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Review on concrete nanotechnology
ABSTRACT
The study of the application of nanotechnology in the construction industry and building
structures is one of the most prominent priorities of the research community. The outstand-
ing chemical and physical properties of nanomaterials enable several applications ranging
from structural reinforcement to environmental pollution remediation and production of
self-cleaning materials. It is known that concrete is the leading material in structural appli-
cations, where stiffness, strength and cost play a key role in the high attributes of concrete.
This paper reviews the literature on the application of nanotechnology in the construction
industry, more particularly in concrete production. The paper first presents general infor-
mation and definitions of nanotechnology. Then, it focuses on the most effective nano-
additives that readily improve concrete properties, such as (i) nano-silica and silica fume,
(ii) nano-titanium dioxide, (iii) iron oxide, (iv) chromium oxide, (v) nanoclay, (vi) CaCO3,
(vii) Al2O3, (viii) carbon nanotubes and (ix) graphene oxide. Besides summarizing the
main nanomaterials used in concrete production as well as the results achieved with each
addition, some future potential consequences of nanotechnology development and orienta-
tions to explore in construction are discussed.
Keywords: Nanotechnology; concrete; nanomaterials; cement; composites
1
1. Nanotechnology and concrete - General aspects
The nanotechnology revolution experienced in the last few years has had a huge impact on
different science fields (chemistry, engineering, biology), also affecting the construction
industry. Conceptually, nanotechnology may be defined as the ability to create new struc-
tures at the smallest scale, using tools and techniques that allow understanding and manipu-
lating matter at nanoscale, generally from 0.1 to 100 nm (Zhu et al., 2004).
Although this is the most used definition, a size limitation of nanotechnology to a below
100 nm range seems to exclude numerous materials and devices, particularly in the phar-
maceutical area. For that reason, some experts disagree with a rigid definition based on a
sub-100 nm size. To avoid this divergence, Bawa et al. (2005) proposed a definition uncon-
strained by any arbitrary size limitations: “… The design, characterization, production, and
application of structures, devices, and systems by controlled manipulation of size and
shape at the nanometer scale (atomic, molecular, and macromolecular scale) that produc-
es structures, devices, and systems with at least one novel/superior characteristic or prop-
erty…”. Nano-structures and nano-modifications may lead to completely distinct compo-
site materials at a macroscopic scale, reflected as well in their properties and performance.
The range of application of nanotechnology is, for this reason, very large. Within the con-
struction industry, one of the most important fields where the application of nanotechnol-
ogy is fairly clear relates with concrete production. Concrete is a composite material at
macroscale but its properties can also be improved at meso and nanoscale. In fact, nano-
technology has a high potential to contribute to the understanding of concrete’s behav-
iour, in order to improve its mechanical properties and reduce ecological and construction
materials production costs (Raki et al., 2010).
2
Figure 1 allows drawing some comments on the research evolution in the field of nano-
technology in concrete. Figure 1 shows the evolution of the number of publications indexed
in SCI Web of Knowledge per year, since 2000, and corresponding to keywords “concrete
and nano” in searched “Topic”. It is easily seen that the works on concrete nanotechnology
rapidly increased from 1 in 2000 to 133 in 2013. The number of published works steadily
increased from 2000 to 2009, but from 2009 to 2011 it displayed a huge rise mainly due to
the advent of nanomaterials “from labs to society”, through information media. From 2011
till 2013, the number of published works is nearly the same, maybe as a result of some un-
successful research projects. However, the number of current research teams working on
the concrete nanotechnology is high
Concrete’s nano-modification may be made in one or all of the phases: solid phase, liquid
phase or in liquid-solid interfaces, which is possible because of its porous liquid-solid
composition (Garboczi, 2009; Sanchez and Sobolev, 2010). The main improvements re-
sulting from these nano-modifications, also known as nano-engineering, include (i) better
cement hydration, (ii) higher compressive or tensile strength, (iii) higher ductility and ener-
gy dissipation, and (iv) enhanced ability to control cracking and shrinkage phenomena. The
high complexity associated to structures manipulation at nanoscale makes this a field going
through intense development and research. This high complexity is quite visible in the sev-
eral cementitious and bituminous products that have been developed, where some of the
properties mentioned above were improved. Examples range (i) from UPHC (Ultra High
Performance Concrete, e.g. Lehmann et al., 2009; Stengel, 2009) to CHHC (Carbon
Hedge Hog Cement, e.g. Cwirzen et al., 2009), (ii) from autoclaved aerated concrete
(Laukaitis et al., 2012) to self-compacted lightweight concrete (Madandoust et al., 2011)
3
and, still, (iii) from calcium-leached cement-based materials (Bernard et al., 2003) to recy-
cled aggregates concrete (Li et al., 2012). On the one hand, these improvements have been
achieved thanks to the nanomanipulation of hydration products of concrete, such as C-S-
H nanoparticles, which have enabled the production of hardening accelerators, such as
Master X-seed, by BASF Construction Solutions (2014). These products gave different
benefits such as early strength acceleration at low, ambient and heat curing temperatures,
improved concrete durability or reduced water absorption. On the other hand, the im-
provements in concrete properties have resulted from the addition of new nanoparticles in
concrete mixes mainly by replacement of cement. This paper will mainly focus this sec-
ond topic. Thus, the main purpose of this article is three-fold: (i) to review the state-of-
the-art on the use of nanoparticles in concrete’s and cement’s based materials production,
(ii) to present the main results obtained in these nanocomposite materials and (iii) to sug-
gest/predict future developments in this research area. All the techniques developed in
this nanotechnology field have as their main purpose the manipulation of concrete’s
structural composition in order to improve the performance of bituminous and cementi-
tious products. These improvements have been achieved, to a great extent, by the addition
of nanoparticles in cement and concrete’s matrix constitution. To the authors’ knowledge,
the most effective nanoparticles for concrete production are:
• Nano-silica and silica fume
• Titanium dioxide
• Iron III oxide
• Chromium III oxide
• Nanoclay
4
• Calcium carbonate
• Alumina
• Carbon nanotubes
• Graphene oxide
The following sections summarize the recent progress in nano-modification of cement-
based composite materials and their influence on concrete behaviour.
2 Nanosilica and Silica Fume
Regarding the application of nanotechnology in concrete, Nano-Silica (NS) or silicon diox-
ide (SiO2) and its colloidal form named as Silica Fume (SF) have attracted considerable
attention from the scientific and technical communities. Their remarkable properties justify
the large number of studies that have been carried out in the last years (Allen and Living-
ston, 1998; Hooton et al., 1996; Sabir, 1995). In fact, the application of SF has been exten-
sively reported in the research community with proved results and effective implementa-
tion. The advantages of using SF include high early compressive strength, high tensile,
flexural strength and modulus of elasticity, enhanced durability, low permeability, among
other. For example, Behnood and Ziari (2008) reported improvements up to 25% in com-
pressive strength for heat and unheated specimens with 10% wt% cement replacement.
Igarashi et al. (2005) evaluated the capillary porosity and pore size distribution in high-
strength concrete containing 10 wt% of silica fume at early ages. It was concluded that
concrete with SF has fewer coarse pores than ordinary concrete, thus a reduction of porosi-
ty was observed due to the micro dimension of these particles. Taking advantages of these
potentialities of the use of SF, its application in the production of high-performance con-
crete for higway bridges, parking decks or marine structures was analysed (Siddique,
5
2011). The opportunity of applying nanotechnology resulted in a rise of interest on the ap-
plication of these particles with smaller size in concrete production (e.g. nano-silica).
In concrete, NS and SF may work at two levels. The first level corresponds to the chemical
effect triggered by the pozzolanic reaction of silica with Calcium Hydroxide (CH) (Singh et
al., 2013). This produces additional Calcium Silicate Hydrate (C-S-H) gel which is the
main constituent for the strength and density in the harden binder paste (Figure 2). Poz-
zolanic reactivity is highly increased by higher surface area of pozzolanic particles, which
then increases the rate of the pozzolanic activity (Chong et al., 2012). The second level is a
physical effect because NS is about 100 times smaller than cement. It can (i) fill the re-
maining voids in the young and partially hydrated cement paste, (ii) increase its final densi-
ty, (iii) reduce its porosity and permeability and (iv) decrease the weight of cement used in
the mix (Quercia and Brouwers, 2010).The published experimental results reflect how the
inclusion of these nanoparticles may influence the mechanical and durability properties
of concrete, and a lot of work has been done in this field. Rashad (2014) presented an
extensive overview on the effect of NS on the main properties of traditional cementitious
materials and alkali-activated fly ash. Using NS in concrete production has a high poten-
tial to improve a wide range of fundamental properties in concrete, such as (i) strength,
(ii) workability and setting time, (iii) heat of hydration, (iv) fire and abrasion resistance or
leaching and behaviour under aggressive environments. Regarding concrete strength, it
has been shown that compressive and flexural strength may increase up to 75% with the
addition of small amounts of NS (0-10%). Shakhmenko et al. (2013) tested the effect on
cement’s paste mechanical properties by replacing cement with different amounts of SF
and NS. A cement/SF paste at 2% of cement mass sample was prepared and different
6
samples of 2% of cement mass of SF and NS non calcined (HF0), NS calcined at 400 oC
(HF400) and NS calcined at 1000 oC (HF1000) were tested.. The results showed that
mixes containing SF and SF compositions with NS particles demonstrated higher values
of compressive strength (more than 3 times higher at early ages and approximately 15%
at 28 days) and long-term hardening effect compared to pure cement paste (CEM).These
higher values of compressive strength occur at all ages of hardening but the differences
are clearly visible in the early stages, as shown in Figure 3 where the 1-day compressive
strength results are summarised. Figure 3 shows that the higher value of 1-day compres-
sive strength was 54.0 MPa, obtained for samples with SF and NS calcined at 400 oC
(HF400). The remarkable reduction observed for samples with SF and NS calcined at
1000 oC (HF1000) is mainly explained by lower specific surface of this sample compared
to others, due to the particle melting observed during the calcining process. Jalal et al.
(2012) tested mechanical, rheological, durability and microstructural properties of high-
performance self-compacting concrete (HPSCC) incorporating micro SiO2 and NS replacing
a fraction of Portland cement. Different amounts of micro silica and NS and a blend of micro
and nanosilica were tested as 10%, 2% and 10% + 2% respectively. The w/b ratio was kept
constant at 0.38 and different binder contents were tested. It was concluded that the replace-
ment by 2% NS in binary mixes increased the compressive strength for a binder content of
400 kg/m3 by 45%, 55%, 70% and 73% at 3, 7, 28 and 90 days respectively. In this context,
efforts have been made to establish an optimum content of NS that gives concrete the highest
compressive strength. It is almost consensual that, to avoid the agglomeration effect, the per-
centage of NS in concrete should not be more than 10%. Some authors (Kuo et al., 2006a)
reported that 2% is the optimum content of NS, others reported 3% (Qing et al., 2006) and
7
6% (Qing et al., 2007). However, the results are affected by so many factors such as curing
conditions, w/b ratio, nanoparticle size or chemical admixtures, that it is hard to establish the
optimum content (Rashad, 2014).
Apart from strength, using NS in concrete also has high impact on other properties. The
addition of NS particles was found to influence hydration behaviour and led to differ-
ences in the microstructure of the hardened paste. A good dispersion of NS particles in
the cement mortar led to a denser microstructure and accelerated the hydration process of
the cement paste. However, as nanoparticles are easy to agglomerate due to their great
surface energy, large quantity of these particles cannot be uniformly dispersed. In that
case it may result in voids and weak zones formation (Singh et al., 2013). Li et al. (2004)
experimentally studied the mechanical properties of nano-Fe2O3 (NF) and NS cement
mortars. Nanoparticles contents in the mortar specimens were 3, 5 and 10% by weight of
cement. Apart from an increase of compressive strength of the specimens, a SEM (Scan-
ning Electron Microscope) comparative study of the microstructure between cement mor-
tar mixed with nanoparticles and plain cement mortar showed that NF and NS filled up
the pores and reduced CaOH compound within the hydrates. The texture of hydrates
products was denser, uniform and compact which explains the extremely good perfor-
mance of these products. Jo et al. (2007) studied the heat of hydration of mixes modified
with NS. Cement was partially replaced with NS at levels of 0% and 10% by weight. Re-
sults showed that the addition of NS in the mix increased the amount of heat involved
during setting and hardening of cement. Also Hou et al.( 2013) tested different samples of
cement pastes with 0%, 0,5%, 1% and 5% addition of colloidal NS. The results suggested
that the addition of NS increased both the hydration peak temperature and the reaction
8
rate. The increase of the rate of hydration highly depends on the surface area of NS parti-
cles added to the mixes. NS particles act as nucleation sites that accelerate the hydration.
