WO2023104349A1

WO2023104349A1 - Grinding aid

Info

Publication number: WO2023104349A1
Application number: PCT/EP2022/054933
Authority: WO
Inventors: Ugur Semih AYTAC; Ahmet ERDAL
Original assignee: Fosroc Yapi Kimyasallari Sanayi Ve Ticaret Anonim Sirketi
Priority date: 2021-12-06
Filing date: 2022-02-28
Publication date: 2023-06-15

Abstract

The invention provides the use of a metabisulfite salt in a grinding aid for cement, wherein the metabisulfite salt is either the sole sulfate or is the majority sulfate, by weight, that is present in the grinding aid, and wherein the grinding aid comprises the metabisulfite salt in an amount of 6wt% or more. The metabisulfite salt is an alkali metal salt or an alkaline earth metal salt, especially sodium metabisulfite or calcium metabisulfite.

Description

GRINDING AID

Field of the Invention

The present invention relates to a grinding aid for cement.

Background of the Invention

Concrete is a construction material formed from a mixture of cement, aggregates (sand and stone) and water. The water used in concrete activates the cement, which acts as the binding agent. The aggregates (coarse and fine) in the mix are bound together by the cement as it sets and cures to produce a hardened concrete.

The cement may commonly be hydraulic cement, such as Portland cement. Portland cement (also known as Ordinary Portland Cement or OPC) may be defined as a cementitious material meeting the requirements of ASTM Cl 50 or the requirements of European Standard EN 197-1.

Portland cement is prepared by heating a mixture of raw components (including calcium carbonate, aluminium silicate, silicon dioxide and miscellaneous iron oxides) to a sintering temperature (usually about 1450°C), resulting in the formation of clinker. Portland cement clinker is formed by the reaction of calcium oxide with acidic components to give primarily tricalcium silicate, dicalcium silicate, tricalcium aluminate, and a ferrite phase “C4AF” (tetracalcium aluminoferrite).

This clinker is ground together with calcium sulphate (usually in the form of gypsum) in a grinding mill to provide the cement in the form of a fine, homogeneous powder. Other additives or cement replacements can be incorporated before or after the milling process. These include fillers and OPC replacements, such as calcium carbonate and other minerals, ground granulated blast furnace slag, natural pozzolans, pulverised fuel ash (PFA), and coal gangue. The components that form the cement powder (clinker, calcium sulphate, and optional additives such as fillers and cement replacements) may be referred to as the cement composition.

A grinding aid can be used to reduce the amount of energy required to grind the clinker, and therefore can improve the efficiency of the grinding stage, and/or improve the hydration of the clinker, leading to an improved quality product. A grinding aid can reduce the energy requirements during grinding and can provide a uniform free flowing cement powder with reduced tendency to form lumps during storage.

Thus, it is well-known in the art for a grinding aid to be added to the clinker and the calcium sulphate in the grinding mill during the grinding stage. The grinding aid is introduced into the mill in a small quantity and inter-grinds with the clinker.

A well-known grinding aid in the art is triethanolamine (TEA). Other alcohol amines are also useful, such as triisopropanolamine (TIPA), tetrahydroxyethylethylene diamine (THEED), diethanolisopropanolamine (DEIPA), and methyldiethanolamine (MDEA). Other materials, such as glycols, (e.g. diethylene glycol, triethylene glycol, ethylene glycol, propylene glycol, polyethylene glycol, glycerol) and gluconates have also been used as grinding aids. Modified sugars such as molasses, vinasse and dextrins can also be used as grinding aids.

Sodium thiosulfate has been described for use as a grinding aid. CN106673479A discloses a cement grinding aid, which is described as allowing a higher content of coal gangue to be used in the cement composition and improving the abrasion resistance of the coal gangue, whilst not adversely affecting the early and late strength of the cement. This cement grinding aid comprises, in parts by weight: 1-15 parts of chloride salts, 1- 20 parts of sulfate (especially sodium thiosulfate), 5-30 parts of alcohols, 5-60 parts of modified alcohol amines, and a balance of water. The chloride salts are taught as playing an important role in improving the utilization efficiency of coal gangue and enhancing the early strength of the cement.

It can be a problem to obtain good early-stage strength enhancement whilst also achieving good later stage strength enhancement. Some grinding aids achieve good strength enhancement at one stage but not the other.

