Application Of Nanotechnology In Civil Engineerings Engineering Essay

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This paper introduces the potential for the application of nanotechnology in the area of construction. It also includes the introduction of nanotechnology and the innovations carried out around the world using different types of nano materials in cement based construction material. The application of nanotechnology in the area of cement concrete and their mechano-chemical activation of cement based materials has been observed to improve the toughness, shear, tensile and flexural strength of cement based materials. A better understanding and engineering of cement-based material at nano-level will spawn a new generation of construction materials with enhanced properties

Index Terms-Nano materials, nanotechnology, construction technology.

INTRODUCTION

NANOSCIENCE is the study of extremely small things that can be used across all the other science fields, such as chemistry, biology, physics, materials science, and engineering. Nanotechnology is not just a new field of science and engineering, but a new way of looking at and studying. The ideas and concepts behind nanoscience and nanotechnology started with a talk entitled "There's Plenty of Room at the Bottom" by physicist Richard Feynman at an American Physical Society meeting at the California Institute of Technology (CalTech) on December 29, 1959, long before the term nanotechnology was used. In his talk, Feynman described a process in which scientists would be able to manipulate and control individual atoms and molecules. Over a decade later, in his explorations of ultraprecision machining, Professor Norio Taniguchi coined the term nanotechnology. It wasn't until 1981, with the development of the scanning tunneling microscope that could "see" individual atoms, that modern nanotechnology began. [1]

Nanotechnology

Nanotechnology is the engineering of functional systems at the molecular scale [2]. Generally, nanotechnology deals with developing materials, devices, or other structures possessing at least one dimension sized from 1 to 100 nanometres. One nanometer (nm) is one billionth, or 10−9 of a meter Nano.

Engineering could potentially lead to a surplus of revolutionary materials and products that could benefit areas from aerospace to everyday life. Nanoengineering could lead to practical applications like self-cleaning paint, aero-planes with skins that de-ice themselves and adjust to different aerodynamic environment. Fluids containing suspension of nanometer-sized particles (nanofluids) are being studied due to their enhanced thermal properties. [3]

Nanomaterial

Composites made from particles of nano-size ceramics or metals smaller than 100 nanometers can substantially become much stronger than predicted by existing materials-science models. For example, metals with a grain size of around 10 nanometers are as much as seven times harder and tougher than their ordinary counterparts with grain sizes in the hundreds of nanometers. The properties of materials can be different at the nanoscale for two main reasons:

First, nanomaterials have a relatively larger surface area when compared to the same mass of material produced in a larger form. This can make materials more chemically reactive (in some cases materials that are inert in their larger form are reactive when produced in their nano scale form), and affect their strength.

Second, quantum effects can begin to dominate the behavior of matter at the nanoscale particularly at the lower end affecting the optical, electrical and magnetic behaviour of materials. Materials can be produced that are nanoscale in one dimension (for example, very thin surface coatings), in two dimensions (for example, nanowires and nanotubes) or in all three dimensions (for example, nano particles).

Nanomaterials can be constructed by 'top down' techniques, producing very small structures from larger pieces of material, for example by etching to creTate circuits on the surface of a silicon microchip. They may also be constructed by 'bottom up' techniques, atom by atom or molecule by molecule. One way of doing this is self-assembly, in which the atoms or molecules arrange themselves into a structure due to their natural properties. Crystals grown for the semiconductor industry provide an example of self assembly, as chemical synthesis of large molecules. A second way is to use tools to move each atom or molecule individually. Although this 'positional assembly' offers greater control over construction, it is currently very laborious and not suitable for industrial applications. [4].

One-dimensional nano materials, such as thin films and engineered surfaces, were developed and used for decades in fields such as electronic device manufacturing, chemistry and engineering.

Two dimensional nano materials such as tubes and wires have generated considerable interest among the scientific community in recent years. In particular, their novel electrical and mechanical properties are the subject of intense research.

Applications in Engineering [4]

Nanotechnology can be described as revolutionary discipline in terms of its possible impact on industrial applications. Nanotechnology offers potential solutions to many problems using emerging nano-techniques. 

