Magnesia Cement Research Articles

Experimental and theoretical research on flexural performance of truss reinforced concrete two-way composite slab with prefabricated baseplate

This paper presents experimental and theoretical research on a novel truss reinforced composite concrete two-way slab using full-scale testing. In contrast to conventional composite slabs, the precast concrete layer with a thickness greater than 60 mm is replaced by a high toughness prefabricated inorganic baseplate with a thickness of 12 mm. The baseplate options include glass fiber and magnesium cement board, as well as fiber cement board. Four full-scale two-way slabs were subjected to eight points simulated uniform vertical loads, comprising one conventional truss reinforced concrete two-way slab (RCS) and three truss reinforced concrete composite two-way slabs with prefabricated baseplates (RCSB). The test results indicate that the failure mode of the truss reinforced concrete composite two-way slab with baseplate is similar to that of a common truss reinforced concrete two-way slab. However, a rectangular yielding region appears at the central part, instead of a single yielding line. The cracking load and ultimate load are increased due to the effect of prefabricated baseplate. Moreover, the beneficial effect of glass fiber and magnesium cement board is superior to that of fiber cement board. Finally, the calculation methods for determining the cracking load and ultimate bearing capacity of truss reinforced concrete composite two-way slabs with baseplates were improved, and the calculated results are in good agreement with experimental data.

PROPERTIES AND CHARACTERIZATION OF MAGNESIUM OXYCHLORIDE CEMENT AS CARBON CAPTURE MATERIAL

Greenhouse gas emissions produced by steam-powered electric plants can trigger damage to the atmosphere and increase the average surface temperature below it, resulting in global warming as a manifestation of the operation of power plants. A material is needed to capture carbon dioxide (CO2) gas produced by the power plant. Magnesium oxychloride (MOC) cement, commonly called Sorel cement, has the potential to be used as a carbon capture material. MOC is synthesized from magnesium oxide (MgO), magnesium chloride (MgCl2), and water (H2O). This study aimed to find the optimum ratio of MgO:MgCl2:H2O to produce the MOC with highest mechanical properties ranged from 1:1:1, 2:1:1, and 3:1:1. To determine the performance of the resulting MOC, physical, mechanical, X-ray diffraction (XRD), and scanning electron microscope (SEM) characterization tests were carried out. MOC with the highest mechanical properties was exposed to a high CO2 gas environment to determine its carbon capture performance. The mechanical testing shows that the best ratio of MgO:MgCl2:H2O was 3:1:1. This produces a hardness value of 43 VHN, a compressive strength of 57 MPa, a flexural strength of 46 MPa, and a modulus of elasticity of 2 GPa. The MOC 3:1:1 shows a CO2 gas capture effectiveness of 36% after 7 days, proven by XRD and SEM. The results of the tests carried out show that MOC has the potential to reduce carbon emissions produced by the steam-powered electric plant industry.

Performance of Pozzolan-Based Reactive Magnesia Cement Mixes against Sulphate Attack

Reactive magnesia cement (RMC) has gained interest due to its lower production temperatures when compared to Portland cement. In this study, the performance of pozzolan-based RMC concrete samples against sulphate attack was examined. Cube samples, after being removed from their moulds, were stored in a CO2-rich environment to gain compressive strength. Information obtained from XRD showed the formation of Mg carbonates in different forms. The use of fly ash and slag in large volumes reduces the environmental impact of concrete, but the use of these components have been found to greatly affect the formation of Mg carbonates in RMC mixes. This is mainly due to their filler effects. The coexistence of Ca- and Mg-based products was found in the slag-RMC mixes. The concrete samples based on RMC underwent mass and strength losses when stored in a MgSO4 solution for up to 12 weeks. The removal of Mg from the microstructure of these samples was confirmed using SEM analysis. The use of the most widely used pozzolans at 50% by weight of the binder greatly affected the carbonation mechanism of the RMC mixes. This finding suggests that they should be limited in the design of Mg-based products that harden under CO2-rich conditions.

