https://orcid.org/0009-0002-8410-9195
Figures
Abstract
Backfill materials are used in underground engineering to fill voids and buried excavated parts. In this study, solid waste was utilised as a raw material mixed with different amounts of polypropylene fibres to determine the optimal sodium hydroxide content, water—solid ratio, and fibre content. The uniaxial compressive strength (UCS) of the produced backfill materials was measured, and the interfacial structures were analysed via scanning electron microscopy. The results revealed that the mechanical properties of the backfill materials were influenced in the order sodium hydroxide doping > water—solid ratio > fibre doping. The optimal material composition corresponded to a sodium hydroxide content of 3%, water—solid ratio of 0.28, and fibre content of 5 ‰. The slag produced a C—S–H gel. Meanwhile, the fly ash and gangue contained large amounts of aluminium, which formed hydrated aluminosilicates. The addition of polypropylene fibres reduced the number of internal defects in the backfill structure and increased the UCS.
Citation: Sha X, Cheng C, Pan G, Zhu Z, Qi C, Chen W (2024) Mechanical properties of fibre-reinforced geopolymer-cemented tailings used as backfill. PLoS ONE 19(12): e0314617. https://doi.org/10.1371/journal.pone.0314617
Editor: Parthiban Kathirvel, SASTRA Deemed University, INDIA
Received: May 19, 2024; Accepted: November 11, 2024; Published: December 5, 2024
Copyright: © 2024 Sha et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: All relevant data are within the paper and its Supporting information files.
Funding: The author(s) received no specific funding for this work.
Competing interests: The authors have declared that no competing interests exist.
1. Introduction
Iron tailings sand is discharged worldwide as beneficiation waste at a rate of more than 10 billion tons per year; however, the utilisation rate of tailings in China is only 7%. Therefore, the comprehensive recycling of iron tailing sand is a highly important task [1, 2]. Blast furnace slag is a type of solid waste, and its large stockpiling amount is hazardous to the environment, and represents a waste of resources [3]. Fly ash is a volcanic ash material. When this material is discharged into a water system, it causes the siltation of rivers, and the toxic chemicals present in sly ash may harm human beings and other living organisms [4, 5].
The comprehensive utilisation of iron tailing sand worldwide has received significant attention from researchers. For example, it has been widely used as a concrete filler [6], road base material [7–9], and filling material [10–12]. Sun et al. [13, 14] prepared a fly ash geopolymer gangue aggregate filling body by using fly ash as a cementitious material and established a deformation localisation law of the filling body via a digital scattering correlation method. Wang et al. [15] used limestone tailings sand to prepare a limestone tailings-based cementing material and improved its performance by optimising the pore structure. Qiu et al. [16] used the emerging microbial‑induced carbonate precipitation technology to promote iron tailing consolidation and determined the strength difference between a blank group and the microbially cemented iron tailing-based backfill. Zhang et al. [17] tested the activity of ultrafine tailings by using ultrafine tailings to prepare clinker-free backfill and exploring its filling performance and hydration mechanism. Although multiple studies on alkali-excited cementitious materials have been conducted, such materials have rarely been applied in practice because factors affecting their performance have not been investigated systematically. Freeze—thaw damage is a destructive process that occurs periodically owing to the freezing and expansion forces, which change the strength and other mechanical properties of a rock mass. Li et al. [18] analysed the influence of geometrical characteristics of fissures on the strength of rock bodies by performing freeze—thaw cycle and uniaxial compression experiments. Moreover, the authors established a deterioration model for the freeze—thaw loaded fissured rock based on the microscopic damage and macroscopic statistical theories to elucidate the damage deterioration mechanism of the fissured rock body under the coupling effect of freezing, thawing, and loading. Fu et al. [19] prepared high-performance alkali slag concrete (ASC) using a composite slag exciter, Na2SiO3, and NaOH and investigated its freeze—thaw durability, microstructure, performance, and variation rules of internal damage variables after freezing and thawing. They also modelled ASC damage by conducting freeze—thaw cycling tests, scanning electron microscopy (SEM) observations, and energy spectrum analyses. Chen et al. [20] performed road performance and freeze—thaw cycle tests on pulverised clay and its cured soil using alkali-excited materials as the curing agents. The microscopic characteristics of the cured soil were investigated via SEM and X-ray diffraction (XRD), and the effect of the alkali-excited materials on the road performance index and freeze—thaw resistance characteristics of the pulverised clay were explored.
