A method for mix proportion design of composite cement based on three volcanic ash components

Abstract

The application discloses a kind of based on three trass components composite cement mix design method.The application in the present application is prepared based on three trass components composite cement by using fly ash, pumice and trass to replace up to 50% of Portland cement under the condition of alkaline activator, and by orthogonal test design sample of Taguchi, the signal-to-noise ratio S / N of different levels of each factor is calculated and evaluated using variance analysis ANOVA, to determine the level and factor of the greatest performance impact, and obtain the best mix proportion of three trass components based composite cement.The application of up to 50% of three trass components replaces OPC, while maintaining a certain proportion of OPC to help initial setting, avoids the use of high temperature curing, the design method of the application not only provides a new type of cement for engineering projects, but also significantly reduces environmental impact.

Description

Technical Field

[0001] This invention relates to the field of cement technology, and specifically to a method for designing the mix proportion of composite cement based on three volcanic ash components. Background Technology

[0002] Cement production and use are indispensable in the modern construction industry, but they also come with significant environmental impacts, particularly in terms of greenhouse gas emissions and energy consumption. The traditional production process of Ordinary Portland Cement (OPC) involves high-temperature calcination of natural raw materials such as limestone and clay. This process not only consumes large amounts of energy but also generates significant amounts of CO2, SO2, and NO. x Greenhouse gases, etc. It is estimated that a considerable amount of greenhouse gases are released for every kilogram of clinker produced. In addition, the entire production process, from the extraction of raw materials to the grinding of the final product, is extremely energy-intensive, putting pressure on the exploitation of natural resources.

[0003] To address these challenges, researchers and industry have begun seeking more environmentally friendly, efficient, and sustainable cement production methods. One such direction is the development of blended cement, which reduces greenhouse gas emissions and energy consumption by replacing a portion of OPC (oligomeric protons). Blended cement typically utilizes pozzolanic materials, such as fly ash and blast furnace slag, to replace up to 40% of OPC. While this approach reduces environmental impact to some extent, it also introduces performance issues, such as decreased workability, reduced strength, and increased demand for water and additives.

[0004] Alkaline activated cement is another alternative that completely replaces OPC by using industrial waste as raw materials. This type of cement requires specialized knowledge to produce the alkaline solution and has higher energy demands due to the thermosetting process. While they perform well in reducing greenhouse gas emissions, they exhibit poor workability in certain situations and lower compressive strength compared to conventional cement. Against this backdrop, further development of blended cements is particularly important. Summary of the Invention

[0005] To address the problems existing in the aforementioned background technology, this invention designs a new generation of composite cement based on three volcanic ash components. This cement can replace up to 50% of OPC while maintaining a certain proportion of OPC to aid initial setting and avoid the use of high-temperature curing. It uses natural or artificial volcanic ash materials as raw materials and alkaline activators as activators. Based on the requirements of actual engineering for cement mechanical properties, the mix proportion of the composite cement is determined using the Taguchi orthogonal experimental method. This results in a 7-day compressive strength similar to conventional cement, a 28-day compressive strength at least 70% of conventional cement, and as time progresses, the later-stage strength of the composite cement gradually increases to the strength level of conventional cement, while also reducing environmental impact.

[0006] To achieve the above-mentioned objectives, the present invention proposes the following technical solution:

[0007] A mix design method for composite cement based on three pozzolanic components is disclosed. The composite cement is prepared by adding three pozzolanic active components to ordinary Portland cement (OPC) and mixing them in the presence of a powdered alkaline activator. Through Taguchi orthogonal design and detailed experiments, the mix proportion of the composite cement based on the three pozzolanic components is effectively determined, demonstrating that the composite cement has performance comparable to or better than that of traditional cement, including in terms of hardening, strength and durability, so that the mechanical properties of the prepared composite cement can meet the design requirements.

[0008] Specifically, the mix design method includes the following steps:

[0009] (1) Raw material selection: Three types of volcanic ash components, cement and activator are used as raw materials for composite cement. Among them, the three types of volcanic ash components are fly ash, pumice and volcanic ash, the cement is ordinary Portland cement (OPC) and the activator is powdered alkaline activator.

[0010] (2) Taguchi orthogonal experimental design was carried out on the mix proportion of composite cement: the key factors affecting the performance of composite cement were determined to be fly ash, pumice, volcanic ash, ordinary Portland cement (OPC) and activator. For each factor except ordinary Portland cement (OPC) and activator, at least seven different levels were selected; for activator, at least four different levels were selected. The experimental scheme was designed using Taguchi orthogonal arrays to ensure that all combinations of factors and levels were considered in the fewest possible number of experiments. The selection of orthogonal arrays depended on the number of factors and the number of levels of each factor. After selecting a suitable Taguchi orthogonal array, the experimental samples were prepared according to the permutations and combinations in the table.

[0011] (3) Conduct experiments and collect data: Based on the experimental scheme designed by Taguchi orthogonal array in step (2), prepare corresponding composite cement samples based on three volcanic ash components, test their mechanical properties, and collect the test results of all experimental samples.

[0012] This composite cement is prepared by mixing ordinary Portland cement with three types of volcanic ash components under the condition of powdered alkaline activator;

[0013] (4) Data analysis: The signal-to-noise ratio (S / N ratio) of the Taguchi orthogonal method was used to analyze the experimental data. The higher the S / N ratio, the better the stability and performance of the experimental results. The S / N ratio was calculated for different levels of each factor to determine which level had the greatest impact on performance. At the same time, analysis of variance (ANOVA) was used to evaluate the degree and significance of the influence of each factor on the experimental results.

[0014] (5) Determination of optimal mix proportion: Based on the S / N ratio and ANOVA analysis results in step (4), determine the optimal level of each factor that meets the performance requirements. By combining these optimal levels, the optimal factor level combination can be obtained, thus obtaining the optimal mix proportion based on the three-volcanic ash component composite cement.