Influence of compaction direction on selected thermal and moisture properties of a lightweight composite based on magnesium binder and organic filler

An alternative binder in thermal insulation composites based on hemp shives is magnesium cement. It provides higher mechanical strength of the composite in comparison to the lime binder. Thanks to this, it is possible to reduce the amount of binder in relation to the shives, and as a result, obtain a lower density and better thermal insulation parameters. The process of compacting the composite mixture determines many of its properties. The longitudinal shape of the shives causes that during compaction they are arranged mainly perpendicular to the direction of compaction. The unidirectional course of the fibers in the shives determines the anisotropic nature of both the shives and the composite. The article presents the results of tests of thermal conductivity and capillary rise of the compacted composite in the direction perpendicular and parallel to the heat flux and moisture transport. A composite with a low binder content, characterized by a density of about 250 kg/m3, was tested. The direction of the mix compaction had an impact on the differences in the obtained results. This phenomenon can be used, for example, in the production of blocks or other prefabricated elements, using the appropriate direction of compaction depending on the expected properties and applications of the composite.

Comparison of magnesium oxysulfate (MOS) cement and reactive magnesia cement (RMC) under different curing conditions: Physical properties, mechanisms, and environmental impacts

The potential of MgO cement as a low-carbon alternative is widely acknowledged. However, there has been no systematic comparison of the physical properties, mechanism and environmental impact between reactive MgO cements (RMC) and MOS Cement. This study investigated the hydration and carbonization processes of RMC and MOS cement within the range of reactive MgO/MgSO4 molar ratio from 7 to 350. Results showed that different curing conditions had different impacts on RMC and MOS. Specifically, the density of both materials exhibited an increase, but the strength of RMC was enhanced while that of MOS decreased. Although the carbonate and 517 phases can coexist in MOS specimens under carbonization curing, their combination resulted in a notable strength decrease. Carbon footprint analysis showed that RMC cement had certain advantages in carbon emissions over the entire life cycle. Overall, these research outcomes provided valuable guidance for the design of RMC and MOS cement.

Pore structures and interfacial properties between hydrated magnesia carbonates-modified recycled aggregate and reactive magnesia paste

To further increase the sustainability of reactive magnesia cement (RMC) concrete while not compromising their overall strength, this study used the carbonation technique to pretreat recycled aggregates during the preparation of RMC-based samples, and their strength, pore structures and carbonation degrees were assessed by the compression test, XRD, TG-DTG, FTIR and X-CT. Greater carbonation degrees are considered to contribute to the strength improvement due to the formation of interconnected and well-developed carbonates and reduced porosity in RMC-based samples. However, this study shows that lower w/c ratios, which greatly refined their pore structures, favor the improved mechanical performance of RMC-based samples, albeit their carbonation degrees are lower. In addition, the much weaker correlation between the carbonation degree and strength of RMC-based samples could also be explained by the formation of different types of hydrated magnesium carbonates (HMCs), where samples containing nesquehonite (∼needle-like HMCs), albeit their carbonation degrees could be lower, reveal better strength than samples with hydromagnesite (∼rosset-like HMCs). Therefore, using pretreated recycled aggregates in RMC-based samples delayed their inside CO2 diffusion when they were cured in CO2, which slowed down their strength development, but when cured in air, RMC-based samples containing pretreated recycled aggregates reveal better strength owing to their more compacted pore structures. This study could also prove that CO2 diffusion among RMC-based samples could be through the pores within ITZs instead of capillary pores resulting from water.

Influences of engineering spoil on the properties and microstructure of 3D printable magnesium cement

Using magnesium cement to solidify engineering spoil (ES) is an eco-friendly option for disposing of solid waste. This paper proposes a novel type of magnesium cement for 3D printing (MC-3DP) using ES as an additive to magnesium oxychloride cement (MOC). The effect of the ES on the mechanical properties and water resistance of the MC-3DP paste and mortar were investigated. The MC-3DP paste was subjected to a hydration heat test and microscopic tests (X-ray diffraction and scanning electron microscopy). The 3D printing properties of the MC-3DP paste were evaluated, including the open time, flowability, extrudability, buildability, and hardened properties. The results showed that the ES improved the MC-3DP’s mechanical properties and water resistance. The results of the hydration heat test, XRD analysis, and SEM analysis revealed that the addition of ES did not result in new hydration products in the MC-3DP paste. Instead, the ES served as a filler and improved the performance of MC-3DP. Additionally, the ES addition significantly improved the printing properties of the MC-3DP paste, and the degree of improvement increased with the ES content. Our results provide new insights into developing methods to upcycle ES.

