305
suggested that the specific ways that nanoparticles organize themselves within the mixture are an extremely efficient close-packing
structure. Expectations are that shear and tensile strengths as well
as toughness will be improved. Other anticipated process improvements include increasing liquid viscosities so that grain suspension
is enhanced, which in turn improves workability.
Experiments with nanomaterials in mortars and concretes have
been limited, but results are promising. Nanosized iron oxides and
nanosilicas have been found to improve strength beyond what has
been obtained with silica fume. Mixture design is quite complex,
so other needed properties, such as slump flow, are not adversely
affected, nor are their undesirable side effects, such as bleeding or
segregation. General workability has been improved. Though experiments so far are few, the prospects for improvements in various
areas look very promising. Efforts have already been made to commercialize nano-based admixtures in liquid form to be used as an
admixture.
As mentioned, cracking under tension stresses has long been one
of the driving material characteristics of designing concrete shapes.
There have been seemingly uncountable numbers of experiments
with mixing in various fibrous materials, such as various polymeric
strands or metallic fibers, into concrete mixtures with the intent
of creating a generally homogeneous concrete composite that has
crack-arresting characteristics. In addition to dispersion approaches,
various layered approaches have also been tried. Some have been
more or less successful for particular applications, but many problems with fiber approaches remain and prevent them from being
widely used in many larger applications. Concrete paste is highly
alkaline and can attack many embedded materials. Bonds are very
problematic. Strengths are low. For building- or bridge-scale structural elements, traditional steel reinforcing remains the primary
solution. Though nanomaterial experiments have suggested some
welcome increases in fundamental tension strengths, cracking
under large stress levels still remains problematic and poses a particular challenge to researchers in this area.
A particularly interesting approach to the cracking problem has
been the exploration of “self-healing” or “self-repairing” concretes.
As described in much more detail in Section 10.2, these interesting materials have been explored at the University of Illinois since
the early 1990s, and this work has also spawned comparable
approaches with other materials. The general approach consists of
developing small, dispersed encapsulated particles or tubes inside
Structural and Mechanical Environments
suggested that the specific ways that nanoparticles organize themselves within the mixture are an extremely efficient close-packing
structure. Expectations are that shear and tensile strengths as well
as toughness will be improved. Other anticipated process improvements include increasing liquid viscosities so that grain suspension
is enhanced, which in turn improves workability.
Experiments with nanomaterials in mortars and concretes have
been limited, but results are promising. Nanosized iron oxides and
nanosilicas have been found to improve strength beyond what has
been obtained with silica fume. Mixture design is quite complex,
so other needed properties, such as slump flow, are not adversely
affected, nor are their undesirable side effects, such as bleeding or
segregation. General workability has been improved. Though experiments so far are few, the prospects for improvements in various
areas look very promising. Efforts have already been made to commercialize nano-based admixtures in liquid form to be used as an
admixture.
As mentioned, cracking under tension stresses has long been one
of the driving material characteristics of designing concrete shapes.
There have been seemingly uncountable numbers of experiments
with mixing in various fibrous materials, such as various polymeric
strands or metallic fibers, into concrete mixtures with the intent
of creating a generally homogeneous concrete composite that has
crack-arresting characteristics. In addition to dispersion approaches,
various layered approaches have also been tried. Some have been
more or less successful for particular applications, but many problems with fiber approaches remain and prevent them from being
widely used in many larger applications. Concrete paste is highly
alkaline and can attack many embedded materials. Bonds are very
problematic. Strengths are low. For building- or bridge-scale structural elements, traditional steel reinforcing remains the primary
solution. Though nanomaterial experiments have suggested some
welcome increases in fundamental tension strengths, cracking
under large stress levels still remains problematic and poses a particular challenge to researchers in this area.
A particularly interesting approach to the cracking problem has
been the exploration of “self-healing” or “self-repairing” concretes.
As described in much more detail in Section 10.2, these interesting materials have been explored at the University of Illinois since
the early 1990s, and this work has also spawned comparable
approaches with other materials. The general approach consists of
developing small, dispersed encapsulated particles or tubes inside
Structural and Mechanical Environments