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Myriad Manifestations of Concrete (Dr. Manamohan R Kalgal)

Special Issue - eMagazine

Introduction

Concrete is one of the most versatile and durable construction materials that have been in use for centuries now in one form or the other. Present day concretes provide innumerable applications with very few limitations. Concrete is ubiquitous in our built environment - be it in buildings, roads, bridges, railways, or dams. Fifty years ago, the world’s concrete consumption was 1 tonne per capita (world population then was around 3 billion) whereas today, it is estimated to be around 3 tonnes per capita (present population being in excess of 7 billion)! Global growth in concrete consumption is partly due to the rapid industrialization of developing countries such as China and India. In the developed world, demand is driven more by the need to replace, repair and retrofit existing structures. Concrete is considered to be a sustainable material for construction in comparison to the available alternatives of similar virtues.

Virtues of Concrete

By substitution for the cementitious and aggregate phases, the finished product can be tailored to its application with varying strength, density, or chemical and thermal resistance properties. Concrete can be made with Supplementary Cementing Materials (SCMs) like fly-ash, slag etc., which are marginal materials or with blended cements containing SCMs thus reducing the Portland cement content leading to reduction in carbon footprint.  

Concrete means different things to different stakeholders

• For Architects, Concrete offers a dramatic range of colours, finishes and unlimited design possibilities, while creating a structure that provides superior environmental and energy performance. Cost-effective, energy efficient and aesthetically pleasing, concrete structures deliver increased client satisfaction.
•  For Engineers, Concrete offers many ways to achieve state-of-the-art environmental and energy performance. Designs that take advantage of the thermal mass, ease of construction and structural integrity of concrete have resulted in many award-winning projects.
• For Developers, Concrete offers a competitive building solution based on first cost, long-term economic benefits, energy efficiency, lower maintenance and overall operating costs as well as opportunities for future reuse - should the occupancy of the building change. 
• For Owners, Concrete offers both aesthetic appeal and cost effectiveness. Its strength and natural thermal mass result in a building that has low maintenance costs and high operating energy efficiency.

An attempt is made here to cover a few of the innumerable varieties of concrete and the present/future possibilities of exploiting its potential.

Special Concretes

Special concrete is defined as a concrete that has been specially designed to achieve one or more properties, behavior, composition or performance to be different, usually superior, compared to conventional concrete.

• With special concretes, possibilities are endless
• Special concretes can even be designed and specified, specifically for a project or an application.
• Special concretes need special care and control to achieve the desired properties

High performance Concrete, High Strength concrete, Self-compacting concrete, High Volume Fly-ash Concrete, Fiber Reinforced Concrete, Foam Concrete, Self-curing Concrete, Smart Concrete, Controlled Low Strength Concrete, Pervious concrete, Self Healing concrete, Anti-washout concrete, coloured and decorative concretes etc., are some of the manifestations of present day concrete.

Some, among the multitude of special concretes, are discussed in the following paragraphs:

High Performance Concrete (HPC)

The word High Performance denotes something more than what is achieved on a routine basis and involves a specification that often requires the concrete to meet several criteria. As per American Concrete Institute (ACI) definition, HPC is a concrete meeting special combinations of performance and uniformity requirements that cannot always be achieved routinely when using conventional constituents, mixing, placing and curing practices. A high-performance concrete usually has certain characteristics that are developed for a particular application and environment.

• A high-strength concrete is always a HPC, but an HPC need not always be a high-strength concrete.
• High-performance concretes are more sensitive to changes in constituent material properties than conventional concretes.
• Variations in the chemical and physical properties of the cementitious materials and chemical admixtures need to be carefully monitored.
• Substitutions of alternate materials can result in changes in the performance characteristics that may not be acceptable for HPC.
• The mix proportions are location specific.
• Many trial batches are usually necessary before a successful mix is developed. This means that a greater degree of quality control is required for the successful production of HPC
• RMC plants are generally ideal to handle the above issues.

Self Compacting Concrete (SCC)

    

SCC is defined as a category of High Performance Concrete that has excellent deformability in the fresh state, high resistance to segregation that can be placed and compacted under its self weight without applying external compaction effort.

