Hydration Products Research Articles

Degradation mechanism and strength prediction of aeolian sand concrete under sulphate dry-wet cycles

In this paper, aeolian sand (AS) with different contents (0 %, 25 %, 50 %, 75 % and 100 %) was used as fine aggregate to prepare aeolian sand concrete (ASC). The effects of AS content and dry-wet cycle (DWC) times on the durability of ASC under sulfate (5 % Na2SO4) erosion conditions were investigated by DWC tests. The mass loss rate, compressive strength loss rate and relative dynamic elastic modulus (RDEM) were used as the macroscopic performance evaluation indexes, while the damage degradation mechanism of ASC was revealed by combining the microscopic technical means such as SEM, XRD, TG-DSC and NMR. The results show that the macroscopic properties of ASC under the action of DWC of sulphate all show the first increase and then decrease, as when the dosage of AS is below 50 %, the "bead effect" and "padding effect" of AS can further improve the internal densification of ASC, thus effectively resisting external sulphate erosion. During sulphate erosion, SO42- firstly reacts with cement hydration product Ca(OH)2 to generate erosion products such as Ettringite (AFt) and fills them within the original defects, with short-term rnhancement of macroscopic properties. As the DWC continue, the excessive erosion products accumulated, resulting in the destruction of pore structure and extension through the phenomenon, the matrix compactness is reduced, and the macroscopic properties degraded. The grey entropy correlation analysis yielded that the grey entropy correlation grade of bound fluid saturation, harmless pore percentage and less harmful pore percentage with compressive strength were all above 0.8, and the GM(1,4) strength prediction model established on the basis of the above pore structure parameters has a high prediction accuracy, and the relative errors between the predicted strength values and the actual strength values are within 10 %, and the research results can provide certain theoretical support for the study of the durability of ASC in sulfate erosion environment.

Effect of nano-Ti-Li-Al hydrotalcite-like on the hydration and hardening properties of sulfoaluminate cement-based materials

The use of sulfoaluminate cement-based materials (SCBMs) in grout reinforcement projects is common, and they also perform well in road repair and other facilities. To obtain high workability and permeability, a large water-to-cement ratio is generally used, which reduces the early mechanical properties of SCBMs. The early mechanical properties of cement-based materials can be improved by adding nanomaterials. The cement hydration product monosulfate (AFm) belongs to the hydrotalcite-like family, which is also called layered double hydroxide (LDHs). At present, there is no literature on the influence of nano-Ti-Li-Al layered double hydroxide materials (TiLiAl-LDHs) on SCBMs. In this study, two types of nano -TiLiAl-LDHs with different Ti/Li/Al molar ratios (Ti1Li3Al4-LDHs and Ti2Li3Al4-LDHs) were synthesized. Nano-Ti1Li3Al4-LDHs promoted the hydration of the slurry and improved the early mechanical properties of SCBMs to a greater extent than nano-Ti2Li3Al4-LDHs. However, the cause of this phenomenon remains unclear. Nano-TiLiAl-LDHs act as nucleation sites for ettringite (AFt) and AFm, both of which are cement hydration products. Among them, Ti1Li3Al4-LDHs preferentially provided nucleation sites for AFt, whereas Ti2Li3Al4-LDHs preferentially provided nucleation sites for AFm. Ti1Li3Al4-LDHs and Ti2Li3Al4-LDHs can release titanium, lithium, and carbonate ions in the SCBMs paste, and Ti1Li3Al4-LDHs release more lithium ions (up to 50 mg/L) while Ti2Li3Al4-LDHs release more titanium ions (up to 100 mg/L). Li+ can consume AlO2− and OH− in the slurry and form amorphous lithium aluminum compounds. Although Li+ inhibits the formation of AFt products, it promotes the hydration of anhydrous calcium sulfoaluminate (ye’elimite). Ti4+ reacts with OH− to form a complex that inhibits the formation of AFt, thus reducing the hydration of SCBMs. CO32− promotes the formation of calcium carbonate and indirectly promotes the dissolution of ye’elimite and gypsum. The nucleation effect and release of titanium, lithium, and carbonate ions acted synergistically to influence the hydration and hardening processes of SCBMs. Compared with Ti2Li3Al4-LDHs, Ti1Li3Al4-LDHs has a greater ability to enhance the hydration and mechanical properties of the slurry owing to its strong nucleation and release of higher concentrations of lithium ions and lower concentrations of titanium ions.

