PUMPED CONCRETE

Guidance Notes

S A Reddi

Preamble

Pumped concrete does not require any additional cement whatsoever

Control of workability is the prime important

The slump should be in the range of 90 to 120mm. Individual slump measurements

may vary up to plus/minus 25mm as per the IS Codes. Thus while the average

slump should be between 90 and 120mm, odd individual values may go up to

155mm. The average should not exceed 120mm.

The desired slump shall be achieved not by increasing the water content but by

choosing proper quality of admixtures. The dosage of admixtures should normally

be by 1& but under no circumstances it should not exceed two percent (by weight of

cement).

Control of quality of sand is very vital. Sand conforming to any one of the four

Zones may be used for pumping concrete. However, no silt content should be

permitted. If the sand as received contains silt, the same should be washed

thoroughly.

Depending on the coarseness or fineness of the sand, the percentage of sand among

the aggregates should be adjusted suitably, based on trial mixes.

The coarse aggregates should be reasonably cubical or ferial in shape. Ferial

aggregates such as river shingle gives the best results for pumped concrete. Ferial

aggregates consume less sand and less water and wear and tear on the batching plant

is also less.

Before commencement of pumping, the dry pipelines should be primed (buttered)

using cement water mix. The amount of cement used for priming will depend on

the length of the pipeline. The manufacturers recommendations may be followed.

Schwing Recommendations :

- Lubricating mix is feed into charging hopper with the concrete pump

switched off and pushed into the pipeline immediately before the first

regular concrete mix is pumped. This activity should be done first before

starting the concrete pumping on any day and should be repeated whenever

there is an interruption in concreting.

- Minimum quantities of lubricating mixes for truck mounted pump with

30m pipelines, 100 Kg. of cement may be used.

- For stationery pumps with up to 200m length of pipeline, 500 Kg. of

cement should be used

- Lubricating mixes should be pumped into the formwork and not

discharged outside.

For details on Guidance on Pumping, please refer to the publication

"Pumping Concrete and Concrete Pumps" brought out by Schwing. Copies are

available complimentary from Schwing. Every site involved in pumping concrete

should have copy of this publication

Use of Fly-ash / Slag

For the pumping to be effected, certain minimum quantity of finer materials

(cement, fly-ash or slag plus fine fraction of sand passing through 300 microns is

required. The minimum quantity required is 450 Kg. per cum of concrete. Fly-ash /

slag is necessary to get continuous grade of fine materials including cement in the

concrete mix.

For example, the following composition of fine materials is O.K. :

Cement 250 Kg.

Fly-ash / slag 80 Kg.

Sand passing through 300 microns 120 Kg.

TOTAL 450 Kg

Minimum cement content for pumping concrete is same as minimum cement content

specified for normal concrete. The phrase "cement content" includes cement and

fly-ash / slag. In the above example, the minimum cement content works out to 250

Kg. + 80 Kg. equivalent to 330 Kg. This satisfies the IS Codes requirements for

structures (other than bridges). For bridges, the suggested values will be cement

300Kg., fly-ash 100 Kg. plus fine fraction of sand as available. This satisfies the

cementicious content requirements of 450 Kg.

The phrase "Minimum Cement Content" in the Codes and Specifications includes

cement + mineral admixtures such as fly-ash / slag, etc.

As per Note No.1 – Table 5 of IS:456-2000 pertaining to Minimum Cement Content,

the "Cement Content" prescribed in the Table is irrespective of Grade of Cement

and it is inclusive of additions mentioned in Clause 5.2. The following additions are

mentioned :

- 5.2.1 : Pozzolanas

- 5.2.1.1 : Fly – ash (pulverized fuel ash)

- 5.2.1.2 : Silica Fume

- 5.2.2 : Ground Granulated Blast Furnace Slag

Pipeline

The pipeline should be as far as possible be laid in one straight line without the use

of any bends. Use of bends will increase the friction and reduce the effectiveness of

pumping.

