Question: We know that structural lightweight concrete mixes for pumping should be proportioned with pumping in mind. But assuming we have obtained a good mix design, shouldn't we be concerned about the choice of pump and pipelines?

Answer: ACI Committee 213 makes recommendations on this subject also. They say:

  • Use the largest size pipeline available, preferably at least 5 inches
  • Be sure all lines are the same size, are clean and are buttered with grout
  • Make the size reduction from the pump to the line gradual. For example, don't go from a 10-inch diameter to a 4-inch diameter in 4 feet. Instead, reduce from 10 inches to 6 inches in 8 feet, then from 6 inches to 4 inches in 4 feet.
  • Keep operating pressure low by using a slow rate of placement, as much steel line and as little rubber line as possible, as few bends as possible and by making sure all lines are gasketed and tightly joined

The committee also suggests a field trial attended by representatives of the contractor, concrete producer, architect and engineer, pumping service, testing agency and aggregate supplier so that all the best advice and consultation is available.