Expansive additive for mortar or concrete

Abstract

The present invention relates to the use of a CaMgO2 compound obtained by calcination at a temperature greater than or equal to 1500°C as an expansive additive for mortars or concretes. It also relates to a concrete or mortar composition comprising the CaMgO2 compound obtained by calcination at a temperature greater than or equal to 1500°C.

Description

EXPANSIVE 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 specifically to expansive additives for mortar or concrete designed to compensate for endogenous shrinkage, reduce total shrinkage, and consequently 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, create an adhesive matrix that encases and binds the aggregates through a 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 moisture content and chemical reactions. It represents a dimensional contraction of the cement's volume due to fluctuations in the concrete or mortar's moisture content, 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 varying 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 through evaporation during the plastic phase of concrete or mortar, while it is still deformable. This phenomenon occurs shortly after the concrete is placed or mortar in 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 concrete or mortar, where the material's internal water evaporates. The primary cause of this shrinkage is the evaporation of water present in the capillaries of the hydrated cement matrix, from the surfaces of the 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. This shrinkage 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 manifests itself through the combination of 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, tensile stresses appear within the material. If these stresses exceed the material's tensile strength, cracks form, potentially compromising the structure's durability. While completely eliminating shrinkage is generally complex, it is possible to reduce the risk of cracking and limit crack size.

[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 partially or completely compensates for shrinkage. Three categories of expansive agents are frequently used for this purpose: those based on magnesium oxide (MgO), quicklime (CaO), and calcium sulfoaluminates (CSA).

[0012] Due to the volumetric shrinkage of mortars or concrete materials, cracks typically occur when this shrinkage is constrained, leading to detrimental effects on both the mechanical properties and durability of these materials, ultimately reducing their service life. Therefore, crack prevention 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, Chemical shrinkage-reducing 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 it through the hydration of the expansive additive integrated into the formulation.

[0014] Expansive additives are generally characterized by their ability to induce rapid expansions at early stages. For example, the expansions of CaO and CSA-containing expansive additives occur rapidly at room temperature. At higher temperatures, expansion can occur even earlier. However, under certain circumstances, the effectiveness of conventional expansive additives is limited due to their relatively rapid hydration, which results in expansions within an unhardened liquid space. This is why MgO-based expansive agents, characterized by later expansions, are of particular importance. It is generally accepted that MgO used as an expansive agent 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 cement and concrete in China: past, present and future, Cem. Concrete Res. 57 (2014) 1-12).

[0015] The CaO-based expanding agent typically undergoes rapid expansion, primarily within the first two days, due to its fast hydration. Consequently, it is considered suitable for modern applications that require relatively rapid strength development at an early stage. However, this high reactivity observed at an early stage has negative implications for rheology, due to the strongly exothermic nature of the reaction.

[0016] Compared to the CaO-based expansive agent, the MgO-based one results in slower expansion due to the rate of hydration. The relatively more moderate reaction of MgO offers several advantages, notably 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 Concrete - 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 combination 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] Patent application CN1202038C describes dolomite calcined at a temperature between 1100 °C and 1300 °C for 60 to 120 minutes which can be used as an expanding agent in cement.

[0019] Patent application CN108046621 describes dolomite calcined at a temperature between 800 °C and 1800 °C in the presence of a silicon-containing component, which eliminates the calcium oxide present in the dolomite. Thus the product obtained will be a MgCh compound and will have the same properties.

[0020] Although prior art offers a considerable variety of solutions to shrinkage problems, none of them seems particularly well-suited to effectively and optimally resolving these 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 need for other products such as superplasticizers.

[0021] The inventors discovered that using a CaMgCh compound obtained by calcining a dolomite-rich compound, particularly dolomite, at a high temperature (1500 °C or higher) yielded a particularly effective expansive additive for mortars or concretes, even more effective than the expansive agent (EMA) described in the article by Miao et al., and at lower concentrations (from 3% in the short term (0 to 3 days) and from 6% in the medium term (28 days)) or than dolomites calcined at lower temperatures (1000 °C or 1300 °C), as demonstrated in the examples below. Thus, calcined dolomite emerges as a solution that combines the advantages of both CaO and MgO compounds while mitigating their undesirable effects. High-temperature calcined dolomite thus maintains the strong initial swelling characteristic of CaO, while exhibiting a non-violent reaction and not disturbing the rheology, as observed with MgO.Furthermore, the manufacturing process for such an expansive additive is particularly simple, as it only requires calcining 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

[0022] The present invention therefore relates to the use of a CaMgOz compound obtained by calcination at a temperature greater than or equal to 1500°C as an expansive additive for mortars or concretes.

