“A Scientific Approach for Determining the Workability of

Concrete”

N.AjayResearch Scholar, Dept of Civil Engg, BMSCE.

Dr.S.GirishProfessor, Dept of Civil Engg, BMSCE.

OUTLINEOUTLINE

INTRODUCTIONINTRODUCTION

WORKABILITY OF CONCRETEWORKABILITY OF CONCRETE

RHEOLOGY OF CONCRETERHEOLOGY OF CONCRETE

RHEOMETERSRHEOMETERS

CONCLUDING REMARKSCONCLUDING REMARKS

REFERENCESREFERENCES

WORKABILITY WORKABILITY

“The ease with which concrete can be mixed, placed, consolidated, and finished to a homogenous condition.”

Unless we measure the phenomenon we cannot understand the properties of workability.

Abrams suggested determining a “relative consistency” term calculated by measuring the distance fresh concrete slumped after being molded in cylinder—the slump test.

WORKABILITY (Cont..)WORKABILITY (Cont..)

Empirical Tests

WORKABILITY-DRAW BACKSWORKABILITY-DRAW BACKS

Widely used test is Slump test. Which is directly related to workability and is an empirical test.

Difficult to compare results from one test to another.

Early days of concrete- composed of cement, Aggregate & Water. Lower Water content – Lower slump & higher quality of concrete.

Today - Advance special concrete in industry. Concrete - Admixture ,Manufacturing Sand, Fibers, GGBS etc.

Tattersall Classifies the Workability of Concrete Class-I , Class-II and Class-III.

Tattersall and Banfill pointed out single-point parameter in evaluation of by empirical methods.

Tattersall, splits up the workability test as single-point and multi-point tests based on flow curve relating shear stress and shear rate.

WORKABILITY-DRAW BACKS (Cont..)WORKABILITY-DRAW BACKS (Cont..)

WORKABILITY-DRAW BACKS WORKABILITY-DRAW BACKS (Cont..)(Cont..)

So single point tests are incapable for determining the parameter of fresh concrete.

Multiple tests needed to describe different aspects of workability.

Two concrete with same Slump may flow differently & have different workability.

Yield stress is related to the force required breaking down structure and initiating the flow.

Plastic viscosity describes the resistance to flow once the concrete is flowing.

WORKABILITY (Cont..)WORKABILITY (Cont..) Draw backs of empirical tests- needs a method based on scientific approach.

Workability of concrete is closely related to flow properties.

Also ACI Subcommittee 236-A recommends, “Workability of Fresh Concrete,” based on material science- approach to provide better methods for measuring workability for concretes.

In that approaches several methods are available, but Rheological techniques are most commonly and widely used methods.

CONCRETE RHEOLOGY CONCRETE RHEOLOGY Rheology is the scientific study of the flow and deformation of matter.

Concrete rheology is science which deals with fresh properties of concrete and concrete it consider as fluid.

Two parameters are namely; yield stress and plastic viscosity are needed to describe flow properties.

By using various available models or constitutive equations.

Basic Constitute Relationships for flow • Newtonian fluid is the basic

constitute equation for flow.

CONCRETE RHEOLOGY (Cont..)CONCRETE RHEOLOGY (Cont..)

The Bingham model is most commonly used to represent concrete flow due to it simplicity and its ability to represent the majority of concrete mixtures.

RHEOLOGY MEASUREMENTRHEOLOGY MEASUREMENT To determine the Bingham parameters, there are two possibilities:

The fresh concrete is sheared at high rate before the Rheological test. Then, the shear rate is decreased gradually and the stress is measured. The relationship between the stress and shear rate is plotted and the intercept at zero-shear rate is the yield stress, while the slope is the plastic viscosity.

The stress applied to the material is increased slowly and the shear rate is measured. When the stress is high enough the concrete will start flowing. The point at which the materials flow is the yield stress and the slope of the curve above this stress is the plastic viscosity.

FACTORS INFLUENCING FACTORS INFLUENCING CONCRETE RHEOLOGY CONCRETE RHEOLOGY

RHEOMETERSRHEOMETERS To measure the liquid, suspension or slurry flows in response to applied

forces is measuring by a devices called as Rheometer.

Tattersall for the first time carried out systematic investigations in this field in 1973 and he suggested the use of a 'Two-point test’.

All the rheometers measure the resistance to flow of concrete at varying shear rate conditions.

Rheometers for concrete fall into one of three configurations: coaxial cylinders, parallel plate, and impeller-type.