Since the surface area is higher, so is the rate of hydration.
Moreover, workability and fresh properties of concrete also seem to be highly affected by
using NS in the mixes. The addition of NS to cement pastes demands more water to
maintain its workability (Heikal et al., 2013; Singh et al., 2013). Some authors, such as
Bahadori and Hosseini (2012), Berra et al. (2012) amd Qing et al. (2006), obtained a re-
markable reduction of the mixes workability when NS particles were used. Contrarily to
this reduction of workability, increased cohesion and yield stress in cement pastes were
achieved with NS addition. Superplasticizers have been used to improve the mix’s work-
ability but its quantitative effects on NS reactivity and dispersion of NS particles is still
not clear. In fact, the rheological properties of the fresh cement pastes are complex and
more studies are needed. For example, Kong et al. (2013) studied the rheological proper-
ties of fresh cement pastes with w/c ratio of 0.4 and with 0.5 wt% NP addition. It was
suggested that if the water content is kept constant the addition of NS is believed to pro-
mote the packing of cement particles decreasing the voids between them and increasing
the free water contributing to fluidity in the paste. So, theoretically, addition of NS will
help to improve the workability of the paste. However, the decrease of workability ob-
tained by the majority of authors is explained by the fact that not all the agglomerates act
as fillers that occupy the void space between cement particles and release the free water.
In addition to the high water absorption of NS particles, these agglomerates will not only
act as fillers but also consume some free water that originally contributes to fluidity. It
was also suggested that they also push away the cement particles around them causing an
9
increase of the void space. This behaviour explains the decrease of workability. There-
fore, the influence of NS addition on the rheological behaviour mainly depends on
whether the agglomerates can act as fillers or not. Figure 4 summarizes this fact. The
tests performed suggest that, in most cases, NS agglomeration do not act as filler and
cause a decrease in workability. Therefore, including superplasticizers in the mixes
should be the best solution, even though more results on this issue are needed (Martins
and Bombard, 2012; Senff et al., 2010).
Finally, the addition of NS particles to cement pastes also has consequences on other
properties less crucial to concrete structural performance, such as thermal behaviour,
abrasion resistance or calcium leaching. Concerning the thermal behaviour, the NS addi-
tion to cement pastes significantly improves the thermal stability of the cementitious sys-
tem exposed to temperatures of 500ºC with lesser strength loss. Related to this, Ibrahim
et al. (2012) studied the performance of cement-based materials under temperatures of
400 ºC and 700 ºC where cement was replaced by high-volume fly ash combined with
colloidal NS. A constant w/b ratio of 0.4 was established and the NS/binder ratios were
2.5%, 5% and 7.5%. The results showed an increase of approximately 30% and 20% in
both the compressive and flexural strength of samples with addition of NS before expo-
sure to elevated temperatures. This rise was also observed as the NS content increased.
After exposure to 400ºC, an increase of 70% in compressive strength for 28-days was
observed when NS was used. Contrarily, the flexural strength decreased about 10% after
this exposure. When exposed to higher temperatures (700ºC), a dramatic decrease in both
the compressive and flexural strength (30% and 80%, respectively) was observed.
Furthermore, several tests (Li et al., 2006a; Nazari and Riahi, 2011a; Shamsai et al.,
10
2012) have been performed to study the abrasion resistance of concrete mixes modified
with NS. This property plays a key role when concrete is used in pavements. The results
showed that the abrasion resistance of concrete containing nano-TiO2 (NT) and NS is
significantly improved (100-180%), much more when compared to plain concrete or con-
crete containing polypropylene fibres (30-70%) (Li et al., 2006a). The relationship be-
tween abrasion resistance and compressive strength of concrete also indicates that the
abrasion resistance increases with increasing compressive strength. For example, an im-
provement from 30 MPa to 40 MPa in the compressive strength may reduce 25% the
depth of wear, from 4 mm to 3 mm.
Besides all the properties’ improvements, the environmental and health effects of using
NS should be also considered. There are only a few studies about the environmental be-
havior and effects of NS. Normally it is reported that NS has very little impact on the
environment and its use in the amorphous form is seen as quite safe, in contrast with its
crystalline form (Som et al., 2011). The inhalation of crystalline form of NS may induce
slight inflammation effects in the lungs. Thus, the toxicity of samples and the risk of ex-
posure to these nanoparticles depend on how the amorphous form of NS is contaminated
with crystalline NS. Still, the risk is generally perceived as low.
Considering all aspects, and even if the reasonable cost of NS is taken into account, NS is
nowadays one of the most promising and effective nanomaterials to use in concrete pro-
duction and it is expected to have effective introduction in construction’s industry in the
short-term. “Cuore Concrete” (Pascal Maes, 2014) reflects this reality with the introduc-
tion of NS in concrete production with some of the advantages previously referred.
11
3. Nano-Titanium Dioxide
If compared to nanosilica, the application of TiO2 nanoparticles in cementitious materials is
justified by different reasons. It is well known that the cement industry is responsible for the
emission of high levels of pollutants, such as nitrogen oxides (NOx) and carbon dioxide
(CO2), which has resulted in an emerging need for environmental regulations to stimulate the
development of new strategies to lessen the polluting agents (Cárdenas et al., 2012). In this
respect, combining TiO2 nanoparticles with cement-based construction materials seems to be
a good solution, due to its strong photocatalytic activity, which results in (i) an environmen-
tal pollution remediation, (ii) self-cleaning and self-disinfection, (iii) high stability and (iv)
relatively low cost (Hashimoto et al., 2005). The photochemistry of TiO2 has become a sub-
ject of intese research since Fujishima and Honda (1972) reported the photocatalytic splitting
of water on TiO2 in the 1970s. Since then, the application of TiO2 photocatalysts to construc-
tion materials started to be highly focused (Fujishima et al., 1999). Photocatalytic activity can
be summarized as follows: when exposed to UV irradiation, TiO2 nanoparticles can absorb
photon energy resulting in the promotion of an electron from the valence band to the conduc-
tion band of Titania, which generate “holes” (h+, electron vacancy) in the valence band. This
electron-hole pairs may recombine in a short time to start redox reactions. These reactions
depend on ambient conditions, generating several radicals, such as OH (from oxidation),
H2O2 or O2- (from reduction) when water vapour and oxygen are present around the activated
TiO2. Pollution remediation occurs when these radicals react with harmful substances ab-
sorbed on the TiO2 surface, resulting in the degradation of these substances (e.g. NOx oxida-
tion) and release of harmless substances such as CO2 and H2O (Figure 5) (Agrios and Pichat,
2005; Chen et al., 2012).
12
A self-cleaning effect, i.e. the removal of inorganic substances dirt on surfaces due to rain-
water soaking between this absorbed substance and the TiO2 surface, is obtained by the
photo-induced hydrophilicity of the catalyst surface (Folli et al., 2012). Since the photo-
catalytic activity of TiO2 is influenced by the (i) crystal size, (ii) crystal structure, (iii)
crystallinity and (iv) surface hydroxylation, the use of TiO2 nanoparticles may increase
this activity compared to TiO2 particles. In this sense, several works have been carried
out in order to quantify the consequences of using TiO2 nanoparticles in NOx reduction.
Cárdenas et al. (2012) studied depollution activity of cement pastes samples, added with
0.0%, 0.5%, 1.0%, 3.0% and 5.0% (of dry cement weight) of TiO2 nanoparticles by eval-
uating NOx degradation. Different blend ratios of TiO2 nanoparticles were tested and
measurements were made at two aging times, 65 h and 28 days. The results showed that
all cement pastes containing TiO2 nanoparticles had photocatalytic properties, regardless
of the ratio and the percentage of TiO2 used. Moreover, the samples with 5.0% of addi-
tion showed the highest photocatalytic activity, both at early and later ages. Senff et al.
(2013) designed cement mortar with additions of NS and nano-TiO2 together. Samples
with 0-2wt% of NS, 0-20 wt% of nano-TiO2, 0.45-7wt% of superplasticizer and 0.45-
0.58 w/b weight ratio were tested. Because of nano-TiO2, NOx photocatalytic degradation
up to 1 h under solar light ranged from 65% to 80%. Lucas et al. (2013) studied the way
microstructural changes affect the photocatalytic efficiency of mortars prepared with aer-
ial lime, cement and gypsum binders with the addition of TiO2 nanoparticles. The results
showed that all compositions exhibited high photocatalytic efficiency, although a de-
crease of approximately 25% and 30% in the flexural and compressive strength respec-
tively was observed for higher amounts of additions (2.5 wt% and 5.0 wt%). Despite the
13
efforts of the research community to address the advantages of using TiO2 nanoparticles,
the benefits of using them have not being fully validated by field trials, much more for
higher amounts of additions. For example, the Progress Report “PhotoPAQ” (2012) stat-
ed that the effectiveness and the real impact on air quality of these new technologies have
been demonstrated only in a very limited manner in real-scale applications.
Still and despite some unconformity related to the optimum amount of TiO2 nanoparti-
cles that should be used to increase NOx degradation, some products have been intro-
duced in construction industry such as TioCem (Balte, 2009).
Apart from self-cleaning and NOx degradation, other potentialities of using TiO2 nano-
particles in concrete have been tested. One of them is related to the potential of mixing
TiO2 powders in cement-based materials without additional treatments, due to the porous
structure of the hardened cement pastes or mortars (Chen et al., 2012). It was also demon-
strated that TiO2 was inert and stable during the cement hydration process. Thus, the appli-
cation of these nanoparticles has important consequences on the total porosity and pore size
distribution of the cement pastes. Nazari and Riahi (2011b, 2011c) stated that TiO2 nanopar-
ticles could improve the pore structure of concrete and change the pores size distribution to
harmless or slightly harmful pores.
Moreover, some research has also been conducted to try to understand the effects of the
replacement of cement with nano-TiO2 on the mechanical and performance properties of
hardened cement pastes. Nazari and Riahi (2011b) stated that TiO2 nanoparticles as a par-
tial replacement of cement up to 3 wt% may accelerate C-S-H gel formation, due to an in-
crease of the amount of crystalline Ca(OH)2 at the early stages of hydration. This resulted
in an improvement up to 45% of the compressive strength of concrete. Their conclusions
14
also showed that an increase of TiO2 by more than 3 wt% may have the opposite effect.
This means that the compressive strength may be reduced due to the decrease of crystalline
Ca(OH)2 content required for C-S-H gel formation and unsuitably dispersed nanoparticles
in the concrete matrix. Meng et al. (2012) tested different samples of cement mortars with
w/b ratio of 0.5 and addition of 5% and 10% of TiO2 nanoparticles by weight of binder.
The results indicated that early strength (1 day) increased by 46% and 46% and decreased
by 6% and 9% at 28 days for 5% and 10% of replacement, respectively. These authors con-
cluded that the amount of addition used might have been excessive.
In fact, compared to NS, TiO2 nanoparticles have less potential to increase the compres-
sive strength of concrete and to accelerate C-S-H gel formation since TiO2 is not a poz-
zolanic material. The results showed that the change of pore structure and the improve-
ment of compressive strength could only be attributed to the micro-filling effect of fine
powders, acting as potential nucleation sites for the accumulation of hydration products
and not the increasing amount of hydration products (Chen et al., 2012; Meng et al.,
2012). In that sense, the influence of adding TiO2 nanoparticles to cement-based materi-
als is much more dependent on the wt% added to the mix, when compared to NS for in-
stance. In fact, if TiO2 is added with a non-adequate content, some properties such as
compressive strength may decrease.
