Hydration Mechanism Research Articles

Alkaline-washed phosphogypsum-based cemented paste backfill prepared using steel slag and blast furnace slag: mechanical properties, fluoride immobilization, and hydration mechanism

Phosphogypsum (PG)-based cemented paste backfill (PCPB) is an effective way to deal with the problem of PG storage, but the low strength, high cost, and serious fluoride pollution of PCPB limit the popularization of this technology. Alkaline washing has been proven to be an effective means to decrease fluoride from PG. Steel slag (SS) and ground granulated blast furnace slag (GGBFS) are common materials possessing pozzolanic activity. SS and GGBFS can be employed as cement substitutes under alkaline conditions. This paper proposes the combined heuristic effect of NaOH pretreatment, SS, and GGBFS to improve the strength of alkaline-washed PCPB (APCPB) and the ability of fluoride immobilization. The study results show that alkali washing stimulates the secondary hydration activity of solid waste materials and promotes the formation of hydration products such as AFt and C-S-H so that the UCS value of APCPB increases greatly in the later stages of hydration increases by 309.8% (7.06MPa), and the leaching concentration of fluoride decreases by 21.5% (0.85mg/L). Through microscopic characterization experiments on the APCPB, it was discovered that in the alkaline hydration system, the transformation of C-S-H and AFt into C-A-S-H, F-C-S-H, and F-AFm, coupled with the physical encapsulation of hydration products, are the main factors immobilizing fluoride. This work provides a much-needed supplement to the in-situ cement-free repair technology of PG in mines to develop more lower-carbon and environmentally friendly mixture formulations.

Performance and Hydration Mechanism of Fly Ash Coal-Based Solid Waste Backfill Material Affected by Multiple Factors

Masses of coal-based solid waste like fly ash are emitted during coal combustion, with low utilization rate. Preparing fly ash into backfill material can not only improve waste utilization efficiency, but also repair the cracks in mining areas. In this research, the performance and hydration mechanism of fly ash coal-based solid waste backfill material were investigated through slurry performance experiment, mechanical strength test and microstructure analysis. Besides, the grouting effect of the backfill material was verified by grouting experiment. The research demonstrated that the increase of fly ash to cement ratio (from 0.5 to 1.5) improved the fluidity, viscosity and bleeding rate of the slurry, but prolonged the setting time. The adjustability of backfill material was good, and the compressive strength of specimen reached its highest value of 27.1 Mpa through changing multiple factors. The grouting effect of fine-grained macadam was better than that of coarse-grained macadam. The compressive strength and Young's modulus of the backfill material specimens containing 0.5-1cm macadam were 12.2% and 17.4% higher, respectively, than those with 1-2cm macadam. The primary hydration product of backfill material was gel, which structural elements were Si, Al and Ca. As the curing age increased, the distribution of the three elements became denser, and more gel was formed, corresponding to the changes in the compressive strength of the backfill material. The research offers material source and selection basis for backfilling cracks in mining areas and enhances utilization efficiency of coal-based solid waste.

Activation of ultra-fine steel slag and ground granulated blast furnace slag in alkaline waste solutions via phosphogypsum and calcium carbide slag

This study expands the ways of utilizing multiple solid wastes. The pH value of SRL (soda residue liquid) closely matches that of the cement pore solution, making it a viable substitute for tap water in mixing. Purified PG (phosphogypsum) can serve as an alternative to traditional sulfate activators. CS (calcium carbide slag), currently serves as a widely utilized alkaline activator. PG and CS synergistically activate GGBFS (ground granulated blast furnace slag) in the presence of SS (steel slag) within the SRL environment. A synergistic effect is observed between SS and GGBFS. The test results demonstrate that the composite system achieves a 28-day strength of up to 60 MPa. The effect of SS content on the hydration kinetics, setting time, compressive strength was investigated. To elucidate the role of SS and PG in the reaction, the hydration products were characterized with TGA, XRD and SEM-EDS. The results suggest that the Cl- in SRL undergoes effective immobilization within the system, thereby filling the gel pores as Friedel’s salt (Fs) and facilitating the formation of a dense structure. Q-XRD coupled with TGA was utilized to analyze the changes in crystalline and non-crystalline phases within the system, revealing the hydration mechanism of steel slag activated by physical, chemical, and mineral factors in an alkaline waste solution environment.

