Action of triethanolamine on the hydration of tricalcium aluminate

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Cement and Concrete Research, 3, January 1, pp. 41-54, 1973-01-01

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Action of triethanolamine on the hydration of tricalcium aluminate

Ramachandran, V. S.

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CEMENT and CONCRETE RESEARCH. Vol

.

3 , pp. 41 -54, 1973. Pergamon P r e s s , I n c . P r i n t e d i n t h e U n i t e d S t a t e s .

ACTION O F TRIETHANOLAMINE ON THE HYDRATION O F TRICALCIUM ALUMINATE

V. S. Ramachandran

Division of Building R e s e a r c h , National R e s e a r c h Council of Canada Ottawa KIA 0R6, Ontario, Canada

(Communicated by P. J

.

Sereda)

ABSTRACT

Hydration c h a r a c t e r i s t i c s of t r i c a l c i u m aluminate and t r i c a l c i u m

aluminate -k gypsum w e r e studied following addition of 0. 5, 1. 0,

5. 0 o r 10. 0% triethanolamine (TEA) at a s o l u t i o n / C 3 ~ r a t i o of

1. 0 a f t e r hydration p e r i o d s of 1 t o 60 min. TEA a c c e l e r a t e d the

hydration of C3A t o t h e hexagonal aluminate h y d r a t e and i t s con- v e r s i o n t o the cubic aluminate h y d r a t e . T h e r a t e of hydration i n c r e a s e d with i n c r e a s e d amounts of TEA, which a l s o a c c e l e r a t e d the f o r m a t i o n of ettringite in t h e C3A - g y p s u m - H 2 0 s y s t e m .

S OMMAIRE

L e s c a r a c t C r i s t i q u e s d'hydratation d e l ' a l u m i n a t e d e t r i c a l c i u m

et de l'aluminate d e t r i c a l c i u m -k gypse ont CtC CtudiCes apr'es

l'addition de 0. 5, 1. 0, 5. 0 ou 1070 de trigthanolamine (TEA) dans

un r a p p o r t s o l u t i o n / C 3 ~ de 1. 0 apr'es de pCriodes d'hydratation

allant de 1 2. 60 min. La TEA accCl'ere l'hydratation du C3A en

h y d r a t e d'aluminate hexagonal et s a conversion en h y d r a t e d'aluminate cubique. La vites s e d'hydratation augmente en proportion d i r e c t e de l a quantitC de TEA, qui accCl'ere Cgalement l a f o r m a t i o n de l ' e t t r i n g i t e dans le syst'eme C A-gypse-H 0.

42

ADMIXTURE, TRICALCIUM ALUMINATE, HYDRATION, RATE V o l . 3, No.

1

I n t r o d u c t i o n T r i e t h a n o l a m i n e ( T E A ) i s u s e d i n c e r t a i n a d m i x t u r e f o r m u l a t i o n s i n c o n c r e t e . In t h e w a t e r r e d u c i n g

-

a c c e l e r a t i n g t y p e of a d m i x t u r e T E A h a s b e e n r e p o r t e d t o c o u n t e r a c t t h e e x c e s s i v e r e t a r d a t i o n effect of t h e w a t e r - r e d u c i n g agent. T h e m a i n a d v a n t a g e i n u s i n g T E A i n s t e a d of C a C l i s t h a t it 2 d o e s not p r o m o t e c o r r o s i o n of embedded m e t a l s u s e d i n r e i n f o r c i n g c o n c r e t e . T h e m e c h a n i s m of t h e a c t i o n of T E A i n t h e h y d r a t i o n of p o r t l a n d c e m e n t is not c l e a r . It i s g e n e r a l l y t e r m e d a n a c c e l e r a t o r , but i t h a s not

b e e n c o m p l e t e l y a c c e p t e d a s one (1-4). It i s p o s s i b l e t h a t T E A m a y a c t a s e i t h e r a r e t a r d e r o r a c c e l e r a t o r of h y d r a t i o n of p o r t l a n d c e m e n t , depending on t h e c h e m i c a l and m i n e r a l o g i c a l c o m p o s i t i o n of t h e c e m e n t and t h e a m o u n t of T E A added t o i t . F r o m a p r a c t i c a l standpoint, a d i r e c t s t u d y of t h e influence of T E A on t h e h y d r a t i o n of c e m e n t would b e useful. T h e a d m i x t u r e m a y a c t i n a c o m p l e x w a y t o affect t h e h y d r a t i o n of individual p h a s e s and t h e i r h y d r a t i o n p r o d u c t s , h o w e v e r , and i t s e e m s t o be m o r e m e a n i n g f u l t o i n v e s t i g a t e t h e r o l e of T E A i n t h e h y d r a t i o n of t h e individual, b i n a r y and t e r n a r y s y s t e m s b e f o r e extending t h e s t u d y t o t h e c e m e n t i t s e l f .