Influence of mixing protocols on flow retention of one-part alkali activated slag systems

Poor workability and rapid flowability loss are among several challenges hindering the wider acceptance of alkali-activated slag (AAS) (i.e. shrinkage, efflorescence). Several attempts were made to solve this issue, focusing more on selected ingredients, proportions, type and dosage of admixtures, and addition sequence. This study shifted the focus to mixing protocol, highlighting its potential and effects on AAS flow retention considering mixing duration, sequence, and relaxation time. Various one-part AAS mixtures activated by 6 %, 8 %, and 10 % sodium metasilicate were tested. Mixing protocols were applied for 10–90 min, mixing with and without relaxation time. Mini-slump, flowability-loss rate, setting time, the heat of hydration, rheological properties, and compressive strength were evaluated. Changes in hydration products were also examined by XRD, FTIR and TGA. Pearson correlation coefficient and ANOVA were applied to identify the dominant factors. Results reveal the dependency of the optimum mixing protocol on the used activator dosage. A long mixing period with r intervals was more effective for high activator dosages due to the continuous breakdown of formed hydration products' links. Modifying the mixing protocol did not alter the amount of formed hydration products, regardless of the activator dosage. These findings pave the way to understanding the role played by the mixing protocol in mineral hydration for wider in-situ implementation of AAS and the flourishing potential of the ready-mix AAS market.

Influence of further hydration on UHPC matrix properties

To investigate the evolution laws governing the macroscopic properties of ultra-high-performance concrete (UHPC) matrices under further hydration effect, a further hydration test was performed by varying the cement fineness and slag powder content. The influence mechanism of further hydration on strength was analyzed. The results revealed that the bound water content for further hydration and expansion strain for UHPC matrix with medium fineness cement achieved the minimum values, and the compressive strength reached the lowest value after 21 d of further hydration. Both the bound water content for further hydration and expansion strain showed a tendency to increase with increasing slag powder content, and the higher the slag powder content, the earlier was the peak strength achieved. The volume expansion of further hydration products caused the matrix to crack, and further hydration was manifested as damage effect, resulting in a decrease in strength.

Time-varying moisture characteristics and C-S-H gel properties of concrete in dry and hot environments

The construction of deeply buried tunnels has intensified concerns regarding shrinkage cracking and the long-term performance deterioration of lining concrete in dry-hot environments. These issues are related to the dynamic interconversion of internal moisture states, the changing moisture behavior over time, and the evolution of calcium silicate hydrate (C-S-H) properties. However, the mechanisms underlying these phenomena are not fully understood. This study investigates the dynamics of moisture content across different states, the source and composition of evaporated water, as well as the mechanism of change in the microscopic properties of C-S-H in concrete subjected to dry-hot conditions (40℃ and 60℃) and standard curing environments through tests on water loss rates, chemically bound water, and low-field nuclear magnetic resonance. The findings reveal that at 40℃ and 60℃, hydration products were generated rapidly before mold removal, leading to significant increases in chemically bound water, interlayer water, and gel water, while capillary water was notably consumed. After mold removal, the rate of chemically bound water increase slowed, while interlayer water, gel water, and capillary water evaporated significantly, with gel water comprising 87.27 % and 83.51 % of the evaporated water at 40℃ and 60℃, respectively. From day 1 to day 28, interlayer water, gel water, and capillary water contents decreased significantly, with reductions of up to 85.98 % at 60℃. In dry-hot environments, moisture primarily exists as chemically bound water and gel water, contrasting with standard curing conditions where capillary water is also present. The study concludes that drying of C-S-H gels leads to both positive effects, such as interlayer space compression and increased indentation modulus, and negative effects, including increased microporosity and reduced matric densification, ultimately contributing to the deterioration of long-term mechanical properties.

