Study of Freshened Properties of Self Compacting Concrete by Design of Experiment

Pankaj Shah*1, Hardik Upadhyay*2, Elizabeth George#3

*PG Students, Dept. of Structure Engg., BVM engg. College, Gujarat Technological University

Gujarat, India.1shah2pankaj@yahoo.com2hpupadhyay88@yahoo.in

#Professor, Dept. of Structure Engg., BVM engg .College, Gujarat Technological University

Gujarat, India.3pmgeorge02@yahoo.com

Abstract— The intent of this study is to apply of Design ofExperiments (DOE) techniques in Self Compacting Concrete (SCC) freshened properties studies. Generally, a large number of experiments are usually required as to study the properties of SCC. For that purpose, Box-Behnken design with three –variable and three-level factor to reduce the numbers of experiment isadopted. Three control factors, namely, cement, fly ash, and W/P ratio are used in this experimental work. The mixtures areextensively tested in freshened state and to meet technical requirement of SCC. Three responses (slump flow, V-funnel, L-box) are evaluated.

Keywords—self-compacting concrete, Fly Ash, superplasticizer, viscosity modifying agent (VMA), freshened properties

I. INTRODUCTION

In an experimental study, in order to determine the effects of various factors, which are affecting the results of experiment, different methods and approaches are used. The fundamentals of these methods are the full factorial design and fractional factorial design. In the traditional approach, which is also known as full factorial design, the experiments are performed for each condition, which consists of all factors. In the experiments where the number of factor and their levels are few, the full factorial experimental design may be applied to the design.

Owing to a wide range of variability of material content of Self Compacting Concrete (SCC), generally, a large number of experiments are usually required as to decide a suitable mixture for attaining the targeted requirements of SCC. So, a three-level design for fitting response surface was investigated by Box and Behnken, which can substantially decrease the number of experiments and feasible to study the effect of factors and its interactions.

In this study, the Box-Behnken design approach is proposed to select the optimal mixture proportioning of SCC based on the freshened stage requirement on the slump flow, L-box, and V-funnel time.

II. EXPERIMENTAL DESIGN

A. Materials properties

Ordinary Portland cement of 53 grade available in local market is used in the investigation. The specific gravity of cement was 3.15.class F Fly Ash from wanakbori thermal power station, kheda, Gujarat, was used. Fly Ash for use as Admixture. Specific gravity of fly ash was 2.3. Locally available natural sand with 4.75 mm maximum size was used as fine aggregate, having specific gravity 2.6 and crushed stone with 10mm maximum size having specific gravity 2.9was used as coarse aggregate. A polycarboxylicether (PCE) based super-plasticizer which is brown in color and free flowing liquid having relative density 1.15 complying with ASTM C-494 type F, was used. Glenium stream 2 was used as VMA. Potable water was used for mixing of concrete constituents.

B. Design of Experiment

Many researchers have used Design of Experiment (DOE) techniques to evaluate mix-proportioning effect by selecting trial and optimized proportions. These DOE techniques provide a method to evaluate the effect of different parameters in statically sound manner and with minimum mixture numbers. Models of regression are fitted to the result to each measured response results. A central composite response surface is commonly used approach. Knowledge about the materials and proportioning of SCC is required to select the parameters that can be used in the design of experiment and satisfies the SCC characteristics. Box and Behnken have proposed some three- level design for fitting response surfaces. These designs are formed by combining 2k factorials with incomplete block designs. The resulting designs are usually very efficient in terms of the number of required runs, and they are rotatable or nearly rotatable. Table -1 shows a three-variable Box-Behnken design and Table-2 shows Parameters and their variation levels.

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C. Recording of Responses

The ingredients for the various mixes were weighed and mixing was carried out using rotator type concrete mixer. Precautions were taken to ensure uniform mixing of ingredients. The batching sequence consisted of homogenizing the sand and coarse aggregate for 30 sec, then adding some amount of the mixing water (water+superplasticizer+VMA) into the mixer and continuing to mix. Then after the cement and fly ash were added and mixed for 3 to 4 minutes. Remaining water was then added into the mixer and continued rotation till the SCC was achieved. After getting SCC slump flow, V-funnel and L-box tests were performed to get required responses for fresh concrete properties.

TABLE I A THREE-VARIABLE BOX-BEHNKEN DESIGN

Run x1 x2 x3

1 −1 −1 0

2 −1 1 0

3 1 −1 0

4 1 1 0

5 −1 0 −1

6 −1 0 1

7 1 0 −1

8 1 0 1

9 0 −1 −1

10 0 −1 1

11 0 1 −1

12 0 1 1

13 0 0 0

14 0 0 0

15 0 0 0

TABLE II PARAMETERS AND THEIR VARIATION LEVELS

Cement Fly ash w/p ratioLevels

kg/m3 kg/m3

−1 300 200 1.1

0 325 225 1.2

1 350 250 1.3

D. Developing Design MatrixThe design matrix was developed using the software called

ANOVA. This software increases the analytical power with more statistics by delivering extensive list of algorithms. It also visualizes the data provided with more graphing capabilities. ANOVA offers a large variety of scientific and technical graphs for a desktop statistics package. The selected

design matrix shown in Table IV is a Box-Behnken design consisting of 15 set of coded values. This 15 experimental run allowed the estimation of the linear, quadratic and two-way interactive effect of the process parameters.

