EP4688700A1

EP4688700A1 - Self-levelling mortars containing calcium aluminate cements

Info

Publication number: EP4688700A1
Application number: EP24717668.8A
Authority: EP
Inventors: Olivier Watt; Laurence Martin; Christophe COVENT; Dries DEVLAMINCK
Original assignee: Holcim Technology Ltd
Current assignee: Holcim Technology Ltd
Priority date: 2023-04-05
Filing date: 2024-04-05
Publication date: 2026-02-11
Also published as: CO2025014409A2; MX2025011880A; WO2024209025A1

Abstract

The invention relates to the use of CSA to lower the setting kinetic of an amorphous CAC based self-levelling mortar. The invention further relates to a cement slurry and a self- levelling mortar, wherein the premixed binder comprises: ∙ a cement C, preferably comprising Portland clinker in an amount of at least 30% by weight, preferentially 50% by weight, relative to the total weight of the cement C, ∙ from 0.25 to 7.5 wt.-% of amorphous calcium aluminate cement, CAC, relative to the total weight of the premixed binder, ∙ from 0.25 to 7.5 wt.-% of anhydrite, relative to the total weight of the premixed binder, ∙ from 0.5 to 5 wt.-% calcium sulfoaluminate cement, CSA, relative to the total weight of the premixed binder, ∙ an admixture composition, in a quantity sufficient to provide self-levelling properties to the mortar. The invention further relates to the use of the self-levelling mortar as underlayment or as top layer.

Description

SELF-LEVELLING MORTARS CONTAINING CALCIUM ALUMINATE CEMENTS

FIELD OF THE INVENTION

The invention relates to self-levelling mortars, and the processes for preparing said selflevelling mortars. These mortars are useful in particular as underlayments.

BACKGROUND OF THE INVENTION

Self-levelling mortars are characterized by higher flow characteristics and, in contrast to traditional concrete, do not require the addition of excessive amounts of water for placement. Self-levelling mortars are typically used to create a flat and smooth surface, usually with a compressive strength similar to or higher than that of traditional concrete prior to installing interior floor coverings. The use of self-levelling mortars increased as the degree of flatness and smoothness required for floor covering products has increased, with vinyl goods becoming thinner and floor tiles becoming larger, for example.

The term “self-levelling” is used to differentiate said compositions, usually mortars, from traditional compositions, which are typically stiffer and require more labour to place, requiring for example additional equipment and work.

Self-levelling mortars are mainly used as underlayments or toppings. An underlayment is installed over an existing subfloor to smooth it out and correct any surface irregularities prior to the installation of all types of floor coverings, including sheet vinyl, vinyl composition tile (VCT), wood, ceramic tile and carpet. A topping performs a similar function but acts as the actual finished floor without the need for a floor covering. Some typical applications for concrete toppings include warehouse floors, light industrial applications, retail stores and institutional facilities.

However, no satisfying self-levelling mortars containing amorphous calcium aluminate cements (CAC) is available to date. Indeed, the setting kinetics of CAC is too rapid to allow defects in the surface - for instance due to bubbles - to disappear before setting is complete. This is particularly problematic when several layers of self-levelling mortar compositions are spread at least partly on each other, as self-levelling mortar compositions are produced in small batches on construction sites, and poured one after another.

The present invention thus aims to provide self-levelling mortars containing calcium aluminate cements (CAC) with adapted setting kinetics allowing to limit surface defects, especially when several layers of self-levelling mortars are spread at least in part on each other.

SUMMARY OF THE INVENTION

Surprisingly, the Inventors have discovered that the addition of calcium sulfoaluminate cement (CSA) to an amorphous CAC based premixed binder for self-levelling mortars, lowers the setting kinetic thereof. Indeed, CSA cement is known in the art to shorten setting times, whereas in the present invention, it has the opposite effect.

Therefore, in first aspect, the invention concerns the use of CSA to lower the setting kinetic of an amorphous CAC based self-levelling mortar.

In another aspect, the invention concerns a premixed binder for self-levelling mortar comprising:

• a cement C, preferably comprising Portland clinker in an amount of at least 30% by weight, preferentially 50% by weight, relative to the total weight of the cement C,

• from 0.25 to 7.5 wt.-% of amorphous calcium aluminate cement, CAC, relative to the total weight of the premixed binder,

• from 0.25 to 7.5 wt.-% of anhydrite, relative to the total weight of the premixed binder,

• from 0.5 to 5 wt.-% calcium sulfoaluminate cement, CSA, relative to the total weight of the premixed binder,

• an admixture composition, in a quantity sufficient to provide self-levelling properties to the mortar.

