The present study aimed to investigate the durability and microstructure evolution of road base materials (RBM) prepared from red mud and flue gas desulfurization fly ash. The durability testing ...showed that the strength of RBM with the blast furnace slag addition of 1wt%, 3wt% and 5wt% reached 3.81, 4.87, and 5.84 MPa after 5 freezing–thawing (F–T) cycles and reached 5.21, 5.75, and 6.98 MPa after 20 weting–drying (W–D) cycles, respectively. The results also indicated that hydration products were continuously formed even during W–D and F–T exposures, resulting in an increase of the strength and durability of RBM. The observed increase of macropores (>1 μm) after F–T and W–D exposures suggested that the mechanism of RBM deterioration is pore enlargement due to cracks that develop inside their matrix. Moreover, the F–T exposure showed a greater negative effect on the durability of RBM compared to the W–D exposure. The leaching tests showed that sodium and heavy metals were solidified below the minimum requirement, which indicates that these wastes are suitable for use as a natural material replacement in road base construction.
Red mud is a type of highly alkaline waste residue produced in the process of alumina smelting by the Bayer process. Based on the idea of medium calcium content, solid wastes such as red mud and fly ...ash were used to prepare non-burnt bricks; and the mass ratio of CaO/SiO
2
was selected in the range of 0.88–1.42. Mechanical properties and durability were investigated with a compressive strength test. X-ray diffractometry (XRD), scanning electron microscope (SEM), and Fourier transform infrared spectroscopy (FTIR) techniques were used to characterize the hydration characteristic. The environmental performance was analyzed by Inductively Coupled Plasma Mass Spectrometry (ICP). The results indicated that the mechanical properties and the durability were optimal when the mass ratio of CaO/SiO
2
was 1.23. The hydration products were mostly C-S-H gel, ettringite, Na
4
Ca(Si
10
Al
16
)O
32
·12H
2
O and Ca
3
Al
2
(SiO
4
)(OH)
8
. They were responsible for the strength development, and the CaO/SiO
2
mass ratio of 1.23 had the best polymerized structure. The results of an environmental performance test showed that the heavy metals in the raw materials were well-solidified in the brick. Therefore, this paper provides an effective solution for use of solid wastes in building material.
In this study, SiO2–Al2O3–CaO–MgO steel slag ceramics containing 5 wt % MgO were used for the preparation of ceramic bodies, with the replacement of 5–20 wt % quartz and feldspar by fly ash. The ...effect of the addition of fly ash on the sintering shrinkage, water absorption, sintering range, and flexural strength of the steel slag ceramic was studied. Furthermore, the crystalline phase transitions and microstructures of the sintered samples were investigated by XRD, Fourier transform infrared (FTIR), and SEM. The results showed that the addition of fly ash affected the crystalline phases of the sintered ceramic samples. The main crystal phases of the base steel slag ceramic sample without fly ash were quartz, diopside, and augite. With increasing fly ash content, the quartz diffraction peak decreased gradually, while the diffraction peak intensity of anorthite became stronger. The mechanical properties of the samples decreased with the increasing amount of fly ash. The addition of fly ash (0–20 wt %) affected the optimum sintering temperature (1130–1160 °C) and widened the sintering range. The maximum addition amount of fly ash should be 15 wt %, for which the optimum sintering temperature was 1145 °C, water absorption was 0.03%, and flexural strength was 43.37 MPa higher than the Chinese national standard GBT 4100-2015 requirements.
•The high cost barrier for safe disposal and environmental issues of red mud are discussed.•Economic and environmental advantages of using red mud in road construction over other applications is ...highlighted.•The possibility of using red mud as road base and subgrade material is evaluated.•Effect of different stabilizers on red mud performance was compared.
