**4. Other applications**

new generation of nanotechnology-based microelectromechanical system (MEMS) sensors has emerged as cheaper, more compact, and easier to install sensors than traditional ones. Nanotechnology/microelectromechanical systems were used, for instance, to measure temperature and internal relative humidity of concrete [56] or to detect cracks in concrete structures [57]. Sensors for detecting the structural integrity of concrete were fabricated as wireless cement-carbon nanotube sensors embedded into concrete beams [57]. These CNTs-cement sensors have emerged as a low-cost small wireless sensor with good sensitivity, significant repeatability, and low hysteresis. Moreover, Lebental et al. [58] have developed well-aligned, ultra-thin, dense carbon nanotube membranes to be used as a vibrating membrane in a capacitive micrometric ultrasonic transducers, which could be used in the durability monitoring of porous materials. Kang et al. [59] have fabricated a long biomimetic artificial neuron sensor, with features such as low cost, simple installation, and low weight. Due to low bandwidth and appropriate strain sensitivity, it can be used for the detection of both small and large

Interestingly, Nanni et al. [60] have presented self-sensing nanocomposite rods to be applied as both reinforcing elements and sensors in concrete structures. The self-sensing rods are composed of an internal conductive core, that is, glass fibers embedded in epoxy resin with carbon nanoparticles (CNPs) and an external insulting GFRP skin. The nanocomposite rods have proved to be suitable for self-monitoring of concrete beams under a four-point static

The concept of weighting loads in motion came back then recently with those new materials [61]. The research team conducted tests on compressed blocks of the concrete with carbon nanotubes and registered its performance under static and dynamic loads. The authors registered changes of electrical resistance readings, proving that even micro-strains may be measured by such smart materials. This very recent work demands more calibrating studies;

Outstanding electrical properties and low cost make graphene nanoplatelets (GNPs) an attractive nanomaterial for use in smart self-sensing concrete. As demonstrated by recent

and a thickness of 5.0 nm) decreases more than one order of magnitude the resistivity of tested composites, thus attaining the percolation point, above which GNPs form the continuous conductive network in cement matrix. Interestingly, during the piezoresistive tests under compression, it turned out that no piezoresistive reactions were detected for samples containing 1.6 wt% of GNPs, indicating that conductive network created by tunneling of GNPs is unstable under applied loading. Indeed, the addition of only 6.4 wt% of GNPs has led to a sufficient and stable response of electrical parameters under cyclic loads. Other studies by Lee

and a thickness of 2.6 nm, the percolation threshold was obtained for 3.6 wt% amount of nanomaterial. Tests on samples with different notch depths confirmed the electrically conduc-

A very interesting and novel approach for use in structural engineering is connected with the proposal of Smart Bricks for Structural Health Monitoring of existing, often historical

/g, a diameter of 6.8 μm,

/g, a diameter of 2.6 μm,

strains and cracks in concrete structures, also under dynamic loading.

studies [62], the addition of 1.6 wt% of GNPs (a surface area of 192 m<sup>2</sup>

et al. [63] have revealed that, for GNPs with a surface area of 352 m<sup>2</sup>

bending as well as for concrete cure monitoring.

120 New Uses of Micro and Nanomaterials

still, it proves high potential of nano-concrete.

tive characteristics of manufactured mortar.

Numerous exciting examples of antimicrobial and self-cleaning surfaces as well as energyharvesting applications have also been reported in the last decade [6].

Recently, it has been shown [6, 65] that some nanoparticles possess tremendous antimicrobial properties and can be used to fabricate antimicrobial materials or coatings. In particular, TiO<sup>2</sup> nanoparticles proved to completely damage *Escherichia coli* cells after 1 week under UV irradiation of 1 mW/cm<sup>2</sup> . Moreover, it has been reported that the addition of silver or copper may enhance the photocatalytic activity of nano-titania even under weak UV light [66]. Interestingly, Hochmannova and Vytrasova [67] have presented paints based on aqueous acrylic dispersion with the 5 vol% addition of nano-ZnO, which proved to be a better photocatalytic coatings than the one containing nano-TiO<sup>2</sup> . The normal domestic fluorescent light was sufficient for nano-ZnO to activate the photocatalytic and microbial processes, deactivating the tremendously wide spectrum of bacteria and fungi. Furthermore, the studies on phenylpropyl type interior wall paints incorporating nano-MgO [68] have revealed that, in contrast to paints with nano-TiO<sup>2</sup> and nano-ZnO, nano-MgO possess a sufficient antimicrobial activity in the absence of light irradiation. In addition, the addition of silver nanoparticles to paints and coating effects in significant antimicrobial properties in case of both Gram-positive and Gramnegative bacteria [6, 69]. In case of carbon nanomaterials, SWCNTs can cause physical cell membrane damage and oxidative stress, impacting also metabolic activity and morphology of *E. coli* bacteria [70]. Grover et al. [71] have prepared laccase-based and chloroperoxidase-based paints, incorporating MWCNTs for biocatalytic coatings. These enzyme-nanotube-based paints exhibited a high bactericidal activity against different evaluated bacteria.

