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The influence of different additions on portland cement hydration heat
CEMENT and CONCRETE RESEARCH. Vol. 23, pp. 46-54,1993. Printed in the USA. 0008-8846193. $6.00+.00. Copyright © 1993 Pergamon Press Ltd.
THE ON
M.I.
INFLUENCE OF DIFFERENT ADDITIONS PORTLAND CEMENT HYDRATION HEAT
SAnchez
de Rojas, M.P. LuxAn, M. F r ~ a s and N. I n s t i t u t o E d u a r d o T o r r o j a (CSIC) A p a r t a d o 19002. 28080 - M a d r i d (Spain)
GarcSa
(Refereed) (Received Sept. 3, 1991; in f'mal form Aug. 18, 1992)
ABSTRACT This p a p e r presents the results obtained using the Langavant Calorimeter method on portland cements with d i f f e r e n t a d d i t i o n m a t e r i a l s that are c o m m o n l y used in the m a n u f a c t u r e of commercial cements. The e f f e c t s of these m a t e r i a l s on the h y d r a t i o n heat w i t h r e s p e c t to a c o n t r o l cement were studied. The first hours show that m o s t of the a d d i t i o n s , which present higher activity at e a r l y stages, i n c r e a s e the h y d r a t i o n heat of t h e i r m i x e d c e m e n t s in r e l a t i o n to the c o n t r o l cement. The use of p o z z o l a n s r e d u c e s the heat g i v e n off by the c e m e n t s d u r i n g h y d r a t i o n . H o w e v e r , the r e a c t i o n s of the p o z z o l a n i c m a t e r i a l s w i t h the lime also p r o d u c e heat and the d e c r e a s e s h o u l d not be p r o p o r t i o n a l to the level of c l i n k e r s u b s t i t u t i o n in the m i x e d cements.
Introduction Exothermal the c e m e n t
reactions mass.
take
place
during
cement
hydration
and
heat
This t e m p e r a t u r e v a r i a t i o n , from the initial m o m e n t of setting until the h a r d e n i n g of the cement, c a u s e s s h r i n k a g e w h i c h r e s u l t s in the c r a c k s that can be seen in s o m e c o n s t r u c t i o n s that are made of large m a s s e s of c o n c r e t e or c e m e n t rich m i x t u r e s (I). The s t u d y and measurement of hydration heat is the s u b j e c t of many i n v e s t i g a t i o n s that p r e s e n t results on the behaviour of p o z z o l a n s and fly ashes. Cements with additions of natural p o z z o l a n (2), d i a t o m i t e s (3), slags (4), fly ashes (5), s i l i c a fume (6), etc. have been studied. The additions generally help d e c r e a s e the h y d r a t i o n heat (7) (8). 46
VOI.23,No. 1
Different have also adiabatic differential
HYDKATION CALORIMETRY, ADDITIONS,FOZZOLANS
47
ways of measuring the heat developed during hydration been tested such as the heat solution method (2), and calorimeter (9), as well as conduction calorimetry and calorimeter analysis (5) (10) (11).
This p a p e r p r e s e n t s the results obtained using the Langavant C a l o r i m e t e r method. D i f f e r e n t addition materials that are c o m m o n l y u s e d in the m a n u f a c t u r e of c o m m e r c i a l cements, and the e f f e c t s of t h e s e m a t e r i a l s on the h y d r a t i o n heat w i t h r e s p e c t to a c o n t r o l c e m e n t were studied.
Experimental * Materials The m a t e r i a l s c h o s e n for this to c e m e n t in m o s t c o u n t r i e s .
study
are
those
that
can
be a d d e d
T h e s e m a t e r i a l s were characterized using chemical m i n e r a l o g i c a l a n a l y s e s and the p o z z o l a n i c q u a l i t i e s of the p o z z o l a n i c m a t e r i a l s w e r e t e s t e d (12) (13). a.
Pozzolanic
and chosen
materials
- Natural Pozzolan: This m a t e r i a l has a h i g h silicon, aluminium and iron c o n t e n t w h i c h is e x p r e s s e d as an o x i d e and m a k e s up o v e r 70% of its chemical composition. The principal crystalline c o m p o n e n t is an i m p o r t a n t c o m p o n e n t in eruptive rocks, augite, w h i c h b e l o n g s to the p y r o x e n e family, as well as magnetite and h e m a t i t e (13). - V o l c a n i c Tuff: The principal c o m p o n e n t s of this f e l s p a r s (albite and a n a l c i t e ) and zeolites. The c o n t e n t (8.7%) of this m a t e r i a l is due to its o r i g i n tuff (13).
m a t e r i a l are high alkali - trachitic
- Diatomaceous Earth: The X-ray diffractogram shows the of c a l c i t e and some CT-opal. The earth has a high i g n i t i o n v a l u e (15.8%) and its p r i n c i p a l c o m p o n e n t s are and c a l c i u m o x i d e s / l i m e s t o n e (13).
presence loss on silicon
O p a l i n e Rock: This sedimentary m a t e r i a l is m o s t l y made up of s i l i c a (87.7%). The m i n e r a l o g i c a l a n a l y s i s shows that the s i l i c a takes d i f f e r e n t m e t a s t a b l e forms. The A-opal is practically a m o r p h o u s , and C T - o p a l c o n t a i n t r i d y m i t e , c r i s t o b a l i t e as well as quartz, k a o l i n i t e and s m a l l e r q u a n t i t i e s of m i c a s (13) (14) (15). -
Fly Ash: This is generated in a power plant that uses bituminous and anthracite coal as a power source. The loss on i g n i t i o n v a l u e (0.9%) reflects its low u n b u r n e d content, of w h i c h the m a i n c o n s t i t u e n t s are silicon, a l u m i n i u m and iron, so that it is a fly ash w i t h a low c a l c i u m c o n t e n t (2.9%). The m a i n c r y s t a l l i n e c o m p o n e n t s are quartz, m u l l i t e and h e m a t i t e (16). -
- Rice H u s k Ash: This m a t e r i a l was o b t a i n e d in a p r o t o t y p e o v e n (17). S i l i c a is the main component (91.3%) and the X-ray diffraction analysis indicates a low d e g r e e of crystallinity.