Propped fracture conductivity in shale oil reservoirs: Prediction model and influencing factors

Hydraulic fracturing is the main measure for stimulation of shale oil reservoirs, but the high content of clay minerals, well-developed bedding, and low mechanical strength of shale rock often result in a strong stress sensitivity of propped fractures associated with shale hydration expansion and proppant embedment in fracture wall. Especially under conditions of low sand laying concentration, the fracture conductivity can be greatly reduced. In this paper, a comprehensive prediction model of propped fracture conductivity in shale oil reservoirs was established, which considers the damage mechanisms of proppant compression, embedment, crushing, and shale hydration and expansion. The sensitivity analysis of factors affecting the fracture conductivity indicates that the proppant particle size, involved damage mechanisms, Kozeny-Carman coefficient, proppant layer number, and proppant density are the main factors to determine the fracture width and permeability and further affect the fracture conductivity. Most of the rest factors are related to the specific fracture damage mechanisms. The influence of shale hydration expansion is larger than that of proppant particle compression which is further larger than that of proppant crushing. In a real hydraulic fracture, the fracture width decreases from fracture heel to toe, caused by the non-uniform laying concentration of proppant. For the fracture near the wellbore usually with a large sand laying concentration, the influences of different factors are ranked as follows: proppant particle size > elastic modulus of proppant > fluid pressure > hydration expansion coefficient > filtration depth. For the front of the fracture with a low sand laying concentration, it is easy to close, which is sensitive to all the above factors. To achieve a high and stable fracture conductivity, the anti-swelling agent should be used to prevent shale hydration expansion. Large-size proppants with high elastic modulus should be selected to prop up the front of the fracture, and the decline of bottom-hole flow pressure should be controlled during the depressurized production process. The obtained results have a certain guiding significance for understanding the factors of shale fracture conductivity and the optimization of fracture parameters.

Study on the effect of thermoactivated conditions on the properties of hardened cement powder

The performance of thermoactivated hardened cement powder (HCP) is the basis for studying the performance of thermoactivated recycled concrete powder (RCP). Previous studies have mostly focused on thermoactivated RCP, while thermoactivated HCP is taken as the research object in this paper. The effects of different thermoactivated conditions on the mass loss rate, density, initial and final hardening time, standard consistency water powder ratio, and compressive strength of the test block made from thermoactivated HCP were studied. Furthermore, the mineral composition, microstructure, chemical elements, hydration heat, and hydration products of thermoactivated HCP made from different thermoactivated conditions were analyzed. The test results indicated that the average initial harden time of the 600, 800, 1000, and 1200 °C of thermoactivated HCP are 15, 1160, 85, and 13 min, respectively. In terms of phase change of HCP at different heating temperatures, when the heating temperature reached 800 °C, the diffraction peaks of C-S-H and CaCO3 disappear, while the diffraction peaks of C3S, β-C2S, and αC2S began to appear. AFt and Hydrotalcite are completely decomposed and C-S-H loses adsorbed water with temperature from 35.9 to 201.7 °C. Ca(OH)2 is completely decomposed with temperature from 413.3 to 457.4 °C. CaCO3 is completely decomposed with temperature from 457.4 to 731.6 °C. In terms of changes in the proportion of chemical elements after hydration of thermoactivated HCP, the values of Ca/Si of hydrated cement is 1.78. The average values of Ca/Si after hydration of 1000 and 1200 °C thermoactivated HCP are 3.32 and 3.33, respectively, while the average values of Ca/Si after hydration of 600 and 800 °C thermoactivated HCP are 2.74 and 2.6. These research conclusions provide a foundation for the application of thermoactivated HCP. HIGHLIGHTS The mass loss rate, density, and compressive strength of hardened cement powder made from different heating conditions were studied. The standard consistency water powder ratio, initial and final hardening time of hardened cement powder made from different thermoactivated conditions were analyzed. The mineral composition, microstructure, chemical elements, hydration heat, and hydration mechanism of hardened cement powder made from different thermoactivated conditions were revealed.

