For decades, riders on Raritan Valley Line trains passed a tall smokestack that read “Schering” just east of Union Station opposite the Kean University campus. The towering structure was just one part of a massive 25-building pharmaceutical campus that was used not only by Schering, but also by its successor companies: Schering-Plough and Merck. However, the days of drug research and manufacturing on these 60 acres are history. In recent months, the site has been filled with construction crews as work gets underway for the township’s largest mixed-use development project in years.