SUPERFLUIDIFYING ADDITIVE FOR CEMENTITIOUS COMPOSITIONS

Abstract: The present invention regards a superfluidifying additive for cementitious compositions, comprising an acrylic superfluidifier, an ammonium salt, at least one surfactant, and possibly an antifoaming additive. The present invention moreover comprises high-fluidity and high-workability cementitious compositions premixed in the dry state and cementitious items containing the said superfluidifying agent.

Description: SUPERFLUIDIFYING ADDITIVE FOR CEMENTITIOUS COMPOSITIONS Scope of the invention The present invention regards a superfluidifying additive for cementitious compositions, characterized in that it comprises an acrylic superfluidifier in combination with a cationic additive. Technical problem In order to meet the required specifications in the phase of laying of cementitious items, such as low water/binder ratio, high initial fluidity, maintenance of workability over time, and in order to bestow on the items the desired characteristics, such as high compression strength, durability, and accurate surface finish, the use of superfluidifying additives is recommended. Acrylic superfluidifiers are particularly appreciated in that they have high fluidifying action even at low water/binder ratios and maintain workability of the mixture for periods of time sufficient for the laying of the items, where the laying comprises preparation, transportation and casting of the cementitious composition (e.g., concrete). The use of acrylic superfluidifiers is appreciated not only on grey cements, but above all on white cements. In fact, in the case of white cements, traditional superfluidifiers, such as naphthalene sulphonate-based or lignin sulphonate- based superfluidifiers, lead to significant variations in the typical luminance of the resulting cementitious items. Melamine products would appear to be recommended for their colour; however, they are sometimes unsuitable from the point of view of performance, in that, in combination with white cements, they exert an unsatisfactory fluidifying action already at the initial working times. Superfluidifiers having an acrylic structure present a sufficiently light colour such as to maintain practically unaltered the degree of whiteness of hardened cementitious surfaces; however, at times they may prove unsatisfactory. In fact, although their fluidifying action is high even at low water/cement ratios (e.g., w/c < 0.40), it may be found to be limited to the period alone of preparation of the mixture, considerable losses of workability occurring already within very short times (5-10 minutes) of preparation of the mixture. This problem is graphically illustrated in Figures 1 , 2 and 3, in which the workability data over time are given, respectively, for specimens of paste, mortar, and concrete with addition of acrylic superfluidifying additives. Furthermore, as may be noted in Figure 12, the problem of loss of workability cannot be solved by increasing the dose of the acrylic superfluidifier: on the contrary, the specimen containing the higher dose of acrylate (indicated by the symbol — ♦ — ), albeit possessing high workability at time zero, shows a greater loss of workability than the specimen containing less fluidifier or the specimen not containing any fluidifier. The loss of workability may manifest itself also as considerable stickiness of the fluid mass, which does not enable the operations of transportation, unloading and laying of the concrete to be carried out in a workmanlike manner. The remedy traditionally adopted in this situation consists in adding more water to the cementitious mixture. This, however, proves to be counterproductive in that it results in a greater porosity of the consolidated mass, and hence practically in cements which present a poorer mechanical performance and are more susceptible to phenomena of damp infiltration, degradation, corrosion of the reinforcements, etc. In view of the limits of the prior art highlighted above, there emerges clearly the need for new efficient superfluidifying systems for cements. In particular, the need is felt for superfluidifiers that are able to meet the requirements of fluidity and workability of cementitious compositions which show considerable loss of workability over time when acrylic fluidifers are used. Summary Now the applicant has unexpectedly found that the drawbacks of the known superfluidifying additives referred to above can be overcome by adopting an additive system consisting of an acrylic superfluidifier combined with an ammonium salt corresponding to the structural formula (I), a surfactant, and possibly an antifoaming additive. This additive system, in the form of a multicomponent superfluidifying additive, constitutes a first subject of the invention. The present invention further comprises high-fluidity and high-workability cementitious compositions containing an acrylic superfluidifier, an ammonium salt described by the structural formula (I), a surfactant, and possibly an antifoaming additive. Further aspects of the present invention are represented by premixes in the dry state and cementitious items containing an acrylic superfluidifier, an ammonium salt of formula (I), a surfactant, and possibly an antifoaming additive, by the corresponding preparation procedures, as well as by the use of the above additive system in the fluidification of cementitious mixtures. Description of Figures Figure 1 (reference): gives the slump values of pastes with a base of white cement (Italbianco ®), containing an acrylic additive, expressed as diameter of cone of paste as a function of time: — • — : mixture containing the acrylic additive Mapefluid ® X-404 — ♦ — : mixture containing the acrylic additive Glenium ® 51. Figure 2 (reference) gives the consistency of a specimen of mortar with a base of white cement (Italbianco ®), as a function of time, compared with the same mortar with addition of acrylic superfluidifiers: — • — : mortar as such ; water/binder = 0.62 — ♦ — : mortar + 1.0% Tupole ® SSP 104 ; water/binder = 0.36 — * — : mortar + 1.0% Mapefluid R x 404; water/binder = 0.40 Figure 3 (reference) gives the slump of concrete with a base of white cement (Italbianco ®), with addition of two different acrylic additives, expressed as reduction in height of the cone as a function of time. — ■ — : concrete containing 2% Glenium ® 51 ; water /binder = 0.43 ; — A — : concrete containing 4% of Mapefluid ® X-404; water/binder = 0.45. Figures 4. 5 and 6 give the values of consistency as a function of time of mortars prepared with three different cements (two white cements Italbianco ® and a grey cement 52.5 R), with the addition of additives as follows: — Figure 4: — ♦ — reference: mortar made using white cement Italbianco ® + 1 % Mapefluid ® X-404; water/binder =0.45 — ■ — : mortar made using white cement Italbianco ® premixed with 0.3% of formulation A0 + 1% Mapefluid ® X-404 ; water/binder = 0.45 - Figure 5: — ♦ — reference: mortar made using white cement Italbianco ® + 1.2% Mapefluid ® X-404; water/binder = 0.47 — ▲ — : mortar made using white cement Italbianco ® premixed with 0.3% of formulation AO ; water/binder = 0.47 — ■ — : mortar made using white cement Italbianco ® premixed with 0.2% of formulation AO + 1 % Mapefluid ® X-404; water/binder = 0.47 - Figure 6: — ♦ — reference: mortar made using grey cement 52.5 R + 1 % Mapefluid ® X- 404; water/binder = 0.45 — ■ — : mortar made using grey cement 52.5 R premixed with 0.4% of formulation A0 + 1 % Mapefluid ® X-404; water/binder = 0.45 Figures 7. 