The aim of the present invention is to provide alternatives to currently used grinding aids, whereby said alternatives are more cost-effective but are at least comparable to known grinding aids in terms of their efficacy. It would be desirable for both good early- stage and late-stage strength enhancement to be achieved. Summary of the Invention

The present invention provides, in a first aspect, the use of a metabisulfite salt in a grinding aid for cement, wherein the metabisulfite salt is either the sole sulfate or is the majority sulfate, by weight, that is present in the grinding aid, and wherein the grinding aid comprises the metabisulfite salt in an amount of 6wt% or more, such as 7wt% or more, or 8wt% or more.

The present inventors have surprisingly found that metabisulfite salts, such as sodium metabisulfite, are effective grinding aids. They have only previously been taught as optional additives. It was not previously known that metabisulfite salts act as grinding aids by themselves. CN106673479A only teaches their use as an optional additive in a grinding aid together with other essential active agents (chloride salts, alcohols, and modified alcohol amines) and all of the grinding aids detailed in CN106673479A include sodium thiosulfate.

The present inventors have determined that metabisulfite salts do not need to be used with another sulfate, such as sodium thiosulfate; they are effective grinding aids in their own right. Whilst the metabisulfite salts can effectively be used in blends with other grinding aid materials, they are also effective when used on their own.

This new technical teaching provided by the present invention is advantageous because metabisulfite salts, such as sodium metabisulfite, can be used to partly or fully replace known grinding aid materials (such as TEA) in a grinding aid product. Being able to use less conventional grinding aid material (such as TEA), has the technical benefit of providing a cheaper grinding aid whilst still achieving good results.

In particular, when using the metabisulfite-based grinding aids according to the invention, the resulting concrete obtained from using the grinding aid has good early- stage and late-stage strength. Thus, the materials are effective grinding aids, providing a uniform free flowing cement powder, without having an adverse effect on compressive strength.

Accordingly, the present invention provides valuable cost-effective alternatives to conventional grinding aids. The present invention provides, in a second aspect, a method of obtaining cement, wherein the method comprises the steps of: a) providing cement clinker, and optionally one or more fillers or cement replacements; and b) intergrinding the cement clinker with (i) calcium sulfate and (ii) a grinding aid that comprises a metabisulfite salt, so as to provide a powdered cement, wherein the metabisulfite salt is either the sole sulfate or is the majority sulfate, by weight, present in the grinding aid and wherein the grinding aid comprises the metabisulfite salt in an amount of 6wt% or more, such as 7wt% or more, or 8wt% or more.

The present invention provides, in a third aspect, a method of obtaining a hardened cement, which method comprises the steps of: a) providing cement clinker, and optionally one or more fillers or cement replacements; b) intergrinding the cement clinker with (i) calcium sulfate and (ii) a grinding aid that comprises a metabisulfite salt, so as to provide a powdered cement, wherein the metabisulfite salt is either the sole sulfate or is the majority sulfate, by weight, present in the grinding aid and wherein the grinding aid comprises the metabisulfite salt in an amount of 6wt% or more, such as 7wt% or more, or 8wt% or more; and c) mixing the powered cement with water, so as to provide a hardened cement.

The present invention provides, in a fourth aspect, a method of obtaining concrete or mortar, which method comprises the steps of: a) providing cement clinker, and optionally one or more fillers or cement replacements; b) intergrinding the cement clinker with (i) calcium sulfate and (ii) a grinding aid that comprises a metabisulfite salt, so as to provide a powdered cement, wherein the metabisulfite salt is either the sole sulfate or is the majority sulfate, by weight, present in the grinding aid and wherein the grinding aid comprises the metabisulfite salt in an amount of 6wt% or more, such as 7wt% or more, or 8wt% or more; c) mixing the powered cement with aggregates (e.g. gravel and/or sand) and water, so as to provide concrete or mortar.

The present invention provides, in a fifth aspect, a ground clinker product comprising cement clinker interground with a grinding aid that comprises a metabisulfite salt, wherein the metabisulfite salt is either the sole sulfate or is the majority sulfate, by weight, present in the grinding aid and wherein the grinding aid comprises the metabisulfite salt in an amount of 6wt% or more, such as 7wt% or more, or 8wt% or more. The present invention provides, in a sixth aspect, a cement product comprising cement clinker interground with (i) calcium sulfate and (ii) a grinding aid that comprises a metabisulfite salt, wherein the metabisulfite salt is either the sole sulfate or is the majority sulfate, by weight, present in the grinding aid and wherein the grinding aid comprises the metabisulfite salt in an amount of 6wt% or more, such as 7wt% or more, or 8wt% or more. The cement product may be obtainable (obtained) by the method of the second aspect.

