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1. Introduction
Cementitious composites include various types of concretes and
mortars and represent the most used building materials. In gen-
eral, concrete and mortar mixtures are considered by many re-
searches and practitioners as a homogeneous material. Never-
theless, this classification may change according to the level of
observation (micro, meso and macroscopic level). Those materials
whose homogeneity depends on the observation level are called
multiscale materials. Based on this definition, cementitious com-
posites are considered as typical representatives of multiscale ma-
terials since they can be treated as homogeneous in the macro-
scopic level (cm~m length scale), and as heterogeneous material
in a finer level of observation (nm~cm length scale).
Heterogeneity of cementitious composites at the lower level arises
from both the chemical reactions from the hydration process, [1,2],
and the mechanical mixing of non-reactive components, [3,4].
Moreover, transition zones between the phases and also porosity
are present at each scale of the composite.
The multiscale analysis of a composite involves the following steps:
1
microstructure observation (i.e. determination of morphologi-
cal parameters) and separation of chemically different phases;
2
assessment of mechanical properties of individual phases and
their links to chemical properties;
3
upscaling of properties from the microlevel to a broader scale,
[3,5]. The microstructure observation and determination of
phases can be performed, e.g., by analysis of images obtained
from optical microscopy, scanning electron microscopy (SEM)
or atomic force microscopy (AFM).
Several researches, [4-8], have used these techniques to obtain
morphological and chemical parameters of individual material
phases with great success, and equally as in this paper, the mi-
crostructure analysis has often been supplemented by porosity
measurements obtained by mercury intrusion porosimetry and/or
image analysis, among other methods.
The micromechanical analysis of individual material phases
(nm~mm scale) can be obtained by the nanoindentation technique.
This corresponds to a unique technique which allows the mechani-
cal properties of small volumes at nano and micro level. The prin-
ciple of nanoindentation lies in forcing a very small diamond tip to
the material surface while the changes in the applied load and the
penetration depth are measured simultaneously, [9]. By using this
method, material properties, such as elastic modulus, hardness,
plastic or viscous parameters, can be obtained from experimental
readings for a given material volume, [9-11].
The macrolevel analysis is performed by different types of stan-
dardized macroscopic tests (e.g., by the static compression, ten-
sion or bending and/or by dynamic tests) where the overall mate-
rial properties are obtained on large specimens (cm~m scale).
Transition between the micro and macro levels can be treated with
a micromechanical approach that separates the levels by defining
a characteristic scale and related representative volume elements
(RVE) for each of the levels, [12]. The response of the micromechani-
cally heterogeneous RVE can be averaged through different homoge-
nization techniques, [12-14]. A significant group of analytical methods
is based on the classical Eshelby’s solution of ellipsoidal inclusions
embedded in a matrix, [13], namely the Mori-Tanaka method, the self-
consistent scheme and others, [12]. Numerical homogenizations can
include finite element computations or fast Fourier transformation, [14-
16]. Among the analytical homogenization schemes, the Mori-Tanaka
method, which performance was justified by some researchers when
used for cementitious composites, [3,5,17], is frequently used for its
simplicity and wide applicability in terms of the concentration range of
the multiple phases involved in the analysis.
High performance Cementitious Composite, HPCC, are those
cementitious-based composites, e.g., mortar and concrete, which
meet special performance and comply with uniformity require-
ments that cannot be always achieved by conventional materials
and practices, [18]. By defining the link between microstructure,
micromechanical properties and macroscopic mechanical perfor-
mance of such composite, one can optimize its mechanical proper-
ties in an easier and experimental less expensive way. This pos-
sibility is highly inviting for the concrete industry, since they would
be able to deliver a more predictable product, for example, a high
performance concrete with the desired elastic properties.
In this paper, a combination of nanoindentation technique and ap-
proaches mentioned along these lines has been applied in order to
determine macroscale elastic properties of the high performance
cementitious composites.
2. Experimental program and evaluation
of results
This section highlights the details on the tested materials, mixture
compositions, sample preparation, mixing procedure and tests
performed. The experimental setup for the analysis of mechanical
properties at different levels is also presented.
2.1 Materials
The tests were carried out with mortar mixtures further denoted as C1.
The mortar mixtures contained cement CEM II/A-S 52.5 N (Table 1),
high-range water reducing admixture Stachement 2000, and quartz
285
IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 2
Table 1 – Chemical composition
of CEM II/A-S 52.5 N (wt.%)
%
CaO
57.6
SiO
2
21.1
Al O
2 3
6.2
Fe O
2 3
3.6
MgO
1.7
Na O
2
0.40
K O
2
0.69
SO
3
3.3
–
Cl
0.06
Loss on ignition
1.5
Insolubles
0.3
W. R. L. da Silva | J. Němeček | P. Štemberk