Numerous studies have been conducted on the static and kinetic properties of alkali-excited materials [21–27]. In this study, the sodium hydroxide doping amount, water—solid ratio, and polypropylene fibre content of polypropylene fibre-reinforced backfill materials were optimised using an orthogonal design method to obtain a cementitious material suitable for landfill excavation. Its mechanical properties and microstructure were correlated with the backfill internal structure and strength enhancement mechanism.
2. Materials and testing procedure
2.1 Test materials
The solid raw materials used in this study were tailings, fly ash, and slag. Fuxin tap water was used for testing, and the alkaline exciter was composed of sodium hydroxide granules. Iron tailings sand was obtained from the Fengshuigou tailing pond of the Qidashan ore dressing plant of the Angang Mining Group. Its physical properties are listed in Table 1, and the particle grading curve is shown in Fig 1. Fly ash was obtained from the Rizhao Huaneng Power Plant, and slag was supplied by Henan Yuanheng Environmental Protection Engineering Company Limited. Their chemical compositions were determined using X-ray fluorescence spectrometry. The results are listed in Table 2. The physical properties of the slag are summarised in Table 3. The phase structures of the slag and fly ash were obtained using Rigaku Benchtop XRD (MiniFlex 600) instrument. The resulting diffraction patterns are shown in Fig 2. The particle size distributions of the slag and fly ash were determined using a Bettersize-2000 laser particle size analyser. The curves obtained are shown in Figs 3 and 4. Polypropylene fibres were produced by Shandong Yishun Engineering Materials Co., and their corresponding physical properties are listed in Table 4. Photographs of the raw materials used in this study are shown in Fig 5.
2.2 Testing procedure
A three-factor three-level orthogonal test (L9(34)) was designed to investigate the effects of NaOH dosing (A), water—solid ratio (B), and fibre dosing (C) on the compressive properties of the geopolymer-gelatinised cemented end-sand specimens. The values of each factor are listed in Table 5.
Specimens were prepared according to the test design quality ratio. Appropriate amounts of the raw materials were weighed, placed in a glue sand mixer, and mixed at a uniform speed for 3 min. Water and sodium hydroxide were mixed at an appropriate ratio, cooled to room temperature, and poured into the glue sand mixer. The resulting system was stirred quickly for 3–5 min until the slurry achieved a certain degree of mobility and then uniformly poured into a film tool (φ 50 mm × 100 mm) and vibration-compacted on a vibration table for 24 h. Demoulding was performed in a standard maintenance box after 3, 7, and 28 d of aging. Three parallel specimens were produced for each ratio (Fig 6).
During testing, a WDW-100E testing machine was used to perform uniaxial compression tests on the specimens that satisfied the testing requirements. The loading process illustrated in Fig 7 was conducted in strain control mode at a loading speed of 0.5 mm/min.
3. Test results and analysis
3.1 Test results
Tests were performed according to the experimental design. The uniaxial compressive strengths (UCSs) of the specimens aged for 3, 7, and 28 d were measured to determine the influences of the three factors on the strength of backfill materials in coal mines and their optimal composition. The obtained results are listed in Table 6.
3.2 Polarisation and ANOVA results
Based on the obtained results, the extreme deviation and variance of the mean value of the specimen UCS at the level of each factor were calculated. The influence of each factor on the test results was determined from the extreme deviation, and the significance of each factor was determined from the variance.
The orthogonal test results showing the effects of different factors on the 3-d UCS of the fibre-reinforced geopolymer-cemented tailing (FRGCT) specimens are presented in Table 7.
The orthogonal test results obtained for the 7-d UCS of the FRGCT samples are listed in Table 8.
The orthogonal test results obtained for the 28-d UCS of the FRGCT samples are listed in Table 9.
The results of the test range and variance analysis suggest that the primary and secondary degrees of influence on the sample UCS after 3, 7, and 28 d of aging are the sodium hydroxide content, water—solid ratio, and fibre content. To examine the degree of influence of each factor in more detail, the level of each factor was plotted along the x-axis, and the average UCS was plotted along the y-axis (Fig 8) to determine compressive failure strengths. The following equation was used to calculate range R:
(1)
where R is the range, and Rc is the mean value of the UCS.