In particular embodiments of the premixed binder: o the cement comprises mineral components selected from the group consisting of calcium carbonate, silica, ground glass, solid or hollow glass beads, glass granules, expanded glass powders, silica aerogels, silica fume, slags, ground sedimentary siliceous sands, fly ash, pozzolanic materials, ground construction demolition waste or mixtures thereof, and/or o the amorphous phase content of the amorphous CAC is of at least 60% by weight, relative to the total weight of CAC, and/or o the amorphous calcium aluminate cement I calcium sulfoaluminate cement weight ratio ranges from 2:1 to 1 :3, preferably 1 :1 to 1 :3, even more preferably from 1 :1 to 1 :2, and/or o the admixture comprises a plasticizer and/or superplasticizer and/or viscositymodifying agent, and wherein:

- the plasticizer and/or superplasticizer (expressed in dry extract) is present in a quantity of between 0.01 % and 3 %, preferably between 0.1 % and 2.5 %, with respect to the total weight of the premixed binder, and

- the viscosity-modifying agent content ranges from 0.005 to 2.0 wt.-%, preferably from 0.01 to 1.0 wt.-%, relative to the total weight of premixed binder, and/or o it comprises up to 15% by weight of additives selected from the group consisting of a resin, water reducer, an accelerator, a retarder, a superabsorbent polymer, a pigment, a defoamer and mixtures thereof, relative to the total weight of the self-levelling premixed binder, and/or o the anhydrite/amorphous CAC weight ratio ranges from 1 :2 to 2:1 , preferably from 1.5: 1 to 1 : 1.5. typically, it is of 1 : 1.

In another aspect, the invention concerns a self-levelling mortar comprising the selflevelling premixed binder of the invention, further comprising sand, and typically water. Preferably, the sand content ranges from 30 wt.-% to 50 wt.-% of sand, preferably from 35 wt.-% to 45 wt.-%, relative to the total weight of the self-levelling premixed binder.

In another aspect, the invention concerns the use of the self-levelling mortar of the invention as underlayment or as top layer.

In another aspect, the invention concerns a method of levelling a floor, said method comprising: a) providing the self-levelling mortar of the invention, b) casting or pouring the self-levelling mortar of step a) on the floor and spreading it, c) letting the self-levelling mortar of step c) set.

Advantageously, step c) of letting the self-levelling mortar set comprises a step c1) of laying a cover layer onto the spread self-levelling mortar. Typically, the cover layer is a vinyl sheet, a vinyl composition tile, wood, a ceramic tile or a carpet.

The CAC-based self-levelling mortar of the invention provides the following advantages: The self-levelling mortar is excellent for smoothing and flattening surfaces, in particular interior surfaces The self-levelling mortar has improved adhesion to floor coverings such as tiles, carpets, paint, ...

The final floor has an excellent visual aspect, be it covered with a cover layer or not,

DEFINITIONS

Self-Levelling: Self-levelling compositions of the invention are mortars that self-level under the effect of gravity only. Self-levelling mortar are highly liquid compositions to be poured onto a surface, so as to smooth or flatten surfaces, in particular before installing floor coverings. Typically, after setting has occurred, that the final surface is (almost) perfectly horizontal.

Premixed Binder: A premixed binder refers to a dry composition comprising at least cement and admixture, said composition being suitable to be mixed with water and sand for preparing a mortar.

Mortar: a mortar refers to a composition comprising premixed binder, water and sand, which in the presence of water forms a paste which sets and hardens by means of hydration reactions and processes and which, after hardening, retains its strength and stability even under water. The terms “mortar” and “mortar composition” will have the same meaning in the present disclosure.

Total weight of a composition: As used herein, the “total weight of a composition” is understood as the total weight of the composition in the dry state, i.e. the total weight of the dry matter of the composition, unless otherwise stated.

Cement: The cement comprises or preferably consists of Portland clinker and a source of calcium sulfate. The cement is preferably as defined in the standard NF-EN-197-1 of April 2012, or in the standard NF EN 197-5 published in May 2021. The cements defined in these standards are grouped in 6 different families: CEM I, CEM II, CEM III, CEM IV, CEM V and CEM VI. The cement can also be a CEM I, CEM II, CEM III, CEM IV, CEM V or a CEM VI to which mineral components are further added in a second preparation step. The cement may be any mineral binder that comprises Portland clinker optionally mixed with one or several mineral components as defined below.

Preferably, the calcium sulphate content ranges from 0% to 5% by weight of the cement. The cement is essentially free of a calcium aluminate cement and calcium sulfoaluminate cement.

Calcium sulphate: Calcium sulphate used according to the present invention includes gypsum (calcium sulphate dihydrate, CaSO4.2H2O), hemi-hydrate (CaSC>4.1/2H2O), anhydrite (anhydrous calcium sulphate, CaSOt) or a mixture thereof. Calcium sulphate produced as a by-product of certain industrial processes may also be used.

Mineral component (or mineral addition): the mineral component may designate slag (for example, as defined in the European NF EN 197-1 Standard of April 2012, paragraph 5.2.2), pozzolanic materials (for example as defined in the European NF EN 197-1 Standard of April 2012, paragraph 5.2.3), fly ash (for example, as described in the European NF EN 197-1 Standard of April 2012, paragraph 5.2.4), calcined schists (for example, as described in the European NF EN 197-1 Standard of April 2012, paragraph 5.2.5), material containing calcium carbonate, for example limestone (for example, as defined in the European NF EN 197-1 Standard paragraph 5.2.6), limestone components (for example, as defined in the "Concrete" NF P 18-508 Standard), silica fume (for example, as defined in the European NF EN 197-1 Standard of April 2012, paragraph 5.2.7), siliceous components (for example, as defined in the "Concrete" NF P 18-509 Standard), metakaolin or mixtures thereof. The mineral component may also be ground construction demolition waste.

