WO2021230735A1 - Cement composition for structural health monitoring - Google Patents

Abstract

The invention relates to the construction industry, more particularly to electrically conductive cement-based compositions. A cement mix for producing electrically conductive concrete comprises Portland cement and a carbon-containing component, with the Portland cement constituting 75-95 wt% of the mix and red mud in an amount of 5-25 wt% being used as the carbon-containing component. The purpose of the invention is to provide a mix comprising components that are relatively simple to produce and inexpensive. Moreover, to improve the performance characteristics of the concrete produced from said mix, the electrical conductivity thereof must satisfy certain criteria; more particularly, the electrical resistivity has to be reduced. The technical result consists in reducing the setting time, increasing the compressive strength of a cement slurry, and improving the electrical properties of concrete (i.e. the electrical conductivity), which will enable the main industrial requirements concerning structural health monitoring, vibration control, and the safety and reliability of buildings, to be met. The use in the production of wastes from metallurgy and heat-and-power engineering has a positive environmental impact.

Description

Cement composition for monitoring the state of structures

The invention relates to construction, namely to electrically conductive compositions based on cement.

More than 30 million tons of concrete are produced annually in the world, this fact indicates that concrete is the second most consumed material after water [1]. The combination of the balance of performance (ie strength, durability) and cost determines that concrete is the most demanded building material [2, 3]. Partial replacement of Portland cement with other materials is a widespread practice that has a positive effect on the sustainability of concrete production [4]. Blended cements show promising results in terms of reducing carbon emissions, reducing energy costs and the durability of concrete structures [5-7].

In addition, it is possible to obtain different properties of concrete by adding certain fillers to its matrix. One of these interesting properties is electrical conductivity, which can be increased if a certain amount of conductive materials are introduced into ordinary concrete, in which case the concrete acquires the properties of both a building material and electrical properties. Electrically conductive concrete is widely used as: firstly, a sensor for monitoring the state of structures, secondly, as a protective material against electromagnetic interference, and thirdly, as a deicing material for the runway and airport bridges and the heated floor [8, nine]. The electrical conductivity of concrete has a great influence on such properties of concrete as: self-heating, self-healing and self-diagnosis [10-13]. In this regard, studies of various approaches to improve the electrical properties of concrete while maintaining its mechanical properties are of great interest.

The known composition of electrically conductive concrete, which includes 1-20% Portland cement, 18-85% ash and water (US Patent N ° 6461424 B1, 08.10.2002).

The disadvantage of this material is its low compressive strength - 8.3

MPa.

Known hydraulic mineral additive (RF patent N ° 2365548 C2, 27.08.2009), which can be used directly as cement or hydraulic binder, or they can be combined with any cement materials and hydraulic binders, such as Portland cement, alumina cements, natural and synthetic gypsum, phosphogypsum and mixtures thereof obtained from slag, in particular from steel slag, as well as from dust from industrial furnaces and dust waste from thermal power plants (fly ash).

The disadvantage of this solution is that the manufacture of such additives is accompanied by many complex steps and processes.

Known concrete mix (USSR author's certificate N ° 337360, 05/31/1972) containing Portland cement, metallic silicon and graphite.

The disadvantage of this composition is that metal silicon is used to increase the electrical conductivity, the manufacture of which is a very laborious and energy-consuming process.

The closest analogue of the claimed invention is electrically conductive concrete (RF Patent N ° 2665324 Cl, 08/29/2018), including Portland cement, sand, water and a carbon-containing component, it additionally uses fly ash and hyperplasticizer, with the following ratio of components, wt%: Portland cement 10-14; sand 14-19; fly ash 13-18; carbon-containing component 11.8-15.8; hyperplasticizer 0.2; water 42. In this case, thermosite sand is used as sand, and carbonaceous sludge of aluminum production is used as a carbon-containing component. In addition, all dry components undergo mechanochemical activation in a vario-planetary mill to a specific surface area of 550 m ² / kg.

