Method of producing a hydraulic cement composition

Abstract

A method of producing a hydraulic cement composition, comprising - providing a raw material that comprises > 18 wt.-% kaolinite, ≥ 15 wt.-% calcite and a combined content of muscovite and illite of < 20 wt.-%, - calcining the raw material to obtain a pozzolanic material, - mixing the pozzolanic material with Portland cement clinker so that the cement composition comprises > 50 wt.-% of the pozzolanic material and < 45 wt.-% of the Portland cement clinker.

Description

[0001] Method of producing a hydraulic cement composition

[0002] The invention refers to a method of producing a hydraulic cement composition . Further, the invention refers to a hydraulic cement composition .

[0003] Cement production is one of the most signi ficant sources of anthropogenic carbon dioxide ( CO2 ) emissions , accounting for approximately 7- 8 % of global CO2 emissions . This is primarily due to the fact that the production of traditional Portland cement involves the calcination of limestone ( calcium carbonate ) , a process that releases a signi ficant amount of CO2 • Furthermore , the energy-intensive nature of cement production, which often involves burning fossil fuels , contributes additional CO2 emissions .

[0004] Low-carbon cements , also known as green or sustainable cements , have been developed to address these environmental concerns . These types of cements aim to signi ficantly reduce the carbon footprint associated with cement production . This is achieved by altering the composition and manufacturing process of the cement , in order to decrease the amount of CO2 produced per unit of cement produced .

[0005] One of the main ways in which low-carbon cements achieve this reduction is by replacing some of the clinker with other materials . Examples of such substitutions include the use of industrial byproducts such as fly ash and slag, as well as naturally occurring materials like poz zolana, or calcined clays . An example of a low-carbon cement is the Limestone Calcined Clay Cement ( LC3 ) , a composite binder comprising clinker, calcined clay, limestone , and gypsum . However, the practical implementation of low-carbon cement production based on calcined clay presents several challenges . Foremost among these is the requirement for the raw clay used to produce the calcined clay component of the cement to have a high content of kaolinite , typically no less than 40% . Unfortunately, it is not uncommon to encounter clay materials with kaolinite contents below this threshold, typically not exceeding 25% . This low percentage makes them unsuitable for the production of low-carbon cement under conventional conditions .

[0006] Kaolinite has a layered silicate structure , composed of alternating layers of tetrahedral sheets of silica and octahedral sheets of alumina linked with each other by oxygen atoms . When kaolinite is heated during the calcination process , a sequence of reactions occurs leading to the dehydroxylation ( loss of water ) and trans formation of the kaolinite into an amorphous material known as metakaolin .

[0007] Metakaolin is highly reactive in a cementitious environment . It reacts with calcium hydroxide (produced during the hydration of Portland cement ) in a process known as poz zolanic reaction, forming calcium silicate hydrates ( C-S- H) , calcium aluminate hydrates and calcium aluminate silicate hydrates . All these products contribute signi ficantly to the compressive strength of the cement . They are the main binders in concrete and responsible for the strength development . The greater the volume of binders produced, the higher the compressive strength of the resulting cementitious matrix . Therefore , a higher kaolinite content , which leads to more metakaolin, allows for more binder formation and results in higher compressive strength . Thus, the requirement for high kaolinite content in the clay used for low-carbon cement production is tied directly to the contribution of the resulting metakaolin to the mechanical performance of the cement, particularly its compressive strength. Using clay with a lower kaolinite content without compensating for the decrease in reactivity could lead to a drop in the cement's mechanical performance.

[0008] One potential solution to this problem was proposed in FR 3084665 Bl. The patent suggests the use of clay with a kaolinite content of less than 25%, but with a significant amount of muscovite and / or illite, constituting at least 20%, to make a cementitious material. However, when the cementitious material produced in this manner is used in a cement formulation where the Portland cement (CEM I) component is less than 70%, the mechanical performance of the resulting composite cement suffers a significant decrease. This substantial drop in performance prevents the production of a low-clinker or low-CEM I cement with acceptable performance characteristics using such clay materials.