Red mud is highly alkaline slurry produced during alumina extraction from bauxite. Its disposal generates serious environmental pollution. The best way to solve red mud disposal issues is to develop economic utilization technologies that consume significant amounts of red mud. This paper reviews the possibility of utilizing red mud as a road base material, weak subgrade soil stabilizer as well as a subgrade material. Results showed that red mud can be used for those purposes. It was also found that the stabilizing content needed to meet a certain standard differs due to differences in requirements from one country to another. Therefore, there is a need to design proportions with UCS, CBR, leaching characteristics required by the country in which red mud is intended for use. The effect of various stabilizers on performance of red mud is discussed and it transpired that lime showed the best performance followed by dolime fine, ground granulated blast furnace slag, cement kiln dust and fly ash. Findings indicated that red mud shows better performance as a subgrade material than natural soil. Also the synergistic use of red mud and other wastes also improves the mechanical and durability properties of the material compared with using red mud alone. Based on mechanical, economic and environmental benefits, it is recommended to use red mud in road base structure rather than in subgrade despite higher red mud consumption in subgrade than in road base. The scope for future research in this area is also suggested.
•The cementitious material was proposed to dispose electrolytic manganese residue.•Amorphous C-S-H gel, ettringite are responsible for the development of strength.•The cementitious material has well ...polymerized SiO4 structure.•Leaching test shows the cementitious material is environmentally acceptable.
Clinker, blast furnace slag (BFS) and electrolytic manganese residue (EMR) were used to make the cement-based cementitious material (CCM) in this research. The activation effect of EMR with different content on the early activity of BFS was studied. The mechanical properties were analyzed by cement mortar test. The hydration characteristics were investigated by XRD, SEM, 29Si NMR and other micro-analysis methods. The results indicate that the early strength of CCM can be greatly improved when the content of EMR is 15%. The microscopic analysis of XRD, SEM and 29Si NMR show that the secondary hydration reaction of BFS was accelerated by the sulfate, and more BFS was depolymerized, which resulted in a significant increase in ettringite (AFt) and C-S-H gel production at 3d. Meanwhile, the consumption of Ca(OH)2 increases. The pore diameter becomes smaller and the structure is more compact. Leaching test results show that NH3–N and heavy metals are well solidified in the cementitious material, which shows a good environmental performance. This research provides an effective path for the disposal of EMR and sulfate activating to pozzolanic materials.
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•A complete design, preparation and application of permeable brick is detailed.•Heavy metals in electrolytic manganese residue is effectively solidified.•The permeable brick yields ...excellent properties and environmentally acceptable.•The industrial production achieved the preferable results.
The present study aims to prepare non-sintered permeable bricks using significant amount of electrolytic manganese residue (EMR), discharged by electrolytic metal manganese industry. Mechanical and environmental properties were investigated. The microstructure was analyzed by means of XRD, FTIR, TG-DSC and SEM-EDS. It was observed that the splitting tensile strength and permeability coefficient of the optimum proportion were 3.53 MPa and 3.2 × 10−2 cm/s respectively. The main hydration products were found to be ettringite, C-S-H, aluminosilicates and C-A-S-H. The leaching test showed that Mn, Pb, Cd, total Cr and NH3-N in the non-sintered permeable bricks were solidified up to concentrations lower than groundwater standard. In addition to that, the NH3-N produced during the process was transformed into ammonia water which was in turn recycled and reused in manganese electrolysis. Besides, non-sintered permeable bricks have been produced at large scale and applied successfully as pavement materials in Songtao, China. Therefore, the use of EMR to produce non-sintered permeable bricks possesses important environmental and economic significance because the process not only utilizes large quantities of EMR and saves EMR disposal cost, but also saves a lot of natural resources and improves the urban environment.
The utilization of electrolytic manganese residue (EMR) in synergy with red mud (RM) and other solid wastes as road base materials (RBM) was investigated in this research. The chemical composition, ...mechanical properties, the hydration behavior, pore structure and environmental friendliness performance of the RBM with different Ca/Si ratios were investigated. The hydration characteristics were analyzed by XRD, FTIR, TG, 29Si MAS-NMR and SEM-EDX technique; the pore structure was investigated by MIP, and environmental properties were texted by ICP. The results showed that the optimal proportion of Ca/Si is within the range of 0.91–1.17. After curing for 7 d, the unconfined compressive strength (UCS) of RBM can reach the highest strength requirement (class I) of 5–7 MPa for road base in Chinese standards. The best mechanical properties and polymerized structure were obtained for a Ca/Si ratio = 0.95 and the main hydration products are C-A-S-H gel, ettringite (AFt) and CaAl2Si2O8·4H2O, which promote the development of strength. The leaching test results indicated that the heavy metals can be efficiently solidified, and meet the Chinese groundwater standards GB14848-2017. This study provides a direction for the large-scale and effective utilization of EMR.
