NEW FOAMED CONCRETE
The present invention relates to a foamed concrete and to foamed compositions
used to prepare it.
Many types of construction materials exist that are intended for carcassing works
in the form of masonry blocks. Such materials include clay-based material (for example
hollow or alveolar bricks such as Monomur™), cement materials (for example solid
concrete blocks or hollow concrete blocks) or organic materials (for example hemp such
as Chanvribloc™).
Of these blocks, lightweight concrete blocks are advantageous for many
applications by virtue of, for example, their thermal insulation properties. Lightweight
concrete is a concrete which is lighter than conventional concrete due, for example, to
the pores or empty spaces it contains. Such pores or empty spaces are due to the
presence of air in the concrete, which forms bubbles. It is possible to produce from 1m3
of raw material, approximately 5m3 of a finished concrete product, which is a block
composed of 20% of solid materials and 80% of air (for a block having a density of
400kg/m 3) .
One difficulty in the production of lightweight concrete blocks is to secure both
lightness and mechanical strength in the block. The most widespread means of
producing lightweight cement materials to make foamed blocks are:
a) to generate a gas by chemical reaction between an aluminium powder and a
reactant rich in lime, in a mixture comprising sand and cement during the setting of the
concrete;
b) to produce an aqueous foam (by introducing air into a mixture of water and
foaming agent) and to inject the foam into a cement paste; or
c) to aerate a cement paste directly in a mixer.
However, such processes are not always satisfactory. The first process, due to its
complexity, does not provide sufficient control of the density. The second requires the
addition to the cement paste of water as part of the foam, which naturally fluidizes the
paste, but to the detriment of the final mechanical properties. The third process does not
provide a sufficiently robust foam. In the last two cases, the required low fluidity is
obtained by known means, which involves the use of fluidizing and/or water-reducing
agents, and sometimes by optimization of the granulometry of the mix of powders.
Although the use of fluidizing agents (such as superplasticizers) does result in improved
fluidity, this is generally associated with a high segregation of the particles, as well as an
increased tendency to generate lumps, which prejudices the mechanical strength of the
solid material produced.
The problem which the invention seeks to solve is to simplify the production of
foamed concrete; to facilitate the production of fluid cement pastes having low
water/cement and water/solid ratios; and/or to secure good thermal and mechanical
properties for the foamed concrete.
Unexpectedly, the inventors have discovered that the joint use, in specific ratios, of
a specific known accelerator, and a foaming agent produces a synergistic effect,
increasing the fluidity of a cement paste. The increase in fluidity facilitates pumping of
the paste and also facilitates foaming, for example in high shear rate mixers.
The invention seeks to provide at least one of the following:
foamed concrete which can be used, for example as pre-cast blocks, in the
building or construction industries (including civil engineering, and roads) and which can
be pre-cast in plants (for example ready-mix concrete mixing plants) or on job sites;
foamed concrete of low density; foamed concrete having good thermal, acoustic
and/or mechanical properties;
cement slurries for preparing foamed concrete, the slurries having a low water
content compared to the same slurry without the admixtures used in the invention;
foamed concrete blocks which make it possible to substantially reduce thermal
bridging at, for example, slab edges, cross walls, wall ties and lintels (it may be possible
to reduce indoor or outdoor insulation);
foamed concrete blocks produced by moulding and setting at ambient
temperature, followed by hardening, for example under ambient conditions (for example
without heating), thereby reducing the energy necessary for their production and the
associated emissions of C0 2; and/or
foamed concrete with improved resistance to cracking when compared with known
blocks of similar density.
The present invention accordingly provides a foamed concrete having a density
from 200 to 800kg/m 3 comprising by mass relative to the total mass of the concrete
- a cement;
- water;
- from 0.01 to 5% of a water-reducing agent, plasticizer or superplasticizer;
- from 0.45 to 5% of a foaming agent relative to the amount of water;
- a water-soluble calcium salt;
comprising inorganic, e.g. mineral, particles from 0.1 to 300 mhi in size (preferably
selected from calcium carbonate, silica fume, slag, fly ash, pozzolan, glass and siliceous
fillers and mixtures thereof), the ratio of foaming agent to calcium salt being from 0.3 to
0.8; the foamed concrete comprising 10% or more by mass of slag.
In this specification including the accompanying claims the ratio of 0.3 to 0.8 is
calculated on the basis of anhydrous calcium chloride as the calcium salt. When a
different calcium salt is used the mass of calcium salt used to calculate the ratio is
the mass expressed in terms of the equivalent mass of anhydrous calcium chloride.
