Effect of curing regimes on microstructural and strength characteristics of UHPC with ultra-fine fly ash and ultra-fine slag as a replacement for silica fume

• Published in: Arabian journal of geosciences 2022-02, Vol.15 (4), Article 345
• Main Authors: Shanmugasundaram, Athibaranan, Jayakumar, Karthikeyan
• Format: Article
• Language: English
• Subjects: Backscattering; Calcium; Calcium silicate hydrate; Compressive strength; Concrete; Curing; Curing (processing); Earth and Environmental Science; Earth science; Earth Sciences; Electron microscopy; Feasibility studies; Flexural strength; Fly ash; Gels; Heat; Heat treatment; Heat treatments; Hydrates; Mechanical properties; Mercury; Microstructure; Original Paper; Scanning electron microscopy; Silica; Silica fume; Silicates; Silicon dioxide; Slag; Steam curing; Substitutes; Tests; Ultra high performance concrete
• ISSN: 1866-7511; 1866-7538
• DOI: 10.1007/s12517-022-09617-y

This paper discusses the feasibility of using ultra-fine slag (US) and ultra-fine fly ash (UF) as a silica fume substitute in ultra-high-performance concrete (UHPC). Initially, a control mix (including silica fume) was arrived at using a trial-and-error approach, and silica fume was substituted with US and UF by 0, 25%, 50%, 75%, and 100% in the obtained mix. Curing regimens for the control, UF, and US replacement specimens include normal curing, steam curing, and heat curing. In this work, the mechanical and microstructural performance of control, US, and UF substituted specimens is investigated. Compressive, split tensile, and flexural strength tests were used to evaluate the mechanical properties. Backscattered scanning electron microscopy (BSE-SEM) and mercury intrusion porosimeter (MIP) tests were used to conduct microstructural investigations. The mechanical investigation demonstrates that when subjected to steam or heat treatment curing, the properties of control, and UF- and US-replaced specimens are equivalent, even at 100% replacement. When compared to control specimens, and UF- and US-replaced concrete exhibits slightly inferior performance at normal or water-cured specimens, which is compensated by a maximum increase in strength up to 52% by steam and heat curing on UF- and US-replaced concrete. As a result, UHPC replaced with UF and US, proved to be very effective, particularly under thermal curing regimes. The BSE-SEM and MIP tests also show that all UHPC specimens have a dense microstructure due to the formation of dense calcium silicate hydrate gel.