8/13/2019 Koehler Rheology v1
1/32
Tenth CANMET/ACI International Conference on Recent Advances in
Concrete Technology and Sustainability Issues
Use of Rheology to Design, Specify, and
Manage Self-Consolidating Concrete
Eric Koehler
W.R. Grace & Co.
8/13/2019 Koehler Rheology v1
2/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 2
Outline
Rheology
Definition Measurement
SCC Rheology
Specification
Design
Management
Case Studies
Formwork pressure
Segregation resistance
Pumpability
8/13/2019 Koehler Rheology v1
3/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 3
Concrete Rheology
Rheology is the scientific description offlow.
The rheology of concrete is measuredwith a concrete rheometer, whichdetermines the resistance of concreteto shear flow at various shear rates.
Concrete rheology measurements are
typically expressed in terms of theBingham model, which is a function of:
Yield stress: the minimum stress to initiateor maintain flow (related to slump)
Plastic viscosity: the resistance to flow onceyield stress is exceeded (related to
stickiness) Concrete rheology provides many
insights into concrete workability.
Slump and slump flow are a function ofconcrete rheology.
Shear Rate, (1/s)
ShearStress,
(Pa)
Re
sults
The Bingham Model
0
slope = plastic viscosity ()
intercept = yield stress (0)
Flow Curve
8/13/2019 Koehler Rheology v1
4/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 4
Workability and Rheology
Workability: The ease with which[concrete] can be mixed, placed,
consolidated, and finished to ahomogenous condition. (ACIDefinition)
Workability tests are typicallyempirical
Tests simulate placement condition andmeasure value (such as distance or
time) that is specific to the test method
Difficult to compare results from one testto another
Multiple tests needed to describedifferent aspects of workability
Rheology provides a fundamental
measurement Results from different rheometers have
been shown to be correlated
Results can be used to describe multipleaspects or workability
ACI 238.1R-08 report describes 69
workability and rheology tests.
8/13/2019 Koehler Rheology v1
5/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 5
Concrete Flow Curves (Constitutive Models)
0
ba 0
ba
ba
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 specificapplications (e.g. pumping)
Very stiff concrete behaves more as a solid than a liquid. Suchmixtures are not described by these models.
8/13/2019 Koehler Rheology v1
6/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 6
Concrete Rheology: Non-Steady State
Static Yield Stress
minimum shear stress to initiate flow fromrest
Dynamic Yield Stress
minimum shear stress to maintain flow afterbreakdown of thixotropic structure
Plastic Viscosity
change in shear stress per change in shearrate, above yield stress
Thixotropyreversible, time-dependent reduction inviscosity in material subject to shear
Shear Rate (1/s)
ShearStress(P
a)
Time (s)
Torque(
Nm)
concrete sheared at constant, low rate
Flow Curve Test
Stress Growth Test
concrete sheared at various rates
maximum stress from rest
= static yield stress
area between up and down
curves due to thixotropy
slope = plastic viscosity
intercept =dynamic
yield stress
Concrete exhibits different rheology
when at rest than when flowing.
Thixotropy is especially critical in highly flowable concretes.
8/13/2019 Koehler Rheology v1
7/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 7
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
8/13/2019 Koehler Rheology v1
8/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 8
Thixotropy Manifestation in Concrete Delivery
Change in yield stress from mixing through delivery and placement
Dynamic Yield StressFull Breakdown,No Thixotropy
Static Yield Stress of
Non-Agitated SCCNo Breakdown, Full
ThixotropyStatic Yield Stress
of SCC During
Placement
Time from Mixing
YieldStress
Concrete is partiallyagitated during transit,
preventing full build-upof at-rest structure
Concrete is discharged into formsresulting shearing causes full
breakdown of at-rest structuretu
Concrete is in formwork;at-rest structure rebuildsand static yield stressincreases
8/13/2019 Koehler Rheology v1
9/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 9
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)
Coaxial Cylinders Parallel Plate Impeller
Typical Rheometer Geometry Configurations
8/13/2019 Koehler Rheology v1
10/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 10
Concrete Rheometers
Tattersall Two-Point Rheometer IBB Rheometer ICAR Rheometer
BML ViscometerBTRHEOM Rheometer
8/13/2019 Koehler Rheology v1
11/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 11
ICAR Rheometer
Example Test ProtocolsStress Growt h Test
Protocol: rotate vane at 0.05 rps, concrete maintained at rest
before test
Results: static yield stress (peak stress)
Flow Cu rve TestProtocol: 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)
Vane Geometry
H: 5 in (125 mm)
D: 5 in (125 mm)
ICAR rheometer was used for the case studies described in this presentation.
