GB2378946A

GB2378946A - Preparation of an admixture for cementitious compositions

Info

Publication number: GB2378946A
Application number: GB0120699A
Authority: GB
Inventors: Paul Griffin; Ian Gibb
Original assignee: RMC GROUP PLC
Current assignee: RMC GROUP PLC
Priority date: 2001-08-24
Filing date: 2001-08-24
Publication date: 2003-02-26
Also published as: AU2002326017A1; WO2003018505A3; GB0120699D0; WO2003018505A2; EP1419121A2

Abstract

An admixture for a cementitious composition, comprising water, at least one viscosity modifying agent, and at least one plasticiser, is prepared by providing a pre-mixture comprising water, viscosity modifying agent, and a first portion of plasticiser, then mixing the pre-mixture with a second portion of plasticiser. The plasticiser is preferably a polyacrylate polymer superplasticiser comprising from 15 to 90 wt% of the admixture. The viscosity modifying agent may be a polysaccharide such as welan gum, present in the final admixture at 0.1% to 2%. The admixture has a pH of & — 10 and has a solids content of 15 to 40.0wt%. Mono-propylene glycol is used as a dispersing agent in the admixture. The admixture may also contain a dispersing agent, a defoamer, a buffer, a retarder, pH adjuster, a biocide, a preservative, a base, and accelerator or an air entraining agent.

Description

An Admixture for Cementitious Compositions The present invention relates to admixtures for cementitious compositions and, in particular, to a single dose admixture for cementitious compositions.

The present invention also provides a method for preparing such admixtures.

The term "cementitious compositions" herein refers to any cement, concrete, artificial or natural stone, mortar, grout, aggregate, slurry compositions or mixtures thereof.

Preferred cementitious compositions include concrete such as self-compacting concrete, cementitious mortar or grout, or chalk slurries.

Self-compacting concrete is particularly preferred.

Concrete is comprised principally of cement, coarse aggregate, fine aggregate and water. The strength of the concrete is linked to the water cement ratio (w/c ratio). A low w/c value corresponds to a high strength. A low strength aggregate will produce a lower strength concrete. Aggregates are classified according to their type, shape and particle size.

They are embedded in a matrix of cement paste.

Examples of naturally occurring aggregates are, processed land based and marine gravels and crushed rocks such as limestones and granites. Aggregates can be sub-divided into coarse and fine fractions and are combined proportionally to a desired overall particle distribution for a concrete mixture.

In the production of concrete using"hydraulic" cement, the addition of water initiates the chemical process associated with the setting and hardening of the cement paste. This crystallisation reaction is known as hydration. Ideally the aggregates are evenly coated with the cement paste thus binding the whole mass together.

The most commonly used cement, especially in the UK, is Portland cement; this is often blended or mixed with other hydraulic cement materials such as ground granulated blast furnace slag and pulverised fuel ash (fly-ash) to obtain specific concrete characteristics.

Portland cement is made from a mixture of approximately 75% of a calcareous material such as limestone or chalk and 25% of a siliceous material such as clay or shale. Both materials are intimately mixed and together with some minor components are heated (burned) to a high temperature at which they fuse together. The resultant clinker is finely ground to form Portland Cement.

Portland cement is a complex mixture of multicomponent, mineral solid-solutions. Among these, are compounds of calcium silicate and calcium aluminate that hydrate in the presence of water. The essential binding component has been identified as calcium silicate hydrate (CSH).

Whilst the basic formulation of a concrete mix approximates to 80% aggregate, 15% cement and 5% water, most commercially produced concretes are specially designed mixes. These mixes are produced for specific applications or to have specific properties, for example for placing underwater and for placing by concrete pumping and for other purposes.

These concrete types may incorporate small amounts of chemicals known as admixtures. Admixtures modify one or more specific properties of the fresh or hardened concrete.

For example, a retarding admixture will defer the setting of the concrete. This is useful when slow rates of placement are envisaged or for placing under high summer temperatures.

Other admixtures are used to control properties such as water permeability, concrete consistence, water demand and resistance to freeze/thaw damage.

The workability of concrete is related to the water: cement ratio and the mix constituents including the particle size distribution of aggregate and cement particles. For a given aggregate: cement ratio, the higher the water: cement ratio, generally the more workable is the concrete.

Despite the advantages of high workability, a high water: cement ratio can, however, adversely affect the strength of the concrete. For example, if excess free water is present, which has not been absorbed into the aggregate and cement or is not adsorbed and used in the hydration reaction, this leaves voids in the hardened concrete as it dries out. The result of this is lower strength and increased porosity leading to a potential reduction in the durability of the

concrete in the structure. Additionally, excess water can result in segregation of the mix during placement.

Accordingly, it is desirable to produce highly workable concrete without significantly increasing the water: cement ratio.

