# Experimental Insights into Concrete Flow-Regimes Subject to Shear-Induced Particle Migration (SIPM) during Pumping

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Theoretical Background

#### 2.1. Rheology of Concrete—Single-Phase Fluid or Multiphase Suspension?

#### 2.2. Pumping of Concrete—Modeling as Two Immiscible Single-Phase Fluids or MultiPhase Suspension with Varying Rheological Properties?

^{3}/s) in a pipeline of length $L$ (m) and radius of ${R}_{Pipe}$ (m) can be represented according to Equation (6) [23]:

## 3. Materials and Methods

#### 3.1. Materials

#### 3.2. Rheological Measurements

^{−1}in the sample. For data evaluation, the methods listed in Table 2 were used. R

_{o}, R

_{i}, and H correspond to outer and inner radii, and the height of the sampling volume, respectively.

^{−7}Pa shear stress. Obviously, differences in the values of yield stress and plastic viscosity should be considered only if measured above the resolution range. Table 2 provides torque resolutions for both devices.

^{3}/h for CVC and 540 m

^{3}/h for SCC mixtures [32]. Indeed, the Sliper device can mimic the pressure loss per unit length of pipe, concrete flow behavior, including the hydrodynamics and particle–particle interaction, very well, and in addition predict the necessary pumping pressure for a given flow rate [37]. More information on data analysis can be found in [7,36].

#### 3.3. Methodologies for Capturing the Lubricating Layer and Shear-Induced Particle Migration

#### 3.3.1. Quantification of Radial/Angular Displacement of Aggregates in Fresh Concrete

#### 3.3.2. Sampling of Pumped Concrete

#### 3.3.3. X-ray Microcomputed Tomography (μCT)

## 4. Results and Discussion

#### 4.1. Impact of Aggregates’ Volume-Fraction on Rheological Properties of Concrete and Constitutive Mortar

#### 4.2. Concrete Rheology during Pumping

#### 4.3. Experimentally Determined Thickness of Lubricating Layer

- With an increasing volume-fraction of coarse particles, the thickness of the lubricating layer decreases: the migration of coarse particles is hindered when the local volume-fraction of particles in the neighboring region reaches $0.8{\varphi}_{c}$ [3,9]. With a larger $\varphi $, the equilibrium is reached faster and closer to the pipe wall; see Equation (8). Hence, a thinner lubricating layer develops (${e}_{LL.S37}>{e}_{LL.S42}>{e}_{LL.S47}$ and ${e}_{LL.C42}>{e}_{LL.C47}>{e}_{LL.C52}$) [3].
- With an increasing rate of discharge, the thickness of the lubricating layer increases: at higher discharge rates, shear rate, and its changes with respect to radial axis ($\dot{\gamma}$ and $\partial \dot{\gamma}/\partial r$, as described by Equation (7)) increase, and so does the intensity of particle migration. Since higher discharge rates were measured for CVC than for SCC (${Q}_{max,CVC}=3{Q}_{max,SCC}$), a thicker LL could be determined for CVC (${e}_{LL,C42}>{e}_{LL,S42}$ and ${e}_{LL,C47}>{e}_{LL,S47}$), despite the fact of self-compacting concrete’s containing in general a higher volume-fraction of fine particles in comparison to conventional concrete (${\varphi}_{total,CVC}<{\varphi}_{total,SCC}$); see Figure 9. The total content of fine particles, including binder and fine sand, in S42 and S47 was 4.59% and 4.29% higher than that in C42 and C47, respectively.

#### 4.4. Particle Distribution in Radial Direction

- The number of traceable particles within the range 1–2 mm was often limited to one-fourth (1/4) of the expected values (expected: ${\varphi}_{1-2}=0.0886$, measured values: $0.0235$ for S47 and $0.0223$ for C47). Therefore, the tracking of particles smaller than 2 mm in this method would not provide any additional information.
- The average surface area fractions for the particle groups 2–4 mm and 4–8 mm are larger than the expected values for both mixtures, expected: ${\varphi}_{2-4}=0.0886$ and ${\varphi}_{4-8}=0.1226$. On the contrary, for the particle group 8–16 mm, the average surface area is always less than expected. This is due to the irregular shape of the particles and their random orientation in the target cross-section.
- For particle size ranges 2–4 mm, 4–8 mm, and 8–16 mm a clear peak can be observed. It seems that the larger the particles are, the greater the distance of the peak to the pipe wall. Furthermore, the peaks are shifted from the maximum aggregate size for each group. This indicates that both wall-effect and SIPM influenced the radial displacement of the particles.

