GB2077251A

GB2077251A - Slag Cement Composition

Info

Publication number: GB2077251A
Application number: GB8018811A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-06-09
Filing date: 1980-06-09
Publication date: 1981-12-16
Also published as: GB2077251B

Abstract

A new high sulphate slag cement with a Blaine specific surface ratio of 4500-5500 cm<2>/g, consists of water-granulated blast furnace slag (80-85%) which contains the following ingredients as indicated; CaO (40-50%), Al2O3 (14- 20%), SiO2 (30-35%), MgO (5-8%) and, in addition to the slag described above, the additional following ingredients; CaSO4 (13-17%), Portland cement (1.5-2.5%), organic carbonic acid or its alkali metal salts (0.1- 0.5%), water-soluble highly polymerized compounds (0.03- 0.6) e.g. methyl cellulose sodium stearate, and sodium benzene sulphate, and sodium sulphate (0.6-2%). The basicity of the slag may be increased by heating with Al2O3 and/or CaO and regranulating with water.

Description

SPECIFICATION A High Sulphate Slag Cement and the Method for Manufacturing This Cement It is a matter common knowledge that watergranulated blast furnace slag has a tendency to harden because the effects of hydration. Utilizing this property, this type of slag is mixed with Portland cement clinkers and pulverized to make low cost blast furnace slag and steel-making slag cement. However, in such cases, watergranulated slag by itself required relatively long periods of time to harden and does not acquire sufficient strength so that such slag tends to be used as an extender for Portland cement and the slat contents of such cements tend to be around 30% or less.

In addition to the type of slag cements referred to above, there is another well-known type of high sulphate slag cement known as the Sealithor variety, but it is not possible to make such a cement in quantity in Japan since suitable watergranulated blast furnace slag cannot be obtained, coagulation and hardening of such cements require relatively long periods of time and the surfaces of such cements, when hardened tend to develop weak areas so that such cements are, in actual practice, not widely used.

This invention relates to slag cement and its manufacture, or stated more specifically special high sulphate slag cements and methods used in their manufacture.

This invention consists of a new type of high sulphate blast furnace slag which hardens rapidly and does not develop weak surface areas, and the methods used to make such a type of cement.

High sulphate slag cements known up to the present time, as represented by the Sealithor variety, not only require water-granulated slags not readily available in Japan but do not begin to coagulate for approximately five hours and the coagulation stage does not end for approximately ten hours. Hardening requires relatively long periods of time and hardening of the surface areas is unsatisfactory with weak areas frequently developing.

The invention which is the subject of this patent application consists of a high sulphate slag cement for practical use. This cement begins to coagulate in 1-3 hours. Coagulation ends after 4-6 hours of time have elapsed. Weak surface areas do not develop so that forms with sharp angles can be cast.

The cement which is the subject of this patent application is a powdered mixture with a Blaine specific surface ratio of 4500-5500 cm2/g and consisting of water-granulated slag in the amount of 8085% (such slag, containing CaO (40 50%), Al2OB (14-20%), SiO2 (30-35%), MgO (58%)) or, preferably 8285%, plus CaSO4 (13-17%), Portland cement (1.52.5%), organic carbonic acid or alkali metal salts (0.1- 0.5%), water-soluble highly polymerized compounds (0.030.6%) and sodium sulphate (0.6-2%).

The method of manufacturing this cement consists of pulverizing and mixing blast furnace siag or blast furnace slag to which Al2O3 and/or CaO have been evenly added, mixed and which has then been reheated so that the slag particles recoalesce and then, which has been regranulated using water, in amount of 8085% of the total (preferably 8285%), with additional ingredients such as CaSO4 (13-17%), Portland cement (1.5-2.5%), organic carbonic acid or alkali metal salts (0.10.5%), water-soluble high polymerized compounds (0.030.6%) and sodium sulphate (0.62%) to produce a powdered mixture with a Blaine specific surface ratio of 4500-5500 cm2/g.

In the manufacture of the high sulphate slag cement which is the subject of this patent application, the chemical structure of the slag is important. It is necessary to utilize slag which has high basicity and which contains CaO (40-50%), Al2O3 (14-20%), SiO2 (3035%) and MgO (58%). However, at the present time, slag which is readily available in Japan typically has such ingredients as CaO (40-43%), Al2O3 (14-16%), SiO2 (30-35%), MgO (5-8%), TiO2 (0.5%), S (1.0%) and FeO (0.2%). Thus, as a slag for making the slag cement which is the subject of this patent application, it barely satisfies the lower limit for required basicity. When basicity is low, the time required for hardening increases and strength decreases.Therefore, it is desirable to increase the basicity of such water-granulated blast furnace slag.