The present invention provides, in a seventh aspect, a hardened cement product comprising a cement product as defined in the sixth aspect that has been hardened by mixing with water. The hardened cement product may be obtainable (obtained) by the method of the third aspect.

The present invention provides, in an eighth aspect, a concrete or mortar product comprising a cement product as defined in the sixth aspect that that has been mixed with aggregates (e.g. gravel and/or sand) and water. The concrete or mortar product may be obtainable (obtained) by the method of the fourth aspect.

The present invention provides, in a ninth aspect, a grinding aid that comprises:

• 6-90wt% of metabisulfite salt, e.g. from 8-75wt%, or from 10-60wt%;

• 0-75 wt% additional grinding aid materials selected from the group consisting of: alcohols and esters thereof, amino alcohols, sugars and modified sugars; e.g. from 2-70wt%, or from 5-65wt%;

• no more than 5wt% of sulfate that is not metabisulfite salt; e.g. not more than 3wt% or not more than 2wt%;

• 0-10wt% optional additives, e.g. de-foamers and/or colorants; and

• a balance of water.

The additional grinding aid materials may suitably be as described further below, in the Detailed Description of the Invention.

It is preferred that the total amount of metabisulfite salt plus additional grinding aid material is from 20 to 90wt% of the grinding aid, e.g. from 25 to 85wt% of the grinding aid, or from 30 to 80wt% of the grinding aid. In one embodiment, the total amount of metabisulfite salt plus additional grinding aid material is from 35 to 75wt% of the grinding aid or from 35 to 70wt% of the grinding aid.

The grinding aid of the ninth aspect may be used in the use of the first aspect or may be used in the method of any of the second to fourth aspects or may be present in the product of any of the fifth to eight aspects.

In all aspects of the invention, the metabisulfite salt may suitably be an alkali metal salt or an alkaline earth metal salt. In a preferred embodiment the metabisulfite salt is sodium metabisulfite or calcium metabisulfite, especially sodium metabisulfite (SMBS).

In all aspects of the invention, the cement clinker may optionally be used with one or more fillers or cement replacements. These include natural pozzolans, fly ash (e.g. pulverised fuel ash), slag (e.g. ground granulated blast furnace slag), burnt shale, silica fume, limestone, and coal gangue. In one embodiment, however, coal gangue is not present.

Detailed Description of the Invention

In the present invention, a metabisulfite salt is used as a grinding aid. The metabisulfite salt is suitably inorganic and may preferably be an alkali metal salt or an alkaline earth metal salt, for example a potassium, calcium or sodium salt. In a preferred embodiment the metabisulfite salt is sodium metabisulfite or calcium metabisulfite, especially sodium metabisulfite (SMBS).

The metabisulfite, e.g. sodium metabisulphite, may suitably be provided in the form of a powder or in the form of a solution, especially an aqueous solution, e.g. as a 30-60 or 30-50% wt/wt solution in water, such as a 35-45% wt/wt solution in water. In embodiments, the sodium metabisulphite may be provided in a non-food grade form, as this is more cost-effective. Thus there may, for example, be ppm level impurities of metal ions such as Fe ions.

The grinding aid may only include metabisulfite salt as the active agent. However, it is envisaged that the grinding aid may usefully comprise the metabisulfite salt together with other grinding aids and/or other cement additives. The present invention has determined that metabisulfite salts such as sodium metabisulfite are compatible with many other compounds and can therefore be used with these compounds to achieve the desired effects, e.g. in terms of efficiency of the grinding process and/or characteristics of the end product.

The grinding aid comprises the metabisulfite salt in an amount of 6wt% or more, such as 7wt% or more, or 8wt% or more, or 9wt% or more. For example, the grinding aid may comprise the metabisulfite salt in an amount of 10wt% or more, or 15wt% or more, or 20wt% or more; in one preferred embodiment the amount may be 25wt% or more, or 30wt% or more, such as 35wt% or more.