[0015] (6) Experimental verification: In order to verify the effectiveness of the obtained optimal mix ratio, composite cement samples can be prepared using this mix ratio and performance tests can be conducted. If the test results meet the expected goals, it indicates that the optimal mix ratio is effective.

[0016] Furthermore, the alkaline activator described in this invention, as a chemical reaction activator, is sodium sulfate (Na2SO4) or potassium sulfate (K2SO4) with a purity >96%.

[0017] Furthermore, the ordinary Portland cement (OPC) described in this invention is from the CEMEX brand, with an equivalent particle size of 10-30 micrometers, preferably a D50 (average particle size) of 17.41 micrometers.

[0018] Furthermore, the fly ash (FA) described in this invention is type F according to ASTM C618 standard, originates from a thermal power plant, and is ground to a D50 of 23.08 micrometers in a DM-1 type vibrating ball mill. Fly ash (FA) is a fine particle produced during the combustion of coal. It can be used as a filler in concrete to improve its density and durability. Simultaneously, the silicates and aluminates contained in FA can undergo a hydration reaction in an alkaline environment to generate a gel similar to cement paste, thereby enhancing the strength of the concrete.

[0019] Furthermore, the volcanic ash (VA) described in this invention is natural volcanic ash with a D50 of 20.72 micrometers after grinding. Volcanic ash (VA) is a fine particulate matter ejected from the crater during a volcanic eruption. Due to its high silicate and aluminate content, VA can act as an active admixture in concrete, improving its strength and durability through the Poisson effect. Simultaneously, the fine particles of VA can also serve as microfillers, enhancing the density and uniformity of concrete.

[0020] Furthermore, the pumice Tepojal (TPJ) described in this invention is a pumice-like rock originating from volcanic magma, possessing high porosity and lightweight properties, with a D50 of 18.97 micrometers after grinding. Pumice (TPJ) is a natural, lightweight, porous volcanic glass with excellent thermal insulation and fire resistance. Introducing TPJ into concrete can reduce structural weight, while its porous structure helps improve the sound insulation and thermal insulation properties of concrete. In addition, the porous structure of TPJ can promote moisture distribution within the cement matrix, which is beneficial to the cement hydration reaction.

[0021] The particle size of the components described in this invention was measured using a Microtrac S3500 particle size analyzer under wet conditions.

[0022] Furthermore, the optimal level of the activator in step (5) of the present invention is 0 to 4%, and not 0, and the mass ratio is based on the total mass of the three volcanic ash components, cement and activator.

[0023] Furthermore, the optimal factors in step (5) of the present invention are the simultaneous presence of fly ash, pumice, volcanic ash, ordinary Portland cement and activator. The optimal mass ratio between the three volcanic ash components and ordinary Portland cement is 1:1, the optimal mass ratio of fly ash, volcanic ash and pumice is 1:1:3, and the mass ratio of activator is 4%.

[0024] The present invention also provides a composite cement based on three volcanic ash components prepared by the above-mentioned proportioning design method, which is prepared by mixing ordinary Portland cement with fly ash, pumice and volcanic ash under the condition of powdered alkaline activator.

[0025] The present invention also provides an application of the above-mentioned composite cement based on three volcanic ash components in concrete.

[0026] This invention utilizes natural volcanic ash materials (such as pumice and volcanic ash) and artificial volcanic ash materials (such as fly ash) to replace most of Portland cement. This method of preparing composite cement not only reduces greenhouse gas emissions and energy consumption but also increases the density of the cement matrix. Furthermore, by using three different admixtures—fly ash (FA), pumice (TPJ), and volcanic ash (VA)—to replace up to 50% of ordinary Portland cement (OPC), this invention not only helps reduce the carbon footprint of the construction industry but also improves the durability and performance of concrete. Simultaneously, the Taguchi orthogonal method is used to determine the mix proportions of the composite cement, resulting in composite cement that meets performance requirements. This method helps reduce time and energy consumption during manufacturing, providing a product that efficiently utilizes activators and natural volcanic ash materials, aiming to achieve the highest performance results based on compressive strength and microstructure, thus serving as an alternative building material.

[0027] To reduce cement usage and reduce energy waste by replacing cement with multiple pozzolanic components, this invention employs the Taguchi orthogonal method to design precise experiments, effectively determining the mix proportion of composite cement based on three pozzolanic components. This allows the prepared composite cement to achieve similar high-performance compressive strength as conventional cement. Furthermore, concrete prepared using the mix design method described in this invention exhibits superior performance. This novel concrete not only possesses higher compressive strength in the later stages but also demonstrates better durability and impermeability, largely due to the synergistic effect of the three materials. From a mechanistic perspective, the synergistic effect of the three pozzolanic components is mainly reflected in three aspects: First, the physical effect, where admixtures of different particle sizes can tightly fill the voids in the cement matrix, improving the density of the concrete; second, the chemical effect, where silicates and aluminates in the admixtures undergo secondary hydration reactions with calcium ions in the cement, generating additional hydrated calcium silicate (CSH) gel, enhancing the microstructure of the concrete; and third, the microscopic effect, where the fine particles of the admixtures can improve the uniformity of the cement paste at the microscopic level, reducing the formation of microcracks. The combined effect of these three factors makes concrete based on the three pozzolanic components superior to traditional cement concrete in multiple performance indicators, providing a new sustainable development solution for the building materials field. Furthermore, XRD, TGA-DTG, and FTIR analyses further confirm that the aforementioned synergistic effect not only promotes the generation of more bound water but also helps to form a more stable gel structure, thereby significantly improving the overall performance of the material. Attached Figure Description

[0028] Figure 1 The volcanic ash characteristics of the three volcanic ash components used in this invention.