48
MI. S~inchez de Rojas et al.
Vol. 23, No. 1
M o s t of the silica present in t h i s a s h is and only a small percentage takes the form tridymite. b.
Non-Pozzolanic
in an a m o r p h o u s f o r m of c r i s t o b a l i t e and
Material
- L i m e s t o n e F i l l e r : T h e m a i n c o m p o n e n t is c a l c i t e . The a n a l y s i s f o u n d s m a l l q u a n t i t i e s of s i l i c a a n d a l u m i n a . c.
Base
chemical
Cement
A c c o r d i n g to the Spanish UNE 80 301 standard (18), t h e b a s e c e m e n t is a T y p e 1/45 A c e m e n t w i t h a c l i n k e r c o n t e n t e q u a l to or a b o v e 9 5 % t h a t c a n h a v e up to 5% a d d i t i o n a l c o m p o n e n t s .
* Mixtures First, the materials were subjected to a grinding process so that all of them presented a specific Blaine surface of between 4,500 and 5,000 cm2/g. Grain fineness strongly influences hydration heat, particularly during the initial moments of the test. The mixtures were prepared guarantee their perfect granulometry. The cement mixtures to Type V on the given in the Spanish Mixtures addition
in a homogeneity
high
were designed to cover bases of the allowable standards.
w e r e m a d e up proportions:
by w e i g h t in 100/0; 80/20;
speed and
a
powder safeguard
range addition
mixer to their
from Type percentages
the following base 70/30; 50/50;
cement 40/60
II
to and
30/70. * Method The method given for determining hydration heat in the Spanish standard (19) is based on the Langavant Calorimeter (20), the same as in France and Luxemburg. This method, like those used in other countries, is presently under discussion by the Low Heat Cements Working Group of the Technical Committee TC-51 of the European Standardization Committee (CEN). The purpose of this committee is the unification of the different criteria for the measurement of hydration heat in order to establish values for low hydration heat cements. This semi-adiabatic method consists in quantifying the heat generated during cement hydration using a Dewar f l a s k , or, more exactly, a thermally isolated bottle. Since the exterior conditions are very influential, the test is c a r r i e d o u t in a p e r f e c t l y c l i m a t i z e d r o o m at 2 0 " C ± 2°C. F o r t h i s p u r p o s e the c e m e n t u n d e r s t u d y is u s e d to m a k e up a t e s t m o r t a r t h a t is p l a c e d in a c l o s e d v e s s e l w h i c h in t u r n is p l a c e d w i t h i n the i s o l a t e d bottle. The mortar temperature during the c o u r s e of h y d r a t i o n is c o m p a r e d with that of a t h e r m a l l y i n e r t m o r t a r (one w h i c h was m i x e d u p e a r l i e r , at l e a s t three months
Vol. 23, No. 1
before
another
HYDRATION CALORIMETRY, ADDITIONS, IK)Z7_DLANS
test, f o l l o w i n g isolated bottle
the same standard) is u s e d as a s t a n d a r d
49
and the control.
content
in
The m e a s u r e m e n t s were m a d e o v e r five days as is i n d i c a t e d in the s t a n d a r d (19), since the heat i n c r e a s e is o b s e r v e d to be v e r y low at l a t e r times, and also since the relative error of the m e a s u r e m e n t i n c r e a s e s b e y o n d that time. Results
and
Discussion
The s t u d y c o n t e m p l a t e s two different aspects of the i n f l u e n c e that the d i f f e r e n t additions and their proportions in the p r e p a r e d c e m e n t m i x e s h a v e on h y d r a t i o n heat. I.
EFFECT
OF THE
DIFFERENT
ADDITIONS
ON HYDRATION
HEAT
F i g u r e 1 shows the e v o l u t i o n of the h y d r a t i o n heat over 5 days (120 hours) in the different cement preparations with different m a t e r i a l s at a c e m e n t / a d d i t i o n p r o p o r t i o n of 70/30. S i n c e all of the materials are incorporated in the same p e r c e n t a g e , the e f f e c t of e a c h m a t e r i a l on the h y d r a t i o n heat in r e l a t i o n to the p o r t l a n d c e m e n t base, w h i c h is the same in all of m i x t u r e s , can be seen. HEAT OF HYDRlfflON ( J / g ) 860
800-
260
-
200
-
110
-
!
1 O0 -
60
- #
..........................
F 0 0
I
I
i
i
i
10
20
a0
40
l0
i
l
i
i
I
i
SO
70
S0
e0
100
110
~E N.PO~.ZOL AN
--~-- V O L T U F F
FLY ASH
-~-
W0
(houre) -~
RIOE HUSK ASH ~
Fig. i.- H E A T Mixed Cements
i ~0
OI~L.ROOK
- G - DIATOMITE EARTH
LIME81"ONE
- K - BASE 0EMENT
OF H Y D R A T I O N O V E R and Base P o r t l a n d
TIME Cement
The first 5 h o u r s (Fig. 2) s h o w that most of the a d d i t i o n s , w h i c h present higher activity at e a r l y stages, i n c r e a s e the h y d r a t i o n heat of t h e i r m i x e d c e m e n t s in r e l a t i o n to the c o n t r o l cement, and a c c e l e r a t e the appearance of the maximum thermal effect. T h i s p h e n o m e n o n is not observed in the cements that c o n t a i n l i m e s t o n e or fly ash.