The grinding aid may suitably comprise the metabisulfite salt in an amount of from 6wt% to 90wt%, or from 7wt% to 80wt%, such as from 8wt% to 75wt%. The amount may, in one embodiment, be from 8wt% to 70wt%, or from 10wt% to 60wt%.

As noted above, it has surprisingly been determined that the metabisulfite salt is effective as a grinding aid by itself and in particular it does not require the presence of chloride salts.

Thus, in one embodiment, the grinding aid comprises chloride salts in an amount of 5wt% or less, such as 2wt% or less, preferably less than lwt%, such as 0.5wt% or less or 0.1wt% or less. Examples of chloride salts include sodium chloride and potassium chloride. In one embodiment the grinding aid may contain no chloride salts.

In addition, because the metabisulfite salt is effective as a grinding aid by itself it does not require the presence of other sulfates, and when other sulfates are present these are included in smaller amounts (by weight) than the metabisulfite salt.

The grinding aid may, in one embodiment, comprise sulfates that are not metabisulfite salts in an amount of 5wt% or less, such as 2wt% or less, preferably less than lwt%, such as 0.5wt% or less or 0.1wt% or less. In one embodiment the grinding aid may contain no sulfates that are not metabisulfite salts. In one embodiment, the grinding aid comprises thiosulfate salts in an amount of 5wt% or less, such as 2wt% or less, preferably less than lwt%, such as 0.5wt% or less or 0.1wt% or less. Examples of thiosulfate salts include sodium thiosulfate and potassium thiosulfate. In one embodiment the grinding aid may contain no thiosulfate salts.

The metabisulfite salt is either the sole sulfate or is the majority sulfate, by weight, present in the grinding aid. Thus, the grinding aid may comprise metabisulfite salt in an amount that is at least lwt% more than the amount of sulfates that are not metabisulfite salts, such as at least 2wt% more, or at least 5wt% more, or at least 6wt% more, or at least 8wt% more, or at least I0wt% more.

The grinding aid may include one or more (such as two or more, or three or more) additional grinding aid materials. These may suitably be materials known in the art to be effective as grinding aids. In one embodiment, the grinding aid comprises 2wt% or more of said additional grinding aid materials, such as 5wt% or more, e.g. from 2 to 75wt%, or from 3 to 70wt%, or from 5 to 65wt%, or from 10 to 60wt%.

In one embodiment, one or more additional grinding aid materials may be present that are selected from the group consisting of: alcohols and esters thereof, amino alcohols, sugars and modified sugars.

For example, one or more additional grinding aid materials may be present that are selected from the group consisting of:

• glycols, triols, polyols and esters thereof; e.g. diethylene glycol, triethylene glycol, ethylene glycol, propylene glycol, polyethylene glycol; glycerol (glycerine); and acetins such as monoacetin (2,3-dihydroxypropyl acetate);

• amino alcohols; e.g. triethanolamine (TEA), diethanolisopropanolamine (DEIPA), triisopropanolamine (TIPA), tetrahydroxyethylethylene diamine (THEED) and methyldiethanolamine (MDEA);

• sugars and modified sugars (including sugar acid salts); e.g. glucose, sodium gluconate, potassium gluconate, molasses, vinasse, and dextrins (e.g. yellow dextrin and/or maltodextrin). In one embodiment, one or more additional grinding aid materials may be present that are selected from the group consisting of: glycols, glycerol, amino alcohols, glucose and gluconate salts, and molasses.

In one embodiment, one or more additional grinding aid materials may be present that are selected from the group consisting of: TEA, TIPA, DEIPA, ethylene glycol, propylene glycol, glycerine, glucose and sodium gluconate. In one embodiment, one or more additional grinding aid materials may be present that are selected from the group consisting of: TEA, TIPA, DEIPA, ethylene glycol, sodium gluconate and glycerine. In one embodiment, the grinding aid comprises from 2 to 75wt%, or from 3 to 70wt%, or from 5 to 65wt%, of said additional grinding aid materials.

The metabisulfite salt (e.g. SMBS) may be the majority component that is an active grinding aid material. In one embodiment, therefore, the grinding aid comprises more metabisulfite salt, by weight, than any other additional grinding aid materials that are present. However, this is not essential. It will be appreciated that there can be value (e.g. reduced costs) in reducing the amount of conventional grinding aid material (e.g. TEA), even if overall the conventional grinding aid is still the majority component that is an active grinding aid material.