Exploring properties and hydration mechanisms in clinker-free cement formulated from steel industry solid waste using the extreme vertices method

The development of clinker-free cementitious binders (CFCB) using industrial solid waste has attracted widespread attention due to their environmental and cost benefits. This study developed a CFCB using ground blast furnace slag (GBFS), steel slag (SS), and flue gas desulfurization gypsum (FGDG) as raw materials, utilizing an extreme vertex design method. The study systematically assessed the effects of each component on the CFCB's properties, hydration behavior, and microstructure, and based on these findings, further elucidated its hydration mechanism using thermodynamic simulations. Results indicated that FGDG played a critical role in regulating the fluidity of the fresh pastes and the compressive strength of the hardened pastes. GBFS enhanced the development of compressive strength, while the high-activity aluminates in SS enhanced the early-stage compressive strength. Thermodynamic simulations and experimental results confirmed that reactive aluminates and sulfates led to the formation of expansive hydration products AFt and AFm, with volume expansion peaking around 10 d. As the hydration reaction progressed, the number of aluminates participating in the reaction gradually increased, promoting the formation of C-A-S-H, hydrogarnet, and hydrotalcite, as well as the transformation of AFt into AFm. Comprehensive analysis suggested that within the GBFS–SS–FGDG system, the proportion of FGDG should not be less than 10 %, the content of GBFS should be controlled between 50 and 57.5 %, and the content of SS should not exceed 37.5 %. This study revealed the hydration mechanisms within the GBFS–SS–FGDG system, emphasizing the critical roles of each component.

Development and Characterization of Alkali-Activated Lithium Slag-Fly Ash Composite Cement

As the demand for environmental sustainability grows in the global construction industry, traditional cement production faces significant challenges due to high energy consumption and substantial CO2 emissions. Therefore, developing low-carbon, high-performance alternative cementitious materials has become a research focus. This paper proposes a new low-carbon cement (alkali-activated lithium slag-fly ash composite cement, ALFC) as a substitute for traditional cement. First, the alkali activation reactivity of lithium slag (LS) is enhanced through calcination and grinding, revealing the reasons behind its improved reactivity. Then, alkali-activated LS and fly ash were partially used to replace cement to prepare ALFC, and the effects of the water-to-binder ratio (W/B), LS content, and NaOH addition on the flowability and mechanical properties of ALFC were investigated. XRD, SEM/EDS, and TG/DTG analyses were conducted to examine its hydration products and microstructure, revealing the hydration mechanism. The results show that the flowability of ALFC increases with W/B but decreases with a higher LS content. When W/B is 0.325 and the LS content is 25 wt.%, flowability reaches 200 mm, meeting construction requirements. LS calcined at 700 °C for 1 h significantly enhanced ALFC’s 90-day flexural and compressive strengths by 39.73% and 58.47%, respectively. The primary hydration products of ALFC are C-S-H, N-A-S-H, and C-A-S-H gels, with their content increasing as the NaOH concentration rises. The optimal NaOH concentration and LS content for ALFC are 2 mol/L and 25 wt.%, respectively.

Effects of composite alkaline activator on mechanical properties and hydration mechanism of cemented paste backfill with cement kiln dust

To address the low utilization rate and environmental pollution of mine tailings (MT) and cement kiln dust (CKD), a CKD-based cemented paste backfill (CPB) material was prepared using quicklime (CaO) and sulfate (DH-7) as a composite alkaline activator (CAA), with CKD and slag as the cementitious material and MT as the aggregate. The optimal dosage of the new CAA was determined through unconfined compressive strength (UCS) analysis. The reaction products, pore structure, and cation dissolution ability of CKD-based CPB activated by CAA were investigated, analyzing the mechanism of strength enhancement. The results showed that the CAA enhanced the compressive strength of CKD-based CPB by improving the reactivity of calcium hydroxide. The addition of the CAA led to elevated the dissolution concentration of cations such as Ca and Si within the system, accelerating both the alkali activation reaction rate and the nucleation rate of the calcium aluminosilicate hydrate (C–(A–)S–H) gel. Furthermore, with the increase in CAA content, the pore structure of CKD-based CPB became more complex. Therefore, this study may provide novel insights into the preparation of cost-effective CPB materials with a high CKD content.

