Hydration Activity Research Articles

Effect of direct electric curing on the mechanical properties, hydration process, and environmental benefits of cement-steel slag composite

Steel slag (SS) is a solid waste produced from the steelmaking process. The weak early hydration activity of steel slag limits its application in cementitious materials. This study attempts to improve the early-age performance of cement-SS composite by direct electric curing (DEC) to broaden the application of SS in cementitious materials. Specifically, The study involves continuous monitoring of performance changes of the specimens over time, with a particular focus on early-age characteristics. The change in strength and capillary water absorption of the hardened paste are evaluated. The pore size distribution and content are investigated by BET, and the effects of DEC on the hydration process of cement-SS composite are determined by XRD, TG, and BSE. The results demonstrate that DEC effectively improves the early-age strength of specimens. The 1d strength of the specimens increased by more than 50% at 50% steel slag dosage. Additionally, DEC effectively reduces the pore size. DEC does not change the type of hydration products of the paste but effectively accelerates the hydration process of the cement-SS composite. This accelerated reaction leads to a notable increase in calcium hydroxide and bound water content at an early age, consequently improving the degree of hydration reaction in steel slag. SEM-BSE analysis revealed changes in the atomic composition of the C-S-H gel near the SS, accompanied by blurred boundaries in the morphology of SS particles. Moreover, this study analyzes the economic and environmental benefits of using cement-steel slag composite with DEC. Considering the strength factor, the cost required to obtain a unit strength by DEC is only 55.88%-71.28% of that required with standard curing method. Simultaneously, carbon emission is reduced by 28.79%-44.16%. Thus, DEC is a sustainable and practical method for promoting the utilization of steel slag in cementitious materials, offering both economic and environmental benefits.

The role of P2O5 on the stability of β-C2S in AOD slag based on the improvement of hydration activity

The original AOD slag in the cold state contained more than 50 wt% low-hydration activity γ-C2S, which significantly affects the hydration activity. Therefore, the effect of the typical crystal stabilizer P2O5 on the formation of a new phase and the enhancement in the mass fraction of high hydration activity β-C2S in AOD slag were studied, and the internal factors that controlled the doping preference and influenced the hydration activity of the crystal stabilizer P2O5 were revealed. When the addition of P2O5 was 0.6 wt%, the mass fraction of β-C2S in AOD slag was increased by 50.8 wt%. The P5+ and its oxide P2O5 entered the lattice of C2S in solid solution, causing lattice distortion. After P doping, the charge energies of the Ca, Si and O atoms shifted toward the low energy direction by approximately 5 eV, which increased the stability of the electronic structure. In addition, P doping changed the delocalization of the CBM in the pure phase, partially located the LDOS of the VBM and CBM, and increased the numbers of nucleophilic and electrophilic attack sites, thus improving the hydration activity of β-C2S.

Effect of Hydroxypropyl methyl cellulose (HPMC) on rheology and printability of the first printed layer of cement activated slag-based 3D printing concrete

Nowadays, Ground Granulated Blast Furnace Slag (GGBFS) is generally used to replace cement for reducing carbon emissions, but due to its low hydration activity and unstable working performance in the early stage, it is difficult to apply in 3D printed concrete (3DPC) as the main binder. In this study, a combination of ordinary Portland cement and calcium sulfoaluminate cement was used to activate GGBFS. In the presence of 0.2 wt% polycarboxylate superplasticizer (PCE), in order to achieve high-precision printing, hydroxypropyl methyl cellulose (HPMC) was used. The rheological properties of mortar were evaluated by the slugs-test and a rotational rheometer. The results show that the yield stress and thixotropy of slag cement-based 3D printing concrete are significantly increased, with addition of HPMC. The slugs-test shows its advantages in measuring rheological properties, such as superior repeatability of rheological data and a better association with 3D printing performance. Pumpability, extrudability, and buildability of the first printed layer of slag cement-based 3DPC were evaluated using pumping pressure, horizontal printing, and vertical printing. The results show that, with a 0.15 wt% HPMC, the 3D printing properties of the first layer are greatly improved, a stable and high-precision slag cement-based 3DPC can be developed, and the relationship between rheological properties and 3D printing performance can be established.

