The invention relates to a method in dry- shake coat- ing of a concrete floor as set forth in the preamble of an independent claim directed thereto .

Concrete floors with a dry shake finish, i.e. dry- shake floors, are commonly used in projects where the floor surface is required of abrasion resistance and strength. By reason of benefits obtained thereby, the dry shakes are particularly employed in heavy indus - trial applications, in which the concrete slabs are subjected to heavy impact and wheel loads and of which is required excellent flatness and abrasion re- sistance . It is because of these benefits that major advantages are also gained by dry shakes in the case of more lightly loaded concrete floors . Further, es- pecially when using fiber- reinforced concrete, it is by the application of dry shakes that the amount of fibers left on the surface of floor concrete can be reduced for a neater end result .

Dry shakes are floor surface hardeners , which are composed of mixtures of extra hard aggregates, cement and various additives and by which is obtained a sur- face abrasion resistance as high as fivefold with re- spect to a surface of just concrete . The dry shake materials have a grain size typically within the range of 0-4mm and differ from each other in terms of their aggregate materials . Typically employed aggre- gates include corundum, quartz, metallurgical slag, metal , silicon carbide or combinations of the above . Some products also involve the use of diabase , ena- bling especially the toughness of a dry shake to be increased.

On the other hand, the cement used in dry shakes is typically one with a high grade of strength. In this regard, it has been a highly common practice to use traditional Portland cement containing 95% Portland clinker and 5% minor additional constituents . In col- ored dry shakes , Portland cement is replaced with purer-than-that white cement capable of providing a more uniform color result . The hues of dry shakes are produced by using, among others , various inorganic color pigments .

The performance of a dry shake in concrete floor is based on a reaction of the cement within the dry shake with water by virtue of the very strong hydroscopicity of cement , enabling its reaction with water to generate heat and calcium silicate com- pounds . The cement within a dry shake material reacts with moisture present at the surface of concrete so as to "suck" moisture into itself , whereby, together with mechanical processing of the floor surface, the dry shake material builds a hard, water- insoluble and monolithic structure with the base concrete .

At the start of a dry-shake coating process , it is typically necessary that the cast and floated base concrete be subjected to early aftercare, the purpose being, among other things , to reduce plastic shrink- age in base concrete, to diminish reticular cracking in concrete surface, and to improve adherence of dry shake to substrate . The early aftercare is typically carried out with an early aftercare agent , which, in reference to what is presented in fig. la, is sprayed onto the surface of a base concrete floated after the casting. In this regard, it is also possible to em- ploy a plastic sheet or a filter fabric to be laid on top of the base concrete .

The application of a dry shake is carried out with a separate dispensing machine , a dispensing cart or by using a traditional concrete placer . When the appli- cation of a dry shake is performed with a dispensing cart or a traditional concrete placer, the surface of base concrete must be floated prior to spreading the dry shake . On the other hand, when the application of a dry shake is carried out with a dispensing machine , it is necessary that spreading of the dry shake be performed immediately over the surface of leveled and vibrated base concrete . Because the surface of base concrete is not in this case opened by grinding, the moisture migrated to the surface of base concrete in the wake of vibration must be sufficient for a dry shake to be applied, which is why spreading of the dry shake must take place as quickly as possible af- ter vibration.

After the application of a first dry shake layer, the dry shake surface must be troweled prior to applying a second dry shake layer thereon . After the second dry shake layer has absorbed moisture in itself from the underlying layer, its surface will be troweled after which the final surface smoothness and density is achieved typically by mechanical steel blade troweling, by using a so-called walk-behind and/or ride-on trowel machine . Steel blade troweling, i.e. o-called honing or blade-polishing, must be performed typically 2-3 times for providing a floor surface which is dense and for removing small irregularities therein should this be warranted by intended use of the floor.

The actual aftercare of a dry-shake coated concrete floor must be initiated immediately after completing the final troweling cycle, the purpose being to pre- vent excessively rapid drying of the base concrete and the dry shake finish and to provide optimal hard- ening conditions for the dry shake floor. Aftercare can also be used for protecting the floor surface e.g. against knocks and soiling. Aftercare is typi- cally performed with a sprayable aftercare agent , a plastic sheet, a wettable filter fabric , a water spray or a combination of these . The selection of an aftercare method is a result of condition factors as well as the size of an area to be covered.

