1. Eric Koehler W.R. Grace & Co.
April 15, 2017
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

2. Outline Rheology SCC Rheology Case Studies Definition Measurement
April 15, 2017
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

3. Concrete Rheology Shear Stress, (Pa) Shear Rate, (1/s)
April 15, 2017
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:
Yield stress: the minimum stress to initiate or maintain flow (related to slump)
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.
Results
Flow Curve
The Bingham Model
Shear Stress, (Pa)
slope = plastic viscosity (m)
intercept = yield stress (t0)
Shear Rate, (1/s)
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues

4. Workability and Rheology
April 15, 2017
Workability and Rheology
ACI 238.1R-08 report describes 69 workability and rheology tests.
Workability: “The ease with which [concrete] can be mixed, placed, consolidated, and finished to a homogenous condition.” (ACI Definition)
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

5. Concrete Flow Curves (Constitutive Models)
April 15, 2017
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.
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues

6. Concrete Rheology: Non-Steady State
April 15, 2017
Concrete Rheology: Non-Steady State
Flow Curve Test
concrete sheared at various rates
Concrete exhibits different rheology when at rest than when flowing.
area between up and down curves due to thixotropy
Shear Stress (Pa)
Static Yield Stress
minimum shear stress to initiate flow from rest
Dynamic Yield Stress
minimum shear stress to maintain flow after breakdown of thixotropic structure
Plastic Viscosity
change in shear stress per change in shear rate, above yield stress
Thixotropy
reversible, time-dependent reduction in viscosity in material subject to shear
slope = plastic viscosity
intercept = dynamic yield stress
Shear Rate (1/s)
Stress Growth Test
concrete sheared at constant, low rate
maximum stress from rest
= static yield stress
Torque (Nm)
Thixotropy is especially critical in highly flowable concretes.
Time (s)
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues

7. Thixotropy Manifestation in Rheology Measurements
April 15, 2017
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

8. Thixotropy Manifestation in Concrete Delivery
April 15, 2017
Thixotropy Manifestation in Concrete Delivery
Change in yield stress from mixing through delivery and placement
Static Yield Stress of
Non -
Agitated SCC
No Breakdown, Full
Static Yield Stress
Thixotropy
of SCC
During
Placement
Concrete is
in formwork; a t -
rest structure rebuilds
Yield Stress
and
static yield stress
increases
Dynamic Yield Stress
Full Breakdown,
No Thixotropy
Time from Mixing
Concrete is
partially
agitated during transit ,
Concrete is discharged into forms
preventing full build - up
resulting shearing causes full
of at -
rest structure
breakdown of at-rest structure t u
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues

9. Rheology Measurement: Typical Geometry
April 15, 2017
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

10. Tattersall Two-Point Rheometer
April 15, 2017
Concrete Rheometers
Tattersall Two-Point Rheometer
IBB Rheometer
ICAR Rheometer
BTRHEOM Rheometer
BML Viscometer
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11. ICAR Rheometer Example Test Protocols Vane Geometry
April 15, 2017
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
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)
H: 5 in (125 mm)
D: 5 in (125 mm)
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12. Conventional Concrete
April 15, 2017
SCC Rheology
Conventional Concrete
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
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 m t0
Similar plastic viscosity
Shear Stress, (Pa)
Near zero yield stress
SCC m t0
Shear Rate, (1/s)
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

13. April 15, 2017
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

14. Test requirements vary between lab and field.
April 15, 2017
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)
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.
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15. April 15, 2017
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
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

16. April 15, 2017
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 %)
Higher powder content (cementitious and non-cementitious, >700 lb/yd3)
Low water/powder ratio ( )
Polycarboxylate-based HRWR (to achieve high slump flow)
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues

