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I

Research and Development Laboratories

of the

Portland Cement Association

RESEARCH DEPARTMENT

 ULLETIN 9

Structure and Physical Properties

of

 ardened Portland ement Paste

 Y

T C POWERS

MARCH 1958

CHIC GO

Au t hor iz ed R ep ri nt f rom

J OU RNAL OF TH E AM ER IC AN C ER AMI C S OC IE TY

v ol . 41,

P.

1

(1958)

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VOL. 41, NO. 1

JOURNAL

o th

American Ceramic Society

JANUARY I r 1958

Structure and physical properties of Hardened

portland Cement Paste

by T. C, POWERS

Research md Development Oivision, Portland Cement Association, Chicago, I ll inois

M et hod s of s tu dy in g t he s ubm icr os copi c s tr uc-

t ur e of P or tla nd cem en t pa st e a r e d es cr ibed , a nd

d ed uct ion s a bou t s tr uct ur e a r e pr es en ted . Th e

m ain com ponen t, cem en t gel, is deposit ed in

water 611ed space within the visible boundaries

of a body of pa st e. S pa ce t illed w it h gel con -

t ains gel pores; spa ce not t iled by gel or ot her

solid material is capillary space. I Iygroscopicity

of cement gel and capillary pores accounts for

various aapects of the propert ies and behavior

of concrete. Da ta on gel a nd pa ste st r r rc-

tn re are used in discussing strength permeabil

ity volume stability and action of frost.

1. Introduction

I

N

t h e p ar la n ce of t h e ce me nt i nd us tr y , a m ix tu re of P or t -

l a nd ce me nt a n d w a t er i s ca l le d ce me nt p as te ; t h e c h em -

i ca l r ea c t io ns o f t h e co mp on en t s o f P o rt l a nd ce m en t w i t h

w a t e r a r e s po ke n o f co ll ect i ve ly a s ce m en t h y dr a t io n; h y dr a -

t ion of cem en t ca u ses t he pa st e t o h ar den a nd t hu s t her e is

t h e t e rm 6h a r de ne d P o rt l a nd ce me nt p a st e .”

S t nd ies of t h e s t rn ct u re a n d p rop er t ies o f h a rd en ed p as te

b eg a n i n t h e P or t la n d C em en t As soci at ion l ab or a t or ie s i n

a bout 1936. The purpose w as t o bridge a ga p bet ween

ce me nt ch em is t ry a n d con cr et e t ech nol og y, I t s ee med t h at

e st a b li sh in g t h e r el a t io n b et w e en p ro pe rt i es o f t h e p a st e a n d

ch em i ca l co ns t it u t io n o f ce m en t on t h e on e h a n d a n d b et w e en

p rop er t ie s of p as t e a n d p rop er t ie s o f con cr et e on t be ot h er

h a nd m ig ht a ccom pl is h t h is p ur pos e. R es ul ts a r e g ra d ua ll y

f ulf il l in g th a t h ope .

Th e a m ou n t o f w a t e r a b so rb ed b y d r y l r a st e i nd ica t e d t h a t

t h e p a s t e w a s h ig h ly p or ou s , a n d a t f ir s t t h e p hy s ica l s t r uc t ur e

o f h a r d en ed p a st e w a s t b or r gh t o f i n t e rm s o f p or e s.

‘~heories

p er t a in in g t o ca pi ll ar ie s w e r e u se d. I n a bou t 1939 t h e con -

c ep t c ha n g ed , a n d p or e s w e r e t h ou g ht o f a s s pa ce s a m o ng p a r -

t icl es (i nt er st it ia l s pa ce s). Th is ch a ng e m a rk ed t h e h eg in -

n in ,g of pr og ress. Th e t heor y of B ru na uer , E mm et t, a nd

Tell er l w a s u sed t o in ter pr et da t a on a ds or pt ion of w a ter

v a por b y p re dr ie d p as te , a n d t h is a pp li ca t ion of t h e t be or y ,

s ti ll i n con st a n t u se , t u r ne d o ut t o be a m os t v a lu a bl e t ool f or