[0023] In this application, the expressions "between ... and ...", "from ... to ..." and "included in the range >......", should be understood to include the limits unless explicitly stated otherwise.

[0024] For the purposes of this invention, "CaMgCh compound obtained by calcination at a temperature greater than or equal to 1500°C" means a mixed CaO.MgO oxide obtained by calcination of a dolomite-rich compound (CaMg CCh) and / or a huntite-rich compound (Mg3Ca(CO3)4) at a temperature greater than or equal to 1500°C. Throughout the remainder of this application, the terms "CaMgOz compound obtained by calcination at a temperature greater than or equal to 1500°C", "CaMgOz compound obtained by calcination of a dolomite-rich compound and / or a huntite-rich compound at a temperature greater than or equal to 1500°C", "CaMgOz compound obtained by calcination", "CaMgOz compound according to the invention", "calcined CaMgCh compound", or simply "CaMgCh compound" shall be used interchangeably to refer to the same compound.

[0025] For the purposes of this 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.

[0026] 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.

[0027] Most advantageously, the dolomite and / or huntite-rich compound according to the invention is a dolomite-rich compound, more advantageously a dolomite-rich ore.

[0028] Advantageously, the calcined CaMgCh 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.

[0029] Advantageously the calcined CaMgCh 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.

[0030] 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.

[0031] 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:

[0032] CaMg(CO3)2CaO / MgO + 2CO2(1)

[0033] The calcination of dolomite- and / or huntite-rich compounds can be carried out in a single step or in several steps, particularly in two steps, with, for example, an initial calcination at a low temperature (e.g., 750–1100 °C) followed by calcination at a temperature of 1500 °C or higher. The first step can thus aim to change the chemical composition by removing most 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."

[0034] In an advantageous embodiment the calcination temperature is between 1500 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.

[0035] Increasing the calcination temperature will impact 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 CaMgCh compound according to the invention has an actual density greater than or equal to 3.18, more advantageously greater than or equal to 3.20, in particular greater than or equal to 3.22, and even more advantageously greater than or equal to 3.30, in particular greater than or equal to 3.31. This density is measured in particular using a gas pycnometer, more specifically the Ultrapyc 3000 model.Advantageously, the LOI (loss on ignition) of the CaMgOz compound according to the invention, measured by the mass loss after 2 hours at 1050°C, is less than or equal to 4.5%, in particular less than or equal to 4.0%, more particularly less than or equal to 3.0%, and even more particularly less than or equal to 2.6%. The LOI allows for the measurement of the amount of residual carbonate of the CaMgOz compound according to the invention.

[0036] In an advantageous embodiment, the CaMgOz compound according to the invention is used in solid form, advantageously in powder form. Advantageously, the CaMgOz 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.

[0037] The CaMgCh 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 such as hexylene 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.

[0038] Advantageously, the inventors discovered that a synergistic effect exists when the CaMgCh 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, or with a shrinkage-reducing admixture (SRA), such as a glycol, particularly an alkylene glycol such as hexylene glycol, more specifically as described in US patent 8784558, or polyalkylene glycol. Thus, advantageously, the CaMgCh compound according to the invention is used in combination with such an additive.

[0039] In cases where the CaMgCh 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 (e.g., a shrinkage-reducing additive), it can be absorbed onto the particles of the CaMgCh compound according to the invention before use. This combination can thus form a dry powder.

[0040] In an advantageous embodiment, the CaMgCh 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.

[0041] In a particularly advantageous embodiment, the CaMgCh compound according to the invention is used without any other expanding additive and / or without any shrinkage reducing additive and / or without any water-retaining additive.

[0042] Advantageously, the CaMgCh compound according to the invention is used at a temperature between 5 and 40 °C, in particular at atmospheric pressure.

[0043] Advantageously, the CaMgCh 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.

[0044] The concrete or mortar according to the invention comprises cement. Advantageously, it is construction cement, more advantageously chosen from Portland cement, aluminous cement, blast furnace cement, pozzolanic cement and mixtures thereof, and even more advantageously from Portland cement. Advantageously, the cement according to the invention is not a petroleum cement such as Class G cement.

[0045] 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.

[0046] The present invention also relates to a concrete or mortar composition comprising the CaMgCh compound according to the invention as defined above.

[0047] The composition of concrete or mortar according to the invention can therefore include a content of CaMgCh compound 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.

[0048] 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 Portland cement. In particular, the cement in the composition according to the invention is not a petroleum cement such as Class G cement.

[0049] The composition of concrete or mortar according to the invention comprises sand and water.

[0050] The composition of concrete or mortar 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.

[0051] Advantageously, the inventors discovered that a synergistic effect exists when the CaMgCh 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 CaMgCh compound according to the invention and the water-retaining additive as described above.

