Magnesia Cement Research Articles

Influence of municipal solid waste incineration bottom ash on the hydration and carbonation behavior of reactive magnesia cement

This study investigates the effects of Municipal solid waste incineration bottom ash (MSWIBA) on the hydration and carbonation behavior of reactive magnesia cement (RMC). The results indicate that the incorporation of MSWIBA accelerates the early hydration rate of RMC due to its dilution and nucleation effects. However, excessive MSWIBA content formed layered double hydroxides (LDH) inhibiting the hydration of magnesium oxide cement. Furthermore, while a 5% addition of MSWIBA enhances the compressive strength of RMC after carbonation, higher contents lead to a reduction in post-carbonation strength and long-term durability due to the formation of microcracks from hydrogen gas generation and the expansion from carbonation products. Additionally, the carbonation process is affected by LDH, which hinders the crystallization of hydromagnesite and favors the formation of more amorphous phases. The findings suggest that while MSWIBA can be beneficial at low dosages, its excessive use may compromise the long-term performance of RMC.

Long-term mechanical performance of fly ash-incorporated reactive magnesia cements

In this research, after producing reactive magnesia directly from calcination of magnesite, reactive magnesia specimens with fly ash were prepared and cured in two different environments to investigate their long-term mechanical performance by carbonation. To investigate the effect on their microstructures of carbonation, the XRD profiles of the samples were also obtained and investigated. It is found that the strength of reactive magnesia samples is highly affected by the addition rate of reactive magnesia and the curing regime. In spite of the presence of the nesquehonite (MgCO3.3H2O) in the reactive magnesia cements having no portland cement, any type of magnesium carbonate crystal was not found for the cements with portland cement in carbon dioxide curing. The strength increase in reactive magnesia cements can be due to the incorporation of Mg2+ ions to the calcite crystals.

Investigating key factors for superior CRMC-based mortars cured under CO2 pressurized environment

An exploratory programme was undertaken to individually test the influence of reactive magnesia to waste-based material (biomass fly ash) ratio, water to solids in binder ratio, static compaction pressure, accelerated carbonation curing period, and curing temperature, on the compressive strength results of Carbonated Reactive Magnesia Cement (CRMC)-based mortars. Subsequently, the observed optimal conditions of each parameter were combined to assess their influence when applied together. A total of twenty-four mixture labels were designed, with specimens moulded under static compaction pressure and subjected to a pressurized accelerated carbonation curing under controlled conditions. The devised mortars were evaluated through compressive strength tests, and the microstructure was carried out through TG-DTG, ATR-FTIR, XRD, SEM-EDX, and MIP analyses. The results demonstrated that none of the tested influencing factors can be exclusively considered as the sole determinant for the compressive strength outcomes. Thus, this study highlights the importance of thoroughly considering any modifications in both mixture design and accelerated carbonation curing conditions to achieve the optimal properties of CRMC-based mortars. Additionally, the devised CRMC-based mortars exhibited favourable binding properties with biomass fly ashes, allowing for its secondary use and contributing to waste circularity by avoiding landfill disposal, supporting the development of the waste circularity and CO2 sequestration through mineralization in carbonated materials.

Investigation of non-uniform carbonation in strain-hardening magnesia composite (SHMC) and its impacts on fiber-matrix interface and fiber-bridging properties

Unlike Portland cement, the reactive magnesia cement (RMC) develops its strength via carbonation. Non-uniform microstructure and properties due to the varied carbonation degree across cross-section depth have thus been observed. However, the existing micromechanics design theory employs uniform material properties (cementitious matrix and fiber-matrix interface characteristics) to design strain-hardening composites. This research investigated such non-uniform carbonation in a strain-hardening magnesia composite (SHMC) and its impacts on fiber-matrix interface and fiber-bridging properties. Results showed that mineral phase composition (of the cementitious matrix) and fiber-matrix interface properties across cross-section depth are highly non-uniform in SHMC due to varied carbonation degrees. The outer layer exhibited a much higher carbonation degree with significantly stronger fiber-matrix friction, while the inner core showed negligible carbonation with distinct fiber-matrix properties. Insights gained from the micro-scale investigation were used to calculate the fiber-bridging constitutive law of SHMC with non-uniform carbonation across cross-section depth and to assess its strain-hardening performance. This investigation highlights the importance and necessity of considering non-uniform carbonation in the modeling and design of SHMC. The study presents a framework for the consideration of non-uniform micromechanical parameters in the design of strain-hardening cementitious composites.

