Abstract: A trailer for use on standard highway systems and having a hopper with a central conveyor belt system forming the floor and two independent, non-linear sides is disclosed for transporting particulate materials such as asphalt, gravel, or low-slump concrete and delivering such materials in a controlled manner to the point of use. The sides of the hopper are formed as segments having a conic section geometry, i.e. circle, ellipse, hyperbola, or parabola. Such hopper sides have different tangential angles for all points on the surface and different rates of change of said angles per unit distance along the side, depending upon the conic segment selected. This design has the novel and unexpected result of producing a vortexing, or mixing, effect on the particulate material, both when it is loaded into the hopper and during transport.