Enhancement of artificial tuff sand by permeated nano crystallization and the application on ecological UHPC as aggregate

To meet the challenge on dredging limitation of natural sand, the low grade tuff sand (TS) was selected as aggregate to prepare tuff ultra-high performance concrete (TUHPC). The TS was pre-improved with nano permeated crystallization method, and replaced river sand with different ratio. The performance of treated TS and their effects on TUHPC were both investigated. The results shown that, the physical performance of treated TS was all improved, more nano-sized products were filled in TS pores and surface. The flowability of TUHPC was affected by different methods and TS ratio, but the strength was all improved with treated TS, and reached the maximum increasement of 34.5%. The generated orthosilicic acid was hydrolyzed to form a 3D network gel product, refine the pore structure and reacted with cement to enhanced the bond strength. The ITZ became more regular and spherical with treated TS, and the hardness was increased as well as the width became narrow. The hydration products in ITZ were more compact, with lower Ca/Si. • The physical properties of TS were all improved after permeated crystallization treatment; • The porosity of TS was decreased 35% for maximum; • The strength of TUHPC at each substituted ratio was improved with modified TS than raw one; • The ITZ became more spherical with higher hardness and modulus; • The width of ITZ was reduced from 30 μm to 20 μm, and lower Ca/Si in ITZ hydration products.