Porosity measurements of some hydrated cementitious systems by high pressure mercury intrusion : microstructural limitations

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Porosity measurements of some hydrated cementitious systems by

high pressure mercury intrusion : microstructural limitations

Beaudoin, J. J.

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of

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recherches du Canada

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Ser

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N21d

1 CEMENTITIUUS

SYSTEMS BY

HIGH

PRESSURE

MERCURY

INTRUSION

-

MICROSTRUCIW

RAL

LIMITATTONS

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frotn:

Cement

and

Concrete Research

Vol.

9 ,

No,

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November

1979

p.

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781

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Paper

No.

868

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Research

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CEMENT

and

CONCRETE RESEARCH. Vol. 9, pp. 771-781, 1979. Printed

in

the U.S.A. 0008-8846/79/060771-11$02.00/0 Copyright ( c )

1979

Pergarnon Press, Ltd.

POROSITY MEASUREMENT OF SOME HYDRATED CEMENTITIOUS SYSTEMS

BY

HIGH PRESSURE MERCURY INTRUSION-MICROSTRUCTURAL LIMITATIONS

J

.

J

.

Beaudoin

Research Officer, Materials Section, Division of Building Research, National Research Council of Canada, Ottawa, Canada KIA OR6

(Communicated by

J.

Skalny) (Received Sept.

11 ,

1979)

ABSTRACT

,

I

Porosity measurements using both mercury intrusion and helium

pycnometric methods are reported for several different hydrated cementitious systems. Significant differences in porosity

values, where they arise, are explained in terms of microstructural limitations of the matrix material. Several mechanisms that

affect mercury intrusion results are discussed.

Les mesures de la porositg 1 l'aide de deux msthodes, la pgngtration du mercure et la pycnomgtrie Zi l'hglium sont rapportges pour

plusieurs systsmes de cgrrtents hydratgs diffgremment. Les differences significatives des valeurs de porosits, lorsqu'elles apparaissent, sont expliquges en termes de limites micro-structurales du matgriau de la gangue. Plusieurs mgcanismes qui influencent les rgsultats de la pgngtration du mercure sont discutEs.

Introduction

Opinion regarding meaningful techniques for porosity measurement of hydrated portland cement paste is varied (1,2]. Some research demonstrated that portland cement paste is not a stable adsorbent when water is used as adsorbate; this led to the use of helium pycnometric method of porosity

measurement (3). In the helium pycnometric method, samples are conditioned at 11 per cent RH to avoid dissociation of hydrates (due to further removal of water on drying) prior to volume displacement with helium.

Porosity values (for most cement pastes) as determined by helium pycnometry are similar to capillary porosity values

-

the remnants of water-filled space existing between cement grains at time of setting

-

as calculated by Helmuth (4); modulus of elasticity versus porosity curves for portland cement paste were identical when porosity was calculated as capillary porosity or was determined by helium pycnometry (5)

.

Previous work on the diffusion of helium into the microstructure of

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Vol. 9 , No.

6 J. J .

Beaudoin

t h a t supported t h e argument t h a t h y d r a t e d p o r t l a n d cement p a s t e was a l a y e r e d m a t e r i a l and t h a t g e l p o r e s ( i n t e r n a l p o r o s i t y o f h y d r a t i o n p r o d u c t s them-

s e l v e s ) a n d / o r p o r e s s m a l l e r t h a n c a p i l l a r y p o r e s d i d n o t e x i s t ( 6 ) . Thus o r g a n i c f l u i d s ( e . g . , methanol), c a p a b l e of f i l l i n g t h e c a p i l l a r y pore system, were c o n s i d e r e d s u i t a b l e d i s p l a c e m e n t media.

Winslow and Diamond, Young, Auskern and o t h e r s used mercury p o r o s i m e t r y t o s t u d y t h e e v o l u t i o n o f p o r o s i t y i n p o r t l a n d cement and c i t e d SEM work on h y d r a t e d cement t o s u p p o r t t h e i r f i n d i n g s ( 7 , 8 , ' 9 ) . These a u t h o r s d i s c u s s e d t h e l i m i t a t i o n s o f t h e governing r e l a t i o n s h i p between pore s i z e and i n t r u s i o n p r e s s u r e . However, p o s s i b l e e f f e c t s such a s c o m p r e s s i b i l i t y o f p o r e space and s t r u c t u r a l damage t o t h e m a t r i x m a t e r i a l a t h i g h p r e s s u r e s have n o t been d i s c u s s e d i n t h e cement l i t e r a t u r e .

The purpose o f t h i s s t u d y was t o p r o v i d e d a t a t o e n a b l e a r e a s s e s s m e n t of t h e mercury i n t r u s i o n method a s a technique , f o r measuring t o t a l c a p i l l a r y p o r o s i t y o f s e v e r a l cement systems and t o compare t h e p o r o s i t y r e s u l t s w i t h

t h o s e o b t a i n e d by helium pycnometry

.