Examples of siliceous components are ground glass, solid or hollow glass beads, glass granules, expanded glass powder.

Amorphous calcium aluminate cement (amorphous CAC): amorphous calcium aluminate cement comprises amorphous hydraulic phases having a C/A molar ratio ranging from 0.3 to 15, preferably from 0.5 to 12. The amorphous phase content is of at least 60% by weight and therefore the crystallization phase content is lower than or equal to 40% by weight, relative to the total weight of CAC. The amorphous phase content is preferably at least 65 wt.-%, at least 70 wt.-%, at least 75 wt.-%, at least 80 wt.-%, at least 85 wt.-%, at least 90 wt.-%.

In cement chemist notation, primary compounds are represented by C for CaO, S for SiC>2, A for AI2O3, $ for SO3, F for Fe2C>3, which will be used throughout the present text, unless otherwise indicated. Calcium aluminate cements may further comprises at least one crystalline phase selected from CA, C12A7, C3A, C11A7CaF2, C2A(1-x)Fx (with x a member of ]0, 1]), or mixtures thereof. Calcium aluminate cements preferably comprise at least C12A7 phase. Amorphous CAC is further characterized by an alumina (AI2O3) content ranging from 3 to 70% by total weight of the CAC, preferentially ranging from 7 to 50% by weight and better ranging from 20 to 30% by weight.

The CAC is essentially free of a cement as defined before, of sulfates, and of CSA as defined below.

Amorphous CAC based composition: as used herein, an amorphous CAC based composition is understood as a composition comprising amorphous CAC, and cement.

Calcium sulfoaluminate cement (CSA): Calcium sulfoaluminate cements are calcium aluminate cements that further comprise sulfates, generally in the form of C4A3$ (ye’elimite in the cement chemist notation), which forms at least 50 % of the weight of CSA cement. The CSA is essentially free of cement and of CAC as defined before.

Essentially free of: As used herein, a material is “essentially free of” a particular component when the component is present in a very low content, usually 5% by weight or less, compared to the total weight of the material, more especially below 1 % by weight. For instance, a cement is essentially free of calcium aluminate cement when calcium aluminate cement is present in the cement in an amount of less than 5 wt.-% or preferably 1 wt.-% of the total weight of cement. For instance, a cement is essentially free of calcium sulfoaluminate cement when calcium sulfoaluminate cement is present in the cement in an amount of less than 5 wt.-% or preferably 1 wt.-% of the total weight of cement.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

1. Cement used for the self-levelling mortar

The invention concerns a premixed binder for self-levelling mortar comprising:

• from 0.25 to 7.5 wt.-% of amorphous calcium aluminate cement, CAC, relative to the total weight of the premixed binder, • from 0.25 to 7.5 wt.-% of anhydrite, relative to the total weight of the premixed binder,

• an admixture, in a quantity sufficient to provide self-levelling properties to the mortar.

The premixed binder of the invention thus comprises three cements of different nature:

1 ) the cement C, as defined above and below, and essentially free of CAC and CSA,

2) amorphous calcium aluminate cement, also referred to as “amorphous CAC”

3) calcium sulfoaluminate cement, also referred to as “CSA”.

Cement C

The cement C has the definition provided above for “cement”. The cement C is essentially free of a calcium aluminate cement and calcium sulfoaluminate cement. The cement C preferably comprises Portland clinker in an amount of at least 30% by weight, preferentially 50% by weight relative to the total weight of the cement C.

The cement C as used in the invention may be any type of cement comprising Portland clinker, whatever its chemical composition is, and whatever its alkaline content.

Therefore, one of the advantages of the invention is not having to select a specific type of cement comprising Portland clinker. Advantageously, the cement C used in the invention is selected from the cements readily available on the market.

Advantageously, the cement C is a CEM I or CEM II, optionally further mixed with mineral components, and preferably comprising at least 30 wt.-%, preferentially 50 wt.-%, or more of Portland clinker, relative to the total weight of cement C.

As mentioned above, the cement C may comprise mineral components (or mineral additions) as defined above. Suitable mineral components are preferably selected from calcium carbonates such as limestone, silica, ground glass, solid or hollow glass beads, glass granules, expanded glass powders, silica aerogels, silica fume, slags such as granulated blast furnace slag, ground sedimentary siliceous sands, fly ash, pozzolanic materials, construction waste or mixtures thereof.

