Mineral additive for cement, useful for preparing ready-mix concrete.

Abstract

MINERAL ADDITION FOR CEMENT USEFUL IN THE PREPARATION OF READY-MIX CONCRETE. Mineral addition for cement comprising: 10% to 90% (w / w) sulfoaluminate clinker; 10% to 90% (w / w) natural rapid-setting cement; and 1% to 50% anhydrite C$; said mineral addition being free of setting accelerators or retarders. Cementitious composition comprising said addition and ready-mix concrete prepared from said cementitious composition.

Description

Title of the invention: Mineral additive for cement useful for the preparation of ready-mix concrete

[0001] The present invention relates to a new mineral addition for cement enabling the acceleration of the setting of ready-mix concrete.

[0002] Concrete is the most widely used construction material in the world. It has two successive states: a plastic or fluid phase allowing it to be used by molding, then a hardening and strength-building phase which allows it to reach its mechanical performance compatible with the construction of civil engineering works and various buildings.

[0003] Concrete is generally composed of a hydraulic binder, aggregates, water, and possibly admixtures. Water participates in the two successive phases of concrete's life. It contributes to obtaining the plastic or fluid phase by forming a paste with the hydraulic binder and subsequently participates in the setting mechanisms that lead to the concrete's performance qualities.

[0004] The setting mechanisms of a hydraulic binder depend on its nature. Generally, setting proceeds through a succession of solubilization reactions and precipitation of new chemical species. These new chemical species, essentially crystals, grow and coalesce in such a way that their interlocking ensures the continuity of the material, leading to its rigidification. This chain of reactions is commonly called hydration.

[0005] Concrete is commonly made using cements as hydraulic binders. The nature of these cements does not call into question the general principles described above but determines the formulation rules and in particular the quantity of water.

[0006] The most commonly used concrete to date is ready-mix concrete, that is, concrete prepared on an industrial site, i.e., a concrete plant, and then transported, in its fresh state, in a mixer truck to the construction site where it will be used. Ready-mix concrete is used for the construction of buildings, individual or multi-family housing, civil engineering structures, or roads.

[0007] “BPEs” offer numerous advantages, including: - time saving and ease of implementation; - cost reduction; - use of concrete of consistent quality, perfectly suited to the needs of the construction site; and - delivery in a single shipment of a sufficient quantity of concrete to allow the work to be carried out without rework of concrete pouring or risk of cracks.

[0008] Once prepared at the concrete plant, the concrete is transported to the placement site, with transport times varying from 20 to 90 minutes. Consequently, ready-mix concrete must have sufficient workability (i.e., the quality reflecting a concrete's suitability for placement) to ensure that its characteristics are maintained in the fresh state, thus limiting the use of rapid-setting concretes.

[0009] Standard concrete does not develop high mechanical strength at an early age. A curing time of several days is sometimes necessary to develop minimum mechanical strength, which is incompatible with certain construction projects, particularly during the renovation of parking lots or roads, in the railway sector (ballasting, anchoring of columns, station platforms), in the road sector (backfilling of trenches, toll plazas, logistics docks), in civil engineering (tunnel foundations, structural transition slabs), or even in the building sector (rapid formwork removal). The waiting time does not allow for optimizing the reuse of the concrete or for quickly restoring road traffic. In this case, the use of rapid-setting concrete is necessary. These problems are compounded when placing concrete in cold weather.

[0010] To prepare these rapid-setting concretes, setting accelerators are generally added to the concrete mixing water. Examples of setting accelerators include soluble organic or inorganic salts such as chlorides, bromides, fluorides, carbonates, nitrates, silicates, aluminates, calcium formate, or calcium acetate. These setting accelerators, often used in cold weather and added to Portland cements (OPC), do not, however, guarantee a rapid increase in cement strength. In particular, they are insufficient to achieve compressive strengths of 4 MPa at 4 hours in cold weather (5°C).

[0011] Aluminous cements (CACs) are also used to develop rapid-curing systems when mixed with Portland cement for applications such as floor coatings or fast-setting tile adhesives. However, since these cements are subject to reversion phenomena, they cannot be used for civil engineering structures.

