{"paper_id":"3a8ec3c1-bb66-4e90-90b3-e63e8645b9c1","body_text":"Preparation of coal gangue based geopolymer and electrical conductivity studies | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Preparation of coal gangue based geopolymer and electrical conductivity studies Wenhua Zha, Wenfang Lv, Jielian Li, Tao Xu, Denghong Chen This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4691610/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Geopolymers are both an effective way to achieve solid waste utilization of coal gangue and an environmentally friendly alternative to ordinary Portland cement. At the same time, the rich ionic content of geopolymers gives them superior conductivity, which makes them potentially valuable for applications in a variety of fields such as nondestructive testing, ice and snow melting, and electromagnetic shielding. However, the influence of external factors on its conductivity is still unclear, which limits its wide application in construction. In this study, coal gangue and slag are used to prepare geopolymer under alkaline excitation conditions, and the influence laws of alkali equivalent, slag substitution rate, modulus and water-cement ratio on its consistency, compressive strength and resistivity are investigated, and the changing law of resistivity of specimens with the curing ages and water content are also explored. It is found that the compressive strength is affected by alkali equivalent, slag substitution rate, modulus and water-cement ratio. When the alkali equivalent, slag substitution rate, modulus and water-cement ratio are taken to 12%, 55%, 1.2, 5 or12%, 45%,1.2, 4 respectively, the compressive strength at 28 days could be more than 80 MPa. Resistivity is first decreased and then increased with increasing alkali equivalent, increasing slag substitution rate, or increasing modulus, and is decreased with increasing water-cement ratio, and all of them are increased with increasing curing ages. At the age of 7 days, it is most significantly affected by alkali equivalent, while after the age of 14 days, it is more significantly affected by modulus and slag substitution rate than alkali equivalent; the effect of water-cement ratio is smaller at different ages. In addition, the resistivity is shown to increase significantly with decreasing water content, and the resistivity is increased by nearly 5–6 orders of magnitude when the specimens are transformed from the surface-dry state to the dry state. Earth and environmental sciences/Environmental sciences Physical sciences/Energy science and technology Physical sciences/Engineering Physical sciences/Materials science Coal gangue Solid waste utilization Geopolymer Compressive strength Electrical resistivity Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Introduction Coal gangue is a solid waste discharged during coal mining, which has accumulated more than 7 billion level in China, and its encroachment on land resources and leaching of heavy metals are causing a serious imbalance in the ecosystem of mining areas 1,2 . According to the latest data released by the China Resources Recycling Association, the comprehensive utilization rate of China's coal gangue is less than 60%, to enhance the comprehensive utilization rate of coal gangue has also become a top priority for the realization of green coal mining 3 . Geopolymer is an inorganic cementitious material obtained from silica-aluminum minerals by alkaline solution excitation at room temperature 4 , which has excellent properties such as early strength, high temperature and acid and alkali corrosion resistance, as well as the advantages of lower energy consumption and CO 2 emission, and therefore becomes a research hotspot in the field of solid waste resource utilization 5–7 . Coal gangue is rich in aluminum-silicate mineral fractions, among which the content of SiO 2 and Al 2 O 3 is as high as 60% ~ 95%, which is highly potential for the preparation of geopolymers 8,9 . It is found that replacing part of the coal gangue with slag could accelerate the generation of C-S-(A)-H gel crystals, thereby refining the internal structure, resulting in a significant increase in the compressive strength of the geopolymer 10,11 . For example, Ma et al suggested that when the slag substitution rate is increased to 20%, the compressive strength of geopolymer is much higher than that of P.O42.5 cement, which is gradually viewed as a substitute for cement 12 . In addition, compared to cement, the matrix pore fluid of geopolymer is rich in ions and has a higher porosity in the range of very small pores (< 6 nm), thus determining its superior electrical conductivity 13,14 . For example, Rovnaník et al. compared the properties of geopolymer with those of cement and found that the conductive properties of geopolymer are significantly better than those of cement. Moreover, the geopolymers show significant self-monitoring properties, while the self-inductive properties of the cement does not meet requirements of the application 15 . A similar conclusion is reached by S. Vaiday et al. that the electrical conductivity of carbon fiber-geopolymer is much better than that of carbon fiber-cement 16 . It can be seen that geopolymers have the potential value of preparing conductive concrete, which in turn can be applied in a number of fields such as non-destructive testing 17 , ice and snow melting 18 , electromagnetic shielding 19 , building heating 20 and lightning protection 21 . More notably, the coal gangue itself exists a large number of active groups, thereby also improving the conductivity of the material considerably 22,23 . However, the current research on coal gangue based geopolymer mainly focuses on how to improve the mechanical strength and be used as a cement replacement product, while relatively little research has been done on their electrical conductivity. Resistivity is a key indicator of the electrical conductivity of geopolymers, and its level is closely related to the differences in the internal structure of the matrix, such as microstructure, pore structure, porosity, and pore size distribution 15 . At the same time, the resistivity is shown to be a function of content of ionic liquid and the migration of ions in the pore solution 24,25 . Studies shown that geopolymer slurries are composed of three-dimensional aluminosilicates, which are more homogeneous 26 . And it has been reported that for homogeneous materials or materials of single-phase composition, the resistivity decreased with increasing densification 27 . Also, P.J. Tumidajski et al. argued that dense microstructures are capable of generating more electronic circuits, resulting in lower resistivity 28 . However, J.M Cai 29 et al found that the addition of slag to fly ash -based geopolymers or metakaolin-based geopolymers could accelerate the hydration reaction, which in turn promoted the generation of C-(A)-S-H gels and filled the internal structure. But at the same time, it also resulted in the consumption of OH − ions and SiO 3 2− ions in the pore space increased. Therefore, due to the addition of slag, the microstructure is made denser, but the content of conductive ions in the pores is reduced, still resulting in higher resistivity. It can be seen that changes in the resistivity of geopolymer caused by external factors are not always a simple process. Thus, resistivity as a fundamental physical behavior of geopolymers still needs to be discussed and studied more comprehensively. In this study, the geopolymer is prepared by using coal gangue and slag under alkaline excitation. The effects of alkali equivalent, slag substitution rate, modulus and water-cement ratio on geopolymer's consistency, compressive strength and resistivity are investigated. The changes of the resistivity of the specimen with the curing age and water content are further discussed. It provides theoretical guidance for resource utilization of coal gangue and engineering applications of geopolymers. Experimental Raw materials The samples of coal gangue used in the test are non-spontaneous combustion coal gangue (CG) from Jiangxi mining area. The samples are crushed, ground and sieved to obtain the raw coal gangue powder with particle size below 200 mesh (0.075 mm), and then calcined at 700°C for 4 hours in the muffle furnace to obtain the coal gangue powder for test (the uncalcined and calcined coal gangue powder is shown in Fig. 1 ). S95 grade slag powder is introduced as a calcium source 10 . The main chemical compositions of the two materials are shown in Table 1 . It can be seen that the accumulated content of SiO 2 and Al 2 O 3 in the coal gangue is greater than 70%, which is considered to have some volcanic ash effect 30 . The mineral compositions in slag and calcined coal gangue analyzed by X-ray diffraction (XRD) are shown in Fig. 2 . It can be seen that the main mineral components of calcined coal gangue are quartz and muscovite, and the main mineral components of slag are calcium-aluminum yellow feldspar and calcium-magnesium yellow feldspar. The alkali exciter for the test is obtained by configuring sodium-based water glass with a modulus of 2.2 and sodium hydroxide (analytically pure) with a purity of 96%. Note that after mixing, the alkali exciter is cooled to room temperature for at least 24 hours before use. River sand is also used as a fine aggregate with a fineness modulus of 2.75 and the content of SiO 2 over 97%. Tap water of Nanchang was used as test water. Table 1 The main chemical composition (by mass/%) of calcined coal gangue and slag. Materials SiO 2 Al 2 O 3 CaO MgO SO 3 K 2 O Fe 2 O 3 Na 2 O P 2 O 5 Others CG 53.47 17.75 0.35 15.44 -- 7.05 0.16 4.51 1.27 -- SG 33.06 15.04 39.29 9.96 1.90 -- -- -- -- 0.75 Mixes design and specimens preparation In this study, geopolymers are prepared using single factor test, and compressive strength and resistivity are utilized to evaluate the mechanical and electrical conductivity of the specimens, respectively. The experiment involves four single factors that could affect the mechanical and electrical conductivity of the specimen, each single factor involves five levels of factors, a total of 20 sets of specimens were prepared, to study the alkali equivalent (mass fraction of Na 2 O to cementitious material: 8%, 10%, 12%, 14%, 16%), slag substitution rate (0%, 15%, 30%, 45%, 55%), modulus (molar ratio of SiO 2 to Na 2 O in alkali exciters: 0.8, 1.0, 1.2, 1.4, 1.6), and water-cement ratio (0.45, 0.45, 0.50, 0.55, 0.60) on compressive strength and resistivity. In the test, when studying the effect of one single factor on the performance of specimen, the test parameter of slag substitution rate is selected according to 45%, and the remaining other single factors are selected according to the intermediate level of their design (the details of all samples is shown in Table 2 ). The process for sample preparation: firstly, water, sodium hydroxide, water glass according to Table 2 to prepare exciter for the test, stirred thoroughly and then placed the solution at room temperature aging for 24 hours standby; then, coal gangue, slag and sand were poured into the stirring pot and stirred at low speed for 3 min; then the alkaline exciter after aging was poured into the stirring pot, stirred at low speed for 2 min, and then stirred at high speed for 3 min. The freshly mixed slurry was injected into molds with dimensions of 40 mm × 40 mm × 160 mm and 40 mm × 40 mm × 40 mm, respectively. Next, after the sample was vibrated, their surface was covered with plastic wrap. After curing for 24 hours in a natural environment, the molds were demolded, and then specimens transferred to a water tank at 20 ± 1℃ for curing until the specified age for mechanical and electrical conductivity tests (the preparation scheme for the sample is shown in Fig. 3 . Table 2 Details of all samples Sample No. CG/w% SG/w% Water/w% NaOH/w% water glass/w% Sand/w% N8 55 45 32.5 4.9 31.0 300 N10 28.1 6.2 38.8 N12 23.7 7.4 46.5 N14 19.3 8.6 54.3 N16 15.0 9.8 62.0 S0 100 0 23.7 7.4 46.5 S15 85 15 23.7 7.4 46.5 S30 70 30 23.7 7.4 46.5 S60 40 60 23.7 7.4 46.5 M8 55 45 30.3 9.4 34.9 M1.0 28.1 8.7 38.8 M1.4 19.3 6.0 54.3 M1.6 15.0 4.7 62.0 W4.0 55 45 13.7 7.4 46.5 W4.5 18.7 7.4 46.5 W5.5 28.7 7.4 46.5 W6.0 33.7 7.4 46.5 Workability The consistency of the geopolymer is tested according to the provisions in JGJ/T 70-2009 Standard for Test Methods of Basic Properties of Building Mortar. Compression strength The SHT4305 electro-hydraulic servo universal testing machine is used to test the compressive strength of the specimens, as shown in Fig. 4 a. The testing process is carried out according to the Method for Testing the Strength of Cementitious Sand (GB/T 17671 − 2021), and the loading rate is set to 2400 N/s. Microstructural Mineral composition analysis of slag and calcined gangue is carried out using a D8-advance (Fig. 4 b) polycrystalline X-ray diffractometer with a voltage of 40 kv, 2θ from 10°/20° to 80°, a step size of 0.02°, and a scanning speed of 5°/min. The fragments of geopolymers from the tests of compressive strength were collected and analyzed for micro-morphology using a FEI Nova NanoSEM 450 (Fig. 4 c) scanning electron microscope (SEM). The elemental content of the specimens was quantitatively analyzed using an energy spectrometer (EDS). Electrical resistivity The two-electrode method is used to test the resistivity of specimen 29 . The size of the specimen is 40 mm×40 mm×40 mm, the material for electrode is stainless steel wire mesh with the size of 30 mm×60 mm, and electrodes are inserted into the interior of the specimen at intervals of 20 mm (the dimensions of the specimen is shown in Fig. 5 a). The circuit tested is a 3V DC power supply connects in series with the resistance boxes and the sample to be tested, and the voltage across the resistance boxes is recorded with a voltmeter (schematic diagram of the circuit tested is shown in Fig. 5 b). In order to minimize the error of test, three specimens are designed for each group and the average value of their