The results also shown that the use of TiO2 nanoparticles improves the resistance to water
permeability of concrete when it is mixed in cement pastes, although those improvements
were achieved for a maximum replacement level of 2.0 wt% of nano-TiO2 (Nazari and
Riahi, 2011b). Moreover, if these nanoparticles are coupled with concrete with low water-
cement ratio, the microstructure in the interfacial transition zones can be improved and,
15
therefore, the value of strengthening gel, resulting also in a decrease of the water permea-
bility. These results finally show that the workability and setting time of fresh concrete
decreases as the amount of TiO2 nanoparticles used increases (Figures 6, 7). Therefore, it is
important to identify how the basic properties of the TiO2 nanoparticles modify cement
pastes before its application at a large scale, because the amount of TiO2 in these materials
is limited according to their final properties. These aspects have been the object of many
studies, aimed to determine the TiO2 specific amounts that can be more advantageous for
the mechanical and thermal properties of concrete (Matějka et al., 2009).
The reasons presented before, as well as the relatively low cost of adding TiO2 nanoparti-
cles to concrete (when compared to others), justify its application and introduction in the
construction industry. The photocalytic activity of TiO2 nanoparticles leading to NOx
degradation seems to be route with better prospects. Beyond some unconsistent results on
its use in cement based materials, the arisal of other methods to decrease NOx pollution
represent major challenges that the application of these nanoparticles have to face. For
example, Krou et al. (2013), suggested other mechanisms to decrease NOx pollution
based on the abilty of some main hydrates (such as Ca(OH)2) to trap NO2 or by the addi-
tion of activated carbon with remarkable absorbent properties. Moreover, similarly to the
human and environment effects of using NS nanoparticles, TiO2 shows reduced or negli-
gible biological effects, although some inflammatory effect may be observer after inhala-
tion of these types of nanoparticles (Som et al., 2011).
Still, some “self-cleaning” and “depolluting” concrete products with TiO2 nanoparticles
are already being produced and used in some facades of buildings and in paving materials
for roads, namely in Europe and Japan (Sanchez and Sobolev, 2010).
16
4. Iron III Oxide
The structural safety of buildings in service is an importance vector in the construction in-
dustry. Monitoring and controlling materials and building performance during their life
cycle should be guaranteed. For this purpose, several techniques have been used, including
embedded or attached sensors that have raised increasing interest. Currently, these types of
sensors continue to be the most effective technique to ensure buildings safety. However,
the opportunity of developing concrete that can sense its own strain and damage has
opened new opportunities in this subject. The advantages of producing concrete with self-
monitoring characteristics are great: greater durability, absence of mechanical property
degradation due to the embedment of sensors and relatively low cost (Li et al., 2004b). In
this issue, Iron III Oxide, also known as Hematite, plays a key role. Iron III Oxide is an
oxide of iron. Iron has two oxidation states and to denote which kind of ion forms on disso-
ciation, iron is named as Iron II or Iron III. Fe2O3 has three iron ions, thus it is called Iron
III Oxide. The addition of Fe2O3 nanoparticles (NF) may play an important role due to its
electrical properties. Several studies have been made in order to evaluate the influence of
NF in self-diagnostic ability of stress and damage. Li et al. (2004b) tested different samples
of cement mortar with w/b ratio of 0.5 and additions of nF at 3%, 5% and 10% by weight
of binder. The results indicated that cement mortar with NF is able to sense its own com-
pressive stress in the elastic and inelastic regimes thanks to their ability to change the vol-
ume electric resistance as the applied load changes. Moreover, it has been shown that NF
particles do not decrease the resistivity of cement mortar, which is beneficial for the dura-
bility of reinforced concrete structure. However, more tests are needed to clearly quantify
this influence of NF on the self-monitoring ability.
17
More specifically, NF may also play an important role in the production of the called heav-
yweight concrete. This type of concrete is widely used for radiation shielding of nuclear
reactors and other structures that require radiation impermeability. Hematite, due to its high
volumic weigth (4.0-4.5 g/cm3), is as a potential candidate to be added as a dispersed
phase. There are several reports on radiation shielding properties of concrete containing
hematite. For example, Gencel et al. (2010) investigated the physical and mechanical prop-
erties of concrete with hematite materials, with focus on workability and durability. Re-
garding the mechanical properties, it was found that there was only a minor effect of hema-
tite added to concrete on its essential properties, namely the compressive strength which
did not differ from that of plain concrete. On the other hand, it has been shown that it had
high impact on other properties, like shrinkage. With the addition of hematite at 50% by
weight of aggregate a decrese of approximetaly 80% was observed in shrinkage for 15
days. In fact, this is an important property in radiation-shielding concrete. With the reduc-
tion of stresses resulting from drying shrinkage, the cracking also effect tends to decrease.
However, for 50% replacement, the beginning of segregation was observed, which indicat-
ed the use of hematite in smaller contents. Still, the opportunity of using NF for this specif-
ic type of concrete should be seriously considered.
Additionally, other tests have been performed in order to assess the influence of NF on
other mechanical and rheological properties of concrete, such as water absorption, com-
pressive strength and workability. Nazari and Riahi (2010a) investigated the percentage
and rate of water absorption, workability and setting time of binary blended concrete with
partial replacement of cement by 0.5, 1.0, 1.5 and 2.0 wt% of NF. The results indicated
that the resistance to water permeability increased up to a maximum replacement of
18
2.0%. Contrarily, the workability and setting time of fresh concrete decreased by increas-
ing the content of NF. Nazari and Riahi (2010b) tested the compressive strength and
workability of concrete with addition of NF with average diameter of 15 nm. Different
contents were used: 0.5%, 1.0%, 1.5% and 2.0% by weight. The results showed an in-
crease of 15% in the ultimate strength of concrete for a maximum replacement level of
1.0%. Contrarily, the workability decreased with increasing content of NF for a maxi-
mum of 8 cm to 3 cm in the concrete slump test, when 2.0% by weight was replaced.
However, more studies are needed on this issue to quantify the influence of NF on the
mechanical properties of concrete. The limited number of studies may be justified by the
existence of other nanoparticles with higher positive impact on these properties. For this
reason, self-monitoring and self-sensing seems to be the property with the best potential
advantage concerning the use of NF in concrete structures.
5. Chromium III Oxide
Chromium III oxide is the inorganic compound of the formula Cr2O3. It is one of principal
oxides of chromium and is used as a pigment. In comparison with SiO2 and TiO2, the use
of Cr2O3 nanoparticles (NCr) in the cement matrix is referred in fewer studies and, there-
fore, less results and applications are known. This may be explained by the inherent proper-
ties and potential of NCr, which are clearly less appealing than those of other nanoparticles.
Nevertheless, there are several reports on the incorporation of these nanoparticles in con-
crete specimens. The aim of the majority of these studies is to investigate the mechanical
properties and water permeability of concrete materials containing different contents of
NCr (Nazari and Riahi, 2010c, 2010d, 2011d).
Nazari and Riahi (2011d) tested some samples of concrete with NCr and their results showed
19
that these specimens have higher strength than those without these nanoparticles at every
curing age. More particularly, the replacement of cement with NCr with average size of 15
nm up to a maximum limit of 2.0% improved the mechanical properties of concrete, although
the optimum level of NCr was achieved for 1.0% for the specimens cured in water where an
improvement of 15% in compressive strength at 28 days was achieved. The influence of
these nanoparticles on both flexural strength and splitting tensile strength has also been
shown. The results showed an increase of these properties in NCr blended concrete when
added in the right amounts. For example, at 28 days, for an optimum replacement value of
NCr of 1.0%, an increase of more than 50% in the splitting tensile strength was observed.
The effects of using NCr are lower in the flexural strength (approximately 5%-10%), particu-
larly for the specimens cured in water. However, these positive effects of NCr may be justi-
fied by the additional formation of C-S-H gel in the presence of these nanoparticles.
Similarly to TiO2 nanoparticles, it was also shown that incorporating NCr in the cement
matrix improves other important properties. A reduction of water absorption was also
observed in the samples with these nanoparticles. This decrease may result from a reduc-
tion of the amount of pores when NCr is added to the cement matrix, due to its filler ef-
fect. Thus, the pore structure of self-compacting concrete containing NCr is improved,
also increasing the content of all mesopores and macrospores (Nazari and Riahi, 2010d).
Apart from the advantages of using NCr, important reasons may justify a slowdown in
the investigations and its use in construction industry, namely in concrete. On one hand,
chromium leaching is known to be a problematic issue to the durability of concrete due to
the release of Cr(VI). On the other hand, toxicity concerns have emerged in the last years,
which have justified its decreasing use for pigments and paints (Assem and Zhu, 2007).
20
Thus, NCr seems not to be the best option if other types of nanoparticles with similar or
higher potentialities are available.
6. Nanoclay
Using Nanoclay (NCl) to reinforce cement-based composites has raised much attention to
academic and industrial sectors due to the addition of small amount of nanoclay could sub-
stantially enhance the mechanical properties of concrete. Many studies have targeted the
applications of clay in cement composites and several enhancements on concrete’s proper-
ties were achieved. However, fewer studies were assessed to evaluate the effects of use
nanoclays (NCl) on the mechanical properties and durability of cement based composites.
Clay belongs to a wider group of minerals and may be simply described as hydrous sili-
cates (Uddin, 2008). They also can be referred as hydrous aluminium phyllosilicates with
variable amounts of iron, magnesium, alkali metals and alkaline earths. Clay minerals are
characterized by their fine-grained natural structure with sheet like geometry. Individually,
natural clay particles are micron and sub-micron in size, and the base structure is composed
of crystalline layers of aluminum phyllosilicates with thicknesses on the order of 1 nm. In
the literature, clay minerals are divided into four major groups mainly depending on the
variation in the layered structure. These include the kaolinite group, the montmorillo-
nite/smectite group, the illite and the chlorite group (Hillier, 2003). Among them, kaolinite
group and montmorillonite/smectite group are widely referred when use fillers in concrete
production is studied (Chang et al., 2007; Gaucher and Blanc, 2006; Gruber et al., 2001;
Kuo et al., 2006b; Morsy et al., 1997; Siddique and Klaus, 2009). The kaolinite group has
different members, such as kaolinite, dickite or nacrite, each with a
la Al2Si2O5(OH)4. This means that these members have the same formula but different
21
structures (Uddin, 2008). Contrarily, the montmorillonite group is larger than the kaolinite
group and the general formula of its chemical structure is
(Ca,Na,H)(Al,Mg,Fe,Zn)2(Si,Al)4O10(OH)2XH2O. The layer structure contains silicate lay-
ers, sandwiching an aluminium oxide/hydroxide layer (Al2(OH)4).
In the presence of silica and aluminium, clay particles may act as “nuclei” of hydration,
possess high pozzolanic behaviour (as well as nano-SiO2) and can fill the voids in the
cement matrix increasing the overall concrete performance. Even if the use of metakaolin
(belonging to kaolinite group) (Dhinakaran et al., 2012; Paiva et al., 2012; Siddique and
Klaus, 2009) and montmorillonite (Kuo et al., 2006c) particles at micro-scale in concrete
production is well reported, nano-engineering in clays is gaining interest in the research
community. The large surface area of these nanoparticles and their abundance because of
their small size can facilitate the chemical reactions to produce a dense cement matrix
with more calcium silicate hydrate (C-S-H) and less calcium hydroxide.
The influence of NCl particles in concrete is mostly related with the mechanical proper-
ties, thermal behaviour and microstructure of cement mortars. Morsy et al. (2010) studied
the effects of NCl on the mechanical properties and microstructure of Portland cement.
Nano-metakaolin (NMK) was prepared by thermal activation to blend in cement prepara-
tion. Ordinary Portland cement was used and it was partially replaced by NMK at 0, 2, 4,
6 and 8% by weight of cement. The w/b ratio was established at 0.5. The results showed
that the compressive and tensile strength of the cement mortars with NMK was higher
than that of plain cement mortar with the same w/b ratio. The tensile strength increased
49% relative to the control mortar and the compressive strength was 7% higher for 8%
NMK replacement. Moreover, SEM observations confirmed that the NMK was not only
22
acting as filler but also as an activator to promote hydration process, confirming its high
pozzolanic activity (Figure 8). Chang et al. (2007) studied the compressive strength and
permeability of the cement paste when nano-montmorillonite is used. Different contents
of nano-montmorillonite were used: 0.0%, 0.2%, 0.4%, 0.6% and 0.8% of cement weight.
