IN-LINE RHEOLOGICAL MEASUREMENTS OF CEMENT BASED GROUTS USING THE UVP-PD METHOD

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IN-LINE RHEOLOGICAL MEASUREMENTS OF CEMENT BASED GROUTS USING THE UVP-PD METHOD

BeFo Report 99

Md. Mashuqur Rahman Ulf Håkansson

ROCK ENGINEERING RESEARCH FOUNDATION STIFTELSEN BERGTEKNISK FORSKNING


IN-LINE RHEOLOGICAL MEASUREMENTS OF CEMENT BASED GROUTS USING THE UVP-PD METHOD -

A Pre-Study


Md. Mashuqur Rahman, KTH

Ulf Håkansson, KTH & Skanska AB


BeFo Report 99

Stockholm 2011 ISSN

ISRN BEFO-R–99–SE


‌Förord

Forskning om injektering har under trettio år varit ett prioriterat område inom undermarksbyggandet. Under denna tid har injekteringstekniken utvecklats från experimentell verksamhet till ingenjörsvetenskap. Tillämpningen har dock gått långsammare till följd av att nyckelfrågor förblivit olösta. En sådan fråga är styrningen och kontrollen av materialets reologiska egenskaper som påverkas av en rad olika faktorer och avgör strömningsegenskaper. De reologiska egenskaperna förändras dessutom över tid under injektering vilket man idag saknar möjlighet att kontinuerligt kontrollera.

Reologiska egenskaper kan mätas med ultraljud, och sådana tekniker har framgångsrikt tillämpats inom bl. a. livsmedelsindustri och sjukvård. I detta projektområde där målet är att kunna styra injekteringsprocessen i realtid har samverkan initierats med livsmedelsinstitutet (SIK) som är världsledande på området. SIK tillhör SP som har samarbetsavtal med KTH vilket passar väl in för att utnyttja SP:s resurser inom högskoleforskningen.

Möjligheten att mäta reologiska egenskaper ”in-line” i injekteringsprocessen, utan kontakt med cementsuspensionen, efterlystes redan i Ulf Håkanssons doktorsavhandling ”Rheology of Fresh Cement-Based Grouts” KTH 1993 (och SveBeFo rapport 15 1994) och ser nu ut att kunna förverkligas. Det blir då möjligt att styra bruket bättre, ändra dess egenskaper och mer effektivt kvalitetssäkra det använda bruket. En av de saknade nycklarna inom forskningsområdet (RTGC) ”real time grouting control” ser därmed ut att kunna lösas och skapa praktiska möjligheter för effektivare tätning av berg under mark.

Denna rapport, den första i BeFo:s rapportserie skriven på engelska med svensk sammanfattning, är författad av doktoranden Md. Mashuqur Rahman & Professor Ulf Håkansson, båda på KTH.

Stockholm i september 2011 Mikael Hellsten

‌SUMMARY

In underground construction grouting is used to seal tunnels and caverns against excessive water inflow and to limit the lowering of the surrounding groundwater table. Rheological properties of the grout used, such as viscosity and yield strength, play a fundamental role in design and execution, but no method has yet been developed to measure these properties in-line during field work. For the first time, the in-line rheometry method combining the Ultrasound Velocity Profiling (UVP) technique with Pressure Difference (PD) measurements, known as “UVP-PD”, was tested successfully for continuous in-line measurements of concentrated micro cement-based grouts. The test set-up consisted of a combination of an experimental “flow loop” and a conventional field grouting rig – UNIGROUT, from Atlas Copco. The velocity profiles were measured directly in-line, and the obtained rheological properties were subsequently compared with off-line measurements using a conventional rotational rheometer. In this work, the UVP-PD method was demonstrated to be a promising new in-line tool for the determination of rheological properties of commonly used cement- based grouts.


KEY WORDS: Grouting, Rheology, In-line rheometry, Cement grouts, Cement suspensions, UVP-PD method Ultrasound velocity profiling, Flow profiling

‌SAMMANFATTNING

Injektering används inom undermarkabyggande för att täta tunnlar och bergrum mot stora vattenflöden eller för att begränsa avsänkningen av grundvattennivåer för att förhindra sättningar. Reologiska parametrar, såsom viskositet och flytgräns, har en fundamental betydelse för injekteringsdesign och utförande, men ännu har inte någon metod utvecklats för att kunna mäta dessa egenskaper kontinuerligt ”in-line”, under pågående injektering. För första gången har nu en metod som kombinerar hastighetsprofiler, uppmätta med ultraljud, med mätning av tryckfall – den sk. ”Ultrasound Velocity Profiling” (UVP) metoden med ”Pressure Difference” (PD) använts. Lyckade försök har utförts på en cementsuspesion baserat på mikro cement. Försöksutrustningen har bestått av en ”flödes slinga” för ultraljudsmätning samt en konventionell injekteringsutrustning, UNIGROUT, från Atlas Copco. De reologiska parametrarna uppmätes direkt ”in-line” och jämfördes sedan med mätningar utförda med en vanlig rotationsviskometer. Resultaten visar tydligt att detta är en lovande metod för att direkt bestämma de reologiska parametrarna för cement baserade injekteringsmedel i samband med en verklig injektering i fält.


‌TABLE OF CONTENTS

Preface. . . . . . . . . . i

Summary. . . . . . . . . . iii

Table of Contents . . . . . . . . v

  1. Introduction . . . . . . . . 1
  2. Objectives and Limitations. . . . . . . 3
    1. Objectives . . . . . . . . 3
    2. Limitations . . . . . . . . 3
  3. Ultrasound Physics . . . . . . . . 5
    1. Introduction . . . . . . . . 5
    2. Sound velocity in fluids . . . . . . . 5
      1. Attenuation of ultrasound waves 8
      2. Acoustic impedance 8
      3. Propagation of ultrasound through the interface between two layers 8
      4. Ultrasound transducers . . . . . . 10
  4. Principles of Ultrasound Velocity profiling (UVP) . . . 13
    1. Ultrasound doppler theory . . . . . . 13
    2. Principles of ultrasound doppler velocimetry (UDV) . . . 14
      1. General principles 14
      2. Velocity estimation using time/frequency domain based signal processing 20
      3. UVP monitor . . . . . . . . 21
  5. UVP-PD Method . . . . . . . . 23
    1. Introduction . . . . . . . . 23
    2. Principles of UVP-PD . . . . . . . 23
    3. Data acquisition and software . . . . . . 24
    4. Acoustic characterization . . . . . . 26
    5. Previous studies based on UVP-PD method . . . . 27
  6. Materials . . . . . . . . . 31
    1. Micro cement . . . . . . . . 31
    2. Additive . . . . . . . . . 32
    3. Sample preparation . . . . . . . 33
  7. Experimental Set up . . . . . . . 35
    1. Flow loop characteristics . . . . . . . 35
      1. UNIGROUT E22H . . . . . . . 36
      2. LOGAC . . . . . . . . 38
      3. UVP-PD instruments . . . . . . . 39
    2. Experimental Procedure . . . . . . . 41
    3. Off line measurement instruments . . . . . 42
      1. ARES G2 rheometer. . . . . . . . 42
      2. Brookfield DV-II+ pro (LV) viscometer . . . . 42
  8. Results . . . . . . . . . 45
    1. Acoustic measurements . . . . . . . 45
    2. Velocity profiles measured by UVP . . . . . 49
      1. In-line velocity profiles fitted with Herschel-Bulkley model . 54
      2. Rheology by gradient method . . . . . 58
    3. Flow curves from in-line measurements . . . . . 60
    4. Shear rate dependent viscosity. . . . . . . 63
    5. Comparison of volumetric flow rate . . . . . 64
    6. Off-line measurements . . . . . . . 65
  9. Conclusion and Recommendations for Future Work . . . 69
    1. Conclusion . . . . . . . . 69
    2. Recommendations for future work . . . . . 70
  10. References . . . . . . . . . 71