This has led to the widespread use of admixtures known as plasticisers and more recently, to the use of superplasticisers. Plasticisers and superplasticisers impart increased workability when added to concrete, without the necessity of the addition of water to help achieve the effect.

Plasticisers tend to be formulated from modified lignosulphonates and hydroxycarboxylic acids. The lignosulphonates may be derived from fermented wood, for example, spruce.

Superplasticisers fall generally into the categories of sulphonated melamine-formaldehyde (SMF) condensates; sulphonated naphthalene-formaldehyde (SNF) condensates; modified lignosulphonates; acid amide/polysaccharide mixtures and other high molecular weight hydroxylated polymers and copolymers.

SMF and SNF superplasticisers are thought to operate by the action of electrostatic repulsion, which results in rapid dispersion of cement particles.

This increases the mobility of the cement paste requiring no additional water for a significant increase in concrete workability.

When concrete is placed into formwork, and especially when there is reinforcement, air can be trapped and, this results in voids or honeycombing. A Self Compacting Concrete (SCC), which has better

deformability and resistance to segregation and can be filled in heavily reinforced formwork without vibrators, has recently been developed. SCC can be placed in the same way as ordinary concrete but without the need for any vibration. Pseudo-plastic in nature, SCC passes around reinforcement, without segregation or bleeding, and at the same time expels entrapped air and so reduces excess voids and honeycombing. An important advantage of SCC is that it obviates compaction.

Generally, SCC properties are obtained by using admixtures in conjunction with careful mix design.

The main admixture used in SCC is a superplasticiser, and this may be supplemented with a viscosity modifying agent (VMA).

Superplasticisers are used to achieve high fluidity and reduce the water: cement ratio.

SCC has tended to rely on plasticisers based on polyacrylate polymers known as polycarboxylic ethers (PCE). These superplasticisers are believed to operate by a mechanism of steric hindrance rather than electrostatic repulsion.

A viscosity modifying agent may be incorporated to enhance the yield value and viscosity of the mixture, hence reducing bleeding, segregation and settlement. Examples of viscosity modifying agents include polysaccharides and nanosilica. The usual polysaccharide is welan gum, which is added as a powder or as a suspension in oil in very small quantities.

However, the addition of these separate admixtures (i. e. superplasticisers and viscosity

modifying agents) has contributed to making the preparation of SCC problematic. These ingredients are not standard stock in concrete plants, and traditional concrete plants are not designed to handle the addition of small quantics of powder like welan gum.

It has therefore been proposed to provide all desired ingredients in a single admixture. Such "one shot" admixtures are more easily handled by existing dispensing equipment on concrete plants. Until now, it has not been possible to produce a stable mix of polyacrylate based superplasticiser and welan gum.

Moreover, the production of a mix by adding a small amount of viscosity modifying agent to a large quantity of plasticizer is problematic on an industrial scale due to difficult homogenization.

It would therefore be desirable to provide a suspension of a superplasticiser and a viscosity modifying agent which is stable over time and easily usable on an industrial basis.

Accordingly, the present invention provides a process for the preparation of an admixture for a cementitious composition, said admixture comprising water, at least one viscosity modifying agent, and at least one plasticiser, the process comprising the steps of: (i) providing a pre-mixture comprising water, viscosity modifying agent, and a first portion of plasticiser, (ii) mixing the pre-mixture from step (i) with a second portion of plasticiser.

The plasticiser in the pre-mixture of step (i) will generally be the same as the plasticiser mixed with the pre-mixture in step (ii), although a different plasticiser may be used in step (ii); also, the plasticiser used in step (i) may be a blend of two or more plasticisers.

As used therein, the term"plasticiser"means any admixture which, without affecting the consistence, permits a reduction in the water content of a given concrete mix, or which without affecting the water content increases the slump/flow or produces both effects simultaneously. Admixtures which increase the slump/flow without affecting the water content are preferred.

As used therein, the term"plasticiser"refers to any water reducing admixture meeting the requirements as defined by the British Standards, BS5075, Part 1,1982.

Preferably, the plasticiser is a superplasticiser. As used therein the term "superplasticiser"means any admixture which without affecting the consistence, permits a high reduction in the water content of a given concrete mix or which, without affecting the water content increases the slump/flow considerably or produces both effects simultaneously. Admixtures which considerably increase the slump/flow without affecting the water content are preferred.

As used therein, the term"superplasticiser" refers to any superplasticising admixture meeting the requirements as defined by the British Standards, BS 5075, Part 3,1985.

Suitable superplasticisers include polycarboxylate polymers, SMF condensates, SNF condensates, modified lignosulfates and amid/polysaccharide mixtures, their derivatives and mixtures thereof, and other high molecular weight hydroxylated polymers and copolymers, such as those described by Ramachandran et al,"Superplasticisers : properties and applications in concrete."Preferably, the superplasticisers are polycarboxylate polymers such as those described by Bradley et al, Cem. Concr.