#### 4.5. Evaluation of Surface Profile during Sliper Tests

^{3}/s). $\Delta P$, $R,$ and $\eta $ are pressure loss per unit length (Pa/m), the radius of the pipe (m), and the viscosity of the Newtonian fluid (Pa·s). Equation (10) shows that the focal width of the velocity parabola is directly proportional to the ratio between the pressure loss and apparent viscosity $\Delta P/\eta $. To check whether this holds for non-Newtonian fluids as well, the inverse of plastic viscosity and the normalized radial velocities are compared in Figure 12a. The results show good correlation between these two parameters. The non-zero ordinate intercept is due to the formation of the plug during concrete flow.

## 5. Conclusions and Outlook

- The Bingham rheological parameters of concrete increase with increasing aggregates’ volume-fraction ($\varphi $). For CVC the changes are pronounced in the yield stress values in the first place, while in the case of SCC it is the plastic viscosity, which alters significantly.
- The thickness of the lubricating layer was measured on hardened concrete samples investigated after performing the Sliper tests. The thickness of the lubricating layer was not constant for the concrete compositions under investigation and varied under different discharge rates. The thickness of the lubricating layer increases with decreasing aggregate volume-fraction and with increasing discharge rate.
- The analytical thickness of the lubricating layer can be calculated using the rheological properties of concrete bulk and the lubricating layer and the output of Sliper. However, these values do not represent reality. The analytical thickness is suitable for eliminating the device-dependency of experimental rheological parameters for analytical or numerical modeling of the pumping process.
- Concrete plastic viscosity is the most influential parameter affecting the shape of the parabolic curve of velocity profile.
- In modern concretes with high volume-fractions of solid particles, the shear-induced particle migration can be severe enough to influence the local rheological properties of the pumping concrete and therefore, must be taken into consideration. In such cases, conventional analytical models using the rheological parameters obtained by means of concrete rheometers, are not sufficiently reliable to predict concrete pumping behavior.

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

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**Figure 2.**(

**a**) ConTec 5 viscometer, (

**b**) HAAKE MARS II rheometer, and (

**c**) Sliding pipe rheometer (Sliper).

**Figure 3.**Displacement of four coarse aggregates in C47 between two frames no. (

**a**) #90 and (

**b**) #110; vertical velocity in the Sliper test was 0.72 m/s.

**Figure 6.**Visible particles larger than one mm for determination of the particle distribution for S47.

**Figure 7.**The 2D images for (

**a**) C47 and (

**b**) S42 and computed 3D images for (

**c**) C47 and (

**d**) S42. The red circles mark the visible aggregates.

**Figure 8.**Yield stress and plastic viscosity for (

**a**) mortar and (

**b**) concrete. Arrows indicate the increase in reduced volume-fraction $\varphi /{\varphi}_{c}$.

**Figure 9.**Required pressure for pumping one meter of concrete in a DN125 pipe with the desired discharge rate. The relation between pressure loss and discharge rate as well as R

^{2}are given as range equations, showing minimum and maximum values.

**Figure 10.**Comparison between experimentally and analytically determined thicknesses of the lubricating layer for all concretes under investigation.

**Figure 11.**Surface area occupied by different groups of particles over the radial direction after pumping for (

**a**) S47 and (

**b**) C47. The overall average for each size is listed on the right side of the graph.

**Figure 12.**(

**a**) Relation between normalized radial velocity at $\Delta {P}_{max}=22.996$ kPa/m according to the pressure sensor from Sliper and the inverse of bulk viscosity and (

**b**) velocity profiles determined analytically.

**Table 1.**Compositions of concretes under investigation and their constitutive mortars as well as the concretes’ properties in the fresh and hardened states.

