Pumex inglese 2

CARMINATI STAMPATORE ALMÈ BG
Share Capital € 3.873.427
loc. Porticello
98050 Acquacalda di Lipari (ME) - Italy
V.A.T. No. IT00071230833
Ph. +39 090 9821126 PBX 3 lines
Fax +39 090 9821044
Sales Offices:
V. M. Macchi, 26 - 20124 Milano - Italy
Ph. +39 02 66710195
Fax +39 02 66713062
E-mail: pmxxomm@tin.it
http://www.pumex.it
Lipari Pumice
The genuine Italian natural pumice
Certificate No. 7245/02/S
Italian leader in the production
and supply of Lipari pumice
Share Capital € 3.873.427
loc. Porticello
98050 Acquacalda di Lipari (ME) - Italy
V.A.T. No. IT00071230833
Ph. +39 090 9821126 PBX 3 lines
Fax +39 090 9821044
Sales Offices:
V. M. Macchi, 26 - 20124 Milano - Italy
Ph. +39 02 66710195
Fax +39 02 66713062
E-mail: pmxxomm@tin.it
http://www.pumex.it
CONTENTS
PHYSICAL AND CHEMICAL CHARACTERISTICS
OF LIPARI PUMICE
2
3
4
4
5
5
6
6
7
8
8
8
Chemical composition and structure
Suggested application of Pumice
Physical structure
Resistance to water and to chemical attack
True density and apparent density
Resistance to pressure (mechanical resistance
of Lipari pumice granules)
Hardness according to Mohs’ scale
Specific surface
Absorption of polar and non-polar liquids
Colorimetric characteristics
Refractive index
Free silica and pneumoconiosis (silicosis)
LIPARI PUMICE IN THE BUILDING INDUSTRY
Pumice aggregates for building
9
9
10
10
Grades and particle size distribution
Apparent density and absolute porosity
Water absorption
Granular form
LIGHT WEIGHT PUMICE CONCRETE
10
10
10
11
11
11
12
12
12
12
12
12
1
General considerations
Addition of cement
Water addition
Resistance to pressure
Shrinkage and thermal linear expansion
Thermal insulation
Improvement of thermal insulation of walls
Sound insulation
Water absorbency and capillary action
Resistance to fire
Resistance to freezing
Adherence of plaster
PHYSICAL AND CHEMICAL
CHARACTERISTICS
OF LIPARI PUMICE
Chemical composition and structure
Lipari pumice is a complex natural
silicate, consisting mainly of silica
(SiO2) but also containing oxides of
various elements, notably aluminum
(Al2O3), titanium (TiO2), iron (FeO,
Fe2O3), manganese (MnO), sodium
(Na2O) and potassium (K2O).
Chemical analysis shows thaI Lipari
pumice is superior to pumice from
many other geographical locations
due to its high silica content, which
generally exceeds 70% (g/100g)
compared with a range of 50 - 65%
for pumice from other sources. The
higher silica content has
considerabIe influence on the quality
of the pumice. ln particular it increases the hardness of the material and
its resistance to chemical attack
because the longer siliceous chains
(-Si-O-Si-O-Si) resuIt in the aIkaline
sodium and potassium ions being
more firmly attached.
Lipari pumice for industrial use is produced in two types, known as
“PeerIess” or white pumice and
“Lapillo” or black pumice with some
slight difference in chemical composition.
The “Peerless” type which is produced by grinding pumice rock with an
apparent density of less than 500
grams per litre, contains more silica,
sodium and potassium with lower
percentages of iron, calcium ond
magnesium.
“Lapillo” pumice is produced from
material with an apparent density
higher than 500 grams per litre and
contains a proportion of a dark,
magnetic material that can be removed by a patented process. Under
microscopic examination the dark
portion is seen to be opaque, and
coloured black, rust red or green.
This material, therefore, is a form of
magnetite or similar oxide rather than
a silicate.
X-ray analysis carried out with an
EDAX type microanalyser (x-ray
Chemical analysis of Lipari pumice
SiO2
Al2O3
TiO2
Fe2O3
FeO
MnO
CaO
MgO
Na2O
K2O
P2O5
CO2
SO3
H2O+
2
White pumice g/100 g
71,75
12,33
0,11
1,98
0,02
0,07
0,70
0,12
3,59
4,47
0,008
0,10
0,18
3,71
Black pumice g/100 g
70,90
12,76
0,14
1,75
0,64
0,09
1,36
0,60
3,23
3,83
0,015
0,04
0,21
3,88
energy dispersive analysis) shows
the presence of the element lanthanum (La) in Lipari pumice. As the
lower analytical limit of the EDAX
system is 500 ppm, it is possible that
traces of other elements at lower
levels also exist.
Lipari pumice contains approximately
4% of water which is chemically combined (combined water). The presence of H2O+ suggests that during the
volcanic formation process, the viscosity of the magma incrensed suddenly (possibly caused by a sharp
lowering of temperature) preventing
complete evaporation of the water
which therefore combined with the
silica in the molecular state. SCHOLZE indentifies three types of combined or structural water:
– Type A, consisting of groups OH–
free, removable at temperatures
between 280° and 400°C (weak
bond).