Pipeline should be laid either vertically or horizontally or a combination thereof.

Under no circumstances the pipelines should be laid at an angle elevation or plain.

Normally the pipeline diameter should be 125mm and this will admit concrete with

maximum coarse aggregate size of 40mm. If the maximum size is only 20mm

concrete pipeline, 100mm diameter is adequate. 100mm pipeline is lighter to handle

and much more efficient, but this will require vigorous control over maximum

aggregate size.

Cleaning of Pipeline

On completion of each pumping activity, the pipelines should be thoroughly cleaned

using the rubber balls and water under pressure, provided for the purpose. The ball

may be pushed using either high pressure water pump or compressed air.

Batching Plant Producing Pumped Concrete

The moisture content of sand should be scrupulously monitored. This is best done by

fixing moisture props at the sand inlet as a part of a batching plant equipment. This item

should be included while purchasing any batching plan…

Workability of Concrete for Pumping

The workability of concrete does not depend on the W/C ratio or the .water content in

concrete using superplasticizers. The workability depends upon the amount of cement

paste. The workability .of freshly mixed concrete continuously changes from the time it

leaves the mixer till the slump becomes zero.

In view of continuous reduction in workability from the time water is added to the mix in

the batching plant, it is necessary to limit the time permissible from the time of adding

water to the mixer till the time of pumping concrete. Thus should not normally exceed one

hour in winter and thirty minutes in summer. In the case of Ready Mixed Concrete, the

provisions of IS : 4926, Indian Standards Ready Mixed Concrete – Code of Practice shall

be followed. Any concrete made in a batching plant away from the site, either in the

Company’s own plant or by Ready Mixed Concrete supplier is treated as Ready Mixed

Concrete

As per Clause 5.2.2. of the Code, concrete shall be discharged from the truck mixer within

two hours of the time of loading which shall start from adding the mixing water to the dry

mix of cement and aggregate or of adding the cement to the wet aggregate whichever is

applicable

Aggregates

Any aggregate conforming to IS : 383 is suitable for pumped concrete. Both river gravel

and / or crushed stones may be used; however, river gravel is preferred as it consumes less

water and less cement. Sand conforming to any one of the four grading zones may be used

for pumped concrete

Fine Material Content

The fines content is composed of cement, mineral admixtures and the fraction of sand

passing through 300 microns. The recommended content of fines for a pumpable

concrete is minimum of 400 Kg. per cum for concrete using river gravel, In case of

crushed or flaky material this quantity has to be increased by ten percent (Pumping

Concrete and Concrete Pumps, published by Schwing). Fly ash or crusher dust are

suitable for the increase of fines content.

The maximum size of aggregate of 20 or 40mm does not affect the pumpability of

concrete. However, the maximum size of aggregate determines the diameter of the

pumping cylinder, and the size of the delivery pipeline. 125mm dia. pipeline is suitable for

concrete with maximum size of aggregate 40mm. Concrete with a maximum size

aggregate of 63mm requires the pipeline diameter of 150mm.

Cement Content of Pumpable Concrete

Ordinary Portland cement is more suitable than slag cement, because of better water

retaining properties. The minimum cement content for any mix given in the Contract

Specification is sufficient for pumping concrete . As per Schwing “Pumpable Concrete has

a minimum cement content of 240 Kg. per cum with a maximum aggregate size of 32mm.

It must be increased by 10% in case of a maximum size of aggregate of 16mm.

Concrete Admixtures for Pumped Concrete

Typically, the pumped concrete should have a slump of about 100mm at the pumping

point. Blockages / segregation of concrete may take places if the slump value is lower or

higher. In the case of higher slumps, segregation occurs frequently.

The superplasticizers should be carefully chosen for the slump retention capability.

Normally concrete should be pumped within thirty minutes of mixing. Any longer

interval will require superior quality of admixtures capable of higher slump retention,

involving extra expenditure.