Recycling gold mine tailings into eco-friendly backfill material for a coal mine goaf: Performance insights, hydration mechanism, and engineering applications

Recycling gold mine overflow tailings for coal mine filling is crucial for sustainable mining. In this work, an eco-friendly, performance-controllable overflow tailings-fly ash-based backfill material is developed for coal mine filling. The effects of three critical factors, namely, the slurry concentration (SC), cement-sand ratio (C:S), and tailings-fly ash ratio (T:F), on the workability and uniaxial compressive strength (UCS) properties of the novel backfill material are thoroughly investigated, and an optimization of the corresponding formulation is conducted. The optimal formula for the backfill is determined to be a CS of 60 %, a C:S of 0.10, and a T:F of 6:6. The hydration mechanism of the chosen typical mixtures is analyzed via X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy, and the results show that a needle-like Aft gel, identified as the major gelatinous product, is intricately intertwined to create an intricate network structure. As the T:F increases, the content of calcium and silicon oxide initially decreases but then increases, and the optimal mixture reaches a minimum value of 63.66 %. The optimum specimen exhibits a peak wavenumber at 1109.46 cm−1 involving a Si-O stretching vibration bond. A comprehensive filling program at the Liangjia Coal Mine is successfully implemented. Approximately 0.27 tons of overflow tailings are utilized for every ton of backfills. The underground core-pulling backfill achieves a peak uniaxial compressive strength (UCS) of 7.56 MPa after 28 d, surpassing design requirements and showing promise for coal mine filling applications. This study is expected to achieve the transformation of a coal mine goaf into a gold mine tailings pond.

Assessment of waste eggshell powder as a limestone alternative in portland cement

The decarbonization of the concrete industry is an ongoing pursuit. One solution towards this goal is the use of limestone powder in portland cement. Waste eggshell has tremendous potential as an alternative calcite filler in cement due to its similarities with limestone. In this research, the feasibility of adding 15% and 35% ground eggshell in portland cement to make cement mortars was investigated. The hydration mechanism of eggshell and limestone blended cements was compared through the heat of hydration, phase assemblage, electrical resistivity, compressive strength, and shrinkage measurements. The experimental results showed that cement mortars with ground eggshell attained similar compressive strength as that with limestone. However, eggshell mixtures demand more mixing water to compensate the hydrophobicity of the eggshell membrane. The high calcite content in both eggshell and limestone accelerates the hydration of cement at 15% replacement, but ground eggshell retards cement hydration at 35% replacement due to the dominant influence of the membrane. Overall, eggshell waste is a feasible sustainable alternative to limestone powder at up to 15% portland cement replacement levels. Lifecycle assessment and cost analysis showed that adding 15% ground eggshell in cement concrete further reduces its embodied carbon and energy and cost compared to cement concrete containing limestone powder.

Study on the hydration characteristics and mechanical properties of recycled powder-slag powder-cement system

This study systematically investigated the influence of different blending ratios of recycled powder and slag powder on hydration heat evolution and mechanical properties. Various modern microscopic testing techniques were employed to quantitatively characterize hydration products and microstructures, revealing their hydration mechanisms. The results indicate that both recycled powder and slag powder can accelerate the early hydration rate. When recycled powder and slag powder are co-blended, their early hydration rate and cumulative heat release surpass those of specimens with single additions of recycled powder. Moreover, the mechanical properties in the later stage are superior to those of specimens with single additions of recycled powder. At 60d, the PRS70–1–2 in the multi doped recycled powder and slag powder system even exceeds that of the uni doped SL system, but is much higher than that of the uni doped RP system，the compressive strength of the multi doped recycled powder and slag powder system increased by 25.5 %, 37.1 % and 36.9 %, respectively, compared with that of the uni doped RP system. Specimens with single additions of recycled powder and slag powder have a relatively high proportion of harmful and very harmful pores. At 28d, the porosity of the multi doped recycled powder and slag powder system decreased by 19.2 %, 24.2 % and 14.8 %, respectively, compared with that of the uni doped RP system. However, when recycled powder and slag powder are co-blended, the proportion of harmful and very harmful pores decreases, while the proportion of less harmful and harmless pores increases. This leads to an overall reduction in porosity and an improvement in mechanical properties.

