Paper Title (use style: paper title)

APSEC-ICCER 2012 Candra Irawan et. al. 2 – 4 October 2012 | Surabaya, Indonesia

Prediction of Fly Ash-Concrete Strength under Steam Curing with Maturity Method Candra Irawan

Januarti Jaya Ekaputri

Department of Civil Engineering Faculty of Civil Engineering and Planning ITS Surabaya Indonesia 60111 [email protected]


Pujo Aji

Triwulan



Abstract— The addition of fly ash and the use of steam treatment (steam curing) conducted concrete production more economical. The prediction of concrete compressive strength in Indonesia was provided in PBI 1971. This code was used for predicting strength of normal concrete. However, it was less accurate to predict the compressive strength of concrete containing fly ash with steam curing. This paper presents the prediction result of compressive strength concrete at ages 7, 14 and 28 days based on the compressive strength data and timetemperature age factor at 1 and 2 day. Cylindrical concrete specimens were made from a mixture of fly ash class F and treated with steam curing. The result show that the value of compressive strength prediction error between the actual compressive strength was of less than 5% at 7 and 28 days for all specimens. Whereas, the error of the samples at 14 days was above 5%, but less than 10%. Keywords-prediction of compressive strength, fly ash, steam curing, maturity

I.

concrete will increase as well as increasing concrete temperature [2]. A research conducted by Triwulan et al in 1998 resulted appropriate temperature steam curing both normal concrete and fly ash concrete was about 70 °C. Using steam curing treatment obtained high compressive strength concrete early age. The addition of fly ash and the use of steam curing conducted concrete production more economical, both in terms of time and cost. Concrete would be more economically if concrete strength after casting could be controlled. It was important to ensure the concrete quality. Prediction of concrete compressive strength in Indonesia was provided in the table 4.1.4 PBI 1971. The coefficient in this code was used to predict strength of normal concrete using ordinary cement or cement with high early strength [4]. Thus, PBI 1971 was less accurate to predict the compressive strength of concrete made from fly ash mixture under steam curing treatment. TABLE I PREDICTION C OEFFICIENT OF COMPRESSIVE CONCRETE STRENGTH IN PBI 1971 [4]

INTRODUCTION

The use of fly ash as an admixture in concrete has been widely used, both in precast concrete or cast in place concrete [1]. The advantages of using fly ash are improving workability, making the concrete more impermeable, and certainly replacement cement with fly ash is more economical than using pure cement [2]. The addition of fly ash in concrete also increases durability of concrete against corrosive environment, as well as increases the strength of concrete. The using of fly ash in concrete delayed setting time as well as reducing heat of cement hydration [3]. Decreasing of heat hydration cement in concrete with fly ash resulted the development of concrete strength to be longer than normal concrete. One way to speed up the process of hydration was treat the concrete using the medium vapor (steam curing). Steam curing made the rate hydration of

Age, day

3

7

14

21

28

90

365

Ordinary cement

0.4

0.65

0.88

0.95

1

1.2

1.35

Early high strength cement

0.55

0.75

0.9

0.95

1

1.15

1.2

Day (2006) proposed maturity method to predict the compressive strength of concrete [2]. Maturity method was a prediction method of concrete compressive strength based on the temperature and compressive strength of concrete data at early ages (1 to 7 days). Maturity method was a method based on measuring the temperature inside the concrete. However the concrete conditions, both materials and treatment method as long as

1 ISSN XXXX-XXXX “Sustaining the World with Better Structures & Construction Practice”

APSEC-ICCER 2012: Candra Irawan, Pujo Aji, Januarti Jaya Ekaputri and Triwulan

known the record of concrete temperature, thus the compressive strength can be predicted. Therefore this method was useful to predict the concrete compressive strength using fly ash under steam curing. Basically, there were two stages in prediction of compressive strength using maturity method. The first, develop the maturity curve. Maturity curve was a curve which represented the relationship between time-temperature factor and concrete compressive strength. Using maturity curve could be determined a maturity function. Second, predict the concrete compressive strength at particular ages of concrete using maturity function [5]. The research was conducted to study the accuracy of the maturity method to predict the compressive strength of concrete with fly ash mixture under steam curing with a maximum temperature of 70° C. compressive strength of concrete to be predicted was at the age of 7, 14 and 28 days (referred to as the target age predictions). While the initial age data was used as the basis data for prediction the compressive strength of concrete is the age of 1 and 2 days (referred to as early age).