[0012] However, the use of such additives in Portland concrete for preparing ready-mix concrete does not allow for a sufficiently rapid increase in mechanical strength, especially in winter when the temperature slows down the setting of the cement. Furthermore, the accelerator dosage at the batching plant is rather imprecise and, consequently, does not produce the expected results.

[0013] Thus, at the date of the present invention it remains necessary to identify new additives to regulate the setting of concretes but not presenting the aforementioned disadvantages and allowing the preparation of "RBCs" exhibiting sufficient workability upon delivery on site and allowing a rapid increase in strength during their use, without requiring the addition of accelerator or retarder of setting.

[0014] However, it has now been found quite surprisingly that a mineral addition comprising a sulfoaluminate clinker (KSA), a natural prompt cement (CNP) and anhydrite (C$) could be used as a setting accelerator and, when added to a Portland cement, made it possible to prepare a "BPE" having a setting time compatible with maintaining workability allowing its use on site after transport and developing mechanical strengths in the very short term after the end of setting without the addition of a setting accelerator type additive being necessary.

[0015] Thus, the present invention relates to a mineral additive for cement comprising: - from 10% to 90% (w / w) of sulfoaluminate clinker (KSA); - 10% to 90% (w / w) natural rapid cement (NRC); and - from 1% to 50% anhydrite C$;

[0016] said mineral addition being free of setting accelerator or setting retarder.

[0017] The mineral additive according to the invention allows, once added to Portland cement, to Prepare a ready-mix concrete (RMC) with a setting time compatible with maintaining workability for on-site use after transport, and developing mechanical strength very quickly after setting without the need for accelerators or retarders. Furthermore, adding the mineral admixture to the powdered cementitious mix rather than to the mixing water makes the concrete formulations more robust and allows for high mechanical performance in the short term.

[0018] Within the scope of the present invention:

[0019] - the term "cementitious composition" means any composition based on cement capable of being used for the preparation of a building material, in particular concrete;

[0020] - "Portland cement" means any cement based on classified Portland clinker such as EMC I, II, III, IV or V, VI according to the standards NF EN 197-1, 197-5 and 197-6;

[0021] - "Natural quick-setting cement" means any hydraulic binder that sets and Rapid hardening conforming to standard NF P 15-314: 1993 in force at the date of the present invention. Preferably, "natural rapid cement" means a cement prepared from a clinker comprising: • from 0% to 20% of C3S; • 20% to 60% C2S; • 2% to 12% of C4AF; • 1% to 10% of C3A; • 0 to 10% of Ci2A7 (mayenite); • 10% to 20% CaCO3 (calcite); • 10% to 15% of Ca5(SiO4)2CO3 (spurrite); • 3% to 10% sulfate phases: yeelimite C4A3$, langbeinite (K2Mg2(SO4) 3, anhydrite (CaSO4); and • 10% to 20% of lime, periclase, quartz and / or one or more amorphous phases;

[0022] - the term "sulfoaluminate clinker" means any clinker obtained by firing a mixture comprising the following compounds: • CaCO3; • A12O3 and / or A1(OH)3; • CaSO4; • SiO2; and • Fe2O3.

[0023] Preferably, "sulfoaluminate clinker" means a clinker comprising: • from 5 to 25% of C2AxF(i_x), with x varying from 0.2 to 0.8; • 15 to 35% of C4A3 y$Fy with y varying from 0 to 0.5; and • 10 to 35% C2S;

[0024] - the term "granulate" means all the inert mineral grains which, according to their dimensions (up to 125 mm), belong to one of the following 5 families: sands, sands, gravels, pebbles and ballast;

[0025] - The term "setting accelerator" means any compound that reduces the Setting time of concrete according to standard NF EN 934-2. In particular, a setting accelerator is defined as any product that promotes the hydration of the binder in order to reduce the transition time of concrete, grout, or mortar from a plastic to a rigid state by modifying the solubilities and dissolution rates of the various cement constituents. Examples of setting accelerators include NaSiO3, NaOH, Na2SO4, Na2CO3, CaCl2, K2SO4, KOH, Ca(NO3), or, more generally, any chemical compound containing alkali or alkaline earth metals;

[0026] - The term "setting retardant" means any compound that increases the start time of transition of the cement mixture, to go from plastic state to rigid state according to standard NF EN 934-2 + Al of August 2012;

[0027] - "superplasticizer" means any compound according to standard NF EN 934-2 + Al of August 2012, which, without changing the consistency, makes it possible to greatly reduce the water content of a given concrete, or which, without altering the water content, considerably increases its slump / spread, or which produces both effects simultaneously; and

[0028] - the term "ready-mix concrete" or "RMC" means any concrete delivered in a fresh state according to the NF EN 206 + A2 standard of March 2021.