[0052] In an advantageous embodiment, the concrete or mortar composition according to the invention does not include blast furnace slag and / or superabsorbent polymer and / or calcined magnesite and / or calcined magnesium-rich ore and / or siliceous mineral.

[0053] In a particularly advantageous embodiment, the concrete or mortar composition according to the invention does not include any other expansive additive besides the CaMgCh compound according to the invention and / or shrinkage reducing additive and / or water retaining additive.

[0054] Advantageously, concrete or mortar having the composition according to the invention is intended for construction, in particular durable concretes intended to marine environments, concretes used in reservoirs, ready-mix concretes, architectural concretes, self-placing concrete, shotcrete, concrete made from recycled aggregates, concretes without shrinkage joints for industrial slabs, repair mortars, sealing and anchoring mortars, packing mortars, screeds or leveling compounds.

[0055] 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 CaMgCh compound according to the present invention is added simultaneously with the cement to the composition according to the present invention.

[0056] 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

[0057] Figure 1 represents the evolution of 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).

[0058] Figure 2 represents the evolution of expansion / shrinkage 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).

[0059] Figure 3 shows the evolution of expansion / shrinkage in pm / m under drying 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).

[0060] Figure 4 represents the evolution of the flexural 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).

[0061] Figure 5 represents 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).

[0062] Figure 6 represents the evolution of the expansion / shrinkage in pm / m under endogenous conditions as described in example 2 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 4%, 5% or 6% (examples 4 to 6) by mass relative to the total mass of cement prepared under the conditions of example 2, - not containing calcined dolomite (control) (Comparative example 1), - 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, - containing a magnesite-rich ore (MgCCh) 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 or - containing a calcium carbonate rich ore (CaCCh) calcined at a temperature of 1000 °C (C1000) 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.

[0063] Figure 7 represents the evolution of the expansion / shrinkage in pm / m under endogenous conditions as described in example 2 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 4%, 5% or 6% (examples 4 to 6) by mass relative to the total mass of cement prepared under the conditions of example 2, - not containing calcined dolomite (control) (Comparative example 1), - 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, - containing dolomite calcined at a temperature of 1300 °C (D1300) in a content of 4%, 5% or 6% (comparative examples 6a, 6b and 6c) by mass relative to the total mass of cement prepared under the conditions of example 2 or - containing calcined dolomite according to the invention at a temperature of 1500 °C (DI 500) in a content of 4%, 5% or 6% (examples 7 to 9) by mass relative to the total mass of cement prepared under the conditions of example 2.

[0064] Figure 8 represents the evolution of the slump for different additions under the conditions 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 mass total cement prepared under the conditions of example 2, - not containing calcined dolomite (control: Comparative example 1), - containing dolomite calcined at a temperature of 1000 °C (D1000) in a content of 6% (comparative example 2c) by mass relative to the total mass of cement prepared under the conditions of example 2, - containing a magnesite-rich ore (MgCCh) calcined at a temperature of 1000 °C (M1000) at a content of 6% (comparative example 3c) by mass relative to the total mass of cement prepared under the conditions of example 2, - containing a calcium carbonate-rich ore (CaCCh) calcined at a temperature of 1000 °C (C1000) to a content of 6% (comparative example 4c) by mass relative to the total mass of cement prepared under the conditions of example 2 or - containing a magnesite-rich ore (MgCCh) 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 (CaCCh) 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.

[0065] Figure 9 represents the evolution of the slump for different additions under the conditions 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, - not containing calcined dolomite (control: Comparative example 1), - containing dolomite calcined at a temperature of 1000 °C (D1000) in a content of 6% (comparative example 2c) by mass relative to the total mass of cement prepared under the conditions of example 2, - containing dolomite calcined at a temperature of 1300 °C (D1300) in a content of 6% (comparative example 6c) by mass relative to the total mass of cement prepared under the conditions of example 2 or - containing calcined dolomite according to the invention at a temperature of 1500 °C (D1500) in a content of 6% (example 9) by mass relative to the total mass of cement prepared under the conditions of example 2.

[0066] Figure 10 shows the times required to reach the beginning and end of setting after the addition of water (in min) measured under 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, - not containing calcined dolomite (control: Comparative example 1), - containing dolomite calcined at a temperature of 1000 °C (D1000) in a content of 6% (comparative example 2c) by mass relative to the total mass of cement prepared under the conditions of example 2, - containing a magnesite-rich ore (MgCCh) calcined at a temperature of 1000 °C (M1000) at a content of 6% (comparative example 3c) by mass relative to the total mass of cement prepared under the conditions of example 2, - containing a calcium carbonate-rich ore (CaCCh) calcined at a temperature of 1000 °C (C1000) to a content of 6% (comparative example 4c) by mass relative to the total mass of cement prepared under the conditions of example 2 or - a mortar composition containing a magnesite-rich ore (MgCCh) 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 (CaCCh) 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.

