Mineral additive for cement, suitable for use in preparing a ready-mixed concrete

Abstract

The invention relates to a mineral additive for cement, comprising: - 10% to 90% (w / w) sulfoaluminate clinker; - 10% to 90% (w / w) Prompt natural cement; and - 1% to 50% anhydrite C$; said mineral additive being free from accelerators and set retarders. The invention also relates to a cementitious composition comprising the aforementioned additive, and ready-mixed concrete prepared from said cementitious composition.

Description

[0001] MINERAL ADDITIVE FOR CEMENT USEFUL FOR PREPARING READY-MIX CONCRETE. The present invention relates to a new mineral additive for cement that accelerates the setting of ready-mix concrete. Concrete is the most widely used construction material in the world. It has two successive states: a plastic or fluid phase that allows it to be molded, and then a hardening and strength-building phase that allows it to reach its mechanical performance, compatible with the construction of civil engineering structures and various other buildings. Concrete is generally composed of a hydraulic binder, aggregates, water, and possibly admixtures. Water participates in both 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.The setting mechanisms of a hydraulic binder depend on its nature. Generally speaking, setting proceeds through a succession of solubilization and precipitation reactions of new chemical species. These new chemical species, primarily 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. Concrete is commonly made using cements as hydraulic binders. The nature of these cements does not invalidate the general principles described above but does influence the formulation rules, particularly the amount of water. The most commonly used concrete today is ready-mix concrete, or "RMC," that is, concrete prepared on an industrial site.a "concrete batching 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 collective housing, civil engineering structures, or roads. Ready-mix concrete offers many advantages, including: - time savings 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 trip of a sufficient quantity of concrete to complete the work without construction joints or risk of cracking. Once prepared at the concrete batching plant, the concrete is transported to the placement site, with transport times varying from 20 to 90 minutes. Consequently, ready-mix concrete must have good workability (i.e.The quality of concrete (describing its suitability for placement) is sufficient to guarantee that its characteristics are maintained in the fresh state, thus limiting the use of rapid-setting concretes. Standard concretes do not develop high mechanical strengths at an early age. A curing time of several days is sometimes necessary to develop minimum mechanical strengths, 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 in the building sector (rapid formwork removal). This waiting time prevents the optimization of formwork reuse times or the rapid restoration of road traffic.In this case, the use of rapid-setting concrete is necessary. These problems are compounded when placing concrete in cold weather. To prepare this rapid-setting concrete, setting accelerators are generally added to the 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).Aluminous cements (CACs) are also used to develop rapid-hardening systems when mixed with Portland cement for applications such as floor coverings or fast-setting tile adhesives. However, because these cements are subject to reversion phenomena, they cannot be used for civil engineering structures. Furthermore, the use of such additives in Portland concrete to prepare ready-mix concrete does not allow for a sufficiently rapid increase in mechanical strength, especially in winter when the temperature slows the cement setting process. In addition, the accelerator dosage at the batching plant is rather imprecise and, consequently, does not produce the expected results.Thus, at the date of the present invention it remains necessary to identify new additives to regulate the setting of concrete but not presenting the aforementioned disadvantages and allowing the preparation of "RBC" having sufficient workability when delivered on site and allowing a rapid increase in strength when used, without requiring the addition of accelerator or retarder setting.However, it