Poor quality of vibration of concrete, in congested locations, has often been a shortcoming of traditional concrete. In such situations, SCC which flows under its self weight and does not require any external vibration, has revolutionized the concrete placement. SCC allows easier pumping - even from bottom up, flows into complex shapes, transitions and inaccessible spots and minimizes voids around embedded items to produce a high degree of homogeneity and uniformity. Since SCC flows easily, self-levels with minimal consolidation, placement is quick and easy, saving placement time, vibration equipment and time, labour and equipment wear and tear. SCC's potential for high early form stripping strength and smooth finish mean faster turnaround and minimal cosmetic repairs and a positive impact on maintaining projects on schedule. By eliminating the need for consolidation, SCC results in fewer safety and noise concerns and costs.

The mortar or paste in SCC requires high viscosity as well as high deformability. This can be achieved by the employment of a super plasticizer with or without a viscosity modifying agent, resulting in a low water-powder ratio for high deformability.

Self-compacting concrete is gradually becoming the preferred formulation worldwide for many applications such as foundations, floors, walls and complex structures. It combines great strength and superb finishes with improved productivity, providing outstanding construction solutions.

RMC plants where constant and superior quality control can be maintained are the ideal source for SCC. In order for self compacting concrete to be used as a standard concrete rather than a special one, new systems for its design, manufacturing and construction with SCC are being established. A system by which SCC can be supplied by RMC manufacturers would involve testing of self compactability, mix-design method, acceptance testing method at job site, development/use of new type of powder or admixture suitable for SCC.

High Volume Fly Ash (HVFA) Concrete

In the modern construction practice 15%-20% of fly ash by mass of the cementitious material is now commonly used in developed countries. Higher amounts of fly ash, of the order of 25%-30%, are recommended when there is a concern for thermal cracking, alkali-silica expansion, or sulfate attack. In HVFA concrete, the proportion of fly ash in the total cementitious materials is kept in the range of 50-60%. Such high proportions of fly ash are not readily accepted by the construction industry due to a slower rate of strength development at early age.

HVFA concrete system overcomes the problems of low early strength to a great extent through a drastic reduction in the water-cementitious materials ratio by using a combination of methods, such as taking advantage of the super-plactisizing effect of fly ash when used in large volumes, the use of a chemical super-plactisizer, and a judicious aggregate grading. Consequently, properly cured high-volume fly ash concrete products are very homogenous in microstructure, virtually crack-free, and highly durable. Because there is a direct link between durability and resource productivity, the increasing use of high volume concrete will help to enhance the sustainability of the concrete industry.

HVFA concrete offers a holistic solution to the problem of meeting the increasing demands for concrete in the future in a sustainable manner and at a reduced or no additional cost, and at the same time reducing the environmental impact of two industries that are vital to economic development namely the cement industry and the coal-fired power industry. The technology of HVFA concrete is especially significant for countries like China and India, where, given the limited amount of financial and natural resources, the huge demand for concrete needed for infrastructure and housing can be easily met in a cost-effective and ecological manner.

HVFA concrete should only be produced in an RMC facility or on projects having batching-mixing plant wherein sufficiently high level of quality control measures are exercised

Fibre Reinforced Concrete (FRC)

Fibre-reinforced concrete is conventional concrete to which discontinuous discrete fibres are added during mixing, so as to enhance the properties of the concrete, such as tensile and flexural strength, ductility, toughness and crack resistance

Improvement of properties of concrete by addition of fibres, governed by three main factors:

• Physical properties of concrete matrix and fibres.
• Uniform distribution of fibre throughout the matrix &
• Bond strength between concrete and fibre.

Benefits of adding fibre to concrete are:

• Improvement of pseudo-ductility of concrete
• Crack arrest and crack control
• Increase in deformability and hence ultimate strength of concrete.
• Improvement in tensile strength and stiffness.
• Better energy absorption properties
• Resistance to impact and fatigue loading.

Depending what performance is expected, fibres of different source and aspect ratios(length/diameter) are added in required quantity. Fibers have been produced from steel, carbon, glass, plastic, polypropylene, nylon, rayon, asbestos and also from natural materials such as cotton, coir, sisal and baggasse.  For structural applications using concrete, steel and glass fibers are generally used, since they possess high modulus of elasticity and lead to strong and stiff composites.