Depending on the strong interdisciplinary character of nanotechnology there are many research fields and several potential applications that involve nanotechnology.

Nanosized titanium dioxide and zinc oxide are currently used in some sunscreens, as they absorb and reflect ultraviolet (UV) rays and yet are transparent to visible light and so are more appealing to the consumer.

An important use of nano particles and nano-tubes is in composites, materials that combine one or more separate components and which are designed to exhibit overall the best properties of each component.

Clays containing naturally occurring nano particles have long been important as construction materials and are undergoing continuous improvement.

Cutting tools made of nanocrystalline materials, such as tungsten carbide, tantalum carbide and titanium carbide, are more wear and erosion-resistant, and last longer than their conventional (large-grained) counterparts.

Incorporating nano particles in paints could improve their performance. 

The potential of nano particles to react with pollutants in soil and groundwater and transform them into harmless compounds is being researched. In one pilot study the large surface area and high surface reactivity of iron nano particles were exploited to transform chlorinated hydrocarbons (some of which are believed to be carcinogens) into less harmful end products in groundwater.

CNTs have exceptional mechanical properties, particularly high tensile strength and light weight. An obvious area of application would be in nano-tube reinforced composites, with performance beyond current carbon-fibre composites.

Nano-materials in concrete & construction

Carbon nanotubes (CNTs) and carbon nanofibers (CNFs)

Due to their exceptional mechanical properties, carbon nanotubes (CNTs) are considered to be one of the most promising reinforcing materials for the next generation of high-performance nano-composites.

On investigating the reinforcing effect of highly dispersed multiwall carbon nanotubes (MWCNTs) in cement paste matrix has shown that the MWCNTs were effectively dispersed in the mixing water by using a simple, one step method utilizing ultrasonic energy and a commercially available surfactant. Small amounts of effectively dispersed MWCNTs can significantly increase the strength and the stiffness of the cementitious matrix, lower amounts of long MWCNTs (0.025-0.048 wt.%) provide effective reinforcement than higher amounts (close to 0.08 wt.%) of short MWCNTs, due to their small diameters (20-40 nm) MWCNTs appear to specifically reduce the amount of fine pores. [34]

To overcome the obstacle of getting a good dispersion of carbon nanomaterials in a matrix, a simple one-step process of synthesis is done to create a novel cement hybrid material (CHM), where in CNTs and CNFs are attached to the cement particles. The CHM has been proven to increase 2 times the compressive strength and 40 times the electrical conductivity of the hardened paste, i.e. concrete without sand.[5]

Reinforced cement mortar composite round bars with carbon fibers (CFs) and MWCNTs shown that the load carrying capacity of composite bars under direct tension is substantially higher than the plain controlled bar. [6]

Effective dispersion of different length MWCNTs in water can be achieved by applying ultrasonic energy in combination with the use of a surfactant. For a constant ratio of surfactant to MWCNTs, the effects of MWCNT type (short and long) improve the nano- and macromechanical properties of cement paste.[7]

Cement matrix composites prepared by adding MWCNTs 0.5% wt of cement, using MWCNTs prepared by as-grown (g-CNTs), annealed (a-CNTs) and carboxyl functionalized (f-CNTs), shows that while high temperature annealing treatments remove lattice defects from the walls of CNTs, hence improving their mechanical strength, acid oxidative treatments increase chemical reactivity of pure material, consequently chemical bonds between the reinforcement and the cement matrix are supposed to enhance the mechanical strength. Flexural and compressive tests showed a worsening in mechanical properties with functionalized MWCNTs, while a significant improvement is obtained with both as-grown and annealed MWCNTs as shown in the Table-1. This behavior was justified taking into account that functionalized CNTs were so hydrophilic to absorb most of the water contained in the cement mixture, hence hampering the proper hydration of the cement paste [8]

Table 1

Sample

Modulus of Rupture (MPa)

Compression Resistance (kN)

Plain Cement (PC)