s tud yin g ph ysica l s t ructure ,

B y t h e B r u n a ue r-E m m et t -Te ll er m et h od , i nt e rn a l s u rf a ce

a r ea w a s m e a su re d a n d t h en t h e o r de r o f s iz e of t h e s ol id p a r-

t it les com pos in g h a rd en ed p as te w a s com pu t ed . Th is w a s

f ir st a ccom pl is he d i n a bou t 1940, Th e t h er m od yn a mi cs of

a d sor pt ion a n d t be f re ez in g of w a t er i n h a rd en ed p as t e a ls o

w er e s tu di ed . S u ch s t ud ie s w er e coor di na t ed w it h e xp er i-

m en t a l a n d t h eo re t ica l s t u di es o f s u ch p hy s ica l p r op er t ie s a s

s t rength , permea bi li ty , a n d v olume c ha n ge .

Aft er a w a rt im e h ia t us , w or k w a s r es um ed a nd n ew t ech -

n iq ues w er e gr adua l]y a dded t o t he old on es. An exper i

m en t al s t ud y of p er me ab il it y h a s b e en u nd er w a y on a p a rt -

t i me b a si s f or a b ou t 11 y e a r s, a n d s t u di es o f v ol um e ch a n ge s,

espec ia l ly th ose c a used b y f reez in gof wa ter in h a rd ened pa s te ,

h a ve b ee n e sp eci al ly i nt en si ve. X-r a y t ech ni qu es a r e n ow

a p pl ie d t o a l m os t a l l a s pe ct s o f s t n di es o f s t r uct u r e, D i ff r a c.

t i on h a s b ee n e ff ec ti ve i n e st a b li sh in g t b e s t oi ch io me t ry , a n d

s tr uct ur e of t he s oli d ph as es of t he pa st e, a nd sm a ll-a ng le

s ca t t e ri ng h a s b ee n u s ed r ece nt l y f or m ea s u ri ng s pe ci fi c s u r-

f a ce . E l ec t ro n-o pt i c a n d e le ct r on -d if fr a ct i on t e ch n iq u es a r e

n ow b ein g a pplied .

P res en ted a t th e F i fty- .V in th A nn ua lMeet in g , Th e Americ a u

C e ra m i c S o ci et y , D a l la s , Te xa s , M a y 8, 1957 (B a s i c S c ie nce

Division,N-o.44). Received May 7, 1957;r evisedcopy received

October 2,1957.

Th e a n th er is ma n a ger ,B a s ic Res ea rch Sec t ion, Resea rch a n d

Development Division, Portland Cement Associa tion.

LSteph eu B run a uer ,Ad s orpt io ll o f Ga s es a n d V a pors, Vol. 1 .

P r i n ce t on U n i ve rs it y P r e ss , P r i nce t on , 1943. 511 P P . ; C e nw n .

.4b tr,, 23 [11]204(1944).

1

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Ceramic Sociely-Powers Vol. 41, No.

Ftg. 1 Smplafied model o f porte rlruciure. Ge l paiticles

are

repre-

sented or

needles

or platel; designoler capillary cavltier.

Co OHIj

cryrtols unhydrated cement and minor hydrates

ore

no1 represented.

A theoretical paper about freezing of water in hardened

paste based results of studies of physical structure was

published in 1945,' but a comprehensive sta tement about the

structure and physical properti'& did not appear until 194i.'

Since then the program has produced other papers.

The following is a brief statement about the principal con-

cepts developed during the course of this work.

II

Structure of Paste

Fresh cement paste is a network of particles of cement in

water.

The paste is plastic, and it normally remains thus

for an hour or more, during which period i t bleeds ; i.e.,

there is a small amount of sedimentation.' After this rela-

tively dormant period, the plastic mass sets and thereafter

the apparent volume of the paste remains constant, except

for microscopic but technically important variations caused

by changes of temperature or moisture content, or by reac-

tions with atmospheric C01.

