Search

In the field of architecture and construction, foam cement has been gradually gaining popularity due to its outstanding attributes of reduced weight, carbon footprint, and potential thermal insulation effects. However, relying solely on the thermal insulation provided by the foam in foam cement lacks the capability to store and release heat. In this paper, a novel approach is proposed by directly incorporating paraffin into foam cement with non-continuous pores, creating a phase change foam cement. The addition of paraffin to foam cement, facilitated by the presence of surfactants in foam, allows the paraffin to disperse. In contrast, if paraffin is directly added to cement without the foam, it tends to aggregate. The internal pore structure, thermal performance, phase change temperature, and relaxation distributions were investigated through equipment such as scanning electron microscope (SEM), thermal conductivity meter, differential scanning calorimetry (DSC), and H 1 nuclear magnetic resonance (NMR). Results indicate that paraffin/foam cement plays a dual function, effectively storing and releasing energy, significantly enhancing its thermal insulation performance. Particularly, the incorporation of 10 vol% paraffin content results in a notable 21.8 % reduction in the thermal conductivity, for foam cement with a density of 600 kg/ m 3. This is attributed to the heat storage capability of the phase-change paraffin, which absorbs heat as the surrounding temperature rises, synergistically collaborating with the foam. This presents a novel perspective for the development of green and energy-efficient building materials, contributing to the realization of sustainable energy utilization in the construction industry. • The nanoparticle-enhanced stable foam maintains stability in paraffin and cement slurry. • A novel building material composed of paraffin and foam cement, exhibiting both energy storage capabilities and superior thermal insulation performance. [ABSTRACT FROM AUTHOR]

The passivation and chloride-induced corrosion behavior of aluminum alloys (AAs) 2014, 5083, and 6061, as a key component in aluminum alloy–concrete composite, were investigated in a pore solution of portland cement paste via electrochemical methods, scanning electron microscopy (SEM), and Raman spectroscopy. Results show that AA6061 presents the highest corrosion resistance due to the formation of uniform α-Al(OH)3 layer on both aluminum matrix and intermetallic phases. AA6061 shows the highest chloride threshold value while exhibiting the lowest corrosion resistance when chloride concentration is above the threshold. Different mechanisms of protection and chloride-induced corrosion for the three aluminum alloys in pore solution are proposed. [ABSTRACT FROM AUTHOR]

Limestone calcined clay cement (LC3) has emerged as a promising alternative to traditional Portland cement (PC), offering reduced carbon dioxide emissions and improved mechanical and durability-related properties. However, concerns persist regarding the durability of reinforced LC3 concrete, particularly its lower critical chloride threshold and carbonation resistance. To address this issue, aluminium alloys were suggested to be used as an alternative reinforcement. This study investigates the passivation behaviour of aluminium alloys in LC3 and compares it with that in PC. Electrochemical measurements indicate that LC3 paste exhibits higher resistance and forms a more compact film compared to PC paste, suggesting its more protective property. XRD, Raman spectroscopy, and SEM analysis provide insights into the chemical composition and thickness of the films formed on the surfaces of aluminium alloys. This study enhances our understanding of the passivation mechanisms of aluminium alloys in LC3, facilitating their potential application in LC3-based structures. • Electrochemical analysis confirmed higher corrosion resistance in LC3 paste. • Distinct film compositions were found between PC and LC3 pastes. • The film was thick, porous film in PC and thin and dese film in LC3. [ABSTRACT FROM AUTHOR]

This study investigates the passivation behaviour and mechanism of mild steel embedded in low-heat Portland cement (LHC) paste. Results show that, compared to ordinary Portland cement (OPC), LHC has a significantly lower alkalinity at early stage and thus a lower passivity of mild steel embedded is obtained in LHC. This is explained by the formation of thinner passive film with higher contents of Fe2+ oxides in LHC at the early stage. Nevertheless, the passivity of mild steel in LHC becomes higher than that in OPC at later stage due to formation of a passive film in LHC with an identical thickness and higher content of Fe2+ oxide compared to that in OPC. • Effect of Initial low pH of LHC paste on passivity of steel embedded is revealed. • Initial low pH of LHC leads to lower initial passivity of mild steel than that in OPC. • Prolonged curing leads to a higher passivity of mild steel in LHC than that in OPC. • Lower initial passivity in LHC is due to less formation of iron oxide/hydroxide. • Initial high Fe2+ content and film thickening benefit passivity in LHC at 28 days. [ABSTRACT FROM AUTHOR]

Magnesium Potassium Phosphate Cement (MKPC) as a protective binder for steel rebars has been well-established. However, corrosion performance of steel rebars in MKPC subjected to carbonation is still unknown. This investigation aimed at revealing the impact and mechanism of carbonation on corrosion performance of steel rebars in MKPC using electrochemical techniques and surface analyses. The findings indicate that, unlike Portland cement (PC) system, carbonation positively influences corrosion performance of steel rebars when embedded in MKPC, as demonstrated by comparable (M/P = 7) or even higher (M/P = 12) corrosion resistance values. Under carbonation, the ingressive CO 2 reacts with Mg-bearing phases in MKPC to form nesquehonite with a higher pH, while the MgO still keep supersaturated. The resultant increase in pH facilitates formation of ferrous oxide and iron phosphate/borate within oxide film developed on steel surface, which enhances protective capability of oxide film and consequently improves the corrosion resistance of the steel rebars. [ABSTRACT FROM AUTHOR]