Aggr. , 8: 68-75 (1986); in particular, polyacrylate copolymers and derivatives thereof comprising (co)- polymerized units of acrylic acid and/or maleic acid or derivatives thereof are preferred. According to a still more preferred embodiment, said (co)-polymerized units include a poly-ether side chain such as polyethylene oxide. Polycarboxylic ethers (PCE) and derivatives thereof are preferred; polycarboxylate from the Sokalan range such as Sokalan HP 80, manufactured by BASF are particularly suitable.

Sokalan HP 80-ils an aqueous solution of PCE, having a solids content of approximately 39 wt. %.

Other suitable products may include other products from the Sokalan range such as CP5 (maleic acidacrylic acid co-polymer, Na salt), CP7 (maleic acidacrylic acid co-polymer, Na salt), CP9 (maleic acidolefin co-polymer co-polymer, Na salt), CP10 (modified polyacrylic acid, Na salt), PA20 (polyacrylic acid, Na salt), PA40 (polyacrylic acid, Na salt), PM101 (maleic acid co-polymer, Na salt), or products based on phosphate ethers such as Marphos TS615P, also available from BASF.

Optionally, the PCE solution can also contain an integral defoamer. Also, part of PCE may be replaced by a conventional superplasticiser, for

example sulfonated naphthalene formaldehyde, such as Galoryl LH220&commat;.

Viscosity modifying agents useful in the practice of the present invention include polysaccharides and/or nanosilica. According to a preferred aspect, welan gum is used as the viscosity modifying agents. Welan gum is a heteropolysaccharide, which can be used as a powder such as Kelco-Crete K1C376 supplied by CP Kelco UK Limited.

If appropriate, additional ingredients such as defoamer, usually used in connection with plasticisers to ensure or improve plasticising properties may be required.

Typically, from 2 to 30 wt. % of plasticiser, said percentage being expressed with reference to the plasticiser's solids content, is comprised in the premixture of step (i), with the remaining 98 to 70 wt. % being mixed with the pre-mixture in step (ii).

Typically, if a 39% suspension is used, such as Sokalan HP 80, from 3 to 7 wt. % of the superplasticiser's solids content is comprised in the pre-mixture of step (i), with the remaining 97 to 93 wt. % of the superplasticiser's solids content being mixed with the pre-mixture in step (ii).

The premixture of step (i) preferably satisfies the following relationship: Weight of solids in premix 10 to 17 % Weight of water and plasticiser (preferably from 11 to 16 %, more preferably from 12 to 15 %).

The pH of the admixture is preferably 10, more preferably from 6 to 10, still more preferably from 7 to 9. It has been found that maintaining the pH of the admixture to 10 results in a particularly stable suspension.

The solids content in the admixture is preferably from 15 to 40.0 wt. %, more preferably from 19 to 37.0 wt. %.

In the final product, the weight percentage of the viscosity modifying agent to the final product is preferably from 0.1% to 2%, more preferably from 0. 25% to 1%.

The admixture may contain one or more additional ingredients, for example one or more of a dispersing agent, a defoamer, a buffer, a retarder, a pH adjuster, a biocide, a preservative, a base, an accelerator, and/or an air entrainer.

A preferred dispersing agent is mono-propylene glycol.

The present invention also provides a process for the preparation of a cementitious composition, wherein an admixture as herein defined is added to the composition in a single dose (i. e."one shot"). The cementitious composition may be concrete, preferably a self compacting concrete.

The present invention further provides an admixture for a cementitious composition comprising an aqueous solution of:

(a) from 15 to 90 wt. % of one or more plasticisers said percentage being expressed with reference to the plasticiser's solids content, (b) from 0.1 to 2 wt. % of one or more viscosity modifying agents, and (c) water, wherein the pH of the aqueous solution is from 6 to 10.

Typically where the plasticiser is in the form of an aqueous solution, the figures recited in (a), which refer to the plasticisers'solid content correspond to approximately 80 to 90%, when expressed with reference to the suspension of plasticiser.

According to the present invention, stable admixtures have been prepared for the first time.

Stability may be assessed having regard to the tendency of the constituents to separate out of solution while the admixture is standing. In the prior art admixtures, the viscosity modifying agent tends to drop out of suspension. Usually, the admixtures according to the present invention show little or substantially no separation over a period of time. In particular, the admixtures are stable typically for at least 24 hours, more typically at least 2 days, still more typically at least 7 days.

Indeed, the admixtures may be stable for over 6+ months.

Preferably, the plasticiser is a superplasticiser as defined above.

In a preferred embodiment, the admixture comprises from 15 to 40 wt. % of one or more plasticisers, said percentage being expressed with reference to the plasticiser's solids content, from

0.1 to 2 wt. % of one or more viscosity modifying agents, up to 7 wt. % (preferably up to 5 wt. %) of one or more of a dispersing agent, a defoamer, a buffer, a retarder, a pH adjuster, a biocide, a preservative, preservatives, a base, a buffer, an accelerator, and/or an air entrainer, and the balance water.