The exploration of effect for nano-Al2O3 on solid waste based superfine tailings cemented paste backfill: Pyrolysis property, hydration mechanism and environmental risk

Resource utilization of superfine tailings has become a key research direction in filling mining. This study analyzes the mechanical properties, pyrolysis mechanism and hydration mechanism of nano-Al2O3(NA)-doped solid waste based superfine tailings cemented paste backfill (SWSCPB) by multiple microscopic characterization methods and pyrolysis kinetic theory. The results show that the main temperature interval for the pyrolysis of SWSCPB to happen is 280–900 °C, which is divided into two stages of dehydroxylation and decarbonization. The apparent activation energy(E) and pre-index factor(A) of pyrolysis are higher than those of NA0 and NA2 at 1 % NA dosage, indicating that NA increases the energy barrier of pyrolysis, the percentage of activated molecules, and the collision probability of hydration products in SWSCPB, but decreases due to agglomeration at exceeds 1 % NA dosage. NA can enhance macroscopic strength of SWSCPB, with the highest strength at 1 % NA dosage. Compared with NA0 and NA2, more hydration products such as AFt and C-(A)-S-H are present in NA1, and the distribution of Q2 and Q4 in C-(A)-S-H is more pronounced, with a higher degree of polymerization, a stronger tendency for the conversion of non-bridging to bridging oxygen bonds, and fewer pores in the microstructure of SWSCPB. The NA dosage can provide more nuclei for the formation of AFt, C-(A)-S-H in SWSCPB, and can also promote the replacement of Si by Al for the conversion of C-S-H to C-(A)-S-H with higher polymerization. In addition, the leaching risk and mechanism of heavy metal ions from SWSCPB are preliminarily explored in combination with leaching experiments. The results provide new insights and guidance for the application of SWSCPB in filling mining under cleaner production targets.

Hydration mechanism and potential as solid-state electrolytes in sodium chloride-magnesium phosphate composite

This study explores the feasibility of NaCl based magnesium phosphate cement (NaCl-MPC) composites as a solid electrolyte for energy storage applications by analyzing the physical, mechanical, hydration and electrochemical properties of composites. The results indicated that the incorporation of NaCl greatly improved the mechanical properties and ionic conductivity of composites, demonstrating enhanced electrochemical stability, making it a promising energy storage material. NaCl induced complex physical and chemical interactions within the MPC system by facilitating the filling of micropores and microcracks, providing the additional nucleation sites and converting intermediate products into struvite. NaCl also reacted chemically in the MPC system to produce small amounts of hazenite crystals. These effects ultimately led to the densification of the microstructure of MPC and significantly improved its mechanical properties. Generally, the improvement of ionic conductivity of solid electrolytes compromises their mechanical properties. However, the NaCl-MPC composites in this study showed significant improvement both in ionic conductivity and mechanical properties, highlighting their potential for advanced energy storage applications.

Study on the mechanism of early strength strengthening and hydration of LC3 raised by shell powder

Limestone calcined clay cement (LC3) was considered the most promising low-carbon alternative to OPC (Ordinary Portland Cement). Due to the relatively low proportion of cement clinker and the delayed reaction of calcined clay led to low early compressive strength. In this study, shell powder was used as a carbonate filler to replace limestone with the aim of enhancing the early strength of LC3. Because the solubility of shell powder in pore solution was lower than that of limestone. The generation of CO3-AFm was delayed and the dissolution of Mg2+ from shell powder promoted the formation of hydrotalcite. The differences in carbonate types had diverse effects on the hydration mechanism with cement clinker and MK, inducing the transformation of C-(A)-S-H gels in the system from decalcification to a higher Si/Ca ratio.

Jet cavitation-enhanced hydration method for the preparation of magnesium hydroxide

During the preparation of magnesium hydroxide via the hydration method, in-situ growth and agglomeration often inhibit the reaction. This study used active magnesium oxide as the raw material and employed jet cavitation technology to enhance the hydration process. Based on the growth process of magnesium hydroxide, the mechanism of jet-enhanced hydration was analyzed. The effects of reaction temperature (T), reaction time (t), solid-liquid ratio (s), and cavitation number (σ) on the hydration rate were investigated. An L25(54) orthogonal experiment explored the significance of each factor's impact on the hydration rate. The hydration products were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and a specific surface area analyzer. Results indicate that the factors affecting the hydration rate, in order of significance, are cavitation number > reaction temperature > solid-liquid ratio > reaction time. The optimal process parameters were determined to be a reaction temperature of 70 °C, reaction time of 80 min, solid-liquid ratio of 1:12, and cavitation number of 0.42. Under these conditions, the hydration rate reached 94.87 %, producing well-dispersed lamellar magnesium hydroxide with a narrow particle size distribution (median particle size D50 = 4.511 μm) and a BET specific surface area of 11.345 m²/g.