E a r l i e r w o r k on t h e effect of d i f f e r e n t a m o u n t s of T E A on t h e h y d r a t i o n of t r i c a l c i u m s i l i c a t e h a s r e v e a l e d a n u m b e r of p o i n t s (5). R e g a r d l e s s of t h e method of a n a l y s i s , DTA, TGA, X - r a y o r c h e m i c a l a n a l y s i s , t h e amount of l i m e found a t a n y t i m e i n a s a m p l e t r e a t e d w i t h T E A i s l e s s t h a n t h a t found i n a n u n t r e a t e d s a m p l e . Addition of T E A t o t r i c a l c i u m s i l i c a t e a l s o i n c r e a s e s t h e induction o r d o r m a n t p e r i o d , p r o m o t e s t h e f o r m a t i o n of a c a l c i u m s i l i c a t e h y d r a t e with a h i g h e r C ~ O / S ~ O r a t i o , and e n h a n c e s t h e f o r m a t i o n of n o n - 2 c r y s t a l l i n e C a ( 0 H ) 2' T h e e a r l y s e t t i n g c h a r a c t e r i s t i c s of p o r t l a n d c e m e n t a r e influenced by t h e t r i c a l c i u m a l u m i n a t e (C A) p h a s e . A l i t e r a t u r e s u r v e y h a s i n d i c a t e d t h a t 3 p r a c t i c a l l y no w o r k h a s b e e n r e p o r t e d on t h e influence of T E A on t h e h y d r a t i o n of C A. C i a c h and Swenson s t u d i e d t h e m o r p h o l o g i c a l c h a n g e s o c c u r r i n g i n 3 C A i n t h e p r e s e n c e of 0. 5% T E A a t 5 m i n , 1 h r , 4 h r and t h e r e a f t e r

(6).

3 T h e y concluded t h a t i n t h e f i r s t few d a y s t h e h y d r a t i o n p r o c e s s of C A p a s t e 3

V o l . 3, N o .

1

4 3 ADMIXTURE, T R I C A L C I U M A L U M I N A T E , H Y D R A T I O N , R A T E

with T E A i s s i m i l a r t o t h a t of a p a s t e without i t . T r i c a l c i u m a l u m i n a t e r e a c t s r a p i d l y with w a t e r and i s t h e r e f o r e u s e f u l i n studying t h e h y d r a t i o n p r o c e s s a t v e r y e a r l y t i m e s . A s D i f f e r e n t i a l T h e r m a l A n a l y s i s i s known t o b e e m i n e n t l y s u i t e d t o following h y d r a t i o n c h a r a c t e r i s t i c s of C A (7), i t w a s ₃ u s e d i n t h e w o r k now r e p o r t e d of t h e h y d r a t i o n of C A and ₃ C ₃ A - g y p s u m m i x - t u r e s f o r p e r i o d s of 1 t o 60 m i n u s i n g different a m o u n t s of T E A . E x p e r i m e n t a l M a t e r i a l s T r i c a l c i u m a l u m i n a t e of high p u r i t y w a s p r e p a r e d by c a l c i n a t i o n of

CaCO and A1 0 T h e s a m p l e w a s ground t o p a s s a 200 - m e s h s i e v e and h a d

3 2 3' a Blaine s u r f a c e a r e a of 4350 s q ~ m / ~ . F r e e l i m e w a s s c a r c e l y d e t e c t a b l e by X - r a y . Only v e r y f a i n t l i n e s of C A could b e d i s c e r n e d . T h e c h a r a c t e r i s - 12 7 t i c s of C A have a l r e a d y b e e n r e p o r t e d (8). T r i e t h a n o l a m i n e of c e r t i f i e d 3

g r a d e (supplied by F i s h e r Scientific G O . ) and a r e a g e n t g r a d e gypsum w e r e u s e d .

