# Mathematical Modelling For Strength Characteristics Of Fly Ash Concrete

DOI : 10.17577/IJERTV1IS7048

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#### Mathematical Modelling For Strength Characteristics Of Fly Ash Concrete

International Journal of Engineering Research & Technology (IJERT)

ISSN: 2278-0181

Vol. 1 Issue 7, September – 2012

*Suganya.S, **B.Hagnesh, A.Gandhimathi^, Dr.T.Meenambal@

*UG Student, Dept. of Civil Engineering, Government College of Technology, Coimbatore, Tamilnadu, India

**UG Student, Dept. of Civil Engineering, Jansons College of Technology, Coimbatore, Tamilnadu.

^Asso.Prof, Dept. of Civil Engineering, SNS Institute of Technology,

@Prof, Dept. of Civil Engineering, Government College of Technology,

.

ABSTRACT

Cement is a fundamental raw material used in construction. Production of cement releases large amount of CO2 which is a major cause for the global warming issue. Hence calculated percentage of cement can be replaced by other materials such as fly ash, rice husk ash, meta kaolin, silica fume, geo-polymer etc. without cutting down much the strengths of concrete. Fly ash is one of the most normally preferred substitutes for cement because concrete workability and durability are enhanced by fly ash by their small size and round shape. A mathematical model was constructed using SPSS software for the strength characteristics like compressive strength, flexural strength and split tensile strength when cement is replaced with fly ash at a range of 0% to 50 %. As the percentage of replacement of fly ash in the concrete increases, the strength characteristics decrease. Water content and cement/aggregate ratio are the main parameters which influence the strength characteristics. A comparative study between the results obtained from the laboratory and SPSS has been made and it is found that the differences between these two values are minimum.

#### cylinders, beams, mathematical modeling, SPSS software.

1.0 INTRODUCTION

Fly ash is the mineral residue produced during combustion of coal, and comprises the fine particles that rise with the flue gases. Fly ash comes primarily from coal-fired electricity generating power plants. These plants grind coal to powder fineness before it is burned.

Effective utilization of wastes should be carried out in a profitable manner thereby reducing the volume of waste. The disposal of fly ash has become mandatory as it poses a serious environmental issue. In India, out of the more than 110 million tons of fly ash produced annually, the unused fly ash occupies vast track of valuable land as ash ponds. It is being used in production of concrete by partial (only 20-25 %) replacement of cement. As per the recommendation of IRC: SP : 62-2004, the fly ash content as partial replacement of ordinary Portland cement can be up to 35 %.

2.0 LITERATURE REVIEW

Some important observations of the review are presented

Charles Berryman, Jingyi Zhu, Wayne Jense, Maher Tadros (2005) .concluded that Test cylinders with varying percentages of Class C (25- 65%) and Class F (25-75%) fly ash and a water- reducing admixture (WRA) were created under field manufacturing conditions and tested for 7-

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International Journal of Engineering Research & Technology (IJERT)

ISSN: 2278-0181

Vol. 1 Issue 7, September – 2012

day compressive strength. Seven-day compressive strength for the concrete/fly ash/WRA was found to be highest when the concrete mix included approximately 35%'Class C or 25% Class F fly ash

Binod Kumar, Tike G.K, Nanda P.K (2007) in their laboratory test results showed that fly ash concrete mixtures containing 50-60% fly ash can be designed to fulfill the requirement of strength and workability suitable for cement concrete pavement construction. At all w-cm ratios, the concrete mixture containing 60% OPC and 40% fly ash developed maximum strength at the age of 90 days and beyond

3.0 MATERIALS AND METHODS

Fly ash is comprised of the non- combustible mineral portion of coal. When coal is consumed in a power plant, it is first ground to the fineness of powder. Blown into the power plants boiler, the carbon is consumed leaving molten particles rich in silica, alumina and calcium. These particles solidify as microscopic, glassy spheres that are collected from the power plants exhaust before they can fly away. Thus fly ash is a residue generated in combustion that rises with the flue gases and is captured by electrostatic precipitators or other particle filtration equipment.

Using the different mixes the concrete moulds are prepared and are tested for strengths after curing in 7, 28, 56, 90 days. The split tensile and compressive strengths are determined using the Compression Testing Machine (CTM).

4.0 EXPERIMENTAL RESULTS AND DISCUSSION

1. Concrete mix design

Cement is partially replaced by fly ash in the range of 0% to 50%. Detailed mix proportions as per IRC: 44-2008are given below. Results of compression strength test, split tensile strength and flexural strength on these mixes test are listed (Table2,3,4.).

2. Mix Proportions as per IRC: 44-2008

The mix proportions are designed as per IRC 44-2008 and cement is replaced by fly ash in increasing steps of 10% for the same quantity of fine aggregate, coarse aggregate and water(Table 1)

 Mix % of fly ash cont ent Ce men t (kg) Fly ash (kg) Fin e agg reg ate (kg) Coa rse agg reg ate (kg) Wat er (lit) M1 0 412. 00 0 679 121 6 159 M2 10 359. 42.9 679 121 23 7 6 159 M3 20 334. 56 89.6 5 679 121 6 159 M4 30 298. 129. 679 121 87 12 6 159 M5 40 258. 168. 679 121 159 25 36 6 M6 50 221. 207. 679 121 159 32 96 6

(Table 1) The mix proportions

 Mix % of Fly Ash Compressive strength (MPa) 7 days 28 days 56 days 90 days M1 0 29.26 42.39 44.51 45.65 M2 10 28.65 40.54 43.06 45.31 M3 20 25.32 38.35 41.26 42.21 M4 30 22.45 37.28 40.31 41.62 M5 40 18.85 32.28 37.07 40.76 M6 50 14.24 28.47 34.54 39.52

(Table 2) Compressive strength result of flyash concrete.

