Hardened portland cement pastes of low porosity III. Degree of hydration. Expansion of paste. Total porosity

CEMENT and CONCRETERESEARCH. Vol. 2, pp. 463-480, 1972. Pergamon Press, Inc. Printed in the United States.

HARDENED PORTLAND CEMENT PASTES OF LOW POROSITY III.

DEGREE OF HYDRATION. EXPANSION OF PASTE. TOTAL POROSITY.

Ivan Odler*, Marvin Yudenfreund**, Jan Skalny***, and Stephen Brunauer Department of Chemistry Clarkson College of Technology Potsdam, New York 13676 (Communicated by D. M. Roy)

ABSTRACT The d e g r e e of hydration, the expansion during hydration, and the total porosity of low-porosity portland cement pastes were investigated at hydration t i m e s ranging from 1 hour to 180 days. The effects of the type of cement (Type I and II), the grinding aid, the surface of the cement, the w a t e r - c e m e n t ratio (0. 2 and 0.3), and the t e m p e r a t u r e of hydration (5 °, 25 ° and 50°C) were d e t e r m i n e d .

Le degr~ de la hydratation, la expansion pendant la hydratation, et la total poroslte des p~tes de bas porosLte de Portland ciment 6tainet examin~ en d~tail ~t las perlode de la hydratation "St la porte~ de une heure au cent quatre-vingts jours. Les effets du type du ciment (Type I e t II), la aide de g r i n c e r , la surface du ciment, la proportion d'eau au ciment (0. 2 et 0.3), et la t e m p e r a t u r e de la hydratation (5 °, 25 ° et 50°C) ~tainent determLne. •

•

t

•

J

1

* P r e s e n t a d d r e s s : Westvaco R e s e a r c h Center, North Charleston, South Carolina. * * P r e s e n t a d d r e s s : Atlas Chemical Industries, Wilmington, Delaware. * * * P r e s e n t a d d r e s s : M a r t i n - M a r i e t t a Corporation, R e s e a r c h Institute for Advanced Studies, Baltimore, Maryland 21227.

463

464

Vol. 2, No. 4 LOW POROSITY, CEMENTPASTES, HYDRATION, EXPANSION Introduction This is the third of a s e r i e s of papers, which p r e s e n t the r e s u l t s of four and a

half y e a r s of r e s e a r c h on low-porosity portland cement pastes.

The r e s e a r c h was

sponsored by the Engineering R e s e a r c h and Development Bureau of the New York State Department of Transportation, in co-operation with the U.S. Department of Transportation, Federal Highway Administration, Bureau of Public Roads.

The opinions, findings, and

conclusions expressed in this paper are those of the authors, and not n e c e s s a r i l y those of the State of New York o r the Federal Highway Administration. The f i r s t paper of the s e r i e s dealt with the m a t e r i a l s and the experimental methods used in the r e s e a r c h (1), and it will be r e f e r r e d to as paper I.

The second paper dealt

with the exploratory phase of the r e s e a r c h , and with the investigation of the dimensional changes of the pastes (2), and it will be r e f e r r e d to as paper H.

The p r e s e n t paper d i s c u s s e s

the degree of hydration, the expansion of the pastes during hydration, and the total porosity of the pastes. Degree of Hydration 1.

In equation {5), paper I, the degree of hydration, x, was defined as w n / < ,

i. e . , the nonevaporable water at any given age of the paste divided by the nonevaporable water at complete hydration.

This procedure r e q u i r e s justification.

If the compounds in cement hydrate at different r a t e s , then from the scientific point of view the degree of h~l ration of cement as a whole has not much meaning.

But

from the practical point of view it is very meaningful, because the strength of the paste and its volume changes are determined by the degree of hydration of the paste. In the hydration, a gel is produced, which is called cement gel. A gel is a coherent m a s s of v e r y small p a r t i c l e s , which have colloidal dimensions.

Most of the cement gel is

a calcium silicate hydrate, produced in the hydration of C3S and C2S.

Brunauer named

this tobermorite gel, because it exhibits certain s i m i l a r i t i e s to the natural m i n e r a l toberm o r i t e , and even g r e a t e r s i m i l a r i t i e s to synthetic t o b e r m o r i t e s .

Recently the l e s s definite

t e r m "C-S-H gel" was adopted by cement chemists, but because m o s t of the work on this substance is found in the publications of Brunauer and his eoworkers, the t e r m t o b e r m o r i t e gel was retained in the p r e s e n t and subsequent papers in o r d e r to avoid confusion. T o b e r m o r i t e gel is the m o s t important constituent of hydrated cement.

Although some

of the other hydration products m a y have some cementing properties, by far the m o s t important cementing m a t e r i a l is t o b e r m o r i t e gel.

Thus, this gel is p r i m a r i l y responsible

Vol. 2, No. 4

465 LOW POROSITY, CEMENTPASTES, HYDRATION, EXPANSION

fDr the strength of hardened cement paste, m o r t a r , and concrete. T o b e r m o r i t e gel m a y contain small amounts of aluminum, iron, magnesium and other ions as impurities, but t h e s e have little o r no effect on its p r o p e r t i e s .

In normal

cement p a s t e s , the SiO 4 m a y be replaced to a limited extent by SO4, and this may reduce the c o m p r e s s i v e strength.

Copeland and Kantro (3) showed that the c o m p r e s s i v e strength

of hydrated C3S p a s t e s is reduced to 56% of its value when the m o l a r ratio SO3/SiO 2 is 0. 1. The sulfate ions come from gypsum, and the low-porosity p a s t e s contain no gypsum.

The

r e a s o n why sulfate substitution is mentioned h e r e is that lack of sulfate substitution in l o w - p o r o s i t y p a s t e s m a y be one factor, though probably not a v e r y important one, in p r o ducing the v e r y high c o m p r e s s i v e strengths in comparison with normal pastes. The extent of substitution of impurities in the t o b e r m o r i t e gel produced in the hydration of c e m e n t s is unknown. Because of this, they will be left out of consideration, and the gel will be r e g a r d e d as composed of CaO, SiO 2, and H20 only.

