Expanding additive for mortar or concrete

Abstract

Expansive additive for mortar or concrete. The present invention relates to the use of a CaMgO2 compound obtained by calcination at a temperature of 1300°C or higher as an expansive additive for mortars or concretes. It further relates to a concrete or mortar composition comprising the CaMgO2 compound obtained by calcination at a temperature of 1300°C or higher.

Description

Title of the invention: Expanding additive for mortar or concrete technical field

[0001] The present invention relates to the field of the construction industry and in particular to the field of the concrete and mortar industry, which faces problems of shrinkage and / or cracking at an early age. It relates in particular to expansive additives for mortar or concrete which aim to compensate for endogenous shrinkage, to reduce total shrinkage and, consequently, to minimize cracking of cementitious materials at an early stage of their development. Previous technique

[0002] Concrete and mortar, resulting from the combination of cement, water, and fine or coarse aggregates, generate an adhesive matrix that encapsulates and binds the aggregates following the chemical reaction between the cement and water. A frequently studied aspect of concrete and mortar is their shrinkage phenomenon.

[0003] Concrete and mortar shrinkage is defined as a decrease in volume resulting from variations in its moisture content and chemical reactions. It represents a dimensional contraction of the cement volume due to fluctuations in the moisture content of the concrete or mortar, whether in its plastic state or before hardening. Water evaporation is triggered by a hydration process, an intrinsic mechanism, or environmental phenomena.

[0004] A thorough understanding of shrinkage is essential to anticipate and evaluate the long-term performance of the material, particularly with regard to its strength, stability and ability to maintain its structural and functional properties under various environmental conditions.

[0005] There are four types of shrinkage in concrete or mortar, namely plastic shrinkage, drying shrinkage, endogenous shrinkage and thermal shrinkage.

[0006] Plastic shrinkage results from the decrease in water volume due to evaporation during the plastic phase of concrete or mortar, while it is still deformable. This phenomenon occurs shortly after the concrete or mortar is placed in the formwork. The magnitude of plastic shrinkage is proportional to the amount of water evaporated, with a typical magnitude of 1 mm / m. Factors influencing this type of shrinkage include a high water / cement ratio, dry air, high ambient temperature, and excess water in the concrete or mortar.

[0007] Drying shrinkage is a localized desiccation phenomenon that begins at the surface of the concrete or mortar, where the internal water of the material evaporates. The main cause of this shrinkage is the evaporation of water present in the capillaries of the matrix. Hydrated cement evaporates from the surfaces of concrete or mortar exposed to ambient air. Evaporation occurs as soon as the relative humidity of the ambient air is lower than that within the capillary network of the concrete or mortar. The tensile forces generated in the menisci inside the concrete induce contraction of the material.

[0008] Endogenous shrinkage arises from the disparity between the volume of the hydrates formed and that of the initial components (water + cement). This disparity generates a post-setting volumetric contraction of the concrete or mortar. It should be noted that hydration reactions are independent of environmental conditions. After setting, capillary voids emerge in the hydrated cement matrix, inducing a reduction in the internal moisture content (self-desiccation). This process leads to a reorganization of water within the cement matrix, causing a contraction identified as endogenous shrinkage. The latter has two sources: chemical shrinkage, also known as "Le Chatelier shrinkage," and self-desiccation shrinkage of physical origin.

[0009] Thermal shrinkage, the last type of shrinkage, is associated with a decrease in the ambient temperature of the concrete or mortar after it has set. The heat released during setting generates an exothermic chemical reaction, but after this phase, the concrete or mortar expands due to the drop in ambient temperature. This expansion is followed by thermal contraction, leading to deformations and cracks.

[0010] The phenomenon of total shrinkage is manifested by the combination of these various types of shrinkage that occur simultaneously or sequentially within cementitious materials. When these deformations are constrained by external elements such as reinforcement or slabs, this leads to the appearance of tensile stresses within the material. If these stresses exceed the tensile strength of the material, cracks form, which can compromise the durability of the structure. In general, completely eliminating the shrinkage phenomenon is complex, but it is possible to reduce the risk of cracking and limit the size of the cracks.

[0011] Various strategies can be considered to minimize shrinkage phenomena. A widely adopted approach to mitigating endogenous shrinkage involves the integration of expansive agents, which induce expansion of the cementitious matrix on a macroscopic scale (Yang, L., Shi, C., Wu, Z. (2019). Mitigation techniques for autogenous shrinkage of ultra high-performance concrete - A review. Composites Part B, 178, 107456). This expansion thus makes it possible to partially or totally compensate for the shrinkage. Three categories of expansive agents are frequently used for this purpose, namely those based on magnesium oxide (MgO), quicklime (CaO), and calcium sulfoaluminates (CSA).

[0012] Due to the volumetric shrinkage of mortars or concrete materials, cracks generally occur when the shrinkage is constrained, resulting in effects These cracks are detrimental to both the mechanical properties and the durability of these materials, ultimately reducing their service life. Therefore, preventing cracks is a prerequisite for preserving the durability of structures. To mitigate shrinkage cracks in concrete or mortar, numerous strategies have been developed, primarily including: - The partial replacement of Portland cement (OPC) with additional cementitious materials (SCM) such as fly ash and limestone. - Adding additives / products to the concrete or mortar mix: Incorporation of fibers, shrinkage-reducing chemical agents, expansive additives - The application of an external or internal treatment, for example using super-absorbent polymers or saturated lightweight aggregates.

[0013] The present invention focuses on the most efficient approach to mitigating the shrinkage of concrete and mortar by compensating for the latter through the hydration of the expansive additive integrated into the formulation.