[0029] Figure 2 The compressive strength of the mono-, binary, and ternary composite cement systems without alkaline activators described in this invention and the mono-composite cement systems containing different alkaline activators are given.

[0030] Figure 3 The compressive strength of the binary and ternary composite cement systems containing 1% Na2SO4 described in this invention and the blank sample.

[0031] Figure 4 The compressive strength of the binary and ternary composite cement system containing 4% Na2SO4 described in this invention.

[0032] Figure 5 The compressive strength of the binary composite cement system containing different alkaline activators described in this invention.

[0033] Figure 6 The compressive strength of the Taguchi orthogonal experimental samples 1-16 described in this invention is given, and the alkaline activator is Na2SO4.

[0034] Figure 7 The compressive strength of Sample 1 and Sample 11 of the present invention at 28, 90 and 180 days, respectively.

[0035] Figure 8 This invention relates to the isothermal calorimetric determination of TPJ by different alkaline activators.

[0036] Figure 9 This invention relates to the isothermal calorimetric determination of OPC by different alkaline activators.

[0037] Figure 10 The present invention uses the 4% Na2SO4 isothermal calorimetry method to determine different ratios of the binder.

[0038] Figure 11 The OPC / W and OPC / 4n 1 and 28-day XRD of the present invention, wherein A-Alite; B-Belite; C-Calcite; E-Ettringite; F-Ferrite; Mc-Monocarbonate; P-Portlandite.

[0039] Figure 12 The XRD patterns of the OPC-FA-VA / W and OPC-FA-VA / 4N mixed cements described in this invention are observed at 1 day and 28 days, where A = Alite; C = Calcite; E = Ettringite; M = Mullite; Mc = Monocarbonate; P = Portlandite; Q = Quartz; Sa = Sanidine; and T = Albite.

[0040] Figure 13 The Portlandite content (left) and bound water (right) of the OPC / W and OPC / 4N mixture described in this invention at 1 day and 28 days.

[0041] Figure 14 The Portlandite content (left) and bound water (right) of the OPC-FA-VA / W and OPC-FA-VA / 4N mixture described in this invention are shown at 1 day and 28 days.

[0042] Figure 15 The Portlandite content (left) and bound water (right) of the OPC-FA-VA / 4N and OPC-FA-VA / 4K mixture described in this invention are shown at 1 day and 28 days.

[0043] Figure 16 This refers to the mixture of OPC-FA / 4N with OPC-VA / 4N with OPC-FA-VA / 4 days as described in this invention.

[0044] Figure 17 The Portlandite content and bound water of the OPC-FA-TPJ / 4N and OPC-FA-VA / 4N mixture described in this invention are measured at 1 day and 28 days.

[0045] Figure 18 The FTIR values ​​of the different composite cement systems described in this invention are on day 1 and day 28. Detailed Implementation

[0046] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way.

[0047] Example

[0048] A method for designing the mix proportion of composite cement based on three volcanic ash components includes the following steps:

[0049] (1) Raw material selection: Three types of volcanic ash components, cement and activator are used as raw materials for composite cement. Among them, the three types of volcanic ash components are fly ash, pumice and volcanic ash, the cement is ordinary Portland cement (OPC) and the activator is powdered alkaline activator.

[0050] (2) Taguchi orthogonal experimental design for the mix proportion of composite cement: The key factors affecting the performance of composite cement are fly ash, pumice, volcanic ash, ordinary Portland cement and activator. For each factor, four different levels are selected. The Taguchi orthogonal array is used to design the experimental scheme to ensure that all factors and levels are considered in the fewest possible number of experiments. The selection of the orthogonal array depends on the number of factors and the number of levels of each factor. After selecting a suitable Taguchi orthogonal array, the experimental samples are prepared according to the permutations and combinations in the table. The specific Taguchi orthogonal experimental samples are shown in Table 1.

[0051] (3) Conduct experiments and collect data: Based on the experimental scheme designed by Taguchi orthogonal array in step (2), prepare corresponding composite cement samples based on three volcanic ash components, test their mechanical properties, and collect the test results of all experimental samples.

[0052] This composite cement is prepared by mixing ordinary Portland cement with three types of volcanic ash components under the condition of powdered alkaline activator;

[0053] (4) Data analysis: The signal-to-noise ratio (S / N ratio) of the Taguchi orthogonal method is used to analyze the experimental data. The higher the S / N ratio, the better the stability and performance of the experimental results. The S / N ratio is calculated for different levels of each factor to determine which level has the greatest impact on performance. In addition, analysis of variance (ANOVA) can be used to evaluate the degree and significance of the influence of each factor on the experimental results.

[0054] (5) Determination of optimal mix proportion: Based on the S / N ratio and ANOVA analysis results in step (4), determine the optimal level of each factor that meets the performance requirements. By combining these optimal levels, the optimal factor level combination can be obtained, thus obtaining the optimal mix proportion based on the three-volcanic ash component composite cement.

[0055] (6) Experimental verification: In order to verify the effectiveness of the obtained optimal mix ratio, composite cement samples can be prepared using this mix ratio and performance tests can be conducted. If the test results meet the expected goals, it indicates that finding the optimal mix ratio is effective.

[0056] The alkaline activator described herein is sodium sulfate (Na2SO4) with a purity >96%, used as a chemical reaction activator.

[0057] The fly ash (FA), which is type F according to ASTM C618 standard, comes from a thermal power plant and is ground to a D50 of 23.08 micrometers in a DM-1 type vibrating ball mill.

[0058] The volcanic ash (VA) is natural volcanic ash, and its D50 after grinding is 20.72 micrometers.

[0059] The pumice (TPJ) is a pumice-like rock originating from volcanic magma, ground to a D50 of 18.97 micrometers.

