2.7　Concrete Slab Construction Operation

2.7.1　Prestressed reinforcement preparation

Prestressed reinforcement shall be cut to length mechanically，instead of being cut by welders.For the prestressed reinforcement used for every pedestal，its length deviation shall be controlled within two over ten thousand.

2.7.2　Rebar grouping and embedded parts installation

1.Rebar shall be processed in normal temperature，the size shall be checked as per design drawings，the cut shall be parallel and level，both ends shall be without bending，and the blanking length shall comply with design requirement（Table 5）.

2.The upper and lower reinforcement grid shall be weaved on special formwork，both longitudinal and transverse reinforcement shall be insulation treated according to design requirement，with resistance value no less than 2 MΩ among reinforcement.

3.The insulation hear shrinkable pipe shall be installed on the special formwork，the hose spacing shall comply with design requirement，and allowable deviation shall be ±5mm.

4.When the reinforcement group is installed into the formwork，the seven layers of reinforcement（except theprestressed reinforcement of diameter 10mm and fine rolled deformed bar of diameter 20mm）shall be insulation treated，the resistance value shall be no less than 2 MΩ among reinforcement.

5.The position of reinforcement in formwork shall comply with design requirement（Table 6）.

6.All the embedded parts in track slab shall be correctly positioned according to the position and spacing requirement of design drawings，and shall be firmly installed，to ensure the concrete not to displace in vibration forming.

2.7.3　Prestressing force application

1.Before every tension，the anchor cylinder and anchor blade of the anchorage device shall be inspected and cleaned up.

2.Prestressed reinforcement adopts integral tensioning style.The tension is divided into two stages，the initial tensioning shall reach 20％ of the design value，the middle baffle shall be installed and locked on the model；final tensioning shall reach the design value，once tensioning is completed，the adjustable ring shall be applied to lock the hydraulic cylinder and to release pressure.

3.The prestressing force adopts double control，which is subject to the tension reader，and the elongation value of prestressed reinforcement shall be used for verification.The deviation of actual tensioning force and elongation with the design value shall not be more than 5％，and the deviation of actual tensioning force of single piece of prestressed reinforcement with the design value shall not be more than 15％.

4.The tensioning record shall be completely and correctly filled out.

5.In tensioning process，the deviation for piston elongation at the same end of the jack shall not be more than 2mm，and the deviation for piston elongation at the other end of the jack shall not be more than 4mm.

6.The tensioning equipment shall be calibrated integrally，and the tensioning force of single piece of reinforcement shall be tested periodically.

2.7.4　Concrete batching and pouring

1.The high efficiency slushing agent and the mineral admixtures which can improve concrete performance shall be used as concrete material，the total cementing material in concrete should not be more than 480 kg/m3，and water consumption shall not be more than 150 kg/m3.

2.The raw material of concrete shall be weighed in accordance with working mix proportion，the material measurement shall comply with the requirement ofGuide for Construction Technology of Railway Concrete Engineering（Tiejianshe [2010]No.241）.

3.The position and spacing of reinforcement and embedded parts shall be confirmed before concrete pouring，meanwhile，the 500 V mega meter shall be used to confirm the insulation performance of the reinforcement framework，the resistance value of different layers of reinforcement shall be no less than 2 MΩ.

4.Before concrete pouring，the position of grounding reinforcement and grounding terminal as well as the welding quality shall comply with design requirement.

5.Track slab concrete shall be of good compactibility，the reinforcement and embedded parts shall be ensured in correct position during concrete pouring，and the pouring time for every single piece of track slab should not be more than 20min.

6.The formwork temperature shall be within 10～30℃for track slab concrete pouring；when the formwork temperature is too low or too high，the corresponding heating measures or cooling measures shall be taken.

7.The temperature of concrete mixture for track slab shall be controlled within 5～30℃when being put into the formwork.

8.The position and quantity of heightened embedded parts which are pressed into concrete shall meet design requirement，the allowable deviation for position shall be（0，-3）mm.

9.After the completion of pouring forming for every single track slab（4 h），under the premise that the edge and corners of embedded parts are complete and slab doesn’t crack，the wire partition of middle baffle between the formworks shall be taken out from the concrete.

10.After the completion of pouring forming for every single track slab（0.5 h）and before preliminary solidification，the concrete surface of track slab shall be brushing finished，the brushing depth shall be 1～2mm.

11.The durability test shall be carried out before trial production on freezing resistance test piece and electric flux test pieces，which are fabricated one each for selected cement，aggregate，mineral admixture and additive.

12.Periodical inspection：during concrete pouring forming process for the last track slab of every production line，the concrete shall be sampled and 3 groups of test pieces shall be fabricated for compressive strength test about concrete demolding and day 28 compressive strength test.Every half a month，1 group of test pieces shall be fabricated for day 28 concrete elasticity modulus test.The test pieces for compressive strength test shall be curing simultaneously，and the test pieces of day 28 shall be standard curing.

