A note on volume changes in the lime-silica reaction

A note on volume changes in the lime-silica reaction

CEMENT and CONCRETERESEARCH. Vol. 3, pp. 833-836, 1973. Pergamon Press, Inc. Printed in the United States. NOTES A NOTE ON VOLUME CHANGES IN THE L...

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CEMENT and CONCRETERESEARCH. Vol. 3, pp. 833-836, 1973. Pergamon Press, Inc. Printed in the United States.

NOTES

A NOTE ON VOLUME

CHANGES

IN THE L I M E - S I L I C A

REACTION

M. J. P u r t o n Celcon Ltd., Rectory Road, Grays, Essex, RMI7 6AP, England.

ABSTRACT

Volume

changes

occurring

calcium h y d r o s i l i c a t e

d u r i n g the formation

phases

in autoclaved

lime products have been calculated. in the v o l u m e

of the solid phase

ding decrease

in porosity)

formation

of C-S-H(II)

An increase

o c c u r s with the

decrease

and is

in the v o l u m e

of the solid phase with the formation tobermorite, changes

gyrolite

correspond

quartz-

(and a correspon-

and C-S-H(I)

followed by a s u b s e q u e n t

of

of

or xonotlite.

to strength

These

changes

in the

system. Recent cementiceous

interest materials

on volume c h a n g e s phases

in

strength-porosity has

during

in a u t o c l a v e d

prompted the

the

formation

lime-silica

The h y d r o s i l i c a t e s

relationships following of

in

observations

calcium

hydrosilicate

products.

in these products

are not u s u a l l y

formed

directly but tend to occur in a series: C2SH(A ) - C-S-H(II)

- C-S-H(I)

- tobermorite

- gyrolite

-

xonotlite. Not all reactions

conform p r e c i s e l y

is only found in specimens

to this series;

with high lime contents

tends to occur as an a l t e r n a t i v e 833

to t o b e r m o r i t e

C2SH(A )

and gyrolite

or xonotlite.

2.24

2.1 2.1 2.1 2.1

= 1.5)

(cn/s

(CH/S = 1 . 0 )

(C./S = 0.8)

0.27 0.45

(a) (b)

g excess

g excess

water

water

1.82

2.7

2.24

(xonotlite)

2.73

2.24

2.4

C2S3H 2 ( g y r o l i t e )

2.18

2.24

2.27

1.82

1.21

0.91

o.91

g

S

Weight

2.4

C6S6H

1

evolved

evolved

3.61 b

4.97

4.42

4.51

4.O6

3.45

3.15

2.88 a

g

phase

C-S-H

1.03

1.00

0.59

0.82

1.00 1.00

0.86

0.69

0.46

0.34

0.34

cm 3

s

1.69

2.03

1.82

1.86

1.69

1.46

1.34

1.34

cm 3

1.34

2.o7

1.84

2.15

1.93

1.64

1.5o

1.o3

phase cm 3

(cti+s) c-s-n

Volume Volume Volume

Mixes

l.oo

1.oo

1.oo

1.oo

1.oo

cm 3

CH

Volume

Quartz-Lime

Weight

in ~utoclaved

C5S6H 5 ( t o b e r m o r i t e )

2.24

2.24

2.24

2.24

g am - 3

2.8

g

Density

phase

C2SH(A) C-S-H (CH/S ~ 2 . 0 )

CH

Assumed

Weight

Changes

Hydrosilicate

Volume

TABLE

-20.8

+ 2.0

+ 1.1

+15.7

+14.7

+12.9

+11.7

-23.5

fo

change

Volume

m Oo

Z O

O~

Z O

Co

O

4~

OO

Vol. 3, No. 6

835 NOTES

Table

1 shows,

individual

in order of formation,

hydrosilicate

1 cm 3 (2.24g)

phases

derived

of calcium hydroxide.

assumed to react stoichimetrically quartz

(density

whose volume

the volume

from a unit volume of

The calcium hydroxide

2.65 g c m -3) to form the given hydrosilicate

is calculated

from published

of the tobermorite

by Crennan,

and Taylor

Dyczek

density figures

group the values

entering the reaction

gyrolite

and C-S-H(I),

of the specimens

C-S-H(II) C-S-H(I)

and C-S-H(I)

for C2SH(A ) and xonotlite.

low strength,

increases with the formation

in strength

the of

occurs with the formation

calcium silicate brick nor aerated concrete in volume on autoclaving,

changes must affect the porosity

It is concluded,

therefore,

hydrosilicate

to changes

changes

specimens.

associated with

show any gross changes

above volume

and

or gyrolite.

Since neither specimens

for tobermorite

up to a maximum with a low C/S ratio

and a decrease

of tobermorite

calcium

1-2% increase

of calcium silicate

C2SH(A ) is generally strength

for the solid

changes can be correlated with observed

in the strength

assumed

is of the order of 12-16% increase

and over 20% decrease

These volume

(I).

(2) have been used.

It can be seen that the change in volume

for C-S-H(II)

is

with silica in the form of

For hydrosilicates

phases

of

that strength

specimens may,

the

of the system.

changes

in autoclaved

in part at least,

be due

in the porosity of the system.

It is further noted that these values depend on the assumed density for the C-S-H(II) and C-S-H(I) phases. Imperfections measurement

in the crystal structure

make accurate

phases extremely

difficult

density

and problems of

determinations

and the figure quoted is based on

that of 2.00 - 2.20 g cm -3 for the closely mineral plombierite and C-S-H(I)

related natural

In spite of this uncertainty

C-S-H(II)

are still likely to be less dense and give rise to

a greater volume Autoclaved hydrate,

(3).

for these

C6S2H3,

increase than for tobermorite. specimens

containing

tricalcium

silicate

do not appear to fit this strength-volume

836

Vol. 3, No. 6 NOTES

change

relationship

(4). Acknowledgment

The author wishes comments

to thank Professor

on the densities

H.F.W.

of hydrosilicates

Taylor for

of the tobermorite

group. References i.

L. Heller and H.F.W.

Taylor,

the Calcium Silicates, 2.

J.M.

Crennan,

and C o n c r . 3.

J.

4.

B. V.

J.R.L.

Res.,

D. M c C o n n e l l ,

Soc.

Imlach

~,

Crystallographic

H.M.S.O.,

Dyczek and H.F.W.

277

Hin.Hag.

(1956) Taylor,

Cement

(1972) 30,

and H.F.W. T a y l o r ,

71, 81 (1972)

London

Data for

672

(1955)

Trans. and J.

Brit.

Ceram.