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Sunday, December 7th, 2014
1:30 pm to 2:30 pm
Harley Nethken PE PTlf: [email protected]
Jonnie Deremo: [email protected]
Richard Zaino: [email protected]
TENNIS COURT POST-TENSION CONCRETE
SLAB
DO’S & DON’TS
THE DO’S AND DON’TS
The Do’s
• Foam wrap all posts that are in the PT slab, full depth of concrete
• Pocket formers tight against forms / check during pour and keep clean
• Rebar @ corners, especially diagonal corners.
• Minimum of 6” concrete coverage beyond posts in slab
• Expansion joints at walls to allow for slab expansion during hot temperatures
• Make sure to lift and chair up cables when using a laser screed
• Make sure plastic covers old court completely when pouring over old courts
• If pouring on top of a retaining wall place a
wood chamfer strip at bottom the perimeter turn down to help create separation between them.
• Place a 24 hour pre-stress on cables
The Don’ts
• Do not allow new concrete to touch any other solid structures beneath
• Do not place/pour turn down up against an old court during overlay’s
• Do not pour if weather is sketchy…wind, rain etc….
• Do not pour on Monday’s
5 KEY POINTS FROM THE POST-TENSIONING INSTITUTE
DESIGN AND CONSTRUCTION OF POST-TENSIONED SPORTS
• The geometry of a slab, and the various elements that can restrain a slab and prevent it from shortening under prestressing force, play a critical role in the successful construction of the post-tensioned sport courts.
• The design provide for a minimum residual compressive stress at the plan center of the slab of 100 psi. (some prefer 150 psi or slightly higher)
• Minimum allowed thickness is 4”, minimum recommended concrete strength at 28 days is 3000 psi., initial stressing strength of 2000 psi as soon as possible after concrete placement.
• 80% jacking force of the tendons minimum ultimate tensile strength (MUTS). A temporary jacking force of 80% is the maximum force allowed by code and is not to be exceeded during the stressing operations.
• Consideration of slab/sub-grade friction: Even if polyethylene sheeting is not required or specified as a vapor retarder, it may prove desirable to utilize it to reduce the friction coefficient. Caution should be exercised if polyethylene sheeting is used when placing concrete in hot weather. Mixing water will tend to evaporate more quickly at the surface than at the soffit, causing the slab to have a higher rate of shrinkage in the top and the bottom. This can lead to non-uniform curing of the slab section and can result in curling and surface shrinkage cracking.
PLANNING AND DESIGN CHECKLIST
• Size of slab
• Spacing of cables
• Clearance for stressing cables
• Cable drawing
• Sequence of stressing
• Concrete mix design
• Concrete supplier
• Timing, start and finish
• Boom pump, trailer pump or tele-belt
• Access
• Inspections
INSTALLATION CHECKLIST
• Proper number of cables
• Cable locations
• Cable spacing
• Edge details
• Compacted base
• Vapor barrier
• Net posts, fence posts or light standards details
• Cross members tied
• Cables secured to forms
• Minimum cable length beyond form
• Cable cleared at key joints
CONCRETE PLACEMENT CHECKLIST
• Cables chaired
• Ends supported
• Sheathing whole
• Anchor wedges horizontal
• Cables clearing posts
• Vapor barrier complete, check for tears in plastic and tape
STRESSING CHECKLIST
• Clean pockets
• Set wedges
• Mark Cables
• Stress cables
• Measure cables
• Cut cables
• Paint ends, place caps
• Grout pockets
COURT SLAB PREPARATIONS
• Subgrade slope and compaction
• Form work
• Sleeves
• Base materials, compaction
• Uniform slab thickness
• Vapor Barrier
• Post-tension cables
• Key Joint
• Expansion joint with cap
• Isolating posts, fence, bench, shade structure, sleeves
• Access for concrete placement
• Clean out container
• Staging for equipment,
CONCRETE PLANNING & SPECIFICATIONS
• Strength
• Slump
• Additives
• Total cubic yards
• Truck spacing
• Wash out container for read-mix trucks and pump
CONCRETE PLACEMENT
• Finishing equipment
• Crew
• Pump or Tele-belt
• Timing
• Planning start and finishing
• Curing
• Supplier
• Finish
ASTM GUIDELINES
• ASTM A-416: Pre-stressing steel requirements
• ASTM C-33: Non-reactive aggregate concrete
POST-TENSION GLOSSARY
Restraint-to-Shortening (RTS): Subgrade friction, keying, none isolated posts
Residual Compressive Stress: Factor used for cable spacing, minimum 100 psi at center of
slab.
