Preparation Of Cement Research Articles

Preparation of magnesium potassium phosphate cement from magnesite tailings under lower calcination temperature

The identification of a more economical source of magnesium, coupled with reduced preparation costs, is essential for enhancing the competitiveness of magnesium potassium phosphate cement (MKPC) production. This study explores the utilization of magnesite tailings, waste materials produced during the mining and ore dressing process of magnesite, as raw materials for the preparation of low-cost dead-burnt magnesium oxide (MgO-T) at comparatively low calcination temperatures. The research demonstrated that impurities, specifically silicon and calcium, formed compounds with MgO during calcination, leading to the encapsulation of certain MgO particles. This encapsulation reduced both the specific surface area and hydration activity of the MgO. Despite the calcination temperature of 1100 °C being significantly lower than that of commercial dead-burnt MgO (MgO-C) at 1700 °C, MgO-T exhibited lower activity compared to MgO-C, which rendered it more suitable for the production of MKPC. Under optimal conditions, characterized by a molar ratio of magnesium to phosphorus (M/P) of 3, a borax retarder content of 15%, and a water-cement ratio of 0.15, the MKPC prepared using MgO-T demonstrated an initial setting time exceeding 60min and achieved a compressive strength of up to 79.6MPa. XRD and microstructural analyses revealed that struvite-K was the primary strength phase; however, the porosity of the specimens had a more pronounced effect on strength. By producing lower activity MgO at reduced calcination temperatures, this method obviates the need for complex purification processes when utilizing magnesite tailings, thereby decreasing the costs associated with MKPC preparation and presenting promising applications for the future.

Performance variations of light burned magnesia under different calcination parameters and its effects on magnesium oxysulfate cement preparation

This study systematically investigated the impact of different calcination temperatures and holding times on MgO reactivity, as well as the influence of varying reactivity and lattice distortion of MgO on the properties of magnesium oxysulfate cement (MOSC). Results indicated that at temperatures of 700–900℃, magnesite underwent decomposition, resulting in increased lattice distortion, and heightened reactivity. At temperatures of 1000–1100℃, magnesia began sintering, nucleating, and experienced reduced crystal distortion, leading to decreased reactivity. Notably, the appearance of the pseudomorphic mother rock at calcination temperatures of 900℃ and 1000℃ was associated with decreased magnesia reactivity. Moreover, the compressive strength of MOSC prepared using MgO calcined at 900℃ for 6 h increased to 77 MPa after 28 d of air curing. The hydration reactivity and lattice distortion of MgO could be regulated through changing the calcining temperature and holding time, which provided a theoretical basis for the preparation of magnesium oxysulfate cement with excellent mechanical properties.

Feasibility study on the preparation of ternary blended cements with low-kaolinite calcined coal gangue and limestone

This paper presents a feasibility study on the production of ternary blended cements with low-kaolinite calcined coal gangue (CCG) and limestone, considering kaolinite contents varying from 11.7 % to 40.6 % in coal gangue (CG). The ternary systems were designed with 15 %, 30 %, 45 % and 60 % by mass of cement replaced by CCG and limestone with a fixed mass ratio of 2:1. The fluidity and compressive strength of the mortars were measured, followed by the strength efficiency analysis combined with CO2 emission. The potential hydration mechanism was revealed by analysing the hydration kinetics, hydrates and microstructural evolution of these ternary pastes. The results showed that it is possible to use low-kaolinite CCG and limestone to prepare ternary blended cements with adequate mechanical strength that can fulfill the 28-day strength requirement of 32.5 or 42.5 grade cement. In addition, Increasing the kaolinite content in CG can increase the substitution of cement up to 60 %. Microstructural studies indicated that the compressive strength of these ternary mortars at 3 and 7 days was mainly dominated by cement hydration and the pozzolanic reaction between CCG and portlandite (CH), respectively. The precipitation of carboaluminates from the synergy of CCG and limestone significantly reduced critical pore size and increased the volume fraction of fine capillary pores from 7 days, well supporting the strength development of the ternary mortar. The findings of this work underscores the potential of using low-kaolinite CCG as a supplementary cementitious material (SCM) to reduce carbon footprint in the field of construction, and also in contributing to a high-value green utilization of solid waste.

