Construction and Building Materials 61 (2014) 18–23

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Construction and Building Materials

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Effects of an externally imposed electromagnetic field on the formationof a lubrication layer in concrete pumping

http://dx.doi.org/10.1016/j.conbuildmat.2014.02.0710950-0618/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author. Tel.: +82 31 330 6418; fax: +82 31 336 9705.E-mail address: kwon08@mju.ac.kr (S.H. Kwon).

Myoung Sung Choi a,b, Yu Seung Kim c, Jae Hong Kim d, Jeong-Su Kim e, Seung Hee Kwon f,⇑a Civil Engineering Research Team, Daewoo Institute of Construction Technology, Suwon 440-210, South Koreab Dept. of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-701, South Koreac Korea Testing and Measurement Group, Seoul 137-855, South Koread School of Urban and Environmental Engineering, Ulsan National Institute of Science and Technology, Ulsan 689-798, South Koreae Hanwha Research Institute of Technology, Hanwha E&C, Daejeon 305-804, South Koreaf Dept. of Civil and Environmental Engineering, Myongji University, Yongin 449-728, South Korea

h i g h l i g h t s

� It needs to improve efficiency of concrete pumping in a large scale construction.� The externally imposed electromagnetic field enhances the pumpability of concrete.� The properties of the lubrication layer are changed by the electromagnetic field.

a r t i c l e i n f o

Article history:Received 13 December 2013Received in revised form 20 February 2014Accepted 26 February 2014Available online 21 March 2014

Keywords:PumpabilityLubrication layerElectromagnetic fieldConcrete

a b s t r a c t

During concrete pumping, a lubrication layer is formed at the interface between the concrete and thepipe. The pumpability highly depends on the characteristics of this layer. In this study, a method toenhance the pumpability by externally imposing an electromagnetic field on the pipe was suggestedand experimentally verified. The electromagnetic field activates the free movement of the water mole-cules so that the layer is expected to become more slippery. Pumping tests with a 1000 m long pipelinewere conducted with and without applying an electromagnetic field. When the electromagnetic field wasimposed, the same discharge rate could be obtained with a 30% reduction in the pump pressure, and a15% increase in the velocity under the same pump pressure was observed. The tests revealed that theimposition of an electromagnetic field was very effective in improving the pumpability.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Since concrete pumping was first introduced in the 1930s, it hasbecome a commonly used technique to transport fresh concrete forplacing in construction sites. Concrete pumping offers notableadvantages such as allowing casting in difficult to access locations,reducing casting durations, and allowing continuous concrete cast-ing. However, in the construction of large scale structures such ashigh-rise buildings, super long bridges, and long-distance tunnels,it is still challenging to transport concrete by pumping because ofthe limited capacity of existing pumps and inadequate technolog-ical solutions to enhance the pumpability through altering theconcrete mix.

Various studies [1–13] have indicated that the dominant factorwhich facilitates the pump is the lubrication layer formed at theinterface between the concrete and the wall of the pipe. The exis-tence of this layer was first suggested by Alekseev [5] and Weber[6] and there have since been numerous attempts to estimate itsproperties. Morinaga [7] also noted that, from a theoretical pointof view, when considering only the rheological parameters of theconcrete itself, the pumping of concrete would not be possiblewithout the formation of this slippage layer. Sakuta et al. [8] wentfurther and demonstrated that the flow properties of the bulk con-crete are irrelevant to the pipe flow of pumped concrete. The onlyproperties that matters in concrete pumping are those related tothe ability of the material to form this layer. Jacobsen et al. [9] usedcolored concretes in a pipe to directly observe their flow profiles.The results demonstrated the existence of a high velocity and pasterich zone at the vicinity of the wall of the pipe. A study by Kaplanet al. [10] on predicting pumping performance demonstrated that

(b) After electromagnetic treatment

(a) Before electromagnetic treatment

Fig. 1. Schematic structure of the molecule clusters of water.

M.S. Choi et al. / Construction and Building Materials 61 (2014) 18–23 19

the lubrication layer is a major factor in facilitating concrete pump-ing, because the layer has a significantly lower viscosity and yieldstress than concrete. They also developed a test instrument called atribometer that can measure the friction stress at the wall of thepipe. Choi et al. [11] tried to directly measure the velocity of lubri-cation layer for full size pumping circuits using an ultrasonic veloc-ity profiler (UVP) and Jo et al. [12] and Choi et al. [13] simulated theformation of the lubrication layer in the concrete flow inside thepipe considering the shear-induced particle migration. As brieflysummarized herein, most studies on concrete pumping have fo-cused on evaluation of the lubrication layer to estimate the pum-pability of concrete.

