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The First International Proficiency Testing Conference Sinaia, România 11 th 13 th October, 2007 355 SOFTWARE-ENHANCED METHOD FOR RAPID DETERMINATION OF THE EARLY HEAT OF HYDRATION OF CEMENT CEM II/A AND B–S TO PREDICT THE 28-DAY COMPRESSIVE STRENGTH Maria Ioan 1 , Liliana Radu 1 , Constanta Mandoiu 2 1 CEPROCIM SA, 6 bd Preciziei, Code: 062203, Bucharest, Romania; 2 CARPATCEMENT HOLDING SA, Fieni, Romania 1 [email protected], 2 [email protected] Abstract The paper dealt with prediction of the 28-day compressive strength of cement by a rapid method of determining the early heat of hydration. The early heat of hydration and the standard strength of cement being determined on a number of cements may serve for establishing a correlation to predict the 28-day strength. The relation needs validation on a greater number of cements of the same type and manufacturer. The investigations involved the following steps: i) determining the standard strength as per SR EN 196–1, ii) determining the early heat of hydration by a calorimeter enhanced with 1-minute temperature increase monitoring software, iii) establishing a correlation equation, and iv) validating the correlation on 70 cements CEM II/A and B–S. The rapid estimation of the 28-day strength of cement CEM II/A and B–S with a precision of ±2.5 MPa is a versatile tool in the cement manufacturing process. The same algorithm may be applied and validated for any cement sort. Key words Cement, early heat of hydration, rapid method, prediction, standard strength 1 INTRODUCTION The paper aimed at establishing correlations between the heat of hydration and the strength of cement so as to enhance quality parameters and management in cement plants and streamline information transfer from testing laboratories to end-users. Solacolu [1] suggested the need of a rapid assessment of the cement strength by processing experimental information using charts of equal strength and modular
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Page 1: SOFTWARE-ENHANCED METHOD FOR RAPID …prev.pt-conf.org/proceeding/51_Ioan_RDE_P_P0094.pdf · compressive strength as determined on thermally cured mortar specimens. ... g—vacuum

The First

International Proficiency Testing Conference

Sinaia, România 11th − 13th October, 2007

355

SOFTWARE-ENHANCED METHOD FOR RAPID DETERMINATION OF THE EARLY HEAT OF HYDRATION OF CEMENT CEM II/A AND B–S

TO PREDICT THE 28-DAY COMPRESSIVE STRENGTH

Maria Ioan1, Liliana Radu1 , Constanta Mandoiu2

1CEPROCIM SA, 6 bd Preciziei, Code: 062203, Bucharest, Romania; 2CARPATCEMENT HOLDING SA, Fieni, Romania

1 [email protected], 2 [email protected] Abstract The paper dealt with prediction of the 28-day compressive strength of cement by a rapid method of determining the early heat of hydration. The early heat of hydration and the standard strength of cement being determined on a number of cements may serve for establishing a correlation to predict the 28-day strength. The relation needs validation on a greater number of cements of the same type and manufacturer. The investigations involved the following steps: i) determining the standard strength as per SR EN 196–1, ii) determining the early heat of hydration by a calorimeter enhanced with 1-minute temperature increase monitoring software, iii) establishing a correlation equation, and iv) validating the correlation on 70 cements CEM II/A and B–S. The rapid estimation of the 28-day strength of cement CEM II/A and B–S with a precision of ±2.5 MPa is a versatile tool in the cement manufacturing process. The same algorithm may be applied and validated for any cement sort. Key words Cement, early heat of hydration, rapid method, prediction, standard strength 1 INTRODUCTION The paper aimed at establishing correlations between the heat of hydration and the strength of cement so as to enhance quality parameters and management in cement plants and streamline information transfer from testing laboratories to end-users. Solacolu [1] suggested the need of a rapid assessment of the cement strength by processing experimental information using charts of equal strength and modular

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Maria Ioan, Liliana Radu, Constanta Mandoiu: Software-enhanced method for rapid determination of the early heat of hydration of cement CEM II/A and B-S to predict the 28-day compressive strength