Materials | Density (kg/m^{3}) | Dosage (kg) for 1 m^{3} of Concrete | ||||||||
---|---|---|---|---|---|---|---|---|---|---|

C42 | C47 | C52 | C47c | S37 | S42 | S47 | S42c | |||

Constitutive mortar | CEM III/A 42.5 N | 2990 | 425 | 388 | 351 | 388 | 392 | 361 | 330 | 361 |

Fly ash | 2200 | - | - | - | - | 239 | 220 | 201 | 220 | |

Quartz powder | 2680 | 57 | 52 | 47 | 52 | 52 | 48 | 44 | 48 | |

Quartz sand 0.06–0.2 * | 2650 | 57 | 52 | 47 | 52 | 52 | 48 | 44 | 48 | |

Quartz sand 0–1 * | 2650 | 456 | 416 | 376 | 416 | 420 | 387 | 354 | 387 | |

Water | 1000 | 211 | 192 | 173 | 192 | 180 | 166 | 152 | 166 | |

Superplasticizer (SP) | 1056 | 3.48 | 3.18 | 2.87 | 3.18 | 11.14 | 10.26 | 9.38 | 10.26 | |

Aggregates | Quartz sand 1–2 * | 2650 | 210 | 235 | 260 | 260 | 185 | 210 | 235 | 210 |

Quartz sand 2–4 * | 2650 | 210 | 235 | 260 | 260 | 185 | 210 | 235 | 210 | |

Quartz gravel 4–8 * | 2650 | 290 | 325 | 360 | 360 | 255 | 290 | 325 | 290 | |

Quartz gravel 8–16 * | 2650 | 403 | 451 | 500 | - | 355 | 403 | 451 | - | |

Basalt 8–11 * (crushed) | 2900 | - | - | - | 197 | - | - | - | 176 | |

Basalt 11–16 * (crushed) | 2900 | - | - | - | 300 | - | - | - | 268 | |

w/b (-) | 0.50 | 0.50 | 0.50 | 0.50 | 0.30 | 0.30 | 0.30 | 0.30 | ||

SP % bwob ** | 0.72 | 0.72 | 0.72 | 0.72 | 1.77 | 1.77 | 1.77 | 1.77 | ||

$\varphi $ of agg. (> 1mm) (-) | 0.42 | 0.47 | 0.52 | 0.47 | 0.37 | 0.42 | 0.47 | 0.42 | ||

$\varphi /{\varphi}_{c}$ (> 1mm) (-) | 0.585 | 0.654 | 0.724 | 0.667 | 0.515 | 0.585 | 0.654 | 0.596 | ||

FT/SF for concrete ^{†} (mm) | 640 | 545 | 450 | 530 | 720 | 680 | 600 | 650 | ||

FT for constitutive mortar ^{‡} (mm) | 260 | 260 | 240 | 240 | 300 | 290 | 250 | 250 | ||

Air content (%) | 1.7 | 2.7 | 1.3 | 1.6 | 0.7 | 0.8 | 0.4 | 1.0 | ||

Density (kg/m^{3}) | 2340 | 2320 | 2390 | 2370 | 2320 | 2360 | 2370 | 2410 | ||

Compressive strength at 28 d (MPa) | 54.3 ± 1.3 | 50.8 ± 1.0 | 48.6 ± 1.1 | 53.7 ± 0.6 | 76.9 ± 1.6 | 78.6 ± 2.0 | 72.1 ± 0.7 | 81.1 ± 1.1 |

^{†}Flow table spread (FT) for conventional vibrated concrete (CVC) based on DIN EN 12350-5 [29] or slump flow (SF) for self-compacting concrete (SCC) based on DIN EN 12350-8 [30].

^{‡}Flow table spread (FT) for constitutive mortars based on DIN EN 459-2 [31], with 15 strokes for conventional mortars and without stroke for self-compacting mortars.

Device | Material | Geometry | Testing Profile | Transformation Equation | Torque Resolution | Angular Resolution |
---|---|---|---|---|---|---|

ConTec 5 viscometer * | Concrete | Serrated beater ${R}_{o}$ = 145 mm ${R}_{i}$ = 100 mm $H$ = 120 mm | Hysteresis loop with rotational velocity range: 0.02 to 0.62 rps | Reiner-Riwlin [1,2]: $\begin{array}{c}T=G+H\xb7N\hfill \\ {\tau}_{0}=\frac{G}{4\pi h}\left(\frac{1}{{R}_{i}^{2}}-\frac{1}{{R}_{o}^{2}}\right)\frac{1}{\mathrm{ln}\left({R}_{o}/{R}_{i}\right)}\hfill \\ \mu =\frac{H}{8{\pi}^{2}h}\left(\frac{1}{{R}_{i}^{2}}-\frac{1}{{R}_{o}^{2}}\right)\hfill \end{array}$ | 0.1 Nm | 126 mrad |

HAAKE MARS II rheometer ** | Mortar | Hollow vane ${R}_{o}$ = 35 mm ${R}_{i}$ = 26 mm $H$ = 50 mm | Hysteresis loop with rotational velocity range: 0.01 to 0.50 rps | Affine translation and calibration by reference materials [33] | 0.1 nNm | 12 nrad |

**Table 3.**The Bingham rheological parameters for CVC and the modified Bingham (MB) rheological parameter for SCC mixtures.

