Reactive Magnesia Cement Research Articles

Tensile behavior of strain-hardening cementitious composites after self-healing based on a novel fiber-bridging model considering preloading and reloading

The self-healing of strain-hardening cementitious composites (SHCCs) causes the recovery of the debonded fiber-to-matrix interface by the products of autogenous healing (mainly calcium carbonates). The recovery of chemical bond Gd has been detected in the reactive magnesia cement (RMC)-based SHCC (SHMC), and the recovery of frictional bond τ0 has been detected in both SHMCs and normal SHCCs. While these phenomena can significantly alter the fiber-bridging σ-w relationship in SHCCs, they have not been quantified in any existing analytical models. In this work, we present a new fiber-bridging model that captures the effect of self-healing of RMC-based SHCC. On the single-fiber level, the debonding and slip-hardening of the fiber-to-matrix interface induced by a tensile preloading as well as the recovery of the interface properties by self-healing are coherently quantified in a clear kinetic process. On the fiber-bridging level, the tensile stress vs. crack width curve is formed by summing individual fibers’ tensile load vs. displacement relationship. The modeling results can well capture the fiber-bridging behavior of the self-healed SHCC specimens. Further, a parametric study is conducted to investigate the tensile behavior of SHCC after self-healing. The effects of preloading levels, recovered τ0, and fiber strength are discussed.

An efficient microbial sealing of rock weathering cracks using bio-carbonation of reactive magnesia cement

Bio-carbonation of reactive magnesia cement (RMC) was proposed as a promising strategy to stabilize the weathered stone grains for the efficient sealing of rock weathering cracks near surface. The physical and mechanical properties of the sandstone grains stabilized by bio-carbonation of RMC was first investigated to verify the feasibility of applying the method to the rock weathering cracks when subjected to the condition of compression failure. Except for initial water content, RMC content and urea concentration, two new effects including bacteria concentration and bacteria solution composition on the underlying stabilization mechanism were systematically studied. The experimental results showed that bio-carbonation of RMC can effectively stabilize the sandstone grains. The highest unconfined compressive strength (UCS) of bio-carbonated sample was up to 5.5 MPa, which was 7.8 times higher than that of the sample stabilized by RMC hydration only. UCS increased as the RMC content and bacteria concentration increase, while the effects of initial water content and urea concentration were opposite. The dry density, resistance of water absorption, electrical resistivity and P-wave velocity were in proportion to the UCS. The effect of bacteria solution composition indicated that the well stabilization performance can be attributed to the coupling effect of the biomolecules and bacteria. Biomolecules-induced amorphous brucite can form a dense structure to fill the pore spaces. Bacteria-induced hydrated magnesium carbonates (HMCs) can form a stable spatial network structure with high cementation strength. The bacteria and biomolecules inhibited the air-based carbonation but facilitated the bacteria-based bio-carbonation and made the microstructure denser. A better bio-carbonation effect and stabilization performance can be obtained by increasing bacteria activity, such as increasing bacteria concentration or using low concentration of urea.

Performance buildup of reactive magnesia cement (RMC) formulation via using CO2-strengthened recycled concrete aggregates (RCA)

Reactive magnesia cement (RMC) is gaining research interest as a low-carbon cement, yet the impacts of recycled concrete aggregates (RCA) on the performances of RMC formulations are rarely researched. In this study, the carbonated/un-carbonated RCA was involved in preparing RMC samples, and three w/c ratios (∼0.55, 0.6 and 0.65) were also adopted. The mechanical performances, mineral phases and pore structures of samples are also unveiled. The results indicate that irrespective of curing conditions, RMC samples with carbonated RCA reveal the best 28 d strength (∼46.79 MPa), and a faster strength gaining was also seen. The improved mechanical performances of RMC samples with carbonated RCA are related to the refined microstructure owing to their smaller number of large pores. The above findings highlight the benefits of the pre-carbonation process in RCA treatment. In addition, using carbonated RCA in RMC samples could increase their hydration degree, but their carbonation process is slowed down, resulting from their denser internal microstructure. Finally, concerning the strength development of RMC samples, their pore structures could be more important than other factors (e.g., carbonation degrees of samples).

