The flow of helium into the interlayer spaces of hydrated portland cement paste

(1)

Publisher’s version / Version de l'éditeur:

Cement and Concrete Research, 1, May 3, pp. 285-300, 1971-05-01

READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.

https://nrc-publications.canada.ca/eng/copyright

Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.

Questions? Contact the NRC Publications Archive team at

PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information.

NRC Publications Archive

Archives des publications du CNRC

This publication could be one of several versions: author’s original, accepted manuscript or the publisher’s version. / La version de cette publication peut être l’une des suivantes : la version prépublication de l’auteur, la version acceptée du manuscrit ou la version de l’éditeur.

For the publisher’s version, please access the DOI link below./ Pour consulter la version de l’éditeur, utilisez le lien DOI ci-dessous.

https://doi.org/10.1016/0008-8846(71)90004-4

Access and use of this website and the material on it are subject to the Terms and Conditions set forth at

The flow of helium into the interlayer spaces of hydrated portland

cement paste

Feldman, R. F.

https://publications-cnrc.canada.ca/fra/droits

L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.

NRC Publications Record / Notice d'Archives des publications de CNRC:

https://nrc-publications.canada.ca/eng/view/object/?id=fc8098d6-3d66-4483-a3b0-8ef6036c4b7a https://publications-cnrc.canada.ca/fra/voir/objet/?id=fc8098d6-3d66-4483-a3b0-8ef6036c4b7a

(2)

(3)

(4)

CEMENT and CONCRETE RESEARCH. Vol

.

1

,

pp. 285-300, 1971

.

Pergamon Press, 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 .

THE FLOW O F HELIUM INTO THE INTERLAYER SPACES O F HYDRATED PORTLAND CEMENT PASTE

R. F. F e l d m a n

Division of Building Re s e a r c h , National R e s e a r c h Council of Canada Ottawa, 7, Ontario, Canada

(Communicated by G. L. Kalousek)

ABSTRACT

A helium flow technique h a s been worked out whereby the changes o c c u r r i n g t o hydrated portland cement a s a r e s u l t of the r e m o v a l of i n t e r l a y e r w a t e r can be m e a s u r e d . R e s u l t s w e r e obtained a t w a t e r - c e m e n t r a t i o s of 0.4, 0.6, 0.8 and 1.0. "Solid volume" m e a s u r e m e n t s w e r e a l s o m a d e . It was concluded that the s p a c e s into which helium flowed w e r e i n t e r l a y e r s p a c e s and not fixed- dimension, narrow-necked p o r e s . This work supported the m e c h a n i s m d i s c u s s e d in the new m o d e l of hydrated portland

cement on the sequence of w a t e r r e m o v a l f r o m the i n t e r l a y e r s p a c e s and subsequent collapse of t h e s p a c e s . An e s t i m a t e of the density of the f i r s t 5. 25% of the w a t e r removed f r o m the 11% R. H. condition w a s m a d e ; t h i s was 1.27 5 _{0.08 g m / c c .}

SOMMAIRE

On a ClaborC une technique de flux dlhClium qui p e r m e t d e m e s u r e r l e s changements qui prennent place dans une p t t e d e ciment p o r t - land hydrate

5

l a s u i t e d e l'enl'evement de l'eau dans l e s couches intermCdiaires. Des r g s u l t a t s ont CtC obtenus pour d e s r a p p o r t s eau:ciment d e 0.4, 0.6, 0.8 e t 1.0. Des m e s u r e s du "volume solide" ont a u s s i CtC f a i t e s . On a conclu que l e p a s s a g e d e llhClium s e f a i s a i t dans l e s couches i n t e r m e d i a i r e s e t non dans d e s p o r e s Ctroites e t d e dimensions fixes. C e t t e Ctude appuie l e mCcanisme discutC du nouveau mod'ele d e ciment portland hydratk

s u r l a s6quence d e l'enlkvement de l ' e a u d a n s l e s couches i n t e r

-

mCdiaires e t l ' a f f a i s s e m e n t subskquent d e s e s p a c e s . Un estimC de l a densit6 du p r e m i e r 5.2570 de l ' e a u enlevCe aux conditions d e 11

%

d8humiditC r e l a t i v e a CtC fait; l a valeur Ctait d e 1. 27 5 _0.08 g m / c c .

(5)

CEMENT PASTE, POROSITY, HELIUM FLOW V o l . 1, No.

3

Introduction

Scientific i n t e r e s t in e x p e r i m e n t s t h a t provide information on the n a t u r e of hydrated portland c e m e n t p a s t e i s c u r r e n t l y c o n s i d e r a b l e , owing t o a r e c e n t l y d e s c r i b e d new m o d e l f o r hydrated portland cement ( 1 ) and subsequent d i s c u s s i o n s ( 2 , 3).

The new m o d e l r e c o g n i z e s t h a t the hydrated c a l c i u m s i l i c a t e s in portland c e m e n t a r e l a y e r - s t r u c t u r e d , and m a n y of the p r o p e r t i e s of h y d r a t

-

ed portland c e m e n t can be a s c r i b e d t o this. P r e v i o u s physical m e a s u r e - m e n t s such a s density and w a t e r sorption d e t e r m i n a t i o n s did not take into account the fact t h a t the d - d r i e d h y d r a t e s can r e h y d r a t e when r e - e x p o s e d t o w a t e r vapor; thus m a n y accepted p r o p e r t i e s and p a r a m e t e r s had t o be r e - a s s e s s e d o r r e v i s e d . In addition, i t i s now c o n s i d e r e d that the p r o p e r t i e s that led t o the notion of " g e l - p o r e s t t a r e i n f a c t due t o i n t e r l a y e r s p a c e s .

Studie s involving length and s o r p t i o n scanning i s o t h e r m s ( 4 ) have shown t h a t up t o 8070 of the length change in the c o u r s e of a sorption i s o - t h e r m d e t e r m i n a t i o n i s due t o i n t e r l a y e r hydration o r dehydration.