The problem of

determining the composition of t o b e r m o r i t e gel in hydrated c e m e n t s is complicated enough even without considering the impurities, as will be d i s c u s s e d later. Some of the other hydration products may also have gel-like p r o p e r t i e s , but they will not be d i s c u s s e d here.

The t o b e r m o r i t e gel and other hydration products deposit

on the unhydrated cement grains, and at an e a r l y age diffusion through the gel coating b e c o m e s the rate determining step.

This will be d i s c u s s e d in detail later.

Because the

coating deposits indiscriminately on the unhydrated grains, when diffusion d e t e r m i n e s the rate, the rate c e a s e s to depend on the nature of the individual cement compounds. the p r e s e n t discussion, the four m a j o r compounds will be considered: and C4AF

In

C3S, C2S, C3A

In both the Type I and Type II clinker used by us, these four compounds con-

stitute 98% of the total weight. hydration a r e v e r y different.

When the compounds hydrate individually, their r a t e s of When other compounds a r e present, the rate of hydration

b e c o m e s different from the individual rates; thus, in cement, the four compounds hydrate at different r a t e s than by t h e m s e l v e s .

However, when the rate of diffusion

through the gel coating b e c o m e s the rate determining step, the differences disappear, and the cement hydrates as a single compound. 2.

P o w e r s and Brownyard found that Vm/W n was constant for a given cement

from 1 day of hydration to nearly complete hydration (4)

The value of Vm, the BET

m o n o l a y e r coverage, was determined by w a t e r vapor adsorption (5).

The quantity V

m gives the number of water m o l e c u l e s n e c e s s a r y to c o v e r the entire surface with a single adsorbed layer; thus, it is a m e a s u r e of the total surface of the hydrated paste.

Because

466

Vol. 2, No. 4 LOW POROSITY, CEMENTPASTES, HYDRATION, EXPANSION

the surface of the unhydrated cement is negligible compared to the surface of the hydration products, and because practically all of the surface r e s i d e s in the cement gel, V is a m m e a s u r e of the gel produced in the hydration. The quantity w is a m e a s u r e of the total n amount of all hydrated compounds. The conclusion from the constancy of Vm / w is that n the gel produced is a constant fraction of the total hydration products. Because the different compounds contribute differently to the total surface area, the additional conclusion is that from 1 day to complete hydration the nature of the hydration products r e m a i n s the same. Verbeck and his coworkers determined the heats of hydration from 1 day to complete hydration, and found that A H / w n, the ratio of the heat of hydration to the combined water remained constant (6). Because the heats of hydration of the four m a j o r cement compounds a r e very different, Verbeck' s r e s u l t s also indicate that the nature of the hydration products r e m a i n s the same from 1 day on. Copeland explained the above r e s u l t s by proposing that the m a j o r compounds hydrate at equal fractional rates; i . e . , if at a given time a fraction x of C3S is hydrated, the degree of hydration of the three other m a j o r compounds is also x (6). h y d r a t e s as a single compound.

In other words, cement

This hypothesis does explain the above r e s u l t s , but

Copeland himself exploded his hypothesis by determining the d e g r e e s of hydration of the m a j o r compounds at various hydration t i m e s by X - r a y quantitative analysis.

For the two

cements that he investigated, he found that the compounds did not hydrate at equal fractional r a t e s in the f i r s t seven days, but after that they hydrated at approximately equal fractional rates. In the discussion of the hydration of the low-porosity cement pastes it will be a s s u m e d that the compounds in the cement hydrate at equal fractional r a t e s from 1 day to ultimate hydration, which means that the cement hydrates as a single compound. a r e three r e a s o n s for this.

There

In the f i r s t place, the X - r a y data are e x t r e m e l y m e a g e r , and

they are partly contradictory.

F u r t h e r m o r e , they were obtained for cement pastes of

higher porosities and not for low-porosity pastes.

In the second place, because of the

low-porosity plus the additives, the hydration products begin to exert t h e i r r a t e - r e t a r d i n g influence at an e a r l i e r time than in pastes of higher porosities.

After the coating on the

unhydrated grains makes diffusion the r a t e - c o n t r o l l i n g step, it c e a s e s to m a t t e r what the nature of the compound under the coating is, and all compounds hydrate at the same rate. In the third place, in view of the fact that no X - r a y analysis data a r e available for the low-porosity pastes, there is no other way to handle the data except by a s s u m i n g that the cement hydrates as a single compound from 1 day on.

Even though during the f i r s t

Vol. 2, No. 4

467 LOW POROSITY, CEMENT PASTES, HYDRATION, EXPANSION I1.7 - -

it

o.6

S

"O.S

i 0.4

Fig. 1 - Degree of hydration from 1 hour to 7 days. 25°C, w/c = 0.2.

/

..,e

o.i

O.O

ii I

|

I

TIME

7

(DAYS)

day the compounds in the cement hydrate at different r a t e s , and so the cement does not hydrate as a single compound, the degree of hydration was still calculated from Wn/W: . This method of calculating x gave only a rough approximation for the f i r s t day, but there was no better method available to us. 3.

Four grinding aids were used in the p r e s e n t experiments:

(DEC}, Reax 70, TMN and AR-100. t r a d e names.

diethyl carbonate

The f i r s t is a pure compound, the three o t h e r s have

Their approximate composition was given in paper I(1).

grinding aid was 0.5 % of the weight of the clinker.

The quantity of

The Type I pastes contained also

1.0% calcium lignosulfonate and 0.5% potassium carbonate; the Type II pastes contained 0.5% of calcium lignosulfonate and 0.5% potassium carbonate.

In the reporting of the

r e s u l t s , the p a s t e s will be designated by the grinding aid and the type of the cement.

Thus,

the designation DEC II will mean that the Type II clinker was ground with diethyl carbonate. The degree of hydration was d e t e r m i n e d for four sets of Type II and one set of Type I p a s t e s at 25°C.