Experimental M a t e r i a l s

A b r i e f d e s c r i p t i o n of t h e m a t e r i a l s used i n p r e p a r i n g specimens f o r t h i s s t u d y f o l l o w s . P r e p a r a t i o n d e t a i l s a r e given i n T a b l e I .

1 . Normal Type I p o r t l a n d cement was mixed with water a t v a r i o u s water-cement r a t i o s t o p r e p a r e p a s t e samples.

2. Magnesium o x i d e and magnesium c h l o r i d e s o l u t i o n (chemical and p h y s i c a l s p e c i f i c s a r e given i n (10)) were used t o p r e p a r e magnesium o x y c h l o r i d e cement p a s t e a t s e v e r a l s o l u t i o n - s o l i d r a t i o s .

3 . Magnesium o x i d e and magnesium s u l f a t e s o l u t i o n s (chemical and p h y s i c a l s p e c i f i c s a r e given i n ( 1 1 ) ) were used t o p r e p a r e magnesium o x y s u l f a t e cement p a s t e s a t s e v e r a l s o l u t i o n - s o l i d r a t i o s .

4 . J e t S e t cement, s u p p l i e d by Huron Cement Co., Alpena, Michigan, (chemical and p h y s i c a l s p e c i f i c s a r e g i v e n i n ( 1 2 ) ) was used t o p r e p a r e cement p a s t e s w i t h and w i t h o u t CaC12 a d d i t i o n s .

5 . Vycor g l a s s h a v i z g p o r e volume 26 p e r c e n t , s u r f a c e a r e a 175 m 2 / g and pore r a d i u s a b o u t 25A, was used.

6 . A commercially a v a i l a b l e l a t e x s o l u t i o n ( p o l y a c r y l i c l a t e x s o l u t i o n

c o n t a i n i n g a p p r o x i m a t e l y 50 p e r c e n t l a t e x s o l i d s ) was mixed w i t h p o r t l a n d cement i n v a r y i n g c o n c e n t r a t i o n t o produce l a t e x based cement p a s t e s having a wide r a n g e o f latex-cement r a t i o s and water-cement r a t i o s . 7 . Fly a s h from n i n e d i f f e r e n t s o u r c e s was used t o p r e p a r e cement-fly a s h

(50/50 by weight) m i x t u r e s f o r a u t o c l a v i n g . Chemical composition and p h y s i c a l c h a r a c t e r i s t i c s o f f l y a s h a r e g i v e n e l s e w h e r e (13).

Methods

Helium comparison pycnometry

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TABLE I

P r e p a r a t i o n D e t a i l s f o r Various Cement Pastes Used i n This P o r o s i t y Study Sys tem P r e p a r a t i o n and Curing Conditions Hydrated P o r t l a n d Cement

Magnesium Oxychloride Cement

Magnesium Oxysulfate Cement

Jet S e t Cement

Jet S e t Cement + 1, 2, 5% CaC12

Portland Cement-Latex Mixtures

Water-cement r a t i o = 0.25, 0.35, 0.40, 0.50, 0.60 Moist cured 2

-

7 y e a r s . S o l u t i o n - s o l i d r a t i o = 0.59, 0.64, 0.71, 0.77, 0.86 conditioned a t 50% RH f o r s e v e r a l months S o l u t i o n s p e c i f i c g r a v i t y = 1.18 S o l u t i o n - s o l i d r a t i o = 0.59, 0.72, 0.84, 0.96, 1.07, 1.43 conditioned a t 50% RH f o r s e v e r a l months S o l u t i o n s p e c i f i c g r a v i t y = 1.30 Water-cement r a t i o = 0.53, 0.73, 0.88

Moist cured 3 - 7 days then a t 11% RH f o r s e v e r a l weeks Water-cement = 0.53, 0.57, 0.73, 0.88

Moist cured 3

-

7 days t h e n a t 11% RH f o r s e v e r a l weeks

S e r i e s

1 100% RH 1 mo +11% RH S o l u t i o n 50% s o l i d s ; water-cement . I 2 5

-

,500; latex-cement .I25

-

.SO0 I T 100% RH 1 mo+11% RH S o l u t i o n 25% s o l i d s ; water-cement .225

-

.600; latex-cement .075

-

.200

I11 100% RH 1 d + l l % RH S o l u t i o n 25% s o l i d s ; water-cement .I50

-

.150

IV

100%

RH

1 d + l l % RH S o l u t i o n 50% s o l i d s ; water-cement .150

-

.350; latex-cement ,150

-

.350 V 57% RH 1 mo+11%

RH

S o l u t i o n 12.5% s o l i d s ; water-cement .220

-

,440; latex-cement . 0 3 1 - .062

YI

57% RH 1 m o + l l %

RH

S o l u t i o n 33.3% s o l i d s ; water-cement . I 6 8

-

. I 6 7 Autoclaved Portland Cement-Fly Ash Water-solid r a t i o = 0.22, 0.26, 0.30, 0.35, 0.40, 0.45

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774 Vol.

