利用煅烧硅藻土制备高稳态超高性能混凝土基体研究

超高性能混凝土(UHPC)早期自收缩大,使结构存在收缩开裂风险,掺入天然多孔活性粉料以激发其火山灰和内养护协同效应可有效降低UHPC自收缩,改善基体体积稳定性。本文利用煅烧硅藻土以一定体积分数(3%、6%、9%)置换水泥制备UHPC基体,并对其新拌性能、力学性能、自收缩、耐久性能及孔结构与微观结构进行了系统评价。结果表明:掺入煅烧硅藻土能显著改善UHPC力学性能和体积稳定性,并进一步提升其耐久性能;掺入煅烧硅藻土UHPC基体孔结构得到优化,孔隙率降低,孔径细化;掺入煅烧硅藻土UHPC基体中C-S-H凝胶平均Ca/Si比下降,C-S-H(I)占比提高,水化产物结构及致密性改善。优化设计条件下,UHPC基体56 d抗压强度提高9%,56 d抗折强度提高18%,7 d自收缩下降29%,28 d快速氯离子迁移系数下降35%,28 d电通量下降27%。

Preparation of High Stability Ultra-High Performance Concrete Matrix with Calcined Diatomite

The large early autogenous shrinkage of ultra-high performance concrete (UHPC) will put the concrete at cracking risk, and adding natural porous active powders to stimulate the synergistic effect of pozzolan and internal curing can effectively reduce the shrinkage deformation and improve the volume stability of UHPC matrix. In this study, UHPC matrix was prepared by replacing cement with calcined diatomite in a certain volume fraction (3%, 6%, 9%), its macro performances such as fresh behaviors, mechanical properties, autogenous shrinkage, durability, and microscopic characteristics such as pore structure and microstructure were investigated. The results show that the incorporation of calcined diatomite significantly improves the mechanical properties and volume stability of UHPC matrix, and further enhances its durability. The pore structure of UHPC matrix with calcined diatomite is optimized, the porosity is reduced and the pore diameter is refined. The average Ca/Si ratio of C-S-H gel in UHPC matrix with calcined diatomite decreases, the proportion of C-S-H (I) increases, and the compactness of hydration products is improved. With the optimized design, the 56 d compressive strength of UHPC matrix increases by 9%, 56 d flexural strength increases by 18%, 7 d autogenous shrinkage decreases by 29%, 28 d rapid chloride ion migration coefficient decreases by 35%, and 28 d electric flux decreases by 27%.