Enhanced autogeneous self-healing of MgO blended composites incorporating with silica fume

Many studies have been conducted on the autogeneous self-healing either using pozzolan or MgO approaches. It is well accepted that MgO adversely affects strength development particularly at an early age. Nevertheless, MgO is well accepted mineral admixture that has a promising self-healing ability for cement-based composites. Numerous efforts have been conducted in overcome the shortcoming of the strength of cement composites due to MgO. Various findings and studies have shown that incorporating MgO with pozzolans can be detrimental to the strength of cement composites; this includes any cement-based material that is incorporated with MgO. Thus, it is necessary to evaluate an appropriate blended cements in combination with MgO that possesses a self-healing ability without compromising its strength development. The study evaluated autogenous self-healing of magnesium oxide (MgO) blended mortar containing silica fume. 5% silica fume was applied into 5%MgO blended cements and for systematic analysis, effect of each single binder was also evaluated independently. A single crack was fabricated at 7-day and then, the healing ability was evaluated based on flexural strength test, crack sealing and microstructural analysis. Furthermore, ANOVA was employed to evaluate the significance of enhancement method to the MgO blended cement. The finding indicated that silica fume slightly enhanced self-healing of mortar. Similarly, statistical analysis confirmed that the autogenous self-healing of MgO cement is more pronounced with the addition of silica fume.

A novel bio-carbonation method of reactive magnesia with urea pre-hydrolysis for geomaterial stabilisation

This study proposes a novel bio-carbonation method of reactive magnesia cement (RMC) with urea pre-hydrolysis for geomaterial stabilisation. Urea pre-hydrolysis in the bacterial solution before mixing with RMC produces more carbonate and ammonia, facilitating the RMC bio-carbonation to form more hydrated magnesia carbonates (HMCs), the dominant product that contributes to strength gain. The effect of urea pre-hydrolysis on the engineering performance of bio-carbonated samples is investigated through a series of RMC bio-carbonation geomaterial stabilisation tests with various pre-hydrolysis times and urea concentrations. The results show that the proposed method can improve material utilisation, enhance the RMC bio-carbonation reaction and promote geomaterial stabilisation performance. The relationships between the unconfined compressive strength (UCS) of bio-carbonated samples and the amount of HMCs are studied using a proposed indicator, the degree of carbonation (DC). However, the strength increment is not monotonically related to the amount of HMCs. The optimal pre-hydrolysis time is 6–12 h for bio-carbonated samples with UCS up to 3·79 MPa, and the maximum UCS increase in the samples is up to 404·42%. The critical DC values are in the range 0·23–0·36 with varying urea concentrations. The proposed method has implications for the design of bio-carbonated RMC in field applications.

Recovery of ultra-high purity reactive magnesia from reject brine and its comparison with commercial magnesia

CO2 emissions and energy consumption associated with ordinary Portland cement production have increased the urgency for the development of alternative construction materials. Reactive magnesia cement (RMC) has been widely studied in the recent years due to the lower calcination temperature used during its production and its ability to permanently sequester CO2. In addition to the calcination of magnesite, reactive MgO, the main component of RMC, can also be synthesized from reject brine, which is rich in Mg2+. However, the presence of other components such as calcium in reject brine leads to the precipitation of other mineral phases together with Mg(OH)2, thereby reducing the purity of the final product. With the goal of improving the purity and yield of MgO synthesized at the end of this process, this study proposed a selective precipitation approach under a controlled pH. An optimum condition was determined for the synthesis of magnesium oxalate dihydrate with an ultra-high purity of 99.6 % and a high magnesium recovery rate of 94.1 %. Reactive MgO with a specific surface area of 30.2 m2/g was obtained after the calcination of the synthesized magnesium oxalate dihydrate at 700 °C for 2 h, which was higher than some of the commercially available MgO powders.