9,

No.

6

J . J .

Beaudoin

d e s c r i b e d elsewhere ( 1 ) . S o l i d volume i s measured e n a b l i n g t h e d e t e r m i n a t i o n of p o r o s i t y when t h e a p p a r e n t volume i s c a l c u l a t e d from sample geometry o r measured b y an a l t e r n a t e means. The s o l i d volume i s t h e i n s t a n t a n e o u s volume measured when helium i s f i r s t a d m i t t e d t o t h e system and i s n o t t o be confused with any time-dependent helium d i f f u s i o n which may s u b s e q u e n t l y o c c u r .

Mercury Porosimetry

i

P o r o s i t y measurements f o r a l l samples were determined u s i n g an Aminco Porosimeter c a p a b l e o f i n t r u s i o n p r e s s u r e s up t o 407 MPa. Each h y d r a t e d p o r t l a n d cement sample was t e s t e d a f t e r c o n d i t i o n i n g t o v a r i o u s m o i s t u r e c o n d i t i o n s from 11 p e r c e n t RH t o D-dry. Samples c o n d i t i o n e d a t 11 p e r c e n t

RH were pumped i n t h e i n s t r u m e n t u n t i l a vapor p r e s s u r e o f 50 pm Hg was reached. Porous g l a s s was t e s t e d i n D-dry c o n d i t i o n . Magnesium o x y c h l o r i d e and o x y s u l f a t e cement c o n d i t i o n e d t o 11 p e r c e n t RH were s u b j e c t e d t o vacuum d r y i n g mm Hg f o r 1-2 h) p r i o r t o t e s t . Latex-cement m i x t u r e s and auto- c l a v e d c e m e n t - f l y a s h m i x t u r e s , p r e v i o u s l y c o n d i t i o n e d t o 11 p e r c e n t RH, were vacuum d r i e d mm Hg) f o r s e v e r a l hours p r i o r t o t e s t . Many of t h e s e

samples were a l s o D-dried. Before e v e r y p o r o s i m e t e r t e s t r u n a helium pycnometric t e s t was performed w i t h t h e same sample having t h e same m o i s t u r e c o n d i t i o n s .

R e s u l t s

P o r o s i t y d a t a a r e p r e s e n t e d i n t h r e e f i g u r e s ( F i g u r e s 1, 2, 3) wherein t o t a l p o r o s i t y a s measured by mercury p o r o s i m e t r y i s p l o t t e d a g a i n s t t o t a l p o r o s i t y measured by helium pycnometry

.

In F i g u r e 1 d a t a from t h e f o l l o w i n g cement p a s t e sys-cems i s p l o t t e d : h y d r a t e d p o r t l a n d cement, magnesium o x y c h l o r i d e cement, magnesium o x y s u l f a t e cement, J e t S e t cement and J e t S e t cement c o n t a i n i n g a d d i t i o n s of CaC12. A

porous g l a s s r e s u l t i s a l s o p l o t t e d . Data f o r h y d r a t e d p o r t l a n d cement, J e t S e t cement w i t h CaC l 2 a d d i t i o n s and t h e h i g h p o r o s i t y magnesium o x y c h l o r i d e sample l i e on t h e l i n e of e q u a l i t y f o r p o r o s i t i e s g r e a t e r t h a n 21 p e r c e n t .

A t p o r o s i t i e s l e s s t h a n 21 p e r c e n t (helium method) d a t a f o r h y d r a t e d p o r t l a n d

cement and magnesium o x y c h l o r i d e cement i n d i c a t e lower p o r o s i t y by mercury method t h a n by t h e helium method. The l a r g e s t d i f f e r e n c e f o r p o r t l a n d cement was 8 p e r c e n t mercury p o r o s i t y * t o 13 p e r c e n t helium p o r o s i t y o r 38.5 p e r c e n t . L a r g e s t d i f f e r e n c e f o r magnesium o x y c h l o r i d e cement was 6 p e r c e n t mercury p o r o s i t y t o 17 p e r c e n t heliwn p o r o s i t y o r 6 4 . 5 p e r c e n t of pore space a c c e s s i b l e t o helium b u t n o t a v a i l a b l e t o mercury. The porous v y c o r g l a s s sample had 18 p e r c e n t mercury p o r o s i t y and 26 p e r c e n t helium p o r o s i t y o r 30.8 p e r c e n t helium p o r e space n o t a v a i l a b l e t o mercury. Data f o r magnesium o x y s u l f a t e cement p a s t e a l l l i e above t h e l i n e of e q u a l i t y ; a s helium p o r o s i t y i n c r e a s e s t h e d i f f e r e n c e between mercury and helium p o r o s i t y i n c r e a s e s , ( a t 32 p e r c e n t mercury p o r o s i t y helium p o r o s i t y i s 1 3 . 5 p e r c e n t g i v i n g a

