Mechanical properties and constitutive model of fibre-reinforced high-performance class-F fly ash foam concrete

Fibre-reinforced high-performance fly ash foam concrete (FHFC) has broad engineering application prospects owing to its lightweight and high-strength, energy-saving, heat preservation and environmental protection characteristics. Its mechanical properties and constitutive models can serve as an important basis for engineering structural design, numerical analysis and structural reliability monitoring. Aimed at exploring the influence of different factors on the physical and mechanical properties of FHFC and its stress–strain constitutive relationship, the dry density, cube compressive strength, splitting tensile strength and axial compressive strength of 27 groups of FHFC with different mixture proportions were measured and analysed. The primary and secondary relationships of the water–binder ratio, sand–binder ratio and replacement rate of fly ash to cement on the physical and mechanical properties of FHFC were studied. The failure mechanism of FHFC under uniaxial compression was discussed and a two-stage phenomenological constitutive model of FHFC was established through theoretical derivation. The results show that sand–binder ratio and water–binder ratio are the main factors affecting the physical and mechanical properties of FHFC. The stress–strain curve shows the characteristics of stages, namely, the elastic–plastic stage, the stress upswing stage, the plastic plateau stage and the failure stage. The influence of each factor on the elastic–plastic stage of the stress–strain curve shows obvious regularity, but the influence on the plastic stage is complex, and the regularity is not significant. The established two-stage phenomenological constitutive model is in good agreement with the stress–strain curve obtained from the test, and it can more accurately predict the uniaxial compression response of FHFC. The model can be used for the theoretical calculation of the bearing capacity of high-strength foam concrete structural members and even serve as an important basis for the engineering application of high-strength foam concrete.