[0014] Expanding additives are generally characterized by their ability to induce rapid expansions at early stages. For example, the expansions of CaO and CSA-containing expanding additives occur rapidly at room temperature. At higher temperatures, expansion can occur even earlier. However, under certain circumstances, the effectiveness of conventional expanding additives is limited due to their relatively rapid hydration, which leads to expansions in an unhardened liquid space. This is why MgO-based expanding agents, characterized by later expansions, are of particular importance. It is generally accepted that MgO used as expanding agents should preferably be of the "light burned" type, i.e., calcined between 700 and 1100 °C and in all cases at a temperature < 1200 °C. A temperature of 1050 ±50 °C is even recommended (L. Mo, M. Deng, M.Tang, A. Al-Tabbaa, MgO expansive cernent and concrète in China: past, présent and future, Cem. Concr. Res. 57 (2014) 1-12). .

[0015] The CaO-based expanding agent generally induces rapid expansion, primarily within the first two days, due to its rapid hydration. Consequently, it is considered compatible with modern applications that exhibit relatively rapid strength development at an early stage. However, this high reactivity observed at an early stage has negative repercussions on the rheology, due to the strongly exothermic nature of the reaction.

[0016] Compared to the CaO-based expanding agent, the MgO-based one results in slower expansion due to the relatively more moderate hydration rate of MgO. This offers several advantages, including a less violent and less exothermic reaction than that observed with CaO, thus reducing, or even eliminating, the negative impact on rheology. However, the expansion magnitude associated with the use of MgO is generally lower than that observed with CaO.

[0017] The article by Miao et al. (“Shrinkage and cracking behavior of high performance concrete containing an MGO-CAO composed expansive agent”, International RILEM Conference on Use of Superabsorbent Polymers and Other new Additives in Concrète - August 15-18, 2010, Technical University of Denmark, Lingby, Denmark) describes the use in Portland cement of a new expansive agent (EA) consisting of a mixture of MgO calcined at 750-850 °C, MgO calcined at 1050-1150 °C and CaO calcined at 1200-1400 °C comprising a CaO / MgO ratio of 37.1 / 50.68. First, it should be noted that this new expansive agent is always used in association with a superplasticizer (polynaphthalene sulfonate) in order to maintain acceptable rheology, which represents a significant additional cost. Thus, this document does not suggest at any point that it can be used alone.Furthermore, this document clearly states that MgO calcined at 750-850 °C is considered highly active due to its relatively high hydration rate, while MgO calcined at 1150 °C is considered weakly active because of its slower hydration rate. This expanding agent is used at a concentration of 8% by mass. The problem associated with this new expanding agent is that it results from a mixture of three expanding agents, each calcined at different temperatures. Its manufacturing process is therefore complex.

[0018] Although the prior art offers a considerable variety of solutions to shrinkage problems, none of them appears to be particularly well-suited for effectively and optimally resolving these shrinkage issues. It would therefore be worthwhile to find new expansive agents with a superior effect to those of the prior art, which can be easily manufactured and used alone in cements without the mandatory presence of other products such as superplasticizers.

[0019] The inventors discovered that the use of a CaMgO2 compound obtained by calcining a dolomite-rich compound, particularly dolomite, at high temperature made it possible to obtain a particularly effective expansive additive for mortars or concretes, even more effective than the expansive agent (MC) described in the article by Miao et al., and this at lower concentrations (from 3% in the short term (0 to 3 days) and from 6% in the medium term (28 days)), as demonstrated in the examples below. Thus, calcined dolomite emerges as a solution that reconciles The advantages of both CaO and MgO are combined while mitigating undesirable effects. High-temperature calcined dolomite maintains the strong initial swelling characteristic of CaO, while exhibiting a non-aggressive reaction and not disrupting the rheology, as observed with MgO. Furthermore, the manufacturing process for such an expansive additive is particularly simple, requiring only calcination of the entire product at the same temperature. Finally, this expansive additive can be used alone without the mandatory presence of a superplasticizer. Description of the invention

[0020] The present invention therefore relates to the use of a CaMgO2 compound obtained by calcination at a temperature greater than or equal to 1300°C as an expansive additive for mortars or concretes.

[0021] In this application, the expressions "between ... and ...", "from ... to ..." and "included in the range ......." shall be understood to include the limits unless explicitly stated otherwise.

[0022] For the purposes of this invention, "CaMgO2 compound obtained by calcination at a temperature greater than or equal to 1300°C" means a mixed CaO.MgO oxide which has been obtained by calcination of a compound rich in dolomite (CaMg(CO3)2) and / or huntite (Mg3Ca(CO3)4) at a temperature greater than or equal to 1300°C. The terms "CaMgO2 compound obtained by calcination at a temperature greater than or equal to 1300°C", "CaMgO2 compound obtained by calcination of a compound rich in dolomite and / or huntite at a temperature greater than or equal to 1300°C", "CaMgO2 compound obtained by calcination", "CaMgO2 compound according to the invention" or "calcined CaMgO2 compound" or even "CaMgO2 compound" shall be used interchangeably to designate the same compound.

[0023] For the purposes of the present invention, "dolomite and / or huntite rich compound" means a compound containing more than 50% by mass of dolomite and / or huntite, advantageously more than 70% by mass of dolomite and / or huntite, even more advantageously more than 90% by mass of dolomite and / or huntite, in particular more than 95% by mass of dolomite and / or huntite, more particularly more than 98% by mass of dolomite and / or huntite, relative to the total mass of the compound.

[0024] Advantageously the dolomite and / or huntite rich compound according to the invention is a dolomite and / or huntite rich ore, even more advantageously it is a dolomite.

[0025] Particularly advantageously, the dolomite and / or huntite-rich compound according to the invention is a dolomite-rich compound, more advantageously a dolomite-rich ore.

[0026] Advantageously, the calcined CaMgO2 compound according to the invention is calcined dolomite. For the purposes of the present invention, "calcined dolomite" means the product obtained after calcining dolomite at the temperature according to the invention.

