Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-11-27
2003-08-05
Egwim, Kelechi (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S543000, C106S737000, C106S788000
Reexamination Certificate
active
06602935
ABSTRACT:
The present invention relates to aqueous suspensions including precipitated silica and to their use in the preparatin of compositions based on cement or on similar inorganic binder or compositions derived therefrom.
The invention applies to all types of compositions including an inorganic binder such as cement, a slag or the like, as base ingredient or in combination with other constituents.
For the purpose of the present description “cement composition” will be intended to mean a composition based on cement or any other similar inorganic binder and water. These compositions constitute products which are used as they are, especially as coating, or else which are intended to incorporate especially inorganic fillers of variable particle size.
Such compositions enclosing an inorganic binder and an inorganic filler in granulate form are considered very generally as concretes.
Although the specialist customarily describes concrete more specifically as a composition in which the inorganic filler is based on relatively coarse granulates (of the order of 4 to 15 mm), and mortar as a composition in which the inorganic filler is based on less coarse granulates (smaller than 4 mm), the term “concrete” will be employed in the present description without any distinction to denote all kinds of compositions, whatever their particle size, in order to simplify the description.
It is desirable to have the ability to control the properties of these various compositions both during their manufacture and their use, as well as the products derived therefrom after setting.
Thus, concrete compositions for large structures (production of walls, veils, posts, cement finishes, slabs, industrial floors) must satisfy individual requirements with regard to:
rapid setting kinetics for early removal of shuttering;
low plastic shrinkage and absence of cracks particularly in the case of cement finishes;
good mechanical properties at 28 days;
durability (resistance to abrasion, low permeability to gases and to liquids);
leakproofing in the particular case of the underground concretes or marine concretes in contact with water.
In addition, the concretes may either be manufactured on the work site or manufactured in a central plant and transported to the site of use (concrete ready for use). In order that the composition may retain acceptable properties, even for a short period, its stability in the hydrated state must be ensured, especially by preserving its fluidity intact and by limiting the segregation of the materials in suspension.
More specifically, architectural concretes, that is to say visible concretes, must additionally satisfy requirements where aesthetics are concerned:
homogeneous surface appearance;
reduction of efflorescences which form surface salt deposits (in particular in the case of acid-treated concretes).
Prefabricated concretes for the production of facade components, paving stones, slabs and pipes must more particularly have a low permeability to gases and to liquids for an optimum durability, as well as the same aesthetic properties as the architectural concretes for the visible components.
The mortar or rendering compositions for the secondary work (finishing renderings, smoothing renderings, facade renderings, adhesive mortars, spray renderings) must themselves also satisfy a certain number of individual requirements:
good water retention to avoid the loss of water by entry into the porous substrate or by preferential surface drying (risk of cracking and of surface powder formation);
good adhesiveness to the substrate;
resistance to abrasion and impact strength;
good fluidity combined with good water retention (especially in the case of smoothing renderings), these contradictory properties being difficult to obtain together.
In general, during the utilization, critical parameters are the fluidity to ensure the processing, the degree of bleeding or the adhesiveness to the substrate and water retention.
To satisfy these requirements, appropriate additives are usually incorporated into cement compositions or in compositions derived therefrom. However, it is not rare for an additive to produce, besides the positive effect for which it is employed, a detrimental effect on another property. Thus, a plasticizing agent may improve the fluidity of a composition, but the high contents sometimes necessary to reach the desired result very clearly promote bleeding and diminish the setting kinetics and hence the acquisition of mechanical strength at an early age (fight against cracking, suitability for removal of shuttering, early commissioning, etc.).
Similarly, setting retarders which allow a composition to be conserved and transported for a certain time after its preparation also have a very marked effect on bleeding and on the setting kinetics.
Such difficulties appear in particular in the case of cement-based compositions and of self-levelling fluid concretes which, according to conventional specifications, must exhibit strict rheological characteristics in respect of settling (measured with the Abrams cone) or static or dynamic spreading.
The solutions which make it possible to obtain fluid concretes or mortars, and which are known so far, consist either in optimizing the particle size curve by the introduction of fines or of ultrafines as described in patent EP-A-0 184 386, this solution exhibiting, besides the awkwardness of making it necessary to handle large quantities of powder, the disadvantage of being highly sensitive to small variations in the content or quality of the products employed, which in practice makes it difficult to employ on a work site, or to add large quantities of plasticizers, retarders and optionally water-retaining agents to maintain the handleability of the material for a sufficient period, which generally entails a delay in setting which impairs the efficiency of the work site (delayed removal of shuttering or need for finishing in the case of early shuttering removal) and a great sensitivity to small changes around the optimized composition.
In practice, one is often confronted with problems of prohibitive decrease in the handleability in the event of metering error, of segregation of the mortar or of the concrete, of high bleeding, of lengthening of the setting time and of lowering of the final mechanical properties, in particular in the event of overdosing with water.
In fact, it is found very difficult to produce cement compositions or compositions derived therefrom, which meet all the essential requirements that are desired with a view to an application.
From U.S. Pat. No. 5,149,370 and GB-2 212 489 it was known to improve the bleeding and segregation properties of compositions by adding silica sols thereto. However, the properties of these compositions were still inadequate.
The present invention proposes to meet this demand for improved additives which make it possible to combine a number of advantageous properties from among those referred to above.
The aim of the invention is to provide a new additive for cement compositions or compositions derived therefrom, making it possible to decrease the bleeding and segregation effects of the concrete compositions.
A further object of the invention is to provide an additive making it possible to combine an improved fluidity, good water retention, even in the case of high contents of water and/or of fluidizing or plasticizing agents, and to impart a good durability to the set product, especially a reduction in the permeability to water and to gases, making it possible to reduce the efflorescences.
To this end, a further object of the invention is an aqueous suspension including a mixture of at least one aqueous suspension of precipitated silica and of at least one latex, in which the said aqueous suspension of precipitated silica has a solids content of between 10 and 40% by weight, has a viscosity lower than 4×10
−2
Pa s at a shear of 50 s
−1
, and, after centrifuging at 7500 revolutions per minute for 30 minutes, produces a supernatant containing more than 50% of the weight of the silica initia
Frouin Laurent
Prat Evelyne
Egwim Kelechi
Rhodia Chimie
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