Effect of Carbonation Treatment on the Strength and CO2 Uptake Rate of Composite Cementitious Material with a High Steel Slag Powder Content.

As a major steel producer, China is now eager to develop feasible solutions to recycle and reuse steel slag. However, due to the relatively poor hydration activity of steel slag, the quantity of steel slag used as a supplemental binder material is limited. In order to improve the cementitious properties of steel slag, the strength and carbonation degree of the high-content steel slag powder-cement-metakaolin composite cementitious material system under CO2 curing conditions were investigated. The compressive strengths of the mortar specimens were tested and compared. The carbonation areas were identified and evaluated. A microscopic analysis was conducted using X-ray diffraction (XRD), thermogravimetry analysis (TG), and scanning electron microscopy (SEM) to reveal the chemical mechanisms. The results showed that CO2 curing significantly increased the early strength as the 3D compressive strength of the specimens increased by 47.2% after CO2 curing. The strength of the specimens increased with increasing amounts of metakaolin in a low water-to-binder ratio mixture. The 3D compressive strength of the specimens prepared with 15% metakaolin at a 0.2 water-to-binder ratio achieved 44.2 MPa after CO2 curing. Increasing the water-to-binder ratio from 0.2 to 0.5 and the metakaolin incorporation from 0% to 15% resulted in a 25.33% and 19.9% increase in the carbonation area, respectively. The calcium carbonate crystals that formed during carbonation filled the pores and reduced the porosity, thereby enhancing the strength of the mortar specimens. The soundness of the specimens after CO2 curing was qualified. The results obtained in the present study provide new insight for the improvement of the hydration reactivity and cementitious properties of steel slag powder.

Effects of 1,2,3-Propanetricarboxylic acid on the hydration and microstructure of fluorogypsum

Aiming at the issues of poor hydration activity, long setting time, and low early strength in industrial by-product fluorogypsum (FG), 1,2,3-propenyltricarboxylic acid (PA) was utilized to enhance its reactivity. The mechanism was investigated using modern analytical techniques such as XRD, 1H low-field NMR, and FTIR spectroscopy. The results indicate that the incorporation of PA can significantly augment the rate of FG hydration and enhance its hydration activity. The optimal concentration of PA was determined to be 0.008%. The FG paste exhibited a reduction in setting time by approximately 500 min compared to the control sample. Furthermore, the flexural and compressive strengths increased by 29.6% (reaching 3.5 MPa) and 40.2% (reaching 40.1 MPa), respectively, after a curing period of 28 d. Through the process of physical adsorption, PA facilitates the transformation from anhydrite (CaSO4-II) to dihydrate gypsum (CaSO4·2H2O). Subsequently, PA promotes the growth of dihydrate gypsum crystals along each crystal axis, resulting in the formation of regular hexagonal prisms. The prismatic crystals of dihydrate gypsum are arranged in a closely packed, layered structure that results in reduced pore and porosity content, and enhanced mechanical strength.

Understanding the improvement of Mg-rich electrical ferronickel slag on magnesium potassium phosphate cement's performance

Electrical ferronickel slag (EFS), a Mg-rich slag from nickel-iron alloy production, is conventionally recycled by blending it with Portland cement as mineral admixtures. However, the low hydration activity of EFS will lead to severe negative effects on cement. To enhance the reuse value of EFS, this study comprehensively investigated the potential of using EFS in magnesium potassium phosphate cement (MKPC), from properties into hydration mechanisms. A variety of characterization techniques, combined with thermodynamic modelling, were applied. The results demonstrate that incorporating EFS effectively increases compressive strength and refines pore structure at all ages. This improvement is mainly attributed to the additional reaction of Mg2SiO4 and amorphous phases from EFS. Mg2SiO4 reacts at low pH and amorphous fractions are involved at higher pH to generate new products magnesium silicate hydrate M-S-H or magnesium aluminosilicate M-A-S-H gel. The findings will provide insight into the role of Mg-rich pyrometallurgical slags in MKPC systems.

Potential Role of GGBS and ACBFS Blast Furnace Slag at 90 Days for Application in Rigid Concrete Pavements.