However, this cannot be accomplished merely by adding Al203 and CaO and pulverizing them with the slag since this will have a negative effect on hardening time and strength.

Rather, the manufacturing process which is the subject of this patent utilizes a new method of obtaining slag of suitable characteristics, namely adding Al2O3 and/or CaO, mixing them with the slag particles, then heating and refusing the particles and regranulating the resulting slag by using water.

When slag of insufficient basicity is to be used to make the slag cement which is the subject of this patent, the use of the process described above, i.e., addition of Al2 and/or CaO-mixing- heating to cause recoalescence of the slag particles-regranulation using water becomes a necessary part of the overall manufacturing process. Likewise, if slag of sufficient basicity is available, this portion of the overall process becomes unnecessary.

The amount of slag used to make the slag cement which is the subject of this patent is 8085% of total weight, preferably 8285%. The ingredient CaSO4, i.e., gypsum, can be anhydride plaster of Paris or aqueous. Lime from antipollution devices aimed at removing SOx from stack gas can be used. The amount of CaSO4 used (calculated as anhydride) is 1317%. If CaS04.2H20 is used, the volume becomes 1622%. The amount of Portland cement used is 1.52.5% (preferably 2.5%).

Examples of "organic carbonic acids or alkali metal salts" would be sodium tartrate, citric acid, sodium citrate, etc. The amount used is 0.10.5%. These organic carbonic acids or alkali metal salts works to speed coagulation and hardening.

Examples of "water soluble highly polymerized compounds" are methyl-cellulose, sodium stearate in the metallic soap category or laurate such as sodium benzene sulphate. The amount used is 0.030.6%. In the case of the metallic soaps such as methyl-cellulose, the amount used is 0.10.6%. For sodium benzene sulphate, the amount is 0.030.06%. Overuse of laurates such as sodium benzene sulphate has the effect of slowing coagulation and hardening, but raises strength so that the amount used depends on the use of the final product.

Regarding the organic carbonic acids and their alkali metal salts, and the highly polymerized compounds, mentioned above, one of each can be used or several types of each can be used in combination.

The amount of sodium sulphate used is 0.62%.

The high sulphate which is the subject of this patent application has a Blaine specific surface ratio of 4500-5500 cm2/g is desirable. If the ratio is lowerthan 4500, the time required for hardening rises. In contrast, if the ratio is raised above 5500, the costs outweigh the benefits.

As a way of understanding the high suphate slag cement manufacturing method described above, either water granulated blast furnace slag; or such slag to which Awl203 and/or CaO has been added and mixed in, then heated so that the particles of slag have recoalesced and then have been regranulated, should be mixed with gypsum, Portland cement, organic carbonic acid or its alkali metal salts, the stipulated water-soluble highly polymerized compounds and sodium be pulverized until the specified Blaine specific surface ratio is obtained or, rather the various ingredients, singly or in various combinations should be pulverized in the specified proportions and mixed together to obtain a mixture with the specified Blaine specific surface ratio.

The high sulphate slag cement described in this patent application, when compared to the well-known Sealithor cement, is noticeably better for its faster coagulation and hardening. The technical reasons for this are not sufficiently clear at the present time, but the inventor has offered the possible explanations below although the invention and its related claims are in no way bound by these possible explanations.

In way of possible explanation, it is thought that when the high sulphate slag cement which is the subject of this patent is mixed with a suitable amount of water, the dissociation of the organic carbonic acids and alkali metal salts causes, directly or indirectly, the stimulation of a slag dissolving action based on Na2O and K2O. The carbonic acid also works to dissolve the gypsum.

This causes the formation of Ca (OH)2 which in turn causes the formation of a highly alkaline solution. The liquidation of the CaO and Al203 contained in the slag and the increased concentration of the CaSO4 in solution cause an increase in the probability of molecular collision in the liquid phase which in turn hastens the reaction. This prevents the formation of a silica gel, containing SiO2, which salts out, is dense and wiil not allow water to penetrate. Rather, a silica gel of rather coarse porous texture is formed which improves the penetration of water and aids the formation of ettringite (3CaO.Al2O3.CaSO4.32H2O) and calcium silicate hydrates.As the reaction progresses, the level concentration of the liquid phase CaO.AI203.SO4 drops, and the formation of an alumina hydrate (Al203.3H2O) takes place. This hydrate and the SiO2 gel form particles of a chrystalline nature on the surface of the siag particles. The ions cause the gel particles to align themselves in a net-like form which fills in the gaps in the attringite and knit together. This series of reactions are speeded up based on the rapid hydrolysis of the solute caused by the catalytic action of the additives, because saturation at the liquid phase ceases.

