These are relatively common in washable aprons and can be seen in many elevated suburban sections. It's a system called 'Rheda', named after a German town where it was first implemented.
It provides a lot of benefits compared to normal ballasted tracks, (like the advantage you pointed out), but is typically seen only in high speed rail due to it's higher cost of construction. Also, it requires a continuous concrete bed which, while durable and less maintenance intensive, is rather non-flexible and costly to modify.