New magnesium cement optimized in MgO-K2HPO4-SiO2 system and its hardening performance

Silica fume (SF) is commonly used in producing magnesium potassium phosphate cement (MPC) and magnesium silicate hydrate cement (MSHC). However, its roles in magnesium cement would differ from each other when mono hydrogen phosphate was involved. This paper aims to find optimized compositions in MgO-K2HPO4 DKP- SF system with comprehensive considerations of the micro and macro performances. Ternary contour maps were designed to determine the optimized proportions of MgO, DKP and SF. The hydration reaction mechanism was analyzed with a variety of techniques including XRD, SEM, TG-DTG and NMR. Magnesium cement containing 60–75 % dead-burnt MgO, 10–25 % DKP and 12.5–25 % SF exhibited excellent compressive strength and volume stability. K-struvite and M-S-H were confirmed to promote the hydration and hardening performance of the blended MgO-DKP-SF system with optimized proportions. An excess of soluble K+ from DKP may precipitate as KOH and then dissolute in solution, increasing pH and release of Si from SF.

Saponitecontaining Waste from Mining and Processing Companies as a Raw Material Reserve for the Building Materials Industry

A new promising direction for recycling the large-scale saponitecontaining waste from the JSC Severalmaz mining processing company is presented, the storage of which can negatively affect the ecological situation of the region and increases the risk of environmental pollution. It has been found that saponitecontaining material (SCM) in terms of MgO content can be considered as a medium-magnesian technogenic raw material for the production of magnesium cement. It has been shown that the main conditions for obtaining effective solutions based on saponite binder are as follows: the sealer is an aqueous solution of magnesium chloride at concentration of 8% and the water-to-solid ratio of 0.4. Cube samples were obtained based on a binder made from thermally modified saponite powder, taking into account the above factors, with a compressive strength of 5.78 MPa at density of 1600 kg/m3. It has been confirmed that the implementation of the above technological methods makes it possible to obtain structural thermal insulating concrete that meets the requirements of the relevant GOST.

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.

Assessment of the properties of mortars made of sorel cement

The purpose of laboratory tests was to determine the effect of sodium silicate and selected hydrophobic agents on the basic physical parameters and freeze-thaw durability of mortars made with Sorel cement in variable proportions. In order to determine the mortars’ parameters, samples of the dimensions of 4x4x16 cm and boards of the diameters of 1x4x16 cm were prepared. Parameters such as water absorption, capillary absorption, compressive and flexural strength and frost resistance were tested. Mortar supplemented with sodium silicate in the quantity of 2.6% of all components demonstrated the best properties. None of the other hydrophobic agents that were used to mitigate the negative effects of water on Sorel cement mortars demonstrated such positive properties. Flexural strength tests of all mortar batches, performed on cuboid samples and boards of the thickness of 1 cm, demonstrated a similar improvement in strength. The lowest value of compressive strength was recorded for the reference batch at 46.6 MPa, whereas the highest value was recorded for the second batch containing sodium silicate, at 49.8 MPa. During the testing of frost resistance, the lowest reduction of compressive and flexural strength was recorded for the reference mortar and for mortar with sodium silicate. All mortars were varied in the MgO/MgCl2 ratio and the total amount of water, the observed effects may be caused by other variables. However it is possible to notice the positive effect of selected hydrophobic agents.