7.5

104 20

PC + g-CNTs

10.1

115 18

PC + a-CNTs

8.2

122 14

PC + f-CNTs

2.9

15 3

MWCNTs modified by using a H2SO4 and HNO3 mixture solution can improve the flexural strength, compressive strength (as shown in the Table-2) and failure strain of cement matrix composites. It is found that there are interfacial interactions between carbon nanotubes and the hydrations (such as C-S-H and calcium hydroxide) of cement, which will produce a high bonding strength between the reinforcement and cement matrix. The mineralogy and microstructure analysis show that carbon nanotubes act as bridges across cracks and voids, which guarantees the load-transfer in case of tension. Also a significant decrease in volume electrical resistivity and a distinct enhancement in compressive sensitivity was noticed. [9] [39]

Table - 2

Sample

Compressive Strength (MPa)

Flexural Strength (MPa)

Cement sand Mortar (CM)

52.27

6.69

CM + untreated

carbon nano fibers

47.51

8.14

CM + treated CNT

62.13

8.37

It has been found that carbon nanotubes accelerate the hydration process (with a proper dispersion), obtaining reinforcements in compression and flexural strength at 3 and 7 days and 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.[10]

The nanofibers not only improve the fracture properties of cement matrix, by controlling the matrix cracks at the nanoscale level, they also improve the early age strain capacity of the cementitious matrix producing a high performance nanocomposite.[17]

There is 2-fold increase in the compressive strength of the cement paste prepared from the dispersion of acetone-washed functionalized few walled carbon nanotubes (FWCNTs), which is believed to occur due to the chemical interaction between cement matrix and functional groups (-COOH and -OH). Utilization of unwashed FWCNTs led to a marginal improvement of mechanical properties of the cement pastes, whereas surfactant-treated functionalized FWCNT dispersions only worsened the mechanical properties. [18]

The blended cement : sand (1:2) consisting of ordinary Portland cement, carbon nanotubes and exfoliated nano metakaolin(NMK) using water/binder ratio of 0.5 wt.% of cement showed that, the replacement of OPC by 6 wt.% NMK increases the compressive strength of blended mortar by 18% compared to control mix and the combination of 6 wt.% NMK and 0.02 wt.% CNTs increased the compressive strength by 29% but addition of CNTs by 0.1% leads to decreases in the compressive strength.[26]

In hybrid CNF /silica fume cement composites, silica fume (SF) facilitated CNF dispersion due to its small particle size and improved the interfacial interaction between the CNFs and the cement phases. The addition of CNFs to SF cement pastes did not show any net change in the compressive and splitting tensile strengths of the composites for all CNF loadings. [31]

CNTs and CNFs can be synthesized on clinker and silica fume particles in order to create a low cost cementitious nano structured material. The synthesis carried out was in situ chemical vapor deposition (CVD) process using converter dust, an industrial byproduct, as iron precursor. The use of these materials reduces the cost, with the objective of application in large-scale nano structured cement production. Some enhancement in the mechanical behavior of cement mortars was observed due to the addition of these nano-size materials. The contribution of these CNTs/CNFs to the mechanical strength of mortar specimens is similar to that of high quality CNTs incorporated in mortars by physical mixture. [51]

CNTs are promising sensor material for health monitoring of concrete structures by acting as a conductive filler to fabricate piezoresistive cement-based sensors .The CNT-filled cement-based sensors have stable and reversible piezoresistive responses when the compressive stress amplitude is lower than 10 MPa. The piezoresistive responses of the sensors are almost free from the effect of loading rate when the loading rate is lower. After the loading rate exceeds a threshold, it will affect the piezoresistive responses of the sensors, and the effect extent increases with the loading rate. The relationship between input (compressive stress) and output (change in electrical resistance) of the sensors is linear. [40]

A very small dosage of MWCNTs can help decrease water sorptivity coefficient, water permeability coefficient, and gas permeability coefficient of cement mortar composites prepared by applying ultrasonic energy in combination with the use of surfactants (sodium dodecylbenzene sulfonate and sodium dodecyl sulfate).[47]

CNTs and CNFs are promising materials for the next-generation high-performance structural and multi-functional composite materials. The use of carbon nano's not only improves the mechanical property but also accelerate the hydration process and crack resistant property. The Piezo-resistive property of the CNT can be harvested to make a health monitoring system for the structure. However, one of the largest obstacles to create strong, electrically or thermally conductive CNT/CNF composites is the difficulty of getting a good dispersion of the carbon nanomaterials in a matrix and the cost involved. Already various researches are on to overcome these huddles.