In practice, the most common problems with dry-shake floors are as follows :

- excessively small amount of dry shake (kg/m ² ) ,

- dry shake has not adhered to base concrete every- where in a uniform manner (hollow tapping sound) ,

- color differences in dry shake , and

- differences in abrasion resistance .

Reasons for the above problems are typically as fol- lows : - excessively low moisture in base concrete ,

- diverse casting conditions (wind, sunshine, rain) ,

- use of plasticized concrete mass (in an effort to lower the water/cement-ratio of base concrete) ,

- use of air-entraining agent in base concrete mass, and

- use of blast-furnace slag, fly ash or excessively fine aggregate in base concrete mass .

In addition, if the white or light-colored dry shake surface is intended to be subsequently diamond-honed or polished for creating sufficient uniformity and gloss, it is highly critical that the amount of a dry shake material be at least 10 k/m ² . In case the amount of an employed coating is e . g. 4-6 kg/m ² , there is a high risk of the dry shake surface being completely or partially removed in the honing process so to ex- pose the metal fibers of e.g. an SFRC (Steel Fiber Reinforced Concrete) floor . Neither is an excessively thin dry shake surface capable of retaining its color but is discolored owing to the underlying concrete structure while being troweled.

It is an objective of the method according to the present invention to provide a decisive improvement regarding the foregoing problems and to thereby raise substantially the available prior art . In order to attain this obj ective, the method according to the invention is principally characterized by what has been presented in the characterizing clause of an in- dependent claim directed thereto. Most noteworthy important benefits offered by a meth- od of the invention include its simplicity and effec- tiveness, by virtue of which it is possible to pro- vide in the most diverse of installation conditions and in view of the most demanding of intended appli- cations a dry shake floor optimal in terms of both physical and visual properties thereof . This is ena- bled by ensuring a mutual bond for the underlying floor structure and a dry shake layer to be spread at each time by applying a silica-based medium on top of the dry shake layer spread over the underlying floor structure and by then troweling the discussed dry shake layer, which first of all impedes evaporation of water from the surface of base concrete or under- lying dry shake and secondly seals the surface of the discussed dry shake layer in a manner consistent with an early aftercare agent . Consequently, the bonding of a base concrete mass or underlying dry shake layer to the next dry shake layer takes place in an overall consistent manner while its surface also remains fresh as the silica-based medium reacts with the ex- cess lime of cement , thereby expediting formation of the surface .

Furthermore , it is by using preferably a nanosilica- based medium, i.e. so-called nanosilica, that a re- markable assistance is provided in terms of the spreading of e.g. three or more superimposed dry shake layers without a risk of inadequate mutual bonding between dry shake layers as the dry shake layers are allowed to moisten sufficiently and with sufficient uniformity throughout . In particular, the use of nanosilica makes it possible to reach a dry shake dosage as high as 10-15 kg/m ² , thereby further improving the strength of a dry shake surface and smoothing the color differences yet without increas- ing the duration of floor surface processing .

A further advantage gained by a silica-based medium in the processing of a dry shake layer is the fact that it does not impair the strength of base concrete as its use does not result in excessive migration of moisture into the base concrete . This is by virtue of the fact that nanosilica works in the above -discussed processing as a so-called primer and reaction accel- erator, whereas the use of water in this connection increases a risk of the excessive "contraction" of base concrete and makes the dry shake material diffi- cult to finish while the same time also impairing the abrasion resistance of a presently constructed dry shake surface .

As the method of the invention enables a dry shake layer thickness significantly greater than the pre- sent one (typically about 3-6 kg/m ² ) for a concrete floor, the constructed dry shake floor can also be diamond polished. A common problem in relation to dry shake floors constructed with currently available technology is that the dry shake material will be honed partially or completely in such a way that, be- cause of the translucency of base concrete, the dry shake surface becomes spotted or mottled.

The colloidal silicate liquid contains pure silica in the form of sufficiently small nanoparticles so as to enable its penetration into the pore structures of a dry shake material . The colloidal calcium silicate forms in the pore structures new calcium silicate hy- drate (CSH/Calcium Silicate Hydrate) , which bonds not only to calcium silicate hydrate present in the pre- viously processed dry shake surface but also to other silicates and to itself . When used in the addition of dry shake layers, the colloidal silica reacts, bonds and thereafter uses the bonded silicate as a growth medium for material layers to be processed later. Other silicate densifiers (such as lithium, sodium and potassium) do not work in a similar fashion, which is why the similar use thereof is not possible when processing dry shake layers on top of each oth- er.