[0009] The amount of cement that can be replaced depends on the physico-chemical properties and the availability of supplementary cementitious materials (SCMs) . Among the various SCMs available, blast furnace slag is the only material that can be used alone as the main constituent for the formulation of cements (CEM III / B) with a very low clinker factor (0.2-0.35) and achieving a strength class of 42.5 N, according to EN 197-1:2011. The world-wide availability of blast furnace slag is estimated to be around 5-10% of the annual cement production. Therefore, there is a strong need for alternative sources of cementitious material that are abundantly available in the world and can reduce the clinker factor in cement to <0.45, preferably <0.40 with a strength class of 42.5 N.

[0010] The present invention therefore aims to enable the production of a low-carbon cement that minimizes the clinker factor and can achieve a strength class of 42.5N.

[0011] To solve this object, the invention provides a method of producing a hydraulic cement composition, comprising providing a raw material that comprises > 18 wt.-% kaolinite, > 15 wt.-% calcite, preferably > 15 wt.-% calcite, and a combined content of muscovite and illite of < 20 wt.-%, calcining the raw material to obtain a pozzolanic material , mixing the pozzolanic material with Portland clinker so that the hydraulic cement composition comprises > 50 wt.-% of the pozzolanic material and < 45 wt.-% of the Portland clinker .

[0012] The invention is based on the surprising finding that it is possible to produce cement with a strength class of 42.5 N according to EN 197-1 2011 with a clinker factor of < 0.45, preferably 0.30-0.40, using a pozzolanic material present in an amount of more than 50% of the cement composition.

[0013] The pozzolanic material is produced by calcining a raw material having a relatively low kaolinite content, so that a wide range of naturally occurring raw materials can be used. In particular, it has been found that the raw material must have certain minimum amounts of kaolinite and calcite and a maximum amount of muscovite and illite in order to obtain a pozzolanic material by calcining the raw material, said pozzolanic material having sufficient reactivity to achieve a strength class of 42.5N at a low clinker content. According to the invention, the raw material shall comprise > 18 wt.-% kaolinite, > 15 wt . % calcite, preferably > 15 wt.-% calcite, and a combined content of muscovite and illite of < 20 wt.-%.

[0014] According to a preferred embodiment, the raw material comprises > 20 wt.-%, preferably > 25 wt.-%, calcite.

[0015] According to a preferred embodiment, the raw material comprises > 25 wt.-%, preferably > 30 wt.-%, kaolinite.

[0016] The upper limit for the calcite content of the raw material is preferably 30 wt.-%.

[0017] As to the kaolinite content, a preferred embodiment provides that the raw material comprises < 40 wt.-% kaolinite.

[0018] Preferably, the raw material comprises a combined content of muscovite and illite of 10-20 wt.-%.

[0019] For the purpose of the invention, the pozzolanic material may be obtained by either calcination of natural marl and / or natural marlstone alone or by combined co-calcination of natural marl / marlstone with kaolinitic clay. In the embodiment when marl and / or marlstone is co-calcined with clay, the mixture of natural marl / marlstone and kaolinitic clay may preferably comprise 35-55 wt.-% natural marl / marlstone and 45-65 wt.-% kaolinitic clay.

[0020] Kaolinitic clay is understood to refer to a clay that has a kaolinite content of at least 40 wt.-%, preferably at least 50 wt . -% . Natural marl or marlstone is a carbonate-rich mud or mudstone which contains variable amounts of clays and silt. Naturally occurring marl / marlstone can have different mineralogical compositions, but for the purpose of the instant invention the marl / marlstone when used as the only component of the raw material, shall comprise > 18 wt.-% kaolinite, > 15 wt.-% calcite, preferably > 15 wt.-% calcite, and a combined content of muscovite and illite of < 20 wt.-%. In addition, natural marl or marlstone may preferably have a quartz content of 15-35 wt.-%.