[0029] In the context of the present invention, the following notations are adopted to designate the mineralogical components of cement:

[0030] - C represents CaO;

[0031] - A represents A12O3;

[0032] - F represents Fe2O3;

[0033] - S represents SiO2; and

[0034] - $ represents SO3.

[0035] Finally, within the framework of the present invention, the proportions expressed in % correspond to mass percentages in relation to the total weight of the entity (e.g. cement, earth etc.) considered.

[0036] The present invention therefore relates to a mineral additive for cement comprising a KSA, a CNP, and anhydrite (C$), said mineral additive being free of setting accelerators or retarders. Preferably, the mineral additive according to the invention has the following characteristics, chosen alone or in combination: - the mineral addition comprises from 20% to 80% (w / w) of sulfoaluminate clinker, preferably from 30% to 70% (w / w) of sulfoaluminate clinker, most preferably from 40% to 60% (w / w) of sulfoaluminate clinker; - the mineral addition comprises 20% to 90% (w / w) of natural rapid-setting cement, preferably 40% to 90% (w / w) of natural rapid-setting cement, and most preferably 60% to 90% (w / w) of natural rapid-setting cement; and - the mineral addition comprises 2% to 40% (w / w) of anhydrite C$, preferably 5% to 30% (w / w) of anhydrite C$, most preferably 8% to 20% (w / w) of anhydrite C$; and / or - the mineral addition is intended to be added to Portland cement.

[0037] The mineral additives described above can therefore be used as setting accelerators. Thus, the present invention also relates to the use of a mineral additive as defined above as a setting accelerator.

[0038] Mineral additives can therefore be added to Portland cement to obtain a cementitious composition suitable for preparing ready-mix concrete (RMC) with a setting time compatible with maintaining workability for on-site use after transport and developing mechanical strength very quickly after setting, without the need for the addition of a setting accelerator. Thus, the present invention also relates to a cementitious composition comprising: - 40% to 99% (w / w) Portland cement (OPC); and - from 1% to 60% (w / w) of a mineral addition as defined above;

[0039] said cementitious composition being free of setting accelerator.

[0040] Preferably, the cementitious composition according to the invention has the following characteristics, chosen alone or in combination: - the cementitious composition comprises 45% to 95% (w / w) Portland cement, preferably 60% to 90% (w / w) Portland cement, and most preferably 65% ​​to 85% Portland cement; and / or - the cementitious composition comprises from 5% to 55% (w / w) of the mineral addition described above, preferably still from 10% to 40% (w / w) of the mineral addition described above, most preferably from 15% to 35% (w / w) of the mineral addition described above.

[0041] The cementitious composition according to the present invention can therefore be used to prepare ready-mix concrete free of accelerators or retarders. To this end, any process known to those skilled in the art can be implemented. By way of example, one process comprising the following steps may be cited: - mixing Portland cement and the mineral addition according to the invention to make a premix; - siloing of said premix in a BPE plant; and - mixing of the premix with water, aggregates and a superplasticizer type rheology agent.

[0042] Finally, the present invention also relates to a ready-to-use concrete comprising: - 13% to 19% (w / w) of a cementitious composition as described above; - 74% to 82% (w / w) of aggregate; - 4% to 6% (w / w) water; and - 0.5% to 0.9% superplasticizer;

[0043] said ready-to-use concrete being free of setting accelerator.