resistivity is taken as the final result. In addition, to eliminate the effect of water on the resistivity of the specimens, constant humidity is maintained during the test. Resistance of the specimen: $$\\:R=\\frac{U-{U}_{1}}{{U}_{1}/{R}_{1}}$$ 1 Where: R is the resistance of the test piece to be tested (Ω); R 1 is the constant value resistance (Ω); U is the supply voltage (V); U 1 is the voltage at the ends of the constant value resistance (V). Resistivity of the specimen: $$\\:\\rho\\:=\\frac{R*S}{L}$$ 2 Where: ρ is the specimen resistivity (Ω. m); S is the cross-sectional area of the current through the specimen (m 2 ); L is the distance between the two electrodes (m). The specimens are removed from the water tank and placed in the muffle furnace at 45°C for 48 hours. The drying resistivity is tested to study the effect of water content on resistivity. The change rate of resistance (FCR) is calculated according to Eq. ( 3 ). $$\\:FCR=\\frac{△p}{{p}_{0}}=\\frac{{p}_{i}-{p}_{0}}{{p}_{i}}$$ 3 Where △p is the change in resistivity (Ω. m); p i is the resistance value of the specimen after the change by water content (Ω. m); p 0 is the initial resistance value of the specimen (Ω. m). Results and discussion Consistency As shown in Fig. 6 , the consistency of the geopolymer is closely related to the dosage of all four factors (alkali equivalent, slag substitution rate, modulus and water-cement ratio). The consistency of specimen is decreased with increasing alkali equivalent and increased with increasing slag substitution rate, increasing modulus and increasing water-cement ratio. As can be seen in Fig. 6 , the consistency of thirteen groups of specimens, including N10, N12, N14, S15, S30, S45, S60, M1.2, M1.4, W4.0, W4.5, W5.0, W5.5, is in the range of 7 cm ~ 11 cm, which meets the basic requirements of the consistency of mortar in Chinese standard (GB/T 25181 − 2019) and conditions of actual construction in China 31 . Compressive strength Figure 7 describes the compressive strength for geopolymers with different factor (alkali equivalent, slag substitution rate, modulus and water-cement ratio). It is found that the compressive strength of the specimens is increased and then decreased with the increase of alkali equivalent (Fig. 7 a), and the compressive strengths at 7 days and 28 days reached the maximum value when the alkali equivalent was taken as 10%, which increased by 53.62% and 60.99% compared with that when the alkali equivalent is 16%. OH − ions provide an alkaline environment for the hydration reaction and accelerate the dissolution of active units such as [AlO 4 ] 5− ions and [SiO 4 ] 4− ions in the precursors 32 . Thus, the hydration reaction is facilitated, thus the amount of gelling products generated is increased and the internal structure is filled, resulting in higher compressive strength. However, when OH − ions are in excess, the rate at which the structure of the precursor is destroyed and the rate at which the hydration products are formed are too fast 33 . Therefore, the products do not have time to diffuse and adhere to the surface of precursor to form a protective film, so that the later reaction process is blocked. Thus, the compressive strength is reduced by too high alkali equivalent. The compressive strength of the geopolymer is significantly increased with increasing slag substitution rate (Fig. 7 b). When the slag substitution rate is reached 60%, the compressive strength of the specimens under the age of 7 days and 28 days is as high as 66.07 MPa and 81.33 MPa, respectively, which is 374.38% and 226.72% higher than that of the all-gangue based geopolymer, indicating that the compressive strength of the specimens is greatly affected by the slag substitution rate. This is due to the fact that the content of Ca 2+ in the system is continuously increased with the increase of slag substitution rate, and more [AlO 4 ] 5− and [SiO 4 ] 4− units in the pores are combined to produce C-S-H and C-A-S-H gel crystals. Meanwhile, the high charge density of Ca 2+ ions drives gel precipitation to from the formation of the three-dimensional disordered mesh that fills the internal structure of the geopolymer 12 , and ultimately the compressive strength of the geopolymer is improved. The compressive strength of the geopolymer is increased and then decreased with increasing modulus (Fig. 7 c). The maximum compressive strength of the geopolymer is obtained when the modulus is 1.4. As can be seen in Fig. 8 , the specific surface area of the micelles in the alkali exciters is increased with increasing modulus, resulting in an enhanced ability of the micelles to adsorb silica-oxygen anion groups, metal ions, and polymerization products. Thus, OH − ions penetrate into the precursor material more easily, so that the later hydration process is promoted. Eventually, a dense and stable internal structure is formed, leading to an increase in compressive strength. However, an increase in modulus also means a relative decrease in the content of OH − ions in the pores, and when its content is not enough to drive the active units to dissolve, the compressive strength of the geopolymer is decreased 34 . Therefore, the compressive strength is significantly decreased when the modulus is taken to 1.6. The compressive strength of the geopolymer is reduced with the increasing water-cement ratio (Fig. 7 d). The free water content within the geopolymer is increased with the increase of the water-cement ratio, resulting in the increase of pore size and the number of pores, and the internal densification and stability of the geopolymer is reduced, so that the compressive strength of the geopolymer is decreased. In addition, an increase in the water-cement ratio causes the concentration of alkali exciter to be reduced, which may also induce lower compressive strength. It is worth noting that when the water-cement ratio is 4.0, the compressive strength of geopolymer at 28 days is reached 80.10 MPa, which is similar to that of geopolymer when the slag substitution rate is 60%. This shows that the appropriate reduction of the water-cement ratio, not only to obtain a higher compressive strength, but also to increase the utilization rate of coal gangue, maximizing the realization of its secondary high-value utilization. Resistivity Influence of ratios of geopolymer The effect of alkali equivalent on resistivity is shown in Fig. 9 a. It can be seen that the resistivity is decreased and then increased with increasing alkali equivalent. As can be seen in Eq. 4, the alkali exciter undergoes hydrolysis in contact with water to produce NaOH as well as Si (OH) 4 , and NaOH exists in the pore solution in free states such as Na + and OH − ions. 2Na 2 O· n SiO 2 + 2( n -1) H 2 O→4NaOH + n Si(OH) 4 ( 4 ) However, Na + ions act as charge balancers, and a small amount of Na + ions bind to the active units to produce N-A-S-H gels, while a large amount of Na + ions remain in the free state in the pore solution 35 . Therefore, the amount of ionic liquid in the pores is enlarged with the increase of equivalent, which leads to the increase of carrier concentration, resulting in the enhancement of ionic conductivity. However, in combination with the test results of alkali equivalent on compressive strength, it is concluded that the hydration process was seriously inhibited when the alkali equivalent was increased to 16%, and the internal structural densification is reduced (Fig. 9 a), which is unfavorable for migration of ions. Carrier concentration and ion mobility are the main factors affecting ionic conductivity 24 , thus only increasing the equivalent in the appropriate interval could reduce the resistivity. The effect of slag substitution ratio on resistivity is shown in Fig. 9 b. It can be seen that the resistivity is decreased and then increased with increasing slag substitution ratio, and the minimum of resistivity was obtained at slag substitution rate of 15%. As can be seen in Fig. 9 b, When the slag substitution rate is 0, there are penetrating cracks in the specimen, and the internal structure is seriously degraded. When the slag substitution rate reaches 15%, the number of cracks inside the specimen is significantly reduced, and it shows a short and fine morphology, and the density and integrity of its microstructure are significantly improved. The microstructure of the geopolymer has a significant effect on its resistivity, and a compact and dense structure could generate more electronic circuits, resulting in a lower resistivity. Therefore, when the substitution rate is less than 15%, the density of the structure is increased with increasing slag substitution rate, and thus the resistivity is shown to be significantly reduced with the increase of substitution rate. After that, the phenomenon of resistivity being increased with increasing substitution rate may be attributed to two reasons. Firstly, the reaction rate of alkali exciters with slag is much faster than that with coal gangue, resulting in a sharp decrease in the concentration of conductive ions 36,37 . Therefore, although the addition of slag makes the microstructure denser, it reduces the content of conductive ions in the system. Secondly, the presence of active groups on the surface of coal gangue could improve the conductivity of the geopolymer, but the number of active groups is reduced with the increase of slag substitution rate, resulting in an increase in resistivity. The effect of modulus on resistivity is shown in Fig. 9 c. It can be seen that the resistivity is decreased and then increased with increasing modulus. The resistivity of modulus taken 0.8 and 1.6 increased by 71.42% and 90.24% respectively as compared to modulus taken 1.0. As can be seen in Fig. 9 c, the compressive strength at 28 days does not reach 42.5 MPa when the modulus is taken as 0.8 and 1.6, indicating that the internal structure is severely degraded, and thus the migration of ionic is suppressed, so the resistivity of specimen is larger. When the modulus is taken between 1.0 and 1.4, the resistivity is increased with the increase of modulus, which may be due to the increase of modulus promoting the hydration reaction, thus the consumption of ions is increased and the concentration of internal carriers is reduced, resulting in the increase of resistivity. The effect of water-cement ratio on resistivity is shown in Fig. 9 d. It can be seen that the resistivity is decreased with increasing water-cement ratio. This phenomenon is attributed to pore connectivity and water saturation. The connectivity porosity inside the matrix is a key factor affecting diffusion of ions, and more connectivity porosity means easier diffusion of ions, thus more favorable for ions to migrate and diffuse in the capillary channels filled with free water 38,39 . Therefore, the increase in the water-cement ratio causes the connectivity porosity of matrix (Fig. 9 d, Fig. 10 ) and free water content to be increased, resulting in lower resistivity. Influence of Curing Ages The effect of curing ages on resistivity is shown in Fig. 11 . It can be seen that the resistivity is increased with increasing age. The above phenomenon could be attributed to two reasons. Firstly, the hydration reaction of the geopolymer takes a period of time. At early age, the free ions such as Ca 2+ , K + and SO 4 2− ions are high inside the pores, and the ions are gradually consumed with the extension of curing ages. Secondly, when the age is prolonged, the free water in the pores is continuously absorbed by the hydration reaction and forced to be in the form of crystal-water. Therefore, the content of ionic liquid is decreased with age, resulting in a weakening of ionic conductivity and thus an increase in resistivity. The SEM micrograph of raw materials and specimen (N12) at 7 days and 28 days of age are shown in Fig. 12 . Comparing Fig. 12 c and Fig. 12 d, it can be seen that at 7 days of age, the amount of internal gelation and flocculation hydration products is low, but at 28 days of age, there is a significant increase in internal agglomerates and flocculation gel crystal products as well as spongy hydrated calcium-aluminum particles, and the densification of the internal structure is improved. Further comparing the SEM images of the specimens of N12 at 7 and 28 days for the paste (Fig. 11 e and Fig. 11 f), it can also be clearly found that the amount of hydration products and the densification of the internal structure were significantly enhanced with increasing age. That is to say, the hydration reaction inside the matrix is still going on after 7 days of age, and the consumption of ionic and the transformation of free water to crystal-water also exist, so the content of ionic liquid is still reduced. The decrease in ionic liquid leads to a deterioration of ionic conductivity, which is consistent with the results of the change in resistivity. In addition, the density and integrity of internal structural is enhanced leading to higher the development of strength, which is also consistent with the results of compressive strength with age. The XRD diffractograms and EDS spectra of specimen (N12) are shown in Fig. 13 . As shown in Fig. 13 a, a small sharp peak is found near 29.5°, which could correspond to the C-S-H and C-A-S-H gel products generated by the reaction, as shown against the standard diffraction pattern. Then in the EDS spectra, it is found that the product is mainly composed of elements such as C, O, Si, Al, and Ca, which is consistent with the results of the XRD spectra. It is inferred that the hydration products are between C-S-H and C-A-S-H or mixtures thereof, which is similar to the experimental results of Ma et al 12 . It can be further found by EDS spectroscopy that at the age of 7d (Fig. 12 a), the ratios of Ca/Si and Al/Si in the products are 0.67 and 0.38, respectively. However, at 28 d of age (Fig. 12 b), the ratios of Ca/Si and Al/Si are 0.58 and 0.40, respectively. Decreased the ratio of Ca/Si and increased the ratio of Al/Si indicate a gradual transition from C-S-H gels