[0067] Figure 11 shows the times required to reach the beginning and end of 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) at a content of 6% (example 6) by mass relative to the total mass of cement prepared under the conditions of example 2, - not containing calcined dolomite (control: Comparative example 1), - containing dolomite calcined at a temperature of 1000 °C (D1000) in a content of 6% (comparative example 2c) by mass relative to the total mass of cement prepared under the conditions of example 2, - containing dolomite calcined at a temperature of 1300 °C (D1300) in a content of 6% (comparative example 6c) by mass relative to the total mass of cement prepared under the conditions of example 2 or - containing calcined dolomite according to the invention at a temperature of 1500 °C (D1500) in a content of 6% (example 9) by mass relative to the total mass of cement prepared under the conditions of example 2.

[0068] Figure 12 represents the evolution of the spreading for different additions under the conditions as described in example 3 as a function of time for a composition of the "self-leveling undercoat" type: - containing calcined dolomite according to the invention at a temperature of 2000 °C (D2000) in a content of 6% by mass relative to the total mass of cement prepared under the conditions of Example 3, - not containing calcined dolomite (control), - containing dolomite calcined at a temperature of 1000 °C (D1000) in a content of 6% by mass relative to the total mass of cement prepared under the conditions of example 3, - containing dolomite calcined at a temperature of 1300 °C (D1300) in a content of 6% by mass relative to the total mass of cement prepared under the conditions of example 3 or - containing calcined dolomite according to the invention at a temperature of 1500 °C (DI 500) in a content of 6% by mass relative to the total mass of cement prepared under the conditions of example 3.

[0069] Figure 13 shows the evolution of compressive strength in MPa under the conditions described in Example 4, 1 day, 7 days, or 28 days after the preparation of a "base coat" type composition "Self-levelling": - containing calcined dolomite according to the invention at a temperature of 2000 °C (D2000) in a content of 5% by mass relative to the total mass of cement prepared under the conditions of Example 4, - containing no additives (control), - containing a glycol-type SRA shrinkage reducing agent at a concentration of 2% by mass relative to the total mass prepared under the conditions of Example 4 or - containing calcined dolomite according to the invention at a temperature of 2000 °C (D2000) in a content of 5% by mass relative to the total mass of cement and a glycol-type shrinkage reducing agent SRA in a content of 2% by mass relative to the total mass prepared under the conditions of Example 4.

[0070] Figure 14 represents the evolution of the expansion / shrinkage in pm / m under endogenous conditions as described in example 4 as a function of time of a "self-leveling underlayer" type composition: - containing calcined dolomite according to the invention at a temperature of 2000 °C (D2000) in a content of 5% by mass relative to the total mass of cement prepared under the conditions of Example 4, - containing no additives (control), - containing a glycol-type SRA shrinkage reducing agent at a concentration of 2% by mass relative to the total mass prepared under the conditions of Example 4 or - containing calcined dolomite according to the invention at a temperature of 2000 °C (D2000) in a content of 5% by mass relative to the total mass of cement and a glycol-type shrinkage reducing agent SRA in a content of 2% by mass relative to the total mass prepared under the conditions of Example 4.

[0071] Figure 15 represents the evolution of expansion / shrinkage in pm / m under drying conditions as described in example 4 as a function of time of a "self-leveling undercoat" type composition: - containing calcined dolomite according to the invention at a temperature of 2000 °C (D2000) in a content of 5% by mass relative to the total mass of cement prepared under the conditions of Example 4, - containing no additives (control), - containing a glycol-type SRA shrinkage reducing agent at a concentration of 2% by mass relative to the total mass prepared under the conditions of Example 4 or - containing calcined dolomite according to the invention at a temperature of 2000 °C (D2000) in a content of 5% by mass relative to the total mass of cement and a glycol-type shrinkage-reducing agent (SRA) in a content of 2% by mass relative to the total mass prepared under the conditions of the example 4.

[0072] Figure 16 shows the evolution of compressive strength in MPa under the conditions described in example 5, 7 days or 28 days after the preparation of a "self-leveling undercoat" type composition: - containing calcined dolomite according to the invention at a temperature of 2000 °C (D2000) in a content of 6% by mass relative to the total mass of cement prepared under the conditions of Example 5, - containing no additives (control), - containing a glycol-type SRA shrinkage reducing agent at a concentration of 2% by mass relative to the total mass prepared under the conditions of Example 5 or - containing calcined dolomite according to the invention at a temperature of 2000 °C (D2000) in a content of 5% by mass relative to the total mass of cement and a glycol-type shrinkage-reducing agent (SRA) in a content of 2% by mass relative to the total mass prepared under the conditions of the example 5.

[0073] Figure 17 represents the evolution of expansion / shrinkage in pm / m under endogenous conditions as described in example 5 as a function of time of a "self-leveling underlayer" type composition: - containing calcined dolomite according to the invention at a temperature of 2000 °C (D2000) at a concentration of 5% by mass relative to the total mass of cement prepared under the conditions of example 5, - containing no additives (control), - containing biochar at a content of 6% by mass relative to the total mass of cement prepared under the conditions of example 5, - containing Starvis 3050 F marketed by BASF SE at a concentration of 2.2% by mass relative to the total mass of cement prepared under the conditions of example 5, - containing calcined dolomite according to the invention at a temperature of 2000 °C (D2000) in a content of 6% by mass relative to the total mass of cement and biochar in a content of 6% by mass relative to the total mass of cement prepared under the conditions of Example 5 or - containing calcined dolomite according to the invention at a temperature of 2000 °C (D2000) in a content of 6% by mass relative to the total mass of cement and Starvis 3050 F marketed by BASF SE in a content of 2.2% by mass relative to the total mass of cement prepared under the conditions of Example 5. EXAMPLES Example 1: compositions according to the invention - dolomite calcined at 2000°C

[0074] One of the calcined dolomites 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.

[0075] [Table 1]

[0076] D2000 also has a LOI (loss on ignition, measured by the mass loss after 2h at 1050°C) of 2.6% and a true density (measured with the Ultrapyc 3000 model gas pycnometer) of 3.31.

[0077] 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. Mechanical and shrinkage properties were evaluated on standardized prismatic specimens measuring 40 x 40 x 160 mm, manufactured using molds with three compartments of these dimensions. Measuring devices, called pads, were attached to the ends of each mold compartment and subsequently positioned at the ends of the specimens once the mortar had set. These pads allow for the installation of the shrinkage meter sensors to facilitate measurements (Reference shrinkage pad: LPLOT-4x4x16 from the company "Recherches et Réalisations Remy").

[0078] 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 specimens stored in water at 20°C.

[0079] 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 for each test specimen. The EN 196-1, 2016 standard recommends the use of CEN reference sand, the particle size of which is regulated and defined by this same standard (Table 2), and which is sold in 1350 g bags specifically for this purpose.

[0080] [Table 2]

[0081] 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 optionally the additive (calcined dolomite according to the invention) into the mixing bowl, followed by mixing at low speed (rotation: 140 min 1planetary 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. - Resumption of high-speed mixing 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.

[0082] 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.

[0083] Thus, the composition used per batch is as follows: - CEM I 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)

[0084] Table 3 below presents the seven formulations that were tested under each of the three conditions:

[0085] [Table 3]

[0086] The use of control samples (control: comparative example 1) is essential to evaluate the effectiveness of the compensation for the shrinkage of the compositions according to the invention incorporating the compound CaMgCh according to the invention.

[0087] Shrinkage was monitored using the 3R Mixed Deformometer, in accordance with standard NF P15-433, 2023, under three distinct experimental conditions: endogenous, underwater, and drying. Under endogenous conditions, mortar samples were demolded 8 hours after pouring, wrapped in aluminum foil, and then stored at 20°C with 50% relative humidity. For underwater conditions, mortar samples were fully immersed in water at 20°C immediately after demolding, 8 hours after pouring. Finally, for drying conditions, mortar samples were demolded after 8 hours and stored at 20°C with 50% relative humidity.

[0088] The results are presented in figures 1 to 3.

[0089] In addition to monitoring shrinkage, an evaluation of mechanical properties, more specifically of resistance to bending and compression, was carried out according to the EN 196-1, 2016 standard using the 250 / 15 KN automatic compression machine of Class A and 1 from the company Controlab.

[0090] The results are presented in figures 4 and 5.

[0091] In light of the results obtained, the CaMgCh 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 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 in any way, and in some cases, may even have a positive impact. - dolomite calcined at 1500°C

[0092] Dolomite calcined at 1500 °C 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 1500 °C. It will be referred to as D1500 in the remainder of this example.

[0093] D1500 also has a LOI (loss on ignition, measured by the mass loss after 2h at 1050°C) of 3.7% and a true density (measured with the Ultrapyc 3000 model gas pycnometer) of 3.22.

[0094] Table 4 below presents the three formulations that were subsequently tested.