Innovative strategies for time-release PCE design and cement paste flowability control

Extending the retention time of cement paste flowability with the addition of admixtures containing slow-release components is standard practice for ensuring the continued building quality of cement-based materials. This study aims to control the release rate of PCE and enhance its time-varying dispersion effect in fresh cement paste by utilizing Time-dependent Release PCEs (TRPCEs) with varying side-chain structures. The structural characterization of the synthesized TRPCEs was investigated using GPC (Gel Permeation Chromatography), FTIR (Fourier Transform Infrared Spectroscopy), and 1H NMR (Proton Nuclear Magnetic Resonance) techniques. Furthermore, experiments were carried out on time-varying flowability with different dosages of TRPCEs to investigate the flowability changes under the time-varying release effect. The influence of TRPCEs on cement hydration was examined using isothermal calorimetry by measuring the early hydration heat of cement paste. The time-dependent adsorption behaviors of TRPCEs were also examined using a TOC (Total Organic Carbon) analyzer. The findings show that TRPCEs have a minor effect on the cement hydration process's rapid reaction period but little effect on its induction and acceleration periods because of variations in the initial dispersion effect. Additionally, the adsorption behaviors of TRPCEs on cement particles vary significantly due to the hydrolysis of slow-release groups. The varying adsorption and consumption of TRPCEs on cement particles and hydration products in different hydration phases are key controlling factors for the time-varying flowability changes in cement paste. Finally, this innovative approach offers a novel perspective for designing and preparing new types of PCEs with a strong capability for time-varying flowability retention.

Characterization of sulfate-driven deterioration through the microstructural and nanomechanical characteristics of the components of cement paste

The hydration reaction products of Portland cement are primarily responsible for all the characteristics of concrete. When sulfate agents attack the reaction products, their chemical and microstructural alterations are highly complex, necessitating fundamental knowledge across various length–time scales. In this study, nanomechanical properties were incorporated into microstructural and chemical analyses at varying sulfate exposure levels to investigate the sulfate-driven deterioration of Portland cement paste. The nanomechanical characteristics were observed using a nanoindentation test following cement paste was exposed to MgSO4. Microstructural and chemical analyses of the impact of sulfate exposure on the hydration products were performed. According to the statistical deconvolution of the nanoindentation data, the elastic modulus of the calcium silicate hydrate (C-S-H) gel progressively declined with increasing exposure period to MgSO4 solution according to the statistical deconvolution of the nanoindentation data. In contrast, the volume percentage of pores gradually increased. The changes in the elastic modulus were linearly related to the Ca/Si molar ratio of the C-S-H gel. New phases and microcracks due to exposure to MgSO4 were observed. The experimental research undertaken in this study suggested that one of the primary reasons for the decrease in the macroscopic characteristics of cement concretes when they encounter MgSO4 is the decalcification of C-S-H gel, which is mechanically, morphologically, and chemically described.

Development of a sustainable stabilized macadam road base using steel slag as supplementary cementitious material

As the main waste product of iron and steel industry, steel slag possesses considerable cementitious activity, making it a promising alternative to cement in Cement Stabilized Macadam (CSM). However, CSM was inevitably exposed to groundwater and rainwater when served as the pavement base course, leading to concerns over poor early strength and potential pollutant leakage, which are the main factors that may hinder the widespread utilization of steel slag in CSM base. To address these issues, this study investigated the feasibility of using steel slag powder to produce CSM. Steel Slag Powder-Cement Stabilized Macadam (SSCSM) samples were prepared and the hydration products, microstructure, mechanical properties, water damage resistance and heavy metal ions leaching behavior were investigated. The results show that the nucleation effect of steel slag powder accelerates the early hydration, but the C-S-H produced by hydration is not sufficient to form a stable hydration product network, so the microstructure of SSCSM is looser than that of CSM. The addition of steel slag powder improved the shrinkage performance of SSCSM, and the mechanical properties and heavy metal ion leaching concentration of SSCSM meet the engineering application requirements when the steel slag powder replacement level does not exceed 30 %. It was also found that the addition of steel slag powder promoted the development of pores in SSCSM samples after dry-wet cycles, resulting in the reduction of water damage resistance. Compared with conventional CSM, the use of SSCSM can not only reduce 4 % of raw material cost and 23.5 % of equivalent CO2 emission, but also mitigate the heavy metal ions leaching risk associated with steel slag, making it an effective and sustainable solution for steel slag recycling.

