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VALIDATION OF ACCELERATED CURING TANK

Suraj T V1, Dhanya Krishnan

2

1M Tech Student,

2Assistant Professor, Department of Civil Engineering,

AmalJyothi College of Engineering Kerala, (India)

ABSTRACT

The compressive strength of cement concrete obtained after 28 days of moist curing is used in the quality

control of constructions. However, for economical quality control, for reworking before the concrete gets

hardened and for reducing the waiting time, finding the 28-day compressive strength at an earlier time with a

reasonable accuracy is necessary. The 28-day compressive strength of a concrete can be estimated early by

finding the strength at an early age with accelerated curing. For the prediction of 28-day compressive strength

previously established correlation curve between the early strength with accelerated curing and 28-day strength

standard method is being suggested by IS: 9013-1978. Major research world has proved that substantial

portion of compressive strength is attained due to accelerated curing and accelerated curing techniques can be

used for early prediction of compressive strength of concrete. During review of literatures it is observed that

there is limited work in the effect of curing period and curing techniques and the strength and performance

aspect of concrete. In this work an attempt is made to study the relation between accelerated curing strength

and normal curing strength and influence of type of cement, age and type of curing on different grades of

concrete.

Keywords: Concrete, Compressive strength, Accelerated Compressive strength, Accelerated Curing

Accelerated Curing Tank, Ordinary Portland cement, Portland Slag cement, Portland Pozzolana

cement.

I. INTRODUCTION

The role of concrete as the most versatile manmade building material is likely to continue for many more

decades. While the basic ingredients of concrete normally remain the same, its properties change considerably

with the proportioning of these ingredients. With a variety of cement types available in the market the

importance of designed mixes over the nominal mixes is on the increase these days. A designed mix of concrete

is highly desirable even for ordinary concrete works to achieve quality and economy. In fact, the latest Indian

standards do not recommend at all the use of nominal mixes for reinforced concrete works. In India, it is

difficult to get materials from the same source throughout the construction period. Each time when the

materials (especially cement) change, a fresh design is to be done. Quality of concrete in construction works is

calculated in terms of its 28 days compressive strength. This procedure requires 28 days of moist curing before

testing. Actually it may take much more time for procurement of materials, preparations etc which is too long

period to be of any value for either quality control on concrete construction or timely corrective measures.The

need for having a reliable and fast method for evaluating controlled concrete in the field using accelerated

curing techniques was recognized. Predicting 28-day compressive strength of concrete is an important research

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task for many years. The compressive strength of cement concrete obtained after 28 days of moist curing is used

in the quality control of constructions. However, for economical quality control, for reworking before the

concrete gets hardened and for reducing the waiting time, finding the 28-day compressive strength at an earlier

time with a reasonable accuracy is necessary. The 28-day compressive strength of a concrete can be estimated

early by finding the strength at an early age with accelerated curing. For the prediction of 28-day compressive

strength previously established correlation curve between the early strength with accelerated curing and 28-day

strength standard method is being used suggested by IS: 9013-1978.

In spite of all its advantages, the time factor is one major cause for the construction engineers to be hesitant to

go for proper mix designs. In India, it is difficult most of the time to get materials from the same source

throughout the construction stage. When source of material change it is necessary to go for new mix design

which causes delay in execution. The method developed by the national council for building materials based on

accelerated curing of concrete (IS: 9013-1978, reaffirmed in 2004) is apparently an exciting solution to this

problem as it can produce the results in two to three days. An inquest is made here to the reliability of this

method on practical problems.It is established that a statistically significant correlation exists between its 28-

days strength and accelerated strength. Hence, the mix design procedure is exactly the same as described for

normal design of concrete mixes and the only difference is that the 28-days can be determined on the next day

(as described in accelerated test procedure) of casting of cubes and then can be compared with the required

target strengths.

IS-9013 was originally formulated in 1978, when the cement available in the market was mainly OPC (IS-269).

Now a lot of varieties of cements are available. During the detailed literature survey which is being explained in

the following chapter the author feels that it is worth doing the study for at least four categories of cement viz.

OPC 53 grade (IS-12269),OPC 43 grade(IS-8112:1989), PPC (IS-1489-Part-1) and PSC (IS-455). It is also

necessary to conduct the study for different grades of concrete.