Titanium Di Oxide (Tio2)

The abrasion resistance of concrete pavement containing nano-particles nano-TiO2 ,nano-SiO2 and polypropylene (PP) fibers indicate that the abrasion resistance of concretes containing nano-particles and PP fibers is significantly improved. However, the indices of abrasion resistance of concrete containing nano-particles are much larger than that of concrete containing PP fibers. The abrasion resistance of concrete containing nano-TiO2 is better than that containing the same amount of nano-SiO2. The extent of abrasion resistance of concrete decreases with increase in nano-particles content. Also, the abrasion resistance of concrete increases with increasing compressive strength. Table-3 shows the flexural and compressive strength of different mixes. [12]

Table - 3

Mix type

Flexural Strength, MPa

Compresive Strength, MPa

Plain concrete

5.46

59.08

PP 0.6 kg/m3

5.99

61.02

PP 0.9 kg/m3

6.6

63.29

nano-SiO2 1% by wt

5.69

66.36

nano-SiO2 2% by wt

5.36

61.16

nano-TiO2 1% by wt

6.02

69.73

nano-TiO2 3% by wt

5.62

66.62

nano-TiO2 5% by wt

5.28

60.00

Cement mortar containing nano-TiO2 indicated that strength of cement mortar at early ages increased a lot and the fluidity and strength at evening ages decreased. It seemed that the main reason for the improvement of strength is the decrease and modification of orientation index for the nucleus function, not the increasing amount of hydration products. Results also indicated that it was useful to modify the fluidity and the strength at evening ages of the cement mortar with nano-TiO2 by adding super plasticizer and slag powder into cement mortar. [22].The total porosity of the cement paste decreases and the pore size distribution were also altered. The acceleration of hydration rate and the change of microstructure also affected the physical and mechanical properties of the cement-based materials and more water is required to maintain a standard consistency due to the addition of the nano-TiO2. the nano-TiO2 acted as a catalyst in the cement hydration reactions.[27]

The split tensile strength increases with adding nano-TiO2 particles up to 1.0%, when water cured and using 2.0% TiO2 nano particles decreases the split tensile strength to a value which is near to the control concrete. On the other hand, for the specimens saturated in limewater, the split tensile strength increases by adding up to 2.0 wt.% TiO2 nano particles. [37]

Also it has been found that TiO2 nano particles up to maximum replacement level of 2.0% produces concrete with improved flexural strength and water permeability when the specimens cured in saturated limewater with respect to the specimens cured in water. Table-4 shows the flexural strength of different mixes. The optimal level of nano-TiO2 particles is up to 1.0% when water cured. TiO2 nano particles can improve the filler effect and also the high pozzolanic action of fine particles increases substantially the quantity of strengthening gel. Although the limewater curing medium could not improve the compressive strength of concrete with respect to the water curing medium, incorporating nano particles could cause more strength and resistance to water permeability for the specimens cured in saturated limewater with respect to the specimens cured in water. [42]

