Functional ultra-high performance concrete with sisal fibre for nuclear containment: Mechanical, impact, and high-temperature performance

Severe nuclear accidents entail the peril of falling molten corium onto the sacrificial concrete basemat, jeopardizing containment vessel integrity through structural compromise and potential radioactive release. Traditional sacrificial concrete poses challenges due to its limited strength and susceptibility to explosive spalling under extreme thermal stress. To reduce such risks, this research produced a functional ultra-high performance concrete (FUHPC) based on sisal fibre, which combines blast resistance, impact resistance and sacrificial properties. Using a Modified Andreasen and Andersen (MAA) model for mix design, a systematic study was conducted on the effects of different sisal fibre content on the mechanical properties, impact resistance, and high-temperature performance of FUHPC. The results indicate that when the fibre volume fraction is 0.6 vol%, the material properties are synergistically enhanced: (1) Flexural strength, compressive strength, elastic modulus and impact resistance were 25.72 MPa, 153.13 MPa, 48.30 GPa and 243.26 MPa respectively, representing increases of 19.74%, 16.03%, 15.77% and 16.96% compared to the control group. (2) Chloride ion migration coefficient decreased by 19.47%, and dry shrinkage rate decreased by 10.14%; (3) Microstructural analysis revealed that sisal fibres effectively refined the pores and formed a crack-blocking network, significantly enhancing the matrix density; (4) After exposure to 1000°C high temperatures, sisal fibres shrink to form interfacial gaps. Their natural tubular structure, combined with micro-cracks caused by thermal shrinkage, constructs a multi-scale steam channel network. This unique pore structure effectively dissipates internal steam pressure, preventing high-temperature explosions. Additionally, the free water content of FUHPC is below 5%, meeting the requirements for sacrificial concrete. Comprehensive performance evaluation determined that the optimal admixture ratio of sisal fibre is 0.6 vol%. This study provides a new approach for the development of explosion-resistant, impact resistance nuclear safety protection infrastructure. • Mixture of FUHPC was designed via MAA particle packing model. • Mechanical and impact resistance properties of FUHPC were improved via sisal fibre. • Pore structure of FUHPC were improved by sisal fibre. • High-temperature properties of FUHPC were improved via sisal fibre. • Optimal amount of sisal fibre in FUHPC was determined to be 0.6 vol%.