II. ACCELERATED CURING

2.1 Accelerated Test Procedure

After % humidity and 27+2 0C temperature for 23 hours + 15 minutes (time should be counted from the time of

addition of water to the ingredients). The specimens shall then be gently lowered into the curing tank containing

boiling water and shall be kept in that condition for 3 ½ hours + 5 minutes. Then the specimens shall be

removed from the boiling water, removed from the mould and cooled by immersing in water (27+2 0C

temperature) for 2 hours. The specimens shall then be tested for compressive strength. The age of the cubes at

the time of testing shall be 28 ½ hours + 20minutes.

Based on the method of accelerated curing of concrete (IS: 9013-1978), the national council for building

materials has developed a method which can give the required design in a time in 2 days. As per the procedure

described in IS-9013, the cubes are transferred to the boiling water without removing it from mould. For

developing new correlation equation, 72 sets of specimen made with different grades of cement. 24 set of

specimen with water cement ratio 0.45. 24 set of specimen with water cement ratio 0.50. 24 set of specimen

with water cement ratio 0.55. It is established that a statistically significant correlation exists between the 28-

days strength and accelerated strength of concrete. Tests conducted on different grades of concrete, and using

different brands of cements from different parts of the country. Based on this correlation, the 28 days strength

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of concrete can be worked out based on its accelerated strength. The determination accelerated strength takes

only a couple of days. The accelerated curing is done using a standard curing tank [conforming to IS: 9013-

1978reaffirmed in 2004].

2.2 Accelerated Curing Tank

Fig 1: Sectional View of Accelerated Curing Tank

Fig 1 shows sectional elevation of accelerated curing tank. The boiling water method is used for rapid design of

concrete mixes. After the specimens are cast (150mm cubes), they should be kept in a humid environment (90%

humidity and 27+2 0C temperature for 23 hours + 15 minutes (time should be counted from the time of addition

of water to the ingredients). The specimens shall then be gently lowered into the curing tank containing boiling

water and shall be kept in that condition for 3 ½ hours + 5 minutes. Then the specimens shall be removed from

the boiling water, removed from the mould and cooled by immersing in water (27+2 0C temperature) for 2

hours. The specimens shall then be tested for compressive strength. The age of the cubes at the time of testing

shall be 28 ½ hours + 20minutes.

Fig 2. Pictorial View of Accelerated Curing Tank

Fig 2. shows accelerated curing tank. Accelerated curing of concrete hastens the process of hydration of cement

and as a result, a substantial proportion of the strength to be attained in 28 days under normal curing conditions

is achieved within a shorter time. The rate and extend of hydration of cement under a particular curing regime

depend mainly upon the chemical composition of cement, water cement ratio, and mix proportions, which are

considered to be important parameters in the correlation of results from compressive strength tests on specimens

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cured by accelerated curing method and normal curing method. The variability arising from the curing regime to

be adopted is eliminated by standardizing them Fig.3 shows typical relation between accelerated and 28 day

compressive strength of concrete as suggested in the IS: 9013 .The typical correlation curves is based on series

of test result conducted at the Cement Research Institute of India.

Fig 3. Typical Relation Between Accelerated and 28-Day Compressive Strength of Concrete

(Boiling Water Method)

III. MATERIALS AND METHODS

3.1 Introduction

The materials used in this study are cement, fine aggregate, coarse aggregate . All the materials used were tested

as per standard procedures to assess their engineering properties and the results were compared with those in the

relevant IS code (IS: 4031, IS1480, IS 2386 part III & part IV, IS 3495 part I) as explained in following

sections. In this investigation four types of cement used. Standard consistencies, initial and final setting time,

Fineness, compressive strength are experimented for assessing the properties of each type of cement. Specific

gravity and particle size distribution are also experimented to assess the properties of aggregates. After material

characterization was completed mix design process started

3.2 Material Characterization

3.2.1 Cement

(a) Ordinary Portland cement Grade-43 IS 8112: 1989

(b Ordinary Portland cement Grade IS 12269: 1987

(c) Portland Slag Cement IS 455: 1989

(d) Portland Pozzolana cement IS1489 (Part-1): 1991

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Table 1 : Properties of Cement

Sl.

No.

Characteristics

Cement

IS Limits

OPC 43 OPC53 PPC PSC

1 Fineness 5% 5% 6% 5.5% <10%,

IS:1489-PART-I

2 Standard consistency 29.44% 29.72% 31.94% 28.92% IS:4031(Part4) -1988

3 Initial setting time( minutes)

180

225

190

256

IS:1489-PART-I

> 30 min

4 Final setting time (minutes) 370 440 325 407 IS:1489-PART-I

< 600 min

5 Specific gravity 3.15 2.95 2.95 3.15 IS:4031:1988

3 to 3.15

6 Compressive strength at 7 days

(N/mm2)

25.22 37.20 23.33 26.92

IS:4031:1988

3.2.2 Aggregates

Fine Aggregate : The fine aggregate used was M sand from nearest source. Common physical properties of

aggregates such as bulk density, void ratio, porosity etc. relevant to the behavior of aggregates in concrete were

assessed.