Parameters | Mixture | ||||||||
---|---|---|---|---|---|---|---|---|---|

C42 | C47 | C52 | C47c | S37 | S42 | S47 | S42c | ||

Concretemortar | Yield stress (Pa) | 65 | 120 | 270 | 160 | 4.0 | 5.0 | 6.0 | 5.5 |

Plastic viscosity (Pa·s) | 20 | 25 | 35 | 30 | 30 | 60 | 130 | 80 | |

Non-linear term of MB (Pa·s^{2}) | - | - | - | - | 5.5 | 5.0 | 1.0 | 5.5 | |

Mortar | Yield stress (Pa) | 21 | 21 | 30 | 27 | 2.0 | 2.5 | 6.0 | 5.0 |

Plastic viscosity (Pa·s) | 1.4 | 1.0 | 1.3 | 1.6 | 3.2 | 3.5 | 7.0 | 5.5 | |

Non-linear term of MB (Pa·s^{2}) | - | - | - | - | 0.3 | 0.2 | 0.5 | 0.6 |

Mixture | C42 | C47 | C52 | C47c | S37 | S42 | S47 | S42c |
---|---|---|---|---|---|---|---|---|

${e}_{LL}$(mm) | 1.63 | 0.96 | 1.17 | 1.71 | 1.58 | 1.57 | 2.83 | 1.31 |

Standard deviation (mm) | 0.18 | 0.10 | 0.14 | 0.12 | 0.11 | 0.10 | 0.44 | 0.12 |

Mixture | C42 | C47 | C52 | C47c | S37 | S42 | S47 | S42c |
---|---|---|---|---|---|---|---|---|

${e}_{LL}$(mm) | 1.11 | 1.04 | 0.98 | 1.25 | 1.22 | 0.95 | 0.78 | 1.06 |

Standard deviation (mm) | 0.79 | 0.99 | 0.81 | 0.84 | 0.95 | 0.71 | 0.66 | 0.79 |

**Table 6.**Average radial and vertical velocity of surface, and the plug radii for specified pressure loss.

Mixture | C42 | C47 | C52 | C47c | S37 | S42 | S47 | S42c |
---|---|---|---|---|---|---|---|---|

$\mathrm{Pressure}\mathrm{loss}\Delta P$ (mbar/m) | 153.89 | 184.90 | 226.20 | 194.84 | 163.72 | 229.96 | 277.14 | 185.39 |

$\mathrm{Average}\mathrm{vertical}\mathrm{velocity}{\upsilon}_{z,avg}$ (cm/s) | 71.69 | 72.18 | 68.13 | 72.18 | 21.93 | 28.14 | 27.73 | 17.00 |

$\mathrm{Average}\mathrm{radial}\mathrm{velocity}{\upsilon}_{r,avg}$(cm/s) | 7.93 | 6.53 | 4.31 | 4.24 | 3.90 | 1.85 | 0.00 | 1.85 |

Exp. ${R}_{plug}$(cm) | 0 | 0 | 0 | 0 | 0 | 0 | 5.53 | 0 |

Analyt. ${R}_{plug}$(cm) | 0.84 | 1.30 | 2.39 | 1.64 | 0.04 | 0.04 | 0.04 | 0.04 |

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**MDPI and ACS Style**

Fataei, S.; Secrieru, E.; Mechtcherine, V.
Experimental Insights into Concrete Flow-Regimes Subject to Shear-Induced Particle Migration (SIPM) during Pumping. *Materials* **2020**, *13*, 1233.
https://doi.org/10.3390/ma13051233

**AMA Style**

Fataei S, Secrieru E, Mechtcherine V.
Experimental Insights into Concrete Flow-Regimes Subject to Shear-Induced Particle Migration (SIPM) during Pumping. *Materials*. 2020; 13(5):1233.
https://doi.org/10.3390/ma13051233

**Chicago/Turabian Style**

Fataei, Shirin, Egor Secrieru, and Viktor Mechtcherine.
2020. "Experimental Insights into Concrete Flow-Regimes Subject to Shear-Induced Particle Migration (SIPM) during Pumping" *Materials* 13, no. 5: 1233.
https://doi.org/10.3390/ma13051233