Nanoscience and nanoengineering of cement-based materials - Nanotechnology in Eco-efficient Construction - page 11

Timber (pine)

PVC

Glass

Copper (virgin)

Concrete (30 MPa)

Cement

Aluminum (recycled)

Aluminum (virgin)

0 50 100 150 200 250

Embodied energy (MJ/kg)

2.3 Embodied energy consumption of some common construction
materials. Data from Alcorn (2003).

the process signifi cant amounts of CO 2 into the atmosphere. It is estimated
that for every tonne of cement produced, approximately a tonne of CO 2 is
released in the atmosphere. About 60% of that is allocated to the chemical
reactions that occur when limestone is heated in the kiln (calcination) with
the remaining 40% admitted to energy generation through fossil fuels usage
for kiln heating and clinker grinding. As a result, cement production is one
of the major carbon dioxide contributors in the Earth's atmosphere. Esti-
mates suggest that the industry is responsible for approximately 7% of
global CO 2 emissions. Furthermore, while concrete structures are generally
thought to be 'eternal', they have life-spans that range between 50 and 100
years, depending on the material quality and environmental conditions in
use. As a result, the durability performance of the majority of the world's
infrastructure is gradually decaying, posing signifi cant sustainability con-
cerns for various governments.
These recent sustainability concerns provide important drivers for the
further understanding and development of this very important material.
Recent advances in experimental and theoretical nanomechanics provide
new avenues for material decoding (nanoscience) and material optimiza-
tion for specifi c applications (nanoengineering). The fundamental idea of
the efforts that have been in effect over the last decade or so is to develop
the material science approach that will link the initial synthesis and process-
ing conditions with the evolving microstructure and the resulting macro-
scopic response. An elegant scientifi c methodology equivalent to the one
used in industrial metals and ceramics is currently lacking. The microstruc-
ture-property approach is adopted such as to provide scientifi c interpreta-
tions for the macroscopic mechanical, physical, and chemical responses
observed in practice.

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