Predicting Compressive Strength Development of Concrete with GGBFS using Chemical Reaction Rate Seung-Yup Lee1, Han-Seung Lee1,*, Hyun-Min Yang1, Mohamed A. Ismail1, Mohd Warid Hussin2 1
Dept. of Architectural Engineering, Hanyang University, 1271 Sa 3-dong, Sangrok-gu, Ansan 426-791, Republic of Korea 2 Construction Research Centre (UTM CRC), Institute of Smart Infrastructure and Innovative Construction, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia *Corresponding Author:
[email protected]
ABSTRACT Blast-Furnace Slag is commonly used in combination with Portland cement in concrete for many applications. Concrete with blast furnace slag (BFS) shows varied strength development properties different from normal concrete. Therefore, a precise prediction of compressive strength using a full maturity model is desired. The purpose of this study is to predict the compressive strength of concrete with BFS by calculating the apparent activation energy (E a ) for each BFS replacement ratio. The activation energy was applied to the equivalent age model, and then the Carino model was used. The method of Carino Model is used in this study for predicting compressive strength of concrete with BFS. Results of experiments show that compressive strength at early-age generally decreases as BFS replacement ratio increases and curing temperature decreases. Meanwhile, it is found that coefficient of determination is above 0.91 regardless of BFS replacement ratio. Finally, the compressive strength of concrete with BFS was successfully predicted. Keywords: ground granulated blast furnace slag, concrete, compressive strength, apparent activation energy, rate constant
1. INTRODUCTION Recently, the Korean government has announced the concept of future-oriented low-carbon green growth as the nation's new vision in order to overcome the issues of human resources and climate change. Accordingly, the utilization of slag as an industrial by product is increasing as part of low-carbon green growth with respect to concrete industry. Ground granulated blast furnace slag (BFS) is one of the most promising building material and is being used the most. Blast-Furnace Slag is commonly used in combination with Portland cement in concrete for many applications [1-2]. Generally, the maturity model used for predicting the development of the compressive strength of concrete is assumed to have a linear relationship with temperature, and a nonlinear relationship with the chemical reaction rate of cement [3-8]. With regards to the range of curing temperatures and the accuracy of the prediction, the equivalent age model, which incorporates the chemical reaction rate of cement, is mainly used for the interpretation of strength development [9-11]. In this chemical reaction rate model, the apparent activation energy (E a ) is an important element in considering the effect of curing temperature on the hydration reaction. E a can be indirectly calculated by using compressive strength, as suggested in ASTM C 1074-11[12]. In addition, various other calculation methods are currently being used, such as the method of calculation in which setting time substitutes for Arrhenius plot. The advantages and disadvantages of each method have been reported [8] [13]. In this regards, the calculation methods for Ea in the equivalent age model are established for normal concrete and are being applied to strength prediction models. However, concrete with blast furnace slag (BFS) exhibits a number of differences concerning the strength development properties under the general temperature condition, because of a reduction in early age compressive strength development, owing to a retardation of the setting. As a result, 1
precise prediction of compressive strength of concrete with BFS by using a full maturity model is desired. Therefore, research into the prediction of compressive strength of concrete with BFS by evaluating E a at each BFS replacement ratio is required. The purpose of this study is to predict the compressive strength of concrete with BFS by calculating the apparent activation energy (E a ) for each BFS replacement ratio. 2. PREDICTION OF COMPRESSIVE STRENGTH 2.1. Apparent activation energy (Ea) Apparent Activation energy refers to the minimum amount of energy required for the reaction to occur. However, to be more precise, it can only be represented as the apparent activation energy (E a ), because the hydration reaction of cement is a complex process of simultaneous reactions involving several minerals [17]. The method for obtaining apparent activation energy required for hydration reaction of cement is suggested in ASTM C 1074-11 and hydration reaction of Portland cement can be explained by using this apparent activation energy. E a can then be acquired from the above Eq. 1. After plotting ln (k T ) and 1/T from the experimental data, the gradient of the equation from the linear regression becomes E a /R, and E a can be obtained from this ratio.
ln kT = ln A −
Ea 1 ⋅ R T
(1)
2.2. Prediction model of compressive strength of concrete The most vital element of the Carino model (Eq. 2) [4] [7] [8] is the correlation between rate constant (k t ) and curing temperature.