Chemical reactions between components of cement and

water produce new solid phases.6 One of them is crystalline

calcium hydroxide and another, the predominant one, micro-

scopically amorphous, is cement gel.

Cement gel is composed of gel particles and interstices

among those particles, called gel pores. The solid part of the

gel contains approximately 3Ca0.2Si0,.3H20. It s crystal

structure, although highly disorganized, approximates that of

tobermorite. Cement contains Al and Fe atoms as well as

calcium and silicon atoms. They seem to play a relatively

minor role as structural units but a more important role in

determining rates of reaction.

ee refereure 4) of Bibliography on

p. 6

his issue.

a

See reference (7)of Bibliography.

The Brunauer-Emmett-Teller method gives the specif

surface of the solid par t of the gel as about

iM

m.' per cm.Jo

solid. This is equal to the specific

surface

of a sphere havin

a diameter of 86 a.u. The figure for specific surface was co

firmed recently by s&-angle scattering of

X

rays.

As seen with the electron microscope, cement

gel

consis

mostly of fibrous particles with straight edges.

Bundles o

such fibers seem to form

a

cross-linked network, containin

some more or less amorphous interstitial material.

The structure of paste is not identical with the structu re

gel. Space within the visible boundaries of a specimen

paste contains gel, crystals of calcium hydroxide, some min

components, residues of the original cement, and residues

the original water-filled spaces in the fresh paste.

The

residues of water-filled space exist in the hardened paste

interconnected channels or, if the structure is dense enoug

as cavities interconnected only by gel pores.

These residu

submicroscopic spaces are called capillary pores, or capillar

cavities.

Thus two classes of pores within the boundaries of a bod

of paste are recognized: (1) gel pores, which are a chara

teristic feature of the structure of gel, and

2)

capillaty por

or cavities, representing space not filled by gel or other sol

components of the system. Figure shows

a

model of th

concept of structure.

All the spaces, gel pores arid capillary cavities, are su

microscopic. This fact, together with the hpdrophile chara

ter of the solid phase, amounts for the hygroscopicity of past

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J a n ua r y 1958

Pro fier t ies o f

Hardened

Por t l a nd Cemen t Paste

3

1

0 -

Mi x

x- II

A-

,’

 

0,2 0.4 0.6

0.8

1.0

Gel -Space Ratio (X)

Fig. 3. Compresske strength w. gel-space raiio for cement-sand mortars.

f. = compressive strength (lb, per s.+ in,); x = gel-space ratio.

Th e p rod uc ts f rom 1 cm ,~ of ce men t r eq u ir e a l it t le m or e

t h a n 2 cm .s of s p~ c e. Th er ef or e, t h e v ol um e of w a t er -f il led

s pa c e i n f r es h p a s te m u st e xc ee d t w i ce t h e a h e ol ut e v o lu m e o f

cem en t, or s om e of t he ot ig in a l cem en t m us t r em a in u nh y-

d ra t ed . C em en t gel ca n be pr od uced on ly in w a ter -filled

cap il [a r y cav it i es , and

when all those cavities

b ec a me f ul l, n o

f ur t he r h y d ra t ion of ce me nt ca n oc cu r, F ig ur e 2 i ll us t ra t es

b ow h y d ra t i on p r od u ct s g r a du a l ly r ed u ce t h e a m ou n t o f c a pi l-

l a r y s pa c e, a n d i n s om e c a se s e l im in a t e i t .

Ill. Strength

As ju st in dica t ed , cem en t g el is r eg a rd ed a s a s olid s ub -

s t a n ce h a v in g a c ha r a c t er is t ic r el a t iv el y h i gh p or os it y . F r om

t h e a s s um pt i on t h a t t h is s u bs t a n ce h a s i n t r in s ic s t r en g t h d e-

pen din g on it s com posit ion a nd s tr uct ur e, a nd t ha t t he

s t re ng t h o f t be g el i s t h e s ol e s ou rce of t h e s t re ng t h of h a r d-

e ne d p as t e, i t f ol low s t h a t t h e s t r en gt h of a s peci me n o f p a st e

s hou ld h e r el a ted t o t h e a m ou nt of g el w i tb in i ts b ou nd a ri es .

