Fly ash from a coal power plant and waste glass were used to produce glass-ceramic composites. The addition of 50% flask glass to fly ash increased bending strength from 9 MPa to 77 MPa and elastic modulus from 6 GPa to 29 GPa. Porous composites made with polyurethane foam had 70% porosity, 3.5 GPa elastic modulus and 6 MPa bending strength. The composites showed good durability in acid with less than 0.05% mass loss, making them suitable for applications like filters or insulation.

1. Bulletin of the Chemists and Technologists of Macedonia, Vol. 23, No. 2, pp. 157–162 (2004)
GHTMDD – 448 ISSN 0350 – 0136
Received: May 11, 2004 UDC: 666.1 : 666.3/.7
Accepted: October 18, 2004
Original scientific paper
UTILISATION OF FLY ASH AND WASTE GLASS IN PRODUCTION
OF GLASS-CERAMICS COMPOSITES
Bianka Mangutova1
, Biljana Angjuševa1
, Darko Miloševski1
, Emilija Fidan~evska1
,
Jörg Bossert2
, Milosav Miloševski1
1
Faculty of Technology and Metallurgy, Ss Cyril and Methodius University,
P. O. Box 580, MK-1001 Skopje, Republic of Macedonia
2
Friedrich Schiller University, Institut of Materials Science and Technology,
Lobdergraben 32, Jena 07743, Germany
milo@unet.com.mk
Glass-ceramics composites were produced utilising fly ash from coal power stations and waste glass from TV
monitors, windows and flasks. The addition of 50% flask glass in the fly ash, increases the bending strength and E-
modulus from 9 ± 3 to 77 ± 3 MPa and 6 ± 2 to 29 ± 3 GPa, respectively. Using polyurethane foam as a creator of
porous structure, the obtained porous composites, consisted of fly ash–glass, had the porosity of 70 ± 5 %. E-
modulus and bending strength of the porous systems, obtained by polyurethane foam, were 3.5 ± 1.2 GPa and 6 ± 2
MPa, respectively. The porous materials had a durability (mass loss) of 0.03 – 0.05 % in 0.1 M HCl, which charac-
teristic is identical with the durability of the dense composites.
Key words: glass-ceramics; waste; fly ash; porosity; E-modulus, bending strength
1. INTRODUCTION
Every year about 500 000 tons of the coal
mining waste are produced at the thermal electric
power station “Oslomej” in the Republic of Mace-
donia. This waste is the result of burning of the
coal in the temperature range of 1100 to 1600 o
C.
Due to the burning procedure coal waste is avail-
able in the fine powder form. The waste is classi-
fied according to the size of particles. Waste with
the diameter not bigger than 0.1 mm is taken as fly
ash, and the others belong to slag-ashes and slags.
Their recycling is one of the tasks in the field of
the environment protection which should be solved
in near future. One kind of fly ash contains Fe2O3,
Al2O3, SiO2, MgO, Na2O as the main constituents
and a small amount of ecologically risky oxides as
MnO and PbO. Three kinds of waste glass were
taken from the dump. They are uniform in their
composition and may be considered in correspo-
dence with the original glass. The combination of
the fly ash with waste glass under controlled sinter-
ing procedure gave bulk or highly porous materials
with surface or/and bulk crystallization. The struc-
ture of glass-ceramics built in this way may pre-
vent the migration of ecologically risky elements
into environment due to corrosion or friction [1, 2].
