Chemical Reaction Bonding CEB

8/11/2019 Chemical Reaction Bonding CEB

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Chemical Reaction onding of

Earth Mud uilding locks

J. L.

Gumaste and B.C. Swain

Regional Research Laboratory

Bhubaneswar

75

013 Orissa)

In recent years, chemical reaction bonding has been tried for

the production of building

materials.

Sodium hydroxide

and

orthophosphoric acid were

used

as chemical binders in this

~ n v e s t i g a t i o n These chemical binders are

uniformly

dispersed

n

earth

mud at

a

concentration

level of 1.0 and 2.0 wt NaOH,

and 0.2, 0.5 and 1.0 wt H

3

P0

4

in presence of 10-12

wt moisture

in separate batches. The

homogeneously

mixed mass is

com-

pacted into blocks which are dried at

room

temperature and

373 K for 1 h and subsequently reaction bonded at 573, 673, 773

and 873 K for 1h in air. The earth mud

building block

consisting

of 1 (by

weight)

NaOH + 0.2 H

3

P0

4

and

reaction

bonded at

673 K

for

1 h

shows

CCS of 8.0 MPa. Hand

compacted

earth

mud

~ u i l d i n g block consisting of 1 NaOH and 0.5 H

3

P0

4

,

which

is

f1red at 673 K for 1 h in air, shows CCS

of

6.0 MPa. The above

mentioned

building

blocks show good

resistance

to

water

swell-

ing and

fluctuations in environmental conditions.

Introduction

In

chemical reaction bonding, a chemical binder

is

mixed

with a matrix clay, the binder reacts with the surface of the

grains of clay forming a layer of cementitious chemicals

on

their surfaces which during sintering under the influ

ence of heat and residual pressure

in

the green body, de

velops bonds between the grain junctions. Stephen et a/.

1

have described the chemical and structural evolution of

sol-gel derived hy&oxyapatite thin film under rapid thermal

processing. Semler et a/.

2

have investigated hydraulic set

ting behaviour of a mixture of portland cement and

orthophosphoric acid. Peter et

a/.

3

have studied reaction

setting behaviour of Ca

3

(P0

4

h s )

and

Si0

2

s)

mixture

in

aqueous suspension of potassium dihydrogen phosphate.

The chemical composition of the earth mud has been

established

as

Si0

2

6070,

Al

2

0

3

10-15, Fe

2

0

3

812, GaO

3-5, Ti02 1-3, Na20 2-3, MgO 1-2 and P

2

0

5

0.2 (all wt ).

The constituents of earth mud like

Ti0

2

, Fe

2

0

3

,

Ai

2

0

3

react

with H

3

P0

4

binder to form respective phosphates which

bind the matrix grains as has been reported by several

workers.

4

7

But

in

case of NaOH, liquid phase glassy

binders are generated during sintering which bind the grains

of the matrix. At low concentration level of binder, hydro

phobic surface groups are developed

on

the surface of the

grains.

In

the present investigation,

an

attempt has been made

to

produce building blocks

by

conventional hand moulding

as

well

as

pressure compaction of homogeneous powder

mixtures consisting of orthophosphoric acid and sodium

hydroxide binders.

Experimental

A common earth mud of chemical assay Si0

2

60-70,

AI203

10-15, Fe20

3

7-9, GaO 1-3, MgO 1.2, Na

2

0 1-3,

Ti0

2

1-3,

P20s

0.2 and LOI6-7 (all wt ) was used as a bulk raw

material and orthophosphoric acid and sodium hydroxide

4

were used as chemical binders. This earth mud was sieved

through 24 mesh BSS sieve to separate out organic root

matter and coarse pebbles.

The sieved and dried earth mud was mixed with

orthophosphoric acid at a concentration of 0.2, 0.5, 1.0 and

2.0 in presence of 0.5, 1.0 and 2.0 wt sodium hydroxide

and 10-12 wt moisture. These ingredients were mixed i(l

a plastic beaker to prepare homogeneous batches.

Similarly, batches with only phosphoric acid and sodium

hydroxide were also made. These homogeneous mixtures

were hand compacted

in

a steel die of 25.0

mm

internal

diameter and 100.0

mm

bore length. Similar green pellets

were prepared by applying 50.0 MPa pressure using a

hydraulic press. The green bodies obtained were dried at

room temperature for 48 h in air. These pellets

W9re

charged into the hearth of a high temperature SiC pit type

furnace and dried at 373 K for 1 h and further reaction

bonded at temperatures of 573, 673, 773, 873 K for 1 h

in

air.

The density of the reaction bonded earth mud blocks

was measured geometrically. The open porosity of the

reaction bonded building blocks was measured

by

immers

ing the sample in distilled water for 24

h,

the

~ i n in

weight

of the sample was taken as the volume of open porosity.

