Post Tension Slabs(PT slabs) Part 2 POST TENSION INSTALLATION.

Hello every one,
After we all got an idea from the last two parts, 


Today we will explain how to install PT slab.

The components of PT system was mentioned in the above links.

1-Anchorage system. 

2-Strands. 

3-Duct.

4-Bar Chair.

Initially and before starting in PT slab all form work should be completed and checked by safety team and scaffolds team to make sure zero harms. SAFETY FIRST 

After receiving the materials at site and checking the materials to be matched with the project specs then the workers can start preparing for the work like cutting the strands at the required length if they will use manual strand pushing and preparing the anchors with recess even it's made from polystyrene or rubber.

Slab edge to be marked by the surveyor and slab edge to be fixed prior to start duct installation.

POST TENSION SLAB INSTALLATION.

Step 1:- marking f anchor location on the side shutter and make holes at required anchor height which will be mentioned in design drawings.

Step 2:- marking of tendon locations on the shutter to be by the PT supervisor and prior to any RFT, Post Tension tendons to be marked at the mentioned locations as per the design approved drawings and showing the dead and live ends locations, the first line to be taken from fixed point like shear wall or the slab edge which is marked earlier by the surveyor. 

that is the marking on top of the shutter and before any RFT installation.

that is the main reason of slab marking, it's reflecting the tendons location in the slab soffit to avoid drilling in tendons locations.

after slab marking completion the slab to be handed over to steel fixer to start fixing the bottom bars.

Step 3:- tendon laying to be at the marked locations as per the design.

Step 4:- strand pushing in the ducts, that can be manual or using strand pushers depending on the tendon length, if the tendon length is less than 25 meter it can be pushed manually but if it is more than 25 meter it's better to use strand pusher to reduce the number of workers and time.

Step 5:- profiling, here i mean by profiling is to make the PT tendon profile as required by design by using bar chairs in the marked locations as shown in the below figure.

 

Step 6:- fixing the grouting pipes in the grout vents in PT anchors and at the end of each tendon then in the middle if required.

 in case of tendon length more than 25 meter intermediate grout pipe to be fixed as shown in the below figure.

Step 7:- slab concreting, in case of PT slab the supervision team must care about the grouting pipes during concreting to avoid any blocking of it. Also duct connections must be secured to avoid any concrete mix to go throw the duct.

Step 8:- after concreting and opining of the side shutter PT team will start to remove the recess and prepare for stressing process by fixing the anchor block and wedges.

Step 9:- slab stressing, it's the most important and dangerous part in PT slabs. after the concrete getting the required strength then the final force can applied to the strands which is equal 0.08 of breaking load of the strands (depends on strand diameter) 

 - PT team to insert the stressing jack firmly onto the strand and start applying the force gradually and to be monitored by the gauge.

then repeat the same for all strands in the tendon.

In case of double life end stressing (in tendon more than 33 meters)

the worker should apply only 30% of final load at the first side then apply the full load(100% of final load) on the other side.

 - Measuring of strands elongation for all strands and compare it with the theoretical elongation (to be given by designer), the tolerance is  ±7% as per ACI code.

Step10:- cutting the excess strands using a disc cutter and fill the anchor recesses using concrete patching material.

Step 11:- grouting of PT tendons by filling the tendons by grouting flow able material throw the grouting pipes using high pressure pumps to ensure filling all tendons, the grout to be injected from throw the pipe to come from the other side then lock off the pipes.
at minimum three days later PT team can cut the grout tubes at the slab surface.

Now the post tension team can handover the slab to the Clint.