Table 2: Properties of Fine Aggregate

Characteristics Loose Compacted

Specific gravity 2.70 2.75

Bulk density 1593(kg/m3) 1602 (kg/m

3)

Porosity 0.428 0.382

Void ratio 0.748 0.618

Grading zone Zone II

Fineness modulus 2.27

Bulking Max bulking at 4% moisture content

Coarse Aggregates : The types of coarse aggregates 20 mm were used. The test conducted on coarse aggregates

are specific gravity, bulk density, water absorption, porosity, void ratio, grading along with crushing strength, as

per IS 2386-1970 Vol.III

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Table 3. Properties of Coarse Aggregate

Sl.No. Characteristic loose Compact IS Code

1 Specific gravity 3.12 3.12 IS 12269-1987

2 Bulk density 1502 1780

3 Porosity 0.487 0.433

4 Void ratio 0.949 0.762

5 Water absorption 0.33%

6 Fineness modulus 2.104

7

Crushing value 23.69%

Not to exceed 30%

for aggregate used

for concrete used

for wearing surfaces

and 45% for other

uses IS : 2386

partIV-1963

Abrasion 25.4%

Impact 16.31%

IV. EXPERIMENTAL STUDY

Mix design process and tests conducted to achieve the objective of this investigation are explained in detail.

After material characterization was completed mix design process started. To investigate the reliability of

prediction of compressive strength at an early age cubes, of same sample were tested after two methods two

methods of curing :

1. Accelerated curing: Boiling water method as per the IS: 9013 as described in 2.2.1 of this report was

adopted for one set of sample.

2. Conventional curing: Another set of cubes tested after normal curing for 28 days by immersing in cold

water at room temperature, after removing from mould after 24 hours

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Table 4. Details of Mix Design (Quantity of Materials per Cubic Meter of Concrete).

Sl. No.

Cement

Type

W/C

Ratio

Water

Liter

Fine

Aggregate

Kg.

Coarse

Aggregate

Kg.

Cement

Kg.

Mix proportion

No. of

specimen

1 OPC 53 0.55 202 702.36 1324.40 364 1:1.93:3.64 6

2 OPC 53 0.5 202 690.51 1301.90 400 1:1.73:3.25 6

3 OPC 53 0.45 202 676.04 1274.60 444 1:1.52:2.87 6

4 OPC 53 0.4 202 660.24 1245.23 462 1:1.42:2.69 6

5 OPC 43 0.55 200 675.45 1140 363.63 1:1.86:3.14 6

6 OPC 43 0.5 200 647.04 1139.15 400 1:1.62:2.85 6

7 OPC 43 0.45 200 616.80 1133.25 444.44 1:1.39:2.55 6

8 OPC 43 0.4 200 645.97 1118.17 425.53 1:1.52:2.62 6

9 PPC 0.55 202 695.96 1124.64 388.46 1:1.79:2.9 6

10 PPC 0.5 202 670.23 1120.48 420.83 1:1.52:2.66 6

11 PPC 0.45 202 649.97 1114.84 448.89 1:1.48:2.48 6

12 PPC 0.4 200 574.27 1101.62 500 1:1.14:2.20 6

13 PSC 0.55 200 667.73 1126.96 363.64 1:1.84:3.10 6

14 PSC 0.5 200 638.76 1124.57 400 1:1.60:2.81 6

15 PSC 0.45 200 607.85 1116.8 444.44 1:1.37:2.51 6

16 PSC 0.4 200 574.27 1101.62 500 1:1.14:2.20 6

Total Number of cubes casted =96

Table 5.Slump

V. RESULT AND DISCUSSION

Results of the compressive strength test conducted as per the IS: 516 is being described through the following

sections. Based on the mix design twelve mix proportions were considered in this experiment. For each set six

number of cubes casted first set of three cubes tested at 28 hour after accelerated curing process and second set

of three cubes tested at 28 day after conventional curing process

Sl.No. Type of

Cement

W/C Ratio

0.4

Slump in

Mm

W/C Ratio

0.45

Slump in

Mm

W/C Ratio

0.50

Slump in

Mm

W/C Ratio

0.55

Slump in

Mm

Perm.limits

for medium

workability

Mm

1 OPC43grade 7.5 8 8.5 9 7.5-10

2 OPC53grade 7.6 8.1 8.2 9 7.5-10

3 PPC 7.9 7.9 8.5 9.3 7.5-10

4 PSC 7.8 8 8.6 9.5 7.5-10

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Table.6.Compressive Strength