2.7.5　Concrete curing

The temperature keeping curing system shall be adopted for concrete curing，the concrete shall be covered curing immediately upon completion of pouring forming；during curing period，the highest temperature of track slab concrete core shall not exceed 55℃.

2.7.6　Prestressed reinforcement tensioning，track slab formwork removal and delaying curing

1.Inprestressed reinforcement tensioning，the compressive strength of concrete shall not be less than 80％ of design strength，and shall not be lower than 48 MPa.

2.The prestressed reinforcement shall adopt integral tensioning style，and 4 jacks shall function synchronously in tensioning process.

3.Once the prestressed reinforcement tensioning is completed，the prestressed reinforcement in the formwork at 1/2 tensioning pedestal shall be cut off，then the prestressed reinforcement in the formwork at 1/4 and 3/4 tensioning pedestal shall be cut off，and finally all the other prestressed reinforcement in the formwork shall be cut off.The prestressed reinforcement with stress shall not be cut off at any position.

4.The vacuum lifting device shall be applied for track slab formwork removal，after confirmation that all the fastening devices are removed from the components and the formwork，the track slab shall be slowly hoisted to avoid impact on the track slab.

5.The track slab shall be delaying curing on the special bracket in the workshop after being removed.The delaying curing shall last 24 h，on every bracket 3 layers of track slabs shall be placed with 4 cushion blocks for each layer.The allowable deviation for the height of cushion block is ±2mm，the bearing surface shall be parallel，and the error shall be controlled within 2mm.The track slab shall be covered in delaying curing.

6.In track slab formwork removal，the temperature difference between track slab surface with the ambient temperature shall be not over 20℃.The track slab shall be covered immediately upon being removed.The covering shall be removed when the temperature difference between track slab surface with the ambient temperature shall be not over 15℃，and the track slab shall be transported outside for storage.

2.7.7　Semi-finished slab（semi-manufactured slab）storage

1.The storage time for semi-finished slab should not be less than 1month.

2.Every stack of semi-finished slab shall not be more than 12 layers，cushion blocks shall be placed between the slab and the storing foundation as well as layers，and the cushion blocks shall be vertically aligned.

3.The storing foundation for semi-finished slab shall be solid and flat，and the storing foundation shall be periodically inspected.

2.7.8　Track slab polishing

1.The automatic measuring system of the grinding machine will test the original parameters of the rail bearing platform for the semi-finished slabs，which shall be compared with the design parameters of the finished slabs，by this way the polishing amount will be calculated finally.

2.The automatic controlling system of the grinding machine will polish the rail bearing platform according to design requirement，and the polishing times will be determined based on the precision parameters for the semi-finished slabs and the parameters of 20 rail bearing platforms.

3.The automatic measuring system of the grinding machine will inspect the finished slabs after polishing individually，and form inspection record.

2.7.9　Track slab measurement

By measurement for track slab，the deformation of the formwork for track slab as well as the working accuracy of CNC grinding machine can be monitored and grasped.The formwork and the grinding machine shall be repaired and maintained if necessary.

1.In normal production process，the semi-finished slabs produced by every set of formwork shall be measured by the total station once a month.

2.In normal polishing process，one piece of finished track slab shall be measured by the total station every week.

3.When the measuring data of the grinding machine has some problems or measuring errors occur，the total station shall be used to measure once again.

2.7.10　Preinstallation of fastners

1.The fastners shall be preinstalled in yard after track slabs are polished.

2.Before the preinstallation of fastners，the water absorbing machine shall be used to suck out the water inside the embedded sleeves.

3.The quantitative grease filling unit shall be applied to fill the grease into the embedded plastic sleeves.

4.The electric torque wrench shall be applied to installfastners，the specific installation requirement shall comply with related provisions.

2.7.11　Insulation detection

The track slab shall be insulation detected upon fastners being installed.The detecting device shall be intelligent bridge tester.

The detection contents include electrical resistance and electrical inductance.When Rdetection≤16.5MΩ，12.75μH≤Ldetection≤13.75μH，the insulation performance of the track slab is qualified.

2.7.12　Finished track slab storage

1.In finished slab storage area，every 9 pieces of track slabs，as 1 stack，shall be placed on the pedestal with 3 points forming the same surface.The ground bearing capacity must be taken into account for the pedestal design，the foundation shall be enlarged，or backfilling and punning measures shall be taken if necessary.

2.Four cushion blocks shall be placed between two layers of track slabs as well as between slabs and the pedestal，the cushion blocks shall be respectively placed at the second pre-splitting crack and the eighth pre-splitting crack，and the cushion blocks shall be vertically aligned，to prevent the track slabs from twist deformation.

3.The cushion block specification is 200mm×200mm×150mm，height error is ±2mm，the bearing surface shall be of the same plane，and the plane error shall be controlled within 2mm.

4.In track slab storage period，the finished track slab shall be inspected anytime and once a week，mainly for deformation of cushion block and concrete pedestal，or any breakage of track slab outline，the problems shall be settled immediately once being detected.