By virtue of the increased layer thickness it is pos- sible to subject a processed dry shake surface to di- amond grinding "from deeper" and to achieve a so- called flat mosaic concrete or terrazzo surface, which has not been possible with currently available technology.

When treating the dry shake coating layer/layers with colloidal silica, the compression strength develops more rapidly and the surface density improves be- cause, by virtue of the colloidal silica, there will be no unreacted cement left in the dry shake . This, on the other hand, makes it possible that the dry shake surface be honed as early as 1-7 days after casting. It should be noted in this respect that the honing of ordinary untreated concrete cannot be per- formed at present earlier than 21-28 days after cast- ing . Other preferred embodiments for a method of the in- vention have been presented in the dependent claims directed thereto .

In the following description, the invention will be illustrated in detail while referring to the accompa- nying drawing, which shows, with a series of figures la-lf and by way of one preferred example, various processing stages for a method of invention.

The invention relates to a method in the dry shake coating of a concrete floor, whereby an applied and, as shown in fig. la, floated floor concrete mass B is first of all subjected to early aftercare, most pref- erably by spraying its surface with an early after- care agent . In this connection, if necessary, after floating the floor concrete mass , on top of the floor concrete mass is applied, on a principle appearing from figs . lc and le, a dry shake material K for two or more superimposed dry shake layers Kl, K2, in which connection the surface of the currently under- lying dry shake layer Kl is troweled prior to spread- ing the next dry shake layer K2 to be processed thereupon. Thereafter, the lastly processed dry shake layer K2 of the concrete floor is troweled and the concrete floor is subjected to actual aftercare, e.g. with an aftercare agent , water spraying, plastic sheet, filter fabric protection, or the like . The ap- plication of the underlying dry shake layer Kl is followed by spreading over its surface, on a princi- ple appearing from figs . lc and le, a water soluble silica-based medium V prior to and/or during the course of troweling this particular dry shake layer and prior to the application of the overlying dry shake layer K2 to be spread thereupon, which, on the other hand, ensures that excessive underside migra- tion of moisture in the dry shake structure is not allowed to occur yet the applied dry shake layer nev- ertheless obtains sufficient moisture for its own curing process .

In a preferred embodiment for a method of the inven- tion, the processing of the superimposed dry shake layers Kl, K2 is implemented by using the nanosilica- based medium V, it being by virtue of the medium' s fineness that optimization of both the homogeneous distribution of moisture in the dry shake layer and the optimal curing of the dry shake structure is achieved.

In a further preferred embodiment of the method, the final dry shake structure of a concrete floor is con- structed from three or more layers processed on top of each other, each dry shake layer being treated with the medium V prior to troweling and, as present- ed in figs . Id and If, also during the course of troweling, if necessary, which further enables a dry shake dosage of e.g. 10-15 kg/m ² when assembling the dry shake structure of a concrete floor. Thereby is enabled the construction of a concrete floor featur- ing a dry shake structure remarkably thicker than those available at present .

In a further preferred embodiment for a method of the invention, the early aftercare of a floor concrete mass or base concrete B, as presented in fig . la, is conducted by using a water soluble silica- or sili- cate-based early aftercare agent , whereby the surface of the floor concrete mass treated therewith is sealed, on a principle shown in fig. lb, mechanically with a manual trowel tool such as a bull float or the like .

In a further preferred embodiment for a method of the invention, the actual aftercare of the completed dry shake floor or the subsequently conducted service or maintenance procedure for the dry shake floor is con- ducted by treating its surface with diamond honing, which, in the case of dry shake floors manufactured with current technology, is not necessarily possible because of a varying or excessively small thickness of the dry shake structure .

It is obvious that the invention is not limited to the above-described or -explained embodiments but can be varied within the basic concept of the invention in a myriad of diverse ways, depending e.g. on cur- rent casting conditions, employed concrete masses and dry shake materials , as well as on properties re- quired of currently constructed concrete floors .