Effect of magnesium-to-phosphate (M/P) ratio on the corrosion resistance of magnesium alloys embedded in magnesium phosphate cement pastes was studied via electrochemical methods and surface characterizations in this study. Results show that corrosion resistance of magnesium alloy increased with the increased M/P ratio. pH played a dominant role in protective capability of oxide film formed on magnesium alloy. M/Ps 7 and 12 leads to formation of oxide film mainly consisting of magnesium phosphates. In contrast, an oxide film composed of magnesium and aluminium oxide/hydroxide formed in M/P 17, possibly with adsorption of phosphate ions which further enhances the corrosion resistance. [ABSTRACT FROM AUTHOR]

• Passivity of mild steel embedded in MKPC-CSA blended paste were investigated. • CSA addition significantly influences the degree of passivity. • Passivity increases with increased CSA addition and 30% CSA addition leads to a much higher passivity. • 30 % CSA addition benefits the precipitation of phosphate ions and formation of Fe2+ oxide in passive film. This study did a pioneer work focused on the passivation of mild steel embedded in magnesium potassium phosphate cement (MKPC)-calcium sulphoaluminate cement (CSA) blended paste via electrochemical measurements and materials characterization techniques. Results showed that 30 % CSA addition in MKPC leads to a passivity of mild steel much higher than that in Portland cement (PC) paste. The passivity of mild steel increased with an increase in CSA content in MKPC paste due to an increase in pH and phosphate concentration in pore solution. The formation of iron phosphate and Fe2+ oxide in passive film of MKPC-30 %CSA contributes to its highest passivity. [ABSTRACT FROM AUTHOR]

This study investigated the chloride-induced depassivation and corrosion of mild steel in the magnesium potassium phosphate cement (MKPC) pore solutions at different magnesia-to-phosphate (M/P) ratios via several electrochemical methods and surface characterisations. Results showed that although the pH of MKPC is much lower than that of PC, the corrosion resistance of mild steel is significantly higher, with critical chloride values in MKPC being several orders higher than that in PC. Chloride-induced corrosion resistance increases with increasing M/P ratios. Whilst both pH and HPO 4 2-/PO 4 3- ions influence the formation of corrosion products, the pH plays a dominant role in the corrosion resistance. • Mild steel in MKPC shows much higher critical chloride values than that in PC. • Corrosion resistance increases with increasing magnesia-to-phosphate (M/P) ratio. • The corrosion resistance of mild steel is mainly determined by pH of MKPC, i.e., M/P. • The PO 4 3- ions in MKPC can inhibit the chloride-induced corrosion of mild steel. • Different corrosion mechanisms are proposed for mild steel in MKPC with low and high M/P. [ABSTRACT FROM AUTHOR]

• Corrosion resistance of Mg-Al-Zn magnesium alloy embedded in Portland cement paste was studied. • Mg-Al-Zn magnesium alloy in PC exhibits a much higher corrosion resistance than 6061 aluminium alloy. • Corrosion resistance of Mg-Al-Zn specimen increases with increased duration in PC paste. • Compact Mg(OH) 2 film and Mg(OH) 2 + Ca 2 SiO 5 precipitates forms on the surface of Mg substrate. • Compact manganese oxide forms on the surface of Al-Mn second phase in Mg-Al-Zn magnesium alloy. Corrosion resistance of Mg-Al-Zn magnesium alloy (AZ41) embedded in PC paste was investigated with 6061 aluminium alloy (AA6061) as s control. Electrochemical methods were adopted to assess the corrosion resistance of AZ41 and AA6061 and surface characterizations were carried out to obtain the morphology and composition of oxide films formed. Results show that the corrosion resistance of AZ41 is obviously higher than that of AA6061 in PC paste due to the formation of a much more compact and thinner oxide film on AZ41. The oxide films on AZ41 and AA6061 are both n-type semiconductors. The oxide film formed on AZ41 mainly consists of uniform Mg(OH) 2 layer and Mg(OH) 2 + Ca 2 SiO 5 particles on AZ41 substrate as well as manganese oxide on Al-Mn second phase, while the oxide film formed on AA6061 is mainly composed of AlOOH, Ca 2 Al 2 O 4 and Ca 2 SiO 5. [ABSTRACT FROM AUTHOR]

• Corrosion inhibition in carbonated solution with Cl- was studied. • A mixture of BTA and Na 2 HPO 4 effectively inhibit corrosion of carbon steel. • BTA inhibitor acts as anodic inhibitor, while Na 2 HPO 4 acts as a mixed type. • Different inhibition mechanisms were identified for two inhibitors. • Formation of hydrogen bonding contributes to synergistic inhibiting. The synergetic inhibiting effect of benzotriazole (BTA) and Na 2 HPO 4 for the corrosion of reinforcing steel in the chloride-contaminated carbonated solutions was preliminarily investigated by electrochemical measurements, as well as X-ray photoelectron spectroscopy and scanning electron microscopy/energy dispersive X-ray techniques. Results show that a mixture of BTA and Na 2 HPO 4 acts as an anodic inhibitor. An optimum enhanced inhibition efficiency was obtained for a mixture of 0.05 M BTA and 0.05 M Na 2 HPO 4. The synergistic inhibiting mechanism for steel was proposed, which was by forming a protective film consisting of Fe n (BTA) m complex and iron phosphates, as well as hydrogen bonding between them on the steel surface. On the contrary, a mixture of unequal amount of BTA and Na 2 HPO 4 showed an antagonistic effect on corrosion inhibition resulting from the competition between the phosphate ions and BTA- on the steel surface. [ABSTRACT FROM AUTHOR]

