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Ultra-lightweight foamed geopolymer (UFG) based on fly ash-metakaolin blends with its density of between 150 kg/m 3 and 300 kg/m 3 was successfully prepared by the mixed foaming method of chemical foaming. In the present study, the properties and characteristics of UFG were investigated by designing and optimizing the components of fly ash, metakaolin, alkaline activator, foam stabilizer and foaming agent (H 2 O 2 ), as well as the curing temperature. The results showed that foamed geopolymer with curing age of 7 days presented its dry density between 150 kg/m 3 and 300 kg/m 3 , the mean pore size between 0.57 mm and 1.13 mm, the porosity between 71.8% and 84.5%, the thermal conductivity between 0.0622 W/(m·K) and 0.0852 W/(m·K) and the compressive strength between 0.68 MPa and 2.23 MPa, showing better mechanical properties than the traditional portland cement foamed concrete with the same density. It is also found that curing temperature at 55 °C for 12 h seemed to substantially improve the compressive strength of UFG which is 1.91 MPa compared to curing at 25 °C for the same period of time. [ABSTRACT FROM AUTHOR]

• The fluidity of UHPCC fresh mortar is directly related to ST-GNPs content. • The effect of ST-GNPs on the microstructure change of the UHPCC is investigated. • The introduction of ST-GNPs is confirmed to reduce the resistivity of UHPCC. • The self-perceived performance of UHPCC with ST-GNPs has been evaluated. An ultra-high-performance cement-based composite (UHPCC) with excellent mechanical behaviors and self-perceived properties was successfully prepared in this work. The effects of silane-treated graphene nano-platelets (ST-GNPs) on the fluidity, porosity, degree of hydration, mechanical behaviors, and self-perceived properties of UHPCC were investigated. The results revealed that the fluidity of UHPCC fresh mortar is directly related to ST-GNPs content. The fluidity decreases as the amount of ST-GNPs increases. Furthermore, when the amount of ST-GNPs was 0.05%, the porosity of UHPCC was found to be 11.5%, and the compressive strength and flexural strength reached the maximum value of 142.5 MPa and 23.8 MPa, respectively. Additionally, the microstructure of the UHPCC was investigated. Also, it was indicated that the introduction of ST-GNPs could enhance the transformation of fibrous calcium silicate hydrate (C–S–H) gel into petal-like hydration products, which has the tendency to continuous interpenetration. Further, the introduction of ST-GNPs is confirmed to reduce the resistivity of UHPCC from 18.85 kΩ·m to 6.26 kΩ·m. Finally, the self-perceived performance of UHPCC with 0.05% ST-GNPs was observed to be about double that of UHPCC without ST-GNPs, which indicates that the UHPCC prepared by adding ST-GNPs has excellent self-perceived performance. [ABSTRACT FROM AUTHOR]

• Thermodynamic cement hydration models were proposed to calculate hydration products over time. • The phase equilibrium model and the surface complexation model were unified to describe the chloride binding isotherm. • Influences of sulfate on the chemically bound chloride and physically adsorbed chloride were studied. • The evolution of Friedel's salt and ettringite was tested and verified by the thermodynamic model. This paper mainly investigates the chloride binding capacity of cement paste immersed in chloride and various chloride-sulfate solution. Taking into account the influence of sulfate on the chemically bound and physically adsorbed chloride, a thermodynamic model consisting of hydration model, phase equilibrium model and surface complexation model is established to describe the chloride binding behavior. The formation of Friedel's salt and ettringite in chloride-sulfate solution are tested by XRD and simulated by the thermodynamic model. The model result of chloride binding behavior in chloride and chloride-sulfate solution are in good agreement with the experimental results. Physically absorbed chloride ions and chemically bound chloride ions are calculated quantitatively. The formation of Friedel's and Kuzel's salt are reduced by the presence of sulfate as well as the chloride adsorbed on C-S-H. The evolution of Friedel's salt and ettringite is closely related to chloride and sulfate concentrations, which is confirmed by the experiment and the proposed model. The thermodynamic model proposed in this paper can be useful to effectively describe the interaction between chloride and sulfate on cement paste. [ABSTRACT FROM AUTHOR]