Production of artificial pumice from glass
and paper sludge ash
Peter Bi
Department of Civil and Environmental Engineering
Imperial College London
ABSTRACT
Paper sludge ash obtained from incineration of paper sludge and waste glass have been milled,
uni-axially pressed and sintered at different temperatures. The artificial pumices produced were
investigated by scanning electron microscopy (SEM). Mechanical properties assessed included
water absorptions and density. Effects of sintering temperature, pressing pressure, pressing
duration, raw materials milling time have been investigated. The optimum artificial pumice contains
90% glass and 10% PSA. It has been ball milled for 8 hours, pressed at 40kPa for 20 seconds and
sintered at 800◦C. This produced a uniformly distributed fine pores structure with a mean density
of 0.86
, water absorption of 65%.The research indicates that artificial pumice from PSA and
waste glass has comparable properties to commercial available pumice. This simple approach
represents a technically and commercially feasible option for PSA that contributes to the
development of long term sustainable, resource efficient reuse applications for PSA.
markets in the construction industry have led
to an increasing demand for lightweight
aggregates.
Furthermore,
lightweight
materials can have various other commercial
applications such as abrasive, concrete
admixture and aggregate, horticulture and
landscaping, absorbent in removing target
pollutants, filtration and laundry stone washing
(Farizoglu, 2003; Njau,. 2003; Rao , 2003).
To relieve pressure on the demand for natural
pumice, secondary materials should be
considered in the production of artificial
lightweight materials. Natural resources are
finite; and extracting and processing pumice is
very damaging and polluting for the natural
environment.
1. Introduction
Lightweight materials occur in nature or they
can be industrially manufactured. The raw
materials most frequently used for their
production are clay and sedimentary rocks
such as slates and shales (Conley, 1948;
Riley, 1951) or zeolitic tuffs (Gennaro, 2007;
Gennaro 2004). Industrial by-products such
as fly ash (Huang, 2007; Aineto, 2005) bottom
ash
(Anagnostopoulos,
2009;
Anagnostopoulos.
2010),
sludge
(Cheeseman, 2005; Laursen, 2006; Tsai,
2006) and waste glass (Cheeseman, 2010;
Ducman,
2002)
have
also
attracted
considerable interest.
A substantial volume of paper sludge ash
(PSA) is generated from the newsprint,
packaging and paperboard manufacturers.
According to the Confederation of Paper
Industries, a total of 125,000 tonnes of PSA
was produced by mills in 2006, of which
88,000 tonnes were sold to a number of end
markets in the UK and 37,000 tonnes were
landfilled (Environment Agency, 2008). In the
next few years, government plans to upgrade
some of the existing mills and construct
additional mills in England. The quantity of
PSA is expected to increase to 300,000
tonnes per annum as manufacturers of
magazine-grade paper and high quality
World pumice production was estimated to be
17.1 million tonnes in 2010. The EU holds a
significant part of the world supply (70% in
2010). United States of America (USA)
consumes 0.43 million tonnes of pumice, 10%
of which is being imported. Greece and
Turkey remained the dominant import sources
to the USA, representing 72% and 20% of the
total imported amount respectively. Because
of their cellular structure, light weight, and
insulating properties significant quantities of
pumice have been incorporated into
construction materials since the Roman
Empire (Meisinger, 1985). The recent growing
1
packaging board increase
biomass energy systems.
their
use
of
secondary glass is therefore an area that
merits attention.
Paper sludge consists of short cellulose
fibres, water, ink, soap and other minerals
separated from the recycled paper feedstock.
Despite the low heat value of mechanically
dewatered paper sludge due to their high
moisture and ash content; it can still be cocombusted with reject plastic and other
biomass to generate energy as a result of the
increasing costs of landfill and other forms of
waste management, together with increasing
costs of gas and electricity. PSA is a residue
left behind from the incineration of paper
sludge and other input materials from the
recycling of newspaper-related products. It is
a highly alkaline calcium alumino-silicate fine
granular material and its moisture content is
usually less than 0.1%.
A range of waste materials has been tested
for producing lightweight aggregates including
lignite coal fly ash (Cheeseman, 2010;
Anagnostopoulos, 2009), incinerator bottom
ash (Cheeseman, 2004), heavy metal sludge
cake and mining residues (Huang, 2007),
sewage sludge ash (Cheeseman, 2005), rice
hush ash (Chindaprasirt, 2009). Notable
studies have demonstrated the potential of
manufacturing lightweight aggregates from
waste glass (Ducman, 2002; Cheeseman,
2010) as well as using recycled glass cullet as
aggregates in concrete mixtures (Topçu,
2003; Shayan, 2004; Chidiac, 2011;
Cheeseman, 2010).
