[001 ] The present invention relates to the use of methyldiethanolamine as a grinding aid for cement and to methods of grinding cement clinker, and optionally fillers or cement replacements, with methyldiethanolamine, as well as to methods of obtaining cement in which methyldiethanolamine is used as a grinding aid and methods of obtaining concrete and mortar products therefrom.

Background to the Invention

[002] In the field of cement technology various additives are used at different stages of the manufacturing process to achieve the desired properties and improve the efficiency of the process. One such additive is a grinding aid, which is used during the stage of grinding the cement clinker in a grinding mill. A grinding aid is used to reduce the amount of energy required to grind the clinker and therefore can improve the efficiency of the grinding stage. Grinding aids can also improve the hydration of the clinker, leading to an improved quality product.

[003] In the present invention the term cement is used to refer to 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 CI 50 or the requirements of European Standard EN197.1.

[004] 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).

[005] The grinding stage involves grinding this clinker 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 additives or cement replacements may be selected from fillers and OPC replacements, such as calcium carbonate and other minerals, ground granulated blast furnace slag, natural pozzolans and pulverised fuel ash (PFA). 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.

[006] Wherever reference is made to "cement" in the present application, this refers to hydraulic cement, such as Ordinary Portland Cement (OPC), which may optionally be a blended cement, i.e. one which comprises one or more fillers or cement replacements. [007] A well known grinding aid in the art is triethanolamine (TEA). Other materials, such as glycols, (e.g. diethylene glycol (DEG)), triisopropanolamine (TIPA), tetrahydroxyethylethylene diamine (THEED), gluconates and dispersants have also been used. These grinding aid materials are introduced into the mill in small quantities and inter-grind with the clinker.

[008] The present invention has identified a new grinding aid that can provide desirable properties in the end product.

Summary of the Invention

[009] The present invention provides, in a first aspect, the use of methyldiethanolamine as a grinding aid for cement.

[010] Methyldiethanolamine (MDEA) has the chemical formula

CH ₃ N-(C ₂ H ₄ OH) ₂

and is known in the art for use as an admixture for accelerating the early hydration time of cement.

[01 1 ] Surprisingly, it has been now found that methyldiethanolamine is an effective grinding aid for cement which furthermore gives rise to significant compressive strength enhancement both at an early stage and at a late stage. As is conventional in this art, the compressive strength is measured at timescales determined in terms of number of days after mixing the cement with water and allowing the cement to set, and, unless stated otherwise, early stage strength enhancement refers to measurements taken at 1 and 3 days whilst later stage strength enhancement refers to measurements taken 7 and 28 days. [012] Early strength is often a problem with blended cements of lower OPC clinker content, for example where the cement composition has a clinker content of 90wt% or less, especially 85wt% or less. In particular, where the cement composition includes one or more fillers or cement replacements at a level of 10wt% or more, such as in a range of from 10 to 50wt%, in addition to clinker and calcium sulphate, the use of the present invention can be highly beneficial in enhancing early stage strength.

[013] It can also 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 present invention permits good strength results to be achieved at both early and late stages.

[014] The present invention therefore is beneficial in a number of ways.

[015] As is conventional for a grinding aid, the methyldiethanolamine can reduce the energy requirements during grinding and provide a uniform free flowing cement powder with reduced tendency to form lumps during storage. It is exemplary in this effect.

[016] Accordingly, the present invention provides methyldiethanolamine for use as a strength enhancing grinding aid for cement, in particular wherein the compressive strength is enhanced at both early stages (e.g. at 1 and/or 3 days) and late stages (e.g. at 7 and/or 28 days).

[017] The present invention also provides methyldiethanolamine for use as a strength enhancing grinding aid for blended cements, such as cement compositions having a content of fillers and/or cement replacements of 10wt% or more. In particular the compressive strength is enhanced at early stages (e.g. at 1 and/or 3 days) by the use of the methyldiethanolamine.

[018] The present invention provides, in a second aspect, a method of grinding cement clinker, which method comprises the steps of:

- providing cement clinker; and

- intergrinding the cement clinker with a grinding aid comprising methyldiethanolamine. [019] The present invention provides, in a third aspect, a method of obtaining cement, which method comprises the steps of:

- providing cement clinker; and

- intergrinding the cement clinker with calcium sulphate and a grinding aid comprising methyldiethanolamine, so as to provide a powdered cement.