8 and 9 give the slump values of concretes, expressed as reduction in the height of the cone as a function of time: - Figure 7 gives the data of Table 5 for specimens of concrete obtained by premixing the formulation A0 with white cement Italbianco ®: specimens 1 , 2 and 3 contain the acrylic additive and the formulation A0, and specimen C1 the formulation A0 alone: — ♦ — : specimen 1 ; — □ — : specimen 2 ; — — : specimen 3 ; — X — : specimen C1 . - Figure 8 gives the data of Table 6 for specimens obtained by mixing with white cement the metakaolin to which the formulation A0 had been pre-added: specimens 5-8 contain the acrylic additive and the formulation A0, and specimens C2-C3 contain the formulation A0 alone: — ♦ — : specimen 5 ; — D — : specimen 6 ; — ■ — : specimen 7 ; — • — : specimen 8 ; — A — : specimen C2 ; — X — : specimen C3 ; - Figure 9 gives the slump values of Table 6 for the specimens of concrete 7 and 8 referred to above, compared with a specimen of concrete to which the acrylic additive alone had been added: — ■ — : specimen 7 ; — • — : specimen 8 ; — X — : specimen with addition of the acrylic additive alone (3% of acrylic additive; water/binder = 0.4). Figures 10 and 11 give the values of compression strength of test specimens of concrete as a function of time: - Figure 10 gives the data of Table 7 for specimens of concrete obtained by premixing the formulation AO with white cement Italbianco ®: specimens 1 , 2, 3 and 4 contain the acrylic additive and the formulation AO, whilst specimen C1 contains the formulation AO alone: H : specimen 1 ; : specimen 2 ; ^ : specimen 3 ; ffl: specimen 4 ; [J] : specimen C1 ; - Figure 11 gives the data of Table 8 for specimens of concrete obtained by pre- dispersion of the formulation AO in the metakaolin: V Ά : specimen 5 ; I — I : specimen 6 ; Hi : specimen 7 ; LJ. : specimen 8 ; Ξ : specimen C3. Figure 12 (reference) Consistency of a specimen of mortar with a base of white cement (Italbianco ®) as a function of time, compared with the same mortar with addition of an acrylic superfluidifying additive: — A — mortar as such, w/c = 0.60; — ■ — mortar + 1 % of acrylic superfluidifier (Superflux 2000AC), w/c ratio = 0.45; — ♦ — mortar + 1.3% of acrylic superfluidifier (Superflux 2000AC), w/c ratio = 0.41. Figures 13. 14. 15 and 16 Consistency as a function of time (workability curve) of white cement-based mortar specimens (EXAMPLE II), prepared with same w/c ratio of 0.45 and with addition of the additive system, as compared to the same mortar with addition of acrylic superfluidifier alone. Fig. 13 — ■ — Reference: mortar with addition of 1% of acrylic superfluidifier (Superflux 2000AC); — ♦ — mortar with addition of 0.3% of formulation A1 + 1% of acrylic superfluidifier (Superflux 2000AC); — A — mortar with addition of 0.3% of formulation A2 + 0.8% of acrylic superfluidifier (Superflux 2000AC). Fig. 14 — ■ — Reference: mortar with addition of 1 % of acrylic superfluidifier (Mapefluid X404); — A — mortar with addition of 0.3% of formulation A3 + 1 % of acrylic superfluidifier (Mapefluid X404); — ♦ — mortar with addition of 0.3% of formulation A4 + 1 % of acrylic superfluidifier (Mapefluid X404); — X — mortar with addition of 0.3% of formulation A5 + 1 % of acrylic superfluidifier (Mapefluid X404). Fig. 15 — ■ — Reference: mortar with addition of 1% of acrylic superfluidifier (Mapefluid X404); — ♦ — mortar with addition of 0.3% of formulation A6 + 1 % of acrylic superfluidifier (Mapefluid X404); — A — mortar with addition of 0.3% of formulation A7 + 1 % of acrylic superfluidifier (Mapefluid X404); Fig. 16 — ■ — Reference: mortar with addition of 1 % of acrylic superfluidifier (Mapefluid X404); — A — mortar with addition of 0.3% of formulation A8 + 1 % of acrylic superfluidifier (Mapefluid X404); — ♦ — mortar with addition of 0.3% of formulation A9 + 1% of acrylic superfluidifier (Mapefluid X404). Figures 17 and 18 Consistency as a function of time of specimens of mortar with a base of grey cement 52.5 R (EXAMPLE III), prepared with the same w/c ratio of 0.45 and with addition of the additive system, as compared to the same mortar with addition of acrylic superfluidifier alone. Fig. 17 — ■ — Reference: mortar with addition of 1% of acrylic superfluidifier (Superflux 2000AC); — ♦ — mortar with addition of 0.5% of formulation A1 + 0.5% of acrylic superfluidifier (Superflux 2000AC). Fig. 18 — ■ — Reference: mortar with addition of 1 % of acrylic superfluidifier (Superflux 2000AC); — ♦ — mortar with addition of 0.5% of formulation A10 + 0.5% of acrylic superfluidifier (Superflux 2000AC); — A — mortar with addition of 0.5% of formulation A11 + 0.5% of acrylic superfluidifier (Superflux 2000AC). Figure 19 Slump loss of a specimen of white cement-based concrete (EXAMPLE IV), prepared with same w/c ratio of 0.38 and with addition of the additive system, as compared to the same concrete with addition of acrylic superfluidifier alone. — ■ — Reference: concrete with addition of 2.5% of acrylic superfluidifier (Mapefluid X404); — A — Concrete with addition of 0.65% of formulation A5 + 2% of acrylic superfluidifier (Mapefluid X404). Detailed description of the invention The subject of the present invention is an additive system for cementitious compositions, comprising at least one acrylic superfluidifier, at least one ammonium salt of formula (I), at least one surfactant, and possibly at least one antifoaming additive. The first element of the present additive system consists of one or more ammonium salts corresponding to the following structural formula (I): Ri + R 4 N R 2 X " R 3 (I) where: R 1 ; R 2 , R 3 , independently of one another, are chosen from among: • hydrogen, • a saturated or unsaturated, linear or branched alkyl group having from 1 to 22 carbon atoms, preferably from 1 to 16, • a polyoxyalkylene chain containing n repetitive units of structural formula (II), and m repetitive units of structural formula (III) [ 0-CH 2 -CH 2 ] [ 0-CH 2 -CH ] I CH 3 (H) (III) where m and n, independently of one another, are integers comprised between 0 and 50, and ( + n) is an integer comprised between 2 and 50, and where the said units may be present randomly in the said chain; • a saturated or unsaturated, linear or branched alkyl group having from 1 to 22 carbon atoms, preferably from 12 to 18, possibly substituted with one or more polyoxyalkylene chains as defined above; and R 4 is chosen from between: • a group having -(CH 2 ) P N R 5 R 6 structure, where p is an integer comprised between 1 and 7, and in which R 5 and R 6 may be, independently of one another: (i) hydrogen, (ii) saturated or unsaturated, linear or branched alkyl groups having from 1 to 22 carbon atoms, or (iii) a polyoxyalkylene chain as defined above; • a saturated or unsaturated, linear or branched alkyl group having from 1 to 12 carbon atoms, preferably from 1 to 4; and where X " is an anion which neutralizes, either partially or