The above mentioned facts as well as past
research findings conclude that PSA and
secondary
glass
constitute
potential
candidates for the production of artificial
pumice-like materials with properties similar to
those of currently available natural pumice. To
this end, the object of this research is to
investigate the potential of a binary glass-PSA
system for the production of pumice-like
materials and provide a better understanding
of key factors affecting the properties of the
end-product.
Current and potential markets for PSA depend
on its composition and, in particular, its lime
concentration. There is a potential for PSA to
be used in a range of applications including as
a liming agent applied to agricultural land, as
a desiccant for animal bedding, stabilising
sewage sludge and in block manufacture, as
cement replacement material. The feasibility
for PSA to be used in new applications
depends on the specification, cost and
restriction from relevant legislation.
2. Material and methodology
The UK reported an amount of 550,000
tonnes of waste glass resulting from wine
bottles in 2007. Around 80 per cent of the
wine bottles were imported. In both the short
and long term, these imports are expected to
increase since glass remains one of the most
appealing packaging options for brand
owners, retailers and consumers. The majority
of glass packaging produced in the UK is
clear, and high levels of clear glass are
exported, mostly as filled whisky bottles.
There is limited UK green glass production but
high imports of green glass. This results in a
colour imbalance for the residual glass byproducts. The increase of mixed glass
exacerbates the situation. Despite of the
colour imbalance issue, FEVE (the European
Container Glass federation) has reported that
the growth of recycling rate increased
dramatically from 29% in 2000 to 62% in 2009
(British Glass, 2011). The development of
higher value alternative products for
2.1 Properties of materials
In the present study, mixed colour glass cullet
was received from Day Group Ltd. It is
essentially a mix of coloured glass obtained
from crushing glass containers such as wine
bottles and jam jars separated and collected
by local authorities recycling units. This postconsumer waste glass is tested according to
BS 7533-3:2005 (Code of Practice for Laying
Precast Concrete Paving Blocks and Clay
Pavers for Flexible Pavements), and meets
the grading requirements of that Standard.
The material was of non-significant fibre
contamination, graded through a 1.00 mm
sieve. The glass cullet fraction that passed
through the sieve would be used for further
processing. Its chemical composition is
presented in Tables 1.
2
Paper Sludge Ash (PSA) is supplied from
Aylesford Newsprint Ltd. PSA is generated
from the combustion of paper sludge in an onsite combustor. It is the secondary products at
Aylesford Newsprint which utilizing the waste
materials from the papermaking process. It is
a heterogeneous, complex mix of crystalline
phases (Table 2).
evaluated by preparing different blends and
milling them for 8 hours. Finally, the effect of
temperature was evaluated for the mixes.
Ball milling involves horizontal rotation of the
cylindrical container so that the grinding
media and solid materials cascade. Traditional
wet ball milling was introduced to reduce the
particle size distribution of the glass cullet for
sintering process. Wet milling produces a
relatively broad particle size distribution and is
widely used in the ceramics industry.
Moreover, it produces homogenous slurry
suitable for subsequent processing. Particles
are fractured by the mechanical impact of the
grinding media. A batch of 500g of glass cullet
and PSA is milled for different time durations.
500g of tap water is added along with 2500g
of high density alumina balls. The amount of
water and milling balls are fixed. The rotation
speed is set to be 5 rpm.
Table 1 Chemical composition of glass (Devaraj et
al., 2009)
Major oxides
SiO2
CaO
Na2O
MgO
Al2O3
K2O
Fe2O3
SO3
wt %
75.8
12.0
7.3
2.3
1.4
0.6
0.3
0.2
Table 2 Oxides composition of PSA
Oxide
%
CaO
61.16
SiO2
21.18
Al2O3
12.6
MgO
2.81
Fe2O3
0.934
K2O
0.392
TiO2
0.293
SO3
0.223
P2O5
0.14
SrO
0.136
ZrO2
0.0352
CuO
0.033
MnO
0.033
After the ball milling, sludge is dried for 24 h
at 105 °C (Gallenkamp Hotbox oven).
