Mortar and Concrete Reinforced with
Nanomaterials
J. Vera-Agullo, V. Chozas-Ligero, D. Portillo-Rico, M.J. García-Casas,
A. Gutiérrez-Martínez, J.M. Mieres-Royo, and J. Grávalos-Moreno1
Abstract. In this work, several nanomaterials have been used in cementitious matrices: carbon nanofilaments (either multiwall nanotubes or nanofibers), nanosilica
and nanoclays. The physico-chemical behavior of these nanomaterials at three different levels has been analyzed: cement paste, mortar and concrete. It has been determined the setting times, the workability, the mineralogical structure and the
dispersion of the nanomaterials in the cement matrix by ESEM/EDX , the percentage of hydration by TGA and the mechanical properties of mortar and concrete at
3, 7, 28 and 56 days. It has been found that almost all the nanomaterials used in
this study accelerate the hydration process (with a proper dispersion), obtaining reinforcements in compression and flexural strength at 3 and 7 days (between 20
and 40 %). At 28 days, it has been observed that carbon nanotubes and nanofibers
exhibit a reinforcement in the flexural strength (more than 25%), due to their fibrilar structure. Reinforcements, either in compression or flexural strength, have
been reached with nanosilica (between 20 and 40 %); indeed, pozzolanic activity
has been confirmed with nanosilica.
1 Introduction
One of the most desired properties of nanomaterials in the construction sector is
their capability to confer a mechanical reinforcement to cement based structural
materials. Three main objectives are considered: a very high-strength concrete for
specific applications can be obtained with the use of nanomaterials. Reduce the
amount of cement needed in concrete in order to obtain similar strengths, decreasing the cost and the environmental impact of construction materials. And moreover, by means of the addition of several types of nanomaterials a high-strength
concrete can be obtained at shorter times, reducing the construction periods.
J. Vera-Agullo, V. Chozas-Ligero, D. Portillo-Rico, M.J. García-Casas,
A. Gutiérrez-Martínez, J.M. Mieres-Royo, and J. Grávalos-Moreno
ACCIONA Infraestructuras
e-mail: [email protected]
http://www.acciona.es/
384
J. Vera-Agullo et al.
Besides these objectives, there are other functionalities that can be obtained
with the addition of nanomaterials to concrete. Self-cleaning facade with the
addition of titania nanoparticles to the mortar [1]; and self sensing cementitious
composites [2] or EMI shielding [3] by the addition of conductive nanomaterials
(carbon nanotubes, carbon nanofibers or carbon black). Nanomaterials have a
huge potential in the construction sector and new applications appear every year.
Mechanical improvements in cementitious matrices by the addition of nanomaterials have been obtained and have been reported in the literature. The compressive strength at early ages and the flexural modulus increased with the addition of
nanoalumina to cementitious composites [4, 5]. Abrasion resistance [6] and flexural fatigue performance [7] can be improved with the use of titania nanoparticles
and nanosilica.
Nanosilica is being used recently in the construction sector because of its best
performance compared to the conventional silica fume [8]. It has been demonstrated by several authors that nanosilica particles increased the hydration process
[9, 10], thus increasing the mechanical properties at 3 days [9]. Nanosilica works
as a nucleation site for the early C-S-H precipitation and shortens the induction
period [8-10]. Moreover, the pozzolanic effect of nanosilica takes place in a large
extent in the paste-aggregate interface, thus improving the interface structure [8].
Unlike the nanosilica, carbon nanofilaments (either carbon nanotubes [11] or
carbon nanofibers [12, 13]) are not being used yet in cementitious composites with
structural purposes in the construction sector. Researchers are doing an increasing
effort to elucidate the potential of carbon nanofilaments as reinforcement in cementitious matrices; however, there are still very few works related to cementitious composites reinforced with carbon nanofilaments compared to the huge
amount of works regarding to polymer composites. Ying Li et al. [14] found that
the compressive strength increases up to 19%, while the flexural strength increases
up to 25% in mortars by the means of the addition of carbon nanotubes at 0.5% in
weight with respect to the cement content; moreover, the failure strain was increased and the porosity reduced.
This work shows the main results of mechanical reinforcement obtained with
the use of nanomaterials (nanosilica, carbon nanofibers and nanotubes). The
analysis of the influence of the nanomaterials in the cementitious matrices has
been carried out at three different levels: cement paste, mortar and concrete.
2 Experimental
2.1 Materials
The nanosilica used in this work is currently under development in a pilot plant;
the silica nanoparticles have a diameter between 3 and 15 nm and a BET surface
2
area between 20 and 1000 m /g. The two types of carbon nanofilaments used in
this study are: GANF carbon nanofibers and Graphistrength C100 MWNTs.