17. April 15, 2017
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

18. Effects of Materials and Mixture Proportions on Rheology
April 15, 2017
SCC: Design
Effects of Materials and Mixture Proportions on Rheology
Yield Stress
Plastic Viscosity
Aggregate max. size (increase) 
Aggregate grading (optimize)
Aggregate angularity 
Aggregate shape (equidimensional)
Paste volume (increase)
Water/powder (increase)
Fly ash
Slag 
Silica fume (low %)
Silica fume (high %)
VMA
HRWR
AEA
Silica Fume
HRWR
Plastic Viscosity (Pa.s)
AEA
Water
Yield Stress (Pa)
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

19. April 15, 2017
SCC: Design
3 Different HRWRs | Same Slump Flow | Same Mix Design | Different Rheology
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.
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues

20. April 15, 2017
SCC: Design
Concrete can be modeled as a concentration suspension. These model can be used to design mixture proportions.
=solid volume concentration
=viscosity of suspension
=Huggins coefficient
=viscosity of suspending medium
=intrinsic viscosity
ICAR Mixture Proportioning Procedure
Factors
Sub-Factors
Aggregates
Maximum Size
Grading
Shape
Paste Volume
Filling Ability
Passing Ability
Robustness
Paste Composition
Water
Powder
Air
Based on concrete as concentrated suspension of aggregates in paste
Includes equation for calculating required paste volume.
Reference: Koehler, E.P., Fowler, D.W. (2007). “ICAR Mixture Proportioning Procedure for SCC” International Center for Aggregates Research, Austin, TX.
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21. April 15, 2017
SCC: Management
The workability box is an effective way to ensure production consistency
Definition: Zone of rheology associated with acceptable workability (self-flow and segregation resistance)
Mixture proportions affect rheology; therefore, controlling rheology is an effective way to control mixture proportions
Workability boxes are mixture-specific
SCC encompasses a wide range of materials and rheology
Rheology appropriate for one set of materials may be inappropriate for another set of materials
Larger workability box corresponds to greater robustness
Example
Requires Vibration
Good
Segregation
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues

22. SCC Case Studies Formwork pressure Segregation resistance Pumpability
April 15, 2017
SCC Case Studies
Formwork pressure
Segregation resistance
Pumpability
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues

23. SCC Case Study: Formwork Pressure
April 15, 2017
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

24. SCC Case Study: Formwork Pressure
April 15, 2017
SCC Case Study: Formwork Pressure
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
Results confirm that high static yield stress reduces formwork pressure.
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
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25. SCC Case Study: Formwork Pressure
April 15, 2017
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

26. SCC Case Study: Segregation Resistance
April 15, 2017
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
Equation
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,
Jossic, L., and Magnin, A. (2001). “Drag and Stability of Objects in a Yield Stress Fluid,” AIChE Journal, 47(12)
Saak, A.W., Jennings, H.M., and Shah, S.P. (2001). “New Methodology for Designing Self-Compacting Concrete,” ACI Materials Journal, 98(6),
Buoyancy + Resisting Force
-Paste rheology
-Paste density
-Aggregate morphology
-Neighboring aggregates (lattice effect)
Reference: Koehler, E.P., and Fowler, D.W. (2008). “Static and Dynamic Yield Stress Measurements of SCC” Proceedings of SCC 2008, Chicago, IL.
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27. SCC Case Study: Segregation Resistance
April 15, 2017
SCC Case Study: Segregation Resistance
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.
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28. SCC Case Study: Pumpability
April 15, 2017
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
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
sheared region
flow
plug flow region
shear stress = yield stress
Buckingham-Reiner Equation
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29. SCC Case Study: Pumpability
April 15, 2017
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
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30. SCC Case Study: Pumpability
April 15, 2017
SCC Case Study: Pumpability
Duke Energy Building, Charlotte, NC
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues

31. SCC Case Study: Pumpability
April 15, 2017
SCC Case Study: Pumpability
Duke Energy Building, Charlotte, NC
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
Reduced pump stroke time confirmed in field mix with VMA
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues

32. April 15, 2017
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
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues