EP4688696A1 - Methods for making supplementary cementitious materials from low grade clay and compositions made therefrom - Google Patents

Abstract

Methods of making supplementary cementitious material (SCM) from low-grade clay are provided. The methods include contacting low-grade clay with an effective amount of an alkali metal compound and mixing; (ii) calcining the mixture at about 600 °C for about 60 mins; and optionally, (c) grinding the calcined clays, optionally in the presence of isopropanol. SCM produced from alkali-fused low-low grade clay is provided. The SCM show showed high strength with a compressive strength after 28 days of curing between about 30 to about 50 MPa and an SAI in the range of about 75% to 109% indicating these samples satisfy the strength requirement of ASTM C618.

Description

ATTORNEY REF #: UTSB 23-12 PCT METHODS FOR MAKING SUPPLEMENTARY CEMENTITIOUS MATERIALS FROM LOW GRADE CLAY AND COMPOSITIONS MADE THEREFROM CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of and priority to U.S.S.N. 63/493,808, filed April 3, 2023, which is incorporated by reference herein in its entirety. FIELD OF THE INVENTION This invention is generally in the field of supplementary cementitious materials. STATEMENT REGARDING FEDERALLY FUNDED RESEARCH This invention was made with government support under W911NF2010308 awarded by Defense Advanced Research Projects Agency. The government has certain rights in the invention. BACKGROUND OF THE INVENTION Concrete produced using Ordinary Portland Cement (OPC) as the primary binder has significant negative impact on the environment ^[1,2]. The negative environmental impacts of concrete can be reduced by replacing OPC with supplementary cementitious materials (SCMs)^[2]. Studies have shown that SCMs can be used to improve concrete’s workability, long- term strength, durability, and sustainability^[3–6]. The availability of natural pozzolans such as tuffs and zeolites are confined to certain geographical locations. The conventional SCMs like coal fly/bottom ash, different types of slags, solid waste incineration ash, ashes from agricultural sources, and wollastonite are not readily available throughout the world^[7–11]. Additionally, the 3availability of one of the most widely used SCM- coal fly ash, is currently declining due to the closing of coal-based power plants^[12]. Calcined clay can be a viable candidate in this regard because of its wide availability across the world^[13,14]. The common clay deposits contain a blend of primarily kaolinite, montmorillonite, and illite/smectite type clay minerals in addition to various non-clay or impure minerals (e.g., quartz, feldspar, etc.). Among the clay minerals, kaolinite shows superior reactivity after thermal, mechanical or chemical activation^[15–17]. The most reactive calcined clay product is metakaolin, formed by the de-hydroxylation of kaolinite above 600 °C^[17–19]. The 1 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT limiting factor in the pozzolanic reactivity of calcined clay is considered to be the kaolinite content^[20]. Based on the kaolinite content, common clay deposits can be categorized as high (>65% kaolinite content), medium (40% ~ 65% kaolinite content), and low grade (< 40% kaolinite content) kaolin clays^[21–23]. The high-grade kaolin sources are fewer in number compared to its application in various fields for instance the cement, paper, whiteware, and refractories industries which are reflected in limited availability and relatively high prices for metakaolin in comparison with other SCMs^[23]. Considering the availability, transportation cost, and energy-intensive clay purification expenses, locally available low-grade kaolin clays can be a suitable source for SCM production^[21]. It is an object of the present invention to provide methods for making supplementary cementitious material from low-grade clay. It is also an object of the present invention to provide supplementary cementitious material made from low-grade clay SUMMARY OF THE INVENTION Methods of making supplementary cementitious material (SCM) from low-grade clay are provided. The methods preferably adopt the alkali fusion route. The methods include (i) contacting low-grade clay with an effective amount of an alkali metal compound and mixing; (ii) calcining the mixture at a temperature between about 600 ^oC to about 850 ^oC, for example, at a temperature of about 600 ^oC, 650 ^oC, 700 ^oC, or about 750 ^oC; and optionally, (c) grinding the calcined clays, optionally in the presence of isopropanol. Exemplary alkali metal compound that includes but not limited to the hydroxide, carbonate, aluminate and silicate of group 1 metals, preferably sodium (Na⁺) and potassium (K⁺). In one preferred embodiment, the alkali metal compound at effective amounts preferably does not result in the formation of nepheline (where the Na to Al ratio is higher than the alkali fused clay particles) as determined by X-ray Diffraction (XRD) patterns of the powdered product. The alkali metal compound can be used at a concentration between about 1-25 weight (wt) %. Preferably, the alkali metal compound is used at a concentration between about 2.5 to about 10 wt %, preferably from about 2.5 wt % to about 5 wt % and more preferably, about 2.5 wt %. 2 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT SCM produced from alkali-fused low-low grade clay are provided. The SCM showed high strength and satisfy the strength requirement of ASTM C618showing a compressive strength after 28 days of curing between about 30 to about 50 MPa, in some form, between about 30 and 45 MP, for example, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44 or 45 MPa and an SAI in the range of about 75% to 109% indicating these samples satisfy the strength requirement of ASTM C618. According to ASTM C618, the sample containing supplementary cementitious material (SCM) must achieve a minimum compressive strength of 75% of the control (pure OPC) batch either at 7 days or at 28 days, or both. BRIEF DESCRIPTION OF THE DRAWINGS FIG.1A-1B show Particle size distribution of the samples (FIG.1A) cumulative distribution and (FIG.1B) differential distribution. FIG.2A-2B show high-temperature X-Ray Diffraction patterns of (FIG.2A) control and (FIG.2B) 10% NaOH dosage samples. K: Kaolinite, Q: Quartz, C: Calcite, I: Illite, M: Mullite. N: Nepheline. FIG.3 shows Derivative thermogravimetric (DTG) plots for clay mixed with different NaOH dosages. FIG.4 Shows X-ray powder diffraction of the sample with and without calcination and different alkali hydroxide dosages. Here, I: Illite (PDF #00-002-0056), K: Kaolin (PDF #96-155-0599), N: Nepheline (PDF #00-002-0637), Q: Quartz (PDF #00-002-0471), C: Calcite (PDF#96-210- 0993), S: Sodium silicate (PDF #96-154-2121). FIG.5 shows FTIR spectra of the samples with and without calcination and different alkali hydroxide dosages. FIG.6 shows ²⁹Si NMR spectra of control, % NaOH, and 20% NaOH specimen. FIG.7A-7B show dissolution of Al (FIG.7A) and Si (FIG.7B) of the alkali fused clays with time. FIG.7C shows Dissolution of Si of pure quartz. FIG.7D shows dissolution of Al (left panel) and Si (right panel) of pure kaolin (> 80% purity). FIG.8A-8B show R³ test results: (FIG.8A) total heat release and (FIG.8B) heat flow for 168 hours. 3 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT FIG.9 shows portlandite consumptions by the alkali fused clays after 168 hours of curing of the R3 sample. FIG.10A shows compressive strength of the SCM prepared with 20% replacement of the OPC by calcined low-grade clay samples with and without alkali hydroxide dosages and (FIG.10B) modified strength activity index (SAI) over different curing duration. FIG.11 shows XRD patterns of the paste samples prepared with and without calcined clays (20% replacement level) after 28 days of curing. Here, E: ettringite (PDF #96-901-2923), M: monosulfate, P: portlandite (PDF #96-900-6833), Q: quartz (PDF #00-002-0471), C: calcium silicate hydrate, Ca: calcite (PDF #96-900-0575), A: alite (PDF 96-901-6126), B: belite (PDF #96-154-6029). FIG.12 shows comparison of % expansion due to alkali-silica reaction (ASR) of alkali fused clay used as SCM. FIG.13A-13B show comparison of (FIG.13A) R³ total heat flow and (FIG.13B) portlandite consumption of alkali-activated and alkali fused clay samples. FIG.14 shows particle size (d50) of the solid precursors prepared via alkali fusion. FIG.15A-15J show BSE images and EDS of precursor prepared via alkali fusion, (FIG.15A-15C) control, (FIG.15D-15F) 5% NaOH, (FIG. 15G-15J) 25% NaOH sample. DETAILED DESCRIPTION OF THE INVENTION I. DEFINITIONS “Low-grade lay as used herein is based on the kaolinite content, and it refers to clay with < 40% kaolinite content as measured by thermogravimetric analysis (TGA) and quantitative X-ray diffraction (XRD) using the Rietveld refinement method. II. METHOD OF MAKING The disclosed methods use an alkali fusion process. Alkali fusion is traditionally used for extracting metals from solid wastes^[24–28]. This process involves solid-state reactions between alumina or silica-bearing minerals with hydroxides or carbonates of AAEM species at a temperature ranging from 180 to 950℃^[29–31]. During this process, the 4 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT 5AAEM ions decompose and subsequently modify the aluminosilicate or silicate network to increase the degree of amorphization^[32] and form new phases with higher dissolution rates^[33]. The AAEM species can play a dual role in the aluminosilicate network as charge compensators to balance the negative charge caused by the substitution of Si by Al, or as network modifiers where they disrupt Si-O-Si bonds and form non-bridging oxygens (NBOs)^[34]. As a network modifier, AAEM species cause depolymerization of the aluminosilicate network (i.e., increased NBO), which then improves the reactivity of the amorphous aluminosilicates^[35]. Alkali fusion was also used in the past to produce zeolites from relatively poor-quality coal fly ash [36], clay^[37–39], and various types of incineration ash^[40]. Previous studies have that co-calcination with AAEM additives led to the conversion of various crystalline minerals, including gehlenite, mullite, 63 quartz, and talc into soluble and amorphous aluminosilicates^[33,41,42]. Accordingly, the reactivity of low-grade clay can potentially be improved by such an alkali- fusion or co-calcination process. A recent study^[43] evaluated the effectiveness of co-calcining clays with dolomites to produce SCM. The authors concluded that the co-calcination of kaolinitic clays with dolomites enables applying relatively high temperatures (~ 950℃) while also achieving enhanced reactivity. A recent study showed that co-calcination (alkali fusion) with a high dosage of NaOH (more than 10%) and at a relatively high temperature negatively affects the reactivity of kaolinite-rich clays due to the formation of crystalline nepheline. The past study also revealed that alkali fusion can potentially reduce the dehydroxylation temperature requirement of 2:1 clay mineral (e.g., bentonite) [44]. Previous methods have used starting materials (pure-grade clay that are different from the disclosed methods (low-grade clay) and/or methods that require much higher temperature. Of note, there are significant chemical difference between low, mid and high grade clay, such that one would not expect that a method which works with high grade clay can be extrapolated to low grade clay successfully. The key difference between high and low- grade clay is the kaolinite content. A clay deposit containing more than 65% kaolinite is considered as high-grade clay, whereas with kaolin content less 5 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT than 40% is considered low-grade clay [14]. Among the associated non-clay minerals, different forms of quartz is the most common. The disclosed methods result in quartz reacting to some extent apart from the clay compound. From ²⁹Si NMR, the presence of Q⁰ peak proves the depolymerization of quartz. The alkali fusion of pure quartz showed that the dissolution of reactive Si improved after co-calcination (7C). By contrast, in the case of high-grade clay, the quantity of the associated minerals is less than 35%. Co-calcining kaolin (>80% pure) with 10% NaOH reduced the dissolution of reactive Al and Si (Figure 7D). By contrast, the disclosed methods employ low-grade clay as the starting material and successfully provide SCM from low-grade clay at a relatively low temperature (~ 600℃). The disclosed method highlights the role of alkali metal compounds such as NaOH on the dehydroxylation temperature of clay minerals (Figure 3). The in-situ XRD (Figure 2A-2B) and DTG (Figure 3) plots revealed that the presence of NaOH lowered the temperature required for dehydroxylation and merged the dehydroxylation temperature peaks for kaolinite and illite. Therefore, the disclosed methods: (i) enable increased use of common clays with mixed mineral contents by enabling calcination at specific temperatures (for example, between about 600 ^oC and about 850 ^oC ) with superior reactivity and (ii) reduce the energy requirement (thus, carbon footprint) of calcined clays by reducing the calcination temperature. Most importantly, the pathway of utilizing low-grade clays can ensure an abundant supply of SCM to enhance the sustainability and durability of Portland cement-based composites throughout the world. The methods include (i) contacting low-grade clay with an effective amount of an alkali metal compound and mixing; (ii) calcining the mixture at a temperature between about 600 ^oC and about 850 ^oC for about 60 mins; and optionally, (c) grinding the calcined clays, optionally in the presence of isopropanol. Exemplary alkali metal compound that include but not limited to the hydroxide, carbonate, aluminate and silicate of group 1 metals, preferably sodium (Na+) and potassium (K+). The selection of Group I metal alkali compounds is based on the observation that Group II compounds such as Mg (OH)₂ does not have any effect on the molecular arrangement of the 6 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT aluminosilicate network formed in the calcined-clay batches. That is why Mg (OH)₂ did not reduce the polymerization of the aluminosilicate network. The role of Mg (OH)2 is presumably a physical effect, where the formation of periclase covered the calcined clay surface, causing a decrease in reactive surface area, which therefore reduced the dissolution of both Si and Al. In one preferred embodiment, the alkali metal compound at effective amounts preferably does not result in the formation of nepheline, as determined by X-ray Diffraction (XRD) patterns of powdered (See FIG.4). X-ray Diffraction (XRD) patterns of the powdered samples can be obtained as demonstrated in the Examples (incorporated herein by reference) using a Cu-Kα source. The diffraction patterns are obtained for the 2θ range from 5° to 60° using a step size of 0.03 (2θ) per second. In one preferred embodiment, the alkali metal compound at effective amounts preferably does not result in excessive expansion due to the alkali silica reaction, as determined by ASTM 1260. The alkali metal compound is used at a concentration between about 1-25 weight (wt) %. Preferably, the alkali metal compound is used at a concentration between about 5 to about 10 wt %and more preferably, about 5 wt %. The disclosed methods do not involve alkali activation and do not result in alkali-activated materials (AAM). There are two primary differences between the disclosed methods and alkali activation, which results in AAM: First, the production of AAM involves direct mixing and/or grinding of activators and solid precursors which may not need any calcination^[50,80–85]. Accordingly, one of the key differences is that the alkali- fusion focuses on enhancing Si and Al dissolution from the aluminosilicate (or silicates) network of calcined clays by modifying the intrinsic molecular arrangements of the network (i.e., network polymerization, solid phase alteration). In contrast, AAM relies on enhancing the Si and Al dissolution from aluminosilicate networks by increasing the alkalinity of the pore solution. Therefore, the fundamental reaction mechanisms of these two approaches are expected to be different. Second, the alkali dosage used in AAM mixes can be significantly higher (up to 30% by wt.[86–88]) than effective dosages exemplified in the present studies (up to 25% by wt.). 7 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT In some forms, the method results in merging of the dehydration peaks for kaolinite and illite as measured by in-situ XRD. In some forms, the dehydroxylation starts at a lower temperature (below 300 ^oC). In some forms, the dehydration of kaolinite and illite occurs at about 400 ^oC. III. COMPOSITIONS Supplementary cementitious materials made from low-grade materials are provided. The Supplementary cementitious materials are made from a method that includes: (i) contacting low-grade clay with an effective amount of an alkali metal compound and mixing; (ii) calcining the mixture at about 600 ^oC for about 60 mins; and optionally, (c) grinding the calcined clays, optionally in the presence of isopropanol. As observed from XRD, Quartz, illite, calcite, and kaolinite are the dominant phases present in the raw low-grade clay mix. In some forms, the peak intensities of illite and quartz were reduced compared to the raw low grade clay mix and/or a control (calcined low-grade clay where the calcination does not include the addition of an alkali metal compound). Compared to control/control samples as used herein refers to low-grade clay, calcined without the presence of an alkali metal compound, under the same calcination conditions as a sample co-calcined in the presence of an alkali metal compound i.e., the only variable in the calcination process is the presence or absence of a metal alkali compound. In some forms, a mullite and/or illite peak is absent. Such reduced peak intensities were attributed to the formation of the amorphous aluminosilicate phase and sodium silicate formation. Co-Calcining low grade clay in the presence of alkali metal compounds as disclosed herein increases the number of non-bridging oxygen (NBO) sites in the final aluminosilicate or silicate network. Such, increase in the NBO is expected to increase the reactivity of the amorphous aluminosilicate phase Thus, in some forms, the compositions show lower polymerization of the calcined low grade clay when compared to the same clay sample calcined without the addition of the same alkali metal compound, as measured by FTR. Fourier Transform Infrared Spectroscopy (FTIR) carried out as demonstrated in the Example, out using a Nicolet iS50 FTIR equipped with an attenuated total reflectance (ATR) accessory. The frequency range can be 400–4000 cm at a resolution of 4 cm . In general, peak at a lower wavenumber indicates lesser 8 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT degree of polymerization of the aluminosilicate or silicate network. From Figure 5, it can be observed that the Si-O bond present in the control batch shows a broad peak at around 1000 cm^-1. For the alkali fused batches, with increasing dosage of NaOH, the ν3 band shifted to a lower wavenumber. This indicates the alkali fusion process reduced the overall silicate polymerization of the calcined clays, and therefore, confirms that the added Na + acted as a network modifier primarily. In some forms, the disclosed supplementary cementitious materials show reduced amounts of uncalcined illite, compared to the same clay sample calcined without the addition of the same alkali metal compound, as observed by ²⁹Si NMR spectra. As demonstrated in the Examples, for the control sample, the major peaks at – 94286 ppm, –100 ppm, and –108.4 ppm corresponding to Q3(1Al) i.e., [Si(OSi)3(Al)], Q3 i.e., [Si(OSi)3(OH)], and Q4 i.e., [Si(OSi)4], respectively, are originated from illite. The Q4 at - 108.4 ppm also indicates the presence of quartz. The minor peaks at –91.4, –95.6 and – 100 ppm are assigned to the amorphous aluminosilicate formed by the calcined of kaolinite. See FIG.6. In some forms, the alkali metal fused compositions disclosed herein show reduced intensity of the peaks at around -94 ppm, -100 ppm, and -108.4 ppm, all of which correspond to uncalcined illite, while the last peak also represent quartz. In some forms, the alkali metal fused compositions disclosed show peak formation at around -65 to -70 ppm and – 85 ppm. Both of these peak locations are assigned to the formation of sodium silicate (water glass). Alkali metal fused clays showed the presence of Si NMR peaks at the lower range indicating a reduced polymerization of these samples compared to the control samples. In some forms, the disclosed supplementary cementitious materials show improved pozzolanic properties compared to control samples. The dissolution of reactive Al and Si is a key factor in determining the pozzolanic properties of SCM. Studies showed that in the reaction of a silicate‐rich SCM in hydrating OPC blend, the dissolution of silicate species from the SCM particles is the initial rate‐controlling step [64,65]. When the solid precursors are exposed to an alkaline environment, the hydroxide ions break the aluminosilicates down to terminal Si–O bonds and leave silanol groups on the surface of the main structures, and these silanol groups, when ion-paired by alkali cations would weaken the adjacent Si-O bonds so that cleavage takes place to facilitate further 9 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT dissolution [66–68]. See FIG.7A and 7B. In some forms dissolution of Al and Si for the disclosed composition increases when compared to control, when measured after 1 day, 7 days or 14 days, as determined using inductively coupled plasma - optical emission spectrometry (ICP-OES). An Exemplary method is exemplified in the Examples, under “ICP-OES”, incorporated herein by reference. In some forms, the disclosed compositions have a compressive strength at 28 days of curing that is greater than 26 MPa, preferably, greater than 28 MPa, for example, ranging from about 30-35 MPa and/or a strength activity index (SAI) over 70 %, for example, 75, 85, 95, 100, 105, 110% with all intermediate numbers included. The compressive strength can be measured for 50 mm × 50 mm × 50 mm mortar cube prepared as per ASTM C311 [47] where 20% of Ordinary Portland Cement (OPC) Type I/III was replaced by SCM (calcined clay mixes), as described under “Compressive Strength” in the Examples (Incorporated herein by reference). The strength activity index is defined as the percentage of strength achieved by the samples containing supplementary cementitious material at 7 and 28 days with respect to the control (pure OPC) samples. The present invention will be further understood by way of the following non-limiting examples. EXAMPLES Materials and methods Experimental methods In-situ high temperature X-ray diffraction (HT-XRD) In-situ HT-XRD patterns were collected for powder samples for the 2θ range of 5° to 60° while 8 continuously heating at a rate of 2℃ per min. The HT-XRD patterns were collected at 15 minutes time intervals. The two-theta step size was 0.03. X-ray diffraction X-ray Diffraction (XRD) patterns of the powdered samples were obtained using a Cu-Kα source. The diffraction patterns were obtained for the 2θ range from 5° to 60° using a step size of 0.03 (2θ) per second. FTIR Fourier Transform Infrared Spectroscopy (FTIR) was carried out using a Nicolet iS50 FTIR equipped with an attenuated total reflectance (ATR) 10 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT accessory. The frequency range was 400–4000 cm at a resolution of 4 cm . Each spectrum presented in this paper is an average of 32scans. 2⁹Si Solid state nuclear magnetic resonance (NMR) All the Si solid-state NMR experiments were conducted at the SCS NMR Facility of the University of Illinois at Urbana-Champaign, at room temperature, at 7.05 T on a Varian Unity Inova 300 MHz spectrometer operating at a resonance frequency of ν0 (29Si) = 59.6 MHz. A Varian/Chemagnetics 7.5mm double-resonance APEX HX magic-angle spinning (MAS) probe 1 was used for all the MAS experiments under a spinning rate of 4 kHz and TPPM 1H decoupling. All samples were finely ground and packed into 4 mm o.d. standard zirconia rotors (typically around 210-580 mg). Experimental silicon chemical shift referencing, pulse calibration and setup were done using powdered octakis(trimethylsiloxy)silsesquioxane (Q8M8), which has a chemical shift of 11.45 ppm, relative to the primary standard, TMS at 0 ppm. The Si pulse width used was 1.5 μs, corresponding to a 45-degree pulse. A recycle delay of 30s was used and 1920 scans were acquired for each sample. ICP-OES The dissolution rate of Al and Si was determined using inductively coupled plasma - optical emission spectrometry (ICP-OES). For this, 0.1 g of the solid precursor was taken with 40 mL of DI water of pH 13.5 (liquid: solid = 400:1). The solutions were prepared in plastic centrifuge tubes and after sample preparation, those were placed on a tube-rocker (at 25 rpm) so that no solid particles deposited and ensuring proper dissolution. At 1, 7, and 14 days, the solutions were extracted for dissolution rate monitoring. A total number of six standard solutions were taken for calibration (0 ppm, 0.5 ppm, 5 ppm, 10 ppm, 20 ppm, 50 ppm) prior to the measurements. The selected wavelength for Al and Si were 396.153 nm and 288.158 nm respectively. Each result presented in this study was an average of three consecutive readings. R³ test The R test method was carried out as per standard ASTM C1897 [45]. Each of the calcined clay was mixed with Ca(OH)2 and CaCO3 (clay: Ca(OH)2 = 1:3 and CaCO3 : clay = 1: 2 ). The pore solution was prepared by dissolving 4.00 g of KOH and 20.0 g of K²SO⁴ in 1.00 L of deionized water. The solution was added to the solid mixture where the solution to solid ratio was 1.2. All the materials along with vials were kept at 40 ^oC oven at least for 24 hours before 11 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT mixing. After mixing, 15g ± 0.01g sample was transferred to the vials and placed in the isothermal calorimeter (TAM AIR) at 40C. For this measurement, deionized water was used as a reference. The 130 measurements were collected for 168hr. Thermogravimetric analysis (TGA) To monitor the portlandite consumption using thermogravimetric analysis (TGA), the paste samples from the R3 test were utilized at 7 days. Isopropanol was used to stop the hydration of the cement paste samples after 7 days of sealed curing following the solvent exchange method. The commercially available TGA 550 TA instrument was used for this purpose. In this study, paste 136 samples were first ground using a mortar and pestle, and then approximately 35 ~ 40 mg of ground powder sample was loaded into a platinum pan and kept in an isothermal condition at around 25°C for 5 minutes. Then the temperature of the TGA chamber was increased to 980°C with a ramp of 15°C per minute. N2 gas was purged in the entire process. For monitoring portlandite consumption, the mass loss over 400 ^oC to 500 ^oC temperature range was taken [10, 46]. Initially, for a few batches, three replicate samples were tested through TGA to validate for any deviation in carbonation across samples. The test result deviations were less than 2% by weight of the samples. Due to the low 143 deviation, TGA was performed with only one sample for the remainder of the batches. Compressive strength The compressive strength was measured for 50 mm × 50 mm × 50 mm mortar cube prepared as per ASTM C311 [47] where 20% of Ordinary Portland Cement (OPC) Type I/III was replaced by 1 SCM (calcined clay mixes). ASTM-graded standard sand and deionized water were used to prepare mortar cubes. The water to binder ratio was 0.485. Samples were cured in saturated lime 149 water at room temperature (23 ^oC ± 1^oC). Compressive strengths were determined after 7, 14, and 28 days of curing as per ASTM C109 [48]. Alkali-Silica Reaction (ASR) 152 The alkali silica reaction (ASR) test was done as per the guidelines of ASTM C1260 [49]. Type 33 alkali-borosilicate glass, supplied by NBS, Vitro minerals was used as the reactive aggregates. The sample preparation 12 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT and curing regime were done as per the ASTM standard recommendations. The expansion due to ASR was measured in terms of change in length by an average of three specimens for each binder-aggregate combination daily for 16 days. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) For Backscattered Electrons (BSE) imaging, the alkali fused precursors (powder) were impregnated in an epoxy resin and then lapped/ polished to obtain a mirror-like surface finish. The polished samples were coated with Gold (Au)-Platinum (Pt) before capturing the SEM images. The BSE images were obtained using the Hitachi 3000N SEM. The instrument was operated in high-vacuum mode with a 25-kV accelerated voltage and a working distance of about 15 mm. The EDS data points were collected using the same working distance. Raw materials Table 1: Oxide contents of the raw materials mass %. chemical composition of the clay was determined from XRF (Rigaku NEXCG) and is presented in Table 1. This clay was found to contain less than 30% kaolinite and 15 -20 % illite as measured using TGA and XRD (Rietveld refinement using 10% corundum as internal standard). The moisture content of the raw clay was found to be 15% when calculated using the following formula. moisture (%) = wt of wet clay-wt of dry clay × 100 wt of dry clay Different NaOH dosages were added to the raw clay sample according to Table 2 and mixed for 90 min in the planetary ball mill for uniform blending and then calcined at 600 ^oC for 60 min in a muffle furnace. 13 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT The clays were ground again in the ball mill for around 150 min to ensure uniform particle size (Figure 1A-1B). Laboratory-grade isopropanol was used (2% by weight) as a grinding aid. The obtained powder was used as the SCM in this study. Particle size distributions of the materials were determined through laser diffraction. The alkali fused batches with NaOH dosage of higher than 15% had relatively smaller diameter (d50) particles (Figure 14). The BSE images of the alkali-fused precursors (control, 5%, and 25% NaOH) are presented with EDS points in Figure 15A-J. All of the samples contained unaltered quartz (SiO2) (Figure 15C, F, J). In Figure S.2a, there are distinct 2 layers of clay particles, the inner particles are denser and more compact compared to the outer layer. This could be the result of grinding after calcination. The outer layer particles got affected and produced finer and more dispersed particles while some of the inner layer particles remained as it is. The 5% NaOH (Figure 15E) and 25% NaOH (Figure 15H) alkali fused sample had Na bound with the clay particles. In 25% NaOH sample, there was the formation of nepheline (Figure 15I) where the Na to Al ratio was higher than the alkali fused clay particles (Na/Al was around 2.28 for nepheline whereas Na/Al ranged from 0.26 to 0.66 for 25% NaOH fused clay). Table 2: Material mix details In some experiments, the low-grade impure clay was co-calcined with 0%, 2.5%, 5%, and 10% NaOH (by wt) of the clay in a laboratory muffle furnace at 400^oC, 500^oC, 600^oC, and 850^oC. The lower temperature threshold was selected to ensure the decomposition of NaOH (>320°C) and its reaction with the aluminosilicate, while the upper limit of 850°C was chosen to prevent crystallization of the clay and the subsequent reduction in surface are. The raw clay and solid NaOH pellets were ground in the planetary ball mill at a speed of 14 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT 2520 rpm for 90 minutes before and 150 minutes after calcination. The particle sizes of the alkali-fused SCM are presented in Figure 1A-1B. The samples exhibited a similar range of particles with d50 ranging from 4 to 11 µm. However, the 2.5%, 10% NaOH sample calcined at 400 ^oC and 2.5% NaOH containing sample calcined at 500 ^oC showed comparatively finer particles (d50 = 2 ~3 µm). Results Effects of NaOH on the calcination process Figure 2 shows the in-situ XRD patterns of the clay collected while heating it up to 1000℃. The decomposition and formation of different phases are marked using red and black arrows, respectively. Without the presence of NaOH (Figure 2A), it can be observed that the kaolinite peak disappeared at around 550℃. Illite and calcite peaks were diminished at around 630 and 720℃, respectively. The relatively low decomposition temperature observed here compared to the literature [19] is due to the fast-heating rate used in the experiments. Mullite peaks appeared due to the recrystallization of kaolin at around 680℃. This finding demonstrates a narrow temperature gap (50℃ gap in this study) between the dehydroxylation of illite and recrystallization of kaolinite. For the sample containing 10% NaOH (Figure 2B), kaolinite, and illite peaks were diminished at around 480℃, and 620℃, respectively. The formation of mullite was not observed to form in this sample. However, nepheline (crystalline sodium aluminosilicate, Na3K(Al4Si4O16)) peaks started appearing at around 850℃, which is more than 100℃ after the dehydroxylation of illite. In the later part of this study, the crystallization temperature of nepheline was found to be dependent on the NaOH dosage. The addition of alkali metal compounds exemplified herein using NaOH is a pathway to reduce the dehydroxylation temperature of clay minerals while increasing the recyclization temperature. The DTG plots of the common clays with various NaOH dosages are given in Figure 3. The dehydration peak of the NaOH-containing samples showed relatively higher weight loss indicating the presence of higher moisture in the former samples compared to the control sample. The DTG peaks in the temperature range of 400 to 700℃ were assigned to the dehydroxylation peaks for kaolinite and illite, and the decarbonation peak for 15 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT calcite based on the literature data [50,51]. Worthy to note, illite typically exhibits a broad dehydroxylation temperature range of 450 to 700℃ [52], and thus, it is difficult to separate it from the decarbonation of carbonates. Regardless, considering the in-situ XRD observation (Figure 2A-2B), the illite and calcite peaks were marked separately in Figure 3. Interestingly, after adding 5% NaOH, the dehydroxylation peaks for kaolinite and illite were merged. Additionally, the dehydroxylation started at a lower temperature (below 300℃) and nearly completed by 600℃. With the addition of 10 or 15% NaOH, the combined dehydroxylation peak further shifted to a lower temperature of around 400℃. With 20 or 25% of NaOH addition, there was an additional peak formed at around 750℃. This new peak was attributed to the decarbonation of sodium carbonate, which may have formed due to the presence of excess NaOH. Important to note that the initial calcite decarbonation peak in the range 600 to 700℃ remained mostly unaltered due to the addition of NaOH. Effect of alkali fusion on aluminosilicate Effect on the crystal structure of raw materials for different NaOH Dosage The XRD spectra of raw, control and alkali fused calcined clays are presented in Figure 4. The calcination was performed at 600℃ in a muffle furnace. As observed from the XRD, Quartz, illite, calcite, and kaolinite are the dominant phases present in the raw clay mix. The control samples showed a slightly increased intensity for quartz and illite after calcination at 600℃, which is due to the overall reduction in amorphous content (e.g., decomposition of organic matter). The peak intensity for kaolinite and illite was slightly reduced in the control batch. For the alkali fused batches, the peak intensities of illite and quartz were reduced with increasing NaOH dosage. Specifically, the illite peak completely disappeared for the 15% alkali fused sample. Such reduced peak intensities were attributed to the formation of the amorphous aluminosilicate phase and sodium silicate formation. However, for a NaOH dosage of more than 15%, nepheline was observed to form. Nepheline is a crystalline sodium aluminosilicate phase with negligible reactivity [53,54]. Therefore, the 16 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT formation of this phase can negatively affect the reactivity of calcined clays. The above finding show that with the addition of metal alkali, it is possible to convert typically inter phase present in common clays (i.e., quartz in this case) to reactive silicate or aluminosilicate phase. Observations from Fourier Transformed Infrared (FTIR) Spectra Figure 5 illustrates the FTIR spectra of raw clay, calcined clay, and