[0095] [Table 4] Example 2: Comparison of the dolomites according to the invention (D2000 and D1500) with compositions containing MgO, CaO or a mixture of MgO+CaO or dolomite calcined at 1000 °C or 1300 °C

[0096] Dolomites calcined at 1000 °C (D1000) or 1300 °C (D1300) have the same composition as that indicated in Table 1 above. The only difference compared to the calcined dolomite according to the invention is their calcination temperature, which is only 1000 °C or 1300 °C.

[0097] D1000 also has a LOI (loss on ignition, measured by mass loss after 2h at 1050°C) of 7.1% and a true density (measured with the Ultrapyc 3000 gas pycnometer) of 3.06. D1300 has a LOI (loss on ignition, measured by mass loss after 2h at 1050°C) of 4.6% and a true density (measured with the Ultrapyc 3000 gas pycnometer) of 3.15.

[0098] The MgO used in the comparative example compositions is a mineral powder resulting from the calcination of a magnesite-rich ore (MgCOs) at a temperature of 1000°C (M1000). This thermal transformation aims to produce magnesium oxide, accompanied by the release of carbon dioxide (CO2), according to the reaction: MgCOs + Calcination temperature → MgO + CO2

[0099] Table 5 below shows the chemical composition of the magnesium used, in percentages by mass relative to the total mass of magnesium.

[0100] [Table 5] Tl

[0101] The CaO used in the comparative example compositions corresponds to a mineral powder resulting from the calcination of a calcium carbonate-rich ore (CaCCh) at a temperature of 1000°C (C1000). 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

[0102] Table 6 below shows the chemical composition of the quicklime used, in percentages by mass relative to the total mass of quicklime.

[0103] [Table 6]

[0104] The performance of the formulations incorporating CaMgU2 according to the invention (D2000 and D1500) 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) or at 1300°C (D1300) (comparative examples 2 and 6).

[0105] Referring to Example 1, it is observed that the mechanical properties do not undergo major disturbances following the incorporation of CaMgCh 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 performed. Regarding rheological characterization, two distinct experimental protocols were executed: determination of setting time and performance of the slump test.

[0106] In the context of monitoring deformation (whether shrinkage or swelling), monitoring was carried out on several formulations, including a control group (Table 7) as well as additions of C1000, M1000, D1000, D1300, D1500 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, 2c, 6a, 6b and 6c).

[0107] Table 6 thus presents the constituents of the standardized mortars tested in grams.

[0108] [Table 7]

[0109] Regarding the determination of setting time, the experiments were carried out in accordance with standard NF P15-431, 1994. The slump test was performed using a 15 cm high cone. Both setting time and slump testing were performed using the formulations presented in Table 8 below (as a percentage by mass relative to the total mass of cement or in grams).

[0110] [Table 8] [YES] The shrinkage phenomenon was monitored on three samples for each formulation, at each percentage addition level. The average of the measurements of these three samples is shown in Figures 6 and 7, illustrating the progression of deformation (whether shrinkage or expansion) over time for the various formulations studied.

[0112] 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 negatively impact the rheology. Thus, this test offers the advantage of evaluating the impact of the additive on 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.

[0113] 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 9 below.

[0114] [Table 9]

[0115] In addition to the initial measured subsidence, Figures 8 and 9 show the evolution of this subsidence in cm as a function of time in minutes. [Setting time: Similar to the slump test, setting time evaluation can be used to assess the reactivity of additives incorporated into 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.]

[0117] In this perspective, monitoring of the setting time of the different formulations according to the standard EN 480-2, 2006 (using the Vicat manual prisometer from the company Recherches et Réalisations Remy and a mold with dimensions: Height: 40 mm; inner diameter of the top: 70 mm; inner diameter of the bottom: 80 mm) was carried out until all reached the stage of complete setting.

[0118] Figures 10 and 11 show the times required to reach the beginning and end of setting for the different formulations. [01191Conclusion: 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.

[0120] Furthermore, all formulations containing calcined dolomite show, after 28 days, a lower shrinkage than the control formulation without additive.

[0121] At a constant calcination temperature, increasing the addition rate (from 4% to 6%) consistently improves shrinkage reduction, suggesting a positive influence of the dosage. However, while the dosage plays a role, it is primarily the calcination temperature that determines the effectiveness of the compensation: dolomites calcined at temperatures of 1500°C or higher show the most significant performance in limiting shrinkage, even swelling.

[0122] In terms of settling, a smaller initial decrease compared to the control formulation could indicate an increasingly vigorous reaction, potentially exacerbating the negative impact of adding this additive on 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 rheology. Indeed, the initial settling of the formulation containing C1000 is almost half that of the control formulation. In contrast, the formulation using D2000 (example 6) offers a dual advantage, compensating for shrinkage without any noticeable effect on rheology.