Table - 4

Concrete Specimen

Flexural Strength, MPa

28 days

90 days

Control - W

4.4

4.7

with nano-TiO2 0.5% by wt - W

5

5.4

with nano-TiO2 1% by wt - W

5.3

6

with nano-TiO2 1.5% by wt - W

5.1

5.5

with nano-TiO2 2% by wt - W

4.9

4.8

Control - LW

4.1

4.2

with nano-TiO2 0.5% by wt - LW

5.6

5.7

with nano-TiO2 1% by wt - LW

6.1

6.2

with nano-TiO2 1.5% by wt - LW

6.4

6.4

with nano-TiO2 2% by wt - LW

6.8

6.9

W-specimen cured in water

LW - specimen cured in saturated lime water

When ground granulated blast furnace slag (GGBFS) and TiO2 nano particles are replaced with Portland cement by replacing 45 wt% of ground granulated blast furnace slag and up to 4.0 wt% TiO2 nano particles, the TiO2 nano particle as a partial replacement of cement up to 3.0 wt% could accelerate C-S-H gel formation as a result of increased crystalline Ca(OH)2 amount at the early age of hydration and hence increase strength and improve the resistance to water permeability of concrete specimens. Table-5 shows the flexural and compressive strength of different mixes. Also several empirical relationships have been presented to predict flexural and split tensile strength of the specimens by means of the corresponding compressive strength at a certain age of curing.[46]

Table - 5

Sample designation

nano-TiO2 (%)

Compressive strength (MPa)

Flexural strength (MPa)

28 days

28 days

C0-GGBFS

0

43.7

5.4

N1-GGBFS

1

49.9

5.7

N2-GGBFS

2

55.3

6.2

N3-GGBFS

3

59.6

6.9

N4-GGBFS

4

56.1

6.3

Addition of TiO2 can improve the mechanical properties including abrasion resistance and provide an early strengthening. The drawback is the cost involved.

Silicon Di Oxide (SiO2)

Mortars prepared with nano-SiO2 synthesized by sol-gel method demonstrate an increase in compressive strength at early stages of hardening followed by the strength reduction at later age (vs. the reference). Addition of super plasticizer improved the compressive strength by 15-20%, reaching up to 144.8 MPa at 90- day age. Mechano-chemical activation was found to be an effective method to improve the strength of cement-based materials. The developed high-performance cements demonstrate the 28-day compressive strength at the range of 93 - 115 MPa, which is higher than 72 - 89 MPa, the strength of reference cements.[11]

Addition of silica nano particles into the systems of cement-sand-water revealed that nano additive affects the density, the rate of strength development, and the final compressive strength of cement. [29]

When nano-SiO2 produced by pyrolysis and with specific area of 200 m2/g has been added at different percentages to high-strength cement pastes. These pastes were tested for their mechanical and structural properties at different ages. The specimens with high nano-SiO2 content, presented lower strength in relation to the other samples. There was 25% average increase in compressive strength when 0.5% nano-SiO2 was added compared to the reference samples. This increase was 20% in the case of 1% and 2% nano-SiO2 content. The specimens with superplasticizer exhibited higher strength values. [28]

Nano particles can be electro kinetically inserted to reduce the permeability of hardened cement paste. When colloidal nano particles were electrokinetically transported into hardened cement paste pores, they underwent chemical reactions resulting in reduced permeability. 20 nm silica and 2 nm alumina particles were combined with simulated pore fluids to assess precipitate production. One precipitate formed was C-S-H, the binder material native to Portland cement paste.[24]

The Al2O3 nano particles could form C-F-H gel which contributes to strengthening the specimens. But it seems that the power of strengthening of C-F-H gel is not as high as C-S-H gel. [13]

The use of industrial waste glass with colloidal silica has shown some improvements to Mortar. Mix contained 20 wt.% waste glass and 3 wt.% colloidal silica(CS), revealed the highest compressive strength, where it recorded a 31% increase in compressive strength and 55% increases in flexural strength compared to the control specimen. The addition of CS has great potential to accelerate the pozzolanic reaction. It seems that their nano-size allows them to react more readily with the calcium hydroxide, thereby increasing calcium silicate hydrate conversion at 28 days of hydration. [19]

SCC made with the addition of micro silica and nano silica show that properties like compressive strength, flexural strength can be increased, also shrinkage and swelling values can be reduce. [21]

A SCC mix prepared by adding micro silica powder and nano silica solution showed that the engineering properties of SCC mixes could not be improved by adding only nano silica. However, a satisfactory behavior can be achieved using micro silica in the SCC mixes. But by adding both micro silica and nano silica to the SCC mixtures, the best effect on the engineering properties can be obtained comparing to the control mixes. [15]