More preferably, the admixture comprises from 19 to 37 wt. % of a polycarboxylic ether, said percentage being expressed with reference to the plasticiser's solids content, from 0.5 to 1 wt. % of welan gum, up to 5 wt. % of one or more of a dispersing agent, a defoamer, a buffer, a retarder, an accelerator, a pH adjuster, a biocide, a preservative, a base and/or an air entrainer, and the balance water, wherein the pH is from 6.5 to 9.5.

The present invention also provides a cementitious composition which comprises an admixture as herein defined. The cementitious composition may be concrete, for example a self compacting concrete.

The present invention still further provides a method of reducing separation in an admixture for a cementitious composition, said admixture comprising water, at least one viscosity modifying agent, and at least one plasticiser, the method comprising the steps of: (i) providing a pre-mixture comprising water, viscosity modifying agent, and a first portion of plasticiser, (ii) mixing the pre-mixture from step (i) with a second portion of plasticiser.

The present invention also provides for the use of mono-propylene glycol as a dispersing agent in an admixture for a cementitious mixture.

The present invention also provides a polysaccharide suspension comprising mono-propylene glycol.

Preferably, the plasticiser is a superplasticiser as defined above.

The mixture according to the present invention may, if desired, include one or more additional ingredients. Examples of additional ingredients include the following: - Retarders such as sodium gluconate and other major retarders such as sugars and phosphates.

Defoamers to remove the air that superplasticisers naturally entrain. The defoamers may also help to buffer the suspension. Suitable defoamers include Lumiten EL (manufactured by BASF), Pluronic PE9200 (manufactured by BASF), Degressal SD20 (manufactured by BASF), Foamaster (manufactured by Henkel), TBP (manufactured by Bayer).

- Preservatives, such as biocides, including Glutaraldehyde (manufactured by BDH), Nippacide TBX (manufactured by Nipa Laboratories Ltd), Preventol D2 (manufactured by Bayer).

- Bases, such as sodium hydroxide (NaOH), which helps to breakdown any flocks of viscosity modifying agent formed.

- Dispersing agents to aid the dispersion of the viscosity modifying agent."Dispersing agent"herein refers to any agent to promote uniform and maximum separation of solid particles in a suspending medium. It has surprisingly been found that monopropylene glycol is a particularly efficient dispersing agent, in particular for dispersing polysaccharides and more specifically welan gum; - Accelerators to increase the rate of stiffening or setting of the concrete or to increase the rate of hardening and early strength again. Usual accelerators include calcium chloride (although generally not used in concrete containing embedded metal) and a range of chloride free accelerators (CFA), such as calcium nitrate, calcium fornate or calcium thiocyanate.

The optional ingredients such as the dispersing agent, defoamer, buffer and retarder may be added to the pre-mixture before the second portion of the plasticiser is added, while optional ingredients such as bases and preservatives may be added after the second portion of the superplasticiser has been added.

According to a further aspect, the present invention also provides a process for the preparation of a pre-mixture as herein described, the process comprising mixing water, a plasticiser, and a viscosity modifying agent, wherein the amount of plasticiser is such that the total solids content of the premix expressed as a percentage of the premix is from 10 to 17 wt. %.

According to a preferred embodiment, the solids contents of the premix is approximately 15%.

Preferably, the plasticiser is a superplasticiser as defined above.

It has surprisingly been found that stabilized suspensions may be achieved by preparing, in a first step, a pre-mixture of a small amount of the superplasticiser with all or substantially all of the viscosity modifying agent. While not wishing to be bound by theory, it is believed that this process enables the viscosity modifying agent to be partially hydrated, thereby resulting in greater stability.

A stabilized pre-mixture is preferably achieved by mixing part plasticiser and the viscosity modifying agent; the plasticiser dosage required to give the required solids content in the premix can be determined in accordance with the following formula:

QZ Initial plasticiser dosage= y Q (l Y) 100

where Q=desired solids content (%) in premix, Y=solids content (%) of plasticiser in PCE, and Z=initial added (%) water.

If the solids content of the premix is within the above specified range, then this allows the supplementation of an additional amount of plasticiser, as required, to produce a stable, usable suspension. More particularly, if the solids content of the premix is from 12 to 17 wt. %, then it is possible to produce a particularly stable product.

Other ingredients may be added during the preparation of the pre-mixture. In particular, sodium

gluconate may be added when preparing the pre-mixture, or before adding the rest of the plasticiser to the final product. Traditionally, the dispersing agents, defoamers can be added between steps i) and ii).

The processes according to the present invention may be carried out at ambient temperature.

The processes may be carried out using a conventional high speed, high shear mixer such as IKA stirrer, type ST DV S2 on a laboratory scale basis; or any other mixers appropriate to industrial full-scale.