– Type B, consisting of groups OH–
chemically bound to two tetrahedrons of silica and removable at
temperatures between 400° and
550°C (strong bond)
– Type C, consisting also of groups
OH– but more strongly bound to
two tetrahedrons of silica and
removable only at temperatures in
excess of 650°C (very strong
bond).
By removing the combined water by
heating it is possible to modify the
chemical and physical characteristics
of the pumice. For example, after
removal of the combined water, the
silica content of Lipari pumice increases to approximately 75%.
According to test method DIN 4226
(test with 3% caustic soda solution)
Lipari pumice is free from organic
matter. Solubility in carbon tetrachioride (CCI4) is Iess than 0,01%.
According to test method ASTM C
289-71 (Standard test for potential
reactivity of aggregates), Lipari pumice contains approximately 200 mmol
of soluble siIica/dm3. The chemical
structure of pumice is determined by
the presence of monovalent and
polyvalent ions of potassium, sodium,
calcium, titanium, magnesium, aluminum etc. in the network of silica.
These are arranged irregularly thus
creating an amorphous structure.
The silica is made up of silicon and
oxygen in the atomic ratio of 1:2. The
silicon is tetravalent and has an ionic
ray of 0,39Å (GOLDSCHMIDT), the
oxygen is bivalent and has an ionic
ray of 1,32Å. The distance between
the atoms of the oxygen and the silicon is 1,63Å (WARREN et al), which
is less than the sum of the ionic rays.
The bond between siIicon and oxygen is, therefore, strong. By adding
potassium oxide and sodium oxide to
the silica, the following may be obtained.
Si-O-Si- + K2O ➙ -Si-O-K + -Si-O-K
Si-O-Si + Na2O ➙ -Si-O-Na + -Si-O-Na
The siIicous chains in the network
are interrupted and consequently
reduce mechanical resistance and
resistance to chemical agents of the
silicate. Similarly the addition of calcium oxide gives.
-Si-O-Si- + CaO ➙ - Si-O-Ca-O-Si-
Calcium also interrupts thc continuity
of thc siIiceous network but as it
employs a bivalent cation, its bond
with the oxygen in the siIicon dioxide
is stronger than that of potassium or
sodium.
Potassium, sodium and caIcium are
known as “network modifiers”, whereas silica and phosphorus are “network former” .
Aluminum, which is present in pumice in considerable quantity, can be
part of its chemical structure in the
capacity of either a network modifier
or a network former. A molecule of
Al2O3 can replace two molecules of
SiO2 if the third valency is saturated
by one alkaline ion, for example, of
sodium or potassium. For this to
occur and for aluminum oxide to
function completely as a network former, it is necessary, that the molecular ratio be equal to 1. In Lipari pumice thc molecular ratio R2O: Al203 is
0.8. The negative action of the alkaline ions on the chemical structure
(weakening of the siliceous network)
is, therefore, compensated.
Chemical structure of pumice
Suggested Applications of Pumice
PRODUCT
APPLICATION
NOTES
1/O N - 2/0 N
Metal, Plastic, Polyester Buttons and Glass Surface
Polishing
For Polishing/finishing of Various Surfaces
3/0 B - FFF - XXX
Metal, Plastic, Polyester Buttons, Acetate Eyeglass
Frames and Glass Surface Finishing
For Polishing/finishing of Various Surfaces
FF - FFF
Hand Soap
For Deep Cleaning and Removal of Grease,
Oil etc.
01/2 B - G 1/2 - G1
Hand Pastes / Exfoliant Creams
FF - 6/0 N
Dental Supplies and Pastes
XXX - FF - FFF
G 325
10/12 B - 8/12 BF - 8/12 B
Filler for:
Plastic, Paints
Automotive Underboy Sealant
Magnesic Grinding Wheels
As Above (for
Stronger Use)
For Body
Treatments
For the Manufacturing of Dental Prosthesis
and Dental-work Supplies
For Anti-slide Paints
For Soundproofing of Cars
For Stone Surface Polishing/finishing
10/12 B - 8/12 BF - 6/8 B
Filter Media
For Water Treatment for Human Consumption
Pellets
A-M-N-P-Q
Support for Catalysts
Thanks to High Content of Silicon Bioxide
10/12 B
Support for Pesticides
Due to its High Porosity it’s Suitable for the
Absorption of Various Chemicals
FF - 3/0 B
Buffing Treatment on Leather
Very Effective for Dry Tanning Process
TBP (4-6 cm)
TBM (6-8 cm)
TBG (8-10 cm)
Mouse - Shaped Pieces for Personal Beauty-care
Handmade Shaped Pieces to Care for Hands
and Feet
GM - PEZ - PG
From 1-2 cm
To 5 cm. approx.