Incorporating blast furnace slag into the composition of paving concrete can be one of the cost-effective ways to completely eliminate by-products from the pig iron production process (approximately 70% granulated slag and 30% air-cooled slag). The possibility to reintroduce blast furnace slag back into the life cycle will provide significant support to current environmental concerns and the clearance of tailings landfills. Especially in recent years, granulated and ground blast furnace slag (GGBS) as a substitute for cement and air-cooled blast furnace slag (ACBFS) aggregates as a substitute for natural aggregates in the composition of concretes have been studied by many researchers. But concrete compositions with large amounts of incorporated blast furnace slag affect the mechanical and durability properties through the interaction between the slag, cement and water depending on the curing times. This study focuses on identifying the optimal proportions of GGBS as a supplementary cementitious material (SCM) and ACBFS aggregates as a substitute to natural sand such that the performance at 90 days of curing the concrete is similar to that of the control concrete. In addition, to minimize the costs associated with grinding GGBS, the hydration activity index (HAI) of the GGBS, the surface morphology, and the mineral components were analyzed via X-ray diffraction, scanning electron microscopy (SEM), energy dispersive spectrometry (EDX), and nuclear magnetic resonance relaxometry (NMR). The flexural strength, the basic mechanical property of road concretes, increased from 28 to 90 days by 20.72% and 20.26% for the slag concrete but by 18.58% for the reference concrete. The composite with 15% GGBS and 25% ACBFS achieved results similar to the reference concrete at 90 days; therefore, they are considered optimal percentages to replace cement and natural sand in ecological pavement concretes. The HAI of the slag powder with a specific surface area equivalent to that of Portland cement fell into strength class 80 at the age of 28 days, but at the age of 90 days, the strength class was 100. The results of this research present three important benefits: the first is the protection of the environment through the recycling of two steel industry wastes that complies with European circular economy regulations, and the second is linked to the consequent savings in the disposal costs associated with wastefully occupied warehouses and the savings in slag grinding.

Investigations for a Yarrowia-Based Biorefinery: In Vitro Proof-of-Concept for Manufacturing Sweetener, Cosmetic Ingredient, and Bioemulsifier

Yarrowia lipolytica is a widely used microorganism in biotechnology since it is capable of producing a wide range of products (lipase, citric acid, polyols). A less-studied related strain is Y. divulgata, which is also capable of erythritol production in even higher concentration than most Y. lipolytica wild strains from glycerol as renewable feedstock. Thus, the aim of this work was to investigate Y. divulgata’s complex utilisation based on erythritol fermentation from glycerol to establish a Yarrowia-based biorefinery in which both the fermentation broth and separated cells are converted into high added-value products (erythritol, bioemulsifier, cosmetic ingredient, i.e., skin moisturizer). An important parameter of erythritol fermentation is an adequate oxygen level, so both the constant oxygen level and oxygen absorption rate were investigated regarding the three target products. DO (dissolved oxygen) = 10, 20, 30, 40% was examined in the bioreactor, and a KLa range of 18–655 h−1 was investigated in both the bioreactor and in different types of shaking flasks, applying two different glycerol levels (100–150 g/L). The results showed that the Yarrowia divulagata NCAIM 1485 strain could produce one of the highest amounts of erythritol (44.14 ± 1 g/L) among wild-type yeasts from 150 g/L glycerol beside a KLa value of 655 h−1. Cell-lysates skin hydrating activity was the highest (12%) when DO = 20% (KLa 26.4 h−1) was applied. In all cases, the collected samples had an emulsification index above 69% which did not decrease below 54% after 24 h, showing good stability. Since Y. divulgata fermentations resulted in three high added-value products at the same time from a renewable raw material (glycerol), we concluded that it is suitable for complex utilisation in a microbial biorefinery, since the fermentation broth can be used for the isolation of a sweetener and bioemulsifier; meanwhile, the separated cells can be processed for cosmetic application as a skin moisturizer.

