Effect of Condensed Silica Fume on the Steel-Concrete Bond

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Title: Effect of Condensed Silica Fume on the Steel-Concrete Bond

Author(s): Odd E. Gjorv, Paulo J. M. Monteiro, and P. K. Mehta

Publication: Materials Journal

Volume: 87

Issue: 6

Appears on pages(s): 573-580

Keywords: bond (concrete to reinforcement); cement pastes; compressive strength; microstructure; morphology; porosity; pullout tests; silica fume; Materials Research

Date: 11/1/1990

Abstract:
The objective of this work was to study the effect of condensed silica fume (CSF) on the mechanical behavior of the steel-concrete bond, and on the microstructure of the steel-cement paste transition zone. The mechanical behavior was studied by using the ASTM C 234 pullout test on concrete of varying compressive strengths (5000, 6000, 9000, and 12,000 psi)and varying contents of CSF (0, 8, and 16 percent by weight of cement). The effect of CSF on the steel-cement paste transition zone was studied in small composite sections by using scanning electron microscopy and X-ray diffraction analysis. Increased additions of CSF up to 16 percent by weight of cement showed an improving effect on pullout strength, especially in the high compressive strength range of the concrete. The presence of CSF affected the morphology and microstructure of the steel-cement paste transition zone. Thus, both porosity and thickness of the transition zone were reduced. The observed effect of CSF may be explained by several mechanisms: reduced accumulation of free water at the interface during specimen casting; reduced preferential orientation of CH crystals at the steel-paste transition zone; and densification of the transition zone due to pozzolanic reaction between CH and CSF.