Fig 8 shows that with an increase in NaOH content, the UCS exhibits a gradually increasing trend. At a NaOH content of 3%, the UCS of the sample aged for 28 d reaches a local maximum. This occurs because at a low alkali amount, the driving force of the polymerisation reaction is low, and the degree of polymerisation of the generated product is low, resulting in an insufficiently dense material structure after hardening. With an increase in alkali content, the pH of the polymerisation reaction increases. A higher solution pH promotes the dissolution of Ca, Si, Al, and other elements, causing the dissolution of a larger amount of grey bodies, which produces silicate and aluminate monomers, accelerating the polymerisation reaction, generating a larger gel amount, and increasing the UCS. As shown in Fig 8, the UCS of the studied samples first increases and then decreases with an increase in the water—binder ratio. An appropriate water—binder ratio can increase the activity of the slag and fly ash and promote the polymerisation reaction; hence, the UCS of the geopolymer reaches a maximum. However, when the water—binder ratio is substantially high, although the fly ash and slag cementitious materials can be fully polymerised, the water content in the alkali solution is extremely high, resulting in a decrease in the pH of the alkali solution, which is detrimental to the fly ash and slag activity. The dissolution rate of the elements in the raw materials decreases, which reduces the reaction rate of the system and reaction degree. Meanwhile, the amount of the hydration products formed and structural compactness decrease, which ultimately decreases the specimen strength. However, the amount of free water in the solid waste matrix paste system gradually increases, and the excess free water remains inside the system. When water evaporates, voids are generated inside the sample structure; consequently, internal defects are created, and the geopolymer compactness and UCS are reduced. These voids lead to an uneven stress distribution when the sample is subjected to an external force, and the stress is concentrated near the voids, which quickly destroys the sample. Fig 8 also shows that with an increase in the fibre content, the UCS first increases and then decreases. At a low fibre content, the fibres inside the matrix are discrete, and their effect is weak. After increasing the fibre content, the fibres form a three-dimensional staggered structure, which helps absorb energy under loading. However, when the fibre content is too high, fibres easily tangle into groups inside the specimen; as, these do not contribute to the specimen tensile properties the UCS decreases.
The optimal level combination determined from the orthogonal test range and variance analysis results is A3B2C2, which corresponds to a NaOH content of 3%, water—solid ratio of 0.28, and fibre content of 5‰.
3.3 FRGCT failure process
The numerical simulation of the failure mode evolution process of FRGCT specimens is shown in Figs 9–12. During the loading process of the specimens, cracks developed in three stages. Initially, the loading was in the linear-elastic stage, followed by the yield stage. Small cracks appeared on the surface of the FRGCT specimen. As the deformation continued to increase, the cracks in the FRGCT specimen gradually increase and became more connected, with the overall failure mode presenting shear failure.
Under loading, the particles inside the FRGCT specimen are displaced in different directions, and numerous shear cracks form in the specimen body. For the well-cemented polymer specimens doped with fibres, damage occurs only under large loads when particles inside the polymer are sufficiently compacted, and apparent shear slip surfaces are present in the polymer structure. At a low fibre content, the specimen tends to undergo crushing damage, whereas at a high fibre content, the specimen tends to undergo shear damage. The displacement vector field distribution based on a discrete element model reflects the stable mechanical response of polypropylene fibres. When the fibre content is low, the bond strength between the particles is low, and internal particle dislocation and slip are prone to occur. Thus, the failure probability is high. With the increase in fibre content, the cracks inside the sample during failure become finer, indicating that the incorporation of polypropylene fibres into the backfill can improve its anti-cracking ability, effectively increasing the energy absorption capacity during deformation and specimen deformation resistance; thus, the geopolymer–fibre backfill material exhibits high toughness and UCS.
3.4 Stress–strain curve analysis
The stress–strain curve of the FRGCT-8 specimen recorded during loading is depicted in Fig 13.
Uniaxial compressive stress–strain curves are frequently used in force analyses and theoretical calculations. To simplify the analysis procedure, dimensionless coordinates, i.e. x = ε/εp, y = σ/σp, were employed, where εp is the average peak strain, ε is the sample strain, ε is the average peak stress, and σp is the sample stress.
