WATER-STEADY SOREL ZEMENTZUSAMMENSETZUNG

The invention e.g. refers to a water-steady SoreI Zementzusammensetzung on the basis of mixtures of MgO, MgCIs and inorganic fillers, like quartz sand. SoreI cement is a name for different masses, which contain magnesia (MgO) and magnesium chloride (MgCI2) as basic elements in an aqueous solution. In the hardened condition these basic elements of SoreI masses are present in the form of Magnesiumoxidchloddhydrat. SoreI cement becomes harder and ties more rapidly than Portland cement, has however only limited water firmness. The magnesium oxide chloride hydrate crystals, which form the substantial component of the SoreI cement, exhibit strong structural similarity with gypsum. Between the crystals it comes to no genuine connection, and the physical characteristics of the cement depend on the penetration of the crystals untereinanto. The adhesion between the crystals is practically eliminated by water. In order to make water-steadier Soren Zementmassen, already one suggested forming by additive of phosphates and aluminates insoluble Magnesiumsalze. Such additives lead however to a reduction of the hardening speed. It is further well-known to make SoreI Zementmassen more water resistant by a set of fillers. From the DE-PS 29 22 815 is it admits become to add Ethylsilicat and glass fibers of the mass whereby a special procedure way for the hardening by precipitation is suggested. In accordance with these DE-PS 29 22 815 as Kristallkeimbildner a Vorgemischmasse is used in a incipient crystal-forming quantity, which if necessary covers a reaction product of water, magnesium oxide and magnesium chloride. The magnesium oxide is here in the magnesium chloride solution soluble, and from a surfeited solution of MgO fails 2 in the consequence mg (OCI). Depending upon speed of the precipitation develops more or less nadelige crystal structure, which leads to a felting of the structure. It is well-known that additives of silicic acid and of ammonium phosphate lower the water solubility. In the EP 419,449 A already one suggested, to a SoreI Zementzusammensetzung of the kind initially specified 5 to 15 Gew,% of an inorganic cation exchanger, to add how e.g. active silicic acid or Ziolith related to magnesium oxide. The use of a such cation exchanger leads here to the reduction of the concentration at magnesium ions in the solution and in the consequence to an improvement of the homogeneity and the hardening by precipitation of the mass. The use of such additives is however in particular if the SoreI Zementzusammensetzung is to find as bonding agents for grinding wheels use, borders subjected. With to high activity it can come to an overheating and to cracking. The invention aims now off to train a Soren Zementzusammensetzung further of the kind initially specified in such a way that overheatings and cracking are avoided also with highly pure magnesium oxide and further the hardening by precipitation and homogeneity are improved. At the same time the Erlindung aims off to make the SoreI mass more easily processable and to make altogether a tying possible at lower temperature. Finally manufactured stones are to exhibit a higher hardness even with smaller magnesium oxide content from such masses. For the solution of this task the water-steady Soren composition according to invention of the kind initially specified consists essentially of that related to MgO 3 to 40 Gew,% sourly activated Bentonit is added. Surprisingly it showed up that a such water-steady SoreI Zementzusammensetzung ties at lower temperature and leads to a higher hardness. Altogether further a smaller swelling and thus a better resistance to deformation were obtained. The assigned Bentonit leads to a tixotropen SorelMasse, which is more easily processable than well-known Soren Zementmassen. The MgOHs education arising with the setting leads to strong swelling. Also the sourly activated Bentonit pours in water, whereby however altogether a substantially smaller water absorption and a much smaller swelling observe; 5 becomes. The sourly activated Bentonit closes the pinholes by sources of Soren cement and due to improved plastic characteristics a permanent and hard surface is created. In favourable way the composition is selected in such a way according to invention that 5 to 20 Gew,%, preferably about 10 Gew,%, sourly activated Bentonit is added. Within this range could optimal values for the pressure strength, which beginning of setting, which swelling, and the flectional resistance to extension are found. For the activation of the Bentonits with advantage it is proceeded in such a way that Bentonit with HCI is activated. While with well-known SoreI Zementmassen with magnesium oxide with a purity of over 90 Gew,% an extremely high activity and thus very high setting temperatures as well as the danger by cracking were observed, magnesium oxide with higher purity can be used for the production of grinding wheels in the context of the Soren Zementzusammensetzung according to invention ss. Also the expenditure for the meals of the additives can be substantially reduced in the context of the SorelZementzusammensetzung according to invention. During well-known compositions substantially finer grinding presuppose, are sufficient it, if Bentonit on grain size smaller 60 /J. husbands RK is used 402,729 B, so that a separate additional meal procedure can be void. Magnesite can together with Bentonit will grind and on a Feinmahlen can be done without. The SoreI compositions in accordance with the invention can be used with advantage for the production of grinding wheels or screeds. The invention is more near described in the following on the basis the design. In this Fig.1 shows the dependence of the pressure strength on the additive at sourly activated Bentonit, Fig.2 the beginning of setting as a function of the additive at sourly activated Bentonit, Fig.3 the decrease and/or the swelling with the additive of sourly activated Bentonit and Fig.4 the flectional resistances to extension as a function of the additive at sourly activated Bentonit. Out of a SoreI cement after the state of the art standard right parallelepipeds with a surface area were poured by 4 x 4 cm. The SoreI cement consisted here of a mixture of 375 g magnesium oxide (K 10/21), 1125 g quartz sand and 290 ml a magnesium chloride caustic solution with 26 " I in the design now on the basis such standard right parallelepipeds measured physical dimension is illustrated. Here it points itself to Fig.1 that within the range between 5 and 10 Gew,% additive at sourly activated Bentonit is obtained related to the magnesium oxide content a maximum at pressure strength. As evident from Fig.2, the beginning of setting with increasing quantity of sourly activated Bentonit rises. The setting delay adheres however up to an additive of 15 (3ew,% to sourly activated Bentonit quite in justifiable orders of magnitude, whereby a smaller setting temperature is obtained at the same time. As evident from Fig.3, an additive of over 5 Gew,% at sourly activated Bentonit leads to a salient decrease of the swelling, whereby extremely low values are already obtained with an additive of Gew.% at sourly activated Bentonit related to MgO. In Fi-g.4 again the salient improvement of the flectional resistance to extension is evident with additives of more than Gew,% at sourly activated Bentonit. Just like in Fig.1 here the lower curve shows the attainable values after 33 of tägiger storage in the water and the upper curve the drying of obtained values.