d i f f e r e n c e of 137 p e r c e n t ) . J e t S e t cement r e s u l t s a l l l i e above t h e l i n e o f e q u a l i t y w i t h maximum d i f f e r e n c e of approximately 20 p e r c e n t .

I n F i g u r e 2, p o r o s i t y d a t a from t h e portland-cement l a t e x m i x t u r e s a r e p l o t t e d . R e s u l t s a r e d e s c r i b e d a s f o l l o w s :

*

P o r o s i t i e s measured by mercury p o r o s i m e t r y method w i l l b e r e f e r r e d t o a s mercury p o r o s i t y ; p o r o s i t i e s measured by helium pycnometry w i l l be r e f e r r e d

t o a s helium p o r o s i t y .

(8)

V o l . 9, No. 6

POROSITY, MERCURY INTRUSION, HELIUM PYCNOMETRY

0 HYDRATED PORTLAND CEMENT PASTE

1

MAGNESIUM OXYCHLORIDE CEMENT PASTE

I

-

0 MAGFIES IWYI OXYSUPFATE CFMEM PASTE /

-

'

5

L I N E OF , U ~ Q U A L I ~ Y - / a

-

[ P O R O U S C L A S S I

-

JET SET CEMENT PASTE

"

JET SET CEMENT P4STE

-

/' + I l. 2. 5SCaCI2 1 P O R O S I T Y I H E L I U M P Y C N O M E T R Y I . % FIG. 2 I

-

Mercury p o r o s i t y vs helium p o r o s i t y

=

-

f o r s e v e r a l cement- l a t e x m i x t u r e s FIG. 1 Mercury p o r o s i t y v s h e l i u m p o r o s i t y f o r s e v e r a l i n o r g a n i c c e m e n t i t i o u s s y s t e m s

I

C E M E N T - L A T E X M I X T U R E S /

I

/ > L A T E X I C E M E N T R A T I O + 1 > W A T E R I C E M E N T R A T I O -S ,// LlNE OF .'O 30 E P U ~ L I T Y ~ ' / /

,'.

I

P

/ / 0 I I I I 1 0 1 0 2 0 3 0 4 0 5 0 6 0 P O R O S I T Y ( H E L I U M P Y C N O M E T R Y I . R 5 0

-

4 0 3 0 F L Y A S H 0 1 . 2 2 0 / 0 3 / . 4 / ₀₅ FIG. 3 Mercury p o r o s i t y v s helium p o r o s i t y f o r a u t o c l a v e d cement-fly a s h m i x t u r e s / I I I I I

1

0 1 0 2 0 3 0 4 0 5 0 h0 P O R O S I T Y ( H E L I U M P Y C N O M E T R Y I . %

(9)

776

V o l . 9 ,

No.

6 J . J .

Beaudoi

n

S e r i e s I From latex-cement r a t i o 0.50 t o 0.28 mercury p o r o s i t y i s approximately 8 t o 10 p e r c e n t l e s s t h a n helium p o r o s i t y , t h e d i f f e r e n c e between t h e methods b e i n g a p p r o x i m a t e l y 30 p e r c e n t a t a helium p o r o s i t y of 30 p e r c e n t . From latex-cement r a t i o 0.28 t o 0.15 t h e change i n mercury p o r o s i t y i s small whereas t h e helium p o r o s i t y d e c r e a s e s t o about 10 p e r c e n t .

A t helium p o r o s i t i e s l e s s t h a n 20 p e r c e n t mercury

p o r o s i t i e s become l a r g e r t h a n t h o s e measured by helium. A t

3 p e r c e n t helium p o r o s i t y ( l a t e x - c e m e n t r a t i o = 0.15)

mercury p o r o s i t y i s 433 p e r c e n t l a r g e r t h a n helium p o r o s i t y . S e r i e s I 1 t o IV R e s u l t s f o r S e r i e s I 1 t o IV samples f o l l o w a s i m i l a r t r e n d

t o S e r i e s I r e s u l t s . There a r e some v a r i a t i o n s i n t h e v a l u e o f latex-cement r a t i o a t which t h e r e g i o n o f small changes i n mercury p o r o s i t y w i t h l a r g e changes i n helium p o r o s i t y b e g i n s .

