yield stress and viscosity
TRANSCRIPT
![Page 1: Yield Stress and Viscosity](https://reader034.vdocuments.net/reader034/viewer/2022050801/544a8d67b1af9f884f8b490a/html5/thumbnails/1.jpg)
Overview of ACI 238.1 R-08
Report on Measurements of Workability and Rheology of
Fresh Concrete
Chiara F. Ferraris, NIST USA
![Page 2: Yield Stress and Viscosity](https://reader034.vdocuments.net/reader034/viewer/2022050801/544a8d67b1af9f884f8b490a/html5/thumbnails/2.jpg)
Importance
Fresh concrete properties are related to the properties of hardened concrete. Poor placement or consolidation leads to problems of durability and placement.Fresh concrete properties are not always properly measured or predicted.
![Page 3: Yield Stress and Viscosity](https://reader034.vdocuments.net/reader034/viewer/2022050801/544a8d67b1af9f884f8b490a/html5/thumbnails/3.jpg)
Workability
that property of freshly mixed concrete or mortar that determines the ease with which it can be mixed, placed, consolidated, and finished to a homogenous condition.
![Page 4: Yield Stress and Viscosity](https://reader034.vdocuments.net/reader034/viewer/2022050801/544a8d67b1af9f884f8b490a/html5/thumbnails/4.jpg)
Classes of workability measurement (Tattersall 1991)
Class I qualitativeWorkability, flowability,
compactability, finishability, pumpability, etc.
To be used only in a general descriptive way without any attempt to quantify
Class II quantitative empiricalslump, compacting factor, Vebe
time, flow table spread, etc.
To be used as a simple quantitative statement of behavior in a particular set of circumstances
Class III quantitative fundamentalviscosity, mobility, fluidity, yield
value, etc.
To be used strictly in conformity with standard definitions
![Page 5: Yield Stress and Viscosity](https://reader034.vdocuments.net/reader034/viewer/2022050801/544a8d67b1af9f884f8b490a/html5/thumbnails/5.jpg)
Report ACI 238: Main Goal
How to select the proper test for the application at hand?How to interpret the results obtained to predict the performance of the concrete in the field in the fresh state?
![Page 6: Yield Stress and Viscosity](https://reader034.vdocuments.net/reader034/viewer/2022050801/544a8d67b1af9f884f8b490a/html5/thumbnails/6.jpg)
Workable concrete
no flow (zero-slump) flow like a liquid (self-consolidating concrete [SCC])Anything in between
It depends on the application!!
![Page 7: Yield Stress and Viscosity](https://reader034.vdocuments.net/reader034/viewer/2022050801/544a8d67b1af9f884f8b490a/html5/thumbnails/7.jpg)
Example of applications
Use of gyratory tester to measure workability of no-slump concreteUsing rheological measurements to solve problem with flooring groutsMeasuring batch-to-batch consistency of self-consolidating concreteTroubleshooting self-consolidating concrete mixtures
![Page 8: Yield Stress and Viscosity](https://reader034.vdocuments.net/reader034/viewer/2022050801/544a8d67b1af9f884f8b490a/html5/thumbnails/8.jpg)
WorkabilitySlumpSlump flowStability staticFilling capacityPassing ability
ViscosityYield stress
Rheology
Torque
gapTorque
R1
R2
![Page 9: Yield Stress and Viscosity](https://reader034.vdocuments.net/reader034/viewer/2022050801/544a8d67b1af9f884f8b490a/html5/thumbnails/9.jpg)
Definitions
Some concepts
![Page 10: Yield Stress and Viscosity](https://reader034.vdocuments.net/reader034/viewer/2022050801/544a8d67b1af9f884f8b490a/html5/thumbnails/10.jpg)
Bingham Model
γττ &μ+= 0Yield Stress Plastic Viscosity
Shear StressShear rate
Yield stressSt
ress
Shear strain rate
Plastic Viscosity
![Page 11: Yield Stress and Viscosity](https://reader034.vdocuments.net/reader034/viewer/2022050801/544a8d67b1af9f884f8b490a/html5/thumbnails/11.jpg)
Bingham model conceptSt
ress
Shear strain rate
Yield stress = Slump
Stre
ssShear strain rate
Plastic Viscosity
Same Yield Stress BUT
Different Plastic Viscosity
Same Plastic Viscosity BUT
Different Yield Stress
![Page 12: Yield Stress and Viscosity](https://reader034.vdocuments.net/reader034/viewer/2022050801/544a8d67b1af9f884f8b490a/html5/thumbnails/12.jpg)
Dilatant/shear thickening
Shear rate
Bingham
Newtonian
Pseudoplastic/shear thinningSh
ear
stre
ssFlow Curves
Herschel-Buckley
![Page 13: Yield Stress and Viscosity](https://reader034.vdocuments.net/reader034/viewer/2022050801/544a8d67b1af9f884f8b490a/html5/thumbnails/13.jpg)
Viscosity definition
i
ini γ
τη
&=
Stre
ss
Shear strain rate
iτ
iγ&
![Page 14: Yield Stress and Viscosity](https://reader034.vdocuments.net/reader034/viewer/2022050801/544a8d67b1af9f884f8b490a/html5/thumbnails/14.jpg)
Non-Newtonian Viscosity
0102030405060708090
100
0 10 20 30 40 50
15 min85 min105 min125 min
Shear stress (1/s)
Non
-New
toni
an V
isco
sity
(Pa.
