Exploratory studies of the utilization of sulfur in autoclaved products

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Cement and Concrete Research, 4, 2, pp. 177-192, 1974-03

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Exploratory studies of the utilization of sulfur in autoclaved products

Beaudoin, J. J.; Sereda, P. J.

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CEMENT and CONCRETE RESEARCH. Vol. 4 , pp. 177-192, 1974. Pergamon P r e s s , I n c . P r i n t e d i n t h e United S t a t e s .

EXPLORATORY STUDIES O F T H E UTILIZATION O F SULFUR IN AUTOCLAVED PRODUCTS

J. J. Beaudoin and P. J. S e r e d a

I/

M a t e r i a l s Section, Division of Building R e s e a r c h , National R e s e a r c h Council of Canada

OTTAWA (Communicated by G .

L .

Kalousek) (Received November 1 9 , 1973) ABSTRACT A significant i m p r o v e m e n t in t h e c o m p r e s s i v e s t r e n g t h of c e m e n t p a s t e autoclaved a t 2 1 6 0 ~ and 300 p s i s t e a m p r e s s u r e

h a s been obtained with 1 t o 2 p e r c e n t s u l f u r additions. P h y s i c a l p r o p e r t i e s s u c h a s N, s u r f a c e a r e a , p o r e s i z e d i s t r i b u t i o n , f i r s t d r y i n g s h r i n k a g e , density, p o r o s i t y and m i c r o h a r d n e s s p r o v i d e evidence that t h e addition of s u l f u r p r o d u c e s p r o p e r t i e s a p p r o a c h i n g t h o s e of n o r m a l l y h y d r a t e d p a s t e . In autoclaved m o r t a r s s u l f u r additions a p p e a r to r e d u c e t h e bond between the autoclaved product and s i l i c e o u s a g g r e g a t e , although t h e a d - vantage of s u l f u r in t h e p a s t e i s s t i l l evident. Strengthening of t h e p a s t e (due t o s u l f u r addition) was fully r e a l i z e d when l i m e s t o n e fine a g g r e g a t e w a s u s e d .

On a obtenu, g r % c e 5 _{l'addition d e 1}

5

_{2 pour cent d e s o u f r e , une}

a m e l i o r a t i o n i m p o r t a n t e d e l a r e s i s t a n c e

5

_{l a c o m p r e s s i o n d e}

l a p%te d e ciment m i s e en autoclave

5

_{216°C e t 'a 300 lv/p2 d e}

p r e s s i o n d e vapeur. L e s p r o p r i e t e s physiques t e l l e s que l ' a i r e d e s u r f a c e 'a l'azote, l a r e p a r t i t i o n d e s p o r e s , l e r e t r a i t dlti au p r e m i e r s e c h a g e , l a d e n s i t e , l a p o r o s i t e et l a m i c r o d u r e t C i n - diquent que l'addition d e s o u f r e e n t r a r n e d e s p r o p r i e t e s s e r a p - p r o c h a n t d e c e l l e s d e l a p%te h y d r a t t e n o r m a l e m e n t . L'addition d e s o u f r e au m o r t i e r m i s en autoclave s e m b l e r C d u i r e l ' a d h e r - ence e n t r e l e produit d'autoclave et l e granulat silicieux, bien que l'avantage du s o u f r e dans l a p%te soit e n c o r e evident.

L'addition d e s o u f r e a u g m e n t e n e t t e m e n t l a r e s i s t a n c e d e l a p%te l o r s q u l o n u t i l i s e du granulat fin.

Vol.

4, No.

2

AUTOCLAVING

,

SULFUR, CEMENT PASTES, MORTARS

Introduction

As t h e supply of e l e m e n t a l sulfur in Canada i s expected t o r e a c h 50

million tons by 1980 (1), the challenge t o find new ways t o u s e t h i s m a t e r i a l

i s g r e a t . The s t u d i e s now r e p o r t e d w e r e fundamental in approach; t h e y w e r e undertaken in a n attempfto p r o v i d e a b a s i s for developing autoclaved c o n c r e t e

of s u p e r i o r p r o p e r t i e s with portland c e m e n t

-

sulfur b i n d e r s . One of the p r o -

b l e m s with autoclaved c e m e n t p a s t e s i s t h a t t h e y a r e i n f e r i o r b i n d e r s due t o

t h e f o r m a t i o n of a l p h a dicalcium s i l i c a t e h y d r a t e . P o r t l a n d cement

-

sulfur

p a s t e s , without r e a c t i v e s i l i c e o u s p o w d e r s , w e r e used a s a f i r s t b a s i c s t e p in the o v e r - a l l investigation. M o r t a r s u s i n g s i l i c e o u s and c a l c i t e s a n d s , without finely ground r e a c t i v e s i l i c e o u s m a t e r i a l s , w e r e studied a s well a s c e m e n t

-

f l y a s h and c e m e n t

-

sand

-

fly a s h m i x t u r e s .