[020] The present invention provides, in a fourth aspect, a method of obtaining a hardened cement, which method comprises the steps of:

- providing cement clinker;

- intergrinding the cement clinker with calcium sulphate and a grinding aid comprising methyldiethanolamine, so as to provide a powdered cement; and

- mixing the powered cement with water, so as to provide a hardened cement. [021 ] The present invention provides, in a fifth aspect a method of obtaining concrete or mortar, which method comprises the steps of:

- providing cement clinker;

- intergrinding the cement clinker with calcium sulphate and a grinding aid comprising methyldiethanolamine, so as to provide a powdered cement;

- mixing the powered cement with aggregates (e.g. gravel and/or sand) and water, so as to provide concrete or mortar.

[022] The present invention provides, in a sixth aspect, a ground clinker product comprising cement clinker interground with methyldiethanolamine.

[023] The present invention provides, in a seventh aspect, a cement product comprising cement clinker interground with calcium sulphate and methyldiethanolamine.

[024] The present invention provides, in an eighth aspect, a hardened cement product comprising a cement product of the seventh aspect that has been hardened by mixing with water.

[025] The present invention provides, in a ninth aspect, a concrete or mortar product comprising a cement product of the seventh aspect that has been mixed with aggregates (e.g. gravel and/or sand) and water. [026] 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 and limestone.

Detailed Description of the Invention

[027] The following preferred features apply to each of the aspects of the invention, where appropriate.

[028] The methyldiethanolamine may be provided in the form of a free base. The methyldiethanolamine may, however, optionally be provided in the form of a salt thereof, for example it may be provided in the form of a sulphate, nitrate, chloride, nitrite, phenolate, acetate or gluconate salt. The methyldiethanolamine may also optionally be provided in its ester form, because upon addition to the high pH of a hydrating cement it will undergo hydrolysis and revert back to the alcohol. The methyldiethanolamine may, for example, be provided in the form of an ester of an organic acid, such as a carboxylic acid; preferably a C1 -C5 carboxylic acid, more preferably a CI , C2 or C3 carboxylic acid.

[029] The methyldiethanolamine may optionally be used together with other grinding aids and/or other cement additives. Methyldiethanolamine is highly beneficial in that it is compatible with many other compounds and can therefore be used with these compounds to achieve the desired effects in terms of efficiency of the process and/or characteristics of the end product.

[030] In one embodiment, the methyldiethanolamine is used together with one or more (such as two or more, or three or more) other grinding aid. The grinding aids may, for example, be one or more grinding aid selected from: glycols (such as diethylene glycol, triethylene glycol, ethylene glycol, propylene glycol or polyethylene glycol), polyols and esters thereof (e.g. glycerol and monoacetin), gluconates, diethanolisopropanolamine, triisopropanolamine, acetic acid, polycarboxylates, naphthalene sulphonates, lignosulphonates, urea, acetyl urea and diacetyl urea. However, other grinding aids may equally be considered. [031 ] The methyldiethanolamine may optionally be used together with other components conventionally used in grinding aids, such as carriers or solvents (e.g. water). De-foaming agents may also optionally be used in order to control the density of the product.

[032] The methyldiethanolamine may suitably be used in amounts known in the art for grinding aids, such as l OOOppm 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 900ppm, such as from 10 to 800ppm, e.g. from 50 to 700ppm, such as from 75 to 600ppm or from 100 to 500ppm or from 150 to 400ppm.

[033] 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 l OOOppm). 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.

[034] The cement clinker is preferably a Portland cement clinker. In one embodiment it may be a Portland cement clinker containing 1 weight % or more tetracalcium aluminoferrite (C4AF), e.g. containing 2 weight % or more, 3 weight % or more, 4 weight % or more, or 5 weight % 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 weight % or less tetracalcium aluminoferrite (C4AF), such as 0.05 weight % or less.

[035] 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.

[036] 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. [037] The methyldiethanolamine 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 methyldiethanolamine and the cement clinker are added into the grinding equipment using a single conveyor.

[038] The methyldiethanolamine may be added into the grinding equipment before the calcium sulphate, simultaneously with the calcium sulphate or after the calcium sulphate.

[039] Any additional grinding aids used with the methyldiethanolamine, as discussed above, may be pre-mixed with the methyldiethanolamine before use, or may be added into the grinding equipment before the methyldiethanolamine, simultaneously with the methyldiethanolamine or after the methyldiethanolamine.

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

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

[042] In one embodiment, the temperature during the intergrinding is controlled, e.g. such that there is a mill exit temperature within a few degrees of 1 15°C, such as from 1 10 to 120°C. In another embodiment, the mill temperature is not controlled.

[043] 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.

