An improved supplementary cementitious materials

Abstract

The invention relates to an improved supplementary cementitious material (SCM), which has favourable properties for being used in cement production. The SCM comprises: SiO2 32 - 46 CaO ≤ 6 Al2O3 4 - 14 MgO ≤ 4 ZnO ≤ 1.5 Na2O ≤ 1.5 Fe2O3 ≤ 10 impurities ≤ 4 FeO* balance, wherein the presence of Fe in all oxidation states is expressed as FeO*. The reactivity of the SCM is 300 -700 J / g SCM, which is the cumulative heat release measured by isothermal calorimetry according to ASTM C1897-20.

Description

[0001] AN IMPROVED SUPPLEMENTARY CEMENTITIOUS MATERIALS

[0002] TECHNICAL FIELD

[0003] The present invention is related to an improved supplementary cementitious material (SCM), which has favourable properties for being used in cement production.

[0004] BACKGROUND TO THE INVENTION

[0005] The production of cement is a major contributor to climate change. It has therefore been a strive to find replacement materials, which have lower CO2 emissions. Such materials are generally referred to as supplementary cementitious materials (SCM). The term “supplementary cementitious material (SCM)” refers to an inorganic material that contributes to the properties of a cementitious mixture through hydraulic or pozzolanic activity, or both. SCM products are known in the art and include ground granulated blast furnace slag (GGBFS), fly ash, copper slag and silica fume. SCM can be used individually with Portland or blended cement or in different combinations.

[0006] The term “pozzolanicity” refers to the SCM material’s hydraulic, and / or pozzolanic activity and relates to the ability of the SCM material to combine with lime in the presence of water and Ca(OH)2 to form a cement. Such activity can be studied by the R3(“Rapid, Relevant and Reliable”) Rilem test, in the following the R3method, in which isothermal calorimetry is used to determine the heat of hydration of hydrating pastes composed of the SCM and calcium hydroxide. The results of this test strongly correlate with the strength of the mortar. The heat of the cement reaction is used to determine the reactivity of the SCM.

[0007] The suitability for use in cement increases with the reactivity. However, a drawback of many of the existing supplementary cementitious materials (SCM's) is that the reactivity is much lower than that of cement. High reactivity SCM's on the other hand have other draw backs like limited availability and / or high costs.

[0008] In addition, the pozzolanic reactivity depends on a number of different parameters with interdependencies such as the degree of crystallinity, glass structure, thermal history, granulometric properties, surface area, chemical composition and the like. Accordingly, it is not a straightforward task to improve the pozzolanic reactivity of a SCM.

[0009] WO2016156394 Al is directed to an improved slag from non-ferrous metal production, which can be used in concrete and / or cement, i.e. a SCM, and discloses a slag composition with an improved hardening rate.

[0010] WO2023052611 Al is directed to a SCM comprising iron silicate and having an amorphous matrix of at least 95 % by weight. The materials in the examples of WO2023052611 Al were tested with an R3method for the cumulative normalized heat produced in 168 hours (7 days). A maximum value of 65 J / g powder was obtained for a slag rich in SiCh.

[0011] JP2018172260 A is directed to a SCM obtained by pulverizing massive copper slag comprising 35 - 55 wt.% Fe2O3 and having a specific surface area of 0.2 - 0.5 m2 / g.

[0012] SUMMARY OF THE INVENTION

[0013] It is an object of the present invention to provide an iron silicate based supplementary cementitious material (SCM) with an improved reactivity expressed as the cumulative heat produced in 168 hours (7 days) by the R3method.

[0014] In this respect, the term “cementitious material” refers to an inorganic material, or a mixture of inorganic materials, that sets and develops strength by the chemical reaction with water by formation of hydrates. Portland cement is the most commonly used cementitious material in industry today. It is defined by the European Standard EN 197-1 as a hydraulic material, which shall consist of at least two-thirds by mass of calcium silicates, (3 CaO SiCE, and 2 CaO SiCE), the remainder consisting of aluminium- and iron-containing clinker phases and other compounds. The ratio of CaO to SiCh shall not be less than 2.0. The magnesium oxide content (MgO) shall not exceed 5.0% by mass.