Carment: Magnesium Cement From Glass Waste As A Solution To The Cement Industry's Carbon Emission Problems

Carment: Magnesium Cement From Glass Waste As A Solution To The Cement Industry's Carbon Emission Problems

Dredged marine soil stabilization using magnesia cement augmented with biochar/slag

Dredged marine soils (DMS) have poor engineering properties, which limit their usage in construction projects. This research examines the application of reactive magnesia (rMgO) containing supplementary cementitious materials (SCMs) to stabilize DMS under ambient and carbon dioxide (CO2) curing conditions. Several proprietary experimental tests were conducted to investigate the stabilized DMS. Furthermore, the carbonation-induced mineralogical, thermal, and microstructural properties change of the samples were explored. The findings show that the compressive strength of the stabilized DMS fulfilled the 7-d requirement (0.7–2.1 MPa) for pavement and building foundations. Replacing rMgO with SCMs such as biochar or ground granulated blast-furnace slag (GGBS) altered the engineering properties and particle packing of the stabilized soils, thus influencing their performances. Biochar increased the porosity of the samples, facilitating higher CO2 uptake and improved ductility, while GGBS decreased porosity and increased the dry density of the samples, resulting in higher strength. The addition of SCMs also enhanced the water retention capacity and modified the pH of the samples. Microstructural analysis revealed that the hydrated magnesium carbonates precipitated in the carbonated samples provided better cementation effects than brucite formed during rMgO hydration. Moreover, incorporating SCMs reduced the overall global warming potential and energy demand of the rMgO-based systems. The biochar mixes demonstrated lower toxicity and energy consumption. Ultimately, the rMgO and biochar blend can serve as an environmentally friendly additive for soft soil stabilization and permanent fixation of significant amounts of CO2 in soils through mineral carbonation, potentially reducing environmental pollution while meeting urbanization needs.

Effect of printing strategies on the properties of product in selective Sorel cement activation

PurposeParticles bed binding by selective cement activation (SCA) method is a computer-aided manufacturing (CAM) technique used to produce cementitious elements. A computer-aided design file is sliced to generate G-codes before printing. This paper aims to study the effect of key input parameters for slicer software on the final properties of printed products.Design/methodology/approachThe one factor at a time (OFAT) methodology is used to investigate the impact of selected parameters on the final properties of printed specimens, and the causes for the variations in outcomes of each variable are discussed.FindingsFiner aggregates can generate a more compact layer, resulting in a denser product with higher strength. Fluid pressure is directly determined by voxel rate (rV); however, high pressures enable better fluid penetration control for fortified products; for extreme rVs, residual voids in the interfaces between successive layers and single-line primitives impair mechanical strength. It was understood that printhead movement along the orientation of the parts in the powder bed improved the mechanical properties.Originality/valueThe design of experiment (DOE) method assesses the influence of process parameters on various input printing variables at the same time. As the resources are limited, a fractional factorial plan is carried out on a subset of a full factorial design; hence, providing physical interpretation behind changes in each factor is difficult. OFAT aids in analyzing the effect of a change in one factor on output while all other parameters are kept constant. The results assist engineers in properly considering the influence of variable variations for future DOE designs.

Investigation of the viscoelastic evolution of reactive magnesia cement pastes with accelerated hydration mechanisms

Viscoelasticity of reactive magnesia cement (RMC) pastes containing 3 different hydration agents (HCl, Mg(CH3COO)2 and MgCl2) were investigated. Amplitude sweep, frequency sweep and time sweep of RMC pastes were examined within 3 h of hydration. Time-dependent evolution of storage modulus, loss modulus, phase angle, and shear stress were recorded. Measurements of pH, isothermal calorimetry, XRD, TG-DTG and FTIR were used to analyze hydration reaction and products. Addition of hydration agents (HAs) accelerated the growth rate of storage modulus/loss modulus over time. MgCl2 demonstrated the greatest acceleration influence, also reflected in non-destructive structural build-up and buildability related to 3D printing applications. Addition of MgCl2 and HCl advanced the initial setting time of RMC pastes to 100–110 min, during which yield stress reached maximum, and decreased afterwards. Within 3 h of hydration, pastes containing MgCl2 revealed lowest pH, highest heat release and brucite concentration. HAs inclusion precipitated brucite away from MgO particles in the bulk solution, creating a bridge between MgO particles and enabling denser microscopic network structure.

