1 Introduction
The search for new compounds that help improve the mechanical conditions of construction materials has led to the development of concretes with high mechanical properties, fire resistance, and impact resistance, through the use of nanomaterials [1], It is well known that cement is a material widely used in the construction industry, much of this material is used for the manufacture of concrete, which has many advantages to resist compressive loads, but very prone to cracking when exposed. to tension [2], This is why in recent years the use of new innovative methods such as the use of nanomaterials has made it possible to improve the properties of cementitious compounds; however, there are still some unforeseen issues with the dosages [3]. Currently, with the implementation of nanoparticles as an additional material in the designs of concrete mixtures, better results have been obtained in the fresh properties of concrete, since it improves its mechanical characteristics, in addition to positively influencing the increase in durability [4]. Now, in order to know the current advances in this field, studies on the influence of nanomaterials in different areas of the construction industry have been compiled [5].
Technologies to improve the properties of concrete have entered a stage, known as the era of smart concrete, it is in this where nanotechnology unleashed development in order to improve certain characteristics [6]. The manufacture of concrete with the addition of nanotechnology aims to have a higher density to reduce the number of pores it contains, thus reducing the attack of sulfates, as well as increasing its resistance to impact loads [7]. Nanomaterials speed up the hydration rate in the initial stage, increase the absorption of water due to its surface, reducing the free water available [8] Currently nanomaterials are constantly studied, due to the different applications in different areas that go from semiconductors to energy, textiles and construction. [9]. Recent research showed that a small addition of nanoparticles, carbon nanotubes (CNT) and nano titanium dioxide (TiO2), have improved the 28-day resistance of cement mortar when added in optimized amounts, and the same optimization for reinforced concrete, producing very good results. However, long-term resistance differs due to poor control of the degree of freedom of its valence electron, that is, nanomaterials tend to oxidize in the long term. [10]
Following the arrival of nanotechnology in India, considerable amounts of research have been found involved in the search for new and efficient materials on the nano scale (10 ^ (- 9) m) [11]. These materials may revolutionize construction in the not too distant future, in fact, it was nanotechnology that completely changed electronics and computing. So it is considered that this can also revolutionize the construction sector. Currently there are successful applications based on nanotechnology that would have been almost impossible without the use of nanoparticles [12].
Recent research studies the problems of the production of construction materials, particularly concrete, and their treatment through the use of nanotechnologies, the general mechanisms of formation of the structure of a set cement and the influence of a treatment of its components. [13]. In an undefined way on the modification of the properties of reinforced concrete, adding nanomaterials are still in a laboratory phase [14].
There are nanomaterials that have unusual properties, among them we have ultrafine powder, which has magnetic, mechanical, electrical and optical properties compared to traditional granular materials. Despite being a relatively new material, it has applications with promising results in construction, which is why it can be used to improve concrete performance, such as silica fume that provides better strength and durability due to its lower granularity and high activity [15]. However, its production is low and its price is high. Generally, silica fume is not considered when the strength of concrete is less than 80 MPa, with the increasing demand for concrete, nanotechnology has produced nanomaterials to replace silica fume, which are widely used in concrete due to their nano special effects [16].
The emergence of nanotechnology in the cement industry has already shown a notable impact on mechanical properties and reveal that nanomaterials improve the performance of reinforced concrete, resulting in High Performance Concrete (HPC) or Ultra High Performance Concrete (UHPC) and in turn, makes concrete durable [17].
In the construction sector, it is constant to deal with soils with unsuitable properties for civil engineering projects. Problem soils generally need special treatment to improve their properties [18], To improve certain characteristics, a process known as soil stabilization is used, normally it is carried out with chemical additives such as cement, lime, but which usually cause alkaline environments, due to the increase in Ph in the soil. [19], Therefore, new alternatives are currently being sought for soil stabilization, focusing on the use of nanomaterials to improve resistance to unconfined compression., [20,21] and the variation of the Atterberg limits, hydraulic conductivity, Ph, density and specific gravity [22].
Nanomaterials have a promising future, among the best known are: colloidal silica, bentonite and laponite, these present a satisfactory effect in mitigating liquefaction for sandy foundations, and the carbon nanotube has the ability to increase compressive strength without confining [23]. Colloidal silica is the closest market application, despite the advantages of nanomaterials adopted as additives for soil improvement, they are known for not causing interactions with different biological objects at the cellular level. Studies on nanomaterials as an additive to treat geotechnical problems in soils are very promising and may intensify the relationship between sustainable development and engineering [24].