[0027] Advantageously the calcined CaMgO2 compound comprises a CaO / MgO mass ratio between 50 / 45 and 65 / 30, advantageously between 56 / 43 and 62 / 36, more advantageously it is 58 / 40.

[0028] For the purposes of this invention, "dolomite-rich ore" means an ore containing more than 50% by mass of dolomite, advantageously more than 70% by mass of dolomite, and even more advantageously more than 90% by mass of dolomite, in particular more than 95% by mass of dolomite, and more particularly more than 98% by mass of dolomite, relative to the total mass of the ore. Advantageously, the ore may also include iron oxide Fe2O3, aluminum oxide Al2O3, silicon dioxide SiO2, potassium oxide K2O, and / or sulfur oxide SO3. Advantageously, the dolomite-rich ore according to the invention is dolomite.

[0029] The thermal transformation by calcination of dolomite aims to produce a mixed oxide, CaO.MgO, accompanied by the release of carbon dioxide (CO2), according to the following reaction:

[0030] CaMg(CO3)2 -> CaO / MgO + 2CO2 (1)

[0031] The calcination of the dolomite and / or huntite-rich compound can be carried out in a single step or in several steps, particularly in two steps, with, for example, a first calcination at a low temperature (e.g., 750–1100 °C) followed by a calcination at a temperature of 1300 °C or higher. The first step can thus aim to change the chemical composition by removing the majority of the CO2, while the second step can primarily aim to modify the crystalline structure of the material. This second step is sometimes called “sintering.”

[0032] In an advantageous embodiment the calcination temperature is between 1300 and 2500°C, advantageously between 1500 and 2400°C, more advantageously between 1700 and 2300°C, even more advantageously between 1800 and 2200°C, more particularly between 1900 and 2100°C, in particular it is 2000°C.

[0033] Increasing the calcination temperature will affect the physicochemical properties of the mixed oxide, CaO.MgO. This results in particular in a decrease in the amount of residual carbonate, an increase in the actual density, and an increase in the size of the crystallites. Thus, advantageously, the CaMgO2 compound according to the invention has an actual density greater than or equal to 3.12, more advantageously greater than or equal to 3.20, even more advantageously greater than or equal to 3.30, and in particular greater than or equal to 3.31. This density is measured in particular using a gas pycnometer, specifically the Ultrapyc 3000 model. Advantageously, the LOI (loss on ignition) of the CaMgO2 compound according to the invention, measured by the mass loss after 2 hours at 1050°C, is less than or equal to 6.0%, advantageously less than or equal to 5.5%, more advantageously less than or equal to 5.0%, even more advantageously less than or equal to 4.0%, and even more advantageously less than or equal to 3.0%, in particular less than or equal to 2.6%. The LOI allows for the measurement of the amount of residual carbonate of the CaMgO2 compound according to the invention.

[0034] In an advantageous embodiment, the CaMgO2 compound according to the invention is used in solid form, advantageously in powder form. Advantageously, the CaMgO2 particles according to the invention have a size of less than 500 µm (40 mesh), more advantageously less than 140 µm (100 mesh). This size is measured by sieving or by laser particle size analysis.

[0035] The CaMgO2 compound according to the invention can be used alone or in combination with an additive selected from: - at least one other expansive additive, such as calcium sulfoaluminate (CSA), MgO and / or CaO; - at least one shrinkage-reducing admixture (SRA), such as a glycol, in particular an alkylene glycol more specifically as described in US patent 8784558, or polyalkylene glycol - at least one water-retaining additive, such as a superabsorbent polymer (SAP), cellulose or cellulose ether, starch or starch ether, diatomaceous earth, biochar, or amorphous silica - at least one plasticizing or superplasticizing polymer such as a lignosulfonate, a polynaphthalene sulfonate, or a polycarboxylic ether (PCE) - and a mixture of these.

[0036] Advantageously, the inventors discovered that a synergy exists when the CaMgO2 compound according to the invention is used in combination with a water-retaining additive, such as a superabsorbent polymer (SAP), cellulose or cellulose ether, starch or starch ether, diatomaceous earth, biochar, or amorphous silica. Thus, advantageously, the CaMgO2 compound according to the invention is used in combination with such an additive.

[0037] In the case where the CaMgO2 compound according to the invention is combined with an additive, it can be in the form of a premix. For example, if the additive is liquid (for example, if it is a shrinkage-reducing additive), it can be absorbed onto the particles of the CaMgO2 compound according to the invention before its use. This combination can thus form a dry powder.

[0038] In an advantageous embodiment, the CaMgO2 compound according to the invention is not used in association with blast-furnace slag and / or a superabsorbent polymer and / or calcined magnesite and / or a calcined magnesium-rich ore and / or a siliceous mineral.

[0039] In a particularly advantageous embodiment, the CaMgO2 compound according to the invention is used without any other expansive additive and / or without a shrinkage reducing additive and / or without a water-retaining additive.

[0040] Advantageously, the CaMgO2 compound according to the invention is used at a temperature between 5 and 40 °C, in particular at atmospheric pressure.

[0041] Advantageously, the CaMgO2 compound according to the invention is used in a content of between 0.1 and 15% by mass, advantageously between 0.5% and 10% by mass, more advantageously between 1% and 7% by mass, relative to the total mass of the cement.

[0042] The concrete or mortar according to the invention comprises cement. Advantageously, this is construction cement, more advantageously selected from Portland cement, aluminous cement, blast furnace cement, pozzolanic cement and mixtures thereof, and even more advantageously, Portland cement. Advantageously, the cement according to the invention is not a petroleum cement such as Class G cement.

[0043] In another advantageous embodiment, the concrete or mortar according to the invention is intended for construction, in particular it is durable concretes intended for marine environments, concretes used in reservoirs, ready-mix concretes, architectural concretes, self-placing concrete, shotcrete, concrete based on recycled aggregates, shrinkage-joint-free concretes for industrial slabs, repair mortars, sealing and anchoring mortars, packing mortars, screeds or leveling compounds.