The grinding aid may include one or more carriers and/or solvents (e.g. water). Preferably the grinding aid is provided as a solution or suspension in water. In one embodiment, the grinding aid includes 5wt% or more of carrier and/or solvent, such as I0wt% or more, e.g. from 5wt% to 70wt% or from 10wt% to 60wt% of carrier and/or solvent, e.g. water.

It may optionally be that other additives may be present in the grinding aid, e.g. in amounts of I0wt% or less, such as 5wt% or less, 3wt% or less or 2wt% or less; e.g. from 0.5 to 10wt% or from 1 to 8wt% or from 1 to 5wt%. These other additives may be materials known in the art for use in grinding aids, e.g. surfactants (air entraining agents and/or defoamers) and/or biocides and/or colorants. These other additives are not intended to be active grinding aid materials; they are agents that provide other functionalities. The grinding aid may be added in amounts known in the art for grinding aids. As will be appreciated by the skilled reader, grinding aids are used in lower amounts than other cement additives such as set accelerators (which are used in amounts of over Ikg/tonne). Further, the grinding aids are added into the grinding mill with the clinker rather than being added to the cement itself. Cement additives such as set accelerators are added as an admixture to powdered cement prior to, together with, or after, the addition of water to harden the cement.

In one embodiment, the grinding aid is used in amounts known in the art for grinding aids, such as lOOOppm or less, (when considered as a weight of solid product with reference to the total weight of clinker), e.g. 900ppm or less or 800ppm or less; preferably from 5 to lOOOppm, such as from 10 to 950ppm, e.g. from 50 to 900ppm, such as from 75 to 800ppm, or from 100 to 750ppm, or from 150 to 700ppm.

In one embodiment, the metabisulfite salt is added in an amount of lOOOppm or less, (when considered as a weight of solid product with reference to the total weight of clinker), e.g. 900ppm or less or 800ppm or less; preferably from 5 to lOOOppm, such as from 10 to 950ppm, e.g. from 50 to 900ppm, such as from 75 to 800ppm, or from 100 to 750ppm, or from 150 to 700ppm.

The cement clinker may, in one embodiment, be a Portland cement clinker. In one embodiment it may be a Portland cement clinker containing 1 wt% or more tetracalcium aluminoferrite (C4AF), e.g. containing 2 wt% or more, 3 wt% or more, 4 wt% or more, or 5 wt% or more tetracalcium aluminoferrite (C4AF). In another embodiment it may be a cement clinker containing no, or substantially no, tetracalcium aluminoferrite (C4AF); for example it may contain 0.1 wt% or less tetracalcium aluminoferrite (C4AF), such as 0.05 wt% or less.

The cement clinker may optionally be used with one or more fillers or cement replacements. These additional materials may be pre-mixed with the cement clinker or may be added into the grinding equipment before the cement clinker, simultaneously with the cement clinker or after the cement clinker.

The grinding of the clinker may be carried out in any suitable grinding equipment. Grinding mills, such as ball mills or roller mills, (e.g. as described in US 6 213 415) may be mentioned for use in this regard. Combinations of different mill types or of mills with different sized grinding media may also be used.

The grinding aid may be added into the grinding equipment before the cement clinker, simultaneously with the cement clinker or after the cement clinker. In one embodiment, the grinding aid and the cement clinker are added into the grinding equipment using a single conveyor.

The grinding aid may be added into the grinding equipment before the calcium sulfate, simultaneously with the calcium sulfate or after the calcium sulfate.

Any additional grinding aids used with the metabisulfite salt grinding aid may be premixed with the metabisulfite salt grinding aid before use, or may be added into the grinding equipment before the grinding aid, simultaneously with the grinding aid or after the grinding aid.

The intergrinding of the cement clinker may be carried out under conventional conditions and for any suitable length of time.

The grinding may suitably be carried out in a closed-circuit mill, where the feed and discharge are continuous.

In one embodiment, the temperature during the grinding is controlled, e.g. such that there is a mill exit temperature within a few degrees of 105°C, such as from 100 to 110°C. In another embodiment, the mill temperature is not controlled.

The throughput in the grinding mill may suitably be from about 20 to over 200 tons per hour, e.g. from about 20 to 120 tons per hour or more. However, it will be appreciated that this can be selected as required, depending on the size of mill, its design and the fineness of cement that is required.