The w/c ratio was fixed at 0.55. Results indicated that, after 28 days, the optimal amounts
of nano-montmorillonite were found to be 0.6% and 0.4% by weight of cement, where
cement paste composites had the highest compressive strength (20% higher) and the low-
est permeability coefficient (25% lower) at 28 days.. The impact on the coefficient of
permeability was, therefore, higher compared to that on compressive strength. Denser and
more stable bonding structures were also found.
Farzadnia et al. (2013) studied the mechanical properties, flowability, thermal behaviour
and durability of mortars containing 1%, 2% and 3% of halloysite nanoclay. Halloysite
NCl, belonging to the kaolinite group, is a two layered aluminosilicate with predominant-
ly hollow nanotubular structure. Results from its use in mortars showed that the compres-
sive strength and gas permeability of samples improved up to 24% and 56% with 3% and
2% halloysite NCl, respectively.
From the results reported, NCl particles have shown high potential in enhancing the me-
chanical performance, reducing permeability and shrinkage of concrete in accordance with
those of NS. However, the main concern in the use NCl in concrete is related with an in-
creased water demand of the mix that has to be controlled (Morsy et al., 2011). Clay parti-
cles are typically highly hydrophilic, which makes this control an important issue. Moreo-
ver, enhanced workability and flowability are needed in concrete production, but without a
decrease in its mechanical properties (Sanchez and Sobolev, 2010). Nevertheless, the po-
23
tential of these nanoparticles in addition to a relatively low-cost may justify further devel-
opments in this area.
7. Calcium carbonate
Calcium carbonate (CaCO3), or simply NCa, is a common substance found in rocks in all
parts of the world, and is the main component of shells of marine organisms. It is created
when Ca ions in hard water react with carbonate ions creating limescale. Ground limestone is
a sedimentary rock composed largely of the minerals calcite and aragonite, which are differ-
ent crystal forms of calcium carbonate. Ground limestone has been used in the last years to
replace part of ordinary portland cement (OPC) in concrete. Energy conservation and natural
resources concerns, in addition to ground limestone having lower costs than OPC, justified its
use in the concrete industry (Sato and Beaudoin, 2006). However, a high number of studies
have been made in recent years reporting positive effects of NCa addition on different con-
crete properties, such has the hydration and strength development of concrete (Ali et al.,
2013; Ingram and Daugherty, 1991; Péra et al., 1999). The effect on the rate of hydration has
been highly focused. It was concluded that the hydration process was accelerated by the addi-
tion of finely ground CaCO3 that acts as a nucleation site on which cement hydration products
form. This micro-physical effect results in a higher development rate of mechanical proper-
ties. The introduction of nanotechnology explores the benefits of using NCa with higher sur-
face area, which promotes hydration reactions with relatively reasonable cost. This leads to
lower amounts of NCa used with similar, if not enhanced, properties. An increasing number
of studies on this issue have been reported in the last few years. Camiletti et al. (2013) tested
the effects of NCa on the early-age properties of ultra-high performance concrete (UHPC)
with addition of NCa at 0%, 2.5%, 5%, 10% and 15% by weight of cement. The results
24
showed that NCa improved the flowability of UHPC mixes, which also exhibited better
workability than other accelerating admixtures. A strong acceleration effect on the early-age
setting and hardening process was observed. Moreover, mixes incorporating NCa showed
comparable or better early-age compressive strength results, except a high dosage of NCa
(>15%) that exhibited a decrease in compressive strength. From the performance and eco-
nomic viewpoint, it was concluded that adding 5% to 10% NCa was the best choice. Sato and
Beaudoin (2010) tested the influence of NCa on the acceleration of hydration of OPC, de-
layed by the presence of high volumes of supplementary cementitious materials, particularly
high volumes of ground granulated blast-furnace slag. Results indicated that the hydration of
OPC was significantly accelerated by the addition of NCa: the greater the amount of the addi-
tion, the greater was the accelerating effect. The microhardness and modulus of elasticity at
the early-stage of the hydration also increased significantly. Admixtures of OPC containing
ground granulated blast-furnace slag with 20% NCa addition increased microhardness values
from 30 MPa to nearly 140 MPa, close to that of the control OPC at 28 days. The effect is
less marked in the modulus of elasticity, but an increase of approximately 10% was ob-
served.Xu et al. (2011) evaluated the effects of NCa on the compressive strength and micro-
structure of high-strength concrete with standard curing (21 ± 1 ℃) and low curing tempera-
tures (6.5 ± 1 ℃). The results showed that 1% and 2% of NCa improved the strength of con-
crete by 13% and 18% with standard curing temperatures and by 17% and 14% with low
curing temperature at the age of 3 days.
For these reasons and considering the relatively low cost of NCa compared to other na-
nomaterials, its introduction in the construction industry is foreseeable, particularly when
strength at early ages is very important. However, more research is needed since the
25
study of NCa addition is relatively recent.
8. Alumina
Aluminium III oxide (Al2O3) is a chemical compound of aluminium and oxygen and it is
the most commonly occurring of several aluminium oxides. It is commonly called alumi-
na (nAl) and it has been shown to potentially improve the properties of concrete. It has
been stated that using nAl as a partial replacement of cement leads to C-A-S (calcium
aluminum silicate) gel formation in concrete, thanks to the reaction of nAl with calcium
hydroxide produced during hydration of calcium aluminates (Behfarnia and Salemi,
2013). The rate of this reaction is proportional to the surface area available to react. This
possibility justified several studies on the use of nAl with high purity and finesses value
to improve the properties of concrete. However, when compared to other nanoparticles,
much less studies were reported in the literature. The main reason for this lack of research
works, is the limited effect that nAl has on the compressive strength of concrete. Nazari
and Riahi (2011e) tested different samples with different contents of nAl particles with
average size of 15 nm. The w/b ratio for all mixes was set at 0.40 and the cement re-
placement was 0.5%, 1.0%, 1.5% and 2.0% by weight. The results showed that the com-
pressive strength increased approximately 10% with nAl for all ages (7, 28 and 90 days)
up to 1.5% replacement and then decreased for values near to those obtained without any
addition, although for 2.0% replacement it was still higher than those of the plain cement
concrete. Contrarily, Barbhuiya et al. (2014) replaced OPC by nAl powder at 2% and 4%
by weight with a w/b ratio of 0.4. The results showed no changes in compressive strength
with this addition, especially at the early ages (Figure 9).
Behfarnia and Salemi (2013) tested different samples containing 1%, 2% and 3% of nAl
by weight of cement with a w/b ratio of 0.48. The results showed a limited increase of
26
compressive strength of 2.6% (7-day), 6% (28-days) and 9% (120-days). Experimental
conditions, preparation technology or inadequate mix amounts of nAl may explain this
trend (Nazari and Riahi, 2011e).
Despite this limited influence on compressive strength, nAl might have positive effects
on other properties, and these possibilities have to be further explored. Li et al. (2006b)
investigated the effect of nAl on the elastic modulus of cement composites with various
volume fractions (3%, 5% and 7%) with a w/b ratio of 0.4. The results showed that the
elastic modulus of composites significantly increased by 143% at 28 days when the nAl
fraction was 5%. Moreover, increased compactness interfacial transition zone (ITZ) and
decreased porosity were observed. Also, Barbhuiya et al. (2014) observed a much denser
microstructure with the addition of nAl to the cement matrix. Its addition also decreased
the water absorption and chloride penetration, improving the durability of concrete. Even
so, more studies are needed to clearly quantify the effects of the use nAl particles on con-
crete properties. This will be a major challenge in the near future.
9. Carbon nanotubes
Carbon nanotubes (CNTs) are probably one of the most promising materials of the 21st centu-
ry, due to their higher mechanical properties compared to all other types of nanomaterials.
Their applications are innumerous, either from biology to chemistry or from electronics to
medicine. Clearly, the construction industry may be added to these research areas. Within this
scope, CNTs have been introduced in several types of matrices (polymeric, metallic, cementi-
tious) and produced an improvement of the mechanical properties of structural materials
(Chaipanich et al., 2010; Soliman et al., 2012). In fact, the CNT properties justify such a
wide application. CNTs are tubular nanostructures with a diameter of a few nanometers and a
27
large length/diameter aspect ratio. Its atomic structure consists of a single or several concen-
tric hexagonal lattices of carbon atoms linked by sp2 bonds and separated by 0.34 nm. Three
main techniques were reported in CNT production: arc-discharge, laser ablation and catalytic
growth (Popov, 2004). Due to the hexagonal lattice and sp2 bonds between carbon atoms,
CNTs have highly advantageous properties. It is widely accepted that CNTs have a Young
modulus around 1.0 TPa (Sinnott and Andrews, 2001), which is five times higher than that
of steel (Silvestre et al., 2012), and a tensile strength around 50-100 GPa. In research, two
types of carbon nanotubes were reported: single-walled carbon nanotubes (SWCNT) and
multi-walled carbon nanotubes (MWCNT), whose differences remain mainly in their overall
thickness (Figure 10). It has also been shown by Faria et al. (2011) and Silvestre (2012)that
CNTs only exhibit these impressive mechanical properties under tensile loading. If submitted
to compressive loading, twisting or combinations of these, CNTs buckle locally and their
stiffness and strength decrease (Figure 11). Compared to SWCNTs, MWCNTs seem to be
more heterogeneous and their characterization and study are more complex. Furthermore,
theoretical calculations and experimental results on SWCNT show that this type of CNTs has
more desirable mechanical, thermal, photochemical and electrical properties (Lam et al.,
2006). For instance, MWCNTs are slightly lower in strength and stiffness than SWCNTs.
However, MWCNTs are (i) less prone no buckling phenomena because of van der Waals
forces between different tube walls and (ii) also less expensive and easier to produce with its
multiple walls, which certainly justifies their wider applications (Soliman et al., 2012) in
strengthening other materials.
The high aspect ratio of CNTs might be responsible for nanocracks decrease and, there-
fore, demand higher energy for crack propagation. Moreover, due to the small diameter
28
of CNTs, fiber spacing is also small (Konsta-Gdoutos et al., 2010a) if a uniform disper-
sion of CNT is achieved. Depending on their specific structure, these nano materials can
be either metallic conductors or semiconductors (Li et al., 2005). Thus, CNTs can also be
used to increase the conductivity of the composite material.
An important aspect in the study of addition of CNTs for mechanical improvement of
materials is their dispersion in the reinforced matrix. In fact, the effective use of CNTs in
nano composites depends on the ability to disperse CNTs within the matrix without re-
ducing their aspect ratio. In order to overcome this problem, many mechanical/physical
methods were developed in the last few years. These techniques range from ultrasoni-
cation to surfactant addition, from high shear mixing to melt blending or also chemical
modification through functionalization. For instance, Li et al. (2005) proposed a H2SO4
and HNO3 mixture solution where multi-walled CNTs were added. Soliman et al. (2012)
have used MWCNTs dispersed in a styrene butadiene rubber (SBR) matrix before mixing
the matrix with cement, also adding surfactants that have successfully enhanced the dis-
persion and functionality of MWCNTs in SBR. However, some of these techniques have
a high aqueous content, corresponding to the mixing water. Because of this, Metaxa et al.
(2012) presented a method to prepare highly concentrated MWCNT suspensions that
result on a reduction of the admixture’s volume required in cement-based materials. This
method is based on a centrifugal process that can reduce the quantity of water of suspen-
sions (Figures 12 and 13). The results showed an increase of the concentration of the
MWCNT suspensions by a factor of five, with the application of this method. In this way,
the dilution of these highly concentrated MWCNT suspensions in nanocomposites results
in materials with similar properties when compared to samples prepared using non-
29
concentrated suspensions. This method has the additional possibility of being used in
large-scale production of MWCNT admixtures for cementitious materials.