totally, the charge of the ammonium ion. X " ions preferred for the purposes of the invention are the hydroxide ion and the R 7 -COO " ion, in which R 7 is a saturated or unsaturated, linear or branched alkyl group having from 1 to 22 carbon atoms, preferably from 9 to 20, such as the oleate, stearate or linoleate ion. The ammonium salt of structure (I) is obtained through partial or total salification of an amine by a protonic acid, used in any molar ratio. Preferred ammonium salts according to formula (I) are those in which the cation is represented by: triethyl ammonium, tetramethyl ammonium, hexadecyltrimethyl ammonium, or else the ammonium ions derived from an ethoxylated primary amine and containing a C 14 -C 18 alkyl chain, such as the products marketed by D.A.C. under the name Diammin. The above polyoxyalkylene chains are bound to the compound of formula (I) by means of the oxygen atom of the last oxyethylene unit (II) or oxypropylene unit (III), whilst the terminal unit at the other end of the chain has a CH 3 -CH 2 -O- structure (in the case of oxyethylene chains) or a CH 3 -CH 2 -CH 2 -0- structure (in the case of oxypropylene chains). Preferably, the polyoxyalkylene chain consists of n units of formula (II) where n is comprised between 2 and 15. When R 4 is a group of -(CH 2 ) P N R 5 R 6 structure, the nitrogen atom belonging to it may, according to the environmental pH, be present in the neutral form, as represented above, or in the form of -(CH 2 ) P NH + R 5 R 6 ammonium ion. In the latter case, the compound of formula (I) is in the form of a bivalent di-ammonium cation. A preferred class of ammonium salts included in the general formula (I) is that in which the ammonium ion corresponds to the structural formula (la) + R 5 NH -(CH 2 ) n -NH 3 (la) where R 5 and n have the meanings specified above; preferably, R 5 is a saturated or unsaturated, linear or branched alkyl group containing from 8 to 22 carbon atoms. The ammonium ion of formula (la) is either partially or totally neutralized by the X " anion, where X has the meanings specified above. Also the derivatives of formula (la) may appear in the form indicated above of di-ammonium salts, i.e., where also the nitrogen atom bound to R 5 is in the protonated form. Preferred ammonium salts of formula (la) are diamine dioleates, marketed by the firm C.E.C.A. under the name of lnipol. The second element of the additive system which is the subject of the present invention consists of one or more surfactants. The surfactant may be any surfactant, ionic or cationic, amphoteric or non-ionic. Preferably, a non-ionic surfactant is used, with a hydrophilic-lipophilic balance (HLB) value of between 5.5 and 15. Among non-ionic surfactants, those having a polyoxyethylene and/or polyoxypropylene structure may be cited, in particular those containing from 2 to 9, for example 5 or 6, ethylene oxide units, generally alkoxylated at least at one end of the polymer chain, for example polyoxyethylene glycol mono-ethers with a fatty alcohol, having, for example from 8 to 22 carbon atoms, or with a phenol possibly substituted with at least one C 8 -C 22 alkyl residue, for instance nonyl. Examples of non-ionic surfactants useful for the purposes of the present invention are the nonylphenol polyoxyethylene having 5 ethylene oxide units marketed by CONDEA Chimica D.A.C. under the name Nonfix 5, and the nonylphenol polyoxyethylene having 6 ethylene oxide units marketed by WITCO Chimica D.A.C. under the name Syntopon A. Further examples of non-ionic surfactants are alcohols, preferably linear ones, ethoxylated with 3-8 moles of ethylene oxide, or else isodecyl alcohol ethoxylated with 4-8 moles of ethylene oxide. These products are marketed by D.A.C under the name Biodac® (e.g., Biodac 2/32). Among anionic surfactants may be cited Fenopon ® 128 (GAF), having an R 8 O(CH 2 CH 2 0) n . 1 CH 2 CH 2 OS0 3 " NH 4 + structure. Examples of cationic surfactants are the compounds of formula R 8 N(CH 3 ) 2 CH 2 C 6 H 5 .Cl" (R 8 is H or C,-C 4 alkyl), marketed by C.E.C.A. under the name Noramium ® . The third element of the additive system which is the subject of the present invention consists of one or more acrylic superfluidifying additives. Belonging to this class are additives containing polymers, terpolymers or copolymers of acrylic acid or methacrylic acid, or other carboxylic acids or corresponding anhydrides containing a polymerizable ethylene unsaturation (for example, fumaric acid, oleic acid, itaconic acid, crotonic acid, aconitic acid, sinapic acid, mesaconic acid, undecylenic acid, angelic acid, hydroxyacrylic acid, maleic anhydride), or the corresponding salts and esters, and their mixtures. Examples of acrylic polymers and copolymers useful for the purpose of the present invention are given below, with the bibliographical references describing them, incorporated for reference in the present patent application: - copolymers between a) acrylic or methacrylic acid and b) a hydroxy-(C 2 -C 3 )-alkyl ester of the acrylic or methacrylic acid, described in EP-A-303,747 ; - mixtures comprising at least one copolymer of alkenyl ethers of formula (I), at least one polyalkenyl ether of formula (II), and maleic anhydride, the corresponding products of hydrolysis or the salts of said products of hydrolysis, described in EP-A-619.277; - superplasticizing additives obtained by terpolymerizing the monomers of formula (IV), (V) or (VI), described in EP-A-612.702; - copolymers of formula (I) described in JP 6048797; - polymer salts formed by reaction of a polycarboxylic acid with an acrylic polymer containing nitrogen, typically in aqueous solution, described in FR 2.656.297; - polymeric compositions of a maleic acid mono-ester with a compound of formula (I), and of a monomer of formula (II), defined in FR 2.668.773 ; - copolymers in the form of free acids or salts, containing three types of monomers, defined in FR 2.671.090 ; - dispersing agents comprising water-soluble vinyl copolymers obtained by radical co-polymerization in aqueous solution of monomers of formulas (1 ), (2), (3), (4), and (5), described in EP-A-590.983; - water-soluble vinyl copolymers represented by linear copolymers between vinyl acetate and N-substituted maleamic acid, having formula (A), described in EP- A1 -604.676 ; - copolymers of the monomers A), B), C) and D), defined in EP-A1 -610.699; - polymers or copolymers of ethylene carboxylic acids chosen from among acrylic acid, methacrylic acid, fumaric acid, aleic acid, itaconic acid, crotonic acid, aconitic acid, sinapic acid, mesaconic acid, undecylenic acid, angelic acid, hydroxyacrylic acid, and maleic anhydride, described in FR-A1 -2.699.915; - an additive for the control of fluidity of cementitious compositions, containing at least one copolymer made up of a monomer a) of an ester of alkylene-glycol monomethacrylic acid of formula (I) and a monomer b) of a methacrylic acid of formula (II), or else a copolymer made up of a monomer d) having a base of an alkoxypolyalkylene-glycol monomethylallyl ether of formula (III) and a monomer b) having a base of methacrylic acid of formula (IV), defined in FR -A1 -2.706.447; - copolymers or corresponding salts containing i) 33-95 mol% of a carboxylic acid with