“Stone Wash” Industrial Treatment for Denim
Various Sizes for Industrial Laundries
LUMPS
Manual Surface Polishing
Many Various Sizes
Pumex
S.p.A.
3
Physical structure
The physical structure of pumice can
be defined as a rigid foam of spherical and/or pseudopolyhedric structure
with fine pores delineated by thin layers of silica substance.
Void volume can be as high as 85%.
In the spherical and pseudopolyhedric form, each pore is delineated
by a thin layer of its own silicate,
while the walls delineating the pores
in a true polyhedric form are common
to many pores. Figures 1, 2 and 3
stow the macro and microstructure of
Lipari pumice. The macrostructure is
characterised by pores of variable
size from the optical limit of the
human eye up to 20-30 mm.
Scanning with an electron microscope clearly demonstrates the close
physical structure of the silicate and,
moreover, measures the dimensions
of the micropores and the thickness
of the enclosing substance (wall
thickness) without resorting to complete analytical methods.The micropores of Lipari pumice have an irregular but uniform diameter which at
times is less than 5 microns, while
the surrounding walls have a thickness of about 1 micron. The average
length of the micropores is some
1500 microns. Pumice grains larger
4
than 1500 microns therefore have
closed pores, that are not open to the
exterior. This fine porous structure
gives Lipari pumice good elasticity
which is responsible for its soft abrasive character and excellent mechanical workability (Lipari pumice may be
riveted, sawn etc.).
Spherical structure
Resistance to water
and to chemical attack
Pseudopolyhedric
structure
For practical purposes pumice can be
regarded as chemically inert inasmuch as it is insoluble in water, in
acids and in alkalis, with the exception of hydrofluoric acid (HFI). In reality, however, it has a significant superficial chemical activity. Due to the
presence of combined water (groups
-OH) and of mono- and polyvalent
ions in its chemical structure it can,
for example, chemically bind organic
and inorganic substances. The pH of
a suspension of pumice in water is
slightly alkaline, even though it contains more than 70% silica and is,
therefore, derived from an acid
magma. Pumice is not soluble in
water but is hydrolysed: At first the
hydrolysis of the bonds takes place Si-O-Me (Me = alkaline metal or alkaline earth) and the formation of
groups -Si-OH and of metal hydroxides (for example, NaOH, KOH, Ca
(OH)2 etc.) can be observed.
Polyhedric structure
Spherical-pseudopolyhedric-polyhedric
structure
Schematic diagrams of different types of
cellular structures according to MANEGOLD, SCHOLTAN & BOHME.
The cellular structure of pumice is spherical and/or pseudopolyhedric.
A gelatinous layer is formed on the
surface of the pumice granules,
which contains the new groups -SiOH and the original groups -Si-O-Me.
If the alkaline products of hydrolysis
are then not removed, hydrolysis is
repressed and is followed by alkaline
attacks of the groups -Si-O-Si-O-Si
(siliceous network). In acid solutions
an ionic change between the alkali
metals and/or alkali earths of the
pumice and the protons (H+, alternatively H3O+) of the solution, is
observed. Alkaline solutions attack
the bonds -Si-O-Si-O-Si which are
replaced by the formation of groups Si-O-Me- and -Si-OH. Attack by alkalis is more intense than that by water
or acids.
The latent hydraulic qualities of
pumice (pozzolanic characteristics)
are therefore, explained by the attack
on the siliceous network by alkalis
and the consequent formation of soluble silica. In a mixture of pumice,
portland cement and water, part of
the silica from the pumice reacts with
the calcium silicate. The formation of
calcium silicate brings about a slow
increase in the mechanical resistance
of the concrete.
This reaction is extremely protracted
and can last several years. Lipari
pumice is less vulnerable to chemical
attack because it, generally, has a
higher silica content than other
pumice and its pozzolanic character-
5
istics are not very marked. The pozzolanic activity of pumice can be
shown by measuring the resistance
to pressure of a concrete, and of the
same concrete to which pumice powder has been added. The values
found by this test method for Lipari
pumice are shown in the adjoining
graph. The cement used for this test
was type Portland PZ45F and for the
comparison a mixture of 80% of the
same cement and 20% white pumice
with a particle size less than 100
microns and a surface area according to BLAINE of 3130 cm2/g. The initial lower mechanical resistance of
the blend of cement, pumice and
water is caused by the greater quantity of water added to the mixture.
LISH & TURNER it is also possible to
roughly calculate the density of
pumice from its chemical composition
according to the formula 1/d = 1/100
p’/d’ where d = density, p’ = percentage of the compound, and d’ = factor
according to ENGLISH & TURNER.
(Na2O = 3.47 - MgO = 3.38 - Ca0 =
5.0 Al2O3 = 2.75 - SiO2 = 2.20). The
value calculated on the basis of this
formula for the Lipari white pumice is
2310 kg/m3, and for the black pumice
2319 kg/m3. The apparent density of
pumice granules, grains or powders is
dependent upon the volume of the
voids within and between the particles, and therefore upon the particle
size and form. The apparent density
of Lipari pumice varies between about
400 and 900 kg/m3.