Generally on a laboratory scale basis, the viscosity modifying agent is added slowly under vigorous stirring (approximately 750 rpm) as to avoid the formation of lumps. When addition is completed, the speed of the mixer may be increased to approximately 1000 rpm and stirring may be continued so as to allow the product to thicken. Corresponding mixing speeds appropriate to larger scales can be routinely determined by one skilled in the art seeking to carry out the present process on a full-scale industrial basis.

The present invention also provides for the use of the suspensions as herein described as admixtures for cementitious compositions. Cementitious compositions comprising the admixtures as herein described are a further aspect of the present invention. According to a preferred aspect, the present invention more specifically refers to concrete. According to a more preferred aspect, the present invention more specifically refers to Self Compacting Concrete (SCC).

It has also been found that monopropylene glycol may be added to the admixture to disperse the

viscosity modifying agent. According to a further aspect, the invention provides for the use of monopropylene glycol as a dispersing agent in a polysaccharide suspension. According to yet a further aspect, polysaccharide suspensions comprising monopropylene glycol are also encompassed by the present invention.

The present invention will be further understood with reference to the following experimental examples.

Example 1

Item No. Raw Material % wt 1 Water 9.50 2 Sokalan HP80 4.22 3 Sodium gluconate 1.00 4 Propylene glycol 2.50 5 Defoamer 0.30 6 K1C376 0.50 7 Sokalan HP80 81.68 8 Biocide 0.30 9 Sodium hydroxide (47%) 0.00 Sokalan HP80 is the trade name of a PCE available from BASF. It has a solids content of approximately 39%.

The sodium gluconate acts as a retarder.

The propylene glycol acts to aid dispersions of the welan gum.

K1C376 is for Kelco-crete K1C376, which is the trade name of a welan gum available from CP Kelco UK Ltd.

The biocide acts as a preservative.

The sodium hydroxide helps break down the flocks of welan formed (see other examples).

Equipment IKA stirrer, type ST DV S2 having a speed range of 50- 200 rpm.

Dissolver blade.

Process 1. Add the water in to the mixing vessel and commence stirring at 750 rpm.

2. Add item 2 and continue to stir. This provides a solids content of 12 wt. % (i. e. weight of solids in the PCE (39% of 4.22 = 1.65), divided by the total weight of the PCE and water (4.22 and 9.5).

3. Add item 3 slowly, and stir until dissolved.

4. Add item 4 and stir for 5 min.

5. Add item and continue to stir for 5 min.

6. Add item 6 slowly, so as to stop the formation of lumps, and increase the speed of the mixer to 1000 rpm. Continue to mix at this speed for 20 min. This will allow the product to thicken.

7. Add in slowly item 7, so as to produce a homogeneous product free from any lumps, and reduce the mixer speed to 750 rpm.

8. Add item 8 and continue to mix for 15 min.

Results

Aspect: Opaque straw coloured suspension.

S. G. at 20 C : 1.118 Solids: 35.9% pH: 7.00 Stability: + 7 months Example 2A & B

Item No. Raw Material % wt 1 Water 10.30 2 Sokalan HP80 4.58 3 Sodium gluconate 1.00 4 Propylene glycol 2.50 5 Defoamer 0.30 6 K1C376 1.00 7 Sokalan HP80 80.02 8 Biocide 0.30 9 Sodium hydroxide (47%) (Form A) 0.00 (Form B) 0.70 Note: Total %Wt. for Form B equals 100.70 Equipment IKA stirrer, type ST DV S2 having a speed range of 50- 200 rpm.

Dissolver blade.

Process 1. Add water in to mixing vessel and commence stirring at 750 rpm.

2. Add item 2 to this and continue to stir (this will provide a 12% solution).

3. Add item 3 slowly, and stir until dissolved.

4. Add item 4 and stir for 5 min.

5. Add item 5 and continue to stir for 5 min.

6. Add item 6 slowly, so as to stop the formation of lumps, and increase the speed of the mixer to 100 rpm. Continue to mix at this speed for 20 min. , this will allow the product to thicken.

8. Add item 8, followed by item 9 if appropriate, and continue to mix for 15 min.

Results Aspect: Opaque straw coloured suspension.

S. G at 20 C : 1.116 Solids: 35. 3% pH: (A) 7.00, (B) 9.4 Stability: + 7 months Example 3

Item No. Raw Material % wt 1 Water 6.95 2 Sokalan HP80 3.09 3 Propylene glycol 2.00 4 Defoamer 0.10 5 Kl376 0.25 6 Sokalan HP80 86.61 7 Sodium gluconate 0.70 8 Biocide 0.30 9 Sodium hydroxide (47%) 0.60

Equipment IKA stirrer, type ST DV S2 having a speed range of 50 200 rpm.

Dissolver blade.

Process 1. Add water in to mixing vessel and commence stirring at 750 rpm.