• Inhibitive effect of MoO 4 2− on AA6061 aluminium alloy is related to its concentration. • Low concentration of MoO 4 2− does not play a role in corrosion inhibition. • 10 mM MoO 4 2− exhibits an optimum corrosion inhibition efficiency. • Inhomogeneous Al-Mg-Si-O(H) and Al-Ca-Mo(VI)-O(H) forms in 30 mM MoO 4 2−. Corrosion inhibition of MoO 4 2− for AA6061 aluminium alloy in simulated concrete pore solutions was investigated. Electrochemical methods were adopted to assess corrosion behaviour of AA6061 and surface characterizations were employed to obtain composition and morphology of oxide layers. Results show that low concentration (6 mM) of MoO 4 2− cannot inhibit corrosion, while MoO 4 2− of 10–30 mM effectively inhibits corrosion, which obeys Langmuir adsorption isotherm. MoO 4 2− acts as an anodic inhibitor. 10 mM MoO 4 2− exhibits an optimum corrosion inhibition efficiency. A uniform oxide layer consisting of Al-Ca-Mo(V)-O(H) complexes forms in moderate concentration of MoO 4 2− (10 mM). Inhomogeneous oxide layer consisting of Al-Mg-Si-O(H) and Al-Ca-Mo(VI)-O(H) complexes forms in high concentration of MoO 4 2− (30 mM). [ABSTRACT FROM AUTHOR]

• Mild steel in MKPC showed comparable or even higher passivity than that in PC. • The passivity increases with increasing magnesium-to-phosphate (M/P) ratio. • The quality of passivation was dominated by pH of MKPC rather than phosphate ions. • Two passivation mechanisms were proposed for low and high M/P ratios, respectively. The low pH of magnesium potassium phosphate (MKPC) has raised concerns over its capability to protect reinforcing steel. The passivation of mild steel in MKPC pore solutions was investigated in this study via electrochemical measurements, XPS and Raman spectroscopy. Results show that the passivity of mild steel in MKPC was comparable or even better than that in Portland cement. Although the passivity was dominated by the pH of MKPC, it also increases with increasing magnesium-to-phosphate (M/P) ratios. The formation of iron phosphate in the low pH MKPC (such as M/P 7) also made additional contributions to the passivity of steel. [ABSTRACT FROM AUTHOR]

• An optimum proportion of DSP and BTA as mixed inhibitors is proposed for carbonation-induced corrosion of rebar. • The role of DSP as a cathodic inhibitor and BTA as an anodic inhibitor are identified. • The antagonistic effect is observed in the mixture of DSP and BTA when high content of BTA is added. The corrosion inhibition of a combination of Na 2 HPO 4 (DSP) and benzotriazole (BTA) for rebar in carbonated concrete pore solutions was investigated. Electrochemical methods were adopted to assess the corrosion behaviour of rebar thermodynamically and kinetically. Also, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to detect the composition of oxide films formed on the rebar surface and the surface morphology of rebar, respectively. Results show that there exists an optimum proportion of DSP and BTA to execute the highest corrosion inhibition efficiency. The mixture of DSP and BTA acts as a mixed-type inhibitor, in which DSP behaves as the cathodic inhibitor and BTA acts as the anodic inhibitor. The adsorption of BTA obeys Langmuir adsorption isotherm. High content of BTA could compete with DSP, which leads to low inhibition efficiency. [ABSTRACT FROM AUTHOR]

Magnesium phosphate cement (MPC) is a promising alternative cement. However, the rheological property of this new binder is still to be explored. In this study, Response Surface Methodology (RSM) was adopted with Central Composite Design (CCD) to establish mathematical models describing the rheological characteristics of MPC in terms of initial mini slump (Y1), mini-slump loss (Y2), yield stress (Y3) and plastic viscosity (Y4), as a function of three independent variables, namely, water-to-solid ratio (W/S ratio, X1), MgO to MKP ratio (M/P ratio, X2) and borax dosage (X3). The results show that the M/P ratio and borax dosage could significantly affect the yield stress and mini-slump loss of MPC, while the W/S ratio was the significant coefficient influencing plastic viscosity and initial mini slump. The numerical optimised values of X1, X2 and X3 were 0.280, 7.528 and 0.170, respectively, and an MPC paste with desirable rheological characteristics (Y1 161.858 mm, Y2 11.282, Y3 0.680 Pa, Y4 0.263 Pa·s) with the highest desirability of 0.867 can be obtained. [ABSTRACT FROM AUTHOR]

The application of coal gangue in construction materials faces challenges due to its inherent structural looseness, elevated porosity, and high carbon content. This study encapsulated coal gangue aggregates (CGAs) with a fly ash-cement slurry, varying the content of fly ash (0 %, 10 %, 20 %, and 30 %) and maintaining a water-to-cement ratio of 0.35. These aggregates were subjected to a curing process within an environment containing a CO 2 concentration of 20 %, 0.1 MPa pressure, 70 % humidity, and a temperature of 20°C. The study delved into examining how the combination of fly ash-cement slurry encapsulation and CO 2 mineralization impacts the physical properties and microstructure of CGAs, focusing on understanding the influence and mechanism behind the synergistic effects. Findings reveal that following the encapsulation process using a fly ash-cement slurry, CGAs exhibit a higher apparent density, a reduced crushing value, but a notable increase in water absorption rate. Notably, treatment with 10 % fly ash-cement slurry and CO 2 mineralization increased the apparent density by 3.85 %, reduced the crushing value by 39.57 %, and limited the increase in water absorption rate to 9.9 %. Additionally, the elastic modulus of the enhanced aggregates rose by 12.73 %. This can be attributed to the formation of a significant quantity of C-S-H gel and CaCO 3 products as a result of the interplay between the encapsulated fly ash-cement slurry and CO 2 mineralization. This process effectively occupied the voids within the coal gangue. Consequently, CO 2 mineralization enhanced the interfacial transition zone between the slurry and coal gangue, ultimately leading to improved coal gangue's mechanical performance. ● Synergy of 10 % fly ash-cement slurry encapsulation and CO 2 mineralization improved the mechanical properties of coal gangue. ● CO 2 mineralization enhanced the interfacial transition zone (ITZ) between the slurry and coal gangue. ● The modulus of elasticity of gangue aggregate increased by an average of 12.73% and the hardness increased by an average of 13.88% after CO 2 mineralization. [ABSTRACT FROM AUTHOR]