F u r t he rm or e, a n a s s um pt i on t h a t t h e r el a t iv e s t r en g t h o f t h e

p a st e d ep en d s on t h e d eg r ee t o w h i ch g el f il ls t h e s pa c e a v a i l-

a b le t o i t l ea d s t o t h e es t a bl is hm en t of a n e mp ir ica l r el a ti on -

s hi p b et w een t h e p or os it y a n d t h e s t re ng t h o f a pa s t e.

Th e d eg ree t o w h ich g el f ill s a va ila ble s pa ce ca n be ex -

pr es sed a s a r at io of volu me of gel t o volu me of a va ila ble

s pa c e. A t y pi ca l r el a t io ns h ip b et w e en c om pr es s iv e s t r en g t h

a n d g el -s pa ce r a t io i s s h ow n i n F ig . 3. Th e s pe ci me ns r ep re -

Capillary

Porasity

f ig. 4. Permeab il it y vs. c .p il lo ry poros ity for cement paste . Dif fe rent

symbol, desion.ate different cements,

Table 1. Compari son of Permeabili ti es of Rocks and Cement

Pastes

Perz;o:p

Kind of rock (dawm)

W.ter.cenlent

auo*

——

De nse t r ap

Qu ar t z d i or i t e

Marble

Marble

G r ani t e

Sandstone

G r ani t e

* Water-cement

abil i tya srock.

rat io

2,57 X 10+

8 .56 X 10 -9

2. 49 X 10-8

6. 00 X 10-7

5 .5 7 X 1O+

I ,2S X I O+

1 .62 X 1 0-6

of m a t ur e p a st e

0.38

.42

,48

.66

70

:71

.71

h a vi ng s a me

perme-

s en ted t h er e con ta in a g gr eg at es , a n d w h a tev er ef fect t h e

a g g re ga t e + $ o n s t r en g t h i s a l s o r ef le ct e d

in

tbe character ist ics

of t he em pm ca l cu rv e. I t is ev id en t t ha t t he g el-s pa ce r a t io

is t he d om in an t va ria ble, a nd t ha t s tr en gt h in cr ea ses in

d ir ec t p ro po rt i on t o t h e c ub e o f t h e i n cr ea s e d g e l -s pa c e r a t i o,

The nu m er i ca l coe f fi ci e nt p r obably d e pe nd s p r inc ip a l ly o n t he

in tr in sic s tr en gt h of t he gel pr od uced by t his pa rt icu la r

c em en t , a n d i t w o ul d b e d i ff er en t f or a d i ff er en t c em en t ,

As t o t h e

source

of s t re ng t h o f t be g el i ts el f, t h er e is n o a d e-

q ua t e t h eor y . I t i s p e rh a ps a f a ir s pe cu la t ion t o a s su me t h a t

s t r en g t h a r i se s f ro m t w o g en er a l k i n ds o f c oh es iv e b on d s: (1 )

p hy s ic a l a t t r a ct i on b et w e en s ol id s u rf a ce s a n d (2 ) c he mi ca l

bon ds . S in ce gel por es a re on ly a bout 15 a u. w id e on t he

a v er a g e, i t s ee ms t h a t L on d on -v a n d er Wa a l s f or ce s ou g ht t o

t en d t o d ra w t h e s u r fa c es t o ge th er or a t l ea s t t o h ol d t h e p a r-

t icl es i n p os it ion s of l ea s t p ot en t ia l e ner gy . I n e it h er ca s e,

t h os e f or ce s g iv e r is e t o coh es ion , S in ce

water

c a nn ot d is -

p er se g e l p ar t i cl es , i .e ., s i nce ce m ent g e l be lo ngs i n t he l im i t ed -

s w el li ng c a t eg os y , i t s ee ms t h a t t h e p a r ti cl es a r e c he mi ca l ly

b on ded t o ea ch ot her (cr os s-l in ked ). S uch b on ds , m uch

e tr on ge r t h a n t be v a n d er Wa a l s b on d s, a d d s ig ni fi ca n t ly t o