An experimental study of mitigating coastal dune erosion by using bio-carbonization of reactive magnesia cement

Due to coastal storm surge and wave or man-made activities, widespread coastal erosion events are emerging. In this study, the feasibility of bio-carbonation of reactive magnesium cement (RMC) to mitigate coastal erosion was investigated by conducting laboratory-scale wave erosion tests. The accumulative erosion volume (V), erosion resistance duration (Dre), and volume erosion rate (VIS) were calculated to evaluate the erosion resistance of sand dunes with the different cement thickness (T = 3 mm, 4 mm, and 5 mm) and RMC content (R = 1%, 1.5%, and 2%). The surface penetration resistance and the cementation product content (brucite/hydrated magnesia carbonates (HMCs)) were also measured to assess the effectiveness of bio-carbonation in sand dunes. Results show that in comparison with RMC hydration, the VIS decreased by 77%, Dre increased by 333%, and peak penetration resistance increased by 42% after the bio-carbonation treatment of sand dunes. Further improvements in these results were obtained with increasing T or R. Given varying T or R, we identify two types of erosion process responses under wave action. For bio-carbonation treatment with higher T or R, the erosion process response follows four phases. In contrast, for hydration treatment, or bio-carbonation treatment with lower T or R, Phase II does not exist because of small crust thickness or weak bond. The presentation of Phase II effectively delays the slope failure depending on larger erosion volume (V ≥ 93 cm3) and turns sudden into flexible failure. Scanned electron microscopy observations further revealed that HMCs formed by RMC bio-carbonation provided better filling and cementation effects than brucite formed by RMC hydration, however, massive amounts of HMCs concentrated in the shallow surface layer, causing hindered penetration and reducing the number of cementation products at higher depths.

The role of biomass bottom ash in Carbonated Reactive Magnesia Cement (CRMC) for CO2 mineralisation

This work evaluates the incorporation of biomass bottom ashes on Carbonated Reactive Magnesia Cement-based (CRMC) mortars. For this purpose, four mixtures were designed to verify the influence of biomass bottom ash as partial or total sand replacement. The specimens were moulded through static compaction pressure and submitted to an accelerated carbonation curing period of 24 h under controlled conditions. The devised mortars were evaluated through mass, dimension, pH measurements, and compressive strength tests. Furthermore, TG-DTG, SEM, FT-IR, XRD, and MIP analyses were performed to investigate the microstructure of the materials developed in this study. Therefore, the devised mortars reached compressive strength results from 9.9 to 24.5 MPa. The TG-DTG, FT-IR, SEM, and XRD analyses support the formation of HMCs in all mixture designs being their volume carbonated in different degrees. Finally, the use of fine particles of biomass bottom ash collaborated for compressive strength enhancement and higher CO2 uptake degree while larger particles do not.

Stabilization of dredged sludge using bio-carbonation of reactive magnesia cement method

Stabilization of dredged sludge using bio-carbonation of reactive magnesia cement method

Study on the viability of unprotected bacterial spores directly embedded in a reactive magnesia cement matrix for potential crack healing

Due to the harsh environment of Portland cement (PC), bacteria spores are often protected by porous carriers or encapsulated with soft materials before incorporated in PC concrete for self-healing. However, this often leads to strength reduction of concrete and higher cost. This paper investigated the feasibility of direct addition of unprotected bacteria spores into reactive magnesia cement (RMC) for potential crack healing via microbial-induced carbonate precipitation (MICP) of Bacillus cohnii with magnesium lactate. To examine the bacteria survival and precipitation capability in the matrix, spores were incorporated directly into RMC pastes. Strong MICP evidenced by the massive formation of nesquehonite to fully close the crack was observed in the hardened RMC paste with unprotected bacteria spores addition, which was associated with the high viability of bacteria in dry and low alkaline RMC environment. This study presented a novel finding for the feasibility of the direct incorporation of unprotected bacteria spores for potential crack healing.

Valorization of Water-Based Drill Cuttings through the Bio-Carbonation Approach

This study proposed a novel bio-carbonation method to recycle water-based drill cutting (WDC) to prepare samples, which contains reactive magnesia (MgO) cement (RMC), ground granulated blast furnace slag (GGBS), and fly ash (FA), with the adoption of microbially induced carbonate precipitation (MICP). Through the investigation of some parameters (i.e., GGBS content, FA content, and curing time), the microstructures and strength development of bio-carbonated RMC-based WDC samples were evaluated. The preliminary results revealed that bio-carbonated RMC-based WDC samples outperformed the control group (i.e., without bio-carbonation) in terms of the 28-day strength (i.e., 9.8 MPa versus 4.4 MPa), which can be assigned to formation of the carbonates, that is, hydrated magnesium carbonates (HMCs). Further, in addition to the identification of HMCs, the microstructural analysis also revealed a continuous carbonate network due to the presence of HMCs, which accounts for the strength boost of samples.