Mechanical and shrinkage properties of alkali-activated mortars with graphite tailings

To improve the problems of high CO2 emission generated by the preparation of silicate cement, large accumulation of solid waste, and depletion of natural sand resources, this paper investigates the effect of pozzolanic effect of graphite tailings (GT) on the mechanical properties, shrinkage properties and microstructure of alkali-activated mortar, and less research has been done on this related content. This paper partially replaced the natural sand with GT, and completely replaced the cement with fly ash and slag to prepare alkali-activated fly ash-slag (AAFS) mortar. The consequences of GT replacement rate on the mechanical and shrinkage characteristics of AAFS mortar were analyzed. In addition, X-ray diffraction (XRD), mercury-in-pressure (MIP), and nuclear magnetic resonance (29Si MAS NMR) were used to examine the hydration degree, pore structure, and hydration products of AAFS mortar. The results demonstrated when the Na2O content was 7 % and the activator modulus was 1.0, the test group's 28-day flexural and compressive strengths at a 20 % GT replacement rate were increased by 19.49 % and 14.45 %, respectively, compared to the test group without GT. The appropriate quantity of GT reduced the AAFS mortar's drying shrinkage and increased the AAFS mortar's self-shrinkage. According to the microstructure analysis, GT had a pozzolanic effect: moderate doping of GT promoted the hydration reaction of precursors, improved the amount of C-(A)-S-H gel product generated, and improved AAFS mortar's mechanical and shrinkage properties.

Comparative analysis of the quality of the cement mantle in hip hemiarthroplasty after femoral neck fracture between three different surgical approaches: a single-center retrospective observational study.

Achieving the initial stability of implants is necessary for hip hemiarthroplasty (HHA), especially in elderly patients, and this can be achieved with a cement mantle of quality. The direct anterior approach (DAA) for HHA lately has shown positive results. However, evidence is lacking of HHA in elderly patients with osteoporosis after femoral neck fracture (FNF). This study compares differences in cement mantle quality after HHA, its complications, radiological outcomes and functional status in elderly patients with FNF intervened through different approaches. A non-interventional, retrospective case-control study was conducted. 150 cases were selected based on the surgical approach (DAA, DLA and PLA) in a 1:1:1 proportion between 2018 and 2019. Under 75years old suspicion or confirmation of a pathological fracture were excluded. Antibiotic-loaded cement was utilized. Cement preparation involved vacuum centrifugation and standard instructions for preparation canal and filling, and prosthesis placement were followed. No statistically significant differences in cement mantle quality, radiological outcomes, and the majority of the postoperative complications and functional status considering the surgical approach (p > 0.05). However, the DAA was associated significantly with shorter hospital stays (8.3days vs 11.3 and 13days for DLA and PLA) a decrease in postoperative blood transfusion (22% vs 34% and 53%), and lower rate of loss of walking (8% vs 20% and 28.6%). The DAA for HHA in patients with FNF provides a high-quality cement mantle, similar to other approaches. Also, the DAA shows advantages like shorter hospital stays and lower transfusion rates in elderly patients.

Preparation and characterization of alkali-activated Pisha sandstone-slag composite cement

