Builtconstruct

Saturday, August 25, 2018

Smart Nanomaterials in Construction Industry and Their Applications

Concrete, steel, glass, and timbers are the most common materials, being used in the field of modern construction. In the following table, some important characteristics of the above-mentioned materials are tabulated.

Material	Young’s Modulus (GPa)	Tensile Strength (GPa)	Density (g.cm-3)
Concrete	30	0.007	2.3
Steel	208	1.0	7.8
Glass	50-90	Negligible	2-8
Timber	16	0.008	0.6

If we compare these properties with those of a carbon nanotube, the results are astonishing. A carbon nanotube has a Young’s modulus of 1054 GPa, a tensile strength of 150 GPa and a density of 1.4 g-cm-3. Thus a carbon nanotube has strength of 150 times that of steel and at the same time approximately six times more lighter.

Based on the above statistics, it was thought (in UK Delphi Survey 1990), that the Construction industry would benefit the most from Nanotechnology. However, Construction industry lags behind other industrial sectors in terms of appealing investment from large corporate sectors.

Nanotechnology is a technology that enables to develop materials with improved or totally new properties. It is an extension of the sciences and technologies already developed for many years to examine the nature of our world at an ever smaller scale. A nanometer is one billionth of a meter.

Nanoparticles is defined as a particle that has at least one dimension less than 100 nm. The size of the particle is very important because at the length scale of the nanometer, i.e. 10-9 m, the properties of the material actually become affected.

Carbon nanotubes and nanofibers present an important classification of nanomaterials. They are made from Graphene. Graphene is defined a monolayer of carbon atoms packed into a honeycomb lattice. It can also be defined as an atomic-scale chicken wire made of carbon atoms and their bonds.

If graphene layers are arranged as stacked cones, cups or plates, it is known as Carbon nanofibers (CNF) and if the grapheme layers are wrapped into perfect cylinders, they are termed as Carbon nanotubes (CNT).

Graphene layer, Carbon Nanotubes, and Carbon Nanofibers

Nanocomposites are produced by adding nanoparticles to a bulk material in order to improve the bulk material properties. Materials reduced to nano-scale can suddenly show very different properties compared to what they exhibit on a macroscale, enabling unique applications. For instance, opaque copper substances become transparent and inert platinum materials attain catalytic properties.

Nanotechnology is a dynamic research field that covers a large number of disciplines including construction industry. Concrete is a material most widely used in construction industry. Concrete is a cement composite material made up of Portland cement, sand, crush, water and sometimes admixtures.

Interest in nanotechnology concept for Portland-cement composites is steadily growing. The materials such nano-Titania (TiO2), Carbon nanotubes, nano-silica (SiO2) and nano-alumina (Al2O3) are being combined with Portland cement. There are also a limited number of investigations dealing with the manufacture of nano-cement.

The use of finer particles (higher surface area) has advantages in terms of filling the cement matrix, densifying the structure, resulting in higher strength and faster chemical reactions (e.g. hydration reactions).

Nano-cement particles can accelerate cement hydration due to their high activity. Similarly, the incorporation of nano-particles can fill pores more effectively to enhance the overall strength and durability. Thus nanoparticles can lead to the production of a new generation of cement composites with enhanced strength, and durability.

According to researchers, following is a list of areas, where the construction industry could benefit from the nano-technology.

Replacement of steel cables by much stronger carbon nanotubes in suspension bridges and cable-stayed bridges
Use of nano-silica, to produce dense cement composite materials
Incorporation of resistive carbon nanofibers in concrete roads in snowy areas
Incorporation of nano-titania, to produce photocatalytic concrete
Use of nano-calcite particles in sealants to protect the structures from aggressive elements of the surrounding environment
Use of nanoclays in concrete to enhance its plasticity and flowability.
Urban air quality could be improved by if the civil structures are treated with nano TiO2

New Jubilee Church (Rome, Italy) made of nano photocatylatic concrete

Cable-Stayed and Suspension bridges

New Jubilee Church (Rome, Italy) made of nano photocatalytic concrete

Photocatalytic Self-Cleaning Concrete – Properties, Applications, Advantages

What is Photocatalytic Self-Cleaning Concrete?

