Effect of mica addition on the microstructure of Portland cement paste

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Effect of mica addition on the microstructure of Portland cement paste

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Ser

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N21d

Natronal Research

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Construction

construction

Effect of Mica Addition on

the

Microstructure of Portland

Cement Paste

by J.J. Beaudoin

Reprinted from

Cement and Concrete Research

Vol. 16, No. 4, 1986

p. 554

-

560 (IRC

Paper No. 1407)

Price $2.00

NRCC 26401

N R C

-

CiSTl

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Pour dgterminer l'effet de l'addition de mica sur la microstructure de la p&e de ciment,

on

a observ6 les modifications survenues dans des Bprouvettes hydrathe pendant des psriodes atteignant cinq ans au niveau de la rbpartition des pores par tailles, de la porositb, de la teneur en eau captive et de la rbpartition des particules

CH

selon la dimension. Les changemente microstructurels dgpendaient du rapport eau-ciment et de la quantit6 de mica ajoutge.

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CEMENT and CONCRETE RESEARCH. Vol. 1 6 , pp. 554-560, 1986. P r i n t e d i n t h e USA. 0008-8846186 $3.00+00. Copyright ( c ) 1986 Pergamon J o u r n a l s , L t d .

BPPECT OF MICA ADDITION ON THE MICKOSTKUCTUKE OF PORTLAND CEMENT

PASTE

1.1. Beaudoin

I n s t i t u t e f o r Uesearch i n C o n a t n ~ c t i o n , N a t i o n a l Research C o u n c i l of Canada, Ottawa, Canada, KIA OR6

(Communicated by F.H. Wittmann) (Received A p r i l 24, 1986) ABSTRACT

I n a s s e s s i n g t h e e f f e c t of mica r e i n f o r c e m e n t on cement p a s t e m i c r o s t r u c t u r e , m o d i f i c a t i o n s t o p o r e - s i z e d i s t r i b u t i o n , p o r o s i t y , non-evaporable w a t e r c o n t e n t , and CH p a r t i c l e s i z e d i s t r i b u t i o n were o b s e r v e d f o r samples h y d r a t e d f o r up t o f i v e y e a r s . M i c r o s t r u c t u r a l changes were dependent on water-cement r a t i o and amount of mica added.

I n t r o d u c t i o n

There h a s been i n t h e p a s t decade a p r o l i f e r a t i o n of new p r o d u c t s marketed f o r c o n c r e t e r e p a i r ( I ) . I n r e c o g n i t i o n of t h e s e r i o u s s t a t e of d e t e r i o r a t i o n of c o n c r e t e s t r u c t u r e s s u c h a s p a r k i n g g a r a g e s and b r i d g e d e c k s , many o f t h e s e p r o d u c t s i n c l u d e f i b r e - r e i n f o r c e d cement syntems. The a d d i t i o n of a r e i n f o r c e m e n t ( f i b r e o r f l a k e ) t o a p o r t l a n d cement-based m a t r i x

g e n e r a l l y r e s u l t s i n a n i n c r e a s e of e i t h e r o r b o t h f l e x u r a l s t r e n g t h and toughnesq, p r o p e r t i e s h i g h l y d e s i r a b l e i n a r e p a i r . Composite t h e o r y , u s u a l l y some form o f m i x t u r e r u l e , i s g e n e r a l l y a p p l i e d t o p r e d i c t t h e b e h a v i o u r of t h e m a t e r i a l s ( 2 ) .

Composite t h e o r y , however, h a s normally been a p p l i e d w i t h o u t

c o n s i d e r a t i o n f u r changes t o t h e m a t r i x , i n c l u d i n g m i c r o s t r u c t u r a l change9 brought a b o u t by t h e r e i n f o r c e m e n t . Such changes may d e t e r m i n e d u r a b i l i t y a s w e l l a s s t r e n g t h and toughness. A s mica f l a k e s have heen found t o be a u s e f u l

rrinforcemnent f o r p o r t l a n d cement m a t r i c e s ( 3 1 , i t was t h e o b j e c t i v e of t h e p r e s e n t work t o d e f i n e t h e i r e f f e c t on t h e m a t r i x ~ n i c r o s t r u c t u r e of cement composites moist cured f o r p e r i o d s o f up t o f i v e y e a r s .

