Use of Rheology to Design, Specify, and
Manage Self-Consolidating Concrete
Eric Koehler
W.R. Grace & Co.
Tenth CANMET/ACI International Conference on Recent Advances in
Concrete Technology and Sustainability Issues
Outline
 Rheology
• Definition
• Measurement
 SCC Rheology
• Specification
• Design
• Management
 Case Studies
• Formwork pressure
• Segregation resistance
• Pumpability
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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Concrete Rheology
 Rheology is the scientific description of
flow.
 The rheology of concrete is measured
with a concrete rheometer, which
determines the resistance of concrete
to shear flow at various shear rates.
 Concrete rheology measurements are
typically expressed in terms of the
Bingham model, which is a function of:
• Plastic viscosity: the resistance to flow once
yield stress is exceeded (related to
stickiness)
 Concrete rheology provides many
insights into concrete workability.
• Slump and slump flow are a function of
concrete rheology.
 
Shear Stress,  (Pa)
• Yield stress: the minimum stress to initiate
or maintain flow (related to slump)
Results
Flow Curve
The Bingham Model
   0  
slope = plastic viscosity ()
intercept = yield stress (0)
   (1/s)
Shear Rate,
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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Workability and Rheology
 Workability: “The ease with which
[concrete] can be mixed, placed,
consolidated, and finished to a
homogenous condition.” (ACI
Definition)
ACI 238.1R-08 report describes 69
workability and rheology tests.
 Workability tests are typically
empirical
• Tests simulate placement condition and
measure value (such as distance or
time) that is specific to the test method
• Difficult to compare results from one test
to another
• Multiple tests needed to describe
different aspects of workability
 Rheology provides a fundamental
measurement
• Results from different rheometers have
been shown to be correlated
• Results can be used to describe multiple
aspects or workability
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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Concrete Flow Curves (Constitutive Models)
 Flow curves represent shear stress vs. shear rate
 Bingham model is applicable to majority of concrete
 Other models are available and can be useful for specific
applications (e.g. pumping)
 Very stiff concrete behaves more as a solid than a liquid. Such
mixtures are not described by these models.
   0  a b
   0  
b
  0  a0 
a b
  
b
  0  a0 
a b
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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Concrete Rheology: Non-Steady State
Flow Curve Test
Concrete exhibits different rheology
when at rest than when flowing.
Static Yield Stress
minimum shear stress to initiate flow from
rest
Shear Stress (Pa)
concrete sheared at various rates
area between up and down
curves due to thixotropy
slope = plastic viscosity
Dynamic Yield Stress
minimum shear stress to maintain flow after
breakdown of thixotropic structure
intercept =
dynamic
yield stress
Plastic Viscosity
Thixotropy
reversible, time-dependent reduction in
viscosity in material subject to shear
Stress Growth Test
concrete sheared at constant, low rate
Torque (Nm)
change in shear stress per change in shear
rate, above yield stress
Shear Rate (1/s)
maximum stress from rest
= static yield stress
Thixotropy is especially critical in highly flowable concretes.
Time (s)
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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Thixotropy Manifestation in Rheology Measurements
 Increase in shear rate causes
gradual breakdown of
thixotropic structure
 Decrease in shear rate allows
re-building of thixotropic
structure
 Change in shear stress due to
change in thixotropic structure
must be taken into account
when:
• Measuring rheology