50
M-I. S ~ c h e z de Roj~ et al.
HF.X7 O F H Y O I t / ~ ' I O N
Vol. 23. No. 1
(J/g)
860
IO0
280
.
IOo
14o
1{}o-
$o-
0
o
i
i
i
!
!
!
i
!
!
i
i
I
a
2
s
4
is
4
1,
•
•
Io
11
s2
m
.*4E (kure) N.PORZOI.AN --X--- F L Y A S H
--4-- V O L . T U F F ~
RIOE HUSK
Fig. 2.- H E A T Mixed cements
AIIH
-]((-- ~
~
DIIQ'OMITE EARTH
-,t3,- L I M E i T O N E
-K-
BASE GEMENT
OF H Y D R A T I O N (12 H O U R S ) and Base P o r t l a n d c e m e n t
Nevertheless, after 5 hours and during the next 7 hours the strongly exothermic reactions and the ascendent slope for the high curves exemplify how the base cement produces higher hydration heat in comparison with the mixed cements. O v e r time the a c t i v i t y of the a d d i t i o n m a t e r i a l c o n t i n u e s to p l a y an i m p o r t a n t role. The o p a l i n e rocks and the d i a t o m a c e o u s earth, a d d i t i o n s w h i c h react q u i c k l y w i t h lime (13) and give rise to e x o t h e r m i c r e a c t i o n s lose less h y d r a t i o n heat than the fly ash, w h i c h e x p r e s s e s its p o z z o l a n i c c a p a c i t y on a m u c h l a r g e r scale (16), the same as the rice husk ash. On the o t h e r hand, the limestone, w h i c h can react with the cement and give rise to carboaluminates (7), also acts more slowly. II.
S T U D Y OF HYDRATION
THE HEAT
INFLUENCE
OF
THE
ADDITION
PERCENTAGE
ON
To c h e c k the i n f l u e n c e of the p e r c e n t a g e of the a d d i t i o n s on the cement mixtures, different mixtures with different addition p e r c e n t a g e s were made up. This s t u d y is c a r r i e d out n a t u r a l and a r t i f i c i a l .
with
two
types
of p o z z o l a n i c
material:
O p a l i n e rock was chosen as a n a t u r a l p o z z o l a n since it p r e s e n t s the g r e a t e s t p o z z o l a n i c a c t i v i t y at early ages. Fly ash was c h o s e n as an artificial p o z z o l a n since its b e h a v i o u r at early ages c o n t r a s t e d w i t h the n a t u r a l m a t e r i a l and shows low activity. Base c e m e n t / a d d i t i o n m i x t u r e s were p r e p a r e d w i t h o p a l i n e rock in the p e r c e n t a g e s of 80/20, 70/30 and 60/40, w h i c h r e p r o d u c e d the T y p e s II and IV cements of the Spanish standard (18). The m i x t u r e s made w i t h fly ash a d d i t i o n w e r e the following: 50/50,
Vol. 23, No. 1
HYDRATION CALORIMETRY, ADDITIONS,P(YZZDLANS
51
HER'INO (1~) 4O
SO
...........
10 ~
.....
0
0
!
I
I
I
I
I
I
I
I
I
I
I
10
IPO
80
40
60
IlO
70
80
90
100
110
'1~0
180
AaE (hours)
00/40
Fig.
--]-- 70/30
--X(- 80/20
3.- H E A T I N G
"{3-100/0
OVER Rock
Opaline
TIME
40/60 and 30/70, w h i c h were s i m i l a r to the m i x e d The base c e m e n t used in each case was d i f f e r e n t , b e l o n g e d to Type 1/45 A (18). These p r o p o r t i o n s r e p r o d u c e the e x i s t i n g w i d e range in m o d e r n c e m e n t F i g u r e 3 gives the h e a t i n g of the mixtures rock and F i g u r e 4 gives the figures for the
c e m e n t Type V. although both were c h o s e n to additions.
prepared with opaline fly ash cement.
HEATING (°0)
40
80
20
'i
-"
i
~'-
! 10
20
80
40 80/70
Ii0
I10 70 M E (llHmro)
--4-- 4 0 / 0 0
~
Fig. 4.- H E A T I N G Fly
ash
8,0
60/60
I10
~
OVER
100
10010
TIME
110
110
1:10
52
M.I. S~nchcz de Rojas et al.
Vol. 23, No. 1
The use of pozzolans reduces the heat given off by the cements during hydration. However, the reactions of the pozzolanic material with the lime also produce heat and should be taken into account since the decrease is not proportional to the level of clinker substitution in the base cement.