From the values of volume of open porosity and total

volume of block, the percentage open porosity was calcu

lated. The cold crushing strength of the reaction bonded

block was measured using ring type compression testing.

machine.

The characterization of the phases present

in

the reac

tion bonded earth mud pellet blended with

2

H

3

P0

4

and

reaction sintered at 573 K

in

air for 1

h,

was carried out

using Phillips APD-15 XRD spectrometer employing CuK

radiations and graphite monochromator.

The microstructure of the fracture surfaces of the

reaction bonded earth mud building block was observed

using Nomaraski phase contrast optical microscope at a

magnification of 100

x

The environmental stability of the reaction sintered earth

mud building block was determined by immersing

the

pellets

in

water and the variation of pH of immersion water

was measured at regular intervals of 7 days for

the

prolonged time durations of three months. The dimensional

stability was measured by measuring dimensions of

the

blocks immersed

in

water at regular interval of

2

days for

over a period

.of

three months.

Results and Discussion

The variations of physical and mechanical properties

of hand compacted and reaction sintered building

blocks

TRANSACTIONS OF THE INDIAN CERAMIC SOCIETY


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oo

iii

'

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-c ;.

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; ; ~

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..,

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NO

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..;

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-c

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.,

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60 48

36 24 12

6

20

(degree)

Fig. 1 - XRD spectrum of building blocks sintered at 573 K in air

for 1 h (composition : 2.0 % H

3

P0

4

and balance earth mud).

are

shown in Table

I.

The CCS increases with the increase

in binder concentration and reaction bonding temperature.

An addition of double dopants like H

3

P0

4

and NaOH

increases the CCS of building blocks which could be

attributed to formation of Na

3

P0

4

1iquid phase during mixing

time

and further formation of sodium metaphosphate at

the grain junctions during bonding.

Table

II

shows the variation of physical and mecha"ical

properties of pressure compacted building blocks which

were reaction sintered at different temperatures and time

durations. The increase in sodium hydroxide concentration

increases the CCS probably due to the formation of ceramic

phases like metaphosphate, strengite etc.

Figure 1 shows the XAD spectrum of reaction sintered

(573 klh) building bloc:.: consisting of 2.0 H

3

P0

4

The XRD

peaks indicate the formation of phosphate phases like

CaSi

3

(P0

4

)

4

,

Fe(P0

5

)a,

CaAI(P0

4

)a

and AIP0

4

.

The forma

tion of these compounds at the grain interjunctions is the

probable cause of strength development.

Table I : Physical and

mechanical

properties of reaction

bonded

earth mud building

blocks

prepared by hand

moulding and slnterlng at 673 K in air for 1 h

Composition*

Density

Open porosity

ccs

(wt%)

(g.cm-

3

)

(%) (MPa)

0.5 H3

P0

4 2.04 17.0 3.5

0.5 NaOH

+

2.00

16.5 5.0

1.0 H3P04

1.0 H

3

P0

4

2.06

16.0

6.0

1.0 NaOH

+

2.04 16.5 6.0

0.5 H3P04

1.0 NaOH +

2.09 13.3 9.5

1.0 H

3

P04

2.0 NaOH

+

2.04 12.8 10.0

1.0 H3P04

balance earth mud

VOL

60

(

11

JANUARY - MARCH 2001

Table II : Physical and

mechanical

properties

of

reaction

bonded earth

mud

building blocks, compacted at 50.0 MPa

reaction sintered in air for 60 min

Composition* Reaction

Density

Open porosity

ccs

(wt%)

sintering

(g.cm-

3

)

(%)

(MPa)

temperature

(K)

Earth mud

673 2.19

16.5

2.7

0.2 H

3

P04 773

2.05 16.2

6.5

0.5 H

3

P0

4

573

2.04 16.04

2.8

1.0 H

3

P0

4

573 2.08

16.0

7.0

1.0 NaOH + 673

2.15 13.7

8.0

0.2 H

3

P0

4

1.0 NaOH

773 2.00

15.7 14.0

1.0 NaOH

573 2.13

13.7

11.0

2.0 NaOH

673 2.17

13.0 18.0

2.0 NaOH 873

2.17 12.6

19.5

balance earth mud

Fig.

2

Photomicrograph of reaction sintered earth mud blocks :

(a) consi lting of 2.0% H

3

P0

4

binder which is reaction sintered at

573

Kin

air for 60 min (1 00 x) and (b) consisting of 10% H

3

P0

4

binder and reaction sintered at 573 K in air for 60 min (1 00 x).

5


4/4

i

:X:

Q

60

50

40

30

20

10

0

0

30

60

90 120 150 180

TIME(DAVS)

Fig. 3 -Variation of pH of immersion water with time reaction

bonded earth mud building blocks, reaction bonded at

673 K in air for 60 min at a binder cone. of 0.5%

NaOH + 0.5% H3PO (0) and 0.5% H3PO ().