Due to its high density, the high strength concrete does not permit water vapours to go out during fire, leading to spalling off of concrete cover and damage to concrete members. Addition of 2kg polypropylene fibres per m³ of high strength concrete mix is said to increase fire resistance. At high temperature during fire, these fibres melt and leave pores for water vapours to escape from the concrete surface, thus preventing spalling and damage,

In India, the use of fibres has been limited to synthetic fibers largely for mitigating shrinkage/surface cracks. Use of fibres for structural applications is slowly picking up for large industrial floors. Steel fibres offer excellent enhancement in shear capacity and energy absorption during dynamic loading conditions. 

Foam Concrete

Foam concrete is a lightweight, free-flowing material that is ideal for many applications, and can have a range of dry densities (typically 400-1600kg/m³) and strengths (1-15MPa). It can be easily placed, by pump if necessary, and does not require compacting, vibrating or levelling. Foam concrete also has excellent resistance to water and frost, and provides a high level of sound and thermal insulation. It is very versatile, since it can be tailored for optimum performance and minimum cost by choice of a suitable mix design

Applications of Foam Concrete are:

• Road sub-bases (recent application in places where soil is unstable)
• Trench filling (for easy removal in future in case of service lines)
• As heat insulating materials for roofs of residential and Industrial buildings.
• Pre-cast panels for non-load-bearing partition walls, to give lightweight and sound insulated construction.
• Light weight-filling material for achieving slopes to facilitate drainage.
• To make complicated shapes for architectural facing work, because of high flowing and moulding ability without adding significantly to structural dead weight.

Flowable Fill

It is also called Controlled Low Strength Material (CLSM) or “liquid soil” in colloquial terms. It is a backfill product that flows as easily as thick pancake batter and is self-leveling. Its consistency is like that of a slurry or lean grout, yet several hours after placement the material is hard enough to support traffic loads without settling. It has a strength range of 1.5 – 9 MPa. Density of the material ranges from 1400 – 2000 kg/m³. CLSM can replace compacted soil as structural fill or backfill in many applications. It is ideal for use in tight or restricted- access areas where placing and compacting soil or granular fill is difficult or even impossible, viz. filling voids under existing pavements, buildings, or other structures, backfilling narrow trenches filling abandoned underground structures such as culverts, pipes, tunnels, storage tanks, wells, and sewers. Often it is used for trench filling of service lines etc to enable easy removal later and where durability is not expected to be a defining property of the material. A constant supply of material will make it flow horizontally a distance of 90 m or more. Flowable fill also has the advantage of displacing any standing water left in a trench. Flowable fill can be made with very high amounts of non-standard materials.

Flowable fill is an ideal pavement base material because it will not settle or rut under loads. It can be placed quickly and support traffic load within hours of placement thereby minimizing repair time and allowing a rapid return of traffic. Costs may be equal or less than the cost of using standard compacted backfill.

Pervious Concrete

Pervious concrete is a special type of concrete with a high porocity used for concrete flat work. It allows water to pass through for drainage, yet it maintains its strength. Possible uses include pedestrian walkways, parking lots, drainage structures and lakeside homes.  

Pervious Concrete, also known as no-fines or low fines concrete, pervious concrete is a mix of Portland cement, coarse aggregate, water and admixtures. Because there is little or no sand in the mix, the pore structure contains many voids that allow water and air to pass through. It typically has a voids content of 15% to 35%. This ensures that the concrete has the unique ability to allow storm water to pass through its mass into the ground underneath. Pervious concrete offers significant environmental benefits as it reduces the requirement for drainage facilities. Further it facilitates the recharge of ground water and the filtration process purifies the water as it percolates below.

Building owners are realizing better land utilization and LEED credits with pervious concrete parking lots. Pervious concrete applications can be used as an alternative to complex drainage systems and water retention areas reducing storm water runoff.