Flow curve area

Stress growth
• Proportioning concrete for
applications
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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Thixotropy Manifestation in Concrete Delivery
Yield Stress
Change in yield stress from mixing through delivery and placement
Static Yield Stress of
Non-Agitated SCC
No Breakdown, Full
Thixotropy
Concrete is in formwork;
at-rest structure rebuilds
and static yield stress
increases
Concrete is partially
agitated during transit,
preventing full build-up
of at-rest structure
Static Yield Stress
of SCC During
Placement
Dynamic Yield Stress
Full Breakdown,
No Thixotropy
Time from Mixing
Concrete is discharged into forms
resulting shearing causes full
breakdown of at-rest structure
tu
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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Rheology Measurement: Typical Geometry
 Rheometers must be uniquely designed for concrete (primarily
due to large aggregate size)
 Results can be expressed in relative units (torque vs. speed) or
absolute units (shear stress vs. shear rate)
Typical Rheometer Geometry Configurations
Coaxial Cylinders
Parallel Plate
Impeller
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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Concrete Rheometers
Tattersall Two-Point Rheometer
BTRHEOM Rheometer
IBB Rheometer
ICAR Rheometer
BML Viscometer
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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ICAR Rheometer
ICAR rheometer was used for the case studies described in this presentation.
Vane Geometry
Example Test Protocols
Stress Growth Test
Protocol: rotate vane at 0.05 rps, concrete maintained at rest
before test
Results: static yield stress (peak stress)
Flow Curve Test
H: 5 in (125 mm)
D: 5 in (125 mm)
Protocol: Immediately after stress growth test, increase vane
speed in 8 increments from 0.05 to 0.50 rps, maintain 0.50 rps
for 20 s, reduce speed in 8 increments from 0.50 to 0.05 rps
Results: thixotropy (area between up and down curves), dynamic
yield stress (intercept of down curve), plastic viscosity (slope of
down curve)
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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 SCC is designed to flow under its own
mass, resist segregation, and meet
other requirements (e.g. mechanical
properties, durability, formwork
pressure, pump pressure)
 Compared to conventional concrete,
SCC exhibits:
• Significantly lower yield stress (near zero):
allows concrete to flow under its own mass
• Similar plastic viscosity: ensures
segregation resistance
 Plastic viscosity must not be too high
or too low
 
Shear Stress,  (Pa)
SCC Rheology
Conventional
Concrete

0
Similar plastic
viscosity
Near zero
yield stress
SCC

0
   (1/s)
Shear Rate,
• Too high: concrete is sticky and difficult to
pump and place
• Too low: concrete is susceptible to
segregation
 Thixotropy is more critical for SCC due
to low yield stress
Yield stress is the main difference between SCC and conventional concrete.
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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SCC: Specification
 SCC workability is described in terms of the following:
• Filling ability
• Passing ability
• Segregation resistance (stability)

Static segregation resistance

Dynamic segregation resistance
 Each property should be evaluated independently
 Minimum requirements for each property vary by application
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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SCC: Specification
ASTM tests are available to measure the three SCC properties independently.
Filling Ability
Passing Ability
Segregation Resistance
Slump Flow
ASTM C 1611
J-Ring
ASTM C 1621
Column Segregation
ASTM C 1610
Test requirements vary between lab and field.
Property
Laboratory
(Pre-Qualification)
Field
(Quality Control)
Filling Ability
(Slump Flow)
Yes.
Yes. Provides indirect measurement of yield
stress and plastic viscosity.
Passing Ability
(J-Ring)
Yes.
No. Depends primarily on aggregates, paste
volume, slump flow.
Segregation Resistance
(Column Segregation)
Yes. Check robustness across typical changes
in materials (especially water)
No. Variations mainly depend on paste
rheology (water).
By confirming robustness in lab and closely controlling materials, fewer tests may be needed in field.
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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SCC: Specification
Empirical workability tests are a function of rheology.
Rheology provides greater insight into workability.
Slump flow vs. yield stress for single
mixture proportion, variable HRWR
T20 vs. plastic viscosity
10
2
R = 0.90
9
8
T20 (s)
7
6
5
4
3
2
1
0
0
30
60
90
120
Plastic Viscosity (Pa.s)
Reference: Koehler, E.P., Fowler, D.W. (2008). “Comparison of Workability Test
Methods for Self-Consolidating Concrete” Submitted to Journal of ASTM International.
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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SCC: Design
 Compared to conventional concrete, SCC proportions typically
exhibit:
• Lower coarse aggregate content (S/A = 0.50 vs. 0.40)
• Smaller maximum aggregate size (3/4” or less vs. up to 1 ½”)
• Higher paste volume (28-40% vs. 25-30%)
• Higher powder content (cementitious and non-cementitious, >700 lb/yd3)
• Low water/powder ratio (0.30-0.40)
• Polycarboxylate-based HRWR (to achieve high slump flow)
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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SCC: Design
Both the mixture proportions and the admixture can be tailored to
the application.
• Precast vs. ready mix
• SCC vs. conventional concrete
• Formwork pressure
• Pumpability
• Segregation resistance
• Mixing
• “Stickiness” and “Cohesion”
• Form surface finish
• Finishability
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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SCC: Design
Effects of Materials and Mixture Proportions on Rheology
Plastic Viscosity (Pa.s)
Aggregate max. size (increase)
Aggregate grading (optimize)
Aggregate angularity
Silica Fume
HRWR
Aggregate shape (equidimensional)
Paste volume (increase)
Water/powder (increase)
AEA
Fly ash
Slag
Water
Silica fume (low %)
Silica fume (high %)
Yield Stress (Pa)
VMA
HRWR
AEA
Yield
Stress
Plastic
Viscosity


