The mineral components are preferably in the form of particles having a Dv90 of 200 pm or less, and more preferably a Dv97 of 200 pm or less. Particle size can be measured by laser granulometry using for example a Malvern MS2000. Mineral components of different natures (calcareous, siliceous, fly ash, silica fume) may be used in the cement C. The mineral components include calcareous, siliceous, and silico-calcareous materials. They include natural, artificial, waste and recycled materials. The mineral components may also comprise, for example, wood.

Typically, the mineral components content of the premixed binder ranges from 0 to 70 wt-%, preferentially from 10 to 50 wt-%, relative to the total weight of the premixed binder. In a particular embodiment, the premixed binder for self-levelling mortar comprises 50 wt.-% or more, preferably 60 wt.-% or more, even more preferably 70 wt.-% or more, of cement C relative to the total weight of the premixed binder. The premixed binder for self-levelling mortar preferably comprises up to 85 wt.-% of cement C relative to the total weight of the premixed binder.

Amorphous CAC

The premixed binder comprises from 0.25 to 7.5 wt.-%, preferably from 0.3 to 3.0 wt.-%, even more preferably from 0.4 to 2.0 wt.-% of amorphous CAC relative to the total weight of premixed binder.

Amorphous CAC usually accelerates setting times of the mortars.

Anhydrite

The premixed binder comprises from 0.25 to 7.5 wt.-% of anhydrite, preferably from 0.3 to 3.0 wt.-%, even more preferably from 0.4 to 2.0 wt.-%, relative to the total weight of the premixed binder.

Preferably, the anhydrite/amorphous CAC weight ratio ranges from 1 :2 to 2:1 , preferably from 1.5: 1 to 1 : 1.5. typically, it is of 1 : 1.

Anhydrite is or consists essentially of anhydrous calcium sulphate (CaSOt). It may be obtained by calcination of gypsum, under temperatures sufficiently high for the gypsum to be completely dehydrated. There are different types of anhydrites: anhydrite I, anhydrite II and anhydrite III. The type of compound formed depends on the implemented calcination method and the gypsum calcination temperature.

Anhydrite may be natural (rock which must be ground before use) or synthetic (e.g. byproduct during the manufacture of hydrofluoric acid).

CSA The premixed binder comprises from 0.5 to 5 wt.-%, preferably from 0.8 to 4.0 wt.-%, even more preferably from 1 .0 to 3.5 wt.-% of CSA relative to the total weight of premixed binder.

Advantageously, the premixed binder of the invention has an amorphous CAC/CSA weight ratio ranging from 2:1 to 1 :3, preferably 1 :1 to 1 :3, even more preferably from 1 :1 to 1 :2.

Calcium sulfate

The composition may further comprise calcium sulfate. Calcium sulfate used includes gypsum (calcium sulfate dihydrate, CaSO4.2H2O), hemi-hydrate (CaSO4.1/2H2O), anhydrite (anhydrous calcium sulfate, CaSO4) or a mixture thereof. The gypsum and anhydrite exist in the natural state. Calcium sulfate produced as a by-product of certain industrial processes may also be used.

The premixed binder may comprise from 0.5 to 5% by weight, compared to the total weight of the premixed binder, of calcium sulfate. This is the content of calcium sulfate added in addition to the calcium sulfate already present in the cement C.

Admixture

The premixed binder further comprises an admixture composition, aiming to modify the rheological properties of the mortar obtained by mixing the premixed binder with sand and/or filler. The admixture may also influence the setting time.

The admixture is added, for example, either in the mortar, preferably in a water-soluble sachet, or with a portion of the water, or in the premixed binder composition, or in multiple vectors.

The admixture preferably comprises at least one rheology agent. The rheology agent helps to prevent bleeding and segregation. It can also improve robustness of the resulting mortar.

The admixture may also comprise water reducing agents (i.e., plasticizers and/or superplasticizers) and viscosity modifying agents (VMAs).

A plasticizer or a superplasticizer is an additive which, by its addition, helps reduce the demand for water and maintain the fluidity/rheology of the paste.

By way of example of plasticizers, mention may be made of lignosulphonates, hydroxycarboxylic acids, carbohydrates, and other specific organic compounds, for example glycerol, polyvinyl alcohol, sodium alumino-methyl-siliconate, sulfanilic acid and casein as described in the Concrete Admixtures Handbook, Properties Science and Technology, V.S. Ramachandran, Noyes Publications, 1984. Superplasticizers have been generally classified into four groups: sulfonated naphthalene-formaldehyde (SNF) condensates (generally a sodium salt); sulfonated melamine-formaldehyde (SMF) condensates; modified lignosulfonates (MLS); and the others. More recent superplasticizers include polycarboxylic compounds such as polycarboxylates, e.g. polyacrylates. Acrylic copolymer-based superplasticizers may also be used, preferably these are polymers comprising a chain with a polycarboxylic function, optionally salified, to which another group (e.g. of the polycarboxylate or polyoxyethylene type) is attached. A superplasticizer is preferably a new generation superplasticizer, e.g. a copolymer containing polyethylene glycol as a grafted chain and carboxylic functions in the main chain like a polycarboxylic ether. Polycarboxylates, such as polycarboxylate ether (PCE) are particularly suitable. Advantageously, the superplasticizer is a polycarboxylate, in particular a polycarboxylate ether or ester. Advantageously, the superplasticizers are polycarboxylates that have at least the following three repeating units: an acrylic unit, a methacrylic acid unit, and a unit formed of a long chain of polyethers. These types of dispersing agents or superplasticizers are very effective, especially for improving fluidity. A high dispersion efficiency also helps reduce the quantity of superplasticizers used and has an economic benefit given that the carboxylate-based product is relatively expensive. Sodium polycarboxylate-polysulfonates and sodium polyacrylates may also be used. Phosphonic acid derivatives and polycarboxylates having phosphate groups, may also be used. Sodium polycarboxylate-polysulfonates and sodium polyacrylates may also be used.