to C-A-S-H gels with increasing age 40 . It is confirmed that Ca 2+ ions produced by the dissolution of slag under the action of alkali are consumed during the reaction, while Al 3+ ions produced by dissolution are further involved in the reaction. This also indicates to some extent that the extension of age increases the consumption of ionic, resulting in an increase in specimen resistivity. In addition, in order to explore the changing law of the degree of influence of four factors on resistivity with age, such as alkali equivalent (N), slag substitution rate (S), modulus (M) and water-cement ratio (W), the specimens under the difference of ages are subjected to range analysis, and the results are shown in Fig. 14 . R' is range of a particular factor and the expression is shown in Eq. 5 : $$\\:{R}^{’}={max}({p}_{i})-{min}({p}_{i})$$ 5 Where: p i is the actual test indicator corresponding to the i level of a factor. As can be seen in Fig. 14 , the relationship between the effects of the four factors on the resistivity of the specimens for 7 days is N > M > S > W; the relationship for both 14 days and 28 days is M > S > N > W. At different ages, the influence of W on resistivity was lower than that of other factors. And with the increase of age, the influence of N on resistivity is decreased, and the influence of M and S on resistivity is increased. This is mainly due to the fact that there are two ways of “external introduction” and “internal consumption” of N to affect the content of ionic liquid of the matrix compared to M and S. Increasing N means the content of Na + ions in the pores increased. What's more, the content of Na + ions in the pores is nearly 10 3 mmol/L higher than that of other ions 35 . Therefore, compared with the difference in resistivity caused by the consumption of hydration reaction, the difference in resistivity brought about by the difference in the content of externally introduced ions is greater. And the difference in the content of externally introduced ions is created when the alkali exciter was added, and therefore, the effect of N on resistivity is more significant at the early age. Influence of Water Content The effect of water content on resistivity is shown in Fig. 15 . It can be seen that the resistivity is increased with increasing ages. When the specimen is changed from the surface dry state to the dry state, the resistivity of different ratios is increased by nearly 5 ~ 6 orders of magnitude, and the value of FCR is reached 10 4 , indicating that the conductivity of the specimen is significantly affected by the water content, and the ambient humidity can affect the resistivity of specimen by influencing the water content. Reduced water content restricts the diffusion of ions, resulting in increased resistivity 41 . The free water in the pores is the carrier of the migration and diffusion of ions, and the decrease in water content results in the internal channels, which were filled with free water, becoming anhydrous. Conclusions In this study, geopolymers ware prepared using single factor test, and consistency, compressive strength and resistivity are utilized to evaluate the workability, mechanical and electrical conductivity of the specimens, respectively, and the changes of the resistivity of the specimen with the curing age and water content are further discussed. Based on the experimental results, the following conclusions may be drawn: ( 1 ) The consistency of 13 groups of specimens, including N10, N12, N14, S15, S30, S45, S60, M1.2, M1.4, W4.0, W4.5, W5.0, W5.5, etc., is within the range of 7 cm ~ 11 cm. They meet the basic requirements for the consistency of the mortar of the Chinese standard (GB/T 25181 − 2019) and the actual construction conditions in China. ( 2 ) The compressive strength of the specimens was first increased and then decreased with increasing alkali equivalent and increasing modulus, increased with increasing slag substitution ratio, and decreased with increasing water-cement ratio. Among them, the compressive strengths of the specimens at 28 days were elevated to more than 80 MPa when the alkali equivalent, slag substitution ratio, modulus and water-cement ratio were taken as 12%, 45%, 1.2 and 4 respectively and 12%, 55%, 1.2 and 5 respectively. ( 3 ) The resistivity of the specimens was first decreased and then increased with increasing alkali equivalent, increasing slag substitution ratio and increasing modulus, and was reduced with increasing water-cement ratio. And due to the content of ionic liquid in the pore space is reduced with age, the resistivity is increased with age. In addition, the effect of water-cement ratio on resistivity is minimized at different ages, while the alkali equivalent is attenuated with increasing age. ( 4 ) The resistivity was significantly increased with decreasing water content, due to the diffusion of ions is limited by the decrease in water content. In particular, the values of FCR for different samples are as high as 10 4 when the specimens are transformed from the face-dry state to the dry state. Declarations Competing interests The authors declare that they have no known conflicts of interest that might influence the work reported in this paper. Author Contribution Wenhua Zha designed and directed this project. Wenfang Lv: Measurements, Forma analysis, Investigation, Writing – original draft. Jielian Li and Tao Xu: Measurements. Denghong Chen: Data curation. Wenhua Zha: provided suggestions for the project. All the authors discussed the results and commented on the manuscript. Acknowledgements The authors gratefully acknowledge the financial support for this research provided by the National Natural Science Foundation of China (Grant No. 52264003), Double Thousand Plan Support Project of Jiangxi Province (Grant No. DHSQT22021002). Data Availability The datasets generated and/or analysed during the current study are not publicly available due [REASON WHY DATA ARE NOT PUBLIC] but are available from the corresponding author on reasonable request. References Gao, S., Zhao, G., Guo, L., Zhou, L., Yuan, K. Utilization of coal gangue as coarse aggregates in str-uctural concrete. Construction and Building Materials 268: 121212 (2021). Wang, Q., Zhu, L., Lu, C., Liu, Y., Yu, Q., Chen, S. Investigation on the effect of calcium on the properties of geopolymer prepared from uncalcined coal gangue. Polymers 15(5): 1241 (2023). Zhang, B., Yang, K., Zhang, K., Wang, Q., Wu, N. 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Effects of mix design parameters on heat of geopolymerization, set time, and compressive strength of high calcium fly ash geopolymer. Construction and Building Materials 228: 116763 (2019). Lu, Y., Song, L., Xu, Y., Duan, P., Wang, X. Microstructure and Efflorescence Resistance of Metakaolin Geopolymer Modified by 5A Zeolite. Materials 16(22): 7243 (2023). Puligilla, S., Mondal, P. Role of slag in micro- structural development and hardening of fly ash-slag geopolymer. Cement and concrete Research 43: 70-80 (2013). Nath, S. K. Geopolymerization behavior of ferrochrome slag and fly ash blends. Construction and Building Materials 181: 487-494 (2018). He, R., Ma, H., Hafiz, R. B., Fu, C., Jin, X., He, J. Determining porosity and pore network connectivity of cement-based materials by a modified non-contact electrical resistivity measurement: Experiment and theory. Materials & Design 156: 82-92 (2018). Zhao, R., Weng, Y., Tuan, C. Y., Xu, A. The influence of water/cement ratio and air entrainment on the electric resistivity of ionically conductive mortar. Materials 12(7): 1125 (2019). Tian, Y., Wang, Y., Chai, H., Zhao, L., Sun, H., Zhang, H. Study on the properties and interfacial transition zone of coal gasification slag aggregate and mineral powder geopolymer mortar. Construction and Building Materials 414: 134864 (2024). Wang, L., Aslani, F. Electrical resistivity and piezoresistivity of cement mortar containing ground granulated blast furnace slag. Construction and Building Materials 263: 120243 (2020). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {\"props\":{\"pageProps\":{\"initialData\":{\"identity\":\"rs-4691610\",\"acceptedTermsAndConditions\":true,\"allowDirectSubmit\":true,\"archivedVersions\":[],\"articleType\":\"Article\",\"associatedPublications\":[],\"authors\":[{\"id\":329442114,\"identity\":\"d965289d-353a-462a-8f7e-b42a414b4eb5\",\"order_by\":0,\"name\":\"Wenhua Zha\",\"email\":\"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAoElEQVRIiWNgGAWjYDACCQY2BoYKCTl+ErWcsTCWbCBJC2NbReIGorUY3G5/9uDnPAnGDQzMDx/dIErLnQPphr3bJJjNGdiMjXOI0WJ2I+GYBO82CTbLBh42aSK1JLZJ/p0jwWNwgHgtyWzSvA0SEsRrsb+RxiYtc0zCQLKZWL9Izkh/Jvmmpq6+n7354WOitCAAM2nKR8EoGAWjYBTgAwD/sixOA0vf8gAAAABJRU5ErkJggg==\",\"orcid\":\"\",\"institution\":\"East China University of Technology\",\"correspondingAuthor\":true,\"prefix\":\"\",\"firstName\":\"Wenhua\",\"middleName\":\"\",\"lastName\":\"Zha\",\"suffix\":\"\"},{\"id\":329442118,\"identity\":\"425e4ba5-abd4-499e-9116-f1ec2f1aa146\",\"order_by\":1,\"name\":\"Wenfang Lv\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"East China University of Technology\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Wenfang\",\"middleName\":\"\",\"lastName\":\"Lv\",\"suffix\":\"\"},{\"id\":329442120,\"identity\":\"88b4ca02-c432-4368-9689-2bdccf63758d\",\"order_by\":2,\"name\":\"Jielian Li\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"East China University of Technology\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Jielian\",\"middleName\":\"\",\"lastName\":\"Li\",\"suffix\":\"\"},{\"id\":329442123,\"identity\":\"042bbb25-2fa3-4aa1-9263-1ada557c3e04\",\"order_by\":3,\"name\":\"Tao Xu\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"East China University of Technology\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Tao\",\"middleName\":\"\",\"lastName\":\"Xu\",\"suffix\":\"\"},{\"id\":329442126,\"identity\":\"63135ec8-982d-4c51-adaa-877677684f25\",\"order_by\":4,\"name\":\"Denghong Chen\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Anhui University of Science and Technology\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Denghong\",\"middleName\":\"\",\"lastName\":\"Chen\",\"suffix\":\"\"}],\"badges\":[],\"createdAt\":\"2024-07-05 10:31:41\",\"currentVersionCode\":1,\"declarations\":\"\",\"doi\":\"10.21203/rs.3.rs-4691610/v1\",\"doiUrl\":\"https://doi.org/10.21203/rs.3.rs-4691610/v1\",\"draftVersion\":[],\"editorialEvents\":[],\"editorialNote\":\"\",\"failedWorkflow\":false,\"files\":[{\"id\":61405106,\"identity\":\"befeea78-56ea-41f3-a144-5948166ed346\",\"added_by\":\"auto\",\"created_at\":\"2024-07-30 10:48:37\",\"extension\":\"png\",\"order_by\":1,\"title\":\"Figure 1\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":563115,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eApparent color change of coal gangue before and after being calcined\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"floatimage1.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-4691610/v1/c1a827c4d9620881e6bfb97e.png\"},{\"id\":61405103,\"identity\":\"e1f75fee-9ecb-4c9c-a551-638d431ad4be\",\"added_by\":\"auto\",\"created_at\":\"2024-07-30 10:48:37\",\"extension\":\"png\",\"order_by\":2,\"title\":\"Figure 2\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":108657,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eXRD diffractograms of raw materials: \\u003cstrong\\u003ea:\\u003c/strong\\u003eCG; 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\\u003cstrong\\u003eb:\\u003c/strong\\u003e EDS spectra at 7 days of age; \\u003cstrong\\u003ec\\u003c/strong\\u003e: EDS spectra at 28 days of age\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"floatimage13.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-4691610/v1/29367b62e11c71a48221a6c2.png\"},{\"id\":61405116,\"identity\":\"2a7aadff-aa18-47d3-9815-f438d99b34cf\",\"added_by\":\"auto\",\"created_at\":\"2024-07-30 10:48:38\",\"extension\":\"png\",\"order_by\":14,\"title\":\"Figure 14\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":106814,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003erange analysis of geopolymer at different curing ages\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"floatimage14.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-4691610/v1/4de40cc2ad33125145871ec0.png\"},{\"id\":61405113,\"identity\":\"85c081c8-55db-4cc0-aca1-648961179ec2\",\"added_by\":\"auto\",\"created_at\":\"2024-07-30 10:48:38\",\"extension\":\"png\",\"order_by\":15,\"title\":\"Figure 15\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":383549,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eResistivity for geopolymers with different water content:\\u003cstrong\\u003e a: \\u003c/strong\\u003ealkali equivalent;\\u003cstrong\\u003e b: \\u003c/strong\\u003eslag substitution rate; \\u003cstrong\\u003ec: \\u003c/strong\\u003emodulus; \\u003cstrong\\u003ed:\\u003c/strong\\u003e water-cement ratio\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"floatimage15.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-4691610/v1/a59ba50c3db59e2629dbe2a9.png\"},{\"id\":64806426,\"identity\":\"f88e25b6-7d18-47a1-bbdc-9458afe6377d\",\"added_by\":\"auto\",\"created_at\":\"2024-09-19 04:34:38\",\"extension\":\"pdf\",\"order_by\":0,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"manuscript-pdf\",\"size\":7239269,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"manuscript.pdf\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-4691610/v1/e3f673c7-236b-4200-ad9b-8940b54d78de.pdf\"}],\"financialInterests\":\"No competing interests reported.\",\"formattedTitle\":\"Preparation of coal gangue based geopolymer and electrical conductivity studies\",\"fulltext\":[{\"header\":\"Introduction\",\"content\":\"\\u003cp\\u003eCoal gangue is a solid waste discharged during coal mining, which has accumulated more than 7\\u0026nbsp;billion level in China, and its encroachment on land resources and leaching of heavy metals are causing a serious imbalance in the ecosystem of mining areas\\u003csup\\u003e1,2\\u003c/sup\\u003e. According to the latest data released by the China Resources Recycling Association, the comprehensive utilization rate of China's coal gangue is less than 60%, to enhance the comprehensive utilization rate of coal gangue has also become a top priority for the realization of green coal mining\\u003csup\\u003e3\\u003c/sup\\u003e.