Non-sintered ceramsite from alkali-activated gasification slag for adsorption through the regulation of physical properties and pore structure

With the development of the coal gasification industry, the comprehensive utilization of coal gasification fine slag (CGFS) has become increasingly important. This study explored the potential of producing non-sintered ceramsite by combining CGFS with blast furnace slag (BFS). The impacts of the alkali activator modulus, dosage, and BFS-CGFS ratio on the ceramsite's cylinder compressive strength, bulk density, apparent density, water adsorption ratio, hydration products, microstructure, and adsorption capacity were investigated. Moreover, the leaching behavior of heavy metals in acidic environments and the production costs were evaluated. The results indicated that the modulus and dosage of the alkali activator, along with the BFS-CGFS ratio, significantly affected the properties of the ceramsite. The cylinder compressive strength, bulk density, and apparent density of the ceramsite increased with the increase in the alkali activator dosage and modulus, but decreased as the BFS-CGFS ratio decreased. The water absorption rate behaved oppositely. With increasing alkali activator modulus and dosage, the ceramsite's adsorption capacity for iodine, CODCr, and methylene blue first increased and then decreased, peaking at a modulus of 1.4 and a dosage of 12%, respectively. A reduced BFS-CGFS ratio increased the adsorption capacity of the ceramsite for iodine and CODCr. Considering both mechanical and adsorption properties, the optimal composition for the ceramsite was found to be an alkali activator modulus of 1.4, a dosage of 12%, and a CGFS content of 70%. With this ratio, the use of ceramsite would not result in secondary environmental pollution. This study not only provided a new approach to enhance the utilization of CGFS but also avoided the use of calcination processes in producing ceramsite, demonstrating its potential in reducing environmental impact.

New elucidating into the microstructural evolution mechanisms and micromechanical properties of C4AF and gypsum synergistic hydration

Increasing the C4AF content significantly enhances the sulfate and impact resistance of Portland cement-based materials. However, the research on the microstructural evolution mechanisms and micromechanical properties of the binary synergistic hydration products of C4AF and gypsum is not yet sufficiently deep. This study employed thermodynamic simulations, phase structure characterization, and nanoindentation techniques to investigate the microstructure evolution of gypsum-assisted C4AF hydration. Results indicated that the final hydration product of C4AF, C3(A,F)H6, formed through the stacking of lamellar OH-AFm phases. The addition of gypsum altered the formation pathway of C3(A,F)H6, causing it to precipitate directly from an amorphous iron-aluminum gel, which resulted in smaller particles with higher crystallinity. Gypsum also filled pores in the hydration products, thereby positively influenced their micromechanical properties.

Chemical shrinkage characteristics and prediction model of desulfurization electrolytic manganese residue-cement composite slurries

To reveal the chemical shrinkage (CS) characteristics of desulphurized electrolytic manganese residue (D-EMR) cement composite slurries, the CS was measured for slurries with different water-cement ratios (0.3 and 0.4) and varying D-EMR content (0 wt%, 5 wt%, 10 %, 15 wt%, 20 wt%, 25 wt%, and 30 wt%) using the expansion method. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and backscattered electron (BSE) image analysis were used to investigate the hydration products and pore porosity at different stages. In addition, the correlation between CS and hydration products was simulated using GEMS thermodynamics. The results indicate that as the water-cement ratio increases, the CS of D-EMR cement composite slurries increases significantly. At a water-cement ratio of 0.4, the CS decreases with increasing D-EMR replacement levels before 1829 h of hydration, but this trend reverses after 1829 h. At 8 days, the CS values for replacement levels of 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, and 30 wt% were 97.2 %, 94.9 %, 87.3 %, 84.4 %, 81.5 %, and 78.6 % of those of the pure cement pastes, respectively. The corresponding limiting chemical shrinkage values were 0.0712 mL/g, 0.0725 mL/g, 0.0742 mL/g, 0.0756 mL/g, 0.0769 mL/g, and 0.0780 mL/g. Finally, the prediction of long-term CS of D-EMR cement composite slurries is well described by both hyperbolic function prediction and thermodynamic simulations. These findings provide valuable theoretical support for the use of D-EMR as a supplementary cementitious material in construction.