The equation for the rising segment of the FRGCT stress–strain curve is [22] as follows:
(2)
The equation for the descending section of the stress–strain curve of the FRGCT sample can be written as follows:
(3)
The slope of curve is the elastic modulus of materials:
(4)
At x = 1 and dy/dx = 0, the derivative of (2) is
(6)
By substituting a, b, and c into (2), the equation for the rising section of curve of the FRGCT sample can be written as follows:
(8)
Eqs (2) and (3) were used to fit the complete stress–strain curves of the FRGCT specimens under uniaxial compression. The fitting curve, experimental curve, a value, d value, and fitting correlation are shown in Fig 14 (owing to the limited space, only the fitting data for the FRGCT-7, FRGCT-8, and FRGCT-9 specimens are provided in this paper). The fitting procedureindicates that the mass content range of polypropylene fibres was 4 ≤ Vf ≤ 6%, a = −0.144, and d = 4.881. Thus, the equation for the rising section of the curve of the FRGCT sample is as follows:
(9)
The equation for the descending section of t curve of the FRGCT sample is as follows:
(10)
4. Microscopic characterisation of backfill materials
As shown in Figs 15–17, observations using electron microscopy reveal that the overall structure of the hydration products is considerably dense. Compared to the 3-d hydration products, the hydration products at 28-d have a more compact overall structure, presenting an amorphous form, and are covered with a large amount of hydration gel. Regardless of curing age, the hydration products contain fly ash particles. In the 3-d hydrated paste, most fly ash particles have relatively smooth surfaces and form many rod-like hydration products, with a weaker bond between the hydration products and the particles. However, in the 28-d hydration products, the surface of the fly ash particles is covered with a large amount of hydration products, and these particles are tightly wrapped by the hydration products.
The fly ash was rich in aluminium, forming hydrated aluminosilicates with a shelf structure, which primarily contributed to the later strength of the backfill material. In contrast, the slag functioned as a calcium source, leading to the formation of a C–S–H gel, which was necessary for the early strength of the backfill material. Furthermore, the flowability of the mixture was enhanced by the flat surface of the fly ash particles. Consequently, the combination of these two materials exhibits high strength and workability.
The microstructures of the FRGCT specimens with different doping ratios after destruction were observed using SEM. Local magnification was performed by changing from a low-magnification mode to a high-magnification mode when a typical region was investigated, and sample photos were recorded. The SEM images used in this investigation have magnifications ranging from 100× to 1000×.
The SEM image of the ground polymer with 4‰ fibres is presented in Fig 18. The figure shows that the fibres embedded into the matrix of the cementitious material, randomly distributed, and highly discrete. During the initial phase of the FRGCT specimen aging process, hydrides continue to form and fill the spaces between the fly ash particles and between fibres and fly ash particles, enhancing their interfacial cohesiveness. Fibres and tailings sand particles are mixed by extrusion and wrapping. Isolated fibres of low fibre content are buried with increasing grip area when they are firmly enveloped in fly ash particles. The fibres are in the tensile condition when the specimen is deformed or damaged by an external load, and the relative displacement of the particles is reduced owing to the bonding and friction forces that limit their relative sliding movements.
The SEM image of the specimen with a fibre content of 5‰ is shown in Fig 19. Fibres in the polymer matrix exhibit a uniformly chaotic crisscross distribution, which is similar to that of the roots embedded in soil, to form a more stable three-dimensional spatial structure. When fly ash sand particles are under the action of an external load causing the misalignment and rearrangement of the fibre network, they disperse the load to other areas of the specimen more effectively, reducing stress concentration by bearing stress, thereby improving the specimen stability. The hydration reaction between fly ash particles, tailings sand particles, and fibres forms crystalline products and crystals adhering to the fibre surface (Fig 19). The hydration products blend to form a porous dense mesh structure that strengthens the interfacial contacts between the fly ash particles and the fibres as well as their adherence. Simultaneously, discrete fibres are cemented into a mesh structure and a zone of anchoring is formed around them by the fibre-wrapped hydrated crystals, which resemble hard shell layers in shape. This process increases the stiffness of the fibres, which increases the adhesion and stabilization of the fibres and fly ash particles in the non-homogeneous material. Consequently, the toughness and integrity of the geopolymer—fibre backfill material are increased because the formation and development of cracks are effectively suppressed and the fibres and fly ash particles do not easily slide relative to each other under loading.
Fibres are less evenly distributed and have a lower degree of dispersion in the sample when the fibre content reaches 6% (Fig 20); the degree of cementing hydration between particles is greatly decreased. In Fig 20, some of the fibres are orientedparallel to one another, and the fibres are partially out of contact with the polymerised products, which reduces the gripping area. The gelling material matrix be-comes looser and the overall performance of the material deteriorates because the water-containing compounds are unable to fill the spaces between the particles and fibres during the hydration reaction. The overall structure of the sample is rapidly destroyed when subjected to an axial load because the overlaid weak layer’s fibres slip and break, with a minimal reinforcing effect.