polymerizable ethylene unsaturation, and ii) 5-67 mol% of a carboxylic-acid ester with polymerizable ethylene saturation, as described in US 5,047,087 and in US 4,473,406, in which the unsaturated carboxylic acid is preferably acrylic acid, methacrylic acid, crotonic acid, fumaric acid, itaconic acid, citraconic acid, aconitic acid or maleic acid. The acrylic additive is, for example, chosen from among the commercial products listed below, together with the corresponding manufacturer's name, and, where available, with the type of polymer or copolymer contained in these products and the bibliographical references regarding their structure and preparation, incorporated for reference in the present patent application:: Mapefluid ® X-404 (Mapei, polyethylene oxide and copolymer of sodium methacrylate and polyethylene oxide methacrylate, EP-A-612.702); Tupole ® SSP-104 (Takemoto Oil & Fat, terpolymer consisting of sodium acrylate, sodium methacrylate and polyethylene oxide, EP-A-590.983); Darex Super ® 200 (Denka Grace, copolymer between ethylene oxide and maleic anhydride, EP-A-0619277); Narlex ® LD-36V and LD-38SF (National Starch, acrylic acid copolymers, USP 4.473.406); Glenium ® 51 (MAC-MTB, ethers of polycarboxylic acids, FR-2.656.297), Sokalan ® HP 80 (BASF). Other examples of commercial acrylic-based additives useful for the purposes of the present invention are Cimfluid ® 2000 AC (AXIM, polyethylene oxide and copolymer of sodium methacrylate and polyethylene oxide methacrylate); PPE 1179 (National Starch & Chemical, copolymers of acrylic acid partially neutralized with triethanol amine); CAD-8000 (Kao Corporation); Tupole ® HP-11 (Takemoto Oil & Fat, polycarboxylic acid); CM 1142 (Bozzetto); Superflux ® 2000 AC (Italeux, polyethylene oxide and copolymer of sodium methacrylate and polyethylene oxide methacrylate). The additive system which is the subject of the present invention preferably contains at least one antifoaming additive. The antifoaming additive may be chosen from among various antifoaming additives for cements; for example, it may be a copolymer between units of ethylene oxide and propylene oxide, etherified at the start of the polymer chain with a C 2 -C 20 aliphatic alcohol, as described in the international patent application PCT/EP97/00026 in the name of the present applicant, having in particular a molecular weight of approximately 1050, a propylene oxide unit / ethylene oxide unit ratio of 3, etherified with an aliphatic alcohol having from 10 to 14 carbon atoms, typically 13, such as the product Airplast ® , marketed by Hispano Quimica. In addition, the antifoaming agent may be a polymer obtained by direct condensation between stearic acid and propylene oxide, such as the product Koster ® K/9 P, marketed by D.A.C. Further subjects of the invention are the following: high-fluidity and high- workability cementitious compositions containing the additive system described above, and the process for their preparation; dry pre-mixes containing the additive system described above, suitable for forming the aforementioned cementitious compositions; cement items made starting from the above-mentioned cementitious compositions; and use of the additive system described above in the fluidification of cementitious compositions. In the present text, by cementitious compositions are meant cementitious mixtures comprising at least one hydraulic binder, water, and possibly: one or more inert aggregates, and/or one or more mineral additives, and/or fibres for cement, and/or one or more conventional additives. By hydraulic binder is meant a material in the form of powder in the dry state, which, when mixed with water, yields plastic mixtures able to solidify and harden over time. By cements are meant in particular those included in the UNI ENV 197.1 standard. The cementitious compositions are divided into pastes (compositions devoid of inert aggregates) and conglomerates (compositions containing at least one inert aggregate). The conglomerates in turn are divided into mortars (containing fine aggregates, for example sand) and concretes (containing both fine aggregates and coarse aggregates, such as gravel, pebbles, and crushed stones, chosen, for example, from among those classified according to the UNI 8520 standard). The present invention refers in particular to mortars and concretes. By mineral additive is meant any type of finely ground inorganic material that may be added to the concrete to bestow on it better characteristics of resistance and durability. The additives may be inert, porcelain-type, or with latent hydraulic activity. For the purposes of the present invention, preferred mineral additives are metakaolin, limestone, fly ash, blast-furnace slag, porcelain (either natural or artificial), and fine silica. The fibres for cements may be natural or artificial, inorganic or organic. Examples of inorganic natural fibres are: asbestos, sepiolite and wollastonite; examples of organic natural fibres are: cotton, wool, jute, flax, hemp, sisal, and cellulose fibres; inorganic artificial fibres include, for example: glass, rock, slag, basalt, ceramics, calcium silicate, silicon carbide, and carbon; organic artificial fibres may be, for example: nylon, rayon, polyacrylonitrile, polyvinyl alcohol, polyethylene, and polypropylene. Further fibres for cements may be of a metallic nature, for example steel. Conventional additives are those normally contained in cementitious compositions, such as: retarders, accelerators, water reducers, pumping adjuvants, and corrosion inhibitors. A further subject of the present invention is represented by dry pre-mixes containing the superfluidifying additives described above. The dry pre-mixes are compositions in the dry state which, by the addition water, are directly converted into cementitious compositions ready for laying. Hence, the dry pre-mixes comprise at least one hydraulic binder as defined above, and possibly one or more inert aggregates, fibres for cements, and/or one or more mineral additives, and/or conventional additives, as defined above. Further examples of conventional additives are: shrinkage compensators, aerating agents, water retainers (e.g., cellulose ethers), retarders or accelerators. By cementitious items are meant items obtained from cementitious compositions prepared, laid and left to harden. Particular embodiments of the present invention are represented by cementitious compositions, cementitious items, and dry pre-mixes containing the additive that is the subject of the present invention and at least one photocatalyst able to oxidize, in the presence of light, air and environmental humidity, the polluting substances present in the environment. In the said compositions, cementitious items or dry pre-mixes, the photocatalyst is preferably represented by titanium dioxide or one of its precursors, prevalently (for example for at least 70%) in the form of anatase. Preferably, the photocatalyst is distributed evenly in the entire cementitious mass. In this case, the cementitious items contain the photocatalyst in bulk, thus avoiding the need for application of cementitious coatings containing the photocatalyst. Examples of pre-mixes, compositions and items containing in bulk particles of photocatalyst