Reactive MgO Research Articles

Hydration and microstructural characteristics of MgO in the presence of metakaolin and silica fume

The characteristics of the hydration products and microstructural development of reactive MgO in the presence of metakaolin (MK) and silica fume (SF), along with thermodynamic modelling, are presented in this paper. The hydration products were characterized at different ages from 1 to 90 days. The hydration of MgO-MK mixes showed the formation of hydrotalcite like phase along with brucite and M-S-H. Coexistence of M-S-H and hydrotalcite was predicted from thermodynamic modelling in a system comprising of MgO, SiO2 and Al2O3. The voluminous nature of the hydration products helped in the development of a low porosity microstructure in MgO-MK mixes. The effects of a denser microstructure were evident from higher compressive strength across all ages and mix compositions compared to MgO-SF mixes. The bound water content of the hydration products showed a reasonable relationship with the compressive strength for both SF and MK mixes.

Using MgO activated slag and calcium bentonite slurry to produce a novel vertical barrier material: Performances and mechanisms

Slag-cement–bentonite (SCB) slurry has been widely used for the construction of vertical cutoff walls to restrain the movement of groundwater at contaminated sites. However, the conventional cement-based slurry needs a long time to evolve satisfactory performance along with a relatively high environmental load. This paper proposes an innovative material for the self-hardening slurry system, consisting of reactive MgO, slag, bentonite and lots of water. The properties of fresh slurry, unconfined compressive strength (UCS) and permeability of the MgO activated slag and bentonite (MASB) slurry are investigated in comparison with SCB slurry. The results indicate that compared with SCB slurry, MASB slurry with appropriate proportions has comparative fresh properties, but possesses higher UCS and much lower hydraulic conductivity (close to 1.0 × 10−10 m/s) at a later age. A massive formation of expansive hydration products (hydrotalcite phases) could satisfactorily fill in the voids of matrix, leading to a dense microstructure which is responsible for the excellent mechanical and penetrative performance of MASB slurry. The overall findings from this study well demonstrate that the developed MASB slurry holds great potential as a novel, eco-friendly and cost-effective material in the construction of vertical cutoff walls.

Investigation of chloride penetration in carbonated reactive magnesia cement mixes exposed to cyclic wetting–drying

The effect of chloride attack on carbonated reactive MgO cement (RMC) samples containing fly ash (FA) and ground granulated blast-furnace slag (GGBS) under cyclic wetting and drying was studied. Porosity, sorptivity and chloride profile observations were carried out in parallel to the XRD, TGA and SEM analyses performed before and after exposure. Inclusion of SCMs increased the resistance of RMC samples by lowering the porosity and leading to the formation of various phases such as bischofite, hydrotalcite and calcite, in addition to Mg-carbonates. Mg-carbonate phases such as hydromagnesite and artinite remained relatively stable, whereas a small reduction in nesquehonite content was observed after exposure. Resulting formulations presented improved durability and lower environmental impacts.

Performance of Mortars with Commercially-Available Reactive Magnesium Oxide as Alternative Binder.

This paper intends to analyze the performance of mortars with reactive MgO, as a sustainable alternative to cement. Six different MgOs from Australia, Canada, and Spain were used in the production of mortars as partial substitutes for cement, namely 5%, 10%, 15%, 20%, and 25% (by weight). MgOs with different levels of reactivity were used to analyze its influence on the performance of MgO mortars. In order to evaluate the mechanical performance of these mortars, compressive strength, flexural strength, dynamic modulus of elasticity, and ultrasonic pulse velocity tests were performed. Compressive strength tests showed that the use of 25% reactive MgO can cause a decrease of this property of between 28% and 49%. The use of reactive MgO affected the other mechanical properties less. This paper also intends to analyze the durability performance of mortars with reactive MgO. To that effect, water absorption by capillarity was assessed. In this research, the effect of using MgO on the shrinkage was also analyzed. It was found that shrinkage may decrease by more than a half in some cases.

