Magnesium Oxychloride Cement Concrete Research Articles

A Study on Compressive Strength and Micro Structural Properties of Magnesium Oxychloride Cement Concrete Under Varying Temperatures of Magnesium Oxide

Abstract: Construction is a huge consumer of natural resources and a considerable contribution in terms of CO2 emissions. Manufacturing cement and construction materials was shown t be source of the most greenhouse gas emissions. This study looks at whether magnesium oxychloride cement (MOC) may be used as a concrete alternative to standard Portland cement to lessen the environmental effect of the building sector. The research process involves a thorough review of the literature, an experimental investigation, and an internal structural analysis based on the optimal molar ratio. In this investigation, MOC cement concrete was mixed with magnesium powder at varied temperatures. The use of heated magnesium oxide powder produces the first set of results. Finally, a change was made to increase compressive strength of MOC cement concrete. To stimulate the reaction or gel formation, heat was applied to MgO powder at various temperatures and added to the manufacturing of MOC cement to improve the compressive strength. The molar ratio is chosen from the journal for optimum mixing and simple casting of concrete cubes. SEM and EDAX are utilized to analyze the microstructure of the various raised temperature samples. The MgO, phases 3 and 5, are apparent as double and triple ribbons with shared boundaries with water molecules and chloride anions in the SEM images, showing that the strength has increased due to these phases. EDAX shows the proportion of elemental weight in the sample

Internal corrosion cracks evolution in reinforced magnesium oxychloride cement concrete

In view of the difficulty of identifying internal micro corrosion-induced cracks in concrete and the poor accuracy of quantitative analysis, which results in inaccurate results regarding the law of formation of internal cracks, reinforced magnesium oxychloride cement concrete (RMOCC) was subjected to a galvanostatic acceleration test, and X-CT technology was combined with the support vector machines (SVM) identification algorithm and grey-level co-occurrence matrix (GLCM) theory. Using the SVM algorithm and GLCM theory, the internal average crack width of concrete and the contrast, correlation, angular second moment (ASM) and inverse difference moment (IDM), which characterise the change in slice texture information, were used as degradation parameters. Using the average internal crack width and IDM as the degradation index, a reliability degradation competition failure analysis was conducted to study RMOCC's law of internal crack formation. The results showed that the SVM algorithm had a greater than 95% accuracy in recognising cracks. In the entire corrosion-induced crack formation process, IDM and the average internal crack width values were consistent with the normal distribution. Through reliability degradation competition failure analysis between IDM and the average crack width value, the average crack width calculated with SVM is more suitable for the degradation analysis of internal corrosion-induced cracks in RMOCC.

Prediction of Water Resistance of Magnesium Oxychloride Cement Concrete Based upon Hybrid-BP Neural Network.

To obtain the magnesium oxychloride cement concrete (MOCC) ratio with excellent water resistance quickly and accurately, a BP neural network (BPNN) model with a topology structure of 4-10-2 was designed, and the PSO (particle swarm optimization), GWO (gray wolf optimization), and WOA (whale optimization algorithm) algorithms were used to optimize the model. The input layer parameters of the model above were n(MgO/MgCl2), Grade I fly ash, phosphoric acid (PA), and phosphate fertilizer (PF) content, and the output layer was the MOCC's compressive strength and softening coefficient. The model had a dataset of 144 groups, including 100 training set data, 22 verification set data, and 22 test set data. The results showed that the PSO-BPNN model had the highest predictive accuracy among the four models, with a mean R2 of 0.99, mean absolute error(MAE) of 0.52, mean absolute percentage error(MAPE) of 0.01, and root mean square error (RMSE) of 0.73 in predicting compressive strength, and a mean R2 of 0.99, MAE of 0.44, MAPE of 0.01, and RMSE of 0.62 in predicting the softening coefficient. The results showed that using the PSO-BPNN to predict the compressive strength and softening coefficient of MOCC is feasible and can provide theoretical guidance for designing the MOCC mix.