I n F i g u r e 3, t h e cement-fly a s h m i x t u r e d a t a a r e p l o t t e d . A'fiove 30 p e r c e n t helium p o r o s i t y t h e d a t a a r e g e n e r a l l y c l u s t e r e d around t h e l i n e of e q u a l i t y . Below 30 p e r c e n t helium p o r o s i t y mercury p o r o s i t y i s g r e a t e r t h a n helium p o r o s i t y ; t h e d i f f e r e n c e between t h e two methods i n c r e a s e s a s p o r o s i t y d e c r e a s e s . The l a r g e s t d i f f e r e n c e was o b t a i n e d a t 8 p e r c e n t helium p o r o s i t y when t h e mercury p o r o s i t y was 21 p e r c e n t , i . e . , 162.5 p e r c e n t d i f f e r e n c e .

D i s c u s s i o n

The ' r e s u l t s of t h i s s t u d y i n d i c a t e t h a t p o r o s i t y a s measured by mercury i n t r u s i o n method can b e s i g n i f i c a n t l y d i f f e r e n t from p o r o s i t y measured b y helium pycnometry. P o r o s i t y (by mercury i n t r u s i o n ) can be s i g n i f i c a n t l y g r e a t e r o r l e s s t h a n helium p o r o s i t y depending on t h e c e m e n t i t i o u s system s t u d i e d . 0 Hydrated P o r t l a n d Cement A s water-cement r a t i o d e c r e a s e s

-

I t h e p r o p e r t i e s o f t h e h y d r a t e d s o l i d change ( 1 4 ) . There i s e x p e r i m e n t a l

-

U U

evidence t o s u g g e s t t h a t i n low &u 2

water-cement r a t i o p a s t e s empty ,= u + space

-

k i n k s

-

e x i s t s between t h e z - 3 s h e e t s o f t h e l a y e r e d s i l i c a t e s I (3,6,15-18.) These o b s e r v a t i o n s 3

-

2 a r e a s f o l l o w s : w = 4 (1) S i g n i f i c a n t l y lower s o l i d d e n s i t i e s i n s p i t e o f t h e p r e s e n c e 5 0 10 20 30 4 0 50 6 0 o f some h i g h d e n s i t y unhydrated cement. S o l i d d e n s i t i e s o f t h e T I M E , h

product d e c r e a s e from approximately

2.30 g / c c f o r water-cement r a t i o FIG. 4 0.80 t o 2.16 g/cc f o r water-cement Helium i n t a k e v s t i m e f o r h y d r a t e d r a t i o 0.25. p o r t l a n d cement p a s t e (2) S i g n i f i c a n t l y l a r g e r h y d r a u l i c r a d i u s c a l c u l a t e d by u s i n g 600-S and n o t SH20-SN2 i n t h e e x p r e s s i o n N2

iYH2-,-VN2 /600-S

1.

S and S a r e s u r f a c e a r e a s measured by n i t r o g e n and

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777 POROSITY, MERCURY INSTRUSION, HELIUM PYCNOMETRY

water vapor adsorption; VHqO and VNq are the pore volumes measured with water

- - L - " L

and nitrogen respectively. Winslow and Diamond (19) have masured an internal surface area for hydrated cement paste of approximately 670 m2/g (on dry weight of paste basis).

(3) Significantly larger helium flow into interlayer space than can be accounted for by removal of water alone. The total helium inflow for specimens conditioned at 11 percent RH increases significantly when water- cement ratio is below 0.40 (Fig. 4). Analysis of the volume change parameter, VV-VD, versus weight loss curves (20) enables an accounting for the volume previously occupied by the water which has been removed. Water densities should be approximately 1.0-1.2 g/cc. When excess helium flow occurs calculations give values for water density which are too low indicating helium is flowing into space in excess of that which was occupied by water. In other words for low'water-cement ratio pastes some helium is diffusing into empty space between the CSH sheets. It is this space which is referred to as 'kinked' space.

(4) Calculations by Feldman (portland cement paste, W/C equals 0.60) indicate the ratio of the total 'pore' volume to monolayer volume 1.32 (3,6).

ratio for perfectly parallel, smooth (no kinks) plates would be 1.00. Assuming a hydraulic radius of 10i for W/C equals 0.60 this ratio would be 3.7 for spheres and 3.6 for cylinders.