Minimum Ultimate Tensile Strength (MUTS): Standard to which cables are stressed to 80%.
Final Effective Force per tendon: Factor for calculating tendon spacing
TENNIS COURT POST-TENSION CONCRETE QUESTIONS
1. Who and what factors determine cable spacing?2. What is good, better, best cable spacing for a tennis court 60’ x 120’?3. Same question for double courts, triple courts, 120’x120’ and 120’ x 180’?4. When do you need to or have to stress cables from both ends or sides of a tennis court pt slab?5. Why stress from both ends of cables?6. What varies from one manufacturer of cables to another manufacturer of cables?7. Are all manufacturer of cables the same, are some better, what makes for a good, better, best cable?8. How long do cables keep compressing a court slab? What is the life of a post-tension tennis court slab?9. Are all vapor barriers the same, one sheet verse two sheets, what’s the best method, thickness for vapor barrier?10. What concrete strength is ideal for a tennis court post-tension slab?11. Is it okay to have cables in only one direction? When is it okay? What is the advantages or disadvantages?12. Is it okay to place a partial stress on cables the day after placing concrete? Do you need a strength test before
stressing cables? 13. What do you do if one cable will not stress? What happens if a pt anchor pops through the top of concrete surface?14. What is the minimum concrete coverage over a pt cable? What is the minimum concrete strength for a tennis court
pt slab? 15. How long can you wait to stress the pt cables?16. What is the minimum thickness for a tennis court pt slab? What is the maximum thickness for a tennis court pt
slab? What is the minimum thickness for the tennis court pt court edge? What is the maximum thickness for the tennis court pt court edge?
17. What is the maximum spacing of cables for a tennis court pt slab?18. Do we need key joints at the net line and or between multiply courts?19. What is the best way to finish the concrete edges between concrete pour strips and pt slab? 20. Is there a maximum size rock in the ready-mix design?21. What ASTM standards apply to tennis court post-tension concrete slabs?22. What is the proper concrete finish for the concrete pt slabs? Best method for curing tennis court pt slabs?23. How much do you separate or space around fence posts, light standards, bench legs or other equipment placed in
or at edge of the tennis court pt slab?24. Should we have deepen footings or concrete grade beams for the tennis court pt slabs?25. What thickness of expansion joint should we place between the tennis court pt slab and walls?26. Can we build a tennis court pt slab over a wall? What design issues do we need to consider?
EDGE DETAIL WITH SPEED DOWELS FOR STEEL REBAR
DOWELS TO TIE INTO CONCRETE POUR STRIP
FENCE POST RADIUS BLOCK OUT
STYROFOAM FENCE POST BLOCK OUT
SQUARE CONCRETE BLOCK OUT FOR FENCE
POST
RADIUS CONCRETE BLOCK OUT FOR FENCE
POST
EDGE DETAILS
KEY JOINTS AND SHADE SHELTER POSTS
BLOCK OUTS
EXPANSION FELT AT WALL AND WRAPPED
FENCE POSTS
CIRCULAR BLOCK OUTS FOR FENCE POSTS
AT WALL LOCATIONS
DOUBLE WRAPPED FENCE POST
SLAB EDGE
WRAPPED FENCE POST AND VAPOR BARRIER
