Page 484 - New Trends in Eco efficient and Recycled Concrete

434 New Trends in Eco-efficient and Recycled Concrete

Figure 14.5 TEM images of C S H with different morphology: (A) fibrillar outer
C S H; and (B) sheet-like outer C S H (arrows indicate the C S H phenograin/outer
product boundary) (Richardson, 2004). Magnification of (C) globular nanoparticles of
phenograin C S H(Zhang et al., 2004); (E) tobermorite-like fibrilles of outer C S H
(Richardson, 2004); (F) jennite-like foils of outer C S H(Richardson, 2004). (D) AFM
image showing a C S H domain with highly ordered structure (Sanchez and Sobolev,
2010), adapted. TEM, Transmission electron microscopy; AFM, Atomic force microscopy.

layer morphology is analogous to that of tobermorite or of jennite depending on the
starting chemical composition (Pellenq et al., 2008; Richardson, 2008; Papatzani
et al., 2015). Outer C S H has fibrillar morphology (Fig. 14.5E) at high
Ca/(Si 1 Al) ratio, which is associated to tobermorite-based structure (Richardson,
2008). At low Ca/(Si 1 Al) ratio it has sheet-like morphology (Fig. 14.5F) associ-
ated to jennite-based structure (Richardson, 2008). Either way, outer C S H
shows variable packing density, decreasing with the distance from the grain surface
(Scrivener and Nonat, 2011).
CH. CH is a crystalline product with well-defined stoichiometry, Ca(OH) 2 .Itpre-
cipitates as irregular deposits of variable size (up to several micron), both inter-
mingled in the groundmass and around phenograin C S H(Franus et al., 2015). CH
precipitates as euhedral crystals, clearly sighted during observation of cement fracture
surfaces. CH crystals are most often hexagonal (Fig. 14.6A), although depending on
hydration age, available free space for crystallisation (w/c) and type of admixtures
and additives present they can evolve to massive agglomerates (Fig. 14.6B), eventu-
ally with columnar morphology (Fig. 14.6C) (Franus et al., 2015).