[0021] In a preferred embodiment, the natural marl / marlstone suitable for the invention has a chemical composition comprising the following compounds:

[0022] SiO235 - 45 wt.-%

[0023] A12O36 - 15 wt.-%

[0024] Fe203 2 - 5 wt.-%

[0025] CaO 15 - 30 wt.-% the rest comprising LOI (loss on ignition) and compounds including MgO, K2O, Na2O, SO2, TiO2, Mn2O3, P2O5, Cr2O3, ZrO2and SrO.

[0026] Any content of kaolinite, illite, muscovite, and calcite or any other mineral phase indicated in wt.-% are measured by QXRD Rietveld method. Quantitative X-ray diffraction (XRD) measurements were made of powdered samples which were hand ground to pass a 63 pm sieve. A D8 Advance X-ray Diffractometer from Bruker was used which was operated using Cu Ka radiation at an acceleration voltage of 25 kV and a current of 40 mA, scanning at 20 range of 3-65°, with 4336 steps and a counting time of 0.135 s per step, rotation of the sample. The quantification of the phases present in the samples was achieved by Rietveld refinement using Topas Academic v6 software. The chemical composition was measured by X-ray Fluorescence (XRF) .

[0027] The step of calcining the raw material is carried out in such a way as to obtain a pozzolanic material, i.e. a material with pozzolanic properties. Such material is characterized by having little or no cementitious value but which, in finely divided form and in the presence of water, reacts chemically with calcium hydroxide at ordinary temperatures to form compounds with cementitious properties.

[0028] According to a preferred embodiment of the invention, calcining the raw material is performed at a temperature of 700-900°C in order to obtain a pozzolanic material. The calcination at said temperature is carried out in order to have the kaolinite component of the raw material at least partially transform to metakaolin. Preferably, the calcination step is carried out so that at least 70 wt.-% of the kaolinite has completely transformed into metakaolin. Preferably, the co-calcination of the raw material should not be done at a temperature above 900°C as this would lead to the production of a dead-burnt material that has less pozzolanic reactivity. Preferably, the calcination step is carried out at a temperature of 700-900°C over a time period of 15-240 minutes, preferably at a temperature of 700-900°C over a time period of 15-180 minutes, even more preferably at a temperature of 700-900°C over a time period of 60-180 min.

[0029] The calcination step preferably results in that the pozzolanic material comprises an amorphous phase in an amount of > 20 wt.-%, preferably > 28 wt.-%. Further, the pozzolanic material may preferably have a calcite content of < 12 wt.-%, preferably < 5 wt.-%, more preferably < 2 wt.-%.

[0030] Several prior art methods may be used for calcining the raw material, with the choice of the method being determined by factors such as the scale of production, the specific nature of the raw materials, and the desired characteristics of the final product.

[0031] According to one alternative a rotary kiln calcination is carried out. This involves feeding the raw material into a rotating cylindrical furnace, where it is heated to the desired temperature range of 700-900°C. The rotation of the kiln ensures thorough mixing and even heating of the material, promoting consistent and efficient decarbonation of the calcium oxide source, such as limestone, and dehydroxylation of the clay minerals.

[0032] Alternatively, a vertical shaft kiln may be used for calcination. The raw material is loaded at the top of a tall, vertical furnace and heated as it descends through the kiln, undergoing the necessary chemical transformations.

[0033] Alternatively, a fluidized bed calcination may be used, which is a method wherein the raw material is suspended in a rising flow of hot gas. This ensures very high heat and mass transfer rates, providing rapid, uniform calcination.

[0034] According to a preferred embodiment of the invention, the raw material, before being subjected to the step of calcining, is ground to a particle size characterized by a D90 < 200pm, preferably < 100pm. This enhanced surface area facilitates more efficient heat transfer and chemical interactions during the calcination process, leading to more effective dehydroxylation of clay minerals.

[0035] The D90 corresponds to the 90th centile of the volume distribution of particle sizes, i.e. 90% of the volume consists of particles for which the size is less than the measured value. The D90 of particles is generally determined by laser diffraction. The particle size distribution of the different powders are obtained with a laser Malvern MS2000 granulometer . The measurement is carried out in a suitable medium (for example, in an aqueous medium) ; the size of the particles should be comprised between 0.02 pm and 2 mm. The light source consists of a red He-Ne laser (632 nm) and a blue diode (466 nm) . The optical model is the Fraunhofer one, the computation matrix is of the polydisperse type.

[0036] A measurement of background noise is first of all carried out with a pump rate of 2,000 rpm, a stirring rate of 800 rpm and a measurement of noise over 10 s, in the absence of ultrasonic waves. It is then checked that the light intensity of the laser is at least equal to 80%, and that a decreasing exponential curve is obtained for the background noise. If this is not the case, the lenses of the cell have to be cleaned. A first measurement is then carried out on the sample with the following parameters: pump rate of 2,000 rpm, stirring rate of 800 rpm, absence of ultrasonic waves, obscuration limit between 10 and 20%. The sample is introduced in order to have an obscuration slightly greater than 10%. After stabilization of the obscuration, the measurement is carried out with a duration between the immersion and the measurement set to 10 s. The measurement duration is of 30 s (30,000 analyzed diffraction images) . In the obtained granulogram, the fact that a portion of the population of the powder may be agglomerated should be taken into account .

[0037] Next, a second measurement (without emptying the tank) is carried out with ultrasonic waves. The pump rate is brought to 2,500 rpm, the stirring to 1,000 rpm, the ultrasonic waves are 100 % emitted (30 Watts) . This rate is maintained for 3 minutes, and then one returns to the initial parameters: pump rate 2,000 rpm, stirrer rate of 800 rpm, absence of ultrasonic waves. After 10 s (for removing the possible air bubbles) , a measurement is made for 30 s (30,000 analyzed images) . This second measurement corresponds to a powder deagglomerated by ultrasonic dispersion. Each measurement is repeated least twice in order to check the stability of the result. The apparatus is calibrated before each working session by means of a standard sample (silica CIO Sifraco) the grain size curve of which is known. All the measurements shown in the description and the announced ranges correspond to the values obtained with ultrasonic waves.

[0038] As mentioned before, the invention allows achieving a high clinker substitution rate, wherein the hydraulic cement composition comprises > 50 wt.-% of pozzolanic material and < 45 wt.-% of Portland clinker. Preferably, the hydraulic cement composition comprises > 50 wt.-% of the pozzolanic material and only 30-40 wt.-% of the Portland clinker.

[0039] Preferably, the hydraulic cement composition comprises > 60 wt.-% of the pozzolanic material, such as 60-70 wt.-% pozzolanic material, and 30-40 wt.-% of the Portland clinker. Preferably, the hydraulic cement composition comprises a minimum content of Portland clinker or 20 wt.-%.

[0040] In order to control the initial rate of reaction of the hydraulic cement composition after the addition of water, a suitable amount of calcium sulfate may be added to the composition. In particular, a source of calcium sulfate is preferably added so that the cement composition comprises 2- 5 wt.-% of the source of calcium sulfate.

[0041] According to a second aspect, the invention provides a hydraulic cement composition, comprising < 45 wt.-% Portland cement clinker, and > 50 wt.-% of a pozzolanic material obtained by calcining a raw material that comprises > 18 wt . - % kaolinite, > 15 wt . % calcite, preferably > 15 wt.-% calcite, and a combined content of muscovite and illite of < 20 wt.-%. Hence, a low-carbon cement is provided that has a reduced clinker content and that, due to the presence of the pozzolanic material, still has an acceptable compressive strength. In particular, the hydraulic cement of the invention has an improved compressive strength when compared to a reference cement that comprises the same amount of pozzolanic material, where the pozzolanic material is calcined clay only.

[0042] Preferably, the hydraulic cement may comprise 20-45 wt.-%, preferably 30-40 wt.-%, Portland cement clinker. The term "Portland cement clinker" refers to a type of hydraulic cement that sets, hardens, and adheres to other materials to bind them together. The primary components of Portland cement clinker are calcium, silicon, aluminum, and iron, which are typically derived from limestone, clay, and other natural materials. These materials are crushed, combined, and heated in a kiln to a high temperature to produce clinker . This clinker is then ground into a fine powder, often with a small amount of gypsum added to control the setting time of the final product .