[0044] The present invention also relates to a concrete or mortar composition comprising the CaMgO2 compound according to the invention as defined above.

[0045] The composition of concrete or mortar according to the invention can therefore include a content of compound CaMgO2 according to the invention of between 0.1 and 15% by mass, advantageously between 0.5% and 10% by mass, more advantageously between 1% and 7% by mass, relative to the total mass of the cement.

[0046] The concrete or mortar composition according to the invention comprises cement. Advantageously, this is construction cement, more advantageously selected from Portland cement, aluminous cement, blast furnace cement, pozzolanic cement and mixtures thereof; even more advantageously, it is the Portland cement. In particular, the cement of the composition according to the invention is not a petroleum cement such as class G cement.

[0047] The concrete or mortar composition according to the invention comprises sand and water.

[0048] The concrete or mortar composition according to the present invention may further comprise an additive selected from: - at least one other expansive additive, such as calcium sulfoaluminate (CSA), MgO and / or CaO; - at least one shrinkage-reducing admixture (SRA), such as a glycol, in particular an alkylene glycol more specifically as described in US patent 8784558, - at least one water-retaining additive, such as a superabsorbent polymer (SAP), cellulose or cellulose ether, starch or starch ether, diatomaceous earth, biochar, or amorphous silica - at least one plasticizing or superplasticizing polymer such as a lignosulfonate, a polynaphthalene sulfonate, or a polycarboxylic ether (PCE) - and a mixture of these.

[0049] Advantageously, the inventors discovered that a synergy exists when the CaMgO2 compound and a water-retaining additive, such as a superabsorbent polymer (SAP), cellulose or cellulose ether, starch or starch ether, diatomaceous earth, biochar, or amorphous silica, are both present in the concrete or mortar composition according to the present invention. Thus, advantageously, the concrete or mortar composition according to the present invention comprises the CaMgO2 compound according to the invention and the water-retaining additive as described above.

[0050] In an advantageous embodiment, the concrete or mortar composition according to the invention does not include blast-fumace slag and / or superabsorbent polymer and / or calcined magnesite and / or calcined magnesium-rich ore and / or siliceous mineral.

[0051] In a particularly advantageous embodiment, the concrete or mortar composition according to the invention does not include any other expansive additive apart from the CaMgO2 compound according to the invention and / or shrinkage reducing additive and / or water retaining additive.

[0052] Advantageously, concrete or mortar having the composition according to the invention is intended for construction, in particular durable concretes for marine environments, concretes used in reservoirs, ready-mix concretes, architectural concretes, self-compacting concrete, shotcrete, concrete based on recycled aggregates, and joint-free concretes for industrial slabs. repair mortars, sealing and anchoring mortars, packing mortars, screeds or leveling mortars.

[0053] The composition according to the present invention is prepared by methods well known to those skilled in the art, in particular by mixing the various ingredients and kneading them to obtain a paste. Advantageously, the CaMgO2 compound according to the present invention is added simultaneously with the cement to the composition according to the present invention.

[0054] The present invention will be better understood upon reading the description of the figures and examples that follow, which are given by way of non-limiting illustration. Brief description of the drawings

[0055] [Fig. 1] The [Fig. 1] represents the evolution of the expansion / shrinkage in pm / m under endogenous conditions as described in Example 1 as a function of time of a mortar composition containing calcined dolomite according to the invention at a temperature of 2000 °C (D2000) in a content of 1%, 2%, 3%, 4%, 5% or 6% (Examples 1 to 6) by mass relative to the total mass of cement prepared under the conditions of Example 1 or of a mortar composition not containing calcined dolomite (control: Comparative Example 1).

[0056] [Fig.2] Fig.2 represents the evolution of the expansion / contraction in pm / m following complete immersion in water under the conditions as described in Example 1 as a function of time of a mortar composition containing calcined dolomite according to the invention at a temperature of 2000 °C (D2000) in a content of 1%, 2%, 3%, 4%, 5% or 6% (Examples 1 to 6) by mass relative to the total mass of cement prepared under the conditions of Example 1 or of a mortar composition not containing calcined dolomite (control: Comparative Example 1).

[0057] [Fig. 3] [Fig. 3] represents the evolution of the expansion / contraction in pm / m under conditions drying as described in Example 1 as a function of time of a mortar composition containing calcined dolomite according to the invention at a temperature of 2000 °C (D2000) in a content of 1%, 2%, 3%, 4%, 5% or 6% (Examples 1 to 6) by mass relative to the total mass of cement prepared under the conditions of Example 1 or of a mortar composition not containing calcined dolomite (control: Comparative Example 1).

[0058] [Fig.4] Fig.4 represents the evolution of the flexural strength in MPa in the conditions as described in Example 1, 7 days or 28 days after the preparation of a mortar composition containing calcined dolomite according to the invention at a temperature of 2000 °C (D2000) in a content of 1%, 2%, 3%, 4%, 5% or 6% (Examples 1 to 6) by mass relative to the total mass of cement prepared in the conditions of example 1 or of a mortar composition not containing calcined dolomite (control: Comparative Example 1).

[0059] [Fig. 5] Figure 5 shows the evolution of the compressive strength in MPa under the conditions as described in Example 1, 7 days or 28 days after the preparation of a mortar composition containing calcined dolomite according to the invention at a temperature of 2000 °C (D2000) in a content of 1%, 2%, 3%, 4%, 5% or 6% (Examples 1 to 6) by mass relative to the total mass of cement prepared under the conditions of Example 1 or of a mortar composition not containing calcined dolomite (control: Comparative Example 1).