The Effect of Removing Hard-to-Grind Minerals from Steel Slag on Efficient Grinding and Hydration Activity

The Effect of Removing Hard-to-Grind Minerals from Steel Slag on Efficient Grinding and Hydration Activity

Recycling of waste magnesia refractory brick powder in preparing magnesium phosphate cement mortar: Hydration activity, mechanical properties and long-term performance

Waste magnesia refractory bricks (MRBs) that remain from industrial production are landfilled in large quantities or recovered to prepare recycled bricks with low added value. In consideration of the significant level of magnesia in waste bricks, this work proposes to extract and recover magnesia from spent bricks for manufacturing magnesium phosphate cement mortar (MPCM). The essential attributes of recycled magnesia (RM) and its influence on the workability, hydration temperature rise, mechanical properties, phase evolution, long-term performance and microstructure of MPCM were analyzed. The results reveal that RM significantly prolongs the setting time and reduces the overall hydration heat release, which is beneficial to the application in large-scale engineering. The compressive strength of MPCM prepared by RM (MPCMRM) initially grew and then decrease with the increase of magnesia to phosphate ratio (M/P ratio). The optimal performance was observed at M/P = 4, and the compressive strength cured for 3 h and 28 d were 39.1 MPa and 68.5 MPa respectively. While the mechanical properties of MPCMRM were marginally inferior to those of dead-burned magnesia (DM), it was found to satisfy the early and long-term strength requirements of engineering repair materials. In addition, MPCMRM did not generate new mineral phases, and the crystal morphology of hydration products (struvite) was worse than that of mortar prepared by DM. MPCMRM also exhibits excellent water resistance and volume stability due to the crystal characteristics of low-activity RM. It seems that RM can completely replace DM to prepare MPCM and achieve satisfactory performance, which not only reduces the cost of repair materials, but also provides a fresh approach for the recycling of waste MRBs.

Physical-chemical coupling excitation of low activity coal gasification slag solid waste and its application as a backfill cementitious material

To realize the green mining and clean utilization of coal resources, environmental issues such as coal mine subsidence and coal gasification slag (CGS) solid waste storage require urgent resolution. High residual carbon and low activity serve as bottlenecks for CGS to achieve safe, efficient and resourceful consumption. Therefore, in this study, we proposed the concept of graded utilization of CGS and conducted a study on physical–chemical coupling to stimulate the hydration activity of CGS. We prepared a modified coal gasification slag-based cement paste backfill material (MCGS-CPB) to meet the technical requirements of coal mine backfilling. Through various experimental tests and microscopic characterization methods (uniaxial compressive strength, hydration heat and microscopic tests, etc.), we elucidated the modification mechanism of CGS, and the synergistic reaction law of MCGS-CPB was clarified. The following results were obtained. (1) The best excitation approach for CGS hydration activity was salt modification, and the early strength of MCGS-CPB prepared with CGS excited by sodium sulfate (SS) developed rapidly, while the later strengths showed expansion and deterioration. The strength development of MCGS-CPB prepared by CGS activated with calcium chloride (CC) was relatively stable, and the excitation effect was ideal. (2) The salt modification of CGS had a significant effect on the early hydration process of MCGS-CPB. The durations of the initial dissolution, acceleration, deceleration and slow reaction stages were prolonged, and the duration of the induction stage was shortened, while the hydration heat release rate increased. (3) The salt modification of CGS had a significant effect on the microstructure of MCGS-CPB, primarily due to the difference in excitation effect of salt modification on CGS on pozzolanic activity. This study provided theoretical guidance for the safe, efficient and resourceful utilization of CGS.

Repurposing of World-Approved Drugs for Potential Inhibition against Human Carbonic Anhydrase I: A Computational Study.

Human carbonic anhydrases (hCAs) have enzymatic activities for reversible hydration of CO2 and are acknowledged as promising targets for the treatment of various diseases. Using molecular docking and molecular dynamics simulation approaches, we hit three compounds of methyl 4-chloranyl-2-(phenylsulfonyl)-5-sulfamoyl-benzoate (84Z for short), cyclothiazide, and 2,3,5,6-tetrafluoro-4-piperidin-1-ylbenzenesulfonamide (3UG for short) from the existing hCA I inhibitors and word-approved drugs. As a Zn2+-dependent metallo-enzyme, the influence of Zn2+ ion models on the stability of metal-binding sites during MD simulations was addressed as well. MM-PBSA analysis predicted a strong binding affinity of -18, -16, and -14 kcal/mol, respectively, for these compounds, and identified key protein residues for binding. The sulfonamide moiety bound to the Zn2+ ion appeared as an essential component of hCA I inhibitors. Vina software predicted a relatively large (unreasonable) Zn2+-sulfonamide distance, although the relative binding strength was reproduced with good accuracy. The selected compounds displayed potent inhibition against other hCA isoforms of II, XIII, and XIV. This work is valuable for molecular modeling of hCAs and further design of potent inhibitors.