This causes, it is theorized, the more rapid beginning of coagulation and its more rapid completion.

Further, like the additive metallic soaps, methyl-cellulose and the laurates such as sodium benzene sulphate, the highly polymerized compounds dissolve and form a film on the surface of the hardening cement which cuts off its exposure to the surrounding air, thus preventing the formation of weak areas in the surface and stimulating the dispersion of the cement particles and causing a camping effect so that the density and strength of the cement are heightened.

As curing takes place, the structures of the hydrates become fixed and coalesce, giving the cement stability and the ability to resist water.

Following is a description by way of example only and with reference to the following examples of methods of carrying the invention into effect. In this specification percentages referred to are, unless otherwise stipulated, percentages by weight.

Example &num;1 Slag was obtained from Shin-Nihon Seitetsu's Hirohata mill. The composition was CaO (41.8%), Al203 (14%), SiO2 (34%), MgO (7%), MnO (0.5%), TiO2 (1.0%), S (1.0%), FeO (0.2%). This blast furnace slag, with an calcination loss of 0.5% and chemical structure basicity of 1.85, was pulverized to a Blaine specific surface ratio of 5000 cm2/g using a pulverizer (carbon steel stainless alloy rod and ball) belonging to Chuo Kakoki K.K. (Toyota-shi, Aichi Pref.). This pulverized slag came to 83% of the total by weight. To this was added calcinated gypsum (used for stack gas SOx removal) in the amount of 18% (13.8% converted to the anhydrous form) The CaSO4.2H2O contained had a purity rating of 96.497.8%. (This CaSO4 solution had an overall chemical composition as follows: CaO (32.333%), SO3 (44.8-45.5%), H2O (20.7- 20.9%), Fe203 (0.05-0.12%), S (0.05-0.92%), CO2 (0.41-0.82%), Cl (0.03-0.05%), H2SO4 (0.07%), water soluble alkalis (0.07-0.23%), MgO (0.01%), Altos (0.01%)). In addition, the following substances were added:Portland cement (2%), citric acid (0.2%), metallic soap (0.1%), sodium sulphate (0.6%), methyl-cellulose (0.1%). The ingredients were well mixed together and a high sulphate slag cement was then made.

Water was added and mixed with the cement to obtain a W/C ratio of 25% which was then poured into a mold. The surrounding air temperature was 1 0-200C and the relative humidity was 78%.

Coagulation began in approximately 1.5 hours and ended after a total elapsed time of 4.5 hours.

A film formed on the surface of the concrete form and devitrofication occurred. The form was removed from the mold 24 hours later. Weak areas in its surfaces could not be detected. The upper surface was milk-white in appearance. The bottom surface had a blue-green hue. The form was placed in water for 27 days and when measured on the 28th day, no signs of swelling or shrinkage were noted.Compression strength testing produced the following results: Day 3 378 kg/cm2 Day 14 502 kg/cm2 Example &num;2 Slag of the type used in Example #1 (83%), calcinated gypsum (18%) and Portland cement (2%) were mixed together and then calcium stearate (0.45%), methyl-cellulose (0.1%), sodium tartrate (0.21%), sodium sulphate (0.6%) and potassium citrate (K3C6HsO7.H20, 0.2%) were added and all ingredients were mixed together.

Then water (w/c 28%) was added and the resulting cement was mixed and poured into a mold. The surrounding temperature was 10 20% (and relative humidity was 78%).

Coagulation began after 2 hours and ended after 5 Hours. A film formed on the surface of the form and devitrofication occurred. The form was removed from the mold after 24 hours. The bottom surface was green. The upper surface was greenish blue. The form was placed in water for 14 days. The bluish hue deepened and the surface become shiny. Neither swelling or shrinking in size could be detected and after drying the form by exposure to the surrounding air, no changes in appearance or physical size took place.

