ISSN: 0149-6123
Page Count: 8

Comparative Study of the Microstructures of Normal and Very High-Strength Concretes
Aïtcin, P-C
Professeur titulaire, Faculté des sciences appliquées, Université de Sherbrooke, Québec

Sarkar, SL
Attaché de recherche, Faculté des sciences appliquées, Université de Sherbrooke, Québec

Abstract

The microstructure of a normal concrete with water/cement ratio (W/C) = 0.56 (f′c at 28 days = 31.8 MPa or 4610 psi) was compared with two series of very high-strength concretes (up to 118 MPa or 17 120 psi), one made with Type III cement and the other with the same Type III cement plus 6 to 10% silica fume. These concretes were water cured for 91 days. Their microstructural examination was undertaken using mercury porosimetry and scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDXA).

Similarities and differences are described in detail. Basically, both are composed of calcium silicate hydrates (C-S-H) and calcium hydroxide (C-H), but their proportions and morphology are quite different. The composition and types of C-S-H also vary. Significant differences in porosity and aggregate-cement bonding are present. Chloride ion permeability tests indicate the very high-strength concretes to be as impervious as polymer-impregnated types.

Keywords:
very high-strength concrete, compressive strength, microstructure, SEM-EDXA, mercury porosimetry, cement, aggregate, C-H, C-S-H, silica fume, condensate of formaldehyde and naphthalene sulfonate superplasticizer, chloride ion permeability

Paper ID: CCA10070J
DOI: 10.1520/CCA10070J
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