TYPES OF RHEOMETERS TYPES OF RHEOMETERS Two-Point Test

BML

BTRHEOM

CEMAGREF-IMG

IBB

THE TWO-POINT RHEOMETER THE TWO-POINT RHEOMETER

FIGURE : GENERAL ARRANGEMENT OF THE TWO-POINT TEST

Impeller imparts stirring action in a bowl of concrete, and driving torque (T) is measured.

THE BML RHEOMETERTHE BML RHEOMETER

FIGURE(A) SHOWS THE CONTEC BML (B) INNER AND OUTER CYLINDER

Inner cylinder measures torque as the outer cylinder rotates at variable angular velocity.

Fully automated and is controlled by computer software called FreshWin.

THE BTRHEOM RHEOMETER THE BTRHEOM RHEOMETER

FIGURE : THE BTRHEOM RHEOMETER SHOWING THE BLADES AT THE TOP AND BOTTOM OF THE BUCKET CONTAINING THE CONCRETE.

Software program, ADRHEO, operates the device, records data, and computes the rheological parameters.

THE IBB RHEOMETER THE IBB RHEOMETER

FIGURE : PICTURE OF IBB RHEOMETER

Fully automated and uses a data acquisition system to drive an impeller rotating in fresh concrete. The yield stress and plastic viscosity, are displayed on the screen.

Measuring workability of fresh concrete based rheological properties is a more basic fundamental scientific approach to address an limitation of empirical test in the back drop of development of new type of special concrete.

Mixes can be differentiate based on the values of rheological parameters.

Using rheological parameters new mathematical models and mix design procedure can be proposed.

CONCLUDING REMARKSCONCLUDING REMARKS

1. K.T. Yucel1 etal,” Comparing Fresh Concrete Workability Using Experimental Studies and Theoretical Statements”.

2. Koehler, P. Eric and Fowler, W. David, “Quality of Qualification of Concrete Workability By Means of the Vibrating Slope Apparatus”, ICAR 105-2, 2003.

3. G. Sam Wong, etal “Portland-Cement Concrete Rheology and Workability: Final Report”, FHWA-RD-00-025, January 2000.

4. Koehler, P. Eric and Fowler, W. David, “Summary of Concrete Workability Test Methods”, ICAR 105-2003.

5. P.F.G. Banfill, “The rheology of fresh cement and concrete-A review” 11th international Cement Chemistry Congress, Durban, 2003.

6. Tattersall.G.H. Workability and Quality Control of Concrete. London: E. & F. N. Spon; 1991.

7. Ferraris C.F, “Measurement of rheological properties of high-performance concrete: state-of-the-art report, National Institute of Standards and Technology”, NISTIR 5869, Vol.104, pp 461-478, September–October 1999.

8. F. de Larrard, C. F. Ferraris, and T. Sedran, “Fresh Concrete: A Herschel-Bulkley Material”, Mater. Struct. 31, 494-498 (1998).

9. Q.D. Nguyen and D.V. Boger, “Yield stress measurement for concentrated suspensions”, Journal of Rheology, Vol. 27, No. 4, Pp 321-349, 1983.

10. V. Hackley and C.F. Ferraris, “The Use of Nomenclature in Dispersion Science and Technology”, (Special Report 960-3). Gaithersburg, MD: National Institute of Standards and Technology, 2001.

11. Ferraris, Chiara. F., and Brower, Lynn E., Comparison of concrete rheometers Concrete International, pp 1-66, 2000.

12. Tattersall.G.H., Banfill, P.F.G.: The rheology of fresh concrete, First edition, Pitman, Boston, London, Melbourne, 1983.

13. P.J.M. Bartos, Workability and Rheology of Fresh Concrete: Compendium of Tests, Report of Technical CommitteeTC145 WSM, RILEM.

14. S. Girish, C. Indumathi, JagadishVengala and R.V. Ranganath, “Rheological Properties of Self-Compacting Concrete using Direct Shear Box”, The Indian Concrete Journal, Vol. 83, No. 8, pp 47-53, 2009.

15. S.Girish and B.S. Santhosh, ”A Unique Procedure for Finding the Rheological Properties of Fresh Portland Cement Concrete using Concrete Shear Tests”, RILEM, pp365-372.

16. S.Girish and B.S. Santhosh, “Determination of Bingham Parameters of Fresh Portland Cement Concrete Using Concrete Shear Box”, Bonfring International Journal of Industrial Engineering and Management Science, No.4, pp 84-90, December 2012.

17. S.Girish and B.S. Santhosh, “Concrete Shear Test: A new tool for determining rheological properties of fresh Portland cement concrete”, Advance in Civil Engineering and Building Materials, pp289-293, 2013.

REFERENCESREFERENCES

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