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Recently, the use of aeolian sand for producing ultra-high-performance concrete (UHPC) was introduced. Preliminary investigations suggested that it was feasible to use aeolian sand to produce UHPC....

Aiming to investigate the mix design of eco-friendly UHPC with supplementary cementitious materials and coarser aggregates, we comprehensively studied the workability, microstructure, porosity, compressive strength, flexural strength, and Young’s modulus of UHPC. Relationship between compressive strength and Young’s modulus was obtained eventually. It is found that the compressive strength, flexural strength, and Young’s modulus of UHPC increase by 19.01%, 10.81%, and 5.99%, respectively, when 40wt% cement is replaced with supplementary cementitious materials. The relationship between compressive strength and Young’s modulus of UHPC is an exponential form.

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&ndash, 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&ndash, 16.83%, 11.26&ndash, 26.62%, 15.63&ndash, 29.54%, and 5.84&ndash, 12.25%, respectively, (3) the resistance of the UHPC to penetration of chloride ions increased, and the freeze&ndash, 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.

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&rsquo, s modulus of the designed UHPC samples were in the ranges of 163.9&ndash, 207.0 MPa, 18.0&ndash, 32.2 MPa, and 49.3&ndash, 58.9 GPa, respectively, (2) the compressive strength, flexural strength, and Young&rsquo, 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&ndash, Young&rsquo, 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.

In this paper, the feasibility of using urea as an additive to prepare low exothermic concrete is studied. The effect of different urea contents (0%, 5%, 10%, 15%) urea on the hydration process and the microstructure of the cementitious materials were investigated systematically. The experimental results show that urea has an obvious retarding effect on the early hydration of cement. The curve of the hydration heat release was significantly reduced and delayed with the urea content increased. The early strength of the concrete decreased significantly. Urea has almost no effect on the compressive strength of concrete at 28 days of age. The actual water-to-binder ratio is lowered, and the hygroscopicity and recrystallization of urea are the main reasons for shrinkage reduction and even micro-expansion of concrete. Scanning electron microscope (SEM) and X-ray diffractometer (XRD) results show that urea does not change the cement hydration products. The total amount of chemically bound water and the degree of hydration of the sample show that urea has a greater inhibitory effect on early hydration of cement and less effect on hydration in a later stage. The results of mercury intrusion porosimetry (MIP) show that the total porosity of cement paste has a consistent trend with mechanical properties. When the content of urea in concrete exceeds 10%, white crystals appear inside of concrete. The Fourier Transform Infrared Spectrometry (FT-IR), Differential thermal analysis (TG-DSC) and SEM result show that crystalline product is produced by urea crystallization.