabongradeis
verysimilartousingreinforcingsteel,exceptfor
thetensioningstep.
5

6. Post Tension slab
•Posttensionedslabcancontainlessconcrete20%-30%.
•Posttensionedslablessreinforcement&lesscomplicated
rebarshapingthenconventionalconcreteslabs.
•Thicknessofposttensionslab100mm-150mmand
conventionalslab120mm-200mm.
•Underthefullserviceloaddeflection<250or40mm
whicheverissmaller.
•Possibletoachieve70%ofspecifiedconcreteconcrete
strengthwithinadayortwodaybyusinghighstrength
concrete.
•Toobtainmaximumbenefitfromposttensionedslab
itisrecommendedthattheyareincorporatedintothe
buildingstructureatearlydesignstage.
6

7. Post tension slab used in various
Construction Project
▪Residential building
▪Commercial building
▪Shopping mall
▪Hospital
▪School
▪Stadium
▪Car Parks
▪Transfer structure
7

8. Post Tension slab construction
Design
Layout
Installation
of strands
and
Tendons
Concreting
Stressing
Grouting

9. Design and layout of Post Tension slab
construction
•Detailing system and
equipment used
•Layout plan
Design
•Selection of Contractor
whichprovide sound and
reliable construction
•Installing the tendon
Strand
Installation

10. Strand Installation
Strands

11. 11
Shutteringandframeworkarelaiddown&connected
togetherandsealed
Live and dead stressing anchorage are fixed
Trained Post tensioning installer is fixed.
The strands either mechanically or by hands are stressed
while opposite end monitors. Strands length at the
opposite end depends on tendon length
Fix the Dutch Chair according to the design specified.
After installing strands, tendons and Dutch chair are
carefully checked

12. 12
Live Anchorage Dead Anchorage
Dutch chair

13. 13
Concreting
▪Surface should be free
from debris and other
matter
▪Concrete should be
poured
▪Monitor concreting
process to ensure no
damage to arrangement
of strands, dutchchair
and tendon

14. 14
After concrete attain the sufficient
strength, shutter should be removed.
Anchorage heads & wedges are installed.
Stressingstageischeckedandmonitoredregularly
andrigorousinspectionisinsuredthatslabshould
remainsafeandalsotendonscarrythedesignload.
Beforestressingstarts,workareashould
beisolatedandauthorizedpersongetthe
access
Calibrated and certified equipment should
be used
Stressing

15. 15
Initialstressshouldbeappliedtoinduceananti
crakesforceintheconcretetypically48to72hrs
afterthepouringandwhentheconcretereachthe
requiredDesignstrength.
Eachindividualtendonisstressedinasingle
smoothactionandthentendonlocksoff.
Aftercompletionofstress,extendedlengthof
eachtendonismeasured(Extendedlength
indicatethatstrengthoftendonagainstthe
initialstress.)
Aftertheapproval,eachtendonshouldbecut
andpacked.Allductsarefilledbynon
shrinkingmortarandthengroutingtakes
place.
Stressing

16. 16
Stressed tendon bar Measured extended length of tendon
Measured extended length of tendon Filling duct with motor

17. 17
Grouting
Createthebondbetweenstrandandthe
tendons,eachstrandisfirstairtestedby
blowingcompressedairthroughtheducts
toensuregroutscanflowfreely.
Grout specified by w/c ratio
Groutstemperatureisregulatedand
checkedbyProbeThermometer.Mortar
temperaturemustbe>3
o
Cotherwise
specialcoldweatherprocedurecanbe
implemented.
Onedayaftergrouting,groutventis
checkedtoinsurethatgroutsisstill
presentonlythenPlasticgroutventtubeis
removed.

18. 18
Test carried out on Grout
Groutfluidity
Wicktest-measurebleedleveland
volumechange
Strength test-Grout specimen
prepared and check independent
Schupackpressuretest

19. 19
Grout fluidity Wick test-measure
Schupackpressuretest

20. 20
Strength Test
Sample for Compressive Strength Checked bond between tendon and grout

21. 21
Advantage of Post-tension slab
Lighter Structure
Extra vertical spaced

22. 22
Advantage of Post-tension slab
Greater flexibility
▪Load carried by column only
▪Enhance the deflection control
▪ItsallowsArchitecttointroduce
partitionwallsanywhererequired,
thisallowsownertochangethesize
ofroomlayout
Easy to maintenance
▪Greater cracks resistance
▪Durable & low maintenance
finished

23. 23
Advantage of Post-tension slab
Reduced Cost
▪Faster Construction
▪Low material cost
Smaller Carbon footprint
▪Requirement of concrete
compare to normal slab so less
emission of CO2 in atmosphere

24. Department of Civil Engineering
Indian Institute of Technology Kanpur
A course on Hydration, porosity and strength of cementitiousmaterials under the Massive Open Online Courses initiative
Dr Sudhir Misra
Dr KV Harish Courtesy: M.S. Shetty