Optimization of Silica Fume, Fly Ash and Amorphous Nano-Silica in Superplasticized High-Performance Concrete

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Title: Optimization of Silica Fume, Fly Ash and Amorphous Nano-Silica in Superplasticized High-Performance Concrete

Author(s): M. Collepardi, S. Collepardi, U. Skarp, and R. Troli

Publication: Special Publication

Volume: 221

Issue:

Appears on pages(s): 495-506

Keywords: carbonation; chloride diffusion; fly ash; high-performance concrete; self-compacting concrete; silica fume; steam-curing; superplasticizer; ultra-fine amorphous colloidal silica

Date: 5/1/2004

Abstract:
The influence of some pozzolanic additions—such as silica fume, fly ash and ultra-fine amorphous colloidal silica (UFACS)—on the performance of superplasticized concrete was studied. Superplasticized mixtures in form of flowing (slump of 230 mm) or self-compacting concretes (slump flow of 735 mm) were manufactured all with a water-cement ratio as low as 0.44, in order to produce high-performance concretes (HPC). They were cured at room temperature (20°C) or steam-cured at 65°C in order to simulate the manufacturing of pre-cast members. Concretes with ternary combinations of silica fume (15-20 kg/m3), fly ash (30-40 kg/m3) and UFACS (5-8 kg/m3) perform better—in terms of strength and durability—than those with fly ash alone (60 kg/m3) and approximately as those with silica fume alone (60 kg/m3). Due to the reduced avail-ability of silica fume on the market, these ternary combinations can reduce by 60-70% the needed amount of silica fume for each pre-cast HPC element at a given performance level. Moreover, at later ages the strength reduction in steam-cured concretes with respect to the corresponding concretes cured at room temperature, is negligible or much lower in mixtures with the ternary combinations of pozzolanic additions.