放射光回折システムの高機能化と機能性材料の開発研究

Driven by improvement of the computer speed and tremendous efforts of crystallographers and equipment manufacturers, X-ray structure analysis has recently become relatively easy and requires no specialized knowledge. On the other hand, synchrotron radiation diffraction experiments have mainly aimed at advanced structural analysis, including electron density analysis, taking advantage of stable and intense X-rays. In recent years, demand for the use of the facility in the materials field has increased, but researchers unfamiliar with synchrotron radiation experiments have felt difficulty in use. Based on my experience in developing conventional diffractometers and software at the equipment manufacturer where I worked after obtaining my degree, I have promoted the development of advanced synchrotron radiation X-ray diffraction systems at SPring-8, a large synchrotron radiation facility. In particular, I have been responsible for the single crystal structure analysis beamline（BL02B1）and the powder diffraction beamline（BL02B2）, which have a wide range of user groups and diverse requirements for instrumental performance, and engaged in instrument development. In addition, I have also worked on structural analysis of functional materials and clarified their structure-function relationships. Among them, I introduce fruitful results on generation process of magnesia cement and design of spin crossover Fe（II）complexes. I believe that such upgrading of synchrotron radiation diffraction systems and development research of functional materials could not be performed without hardware and software knowledge which I learned at the equipment manufacturer.

Geomechanical performances of geocell reinforced retaining wall backfilled with magnesia-based cement stabilized marine fill

Cement-stabilized soil retaining wall structures are becoming increasingly popular for high-speed railway lines. However, the widely used Portland cement is heavily associated with carbon dioxide (CO2) emissions. Additionally, the rising cost and scarcity of sand traditionally used as fill material is becoming a concern. Besides, the geomechanical performances of the cement-stabilized soil retaining walls using three-dimensional (3-D) finite element method (FEM) numerical analysis have seldom been investigated. To address these issues, this study investigates the geomechanical performances of geocell-reinforced soil (GRS) backfilled with magnesia-based cement-stabilized marine fill using the nonlinear stress-strain relationship and 3-D FEM models as an alternative to the traditional earth GRS walls. The study finds satisfactory results regarding stability, deformation, and settlement. Only nominal facing reinforcements may be required as the magnesia cement mechanically stabilizes the fill. Moreover, the strength and stiffness properties improve with increased curing duration. The safety factors and observed displacements were within acceptable limits. However, the critical region for the cement-stabilized marine fill GRS wall showing a rupture zone was identified at the toe of the structure. Finally, the study developed a load-displacement model for settlement predictions and uncertainty interpretations, and explained the strength development and deformation mechanisms. The results suggest that cement-stabilized soil retaining walls using magnesia-based cement could be a viable alternative to traditional earth GRS walls, while mitigating environmental concerns and reducing costs.

Investigation of mechanical and insulation properties of Sorel cement binding light concrete

In this study, some mechanical and insulation properties of light concrete with Sorel cement were investigated by using Sorel cement, which is an alternative to cements used in the market. In addition, samples were produced by substituting some additives separately into the Sorel cement mixtures in order to evaluate the waste materials in the inactive state and to improve some of the mechanical and insulation properties of the Sorel cemented samples. In this study the flexural and compressive strengths, thermal conductivity, thermal resistance, ultrasound transition velocity, unit weight, water absorption and apparent porosity, bulk expansion, alkali silica reaction (ASR), surface area analysis (BET) and microstructures of samples were investigated. The reference samples were Sorel cement (SC), the other samples were made of mixtures of SC, pumice (P), air-entraining additive (AEA), Afşin Elbistan fly ash (AEFA), wood and corncob shavings (WS, CS). According to the findings, it can be said that while the flexural and compressive strength of the lightweight aggregate samples decreased compared to the reference sample, there were improvements in heat and sound insulation properties. The determined values differed according to the type and ratio of lightweight aggregates. It was observed that the increase in the ambient temperature of the SC samples had a positive effect on the flexural and compressive strength values up to 100 °C, while it caused a decrease in the strength values after a certain temperature. It was seen that the strength values of SC samples kept in water decreased due to the cracks formed. The results showed that the samples produced with Sorel cement had high strength. Sample strengths produced with pumice used as aggregate are higher than those with wood chips and corncob sawdust. It was determined that Sorel cement could not be used together with AEFA because the samples were shattered. No incompatibility was observed with AEA and WS additives either; however, the strength value was low in those with CS added.