Afterwards, the dried material is grounded
using mortar and pestle. Then the crushed
powders are separated using a 300 μm
stainless steel sieve to remove coarse
particles unsuitable for preparing samples.
The powder fraction being less than 300 μm
would be used for uniaxial press to form a tilt.
(Nannetti Hydraulic Press MIGNON S). The
pressing pressure and pressing time would be
varied.
2.2 Preparation of samples
Once the tilts were prepared, they can be
rapidly fired at the final temperature for 20
minutes (Lenton Furnace). The refractory
block for holding the tilts had been pre-heated
at the final sintering temperature. After
sintering, the tilts were taken out and allowed
to cool down at room temperature. The
experimental systematic outline is depicted in
Figure 1.
Based on practical experience and theoretical
understanding the most crucial factors
foreseen to determine the properties of
samples are: (i) weight percentage content of
different raw materials, (ii) particle size of raw
materials, (iii) sintering temperature. In
additional, pressing pressure and time were
also included in the design of the
experiments. All the milled powders were
pressed at pressures ranging from 40 to 90
kPa, sintered at 700, 800, 900 °C. Pressing
times of 10 seconds and 20 seconds were
tried on the 90% glass and 10% PSA
samples, ball milled for 8 hours. The influence
of fineness of raw materials on the properties
of artificial pumice was evaluated by using
different milling times on the 90% glass and
10% PSA samples. The impact of PSA
content on the pumice properties was
3
Raw materials
(Glass cullet,
PSA)
Pulverisation
(Ball milling)
samples. A small sieve was placed at the top
of the tested sample to ensure full immersion.
The samples were under water for 24 hours.
The formula for density calculation is shown:
[Eq.2]
Water
Where mdry is the dry mass, mimm is the
immersed mass for samples impregnated by
immersion under vacuum for 24 hours, msat is
the saturated surface-dry mass of pellets in air
and ρw is the density of water.
Drying
(105°C for 24 hours)
Sieving
(Less than 300 μm)
2.3.3 Water absorption
The water absorption (WA24) was calculated
as a percentage of the dry mass in
accordance with the following formula:
Pressing
(Uniaxial press for 10 or 20 seconds)
[Eq. 3]
Sintering
(700, 800 and 900
°C)
The water absorption (WA24) is defined in BS
EN 1097-6 (British Standards Institution,
2000) as the increase in the mass of the
sample (oven dried) due to the water
absorbed in the open pores of the particle.
Artificial pumice tilt
2.3.4
Scanning electron microscopy (SEM) was
used to examine the microstructure of
fractured surface of the sintered samples
(sample ID: PSA20_8_900_70_2). The
chosen sample comprises of 90% glass
and 10%PSA, pressed at 70 kPa with a
900°C firing temperature, 8 hours ball
milled.
Figure 1.Experimental process for artificial pumice
tilts at laboratory-scale.
2.3 Characterisation of sintered products
2.3.1 Expansion
The expansion is expressed as a percentage
of the difference of initial thickness and final
thickness of tilt divided by the initial thickness.
The formula used is shown below:
In SEM a beam of electrons strikes the
specimen and penetrates into a depth
depending on the energy of the beam and
the nature of the sample. The interaction
produces various emissions, which can
provide different types of data depending
on the detector used. Backscattered
electrons are highly energetic electrons,
while secondary electrons can knock
electron out of their orbits around an atom,
with enough energy to escape from the
sample. The backscattered detectors
produce an electron micrograph that
indicates the difference in average atomic
mass between the phases, while
secondary detectors produce
topographical micrographs of the sample.
[Eq. 1]
Where Di and Df are the measured thickness
of tilt before and after firing respectively. A
digital calliper was used to take four
measurements for Di and Df of each pellet.
The arithmetic mean of those measurements
was substituted back into Equation 1.
2.3.2
Scanning electron microscopy
Density on an oven-dried basis
The dry density of the sintered tilts was
determined using Archimedes Principle.
(Kourti & Cheeseman, 2010) 6 small piece
samples were taken from each sintered tilt.
Degased water was used to immerse the
4
3. Test result and discussion
d
3.1 Microstructure
Figures 2 shows the microstructure of the samples
consisting of 90% glass – 10% PSA after the raw
material had been milled for 8 hours, pressed at
75kPa and sintered at 900 ºC, and that of the
commercially available pumice (Lava Rock Ltd).
a
Figure 2.SEM microphotographs of samples made
out of 90% - 10% PSA sintered at 800 ºC and Lava
Rock pumice. a: general review of ‘artificial’ pumice
; b: closed-up view of inner pores of the ‘artificial’
pumice; c: general view of Lava Rock pumice; d:
closed-up view of Lava Rock pumice.