Hydration

C A w a s mixed with double-distilled w a t e r a t a

water/^

A r a t i o of

3 3

1. 0, p l a c e d i n tightly c o v e r e d polyethylene c o n t a i n e r s and r o t a t e d continu-

o u s l y o v e r r o l l e r s , At s p e c i f i e d i n t e r v a l s , which v a r i e d f r o m a few m i n u t e s

t o 1 h r , e a c h s a m p l e w a s p l a c e d i n a n e x c e s s of cold a c e t o n e , f i l t e r e d by

washing with cold acetone, and s u b s e q u e n t l y evacuated f o r 2 4 h r u s i n g liquid

a i r i n t h e t r a p . C a r e w a s t a k e n t o p r e v e n t contamination with CO A s i m i l a r 2' method w a s followed f o r h y d r a t i o n e x p e r i m e n t s i n t h e p r e s e n c e of 0. 5, 1. 0 and 5. 0% T E A a t a solution/C A r a t i o of 1. 0. 3 T h e influence of T E A on t h e h y d r a t i o n c h a r a c t e r i s t i c s of C A-gypsum 3 m i x t u r e s w a s studied a s d e s c r i b e d above. T h e C ~ / ~ y p s u m r a t i o w a s e i t h e r 3

20 o r 4, and thorough mixing w a s achieved with a Wig-1 -bug v i b r a t o r . T e c h n i a u e

A l l s a m p l e s w e r e s u b j e c t e d t o D i f f e r e n t i a l T h e r m a l A n a l y s i s , and s o m e t o conduction c a l o r i m e t r i c , X - r a y d i f f r a c t i o n and scanning e l e c t r o n m i c r o s c o p e investigations.

44

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ADMIXTURE, TRICALCIUM ALUMINATE, HYDRATION, RATE

DTA w a s c a r r i e d out i n a i r and i n a flow of N u s i n g a n a p p a r a t u s 2

supplied by R. L. S t o n e and Co. T h e h e a t i n g r a t e w a s m a i n t a i n e d a t 1 0 * l ° C .

In e a c h r u n 100 m g of t h e s a m p l e w a s u s e d t o f a c i l i t a t e a r e a s o n a b l e c o m p a r i - s o n of t h e r e l a t i v e i n t e n s i t i e s of t h e r m a l e f f e c t s developed a t d i f f e r e n t s t a g e s of h y d r a t i o n . D i f f e r e n t i a l t e m p e r a t u r e i s plotted on t h e y - a x i s of t h e t h e r m o - g r a m s . X - r a y p h o t o g r a p h s w e r e obtained by a N o r e l c o unit u s i n g a Debye- S c h e r r e r c a m e r a of d i a m e t e r 114. 6 m m

A conduction c a l o r i m e t e r containing s i x c h a m b e r s , supplied by t h e I n s t i t u t e of Applied P h y s i c s , Delft, w a s u s e d t o d e t e r m i n e t h e r a t e of h e a t

development of C A and C A

+

gypsum h y d r a t e d a l o n e and i n t h e p r e s e n c e of

3 3

T E A . Although t h e c h a m b e r s w e r e c o a t e d with teflon t h e h y d r a t e d p r o d u c t s

tended t o s t i c k t o t h e s u r f a c e s o t h a t polyethylene l i n e r s w e r e u s e d . T h e s e n s i t i v i t y of t h e c a l o r i m e t e r w a s 20 ~ v / w ; t e m p e r a t u r e of t h e bath, 2 5 ° C . E x a m i n a t i o n of t h e h y d r a t e d s a m p l e s w a s a l s o c a r r i e d out by e l e c t r o n m i c r o - s c o p e u s i n g a C a m b r i d g e S t e r e o s c a n M a r k 2A unit. R e s u l t s and D i s c u s s i o n H y d r a t i o n of C A i n t h e P r e s e n c e of T E A 3 F i g u r e 1 r e f e r s t o t h e t h e r m a l c u r v e s of C A h y d r a t e d f o r 1. 5, 10, 3 30 and 60 m i n a t a w a t e r / C A r a t i o of 1. 0. C u r v e s of T E A w e r e obtained a t 3

0. 5, 1. 0 o r 5. 0% by m i x i n g with r e q u i r e d a m o u n t s of A1203. Unhydrated

C A d o e s not i n d i c a t e any t h e r m a l inflection and i s not shown. At 1 m i n t h e 3 C3A s a m p l e e x h i b i t s e n d o t h e r m a l e f f e c t s a t about 150 a n d 250°C (8, 9 ) . t y p i c a l of a m i x t u r e of hexagonal d i c a l c i u m a l u m i n a t e h y d r a t e , 2 C a 0 . A 1 2 0 3 . 8 H 2 0 (C2AH ) 8 and t e t r a c a l c i u m a l u m i n a t e h y d r a t e , 4CaO. A1 0

.