Carbon nanoparticles can be used as a superplasticizer additive that increases the tensile and flexural rupture properties of concrete. [25]. Nanotechnologies are currently considered the most active, with innovative science and useful applications in the construction sector, it has been shown that nano-materials have their application in rigid pavements, with results of improvements in their compression, flexural and modulus properties. elasticity, there is the possibility of improving the properties of cement bricks by using Nanomaterials such as Nano Alumina NA, Nano Ferrite NF and Nano Copper NC [26]
The substitution of natural aggregates in concrete mixtures, as a source of solution to global warming generated by concrete waste extracted from constructions, on roads in cold regions with constant snowfall, the use of hydrophobes is recommended in the maintenance of the pavement, which has greater efficiency, reducing the adherence of ice to the structural mat, reducing the risk of accidents [27]
The asphalt that is used in the paving of roads, is usually prone to failure due to cracking or in any case due to deformations caused by traffic and / or environmental factors. [28], For example, the formation of grooves in the asphalt surface usually occurs due to exposure to high temperatures, which soften the asphalt binder, therefore the properties of this material play a fundamental role in the final performance of the pavement layer. [29,30] while cracking usually occurs due to a hardening of the asphalt binder due to low temperatures [31], therefore the performance and duration of the asphalt layer depends a lot on the development and / or behavior of the binder in the face of traffic loads and climatic changes; Based on these problems, different techniques or methods have been proposed to modify the asphalt binder in order to counteract the aforementioned problems, among them the use of polymers and nanomaterials stand out [32].
Although the modification of the properties of the binder through the use of polymers has provided satisfactory results, but its high cost represents a disadvantage for its application [33], While the application of nanomaterials for the modification of the properties of the binder have a lower cost of between 20-30% approximately, and have shown that they can help combat several problems related to the behavior of the mixture, studies show that the use of Nanomaterials such as Nanosilica, leads to a reduction in ductility and penetration value, increases the softening point resulting in a higher viscosity compared to common asphalt [34].
It is known that asphalt is a material very prone to aging when it is exposed to heat, oxygen and solar radiation, the asphalt binder as it ages becomes more rigid and brittle, losing the adhesion of the aggregates, triggering pavement failures, shortening its lifespan [35]. During the aging process, physical reactions occur (evaporation of light components), and chemical reactions (oxidation, dehydrogenation, isomeration, etc.) [36]. Recent studies show that nanomaterials improve viscoelastic responses, resistance to high temperatures, resistance to aging of asphalt binders [37]
According [38], The use of Nanosilica in the asphalt binder improves the anti-aging properties and resistance to deformation, this change is due to intermolecular forces in the asphalt.
Soil stabilization, which involves improving shear strength, increasing stiffness and decreasing plasticity, as well as reducing volumetric change [39], They are commonly treated with chemical additives such as the application of lime, cement or industrial waste such as fly ash, although their results are positive [40], they carry the disadvantage of being highly polluting products, which is why they are currently looking for more environmentally friendly materials. [41]. For this reason, studies are currently being carried out on the application of nanomaterials to improve problem soils. [42], which show promising results, such as carbon nano tubes (CNT) that due to its fine structure, high strength and modulus of elasticity, elastic and ductile behavior, make it a suitable material to be used in soil stabilization. [43], Although its application to be used as a soil stabilizer is still in the laboratory study stage, but it is already known that it can increase the plasticity index, increase the compression and swelling index as well as increase the resistance to hydraulic conductivity.
4. Conclusions
The use of nanomaterials in concrete is shown as a viable option, due to the results shown by different studies, so much so that, with relatively low addition percentages ranging from 0.15% to 4%, it is possible to increase the resistance to compression, impact resistance and sulfate attack, as well as increasing tensile strength with the application of nanomaterials such as carbon nanotubes.
The use of nanomaterials such as Nanosilica in soil stabilization achieves positive results in unconfined compression resistance tests, with an addition percentage of 0.1% of the soil mass, and during the first 7 days of curing the increase in the resistance is fast and subsequently the increase is gradual, on the other hand the stabilization with nanocalcium carbonate also achieves good results in the unconfined compressive strength tests, since with an addition percentage of 0.2% it is possible to increase the results , this value being the optimal content.
The use of Nanosilica considerably reduces the penetration and ductility in the asphalt, that is, the softening and viscosity of the binder is improved. In addition, the resistance to the formation of grooves is increased, and anti-aging properties improve, it should be noted that the dispersion of the nanomaterials within the asphalt mixture is important since it influences the final result, since the type of preparation is related that is done.
With the application of nanomaterials in the asphalt, it is concluded that in the tests of resistance to compression of an asphalt mixture with the addition of Nanosilica, it improves in humid and dry conditions, with an action percentage of 0.4% the resistance to traction, resistance to humidity and an increase in the modulus of rigidity is obtained. In the preparation of mortars, the uses of nanomaterials decrease the setting time, and influence the plasticity of the mixture, the smaller the nono material, the more water will be required in the design, so much so that with the use of Nanosilica increases the water requirement. To increase the fluidity of the mixture with the presence of nanomaterials, the use of plasticizers can be used, as long as they guarantee a correct dispersion and without limiting the performance of the nanomaterials.
Nanomaterials in the construction industry can be a good alternative from a sustainable point of view, in order to reduce the indiscriminate use of non-renewable resources used in the manufacture of materials used in construction, studies show that with the application of nanomaterials, positive results are obtained in the improvement of the mechanical properties of concrete such as increased compressive strength and tensile strength, in the stabilization of soils improvements are obtained in unconfined compressive strength and increased at the limit of plasticity in use to treat asphalt problems such as grooving, cracking and warping.