The intergrinding of the cement clinker may be carried out with any suitable amount of calcium sulfate; for example from 1 to 15wt% of the interground components may be calcium sulfate, such as from 3 to 10wt%. As is known in the art, small amounts of calcium carbonate (limestone) and other minerals are often present during the intergrinding. For example, up to 10wt% calcium carbonate and up to lwt% or more, e.g. up to 5wt%, of other minerals may be present during the intergrinding.

Any optional fillers or cement replacements, e.g. pozzolans, fly ash (such as pulverised fuel ash), or limestone, or coal gangue, may be present during the intergrinding. For example, up to 40wt% or more of cement replacements may be present during the intergrinding. In one embodiment, from 0 to 50wt% of cement replacements are present during the intergrinding, such as from 1 to 40wt%. In one embodiment, it may be that fillers and cement replacements are present in the inter-ground cement composition in an amount of from 1 to 50wt% or from 1 to 45wt% or from 1 to 40wt%; for example they may be present in an amount from 5 to 50wt%, e.g. from 5 to 45 wt% or from 5 to 40wt%, such as from 10 to 40wt%. Preferably the amount is 50 wt% or less, or 45 wt% or less, or 40 wt% or less, preferably 20wt% or less, or 15 wt% such as less, or 10 wt% or less. For example, the amount may be from 1 to 20 wt%, such as from 1 to 15 wt%, or from 1 to 10 wt%.

The amount of clinker (e.g. OPC clinker) present in the inter-ground cement composition may be 40 wt% or more, or 50 wt% or more, such as 70 wt% or more. Preferably the amount is 80 wt% or more, such as 85 wt% or more. For example, it may be from 40 to 99wt%, such as from 45 to 99wt% or from 50 to 95wt%. In one embodiment, it may be from 70 to 99wt%, e.g. from 80 to 98wt%, or from 85 to 95wt%.

In one embodiment of the invention the cement composition comprises: from 1 to 15wt% calcium sulfate, such as from 3 to 10wt% from 40 to 99wt% clinker (e.g. OPC clinker), such as from 50 to 95wt% from 0 to 50wt% filler and cement replacements, such as from 1 to 40wt%.

In particular, in one embodiment the cement composition comprises: from 1 to 15wt% calcium sulfate, such as from 3 to 10wt% from 40 to 98wt% clinker (e.g. OPC clinker), such as from 70 to 95% from 1 to 50wt% filler and cement replacements, such as from 2 to 10wt%. In one embodiment, one or more cement additive is added to the powdered cement that is obtained from the intergrinding. These may, for example, be one or more additive selected from retarders, corrosion inhibiting agents, anti-foaming agents, air entraining agents, water-reducing agents, fluidizers, agents to reduce segregation, set accelerators, anti-freezing agents, cold-resisting agents, shrink reducing agents, heat of hydration inhibitors, alkali aggregate reaction inhibitors, or expansive agents.

In relation to the concrete or mortar product, the ratios of cement product, aggregates (e.g. gravel and/or sand) and water used may be conventional, e.g. in accordance with ASTM C109.

Examples

General procedure

Cement clinker, gypsum and limestone, in a weight ratio of 90:5:5 respectively, were ground in a laboratory ball mill. The total number of revolutions was set to 4500 and this took around 40 minutes to complete.

The grinding was carried out either in the presence of no grinding aid (control) or in the presence of a grinding aid.

The materials used in the examples were all obtained from commercial suppliers.

The powdered cement as obtained from the grinding step was then cured with water.

Mechanical strength measurements were carried out on 40 mm cubes of the cured cement mortar thus obtained after 2, 7 and 28 days. In each case three samples were tested, and the mean result was calculated.

The tests carried out were all according to EN standards, in particular:

- EN 196-1 Methods of testing cement - Determination of strength

Example 1 : SMBS as a grinding aid

A grinding aid “SMBS-A” was prepared which was a 50wt% solution of sodium metabisulfite in water. The grinding aid was used in an amount of 300g/tonne. The effectiveness of this material was compared to a control (no grinding aid).

SMBS-A was found to be an effective grinding aid, providing a uniform free flowing cement powder.

Table 1

The resulting concrete obtained from using the grinding aid had good early-stage and late-stage strength; in each case the values were improved as compared to the use of no grinding aid.

Example 2: SMBS compared to TEA

A grinding aid “SMBS-B” was prepared which was a blend of sodium metabisulfite (provided as a 35wt% aqueous solution) and a colorant.