It was postulated that during t h e autoclaving p r o c e s s , sulfur would melt, flow into i n t i m a t e contact with newly f o r m e d hydration p r o d u c t s , and poly- m e r i z e . T h e m e r i t s of s u l f u r in t h i s s t a t e would then be i m p a r t e d t o t h e composite. It was hoped that t h e i n t i m a c y of s u r f a c e - t o - s u r f a c e contiguity between sulfur and m i c r o s t r u c t u r e would not only provide s t a b i l i t y but a l s o d e l a y t h e t r a n s f o r m a t i o n of p o l y m e r i c s u l f u r t o t h e S a o r c r y s t a l l i n e f o r m .

The p o s s i b i l i t y of c h e m i c a l o r topochemical r e a c t i o n a s well a s l a t t i c e substitution o r e n t r a n c e into solid solution m a y p r e s e n t other b a s e s on which t o a s s e s s e x p e r i m e n t a l r e s u l t s .

E x p e r i m e n t s with Cement P a s t e Autoclaving

To e n s u r e a r e l a t i v e l y high d e g r e e of p o l y m e r i z a t i o n of s u l f u r a s well a s rapid hydration of c e m e n t , t h e autoclaving r e g i m e followed t h a t of ASTM

C151. Essentially, t h e s a m p l e s w e r e heated f r o m r o o m t e m p e r a t u r e t o 216°C

and 300 p s i s t e a m p r e s s u r e w h e r e t h e y r e m a i n e d f o r 3 h o u r s . While t h e autoclave was being heated t h e s u l f u r had sufficient l a g t i m e in t h e low v i s - c o s i t y liquid s t a t e (120 t o 1 4 0 ° C ) t o p e r m e a t e t h e m i c r o s t r u c t u r e ; and a s i t

was finely divided and w e l l d i s p e r s e d throughout t h e m i x t h e effect of t o r

-

AUTOCLAVING, SULFUR, CEMENT PASTES, MORTARS V o l . 4, N o . 2

Mixes

Two-in. cubes were cast from the mixes outlined in Table 1 and moist cured for 24 hours p r i o r to autoclaving. At least t h r e e cubes were cast for every t e s t condition. TABLE 1 C e m e n t P a s t e M i x e s Mix 1 2 3 4 5 6 7 8 9 10 1 1 12 W / C Ratio 0. 30 0. 30 0. 30 0. 30 0. 30 0. 30 0. 35 0. 35 0. 35 0. 35 0. 35 0. 35 70 Sulfur ;" 0 1/2 1 1-1/2 2 10 0 1/2 1 1-1/2 2 10 -" Sulfur e x p r e s s e d a s 70 by weight of c e m e n t .

Results and Discussion

Figure 1 illustrates quite conclusively that a 2 percent sulfur addition

increased strength by approximately 7 5 percent. It was surprising that the 1 percent addition had no positive ef-

fect. This trend of increased CA

a 5 strength with the addition of 1 p e r - c e n t m o r e s u l f u r w a s observedfor

both water -cement ratios and sug-

_g

W W/C

P: 0-0 0 . 3 0

gests that elemental sulfur may be

acting a s an admixture to alter the 0-0 0 . 3 5

nature of the cement paste m i c r o -

structure in a beneficial way. The

2

U

A U T O C L A V E D PASTE

effect of calcium chloride on the Z I ~ O C , 3 H R

28 -day strength development in C,S

s

pastes b e a r s a distinct similarity to o 2 4 6 8 1 0

S U L F U R ( B Y WT O F CEMENT), %

the effect of sulfur on the strength of _-

FIG. 1

autoclaved cement paste (w/C = 0.30) _{Compressive strength of auto-}

-

(2). P a s t e s containing either admix- claved paste containing sulfur.

t u r e show a decrease in strength for additions greater than 2 percent. It

appears, therefore, that calcium chloride i s not unique in providing optimum

AUTOCLAVING, SULFUR, CEMENT PASTES, MORTARS V o l . 4, N o . 2 p h y s i c a l m e a s u r e m e n t s was m a d e t o identify changes in p h y s i c a l p r o p e r t i e s . P h y s i c a l P r o p e r t i e s

N2 s u r f a c e a r e a . Nitrogen s u r f a c e a r e a s i n c r e a s e d l i n e a r l y with sulfur a d d i -

tion. They w e r e 9, 13 and 2 4 m2/g, r e s p e c t i v e l y , f o r 0, 2 and 10 p e r c e n t s u l -

fur additions.

P o r e s i z e distribution. F i g u r e 2 shows quite c l e a r l y t h a t t h e distribution of

p o r e s , a s d e t e r m i n e d by Hg p o r o s i m e t r y , i s s y s t e m a t i c a l l y changed f r o m a c o a r s e t o a fine d i s t r i b u t i o n a s sulfur content i n c r e a s e s .