are those described in the international patent application WO 98/06601 (PCT/EP97/04008), incorporated by reference in the present application. The high-fluidity and high-workability cementitious compositions that are the subject of the present invention contain the components of the additive system preferably in the following weight percentages which refer to the weight of the hydraulic binder in the dry state: ammonium salt: from 0.04% to 1%, more preferably 0.12% - 0.30%; surfactant: between 0.04% and 1 %, more preferably 0.12%-0.30%; antifoaming agent: between 0.02 % and 0.3%, more preferably 0.06 -0.15%; acrylic superfluidifier: from 0.3% to 3%, more preferably between 0.5% and 2.5%. The additive system that is the subject of the invention is preferably produced in the form of two separate formulations, A and B, which may be added separately to the cementitious compositions, where: formulation A comprises the ammonium salt of formula (I), the surfactant, and the possible antifoaming additive; formulation B comprises the acrylic superfluidifier. Typically, formulation A contains the following weight quantities for ammonium salt a), surfactant b) and antifoaming agent c): from 2 to 6 parts by weight, for example, 4 parts by weight of a); from 2 to 6 parts by weight, for example 4 parts by weight of b) ; from 1 to 4 parts by weight, for example 2 parts by weight of c). In order to obtain a volume of additive such as to facilitate the operations of incorporation into cements, formulation A may be added to suitable quantities of the filler material ("mineral additive", for example metakaolin) required for preparing the cementitious compositions or the pre-mixes. Preparation of the cementitious compositions is according to conventional procedures and using conventional equipment, by mixing the hydraulic binder and remaining ingredients with water, typically in ambient conditions, for example at a temperature of between approximately +10°C and +40°C, for example between +15° and +25°C. The elements of the additive system are incorporated in the cementitious mixtures at any stage of the preparation of the latter, preferably in the form of two separate fractions (formulations A and B). The temperature at which formulation A is added depends upon the viscosity of the formulation itself. In the case of high viscosity, formulation A may be previously heated to a temperature generally ranging from 30°C to 40°C. Formulation A is preferably premixed with the hydraulic binder in the dry state, or with a mineral filler in the dry state, before being mixed with water and before the remaining ingredients are added. Preferably, formulation A is pre-dispersed dry in a mineral filler, such as metakaolin, and the resulting material is then evenly dispersed in the hydraulic binder. In particular, formulation A may be premixed with the total quantity of filler required for the preparation of the cementitious mixture, this quantity ranging, for example, from 5 wt% to 15 wt%, and typically being approximately 10 wt% with respect to the weight of the hydraulic binder in the dry state. Preferably, formulation A is added to an aliquot of the total filler required for the mixture, the so-called "master", which may vary, for example, from approximately 1% to 5%, being for example approximately 2.5 wt% with respect to the weight of the hydraulic binder in the dry state. The pre-dispersion of formulation A in an aliquot of filler enables a considerable reduction in the volumes of materials to be pre-mixed, at the same time facilitating also the subsequent phase of homogenisation with the cement. The homogenisation of the "master" with the cement, and the possible addition of the mineral extenders (inert aggregates and mineral additives) may also be carried out directly in the concrete mixer, by dry-premixing all the solid components of the cementitious composition for approximately 2-3 minutes, and subsequently adding the quantity of water and of formulation B (acrylic superfluidifier) necessary for preparing the composition. This system is even more advantageous because it enables slow volumes of mineral extender to be handled and is thus suited for the preparation of concretes in either fixed or mobile (i.e., truck) concrete mixers. Formulation B (acrylic additive) is preferably incorporated in the cementitious mixture at the end, as final ingredient, being typically added to the mixing water, which is preferably added in portions to the cementitious mixture containing the remaining ingredients. The superfluidifying compositions according to the present invention afford the following unexpected advantages: - they enable cementitious mixtures, for example concretes, to be obtained that are endowed with satisfactory characteristics of workability and fluidity both at the initial working times and subsequently, for at least 30-45 minutes, corresponding in particular to a workability according to class S4 of the UNI 9858 standard for at least 30-45 minutes; - they enable low water/binder weight ratios to be adopted, in particular ratios not higher than 0.4, for example approximately 0.35-0.4 parts by weight of water per part by weight of cement (hydraulic binder) in the dry state; - they enable cementitious compositions, in particular concretes, to be obtained that are endowed with high mechanical strength, presenting, for example, values of compression strength at 1 , 2, 7 and 28 days of at least 35, 50, 65, and 70 MPa , respectively, typically of between 35 and 40 MPa at 1 day, between 45 and 55 MPa at 2 days, between 50 and 60 MPa at 3 days, between 60 and 70 MPa at 7 days and between 70 and 85 MPa at 28 days; - in particular, they enable values of mechanical strength to be obtained at 28 days that are unexpectedly higher than those of the specimens containing formulation A alone, for example values of compression strength at 28 days of at least 70 MPa; - they enable cementitious compositions, in particular concretes, to be obtained with values of absolute gravity of at least 2400 kg/m 3 , corresponding to air contents lower than 1 % volume/volume. The percentage of air was calculated on the basis of the values of the absolute gravity determined according to the UNI 6394 standard, Part 1. Below are given a few examples in order to provide a non-limiting illustration of the present invention. EXPERIMENTAL PART EXAMPLE I: Tests on concrete Materials 1. Cement: Italbianco ® CEM 52.5 R (Italcementi), the chemical analysis of which is given in Table 1 350 kg/m 3 TABLE 1 - Cement CEM 52.5R ITALBIANCO ® (ITC) Chemical analysis Fire loss 3.87% w/w Luminance 89.9% Dominant wavelength 569 nm Purity 2.3% w/w X-ray spectrometric analysis Si0 2 21.66% w/w Al 2 0 3 3.63% w/w Fe 2 0 3 0.16% w/w CaO 65.00% w/w MgO 1.05% w/w SO 3 3.26% w/w Na 2 O 0.67% w/w K 2 0 0.14% w/w SrO 0.06% w/w Mn 2 0 3 <0.04% w/w P 0.10% w/w Ti0 2 0.03% w/w w/w = weight/weight 1A. Water/binder ratio: in the present text is meant the weight ratio between the mixing water and the sum of the cement and possible metakaolin or other filler. 