alkali fused clay with different doses of alkali. The FTIR spectra for silicates or aluminosilicates exhibit a broad absorption between 800 cm^-1 and 1200 cm^-1 which corresponds to the asymmetrical stretching vibration (ν3) of the Si-O bond present in silicate [55]. The peaks representing silicate units with various degrees of polymerization (Qⁿ, n = 0,1,2,3,4) are overlapped in the 800 to 1200 cm^-1 range and deconvolution is required to separate those peaks. In general, peak at a lower wavenumber indicates lesser degree of polymerization of the aluminosilicate or silicate network. From Figure 5, it can be observed that the Si-O bond present in the control batch shows a broad peak at around 1000 cm^-1. For the alkali fused batches, with increasing dosage of NaOH, the ν3 band shifted to a lower wavenumber. This indicates the alkali fusion process reduced the overall silicate polymerization of the calcined clays, and therefore, confirms that the added Na ⁺ acted as a network modifier primarily. Thus, co-calcining clay herein with NaOH increases the number of non-bridging oxygen (NBO) sites in the final aluminosilicate or silicate network. Such, increase in the NBO is expected to increase the reactivity of the amorphous aluminosilicate phase [54, 56, 57]. Worthy to note, the FTIR peak at 1440 cm^-1 indicates C-O bending vibration and exists in all the specimens. This shows that calcination at 600 °C for 60 minutes is insufficient for the complete decomposition of CaCO3. Observations from the 29Si NMR Spectra 2⁹Si NMR spectra of calcined clays are presented in Figure 6. The peaks were assigned to different silicate species based on the literature [58– 61]. For the control sample, the major peaks at – 94 ppm,–100 ppm, and – 108.4 ppm corresponding to Q³(1Al) i.e., [Si(OSi)3(Al)], Q³ i.e., [Si(OSi)₃(OH)], and Q⁴ i.e., [Si(OSi)₄], respectively, are originated from illite [61]. The Q⁴ at -108.4 ppm also indicates the presence of quartz. The minor peaks at –91.4, –95.6 and –100 ppm were assigned to the amorphous 17 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT aluminosilicate formed by the calcined of kaolinite [60]. The alkali fused clay with 10% NaOH showed significantly different NMR spectra compared to the control batch. Specifically, the 10% NaOH batch showed reduced intensity of the peaks at around -94 ppm, -100 ppm, and -108.4 ppm, all of which correspond to uncalcined illite [61], while the last peak also represent quartz. The 10% NaOH alkali fused batch also showed new peak formation at around -65 to -70 ppm and – 85 ppm. Both of these peak locations were assigned to the formation of sodium silicate (water glass)[59]. Additionally, the peak intensity at around -90 ppm was increased. This peak was assigned to Q⁴ (3Al) i.e., [Si(OSi)(3Al)], which can originate from amorphous aluminosilicate [58,60] and/or nepheline [62]. For the alkali fused clay with 20% NaOH, the Q4 peak was shifted from -108 ppm to -104 ppm. Additionally, intensities of the peaks corresponding to Q1 (~80 ppm), Q² (~85 ppm), and Q⁴ (3Al) (~96 ppm) were increased, which was attributed to the increased formation of sodium silicate and amorphous aluminosilicate phases. Overall, the alkali fused clays showed the presence of ²⁹Si NMR peaks at the lower range indicating a reduced polymerization of these samples compared to the control batch. Performance of alkali-fused clays as SCMs Dissolution of Al and Si The dissolution of reactive Al and Si is a key factor in determining the pozzolanic properties of SCMs [63]. Studies showed that in the reaction of a silicate‐rich SCM in hydrating OPC blend, the dissolution of silicate species from the SCM particles is the initial rate‐controlling step [64, 65]. When the solid precursors are exposed to an alkaline environment, the hydroxide ions break the aluminosilicates down to terminal Si–O bonds and leave silanol groups on the surface of the main structures, and these silanol groups, when ion-paired by alkali cations would weaken the adjacent Si-O bonds so that cleavage takes place to facilitate further dissolution [66–68]. Figure 7A-B represents the dissolution of Al and Si from the clay samples with and without NaOH dosages after 1, 7, and 14 days. Both the Al and Si dissolution increased significantly after calcination (with and without NaOH) compared to the raw sample and hence indicating the enhanced pozzolanic activity of the samples. The Al dissolution (Figure 7A) increased by 68%, 76 18 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT %, and 65% after 14 days for 15%, 0%, and 25% NaOH batches, respectively, compared to the control specimen. The maximum Al dissolution was obtained from 20% NaOH-containing batch (148.4 mg/L). The Si dissolution (Figure 7B) also improved with the increase in NaOH content with time. The 20% dosage of NaOH-containing batch showed the maximum Si dissolution after 14 days (336 mg/L) which is 67.83% higher than the control specimen. The amorphization of the clay components, specifically illite in the presence of high alkali content (Figure 4), depolymerized the aluminosilicate network (Figure 5), and the formation sodium silicate formation were attributed to the enhanced Al and Si dissolution of the samples. Rapid, relevant, and reliable (R³) method The rapid, relevant, and reliable (R³) test is a well-known method to represent the pozzolanic activity of a wide range of SCMs [69, 70]. Using this test method and its modified versions, the SCMs can be categorized into inert, pozzolanic, highly pozzolanic, and more hydraulic based on the total heat release and portlandite consumption data [71,72]. Figure 8A represents the total heat release over 168 hours of calcined clays as obtained using the R³ method. The raw low-grade clay sample showed the lowest heat release compared to all other samples indicating its lower reactivity. The 15% NaOH (191.58 J/g) and 25% NaOH (192.37 J/g) batches had similar heat releases, which were higher than all other samples. With the increase in the NaOH content, the heat release also increased. The dissolution of the aluminosilicate precursor and subsequent precipitation of the reaction product was represented in Figure 8B. The 10% NaOH batch showed the highest peak of dissolution (the first peak), followed by 15% NaOH. All other batches except the raw sample showed similar dissolution within the first 2 hours. The raw sample and 10% NaOH sample did not show any distinct peak after dissolution. The 25% NaOH sample showed a faster formation of reaction product peak than all other samples which can be related to higher Si dissolution that readily reacted with portlandite. All these clays fall into the ‘Pozzolanic, less reactive’ category as their total heat is more than 120 J/g but less than 370 J/g according to the literature [72] except 19 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT for raw clay which is in the ‘inert’ category as the total heat of this sample was < 120 J/g. Portlandite consumption The portlandite consumptions by the calcined clays were utilized for depicting the pozzolanic reactivity [73–75]. The samples obtained from the R3 test after 7 days were utilized to determine the portlandite consumption. The hydration reaction of the samples was arrested following the solvent exchange method and then the thermogravimetric analysis was performed to determine the portlandite consumption of the samples [76]. Initially, 66.67g of calcium hydroxide [Ca(OH)₂] per 100g of total solid from the R³ test was added to the mixture as per the R3 test standard requirement. The amounts of Ca(OH)2 present in the samples were determined by integrating the derivative of thermogravimetric (DTG) peak in the temperature range of 400 to 500 ^oC [46], which was then deducted from the initial amount to determine the Ca(OH)2 consumption. Figure 9 represents the quantity of portlandite that was consumed after 7 days in g per 100g of solid. It is evident that the relation between portlandite consumption and NaOH dosages is linear. The 15%, 20%, and 25% batches consumed around 65% of the total portlandite within 7 days. The reason for increased reactivity is the increased dissolution of Si, and Al for the alkali fused batches which reacted with Ca(OH)₂ and formed calcium silicate hydrate (C-S-H) [73,75] and in the presence of Al, calcium aluminum silicate hydrate (C-A-S-H). The 10% dosage of NaOH-containing batch had 58% consumption of Ca(OH)₂. The calcined batch without any NaOH and 5% NaOH containing batch had almost similar consumption of portlandite and the raw clay had the lowest one indicating its lowest reactivity. Compressive strength and Strength Activity Index (SAI) Figure 10A and 10B represents the compressive strength and strength activity index (SAI), respectively, of different batches after 7, 14, 28, and 56 days of curing. It is evident from the pozzolanic test (R³ test and portlandite consumption) results, that the raw clay does not show pozzolanic reactivity and for this reason, it was not used for monitoring the mechanical performance. The compressive strength and SAI of the control batch was around 15 MPa and 50%, respectively, after 7 days of curing. After 28 days 20 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT of curing, the control