A highly crystalline structure can be observed
for the Lava Rock pumice, it is a combination
of small and larger crystals forming the inner
structure of the specimen tested with different
orientation patterns. Most of the crystals seem
to be cracked while some others remain intact
within the body of the sample. In terms of
crystal shape, flat rectangular-shaped crystals
can be observed with a size of approximately
10-15 µm. The material is porous due to
significant crystal roughness.
b
On the other hand, distinct pores can be
observed for the ‘artificial’ pumice. The size of
the pores ranges from 5-60 µm. Pores are not
interconnected while uniformly distributed
along the body of the material. The surface of
the pores is smooth attributed to the viscous
phases formed during sintering as glass
softens to effectively encapsulate the gases
generated from the PSA fine particles in the
tilt.
c
3.2 Effect of firing temperature on
properties of product
Effect of firing temperature on density and
water absorption for 8 hours milled samples
pressed at 90 kPa are shown in Figures 3.
Pumice data are plotted along in all graphs for
immediate comparison.
5
The graphs show that an increase in
temperature decreased the densities of
products contain higher glass content, for
instance, 80% and 90% glass tilts. However,
the densities of samples consist of lower glass
percentage such as 60% and 70% glass
pumice increase with increasing temperature.
Obtaining denser structures of samples
contain higher percentage of PSA can be
attributed to the excessive glass formation at
higher temperatures. This densification of
pumice increased the crushing strength.
Carbon dioxide is released from carbon
compounds at 700 ◦C. Gas forming reaction
of
takes place at 1100 ◦C. Since our
firing temperature range is from 700 ◦C to
900◦C. Therefore gas evolves from
instead of
causes the bloating effect.
High concentration of calcium containing
minerals is found in PSA compare to glass
cullet. The major crystalline phases exist in
glass is
. The melting temperature and
viscosity of
is higher than that of calcium
containing minerals. Thus, it is expected that
the melting temperature of glass cullet would
be higher than that of PSA, leading to a lower
melting point of the mixture.
At 700◦C,
sintering temperature is not high enough for
the formation of liquid phase. The gas
produced cannot be trap inside the material.
Voids were filled up by the melting minerals
through capillary action. At the temperature of
maximum densification, all of the pores would
be eliminated by creating more melting
minerals. Once the level of viscosity was high
enough to hold the gas at higher temperature
and there were still enough available gas
generating minerals, density of the product
with higher PSA content would decrease with
increase expansion. However, it is possible
that the adequate glassy phase cannot
effectively develop regardless of sintering
temperature due to the presence of high
percentage of PSA. As the temperature
increases, it can be seen from Figure 3a that
the densification rate was decreased. This
effect can be observed more obvious from
Figure 3b. These data suggest that possible
that there were some pores structures have
been created. However, the quantity of pores
was not great enough to compensate the
degree of densification. If the products were
sintered at higher temperature, for instance
1000◦C or 1100◦C, decrease in density would
be expected to occur.
Figure 3.Effect of firing temperature on density
(a) and water absorption (b) for 8 hour-ball
milled samples pressed at 90kPa.
6
Although the quantity of gas forming agents
reduces for artificial pumice contains lower
PSA content, but the glassy phase developed
at higher temperature effectively traps the gas
generated. The combination of the internal
combustion of the organic mineral and the
highly viscous liquid phase results the density
decrease in increasing temperature. As the
expanding mineral is rapidly consumed, the
reduction rate of the density drops. Therefore,
it is possible for the high glass content
samples to increase in density after minimum
density is achieved at higher temperature as
no pores are produced whereas more
minerals are melted to fill up the void space.
a
3.3 Effect of pressing pressure and
pressing time on properties of product
It can conclude that pressing time only has a
small influence on the performance of the
product as long as the tilts have been pressed
for enough duration so that they do not fall
apart easily. The effect of pressing pressure is
more substantial. For all the samples
processed at 700◦C, the density remains
constant regardless of the presence of large
errors at lower pressure in the range of 40kPa
to 90kPa. This argument is also evident by the
WA data with less measured error. As the
sintering temperature increases to 800◦C, the
density of all samples decreases with
increasing pressing pressure. Denser particle
arrangement leads to more expansion of the
sintered tilts as more gas is encapsulated
inside the material. The reduction rate is
greater for pumices contain less PSA, for
example 90% and 80% glass samples due to
the formation of higher glassy phase. Tilts with
higher PSA content at 900◦C exert the same
behaviour. However, denser matrix of samples
lower percentage of PSA can be achieved by
increasing the pressing pressure at 900◦C.