has now been discovered, quite surprisingly, that a mineral additive comprising sulfoaluminate clinker (KSA), rapid natural cement (CNP), and anhydrite (C$) can be used as a setting accelerator and, when added to Portland cement, allows the preparation of a ready-mix concrete (RMC) with a setting time compatible with maintaining workability for on-site use after transport and developing very short-term mechanical strength after setting without the need for the addition of a setting accelerator. Thus, the present invention relates to a mineral additive for cement comprising: - 10% to 90% (w / w) sulfoaluminate clinker (KSA); - 10% to 90% (w / w) rapid natural cement (CNP); and - 1% to 50% anhydrite (C$); said mineral additive being free of setting accelerators or setting retarders.The mineral additive according to the invention, when added to Portland cement, allows for the preparation of a ready-mix concrete (RMC) with a setting time compatible with maintaining workability, enabling its use on-site after transport and developing very short-term mechanical strength after setting, without the need for the addition of setting accelerators or retarders. Furthermore, adding the mineral additive to the powdered cementitious mix rather than to the mixing water of the concrete makes the concrete formulations more robust and allows for high short-term mechanical performance.In the context of the present invention: - "cementary composition" means any cement-based composition that can be used for the preparation of a construction material, in particular concrete; - "Portland cement" means any Portland clinker-based cement classified as CEM I, II, III, IV or V, VI according to standards NF EN 197-1, 197-5 and 197-6; - "natural rapid cement" means any hydraulic binder with rapid setting and hardening conforming to standard NF P 15-314: 1993 in force at the date of the present invention.Preferably, "natural quick-setting cement" designates a cement prepared from a clinker comprising:^ 0% to 20% of C3S;^ 20% to 60% of C2S;^ 2% to 12% of C4AF;^ 1% to 10% of C3A;^ 0% to 10% of C12A7 (mayenite);^ 10% to 20% of CaCO3 (calcite);^ 10% to 15% of Ca5(SiO4)2CO3 (spurrite);^ 3% to 10% of sulfate phases: C4A3, langbeinite (K2Mg2(SO4)3, anhydrite (CaSO4); and^ 10% to 20% of lime, periclase, quartz and / or one or more amorphous phases; - by " sulfoaluminous clinker » any clinker obtained by the firing of a mixture comprising the following compounds:. ^ CaCO3 ; ^ Al2O3 and / or Al(OH)3; ^ CaSO4 ; ^ SiO2 ; and Fe2O3.Preferably, "sulfoaluminous clinker" designates a clinker comprising:^ 5 to 25% of C2AxF(1-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% of C2S;- "aggregate" means any mineral or bio-based aggregate;- "mineral aggregate" means all inert mineral grains which, according to their dimensions (up to 125 mm), belong to one of the following 5 families: sands, gravels, crushed stone and ballast;- "bio-based aggregate" (or "plant-based aggregate") means any aggregate of plant origin essentially composed of cellulose, hemicellulose and / or lignins.Preferably, "bio-based granulate" means a plant granulate chosen from:^ seed hairs of seeds, in particular cotton,^ bast fibers from plant stems such as hemp fiber, flax fiber, nettle fiber; ^ the woody part of the stem such as hemp hurds, flax shives, wood chips or miscanthus;^ cork such as cork pellets;^ fibers extracted from leaves or trunk, in particular sisal; and^ fruit husks such as nuts, and in particular coconut, or cereal husks such as rice.Preferably, "bio-based aggregate" refers to a plant-based aggregate chosen from cotton, hemp fiber, hemp shives, flax shives, wood chips, cork beads, miscanthus, sisal, coconut husks, straw, rapeseed, rice husks, sunflower, reed, and / or cattail; - "setting accelerator" means any compound that reduces the setting time of concrete according to standard NF EN 934-2. In particular, a setting accelerator means any product that promotes the hydration of the binder in order to decrease the transition time of concrete, grout, or mortar from a plastic to a rigid state by modifying the solubilities and the dissolution rate 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; - "Setting retarder" means any compound that increases the time it takes for the cement mixture to transition from a plastic to a rigid state according to standard NF EN 934-2 + A1 of August 2012; - "Superplasticizer" means any compound according to standard NF EN 934-2 + A1 of August 2012, which, without changing the consistency, significantly reduces the water content of a given concrete, or which, without changing the water content, considerably increases its slump / spread, or which produces both effects at the same time; and- we mean by “ready-mix concrete” or “RMC” any concrete delivered in a fresh state according to the NF EN 206 + A2 standard of March 2021.In the context of the present invention, the following notations are adopted to designate the mineralogical components of cement: - C represents CaO; - A represents Al2O3; - F represents Fe2O3; - S represents SiO2; and - $ represents SO3. Finally, in the context of the present invention, the proportions expressed as % correspond to mass percentages relative to the total weight of the entity (cement, soil, etc.) considered. The present invention therefore relates to a mineral additive for cement comprising a KSA, a CNP, and anhydrite (C$), said mineral additive being free of setting accelerators or retarders.Preferably, the mineral addition according to the invention has the following characteristics, chosen alone or in combination: - the mineral addition comprises from 20% to 80% (w / w) of sulfoaluminate clinker, preferably still from 30% to 70% (w / w) of sulfoaluminate clinker, most preferably from 40% to 60% (w / w) of sulfoaluminate clinker; - the mineral addition comprises from 20% to 90% (w / w) of natural rapid cement, preferably still from 40% to 90% (w / w) of natural rapid cement, most preferably from 60% to 90% (w / w) of natural rapid cement; and - the mineral addition comprises 2% to 40% (w / w) of anhydrite C$, 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. The mineral additions described above can therefore be used as a setting accelerator.Thus, the present invention also relates to the use of a mineral additive, as defined above, as a setting accelerator. The mineral additive can therefore be added to Portland cement to obtain a cementitious composition for preparing ready-mix concrete (RMC) with a setting time compatible with maintaining workability for on-site use after transport and developing very short-term mechanical strength after setting, without the need for the addition of a setting accelerator. The present invention also relates to a cementitious composition comprising: - 40% to 99% (w / w) Portland cement (OPC); and - 1% to 60% (w / w) of a mineral additive as defined above; said cementitious composition being free of setting accelerator.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, most preferably 65% ​​to 85% Portland cement; and / or - the cementitious composition comprises 5% to 55% (w / w) of the mineral addition described above, preferably 10% to 40% (w / w) of the mineral addition described above, most preferably 15% to 35% (w / w) of the mineral addition described above. 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.As an example, one can notably cite a process comprising the following steps:- mixing of Portland cement and mineral addition according to the invention to produce a. prémix ;- placing said premix in a silo in a ready-mix concrete plant; and - mixing the premix with water, aggregates and a rheology agent of the superplasticizer type. Finally, the present invention also relates to a ready-mix 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) of water; and - 0.5% to 0.9% of superplasticizer; said ready-mix concrete being free of setting accelerator.Preferably, the present invention relates to a ready-mix concrete as defined above having the following characteristics, chosen alone or in combination: - the 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; - the ready-mix concrete comprises 74% to 82% (w / w) of aggregate, most preferably 76% to 80% (w / w) of aggregate, most preferably 77.5% to 78.5% (w / w) of aggregate; and / or - the ready-mix concrete comprises 4% to 6% (w / w) water, preferably 4.5% to 5.5% (w / w) water, most preferably 4.8% to 5.2% (w / w) water. The present invention may be illustrated, without limitation, 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: Natural cement PROMPT VICAT; - KSA: Alpenat CK VICAT; and - C$: micronized Lorraine anhydrite. The phase compositions of the cements used are reported in Table 1 below.