P R E S S U R E . P S I

D l A M E T E R , fY

FIG. 2

P o r e s i z e distribution of autoclaved p a s t e s containing s u l f u r .

F i r s t drying s h r i n k a g e . S a m p l e s of autoclaved p a s t e (initially at 100 p e r c e n t

RH) w e r e equilibrated a t 11 p e r c e n t RH and simultaneous length change m e a -

s u r e m e n t s taken. F i g u r e 3 d e m o n s t r a t e s t h e proportionality of f i r s t drying s h r i n k a g e with s u l f u r content. It i s evident that the sulfur additive a l t e r s t h e m i c r o s t r u c t u r e significantly and t h a t length change f o r t h e p a s t e with 10

V o l . 4, No. 2

AUTOCLAVING, SULFUR, CEMENT PASTES, MORTARS

p e r c e n t s u l f u r additive a p p r o a c h e s t h a t of a n o r m a l l y h y d r a t e d p a s t e with W/C = 0. 25. Density. D e n s i t i e s d e t e r - mined b y h e l i u m d i s p l a c e - m e n t w e r e 2. 639 and 2. 490, r e s p e c t i v e l y , f o r p a s t e with 0 and 1 0 p e r c e n t s u l - f u r a d d i t i o n s . D e n s i t i e s of n o r m a l l y h y d r a t e d p a s t e u s u a l l y r a n g e f r o m 2. 00 t o 2. 20 (3). T h i s o f f e r s f u r - t h e r evidence t h a t t h e a d d i - tion of s u l f u r b r i n g s t o t h e autoclaved p a s t e p r o p e r

-

t i e s a p p r o a c h i n g t h o s e of n o r m a l l y h y d r a t e d c e m e n t p a s t e . P o r o s i t y . S a t u r a t e d p a s t e s a m p l e s w e r e weighed in d a m p - d r y condition in a i r , 0 1 1 1 1 1 1 1 1 I I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 A U T O C L A V E D - 0'1 SULFUR w / c = 0 3 5 - A U T O C L A V E D 2 7 SULFUR X 1

-

- A U T O C L A V E D 25 - 30 - S H R I N h A G E VS T I M E H Y D R A T E D l o o o / -I lo/ RH I I I 1 i l l 1 1 1 1 1 1 1 1 1 0 . 0 1 0 . 1 1 . 0 1 0 TIME, D A Y S FIG. 3 Fir s t d r y i n g s h r i n k a g e of autoclaved p a s t e s containing s u l f u r .

weighed in w a t e r , t h e n D - d r i e d . T h e D-dried s a m p l e s w e r e vacuum s a t u - r a t e d in m e t h a n o l and r e - w e i g h e d . T a b l e 2 r e c o r d s t h e r e s u l t s T A B L E 2 Methanol Volumes Hg Sample:: V W a t e r V Methanol V W a t e r 15, 000

70

70

V Methanol

70

:: E a c h value i s t h e a v e r a g e of five d e t e r m i n a t i o n s .

182 V o l . 4, No. 2 AUTOCLAVING, SULFUR, CEMENT PASTES, MORTARS

It i s significant that Water i s approximately unity, even a f t e r D-drying,

V Methanol

f o r p a s t e with 0 p e r c e n t sulfur. This suggests that during autoclaving t h e

l a y e r s approach a s t a t e of complete collapse and that w a t e r removed on D- drying i s essentially adsorbed water (4). On r e -saturation with methanol t h e volume adsorbed i s equal t o that f o r water; methanol apparently occupies

s i t e s s i m i l a r t o those occupied by w a t e r on t h e external s u r f a c e s of t h e l a y e r s . With the addition of sulfur t h e l a y e r e d system i s modified t o the extent that the volume of w a t e r adsorbed i s 16 and 33 p e r c e n t g r e a t e r than that f o r methanol. This i s f u r t h e r evidence that modification of t h e m i c r o s t r u c t u r e

is such that i t approaches that of n o r m a l l y hydrated p a s t e . It i s s u r p r i s i n g

that strength i s not i n c r e a s e d although s u r f a c e a r e a continues t o change in t h e region 2 t o 10 p e r c e n t sulfur addition.

Microhardness. Table 3 gives values of m i c r o h a r d n e s s and strength f o r

W/C = 0. 30 paste. A Leitz m i c r o h a r d n e s s testing machine with a Vickers

indenter was used (5).

TABLE 3

Values of Microhardness and Strength f o r W/C

=

0. 30 P a s t e

Sample* Microhardness Strength

(kg/mm2) (PS i)

0% S

9.

4 2940

*

Average of a t l e a s t t h r e e determinations.

It i s c l e a r that with the addition of sulfur subsequent autoclaving of cement p a s t e increased t h e h a r d n e s s of the m a t e r i a l . This appears to have a direct relation t o the c o m p r e s s i v e strength of the m a t e r i a l .