Further possible applications for pervious concrete

• Airport tarmac and terminal edge strips: So much rain water is converted to storm water at airports because of the vast amount of paving for runways, ramps, tarmacs and gate areas. If some of that can be paved with pervious concrete, much rain water will reach the aquifer.
• Curbs, gutters and bicycle path strips: This is another way to divert a tremendous amount of water from the storm water sewers. Consider: A 3' wide by 150' long strip of pervious concrete upstream from a catch basin could return over 25,000 gallons of water per hour to the aquifer, diverting it from surrounding bodies of water. This estimate is based upon percolation rate of 1 gallon per minute per square foot.
• Playground bases: A well constructed pervious concrete system covered with shredded tire mulch can provide a well drained easily maintained playground surface.
• Drainage ditch linings.
• Sound absorption walls for highways.
• Well linings
• Seawalls
• Sewage treatment plant - sludge beds etc.

Ultra High Performance Concrete (UHPC)

First developed in the early 1990’s by Bouygue’s laboratory in France, UHPC (also called Reactive Powder Concrete – RPC) consists of a special concrete where its microstructure is optimized by precise gradation of all particles in the mix to yield maximum density. At the level of maximum compressive strength of concrete, the coarse aggregate becomes the weakest link in concrete. In order to increase the compressive strength of concrete even further, the only way is to remove the coarse aggregate. This philosophy has been employed in RPC. It is a material which can resist direct primary tensile stresses and having the potential to structurally compete with steel.

UHPC is a high-strength, ductile material formulated by combining Portland cement, silica fume, quartz flour, fine silica sand, high-range water reducer, water, and steel or organic fibers. The material provides compressive strengths up to 200 MPa and flexural strengths up to 50 MPa.

The materials are usually supplied in a three-component premix: powders (Portland cement, silica fume, quartz flour, and fine silica sand) pre-blended in bulk-bags; super-plasticizers; and organic fibers. The ductile behavior of this material is a first for concrete, with the capacity to deform and support flexural and tensile loads, even after initial cracking. The use of this material for construction is simplified by the elimination of reinforcing steel and the ability of the material to be virtually self placing or dry cast.

The superior durability characteristics are due to a combination of fine powders selected for their grain size (max. size 600 microns) and chemical reactivity. The net effect is a maximum compactness and a small, disconnected pore structure leading to very low permeability and very high durability.

Self-curing Concrete

It is very well known that hydration of cement (which leads to gain of strength in concrete) occurs in the presence of moisture and to ensure the hydration of almost all particles of cement, it is essential to make available the moisture for a longer period. The mixing water tends to move from inside the body of concrete to the surface during hydration primarily due to the heat generated in the interior of concrete. Non availability of water may also lead to autogenous deformation and early micro-cracking.  Adding more water during mixing increases segregation, bleeding, porosity and reduces strength. Thus external curing is resorted to. Several methods like water ponding (where possible), covering with wet hessian/ gunny bags, plastic sheets, curing compounds etc., are used to  create a barrier for evaporation of water. It is known that in many cases the curing is not easy (viz. tall vertical surfaces, inaccessible places etc.) and in many other, curing is simply neglected leading to serious problems.

In order to mitigate this problem, efforts are on to find methods of reducing (if not avoiding) the necessity of external curing. This is being attempted by a process known as Internal Curing or Self Curing of concrete. ACI states, “internal curing refers to the process by which the hydration of cement occurs because of the availability of additional internal water that is not part of the mixing water.”  This is enabled by creating what can be called as internal reservoirs of water in the form of saturated porous aggregates (viz. light weight aggregates), superabsorbent polymers, saturated wood powders/fibres etc. Super absorbent polymers are a group of polymeric materials that have the ability to absorb a significant amount of liquid from the surroundings and to retain the liquid within their structure without dissolving. The most common application of these polymers is in super absorbent disposable diapers!

A few water-soluble chemicals (like polymeric glycols) are also available which can reduce the water evaporation from within the hydrating concrete creating self curing conditions.

Important applications of this concept of self curing would be concrete pavements, precast concrete operations, parking structures, bridges,  projects where high performance/high strength concretes are used and architectural concretes. 

Self Healing Concrete

Autogenous healing is the natural process of crack repair that can occur in concrete in the presence of moisture, and the absence of tensile stress. The repair is enabled by a combination of mechanical blocking by particles carried into the crack with the water and the deposition of calcium carbonate from the cementitious material.

Autogenous healing has practical applications for closing dormant cracks in a moist environment, such as may be found in mass structures and in water retaining or watertight structures. It is said that cracks up to 0.2 mm wide will autogenously seal within 28 days; cracks up to 0.1 mm will seal within 14 days.