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4 J ou rn al of T he Am e ri ca n C er a m ic Society l’ow ers Vol. 41, No. 1

ov er -a l l s t re ng t h; t h er e i s g ood r ea s on t o b el iev e, h ow ev er ,

t h at on ly a s ma ll f ra ct ion of t h e b ou nd a ry o f a g el p ar t icl e i s

ch em i ca l ly b on de d t o n ei gh bo ri ng p a rt i cl es a n d t h a t p hy s ica l

b on ds a r e p rr ha p s t h e m or e i mp or t a nt . P e rt i ne nt e vi de nce

i s t h a t c on ve r ti n g g el t o w e ll -o rg a n iz ed cr y st a l s b y c ur i ng i n

s t ea m a t a b ou t 400” F . d es t r oy s co he si on .

IV. Poros ity and Permeab il ity

kry s ol id com pos ed of p ar t icl es r a nd om ly a g gr eg a te d i s

bot h por ou s a nd per mea ble. S in ce cem en t pa st e h as s uch

S Ir ucb ur e, it i s in tr in sica lly p or ou s a nd per mea ble. Th e

d en se st p os si bl e com pl et el y h yd ra t ed ce me nt pa s te h a s a

p or os it y of a bou t 2(Y Y0. Th e p or os it y of p as t e a s a w h ol e i s

u s ua l ly g r ea t e r, a n d i t d ep en cl s o n t h e o ri gi na l w a t e r co nt e nt

a nd cm Lhe ext en t t o w hich s pa ce ba s becom e fil led w it h

h yd ra t ion p rod uC t S , I t d ep en ds , t h er ef or e, on t h e or ig in a l

wa te . r -c emen tra t io a n d c mth e c on d it ion s of c ur in g .

Th e p er me ab il it y of a g ra n ul a r s ol id d ep en ds on p or os it y

a n d o n t h e s i ze a n d s ha p e of t h e p or es . I n s uch s ol id s, s iz e of

p or e ca n b e e xp re ss ed i n t er m s of h yd ra u li c r a di us , w h ich i s

t he q uot ien t of w a ter -f ill ed s pa ce by t he bou nd ar y a rea of

t h a t s pa ce . K now i ng t h e p or os it y of a p as t e a n d t h e s pe ci fi c

s u rf ia c eo f t h e g el i t co nt a i ns , o ne c a n ca l cu la t e t h e h y dr a u li c

r a di us , Th e h yd ra u li c r a d iu s of t h e p or es i n t h e g el i ts el f i s

fou nd t o h e a b ou t 5 a u . R es is ta nce t o f low t hr ou gh p or es s o

sm all is exceed bI gly h igh . Mea su rem en ts sh ow t ha t t he

c oe t il ci en t o f p er m ea b il it y o f t h e g el i t se lf i s a b ou t 7 X 10– ’1

dareys.“

Th e p er m ea b il it y o f p a st e a s a w h ol e d e pe nd s m os t ly o n i t s

ca pill ar y p or os it y, f or t he r es is ta nce t u f low t hr ou gh t he

ca pi ll a ry ca vi ti es i s n m ch s ma l le r t h an t h at t h rou gh t h e g el .

Th e rela t ions h ip b etween permea bi l ity a n d c a pi l la ry porosi ty

is sh ow n in F ig. 4. P a st e s uch a s is pr odu ced n or ma lly in

con cr et e of g ood q ua lit y h x. s a ca pi lla r y por os it y of 30 t o

40~ o a nd, a s seen in P ig, 4, is fr om 20 t o 100 t im es a s per -

m ea bl e a s ce me nt g el i ts el f. I t i s, h ow ev er , l es s p er m ea b le

t h a n m a n y n ~ lu ra l r a ck s, a s m a y be s ee n by t h e d a ta s how n i n

Ta b le I .

