3.1.4.6 PACT system
The PACT slab track system was developed in Britain and first constructed in 1969 at Radcliffe for testing purposes (Round8). It is consisted of a continuous paved unreinforced concrete layer on which a paved, profiled continuous reinforced track slab is based (Bastin31). The connection between these two layers is achieved by shear links in the reinforcement of the upper slab (Round8). This system has a 22.9 cm thick concrete slab that is 2.43 m wide (Canadian Pacific Railway) (Bilow,Gene & Randich9). After the curing of concrete is complete, holes are drilled (diamond-core) and the continuous welded rail is laid on a continuous rail pad and fixed to inserts embedded in the slab (Bilow,Gene & Randich9, Bastin31). Although it was designed for high speed lines, this has not happened. It has mainly used in tunnels (wet tunnels) because of its low construction height and low maintenance needs comparing to ballasted track. The maximum speed in a PACT system nowadays does not exceed the 150 km/h (Round8). Although this system was at the forefront of slab track development, the lack of any significant new construction in Britain did not allow for many further developments. The PACT system is outdated for the current standards and high speed train demands (Bastin31). The advantages of this system are the low construction costs and the high quality geometry. The disadvantages are, that requires special laying equipment, the out-dated construction method (bottom-up) combined with the continuous support of the rail make it harder to achieve the levels of accuracy required for high speed, as well as that the drainage is often hindered resulting to debris collection which lead to corrosion of the railway fastenings (Round8, Bastin31). The exact dimensions and structural features of the PACT system are schematically illustrated in figure 56.
Figure 56: PACT slab track system (* Depth D at real seat varies: typically 150-250 mm. Similarly depth of the base slab varies depending on site conditions: 300mm minimum) (Bastin31).