Development of a consistent geochemical model of the Mg(OH)2–MgCl2–H2O system from 25°C to 120°C

The formation of magnesium chloride-hydroxide salts (magnesium hydroxychlorides) has implications for many geochemical processes and technical applications. For this reason, a thermodynamic database for evaluating the Mg(OH)2–MgCl2–H2O ternary system from 0 °C–120 °C has been developed based on extensive experimental solubility data. Internally consistent sets of standard thermodynamic parameters (ΔGf°, ΔHf°, S°, and CP) were derived for several solid phases: 3 Mg(OH)2:MgCl2:8H2O, 9 Mg(OH)2:MgCl2:4H2O, 2 Mg(OH)2:MgCl2:4H2O, 2 Mg(OH)2:MgCl2: 2H2O(s), brucite (Mg(OH)2), bischofite (MgCl2:6H2O), and MgCl2:4H2O. First, estimated values for the thermodynamic parameters were derived using a component addition method. These parameters were combined with standard thermodynamic data for Mg2+(aq) consistent with CODATA (Cox et al., 1989) to generate temperature-dependent Gibbs energies for the dissolution reactions of the solid phases. These data, in combination with values for MgOH+(aq) updated to be consistent with Mg2+-CODATA, were used to compute equilibrium constants and incorporated into a Pitzer thermodynamic database for concentrated electrolyte solutions. Phase solubility diagrams were constructed as a function of temperature and magnesium chloride concentration for comparisons with available experimental data. To improve the fits to the experimental data, reaction equilibrium constants for the Mg-bearing mineral phases, the binary Pitzer parameters for the MgOH+ — Cl− interaction, and the temperature-dependent coefficients for those Pitzer parameters were constrained by experimental phase boundaries and to match phase solubilities. These parameter adjustments resulted in an updated set of standard thermodynamic data and associated temperature-dependent functions. The resulting database has direct applications to investigations of magnesia cement formation and leaching, chemical barrier interactions related to disposition of heat-generating nuclear waste, and evaluation of magnesium-rich salt and brine stabilities at elevated temperatures.

Effect of internal moisture content (IMC) on the CO2 sequestration efficiency of hollow natural fiber (HNF)-reinforced reactive magnesia cement (RMC) composites

The incorporation of minor hollow natural fibers (HNF) can significantly accelerate the CO2 diffusion in reactive magnesia cement (RMC). The CO2 diffusivity in HNF is highly related to its internal moisture content (IMC), which subsequently affects the carbonation process of HNF-RMC, but this is outside the scope of the existing studies. Therefore, this work investigates the effect of IMC on carbonation, strength, and microstructure of HNF-RMC composites. HNF-RMC mortar specimens are dried to different levels of nominal IMC (0–100%), and cured under high CO2 concentration for carbonation. Following the curing, the matrix composition was characterized with varying techniques (QXRD, TGA, FTIR, and acid digestion) for quantifying the CO2 sequestration; the compressive strength at different depths was determined with uniaxial compressive test; the microstructure was examined with SEM/ESEM. The results show that the carbonation depth is increased by three to four times by reducing the IMC to 0%. The effects of varying IMC on local carbonation and strength are distinct in the shallow (0–20 mm) and middle/deep region (20–100 mm). In the shallow region, inadequate CO2 dissolution is the limiting factor, these performances decreased with the increasing desiccation. In the deeper regions, moisture absorption by HNF decreased the CO2 diffusivity, hence the CO2 availability is the limiting factor, and these performances increased with the desiccation. These observations suggest that the understanding that carbonation maximizes at a medium moisture level is not valid in HNF-RMC–controlling the moisture can be important for improving the CO2 sequestration and consequent mechanical strength.

Enhancing carbonation and thermal insulation of reactive magnesium oxide cement (RMC)-based 3D printable pastes with cenospheres

Reactive magnesium oxide cement (RMC) has been proposed as a sustainable alternative to ordinary Portland cement (OPC) due to its lower production temperature and ability to permanently sequester carbon dioxide (CO2) through carbonation. However, mixtures with only RMC can have significantly reduced CO2 absorption capacity due to limited CO2 diffusion, thereby compromising the performance of RMCs. This paper demonstrates the adoption of cenospheres, an industrial waste, as a lightweight filler in RMC-based 3D printable composites to enhance carbonation and improve thermal insulation. This work investigates the effect of incorporating different dosages of cenospheres on the rheological properties, compressive strength, thermal conductivity, and microstructural development of the RMC mixtures using X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The study reveals that substituting 30 % of RMC with cenospheres not only improves the printability and carbonation of the composite but also results in a 16 % reduction in density, achieving 1.72 g/cm³, and reduces the thermal conductivity by 59 % compared to the control without cenospheres to 0.63 W/(m·K). The findings provide valuable insights for developing lightweight 3D printable RMC-based composites.