\\u003c/p\\u003e \\u003cp\\u003eGeopolymer is an inorganic cementitious material obtained from silica-aluminum minerals by alkaline solution excitation at room temperature\\u003csup\\u003e4\\u003c/sup\\u003e, which has excellent properties such as early strength, high temperature and acid and alkali corrosion resistance, as well as the advantages of lower energy consumption and CO\\u003csub\\u003e2\\u003c/sub\\u003e emission, and therefore becomes a research hotspot in the field of solid waste resource utilization\\u003csup\\u003e5\\u0026ndash;7\\u003c/sup\\u003e. Coal gangue is rich in aluminum-silicate mineral fractions, among which the content of SiO\\u003csub\\u003e2\\u003c/sub\\u003e and Al\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e3\\u003c/sub\\u003e is as high as 60% ~ 95%, which is highly potential for the preparation of geopolymers\\u003csup\\u003e8,9\\u003c/sup\\u003e. It is found that replacing part of the coal gangue with slag could accelerate the generation of C-S-(A)-H gel crystals, thereby refining the internal structure, resulting in a significant increase in the compressive strength of the geopolymer\\u003csup\\u003e10,11\\u003c/sup\\u003e. For example, Ma et al suggested that when the slag substitution rate is increased to 20%, the compressive strength of geopolymer is much higher than that of P.O42.5 cement, which is gradually viewed as a substitute for cement\\u003csup\\u003e12\\u003c/sup\\u003e.\\u003c/p\\u003e \\u003cp\\u003eIn addition, compared to cement, the matrix pore fluid of geopolymer is rich in ions and has a higher porosity in the range of very small pores (\\u0026lt;\\u0026thinsp;6 nm), thus determining its superior electrical conductivity\\u003csup\\u003e13,14\\u003c/sup\\u003e. For example, Rovnan\\u0026iacute;k et al. compared the properties of geopolymer with those of cement and found that the conductive properties of geopolymer are significantly better than those of cement. Moreover, the geopolymers show significant self-monitoring properties, while the self-inductive properties of the cement does not meet requirements of the application\\u003csup\\u003e15\\u003c/sup\\u003e. A similar conclusion is reached by S. Vaiday et al. that the electrical conductivity of carbon fiber-geopolymer is much better than that of carbon fiber-cement\\u003csup\\u003e16\\u003c/sup\\u003e. It can be seen that geopolymers have the potential value of preparing conductive concrete, which in turn can be applied in a number of fields such as non-destructive testing\\u003csup\\u003e17\\u003c/sup\\u003e, ice and snow melting \\u003csup\\u003e18\\u003c/sup\\u003e, electromagnetic shielding\\u003csup\\u003e19\\u003c/sup\\u003e, building heating\\u003csup\\u003e20\\u003c/sup\\u003e and lightning protection\\u003csup\\u003e21\\u003c/sup\\u003e. More notably, the coal gangue itself exists a large number of active groups, thereby also improving the conductivity of the material considerably\\u003csup\\u003e22,23\\u003c/sup\\u003e. However, the current research on coal gangue based geopolymer mainly focuses on how to improve the mechanical strength and be used as a cement replacement product, while relatively little research has been done on their electrical conductivity.\\u003c/p\\u003e \\u003cp\\u003eResistivity is a key indicator of the electrical conductivity of geopolymers, and its level is closely related to the differences in the internal structure of the matrix, such as microstructure, pore structure, porosity, and pore size distribution\\u003csup\\u003e15\\u003c/sup\\u003e. At the same time, the resistivity is shown to be a function of content of ionic liquid and the migration of ions in the pore solution\\u003csup\\u003e24,25\\u003c/sup\\u003e. Studies shown that geopolymer slurries are composed of three-dimensional aluminosilicates, which are more homogeneous\\u003csup\\u003e26\\u003c/sup\\u003e. And it has been reported that for homogeneous materials or materials of single-phase composition, the resistivity decreased with increasing densification\\u003csup\\u003e27\\u003c/sup\\u003e. Also, P.J. Tumidajski et al. argued that dense microstructures are capable of generating more electronic circuits, resulting in lower resistivity\\u003csup\\u003e28\\u003c/sup\\u003e. However, J.M Cai\\u003csup\\u003e29\\u003c/sup\\u003e et al found that the addition of slag to fly ash -based geopolymers or metakaolin-based geopolymers could accelerate the hydration reaction, which in turn promoted the generation of C-(A)-S-H gels and filled the internal structure. But at the same time, it also resulted in the consumption of OH\\u003csup\\u003e\\u0026minus;\\u003c/sup\\u003e ions and SiO\\u003csub\\u003e3\\u003c/sub\\u003e\\u003csup\\u003e2\\u0026minus;\\u003c/sup\\u003e ions in the pore space increased. Therefore, due to the addition of slag, the microstructure is made denser, but the content of conductive ions in the pores is reduced, still resulting in higher resistivity. It can be seen that changes in the resistivity of geopolymer caused by external factors are not always a simple process. Thus, resistivity as a fundamental physical behavior of geopolymers still needs to be discussed and studied more comprehensively.\\u003c/p\\u003e \\u003cp\\u003eIn this study, the geopolymer is prepared by using coal gangue and slag under alkaline excitation. The effects of alkali equivalent, slag substitution rate, modulus and water-cement ratio on geopolymer's consistency, compressive strength and resistivity are investigated. The changes of the resistivity of the specimen with the curing age and water content are further discussed. It provides theoretical guidance for resource utilization of coal gangue and engineering applications of geopolymers.\\u003c/p\\u003e\"},{\"header\":\"Experimental\",\"content\":\"\\u003cdiv id=\\\"Sec3\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003eRaw materials\\u003c/h2\\u003e \\u003cp\\u003eThe samples of coal gangue used in the test are non-spontaneous combustion coal gangue (CG) from Jiangxi mining area. The samples are crushed, ground and sieved to obtain the raw coal gangue powder with particle size below 200 mesh (0.075 mm), and then calcined at 700\\u0026deg;C for 4 hours in the muffle furnace to obtain the coal gangue powder for test (the uncalcined and calcined coal gangue powder is shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003e). S95 grade slag powder is introduced as a calcium source\\u003csup\\u003e10\\u003c/sup\\u003e. The main chemical compositions of the two materials are shown in Table\\u0026nbsp;\\u003cspan refid=\\\"Tab1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003e. It can be seen that the accumulated content of SiO\\u003csub\\u003e2\\u003c/sub\\u003e and Al\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e3\\u003c/sub\\u003e in the coal gangue is greater than 70%, which is considered to have some volcanic ash effect\\u003csup\\u003e30\\u003c/sup\\u003e. The mineral compositions in slag and calcined coal gangue analyzed by X-ray diffraction (XRD) are shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003e. It can be seen that the main mineral components of calcined coal gangue are quartz and muscovite, and the main mineral components of slag are calcium-aluminum yellow feldspar and calcium-magnesium yellow feldspar.\\u003c/p\\u003e \\u003cp\\u003eThe alkali exciter for the test is obtained by configuring sodium-based water glass with a modulus of 2.2 and sodium hydroxide (analytically pure) with a purity of 96%. Note that after mixing, the alkali exciter is cooled to room temperature for at least 24 hours before use.\\u003c/p\\u003e \\u003cp\\u003eRiver sand is also used as a fine aggregate with a fineness modulus of 2.75 and the content of SiO\\u003csub\\u003e2\\u003c/sub\\u003e over 97%. Tap water of Nanchang was used as test water.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003e \\u003cdiv class=\\\"gridtable\\\"\\u003e\\u003ctable float=\\\"Yes\\\" id=\\\"Tab1\\\" border=\\\"1\\\"\\u003e \\u003ccaption language=\\\"En\\\"\\u003e \\u003cdiv class=\\\"CaptionNumber\\\"\\u003eTable 1\\u003c/div\\u003e \\u003cdiv class=\\\"CaptionContent\\\"\\u003e \\u003cp\\u003eThe main chemical composition (by mass/%) of calcined coal gangue and slag.\\u003c/p\\u003e \\u003c/div\\u003e \\u003c/caption\\u003e \\u003ccolgroup cols=\\\"11\\\"\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c1\\\" colnum=\\\"1\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"char\\\" char=\\\".\\\" class=\\\"colspec\\\" colname=\\\"c2\\\" colnum=\\\"2\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"char\\\" char=\\\".\\\" class=\\\"colspec\\\" colname=\\\"c3\\\" colnum=\\\"3\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"char\\\" char=\\\".\\\" class=\\\"colspec\\\" colname=\\\"c4\\\" colnum=\\\"4\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"char\\\" char=\\\".\\\" class=\\\"colspec\\\" colname=\\\"c5\\\" colnum=\\\"5\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c6\\\" colnum=\\\"6\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c7\\\" colnum=\\\"7\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c8\\\" colnum=\\\"8\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c9\\\" colnum=\\\"9\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c10\\\" colnum=\\\"10\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c11\\\" colnum=\\\"11\\\"\\u003e\\u003c/div\\u003e \\u003cthead\\u003e \\u003ctr\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eMaterials\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eSiO\\u003csub\\u003e2\\u003c/sub\\u003e\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eAl\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e3\\u003c/sub\\u003e\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003eCaO\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003eMgO\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003eSO\\u003csub\\u003e3\\u003c/sub\\u003e\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003eK\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003eFe\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e3\\u003c/sub\\u003e\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c9\\\"\\u003e \\u003cp\\u003eNa\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c10\\\"\\u003e \\u003cp\\u003eP\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e5\\u003c/sub\\u003e\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c11\\\"\\u003e \\u003cp\\u003eOthers\\u003c/p\\u003e \\u003c/th\\u003e \\u003c/tr\\u003e \\u003c/thead\\u003e \\u003ctbody\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eCG\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e53.47\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e17.75\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e0.35\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e15.44\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e--\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003e7.05\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e0.16\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c9\\\"\\u003e \\u003cp\\u003e4.51\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c10\\\"\\u003e \\u003cp\\u003e1.27\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c11\\\"\\u003e \\u003cp\\u003e--\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eSG\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e33.06\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e15.04\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e39.29\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e9.96\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e1.90\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003e--\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e--\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c9\\\"\\u003e \\u003cp\\u003e--\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c10\\\"\\u003e \\u003cp\\u003e--\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c11\\\"\\u003e \\u003cp\\u003e0.75\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003c/tbody\\u003e \\u003c/colgroup\\u003e \\u003c/table\\u003e\\u003c/div\\u003e \\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec4\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003eMixes design and specimens preparation\\u003c/h2\\u003e \\u003cp\\u003eIn this study, geopolymers are prepared using single factor test, and compressive strength and resistivity are utilized to evaluate the mechanical and electrical conductivity of the specimens, respectively. The experiment involves four single factors that could affect the mechanical and electrical conductivity of the specimen, each single factor involves five levels of factors, a total of 20 sets of specimens were prepared, to study the alkali equivalent (mass fraction of Na\\u003csub\\u003e2\\u003c/sub\\u003eO to cementitious material: 8%, 10%, 12%, 14%, 16%), slag substitution rate (0%, 15%, 30%, 45%, 55%), modulus (molar ratio of SiO\\u003csub\\u003e2\\u003c/sub\\u003e to Na\\u003csub\\u003e2\\u003c/sub\\u003eO in alkali exciters: 0.8, 1.0, 1.2, 1.4, 1.6), and water-cement ratio (0.45, 0.45, 0.50, 0.55, 0.60) on compressive strength and resistivity. In the test, when studying the effect of one single factor on the performance of specimen, the test parameter of slag substitution rate is selected according to 45%, and the remaining other single factors are selected according to the intermediate level of their design (the details of all samples is shown in Table\\u0026nbsp;\\u003cspan refid=\\\"Tab2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003e).