Nano Concret

NANO concrete

 

THOMAS BRITTO(8807423228)

Thomasbritto3@gmail.com

Abstract

Nanoconcrete  is one of the most active research areas that encompass a number of disciplines including civil engineering and construction materials, Currently, the most active research areas dealing with cement and concrete are: understanding of the hydration of cement particles and the use of nano-size ingredients such as titanium oxide, silica, carbon nanojubes, and nano- sensors. if cement with nano-size particles can be manufactured and processed, it will open up a large number of opportunities in the field of ceramics, high strength composites etc. it will elevate the status of Portland cement to a high tech material in addition to its current status of most widely used construction material. The main objective of this paper is to outline some of the applications of nanotechnology in concrete and comparing this concrete with the ordinary concrete

Contents

1.       Introduction

2.       Applications Of Nanotechnology

3.       Cuore Concrete Nano Silica

4.       Titanium Dioxide

5.       Carbon Nano Tubes

6.       Polycarboxylates

7.       Nano Sensors

8.       Benefits Of Nanotechnology

9.       Results And Proof

10.    Conclusions

11.    References

INTRODUCTION:

"Nano technology is the study of the control of matter on an atomic and molecular scale. It deals with the size 100 nanometers or smaller, and involves developing materials or devices within that size".

A long time used material m concrete is for the first time fully replaced by a nano maternal. lt is well known m physics and chemistry that a well designed and developed nano material produces better and cheaper cost results than traditional materials.

Micro silica has been one of the world's most widely used products for concrete for over eighty years. Its properties allowed high compressive strength concretes; water and chemical resistant concretes, and they have been part of many concrete buildings that we see nowadays. Its disadvantage, though, has been its relatively high cost and contamination, which affects the environment and the operators' health. As micro silica, as a powder, is thousand fold thinner than cigarette smoke. Operators must take special precautions to avoid inhaling micro silica and not to acquire silicosis, an irreversible d.sease.hcnce to over come all tese above ill-effects of micro silica, nanotechnology was introduced in the world of concrete.

Nanotechnology and Concrete

Concrete is probably unique in construction in that it is the only material exclusive to the business and therefore is the beneficiary of a fa.r proportion of the research and development money from industry. The following section describes some of the most promising applications of nanotechnology in construction that are being developed or are even available today.

Some of the applications of nanotechnology are:

•         Cuore concrete- nano silica

•         Titanium dioxide

•         Carbon nanotubes

•         polycarboxylates

•         Nano-sensors

Cuore concrete nano-silica

Fig – Showing the mixing of nano silica in concrete

physics,   chemistry  and  recent   nanotechnology   advances, the challenge was fulfilled.Lab tests and production tests proved that the nano silica did not contaminate (because its state), but it also produced better results than micro silica, and a litre bottle of the product was equivalent to a barrel full of micro silica, extra cement and super plasticizing additives.Silica (SiCte) is present in conventional concrete as part of the normal mix. However, one of the advancements made by the study of concrete at the nanoscale is that particle packing in concrete can be improved by using nano-silica which             leads to a densifying of the micro and nanostructure resulting in improved mechanical properties.   Nano-silica   addition   to   cement   based   materials   can   also   control   the degradation of the fundamental C-S-H (calcium-silicatehydrate) reaction of concrete caused by calcium leaching in water as well as block water penetration and therefore lead to improvements in durability. Related to improved particle packing, high energy milling of ordinary Portland cement (OPC) clinker and standard sand, produces a greater particle size diminution with respect to conventional OPC and, as a result, the compressive strength of the refined material is also 3 to 6 times higher (at different ages). Fly ash not only improves concrete durability, strength and, importantly for sustainability, reduces the requirement for cement, however, the curing process of concrete is slowed by the                addition of fly ash and early stage strength is also low in comparison to normal concrete. With the addition of SiCh nanoparticles part of the cement is replaced but the density and strength of the fly-ash concrete improves particularly in the early stages. Research into hematite (Fe20;,) nanoparticles added to concrete has shown that they also increase strength   as   well   as   offering   the   benefit   of monitoring   stress   levels   through   the measurement of section electrical resistance.

Because of its innovation the nano silica was tested for over a year in the world's largest subterranean copper mine to prove its long term characteristics. Cuore concrete takes care of the environment, the concrete and the operators' health. It is the first nano product that replaced the micro sihca.Cuore concrete surpassed the expectations of its design and gave concrete not only the high initial and final resistance but in addition, plasticity, impermeability, minor final cost of work, and cement savings of up to 40%. Also, it lowered the levels of environmental contamination

 In high compressive strengths concretes (H-70), Cuore concrete is 88% more efficient than micro silica, added to concrete and super plasticizers. ( For an average 9,43 Kg. of Cuore concrete Nanosilica, 73Kg. of all the others additives are used).

The production cost of is drastically lower than using the traditional production method or formulas.

