Title: The Development of Microstructure of Portland Cement Mortars - From the Fresh to the Hardened State

Author(s): Knut O. Kjellsen, Sidney Diamond

Publication: NCR

Volume: 45

Issue: 2

Appears on pages(s): 15-24

Keywords: Portland cement, fresh mortar, hardened mortar, microstructure, SEM

DOI:

Date: 6/15/2012

Abstract:
SEM-BSE examination of freshly-mixed, early age and late age Portland cement mortar specimens are reported. Freshly mixed mortars reveal complex features that appear to influence subsequent development of the hardened state microstructure. The larger cement grains were found to be distributed in-homogeneously within the paste of the freshly-mixed mortars, ‘pockets’ of paste being either relatively densely packed with large cement grains, or largely bereft of such grains. These ‘pockets’ gave rise to either ‘densely packed patches’ or ‘porous patches’ in the hardened mortars. Local indications of ITZ were occasionally observed in our visual examination. The microstructure of freshly-mixed mortar also contains layers of entirely water-filled space a few micrometers thick in the paste immediately adjacent to many sand grain surfaces. After a few hours, sparse deposits of calcium hydroxide, and later C-S-H and presumably other reaction products, may form in these spaces.