\\u003c/p\\u003e \\u003cp\\u003eThe process for sample preparation: firstly, water, sodium hydroxide, water glass according to Table\\u0026nbsp;\\u003cspan refid=\\\"Tab2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003e to prepare exciter for the test, stirred thoroughly and then placed the solution at room temperature aging for 24 hours standby; then, coal gangue, slag and sand were poured into the stirring pot and stirred at low speed for 3 min; then the alkaline exciter after aging was poured into the stirring pot, stirred at low speed for 2 min, and then stirred at high speed for 3 min. The freshly mixed slurry was injected into molds with dimensions of 40 mm \\u0026times; 40 mm \\u0026times; 160 mm and 40 mm \\u0026times; 40 mm \\u0026times; 40 mm, respectively. Next, after the sample was vibrated, their surface was covered with plastic wrap. After curing for 24 hours in a natural environment, the molds were demolded, and then specimens transferred to a water tank at 20\\u0026thinsp;\\u0026plusmn;\\u0026thinsp;1℃ for curing until the specified age for mechanical and electrical conductivity tests (the preparation scheme for the sample is shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig3\\\" class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003e.\\u003c/p\\u003e \\u003cp\\u003e \\u003cdiv class=\\\"gridtable\\\"\\u003e\\u003ctable float=\\\"Yes\\\" id=\\\"Tab2\\\" border=\\\"1\\\"\\u003e \\u003ccaption language=\\\"En\\\"\\u003e \\u003cdiv class=\\\"CaptionNumber\\\"\\u003eTable 2\\u003c/div\\u003e \\u003cdiv class=\\\"CaptionContent\\\"\\u003e \\u003cp\\u003eDetails of all samples\\u003c/p\\u003e \\u003c/div\\u003e \\u003c/caption\\u003e \\u003ccolgroup cols=\\\"7\\\"\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c1\\\" colnum=\\\"1\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"char\\\" char=\\\".\\\" class=\\\"colspec\\\" colname=\\\"c2\\\" colnum=\\\"2\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"char\\\" char=\\\".\\\" class=\\\"colspec\\\" colname=\\\"c3\\\" colnum=\\\"3\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"char\\\" char=\\\".\\\" class=\\\"colspec\\\" colname=\\\"c4\\\" colnum=\\\"4\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"char\\\" char=\\\".\\\" class=\\\"colspec\\\" colname=\\\"c5\\\" colnum=\\\"5\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"char\\\" char=\\\".\\\" class=\\\"colspec\\\" colname=\\\"c6\\\" colnum=\\\"6\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c7\\\" colnum=\\\"7\\\"\\u003e\\u003c/div\\u003e \\u003cthead\\u003e \\u003ctr\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eSample\\u003c/p\\u003e \\u003cp\\u003eNo.\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eCG/w%\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eSG/w%\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003eWater/w%\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003eNaOH/w%\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003ewater glass/w%\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003eSand/w%\\u003c/p\\u003e \\u003c/th\\u003e \\u003c/tr\\u003e \\u003c/thead\\u003e \\u003ctbody\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eN8\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\" morerows=\\\"4\\\" rowspan=\\\"5\\\"\\u003e \\u003cp\\u003e55\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\" morerows=\\\"4\\\" rowspan=\\\"5\\\"\\u003e \\u003cp\\u003e45\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e32.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e4.9\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e31.0\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c7\\\" morerows=\\\"16\\\" rowspan=\\\"17\\\"\\u003e \\u003cp\\u003e300\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eN10\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e28.1\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e6.2\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e38.8\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eN12\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e23.7\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e7.4\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e46.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eN14\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e19.3\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e8.6\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e54.3\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eN16\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e15.0\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e9.8\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e62.0\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eS0\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e100\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e0\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e23.7\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e7.4\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e46.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eS15\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e85\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e15\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e23.7\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e7.4\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e46.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eS30\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e70\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e30\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e23.7\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e7.4\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e46.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eS60\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e40\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e60\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e23.7\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e7.4\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e46.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eM8\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\" morerows=\\\"3\\\" rowspan=\\\"4\\\"\\u003e \\u003cp\\u003e55\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\" morerows=\\\"3\\\" rowspan=\\\"4\\\"\\u003e \\u003cp\\u003e45\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e30.3\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e9.4\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e34.9\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eM1.0\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e28.1\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e8.7\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e38.8\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eM1.4\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e19.3\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e6.0\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e54.3\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eM1.6\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e15.0\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e4.7\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e62.0\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eW4.0\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\" morerows=\\\"3\\\" rowspan=\\\"4\\\"\\u003e \\u003cp\\u003e55\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\" morerows=\\\"3\\\" rowspan=\\\"4\\\"\\u003e \\u003cp\\u003e45\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e13.7\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e7.4\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e46.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eW4.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e18.7\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e7.4\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e46.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eW5.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e28.7\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e7.4\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e46.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eW6.0\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e33.7\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e7.4\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e46.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003c/tbody\\u003e \\u003c/colgroup\\u003e \\u003c/table\\u003e\\u003c/div\\u003e \\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec5\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003eWorkability\\u003c/h2\\u003e \\u003cp\\u003eThe consistency of the geopolymer is tested according to the provisions in JGJ/T 70-2009 Standard for Test Methods of Basic Properties of Building Mortar.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec6\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003eCompression strength\\u003c/h2\\u003e \\u003cp\\u003eThe SHT4305 electro-hydraulic servo universal testing machine is used to test the compressive strength of the specimens, as shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig4\\\" class=\\\"InternalRef\\\"\\u003e4\\u003c/span\\u003ea. The testing process is carried out according to the Method for Testing the Strength of Cementitious Sand (GB/T 17671\\u0026thinsp;\\u0026minus;\\u0026thinsp;2021), and the loading rate is set to 2400 N/s.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec7\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003eMicrostructural\\u003c/h2\\u003e \\u003cp\\u003eMineral composition analysis of slag and calcined gangue is carried out using a D8-advance (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig4\\\" class=\\\"InternalRef\\\"\\u003e4\\u003c/span\\u003eb) polycrystalline X-ray diffractometer with a voltage of 40 kv, 2θ from 10\\u0026deg;/20\\u0026deg; to 80\\u0026deg;, a step size of 0.02\\u0026deg;, and a scanning speed of 5\\u0026deg;/min.\\u003c/p\\u003e \\u003cp\\u003eThe fragments of geopolymers from the tests of compressive strength were collected and analyzed for micro-morphology using a FEI Nova NanoSEM 450 (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig4\\\" class=\\\"InternalRef\\\"\\u003e4\\u003c/span\\u003ec) scanning electron microscope (SEM). The elemental content of the specimens was quantitatively analyzed using an energy spectrometer (EDS).\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec8\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003eElectrical resistivity\\u003c/h2\\u003e \\u003cp\\u003eThe two-electrode method is used to test the resistivity of specimen\\u003csup\\u003e29\\u003c/sup\\u003e. The size of the specimen is 40 mm\\u0026times;40 mm\\u0026times;40 mm, the material for electrode is stainless steel wire mesh with the size of 30 mm\\u0026times;60 mm, and electrodes are inserted into the interior of the specimen at intervals of 20 mm (the dimensions of the specimen is shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig5\\\" class=\\\"InternalRef\\\"\\u003e5\\u003c/span\\u003ea). The circuit tested is a 3V DC power supply connects in series with the resistance boxes and the sample to be tested, and the voltage across the resistance boxes is recorded with a voltmeter (schematic diagram of the circuit tested is shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig5\\\" class=\\\"InternalRef\\\"\\u003e5\\u003c/span\\u003eb). In order to minimize the error of test, three specimens are designed for each group and the average value of their resistivity is taken as the final result. In addition, to eliminate the effect of water on the resistivity of the specimens, constant humidity is maintained during the test.\\u003c/p\\u003e \\u003cp\\u003eResistance of the specimen:\\u003cdiv id=\\\"Equ1\\\" class=\\\"Equation\\\"\\u003e\\u003cdiv format=\\\"TEX\\\" class=\\\"mathdisplay\\\" id=\\\"FileID_Equ1\\\" name=\\\"EquationSource\\\"\\u003e\\n$$\\\\:R=\\\\frac{U-{U}_{1}}{{U}_{1}/{R}_{1}}$$\\u003c/div\\u003e\\u003cdiv class=\\\"EquationNumber\\\"\\u003e1\\u003c/div\\u003e\\u003c/div\\u003e\\u003c/p\\u003e \\u003cp\\u003eWhere: \\u003cem\\u003eR\\u003c/em\\u003e is the resistance of the test piece to be tested (Ω); \\u003cem\\u003eR\\u003c/em\\u003e\\u003csub\\u003e\\u003cem\\u003e1\\u003c/em\\u003e\\u003c/sub\\u003e is the constant value resistance (Ω); \\u003cem\\u003eU\\u003c/em\\u003e is the supply voltage (V); \\u003cem\\u003eU\\u003c/em\\u003e\\u003csub\\u003e\\u003cem\\u003e1\\u003c/em\\u003e\\u003c/sub\\u003e is the voltage at the ends of the constant value resistance (V).\\u003c/p\\u003e \\u003cp\\u003eResistivity of the specimen:\\u003cdiv id=\\\"Equ2\\\" class=\\\"Equation\\\"\\u003e\\u003cdiv format=\\\"TEX\\\" class=\\\"mathdisplay\\\" id=\\\"FileID_Equ2\\\" name=\\\"EquationSource\\\"\\u003e\\n$$\\\\:\\\\rho\\\\:=\\\\frac{R*S}{L}$$\\u003c/div\\u003e\\u003cdiv class=\\\"EquationNumber\\\"\\u003e2\\u003c/div\\u003e\\u003c/div\\u003e\\u003c/p\\u003e \\u003cp\\u003eWhere: \\u003cem\\u003eρ\\u003c/em\\u003e is the specimen resistivity (Ω. m); \\u003cem\\u003eS\\u003c/em\\u003e is the cross-sectional area of the current through the specimen (m\\u003csup\\u003e2\\u003c/sup\\u003e); \\u003cem\\u003eL\\u003c/em\\u003e is the distance between the two electrodes (m).\\u003c/p\\u003e \\u003cp\\u003eThe specimens are removed from the water tank and placed in the muffle furnace at 45\\u0026deg;C for 48 hours. The drying resistivity is tested to study the effect of water content on resistivity. The change rate of resistance (FCR) is calculated according to Eq.\\u0026nbsp;(\\u003cspan refid=\\\"Equ3\\\" class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003e).\\u003cdiv id=\\\"Equ3\\\" class=\\\"Equation\\\"\\u003e\\u003cdiv format=\\\"TEX\\\" class=\\\"mathdisplay\\\" id=\\\"FileID_Equ3\\\" name=\\\"EquationSource\\\"\\u003e\\n$$\\\\:FCR=\\\\frac{△p}{{p}_{0}}=\\\\frac{{p}_{i}-{p}_{0}}{{p}_{i}}$$\\u003c/div\\u003e\\u003cdiv class=\\\"EquationNumber\\\"\\u003e3\\u003c/div\\u003e\\u003c/div\\u003e\\u003c/p\\u003e \\u003cp\\u003eWhere \\u003cem\\u003e△p\\u003c/em\\u003e is the change in resistivity (Ω. m); \\u003cem\\u003ep\\u003c/em\\u003e\\u003csub\\u003e\\u003cem\\u003ei\\u003c/em\\u003e\\u003c/sub\\u003e is the resistance value of the specimen after the change by water content (Ω. m); \\u003cem\\u003ep\\u003c/em\\u003e\\u003csub\\u003e\\u003cem\\u003e0\\u003c/em\\u003e\\u003c/sub\\u003e is the initial resistance value of the specimen (Ω. m).