Seligmann ( 5 ) h a s analyzed NMR m e a s u r e m e n t s of o t h e r s and h i s own and h a s shown that a l a r g e portion of what w a s c o n s i d e r e d to be physically a d s o r b e d w a t e r i s i n t e r l a y e r w a t e r . Verbeck and Helmuth

( 6 )

have gone f u r t h e r and concluded that the w a t e r that w a s f o r m e r l y c o n s i d e r e d t o be gel w a t e r i s i n t e r l a y e r w a t e r , and t h a t g e l p o r e s a r e in f a c t i n t e r l a y e r s p a c e s .

At t h i s s t a g e i t w a s i m p o r t a n t t o follow by s o m e e x p e r i m e n t a l technique the changes t o the solid t h a t r e s u l t f r o m the r e m o v a l o r r e p l a c e - m e n t of the i n t e r l a y e r w a t e r i n o r d e r t o confirm i t s existence. The helium flow technique developed f o r t h i s p u r p o s e and t h e r e s u l t s obtained with i t a r e the subject of t h i s p a p e r . E x p e r i m e n t a l M a t e r i a l s ( a ) P o r o u s s i l i c a g l a s s - - P o r o s i t y i s approximately 5070 by volume 2 m a d e up a l m o s t e n t i r e l y of p o r e s 2 5 1 r a d i u s ; the s u r f a c e a r e a i s 180 m

/gm.

(6)

V o l . 1, No. 3

CEMENT PASTE, POROSITY, H E L I U M FLOW

( b ) Compacts of reagent g r a d e NaC1 - - P o r o s i t y v a r i e d f r o m 18 t o 2

0% by volume. Surface a r e a was l e s s than 0. 5 m / g m .

( c ) Compacts of r e a g e n t g r a d e C a ( 0 H ) - - P o r o s i t y v a r i e d f r o m 46 2 2

t o 8% by volume. Surface a r e a was 15 m / g m .

(d) A Type I portland cement was p a s t e -hydrated a t w a t e r - c e m e n t r a t i o s 0.4, 0.6, 0.8 and 1.0, i n cylinders 3 . 2 c m i n d i a m e t e r f o r 2. 5 y e a r s . D i s c s 1.25 m m thick w e r e cut f r o m t h e s e and w e r e used a s the s a m p l e s f o r helium flow m e a s u r e m e n t s .

The compacts fabricated i n ( a ) , (b) and ( c ) w e r e of the s a m e d i m e n - sions. The analysis of the cement h a s been published previously ( 4 ) .

Helium Comparison P y c n o m e t e r

As shown i n F i g u r e 1 , the s a m p l e i s placed in a cylinder which i s then evacuated. Helium i s allowed t o f i l l the two cylinders a t approximately

1 atrn. The cylinders a r e then isolated and c o m p r e s s e d t o 2 atrn by m o v - ing the r e f e r e n c e piston t o the f o r w a r d fixed position ( F i g u r e 1 ) ; in doing t h i s the volume i s exactly halved and the p r e s s u r e i s doubled. The s a m p l e

D I F F E R E N T I A L

FIG. 1

Simplified s chematic d i a g r a m of helium comparison pycnometer.

S A M P L L C U P

piston i s moved simultaneously with the r e f e r e n c e piston, and by r e f e r e n c e t o the differential p r e s s u r e indicator, the p r e s s u r e in the two cylinders i s kept the s a m e .

In the actual e x p e r i m e n t the sample i s evacuated for 10 m i n and helium i s then admitted t o the sample f o r 1 5 s e c . P r e s s u r e equalisation between the cylinders and c o m p r e s s i o n take a f u r t h e r 1 min:45 s e c . As

(7)

CEMENT PASTE, POROSITY, H E L I U M FLOW V o l . 1, No. 3

soon a s c o m p r e s s i o n t o 2 a t m i s complete, helium flow readings begin. The sample cylinder i s always r e t u r n e d to 2 a t m before a reading i s taken by comparing with the r e f e r e n c e cylinder through the d i f f e r e n t i a l manometer. Flow i s plotted a s m i l l i l i t e r s of helium a t 2 a t m p e r 100 gm of sample and a s a function of t i m e .

G e n e r a l P r o c e d u r e

The s a m p l e s w e r e heated under vacuum before a run, in a s e p a r a t e vacuum v e s s e l . After a p r e s c r i b e d period of t i m e d r y a i r was allowed t o e n t e r the v e s s e l and the sample was t r a n s f e r r e d to the pycnometer's sample cylinder in a gloved box d r i e d with magnesium perchlorate. The sample, except in the c a s e of porous g l a s s , was in the f o r m of s e v e r a l d i s c s a s a l r e a d y d e s c r i b e d , the total weight varying f r o m 15 to 30 gm. P o r o u s g l a s s was in the f o r m of broken tube, 2 -rnm wall thickness and 2.5 c m in d i a m e t e r . The runs on the hydrated cement w e r e done a t different m o i s - t u r e contents. At fir s t m o i s t u r e was removed by evacuation alone and then by heating a t i n c r e a s i n g t e m p e r a t u r e s and f o r different periods of time.

The sample was weighed a f t e r the helium flow r u n which extended over 40 h r , s o the change in flow c h a r a c t e r i s t i c s could be plotted a s a function of weight change. Some runs w e r e a l s o p e r f o r m e d using nitrogen a s the fluid.

The i n s t r u m e n t itself exhibited a s m a l l leak r a t e , but t h i s was determined before the e x p e r i m e n t s . All runs w e r e performed in a t e m p e r a t u r e -controlled l a b o r a t o r y a t 22°C.

The standard p r o c e d u r e was followed with t h e s e m a t e r i a l s using only helium a s the fluid. It was found that the flow r a t e was of the s a m e o r d e r a s the blank run (< 0.100 m l f o r 40 h r ) and was independent of the porosity of the compact. Density calculations ( f r o m Boyle's law) w e r e m a d e by assuming that the value obtained d i r e c t l y a f t e r c o m p r e s s i o n was

(8)

V o l .

1,

No.