E x p e r i m e n t a l M a t e r i a l s

Cement: P o r t l a n d cement comnposition: C3S = 51.4%; C2S = 20.3%; C3A = 12.7%; C,,AF

-

6.7% and CaSO,, = 5.4% a s c a l c u l a t e d by t h e Bogue method.

Mica: A p h l o g o p i t e t y p e m i n e r a l w i t h high-aspect r a t i o ; p h y s i c a l and chemical p r o p e r t i e s of t h e f l a k e s have been p u b l i s h e d (3).

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Vol. 1 6 , No.

4

555 MICA, REINFORCEMENT, MICROSTRUCTURE, CEMENT PASTE, PORE STRUCTURE

Mixes: Cement p a s t e mixes w i t h water-cement r a t i o s of 0.25-0.70 and mica c o n t e n t of 0-7% by volume were h y d r a t e d i n l i m e - s a t u r a t e d w a t e r f o r up t o f i v e yearn. Mix d e t a i l s a r e provided e l s e w h e r e ( 3 ) .

Technique

P o r o s i t y and p o r e - s i z e d i s t r i b u t i o n s were determined by mercury i n t r u s i o n cunder p r e s s u r e s up t o 408 MPa, u s i n g an American Instrument CO. p o r o s i m e t e r .

Non-evaporable w a t e r c o n t e n t was determined by TGA, employing a 1090 Dupont Thermal Analyzer c o n t a i n i n g a 951 TGA a c c e s s o r y .

Leaching of CH from mica-cement specimens ( s l i c e d 0.030 pm t h i c k ) was accomplished w i t h p a r t i a l l y - s a t u r a t e d lime s o l u t i o n s a c c o r d i n g t o t h e method developed by Ramacliandra8l and Polomark ( 4 ) . Leaching time was a t l e a s t 30 days; i t s e f f i c i e n c y was checked by TGA.

E s t i m a t i o n s of CH c o n t e n t were v e r i f i e d by DSC. A Oupont 1090 t h e r m a l a n a l y s i s system was used.

R e s u l t s and D i s c u s s i o n P o r e - s i z e d i s t r i b u t i o n P o r e - s i z e d i s t r i b u t i o n f o r m i c a - r e i n f o r c e d cement p a s t e specimens h y d r a t e d f o r Eive y e a r s 25 i s p r e s e n t e d i n F i g u r e 1. Mica a d d i t i o n g e n e r a l l y r e s u l t s i n 1 5

g r e a t e r pore volume above a p o r e _... d i a m e t e r g r e a t e r t h a n 0.10 pa. T l ~ e

t h r e s h o l d v a l u e of t h e c o n t r o l samples ( p o r e s i z e a t which the,

i n i t i a l mercury i n t r u s i o n r a t e 3 0 changes s i g n i f i c a n t l y ) a l s o 25 i n c r e a s e s w i t h w/c r a t i o from

-

.

2 0 0.05 pm a t w/c = 0.35 t o 0.30 pm 3 1 5 a t w/c = 0.70. Yores g r e a t e r t h a n $ 1 0 0.30 pm were d e t e c t e d o n l y i n mica-

"

5 r e i n f o r c e d i n a t e r i a l (wlc = 0.70). " _{2 0}0 Many p o r e s e x i ~ t i n t h e i n t e r f a c e a 1 5

zone, between t h e bulk m a t r i x and

1 0 t h e mica s u r f a c e s where p r o p e r t i e s a r e dependent on w/c r a t i o and 5 0 c!rring c r > ~ i d i t i o n s _- ( 5 ) . 1 5 r r f r t

,

, ,

.

t T o t a l p o r o s i t i e s e x p r e s s e d a s pore volune p e r u n i t volume of p a s t e

5

"/A,,,

-.

, ,

,

( c o r r e c t i o n s a r e made f o r t h e

,

volume of mica i n a g i v e n s a m p l e ) l o -

a r e g i v e n i n Table 1. The cement m a t r i x (w/c

.