Based on these important aspects about the general properties and applications of CNTs,
several results have been presented concerning their addition to cement-based materials.
One of the most reported studies is related to the increase of the compressive and flexural
strength of fly ash mortars and Portland cement, cement paste or all other cement compo-
sites (Chaipanich et al., 2010; Sanchez et al., 2009; Soliman et al., 2012). An explanation
for this behaviour is that the functionalized CNTs could provide bond between the COOH
groups of nanotubes and the calcium silicate hydrate phase (C-S-H) of the cement matrix,
which enhanced the stress percolation, thus increasing the load-transfer efficiency from
cement matrix to the reinforcement (Chaipanich et al., 2010). Some investigations on the
reinforcing effect of MWCNTs in a cement matrix (w/c = 0.5) suggested that the cement
paste matrix reinforced with CNTs can increase its flexural strength and Young’s modulus
by 25% and 50%, respectively (Konsta-Gdoutos et al., 2010b; Metaxa et al., 2009; Shah et
al., 2009). More particularly, Konsta-Gdoutos et al. (2010b) found that small amounts of
well dispersed MWCNTs (0.025–0.08 wt% of cement) can highly increase the strength and
the stiffness of the cementitious matrix (25-30%). However, the majority of the results pre-
sented show lower values of flexural strength and Young’s modulus enhancement (10-
25%) (Habermehl-Cwirzen et al., 2008).
Nanoindentation results also suggest that MWCNTs can strongly modify and reinforce the
nanostructure of cementitious matrix, thanks to a higher amount of high stiffness C-S-H
and a decrease of nanoporosity. In fact, some techniques such as SEM micrographs showed
good interaction between CNTs and cement matrix, with CNTs functioning as filler. This
30
results on a denser microstructure and higher strength when compared to cement compo-
sites without CNTs, mainly due to the small diameter of these nanotubes that reduces the
number of fine pores. However, the strength of fly ash cement mixes is lower than that of
Portland cement, because of lower strength development in fly ash cement because of its
long-term pozzolanic reaction (Chaipanich et al., 2010).
In this review, it is also important to refer some drawbacks in the success of CNT rein-
forcement, i.e. research works in which improvement was not achieved. Musso et al.
(2009) reported that flexural and compressive tests performed on cement composite with
addition of functionalized CNTs showed a significant performance decrease when com-
pared to plain cement. Sáez de Ibarra et al. (2006) also obtained samples with worse me-
chanical properties than the plain cement paste, especially when no CNTs dispersion
method was used. This behaviour is justified by the fact that CNT are so intrinsically hy-
drophilic that they absorb most of the water contained in the cement mix, negatively in-
fluencing a proper hydration of the cement paste.
CNTs can also increase the conductivity of cementitious materials, adding to the fact that
cement-based materials are also piezoresistive which means that excellent sensors can be
produced for cement structures monitoring. These sensors can easily sense micro-
cracking and failure (Azhari and Banthia, 2012). In this context, some studies have been
presented showing how advantageous the addition of CNTs can be. Li and Chou (2004)
used SWCNT-based sensors in order to measure strain and pressure at the nanoscale. In
fact, CNTs change their electronic properties when subjected to strains. Using this strain
sensing characteristic of CNTs, it is possible to develop excellent sensors to measure
these particular properties (Dharap et al., 2004). The results indicate that the resonant
31
frequency shift is linearly dependent on the applied axial strains or transverse pressure
that suggests the potential of such films for multidirectional and multiple location strain
sensors in the macroscale.
Regarding the environmental risks of using CNTs, the possible adverse effects of its use
have been widely assessed. However, there are a lot of contradictory data that increases
the uncertaintiy and secticispm of consumers. Besides the risks of inhalation of these na-
nomaterials, some authors (Grubek-Jaworska et al., 2006 and Lam et al., 2006) reported
that exposure to CNTs may cause an inflammatory reaction while others (Kagan et al.,
2006) suggested that these effects were due to the presence of contaminants in the sam-
ples and not due to the CNTs directly.
For all these reasons much work is still needed to fully understand and evaluate the bene-
fits and potentialities of CNTs in cement composites. There is still a lack of studies estab-
lishing the optimum values of CNT and dispersing agents in the mix design parameters,
although research in this direction is under progress - see the work by Yazdanbakhsh and
Grasley (2012). In fact, if better dispersions of CNTs in the cement paste were achieved
(based on surface treatment of CNT, optimum physical blending or the use of surfac-
tants), an enhancement in cement composites performance would be expected. In that
sense, Collins et al. (2012) reported the results of several investigations on the dispersion,
workability and strength of CNTs aqueous and CNT-OPC paste mixes. These mixes were
produced with and without various dispersants compatible as admixtures in the manufac-
ture of concrete, such as butadiene rubber or polycarboxylates. All of these composites
were tested and a broad range of workability responses was measured with the main ob-
jective of achieving results for CNTs dispersion in hardened pastes.
32
10. Graphene oxide
Graphene is a two-dimensional, crystalline allotrope of carbon. In graphene, carbon atoms
are packed in a regular sp2-bonded hexagonal structure, with a C-C bond length of 0.142 nm.
A SWCNT can be viewed as graphene sheet rolled into a cylindrical shape to form the tube.
Graphene may be viewed as a one-atom thick layer of graphite. On the other hand, graphene
sheets stack to form graphite with an interplanar spacing of 0.335 nm. While graphite is a
three-dimensional carbon based material made up of millions of layers of graphene, graphite
oxide is a little different. By the oxidation of graphite using strong oxidizing agents, oxygen-
ated functionalities are introduced in the graphite structure which not only expand the layer
separation, but also makes the material hydrophilic. This property enables the graphite oxide
to be exfoliated in water using sonication, ultimately producing single or few layer graphene,
known as graphene oxide (GO). The main difference between graphite oxide and GO is, thus,
the number of layers. While graphite oxide is a multilayer system, in a GO dispersion a few
layers flakes and monolayer flakes can be found.
One of the advantages of the GO is its easy dispersability in water and other organic solvents,
as well as in different matrixes, due to the presence of the oxygen functionalities. This re-
mains as a very important property when mixing the material with cement matrices when
trying to improve their electrical and mechanical properties. On the other hand, in terms of
electrical conductivity, GO is often described as an electrical insulator, due to the disruption
of its sp2 bonding networks. In order to recover the honeycomb hexagonal lattice, and with it
the electrical conductivity, the reduction of the GO has to be achieved. It has to be taken into
account that once most of the oxygen groups are removed, the reduced GO obtained is more
difficult to disperse due to its tendency to create aggregates.
33
Graphene oxide (GO) is probably the most prominent nanomaterial whose application in
construction industry should be taken as a very meaningful research field in the next years. In
fact, its application in reinforcement of concrete for structural applications is still to be re-
ported, although the first steps have already been taken. Like other nanomaterials, GO has a
large theoretical specific surface area (2630 m2/g) and high Young’s modulus (around 1
TPa), similar to that of CNTs. In addition, it also has high thermal conductivity and excellent
electrical conductivity, which results in a broad range of potential applications (Zhu et al.,
2010). For example, taking advantage of its thermal and electrical conductivity properties,
Wang et al. (2008) proposed a transparent, conductive, and ultrathin graphene films, as an
alternative metal oxides window electrodes for dye-sensitized solar cells. That is indeed the
most studied application of GO in the construction industry, although much more work has
been done in other science fields, such as that of chemistry and biomedical engineer (Dreyer
et al., 2009). However, Duan (2012) developed a novel method to reinforce concrete con-
struction materials based on the incorporation of GO in a cementitious matrix, resulting in an
enhancement of its strength and durability. Laboratory results showed that only 0.05% of GO
incorporation in cement matrix improve flexural strength of an OPC matrix around 50% and
compressive strength from between 15% and 33% (Figure 14(a)). Also a decrease in total
porosity was registered with the addition of these nanomaterials (Figure 14(b)). This technol-
ogy is owned by Monash University and is protected by Patent PCT/AU2012/001582.
Babak et al. (2014) synthesized GO using exfoliation of graphite oxide prepared by a
colloidal suspension route. They used it to fabricate GO-cement nanocomposites by
means of an ultrasonic method and concluded that the use of an optimal percentage
(1.5 wt%) of GO nanoplatelets caused a 48% increase in the tensile strength of the ce-
34
ment mortar specimens. Using FE-SEM observation of the fracture surface of the sam-
ples containing 1.5 wt% GO, these authors revealed that the GO nanoplatelets were well
dispersed and no GO agglomerates were seen in the matrix. Babak et al. (2014) showed
the growth of C-S-H gels in GO cement mortar because of the nucleation of C-S-H by the
GO flakes. Due to the higher surface energy and the presence of hydrophilic groups on
the GO surfaces, the hydrated cement products deposited on the GO flakes acted as a
nucleation site. The results by Babak et al. (2014) indicated that the main reason for the
observed high bond strength was the nucleation of C-S-H by the GO flakes and its for-
mation along them. FE-SEM observation also revealed microcracks in the GO flakes,
implying that the GO flakes stretched across microcracks in the mortar (Figure 15 (a)).
The breakage observed indicated that very high stresses were applied to the GO flakes.
Because the theoretical tensile strength of GO flake is very high, more GO flakes are
needed to carry stresses. The tensile strength of specimens containing 2 wt% GO flakes
was much less than that of the control samples, because GO is hydrophilic enough to ab-
sorb most of the water contained in the cement mortar, (i) hampering the proper hydra-
tion of the cement mortar and (ii) making dispersion of the GO within the matrix diffi-
cult. This hypothesis raised by Babak et al. (2014) was confirmed by the 24.7% increase
obtained in the tensile strength of specimens containing 2 wt% GO at a water/cement
ratio of 0.5 compared with that of the sample containing 2.0 wt% GO at a water/cement
ratio of 0.4 (Figure 15 (b)).
Although much work remains to be done in developing reliable characterization of GO-
reinforcement of concrete and studying rigorously its mechanical properties, the unam-
35
biguous advantages of GO increase the expectations of further developments in concrete
technology and its future structural applications.
11. Concluding remarks and future perspectives
Having presented some of the most relevant and recent research works that has been car-
ried out on the application of nanotechnology in the construction industry, it is possible to
conclude that the potential of concrete nanotechnology will certainly be the key to a new
construction’s paradigm. Concrete production is responsible for high levels of CO2 emis-
sions among many others pollutants. In that sense, the application of nanomaterials in the
construction industry should be considered not only to improve the physical and mechani-
cal material properties, but also for environmental protection and energy saving. Experi-
mental techniques have been developed, which made the characterization of material prop-
erties easier and reliable. Concerning the nanomodification of cement-based materials, tita-
nium dioxide, nanosilica, nanoclay, carbon nanotubes a graphene oxide are the nanomateri-
als with higher potentialities. Their advantages may be summarized as follows:
• Enhancement of concrete (compressive and flexural) strength;
• Reduction of the total porosity;
• Acceleration of C-S-H gel formation;
• Enhancement of Young’s modulus;
• Environmental pollution remediation, self-cleaning and self-disinfection.
From all the nanomaterials presented, nanosilica seems to be the nanomaterial that more
advantageous when production of concrete with high compressive strength is needed. Car-
bon nanotubes have impressive mechanical properties that can play an important role in
this issue, but the high cost of production and use of these nanostructures in concrete pre-
36
vent massive use in the construction industry. On the other hand, when environmental pol-
lution remediation, self-cleaning and self-disinfection issues are taken into account, titani-
um dioxide nanoparticles are definitely the nanomaterials with more advantages.
Nevertheless, other nanomaterials have come up in recent research works such as the
application of graphene oxide, but its high costs are also an issue barring its introduction
in the construction industry. In fact, the cost of nanotechnology is still seen as one of the
main barriers to implementation of nanoproducts. Besides the cost of nanomaterials, the
initial investment necessary has a major impact on this cost, despite the long-term bene-
fits that could be obtained through the use of these products. Effectively, the costs of
equipments and technologies are relatively high due to the complexity of the equipment
used for the preparation and characterization of these products. Expectations are that
costs will decrease over time, as manufacturing technologies improve and demand in-
creases. It is a challenge to the construction industry to solve production and distribution
problems to provide solutions to the general public at a reasonable cost.