Construction and demolition waste stabilization through a bio-carbonation of reactive magnesia cement for underwater engineering

Bio-carbonation of reactive magnesia cement (RMC), an innovative and potentially sustainable cementing technology, has been proposed as a promising strategy to stabilize the construction and demolition wastes (CDW) for underwater engineering. A series of underwater bio-carbonation experiments on CDW samples with various RMC content and bacteria concentration were conducted to verify the feasibility of the method. Experimental results showed that bio-carbonation of RMC had the ability to stabilize CDW subjected to the underwater environment. The unconfined compressive strength (UCS) of the bio-carbonized CDW samples was up to 1006.04 kPa with 12% of RMC content, which was 11.2 times of samples stabilized by RMC hydration only. The stabilization effect was facilitated by the increase of the RMC content and bacteria concentration. The UCS of the sample with 12% of RMC content was 10.64 times as much as that of the sample with 4% of RMC content. The UCS of the sample stabilized with concentrated bacteria solution was increased by 218.19%. The high RMC content and bacteria concentration also changed the sample failure characteristics from ductileness to brittleness. Based on the measurements of the degree of carbonation (DC), urea utilization ratio (UUR), and microstructure observations, the CDW stabilization mechanism through the bio-carbonation of RMC was discussed. The increasing UCS of the bio-carbonized CDW samples can be attributed to the formation of the brucite and hydrated magnesia carbonates (HMCs) by the combined effects of hydration of RMC and the carbonation of brucite. The formed brucite and HMCs provide excellent filling, bonding, and coating effects between the CDW particles than that of brucite only. The higher RMC content and bacteria concentration promote the urea hydrolysis and RMC carbonation processes, resulting in forming more brucite and HMCs. The large amount of HMCs forms a stable spatial network structure that facilitates stabilization performance and improves the mechanical properties. The coupling effect of the high adsorption characteristic of RMC, CDW, and the fast bio-carbonation ratio makes it possible for the proposed method to be applied to underwater engineering.

Feasibility for co-utilisation of Carbonated Reactive Magnesia Cement (CRMC) and industrial wastes in circular economy and CO2 mineralisation

The increased concern about climate change is leading to the growth of research interest in alternatives to mitigate its effect. Such trend is also observed in the materials and building technologies field, where among the many possible alternatives. Cementitious composites with a lower CO2 footprint have been recently developed to incorporate waste in their composition, with the capability to adsorb CO2. This study evaluates the feasibility of incorporating seven different wastes sources as filler and/or magnesia replacement in Carbonated Reactive Magnesia Cement (CRMC)-based mortars. CRMC-based mortars were designed to incorporate reactive magnesia and waste powders, by the volume ratio of three to one (sand to paste). The mortar specimens were cast by static compaction pressure and cured through accelerated carbonation curing for 24 h at controlled conditions. The performance of CRMC-based mortars was evaluated by compressive strength and microstructural examination. TG-DTG and FT-IR analysis were used to investigate the carbonation effectiveness through the specimens' volume. The results showed that the designed mortars embodying waste have achieved strength values of 8.5 to 14.6 MPa and the carbonation took place at the whole volume independently of the waste-based material used. The compressive strength results were found to be influenced by the pH of the raw materials. The study demonstrated that CRMC-based mortars have good binding properties with the different wastes investigated with the capability of adsorbing CO2 the surrounding environment into the cementitious matrix. It provides innovative solutions for the circular economy in the construction sector aside to sequestrate carbon within the built environment.

Incorporating hollow natural fiber (HNF) to enhance CO2 sequestration and mechanical properties of reactive magnesia cement (RMC)-based composites: Feasibility study

Reactive magnesia cement (RMC) hydrates and carbonates to harden, which can sequestrate CO2 from ambient air. However, the application of RMC-based composites in construction material is still limited by the inadequate CO2 diffusion through the dense microstructure of MgO carbonates. This work for the first time investigates and demonstrates the feasibility of utilizing hollow natural fibers (HNFs) to enhance the carbonation and mechanical properties of RMC. In this study, 2 vol.% sisal or PVA microfibers were added RMC-based matrix to make fiber-reinforced composites. The compressive test shows that addition of sisal fibers significantly enhanced the 14-day compressive strength (10 % CO2 curing) from 20.9 MPa to 39.3 MPa, while PVA fibers only marginally enhanced the strength to 25.0 MPa; the carbonation test of the composites, e.g., phenolphthalein color indication, FTIR, and XPS, shows that the lumens in the natural fibers served as the pathway for CO2 penetration, which significantly increased the carbonation depeth and degree and thus the material strength. The tensile strength of sisal fibers were tested after conditioning in oversaturated Mg(OH)2 or Ca(OH)2 solution, the result shows that the fibers deterioration in RMC-based matrix is minimal, almost neglible compared to that in Portland cement (PC)-based composites. Collectively, these experimental results indicate that RMC and HNF are complementary to each other and can potentially make a new class of sustainable building materials.