[0060] [Fig. 6] Fig. 6 represents the evolution of the expansion / contraction in pm / m under conditions endogenous as described in example 2 as a function of time: - a mortar composition containing calcined dolomite according to the invention at a temperature of 2000 °C (D2000) in a content of 4%, 5% or 6% (examples 4 to 6) by mass relative to the total mass of cement prepared under the conditions of example 2, - of a mortar composition not containing calcined dolomite (control) (Comparative example 1) - a mortar composition containing dolomite calcined at a temperature of 1000 °C (D1000) in a content of 4%, 5% or 6% (comparative examples 2a, 2b and 2c) by mass relative to the total mass of cement prepared under the conditions of example 2 - a mortar composition containing a magnesite-rich ore (MgCO3) calcined at a temperature of 1000 °C (M1000) in a content of 4%, 5% or 6% (comparative examples 3a, 3b and 3c) by mass relative to the total mass of cement prepared under the conditions of example 2 - of a mortar composition containing a calcium carbonate rich ore (CaCO3) calcined at a temperature of 1000 °C (Cl000) in a content of 4%, 5% or 6% (comparative examples 4a, 4b and 4c) by mass relative to the total mass of cement prepared under the conditions of example 2.

[0061] [Fig.7] Fig.7 represents the evolution of the subsidence for different additions in the conditions as described in example 2 as a function of time for: - a mortar composition containing calcined dolomite according to the invention at a temperature of 2000 °C (D2000) in a content of 6% (example 6) by mass relative to the total mass of cement prepared under the conditions of example 2, - a mortar composition not containing calcined dolomite (control: Comparative Example 1) - a mortar composition containing dolomite calcined at a temperature of 1000 °C (DI000) at a content of 6% (comparative example 2c) by mass relative to the total mass of cement prepared under the conditions of example 2 - a mortar composition containing a magnesite-rich ore (MgCO3) ) calcined at a temperature of 1000 °C (M1000) to a content of 6% (comparative example 3c) by mass relative to the total mass of cement prepared under the conditions of example 2 - a mortar composition containing a calcium carbonate (CaCO3) rich ore calcined at a temperature of 1000 °C (Cl000) at a content of 6% (comparative example 4c) by mass relative to the total mass of cement prepared under the conditions of example 2 - a mortar composition containing a magnesite-rich ore (MgCO3) calcined at a temperature of 1000 °C in a content of 2.4% by mass relative to the total mass of cement and a calcium carbonate-rich ore (CaCO3) calcined at a temperature of 1000 °C in a content of 3.6% by mass relative to the total mass of cement (C1000 + M1000: comparative example 5) prepared under the conditions of example 2.

[0062] [Fig. 8] Figure 8 represents the setting time (in mm) measured using the Vicat needle as a function of the time after the addition of water under the conditions described in Example 2 for: - a mortar composition containing calcined dolomite according to the invention at a temperature of 2000 °C (D2000) in a content of 6% (example 6) by mass relative to the total mass of cement prepared under the conditions of example 2, - a mortar composition not containing calcined dolomite (control: Comparative Example 1) - a mortar composition containing dolomite calcined at a temperature of 1000 °C (DI000) at a content of 6% (comparative example 2c) by mass relative to the total mass of cement prepared under the conditions of example 2 - a mortar composition containing a magnesite-rich ore (MgCO3) ) calcined at a temperature of 1000 °C (M1000) to a content of 6% (comparative example 3c) by mass relative to the total mass of cement prepared under the conditions of example 2 - a mortar composition containing a calcium carbonate (CaCO3) rich ore calcined at a temperature of 1000 °C (Cl000) at a content of 6% (comparative example 4c) by mass relative to the total mass of cement prepared under the conditions of example 2 - a mortar composition containing a magnesite-rich ore (MgCO3) calcined at a temperature of 1000 °C in a content of 2.4% by mass relative to the total mass of cement and a calcium carbonate-rich ore (CaCO3) calcined at a temperature of 1000 °C in a content of 3.6% by mass relative to the total mass of cement (C1000 + M1000: comparative example 5) prepared under the conditions of example 2.

[0063] [Fig.9] Figure [Fig.9] represents the times required to reach the start and end of the setting after the addition of water (in min) measured under the conditions as described in Example 2 for: - a mortar composition containing calcined dolomite according to the invention at a temperature of 2000 °C (D2000) in a content of 6% (example 6) by mass relative to the total mass of cement prepared under the conditions of example 2, - a mortar composition not containing calcined dolomite (control: Comparative example 1) - a mortar composition containing dolomite calcined at a temperature of 1000 °C (DI000) at a content of 6% (comparative example 2c) by mass relative to the total mass of cement prepared under the conditions of example 2 - a mortar composition containing a magnesite-rich ore (MgCO3) ) calcined at a temperature of 1000 °C (M1000) to a content of 6% (comparative example 3c) by mass relative to the total mass of cement prepared under the conditions of example 2 - a mortar composition containing a calcium carbonate (CaCO3) rich ore calcined at a temperature of 1000 °C (Cl000) at a content of 6% (comparative example 4c) by mass relative to the total mass of cement prepared under the conditions of example 2 - a mortar composition containing a magnesite-rich ore (MgCO3) calcined at a temperature of 1000 °C in a content of 2.4% by mass relative to the total mass of cement and a calcium carbonate-rich ore (CaCO3) calcined at a temperature of 1000 °C in a content of 3.6% by mass relative to the total mass of cement (C1000 + M1000: comparative example 5) prepared under the conditions of example 2.

[0064] EXAMPLES Example 1#: compositions according to the invention

[0065] The calcined dolomite used in the context of the present invention, after calcination at a temperature of 2000 °C, has the chemical composition indicated in Table 1, expressed as mass percentages relative to the total mass of the calcined dolomite. It will be referred to as D2000 in the remainder of this example.