Bioinspired synthesis of micelle-templated ultrathin silica-layered mesoporous nanoparticles with enhanced mass transfer and stability for biocatalysis

Bioinspired enzyme encapsulation technologies have received increasing attention in sustainable development owing to the enzyme protection from external stressors while mimicking the cellular environment and structure. In this study, we developed a diatom-inspired synthesis of ultrathin silica-layered nanoparticles directed by silica-forming R5 peptide- and carbonic anhydrase (CA)-functionalized micelles. Each CA and R5 peptide was covalently conjugated with N-hydroxysuccinimide (NHS)-ester-modified hydrophilic ends of the triblock copolymer F127 (F127–CA and F127–R5). F127–CA/R5 micelles were prepared by controlling the molar ratio of F127–CA and F127–R5. F127–CA/R5 micelle@silica nanoparticles (SiNPs) were synthesized through R5 peptide-catalyzed silicification of the F127–CA/R5 micelle in a two-phase system. F127–CA/R5 micelle@SiNPs exhibited uniform and monodisperse particles with a size of 17 nm, indicating the formation of a ∼1.5-nm ultrathin and mesoporous silica layer compared with F127–CA/R5 micelle. F127–CA/R5 micelle@SiNPs exhibited almost identical KM and kcat values in CO2 hydration activity compared with the free enzyme. In addition, F127–CA/R5 micelle@SiNPs also showed enhanced stability compared to free ngCA under the operation condition of CO2 capture and sequestration with good storage stability. These results indicated that an ultrathin and mesoporous silica layer on the micelle could protect enzymes from external environments while minimizing limited mass transfer. Thus, our strategy could offer a new direction for enzyme-based green chemistry in practical applications, providing enhanced mass transfer and stability.

Molecular Dynamics Study of Silica Nanoparticles and CO2-Switchable Surfactants at an Oil-Water Interface.

Adsorbing CO2-sensitive surfactants on the surface of nanoparticles is an important strategy for preparing stimuli-responsive Pickering emulsions. However, the microscopic mechanisms are still limited, owing to a lack of intuitive understanding at the molecular level on the interactions between nanoparticle and switchable surfactants at the oil-water interface. We employed the molecular dynamics (MD) simulations to explore the mechanism behind the reversible emulsification/demulsification of a Pickering emulsion stabilized by silica nanoparticles (NPs) and CO2-switchable surfactants, named N-(3-(dimethylamino)propyl)alkyl amide (CPMA). MD results show that the protonated surfactant CPMAH+ has strong hydrophilicity, forming an adsorption layer at the oil-water interface. The ionic surfactants can be tightly adsorbed on NP surface through electrostatic interactions. Thus, the formed colloid particle has both hydrophobic and hydrophilic properties, which is a key factor in stabilizing emulsion. When CPMAH+ molecules were deprotonated to CPMA, the hydration activity of the headgroups reduced greatly, inducing a mixture with oil molecules. There are still a certain number of CPMA molecules residing at the oil-water interface due to the hydrophilic amine groups. The results from repeated simulations show that NP can either stay in the water phase or locate at the interface. Even NP was finally adsorbed on the interface and combined with CPMA or oil molecules, the adsorption configuration of CPMA on the NP surface was essentially different from that of CPMAH+. The potential of mean force confirmed that the combination between NP and CPMA is quite unstable due to the disappearance of electrostatic attraction. Different binding configurations and stability between NP and CPMA or CPMAH+ were the fundamental reason for the reversible emulsification/demulsification of Pickering emulsion.

3D-printed hydrogels dressings with bioactive borate glass for continuous hydration and treatment of second-degree burns.