2. Aggregates Light white marble from the Apuane Alps of the area of Carrara, divided into 10 distinct sizes; continuous-type granulometric curve with granulometric maximum - 20 mm 1900 kg/m 3 3. Mineral extenders: Metakaolin Metastar ® 501 ECC: 10 wt% with respect to the cement: 35 kg/m 3 4. Photocatalyst: Titanium dioxide A-HR ® micron Tioxide 7 kg/m 3 5. Superfluidifying composition: Formulation AO, liquid; w/w % with respect to the dry cement: 0.5%-1.3% B) Formulation B: commercial acrylic additive Mapefluid ® X-404; w/w % with respect to the dry cement: 1.5%-2.0% C) small quantities of antifoaming agent Airplast ® 251 Equipment: 1. For the preparation of the pre-mixes: - "blendor" mixer with 1 -litre beaker (Waring) - 5-litre intensive mixer (Eirich) 2. For the preparation of the concrete: 50-litre vertical-axis concrete mixer, with rotating movement Method of addition of additives to the mixtures: a) Dry pre-mixing of formulation A with the cement: In a laboratory "blendor", quantities of cement sufficient for the preparation of the concrete were prepared. All the cement required for the mixture received addition of formulation A. b) Pre-dispersion of formulation A in the metakaolin: Two distinct methodologies were adopted, using a laboratory blendor: i) in the first case, formulation A was dispersed in the entire volume of the metakaolin required for the preparation of the concrete (10 wt% with respect to the cement); ii) in the second case, formulation A was dispersed in lower quantities of metakaolin, corresponding to 5 wt% and 2.5 wt% with respect to the cement in the dry state. After the above addition, the metakaolin was mixed with the cement necessary for the preparation of the concrete, using an Eirich intensive mixer. - Formulation B (acrylic superfluidifie : The additive B was added directly in the concrete mixer as the last component, together with the antifoaming agent. Reference cementitious compositions containing the acrylic additive alone (formulation B). Various specimens of cementitious compositions were prepared which had a base of white cement Italbianco ® (Italcementi) (pastes, mortars and concretes) and contained the acrylic additive alone, and reference compositions devoid of the said additive, having the characteristics specified above in the legends of Figures 1 , 2 and 3. Concretes containing the multicomponent additive system of the present invention (formulation A + formulation B) and reference compositions containing formulation A alone Various specimens of concrete were prepared by mixing the hydraulic binder and the remaining ingredients with water, in the quantities specified above, in ambient conditions (approximately +20°C to +30°C). The proportioning of the additives, with reference to the commercial products as such, and the water/hydraulic binder ratios are given in Tables 2 and 3 for to the two procedures of addition of formulation A described above. Specimens from 1 to 8 are concrete specimens according to the present invention; specimens C1 , C2, and C3 are reference concrete specimens containing the additive A alone and without acrylic superfluidifier. TABLE 2 - Cement dry-premixed with formulation A TABLE 3 - Cement dry-premixed with metakaolin to which formulation A had been previously added Analysis of the characteristics of the mixtures Fresh-state tests: Determinations of absolute gravity, slump over time, and behaviour under vibration were carried out on mixtures of concretes prepared as described above in the fresh state (i.e., within approximately 60 minutes of mixing the corresponding ingredients with water). The absolute gravity was determined according to the UNI 6394 Standard, Part 1. The behaviour under vibration was determined by assessing visually the degree of segregation of the mixtures. The workability loss was evaluated by measuring the slump ("slump test") according to the UNI 9418 standard, at the times indicated in the Table. Table 4 presents the values of absolute gravity, in kg/m 3 , and behaviour under vibration expressed as excellent, good, satisfactory or poor. TABLE 4 Legend: +++ excellent ++ good + satisfactory - poor Results - The absolute gravity value generally proved higher than 2400 kg/m 3 , corresponding to an air content lower than 1 % volume/volume. The behaviour under vibration was on average good, and satisfactory only for a few mixtures. The reference specimens C1-C3 presented an unsatisfactory behaviour under vibration, or in any case a behaviour inferior to that of the concrete specimens containing the superfluidifying composition according to the present invention. Slump Test: The slump values, expressed as reduction in the height in centimetres of the cone of concrete are given in Tables 5 and 6 and presented in graphic form in Figures 7, 8 and 9. TABLE 5 - Cement dry-premixed with formulation A TABLE 6 - Cement dry-premixed with metakaolin to which formulation A had been added Results The use of formulation A in combination with the acrylic additive B significantly reduced the workability loss over time, which, instead, was found when the acrylic additive B alone was used, as illustrated in Figure 9. The use of 0.65% of formulation A plus 1.8% of formulation B, with formulation A dry-premixed with cement or metakaolin, enabled the concrete to be maintained in the consistency class S4 up to approximately 45 minutes. It was possible to operate with a water/binder ratio < 0.4 Tests in the hardened state Compression strength - Various specimens of concrete were prepared according to the UNI 6127 standard. Compression strength was determined according to the UNI 6132-72 standard. The results obtained are presented in Tables 7 and 8, and in Figures 10 and 11. TABLE 7 Cement dry-premixed with formulation A TABLE 8 Cement dry-premixed with metakaolin to which formulation A had been added ** not ejectable at expiry of 24 h Comments on results The concretes prepared with the superfluidifying composition comprising 0.65% of formulation A plus 1.8% of formulation B, in which formulation A had been premixed with metakaolin, presented compression strength values at 1 , 2, 3 and 7 days of 36-40, 52-57, 56-61 and 66-73 MPa, respectively, with compression strength values at 28 days of 75 MPa or higher. At 1 day, the compression strength was 10-15% lower than that of a concrete having the same composition and the same water/binder ratio (at 20°C). However, already at 30 hours the values were similar, in the region of 45 MPa (at 20°C). It is important to note that the reference specimens containing formulation A alone show compression strength values at 28 days that are significantly lower than those of the specimens according to the present invention, containing both formulation A and formulation B. Retarding effect: Formulation A in quantities as low as 1.3% (specimen C3) yields retardation in setting/hardening such as not to enable ejection of the test specimens at 24 hours. At 40 hours the compression strength values were lower than those of the test specimens containing 0.65% of formulation A plus 1.8% of formulation B (specimens 6, 7, 8) prepared with water/cement ratios that were equal or even higher. Specimen C3 at 2 days showed a compression strength R c lower than that of specimens 6, 7, and 8 at 24 hours. The use of formulation A made possible the utilization of acrylic superfluidifiers in the white cement-based cementitious mixtures, thus eliminating