SEM Micrographs

In the p a s t e the m a j o r f e a t u r e in the p r e s e n c e of sulfur (1 0 ~ e r c e n t ) appeared t o be i n t e r s p e r s e d , i r r e g u l a r , platy m a s s e s . Typical micrographs

Vol. 4, No.

2

1 8 3

AUTOCLAVING, SULFUR, CEMENT PASTES, MORTARS

a r e shown i n F i g s . 4 (A t o

c ) .

In c o n t r a s t , t h e morphology of t h e autoclaved

p a s t e without sulfur ( F i g s . 4 (D and E) ) w a s e s s e n t i a l l y f r e e of p l a t y m a t t e r .

FIG. 4

Scanning e l e c t r o n m i c r o g r a p h s of

autoclaved p a s t e ; A, B, C with 10

p e r c e n t s u l f u r addition; D, E, with n o s u l f u r addition.

1 8 4

AUTOCLAVING

,

SULFUR, CEMENT PASTES, MORTARS V o l . 4 , N o . 2

Differential T h e r m a l A n a l y s i s

Differential t h e r m a l a n a l y s i s w a s c a r r i e d out u s i n g t h e Du Pont 900 T h e r m a l A n a l y s e r . F i g u r e 5 gives t h e DTA t r a c e s of s u l f u r and p a s t e c o n - taining 0, 2 and 10 p e r c e n t s u l f u r , r e s p e c t i v e l y . Distinguishing f e a t u r e s include: I l l I I 1 I I I I

I

-

A U T O C L A V E D C E M E N T PASTE 2 1 6 " C , 3 HR I I I I I I I I I I

I

I

200 4 0 0 6 0 0 8 0 0 1 0 0 0 T E M P E R A T U R E . 'C FIG. 5 Differential t h e r m a l a n a l y s i s of autoclaved c e m e n t p a s t e con

-

taining sulfur. (1) t h e l i m e p e a k d i s a p p e a r s in t h e p r e s e n c e of 10 p e r c e n t s u l f u r ,

'

(2) t h e r e i s a s m a l l e x o t h e r m a l p e a k a t a p p r o x i m a t e l y 820 t o 830°C in t h e p r e s e n c e of 10 p e r c e n t s u l - f u r . It i s p o s s i b l e t h a t t h e a b s e n c e of a l i m e peak a t 10 p e r c e n t sulfur content indicates t h a t t h e l i m e h a s gone into t h e f o r m a t i o n of a high l i m e p r o d u c t . R e s u l t s f r o m m e - c h a n i c a l m i x t u r e s of l i m e and s u l -

f u r indicate that l i m e does not i n t e r -

a c t with s u l f u r during t h e DTA run. F i g u r e 6, h o w e v e r , shows a DTA r u n on a 1:l m i x t u r e of l i m e and s u l f u r autoclaved p r i o r t o DTA. In c o n t r a s t , t h e r e i s a n e x o t h e r m a l p e a k at a p p r o x i m a t e l y 795 t o 800°C and a s m a l l endothermic p e a k a t about 465°C. F o r t h i s p a r t i c u l a r 1: 1 m i x t u r e t h i s might s u g g e s t t h e p r e s e n c e of calcium sulfide. It i s of i n t e r e s t that t h e e x o t h e r m a l p e a k probably r e s u l t s f r o m t h e autoclaving p r o c e s s and not f r o m t h e enthalpic effect of t h e DTA r u n i t s e l f . T h e r m o p r a v i m e t r i c Analysis

T a b l e 4 t a b u l a t e s d a t a e s t i m a t e d f r o m c u r v e s of t h e r m o g r a v i m e t r i c

V o l . 4, N o . 2 1 8 5 AUTOCLAVING, SULFUR, CEMENT PASTES, MORTARS

FIG. 6 Differential t h e r m a l a n a l y s i s of m i x t u r e s of l i m e and sulfur. I I I I I I

I

M I X T U R E S O F C a ( O H ) : , A N D S U L F U R A - A U T O C L A V E D S U L F U R 0 - M E C H A N I C A L M I X T U R E O F L l M E A N D S U L F U R C - A U T O C L A V E D M I X T U R E O F L l M E A N D S U L F U R

.

1 1 1 1 I I I I 200 400 6 0 0 800 1000 T E M P E R A T U R E . " C TABLE 4 Calculations f r o m TGA T r a c e s f o r Autoclaved P a s t e s

Sample Ca(OH)a Total Weight W720

-

W l ~ ~ ~

L o s s

70

Ignited

OJo

Sulfur Weight

70

D - d r y

70

70

of Total

X - r a y Diffraction

X - r a y diffraction a n a l y s e s w e r e p e r f o r m e d using a P h i l i p s powder c a m - e r a (PW 1024). T h e m i n e r a l s identified in autoclaved p a s t e containing 0, 2

V o l . 4, N o . 2 AUTOCLAVING, SULFUR, CEMENT PASTES, MORTARS

and 10 p e r c e n t sulfur w e r e t o b e r m o r i t e , aC,SH and Ca(OH),. T h e r e was

evidence a l s o of xontolite i n p a s t e s containing 0 and 2 p e r c e n t s u l f u r additions.