Recent advances in additive manufacturing have led to the development of innovative solutions for tissue regeneration. Hydrogel materials have gained significant attention for burn wound treatment in clinical practice among various advanced dressings due to their soothing and moisturizing activity. However, prolonged healing, pain, and traumatic removal due to the lack of long-term wound hydration are some of the challenges in the treatment of second-degree burn wounds. In this study, 3D-printed dressings were fabricated using gelatin, alginate, and bioactive borate glass (BBG) using an extrusion-based bioprinter. After ionic crosslinking, the 3D-printed dressings were characterized for mechanical properties, degradation rate, hydration activity, and in vitro cell viability using human fibroblasts. The results demonstrated that in 3D-printed dressings with 20 wt% BBG, Young's modulus increased by 105%, and 10-day degradation rate decreased by 62%. Addition of BBG prevented the burst release of water from hydrogel dressings and enabled the continuous water release for up to 10 days, which is crucial in treating second-degree burn wounds. 3D-printed hydrogel dressings with BBG showed long-term cell viability that can be a result of the accumulative release of therapeutic ions from BBG particulate. The in vivo wound healing functionality of the dressings was investigated using a rat model with a second-degree burn wound. Our animal study showed that the 3D-printed dressings with BBG exhibited faster wound closure, non-adhesive contact, non-invasive debridement, and non-traumatic dressing removal. Histological analysis suggested that 3D-printed dressings contributed to more uniform re-epithelialization and tissue remodeling compared to the non-printed hydrogels of the same compositions. Critically, 3D-printed dressings with BBG led to significant regeneration of hair follicles compared to the 3D-printed hydrogel, non-printed hydrogel, and the control groups. The superior outcome of the 3D-printed hydrogel-BBG20 dressings can be attributed to the bioactive formulation, which promotes moist wound healing for longer time periods, and the non-adhesive porous texture of the 3D-printed dressings with increased wound-dressing interactions. Our findings provided proof of concept for the synergistic effect of bioactive formulation and the porous texture of the 3D-printed hydrogel dressings incorporated with BBG on continuous water release and, consequently, on second-degree burn wound healing.

Increase in volume stability of RO phases in steel slag by combined treatment of alkali and dry carbonation

RO phases account for 8.5–16.9 wt% of steel slags and exhibit delayed hydration activity, which may result in poor volume stability of steel slags (SS). Treatment of alkali activator (sodium silicate) followed by dry carbonation technology (ADC) was conducted on synthetic RO phases with various molar ratios of FeO, MgO, and MnO to promote its early hydration activity. Results show that 28 d compressive strength of mortar added by ADC_SS is 19.67% higher than that of added untreated SS and 26% decrease in expansion rate. Hydration degree of RO phases increases obviously during alkali treatment from 10.6% to 21.7% (RO-6), and is further stimulated by subsequently carbonation (reaching 44.1%), both resulting in much consumption of expansive component (i.e., MgO) in RO phases. The early hydration activity of cement promoted by adding ADC_RO phase/SS, which mainly attributes to the nucleation effect of hydration and carbonation products (i.e., Mg(OH)2, pyoaurite, and MgCO3·3H2O). The alkali excitation reaction of silica gels produced during carbonation as well as the formation of monocarboaluminate further contribute to the strength gain. ADC_SS used as admixture for cement makes pastes have advantage of higher strength, higher hydration rate, lower heat release, and less expansion rate compared to the system contained untreated SS. ADC may be a potential method to treat SS and makes SS to be used as admixture for Portland cement.

Mechanism research on surface hydration of Fe(II)-doped kaolinite, insights from molecular dynamics simulations

To investigate the micro-influence mechanism of Fe(II) doping on the surface hydration of kaolinite, molecular dynamics (MD) simulation method was utilized to simulate the interaction between H2O and Fe(II)-doped kaolinite (referred to as Fe(II)-Kao) surface under different conditions. Results demonstrate that the H2O can be adsorbed on Fe(II)-Kao surfaces, forming a hydration film composed of three H2O layers with a thickness of 8–10 Å. As the thickness of the H2O layer increased on Fe(II)-Kao surfaces, the interfacial effect between H2O and the surface gradually weakened. Furthermore, the interaction between H2O and Fe(II)-Kao (001¯) surface is weaker compared to that on the Fe(II)-Kao (001) surface. Additionally, the presence of Fe(II) doping enhanced the hydration of the kaolinite surface. The micro-influence mechanism of Fe(II) doping on the surface hydration of kaolinite can be attributed to the enhancement of the interface effect between equilibrium cations (such as Na(I)) and the surface, resulting in an increased ion hydration at the kaolinite surface. Overall, Fe(II) doping tends to promote the surface hydration of kaolinite. The elucidated mechanism of how impurity defects affect the surface hydration activity of kaolinite can provide theoretical support for tailings separation and wastewater treatment.