The disadvantage of this solution is that a complex plasticizer is used in the composition.

The problem solved by the claimed invention is to develop a mixture that includes relatively easy to manufacture and, as a consequence, inexpensive components. At the same time, the strength characteristics of such a mixture should not be inferior to those of the above solutions. In addition, in order to improve the performance of concrete made from such a mixture, its electrically conductive properties must meet certain criteria, namely, it is necessary to reduce its electrical resistivity.

The technical result achieved as a result of solving the problem is to reduce the setting time, increase the compressive strength of the cement slurry, improve the electrical properties of concrete (i.e. electrical conductivity), which will ensure the basic industrial needs associated with monitoring the state of structures, with vibration control , safety and security of buildings. Also, the use of metallurgy and thermal power waste in the production has a positive effect on the environmental situation. Studies of the electrical conductivity of concrete have attracted the attention of many researchers over the past few decades [14-17]. The electrical properties of concrete are manifested as a result of the inclusion of such additional phases (fillers), which dramatically improve the electrical properties of the final material [18]. Researchers such as Han, Chiarello, Materazzi, Bantia and Azhari use carbon fibers, tubes, pure graphite powder and graphene in various dosages to increase the conductivity of concrete [19-21]. However, the high cost of these nanofillers is the main reason for the limitation of their use. On the other hand, some researchers have achieved low electrical resistivity by using industrial waste and by-products as fillers [22]. These wastes are rich in aluminum oxide, silicon oxide and iron oxide, which makes them good candidates for use as conductive additives in concretes and mortars [23, 24]. All these studies show good results, but the drawback of these studies is that these formulations were based on the use of complex plasticizers and additives, in addition to using various approaches to reduce the influence of van der Waals forces [25] in order to achieve an even distribution electrically conductive aggregates and homogeneity in concrete [26]. Improving the electrical properties of concrete (ie, electrical conductivity) will meet the basic industrial needs associated with monitoring the condition of structures, vibration control, safety and reliability of buildings, as well as the growing costs of managing extensive infrastructure in developed countries [27-29]. Conductivity of concrete can be easily related to its resistivity, which can be an indicator for assessing the characteristics of concrete [30].

The present invention is directed to improving the electrical conductivity of concrete by using; red mud. Bauxite residues, like steel sludge, are mainly composed of iron oxides and aluminum oxide. Thus, it is possible to use red mud as a functional filler, which not only improves the conductivity of concrete, but also increases its mechanical properties.

In the composition of the claimed mixture, the content of Portland cement is in the range of 75-95% by weight, and the content of red mud varies in the range of 5-25% by weight.

In the claimed cement mixtures, red mud (KSH) is also used to partially replace Portland cement in various dosages. Brief description with links to drawings.

Figure 1 - Graph of particle size distribution;

Figure 2 - Solution preparation process;

Figure 3 - XRF results: KSh;

Figure 4 - Arrangement of electrodes on the sample;

Figure 5 - (a) Compressive strength test, and (b) electrical resistance measurement;

Figure 6 - Maximum change in resistivity during loading of the samples;

Figure 7 - Relative change in resistivity during cyclic loading (a) with 20% red mud (b) with 25% red mud.

In order to confirm the presence of the above properties in the claimed invention, samples were studied.

The chemical composition of Type I Portland cement (PC) and red mud, which was determined using X-ray fluorescence spectrometry (XRF), is presented in Table 1. In red mud, the weight ratio of silica to alumina (S1O ₂ / AI ₂ O ₃ ) and oxide silicon to calcium oxide (SiCb / CaO) was found to be 0.46 and 0.50, respectively.