Only i n t h e autoclaved p a s t e containing 10 p e r c e n t s u l f u r was t h e r e evidence of CSH (11).

X - r a y diffraction indicated t h e p r e s e n c e of negligible amounts of c r y s

-

t a l l i n e sulfur in autoclaved p a s t e a t 30 d a y s , suggesting t h a t c o n v e r s i o n of s u l f u r f r o m t h e p o l y m e r i c f o r m t o t h e o r t h o r h o m b i c f o r m i s negligible at room t e m p e r a t u r e . T h i s i s i n a g r e e m e n t with equal s t r e n g t h s f o r autoclaved p a s t e with sulfur a t 30 d a y s .

M o r t a r with Sulfur Additions

T h e f i r s t p h a s e of t h i s investigation showed t h a t s u l f u r h a s a m a j o r effect

on t h e s t r e n g t h and p r o p e r t i e s of autoclaved p a s t e . It i s known t h a t auto

-

claving of m o r t a r containing s i l i c e o u s sand r e s u l t s in a l a r g e i n c r e a s e in s t r e n g t h when c o m p a r e d with t h e s a m e m o r t a r hydrated a t n o r m a l conditions b e c a u s e of t h e pozzolanic effect (owing t o t h e i n c r e a s e i n t h e bond between

A U T O C L A V E D M O R T A R C U B E S

I

A / C = 2 . 7 5 : 1 , W / C = 0 . 5 0 0 -R O - O

I

0 - O O T T A W A S A N D A N N E A L E D i l O ° C / 2 HR

I

0-0 N A T U R A L S A N D - .-0 O T T A W A S A N D 1 5 0 ° C / 6 HR A-A L I M E S T O N E F I N E A G G S U L F U R ( B Y W T O F CEMENT). % FIG. 7 sand and c e m e n t p a s t e ) . T h e second p h a s e w a s designed t o show whether both t h e beneficial effect of s u l f u r on c e m e n t p a s t e and t h e pozzolanic r e a c t i o n with sand could b e r e a l i z e d t o g e t h e r . F i g u r e 7 c l e a r l y i l l u s t r a t e s that f o r m i x e s 1, 4 and 5 ( T a b l e 5) t h e r e i s up t o 50 p e r c e n t d e c r e a s e i n s t r e n g t h f o r a wide r a n g e of a g g r e g a t e - c e m e n t r a t i o s when sulfur i s p r e s e n t . F i g u r e 8 plots c o m p r e s s i v e s t r e n g t h v e r s u s sulfur content f o r m i x e s 1, 2

and 3. Mixes with both n a t u r a l sand

and Ottawa sand exhibit up t o 50 p e r

-

C o m p r e s s i v e s t r e n g t h of autoclaved cent d e c r e a s e i n s t r e n g t h in t h e p r e -

V o l . 4, No. 2 1 8 7

AUTOCLAVING

,

SULFUR, CEMENT PASTES, MORTARS

f o r 2 h o u r s a f t e r autoclaving a t 2 1 6 0 ~ had l i t t l e effect on t h i s t r e n d ; and low- p r e s s u r e s t e a m c u r i n g (150°C f o r 6 h o u r s ) g a v e no significant change in

s t r e n g t h f o r m o r t a r containing s u l f u r . In a l l t h e e x p e r i m e n t s , m o r t a r m a d e with s i l i c e o u s a g g r e g a t e exhibited l a r g e s t r e n g t h d e c r e a s e s when autoclaved i n t h e p r e s e n c e of s u l f u r . With n o s u l f u r it showed 100 p e r c e n t i n c r e a s e when t h e t e m p e r a t u r e of r e a c t i o n was i n c r e a s e d f r o m 150 t o 21 6 ° C . When c r u s h e d l i m e s t o n e w a s u s e d a s a fine a g g r e g a t e , s u l f u r i n c r e a s e d t h e s t r e n g t h of t h e autoclaved p r o d u c t b y a p p r o x i m a t e l y 50 p e r c e n t , showing t h a t t h e b e n e f i c i a l effect of s u l f u r on p a s t e i s r e t a i n e d . T h i s f a c t a l l o w s one t o p o s t u l a t e t h a t t h e r e i s a s u r f a c e r e a c t i o n a n d / o r modification between t h e s i l i c a and t h e p a s t e in t h e p r e s e n c e of s u l f u r . F i g u r e 9 i l l u s t r a t e s t h a t s u l f u r c a n b e b e n e f i c i a l i f sand i s p a r t i a l l y r e -

placed (Mixes

6

and 7) b y f l y a s h . F o r a 50/50 r e p l a c e m e n t t h e r e i s about a