[0015] DETAILED DESCRIPTION

[0016] The inventors of the present invention have carried out an extensive research program and have found that it is under certain circumstances possible to improve the pozzolanic reactivity of an iron silicate based SCM by carefully controlling the chemical composition of the SCM and subjecting the SCM to a specific treatment. Surprisingly, an unsurpassed pozzolanic reactivity as determined by the R3method could be obtained.

[0017] The chemical composition of the SCM has to be controlled within the limits set out in the independent claim.

[0018] The importance of the separate constituents and their interaction with each other as well as the limitations of the ingredients of the claimed SCM are briefly explained in the following. All percentages for the chemical composition of the SCM are given in weight % (wt. %) throughout the description. The amounts of the microstructural constituents are given in volume % (vol. %).

[0019] The broadest aspect of the invention is set out in claim 1. The inventive idea is valid for the whole scope of claim 1. Upper and lower limits for one or more of the chemical constituents may be freely combined within the limits set out in claim 1 in order to form a more limited range for the one or more elements. This may be necessary in order to delimit the invention over the prior art. Accordingly, multiple combinations are expressly allowable for all constituents defined in claim 1 and there is no need or pointer for a certain combination, because such a combination solely leads to a limitation of the scope of protection and not to a new invention. It is also allowable to form a new range for an element by the combination of two different values of an upper range or by the combination of two different values of a lower range.

[0020] The arithmetic precision of the numerical values can be increased by one or two digits for all values given in the present application. Hence, a value reported as e.g. 0.1 % can also be expressed as 0.10 or 0.100 %.

[0021] The starting material used for producing the inventive supplementary cementitious material may be based on a ferro silicate slag but it is also possible to mix different starting materials to obtain the desired composition. Iron-rich ferro silicate slags originate for instance from copper and lead production. The composition of these slags varies considerably depending on the starting materials, which may be ore or scrap. The inventive SCM can be produced by modifying the composition of a copper slag to fall within the limits set out in the independent claim.

[0022] The supplementary cementitious material may contain conventional residual elements or impurities, which are not intentionally added but originate from the raw materials, the refractories or from the atmosphere during the processing. The term impurities includes all type of impurities such as metals, non-metals, oxides and sulphides.

[0023] The effect of the different oxides on the slag structure, the viscosity, the crystallization during cooling and on the reactivity is intricate in that it would appear that there exists a complex relationship between the individual components, which is not fully understood.

[0024] The limits for the individual constituents set out in this application are based on an extensive theoretical analysis and experimental work to understand the dependency between the parameters that influences properties but the applicant does not want to be bound of theory concerning the effect of the different constituents.

[0025] The limits of the constituents are set out below (wt.%):

[0026] SiO2

[0027] SiO2is the main net-work former and is necessary for obtaining an amorphous matrix. The lower limit is 32 % and may be set to 33, 34, 35, 36, 37, 38, 39 or 40 %.

[0028] The upper limit is 46 % and may be set to 45, 44, 43 or 42 %.

[0029] FeO*

[0030] FeO* constitutes the balance in the ferro silicate slag, wherein the presence of Fe in all oxidation states is expressed as FeO*. The content of FeO* should preferably be balanced to the content of SiO2in order to obtain a desired ratio of FeO* / SiO2.

[0031] It should preferably be balanced to the content of SiO2in order to obtain a desired ratio of FeO* / SiO2. The amount of FeO* is preferably in the range of 35 - 51 %. FeiOs

[0032] The amount of Fe2O3 should be low. The maximum content is 10 % and may be set to 9, 8, 7, 6, 5, 4, 3, 2 or 1 %. The reason for restricting the amount of Fe2O3 is related to the fact that Fe2C>3 may lead to an undesired crystallisation, which reduces the reactivity of the SCM. Further possible effects of high amounts of Fe2<)3 may be an undesirable high polymerization of the glassy amorphous phase and possibly a lower reactivity due to passivation of the surface of the SCM.

[0033] FeO* / SiO2

[0034] The ratio FeO* / SiO2 is 0.7 - 1.7 and should preferably be 0.76 - 1.37. A low ratio increases the propensity to form tridymite and cristobalite upon cooling. A high ratio increases the propensity to precipitate fayalite and / or spinel during cooling. Accordingly, the ratio can be used in order to avoid or minimize the amount of precipitates in the amorphous matrix.

[0035] The lower limit may be 0.8, 0.85, 0.9 or 0.95. The upper limit may be 1.35, 1.3, 1.25, 1.2, 1.15, 1.1 or 1.05.

[0036] CaO

[0037] CaO is generally considered as a chain breaking element that causes depolymerization of the slag. However, the experimental results indicate that CaO may have a negative effect on the reactivity.

[0038] The lower limit is 0 % and may be set to 0.5, 1, 1.5, 2, 2.5 or 3 %.

[0039] The upper limit is 6 % and may be set to 5.5, 5, 4.5, 4, 3.5 or 3 %.

[0040] AI2O3

[0041] The effect of AI2O3 is not fully understood but the results of the extensive experimental program performed by the applicant indicate that a fairly high content of AI2O3 could be beneficial to the reactivity, possibly by increasing the amorphous content in the quenched material and / or to increase the polymerization of the liquid slag.

[0042] The lower limit is 4 % and may be set to 4.5, 5, 5.5, 6, 6.5, 7, 7.5 or 8 %.

[0043] The upper limit is 14 % and may be set to 13.5, 13, 12.5, 12, 11.5, 11, 10.5, 10, 9.5 or 9 %.

[0044] MgO

[0045] MgO may enter the slag from chrome-magnesite and other MgO containing refractories used.

[0046] The effect of MgO and its impact on reactivity is not fully understood. The lower limit is 0 % and may be set to 0.5, 1 or 1.5 %.

[0047] The upper limit is 4 % and may be set to 3.5, 3, 2.5 or 2 %.

[0048] ZnO

[0049] The upper limit is 1.5 % and may be set to 1.4, 1.3, 1.2, 1.1, 1.0, 0.95, 0.9, 0.85 or 0.8 %.

[0050] Na2O

[0051] Na2O is a flux that heavily reduces the viscosity of the molten slag as well as the melting temperature and is therefore an undesired component in the present invention.

[0052] The upper limit is 1.5 % and may be set to 1.4, 1.3, 1.2, 1.1, 1.0, 0.95, 0.9, 0.85 or 0.8 %.

[0053] Impurities

[0054] The supplementary cementitious material may contain conventional residual elements or impurities, which are not intentionally added but originate from the raw materials, the refractories or from the atmosphere during the processing. The term impurities include all type of impurities such as metals, non-metals, oxides and sulphides. Accordingly, a nonlimiting list of impurities embraces: MnO, K2O, Cr2Os, Cu2O, Sb20s, Pb2Os, TiO2, P2Os, SO3, S and Cu as well as the elements As, Bi, Cd, Hg, Ni, Mo, V, Zr, Ba, Sr and / or the compounds thereof. The upper limit is 4 % and may be set to 3.5, 3, 2.5, 2, 1.5 or 1 %.

[0055] However, for environmental reasons and / or for improving the Cu recovery, it may be beneficial to restrict the upper limit of S to 1.0 %. The upper limit may be set to 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3 or 0.2 %.

[0056] The chemical composition was determined by X-ray fluorescence (XRF) spectrometry on pressed powder samples. Powder X-ray (XRD) diffraction was used to determine the mineralogical composition of the material.

[0057] The fraction of amorphous material in the samples was determined using Rietveld powder X- ray diffraction (XRD) with an internal standard of calcite (99.5 % CaCOfl.

[0058] The specific surface area of the powder was determined by the Brunauer, Emmett and Teller (BET) method. The BET surface area is generally in the range of 0.5 - 2.5 m2 / g. The lower limit may be set to 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5 or 1.6 m2 / g. The reactivity assessment was made by the R3method as the cumulative heat release measured by isothermal calorimetry after 168 h according to ASTM Cl 897-20.

[0059] The SCM material of the present invention has been shown to exhibit a high pozzolanic reactivity. Herein, term “pozzolanic reactivity” refers to the SCM material’s hydraulic, and / or pozzolanic activity and relates to the ability of the SCM material to combine with lime in the presence of water and Ca(OH)2 to form a cement.

[0060] In the present application the reactivity of the SCM is determined by using the standard test method for measuring the cumulative heat evolved during 168 h using the Rilem R3isothermal calorimetry method as set out in ASTM C 1897-20.

[0061] The reactivity of the SCM measured as the cumulative heat release measured by isothermal calorimetry after 168 h according to ASTM C1897-20 is 300 -700 J / g SCM. The lower limit may be set to 310. 320, 330, 340, 350, 360, 370 or 380 J / g SCM. The upper limit may be set to 690, 680, 670, 660, 650, 640, 630, 620, 610, 600, 590, 580, 570, 560 or 550 J / g SCM.

[0062] EXAMPLE 1

[0063] A supplementary cementitious material of the present invention was prepared by melting and water granulation followed by milling in a planetary ball mill to BET surface area of 1.04 m2 / g. The milling was performed in a FRITSCH pulverisette 7 planetary mill equipped with eighteen 45 mL tungsten carbide grinding balls of 10 mm diameter at 600 RPM.

[0064] The inventive material had the following composition in wt. %:

[0065] SiO236

[0066] FeO* 54

[0067] CaO 1

[0068] AI2O3 8

[0069] MgO 1

[0070] FeO* / SiO21.5 The reactivity was measured as the cumulative heat after 7 days (168 hours) by the R3isothermal calorimetry and was found to be 396 J / g SCM. The inventive material was fully amorphous.

[0071] EXAMPLE 2

[0072] A comparative supplementary cementitious material was prepared by melting and water granulation followed by milling in a planetary ball mill to a BET surface area of 1.11 m2 / g. The milling was performed in the same way as for Example 1.

[0073] The material had the following composition in wt. %:

[0074] SiO227

[0075] FeO 64

[0076] CaO 1

[0077] AI2O3 7

[0078] MgO 1

[0079] FeO / SiCh 2.4

[0080] The reactivity was measured as the cumulative heat after 7 days (168 hours) by the R3isothermal calorimetry and was found to be 320 J / g SCM. The material was found to have a crystalline content of 10 % in an amorphous matrix.

[0081] EXAMPLE 3

[0082] The effect of the content of CaO of the supplementary cementitious material on the specific surface area after milling for 15 minutes in a planetary ball mill was examined. The starting material was prepared by melting and water granulation. The milling time was selected for avoiding agglomeration, which tends to occur after additional milling. The milling was performed in the same way as for Example 1.

[0083] Inventive Comparative

[0084] SiO241 36

[0085] FeO* 49 45 CaO 1 10

[0086] AI2O3 8 8

[0087] MgO 1 1

[0088] FeO* / SiO21.2 1.2

[0089] BET (m2 / g) 1.7 1.1

[0090] The results obtained indicate that the comparative slag with the higher content of CaO was more resilient to milling and resulted in a much lower specific surface area than the inventive material.

[0091] The reactivity was measured as the cumulative heat after 7 days (168 hours) by the R3isothermal calorimetry according to ASTM C1897-20 and was found to be 360 J / g SCM for the inventive material and 290 J / g SCM for the comparative material.

[0092] Accordingly, the inventive material was easier to mill and the reactivity assessment measured by the R3method revealed that the inventive material had a higher reactivity.

[0093] EXAMPLE 4

[0094] The effect of the content of AI2O3 of the supplementary cementitious material on the specific surface area after milling for 15 minutes in a planetary ball mill was examined. The milling was performed in the same way as for Example 1. The starting material was prepared by melting and water granulation. The milling time was selected for avoiding agglomeration, which tends to occur after additional milling.

