Rail mounted volumetric mixers have been used since the time of the original Daffin mixers.
It can be extremely difficult and cumbersome to mount a batch plant on a rail car. In many cases it is easier to the mixer to the site rather then making multiple trips back and forth to a batch plant. Transport time and ultimate concrete quality can be an issue as it is easier to produce it fresh at the pour site vs. having to spend time going back and forth to a central location. The two major areas where this application is need is in for the rail system it self and the remote tunnels where construction is being performed. Most often the tunnel work involves some type of shotcrete or gunite application.
Rail mounted volumetric mixers have been used since the time of the original Daffin mixers. While there are more parameters and specifications to there are several manufacturers who still have the technology and expertise to accommodate this specialty work.