batch a compressive strength and SAI of around 26 MPa and 70%, respectively. Therefore, this low-grade calcined clay does not satisfy the requirements of ASTM C 618. On the other hand, all of the alkali- fused batches showed relatively higher strength. High compressive strengths of 34.18 MPa (15% NaOH) were obtained after 28 days of curing. At this curing age, all the alkali fused clay batches showed strength in a similar range (30 ~ 34 MPa) indicating their similar performance. The SAI of all the alkali fused batches were in the range of 75% to 109% indicating these samples satisfy the strength requirement of ASTM C618. The relatively low SAI of the alkali-fused batch containing 25% NaOH was lower after the nepheline formation in this batch. Mineralogy of the hydration reaction products The mineralogy of the paste samples prepared with alkali fused samples as SCM (20% replacement of OPC) with water to binder ratio of 0.485 (same as the mortar sample) is illustrated in Figure 11 after 28 days of curing. The pure OPC sample had a significant quantity of portlandite whereas, in the SCM samples, the portlandite peak intensity got reduced which is the result of portlandite consumption by the alkali-fused calcined clay materials. The 5% NaOH-containing sample showed the lowest portlandite peak which indicates its superior pozzolanic property in the OPC system. In addition to portlandite, calcium silicate hydrate (C-S-H), calcite (CaCO3), ettringite [Ca6Al2(SO4)3(OH)12⋅26H2O], and a trace amount of monosulfate [Ca4Al2O6(SO4).14H2O] [77] and unreacted alite (C3S) and belite (C2S) were also present in the system. The presence of reactive Al from the calcined clay favored the formation of AFm-type phases [78,79]. The quartz (SiO2) was present in the raw material, and due to its inert nature, it remained unchanged in the paste samples after 28 days of curing. Role of Alkali-fused clays in alkali silicate reactivity The expansion due to alkali silica reaction are expressed in terms of change in length are shown in Figure 12. After 16 days of exposure conditions, it was found that the calcined clay batch, represented as the "control" batch in Figure 12, has the lowest rate of expansion. When compared with the OPC sample (does not contain calcined clays), the control batch showed a percentage reduction in expansion by 99%. For the alkali 21 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT fused batches, the expansion was higher compared to the control batch (contains low-grade calcined clay). For the samples containing alkali-fused clays, the expansion was higher in the early days of exposure and decreased after 16 days compared to OPC batches. In this case, 5%, 10% & 20% NaOH alkali fused batches showed percentage reduction with respect to OPC batches as 76%, 48% and 23% respectively. Therefore, it can be concluded that after 16 days of exposure conditions, the 5% dosage of alkali-fused batches showed a lower expansion rate than the OPC batches. As per the ASTM standard, after 16 days of casting, an expansion rate of less than 0.10%, indicates innocuous behavior, whereas expansions between 0.10% and 0.20% can be innocuous and deleterious; and expansions more than 0.20% indicate potentially deleterious expansion in field performance. Therefore, the graph shows that the expansion of the control batch and 5% NaOH alkali fused batches are innocuous whereas, the expansion of OPC, 10% NaOH alkali-fused batches which are close to 0.20% expansion shows innocuous and deleterious performance. The 20% NaOH alkali-fused batch shows higher expansion rate than 0.20%, indicating potentially deleterious expansion in field performance. Therefore, 5% alkali-fused clay can be used as an of the composite. Differences between alkali-fusion and alkali-activation The traditional approach of accelerating the cementation of aluminosilicates using alkalis is known as alkali activation and the composites are known as alkali-activated materials (AAM) or geopolymers. Considering the role of AAEM in this study, the question arises how alkali- fusion compares to the traditional AAM. There are two primary differences: First, the production of AAM involves direct mixing and/or grinding of activators and solid precursors which may not need any calcination [50,80– 85]. Accordingly, one of the key differences is that the alkali-fusion focuses on enhancing Si and Al dissolution from the aluminosilicate (or silicates) network of calcined clays by modifying the intrinsic molecular arrangements of the network (i.e., network polymerization, solid phase alteration). In contrast, AAM relies on enhancing the Si and Al dissolution from aluminosilicate networks by increasing the alkalinity of the pore solution. Therefore, the fundamental reaction mechanisms of these two approaches are 22 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT expected to be different. Second, the alkali dosage used in AAM mixes can be significantly higher (up to 30% by wt.[86–88]) than the target dosages used in the present study (up to 25% by wt.). As observed from the Si dissolution, a high dosage of alkali can in fact reduce the reactivity of the alkali fused calcined clays due to the formation of nepheline. To highlight the difference, R³ heat release (ASTM C1897) and portlandite consumptions were determined for the calcined clay activated with 10% and 20% NaOH by adding these additives after calcining the clays. The results were compared with those obtained for the same clay co-calcined (i.e., alkali-fused) with the same dosages of NaOH. The R³ heat release and portlandite consumption by the calcined clays with NaOH activators were found to be lower (i.e., poorer reactivity) than the alkali fused batches (Figure 13A-13B). The alkali- activated batches showed poorer reactivity compared to the control batch, which could be because the presence of NaOH in pore solution can decompose CaCO3 (present in R³ test material) and convert to Ca(OH)2 [89]. Regardless, the findings (Figure 13A and 13B) indicate that the alkali-fused clay batches perform substantially different than those of alkali-activated. Effect of different calcination temperatures and NaOH dosages on the pozzolanic properties Dissolution of Al and Si Upon encountering the pore solution, the precursors initiate the dissolution of Al and Si from the SCMs in a cementitious composite. The level of pozzolanic reactivity can be potentially evaluated by the extent of dissolution, with higher reactivity leading to increased dissolution of Si and Al. The Al and Si dissolution from the SCM samples prepared by alkali thermal fusion with different dosages of NaOH at different temperatures are presented in Figure 5. The samples calcined at 400 ^oC were not considered for comparing the pozzolanic properties. The exclusion of samples calcined at 400°C was based on its higher leaching rate of free Na2O, rendering the system inefficient. The results indicate that the dissolution of both Al and Si increased with the increase in the calcination temperature, dosages of NaOH, and time. The Si dissolution was increased by 55% and 76% for 10% NaOH samples calcined at 500 ^oC and 600 ^oC. Nonetheless, for 850 ^oC, a different trend was observed. At this temperature, with the increase in the NaOH 23 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT dosages, both Al and Si dissolution decreased. The samples calcined at 850°C without any additives exhibited the highest dissolution of Al (123.34 mg/l) and Si (228.2 mg/l) after 14 days. This suggests that, at this elevated temperature, the efficacy of NaOH addition in promoting Al and Si dissolution was limited. This limitation may be attributed to the role of NaOH in fostering the formation of crystalline aluminosilicates, as evidenced by XRD analyses. Portlandite consumption Portlandite consumption of the samples Sample name Portlandite consumed (g/100 g of binder) Portlandite is one of the major hydration products of an OPC system. When SCMs are introduced into the matrix, the Al and Si from the SCM dissolve into the pore solution, interacting with the portlandite to generate 24 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT pozzolanic reaction products. The extent of pozzolanic reactivity of an SCM directly influences the dissolution of Al and Si, leading to a corresponding increase in portlandite consumption when the SCM with higher reactivity is incorporated. The Table above presents the portlandite consumption of the paste samples containing 20% alkali-fused SCM. The consumption of portlandite showed a rise after 28 days of hydration in contrast to the 7-day hydration period, suggesting a prolonged pozzolanic reactivity over time. The maximum portlandite was consumed by the samples calcined at 850^oC without NaOH (6.81 g/100g of binder). With the increase in NaOH dosages at this temperature, the portlandite consumption decreased. This result is in line with the Al and Si dissolution results. The samples with 10% NaOH calcined at higher temperatures (> 500^oC) showed less consumption of portlandite. This indicates that a higher dosage of NaOH (> 5%) is not effective when calcined at a higher temperature. The samples calcined at 500 ^oC showed very similar portlandite consumptions, which did not increase