 Mix % of Fly Ash Flexural strength (MPa) 28 days 56 days 90 days M1 0 4.85 5.01 5.23 M2 10 4.63 4.95 5.12 M3 20 4.52 4.90 5.03 M4 30 4.36 4.83 4.97 M5 40 3.94 4.58 4.72 M6 50 3.51 4.14 4.36

(Table 3) Flexural strength results of fly ash concrete

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International Journal of Engineering Research & Technology (IJERT)

ISSN: 2278-0181

Vol. 1 Issue 7, September – 2012

4.3 COMPARATIVE STUDY OF COMPRESSIVE STRENGTH OF FLY ASH CONCRETE

The comparative study has been made between the experimental value and the theoretical values

theoretical vs experimental (56 days)

compressive strength at 56 days (Mpa)

60

which are derived from the SPSS software.

theoretical vs experimental (7 days)

40

20

0

0 20 40

% of fly ash

experimental backward forward stepwise

compressive strength at 7 days (Mpa)

30

20

10

0

0 20 40

% of fly ash

experimental backward forward stepwise

Figure 3 Comparative study of theoretical and experimental values for compressive strength at 56 days

compressive strength at 90 days (Mpa)

theoretical vs experimental (90 days)

60

Figure 1.Comparative study of theoretical and experimental values of compressive strength at 7 days

theoretical vs experimental (28 days)

40

20

0

0 20 40

% of fly ash

experimental backward forward stepwise

compressive strength at 28 days (Mpa)

60

40

20

0

0 20 40

% of fly ash

experimental backward forward stepwise

Figure 4 Comparative study of theoretical and experimental values for compressive strength at 90 days

The replacement of cement with fly ash ranges from 0 % to 50 % and the compressive strength at 7, 28, 56 and 90 days are considered in this comparison( figure 1,2,3,4). The experimental values and the results from three different regression methods are compared and it is clear that the differences in values between

Figure 2.Comparative study of theoretical and

experimental values for compressive strength at 28 days

For compressive strength at 28 days the parameters influencing the strength in forward and stepwise regression are same.

experimental results and the theoretical results from the software is minimum.

From the result it has been noted that the forward regression and the stepwise regression is giving the same values and parameters affecting the strength are same. The backward regression is the method which gives more number variable which

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International Journal of Engineering Research & Technology (IJERT)

ISSN: 2278-0181

Vol. 1 Issue 7, September – 2012

is affecting the strength properties hence the backward method can be adopted.

theoretical vs experimental (90 days)

4.4. COMPARATIVE STUDY OF FLEXURAL STRENGTH OF FLY ASH CONCRETE

Experimental values for flexural strength for 28, 56, 90 days are compared with the theoretical results obtained from the software.

6

flexural strength at 90 days (Mpa)

4

2

0

0 20 40

% of fly ash

experiment al

backward forward stepwise

In flexural strength, the forward regression and stepwise regression is giving the same parameters which affects the split tensile strength. In the case of backward regression model more number of parameters are involved in strength characteristics and hence it is the best method.

flexural strength at 28 days (Mpa)

theoretical vs experimental (28 days)

Figure 7 Comparative study of theoretical and experimental values of flexural strength at 90 days

From the figures(5,6,7) it is clear that the difference in values between the experimental value and the theoretical values obtained from the SPSS are minimum and the backward regression can be adopted.

1. CONCLUSIONS

6

4

2

0

01020304050

% of fly ash

experimenta l

backward forward stepwise

The following conclusions are arrived based on the results obtained from the regression model using SPSS software.

1. Water content and cement/ TA are the main parameters which are influencing the strength characteristics.

2. The difference in values of strength characteristics such as compression,

Figure 5 Comparative study of theoretical and experimental values of flexural strength at 28 days

theoretical vs experimental ( 56 days)

flexural, which were obtained from the laboratory and the predicted value from SPSS software is minimum.

3. As the percentage of fly ash increases, the strength characteristics of concrete containing fly ash slightly reduce.

flexural strength at 56 days (Mpa)

6

4

2

0

0 20 40

% of fly ash

experiment

al backward

forward stepwise

4. Even though, strength characteristics decrease slightly, the nominal replacement of fly ash in cement reduces the wastage disposal problem.

ACKNOWLEDGEMENT

We express our sincere gratitude and indebtedness to Er. Jino John, Asso. Prof. i n C i vi l E n gi ne er i n g, Sr i Kr i s h na C ol l e ge

Figure 6 Comparative study of theoretical and experimental values of flexural strength at 56 days

o f Techn ol o gy, C oi mbat or e , Ta mi l n adu , f or hi s val u a bl e s u g ges t i ons and gui d an ce.

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International Journal of Engineering Research & Technology (IJERT)

ISSN: 2278-0181

Vol. 1 Issue 7, September – 2012

REFERENCES

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2. Binod Kumar, Tike G.K, Nanda P.K, Evaluation of properties of high volume fly ash concrete for pavements Journal of Materials in Civil Engineering, Vol.19 (10), October 2007.

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