Synthesis of a chitosan-based superabsorbent polymer and its influence on cement paste

To address the challenge of adaptability between cement-based materials and conventional superabsorbent polymers (sodium polyacrylate, Na-PA), a chitosan-based superabsorbent polymer (CSP) with high salt and alkaline resistance was synthesized, and the optimal synthesis process was determined by a single-factor method. The macroscopic performance and microstructure of CSP and Na-PA were compared, and their influences on cement paste were studied. The results show that CSP exhibits a gradual swelling process during water absorption, which is independent of the solution environment. The poriferous structure of CSP allows it to form a network composed of gel membranes. The introduction of amide group enhances the resistance of CSP to salt and alkaline conditions. The autogenous shrinkage of cement paste is mitigated by CSP, with a superior effect compared to Na-PA. The longer desorption time of CSP allows it to promote cement hydration for a longer period, reducing the loss of compressive strength. The heat release, chemically bound water and hydration products (portlandite and amorphous substances) of CSP pastes are higher than those of Na-PA pastes. The water desorption from CSP fills some middle capillary pores and mesopores, leading to the pores in the hardened cement paste being more concentrated in smaller sizes.

Mineral effects on methane hydrate formation and distribution in sand sediments

Methane hydrate is a promising energy resource widely occurring in the world, but the formation and distribution of methane hydrate in marine sediments with complex minerals remains unclear. Due to the small pore space and fine-grained size of clay minerals, the contact relationship between methane hydrate and clay mineral surface under excess water has not been characterized fully, which is required to investigate the mineral effect on methane hydrate formation. In this study, cryo-SEM was applied to observe the distribution of methane hydrate synthesized in pure quartz sands and the quartz sands mixed with montmorillonite or illite separately. According to the results of the research, methane hydrate dispersedly forms in the pore space away from and on the surface of quartz under a local excess water condition. In addition, methane hydrate occurs away from montmorillonite in pores with excess water and contacts the edge of montmorillonite under a local excess-gas condition. Moreover, methane hydrate was only observed to form away from illite aggregates in the pore with residual water. Montmorillonite and illite influence the preferable distribution of methane hydrate to occur away from mineral surface in excess water condition. In the sediments composed of different minerals, methane hydrate forms stochastically in the pore space and grows up individually. As a result, the findings of this study significantly expand the understanding of the formation and distribution of methane hydrate in marine sediments and the prediction of physical properties of hydrate-bearing sediments, and provide insights into natural gas hydrate exploration and production.

Recycling single use surgical face mask waste for reinforcing cement-treated/untreated dredged marine sediments: Strength, deformation and micro-mechanisms analysis

To prevent the transmission of airborne infectious diseases (SARS, H1N1, COVID-19, and influenza), the use of disposable surgical face masks has increased dramatically in the past few years. To mitigate the environmental consequences associated with mask waste, implementing circular economy strategies with the reuse of mask waste is a sustainable method. This study explores an innovative way to reuse mask fiber (MF) with dredged sediment waste together as road construction materials. First, the MF was introduced into cement-treated/untreated dredged marine sediment mixtures with different content and lengths. Then, a variety of laboratory tests were carried out to explore the basic physical and chemical characterization of raw materials and the development of mechanical properties of mixtures. In addition, the intrinsic mechanism of MF inclusion on cement-treated sediments was analyzed by scanning electron microscope (SEM) test. The results show that the inclusion of MF significantly improves the unconfined compression strength (UCS) and splitting tensile strength (STS) of both treated and untreated specimens. The highest UCS and STS values are at the condition with an MF content of 0.25%, a length of MF of 2 cm, and a curing time of 28 days. The combined strength increase caused by cement-MF together inclusion is much greater than the strength increase caused by either of them separately. It was also found that the elastic modulus (E50) decreased with the inclusion of MF. Furthermore, the addition of MF changes the brittle behavior of the specimens, which also improves the ductility and residual strength of the specimens. The SEM analysis demonstrates the microstructure of MF and MF-reinforced specimens. The creation of a stable and interconnected microstructure is largely attributed to the bridging impact of MF and the binding effect of hydration products, which significantly improves the mechanical behavior of specimens. The MF-reinforced cement-treated sediment could be an innovative, environmentally friendly, and economical material for road construction.