Effect of hollow natural fiber (HNF) content on the CO2 diffusion, carbonation, and strength development of reactive magnesium cement (RMC)-based composites

Reactive magnesia cement (RMC) is an emerging class of green cement that hardens by sequestering CO2. However, CO2 diffusion into RMC is restricted to a few millimeters by the carbonation-induced dense microstructure on the outer layer, which severely slows down the strength growth and CO2 sequestration. To address this issue, this work employed hollow natural fibers (HNFs) to facilitate CO2 diffusion into the deep regions of RMC. The effects of HNFs contents on the mechanical strength development, holistic porosity, CO2 sequestration, CO2 diffusivity, and microstructure of RMC were investigated through different techniques. The findings revealed that the compressive strength could be more than doubled with the addition of adequate sisal fiber. Moreover, the CO2 sequestration and diffusivity could be continuously enhanced with the increasing HNFs content. However, overdosage of HNFs could induce a higher porosity and additional defects, which slightly compromises the mechanical strength. Finally, the durability of HNFs in simulated RMC and Portland cement (PC) environment was compared by accelerated aging test, showing that the alkaline-induced deterioration of HNFs could be almost eliminated in RMC. Therefore, this preliminary study reinforces the function of RMC as a carbon reservoir and lays the foundation for the large-scale utilization of HNFs in RMC.

The effect of depth-dependent carbonation on the interfacial strength between GFRP reinforcement bar and reactive magnesia cementitious composites

Reactive magnesia cement (RMC) is an emerging class of low-alkaline and CO2-sequestering binder, which can mitigate the deterioration of GFRP reinforcements induced by a high-alkaline environment, e.g., in Portland cement. This study investigated the slip behavior of GFRP rebar embedded in RMC composite, which varies with carbonation depth significantly. The variation of the interfacial bond was determined by a specially designed push-out test of the GFRP core; the variation of the carbonation degree and microstructure was examined by SEM-EDX, MIP, XRD, TGA, FTIR, and acid digestion tests. Both properties demonstrated a similar trend, decreasing rapidly with increasing depth. A new finite element model that considers the depth-dependency of the matrix compositions and the rebar-to-matrix interfacial bond is established. It can predict the constitutive bond-slip behavior of a long GFRP rebar embedded in an RMC composite with non-uniform carbonation.

Efficient stabilization of dredged sludge with high water content using an improved bio-carbonation of reactive magnesia cement method

This study proposed an improved bio-carbonation of reactive magnesia cement (RMC) method for dredged sludge stabilization using the urea pre-hydrolysis strategy. Based on unconfined compression strength (UCS), pickling-drainage, and scanning electron microscopy (SEM) tests, the effects of pre-hydrolysis duration (T), urease activity (UA) and curing age (CA) on the mechanical properties and microstructural characteristics of bio-carbonized samples were systematically investigated and analyzed. The results demonstrated that the proposed method could significantly enhance urea hydrolysis and RMC bio-carbonation to achieve efficient stabilization of dredged sludge with 80% high water content. A significant strength increment of up to about 1063.36 kPa was obtained for the bio-carbonized samples after just 7 d of curing, which was 2.64 times higher than that of the 28-day cured ordinary Portland cement-reinforced samples. Both elevated T and UA could notably increase urea utilization ratio and carbonate ion yield, but the resulting surge in supersaturation also affected the precipitation patterns of hydrated magnesia carbonates (HMCs), which weakened the cementation effect of HMCs on soil particles and further inhibited strength enhancement of bio-carbonized samples. The optimum formula was determined to be the case of T = 24 h and UA = 10 U/mL for dredged sludge stabilization. A 7-day CA was enough for bio-carbonized samples to obtain stable strength, albeit slightly affected by UA. The benefits of high efficiency and water stability presented the potential of this method in achieving dredged sludge stabilization and resource utilization. This investigation provides informative ideas and valuable insights on implementing advanced bio-geotechnical techniques to achieve efficient stabilization of soft soil, such as dredged sludge.