Experimental Study on the Protection of an Asphalt Coating to Reinforcement in Magnesium Oxychloride Cement Concrete

To mitigate the corrosion of steel bar in magnesium oxychloride cement concrete (MOCC), an asphalt coating is used for protection. According to the service environment in the Salt Lake area of western Qinghai, China, a solution immersion test on MOCC was performed. The test results showed that, after soaking for 2160 days, the corrosion current density icorr was 7.88 µA/cm2, and RC was 113.51 Ω for group A and icorr is 0.08 µA/cm2 and RC is 842.57 Ω for group B. The time parameters for groups A and B fell in the high-frequency range of 103–105 Hz and low-frequency range of 10−2 to 10−1 Hz. The relative dynamic moduli of the elasticity evaluation parameters ω1 and ω2 were 0.942 and 0.959 and 0.946 and 0.962 for groups A and B, respectively, at 2160 days, exhibiting a downward trend on the whole. Fourier transform infrared spectroscopy and microscopic testing revealed that the corrosion of the chloride solution on asphalt was mainly the corrosion of chloride in the interior of the asphalt and that the invaded salt provided a channel for the water solution to invade into the interior.

Research and Engineering Application of Salt Erosion Resistance of Magnesium Oxychloride Cement Concrete.

Aiming at the problem that ordinary cement concrete is subjected to damage in heavy saline soil areas in China, a new type of magnesium oxychloride cement concrete is prepared by using the gelling properties of magnesium oxychloride cement in this study, and the erosion resistance of the synthesized magnesium oxychloride cement concrete in concentrated brine of salt lakes is studied through the full immersion test. The effects of concentrated brine of salt lakes on the macroscopic, microscopic morphology, phase composition and mechanical properties of magnesium oxychloride cement concrete are investigated by means of macro-morphology, erosion depth, SEM, XRD and strength changes. The salt erosion resistance mechanism of magnesium oxychloride cement concrete is revealed. The results demonstrate that under the environment of full immersion in concentrated brine of salt lakes, there is no macroscopic phenomenon of concrete damage due to salt crystallization, and the main phase composition is basically unchanged. The microscopic morphology mostly changes from needle-rod-like to gel-like. Due to the formation of a new 5·1·8 phase on the surface layer and the increase in compactness, its compressive strength has a gradual increase trend. Based on the engineering application of magnesium oxychloride cement concrete, it is further confirmed that magnesium oxychloride cement concrete has excellent salt erosion resistance and good weather resistance, which provides theoretical support for future popularization and application.

Long-term mechanical properties and micro mechanism of magnesium oxychloride cement concrete

According to the C20 Portland cement concrete (PCC) batching standard, magnesium oxychloride cement concrete (MOCC) is made using bischofite from salt lakes and light-burned magnesium oxide as the main raw materials. In this work, the mechanical properties of MOCC (setting time and compressive and flexural strengths) were tested. The rules governing the phase composition and microstructure changes of the hydration products were analysed using X-ray diffraction and scanning electron microscopy. The results showed that MOCC solidifies rapidly, has high early compressive and flexural strengths and exhibits excellent long-term mechanical properties, far superior to those of the same grade of C20 PCC. The main phase at different curing times was found to be 5Mg(OH)2.MgCl2.8H2O (5.1.8). With hydration from 7 to 365 d, the amount of 5.1.8 fluctuated between 30% and 37% and the microscopic crystal morphology of the MOCC changed significantly. Importantly, fibre-like and rod-like crystals were observed to transform into their respective gel phases from 180 to 270 d. This phenomenon explains the fact that the content of 5.1.8 was the lowest but the mechanical strength of MOCC was the highest at 180 and 270 d. It was also confirmed that 5.1.8 gel is one of the main strength phases.

Water resistance and a comprehensive evaluation model of magnesium oxychloride cement concrete based on Taguchi and entropy weight method

In this paper, phosphoric acid (PA) and fly ash (FA) were added to improve the water resistance of magnesium oxychloride cement concrete (MOCC). The effects of the single or compound addition of PA and FA on the compressive strength and internal deterioration based on Taguchi method, water resistance, phase composition, and microstructure were studied in detail by means of compression test, relative dynamic elasticity modulus test, X-ray diffraction (XRD) and scanning electron microscope (SEM). Furthermore, a comprehensive evaluation model of MOCC was established on the base of entropy weight method, and the critical value of its comprehensive water resistance coefficient was given. The results showed that the single or compound addition of PA and FA decreased the compressive strength of MOCC but led to an increase in the water resistance. The water resistance of MOCC with the combination of PA and FA was better than that with single-doped PA or FA, and the water-resistant effect of FA was far less than that of PA. It was also noted that the above conclusions were mutually validated by multiple methods. Besides, the comprehensive evaluation model could reduce the test error, improve the reliability of test analysis, and effectively evaluate the water resistance of MOCC. For MOCC, the critical value of comprehensive water resistance coefficient was 0.80.