[0095] Inventive Comparative

[0096] SiO233 37

[0097] FeO* 52 58

[0098] CaO 1 1

[0099] AI2O3 13 3

[0100] MgO 1 1

[0101] FeO* / SiO21.6 1.6 BET (m2 / g) 1.1 0.9

[0102] The results obtained indicate that the comparative slag with the lower content of AI2O3 was more resilient to milling and resulted in a lower specific surface area than the inventive material.

[0103] The reactivity was measured as the cumulative heat after 7 days (168 hours) by the R3isothermal calorimetry according to ASTM C1897-20 and was found to be 360 J / g SCM for the inventive material and 240 J / g SCM for the comparative material. The materials were examined by XRD and both materials were found to be fully amorphous.

[0104] Accordingly, the inventive material was easier to mill and the reactivity assessment measured by the R3method revealed that the inventive material had a higher reactivity.

[0105] EXAMPLE 5

[0106] The effect of the contents of iron oxide and silica expressed as FeO* / SiO2 of the supplementary cementitious material on the specific surface area after milling for 15 minutes in a planetary ball mill was examined. The milling was performed in the same way as for Example 1. The starting material was prepared by melting and water granulation. The milling time was selected for avoiding agglomeration, which tends to occur after additional milling.

[0107] Inventive Comparative

[0108] SiO241 26

[0109] FeO* 49 64

[0110] CaO 1 1

[0111] AI2O3 8 8

[0112] MgO 1 1

[0113] FeO* / SiO21.2 2.4

[0114] BET (m2 / g) 1.7 0.7

[0115] The results obtained indicate that the comparative slag with the higher ratio of FeO* / SiO2 was more resilient to milling and resulted in a much lower specific surface area than the inventive material. The materials were examined by XRD and the inventive material was found to have an amorphous content of 98.5 vol. %, whereas the amorphous content of the comparative material was 94.4 vol. %.

[0116] The reactivity was measured as the cumulative heat after 7 days (168 hours) by the R3isothermal calorimetry according to ASTM Cl 897-20 and was found to be 350 J / g SCM for the inventive material and 230 J / g SCM for the comparative material.

[0117] Accordingly, the inventive material was easier to mill and the reactivity assessment measured by the R3method revealed that the inventive material had a higher reactivity.

[0118] EXAMPLE 6

[0119] The effect of the contents of iron oxide and silica of the supplementary cementitious material on the specific surface area after milling for 15 minutes in a planetary ball mill was examined. The milling was performed in the same way as for Example 1. The starting material was prepared by melting and water granulation. The milling time was selected for avoiding agglomeration, which tends to occur after additional milling.

[0120] Inventive Comparative

[0121] SiO236 26

[0122] FeO* 54 64

[0123] CaO 1 1

[0124] AI2O3 8 8

[0125] MgO 1 1

[0126] FeO* / SiO21.5 2.4

[0127] BET (m2 / g) 1.1 0.7

[0128] The results obtained indicates that the comparative slag with the higher ratio of FeO* / SiO2was more resilient to milling and resulted in a lower specific surface area than the inventive material. The materials were examined by XRD and the inventive material was found to be fully amorphous whereas the amorphous content of the comparative material was 94.4 vol. %. EXAMPLE 7

[0129] The effect of the contents of SiO2and CaO of the supplementary cementitious material on the specific surface area after milling for 15 minutes in a planetary ball mill was examined. The milling was performed in the same way as for Example 1. The starting material was prepared by melting and water granulation. The milling time was selected for avoiding agglomeration, which tends to occur after additional milling.

[0130] Inventive Comparative

[0131] SiO235 30

[0132] FeO* 55 51

[0133] CaO 1 10

[0134] AI2O3 8 8

[0135] MgO 1 1

[0136] FeO* / SiO21.6 1.7

[0137] BET (m2 / g) 1.1 1.0

[0138] The results obtained indicates that the comparative slag with the higher content of CaO and lower content of SiO2was more resilient to milling and resulted in a lower specific surface area than the inventive material. The materials were examined by XRD and the inventive material was found to be fully amorphous whereas the amorphous content of comparative material was 97.1 vol. %.