. = 0.70) c o n t a i n i n e 5%

-

mica has l e s s t o t a l pore volume 2 0 . 2 0. 0 2 0 . 0 0 2

( o v e r t h e e n t i r e pore s i z e r a n g e ) PORE D I A M ' E T E R , , ~ ~

than m a t r i c e s c o n t a i n i n g l e s s mica

(1-3%), i n d i c a t i n g t h a t mica does FTG. I. P ~ r e s i z e d i s t r i b u t i o n of not n e c e s s a r i l y i n c r e a s e t o t a l cement p a s t e s a m l ~ l e s ( w i t h and w i t h o u t p o r o s i t y a t h i g h e r w/c r a t i o s . The mica) h y d r a t e d f o r f i v e y e a r s w i t h t o t a l p a r e volume of specimens d i f f e r e n t amounts of mica.

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556 Val. 1 6 , No. i J.J. Beaudoin 0 . 2 2 F I G . 2. Non-evaporable w a t e r v e r s u s mica c o n t e n t f o r cements h y d r a t e d f o r ( a ) f i v e y e a r s and ( b ) 35 d a y s + a WIC = 0.50

5

0.19 0 . 1 7 0. 19 mica c o n t e n t i s a l s o l e s s t h a n t h a t f o r t h e c o n t r o l sample c o n t a i n i n g no mica. Non-evaporable w a t e r c o n t e n t P l o t s of Wn (non-evaporable 4 w a t e r c o n t e n t ) v e r s u s mica c o n t e n t f o r samples h y d r a t e d f a r 35 d a y s and Q

2

0 . 1 4 f i v e y e a r s a c e p r e s e n t e d i n F i g u r e 2. I n g e n e r a l , W n d e c r e a s e s

5

0 . 1 3 Z

\.

w i t h mica f l a k e a d d i t i o n , a l t h o u g h 0. 12 a t t h e l o w e s t w/c r a t i o (0.25) Wn

.-

0.25 a p p e a r s t o be independent of i t . 0. 1 1 R e g r e s s i o n c u r v e s of W v e r s u s m a t r i x p o r o s i t y ( f o r 3? d h y d r a t i o n ) 0. 1 0 ₀ ₁ ₂ ₃ ₄ ₅ ₆ _, ₇ ₈ ₉ a r e g i v e n i n F i g u r e 3 f o r W / C = 0.25-0.50, f o r which F L A K E VOLUME, % c o r r e l a t i o n c o e f f i c i e n t s were g r e a t e r t h a n 90%. Values of W n o v e r most of t h e p o r o s i t y range were

g e n e r a l l y l e s s when mica was added t o t h e p a s t e . A t a g i v e n p o r o s i t y , Wn d e c r e a s e d w i t h p e r c e n t a g e o f mica. A s t m i l a r e f f e c t h a s been o b s e r v e d w i t h a d d i t i o n o f g l a s s f i b e r s ( 6 ) .

Some workers have p o s t u l a t e d t h a t CH p a r t i c l e s i n cement p a s t e a c t a s n u c l e a t i o n s i t e s f o r C-S-H growth ( 7 ) . Mica a f f e c t s t h e d l s t r t h v ~ t i . o n of CH

p a r t i c l e s i n cement p a s t e , e . g . , i n t e r f a c e r e g i o n s i n mica cements a r e CH-rich (2)., A m o d i f i c a t i o n of t h i s n u c l e a t i o n p r o c e s s i n t h e p r e s e n c e of mica r e l n f o e < : e t r ? r ~ t <nay be one e x p l a n a t i o n f o r lower r a t e s of h y d r a t i o n . It i s p o s s i b l e t h a t mica enhances t h e e a r l y c r y s t a l l i z a t i o n o f CH 8 0 t h a t t h e

n u c l e a t i o n e f f e c t of CH ( w i t h l a r g e s u r f a c e f a c e e n e r g y ) i s reduced.

T a b l e 1. P o r o s i t y

(XI

of Mica Cements Hydrated f o r F i v e Years

-

--

- - - -

- - -

-

Mica 0.50 % 0.70 0.60 W/ c 0.40 0.35

-- - -

-

--

- -

-

--

-

- --

0 32.0 26.0 17.0 11.5 8.0 1 35.9 25.8 18.7 12.8 8.6

(7)

-

( o v e r t h e s i z e r a n g e 2-0.2 pm) f o r W / C = 0.79 a r e p r e s e n t e d i n F i g u r e 6. The l a r g e s t volume of CH p a r t i c l e s o c c u r s i n t h e s i z e r a n g e 0.8-0.6 pm f o r mica a d d i t i o n s up t o 2% and

i s

g r e a t e s t f o r t h e c o n t r o l samples. The range f o r maximum CH volume s h i f t s t o 0.6-0.4 pm f o r 3 and

G%

mica. The p a r t i c l e s i z e r a n g e s f o r maximum CH volume f o r wlc = 0.60, 0.50 and 0.40 ( h i s t o g r a m s a r e not p l o t t e d ) a r e 0.6-0.4, 0.4-0.3, and 0.3-0.2 pm, r e s p e c t i v e l y . C o n t r o l samples f o r t h e s e w/c I

1

Vol. 1 6 , No.