This study explores the development of a novel alkali-activated cementitious material (APKC) using Pisha sandstone and slag as the main raw materials, offering a sustainable alternative to traditional cement. The APKC's flowability and mechanical properties are comparable to those of ordinary Portland cement (OPC), but it is significantly more cost-effective, with lower carbon emissions and energy consumption. Specifically, at a water-to-binder (w/b) ratio of 0.3, with an optimal activator content of 17.5 % and a Pisha sandstone-to-slag ratio of 1:1, APKC achieves excellent performance: a flowability of 195 mm, and 28-day compressive and flexural strengths of 59.1 MPa and 9.96 MPa, respectively. Moreover, the production of one ton of APKC reduces costs to 64.01 %, carbon emissions to 22.76 %, and energy consumption to 28.56 % of those associated with one ton of OPC, highlighting its potential as a viable replacement in engineering applications. The primary hydration products of APKC include hydrotalcite, C,N-A-S-H gels, C-S-H gels, and natrolines. It is crucial to maintain the alkali activator content and Pisha sandstone-to-slag ratio within optimal ranges, as insufficient alkali dosage or an excessive Pisha sandstone-to-slag ratio can diminish the mechanical properties by reducing hydration product content. Conversely, too much alkali activator can lead to high-porosity hydration products due to the dissolution of Al in C,N-A-S-H gels.

Study on the preparation and properties of high-performance foamed cement by multi-factor optimization

The promotion of high-performance foamed cement in engineering is consistent with the objectives of energy conservation and sustainable development. In this work, the effects of the water–binder ratio, foam–grout ratio, mineral powder content and magnesium oxide content on the performance of foamed cement were studied. High-performance foamed cement was prepared considering the above four factors. The results indicated that the pore structure of the foamed cement was effectively modified by adjusting the water–binder and foam–grout ratios, while its compressive strength increased and its setting time decreased when mineral powder and magnesium oxide were added. Pore structure and scanning electron microscopy experiments revealed that the surface of the high-performance foamed cement was covered with many hydration products of mineral powder and magnesium oxide, resulting in a more compact and uniform structure. Simultaneously, these hydration products effectively filled pores with diameters ranging from 0 to 0.2 mm in the high-performance foamed cement, refining its pore structure and thereby enhancing its waterproof performance and drywet cycling stability. Compared with those of commercial foamed cement, the setting time of the high-performance foamed cement was 23.48 % shorter, and its compressive strengths at 1 d and 7 d were 245.78 % and 178.62 % greater, respectively. Furthermore, the production cost per cubic meter of the high-performance foamed cement was 107.29 RMB less than that of ordinary cement. In brief, the high-performance foamed cement can be widely used in a variety of engineering applications because of its performance and economic benefits.

Injectable bone cement based on magnesium potassium phosphate and cross-linked alginate hydrogel designed for minimally invasive orthopedic procedures

Bone cement based on magnesium phosphate has extremely favorable properties for its application as a bioactive bone substitute. However, further improvement is still expected due to difficult injectability and high brittleness. This paper reported the preparation of novel biocomposite cement, classified as dual-setting, obtained through ceramic hydration reaction and polymer cross-linking. Cement was composed of magnesium potassium phosphate and sodium alginate cross-linked with calcium carbonate and gluconolactone. The properties of the obtained composite material and the influence of sodium alginate modification on cement reaction were investigated. Our results indicated that proposed cements have several advantages compared to ceramic cement, like shortened curing time, diverse microstructure, increased wettability and biodegradability and improved paste cohesion and injectability. The magnesium phosphate cement with 1.50% sodium alginate obtained using a powder-to-liquid ratio of 2.5 g/mL and cross-linking ratio 90/120 of GDL/CC showed the most favorable properties, with no adverse effect on mechanical strength and osteoblasts cytocompatibility. Overall, our research suggested that this novel cement might have promising medical application prospects, especially in minimally invasive procedures.

Study on the Preparation and Compressive Strength of Boron Mud-Based Basic Magnesium Sulfate Cement.