Reference: Koehler, E.P., Fowler, D.W. (2007). “ICAR Mixture Proportioning
Procedure for SCC” International Center for Aggregates Research, Austin, TX.
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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SCC: Design
3 Different HRWRs | Same Slump Flow | Same Mix Design | Different Rheology
w/c = 0.35
w/c = 0.35
250
PC 068
20
15
10
PC 068
PC 059
PC 915
Dynamic Yield Stress (Pa)
Slump Flow (inches)
25
5
PC 059
200
PC 915
150
100
0
50
0
0
30
60
90
120
0
60
90
120
w/c = 0.35
120
0.45
PC 068
PC 068
PC 059
PC 915
80
60
40
Thixotropy (Nm/s)
100
30
Elapsed Time (Minutes)
Elapsed Time (Minutes)
Plastic Viscosity (Pa.s)
Reference: Jeknavorian, A., Koehler, E.P., Geary, D., Malone, J. (2008).
“Concrete Rheology with High-Range Water-Reducers with Extended
Slump Flow Retention” Proceedings of SCC 2008, Chicago, Illinois.
30
0.40
PC 059
0.35
PC 915
0.30
0.25
0.20
0.15
0.10
20
0.05
0.00
0
0
30
90 Issues 120
0
30
60
90
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Recent Advances in Concrete
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Elapsed Time (Minutes)
Elapsed Time (Minutes)
19
SCC: Design
Concrete can be modeled as a concentration suspension. These model can
be used to design mixture proportions.
=solid volume concentration
=Huggins coefficient
=viscosity of suspension
=viscosity of suspending medium
=intrinsic viscosity
ICAR Mixture Proportioning Procedure
• Based on concrete as concentrated
suspension of aggregates in paste
• Includes equation for calculating
required paste volume.
Factors
Aggregates
Paste Volume
Reference: Koehler, E.P., Fowler, D.W.
(2007). “ICAR Mixture Proportioning
Procedure for SCC” International Center for
Aggregates Research, Austin, TX.
Paste Composition
Sub-Factors
Maximum Size
Grading
Shape
Filling Ability
Passing Ability
Robustness
Water
Powder
Air
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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SCC: Management
 The workability box is an effective
way to ensure production
consistency
Example
50
Low Flow
 Mixture proportions affect
rheology; therefore, controlling
rheology is an effective way to
control mixture proportions
 Workability boxes are mixturespecific
• SCC encompasses a wide range of
materials and rheology
• Rheology appropriate for one set of
materials may be inappropriate for
another set of materials
Plastic Viscosity (Pa.s)
Definition: Zone of rheology
associated with acceptable workability
(self-flow and segregation resistance)
45
Good
40
Segregation
Requires Vibration
35
30
Good
25
20
15
Segregation
10
5
0
0
50
100
150
Yield Stress (Pa)
• Larger workability box corresponds to
greater robustness
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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SCC Case Studies
 Formwork pressure
 Segregation resistance
 Pumpability
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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SCC Case Study: Formwork Pressure
 Formwork pressure is related to
concrete rheology
• Pressure is known to increase with slump
• SCC often exhibits high formwork
pressure due to its high fluidity
 Concrete is at rest in forms, therefore,
static yield stress is relevant
• Static yield stress is affected by dynamic
yield stress and thixotropy
• SCC is placed in lifts, which takes
advantage of thixotropy
 SCC must be designed to flow under
its own mass and exert low formwork
pressure
• Low dynamic yield stress (self flow)
• Fast increase in static yield stress
(reduced formwork pressure)
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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Mix 2 (Increased
CA)
Mix 3 (Lower w/cm,
Different Admix)
500
400
300
200
100
0
0
20
40
60
80
100
Time from Placement, Minutes
120
40
0.8
Mix 1 (Base)
0.7
Peterborough Trial 2 - July 12, 2006
Concrete temperature 20C
35
Mix 2 (Increased
CA)
Mix 3 (Lower w/cm,
Different Admix)
0.6
0.5
30
Lateral Pressure (kPa)
Mix 1 (Base)
0.4
0.3
0.2
0.1
25
20
15
Cell 13 (Hyd.Pres. 36.1 kPa)
Cell 14 (Hyd.Pres. 63.5 kPa)
Cell 15 (Hyd.Pres. 91.1 kPa)
Cell 16 (Hyd.Pres. 98.7 kPa)