The w a t e r - c e m e n t ratio was 0.20.

The r e s u l t s f r o m 1 hour to

7 days a r e shown in Fig. 1, and from 1 day to 90 days in Fig. 2. As Fig. 1 shows, in the e a r l y stages of hydration, the grinding aid has a strong influence on the rate of hydration. f a s t e r than the two o t h e r s .

Of the four s e t s of Type II pastes, two hydrate much

After 1 day, the d e g r e e s of hydration range f r o m 0. 075 for

the TMN H paste to 0.47 for the Reax II paste, a 6 fold difference.

Another thing to note is

that the degree of hydration of the DEC I paste is only about one-third of the degree of hydration of the DEC II paste a f t e r 1 day. The details of the m e c h a n i s m of hydration of low-porosity pastes will be discussed

468

Vol. 2, NO. 4 LOW POROSITY, CEMENT PASTES, HYDRATION, EXPANSION

"i°i

•

__

I11¢ T

0

- -

omc !

O

C)

8o-

O

-

~

-t.onl

-

ImAX YO It

- -

v"o~ ,1[

1,4

~"

'

I0

Ii

TIME

SO

9O

(DAYS)

Fig. 2 Degree of hydration from 1 day to 90 days. 25Oc, w/c = 0.2. l a t e r , but certain features of the p r o c e s s will be pointed out now.

The t h r e e lowest curves

of Fig. 1 show that a f t e r a small amount of hydration, a period of very slow hydration follows.

This is called the "dormant period".

The hydration products, the grinding

aid, and calcium lignosulfonate jointly form a coating on the unhydrated cement grains, through which the diffusion is slow, and so the hydration becomes very slow.

No ex-

p e r i m e n t s were p e r f o r m e d to a s c e r t a i n whether the diffusion of water through the coating to the unhydrated grains or the diffusion of the ions of the hydration products through the coating outward was the slower p r o c e s s .

As far as the investigations reported in this s e r i e s

of papers go, this m a k e s no difference; consequently, for the sake of simplicity, we will talk about the diffusion of water through the coating.

The fact that the d o r m a n t period does

not begin at zero time shows that the hydration products constitute a p a r t of the coating. Actually, n o r m a l cement pastes, without grinding aid and lignosulfonate, always exhibit a dormant period.

The role of the lignosulfonate in the coating is seen by comparing the

DEC I and DEC II pastes.

The Type I pastes contain 1% lignosulfonate; the Type II pastes

contain 0.5% lignosulfonate. The double amount of lignosulfonate causes the r e t a r d e d hydration of the Type I pastes.

The role of the grinding aid is seen by comparing the

Reax IT and DEC II pastes with the TMN II and AR-100II pastes. form a coating much l e s s pervious to water than the f i r s t two.

Obviously the last two in fact, no d o r m a n t period

appears in Fig. 1 for the Reax II and DEC IT pastes; thus, if there is any d o r m a n t period at all, it is less than 1 hour.

Vol. 2, No. 4

469 LOW POROSITY, CEMENTPASTES, HYDRATION, EXPANSION

~5 O J~t

0.6

r.~ o 0.4

8 1,4

DEC •

0.2

0,0 0

I IO

i 20

HYDIt&TliD

0

J~c

0

~tJ" C SOe C

AT

J ~0

TIHE (DAYS) F i g . 3 - Degree of hydration of DEC II pastes from 1 day to 180 days at 5 °, 25 ° and 50°C. w / c = 0.2.

During the dormant period, there is a slow hydration.

Because the hydration

products have a l a r g e r volume than the unhydrated grains, a p r e s s u r e builds up under the coating.

The p r e s s u r e eventually ruptures the coating; water a c q u i r e s d i r e c t a c c e s s to

the unhydrated grains, and the reaction speeds up. between the d e g r e e s of hydration b e c o m e s smaller.

This is seen in Fig. 1.

The difference

After 7 days, the highest value of

x is 0.67 for the Reax II paste, and the lowest value is 0.50 for the AR-100II paste; the difference is only 25~0. As Fig. 2 shows, the d i f f e r e n c e s continue to become smaller.

After

90 days, the d e g r e e s of hydration of the four Type II p a s t e s a r e between 0.725 and 0.75, and the d e g r e e of hydration of the Type I paste is 0.68.

These values a r e close to the ultimate

d e g r e e s of hydration that these l o w - p o r o s i t y p a s t e s can reach, as will be d i s c u s s e d in a future paper. 4. figures.

The effect of t e m p e r a t u r e on the rate of hydration is shown in the next three The w a t e r - c e m e n t ratio was 0, 20.

As one would expect for normal chemical

reactions, the hydration is f a s t e r at higher t e m p e r a t u r e s during the early stages of hydration, and as the ultimate d e g r e e of hydration is approached, the rate d e c r e a s e s . Fig. 3 shows the d e g r e e of hydration as a function of time at 5 °, 25 °, and 50°C for the DEC II p a s t e s .

The d o r m a n t period at 5°C l a s t s for at l e a s t 3 days, but it is not

noticeable at the two higher t e m p e r a t u r e s . dormant period was l e s s than 1 hour.

It was seen in Fig. 1 that at 25°C the

With increasing t e m p e r a t u r e , the dormant period

s t a r t s at an e a r l i e r age, and it is of s h o r t e r duration. Fig. 4 shows the d e g r e e of hydration as a function of time at 5 °, 25 °, and 50°C for the Reax II p a s t e s from 1 day to 90 days of hydration.

Reax 70 f o r m s a coating m o r e

pervious to w a t e r than that formed by diethyl carbonate; consequently, the dormant

470

Vol. 2, No. 4 LOW POROSITY, CEMENTPASTES, HYDRATION, EXPANSION

Q,7

0

Fig. 4 - D egree of hydration G.4

of Reax 70 H p a s t e s f r o m 1 day to 90 days at 5 °, 25 °, 50oc. w / c = 0.2.

e,J 70 E

iiiX

M GJ

• I

AT

$o C 2~C

0.1

ool I

XYO|AT'O

O

I ?