8/13/2019 Koehler Rheology v1
12/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 12
SCC Rheology
SCC is designed to flow under its ownmass, resist segregation, and meetother requirements (e.g. mechanicalproperties, durability, formworkpressure, 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: ensuressegregation resistance
Plastic viscosity must not be too highor too low
Too high: concrete is sticky and difficult topump and place
Too low: concrete is susceptible tosegregation
Thixotropy is more critical for SCC dueto low yield stress
Shear Rate, (1/s)
ShearStress,
(Pa)
0
0
Similar plastic
viscosity
Near zero
yield stress
Conventional
Concrete
SCC
Yield stress is the main difference between SCC and conventional concrete.
8/13/2019 Koehler Rheology v1
13/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 13
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
8/13/2019 Koehler Rheology v1
14/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 14
SCC: Specification
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).
Slump FlowASTM C 1611
J-RingASTM C 1621
Column SegregationASTM C 1610
Filling Ability Passing Ability Segregation Resistance
Test requirements vary between lab and field.
ASTM tests are available to measure the three SCC properties independently.
By confirming robustness in lab and closely controlling materials, fewer tests may be needed in field.
8/13/2019 Koehler Rheology v1
15/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 15
SCC: Specification
Slump flow vs. yield stress for single
mixture proportion, variable HRWR
R2= 0.90
0
1
2
3
4
5
6
78
9
10
0 30 60 90 120
Plastic Viscosit Pa.s
T20(s)
T20vs. 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.
Empirical workability tests are a function of rheology.
Rheology provides greater insight into workability.
8/13/2019 Koehler Rheology v1
16/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 16
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 )
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)
8/13/2019 Koehler Rheology v1
17/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 17
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
8/13/2019 Koehler Rheology v1
18/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 18
SCC: Design
Reference:Koehler, E.P., Fowler, D.W. (2007). ICAR Mixture Proportioning
Procedure for SCC International Center for Aggregates Research, Austin, TX.
YieldStress
PlasticViscosity
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
Yield Stress (Pa)
PlasticViscos
ity(Pa.s
)
AEA
Silica FumeHRWR
Water
Effects of Materials and Mixture Proportions on Rheology
8/13/2019 Koehler Rheology v1
19/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 19
SCC: Design
0
5
10
15
20
25
30
0 30 60 90 120
Elapsed Time (Minutes)
SlumpFlow
(inches)
PC 068
PC 059
PC 915
w/c = 0.35
0
50
100
150
200
250
0 30 60 90 120
Elapsed Time (Minutes)
D
ynamicYieldStress(Pa)
PC 068
PC 059
PC 915
w/c = 0.35
0
20
40
60
80
100
120
0 30 60 90 120
Elapsed Time (Minutes)
PlasticViscosity(P
a.s)
PC 068
PC 059
PC 915
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0 30 60 90 120
Elapsed Time (Minutes)
Thixotropy(Nm/s)
PC 068
PC 059
PC 915
w/c = 0.35
3 Different HRWRs | Same Slump Flow | Same Mix Design | Different Rheology
Reference:Jeknavorian,
A.,Koehler,E.P.,
Geary,
D.,
Malone,
J.