the drastic loss of workability observed in the first 10 minutes of working when the acrylic additive B alone was used. In the experimental conditions adopted, the optimal proportioning of the two products was as follows: 0.65% of formulation A plus 1.8% of formulation B; this made it possible to maintain the concrete in the consistency class S4 up to approximately 45 minutes. The favourable results obtained by dry premixing of formulation A with an aliquot of metakaolin, corresponding to 2.5 wt% with respect to the cement, are particularly important for the industrial application of the superfluidifying compositions studied: with this addition procedure, the volumes of metakaolin to which formulation A is to be added undergo, in fact, a significant reduction, and at the same time the homogenization in the industrial plant of the "master" is rendered more effective. The properties of the additive system according to the invention may be further highlighted in the ensuing Examples II and III , which refer to measurements of consistency over time carried out according to the UNI 7044 standard. These measurements represent an index of the workability of the cementitious mixtures. Example IV refers to slump measurements according to UNI 9418 standard, carried out on concrete. EXAMPLE II This consisted of a series of tests carried out on mortar. Each mortar was prepared with the following ingredients: 450 g of white cement CEM 52.5R (Italbianco ®); 1350 g of aggregate: light white marble form the area of Carrara, divided into two sizes, of 0-1 mm and 1-3 mm. The mortars were prepared according to the EN 196/1 standard, using a Hobart mixer. The results, expressed as workability curves, are shown in graphic form in Figures 4 and 5, and 13-16. To each mortar the fluidifying-effect additive system was added. The latter consisted of: formulation A0, dry pre-mixed in a laboratory blendor; an acrylic superfluidifier, again added to the mixing water. The doses of the additives are expressed as weight percent with respect to the weight of the cement. Formulation A was prepared at the moment of use, by mixing the components in the relative percentage ratios indicated in Table 9. The components used in the formulations are commercially available products. The ammonium salts of formula (I) that are the subject of the present invention were prepared by mixing components 1 and 2 indicated in the Table. Formulation A0 contained an ammonium salt of formula (la) consisting of a diamine dioleate (product commercially available under the name INIPOL 002). EXAMPLE III This consisted of a series of tests carried out on mortar. Each mortar was prepared with the following ingredients: • 450 g of grey cement CEM I 52.5R (Ultracem); • 1350 g of aggregate: German-type normalized silica sand, in compliance with the EN I 196/1 standard. The preparation procedures for the mortars and for addition of the additives were the same as those adopted for Example I. The results are given in the graphs of Figures 6 and 17-18. EXAMPLE IV This consisted of a test carried out on concrete. The concrete was prepared with the following ingredients: • 350 kg/m 3 of white cement CEM 52.5R (Italbianco ®); • 1900 kg/m 3 of aggregate: light white marble from the area of Carrara, divided into ten different sizes; continuous-type granulometric curve, with granulometric maximum of 20 mm; • 35 kg/m 3 of mineral extenders: metakaolin Metastar 501 ECC; • 7 kg/m 3 of photocatalyst: titanium dioxide A-HR micron Tioxide. Formulation A5 was pre-mixed with the metakaolin. The acrylic superfluidifier was added to the mixing water. The result is given in the graph form in Figure 19.

Claims: CLAIMS 1 . Superfluidifying additive for cementitious compositions, comprising: (i) at least one ammonium salt of formula (I), Ri + R 4 N R 2 X " R 3 (I) in which R R 2 , R 3 , independently of one another, are chosen from among: • hydrogen, • a saturated or unsaturated, linear or branched alkyl group having from 1 to 22 carbon atoms; • a polyoxyalkylene chain containing n repetitive units of structural formula (II), and m repetitive units of structural formula (III) [ 0-CH 2 -CH 2 ] [ 0-CH 2 -CH ] I CH 3 (II) (III) where m and n, independently of one another, are integers comprised between 0 and 50, and (m + n) is an integer comprised between 2 and 50, and where the said units may be present randomly in the said chain; • a saturated or unsaturated, linear or branched alkyl group having from 1 to 22 carbon atoms, possibly substituted with one or more polyoxyalkylene chains as defined above; R 4 is chosen from between: • a group having -(CH 2 ) P N R 5 R 6 structure, where p is an integer comprised between 1 and 7, and in which R 5 and R 6 may be, independently of one another: (a) hydrogen, (b) saturated or unsaturated, linear or branched alkyl groups having from 1 to 22 carbon atoms, or (c) a polyoxyalkylene chain as defined above; • a saturated or unsaturated, linear or branched alkyl group having from 1 to 12 carbon atoms; and X " is an anion which neutralizes, either partially or totally, the charge of the ammonium ion; (I) at least one acrylic superfluidifier; at least one surfactant; and possibly one or more antifoaming agents. 2. Additive according to Claim 1 , where the substituents R 1 ; R 2 , R 3 , in formula (I), independently of one another, are chosen from among: hydrogen, a saturated or unsaturated, linear or branched alkyl group having from 1 to 16 carbon atoms, a polyoxyalkylene chain as defined above, where m is equal to 0, and n is comprised between 2 and 15, a saturated or unsaturated, linear or branched alkyl group having from 12 to 18 carbon atoms, possibly substituted with one or more polyoxyalkylene chains as defined above, where m is equal to 0, and n is comprised between 2 and 15. 3. Additive according to Claim 1 , where the ammonium ion represented in formula (I) is chosen from among: triethylammonium, tetramethylammonium, hexadecyltrimethylammonium, or else an ion of formula (la), where R 5 and n have the meanings indicated above + R 5 NH -(CH 2 ) n -NH 3 (la) 4. Additive according to any one of Claims 1-3, where X " represents at least one anion chosen from between OH " and R 7 -COO " , in which R 7 is a saturated or unsaturated, linear or branched alkyl group having from 1 to 22 carbon atoms. 5. Additive according to Claim 4, where X " represents at least one anion chosen from among oleate, stearate or linoleate. 6. Additive according to any one of Claims 1-5, where the surfactant (iii) is a nonionic surfactant having a hydrophilic/lipophilic balance (HLB) of between 5.5 and 15. 7. Additive according to any one of Claims 1-6, formulated in two separate compositions A) and B), having the following compositions: Formulation A): containing the ammonium salt (i) , surfactant (iii) , and possibly the antifoaming agent (iv) ; Formulation B): containing the acrylic superfluidifier (ii). 8. Additive according to Claim 7, in which formulation A) is diluted with an inert filler material. 