The microstructure formation of C-S-H in the HPC paste from nano-scale feature

AbstractThe nano to micro scale morphology of calcium silicate hydrate (C-S-H) in cement paste with water/cement ratio similar to high performance concrete was characterized by field emission transmission electronic microscopy. It is found that foiled C-S-H is prevalent in outer products (Op) and forms various morphologies with the reduction of free space; first, foils curl up as cigar-like needles; occasionally, foils interleave or stick together, partly forming a honeycomb structure; mostly, lamellar foils pack or crumple thus the paste become a denser matrix. The fibrous C-S-H with diameter around 2.5 nm in Op has certain crystallinity interleaving in the matrix. Amorphous matrix dominates in inner products (Ip), C-S-H granules with diameter of around 2.5 nm pack into a denser bulk, and irregular nanocrystalline regions of about 6 nm present randomly in this matrix. A hypothesis model on fundamental unit of 2–3 nm particles assembling into various dimension nano-features is put forward.