26 p e r c e n t i n c r e a s e in s t r e n g t h a t 2 p e r c e n t s u l f u r content. F o r a 25 p e r c e n t r e p l a c e m e n t t h e r e i s a p p r o x i m a t e l y a 15 p e r c e n t i n c r e a s e i n s t r e n g t h a t 2 p e r c e n t s u l f u r content. T A B L E 5 Cement/A g g r e g a t e Mixes No. A g g r e g a t e P r o p o r t i o n s

w

/c

1 Ottawa sand 1:2. 75 C / A 2. Ottawa sand 1: 1 . 00 C / A 3 Ottawa sand 3 : l . 00 C / A 4 N a t u r a l sand l : 2 . 75 C / A 5 L i m e s t o n e f i n e a g g r e g a t e 1:2. 75 C / A

Ottawa s a n d and f l y a s h C:S:fly a s h

1:2. 06:O. 68

W

- -

- 0. 382 C t a s h

Ottawa sand and f l y a s h C:S:fly a s h

1 : l . 37: 1. 37

W

--

_{- 0 . 2 7 1}

188 V o l . 4, N o . 2 AUTOCLAVING, SULFUR, CEMENT PASTES, MORTARS

Effect of Sulfur in the P r e s e n c e

of Siliceous Aggregate

-

CT)

n 5

F u r t h e r comment on the r e l a t i o n s

p r e s e n t e d in F i g u r e s 1 and 7 m a y s e r v e

0

t o c l a r i f y t h e effect of sulfur on the Z w

E engineering s t r e n g t h of autoclaved

r,

3 W > m o r t a r containing siliceous a g - - CT) CT) w 2 g r e g a t e . E a 5 0

T h e r o l e sulfur plays in enhancing

t

A U T O C L A V E D M O R T A R C U B E S 00,- S U L F U R - oIc----020b S U L F U R O-OIOoo S U L F U R q I - the c o m p r e s s i v e s t r e n g t h of autoclaved

I

p a s t e i s c l e a r l y i l l u s t r a t e d in F i g u r e 1.

,,

1

I I I

I

F i g u r e 7 d e m o n s t r a t e s t h e attainment 0. 3 3 1. 0 2. 0 2. 7 5 A G G R E G A T E I C E M E N T

of added s t r e n g t h owing to pozzolanic

FIG. 8

S U L F U R ( B Y W T O F C E M E N T ) , %

C o m p r e s s i v e s t r e n g t h vs a g g r e g a t e -

cement r a t i o of autoclaved m o r t a r cubes containing sulfur.

activity in t h e p r e s e n c e of a siliceous

p h a s e . In the p r e s e n c e of both sulfur

and a siliceous phase, however, the

s t r e n g t h of the composite r e v e r t s t o

that of cement p a s t e alone. In effect,

sulfur with s i l i c a negates the advan

-

t a g e offered by pozzolanic activity.

That this i s due to t h e fact that sulfur

coats t h e a g g r e g a t e and in itself im

-

p a r t s poor bond c h a r a c t e r i s t i c s to t h e

a g g r e g a t e - m a t r i x i n t e r f a c e i s im -

probable; examination of thin sections

revealed l i t t l e or no sulfur a t t h e

FIG. 9 a g g r e g a t e m a t r i x i n t e r f a c e . T h e

C o m p r e s s i v e s t r e n g t h of autoclaved autoclaved product, modified in t h e

m o r t a r containing sulfur and

flv a s h , p r e s e n c e of s u l f u r , m a y simply have

V o l . 4, N o . 2

AUTOCLAVING, SULFUR, CEMENT P A S T E S , MORTARS

T h e n a t u r e and p r e s e n c e of t h e nullifying m e c h a n i s m a p p e a r s t o be d e - pendent on t h e inclusion of a s i l i c e o u s a g g r e g a t e in t h e m a t r i x . T h e negative

effect of s u l f u r i s a b s e n t in t h e p r e s e n c e of l i m e s t o n e fine a g g r e g a t e . T h e m a j o r d i f f e r e n c e between m o r t a r m a d e with l i m e s t o n e f i n e a g g r e g a t e and m o r t a r m a d e with s i l i c e o u s a g g r e g a t e i s t h e a b s e n c e in t h e f o r m e r of a n y pozzolanic r e a c t i o n d u r i n g autoclaving.