•The application of road base material utilizing EMR was proposed.•The road base material shows excellent mechanical properties when Ca/Si = 0.95.•The road base material has well polymerized SiO4 structure.•Leaching test shows the road base material is environmentally friendly.•This research is well applied to practical production.
•Synergistic effect of EMR, RM and CS was proposed.•Excellent mechanical and durability performance obtained under synergistic action.•The EMR-RM-CS hydrated paste has well polymerized SiO4 ...structure.•AlIV and AlVI both exist in the synergistic system.•Heavy metals can be well solidified by the road base material.
The present study was designed to prepare the road base material by using electrolytic manganese residue (EMR), red mud (RM) and carbide slag (CS) as main raw materials. The mix was optimized and mechanical properties, durability, strength formation mechanism and environmental behavior were investigated. X-ray diffraction (XRD), Mercury intrusion porosimetry (MIP), 29Si and 27Al magic-angle spinning (MAS) nuclear magnetic resonance (NMR) and electron probe microanalysis method (EPMA) were used for microstructure characterization. The results show that after curing for 7 days, the EMR-RM-CS exhibited the highest unconfined compressive strength (UCS), showed the best durability, the best pore diameter distribution and critical pore size. Hydration characteristics reveal that C-A-S-H gel and AFt are generated in EMR-RM-CS, which is positive to the form of UCS and durability. 29Si analysis demonstrates that the synergy of EMR, RM and CS has the best polymerized structure. Al in the hydrated pastes exists in the form of AlIV and AlVI, and one part of the dominant AlIV is activated and another one is converted to AlVI. The leaching results meet the Chinese groundwater standards which indicate that EMR-RM-CS system can well solidify the heavy metals. The road base material prepared by EMR not only consumes a significant quantity of solid wastes but also provides a new idea for the synergistic utilization of solid wastes.
The present study investigated the possibility of co-immobilization of caesium and strontium containing waste by metakaolin-based (MK) geopolymer. 4% of CsNO3 and 4% of Sr(NO3)2 by weight were used ...as simulants for radioactive Cs and Sr. The effect of Cs and Sr on the geopolymerization kinetics was determined via isothermal calorimetry. Furthermore, the evolution of mechanical properties, microstructure, and mineralogy was analysed. The results showed that Cs exerted no noticeable effect on reaction kinetics while Sr lowered the geopolymerization degree of MK geopolymer due to part of OH− from the activating solution being consumed by Sr2+, thereby reducing the activating capacity of pore solution. In addition, the pore structure analysis showed that the incorporation of Sr coarsened the microstructure of MK geopolymer while no significant change was observed with Cs. The phase analysis showed that no new phase was formed because of Cs or Sr incorporation. The mechanical properties decreased with Cs and Sr addition and a higher strength loss was observed for Sr-bearing geopolymers than that of Cs-bearing matrices. The strength reduction in Cs-bearing matrices is associated with the accompanying nitrate ions while a more pronounced strength reduction in Sr-bearing specimens is due to the synergistic effect of nitrates and Sr2+ on the geopolymerization. Despite that, the compressive strengths for all tested MK recipes met the minimum Belgian waste form acceptance criteria indicating that MK geopolymer preserved sufficient strength even at high Cs and Sr waste loadings. Thermodynamic modelling based on speciation and saturation index revealed that Cs+ was mainly bound through ion exchange, whereas Sr2+ largely precipitated as SrCO3. More importantly, it was observed that the co-immobilization of Cs and Sr by MK geopolymer is largely influenced by Sr behaviour. Based on the findings, it can be concluded that MK geopolymer is an excellent host material for Cs and Sr-based waste.
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