Effect of Low Nesquehonite Addition on the Hydration Product and Pore Structure of Reactive Magnesia Paste.

Reactive magnesia cement is considered an eco-efficient binder due to its low synthesis temperature and CO2 absorption properties. However, the hydration of pure MgO-H2O mixtures cannot produce strong Mg(OH)2 pastes. In this study, nesquehonite (Nes, MgCO3·3H2O) was added to the MgO-H2O system to improve its strength properties, and its hydration products and pore structure were analyzed. The experimental results showed that the hydration product changed from small plate-like Mg(OH)2 crystals to interlaced sheet-like crystals after the addition of a small amount of Nes. The porosity increased from 36.3% to 64.6%, and the total pore surface area increased from 4.6 to 118.5 m2/g. At the same time, most of the pores decreased in size from the micron scale to the nanometer scale, which indicated that Nes had a positive effect on improving the pore structure and enhancing the compressive strength. Combined with an X-ray diffractometer (XRD), a Fourier transform infrared spectrometer (FTIR), and a simultaneous thermal analyzer (TG/DSC), the hydration product of the sample after Nes addition could be described as xMgCO3·Mg(OH)2·yH2O. When Nes was added at 7.87 and 14.35 wt%, the x-values in the chemical formula of the hydration products were 0.025 and 0.048, respectively. These small x-values resulted in lattice and property parameters of the hydration products that were similar to those of Mg(OH)2.

Unlocking the role of recycled aggregates in the performance enhancement and CO2 capture of reactive magnesia cement formulations

The use of recycled aggregates (RCAs) could further enhance the sustainability of reactive magnesia cement (RMC) formulations, but the performances of RMC-RCA are still unknown to researchers. Therefore, in this study, the strength development of CO2-cured RMC-RCA was explored for the first time, and the strength variation among groups was further interpreted by microstructural analyses. The initial results show that compared with samples with natural aggregates (NAs), a 28 d strength boost (i.e., 37 vs. 15 MPa) in RMC-RCA can be observed. The strength improved in RMC-RCA could be related to its refined microstructures, ITZs and larger carbonation depths, which resulted from the easiness of CO2 penetration within samples. Then the presence of porous ITZs in RCA contributes to better CO2 diffusion, as described in the proposed revised CO2 diffusion model. Overall, while enabling a pronounced CO2 capture potential of RMC concrete, this preliminary study could pave the path for the upcycling of RCAs in RMC concrete on a large scale.

Understanding the role of seeds in reactive magnesia cement (RMC) formulations

AbstractNucleation effects of seeds in reactive magnesia cement (RMC) systems have been reported, but this process has never been directly observed. In this study, different types and contents of seeds were introduced in RMC formulations. Results show that seeded RMC samples revealed accelerated hydration/carbonation that led to their more rapid strength development, and the use of magnesite outperformed other seeds given their overall performances, as explained by their more homogenous microstructures. Further, in the model solution, the amount of Mg2+ ions adsorbed onto seeds particles continuously increased with the increment of Mg2+ concentrations, confirming the nucleation effects of seeds in RMC formulations directly, and seeds surfaces revealed a much higher affinity for Mg2+ ions than other ions due to their acid‐base interactions. Therefore, the use of seeds could act as accelerators that shorten the curing period of RMC‐based concrete products on a large scale.