Abstract:
Nanotechnology is one of the most active
research areas that include a number of disciplines including civil engineering
and construction materials. Nanotechnology is the understanding, control, and restructuring
of matter on the order of nanometers (i.e., less than 100 nm) to create materials
with fundamentally new properties and functions. Nanotechnology encompasses two
main approaches: (i) the
‘‘top down” approach, in which larger structures are reduced in size
to the nanoscale while maintaining their original properties or deconstructed from
larger structures into their smaller, composite parts and (ii) the ‘‘bottom-up”
approach, also called ‘‘molecular nanotechnology” or ‘‘molecular manufacturing,”
in which materials are engineered from atoms
or molecular components through a process of assembly or self-assembly. Traditionally
nanotechnology has been concerned with developments in the fields of microelectronics,
medicine and material sciences. However the potential for applications of many developments
in the nanotechnology field in the area of construction engineering is growing.
NanoTechnology and Concrete
Concrete, the most ubiquitous material in the world, is a nanostructured,
multi-phase, composite material that ages over time. It is composed of an amorphous
phase, nanometer to micrometer
size crystals,
and bound water. The
amorphous phase, calcium–silicate–hydrate
(C–S–H) is the ‘‘glue” that holds concrete together and is itself a nanomaterial. Viewed from the bottom-up,
concrete at the nanoscale is a composite of molecular
assemblages, surfaces
(aggregates, fibres), and chemical
bonds that interact through local chemical reactions, intermolecular forces, and
intraphase diffusion. Properties
characterizing this scale are
molecular structure; surface functional groups; and bond length, strength (energy), and density. The structure of the amorphous and crystalline
phases and of the interphase boundaries originates from this scale. The properties
and processes at the nanoscale define the interactions that occur between particles
and phases at the microscale and the effects of working loads and the surrounding
environment at the macroscale. Processes occurring at the nanoscale ultimately affect
the engineering properties and performance of the bulk material.
At the basic
science level, much analysis of concrete is being done at the nano-level in order
to understand its structure using the various techniques developed for study at
that scale such as Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM)
and Focused Ion Beam (FIB). This has come about as a side benefit of the development
of these instruments to study the nanoscale in general, but the understanding of
the structure and behaviour of concrete at the fundamental level is an important
and very appropriate use of nanotechnology. One of the fundamental aspects of nanotechnology
is its interdisciplinary nature and there has already been cross over research between
the mechanical modeling of bones for medical engineering to that of concrete which
has enabled the study of chloride diffusion in concrete (which causes corrosion
of reinforcement). Concrete is, after all, a macro-material strongly influenced
by its nano-properties and understanding it at this new level is yielding new avenues
for improvement of strength, durability and monitoring.
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