It is possible to recycle existing foamed concrete of the invention for reuse in the
production of new foamed concrete. The existing foamed concrete is crushed using
low energy crushing means to produce a particulate material generally having a
particle size from 200 to IOOOmhi . Up to about 10% by mass of the particulate
material can be incorporated into new foamed concrete, relative to the mass of the
new foamed concrete.
When the water-reducing agent, plasticizer, superplasticizer or foaming agent is
used in solution, the amount is the amount of active ingredient in the solution.
The calcium salt may be a hydrate or anhydrous: when a hydrate is used the
amount is expressed in terms of the anhydrous material.
The foaming agent is preferably an anionic foaming agent, for example a sulfonate
or sulfate, and is more preferably selected from an alkyi sulfonate, an alkyi ether
sulfonate, a hydroxyalkyl ether sulfonate, an alpha olefin sulfonate, an alkyi
benzenesulfonate, an alkyi sulphate, an alkyi ether sulphate, a hydroxyalkyl ether
sulphate, an alpha olefin sulphate and an alkyi benzenesulphate, or a mixture thereof.
The alkyi sulphate or alkyi ether sulphate preferably has the formula:
C H2n+1-(OCH2CH2)m-OS0 3M (I)
in which n is from 8 to 14, the grouping CnH2n+ i is linear or branched, m is from 0 to 15,
and M represents an alkali metal. M preferably represents sodium or potassium, more
preferably sodium; m is preferably from 0 to 10, for example 0 to 9.
The preferred foaming agent is a linear or branched alkyi ether sulphate of formula
(I) in which n is from 8 to 12, preferably from 10 to 12, for example 9 to 11, and m is
from 1 to 6.
The grouping CnH2n+1 is preferably linear.
The foaming agent may be a mixture of alkyi ether sulphate and alkyi sulphate.
Each alkyi ether sulphate and alkyi sulphate may itself be a mixture of compounds
according to formula (I).
The term "water-soluble calcium salt" in this specification including the
accompanying claims is to be understood as a salt having a solubility in water at 20°C
greater than 2g/100ml. Such salts generally have an anion which is acceptable for use
in cement-containing aqueous compositions at the concentrations used in the invention.
The water-soluble calcium salt is preferably calcium chloride, calcium nitrite, calcium
nitrate, calcium formate, calcium acetate or a mixture thereof. Calcium chloride, calcium
formate and calcium nitrate are preferred.
The water-soluble calcium salt used in the invention may be in a solid, e.g.
powder, or liquid, e.g. aqueous solution, form.
The ratio of foaming agent to water-soluble calcium salt is preferably from 0.4 to
0.8, for example 0.45 to 0.75, preferably from 0.45 to 0.65, more preferably from 0.45 to
0.6, most preferably from 0.45 to 0.55.
The foamed concrete according to the invention preferably has a density from 300
to 700kg/m 3, more preferably from 400 to 600kg/m 3, most preferably from 450 to
550kg/m 3.
The foamed concrete of the invention generally comprises from 30 to 90% by
volume of a gas, e.g. air, more preferably from 60 to 80% by volume. The air may be in
the form of micro-cells and give the block an alveolar structure providing thermal
insulating properties ("distributed insulation"). The micro-cells may be, for example, 0.5
to 1mm in size. The air is generally trapped homogeneously in the mass of the material
and assumes an insulating role.
Cements suitable for use in the present invention include Portland cement,
calcium aluminate cement, magnesium based cement, calcium sulfo-aluminate cement,
and mixtures thereof.
The preferred Portland cements are those defined in the EN 197-1 Standard, more
preferably cements comprising calcium carbonate, silica fume, slag, fly ash, pozzolan,
glass or siliceous filler or mixtures thereof. Such cements include Portland cement (CEM
I); Portland slag cement; Portland-silica fume cement; Portland-pozzolana cement;
Portland-fly ash cement; Portland-limestone cement; and Portland-composite cement
preferably comprising calcium carbonate, silica fume, slag, fly ash, pozzolan, glass or
siliceous filler or mixtures thereof; pozzolanic cement; and composite cement. It will be
understood that the mineral particles present in the foamed concrete of the invention
may already be present in the cement if a blended cement is used.
The preferred calcium aluminate cements are, for example, the Ciments Fondus®,
the aluminate cements, and cements according to the NF EN 14647 Standard.
The preferred magnesium based cements may include magnesium carbonates,
magnesium oxide or magnesium silicates, for example as disclosed in US patent
n°4,838,941 .
The preferred cement for use in the invention is a Portland cement, either alone or
in combination with any one of the other aforementioned cements, for example a
calcium sulfoaluminate cement. The ratio of cement (expressed as ground clinker) to the
inorganic particles in the foamed concrete of the invention is preferably from 30/70 to
50/50, more preferably 35/65 to 50/50, most preferably about 35/65.
