1. Mix design

Cement content

The right cement must be used to ensure that the required properties are obtained. But for a maximum particle diameter of 32 mm, it should be at least 300 kg per m3 of concrete. For crushed aggregate, the cement content must be increased by about 10% due to the larger specific particle surface.

Note:  Good pumpability is not determined by the cement content alone but by the cement paste (cement + fines + water).

Fines content

The fines content < 0,125 mm with rounded gravel/sand material should be not less than 350 kg/m3 of concrete. If crushed aggregate is used or it is necessary to have recourse to secondary raw materials (such as from excavation or demolition material), the fines content should be increased by 25 to 50 kg/m3. Lack of fines should be offset not by increasing the sand content, but by correct use of concrete admixtures (e.g. SikaFume, fly ash, hydraulic lime etc.) or possibly by slightly increasing the cement content.On the basis of many years site experience, the following fines contents (diameter < 0,125 mm) are recommended for trouble-free pumping.

Lack of fines can be offset by the addition of Sika® Pump.

Particle-size distribution curve

A poor aggregate particle size distribution causes problems with pumping and placement of the concrete.The granulometry made up of the individual fractions (0-4mm; 4-8mm; 8-16mm; 6-32mm) should be in the range of the upper curve. A continuously developed particle-size distribution curve is more pumpable than a sieve curve deficient in certain particle sizes.It is recommended, however, that the 4-8 mm fraction be kept low and the 8-30 mm fraction increased.
Fluctuations in the particle-size distribution curve and resultant problems in pumping can be compensated for by Sika® Pump.

2. Fresh concrete

The fresh concrete should have a soft consistency and good internal cohesion should be guaranteed. Concrete with insufficient fines or too high a W/C ratio tend to blead, which can cause too high pump pressures and blockages.
The use of a superplasticizer of the sikament type reduces unnecessary excess water and the addition of the Sika® Pump pumping agent greatly improves the internal cohesion. For these cohesive concrete mixes. The fresh concrete consistency should be measured by a dynamic test method such as compacting factor “Walz”.

Note
Air-entrained concrete can only be produced in the “soft plastic” consistency range. Air entrainment is much more difficult in stiff plastic concrete (Walz value S < 1,20); flow concrete (Walz value S < 1,04) loses a large proportion of the entrained air under mechanical power (pumping, vibrating etc.). Standard air-entrained concrete (3-6% voids) with good internal cohesion, such as can be produced with Sika Fro-V5-A, can also be pumped over long distances without significant air-pore losses.

3. Low pump pressures

Compliance with the minimum requirements laid down in the standard, together with a good particle-size distribution curve and round aggregate, ensures that there is sufficient lubricating film (cemen, water and very fine sand) to give soft pumping at low pressures. If the particle grading is not good (broken aggregate, secondary raw materials, highly absorbent aggregates etc.) it is essential to increase film and improve the flowability.
Corrections in the mix design (see section 1) and the use of Sika® Pump pumping agent enable the friction drag on the pipe walls to be reduced, which results in lower pump pressures combined with a higher pumping output.

4. Equipment wear

When starting up the concrete pump, a mortar mix with a high content of fines should be pumped, as this draws a fine lubricating film along the dry pipe surface (lubricating mix).By reducing the friction drag on the pipe walls and improving the flowability of the concrete, the required pumping pressure in decreased and the hydraulics and mechanics of the pump are spared.
By adding Sika®Pump, discontinuous, jerky pumping is prevented, which greatly reduces the wear on the pump and piping. The life of the pumping  equipments is extended and its breakdown times are kept to a minimum.