Use of microbial carbonation process to enable self‑carbonation of reactive MgO cement mixes

The low hydration and carbonation of reactive MgO cement (RMC) under ambient conditions causes prolonged setting and low compressive strengths (~4 MPa). This study proposed a unique technique which led to the enhancement of the hydration and carbonation processes via the synergistic combination of microbial carbonation process (MCP) with a hydration agent (HA) that enabled the self‑carbonation of RMC-based mixes without using of any special curing environments. Through hydrolysing urea (CO(NH2)2) using ureolytic bacteria, CO32− ions were produced to facilitate the carbonation of dissolved Mg2+ ions to form hydrated magnesium hydroxy carbonates (HMHCs). The self‑carbonation of RMC enabled by the MCP resulted in formation of brucite with a poor crystallinity and its rapid conversion into HMHCs, which improved the setting time and compressive strength of RMC-based samples. The simultaneous use of MCP with 2 M urea and HA revealed HMHCs with improved morphologies, resulting in the highest compressive strength (~15 MPa).

Mechanical and microstructural changes in reactive magnesium oxide cement-based concrete mixes subjected to high temperatures

This study investigated the mechanical, microstructural, and chemical changes in reactive MgO cement-based concrete cured under ambient and accelerated carbonation conditions, followed by exposure to high temperatures. The compressive strength of the ambient-cured samples increased from 10 to 30 MPa when subjected to up to 200 °C, induced by increased hydration of the remaining MgO. The accelerated formation of brucite at 50 °C also enhanced the compressive strength of the carbonated samples (58 vs. 65 MPa). A relatively stable performance (~56 MPa) was observed at temperatures ranging between 100 and 300 °C for the carbonated samples, associated with additional formation of brucite and transition of nesquehonite and hydromagnesite to artinite. The hydrated magnesium carbonates (HMCs) forming around brucite acted as barriers and delayed its dehydroxylation. The decomposition of brucite and HMCs at 400 °C caused a porous microstructure and a low residual strength (5–8 MPa) in both the ambient-cured and carbonated samples.

Urolithin A alleviates advanced glycation end-product formation by altering protein structures, trapping methylglyoxal and forming complexes.

Urolithin A (UroA) is a first-in-class natural compound derived from the gut microbiota-derived metabolites of ellagitannins. This research for the first time evaluates the mechanisms of UroA inhibiting advanced glycation end-product (AGE) formation by fluorescence spectroscopy, molecular docking, liquid chromatography (LC) and LC-Oribitrap tandem mass spectrometry. The results indicated that UroA exhibited a good suppression effect on the formation of AGEs in human serum albumin (HSA)-fructose and HSA-methylglyoxal (MGO) systems. Further mechanism analysis revealed that UroA alleviated AGE formation by changing the conformational structure of HSA, trapping reactive MGO to form mono-MGO-UroA complexes, promoting the exposure of chromophores to a more hydrophobic micro-environment, and forming stable UroA-HSA complexes. UroA bound with HSA in an equimolar manner, the binding was an exothermic spontaneous process, subdomain IIIA was the preferred binding pocket, and hydrogen bonding, hydrophobic interactions and van der Waals forces were the major interaction forces. The number of glycation sites detected in glycated HSA was reduced by 1 and 2, respectively, when 181.82 and 363.64 μM UroA was added. These could provide an insight into the mechanism of UroA inhibiting HSA glycation, and highlight its value as a promising glycation inhibitor in the prevention of diabetic complications.

The engineering properties and reaction mechanism of MgO-activated slag cement-clayey sand-bentonite (MSB) cutoff wall backfills

An innovative cutoff wall backfill consisting of reactive MgO, ground granulated blast furnace slag (GGBS), bentonite and local clayey sand (MSB) was developed recently for land remediation applications. This paper investigates the engineering characteristics (e.g. strength and permeability) and reaction mechanisms of the MSB backfills with various MgO-activated GGBS (i.e., the binder) and bentonite contents. A series of analytical techniques are employed to identify the hydration products in this complex system. The engineering properties are tested via the unconfined compressive strength (UCS) test and flexible-wall permeation test. Results show that UCS and dry density decrease with increasing bentonite content, while the opposite trends are observed when increasing the binder content. The UCS values increase with curing time and become plateaued after ∼90 days. Meanwhile, the hydraulic conductivity (k) decreases distinctly with the increase of the binder content and bentonite content. All backfills reach UCS of >100 kPa UCS and k <10−8 m/s at 28 days while curing for 90 days leads to increase of UCS by >1.5 times and reduction of k by nearly one order of magnitude. The major hydration products of MSB backfills are identified as hydrotalcite-like phases (Ht), calcium silicate hydrates (C-S-H), monosulfate (AFm) and portlandite (CH). The hydration products, binding adjacent soil particles, filling pores, together with the swelling of bentonite, contribute to the mechanical performance and impermeability of the backfills.

Production of reactive magnesia from desalination reject brine and its use as a binder

This study investigated the feasibility of producing reactive MgO cement from reject brine obtained from a desalination plant and evaluated its use as a binder in comparison to a commercial MgO. The mechanical performance of the samples cured under carbonation conditions for up to 28 days were further supported by x-ray diffraction (XRD), thermogravimetric analysis/differential scanning calorimetry (TGA/DSC) and field emission scanning electron microscopy (FESEM) analyses. Samples involving synthetic MgO revealed higher strengths than those with commercial MgO, in line with the higher reactivity of the former. The increased dissolution of synthetic MgO led to its enhanced hydration and carbonation, resulting in samples with denser structures and improved performances. The findings highlighted issues regarding the large-scale production of MgO from reject brine and CO2 emissions of this process. The major environmental impact was associated with the production of the alkali base (NaOH), which could be improved via the identification of sustainable alkali sources used during production. Overall, the production of MgO from reject brine can save natural resources and pave the way for the sequestration of CO2 as stable carbonates in cement-based mixes.

Effect of reactive MgO on hydration and properties of alkali-activated slag pastes with different activators

Activator type significantly affects the properties of alkali-activated slag (AAS) cement. Reactive MgO may have different effects on AAS cement activated with different activators. Four activators, sodium hydroxide (NaOH), water glass (WG), sodium carbonate (Na2CO3) and sodium sulfate (Na2SO4) were used in the present paper. The effect of reactive MgO on the fluidity, setting time of AAS paste and the compressive strength of AAS mortar was studied. The hydration process was assessed with pH and hydration heat. Microstructure and hydrates were also characterized by XRD, SEM and EDS. The results show that the addition of reactive MgO decreases the fluidity and setting time of AAS paste regardless of activator type. In NaOH activated slag, the compressive strength decreases with the increase of reactive MgO. While in the other three activators, there exists an optimal reactive MgO content of about 4%–6%. Now the compressive strength is higher. Reactive MgO increases the pH, heat evolution rate and cumulative hydration heat of AAS cement. Hydrotalcite and C-(A)-S-H gel are the main hydration products. More hydration products are promoted by reactive MgO, which results in the densification of AAS matrix. The above changes due to reactive MgO are especially remarkable for Na2CO3 and Na2SO4 activated AAS cement. AFt is more likely to be formed than hydrotalcite in Na2SO4 activated slag and reactive MgO enhances this trend. Reactive MgO is especially suitable for Na2CO3 and Na2SO4 activated AAS cement. It can accelerate the hydration, adjust the fluidity and setting time, and improve the mechanical properties to a reasonable degree.

Enhancing the performance of MgO-activated slag-fly ash mixes by accelerated carbonation

This study focused on the development of reactive MgO (RM) activated-GGBS binders containing fly ash (FA). Performance of these binders was aimed to be improved by enhancing the hydration of RM and dissolution of GGBS and FA via high temperature pre-curing (HTPC); and conversion of unreacted phases into carbonates via carbonation. Spherical FA particles mitigated inter-particle surface frictions and improved flow. Although the use of HTPC accelerated the hydration of MgO, rapid precipitation of brucite hindered the dissolution of GGBS and FA and formation of associated hydration products. Transformation of RM into hydrated magnesium carbonates (HMCs) under carbonation led to significant improvements in sample performance via the pore filling effect and binding strength provided by HMCs, despite the degradation of ettringite and C-(A)-S-H during carbonation. Inclusion of 12 % FA resulted in comparable strengths to the control sample, highlighting the feasibility of incorporating FA within RM activated-GGBS samples without compromising performance.