CO2-sequestering ability of lightweight concrete based on reactive magnesia cement and high-dosage biochar aggregate

Lightweight concrete is widely used in non-structural components of buildings, e.g., partition wall bricks. Most current lightweight concretes engage Portland cement and lightweight aggregates. In this study, lightweight concretes based on reactive magnesia cement (RMC) and high amount of biochar aggregates (up to 508 kg/m3, 61 vol% of the concrete) are developed. The new material demonstrates the ability to sequestrate massive amounts of CO2 from ambient air, and thus has the potential to be used for greener non-structural applications. The CO2 sequestration during curing under high-concentration CO2 (10 %), which is mainly via the RMC carbonation, is determined by acid digestion. The CO2 sequestration during service under ambient CO2 concentration (0.1%, or 1000 ppm), which is via the continued carbonation of RMC and the adsorption of biochar, is determined by monitoring the removal of CO2 in situ; particularly, the CO2 sequestrations by the RMC and the biochar are determined separately. The effect of varying biochar content and CO2 curing time on the overall CO2 sequestering ability of the concrete are studied, together with the variation of the local CO2 sequestration with carbonation depth in the concrete. Based on the experimental results, the new concretes are seen to achieve adequate mechanical properties for non-structural application. They can permanently sequestrate a significant amount of CO2 during the curing phase (0.2–0.3 g per gram RMC), and constantly sequestrate noticeable amounts of CO2 during the service stage (1–12 mg per gram RMC, 1 mg per gram biochar). The incorporation of porous biochar not only decreases the material density, but also improves the RMC carbonation by accelerating CO2 penetration, while the RMC barely influences the biochar adsorption. However, the RMC carbonation ability permanently vanishes with curing age, whilst the biochar adsorption decreases marginally with the curing age.

Autogenous healing of the interface between hollow natural fiber (HNF) and reactive magnesia cement (RMC) matrix

The fiber-matrix interface healing determines the restoration of tensile strength of fiber reinforced cementitious composites (FRCCs). This work first-timely investigates the autogenous healing of debonded interface between hollow natural fiber (HNF) and reactive magnesia cement (RMC) matrix and subsequent tensile strength recovery. HNF-RMC single-fiber specimens are preloaded to induce interfacial debonding, and then conditioned under water-air cycles for healing. The healing-induced recovery of the interfacial properties in the HNF-RMC group are significantly higher than the control PVA-RMC and PVA-PC groups. Tensile test of notched FRCCs demonstrated that the tensile strength of HNF-RMC can be more than doubled after cracking-healing, and its healing efficiency is around 50% higher than that of PVA-PC and PVA-RMC. Based on microstructural characterization in situ and finite element modeling, the increased healing degree is attributed to two new mechanisms related to the special porous microstructure of HNF. First, the lumens and micropores within cell of HNF can be the pathway for CO2 and water penetration, which promotes the formation of healing products (e.g., hydrated magnesium carbonates) within fiber-matrix interface and hence the recovery of chemical and frictional bonds. Second, the healing products formed within lumens caused lateral fiber expansion, and thus prominently enhanced the frictional bond.

Influence of natural fibers on hydration and carbonation of reactive magnesium oxide cement (RMC)

This study offers insights into the influence of cellulose fibers at 0, 0.25, and 0.5 vol% on the hydration and carbonation of reactive magnesium oxide cement (RMC). The cumulative heat increased with the fiber content, attributed to the nucleation and possibly internal curing effects of the fibers. The reinforcing action provided by the fibers also improved the mechanical performance of the air-cured samples, yet the compressive strength under 20% CO2 and 80% RH was maximized at 0.25 vol%. At 0.5 vol%, the contents of brucite and carbonates were reduced due to confinement and crack control, which restricted the growth of brucite and CO2 diffusion. The carbonation phase was mainly poorly crystalline or amorphous, marked by a fused structure and with a thermal decomposition peak at approximately 405 °C. The cellulose fibers with a porous cell wall and cavity provided a pathway for enhanced CO2 diffusion, resulting in concentrated carbonates at the fiber-matrix interface.

