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Manufacturing Ultra High Performance Concretes by Silica Fume, Ultra Fine Fly Ash and Metakaolin Addition



Author(s)

Tony Song, Ion Dumitru and Bob Bornstein

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DOI:10.17265/2161-6213/2017.5-6.003

Boral Construction Materials, Australia

SF (silica fume) has been widely used in high performance concrete manufacturing due to its pozzolanic reactivity and the filler effect of ultra-fine particles. Recently ultra-fine grades of fly ash and metakaolin have been assessed and compared with SF concretes. This paper evaluates four commercially available products in manufacturing high performance concrete, including two SF (control I and II), one ultra-fine fly ash and one ultra-fine metakaolin. The study firstly assessed the properties of each raw material, including the loss of ignition, particle size distribution, relative water demand, relative strength, available alkali, and pozzolanic index. Concrete trial mixes were further carried out to assess the concrete properties, including workability by slump, compressive strength development up to 91 days, drying shrinkage up to 91 days, durability in terms of sorptivity and rapid chloride migration coefficient tests NT 492. The study has concluded that at a given workability (slump of 200 mm), the concrete with ultra fine fly ash required about 15-25 kg/m³ less water, and achieved about 5-20 MPa higher compressive strength in 91 days, depending on the type of the SF used as the control. The sorptivity and chloride migration coefficient data show that concrete with ultra fine fly ash can achieve similar durability properties with SF used as control. The concrete with ultra-fine metakaolin requires similar water to control I and about 9 kg/m³ more water than control II. The ultra-fine metakaolin concrete develops higher strength than control I, with similar compressive strength when compared to control II mix. This concrete mix has the lowest drying shrinkage than both controls and ultra-fine fly ash concretes. In terms of durability properties (sorptivity and chloride diffusion tests), concrete with ultra-fine metakaolin showed the best performance, especially at early age (i.e. 28 days). Therefore, it is possible to manufacture high performance concrete with ultra-fine fly ash or ultra-fine metakaolin to replace SF.

SF, ultra-fine fly ash, ultra-fine metakaolin, high performance concrete.