Размер частиц материалов был определен при помощи электростатического классификатора TSI Electrostatic Classifier, результаты анализа представлены на фигуре 1. В целом, тонкость помола (удельная площадь поверхности) конечного продукта зависит от способа измельчения (измельчение при помощи шаровой мельницы, планетарной мельницы или криомельницы). Table 1 Chemical composition of materials (%)

The particle size of the materials was determined using a TSI Electrostatic Classifier, the analysis results are shown in Figure 1. In general, the fineness (specific surface area) of the final product depends on the grinding method (grinding with a ball mill, planetary mill or cryo mill).

For this study, the red mud was ground using a laboratory ball mill to a size of less than 1 mm, and then further disintegrated using a nanomill to nanosized.

The mass ratios of red mud used for the production of cement mixtures were 5, 10, 15, 20 and 25% of the total weight of Portland cement, as shown in Table 2. A laboratory mixer was used to mix materials (cement, red mud, quartz sand and water). (mixer). These ratios have been designed to provide chemical composition and sufficient electrical conductivity. Before the addition, the red mud was milled for 2 hours using a ball mill at 65 rpm and a material to balls ratio of 25%. Disintegration was carried out for 2 hours in a nanomill using zirconium blasting bodies. The ratio of water and cement in the slurry was selected so that the spread of the slurry was 110 ± 5% in accordance with ASTM C1437 [32]. The resulting water to cement ratios ranged from 0.50 to 0.56. Sample preparation was carried out in the following sequence, as shown in figure 2: (1) the required amount of red mud is premixed with a certain amount of water using a laboratory ultrasonic stirrer (homogenizer) at a speed of at least 1000 rpm for 15 minutes, (2) after which this slurry is added to Portland cement, and the cement paste is mixed for three minutes at low speed, (3) gradually adding quartz sand with a sand / cement ratio of 2.75 for all samples, and then the solution is left at rest for 90 seconds, (4) and then the entire solution is mixed at medium speed for 60 s.

The samples were filled in cubic shapes with sides of 50 mm in accordance with ASTM C 109 [33]. Two copper plates (25 x 50 x 0.2 mm) were used as embedded electrodes, which were placed in the samples at a distance of 10 mm from the edges of each cube during the molding of the samples. Copper foil 0.07 mm thick was used as an external electrode; it was glued with conductive silver paint from opposite ends of the cube. The samples were shaken on a vibrating table to reduce air bubbles and provide compaction. After 24 hours the samples were deformed and placed in a curing chamber at a temperature of 20 ° C and a relative humidity of 95%.

Table 2. Description of the composition of the samples and the water-cement ratio.

To assess the effectiveness of the resulting cement mixtures, measurements of electrical resistance, setting time, and compressive strength were carried out, where ordinary Portland cement (OPC) was used as a reference value. The mineralogical composition of cement mixtures was determined using the method of X-ray diffraction analysis. For this analysis, a Bruker D8 diffractometer was used, equipped with a Cu-emitter, operating at a voltage of 40 kV and a current of 30 mA, the scanning angle range of 20 was set within 5-60 °. Scanning mode: continuous fast PSD with a counting time of 0.2 s at each step.

The pH measurement of a 1% aqueous solution was carried out using a Fisher Scientific Accumet AB15 instrument. For this test, 1 gram of cement mixture was dissolved in 100 grams of distilled water. The solution was placed in an agitator (shaker) for 30 minutes at a speed of 200 rpm. Then, the solution was left in a calm state for 30 minutes and after which the pH values were measured.

Compressive strength of 50 mm cube slurry samples was determined according to ASTM C 109 over curing periods of 3, 7 and 28 days [34] using a FORNEY laboratory press as shown in FIG. 5 (a). Three specimens were tested for each period, then the average value of the compressive strength was determined. The initial and final setting times of cement pastes were measured in accordance with ASTM C191 using a Vic apparatus [35], the amount of water for the setting time measurement was chosen to obtain a normal consistency according to ASTM C 187 [36].