(2008).
ConcreteRheologywithHigh-RangeWater-ReducerswithExtended
Slum
pFlow
RetentionProce
edingsofSCC
2008,
Chicago,
Illinois.
8/13/2019 Koehler Rheology v1
20/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 20
SCC: Design
Concrete can be modeled as a concentration suspension. These model can
be used to design mixture proportions.
=Huggins coefficient
=solid volume concentration
=intrinsic viscosity
=viscosity of suspension
=viscosity of suspending medium
Factors Sub-Factors
Aggregates
Maximum Size
Grading
Shape
Paste Volume
Filling Ability
Passing Ability
Robustness
Paste Composition
Water
Powder
Air
Reference:Koehler, E.P., Fowler, D.W.
(2007). ICAR Mixture Proportioning
Procedure for SCC International Center for
Aggregates Research, Austin, TX.
ICAR Mixture Proportioning Procedure
Based on concrete as concentrated
suspension of aggregates in paste
Includes equation for calculatingrequired paste volume.
8/13/2019 Koehler Rheology v1
21/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 21
SCC: Management
The workability box is an effectiveway to ensure production
consistencyDefinition:Zone of rheologyassociated with acceptable workability(self-flow and segregation resistance)
Mixture proportions affectrheology; therefore, controlling
rheology is an effective way tocontrol mixture proportions
Workability boxes are mixture-specific
SCC encompasses a wide range ofmaterials and rheology
Rheology appropriate for one set ofmaterials may be inappropriate foranother set of materials
Larger workability box corresponds togreater robustness
0
5
10
15
20
25
30
35
40
45
50
0 50 100 150
Yield Stress (Pa)
PlasticVisco
sity(Pa.s
)
Low Flow
Good
Segregation
Example
Requires Vibration
Segregation
Good
8/13/2019 Koehler Rheology v1
22/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 22
SCC Case Studies
Formwork pressure
Segregation resistance
Pumpability
8/13/2019 Koehler Rheology v1
23/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 23
SCC Case Study: Formwork Pressure
Formwork pressure is related toconcrete rheology
Pressure is known to increase with slump
SCC often exhibits high formworkpressure due to its high fluidity
Concrete is at rest in forms, therefore,static yield stress is relevant
Static yield stress is affected by dynamicyield stress and thixotropy
SCC is placed in lifts, which takesadvantage of thixotropy
SCC must be designed to flow underits own mass and exert low formworkpressure
Low dynamic yield stress (self flow)
Fast increase in static yield stress(reduced formwork pressure)
8/13/2019 Koehler Rheology v1
24/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 24
SCC Case Study: 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
0
100
200
300
400
500
600
0 20 40 60 80 100 120
Time from Placement, Minutes
DynamicYieldStress(Pa)
Mix 1 (Base)
Mix 2 (IncreasedCA)
Mix 3 (Lower w/cm,Different Admix)
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 20 40 60 80 100 120
Time from Placement, Minutes
ThixotropicBreakdownArea(Nm/s)
Mix 1 (Base)
Mix 2 (IncreasedCA)
Mix 3 (Lower w/cm,
Different Admix)
Peterborough Trial 2 - July 12, 2006
Concrete temperature 20C
-10
-5
0
5
10
15
20
25
30
35
40
11.0 11.5 12.0 12.5 13.0
Time (Hour + Decimal)
LateralPressure(kPa)
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)
Peterborough Trial 3 - Sept 20, 2006,
Concrete temperature 21C
-20
0
20
40
60
80
100
10.0 10.5 11.0 11.5 12.0 12.5 13.0
Time (Hour + Decimal)
Lateral
Pressure(kPa)
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)
Mix 1 and 2: Fast increase in yield stress and thixotropylow
formwork pressure
Mix 3:Slow increase in yield stress and thixotropyhigh formwork
pressure
Results confirm that high static yield stress
reduces formwork pressure.