F i g u r e s 5 and 6 study d i f f e r e n c e s in the r e l a t i o n between the a d d i t i o n p e r c e n t a g e in the p r e p a r e d m i x e s and the d e c r e a s e of the h y d r a t i o n heat (by p e r c e n t a g e s ) p r o v o k e d by the i n c o r p o r a t i o n of each of the a d d i t i o n s , in r e l a t i o n to the base cement. The h y d r a t i o n r e f e r e n c e and
heat of the a d d i t i o n - f r e e is g i v e n a v a l u e of I00%.
cement
is
taken
as
a
This study was c a r r i e d out at the times at w h i c h the heat c u r v e s r e a c h e d their maximum, since, as has b e e n n o t e d earlier, at e a r l y times the p o z z o l a n i c material usually increased the hydration heat in c o m p a r i s o n w i t h the base cement, and a f t e r 48 h o u r s the t e m p e r a t u r e b e g a n to s t a b i l i z e itself and the heat g i v e n off was not v e r y s i g n i f i c a n t . Its i n c r e a s e s the test error m a r g i n and allows m i n i m u m v a r i a t i o n s in the heat p r o d u c e d by the p o z z o l a n i c m a t e r i a l s to c o m p e n s a t e for the p e r c e n t a g e of c e m e n t s u b s t i t u t e d in the p r e p a r a t i o n of the mixes. Figure 5 shows that the i n f l u e n c e of the o p a l i n e rock at 12 hours on the p e r c e n t a g e of d e c r e a s e of heat is proportional to the c o n t e n t of the addition in m i x e d cements, i n d i c a t i n g that the p r e d o m i n a n t e f f e c t is the elimination of the cement by s u b s t i t u t i n g it w i t h the addition. N e v e r t h e l e s s , over time and until h y d r a t i o n heat in r e l a t i o n w i t h the lower.
48 hours, base c e m e n t
decrease in the progressively is
H Y D R I I Z I O N HE/Or DECREASE ( % )
1 O0
60
" ..........................................................................................................................................................................................
40
....
2o
......
~
I
0
10
:
-
I
-
~
................. ~
I ~4......,@__ I
i
I
20
,
................................................
i
25
80120
Fig.
I -,--.._.~
.---~::::.--:-....--:--:--.-
15
....................................................................................................
:-----~.----"T
i
i
30 ~ E (Imuro)
86
I
70150
i
40
:~
................ , ......
l
46
60
60•40
5.- R A T I O B E T W E E N THE A D D I T I O N P E R C E N T A G E AND THE D E C R E A S E OF THE H Y D R A T I O N H E A T O p a l i n e rock
Vol.23.No. 1
HYDRATION CALORIMETRY,ADDITIONS,POZZOLANS
HF.IQ D E O R ~
HY~ION
53
(,)
100"
80
...................................................................................................................................................................................
~--~..~_...~_
/
'
4 0 t .................................................................... /
~
.............................."~...........................................
i
0
10
i
1
i
i
|
|
i
15
20
26
80
86
40
46
60
N3E (boure)
60/50
Fig.
6.-
- 4 - - 40•60
:(( 80170
RATIO BETWEEN THE ADDITION PERCENTAGE AND THE DECREASE OF THE HYDRATION HEAT Fly ash
Fly ash, Fig. 6, is similar to the above, although, since the p o z z o l a n i c a c t i v i t y of this m a t e r i a l is slower than the former, it takes l o n g e r to c o m p e n s a t e the d e c r e a s e in heat c a u s e d by the s u b s t i t u t i o n of c e m e n t w i t h fly ash. C o n s t r u c t i o n s done w i t h cements that contain fly ash (low calcium) p r e s e n t an evolution of hydration heat that is p r i n c i p a l l y i n f l u e n c e d by the decrease in the proportion of c e m e n t in the mixture. The p r o p o r t i o n a l i t y b e t w e e n the d e c r e a s e of the h y d r a t i o n heat and the p e r c e n t a g e of addition will he g r e a t e r than w h e n n a t u r a l a d d i t i o n s are used, w h i c h have g r e a t e r r e a c t i v i t y at e a r l i e r ages. N e v e r t h e l e s s , the use of fly ashes, w h i c h may be f a v o u r a b l e in r e g a r d s to the h y d r a t i o n heat, w h i c h d e c r e a s e s , does not improve the m e c h a n i c a l s t r e n g t h s of the mixed c e m e n t s and c o n c r e t e s .
References
1.-
R.
SPRINGENSCHMID.
2.- A. RIO, A. CELANI, 232 (1964).
Zement
Kalk
A. MIELE.
n.
L'Ind.
MALHOTRA.
of
Cem.,
n.
4,
III,
223-
K. KOKUBU, S. TAKASHASHI, H. ANZAI. 3 r d CANMET/ACI I n t . C o n f e r e n c e on Fly Ash, Silica Fume, Slag, and Natural P o z z o l a n s in C o n c r e t e , 2, 1361-1376, T r o n d h e i m (1989).
V.M.
Chem.
Cem.,
(1991).
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ELOLA,
the
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J.GRZYMEK. 7th Int. 71. Paris (1980).
A.
on
3,
3.-
5.- E. DOUGLAS,
Congr.
Gips,
3rd C A N M E T / A C I
IV/66-
Int.
54
M.I. S ~ c h e z de Rojas et al.
C o n f e r e n c e on Fly Ash, P o z z o l a n s in Concrete, T r o n d h e i m , (1989). 6.-
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Slag, and Natural Papers, 618-640.
D.M. ROY. 3 r d CANMET/ACI I n t . Conference on Fly Fume, Slag, and Natural Pozzolans in Concrete, Trondheim (1989).
7.- F. MASSAZZA. 7th Int. 96, Paris (1980).
Congr.
8.- H. UCHIKAWA. 8th Int. Congr. 280. Rio de J a n e i r o (1986).
on
the Chem.
on the Chem.
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of Cem.,
of
Cem.,
IV,
i,
85-
249-
9 . - U. COSTA. I i Cemento, 2, 75- 91 (1979). i0.- G. OLIEW, W. WIEKER. 7th Int. C o n g r e s s Cement, IV, 291-294. Paris (1980). Ii.- C.H. BLAND, J.H. 359-361 (1991). 12.- M.P. LUXAN, Construcci6n,
SHARP.
Cement
and
on the C h e m i s t r y
Concrete
M.I. SANCHEZ DE ROJAS. 35, n. 200, 3-13 (1985).