Recycling of phosphogypsum for low-carbon cement: Clinker production, mechanical properties and hydration mechanism

The emission of solid waste phosphogypsum (PG) imposes significant environmental stress. Utilizing PG to produce sulfoaluminate cement (SAC) offers a dual benefit of consuming PG and enhancing resource recycling. This study focuses on preparing a low-carbon phosphogypsum-based SAC (PGSAC) using PG. PGSAC clinker was successfully synthesized with 19.7 % calcined PG as a raw material at a calcination temperature of 1200 °C. Notably, the production temperature of PGSAC clinker was 70 °C lower than that of conventional SAC clinker, resulting in a 10 % reduction in fuel consumption and a 15.5 % reduction in electricity usage. Incorporating PG into the clinker to prepare PGSAC significantly enhanced the 3-day compressive strength of PGSAC mortar by 24.8 % and 18.3 % at 10 % and 20 % PG levels, respectively. Additionally, the setting time for PGSAC was notably extended by 30.77 % and 80.77 % at the respective PG contents. Compared to dihydrate gypsum specimens, the setting time of PGSAC paste with added PG was prolonged by 7.7 % (10 % PG) and 30.77 % (20 % PG). The introduction of PG resulted in a decrease in the pH of PGSAC, an advancement in dissolution exothermic reactions, and an increase in AFt formation during hydration. PG influenced cement hydration by accelerating the hydrolysis of clinker minerals, promoting AFt generation, and forming insoluble phosphate. In summary, PG can be a retarder for PGSAC and enhance cementitious strength, with an optimal dosage range of 10%–20 %. For each ton of R·SAC 42.5 grade PGSAC, 208 kg of calcined PG and 200 kg of PG were utilized, leading to a 19 % reduction in CO2 emissions. The findings of this research advocate for the application of PG in SAC, thereby promoting increased utilization of PG and contributing to environmental sustainability.

Towards a sustainable thermodynamic optimization solution for preparing unburned low-carbon bricks from low-activity tailings

Basalt tailings, as an important type of solid waste in the mining industry and quarries, are mainly stacked in the open air or buried, causing huge potential harm to the environment and society. In this work, we propose a sustainable and promising utilization method for such low alkali activated tailings. A thermodynamic optimization solution and a design model for unburned low-carbon bricks composed entirely of solid waste were established, and the macro-microscopic mechanisms of hydrate formation and durability were comprehensively analyzed. Firstly, the thermodynamic reaction kinetics of the full chemical composition of basalt tailings modulated by fly ash were used to investigate the effects of different reaction material ratios on hydration products. Then, a new optimization design method of chemical thermodynamics model of alkali excitation was proposed. Further, the hydration mechanism of geopolymer was qualitatively and quantitatively analyzed via test of mechanics, XRD, FTIR, SEM and AFM. The calculation results were very consistent with experimental research, and the basalt-based fly ash-modulated geopolymer brick through optimization met the requirements of durability, especially from the viewpoint of excellent high-temperature resistance. Finally, the life cycle assessment (LCA) method was adopted to analyze the carbon emission reduction potential of current eco-friendly bricks. The carbon emissions were approximately 15.6 % of that of sintered shale hollow bricks and 19.4 % of that of aerated concrete building blocks. Thermodynamic optimization design of alkali activated low-activity tailings unburned bricks technology is one-stone-for-two-birds strategy, which can effectively optimize the process of making bricks from tailings.

Performance and hydration mechanism of MSWI FA-barium slag-based all-solid waste binder

Barium slag (BS) and municipal solid waste incineration fly ash (MSWI FA) are hazardous wastes produced in large quantities, with heavy metals such as Ba, Pb, and Cr significantly exceeding acceptable levels, posing a threat to the ecological environment and living organisms. The development of technologies for the harmless disposal and resource utilization of hazardous waste is a current research focus. This study used BS, blast furnace slag (BFS), MSWI FA, and flue gas desulphurized (FGD) gypsum to replace cement in the preparation of solid waste-based binder. The results indicated that the optimal mass ratio was BS: BFS: FGD gypsum: MSWI FA = 14 %:56 %:20 %:10 %. The compressive strengths of the binder at 3, 7,and 28 days were 23.7 MPa, 30.76 MPa, and 38.65 MPa, respectively. Chinese standard HJ557–2010 was adopted to carry out heavy metal leaching experiment on raw materials, the immobilization efficiency of heavy metals Ba, Pb, and Cr were 99 %, 99 %, and 96 %, respectively, and the leachate toxicity was below the Class III groundwater limit. XRD, FT-IR, TG-DSC, XPS, SEM-EDS and other experimental methods were used to study the effect of BS content on the properties of cementable materials. An appropriate amount of BS hydrolyzes during hydration, releasing Ba²⁺ and OH⁻ ions, which activated the BFS, producing AFt and C–(A)–S–H gel. These products interweaved with material particles to fill the pore spaces, enhancing the binder’s mechanical strength and heavy metal immobilization capability. However, when excessive BS was added, the hydration products favored the formation of FS, leading to a decline in binder performance.

