Zou D H, Zhang Y S, Xiao L T,et al.Effect of short-chain alkyl silane-modified supplementary cementitious materials on the workability and mechanical properties of ultra-high-performance concrete[J].Journal of Henan Polytechnic University(Natural Science) ,2026,45(6):185-192.

doi:10.16186/j.cnki.1673-9787.2024070028

Received:2024/07/08

Revised:2024/10/10

Published:2026/10/09

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

Zou Dinghua1, Zhang Yisheng1,2, 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 poor workability of ultra-high-performance concrete （UHPC） resulting from its low water-to-binder ratio and the hydrophilicity of silica fume was the focus of this study. The feasibility of improving the workability of UHPC by using short-chain alkyl silane-modified supplementary cementitious materials （SCMs） was investigated. Methods Silica fume and fly ash were surface-modified using propyltriethoxysilane （PTOS） and octyltriethoxysilane （OTES）， respectively. The slump flow and T400， defined as the time required for fresh UHPC to spread to 400 mm， were measured for UHPC mixtures containing unmodified and modified SCMs. The pozzolanic reaction of modified SCMs and their effects on the properties of UHPC were analyzed by measuring hydration heat， non-evaporable water content， compressive strength， and flexural strength.  Results The results showed that the incorporation of modified SCMs significantly improved the workability of UHPC， and PTOS-modified SCMs showed a greater improvement in workability than OTES-modified SCMs. The hydrophobicity of silanes inhibited the pozzolanic reaction of SCMs at the ages of 1 and 3 days. This inhibition delayed and reduced the main hydration heat evolution peak of modified UHPC. Consequently， the hydration products and early-age strength of UHPC incorporating silane-modified silica fume decreased. However， silane-modified fly ash had a relatively minor effect on the early-age hydration heat evolution and hydration product formation of UHPC. PTOS promoted the formation of hydration products after 3 days and improved the strength of modified UHPC after 3 days. At 28 days， the strength of UHPC containing PTOS-modified SCMs was comparable to that of the control group， whereas UHPC containing OTES-modified SCMs exhibited lower amounts of hydration products and lower strength than the control group.  Conclusions Short-chain alkyl silane-modified SCMs significantly improved the workability of fresh UHPC， increased the slump flow， and had only a slight influence on early-age strength.

Key words: ultra-high-performance concrete ;supplementary cementitious materials; alkyl silane; surface modification