True density and apparent density
Resistance to pressure
The density of a body principally
depends upon its chemical composition. Additionally, but to a Iesser
extent, the density of the silicate is
influenced by the speed of cooling of
the fused mass. Silicates cooled
slowly have a higher density than
those cooled quickly. The density of
Lipari white pumice is approximately
2313 kg/m3, and of Lipari black
pumice approximately 2356 kg/m3.
These figures are obtained by analysis of pumice dust with particle size
equal to or less than 63 microns,
dried at 105°C. According to ENG-
The resistance to pressure of pumice
can be determined indirectly by
measuring the degree of degradation
according to method DIN 53109
and the modified process according
to HUMMEL. This analytical method
takes into account not only the
mechanical resistance of the silicate
but also the influence on it by the
shape of the grains (granular morphology). For example, grains of elongated form are more readily broken
down under pressure than round
grains of the same silicate.
Compressive strength
of Lipari pumice granules
200
100
Resistance to pressure (kg/cm2)
300
The analytical process consists of
pressing 0,5 litres of dry pumice with
particle size 7 to 15 mm according to
method DIN 1604 so that a maximum
pressure of 5 tons is reached in 60 to
90 seconds. The granulate so treated
Is then classified on sieves with mesh
sizes of 7, 3 and 1 mm. The sum of
the residues on the three sieves is
divided by 100 to obtain the degree of
fineness before and after the application of pressure.
The difference between the degree of
fineness before and after the application of pressure is the so-called
“degradation under pressure”. By this
method a granulate of Lipari pumice
has a degradation under pressure of
0,765. This corresponds to a resistance to pressure of over 20 N/mm2
(200 kg/cm2) which is a high figure.
This value is not indicative of the
resistance to pressure of a single
grain of pumice but rather of the totality of the grains.
Hardness according
to Mohs’ scale
0
Resistance to pressure (N/mm2)
Degree of degradation under pressure
Mohs’ scale lists minerals tale (1),
gypsum (2), calcium carbonate (3),
calcium fluorite (4), apatite (5),
feldspar (6), quartz (7), topaz (8), sapphire (9) and diamond (10) according
to their degree of hardness on the
principle that a mineral of a certain
hardness scratches a softer mineral
and in turn is scratched by a harder
mineral. For example, feldspar (Mohs’
hardness 6) scratches talc, gypsum,
calcium carbonate, calcium fluorite
and apatite (Mohs’ hardness 1-5) and
is scratched by quarz, topaz, sapphire
and diamond (Mohs’ hardness 7-10).
Mohs’ hardness depends upon the
direction of scratching, and can be
determined only upon compact bodies. Due to its finely porous structure it
is not possible to determine the Mohs’
hardness of pumice in its natural form.
It could only be exactly determined on
a mass of the silicate after fusion.
Nevertheless, it is estimated that the
hardness of pumice is approximately
5-6.
Specific surface
The specific surfaces of Lipari pumice
determined according to the B.E.T.
(BRUNAUER, EMMET & TELLER)
method and test method DIN 66132Determination of The specific surface
of solids by means of absorption of
nitrogen (HAUL & DUMBGEN) on
grains 151 - 209 microns, dried at
105°C, is typically 0,6 m2/g.
Water absorption of various
Lipari pumice grades
Portland cement PZ45F
Pumice/cement mixture
Water absorption (g 100/g)
Days
Black Pumice
White Pumice
1
The compressive strength of Lipari pumice is
due t uts particular chemical composition and its
physical and chemical structure (over 70% silica
and high relationship between network former
and network modifier) - markedly superior to
pumice from other sources.
6
Particle size (µm)
Absorption of polar
and non-polar liquids
A liquid in contact with a solid body is
absorbed. The absorptive capacity of
a solid depends upon a number of
factors, e.g. specific surface, physical
structure (in the case of finely porous
pumice), chemical structure
(hydrophilic and hydrophobic characteristics) etc. In general the capacity to
absorb is directly proportional to a
solid’s surface area, which often
depends upon particle size. A cube
with sides of 1 cm has a surface area
of 6 cm2. By dividing this cube into
smaller cubes of 0,001 mm the surface area becomes 6 m2 and continuing the division to obtain cubes with
sides of 0,00001 mm (size of colloidal
matter) the resulting surface is 600 m2.
Pumice because of its fine porous
physical structure does not directly follow this rule. The micropores of Lipari
pumice have an average diameter of
5 microns and an average length of
1500 microns. Granules of a size
greater than 1500 microns therefore
contain pores which do not communicate with the exterior. Thus, in contact
with a liquid, if the density of the granules plus liquid absorbed is less than
the density of the liquid, they will float.