Appendix A . . . . . . . . . 77

Appendix B . . . . . . . . . 85

  1. ‌INTRODUCTION

    In underground construction, grouting is used to seal tunnels and caverns against excessive water inflow or to limit the lowering of the groundwater table, by injecting a grout into joints and fractures in the rock. A lowered groundwater level can have adverse environmental impact or it can increase the risk of settlement to adjacent buildings. Most infrastructure projects today are located in urban areas and the cost to avoid groundwater related problems can constitute a large portion of the total project cost.Performed grouting work is often based on rules of thumb and despite the fact that extensive research has been conducted for the last 25 years in Sweden, practical implementation of the result has so far been rather limited.The rheological properties, such as viscosity and yield strength, of the used grouts play a fundamental role in grouting and difficulties in the measurement of the rheological properties of cement based suspensions, are well known (Håkansson, 1993). However, testing methods that deliver a continuous in-line measurement of the properties as well as their change with time are still lacking. Measurements are today made with rather primitive methods, developed many years ago, mainly in order to verify and fulfil stipulated quality criteria. The activity itself often implies a stop and disruption of the ongoing grouting and it is frequently difficult to achieve quality assured results.Modern grouting rigs are today equipped with monitoring devices for continuous measurement of flow and pressure and the output constitutes an important means for quality control and steering of a grouting operation. However, as pointed out in his thesis, Håkansson (1993) concluded that future improvements of grouting equipment should also involve continuous in-line monitoring of the rheological properties. This holds true even more today since the latest development regarding design and steering of a grouting operation necessitates an accurate and reliable determination of the rheological properties, as well as their change with time. In recent work regarding design and steering of a grouting operation (Gustafson and Stille, 2005) it is shown that an accurate and reliable determination of the rheological properties, as well as their change with time is important. The authors showed that the characteristics grouting time depends on the pressure, viscosity and yield stress and that it is also independent of the joint aperture, according to following equationt6 g  p0 20This means that the designer can choose the grouting time scale at his own choice and that the necessity of continuously in-line monitoring of the rheological properties therefore becomes important. It is interesting to note that the equation above includesthe viscosity in the nominator and the yield stress in the denominator, to the power of two, emphasising the importance of the rheological properties.A promising contribution towards in-line measurements of cement-based grouts is the so-called “Ultrasound Velocity Profiling (UVP) – Pressure Difference (PD)” method, used by various other industries (Takeda, 1986). The UVP-PD method has recently been successfully used on other industrial suspensions, such as food, paper pulp and mine tailings (Ouriev, 2000, Kotzé, 2007, Birkhofer, 2007 and Wiklund, 2007). One of the major advantages, compared to conventional rotational or capillary rheometers, is that the measurement is conducted continuously in-line and that it is non-invasive, i.e. there is no measuring device in contact with the suspension itself. Output from the device is an image of the actual velocity profile from which either the flow curve, i.e. shear stress vs. shear rate, can be found directly or the rheological model determined by various curve-fitting procedures. Once the velocity profile is found, the flow rate can be determined by integration and subsequently compared with the measurements from ordinary flow rate instruments. An interesting feature of this method is that parameters, such as the yield strength and the shear rate, can be measured directly from the image of the velocity profile. The shear stress, however, must be estimated from the pressure drop over a certain distance of the pipe by using conventional pressure transducers.The development of an in-line measurement procedure, based on ultra-sound, implies that it can be possible to control the properties and early determine if the grout is starting to hydrate or if it is by some other mechanism achieving unwanted flow characteristics. It is envisaged that the monitoring device in the future can be mounted on one of the pipes on the grouting rig for continuous measurements of the properties throughout the entire grouting operation. The results can be stored digitally, the same way as pressure and flow is stored today, and used to steer the grouting operation as well as quality assure the used grouts.The applicability of the in-line UVP-PD method for the measurement of rheological properties of grouts has been reported previously in a pre-feasibility study (Håkansson and Rahman, 2009).

  2. ‌OBJECTIVES AND LIMITATIONS

    1. ‌Objectives

      The main objective of this study was to verify the feasibility of the ultrasound velocity profiling – pressure difference (UVP-PD) method for measuring the velocity profiles of commonly used cement based grouts directly in-line. The UVP-PD data was subsequently used to evaluate how accurate and effective it is in determining the rheological properties of grouts with different water-cement ratios. A standard cement grout mixing equipment, UNIGROUT E22H and LOGAC flow meter, was used to keep the conditions similar to the ones in the field. Secondary objectives of the investigation were to determine the following:
      1. Velocity of sound using the customized flow loop.
      2. Rheological properties by curve fitting to the velocity data.
      3. Shear rate, yield stress and viscosity directly from the velocity profiles by the gradient method.
      4. ​Flow curves, i.e. shear stress vs. shear rate, by the two different methods given above.
      5. Volumetric flow rate by integrating the velocity profiles and comparing the results with a conventional flow meter (LOGAC).
      6. Rheological properties from off-line measurements by a conventional rheometer.

    2. Limitations

‌This was the first time the UVP-PD method was used for measuring the rheological properties of cement based grouts. The set up was also different from previous measurements and studies using the UVP-PD application. Limitations involved in the current work are described below.

In order to have accurate measurements of velocity profiles and subsequent determination of rheological properties, it is very important to have a stable flow through the flow loop. The UNIGROUT E22H is equipped with a piston type of pump and as a consequence, the movement of the piston and variations of pressure creates high fluctuations in the flow rate which, was observed in all the measured velocity profiles.

Ball valves mounted on the UNIGROUT E22H were used to change the flow rate. The ball valves are simple and crude, making it difficult to control the flow rate accurately enough for this type of measurements.

In the measurements, only 4 MHz transducers were used and this creates limitations with respect to signal penetration when using dense grouts, i.e. low w/c ratios.