1 3 H 2 0 (C AHl3). 2 3 4

A t about 5 m i n a l l s a m p l e s show a l a r g e e n d o t h e r m a l effect a t about 300°C, followed by a s m a l l e r e n d o t h e r m b e t w e e n 400 and 500°C. T h e s e i n f l e c t i o n s a r e t y p i c a l of t r i c a l c i u m a l u m i n a t e h e x a h y d r a t e

3 C a 0 . A1203. 6 H 2 0 (C3AH ) 6

V o l . 3 , N o .

1

4 5 ADMIXTURE, T R I C A L C I U M A L U M I N A T E , HYDRATION, RATE

u

u

I l l 1 l l 1 1 i : u

0 - T t A 0 57 T E A 1 0‘ T E A 5 - T E A

FIG. 1

Hydration of C A with Different Amounts of Triethanolamine

3

and r e p r e s e n t a stepwise dehydration of

6

_{m o l e s of H 0.}

2

The intensity of t h e peaks i n c r e a s e s a s hydration p r o g r e s s e s . Data

r e v e a l that C A h y d r a t e s t o the hexagonal aluminate hydrate p h a s e immediately

3

on contact with water and that i t t r a n s f o r m s t o t h e cubic f o r m within 5 min. The r a t e of formation of the hexagonal aluminate hydrate and i t s t r a n s f o r m a - tion t o the cubic f o r m depend on t e m p e r a t u r e and water/C A ratio. At a low

3

water/^

A r a t i o of 0. 12 i t m a y be 2 h r before t h e hexagonal f o r m t r a n s f o r m s 3

t o the cubic f o r m

(9).

C3A s a m p l e s containing 0. 5, 1. 0 o r 5.070 TEA show t h e r m a l c h a r a c -

t e r i s t i c s different f r o m those of untreated C A. At 1 min, 0. 5 and 1. 070 TEA

3

p r o m o t e t h e formation of l a r g e r amounts of hexagonal aluminate hydrates, a s evidenced by t h e g r e a t e r intensity of the peak a t about 150°C (revealing

thereby t h a t a c c e l e r a t i o n of hydration of C A h a s taken place). The endo- 3

t h e r m a l effect a t about 250°C does not i n c r e a s e i n proportion t o that a t about 150°C because of t h e masking effect of t h e exothermal effect of TEA o c c u r r i n g between 200 and 300°C. At 5.070 TEA t h e r e i s a l a r g e amount of C AH even

3

6

a t 1 min, indicating that a c c e l e r a t i o n of hydration of C A i s enhanced by 3

46

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A D M I X T U R E , T R I C A L C I U M A L U M I N A T E , H Y D R A T I O N , R A T E

i n c r e a s e d amount of TEA. It w a s difficult, b e c a u s e of t h e e x p e r i m e n t a l l i m i t a t i o n s of stopping h y d r a t i o n efficiently within a few s e c o n d s , t o confirm

whether C A

+

57'0 T E A f o r m e d a hexagonal a l u m i n a t e h y d r a t e a s a p r e l u d e t o

3

f o r m a t i o n of t h e cubic f o r m .

C A

+

57'0 T E A shows a n e x o t h e r m a l effect between 400 and 5 0 0 ° C a t

3

60 m i n of hydration, a n effect not r e a d i l y a p p a r e n t i n o t h e r s a m p l e s . T h i s p e a k cannot be a t t r i b u t e d t o t h e oxidation effect of f r e e T E A b e c a u s e f r e e T E A

exhibits e x o t h e r m a l p e a k s between 200 and 300" C. Leaching of t h e s a m p l e

with ethyl alcohol does not r e m o v e t h e e x o t h e r m i c peak. F r e e T E A i s soluble i n alcohol and i t m a y be i n f e r r e d t h a t T E A r e a c t s with t h e a l u m i n a t e h y d r a t e t o exhibit t h e e x o t h e r m i c effect a t about 450°C. C a l c i u m lignosulfonate i s

shown t o be i r r e v e r s i b l y a d s o r b e d by t h e C AH p h a s e (10). 3 6 T h e a b s e n c e of e x o t h e r m i c p e a k s i n a l l o t h e r s a m p l e s m a y be due t o one o r m o r e of t h e following c a u s e s : ( 1 ) T h e amount of C AH f o r m e d i n o t h e r s a m p l e s i s l e s s and h e n c e l e s s T E A 3 6 i s bound. ( 2 ) A l a r g e r contact t i m e m a y b e r e q u i r e d f o r r e a c t i o n of t h e T E A admixture. ( 3 ) T E A m a y e x i s t i n t h e f r e e f o r m .