Example &num;3 To slag (similar to that used above), CaSO4.2H2O and Portland cement were added calcium stearate (0.3%), methyl-cellulose (0.3%), potassium citrate (0.21%) and sodium sulphate (0.6%). These ingredients were blended together and water was added (w/c 26%) and mixed with the ingredients. Then the cement was poured into a moid. the temperature was 1 0-200C and the humidity was 78%. Coagulation began one hour and fifty minutes had elapsed and ended after five hours elapsed time. A film formed on the surface.

No bridging water was present and devitrofication occurred. The form was removed from the mold after 24 hours. The surface was milk-white in color, the bottom was spotted blue. No weak areas could be detected in the surface.

Example &num;4 Slag similar to that used in Example &num;1, CaSO4.2H2O and cement were blended together.

To this mixture was added methyl-cellulose (0.3%), calcium stearate (0.2%), sodium sulphate (0.7%), potassium citrate (0.2%), and sodium benzene sulphate (0.01%). All ingredients were blended together and then mixed with water (w/c 25%). The resulting cement was poured into a mold. The surrounding temperature was 200C, humidity was 78%. Coagulation began after two hours and forty minutes and ended after five hours and twenty minutes. A film formed on the surface of the form and a small amount of bridging water was detected. After 24 hours, the form was removed from the mold. No weak areas were detected on the surface of the form. The corners were sharp and the surface was white, the bottom pale blue. After air-drying, the pale blue color faded, but hardening was good.After air drying for seven days and submergence in water for 28 days, no swelling, shrinking or cracking had occurred and corners remained sharp.

In addition to the four examples described above, an additional seven samples of similar chemical composition were made and similar results were obtained. For one sample, the amount of sodium benzene sulphate was greatly increased and the percentage of water was also significantly increased. Hardening took longer, but sufficient strength was obtained.

To increase the basicity of the blast furnace slag CaO and Al203 used were added to slag of the type used in Example &num;1. The slag particles were heated and recoalesced, then regranulated by using water. In this manner, a slag was obtained that had a chemical composition as follows: CaO (45.01%), Al203 (18.28%), SiO2 (29.87%), MgO (6.10%), MnO (0.25%), TO2 (0.4%), S (0.7%), Fe203 (0.10/a), (ignition loss was not measured) and a basicity of 2.32. This slag (83%) was mixed with Portland cement (2%), CaSO4.2H2O (19%, calculated as CaSO4, 14.6%), methyl-cellulose (0.15%), calcium stearate (0.2%), sodium sulphate (0.6%), and potassium citrate (0.1%) in a stainless steel drum and pulverized to obtain a Blaine specific surface ratio of 5000 cm2/g. Then a suitable amount of water was mixed in and the resulting cement was poured into a mold. Hardening took place at 10200C and relative humidity of 78%. When the form was removed from the mold 24 hours later, no weak surface areas could be detected. The color was deep blue. After 27 days in water, in the 28th day no swelling, shrinking or cracking could be detected strength was measured at 600 kg/cm2.

Claims

1. A new high sulphate slag cement with a Blaine specific surface ratio of 4500-5500 cm2/g, consisting of watergranulated blast furnace slag (80-85%) which contains the following ingredients as indicated: CaO (40-50%), Al2O3 (14-20%), SiO2 (30 35%), MgO (5-8%) and, in addition to the slag described above, the additional following ingredients; CaSO4 (13-17%), Portland cement (1.5

2.5%), organic carbonic acid or its alkali metal salts (0.10.5%), water-soluble highly polymerized compounds (0.03-0.6) and sodium sulphate (0.6-2%).

2. A cement as claimed in claim 1 wherein the proportion of water-granulated blast furnace slag content is 82-85% by weight and the proportion of Portland cement is 22.5% by weight.

3. A cement as claimed in claim 1 and substantially as described in any one of the specific examples hereinbefore set forth.

4. A method of manufacturing a high sulphate slag cement in a powder mixture state having a Blaine specific surface ratio of 4500-5500 cm2/g which method comprises mixing, crushing and pulverizing the following specific ingredients in the quantities indicated; water granulated blast furnace slag (composed of CaO (40-50%), Al203 (14-20%), SiO2 (30-35%) and MgO (5-8%) in the amount of 80-85%, CaSO4 (13-17%), Portland cement (1.5-2.5), organic carbonic acid or its alkali metal salts (0.10.5%), water soluble highly polymerized compounds (0.03-0.6%) and sodium sulphate (0.6- 2%).

5. A method as claimed in claim 4 by adding Al2O3 and/or CaO to water-granulated blast furnace slag, mixing, refusing the slag particles and regranulizing them using water.