Self cleaning concrete is produced by adding catalytic material to the concrete mixture. It is a new construction material that has been developed in the past three decades. The most prominent properties of the type of concrete is self cleaning ability.

Not only does it preserve façade appearances of structure but also it decomposes most of gases that emits from car exhaust and those produced because of emitted gases with rainwater.

The self-cleaning property is obtained by adding an additive to concrete which is called catalytic material which has a white color. An example of catalytic material is the titanium oxide as shown in Figure-1.

Fig.1: Titanium Dioxide

Self-cleaning begins when this material is activated, and catalytic material activation will start due to energy that is received from sunlight (it also can be activated using artificial lights).

When titanium oxide activates, a charge of separation electrons will be generated which will spread over photocatalytic concrete surface and decompose organic compounds on the concrete surface.

Properties of Photocatalytic Self-Cleaning Concrete

The properties of concrete both at plastic and hardened stage would not decline by adding photocatalytic materials. Slump, air content, unit weight, set-time, workability, permeability, flexural strength, and compressive are like ordinary concrete provided that proper guidelines are employed.

Advantages of Photocatalytic Self-Cleaning Concrete

The most outstanding properties of this type of concrete is self cleaning. This lead to maintain aesthetical appearance of structures for a long time.

Photocatalytic materials used in the production of photocatalytic concrete will help in decomposition of harmful gases such ozone, and other detrimental gases that produced because of emission gasses with rain water. This is specifically significant in great and congested cities.

So, it will decline environmental pollution greatly and save lives of many generations to come.

Photocatalytic self-cleaning concrete reflect majority of heat coming from the sun. Consequently, it helps the surface of the structure to retain its low temperature during summer season.

It reduces air temperature in urban environment and eventually reduces quantity of smoke.

Fig.2: Photocatalytic materials reduce pollution

Disadvantages

It may not be suitable for interior applications since it needs light to be activated. However, artificial light may decline this disadvantage to a certain extent.
Photocatalytic self cleaning concrete cannot be labeled graffiti proof since various paints are ultraviolet resistant and become a barrier between sunlight and concrete surface.

Application of Photocatalytic Self-Cleaning Concrete

There are several applications of photocatalytic concrete which include:

It is used in the construction of various structures
It is used in the construction of roads. This is greatly helpful since it decompose some of the gasses while they are emitted from car exhausts.
It is used in the construction of bridge structure and maintains its visually pleasant appearances.
Photocatalytic cement can be used to produce mortar, pavement plasters, and precast elements.
Concrete sidewalks
Tilt-up concrete panels
Noise barriers for roads and highways

Examples of using photocatalytic self-cleaning concrete in the world

New jubilee church structure photocatalytic concrete

Fig.3: New jubilee church structure in Rome which is anticipated to remain clean and keep its aesthetical appearance for many years to come

Fig.4: Photocatalytic are used in Japan to keep paving, clean and to reduce the effect of air pollution

Fig.5: Air France company head office structure in France, photocatalytic concrete used in the construction

Fig.6: The Milan Expo

What is Pile Drivability? Factors Influencing Pile Drivability and its Evaluation

What is pile drivability?

It is the ability of the pile to be driven to a designated depth without suffering without sustaining damages. The ultimate resistance of soil against a pile, which is driven without suffering any damages using suitable driven equipment, specify a limit for pile drivability.

Fig.1: Pile Driving

Factors Influencing Pile Drivability

There are two major drivability features that a pile need to meet namely pile stiffness and pile strength. The pile need to have adequate stiffness to be able to transfer sufficient driving force that overcomes soil resistance. Regarding pile strength, it should be large enough so as the pile can withstand the driving force without suffering any damages.