Life Prediction and Long-Term Durability of Coated Steel Bars in Magnesium Oxychloride Concrete

The solution to the problem of corrosion of the steel bars in magnesium oxychloride cement concrete (MOCC) is to apply a coating that protects the steel. To investigate the coating’s long- term protective effect on the steel, a solution immersion accelerated corrosion test was carried out on coated reinforced MOCC for up to 2,160 days. Electrochemical tests were conducted every 90 days to measure the polarization curve and AC impedance during the steel bars’ corrosion process. Then, the corrosion current density that characterizes the corrosion of a coated steel bar was used as a degradation index, and the time to the coated steel bar’s corrosion was predicted based on the Wiener function. It was concluded that after 2,160 days of solution immersion, the coated steel bars’ corrosion current density was 0.063 µA·cm−2, indicating that the coating protected the steel bars in MOCC from corrosion well. Thdroughout the immersion process, the specimen’s corrosion current density showed a steady and increasing trend, and its polarization impedance showed a volatile growth trend. The degradation of the coated steel bars also obeyed the Wiener degradation process, and the bars reached a severely rusted state at 21,800d with a corrosion time of R0.6(t) is 10,650d.

Predicting the Life of BNC-Coated Reinforced Concrete Using the Weibull Distribution

Aiming at addressing the corrosion of reinforcing steel bars by chloride (Cl−) ions contained in magnesium oxychloride cement concrete, it is proposed to use a double corrosion-resistant Bei Nai Si...

Durability of organic coated reinforced magnesium oxychloride cement concrete

AbstractZinc‐rich coating as a sacrificial anode provides cathodic protection for steel bars, so it can provide protection only for the steel bars for a certain period of time, and fundamentally cannot solve the problem of steel bar corrosion in magnesium oxychloride cement concrete (MOCC). However, the organic coating protects the steel by its own shielding. Therefore, organic coated reinforced MOCC (ORMOCC) is more adaptable in western saline soil and salt lake areas. ORMOCC's durability degradation process includes four aspects, but its durability degradation model under those four factors has not been studied. Therefore, combined with the environment of western salt lakes and saline soil, the solution immersion test was performed on ORMOCC, and the durability degradation of steel bars was studied with electrochemical tests. The degradation durability of organic coatings was studied by Fourier transform infrared spectroscopy. Crack formation and the mass loss of MOCC were studied by ultrasonic and quality tests, taking the four corresponding parameters as degradation indicators. Based on the four‐dimensional Copula function, the degradation model of ORMOCC under four degradation factors was established. The results showed that the four‐dimensional Copula function can describe the durability degradation process of ORMOCC under the influence of the four factors well, and it reaches the damage state at approximately 12,450 days.

Meso-damage evolution analysis of magnesium oxychloride cement concrete based on X-CT and grey-level co-occurrence matrix

X-CT technology can be used to analyse the internal damage to concrete due to rust expansion. However, the original X-CT slice of the internal damage of the concrete can only be used to quantitatively analyse the internal damage in the specimen. The X-CT pictures of the concrete cannot deeply excavate the slight changes in the concrete specimens before and after damage due to rust expansion. As a texture feature analysis method, grey-level co-occurrence matrices (GLCM) have the ability to deeply mine the subtle grey-scale changes of original X-CT pictures. Therefore, this paper coupled X-CT and GLCM to analyse the internal damage in magnesium oxychloride cement concrete due to rust expansion. The four characteristic values of GLCM—contrast, correlation, energy and homogeneity—are used to reflect the internal concrete damage’s evolution. The results show that there is a significant exponential relationship between the surface crack formation and the internal volume growth of the specimen. The contrast value gradually increases during the concrete damage process, while the correlation, energy and homogeneity values gradually decrease during this process, and these four eigenvalues all follow the normal distribution. By using these four characteristic values to analyse the reliability of concrete specimens, it is concluded that homogeneity can be better used to evaluate the internal damage of concrete specimens. The peak bandwidth of matrix in a color heat map decreases gradually and extends along the main diagonal of the matrix in the process of specimen damage that can be used to accurately reflect the damage to the concrete due to the rust expansion force.