[0043] In the following, the invention will be described in more detail with reference to the following examples .

[0044] Examples according to the invention

[0045] In the following examples , three di f ferent raw material compositions were used . The raw material is either comprised of natural marlstone alone ( raw material composition 1 ) or comprised of a mixture of raw kaolinitic clay and natural marlstone ( raw material compositions 2 and 3 ) , as shown in Table 1 .

[0046] Table 1 : Raw material compositions according to the invention

[0047] The mineralogical composition of marlstone was determined with the Quantitative X-ray Di f fraction ( QXRD) using the Rietveld method . The chemical composition was measured by X- ray Fluorescence (XRF) . The composition of marlstone used as raw material composition 1 is summari zed in Table 2

[0048] Table 2 : Chemical and mineralogical composition of raw material composition 1

[0049] The Rwp (weighted profile R value ) given in the last line of Table 1 is the value that indicates how good or bad the predicted fitting is as compared to the experimental setting . The lower this value the better the prediction .

[0050] Table 3 discloses the chemical and mineralogical composition of marlstone and kaolinitic clay used to prepare raw material compositions 2 and 3 .

[0051] Table 3 : Chemical and mineralogical composition of natural marlstone and kaolinitic clay used to prepare raw material compositions 2 and 3

[0052]

[0053] The raw materials were calcined under industrial conditions in a rotary kiln at 777 -825° C , which converted the raw materials into pozzolanic materials. Thereby, raw material composition 1 was calcined to obtain pozzolanic material composition 1, raw material composition 2 was calcined to obtain pozzolanic material composition 2, and raw material composition 3 was calcined to obtain pozzolanic material composition 3. The chemical and mineralogical compositions of the pozzolanic compositions 1, 2 and 3 after calcination at 800°C are given in Table 4.

[0054] Table 4 : Chemical composition and mineralogical composition of pozzolanic material 1, 2 and 3

[0055]

[0056] The pozzolanic material compositions 1, 2 and 3 were used to produce a low-clinker cement composition by mixing the pozzolanic material with an Ordinary Portland Cement CEM I 52.5 N, complying with the European Standard EN 197-1.

[0057] Table 5 summarizes the composition of the hydraulic cements according to the invention.

[0058] Table 5: Composition of low-clinker cements

[0059] A standard mortar according to EN 196-1 was produced on basis of the low-clinker cements show in Table 5. The composition of the mortar was 450 g of cement, 225 g of water and 1350 g of sand. Mortar 1 contained a low-clinker cement produced with pozzolanic material composition 1. Mortar 2 contained a low-clinker cement produced with pozzolanic material composition 2. Mortar 3 contained a low-clinker cement produced with pozzolanic material composition 3.

[0060] The compressive strength development of mortars 1, 2 and 3 was measured according to EN-196-1. Fig. 1 shows the compressive strength after 1 days, 7 days and 28 days. As seen in Fig 1, the strength class of 42.5 N as per EN 197-1 can be obtained by replacing CEM I with 62.5% of the pozzolanic material produced by calcining natural marlstone or a mixture of natural marlstone and a kaolinitic clay.

[0061] Comparative examples

[0062] Comparison of low-clinker cements according to the invention with pozzolanic compositions with cements manufactured using common SCMs

[0063] This section compares the performance of cements according to the invention against cements manufactured using common supplementary cementitious materials (SCMs) , namely blast furnace slag and fly ash. The chemical composition of blast furnace slag and fly ash used in this example section is given in Table 6. The slag is mainly amorphous with broad diffraction hump centered around 30° 2theta, while fly ash contains some crystalline phases like mullite (9.5%) , quartz (3.5%) and hematite (0.5%) along with the amorphous phase (83.7%).

[0064] Table 6: Chemical composition [wt.%] of SCMs The compositions of low-clinker cements containing the SCMs of Table 6 are given in Table 7 .

[0065] Table 7 : Composition of low-clinker cements with di f ferent

[0066] SCMs .