The direct discharge of boron mud poses significant environmental hazards to soil and groundwater. Despite extensive research efforts, the reprocessing of boron mud has not yielded significant advancements. Recently, the development of magnesium cement has spurred interest in the reutilization of boron mud. However, the direct treatment of boron mud remains challenging, necessitating pre-treatment in most studies to achieve substantial results. Consequently, research on the direct incorporation of untreated boron mud is scarce. This study explores the feasibility of using uncalcined boron mud as a base material in basic magnesium sulfate cement (BMSC), composed of lightly calcined magnesia and magnesium sulfate heptahydrate. The effects of varying boron mud content on the compressive strength of the BMSC system were investigated. The results indicate that the 5·1·7 phase is the primary strength phase of BMSC. When the boron mud content is 30%, the uncalcined boron mud has a minimal impact on the formation of the 5·1·7 phase. Additionally, the 28 days compressive strength of BMSC-B30 showed a slight difference compared to the control group BMSC-C, registering at 66.7 MPa. TG-DSC analysis revealed that the presence of a small amount of boron mud inhibits the micro-expansion trend of the BMSC structure. Furthermore, XRD and SEM analyses confirmed that the addition of uncalcined boron mud does not significantly alter the phase structure of the 5·1·7 phase in BMSC. This study provides a foundational basis for the long-term development of direct boron mud treatment.

Preparation and investigation of heat insulation materials with microorganism-assisted foaming

This study aims to explore the feasibility of foamed cement preparation by microbial liquid. Specimens containing glass beads were employed for comparison with microbial foamed cement, and the characterization and evaluation of these samples were conducted using techniques such as TGA, XRD, micro-CT, thermal conductivity measuring instrument and SEM. The results revealed that the porosity of the microbial foamed specimens could reach 25.3 %, and compared to the thermal conductivity of 1.06 W/mK for the normal samples, microbial foamed cement could reach 0.58 W/mK. Furthermore, the strength of the foamed cement with bacterial solution was the lowest, and the strength at 7 days was almost the same as that at 28 days. This is attributed to the high concentration of the bacterial solution impacting the stabilization of the C-S-H gel, thereby hindering the further hydration of cement particles. Nevertheless, for production blocks used in non-load-bearing structures, the strength proved to be adequate, and significant time savings can be achieved.

Study on mechanical properties of E-glass mat reinforced basic magnesium sulfate cement thin-slab

To achieve sustainable development and reduce the carbon footprint in building material production, the E-glass fiber mat was impregnated with basic magnesium sulfate cement (BMSC) by lamination impregnation. This process reduces environmental pollution from cement preparation, increases fiber volume content, and enhances the mechanical properties of cementitious composite materials. The study examined axial tensile, four-point bending resistance, drop weight impact resistance and pendulum impact resistance of BMSC thin-slab reinforced with dispersed short glass fiber (SGF), short glass fiber mat (SGFM) and continuous glass fiber mat (CGFM) of varying gram weights. The results show that the mechanical properties of BMSC thin-slab reinforced with fiber mat are much higher than those of SGF reinforced thin-slab. The tensile strength of BMSC thin-slab reinforced with CGFM is higher than that of BMSC thin-slab reinforced with SGFM at the same gram weight, and the tensile strength increases as the weight of CGFM increases. Specifically, the axial tensile strength of BMSC thin-slab reinforced with 450 g of CGFM is nearly 8 times higher than that of SGF reinforced BMSC thin-slab. BMSC thin-slab reinforced with 450 g of CGFM has the maximum proportional limit load and bending strength. The impact strength and toughness indexes of BMSC thin-slab reinforced with CGFM are the highest, followed by SGFM reinforced BMSC thin-slab. The addition of 300 g CGFM significantly enhanced flexural toughness during the early stage of thin-slab cracking, while 450 g CGFM showed significant improvement in flexural toughness during the middle and late stages of cracking. When comparing thin-slabs with the same glass fiber volume ratio, those reinforced with 450 g CGFM exhibited the best impact resistance. SEM results indicated superior adhesion between 450 g CGFM and the cement matrix, as well as between adjacent CGFM layers, with fiber breakage being the main cause of specimen failure.