The water/cement (W/C) ratio (in which cement is expressed as ground clinker) in
the foamed concrete of the invention is preferably from 0.3 to 0.9, more preferably 0.4 to
0.7, most preferably about 0.45.
The amount of water reducing agent, plasticizer or superplasticizer is preferably
0.01 to 0.2%, more preferably 0.02 to 0.08%.
The water/cement weight ratio of the foamed concrete according to the invention
may vary depending, inter alia, on water demand of the mineral particles used. The
water/cement ratio is defined as the weight ratio of the amount of water (W) to the
weight of the cement (C). In the Concrete Admixtures Handbook, Properties Science
and Technology, V.S. Ramachandran, Noyes Publications, 1984:
A water reducer is defined as an additive which reduces the amount of mixing water of
concrete for a given workability by typically 10 - 15%. Water reducers include, for
example lignosulphonates, hydroxycarboxylic acids, carbohydrates, and other
specialized organic compounds, for example glycerol, polyvinyl alcohol, sodium
alumino-methyl-siliconate, sulfanilic acid and casein.
Superplasticizers belong to a new class of water reducers chemically different from the
normal water reducers and capable of reducing water contents by about 30%. The
superplasticizers have been broadly classified into four groups: sulphonated
naphthalene formaldehyde condensate (SNF) (generally a sodium salt); or sulphonated
melamine formaldehyde condensate (SMF); modified lignosulfonates (MLS); and others.
More recent superplasticizers include polycarboxylic compounds such as polyacrylates.
The superplasticizer is preferably a new generation superplasticizer, for example a
copolymer containing polyethylene glycol as graft chain and carboxylic functions in the
main chain such as a polycarboxylic ether. Sodium polycarboxylate-polysulphonates
and sodium polyacrylates may also be used.
Preferably, the foamed concrete according to the present invention comprises a
superplasticizer, for example a PCP superplasticizer. The term "PCP" or
"polycarboxylate polyoxide" is to be understood according to the present invention as a
polymer or copolymer of acrylic and/or methacrylic acids, and of their esters of
poly(ethylene oxide) (PEO).
The foamed concrete of the invention preferably does not comprise an antifoaming
agent. Some commercial superplasticizers may contain antifoaming agents and
may be unsuitable for use in the invention.
The inorganic particles in the foamed concrete of the invention are preferably
calcium carbonate, silica fume, slag, fly ash, pozzolan, preferably a naturally-occurring
pozzolan, glass, e.g. as crushed glass or beads, and siliceous fillers, or mixtures
thereof.
Suitable particles comprising fly ash include those from North America (Lafarge, Will
County, Illinois): particle size D5o=6^m.
Suitable particles comprising a pozzolan include Superpozz from South Africa: particle
size D5o=3^m.
Suitable particles comprising a naturally-occurring include pozzolan from Greece (Yali):
particle size D5o=10^m.
The inorganic particles vary in their thermal conductivity. In general slag has a
lower thermal conductivity than fly ash which has a lower thermal conductivity than
naturally-occurring pozzolan which has a lower thermal conductivity than limestone.
The inorganic particles are preferably from 1 to IOOmhh , for example from 1 to
dqmhh in size. The D 0 of the particles is preferably from 1 to 4mh . The D50 of the
particles is preferably from 4 to 20mh , more preferably from 6 to 15mh . The D90 of the
particles is preferably from 12 to IOOmhh .
Preferably, the concrete of the invention further comprises hydrated, hemi
hydrated or anhydrous calcium sulphate.
Preferably, the foamed concrete of the invention further comprises lime.
The foamed concrete of the invention preferably further comprises a foamstabilizing
agent, for example a betaine, an amine oxide or a fatty amide.
Other additives may also be used, for example a retarder, e.g. citric acid.
The invention also provides a process for the production of a foamed concrete
according to the invention which process comprises:
(a) mixing :
a cement;
water;
from 0.01 to 5% of a water-reducing agent, plasticizer or
superplasticizer;
from 0.45 to 5% of a foaming agent relative to the amount of
water;
a water-soluble calcium salt;
inorganic, e.g. mineral, particles from 0.1 to 300mhi in size
(preferably selected from calcium carbonate, silica fume, slag, fly
ash, pozzolans, glass and siliceous fillers and mixtures thereof),
the ratio of foaming agent to calcium salt being from 0.3 to 0.8;
(b) introducing a gas, preferably air, into the mixture obtained in step (a)
to form a foamed concrete; and optionally
(c) moulding the foamed concrete and letting it set.
A foamed concrete element (i.e. a foamed concrete in shaped form), for example a
block, may thus be obtained.