3

₂₈₉

CEMENT PASTE, POROSITY, HELIUM FLOW

c o r r e c t . Results c o r r o b o r a t e d t h i s and indicated that the helium g a s had completely e n t e r e d the p o r e s r e g a r d l e s s of the porosity.

P o r o u s G l a s s

The s a m e r e s u l t a s above was obtained f o r porous g l a s s when helium was u s e d a s a fluid, but when nitrogen was used, i t w a s found that the

"apparent volume" was v e r y low, giving an abnormally high value f o r density. It was concluded that nitrogen was adsorbing on the clean porous g l a s s s u r f a c e during the c o m p r e s s i o n f r o m 1 t o 2 a t m o s p h e r e s .

The lack of flow when helium was u s e d was significant. The density value w a s r e a l i s t i c and i t w a s apparent that helium v e r y rapidly e n t e r e d the p o r e s even when t h e s e w e r e 25A r a d i u s .

Hydrated P o r t l a n d C e m e n t

Two s e t s of s a m p l e s w e r e used a t the four w a t e r - c e m e n t r a t i o s of 0 . 4 , 0 . 6 , 0.8 and 1.0. One s e t was d r i e d t o what had been previously d e t e r m i n e d by conventional techniques t o be equivalent t o the d - d r i e d s t a t e ( 4 ) ; the other s e t was d r i e d well beyond the d - d r i e d s t a t e . All the s a m p l e s had been initially equilibrated over concentrated NaOH solution ( 1 170 R. H. ) i n d e s i c c a t o r s for a m i n i m u m of 6 m o n t h s . The f i r s t helium flow r u n was done a t t h i s s t a t e and the s a m p l e s w e r e then d r i e d in 10 t o 12 s t e p s , a helium flow run being done a t e a c h step. The f i r s t s e t l o s t a total of about 8.2% based on the weight a t 1170 R.H. and the second s e t about 10.870. In g e n e r a l i t took f r o m 40 t o 50 days until the final stage of drying.

Helium Flow a s a Function of T i m e

F i g u r e 2 p r e s e n t s the flow of helium v e r s u s t i m e f o r the w a t e r

-

c e m e n t r a t i o 0.4 (weight l o s s t o 10.8%). The c u r v e s f o r a l l the w a t e r - cement r a t i o s a m p l e s a r e s i m i l a r ( w a t e r - c e m e n t r a t i o s of 0.6, 0.8 and 1.0, not shown). The c u r v e s i n F i g u r e 2 can be divided into t h r e e types. The c u r v e f o r the sample a t 1170 R R . H. and the subsequent two c u r v e s up t o a weight l o s s of 1.92% show a v e r y rapid helium flow f o r approximately the f i r s t 50 m i n . F r o m about 8 t o 10 h r onward t h e r a t e i s no g r e a t e r than that

(9)

CEMENT PASTE, POROSITY, H E L I U M FLOW

V o l .

1,

No. 3

of the blank r u n , and one can a s s u m e t h a t helium i s no longer flowing into the s a m p l e . This i s the f i r s t type of c u r v e , designated Type I. F u r t h e r weight l o s s up to 4 o r 570 yields c u r v e s which show even m o r e rapid helium flow a t the e a r l y p e r i o d s and a l e s s rapid d e c r e a s e in r a t e , the r a t e a t 10 h r

s t i l l being significant, but insignificant a t 40 h r . Beyond t h i s point, up t o a weight l o s s of 6 t o 770, one o b s e r v e s t h e second type of c u r v e (Type

II),

FIG. 2

Helium flow into 0 . 4 w a t e r - c e m e n t r a t i o cement p a s t e at different w a t e r contents, a s a function of time.

5 10 15 20 25 30 35 40

TIME. H O U R S

w h e r e the r a t e in the f i r s t 50 m i n b e c o m e s l e s s than in the previous condition, but t h e r e i s a c r o s s o v e r of c u r v e s a t a l a t e r period, with m o r e helium penetrating ultimately. The r a t e a t 40 h r at 670 weight l o s s now exceeds that of the blank r u n and i t a p p e a r s that a t 40 h r helium has not yet fully penetrated. Beyond 6 to 770 weight l o s s i s the t h i r d type of c u r v e (Type

HI),

which shows a l o s s in r a t e with weight l o s s before 1 h r and a net d e c r e a s e in helium flow a t 40 h r . F u r t h e r weight l o s s beyond 770 shows the r a t e d e c r e a s i n g a t both the e a r l y and l a t e p e r i o d s . The r a t e a t 10.82% weight l o s s a f t e r 40 h r i s quite low even though little penetration h a s

(10)

Vol.

1 ,

No.

3 CEMENT PASTE, POROSITY, HELIUM FLOW

W E I G H T L O S S . I O N D R Y I N G W E I G H T L O S S , I O N D R Y I N G

FIG. 3 FIG. 4

Helium flow a t 50 m i n and 40 h r , Helium flow a t 50 m i n and 40 h r , plotted a s a function of weight l o s s plotted a s a function of weight l o s s f o r 0.4 w a t e r -cement r a t i o cement f o r 0.

6

w a t e r - c e m e n t r a t i o cement

paste. paste.