Cement grouts were tested both with and without SetControl II. However, since the main objective was to determine the feasibility of the UVP-PD method, no actual comparisons were within the scope of this work. The sampling time and other conditions were not identical, which means that the results with or without SetControl II cannot readily be compared.

Off-line measurements were performed by using a rotational rheometer. However, it was out of the scope of work to thoroughly compare the results between in-line and off- line measurements and to observe the change of the rheological properties over time. As most of the sampling time and other conditions were not identical between the two methods, the results of the off-line measurements are only indicative and are shown as a separate result for convenience.

  1. ‌ULTRASOUND PHYSICS‌

    1. ‌Introduction

      Sound waves propagate through air or water by mechanical vibration, i.e. by the transmission of energy through the molecules of a medium. Every molecule transfers the energy to other molecules but remains in the same position after transferring the energy. The energy passes in the form of a sound wave, which can propagate transversely or longitudinally. Transverse waves are also called shear waves and they are the most easily propagated waveform in nature. Sound waves can propagate both longitudinally and transversely in solids but fluids only support longitudinal propagation.Ultrasound is defined as any sound wave with frequencies higher than the human hearing threshold, i.e. in the range 20 kHz. The amplitude of a sound wave comes from the change of air pressure in the wave and it is a degree of motion of the air molecules. The frequency of a sound wave is the number of the waves passing through a point in one second. Intensity is the average rate of flow of energy per unit area perpendicular to the direction of propagation. Wavelength is the distance between the two successive peaks of the wave. The sound velocity can be determined from the product of the frequency and the wavelength by the following equationc  f ………………..3.1where,c  Acoustic velocity in the medium (m/s)  Acoustic wavelength (m)f  Frequency (Hz)

    2. Sound velocity in fluids

      Sound velocity in gases can be measured very accurately by the molecular theory. Due to the higher compressibility, the density of the gas varies in the same way as the change of pressure. But in case of solid the density remains partially constant. The pressure and the density are the same throughout the entire volume of a gas in equilibrium state. If the pressure of the gas is distributed the pressure gradient increases and a volume element gains some motion. Adiabatic linear bulk modulus of elasticity is used to show the change of pressure per unit change of density in gases. It can be expressed as   dP ………………..3.2 AD 0  d ‌whereAD = adiabatic linear bulk modulus of elasticity (N/m2)0 = equilibrium density (kg/m3)The adiabatic linear bulk modulus of elasticity indicates the stiffness of the gas medium and their changes in volume when distributed at a constant temperature. The compressibility of liquid is lower than gases but still this theory can be used with a modified volumetric modulus of elasticity. The propagation of ultrasound in a liquid is nearly an adiabatic process. The compressed regions possess more heat than the relaxed zones in the liquid where sound is propagating. The inverse of the adiabatic linear bulk modulus of elasticity is known as the compression coefficient and can be expressed as  1   1   d ………………..3.3dPAD Ad 0  p  0The velocity of sound wave propagating in liquids can be expressed asAD01AD 0c  ………………..3.4Wherec  Sound velocity in liquid (m/s)
      1. Attenuation of ultrasound wavesThe ultrasound waves are attenuated as some of the energies are refracted or scattered. If we know the wave amplitude for a propagating distance, the attenuation of an ultrasound wave can be determined. The damping of an ultrasound wave propagating in a certain distance can be characterized by the spatial attenuation coefficient, 0 ,expressed as     1  dAMax ………………..3.50  A  dx  Max  whereAMax = wave amplitude of the transmitted ultrasound wave‌The amplitude of an ultrasound wave reduces following an exponential law which is expressed asand is shown in Figure 3.1.AMax0ct A  eMax 0………………..3.6
        Figure 3.1 Attenuation of an Ultrasound Wave (Ouriev, 2000) Figur 3.1 Dämpning av ultraljudvågen (Ouriev, 2000)The attenuation coefficient depends on the material which is important in choosing the pipe materials for the UVP-PD test. Materials with a high attenuation coefficient should be avoided.
      2. Acoustic impedanceAcoustic impedance is a physical property of a material and an important factor for optimizing the energy transfer from one medium to another. It determines the refraction and transmission of energy at the boundary between two successive media.The acoustic impedance can be expressed asZ=ρ×cwhere………………..3.7Z  Acoustic impedance (kg/m2s = Ray) c = sound velocity (m/s)ρ= density of transmitting medium (kg/m3)It is possible to obtain the non-invasive measurements through a pipe wall if the acoustic impedance of the wall material is greater than the acoustic impedance of the liquids used.
      3. ‌Propagation of ultrasound through the boundary between two layersReflection and refraction occurs when ultrasound waves pass through the boundary of two layers. While passing through the boundary, the ultrasound waves will reflect and refract at different angles. The angles depend on the acoustic properties of the two materials. A correlation between the incident angle and refractive angle is established by Snell’s equation, which was established for optics but found valid for all wave propagation and expressed asSin1 Sin2 c1 c2………………..3.8where1 = angle of incidencec1= sound velocity in medium 12 = angle of refractionc2= sound velocity in medium 2The equation is explained by Figure 3.2.
        Figure 3.2 Ultrasound wave propagating through two materials Figur 3.2 Ultraljudvåg genom två olika materialThe ultrasound propagates from layer 1 to layer 2 with an incidence angle 1and it isrefracted in layer 2 with a refraction angle of 2 . From Snell’s law we can say that the higher the sound velocity in layer 2 the larger the refraction angle 2 will be.1While propagating through the boundary layers the ultrasound wave will lose some energy due to the acoustic impedance of the materials. In Figure 3.2 the incidence intensity of the ultrasound wave at layer 2 is I1 and transmitted intensity at layer 2 is I2. The reflective intensity at layer 1 is I  and the initial intensity of the ultrasound wavecan be expressed as1I1  I2  I ………………..3.9A reflection coefficient can be expressed asI 1r   1  I1………………..3.10‌A transmission coefficient can be written as1  I2………………..3.11I1The total acoustic energy at the boundary of two layers consists of the incidence intensity, transmitted intensity and reflective intensity expressed asr   1……………….3.121 1The reflection coefficient can be shown as the function of the material acoustic impedance and the corresponding angles and can be expressed as z  z 2r      1         2 ………………..3.131 21  z  z From equation 3.12 and 3.13 it can be shown thatr  1  4z1z2………………..3.141 1 z  z 21 221The incident wave will be fully reflected when θ =900 . The corresponding  is knownas the critical angle. According to Snell’s law when the wave is propagating from a lower wave velocity medium to higher wave velocity medium, the critical angle can be achieved. The maximum angle of incidence can be expressed as  arcsin  c1 ………………..3.15c1   2 The critical angle is an important factor for non-invasive measurements through the pipe wall. The critical angle varies intensively in different materials and the value of critical angle must be check for testing materials before the experiments.
      4. Ultrasound transducerTransducers are used to emit ultrasound signals and transducers developed by Met Flow, SA has been used by most of the studied authors (Wiklund 2007, Birkhofer, 2007, Kotze 2007). Transducer frequencies are available for 0.5, 1, 2, 4 and 8 MHz. The ultrasound generated by the transducer is divided into two fields- near field and far field. In the near field, measurements are avoided because ultrasound measurements are unstable in this region. The acoustic sound field is irregular here and acoustic wavesoscillate along the axis of the propagation. The near field region starts in front of the transducer and continues until the maximum acoustic intensity. The near field distance can be expressed asD2f N      0 4c………………..3.16whereN = near field distance (m)D = active element diameter (m)f0 = basic ultrasound frequency (Hz)c = sound velocity (m/s)The acoustic wave propagation from an ultrasound transducer is shown in Figure 3.3
        Figure 3.3 Schematic diagram of the sound wave generation from an ultrasound transducer (Met-Flow, 2000)Figur 3.3 Schematiskt diagram av ljudvåg från en ultraljuds givare (Met-Flow, 2000)The near field distance, N, is the natural focal point of the transducer.Transducers are fixed in the flow adapter in order to measure the pipe flow with as low interference as possible. Transducers can be set with direct contact with the liquid material. Different kinds of transducer setups for non-invasive measurements used in different publications are as follows (Wiklund, 2007).Several ultrasound transducers, 1-3 can be used and the data’s are combined. For non- invasive measurement an acoustic coupling material has to be used. Small errors in doppler angle determination can lead to a large error when all transducer’s data’s are combined.Transducers can be mounted in the pipe through small as shown in Figure 3.4. They are installed in such a manner that the near field region is equal to the distance between the transducer and the pipe wall. This is done to avoid measurements in near field zone where it is irregular and not fully developed. If the transducer is mounted inside the pipe wall then there will be loss of ultrasound energy and the doppler angle will be incorrect due to the refraction of ultrasound wave in the pipe wall. It has found that it is possible to achieve good results when the transducer is in direct contact with the fluid. Two transducers are used in the opposite direction to also perform acoustic measurements in addition to the velocity profiles.A thin wall membrane, e.g. polymethyl methacrylate (PMMA), can be used in the near field region to separate the transducers from the fluid inside the pipe.
        Figure 3.4 Schematic diagram of flow adapter cell with two transducers Figur 3.4 Schematiskt diagram av flödes adapter med två givare

