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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
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
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
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-
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-
iour, in order to improve its mechanical properties and reduce ecological and construction
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
Concretes nano-modification may be made in one or all of the phases: solid phase, liquid
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
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
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 concretes and cements 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 concretes
tious products. These improvements have been achieved, to a great extent, by the addition
Titanium dioxide
Nanoclay
4
Calcium carbonate
Alumina
Carbon nanotubes
Graphene oxide
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
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
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
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
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.
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
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-
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)
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.
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 mixs 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-
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
should be the best solution, even though more results on this issue are needed (Martins
Finally, the addition of NS particles to cement pastes also has consequences on other
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 500C with lesser strength loss. Related to this, Ibrahim
400 C and 700 C 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 400C, 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 (700C), 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
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-
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-
short-term. Cuore Concrete (Pascal Maes, 2014) reflects this reality with the introduc-
11
3. Nano-Titanium Dioxide
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 (Crdenas et al., 2012). In this
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
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
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,
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.
Crdenas 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
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-
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
Moreover, some research has also been conducted to try to understand the effects of the
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
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
The results also shown that the use of TiO2 nanoparticles improves the resistance to water
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 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
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-
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-
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
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
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
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-
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
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
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
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
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
the optimum level of NCr was achieved for 1.0% for the specimens cured in water where an
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,
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
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
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
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
la Al2 Si2 O5 (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
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
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.
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
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
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
Farzadnia et al. (2013) studied the mechanical properties, flowability, thermal behaviour
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
From the results reported, NCl particles have shown high potential in enhancing the me-
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-
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; Pra 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-
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
For these reasons and considering the relatively low cost of NCa compared to other na-
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
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
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
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
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-
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-
(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
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
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
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.
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,
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
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 Youngs 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 (0.0250.08 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 Youngs modulus enhancement (10-
Nanoindentation results also suggest that MWCNTs can strongly modify and reinforce the
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
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
pared to plain cement. Sez 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-
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
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
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-
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-
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-
were tested and a broad range of workability responses was measured with the main ob-
32
10. Graphene oxide
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
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
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
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
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 Youngs 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-
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-
means of an ultrasonic method and concluded that the use of an optimal percentage
(1.5wt%) 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 1.5wt% 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 2wt% 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
ratio of 0.5 compared with that of the sample containing 2.0wt% GO at a water/cement
reinforcement of concrete and studying rigorously its mechanical properties, the unam-
35
biguous advantages of GO increase the expectations of further developments in concrete
Having presented some of the most relevant and recent research works that has been car-
conclude that the potential of concrete nanotechnology will certainly be the key to a new
constructions 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-
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-
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
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-
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
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.
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FIGURE CAPTIONS
Figure 1 - Number of publications per year indexed in SCI Web of Science matching
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)
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
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
Figure 7 - Influence of TiO2 nanoparticles on the initial setting time of cement paste
54
nanoclay. Numbers indicate: 1 = [Ca(OH)2] crystals, 2 = pores and 3= C-S-H
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-
Figure 13 - MWCNT suspensions ultra-centrifuged for: (a) 30 min; (b) 45 min; (c) 60 min
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
Figure 15 - (a) FE-SEM images of cement mortar containing 1.5 wt by weight of cement
a GO flake under tensile stresses (b) Tensile strength results of cement mortar
55
140 133 130 133
120
99
Number o SCI WoSc Publications 100
80
63
56
60 50
40 33
24
17 17
20
1 3 3
0
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
Year
Figure 1 - Number of publications per year indexed in SCI Web of Science matching
56
+ 2 + 2 2+ + 2 4 2 + 2 4 2 +
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-
61
Figure 7 - Influence of TiO2 nanoparticles on the initial setting time of cement paste
62
Figure 8 - SEM micrographs of (a) nanocomposites containing 1% by weigth of cement
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
66
Figure 12 - Schematic gure showing the progress of sedimentation of nanomaterials
67
Figure 13 - MWCNTs suspensions ultra-centrifuged for: (a) 30 min; (b) 45 min; (c) 60 min
68
(a) (b)
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
70