[0123] The results presented in Figure 9 show that dolomites calcined at temperatures of 1500 °C or higher preserve a The mixture had a good consistency compared to the control. However, those calcined at lower temperatures tended to reduce slump, indicating a loss of fluidity and an increase in the mortar's rigidity.

[0124] 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 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 rheology similar to that of the control formulation.

[0125] The results shown in Figure 11 indicate that formulations containing dolomite calcined at temperatures of 1500 °C or higher exhibit a setting time similar to that of the control, suggesting a negligible influence of the additive on the rheology of the mixture. Conversely, dolomites calcined at lower temperatures result in a marked decrease in the initial and final setting times, reflecting a significant effect on the rheology.

[0126] These various results clearly demonstrate that the use of the compound CaMgCh calcined at high temperature (at a temperature of 1500 °C or higher) is particularly advantageous as an expansive additive for mortars or concretes. These results are significantly superior to those obtained using dolomite calcined at lower temperatures (1000 °C: D1000 and 1300 °C: D1300), or to the combination of CaO and MgO (C1000 + M1000), or even to CaO (C1000) or MgO (M1000) taken separately. Example 3: “Self-Leveling Underlayment” (SLU) type formulation.

[0127] The tested formulation is detailed in Table 10 below. The preparation process is identical to that of Example 1.

[0128] [Table 10] (1) Polycarboxylate-based superplasticizer (PCE - PolyCarboxylate Ether) (MasterGlenium SKY 800 marketed by Master Builders Solutions).

[0129] The formulation without calcined dolomite (control) and the formulation with 6% by mass of D1000, D1300, D1500 or D2000 cement were tested in a smear test.

[0130] The slump test (also called the "flow test") is different from the slump test. Both tests are used to evaluate the consistency of concrete or mortar, but they do not apply to the same types of mixtures.

[0131] The slump test is used for plastic mixes, that is, mixes with a certain degree of stability. It consists of filling a truncated cone, then removing it vertically to measure the height of the concrete's slump under its own weight.

[0132] The slump test, on the other hand, is suitable for fluid or very fluid mixtures, such as certain self-compacting mortars or highly permeable concretes. It does not measure height but rather the diameter of the material's spread on a flat plate after lifting the cone. It thus provides an indication of the mixture's ability to flow without vibration.

[0133] The results are shown in Figure 12.

[0134] Conclusion: The graph presented illustrates the evolution of the spread (expressed in centimeters) over time (8, 45, and 90 minutes) for different mortar formulations. These formulations incorporate dolomites calcined at various temperatures (1000°C, 1300°C, 1500°C, and 2000°C). To evaluate the impact of adding these dolomites on the rheology of the mixture, a control formulation, containing no dolomite, was used as a comparative reference.

[0135] Dolomite calcined at the lowest temperature (1000°C) induces the greatest reduction in spread compared to the control, indicating a significant loss of fluidity. This influence gradually decreases with increasing calcination temperature: dolomite calcined at 1300°C shows a moderate impact, followed by dolomite calcined at 1500°C, whose effect is even less pronounced. [0136JII It is particularly noteworthy that, from a calcination temperature of 1500°C or higher, the impact of adding dolomite on reducing slump becomes less and less significant. With dolomite calcined at 2000°C, the mortar slump is very close to that observed for the control formulation, reflecting almost identical rheological behavior.

[0137] This trend indicates that the calcination temperature plays a crucial role in the physicochemical properties of dolomite, in turn affecting its interaction with the cementitious matrix. These results demonstrate that using highly calcined dolomites (> 1500°C) limits, or even eliminates, the negative impact on mortar workability. Example 4: Combined effect between a dolomite according to the invention and a shrinkage reducing agent (SRA).

[0138] The same Self-Leveling Underlayment (SLU) formulation as in Example 3 was used, varying only the type of additive incorporated. Four formulations were studied: a control formulation without additive, a formulation containing 5% D2000 (as a percentage of cement mass), another containing 2% glycol-type SRA, specifically hexylene glycol (Glycolic Shrinkage Reducing Agent (SRA), Brand Name: Serenis; Supplier: Chryso) (as a percentage of total mass), and finally a combined formulation incorporating both 5% D2000 (as a percentage of cement mass) and 2% glycol-type SRA, specifically hexylene glycol (Glycolic Shrinkage Reducing Agent (SRA), Brand Name: Serenis; Supplier: Chryso) (as a percentage of total mass).

[0139] The compressive strength of these formulations, according to EN 196-1, 2016, was tested using Controlab's 250 / 15 kN automatic compression machine, Class A and 1. The results are shown in Figure 13.