s)i
ini γ
τη
&=
Amziane S., Ferraris C.F. “Cementitious Paste Setting Using Rheological and Pressure Measurements”, ACI Materials Journal, vol. 104 #2, 2007 pp. 137-145
![Page 15: Yield Stress and Viscosity](https://reader034.vdocuments.net/reader034/viewer/2022050801/544a8d67b1af9f884f8b490a/html5/thumbnails/15.jpg)
Yield stressA critical shear stress value below which an ideal plastic or
viscoplastic material behaves like a solid (that is, will not flow).
Once the yield stress is exceeded, a plastic material yields (deforms plastically), while a viscoplastic material flows like a liquid.
Time
Stre
ss
B
A
Time
Stre
ss
B
AA=Yield stressB= related to viscosity
Stress Controlled
Shear rate
![Page 16: Yield Stress and Viscosity](https://reader034.vdocuments.net/reader034/viewer/2022050801/544a8d67b1af9f884f8b490a/html5/thumbnails/16.jpg)
Yield stress
Time
Stre
ss AB
Time
Stre
ss
Time
Stre
ss AB
Yield stress is between A & B
B is taken as the yield stress as it is easily determined
A=Yield stressB= related to viscosity
Stre
ss
Shear rate
B
A* *
****
Stre
ss
Shear rate
B
A* *
****
Shear rate
B
A* *
****
Stress Growth
Bingham
![Page 17: Yield Stress and Viscosity](https://reader034.vdocuments.net/reader034/viewer/2022050801/544a8d67b1af9f884f8b490a/html5/thumbnails/17.jpg)
Segregation
BleedingSegregationSeparationStability – stability, dynamic– stability, static
AggregateWater
Cement/particles
![Page 18: Yield Stress and Viscosity](https://reader034.vdocuments.net/reader034/viewer/2022050801/544a8d67b1af9f884f8b490a/html5/thumbnails/18.jpg)
Segregation - Rheology
Yield stress and viscosity
Yield stress > Weight of aggregateAggregate stable
Yield stress < weight of aggregateSedimentation
Depends on viscosity how fast the aggregate will settle
![Page 19: Yield Stress and Viscosity](https://reader034.vdocuments.net/reader034/viewer/2022050801/544a8d67b1af9f884f8b490a/html5/thumbnails/19.jpg)
Consolidation From SCC to no-slump concrete
SCC: – low yield stress
• Flow on its own weight– high viscosity
• Cohesion, avoid segregation
No-slump concrete:– High yield stress
• Vibration reduced yield stress– Viscosity
![Page 20: Yield Stress and Viscosity](https://reader034.vdocuments.net/reader034/viewer/2022050801/544a8d67b1af9f884f8b490a/html5/thumbnails/20.jpg)
Finishingleveling, smoothing, consolidating, andotherwise treating surfaces of fresh or
recently placed concrete or mortar to produce desired appearance and service.
No standard tests; Related toThe viscosity of the paste?Bleeding (yield stress/viscosity of bulk)?
![Page 21: Yield Stress and Viscosity](https://reader034.vdocuments.net/reader034/viewer/2022050801/544a8d67b1af9f884f8b490a/html5/thumbnails/21.jpg)
Consistencythe degree to which a freshly mixed concrete, mortar, grout, or cement paste resists deformation
– Normal: Meets requirements for application– Plastic: deformation would be sustained
continuously in any direction without rupture.– wettest stable: maximum water content at
which cement grout and mortar will adhere to a vertical surface without sloughing.
![Page 22: Yield Stress and Viscosity](https://reader034.vdocuments.net/reader034/viewer/2022050801/544a8d67b1af9f884f8b490a/html5/thumbnails/22.jpg)
Outline of reportChapter 1 —IntroductionChapter 2 —Rheological terms related to concreteChapter 3 —Test methods, (Koehler)
Chapter 4 —Factors affecting workability of concrete, (Billberg)
Chapter 5 —Examples of using workability test methods (Daczko, Khayat)
![Page 23: Yield Stress and Viscosity](https://reader034.vdocuments.net/reader034/viewer/2022050801/544a8d67b1af9f884f8b490a/html5/thumbnails/23.jpg)
Acknowledgements
All members of ACI 238– Former ACI 236A