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Advances in Concrete Construction
  Volume 9, Number 5, May 2020 , pages 449-457

Effects of subsequent curing on chloride resistance and microstructure of steam-cured mortar
Yuquan Hu, Shaowei Hu, Bokai Yang and Siyao Wang

    The influence of subsequent curing on the performance of fly ash contained mortar under steam curing was studied. Mortar samples incorporated with different content (0%, 20%, 50% and 70%) of Class F fly ash under five typical subsequent curing conditions, including standard curing (ZS), water curing(ZW) under 25oC, oven-dry curing (ZD) under 60oC, frozen curing (ZF) under -10oC, and nature curing (ZN) exposed to outdoor environment were implemented. The unsteady chloride diffusion coefficient was measured by rapid chloride migration test (RCM) to analyze the influence of subsequent curing condition on the resistance to chloride penetration of fly ash contained mortar under steam curing. The compressive strength was measured to analyze the mechanical properties. Furthermore, the open porosity, mercury intrusion porosimetry (MIP), x-ray diffraction (XRD) and thermogravimetric analysis (TGA) were examined to investigate the pore characteristics and phase composition of mortar. The results indicate that the resistance to chloride ingress and compressive strength of steam-cured mortar decline with the increase of fly ash incorporated, regardless of the subsequent curing condition. Compared to ZS, ZD and ZF lead to poor resistance to chloride penetration, while ZW and ZN show better performance. Interestingly, under different fly ash contents, the declining order of compressive strength remains ZS>ZW>ZN>ZD>ZF. When the fly ash content is blow 50%, the open porosity grows with increase of fly ash, regardless of the curing conditions are diverse. However, if the replacement amount of fly ash exceeds a certain high proportion (70%), the value of open porosity tends to decrease. Moreover, the main phase composition of the mortar hydration products is similar under different curing conditions, but the declining order of the CS-H gels and ettringite content is ZS>ZD>ZF. The addition of fly ash could increase the amount of harmless pores at early age.
Key Words
    steam-cured mortar; subsequent curing condition; fly ash; chloride resistance; microstructure
Yuquan Hu: College of Civil and Transportation Engineering, Hohai University, 1 Xikang Road, Nanjing, China
Shaowei Hu: School of Civil Engineering, Chongqing University, 174 Shazheng Road, Chongqing, China
Bokai Yang: The College of Mechanics and Materials, Hohai University, 8 Fucheng West Road, Nanjing, China
Siyao Wang: School of Water Resources and Hydropower Engineering, Wuhan University,8 Donghu South Road, Wuhan, China

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