[0140] The monitoring of shrinkage using the 3R Mixed Deformometer and according to the NF P15-433, 2023 standard was carried out according to two distinct experimental modalities: endogenous and drying under the same conditions as in example 1. The results are presented in figures 14 and 15. [01411Conclusion: The evaluation of mechanical performance shows that the compressive strength of the control formulation (without the addition of dolomite or SRA) is systematically superior to that of the formulation containing only SRA, and remains slightly superior to or equivalent to that of the formulations incorporating dolomite alone (D2000), regardless of the measurement age.

[0142] However, it is particularly noteworthy that combining dolomite calcined at 2000°C with SRA generates a significant synergistic effect. This combination allows the compressive strength of the control formulation to be reached, or even exceeded, at all test intervals. The observed increase is on the order of 15%, highlighting a notable enhancement of mechanical properties thanks to this combination.

[0143] In terms of physicochemical behavior, particularly with regard to shrinkage, this coupling does not cause any detrimental effects. On the contrary, it helps to improve shrinkage compensation capacity, which is a major advantage for formulations designed to limit dimensional deformations while maintaining, or even improving, mechanical performance.

[0144] These results demonstrate that the combination of highly calcined dolomite (D2000) with a shrinkage reducing agent constitutes an innovative and efficient solution for the optimization of cementitious materials. Example 5: Combined effect between a dolomite according to the invention and a water-retaining agent.

[0145] The same Self-Leveling Underlayment (SLU) formulation as in Example 3 was used, varying only the type of additive incorporated. Six formulations were studied: - a control formulation without additives, - a formulation containing 6% of D2000 (as a percentage of the mass of cement), - another containing 6% biochar (Supplier: La carbonerie; Brand: Carbovia) (as a percentage of the mass of cement), - another containing 2.2% of Starvis 3050 F (water-soluble polymer marketed by BASF SE) (as a percentage of the mass of cement), - a combined formulation incorporating both 6% D2000 (as a percentage of the cement mass) and 6% biochar (Supplier: La Carbonerie; Brand: Carbovia) (as a percentage of the cement mass) and - a combined formulation incorporating both 6% of D2000 (as a percentage of the mass of cement) and 2.2% of Starvis 3050 F (water-soluble polymer marketed by BASF SE) (as a percentage of the mass of cement).

[0146] The compressive strength of these formulations, according to EN 196-1, 2016, was tested using Controlab's 250 / 15 kN automatic compression machine, Class A and 1. The results are shown in Figure 16.

[0147] The monitoring of shrinkage using the 3R Mixed Deformometer and according to the standard NF P15-433, 2023, was carried out according to a distinct experimental modality: endogenous under the same conditions as in example 1. The results are presented in figure 17. [01481Conclusion: Analysis of compressive strength (measured at 7 and 28 days) shows that the control formulation (without additives) exhibits slightly higher or equivalent mechanical strength to the formulation incorporating 6% dolomite calcined at 2000°C. In contrast, the formulation containing 2.2% Starvis consistently shows lower strength than the control. It is nevertheless noteworthy that the isolated addition of biochar maintains comparable mechanical performance.] to those of the control. However, despite this ability to preserve mechanical properties, biochar has a very weak effect on shrinkage compensation, which limits its usefulness when shrinkage reduction is sought.

[0149] However, the results clearly demonstrate a synergistic effect when dolomite D2000 is combined with biochar, or when dolomite D2000 is combined with Starvis 3050F. Specifically, these two combinations not only compensate for the loss of strength observed with the individual additions, but also surpass the compressive strength of the control formulation at both 7 and 28 days. This increase is on the order of 10 to 15% at 28 days.

[0150] These results demonstrate that coupling D2000 dolomite with an organic additive, such as biochar or Starvis, generates a significant mechanical benefit.

[0151] Furthermore, it is important to emphasize that this improvement in mechanical performance is accompanied, according to parallel observations on shrinkage monitoring, by maintained, or even improved, shrinkage compensation efficiency. The D2000 + Starvis combination, in particular, stands out as a high-performance solution that reconciles increased mechanical strength with effective shrinkage control.

Claims

Demands

1. Use of a CaMgCh compound obtained by calcination at a temperature greater than or equal to 1500°C as an expansive additive for mortars or concretes.

2. Use according to claim 1, characterized in that the CaMgCh compound 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 1500 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 compound CaMgCh comprises a CaO / MgO mass ratio 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 CaMgCh 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, concretes used in reservoirs, ready-mix concretes, architectural concretes, self-placing concrete, shotcrete, concrete made from recycled aggregates, shrinkage-joint-free concretes for industrial slabs, repair mortars, sealing and anchoring mortars, packing mortars, screeds or leveling compounds.

9. Concrete or mortar composition comprising the CaMgCh compound obtained by calcination at a temperature greater than or equal to 1500°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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