Apart from antibacterial surfaces, the addition of nanomaterials may also enhance the selfcleaning abilities of construction materials. Self-cleaning surfaces are mainly classified into two categories: hydrophobic and hydrophilic surfaces. As reported by previous studies [72–74], nano silica may be used to fabricate transparent superhydrophobic films and coatings on glass. The nanoporous structure made out of nano-SiO<sup>2</sup> also possesses antireflection properties [72, 73]. Hydrophobic surfaces were also developed with the use of carbon nanotubes (CNTs). Transparent, conductive, and superhydrophobic films incorporating CNTs were prepared on a glass substrate using, for instance, fluoropolymer-grafted MCWNTs [75] or CNTs produced by plasma-enhanced chemical vapor deposition and functionalized by a 1H,1H-2H,2H perfluorodecyl-trichlorosilane and hexane mixture [76]. Nanoparticles used typically in hydrophilic surfaces are materials with photocatalytic properties. Tan et al. [77] have revealed that transparent TiO<sup>2</sup> films fabricated by the growth of TiO<sup>2</sup> nanotube arrays on glass substrate have exhibited a higher photocatalytic activity than nanoparticulate TiO<sup>2</sup> thin films due to a higher surface area. Interestingly, Pan et al. [78] have presented nanofiber-based TiO<sup>2</sup> films with stable super-amphilicity, which possessed superhydrophilic properties even after 240 days in the absence of UV irradiation. It is worth noting that the effect of various forms of TiO<sup>2</sup> [79] as well as the interaction between TiO<sup>2</sup> and pigments has been investigated in the case of cement mortars [80]. Mortar with the addition of 3% of anatase powder and 2% of anatase suspension has emerged as a commercially attractive material with optimal photoactivity [79].

**Nanomaterial Effect on the properties of building materials References**

Refined microstructure and porosity

Refined microstructure and porosity Enhanced corrosion resistance Enhanced frost resistance Self-cleaning properties

Refined microstructure and porosity Enhanced corrosion resistance Increased impermeability

Refined microstructure and porosity

Self-cleaning properties Antibacterial activity

Reduced shrinkage Self-sensing properties Enhanced corrosion resistance Self-cleaning properties Antibacterial activity

Reduced water absorption Enhanced corrosion resistance Self-sensing properties

Accelerated hydration Reduced water absorption Enhanced corrosion resistance

**Table 1.** Effect of the incorporation of various nanomaterials into building materials.

Silver nanoparticles Antibacterial activity [69] Nano-magnesium oxide Antibacterial activity [68] Nano-zinc oxide Antibacterial activity [67]

Refined microstructure and porosity

Improved performance at elevated temperatures

Improved performance at elevated temperatures

[8, 10, 11] [8, 11] [8] [8] [10] [10] [11]

Nanomaterials in Structural Engineering http://dx.doi.org/10.5772/intechopen.79995 123

[9, 11] [9, 11] [9] [11] [72–74]

[13] [12, 13] [12] [13] [13] [66, 77–80] [66]

[14]

[24] [75, 76] [70, 71]

[19, 52] [19, 52] [19, 52, 62] [53, 62, 63]

[14, 18, 20–24, 27–33] [14, 21, 30–32]

[24, 25, 27, 58, 59, 61]

[41–43, 45, 46, 48–50] [41, 42, 44–46, 48–51]

[44, 47, 48] [50, 51] [51]

Accelerated hydration Reduced water absorption Increased impermeability

Enhanced frost resistance

Nano-alumina Improved mechanical properties

Nano-silica Improved mechanical properties

Nano-titania Improved mechanical properties

Carbon nanotubes Improved mechanical properties

Graphene nanoplatelets Refined microstructure and porosity

Graphene oxide Improved mechanical properties

Nanomaterials as conductive materials have also the potential for energy harvesting. Tests on this issue are conducted in many research centers, not connected with structural engineering. Some of them, especially those connected with obtaining energy from mechanical actions [81] and solar [82] activity, have the potential, which could also be considered in large engineering and special structures made out of smart nanomaterials.
