Effect of ultra-fine fly ash on concrete performance and durability. (10th December 2020)

• Record Type: Journal Article
• Authors: Kara De Maeijer, Patricia; Craeye, Bart; Snellings, Ruben; Kazemi-Kamyab, Hadi; Loots, Michel; Janssens, Koen; Nuyts, Gert
• Is Part Of: Construction & building materials. Volume 263(2021)
• Publication Date: 2020-12-10
• Subjects: Concrete -- Ultra-fine fly ash -- Compressive strength -- Corrosion resistance -- ASR; Building materials -- Periodicals; 624.18
• DOI: 10.1016/j.conbuildmat.2020.120493
• Languages: English
• ISSNs: 0950-0618

Abstract

Highlights: Improved reactivity of ultra-fine fly ash. Increased workability in case of increased fineness of fly ashes. Equal compressive strength of CEMI-FA2-25% to CEMI-REF at the age of 28 days. Positive effect on the resistivity, chloride migration coefficient and ASR. Negative effect on carbonation resistance. Abstract: In the present study ultra-fine fly ash as a novel by-product obtained by a dry and closed separation process was investigated as cement replacement in concrete. The impact of ultra-fine fly ash on material properties was investigated following an upscaling as an approach considering paste, mortar and concrete properties. Two types of cement, Portland cement (CEMI) and slag cement (CEMIII), two types of ultra-fly ashes, one with particle size d90 < 9.3 μm (FA1) and second with d90 < 4.6 μm (FA2) were used. At paste- and mortar- level, cement was replaced at 0%, 15%, 25%, 35% and 50% with FA1 and FA2. At concrete- level, cement was replaced at 0%, 15% and 25% with different ratios of FA1 and FA2. The results at paste- and mortar- level showed that an increased fineness of the fly ash (FA2) contributes to better workability of the mix. For CEMI, the compressive strength of concrete with FA2 at 25% cement replacement was already equal to the reference 0% replacement concrete at the age of 28 days. For CEMIII, the compressive strength of concrete mix with FA1 with 15% and FA2 with 25% cement replacements reached the reference concrete value at the age of 91 days. Regarding the durability, replacing cement with ultra-fine fly ash (FA2) had a positive influence on the resistivity, chloride migration coefficient and alkali-silica reaction (ASR), and a negative influence on the carbonation resistance.