V. i nst abil it y o f Vo lu m e

As w i t h o t hc i col lo id a l h y dr op h il ic m a t er ia l s, ce m en t g el

s h ri nk s a n d s w el ls w i t h c ha n g es i n m oi st u r e co nt e nt , a n d i t s

r es po ns e t o ch a u gc i n t e mp er a t u r e i s co mp le x, N on co ll oi da l

c om p on en t s o f p a st e , a , ld t h e m i ne ra l a g g re ga t e o f co nc re t e,

r es t ra i n m os t of t be s hr in ki ng a n d sw elling of gel, but t h e

r em a i nd er , w h i ch a c co un t s f or s om e ch a r a ct e ri st i c v ol um e

ch a ng es of con cr et e, i s com m er ci a ll y s ig ni fi ca n t . Ty pi ca l

s h r in ka geof put t at c on s ta n t tempera ture, c a used b y d rying

fr om t he sa tur at ed st at e, is sh ow n in F ig. 5, S hr in ka ge is

m anifest ly a com plex fu nct ion of t he ch an ge in r ela tive

h um id it y i n t h e p or es of t h e p as t e.

C l mn e i n v ol um e ca u s ed b y ch a n ge i n t e mp er a t u r e a l so i s

com plex, I n F ig . O t h e d as hed lin e in dica t es t he ch a ng e i n

v oh nn e p rod uce d b y a s low ch a ng e i n t em per a t ur e w it h t h e

s pecim en k ept fu ll y s at ur at ed a t a ll s ta ges of t he ch mg e,

Th is l ine repres en ts t h e ordin a ry th erma l c on tra c t ion s h own ,

[or exa mple, b y meia l ]ic s ol id s .

Th e s olid lin e 4 B is i h e l ocu s for a s pecim en of pa st e n ot

c~ uit e sa tura ted w it h w at er, When such a specimen is

m mlcd , it u nd er goes or di na ry t her ma l con tr a ct ion a “d i rl

a d di t io n a ~ , r in k a ~ e t h a t i s c a ll ed h y gr ot k er w u ds h ri nk a g e,

Th e r m ujI .o: o f s uch s hr in ka g e i s i nd ica t ed b y t h e v er t ica l

d is ta n ce f rom x p oi nt on l in e AB tohe corresponding point

d ir ect l y a b ov e i t on t h e d a sh ed l in e,

Th e l oc us B C ’, s h o w in j~ l a c k o f r ev er s ib il it y , a n d r es id u a l

expa n s ion , i s imlic: l t iv e of s t i ll more c omplexi t ies of b eh a v ior

t b a t a r e n ot d is m is se d h er e .

Th e s t ia t c of s h ri nk in g o r s w el li ng d ep en d s o n t h e a m ou n t

of w a ter a ds or hcd by t he g el, Th is m ay r an ge f rom n on e t o a

m axim um w hich r epr eser lt s a st at e of sa tu ra tion . Tbe

a m ou nt of w a t er t h at g el ’i s a bl e t o a d sor b ju cr ea s es a s t em -

Specimen

OV

w /c = 0. 58

2.4 ~

72

hydrated

I

Vs = 0.49

20 -

16 -

0

1.2

08

8

04 -

0

0

.2

.4

h

.6

,8

1.0

Kg,5. Drying shrinkage of cement pcxte. AVIV = fractional volume

change; V, = solids per unit volume of paste; h = relative humidity.

40 ~

c

~

-40 -

,0

z

.-

=

~ -8o -

/“

,/

 

:

:-120

5@

.5’160

-

A

-200 -

Specimen under Mercury

dur ing test

-240 -

:

F ig . Hydro thermal e ffec t. . cement pmt .,

* A flow r a te of 1 cm , , p er s econ d t h rou gh m srca of 1 s q.

cm.

un der a pr essure gra dien t of 1 a t m . per cm . w it h a

flaid

h a v ing a v isc os i ty equa l to 1 c ent ipois eequa ls 1 d a rcy ,

1

I

i

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.,

J a n ua ry 1958

~ opertiesf

Ha rdened Por t l a nd

C em e nt ~ a s l e

II

\

\

01

i

o

.2 .4

.6

.8

1,0

Relat tve Humid ity

fig . 7 . Hywo herm.1 swelling of cement post.. Two fop c.r.es, data of

Meyers (see footnote 6); boflom curve, data of Virronncwd and van

Thanh [see f.ac.tnote 7).

