1. The effect of yield shear stress on flow resistance
Autumn 2016: Overview of laboratory and
numerical results
Evgeny Ramenskiy

2. Laboratory results – Autumn 2016
Mix number
Sequence number
w/c
SP (SR-N)
fi/c
Filler Grading
Solid volume fraction, Φs
Mini-slump flow
Bingham parameters
Herschel–Bulkley parameters
Measured Flow resistance, λQ
Flow-3D Flow resistance, λQ
Deviation
[cm]
τ0 [Pa]
µ [Pas]
τHB [Pa]
c [Pas]
p [Pa]
[m-% of cem.]
[m-%]
[%] 10
0.4
0.75 %
0.25
Intermediate
0.516
19.40
11.04
0.84
9.26
1.26
0.91
0.861
2.4 % 1 79
1.00 % 4 82
1.25 %
0.515 7 85
1.50 % 88
1.75 % 11
0.32
0.531
15.85
16.79
1.09
14.34
1.67
0.90
0.89
0.905
1.7 % 2 80
20.80
8.32
0.97
8.59
0.92
1.01
0.86
0.880
2.7 % 5 83
0.530
24.75
4.42
0.68
5.53
0.47
0.80
0.827
3.3 % 8 86
26.70
1.69
0.62
3.32
0.33
1.15
0.805
0.4 % 89
28.60
1.63
0.49
2.68
0.30
1.12
0.76
0.766
0.3 % 12
0.39
0.545
13.15 3 81 6 84 9 87
0.544 90 13
0.55
0.45
0.450
26.65
2.73
2.14
0.57
0.605
5.8 % 91 16 94 19 97 22
100 14
0.52
0.490
26.20
3.73
0.27
2.75
0.85
0.618
7.8 % 92
30.15
1.64
0.20
1.30
0.28
0.558
0.7 % 17 95
32.00
1.00
0.17
0.73
0.23
0.93
0.53
0.529
-0.8 % 20 98
35.10
0.14
0.18
0.94
0.503
-3.0 % 23
101
0.489
37.70
0.43
0.10
0.16
0.48
0.446
-7.0 % 15
0.59
0.502
25.05
4.40
3.22
0.56
0.81
0.596
7.7 % 93 18 96 21 99 24
102
Text in white – is data from Summer 2016 cement paste mixes.
Torjus – sick. Several mixes are not included as they don’t represent the whole series overview.
Two series were completed with Rolands help.

3. Exponential reduction of Bingham yield stress with increased SP dosage
This graph describes relationship between yield stress and SP dosage.
As expected…

4. Linear reduction of Bingham plastic viscosity with increased SP dosage
Here we see correlation of plastic viscosity and SP dosage.

5. Linear reduction of flow resistance with increased SP dosage
As a result we see the linear reduction of workability parameter lambda Q with increasing SP dosage.

6. Linear increase of mini slump flow with increased SP dosage

7. Flow resistance deviation varies in matrices with varying w/c ratio
On this graph we see flow resistance deviation of two series of cement paste (i.e. with w/c-ratio 0.4 and 0.55).
Effect of SP dosage on the cement paste varies with varying w/c-ratio.
In case of mixes with w/c-ratio = 0.4, reduction of lambda Q deviation is approximately 1.4%. For w/c=0.55, it is 14.8%. What can contribute to this variation?

8. Objective of the numerical DOE study
The objective of this study is to find out how the flow resistance behaves when simulating concrete matrixes that have a yield stress and plastic viscosity combination that cannot be described by the linear relationship.
The idea with the simulated matrixes is that they could for instance represent a situation where a matrix is not fully saturated with superplasticizer, so that the plastic viscosity could be relative low, but the yield stress could be relatively high.

9. Numerical DOE setup and results
(τ0; µ) 1 2 3 4 5 6 -
1.19; 1.37
6; 1.37
11; 1.37
16.45; 1.37
1.19; 0.84
6; 0.84
11; 0.84
16.45; 0.9
1.19; 0.52
3.5; 0.52
6.13; 0.52
11; 0.5
16.45; 0.5
1.19; 0.38
3; 0.38
4.85; 0.38
6.13; 0.3
11; 0.07
16.45; 0.07
1.19; 0.23
2.64; 0.23
4.85; 0.2
6.13; 0.07
2.64; 0.07
4.85; 0.07
(λQ) 1 2 3 4 5 6 -
0.886
0.901
0.911
0.921
0.822
0.848
0.871
0.743
0.760
0.776
0.838
0.686
0.696
0.712
0.685
0.541
0.601
0.598
0.607
0.490  -
0.452
0.479 - 

10. Numerical DOE results
(λQ) 1 2 3 4 5 6 -
0.886
0.901
0.911
0.921
0.822
0.848
0.871
0.743
0.760
0.776
0.838
0.686
0.696
0.712
0.685
0.541
0.601
0.598
0.607
0.490  -
0.452
0.479 - 
Jon’s conclusion is:
Flow resistance can be used as a single parameter to describe the flow behavior of concrete matrixes if the shear rates of cement paste is of the order of 200 s-1 (Per second) or higher.

11. FlowCyl nozzle analysis?
The pressure gradient created by the fluid weight above the nozzle may not be sufficient for the shear stress to overcome the yield stress in the nozzle.
The FlowCyl nozzle size analysis could be carried out via numerical simulation of matrix with high yield (e.g. <20Pa).
Marsh Cone has two nozzle sizes.
The FlowCyl nozzle size analysis could be carried out via numerical simulation of matrix with high yield (e.g. <20Pa).
The reference distance form the cone to the container of the FlowCyl setup. It would be advantageous to establish the reference distance as it determines the length of the stream, possibly affecting the results.

12. Other concerns
Torque of the mixer isn’t constant for mixes with high viscosity leading to improper mixing of the cement pastes. Can this contribute to the found inconsistency in the flow resistance deviations?

13. Flow-3D Numerical DOE overview
Mix number
Sequence number
Mix density
Bingham parameters
Flow-3D Flow resistance, λQ
[g/cm3]
τ0 [Pa]
µ [Pas]
1_4
103
1930
1.19
0.38
0.887
1_5
104
0.23
0.906
2_3
105
0.52
0.929
2_4
106
3.00
0.605
2_5
107
2.64
0.647
2_6
108
0.07
0.693
3_1
109
1.37
0.458
3_2
110
0.84
0.474
3_3
111
3.50
0.473
3_4
112
4.85
0.861
3_5
113
0.20
0.905
3_6
114
0.927
4_1
115
6.00
4_2
116
0.618
4_3
117
6.13
0.596
4_4
118
0.30
0.397
4_5
119
0.431
5_1
120
11.00
0.521
5_2
121
0.917
5_3
122
0.50
0.950
5_4
123
0.987
6_1
124
16.45
0.764
6_2
125
0.90
0.796
6_3
126
0.842
6_4
127
0.551
The results of the numerical simulation indicates that the flow resistance is a good measure if the shear rates is of the order of 200 s-1 or higher.