356

coordinates, keeping free lime constant, and highlighting the effect of SM and AM on the standard strength. Later, the effect of free lime CaO [2] as well as tricalcium aluminate C3A [3, 4] was taken into consideration. The effect of cement fineness and the contribution of various particle size fractions on short- and long-term strength development was studied as well [5–8]. Moreover, experimental methods were devised for rapid cement strength assessment. To this end, de Squeira Tango [9] presented a method for predicting the compressive strength of hydraulic cement on the basis of the 2- and 7-day compressive strength; Izaguirre [10] presented a method of determining the strength by curing at temperatures exceeding 100°C; and Ioan et al. [11] presented a method of predicting the strength by using the 1-day compressive strength as determined on thermally cured mortar specimens. Although literature failed to indicate any direct correlation between the strength and the heat of hydration of cement, studies carried out in the CEPROCIM testing laboratory on 30 cements CEM I from the same manufacturer revealed a linear correlation y = ax + b, with y being the 28-day compressive strength determined as per standard SR EN 196–1 [12] and x being the early heat of hydration released before reaching the maximum temperature θM. Preliminary investigations on cement mortars were continued on cement pastes based on cement CEM I. Moreover, an accelerator was used to perform a rapid determination [13] of early heat of hydration. The present investigation focused on determining the heat of hydration by using a semi-adiabatic method on cement pastes based on cement CEM II/A, B-S. 2 EXPERIMENTAL 2.1 Materials

a) Cements The laboratory experiments used 70 samples (S) of cement with addition of blast furnace slag (BFS) type CEM II from CARPATCEMENT HOLDING SA, Fieni. Figure 1 shows the oxide composition, the BFS content, and the 28-day compressive strength determined as per SR EN 196-1. b) Sand The sand employed in the investigations was standard sand as per CEN EN 196–1 (France) for determining the 28-day compressive strength. c) Accelerator An accelerator was employed to determine the early heat of hydration QhM released up to attaining the maximum temperature θM. d) Water Distilled water as per SR EN 196–1 was employed for reference testing in determining both the strength and the early heat of hydration.

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Maria Ioan, Liliana Radu, Constanta Mandoiu: Software-enhanced method for rapid determination of the early heat of hydration of cement CEM II/A and B-S to predict the 28-day compressive strength

357

0 10 20 30 40 50 60 70 80 90 100 110 1200

5

10

15

20

25

30

35

40

45

50

55

60

65

Oxi

des,

BFS

(%);

Stre

nght

(MP

a)

Cement samples

CaO SiO2 Al2O3 Fe2O3 MgO SO3 BFS Strenght

Figure1 – Characterisation of the cements 2.2 Working technique

2.2.1 Experimental technique A calorimeter prototype enhanced with software for 1-minute temperature increment monitoring with a precision of ±0.01°C was employed to calculate the early heat of hydration (Fig. 2).

Imagine a prototipului pregatit pentru începerea încercarii

e

f

g

Imagine de ansamblu a prototipului realizat (vedere din plan superior)

a

b

c

d

Figure 2 Calorimeter a—temperature module; b—temperature controller; c—PELTIER cooler; d—fan;

e—reference calorimeter; f—calorimeter; g—vacuum container 2.2.2 Calculation technique Establishing a correlation between the standard strength and the heat of hydration involved two steps: I and II [13]. Step I: Automatic calculation of the early heat of hydration QhM of cement up to attaining the maximum temperature in the calorimeter by using equation (1) (Figure 3).

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Maria Ioan, Liliana Radu, Constanta Mandoiu: Software-enhanced method for rapid determination of the early heat of hydration of cement CEM II/A and B-S to predict the 28-day compressive strength

358

0 10 20 30 40 50 60 70405060708090

100110120130140150160170180190200210

Hea

t of h

ydra

tion,

Tem

pera

ture

Cement samples

Early heat of hydration (J/g)

Maximum temperature ( 0 C)

Figure 3 – Heat of hydration calculated up to attaining the maximum temperature

The early heat of hydration was calculated at 1-minute intervals by means of a software application program attached to the calorimeter. The heat of hydration Q (J/g) was calculated by adding the heat A contained in the calorimeter and the heat B lost in the environment.

