Early age microstructure of the paste-aggregate interface and its evolution

Davide Zampini*, Surendra P. Shah, Hamlin M. Jennings

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

58 Scopus citations

Abstract

The sequence of microstructural changes occurring at the wet paste-aggregate interface is documented at an age as early as 5 min using the environmental scanning electron microscope (ESEM). Unlike other microscopic techniques, the ESEM allows pastes of normal water: cement ratio to be observed at early ages without reducing the paste to a powder. Evolution of the paste-aggregate microstructure is followed up to an age of 24 h. The region adjacent to the aggregate surface contains a phase with a morphology referred to as a "sheaf of wheat" morphology. The same interfacial region in a 10-day-old specimen has a microstructure similar to the interfacial transition zone (ITZ) reported in the literature. Variations of the "sheaf of wheat" morphology due to original water-to-cement ratio, mixing energy, incorporation of silica fume, and drying are documented. As revealed by energy dispersive x-ray analysis (EDS), the microstructure contains significant amounts of calcium and silica. These results indicate that the observed morphology is likely to be a calcium silicate hydrate (C-S-H) product that is a precursor to type I C-S-H. A description of the evolution of the observed microstructural features is presented. The "sheaf of wheat" morphology appears to be a general precursor to morphologies commonly seen in mature pastes.

Original languageEnglish (US)
Pages (from-to)1888-1898
Number of pages11
JournalJournal of Materials Research
Volume13
Issue number7
DOIs
StatePublished - Jul 1998

Funding

The National Science Foundation (NSF) Center for Science and Technology of Advanced Cement-Based Materials is acknowledged for its support through Grant No. CHE9120002. The author also wishes to express his sincere gratitude toward Marina Reider who provided valuable assistance with the microscopy.

ASJC Scopus subject areas

  • General Materials Science
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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