The electrical resistance was measured indirectly by setting the VK Precision 4071 A signal generator to an electrical signal with a voltage of 5 V in the frequency range from 0.1 kHz to 100 kHz, followed by measuring the voltage with a Tektronix TDS 1002 two-channel oscilloscope and the current with a Radio Shark digital multimeter, as shown in figure 5 (6). It should be noted that the 10 kHz signal frequency was chosen as the reference due to the limited bandwidth of the multimeter. Two inner electrodes were used to measure the voltage, and the AC value was measured with two outer film electrodes. To determine the electrical resistance, a four-wire circuit was used, as shown in figure 4, in order to reduce the influence of the contact resistance that occurs when using only two electrodes [37]. The resistance of the solution samples p was calculated using the following formula:

(1) where V and I are voltage and current values, respectively. A and L are the area of the electrodes and the distance between the inner electrodes, respectively.

Below are the results of the research.

Table 3 shows the set time and pH results for each cement mixture. As can be seen, an increase in the content of red mud leads to a decrease in the setting time.

Table 3 Setting time and pH of various cement mixtures

Table 4 presents the results for the compressive strength and electrical resistivity of cement mixtures with a certain content red mud at different curing times: 3, 7 and 28 days. It can be seen that an increase in the content of red mud leads to an increase in compressive strength for all samples in the early and late periods. It is worth noting that at a late aging period (28 days), replacing 25% of Portland cement with KSh gives similar results for OPC with a difference of 0.6%, respectively. Nevertheless, for a holding period of 7 days, a general drop in strength is observed for specimens containing KSH. This observed regression of compressive strength may be due to the presence of crystalline phases of tricalcium silicate and dicalcium silicate in the KS, as shown in figure 3, because these phases are limitedly involved in the hydration process [38, 39].

An interesting trend is observed in the late period of strength development (28 days), when there is a general increase in the compressive strength index. This trend may be due to the presence of calcium oxide, iron oxide, aluminum oxide and titanium oxide in the amorphous phase, which had a positive effect on the compressive strength of the cement slurry [43, 44]. In addition, the presence of these metal ions can contribute to the formation of new crystallization centers and the presence of dicalcium silicate, the crystallization of which takes a longer time, which is also confirmed by a drop in strength in middle age.

Resistivity values in the early and late stages of curing were measured without applying a load to the samples. Changes in the dynamics of electrical resistivity at different curing ages are presented in Tables 5. The samples were not dried before measurements (they were stored continuously until the moment of testing), therefore, an excess water content could contribute to an increase in electrical resistivity over time, due to the presence of ions in water, which is contained in the pores of cement slurry samples [45, 46]. All tested samples show low resistivity (including RAFT), but samples with 25% KSh showed the lowest resistivity, which is possibly provided by electrolytic and electronic conductivity, as described in [47]. The introduction of 25% red mud reduces the electrical resistance of the Portland cement solution by a factor of three, which may be due to the high content of metal oxides (i.e., FerOs) in nano and submicron sizes found in these materials, as shown in Table 1, which is possible even at the end of the curing period, when conductivity is provided by electrons [48]. Table 4 Indicators of compressive strength of samples during standard periods of strength development, MPa

Table 5 Specific electrical resistance to compression of samples during standard periods of strength development, Wm

Sensory properties of cement mixtures

Figure 6 shows the maximum relative changes in electrical resistivity (RR), which were calculated using expression 2:

(2) where and the values of the relative electrical resistance measured at the initial moment and during the loading of the sample, respectively.

During compressive loading, the matrix of the cement sensor is compacted, and in this case the distance between electrons is reduced, which means a decrease in electrical resistance [17]. Thus, the OIS of the samples should have a negative value for the compressive load [49]. In this regard, samples with a high content of red mud showed the most effective results with sensory (self-detecting) properties, and, as expected, samples with 5% red mud do not provide the required resistivity change. In addition, the coefficient of sensitivity to compressive stress was calculated according to formula 3 and the results of the calculations are presented in table 6.

(3) where, and are the maximum values of the relative change in resistivity and the specified voltage value during the loaded state, respectively.