A systematic investigation was undertaken to explore the influence of microstructure evolution in the as-cast, heat-treated, and as-extruded on the corrosion properties of a high-performance Mg-5.6Dy-3.1Ni alloy, which includes two intermediate phases. It was found that degradation rate of both as-cast and heat treated alloys primarily depended on the distribution of the LPSO and Mg 6 Ni intermetallic phases. For the as-extruded alloy, the degradation rate depended on both the distribution of the LPSO and Mg 6 Ni phases and the grain refinement of the matrix. Compared with as-cast alloy, the corrosion barrier was formed and inhibited the corrosion propagation after heat treatment. This was attributed to the network distribution of the LPSO phase, coupled with a uniform distribution of Mg 6 Ni phase. After extrusion, After extrusion, the streamlined distribution of the stripped LPSO phase. This led to a reduced corrosion barrier in the extrusion direction (ED) sample, resulting in a higher degradation rate compared to the transverse direction (TD) sample. Furthermore, the LPSO phase and grain refinement after extrusion provided a denser corrosion product film to retard the degradation rate in the TD sample. A high mechanical properties Mg-5.6Dy-3.1Ni alloy with different degradation rates in the as-cast, heat-treated, and along the extrusion direction and in the transverse direction was developed. • Developed a high strength Mg-Dy-Ni alloy with different corrosion rates by different process conditions. • The mechanism of microstructure evolution on the degradation rate of high-strength Mg-Dy-Ni alloy was elucidated. • The study alloy meet the fracturing tools with high strength and different degradation time demand. [ABSTRACT FROM AUTHOR]

• 6% Cr steel exhibits a protective passive film with Cr oxide/hydroxide layer. • High pitting corrosion resistance is highlighted for 6% Cr steel. • Compact rust layer is formed for 6% Cr steel after natural exposure. The electrochemical performance of a new 6% Cr steel was investigated intensively by means of a broad variety of electrochemical methods (EIS, CV and CPP) and surface characterization techniques (AFM, XPS, EPMA and ESEM/EDS) in simulated concrete pore solution (SCPS) with chlorides. Improved corrosion resistance of 6% Cr steel in SCPS was established by the protective passive film, the high pitting corrosion resistance as well as the compact rust layer, which may shed light on the design of corrosion-resistant reinforcing steels with enhanced corrosion resistance throughout the service life of reinforced concrete structures. [ABSTRACT FROM AUTHOR]

• Three kinds of release agents were attempted on the surface of AZ41 Mg alloy. • Corrosion resistance of AZ41 Mg alloy embedded in Portland cement paste was studied. • Oil-based release agent coated Mg alloy presents the best corrosion resistance. Anticorrosion performance of AZ41 Mg alloy coated with three different kinds of release agents was investigated embedded in Portland cement (PC) paste containing 0.6 M NaCl. Surface characterizations were employed to obtain the surface information after coated with release agents before and after embedment. Meanwhile, electrochemical methods were adopted to assess the corrosion resistance embedded in PC paste. Results demonstrated that water-based release agent led to the corrosion of Mg alloy while the oil-based release agent not only protected the Mg alloy but also exhibited the best demolding effect. Oxide films can be generated on the surface of Mg alloy after coated with release agents. The thin film after applying the water-based release agent was magnesium/aluminium oxide and hydroxide with some talcum (3MgO·4SiO 2 ·H 2 O) particles. Additionally, thin films on the surface of Mg alloy after coated with emulsified and oil-based release agents were magnesium/aluminium oxide and hydroxide. [ABSTRACT FROM AUTHOR]

An anticorrosive CaCO 3 -coated Mg(Al)O passive layer was obtained via the ultrasound-assisted electrodeposition on AZ41 Mg alloy for concrete formwork. Corrosion rate of the CaCO 3 /Mg(Al)O coated AZ41 Mg alloy was lower than 0.005 mmy−1 in Portland cement (PC) system containing 0.6 M NaCl. Ultrasound plays a dual-role in forming a dense Mg(Al)O passivation film and densifying the outer CaCO 3 layer. Furthermore, re-passivation instead of corrosion was observed during the embedment, attributed to the double-layer structure effectively increasing the critical chloride ion concentration for corrosion. Formation and anticorrosion mechanism as well as the role of the passivation film in anticorrosion are discussed. • An anticorrosive bilayer CaCO 3 /Mg(Al)O coating system was prepared on AZ41 Mg alloy. • Ultrasound was used in electrodeposition to assist formation of the coating system. • Outer CaCO 3 plays a dual role of anticorrosion and protection of the inner layer. • Inner Mg(Al)O passivation film can survive and regeneration in corrosive media. • A "dissolution – repassivation" cycle behavior inhibits or mitigates the corrosion. [ABSTRACT FROM AUTHOR]

The Mg 95.34 Gd 2.66 Cu 2 alloy containing profuse solute segregation stacking faults (SFs) phase was prepared through solution treatment and furnace cooling, and its effect on corrosion behavior and corrosion mechanism were investigated. After heat treatment, the microstructure distribution of continuous bulk-shaped Mg 5 (GdCu) phase at grain boundaries and profuse solute segregation SFs phases in the matrix was realized. Compared with the as-cast alloy without SFs phase, the corrosion morphology exhibited that the galvanic corrosion expanded rapidly along the length direction of SFs phase after heat treatment. The Mg 95.34 Gd 2.66 Cu 2 alloy heat treated at 420 °C exhibited the optimal comprehensive performance, with the ultimate compressive strength (UCS), compressive yield strength (CYS) and degradation rate of 437 MPa, 291 MPa, 56.5 mg/(cm2·h), respectively. And the degradation rate increased by 40% compared with the as-cast alloy. • The profuse SFs were prepared in Mg 95.34 Gd 2.66 Cu 2 alloys by heat treatment. • SFs increased the volume fraction of the cathode phase and improved the degradation rate. • A rapid corrosion microstructure distribution model was proposed. [ABSTRACT FROM AUTHOR]