S=
S u kT (t − t 0 ) 1 + kT (t − t 0 )
(2)
where S = compressive strength, S u = ultimate strength, k T = rate constant at curing temperature (T), t = age, and t 0 = age when compressive development starts.
3. EXPERIMENTAL PROGRAM The experimental program and concrete mix proportions are presented in Tables 1 and 2, respectively. W/B is fixed at 0.60, and the BFS replacement ratios are 0%, 10%, 30%, and 50%. Table 1 The experimental program Experimental level W/B Replacement ratio of BFS (%) Curing temperature (°C)
Items 0.60 0, 50 5, 20, 35
Fresh concrete
Slump, air content
Hardened concrete
Compressive strength
2
BFS (%)
W/B
Table 2 Mix proportions of concrete Mix composition (kg/m3) S/A (%) W* BFS C* S* G*
0
0
0.60
46
362
798
SP*
912
217.2
0.012
50
181
181
790
906
* W = water, C = cement, S = sand, G = coarse aggregates, and SP = Superplasticizer
4. APPARENT ACTIVATION ENERGY OF CONCRETE USING BLAST FURNACE SLAG E a obtained from regression equation for calculating E a by k T and the resulting analysis is shown in Figures 1 and 2. Figure 1 shows the relationship between the curing temperature and the rate constant (k T ). It is founded that the rate constant (k T ) increases in the form of an exponential function as the curing temperature increases. 1.4 0%
1.2
50%
R² = 0.9773
1
kt
0.8 0.6 R² = 0.9975
0.4 0.2 0
0
5
10
15
20
25
30
35
40
Curing temperature(℃) Figure 1: The regression equation according to curing temperature 0.0032 0.5
0.0033
0.0034
0.0035
0.0036
0
Ln(kt)
-0.5 -1 -1.5 -2
BFS 0% R² = 0.993 -2.5
BFS 50% R² = 0.9916 -3
1/T (Reciprocal of atbsolute temperature) Figure 2: Arrhenius plot of ASTM C 1074. 3
0.0037
Table 3 lists the values of E a obtained from Figure 2. In case of a BFS replacement ratio of 0%, it is found that E a is similar to the value of 33.5 kJ/mol from existing models (FreislebenHansen) [7], and that E a increases as the replacement ratio increases. Table 3 E a calculated by BFS replacement Ratio ln k T = ln A −
Replacement ratio (%)
W/B
0.60
Ea 1 ⋅ R T
Ea (kJ/mol)
2
lnA
E a /R
R
0
13.15
4017
0.993
33.475
50
14.23
5465
0.992
45.541
5. COMPRESSIVE STRENGTH OF CONCRETE WITH BFS
Compressive strength (MPa)
Compressive Strength according to each curing temperature in BFS replacement ratio is shown in Figures 3 and 4. The results of experiments show that compressive strength at early-age generally decreases as the BFS replacement ratio gets higher and also as the curing temperature gets lower. 36 30 24 18 12
5℃ 20℃
6
35℃
0 0
5
10
15
20
25
30
Age (days)
Compressive strength (MPa)
Figure 3: Compressive strength according to each curing temperature in 0% of BFS replacement ratio. 30 24 18 12 5℃ 6
20℃ 35℃
0 0
5
10
15
20
25
30
Age (days)
Figure 4: Compressive strength according to each curing temperature in 50% of BFS replacement ratio. 4
In particular, in case of a curing temperature of 5°C, the compressive strength at early-age is lower than that of 0% BFS as the replacement ratio increases. It is found that the 28-days strength decreases by 4.8 MPa at replacement ratios of 50%, respectively.
6. THE PREDICTION OF COMPRESSIVE STRENGTH OF CONCRETE WITH BFS BY CARINO MODEL
Compressive strength (MPa)
The method of the Carino Model [4] is used in this study for prediction of the compressive strength of concrete with BFS. Measurements of the compressive strength and corresponding predictions by the Carino model equation are shown for each replacement ratio in Figures 5 and 6. It is found that, in general, the value of prediction is similar to the measured values throughout the time period, but that the compressive strength for early-age at 5°C and equivalent age at 35°C is under-predicted. Meanwhile, it is found that coefficient of determination is over 0.91 regardless of the BFS replacement ratio.