Table 6 Sensitivity coefficient of cement mortars on the 28th day of curing

Figure 7 shows the relationship between the compressive strength and the change in the specific electrical resistance of the cement slurry samples, during repeated cyclic loads of 10 and 18 MPa (45-60% of the breaking load). Figures 7 (a) and 7 (b) show the results for samples containing 20 and 25% red mud, respectively. Percentages of 20% and 25% have been selected here to illustrate the change in resistance. OPC was used as a reference value for comparison. As can be seen, the electrical resistivity of all tested samples decreases with the application of a load. It should be noted that the specific electrical resistance of the RAFT decreased with increasing load up to 360 seconds, then the sample begins to show the opposite tendency, which may be associated with the appearance of significant irreversible damage in the sample structure [50].

The studies carried out allow us to draw the following conclusions.

The effect of a by-product of aluminum production, residual bauxite (red mud), added in various volume fractions to a cement slurry prepared using Type I Portland cement, was studied. Based on the data obtained in this experimental work, the following main conclusions were formulated:

• The introduction of KSH into ordinary Portland cement in an amount of 5-25 wt.% Increases the compressive strength of the cement slurry at an early and late age. WITH on the other hand, the maximum increase in compressive strength was achieved after 28 days with 15 wt% red mud.

• The addition of red mud to the Portland cement slurry in the form of a powder with a particle size of less than 100 nm significantly improved the sensory (self-detecting) properties of the cement slurry. The addition of 15, 20 and 25 wt% KS reduced the relative change in resistivity by 75%, 77% and 78% compared to the control solution (0% red mud), respectively. The electrical conductivity of Portland cement slurry improves with an increase in the mass fraction of red mud.

List of used literature:

1. Monteiro, R., Concrete: microstructure, properties, and materials. 2006: McGraw-Hill Publishing.

2. Mehta, P.K., P.J. Monteiro, and M.-H. Education, Concrete: microstructure, properties, and materials. Vol. 3. 2006: McGraw-Hill New York.

3. Naik, T.R., Sustainability of concrete construction. Practice Periodical on Structural Design and Construction, 2008.13 (2): p. 98-103.

4. Lothenbach, B., K. Scrivener, and R. Hooton, Supplementary cementitious materials. Cement and Concrete Research, 2011.41 (12): p. 1244-1256.

5. Chindaprasirt, P. and S. Rukzon, Strength, porosity and corrosion resistance of ternary blend Portland cement, rice husk ash and fly ash mortar. Construction and Building Materials,

2008.22 (8): p. 1601-1606.

6. Chindaprasirt, P., S. Rukzon, and V. Sirivivatnanon, Resistance to chloride penetration of blended Portland cement mortar containing palm oil fuel ash, rice husk ash and fly ash. Construction and Building Materials, 2008.22 (5): p. 932-938.

7. Chindaprasirt, P., C. Jaturapitakkul, and T. Sinsiri, Effect of fly ash fineness on compressive strength and pore size of blended cement paste. Cement and Concrete Composites, 2005.27 (4): p. 425-428.

8. Sassani, A., et ah, Carbon fiber-based electrically conductive concrete for salt-free deicing of pavements. Journal of cleaner production, 2018.203: p. 799-809.

9. Mingqing, S., et ah, Experimental studies on the indoor electrical floor heating system with carbon black mortar slabs. Energy and Buildings, 2008.40 (6): p. 1094-1100.

10. Zhang, Q. and H. Li. Experimental investigation of road snow-melting based on CNFP self-heating concrete in Behavior and Mechanics of Multifunctional Materials and Composites 201L 2011. International Society for Optics and Photonics.

11. Ounaies, Z. and S.S. Seelecke. Behavior and Mechanics of Multifunctional Materials and Composites 20 IP in Behavior and Mechanics of Multifunctional Materials and Composites

201 P 2011.

12. Dry, C.M. Design of self-growing, self-sensing, and self-repairing materials for engineering applications. in Smart Materials. 2001. International Society for Optics and Photonics.