Mortar and Concrete Reinforced with Nanomaterials
385
GANF material is a commercial helical-ribbon “stacked-cup-like” CNFs, produced by Grupo Antolín Ingeniería (Burgos, Spain). This sample has been deeply
characterized elsewhere [13, 15]. Graphistrength C100 MWNTs consisting of high
purity (> 90%) multi-wall carbon nanotubes are produced in semi-industrial quantities by Arkema. The cementitious materials used in the tests were ordinary Portland cement (CEM I 42,5R and CEM I 42,5R/SR). The fine aggregate used in the
mortar assays was standard silica sand (European standard) in the mortar assays.
Quartize was used as the sand and the coarse rounded aggregates at concrete level.
2.2 Characterization Techniques
The percentage of hydration in the cement has been analyzed by thermogravimetric analysis (TGA). The method is explained elsewhere [16]. Mechanical properties have been measured according to the standards UNE-EN 196 in the case of
mortars and UNE-EN 12390 in the case of concrete.
2.3 Challenges in the Preparation of Nanocomposites
One of the most important challenges in the nanocomposite research is to disperse
properly the nanomaterials into the matrices. Nanomaterials like carbon nanofilaments are usually entangled and grouped in nest. Thus, a great effort has been
done in this work in order to break these agglomerates and disperse the nanofilaments indiviadually. High energy mixing machines have been used to disperse the
nanomaterials into the cementitious matrices.
Other problem related with the use of nanomaterials in cementitious matrices is
the fact that they adsorb a high quantity of water due to their high surface area that
can be hydrophilic in some cases. The challenge is to obtain a good workability
without adding an extra quantity of water.
3 Results and Discussion
Table 1 shows the results of the degree of hydration in cement paste with nanomaterials. It can be seen that the percentage of hydration increases strongly with the
addition of medium % of NS. Carbon nanofibers accelerate the hydration too, but
in a minor extent.
Table 1 Percentage of hydration with and without NS
Sample
% of hydration at 7 days
% of hydration at 28 days
Cement Paste
69.9
75.6
Cement Paste medium % NS
82.2
90.7
Cement Paste low % CNF
71.4
80.2
Cement Paste medium % CNF
75.4
79.0
Cement Paste high % CNF
75.6
82.2
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Moreover, the pozzolanic effect of NS has been confirmed by the thermogravimetric analysis; there is more C-S-H gel and less portlandite than the cement
paste without NS. The portlandite content does not increase at 28 days with respect to the results at 3 days.
The pozzolanic effect and the acceleration of the hydration process improve the
mechanical properties at concrete levels as can be seen in Fig. 1.
80
Control
78,44
75,92
NS medium %
70,5
Compressive strength, MPa
70
62,8
60
50
44,6
40
35,3
30
20
10
0
3
7
28
days
3
Fig. 1 Concrete with a medium % of NS. 350 kg of cement/m
60
Control
CNF low %
CNF medium %
MWNT low %
Compressive Strength, MPa
52,5
53,1
48,8
50
37,3
46,7
45,0
44,8
40
MWNT medium %
51,6 51,6
39,4
42,9
44,0
39,7
37,9
30
20
10
0
3
7
days
Fig. 2 Compressive strength. Mortars loaded with carbon nanofilaments
28
48,5
Mortar and Concrete Reinforced with Nanomaterials
387
Regarding to carbon nanofilaments, it can be seen that both nanofibers and
nanotubes increases the compressive strength at early ages in mortar, especially at
low % in weight (21% at 3 days). However, this increment in the compressive
strength is not kept at 28 days (Fig. 2).
In the case of flexural strength in mortar with carbon nanofilaments (Fig. 3),
the reinforcement is permanent and not only at early ages. There is an outstanding result with a low % in weight of MWNTs at 28 days (27% at 28 days).
The strong fibrilar structure of carbon nanofilaments improves the flexural behaviour of mortars.
12
Control
CNF low %
CNF medium %
MWNT low %
MWNT medium %
10,4
Flexural Strength, MPa
10
7,8
8
6,9
6,8
7,2
7,3
7,6
7,7
8,1
8,1
8,2
8,6
8,9
9,2
7,6
6
4
2
0
3
7
days
28
Fig. 3 Flexural strength. Mortars loaded with carbon nanofilaments
4 Conclusions
As conclusions we can say that:
• Nanosilica fills the voids and makes the cement structure denser, accelerates
the hydration process, has a pozzolanic effect, improves reology and increases the compressive strength.
• Carbon nanofilaments (either carbon nanofibers or nanotubes) accelerate the
hydration process and the compressive strength at early ages. And they improve the flexural strength at 28 days.
Acknowledgments. This work has been partially supported by the CENIT project
DOMINO [http://www.cenitdomino.es], which is funded by Spanish Ministry of Science
and Innovation. The views expressed in this paper are not necessarily those of the
DOMINO consortia.
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