Nanoscience and nanoengineering of cement-based materials - Nanotechnology in Eco-efficient Construction - page 14

The technique further contributed to the study of other chemical con-
stituents of cement paste as well as their chemomechanical stability in time.
The carbonation of calcium hydroxide crystals, prepared using the mica-
replication method, exposed to various environments (combinations of N 2 ,
O 2 , H 2 O, and CO 2 ), has been studied using AFM images. Spherules of
CaCO 3 , the chemical product of the carbonation reactions, have been
observed and the necessary conditions for their formation have been
recorded (Yang et al. , 2003). The technique currently provides reliable
means of seeing at the nanoscale of C-S-H and assists in the quantifi cation
of either modifi cation attempts (e.g., Weiguo et al. , 2011) or in the funda-
mental understanding of chemical formation or degradation phenomena.

Nanoindentation

The advent of instrumented indentation enabled fundamental studies of the
nanomechanical response of metals, ceramics, polymers, and composites
(see, e.g., Oliver and Pharr, 1992, 2004; Fischer-Cripps, 2011). Current tech-
nology allows for contact-based deformation of nanoscale load and dis-
placement resolution and has been leveraged for both general mechanical
characterization of small materials volumes and unprecedented access to
the physics and deformations processes of materials. While nanoindentation
was originally developed for homogeneous metals and ceramics, it was
quickly appreciated that nanoscale resolution can be of signifi cant use to
the decoding of C-S-H structure, the binding phase of all cementitious
materials (Constantinides et al. , 2003; Constantinides and Ulm, 2004).
However, accurate nanomechanical analysis of composites requires
advanced analysis that takes into consideration the multi-phase, multi-scale
nature of the material and its pressure-sensitive mechanical response (Con-
stantinides et al. , 2003; Constantinides and Ulm, 2004, 2007; Ulm et al. , 2005,
2007, 2010; Ganneau et al. , 2006; Trtik et al. 2009; Randall et al. , 2009).
A typical nanoindentation test consists of establishing contact between
an indenter (typically diamond) and a smooth sample (Miller et al. , 2008),
while continuously measuring the load, P and the penetration depth h
(Plate I between pages 162 and 163). Analysis of the P-h response proceeds
by applying a continuum scale model (Fischer-Cripps, 2011) to derive

￿ ￿ ￿ ￿ ￿ ￿

2 S

A c

the indentation modulus M , M = , and indentation hardness H ,

P
A c

max , where S is the unloading slope at maximum depth h max , P max is

H =

the maximum indentation force, and A c is the projected contact area at
h max . Several empirical means to estimate A c exist, either through post-
indentation inspection, geometric idealizations of the probe, or more com-
monly through analysis of the indentation response for a material of