8/13/2019 Koehler Rheology v1
25/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 25
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
8/13/2019 Koehler Rheology v1
26/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 26
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 ofaggregates
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
Reference Equation
Beris, A. N., Tsamopoulos, J.A., Armstrong,
R.C., and Brown, R.A. (1985). Creeping motionof a sphere through a Bingham plastic, Journal
of Flu id Mech., 158, 219-244.
Jossic, L., and Magnin, A. (2001). Drag andStability 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 Self-
Compacting Concrete, ACI Materials Journal,
98(6), 429-439.
Rg fluidsphere )09533.0(0
Rg fluidsphere )124.0(0
Rg fluidsphere 3
40
Buoyancy + Resisting Force
-Paste rheology
-Paste density
-Aggregate morphology
-Neighboring aggregates (lattice
effect)
Gravitational Force-Aggregate density
-Aggregate size Equations relating descent of sphere to rheology
Reference:Koehler, E.P., and Fowler, D.W. (2008). Static and Dynamic
Yield Stress Measurements of SCC Proceedings of SCC 2008, Chicago, IL.
8/13/2019 Koehler Rheology v1
27/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 27
SCC Case Study: Segregation Resistance
0
5
10
15
20
25
30
35
40
45
50
0 20 40 60 80 100Dynamic Yield Stress, 0 min. (Pa)
Plastic
Viscosity,
0min.(
Pa.s
)Column Seg10%
-0.05
0.00
0.05
0.10
0.15
.
0 20 40 60 80 100Dynamic Yield Stress, 0 min. (Pa)
Thixo
tropyy,
0min.
(Nm
/s) Column Seg10%
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.
8/13/2019 Koehler Rheology v1
28/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 28
SCC Case Study: Pumpability
Concrete moves through apump line as a plug
surrounded by a shearedregion at the walls.
Higher viscosity increasespumping pressure, reduces flowrate
Unstable mixes may cause
blocking Pumping concrete in high-rise
buildings presents uniquechallenges
High strength mixes often havelow w/cm, resulting in high
concrete viscosity
Blockage can result in significantjobsite delays
4
00
4
31
341
8 wwLPRQ
Buckingham-Reiner Equation
shearedregion
plug flow
regionflow
shear stress = yield stress
wallatstressshear
radiustube
rateflow
w
R
Q
lengthtube
pressure
L
P
8/13/2019 Koehler Rheology v1
29/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 29
SCC Case Study: Pumpability
Duke Energy Building, Charlotte, NC
52 Story Office Tower (764 ft) with 9 story buildingannex
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 106psi (32 to 55 GPa)
Workability
27 +/- 2 inch spread (690 +/- 50 mm)
To meet compressive strength and elasticmodulus requirements, the high strengthconcrete mixtures were proportioned with:
Low w/c
Silica fume High-modulus crushed coarse aggregate
The resulting mixture exhibited:
High viscosity
High pump pressure
8/13/2019 Koehler Rheology v1
30/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 30
SCC Case Study: Pumpability
Duke Energy Building, Charlotte, NC
8/13/2019 Koehler Rheology v1
31/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues 31
SCC Case Study: Pumpability
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
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0.00 0.10 0.20 0.30
Rotation Speed (rps)
Torq
ue(Nm)
#1: baseline#4: Increase paste vol
#4: +VMA
#5: Increase w/cm
#5: +VMA
#6: Change agg
#6: +VMA
Duke Energy Building, Charlotte, NC
8/13/2019 Koehler Rheology v1
32/32
Tenth CANMET/ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues
Conclusions
Concrete rheology is a useful tool for specifying, designing, and
managing SCC.
Static yield stressimportant for at-rest conditions
Dynamic yield stressimportant for flowing conditions
Plastic viscosityimportant for stickiness and cohesion
Thixotropyimportant 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 tothixotropy) and viscosity
Increased pumpability: reduced plastic viscosity, stable mixture
Top Related