Processing the Fluorocarbon-containing Waste from Electrolytic Aluminum Production

The characteristics of fine fluorocarbon-containing waste from aluminum production are given and the influence of changes in aluminum production technology that have occurred in recent years on the formation structure, composition and properties is analyzed. The currently proposed methods for processing these wastes are reviewed. An assessment of the method for processing fine fluorocarbon-containing waste from aluminum production was carried out on the example of coal foam flotation tailings using the method of causticization with lime milk to produce a product containing synthetic fluorite, used as a mineralizer for the preparation of straight cement. The influence of operating parameters (temperature, process time, dilution) on the completeness of causticization of raw materials has been determined. The greatest influence on the extraction of fluorine into fluorite and sodium into solution is exerted by the liquid to solid ratio (L:S), at that, the yield of fluorite reaching 220 kg per ton of supplied raw material. It has been found that the high alkalinity of the solution allows sodium hydroxide to be extracted from it and used after causticization as a gas cleaning solution.

High-value utilization of boron mud waste: preparation of magnesium oxysulfate cement after primary blank roasting and secondary (NH4)2SO4 roasting

Boron mud, as a typical industrial solid waste, calls for value-added use because of environmental problems caused by stockpiling and waste of considerable magnesium resource. In this work, the primary blank roasted boron mud, as well as the secondary (NH4)2SO4 roasted boron mud were used to prepare magnesium oxysulfate (MOS) cement, then, its characterization and mechanical properties were analyzed and compared systematically. Results showed that the primary blank roasted boron mud can replace 45 % of light burned MgO to prepare MOS cement, whose compressive and flexural strength are 59.0 MPa and 8.0 MPa after curing for 28 d. During the secondary (NH4)2SO4 roasting process of boron mud, MgO and Mg2SiO4 in the primary roasted boron mud transform into MgSO4. The secondary roasted boron mud can replace MgSO4 completely, MOS cement rich in 5Mg(OH)2·MgSO4·7 H2O (517) phase can be obtained with compressive and flexural strength of 70.0 MPa and 9.0 MPa after curing for 28 d. When both of the primary blank roasted and secondary (NH4)2SO4 roasted boron mud are used for preparing MOS cement which compressive and flexural strength are higher than the requirements of the national standard, MgSO4 can be completely derived from the secondary roasted boron mud, the primary blank roasted boron mud can replace up to 35 % of light burned MgO at most, and the total utilization ratio of boron mud is 53.3 wt%. This process not only achieves the high-value utilization of boron mud, but also provides a new thought to prepare MOS cement with high mechanical properties.

Preparation of Injectable Dicalcium Phosphate Bone Cement for Potential Orthopedic Applications

Various natural wastes can be promising for mining more valuable compounds if some specialized extraction techniques are adopted. Hydroxyapatite (HA) is a significant biomaterial that can be extracted from waste bovine bones by heating them at 700 °C and 900 °C. Based on this idea, we made a novel dicalcium phosphate (DCP) bone cement (BC) by extracting HA via the reaction with monocalcium phosphate monohydrate (MCPM) and trisodium citrate. The setting time, injectability, and compressive strength (CS) of this DCPBC were examined using various analytical techniques, such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) attached with energy-dispersive X-ray (EDX) spectroscopy, and Fourier-transformed infrared spectroscopy (FTIR). The phase composition, surface morphology, and chemical compositions of HA and DCP were evaluated. A Gillmore needle apparatus was used to measure the initial and final setting times of the specimens. The CS values of the prepared specimens were determined using INSTRON Series IX. The in vitro dissolution behavior of all samples was evaluated by immersing them in simulated body fluid (SBF) over 7 days at 37 °C. The final setting times of samples 3, 4, and 5 were 20, 24, and 18 min, respectively. In addition, the CS value of sample 1 before immersion in SBF was much lower (1.23 MPa) compared to sample 5 (21.79 MPa) after 7 days of immersion. The CS of the DCP after 3 days of immersion was increased to 33.75 MPa. The in vitro results for the dissolution and bioactivity of HA showed the highest degradation rate after 1 day of immersion and then decreased with the increase in the immersion duration. The HA layer thickness was considerably improved with longer incubation times. The proposed injectable DCP bone cement may have potential in future orthopedic applications.