[0066] [Tables 1] Oxide (%) CaO 58.0 MgO 40.0 Fe2O3 0.5 Al2O3 0.3 SiO2 0.4

[0067] D2000 also exhibits a LOI (loss on ignition, measured by mass loss) after 2h at 1050°C) of 2.6% and an actual density (measured with the Ultrapyc 3000 model gas pycnometer) of 3.31.

[0068] As part of the validation tests, the formulation and characterization of the mortars were carried out in accordance with the guidelines of European standards EN 196-1 of 2016 and NF P15-433 of 1994. The mechanical and shrinkage properties were evaluated on standardized prismatic specimens of dimensions (40 x 40 x 160 mm), manufactured using molds with three compartments of these respective dimensions. Measuring devices, called pads, were attached to the ends of each mold compartment and subsequently positioned at the ends of the test specimens once the mortar had set. These pads allow for the installation of the shrinkage meter sensors to facilitate measurements (Reference shrinkage pad: LPLOT-4x4xl6 from the company "Recherches et Réalisations Remy").

[0069] Regardless of the formulation, each batch contains 450 g of cement, 1350 g of sand, and 225 g of water (in a ratio of 1:3:0.5 by weight for cement, sand, and water, respectively). The only variable between the different formulations is the quantity of additive according to the invention to be added. The cement used is a CEM I class Portland cement, characterized by a minimum compressive strength at 28 days of 52.5 MPa, measured on test specimens stored in water at 20°C.

[0070] In the composition of mortar or concrete, the particle size distribution of the aggregates used influences the shrinkage and strength properties of the material. Therefore, it is essential to use sand of uniform particle size distribution for each test specimen. Standard EN 196-1, 2016, thus recommends the use of CEN reference sand, the particle size distribution of which is regulated and defined by this same standard (Table 2), and which is sold in 1350 g bags specifically for this purpose.

[0071] [Tables2] Dimensions of square miles (mm) 2.00 1.60 1.00 0.50 0.16 0.08 Cumulative residue on sieves (%) 0 7+5 33+5 67+5 87+5 99+1

[0072] The mortar preparation process is carried out using a suitable two-speed mixer (E093N Automatic mortar mixer from the company “controlab”), according to a standardized procedure broken down as follows: - Introduction of water, cement, and possibly the additive (calcined dolomite according to the invention) into the mixing bowl, followed by mixing at low speed (rotation: 140 min⁻¹; planetary motion: 62 min⁻¹) for 30 seconds, - Regular addition of standardized sand into the bowl via a hopper for 30 seconds. - High-speed mixing (rotation: 285 min⁻¹; planetary motion: 125 min⁻¹) for 30 seconds, - Mixing is stopped for 90 seconds, during which time the mortar adhering to the sides and bottom of the bowl is scraped and brought back to the center of the bowl for 30 seconds, - Mixing is resumed at high speed for 60 seconds. - The mortar paste thus obtained is then compacted by impacts on an impact table (the "EO130 standard impact table" from the company "controlab"), in order to remove air from the paste, similar to the vibration of concrete. The mold is fixed to the impact table and the paste is introduced in two layers, each compacted by 60 impacts, in accordance with standard EN 196-1, 2016. - Finally, the excess dough is removed and the mold is covered with cling film to prevent the dough from drying out.

[0073] In order to highlight the intrinsic benefits of calcined dolomite according to the invention, a comparative analysis is carried out between the performance of standardized mortars, acting as controls, and that of mortars incorporating calcined dolomite according to the invention.

[0074] Thus, the composition used per batch is as follows: - CEM 1 cement: 450 g - Standardized sand: 1350 g - Water: 225 g - D2000 (calcined dolomite according to the invention at 2000 °C): 1, 2, 3, 4, 5 or 6% of the mass of the cement (i.e. 4.5, 9, 13.5, 18, 22.5 or 27 g)

[0075] Table 3 below presents the seven formulations that were tested under each of the three conditions:

[0076] [Tables3] Examples Reference W / C (water / cement mass ratio) Cement Standardized Sand Water D2000 (kg / m3) (kg / m3) (kg / m3) (kg / m3) Comp 1 Control 0.5 450 1350 225 0.0 1 (1%) D200 0 0.5 450 1350 225 4.5 2 (2%) D200 0 0.5 450 1350 225 9.0 3 (3%) D200 0 0.5 450 1350 225 13.5 4 (4%) D200 0 0.5 450 1350 225 18.0 5 (5%) D200 0 0.5 450 1350 225 22.5 6 (6%) D200 0 0.5 450 1350 225 27.0

[0077] The use of control samples (control: comparative example 1) is essential to evaluate the effectiveness of the compensation of the shrinkage of the compositions according to the invention incorporating the compound CaMgO2 according to the invention.

[0078] Shrinkage monitoring using the 3R Mixed Deformometer, in accordance with standard NF P15-433, 2023, was carried out under three distinct experimental conditions: endogenous, underwater, and drying. Under the endogenous conditions, the mortar samples were demolded 8 hours after pouring, wrapped in aluminum foil, and then stored at a temperature of 20°C with a relative humidity of 50%. For the immersed conditions, the mortar samples were completely submerged in water at a temperature of 20°C immediately after demolding, 8 hours after pouring. Finally, for the drying conditions, the mortar samples were demolded after 8 hours and stored at a temperature of 20°C with a relative humidity of 50%.

[0079] The results are presented in Figures 1 to 3.

[0080] In addition to monitoring shrinkage, an evaluation of mechanical properties, more specifically of resistance to bending and compression, was carried out according to standard EN 196-1, 2016 using the 250 / 15 KN automatic compression machine of Class A and 1 from the company Controlab.

[0081] The results are presented in Figures 4 and 5.