The effectiveness of this material was compared to a control (no grinding aid) and to two comparative grinding aids “TEA-A” and “TEA-B”, which both contained triethanolamine (TEA).

The grinding aids were each used in an amount of 600g/tonne.

The amounts given in the table below are parts by weight.

SMBS-B was found to be an effective grinding aid, providing a uniform free flowing cement powder.

Table 2

For all grinding aids tested, the resulting concrete obtained from using the grinding aid had good early-stage and late-stage strength; in each case the values were improved as compared to the use of no grinding aid.

The grinding aids according to the invention, based on SMBS, give comparable results to TEA-containing grinding aids. Thus, the present invention provides valuable cost- effective alternatives to conventional grinding aids.

Example 3 : Use of SMBS over a range of doses

A grinding aid “SMBS-C” was prepared which was a 35wt% solution of sodium metabisulfite in water. The grinding aid was used in a range of different amounts, from 200 to lOOOg/tonne.

The effectiveness of this material was compared to a control (no grinding aid).

SMBS-C was found to be an effective grinding aid, providing a uniform free flowing cement powder, for all dosage regimes tested.

Exemplary results are shown below.

Table 3

For all dose regimes tested, the resulting concrete obtained from using the grinding aid had good early-stage and late-stage strength. Therefore, the SMBS-based grinding aid provides flexibility for the user, in that they can increase the amount if needed to assist with efficiency of the grinding stage without a detrimental effect on the strength of the resulting concrete.

Example 4: SMBS compatibility with other grinding aid materials

Grinding aids “SMBS-D” through to “SMBS-K” were prepared. Each used a blend of SMBS (provided as a 35wt% solution in water), a colorant, and further grinding aid materials as an additive.

The grinding aids were each used in an amount of 600g/tonne.

The amounts given in the table below are parts by weight.

Each of the grinding aid blends tested was found to be an effective grinding aid, providing a uniform free flowing cement powder.

Table 4

TEA = triethanolamine ; TIPA = triisopropanolamine; MDEA = methyldiethanolamine ; DEIPA = diethanolisopropanolamine.

For all of the blends tested, the resulting concrete obtained from using the grinding aid had good early-stage and late-stage strength. Therefore, the SMBS-based grinding aid provides flexibility for the user, in that they can blend the SMBS with other grinding aid materials if needed or desired, without a detrimental effect on the strength of the resulting concrete.

Example 5 : SMBS blends compared to TEA blends

Grinding aids “SMBS-L” and “SMBS-M” were prepared, which were blends of sodium metabisulfite (provided as a 35wt% aqueous solution), DEIPA, and crude glycerin.

The effectiveness of these blends was compared to a control (no grinding aid) and to a comparative grinding aid blend “TEA-C”, which contained triethanolamine (TEA), DEIPA, and crude glycerin.

The amounts given in the table below are parts by weight.

The grinding aids were each used in an amount of 600g/tonne.

Table 5

SMBS-L and SMBS-M were both found to be effective grinding aids, providing a uniform free flowing cement powder. For all grinding aids tested, the resulting concrete obtained from using the grinding aid had good early-stage and late-stage strength; in each case the values were improved as compared to the use of no grinding aid.

Claims

1. The use of a metabisulfite salt in a grinding aid for cement, wherein the metabisulfite salt is either the sole sulfate or is the majority sulfate, by weight, that is present in the grinding aid, and wherein the grinding aid comprises the metabisulfite salt in an amount of 6wt% or more.

2. The use of claim 1, wherein the grinding aid comprises the metabisulfite salt in an amount of 8wt% or more.

3. The use of claim 1 or claim 2, wherein the metabisulfite salt is an alkali metal salt or an alkaline earth metal salt.

4. The use of any one of the preceding claims, wherein the metabisulfite salt is sodium metabisulfite or calcium metabisulfite.

5. The use of any one of the preceding claims, wherein the grinding aid comprises chloride salts in an amount of 5wt% or less.

6. The use of any one of the preceding claims, wherein the grinding aid comprises sulfates that are not metabisulfite salts in an amount of 5wt% or less.

7. The use of any one of the preceding claims, wherein the grinding aid comprises one or more additional grinding aid materials that are selected from the group consisting of: alcohols and esters thereof, amino alcohols, sugars and modified sugars.