[0060] In Table 1, the content ratios of FA, VA, TPJ, and OPC are mass ratios, meaning the sum of their mass percentages is 100%. The content of the alkaline activator is also a mass ratio, representing its percentage of the total mass of FA, VA, TPJ, OPC, and the alkaline activator. N / K indicates whether sodium sulfate (Na2SO4) or potassium sulfate (K2SO4) is used as the alkaline activator. Sample 1 is a blank sample comparative example.

[0061] Table 1 Sample Table for Taguchi Orthogonal Experiment

[0062]

[0063]

[0064] Performance testing

[0065] To investigate how different types, proportions, and alkaline activators of pozzolanic ash affect the mechanical properties of mixtures, we prepared and tested a series of cement paste mixtures. Except for a control sample using 100% water-activated OPC, the remaining mixtures contained 50% OPC and were classified into binary, ternary, and quaternary systems. Following ASTM C305, we prepared various mixtures at a cement ratio of 0.6 and poured them into cylindrical molds coated with a release agent for curing. After curing, the samples were cured under controlled temperature and humidity until compressive strength tests were completed at 1, 7, and 28 days. The best-performing samples underwent special treatment to terminate the hydration reaction and were subjected to a series of characterization evaluations, including XRD, TGA-DTG, isothermal calorimetry, FTIR, and pozzolanic activator tests, aiming to deeply analyze the chemical composition, physical properties, and microstructure characteristics of the raw materials, activators, and mixtures.

[0066] (I) Volcanic ash component activity test

[0067] According to ASTM C311 standard, activity tests were conducted on the three volcanic ash components used in this invention to evaluate the volcanic ash potential of the raw materials to be used. Figure 1 The compressive strength of the three volcanic ash components at 7 and 28 days was demonstrated, indicating that all three materials possess the reactivity of volcanic ash and the potential as a cementing material.

[0068] (II) Mechanical property testing

[0069] Compressive strength tests were conducted on the samples in Table 1, and the results are shown in Figures 2-6. Specifically, when the composite cement mixture contains only 50% OPC, the expected compressive strength is at least 8.3 MPa, calculated based on 50% of the reference compressive strength of OPC (27.75 MPa). Experimental results show that the OPC-FA / W mixture exhibits good compressive strength (9.85 MPa) at 1, 7, and 28 days, demonstrating the potential of FA as the most reactive pozzolanic material. However, the binary mixture of TPJ and VA failed to reach a compressive strength of 7 MPa due to insufficient cement or heat to promote its dissolution and reaction. However, the compressive strength of both binary and ternary mixtures significantly improved when alkaline activators, such as 1% and 4% Na₂SO₄, were introduced. In particular, ternary compounds containing 50% OPC + 25% FA + 25% TPJ or VA exhibited compressive strengths exceeding 10 MPa, even reaching 13.88 MPa, under alkaline activating conditions. This is attributed to the synergistic effect of cement hydration and the early reaction of FA promoting the dissolution of TPJ. Figure 6 It can be seen from the data that sample 11 has the highest strength, indicating that it contains three volcanic ash components, OPC, and alkaline activator, and has the best mechanical properties under this ratio.

[0070] also, Figure 2 This study tested the compressive strength of binary and ternary composite cement systems and blank cement under conditions without alkaline activators. The composite cement contained 50% OPC, 50% single pozzolanic component, and any two combinations of pozzolanic components each comprising 25% of the total. The results showed that without the action of an alkaline activator, the strength of OPC combined with any one or two of the three pozzolanic components was significantly lower than that of OPC alone.

[0071] Figure 3 The compressive strength of a composite cement activated mixture with 1% Na2SO4 as the alkaline activator was measured. The mixture consisted of 50% OPC, 50% single pozzolanic component, and any two combinations of pozzolanic components, each comprising 35% of the total. The results showed that under the action of 1% alkaline activator, the strength of the OPC + any two of the three pozzolanic components combination was greater than the strength of the OPC + any single combination.

[0072] Figure 4 The compressive strength of a composite cement activated mixture with 4% Na2SO4 as the alkaline activator was measured. The mixture consisted of 50% OPC, 50% single pozzolanic component, and any two combinations of pozzolanic components, each comprising 35% of the total. The results showed that under the action of 4% alkaline activator, the strength difference between any combination of OPC and the three pozzolanic components and any combination of OPC and two other components became smaller.

[0073] Figure 5 The compressive strength of composite cement activated mixtures with different activators was studied, where OPC accounted for 50% and TPJ for 50%. Results showed that the 28-day strength was significantly improved with 4% Na₂SO₄ compared to 1% Na₂SO₄, 1% K₂SO₄, and 4% K₂SO₄. The addition of alkaline activators, particularly 4% Na₂SO₄, promoted the dissolution of TPJ and VA pozzolanics by increasing the pH of the solution, thereby enhancing the compressive strength of the mixture.

[0074] Figure 7 The figure shows the compressive strength of the composite cement sample and the blank cement sample under optimal mixing conditions at 28, 90 and 180 days, respectively. The figure shows that as time goes on, the compressive strength of the composite cement gradually approaches that of ordinary Portland cement, and its later strength can gradually meet the engineering requirements.

[0075] (III) Isothermal Calorimetry (IC) Measurement

[0076] Isothermal calorimetry (IC) is an analytical technique that studies the hydration kinetics of cement components by measuring the heat released and accumulated over time during a material reaction. This method can be used to compare the effects of different types and concentrations of alkaline activators on the reactivity of cement and pozzolanic materials. Studies have found that, unlike the traditional Portland cement hydration process, the exothermic reaction peak of a 100% pumice (TPJ) mixture after the addition of an alkaline activator is mainly affected by the type and concentration of the activator, exhibiting hydration kinetic characteristics different from OPC. In particular, Na₂SO₄ and K₂SO₄, as activators, can increase heat release and accumulation by up to 100% compared to mixtures without activators. Figure 8 It can be observed that TPJ varies with the type and amount of alkalinity, and activation exhibits only a single exothermic reaction peak. Furthermore, 1% activator addition is more effective than 4%, likely because less activator dissolves more quickly, generating more heat, while excessive activator may inhibit the reaction process. The type of alkaline activator also significantly affects heat generation; Na... + Ion ratio K + Ions generate more heat. These findings complement the compressive strength results analyzed by IC technology, demonstrating the important role of alkaline activators in enhancing the reactivity of pozzolanic ash.