Effect of Weight L o s s on the Volume of Helium Flow

T o i l l u s t r a t e how the helium flow v a r i e s with m o i s t u r e content, the volume that flowed into the s a m p l e a t 50 m i n and a t 40 h r was plotted a s a function of m o i s t u r e removed f r o m the 11% condition. F i g u r e s 3 and 4 show the plots f o r w a t e r - c e m e n t r a t i o s of 0.4 and 0.6, respectively. The only r e a l difference i n the c u r v e s i s that f o r the w a t e r - c e m e n t r a t i o of 0.4 the m a x i m u m inflow was approximately 4.2 m1/100 g m , while f o r w a t e r - c e m e n t

r a t i o s of 0.6, 0.8 and 1.0 t h e m a x i m a w e r e 3.2 and 3.4 f o r 0.6, 3.2 and 3.6 f o r 0.8 and 3.1 and 3.6 f o r 1.0. This includes the two s a m p l e s f o r the w a t e r -cement r a t i o s 0.6, 0.8 and 1.0. The s i m i l a r i t y between the c u r v e s f o r w a t e r - c e m e n t r a t i o s 0.6, 0.8 and 1.0 and how they differ with 0.4 i s not s u r p r i s i n g when one c o n s i d e r s t h e i r s u r f a c e a r e a s a s determined by

L

nitrogen adsorption. T h e s e a r e 30, 55, 51, and 57 m / g m f o r w a t e r - cement r a t i o s of 0.4, 0.6, 0.8 and 1 . 0 , respectively. The plotted points

show s o m e s c a t t e r between the two s a m p l e s f o r l e s s than 270 w a t e r removed, e s p e c i a l l y f o r w a t e r - c e m e n t r a t i o of 0.8, but beyond 270 the a g r e e m e n t i s quite good. They a l l show a d e c r e a s i n g amount of helium inflow a f t e r 50 m i n a t approximately 4 to 4. 570 weight l o s s , while the amount that flowed

(11)

292 V o l . 1 , N o . 3 CEMENT PASTE, P O R O S I T Y , H E L I U M FLOW

in a f t e r 40 h r d e c r e a s e d v e r y steeply a f t e r

6

t o 6. 5% weight l o s s . After 8 to 970 weight l o s s t h e r e i s little f u r t h e r d e c r e a s e in helium flow. This i s just a little beyond the equivalent of the d - d r i e d s t a t e .

Nitrogen Used a s Fluid in P y c n o m e t e r

Nitrogen w a s a l s o used a s the fluid on hydrated portland cement; s o m e of the r e s u l t s a r e shown in F i g u r e 5 f o r the p a s t e p r e p a r e d at a w a t e r - cement r a t i o of 1.0. R e s u l t s indicated little flow of nitrogen into the s m a l l s p a c e s of the sample. The c u r v e f o r the s a m p l e equilibrated a t 1170 R. H. i s little g r e a t e r than a blank run. Since a t 1170 R .

H.

approximately a m o n o - l a y e r of a d s o r b e d w a t e r e x i s t s , the s u r f a c e will not be s o active and

adsorption of nitrogen will d e c r e a s e r e l a t i v e to a b a r e s u r f a c e . The o t h e r c u r v e s shown a r e for the s a m p l e in a f a i r l y well d r i e d s t a t e . In none of the c a s e s does the nitrogen flow c o m p a r e in amount with that f o r helium

( F i g u r e 2) and t h e r e i s little change between 4 and 870 weight l o s s , the final c u r v e being equivalent t o the d - d r i e d state. The l a t t e r c u r v e s can thus be explained by the fact that during drying the m o n o l a y e r of w a t e r i s removed, and i n c r e a s e d adsorption of nitrogen will take place a s a r e s u l t of the c o m p r e s s i o n of the g a s f r o m 1 to 2 a t m . Examination of the c u r v e

r e p r e s e n t i n g a weight l o s s of 8.3370 (approximately d - d r i e d ) r e v e a l s t h a t in the f i r s t 20 m i n u t e s t h e r e i s a high r a t e of nitrogen flow. This r a t e cannot be matched by the equivalent helium curve ( F i g u r e 2) and i t i s believed t o be predominantly adsorption. The r e s u l t s f r o m porous g l a s s showed t h i s even m o r e c l e a r l y and a l s o in the c a s e of hydrated cement the density obtained by nitrogen w a s too high, approaching that of the unhydrated cement. T h i s h a s been mentioned p r e v i o u s l y ( 7 ) . It i s c l e a r then that in m e a s u r i n g the flow of helium into hydrated portland cement one i s m e a s u r - ing flow into s p a c e s which nitrogen cannot p e n e t r a t e , whether t h e s e s p a c e s contain s o m e water o r not. Studies, which will be r e p o r t e d in another paper, have shown that p o r e volumes computed by m e a s u r i n g solid volumes by this helium technique (the value i s taken i m m e d i a t e l y a f t e r c o m p r e s s i o n to 2 atm; flow i s not taken into account) i s the s a m e a s that obtained by methanol pycnometry. This in t u r n has been shown t o give p o r e volumes s i m i l a r t o liquid nitrogen ( 8 ) . Of i n t e r e s t in t h i s p a p e r a r e the n a t u r e of the s p a c e s

(12)

V o l . 1 , N o . 3 293 CEMENT P A S T E , POROSITY, H E L I U M FLOW

t h a t t h e n i t r o g e n and m e t h a n o l m o l e c u l e s do not e n t e r , e f f e c t of r e m o v a l of w a t e r f r o m t h e s p a c e s , and t h e r o l e of w a t e r i n t h e m .