13. Ou, J. and B. Han, Piezoresistive cement-based strain sensors and self-sensing concrete components. Journal of Intelligent Material Systems and Structures, 2009.20 (3): p. 329-336. 14. Kim, S., J. Surek, and J. Baker-Jarvis, Electromagnetic metrology on concrete and corrosion. Journal of research of the National Institute of Standards and Technology, 2011.116 (3): p. 655.

15. Sun, M., W. Staszewski, and R. Swamy, Smart sensing technologies for structural health monitoring of civil engineering structures. Advances in civil engineering, 2010.2010.

16. Han, B., L. Zhang, and J. Ou, Smart and multifunctional concrete toward sustainable infrastructures. 2017: Springer.

17. Banthia, N., S. Djeridane, and M. Pigeon, Electrical resistivity of carbon and steel micro-fiber reinforced cements. Cement and Concrete research, 1992.22 (5): p. 804-814.

18. Han, B., X. Yu, and J. Ou, Self-sensing concrete in smart structures. 2014: Butterworth-Heinemann.

19. Azhari, F. and N. Banthia, Cement-based sensors with carbon fibers and carbon nanotubes for piezoresistive sensing. Cement and Concrete Composites, 2012.34 (7): p. 866-873.

20. Materazzi, A.L., F. Ubertini, and A. D'Alessandro, Carbon nanotube cement-based transducers for dynamic sensing of strain. Cement and Concrete Composites, 2013.37: p. 2-11.

21. Chiarello, M. and R. Zinno, Electrical conductivity of self-monitoring CFRC. Cement and Concrete Composites, 2005.27 (4): p. 463-469.

22. Saafi, M., et ak, Graphene / fly ash geopolymeric composites as self-sensing structural materials. Smart materials and structures, 2014.23 (6): p. 065006.

23. JIA, X., J. QIAN, and Z. TANG, Research on Compression Sensitivity of Steel Slag Concrete [J]. Materials Review, 2008.11.

24. McCarter, W., et ak, Characterization and monitoring of cement-based systems using intrinsic electrical property measurements. Cement and Concrete Research, 2003.33 (2): p. 197-206.

25. Wang, T., et al. Study on the Effects of Carbon Fibers and Carbon nanofibers on Electrical Conductivity of Concrete in IOP Conference Series: Earth and Environmental Science. 2019. IOP Publishing.

26. Danoglidis, P. A., et al., Strength, energy absorption capability and self-sensing properties of multifunctional carbon nanotube reinforced mortars. Construction and Building Materials, 2016.120: p. 265-274.

27. Hooton, R.D. and J.A. Bickley, Design for durability: the key to improving concrete sustainability. Construction and Building Materials, 2014.67: p. 422-430.

28. Shao-peng, W., et al., An improvement in electrical properties of asphalt concrete.

Journal of Wuhan University of Technology -Mater. Sci. Ed., 2002.17 (4): p. 69-72. 29. El-Enein, SA, et al., Electrical conductivity of concrete containing silica fume. Cement and concrete research, 1995.25 (8): p. 1615-1620.

30. Andrade, C., Model for prediction of reinforced concrete service life based on electrical resistivity. IBRACON Mater J, 2005.1 (1): p. 1-5.

31. Bray, E. L., Bauxite and alumina. USGS 2015 Mineral Commodity Summaries, 2016.

32. ASTM, C., Standard test method for flow of hydraulic cement mortar. C 1437, 2007.

33. ASTM, C. 109 / C 109M-99, ". Standard Test Method for Compressive Strength of Hydraulic Cement Mortars (Using 2-in. Or [50-mm] Cube Specimens), ”ASTM International, West Conshohocken, PA, 1999.