Sl.no Type of

Cement

W C Ratio Acc. Curing

strength at

@28 hr N/

mm2

Predicted

Strength

N/mm2

28 Normal

curing strength

N/mm2

1 OPC 53 Grade 0.55 12.39 28.41 31.25

2 OPC 53 Grade 0.55 12.78 29.05 31.75

3 OPC 53 Grade 0.55 12.47 28.54 32.28

4 OPC 53 Grade 0.5 15.18 32.98 39.32

5 OPC 53 Grade 0.5 15.72 33.87 38.79

6 OPC 53 Grade 0.5 15.13 34.53 38.25

7 OPC 53 Grade 0.45 19.12 39.45 40.91

8 OPC 53 Grade 0.45 20.05 40.97 41.78

9 OPC 53 Grade 0.45 19.72 40.43 42.10

10 OPC 53 grade 0.4 22.18 44.46 47.23

11 OPC 53 grade 0.4 22.70 45.32 47.89

12 OPC 53 grade 0.4 23.01 45.82 48.21

13 OPC 43 grade 0.55 13.07 29.52 32.76

14 OPC 43 grade 0.55 13.64 30.45 33.24

15 OPC 43 grade 0.55 13.28 29.86 32.86

16 OPC 43 grade 0.5 15.11 32.87 37.91

17 OPC 43 grade 0.5 16.58 35.28 38.22

18 OPC 43 grade 0.5 15.56 33.61 37.33

19 OPC 43 grade 0.45 18.57 38..54 42.22

20 OPC 43 grade 0.45 18.21 37.95 41.8

21 OPC 43 grade 0.45 17.97 37.56 41.3

22 OPC 43 grade 0.4 19.77 40.51 45.22

23 OPC 43 grade 0.4 20.44 41.61 46.6

24 OPC 43 grade 0.4 19.91 40.74 44.8

25 PPC Flyash 0.55 9.55 23.75 25.14

26 PPC Flyash 0.55 9.82 24.19 26.66

27 PPC Flyash 0.55 9.66 23.99 27.23

28 PPC Flyash 0.5 10.74 25.70 29.96

29 PPC Flyash 0.5 9.45 23.59 32.76

30 PPC Flyash 0.5 9.82 24.19 29.36

31 PPC Flyash 0.45 16.53 35.19 39.76

32 PPC Flyash 0.45 16.21 34.67 39.18

33 PPC Flyash 0.45 15.93 34.22 40.01

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34 PPC Flyash 0.4 18.53 38.47 43.21

35 PPC Flyash 0.4 18.76 38.85 42.96

36 PPC Flyash 0.4 18.21 37.95 42.78

37 PSC 0.55 7.89 21.02 25.11

38 PSC 0.55 8.01 21.22 25.2

39 PSC 0.55 8.12 21.41 24.94

40 PSC 0.5 10.92 25.99 28.66

41 PSC 0.5 11.23 26.51 28.12

42 PSC 0.5 11.52 26.98 28.93

43 PSC 0.45 12.96 29.34 34.66

44 PSC 0.45 13.21 29.75 34.04

45 PSC 0.45 12.86 29.18 35.66

46 PSC 0.4 19.21 39.59 42.43

47 PSC 0.4 19.78 40.53 43.96

48 PSC 0.4 18.96 39.18 42.98

Fig.4. Experimental and Predicted Values of Compressive Strength for Different Grades of

Concrete

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Fig.5. Experimental and Predicted Values of Compressive Strength for OPC 53

Fig 6 : Experimented and Predicted Values for OPC 43

Fig 7: Experimented and Predicted Values for PSC

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Fig 8: Experimented and Predicted Values for PSC

Fig

Fig 9 : Fitted Line Plot for Linear Equation

First attempt to fit a linear equation from the data of experimental study in a scattered plot (Fig.9) equation

obtained is as follows.

R28=12.63+1.587 R1

Even a preliminary observation would reveal that to get a realistic estimate of R28, the constant has to be reduced

considerably. Observing that variation may not be linear, another attempt was made to fit binomial equation Fig

5.3 gives an equation

R28=8.926+2.118 R1-0.017R12

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Fig 10 : Fitted Line Plot for Second Degree Equation.