The foamed concrete will continue to harden with time after setting. The
hardening process need not be fully complete before demoulding. It will be understood
that the element can be demoulded when it has sufficient mechanical strength to retain
its shaped form.
In a preferred embodiment of the invention all of the air introduced in step (b)
remains in the foamed concrete.
The moulded element may be a preform which, after moulding, is cut to produce
an element of the desired shape, e.g. a block. The element is preferably kept in such a
way as to prevent or reduce early loss of water: for example the element may be
covered by a water-impermeable, e.g. plastics sheet; or the element may be allowed to
harden in a humid atmosphere, preferably at a controlled relative humidity, more
preferably greater than 80%, generally for at least 24 hours.
The mixing step in the process of the invention preferably comprises an initial
mixing and, preferably, deflocculation step; preferably the mixture obtained from the
initial mixing and deflocculation is subjected to a further mixing at a high shear rate.
The process according to the present invention preferably does not comprise an
autoclaving step.
The period of time before setting in step (c) of the process of the invention is
preferably from 1 to 7 hours, for example about 2 hours.
The mixing step (a) generally produces a cement slurry.
Generally step (a) is carried out according to one of the following methods:
- the components are added at the same time as the water and/or in the water; or
- the solid components are mixed in a dry form before adding the water.
Preferably the ingredients (except for the foaming agent) and part of the water are
mixed first; at this stage the ingredients are uniformly mixed and deflocculation occurs.
The foaming agent and the remainder of the water are then added and further mixing is
effected. Addition of the foaming agent and the remainder of the water increases the
fluidity of the mixture and facilitates the further mixing, for example at a high shear rate.
The step (b) of introducing a gas may be carried out in different ways, for example
by direct introduction of the gas or by the introduction of a dispersion of a gas phase in a
liquid (a foam), generally an aqueous liquid. A foaming agent is required to produce the
foam. The foaming agent used is preferably anionic or non-ionic; it may be the same as
or different to the foaming agent used in step (a) to prepare the foamed concrete
according to the invention.
According to a feature of the process of the invention, the gas may be introduced
directly into a liquid mixture of the ingredients of the concrete of the invention, for
example before or during mixing at a high shear rate. In particular the process of direct
injection of air described in patent application WO2005/080294 is particularly suitable.
The gas, is introduced under pressure into the mixture obtained in step (a): the
pressure is preferably from 1 to 5 bars gauge. The gas is preferably introduced after the
initial mixing at a low shear rate and before or during the mixing at a high shear rate.
According to a further feature of the invention, the introduction of the gas may be
carried out by the introduction of a dispersion of the gas in a liquid, in particular by
introduction of a gas foam in water. The air dispersion in water may be directly
introduced into the composition according to the present invention then mixed in a static
mixer, in batches or continuously.
The density of the foamed concrete according to the invention may be adjusted by,
for example, adjusting the amount of air introduced at the foaming step and/or adjusting
the speed of the mixer used to produce the foam.
In this feature of the invention the mixture of the step (a) is preferably made at a
concrete mixing plant. The mixture is then placed in a mixer truck (for example a drum
truck) then a foam is added either directly in the truck or directly on the jobsite when the
truck arrives. The foamed slurry is then poured into a mould.
The invention also provides a shaped element, for example a building block
comprising the foamed concrete according to the invention; the use of such a block in
the construction field; the use of such a block in the production of pre-fabricated items
for the construction field; and a pre-fabricated item for use in the construction field
comprising a block according to the invention.
The foamed concrete according to the invention can be used to produce blocks
that are intended for carcassing work and also for light-weight construction works. The
blocks may be in various forms, for example in the form of bricks, such as alveolar
bricks, of various sizes and thicknesses. The blocks have the advantage of being easy
to handle, and in particular of generally being able to be cut with a manual saw. It is also
generally possible to sand the surface of a block for example, using a sanding board if
there is an undesired protrusion.
The foamed concrete according to the invention can also be used to produce castin-
place concrete element including cement-based panels.
The foamed concrete blocks according to the present invention are generally in
the form of a rectangular parallelepiped; they are normally grey in colour. Other colours
are possible by incorporating colouring agents into the mixture used to prepare the
foamed concrete and/or by using a lighter-coloured cement having, for example, a low
iron content. A range comprising blocks, lintels, floor and roof slabs, and panels for
partition walls makes it possible to build a substantially complete house of lightweight
concrete according to the invention. The density of the block can be adapted according
to its function. The laying of the material can be rapid and 3m2/hour may be produced for
a solid wall by assembly using a mortar glue (the "thin joint" laying method which
reduces thermal bridging). It is also possible to assemble the blocks using a known
mortar following a conventional laying procedure.