Potential additives for magnesia-based concrete with enhanced performance and propensity for CO2 sequestration

This study focuses on the development of carbonated reactive magnesia cement (RMC) concrete formulations involving hydromagnesite (H), magnesite (M) and hydration agent (HA). Partial replacement of RMC by H and M stimulated the formation of hydrate and carbonate phases. Use of H increased the rate and degree of hydration, resulting in the formation of a bird nest-like structure containing poorly-crystalline brucite. The higher propensity of this poorly-crystalline phase for carbonation increased the utilisation of RMC as a binder and facilitated its conversion into strength-providing HMCs. Synergistic combination of M and HA led to significant strength gain via increased carbonate content and reduced w/b ratio. Presence of M provided micro-aggregates that facilitated the enhanced formation of large carbonate crystals with improved morphologies, resulting in microstructure densification and 113 % strength increase. Furthermore, partial replacement of RMC with M enabled reduction of natural resources, CO2 emissions and energy consumption associated with RMC production.

Thermal properties and stability of reactive magnesia cement

The unique ability of reactive magnesium oxide cement (RMC) to permanently sequester environmental carbon dioxide (CO2), followed by sufficient strength gain, makes it an attractive material for greener construction. The potential of RMC and its combination with various supplementary materials have been demonstrated for construction by several researchers. In this study, the thermal properties of the RMC-based paste, along with its thermal stability after prolonged and cyclic high-temperature exposure, are reported. The results reveal that, in general, the RMC-based paste samples cured under an ambient environment as well as the ones cured under accelerated carbonation undergo strength gain after cyclic exposure to temperature as high as 300 °C. In terms of thermal properties, the general trend was found to be an increase in the specific heat and a decrease in the thermal conductivity and the thermal diffusivity with increasing temperature for both types of RMC-based paste samples. These results reveal a remarkable ability of the RMC to sustain high temperatures with excellent strength retention making it suitable for high temperature and energy storage applications.

Assessment of the properties and environmental impact of carbonated reactive magnesia containing industrial waste

To achieve the goal of carbon neutrality, carbon capture and storage (CCS) is considered to be an effective approach. This study investigated the microstructural development of reactive magnesia cement-industrial waste (i.e., pulverized fly ash and ground granulated blast-furnace slag) formulations under accelerated carbonation conditions. The density and isothermal calorimetry analyses were supported with microstructural analysis performed. Results showed that pulverized fly ash and ground granulated blast-furnace slag could be activated by reactive magnesia cement, resulting in the formation of phases such as magnesia silicate hydrate, hydrotalcite and hydromagnesite, whose formation was enhanced in the presence of accelerated carbonation. Associated with a low initial pH, samples with pulverized fly ash outperformed samples with ground granulated blast-furnace slag counterparts in terms of their strength development. The study led to the determination of a formulation containing the reactive magnesia cement and pulverized fly ash with a higher mechanical performance than the control group, also highlighting the need for the revision of the adopted carbon footprint calculation to incorporate several critical factors.

Advances in the hydration of reactive MgO cement blends incorporating different magnesium carbonates

Hydration of reactive magnesia cement (RMC) is limited by the formation of a Mg(OH)2 surface-layer on unreacted MgO particles. This study improved RMC hydration by using magnesium acetate (MA), along with hydromagnesite (H) and magnesite (M) as RMC replacements. While MA accelerated hydration and resulted in the formation of needle-like artinite, inclusion of M led to rosette-like crystals. The accumulated nucleation and growth of low-crystallinity Mg(OH)2 on H particles in a bird nest-like arrangement was observed for the first time in literature. This low-crystallinity Mg(OH)2 could be prone to carbonation. The replacement of up to 40% RMC with M in the presence of MA improved the compressive strength of RMC samples by 240%. This performance enhancement was supported by microstructure densification via the compact formation of hydrate and carbonate phases, defining M as a feasible partial RMC substitute.

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.