2. Add item 2 to this and continue to stir (this will provide a 12% solution).

3. Add item 3, and stir for 5 min.

4. Add item 4, and stir for 5 min.

5. Add item 5 slowly as to stop the formation of lumps, and increase the speed of the mixer to 1750-2000 rpm. Continue to mix at this speed for 15 min, this will allow the product to thicken.

6. Add in slowly item 6, so as to produce a homogeneous product free from any lumps, and reduce the mixer speed to 750 rpm.

7. Add item 7 slowly and continue to stir until dissolved.

8. Add item 5, followed by item 9 and continue to mix for 15 min.

Results Aspect: Opaque straw coloured suspension.

S. G at 20 C : 1.21 Solids: 36.8% pH: 8.00 Stability : + 6 months

Example 4

Item No. Raw Material % wt 1 Water 6.85 2 Sokalan HP80 3.04 3 Propylene glycol 2.00 4 Defoamer 0.20 5 K1C376 0.25 6 Sokalan HP80 86.66 7 Sodium gluconate 0. 70 8 Biocide 0.30 9 Sodium hydroxide (47%) 0.60 Equipment IKA stirrer, type ST DV S2 having a speed range of 50- 200 rpm.

Dissolver blade.

Process 1. Add water in to mixing vessel and commence stirring at 750 rpm.

2. Add item 2 to this and continue to stir (this will provide a 12% solution).

3. Add item 3, and stir for 5 min.

4. Add item 4 and stir for 5 min.

5. Add item 5 slowly, so as to stop the formation of lumps, and increase the speed of the mixer to 1750-2000 rpm. Continue to mix at this speed for 15 min, this will allow the product to thicken.

7. Add item 7 slowly and continue to stir until dissolved.

8. Add item 8, followed by item 9 and continue to mix for 15 min.

Results Aspect: Opaque straw coloured suspension.

S. G at 20 C : 1.21 Solids: 36.8% pH: 8.00 Stability: + 6 months Example 5

Item No. Raw Material % wt 1 Water 6.53 2 Sokalan HP80 2.90 3 Propylene glycol 1.98 4 Defoamer 0.20 5 K1C376 0.50 6 Sokalan HP80 86.09 7 Sodium gluconate 1.50 8 Biocide 0.30 9 Sodium hydroxide (47%) 0.60

Note: Total % wt equals 1UU. bU Equipment IKA stirrer, type ST DV S2 having a speed range of 50- 200 rpm.

Dissolver blade.

Process 1. Add water in to mixing vessel and commence stirring at 750 rpm 2. Add item 2 to this and continue to stir (this will provide a 12% solution).

3. Add item 3, and stir for 5 min.

4. Add item 4, and stir for 5 min.

7. Add item 7 slowly and continue to stir until dissolved.

8. Add item 8, followed by item 9 and continue to mix for 15 min.

Results Aspect: Opaque straw coloured suspension.

S. G at 20 C : 1.22 Solids: 36.9% pH: 7.70 Stability: + 6 months

Example 6

Item No. Raw Material % wt 1 Water 8.05 2 Sokalan HP80 4.51 3 Propylene glycol 2.00 4 Defoamer 0.10 5 K1C376 0.25 6 Sokalan HP80 82.69 7 Sodium gluconate 1.50 8 Sodium hydroxide (47%) 0.60 9 Biocide 0.30 Equipment IKA stirrer, type ST DV S2 having a speed range of 50- 200 rpm.

Dissolver blade.

Process 1. Add water in to mixing vessel and commence stirring at 750 rpm.

2. Add item 2 to this and continue to stir (this will provide a 14% solution).

3. Add item 3, and stir for 5 min.

4. Add item 4, and stir for 5 min.

7. Add item 7 slowly and continue to stir until dissolved.

8. Add item 8, followed by item 9 and continue to mix for 15 min.

Results Aspect: Opaque straw coloured suspension S. G. at 20 C : 1.121 Solids: 36. 6% pH: 8.00 Stability: 6 months Example 7

Item No. Raw Material % wt 1 Water 7.75 2 Sokalan HP80 4.34 3 Propylene glycol 2.00 4 Defoamer 0.10 5 K1C376 0.25 6 Sokalan HP80 82. 86 7 Sodium gluconate 1.80 8 Sodium hydroxide (47%) 0.60 9 Biocide 0.30 Equipment IKA stirrer, type ST DV S2 having a speed range of 50- 200 rpm.

Dissolver blade.

Process 1. Add water in to mixing vessel and commence stirring at 750 rpm.