The quantity of plasticizer and/or superplasticizer is very dependent on the nature of the plasticizer and/or superplasticizer and its dilution; however, dosages will be given with 100 % dry extract. The plasticizer and/or superplasticizer (expressed in dry extract) is usually present in a quantity of between 0.01 % and 3 %, preferably between 0.1 % and 2.5 %, with respect to the total weight of the premixed binder.

The superplasticizer is usually added in powder form, but an addition in liquid form is also possible. Addition in liquid form generally allows automated dosage of the additives.

VMAs prevent bleeding and segregation and improve robustness of the cement slurry and mortars.

Viscosity modifying agents are agents able to modify yield stress, viscosity, and thixotropy of the cement slurry. VMAs are also known in the art as viscosity modifying admixtures, viscosity enhancing agents (VEAs), or stabilizing agents (SAs), or yield stress modifying agent.

VMAs are usually biobased polymers, and include: cellulose derivatives, for example water-soluble cellulose ethers, such as the sodium carboxy methyl, methyl, ethyl, hydroxyethyl and hydroxypropyl ethers; alginates; and natural gums such as xanthan, carrageenan, wellan, diutan or guar gum; and starch. Combination thereof may also be used (see for instance https://doi.Org/10.1016/j.cemconres.2021.106646).

Preferably, the viscosity modifying agent is an amphiphilic bio-based polymer.

In a particular embodiment, the VMA is a polymer derived from cellulose. Even more preferably the VMA is chosen among Methyl Cellulose, methylhydroxyethyl cellulose, hydroxypropylmethyl cellulose and mixture thereof. In a preferred embodiment, the VMA comprises or consists of xanthan gum or a polymer derived from xanthan gum, such as diutan gum. Mixtures of polymer derived from cellulose and of xanthan gum or a polymer derived from xanthan gum can also be contemplated.

Preferably, the viscosity-modifying agent content ranges from 0.005 to 2.0 wt.-%, preferably from 0.01 to 1.0 wt.-%, relative to the total weight of premixed binder.

Preferably, the admixture comprises a plasticizer and/or a superplasticizer and/or a VMA. Even more preferably, the admixture comprises a superplasticizer and a VMA.

Additives

Optionally, the premixed binder further comprises up to 15 % of further additives by weight relative to the weight of premixed binder.

When the water reducing agent is used in solution, the quantity is expressed in g of active ingredient per 1 L of solution.

Advantageously, the additives are selected from the group consisting of: a resin, to improve abrasion resistance or surface adhesion of the mortar to a cover layer such as tiles, a pigment, to provide a decorative effect, an accelerator and/or a retarder, to further modify the setting time of the composition, a defoaming agent, to avoid formation of foams and bubbles, and mixtures thereof. Advantageously, the premixed binder further comprises a resin, and preferably up to 10 wt.-% of resin, such as between 1.5 wt.-% and 5 wt.-%, relative to the total weight of premixed binder.

Advantageously, the premixed binder may further comprise an accelerator (or accelerating agent). The accelerator is typically as defined in the standard NF EN 934-2 of September 2012. Suitable accelerators may for example be selected from:

- alkaline metal or alkaline earth metal salts, especially potassium salts, calcium salts and sodium salts wherein the anion may be nitrate, nitrite, chloride, formate, thiocyanate, bromide, or mixtures thereof;

- alkali metal or alkaline earth metal silicates and aluminates, for example sodium silicate, potassium silicate, sodium aluminate, potassium aluminate, or mixtures thereof.

In particular the cement for the self-levelling mortar slurry may comprise a CAC accelerator, such as lithium salts.

Advantageously, it is present in an amount up to 2% by weight relative to the total weight of premixed binder. In other words, the premixed binder may further comprise an accelerator in an amount ranging from 0.2 to 2.0 % by weight, relative to the total weight of the premixed binder.

The additives may also comprise a retarder. Retarders are typically as defined in the standard NF EN 934-2 of September 2012. Suitable retarders may for example be selected from sucrose, alpha hydroxyacids or salts thereof, ethanolamines or salts thereof, and/or catechols and derivatives thereof. Particularly preferred are alpha hydroxyacids and salts thereof, in particular alkali metal salts thereof. The salt may be selected from the group consisting of tartrate, citrate, lactate, malate, benzoate, acetate, and combinations thereof. Typically, the retarder is tartaric acid, calcium or sodium tartrate, citric acid, or calcium and sodium citrate.

