- Mixes that are regularly used in a market area will be the most economical. Consult the lightweight aggregate suppliers for detailed mix design information and material capabilities (i.e., unit weight, strength, etc.).
- Specify 4 to 7 percent air entrainment for pumpability, workability, finishability, and durability.
- Specify the maximum size aggregate rather than specifying individual sizes.
- Allow a higher slump into the pump to accommodate the possible slump loss.
- Have the testing lab run design curves based on the maximum specified slump and air per ACI 301.
- Specify a pre-pump meeting with the following present: engineer, architect, project manager, contractor, ready-mix supplier, lightweight aggregate supplier, testing agency, admixture supplier, and pumping subcontractor.
- On large jobs, these same people that atttended the pre-pump meeting should be present at the first concrete pump placement.
- Specify where concrete should be tested, preferably at the end of the discharge line as per ACI 304.2R.
- Realize that absorbed water does not affect water/cementations materials ratio, as defined in ASTM C125.
- Keep everyone communicating; this is a team effort!
- Use an experienced pumping subcontractor.
- Make arrangements for two ready-mix trucks to unload simultaneously.
- Designate a laborer to help the testing lab inspector.
- Provide a washout area for ready-mix trucks.
- Make use of the ready-mix truck radio when placement delays occur.
- Specify to the ready-mix supplier the number of yards needed per hour, not how many truckloads.
- Check that the pump line has been properly lubricated before placing the concrete.
- Know the required unit weight of the concrete being pumped.
- Order concrete to coincide with actual pumping time, not when the pump arrives at the job site.
- Maintain continuous placement.
- Operator should know the maximum slump allowed.
- Clean steel pump lines with a 5″ minimum diameter should be used; minimize the use of rubber hose at the end of pump lines and avoid reducers if possible.
- Keep the same pump and operator throughout the duration of the job.
- Use a pump whose piston size is as close as possible to the line size to maintain the best performance and minimize slump loss.
- It is necessary to properly lubricate the pump line before placing the concrete.
Ready Mix Producers
- The lightweight aggregate must be prewetted prior to batching using procedures recommended by the lightweight aggregate supplier.
- Check with the lightweight aggregate supplier for a recommended concrete mix design and field correction procedures for pumped concrete.
- The aggregate moisture content and/or unit weight should be checked at regular intervals through the day’s placement. This is necessary for concrete yield control.
- Make drivers aware of admixtures being used for slump control.
- Maintain a minimum of 3″ slump before the addition of high-range water reducing admixture.
- The field inspector shall be ACI Field Technician Grade 1 (or equivalent), per ASTM C94.
- Make sure the inspector has properly calibrated tools including a rolla-meter for volumetric air tests and a proper strike-off plate for unit weight determination.
- On large jobs use the same inspector for all concrete placements.
- The inspector should know fresh unit weight limitations (min & max).
- Place test cylinders immediately upon casting in a curing box protected from vibration per ASTM C31.