2. Add item 2 to this and continue to stir (this will provide a 14% solution).

3. Add item 3, and stir for 5 min.

4. Add item 4, and stir for 5 min.

7. Add item 7 slowly and continue to stir until dissolved.

8. Add item 8, followed by item 9 and continue to mix for 15 min.

Results Aspect: Opaque straw coloured suspension S. G. at 20 C : 1.123 Solids: 36.6% pH: 7.9 Stability: 6 months

Example 8

Item No. Raw Material % wt 1 Water 7.80 2 Sokalan HP80 5.72 3 Propylene glycol 2.00 4 Defoamer 0.00 5 K1C376 0.60 6 Sokalan HP80 81.48 7 Sodium gluconate 1.50 8 Sodium hydroxide (47%) 0.60 9 Biocide 0.30 Equipment IKA stirrer, type ST DV S2 having a speed range of 50- 200 rpm.

Dissolver blade.

Process 1. Add water in to mixing vessel and commence stirring at 750 rpm.

2. Add item 2 to this and continue to stir (this will provide a 16.5% solution).

3. Add item 3, and stir for 5 min.

4. Add item 4, and stir for 5 min.

6. Add in slowly item 6, so as to produce a

homogeneous product free from any lumps, and reduce the mixer speed to 750 rpm.

7. Add item 7 slowly and continue to stir until dissolved.

8. Add item 8, followed by item 9 and continue to mix for 15 min.

Results Aspect: Opaque straw coloured suspension S. G. at 20 C : 1.123 Solids: 36.9% pH: 8.1 Stability: + 2.5 months Example 9

Item No. Raw Material % wt 1 Water 7.90 2 Sokalan HP80 4.95 3 Propylene glycol 2.00 4 Defoamer 0.10 5 K1C376 1.00 6 Sokalan HP80 82.25 7 Sodium gluconate 1. 50 8 Biocide 0.30 Equipment IKA stirrer, type ST DV S2 having a speed range of 50- 200 rpm.

Dissolver blade.

Process 1. Add water in to mixing vessel and commence stirring at 500 rpm.

2. Add item 2 to this and continue to stir (this will provide a 15% solution).

3. Add item 3, and stir for 5 min.

4. Add item 4, and stir for 5 min.

5. Add item 5 slowly, so as to stop the formation of lumps, and increase the speed of the mixer gradually so as to maintain a vortex, up to 1000 rpm. Continue to mix at this speed for 10 min, this will allow the product to thicken.

Reduce the mixer speed to 300 rpm. and mix for 5-10 min.

6. Add in slowly item 6, so as to produce homogeneous product free from any lumps, and continue to increase the mixer speed so as to maintain a vortex, typically up to 750-900 rpm.

7. Add item 7 slowly and continue to stir until dissolved, approx. 30 min.

8. Add item 8, reduce mixer speed to 250 rpm and continue to mix for 15 min.

Results Aspect: Opaque straw coloured suspension S. G. at 20 C : 1.119 Solids: 36.9% pH: 7.0 Stability: + 2 months

Claims

CLAIMS:

1. A process for the preparation of an admixture for a cementitious composition, said admixture comprising water, at least one viscosity modifying agent, and at least one plasticiser, the process comprising the steps of: (i) providing a pre-mixture comprising water, viscosity modifying agent, and a first portion of plasticiser, (ii) mixing the pre-mixture from step (i) with a second portion of plasticiser.

2. A process as claimed in claim 1, wherein the plasticiser in the pre-mixture of step (i) is the same as that mixed with the pre-mixture in step (ii).

3. A process as claimed in claim 1 or claim 2, wherein the plasticiser is a superplasticiser.

4. A process as claimed in claim 3 wherein the superplasticiser is or comprises a polyacrylate polymer or a derivative thereof.

5. A process as claimed in claim 3 wherein the superplasticiser is or comprises a polycarboxylic ether or a derivative thereof.

6. A process as claimed in any one of the preceding claims, wherein the viscosity modifying agent is or comprises a polysaccharide or a derivative thereof.

7. A process as claimed in claim 6, wherein the viscosity modifying agent is or comprises welan gum or a derivative thereof.

8. A process as claimed in any one of the preceding claims, wherein from 2 to 30 wt. % of superplasticiser, said percentage being expressed with reference to the plasticiser's solids content, is comprised in the pre-mixture of step (i), with the remaining 98 to 70 wt. % being mixed with the premixture in step (ii).

9. A process as claimed in claim 8, wherein from 3 to 7 wt. % of plasticiser is comprised in the premixture of step (i), with the remaining 97 to 93 wt. % being mixed with the pre-mixture in step (ii).

10. A process as claimed in any one of the preceding claims, wherein the pre-mixture of step (i) satisfies the following relationship: Weight of solids in the premix = 10 to 17 % Weight of water and plasticiser

11. A process according to claim 10, wherein the pre-mixture of step (i) satisfies the following relationship: Weight of solids in the premix = 11 to 16 % Weight of water and plasticiser

12. A process according to claim 11, wherein the pre-mixture of step (i) satisfies the following relationship: Weight of solids in the premix = 12 to 15 % Weight of water and plasticiser

13. A process as claimed in any one of the preceding claims, wherein the pH of the admixture is 10, preferably from 6 to 10, more preferably from 7 to 9.