Clearly the number of open pores
communicating with the exterior of the
pumice granules will affect the direct
absorption of a liquid. As the average
7
length of the pores of Lipari pumice is
1500 microns, a high absorption can
only be obtained using particles smaller than 1500 microns. This is demonstrated by the graph showing the
water absorption of different particle
sizes of black and white pumice. The
highest absorption (145 g water/100 g
pumice) is given by white pumice with
particles in the range of 151 - 209
microns. Larger particles absorb Iess
water because of the presence of
closed pores within the particles, and
the absorption capacity falls dramatically once the particle size exceeds
1500 microns. The substantially lower
absorption (50 g water/100 g, pumice)
shown for powder finer than 100
microns is due to the destruction of
part of the pores during grinding.
Black pumice absorbs on average
about 30% Iess water than white
pumice. This is caused by the higher
apparent density or by the lower
weight/volume relationship of black
pumice (average proportion
weight/volume black pumice 1:1.6,
white pumice 1:2.2). Even pumice
granules containing a high percentage
of closed pores and therefore floating
(particle size greater than 1500
microns) will saturate in time and sink.
This process of saturation can take
more than ten days and is associated
with hydrolysis of the pumice and the
subsequent attack on the siliceous
network by the alkaline products of
hydrolysis. This characteristic of Lipari
pumice, while of little interest when an
immediate absorptive action is
required, is of great importance for
some other uses, for example in water
treatment and in agriculture.
As well as water and polar liquids in
general (miscible with water), pumice
will absorb non-polar liquids (immiscible with water), but not selectively. To
achieve selective absorption of nonpolar liquids, for example hydrocarbons floating on water or forming an
emulsion with it, pumice can be treated with hydrophobic substances making it water-repellent.
Lipari pumice with particle size in the
range 151 - 209 microns will absorb:
1. Premium petrol (gasoline) - test
method DIN 51600
a) white pumice 63 - 102 g/100g
b) black pumice 55 - 82 g/100g
2. Diesel oil EL - test method DIN
51603
a) white pumice 74 - 116 g/100 g
b) black pumice 50- 79 g/100g
3. Lubricating oil SAE 20
a) white pumice 80 - 150 g/100g
b) black pumice 60 - 101 g/100g
The lower value refers to the quantity
of liquid absorbed by the material up
to the point at which is still flows and
can be removed by normal mechanical means (broom, shovel etc.) without agglomeration. The higher value is
that at which the pumice becomes
saturated.
Colorimetric characleristics
Refractive index
The colorimetric characteristics of
Lipari pumice are as follows:
White pumice
The refractive index for a solid body
expresses the relationship between
the velocity of light in the solid body
and the velocity of light in a standard
medium surrounding the body. The
determination of the refractive index
nD of the vitreous fraction of pumice
is effected by mixing under the optical microscope liquids with varying
refractive indices and equalising their
values with those of the solid particles of pumice dispersed within them,
a procedure determined by compliance wilh the so-called line of BECKE.
The refructive index of the blend of
liquids which equals that of the solid
body is then measured with a refractometer. The refraclive index of Lipari
pumice, both black and white types,
at 25°C (surrounding medium air) is:
1,492 ± 0,001
The refractive index in a vacuum is
obtained by multiplying the value
obtained by a factor of 1,00023.
Trichromatic coordinates
Luminosity factor
MUNSELL notation
x = 0.322
y = 0.338
0.53
0.9Y 7.6/0.5
Black pumice
Trichromatic coordinates
Luminosity factor
MUNSELL notation
x = 0.394
y = 0.339
0.47
0.9Y 7.3/0.7
The data were obtained spectrophotometrically with a geometric measurement 8/D according to test method
DIN 5033. For the calculation of the valency measurement, observation
was conducted at 2° and normalized
illuminant D65. The calculation of the
MUNSELL notation was made for the
normalised illuminant C according to
NEWHALL, NICKERSON and JUDD.
Measurements were carried out on
pumice grains with a particle size in
the range of 151 - 209 microns.
Black pumice is shown to be darker
than white pumice. The figures for
black pumice are, however, influenced by the presence of dark particles
(dark magnetic fraction).
8
Free silica and pneumoconiosis
(silicosis)
Free silica can be defined as silicon
dioxide which is not combined with a
metal oxide to form a silicate (e.g.
aluminum silicate, sodium silicate,
potassium silicate etc., such as the
complex silicate of which pumice is
comprised. The term “free silica”
gives no indication as to the physical
form of the silicon dioxide, whether it
is crystalline or amorphous nor its
particle size. The disease of the
lungs (pneumonoconiosis) known as
silicosis is caused by the crystalline
form of silica (quariz, tridymite, cristobalite) with a particle size below 5
microns. Conversely amorphous silica, which forms silicates with other
elements, as well as crystalline silica
above 5 microns, are relatively harmless (excepting fibrous forms). For
example, the products AEROSIL
(Degussa, Germany) and CABOSIL
(Cabot, U.S.A.) although consisting
of 99,9% silica with a mean particle
size of 1/100 of a micron do not
cause silicosis owing to their physical
form being completely amorphous. In
view of the above, international standards have been established for working environments so that the product of the concentration of airborne
dust less than 5 microns and of the
concentration of crystalline silica
below 5 microns must not exced 0,5.