E. Development of mathematical modelThe response function representing any of the recorded

responses of SCC can be expressed as:

Y = f (C, F, W/P)

C- Cement F- Fly AshW/P- Water paste ratio

The relationship selected being a second-degree response surface expressed as follows:

Y = b0+b1C+b2 F +b3W/P+b11 C.C+b22 F.F +b33 W/P.W/P +b12 C.F +b13 C.W/P +b23 F.W/P

The values of the coefficients were calculated by regression analysis using ANOVA software.

III. RESULT Freshened properties of SCC were observed through slump-flow, flow time, V-funnel, L-box and Segregation Resistance. The values of the regression coefficients give an idea as to what extent the control variables affect the responses quantitatively. In significance coefficient using student t-test can be dropped along with responses to which they are associated without affecting much of the accuracy of the model. TABLE III gives the recommended values for different tests given by different researchers for mix to be characterized as SCC mix. TABLE IV shows mix proportions and observed values of the responses.

TABLE III RECOMMENDED LIMITS FOR DIFFERENT FRESHEND PROPERTIES OF SCC

Sr. No.

Property Range

1 Slump Flow Diameter 500-700 mm 2 T50cm 2-5 sec3 V-funnel (T0 min) 6-12 sec 4 V-funnel (T5 min) 9-15 sec5 L-Box H2/H1 ≥ 0.8

The final models for the various responses as determined by the analysis are represented below:

C8=−1337.29−13.83C+16.83F+3643.75W/P+0.03C.C+0.01F.F−395.83W/P.W/P−0.02C.F−1.0C.W/P−9.50F.W/P

C9=101.048−0.003C−0.205F−112.856W/P−0.0C.C+0.00F.F+16.479W/P.W/P+0.0C.F+0.152C.W/P+0.063F.W/P

C10=−221.94O−0.298C+0.836F+323.950W/P+0.001C.C−0.02F.F−79.250W/P.W/P+0.001C.F−0.260C.W/P−0.258F.W/P

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C11=279.685−1.977C+0.340F+65.563W/P+0.002C.C−0.002F.F−96.708W/P.W/P+0.00C.F+0.352C.W/P+0.143F.W/P

C12=−30.5282−0.0899C−0.0059F+26.8094W/P−0.00C.C+0.002F.F−1.6146W/P.W/P−0.001C.F−0.0455C.W/P−0.0328F.W/P

IV. CONCLUSION

From the result of statistical analysis obtain from ANOVA; it is observed that effect of different parameters like quantity of Fly Ash, quantity of cement and water- powder ratio on the responses namely slump flow, V-funnel, L-box are notsignificant up to 95% confidence level. Hence RSP methodology cannot be applied for the modeling of fresh properties of SCC.

TABLE IV MIX PROPORTIONS AND OBSERVED VALUES OF THE RESPONSES

X1 X2 X3 C8 C9 C10 C11 C12

Cement Fly Ash w/p Slump Test V-Funnel Test L-Box TestMix No.

kg/m3 kg/m3 Flow T50cm T0min T5min (H2/H1)

(mm) (sec) (sec) (sec)

1 300 200 1.2 700 1.98 6.23 12 0.8

2 300 250 1.2 720 0.96 3.61 8.27 0.97

3 350 200 1.2 710 1.53 4.62 8.3 0.84

4 350 250 1.2 670 1.3 4.04 5.63 0.77

5 300 225 1.1 640 3.27 6.2 12.67 0.29

6 300 225 1.3 710 0.9 6.5 7.77 0.67

7 350 225 1.1 680 1.5 4.71 7.57 1

8 350 225 1.3 740 0.65 2.41 6.19 0.93

9 325 200 1.1 410 4.57 10.4 14.3 1.5

10 325 200 1.3 700 0.58 2.88 4.21 0.97

11 325 250 1.1 700 2.82 5.32 7.56 0.87

12 325 250 1.3 680 0.9 1.51 3.43 0.86

13 325 225 1.2 670 1.35 3.53 4.53 0.86

14 325 225 1.2 680 1.85 6.13 10.5 0.67

15 325 225 1.2 680 1.8 6.45 9.5 0.7

All the experiment designed by Box Behnken method to develop the modal for hardened concrete properties satisfied the SCC fresh concrete property requirements.

REFERENCES[1] Montogomery, D.C, 2005. Design and Analysis of

Experiment. 6th Edition, Arizona State University, John Wiley and Sons, Inc., 111 River Street, Hoboken, New Jersey, USA

[2] Jagadish Vengala Sudarsan,M.S and R.V. Ranganath 2003. Experimental Stydy for Obtaining Self-Compacting Concrete. Indian Concrete Journal. J. 77:1261-1266.

[3] Khatib, J.M., 2008. Performance of self- compacting concrete containing fly ash. Construction Bulding Material., 22:1963-1971.

[4] EFNARC, 2002. Specification and guideline for self-compacting concrte. UK., pp: 1-32. http://www.efnarc.org/pdf/sandGforSCC.PDf.

[5] Frank, D., K. Holschemacher and D. Weibe, 2000.Self Compacting Concrete (SCC) time development of the material properties and the bond behavior. LACER no.5.http://www.wilbertprecast.com/documents/scc.pdf

National Conference on Recent Trends in Engineering & Technology

13-14 May 2011 B.V.M. Engineering College, V.V.Nagar,Gujarat,India

National Conference on Recent Trends in Engineering & Technology

13-14 May 2011 B.V.M. Engineering College, V.V.Nagar,Gujarat,India