The foamed concrete according to the present invention generally has good
thermal properties, and in particular low thermal conductivity. The thermal conductivity,
lambda (l) , of a material represents the quantity of heat transferred per unit of surface,
per unit of time per unit of temperature gradient. In the international system of units,
thermal conductivity is expressed in watts per metre Kelvin, (W/m.K). Conventional
concretes have a thermal conductivity at 23°C and 50% relative humidity of between 1.3
and 2.1 . Typical known lightweight structural concretes have thermal conductivities
generally higher than 0.8W/m.K at 23°C and 50% relative humidity. The foamed
concrete according to the present invention generally has a thermal conductivity from
0.05 to 0.6W/m.K, preferably from 0.05 to 0.4W/m.K, more preferably from 0.05 to
0.25W/m.K, most preferably from 0.1 to 0.2W/m.K.
The foamed concrete block according to the present invention generally has good
acoustic properties, and in particular low phonic conductivity.
The foamed concrete according to the invention generally has good mechanical
properties, and in particular good compressive strength. The compressive strength is
generally from 1 to 10MPa, preferably from 2 to 8MPa, more preferably from 2 to 4MPa,
most preferably about 3MPa.
Brief description of the Figures: The accompanying Figures illustrate the invention
without restricting its scope. Figure 1 represents the relationship between the viscosity
and the shear rate for different pastes in which different specific admixtures were added.
The reduction in viscosity values in compositions according to the invention may be
demonstrated by measuring viscosity values in known manner. Viscosity values may be
measured at 23°C in a cylindrical Couette rheometer (Haake RS600), equipped to limit
sliding at the edges (as is common practice in rheometry). A steady state rotation of the
mobile part at a shear rate of typically 400 sec 1 is achieved for 2 minutes. Then shear
rate is allowed to ramp logarithmically ascending from 0 to 200 sec 1 in 70 sec, kept
steady for 10 sec and allowed to ramp logarithmically descending from 200 to 0 sec 1 in
70 sec. Viscosity data are measured in the descent.
Figure 2 is a diagram of a process for the production of a foamed concrete
element according to the present invention with direct introduction of air.
Referring to Figure 2, the process of the invention comprises the preparation of a
batch-made slurry ( 1 ) comprising cement, inorganic particles (additions), admixtures,
water, accelerator (the calcium salt), and a foaming agent. The process comprises
continuous foaming (2) with introduction of air in the dynamic Mondomix mixer, and
finally the pouring/forming of the lightweight concrete (3).
It is to be understood that, unless otherwise specified, in this specification including the
accompanying claims:
1. Percentages are by mass.
2. Compressive strengths are as measured on 10cm by 10cm by 10cm ( 1 litre)
blocks 28 days after their production. During the 28 days the blocks were
covered with a plastics sheet. The blocks were maintained in a drying oven at
45°C and 10% relative humidity for 24 hours before the test. They were then
crushed in a Zwick™ (PRES-018) press raising the pressure at a rate of 1000
Newtons/second until the block broke.
3. Thermal conductivities are as measured on 10cm by 10cm by 10cm ( 1 litre)
blocks 28 days after their production. During the 28 days the blocks were
covered with a plastics sheet. The blocks were maintained in a drying oven at
85°C for 48 hours before the test. Thermal conductivity is measured using a
thermal conductivity measuring device (CT metre). A 1 litre block is cut in half. A
calibrated measurement cell is placed and fastened between two flat sides of the
cut block. The heat is transmitted from the source towards the thermocouple by
the material surrounding the cell. The rise of temperature at the thermocouple
level as well as the energy transmitted by the source of heat, measured as a
function of time, allows calculation of the thermal conductivity of the block
material surrounding the measurement cell.
4. Particle size and size distribution (between 0.02 mhi and 2mm) are as measured
using a Malvern MS2000 laser granulometer. Measurement is effected in
ethanol. The light source consists of a red He-Ne laser (632nm) and a blue diode
(466nm). The optical model is that of Mie and the calculation matrix is of the
polydisperse type.
The apparatus is checked before each working session by means of a standard
sample (Sibelco France (formerly known as Sifraco) C10 silica) for which the
particle size distribution is known.
Measurements are performed with the following parameters: pump speed
2300rpm and stirrer speed 800rpm. The sample is introduced in order to
establish an obscuration between 10 and 20%. Measurement is effected after
stabilisation of the obscuration. Ultrasound at 80% is first applied for 1 minute to
ensure the de-agglomeration of the sample. After about 30s (for possible air
bubbles to clear), a measurement is carried out for 15s (15000 analysed
images). Without emptying the cell, measurement is repeated at least twice to
verify the stability of the result and elimination of possible bubbles.