Thus the higher the concentration of
fine crystalline silica the lower the
concentration of total fine dust which
can be tolerated and vice versa.
Bibliographic sources indicate that
Lipari pumice contains between 2
and 20% of free silica. The authors
do not specify however, whether this
silica is crystalline or amorphous.
Test carried out by the
Staubforschungsinstitut of Bonn
(German Federal Republic) indicate
that Lipari pumice contains no
crystalline silica.
Apparent density
and absolute porosity
The apparent density of pumice granules depends upon the volume of the
voids within the particles and voids
between the particles, and therefore
upon the size and shape of the particles. The apparent density of Lipari
pumice building aggregates varies from
600 up to 900 kg/m3 approximately.
The true density of Lipari pumice is
about 2350 kg/m3. Absolute porosity
deduced from the apparent density and
true density is in the range 62 to 75%.
9
Passing by weight
Pumice Aggregate grade 5-15
Sieves Size
Mesh
Microns
3/4
19.000
5/8
16.000
1/2
12.500
3/8
9.500
4
4.750
Pan
1
Passing by weight
Grades and particle size distribution
Lipari pumice aggregates for building
are produced in a number of grades.
The most frequently requested grades
being 0-10 and 5-15 the paticle size distribution for these grades are as follows:
Cumulative percentage
PUMICE AGGREGATES
FOR BUILDING
Pumice Aggregate grade 0-10
Sieves Size
Mesh
Microns
3/8
9.500
4
4.750
8
2.360
16
1.180
30
600
50
300
100
150
Pan
1
Reference Curve
100
80
47
32
27
24
19
0
Reference Curve
100
97
90
60
15
0
Apparent density of pumice aggregates for building
(+/- 7%)
Bulk density at original moisture content
Pumice is known to be one of the oldest
materials used in construction. The earliest reference to the special properties of
pumice are to be found in Vitruvio’s
compendium of architecture of the first
century B.C. \itruvio describes artificial
agglomerates lighter than water, and
therefore buoyant, containing an inert
pumice-like mass, and he lists among
their other qualities that “they are not
hygroscopic, do not absorb water and
only slightly weigh down the foundations
of the structures”.
At the time of the Ancient Romans,
pumice was largely used in the construction of thermal baths and temples.
The most notable example is the
Pantheon of Rome, where granules of
pumice were used in the construction of
the dome. Lipari pumice granules have
long been exported and esteemed all
over the world for their excellent physical and chemical characteristics. Due to
the present need to conserve energy,
the use of pumice in modern building is
growing continually. Arising from the
increasing use of pumice in construction
is the development of the technology of
light-weight concrete, in which there
remains considerable scope for further
progress, notably in the field of lightweight loadbearing concrete. An important innovation is light-weight pumice
mortar to replace traditional
sand/cement mortar, which markedly
increases the thermal insulation of
masonry with little effect upon its
mechanical strength.
Cumulative percentage
LIPARI PUMICE IN THE BUlLDING
INDUSTRY
0-10 grade
5-15 grade
Pumice building aggregates will
absorb on average approximately
200 litres of water per cubic metre.
This figure has been determined on
samples dried at 105°C for 5 hours.
The graph below shows that absorption does not increase significantly
with time.
Absorbed water (%)
Water absorption
Granular form
Pumice grains are formed in a polyhedron-like shape which indicates
they were formed in the volcano prior
to being erupted. The surface of the
grains is rough, which is an important
characteristic for the adherence of
plaster. Pores communicating with
the external surface are usually
sealed with pumice powder having a
particle size greater than 20 microns,
and therefore have no harmful effect
in the concrete.
LIGHT WEIGHT PUMICE CONCRETE
General considerations
In normal concrete the compressive
strength of the aggregate is greater
than that of the hydraulic bond. The
resistance of the concrete is therefore the resistance of the hydraulically bonded cement, and as is well
known, this is closely related to the
ratio of cement to water. In lightweight concrete, however, the aggregate is less resistant than the binder.
The compressive strength of lightweight concrete is essentially therefore that of the aggregate. In the
case of Lipari pumice, due to its special chemical composition, the granular compressive strength is outstanding (in excess of 200 kg/cm2). For
light-weight concrete with pumice
aggregate, the following rules apply:
• The resistance to pressure
depends particularly on the compressive strength of the aggregate
granules.
Time of soaking (h)
water g/100 g pumice
water g/100 ml pumice
• The resistance of the granules
depends upon their apparent density and upon their form and shape.
• The resistance to pressure of the
concrete depends upon its apparent density.
• The apparent density of the concrete, in turn, largely depends
upon the apparent density of the
aggregate.
• The use of high resistance cement
or the reduction of the
water/cement ratio increases the
compressive strength of mortar;
but the influence on the resistance
of concrete is minimal. An excess
of fine particles in the aggregate
necessitates an increase in the
percentage of cement.
