Nanoscience and nanoengineering of cement-based materials - Nanotechnology in Eco-efficient Construction - page 10

tain stoichiometry. Furthermore, this constituent phase cannot be recapitu-
lated effectively ex-situ ; one has to, therefore, access the properties of C-S-H
in-situ at the length scale where it naturally occurs. Experimental data
report C/S-ratios in the 1.2-2.1 range with an average around 1.75, while
the H content fl uctuates even more. The recent advent of innovative and
powerful experimental techniques provides the cement and concrete com-
munity with an unprecedented opportunity to probe this phase in its natural
environment, understand its behavior, and transfer these ideas to higher
levels through multi-scale models that can deliver the composite concrete
response.

2.1.3 Call for innovation

Despite the ubiquitous presence and extreme importance of concrete for
modern societies, its development over the past decades has had a largely
empirical basis. On one hand, the construction industry is characterized by
risk aversion as the use of materials is dictated by codes or standards, and
therefore it is diffi cult for new products to be introduced into the industry.
On the other hand, the industry itself is highly fragmented 2 and as a con-
sequence very little effort and money is invested by companies on funda-
mental research and development. As a result, our knowledge of this very
important material has remained largely on an empirical basis, and any
fundamental research for understanding and innovation is developing from
isolated efforts primarily in research and educational institutions.
The low cost and wide availability of the material, coupled with its excel-
lent properties such as ability to be shaped, resistance to water and fi re, and
good mechanical properties, have been suffi cient to maintain concrete as
the most used material in the construction industry. Recent environmental
publications, however, raise concerns over the ecological footprint of cement
and as a consequence cement-based materials like concrete. Compared to
steel, aluminum, plastics and other manufactured materials, Portland cement
concrete is generally considered as environmentally friendly (Fig. 2.3).
However, the large volumes of the material produced every year consume
2-3% of the global energy (Juenger et al. , 2011) and approximately 12-15%
of the industrial energy (Ali et al. , 2011). Furthermore, there is a growing
awareness that concrete production and construction practices of today are
not sustainable (Worrell et al. , 2001; Gartner, 2004; Phair, 2006; Damtoft et
al. , 2008; Mehta, 2009).
The production of cement involves heating clay and limestone to 1450°C
which involves the burning of fossil fuels to generate such heat releasing in

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2 According to (Mann, 2006) about 97% of EU construction companies employ fewer than 20
people.