[0082] In view of the results obtained, the CaMgO2 compound according to the invention, and in particular the calcined dolomite according to the invention, demonstrates remarkable performance compared to the reference formulations (comparative example 1) under three distinct conditions: endogenous, complete immersion in water, and drying. Indeed, even at addition levels below 3%, significant alterations were observed. observed in the desired direction, while between 4 and 6% addition, the results become particularly interesting. Regarding mechanical characterization, the results obtained indicate that the incorporation of this product up to 6% does not negatively affect the mechanical properties of the formulations, and in some cases, can even have a positive impact.

[0083] Example 2: comparison with compositions containing MgO, CaO or a mixture of MgO+CaO or dolomite calcined at 1000 °C

[0084] Dolomite calcined at 1000 °C (D1000) has the same composition as that indicated in Table 1 above. The only difference compared to the dolomite calcined according to the invention is its calcination temperature, which is only 1000 °C.

[0085] D1000 also exhibits a LOI (loss on ignition, measured by mass loss) after 2h at 1050°C) of 7.1% and an actual density (measured with the Ultrapyc 3000 model gas pycnometer) of 3.06.

[0086] The MgO used in the comparative example compositions corresponds to a mineral powder resulting from the calcination of a magnesite-rich ore (MgCO3) at a temperature of 1000°C (Ml000). This thermal transformation aims to produce magnesium oxide, accompanied by the release of carbon dioxide (CO2), according to the reaction: MgCO3 + Calcination temperature —> MgO + CO2

[0087] Table 4 below shows the chemical composition of the magnesium used, in percentages by mass relative to the total mass of the magnesium.

[0088] [Tables4] Oxide (%) CaO 1.6 MgO 95.0 Fe2O3 0.5 Al2O3 0.15 SiO2 1.5

[0089] The CaO used in the compositions of comparative examples corresponds to a mineral powder resulting from the calcination of an ore rich in calcium carbonate (CaCO3) at a temperature of 1000°C (Cl000). This thermal transformation aims to produce calcium oxide, accompanied by the release of carbon dioxide (CO2), according to the reaction: CaCO3 + Calcination temperature —> CaO + CO2

[0090] Table 5 below shows the chemical composition of the quicklime used, in percentages by mass relative to the total mass of quicklime.

[0091] [Tables5] Oxide (%) CaO 96.0 MgO 1.5 Fe2O3 0.4 Al2O3 0.1 SiO2 1.3

[0092] The performance of the formulations incorporating CaMgO2 according to the invention (D2000) was compared to that of formulations using products containing C1000 (comparative examples 4), M1000 (comparative examples 3), or a combination of the two (comparative example 5), in order to precisely characterize the advantages of this product. In addition to these substances, a further comparative analysis was conducted by evaluating the results of formulations including additions of dolomite calcined at 1000°C (D1000) (comparative examples 2).

[0093] With reference to Example 1, it is observed that the mechanical properties do not undergo major disturbances following the incorporation of CaMgO2 according to the invention. In this example, the analysis will therefore focus on comparing the different formulations with regard to their ability to compensate for shrinkage, their expansion potential, and their impact on rheology. To evaluate their shrinkage capacity, measurements similar to those used in Example 1 were carried out. Regarding rheological characterization, two distinct experimental protocols were performed: determination of the setting time and the slump test.

[0094] In the context of monitoring deformation (whether shrinkage or swelling), monitoring was carried out on several formulations, including a control group (Table 6) as well as additions of C1000, M1000, D1000 and D2000. The percentages of addition studied were 4%, 5% and 6% by mass relative to the total mass of cement (respectively comparative examples 4a, 4b, 4c, 3a, 3b, 3c, 2a, 2b, and 2c).

[0095] Table 6 thus presents the constituents of the standardized mortars tested in grams.

[0096] [Tableauxô] Constituents Mass per batch (g) Control mortar Cement CEM I 450 Sand 1350 Water 225 Addition (2.4 to 6%) 10.8 to 27

[0097] Regarding the determination of setting time, the experiments were carried out in accordance with standard NF P15-431, 1994. As for the slump test, it was performed using a cone with a height of 15 cm. The setting time and the slump test were carried out using the formulations presented in Table 7 below (as a percentage by mass relative to the total mass of cement or in grams).

[0098] [Tables7] Example Reference Constituents Control C1000 M1000 D1000 D2000 (%) (g) (%) (g) (%) (g) (%) (g) Comp. 1 Control X Comp. 5 C1000+M100 0 X 3.6 16.2 2.4 10.8 Comp. 4 c C1000 X 6.0 27.0 Comp. 3 c M1000 X 6.0 27.0 Comp. 2 c D1000 X 6.0 27.0 Ex 6 D2000 X 6.0 27.0

[0099] The monitoring of the shrinkage phenomenon was carried out on three samples for each formulation, at each percentage level of addition. The average of the measurements of these three samples is shown in [Fig. 6], illustrating the progression of deformation (whether shrinkage or expansion) over time for the various formulations studied.

[0100] Slump Test: This test aims to observe the slump of a cone of mortar or concrete under the effect of its own mass. A greater slump value indicates greater fluidity of the mortar or concrete. This variation in fluidity can be associated with the reactivity of additives. More specifically, a low slump suggests excessive reactivity of the additive, which can have a negative impact on the rheology. Thus, this test offers the advantage of evaluating the impact of the additive on the rheology by comparing the slump with that obtained with the control formulation. The test protocol is as follows: - The 50 x 50 cm support plate and the mold (Cone: bottom diameter: 10 cm; top diameter: 5 cm; height: 15 cm) are slightly moistened, and the mold is securely fixed against the support plate, - The cone is filled in three distinct stages, with each addition representing one-third of the cone's total height, which measures 15 cm. Each layer is carefully compacted by making 25 indentations with the appropriate rod. - Any excess concrete on the final layer is carefully leveled using the compaction rod, - The mold is then removed by lifting it vertically and steadily, taking between 3 and 5 seconds. - Immediately after the mold is removed, the slump is measured by calculating the difference between the height of the mold and the lowest point of the slumped concrete or mortar.