Numerical simulation of gravel packing in multi-branch horizontal wells in hydrate reservoirs based on CFD-DEM coupling

The current single-wellbore gravel packing completion method for hydrate production is limited by its narrow pressure reduction range, leading to reduced production capacity in later stages. To address this, the "branch horizontal well completion with full-wellbore gravel packing and sand control" method has been proposed to significantly expand the pressure reduction range and enhance natural gas production. However, there is a lack of comprehensive studies on gravel packing in branch horizontal wells, the construction design for gravel packing and sand control in branch horizontal wells lacks a solid theoretical foundation. In this study, we establish a CFD-DEM coupled model to simulate gravel packing in single and multi-branch horizontal wellbores, accurately capturing particle movement. We investigate the effects of injection rate, gravel concentration, branch wellbore length, and branch wellbore angle on gravel packing efficiency. The five distinct stages of gravel packing in branch horizontal wells are elucidated. Results indicate that increasing the fluid injection rate, reducing sand concentration, and decreasing both the length and angle of the branch wellbore can significantly improve the packing efficiency. Notably, the filling ratio in the branch wellbore at an angle of 15° was 11.42% higher than that at 30°; As the length of the branch wellbore increases from 1m to 2m, the filling ratio of the branch wellbore decreases significantly. We recommend utilizing a high injection rate (0.6 m³/min), low gravel concentration (3%) to optimize the filling ratio and compaction in both the main and branch wellbores.

The effect of pre-dehydrated magnesium-silicate-hydrate on the properties of the castables bonded with hydrable magnesium carboxylate

This study investigates the effect of pre-dehydrated magnesium-silicate-hydrate (PMSH) on the properties of HMC-bonded castables (HMCC), aiming to enhance the medium-temperature mechanical performance of HMCC through the structural memory characteristics of PMSH. The results indicate that adding M-S-H-300 (PMSH treated at 300 °C) improves the mid-temperature mechanical properties of HMCC. Specifically, the cold modulus of rupture (CMOR) for the samples 300MSH increases by 605.9% at 500 °C and 582.6% at 800 °C compared to control samples due to the excellent thermal stability of M-S-H-300 and a 38.3% improvement in castable sintering performance. Additionally, M-S-H-300 improves the thermal shock resistance and setting properties of HMCC, extending the castable's setting time by 19%. The conductivity test results indicate that the addition of M-S-H-300 inhibits the ionization of HMC, thereby delaying its hydration process. Castables with M-S-H-300 demonstrate higher CMOR and residual strength ratio before and after thermal shock. Further testing reveals that adding M-S-H-300 increased the castable's elastic modulus by 482.6% and fracture toughness by 35.6% after sintering at 1500 °C, enhancing resistance to microcrack propagation during thermal shock. Furthermore, adding M-S-H-300 reduces the aspect ratio of HMC hydration products, optimizing microstructure and reducing porosity. However, this modification slightly decreases the mechanical properties of the green body.