\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003c/div\\u003e\"},{\"header\":\"Results and discussion\",\"content\":\"\\u003cdiv id=\\\"Sec10\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003eConsistency\\u003c/h2\\u003e \\u003cp\\u003eAs shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig6\\\" class=\\\"InternalRef\\\"\\u003e6\\u003c/span\\u003e, the consistency of the geopolymer is closely related to the dosage of all four factors (alkali equivalent, slag substitution rate, modulus and water-cement ratio). The consistency of specimen is decreased with increasing alkali equivalent and increased with increasing slag substitution rate, increasing modulus and increasing water-cement ratio. As can be seen in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig6\\\" class=\\\"InternalRef\\\"\\u003e6\\u003c/span\\u003e, the consistency of thirteen groups of specimens, including N10, N12, N14, S15, S30, S45, S60, M1.2, M1.4, W4.0, W4.5, W5.0, W5.5, is in the range of 7 cm\\u0026thinsp;~\\u0026thinsp;11 cm, which meets the basic requirements of the consistency of mortar in Chinese standard (GB/T 25181\\u0026thinsp;\\u0026minus;\\u0026thinsp;2019) and conditions of actual construction in China\\u003csup\\u003e31\\u003c/sup\\u003e.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec11\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003eCompressive strength\\u003c/h2\\u003e \\u003cp\\u003eFigure\\u0026nbsp;\\u003cspan refid=\\\"Fig7\\\" class=\\\"InternalRef\\\"\\u003e7\\u003c/span\\u003e describes the compressive strength for geopolymers with different factor (alkali equivalent, slag substitution rate, modulus and water-cement ratio). It is found that the compressive strength of the specimens is increased and then decreased with the increase of alkali equivalent (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig7\\\" class=\\\"InternalRef\\\"\\u003e7\\u003c/span\\u003ea), and the compressive strengths at 7 days and 28 days reached the maximum value when the alkali equivalent was taken as 10%, which increased by 53.62% and 60.99% compared with that when the alkali equivalent is 16%. OH\\u003csup\\u003e\\u0026minus;\\u003c/sup\\u003e ions provide an alkaline environment for the hydration reaction and accelerate the dissolution of active units such as [AlO\\u003csub\\u003e4\\u003c/sub\\u003e]\\u003csup\\u003e5\\u0026minus;\\u003c/sup\\u003e ions and [SiO\\u003csub\\u003e4\\u003c/sub\\u003e]\\u003csup\\u003e4\\u0026minus;\\u003c/sup\\u003e ions in the precursors\\u003csup\\u003e32\\u003c/sup\\u003e. Thus, the hydration reaction is facilitated, thus the amount of gelling products generated is increased and the internal structure is filled, resulting in higher compressive strength. However, when OH\\u003csup\\u003e\\u0026minus;\\u003c/sup\\u003e ions are in excess, the rate at which the structure of the precursor is destroyed and the rate at which the hydration products are formed are too fast\\u003csup\\u003e33\\u003c/sup\\u003e. Therefore, the products do not have time to diffuse and adhere to the surface of precursor to form a protective film, so that the later reaction process is blocked. Thus, the compressive strength is reduced by too high alkali equivalent.\\u003c/p\\u003e \\u003cp\\u003eThe compressive strength of the geopolymer is significantly increased with increasing slag substitution rate (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig7\\\" class=\\\"InternalRef\\\"\\u003e7\\u003c/span\\u003eb). When the slag substitution rate is reached 60%, the compressive strength of the specimens under the age of 7 days and 28 days is as high as 66.07 MPa and 81.33 MPa, respectively, which is 374.38% and 226.72% higher than that of the all-gangue based geopolymer, indicating that the compressive strength of the specimens is greatly affected by the slag substitution rate. This is due to the fact that the content of Ca\\u003csup\\u003e2+\\u003c/sup\\u003e in the system is continuously increased with the increase of slag substitution rate, and more [AlO\\u003csub\\u003e4\\u003c/sub\\u003e]\\u003csup\\u003e5\\u0026minus;\\u003c/sup\\u003e and [SiO\\u003csub\\u003e4\\u003c/sub\\u003e]\\u003csup\\u003e4\\u0026minus;\\u003c/sup\\u003eunits in the pores are combined to produce C-S-H and C-A-S-H gel crystals. Meanwhile, the high charge density of Ca\\u003csup\\u003e2+\\u003c/sup\\u003e ions drives gel precipitation to from the formation of the three-dimensional disordered mesh that fills the internal structure of the geopolymer\\u003csup\\u003e12\\u003c/sup\\u003e, and ultimately the compressive strength of the geopolymer is improved.\\u003c/p\\u003e \\u003cp\\u003eThe compressive strength of the geopolymer is increased and then decreased with increasing modulus (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig7\\\" class=\\\"InternalRef\\\"\\u003e7\\u003c/span\\u003ec). The maximum compressive strength of the geopolymer is obtained when the modulus is 1.4. As can be seen in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig8\\\" class=\\\"InternalRef\\\"\\u003e8\\u003c/span\\u003e, the specific surface area of the micelles in the alkali exciters is increased with increasing modulus, resulting in an enhanced ability of the micelles to adsorb silica-oxygen anion groups, metal ions, and polymerization products. Thus, OH\\u003csup\\u003e\\u0026minus;\\u003c/sup\\u003e ions penetrate into the precursor material more easily, so that the later hydration process is promoted. Eventually, a dense and stable internal structure is formed, leading to an increase in compressive strength. However, an increase in modulus also means a relative decrease in the content of OH\\u003csup\\u003e\\u0026minus;\\u003c/sup\\u003e ions in the pores, and when its content is not enough to drive the active units to dissolve, the compressive strength of the geopolymer is decreased\\u003csup\\u003e34\\u003c/sup\\u003e. Therefore, the compressive strength is significantly decreased when the modulus is taken to 1.6.\\u003c/p\\u003e \\u003cp\\u003eThe compressive strength of the geopolymer is reduced with the increasing water-cement ratio (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig7\\\" class=\\\"InternalRef\\\"\\u003e7\\u003c/span\\u003ed). The free water content within the geopolymer is increased with the increase of the water-cement ratio, resulting in the increase of pore size and the number of pores, and the internal densification and stability of the geopolymer is reduced, so that the compressive strength of the geopolymer is decreased. In addition, an increase in the water-cement ratio causes the concentration of alkali exciter to be reduced, which may also induce lower compressive strength. It is worth noting that when the water-cement ratio is 4.0, the compressive strength of geopolymer at 28 days is reached 80.10 MPa, which is similar to that of geopolymer when the slag substitution rate is 60%. This shows that the appropriate reduction of the water-cement ratio, not only to obtain a higher compressive strength, but also to increase the utilization rate of coal gangue, maximizing the realization of its secondary high-value utilization.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec12\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003eResistivity\\u003c/h2\\u003e \\u003cdiv id=\\\"Sec13\\\" class=\\\"Section3\\\"\\u003e \\u003ch2\\u003eInfluence of ratios of geopolymer\\u003c/h2\\u003e \\u003cp\\u003eThe effect of alkali equivalent on resistivity is shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig9\\\" class=\\\"InternalRef\\\"\\u003e9\\u003c/span\\u003ea. It can be seen that the resistivity is decreased and then increased with increasing alkali equivalent. As can be seen in Eq.\\u0026nbsp;4, the alkali exciter undergoes hydrolysis in contact with water to produce NaOH as well as Si (OH)\\u003csub\\u003e4\\u003c/sub\\u003e, and NaOH exists in the pore solution in free states such as Na\\u003csup\\u003e+\\u003c/sup\\u003e and OH\\u003csup\\u003e\\u0026minus;\\u003c/sup\\u003e ions.\\u003c/p\\u003e \\u003cp\\u003e2Na\\u003csub\\u003e2\\u003c/sub\\u003eO\\u0026middot;\\u003cem\\u003en\\u003c/em\\u003eSiO\\u003csub\\u003e2\\u003c/sub\\u003e\\u0026thinsp;+\\u0026thinsp;2(\\u003cem\\u003en\\u003c/em\\u003e-1) H\\u003csub\\u003e2\\u003c/sub\\u003eO\\u0026rarr;4NaOH\\u0026thinsp;+\\u0026thinsp;\\u003cem\\u003en\\u003c/em\\u003eSi(OH)\\u003csub\\u003e4\\u003c/sub\\u003e (\\u003cspan citationid=\\\"CR4\\\" class=\\\"CitationRef\\\"\\u003e4\\u003c/span\\u003e)\\u003c/p\\u003e \\u003cp\\u003eHowever, Na\\u003csup\\u003e+\\u003c/sup\\u003e ions act as charge balancers, and a small amount of Na\\u003csup\\u003e+\\u003c/sup\\u003e ions bind to the active units to produce N-A-S-H gels, while a large amount of Na\\u003csup\\u003e+\\u003c/sup\\u003e ions remain in the free state in the pore solution\\u003csup\\u003e35\\u003c/sup\\u003e. Therefore, the amount of ionic liquid in the pores is enlarged with the increase of equivalent, which leads to the increase of carrier concentration, resulting in the enhancement of ionic conductivity. However, in combination with the test results of alkali equivalent on compressive strength, it is concluded that the hydration process was seriously inhibited when the alkali equivalent was increased to 16%, and the internal structural densification is reduced (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig9\\\" class=\\\"InternalRef\\\"\\u003e9\\u003c/span\\u003ea), which is unfavorable for migration of ions. Carrier concentration and ion mobility are the main factors affecting ionic conductivity\\u003csup\\u003e24\\u003c/sup\\u003e, thus only increasing the equivalent in the appropriate interval could reduce the resistivity.\\u003c/p\\u003e \\u003cp\\u003eThe effect of slag substitution ratio on resistivity is shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig9\\\" class=\\\"InternalRef\\\"\\u003e9\\u003c/span\\u003eb. It can be seen that the resistivity is decreased and then increased with increasing slag substitution ratio, and the minimum of resistivity was obtained at slag substitution rate of 15%. As can be seen in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig9\\\" class=\\\"InternalRef\\\"\\u003e9\\u003c/span\\u003eb, When the slag substitution rate is 0, there are penetrating cracks in the specimen, and the internal structure is seriously degraded. When the slag substitution rate reaches 15%, the number of cracks inside the specimen is significantly reduced, and it shows a short and fine morphology, and the density and integrity of its microstructure are significantly improved. The microstructure of the geopolymer has a significant effect on its resistivity, and a compact and dense structure could generate more electronic circuits, resulting in a lower resistivity. Therefore, when the substitution rate is less than 15%, the density of the structure is increased with increasing slag substitution rate, and thus the resistivity is shown to be significantly reduced with the increase of substitution rate. After that, the phenomenon of resistivity being increased with increasing substitution rate may be attributed to two reasons. Firstly, the reaction rate of alkali exciters with slag is much faster than that with coal gangue, resulting in a sharp decrease in the concentration of conductive ions\\u003csup\\u003e36,37\\u003c/sup\\u003e. Therefore, although the addition of slag makes the microstructure denser, it reduces the content of conductive ions in the system. Secondly, the presence of active groups on the surface of coal gangue could improve the conductivity of the geopolymer, but the number of active groups is reduced with the increase of slag substitution rate, resulting in an increase in resistivity.\\u003c/p\\u003e \\u003cp\\u003eThe effect of modulus on resistivity is shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig9\\\" class=\\\"InternalRef\\\"\\u003e9\\u003c/span\\u003ec. It can be seen that the resistivity is decreased and then increased with increasing modulus. The resistivity of modulus taken 0.8 and 1.6 increased by 71.42% and 90.24% respectively as compared to modulus taken 1.0. As can be seen in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig9\\\" class=\\\"InternalRef\\\"\\u003e9\\u003c/span\\u003ec, the compressive strength at 28 days does not reach 42.5 MPa when the modulus is taken as 0.8 and 1.6, indicating that the internal structure is severely degraded, and thus the migration of ionic is suppressed, so the resistivity of specimen is larger. When the modulus is taken between 1.0 and 1.4, the resistivity is increased with the increase of modulus, which may be due to the increase of modulus promoting the hydration reaction, thus the consumption of ions is increased and the concentration of internal carriers is reduced, resulting in the increase of resistivity.\\u003c/p\\u003e \\u003cp\\u003eThe effect of water-cement ratio on resistivity is shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig9\\\" class=\\\"InternalRef\\\"\\u003e9\\u003c/span\\u003ed. It can be seen that the resistivity is decreased with increasing water-cement ratio. This phenomenon is attributed to pore connectivity and water saturation. The connectivity porosity inside the matrix is a key factor affecting diffusion of ions, and more connectivity porosity means easier diffusion of ions, thus more favorable for ions to migrate and diffuse in the capillary channels filled with free water\\u003csup\\u003e38,39\\u003c/sup\\u003e. Therefore, the increase in the water-cement ratio causes the connectivity porosity of matrix (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig9\\\" class=\\\"InternalRef\\\"\\u003e9\\u003c/span\\u003ed, Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig10\\\" class=\\\"InternalRef\\\"\\u003e10\\u003c/span\\u003e) and free water content to be increased, resulting in lower resistivity.