[0077] Figure 9 Isothermal calorimetry of OPC with different activators showed that the reactions of OPC with different types and amounts of alkalinity were similar. Further analysis revealed that although the cumulative heat of the different mixtures was similar at 1 day, the OPC / 4K (4% K2SO4) mixture exhibited the highest heat release and accumulation, but also the lowest compressive strength. This is likely due to drying shrinkage caused by increased heat, leading to microcracks and reduced compressive strength. Furthermore, binary and ternary mixtures activated with 4% Na2SO4 showed excellent performance in hydration kinetics, particularly at the second exothermic peak in the accelerated zone. Compared to the reference, these mixtures reduced heat release and cumulative heat by more than half, while also reducing setting time. These effects are attributed to the combined effects of the amount of cement in the reaction, the number of free ions in the pozzolanic ash, and the alkaline environment. Finally, by Figure 10 It can be observed that the VA mixture releases more heat in the initial stage of the reaction compared to the TPJ mixture, indicating that the OPC-FA-VA mixture has a better synergistic effect compared to the OPC-FA-TPJ mixture. The ternary mixture produces a higher heat release rate and accumulated heat than the binary mixture, which helps in the dissolution of volcanic ash and the formation of reaction products, thereby improving compressive strength.

[0078] (iv) X-ray diffraction (XRD)

[0079] X-ray diffraction (XRD) analysis provided qualitative information on the mineral and crystalline composition present in various mixtures. This analysis covered multiple aspects, including the behavior of Portland cement (OPC) in alkaline environments, different blended cements (binary and ternary mixtures), and their interactions with different types and concentrations of alkaline activators. Figure 11 XRD analysis revealed peaks in certain anhydrous phases between the 1-day and 28-day samples, pointing to specific reactions in OPC and indicating early crystallization. At 28 days, the OPC / 4N mixture exhibited ferrite and silicate phases, while the OPC / W mixture showed ettringite and monocarbonate phases, reflecting the effect of the alkaline environment and reduced calcium solubility on the reaction. Nevertheless, the use of an alkaline activator was intended to increase the pH and promote pozzolanic dissolution, with the expectation of reducing the formation of expansion products by decreasing cement dosage and increasing pozzolanic concentration.

[0080] Figure 12 XRD analysis of the OPC-FA-VA / W and OPC-FA-VA / 4N mixtures revealed a lower concentration of silicate phases in the water-activated mixture, while peaks of these phases remained in the alkaline-activated mixture, indicating delayed calcium dissolution. Furthermore, the reduction in calcium silicate and the increase in ettringite peaks under both activation methods are likely due to the participation of alumina in the reaction, forming ettringite with calcium silicate and calcium sulfate. XRD analysis of the OPC-FA-VA mixtures with sodium and potassium as activators at 28 days revealed differences between the two. The sodium-activated mixture showed a higher concentration of silicate phases, possibly due to reduced solubility caused by the alkaline environment. However, the diffraction patterns of the two mixtures at 28 days were similar, with only slight differences at certain angles; the potassium mixture retained the orthoclase phase, while the sodium mixture showed ettringite crystals. This suggests that although sodium ions generate less heat, their smaller radius contributes to better zeolization, thereby improving compressive strength. Comparison of OPC-FA / 4N, OPC-VA / 4N, and OPC-FA-VA / 4N mixtures revealed differences in the strength of the crystalline phases in the ternary mixtures, likely due to variations in the proportion of pozzolanic ash. Furthermore, the synergistic reaction between FA and VA favored the polymerization of the ternary mixtures, resulting in higher compressive strength at 28 days.

[0081] Finally, XRD analysis of different types of volcanic ash, specifically OPC-FA-VA / 4N and OPC-FA-TPJ / 4N mixtures, revealed the presence of orthoclase crystals in the VA mixture and ettringite crystals in the TPJ mixture. This demonstrates that TPJ exhibits better reactivity compared to VA. Although both materials have similar compressive strengths and are considered viable alternatives to cement, the VA mixture shows a greater number of minerals potentially involved in long-term reactions.

[0082] (v) Thermogravimetric analysis and thermogravimetric derivatization analysis (TGA-DTG)

[0083] Using TGA-DTG technology, the main phenomena identified included calcium hydroxide or Portlandite and their dehydroxylation, calcium carbonate decarburization, decomposition of sulfoaluminate or CSH gels, and loss of free water. Figure 13 The results show three main peaks, corresponding to the decomposition of evaporable water and hydrates (25–200 °C), the dehydroxylation of portlandite (400–600 °C), and the decarburization of calcium carbonate (600–800 °C). In the comparison of OPC / W and OPC / 4N mixtures, the initial alkaline mixture showed a higher portlandite formation, favoring earlier reactions. At 28 days, the portlandite content was slightly higher, indicating reduced portlandite consumption; the alkaline environment reduced calcium solubility, affecting compressive strength. In the comparison of OPC-FA-VA / 4N and OPC-FA-VA / 4K mixtures, both alkaline activators completely consumed portlandite after 28 days, but the 4N mixture showed more hydration products. Ternary mixture analysis indicated a synergistic effect, increasing hydration product formation and thus enhancing compressive strength. A comparison of the OPC-FA-TPJ / 4N and OPC-FA-VA / 4N ternary mixtures showed subtle differences in the portlandite dehydroxylation peak, despite similar performance. Quantitative analysis of the Portlandite content and hydrate-bound water of the mixture at different age stages showed that the greater the amount of bound water, the greater the increase in hydration products.