[0139] EXAMPLE 8

[0140] The effect of the specific surface area after milling on the reactivity of the inventive slag of Example 3 was examined by milling the starting material for different times in a planetary ball mill in the interval 0-20 minutes. The milling was performed in the same way as for Example 1. It was found that both the BET surface area and the reactivity increased with increasing milling time and that the cumulative heat after 7 days (168 hours) measured by the R3isothermal calorimetry according to ASTM Cl 897-20 and had a strong linear increase with the specific surface area of the type Y = 83X + 226 (R2= 0.97), wherein Y is the reactivity in J / g SCM and X is the BET area in m2 / g. The investigations performed reveal that the composition need to be controlled within the limits of claim 1 for obtaining a high reactivity. It was also found that the depolymerization of the slag, e.g. by a high content of CaO or a high ratio of FeO* / SiO2, resulted in a slag more difficult to mill and thereby to a lower reactivity. Surprisingly, it was also found that AI2O3 appeared to increase the polymerisation and thereby also the reactivity. These results were used to optimize the composition of the claimed SCM.

[0141] INDUSTRIAL APPLICABILITY

[0142] The improved supplementary cementitious material of the present invention has a high pozzolanic reactivity and is a suitable SCM for replacement of CaO in cement and concrete.

Claims

CLAIMS1. A supplementary cementitious material (SCM) consisting of the following components in weight %:SiO232 - 46CaO < 6AI2O3 4 - 14MgO < 4ZnO < 1.5Na2O < 1.5Fe2C>3 < 10 impurities < 4FeO* balance wherein the presence of Fe in all oxidation states is expressed as FeO*, wherein the reactivity of the supplementary cementitious material (SCM) measured as the cumulative heat release measured by isothermal calorimetry according to ASTM C1897- 20 is 300 -700 J / g SCM, and optionally wherein the matrix of the supplementary cementitious material comprises an amorphous phase of at least 92 volume %.

2. The supplementary cementitious material as defined in claim 1, wherein the material fulfils one or more of the following requirements in weight %:SiO237 - 44CaO < 5A12O3 4.5 - 13MgO < 3ZnO < 1.2Na2O < 1.2 impurities < 3and / or wherein the matrix of the supplementary cementitious material comprises an amorphous phase of at least 94 volume %.

3. The supplementary cementitious material as defined in claim 1 or 2, wherein the material fulfils one or more of the following requirements in weight %:SiO240 - 43CaO < 4.5A12O3 4.5 - 12.5MgO < 2.5ZnO < 1.0Na2O < 1.0 impurities < 3 and / or wherein the matrix of the supplementary cementitious material comprises an amorphous phase of at least 96 volume %.

4. The supplementary cementitious material as defined in any of the preceding claims, wherein the material fulfils one or more of the following requirements in weight %:SiO240.5 - 42.5CaO < 4AI2O3 5 - 12MgO < 2ZnO < 0.95Na2O < 0.95 and / or wherein the matrix of the supplementary cementitious material is entirely amorphous.

5. The supplementary cementitious material as defined in any of the preceding claims, wherein the BET specific surface area is in the range of 0.5 - 2.5 m2 / g.

6. The supplementary cementitious material as defined in any of the preceding claims, wherein the reactivity of the supplementary cementitious material measured as the cumulative heat release measured by isothermal calorimetry according to ASTM C1897- 20 is 350 - 600 J / g SCM.

7. The supplementary cementitious material as defined in any of the preceding claims, wherein the reactivity of the supplementary cementitious material measured as the cumulative heat release measured by isothermal calorimetry according to ASTM C1897- 20 is 370 - 550 J / g SCM.

8. The supplementary cementitious material as defined in any of the preceding claims, wherein the ratio FeO* / SiO2 is 0.76 - 1.37, preferably 0.9 - 1.2, more preferably 0.95 -1.1.