        1. ‌PRINCIPLES OF ULTRASOUND VELOCITY PROFILING (UVP)

          1. ‌Ultrasound doppler theory

            Using sound waves for measuring the distance between two points was invented by mankind due to their own need for measuring distances and this method has been continuously developed since the last century. Bats use sound waves for their navigation and to measure the distances to other flying objects. This method involves transmitting sound waves in a medium and measuring the time required to propagate and coming back from the reflecting surface. This type of phenomenon is referred as ‘sonar’. The idea of using acoustic measurements first arose for detecting icebergs after the tragic accident of Titanic in 1912. During the first and second world war lots of military and naval applications of ultrasonic wave and electromagnetic waves, which also use the same principle, were found. A powerful ultrasonic echo sounding device ‘hydrophone’ was introduces and it was the base of medical pulse-echo sonar. Radar was developed by using the radio detection and ranging of electromagnetic waves. Invention of the methodology of non-destructive material testing based on ‘sonar’ is presently one of the most frequently used applications (Wiklund, 2003).In the medical field for blood flow monitoring an instrument was commercially marketed by Novamed, SA, Switzerland. It was possible to record and analyze a large number of signals along the measuring axis and hence instantaneous velocity profiles could be plotted. Takeda used this type of instrument to find out the possibility for general flow measurement of fluids. He found it very promising and the principles are in detail given by Takeda (1986). The limitation with this instrument was that only a limited number of channel/gates were available in which the received echo signal could be stored and analyzed. Consequently, the resolution of the velocity profiles was not good enough. Further work was performed by Takeda and this led to the development of the ultrasound velocity profile monitor (UVP) and the windowing function patented by Takeda (Takeda, 1989, 1991). The UVP monitor is for example, marketed by Met- Flow, Switzerland who also has made further developments on the equipment.The Doppler EffectThe Doppler effect is named after an Austrian physicist, Christian J. Doppler, who first noticed it and gave a lecture on this phenomenon in 1842. When an observer and the source from where the sound wave is originating are in motion with respect to each other, the frequency of the wave to the observer is different than the source. This phenomenon is said to be Doppler shifted and known as the ‘Doppler effect’. It is valid not only for sound waves but also for electromagnetic waves, microwaves, radio waves and visible light. The change of frequency with motion of the source and observer can‌be illustrated easily by the whistle of a train and an observer. If the train and the observer both are static then the driver and the observer both will hear the sound with same frequency and no Doppler shift will occur. But if the train and the observer are in relative motion to each other then a different frequency will be observed and the sound intensity will be changed. The basic frequency of a ultrasonic wave can be expressed by the following equation‌f  c………………..4.1wheref  emitted frequency (Hz)c = velocity of sound wave in the medium (m/s) = wavelength of the emitted ultrasound wave (m)The general Doppler equation when the source and observer are both moving in the direction of wave propagation can be expressed by the following equationf  fc  vobserver ………………..4.2observersource  c  vsource wherevobserver and vsource are the velocity of the observer and source in the direction of wavepropagation, c is the velocity of sound wave in that medium. If the source and observerare moving in the same direction then the values of vobserver and vsource are positive andthey are moving in opposite direction then the values are negative.