T o t a l S p a c e Vacated by W a t e r V e r s u s D e g r e e of D r y i n g ( s e e A p p e n d i x f o r d e f i n i t i o n s ) B e f o r e a s p e c i f i c i n t e r p r e t a t i o n of t h e flow c u r v e s i s m a d e s o m e f u r t h e r a n a l y s i s w i l l be helpful. I n t h e h e l i u m p y c n o m e t r i c technique one m a y obtain a "solid volume" of t h e s a m p l e by using t h e v a l u e obtained by c o m p r e s s i n g t h e g a s i n t h e s a m p l e c y l i n d e r t o 2 atrn. No h e l i u m flow i s t a k e n i n t o account. O n e m a y t h e n p l o t a c u r v e of change i n " s o l i d v o l u m e " ( A V ) w i t h weight l o s s a s shown on F i g u r e 6 ( t h i s weight l o s s i s due t o t h e w a t e r r e m o v e d i n s t e p - b y - s t e p d r y i n g f r o m t h e 11% R . H. s t a r t i n g condition). S i m i l a r l y on F i g u r e s 3 a n d 4 " t o t a l inflow" a t 40 h o u r s h a s b e e n plotted a g a i n s t weight l o s s . T h i s t e r m " t o t a l inflow" now r e f e r s , of c o u r s e , t o t h e h e l i u m flow i n t o t h e s m a l l p o r e s i n t o which n i t r o g e n a n d m e t h a n o l e s s e n t i a l l y cannot e n t e r . Without d i s c u s s i n g a n y i n t e r p r e t a t i o n of t h e c u r v e s i t c a n be o b s e r v e d t h a t r e m o v a l of m o i s t u r e l e a d s t o a change i n "solid volume" and a change i n h e l i u m flow (AD). Adding t h e s e t o g e t h e r a p a r a m e t e r AV-AD i s obtained w h e r e t h e d e c r e a s e i n volume i s a n e g a t i v e AV and i n c r e a s e i n flow, AD, due t o i n c r e a s e d weight l o s s i s r e g a r d e d a s p o s i t i v e . T h i s c a n be r e g a r d e d a s t h e s p a c e v a c a t e d by t h e w a t e r , on t h e a s s u m p t i o n t h a t a t t h e beginning of t h e flow e x p e r i m e n t s l i t t l e h e l i u m e n t e r e d i n t o t h e s m a l l s p a c e s v a c a t e d by t h e w a t e r f o r t h e s h o r t p e r i o d a t 1 a t m and d u r i n g c o m p r e s s i o n . I t i s a s s u m e d t h a t c o r r e c t i o n f o r t h i s a m o u n t i s m a d e f r o m t h e r e s u l t s of t h e f i r s t condition ( t h e s a m p l e c o n - ditioned a t 1170

RR.

H.

) which a r e s u b t r a c t e d f r o m t h e o t h e r s t o obtain AV and AD. It i s a l s o a s s u m e d t h a t t h e h e l i u m d o e s not i n t e r a c t with t h e s u r - f a c e o r o t h e r body f o r c e s and i s a t 2 a t m within a l l t h e s m a l l s p a c e s t h a t w a t e r h a s v a c a t e d .

A s w a t e r i s r e m o v e d f r o m the s a m p l e one would e x p e c t a continual d e c r e a s e i n t h e p a r a m e t e r AV-AD. In F i g u r e 6, AV-AD i s plotted f o r t h e t w o s e t s of s a m p l e s f r o m 0 . 4 t o 1 . 0 and f o r C3S p a s t e h y d r a t e d a t 0. 5 a n d 0 . 8 w a t e r - c e m e n t r a t i o ; f o r t h e C S p a s t e s only u p t o a l o s s of 3 . 570 w a s

3

plotted. T h e p a r a m e t e r AV-AD a p p e a r s l i n e a r u p t o about 5. 570 weight l o s s ( F i g u r e 6). C o n s e q u e n t l y , a l i n e a r r e g r e s s i o n a n a l y s i s w a s applied t o

(13)

V o l

.

1, No. 3 CEMENT PASTE, POROSITY, HELIUM FLOW

0 11% R. H. A-.

a WEIGHI LOSS -4.1268

A z WEIGmLOSS - 6 . W

A Z WEIGHT LOSS ' 8.331%

0 _{0.4 WIC CEMENT PASTE A &}_B

0 0.6 WIC CEMENT PASTE A -

A _{0 . 8 WIC CVnENT PASTE A}

V 1.0 WIC CEMMT PASTE A

t 0.6 WIC CEMENT PASTE B

X 0 . 8 WIC CVnENT PASTE B

T 1.0 WIC CEMENT PASTE B

A 0.5 WIC C j S PASTE A V V S AW 0.4CEMENT PASTE -

1

A V

-

'.

_'.

- - '0 T I M E . H O U R S W E I G H T L O S S , Z I A W I O N D R Y I N G FIG. 5 FIG. 6 N i t r o g e n f l o w i n t o 1 . 0 w a t e r - c e m e n t P l o t o f A V - A D a n d A V a s a f u n c t i o n r a t i o p a s t e a t d i f f e r e n t w a t e r c o n - of weight l o s s f o r 10 d i f f e r e n t t e n t s , a s a function of t i m e . p a s t e s .

t h e points (39 i n a l l ) below a weight l o s s of 5. 370. T h i s s t r a i g h t l i n e i s y = 0.31034 (&O. 15939)

-

0.7886 ( & O m 0 5 0 5 2 ) ~ ~ x being t h e weight l o s s . T h e c o r r e l a t i o n coefficient i s 0.9823 giving a s i g n i f i c a n c e i n the 0.99 l e v e l f o r t h e c o r r e l a t i o n . ( T h e e r r o r s a r e e s t i m a t e d a t t h e 9970 confidence l e v e l . ) If a l l t h e a s s u m p t i o n s a r e c o r r e c t and t h e h e l i u m f i l l e d a l l t h e s p a c e t h a t t h e w a t e r v a c a t e d , t h e i n v e r s e of t h e s l o p e g i v e s t h e d e n s i t y of t h e w a t e r f r o m 0 t o 5. 370 weight l o s s . T h i s value c o m e s t o 1 . 2 7 % 0.08 g m / c c . T h e p a r a m e t e r AV-AD beyond 5.3% weight l o s s t o a p p r o x i m a t e l y 1170 ( F i g u r e 6) s h o w s p r a c t i c a l l y no f u r t h e r d e c r e a s e ; i n f a c t o v e r s o m e r e g i o n s t h e r e i s an i n c r e a s e plotted on F i g u r e 6 f o r t h e 0 . 4 w a t e r - c e m e n t r a t i o p a s t e ) , d e s p i t e t h e f a c t t h a t a f u r t h e r 5.670 of w a t e r h a s b e e n r e m o v e d f r o m t h e s a m p l e . It a p p e a r s t h a t r e m o v a l of w a t e r beyond 5.370 d o e s not c o n f o r m t o t h e m e r e r e m o v a l of w a t e r f r o m p o r e s . T h e c u r v e f o r AV ( F i g u r e 6) shows t h a t b e - tween 5 t o 6% weight l o s s a n i n c r e a s e i n t h e r a t e of change of AV o c c u r s (i. e.