Another barrier to a wider implementation of nanotechonolgy regards health and envi-
ronmental concerns. The effect of various NMs on the natural environment is a subject of
debate within the nanotechnology and environmental research community. Some of the
potential problems on this matter include leakage of materials into groundwater, release
of materials in the air through the generation of dust and exposure to potentially harmful
materials during construction and maintenance operations. Therefore, there are some rea-
sonable concerns about the potential adverse health and environmental effects related to
the manipulation and use of NMs. The wide range of properties that make NMs so useful,
such as their size, shape and surface characteristics, can also cause potential problems if
37
the material is not properly used. For example, nanotechnology-based construction prod-
ucts may cause respiratory problems to construction workers related with the inhalation
of dust and aerossol.
In conclusion and beyond the current excitement and all the expectations about the
use of nanomaterials in the construction industry, further research results are needed in order
to clarify some consequences about the use, production and design that are still not fully un-
derstood.
12. References
Agrios, A.G., and Pichat, P., "State of the art and perspectives on materials and
applications of photocatalysis over TiO2", Journal of Applied Electrochemistry, Vol.
35, 2005, pp. 655–663.
Allen, A.J., Livingston, R.A., "Relationship between differences in silica fume additives
and fine-scale microstructural evolution in cement based materials", Advanced
Cement-Based Materials, Vol. 8, 1998, pp. 118–131.
Ali, A.H., Kandeel, A.M., and Ouda, A.S., "Hydration characteristics of limestone filled
cement pastes", Chemistry and Materials Research, Vol. 5, 2013, pp. 68–73.
Assem, L., and Zhu, H., "Chromium - Toxicological overview", Institute of Environment
and Health, 2007.
Azhari, F., and Banthia, N., "Cement-based sensors with carbon fibers and carbon
nanotubes for piezoresistive sensing", Cement and Concrete Composites, Vol. 34,
2012, pp. 866–873.
Babak, F., Abolfaz, H., Alimorad, R., Parviz, G. “Preparation and mechanical properties
of graphene oxide: cement nanocomposites”, The Scientific World Journal, Vol. 2014,
38
Article ID 276323, 2014.
Bahadori, H., and Hosseini, P., "Reduction of cement consumption by the aid of silica
nano-particles (Investigation on concrete properties)", Journal of Civil Engineering
and Management, Vol. 18, 2012, pp. 416–425.
Balte, G.,"Innovative building materials- reduction of pollutants with TioCem", ZKG
International Ene, 2009, pp. 63–70.
Barbhuiya, S., Mukherjee, S., and Nikraz, H., "Effects of nano-Al2O3 on early-age
microstructural properties of cement paste", Construction and Building Materials, Vol.
52, 2014, pp. 189–193.
BASF Construction Solutions - Master X-Seed 100, “Hardening accelerating admixture
for concrete - EN 934-2:T7”, Version 2, 2014.
Bawa, R., Bawa, S.R., Maebius, S.B., Flynn, T., and Wei, C., "Protecting new ideas and
inventions in nanomedicine with patents", Nanomedicine Nanotechnology Biology
and Medicine, Vol. 1, 2005 pp. 150–158.
Behfarnia, K., and Salemi, N., "The effects of nano-silica and nano-alumina on frost
resistance of normal concrete", Construction and Building Materials, Vol. 48, 2013,
pp. 580–584.
Behnood, A. and Ziari, H., “Effects of silica fume addition and water to cement ratio on
the properties of high-strength concrete after exposure to high temperatures”, Cement
& Concrete Composites, Vol. 30, 2008, pp. 106-112.
Bernard, O., Ulm, F.-J., and Germaine, J.T., "Volume and deviator creep of calcium-
leached cement-based materials", Cement and Concrete Research, Vol. 33, 2003, pp.
1127–1136.
39
Berra, M., Carassiti, F., Mangialardi, T., Paolini, A.E., and Sebastiani, M., "Effects of
nanosilica addition on workability and compressive strength of Portland cement
pastes", Construction and Building Materials, Vol. 35, 2012, pp. 666–675.
Camiletti, J., Soliman, A.M., and Nehdi, M.L., "Effect of nano-calcium carbonate on
early-age properties of ultra-high-performance concrete", Magazine of Concrete
Research, Vol. 65, 2013, pp. 297–307.
Cárdenas, C., Tobón, J.I., García, C., and Vila, J., "Functionalized building materials:
Photocatalytic abatement of NOx by cement pastes blended with TiO2 nanoparticles",
Construction and Building Materials, Vol. 36, 2012, pp. 820–825.
Chaipanich, A., Nochaiya, T., Wongkeo, W., and Torkittikul, P., "Compressive strength
and microstructure of carbon nanotubes–fly ash cement composites" Materials Science
and Engineering: A, Vol. 527, 2010, pp. 1063–1067.
Chang, T.-P., Shih, J.-Y., Yang, K.-M., and Hsiao, T.-C., "Material properties of portland
cement paste with nano-montmorillonite", Journal of Materials Science, Vol. 42,
2007, pp. 7478–7487.
Chen, J., Kou, S., and Poon, C., "Hydration and properties of nano-TiO2 blended cement
composites", Cement and Concrete Composites, Vol. 34, 2012, pp. 642–649.
Chong, J.Z., Sutan, N.M., and Yakub, I., "Characterization of early pozzolanic reaction of
calcium hydroxide and calcium silicate hydrate for nanosilica modified cement paste",
UNIMAS E-J. Civil Engineering, Vol. 4, 2012, pp. 6–10.
Collins, F., Lambert, J., and Duan, W.H., "The influences of admixtures on the
dispersion, workability, and strength of carbon nanotube–OPC paste mixtures",
Cement and Concrete Composites, Vol. 34, 2012, pp. 201–207.
40
Cwirzen, A.; Habermehl-Cwirzen, K.; Nasibulina, L.I.; Shandakov, S.D.; Nasibulin,
A.G.; Kauppinen, E.I.; Mudimela, P.R. and Penttala, V., “CHH cement composite”,
Nanotecnhology in Construction, Vol. 3, 2009, pp. 181-185.
Dharap, P.; Li, Z.; Nagarajaiah, S. and Barrera, E.V., “Nanotube film based on single-
wall carbon nanotubes for strain sensing”, Nanotechnology, Vol. 15, 2004, pp. 379-
382.
Dhinakaran, G., Thilgavathi, S., and Venkataramana, J., "Compressive strength and
chloride resistance of metakaolin concrete", KSCE Journal Civil Engineering, Vol. 16,
2012, pp. 1209–1217.
Dreyer, D.R., Park, S., Bielawski, C.W., and Ruoff, R.S., "The chemistry of graphene
oxide" Chemical Society Reviews, Vol. 39, 2009, pp. 228–240.
Duan, 2012, http://www.monash.edu.au/assets/pdf/industry/graphene-oxide-reinforced-
concrete.pdf.
Faria, B., Silvestre, N., and Canongia Lopes, J.N., "Interaction diagrams for carbon
nanotubes under combined shortening–twisting", Composites Science and
Technology, Vol. 71, 2011, pp. 1811–1818.
Farzadnia, N., Abang Ali, A.A., Demirboga, R., and Anwar, M.P., "Effect of halloysite
nanoclay on mechanical properties, thermal behavior and microstructure of cement
mortars", Cement and Concrete Research, Vol. 48, 2013, pp.9 7–104.
Folli, A., Pade, C., Hansen, T.B., De Marco, T., and Macphee, D.E., "TiO2
photocatalysis in cementitious systems: Insights into self-cleaning and depollution
chemistry", Cement and Concrete Research, Vol. 42, 2012, pp. 539–548.
Fujishima, A., Hashimoto, K. and Watanabe, T., “TiO2 photocatalysis: Fundamentals and
41
application, 1st Edition, 1999.
Fujishima, A. and Honda, K., “Electrochemical photolysis of water at a semiconductor
electrode”, Nature, Vol. 238, 1972, pp. 37-38.
Fujishima, A., Zhang, X., and Tryk, D.A., "TiO2 photocatalysis and related surface
phenomena", Surface Science Reports, Vol. 63, 2008, pp. 515–582.
Garboczi, E., “Concrete nanoscience and nanotechnology: Definitions and applications”,
Nanotecnhology in Construction, Vol. 3, 2009, pp. 81-88.
Gaucher, E.C., and Blanc, P., "Cement/clay interactions - A review: Experiments, natural
analogues, and modeling" Waste Management, Vol. 26, 2006, pp. 776–788.
Gencel, O., Brostow, W., Ozel, C. and Filiz, M., “Concretes containing hematite for use
as shielding barriers”, Materials Science, Vol. 16, 2010, pp. 249-256.
Grubek-Jaworska, H., Nejman, P., Czuminska, K, Przybylowski,T., Huczko, A., Lange,
H., Bystrzejewski, M., Baranowski, P. and Chazan, R., “Preliminary results on the
pathogenic effects of intratacheal exposure to onedimensional nanocarbons”, Carbon,
Vol. 44, 2006, pp. 1057-1063.
Gruber, K.A., Ramlochan, T., Boddy, A., Hooton, R.D., and Thomas, M.D.A.,
"Increasing concrete durability with high-reactivity metakaolin", Cement and Concrete
Composites, Vol. 23, 2001, pp. 479–484.
Habermehl-Cwirzen, K., Penttala, V., Cwirzen, A., "Surface decoration of carbon
nanotubes and mechanical properties of cement/carbon nanotube composites",
Advances in Cement Research, Vol. 20, 2008, pp. 65-73.
Hakamy, A., Shaikh, F.U.A., Low, I.M., "Thermal and mechanical properties of hemp
fabric-reinforced nanoclay–cement nanocomposites", Journal of Materials Science,
42
Vol. 49, 2014, pp. 1684–1694.
Hashimoto, K., Irie, H., and Fujishima, A., "TiO2 Photocatalysis: A historical overview and
Future Prospects", Japanese Journal of Applied Physics, Vol. 44, 2005, pp. 8269–8285.
Heikal, M., Abd El Aleem, S., and Morsi, W.M., " Characteristics of blended cements
containing nano-silica", HBRC Jounal, Vol. 9, 2013, pp. 243–255.
Hillier, S., "Clay Mineralogy", GV Middleton, MJ Church, M Coniglio, LA Hardie, and
FJ Longstaffe eds., Encyclopaedia of sediments and sedimentary rocks: Kluwer
Academic Publishers, Dordrecht., 2003, pp. 139-142.
Hooton, R., Li, Y., Langan, B., Ward, M., "The strength and microstructure of high-
strength paste containing silica fume" Cement, Concrete and Aggregates, Vol. 18,
1996, pp. 112-117.
Hou, P., Kawashima, S., Kong, D., Corr, D.J., Qian, J., and Shah, S.P., "Modification
effects of colloidal nanoSiO2 on cement hydration and its gel property", Composites
Part B: Engineering, Vol. 45, 2013, pp. 440–448.
Ibrahim, R.K., Hamid, R., and Taha, M.R., "Fire resistance of high-volume fly ash
mortars with nanosilica addition" Construction Building Materials, Vol. 36, 2012, pp.
779–786.
Igarashi, SI., Watanabe, A. and Kawamura, M., “Evaluation of capillary pore size
characteristics in high-strenght concrete at early ages”, Cement and Concrete
Research, Vol. 35, 2005, pp. 513-519.
Ingram, K.D., and Daugherty, K.E., "A review of limestone additions to Portland cement
and concrete", Cement and Concrete Composites, Vol. 13, 1991, pp. 165–170.
Jalal, M., Mansouri, E., Sharifipour, M., and Pouladkhan, A.R., "Mechanical, rheological,
43
durability and microstructural properties of high performance self-compacting
concrete containing SiO2 micro and nanoparticles", Materials & Design, Vol. 34,
2012, pp. 389–400.