The basic goal of the present study is to improve concrete pum-pability by manipulating and controlling the properties of thelubrication layer. One possible method to accomplish this is tointroduce an electromagnetic field to the pipe when concrete isbeing pumped. During concrete pumping, a redistribution of parti-cles occurs in the vicinity of the pipe wall [12–16]. As a result, thelubrication layer can therefore be considered as a paste rich zone.This layer consists of water, cement, and fine sand. Water contentin this layer has of course a significant influence on the propertiesof the layer. Various studies [17–22] have shown that usage ofmagnetic field treated water in concrete field can increase theworkability, accelerate the hydration reaction, increase the com-pressive strength, and improve the impermeability and freeze/thaw resistance. Through the magnetic treatment on water, thecharacteristic of concrete could be improved. When applying sameprinciple to concrete pumping, stimulating the movement of watermolecules within the layer by externally imposing an electromag-netic field on the outer surface of the pipe could be an effectivemeans of improving the pumpability.

The objective of this study is to investigate the effects of anexternally imposed electromagnetic field on the formation of thelubrication layer in an experimental way. Full-scale pumping testswith a 1000 m long pipeline were performed with three differentconcrete mixes according to the imposition of an electromagneticfield. A special electronic control device called a Fluid-Liner[23,24] was mounted on the pipe in front of the pump to inducethe electromagnetic field. The pressures inside the pipe and theflow rates were measured during pumping concrete. In addition,the velocity profile near the wall of the pipe was observed with aspecial sensor using ultrasonic waves [11,13]. Based on the test re-sults, the effects of an electromagnetic field on the lubrication layerwere quantitatively analyzed.

Table 1Mixture proportions.

Materials Design strength

Name of the series C40 C50 C60

Cement CEM I 52.5 N, kg/m3 201 225 257Fly ash class F, kg/m3 45 50 57Blast furnace slag, kg/m3 201 225 257W/B ratio 0.38 0.33 0.28Sand, kg/m3 768 736 713Coarse aggregate, kg/m3 873 871 844Polycarboxylate-based HRWRA (%) 0.8 0.9 1.0Slump flow, mm 600 ± 20 620 ± 20 620 ± 20

2. Activation of water molecule movement due toelectromagnetic field

When an electromagnetic field is imposed to the outer surfaceof the pipe, water existing in the lubrication layer can be directlyaffected and activated. Water is a polar substance, and water mol-ecules tend to be attracted to each other by hydrogen bonding andform clusters, as illustrated in Fig. 1(a) [20,25]. The associationsand disassociations of water molecules are in thermodynamicequilibrium. In general, each cluster contains about 100 water mol-ecules at normal temperature [26,27]. Under a magnetic field,magnetic force can break apart water clusters into single moleculesor smaller clusters, as shown in Fig. 1(b), thereby increasing theactivity of water [17–21]. For water with the same or close ioniccomposition, as the cluster size of water becomes smaller, theactivity of the water becomes accordingly higher.

Yu et al. [21] demonstrated that a decrease of the peak width ofNMR (Nuclear Magnetic Resonance) spectroscopy of water provesthat the molecule clusters of water have been reduced by electro-magnetic treatment. Accordingly, the activity of the water after

electromagnetic treatment becomes higher than that of normalwater. Wang et al. [28] pointed out that an electromagnetic fieldaffects water hydrogen bonding and brings about structural andcharge changes of ions in water. Therefore, in the present study,by inducing an electromagnetic field on the lubrication layer,which is significantly controlled by the water present within it,the properties of this layer could be manipulated, leading to im-prove concrete pumpability.

3. Experimental program

3.1. Concrete mixes

Three different concrete mixes were prepared for this study. The mixture pro-portions are listed in Table 1. The cement was CEM I 52.5 N with a density of3150 kg/m3. The sand was natural river sand with a density of 2590 kg/m3 and afineness modulus of 2.81. Sand particles size ranged from 0.08 to 5 mm in size witha water absorption capacity of 2.43%. The coarse aggregate was a limestone aggre-gate material with a water absorption capacity of 0.8%, a density of 2610 kg/m3 andthe fineness modulus of 6.72. The amount of mixing water was corrected to takeinto account the water absorbed by the sand and coarse aggregates. A polycarbox-ylate-based high-range water-reducing admixture (HRWRA) was used. As listed inTable 1, its dosage, marked as % HRWRA, meaning the percentage of admixture rel-ative to the binder content (in weight), was adjusted to obtain the same slump flow.