This phenomenon can be explained by in
terms of expanding agent consumptions.
Even though the liquid phase at 900◦C
provided an appropriate environment for the
capsulation of gas. However, majority of the
calcium minerals was exhausted at this stage.
Hence, further increasing in temperature
cannot create more porosity. On the other
hand, the increasing vitrification leads to
closure of the existing space between
unreacted particles.
b
7
e
c
Figure 4. Effect of pressing pressure on density for
8 hour-ball milled samples containing 30(a), 20(b),
10(c) wt% PSA
f
d
Figure 5. Effect of pressing pressure on water
absorption for 8 hour-ball milled samples
containing 30(d), 20(e), 10(f) wt% PSA
8
3.4 Effect of PSA content on properties of
product
The increase in PSA content for the samples
sintered at 700◦C weakens the dense
structure of artificial pumice since density of
PSA is lower than that of glass and there was
no significant expansion taken place. At 800◦C
and 900◦C, expansions effectively occurred to
reduce the density with increasing glass
content from range 90% to 70%. For 60%
glass tilts, even at higher temperature, the
magnitude of densification still cannot
compete with the combination impact of
density drop due to higher PSA content and
expansion behavior. Therefore, the density
change of samples sintered at 800◦C and
900◦C decreases from PSA content of 30% to
40%.
Figure 6.Effect of PSA content in the mix on
density (a) and water absorption (b) for 8 hour-ball
milled samples, pressed at 90kPa
3.5 Effect of milling time on properties of
product
As it can be seen from Figure 7, density
decreases with increasing ball milling time.
The density reduces significantly for the first 4
hours milling. Then it decreases less rapidly
for the next 4 hours. The density drops much
slower for the final 24 hours milling. Milling
time effectively increases the WA. Finer
particles can fill in the void spaces between
coarse particles, whereby neck growth rate
among particles can be boosted to form
continuous liquid phase, rendering a better
sintering rate. Combustion of fine and
uniformly distributed carbon grains leads to
the formation of a homogeneous porous
structure.
9
are 22.836 and 776.605 μm respectively. A single
distinct peak can be seen for 8 hours and 32 hours
ball milling. The peak for 8 hours ball milling is
sharper than that of 32 hours. The 10% volumes of
particles are approximately 3 μm for 8 and 32
hours durations. The main difference is for the 50%
and 90% volume sizes (Table 3).
Table 3.Particle analysis data for different milling
times
Volume
diameter
2h milling
8h
milling
32h
milling
d10
22.836
2.748
2.924
d50
188.149
42.976
15.181
d90
776.605
248.208
110.338
3.6 Overall performance of samples
The level of water adsorption was positively
related to the density. The decrease of WA
was proportional to increase of the density,
vice versa. The relationship of WA and density
can be visualised from Figure 8. It is not
possible to produce pumice from PSA and
glass far away from this curve. In others
word, it indicates the feasible region of pumice
production out of PSA and glass.
Figure 7.Effect of milling time on density (a) and
water absorption (b) for samples, pressed at 70kPa
The particle size profile of different milling duration
for the preparation of mixtures in experiment-1 was
quite different. All curves; although only have one
single peak, are not symmetric (Figure 8). 2-hour
ball milling produces a width range of grain sizes.
The particle size for 10 and 90 volume percentages
10
An inverse relationship between the two
properties is obvious in Figure 8. Samples
prepared with 10-20 wt% PSA after ball milling
the raw materials for 8 hours fired at 800-900
ºC constitute promising results for a
potentially commercial pumice-like product
with properties comparable to those of natural
pumice.
always been an issue for the UK industry. PSA
used in this research were received from
Aylesford Newsprint Ltd that produces
approximately 10,000 tonnes of PSA annually.
Most of the industrial by-products are
currently disposed in landfills or by
incinerations. Landfill disposal costs in the UK
for active waste rose to £64 per tonne in
2012. It is expected to increase significantly in
the next few years. Therefore, landfill disposal
of this problematic fraction of PSA represents
a significant potential cost. The engineered
pumice provides an excellent alternative to
quarried pumice, being light, strong and
consistent. The combination of resource
sustainability and strong performance makes
the engineered pumice attractive in a wide
range of applications.