I 14

50°C

i lI

] 90

TI:HE (DA~fS)

p e r i o d at 5°C is much s h o r t e r ; it is l e s s than 1 day.

As was seen in Fig. 1, the d o r m a n t

p e r i o d at 25°C was l e s s than 1 hour. Fig. 5 shows the d e g r e e of hydration as a function of time at 5 °, 25 °, and 50°C f o r the DEC I p a s t e s f r o m 1 day to 90 days.

The d o r m a n t peri od at 5°C l a s t s for at

l e a s t 3 days, as f o r the DEC II pastes; thus, the effect of the double amount of lignosulfonate is not shown by the r e s u l t s .

It is possible that the d o r m a n t peri od was l o n g e r f o r the

DEC I p a s t e s than for the DEC H pas t e s , but t h e r e a r e no data between the ages of 3 days and 7 days.

However, the effect of the lignosulfonate at 25°C was m a r k e d , as was seen

in Fig. 1, and d i s c u s s e d e a r l i e r .

The d o r m a n t period of the DEC I p a s t e s was 1 day;

that of the DEC II p a s t e s was l e s s than 1 hour.

At 50°C, the d o r m a n t peri od of DEC I

was l e s s than 4 hours. 5.

The effect of the w a t e r - c e m e n t ratio on the rat e of hydration is shown in

Fig. 6 f o r the DEC I p a s t e s f r o m 1 to 90 days.

At e v e r y age, the d e g r e e s of hydration

of the p a s t e s made with w / c = 0.30 a r e g r e a t e r than those of the p a s t e s made with w / c = 0.20. The u l t i m a t e d e g r e e of hydration is g r e a t e r for the f o r m e r than for the l a t t e r .

The higher

w a t e r - c e m e n t r atio p r o d u c e s p a s t e s of higher total p o r o s i t y , which r e s u l t s in the a c commodation of a l a r g e r quantity of hydration product s. S imilar c o m p a r i s o n s w e r e made f or the DEC H p a s t e s , and the r e s u l t s w e r e qualitatively s i m i l a r to those obtained f or the DEC I p a s t e s . 6.

Some e x p e r i m e n t s w e r e made to d e t e r m i n e the effect of c e m e n t fineness on

the hydration r a t e s .

The Type I and the Type II cl i nker were ground to a Blaine s u r f a c e

of about 4000 c m 2 / g with diethyl carbonate as the grinding aid.

The s a m e amounts of

Vol. 2, No. 4

471 LOW POROSITY, CEMENTPASTES, HYDRATION, EXPANSION

o,7

o,+

Fig. 5 - Deg r ee of hydration of DEC I p as tes f r o m 1 day to 180 days at 5°, 25 ° and 50°C. w / c = 0.2.

DEC I hYDRATED AT

o+,

"tl

° 0

o.i

•

"'

tP

c

141"C

TIME (DAYS)

~

o.i

, ----4

al

~ Fig. 6 - D e g r e e of hydration of DEC I pastes from 1 day to 90 days at 25°C, with w / c = 0. 2

~

m

o, o~ 0,4

DEC I HYDRATED AT 25°C

and 0.3. N

e.I I

7

0

I1#¢ =

L,

•

wo¢ =

La

14

TIME (DAYS)

grinding aid, lignosulfonate and p o t a s s i u m c a r b o n a t e w e r e used as f o r the h i g h - s u r f a c e cement.

The w a t e r - c e m e n t ratio was 0.2, and the t e m p e r a t u r e was 25°C.

A f t e r 4 hours

o f hydration, the DEC II pa s t e made f r o m the h i g h - s u r f a c e c e m e n t had a d e g r e e of h y d r atio n of 2 4 . 0 % , w h e r e a s the l o w - s u r f a c e c e m e n t was hydrat ed only to the extent of 14.7%.

The l o w - s u r f a c e c e m e n t bad a long d o r m a n t period; at the end of 1 day, the

d e g r e e of hydration was still only 15.8%, w h e r e a s the h i g h - s u r f a c e c e m e n t was h y d r a t e d to the extent of 44. 9%. At 3 days, the d i f f e r e n c e was much s m a l l e r ; the values of x w e r e 41.3 and 57.6% f o r the low and h i g h - s u r f a c e c e m e n t , r e s p e c t i v e l y .

Subsequently

the gap continued to becom e n a r r o w e r ; at 14 days, the values of x w ere 68.3 and 70.3%; thus, the d e g r e e of hydration of the l o w - s u r f a c e c e m e n t a l m o s t r e a c h e d that of the highs u r f a c e cement. The influence of the s u r f a c e of the c e m e n t was m uch g r e a t e r f o r the Type I p a s t e s tban f o r the Type II pas t e s .

When the s a m e amount of lignosulfonate was used

f o r the high and l o w - s u r f a c e c e m e n t , i . e . ,

1%, the d e g r e e of hydration of the l o w - s u r f a c e

c e m e n t even a f t e r 14 days was only 23.0%; w h e r e a s the value of x for the h i g h - s u r f a c e c e m e n t was 61.8%.

When the lignosulfonate was cut to half of its value, i . e . , to 0.5%

472

Vol. 2, No. 4 LOW POROSITY, CEMENTPASTES, HYDRATION, EXPANSION

f o r the l o w - s u r f a c e cem e nt , a d e g r e e of hydration of 41.5% was r e a c h e d in 7 days.

At the

s a m e age, the h i g h - s u r f a c e cem e nt , with 1.0%lignosulfonate, had a d e g r e e of hydration of 57.8%. T h e r e a r e no data available beyond 7 days; it is possible that eventually the low- s u r f a c e c e m e n t would r e a c h t h e s ame , o r n e a r l y the s a m e, d e g r e e of hydration as the h i g h - s u r f a c e cement, provided that the f o r m e r contains half as much lignosulfonate as the l a t t e r . Expansion of the P a s t e s The expansions of the p a s t e s w e r e calculated f r o m equation (17) of p a p e r I (1). The equation is

Exp. = 100 ( v

where v

P

p

- v

p theor,

) / Vp

t heor.