[0101] The results illustrating the evolution of the initial slump, measured after 8 minutes following the addition of water, for the various additives used in the formulations are gathered in Table 8 below.

[0102] [Tables8] Example Reference Slump at 8 minutes in cm Comp. 1 Control 6.0 Comp. 5 C1000+M1000 3.6 Comp. 4c C1000 3.1 Comp. 3c M1000 4.2 Comp. 2c D1000 3.9 Example 6 D2000 6.2

[0103] In addition to the initial measured subsidence, [Fig.7] shows the evolution of this subsidence in cm as a function of time in minutes.

[0104] Setting time: Similar to the slump test, the setting time can be used to assess the reactivity of the additives incorporated in each formulation. Indeed, the shorter the setting time of a formulation with an additive compared to that of the reference formulation, the more likely the reaction is to be exothermic, potentially negatively altering the rheology of the mixture.

[0105] In this context, the setting time of the different formulations was monitored according to standard EN 480-2, 2006 (using the Vicat manual prisometer from Recherches et Réalisations Remy and a mold with the following dimensions: Height: 40 mm; top inner diameter: 70 mm; bottom inner diameter: 80 mm). until all reach the stage of complete setting. The results of this observation are presented in [Fig.8].

[0106] Figure 9 shows the times required to reach the start and end of the capture for the different formulations.

[0107] Conclusion: With regard to shrinkage compensation, formulations using D2000 (examples 4 to 6) and C1000 (comparative examples 4a, 4b and 4c) show the best results, followed by D1000 (comparative examples 2a, 2b and 2c) and M1000 (comparative examples 3a, 3b and 3c), which are also effective against shrinkage but to a lesser extent than D2000 and C1000.

[0108] In terms of slump, a smaller initial decrease compared to the control formulation could indicate an increasingly vigorous reaction, which could potentially accentuate the negative impact of adding this additive on the rheology. The data obtained reveal that the introduction of C1000 (comparative example 4c) as an additive to compensate for shrinkage, despite its beneficial effect on this compensation, risks having an adverse impact on the rheology. Indeed, the initial slump of the formulation containing C1000 is almost half that of the control formulation. In contrast, the formulation using D2000 (example 6) offers a double advantage, compensating for shrinkage without any noticeable effect on the rheology.

[0109] The setting time results confirm the conclusions of the slump test. The formulation containing C1000 (comparative example 4c) required a shorter setting time to reach the beginning and end of the set, highlighting the negative impact of C1000 on the rheology. In contrast, the use of dolomite resulted in setting times very close to those of the control formulation, underscoring the dual positive effect of using D2000 (example 6) on shrinkage compensation while maintaining a rheology similar to that of the control formulation.

[0110] These various results clearly show that the use of the compound CaMgO2 calcined at high temperature (at a temperature greater than or equal to 1300 °C) is particularly advantageous as an expansive additive for mortars or concretes. These results are, in particular, far superior to those obtained using dolomite calcined at a lower temperature (1000 °C: D1000), or to the combination of CaO and MgO (Cl000 + Ml000), or even to CaO (Cl000) or MgO (Ml000) taken separately.

Claims

Demands

1. Use of a CaMgO2 compound obtained by calcination at a temperature greater than or equal to 1300°C as an expansive additive for mortars or concretes.

2. Use according to claim 1, characterized in that the compound CaMgO2 is obtained by calcination of an ore rich in dolomite and / or huntite, advantageously by calcination of dolomite.

3. Use according to any one of claims 1 or 2, characterized in that the calcination can be carried out in one or more stages.

4. Use according to any one of claims 1 to 3, characterized in that the calcination temperature is between 1300 and 2500°C, advantageously between 1500 and 2400°C, more advantageously between 1700 and 2300°C, in particular it is 2000°C.

5. Use according to any one of claims 1 to 4, characterized in that the CaMgO2 compound comprises a CaO / MgO mass ratio of between 50 / 45 and 65 / 30, advantageously it is 58 / 40.

6. Use according to any one of claims 1 to 5, characterized in that the CaMgO2 compound is mixed or associated with an additive selected from at least one other expanding additive, at least one shrinkage reducing additive, such as a glycol, at least one water-retaining additive, such as a superabsorbent polymer, at least one plasticizing or superplasticizing polymer such as a polycarboxylic ether (PCE), and a mixture of these.

7. Use according to any one of claims 1 to 6, characterized in that the concrete or mortar comprises a cement selected from Portland cement, aluminous cement, blast furnace cement, pozzolanic cement and mixtures thereof, advantageously Portland cement.

8. Use according to any one of claims 1 to 7, characterized in that the concrete or mortar is intended for construction, in particular in that it is durable concrete intended for marine environments, concrete used in reservoirs, ready-mix concrete, architectural concrete, the self-compacting concrete, shotcrete, concrete made from recycled aggregates, jointless concrete for industrial slabs, repair mortars, sealing and anchoring mortars, packing mortar, screeds or leveling compounds.

9. Concrete or mortar composition comprising the CaMgO2 compound obtained by calcination at a temperature greater than or equal to 1300°C as defined in any one of claims 1 to 6.

10. Concrete or mortar composition according to claim 9, characterized in that it comprises a cement selected from Portland cement, aluminous cement, blast furnace cement, pozzolanic cement and mixtures thereof, more advantageously Portland cement.

11. Concrete or mortar composition according to any one of claims 9 or 10, characterized in that the concrete or mortar is intended for construction, in particular in that it is durable concrete for marine environments, concrete used in reservoirs, ready-mix concrete, architectural concrete, self-compacting concrete, shotcrete, concrete based on recycled aggregates, shrinkage-joint-free concrete for industrial slabs, repair mortars, sealing and anchoring mortars, packing mortar, screeds or leveling compounds.

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