Pumpability of Concrete

Pumpability of Concrete

The pumpability of concrete depends basically on the composition of the mix, the aggregates used and the method of delivery.

As far as the delivery and installation of pumped concrete is concerned, a significant reduction in the pump pressures and an increase in the output can be obtained by the systematic addition of pumping agents, particularly for use with crushed aggregates, secondary raw materials, highly absorbent aggregates etc.

Pumped concrete is used for many different requirements and applications nowadays. A suitable concrete mix design is essential so that the concrete can be pumped without segregation and blocking of the lines.

Composition

·     Aggregate

Max. particle < 1/3 of pipe bore

The fine mortar in the pumped mix must have good cohesion to prevent the concrete segregating during pumping.

·     Cement

Max. particle		Round aggregate		Crushed aggregate
8 mm		380 kg/m³		420 kg/m
16 mm		330 kg/m³		360 kg/m³
32 mm		300 kg/m³		330 kg/m³

·     Water/binder ratio

If the water content is too high, segregation and bleeding occurs during pumping and this can lead to blockages. The water content should always be reduced by using superplasticizers.

·     Workability

The fresh concrete should have a soft consistence with good internal cohesion. Ideally the pumped concrete consistence should be determined by the degree of compatibility.

·     Pumping agents

Difficult aggregates, variable raw materials, long delivery distances or high volume installation rates require a pumping agent. This reduces friction and resistance in the pipe, reduces the wear on the pump and the pipes and increases the volume output.

·     Pump lines

-  80 to 200 mm (normally  100, 125 mm)

- The smaller the, the more complex the pumping (surface/cross-section)

- The couplings must fit tightly to prevent loss of pressure and fines

- The first few metres should be as horizontal as possible and without bends. (This is particularly important ahead of risers.)

- Protect the lines from very strong sunlight in summer

·     Lubricant mixes

The lubricant mix is intended to coat the internal walls of the pipe with a high-fines layer to allow easy pumping from the start.

Conventional mix: Mortar 0–4 mm, cement content as for the following concrete quality or slightly higher. Quantity dependent on andline length

·     Effect of air content on pumped concrete

Freeze/thaw resistant concrete containing micropores can be pumped if the air content remains < 5%, as increased resilience can be generated with a higher air content.