The reaction of calcium aluminates with some basic solutions

Thermochimica Acta, 93 (19851 569-572 Elsevier Science Publishers B.V.. Amsterdam

THE REACTION OF CALCIUN ALUMINATES WIT11 SOi harek

Wieslawa

Garlicki,

Jniversity

of

Lining

BASIC SOLUTIONS

Woculi-Wczelik,

and

Metallurgy,

Cracow,Poland

ABSTXACT The calcium aluuinates hydration in water and Na CO solutions been studied using the microcalorimetry, DTA, TG and2X& methods. position of the liquid and solid phase products have been thereby shed.

have The comestabli-

IRTHODUCTION The

c,ilcium

solutions

are

aluminate of

important

portland

cement,aluminous

of

reactions

these

the

phenomena

tes

with

solutions basic

five

compounds

are

C3A,

of

opinion

then,

rated is

that

these

and

hydration

CA react product.

into

the

hydrating

rate

and

the

anions The

pounds the

of

celorimetry

phase

the

present

during has

been

supplemented

analysis

proceedings

with

hydrates

to of

alumina

to

the

the

in

paper

most

of

congruent

of

by

the used with

was

from

Na2C03

salts

to

H=B20,

8 bssic

and

llquld

are

dynamic That

phase

DTA, TG and XRD methods.

ICTA 85,

Brat&lava

the the

time.

investigation

is

supersatu-

forms

containing

to

to abbre-

authors

the

the

change

investigate

examined

the

from

C AH /lJt/.This hydrate 3 6 system CaO-A1203-H20.

considerable

relation

observation as

explain alumina-

dissolution

hydroxide

CaS04,

the

double

in

as

the

aluminiua of

in

The

cubic

the

introducing

A=Al 2 0 3’

precipitate

water,

hydrated

of

C=CaO,

water.

compound

Na CO solutions 2 3 water. The systems

with

been

with

stable

with

equilibrium

have

of

leaching

where

start

results

and

reaction

also other

of

SO:-,

C3A,

and is

they

the

method.

chemical

of

these

not

reason,

analysis

CA com-

attin thst

These

salts

and

C12A7

reactions

as

hydration eCO and 3

/k-7/.

aim

reactions

The

mixture

formation

rapidly

finally

with

practice The

such

investigations

Al

cements,

hexagonal

transform

the

binders,

The in

salts

0 production. 23 system CaO-Al 0 which correspond 2 3’ We apply the CA, CA29 CA6 /l-2/.

reactions

thermodynamicaly

in

different

several

cements. process

the

the

of

react

metastable and

only

in

with

corrosion.

also of

C ,h,A 7.

chemistry

CJ2A7

the

When C,,2A7

other

the

CA and

solution

the

the

in

the

and of

slag

concrete

occurs

C3A,

water

hardening and

methods

formulae:

used

in

control1 the

some

&co,.

and

to

in

There

the

allow

accompanying

following

viatlons

role

with

cements

alkaline

aluminates

the

reactions

the

reszlts

and

solid

- 570 EXPERIMBNTAL The

calcium

been

have

used

and

CaCO.,

cination

Na2C03

reaction

rhich

the

is

when

then

pure:

They process

ground

are

using

to

were at

the

C3A,

C12A7

synthesized

135O’C

specific

and

as

/after of

CA

a result

the

surface

The

unhydrous

products

Suspension

in the

precal-

3500’50cm2/g

the

stable

When CA and

do not

transform the

the

primary

Na2C03

introduced

phase

composition

calcium

formation

calcium

present

be

in

hydrates

C3AH6.

depends

predominant

phase.

In the

of

it

C4AH,3

and

the

carried

initiate sample,

was of

carried materials

by

chemical

as

an

on the

hydration

method

initial

pro-

,

CaO to

in

the

C,&,

A1203

CA hydra-

hydrating

aluminium

hydroxide.

products

hydration as

form

1 hour

6%

be wetted

analysis

obtained

after

the

results*thus

analysis

aluminates

these

amount

react

phase

data

can

The

composition the

hydration

the

can

with

be

seen

water

When the

- C AH and C3AH6 can be 4 13 metastable products transform from

, the

the

DTA and

qetastable

hydration

TG mrasure-

occurs

C AH and C AH 4 13 2 B at 65 C - C3AH6

alters

the

hydration

of

C3A and

product. to

the

investigated

radically.