To carry out pumping tests in real size pumping circuits, each concrete mix wasproduced in a batch of 2 m3 at a time and dumped into the total 6 m3 mixer anddelivered by a ready-mix concrete company. The mixing procedure was as follows:

Table 2Pump specifications.

Item Content

Model BSA14000HP-DFlow rate (m3/h) 82a/54b

Max. pressure (bar) 185a/260b

Engine house (kW) 350Stroke/min 26a/17b

a Rod side.b Piston side.

20 M.S. Choi et al. / Construction and Building Materials 61 (2014) 18–23

sand and coarse aggregate materials were mixed for 15 s, all other dry componentswere added during 15 s, and water and HRWRA were then added during an addi-tional two minutes of mixing. The total mixing time was 2.5 min.

3.2. Pumping circuit

A horizontal pumping circuit with a length of 1000 m was installed (cf. Fig. 2). Itconsists of nine 180� bends with a radius of curvature equal to 1.0 m and the pipediameter was 125 mm and its thickness was 7.7 mm. The concrete pump is a high-pressure piston pump. The specifications of the model are given in Table 2.

The filling rate of the pump cylinder, which measures the degree of filling in thecylinder per one stroke and directly affects the flow rate, was calibrated from spe-cific experiments carried out prior to the actual concrete pumping [11]. The con-crete was pumped into several 1 m3 reservoirs, which were connected to a linearvariable differential transformer (LVDT). As the pump cylinder volume is known,the filling rate was computed from the LVDT length variation with the designatedstroke times. Through these experiments, the averaged filling rate was found tobe around 75%.

The pumping circuit was equipped with 11 pressure gauges. The detailed loca-tions of the gauges are shown in Fig. 3. The first gauge was located 10 m after thebeginning of the circuit, and the last was located 4 m before the end.

3.3. Ultrasonic velocity profiler (UVP)

In this study, to investigate the thickness variation of the lubrication layerdepending on the induced electromagnetic field, an ultrasonic velocity profiler(UVP) [11,13] was used to carry out non-destructive measurement of the velocityprofile in the pipe using ultrasonic waves at a high resolution. The detailed specifi-cations of the device used in this work are given in Table 3, and more informationabout this device, such as its principle of measurement, the installation of the ultra-sonic probe, and some limitations can be found in earlier works [11,13]. In addition,for application of the UVP using ultrasonic waves, a 1 m transparent engineeredplastic pipe with the same diameter as a standard pipe was installed in the last sec-tion, as shown in Fig. 4.

When ultrasonic waves propagate in a medium containing coarse particles,such as concrete, the ultrasound pulse hits the particles and part of the ultrasoundenergy is scattered and lost for the echo measurement. Thus, as the measuringdepth increases, the amplitude of echoed ultrasound energy decreases. This is espe-cially true for the high frequency ultrasonic waves used in this work. Thus, above agiven depth, the amplitude of echoed ultrasound energy is not sufficiently strong todetect the doppler shift frequency and give access to the velocity profile. Althoughthis limited measurement range does not allow obtaining the full velocity profile inthe cross section, the measured thickness exceeds the expected thickness of thelubrication layer and provides valuable information about the variation of thicknessdepending on an electromagnetic field.

3.4. Pulsating electromagnetic field

To stimulate and manipulate the lubrication layer, an electromagnetic field wasinduced in the pipe while concrete was being pumped as shown in Fig. 5. In order toincrease the efficiency of an electromagnetic field, with the aid of a pulsating cur-rent, it is possible to determine the hydrodynamic variables such as pulse fre-quency, pulse amplitude, and speed of current that will generate sudden changesin the current, especially close to the walls, and even to force a temporary reversalof the current in the pipe, a phenomenon known as the Richardson effect [29,30]. Aspecial feature of this process is the introduction of a variable spectrum of frequen-cies into the current on the pipe to increase the activated motion. With a specialelectronic control device called Fluid-Liner [23,24], the optimal frequency rangeof the magnetic field can automatically be adjusted, harmonized with the conduc-

Fig. 2. Overview of the 1000 m full-scale test setup.

tivity and the speed of the current of the water. Depending on the composition ofmedium, the range lies somewhere between 80 Hz and up to 1.1 kHz. More specificinformation about the device is provided in Table 4.