[0084] Figure 13 Portlandite content and bound water of OPC / W and OPC / 4N mixtures at 1 day and 28 days are shown. Initially, the alkaline mixture promoted the reaction with cement compounds, producing a large amount of hydration products. After 28 days, the hydrated bound water of the alkaline mixture decreased, indicating a reduction in hydration products. The OPC-FA-VA / 4N mixture promoted the early reaction of cement compounds, but not specifically for the formation of CSH gel, but rather by promoting ettringite formation through the reaction with Portlandite. This phenomenon was also observed in the bound water, as the alkaline mixture had a greater amount of bound water at 28 days compared to the water-activated mixture, indicating a reduction in products and therefore a reduction in bound water in the sulfate-activated mixture. In a comparison of OPC-FA-VA / 4N and OPC-FA-VA / 4K mixtures, the effect of alkali metal type on performance was evaluated. Although the amount of bound water differed between the two alkali metals on the first day, the potassium system showed higher Portlandite consumption. Figure 13A synergistic effect analysis of ternary cement blends using two pozzolanic materials was presented, showing that the OPC-VA / 4N blend exhibited higher Portlandite content and bound water on day 1, thus providing the highest compressive strength at 28 days. This explains the improved performance and the attainment of the highest compressive strength in the ternary blend due to the synergistic effect of the two pozzolanic materials.

[0085] exist Figure 14 In the comparison, the OPC-FA-VA / W and OPC-FA-VA / 4N mixtures exhibited different Portlandite contents. Compared to the Na2SO4-activated mixture, the mixture using water as an activator had a higher Portlandite content, but both showed complete consumption of Portlandite after 28 days. Regarding bound water, the alkaline mixture showed the most hydrates on day one, but by day 28, the situation reversed, with the water-activated mixture showing a greater increase in bound water. These findings suggest that the OPC-FA-VA / 4N mixture promoted early cement compound reactions. These reactions were not primarily aimed at the formation of amorphous CSH gel, but rather promoted the formation of ettringite through reaction with available Portlandite, as evidenced by the lower Portlandite content of the alkaline mixture on day one and the higher ettringite content observed in the XRD results. Furthermore, this phenomenon was also reflected in the observation of bound water, as the water-activated mixture produced more amorphous gel through the reaction with Portlandite, thus possessing more bound water at 28 days. In contrast, the amount of bound water in the alkaline mixture containing more ettringite on day 1 was less than that in the water-activated mixture at day 28, resulting in a reduction in the product in the sulfate-activated mixture and thus a decrease in the amount of bound water. The effect of alkali metal type was examined when comparing OPC-FA-VA / 4N and OPC-FA-VA / 4K mixtures. Figure 15 The results showed that the bound water content differed between the two alkali metals on the first day, with sodium exhibiting a higher content, while the potassium system showed higher Portlandite consumption. Supplemental calorimetric analysis revealed that the use of a potassium activator increased the heat generated in the first exothermic peak, explaining the higher consumption of Portlandite by potassium. However, by day 28, considering the smaller radius of sodium, which is beneficial for its zeolization / geometric polymerization and charge density, the bound water of the sodium mixture contained more hydration gel. Regarding synergistic effects… Figure 13The synergistic effect of using two types of pozzolanic materials in ternary cement blends was evaluated by comparing OPC-FA / 4N, OPC-VA / 4N, and OPC-FA-VA / 4N mixtures. By directly quantifying the bound water content of portlandite and hydrates, it was found that the OPC-VA / 4N mixture exhibited a higher portlandite content on day one, allowing for a greater reaction in the blended cement, and it was observed to have the highest amount of bound water on day one. The OPC-FA / 4N mixture showed the lowest compressive strength on day one at 1.73 MPa, consistent with its lower bound water content, while the OPC-FA-VA / 4N mixture acquired more bound water on day one due to the synergistic effect of VA, thus achieving a compressive strength of 1.86 MPa. By day 28, although the amount of portlandite was not observed in any of the mixtures, the hydration kinetics differed for each mixture. Regarding compressive strength, the OPC-VA / 4N mixture exhibited the highest compressive strength on day 1, but decreased to a minimum of 9.98 MPa at day 28. The OPC-FA / 4N mixture showed a compressive strength of 11.13 MPa, while the ternary mixture of OPC-FA-VA / 4N showed the highest compressive strength at 12.41 MPa. This may be controversial because the VA binary mixture has a higher bound water content than the FA mixture. However, the diffraction pattern shows that the OPC-VA / 4N mixture has the highest calcite content, suggesting that some of the Portlandite consumption is due to CO2 entering through the porosity of the sample and reacting with the Portlandite to produce calcite. Furthermore, the comparison with the ternary mixture shows that, despite the improved performance, it exhibits the highest compressive strength due to the synergistic effect of the two pozzolanic materials. This is observable from day 1, where the bound water content exceeds that of the FA binary mixture, and by day 28, it surpasses both binary mixtures, undoubtedly explaining its highest compressive strength.