As the mercury porosity is less than helium porosity it is apparent that mercury cannot enter all the space available to helium. It is possible that there exists trapped micro space between aggregations of CSH sheets (extra layer space) which is accessible to helium but not mercury. 'This space possibly forms as a result of deposition and consolidation of aggregations of CSH layers in confined space such as would be found in low water-cement ratio paste. The geometrical constraints on the deposition of these products is

such that they cannot be deposited in a regular manner. It is postulated that many surfaces would come together or 'mate1 within distances of molecular dimension while other surfaces would provide the boundaries of 'trappedspace'. This may be similar to what Daimon and Kondo (21) refer to as an 'inter- crystallite pore' but it appears to be specific to low water-cement ratio CSH material. This space is not to be confused with 'kinked' space which is interlayer space and not accessible to mercury. Alternatively, there may be a simple sieve effect

-

micropores which permit entry of helium but not mercury; this would not explain, however, why mercury and helium give

comparable values at higher water-cement ratios when the volume concentration of fine pores (<200A diameter) increases with water-cement ratio (7,8,9). This trapped space, if present, appears to be present for only low water- cement ratio pastes. The solid matrix apparently has sufficient strength to resist the hydrostatic stresses imposed on it by mercury at high pressure.

In order to determine if there was any significant error in helium porosity measurement for low water-cement ratio pastes due to any diffusion during the measurement period, porosity measurements for most samples were independently measured using methanol as a displacement fluid. The porosity values were

similar to those determined by using helium and it is felt that possible errors due to diffusion processes are insignificant. Previous work (1) using methanol as a displacement mediwn for porosity measurement had indicated that porosity values were equivalent to those when helium was used as a displacement fluid.

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J . J

.

Beaudoi

n

I t i s noteworthy t h a t mercury p o r o s i m e t r y e x p e r i m e n t s on h y d r a t e d p o r t l a n d cement p a s t e were conducted on samples which had been d r i e d t o v a r i o u s s t a g e s from 1 1 p e r c e n t

RH

t o D-dry. There was no s i g n i f i c a n t d i f f e r e n c e i n t h e p o r e s i z e d i s t r i b u t i o n o r t o t a l p o r e volume i n t r u d e d f o r s a m p l e s ' s u b j e c t e d t o d i f f e r e n t d e g r e e s o f d r y i n g . T h i s i s i n a p p a r e n t c o n f l i c t w i t h t h e r e s u l t s o f Winslow and Diamond ( 7 ) a l t h o u g h t h e i r i n t r u s i o n p r e s s u r e s were o n l y t o 102 MPa.

Magnesium. Oxychloride Cement

With t h e e x c e p t i o n of t h e sample having s o l u t i o n - s o l i d r a t i o = 0.86 a l l o x y c h l o r i d e samples have s i g n i f i c a n t l y g r e a t e r helium p o r o s i t i e s t h a n mercury p o r o s i t i e s . A s p o r o s i t y d e c r e a s e s t h e volume c o n c e n t r a t i o n o f micropores l e s s than 0.005

l

m

i n c r e a s e s f o r t h i s system ( i n c o n t r a s t t o h y d r a t e d p o r t l a n d cement system). Also t h e o x y c h l o r i d e system h a s been shown t o .have h i g h e r s t r e n g t h t h a n t h e p o r t l a n d cement system ( 1 0 ) . The p r o d u c t s of h y d r a t i o n a r e mainly Mg(OH) noand c r y s t a l l i n e o x y c h l o r i d e complexes. I t i s p o s s i b l e t h a t micropores <30A d i a m e t e r ( e s t i m a t e d minimum p o r e d i a m e t e r mercury w i l l e n t e r a t 408 m a ) exist and t h e r e f o r e mercury w i l l n o t e n t e r , whereas helium w i l l

completely f i l l t h e micropore system. There a r e a l s o p o r e s i n t o which helium slowly d i f f u s e s u n t i l p o r e f i l l i n g i s complete. These p o r e s may have

e n t r a n c e s t o o narrow f o r mercury t o e n t e r . Porous Vvcor G l a s s

0

The porous g l a s s h a s an a v e r a g e p o r e d i a m e t e r of a p p r o x i m a t e l y 50A. Helium p e n e t r a t e s a l l t h e p o r e s and a c o r r e c t v a l u e of d e n s i t y can b e determined u s i n g t h e s o l i d volume measured u s i n g helium a s a d i s p l a c e m e n t f l u i d . Mercury was a b l e t o p e n e t r a t e approximately 69 p e r c e n t of t h e pore s p a c e , i n d i ~ a t i n g ~ t h a t t h e remainder of t h e p o r e s had d i a m e t e r s l e s s t h a n a p p r o x i m a t e l y 30A. The s t r e n g t h o f t h e g l a s s i s s u f f i c i e n t t o p r e v e n t c r u s h i n g o f p o r e w a l l s and e n t r y o f mercury i n t o t h e f i n e s t p o r e s . Magnesium O x y s u l f a t e Cement

Unlike o x y c h l o r i d e cement, t h e volume c o n c e n t r a t i o n of f i n e p o r e s f o r o x y s u l f a t e cement i n c r e a s e s a s s o l u t i o n - s o l i d r a t i o i n c r e a s e s . Also t h e d i f f e r e n c e between mercury p o r o s i t y and h e l i u m p o r o s i t y