Jo, B.-W., Kim, C.-H., Tae, G., and Park, J.-B., "Characteristics of cement mortar with
nano-SiO2 particles", Construction and Building Materials, Vol. 21, 2007, pp. 1351–
1355.
Kagan, VE., Tyurina, YY., Tyurin, VA., Konduru, NV., Potapovich, AI, and Osipov,
AN., “Direct and indirect effects of single walled carbon nanotubes on RAW 264.7
macrophages: role of iron”, Toxicology Letters, Vol. 165, 2006, pp. 88-100.
Kong, D., Su, Y., Du, X., Yang, Y., Wei, S., and Shah, S.P., "Influence of nano-silica
agglomeration on fresh properties of cement pastes", Construction and Building
Materials, Vol. 43, 2013, pp. 557–562.
Konsta-Gdoutos, M.S., Metaxa, Z.S., and Shah, S.P., "Highly dispersed carbon nanotube
reinforced cement based materials", Cement and Concrete Research, Vol. 40, 2010a,
pp. 1052–1059.
Konsta-Gdoutos, M.S., Metaxa, Z.S., and Shah, S.P., "Multi-scale mechanical and
fracture characteristics and early-age strain capacity of high performance carbon
nanotube/cement nanocomposites", Cement and Concrete Composites, Vol. 32,
2010b, pp. 110–115.
Krou, N.J., Batonneau-Gener, I., Belin, T., Mignard, S., Horgnies, M. and Dubois-
Brugger, I., “Mechanisms of NOx entrapment into hydrated cement paste containing
activated carbon - Influences of the temperature and carbonation”, Cement and
Concrete Research, Vol. 53, 2013, pp. 51-58.
44
Kuo, W.-T., Lin, K.-L., Chang, W.-C., and Luo, H.-L., "Effects of nano-materials on
properties of waterworks sludge ash cement paste", Jounal of Industrial and
Engineering Chemistry, Vol. 12, 2006a, pp. 702–709.
Kuo, W.-Y., Huang, J.-S., and Lin, C.-H., "Effects of organo-modified montmorillonite
on strengths and permeability of cement mortars", Cement and Concrete Research,
Vol. 36, 2006b, pp. 886–895.
Kuo, W.-Y., Huang, J.-S., and Lin, C.-H., "Effects of organo-modified montmorillonite
on strengths and permeability of cement mortars", Cement and Concrete Research,
Vol. 36, 2006c, pp. 886–895.
Lam, C.-W., James, J.T., McCluskey, R., Arepalli, S., and Hunter, R.L., "A review of
carbon nanotube toxicity and assessment of potential occupational and environmental
health risks" Critical Reviews in Toxicology, Vol. 36, 2006, pp. 189–217.
Laukaitis, A., Kerienė, J., Kligys, M., Mikulskis, D., and Lekūnaitė, L., "Influence of
mechanically treated carbon fibre additives on structure formation and properties of
autoclaved aerated concrete", Construction and Building Materials, Vol. 26, 2012, pp.
362–371.
Lehmann, C.P. and Fontana, U. M., “Evolution of phases and micro structure in
hydrothermally cured Ultra-High Performance Concrete (UHPC)”, Nanotecnhology in
Construction 3, 2009, pp. 287-293.
Li, C.-Y., and Chou, T.-W., "Strain and pressure sensing using single-walled carbon
nanotubes", Nanotechnology, Vol. 15, 2004, pp. 1493-1496
Li, G.Y., Wang, P.M., and Zhao, X., "Mechanical behavior and microstructure of cement
composites incorporating surface-treated multi-walled carbon nanotubes", Carbon,
45
Vol. 43, 2005, pp. 1239–1245.
Li, H., Xiao, H., Yuan, J., and Ou, J., "Microstructure of cement mortar with nano-
particles" Composites Part B: Engineering, Vol. 35, 2004a, pp. 185–189.
Li, H., Xiao, H., and Ou, J., "A study on mechanical and pressure-sensitive properties of
cement mortar with nanophase materials", Cement and Concrete Research, Vol. 34,
2004b, pp. 435–438.
Li, H., Zhang, M., and Ou, J., "Abrasion resistance of concrete containing nano-particles
for pavement", Wear, Vol. 260, 2006a, pp. 1262–1266.
Li, W., Xiao, J., Sun, Z., Kawashima, S., and Shah, S.P., "Interfacial transition zones in
recycled aggregate concrete with different mixing approaches", Construction and
Building Materials, Vol. 35, 2012, pp. 1045–1055.
Li, Z., Wang, H., He, S., Lu, Y., and Wang, M., "Investigations on the preparation and
mechanical properties of the nano-alumina reinforced cement compo site", Materials
Letters, Vol. 60, 2006b, pp. 356–359.
Lucas, S.S., Ferreira, V.M., and de Aguiar, J.L.B., "Incorporation of titanium dioxide
nanoparticles in mortars - Influence of microstructure in the hardened state properties and
photocatalytic activity", Cement and Concrete Research,Vol. 43, 2013, pp. 112–120.
Madandoust, R., Ranjbar, M.M., and Yasin Mousavi, S., "An investigation on the fresh
properties of self-compacted lightweight concrete containing expanded polystyrene",
Construction and Building Materials, Vol. 25, 2011, pp. 3721–3731.
Martins, R.M., and Bombard, A.J.F., "Rheology of fresh cement paste with
superplasticizer and nanosilica admixtures studied by response surface methodology",
Materials and Structures, Vol. 45, 2012, pp. 905–921.
46
Matejka, P.V; Kovár, P.; Bábková,P.; Pøikryl, P.; Mamulová-Kutláková, K. and
Èapková, P., “Utilization of photoactive kaolinite/TiO2 composite in cement-based
building materials”, Nanotechnology in Construction, Vol. 3, 2009, pp. 309-315.
Meng, T., Yu, Y., Qian, X., Zhan, S., and Qian, K., "Effect of nano-TiO2 on the
mechanical properties of cement mortar", Construction and Building Materials, Vol.
29, 2012, pp. 241–245.
Metaxa, Z.S.; Konsta-Gdoutos,M.S. and Shah, S.P., “Carbon nanotubes reinforced
concrete. Nanotechnology of concrete: the next big thing is small”, ACI special
publications, Vol. 267, 2009, pp. 11-20.
Metaxa, Z.S; Seo, J-W T; Konsta-Gdoutos, M.S; Hersam, M.C. and Shah, S.P., “Highly
concentrated carbon nanotube admixture for nano-fiber reinforced cementitious
materials”, Cement and Concrete Composites, Vol. 34, 2012, pp. 612-617.
Morsy, M.S., El-Enein, S.A.A., and Hanna, G.B., "Microstructure and hydration
characteristics of artificial pozzolana-cement pastes containing burnt kaolinite clay",
Cement and Concrete Research, Vol. 27, 1997, pp. 1307–1312.
Morsy, M.S., Alsayed, S.H., and Aqel, M., "Effect of nano-clay on mechanical properties
and microstructure of ordinary Portland cement mortar", International Journal of
Environmental Engineering, Vol. 10, 2010, pp. 21–25.
Morsy, M.S., Alsayed, S.H., and Aqel, M., "Hybrid effect of carbon nanotube and nano-
clay on physico-mechanical properties of cement mortar", Construction and Building
Materials,Vol. 25, 2011, pp. 145–149.
Musso, S; Tulliani, J-M.; Ferro, G. and Tagliaferro, A., “Influence of carbon nanotubes
structure on the mechanical behavior of cement composites”, Composites Science and
47
Technology, Vol. 69, 2009, pp. 1985-1990.
Nazari, A., and Riahi, S., "Assessment of the effects of Fe2O3 nanoparticles on water
permeability, workability and setting time of concrete", Journal of Composites
Materials, Vol. 45, 2010a, pp. 923-930
Nazari, A., and Riahi, S., "Benefits of Fe2O3 nanoparticles in concrete mixing matrix",
Journal of American Science, Vol. 6, 2010b, pp. 102-106
Nazari, A., and Riahi, S., "Computer-aided prediction of physical and mechanical
properties of high strength cementitious composites containing Cr2O3 nanoparticles",
Nano, Vol. 5, 2010c, pp. 301–318.
Nazari, A., and Riahi, S., "Optimization mechanical properties of Cr2O3 nanoparticle
binary blended cementitious composite", Journal of Composite Materials, Vol. 45,
2010d, pp. 943-948.
Nazari, A., and Riahi, S., "Abrasion resistance of concrete containing SiO2 and Al2O3
nanoparticles in different curing media", Energy Buildings, Vol. 43, 2011a, pp. 2939–
2946.
Nazari, A., and Riahi, S., "The effects of TiO2 nanoparticles on properties of binary
blended concrete", Journal of Composites Materials, Vol. 45, 2011b, pp. 1181–1188.
Nazari, A., and Riahi, S., "TiO2 nanoparticles’ effects on properties of concrete using
ground granulated blast furnace slag as binder", Science China Tecnhological
Sciences, Vol.54, 2011c, pp. 3109–3118.
Nazari, A., and Riahi, S., "The effects of Cr2O3 nanoparticles on strength assessments
and water permeability of concrete in different curing media", Materials Science and
Engineering: A, Vol. 528, 2011d, pp. 1173–1182.
48
Nazari, A., and Riahi, S., "Improvement compressive strength of concrete in different
curing media by Al2O3 nanoparticles", Materials Science and Engineering: A, Vol.
528, 2011e, pp. 1183–1191.
Paiva, H., Velosa, A., Cachim, P., and Ferreira, V.M., "Effect of metakaolin dispersion
on the fresh and hardened state properties of concrete", Cement and Concrete
Research, Vol. 42, 2012, pp. 607–612.
Pascal Maes, 2014, http://www.engineeringcivil.com/cuore-concrete-nano-silica.html (last
accessed 11-03-2014).
Péra, J., Husson, S., and Guilhot, B., "Influence of finely ground limestone on cement
hydration", Cement and Concrete Composites, Vol. 21, 1999, pp.99–105.
Popov, V. N., “Carbon nanotubes: properties and application”, Materials Science and
Engineering: R: Reports, Vol. 43, 2004, pp. 61-102.
PhotoPAQ - Demonstration of photocatalytic remediation processes on air quality -
Progress Report, March 2012.
Qing, Y., Zenan, Z., Li, S., and Rongshen, C., "A comparative study on the pozzolanic
activity between nano-SiO2 and silica fume", Journal of Wuhan University of
Technology-Mater Sci. Ed., Vol. 21, 2006, pp. 153–157.
Qing, Y., Zenan, Z., Deyu, K., and Rongshen, C., "Influence of nano-SiO2 addition on
properties of hardened cement paste as compared with silica fume", Construction and
Building Materials, Vol. 21, 2007, pp. 539–545.
Quercia, G., and Brouwers, H.J.H., "Application of nanosilica (nS) in concrete mixtures"
8th Fib PhD Symp. Kgs Lyngby Den, 2010.
Raki, L., Beaudoin, J., Alizadeh, R., Makar, J., and Sato, T., "Cement and concrete
49
nanoscience and nanotechnology", Materials, Vol. 3, 2010, pp. 918–942.
Rashad, A.M., "A comprehensive overview about the effect of nano-SiO2 on some
properties of traditional cementitious materials and alkali-activated fly ash",
Construction and Building Materials, Vol. 52, 2014, pp. 437–464.
Raymond M. Reilly, “Carbon nanotubes: potential benefits and risks of nanotechnology
in nuclear medicine”, Journal of Nuclear Medicine, Vol. 48(7), 2007, pp. 1039–1042.
Sabir, B.B., Wild, S., Bai, J., "Metakaolin and calcined clays as pozzolans for concrete: a
review" Cement and Concrete Composites, Vol.2 3, 2001, pp. 441–454
Sáez de Ibarra, Y., Gaitero, J.J., Erkizia, E., and Campillo, I., "Atomic force microscopy
and nanoindentation of cement pastes with nanotube dispersions", Physica Status
Solidi A , Vol. 203, 2006, pp. 1076–1081.
Sanchez, F., and Sobolev, K., "Nanotechnology in concrete - A review", Construction
and Building Materials, Vol. 24, 2010, pp. 2060–2071.