Effect of nano-Al2O3 on the mechanical and microstructural properties of cement-based grouting material

The mechanical properties and microstructure of cement-based grouting materials are important parameters affecting the quality of geotechnical engineering, which are limited by the properties of added materials. At present, the exploration of nanomaterials has become the development trend of cement-based grouting materials. The results showed that NA can significantly improve the strength of NCBS. The most pronounced effect was observed when the dosage of NA was 1 %; compared with the control group, the strength increased by up to 45.2 %. NA particles accelerate the hydration reaction rate between cement and fly ash, generating a large amount of hydration products to fill the internal voids of NCBS. When the content of NA was 2–4 %, the strength gradually decreased with an increase in the amount of NA addition. The catalytic and microaggregate effect of the NA particles were the primary contributors to the improved NCBS mechanical properties. Aggregated NA particles were the main cause of the decrease in strength. Acicular ettringite, fibrous calcium silicate hydrate, and NA particles are the dominant components that effect the strength and microstructure of NCBSs. By comparing the relationship between NA and the strength of NCBS and the relationship between the curing age and the strength of NCBS, it was found that NA can better reflect the compressive strength of NCBS, and the correlation degree of NA to the strength of NCBS is 76 % higher than that of the curing age.

Enhancement in clinker hydration degrees and later stage-ettringite stability of calcium sulfoaluminate cements by the incorporation of dolomite

The hydration degrees of clinkers and ettringite stability in calcium sulfoaluminate (C A) cements in the presence of externally supplied dolomite were investigated in this study. The mineralogical and microstructural characteristics of C A cements containing different dosages of dolomite were characterized using X-ray diffractometry, Rietveld refinement-based quantification analysis, thermogravimetry analysis, mercury intrusion porosimetry, scanning electron microscopy observation, and energy dispersive spectroscopy point analysis. Furthermore, the binder systems were simulated using thermodynamic modeling to observe the phase changes of hydration products and the underlying hydration kinetics. The incorporation of dolomite accelerated clinker consumption and enhanced the stability of ettringite throughout the testing period, due possibly to the nucleation seeding effect and provision of carbonate ions by dolomite. The modeling outcomes showed the stability of ettringite at later stage by the incorporation of dolomite in the simulated timeframe, yet the active dissolution of dolomite assumed in the modeling procedure overestimated the Mg-bearing hydrates in the samples.

Effect of coupling between sphericalization and maximum coarse particle content on the cement properties

In this paper, spherical cement with different fineness (45 μm sieve residue) and particle size distributions were prepared using a new dry energy-saving vertical grinder (NDEVG), and the properties and mechanism of cement, which was compared with cement made by roller press-ball mill, under the coupling effect of sphericalization and maximum coarse particle content were investigated. The results indicated that NDEVG can optimize the particle size distribution and improve the roundness to above 0.731. Which was beneficial for improving the packing density and reducing the water requirement of normal consistency of cement. In addition, the coupling effect of sphericalization and maximum coarse particle content created convenience for the overlap of hydration products, resulting in an increase of 7.22MPa at the 28d strength and an effective reduction in drying shrinkage and hydration heat release rate. This work provides technical guidance for the high-quality processing of cement and other powder materials.

Enhancing Sustainable Subgrade Engineering Using Soil Tuff for Modifying Iron Tailings Sand: A Comprehensive Engineering Performance and Sustainability Analysis

Soil tuff, an industrial solid waste, can serve as a sustainable alternative to cement for modifying iron tailings sand (ITS). To substantiate this claim, the physical properties, durability and microstructure of soil tuff and cement-modified ITSs were analyzed at different modifier dosages, compaction degrees and maintenance ages, with a comprehensive comparison in the perspective of sustainable built environments. The results indicate that the physical properties of soil tuff-modified ITS (STM-ITS) were significantly enhanced in subgrade engineering applications compared with cement-modified ITS (CM-ITS). In addition, compared with CM-ITS, the hydration products of STM-ITS possessed a smaller amount of Ca(OH)2 and were cemented with surrounding binding products, which resulted in fewer cracks. STM-ITS featured a more stable C–S–H gel than CM-ITS due to a lower Ca/Si ratio, contributing to its higher corrosion resistance. Notably, a sustainability analysis demonstrated that incorporating STM-ITS has physical properties comparable to those of CM-ITS and can be obtained at a significantly lower cost, CO2 emission, and energy consumption. Therefore, this study highlights the potential of soil tuff as a promising eco-friendly option for subgrade engineering, promoting waste usage, improving built environments, and contributing to carbon-neutrality goals. These findings have significant implications for the construction industry and the pursuit of sustainable development.