Preparation and efficacy of antibacterial methacrylate monomer-based polymethyl methacrylate bone cement containing N-halamine compounds.

Our objective in this study was to prepare a novel type of polymethyl methacrylate (PMMA) bone cement, analyze its material properties, and evaluate its safety and antibacterial efficacy. A halamine compound methacrylate antibacterial PMMA bone cement containing an N-Cl bond structure was formulated, and its material characterization was determined with Fourier transform infrared spectroscopy (FT-IR) and 1H-NMR. The antibacterial properties of the material were studied using contact bacteriostasis and releasing-type bacteriostasis experiments. Finally, in vitro and in vivo biocompatibility experiments were performed to analyze the toxic effects of the material on mice and embryonic osteoblast precursor cells (MC3T3-E1). Incorporation of the antibacterial methacrylate monomer with the N-halamine compound in the new antibacterial PMMA bone cement significantly increased its contact and releasing-type bacteriostatic performance against Staphylococcus aureus. Notably, at 20% and 25% additions of N-halamine compound, the contact and releasing-type bacteriostasis rates of bone cement samples reached 100% (p < 0.001). Furthermore, the new antibacterial bone cement containing 5%, 10%, and 15% N-halamine compounds showed good biocompatibility in vitro and in vivo. In this study, we found that the novel antibacterial PMMA bone cement with N-halamine compound methacrylate demonstrated good contact and releasing-type bacteriostatic properties against S. aureus. In particular, bone cement containing a 15% N-halamine monomer exhibited strong antibacterial properties and good in vitro and in vivo biocompatibility.

Preparation and property studies of ferric sulfoaluminate cement based on Bayer red mud and phosphogypsum.

The Bayer red mud (RM) and phosphogypsum (PG) accumulation have caused significant environmental contamination. However, practical and effective resource utilization technologies are still lacking currently. This work aims to develop ferric sulfoaluminate cement (FSAC) employing low-cost materials including Bayer red mud, phosphogypsum, and other materials. This method effectively improves the utilization rate of Bayer red mud and phosphogypsum. Under the premise of ensuring the performance of FSAC, the utilization rate of solid waste can reach up to 48.56%. The effects of different red mud dosages on cement mineral formation, workability, and mechanical properties are investigated. Then, untreated phosphogypsum is adopted as a retarder for FSAC, and the hydration process, working properties, mechanical properties, types of hydration products, and morphology of FSAC are explored. The results suggest that the crystal transformation of Ye'elemite is promoted with the increase of Bayer red mud content. Cubic crystal system Ye'elemite with higher hydration activity is generated, which increases the early strength of cement but greatly reduces the setting time, hindering the later strength growth. Untreated phosphogypsum can effectively delay the early hydration process of FSAC, prolong the setting time of cement, and increase the strength of FSAC in the later stage. When the dosage of Bayer red mud and phosphogypsum is 17.64% and 9.21%, respectively, with phosphogypsum dosage of 20%, the prepared FSAC has satisfactory mechanical properties, and the 3-day and 90-day compressive strengths are 34.6 MPa and 57.1 MPa, respectively. In addition, the study of heavy metal leaching indicates that the FSAC prepared by Bayer red mud, phosphogypsum, and other raw materials will generate no environment pollution, and the solidification of heavy metal elements in the cement slurry is superior.

Influence of Curing Temperature on the Performance of Calcined Coal Gangue-Limestone Blended Cements.