4. Results and discussion

4.1. Pressure measurement

The representative pressure variation according to the timeafter applying an electromagnetic field for concrete C60 case isillustrated in Fig. 6, where the measured pressures are the aver-aged values of the 0 m position which are calculated using a linearextrapolation process with data from pressure gauges at 11 desig-nated positions. As shown in Fig. 6, after the electromagnetic fieldwas induced in the pipe, the measured pressure showed a steadydecreasing trend for a certain period and then reached a steadypressure condition, i.e. the equilibrium condition, which meansthe effects of an electromagnetic field were fully reflected to theconcrete flow along the pipe. These pressure variations indicatedthat the effect of an electromagnetic field on the concrete flowwas simultaneously detected and was also sufficient to influencethe inner material inside the steel pipe, especially the lubricationlayer. When examining the pressure difference depending on anelectromagnetic field, the equilibrium condition pressure afterinducing the effects showed 30% less than that of the original con-dition regardless of the mixture proportion. This represents that byinducing an electromagnetic field, the pressure required to obtainthe targeted flow rate could be reduced by almost 30%; this signif-icant reduction could make it possible to secure pump use for con-crete in the construction of superstructures.

The pressure distributions along the pipeline are plotted beforeand after imposing the electromagnetic field to the same concreteC60 in Fig. 7. Almost 30% pressure drop shown in Fig. 6 took placenot only at the inlet but also along the whole pipeline. Moreover, itis of note that although the electric coils creating an electromag-netic field were mounted only at the front region of the pipe (overa distance of about 20 m), the measured pressures along the entirepipe show an almost linear relationship with an extrapolated ordi-nate at the origin in the investigated regime nearly equal to zero.This indicates that the effects of an electromagnetic field on thepipe in this study might influence the entire length, which meansthat the newly formed lubrication layer due to an electromagneticfield is maintained along the pipe as the concrete passes through it.It was also found that the length of the electric coils and the mag-nitude of the electric field creating an electromagnetic field are suf-ficient to maintain this effect. Moreover, in this regime and in thepumping conditions tested in this study, the pumping pressuredoes not appear to be affected by shear thickening or shear thin-ning [31–34] and does not display any pressure dependency ofthe rheological parameters of the pumped materials [35,36].

4.2. Thickness of lubrication layer

To investigate the thickness variation of the lubrication layeraccording to an electromagnetic field, the axial velocities

Fig. 3. Schematic ground plan of the pumping circuits and the location of pressure gauges.

Table 3Experimental UVP parameters.

Item Content

Frequency (MHz) 8Cycles per pulse 2–32No. of profiles 1024Sound velocity (m/s) 2680 ± 200Doppler angle (�) 85 ± 0.5Spatial resolution (mm) Min. 0.20

Fig. 4. Application point of the UVP and transparent engineered plastic.

Fig. 5. Installment of electric coils at the front part of the pipe about 20 m in lengthto generate an electromagnetic field.

Table 4Fluid Liner specifications.

Item Content

Power consumption (W) 150Switching frequency (kHz) Max. 1.1Design flow velocity (m/s) 2–4Flow rate (m3/h) Max. 360Pipe diameter (m) Max. 1

Fig. 6. Variation of measured pressure over time after applying an electromagneticfield for concrete C60.

M.S. Choi et al. / Construction and Building Materials 61 (2014) 18–23 21

experimentally measured by means of the UVP are illustrated inFig. 8, where the normalized velocity is defined as the relativevelocity to the its own maximum velocity. As shown in Fig. 8, a

dramatic change in the slope can be spotted within a limited zonethat represents the lubrication layer and shear rates (i.e., approxi-mately the slope of the velocity profiles) concentrated in this layerfor all tested cases. In the previous study [11–13], it was found thatwhen the electromagnetic field was not applied, the thickness wasapproximately 2 mm regardless of the mixture proportion in therange studied in this paper. When taking a look at the thicknessof the lubrication layer after inducing an electromagnetic field inFig. 8, it became slightly wider relative to the original thicknessregardless of the mixture proportion. The reason for this changecomes from the fact that due to an electromagnetic field, waterexisting mostly in the lubrication layer is activated with higher en-ergy and is excited, which results in an increase of the activationzone, i.e. the thickness of the lubrication layer. It is moreoverinteresting to note that, based on the experimental results ob-tained with the UVP, the velocity after inducing an electromagnetic

Fig. 7. Pressure distribution along the entire pipeline according to the imposition ofan electromagnetic field for concrete C60.