To address the limited corrosion resistance of magnesium alloys, calcium phosphorus coatings are frequently applied to their surfaces as a means of compensating for this drawback. However, cracking of traditional calcium phosphorus coatings greatly affects their protective properties. In this research, a novel CaHPO 4 ·2H 2 O (DCPD) and CaCO 3 composite coating with no cracks was obtained via a chemical conversion method assisted by ultrasound. DCPD coatings were also fabricated in the same method. All the coatings possess excellent adhesion strength to the substrates. In addition, electrochemical tests results show that the elimination of cracks greatly improves the anticorrosion performance of composite coatings. Optimization of the bath constituents resulted in a reduced reliance on interfacial electrochemical reactions during the co-deposition process, which plays a critical role in attaining the high-quality coating. This innovative composite coating provides a promising avenue for surface treatments of magnesium alloy concrete formwork. • A composite CaHPO 4 ·2H 2 O/CaCO 3 coating via ultrasound treatment on Mg alloy was prepared. • The elimination of cracks in the composite coating significantly enhanced the corrosion resistance. • The Ca/P/C-Ca composite coating shows regrowth performance. [ABSTRACT FROM AUTHOR]

In order to enhance the corrosion resistance of the AZ41 Mg alloy used as concrete formwork, a bilayer CaCO 3 /MgO coating was fabricated on the surface of AZ41 Mg alloy with addition of Ca-EDTA in the chemical conversion solutions. Effect of different Ca-EDTA concentrations on the surface morphology of as-prepared CaCO 3 /MgO coating and corrosion resistance in simulated concrete pore solutions with 3.5 wt% NaCl were investigated. SEM, XPS and XRD were combined to investigate the morphology and composition of the coatings. Electrochemical methods and immersion tests were used to assess the anticorrosion performance of the as-prepared coatings. Results show that an integrated bilayer CaCO 3 /MgO coating can be prepared on AZ41 Mg alloy by the addition of Ca-EDTA. Electrochemical tests reveal that the CaCO 3 /MgO coating prepared at 0.01 M Ca-EDTA possesses the best corrosion resistance at varying concentrations of Ca-EDTA. Ca-EDTA accelerates the release of Mg2+ and further affects both nucleation and growth of CaCO 3 particles. Appropriate addition of Ca-EDTA can simultaneously preserve the stability of CaCO 3 and enhance coating density. • A bilayer CaCO 3 /MgO coating via ultrasound-assisted chemical conversion improve the corrosion resistance of AZ41 Mg alloy. • Addition of disodium calcium of ethylenediamine tetra-acetic acid (Ca-EDTA) can improve the density of CaCO 3 particles. • The CaCO 3 /MgO coating prepared at 0.01 M Ca-EDTA possesses the best corrosion resistance. • Both stable components and a dense structure maybe key factors for a coating to possess outstanding corrosion resistance. [ABSTRACT FROM AUTHOR]

The effects of the high content of erbium (Er) addition (9.5–17 wt%) and short-time low-temperature heat treatment on the microstructure evolution, corrosion behaviors and mechanism of Mg-xEr-1.6Ni alloys have been investigated. After heat treatment, the corrosion rate for various Er content alloys increased by 15.1–338.8% in comparison to as-cast alloys, which was mainly related to the formation of Er-rich phases and the increase the density of laminar γ′ phase. These phases increase the galvanic coupling pairs and provide more corrosion propagation paths, reducing the Er content in the Mg matrix and weakening the corrosion barrier. • Corrosion mechanism of Mg-xEr-1.6Ni alloy with different Er content was revealed. • Corrosion rate increased by 15.1%− 338.8% after low-temperature heat treatment. • Increased corrosion rate is due to formation of Er-rich phase and increased γ′ phase. • This work provides foundation for designing high-degradation Mg alloy. [ABSTRACT FROM AUTHOR]

The corrosion inhibition of EDTA-Ca for mild steel in chloride-contaminated concrete pore solution, with EDTA-Na as comparison, was investigated via several electrochemical methods and surface characterizations. Results show that corrosion inhibition efficiency of EDTA-Ca is higher than that of EDTA-Na. Corrosion inhibition efficiency increased with an increase in EDTA-Ca concentration while decreased with the increased EDTA-Na concentration. EDTA-Ca adsorbs physiochemically on surface of mild steel which obeys Langmuir isotherm, while adsorption of EDTA-Na is physical obeying Freundluich isotherm. A much thinner and more compact oxide film with higher Fe2+ content formed in the presence of EDTA-Ca compared to EDTA-Na. The availability of coordinate bonds for chelation in EDTA-Ca or EDTA-Na plays a critical role in determining the corrosion inhibition efficiency. • Enhanced corrosion inhibition of EDTA-Ca than EDTA-Na for mild steel in concrete pore solution was obtained. • Inhibition efficiency of EDTA-Ca increased with increased concentration. • EDTA-Na adsorbs physically while adsorption of EDTA-Ca is physicochemical. • EDTA-Ca possibly favours formation of insoluble EDTA-Ca-Fe(II) complexes on steel. [ABSTRACT FROM AUTHOR]