Since the core problem of this research is to predict the concrete strength based on an early-age concrete therefore the ASTM C 918-02 [11] is used as a guidline with a slight modification in its prediction equation (3). Fig. 1, shows the relationship cumulative Time Temperature Factor (the x axis is in logarithmic scale) and concrete strength to illustrate the equation (2). Fig. 2 shows the modified prediction equation with both x and y axis in linear scale. ( ) (2) where: = projected strength at maturity index M, = measured compressive strength at maturity index m, = slope of the line, = maturity index under standard curing condition = maturity index of the specimen tested at early age

This research expected to work in construction would be more optimal. Engineers can check the compressive strength of concrete without waiting 28 days and decided to conduct further activities based on these results. This can improve the work efficiency of a contractor. In addition, since the result is more accurate than the quality control and quality assurance of concrete work to be increasing. II. FUNDAMENTAL THEORY The compressive strength of concrete is a complicated property that depends not only upon the intrinsic makeup and workmanship of the concrete, but also varies with its age and the temperature at which it hardens. For many years [6], [7], [8], [9], [10] it has been proposed that the strength of concrete can be related to simple mathematical function of time and temperature so that strength could be assessed by calculation without mechanical testing. Such as function are used to compute what is called the "maturity" of concrete, and the computed value is believed to bear a correlation with the strength of concrete [10].

Fig. 1. The cumulative Time-Temperature vs Concrete Strength (ASTM C918)

[ ( )

( )]

(3)

where: = projected strength at maturity index M = measured compressive strength at maturity index m = a function that relate the Cum TTF and Strength = maturity index under standard curing condition = maturity index of the specimen tested at early age

There are 2 ASTM discusses this maturity method: ASTM C 918-02 “Standard Test method for measuring Early-Age Compressive Strength and Projecting Later-Age Strength”, ASTM C 1074-98 "Standard Practice for Estimating Concrete Strength by the Maturity Method”. The maturity function (ASTM C 1074-98) is used to compute the temperature-time factor as follows: ( )

∑(

)

(1)

where: ( ) = the temperature-time factor at age t, degree-days or degree-hours. = a time interval, days or hours. = average concrete temperature during interval, deg C. = datum temperature, deg C.

Fig. 2. The cumulative Time-Temperature vs Concrete Strength (modified prediction equation)



The function ( f ) in (3) is created to develop the prediction equation (usually in a form of logaritmic function). The objective of steam curing is to accelerate the hydration process by increasing the environment temperature using boiling/hot steamed water. Fig. 3, shows the actual steam curing used in  the experiment. III. METHODS The materials were used in this research was cement type I from Semen Gresik, sand from Lumajang, coarse aggregate from Mojokerto and fly ash class F. Test results XRD of fly ash shown in Fig. 3. The main compound of fly ash were Quartz (SiO2), Hematite (Fe2O3), mullite (Al6Si12O3).

Fig. 3. The result XRD test fly ash

In steam curing process, temperature box steam is raised until 70 deg. Celcius and maintained around 3 hours, then the cooling down process finished at 30 hours. After this process, the concrete were treated under normal curing until the 28th days.

A. Development of prediction equation: - The time and temperature was recorded for 11 samples. The concrete strength was tested at the age of 1 day, 2 days, 7 days, 14 days and 28 days. - The steam curing was applied during the first 20 hours. - The time-temperature factor was analyzed and transformed into cumulative time-temperature factor (Cum TTF). - The Cum TTF and strength were plotted. - The logarithmic function ( ) was found using microsoft excel trendline feature. B. To use the prediction equation to project the concrete based upon early-age strengths to later-age strength. - There were 10 samples to be tested (compressive strength) at the age of 1 day, 2 days (early age data), 7 days, 14 days and 28 days (for validation). - All of the samples were recorded both the time and the temperature. - At this point we have the Cum TTF (m) and Sm (for the age of 1 and 2 days). - The M was found by using the Cum TTF at the age of 1 and 2 days + the rest of time till 28 days multiply by the average temperature.  - Equation 3 is used to find the SM - The compressive strength tested at the age of 7 days, 14 days and 28 days will be compared with the SM IV.