In one embodiment, the premixed binder also comprises a defoaming agent (also called defoamer or anti-foaming agent).

The type of defoaming agent varies. It may notably be based on silicone, fatty alcohols, esters, or polypropylene glycol. The defoaming agent may in particular be selected from the following classes:

- Oil-based defoaming agents, which has an oil as a vehicle. This oil may be mineral or vegetable (except silicone). The defoamer also comprises a wax and/or a hydrophobic silica. Waxes are, for example, ethylene bis stearamide (EBS), paraffin waxes, ester waxes and fatty alcohol-based waxes. Surfactants may also be present; - Powdered defoaming agent. These agents correspond to oil-based agents but on a particulate medium such as silica;

- Water-based defoaming agents. These are generally oils or waxes dispersed in an aqueous base. The oils are white oils or vegetable oils and the waxes are fatty alcohols, fatty acids, esters or the soaps therefrom;

- Silicone defoaming agents. These defoamers have a silicone as the active agent. They may be oil-based or water-based. A hydrophobic silica may be dispersed in the silicone medium. Emulsifiers may be used. Modified silicones such as glycol silicones or fluorosilicones may also be used. The defoaming agent may be a polydimethylsiloxane. Particularly suitable are silicones comprising (RSiOO.5) and (R2SiO) groups. In these formulas, the radicals R, which may be identical or different, are preferably one hydrogen atom or an alkyl group of 1 to 8 carbon atoms, the methyl group being preferred. The number of repeat units is preferably from 30 to 120;

- Glycol type defoaming agents. These agents comprise polyethylene glycol and polypropylene glycol copolymers. They are available on an oily or aqueous base or emulsions;

- Alkyl polyacrylate type defoaming agents. These agents are generally available in a petroleum solvent;

-mixtures thereof.

The quantity of defoaming agent typically ranges from 0.01 wt.-% to 5 wt.-%, preferably from 0.1 wt.-% to 2 wt.-%, calculated with respect to the total weight of premixed binder. The defoaming agent is generally added in powder form, but an addition in liquid form is also possible. Addition in liquid form generally allows automated dosage of the additives.

2. Cement slurry or paste for self-levelling mortar

Water is added to the premixed binder as disclosed above in an amount sufficient to provide the desired flowability and self-levelling properties to the resulting mortar.

Preferably, the water content of the mortar ranges from 16 to 26 wt.-%, more preferably from 18 to 24 wt.-%. Advantageously, the water content is equal to 23 wt.-% relative to the total weight of the mortar including water.

3. Dry mortar

Sand and water are added to the premixed binder, or sand is added to the cement slurry to prepare a mortar. The sands that are used in the mortar are conventional aggregates in conformity with the standard EN 12620 (sands for concrete). In practice, the Dmax is less than 4 mm, preferentially less than 1 mm, and even more preferentially less than 500 pm. The sands include calcareous, siliceous and silico-calcareous materials. The sand may be of different origins, washed alluvial (rolled, semi-crushed or crushed), sands of marine origin, crushed limestone sands (dry or washed), sands of magmatic origin (porphyry, granite), recycling aggregates from the crushing of concretes or other construction materials.

When the sand includes clay, it is advantageous to add inerting agents. Clay inerting agents are compounds that help reduce or prevent the harmful effects of clays on the properties of hydraulic binders. Clay inerting agents include those described in FR 2 948 118, WO 2006/032785 and WO 2006/032786.

Typically, the sand content of the self-levelling mortar ranges from 20 to 80 wt.-%, preferentially from 40 to 60 wt.-%, relative to the total weight of the self-levelling mortar.

The self-levelling mortar, once spread and subjected to the effect of gravity, has no defects visible to the naked eye, namely no apparent bubbles or unevenness.

As used herein, no apparent unevenness means that, once spread and subjected to the effect of gravity, the self-levelling mortar has a substantially even and flat surface. In other words, the exposed (superior) surface of the self-levelling mortar is essentially free of visible reliefs or 3-dimensional motifs.

The self-levelling mortar typically has a good compressive strength. The mortar has a compressive strength of between 15 to 40 MPa after 28 days.

Particular embodiments

Advantageously, the premixed binder comprises or consist of:

• at least 50 wt-% of a cement C, relative to the total weight of the premixed binder, wherein cement C comprises Portland clinker in an amount of at least 30% by weight, preferentially 50% by weight, relative to the total weight of the cement C,

• from 0.3 to 3.0 wt.-% of amorphous calcium aluminate cement, CAC, relative to the total weight of the premixed binder,

• from 0.3 to 3.0 wt.-% of anhydrite, relative to the total weight of the premixed binder,

• from 0.8 to 3.5 wt.-% calcium sulfoaluminate cement, CSA, relative to the total weight of the premixed binder, • an admixture composition, preferably comprising a (super)plasticizer and a VMA, in a quantity sufficient to provide self-levelling properties to the mortar,

• and optionally up to 15 wt.-% additives, relative to the total weight of the premixed binder, selected from the group consisting of a resin, a defoamer, an accelerator, a retarder, and combinations thereof, wherein the self-levelling premixed binder has an amorphous CAC/CSA weight ratio ranging advantageously from 1 :1 to 1 :4, preferably from 1 :1.5 to 1 :3, and an amorphous CAC/CSA weight ratio ranging from 2:1 to 1 :3, preferably 1 :1 to 1 :3, even more preferably from 1 :1 ,5 to 1 :2.