carbonate

can

of

small

Cz2A7

to

- C3A- C&H,2

in

the

C3AH6 phase

merits.

phase with

Namely,

24 hours

liquid

to The

container,

crushed.

hydrated

ratio

aluminate

After

as

The well

in

starting were

allow

equilibrium.

glass

The

or The

measurements

thermal

special

1:lO.

which

containeris

hexagonal

with

in

1.

water to

calorimetric

The

figure

CAHIO is

- C2AHU

detected.

also

in

AleO

tricalcium

the

sealed when

aluminate. the

equal

are

reagents

the

CaO to

redistilled

the

correlates

that

in

ducts

25’C.

the ratio

microcalorimeter,

water

water

ducts.

appears

and

in

liquid

0.05~1 EDTA solution.

reveals,

the

out

to

differential

presented

in

the

carrird

and

with

hydrated

is

materials. sintering

solid

65’C

outgassed

obtained

the

was

polish

immediately

only

and

with were

the

into

C/

hydration

in

In

a

1100

temperatures

tion

initial

mixtures

solution

out

and

the

rentgenogrephically

method/. The

out

as

Al/OH/ at

/Blaine

aluminates

and

detected. carbonate the

reaction

After carbonated In

the

and

case

CAHlO.

products.

system 1 hour calcium of

hydration aluminate

CA the

Later,

the

process aluminium

proC,2A7

hydrate

-

results

in

hydroxide

the

- 571 -

dQ

C3A

dt

H20,25’C --Na2CQ ,25 *C ........... Na2C@ , 65 ‘C

dQ dt

H20,25 “C ---- Na2CQ,25 *C ............ Na2 co3 , 65*C

‘

dQ -

dt

f-420 ,25 *c ---- Na2C03,25k ._+ _ Na2 CO3,65 “C

I

2 4.

time (h)

CA

I

i :

.- ..

FIG

,

4

Heat evolution curves

.. . . I

,

6

,

,

8 for

CjA,

,

10 C

A

Q 7

,

,

,

12 time(h) and CA,

- 572 DISCUSSION The

change

on the

substantial

sition

rate

the

ions

ences

in

as

visible

well

as

the

the

C3A reacts -

induction

layer

quicly

in water

content

in

system

in

the

sing

system

work.

This

analysis pears

is curve

result data

with

the

for

the

the

as

in

a result

is

the

increasing

among

well that

with

the

The

expressed the

the

effects Al

0

23

CAHIO delayed

examined.

the

When the

-

hydration

temperature

microcalorimetric

period

slower.

strongly

highest

correlates

indicating,

relatively

reaction

C3A decopo-

of

-

the

reactions

The

tigh

Cl2 A7 -ii 2 0-Na 2 CO3 should CO are 2 3 practicularly

and

influ-

clearly

the

Na CO solution. 2 3 be underlined.

the

The is

compounds

The

decompo-

also

retard

C.,A grain.

brings

prodocts

above.

to

Na CO solution. 2 3 reveal any dormant as

aluminate

reaction

admixture

with

well

addition

temperature

all

seems

probably

surrounding

CA-H20-Na

temperature

calorimetric

The

Ne2C03

Na2C03

Na2C03

calcium the

mentioned

and

appears

of

the of

phase.

curves

do not as

to

reactions

water.

quickly

proceed

the

the

period

samples

C,.&

liquid

teaperature

with

C3A reacts of

the

a result

composition

microcalorimetric

impermeable

increases,

phase

of

of

rapidly

the

products

course

as

concerning

the in

a function

form

medium

alterations

as

strongly

curves

reaction

concentrations

progress

sition

the

influence the

observed determination nucleation

A1203

The reactions of

effect in

increa-

on microthe

present

and

phase

barrier

disap-

temperature.

REFEBENCgS 1 2

3 4 5

6 7

H.F.b. Taylor, The Chemistry of Cements. Pergamon Press, London 1968 F.&i. Lea, The Chemistry of Cement and Concrete. Chemical Publ. Comp., New York 1971 S.N. Ghosh, Advance in Cement Technology, Pergamon Press,London 1985 Proc, of the 7th Inter. Congr. Chem. Gem., Paris 1980 I. Jawed, J, Skalny, Cem. Concr. 888. L/1978/ 37 G.A.M. Spierings, H.N. Stein, Gem. Concr. Bes. L/1976/ 26.5 G.A.U. Spierings, H.N. Stein, ibid.&/1976/ 487