DE506615C - Process for making improved portland cement - Google Patents

Description

Method of Making Improved Portland Cement One takes generally suggests that the most important constituents of a Portland cement are tricalcium aluminate (3 CaO.A1203), tricalcium silicate (3 Ca0 # SiO2) and beta-dicalcium silicate (a Ca0 # SiO2) are. Less important components are usually magnesium oxide (Mg0) and tricalcium iron oxide (3 Ca0 # Fe20g), while gypsum (CaS04 # Z H20) is often used as additional ingredient is present and carbon dioxide, alkalis, silica and Water in small quantities.

Of these constituents, the tri- and dicalcium silicates have in highly cementing properties; but it is very likely that too Tricalcium aluminates and tricalcium iron oxides to a small extent cementing properties own. However, the tricalcium silicate alone exhibits all of the desirable properties of a real Portland cement. It literally ties off and the addition of one Delay means for regulating this process is usually unnecessary.

In contrast, dicalcium silicate sets only slowly and only hardens afterwards Course of several weeks complete.

As a result, the presence of lower calcium silicates continues the cementing properties of a Portland cement down, it is also desirable that the aluminates and ferrites are only present in it in their highest level. The ratio of silica (Si02) to lime (Ca0) in cement, in short as lime-silica index or factor, is therefore used to assess the quality of the 'cement of particular importance. If the cement consists only of tricalcium silicate, the Lime-silica index 2.8. This is the highest theoretically achievable value; however, as is well known, it was previously not possible to use a cement with a lime-silica index to produce of such value, rather, had to be due to the inevitable presence of the lower calcium silicates the index value must always be lower than 2.8, and therefore the cement wasn't quite good either. The presence of free lime is natural also harmful, and when assessing a cement on the basis of the lime-silica index only the firmly bound lime-silica compounds come into consideration.

Portland cement is the product that, by finely grinding a An intimate mixture of clay and lime that is fired up to the beginning of sintering Substances is obtained, and if in the following the expression normal Portland cement clinker is used, such a product is meant.

The invention now consists in the manufacture of a cement that only the highest grades of lime-silica, lime-alumina and Lime iron oxy contains interconnections, and it is based on the observation that one is one Such cement is obtained by using normal Portland cement clinker, which is of lower grades of lime-silica, lime-alumina and lime-iron oxide compounds, with so much free lime (in the form of calcium carbonate, calcium hydrate or calcium oxide) than theoretically necessary for complete saturation of the acidic constituents is, intimately ground together, then burns again until sintering to form a clinker and finally, as usual, grinds it.

Likewise, the improved Portland cement can also be produced in the manner be that one of the usual starting materials for the production of normal Portland cement from the start more than the normal amount of lime, but not more than the perfect amount Saturation of the acidic constituents is theoretically required, admixing and after firing to an ordinary portland cement clinker that lets it cool then finely grinds and then fires again until sintering.

The new process can either be from normal portland cement clinker or from the raw materials customary in the production of normal porcelain cement or, finally, start with a poorly made portland cement mass that contains an excess of free lime and is therefore more or less unusable is, according to the new process, still processed on a high-quality cement can be. Here, of course, it should be noted that there is an excess of free lime must be avoided in the end product and that the new process therefore only leads to the goal if the cement clinker to be improved does not already contain more lime contains, as to the complete saturation of the acidic components of the cement theoretically is required.

The amount of lime to be added to ordinary cement clinker for the purpose of forming the highest levels of silicate, aluminate and iron oxide compounds can be determined on the basis of an analysis of the clinker according to the formula can be calculated.

The lime can be the clinker in the form of quick lime or one when burning calcium compound passing into quicklime, e.g. B. calcium carbonate, in dry, powdery state or in the form of milk of lime or lime slurry in a suitable manner be added. While it is now known that one-time, arbitrary prolonged burning of a cement mixture, which leads to the stoichiometric Absorption of the acidic constituents contains the required amount of lime, such Saturation can never be achieved, in such a case a free lime can be obtained containing cement clinker, it has surprisingly been found that after the fine grinding and subsequent firing of such a clinker, the during first burning process unbound lime with complete saturation of the acidic constituents and in particular the silica is bound.

This can perhaps be explained by the fact that the one-time burning clumping and agglomeration of the substances as a result of sintering results in the stoichiometric saturation of the silica by lime is a hindrance, being there It can be left open whether this explanation is the correct one. .

The second burning process is when burning normal Portland cement clinker usual way, d. H. until sintering, whereupon the clinker obtained in this way, as usual, to be ground into cement. If necessary, it can be finely ground and distilled be repeated with or without a further addition of lime until complete Saturation of the acidic constituents of the cement has been achieved.

A cement obtainable according to the present method binds on the other hand the well-known Portland cements in a considerably shorter time while achieving a significantly higher strength with complete volumetric stability.

The process is illustrated by the following examples.

Normal, ie in addition to tricalcium silicate still containing dicalcium silicate, Portland cement clinker, e.g. B. Knickerbocker or Houston clinker is mixed with 15% or a sufficient amount of calcium carbonate to saturate the silica, clay and iron oxide, the amount of lime required based on the formula was determined.

The whole is then finely ground and fired again into clinker, whereupon a retarder such as plaster of paris is added, if desired, and the product is ground into cement. The better properties of a cement obtained in this way (Durbin cement) compared to a normal port that is only fired once Knicker- Knicker- Durbin- bocker-bocker-cement ldinker cement Silica .... 23.46 22.36 20.58 Alumina ...... 5.49 5.64 5115 Iron oxide .... 2.89 2.66 3.51 Lime . . . . . . . . . 64.55 63.53 6531 Magnesia .... 3.13 314 3.18 S03. . . . . . . . . . 0.12 1.72 1.51 Strength in kg per cm2 1 day i-3 sand 6.1 12.1 2 - 1-3 - 6.1 15.9 3 - 1--3 - 131 20.4 7-1-3-20.1 30.1

Claims (2)

PATENT CLAIMS: r. Process for the production of improved portland cement, characterized in that normal portland cement clinker, which in addition to tricalcium silicate also contains unsaturated silicate, is added with as much free lime (in the form of calcium carbonate, quick lime or hydrated lime) as to completely saturate the silica, the clay and the Theoretically required iron oxide land cement (Knickerbocker or Houston cement) results from the following comparative analyzes and strength values: Houston- Houston- Durbin- clinker cement Silica .... 24.6o 23.56 21.70 Alumina ...... 5.6o 5.94 6.26 Iron oxide .... 2.72 2.46 2.70 Lime . . . . . . . . . 66.3o 63, go 66.2o Magnesia. ... o, 83 o, 84 o, 86 S03 ......... 0.13 2.03 1.33 Strength in kg per cm ' i day i-3 sand 7.5 17.0 2 - i - 3 - - 2o, 6 3 _ i-3 - 131 - 7 - 1-3 - 18.7 26.5 is borrowed, intimately ground, then burns a second time until sintering and finally grinds again. 2. Modification of the method according to claim r, characterized in that that one starts from a Portland cement clinker containing free lime, its Total lime content is such that it is used to completely saturate the acidic Components (S102, A1203 and Fe203) is theoretically just sufficient.