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Ultra-high-performance concrete (UHPC) has attracted much attention in civil engineering. However, the high deadweight of UHPC limits its application. To reduce the density of UHPC, this study developed an ultra-high-performance lightweight concrete (UHPLC) by combining the use of shale ceramic sand and nano-materials, according to the modified Andreasen and Andersen (MAA) model. Taking advantage of nanotechnology, graphene oxide (GO) was utilized to improve the mechanical performance of UHPLC, and the effects of GO on the workability, mechanical properties, and microstructure of UHPLC were systematically investigated. It was found that: 1) UHPLC with an apparent density of 2022 ∼ 2114 kg/m³ was prepared according to the MAA model; 2) Owing to the addition of GO, the flexural strength, compressive strength, and elastic modulus of UHPLC increased by 6.3 ∼ 22.4%, 7.6 ∼ 16.7%, and 4.1 ∼ 13.0%, respectively; 3) Considering the effects of GO on the mechanical properties and microstructure of UHPLC, the optimal content of GO was 0.06%. [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 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]

• 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]

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]