A CaCO 3 coating with good anticorrosion and self-healing performance was fabricated on the as-prepared MAO coating on the surface of AZ41 Mg alloy via ultrasound-assisted chemical conversion, a DCPD(CaHPO 4 ·H 2 O) coating was also fabricated on the MAO coating as a comparison. Surface characterizations were carried out to obtain the morphology and composition of CaCO 3 coating formed and electrochemical methods were adopted to assess the corrosion resistance of Mg alloy embedded in PC paste. The self-healing property of MAO/CaCO 3 coating was ascribed to the formation of extra calcite. This coating may become a potential target for surface modification of magnesium alloy formwork. • An anticorrosive CaCO 3 coating via ultrasound treatment on MAO coating was prepared. • A compact CaCO 3 + (Mg,Ca)CO 3 +MAO triple layer with a thickness of ∼3 µm. • (Mg,Ca)CO 3 inner layer plays an important role in the anticorrosion. • The MAO/CaCO 3 coating shows good corrosion resistance and self-healing property. [ABSTRACT FROM AUTHOR]

A superhydrophobic anticorrosive CaCO 3 coating was prepared on Mg-Nd alloy by ultrasound-assisted chemical conversion. Results show that the prepared coating consists of an outer durian-peel like CaCO 3 layer and a compact inner (Ca, Mg)CO 3 layer. Ultrasound treatment enhances the homogeneity and decreases the size of CaCO 3 particles in coating, which contributes to its superhydrophobicity. This results in an enhanced anticorrosive property of coating via ultrasonic treatment. Ultrasound possibly accelerates the nucleation of CaCO 3 crystals and assists the removal of hydrogen bubbles. A self-healing property of ultrasonically prepared coating was also obtained due to the formation of vaterite and Ca 3 (OH) 2 (CO 3) 2. • A superhydrophobic CaCO 3 coating via ultrasound treatment on Mg alloy was prepared. • A compacted CaCO 3 + (Mg,Ca)CO 3 dual layer with a thickness of ∼4 µm. • (Mg,Ca)CO 3 inner layer plays an important role in the anticorrosion. • Durian peel-like CaCO 3 surface contributes to the superhydrophilicity. • The UMg coating shows good corrosion resistance and self-healing property. [ABSTRACT FROM AUTHOR]

The microstructure and corrosion behaviors of Mg-Gd–Ni alloys with various long period stacking ordered (LPSO) phase volume fraction and heat treatments were investigated. Compared with as-cast alloys, the corrosion rates increased significantly after heat treatment, and increased with increasing volume fraction of LPSO phase, which may be due to the transformation of continuous bulk reticular LPSO phase to discontinuous rod-like and the precipitation of the lamellar 14 H LPSO phase, changing the corrosion propagation paths and providing more galvanic corrosion points for alloy with high LPSO phase volume fraction, resulting in corrosion rate of MgGd3Ni3 alloy increased significantly by 58.1%. • The corrosion mechanism of Mg-Gd-Ni alloys by change of LPSO phase volume fraction and heat treatment were clarified. • The change of corrosion propagation paths and precipitation of lamellar LPSO phase accelerates the corrosion of the alloys. • Compared toas-cast alloys, the corrosion rates of MgGd 3 Ni 3 alloy increased significantly by 58.1% after heat treatment. [ABSTRACT FROM AUTHOR]

The passive behaviour of new alloy corrosion-resistant steel Cr10Mo1 and plain carbon steel (as a comparison) in simulating concrete pore solutions of different pH (ranging from 13.5 to 9.0) under open circuit potential conditions, was evaluated by various electrochemical techniques: potentiodynamic polarization, capacitance measurements and electrochemical impedance spectroscopy. The chemical composition and structure of passive films were investigated by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). The electrochemical responses of passive films show that Cr10Mo1 steel has an increasing passivity with pH decreasing while carbon steel dose conversely, revealing carbonation does no negative effect on passivation of the corrosion-resistant steel. SIMS reveals that the passive film on the corrosion-resistant steel presents a bilayer structure: an outer layer mainly consisting of Fe oxides and hydroxides, and an inner layer enriched in Cr species, while only a Fe-concentrated layer for carbon steel. According to the XPS analysis results, as the pH decreases, more stable and protective Cr oxides are enriched in the film on Cr10Mo1 steel while Fe oxides gradually decompose. Higher content of Cr oxides in the film layer provides Cr10Mo1 corrosion-resistant steel more excellent passivity at lower pH. [ABSTRACT FROM AUTHOR]

Lamellar long-period stacking order (LPSO) and delaminated bulk-shaped LPSO phases have been introduced into the Mg-Gd-Ni alloys matrix and grain boundaries by adjusting the heat-treatment process to improve the degradation performance. Precipitation of the lamellar LPSO phase in the matrix increased the proportion of the cathode phase, and the corrosion rapidly expanded in the length direction of lamellar LPSO phase, which improved the degradation rate. In addition, the delaminated bulk-shaped LPSO phase provided corrosion channels, which weakened the hindrance of the continuous bulk-shaped LPSO phase to corrosion expansion and further improved the degradation rate. The degradation rate of HT480 reached 19.9 mg/cm2/h in 3 wt% KCl solution at 25 °C, 39% higher than that of as-cast alloy. A new type of rapid degradation model is proposed, namely microstructural distribution of a continuous delaminated bulk-shaped LPSO phase at grain boundaries and of a lamellar LPSO phase within the matrix. • The 14H-type lamellar LPSO phases are precipitated in Mg 96 Gd 2 Ni 2 alloys. • The 14H-type lamellar LPSO phases can act as an effective cathodic phase to accelerate the degradation of Mg alloys. • The delaminated bulk-shaped LPSO phase can effectively reduce the hindering effect on corrosion expansion. • A new type of rapid degradation model is proposed. [ABSTRACT FROM AUTHOR]

