Lubricating suspension for pumping concrete

In a method comprising pumping concrete or mortar through a concrete or mortar pumping system, introducing a lubricating phase into the pumping system prior to the introduction of, or downstream relative to the front edge flow boundry, of said concrete or mortar, wherein said lubricating phase comprises an aqueous suspension of (i) at least one water-dispersed polymer, and (ii) an amorphous silicon dioxide material, and wherein after introduction said lubricating phase is effective for providing a suspension of liquids and solids in the pumping system with a segregation pressure greater than the pressure required to pass the suspension through the pumping system.