(1)

is the actual volume of the paste produced by the hydration of 1 g of cem ent , and

v

is the volume of the paste without expansion. The details of the obtaining of the p theor two t e r m s a r e given in p a p e r I. Because the expansion is obtained as a small d i f f e r e n c e between two l a r g e n u m b e r s , the e r r o r is l a r ge; it is of the o r d e r of 1%.

The d e g r e e of

hydration, x, e n t e r s into the calculation of v

(equations (11) and (13) of p a p e r I), P and b e cau s e the e x p e r i m e n t a l e r r o r in small values of x is r e l a t i v e l y g r e a t e r than in l a r g e values, the e r r o r in the calculated expansions is g r e a t e r at e a r l y ages than at l a t e r ages.

This can be seen in Fig. 7, which shows the expansions of four s e t s of

Type II p a s t e s and one set of Type I paste. the w a t e r - c e m e n t r at i o was 0.20.

The t e m p e r a t u r e of hydration was 25°C;

The points at 1 day show the g r e a t e s t s c a t t e r ; the

s c a t t e r at 3 and 7 days is c o n s i d e r a b l y s m a l l e r , and at l a t e r ages any given set of p a s t e s indicates an a p p r o x i m a t e l y constant value of expansion. The DEC II p a s t e s show a m a x i m u m value of 4.3% expansion at i day, and a m i n i m u m value of 3.5% at 3 days.

The pas t e does not shrink between 1 and 3 days; the d i f f e r e n c e

is due to e x p e r i m e n t a l e r r o r .

The expansion is 4.1% a f t e r 90 days of hydration; thus,

a p p a r e ntly t h e r e is no f u r t h e r expansion a f t e r 1 day of hydration. F o r the DEC I p a s t e s , the expansion is 3.3% at 3 days and 3.5% at 90 days; t h e s e values a r e the s a m e v e r y much within the e x p e r i m e n t a l e r r o r .

The v e r y low value

of 2.0% at 1 day may indicate that the expansion stopped only some t i m e between 1 and 3 days, but the low value m a y also be due to the e a r l i e r d i s c u s s e d e x p e r i m e n t a l e r r o r in the d e t e r m i n a t i o n of x.

S i m i l a r c o n s i d e r a t i o n s apply to the t h r e e o t h e r c u r v e s in Fig. 7.

The 90-day expansion values range f r o m 3.2% for the TMN II past e to 4.5% f o r

Vol. 2, No. 4

473 LOW POROSITY, CEMENTPASTES, HYDRATION, EXPANSION U

Fig. 7 - Expansion, in percent of the volume o f the paste, from 1 day to 180 days. 25°C, w / c = 0.2.

0

NcI

D

IPI¢|

0

llllltlla

4" vmoa I AI--I N •

•

,,~

~

-'

4

mid '

~

TINE (DAYS)

the AR-100 II paste.

This difference is probably g r e a t e r than the experimental e r r o r .

The values for DEC I and DEC II a r e 3.5 and 4.1%, respectively; this difference is p r o bably within the experimental e r r o r . 2.

The t e m p e r a t u r e dependence of the expansion was investigated for the DEC I,

DEC II, and Reax II p a s t e s , p r e p a r e d with w / c = 0.20.

Fig. 8 shows the expansion values

obtained for the DEC II p a s t e s from 1 to 90 days at 5 °, 25 °, and 50°C. at 25°C was d i s c u s s e d before.

The expansion

The expansion at 5 ° continues for a long time, and it

is much g r e a t e r than at 25°C, reaching a value of 7.7% at 90 days.

Apparently, the

paste must acquire a high strength before it can r e s i s t further expansion, and because the p a s t e s at 5°C hydrate m o r e slowly than at the higher t e m p e r a t u r e s , the strength development is also slower. In the expansion of the paste, two opposing factors operate.

The hydration products

have g r e a t e r volume than the unhydrated cement, and because the pore space in the lowp o r o s i t y p a s t e s is limited, the accumulation of the hydration products builds up an internal p r e s s u r e which tends to enlarge the paste, thus increasing the pore volume available for further hydration.

This internal p r e s s u r e is r e s i s t e d by the increasing strength 7

----0

J

l,¢

Fig. 8 - Expansion, in percent of the volume of the paste, from 1 day to 180 days, of DEC H p a s t e s at 5 °, 25 ° and 50°C. w / c = 0.2. I)1¢11 IqVNATIIII AT I~

1

n

p ¢

|

TIHE

(DAYS)

474

Vol. 2, No. 4 LOW POROSITY, CEMENTPASTES, HYDRATION, EXPANSION

of the paste, and after the paste acquires a high enough strength, it also acquires a stable volume.

The fact that p a s t e s of normal p o r o s i t i e s expand much l e s s during hydration

than the low-porosity pastes supports the above hypothesis. The m o s t r e m a r k a b l e observation in Fig. 8 is that the expansion of the p a s t e s hydrated at 50°C exhibit g r e a t e r expansions than those hydrated at 25°C. found for the DEC I and the Reax II pastes, as shown in Table I.

The same was

For the three sets of

pastes, the average expansion at 50°C is 1.0% g r e a t e r than that at 25°C.

This fact cannot

be explained by the hypothesis advanced in the previous paragraph. Fig. 9 suggests an explanation.

It r e p r e s e n t s the expansions of the DEC II pastes

in the f i r s t seven days at the t h r e e t e m p e r a t u r e s .

The expansions after 1 hour a r e 0.8

and 3.4% at 25 and 50°C, respectively; after 2 hours, the expansions a r e 1.2 and 4.0% at 25 and 50°C, respectively,

Thus, the fast rate of hydration and the sudden development of

a large amount of hydration products at 50°C produces a much l a r g e r initial expansion than is produced in the much slower initial hydration at 25°C.

