The fundamental mechanisms underlying the influence of nuclear wastes on concrete properties remain poorly understood, especially at the molecular level. Herein, caesium ions (Cs⁺) are introduced into calcium silicate hydrates (CSH) to investigate its effect using molecular dynamics simulation. Structurally, a swelling phenomenon is observed, attributed to the CSH interlayer expansion as Cs⁺ occupies larger space than Ca²⁺. The diffusion of interlayer water, Ca²⁺ and Cs⁺, following an order of water > Cs⁺ > Ca²⁺, is accelerated with increasing Cs⁺ content, owing to three mechanisms: expanded interlayer space, weakened interfacial interaction, and loss of chemical bond stability. Mechanically, the Young’s modulus and strength of CSH are degraded by Cs⁺ due to two mechanisms^: (1) the load transfer ability of interlayer water and Ca²⁺ is weakened; (2) the load transfer provided by Cs⁺ is very weak. Additionally, a “hydrolytic weakening” mechanism is proposed to explain the mechanical degradation with increasing water content. This study also provides guidance for studying the influence of other wastes (like heavy metal ions) in concrete.

核废料影响混凝土性能的基本机理仍然知之甚少，尤其是在分子水平上。在此，将铯离子（Cs ⁺）引入到水合硅酸钙（CSH）中，以使用分子动力学模拟研究其作用。在结构上，观察到溶胀现象，这归因于CSH ^+的层间膨胀，因为Cs ⁺比Ca ²⁺占据更大的空间。随水> Cs ⁺ > Ca ²⁺的顺序，层间水Ca ²⁺和Cs ⁺的扩散随着Cs ^+的增加而加速含量，这归因于以下三种机理：扩大的层间空间，减弱的界面相互作用以及化学键稳定性的损失。在机械上，Cs ⁺会降低CSH的杨氏模量和强度，其原因有两个^：（1）层间水和Ca ²⁺的负荷传递能力减弱；（2）Cs ⁺提供的负载转移非常弱。此外，提出了一种“水解弱化”机理来解释随着水含量增加而引起的机械降解。该研究还为研究混凝土中其他废物（如重金属离子）的影响提供了指导。