Nanoparticles for high performance concrete (HPC) - Nanotechnology in Eco-efficient Construction - page 38

to the ERMCO 2011 statistics, ready-mixed concrete production lies essen-
tially between C25/30 and C30/37. In addition, only 11% of the concrete
production corresponds to the high performance concrete (HPC) strength
class target. As ERMCO 2001 statistics showed a 10% fi gure for this type
of concrete, it appears that high strength concrete demand has remained
unchanged during the last decade. Normal strength concrete produces less
durable structures which require frequent maintenance and conservation
operations or even complete replacement, with the associated consumption
of additional raw materials and energy. Many degraded concrete structures
were built decades ago at a time when little attention was given to durability
(Hollaway, 2011). It is not therefore surprising that worldwide concrete
infrastructure rehabilitation costs are extremely high.
For example, in the USA, around 27% of all highway bridges are in need
of repair or replacement. In addition, the cost of deterioration caused by
deicing and sea salt is estimated at over US$150 billion (Davalos, 2012). In
the European Union, nearly 84,000 reinforced and pre-stressed concrete
bridges require maintenance, repair and strengthening. This results in an
annual cost of £215 million, not including traffi c management costs (Yan
and Chouw, 2013). Beyond the durability problems caused by imperfect
concrete placement and curing operations, the real problem with the dura-
bility of ordinary Portland cement concrete (OPC) is the intrinsic proper-
ties of the material which has a high degree of permeability. This allows the
ingress of water and other aggressive elements, leading to carbonation and
chloride ion attack, which ultimately result in corrosion (Bentur and Mitch-
ell, 2008; Glasser et al. , 2008). The importance of durability for eco-effi ciency
in construction materials has been described by Mora (2007). The author
stated that increasing concrete durability from 50 to 500 years would reduce
its environmental impact by a factor of 10. It is also worth noting that
according to Hegger et al. (1997), the increase of compressive strength in
concrete would mean a reduction of as much as 50% in the use of reinforced
steel. These are crucial issues in materials effi ciency (Pacheco-Torgal and
Jalali, 2011a; Allwood et al. , 2011), highlighting the need for investigation
into the future production of concretes with high mechanical strength and
high durability.
Nanotechnology involves study at the microcospic scale (1 nm

￿ ￿ ￿ ￿ ￿ ￿

= 1 ×

10 −9 m). Some estimates predict that products and services related to nano-
technology could reach 1,000,000 million euros per year beyond 2015
(Pacheco-Torgal and Jalali, 2011b). The use of nanoparticles to increase the
strength and durability of cementitious composites was predicted by the
report RILEM TC 197-NCM, 'Nanotechnology in construction materials'
(Zhu et al. , 2004), as a research area with high nanotechnology potential.
Since that time, several dozen papers have been published by the Society
of Chemical Industry (SCI) in the fi eld. However, the majority of these