Without s u l f u r , t h e r e f o r e , autoclaved m o r t a r m a d e with s i l i c e o u s a g g r e - gate h a s a m u c h g r e a t e r s t r e n g t h than h a s l i m e s t o n e m o r t a r . As mentioned p r e v i o u s l y , however, s u l f u r enhances t h e s t r e n g t h p r o p e r t y of l i m e s t o n e m o r -

t a r by about 50 p e r c e n t , c o r r e s p o n d i n g roughly to t h e i n c r e a s e in p a s t e s t r e n g t h f r o m s u l f u r .

F l y Ash Additions

T h e p o s s i b i l i t y was explored that t h e f i n e n e s s of t h e s i l i c a might be a

controlling f a c t o r in s t r e n g t h reduction r e s u l t i n g f r o m s u l f u r addition in m o r

-

t a r with s i l i c e o u s a g g r e g a t e . It w a s postulated that a finely divided s i l i c a in the f o r m of fly a s h might p r o v i d e a s o u r c e of pozzolanic a c t i v i t y t h a t would o v e r r i d e any i l l effects f r o m s u l f u r and t a k e advantage of t h e beneficial effects it gives to the p a s t e a l o n e .

T o b e optimally useful s u l f u r should p r o v i d e s t r e n g t h i n c r e a s e a t t h e optimum s i l i c a content, p r e f e r a b l y o v e r t h e c o m p l e t e r a n g e of the w e l l -

established Menzel r e l a t i o n ( 6 ) . F i g u r e 10 plots s t r e n g t h a s a function of fly

a s h content f o r m i x e s containing 0, 2 and 10 p e r c e n t s u l f u r . As noted, both 2 and 10 p e r c e n t s u l f u r additions give l a r g e s t r e n g t h i n c r e a s e s in p a s t e when no a s h i s p r e s e n t . At about 10 p e r c e n t a s h the 2 p e r c e n t sulfur gives no advantage, and a t t h e optimum s i l i c a content it gives about 15 p e r c e n t a d v a n - t a g e . With 10 p e r c e n t s u l f u r t h e r e i s no advantage u n t i l t h e optimum, w h e r e equality i s r e a c h e d . At about 75 p e r c e n t a s h , h o w e v e r , t h e r e i s a p p r o x i

-

m a t e l y 75 p e r c e n t i n c r e a s e in s t r e n g t h f o r 10 p e r c e n t s u l f u r and about 30 p e r c e n t i n c r e a s e f o r 2 p e r c e n t s u l f u r .

SEM M i c r o g r a p h s

1 9 0 V o l . 4, N o . 2 AUTOCLAVING, SULFUR, CEMENT PASTES, MORTARS

akin t o that of a high w a t e r -cement r a t i o l 6 I I I I

A U T O C L A V E D C U B E S

p a s t e ( F i g u r e 11). T h e s t r u c t u r e a p - C E M E N T A N D

F L Y A S H 2 1 b D C / 3 H R

-

p e a r s t o be highly p o r o u s and open and 14-

h a s a t l c a c t u s - l i k e t ' composition, with Z a 12 n e e d l e s emanating f r o m d i s c r e t e c l u s - 0 t e r s of hydration product.

h

c o n t r a s t , ;I 1 10

p a s t e without sulfur ( F i g u r e 4(e)) h a s a

₅

W

distinctly different morphology. I-

* 8 W Differential T h e r m a l Analysis 5 _* * F i g u r e 12 shows DTA t r a c e s f o r t h e r a n g e of a g g r e g a t e - c e m e n t r a t i o s w 0 0 % S U L F U R - 2% S U L F U R t e s t e d . In a l l c a s e s t h e m a x i m u m C. 1 0 % S U L F U R amount of l i m e i s p r e s e n t at 2 p e r c e n t W A T E R / S O L I D S = 0 . 2 8 6 _-

sulfur content; only s m a l l o r negligible

I

I

amounts of l i m e a r e p r e s e n t at 0 and

n

n

10 p e r c e n t s u l f u r content. In c o m - "0 20 4 0 60 80 100

F L Y A S H ( B Y W T O F S O L I D ) , %

p a r i s o n , f o r p a s t e t h e r e i s a m a x i - FIG. 10

mum amount of l i m e without sulfur _{C o m p r e s s i v e s t r e n g t h of autoclaved}

c e m e n t p a s t e containing s u l f u r and fly a s h . and a s i m i l a r a b s e n c e of l i m e a t 10 p e r - c e n t s u l f u r . In t h e m o r t a r (A/C = 2. 75) t h e r e i s an e x o t h e r m i c peak a t 810°C for 10 p e r c e n t s u l f u r , suggesting t h e p r e - s e n c e of t o b e r m o r i t e ; t h i s p e a k i s not p r e s e n t in p a s t e with 0 p e r c e n t s u l f u r . Conclusions 1. T h e s t r e n g t h of autoclaved p a s t e con- taining 2 p e r c e n t s u l f u r i n c r e a s e s by a s FIG

.