All values given in the description and the specified ranges correspond to
average values obtained with ultrasound.
The expression "hydraulic composition" is to be understood according to the
present invention as a mix of a hydraulic binder, with water, optionally aggregates,
optionally admixtures according to the EN 934-2 Standard, and optionally additions. The
expression "hydraulic composition" according to the present invention denotes a
composition in the fresh, set or hardened state. More preferably, the hydraulic
composition according to the present invention is a cement slurry. A hydraulic
composition may for example be a concrete such as self-placing concrete, self-levelling
concrete, self-compacting concrete, fibred concrete, ready-mix concrete, jobsite
concrete, lightweight concrete, pre-cast concrete, or coloured concrete. The expression
"ready-mix concrete" is to be understood according to the present invention as a
concrete having sufficient open workability time to allow for the transport of the concrete
to the jobsite where it will be cast. The term "concrete" according to the present
invention denotes freshly mixed concrete, set concrete or hardened concrete.
The term "addition", is to be understood according to the present invention as the
inorganic particles from 0.1 to 300mhi in size. The term "setting", is to be understood
according to the present invention as the passage to the solid state of the hydraulic
binder by hydration reaction. The setting is generally followed by a hardening period.
The term "hardening", is to be understood according to the present invention as
the acquisition of mechanical strength of a hydraulic binder. The hardening generally
takes place after the end of the setting.
The expression "elements for the construction field", is to be understood according
to the present invention as any element of a construction, for example a floor, a screed,
a foundation, a basement, a wall, a partition wall, a wall lining, a ceiling, a beam, a work
top, a pillar, a concrete block, a block of lightweight concrete, a post, a cornice, a mould,
a coating, a jointing compound, an insulating element (acoustic and/or thermal).
The term slag denotes a slag which: preferably comprises at least two thirds by
mass of glassy slag; preferably has hydraulic properties when activated in known
manner; preferably comprises at least two-thirds by mass of the sum of calcium oxide
(CaO), magnesium oxide (MgO) and silicon dioxide (Si0 2) , the remainder preferably
comprising aluminium oxide (Al20 3) ; the ratio by mass (CaO+MgO)/ (Si0 2) is preferably
greater than one.
The compositions of the invention are referred to as "foamed concrete" in view of
their mechanical properties and the nomenclature generally used in this technological
field. They do, however, differ from conventional concrete in that they do not contain
coarse aggregate.
The following Example illustrates the invention without restricting its scope.
EXAMPLE 1
Materials:
Millifoam H: an anionic foaming agent (alkyl ether sodium sulphate) supplied by the
Huntsman company. Calcium chloride: pure anhydrous CaCI2 from Verre Labo Mula.
The Portland cement in Table 1 is a CEM I 52.5 R cement from the Lafarge Port La
Nouvelle cement plant (Batch No. LHY-3830 or LHY-3867).
The CEM I 52.5 R cement in Table 3 is from China and comprises 80% ground clinker,
13.4% slag with 6.6% filler.
The CEM III cement in Table 3 is Lafarge Le Havre (66% slag + 33% cement).
The inorganic particles in Table 1 are calcium carbonate supplied by the OMYA
company under the brand name of Betocarb HP Entrains in which the D50 is 7.8mh , the
D-io is 1.7mh , the D90 is 93mhi and with a maximum particle size of 200mhi (Batch No.
ADD-0239).
The inorganic calcium carbonate particles in Table 3 are limestone filler from Lafarge,
Nanshan, Chongqing area, China:
The inorganic ground slag particles are from Lafarge, Nanshan, Chongqing area, China:
D50 very close to 10 mhi ; plasticizer is a product comprising a
polycarboxylate polyoxide (PCP) supplied by the Chryso company: it is based on Premia
180 but does not contain an antifoaming agent.
Water: tap water.
Cement slurries
The cement, the inorganic solids and the calcium salt were weighed together on a
scale. The mixing water and the plasticizer (Chrysolab) were then weighed separately.
The Millifoam was weighed separately. All the weighed powders were placed in a mixer
(Rayneri™ MALX-104, Rayneri VMI, model PH602, serial no. 121025) and were stirred
for one to two minutes using the mixer's rotating blade with a planetary motion (17
revolutions/minute). The mixing water comprising the fluidizer was added to the powders
in the pan of the mixer (33 revolutions/minute for one to two minutes, depending on the
volume). A cement slurry was thus obtained, which was stirred for two additional
minutes in the mixer. The mixer was stopped. The pan of the mixer was scraped and the
Millifoam was poured onto the surface of the cement slurry. Mixing was resumed to
incorporate the Millifoam in the slurry (the speed varying from 17 to 25
revolutions/minute for approximately two minutes). The cement slurry obtained
(Formulation A) was ready to be foamed. Table 1 below presents the chemical
composition of Formulation A.