Based on 2010 data, pumice typically sells in
the UK for between £7 and £90 per tonne
depending on the application. The quality of
mixed colour glass is sufficient for the
production.
Therefore it is not difficult to cover various
costs associated with artificial pumice
manufactured from PSA and mixed colour
glass. It is worth noticing that the exact cost
depends on a number of factors such as the
processing technique and location of the
treatment plant. However, based on the
properties of the artificial pumice, there
appears to be potential for this product to
manufacture as a replacement of natural
pumice aggregate.
Figure 9.Relationship between water absorption and
density for all samples prepared including data for Lava
Rock pumice.
3.7 Economical consideration
The technical feasibility of using PSA and
waste mixed color glass in the manufacture of
artificial pumice has been successfully
demonstrated at laboratory scale. Its market
value is considered in detail below.
Rapid industrial and economic developments
in urbanisation cause an increase of waste
volumes. Disposal of industrial residues has
11
Further investigation is required for the full
understanding and optimisation of the
manufacturing process of artificial pumice at
pilot plant scale. Subsequent processing
involving pressing and sintering in a furnace is
expected to be similar to other commercially
available lightweight aggregates that are
typically manufactured from shales, clays and
slates. Pressed tilts can be continuously
delivered to the belt furnace with a hot zone of
designated temperature for firing. The firing
duration can be controlled by the rotation
velocity of the belt. Another hot zone with
glass melting temperature after the sintering
process can be set in order to produce a tilt
with flat surface.

4. Conclusion

Pumice-like material produced from
waste glass and PSA is feasible by
using simple processing techniques
including ball milling, pressing and
sintering.

A 90% glass-10% PSA sample
prepared with raw materials having
been ball milled for 8 hours, pressed at
pressure 40kPa into a tilt and fired at
800 ºC produced the optimum product
with a mean density of 0.86 g/cm3 and
water
absorption
of
65%.
Commercially available pumice had a
mean density of 0.86 g/cm3, water
absorption of 68%.





The research indicates the market for
high quality pumice could be
substantial. It could replace natural
pumice for a wide range of application
such as abrasive, concrete admixture
and aggregate, horticulture and
landscaping, absorbent in removing
target pollutants, filtration and laundry
stone washing.
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to
my supervisor, Professor Chris Cheeseman
for his help and encouragement as well as
detailed and constructive criticism. The
completion of this thesis would not have been
possible without his valuable insight.
An increase in temperature decreased
the densities of products contain
higher glass content, for instance, 8
hours milled, 80% and 90% glass
samples. However, the densities of
samples consist of lower glass
percentage such as 8 hours milled,
60% and 70% glass pumice increase
with increasing temperature.
I am also grateful to Miss Charikleia Spathi for
her support and technical contribution in the
course of this project. Our lively discussions
on several aspects of my research have been
of great benefit for my way of thinking.
REFERENCES
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http://www.environmentagency.gov.uk/static/documents/Business/Tec
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[Accessed 19 April 2012]
The density remains constant for all
the samples processed at 700 ºC,
milled for 8 hours in the pressing
pressure range of 40kPa to 90kPa. As
the sintering temperature increases to
800 ºC, the density of all samples
decreases with increasing pressing
pressure.
British Standards Institution. (2000) BS EN
1097-6:2000. Tests for mechanical and
physical properties of aggregates. Part 6:
Determination of particle density and water
absorption.
London,
British
Standards
Institution.
The increase in PSA content for the
samples milled for 8 hours, sintered at
700 ºC weakens the dense structure of
artificial pumice. At 800 ºC and 900 ºC,
expansions effectively occurred to
reduce the density with increasing
glass content from range 90% to 70%.
British Standards Institution. (2002) BS
13055-1:2002. Lightweight aggregates. Part
1: Lightweight aggregates for concrete, mortar
and grout. London, British Standards
Institution.
Density of 90% glass and 10% PSA
samples sintered at 800 ºC decreases
with increasing ball milling time.
C.R. Cheeseman, G.S. Virdi, (2005)
Properties and microstructure of lightweight
aggregate produced from sintered sewage
sludge ash, Resour. Conserv. Recycl. 45 18–
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Effect of SiO2-Al2O3-flux ratio change on the
12
bloating
characteristics
of
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