The cone test shows that It preserves the cone shape for more than one hour, (with a relation of H2O/Cement=0.5, adding 0.5% of Nano silica of the metric volume of the cement used, it conserved a its circle shape of 60 cm lor two hours, with a lost of only 5%). The nano silica has a plasticity that has been compared to the pohcarboxilate technology. Therefore the use of super plasticizing additives is unnecessary.

•   High workability with reduced water/concrete levels, for example: 0,2.

•   Easy homogenization. The reduction of mixing times allows concrete plants to increase their production

•   Depending on the cement and the formulations used for concrete (tests from value H-30 to H-70), shows that the material provides compressive strengths between 15 MPa and 75 MPa at 1 day; 40 MPa and 90 MPa at 28 days and 48 MPa and 120 MPa at 120 days.

•   Nano silica fully complies with ISO 14001 regulations regarding the environment and health. It preserves operators of the danger of being contaminated with silicosis and does not contaminate the environment.

It successfully passed all the tests and since the beginning of this year it is being commercialized in different parts of the world.

TITANIUM DIOXIDE

Titanium dioxide itself has no toxicity to microbe and the cell. Only after the irradiation of light such as fluorescent or UV light, natural mineral Ti02 activates its unique photo catalytic properties. In the presence of light and humid in the air, titanium dioxide oxidizes, converts complex organic molecules into water and carbon dioxide. Photo catalytic power of titanium dioxide successfully destroys bacteria cell's wall and its membrane, and reacts with cell's components, which inhibits bacteria's activity and ultimately results in the death and decomposition of bacteria, thus eliminating bad odours created by a living or decomposing bacteria and also reduces risk of bacteria spread.

The increase in patents during the last decade indicates a huge interest, especially from Japan and Europe, in the application of Ti02 as photocatalyst in buildmu materials

Regarding the reduction of air pollution due to traffic in urban areas, the application on pavement surfaces or on the building surfaces in cementations materials gives optimal solutions. To increase the efficiency of the photocatalyst, its presence at the surface of the material is crucial. It has to be accessible by sunlight to be activated. Consequently, the pollutant has to be absorbed on the surface and oxidized or reduced to a less harmful element. The goal is to have as much TiC>2 as possible at the surface of the material, without the risk of loosing it by abrasion or weathering. Up till now, the most efficient way to apply the TiC>2 is in a thin layer cementations material, which is placed on the surface. Application in concrete tiles is therefore very suitable: the TiOa can be added to the weathering layer. If the layer is slightly used, new Ti02-particles will be present at the surface. Other applications can be found in architectural concrete. The use of white cement with TiCh at the surface of buildings and construction attribute to the durability of the visual aspect of the building. Due to the photocatalytic action, the whiteness of the building will remain and dirt will be washed away more easily due to the hydrophilic properties or will be decomposed.

Carbon nanotubes

Carbon nanotubes can be visualized as a modified form of graphite. Graphite is formed from many layers of carbon atoms that are bonded in a hexagonal pattern in fiat sheets, with weak bonds between the sheets and strong bonds within them. A CNT can be thought of as a sheet or sheets of graphite that have been rolled up into a tube structure. CNT can be single walled nanotubes (SWNT), as if a single sheet had been rolled up, or multiwalled (MWNT), similar in appearance to a number of sheets rolled together.

              Schematic of a Single Walled Nanotube

A further type of nanoparticle, which has remarkable properties, is the carbon nanotube                (CNT) and current research is being carried out to investigate the benefits of adding CNT's to concrete. The addition of small amounts (1 % wt) of CNT's can improve  the mechanical properties of samples consisting of the main portland cement phase and water.Oxidized multi-walled nanotubes (MWNT's) show the best improvements both in compresstve strength (+ 25 N/rnrm) and flexural strength (+ 8 N/mm₂) compared to the reference samples without the reinforcement. It is theorized the high defect concentration on the surface of the oxidized MWNTs could lead to a better linkage between the nanostructures and the binder thus improving the mechanical properties of the composite rather like the deformations on reinforcing bars. However, two problems with the      addition of carbon nanotubes to any material are the clumping together of the tubes and the lack of cohesion between them and the matrix bulk material. Due to the interaction   between the graphene sheets of nanotubes, the tubes tend to aggregate to form bundles or "ropes" and the ropes can even be entangled with one another. To achieve uniform dispersion they must be disentangled. Furthermore, due to their graphitic nature, there is not a proper adhesion between the nanotube and the matrix causing what it is called sliding. However, when pre-dispersing the nanotubes with gum arable an increase in the mechanical properties is achieved, above all in the case of single walled nanotubes (SWNT's). Additional work is needed in order to establish the optimum values of carbon nanotubes and dispersing agents in the mix design parameters.

The cost of adding CNT's to concrete may be prohibitive at the moment, but work is being done to reduce their price and at such time the benefits offered by their addition to Lementitious materials may become more palatable.

  Nano-sensors

Strain sensors are an integral part of mueh of the lab work completed in structuralengineering. Sensors monitor and quantify the behavior of a test specimen, and provide insight into the reasons behind the behavior. In concrete, strain sensors can be broken down into three main categories

•         External strain sensor

•         Strain gage sensor

•         Embedded strain gage sensor

The most basic category is external strain sensors. These are attached to the exterior of the specimen and typically record the strain at that location very accurately. The disadvantage of these sensors is that the majority of the time the critical location of the specimen is not on the exterior of the specimen, and therefore, the readings provided by these gages are only marginally beneficial.