Table 1
Formulation A
Ingredients
Millifoam H 1.45
CaCI2 0.8
CEM I 52.5 R Cement 40.13
CaC03 39.74
Chrysolab 0.16
Water 17.72
Ratio of Millifoam/CaCb 0.49
Amounts in Table 1 are given in % by mass relative to the tota mass of the formulation.
The amount of Millifoam is the amount of commercial product which contains 27%
of active material. The ratio of Millifoam to calcium chloride given in the Table is of
active material to calcium chloride.
Following the procedure used to prepare Formulation A six further cement slurry
formulations were prepared using the ingredients listed in Table 2 below. Figure 1
shows the relationship between the viscosity and the shear rate for the six cement slurry
formulations Six such formulations were tested as listed in the following Table (the
figures given in the Table are the same as those listed in Figure 1 itself). The sixth
formulation is the same as the fifth and represents a rerun carried out by way of
confirmation: it will be seen that the results are very similar. The two plots for the fifth
and sixth formulations follow each other closely and demonstrate a substantial drop in
viscosity.
Table 2
' The amount of binder is the combined amount of cement and calcium carbonate.
2 Chrysolab
Millifoam H: the percentage is that of the active ingredient itself
All of the compositions contained superplasticizer (Chrysolab). Relative to the use
of superplasticizer alone:
the use of a low dose of calcium chloride (1%) did not significantly reduce viscosity;
the use of a higher dose of calcium chloride ( 1 .82%) led to an increase of viscosity;
Millifoam alone reduced the viscosity;
however the combination of Millifoam with the calcium salt produced a combined effect
by which the viscosity was greatly reduced. In Figure 1 both the ordinate and abscissa
are logarithmic scales: it will be seen that the viscosity can be reduced by a factor of
more than 10.
Lightweight concrete
Lightweight concrete was prepared continuously. Using the procedure to prepare
Formulation A described above, but using the ingredients listed in Table 3, three cement
slurries (Formulations 1, 2 and 3) were prepared. Amounts in the Table are in kg for
1m3.
Table 3
The cement slurry thus obtained was poured into a holding vessel and stirred
using a Rayneri Turbotest mixer (MEXP-101 , Rayneri VMI, model Turbotest 33/300,
serial no.71815) comprising a deflocculating blade (the speed of the blade varied from
1000 revolutions/minutes to 400 revolutions/minutes depending on the volume of slurry).
The slurry was pumped using a volume pump of the Moineau type (off-centre screw
pump, Seepex™ MEXP-413, model BN-025-12, serial no. 243327) at an approximate
flow rate of 1 litre/minute. The slurry was introduced into a foamer (Mondomix™ MALX-
160, Minimondo A05, serial no.P14018-371 15) to which compressed air (supplied by a
Brooks air mass regulator, smart mass flow 5850S, serial no.T55329/028) was added at
a flow rate of 2.75 litres/minute. The flow rate was adapted to the density of the desired
foam at the outlet of the foamer, generally from 1 to 4 litres/minute. The rotation speed
of the foamer was 400 revolutions/minute: the rotation speed was adapted to the density
of the desired foam at the outlet of the foamer and may vary from 250 to 1500
revolutions/minute. The foam thus obtained was used to prepare a lightweight concrete.
Blocks of lightweight concrete
- Block size: 10 X 10 x 10cm (volume 1 litre):
The foams obtained as described above were poured into polystyrene moulds 10
X 10 x 10cm in size at ambient temperature (20 - 23°C). They were stored for 12 to 24
hours, the blocks being covered by a plastic film. They were then demoulded. Blocks
were thus obtained.
- Block size: 25 X 33 x 50cm (volume 4 1.25 litres): (a commercial size block used
for building).
The previously obtained foams were poured into wooden moulds 25 X 33 x 50cm
in size at ambient temperature (20 - 23°C). They were left on stand-by for 12 to 24
hours, the blocks being covered by a plastic film. They were then demoulded. Blocks
were thus obtained.
Mechanical strength
The mechanical strength was tested 7 days and 28 days after making the 1 litre
blocks. The blocks were maintained in a drying oven at 45°C and 10% relative humidity
for 24 hours before the test. They were then crushed by a Zwick™ (PRES-018) press
raising the pressure at a rate of 1000 Newtons/second until the block broke. Table 4
below presents the maximum strengths at the breaking point for blocks made using the
same procedure as for formulations 1, 2 and 3.
