ZOU D H, ZHANG Y S, XIAO L T, et al． Effect of supplementary cementitious materials modified by short chain alkyl-silane on workability and mechanical properties of ultra-high-performance concrete[J]. Journal of Henan Polytechnic University( Natural Science) ， doi: 10.16186/j.cnki.1673-9787. 2024070028.

doi: 10.16186/j.cnki.1673-9787.2024070028

Received： 2024-07-08

Revised： 2024-10-09

Online： 2024-12-25

Effect of supplementary cementitious materials modified by short chain alkyl-silane on workability and mechanical properties of ultra-high-performance concrete (Online)

ZOU Dinghua¹_, ZHANG Yisheng^1,2, XIAO Lutong¹, LOU Guanghui³, ZHANG Haibo¹, ZHU Yu¹

1.School of Materials Science and Engineering, Henan Polytechnic University, Jiaozuo 454003, Henan ,China；2.Henan Academy of Sciences，Zhengzhou 450046, Henan ,China；3.Henan Building Materials Research and Design Institute Co., Ltd,Zhengzhou 450002, Henan ,China

Abstract: Objectives The research presented in this paper aims to survey the feasibility of improving the workability of ultra-high-performance concrete (UHPC) using supplementary cementitious materials (SCMs) modified by alkyl-silane with short carbon chain. Propyltriethoxysilane (PTOS) and triethoxyoctylsilane (TEOS), with carbon chain containing 3 and 8 carbon atoms, respectively, were adopted. Methods Silica fume and fly ash were modified for UHPC preparation. Slump flow and T400, the time for fresh concrete spreading up to 400 mm, of UHPC slurry with and without silane modified SCMs were measured. Effects of the modification on pozzolanic reaction of SCMs and mechanical properties of UHPC were also investigated.  Results The experiment results demonstrated that the workability of UHPC slurry was promoted evidently by PTOS and TEOS modified SCMs. Moreover, the SCMs modified by PTOS showed higher effect than those modified by TEOS. However, the hydrophobicity of the silanes inhibited the pozzolanic reaction of SCMs at 1 and 3 days. This postponed and lowered the main hydration heat peak of UHPC pastes. The amount of the hydration products and the strengths of the UHPC with silanes modified silica fume at 1 and 3 days were decreased thereby. A less impact on main hydration heat peak and amount of the hydration products of UHPC pastes with silanes modified fly ash and plain silica fume was observed at 1 and 3 days. The reduction of the strengths was also lower. The acceleration effect of the POTS facilitated the precipitation of the hydration products after 3 days. The strengths of the UHPC with PTOS modified SCMs were comparable to that of the plain one at 28 days. The higher hydrophobicity of TEOS due to its longer carbon chain enhanced the inhibitory effect on pozzolanic reaction of SCMs, which reduced the amount of the hydration products and strengths of UHPC at 28 days. Conclusions Silica fume and fly ash modified by alkyl silanes with short carbon chain improve the workability of UHPC slurry but had a slight impact on early strength. Silanes facilitate the precipitation of the hydration products at later age. At 28 days, the amount of hydration products and strength of UHPC with PTOS modified SCMs were comparable to that of the plain one.

Key words: Ultra-high-performance concrete (UHPC); Supplementary cementitious materials (SCMs); Alkyl silane; Surface modification; Workability; Strength