          2. Ultrasound doppler velocimetry (UDV)

            1. General principlesThe ultrasound pulsed Doppler velocity profiling technique was originally developed in medical engineering to measure the flow of blood in the human body (Takeda, 1985). The ultrasound is reflected from the surface of the blood particles and by using the principle of the Doppler effect, the particle distribution as well as the velocity profile in a blood vessel can be determined. This method was subsequently extended by Takeda for application in other fields of engineering and the principles are in detail discussed in his literatures (Takeda 1985, 1990, 1995).The principles of ultrasound doppler velocimetry are shown in Figure 4.1. Here the ultrasound transducer is placed at an angle θ with respect to the pipe wall. It emits ultrasound waves and also works as a receiver. When the ultrasound waves hit a particle, some portion of the ultrasound energy scatters and the echoes come back to the transducer.
              Figure 4.1 Principles of ultrasound doppler velocimetry (a) transducer emitting ultrasound wave (b) received ultrasound signal (c) velocity profile (Takeda, 1995)Figur 4.1 Principer för doppler ultraljudsmätning (a) givare för ultraljud (b) erhållen ultraljudssignal (c) hastighetsprofil (Takeda, 1995)In Figure 4.2, the transmission and reflection of an ultrasound wave from the moving particles inside the acoustic beam are shown.
              Figure 4.2 Transmission and reflection from a moving particle inside the acoustic beam (Ouriev, 2000)Figure 4.2 Överföring och reflektion från en partikel i rörelse inom en akusisk signal (Ouriev, 2000)The transducer is static with respect to the reflector particle and if the particle is moving with non-zero velocity into the acoustic wave, then doppler shift occurs. The received signal frequency is doppler shifted and can be expressed asf  fc  vTP ………………..4.3r e c  vTP wherefr is received frequency, fe (or f0 ) is the emitted frequency and vTP is the velocity ofthe target particle. In Figure 4.1, the ultrasound wave transmission and the reflected echo receiving is shown. After The second doppler shift the velocity of the moving reflector particles can be expressed asv  c  fd2fe cos ………………..4.4Here the doppler shifted frequency fd is the difference between the emitted frequencyand the received frequency. The time interval between two consecutive echoes is measured. If the time interval is t between the emission of the pulse and the receptionof the backscattered echo, then the distance of the moving particle from the transducer, x along the measuring axis can be given asx  c  t2………………..4.5The echoes are amplified to come over the attenuation of ultrasound energy loss due to the pipe wall and the liquid materials. The doppler shift frequencies are measured continuously and a velocity profile with velocity v can be obtained as a function of x.Several doppler shifted echoes will be received in a certain time period. This very small time period should be set before the experiment and is known as a ‘gate’. Each gate gives a single value of velocity which is measured from the mean value of total doppler energy of that certain time. The gate is closed after each transmission and the next pulse is transmitted after the previous one has reached its maximum depth. This is known as pulse repetition frequency and the process is repeated until enough gates are available for a complete velocity profile. Windowing function is used to fix the measurement volume and the distance from each other. To obtain a good resolution a large number of gates are desirable. In Figure 4.3, a schematic diagram of a measuring window is shown. In UVP-DUO-MX from Met-Flow SA, Switzerland it is possible to choose upto 2048 gates, as required.
              Figure 4.3 Diagram of measuring window in ultrasound beam (Ouriev, 2000) Figur 4.3 Diagram over “mätfönstret” in en ultraljudssignal (Ouriev, 2000)The sampling frequency and the aliasingAnalog data is received in pulsed doppler ultrasound instruments and the analog signal is converted to digital signal by sampling the signal in certain points. The sampling frequency is the sampling rate per unit time and it is determined from the sampling interval, which is the time between two successive pulse emissions. It is also known asthe pulse repetition frequency, Fprf (Wiklund, 2003). The maximum measurablefrequency is determined by the theorem of ‘Nyquist frequency’. According to this theorem the maximum measurable frequency is less than or equal to the half of the sampling frequency, expressed asfmax Fprf2………………..4.6Here fmax is the Nyquist frequency. If the measured frequency is higher than theNyquist frequency then the lower frequency regions will be overlapped and it will cause distortion. This effect is called aliasing.Maximum depth and maximum velocityThe maximum depth of the ultrasound wave is limited by pulse repeated frequency, Fprf and signal to noise ratio (SNR). The ultrasound echo has to be reflected and then come back to the transducer before emitting a new pulse. The maximum measurable depth isexpressed asPmax   c  2Fprf………………..4.7Here Pmax is the maximum measurable depth, c is the velocity of transmitted pulse in thefluid medium. Consequently for a larger depth, lower frequencies should be used.Since the maximum measurable doppler shift is limited by Nyquist theorem, the maximum velocity is also limited. The maximum detectable velocity is expressed asVmax cFprf4F0………………..4.8Subsequently the limiting condition can be obtained from equation 4.7 and 4.8, expressed asP  V  c2max max8F0………………..4.9We can see that for constant pulse velocity and emitted frequencies, the maximum depth and velocity is dependent on each other (Takeda, 1991). In higher velocities the penetration depth will reduce and vice versa. However higher velocities can be achieved with the same penetration depth by reducing the transducer frequency.Doppler shifted frequency or time-phase lagThe UVP method does not use the doppler shifted frequency (fd) but measure the time- phase lag for the reflection of the emitted US wave for each particle. The pulse repetition frequency ( Fprf ) is used to determine the velocity of the particles. There is an ongoing debate that if it should be called a doppler shifted method.Doppler angleThe Doppler angle is the angle between the ultrasound beam and the direction of the flowing particles inside the pipe. As the ultrasound doppler instruments measure velocities along the ultrasound beam axis, it should be multiplied by a factor 1/cosθ in order to achieve the velocity in the direction of the main flow. An illustration of the doppler angle is shown in Figure 4.4 where both particles are moving with the samevelocity, implying that the travelled distances is the same for both cases.d1andd2 are the distance travelled, relative to the beam direction. If the doppler angle is lower, as we can see in Figure 4.4,1  2 , the perpendicular distance h1 is larger thanh2. A longer perpendicular distance will cause a velocity spread for all the particles inside the beam and generate a spectrum of doppler shift frequencies.
              Figure 4.4 Variation of the velocity spread of the particles with respect to the doppler angle1 &2 (Ouriev, 2000)Figur 4.4 Variation av hastighetsspridning på partiklarna I förhållande till Dopplervinklarna 1 &2 (Ouriev, 2000)The accuracy of the measured velocity is dependent on the pulse doppler spectrum and a narrow spectrum is desirable. Based on available literature, a doppler angle of 600-800 is optimum for the accuracy of velocity estimation (Birkhofer, 2007).
            2. ‌Velocity estimation using time/frequency domain based signal processingDoppler shift frequencies are obtained continuously in order to obtain instantaneous velocity profiles. The change of phase between two consecutive pulses is measured to determine the velocity. Multiple vectors are acquired along a single scan line while the transducer is stationary and the change in phase at every channel along the scan line is calculated. Most commercially available ultrasound equipments are using time domain method. The mean frequency of each channel can be estimated in time domain using the cross correlation of two consecutive pulse emissions.The advantage of the time domain is that it does not require very fast electronics. There are some difficulties in detecting the doppler shift from a single echo for the instruments based on pulse doppler method. As lots of echo receptions are required to obtain the full profile, the time resolution is limited to 10 ms. Time domain algorithms are superior to frequency domain but does not provide the whole spectra. Not so much information about the quality of the measurements are available in time domain which means that the time domain method is found disadvantageous for real time and high time resolution equipments. From frequency domain one can have the spectral distribution of the velocity profile implying that it is actually known in what volume the velocity profiles are measured and the quality of the measurement.In frequency domain, frequency spectrum is obtained from demodulated echo amplitude (DMEA) using fast Fourier transformation (FFT). The average doppler shift frequency at each radial point is calculated by weighted averaging of the frequency spectrum. The velocity in the direction of the flow is obtained from the doppler shifted frequencies as shown in equation 4.4.
            3. UVP monitor‌The UVP monitor is used to measure the velocity profiles continuously during the fluid flow. Ultrasound waves are emitted and received by the transducers and the integrated data acquisition and processing softwares of the UVP monitor delivers the result. It is based on the ultrasound pulse doppler velocimetry principle. Wiklund (2007), Birkhofer (2007), Kotze (2007) used the UVP-Duo instrument of Met-Flow, SA which can emit pulses of 1 to 32 cycles with a base frequency of 0.5 MHz, 1 MHz, 2 MHz, 4 MHz and 8 MHz respectively. The emitted voltage can be 30, 60, 90 and 150 V and the maximum pulse repetition frequency is 1024 Hz. It is possible to use up to 2048 gates per channels in order to obtain a good resolution of the velocity profile. The UVP monitor adjusts the attenuation of the received echo signal as it increases with increased depth. This is possible by using an amplification procedure which follows the exponential law. A detail description of the UVP monitor can be found in Birkhofer (2007) and Met-Flow, 2002.