Research,
of
21,
Materiales
de
13.- M.P. LUXAN, M.I. SANCHEZ DE ROJAS, M.T. M A R T I N PATINO, J. SAAVEDRA. ist Int. R I L E M Congress. Ed. Chapman and Hall. Pore S t r u c t u r e and M a t e r i a l s P r o p e r t i e s , l, 191-194. Paris
(1987). 14.- M.P. LUXAN, M.I. SANCHEZ DE ROJAS, M.T. M A R T I N PATINO, SAAVEDRA. 8th Int. C o n g r e s s on The C h e m i s t r y of Cement, IV, 468-469. Rio de Janeiro (1986).
J.
M.T. M A R T I N PATINO, J. 15.- M.P. LUXAN, M.I. S A N C H E Z DE ROJAS, n. 397. Ed. Instituto SAAVEDRA, F. MADRUGA. Monografia E d u a r d o T o r r o j a (CSIC), p. 46 (1989).
16.- M.P. LUXAN, M.I. C o n c r e t e Research,
SANCHEZ DE ROJAS, 19, 69-80 (1989).
17.- J. SALAS, P. CASTILLO, M.I. M a t e r i a l e s de C o n s t r u c c i 6 n , 18.- N o r m a UNE 80 301: "Cementos. y E s p e c i f i c a c i o n e s " (1988).
SANCHEZ 36, 21-39
M. FRIAS.
DE ROJAS, (1986).
Definiciones,
Cement
J.
and
VERAS.
Clasificaci6n
19.-
N o r m a UNE 80 1 1 8 : " M 4 t o d o s d e E n s a y o d e C e m e n t o s . Ensayos Fisicos: D e t e r m i n a c i 6 n del Calor de Hidrataci6n por Calorimetr~a Semi-adiab~tica (M4todo del Calor~metro de L a n g a v a n t ) " (1986).
20.-
R. ALEGRE. Revue 247-262 (1961).
des
Mat~riaux,
(547),
218-229.
(548)
THE ON
M.I.
INFLUENCE OF DIFFERENT ADDITIONS PORTLAND CEMENT HYDRATION HEAT
SAnchez
de Rojas, M.P. LuxAn, M. F r ~ a s and N. I n s t i t u t o E d u a r d o T o r r o j a (CSIC) A p a r t a d o 19002. 28080 - M a d r i d (Spain)
GarcSa
(Refereed) (Received Sept. 3, 1991; in f'mal form Aug. 18, 1992)
ABSTRACT This p a p e r presents the results obtained using the Langavant Calorimeter method on portland cements with d i f f e r e n t a d d i t i o n m a t e r i a l s that are c o m m o n l y used in the m a n u f a c t u r e of commercial cements. The e f f e c t s of these m a t e r i a l s on the h y d r a t i o n heat w i t h r e s p e c t to a c o n t r o l cement were studied. The first hours show that m o s t of the a d d i t i o n s , which present higher activity at e a r l y stages, i n c r e a s e the h y d r a t i o n heat of t h e i r m i x e d c e m e n t s in r e l a t i o n to the c o n t r o l cement. The use of p o z z o l a n s r e d u c e s the heat g i v e n off by the c e m e n t s d u r i n g h y d r a t i o n . H o w e v e r , the r e a c t i o n s of the p o z z o l a n i c m a t e r i a l s w i t h the lime also p r o d u c e heat and the d e c r e a s e s h o u l d not be p r o p o r t i o n a l to the level of c l i n k e r s u b s t i t u t i o n in the m i x e d cements.
Introduction Exothermal the c e m e n t
reactions mass.
take
place
during
cement
hydration
and
heat
This t e m p e r a t u r e v a r i a t i o n , from the initial m o m e n t of setting until the h a r d e n i n g of the cement, c a u s e s s h r i n k a g e w h i c h r e s u l t s in the c r a c k s that can be seen in s o m e c o n s t r u c t i o n s that are made of large m a s s e s of c o n c r e t e or c e m e n t rich m i x t u r e s (I). The s t u d y and measurement of hydration heat is the s u b j e c t of many i n v e s t i g a t i o n s that p r e s e n t results on the behaviour of p o z z o l a n s and fly ashes. Cements with additions of natural p o z z o l a n (2), d i a t o m i t e s (3), slags (4), fly ashes (5), s i l i c a fume (6), etc. have been studied. The additions generally help d e c r e a s e the h y d r a t i o n heat (7) (8). 46
VOI.23,No. 1
Different have also adiabatic differential
HYDKATION CALORIMETRY, ADDITIONS,FOZZOLANS
47
ways of measuring the heat developed during hydration been tested such as the heat solution method (2), and calorimeter (9), as well as conduction calorimetry and calorimeter analysis (5) (10) (11).
This p a p e r p r e s e n t s the results obtained using the Langavant C a l o r i m e t e r method. D i f f e r e n t addition materials that are c o m m o n l y u s e d in the m a n u f a c t u r e of c o m m e r c i a l cements, and the e f f e c t s of t h e s e m a t e r i a l s on the h y d r a t i o n heat w i t h r e s p e c t to a c o n t r o l c e m e n t were studied.
Experimental * Materials The m a t e r i a l s c h o s e n for this to c e m e n t in m o s t c o u n t r i e s .
study
are
those
that
can
be a d d e d
T h e s e m a t e r i a l s were characterized using chemical m i n e r a l o g i c a l a n a l y s e s and the p o z z o l a n i c q u a l i t i e s of the p o z z o l a n i c m a t e r i a l s w e r e t e s t e d (12) (13). a.
