From this short description, what you say may have been (1) parallel tracks for suburban trains, (2) repair of a short section (say after an accident), (3) real 200 km/h track replacement, in which case I guess there'll be at least an inspection run followed by adjustments!?...

At any rate, the Beijing-Tianjin line is different: it is "FF Bögl" slab tracks supplied (again with technology transfer) by German firm MAX BÖGL (see their page, and photos of the track near Beijing in this pdf).

_{*Lunatic*, n.
One whose delusions are out of fashion.}