• An excess of large particles
increases the total porosity of the
concrete. There is a reduction in
the apparent density and the
resistance to pressure of the concrete.
• The use of sand increases the
resistance of both mortar and concrete. The apparent density of
concrete increases substantially
and there is a reduction in thermal
insulation.
• Due to the pozzolanic nature of
pumice the compressive strength
of the concrete increases with time
and will eventually well exceed the
values measured after 28 days.
Addition of cement
It has been seen that the quality of
the cement and the water/cement
ratio do not markedly influence the
compressive strength of light-weight
pumice concrete. The quantity of
cement added, however, is of considerable importance, particularly in
reinforced concrete where cement
inhibits oxidation of the iron reinforcement. Generally, the ideal addition of
cement should be between 300 and
450 kg per cubic metre of concrete.
Special concrete mixes designed particularly for thermal insulation (that is
where a high compressive strength is
not required) may contain 100 - 150
kg of cement per cubic metre of concrete. An increased addition of
cement will increase the resistance of
fresh concrete. The increase in
resistance after 28 days, however, is
only 50% of that shown by normal
concrete. Every additional 50 kg of
cement per cubic metre of finished
concrete increases the density of the
concrete by 30 kg. Thermal insulation
properties are reduced only slightly.
Water addition
Lipari pumice/cement mixtures
absorb approximately 200 litres of
water per cubic meter. This figure
refers to absorption in the first 30
minutes which is the period of time
during which the concrete is readily
workable, and is based on pumice in
the dry state. Since, however, pumice
as mined contains natural moisture
this percentage of water must be
token into account when calculating
total absorption.
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Resistance to pressure
Literature citations indicate that the
resistance to pressure of Lipari
pumice light-weight concrete varies
between 3 and 15 N/mm2 (30 150
kg/cm2) However, the compressive
strength of Lipari pumice gives considerably higher values than these
which must, therefore, be token into
account. According to PERFETTI the
resistance of Lipari pumice concrete
blocks depends solely upon their
apparent density and can be calculated according to the formula
0,36 d - 251 in which d = apparent
density of the concrete block in
kg/m3. Values of 3 - 15 Newtons per
square millimetre (N/mm2) arc equivalent to apparent densities between
900 and 1300 kg/m3. According to
MUSEWALD it is possible by the
addition of 20% by weight of sand to
obtain pumice concrete blocks with
apparent density in the dry state of
1400 to 1500 kg/m3 and a resistance
to pressure of about 22,5 N/mm2
(225 kg/cm2). However, because the
addition of sand has an adverse
effect on the thermal insulation properties, it is advisable to use an amorphous substance such as pumice
grade 0-5 mm in place of sand.
Shrinkage and thermal linear
expansion
The phenomenon of shrinkage during
setting, caused by physical forces
like the loss of water by evaporation,
ceases in Lipari pumice concrete
after 3 months. With blocks of limited
size it can be accelerated by heat
treatment in an autoclave. Shrinkage
can be countered by using expanding
cements such as pozzolanic cements
with low flux properties or cements
super-sulphated with blast-furnace
slag. After curing, shrinkage is less
than 0,2 mm per metre, which is too
small to cause cracking or other damage. the thermal lincar expansion of
pumice concrete is 0,8 to 1,4 mm/m
per At 1 00°C, according to MUSEWALD.
Thermal Insulation
The thermal insulation properties of
light-weight concrete depends upon
its apparent density, Its permanent
moisture content and the mineralogical composition of the aggregate. At
a density between 800 and 1600
kg/m, concrete has a coefficient of
thermal conductivity of 0,25 up to
0,65 (kcal/mh°C). Wet concrete
does not insulate well because air Is
partially excluded from the pores and
Is replaced by water which has a
thermal conductivity some 25 times
higher.
11
The permanent moisture content of
pumice concrete averages less than
3% (30 kg of water per cubic metre of
concrete). It Is interesting to note that
this figure Is lower than the
water of crystallisation In the cement
which is, according to CZERNIN,
approximately 15% by weight.
In a light weight concrete containing
300 kg of cement per cubic metre,
chemically combined water would be
about 45 kg/m3 which is higher than
the moisture content determined in
light-weight pumice concrete.
Obviously it must be token into
account that the value indicated by
CZERNIN refers to cement produced
by wet grinding. Dry processed material would give a lower figure.
Examination of Lipari pumice by Xray spectrography shows a fully
amorphous structure and a complete
absence of crystalline silica, e.g.
quartz, tridymite, and cristobalite.
Crystalline minerals such as quartz
have a high coefficient of thermal
conductivity, some 4-6 kcal/mh °C.