[044] The intergrinding of the cement clinker may be carried out with any suitable amount of calcium sulphate; for example from 1 to 15wt% of the interground components may be calcium sulphate, such as from 3 to 10wt%. [045] As is known in the art, small amounts of calcium carbonate and other minerals are often present during the intergrinding. For example, up to 5wt% calcium carbonate and up to lwt% or more, e.g. up to 5wt%, of other minerals may be present during the intergrinding.

[046] Any optional fillers or cement replacements, e.g. pozzolans, fly ash (such as pulverised fuel ash), or limestone, 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%.

[047] 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%.

[048] The amount of clinker (e.g. OPC clinker) present in the inter-ground cement composition may be from 40 to 99wt%, such as from 45 to 95wt% or from 50 to 95wt%. In one embodiment, it may be from 40 to 90wt%, e.g. from 45 to 85wt%, or from 50 to 85wt%, or from 55 to 80wt%, or from 60 to 80wt%.

[049] In one embodiment of the invention the cement composition comprises :

from 1 to 15wt% calcium sulphate, 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%.

[050] In particular, in one embodiment the cement composition comprises:

from 1 to 15wt% calcium sulphate, such as from 3 to 10wt%

- from 40 to 90wt% clinker (e.g. OPC clinker), such as from 50 to 85wt%

- from 5 to 50wt% filler and cement replacements, such as from 10 to 40wt%.

[051 ] 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.

[052] 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 CI 09.

Examples

Cement products tested in the Examples 1-3

The examples 1 -3 were carried out using Malaysian clinker and grey cement which when tested had elemental compositions as indicated in Table 1.

Table 1

Example 1 - Grinding of Malaysian clinker

4.75 kg of Malaysian clinker (as characterised above) was ground with 0.25kg of gypsum in a laboratory ball mill in the presence of either no grinding aid (control) or in the presence of 0.45g/kg (450ppm) of a grinding aid as set out in Table 2 below.

It can be seen that I B is a comparative example, using the known grinding agent triethanolamine (TEA). The remaining Examples use methyldiethanolamine (MDEA) in accordance with the invention. Defoamer was used in amounts such that a comparable density was obtained across the Examples, as it is known that density can affect the compressive strength.

Table 2

In each case (including the control, with no grinding aid) the grinding was carried out for 40 minutes. The powdered cement thus obtained was then cured with water.

Mechanical strength measurements were carried out on 50 mm cubes of the cured cement thus obtained after 1 , 7 and 28 days. In each case three samples were tested and the results averaged.

The calculated average (mean) results are shown in Table 3.

Results

Table 3

It can be seen that the products using MDEA as grinding aid, either alone or in combination with other known grinding aids, have good improvements in compressive strength, compared to the control, at 1 , 7 and 28 days. In other words, the use of MDEA as a grinding aid enhances both early and late stage compressive strength. It can be seen that TEA is beneficial for early strength but less so than MDEA for later strength. It can be seen that particularly good results are shown at 7 and 28 days for MDEA based grinding aids, as compared to TEA.

Example 2 - Malaysian clinker with limestone as OPC replacement Malaysian clinker (as characterised above) was ground with gypsum and limestone in the following weight proportions: clinker = 71 %, gypsum = 4%, limestone filler = 25%.

The ground cement was either used directly or mixed with 0.3g/kg (300ppm) of grinding aid. The grinding aid was formulated in the following weight proportions: water 66%, DEG 10%, MDEA 24%.

This test was to assess the extent to which the components of the grinding aid had an impact on the properties of the end product, even if not present during the grinding of the clinker, and also ensured that the effect of particle size was eliminated.

The ground cement products (control and Example) were used to make mortar in accordance with ASTM C 109 (cement 500g, sand 1350g and a 0.52 water to cement ratio, to give flow in the range 105 - 1 15%>). Testing of the concrete products (control and Example) was carried out after 2 days, 7 days and 28 days. In each case two samples were tested and the results averaged.

Results are shown in Table 4.

Results

2 Days 7 days 28 days

Control Weight (g) 282 280.5 285.5 280.5 286 282 kN 37.8 39.75 62.51 66.11 89.55 85.62

N/mm ² 15.12 15.90 25.00 26.44 35.82 34.25

Average 15.51 25.72 35.05 Example Weight (g) 280 284 288 283 283 291 kN 46 44.97 76 74.41 98.6 99.31

N/mm ² 18.40 17.99 30.40 29.76 39.44 39.72

Average 18.19 30.08 39.58

Variation

from 17.35 16.94 12.98 control (%)

Table 4

It can be seen that the concrete product in accordance with the invention shows improved strength at all ages. However, these effects are much less significant than the improvements shown when the MDEA based grinding aid was used as a grinding aid, i.e. present during grinding of the clinker rather than used as an additive to the cement.