The second type of strain gage typically used in concrete is a strain gage that is Placed on the steel reinforcement inside the concrete. These gages can be placed insidethe concrete, so for many applications they are more useful. However, they can only be placed in regions where there is steel reinforcement. Also, these gages provide the strain the steel, not the strain in the concrete.

The third type of strain gage is an embedded strain sensor. These are gages that are cast into the concrete and provide readings of the strain in the concrete at their location.

They must be anchored or bonded to the concrete in order to function properly. They are capable of providing the strain in the concrete at any location and in any direction. There arc embedded strain gages that already exist, but they are typically large and expensi A new material has been developed that has the potential to be used in tins applicat and this study examines the effectiveness of this material. This experimental material is produced using a process called electrostatic self-assembly. The process is completed by building up alternating layers of positive and negatively charged particles. The material is formed into a l/8-in.-thick flexible sheet that exhibits the conductance properties of a metal. This includes changing resistance as the length is changed. It is this property that makes the material potentially useful as a strain sensor. If the sensor can be anchored to a specimen and the resistance of the sensor can be accurately measured, the change in resistance of the sensor should correspond to the strain in the specimen. The experimental material is also very durable. It can withstand large strains and is unaffected by the high pH that occurs in concrete. It is also produced in sheets, so the sensors can be cut to any size or shape that is required. These properties give this new material an advantage over existing embedded strain gages.

Immediate benefits for the user

1)       Cessation of contamination caused by micro silica solid

     particles.

2)       Lower cost per building site.

3)       Concrete with high initial and final compressive and

     tensile strengths.

4)   Concrete with good workability.

5)       Cessation of super plasticizing utilization.

6)       Cessation of silicosis risk.

7)       High impermeability.

8 ) Reduction of cement using Cuore concrete Nanosilice

9)  Cuore concrete nano silica on itself produces nano

     cement.

10)   During the moisturizing reaction of the cement, the

      silica produces CSIl particles, the "glue" of the

      concrete ensuring the cohesion of all the particles.

11) Cuore concrete has a specific surface near to l,000m2/gr (micro silica has only 20m2/gr) and a particle size of 5nm to 250 nm.

As a consequence of its size, Cuore concrete produces nano cristals of CSH, filling up all the micro pores and micro spaces which where left empty in traditional concrete production. Former described function reinforces the concrete structure on levels, thousand times smaller then in the ease of traditional concrete production. This allows the reduction of the cement used and gives the compression needed to reduce over 90 % of the additives used in the production of H-70 concrete.

 Cuore concrete allows to save in between 35% and 50% of the used cement.We do stress that   we recommend to change the formula of the concrete in order to take advantage of the characteristics of the Cuore concrete Nano silica particle.

The results are the proof

1)  Resistance to compression from 40 to 90MPa in 1 day.

2)         Resistance to compression from 70 a 10Q MPa (or more) in 28 days.

3)         Versatile: produces high resistance even with low addition (1 to 1,5 % of the cements weight) and gives self compacting characteristics with higher proportions (2.5 %).

4)         Meets the norms of environmental protection (ISO 14001).

5)         70% less use of additives as traditional silica, super plast.cizers or traditional Fibres.

6)         Equal or minor raw material cost as in traditional production with super plasucizers, and or fibres.

Conclusions

•          Well-dispersed nanoparticies increase the viscosity of the liquid phase, which helps to suspend the cement grains and aggregates, which, in turn, improves the segregation resistance and workability of the system.

•          Nanoparticies fill the voids between cement grains, which results in immobilization of free water (filler effect).

•          Well-dispersed nanoparticies act as centers of crystallization of the cement hydrates, which accelerates the hydration.

•          Nanoparticies favor the fomiation of small-sized crystals (such as calcium hydroxide)

•          Nanosilica participates in the pozzolanic reactions, which results in the consumption of calcium hydroxide and formation of an additional C-S-H.

•          Nanoparticies improve the structure of the aggregate contact zone, which results in better bond between aggregates and cement paste.

•          Nanoprticles improve the toughness, shear, tensile strength and (lexural strength of concrete.

Reference:

·          R.Z.Ma J.Wu, B.Q. Wei, Liang, and D.H. Wu, Journal Of Materials Science, 1998, 33, 5243.

·          24, G.D., Zhan, J.D. Kuntz, J. Wan and A.K. Mukherjee, Nature Materials, 2003, 2,38.

·          Li, G (2004) “Properties of High-Volume Fly Ash Concrete Incorporating Nano-Si02” Cement and Concrete Research, Vol.34, p.1043-1049

About Author:

I am Thomas Britto here to share my experiences in the civil engineering field to all my readers.Today many students are struggling to buy books at high prices. So I decided to start a blog and share my experience and knowledge with all my readers.

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