[0067] The compressive strength values for mortars manufactured using the cements of Table 7 are summari zed in Table 8 .

[0068] Table 8 : Composition of compressive strength of low-clinker cements

[0069] It can be seen that the low-clinker cements according to the invention achieve higher strength values compared to CEM I I I / B slag-based cements ( OPC / Slag-35% / 65% ) .

[0070] Comparison of low clinker cements according to the invention and cements containing calcined kaolinitic clays having a comparable metakaolin content

[0071] This section compares the performance of cements according to the invention against cements manufactured using common supplementary cementitious materials ( SCMs ) , namely calcined clay . The chemical and mineralogical composition of the clays used in this example section is given Tables 9 and 10 . The chemical and mineralogical compositions were determined by using X-ray Fluorescence (XRF) and Quantitative X-ray Di f fraction ( QXRD) using the Rietveld method, respectively .

[0072] Table 9 : Chemical composition [wt . % ] of the raw material compositions according to the invention and raw clays (prior to calcination)

[0073] Table 10: Mineralogical composition [wt.%] of pozzolanic material compositions according to the invention and calcined clays

[0074] The compositions of low-clinker cements containing the SCMs of Table 10 are given in Table 11.

[0075] Table 11: Composition of low-clinker cements with different

[0076] SCMs .

[0077] Fig. 2 shows the compressive strength of standard mortars (EN 196-1) produced using the cements of Table 11 after 1 days, 7 days and 28 days. As seen in Fig 2, at comparable metakaolin contents, samples with the pozzolanic material composition according to the invention reach higher strength values when compared with samples manufactured with calcined kaolinitic clay .

Claims

Claims :

1. A method of producing a hydraulic cement composition, comprising providing a raw material that comprises > 18 wt.-% kaolinite, > 15 wt.-% calcite and a combined content of muscovite and illite of < 20 wt.-%, calcining the raw material to obtain a pozzolanic material , mixing the pozzolanic material with Portland cement clinker so that the hydraulic cement composition comprises > 50 wt.-% of the pozzolanic material and < 45 wt.-% of the Portland cement clinker.

2. Method according to claim 1, wherein the hydraulic cement composition comprises > 50 wt.-% of the pozzolanic material and 30-40 wt.-% of the Portland clinker.

3. Method according to claim 1 or 2, wherein a source of calcium sulfate is added so that the cement composition comprises 2-5 wt.-% of the source of calcium sulfate.

4. Method according to claim 1, 2 or 3, wherein the raw material comprises or consists of natural marl and / or natural marlstone or a mixture of natural marl / marlstone and kaolinitic clay.

5. Method according to claim 4, wherein the mixture of natural marl / marlstone and kaolinitic clay comprises 35- 55 wt.-% natural marlstone and 45-65 wt.-% kaolinitic clay.

6. Method according to any one of claims 1 to 5, wherein the raw material comprises > 20 wt.-%, preferably > 25 wt.-%, calcite .

7. Method according to any one of claims 1 to 6, wherein the raw material comprises < 30 wt.-% calcite.

8. Method according to any one of claims 1 to 7, wherein the raw material comprises < 40 wt.-% kaolinite.

9. Method according to any one of claims 1 to 8, wherein the raw material comprises a combined content of muscovite and illite of 10-20 wt.-%.

10. Method according to any one of claims 1 to 9, wherein the pozzolanic material comprises an amorphous phase in an amount of > 20 wt.-%, preferably > 28 wt.-%.

11. Method according to any one of claims 1 to 10, wherein the raw material, before being subjected to the step of calcining, arise ground to a particle size characterized by a d90< 200pm, preferably d90< 100pm.

12. A hydraulic cement composition, comprising: a) < 45 wt.-% Portland cement clinker, b) > 50 wt.-% of a pozzolanic material obtained by calcining a raw material that comprises > 18 wt.-% kaolinite, > 15 wt . % calcite and a combined content of muscovite and illite of < 20 wt.-%.

13. Hydraulic cement composition according to claim 12, further comprising 2-5 wt.-% of the source of calcium sulfate .

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