-

mercury p o r o s i t y b e i n g s i g n i f i c a n t l y l a r g e r

-

i n c r e a s e s a s s o l u t i o n - s o l i d r a t i o i n c r e a s e s . I t has been shown t h a t t h e mercury p o r o s i t y i s e q u i v a l e n t t o t h e sum o f t h e i n i t i a l helium p o r o s i t y p l u s t h e e x t r a p o r e volume due t o p r e s e n c e of d i s c r e t e empty p o r e s which become a c c e s s i b l e t o helium upon h e a t i n g t h e sample t o 200°C ( 1 1 ) . The o x y s u l f a t e cement m a t r i x i s r e l a t i v e l y weak and it

is a p p a r e n t t h a t mercury can r u p t u r e p o r e w a l l s and e n t e r f i n e p o r e space n o t immediately a c c e s s i b l e t o helium.

J e t S e t Cement

J e t S e t cement w i t h o u t CaC12 i s r e l a t i v e l y weak ( 1 2 ) , t h e volume co-ncentra- t i o n o f micropores i n c r e a s e s w i t h water-cement r a t i o . I t a p p e a r s t h a t mercury can damage p o r e w a l l s and e n t e r f i n e p o r e s . The a d d i t i o n of C a C 1 2 t o J e t S e t cement i n c r e a s e s t h e s t r e n g t h o f t h e m a t r i x and f o r t h e p o r o s i t y r a n g e s t u d i e d t h e r e i s no s i g n i f i c a n t d i f f e r e n c e i n mercury p o r o s i t y and helium p o r o s i t y .

I n g e n e r a l , f o r t h e systems i n F i g . 1, s t r e n g t h i s i n t h e f o l l o w i n g o r d e r : o x y c h l o r i d e > p o r t l a n d cement>Jet S e t cement+CaC12>Jet S e t cement>oxysulfate

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Vol. 9, No.

6

POROSITY, MERCURY INTRUSION, HELIUM PYCNOMETRY

cement. Apparent structural damage to pore walls occurred for the twoweakest matrices. Figure 5 is a plot of microhardness versus porosity (helium) for five systems illustrated in Fig. 1;

the relative strengths of these

matrices are shown. The curves IUUu

0

presented in Fig. 5 are regression lines for the various cement systems; regression analysis data is presented in detail in other papers (22-24). At least ten microhardness measurements are made on each sample tested enabling a better statistical evaluation of results. Correlation coefficients for the microhardness-porosity curves presented are greater than 90%.

i

MAGNESIUM OXYCHLORIDE CEMENT

.-.-.- PORTLAND CEMENI

ccm-• JET SET CEMENT + 1% CaCIZ 0-0-0-0 JET SET CEMENT

---

MAGNESIUM OXYSULFATE CEMENT

Cement-Latex Mixtures

Between 10 to 30 per cent helium porosity there is little change in mercury porosity. At porosities greater than 20 per cent helium,

' 0

2

4 8 1 2 16 23 2 4 2 8 3 2 36 40 44 mercury porosity is less than helium

porosity; at porosities less than P O R O S I T Y . s

20 per cent helium, mercury porosi-

ties are greater than helium. FIG. 5

In general latex-cement ratio Microhardness vs porosity for

decreases as helium porosity several inorganic cernentitious

decreases. It is suggested that systems

latex film is plugging up pores making penetration by mercury more

difficult. At porosities greater than 30 per cent (mercury) a largepercentage of pores are >0.1 pm in diameter. At approximately 20 per cent mercury

porosity a significant percentage of pores have diameters between 0.1 to 0.01 pm. Samples having lowest value of mercury porosity have a large number of pores between 0.01 and 0.003 pm in diameter. 1n other words, as latex- cement ratio increases water-cement ratio increases and the number of fine pores detected by mercury decreases. (In the absence of latex, the number of fine pores increases with water-cement ratio.) The reason for the decrease may simply be that they are plugged or blocked off by latex film and are not

detected by mercury. In the absence of latex

-

at low water-cement ratios

-

there appears to be trapped space not accessible to mercury. In the presence of latex at low water-cement ratios, two possibilities are suggested. Helium diffusion experiments on the latex film alone indicate that the polyacrylic

I latex film itself contains micropores which can be penetrated by slow

1 diffusion of helium. Mercury may be entering some of this space. Penetration

may also be into trapped space between agglomerates of CSH sheets or even into

I

small discrete pores formed during mixing with latex. The latter possibility, however, does not explain why mercury porosity is significantly less than helium porosity at higher latex-cement ratios.

I

AS latex-cement ratio changes there is a possibility that surface energy changes and there may be a change in contact angle of mercury against these surfaces. Any changes in contact angle may have a contributary effect on the volume of mercury intruded (7).