Time‐dependent model and life prediction for reinforcement corrosion in magnesium oxychloride cement concrete

AbstractAn effective approach to make better use of the salt‐brine resistance of magnesium oxychloride cement concrete (MOCC) and reduce “magnesium damage” (the concentrate of magnesium resources) that destroys the ecological balance in salt lake areas is to apply MOCC widely. However, the first problem is the high chloride ion content in MOCC, which corrodes reinforcement easily. Concrete cover depth, the experimental environment, and surface treatment of rebar were considered factors study in reinforcement corrosion in MOCC. Based on the tests conducted, a time‐dependent model for reinforcement corrosion in MOCC was proposed, and its life time (initial corrosion and initial cracking time) was calculated and verified in tests. The results showed that proper coating could inhibit reinforcement corrosion and increase the service life of rebar significantly. Further, the salt lake environment had little influence on reinforcement corrosion in MOCC. For exposed rebar in MOCC, the larger the concrete cover depth, the more serious the reinforcement corrosion, while, for coated rebar, the converse was true. All cases of reinforcement corrosion in MOCC conformed to the logarithmic‐type time‐dependent model before concrete cracking. Accordingly, reinforcement corrosion in MOCC and the excess of magnesium resources are expected to be solved.

Three-dimensional characteristics of steel corrosion and corrosion-induced cracks in magnesium oxychloride cement concrete monitored by X-ray computed tomography

We investigated corrosion-induced crack formation of magnesium oxychloride cement concrete (MOCC) in saline soil. Accelerated corrosion of steel in MOCC occurred through an improved galvanostatic accelerated test. X-ray computed tomography, used to scan the MOCC after curing for 14 days, revealed surface cracks of 0.11 mm, 0.25 mm, and 0.44 mm. Steel corrosion, corrosion distribution and corrosion-induced cracks were investigated, using scanning electron microscope (SEM) study the interface transition zone of MOCC. Results show a good linear relationship between steel volume loss and an increase in crack width; a good exponential relationship between an increase in corrosion-induced crack volume and an increase in crack width; and a good exponential relationship between steel volume loss and an increase in the volume of corrosion products. Corrosion-induced cracks do not necessarily form in the direction of the corrosion distribution. The product of the interfacial transitional zones (ITZs) is needle-shaped, which causes the formation of a weak surface in the ITZs so that corrosion-induced cracks usually develop along those zones.

Environmental Assessment of Magnesium Oxychloride Cement Samples: A Case Study in Europe

This study is the first in the literature to systematically assess the environmental impacts of magnesium oxychloride cement (MOC) samples, which are regarded as a more eco-friendly construction material than Portland cement. The environmental impacts of MOC samples prepared with various molar ratios of MgO/MgCl2∙6H2O and sources of reactive magnesia were obtained via a life cycle assessment (LCA) approach (from cradle to grave), and the obtained outcomes were further compared with the counterparts associated with the preparation of Portland cement (PC) samples. Meanwhile, a sensitivity analysis in terms of shipping reactive magnesia from China to Europe was performed. Results indicated that the preparation of MOC samples with higher molar ratios led to more severe overall environmental impacts and greater CO2 sequestration potentials due to the difference of energies required for the production of MgO and MgCl2∙6H2O as well as their various CO2 binding capacities, whereas in terms of CO2 intensities, the molar ratios in MOC samples should be carefully selected depending on the strength requirements of the applications. Furthermore, various allocation procedures and MgO production processes will greatly influence the final outcomes, and allocation by mass is more recommended. Meanwhile, the environmental impacts associated with the transportation of reactive magnesia from China to Europe can be ignored. Finally, it can be concluded that MOC concrete is no longer a type of ‘low-carbon’ binder in comparison with PC concrete in terms of CO2 emissions, and in view of the single scores and mixing triangles for weighing, MOC concrete can only be identified as a type of more sustainable binder than PC concrete when the main component MgO in MOC samples is obtained through the dry process route rather than the wet process route.

Characterizing properties of magnesium oxychloride cement concrete pavement

The performance of magnesium oxychloride cement concrete (MOCC) in road engineering in the arid region in northwest China was investigated over a two-year period. Two categories of MOCC pavement, light-burnt magnesia concrete road (Road-L) and dolomite concrete road (Road-D), were prepared with light-burnt magnesia and a mixture of light-burnt magnesia and caustic dolomite (1:3 by mass), respectively. Variations in the properties of the MOCC pavement, such as compressive and flexural strength, mineralogical phase, and microstructure, after being exposed to two rainy seasons in the field were monitored. The compressive strength of the cored samples were conducted after being aged for 28 d, and the compressive and flexural strength were tested at ages of 1, 2, 3, 28, 90, 180, 270, 360 and 720 d. The mineralogical phase and microstructure of the pavement were also analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results demonstrate that MOCC pavement obtained desirable compressive and flexural strengths after curing for 3 d for Road-L and 28 d for Road-D. Both of the compressive and flexural strength of Road-L and Road-D decreased slightly after experiencing two rainy seasons, with the major hydration products being 5Mg(OH)2·MgCl2·8H2O (Phase 5) and 3Mg(OH)2·MgCl2·8H2O (Phase 3). The decomposition of Phase 5 is mainly responsible for reducing the mechanical strength of the MOCC pavement.