Fig. 8. Normalized velocity profile near the wall of the pipe.

Fig. 9. Comparison of relative velocity profile according to the imposition of anelectromagnetic field.

22 M.S. Choi et al. / Construction and Building Materials 61 (2014) 18–23

field tends to increase. When taking a look at the variation of therelative velocity, as shown in Fig. 9, where the relative velocity isthe ratio of the velocity to the maximum velocity without theimposition of the electromagnetic field, the velocity after inducingan electromagnetic field increased more than 15% regardless of themixture proportion. This result is also ascribed to activation ofwater and vigorous excitation movement in the lubrication layer.Another possible reason is that by inducing an electromagneticfield, the friction resistance between the lubrication layer and thewall of pipe could be reduced, which in turn would increase theabsolute velocity under the same pressure condition. Ultimately,increased velocity in the lubrication layer caused by an electro-magnetic field results in a higher flow rate. From a practical pointof view, a lower capacity pump could therefore be used to satisfythe required casting speed and make it possible to pump concreteover long distances and to considerable heights. It can therefore benoted that the application of an electromagnetic field in theconcrete pump can increase the pump efficiency by affecting theproperties of the lubrication layer. This makes it possible to over-come pump limitations for the construction of superstructuresand can provide cost savings by permitting the use of a lowerspecification pump that would then be able to satisfy constructionrequirements.

5. Conclusion

When concrete is transported through a pipe, the lubricationlayer that is formed at the interface between concrete and the pipewall plays a dominant role in facilitating concrete pumping. Theconstituents of the layer are very different from those of the innerconcrete. Specifically, the layer resembles a cement paste enrichedzone consisting of water, cement, and fine sand particles. Here,water that exists mostly in the lubrication layer can be activatedwith higher energy by inducing an electromagnetic field, whichchanges the properties of the lubrication layer. In the presentstudy, in order to enhance concrete pumpability, the propertiesof the lubrication layer were manipulated by inducing a pulsatingelectromagnetic field to part of a pipeline. For verification of the ef-fects, 1000 m full scale pump tests according to imposition of anelectromagnetic field were conducted, and the following conclu-sions were obtained.

1. After imposing an electromagnetic field, the measured pressureunder the same flow rate conditions decreased significantly, byalmost 30%, compared with the original pressure.

2. Although the electric coils that create the electromagnetic fieldwere mounted only in a 20 m length region at the front of thepipe, the measured pressures along the entire pipe, i.e.1000 m, showed an almost linear relationship. This indicatesthat the newly formed lubrication layer due to an electromag-netic field is maintained along the pipe as the concrete passthrough it.

3. Investigation of the thickness variation of the lubrication layerafter inducing an electromagnetic field revealed that it becameslightly wider regardless of the mixture proportion. This isascribed to excitation of water that existed mostly in the lubri-cation layer by an electromagnetic field, which resulted in anincrease of the activation zone, i.e. the thickness of the lubrica-tion layer.

4. Moreover, the relative velocity in the lubrication layer afterinducing an electromagnetic field tended to increase. Two pos-sible reasons for this can be considered: excitation of watermovement and reduced friction resistance between the lubrica-tion layer and the wall of pipe. The increased velocity of thelubrication layer can ultimately cause a higher flow rate, whichmeans that the efficiency of the pump is increased.

5. Therefore, the application of an electromagnetic field on theconcrete pump can increase the pumpability by manipulatingthe flow properties of the lubrication layer. This makes it

M.S. Choi et al. / Construction and Building Materials 61 (2014) 18–23 23

possible to overcome the limited capacity of pumps for the con-struction of long and high structures and also can provide costsavings by permitting the use of lower-capacity pumps.

Acknowledgements

This research was supported by the General Individual Researchin General Researcher Program through the National ResearchFoundation of Korea (NRF) funded by the Ministry of Education(Grant No. NRF-2013R1A1A2013470). This research was supportedby a grant from the Construction Technology Innovation Program(12CTIPE12-Secure of green dredged soil, reclamation and 30 Kmtransporting technology) funded by Ministry of Land,Infrastructure and Transport of Korean government.

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