The difference between

the expansions at later ages b e c o m e s much s m a l l e r , but the expansion at 25°C does not catch up with the expansion at 50°C, with the result that t h e r e r e m a i n s a 1% difference between the ultimate expansions. experimental e r r o r .

The dip in the 50°C curve in Fig. 9 is attributed to

The expansion of the 5°C paste was m e a s u r e d only at 1 day and

l a t e r ages. As Table I shows, the DEC I paste shows a slightly g r e a t e r final expansion at 5°C than the DEC 1[ paste, but a s m a l l e r expansion at the two higher t e m p e r a t u r e s . These differences a r e probably not significant; the average value for the t h r e e DEC I p a s t e s is 5.2%, for the DEC II p a s t e s is 5.6%.

Thus, the Type I and Type II pastes,

containing the same grinding aid, show approximately the same expansions.

On the other

hand, the Reax II p a s t e s show a s m a l l e r expansion than the DEC H p a s t e s at all three t e m p e r a t u r e s , so the difference may possibly be significant.

Even if t h e r e is a difference,

Table I ~ n a l Expansions of L o w - P o r o s i t y P a s t e s (w/c = 0.21 Hydration T e m p e r a t u r e

DEC I

DEC II

Reax 70 II

5°0

7.9%

7.7%

6.7%

25°C

3.5

4.1

3.4

50°C

4.2

5.1

4.7

Vol. 2, NO. 4

475 LOW POROSITY, CEMENTPASTES, HYDRATION, EXPANSION

..,..,.o N

z"

Fig. 9 - Expansion, in percent of the volume of the paste, from 1 hour to 7 days, of DEC H pastes at 5 °, 25 ° and 50UCs w / c ~ 0.2.

DI| I

t

N¥1IATI|

AT

:::

:

•

II ° C

! II,,I

I

I

I

7

TIME (DAYS)

it is slight; the a v e r a g e f o r the t h r e e DEC II p a s t e s is 5.6%, for the Reax II p a s t e s 4.9%. 3.

The expansions of the p a s t e s with w / c = 0.3 w e r e s m a l l e r than those of the

p a s t e s with w / c = 0.2, as one would expect.

The 90-day expansion of DEC I was 3.5%

with w / c = 0.20, and 2.8% with w / c = 0.30.

At the s a m e age, the expansion of DEC II

was 4.1% with w / c = 0.20 and 3.2% with w / c = 0.30. The expansions of the pas t e s of the l o w - s u r f a c e c e m e n t s w ere somewhat g r e a t e r than those of the p a s t e s of the h i g h - s u r f a c e c e m e n t s .

Total .Porosity 1. I (1).

The total p o r o s i t y , c , of the past e was calculated f r o m equation (7) of p a p e r

The equation is

W

~=

e V

(2)

P

where w e is the weight o r volume of the e v a p o r a b l e w a t e r (the density is v e r y close to 1), and v

is the volume of t he paste. P t e r m s a r e given in p a p e r I.

The e x p e r i m e n t a l details and the calculation of the two

The total p o r o s i t i e s of four s e t s of Type II p a s t e s and one set of Type I p a s t e s a r e shown in Fig. 10 f r o m 1 hour to 7 days. hydration t e m p e r a t u r e was 25°C. of the paste.

The w a t e r - c e m e n t ratio was 0.2, and the

The total p o r o s i t y is given as the f r a c t i o n of the volume

476

Vol. 2, No. 4

LOW POROSITY, CEMENTPASTES, HYDRATION, EXPANSION

~6 h~B:"-O"~"%,

w

O..-OIIAI t~ | O--.Ae-m, •

Fig. 10 - Total porosity, in percent of the volume of the paste, from 1 hour to 7 days. 25°C, w / c = O. 2.

~

S,$l

TIME (DAYS) As the hydration p r o g r e s s e s , the hydration product s fill up a p a r t of the p o r e volume, and the p o r o s i t y d e c r e a s e s .

However, as Fig. 10 shows, four of the five set s

of p a s t e s show an initial i n c r e a s e in por os i t y.

This is caused by the expansion of the past es.

If the r a t e of expansion is such as to caus e a l a r g e r volume i n c r e a s e than the p o r e volume d e c r e a s e caused by the hydration p r o d u c t s , the net r e s u l t is an i n c r e a s e in porosi t y. The Reax H p a s t e s show only a d e c r e a s e in p o r o s i t y , and the DEC II p a s t e s show the s m a l l e s t i n c r e a s e among the four o t h e r sets. h y d rate f a s t e r than any of the o t h e r s .

Fig. 1 shows that the Reax 1I p a s t e s

The DEC II p a s t e s h y d r a t e a l m o s t as rapidly as

the Reax II p a s t e s , but because of the somewhat sl ow er hydration (Fig. 1), and the s o m e what g r e a t e r expansion of the f o r m e r (Table I), the DEC II p a s t e s show a small i n c r e a s e in p o r o s i t y , w h e r e a s the Reax II p a s t e s show only a d e c r e a s e . The t h r e e o t h e r c u r v e s in Fig. 10 a r e also c o m p l e t e l y in line with the t h r e e o t h e r T a b l e II Final P o r o s i t i e s at D i f f e r e n t T e m p e r a t u r e s 1 Cement paste

2 Temperature °C

3 T i m e of h y d r a t i o n (days)

{w/c = 0 . 2 )

4 D e g r e e of h y d r a tion, x(%)

5 Total porosity, c (%)

DEC I

5 25 25 50

90 90 180 90

64.5 67.7 69.0 71.3

21.5 17.2 16.7 16.5

DE C II

5 5 25 50

90 180 90 90

68.8 71.4 75.4 80.5

23.4 23.0 19.1 18.0

R e a x 70 II

5 25 50

90 90 90

66.3 72.9 81.5

23.4 19.0 17.9

TMN II

25 25

90 180

72.4 74.4

19.1 18.7

A R - 1 0 0 II

25

90

74.4

19.6

Vol. 2, No. 4

477 LOW POROSITY, CEMENT PASTES, HYDRATION, EXPANSION

0,81 •

II| el"

0 eocl l, ll

rn t i l l Will • TIN •

~I

Fig. 11 - Total porosity, in percent of the volume of the paste, from 1 day to 180 days. 25°C, w/c = 0.2.