4

557

MICA, REINFORCEMENT, MICROSTRUCTURE, CEMENT PASTE, PORE STRUCTURE

i

CH P a r t i c l e S i z e D i s t r i b u t i o n

The s i z e d i s t r i b u t i o n of CH p a r t i c l e s i n p a s t e was determined i n t h e f o l l o w i n g manner. A p o r e - s i z e d i s t r i b u t i o n c u r v e was o b t a i n e d u s i n g a sample from which CH had been removed by l e a c h i n g w i t h a p a r t i a l l y - s a t u r a t e d l i m e

s o l u t i o n ( 4 ) . It i s assumed t h a t mercury e n t e r s a l l t h e s p a c e s formed when CH

'

in removed, and t h a t CH p a r t i c l e s i z e is e q u i v a l e n t t o t h e s i z e of t h e v a c a t e d space. A c o r r e s p o n d i n g p o r e - s i z e d i s t r i b u t i o n c u r v e f o r an unleached

companion sample was a l s o o b t a i n e d . A CH p a r t i c l e s i z e d i s t r i b t ~ t i o n c u r v e was t h e n c o n s t r u c t e d by p l o t t i n g t h e d i f f e r e n c e i n c u m u l a t i v e pore volume from t h e p o r e - s i z e d i s t r i b u t i o n c u r v e s s o o b t a i n e d v e r s u s t h e p a r t i c l e s i z e . T y p i c a l p o r e - s i z e d i s t r i b u t i o n s f o r l e a c h e d and unleached cement p a s t e s c o n t a i n i n g 4% mica a r e g i v e n i n F i g u r e 4; t h e c o n s t r u c t e d CH p a r t i c l e s i z e d i s t r i b u t i o n i s

a l s o given. I n g e n e r a l , t h e curve h a s t h r e e r e g i o n s : one of i n c r e a s i n g pore volume, 0-1; one w i t h e s s e n t i a l l y no i n c r e a s e i n p o r e volume, 1-2; and a f i n e

i

pore r e g i o n w i t h i n c r e a s i n g p o r e volume, 2-3. I I CH p a r t i c l e s i z e d i s t r i b u t i o n !

PI(;.

4. T y p i c a l p o r e s i z e and CH p a r t i c l e s i z e d i s t r i b u t i o n f o r m i c a - r e i n f o r c e d cement p a s t e , W / C = 0.60, 4% mica, h y d r a t e d f o r f i v e y e a r s . V f

-

volume % mica

i

c u r v e s f o r f i v e - y e a r mica- 0 . 2 0 I r e i n f o r c e d p a s t e s a r e g i v e n i n + z w 0 . 1 9 - F i g u r e 5. The volume of CH i n c o n t r o l and m i c a - r e i n f o r c e d

₅

_u _{0. 1 8} samples g e n e r a l l y i n c r e a s e s w i t h

=

w l c g r e a t e r r a t i o t h a n f o r 0.20 p a r t i c l e pm. s i z e s S e v e r a l

_E

0 0 . 1 6 - c u r v e s e x h i b i t a low s l o p e between

-

4 0.2 and 0.02 pm a n d an i n c r e a s i n g 5 0. 15 s l o p e between 0.02 and 0.004 pm. L,, Many s a m p l e s , t h e r e f o r e , c o n t a i n 0. 1 4 4 s m a l l amounts o f CH i n t h e Eormer 0 . 1 3 - s i z e r a n g e and, a p p a r e n t l y , l a r g e r a amounts i n t h e l a t t e r . 4 0 . 1 2 -

2

CH p a r t i c l e s i z e h i s t o g r a m s

&

0 . 1 1 - 0. 10-1 5 2 0 25 3 0 3 5 P O R O S I T Y , 4. I I I V t = 0% I / / :