In order to develop new Mg alloys for fracturing tools, Mg-Gd-Cu alloys containing profuse solute segregated stacking faults (SFs) were prepared by appropriate heat treatments and the effect of SFs on corrosion behavior of the alloys was investigated. It was found that the presence of SFs greatly changed corrosion behavior of the Mg-Gd-Cu alloys. Specifically, the alloys containing SFs presented higher initial corrosion rate due to the increased volume fraction of the cathodic phase associated with the SFs; while the rapid formation ability as well as uniform and complete distribution of corrosion films resulted in a lower average degradation rate. • The profuse solute segregated stacking faults were prepared in Mg-Gd-Cu alloys by heat treatment. • The presence of stacking faults greatly changed corrosion behavior of the Mg-Gd-Cu alloys. • Heat-treated alloys exhibited higher initial corrosion rates due to the increased volume fraction of the cathodic phase associated with the stacking faults. • The rapid formation ability as well as uniform and complete distribution of corrosion product films of heat-treated alloy resulted in a lower average corrosion rate. [ABSTRACT FROM AUTHOR]

• SCM with high elastic modulus was developed by using AMP. • Fluidity, microstructure, mechanical strength, and durability of SCM were studied. • DME of SCM was characterized via ultrasonic testing technology. • DME of SCM was increased by 4.37 ∼ 9.97% due to the addition of AMP. • Durability properties of SCM were markedly improved due to the addition of AMP. Cementitious composites are one of the most widely used building materials in civil engineering. However, their low Young's modulus cannot meet the requirements of long-span structures. This work carried out a feasibility study on producing self-compacting mortar (SCM) with high elastic modulus by using Al 2 O 3 micro powder (AMP). Effects of AMP on the workability, microstructure, mechanical properties, and durability properties of SCM were systematically investigated. The dynamic modulus of elasticity (DME) of SCM was characterized via ultrasonic testing technology. It was found that, 1) due to the addition of AMP, the porosity of SCM was reduced by 2.64 ∼ 13.64%, and the threshold pore diameter of SCM was decreased; 2) the flexural strength and compressive strength of SCM were increased by 4.40 ∼ 15.85% and 2.35 ∼ 14.33%, respectively, because of the incorporation of AMP; 3) the drying shrinkage of SCM was reduced by 6.46 ∼ 11.21%, and the chloride migration coefficient of SCM was decreased by 3.38 ∼ 18.64%, due to the addition of AMP; 4) the optimal content of AMP in SCM was 10%, considering the effects of AMP on the microstructure, mechanical properties, and durability properties of SCM; 5) it was feasible to produce SCM with high elastic modulus by using AMP, and the DME of SCM was increased by 4.37 ∼ 9.97%, because of the incorporation of AMP. [ABSTRACT FROM AUTHOR]

• UHPC with high elastic modulus was design by MAA particle packing model. • Workability, microstructure, and mechanical strength of HEMUHPC were studied. • Elastic modulus of HEMUHPC ranged from 40.50 GPa to 47.13 GPa. • Relationship between elastic modulus and compressive strength was a power function. • Optimal content of alumina micro-powder in HEMUHPC was 10%. Elastic modulus is an important parameter in engineering structural design for evaluating the stiffness of concrete members. Ultra-high-performance concrete (UHPC) has excellent mechanical properties and durability, but the relatively low elastic modulus prohibits the widespread use of the UHPC. In this study, high elastic modulus UHPC (HEMUHPC) was designed according to Modified Andreasen and Andersen particle packing model proposed by Funk and Dinger. Effects of alumina micro-powder (the content of alumina is higher than 99%, and the particle size is lower than 100 μ m) on the workability, microstructure, and mechanical properties of HEMUHPC were systematically investigated. The reason for the improvement of elastic modulus of HEMUHPC was revealed by nano indentation test. It was found that, 1) the porosity and threshold pore diameter of HEMUHPC were reduced because of the addition of alumina micro-powder; 2) the flexural strength, compressive strength, and elastic modulus of HEMUHPC were increased by 3.54–11.23%, 8.89–22.83%, and 6.19–16.37%, respectively, due to the addition of alumina micro-powder; 3) the optimal content of alumina micro-powder was 10%, considering its effects on the workability, mechanical properties, and microstructure of HEMUHPC; 4) Nano indentation experiments showed that the elastic modulus of the alumina micro-powder was 90–135 GPa, which is much higher than the elastic modulus of hydration products of HEMUHPC, and thus the elastic modulus of the HEMUHPC matrix could be improved, due to the addition of alumina micro-powder. [ABSTRACT FROM AUTHOR]

• Passivation film thickness of rebar in alkali-activated pore solution were obtained. • Composition of passive film for two kinds of rebars were characterized by XPS. • The protective ability of passive film was deeply analyzed by molecular dynamics. The study on the properties of passive films in alkali-activated slag cement can provide a theoretical basis for the development and application of low-carbon and environmental friendly concrete materials. In this paper, the passivation behaviour of anti-corrosion rebar (AR) and normal reinforcing steel (NR) in sulfur-free simulated pore solutions of alkali-activated slag cement pastes was investigated using electrochemical, microscale techniques and molecular dynamics modelling. Results showed that the formation time, composition and thickness of the passive film were affected by the types of simulated pore solutions. Molecular dynamics further elucidated the reason for difference in the protective ability of passive film in three types of simulated pore solutions. The results of protection capability of two kinds of rebar obtained from molecular dynamics were consistent with those of electrochemical impedance spectroscopy (EIS). [ABSTRACT FROM AUTHOR]