Q 0.14 A,I it, ll

~

n

N

41

N

m

11

N

eO ~1

T]:HE (DAYS)

c u r v e s in Fig. 1.

The DEC I p a s t e s hydrate f a s t e r than the AR-100 II pastes, which in

turn hydrate f a s t e r than the TMN II pastes; the i n c r e a s e in p o r o s i t y is the s m a l l e s t for DEC I among the t h r e e , and it is the l a r g e s t for TMN II.

The AR-100 H and the TMN H

c u r v e s c r o s s each o t h e r at about 3 days of hydration in Fig. 1; they likewise c r o s s each other at the same age in Fig. 10. The total porosities of the five sets of pastes from 1 day to 180 days a r e shown in Fig. 11.

The four sets of Type II pastes show very n e a r l y the same p o r o s i t y at 90 days.

Fig. 2 shows that the d e g r e e s of hydration of the same p a s t e s is also very n e a r l y the same.

However, the d e g r e e of hydration of the DEC I paste at 90 days is somewhat lower

than that of the Type II p a s t e s , and yet the porosity is also lower.

This is p r i m a r i l y

because the volume of the hydration products of the Type I cement is g r e a t e r than that of the Type II cement; also the l a r g e r amount of lignosulfonate in the Type I pastes occupies m o r e pore space than the s m a l l e r amount in the Type II pastes.

The total

p o r o s i t y at 180 days was 16.7 and 18.7% of the paste volume for the DEC I and the TMN II paste, respectively. 2.

The t e m p e r a t u r e dependence of the total porosity was investigated for the

DEC I, DEC II, and Reax II pastes.

The r e s u l t s for theDEC II pastes at 5 °, 25 ° and 50°C

a r e shown in Fig. 12 to 180 days at the lowest t e m p e r a t u r e and to 90 days at the two higher o,01 III1¢|

Fig. 12

- Total porosity, in percent of the volume of the paste, from 1 day to 180 days, of DEC II pastes at 5 ° , 2G° andS0°C, w/c = 0.2.

0 •

t--t o,I I

NTDIIATIO AT

PC tile C II* ¢

Q

:° m

to

m

ee'lm

T ~

(DAYS)

478

Vol, 2, No. 4 LOW POROSITY, CEMENTPASTES, HYDRATION, EXPANSION

t e m p e r a t u r e s . . T h e w a t e r - c e m e n t ratio was 0.2.

Because of the sl ow er hydration at 5°C

(Fig. 3), and because of the l a r g e r expansion (Fig. 9), the p o r o s i t y i n c r e a s e s in the f i r s t 3 days.

At 25°C, the p o r o s i t y i n c r e a s e s v e r y slightly only during the f i r s t 4 hours;

at 50°C, the por0si~y d e c r e a s e s f r o m the start. Table II shows the final p o r o s i t i e s of the p a s t e s at d i f f e r e n t t e m p e r a t u r e s . column 3 shows, 180 day values of c w e r e obtained only f o r t h r e e pastes.

As

For two of

the p a s tes (DEC II at 5°C and TMN II at 25°C) the e values w e r e 0.4% l o w e r at 180 days than at 90 days; f o r one paste (DEC I at 25°C) the d i f f e r e n c e was 0.5%. F o r any of the five s e t s of p a s t e s , without exception, a higher d e g r e e of hydration is always accompanied by a l ow e r final por os i t y, as a c o m p a r i s o n of columns 4 and 5 in Table II shows.

T h e r e is no such s t r i c t c o r r e l a t i o n , when di fferent sets a r e com pared.

It was pointed out bef or e that the DEC I paste of 25°C had a l o w e r d e g r e e of hydration and a lo wer p o r o s i t y than any of the Type II p a s t e s at the same age (90 days). shows that the s ame is t r u e at 5° and 50°C.

Table II

An explanation was advanced for this in

the previous section. The values of x f or the four Type II p a s t e s at 25°C and 90 days range f r o m 72.4 to 75.4% (column 4), and the values of ¢ range f r o m 19.0 to 19.6% (column 5). The values of x f o r TMN II and AR-100 II a r e 72.4 and 74.4% r e s p e c t i v e l y , and the values of e a r e 19.1 and 19.6%, r e s p e c t i v e l y . TMN II, it has the l ow er porosity.

In spite of the l o w e r d e g r e e of hydration of

This can be understood by looking at Fig. 7, which shows

that among the five sets of p a s t e s AR-100 II shows the l a r g e s t expansion, and TMN II has the s malles t.

This explanation may possibly also suffice for accounting for the

d i f f e r e n c e between the r e s u l t s f o r the DEC II and Reax II paste.

In this case, the p o r o s i t i e s

w e re equal within the e x p e r i m e n t a l e r r o r , in spite of the fact that the d e g r e e of hydration of the DEC II paste was higher.

However, the expansion of the DEC II paste was g r e a t e r

than the expansion of the Reax II paste, as was d i s c u s s e d e a r l i e r . N e v e r t h e l e s s , it is v e r y probable that the expansion is not the only f a c t o r in producing a l e s s than p e r f e c t c o r r e l a t i o n between d e g r e e of hydration and total porosi t y. It was as s u med in the di s c us s i on of the d e g r e e of hydration that the sam e hydration p r o ducts were f o r m e d during the e n t i r e hydration p r o c e s s .

In the above c o m p a r i s o n s , it is

also a s s u m e d that the grinding aid has no influence on the nature of the hydration products; in o t h e r words, it is as s um e d that at a given d e g r e e of hydration, the hydration products a r e the same r e g a r d l e s s of the grinding aid.