Calcined clays have a mixed crystalline and amorphous structure with
coefficients of thermal conductivity
about 2 - 3 kcal/mh °C. the coefficient
of thermal conductivity of fully amorphous minerals is markedly lower,
about 1 kcal/mh°C. For Lipari
pumice, due to its amorphous structure and high porosity, the coefficient
of thermal conductivity is: A = 0,09
kcal/mh°C. As previously indicated
the addition of sand to pumice concrete markedly reduces its thermal
insulation. This occurs for two reasons; it increases the apparent density of the concrete and, because its
mineralogical composition is predominantly crystalline, the sand directly
increases the coefficient of thermal
conductivity. the coefficient of thermal
transmittance of light weight pumice
concrete is usually less than 1
kcal/m2h 0C. Thus it can be calculated, as is well known, on the basis of
the formula K = 1/~0,2 + Id/A) where
0,2 is the conventional value of the
thermal resistance of the interface
between two adjoining atmospheres,
d = thickness of the wall and A =
coefficient of thermal conductivity of
the materials employed. For Lipari
pumice concrete blocks with an
apparent density of 1000 kg/m3 the
coefficient A is approximately 0,2
kcal/mh °C. This corresponds to a
coefficient of transmittance K = 0,58
kcal/m2 h °C for a thickness of a
pumice structure of 30 cm. The
response time for Lipari pumice concrete to reach the ideal value is 12
hours Lipari pumice concrete, therefore, insulates extremely well against
heat and cold.
Sound insulation
The porous structure and rough surface
of Lipari pumice provide excellent sound
absorbency.
Resistance to fire
Exposure for 180 minutes of a pumice
concrete block with a thickness of 60 mm
to a flame of 1200 °C: the temperature
of the opposite surface does not exceed
125 °C.
Thermal insulation
The amorphous structure and high
porosity give Lipari pumice excellent
thermal insulating properties.
The thermal conductivity of Lipari pumice
is approximately 0,09 kcal/mh°C
(= 0,105 W/K m).
Improvement of thermal insulation
of walls
By using a light pumice mortar to
replace the usual sand/cement mortar, the thermal insulation of block
walls is markedly improved. The reason for this is, as previously stated,
the coefficient of thermal conductivity
of crystalline minerals such as
quartz, the principal constituent of
sand, which is some 50 times greater
than Lipari pumice. For solid block
walls the improvement is approximately 0,13 kcal/mh °C, for perforated block walls some 0,07 kcal/mh °C.
These improvements are obtained
from a pure pumice mortar of density
less than 1 kg/dm3 and pumice particle size 0-5 mm. The use of light
pumice mortar does not reduce the
strength of the wall nor does it have
any other adverse effect upon the
structure.
Sound Insulation
Although acoustic insulation primarily
depends upon the weight of the
materials forming a construction,
light-weight concrete containing
Lipari pumice has a high absorbency
of sound. This characteristic is entirely due to the particular physical structure of Lipari pumice. Due to the very
thin walls, about 1 micron, dividing
the pores, Lipari pumice has a high
elasticity and absorbs sound and
other vibrations. It is, therefore, an
ideal material for construction in
12
earthquake zones. Lipari pumice concrete has a sound absorbency of 4050 decibels in the frequency range
400 to 3200 Hertz (40-50 dB = sound
absorption factor of 100-316 X).
The ISO index of valuation at 500 Hz
is 47 dB. These values refer to a single wall 16 cm thick faced with 1,5
cm of mortar. Pumice concrete when
left unplastered has an extremely
high sound absorbency due to its
rough surface. It is, therefore, especially recommended for use in industrial buildings to substantially reduce
reflected and transmitted noise.
Water absorbency and capillary
action.
The capillary action of pumice concrete is small. If a pumice concrete
block is placed in 3 cm of water, the
water level in the block will rise to 3,5
cm after 24 hours, to 4 cm after 48
hours and only to 5 cm after 72
hours. The resistance to the diffusion
of water vapour is 2 - 4, dependent
upon the apparent density. This
means that water vapour spreads
across a layer of air of the same
thickness only 2 - 4 times further than
across a pumice concrete wall. In
consequence, constructions in lightweight pumice concrete dry out rapidly while other artificial porous materials stay wet sometimes for several
years, with a resultant major disadvantage to the thermal insulation.
Resistance to fire
Pumice is incombustible. If a pumice
concrete block of thickness 60 mm is
exposed on one side to a flame with
temperature of 1200°C, the temperature of the opposite side will not
exceed = 125°C. Pumice concrete
construction is therefore suitable for
the building of chimneys.
Resistance to freezing
Pumice concrete blocks with resistance to pressure greater than 4
N/mm2 (40 kg/cm2) are resistant to
intense cold.
Samples submerged in water for 48
hours, placed in a freezer at -10°C
for 9 hours and immersed again in
water at 35°C for 15 hours (and submitted to this cycle 20 times) show
no visible signs of damage, deterioration or breakdown.
Adherence of plaster
Pumice aggregates produced and
used for building purposes, due to
their rough surface, provide a very
good key which permits excellent
adherence of conventional plaster to
the walls.
Pumice granules with a particle size
0-5 mm, can be used as an aggregate to produce a special plaster with
excellent thermal insulation and
sound absorbent characteristics as
well as good adhesion to pumice
concrete blocks and to smooth walls.