The utilization of calcined coal gangue (CCG) and limestone for the preparation of blended cement is an efficient approach to address the issue of coal gangue disposal. However, the compressive strength development of blended cement is slow, particularly at high substitution levels of CCG. Therefore, this study aimed to promote the hydration and mechanical properties of the calcined coal gangue-limestone blended cements by increasing the curing temperature. In this study, the samples were cured at two different temperatures, namely 20 and 40 °C. The four groups of samples contained 15 wt.%, 30 wt.%, 45 wt.% and 60 wt.% cement substitutions using CCG and limestone (2:1 mass ratio). The compressive strength, hydration and microstructure were investigated at the ages of 1 to 28 d. X-ray diffraction (XRD) and thermogravimetry (TG) were used to study the hydration behavior of samples. Mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) were used to determine the microstructure of the samples. The results indicate that an increase in curing temperature significantly promotes the compressive strength of the calcined coal gangue-limestone blended cements from 1 to 28 d. The microstructural analysis indicates that increasing the curing temperature not only promotes cement hydration but also facilitates the reaction of CCG, which precipitated more hydrates such as C-A-S-H gel, Hc and Mc. These hydrates are conducive to refining the pore structures and densifying the microstructure, which sufficiently explains the enhanced compressive strength of the calcined coal gangue-limestone blended cements.

Preparation of Calcite-Precipitating Bacteria-Embedded Magnesium Phosphate Cement for Self-Healing Application

The present study was undertaken to check the feasibility of magnesium phosphate cement (MPC) for the immobilization of calcite-precipitating bacteria. An aqueous route of MPC synthesis was followed using magnesium phosphate Mg3(PO4)2 powder and ammonium phosphate solution. The Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) analysis confirmed the synthesis of MPC. The thermal decomposition analysis (TGA) showed decomposition of struvite between 50–60 °C - Paenibacillus sp. NCIM 5410 was used due to its urea hydrolysis ability. pH 9 was found to be optimum for urea hydrolysis. The urea hydrolysis steadily decreased with an increase in temperature from 30 °C to 60 °C. The hydrolysis was seen to increase with an incubation time of up to 72 h and subsequently reduced. The bacteria showed 90% urea hydrolysis at pH 9, 30 °C temperature, and after 72 h. The bacterial spores were incorporated during MPC synthesis, which helped their immobilization. The bacterial spore-containing MPC decomposed around 70 (±0.48)% of urea. Further, calcite precipitation was studied. The precipitate formed due to bacterial action in the MPC crack showed the presence of calcium. The calcite precipitation helped to reduce the water absorption by MPC specimens. The spore containing MPC specimens showed around 2.62 (±0.55) % water absorption. These results suggest that it is possible to synthesize bioactive MPC by immobilizing bacterial spores in MPC.

Effect of surface water on wollastonite carbonation: Activated dissolution and mass transfer

Carbonation of non-hydraulic calcium silicate to produce cement represents a crucial strategy for mitigating carbon emissions in the cement industry. However, the dissolution rate of Ca2+ is the main constraint on the reaction kinetics. In this study, the carbonation of wollastonite (CS) was investigated, with an emphasis on the role of water in the Ca2+ dissolution process. Firstly, we investigated carbonation performance of CS and its influencing factors. Results revealed a significant impact of the water-to-solid (w-s) ratio on carbonation. In the carbonate products, we observed that the dissolution of Ca2+ adsorbed on the particle surface, referred to as “pseudocrystalline replacement”, which can serve as supplementary cementitious material. Additionally, this observation signifies the accordance of Ca2+ dissolution with the electric double layer (EDL) theory. Subsequently, we quantitatively assessed the influence of w-s ratio on carbonation using kinetic models. Based on EDL theory and the kinetic model, we categorized water film effect into three stages and determined the influence of water film thickness on the rate-determining factors of CS carbonation. This provides theoretical support for preparation of CS-based cement. Interestingly, we found that reaction rate constant varies with changes in the w-s ratio, indicating a catalytic role of water. Further analysis using density functional theory demonstrated that the free water combined with the O/Ca sites on CS to form hydroxylated surfaces, thereby decreasing and increasing the abilities of the local and neighboring sites, respectively, to absorb H2CO3. These findings provide a theoretical foundation for the curing method of low-carbon cements and offer a methodology for the preparation of supplementary cementitious materials.

Preparation and Evaluation of Cements Using Spherical Porous β-Tricalcium Phosphate Granules

Preparation and Evaluation of Cements Using Spherical Porous β-Tricalcium Phosphate Granules