,

a n i n c r e a s e d s h r i n k a g e p e r unit weight l o s s ) . I n addition, on F i g u r e 3 t h e h e l i u m flow a t 40 h r s h o w s t h a t a f t e r 5.870 weight l o s s t h e r e i s a v e r y a b r u p t d e c r e a s e i n t h e a m o u n t t h a t h a s flowed i n t o t h e s m a l l s p a c e s of t h e s a m p l e .

(14)

Vol. 1, No.

3

FIG. 7

CEMENT PASTE, POROSITY, HELIUM FLOW

Two different m o d e l s t o explain t h e helium flow c h a r a c t e r i s t i c s of the c e m e n t p a s t e s . ( a ) m o d e l with p o r e s having n a r r o w n e c k s and fixed d i m e n s i o n s ( b ) i n t e r l a y e r m o d e l . liiil D i s c u s s i o n In t h e p r e s e n t a t i o n of r e s u l t s i t w a s s u g g e s t e d t h a t a s p e c i f i c i n t e r - p r e t a t i o n of t h e s e r e s u l t s could be m a d e . I t w a s concluded t h a t t h e flow of helium which w a s being o b s e r v e d in t h e s e e x p e r i m e n t s w a s flow f r o m t h e p o r e s of - 2 0 i r a d i u s , which f i l l r a p i d l y during c o m p r e s s i o n , into s p a c e s which have e n t r a n c e s too s m a l l f o r t h e e n t r a n c e of n i t r o g e n . T h e r e a r e two m o d e l s f o r h y d r a t e d p o r t l a n d cement. One m o d e l h a s a m i c r o s t r u c t u r e with a s m a l l a r e a a c c e s s i b l e t o n i t r o g e n but a c o n s i d e r a b l y l a r g e r a r e a available t o m o l e c u l e s like w a t e r ; t h e l a r g e a r e a i s composed of p o r e s of fixed d i m e n s i o n s with n e c k s of s u c h a s i z e t h a t n i t r o g e n cannot e n t e r ( F i g u r e 7 ( a ) ) . The o t h e r , t h e "new model" f o r h y d r a t e d p o r t l a n d c e m e n t , d o e s not r e c o g n i z e the e x i s t e n c e of t h e s e p o r e s with fixed d i m e n s i o n s , but p o s t u l a t e s the p r e s e n c e of l a y e r e d c r y s t a l s with i n t e r l a y e r w a t e r between adjacent l a y e r s ; the s u r f a c e a r e a d e t e r m i n e d by n i t r o g e n a d s o r p t i o n i s t h e e x t e r n a l a r e a of t h e l a y e r e d c r y s t a l s . As t h e w a t e r i s withdrawn, i n t e r l a y e r . s p a c e i s m a d e available a t f i r s t f o r helium flow, but then collapse of the

l a y e r s o c c u r s i n a m a n n e r not p r o p o r t i o n a l t o t h e l o s s of i n t e r l a y e r w a t e r ( F i g u r e 7 ( b ) ) . It will be shown how t h e l a t t e r m o d e l i s t h e one that b e s t f i t s t h e data.

At 1170 R. H. i t i s a s s u m e d that the s a m p l e s p o s s e s s approximately a m o n o l a y e r of a d s o r b e d w a t e r . R e s t r i c t e d flow into the s a m p l e a t t h i s s t a g e can be d e s c r i b e d by e i t h e r m o d e l , i. e . , flow into n a r r o w - n e c k e d p o r e s o r into p a r t i a l l y d e h y d r a t e d e n t r a n c e s of i n t e r l a y e r s p a c e s . As m o r e w a t e r i s r e m o v e d f r o m t h e s a m p l e an i n c r e a s e i n flow would be expected f r o m both m o d e l s . Volume change can be explained in the e a r l y s t a g e s f o r both

(15)

CEMENT PASTE, POROSITY, HELIUM FLOW

V o l . 1 , No. 3

s u r f a c e w a s being removed. In e i t h e r m o d e l , t h i s can only be u s e d t o explain a s m a l l p a r t of the volume change, however, because the complete monolayer would occupy l e s s than 1 m1/100gm of a s a m p l e (calculated f r o m e x t e r n a l a r e a d e t e r m i n e d by nitrogen adsorption; the s u r f a c e a r e a i s

2

30 m / g m f o r 0 . 4 w a t e r - c e m e n t r a t i o p a s t e ) . Model (b) ( F i g u r e 7) c a n explain t h i s s i n c e one would expect a diminution in "solid volume" a s dehydration p r o c e e d s f u r t h e r into the l a y e r s . P a r t of the volume vacated by the w a t e r f r o m the i n t e r l a y e r s p a c e s i s taken up by a slight collapse of the l a y e r s which c a u s e s a n e x t e r n a l volume change; the r e s t of the volume vacated by w a t e r will r e s u l t in i n c r e a s e d flow of the Type I flow c u r v e s .

T h e s u m of the e x t e r n a l volume change (AV) and change in amount of inflow (AD) ( s a m e a s p a r a m e t e r OV-AD) plotted against the l o s s in weight (OW) f o r the m a n y s a m p l e s ( F i g u r e

6 )

produced a s t r a i g h t line giving a density of 1. 27 g m / c c f o r the w a t e r removed up t o 5 . 2 7 0 ~ Although t h i s r e s u l t by itself i s consistent with m o d e l ( a ) , i t p r o v i d e s evidence against it because, a t t h i s weight l o s s ( 5 . 2 7 0 ) ~ AV i s too l a r g e t o be explained by the fixed-dimension narrow-necked p o r e s of m o d e l ( a ) . The flow c u r v e s and the value of density f o r the w a t e r would be consistent with both m o d e l s up t o about 470 weight l o s s . Beyond t h i s l o s s , however, the flow c u r v e s show a d e c r e a s e i n initial r a t e a l t h o u g h m o r e helium h a s flowed i n a t 40 h o u r s . ( T h e s e c u r v e s w e r e labelled Type

LI

e a r l i e r i n this p a p e r ) . This l a s t fact cannot be explained by m o d e l ( a ) . Indeed, t h e r e i s no m e c h a n i s m in t h i s m o d e l t o account f o r a d e c r e a s e i n flow r a t e o r t o t a l flow. One would e x - pect a n i n c r e a s e in i n i t i a l r a t e and quantity a s the volume of empty s p a c e in the s m a l l p o r e s i n c r e a s e s . A s m o r e w a t e r i s r e m o v e d , i. e . , beyond 670 weight l o s s w h e r e the Type III c u r v e s o c c u r , initial flow r a t e d e c r e a s e s even f u r t h e r ; a t 40 h o u r s the t o t a l quantity of helium that h a s e n t e r e d the s a m p l e now a l s o d e c r e a s e s .

