Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
2000-06-15
2002-07-23
Wood, Elizabeth D. (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106S819000, C423S556000, C423S625000, C423S629000
Reexamination Certificate
active
06423133
ABSTRACT:
The present invention relates to aqueous suspensions comprising at least one alkaline compound (B) in combination with silica and/or alumina, to a process of use in the preparation of these compositions and to their uses in the field of cement pastes, mortars and concretes and in particular as setting and hardening accelerating agent for cements.
Conventionally, in the concrete industries, concrete or mortar layers are applied on a substrate or surface to be concreted with the help of two spraying techniques, one by the dry route and the other by the wet route.
Processes for concrete spraying by the dry route employ a dry mixture comprising all the conventional anhydrous components of a concrete or of a mortar. This is transported to a spray nozzle, where wetting with the mixing water is then carried out. A setting accelerating agent is generally added upstream or at the spray nozzle and the mixture obtained is sprayed onto the surface to be concreted. Unfortunately, with this type of process, a phenomenon of rebound of the concrete occurs which is harmful economically and which, furthermore, represents a risk to the safety of the operator carrying out the spraying.
The process for spraying by the wet route, which employs a cement mixture which is usually thoroughly wetted, allows the two problems mentioned above to be partly solved. However, the presence of an excess amount of water affects the relative density of the concrete or mortar and, on the other hand, the introduction of a setting accelerating agent in order to compensate for this effect is harmful to the mechanical strength over time of the concrete or mortar, once it has been sprayed.
Provision has recently been made, in Patent Applications EP 736,489 and EP 736,501, for the use of mixtures based on silica and on aluminium sulphate, which are provided in the form of a reversible gel, as substitution products for conventional setting accelerating agents in the concrete industries. This type of additive advantageously proves to be less corrosive than conventional setting accelerating agents and is furthermore satisfactory economically. On being present in the sprayed concrete, it significantly reduces the phenomenon of rebound mentioned above.
The Applicant has unexpectedly found a novel family of aqueous compositions based on specific aluminium derivatives which have an even better performance than those disclosed in Patent Application EP 736,501.
The first subject-matter of the present invention is thus an aqueous suspension comprising:
A) silica and/or alumina particles, and
B) a compound of general formula (I):
Al(OH)
a
(SO
4
)
b
(SiO
x
)
c
(Y)
d
(I)
with:
a between 0.1 and 2,
b between 0.3 and 1.5,
c between 0 and 0.1,
d greater than 0.05,
Y chosen from alkali metals and alkaline earth metals,
x between 2 and 4, and its derivatives,
the said compound (B) being present in the suspension at a concentration of at least 1.65 mol/l, expressed as moles of aluminium issued from the said compound.
Y preferably represents a sodium atom.
The Applicant has unexpectedly found that the use of an aqueous suspension as defined above significantly increases the kinetics of curing of cement pastes, concrete or mortar, in comparison with conventional setting accelerating agents.
The examples presented below illustrate more specifically this setting accelerating effect of the suspensions according to the invention.
The compound (B) of general formula (I) comprises soluble species and solid species.
The soluble species are generally ions, indeed polyions, such as hydrolysis complexes, aluminium poly-sulphates, which optionally comprise silicates. The soluble species can be present individually within the solution or adsorbed on the silica or alumina particles.
The solid species are particles, of micron or nanometric size, of Al(OH)
3
, AlOOH and/or Al
3
(OH)
6
(S
4
)
2
Na, for example. In general, at least a portion of these solid species are amorphous, the others being crystal- line. These solid species can be dispersed within the dispersion or can interact with the silica or alumina particles.
According to a preferred embodiment of the invention, the compound (B) exhibits an amorphous structure after having been dried, the said structure representing at least 15% by weight of the compound (B).
More preferably, the compound (B) present in the claimed aqueous suspensions is at least partially in the form of an amorphous dispersed solid.
The amorphous nature of the dispersed solid is, within the meaning of the invention, that determined by X-rays. More specifically, the monitoring method is X-ray diffraction. On the X-ray spectrum, the amorphous nature is reflected by the presence of halos instead of the main lines. Monitoring can be carried out either on the dried suspension or on the suspension as is.
In the first case, the suspension is dried at room temperature so as to remove the free water but to retain the water of constitution of the components of the suspension. The X-ray spectrum obtained on the dry solid opens the way to the amount of crystalline solid and thus, by difference, to the amount of amorphous solid. It is necessary to remove, from this amount of amorphous solid, the amount of silica (it is amorphous) in the suspension, in order to obtain the amount of amorphous compound (B).
In the second case, the X-ray analysis is carried out directly on the aqueous suspension.
More preferably, the indices a and b present in the overall formula of the compound (B) are between approximately 0.75 and 2 and 0.3 and 1.2 respectively.
According to a preferred embodiment of the invention, the said suspension comprises approximately from 2.1 to 3.5 mol/l of aluminium, approximately from 2.25 to 4 mol/l of sulphate and approximately from 0.2 to 3.5 mol/l of silica.
The suspension according to the invention has a pH (measured according to ISO Standard 787/9) of between 2.5 and 4. According to a preferred embodiment of the invention, it has a value of between 3 and 4 and more preferably is of the order of 3.7.
The claimed aqueous suspensions advantageously constitute an optimum with respect to the compromise of the properties desired in the field of cements, mortars and concretes. These properties are accelerated hardening and setting kinetics and an increased mechanical strength of the cured grouts, mortars or concretes incorporating them.
An optimization in one of these kinetics is generally acquired at the expense of the mechanical strength, and vice versa. Surprisingly, the claimed aqueous suspensions significantly accelerate the hardening kinetics, in comparison with a conventional suspension based on a silica/aluminium sulphate mixture, without affecting the long-term mechanical properties of the mortars incorporating them. These properties remain entirely satisfactory. These results are presented in more detail in the examples below.
According to a privileged embodiment of the invention, the aqueous suspension comprises a compound (B) of general formula I in which a has a value of the order of 1.26±0.1, 0.5±0.1 or 0.88±0.1.
The aqueous suspensions comprising a compound (B) of general formula I in which a is between 0.1 and 1.5, with the said suspension comprising approximately from 2.2 to 3.1 mol/l of aluminium and approximately 2.3 to 3.9 mol/l of sulphate, are more particularly preferred.
Mention will very particularly be made, as representative of the claimed aqueous suspensions, of the suspensions described in the examples below.
According to a preferred alternative form of the invention, the claimed aqueous suspensions exhibit a silica concentration of between approximately 0.7 and 2.4 mol/l.
The compound (B) is used in combination, in the aqueous suspensions provided according to the invention, with at least one compound selected from:
a silica, chosen in particular from fumed silicas, precipitated silicas, silica sols, silica gels, pyrogenic silicas, silica compounds of natural or synthetic origin, aluminosilicates, smectites, magnesium silicates, clays, wollastonite, talc, mica, at
Chane-Ching Jean-Yves
Prat Evelyne
Touzet Sylvie
Burns Doane Swecker & Mathis L.L.P.
Rhodia Chimie
Wood Elizabeth D.
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