Without these assumptions, it would be

impossible to handle such a complicated p r o b l e m as the hydration of c e m e n t past es.

It

Vol. 2, No. 4

479 LOW POROSITY, CEMENTPASTES, HYDRATION, EXPANSION L41' 0.44 IIA~I I P I ¢ Z , WO¢ = • . |

O~I

Illl elf ° W-'CSI.I

Fig. 13 Total porosity, in percent of the volume of the paste, from 1 day to 90 days, of DEC I and DEC II pastes. w / c = O. 3. -

25°C,

o t$

U4 U2 |.||

Ui

•

~

~

.~

~o

;o

Io

.

,

TIHK (DAYS)

will be shown in the l a s t paper of this s e r i e s that n e i t h e r assumption is entirely c o r r e c t ; the grinding aid does have some influence on the nature of the hydration products, and the n a t u r e of the hydration products does change slightly with age. Returning now to Table II, it should be noted that the porosity at 90 days and 5 0°C is lower thanthe porosity at 25°C by 4.0, 5.8 and 5.8% for the DEC I, DEC II, and Reax IIpastes. The differences between the porosities at 5 ° and 25 °C are much g r e a t e r ; the 5°C porosities a r e 25.0, 22.5, and 23. l %higher than the 25°Cporosities.

The v a l u e o f x i s higher at 5 0° than at

25 °C, but because of the l a r g e r expansion at 5 0°C, the difference between the porosities is relatively small. On the other hand, the lower degree of hydration plus the much g r e a t e r expansion at 5°C m a k e s the difference between the porosities at 5 ° and 25°C quite large. 3.

The h y d r a t i o n s with a water to cement ratio of 0.3 were investigated only at

25°C and only f o r the DEC I and DEC II pastes.

Fig. 13 shows the porosity r e s u l t s .

It

was shown in Fig. 10 that during the f i r s t day of hydration the porosity i n c r e a s e d for the DEC I p a s t e s with w / c -~ 0.2.

It was shown in Fig. 6 that the DEC I pastes with

w / c = 0.3 hydrate f a s t e r than those with w/c = 0.2.

As a result, the DEC I curve in

Fig. 13 shows a d e c r e a s e in porosity from the beginning.

The DEC H pastes showed

a s m a l l e r i n c r e a s e in p o r o s i t y than the DEC I pastes in Fig. 10, and the DEC II curve in Fig. 13 also shows only a d e c r e a s e in p o r o s i t y from the beginning. A comparison of Figs. 11 and 13 shows that the porosities of both the DEC I and DEC II pastes a r e higher for the pastes of higher w/c.

It is, of course, a long known

fact that i n c r e a s i n g the w a t e r - c e m e n t ratio i n c r e a s e s the porosity.

The porosity at 90

days is 17.2% for the DEC I paste with w / c = O. 2; it is 27.7% with w / c = 0.3. p o r o s i t i e s for DEC H are 19. 1% with w / c -- 0.2, and 31.7% with w/c = 0, 3.

The 90-day

The porosity

for w / c = 0.2 in both c a s e s is somewhat l e s s than two-thirds of the porosity of the pastes with w/c = 0.3. The p o r o s i t y of the DEC I paste at 90 days is s m a l l e r than that of the DEC II

480

Vol. 2, No. 4 LOW POROSITY, CEMENTPASTES, HYDRATION, EXPANSION

paste, as Fig. 13 shows, just as it was found for the pastes with w/c = 0.2. for this a r e the same as for the pastes with w/c = 0.2, discussed e a r l i e r .

The reasons The 90-day

porosity of the DEC I paste is about 90% of that of the DEC II paste at both w a t e r - c e m e n t ratios. 4.

It was pointed out in the discussion of the degree of hydration that the low-

surface cement h y d r a t e s m o r e slowly than the high surface cement in the e a r l y stages. Because for the Type II cement the same amount of diethyl carbonate and lignosulfonate were used r e g a r d l e s s of the surface of the cement, the coating on the low-surface cement was, doubtless, considerably thicker. l o w - s u r f a c e cement.

This resulted in the long d o r m a n t period of the

At 1 day, the degree of hydration of the l o w - s u r f a c e cement was

15.8%, and the porosity was 35.3%.

The degree of hydration of the high-surface cement

was 44.9%, and the porosity was 27.5%.

At 14 days, however, the d e g r e e s of hydration

differed only slightly, as was pointed out before.

The degree of hydration of the low-

surface cement was 68.3%, and the porosity was 21.4%; the degree of hydration of the h i g h - s u r f a c e cement was 70.3%, and the porosity was 20.1%. Acknowledgment The authors wish to e x p r e s s their v e r y deep gratitude to the Engineering R e s e a r c h and Development Bureau of the New York State Department of Transportation and to the Bureau of Public Roads, Federal Highway Administration, U.S. Department of Transportation, for sponsoring the r e s e a r c h on low-porosity cement pastes. References 1.

Marvin Yudenfreund, Ivan Odler, and Stephen Brunauer, Cement and Concrete Research, 2, 3]3 (May 1972. )

2.

M a r v i nYudenfreund, Jan Skalny, Raouf Sh. Mikhail, and Stephen Brunauer, Cement and Concrete Research, 2_, 33] (May 1972. )

3.

L.E. Copelandand D. L. Kantro, "Chemistry of Cement". Proceedings of the Fifth International Symposium, Tokyo, 1968. Volume If, p. 387.

.

T.C. Powers and T.L. Brownyard, Proc. of Am. Concrete Institute, 4__33, 101, 249, 469, 549, 669, 845, 933 (1946-47).

5.

Stephen Brunauer, P.H. Emmett, and Edward Teller, J. Am. Chem. Soc., 6_~0, 309 (1938).

6.

L . E . Copeland, D.L. Kantro, and G.J. Verbeck, " C h e m i s t r y of Cement". Proceedings of the Fourth International Symposium, Washington, 1960. National Bureau of Standards Monograph 43, Volume I, p. 429.