2.6 Key Points of Critical Processes
The fabrication of track slab adopts complete mechanized equipment，the CNC grinding machine in particular is the full automation equipment which integrates electricity，gas，hydraulic pressure，measurement，computation，input and output.
The key（tooling）equipment required for track slab fabrication mainly refers to track slab fabrication formwork，tension equipment，batching plant，feeding equipment and polishing equipment，and the corresponding processes are critical processes like track slab formwork process，track slab tension process，concrete pouring process，track slab polishing process.
2.6.1 Key points of Ⅱ type track slab formwork operation
1.The damping rubber blanket shall remain necessary elasticity under the bracket of track slab formwork，to ensure the track slab can restore after tension releasing when the overall formwork displaces laterally inprestress cutting，and no partial deformation.
2.The wire baffle on track slab formwork is an integral part of the lateral formwork，the position of prestressed rebar is controlled by tension cross beam，due to the installation deviation of the formwork and the tension cross beam，there is certain deformation in construction process.Therefore，the notch of prestressed rebar for the wire baffle shall be adjusted in construction.
3.For the frame design on track slab formwork to install rail bearing groove，the flatness of its reverse side shall reach 0.15mm.The right side shall also reach such requirement in installation，the flatness of 20 rail bearing grooves for one track slab formwork inspected during construction process shall reach 0.3mm，by which whether partial deformation occurs can be judged.
4.The taper of locating pin for rail bearing groove shall match that of locating hole on the formwork，which can ensure the straightness accuracy of the rail bearing groove in case of correct position for locating hole.
5.The position precision of sleeve dowel pin determines the relative position state of the fastners for finished slab，the perpendicularity and straightness accuracy of the sleeve shall be ensured in operation.Meanwhile，the installed sleeve shall be prevented from floating upward and with not bigger resistance to affect the outline of the rail bearing groove in formwork removal operation.Regular formwork testing and inspection becomes quite important，in daily inspection，the roller flower at end of dowel pin shall be valid，and shall not be rotated after installation of plastic sleeves.
6.In formwork installation and usage，the gap，perpendicularity of lateral formwork，dowel pin（sleeve fastener）shall be timely inspected and repaired where cracks possibly occur.
2.6.2 Track slab tension
1.Tension procedure
The total designed tensioning force of the track slab is 4367 kN，the corresponding tensioning force for every oil cylinder is 2183.5 kN，the integral tensioning style shall be adopted and shall be performed simultaneously at both ends of the pedestal，i.e.to push outward with the tension beam installed at both ends of the pedestal to achieve tension purpose.Two 300t jacks shall be mounted at both ends of one tension beam，the four jacks will function simultaneously，the hydraulic pump station providing power shall be connected with computers which can display the piston displacement，tensioning force value of every jack，therefore，both the tensioning force and elongation can be controlled and managed.
2.Total design tensioning force and elongation value calculation for prestressed rebar
1）Total design tensioning force：according to track slab drawing，the tensioning force of single 10mm prestressed rebar shall be 68.3 kN，in view of stress loss for prestressed rebar caused by time and heat treatment，the prestress shall increase 4％.The total design tensioning force shall be calculated as follows：
The tensioning force of 60 pieces of 10mm prestressed rebar：68.3×104％×60=4260（kN）
The tensioning force of 6 pieces of 5mm prestressed rebar：68.3×25÷100×104％×6=107（kN）
Total design tensioning force：4260+107=4367（kN）
2）Total elongation value：the elongation is related to the cross section，elasticity modulus and effective length of the steel wire.The total elongation value shall be calculated as follows：
Net elongation value：68.3×104％÷205÷78.5×73860=326（mm）
Compensation elongation value：80（mm）
Total elongation value：326+80=406（mm）
3.Tensioning system inspection
The tensioning equipment is integrally calibrated，its validity shall not be more than one year，and the tensioning force of every single rebar shall be periodically inspected（10 batches for single line）.
2.6.3 Concrete pouring
Owing to the requirement of track slab manufacturing technology，the concrete pouring for single line shall be completed within 3 h，and the concrete strength shall reach 48 MPa within 16 h.Therefore，the early strengthening water reducing agent shall be used，and the concrete workability，liquidity and air content shall be controlled.
Prior to concrete brushing finish，the bottom surface of track slab shall be flat brushed manually；the remaining air bubble shall be eliminated.When concrete is not sticky，the concrete brushing finish shall be completed appropriately.
The pouring speed shall be controlled in concrete pouring，to prevent air from being pressed into concrete；vibration time shall be determined by site technicians，to ensure the air bubble inside the concrete can be vibrated to concrete surface and eliminated.
In concrete forming process，the solid rubber end seal and steel formwork shall be applied cooperatively，which shall be inspected periodically to ensure their proper functioning.
2.6.4 Track slab polishing
Track slab doesn’t require manpower intervention，but the operators shall be preferably assigned to monitor the movement precision.Because the polishing amount measured by the CNC grinding machine may be bit larger owing to improper positioning of the track slab，the track slab with little polishing amount reserved may become unqualified semi-manufactured slab.
The conversion of polishing data is very critical in polishing process，the line data shall be connected with grinding machine system，the grinding machine will generate theoretical data based on line data，which will be compared with actually tested data，and finally the polishing amount will be calculated.
The measured data of the grinding machine in repairing and commissioning shall be constantly compared with the inspection data of the polished track slab，to ensure the inspection data of the grinding machine is qualified.