significantly over time, except for the 10% NaOH sample. In other experiments, the maximum compressive strength was observed (40 MPa) for the sample containing 2.5% NaOH dosages calcined at 600 ^oC and 5% NaOH dosages at 850 ^oC after 56 days. It is interesting to note that the long-term reactivity of the SCMs calcined at higher temperatures (>500^oC) is more efficient. For 500^oC, the strength did not increase significantly after 28 days of curing. The strength improvement was observed at a maximum of 30% and 28% for 2.5% and 0% NaOH-containing samples calcined at 600^oC, respectively, after 56 days. The reason behind this improved reactivity can be attributed to the fact that, at 600 ^oC in the presence of NaOH, a fraction of inert quartz became reactive silicate, which in the long run improved the reactivity. Strength activity index of 97% was achieved by the sample containing 2.5% NaOH and calcined at 850 ^oC. DISCUSSION The co-calcination of aluminosilicates in presence of alkali hydroxide helps depolymerize the aluminosilicate network and increases non-bridging oxygen (NBO) per tetrahedra [44]. Through a variety of experimental techniques, the presented study confirmed that co-calcining clay with NaOH 25 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT effectively alters the resultant aluminosilicate phases compared to the control batch. Specifically, such alkali fusion reduced the polymerization of aluminosilicates (as observed from FTIR and ²⁹Si NMR) and increased the Al and Si dissolutions. The Al and Si dissolution improved with the increase in NaOH dosage and calcination temperature. Upon calcination at 850oC, the sample without NaOH showed the maximum dissolution of Al and Si. However, with the increase in the NaOH dosages, the Al and Si dissolution was reduced due to the formation of the crystalline phases. Both factors enhanced the reactivity of the alkali-fused clay. The alkali-fused clays with different dosages of NaOH, when used as SCM, attained at least 75% of the compressive strength of OPC at both 7 and 28 days and therefore satisfy the criteria of the Strength Activity Index (SAI) (Figure 10B). Therefore, alkali fusion as disclosed herein provides a new route for the application of low- grade clay as SCM by satisfying the strength requirement of ASTM C 618. The compressive strength was maximum for 2.5% NaOH calcined at 600^oC and 5% NaOH sample calcined at 850 ^oC after 56 days. Considering the pozzolanic properties, efficiency of incorporating alkali in the aluminosilicate network, strength, and the energy requirement for calcination of the clay, 600 ^oC is the optimum temperature, in some forms, for co- calcination of the low-grade clay with NaOH. However, the most interesting observation of this study is the role of NaOH on the dehydroxylation temperature of clay minerals (Figure 3). The in-situ XRD (Figure 2A-2B) and DTG (Figure 3) plots revealed that the presence of NaOH lowered the temperature required for dehydroxylation and merged the dehydroxylation temperature peaks for kaolinite and illite. The dehydroxylation energy requirements were reduced with the increase in NaOH dosages. For both calcination temperatures (600 ^oC and 850 ^oC), the 2.5% dosage of NaOH had the optimum energy consumption considering dehydration and dehydroxylation. Such a technique can, adopted at industrial scale can: (i) enable increased use of common clays with mixed mineral contents by enabling calcination at specific temperatures with superior reactivity and (ii) reduce the energy requirement (thus, carbon footprint) of calcined clays by reducing the calcination temperature. Most importantly, the pathway of utilizing low-grade clays can ensure an abundant supply of SCM to enhance 26 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT the sustainability and durability of Portland cement-based composites throughout the world. Conclusions In this study, locally available low-grade clay was used to produce SCMs via alkali fusion.Clay samples were co-calcined with different dosages of NaOH at 600^oC. However, The co-calcination method is effective at higher temperatures. With increase in the calcination temperature, it can incorporate more Na2O for altering the aluminosilicate network. The following summarizes the present study: I. Dehydroxylation at 600 ^oC in the presence of NaOH helped transform a portion of inert quartz to reactive silica (sodium silicate), which is in good agreement with the findings from ²⁹Si spectra, FTIR, and XRD. II. The presence of alkali helped depolymerize the aluminosilicate network and reduced the dehydroxylation temperature. This thermo-chemical treatment increased amorphous content, which contributed to the higher dissolution of reactive Al and Si. The Si and Al dissolution improved by 67.83 % and 76.37%, respectively, for 20% NaOH sample after 14 days compared to the control sample. III. The pozzolanic properties of the low-grade clay were enhanced by adopting the alkali fusion pathway. The alkali fused system showed 33% higher heat release in the standard R³ test than that of the conventional alkali-activated system (20% NaOH) and 25% more portlandite consumption for the same. The SAI improved by 24.13% for the 15% NaOH dosage alkali fused sample compared to the control sample after 28 days of curing duration. The alkali fused sample with 5% NaOH dosage performed better in terms of alkali-silica reaction when compared to the conventional OPC sample. IV. The maximum compressive strength was observed for 2.5% NaOH calcined at 600^oC. Overall, this work shows that the reactivity of low-grade clay can be enhanced by co-calcining (i.e., alkali fusion) it with alkali hydroxides. For the tested clay, 5% NaOH dosage can be considered appropriate as it provides reactivity improvement without significantly degrading ASR resistance. 27 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT Reference [1] M.-S. Low, Material Flow Analysis of Concrete in the United States, Master of Science in Building Technology, Massachusetts Institute of Technology, 2005. [2] Damtoft, Jet al. Cem Concr Res.38 (2008) 115–127. [3] Jafari, J. , et al. Journal of Materials in Civil Engineering.34 (2022) 04022094. [4] Juenger, et al Cem Concr Res.122 (2019) 257–273. [5] Yang, et al., J Clean Prod.103 (2015) 774–783. [6] Ezziane, et al. ACI Mater J.107 (2010). [7] Aprianti, et al. Constr Build Mater.74 (2015) 176–187. [8] Diaz-Loya, et al. Cem Concr Compos.101 (2019) 44–51. [9] Massazza, Lea’s Chemistry of Cement and Concrete.4 (1998) 471–631. [10] Borno, et al ^{DOI: 10.1520/ACEM20210156} [11] Saladi, et al., Journal of Materials in Civil Engineering 32(12):04020377. [12] Diaz-loya, et al. Cem Concr Compos. (2017) 4–11. [13] Karen Scrivener, Aurelie Favier, Calcined Clays for Sustainable Concrete: Proceedings of the 1st International Conference on Calcined Clays for Sustainable Concrete, in: Proceedings of the 1st International Conference on Calcined Clays for Sustainable Concrete, RILEM Bookseries, Springer, 2015. [14] Scrivener, et al., Cem Concr Res.114 (2018) 49–56. [15] Fernandez, et al., Cem Concr Res.41 (2011) 113–122. [16] Khalifa, et al. Cem Concr Res.132 (2020) 106050. [17] Thanein, et al. Mater Struct.55 (2022) 1–29. [18] Jaskulski, et al., Materials.13 (2020) 4734. [19] Fernandez, et al. Cem Concr Res.41 (2011) 113–122. [20] Du, A. Dixit, S.D. Pang, Potential of Marine Clay for Cement Replacement and Pozzolanic Additive in Concrete, in: Calcined Clays for Sustainable Concrete, Springer, 2020: pp.57–65. [21] Bediako et al. Journal of Engineering.2016:Article ID 7210891 (2016). 28 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT [22] Aras, et al, Clay Miner.42 (2007) 233–244. [23] Alujas, et al, Appl Clay Sci.108 (2015) 94–101. [24] Jian, et al. R Soc Open Sci.5 (2018). [25] Shoppert, et al, Minerals.9 (2019). https://doi.org/10.3390/min9010060. [26] Ishmah et al,, PENDIPA Journal of Science Education.4 (2020) 1–5. [27] Choi, et al,, Sci Rep.9 (2019) 1–8. https://doi.org/10.1038/s41598-019-48767-0. [28] Goguel, et al,, Cem Concr Res.25 (1995) 841–852. https://doi.org/10.1016/0008-8846(95)00075-N. [29] Ma, et al,, Ind. Eng. Chem. Res.49 (2010) 454–458. [30] Wulandari, et al,, Indonesian Journal of Chemistry.18 (2018) 580–586. https://doi.org/10.22146/ijc.25184. [31] Wajima, et al,, International Journal of the Society of Materials Engineering for Resources.23 (2018) 30–35. [32] Xuan, Q et al,, Fuel.189 (2017) 39–45. https://doi.org/10.1016/j.fuel.2016.10.081. [33] Wajima, et al, Int. J. Soc. Mater. Eng. Resour.17 (2010) 47– 52. [34] Shelby, et al,, The Royal Society of Chemistry 2005, 2005. [35] Nie, et al,, Cem Concr Res.138 (2020) 106231. https://doi.org/10.1016/j.cemconres.2020.106231. [36] Tosheva, et al,, J Mater Chem.22 (2012) 16897–16905. https://doi.org/10.1039/c2jm33180b. [37] Ltaief, et al, Eur J Inorg Chem. (2015) 4658–4665. https://doi.org/10.1002/ejic.201500537. [38] Belviso, et al,, Powder Technol.320 (2017) 483–497. https://doi.org/10.1016/j.powtec.2017.07.039. [39] Ma, et al,, Ind. Eng. Chem. Res.49 (2010) 454–458. [40] Wajima, et al,, International Journal of Chemical Engineering and Applications.10 (2019) 184–188. https://doi.org/10.18178/ijcea.2019.10.6.766. 