10
5
0
0
-0.1
0
20
40
60
80
100
11.0
-5
120
Results confirm that high static yield stress
reduces formwork pressure.
12.0
12.5
13.0
-10
100
Peterborough Trial 3 - Sept 20, 2006,
Concrete temperature 21C
Mix 1 and 2: Fast increase in yield stress and thixotropy – low
formwork pressure
Mix 3: Slow increase in yield stress and thixotropy – high formwork
pressure
11.5
Time (Hour + Decimal)
Time from Placement, Minutes
80
Lateral Pressure (kPa)
Dynamic Yield Stress (Pa)
600
Thixotropic Breakdown Area (Nm/s)
SCC Case Study: Formwork Pressure
60
Cell 13 (Hyd.Pres. 36.1 kPa)
Cell 14 (Hyd.Pres. 63.5 kPa)
Cell 15 (Hyd.Pres. 91.1 kPa)
Cell 16 (Hyd.Pres. 98.7 kPa)
40
20
0
10.0
10.5
11.0
11.5
12.0
12.5
13.0
Time (Hour + Decimal)
-20
Reference: Koehler, E.P., Keller, L., and Gardner, N.J. (2007). “Field Measurements of
SCC Rheology and Formwork Pressure” Proceedings of SCC 2007, Ghent, Belgium
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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SCC Case Study: Formwork Pressure
Options to Reduce SCC Formwork Pressure
 Select concrete with fast build-up of static yield stress
• Attributable to thixotropy
• Must achieve concurrent with low dynamic yield stress
 Place concrete in lifts to allow build-up of thixotropic structure
 Limit pour heights and rates based on concrete rheology
 Do not vibrate concrete
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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SCC Case Study: Segregation Resistance
 SCC consists of aggregates suspended in a thixotropic, Bingham
paste
 Paste must exhibit proper rheology to suspend a particular set of
aggregates
• Static yield stress > minimum static yield stress: no segregation
• Static yield stress < minimum static yield stress: rate of descent of aggregate
depends on paste yield stress and viscosity
Gravitational Force
-Aggregate density
-Aggregate size
Equations relating descent of sphere to rheology
Reference
Beris, A. N., Tsamopoulos, J.A., Armstrong,
R.C., and Brown, R.A. (1985). “Creeping motion
of a sphere through a Bingham plastic”, Journal
of Fluid Mech., 158, 219-244.
Buoyancy + Resisting Force
-Paste rheology
-Paste density
-Aggregate morphology
-Neighboring aggregates (lattice
effect)
Jossic, L., and Magnin, A. (2001). “Drag and
Stability of Objects in a Yield Stress Fluid,”
AIChE Journal, 47(12). 2666-2672.
Saak, A.W., Jennings, H.M., and Shah, S.P.
(2001). “New Methodology for Designing SelfCompacting Concrete,” ACI Materials Journal,
98(6), 429-439.
Equation
 0  (0.09533) g  sphere   fluid R
 0  (0.124) g  sphere   fluid R
0 
4
g  sphere   fluid R
3
Reference: Koehler, E.P., and Fowler, D.W. (2008). “Static and Dynamic
Yield Stress Measurements of SCC” Proceedings of SCC 2008, Chicago, IL.
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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0.20
50
Column Seg<10%
Column Seg>10%
45
40
35
30
25
20
15
10
5
Thixotropyy, 0 min. (Nm/s)
Plastic Viscosity, 0 min. (Pa.s)
SCC Case Study: Segregation Resistance
Column Seg<10%
Column Seg>10%
0.15
0.10
0.05
0.00
-0.05
0
0
20
40
60
80
100
Dynamic Yield Stress, 0 min. (Pa)
0
20
40
60
80
100
Dynamic Yield Stress, 0 min. (Pa)
Segregation resistance increased with:
• Higher yield stress (static and dynamic yield stress assumed equal initially)
• Higher plastic viscosity
• Higher thixotropy
Reference: Koehler, E.P., and Fowler, D.W. (2008). “Static and Dynamic
Yield Stress Measurements of SCC” Proceedings of SCC 2008, Chicago, IL.
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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SCC Case Study: Pumpability
 Concrete moves through a
pump line as a “plug”
surrounded by a sheared
region at the walls.
• Higher viscosity increases
pumping pressure, reduces flow
rate
sheared
region
flow
plug flow
region
• Unstable mixes may cause
blocking
 Pumping concrete in high-rise
buildings presents unique
challenges
• High strength mixes often have
low w/cm, resulting in high
concrete viscosity
• Blockage can result in significant
jobsite delays
shear stress = yield stress
Buckingham-Reiner Equation
4