• Producing cement-based sacrificial materials with strontium ferrite is feasible. • Adding strontium ferrite decreases the mechanical properties of cement mortar. • Adding strontium ferrite reduces the drying shrinkage of cement mortar. • Strontium ferrite does not participate in the hydration reaction of cement mortar. • A model between the damage of cement mortar and the temperature is proposed. The safety of nuclear power plant can be improved via core catcher, and cement-based sacrificial materials are widely used in most core catchers because of their simple construction process and the low manufacturing cost. This paper carried out a preliminary investigation to explore the feasibility of using strontium ferrite to prepare cement-based sacrificial materials. The effects of strontium ferrite on the room temperature and high temperature properties of cement mortar were systematically studied in the work. In addition, the damage evolution of cement mortar containing strontium ferrite subjected to elevated temperatures was also identified according to the damage mechanics theory. It was found that, (1) the addition of strontium ferrite led to the deterioration of the mechanical properties, microstructure and pore structure of cement mortar; (2) it was feasible to prepare cement-based sacrificial materials containing strontium ferrite that met the requirements on basic properties like mechanical properties, free water content, volume stability, and the high temperature integrity by controlling the content of strontium ferrite; (3) the correlation between the internal damage of cement mortar and the temperature could be described by Weibull Distribution Model, which provided a basis for the identification and evaluation of serious nuclear power accidents. [ABSTRACT FROM AUTHOR]

The fabrication of high-performance cement-based materials has benefited greatly from the extensive use of graphene and its derivatives. This paper studies the effects of graphene sulfonate nanosheets (GSNSs) on sacrificial cement paste and mortar (the tested materials) and other siliceous sacrificial materials, especially their ablation behaviors and mechanical properties. Decomposition temperatures and differential scanning calorimetry were used to examine how different contents of GSNSs determines the corresponding decomposition enthalpy of the tested materials and their ablation behaviors. Molecular dynamics was also used to clarify the mechanism how the GSNSs work in the CSH (calcium silicate hydrated)/GSNSs composite to increase the resistance to high temperature. The experimental results show that: (1) the contents of GSNSs at 0.03 wt.%, 0.1 wt.%, and 0.3 wt.% brought an increase of 10.97%, 22.21%, and 17.56%, respectively, in the flexural strength of siliceous sacrificial mortar, and an increase of 1.92%, 9.16%, and 6.70% in its compressive strength; (2) the porosity of siliceous sacrificial mortar was decreased by 5.04%, 9.91%, and 7.13%, respectively, and the threshold pore diameter of siliceous sacrificial mortar was decreased by 13.06%, 35.39%, and 24.02%, when the contents of GSNSs were 0.03 wt.%, 0.1 wt.%, and 0.3 wt.%, respectively; (3) a decline of 11.16%, 28.50%, and 61.01% was found in the ablation velocity of siliceous sacrificial mortar, when the contents of GSNSs were 0.03 wt.%, 0.1 wt.%, and 0.3 wt.%, respectively; (4) when considering the ablation velocities and mechanical properties of siliceous sacrificial materials, 0.1 wt.% GSNSs was considered to be the optimal amount; (5) the GSNSs contribute to the reinforced effect of GSNSs on CSH gel through the grab of dissociated calcium and water molecules, and the chemical reaction with silicate tetrahedron to produce S–O–Si bonds. These results are expected to promoting the development of new kinds of siliceous sacrificial materials that contain GSNSs. [ABSTRACT FROM AUTHOR]

Ultra-high-performance concrete (UHPC) has been used as an advanced construction material in civil engineering because of its excellent mechanical properties and durability. However, with the depletion of the raw material (river sand) used for preparing UHPC, it is imperative to find a replacement material. Recycled sand is an alternative raw material for preparing UHPC, but it degrades the performance. In this study, we investigated the use of graphene oxide (GO) as an additive for enhancing the properties of UHPC prepared from recycled sand. The primary objective was to investigate the effects of GO on the mechanical properties and durability of the UHPC at different concentrations. Additionally, the impact of the GO additive on the microstructure of the UHPC prepared from recycled sand was analysed at different mixing concentrations. The addition of GO resulted in the following: (1) The porosity of the UHPC prepared from recycled sand was reduced by 4.45–11.35%; (2) the compressive strength, flexural strength, splitting tensile strength, and elastic modulus of the UHPC prepared from recycled sand were enhanced by 8.24–16.83%, 11.26–26.62%, 15.63–29.54%, and 5.84–12.25%, respectively; (3) the resistance of the UHPC to penetration of chloride ions increased, and the freeze–thaw resistance improved; (4) the optimum mixing concentration of GO in the UHPC was determined to be 0.05 wt.%, according to a comprehensive analysis of its effects on the microstructure, mechanical properties, and durability of the UHPC. The findings of this study provide important guidance for the utilisation of recycled sand resources. [ABSTRACT FROM AUTHOR]

Ultra-high-performance concrete (UHPC) has received increasing attention in recent years due to its remarkable ductility, durability, and mechanical properties. However, the manufacture of UHPC can cause serious environmental issues. This work addresses the feasibility of using aeolian sand to produce UHPC, and the mix design, environmental impact, and mechanical characterization of UHPC are investigated. We designed the mix proportions of the UHPC according to the modified Andreasen and Andersen particle packing model. We studied the workability, microstructure, porosity, mechanical performance, and environmental impact of UHPC with three different water/binder ratios. The following findings were noted: (1) the compressive strength, flexural strength, and Young's modulus of the designed UHPC samples were in the ranges of 163.9–207.0 MPa, 18.0–32.2 MPa, and 49.3–58.9 GPa, respectively; (2) the compressive strength, flexural strength, and Young's modulus of the UHPC increased with a decrease in water/binder ratio and an increase in the steel fibre content; (3) the compressive strength–Young's modulus correlation of the UHPC could be described by an exponential formula; (4) the environmental impact of UHPC can be improved by decreasing its water/binder ratio. These findings suggest that it is possible to use aeolian sand to manufacture UHPC, and this study promotes the application of aeolian sand for this purpose. [ABSTRACT FROM AUTHOR]