Using nanomaterials is a new method to improve concrete material, and graphene or its derivatives are currently the most attractive nanomaterials. This paper aims to experimentally evaluate the effects of graphene sulfonate nanosheets (GSNSs) on physical, mechanical, and thermal properties of sacrificial concrete. The microstructure, porosity, compressive strength, thermal analysis, coefficient of thermal expansion, thermal diffusivity and ablation behaviour of sacrificial concrete with different contents of GSNSs before and during exposure to various temperatures up to 1000 ºC were comprehensively investigated. A new experimental apparatus was proposed and used to measure the compressive strength of sacrificial concrete during elevated temperature exposure. It was found that, (1) the compressive strength, thermal diffusivity, and decomposition enthalpy of sacrificial concrete increased by 10.14-23.11%, 6.51-27.66%, and 7.48%, respectively, when adding 0.1 wt% GSNSs; (2) the porosity and ablation velocity of sacrificial concrete reduced by 2.00-6.00% and 7.48%, respectively, due to the incorporation of GSNSs.

1 / 24 Mechanical and physicochemical properties of ferro-siliceous concrete subjected to elevated temperatures

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The theory of poroelastic behavior in a deformable porous medium containing two immiscible, viscous, compressible fluids was applied to the three‐dimensional consolidation of unsaturated soils. Three coupled partial differential equations were developed that feature the displacement vector of the solid phase and the excess pore water and air pressures as dependent variables. These equations generalize the classic Biot consolidation model, which applies to saturated soils, with effective stress emerging naturally from a pure compliance formulation of the relation between stress and strain. Under uniaxial strain and constant total compaction stress, the equations simplify to two coupled diffusion equations for the excess pore water and air pressures. Analytical solutions describing the response to instantaneous compression under both permeable and semipermeable boundary drainage conditions were obtained using the Laplace transform. Numerical calculations of pore water pressure, effective stress, and total settlement were made for a soil with clay texture as a representative example. The results show that excess pore water pressure dissipates faster at higher initial water content, leading to higher effective stress. The loading efficiency also was found to be highly sensitive to initial water saturation.

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.

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