[0086] exist Figure 16The analysis compared three mixtures: OPC-FA / 4N, OPC-VA / 4N, and OPC-FA-VA / 4N, to explore the synergistic effect of ternary cement blends with two different pozzolanic additions. Quantification of Portlandite and bound water revealed that the OPC-VA / 4N mixture exhibited a higher Portlandite content in the initial stage, promoting more chemical reactions, and also showed the highest bound water content on the first day. In contrast, the OPC-FA / 4N mixture had the lowest compressive strength on the first day, at only 1.73 MPa, consistent with its lower bound water content. The OPC-FA-VA / 4N mixture, due to the synergistic effect of VA addition, showed increased bound water content in the initial stage, achieving a compressive strength of 1.86 MPa. After 28 days, although the Portlandite in all mixtures was completely consumed, their hydration kinetics showed differences. In terms of compressive strength, the OPC-VA / 4N mixture showed the highest initial strength, but dropped to 9.98 MPa after 28 days, becoming the lowest. This was followed by the OPC-FA / 4N mixture at 11.13 MPa, while the OPC-FA-VA / 4N ternary mixture exhibited the highest compressive strength of 12.41 MPa. This result may raise questions because, although the VA mixture had a higher bound water content than the FA mixture, the diffraction pattern showed that the OPC-VA / 4N mixture had the highest calcite content. This could be due to CO2 entering through the sample pores and reacting with Portlandite to form calcite. Furthermore, the comparison of the ternary mixtures indicates that the synergistic effect of the two volcanic ash compounds not only improved performance but also achieved the highest compressive strength. This was evident from the initial stage, where the bound water content exceeded that of the FA binary mixture, and surpassed both binary mixtures at 28 days, clearly explaining the reason for its highest compressive strength.

[0087] Ultimately, through Figure 17 A comparison was made between two ternary mixtures, OPC-FA-TPJ / 4N and OPC-FA-VA / 4N, analyzing their Portlandite percentage and compressive strength. In the initial stages, the TPJ-containing mixture exhibited a compressive strength of 2.24 MPa, higher than the VA-containing mixture's 1.86 MPa, likely due to the earlier reaction of Portlandite with the volcanic ash compounds in the TPJ mixture. By day 28, although the Portlandite had been completely consumed, the TPJ-containing mixture still achieved a compressive strength of 13.17 MPa, higher than the VA mixture's 12.41 MPa. Nevertheless, the VA-containing mixture showed a greater increase in bound water, suggesting that it may exhibit stronger compressive strength in the long term.

[0088] (vi) Fourier Transform Infrared Spectroscopy (FTIR)

[0089] Figure 18By analyzing the infrared spectra of different mixtures in the 400-4000 cm⁻¹ range after curing on day 1 and day 28, the characteristics of the functional groups in the mixtures were revealed, and their identification was compared with theories and literature. From low to high wavenumbers, peaks at 450 cm⁻¹ and 609-615 cm⁻¹ were observed in the early stages, indicating the presence of unreacted silica in the cement, which was confirmed by XRD tests at both time points. In particular, at day 28, both mixtures showed the presence of allite. The 712-714 peak on day 1 and the 873-875, 1415-1422, and 2320-2362 peaks on days 1 and 28 were slightly stronger than those of the OPC / 4N mixture; these peaks correspond to the presence of calcium carbonate (CaCO₃), consistent with the increased calcite content. The significant peak at 954-960 corresponds to CSH hydration products, which are key to the compressive strength of the mixtures, showing the strong reaction of the sulfate-containing mixtures in the early stages. At 28 days, the CSH peak of the 4N mixture showed little change, indicating that the alkaline environment affected the reaction of the compounds. An increase in calcium sulfoaluminate was observed in the 1100–1005 cm⁻¹ range, particularly in the sulfate-containing mixture, suggesting a promoting effect of sulfate on the compound reaction. However, this reaction weakened over time. At the peak of 3638–3640 cm⁻¹, the amount of Portlandite was initially increased in the sulfate-containing mixture, but was relatively less at 28 days. The effect of alkaline activators in the mixed cement was analyzed through evaluation of the OPC-FA-VA / W and OPC-FA-VA / 4N series. The peak at 442–445 cm⁻¹ revealed O-Si-O bonds, while the slight peak at 775–779 cm⁻¹ at 1 day originated from the Si-O-Si bonds of quartz, which disappeared after 28 days. The peaks at 949-962 and the shoulders at 1086-1107 indicate the presence of NASH / CSH / C-(A)-SH gels, which are crucial to the performance of the mixture. Particularly at 28 days, rearrangement of hydration products was observed through peak changes, indicating the formation of CASH gel and (N,C)-ASH. Furthermore, peaks at 874-872, 1418-1431, 2160, 2357-2365, 2899, and 2988 reveal the presence of a calcite phase, consistent with the higher peak intensities observed in the alkaline-activated mixture at 1 day. Therefore, the use of an activator is crucial for promoting the formation of amorphous gel hydration products, especially over the long term, where the alkaline-activated mixture exhibits superior performance compared to the mixture activated only with water.

[0090] Figure 18An comparison of OPC-FA-VA mixtures using sodium (4N) and potassium (4K) as alkaline activators revealed the effect of alkali metal type on compound reactions. The coexistence of NASH, CSH, and C-(A)-SH hydration products was observed at peaks of 956–949 and 1086–1099, with these peaks showing greater intensity and detail at 28 days, indicating rearrangement of amorphous gels and formation of CASH / (C,N)-ASH gels. Despite similar peak values, TGA results showed that the 4N-containing mixture contained more bound water and ettringite on day 1, while the 4K-containing mixture showed a slightly higher bound water content and more cement compounds and volcanic ash at 28 days, suggesting that the increase in bound water may originate from other hydrates. Peaks observed at 872–872, 1429–1443, 2326–2362, 2900, and 2988 cm⁻¹ indicate the presence of carbonates, with calcite being more pronounced in the sodium mixture at day 1 and the potassium mixture at day 28. Furthermore, peaks at 3406 and 3630–3647 reveal the presence of ettringite and bound water, consistent with TGA results. Further, the synergistic effect of the two volcanic ashes in the ternary mixtures was analyzed by comparing OPC-FA / 4N, OPC-VA / 4N, and OPC-FA-VA / 4N mixtures. Observations at peaks at 949–960 and 1080–1094 indicate that the NASH / CSH / C-(A)-SH gel appearing at day 1 stabilizes as CASH and (N,C)-ASH at day 28. Differences in peak intensity, fineness, and shift demonstrate the presence of a synergistic effect, particularly in the amount of amorphous gel. At 28 days, the binary mixture of FA showed increased strength, while the mixture of VA remained unchanged, but the strength of the ternary mixture also increased, suggesting that VA may have initiated the reaction earlier, subsequently being taken over by FA. Analysis of bound water showed that the binary mixture of FA contained the least amount of bound water on day 1, while the binary mixture of VA produced the most bound water at 28 days, which may be related to the formation of ettringite.