        2. ‌UVP-PD METHOD

          1. ‌Introduction

            The term UVP – PD represents Ultrasound Velocity Profiling using Pressure Difference. It consists of the continuous measurement of velocity profiles using ultrasound pulsed doppler velocity profiling and the pressure difference between two certain points. The concept of combining UVP with pressure difference was implemented around 1993 when the Met-Flow UVP monitor became commercially available. The concept is described by Muller (1997) and it is discussed in other literatures, such as Brunn et al (1993), Muller et al (1997) etc. A large number of publications were presented by Ouriev (2000) and recent developments were performed by Wiklund (2007) and Birkhofer (2007).

          2. Principles of the UVP-PD method

            ‌The basic principles of the UVP-PD method come from the capillary viscometry concept originating from a force balance over a cylindrical fluid element in fully developed, steady state, laminar pipe flow. The relationship between the velocity distribution, shear stress, shear rate and (shear rate dependent) viscosity can be shown by Figure 5.1
            Figure 5.1 Link between velocity distribution, shear stress, shear rate and viscosity for a Newtonian fluid (n=1) and shear thinning fluid (n<1)Figur 5.1 Sambandmellan hastighetsfördelning, skjuvspänning, deformationshastighet och viskositet för en Newtonsk vätska (n=1) och en skjuvförtunnande vätska (n<1)Examples of a Newtonian and a shear thinning fluid are shown in the Figure 5.1 for five moving particles (reflectors) inside a pipe. In the first segment we can see the velocity distribution, as measured by UVP over the diameter of the pipe. In the second segmentthe distribution of the shear stress, as measured by the pressure difference (PD) and independent of the velocity profiling is shown. The third segment shows the distribution of the shear rate accross the pipe diameter which is dependent on the first derivative (dv/dr) of the velocity profiles. In the fourth segment the viscosity is shown which is derived from the flow curve, i.e. shear stress vs shear rate.

          3. ‌Data acquisition and software

            The velocity in different points of the pipe is obtained from the velocity profile and the pressure difference, measured by the pressure sensors. By using, e.g. rheological models, the flow curve and other rheological parameters are determined. In general, the UVP-PD setup consists of an UVP DUO monitor, flow adapter with ultrasound transducers, highly accurate pressure sensors for measuring the pressure difference, digital oscilloscope, mass flow meter, volumetric flow meters, water tank and a pump. A pc with data acquisition software is connected and the data acquisition and processing steps are shown in Figure 5.2. The data acquisition steps and the UVP-PD setup varies depending on the type of experiment. A MATLAB (Math Works, Natic, MA, USA) based application with Graphical User Interface (GUI) has been developed by Wiklund et al (2007) for the data acquisition and processing. The tasks that can be performed by this software as shown in Figure 5.2:
            Figure 5.2 Data acquisition and processing flowchart of the UVP-PD method (Wiklund et al, 2007)Figur 5.2 Flödesschema för data insamling och bearbetning med UVP-PD metoden (Wiklund et al, 2007)The data is acquired and stored in the memory as a MATLAB file. It is possible to read a saved MATLAB file associated with the UVP monitor application or raw binary data for post processing. The velocity profile is determined from the power spectra of the baseband signal and the flow curve can be found by using rheological models such as power law, Herschel Bulkley etc or by using the gradient method. The following results can be obtained:
            • Power spectra of a single profile or the average of several profiles including the velocity determination
            • Velocity profile from time domain
            • Rheological properties such as viscosity, yield stress, consistency index such as n, k and plug radius
            • Flow curve, i.e. shear stress vs shear rate
            • Velocity of sound
            • Temperature and flow rate
            • Animations of the velocity profile over time

          4. Acoustic characterization

            ‌The velocity of sound is an important parameter when using the UVP-PD method and If the measured velocity is incorrect, the velocity of the fluid particles will also be incorrect. Individual methods and flow adapters have been developed to measure the sound velocity both off-line and in-line. In Figure 5.3 a schematic diagram of the setup of ultrasound transducers for measuring acoustic properties off-line is shown. Here two transducers are used, one for emitting ultrasound waves and the other working as a receiver.‌
            Figure5.3 Schematic diagram of the transducer setup for the acoustic measurements off-line(Wiklund 2007)Figur5.3 Schematiskt diagram över givarkonfigurationen för akustiska mätningar off- line (Wiklund 2007)This technique is known as ‘pulse echo time of flight’ or ‘acoustic time of flight measurement’. The ultrasound pulse emitting transducer is connected to a UVP monitor and the receiver transducer is connected to an oscilloscope and a master PC. The sound velocity is determined from the measured time of flight ( t ) and the fixed distance between the transducers. The attenuation is measured as peak-peak voltage of transmitted ultrasound and it increases with an increasing concentration of solids in the fluid. Distilled water is used as a reference sample to measure the variation of attenuation and peak-peak voltage. The velocity of sound is temperature dependent and increases approximately 50m/s over the temperature range of 25-500C.The acoustic measurements for the UVP-PD setup is in detail described by Wiklund (2007).

          5. Previous studies based on UVP-PD method

            This section presents a brief overview of various published research work based on the UVP-PD method, see Table 5.1.Table 5.1 Previous studies based on the UVP-PD method Tabell 5.1 Tidigare studier baserade på UVP-PD metoden

            Research

            Group

            Tested Material / Type of work

            Published by


            University Erlangen

            Nurnberg, Germany

            Aqueous Hydroxypropyl Aqueous Polyacrylamide


            Brunn et al, 1993

            4000 ppm Aqueous Polyacrylamide

            Muller et al, 1997

            Flow process of Polyacrylamide solution

            Wunderlich and Brunn, 1999

            Body lotion

            Brunn et al, 2004


            ETH Zurich

            Feasibility studies of UVP-PD method, Semester Work

            Cantz, 1994

            Feasibility studies of UVP-PD method, Diploma Work

            Drost and Wagner, 1994

            PhD Thesis

            Ouriev, 2000

            Chocolate crystallization process

            Ouriev and Windhab, 1999

            Fat crystallization

            Ouriev et al, 1999

            Corn starch in glucose syrup diluted by water (Shear thickening fluid)

            Ouriev, 2002

            Time averaged flow mapping of shear thinning and shear thickening suspensions

            Ouriev and Windhab, 2003

            Transient flow and pressure driven shear flow of highly concentrated suspension

            Ouriev and Windhab, 2002,2003

            Chocolate suspension including cocoa butter with 60% solid in pre-crystallization process

            Ouriev et al, 2004

            PhD Thesis on model and cocoa butter suspension

            Fat crystallization process of cocoa butter

            Birkhofer, 2007 Birkhofer et al, 2007


            SIK, Sweden

            CPUT, South Africa


            Shear thinning surfactant solutions and cellulose suspensions

            Johansson and Wiklund, 2001.