Pozzolanic
and chosen
materials
- Natural Pozzolan: This m a t e r i a l has a h i g h silicon, aluminium and iron c o n t e n t w h i c h is e x p r e s s e d as an o x i d e and m a k e s up o v e r 70% of its chemical composition. The principal crystalline c o m p o n e n t is an i m p o r t a n t c o m p o n e n t in eruptive rocks, augite, w h i c h b e l o n g s to the p y r o x e n e family, as well as magnetite and h e m a t i t e (13). - V o l c a n i c Tuff: The principal c o m p o n e n t s of this f e l s p a r s (albite and a n a l c i t e ) and zeolites. The c o n t e n t (8.7%) of this m a t e r i a l is due to its o r i g i n tuff (13).
m a t e r i a l are high alkali - trachitic
- Diatomaceous Earth: The X-ray diffractogram shows the of c a l c i t e and some CT-opal. The earth has a high i g n i t i o n v a l u e (15.8%) and its p r i n c i p a l c o m p o n e n t s are and c a l c i u m o x i d e s / l i m e s t o n e (13).
presence loss on silicon
O p a l i n e Rock: This sedimentary m a t e r i a l is m o s t l y made up of s i l i c a (87.7%). The m i n e r a l o g i c a l a n a l y s i s shows that the s i l i c a takes d i f f e r e n t m e t a s t a b l e forms. The A-opal is practically a m o r p h o u s , and C T - o p a l c o n t a i n t r i d y m i t e , c r i s t o b a l i t e as well as quartz, k a o l i n i t e and s m a l l e r q u a n t i t i e s of m i c a s (13) (14) (15). -
Fly Ash: This is generated in a power plant that uses bituminous and anthracite coal as a power source. The loss on i g n i t i o n v a l u e (0.9%) reflects its low u n b u r n e d content, of w h i c h the m a i n c o n s t i t u e n t s are silicon, a l u m i n i u m and iron, so that it is a fly ash w i t h a low c a l c i u m c o n t e n t (2.9%). The m a i n c r y s t a l l i n e c o m p o n e n t s are quartz, m u l l i t e and h e m a t i t e (16). -
- Rice H u s k Ash: This m a t e r i a l was o b t a i n e d in a p r o t o t y p e o v e n (17). S i l i c a is the main component (91.3%) and the X-ray diffraction analysis indicates a low d e g r e e of crystallinity.
48
MI. S~inchez de Rojas et al.
Vol. 23, No. 1
M o s t of the silica present in t h i s a s h is and only a small percentage takes the form tridymite. b.
Non-Pozzolanic
in an a m o r p h o u s f o r m of c r i s t o b a l i t e and
Material
- L i m e s t o n e F i l l e r : T h e m a i n c o m p o n e n t is c a l c i t e . The a n a l y s i s f o u n d s m a l l q u a n t i t i e s of s i l i c a a n d a l u m i n a . c.
Base
chemical
Cement
A c c o r d i n g to the Spanish UNE 80 301 standard (18), t h e b a s e c e m e n t is a T y p e 1/45 A c e m e n t w i t h a c l i n k e r c o n t e n t e q u a l to or a b o v e 9 5 % t h a t c a n h a v e up to 5% a d d i t i o n a l c o m p o n e n t s .
* Mixtures First, the materials were subjected to a grinding process so that all of them presented a specific Blaine surface of between 4,500 and 5,000 cm2/g. Grain fineness strongly influences hydration heat, particularly during the initial moments of the test. The mixtures were prepared guarantee their perfect granulometry. The cement mixtures to Type V on the given in the Spanish Mixtures addition
in a homogeneity
high
were designed to cover bases of the allowable standards.
w e r e m a d e up proportions:
by w e i g h t in 100/0; 80/20;
speed and
a
powder safeguard
range addition
mixer to their
from Type percentages
the following base 70/30; 50/50;
cement 40/60
II
to and
30/70. * Method The method given for determining hydration heat in the Spanish standard (19) is based on the Langavant Calorimeter (20), the same as in France and Luxemburg. This method, like those used in other countries, is presently under discussion by the Low Heat Cements Working Group of the Technical Committee TC-51 of the European Standardization Committee (CEN). The purpose of this committee is the unification of the different criteria for the measurement of hydration heat in order to establish values for low hydration heat cements. This semi-adiabatic method consists in quantifying the heat generated during cement hydration using a Dewar f l a s k , or, more exactly, a thermally isolated bottle. Since the exterior conditions are very influential, the test is c a r r i e d o u t in a p e r f e c t l y c l i m a t i z e d r o o m at 2 0 " C ± 2°C. F o r t h i s p u r p o s e the c e m e n t u n d e r s t u d y is u s e d to m a k e up a t e s t m o r t a r t h a t is p l a c e d in a c l o s e d v e s s e l w h i c h in t u r n is p l a c e d w i t h i n the i s o l a t e d bottle. The mortar temperature during the c o u r s e of h y d r a t i o n is c o m p a r e d with that of a t h e r m a l l y i n e r t m o r t a r (one w h i c h was m i x e d u p e a r l i e r , at l e a s t three months
Vol. 23, No. 1
before
another
HYDRATION CALORIMETRY, ADDITIONS, IK)Z7_DLANS
test, f o l l o w i n g isolated bottle
the same standard) is u s e d as a s t a n d a r d
49
and the control.
content
in
The m e a s u r e m e n t s were m a d e o v e r five days as is i n d i c a t e d in the s t a n d a r d (19), since the heat i n c r e a s e is o b s e r v e d to be v e r y low at l a t e r times, and also since the relative error of the m e a s u r e m e n t i n c r e a s e s b e y o n d that time. Results
and
Discussion
The s t u d y c o n t e m p l a t e s two different aspects of the i n f l u e n c e that the d i f f e r e n t additions and their proportions in the p r e p a r e d c e m e n t m i x e s h a v e on h y d r a t i o n heat. I.