Q = A + B (1)

The heat A was calculated using the overall heat capacity c of the calorimeter, the cement weight mc and the temperature increase θt of the cement specimen at the time t.

tcm

cA θ= (2)

The overall heat capacity c of the calorimeter including the cement specimen box and the cement specimen was calculated using eq. (3).

c = 0.8 mc + 3.8 mw + 3.833 macc 0.879 mb + μ (3)

Where: 0.8—specific heat capacity of cement, J/K.g 3.8—specific heat capacity of water, J/K.g 0.879—specific heat capacity of aluminium, J/K.g 3.833—specific heat capacity of CaCl2, J/K.g μ—default heat capacity of the empty calorimeter, J/K mc—weight of cement, g macc—weight of CaCl2, g mw—weight of water, g mb— weight of the cement specimen box, g.

The heat loss was calculated over periods of hydration such as between successive iterations of temperature determination. The calorimeter heat loss coefficient α, expressed in J/h.K, was given by equation (4).

α = a + b⋅θ (4) Where: a, b—calorimeter default constants θ—temperature increase, K.

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Maria Ioan, Liliana Radu, Constanta Mandoiu: Software-enhanced method for rapid determination of the early heat of hydration of cement CEM II/A and B-S to predict the 28-day compressive strength

359

Step II: Establishing a correlation y = ax + b to predict the 28-day compressive strength y as a function of the early heat of hydration x released up to θM. This step involved— – Graphical representation of the 28-day compressive strength (standard strength)

as determined experimentally as a function of the rapidly-determined early heat of hydration released up to attaining the maximum temperature (Fig. 4)

– Plotting the regression curve using equation y = ax + b (Fig. 4) – Calculating the 28-day compressive strength by using the obtained equation, and – Calculating the differences between the experimental data and the calculated

values.

150 160 170 180 190 200 210

32

34

36

38

40

42

44

46

48

50

R = 0.944

28da

y co

mpr

essi

ve s

treng

th, M

Pa

Early heat of hydration, J/g

y = 0.29471*x - 13.05315

Figure 4 - Standard strength vs. rapidly-determined early heat of hydration

Figure 4 presents the correlation between the 28-day strength determined on the 70 samples as per SR EN 196-1 and the early heat of hydration determined as per the rapid method. The early heat of hydration is used for predicting the 28-day compressive strength by means of equation (5).

y = 0,29471 x – 13,05315 (5) 3 RESULTS 3.1 Effect of blast furnace slag addition

Another objective of the experiments was to monitor the effect of the BFS addition on the 28-day compressive strength, the early heat of hydration and the maximum temperature during cement hydration. The data regarding the 28-day compressive strength, the early heat of hydration and the maximum temperature during cement hydration as a function of the BFS content were presented in figures 5, 6 and 7.

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Maria Ioan, Liliana Radu, Constanta Mandoiu: Software-enhanced method for rapid determination of the early heat of hydration of cement CEM II/A and B-S to predict the 28-day compressive strength

360

0 10 20 30 40 50 60 70101214161820222426283032343638404244464850

Slag

(%),

Rc28

(MPa

)

Cement samples

Slag (%) Rc28 (MPa)

Figure 5 - Variation of the 28-day compressive strength (red) and BFS content (black) for the 70 samples

0 10 20 30 40 50 60 70

20

40

60

80

100

120

140

160

180

200

Slag

(%),

QhM

(J/g

)

Cement samples

Slag QhM

Figure 6 - Variation of the early heat of hydration (red) and BFS content (black) for the 70 samples

0 10 20 30 40 50 60 7010

20

30

40

50

60

70

Max

imum

tem

pera

ture

( o C)

Cement samples

Slag (%) Max. temp ( oC)