In s u c h s a m p l e s t h e l a r g e e n d o t h e r m of t h e C3AH effect, commencing a t

6

about 200°C, m a y m a s k t h e e x o t h e r m of t h e f r e e TEA. In t h e C3A

+

070 T E A

s a m p l e s i t m a y be o b s e r v e d t h a t e n d o t h e r m a l deviation of t h e p e a k o c c u r s a t

about 200°C. In s a m p l e s containing T E A t h e deviation o c c u r s beyond a

t e m p e r a t u r e of 200" C.

T h e a c c e l e r a t i n g effect of T E A on t h e h y d r a t i o n of C A was f u r t h e r 3

confirmed by r a t e of h e a t development i l l u s t r a t e d by t h e conduction c a l o r i

-

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1

4

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A D M I X T U R E , T R I C A L C I U M A L U M I N A T E , H Y D R A T I O N , R A T E

a f t e r 10 to 12 min for C A hydrated without 3

TEA, and a s the amount of TEA i s increased, s o i s the r a t e of heat liberation enhanced. The inflection corresponding to the maximum r a t e of heat development o c c u r s e a r l i e r a s the

amount of TEA i s increased from 1. 0 t o 10. 070;

1

the maximum r a t e o c c u r s at only 3, min f o r the sample with 1070 TEA.

The total amount of heat developed in the f i r s t 30 min i s n e a r l y twice a s much for the

4 "

sample with 1070 TEA and about one and one half

2 3

a s mach for t h e sample with 470 TEA a s for corresponsing s a m p l e s containing no TEA. It

IS

should be noted that the r a t e of hydration d e t e r - mined by conduction c a l o r i m e t r y i s not directly

comparable to data obtained through DTA t h e r - r1:1c ? ~ I N U T E C

m o g r a m s because, in the c a l o r i m e t e r , the

sample-solution mixture i s not continuously FIG. 2

agitated during hydration. The method c l e a r l y Conduction C a l o r i m e t r i c

demonstrates the accelerating effect of TEA Curves of 3 C a 0 A1203

With Different Amounts on the hydration of C A.

3 of Added TEA

The exact mechanism of the accelerating effect of TEA on the h y d r a -

tion of C A i s difficult to prove conclusively. On exposure to water C A

3 3

f o r m s hexagonal aluminate hydrates on the s u r f a c e , and the r a t e of reaction a t the s u r f a c e and the p a s s a g e of water through the layer of hexagonal

aluminate hydrates control the o v e r - a l l r a t e of reaction. Triethanolamine is an aminoalcohol and cation active, and it i s possible that it i n t e r f e r e s with the formation of t h e usual protective layer of t h e hexagonal aluminate hydrate on the s u r f a c e of C3A. The formation of a complex of TEA with the hexagonal

phase was not detected in the t h e r m o g r a m s . It i s possible that, i f formed, this complex i s soluble in an aqueous medium.

48

ADMIXTURE, T R I C A L C I U M ALUMINATE, HYDRATION, RATE

Hydration of C,A t Gypsum in t h e P r e s e n c e of TEA

V o l . 3, N o . 1

F i g u r e 3 shows t h e t h e r m a l behaviour of C ₃ A hydrated in t h e p r e s e n c e

of 57'0 gypsum with and without 170 TEA. The unhydrated C A t gypsum m i x - 3

t u r e exhibits a typical endothermal doublet between 100 and 150" C due t o t h e

TEhlPiRATURL c _{stepwise dehydration of gypsum.}

0 100

d

o

o

-

6

"

Even a t 1 m i n of hydration

O M l N

t h e r e i s a c o n s i d e r a b l e diminu- tion of the intensity of t h i s

2 M I N ,

effect, indicating that an appreciable amount of gypsum

h a s r e a c t e d with C A. In

3

addition, a s m a l l endotherm

! O ? < l l N _{develops at about 170" C that}

intensifies with a shift in t h e

I

I peak t e m p e r a t u r e at 30 and

60 min. T h i s peak m a y be a s c r i b e d t o t h e p r e s e n c e of high sulfoaluminate (ettringit e).