The aim of the investigation is to produce
highly porous composites based on the interactions
between fly ash and waste glass from TV monitors,
windows and flasks. In this way the following ad-
vantages are present: the sintering process leads to
the reduction of energy consumption and ecologi-
cally risky components from the waste that are fixed
molecularly in the silicate phase and additionally
inserted in the ceramic matrix, which either have no
toxic inserted components or have them in eco-
compatible concentration. The porous glass-
ceramics obtained in this way which possesses a
foam like structure can be used as filters, thermal
insulation, lightweight structural laminates, dif-
fused aeration, dust collectors, acoustic absorbers
etc. The principle of this procedure was presented

2. 158 B. Mangutova, B. Angjuševa, D. Miloševski, E. Fidančevska, J. Bossert, M. Miloševski
Bull. Chem. Technol. Macedonia, 23, 2, 157–162 (2004)
as multibarrier-concept by Ondracek [3] and basi-
cally investigated for various waste combinations
[4, 5]. This work deals not only with the chemical
inertisation process and combination of waste ma-
terials but also with new application of these waste
materials as highly porous glass ceramics.
2. EXPERIMENTAL PROCEDURE
Chemical analysis of the waste materials was
carried out using an atomic absorption spectropho-
tometer (Rank Hilger, Atom Spek H-1580) and wet
chemical methods. X-ray diffraction (XRD) studies
on the samples were undertaken using a Philips X-
ray diffraction unit (Model PV 105-1) operating at
CuKα-radiation.
Glass from TV monitors (only from screen)
was treated with 12 %HF and NH4F to dissolve all
non glassy elements [6].
The homogenization of the mineral waste and
the glass waste was made in a planetar mill (Fritsch
pulverisette) for 60 min. The particle size distribu-
tion of the sample was determined by sieve analy-
sis. Thermal characteristics were determined by
heating the microscope (Leitz) in the temperature
interval RT-1500 o
C with a heating rate of 10
o
/min. Pressing the samples was performed by the
uniaxial press (Weber Pressen KIP 100). A pres-
sure of 50 MPa was employed to reach green den-
sities of 55 to 60 % of the theoretical density. Sin-
tering was realized in a chamber furnace in air at-
mosphere at the temperature region from 900 to
1150 o
C, using the heating rate of 10 o
/min and
isothermal treatment at the final temperature of 30
to 120 min. The bulk density of the sintered sam-
ples was determined by the water displacement
method according to EN-993. The value of the
theoretical density of the compacts were calculated
based on the composition of the initial mixture and
known densities of the fly ash and glasses.
Mechanical properties (E-modulus and bend-
ing strength) of the dense and porous specimens (8
pieces, 50×5×5 mm) were investigated at room
temperature. The samples were polished with dia-
mond paste of 15 µm and subjected to the 3-point
bending tester Netzsch 401/3 with 30 mm span and
0.5 mm/min crosshead speed. The thermal studies
of the waste and polyurethane foam were per-
formed by DTA/TG (Netzsch STA 409). Linear
thermal expansion of the dense materials was de-
termined by a dilatometer (Netzsch 402E) in the air
atmosphere and the temperature interval of RT-
650-RT. The measurements were performed with a
heating rate of 2 o
/min.
Open celled macrostructures were fabricated
by coating the struts of polyurethane foam with a
ceramic slurry and then firing the resultant struc-
ture to pyrolyse the substrate and sinter the ceramic
system [7, 8]. Commercial polyurethane foam with
density of 25 kg/m3
was used as a substrate. The
slurry contained 55 % solid (fly ash-glass), 27 %
water glass and 18 % Dolapix CE 64 (4 % water
solution). It coherently coated the polyurethane
substrate. The foam was squeezed and dipped into
slurry, looking in that case like a sponge. During
the expansion to the original shape and size, the
foam was impregnated by the mentioned slurry.
After drying, the coated substrates were heated up
to 950 o
C/1 h in a schedule which minimized dis-
ruption during pyrolysis and allowed the ceramic
to achieve high density. This heating schedule con-
sisted of a heating rate of 1 o
/min up to 500 o
C and
rapid heating of 10 o
/min from 500 o
C to 950 o
C,
1 h held at 950 o
C and then cooling in the furnace.
The relative density of the foam material was de-
termined from the ratio of mass and volume.
