Modern pumps are able to cope with most concrete mixes but difficulties can be experienced with concretes made from aggregates that are poorly graded, elongated or flaky. Pumping for large distances horizontally or vertically can lead to high pump pressures and the need for improved lubrication within the lines. Adding a polymer-based pumping aid can modify the cement paste rheology to help provide this enhanced lubrication. Pumping aids can also provide better workability retention for long pumping distances and can be particularly effective if interruptions to pumping are likely and when segregation or stiffening in the line could prevent a restart.
Pumping lightweight aggregate concretes presents problems, particularly if the aggregates are not pre-soaked and fully saturated. The pump pressure drives water into the aggregate, causing the mix to ´dry out´ and block lines. Specifically designed pumping aids can assist by reducing the amount of water that gets absorbed and allowing drier aggregate to be used.