[0044] Preferably, the present invention relates to a ready-mix concrete as defined above having the following characteristics, chosen alone or in combination: - ready-mix concrete comprises 14% to 18% (w / w) of a cementitious composition as described above, 15% to 17% (w / w) of a cementitious composition as described above, most preferably 15.5% to 16.5% (w / w) of a cementitious composition as described above;

[0045]

[0046]

[0047]

[0048]

[0049]

[0050] - Ready-mix concrete comprises 74% to 82% (w / w) aggregate, preferably 76% to 80% (w / w) aggregate, and most preferably 77.5% to 78.5% (w / w) aggregate; and / or - Ready-mix concrete comprises 4% to 6% (w / w) of water, preferably 4.5% to 5.5% (w / w) of water, most preferably 4.8% to 5.2% (w / w) of water. The present invention can be illustrated in a non-limiting way by the following examples. Example 1 - Materials used To prepare the mineral additions and cementitious compositions according to the invention, the following materials are used: - OPC (reference): CEM I 52.5R from Xeuilley; CNP: PROMPT VICAT natural cement; KSA: Alpenat CK VICAT; and - C$: micronized Lorraine anhydrite. The phase compositions of the cements used are reported in the following Table 1. [Tables 1] Phases / constituents (% (w / w)) Cements OPC KSA CNP C3S 49.5 - 2.0 c2s 21.4 28.7 31.3 c3a 10.5 - 2.0 c4af 10.5 - 6.8 C12A7 - - 2.7 c4a3$ - 51.2 2.1 c$ - 0.3 2.5 Gypsum - - - CaCO3 - - 15.7% Spurrite - - 13.6% Other phases - 19.8 21.3% Table 1 - Phase composition of the cements used Example 2 - Mineral Additions Various mineral additions are prepared from the materials in Example 1.

[0051] The compositions of the additions thus obtained are reported in the following Table 2.

[0052] [Tables2] Ingredients Mineral Additive (% w / w) Invention Comparison ABCDEFGH Alpenat CK VI CAT (KSA) 31.6 61.8 0.7 20.8 52.3 40.0 10.8 1.3 PROMPT VIC AT Natural Cement (CNP) 49.4 13.1 91.3 79.1 35.7 44.5 20.2 7.7 Micronized Lorraine Anhydrite (C$) 19 25.1 8 0.1 12 15.5 69 92

[0053] Table 2 - Mineral additive according to the invention Example 3 - Cementitious compositions 3.1 - Compositions

[0054] Different cementitious compositions are prepared by mixing the OPC described in Example 1 with one of the mineral additions A to H described in Example 2.

[0055] The compositions of the cementitious compositions thus obtained are reported in the following Table 3.

[0056] [Tables3] Ingredients Cementitious Composition (% w / w) Ref. Invention Comparison 1 2 3 4 5 6 7 8 OPC 75 75 75 75 75 75 75 75 Mineral Addition A 25 - - - - - - - Mineral Addition B - 25 - - - - - - Mineral Addition C - - 25 - - - - - Mineral Addition D - - - 25 - - - - Mineral Addition E - - - - 25 - - - Mineral Addition F - - - - - 25 - - Mineral Addition G - - - - - - 25 - Mineral Addition H - - - - - - - 25

[0057] Table 3 - Cementitious compositions according to the invention 3.2 - Evaluation of the onset time of intake

[0058] The start time of setting of compositions 1 to 8 is evaluated by studying the heat fluxes obtained by microcalorimetry.

[0059] The reactivity of OPC is first evaluated at 10°C. This will serve as a reference for evaluating the effectiveness of the various additives studied. The initial setting time is obtained by the intersection of the baseline and the tangent to the heat flux curve obtained by isothermal microcalorimetry. The heat of hydration of Portland cement alone at a water / cement ratio of 0.5 is 39 J / g and its initial setting time is 9.4 hours.

[0060] The effectiveness of compositions 1 to 8 is evaluated by isothermal microcalorimetry test at E / C0.5 and 10°C. The setting time corresponds to the time taken by the composition to reach the total heat of the mixture reached 39 J / g.

[0061] The results obtained are reported in Table 4 below.

[0062] [Tables4] Composition Onset of action time (in hours) OPC (reference) 9.4 1 1.6 2 1.0 3 4.8 4 1.3 5 0.7 6 2.0 7 10.0 8 11.0

[0063] Table 4 - Setting time of the compositions of the invention

[0064] The results obtained confirm a clear reduction in the initial setting time for cementitious compositions containing an additive according to the invention compared to the reference (i.e., cement without additives). It is also noted that an additive containing too much anhydrite (C$) does not accelerate setting but, on the contrary, delays it.