[0091] In summary, fly ash (FA), pumice (TPJ), and pozzolanic ash (VA), as admixtures, all meet the chemical composition requirements of ASTM C618 and are considered qualified pozzolanic materials. Regarding compressive strength, the 100% OPC mixture exhibits a decrease in strength in an alkaline environment due to reduced calcium solubility. The binary mixture containing 50% OPC did not reach the expected compressive strength when activated with water alone, but the ternary mixture did. All alkaline-activated mixtures exceeded the strength proportional to their OPC content, with only 50% OPC achieving 75% of the strength of the OPC / W reference mixture. The quaternary mixture, sample 11, reached its maximum compressive strength, making it the optimal formulation. Increasing the alkaline activation dosage from 1% to 4% improved compressive strength, regardless of the type of alkaline ion.

Claims

1. A method for designing the mix proportion of composite cement based on three volcanic ash components, characterized in that, The steps include the following: (1) Raw material selection: Three types of volcanic ash components, cement and activator are used as raw materials for composite cement. Among them, the three types of volcanic ash components are fly ash, pumice and volcanic ash, the cement is ordinary Portland cement and the activator is powdered alkaline activator. (2) Taguchi orthogonal experimental design for the mix proportion of composite cement: The key factors affecting the performance of composite cement are determined to be fly ash, pumice, volcanic ash, ordinary Portland cement and activator. For each factor except ordinary Portland cement and activator, at least seven different levels are selected; for activator, at least four different levels are selected. The experimental scheme is designed using Taguchi orthogonal array to ensure that all combinations of factors and levels are considered in the fewest possible number of experiments. The selection of orthogonal array depends on the number of factors and the number of levels of each factor. After selecting a suitable Taguchi orthogonal array, the experimental samples are prepared according to the permutations and combinations in the table. (3) Conduct experiments and collect data: Based on the experimental scheme designed by Taguchi orthogonal array in step (2), prepare corresponding composite cement samples based on three volcanic ash components, test their mechanical properties, and collect the test results of all experimental samples. This composite cement is prepared by mixing ordinary Portland cement with three types of volcanic ash components under the condition of powdered alkaline activator; (4) Data analysis: The signal-to-noise ratio (S / N ratio) of the Taguchi orthogonal method was used to analyze the experimental data. The higher the S / N ratio, the better the stability and performance of the experimental results. The S / N ratio of each factor at different levels was calculated to determine which level had the greatest impact on performance. At the same time, analysis of variance (ANOVA) was used to evaluate the degree and significance of the influence of each factor on the experimental results. (5) Determination of optimal mix proportion: Based on the S / N ratio and ANOVA analysis results in step (4), determine the optimal level of each factor that meets the performance requirements. By combining these optimal levels, the optimal factor level combination can be obtained, thus obtaining the optimal mix proportion based on the three-volcanic ash component composite cement. (6) Experimental verification: In order to verify the effectiveness of the obtained optimal mix ratio, composite cement samples can be prepared using this mix ratio and performance tests can be conducted. If the test results meet the expected goals, it indicates that the optimal mix ratio is effective.

2. The method for designing the mix proportion of composite cement based on three volcanic ash components according to claim 1, characterized in that, The alkaline activator is sodium sulfate or potassium sulfate with a purity >96%.

3. The method for designing the mix proportion of composite cement based on three volcanic ash components according to claim 1, characterized in that, The ordinary Portland cement mentioned is from the CEMEX brand and has an equivalent particle size of 10–30 micrometers.

4. The method for designing the mix proportion of composite cement based on three volcanic ash components according to claim 3, characterized in that, The D50 of the ordinary Portland cement is 17.41 micrometers.

5. The method for designing the mix proportion of composite cement based on three volcanic ash components according to claim 1, characterized in that, The fly ash, classified as Type F according to ASTM C618, originates from a thermal power plant and is ground to a D50 of 23.08 micrometers in a DM-1 type vibrating ball mill; The volcanic ash is natural volcanic ash, and its D50 after grinding is 20.72 micrometers; The pumice is a pumice-like rock originating from volcanic magma, and it is ground to a D50 of 18.97 micrometers.

6. A method for designing the mix proportion of composite cement based on three volcanic ash components according to any one of claims 3 to 5, characterized in that, The particle size of each component was measured under wet conditions using a Microtrac S3500 particle size analyzer.

7. The method for designing the mix proportion of composite cement based on three volcanic ash components according to claim 1, characterized in that, The optimal level of the activator in step (5) is 0-4%, and not 0. This mass ratio is based on the total mass of the three volcanic ash components, cement and activator.

8. The method for designing the mix proportion of composite cement based on three volcanic ash components according to claim 7, characterized in that, The optimal factors in step (5) are the simultaneous presence of fly ash, pumice, volcanic ash, ordinary Portland cement and activator. The optimal mass ratio between the three volcanic ash components and ordinary Portland cement is 1:1, the optimal mass ratio of fly ash, volcanic ash and pumice is 1:1:3, and the mass ratio of activator is 4%.

9. A composite cement based on three pozzolanic components prepared by the mix design method according to any one of claims 1 to 8, characterized in that, It is prepared by mixing ordinary Portland cement with fly ash, pumice, and volcanic ash under the condition of powdered alkaline activator.

10. The application of the composite cement based on three volcanic ash components as described in claim 9 in concrete.

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