Study on corrosion and anticorrosion of rebar in magnesium oxychloride cement concrete

In order to solve the rapid corrosion problem associated with rebar in magnesium oxychloride cement concrete, an experiment on the corrosion and anticorrosion of rebar is designed. The corrosion and anticorrosion effects of rebar are evaluated through the corrosion current density. A time-varying model of rebar corrosion in magnesium chloride cement concrete is proposed. Based on the time-varying model for rebar corrosion, the initial cracking time with magnesium oxychloride cement concrete is calculated. The results show that the test environment has little effect on exposed-rebar corrosion. The corrosion current density of the coated rebar in a water-soaking environment is greater than that for coated rebar in an indoor natural environment. Greater concrete cover depths cause more severe rebar corrosion. All cases of exposed-rebar corrosion conform to the exponential-type time-varying model, whereas coated-rebar corrosion conforms to the logarithmic-type time-varying model. The corrosion degree of the magnesium oxychloride cement exposed-rebar concrete is much greater than that for magnesium oxychloride cement coated-rebar concrete by two orders of magnitude, showing the feasibility, long-term stability and effectiveness of using coated rebar in magnesium oxychloride cement concrete.

Strength development and micro-mechanism of magnesium oxychloride cement concrete

This paper presents the feature of magnesium oxychloride cement and its particle. Water-resistant admixture and other inorganic materials (silica fume, fly ash and slag) with mix proportion were added to the mix proportion to improve the mechanical properties of magnesium oxychloride cement concrete. By recording the uniaxial compressive strength of concrete at 7–128 days, the influences on the early and late strength of magnesium oxychloride cement caused by different inorganic materials and varied consumption of magnesium chloride solution were analysed. It is shown that the early strength development is fast and the strength with fly ash performs the highest strength; the late strength of concrete reduces because of the scumming of magnesium oxychloride cement, but the strength resumes. Using X-ray diffraction, scanning electron microscope and energy dispersive X-ray spectroscope to investigate the micro-mechanism, the dense gel phase is found in magnesium oxychloride cement concrete with fly ash, which led to the advantage in compressive strength over other samples.

Influence of MgCl<sub>2</sub> Solution Concentration on Strength of Magnesium Oxychloride Cement Concrete

The molar ratio of MgO and MgCl2 affects prominently on the strength of Magnesium Oxychloride Cement Concrete. Different ratios were used to explore the optimum mixture proportion with the highest uniaxial compressive strength. The influence of the MgCl2 solution concentration is presented. XRD (X-ray diffraction) and SEM (scanning electron microscope) was used to analyze the micro-mechanism.

Influence of MgCl<sub>2</sub> Solution Concentration on Strength of Magnesium Oxychloride Cement Concrete

The molar ratio of MgO and MgCl2 affects prominently on the strength of Magnesium Oxychloride Cement Concrete. Different ratios were used to explore the optimum mixture proportion with the highest uniaxial compressive strength. The influence of the MgCl2 solution concentration is presented. XRD (X-ray diffraction) and SEM (scanning electron microscope) was used to analyze the micro-mechanism.

Magnesium Oxychloride Cement Concrete with Recycled Tire Rubber

Either portland cement or magnesium oxychloride cement was used as binders for concretes that incorporated fine rubber aggregate, ranging from 0 to 25 percent by volume. The concretes were tested for their compressive and split tensile strengths to determine whether the use of a magnesium oxychloride cement along with recycled tire rubbers would improve concrete properties. Failure of the concrete around the rubber particles was attributed to tension failure, leading to weak shear failure of the concrete matrix. Both portland and magnesium oxychloride cement concretes lost 90 percent of their compressive strength with 25 percent rubber by volume. The portland cement concrete retained 20 percent of its tensile strength, and the magnesium oxychloride cement concrete retained 35 percent of its tensile strength. Both compressive and tensile strengths of magnesium oxychloride cement rubber concrete were significantly higher than rubberized portland cement rubber concrete.