8. The use of claim 7, wherein grinding aid comprises one or more additional grinding aid materials selected from the group consisting of:

• amino alcohols; e.g. triethanolamine (TEA), diethanolisopropanolamine (DEIPA), triisopropanolamine (TIPA), tetrahydroxyethylethylene diamine (THEED) and methyldiethanolamine (MDEA); • sugars and modified sugars (including sugar acid salts); e.g. glucose, sodium gluconate, potassium gluconate, molasses, vinasse, and dextrins (e.g. yellow dextrin and/or maltodextrin).

9. The use of any one of the preceding claims, wherein the metabisulfite salt is used in amounts of from 5 to lOOOppm, when considered as a weight of solid product with reference to the total weight of cement clinker.

10. A method of obtaining cement, wherein the method comprises the steps of: a) providing cement clinker, and optionally one or more fillers or cement replacements; and b) intergrinding the cement clinker with (i) calcium sulfate and (ii) a grinding aid that comprises a metabisulfite salt, so as to provide a powdered cement, wherein the metabisulfite salt is either the sole sulfate or is the majority sulfate, by weight, present in the grinding aid and wherein the grinding aid comprises the metabisulfite salt in an amount of 6wt% or more.

11. A method of obtaining a hardened cement, which method comprises the steps of: a) providing cement clinker, and optionally one or more fillers or cement replacements; b) intergrinding the cement clinker with (i) calcium sulfate and (ii) a grinding aid that comprises a metabisulfite salt, so as to provide a powdered cement, wherein the metabisulfite salt is either the sole sulfate or is the majority sulfate, by weight, present in the grinding aid and wherein the grinding aid comprises the metabisulfite salt in an amount of 6wt% or more; and c) mixing the powered cement with water, so as to provide a hardened cement.

12. A method of obtaining concrete or mortar, which method comprises the steps of: a) providing cement clinker, and optionally one or more fillers or cement replacements; b) intergrinding the cement clinker with (i) calcium sulfate and (ii) a grinding aid that comprises a metabisulfite salt, so as to provide a powdered cement, wherein the metabisulfite salt is either the sole sulfate or is the majority sulfate, by weight, present in the grinding aid and wherein the grinding aid comprises the metabisulfite salt in an amount of 6wt% or more; and c) mixing the powered cement with aggregates and water, so as to provide concrete or mortar.

13. The method of any one of claims 10 to 12, wherein the grinding aid comprises the metabisulfite salt in an amount of 8wt% or more.

14. A ground clinker product comprising cement clinker interground with a grinding aid that comprises a metabisulfite salt, wherein the metabisulfite salt is either the sole sulfate or is the majority sulfate, by weight, present in the grinding aid and wherein the grinding aid comprises the metabisulfite salt in an amount of 6wt% or more.

15. A cement product comprising cement clinker interground with calcium sulfate and a grinding aid that comprises a metabisulfite salt, wherein the metabisulfite salt is either the sole sulfate or is the majority sulfate, by weight, present in the grinding aid and wherein the grinding aid comprises the metabisulfite salt in an amount of 6wt% or more.

16. A hardened cement product comprising a cement product as defined in claim 15 that has been hardened by mixing with water.

17. A concrete or mortar product comprising a cement product as defined in claim 15 that that has been mixed with aggregates and water.

18. The use, method or product of any one of the preceding claims wherein the cement clinker comprises Ordinary Portland Cement (OPC) clinker.

19. The use, method or product of claim 18 wherein the OPC clinker is used together with one or more fillers or cement replacements.

20. A grinding aid that comprises: • 6-90wt% of metabisulfite salt, e.g. from 8-75wt%, or from 10-60wt%;

• 0-75 wt% additional grinding aid materials selected from the group consisting of: alcohols and esters thereof, amino alcohols, sugars and modified sugars; e.g. from 2-70wt%, or from 5-65wt%; • no more than 5wt% of sulfate that is not metabisulfite salt; e.g. not more than

3wt%, or not more than 2wt%;

• 0-10wt% optional additives, e.g. de-foamers and/or colorants; and

• a balance of water.

21. The grinding aid of claim 20, wherein the total amount of metabisulfite salt plus additional grinding aid material is a) from 20 to 90wt% of the grinding aid, or b) from 25 to 85wt% of the grinding aid, or c) from 30 to 80wt% of the grinding aid.