EFFECT
OF THE
DIFFERENT
ADDITIONS
ON HYDRATION
HEAT
F i g u r e 1 shows the e v o l u t i o n of the h y d r a t i o n heat over 5 days (120 hours) in the different cement preparations with different m a t e r i a l s at a c e m e n t / a d d i t i o n p r o p o r t i o n of 70/30. S i n c e all of the materials are incorporated in the same p e r c e n t a g e , the e f f e c t of e a c h m a t e r i a l on the h y d r a t i o n heat in r e l a t i o n to the p o r t l a n d c e m e n t base, w h i c h is the same in all of m i x t u r e s , can be seen. HEAT OF HYDRlfflON ( J / g ) 860
800-
260
-
200
-
110
-
!
1 O0 -
60
- #
..........................
F 0 0
I
I
i
i
i
10
20
a0
40
l0
i
l
i
i
I
i
SO
70
S0
e0
100
110
~E N.PO~.ZOL AN
--~-- V O L T U F F
FLY ASH
-~-
W0
(houre) -~
RIOE HUSK ASH ~
Fig. i.- H E A T Mixed Cements
i ~0
OI~L.ROOK
- G - DIATOMITE EARTH
LIME81"ONE
- K - BASE 0EMENT
OF H Y D R A T I O N O V E R and Base P o r t l a n d
TIME Cement
The first 5 h o u r s (Fig. 2) s h o w that most of the a d d i t i o n s , w h i c h present higher activity at e a r l y stages, i n c r e a s e the h y d r a t i o n heat of t h e i r m i x e d c e m e n t s in r e l a t i o n to the c o n t r o l cement, and a c c e l e r a t e the appearance of the maximum thermal effect. T h i s p h e n o m e n o n is not observed in the cements that c o n t a i n l i m e s t o n e or fly ash.
50
M-I. S ~ c h e z de Roj~ et al.
HF.X7 O F H Y O I t / ~ ' I O N
Vol. 23. No. 1
(J/g)
860
IO0
280
.
IOo
14o
1{}o-
$o-
0
o
i
i
i
!
!
!
i
!
!
i
i
I
a
2
s
4
is
4
1,
•
•
Io
11
s2
m
.*4E (kure) N.PORZOI.AN --X--- F L Y A S H
--4-- V O L . T U F F ~
RIOE HUSK
Fig. 2.- H E A T Mixed cements
AIIH
-]((-- ~
~
DIIQ'OMITE EARTH
-,t3,- L I M E i T O N E
-K-
BASE GEMENT
OF H Y D R A T I O N (12 H O U R S ) and Base P o r t l a n d c e m e n t
Nevertheless, after 5 hours and during the next 7 hours the strongly exothermic reactions and the ascendent slope for the high curves exemplify how the base cement produces higher hydration heat in comparison with the mixed cements. O v e r time the a c t i v i t y of the a d d i t i o n m a t e r i a l c o n t i n u e s to p l a y an i m p o r t a n t role. The o p a l i n e rocks and the d i a t o m a c e o u s earth, a d d i t i o n s w h i c h react q u i c k l y w i t h lime (13) and give rise to e x o t h e r m i c r e a c t i o n s lose less h y d r a t i o n heat than the fly ash, w h i c h e x p r e s s e s its p o z z o l a n i c c a p a c i t y on a m u c h l a r g e r scale (16), the same as the rice husk ash. On the o t h e r hand, the limestone, w h i c h can react with the cement and give rise to carboaluminates (7), also acts more slowly. II.
S T U D Y OF HYDRATION
THE HEAT
INFLUENCE
OF
THE
ADDITION
PERCENTAGE
ON
To c h e c k the i n f l u e n c e of the p e r c e n t a g e of the a d d i t i o n s on the cement mixtures, different mixtures with different addition p e r c e n t a g e s were made up. This s t u d y is c a r r i e d out n a t u r a l and a r t i f i c i a l .
with
two
types
of p o z z o l a n i c
material:
O p a l i n e rock was chosen as a n a t u r a l p o z z o l a n since it p r e s e n t s the g r e a t e s t p o z z o l a n i c a c t i v i t y at early ages. Fly ash was c h o s e n as an artificial p o z z o l a n since its b e h a v i o u r at early ages c o n t r a s t e d w i t h the n a t u r a l m a t e r i a l and shows low activity. Base c e m e n t / a d d i t i o n m i x t u r e s were p r e p a r e d w i t h o p a l i n e rock in the p e r c e n t a g e s of 80/20, 70/30 and 60/40, w h i c h r e p r o d u c e d the T y p e s II and IV cements of the Spanish standard (18). The m i x t u r e s made w i t h fly ash a d d i t i o n w e r e the following: 50/50,
Vol. 23, No. 1
HYDRATION CALORIMETRY, ADDITIONS,P(YZZDLANS
51
HER'INO (1~) 4O
SO
...........
10 ~
.....
0
0
!
I
I
I
I
I
I
I
I
I
I
I
10
IPO
80
40
60
IlO
70
80
90
100
110
'1~0
180
AaE (hours)
00/40
Fig.