Of course, the total of all components within the premixed binder totals 100 wt.-%.

To form a self-levelling mortar, the premixed binder can then be: mixed with sand, preferably with a sand content of 30 to 50 wt.-% of the weight of mortar,

- water is then added, preferably with a water content of 16 to 26 wt.-% of the weight of mortar.

Typically, the initial setting time of the self-levelling mortar ranges from 30 to 120 minutes, and its final setting time ranges from 40 minutes to 3 hours at room temperature, also when additional accelerators are added.

After setting, the dry mortar preferably comprises, in weight compared to the total weight of the dry mortar: from 50 wt.-% to 70 wt.-% of the premixed binder, preferably from 55 wt.-% to 65 wt.-%, from 30 wt.-% to 50 wt.-% of sand, preferably from 35 wt.-% to 45 wt.-%.

Of course, the total of all components within the dry mortar totals 100 wt.-%.

4. Process for preparing the premixed binder/mortar

Any conventional process for preparing a mortar is suitable to prepare the mortar of the invention.

The cements as disclosed above (cement C, CAC, CSA), anhydrite and optionally calcium sulfate can be mixed, in the contents disclosed above, to for a premix. All or part of the admixtures can be added to the premix.

The premix can then be mixed with sand. All or part of the admixtures can be added to the composition comprising the premix and sand. To prepare the mortar, water can be added, in the content disclosed above, before or during or after addition of sand. All or part of the admixtures can be added to the mixing water.

5. Uses

The invention further concerns the use of the self-levelling mortar of the invention as underlayment or top layer.

More particularly, the invention concerns a method of levelling a floor, said method comprising: a) providing the self-levelling mortar of the invention, b) pouring the self-levelling mortar of step a) on the floor and spreading it, c) Letting the self-levelling mortar of step c) set.

The floor may have defects and be uneven. It may be a concrete, wooden or tiled floor, and may be covered in places with cut back adhesives. Also, the floor may have a sloping.

As explained above, the mortar is left to set long enough to flatten and allow bubbles to migrate out of the mortar.

A gauge rake may be used to move the mortar into place without spreading it too thin. The finishing is preferably done by lightly breaking the surface tension of the setting mortar using a for instance a smoother.

Typically, the thickness of the set self-levelling mortar ranges from 2 mm to 30 mm. When the mortar is used as underlayment, step c) of letting the self-levelling mortar set may comprise a step c1) of laying a cover layer onto the spread self-levelling mortar. Examples of cover layers are a vinyl sheet, a vinyl composition tile, wood, a ceramic tile or a carpet.

METHODS

Measurement of setting time

The setting time is measured according to the standard NF EN 196-3 published in January 2009.

Method for measuring the compressive strength (Cs) of the absorbent mineral composition:

A cement slurry of the invention is typically cast in a mold. The cement slurry is cured for 28 days at 20°C and 100% relative humidity to give a cured absorbent mineral composition. Cubic samples (dimensions 4cm*4cm*4cm) are used for measuring the compressive strength.

A mini press is used for measuring low resistances.

FIGURES

Fig. 1 shows a heat development curve of a reference mortar (dotted line) and of a mortar of the invention (plain line). Y-axis show temperature in °C, while the X-axis shows the time in minutes.

Fig. 2 shows a photograph of the reference mortar after setting. Visual defects such as bubble holes are clearly visible.

Fig. 3 shows a photograph of an example of inventive mortar after setting. The exposed surface is flat and even, with no visual defects.

EXAMPLES

The following non-restrictive example illustrate embodiments of the invention.

Materials

The cement used is a mix of a CEM I 52.5R HER supplied by CBR and a filler (or mineral addition). The mineral addition is a calcium carbonate filler: Calcitec 2000 filler supplied by CARMEUSE.

Amorphous CAC and anhydrite are provided by Leap Fit supplied by IMERYS which is composed of 50 wt.-% amorphous CAC and 50 wt.-% anhydrite.

The CSA is Calumex Quick supplied by Caltra.

The admixture composition makes use of Melfux 2651 F (a superplasticizer), Starvis 3003 F (a VMA, hereinafter “VMA 1”) supplied by BASF as powders, and Kelco-crete DG-F (a VMA hereinafter “VMA 2”) supplied by CP Kelco as a powder.

The accelerator is U2CO3 (calcium aluminate-based accelerator) supplied by RodaChem as a powder with a granulometry of 40 pm or less.

The sand is M32 sand supplied by SIBELCO.