PLACING CONCRETE WITH A TELE-BELT
CONVEYER SYSTEM
TELE BELT PLACEMENT OF READY MIX
CONCRETE
CONCRETE ¼” TOOLED EDGE JOINTS FOR
CHANNEL DRAIN
BLENDED CONCRETE SAW CUT JOINT AT
CHANNEL DRAIN
KEY JOINT AND LIGHT POLE BLOCK OUT
SAW CUT POST TENSION CONCRETE EDGE AT POUR STRIP
NEXT TO WALL WITH EXPANSION JOINT
POST TENSION SLAB OVER CAMERA PIT WALL
POST TENSION SLAB OVER WALL DETAIL
POST TENSION CONCRETE SLAB EDGE AND
CAMERA PIT WALL
NOT ENOUGH ISOLATION OF FENCE POST,
CORNER CONCRETE EDGE SPALLED
SPALLED CONCRETE AROUND CORNER FENCE POSTS
UNWRAPPED FENCE POSTS
CASE STUDY OF RESTRAINED POST TENSION CABLE
TENNIS COURT CONCRETE SLAB OVERLAY
• Post Tension slab placed over an existing tennis court slab
• New concrete post tension slab edge restrained by existing slab
• Material void not installed
• New slab restrained by the existing slab
• Spalling and uplifting of new slab
• Fence posts restrained at concrete slab edges
NEW POST TENSION SLAB LIFTING AND SPALLING AT AREAS
RESTRAINED BY THE EXISTING SLAB
RESTRAINED POST TENSION CONCRETE SLAB
EDGE DETAILS
CONCRETE EDGE DETAILS
CLOSE UP PHOTOS OF EDGE FAILURE
LIFTING OF SLAB EDGE
CRACKING AT EDGE
CONCRETE CRACKING AT EDGE AND FENCE
POST
CONCRETE EDGE SET UP
LACK OF VOID MATERIAL BETWEEN NEW SLAB
AND EXISTING SLAB
SET UP WITH LACK OF VOID MATERIALS OVER
EXISTING SLAB
EDGE DETAIL
CONCRETE FINISHING AT EDGE
EDGE DETAIL
POUR STRIP BETWEEN TWO SLABS
NOT ENOUGH VOID MATERIAL TO ALLOW COMPRESSION OF
THE NEW POST TENSION SLAB
WHAT’S WRONG WITH THIS PICTURE
THERE IS ANOTHER PROBLEM OTHER THEN THE
FOAM VOID, WHAT IS IT?
CRACKS DEVELOPING IN THE NEW SLAB
CLOSE UP OF CRACKS IN SLAB
IMPROPER CONCRETE THICKNESS
GREASE SPOTS , RUSTING, AND CRACKING
IMPROPER CONCRETE THICKNESS
GREASE SPOTS , RUSTING, AND CRACKING
IMPROPER CONCRETE THICKNESS
GREASE SPOTS , RUSTING, AND CRACKING
IMPROPER CONCRETE THICKNESS
GREASE SPOTS , RUSTING, AND CRACKING
IMPROPER CONCRETE THICKNESS
GREASE SPOTS , RUSTING, AND CRACKING
IMPROPER CONCRETE THICKNESS
GREASE SPOTS , RUSTING, AND CRACKING
IMPROPER CONCRETE THICKNESS
GREASE SPOTS , RUSTING, AND CRACKING
EXCESSIVE SLAB LENGTH
ELASTIC SHORTNING , LONG TERM CREEP
-1/8”PER 20’ 200’ = 10/8” OR 5/8’ EACH END
EXCESSIVE SLAB LENGTH
ELASTIC SHORTNING , LONG TERM CREEP
-1/8”PER 20’ 200’ = 10/8” OR 5/8’ EACH END
EXCESSIVE SLAB LENGTH
ELASTIC SHORTNING , LONG TERM CREEP
-1/8”PER 20’ 200’ = 10/8” OR 5/8’ EACH END
EXCESSIVE SLAB LENGTH
ELASTIC SHORTNING , LONG TERM CREEP
-1/8”PER 20’ 200’ = 10/8” OR 5/8’ EACH END
IMPROPER STRESSING
INDEPENDENT INSPECTION & REVIEW
IMPROPER STRESSING
INDEPENDENT INSPECTION & REVIEW
POOR SITE DRAINAGE
POOR MAINTENANCE
POOR SITE DRAINAGE
POOR MAINTENANCE
SUB GRADE DRAG
WEIGHT OF ½ OF THE SLAB “SLIDING” OVER THE SUBGRADE
SINGLE SLAB
EDGES MOVE TOWARD THE CENTER
SLAB MIDDLE IS POINT OF FIXITY
SUB-GRADE DRAG OF MULTIPLE POURS
ENTIRE WEIGHT OF 2nd SLAB “SLIDING” OVER THE SUBGRADE
2nd SLAB IS CAST
NEW SLABS ARE TO BE MOVE TOWARD THE PREVIOUS CAST SLAB
EDGE IS POINT OF FIXITY
MULTIPLE POURS TO BUILD A SINGLE COURT
SLABS UP TO 300’ ARE OFTEN DESIRED THE CORRECT SUBGRADE DRAG MUST BE USED
PROVIDED SHORTING IS ACCOUNTED FOR
CONCRETE OVERLAY EDGE
COMPRESSABLE MATERIAL
EXISTING CONCRETE SLAB