--]-- 70/30
--X(- 80/20
3.- H E A T I N G
"{3-100/0
OVER Rock
Opaline
TIME
40/60 and 30/70, w h i c h were s i m i l a r to the m i x e d The base c e m e n t used in each case was d i f f e r e n t , b e l o n g e d to Type 1/45 A (18). These p r o p o r t i o n s r e p r o d u c e the e x i s t i n g w i d e range in m o d e r n c e m e n t F i g u r e 3 gives the h e a t i n g of the mixtures rock and F i g u r e 4 gives the figures for the
c e m e n t Type V. although both were c h o s e n to additions.
prepared with opaline fly ash cement.
HEATING (°0)
40
80
20
'i
-"
i
~'-
! 10
20
80
40 80/70
Ii0
I10 70 M E (llHmro)
--4-- 4 0 / 0 0
~
Fig. 4.- H E A T I N G Fly
ash
8,0
60/60
I10
~
OVER
100
10010
TIME
110
110
1:10
52
M.I. S~nchcz de Rojas et al.
Vol. 23, No. 1
The use of pozzolans reduces the heat given off by the cements during hydration. However, the reactions of the pozzolanic material with the lime also produce heat and should be taken into account since the decrease is not proportional to the level of clinker substitution in the base cement.
F i g u r e s 5 and 6 study d i f f e r e n c e s in the r e l a t i o n between the a d d i t i o n p e r c e n t a g e in the p r e p a r e d m i x e s and the d e c r e a s e of the h y d r a t i o n heat (by p e r c e n t a g e s ) p r o v o k e d by the i n c o r p o r a t i o n of each of the a d d i t i o n s , in r e l a t i o n to the base cement. The h y d r a t i o n r e f e r e n c e and
heat of the a d d i t i o n - f r e e is g i v e n a v a l u e of I00%.
cement
is
taken
as
a
This study was c a r r i e d out at the times at w h i c h the heat c u r v e s r e a c h e d their maximum, since, as has b e e n n o t e d earlier, at e a r l y times the p o z z o l a n i c material usually increased the hydration heat in c o m p a r i s o n w i t h the base cement, and a f t e r 48 h o u r s the t e m p e r a t u r e b e g a n to s t a b i l i z e itself and the heat g i v e n off was not v e r y s i g n i f i c a n t . Its i n c r e a s e s the test error m a r g i n and allows m i n i m u m v a r i a t i o n s in the heat p r o d u c e d by the p o z z o l a n i c m a t e r i a l s to c o m p e n s a t e for the p e r c e n t a g e of c e m e n t s u b s t i t u t e d in the p r e p a r a t i o n of the mixes. Figure 5 shows that the i n f l u e n c e of the o p a l i n e rock at 12 hours on the p e r c e n t a g e of d e c r e a s e of heat is proportional to the c o n t e n t of the addition in m i x e d cements, i n d i c a t i n g that the p r e d o m i n a n t e f f e c t is the elimination of the cement by s u b s t i t u t i n g it w i t h the addition. N e v e r t h e l e s s , over time and until h y d r a t i o n heat in r e l a t i o n w i t h the lower.
48 hours, base c e m e n t
decrease in the progressively is
H Y D R I I Z I O N HE/Or DECREASE ( % )
1 O0
60
" ..........................................................................................................................................................................................
40
....
2o
......
~
I
0
10
:
-
I
-
~
................. ~
I ~4......,@__ I
i
I
20
,
................................................
i
25
80120
Fig.
I -,--.._.~
.---~::::.--:-....--:--:--.-
15
....................................................................................................
:-----~.----"T
i
i
30 ~ E (Imuro)
86
I
70150
i
40
:~
................ , ......
l
46
60
60•40
5.- R A T I O B E T W E E N THE A D D I T I O N P E R C E N T A G E AND THE D E C R E A S E OF THE H Y D R A T I O N H E A T O p a l i n e rock
Vol.23.No. 1
HYDRATION CALORIMETRY,ADDITIONS,POZZOLANS
HF.IQ D E O R ~
HY~ION
53
(,)
100"
80
...................................................................................................................................................................................
~--~..~_...~_
/
'
4 0 t .................................................................... /
~
.............................."~...........................................
i
0
10
i
1
i
i
|
|
i
15
20
26
80
86
40
46
60
N3E (boure)
60/50
Fig.
6.-
- 4 - - 40•60
:(( 80170
RATIO BETWEEN THE ADDITION PERCENTAGE AND THE DECREASE OF THE HYDRATION HEAT Fly ash
Fly ash, Fig. 6, is similar to the above, although, since the p o z z o l a n i c a c t i v i t y of this m a t e r i a l is slower than the former, it takes l o n g e r to c o m p e n s a t e the d e c r e a s e in heat c a u s e d by the s u b s t i t u t i o n of c e m e n t w i t h fly ash. C o n s t r u c t i o n s done w i t h cements that contain fly ash (low calcium) p r e s e n t an evolution of hydration heat that is p r i n c i p a l l y i n f l u e n c e d by the decrease in the proportion of c e m e n t in the mixture. The p r o p o r t i o n a l i t y b e t w e e n the d e c r e a s e of the h y d r a t i o n heat and the p e r c e n t a g e of addition will he g r e a t e r than w h e n n a t u r a l a d d i t i o n s are used, w h i c h have g r e a t e r r e a c t i v i t y at e a r l i e r ages. N e v e r t h e l e s s , the use of fly ashes, w h i c h may be f a v o u r a b l e in r e g a r d s to the h y d r a t i o n heat, w h i c h d e c r e a s e s , does not improve the m e c h a n i c a l s t r e n g t h s of the mixed c e m e n t s and c o n c r e t e s .
References
1.-
R.
SPRINGENSCHMID.
2.- A. RIO, A. CELANI, 232 (1964).
Zement
Kalk
A. MIELE.
n.
L'Ind.
MALHOTRA.
of
Cem.,
n.
4,
III,
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