A high performance self compacting concrete (HPSCC) was made by replacing a fraction of Portland cement by different amounts of micro silica, nano silica and blend of micro and nano silica as 10%, 2% and 10% + 2% respectively. Three different binder contents as 400, 450 and 500 kg/m3 with a constant water to binder ratio (w/b = 0.38) were investigated. The results showed that the properties improved significantly for the specimens containing micro and nano silica. Improvement of Cl ion percentage and resistivity results in the micro and nano silica blended mixtures was also noticeable. From the microstructure point of view, the SEM micrographs showed more refined and packed pore structure of the concrete containing admixtures especially at longer ages which could lead to enhancement of strength and the durability properties of HPSCC specimens.[30]

A high strength self compacting concrete containing SiO2 improves the strength and water permeability up to 4.0 wt.% of SiO2 nano particles in the cement paste. In addition, SiO2 nano particles are able to act as nano fillers and recover the pore structure by decreasing harmful pores. [43]

The split tensile strength of self compacting concrete with SiO2 nano particles and randomly oriented steel fibers up to 12 wt.% improve the concrete strength. [33]

The split tensile strength of concrete containing ground granulated blast furnace slag (GGBFS) and SiO2 nano particles increases by adding SiO2 nano particles up to 3.0 wt% replacements and then it decreases. SiO2 nano particles could improve the pore structure of concrete and shift the distributed pores to harmless and few-harm pores. [41]

The rate of cement and slag hydration can be accelerated with the incorporation of the nano silica in the high-volume slag cement paste. Compressive strength of the slag mortars were increased with the increase in nano silica dosages from 0.5% to 2.0% by mass. The strengths of the slag mortars were generally increased with the decrease in the particles size of silica inclusions at early age. Ultra-sonication of nano-silica with water is probably a better method for proper dispersion of nano-silica than mechanical mixing method [45] [48]. The length of dormant period was shortened, and rate of cement and slag hydration was accelerated with the incorporation of 1% nano SiO2 in the cement pastes with high volumes of fly ash or slag. The incorporation of 2% nano SiO2 by mass of cementitious materials reduced initial and final setting times by 90 and 100 min, and increased 3- and 7-day compressive strengths of high-volume fly ash concrete by 30% and 25%, respectively, in comparison to the reference concrete with 50% fly ash. Similar trends were observed in high-volume slag concrete. Nano-silica with mean particle size of 12 nm appears to be more effective in increasing the rate of cement hydration compared with silica fume with mean particle size of 150 nm.[49]

The nano SiO2 can improve swelling, shrinking properties of SSC, reduce harmful pores, mechanical properties including abrasion resistance and increase the rate of hydration.

Aluminium Tri Oxide (Al2O3)

Utilizing up to 2.0 wt% Al2O3 nano particles could produce concrete with improved strength and water permeability when the cured in limewater, while this content is 1.0 wt% for the specimens cured in tap water. The high action of fine nano particles substantially increases the quantity of C-S-H gel. In addition, Al2O3 nano particles are able to act as nano fillers and recover the pore structure of the specimens by decreasing harmful pores. [14]

Calcium Carbonate (CaCo3)

The addition of nano-CaCO3 (NC) to cement paste showed that there was no effect on water requirement of normal consistency of cement, the flow ability decreased and the setting time of fresh cement paste was shortened. The flexural and compressive strength of hardened cement paste increased with the addition of nano-CaCO3 and the optimal content of NC is 1%. [20]

Iron Oxide (Fe2O3)

The high performance self-compacting concrete containing Fe2O3 nano particles could accelerate C-S-H gel formation as a result of increased crystalline Ca(OH)2 amount especially at the early age of hydration and hence increase the strength of the specimens. The strength and the water permeability can be improved by adding Fe2O3 nano particles in the cement paste up to 4.0 wt%. In addition, Fe2O3 nano particles are able to act as nano fillers and recover the pore structure of the specimens by decreasing harmful pores to improve the water permeability. [23]