V

v

A s m a l l endothermal effect

u

u

o c c u r r i n g a s a doublet adjacent

OL T I I I E T H A N O L d ? l l N t I ' T H l t T H A N O L A h . l l \ t

FIG. 3 t o t h e ettringite peak m a y

Hydration of C A

f

57'0 Gypsum

With ~ r i e t i a n o l a m i n e

indicate t h e formation of h e x a - gonal aluminate h y d r a t e . The endothermal humps between 250 and 300°C (containing two endothermal effects) m a y r e p r e s e n t t h e e x i s - t e n c e of the hexagonal aluminate h y d r a t e and i t s solid solution with t h e low

sulfoaluminat e.

E t t r i n g i t e i s t h e f i r s t sulfate-containing product that f o r m s in t h e h y - dration of C A with gypsum and c o n v e r t s , subsequently, t o t h e low sulfoalu-

3

m i n a t e f o r m , depending on t h e r a t i o of C A t o gypsum. In C A containing

3 3

57'0 gypsum t h e formation of ettringite, the hexagonal. aluminate hydrate, and conversion of ettringite t o t h e low sulfoaluminate o r solid solution s e e m t o occur together in the f i r s t hour of hydration.

V o l . 3, N o . 1 4 9 ADMIXTURE, T R I C A L C I U M A L U M I N A T E , H Y D R A T I O N , RATE

The C A t gypsum m i x t u r e containing 170 TEA a l s o shows endother-

3

ma1 e f f e c t s s i m i l a r t o those of the m i x t u r e containing no TEA. The r a t e of formation of various h y d r a t e s i s different : gypsum s e e m s t o be

consumed m o r e rapidly; ettringite f o r m s in l a r g e r quantities, even a t 2 min, and continues t o i n c r e a s e up t o 60 min; and the amount of low sulfo- aluminate i s enhanced. T h e s e r e s u l t s a r e evidence that TEA a c t s a s an

a c c e l e r a t o r in the hydration of C A t gypsum m i x t u r e .

3

In o r d e r t o accentuate some of t h e s e effects, a f u r t h e r set of e x -

p e r i m e n t s was c a r r i e d out by hydrating a C A t gypsum m i x t u r e containing

3

25% gypsum ( s e e t h e r m o g r a m s , T E I I P L R A T U R C c

0 1 0 0 3 0 0 5 0 0

Fig. 4). T h e r m a l c u r v e s of C A

m

0+Fr?14u

3 h l l N 0

t gypsum hydrated in the p r e s e n c e

of TEA a r e different from those

without TEA. Hydration s e e m s t o 2,,,

s t a r t in the f i r s t minute of contact

of H 0 with the C A t gypsum

2 3

mixture. At 5 m i n a l a r g e r amount of gypsum h a s disappeared from the sample containing TEA; a t

10 and 30 min it i s evident that the ettringite peak o c c u r r i n g between 150 and 200°C i s m o r e intense. Beyond 30 min t h e two s a m p l e s (with and without TEA)

exhibit almost s i m i l a r intensities.

1

It a p p e a r s that formation of U J

-

0 % T R I E T H A N O L A h l l N E 1% T R I E T H A N O L A h I I N E

ettringite i s a c c e l e r a t e d between 5

FIG. 4

and 10 min in the TEA-treated

Hydration of C A ₃ t 25Y0 Gypsum

sample, w h e r e a s in the untreated With Triethanolamine

s a m p l e t h i s o c c u r s between 10 and 30 min. S i m i l a r t r e n d s m a y be observed

in C A t 5% gypsum m i x t u r e s (Fig. 3 ) . Additional peaks corresponding t o

3

those f o r hexagonal aluminate h y d r a t e s a r e not indicated in the C A

+

2570

3

gypsum m i x t u r e s . Where t h e r e i s an e x c e s s of gypsum, C A p r e f e r e n t i a l l y 3

5 0 V o l . 3, N o . 1 ADMIXTURE

,

T R I C A L C I U M A L U M I N A T E , HYDRATION, RATE

f o r m s t h e sulfoaluminate products. L a r g e amounts of low sulfoaluminate h y d r a t e a r e formed between 10 and 30 min. A s m a l l endothermal effect between 100 and 150°C p e r s i s t i n g t o 60 m i n m a y r e p r e s e n t r e s i d u a l gypsum; it m a y a l s o be contributed t o s o m e extent by the ettringite phase.

T h e a c c e l e r a t i n g influence of TEA in the hydration of C A t gypsum

3

should be reflected in t h e amount of heat developed during the r e a c t i o n and m a y be followed through the conduction c a l o r i m e t r i c c u r v e s ( F i g . 5).