Durability of the glass-ceramics was tested
using standard methods both for glass and ceram-
ics. The durability was determined as a mass lost in
0.1 M HCl, 0.1 M Na2CO3 and distilled water. Af-
ter treatment of 24 h and 30 days, the risky ele-
ments like Zn2+
, and Pb2+
were removed from the
tested materials and analysed by atomic absorbtion
spectroscopy. The measurement of radioactivity of
the fly ashes was performed by gamaspectrometry.
3. RESULTS AND DISCUSSION
The chemical composition of the investigated
wastes is shown in Table 1.
The wastes contain Fe2O3, Al2O3, SiO2, and
CaO as the main constituents and a small amount
of ecologically risky oxides as MnO and PbO.
The values of the radioactivity which is very
important as a property of fly ash, are given in Table 2.
According to the book of regulations the
maximal levels of the radioactive contamination of
the human environment (Sl. list No
8/87), the in-

3. Utilisation of fly-ash and waste glass in production of glass-ceramics composites 159
Glas. hem. tehnol. Makedonija, 23, 2, 157‡162 (2004)
vestigated fly ash can be used as a material in a
civil engineering.
T a b l e 1
Chemical compostion of the fly ash Oslomej and
waste glasses
Oslomej TV glass Window glass Flask glassChemical
composition % wt % wt. % wt % wt
ZnO – 0.06 0.09 –
TiO2 0.77 0.09 0.07 –
SO3 0.67 0.11 0.37 0.41
K2O 1.90 6.40 0.19 2.31
Na2O 0.45 7.10 9.50 8.67
Fe2O3 10.02 0.31 0.31 –
CaO 3.36 1.65 8.96 0.21
MgO 1.21 2.42 4.22 7.34
Al2O3 24.13 3.75 3.38 4.76
SiO2 49.60 58.50 71.50 71.62
PbO 0.01 8.18 – –
CoO 0.01 0.08 0.12 –
CO2 5.90 6.30 1.29 –
BaO – 4.81 – –
B2O3 – – – 4.00
MnO 0.27 – – –
NiO 0.02 – – –
Lost of
ignition 2,69 – – –
T a b l e 2
Results of measurements of radioactivity
of fly ash Oslomej
Fly ash Oslomej
40
K 944.7±206.9
212
Bi 62.8±51.9
212
Pb 115.6±18.6
214
Bi 35.8±16.1
214
Pb 72.5±18.7
228
Ac 83.3±19.4
226
Ra –
137
Cs –
134
Cs –
Following to the XRD, the as-received fly ash
contains small amounts of crystalline phases such
as quartz, mullite, hematite and amorphous phase.
The density of the as-received fly ash was
ρf = 2.42 g/cm3
. The thermal characteristics of the
fly ash and glasses are shown in Table 3.
T a b l e 3
Thermal characteristics of the fly ash and waste
glasses (heating microscopy)
Material Significant
shrinkage
Softening
temperature
Melting
temperature
o
C o
C o
C
Fly ash 1140 1300 1340
TV-glass 600 700 800
Window glass 650 850 950
Flask glass 650 850 960
The sintering studies of the pressed compacts
of fly ash showed the highest relative density of 71
± 1% after sintering at 1050 o
C/2h. Sintering at
higher temperature of 1050 o
C exibits side effects
as bending and degassing.
E-modulus, bending strength and technical co-
efficient of thermal expansion of the fly ash sintered
at 1050 o
C/2h and glasses are shown in Table 4.
T a b l e 4
E-modulus, bending strength and thermal
coefficient of thermal expansion
of the fly ash and glasses
Material E-modulus Bending
strength
Tech. coeff. therm.
expan. 106
GPa MPa o
C
Fly ash 6± 2 9 ± 3 6.45
TV glass 72±8 136±10 10.61
Window glass 51±7 125±10 10.10
Flask glass 53±7 127±10 10.80
For the purpose of aiding the sintering proc-
ess and to encapsulate the particles of industrial
wastes into matrix, compatible with the environ-
ment, waste glasses in quantity of 10 to 60 wt%
have been used. By variation of the temperature
(900–1100o
C) and time (0.5–2h) of sintering, com-
pacts with different density were obtained. Optimal
composition of the waste composites, sintering

4. 160 B. Mangutova, B. Angjuševa, D. Miloševski, E. Fidančevska, J. Bossert, M. Miloševski
Bull. Chem. Technol. Macedonia, 23, 2, 157–162 (2004)
temperature, relative density, E-modulus and bend-
ing strength are shown in Table 5.