Nano Clay

The durability of concrete structures is strongly affected by the ease of water and ion penetration. To overcome this application of polymer/organo clay nano composites as a surface treatment material for concrete structures can be done. Nano clay has a great potential when added with polymers or resins to form a protective coating over concrete surface. [38] [50]

Zinc Oxide (ZnO2)

When Portland cement was partially replaced by ZnO2 nano particles and the specimens were cured in water and saturated limewater the results indicate that ZnO2 nano particles up to maximum of 2.0% produces concrete with improved compressive strength and setting time when the specimens cured in saturated limewater. The optimum level of replacement for cured specimens in water is 1.0 wt%.All indicate that ZnO2 nano particles could improve mechanical and physical properties of the specimens. [36]

ZnO2 nano particles when added partially to self-compacting concrete were able to improve the flexural strength of self-compacting concrete and recover the negative effects of polycarboxylate super plasticizer on flexural strength. ZnO2 nano particle as a partial replacement of cement up to 4 wt.% could accelerate C-S-H gel formation as a result of increased crystalline Ca(OH)2 amount at the early ages of hydration. The increase in the ZnO2 nano particles content more than 4 wt.%, causes reduction in the flexural strength because of unsuitable dispersion of nano particles in the concrete matrix. ZnO2 nano particles up to 4 wt.% could improve the mechanical and physical properties of the specimens. Finally, ZnO2 nano particles could improve the pore structure of concrete and shift the distributed pores to harmless and few-harm pores.[44]

Graphene

Graphene is a new generation of nano particle reinforced polymeric materials as an alternative to fiber-reinforced polymer for the protection of masonry structures against blast loads. The nano particles exfoliated graphene nano platelets (XGnP) and polyhedral oligomeric silsesquioxane (POSS) and the polymer is polyurea. A one-quarter scale physical model of unreinforced masonry walls, spray coated with the nanoparticle-reinforced polymers, are subjected to blast load in the Blast Load Simulator facility. POSS-reinforced polyurea is observed to significantly enhance the performance of masonry walls sustaining blast loads, whereas XGnP reinforcement has only marginal improvement. [35]

Electrokinetic nanoparticle

Electrokinetic nano particle (EN) treatments were employed to mitigate corrosion in reinforced concrete. Electrokinetic nano particle treatments have been demonstrated to reduce the permeability of hardened cement paste by orders of magnitude. The origin of this approach stems from the tendency of particles to flocculate and precipitate when they make contact with pore fluid. The feasibility of a given treatment application is dependent upon the transport properties of the particle and of the cement paste. It is theorized that this process causes particles to fill the initial sections of pores to a large extent before further penetration is achieved.[32]

Electric field can be used to drive pozzolanic nano particles through the capillary pores of concrete and directly to the reinforcement. The intent was to use the nano particles as pore-blocking agents to prevent the ingress of chlorides. Treatment effectiveness was examined for both freshly batched and relatively mature concrete. Also it has been found that microstructural changes attributable to treatment were effective in mitigating reinforcement corrosion in both young and mature concrete.[16]

Nano polazolon

Natural pozzolans are appropriate supplementary cementitious materials in cement and concrete industry. Nanostructures of natural pozzolan were synthesized by simple sonochemical method. Compressive strength tests were performed to evaluate the properties of blended cements incorporating nano natural pozzolan. Under optimized conditions, the nano natural pozzolans seems to have superior reactivity as compared to the bulk natural pozzolan. Also higher compressive strength was obtained for the cement specimen incorporating nano natural pozzolan. [25]

Conclusion

Research into the nanotechnology for construction can lead to structures with superior quality and better life-cycle cost. More research is required in understanding the structural behavior, durability aspect and corrosion studies of the nano composites to pave a way for the studies on the long term effects. The costs of most nanotechnology materials and equipment are relatively high; this can change over time and as manufacturing technologies improve these costs will further decrease. Also other avenues like use of nano materials with micro counterparts, FRPs, pozzolana material can also be researched where the nano materials only acts a catalyst to activate and promote the activation of cement based materials. Health hazard created by construction workers using nano materials have to overcome and feasible methods must be found to convert the research innovation to practical applications.

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