[0065] Example 4 - BPE - Workability and mechanical resistance

[0066] Rapid concretes are formulated with a total binder of 400 kg / m3. This is composed of 100% Portland cement (reference) or 75% Portland cement and 25% of an addition according to the invention.

[0067] The complete compositions of the concretes are reported in the following Table 5.

[0068] [Tables5] Ingredients Concrete 1 (ref.) Concrete 2 OPC (in kg / m3) 400 300 KSA (in kg / m3) - 38.8 CNP (in kg / m3) - 43.2 C$ (in kg / m3) - 15.1 Trisodium citrate (in % binder) - 0.73 Plastiretard 930 (in % binder) - 1 Optima 372 (in % binder) - 2.4 Equalis 250 (in % binder) - 1.2 Aggregates (in kg / m2) 1734 1934 Effective water - Eeff (in kg / m2) 182 138 E / Binder 0.46 0.345

[0069] Table 5 - Rapid setting concretes

[0070] Workability

[0071] The workability of the concrete is measured by measuring the slump using the Abrams cone according to standard NF EN 12350-2. Monitoring it ensures that the slump class is maintained throughout the period from its manufacture to its implementation.

[0072] The results obtained are reported in the following Table 6.

[0073] [Tableauxô] Slump (in mm) Concrete 1 (ref.) Concrete 2 To 210 200 Tq+30 min 210 200 Tq+60 min 210 200 Tq+90 min 210 190 Tq+120 min 210 180

[0074] Table 6 - Workability

[0075] It appears that the S4 class (160 mm - 210 mm) is guaranteed for 120 minutes for the reference concrete as well as for the concrete according to the invention.

[0076] Compressive strength

[0077] The ambient temperature and that of the materials used is 10°C. The mechanical resistances are measured on 15x30 cylindrical specimens. The cylinders are filled in 3 layers tightly packed by vibration.

[0078] Mechanical resistances are obtained according to standard NF EN 12390-3.

[0079] The results obtained are reported in the following Table 7.

[0080] [Tables7] Compressive strength (in MPa) Concrete 1 (ref.) Concrete 2 3h - 6.7 4h - 11.9 5h - 15.3 24h 5.7 22.7 28 days 39.7 63.4

[0081] Table 7 - Compressive strength

[0082] With an equivalent quantity of binder (400 kg / m3) to the reference concrete, the concrete according to the invention exhibits a setting and a rise in strength significantly faster than the latter.

Claims

Demands

1. Mineral addition for cement comprising: - 10% to 90% (w / w) of sulfoaluminate clinker; - 10% to 90% (w / w) of natural prompt cement; and - 1% to 50% of anhydrite C$; said mineral addition being free of setting accelerator or retarder.

2. Mineral addition according to claim 1, characterized in that it comprises from 20% to 80% (w / w) of sulfoaluminate clinker.

3. Mineral addition according to claim 2, characterized in that it comprises from 40% to 60% (w / w) of sulfoaluminate clinker.

4. Mineral addition according to any one of claims 1 to 3, characterized in that it comprises from 20% to 90% (w / w) of natural prompt cement.

5. Mineral addition according to claim 4, characterized in that it comprises from 60% to 90% (w / w) of natural prompt cement.

6. Mineral addition according to any one of claims 1 to 5, characterized in that it comprises from 2% to 40% (w / w) of anhydrite C$.

7. Mineral addition according to claim 6, characterized in that it comprises from 8% to 20% (w / w) of anhydrite C$.

8. Cementitious composition for the preparation of ready-mix concrete comprising: - 40% to 99% (w / w) Portland cement; and - 1% to 60% (w / w) of a mineral addition according to any one of claims 1 to 7; said cementitious composition being free of setting accelerator.

9. Cement composition according to claim 8, characterized in that it comprises from 45% to 95% (w / w) Portland cement.

10. Cement composition according to claim 8 or 9, characterized in that it comprises from 5% to 55% (w / w) of a mineral addition according to any one of claims 1 to 7.

11. Ready-mix concrete comprising: - 13% to 19% (w / w) of a cementitious composition according to any one of claims 8 to 10; - 74% to 82% (w / w) of aggregate; - 4% to 6% (w / w) water; and - 0.5% to 0.9% superplasticizer; said ready-mix concrete being free of setting accelerator.