Bacteria-induced internal carbonation of reactive magnesia cement

With lower calcination temperature, reactive magnesia cement (RMC) can be a potential alternative to the Portland cement. However, RMC concrete requires accelerated carbonation curing from external sources which greatly hinder the wider applications of RMC. This study proposed a bacteria-based method for the strength gain of RMC through internal carbonation. Sporosarcina pasteurii, urea, and yeast extract were used as a carbonation agent for internal carbonation of RMC pastes. Results showed that the flowability of the fresh bio-RMC paste increased by 20% while the initial setting time remained unchanged. Besides serving as the CO2 provider, urea can also function as superplasticizer to reduce the water demand of the bio-RMC pastes. The resulting bio-RMC pastes showed a continuous strength gain with time, demonstrating the feasibility of bacteria-induced internal carbonation of RMC. Microstructure analysis revealed abundant formation of hydrated magnesium carbonates in the bio-RMC pastes, which is responsible for the strength gain of the bio-RMC pastes.

Biocarbonation of reactive magnesia for soil improvement

This paper presents a new microbial technique for soil improvement through microbially induced carbonate precipitation (MICP) incorporating with reactive magnesia cement (RMC). Through a microbially induced carbonate precipitation (MICP) process, hydrated magnesium carbonates (HMCs) are produced due to biological carbonation of hydrated RMC, which then act as cementation agents to bind soil particles. The influence of several parameters including the RMC content, urea content, and water content on the MICP efficiency was investigated. The performance of the biocarbonated RMC-based sand samples was evaluated using unconfined compressive strength and permeability measurements. Microstructural analyses including scanning electron microscope, X-ray diffraction, and thermogravimetric analysis were also performed to understand the mechanisms behind the treatment. Biocarbonated RMC-based sand samples were compared with the biocement-treated samples using the conventional MICP method. The experimental results indicated the formation of different types of biocarbonation phases enabled by the carbonate ions produced by urea hydrolysis via microbial metabolism. These phases, identified as HMCs, have provided strong bonding to loose sand particles to increase its early strength. The HMCs also occupy the pores of sand matrix to reduce its permeability. The unconfined compressive strength gained at 28 days was up to 2.3 MPa, and the reduction in permeability was up to 1.8 × 10−7 m/s among the tests carried out. The obtained findings have demonstrated that the biocarbonation of reactive magnesia approach is effective for soil improvement.

A comparative assessment of chemical stabilisers including waste materials, for the treatment of swelling-shrinking soils

This paper assesses comparatively the performance of a number of innovative soil stabilisers for the treatment of a highly swelling-shrinking soil, against that of commercial calcium lime. The production of lime, a most common soil stabiliser, involves high energy consumption, carbon dioxide emissions and the depletion of natural raw materials. Alternatives are actively sought, in particular industrial wastes and by-product materials or lower energy demand cements e.g. reactive magnesia (MgO) cements. In this paper calcium lime, reactive magnesia, industrial wastes and mixes of these with lime are comparatively assessed, based on a number of conventional measures of the propensity of a soil to swell, i.e. plasticity characteristics and swelling characteristics (swelling strains, swelling pressures, swelling indices). Furthermore, as expansive soils are typically in an unsaturated state hence sensitive to both changes in water content and suction, filter paper testing was performed to provide additional evidence of the effect of the treatments on the swelling/shrinking soil. According to the main findings, for the treatment of swelling shrinking soils, binders coming from the paper recycling industry show most promise as alternatives to lime; reactive magnesia cement had a smaller effect than calcium based stabilisers in improving the swelling-shrinking of the soil, yet it also suppressed swelling and shrinkage considerably; it thus shows potential for use as an alternative to common soil stabilisers (Portland cement and calcium lime) to alleviate the environmental impact of the latter.

Performance of reactive magnesia cement formulations containing fly ash and ground granulated blast-furnace slag

This study investigated the performance of carbonated reactive MgO cement (RMC) and sealed MgO-SiO2 (RMS) concrete formulations. Fly ash (FA) and ground granulated blast-furnace slag (GGBS) replaced half of the binder component in each system. The assessment of hydration mechanisms via isothermal calorimetry was supported by performance evaluation involving the measurement of permeable pores and compressive strength. Samples were also studied via x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and field emission scanning electron microscopy (FESEM). The formation of a continuous carbonate network was responsible for the strength development of RMC samples, whereas hydrate phases such as M-S-H were observed in RMS samples. Partial replacement of RMC with GGBS led to similar performances under carbonation. RMS samples revealed comparable strengths to PC-based samples, highlighting the potential of MgO-SiO2 binders to be used in similar applications without requiring any special curing conditions.