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003c/div\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec14\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003eInfluence of Curing Ages\\u003c/h2\\u003e \\u003cp\\u003eThe effect of curing ages on resistivity is shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig11\\\" class=\\\"InternalRef\\\"\\u003e11\\u003c/span\\u003e. It can be seen that the resistivity is increased with increasing age. The above phenomenon could be attributed to two reasons. Firstly, the hydration reaction of the geopolymer takes a period of time. At early age, the free ions such as Ca\\u003csup\\u003e2+\\u003c/sup\\u003e, K\\u003csup\\u003e+\\u003c/sup\\u003e and SO\\u003csub\\u003e4\\u003c/sub\\u003e\\u003csup\\u003e2\\u0026minus;\\u003c/sup\\u003e ions are high inside the pores, and the ions are gradually consumed with the extension of curing ages. Secondly, when the age is prolonged, the free water in the pores is continuously absorbed by the hydration reaction and forced to be in the form of crystal-water. Therefore, the content of ionic liquid is decreased with age, resulting in a weakening of ionic conductivity and thus an increase in resistivity.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003eThe SEM micrograph of raw materials and specimen (N12) at 7 days and 28 days of age are shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig12\\\" class=\\\"InternalRef\\\"\\u003e12\\u003c/span\\u003e. Comparing Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig12\\\" class=\\\"InternalRef\\\"\\u003e12\\u003c/span\\u003ec and Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig12\\\" class=\\\"InternalRef\\\"\\u003e12\\u003c/span\\u003ed, it can be seen that at 7 days of age, the amount of internal gelation and flocculation hydration products is low, but at 28 days of age, there is a significant increase in internal agglomerates and flocculation gel crystal products as well as spongy hydrated calcium-aluminum particles, and the densification of the internal structure is improved. Further comparing the SEM images of the specimens of N12 at 7 and 28 days for the paste (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig11\\\" class=\\\"InternalRef\\\"\\u003e11\\u003c/span\\u003ee and Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig11\\\" class=\\\"InternalRef\\\"\\u003e11\\u003c/span\\u003ef), it can also be clearly found that the amount of hydration products and the densification of the internal structure were significantly enhanced with increasing age. That is to say, the hydration reaction inside the matrix is still going on after 7 days of age, and the consumption of ionic and the transformation of free water to crystal-water also exist, so the content of ionic liquid is still reduced. The decrease in ionic liquid leads to a deterioration of ionic conductivity, which is consistent with the results of the change in resistivity. In addition, the density and integrity of internal structural is enhanced leading to higher the development of strength, which is also consistent with the results of compressive strength with age.\\u003c/p\\u003e \\u003cp\\u003eThe XRD diffractograms and EDS spectra of specimen (N12) are shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig13\\\" class=\\\"InternalRef\\\"\\u003e13\\u003c/span\\u003e. As shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig13\\\" class=\\\"InternalRef\\\"\\u003e13\\u003c/span\\u003ea, a small sharp peak is found near 29.5\\u0026deg;, which could correspond to the C-S-H and C-A-S-H gel products generated by the reaction, as shown against the standard diffraction pattern. Then in the EDS spectra, it is found that the product is mainly composed of elements such as C, O, Si, Al, and Ca, which is consistent with the results of the XRD spectra. It is inferred that the hydration products are between C-S-H and C-A-S-H or mixtures thereof, which is similar to the experimental results of Ma et al\\u003csup\\u003e12\\u003c/sup\\u003e. It can be further found by EDS spectroscopy that at the age of 7d (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig12\\\" class=\\\"InternalRef\\\"\\u003e12\\u003c/span\\u003ea), the ratios of Ca/Si and Al/Si in the products are 0.67 and 0.38, respectively. However, at 28 d of age (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig12\\\" class=\\\"InternalRef\\\"\\u003e12\\u003c/span\\u003eb), the ratios of Ca/Si and Al/Si are 0.58 and 0.40, respectively. Decreased the ratio of Ca/Si and increased the ratio of Al/Si indicate a gradual transition from C-S-H gels to C-A-S-H gels with increasing age\\u003csup\\u003e40\\u003c/sup\\u003e. It is confirmed that Ca\\u003csup\\u003e2+\\u003c/sup\\u003e ions produced by the dissolution of slag under the action of alkali are consumed during the reaction, while Al\\u003csup\\u003e3+\\u003c/sup\\u003e ions produced by dissolution are further involved in the reaction. This also indicates to some extent that the extension of age increases the consumption of ionic, resulting in an increase in specimen resistivity.\\u003c/p\\u003e \\u003cp\\u003eIn addition, in order to explore the changing law of the degree of influence of four factors on resistivity with age, such as alkali equivalent (N), slag substitution rate (S), modulus (M) and water-cement ratio (W), the specimens under the difference of ages are subjected to range analysis, and the results are shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig14\\\" class=\\\"InternalRef\\\"\\u003e14\\u003c/span\\u003e.\\u003c/p\\u003e \\u003cp\\u003eR' is range of a particular factor and the expression is shown in Eq.\\u0026nbsp;\\u003cspan refid=\\\"Equ4\\\" class=\\\"InternalRef\\\"\\u003e5\\u003c/span\\u003e:\\u003cdiv id=\\\"Equ4\\\" class=\\\"Equation\\\"\\u003e\\u003cdiv format=\\\"TEX\\\" class=\\\"mathdisplay\\\" id=\\\"FileID_Equ4\\\" name=\\\"EquationSource\\\"\\u003e\\n$$\\\\:{R}^{\\u0026rsquo;}={max}({p}_{i})-{min}({p}_{i})$$\\u003c/div\\u003e\\u003cdiv class=\\\"EquationNumber\\\"\\u003e5\\u003c/div\\u003e\\u003c/div\\u003e\\u003c/p\\u003e \\u003cp\\u003eWhere: \\u003cem\\u003ep\\u003c/em\\u003e\\u003csub\\u003e\\u003cem\\u003ei\\u003c/em\\u003e\\u003c/sub\\u003e is the actual test indicator corresponding to the \\u003cem\\u003ei\\u003c/em\\u003e level of a factor.\\u003c/p\\u003e \\u003cp\\u003eAs can be seen in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig14\\\" class=\\\"InternalRef\\\"\\u003e14\\u003c/span\\u003e, the relationship between the effects of the four factors on the resistivity of the specimens for 7 days is N\\u0026thinsp;\\u0026gt;\\u0026thinsp;M\\u0026thinsp;\\u0026gt;\\u0026thinsp;S\\u0026thinsp;\\u0026gt;\\u0026thinsp;W; the relationship for both 14 days and 28 days is M\\u0026thinsp;\\u0026gt;\\u0026thinsp;S\\u0026thinsp;\\u0026gt;\\u0026thinsp;N\\u0026thinsp;\\u0026gt;\\u0026thinsp;W. At different ages, the influence of W on resistivity was lower than that of other factors. And with the increase of age, the influence of N on resistivity is decreased, and the influence of M and S on resistivity is increased. This is mainly due to the fact that there are two ways of \\u0026ldquo;external introduction\\u0026rdquo; and \\u0026ldquo;internal consumption\\u0026rdquo; of N to affect the content of ionic liquid of the matrix compared to M and S. Increasing N means the content of Na\\u003csup\\u003e+\\u003c/sup\\u003e ions in the pores increased. What's more, the content of Na\\u003csup\\u003e+\\u003c/sup\\u003e ions in the pores is nearly 10\\u003csup\\u003e3\\u003c/sup\\u003e mmol/L higher than that of other ions\\u003csup\\u003e35\\u003c/sup\\u003e. Therefore, compared with the difference in resistivity caused by the consumption of hydration reaction, the difference in resistivity brought about by the difference in the content of externally introduced ions is greater. And the difference in the content of externally introduced ions is created when the alkali exciter was added, and therefore, the effect of N on resistivity is more significant at the early age.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec15\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003eInfluence of Water Content\\u003c/h2\\u003e \\u003cp\\u003eThe effect of water content on resistivity is shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig15\\\" class=\\\"InternalRef\\\"\\u003e15\\u003c/span\\u003e. It can be seen that the resistivity is increased with increasing ages. When the specimen is changed from the surface dry state to the dry state, the resistivity of different ratios is increased by nearly 5\\u0026thinsp;~\\u0026thinsp;6 orders of magnitude, and the value of FCR is reached 10\\u003csup\\u003e4\\u003c/sup\\u003e, indicating that the conductivity of the specimen is significantly affected by the water content, and the ambient humidity can affect the resistivity of specimen by influencing the water content. Reduced water content restricts the diffusion of ions, resulting in increased resistivity\\u003csup\\u003e41\\u003c/sup\\u003e. The free water in the pores is the carrier of the migration and diffusion of ions, and the decrease in water content results in the internal channels, which were filled with free water, becoming anhydrous.\\u003c/p\\u003e \\u003c/div\\u003e \"},{\"header\":\"Conclusions\",\"content\":\"\\u003cp\\u003eIn this study, geopolymers ware prepared using single factor test, and consistency, compressive strength and resistivity are utilized to evaluate the workability, mechanical and electrical conductivity of the specimens, respectively, and the changes of the resistivity of the specimen with the curing age and water content are further discussed. Based on the experimental results, the following conclusions may be drawn:\\u003c/p\\u003e \\u003cp\\u003e(\\u003cspan citationid=\\\"CR1\\\" class=\\\"CitationRef\\\"\\u003e1\\u003c/span\\u003e) The consistency of 13 groups of specimens, including N10, N12, N14, S15, S30, S45, S60, M1.2, M1.4, W4.0, W4.5, W5.0, W5.5, etc., is within the range of 7 cm\\u0026thinsp;~\\u0026thinsp;11 cm. They meet the basic requirements for the consistency of the mortar of the Chinese standard (GB/T 25181\\u0026thinsp;\\u0026minus;\\u0026thinsp;2019) and the actual construction conditions in China.\\u003c/p\\u003e \\u003cp\\u003e(\\u003cspan citationid=\\\"CR2\\\" class=\\\"CitationRef\\\"\\u003e2\\u003c/span\\u003e) The compressive strength of the specimens was first increased and then decreased with increasing alkali equivalent and increasing modulus, increased with increasing slag substitution ratio, and decreased with increasing water-cement ratio. Among them, the compressive strengths of the specimens at 28 days were elevated to more than 80 MPa when the alkali equivalent, slag substitution ratio, modulus and water-cement ratio were taken as 12%, 45%, 1.2 and 4 respectively and 12%, 55%, 1.2 and 5 respectively.\\u003c/p\\u003e \\u003cp\\u003e(\\u003cspan citationid=\\\"CR3\\\" class=\\\"CitationRef\\\"\\u003e3\\u003c/span\\u003e) The resistivity of the specimens was first decreased and then increased with increasing alkali equivalent, increasing slag substitution ratio and increasing modulus, and was reduced with increasing water-cement ratio. And due to the content of ionic liquid in the pore space is reduced with age, the resistivity is increased with age. In addition, the effect of water-cement ratio on resistivity is minimized at different ages, while the alkali equivalent is attenuated with increasing age.\\u003c/p\\u003e \\u003cp\\u003e(\\u003cspan citationid=\\\"CR4\\\" class=\\\"CitationRef\\\"\\u003e4\\u003c/span\\u003e) The resistivity was significantly increased with decreasing water content, due to the diffusion of ions is limited by the decrease in water content. In particular, the values of FCR for different samples are as high as 10\\u003csup\\u003e4\\u003c/sup\\u003e when the specimens are transformed from the face-dry state to the dry state.\\u003c/p\\u003e\"},{\"header\":\"Declarations\",\"content\":\"\\u003cp\\u003e \\u003ch2\\u003eCompeting interests\\u003c/h2\\u003e \\u003cp\\u003eThe authors declare that they have no known conflicts of interest that might influence the work reported in this paper.\\u003c/p\\u003e \\u003c/p\\u003e\\u003ch2\\u003eAuthor Contribution\\u003c/h2\\u003e\\u003cp\\u003eWenhua Zha designed and directed this project. Wenfang Lv: Measurements, Forma analysis, Investigation, Writing \\u0026ndash; original draft. Jielian Li and Tao Xu: Measurements. Denghong Chen: Data curation. Wenhua Zha: provided suggestions for the project. All the authors discussed the results and commented on the manuscript.\\u003c/p\\u003e\\u003ch2\\u003eAcknowledgements\\u003c/h2\\u003e \\u003cp\\u003eThe authors gratefully acknowledge the financial support for this research provided by the National Natural Science Foundation of China (Grant No. 52264003), Double Thousand Plan Support Project of Jiangxi Province (Grant No. DHSQT22021002).\\u003c/p\\u003e\\u003ch2\\u003eData Availability\\u003c/h2\\u003e\\u003cp\\u003eThe datasets generated and/or analysed during the current study are not publicly available due [REASON WHY DATA ARE NOT PUBLIC] but are available from the corresponding author on reasonable request.\\u003c/p\\u003e\"},{\"header\":\"References\",\"content\":\"\\u003col\\u003e\\n\\u003cli\\u003eGao, S., Zhao, G., Guo, L., Zhou, L., Yuan, K. Utilization of coal gangue as coarse aggregates in str-uctural concrete. Construction and Building Materials 268: 121212 (2021).\\u003c/li\\u003e\\n\\u003cli\\u003eWang, Q., Zhu, L., Lu, C., Liu, Y., Yu, Q., Chen, S. Investigation on the effect of calcium on the properties of geopolymer prepared from uncalcined coal gangue. Polymers 15(5): 1241 (2023).\\u003c/li\\u003e\\n\\u003cli\\u003eZhang, B., Yang, K., Zhang, K., Wang, Q., Wu, N. Migration transformation, prevention, and control of typical heavy metal lead in coal gangue: a review. International Journal of Coal Science \\u0026amp; Technology 10(1): 85 (2023).