Nanoscience and nanoengineering of cement-based materials - Nanotechnology in Eco-efficient Construction - page 20

that they can effectively transfer the information across several orders of
magnitude in length scale starting from the atomistic C-S-H level to the
decimeter level of concrete structures. While the above described approaches
rely on analytical formulation of the problem, numerical schemes are
also employed which provide more powerful possibilities to tackle with
non-linear phenomena, like strength, creep, permeability, etc. (Hain and
Wriggers, 2008; Smilauer and Bazant, 2010).

2.2.3 Concluding remarks: a framework for
science-based innovation

The fi eld of experimental and theoretical nanomechanics is advancing at a
rapid pace. As the tools of experimentation and the resulting theoretical
frameworks of data analysis are developing, new opportunities for under-
standing and characterization of materials arise. This provides an unprec-
edented opportunity to probe long-used ubiquitous construction materials,
like concrete, that have not been rigorously characterized and modeled in
the past and create a science-based platform for material optimization.
Some ideas and recent developments in the fi eld of cement-based materials
are presented below.

2.3 Nanoengineering of cement-based materials

The process of tailoring the microstructure of cementitious materials to
achieve desirable properties for specifi c applications is termed materials
engineering. When nanoscale features are involved, we refer to this process
as nanoengineering. From the above discussion it becomes apparent that
cement-based materials, which essentially depend on the performance of
C-S-H, are nanoscale materials. Nanoengineering can occur by modifying
this nanoscale phase directly, through some macroscopic synthesis and pro-
cessing means, or by introducing nanoscale additives that can either be inert
or chemically interact with the material in certain ways. Recent develop-
ments in nanotechnology provide ample routes for concrete nanoengineer-
ing, some of which are discussed below.

￿ ￿ ￿ ￿ ￿ ￿

2.3.1 Empirical routes for material development

When reviewing the historical evolution of cementitious materials, it can be
identifi ed that much of their development relied on empirical knowledge
that was achieved through trial and error experimentation. In retrospect,
the degree of optimization that has been achieved in this fashion is rather
impressive. Traditionally, the most used variable for the material characteri-
zation has been the mass ratio of water to cement in the initial mix. It has