p er a t ur e d ecr ea s es , Wh en t em per a t ur e d rop s a n d n o e xt r a

w a t e r i s a v a il a bl e, t h e g el b eco me s r el a t iv el y l es s s a t ur a t ed ,

a nd it s hr in ks . Th e a mou nt of s hr in ka ge t hu s in du ced d e-

pen ds on t he st a te of s at ur at ion of t he g el a nd h en ce on t he

i nt e rn a l h u m i di t y o f t h e s pe ci m en , a s i nt i lca t e d i n F ig . 7,

I n F ,g , 7 t he a mou nt of h yd rot her ma l volu me ch a ng e is

s how n i n r el at ion t o t h e i nt er na l h um id it y o f t h e s pe ci me n.

I t is expr essed a s m illiont hs per deg ree a nd is t ber efm w

n umer ica l ly c ompa ra b le wi th th e ordin a ry th erma lc oef ficient ,

 

S i nce a t y pi ca l v a lu e f or a t h er m a l c o ef fi ci en t i s 11 m i l li on t h s

p er ‘C . , t h es e f ig u re s i nd ica t e t h a t t h e m a x im u m h y gr ot h er -

/

m al s wellin g e ff ect m ay be t w o t o t hr ee t im es a s g rea t a s t he

normal thermal coeklicient.

S u ch e ~ e ct s a p pe a r t o b e u n de rs t a n da b le co ns ec u e n ce s o f

t he coll oi da l s ta t e of t he h yd ra t ion pr od uct s of P or tla nd

ce m en t , A c om p re he ns iv e h y pot h es is a b ou t t h e m ech a n is m

o f v ol um e c ha n g es p r od u ce d b y ch a n ge s i n t e mp er a t u r e a n d

i n t h e h u mi di t y i s n ow b ei ng d ev el op ed .

6 S,

L , M ey er s, <‘Th er ma l

ExpansionCharacteristicsof Hard-

en ed C emen t P a s tes a n d o f Co n cr e t e, ’% Highway Research Bo a r d ,

P r oc ., 3 0, 1 93 -2 03 ( 1 95 0).

7 L . Vir rorm au d a nd N. va n Tha nh , ‘ ‘D ila tom et er w it h a n 0P -

t icd Tr ipod : Test s a nd Result s of E xperim en t s,” ,4 XX.

inst

tech

d ti me nt e t t m u . @bL, 7 , 5 22 -4 0 (1 95 4) (i ll F r en ch )

f ”’o’

 6

5

Fig. 8, Effect of entrained air in cement paste. Upper curve shows

dMl ion prod. cad inpaste conta in ing nobubb les. lower curve shows same

past e w ith en tra ined a ir, A l/ l = fra ct iona l l en gth change .

Vi. Freezing

Wa t er ca n b e ca u se d t o f re ez e i n ca pi ll ar y ca v it ies , b ut i t

ca n not f re ae i n g e l p or es . G e l p or es a p pa r en t ly a r e t oo s ma ll

t o per mit n ucl ea t ion of i ce cr ys ta ls . Th e fr a ct ion of t ot a l

e va por a bl e w a t er t h at ca n b e f r oz en i s a f un ct ion of t em per a -

t u r e a n d t i me , a s w o ul d b e e xp ec t ed f r om d im en s io na l f a ct o rs

a n d t h e e ff ect s o f s ol ut e s i n t h e f re ez a bl e w a t e r .