I

I I I I I I I I Generally, the r a t e of h e a t develop-

ment in T E A - t r e a t e d s a m p l e s i s higher. T h e t o t a l heat developed in

t h e f i r s t 30 min in the C3A t 570

0 - -

gypsum s a m p l e with and without TEA, i s in the r a t i o 1:O. 77; the c o r r e s p o n d -

ing r a t i o for the C A t 2570 gypsum

3

i s 1:O. 9. As h a s a l r e a d y been stated,

t h e r a t e of heat development d e t e r - mined by conduction c a l o r i m e t r y i s not d i r e c t l y c o m p a r a b l e with DTA c u r v e s . T h e c u r v e s , however, demon- s t r a t e t h e r e l a t i v e r a t e s of reaction of

C A t gypsum s a m p l e s with and with-

3 out TEA.

0

0 I 0 20 30 4 0 5 0 No definite conclusions could

TlhlE M I N U T E S

FIG. 5

be drawn f r o m the X - r a y data. 3A l i n e s become somewhat weaker a s

Conduction C a l o r i m e t r i c hydration p r o g r e s s e s . T h e C3A t

C u r v e s of 3 C a 0 A1203

Hydrated in t h e P r e s e n c e gypsum

+

H 2 0

+

570 TEA s a m p l e shows

of C a S 0 4 2H 0 and TEA

2 a broad band in the r a n g e 9 . 8 t o 10A,

not indicated in the untreated s a m p l e s possibly owing t o t h e formation of m o r e e t t r i n g i t e in the TEA-treated sample.

E l e c t r o n m i c r o s c o p i c examination provided observations of morpho

-

logical changes o c c u r r i n g in the s y s t e m a t different p e r i o d s of hydration. In general, the ettringite needles predominated in a l l s a m p l e s during the e a r l y

Vol.

3, No.

1

51

A D M I X T U R E , T R I C A L C I U M A L U M I N A T E , H Y D R A T I O N , R A T E

FIG. 6A FIG. 6B C A

+

Gypsum

+

H 0 a t 5 m i n 2 C A t Gypsum

+

H20

+

TEA (170) 3 3 ( x 1400) 5 m i n ( x 1400) FIG. 6C FIG. 6D C A t Gypsum

+

H

0 a t 5 m i n 3 2 C A t Gypsum t H 3 2 0

+

T E A (170) ( x 3650) 5 m i n ( x 3650)

p e r i o d s of h y d r a t i o n . At 5 m i n t h e C A t 570 gypsum m i x t u r e with TEA

3

indicated a m o r e d e n s e f o r m a t i o n of e t t r i n g i t e n e e d l e s on t h e C A s u r f a c e t h a n ₃

did t h e u n t r e a t e d s a m p l e ( F i g . 6A t o D ) . T h e r e w a s a l s o s o m e indication t h a t

m o r e unhydrated p a r t i c l e s e x i s t in t h e u n t r e a t e d s a m p l e . At 60 m i n of h y d r a - t i o n a p l a t y s t r u c t u r e f o r m e d in a l l s a m p l e s , c o r r e s p o n d i n g t o t h e hexagonal a l u m i n a t e h y d r a t e , low s u l f o a l u m i n a t e o r i t s solid solution (Fig. 6 ~ t o G).

52 V o l . 3, N o . 1 ADMIXTURE, T R I C A L C I U M A L U M I N A T E , HYDRATION, R A T E FIG. 6 E FIG. 6 F C A ₃

+

G y p s u m

+

H 0 a t 60 m i n 2 C A t G y p s u m t 3 H 2 O + T E A (1%) ( x 7500) a t 60 m i n ( x 7500) FIG. 6G C A

+

G y p s u m t H 0

+

T E A (5%) 3 ₂ a t 60 m i n ( x 7500) In t h e h y d r a t i o n of C A t gypsum m i x t u r e s i t i s g e n e r a l l y believed 3 t h a t a l a y e r of h i g h s u l f o a l u m i n a t e f o r m s on t h e a n h y d r o u s C A s u r f a c e and 3 r e t a r d s t h e r e a c t i o n by d e c r e a s i n g diffusion of s u l f a t e i o n s t h r o u g h i t . With t i m e , m o r e s u l f a t e c o m p l e x f o r m s u n t i l t h e l a y e r b r e a k s . It a p p e a r s t h a t t h e addition of T E A i n t e r f e r e s with t h e f o r m a t i o n of a n i m p e r m e a b l e l a y e r of s u l f o a l u m i n a t e b y c o m p e t i n g f o r a d s o r p t i o n on t h e C A s u r f a c e . T r i e t h a n o l a - 3 + t t

++

m i n e is c a t i o n a c t i v e and i s c a p a b l e of r e p l a c i n g A 1 and C a i o n s . T h e p o s s i b i l i t y of t h e f o r m a t i o n of a l e s s c r y s t a l l i n e e t t r i n g i t e i n t h e p r e s e n c e of T E A i s difficult t o p r o v e , but t h e r e i s i n d i c a t i o n of a s t r o n g e x o t h e r m i n t h e

Vol.