Table 4
(1) Maximum strength at the breaking point of the block at 28 days.
(2) The formulations comprised CEM I 52.5 R cement from China as in Table 3 and
slag.
(3) The formulations comprised CEM I 52.5 R cement from China as in Table, slag
and calcium carbonate.
(4) The formulations comprised CEM III Le Havre cement.
Thermal conductivity
The thermal conductivity of the blocks was measured using a thermal conductivity
measuring device (CT metre). The blocks were maintained in a drying oven at 85°C for
48 hours before the test. A 1 litre block was cut in half. A calibrated measurement cell
was placed and fastened between two flat sides of the cut block. The heat was
transmitted from the source towards the thermocouple by the material surrounding the
cell. The rise of temperature at the thermocouple level as well as the energy transmitted
by the source of heat, measured as a function of time, made it possible to calculate the
thermal conductivity of the block material surrounding the measurement cell.
Table 5 below presents the thermal conductivities for the blocks of formulations 4
to 1 .
Table 5

CLAIMS
received by the International Bureau on 20 July 201 1 (20.07.201 1)
1. Afoamed concrete having a density from 200 to 800kg/m 3 comprising by mass
relative to the total mass of the concrete
- a cement;
- water;
- from 0.01 to 5% of a water-reducing agent, plasticizer or superplasticizer;
- from 0.45 to 5% of a foaming agent relative to the amount of water;
a water-soluble calcium salt having a solubility in water at 20°C greater than
2g/100ml;
comprising inorganic particles from 0.1 to 300 m h in size;
the ratio of foaming agent to calcium salt being from 0.3 to 0.8; the foamed concrete
comprising 10% or more by mass of slag particles.
2. The foamed concrete according to claim 1 in which the inorganic particles comprise
calcium carbonate, silica fume, slag, fly ash, pozzolan, glass, siliceous filler ora
mixture thereof.
3. The foamed concrete according to claim 1 or 2 having a density from 300 to
700kg/m 3.
4 . The foamed concrete according to any one of the preceding claimscharacterised in
that the foaming agent is selected from an alkyi sulfonate, an alkyi ether sulfonate, a
hydroxyalkyl ether sulfonate, an alpha olefin sulfonate, an alkyi benzene sulfonate,
an alkyi sulphate, an alkyi ether sulphate, a hydroxyalkyl ether sulphate, an alpha
olefin sulphate and an alkyi benzene sulphate and mixtures thereof.
5. The foamed concrete according to any one of the preceding claims characterised in
that the foaming agent is an alkyi sulphate or an alkyi ether sulphate of the formula
C H2n+1-(OCH 2CH2)m-OS0 3M
in which n is from 8 to 14, the grouping CnH2n+1 is linear or branched, m is from 0 to
15, and M represents an alkali metal.
6. The foamed concrete according to any one of the preceding claims characterised in
that the foaming agent is a linear or branched alkyi ether sulphate of formula (I)
depicted in claim 5in which n is from 10 to 12 and m is from 1 to 6 .
7. The foamed concrete according to any one of the preceding claims characterised in
that the foaming agent is a mixture of alkyi ether sulphate and alkyi sulphate.
8. The foamed concrete according to any one of the preceding claims characterised in
that the water-soluble calcium salt is selected from calcium chloride, calcium formate
and calcium nitrate and mixtures thereof.
9. A process for the production of a foamed concrete according to claim 1 characterised
in that it comprises:
(a) mixing :
a cement;
water;
fromO.01 to 5% of a water-reducing agent, plasticizer or
superplasticizer;
from 0.45 to 5% of a foaming agent relative to the amount of water;
a water-soluble calcium salthaving a solubility in water at 20°C greater
than 2g/100ml;
inorganic particles from 0.1 to 300m h in size;
the ratio of foaming agent to calcium salt being from 0.3 to 0.8;
(b) introducing a gasinto the mixture obtained in step (a) to form a foamed
concrete; and optionally
(c) moulding the foamed concrete and allowing it to set.
10. A process according to claim 9 characterised in that the foamed concrete produced
in step (b) is moulded and allowed to set to produce a preform; and the perform is
cut into blocks.
11. The process according to claim9or 10 characterised in that it does not comprise an
autoclaving step.
12. The process according to claim9 or 10 in which the time before setting in step (c) is
from 1 to 7 hours.
13. The process for the production of a foamed concrete according to any one of
claims9 to 12 characterised in that, after step (c),the foamed concrete is allowed to
harden in a controlled humid atmosphere the relative humidity of which is greater
than 80%.
14. Use of a foamed concrete according to any one of claims 1 to 8in the construction
field.
15. Afoamed concrete according to any one of claims 1 to 8 in shaped form.