Improving the carbonation resistance of Na2CO3-activated slag mixes via the use of reactive MgO and nucleation seeding

When exposed to carbonation, Na2CO3-activated slag (SCAS) concrete demonstrated 53% mass loss and 57% reduction in compressive strength due to the decalcification of C-(A)-S-H. Improvements in the carbonation resistance of SCAS mixes via the inclusion of hydromagnesite seeds (S) and reactive MgO (M) were reported in this study. The conversion of MgO into hydrated magnesium carbonates (HMCs) and the additional formation of hydrotalcite were observed in the presence of these additives. HMCs contributed to the binding network and limited the diffusion of CO2 into the sample. The decalcification of C-(A)-S-H was retarded via the absorption of CO2 in hydrotalcite, producing huntite. These changes in the reaction kinetics of samples involving M and S enabled the retention of hydration products and formation of additional carbonation products, leading to denser microstructures and ~40% increase in compressive strength after carbonation, which was ~10 times higher than the control sample (58 vs. 6 MPa).

Influence of CO2 concentration on the performance of MgO cement mixes

This paper investigated the influence of different CO2 concentrations on the microstructural and mechanical development of reactive MgO cement (RMC) concrete. Combination of various analyses revealed the enhancement of hydrated magnesium carbonate (HMC) phases with relatively superior micro-mechanical properties as the CO2 concentration increased from ambient (~0.04%) to accelerated (5–20%) levels. The higher CO2 diffusion within samples cured under 5–20% CO2 increased the compressive strength by ~5 times. While samples cured under 20% CO2 revealed high early strengths, the formation of a dense HMC layer on the sample exterior led to limitations on further CO2 diffusion. Use of 5% CO2 produced comparable strengths as 20% CO2 at 28 days, highlighting the potential of using lower concentrations. Samples cured under 10% CO2 revealed the best performance at 28 days, thereby defining this environment as the most favorable condition for the development of microstructural and mechanical properties of RMC concrete.

Influence of calcination temperature on the structure and hydration of MgO

The performance of magnesium oxide-based cements and expansion agent closely relates to the reactivity of MgO. This paper systematically investigates the structure and hydration properties of MgO calcined from amorphous magnesite at a wide range of temperatures from 400 to 1150 ℃. XRD, SEM, BET and PSD tests were carried out to determine the structure and particle properties of MgO. The hydration reactivity of MgO was indexed with isothermal calorimeter, DTG, XRD and TEM test. Increasing temperature augments the crystallinity and size of MgO nanograins from about 23.85 nm to 86.37 nm, decreases the specific surface area but makes the particles agglomerate into smaller size. The increasing temperature prolongs the induction period and retards the hydration rate of main peak. The total cumulative heat from complete hydration of MgO is with a similar value of about 800 J/g. The hydration reactivity of MgO can be accurately indexed by its heat release. MgO calcined at 700 ℃ has high reactivity and it dissolves quickly leading to the precipitation of needle Mg(OH)2 initially. The needle brucite has poor crystallinity but it transforms into flake and clavate shape. MgO calcined at 1150 ℃ has very low dissolving rate. The dissolution starts from the (110) truncation at <100> edges, and then the cuts at (111) occur to create an octahedron shape. Some clavate brucite initially precipitates instead of needle brucite during the hydration of low reactive MgO.

Effect of Fly Ash and Reactive MgO on the Engineering Properties and Durability of High-Performance Concrete Produced with Alkali-Activated Slag and Recycled Aggregate

AbstractThis study investigated the engineering properties and durability of high-performance recycled aggregate concrete (HPRAC) specimens. The specimens were prepared using alkali-activated slag ...

Effect of Preconditioning on Carbonated Reactive MgO-Based Concrete Samples

AbstractThis study investigated the influence of preconditioning on the strength and microstructural development of carbonated reactive MgO cement (RMC)-based concrete mixes. The hydration mechanis...