T a b l e 5
Optimal composition of the waste composites,
sintering temperature, relative density (ρrel.),
E-modulus, bending strength (σ)
Composite Sinter. temp. ρrel. E σ
Fly ash – %glass o
C/1h % GPa MPa
Fly ash – 50 % TV glass 1050 90 30 ± 1 76 ± 2
Fly ash – 50 % window glass 1050 92 29 ± 2 73 ± 3
Fly ash – 50 % flask glass 1050 94 29 ± 2 77 ± 3
From the Table 5 it is evident that the compo-
sition fly ash – 50% flask glass sintered at
1050o
C/1h showed the highest relative density.
The variation of E-modulus and the bending
strength of this system with porosity is shown in
Figs. 1 and 2.
Fig. 1. Variation of the bending strength with the porosity
of the system fly ash – 50% flask glass
Fig. 2. Variation of the E-modulus with the porosity
of the system fly ash – 50% flask glass
Approximation of the E-modulus and the
bending strength with porosity are given with
eqs.(1, 2):
E = 37.9 exp (–0.026 Θ) , (1)
σ = 100.1 exp(–0.037 Θ) , (2)
where: Θ – porosity / %; E / GPa; σ /MPa.
In the first approximation, for zero porosity,
E-modulus and the bending strength have values of
Eo = 37.9 GPa and σo = 100.1 MPa
Figures 1 and 2 show that increase of the po-
rosity from 6 to 26 % leads to a 51 % reduction for
σ, and 45 % for E-modulus.
Thermal expansion characteristics of these
investigated systems in the interval RT-600-RT
showed absence of hysteresis effect, that proves
that the systems are in thermal equilibrium [9]. The
temperature dependence of the thermal expansion
in the interval RT-600 o
C can be represented by a
II order polynomial form. Table 6 shows the tem-
perature variation of the physical and the technical
coefficient of thermal expansion.
T a b l e 6
Temperature variation of the physical and the technical coefficient of thermal expansion
Composite ∂(∆ L/Lo)/∂T = f(T) αtech 10–6
/ o
C
Oslomej – 50%TV glass 0.017 – 7.178·10–5
T + 1.097·10–9
T2
8.53
Oslomej – 50% window glass 0.031 – 1.069·10–6
T + 1.303·10–9
T2
8.28
Oslomej – 50% flask glass 0.019 – 7.736·10–5
T + 1.113·10–9
T2
8.62
Durability of the investigated dense materials
(mass lost after 30 days) was determined for ce-
ramics containing only fly ash (F) and the compos-
ites, fly ash – 50 % TV glass (TV50), fly ash –
50 % window glass (W50) and fly ash – 50 % flask
glass (FG50). The composite (TV50) possesses
durability of 0.12 %, (W50) of 0.06 %, (FG50) of
0.07 %, where as (F) possesses durability of 4.54 %
0
20
40
60
80
100
5 10 15 20 25 30
Θ / %
Bendingstrength
5
10
15
20
25
30
35
40
5 10 15 20 25 30
Θ / %
E-modulus

5. Utilisation of fly-ash and waste glass in production of glass-ceramics composites 161
Glas. hem. tehnol. Makedonija, 23, 2, 157‡162 (2004)
in 0.1M HCl. The change in mass in 0.1M Na2CO3
was –0.01 % for (TV50), –0.02 % for (W50),
–0.01 % for (FG50) and –0.07 % for (F). In all in-
vestigated specimens durability in water was
0.001 %. The durability allows the categorization
of these materials to definite classes according to
DIN EN 122. All investigated composites belong
to the class B (visible changes of colour). The
durabilities show that the ceramics meet the re-
quirements of dense unglazed, dust-pressed ce-
ramic tiles according to building ceramic norms
DIN EN 106.