Example 3 - Addition to Grey Cement A grey cement was made using the following weight proportions: pre-ground grey clinker 600 g, sand 1800 g and water 300 g; the cement clinker had the elemental compositions as indicated in Table 1.

Grinding aids as shown in Table 5 were added to the water, in an amount of 0.45g/kg (450ppm), when preparing the cement.

This test was to assess the extent to which the components of the grinding aid had an impact on the properties of the end product, even if not present during the grinding of the clinker.

Table 5

Mechanical strength measurements were carried out on 50 mm cubes of the cured cement thus obtained after 1 , 7 and 28 days. Results are shown in Table 6.

Results Control 3A 3B 3C 3D 3E

Mortar Density 2.23 2.24 2.22 2.21 2.23 2.22

Compressive strength

After 1 day (N/mm ² ) 8.47 9.05 8.54 8.59 9.10 8.64

Variation from control (%) - 6.8 0.8 1.4 7.4 2.0

After 7 days (N/mm ² ) 25.48 27.54 26.34 27.06 27.72 27.08

Variation from control (%) - 8.1 3.4 6.2 8.8 6.3

After 28 days (N/mm ² ) 37.39 40.66 39.00 40.96 39.50 40.99

Variation from control (%) - 8.7 4.3 9.5 5.6 9.6

Table 6

It can be seen that although increases in compressive strength over all ages are exhibited, these are much less significant than the improvements shown when the MDEA based grinding aid was used as a grinding aid, i.e. present during grinding of the clinker rather than used as an additive to the cement.

Example 4 - Blended cements in plant trial

Blended cements were prepared based on the formulations shown in Table 7. The compositions were ground in the presence of three different grinding aids as set out in Table 8 below.

Table 7

Grinding A (Comparative) B (Comparative) C (Invention)

Aid

Commercially Commercially Water (53.7wt%>); sodium available grinding available grinding I aid: lignosulphonate powder (1 aid: containing containing TEA, wt%); triethanolamine chloride, TEA, TIPA TIPA, sulphonated (TEA) 99% cone (12wt%); and glycol napthalene methyldiethanolamine

formaldehyde and (MDEA) (25wt%); polycarboxylate diethylene glycol (8wt%);

tri-n-butyl phosphate (0.3 wt%)

Table 8

In each case the grinding was carried out for 40 minutes in a cement plant, with the powdered cement being cured with water.

Mechanical strength measurements were carried out on samples of the cured cement after 1 , 2, 7 and 28 days. The results are shown in Table 9.

Results

A B C

Mill production (tons per hour) 92 94 102

Blaine (cm /gm) 3400 3488 3460

Residue 45 μ (%) 1.6 1.43 1.3

S0 ₃ (%) 2.7 2.6 2.6

Mill motor power (kWhr) 4120 4101 4230

Power consumption (kWhr/ton) 44.8 43.6 41.5

Initial set (min) 120 120 1 10

Final set (min) 180 170 150

Normal Consistency (%) 29.8 29.5 29.2

Soundness (mm) 1 1 1

Compressive Strength (N/mm ² )

1. 1 day EN 15.98 16.38 19.48

2. 2 days EN 25.16 25.97 29.41

3. 7 days EN 44.8 46.1 47.01

4. 28 days EN 56.72 57.1 1 58.35 Table 9

It can be seen that the grinding aid according to the invention, which includes MDEA, resulted in good early and late stage strength.

In particular, the advantages of high mill throughput and lower power consumption, as well as very good early strength and final strength equivalent to commercially available grinding aids, were observed.

Example 5 - OPC cements in plant trial

Ordinary Portland Cements were prepared based on the formulations shown in Table 10. The compositions were ground in the presence of two different grinding aids as set out in Table 1 1 below.

Table 10

Table 11

In each case the grinding was carried out for 40 minutes in a cement plant, with the powdered cement being cured with water. Mechanical strength measurements were carried out on samples of the cured cement after 1 , 2, 7 and 28 days. The results are shown in Table 12. Results

Table 12

It can be seen that the grinding aid according to the invention, which includes MDEA, resulted in good early and late stage strength.

In particular, the advantages of high mill throughput, very good early strength and final strength equivalent to a TIPA-based grinding aid, were observed.