34. Testing, A.S.f. and M.C.C.-o. Cement, Standard Test Method for Compressive Strength of Hydraulic Cement Mortars (using 2 -in. Or [50-mm] Cube Specimens). 2013: ASTM International.

35. ASTM, Standard test methods for time of setting of hydraulic cement by Vicat needle.

2008.

36. ASTM, Standard test method for normal consistency of hydraulic cement. 2004.

37. Han, B., X. Guan, and J. Ou, Electrode design, measuring method and data acquisition system of carbon fiber cement paste piezoresistive sensors. Sensors and Actuators A: Physical, 2007.135 (2): p. 360-369.

38. Lizarazo-Marriaga, J., P. Claisse, and E. Ganjian, Effect of steel slag and portland cement in the rate of hydration and strength of blast furnace slag pastes. Journal of materials in civil engineering, 2010.23 (2): p. 153-160.

39. Zhang, T., et al., Preparation of high performance blended cements and reclamation of iron concentrate from basic oxygen furnace steel slag. Resources, Conservation and Recycling, 2011.56 (1): p. 48-55.

40. Jiang, Y., et al., Characteristics of steel slags and their use in cement and concrete A review. Resources, Conservation and Recycling, 2018.136: p. 187-197.

41. Baltakys, K., et al., The impact of A1203 amount on the synthesis of CASH samples and their influence on the early stage hydration of calcium aluminate cement. Ceramics International, 2019.45 (2): p. 2881-2886.

42. Wang, J., et al., Influence of the combination of calcium oxide and sodium carbonate on the hydration reactivity of alkali-activated slag binders. Journal of cleaner production, 2018.

171: p. 622-629.

43. Lucas, S., V. Ferreira, and JB De Aguiar, Incorporation of titanium dioxide nanoparticles in mortars Influence of microstructure in the hardened state properties and photocatalytic activity. Cement and Concrete Research, 2013.43: p. 112-120. 44. Fan, W.-J., X.-Y. Wang, and K.-B. Park, Evaluation of the chemical and mechanical properties of hardening high-calcium fly ash blended concrete. Materials, 2015.8 (9): p. 5933-5952.

45. Yoo, D.-Y., L You, and S.-J. Lee, Electrical properties of cement-based composites with carbon nanotubes, graphene, and graphite nanofibers. Sensors, 2017.17 (5): p. 1064.

46. Tian, Z., et al., A state-of-the-art on self-sensing concrete: Materials, fabrication and properties. Composites Part B: Engineering, 2019: p. 107437.

47. Han, B., L. Zhang, and J. Ou, Influence of water content on conductivity and piezoresistivity of cement-based material with both carbon fiber and carbon black. Journal of Wuhan University of Technology -Mater. Sci. Ed., 2010.25 (1): p. 147-151.

48. Fulham-Lebrasseur, R., L. Sorelli, and D. Conciatori, Development of electrically conductive concrete and mortars with hybrid conductive inclusions. Construction and Building Materials, 2020.237: p. 117470.

49. Dong, W., et al., Piezoresistive properties of cement-based sensors: review and perspective. Construction and Building Materials, 2019.203: p. 146-163.

50. Fu, X. and D. Chung, Self-monitoring of fatigue damage in carbon fiber reinforced cement. Cement and concrete research, 1996.26 (1): p. 15-20.

51. Sun, S., et al., Nano graphite platelets-enabled piezoresistive cementitious composites for structural health monitoring. Construction and Building Materials, 2017.136: p. 314-328.

Claims

Claim 1. A cement composition for monitoring the state of structures, including Portland cement and a carbon-containing component, characterized in that the content of Portland cement in it is 75-95% by weight, and the carbon-containing component is red mud in an amount of 5-25% by weight. 2. The composition according to claim 1, characterized in that the weight ratio of silica to alumina (S1O ₂ / AI ₂ O ₃ ) in red mud is 0.46, and silicon oxide to calcium oxide (SiC / CaO) is 0.50 ...