Tracing the Status of Silica Fume in Cementitious Materials Subjected to Deterioration Mechanisms with Raman Microscope

The status and stability of the unreacted silica fume (SF) agglomerates existing in concrete structures subjected to various deterioration environments is largely unknown, but is a critical issue which could cause public concern. This work employed a Raman microscope, which combines the Raman spectroscopy with a light optical microscope, to characterize the phase assemblage in 6-month-old SF blended Portland cement (PC) pastes after 3-month exposure to simulated deterioration mechanisms (viz. carbonation, chloride attack, or sulfate attack), in order to illustrate the status of SF. Unhydrated SF phases, in terms of amorphous silica (Raman shift at about 350–540 cm(−1)), were identified in the SF blended paste samples after being exposed to carbonation and sulfate attack, indicating that there is a potential hazard to the living system, especially the structures undergoing long-term ‘interactions’ with a contiguous environment.