29 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT [41] Wajima, et al, Mater Trans.49 (2008) 612–618. https://doi.org/10.2320/matertrans.MRA2007250. [42] Tosheva, et al, J Mater Chem.22 (2012) 16897–16905. [43] Bullerjahn, et al., Cem Concr Res.134 (2020) 106083. [44] Borno, et al,, Appl Clay Sci.231 (2023). https://doi.org/https://doi.org/10.1016/j.clay.2022.106742. [45] Standard Test Methods for Measuring the Reactivity of Supplementary Cementitious Materials by Isothermal Calorimetry and Bound Water Measurements 1, (n.d.). https://doi.org/10.1520/C1897-20. [46] Scrivener, R. Snellings, B. Lothenbach, A practical guide to microstructural analysis of cementitious materials, Crc Press Boca Raton, FL, USA:, 2016. [47] Standard Test Methods for Sampling and Testing Fly Ash or Natural Pozzolans for Use in Portland-Cement Concrete 1, (n.d.). https://doi.org/10.1520/C0311_C0311M-22. [48] Standard Test Method for Compressive Strength of Hydraulic Cement Mortars (Using 2-in. or [50-mm] Cube Specimens), (n.d.). [49] Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar Method) 1, (n.d.). https://doi.org/10.1520/C1260-21. [50] Khalifa, Ö et al,, Cem Concr Res.132 (2020) 106050. https://doi.org/10.1016/j.cemconres.2020.106050. [51] Ashraf, Constr Build Mater.120 (2016) 558–570. https://doi.org/10.1016/j.conbuildmat.2016.05.080. [52] Hanein, et al, Materials and Structures/Materiaux et Constructions.55 (2022). https://doi.org/10.1617/s11527-021-01807-6. [53] Peng, Z.H. et al,, Constr Build Mater.130 (2017) 103–112. [54] Borno, W. Ashraf, Effects of co-calcining kaolinite-rich clay blends with alkali and alkali earth metal hydroxides, Appl Clay Sci. (n.d.). [55] Ashraf, et al, J Mater Sci.51 (2016) 6173–6191. 9909-4. of the American Ceramic Society.95 (2012) 565–572. [57] Ke, et al, J. of the American Ceramic Society.98 (2015) 5–11. 30 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT [58] Gao, et al,, Ceram Int.43 (2017) 12408–12419. https://doi.org/10.1016/j.ceramint.2017.06.108. [59] Jansson, et al,, AIP Adv.5 (2015). https://doi.org/10.1063/1.4923371. [60] He, et al,, Clay Miner.38 (2003) 551–559. https://doi.org/10.1180/0009855033840114. [61] Luo, et al,, Appl Clay Sci.146 (2017) 325–333. https://doi.org/10.1016/j.clay.2017.06.025. [62] Stebbins, et al,, Defects and Short-range Order in Nepheline Group Minerals: a Silicon-29 Nuclear Magnetic Resonance Study, 1986. [63] Snellings, J. of the American Ceramic Society.96 (2013) 2467–2475. [64] Garg, et al,, Journal of the American Ceramic Society.102 (2019) 7720–7734. [65] Greenberg, J Phys Chem.65 (1961) 12–16. [66] Brady, et al, Geochim Cosmochim Acta.53 (1989) 2823– 2830. [67] Bunker, J Non Cryst Solids.179 (1994) 300–308. [68] Chen, J Solgel Sci Technol.96 (2020) 589–603. [69] Avet, et al,, Cem Concr Res.85 (2016) 1–11. [70] Snellings, Mater Struct.49 (2016) 3265–3279. [71] Suraneni, et al, Cem Concr Compos.83 (2017) 273–278. [72] Suraneni, A et al,, Cem Concr Compos.103 (2019) 331–338. [73] Mejdi, et al, Cem Concr Res.123 (2019) 105790. [74] Wild, et al, Cem Concr Res.27 (1997) 137–146. [75] Hollanders, et al,, Appl Clay Sci.132 (2016) 552–560. [76] Wang, et al,, Constr Build Mater.204 (2019) 458–467. [77] Lee, et al,, Applied Sciences.9 (2019) 5044. [78] Alujas, R et al,, Appl Clay Sci.108 (2015) 94–101. [79] Ashraf, et al,, Appl Clay Sci.230 (2022) 106696. [80] Hajimohammadi, et al,, Waste Biomass Valorization.8 (2017) 225–233.https://doi.org/10.1007/s12649-016-9582-5. [81] Duxson, et al,, J Mater Sci.42 (2007) 2917–2933. https://doi.org/10.1007/s10853-006-0637-z. 31 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT [82] Hajimohammadi, J.L. Provis, J.S.J. Van Deventer, One-Part Geopolymer Mixes from Geothermal Silica and Sodium Aluminate, (2008) 9396–9405. [83] Duxson, et al, Geopolymer Cements, 3869 (2008). https://doi.org/10.1111/j.1551-2916.2008.02787.x. [84] Luukkonen, et al., One-part alkali-activated materials : A review, Cem Concr Res.103 (2018) 21–34. https://doi.org/10.1016/j.cemconres.2017.10.001. [85] Provis, S.A. Bernal, Geopolymers and Related Alkali- Activated Materials, (2014) 299–329. https://doi.org/10.1146/annurev- matsci-070813-113515. [86] Xun, P. Zheng, H. Wang, Synthesis , characterization and mechanisms of one-part geopolymeric cement by calcining low-quality kaolin with alkali, (2015) 699–708. https://doi.org/10.1617/s11527-014- 0350-3. [87] Hajimohammadi, et al,, Waste Biomass Valorization.8 (2017) 225–233. https://doi.org/10.1007/s12649-016-9582-5. [88] Peng, et al, Appl Clay Sci.139 (2017) 64–71. https://doi.org/10.1016/j.clay.2017.01.020. [89] Hanein, et al, Energy Environ Sci.14 (2021) 6595–6604. https://doi.org/10.1039/d1ee02637b. 32 45623665.1

Claims

ATTORNEY REF #: UTSB 23-12 PCT We claim: 1. A method of making supplementary cementitious material (SCP) from low grade clay comprising: contacting low-grade clay with an effective amount of an alkali metal compound and mixing; (ii) calcining the mixture at about 600 ^oC for about 60 mins; and optionally, (c) grinding the calcined clays, optionally in the presence of isopropanol. 2. The method of claim 1, wherein the alkali metal compound is a the hydroxide, carbonate, aluminate or silicate of a group 1 metal. 3. The method of claim 1 or 2 wherein the alkali metal is sodium (Na+) or potassium (K+). 4. The method of any one of claims 1-3, wherein the alkali metal compound is NaOH. 5. The method of any one of claims 1 or 2, wherein the alkali metal compound is KOH. 6. The method of any one of claims 1-5, wherein the alkali earth metal is at a concentration between about 1-25 weight (wt) %. 7. The method of claim 6, wherein the alkali metal compound is used at a concentration between about 1 to about 10 wt %. 8. The method of claim 6, wherein the alkali metal compound is used at a concentration between about 2.5 and about 5 wt %. 9. The method of any one of claims 1-8, wherein the method enhances the Si and Al dissolution in the treated sample, when compared to an untreated control. 10. The method of any one of claims 1-9, wherein the method is effective to merge of the dehydration peaks for kaolinite and illite as measured by in-situ XRD. 11. Supplementary cementitious material (SCM) made from low- grade material by the method of any one of claims 1-10. 12. The SCM of claim 11, wherein the peak intensities of illite and quartz are reduced compared to the raw low grade clay mix and/or a 33 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT control (calcined low-grade clay where the calcination does not include the addition of an alkali metal compound). 13. The SCM of claim 11 or 12, having lower polymerization of the calcined low grade clay when compared to the same clay sample calcined without the addition of the same alkali metal compound, as measured by Fourier Transform Infrared Spectroscopy. 14. The SCM of any one of claims 11-13, comprising reduced amounts of uncalcined illite, compared to the same clay sample calcined without the addition of the same alkali metal compound, as observed by ²⁹Si NMR spectra. 15. The SCM of any one of claims 11-14, comprising sodium silicate (water glass). 16. The SCM of any one of claims 11-15, wherein the dissolution of reactive Al and Si in the SCM is increased when compared to control, when measured after 1 day, 7 days or 14 days, as determined using inductively coupled plasma - optical emission spectrometry (ICP-OES). 17. The SCM of any one of claims 11-16, having a compressive strength at 7, 14 or 28 days of curing that is greater than 26 MPa, preferably, greater than 28 MPa, for example, ranging from about 30-50 MPa 18. The SCM of any one of claims 11-16, having a strength activity index (SAI) over 70 %, for example, about 75, 85, 95, 100, 105, 110% with all intermediate numbers included. 19. The method of any one of claims 1-18, wherein the peak intensities of illite and quartz are reduced compared to the raw low grade clay mix and/or a control (calcined low-grade clay where the calcination does not include the addition of an alkali metal compound). 20. A SCM composition made from low grade clay, having lower polymerization of the calcined low grade clay when compared to the same clay sample calcined without the addition of the same alkali metal compound, as measured by Fourier Transform Infrared Spectroscopy. 34 45623665.1 ATTORNEY REF #: UTSB 23-12 PCT 21. The SCM of claim 20 comprising reduced amounts of uncalcined illite, compared to the same clay sample calcined without the addition of the same alkali metal compound, as observed by ²⁹Si NMR spectra. 22. The SCM of claim 20 or 21 comprising sodium silicate (water glass). 23. The SCM of any one of claims 20-22, wherein the dissolution of reactive Al and Si in the SCM is increased when compared to control, when measured after 1 day, 7 days or 14 days, as determined using inductively coupled plasma - optical emission spectrometry (ICP-OES). 24. The SCM of any one of claims 20-23, having a compressive strength at 7, 14 or 28 days of curing that is greater than 26 MPa, preferably, greater than 28 MPa, for example, ranging from about 30-50 MPa 25. The SCM of any one of claims 20-24, having a strength activity index (SAI) over 70 %, for example, about 75, 85, 95, 100, 105, 110% with all intermediate numbers included. 35 45623665.1