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Vol.

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Beaudoi n

Autoclaved Cement-Fly Ash Mixtures

Mechanical properties and chemical composition'of these systems have been reported elsewhere (13). At helium porosities less than 30 per cent

differences with the larger mercury porosity values increase. The largest differences are observed for the four weakest matrices, preparations 2, 7, 8, 9. Data for the strongest matrix,preparation 3,are nested about the line of equality. In general, for these systems, a greater volume concentration of fine pores is observed for lower water-cement ratios. Only two preparations are significantly weaker than room-temperature cured portland cement paste

-

preparations 8 and 2

-

yet mercury is able to enter space that heliumdoes not.

One explanation i.s that it is possible that in these systems trapped space exists between agglomerations of silicate sheets and that mercury can force its way into these spaces; some microstructural damage is likely. It is suggested that the potential penetrstion of trapped space is greater for less dense, low C/S ratio products. High C/S ratio products have highest solid density and lowest total helium intake as observed in helium diffusion experiments.

I

Conclusions

Porosity of several common cementitious systems, as measured by high pressure mercury porosimetry, may be subject to microstructural limitations. Several mechanisms of pore filling by mercury intrusion are therefore

possible:

(1) Complete filling of pore space according to a pore size-intrusion pressure relationship as is conventionally assumed (7).

I

( 2 ) Structural damage of the relatively weak walls of discrete pores and subsequent entry of mercury into these spaces.

(3) Exclusion or entry of mercury from or into trapped space between

1

aggregations of layered silicates.

(4) Exclusion of mercury from pores or pore entrances which are too small for mercury to penetrate at a maximum intrusion pressure of 408 MPa.

(5) Blocked pore space due to the presence of an interfering phase, e.g., polymer latex film.

(6) Changes in contact angle between mercury and surface. Acknowledgements

The author wishes to thank J.J. Wood for his fine work in conducting all the experiments. Thanks are also due Drs. R.F. Feldman and V.S. Ramachandran for helpful discussions. This paper 'is a contribution from the Division of Building Research, National Research Council of Canada, and is published with the approval of the Director of the uivision.

References 1. R.F. Feldman. Cement Technology

-

3, 5 (1972).

2. R.S.H. Mikhail,

L.E.

Copeland and S. Brunauer. Canadian Journal of Chemistry

-

42, 426 (1964).

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6 POROSITY, MERCURY INTRUSION, HELIUM PYCNOMETRY

3. R.F. Feldman. Cem. Concr. Res. 4, 1 (1974).

_-

4. R.A. Helmuth and D.H. Turk. Highway Res. Board, Washington, Special Report 90, 135 (1966).

5. R.F. Feldman and J.J. Beaudoin. Cem. Concr. Res. 6, 389 (1976).

_-

6. R.F. Feldman. Proc. RILEM/IUPAC Int. Symp. on Pore Structure and

Properties of Materials, C101-C116, Prague (1973).

7. D.N. Winslow and S. Diamond. Journal of Materials,

-

5, 564 (1970). 8. J.F. Young. Powder Technology

-

9, 173 (1974).

9. A. Auskern and

W.

Horn. Journal of Testing and Evaluation,

1,

74 (1973). 10. J.J. Beaudoin and V.S. Ramachandran. Cem. Concr. Res. 5, 617 (1975).

_-

11. J.J. Beaudoin and V.S. Ramachandran. Cem. Concr. Res. 8, 103 (1978).

_-

12. J.J. Beaudoin. To be published.

13. J.J. Beaudoin and R.F. Feldman. Journal of Materials Science,

14,

1681 (1979).

14. R.F. Feldman. Cem. Concr. Res. 3, 777 (1973).

_-

15. .J.J. Beaudoin. Unpublished data.

16. R.F. Feldman. Cem. Concr. Res.

-

3, 107 (1973).

17. R.F. Feldman. Highway Res. Board Record No. 370, 8 (1971)

18. R.F. Feldman and P. J. Sereda. Mat6riaux et Constructions,

1,

509 (1968). 19. D.N. Winslow and S. Diamond. Journal Amer. Ceram. Soc. 57, 193 (1974).

_-

20. J.J. Beaudoin and R.F. Feldman. Cem. Concr. Res. 8, 223 (1978).

_-

21. M. Daimon and R. Kondo. Journal her. Ceram. Soc.

60,

110 (1976). 22. J.J. Beaudoin and V.S. Ramachandran. Cem. Concr. Res. 5, 617 (1975).

_-

23. J.J. Beaudoin and V.S. Ramachandran. Cem. Concr. Res. 8, 103 (1978).

_-

24. R.F. Feldman and J.J. Beaudoin. Cem. Concr. Res.

5,

389 (1976).