PR
4  0  1  0  
1       
Q
8L  3   w  3   w  


4
P  pressure
Q  flow rate
L  tube length
R  tube radius
 w  shear stress at wall
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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SCC Case Study: Pumpability
 Duke Energy Building, Charlotte, NC
• 52 Story Office Tower (764 ft) with 9 story building
annex
• 8 Story Parking Structure 95 ft below street level
 Concrete Mixture Requirements
• Compressive Strength

5,000 psi to 18,000 psi (35 to 124 MPa)
• Modulus of Elasticity

4.6 to 8.0 x 106 psi (32 to 55 GPa)
• Workability

27 +/- 2 inch spread (690 +/- 50 mm)
 To meet compressive strength and elastic
modulus requirements, the high strength
concrete mixtures were proportioned with:
• Low w/c
• Silica fume
• High-modulus crushed coarse aggregate
 The resulting mixture exhibited:
• High viscosity
• High pump pressure
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
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SCC Case Study: Pumpability
Duke Energy Building, Charlotte, NC
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SCC Case Study: Pumpability
Duke Energy Building, Charlotte, NC
5.0
4.5
4.0
Torque (Nm)
3.5
#1: baseline
#4: Increase paste vol
#4: +VMA
#5: Increase w/cm
#5: +VMA
#6: Change agg
#6: +VMA
3.0
 VMA and/or other changes in
mixture proportions were shown to
increase pumpability by reducing
concrete viscosity.
 Role of VMA in reducing viscosity:
• VMA results in shear-thinning behavior

Increased viscosity (thickens) concrete at rest
and at low shear rates: beneficial for reduced
formwork pressure and increased segregation
resistance

Decreased viscosity (thins) at high shear rates:
beneficial for improved pumpability
2.5
2.0
1.5
• Reduced pump stroke time confirmed
in field mix with VMA
1.0
0.5
0.0
0.00
0.10
0.20
0.30
Tenth CANMET/ACI International
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Rotation Speed (rps)
31
Conclusions
 Concrete rheology is a useful tool for specifying, designing, and
managing SCC.
• Static yield stress – important for at-rest conditions
• Dynamic yield stress – important for flowing conditions
• Plastic viscosity – important for stickiness and cohesion
• Thixotropy – important for at-rest conditions
 Rheology can be optimized to ensure concrete performance.
• Self-consolidating concrete: low dynamic yield stress, adequate plastic
viscosity and thixotropy
• Reduced formwork pressure: increased static yield stress (due to
thixotropy)
• Increased segregation resistance: increased static yield stress (due to
thixotropy) and viscosity
• Increased pumpability: reduced plastic viscosity, stable mixture
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