T h e s e r e s u l t s c a n be completely explained by m o d e l (b): a s w a t e r i s removed f r o m the i n t e r l a y e r s p a c e s m o r e s p a c e i s vacated and some collapse o c c u r s . At f i r s t , however, the collapse i s not a s g r e a t a s the space c r e a t e d and helium flow i n c r e a s e s in r a t e . A s e n t r a n c e s t o i n t e r - l a y e r s p a c e s get significantly s m a l l e r , r a t e of flow d e c r e a s e s even though a

(16)

Vol

.

1 , No. 3

297 CEMENT PASTE, POROSITY, HELIUM FLOW

l a r g e r volume of helium can ultimately flow in. Where the weight l o s s i s between 5 and 6% the r a t e of volume change with weight l o s s i n c r e a s e s significantly; t h i s f i t s i n well with the flow c u r v e s and m o d e l ( b ) . T h i s i n c r e a s e d r a t e of shrinkage h a s been indicated i n previous s t u d i e s of length change ( 4 ) and was p a r t of the evidence u s e d f o r constructing t h i s model. F i g u r e s 3 and 4 show how rapidly the r a t e of flow d e c r e a s e s over a v e r y s m a l l weight l o s s range. I t i s believed that i n t h i s region the collapsing l a y e r s not only p r e s e n t "narrow necks" t o the helium a t o m s but a l s o long n a r r o w s l i t s which g r e a t l y r e s t r i c t flow. T h i s i s i l l u s t r a t e d f u r t h e r in F i g u r e 6 which shows t h a t beyond 5. 570 weight l o s s t h e r e i s no f u r t h e r d e c r e a s e i n AV-AD; i n f a c t i t s o m e t i m e s i n c r e a s e s . T h e i n c r e a s e i n shrinkage (-AV) i n t h i s region ( F i g u r e

6 )

does not compensate f o r the d e - c r e a s e i n flow in the p a r a m e t e r AV-AD ( F i g u r e s 2-4).

R e s u l t s f r o m sorption and length-change i s o t h e r m s ( I ) , and m e a s u r e - m e n t of Young's modulus a s a function of sorbed w a t e r , led t o the i d e a t h a t the w a t e r between the l a y e r s of the hydrated s i l i c a t e s played a n a l l -

i m p o r t a n t r o l e , especially the w a t e r i n the middle portion, which, i t w a s thought, controlled the collapse and change i n e l a s t i c p r o p e r t i e s . Signifi- cant closing of the l a y e r s did not o c c u r until the i n t e r i o r portion of the w a t e r w a s expelled. This explains the g r e a t influence of a s m a l l weight l o s s on the r a t e of flow, and the f a i l u r e of p a r a m e t e r (AV-AD) t o continue to d e c r e a s e l i n e a r l y a s a function of weight l o s s . In effect, the collapse of the l a y e r s h a s t r a p p e d space vacated by w a t e r , and helium cannot e n t e r t h i s

space even a f t e r 40 h o u r s of exposure. Thus the new m o d e l a l s o explains the behavior of the AV-AD v e r s u s AW plot; m o d e l ( a ) would p r e d i c t t h i s plot t o continue i n e s s e n t i a l l y a l i n e a r fashion.

Conclusions

( 1 ) A technique i s d e s c r i b e d which m a k e s possible the m e a s u r e

-

m e n t of flow of helium o r nitrogen into hydrated portland cement.

( 2 ) Helium flows rapidly into a l l p o r e s except the i n t e r l a y e r s p a c e s . The m e a s u r e m e n t of helium flow data i s the m e a s u r e m e n t of the r a t e of penetration of helium into i n t e r l a y e r s p a c e s . Nitrogen g a s produces slight,

(17)

298

CEMENT PASTE, POROSITY, HELIUM FLOW V o l . 1 , No. 3

if a n y , p e n e t r a t i o n i n t o t h e s e s p a c e s . ( 3 ) By m e a s u r i n g t h i s p a r a m e t e r f o r t h e s a m e s a m p l e a t d i f f e r e n t l e v e l s of w a t e r c o n t e n t i t i s p o s s i b l e t o s t a t e c o n c l u s i v e l y t h a t t h e s e " s m a l l p o r e s " i n t o w h i c h h e l i u m i s flowing a r e i n t e r l a y e r s p a c e s , not f i x e d - d i m e n s i o n n a r r o w - n e c k e d p o r e s . (4) T h e s e m e a s u r e m e n t s p r o v i d e c o r r o b o r a t i o n t o t h e "new" m o d e l f o r h y d r a t e d p o r t l a n d c e m e n t a n d s u p p o r t t h e m e c h a n i s m on t h e s e q u e n c e of w a t e r r e m o v a l f r o m t h e i n t e r l a y e r a n d how t h i s e f f e c t s v o l u m e change. ( 5 ) T h i s t e c h n i q u e m a k e s p o s s i b l e t h e s t u d y of t h e i n t e r l a y e r n a t u r e of h y d r a t e d p o r t l a n d c e m e n t and t h u s should be helpful i n studying all

p r o p e r t i e s t h a t a r e d e p e n d e n t on t h e n a t u r e of t h e i n t e r l a y e r , s u c h a s f i r s t - d r y i n g s h r i n k a g e .