5. Conclusions
This study examined the effects of various parameters on the UCS of fly ash composite cement samples that were generated through the homogenous mixing of polypropylene fibres with the cementing material. SEM was used to analyse the composite structure’s interfacial interactions at the microscopic level. The following conclusions were drawn based on the results:
- The strength model established using the orthogonal design method exhibited a high accuracy and predictability. The effect of each factor on the backfill material was ranked as follows: sodium hydroxide content > water—solid ratio > fibre content. Moreover, a significant interaction was observed between these parameters, which necessitated the establishment of strict measurement accuracy requirements for the production and use of cementing materials. The optimal mix ratio with a 28-d UCS above 5 MPa was achieved at a sodium hydroxide content of 3%, water—solid ratio of 0.28, and fibre content of 5‰, which satisfies the requirements of deep backfill mining.
- The displacement vector field distribution obtained via discrete element simulations using PFC3D software effectively reflected the real failure form of the studied FRGCT samples after a uniaxial compression test from a microscopic perspective. After adding polypropylene fibres, the peak stress—strain increased, and the maximum value was reached at a fibre content of 5‰, which increased the strength and ductility of the backfill before failure.
- At a fibre concentration of 5‰, the blended system’s fibres were uniformly and randomly dispersed, displaying chaotic distribution features in three-dimensional space, according to SEM observations. Fibres met at several points, and the fibre-reinforced geopolymer matrix adopted a comparatively stable three-dimensional spatial structure. Nevertheless, at reaching a fibre content of 6%, the sample’s homogeneous fibre distribution rapidly diminished due to fibre agglomeration, thereby indirectly reducing the effective contact area between particles and fibres.
The results of this study can serve as a reference for similar studies related to mine management projects.
Acknowledgments
We would like to thank Keith (Shanghai) Business Information Consulting Co., Ltd., for their help with language editing.
References
- 1. Cao L.; Zhou J.; Zhou T.; Dong Z. Tian Z. 2022 Utilization of Iron Tailings as Aggregates in Paving Asphalt Mixture: A Sustainable and Eco-friendly Solution for Mining Waste. J. Clean. Prod. 375, 134126,
- 2. Vilaça A.S.I.; Simão L.; Montedo O.R.K.; Novaes de Oliveira A.P.; Raupp-Pereira F. 2022 Waste Valorization of Iron Ore Tailings in Brazil: Assessment Metrics from a Circular Economy Perspective. Resour. Policy 75, 102477,
- 3. Tripathy S.K.; Dasu J.; Murthy Y.R.; Kapure G.; Pal A.R; Filippov L.O. 2020 Utilisation Perspective on Water Quenched and Air-Cooled Blast Furnace Slags. J. Clean. Prod. 262, 121354,
- 4. Zhao X.; Yang J.; Ning N.; Yang Z. 2022 Chemical Stabilization of Heavy Metals in Municipal Solid Waste Incineration Fly Ash: A Review. Environ. Sci. Pollut. Res. 29, 40384–40402, pmid:35338465
- 5. Blaha U.; Sapkota B.; Appel E.; Stanjek H; Rösler W. 2008 Micro-Scale Grain-Size Analysis and Magnetic Properties of Coal-Fired Power Plant Fly Ash and Its Relevance for Environmental Magnetic Pollution Studies. Atmos. Environ. 42, 8359–8370,
- 6. Chen F.; Zhang L.; Zou C.; Zhu X.; Fang Q.; Xu S. 2022 Study on Influencing Factors of Shear Characteristics of Rock-Fill Concrete Layer of Iron Tailings as Fine Aggregate. Constr. Build. Mater. 345, 128213,
- 7. Niu X.; Sun Y. 2018 Numerical Analysis on Settlement and Stability of Iron Ore Tailings Subgrade. J. Chang’an Univ. 38, 9–16,
- 8. Zhang B. 2024 Durability of low-carbon geopolymer concrete: A critical review. Sustain Mater Techno. 40: e00882,