Victor Li's of Michigan University claims to have developed a self-healing concrete which is based on a material he came up with in 1990 called Engineered Cementitious Composite. He and En Hua Yang improved on this and came up with what is famously known as “bendable concrete”.  It has some of the same ingredients as portland cement, except the coarser bits of the mix are replaced by microfibers. When the composite is stressed, it bends without fracturing. If it does crack, the cracks tend to be less than 50 microns wide--thinner than a human hair. These tiny cracks have the ability to heal themselves.

Li is said to be working on his next project: a concrete that can not only heal itself but also tell you when it has been damaged. A concrete that can talk back to monitoring systems

Some researchers have laced the concrete with bacteria spores that secrete calcium carbonate to fill the cracks and pores, while others embedded glass capillaries with a healing agent, but the process of filling the capillaries with the agent is long and tedious.

Henk  Jonkers of Delft University of Technology in Delft, the Netherlands is trying packing the concrete with bacteria that use water and calcium lactate "food" to make calcite, a natural cement. To keep the spores from activating in the wet concrete mix, and to keep them and their calcium lactate food from affecting the quality of the concrete, Jonkers and his colleagues first set both into ceramic pellets 2 to 4 millimetres wide and then added them to the concrete. Only when tiny cracks form in the concrete – opening up the pellets – and water seeps inside will the bacteria activate and begin to consume the food that has also been freed. As they feed, they combine the calcium with oxygen and carbon dioxide to form calcite – essentially pure limestone.

Michelle Pelletier of University of Rhode Island has tried embedding microencapsulated sodium silicate healing agent directly into a concrete matrix. When tiny stress cracks begin to form in the concrete, the capsules rupture and release the healing agent into the adjacent areas. The sodium silicate reacts with the calcium hydroxide naturally present in the concrete to form a calcium-silica-hydrate product to heal the cracks and block the pores in the concrete. The chemical reaction creates a gel-like material that hardens in about one week. This approach may prove to be cost-effective.

Smart Concrete

A concrete that can take care of its own shortcomings or that can perform as a sensor to help detecting internal flaws in it. The term was first used by Dr. Chung of State University of New York at Buffalo. Smart concrete patented by her is reinforced by carbon fiber as much as 0.2% to 0.5% of volume to increase its sense ability to strain or stress while still has good mechanical properties. Under load, the conductivity decreases but returns to original upon removal of the load. The concrete could thus act as a sensor to

• measure the number, speed and weight of the vehicles moving on concrete highways, and
• detect tiny flaws exhibiting  internal condition of concrete construction, after an earthquake or when overloaded .

• Monitoring can be a real-time and continuous activity

Although this technology has been through extensive laboratory testing, it still needs field testing and it is not yet available in the market.

Another ‘smart concrete’ being talked about is a concrete containing  porous carbon aggregate, available in the form of coke at the steel plant. This imparts good electrical conductivity which can help in room heating, melting of ice on concrete highway and runways when a low voltage current is passed through it.

Sumitomo Osaka Cement and YRP Ubiquitous Networking Laboratory have developed cyber-concrete - a kind of concrete containing RFID tags embedded in concrete, capable of storing data. A special Viewer is used for retrieving stored data, converting it to a language spoken almost instantly.  The main interest of the cyber-concrete is to use it as a tool to manage the data on the safety of the structure - something that is extremely important for a country prone to earthquakes as the Japan. It facilitates the work of the building managers, because the cyber-concrete is capable of storing various data and condiments, such as when, where and how it was manufactured, and the strength and quality. This will result in a more efficient and more reliable security inspection system.

Anti-wash out Concrete

Underwater concreting has been in use for a long time. Basically the concentration has been on  improving the techniques of concrete placement and minimising contact between the water and mortar so as to prevent the concrete from segregating under water.   

Anti-washout underwater concrete is quite different in concept from the methods mentioned above. This approach concentrates on the improved performance of the concrete in the fresh state. An underwater cellulose (like Hydroxy Propyl Methyl Cellulose) or acrylamide based admixture is used to increase the viscosity of the concrete and its resistance to segregation under the washing action of water is enhanced. The tremie and concrete pump placing methods can be additionally deployed.