Influence of aqueous carbonate species on hydration and carbonation of reactive MgO cement

Reactive MgO cement derived from brine could be a low-carbon alternative to Portland cement, as it avoids the need to burn carbon-containing raw materials and it can absorb CO2 gas to form high-strength mineral carbonates. Additionally, the incorporation of a high concentration of aqueous carbonate species can further contribute to its negative CO2 footprint. This paper aims to study the influence of aqueous carbonate species on the hydration and carbonation behavior of reactive MgO cement derived from brine. Although the hydrated MgO exhibited much higher compressive strength in the presence of bicarbonate solution, it still did not exhibit compressive strength sufficient for structural applications (> 10 MPa) under ambient conditions. TGA and XRD results revealed that the carbonate and/or bicarbonate solution altered the hydration degree and morphology of formed Mg(OH)2 but did not form new hydration products. In contrast, when MgO paste was exposed to concentrated CO2 gas (20 % CO2) it produced magnesium carbonates and reached dramatically higher compressive strength, nearly 60 MPa by 28 days. TGA and XRD results suggest that an amorphous phase forms in sodium bicarbonate and sodium sesquicarbonate systems, which plays a key role in the enhancement of compressive strength.

Effects of magnesia expansive agents on the self-healing performance of microcracks in strain-hardening cement-based composites (SHCC)

This contribution presents the self-healing performance of cracks in strain-hardening cement-based composites (SHCCs) containing different amounts of magnesia expansive agents (MEAs) with different reactivities. Specimens were preloaded under a four-point bending test to induce cracks and then exposed to water fog curing conditions. The changes in the crack width before and after curing were measured with a digital microscope, and a water absorption test was also performed to measure the sealing ability of the cracks. The test results show that three reactive MgO expansive agents can significantly improve the crack healing efficiency of SHCC under water fog curing conditions. However, the self-healing effect of the 10 % dosage was not as good as that of the 5% dosage when the reactivity of the MEA was the same, and the MgO expansive agent with a reactivity value of 110 s shows the most promising effect on crack healing. Moreover, it should be noted that the 10 % dosage was too high for the 110 s MgO expansive agent, resulting in poor volume stability.

Carbonated binder systems containing reactive MgO and Portland cement: Strength, chemical composition and pore structure

A sustainable binder system with a capacity to mineralize CO2 can be formulated by reactive MgO and Portland cement (PC). This research studies the properties of mortar specimens made with carbonated MgO-PC systems with a MgO substitution range of 0%–100% in order to evaluate and compare the compressive strength, chemical composition and pore structure. Key results indicate that the carbonation front of mortar subjected to the same curing regime is primarily controlled by the percentage of MgO. The carbonation depth together with the MgO substitution percentage impacts the type of the hydration and carbonation products and their quantity. This affects the mechanical properties and microstructure of the matrix. The compressive strength and pore volume are between of 27.5–84.7 MPa and 2.9%–8.7%, respectively. MgO substitution percentages of 60% and 70% were optimal to achieve both relatively high strength and low porosity. Carbonated MgO-PC binder with 60% MgO was found to possess 20% lower embodied CO2 than that of PC.

The Evaluation of the Stress-Strain Characteristics of MCC Concrete

The MgO-Construction and demolition waste Concrete (MCC) is a green construction material that not only uses the reactive MgO characteristics but also helps the sustainable development approach. In the current study, 30%, 40%, 50%, and 60% of C&DW was substituted for natural aggregate. Also, reactive MgO (2% to 6% wt.) of cement was added to the samples as filler. The mechanical properties of the concrete samples were evaluated after 210 days of curing. The results showed that samples with a sand-to-cement ratio (S/C) of 2.5 have a higher compressive strength than samples with S/C = 3. In addition to compressive strength, the stress-strain and peak strain relationships were evaluated for MCC samples. According to GB50010, the MCC was more ductile than natural aggregate concrete (NAC). Furthermore, new models were suggested for the stress-strain and peak stress prediction. The Field Emission Scanning Electron Microscopy (FESEM) images were assisted for finding proof of MCC structural behavior. The results indicated that the shape of the microstructure has direct effects on energy absorption. Therefore, the use of 2% and 4% MgO in concrete specimens at S/C of 3 and 2.5, increase the energy absorption ability of MCC for specific C&DW aggregate portion.