Pile impedance (EA/C) is the major factor that controls pile drivability. The modulus of elasticity (E) of pile is specified based on the material used for the construction, (C) is the pile wave speed, and (A) is the cross-sectional area of the pile which seems to be the only parameter by which pile drivability can be improved.

The improvement of pile drivability though increasing cross sectional area can be clearly observed when steel pile is selected. For example, the increase of the thickness of steel pipe pile will enhance the pile drivability. However, when the area of reinforced concrete section is increased, the soil resistance would also increase.

Pile driven system features such as speed, stroke, ram weight, and real performance of pile driving system on the construction site would influence pile drivability to a certain extent.

Methods to Assess Pile Drivability

There are three methods used to evaluate pile drivability which include:

Wave equation analysis
Dynamic testing and analysis

Static loads tests

Types of Liner Used for Sewer Sanitary System

There are various types of liners used for sewer sanitary system such as cast in place liners, chemically attached liners and mechanically attached liners which are categorized based on attachment technique and type of material used in the liner production.

These types of liners used in the construction and/or repair of sanitary sewer system will be discussed in the following sections.

Fig.1: Liner used for sanitary sewer pipe system to prevent it from corrosion

Types of Liner Used for Sewer Sanitary System

Cast in Place Sewer Liners

There are various types of cast in place sewer liners which are commercially available to be used. It can be used for new construction and repairing works.

Cast in place liners are attached to sanitary sewer pipes by means of ribs, knobs, and tees which are embedded into concrete or grout. It creates an acid barrier between sewer water and sewer sanitary pipe wall.

Cast in place liner permits the movement of hydrostatic pressure and vapor into sewer pipe without compromising its function which is protection sewer pipe from corrosion.

Regarding cast in place liner performance, the best performance is when liners are attached to precast pipes in factory.

The inside sewer pipe area that recommended to be covered ranges from 300 to 320 degrees. Lesser coverage may lead to pipe deterioration due to sanitary water flow whereas 360 degree coverage could pose health issues.

Finally, it is required to be cautious during liner placement and liner welding which used to attach liners to each other.

Chemically Attached Sewer Liners

Chemically attached liners can be used for new construction and repairing works. It is widely used in rehabilitation works since other types of liners are more economical in the case of new construction.

There are two major forms of chemically attached liners. Firstly, PVC sheet with protrusions on one side that pushed into previously applied epoxy mastic on concrete sewer pipe surface. The epoxy would encircle protrusions and satisfactory bond would be generated between liner and concrete.

Secondly, PVC sheet liner that attached to sewer pipe chemically using polyurethane mastic. There is chemical agent in the PVC sheet that causes chemical fusion between polyurethane mastic and the liner.

Moreover, it is important to bear in mind that concrete pipe surface should be prepared in addition to choose suitable primer under mastic polyurethane or concrete polymer which may be used instead of the mastic.

These Measures will ensure a good bond between sewer pipe and the liner.

Fig.2: Chemically Attached Lining Pipe

Mechanically Attached Sewer Liners

This type of liner is widely used for new construction and it has been applied for countless repairing tasks. The most common type of materials used to manufacture this liner types are PVC and HDPE. However, it can be produced from nearly all types of materials.

The strongest point of mechanically attached liner is its suitability for almost all construction condition. This is because not only does the liner thickness can be changed but also broad ranges of attachment techniques may be employed.

The attachment may vary from small expansion type anchors to stainless steel batten strips with epoxy coat. Design conditions can be easily met with mechanically attached liner since its thickness can be increased to accommodate greater loads.

Similar to cast in place liner, hydrostatic and vapor forces cannot be accommodated, so it is permitted to move into sewer environment through the liner.

It is necessary to pay attention to the liner and sewer pipe interface during installation otherwise hydrostatic relief issue may arise due to chemical reactions. When this liner is designed, all hydraulic conditions should be accounted.

Finally, adequate thickness, hoop strength, attachment security need to overcome expected loads otherwise it would suffer from crucial failures. With regard to attachments, materials used for manufacturing, spacing, type, and size of the attachment play critical role in the safety of the liner.