\\u003c/li\\u003e\\n\\u003cli\\u003eEssaidi, N., Nadir, H., Martinod, E., Feix, N., Bertrand, V., Tantot, O., Rossignol, S. Comparative study of dielectric properties of geopolymer matrices using different dielectric powders. Journal of the European Ceramic Society 37(11): 3551-3557 (2017).\\u003c/li\\u003e\\n\\u003cli\\u003eYu, G., Jia, Y. Preparation of geopolymer composites based on alkali excitation. 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(2023).\\u003c/li\\u003e\\n\\u003cli\\u003eZhao, Y., Zhang, Z., Ji, Y., Song, L., Ma, M. Experimental research on improving activity of calcinated coal gangue via increasing calcium content. Materials 16(7): 2705 (2023).\\u003c/li\\u003e\\n\\u003cli\\u003eFeng, D., Wang, J., Chen, D., Hou, W., Liang, S. Experimental study on municipal solid waste incineration fly ash as a component of coal gangue geopolymer and the feasibility of making geopolymer mortar. Construction and Building Materials 409: 133862 (2023). \\u003c/li\\u003e\\n\\u003cli\\u003eMa, H. Q., Zhu, H. G., Chen, H. Y., Ni, Y. D., Wang, T., Yang, S. Effects and mechanisms of slag reinforced coal gangue geopolymers. In IOP Conference Series: Materials Science and Engineering (Vol. 474, No. 1, p. 012040). IOP Publishing. (2019).\\u003c/li\\u003e\\n\\u003cli\\u003eLuo, T., Wang, Q., Fang, Z. Effect of graphite on the self-sensing properties of cement and alkali-activated fly ash/slag based composite cementitious materials. Journal of Building Engineering 77: 107493 (2023)..\\u003c/li\\u003e\\n\\u003cli\\u003eProvis, J. L., Duxson, P., Van Deventer, J. S., Lukey, G. C. The role of mathematical modelling and gel chemistry in advancing geopolymer technology. Chemical Engineering Research and Design 83(7): 853-860 (2005).\\u003c/li\\u003e\\n\\u003cli\\u003eRovnan\\u0026iacute;k, P., Kus\\u0026aacute;k, I., Bayer, P., Schmid, P., Fiala, L. Comparison of electrical and self-sensing properties of Portland cement and alkali-activated slag mortars. Cement and Concrete Research 118: 84-91 (2019).\\u003c/li\\u003e\\n\\u003cli\\u003eVaidya, S., Allouche, E. N. Experimental evaluation of electrical conductivity of carbon fiber reinforced fly-ash based geopolymer. Smart structures and systems 7(1): 27-40 (2011).\\u003c/li\\u003e\\n\\u003cli\\u003eLi, Y., Hu, B., Gao, Y., Feng, J., Kot, P. Electrical characteristics and conductivity mechanism of self-sensing asphalt concrete. Construction and Building Materials 416: 135236 (2024).\\u003c/li\\u003e\\n\\u003cli\\u003eRahman, M. L., Ceylan, H., Kim, S., Taylor, P. C. Influence of electrode placement depth on thermal performance of electrically conductive concrete: Significance of threshold voltage for long-term stability. Construction and Building Materials 412: 134883 (2024).\\u003c/li\\u003e\\n\\u003cli\\u003eKhalid, T., Albasha, L., Qaddoumi, N., Yehia, S. Feasibility study of using electrically conductive concrete for electromagnetic shielding applications as a substitute for carbon-laced polyurethane absorbers in anechoic chambers. IEEE Transactions on Antennas and Propagation 65(5): 2428-2435 (2017).\\u003c/li\\u003e\\n\\u003cli\\u003eLi, Z., Guo, T., Chen, Y., Yang, W., Ding, S., Hao, M., Liu, J. Electrode Layout Optimization and Numerical Simulation of Cast Conductive Asphalt Concrete Steel Bridge Deck Pavement. Materials 15(19): 7033 (2022).\\u003c/li\\u003e\\n\\u003cli\\u003eHemalatha, T., Sangoju, B., Muthuramalingam, G. A study on copper slag as fine aggregate in improving the electrical conductivity of cement mortar. Sādhanā 47(3): 141 (2022).\\u003c/li\\u003e\\n\\u003cli\\u003eLi, J., Cao, Y., Sha, A., Song, R., Li, C., Wang, Z. Prospective application of coal gangue as filler in fracture-healing behavior of asphalt mixture. Journal of Cleaner Production 373: 133738 (2022).\\u003c/li\\u003e\\n\\u003cli\\u003eZhu, B., Gao, Y., Hao, H., Ji, G., Yang, C., Wang, F., Tian, Y. One-pot synthesis of coal gangue\\u0026ndash;derived NiCG composite for enhancing microwave absorption. Colloids and Surfaces A: Physicochemical and Engineering Aspects 666: 131305 (2023).\\u003c/li\\u003e\\n\\u003cli\\u003eMontanari, L., Tanesi, J., Kim, H., Ardani, A Influence of loading pressure and sample preparation on ionic concentration and resistivity of pore solution expressed from concrete samples. Journal of Testing and Evaluation 49(5): 3482-3505. (2021).\\u003c/li\\u003e\\n\\u003cli\\u003eChen, W., Li, Y., Shen, P., Shui, Z. Microstructural development of hydrating portland cement paste at early ages investigated with non-destructive methods and numerical simulation. Journal of Nondestructive Evaluation 32: 228-237 (2013).\\u003c/li\\u003e\\n\\u003cli\\u003eGuo, L., Liu, J., Zhou, M., An, S. Effect of an alkali activators on the compressive strength and reaction mechanism of coal gangue-slag-fly ash geopolymer grouting materials. Construction and Building Materials 426: 136012 (2024).\\u003c/li\\u003e\\n\\u003cli\\u003eChen, L., Yin, X., Fan, X., Chen, M., Ma, X., Cheng, L., Zhang, L. Mechanical and electromagnetic shielding properties of carbon fiber reinforced silicon carbide matrix composites. Carbon 95: 10-19 (2015).\\u003c/li\\u003e\\n\\u003cli\\u003eTumidajski, P. J., Schumacher, A. S., Perron, S., Gu, P., Beaudoin, J. J. On the relationship between porosity and electrical resistivity in cementitious systems. Cement and concrete research 26(4): 539-544 (1996).\\u003c/li\\u003e\\n\\u003cli\\u003eCai J, Pan J, Li X, et al. Electrical resistivity of fly ash and metakaolin based geopolymers[J]. Construction and Building Materials, 234: 117868 (2020).\\u003c/li\\u003e\\n\\u003cli\\u003eDong, C., Zhou, N., Zhang, J., Lai, W., Xu, J., Chen, J., Che, Y. Optimized preparation of gangue waste-based geopolymer adsorbent based on improved response surface methodology for Cd (II) removal from wastewater. Environmental Research 221: 115246 (2023).\\u003c/li\\u003e\\n\\u003cli\\u003ePi, Z., Huang, S., Xu, J., Chen, Z., Li, H., Shen, Y., Tian, J. The reinforcement mechanism of basalt and polypropylene fibers on the strength, toughness and crack resistance of tailing mortar. Construction and Building Materials 419: 135531 (2024).. \\u003c/li\\u003e\\n\\u003cli\\u003eYe, N., Yang, J., Liang, S., Hu, Y., Hu, J., Xiao, B., Huang, Q. Synthesis and strength optimization of one-part geopolymer based on red mud. Construction and Building Materials 111: 317-325 (2016).\\u003c/li\\u003e\\n\\u003cli\\u003eSha, D., Wang, F., Wang, B., Pan, B. Microstructural and mechanical properties of a high-strength geopolymer based on coal-based synthetic natural gas slag cured at ambient temperature. Journal of Cleaner Production 430: 139657 (2023).\\u003c/li\\u003e\\n\\u003cli\\u003eLing, Y., Wang, K., Wang, X., Hua, S. Effects of mix design parameters on heat of geopolymerization, set time, and compressive strength of high calcium fly ash geopolymer. Construction and Building Materials 228: 116763 (2019).\\u003c/li\\u003e\\n\\u003cli\\u003eLu, Y., Song, L., Xu, Y., Duan, P., Wang, X. Microstructure and Efflorescence Resistance of Metakaolin Geopolymer Modified by 5A Zeolite. Materials 16(22): 7243 (2023).\\u003c/li\\u003e\\n\\u003cli\\u003ePuligilla, S., Mondal, P. Role of slag in micro- structural development and hardening of fly ash-slag geopolymer. Cement and concrete Research 43: 70-80 (2013).\\u003c/li\\u003e\\n\\u003cli\\u003eNath, S. K. Geopolymerization behavior of ferrochrome slag and fly ash blends. Construction and Building Materials 181: 487-494 (2018).\\u003c/li\\u003e\\n\\u003cli\\u003eHe, R., Ma, H., Hafiz, R. B., Fu, C., Jin, X., He, J. Determining porosity and pore network connectivity of cement-based materials by a modified non-contact electrical resistivity measurement: Experiment and theory. Materials \\u0026amp; Design 156: 82-92 (2018).\\u003c/li\\u003e\\n\\u003cli\\u003eZhao, R., Weng, Y., Tuan, C. Y., Xu, A. The influence of water/cement ratio and air entrainment on the electric resistivity of ionically conductive mortar. Materials 12(7): 1125 (2019).\\u003c/li\\u003e\\n\\u003cli\\u003eTian, Y., Wang, Y., Chai, H., Zhao, L., Sun, H., Zhang, H. Study on the properties and interfacial transition zone of coal gasification slag aggregate and mineral powder geopolymer mortar. Construction and Building Materials 414: 134864 (2024).\\u003c/li\\u003e\\n\\u003cli\\u003eWang, L., Aslani, F. Electrical resistivity and piezoresistivity of cement mortar containing ground granulated blast furnace slag. Construction and Building Materials 263: 120243 (2020).\\u003c/li\\u003e\\n\\u003c/ol\\u003e\"}],\"fulltextSource\":\"\",\"fullText\":\"\",\"funders\":[],\"hasAdminPriorityOnWorkflow\":false,\"hasManuscriptDocX\":true,\"hasOptedInToPreprint\":true,\"hasPassedJournalQc\":\"\",\"hasAnyPriority\":false,\"hideJournal\":true,\"highlight\":\"\",\"institution\":\"\",\"isAcceptedByJournal\":false,\"isAuthorSuppliedPdf\":false,\"isDeskRejected\":\"\",\"isHiddenFromSearch\":false,\"isInQc\":false,\"isInWorkflow\":false,\"isPdf\":false,\"isPdfUpToDate\":true,\"isWithdrawnOrRetracted\":false,\"journal\":{\"display\":true,\"email\":\"info@researchsquare.com\",\"identity\":\"researchsquare\",\"isNatureJournal\":false,\"hasQc\":true,\"allowDirectSubmit\":true,\"externalIdentity\":\"\",\"sideBox\":\"\",\"snPcode\":\"\",\"submissionUrl\":\"/submission\",\"title\":\"Research Square\",\"twitterHandle\":\"researchsquare\",\"acdcEnabled\":true,\"dfaEnabled\":false,\"editorialSystem\":\"\",\"reportingPortfolio\":\"\",\"inReviewEnabled\":false,\"inReviewRevisionsEnabled\":true},\"keywords\":\"Coal gangue, Solid waste utilization, Geopolymer, Compressive strength, Electrical resistivity\",\"lastPublishedDoi\":\"10.21203/rs.3.rs-4691610/v1\",\"lastPublishedDoiUrl\":\"https://doi.org/10.21203/rs.3.rs-4691610/v1\",\"license\":{\"name\":\"CC BY 4.0\",\"url\":\"https://creativecommons.org/licenses/by/4.0/\"},\"manuscriptAbstract\":\"\\u003cp\\u003eGeopolymers are both an effective way to achieve solid waste utilization of coal gangue and an environmentally friendly alternative to ordinary Portland cement. At the same time, the rich ionic content of geopolymers gives them superior conductivity, which makes them potentially valuable for applications in a variety of fields such as nondestructive testing, ice and snow melting, and electromagnetic shielding. However, the influence of external factors on its conductivity is still unclear, which limits its wide application in construction. In this study, coal gangue and slag are used to prepare geopolymer under alkaline excitation conditions, and the influence laws of alkali equivalent, slag substitution rate, modulus and water-cement ratio on its consistency, compressive strength and resistivity are investigated, and the changing law of resistivity of specimens with the curing ages and water content are also explored. It is found that the compressive strength is affected by alkali equivalent, slag substitution rate, modulus and water-cement ratio. When the alkali equivalent, slag substitution rate, modulus and water-cement ratio are taken to 12%, 55%, 1.2, 5 or12%, 45%,1.2, 4 respectively, the compressive strength at 28 days could be more than 80 MPa. Resistivity is first decreased and then increased with increasing alkali equivalent, increasing slag substitution rate, or increasing modulus, and is decreased with increasing water-cement ratio, and all of them are increased with increasing curing ages. At the age of 7 days, it is most significantly affected by alkali equivalent, while after the age of 14 days, it is more significantly affected by modulus and slag substitution rate than alkali equivalent; the effect of water-cement ratio is smaller at different ages. In addition, the resistivity is shown to increase significantly with decreasing water content, and the resistivity is increased by nearly 5\\u0026ndash;6 orders of magnitude when the specimens are transformed from the surface-dry state to the dry state.\\u003c/p\\u003e\",\"manuscriptTitle\":\"Preparation of coal gangue based geopolymer and electrical conductivity studies\",\"msid\":\"\",\"msnumber\":\"\",\"nonDraftVersions\":[{\"code\":1,\"date\":\"2024-07-30 10:48:32\",\"doi\":\"10.21203/rs.3.rs-4691610/v1\",\"editorialEvents\":[{\"type\":\"communityComments\",\"content\":0}],\"status\":\"published\",\"journal\":{\"display\":true,\"email\":\"info@researchsquare.com\",\"identity\":\"researchsquare\",\"isNatureJournal\":false,\"hasQc\":true,\"allowDirectSubmit\":true,\"externalIdentity\":\"\",\"sideBox\":\"\",\"snPcode\":\"\",\"submissionUrl\":\"/submission\",\"title\":\"Research Square\",\"twitterHandle\":\"researchsquare\",\"acdcEnabled\":true,\"dfaEnabled\":false,\"editorialSystem\":\"\",\"reportingPortfolio\":\"\",\"inReviewEnabled\":false,\"inReviewRevisionsEnabled\":true}}],\"origin\":\"\",\"ownerIdentity\":\"36b84e96-a173-4bfa-b3d4-5162e240b73f\",\"owner\":[],\"postedDate\":\"July 30th, 2024\",\"published\":true,\"recentEditorialEvents\":[],\"rejectedJournal\":[],\"revision\":\"\",\"amendment\":\"\",\"status\":\"posted\",\"subjectAreas\":[{\"id\":34877437,\"name\":\"Earth and environmental sciences/Environmental sciences\"},{\"id\":34877438,\"name\":\"Physical sciences/Energy science and technology\"},{\"id\":34877439,\"name\":\"Physical sciences/Engineering\"},{\"id\":34877440,\"name\":\"Physical sciences/Materials science\"}],\"tags\":[],\"updatedAt\":\"2024-09-19T04:26:27+00:00\",\"versionOfRecord\":[],\"versionCreatedAt\":\"2024-07-30 10:48:32\",\"video\":\"\",\"vorDoi\":\"\",\"vorDoiUrl\":\"\",\"workflowStages\":[]},\"version\":\"v1\",\"identity\":\"rs-4691610\",\"journalConfig\":\"researchsquare\"},\"__N_SSP\":true},\"page\":\"/article/[identity]/[[...version]]\",\"query\":{\"redirect\":\"/article/rs-4691610\",\"identity\":\"rs-4691610\",\"version\":[\"v1\"]},\"buildId\":\"qtupq5eGEP_6zYnWcrvyt\",\"isFallback\":false,\"isExperimentalCompile\":false,\"dynamicIds\":[84888],\"gssp\":true,\"scriptLoader\":[]}","source_license":"CC-BY-4.0","license_restricted":false}