            Wiklund et al, 2001

            Application of UVP-PD in the food industry

            Wiklund, 2003


            Pulp suspensions

            Wiklund et al, 2004 Wiklund et al, 2006


            Food and industrial suspensions

            Wiklund and Stading, 2008

            Wiklund et al, 2010

            Methodology of UVP-PD technique

            Wiklund et al, 2007

            Mineral suspensions

            Kotze´, 2007

            Carboxy Methyl Cellulose

            Kotze´ et al, 2010


            UC Davis, USA

            Microcrystalline cellulose gel, Xantham gum solution, starch gels, polymer melt

            Powell et al, 2006

            Diced tomatoes suspended in tomato slurries

            Dogan et al, 2002

            Flow of tomato concentrated with three different amount of solid content

            Dogan et al, 2003

            6% (w/w) acid thinned and native corn starch including gel

            Dogan et al, 2005a

            Polymer melt suspensions

            Dogan et al, 2005b

            65.70 Brix corn syrup and 4.30 Brix tomato juice

            Choi et al, 2002

            Matlab based graphical user interface program implemented for UDV based viscometry

            Choi et al, 2005

        3. ‌MATERIALS

          Due to ease of preparation and use, wide availability and a relative low cost, cement- based materials are the most commonly used grouts for permeation grouting. Cement can be divided into two main groups, Portland cement and slag cement, with different chemical composition. Depending on the fineness and maximum particle size, cement can be distinguished as standard or micro-fine cement. For grouting purposes, the trend has been directed to achieving as fine cement particles as possible. However, it has been found that very fine cement are difficult to handle and disperse due to the increased interaction between the particles that comes with increasing specific surface.

          1. Micro cement

            ‌In this work, a relatively fine cement has been used, Cementa Injektering 30. It has been found that this has superior characteristics with respect to penetrability compared to more fine cements (Draganovic, 2010).Particle size distributionCementa Injektering 30 has a particle size distribution where 95 percent of the cement particles are less than 30 μm in size. The particle size distribution is shown in Figure 6.1.‌
            Figure 6.1 Particle size distribution of Cementa Injektering 30 Figur 6.1 Partikelfördelning för Injektering 30Properties of micro cement Injektering 30 are shown in Table 6.1Table 6.1 Properties of Injektering 30 from Cementa Tabell 6.1 Egenskaper för Injektering 30 från Cementa

            Properties

            Description

            Physical properties

            Compact density approximately 3100-3200 kg/m3. Bulk density 800-1500 kg/m3.

            Chemical properties

            MgO maximum 5% by weight. SO3 maximum 3.5% by weight and chloride maximum 0.1% by weight.

            Setting time

            100 minutes

          2. Additive

            Cementa SetControl II (SC) is a high performance setting time regulator and dispersing additive that is especially suitable for grouts based on Cementa Injektering 30, Ultrafin 16 and Ultrafin 12. It is based on sulphonated naphthalene polymers and nitrate. Thecolor of the SetControl II is yellowish brown and its density is 1476 kg/m3, pH value approximately 6 and dry content 45%.

          3. ‌Sample preparation

            A total number of 8 batches were made using w/c ratio 0.8 and 06 with and without SetControl II (SC). Sample preparations for the different batches are shown in Table6.2. The mixing time in the high speed mixer was 4 minutes.Table 6.2 Sample preparation for different w/c ratio Tabell 6.2 Provdata för olika w/c tal

            Batch Number

            w/c ratio

            SetControl II (% by weight)

            1

            0.8

            -

            2

            0.6

            2

            3

            0.8

            -

            4

            0.6

            -

            5

            0.8

            -

            6

            0.8

            2

            7

            0.6

            2

            8

            0.8

            2

        4. ‌EXPERIMENTAL SET-UP

          To investigate the feasibility of the UVP-PD method under practical grouting conditions, it has been important to use as much standard grouting equipment as possible. In order to achieve field like conditions, an ordinary grouting rig has been used, including normal pressure hoses. The grouting rig was placed outside on a parking lot and connected to the UVP-PD equipment, placed under a garage roof, forming a closed experimental flow loop.