[0002] Phases / Constituents Cements (% (w / w) OPC KSA CNPC3S 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 Different mineral additions are prepared from the materials of Example 1. The compositions of the additions thus obtained are reported in the following Table 2. Mineral addition (% w / w) Ingredients Invention Comparison A B CD E F G HAlpenat CK 31.6 61.8 0.7 20.8 52.3 40.0 10.8 1.3 VICAT (KSA) Natural Cement PROMPT 49.4 13.1 91.3 79.1 35.7 44.5 20.2 7.7 VICAT (CNP) Lorraine Anhydrite 19 25.1 8 0.1 12 15.5 69 92 micronized (C$) Table 2 – Mineral Addition According to the Invention Example 3 – Cementitious Compositions 3.1 – Compositions 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.The compositions of the cement compositions thus obtained are reported in Table 3 below. Cement composition (% w / w) Ingredients 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 Table 3 – Cementitious compositions according to the invention 3.2 - Evaluation of the initial setting time The initial setting time of compositions 1 to 8 is evaluated by studying the heat fluxes obtained by microcalorimetry. The reactivity of the OPC is first evaluated at 10°C. It will serve as a reference for evaluating the effectiveness of the various additions 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 / temperature ratio (W / C) of 0.5 is 39 J / g, and its initial setting time is 9.4 hours. The effectiveness of compositions 1 to 8 is evaluated by isothermal microcalorimetry testing at W / C 0.5 and 10°C. The initial setting time corresponds to the time taken by the composition to reach the total heat of the mixture of 39 J / g. The results obtained are reported in Table 4 below. Composition Initial setting 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 11,0Table 4 – Setting Time of the Compositions of the Invention. The results obtained confirm a clear reduction in the 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. Example 4 – Ready-Mix Concrete – Workability and Mechanical Strength. Rapid-setting concretes are formulated with a total binder content of 400 kg / m³. 3 This is composed of 100% Portland cement (reference) or 75% Portland cement and 25% additives according to the invention. The complete compositions of the concretes are given in Table 5 below. 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 (as % binder) - 0.73 Plastitard 930 (as % binder) - 1 Optima 372 (as % binder) - 2.4 Equalis 250 (as % binder) - 1.2 Mineral aggregates1734 1934(in kg / m³) Effective Water - Eeff (in kg / m²) 182 138 E / Binder 0.46 0.345 Table 5 – Rapid Setting Concretes Workability The workability of the concrete is measured by measuring the slump using the Abrams cone according to standard NF EN 12350-2. Monitoring this measurement ensures that the slump class is maintained throughout the period from its production to its placement. The results obtained are reported in Table 6 below. Slump (in mm) Concrete 1 (ref.) Concrete 2 T0 210 200 T0+30 min 210 200 T0+60 min 210 200 T0+90 min 210 190 T0+120 min 210 180 Table 6 – Workability It appears that class S4 (160 mm - 210 mm) is guaranteed for 120 minutes for both the reference concrete and the concrete according to the invention. Compressive strength The ambient temperature and that of the materials used is 10°C. The mechanical strengths are measured on 15x30 cylindrical specimens. The cylinders are made in 3 layers compacted by vibration.Mechanical strengths are obtained according to standard NF EN 12390-3. The results obtained are reported in Table 7 below. 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 Table 7 – Compressive strength With an equivalent quantity of binder (400 kg / m 3 ) compared to the reference concrete, the concrete according to the invention exhibits a setting time and a rise in strength that are significantly faster than the latter.

Claims

CLAIMS 1. A mineral additive for cement comprising: - 10% to 90% (w / w) of sulfoaluminate clinker; - 10% to 90% (w / w) of natural rapid-setting cement; and - 1% to 50% of anhydrite C$; said mineral additive being free of setting accelerators or retarders.

2. A mineral additive according to claim 1, characterized in that it comprises 20% to 80% (w / w) of sulfoaluminate clinker.

3. A mineral additive according to claim 2, characterized in that it comprises 40% to 60% (w / w) of sulfoaluminate clinker.

4. A mineral additive according to any one of claims 1 to 3, characterized in that it comprises 20% to 90% (w / w) of natural rapid-setting 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. Cementitious composition according to claim 8, characterized in that it comprises 45% to 95% (w / w) Portland cement.

10. Cementitious composition according to claim 8 or 9, characterized in that it comprises 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 7. 10 ; - 74% to 82% (w / w) aggregate; - 4% to 6% (w / w) water; and - 0.5% to 0.9% superplasticizer; said ready-mix concrete being free of setting accelerator.