_-

-

FIG. 3. Non-evaporable w a t e r v e r s u s m a t r i x p o r o s i t y f o r mica cements h y d r a t e d t o r 35 days. Vf = volume % mica

I " " ' ' STE WIC

-

0.60; V, ; 4% 8 - CH PRESENT DISTRIBUTION

-

A-B 15

---

0

,

' " 2 0. 2 0. 0 2 P O R E [ P A R T I C L E S I Z E 1 D I A M E T E R , pm

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558 Vol. 1 6 , No. 4

I

.]..I. Deaudoin r a t i o s g e n e r a l l y have t h e l a r g e s t CH volume i n t h e s e ranges. Volumes of CH d e t e r m i n e d by 0% M I C A mercury p o r o s i m e t r y were n e a r l y

...

always h i g h e r t h a n t h o s e

-

. - .

-.

-

.

-

.-

d e t e r m i n e d by USC methods. The ... two were a p p r o x i m a t e l y e q u a l ,

however, i f t h e " f i n e pore" volume

20 ( r e g i o n 2-3 of t h e C o n a t r u c t e d c u r v e , F i g u r e

4)

was s u b t r a c t e d 15 1 0 from t h e t o t a l volume d e t e r m i n e d by p o r o s i m e t r y . DSC v a l u e s of CH volume a r e p l o t t e d a g a i n s t volumes d e t e r m i n e d by t h e c o r r e c t e d mercury p o r o s i m e t r y method i n 1 0 F i g u r e 7. It a p p e a r s t h a t

l e a c h i n g of CH from cement compos- i t e s "opens up" f i n e p o r e s p r e v i - o u s l y i n a c c e s s i b l e t o mercury.

Volumes of CH d e t e r m i n e d by t h e mercury i n t r u s i o n method a r e g i v e n i n T a b l e 2. Nearly a l l t h e f r e e lime was removed from most samples by t h e l e a c h i n g p r o c e s s , a s v e r i f i e d by t h e r m a l methods, but i n a few samples some remained, e.g., w/c

-

0 . 4 0 .

The volume of CH g e n e r a l l y d e c r e a s e s w i t h mica a d d i t i o n f o r W / C 2 0 . 5 0 . _{The e x c e p t i o n}_is_{a t} 4% _{mica c o n t e n t , a t which t h e} p a r t i c l e s i z e c u r v e d o e s n o t f l a t t e n ( F i g u r e 5) and t h e amount of CH may be o v e r e u t i m a t e d . A lower amount of lime w i t h mica a d d i t i o n can be e x p l a i n e d , i n p a r t , by t h e lower v a l u e s of

non-evaporahle w a t e r f o r t h e s e 2 0.2 0.02 0.002 samples ( F i g u r e 8). Higher CH C H P A R T I C L E S I Z E ,

pm

c o n t e n t s wLth 4% _{mica may be due}

t o p o r o s i t y n o t accounted f o r i n

a p p l y i n g c o r r e c t i o n s t o c o n s t r u c - FIG. 5. P a r t i c l e s i z e distribution

t e d p a r t i c l e s i z e d i s t r i b u t i o n of CH i n mica cements. Hydrated f o r curves. A d i f f e r e n c e i n CIS r a t i o f i v e y e a r s of t h e C-S-H formed i n t h e p r e s e n c e of mica would a l s o a f f e c t t h e CH c o n t e n t and non-evaporable c o n t e n t . Conclusion

I , Mica f l a k e s modify t h e p o r e - s i z e d i n t r i b t i t i o n and t u e a l purosity of t h e m a t r i x i n cement c o m p o s i t e s h y d r a t e d f o r f i v e y e a r s . Pores of d i a m e t e r g r e a t e r t h a n 0.30 _{pm a r e dependent on water-cement r a t i o and mica}

c o n t e n t .

2. Addicion of mica f l a k e g c n c r n l l y r e t a r d s h y d r a t i o n of cements. The d e c r e a s e i s dependent on water-cement r a t i o and mica a d d i t i o n .

(9)

Val. 1 6 , No.