F re ez in g of w a t er i n a s a tu ra t ed p as t e ca u se s t h e p as te t o

d il a t e d es t r uc t iv el y u n le ss s pe ci a l s t ep s a r e t a k en t o p r ot e ct

t h e p as t e f r om t h e p re ss ur e t h a t ca u ses d il at ion . Th e p re s-

s u re t h a t c a us es d il a t io n c om p ri se s t w o k in ds : (1 ) h y dr a u li c

pres s ureth a t , d ur ing f reez in g , f orces wa ter a wa y f rom f reez in g

s i tes (th e wa ter-f i lled c a pi l la ry c a vi t ies ) a n d (2 ) osmot ic pres -

s ur e p r od uce d b y w a t er t en di ng t o e nt er p a rt ly f roz en ca p il -

l a ry ca vi ti es . E i th er k in d of p re ss ur e c a n b e con t rol le d b y

f il li n g t h e f r es h p a st e w i t h m i cr os co pi c a i r b ub bl es w h i ch r e -

m a in i n t h e h a rd en ed p as t e. Th e b ub bl es m us t b e s o n u m er -

ou s t ha t t he y a re sepa ra ted by la yer s of pa st e on ly a few

t hou sa ndt hs of a n in ch t hick. E ffect s of s uch bubbles r m

d il a t ion d u ri n g f r e ez in g a r e s h ow n i n F ig . 8,

Wh en t h e a i r h u bb ie s a r e s u ff ic ie nt l y c lo se t og et h er , f r ee z-

i ng pr od uces s hr in ka ge r a th er t ha n d ila t ion . U n der t hes e

c ir cu m st a n ce s s h ri nk a g e i s ca u s ed b y t l -a n s fe r of w a t e r f r om

t h e p as t e t o t h e a ir b ub bl es b y os mos is .

WI. Other Properties

C em e nt g el s u rr ou n ds a n d i sol a t es e a ch n m r co ll oi da l p a r -

t icl e in con cr et e. M ech a ni ca l pr oper ti es of con cr et e a r e

t h er e fo re ch a r a ct e ri ze d b y t h e m e ch a n ica l p ro pe rt i es o f t h e

g el , t o a n i m po rt a n t d eg r ee . S t r es s -s t r a in t i me r el a t io ns h ip s

a r e t o b e ex pl ai ne d l ar ge ly i n t er m s of t h e ch a ra ct er is t ics of

cem en t g el, M os t of t be r es ea r ch n e ed ed in t his fiel d i s y et

t o b e d on e.

VIII. Summary

R es ea r ch s ta r ted i n t he P or tla nd C em en t As socia t ion

l a bor a t or ie s a b ou t 20 y ea r s a g o o n t h e p ro pe rt i es o f P o rt l a nd

c em e nt p a st e p r od u ce d i m po rt a n t b a si c k n ow l ed ge a b ou t t h e

p r op er t i es a n d b eh a v ior o f co nc re t e. Th e p ri nc ip a l r es ew c h

t ech ni qu e w a s w a t er -v a por a d sor pt ion i nt er pr et ed b y t h e

B run a uer-Emmett-Teller th eory . More recen t ly, o th er tech -

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6

J ou r na l of 7 e Amer i ca n Ceramic Society—Powers

Vol. 41, No. 1

n iq ues in clu din g X-r ay a nd elect ron m icr oscopy h ave been of t he m ajor pr od uct of t he r ea ct ion s bet ween P or tla nd

i nt rod uced . K now led ge of t he ph ys ica l a nd ch em ica l c on st i. cem en t a n d w a t er , a n d t o t he s pa t ia l con cen tr a tion of t his

t u t io n o f c em e nt p a st e p r ov id es u s ef ul c on ce pt u a l m od el s f or

p r od u ct (c em e nt g el ). Th e m e ch a n ics a n d p hy s ic a l c h em i st r y

d ea l in g w i t h p r a ct i ca l p r ob le m s, S t r en g t h, p er m ea b il it y , a n d

of fr ost a ct ion in con cr et e w a e est ablish ed in t er ms ~ t be

v ol um e i ns t a bi li t y a r e b a si ca l ly r el a t ed t o t h e co ll oi da l s t a t e

pb yeica l c h a ra cter i st ics of c emen t pa s te,

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f ully t he w or k r eview ed in t he t ext .

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—–,–

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