Figure 7 - Variation of BFS content (black) and maximum temperature θM (red)

in the calorimeter for the 70 samples

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Maria Ioan, Liliana Radu, Constanta Mandoiu: Software-enhanced method for rapid determination of the early heat of hydration of cement CEM II/A and B-S to predict the 28-day compressive strength

361

3.2 Compatibility of calculated strength with experimental data

Data in Figure 3 revealed that the correspondence relation between the 28-day compressive strength values determined experimentally and calculated using the established correlation y = 0.29471x – 13.05315 was of R = 0.944. Figure 8 presents the strength values calculated on the basis of the above equation along with the experimental data. Differences between experimental data and calculated data varied within ±2.5 MPa.

20

30

40

50

60

0 10 20 30 40 50 60 70 80Number of samples

28d

stre

ngth

, MPa

Exp Calc

Max increases: 2.5 MPa

Max decreases: 2.5MPa

Figure 8 - 28-day compressive strength determined experimentally and calculated

using the equation y = 0.29471 x – 13.05315 (x = QhM) 4 CONCLUSIONS The paper dealt with establishing a correlation relation y = ax + b between the 28-day compressive strength y and the rapidly-determined early heat of hydration x of cement by employing a number of 70 samples of cement with addition of blast furnace slag CEM II/A, B-S from CARPATCEMENT HOLDING SA, Fieni. The obtained results revealed differences of ±2.5 MPa between the experimental data and the calculated values. The blast furnace slag addition was found to influence in the same manner both the early heat of hydration and the standard strength. A correlation equation for predicting the standard strength on the basis of the rapidly-determined early heat of hydration is specific to each cement manufacturer and type and sort of cement. The method is new, reproducible and fast, with the time to predict the standard strength for cement CEM II/A and B-S being of 3-4 hours upon manufacture. It may be employed by any cement manufacturer both when changing the formulation and the cement sort.

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Maria Ioan, Liliana Radu, Constanta Mandoiu: Software-enhanced method for rapid determination of the early heat of hydration of cement CEM II/A and B-S to predict the 28-day compressive strength

362

REFERENCES [1] Solacolu, S. : La chimie physique des silicates techniques (in Romanian), 2nd

Edition, Editura Tehnică, Bucharest, 1968 [2] Schmitt-Henko, C. : Effect of clinker composition on setting and early strength

of cement, ZKG International, 26 (2), 63, (1973) [3] Sylla, H.M. :Process Technology of Cement Manufacturing, Bauverlag GmbH,

Wiesbaden, (1993) [4] Shalam, M. Ish; Bentur, A. :Effects of aluminate and sulfate contents on the

hydration and strength of Portland cement pastes and mortars, Cem. Concr. Res., 2 (6), 653, (1972)

[5] Locher F.W. et al : Influence of the fineness of grinding and the particle size distribution on the properties of Portland and blast furnace cements and hydraulic limes, Tonind-Ztg, 90 (12), 547, (1966)

[6] Locher, F.W. :Setting and early strength of cement, ZKG International, 26 (2), 53, (1973)

[7] Teoreanu, I. et al., Concrete Durability (in Romanian), Editura Tehnică, Bucharest, 1982

[8] Locher, F.W. et al : The effect of the particle size distribution on the strength of Portland cement, ZKG International, 26 (8), 349, (1973)

[9] Squeira Tango, C.E. :An extrapolation method for compressive strength prediction of hydraulic cement products, Cem. Concr. Res., 28 (7), 969, (1998)

[10] Izaguirre, J.R. :Procedimiento rapido para identificar las resistencias de los cementos, Cemento Hormigon, 65 (20), 754, (1995)

[11] Ioan, M. et al : A rapid method of determination of the 28-day compressive strength of cement on thermally treated specimens; CEPROCIM Technical Report, 2000

[12] ***, SR EN 196-1:2006, Methods of testing cement. Part 1: Determination of strength

[13] Ioan, M. :CALIST Research Programme, Project No.4217 (2003–2005) [14] ***, SR EN 196-9:2004, Methods of testing cement. Part 9: Heat of hydration.

Semi adiabatic method


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