• Compared to ordinary concrete, anti-washout underwater concrete is highly resistant to the washing action of water, and rarely separates even when dropped under water
• Its yield value is small and viscosity high, so the concrete components never segregate and it displays high fluidity.
• As a result of the high fluidity, filling property and self-leveling ability are improved.
• Almost no bleeding occurs.

 The degree of anti-washout property and flow property differs depending on the brand of anti-washout admixture, even though the main Ingredient may be the same. This it is important to understand the performance of the anti-washout admixture to be used using available reference materials, as well as to confirm that the required quality can be obtained by conducting tests in advance using the chosen materials.

When producing the underwater anti-wash concrete it is necessary to mix this concrete for longer period in a mixer large enough to uniformly disperse the anti-washout admixture. Care should be taken to check the compatibility of this admixture with other admixtures, if any, like Napthalene Supphonates. Also, when concrete pumps are used for placement, the proper planning of appropriate equipment for the distance to be pumped is necessary since the pumping resistance is increased by the higher viscosity.

Decorative Concretes

Concrete is not a mere grey material that could be used as a base for further surface finishes. Endless possibilities of decoration of (not on) concrete surface are possible. Simple integral pigmented concrete is the most common and simple decorative concrete. There are many techniques for surface finishing, that are available to improve the aesthetics

Architectural concrete is becoming more widely used as architects seek ways to enhance the appearance of concrete. Achieving an architectural or decorative appearance usually requires that something different be done to the concrete. It may involve special forms, special finishing techniques, or special ingredients. The plethora of effects is amazing.

 White Cement is almost an essential ingredient in Architectural/decorative concretes. White cement concrete, plain or pigmented, allows for a broad spectrum of colors-from bright whites and pastels to saturated colors. It can be textured, patterned, or shaped to almost any form, allowing architects to be truly creative in their designs. Imagination becomes architectural reality with white cement. Beyond aesthetics, its light colour offers energy efficiency and safety. Whether inside or outside, white cement concrete provides a hard-wearing, durable surface that stands up to heavy use.

Several materials and systems produce stamped concrete, Polished Concrete, Stained Concrete, Stencilled floor, decorative overlays, polished concrete, concrete countertops, vertical overlays, photo engraved concrete etc. These including Translucent Concrete, are indicating immense possibilities and newer manifestations

Some of the decorative concrete systems are briefly introduced here.

Polished concrete

Polished concrete is fast becoming the ultimate no-wax flooring material. Thanks to recent advances in polishing equipment and techniques, contractors are now grinding concrete floor surfaces, whether new or old to a high-gloss finish that never needs waxes or coatings.

Polished concrete is concrete that has been treated with a chemical densifier and ground with progressively finer grinding tools. Stains and dyes are often applied to enhance polished concrete as well as other options such as scoring, creating radial lines, grids, bands, borders, and other designs. Polished concrete is considered a good sustainable design flooring option and a green solution because it makes use of the materials already present.

Stained Concrete

Staining concrete is one of the most popular applications for transforming concrete slabs. Acid based chemical stains are used to achieve rich reath-tones colour schemes resembling natural stone, marble, wood, or even leather, giving a completely custom look to cement floors, concrete driveways, patios, walkways, pool decks, concrete walls etc.  They consist of hydrochloric acid and acid soluble metallic salts. The acid lightly etches the surface, allowing the metallic salts to penetrate easily. Once the stain reacts it becomes permanent part of concrete. The acid based stains are translucent and the and the color they produce will vary depending on the color and condition of the substrate they are applied to. Newer products on the market such as water-based penetrating stains and water- and solvent-based concrete dyes are greatly expanding the artist's palette with colors ranging from soft pastels to vivid reds, oranges, yellows, and purples. The results are limited only by the creativity of those involved in the stained concrete process.

Stencilled Concrete

  

Stenciled concrete is a form of decorative concrete that uses paper patterns embedded into the surface of the concrete. These paper stencils are removed soon after the concrete sets up revealing the pattern of the stencil

Stencils can be used on new concrete or on existing concrete. Stenciling utilizes a blocking technique. A high quality paper stencil is suitable for creating many varied decorative effects in concrete. Stencils for concrete come in a variety of patterns ranging from tile, slate, stone, and many brick patterns. Patterns from drawings, photos, graphics, logos, and even carpet samples can be custom made and transferred to a concrete surface 

Concrete Countertops and furniture

The advantages of concrete as a countertop material range from its physical characteristics to aesthetics — from its durability to its flexibility. Concrete Countertops are either pre-cast in a shop or built on site. Precast has the advantage of better quality due to controlled condition, special casting tables, better curing etc. Cast-in-situ countertops are resorted to to suit client’s particular needs - radius edges, curved corners, etc.