RESULT  AND DISCUSSION

Table 2 shows the Cum TTF and the strength test to build the prediction equation.  TABLE 2 THE CUM TTF AND CONCRETE STRENGTH AT THE AGE OF 1, 2, 7, 14 AND 28 DAYS

Fig. 4. The actual steam curing time-temperature history

There are two important steps to take in order to use the maturity method:

Age, day

Cumulative TTF, deg. Celcius hour

1

1272

2

1973

7

5252

14

9888

28

19005

Concrete Strength, MPa 21.6 21.7 25.8 26.3 32.6 30.2 35.3 35.8 45.4 43.1 44.8

Fig. 5 shows the Cum TTF vs Concrete strength. The function ( f ) that relates the Cum TTF and the compressive strength is f(x) = 7.969*ln(x) - 35.53





V.

Figure 5. The Cum TTF vs Strength

The cumulative TTF at early age 1 and 2 days (m) are 1141 and 1779 °C.hour, respectively. From the experimental data, the M based on early age prediction is: TABLE 2 THE CUM TTF AT TARGET AGE 7, 14 AND 28 DAYS

Early ages, days

Cum. TTF at target age (M) 7 days

14 days

28 days

1

5029

9565

18637

2

5019

9555

18627

Actual strength concrete sample tested at 7, 14 and 28 day are 29.2 MPa, 32.9 MPa and 39.5 MPa, respectively. Using the equation f(x) = 7.969*ln(x) - 35.53, the ( ) and ( ) can be calculated. Table 3 shows the difference (error in %) between the predicted and the sample tested at 7, 14 and 28 days.

Early ages

Day

TABLE 3 THE CUM TTF AND AT THE AGE OF 7, 14 AND 28 DAYS Concrete strength Concrete prediction at target age Error strength (SM) at early 7 14 28 7 14 28 age (Sm) day day day day day day (MPa)

(MPa)

(%)

16.8

28.8

33.7

39.0

2.2

2.5

1.3

18.0

29.8

34.9

40.2

1.9

6.1

1.8

21.1

29.3

34.5

39.8

0.4

4.8

0.7

22.2

30.5

35.6

41.0

4.4

8.3

3.6

1

2

CONCLUSIONS

The Maturity method is an effective method to predict the 7, 14 and 28 days age strength test using as early as 1 and 2 days compressive fly ash-concrete strength test under steam curing condition. To apply this method the prediction equation has to be found from a previous data (time, temperature, compressive strength test). The logarithmic function can be created using a simple microsoft excel program. Equation 3 is ready to be applied to predict the concrete strength. This research gives a great advantage to a precast or concrete industry in Indonesia to control their product at early age of concrete. It gives a better alternative way to predict other than the PBI 71 that uses only age factor to predict the concrete strength. From the experimental result an error below 5 % for 7 and 28 days age target and below 10 % for 14 days age target was achieved so that the prediction was deemed a quiet good success. REFERENCES [1] Triwulan, Raka IGP. and Sadji. (1998) Perubahan Kuat Tekan Pasta dan Beton dengan Fly Ash oleh pengaruh moist dan steam curing. Media Teknik 4 (Nopember) : 66-71. [2] K. W. Day. (2006) Concrete Mix Design, Quality Control and Specification. London and New York: Taylor and Francis. [3] Triwulan, Marwan. (1995) Reaktifitas fly ash (abu terbang ex batu bara) serta pengaruhnya pada perekat beton. Jurnal Teknologi dan Rekayasa Sipil (TORSI) (Nopember) : 29-35. [4] PBI 71, Peraturan Beton Bertulang Indonesia, Direktorat Penyelidikan Masalah Bangunan, Bandung, 1971. [5] ASTM C 1074-98, Standard Test Method for Estimating Concrete Strength by the Maturity Method, 1998. [6] A. G. A. Saul. (1951) Principles Underlying the Steam Curing of Concrete at Atmospheric Pressure. Magazine of Concrete Research (London), V. 2, No. 6. [7] Bergstrom, Sven G. (1953) Curing Temperature, Age and Strength of Concrete. Magazine of Concrete Research (London), V. 5, No. 14. [8] J.D. McIntosh. (1949) Electrical Curing of the Concrete. Magazine of Concrete Research (London), V.1, No. 1. [9] Rastrup, Erik. (1954) Heat of Hydration in Concrete. Magazine of Concrete Research (London), V.6, No. 17. [10] R. W. Nurse. (1949) Steam Curing of Concrete. Magazine of Concrete Research (London), V.1, No. 2. [11] ASTM C 918-02, Standard Test Method for Measuring Early-Age Compressive Strength and Projecting LaterAge Strength, 2002.