Investigation of the mechanical properties of magnesium chloride on magnesium oxide improved kaolin clay

In our study, samples were prepared by mixing 2%, 4%, and 6% MgO doses with the dry weight of kaolin-type low-plastic clay. In each MgO dose, 1% and 2% of the soil weight, respectively, MgCl2 chemicals were added, and all samples were mixed at the optimum water content ratio (16.2%). All components were mixed with a planetary mixer for 10 minutes until homogeneous, and then the mixture was poured to have 25 blows for 5 layers. All samples were cured under room conditions for 3–10 days to be tested on the Unconfined Compression Test. From the results, it was observed that the undrained shear strength of the sample increased as the percentages of MgCl2 and MgO rose. It can be said that the interaction between MgO and MgCl2 contributes to the cementation of the clay, and sorel cement plays a role in the mechanical strengthening of kaolin clay based on its effect on strength development. Extending the curing time also developed the mechanical properties of kaolin clay and improved the hardness of the samples by increasing the elastic modulus. In this way, early failures were attained at early strains, and the ductility of the samples increased. We finally saw that the mixture of MgO and MgCl2 worked well as a building material for kaolin clay. The study also tried to get rid of some of the problems that come up with filling materials used in geotechnical engineering and shoring projects, like swelling, shrinkage, and low mechanical properties.

Interpretable machine learning-based analysis of hydration and carbonation of carbonated reactive magnesia cement mixes

This study explored the influence of different input variables on the hydration and carbonation degree of carbonated reactive magnesia cement (RMC) system by employing six machine learning algorithms. These included support vector machine (SVM), particle swarm optimization-based SVM (PSO-SVM), extreme learning machine (ELM), grey wolf optimizer-based SVM (GWO-SVM), kernel extreme learning machine (KELM), and extreme gradient boosting (XGBoost). The followed approach enabled the deep learning of the relevant database to achieve parameter prediction. Two feature analysis methodologies, i.e. partial dependence plot (PDP) and SHapley Additive exPlanations (SHAP), were applied to uncover the operating laws underpinning the black box operation characteristics of machine learning models. Results revealed that GWO-SVM and XGBoost outperformed all other models in predicting the hydration and carbonation degree of the complete database set (R2 of the total database set was 0.9470/0.9775 and 0.9663/0.9727 for hydration and carbonation degree, respectively). Factors such as carbonation duration, CO2 concentration, pre-curing temperature, and w/b directly influenced the degree of hydration and carbonation. Among them, carbonation duration and CO2 concentration were two of the most influential factors, resulting in the promotion of brucite consumption and accelerating the formation of carbonation products.

Influence of nesquehonite seeds on hydration and carbonation of reactive magnesia cement

Among all carbonation products of reactive magnesia cement (RMC), nesquehonite exhibited the highest CO2 amount of sequestration per molar. Inducing the nesquehonite formation may improve the CO2 sequestration capacity of RMC. In this paper, nesquehonite seeds were introduced to promote the formation of nesquehonite in RMC. The performances of RMCs with 0%, 0.5%, 1%, 1.5% and 2% nesquehonite seeds were studied and compared with that of RMC mixed with hydromagnesite seeds. It was found that the hydration of RMC could be facilitated by nesquehonite seeds, resulting in reduced setting times. The nucleation effect of nesquehonite seeds was demonstrated, resulting in increased nesquehonite formation and carbonation degree. Nesquehonite seeds combined with hydration agent can further promote the compressive strength of RMC through forming more amounts of nesqeuhonite crystals and amorphous hydrated magnesium carbonates. Compared with the hydromagnesite seeds, the nesquehonite seeds showed a more significant increase in the CO2 sequestration capacity of RMC.