Title: Chemical and Physical Effects of Silica Fume on the Mechanical Behavior of Concrete

Author(s): Rachel J. Detwiler and P. Kumar Mehta

Publication: Materials Journal

Volume: 86

Issue: 6

Appears on pages(s): 609-614

Keywords: aggregates; carbon black; cement pastes; chemical analysis; compressive strength; concretes; crack propagation; mechanical properties; modulus of elasticity; physical properties; pozzolans; silica fume; stress-strain diagram; Materials Research

DOI: 10.14359/2281

Date: 11/1/1989

Abstract:
The appropriate use of silica fume improves both the mechanical characteristics and the durability of concrete. However, there is some disagreement among researchers as to whether the mechanisms underlying these improvements depend primarily on the physical or the pozzolanic nature of silica fume. In this work, carbon black, which is physically similar to silica fume but is not pozzolanic, is used to evaluate the relative significance of the physical and the pozzolanic effects. The results show that at age 7 days the influence of silica fume on the compressive strength of concrete may be attributed mainly to physical effects. By age 28 days, both physical and chemical effects become significant. However, even at age 7 days there is a difference in the resistance to subcritical crack growth in the cement paste-aggregate transition zone between silica fume and carbon black mixes. This explains the differences in the shapes of the stress-strain curves.