Figure 2a shows the photomicrograph of reaction

sintered earth mud pellet consisting of 2% H

3

P0

4

which

shows the formation

of

metaphosphate layer

on

the surface

of

silica grains and the formation of complex phosphate

granular material

in

the interstices of silica grains. Figure

2b shows the photomicrograph of reaction sintered earth

mud pellet consisting of 10%

H

3

P0

4

reaction sintered at

573 K for 1

h

A substantial quantity of phosphates of

aluminium and iron

is

formed

in

the inter grain area. These

granular phosphate phases like metastrengite (Fe(P0

4

b

2H

2

0), phosphoferrite (FeP0

4

, berlinite {AIP0

4

} and

griphite {Na

3

P0

4

) are expected to be present

in

the micro

structure. Similarly, phases like seyenite {Na

2

0.AI

2

0

3

2Si0

2

, albite {Na

2

0.2Si0

2

},

anorthite {Na

2

0.Ca0.2Si0

2

}

and mullite

{3AI

2

0

3

.2Si0

2

are expected to form during

reaction sintering of building blocks consisting of earth

mud and 1-2% NaOH chemical binder. Figure 3 shows

the variation of pH of immersion water

in

which various

building blocks were immersed. There is practically no

decrease

in

pH of immersion water with the p r o g ~ s s of

time

whiCh

indicates the better chemical stability of building

blocks

in

aqueous medium.

Conclusions

1 Earth mud building blocks prepared by employing

an optimum binder concentration of 0.2 wt% H

3

P0

4

,

~ o m p b t i o n

pressure of 50.0 MPa and firing temperature

of

773

Kin

air for 1h shows CCS of 6.5 MPa

and

this method

saves cost of fuel by lowering the firing temperature

to

773 K as against the firing temperature of 1273 K

in

the

conventional method.

2

Building blocks produced by employing

an

optimum

compaction pressure of 50.0 MPa, binder concentration

of

1.0% NaOH and fired at 773 K for 1h

in

air show CCS of

14.0 MPa.

3

The building blocks produced using H

3

P0

4

and NaOH

chemical binder show good chemical and environmental

stability.

4

It

is

feasible to produce reasonably strong building

blocks from earth mud by simple hand compaction utilizing

NaOH (0.5 to 1.0 wt%) and H

3

P0

4

(0.2 to 0.5 wt%} chemi

cal binder and such bricks have lower firing temperature of

673 K

in

air for I

h

Acknowledgements:

Authors are thankful to Dr V N. Misra, Director,

RRL; Bhubaneswar for his kind permission to publish this research

work.

References

1 W. Stephen, L.A. Russel, T. A Laptak Carlos, T

L

Suchicital

and B

P

Vincent, Chemical and Structural Evolution of Sol

gel Derived Hydroxy Apatite Thin Film under Rapid Chemical

Processing, J. Am.Ceram Soc., 79 (4) 837-42 (1996).

2 C E Semler, A quick Setting Wollastonite Phosphate Cement,

Am.

Ceram. Soc.Bull.,

55 (11) 983-85 (1976).

3 V Peter and I Vanidler, Hydration Reaction in the System

CaO, P

2

0

5

, Si0

2

, H

2

0,

J Am. Ceram. Soc.,

79 (4) 1124-26

(199F).

4.

A A

Chislyahova, Y. A. Sivikina, A.

P

Khashkova,

V

I

Sadkora and L. G. Povysheva, Investigation of an Aluminium

Phosphate Binder, Sov.

J

Inorganic Materials, 5 (9) 1333-38

(1969).

5 J. L. Gumaste, B. C Swain, B C. Mohanty and J.

S

Murty,

Chemical Reaction Bonding of Building Blocks using Red Mud

and Orthophosphoric Acid Binder,

J

Mat. Sci. Lett., 15, 1667-

68 (1969).

6 M. J. Ohara, J. D. Duga and H. D. Sheets Jr., Studies in Phos

phate Bonding of Ceramics, Am. Ceram. Soc. Bull., 51 (7)

590-95 (1972).

7 M. Hirao, Phosphate Bonded Synthetic Ceramics,

Am Ceram.

Soc. Bull.,

55 (9) 788-79 (1976).

8 J. L Gumaste, B. C. Swain, B C. Mohanty and J S Murty,

Production

of Building

Blocks

from Earth Mud using

Orthophosphoric Acid as a Binder, pp.294-300 in Proc. Inti.

Con . on Non-conventional Constructional Materials (NOCMAT-

97), organized by NRDF and Institute of Advanced Technology

and Environmental Studies, held during 17-19 June (1997).

[MS received

October

3, 2000; revised copy received March 21, 2001)

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Chemical Reaction Bonding CEB