Nanoscience and nanoengineering of cement-based materials - Nanotechnology in Eco-efficient Construction - page 25

Nanocoating

No x

NO 3 -

Water drop

H 2 O

Dirt

TiO 2

Active oxygen

Surface

(a) (b)

2.7 (a) Photocatalytic and (b) self-cleaning mechanisms of TiO 2
nanocomposites.

potential to add new functionalities to infrastructures, i.e., self-cleaning
properties and the ability to remove air pollutants through photocatalysis
(Fig. 2.7). TiO 2 are semiconductors that behave as photocatalysts when
irradiated by ultraviolet (UV) light in the presence of gas or liquid (Serpone
and Pelizzetti, 1989). When mixed with cement, it can photocatalytically
degrade organic pollutants that are, after neutralization, washed away
through the hydrophilic nature of the surface, maintaining at the same time
the aesthetic characteristics of concrete structures, particularly those con-
structed with white cement (Cassar, 2004; Ruot et al. , 2009). TiO 2 has proven
very effi cient in the removal of pollutants such as NOx, aromatics, alde-
hydes, and ammonia, and currently fi nds applications in various infrastruc-
ture projects like pavements, tunnels, buildings, etc. (Guerrini, 2012). A
more detailed exposition of photocatalytic applications is provided in a
separate chapter of this topic.

Cement-polymer nanocomposites

While considerable research effort has been devoted to the study of organic
composites with small amounts of inorganic reinforcements, like polymer-
clay systems, little is known about the consequences of adding small amounts
of organic material in an inorganic matrix, like the C-S-H/polymer system.
This approach constitutes a rather recent and alternative route for concrete
nanocomposites which stems from biomimicry approaches (synthesis of
composites from aqueous routes like many natural biocomposites, e.g.,
tooth, bone, and shells) and relates to the attempt to modify the nanoscale
C-S-H material through organic hybridization (Matsuyama and Young,
1999a,b; Minet et al. , 2006, Franceschini et al. , 2007; Alizadeh et al. , 2011;
Fan et al. , 2012). The process, which has been verifi ed computationally
(Pellenq et al. , 2008), involves grafting organic moieties on the silica layers
through controlled hydrolysis of organo-silane precursor mixtures or by
hydration of anhydrous silicates in silanized polymer solutions. Additional
benefi ts are expected when the organic molecules intercalate the interlayer

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