STANDING 23 metres above the ground, Anantha Guru, the site inspector at an under-construction viaduct of the Mumbai-Ahmedabad High Speed Corridor in Vaktana village near Surat, discusses a “mystery” with a group of engineers. The material that lies sandwiched between the track bed and the track slabs that hold the rails has a “secret ingredient” that allows trains to run at blinding speeds of 320 km per hour. Only the Japanese know what it is, they say. Guru walks towards the Cement Asphalt Mortar (CAM) injection car, a machine brought from Japan that’s being used for the first time on Indian soil. Its task is precise. Before the rails can be laid on the track slab, it creates a 40-100 mm cushioning layer of mortar that absorbs the vibrations generated when trains run at such high speeds. “With this machine, we inject CAM, a mixture of nine ingredients such as cement, asphalt, polymer emulsion, sand, water, and other materials.…