Other additives include: o Na2COs is supplied as a powder by TATA or SOLVAY, which decreases shrinkage and delays the setting time. o L-Tartaric acid (a retarder) is supplied by RFI (food ingredients). o a defoamer: Agitan P804, supplied by MUNZING. o A resin Vinnapas 5014F supplied by WACKER.

Water: tap water Mortars

The following mortars were prepared: The mortar is prepared by mixing all dry ingredients in a static mixer, and then progressively adding all liquid components. The W/C is within the range described herein. Mixing is done for a duration of 5 minutes.

The reference mortar is not according to the present invention as it does not contain CSA. Mortar 1 is a mortar according to the invention, as it comprises cement C, amorphous CAC, CSA and anhydrite.

Results

The results are presented in figures 1 to 3.

Figure 1 shows that the initial setting time is unchanged when 2 parts by weight (around 1.95 wt.-%) CSA is added. However, the final setting is increased, as the slope of temperature as a function of time is not as steep. This means that the mortar takes more time to harden and structure itself, allowing the bubbles and surface defects to migrate out of the mortar.

This is very surprising as CSA are known in the art to be highly reactive, thus accelerating setting times. Here however the addition of CSA has the opposite effect: it reduces heat development.

Figure 2 shows the results obtained with the reference mortar, while Figure 3 shows the results obtained with mortar 1 , after pouring a second batch of 1 liter after 10 minutes.

The mortar of Figure 2 shows bubbles (see left) and unevenness (see centre). In contrast, the surface of the mortar in Figure 3 shows a smooth, flat and even surface.

Claims

1. Use of calcium sulfoaluminate cement (CSA) to lower the setting kinetic of an amorphous calcium aluminate cement (CAC) based self-levelling mortar.

2. Premixed binder for self-levelling mortar comprising:

• a cement C comprising Portland clinker and optionally mineral components, the cement C preferably comprising Portland clinker in an amount of at least 30% by weight, preferentially 50% by weight, relative to the total weight of the cement C,

• from 0.25 to 7.5 wt.-% of amorphous calcium aluminate cement, CAC, relative to the total weight of the premixed binder, the amorphous CAC having an amorphous phase content of at least 60% by weight relative to the total weight of CAC,

3. The premixed binder of claim 2, wherein the cement comprises mineral components selected from the group consisting of calcium carbonate, silica, ground glass, solid or hollow glass beads, glass granules, expanded glass powders, silica aerogels, silica fume, slags, ground sedimentary siliceous sands, fly ash, pozzolanic materials, ground construction demolition waste or mixtures thereof.

4. The premixed binder of claim 2 or 3, wherein the amorphous phase content of the amorphous CAC is of at least 65% by weight, relative to the total weight of CAC.

5. The premixed binder of any of claims 2 to 4, wherein the amorphous calcium aluminate cement / calcium sulfoaluminate cement weight ratio ranges from 2:1 to 1 :3, preferably 1 :1 to 1 :3, even more preferably from 1 :1 to 1 :2.

6. The premixed binder of any of claims 2 to 5, wherein the admixture comprises a plasticizer and/or superplasticizer and/or viscosity-modifying agent, and wherein: - the plasticizer and/or superplasticizer (expressed in dry extract) is present in a quantity of between 0.01 % and 3 %, preferably between 0.1 % and 2.5 %, with respect to the total weight of the premixed binder, and

- the viscosity-modifying agent content ranges from 0.005 to 2.0 wt.-%, preferably from 0.01 to 1.0 wt.-%, relative to the total weight of premixed binder.

7. The premixed binder of any of claims 2 to 6, wherein it comprises up to 15% by weight of additives selected from the group consisting of a resin, water reducer, an accelerator, a retarder, a superabsorbent polymer, a pigment, a defoamer and mixtures thereof, relative to the total weight of the premixed binder.

8. The premixed binder of claim 7, wherein the anhydrite/amorphous CAC weight ratio ranges from 1 :2 to 2:1 , preferably from 1.5:1 to 1 :1.5. typically, it is of 1 :1.

9. A self-levelling mortar comprising the self-levelling premixed binder of any of claims 2 to 9, further comprising sand.

10. The self-levelling mortar of claim 9, wherein the sand content ranges from 30 wt.-% to 50 wt.-% of sand, preferably from 35 wt.-% to 45 wt.-%, relative to the total weight of the self-levelling mortar.

11 . Use of the self-levelling mortar of claims 9 or 10 as underlayment or as top layer.

12. A method of levelling a floor, said method comprising: d) providing the self-levelling mortar as defined in any of claims 9 to 10, e) casting or pouring the self-levelling mortar of step a) on the floor and spreading it, f) Letting the self-levelling mortar of step c) set.

13. The method of claim 12, wherein step c) of letting the self-levelling mortar set comprises a step c1) of laying a cover layer onto the spread self-levelling mortar.

14. The method of claim 13, wherein the cover layer is a vinyl sheet, a vinyl composition tile, wood, a ceramic tile or a carpet.