( 6 ) T h e d e n s i t y of t h e w a t e r c o n s i d e r e d p r e d o m i n a n t l y i n t e r l a y e r c a m e t o 1 . 2 7 f 0 . 0 8 g m / c c . T h i s i s i n l i n e w i t h m e a s u r e m e n t s m a d e on expanding a n d non-expanding c l a y s f o r wat-er c o n t e n t s of l e s s t h a n one m o n o l a y e r ( 9 ) . R e s u l t s f o r s o m e a d s o r b a t e s 30% a b o v e t h e i r bulk v a l u e s a r e a l s o r e c o r d e d i n t h e l i t e r a t u r e ( 1 0 ) . B r u n a u e r e t a1 have r e p o r t e d t h e value f o r t h e a p p a r e n t d e n s i t y of t h e m o l e c u l e of w a t e r i n e x c e s s of C a S i 0 _2H 0 _{a s 1 . 3 9 g m / c c ( 1 1 ) . T h e d e n s i t y r e s u l t t h u s l e n d s s u p p o r t} 3 2 7 ' 2 t o t h e c o n c l u s i o n s m a d e f r o m t h e h e l i u m flow t e c h n i q u e . A c k n o w l e d g m e n t s T h e v a l u a b l e c o n t r i b u t i o n of S. E. D o d s i n o b s e r v i n g a n d r e c o r d i n g t h e p h e n o m e n a i s r e c o g n i z e d h e r e . T h a n k s a r e a l s o given t o D r s . V.S. R a m a c h a n d r a n a n d H. Whitehead f o r h e l p f u l d i s c u s s i o n s . 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 D i v i s i o n of Building Research, N a t i o n a l R e s e a r c h C o u n c i l of C a n a d a , and i s p u b l i s h e d w i t h 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 D i v i s i o n . R e f e r e n c e s

1,

R. F. F e l d m a n and P. J . S e r e d a . A m o d e l f o r h y d r a t e d p o r t l a n d c e m e n t a s d e d u c e d f r o m s o r p t i o n - l e n g t h c h a n g e and m e c h a n i c a l p r o p e r t i e s . M a t C r . C o n s t r . 1 , No. 6, 509 (1968).

_-

(18)

V o l .

1,

N o . 3 299 CEMENT PASTE, P O R O S I T Y , H E L I U M FLOW

2. S. B r u n a u e r , I. Odler and M. Yudenfreund. The new m o d e l of

hardened portland c e m e n t p a s t e . Highw. R e s . Bd. ( t o be published). 3. R. F. F e l d m a n and P. J. S e r e d a . D i s c u s s i o n of p a p e r "The new

m o d e l of hardened portland c e m e n t paste" by S. B r u n a u e r , I. Odler and M . Yudenfreund. Highw. R e s . Bd. ( t o be published).

4. R. F. Feldman. Sorption and length change s c a n n i n g i s o t h e r m s of m e t h a n o l and w a t e r on hydrated portland cement. P r o c . F i f t h Int. Syrnp. Chem. Cement, Tokyo, 1968, P a r t 111, Vol. 111, p. 53.

5. P. Seligmann. Nuclear m a g n e t i c r e s o n a n c e s t u d i e s of the w a t e r in hardened cement paste. J. P o r t l a n d C e m e n t Assoc. R e s . Dev. Lab.

10, No. 1, 52 (1968).

-

6. G. J. Verbeck and R. A. Helrnuth. S t r u c t u r e s and physical p r o p e r t i e s of cement p a s t e s . P r o c . F i f t h Int. Syrnp. Chem.Cement, Tokyo, 1968, Vol.

m,

p. 1.

7. T . C. P o w e r s and T . L o Brownyard. P h y s i c a l p r o p e r t i e s of hardened portland cement paste. P o r t l a n d Cement A s s o c . Res. Lab. Bu11.22. Chicago (1947).

8. R. Sh. Mikhail and S. A. Selirn. Adsorption of o r g a n i c v a p o r s in r e l a t i o n t o the p o r e s t r u c t u r e of hardened portland cement p a s t e s . Highw. R e s . Bd. Spec. Rep. 90, p. 123.

9. R. T o M a r t i n . Adsorbed w a t e r on clay: A review. P r o c . Ninth Nat. Conf. C l a y C l a y M i n e r a l s (1962), p. 28.

10. S. B r u n a u e r . The Adsorption of G a s e s and Vapors. p. 420. P r i n c e t o n University P r e s s (1943).

11. S. B r u n a u e r ,

D o

L . K a n t r o and L. E . Copeland. T h e s t o i c h i o m e t r y of the hydration of @ - d i c a l c i u m s i l i c a t e and t r i c a l c i u m s i l i c a t e a t room t e m p e r a t u r e . J . Am. Chem. Soc. 80, 761 (1958).

_-

Appendix

The following a r e definitions of t e r m s u s e d in the text. Solid Volume

T h i s i s the value obtained f o r solid volume f r o m the helium pycnometer i m m e d i a t e l y a f t e r the helium i s c o m p r e s s e d t o 2 a t m . The solid volume i s c o n s i d e r e d t o exclude a l l p o r e s , but include i n t e r l a y e r s p a c e s which m a y o r m a y not be occupied by w a t e r .

(19)

3 0 0 V o l . 1 , No. 3 CEMENT PASTE, POROSITY, HELIUM FLOW

T h i s r e f e r s t o the change i n solid volume f r o m the volume a t 11% R.H. due t o a w a t e r content change. -AV r e p r e s e n t s a shrinkage.

AD

-

T h i s i s the change, due t o a r e m o v a l of w a t e r f r o m the 11% R. H. condition, in the helium inflow taken a t 4 0 h r . An i n c r e a s e in inflow yields an i n c r e a s e in AD.

AV

-

AD

T h i s r e f e r s t o the n e t effect of the r e m o v a l of i n t e r l a y e r w a t e r and physically i s a volume. When helium can e n t e r a l l t h e vacated i n t e r l a y e r space, t h i s t e r m r e p r e s e n t s the volume which t h e r e m o v e d i n t e r l a y e r w a t e r had occupied.