Sanchez, F..L. and Zhang, C. I., “Multi-scale performance and durability of carbon
nanofiber/cement composites”, Nanotechnology in Construction, Vol. 3, 2009, pp.
345-351.
Sato, T., and Beaudoin, J., "The effect of nano-sized CaCO3 addition on the hydration of
OPC containing high volumes of ground granulated blast-furnace slag" 2nd
International Symposium Advanced Concrete Science Engineering, 2006.
Sato, T., and Beaudoin, J., "Effect of nano-CaCO3 on hydration of cement containing
supplementary cementitious materials", Advanced Cement Research, Vol. 23, 2010,
pp. 1–29.
Senff, L., Hotza, D., Repette, W.L., Ferreira, V.M., and Labrincha, J.A., "Rheological
50
characterisation of cement pastes with nanosilica, silica fume and superplasticiser
additions", Advances in Applied Ceramics: Structural, Functional & Bioceramics,
Vol. 109, 2010, pp. 213–218.
Senff, L., Tobaldi, D.M., Lucas, S., Hotza, D., Ferreira, V.M., and Labrincha, J.A.,
"Formulation of mortars with nano-SiO2 and nano-TiO2 for degradation of pollutants
in buildings", Composites Part B: Engineering, Vol. 44, 2013, pp. 40–47.
Shah, S.P.; Konsta-Gdoutos, M.S.; Metaxa, Z.S. and Mondal, P, “Nanoscale modification
of cementitious materials”, Nanotechnology in Construction, Vol. 3, 2009, pp. 125-130.
Shakhmenko, G., Juhnevica, I., and Korjakins, A., "Influence of sol-gel nanosilica on
hardening processes and physically-mechanical properties of cement paste", Procedia
Engineering, Vol. 57, 2013, pp. 1013–1021.
Shamsai, A., Peroti, S., Rahmani, K., and Rahemi, L., "Effect of water-cement ratio on
abrasive strength, porosity and permeability of nano-silica concrete", World Applied
Sciences Journal, Vol. 17, 2012, pp. 929–933.
Siddique, R., “Utilization of silica fume in concrete: Review of hardened properties”,
Resources, Conservation and Recycling, Vol. 55, 2011, pp. 923-932.
Siddique, R., and Klaus, J., "Influence of metakaolin on the properties of mortar and
concrete: A review", Applied Clay Science, Vol. 43, 2009, pp. 392–400.
Silvestre, N., "On the accuracy of shell models for torsional buckling of carbon
nanotubes", European Journal of Mechanics - A/Solids, Vol. 32, 2012, pp. 103–108.
Silvestre, N., Faria, B., and Canongia Lopes, J.N., "A molecular dynamics study on the
thickness and post-critical strength of carbon nanotubes", Composite Structures, Vol.
94, 2012, pp. 1352–1358.
51
Singh, L.P., Karade, S.R., Bhattacharyya, S.K., Yousuf, M.M., and Ahalawat, S.,
"Beneficial role of nanosilica in cement based materials - A review", Construction and
Building Materials, Vol. 47, 2013, pp. 1069–1077.
Sinnott, S.B. and Andrews, R., “Carbon nanotubes: synthesis, properties, and
applications”, Critical Reviews in Solid State and Materials Sciences, Vol. 26, 2001,
pp. 145–249.
Soliman, E.M.; Kandil, U.F and Taha, M., “The significance of carbon nanotubes on
styrene butadiene rubber (SBR) and SBR modified mortar”, Materials and Structures,
Vol. 45, 2012, pp. 803-816.
Som, C., Wick, P., Krug, H. and Nowack, B., “Environmental and health effects of
nanomaterials in nanotextiles and façade coatings”, Environment International, Vol.
37, 2011, pp. 1131-1142.
Stengel, T., “Effect of surface roughness on the steel fibre bonding in Ultra High
Performance Concrete (UHPC)”, Nanotecnhology in Construction, Vol. 3, 2009, pp.
371-376.
Uddin, F., "Clays, Nanoclays, and Montmorillonite Minerals", Metallurgical and
Materials Transactions A, Vol. 39, 2008, pp. 2804–2814.
Wang, X.; Zhi, L.J. and Mullen, K., “Transparent, conductive graphene electrodes for dye-
sensitized solar cells”, Nano Letters, Vol. 8, 2008, pp. 323-327.
Xu, Q.L., Meng, T., and Huang, M.Z., "Effects of nano-CaCO3 on the compressive
strength and microstructure of high strength concrete in different curing temperature",
Applied Mechanics and Materials, Vol. 121-126, 2011, pp. 126–131.
Yazdanbakhsh, A., and Grasley, Z., "The theoretical maximum achievable dispersion of
52
nanoinclusions in cement paste", Cement and Concrete Research, Vol. 42, 2012, pp.
798–804.
Zhu, W; Bartos, P.J.M.; and Porro, A., “Application of nanotechnology in construction”,
Materials and Structures, Vol. 37, 2004, pp. 649-658.
Zhu, Y.; Murali, S.; Cai, W.; Li, X.; Suk, J.W.; Potts, J.R. and Ruoff, R.S., “Graphene
and graphene oxide: Synthesis, properties, and applications”, Advanced Materials,
Vol. 22, 2010, pp. 3906-3924.
53
FIGURE CAPTIONS
Figure 1 - Number of publications per year indexed in SCI Web of Science matching
keywords “concrete and nano” in searched “Topic”.
Figure 2 - Production of Calcium Silicate Hydrate (C-S-H) via pozzolanic reaction of
silica with Calcium Hydroxide (CH).
Figure 3 - Results of compressive strength in age of 1 day (CEM), paste with SF, paste
with SF and HFO NS (HFO) and paste with SF and HF1000 NS (HF1000)
(Shakhmenko et al., 2013).
Figure 4 - Illustration of the filling effect of NS agglomerates: (a) The smaller agglomerates
act as fillers to release some free water in the gap to enhance the fluidity of the
paste; (b) The larger agglomerates cannot act as fillers; they tend to push away
the particles around them, resulting in an increase of the void space; (c) The
very large agglomerates absorb some free water originally contributing to the
fluidity of the paste (Kong et al., 2013).
Figure 5 - Processes occurring on bare TiO2 particle after UV excitation (Fujishima et al.,
2008).
Figure 6 - Effect of TiO2 nanoparticles on the workability of concrete (N1, N2, N3, and
N4 are the series N blended concrete with 0.5, 1.0, 1.5 and 2.0 wt% of TiO2
nanoparticles, respectively) (Nazari and Riahi, 2011).
Figure 7 - Influence of TiO2 nanoparticles on the initial setting time of cement paste
(Nazari and Riahi, 2011).
Figure 8- SEM micrographs of (a) nanocomposites containing 1 % by weight of cement
nanoclay and (b) nanocomposites containing 3 % by weight of cement
54
nanoclay. Numbers indicate: 1 = [Ca(OH)2] crystals, 2 = pores and 3= C-S-H
gel (Hakamy et al, 2014).
Figure9 - Compressive strength of cement replaced with 0%, 2% and 4% nAl (Barbhuiya
et al., 2014).
Figure 10 - Conceptual diagram of single-walled carbon nanotube (SWCNT) (A) and mul-
ti-walled carbon nanotube (MWCNT) (B) delivery systems showing typical
dimensions of length, width, and separation distance between graphene layers
in MWCNT (Reilly, 2007).
Figure 11 - Collapse modes of CNT submitted to several twisting-compression rates (
φ
is
the twist in rad; u is the shortening in Å; ∆
φ
/∆u is the rate in rad/Å)
Figure 12 - Schematic figure showing the progress of sedimentation of nanomaterials
inside a tube during ultracentrifugation (Metaxa et al., 2012).
Figure 13 - MWCNT suspensions ultra-centrifuged for: (a) 30 min; (b) 45 min; (c) 60 min
(Metaxa et al., 2012).
Figure 14 - (a) Comparison of mechanical parameters of graphene oxide reinforced ce-
ment (GO-OPC) and OPC; the compressive strength of cement paste is 46%
higher and (b) the microstructure of cement paste is finer and denser with the
inclusion of GO sheets (Duan, 2012).
Figure 15 - (a) FE-SEM images of cement mortar containing 1.5 wt by weight of cement
GO at scales of 200 and 2.0 m after 28 days curing, showing microcracks on
a GO flake under tensile stresses (b) Tensile strength results of cement mortar
specimens with GO content (Bakar et al., 2014).
55
Figure 1 - Number of publications per year indexed in SCI Web of Science matching
keywords “concrete and nano” in searched “Topic”.
1 3 3
17
24
17
33
50
56
63
99
133 130 133
0
20
40
60
80
100
120
140
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
Number o SCI WoSc Publications
Year
56
+ 2+ 2→ 2+ + 24
2− +24
2− + −
Figure 2 - Production of Calcium Silicate Hydrate (C-S-H) via pozzolanic reaction of
silica with Calcium Hydroxide (CH).
C-S-H
Ca(OH)2
C-S-H
(additional)
57
Figure 3 - Results of compressive strength in age of 1 day (CEM), paste with SF, paste
with SF and HFO NS (HFO) and paste with SF and HF1000 NS (HF1000) (Shakhmenko
et al., 2013).
58
Figure 4 - Illustration of the filling effect of NS agglomerates: (a) The smaller agglomerates
act as fillers to release some free water in the gap to enhance the fluidity of the paste; (b)
The larger agglomerates cannot act as fillers; they tend to push away the particles around
them, resulting in an increase of the void space; (c) The very large agglomerates absorb
some free water originally contributing to the fluidity of the paste (Kong et al., 2013)
59
Figure 5 - Processes occurring on bare TiO2 particle after UV excitation (Fujishima et al.,
2008).
60
Figure 6 - Effect of TiO2 nanoparticles on the workability of concrete (N1, N2, N3, and
N4 are the series N blended concrete with 0.5, 1.0, 1.5 and 2.0 wt% of TiO2 nanoparti-
cles, respectively) (Nazari and Riahi, 2011).
61
Figure 7 - Influence of TiO2 nanoparticles on the initial setting time of cement paste
(Nazari and Riahi, 2011).
62
Figure 8 - SEM micrographs of (a) nanocomposites containing 1% by weigth of cement
nanoclay and (b) nanocomposites containing 3% by weigth of cement nanoclay. Numbers
indicate: 1 = [Ca(OH)2] crystals, 2 = pores and 3= C-S-H gel (Hakamy et al, 2014).
63
Figure 9 - Compressive strength of cement replaced with 0%, 2% and 4% nAl (Barbhuiya
et al., 2014).
64
Figure 10 - Conceptual diagram of single-walled carbon nanotube (SWCNT) (A) and mul-
ti-walled carbon nanotube (MWCNT) (B) delivery systems showing typical dimensions of
length, width, and separation distance between graphene layers in MWCNT (Reilly, 2007).
65
= 0.0
= 0.09
= 0.20
= 0.35
= 0.60
= 1.30
→ ∞
Figure 11 - Collapse modes of CNT submitted to several twisting-compression rates (
φ
is
the twist in rad; u is the shortening in Å; ∆
φ
/∆u is the rate in rad/Å) (Silvestre et al,
2012).
66
Figure 12 - Schematic figure showing the progress of sedimentation of nanomaterials
inside a tube during ultracentrifugation (Metaxa et al., 2012).
67
Figure 13 - MWCNTs suspensions ultra-centrifuged for: (a) 30 min; (b) 45 min; (c) 60 min
(Metaxa et al., 2012).
68
(a) (b)
Figure 14 - (a) Comparison of mechanical parameters of graphene oxide reinforced ce-
ment (GO-OPC) and OPC; the compressive strength of cement paste is 46% higher and
(b) the microstructure of cement paste is finer and denser with the inclusion of GO sheets
(Duan, 2012).
69
(a)
(b)
Figure 15 - (a) FE-SEM images of cement mortar containing 1.5% by weigth of cement
GO at scales of 200 and 2.0 m after 28 days curing, showing microcracks on a GO flake
under tensile stresses (b) Tensile strength results of cement mortar specimens with GO
content (Bakak et al., 2014).
70