Countertops are made of cement, lightweight aggregates, and a combination of additives (fibres, silica fume, pozzolan, acrylic etc.)  Reinforcement used - structural steel, wire mesh, fiberglass, and/or fibers. Sometimes more than one type of reinforcement is used.

Sinks in homes are kitchen necessities but ones that can add interest to countertops. The sink can be concrete, either integrally cast with the countertop or a separate casting, or it can be metal, porcelain, or composite.

Stamped Concrete

Stamped concrete involves pouring slab concrete for driveways, walkways, patios, etc., and then impressing both patterns and textures onto the concrete before it is fully dry. For many years, a lesser form of stamped concrete was often seen that merely duplicated patterns. But the newer types of stamped concrete impart textures that duplicate many different surfaces such as cobblestones, brick, pavers, wood, seashells, and more. Also, pigment is usually added to stamped concrete to further duplicate the look of such patterns.

The installation consists of pressing molds into the concrete while the concrete is still in its plastic state. Color is achieved by using Dry Shakes or Color Hardeners, Powder or Liquid Releases, Integral Colors or Acid Stains. All these products may be combined to create even more intricate designs. However with time and wear the color dyes may fade and the surface appear patchy and non-presentable. There are many re-coloring options which can completely restore and rejuvenate the color and presentation of faded stamped concrete.

Photo-engraved Concrete

Photo engraved concrete is where using patented  processes,  images and photographs are reproduced onto concrete . For example, using Serilith system, a photograph or design is screen-printed, using a retarder, onto a polystyrene sheet as a layer of tiny dots. The photo-sensitive sheet is then placed into a mould ‘face up’ & concrete is poured on top. Approx. 2 days later, mould is stripped & the unit pressure-washed.

By carefully selecting coloured aggregates and sands, a good reproduction of the photograph or design is obtained. The technique is not restricted to internal and external walls, it can also be used to create photographs or designs onto ceilings or floors.

Transulcent Concrete

By combining concrete with optical fiber, concrete that transmits light has been created, resulting in translucent concrete. Several ways of producing translucent concrete do exist. But all are based on a fine grain concrete (ca. 95%) and only 5% light conducting elements that are added during casting process.

After setting, the concrete is cut to plates or stones with standard machinery for cutting stone materials. The new material is said to retain the strength of regular concrete, but because of the embedded array of glass fibers, can display a view from the outdoors in the form of silhouettes.

This special effect will create the impression that the thickness and weight of a concrete wall has disappeared, giving concrete buildings a light and airy feel. This material significantly expands the possibilities for architectural and engineering design.

Traditional uses

• Translucent blocks suitable for floors, pavements and load-bearing walls
• Facades, interior wall cladding and dividing walls based on thin panels.

Emerging uses / trends

• Partitions
• Furniture
• Light fixtures
• Light sidewalks at night
• Increasing visibility in dark subway stations
• Lighting indoor fire escapes in the event of a power failure
• Illuminating speed bumps on roadways at night 

Closing Remarks

Concrete is indisputably the most versatile construction material which is also sustainable in comparison to the presently available options. It is also a constantly evolving material showing greater and greater potentials which were hitherto unexploited. It is manifesting not only its traditional properties like ease of manufacture, mouldability, compressive strength and thermal comfort, but also the newer properties like environmental friendliness, fracture toughness, ductility, self leveling, self curing, self healing, aesthetics etc. It is up to us to use the capabilities of different special concretes as appropriate to get the best of the benefits and build the best of infrastructure and housing.

Acknowledgements

The author has borrowed liberally material available in the public domain on the internet and the books and papers of eminent authors and thanks all the authorities for the information that is made available. The intention of the article is to comprehensively cover the information available on the subject matter and author claims no copyright or ownership of any of the information collated and presented.