Effect of strontium slag on early hydration and mechanical properties of belite-C4A3$ cement

Belite-calcium sulfoaluminate (Belite-C4A3$) cement is one type of low-calcium clinker with good long-term compressive strength and durability. Yet, its early mechanical property is lower than P·І 42.5. In this paper, the effect of strontium slag on the preparation and performance of belite-C4A3$ cement was investigated. Moreover, the effect of SrO on crystal form and hydration characteristic of silicate minerals was studied. It was found that SrO could improve the early hydration activity of silicate minerals by stabilizing the β-type C2S and M-type C3S. The experiment results showed that the addition of strontium slag improved the burnability of cement, stabilized the high temperature active crystalline form of silicate minerals and promoted its formation, which were benefited to the rapid generation of hydration products and increase of early compressive strength of belite-C4A3$ cement. It was found that the compressive strength of belite-C4A3$ cement at different ages was increased to various degrees under the content of 1∼8% strontium slag. The optimal content of strontium slag was 5%, and its compressive strength of 1, 3, 7 and 28 days was 8.43, 35.83, 71.25 and 103.73 MPa, respectively. Compared with the blank group without strontium slag, the compressive strength was increased by 270%, 210%, 320% and 13%, respectively. This indicated that strontium slag had a significant effect on improving the early mechanical properties of belite-C4A3$ cement.

Improving the hydration activity and volume stability of the RO phases in steel slag by combining alkali and wet carbonation treatments

Poor volume stability of steel slag (SS) is due to the existence of free-CaO, free-MgO, and RO phases. Combined treatments of alkali and wet carbonation (AWC) were conducted on the RO phases to stimulate hydration activity. The hydration degree of AWC_RO phases with MgO molar ratios of 0.84 increased from 10.6 % to 57.6 %. The effects of FeO-MgO-MnO proportions on the hydration activity of RO phases were investigated electronically based on the density functional theory. Results showed that Fe imparted higher inhibition effects on MgO hydration than Mn. The compressive strength of mortar with added AWC_SS was 34.4 % higher than with added untreated SS at 28 days, with an expansion rate decreased from 0.0447 % to 0.0298 %. The main products of AWC_RO phases were Mg(OH)2 and Mg5(CO3)4(OH)2·4H2O, which exhibited seed crystal effects, accelerating the early hydration of cement. This method provides guidance towards a meaningful solution to poor SS volume stability.

Application of concrete produced from reused ready-mixed concrete wastewater filtration residue

During the production of ready-mixed concrete, waste slurry was filtered under pressure to obtain Wastewater Filtration Residue (WFR). Physical and chemical analysis of the WFR was conducted using methods such as XRD, SEM. The flowability and activity index of the cement mortar with composite admixtures, prepared by replacing fly ash (FA) with WFR powder at weight ratios of 0%, 25%, 50%, 75%, and 100%, were tested. Different strength grade concretes were prepared by replacing FA at weight ratios of 0%, 25%, and 50%, and replacing fine aggregate at weight ratios of 0%, 5%, and 10%, in order to analyze the variation of concrete strength. The results indicate the following: 1) The WFR was primarily composed of fine particles with various shapes and loose surfaces, making it suitable for concrete preparation. 2) WFR had poor flowability (59.83%) and hydration activity (51.7%), but FA addition improved both. Increasing FA content enhanced flowability ratio and hydration activity. At 1:1 FA-to-WFR ratio, flowability reached 81.44% and hydration activity reached 75.73%. 3) When WFR replaced FA (25%, 50%) or manufactured sand (5%, 10%) in concrete preparation, the strength of the concrete decreased with an increase in the WFR content. In low-strength grade concrete, the strength reduction was significant when WFR replaced FA. However, the strength reduction was less influenced by the design strength of the concrete when WFR replaced manufactured sand. 4) It was recommended to replace fine aggregate with WFR for concrete preparation, with the replacement ratio not exceeding 10% by weight.