- 9. Sá T.S.W.; Oda S.; Machado Balthar V.K.C.B.L.; Filho R.D.T. 2022 Use of Iron Ore Tailings and Sediments on Pavement Structure. Constr. Build. Mater. 342, 128072,
- 10. He X.; Li W.; Yang J.; Su Y.; Zhang Y.; Zeng J.; et al. 2023 Multi-Solid Waste Collaborative Production of Clinker-Free Cemented Iron Tailings Backfill Material with Ultra-Low Binder-Tailing Ratio. Constr. Build. Mater. 367, 130271,
- 11. Zhang N.; Tang B.; Liu X. 2021 Cementitious Activity of Iron Ore Tailing and Its Utilization in Cementitious Materials, Bricks and Concrete. Constr. Build. Mater. 288, 123022,
- 12. Behera S.K.; Mishra D.P.; Singh P.; Mishra K.; Mandal S.K.; Ghosh C.N.; et al. 2021 Utilization of Mill Tailings, Fly Ash and Slag as Mine Paste Backfill Material: Review and Future Perspective. Constr. Build. Mater. 309, 125120,
- 13. Sun Q.; Tian S.; Sun Q.; Li B.; Cai C.; Xia Y.; et al. 2019 Preparation and Microstructure of Fly Ash Ge-opolymer Paste Backfill Material. J. Clean. Prod. 225, 376–390,
- 14. Sun Q.; Cai C.; Zhang S.; Tian S.; Li B.; Xia Y.; et al. 2019 Study of Localized Deformation in Geopolymer Ce-mented Coal Gangue-Fly Ash Backfill Based on the Digital Speckle Correlation Method. Constr. Build. Mater. 215, 321–331,
- 15. Wang Y.; Li Z.; Jin Q.; Zhang M.; Zhou Z. 2022 High-Efficiency Utilization of Limestone Tailings: Used as Cementi-tious Materials and Fine Aggregate to Prepare Karst Structure Filling Material. Constr. Build. Mater. 316, 125841,
- 16. Qiu J.; Xiang J.; Zhang W.; Zhao Y.; Sun X.; Gu X. 2022 Effect of Microbial-Cemented on Mechanical Properties of Iron Tailings Backfill and Its Mechanism Analysis. Constr. Build. Mater. 318, 126001,
- 17. Zhang M.; Li K.; Ni W.; Zhang S.; Liu Z.; Wang K.; et al. 2022 Preparation of Mine Backfilling from Steel Slag-Based Non-Clinker Combined with Ultra-Fine Tailing. Constr. Build. Mater. 320, 126248,
- 18. Li X.; Lu Y.; Wang Y. 2013 Study on Damage Model of Single-Fractured Rock Mass Under Freeze-Thaw Load Coupling. Chin. J. Rock Mech. Eng. 32, 2307–2315.
- 19. Fu Y.; Cai L.; Cao D.; Wu Y. 2012 Study on Freeze-Thaw Durability and Damage Model of Alkali Slag High-Performance Concrete. Eng. Mech. 23, 103–109.
- 20. Chen R.; Hao R.; Li D.; Bao W.; Lai H. 2022 Study on Road Performance and Freeze-Thaw Resistance of Alka-li-Activated Material Stabilized Low-Liquid-Limited Silty Clay. J. Eng. Geol. 30, 327–337,
- 21. Wang M.; Yan S.; Li Y. 2022 Effects of Fine Iron Ore Tailings Sand and Curing Conditions on Mechanical Properties and Microstructure of High-Strength Alkali-Activated Mortar. Bull. Chin. Ceram. Soc. 41, 2082–2089+2116,
- 22. Zhou Y.; Fall M.; Haruna S. 2022 Flow Ability of Cemented Paste Backfill with Chloride-Free Antifreeze Additives in Sub-Zero Environments. Cem. Concr. Compos. 126, 104359,
- 23. Ma H.; Wu C. 2022 Mechanical and Microstructural Properties of Alkali-Activated Fly Ash-Slag Material Under Sustained Moderate Temperature Effect. Cem. Concr. Compos. 134, 104744,
- 24. Liu M.; Wu H.; Yao P.; Wang C.; Ma Z. 2022 Microstructure and Macro Properties of Sustainable Alkali-Activated Fly Ash Mortar with Various Construction Waste Fines as Binder Replacement up to 100%. Cem. Concr. Compos. 134, 104733,
- 25. Fiala L.; Pommer V.; Böhm M.; Scheinherrova L.; Cerny R. 2022 Self-Heating Alkali Activated Materials: Micro-structure and Its Effect on Electrical, Thermal and Mechanical Properties. Constr. Build. Mater. 335, 127527,
- 26. Nodehi M.; Ozbakkaloglu T.; Gholampour A.; Mohammed T.; Shi X. 2022 The Effect of Curing Regimes on Physi-co-Mechanical, Microstructural and Durability Properties of Alkali-Activated Materials: A Review. Constr. Build. Mater. 321, 126335,
- 27. Lian C.; Wang Y.; Liu S.; Hao H.; Hao Y. 2023 Experimental Study on Dynamic Mechanical Properties of Fly Ash and Slag Based Alkali-Activated Concrete. Constr. Build. Mater. 364, 129912,