11 much a s 75 p e r c e n t . T h i s i n i t s e l f c o n - Scanning _{f i r m s t h a t s u l f u r h a s a m a j o r influence i n} autoclaved m o r t a r containing

V o l . 4, N o . 2 1 9 1 AUTOCLAVING, SULFUR, CEMENT PASTES, MORTARS

t h e final p r o d u c t . F u r t h e r confirmation

of t h e effect of s u l f u r on the h y d r a t i o n A / C o 3 3

product i s offered by t h e following: (1) s u r f a c e a r e a i n c r e a s e , (2) p o r e s i z e t r a n s i t i o n f r o m c o a r s e to fine, A / C - 1 0 0 (3) i n c r e a s e d d r y i n g s h r i n k a g e , (4) VH,o/ V ~OH ~i n c r e a s e , , (5) d i s a p p e a r a n c e of l i m e and a p - I-

a

p e a r a n c e of CSH (11) f o r p a s t e containing 10 p e r c e n t s u l f u r . 2. T h e fact t h a t a r e l a t i v e l y s m a l l amount of s u l f u r p r o d u c e s s u c h m a j o r changes s u g g e s t s t h a t t h e effect i s t h a t of a n a d m i x t u r e . 3. Sulfur c a n be u s e d to p r o d u c e a u t o - claved p a s t e with p r o p e r t i e s a p p r o a c h - 0 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 ing t h o s e of n o r m a l l y h y d r a t e d p a s t e . T E M P E R A T U R E . " C ( N o r m a l l y h y d r a t e d p a s t e i s s t r o n g e r FIG. 12 than autoclaved p a s t e f o r s i m i l a r Differential t h e r m a l a n a l y s i s of a u t o -

m i x e s . ) claved m o r t a r containing sulfur.

4. T h e r e i s a n a p p a r e n t d e c r e a s e in s t r e n g t h of autoclaved m o r t a r i n c o r - p o r a t i n g s u l f u r a s a n additive when i t i s m a d e with a s i l i c e o u s a g g r e g a t e , c o m p a r a b l e t o t h e gain due t o pozzolanic a c t i o n between s i l i c a and p a s t e . 5. T h e r e i s a n a p p a r e n t i n c r e a s e i n s t r e n g t h of autoclaved m o r t a r i n c o r - p o r a t i n g s u l f u r a s a n additive when t h e m o r t a r i s m a d e with a n o n - s i l i c e o u s a g g r e g a t e s u c h a s l i m e s t o n e fine a g g r e g a t e , c o m p a r a b l e t o t h e gain in s t r e n g t h of p a s t e contributed by s u l f u r .

6. T h e ill effects of s i l i c e o u s a g g r e g a t e s on s t r e n g t h of autoclaved m o r t a r

i n t h e p r e s e n c e of s u l f u r a r e p a r t i a l l y o v e r c o m e when s i l i c a ( i n finely divided f o r m ) r e p l a c e s c e m e n t i n such quantity a s w i l l equal o r exceed t h e optimum

1 9 2

AUTOCLAVING, SULFUR, CEMENT PASTES, MORTARS V o l . 4, No. 2

of t h e M e n z e l s t r e n g t h r e p l a c e m e n t function.

T h e f u n d a m e n t a l a p p r o a c h t a k e n h a s d e m o n s t r a t e d t h e c a r d i n a l f e a t u r e s of t h e c e m e n t - s u l f u r s y s t e m d u r i n g autoclaving and indicated t h e p o t e n t i a l f o r f u r t h e r w o r k d i r e c t e d t o w a r d p r a c t i c a l application.

Acknowledgements

The a u t h o r s w i s h t o t h a n k t h e i r c o l l e a g u e s R. F. F e l d m a n and V. S. R a m a c h a n d r a n f o r m a n y helpful d i s c u s s i o n s , and t o acknowledge t h e c o n t r i -

bution of S. Dods, R. M e y e r s , G. P o l o m a r k and E. Quinn f o r a s s i s t i n g with

the e x p e r i m e n t a l work.

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 the Division of Building R e s e a r c h , National R e s e a r c h Council 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 the Division.

R e f e r e n c e s

1. A. H. Vroom. "Sulphur Utilization

-

A Challenge and an Opportunity".

National R e s e a r c h Council of Canada. NRC 12241, 80p. (1971).

2. V. S. R a m a c h a n d r a n . T h e r m o c h i m i c a A c t a

-

3, 343 (1972).

3. R. F. Feldman. C e m . and Concr. R e s . 2, 1, 123 (1972).

_-

4. R. F. Feldman. Sorption and Length Change Scanning I s o t h e r m s of

Methanol and Water on H y d r a t e d P o r t l a n d C e m e n t . P r o c . , Fifth I n t e r n a t .

Syrnp. Chem. C e m e n t , Vol. 111, 53. Tokyo (1968).

5. P. J. S e r e d a . Cem. and Concr. Res. 2, 6, 717 (1972).

_-