4

559

MICA, REINFORCEMENT, MICROSTRUCTURE, CEMENT PASTE, PORE STRUCTURE

C H P A R T I C L E D I A M E T E R . p m

FIG. 6. _{P a r t i c l e s i z e of} CH i n mica cements i n t h e range 2.0

-

0.2 pm. Hydrated f o r f i v e y e a r s ;

W / C = 0.70; Vf = volume X mica

CH V O L U M E , % I H g P O R O S I M E T R Y I

FIG. 7. Comparison of CH e s t i m a t i o n methods f o r mica cements. Method of e s t i m a t i n g CH, u s i n g mercury

p o r o s i m e t r y , and c o r r e c t i o n p r o c e d u r e s a c e e x p l a i n e d i n t e x t

FIG. 8. Volume of CH i n mica cements h y d r a t e d f o r f i v e y e a r s v e r s u s noo- e v a p o r a b l e w a t e r c o n t e n t 2 1 2 0 19 1 8 az 1 7

$

1 6 - L 15 r o _{1 4} 13 I 2 11 1 0 15 I I I

-

W I C 0% _/"

-

0 0. 35 0 0.50 / //

-

/ / -

-

01% //

-

/ / - /

-

/ 70%

-

/ - 0 1 % / / 3% 0 2 % 0 2 +

-

/

//

0 3 % /'

-

/ 0 5 % M I C A / - I I I

-

16 1 7 1 8 19 N O N - E V A P O R A B L E W A T E R , %

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560 Vol. 1 6 , No. 4

J . J . Beaudoin

Table 2. T o t a l Volume ( % ) of CH Determined by Mercury Porosimetry f o r Mica Cements Hydrated f o r F i v e Years

- - --- -

- - -

- - - -

- - -

- -

-

*-

- - - --

- - - -

-

- --

-

-- -

- --

-

- - -

- -

--

-

Mica ( % ) 0.40 12.5**(12.5)

-

12.5**(12.5) 17.0(17.0) 16.0(16.0)

-

---

" E s t i m a t e s i n h r a c k e t s o b t a i n e d by c o r r e c t i n g p a r t i c l e s i z e d i 3 t r i b o t i o n c u r v e s ( s e e t e x t ) . **Not a l l lime l e a c h e d o u r . 3. Mica f l a k e s modlfy t h e s i z e d i s t c i h u t i o n of CH p a r t i c l e s i t ? t h e m a t r i x of

cement composites h y d r a t e d f o r f l v e y e a r s . Maximum p a r t i c l e e i z e i n c r e a s e s w i t h water-cement r a t i o .

4.

The volume p e r c e n t a g e of l a r g e CH p a r t i c l e s i n c r e a s e s a t mica c o n t e n t s g r e a t e r t h a n 2%.

5. CH i n cements p r e v e n t s mercury from e n t e r i n g some of t h e micropores. When t h e CH i a removed, t h e p o r e s a r e a c c e s s i b l e t o mercury.

6. C o n s i d e r a t i o n s h o u l d be g i v e n t o t h e e f f e c t of f i b e r o r f l a k e

r e i n f o r c e m e n t on t h e cement m a t r i x when making long-term p r e d i c t i o n s o f s t r e n g t h and d o r a b i l i t y .

Acknowledgement

The a u t h o r wishes t o thank R. Myers and

F.

G o e r t i n f o r a s s i s t a n c e w i t h t h e e x p e r i m e n t a l work. This paper i s a c o n t r i b u t i o n from t h e I n s t i t u t e f o r Research i n C o n s t r u c t i o n , N a t i o n a l Keaearch Council of Canada.

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I

,

3 (1985). 2. V.S. Kamacharldran, K.P. Feldrnan and .J.

J.

Reaudoin, Concrete S c i e n c e ,

Heyden h Son, 427 p. (1981).

3. ..I.J. Reaudoin, Cem. Concr. R e g .

3,

153 (1983).

4. V.S. Ramachandran and G.M. Polomark, J. Chem. Tech. and B i o t e c h . ,

2,

946 (1982).

5. A. R e n t u r , S. Uiamorld and S. MindBss, 3. Mats. S c i .

c,

3360 (1985).

6. R. Sh. M i k h a i l , M. Abd-El-Khalik and A . H a s s a n e i n , Cem. Concr. R e s .

-

8, 765 (1978).

7. J. Skalny and .J.F. Young, Proc. 7 t h I n t . Congr. Chem. Cem., P a r i s , Paper 11-1, 3 (1980).