By using a polyurethane foam as the creator
of a porous structure, samples of fly ash –50 %
flask glass with a porosity of 70 ± 5 % were fabri-
cated (Fig. 3).
The pores with diameters from 300 to 600 µm
are interconnected. The E-modulus of this system
was 3.5±1.2 GPa, bending strength was 6±2 MPa.
Fractures among the pore walls were not evident.
Durability of this porous system (mass lost) was
0.065% in 0.1M HCl and 0.01% in 0.1M Na2CO3.
The dense composites can be used in the building
industry [1], while the porous composites are a
potential material for producing diffusers which
could be used for water aeration [10].
Fig. 3. Macrostructure of cell foam fly ash – 50% flask glass
(bar 1200 µm)
CONCLUSIONS
Ecologically harmless materials (glass ce-
ramics) can be created from fly ash and waste
glasses.
The addition of 50% flask glass in the fly
ash, increases the bending strength and E-modulus
from 9±3 to 77±3 MPa and 6±2 to 29±2 GPa, re-
spectively.
Approximation of the E-modulus and bend-
ing strength with porosity are given with equations
E = 37.9exp(–0.026Θ) and σ = 100.1exp(–0.037Θ)
Polyurethane foam was used as a creator of
porous structure and the obtained porous compos-
ites consisted of fly ash – glass had the porosity of
70 ±5%.
E-modulus and bending strength of the
porous systems consisted of fly ash-glass were
3.5 ± 1.2 GPa and 6 ± 2 MPa, respectively.
The chemical and physical properties of the
dense material, makes them suitable for a wide
range of applications in the building industry.
AAcckknnoowwlleeddggeemmeenntt:: This work was supported by
the European Community, contract ICA2-CT-2002-
10003-REINTRO in the frame of the INCO COPER-
NICUS program.
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R e z i m e
PRIMENA NA LEBDE^KA PRA[INA I OTPADNO STAKLO VO PROIZVODSTVOTO
NA STAKLO-KERAMI^KI KOMPOZITI
Bianka Mangutova1
, Biljana An|u{eva1
, Darko Milo{evski1
, Emilija Fidan~evska1
,
Jörg Bossert2
, Milosav Milo{evski1
1
Tehnolo{ko-metalur{ki fakultet, Univerzitet "Sv. Kiril i Metodij",
p. fah 580, MK-1001 Skopje, Republika Makedonija
2
Friedrich Schiller University, Institut of Materials Science and Technology,
Lobdergraben 32, Jena 07743, Germany
milo@unet.com.mk
Klu~ni zborovi: staklo-keramika; otpad; lebde~ka pra{ina; porozitet; E-modul; rastvorlivost
Staklo-kerami~kite kompoziti bea dobieni so
primena na lebde~ka pra{ina od termocentralite i
na otpadno staklo od TV monitori, prozorsko i am-
bala`no. So dodavawe na 50% ambala`no staklo vo
lebde~kata pra{ina ja~inata na svitkuvawe i E-
modulot bea zgolemeni od 9 ± 3 na 77 ± 3 MRa i od 6 ± 2
na 29 ± 3 GPa, soodvetno. So upotreba na poliuretan-
ska pena, kako kreator na porozna struktura, bea do-
bieni porozni kompoziti od lebde~ka pra{ina i
staklo, so porozitet od 70 ± 5 %. E-modulot i ja~ina-
ta na svitkuvawe na poroznite sistemi bea 3,5 ±
1,2 GPa i 6 ± 2 MRa, soodvetno. Poroznite materijali
poseduvaat rastvorlivost (zaguba na masa) od 0,03 do
0,05 % vo 0,1 M HCl, identi~no so rastvorlivosta na
gustite kompoziti so ist sostav.