14. A process as claimed in any one of the preceding claims, wherein the solids content in the admixture is from 15 to 40.0 wt. %, preferably from 19 to 37.0 wt. %.

15. A process as claimed in any one of the preceding claims, wherein, in the final product (i), the weight percentage of the viscosity modifying agent to the final product is from 0.1% to 2%.

16. A process as claimed in any one of the preceding claims, wherein, in the final product (i), the weight percentage of the viscosity modifying agent to the final product is from 0.25% to 1%.

17. A process as claimed in any one of the preceding claims, wherein the admixture contains one or more of a dispersing agent, a defoamer, a buffer, a retarder, a pH adjuster, a biocide, a preservative, a base, a buffer, an accelerator and/or an air entrainer.

18. A process as claimed in claim 17, wherein the admixture contains mono-propylene glycol as a dispersing agent.

19. An admixture for a cementitious composition whenever produced by a process as defined in any one of the preceding claims.

20. A process for the preparation of a cementitious composition, wherein an admixture as defined in claim 19 is added to the mixture in a single dose.

21. A cementitious composition comprising an admixture as defined in claim 19.

22. A cementitious composition as claimed in claim 21, which is concrete, preferably a self compacting concrete.

23. An admixture for a cementitious composition, the admixture comprising an aqueous solution of:

t (a) from 15 to 90 wt. % of one or more plasticisers, said percentage being expressed with reference to the plasticiser's solids content, (b) from 0.1 to 2 wt. % of one or more viscosity modifying agents, (c) and water, wherein the pH of the aqueous solution is from 6 to 10.

24. An admixture as claimed in claim 23, wherein the pH of the aqueous solution is from 7 to 9.

25. An admixture as claimed in claim 23 or 24 wherein the solids content of the plasticiser of the aqueous solution is from 19 to 37.0 wt. %.

26. An admixture as claimed in any one of claims 23 to 25 wherein the plasticiser is a superplasticiser.

27. An admixture as claimed in claim 26 wherein the superplasticiser is or comprises a polyacrylate polymer or a derivative thereof.

28. An admixture as claimed in claim 26 wherein the superplasticiser is or comprises a polycarboxylic ether or a derivative thereof.

29. An admixture as claimed in any one of claims 23 to 28, wherein the viscosity modifying agent is or comprises a polysaccharide or a derivative thereof.

30. An admixture as claimed in claim 29, wherein the viscosity modifying agent is or comprises welan gum or a derivative thereof.

31. An admixture as claimed in any one of claims 23 to 30, further comprising one or more of a dispersing agent, a defoamer, a buffer, a retarder, a pH adjuster, a biocide, a preservative, preservatives, a base, an accelerator and/or an air entrained.

32. An admixture as claimed in claim 31, which contains mono-propylene glycol as a dispersing agent.

33. An admixture as claimed in any one of claims 23 to 32, comprising from 15 to 40 wt. % of one or more plasticisers, from 0.1 to 2 wt. % of one or more viscosity modifying agents, up to 7 wt. % (preferably up to 5 wt. %) of one or more of a dispersing agent, a defoamer, a retarder, a pH adjuster, a biocide, a preservative, a base, a buffer and/or an air entrainer, an accelerator and the balance water.

34. An admixture as claimed in any one of claims 23 to 33, comprising from 19 to 37 wt. % of a polycarboxylic ether, from 0.5 to 1 wt. % of welan gum, up to 5 wt. % of one or more of a dispersing agent, a defoamer, a buffer, a retarder, a pH adjuster, a biocide, a preservative, preservatives, a base, an

accelerator and/or an air entrainer, and the balance water, wherein the pH is from 6.5 to 9.5.

35. A cementitious composition which comprises an admixture as defined in any one of claims 23 to 34.

36. A cementitious composition as claimed in claim 35, which is concrete, preferably a self compacting concrete.

37. A method of reducing separation in an admixture for a cementitious composition, said admixture comprising water, at least one viscosity modifying agent, and at least one plasticiser, the method comprising the steps of: (i) providing a pre-mixture comprising water, viscosity modifying agent, and a first portion of plasticiser, (ii) mixing the pre-mixture from step (i) with a second portion of plasticiser.

38. A process for the preparation of a pre-mixture for an admixture for a cementitious composition, the process comprising mixing together water, a plasticiser, and a viscosity modifying agent, wherein the amount of plasticiser is such that the total solids content of the premix expressed as a percentage of the plasticiser and water is from 10 to 17 wt. %.

39. Use of mono-propylene glycol as a dispersing agent in an admixture for a cementitious mixture.

40. A polysaccharides suspension containing monopropylene glycol.

41. An admixture for a cementitious mixture substantially as herein described with reference to any one of the Examples.