Study and optimization of the selectivity of an odorant binding protein-based bioelectronic nose

Over the past two decades, the use of odorant-binding proteins (OBPs) for the development of biosensors and bioelectronic noses (bioeNs) aimed at detecting and analyzing volatile organic compounds (VOCs) has been the subject of considerable research. However, there is a lack of fundamental studies for better understanding the interaction between OBPs and VOCs in gas phase. In this work, we investigated the effect of two key factors, namely relative humidity (RH) level and immobilization technique, on the selectivity of two OBP-based biosensors in gas phase. Concerning the effect of RH, the results showed that our active OBP (wild-type rat OBP3) lost its selectivity at 0% RH but retained good selectivity at 30% and 50% RH. To better understand the effect of this parameter, the hydration mechanism of the OBP was studied both experimentally and through molecular dynamics simulations. The effect of a cysteine residue, genetically added to the N-terminus of OBPs to control their orientation after immobilization on the chip, was evaluated. A significant reduction in selectivity was observed in the absence of cysteine. As expected, the introduction of this amino acid enabled to control the orientation of OBPs, making their binding pocket more accessible to VOCs and favoring specific interactions. Furthermore, we demonstrated that combining OBP-based biosensors with different properties can improve the discrimination capability of our bioeN. Finally, the ability of our system to detect essential oil vapors was tested, providing preliminary evidence that our bioeN is capable of detecting VOCs in complex media.

Mechanical properties and hydration mechanism of nano-silica modified alkali-activated thermally activated recycled cement

The recycling and reuse of waste concrete are crucial for reducing environmental pollution, minimizing resource waste, and lowering carbon emissions. However, current efforts to improve the performance of recycled cement (RC) using the synergistic effects of alkali activation and thermal activation have been suboptimal. Therefore, this study explores the influence of nano-silica (NS) incorporation on the mechanical properties and hydration mechanism of alkali-activated and thermally activated RC. The research focuses on cement mortar with a thermal activation temperature of 750 °C, an RC replacement rate of 30 %, and an alkali content of 6 %. Various analytical techniques, including thermogravimetric analysis (TG-DTG), X-ray diffraction (XRD), and scanning electron microscopy (SEM), were used to evaluate the impact of different NS dosages (1 %, 2 %, 3 %, and 5 %) on the mechanical properties and hydration characteristics of nano-modified alkali-activated and thermally activated RC mortar. The study reveals the mechanism by which NS enhances the microstructure of alkali-activated and thermally activated RC. The experimental results show that as the NS content increases, the compressive and flexural strengths of RC initially increase and then decrease. The optimal strength was achieved with a 2 % NS content, with a 31.5 % increase in compressive strength compared to RC without NS. At this dosage, RC exhibited a higher hydration rate during the acceleration period of hydration. Additionally, the initial hydration heat release rate of RC increased with rising NS content. While NS incorporation did not alter the phase composition of RC, it activated the pozzolanic effect of RC, causing free active substances such as CaO and gypsum in the components to dissolve and react to form Aft at the start of the hydration reaction. The unsaturated bonds (≡Si-O- and ≡ Si-) on the surface of NS absorbed Ca2⁺ and OH⁻ from the RC, promoting the hydration of C2S and C3S. However, excessive NS content (greater than 3 %) led to a decline in RC strength and the formation of more cracks. This is primarily due to the excess NS particles not contributing to an increase in effective nucleation sites, causing agglomeration, an increase in large pores, and a reduction in transition and gel pores, which negatively affected the microstructure and thus reduced the mechanical properties of the RC. Our findings enhance the understanding of the role of nanomaterials in alkali-activated RC and provide valuable insights for further research into high-performance recycled cement materials.