Equation obtained on a second attempt to fit a second degree equation (Fig.10) is as follows

R28 =8.926+211.8R1-0.0017R12.

Table- 7 : Comparison of Predicted Strength Between two Different Correlations: -

Mix Accelerated

Strength at

28 hour R1

N/mm2

28 day

strength

R normal

N/mm2

Predicted Strength

IS:9013 R28 N/mm2

R28 =1.64* Ra +

8.09

Error

%

Predicted Strength

New correlation

R28-new N/mm2

R28-new =8.926+2.118*R1

-0.017 R12

Error

%

1 10.89 35.41 25.95 26.72 29.92 15.5

2 15.11 41.19 32.87 20.20 36.94 10.31

3 14.89 45.33 32.51 28.28 36.59 19.28

4 22.52 51.41 45.02 12.4 47.74 7.13

5 16.89 53.33 35.79 32.88 39.71 25.53

6 21.63 56.15 43.56 22.42 46.55 17.09

VI. CONCLUSION

6.1 Introduction

The main objective of this study was to check the reliability in prediction of 28 day compressive strength of

concrete at an early age (accelerated curing techniques). Based on the experiment following conclusions were

arrived.

Actual compressive strength after conventional curing is greater than the strength predicted(accelerated

curing) using the correlation equation as per IS: 9013.

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Strength varies at different proportions in concrete with different types of cement. In the case of OPC53

grade as strength increases the difference between the actual and predicted strength varies uniformly. As

strength increases the difference between actual and predicted strength increases while OPC43 grade is

considered. Strength of concrete cubes using PPC and PSC varies in similarly. As strength increases

difference decreases. Hence a single linear equation does not help in reliable prediction

As a result of accelerated curing of concrete a substantial portion of the compressive strength to be attained

on 28 day under conventional curing is attained on accelerated curing at early age namely 28 hours in

different grades of concrete. A non linear relation exists between two values which may help in prediction

of compressive strength. When attempted for a binomial correlation, new correlation equation arrived from

results of this experimental study is R28=8.926+2.118 R1-0.017R12

6.2 Achievement of this Research

Through this study it is proved that accelerated curing using boiling water method gives reliable results for

predicting compressive strength at an early age. Regression equation suggested by IS: 9013 is not reliable in

early prediction of compressive strength. Error in early prediction is minimized when attempted with binomial

correlation equation.

REFERENCES

[1] Ali h. Hameed, Civil Department, College of Engineering Diyala University. “The effect of curing

condition on compressive strength in high strength concrete”,Published in Diyala Journal of Engineering

Sciences(2009)

[2] Anton K. Schindler.”The importance of Concrete Temperature Control during Concrete Pavement

Construction in hot Weather conditions” A paper offered for publication at the annual meeting of the

Transport Research Board Washington D C. January 2002.

[3] Brent vollen Weider 2004. Various methods of accelerated curing for concrete applications and their

impact on short term and long term compressive strength CE 241: Concrete technology,Paper-1 –

[4] Bureau of Indian Standards, IS: 10262-2009, Concrete Mix proportioning-Guidelines.

[5] Bureau of Indian Standards, IS: 456-2000, Plain and Reinforced Concrete-Code of practice.

[6] Bureau of Indian Standards, IS: 516-1959 "Methods of Tests for Strength of Concrete",

[7] Bureau of Indian Standards, IS: 9013-1978 (reaffirmed in 2004), “Method of making, curing and

determining the compressive strength of accelerated-cured concrete test specimens”.

[8] Imad Elkhadiri, Marta Palcios,Fracisca Puertas,”Effect Of Curing Temperatureon Cement

Hydration”(2009)

[9] IS: 2386-1963 Methods of Test for Aggregate for Concrete, Bureau of Indian Standards, New Delhi.

[10] IS: 516-1959 Methods of Test for Strength of Concrete, Bureau of Indian Standards, New Delhi.

[11] IS:1199-1959 Methods Of Sampling And Analysis Of Concrete, Bureau of Indian Standards, New Delhi.

V.Jayadevan,V.R.Valsalakumari,O.B.Sufeera,”Reliability of accelerated curing technique for speedy

design of concrete mixes-An Appraisal of IS Code 9013-1978”The Indian Concrete Journal Published by

ACC Ltd Feb.2014 Vol.88-No.2