Post-tension concrete is a method of reinforcing concrete. This concrete has cable conduits cast into it and that cable is stretched, or tensioned, hydraulically after the concrete has hardened. The tension is transferred to the concrete, helping hold it together even better. Post-tensioning provides high strength and stability, but looks just like any other concrete slab.

In collaboration with PCC Post Tension Thailand, Synesis has developed and introduced the bonded post tension slab to clients in the Lao PDR since 2011. Synesis team has wide experience in the application of bonded post-tensioning systems, and was one of the pioneers in the introduction of post tensioning in the Lao PDR. We have given technical advice to lots of consultants regarding post tensioning suitable standards and designs, with a large design and installation team, we are able to complete a full range of design and installation solutions.

Bonded post-tensioned concrete is a method of applying compression after pouring concrete and during the curing process. The concrete is cast around a plastic/steel/aluminum circular/flat duct. A group of tendons/wires/cables are fished through the duct circular/flat and the concrete is poured, Once the concrete has hardened, the tendons are tensioned by hydraulic jacks that react (push) against the concrete member itself. When the tendons have stressed sufficiently, according to the design specifications, they are wedged in position and maintain tension after the jacks is removed; transferring pressure to the concrete, then duct is grouted to protect the tendons from corrosion.


•   Minimum compressive strength of concrete at time of stressing shall not be been than 240 ksc. and age shall not be less than 3 days

•   Jacking force = 75% of ultimate strength ( = 14.07 ton ) but not more than 80% in case of increasing jacking force for restressing process

•   Two sets of stressing equipment are used to stress simultaneously at both ends of tendon, if length of the tendon exceed 30 meteres otherwise only one end is stressing ( the other end is dead end )

•   Elongation of tendon in each floor and the designed values ( elongation ) will be submitted after stressing. The different of overage actual elongation and designed values panel by panel should not be exceeded ± 5% ( ACI 318-99 clause 18.18.1 or EIT 1009 – 34 clause 8.5.1 )

•   Total loss of prestress due to unreplaced broken tendons shall not exceed 2% of total prestress. ( ACI 318-99 clause 18.18.4 or EIT 1009 – 34 clause 8.5.4 )

•   PC. Strand shall be cut by an abrasive disc after the stressing process has been completed and the elongation results have been approved by the Owner Authorized Representative

Architectural aspect

•   Space can be easily allocated for the service purpose. Wall or walls are not required to be on a flat surface, it will not obstruct pipeline system or work system.

•   Reduce the height between the floor and the total height of the building , making the height of the building not exceed legal requirement.

•   Can design buildings with longer interval between each pillar, making the space inside the building spacious and beautiful.

•   Can adjust your utility space interior living space for any occasion.

Structural aspect

•   Post-Tensioned Flat Slab system provides flat and thin floor. The overall weight is less than reinforced concrete floor. As a result, it is possible to reduce the construction cost of foundation work, save the structural wood and construction overhead.

•   Can be designed to have less deflection of the floor, compared to reinforced concrete Flat Slab.

•   Fire resistance is taken into account in the designing of Post-Tensioned Flat Slab by selecting number of hours which will resist to fire , according to the instruction of Post Tensioning Institute (PTI).

•   Can better withstand earthquakes, resistant to cracking, the structure is tough.

Valuable aspect

•   Construction cost per square meter is cheaper than reinforced concrete floor. For areas with a long pillar interval over 6 meters and large building.

•   Save construction time. Construction period takes 7-10 days for one floor.

•   More number of floor at the same height, extending more utility space , can support general force and earthquake less than that of the same number of floor.

Valuable aspect

Step 1: Erect the formwork for post-tension slab.

Step 1: Erect the formwork for post-tension slab.

Step 2: Place the bottom reinforcing steel as in the construction drawing.

Step 3: Lay the tendon and set the profile as show in the shop drawing and install the anchorage.

Step 4: Place the top reinforcing steel as in the construction drawing.

Step 5: Cast concrete slab.

Step 6: Stressing when the concrete compressive strength is more than 240 ksc (cylinder test).

Step 7: Props and formworks can be removed after stressing is completed.

Step 8: Grouting with cement paste.

PTS Installation VDO