30 R² = 0.839
20 5°C
10
20°C 35°C Predicted strength
0 10 100 Equivalent age (days) Figure 5: Compressive strength of concrete and prediction compressive strength according to curing temperature in 0% of BFS replacement ratio.
Compressive strength (MPa)
1
30
20 R² = 0.855
10
5°C 20°C 35°C Predicted strength
0 1
10 100 Equivalent age (days) Figure 6: Compressive strength of concrete and prediction compressive strength according to curing temperature in 50% of BFS replacement ratio. 5
7. CONCLUSIONS The conclusions of this study, which involves the prediction of compressive strength of concrete with BFS in various replacement ratios by use of the chemical reaction rate equation, are as follows: • For concrete with BFS, the compressive strength at the same age was found to increase with an increase in the curing temperature. The compressive strength was found to decrease with higher BFS replacement ratios. • The apparent activation energy by ASTM C 1074-11 at replacement ratios of 0%, 10% and 50% was calculated as 33.475 kJ/mol, 45.541 kJ/mol, respectively with the general trend that E a becomes higher as the replacement ratio increases. • An chemical reaction rate equation method accurately predicts the measured strength value, regardless of the BFS replacement ratio. REFERENCES [1] Report of ACI Committee 233, 2003. Slag Cement in Concrete and Mortar. ACI 233R-03, American Concrete Institute, Farmington Hills, Mich. [2] J. Bijen, 1996. Blast Furnace Slag Cement for Durable Marine Structures, Stichting BetonPrisma, Netherlands. [3] Carino, N. J., 1982. Matunty functions for Concrete. Proceedings, RILEM Internaional Conference on Concrete at Early Ages, Ecole Nationaledes Ponts et Chausses, Paris, 1, 123128. [4] Carino, N. J., 1984. Maturity Method: Theory and Application. Journal of Cement Concrete and Aggregate, ASTM, 6, 2, 61-73. [5] Carino, N. J., Lew, H. S.; Volz, C. K., 1983. Early Age Temperature Effects on Concrete Strength Prediction by the Maturity Method. Journal of ACI, Proceedings, 80, 2, 93-101. [6] Carino, N. J., 1981. Temperature Effects on the Strength-Matunty Relation of Mortar. Report No. NBSIR 81-2244, National Bureau of Standards, Washington, D.C., 90. [7] Freiesleben, H. P.; Pedersen, E. J., 1977. Maturity Computer for Controlled Curing and Hardening of Concrete. Journal of the Nordic Concrete Federation, 1, 21-25. [8] Schindler A. K., 2002. Concrete hydration, Temperature Development and Setting at Early Age., PhD D Dissertation, The university of Texas at Austin, 23~50. [9] Bernhardt, C. I., 1956. Hardening of Concrele at Different Temperatures, Institute for Building Research Copenhagen, Session BII. Proceedings, RILEM Symposium on Winter Concreting, Copenhagen, Danish. [10] Tank R. C.; Carino. N. J., 1991. Rate Constant Functions for Strength Development of Concrete. ACI Material Journal, 88, 1, 74-83. [11] Guo Chengju, 1989. Maturity of Concrete: Method for Predicting Early Stage Strength. ACI Materials Journal, 86, 4, 341-353. [12] ASTM C1074, 2011. Standard practice for estimating concrete strength by the maturity method. Annual Book of ASTM Standards, 4, 2. [13] Roberto C. A. Pinto; Kenneth C. Hover, 1999. Application of Maturity Approach to Setting Times. ACI Materials Journal, 96, 6, 686~691. [14] Saul, A. G. A., 1951. Principles Underlying the Steam Curing of Concrete at Atmospheric Pressure. Magazine of Concrete Research, 2, 6, 127-140. [15] Nurse, R.W., 1949. Steam Curing of Concrete. Magazine of Concrete Research, 1, 2, 79-88. [16] Bergstrom, S. G., 1953. Curing Temperature, Age and Strength of Concrete. Magazine of Concrete Research, Volume. 5, No. 14. [17] Carino, N. J., 1991. The Maturity Method., CRC Handbook on Nondestructive Testing of Concrete, CRC Press., pp.101~14. 6
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