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53

A D M I X T U R E , T R I C A L C I U M A L U M I N A T E , H Y D R A T I O N , R A T E

r a n g e 300 t o 400°C, even a t 1 m i n , i n T E A - t r e a t e d s a m p l e s . T h i s effect i s a b s e n t a t s u b s e q u e n t p e r i o d s of h y d r a t i o n . It m a y r e p r e s e n t a c r y s t a l l i z a t i o n effect of t h e d e h y d r a t e d e t t r i n g i t e . Analogous e x o t h e r m a l effect i n t h e

t h e r m a l c u r v e s of C A. C a C l . 6 H 0 h a s b e e n r e p o r t e d ( 1 1 ) . 3 2 2 C o n c l u s i o n s T r i e t h a n o l a m i n e a c t s a s a r e t a r d e r i n t h e h y d r a t i o n of t r i c a l c i u m s i l i c a t e by extending t h e induction p e r i o d . It a c t s , h o w e v e r , a s a n a c c e l e r a - t o r i n t h e h y d r a t i o n of t r i c a l c i u m a l u m i n a t e , by both i n c r e a s i n g t h e f o r m a t i o n of t h e h e x a g o n a l a l u m i n a t e h y d r a t e s and p r o m o t i n g c o n v e r s i o n t o t h e cubic a l u m i n a t e h y d r a t e . T E A a l s o a c c e l e r a t e s t h e f o r m a t i o n of e t t r i n g i t e i n t h e C A - g y p s u m - H 0 s y s t e m . 3 2 Acknowledgment

T h e a u t h o r i s g r a t e f u l t o P. E. Grattan-Bellew for useful d i s c u s s i o n and acknowledges with t h a n k s t h e v a l u a b l e e x p e r i m e n t a l c o n t r i b u t i o n of

G. M. P o l o m a r k and t h e a s s i s t a n c e of E. G. Quinn and P. J. L e f e b v r e .

T h i s p a p e r i s a c o n t r i b u t i o n f r o m t h e Division of Building R e s e a r c h , National R e s e a r c h C o u n c i l of Canada, and i s published with t h e a p p r o v a l of t h e D i r e c t o r of t h e Division.

R e f e r e n c e s

1. S. M. Royak, V. S. Klemet'eva, and G. M. T a r n a r u t s k i i . Z h u r n a l

P r i k l . Khimii, 43, 8 2 (1970).

_-

2 . ACI C o m m i t t e e 212, A d m i x t u r e s i n C o n c r e t e , J. A m e r . C o n c r e t e I n s t . , 1 6 , 113 (1954).

_-

3. K. E. F l e t c h e r , and M.H. R o b e r t s . C o n c r e t e , 5, 142 (1971).

_-

4. V. S, R a m a c h a n d r a n . (unpublished r e s u l t s ) . 5. V. S , R a m a c h a n d r a n . "fluence of t r i e t h a n o l a m i n e on t h e h y d r a t i o n c h a r a c t e r i s t i c s of t r i c a l c i u m s i l i c a t e P . T o b e published. 6. T . D . C i a c h , a n d E . G , Swenson. C e m e n t C o n c r e t e R e s , , 1, 1 4 3 ( 1 9 7 1 ) .

_-

7. V. S. R a m a c h a n d r a n . Applications of D i f f e r e n t i a l T h e r m a l A n a l y s i s i n

54 V o l . 3, N o . 1 ADMIXTURE, T R I C A L C I U M A L U M I N A T E , HYDRATION, RATE

Cement C h e m i s t r y , C h e m i c a l Publishing Co.

,

New York, pp. 308,

(1969).

8. V. S. R a m a c h a n d r a n and R. F. -Feldman. Cement Technology,

-

2, 121

(1971).

9. R. F. F e l d m a n and V. S. Ramachandran. J. A m e r . C e r a m . S o c . , 49,

-

268 (1966).

10. V. S. R a m a c h a n d r a n and R. F. Feldman. M a t e r i a u x et Constructions,

5, 67 (1971).

-

11. S. J. Ahmed, L. S. Dent G l a s s e r and H. F. W. T a y l o r . P r o c . Fifth