tennis court post-tension concrete slab do's & don'ts

Sunday, December 7th, 2014

1:30 pm to 2:30 pm

Harley Nethken PE PTlf: harley@acadianss.com

Jonnie Deremo: jderemo@generalacrylic.com

Richard Zaino: richard@zainotennis.com

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