9. High-fluidity and high-workability cementitious composition comprising a hydraulic binder, water, and a superfluidifying additive containing: (i) at least one ammonium salt of formula (I), in which R 15 R 2 , R 3 , independently of one another, are chosen from among: • hydrogen, • a saturated or unsaturated, linear or branched alkyl group having from 1 to 22 carbon atoms; • a polyoxyalkylene chain containing n repetitive units of structural formula (II), and m repetitive units of structural formula (III) [ 0-CH 2 -CH 2 ] [ 0-CH 2 -CH ] CH 3 (II) (III) where m and n, independently of one another, are integers comprised between 0 and 50, and (m + n) is an integer comprised between 2 and 50, and where the said units may be present randomly in the said chain; • a saturated or unsaturated, linear or branched alkyl group having from 1 to 22 carbon atoms, possibly substituted with one or more polyoxyalkylene chains as defined above; R 4 is chosen from between: • a group having -(CH 2 ) P N R 5 R 6 structure, where p is an integer comprised between 1 and 7, and in which R 5 and R 6 may be, independently of one another: (a) hydrogen, (b) saturated or unsaturated, linear or branched alkyl groups having from 1 to 22 carbon atoms, or (c) a polyoxyalkylene chain as defined above; • a saturated or unsaturated, linear or branched alkyl group having from 1 to 12 carbon atoms; and X " is an anion which neutralizes, either partially or totally, the charge of the ammonium ion; (ii) at least one acrylic superfluidifier; (liii) at least one surfactant; and (iv) possibly one or more antifoaming agents. 10. Cementitious composition according to Claim 9, containing the following weight percentages of components with respect to the weight of the hydraulic binder in the dry state: from 0.04% to 1% of ammonium salt (i) ; from 0.04% to 1 % of surfactant (iii); from 0.02% to 0.3% of antifoaming additive (iv); from 0.3% to 3% of acrylic superfluidifier (ii). 11. Cementitious composition according to any one of Claims 9-10, in which the hydraulic binder is a white cement. 12. Cementitious composition according to any one of Claims 9-11 , further containing particles of compounds having a photocatalytic action. 13. Cementitious composition according to Claim 12, in which the compound having photocatalytic action is titanium dioxide or one of its precursors, prevalently in the form of anatase. 14. Cementitious composition according to any one of Claims 9-13, represented by a concrete or by a mortar. 15. Cementitious composition according to any one of Claims 9-14, having a water/hydraulic binder weight ratio not higher than 0.4. 16. Procedure for the preparation of a high-fluidity and high-workability cementitious composition, characterized in that a hydraulic binder, the additive described in Claim 1 , and water in suitable quantities are mixed together to obtain a fluid mixture. 17. Procedure according to Claim 16, in which the additive is used in the form of two separate formulations A) and B) having the following compositions: A): containing the ammonium salt (i) , surfactant (iii), and the possible antifoaming additive (iv), possibly mixed with an inert filler material; B): containing the acrylic superfluidifier (ii). 18. Procedure according to Claim 17, comprising the following steps: mixing the formulation A) with the hydraulic binder in the dry state; Dispersing the formulation B) in the mixing water; adding of the mixture obtained in step b- to the mixture obtained in step a-, and stirring until the mixture is homogeneous. 19. Procedure according to any one of Claims 16-18, in which a water/hydraulic binder weight ratio is used that is lower than or equal to 0.4. 20. Pre-mix in the dry state for cementitious compositions, comprising at least one hydraulic binder, and a superfluidifying additive containing: (i) at least one ammonium salt of formula (I), Ri + R 4 N R 2 X " R 3 (I) in which R.,, R 2 , R 3 , independently of one another, are chosen from among: • hydrogen, • a saturated or unsaturated, linear or branched alkyl group having from 1 to 22 carbon atoms; • a polyoxyalkylene chain containing n repetitive units of structural formula (II), and m repetitive units of structural formula (III) [ 0-CH 2 -CH 2 ] [ 0-CH 2 -CH ] CH 3 (II) (HI) where m and n, independently of one another, are integers comprised between 0 and 50, and (m + n) is an integer comprised between 2 and 50, and where the said units may be present randomly in the said chain; • a saturated or unsaturated, linear or branched alkyl group having from 1 to 22 carbon atoms, possibly substituted with one or more polyoxyalkylene chains as defined above; R 4 is chosen from between: • a group having -(CH 2 ) p N R 5 R 6 structure, where p is an integer comprised between 1 and 7, and in which R 5 and R 6 may be, independently of one another: (a) hydrogen, (b) saturated or unsaturated, linear or branched alkyl groups having from 1 to 22 carbon atoms, or (c) a polyoxyalkylene chain as defined above; • a saturated or unsaturated, linear or branched alkyl group having from 1 to 12 carbon atoms; and X " is an anion which neutralizes, either partially or totally, the charge of the ammonium ion; (ii) at least one acrylic superfluidifier; (iii) at least one surfactant; and (iv) possibly one or more antifoaming agents and/or particles of compounds having a photocatalytic action. 21. Cement item, laid and hardened, containing the additive for cements described in Claim 1 , and possibly particles of compounds having a photocatalytic action. 22. Use of an additive comprising: (i) at least one ammonium salt of formula (I), Ri j + R 4 N Ro X " R 3 (I) in which R.,, R 2 , R 3 , independently of one another, are chosen from among: • hydrogen, • a saturated or unsaturated, linear or branched alkyl group having from 1 to 22 carbon atoms; • a polyoxyalkylene chain containing n repetitive units of structural formula (II), and m repetitive units of structural formula (III) [ 0-CH 2 -CH 2 ] [ O-CH 2 -CH ] I CH 3 (II) (III) where m and n, independently of one another, are integers comprised between 0 and 50, and (m + n) is an integer comprised between 2 and 50, and where the said units may be present randomly in the said chain; a saturated or unsaturated, linear or branched alkyl group having from 1 to 22 carbon atoms, possibly substituted with one or more polyoxyalkylene chains as defined above; R 4 is chosen from between: • a group having -(CH 2 ) p N R 5 R 6 structure, where p is an integer comprised between 1 and 7, and in which R 5 and R 6 may be, independently of one another: (a) hydrogen, (b) saturated or unsaturated, linear or branched alkyl groups having from 1 to 22 carbon atoms, or (c) a polyoxyalkylene chain as defined above; • a saturated or unsaturated, linear or branched alkyl group having from 1 to 12 carbon atoms; and X ' is an anion which neutralizes, either partially or totally, the charge of the ammonium ion; (ii) at least one acrylic superfluidifier; (iii) at least one surfactant; and (iv) possibly one or more antifoaming agents, as superfluidifier for cements.

Inventors: CASSAR LUIGI, DE MARCO TIZIANA, GOISIS MARCO, PEPE CARMINE, CASSAR, LUIGI, DE MARCO, TIZIANA, GOISIS, MARCO, PEPE, CARMINE
Applicants: CASSAR LUIGI, GOISIS MARCO, ITALCEMENTI SPA, MARCO TIZIANA DE, PEPE CARMINE, CASSAR, LUIGI, DE MARCO, TIZIANA, GOISIS, MARCO, ITALCEMENTI S.P.A., PEPE, CARMINE
Application year: 1999
Main classification: C04B28
IPC codes: C04B24, C04B40