          1. ‌Flow loop characteristics

            The experimental flow loop consists of the following parts:
            • UNIGROUT E22H, grouting rig
            • LOGAC, pressure and flow meter
            • UVP flow adapter
            • Pressure sensors
            • Temperature sensor
            • Grouting hoses
            • Stainless steel pipes
            A schematic diagram of the flow loop is shown in Figure 7.1. The pressure sensors were mounted on each side of the 4 MHz transducers and separated by a distance of 1.3 meters. Two 10 m and one 2 m grouting hose pipe of 25 mm inner diameter was used. The inner diameter of the stainless steel pipe for the flow adapter was 22.5 mm. All the measurements were performed in ambient temperature of approximately 21 0 C. One ball valve was added close to the agitator to control the flow of the grout mixture when it was returning back to the agitator tank. A lever, was integrated with the mixer to control the flow from the mixer to the agitator. Another ball valve was placed after the pump to control the flow from the agitator to the UVP-PD test section.‌
            Figure 7.1 Schematic diagram of the flow loop Figur 7.1 Schematiskt diagram over försöksuppsättningen
            1. UNIGROUT E22HThe UNIGROUT E22H is a complete grouting rig, manufactured by Atlas Copco, consisting of a mixer, agitator, pump, control unit and the necessary hoses. The rig was used to produce a grout with the same properties as would be the case under field conditions.Grout mixer, Cemix 203HCemix 203H is a high speed colloidal mixer consisting of a container and impeller. After mixing, the grout is pumped in to the agitator. The volume of the mixer is 200 L and the mixing capacity 0-3 m3/h.Grout agitator, Cemag 402HCemag 402H is a slow running agitator consisting of a cylindrical container with angular base and an inclined mixer shaft fitted with two pair of blades. The volume of the agitator is 400L and the rotational speed of the agitator shaft is 60-70 rpm.Grout pump, PumpacPumpac is a hydraulic piston pump based on the double acting pump principle. The pump cylinder diameter is 110 mm and the grout flow capacity is up to 0-120 l/min. Two grout pressure setting levels are available, a low pressure range operated at 2-10 bars and a high pressure range at 8-100 bars. In the presented test, the low pressure range was always used as the transducer connection could only sustain up to 20 bar.The UNIGROUT E22H is shown in Figure 7.2
              Figure 7.2 UNIGROUT E22H used for the experimental work Figur 7.2 UNIGROUT E22H som använts för experimenten
            2. ‌LOGAC‌An Atlas Copco LOGAC 4000 was used, consisting of a computer based recording system for storing and sampling data during a grouting operation. The parameters that can be logged and stored on a PC card are flow, pressure, volume, time and real time, recorded on the card at every 10th seconds. The CFP meter unit consists of an electromagnetic flow meter and a pressure meter. The flow meter operates in a range of 0-200 l/min with a maximum allowed pressure of 40 bar. The LOGAC device was used as a reference, to compare the flow rate with the one achieved by the UVP method. In the presented case the flow rate was always maintained within 15-30 l/min. The LOGAC experiment is shown in Figure 7.3.
              Figure 7.3 LOGAC used for the experimental work Figur 7.3 LOGAC som använts i experimenten7.1.3. UVP-PD instrumentsFlow adapter with ultrasound transducerIn this experiment two 4 MHz ultrasound transducers (TR0405LH-X; Signal-Processing SA, Savigny, Switzerland), high temperature, were fitted with the flow adapter. The flow adapter was made out of stainless steel with an inner diameter of 22.5 mm andwith a pressure limit of 20 bars. The transducers were mounted through cavities in the pipe wall, with a diameter equal to the housing diameter of the transducers. The transducers were installed at a distance equal to the near field distance to avoid this region, where the ultrasound field is highly irregular. The flow adapter and transducer installation used for this experiment is shown in Figure 7.4.These transducers allow measurements directly from the transducer front, implying that more or less zero velocity at the wall can be recorded. The active and outer diameters of the transducers are 5 mm and 8 mm respectively. The transducers were fixed inside the flow adapter in a horizontal plane, to minimize the sedimentation effect, opposite to each other with a doppler angle (between the flow direction and the transducer axis)
              Figure 7.4 Flow adapter with 4MHz transducers used for the experiment Figur 7.4 Flödesadapter med 4 MHz givare som använts i experimentenof 700 and 1100 respectively. The near field distance for these transducers are 7 mm.UVP DUOThe velocity profile measurements were performed with a pulser/receiver instrument, UVP-DUO MX (Met-Flow, SA, Lusanne, Switzerland) model with a multiplexer. The instrument firmware and driver software were modified to allow access to the demodulated echo amplitude data (DMEA; raw data which is not possible to obtain using the standard instruments). The UVP DUO instrument and other hardware devices were connected to a master PC via Ethernet and a DAQ card (National Instruments, ABB). A MatLab based software with graphical user interface (Rheoflow) was used to control all hardware devices for data acquisition, signal processing, visualization of the data and real time monitoring of the rheological properties. UVP data acquisition was implemented using an active X library (Met-Flow, SA). A high speed digitizer card (Agilent Acquiris) was used as an integral part of the data acquisition scheme, enabling simultaneous measurements of the velocity profiles and acoustic properties.Pressure sensorsTwo differential pressure sensors (ABB 256DS, ETP80,ABB Automation Technology Products AB, Sollentuna, Sweden), 45V DC, 20 mA, PS 40 bar were used to measure the pressure difference over a distance of 1.3.UVP-PD experimental parametersThe UVP-PD experimental parameters used for this experiment are shown in Table 7.1.Table 7.1 Experimental parameters for UVP-PD Tabell 7.1 Experiment parametrar för UVP-PD

              Parameter

              Value

              Ultrasound frequency (MHz)

              4

              Cycles per pulse

              2-4

              Voltage (V)

              50-150

              Transducer active element diameter (mm)

              5

              Spatial resolution (mm)

              0.37-0.74

              Repetitions per pulse

              128-512

              Sampling time per profile (ms)

              104-115

              Doppler angle (0)

              Number of Time domain profiles (steady state flow) Number of FFT profiles (steady state flow) Sampling time for pressure difference (ms) Temperature (0C)

              Length of pipe between pressure sensors (m)

              Volumetric flow rate range (l/min)

              70/110

              500

              30

              100

              16-20

              1.3

              15-30

          2. Experimental Procedure

            ‌The experiments were performed in the following steps:
            1. The mixer was filled with water and the whole system was operated with water for several minutes in order to calibrate the distance between the transducers.
            2. The mixer was filled with the required amount of water for a certain water cement ratio. Cement was added after the high speed mixer was switched on.
            3. The mixing was performed for 4 minutes. SetControl II, if used, was added after mixing for 2 minutes.
            4. The mixture was shifted from the the high speed mixer to the agitator.
            5. The pressure level was set for the pump. For these experiments a low range of 1-4 bar pressure was always used.
            6. The mixture was pumped through the system including the LOGAC and the UVP- PD flow adapter. A ball valve was used to regulate the flow rate and keep it between 15- 30 l/min.
            7. The pressure and flow rate was continuously recorded by the LOGAC at every 10 seconds’.
            After starting, the UVP settings were altered and tuned to get the best result. Maximum penetration depth and frequency was optimized to change the pulse repetitions frequency and to measure the prevailing flow rate.

          3. ‌Off-line measurement instrument‌

                1. ‌ARES-G2 rheometerAn ARES-G2 rheometer was used to verify the in-line measurements. It is based on the deformation controlled design, where deformation or shear rate are applied to the same sample via rotating outer cylinder or plate at the bottom. ARES G2 from TA Instruments is a controlled stress, direct strain and controlled shear rate rheometer. ARES G2 uses smart swap geometries with automatic detection including an integrated magnetic cylinder that stores unique geometry information. The information is automatically read and the software is configured with appropriate parameters (type, dimension, material, etc).Experimental parameters are shown in Table 7.2Table 7.2 Experimental parameters for ARES-G2 Rheometer Tabell 7.2 Försöksparametrar för ARES-G2 Rheometer

                  Parameter

                  Remarks

                  Geometry

                  27mm DIN, Concentric cylinder

                  Temperature(0C)

                  20

                  Soak time (s)

                  10

                  Number of flow sweeps

                  2 (low to high shear rate and vice versa)

                  Shear rate(1/s)

                  0.1-1000

                  Points per decade

                  10

                  Equilibration time(s)

                  5

                  Averaging time (s)

                  5

                2. Brookfield DV-II+ pro (LV) viscometer
            Brookfield DV-II+ pro (LV) viscometer from Brookfield Engineering was used for off- line measurements. This experiment was performed at the laboratory of KTH. The experimental parameters are shown in Table 7.3. Measurements were done after mixing the sample for 4 minutes and after agitating for 2 hours respectively. Results of Brookfield viscometer are shown in Appendix A.Table 7.3 Experimental parameters for Brookfi