How Tall is a "Tall" Building??

What is a tall building? How is a building's height measured? What do terms like "supertall" and "mixed-use" actually mean? These and other questions are answered in the CTBUH Height Criteria, the official rules whereby tall buildings are defined and heights are measured.
What is a Tall Building?
There is no absolute definition of what constitutes a “tall building.” It is a building that exhibits some element of “tallness” in one or more of the following categories:
a) Height Relative to Context:                 It is not just about height, but about the context in which it exists. Thus, whereas a 14-story building may not be considered a tall building in a high-rise city such as Chicago or Hong Kong, in a provincial European city or a suburb this may be distinctly taller than the urban norm.
b) Proportion Again, a tall building is not just about height but also about proportion. There are numerous buildings that are not particularly high, but are slender enough to give the appearance of a tall building, especially against low urban backgrounds. Conversely, there are numerous big/large footprint buildings that are quite tall but their size/floor area rules them out as being classed as a tall building.
c) Tall Building Technologies:         If a building contains technologies which may be attributed as being a product of “tall” (e.g., specific vertical transport technologies, structural wind bracing as a product of height, etc.), then this building can be classed as a tall building. Although number of floors is a poor indicator of defining a tall building due to the changing floor to floor height between differing buildings and functions (e.g., office versus residential usage), a building of perhaps 14 or more stories – or more than 50 meters (165 feet) in height – could perhaps be used as a threshold for considering it a “tall building.”
What are Supertall and Megatall Buildings? The CTBUH defines “supertall” as a building over 300 meters (984 feet) in height, and a “megatall” as a building over 600 meters (1,968 feet) in height. As of June 2015 there were 91 supertall and 2 megatall buildings fully completed and occupied globally.
How is the Height of a Tall Building Measured?
The Council on Tall Buildings and Urban Habitat (CTBUH) recognizes tall building height in three categories:
1. Height to Architectural Top: Height is measured from the level1 of the lowest, significant,2 open-air,3 pedestrian4 entrance to the architectural top of the building, including spires, but not including antennae, signage, flag poles or other functional-technical equipment.5 This measurement is the most widely utilized and is employed to define the CTBUH rankings of the "World's Tallest Buildings."
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2. Highest Occupied Floor: Height is measured from the level1 of the lowest, significant,2 open-air,3 pedestrian4 entrance to the finished floor level of the highest occupied6 floor within the building.
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3. Height to Tip: Height is measured from the level1 of the lowest, significant,2 open-air,3 pedestrian4 entrance to the highest point of the building, irrespective of material or function of the highest element (i.e., including antennae, flagpoles, signage, and other functional-technical equipment).
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Footnotes: 1 Level:  finished floor level at threshold of the lowest entrance door. 2 Significant:  the entrance should be predominantly above existing or pre-existing grade and permit access to one or more primary uses in the building via elevators, as opposed to ground-floor retail or other uses that solely relate/connect to the immediately adjacent external environment. Thus, entrances via below-grade sunken plazas or similar are not generally recognized. Also note that access to car park and/or ancillary/support areas are not considered significant entrances. 3 Open-air: the entrance must be located directly off an external space at that level that is open to air. 4 Pedestrian: refers to common building users or occupants and is intended to exclude service, ancillary, or similar areas. 5 Functional-technical equipment: this is intended to recognize that functional-technical equipment is subject to removal/addition/change as per prevalent technologies, as is often seen in tall buildings (e.g., antennae, signage, wind turbines, etc. are periodically added, shortened, lengthened, removed and/or replaced). 6 Highest occupied floor: this is intended to recognize conditioned space which is designed to be safely and legally occupied by residents, workers or other building users on a consistent basis. It does not include service or mechanical areas which experience occasional maintenance access, etc.
Number of Floors The number of floors should include the ground-floor level and be the number of main floors above ground, including any significant mezzanine floors and major mechanical plant floors. Mechanical mezzanines should not be included if they have a significantly smaller floor area than the major floors below. Similarly, mechanical penthouses or plant rooms protruding above the general roof area should not be counted. Note: CTBUH floor counts may differ from published accounts, as it is common in some regions of the world for certain floor levels not to be included (e.g., the level 4, 14, 24, etc. in Hong Kong).
Criteria for Co-joined Buildings A building complex is considered to be a single, co-joined building (as opposed to two separate buildings connected by skybridges or other elements) when 50 percent or more of the total building height is connected. Exceptions to this 50 percent rule can be made in cases where the form of the building creates a coherent arch, creating a singular architectural expression and thus a co-joined building – to be judged by the CTBUH Height Committee.
Building Usage Building vs. Telecommunications Tower: A tall “building” can be classed as such (as opposed to a telecommunications/observation tower) and is eligible for the "Tallest” lists if at least 50 percent of its height is occupied by usable floor area.		To enlarge, click here
Single-function and mixed-use buildings
A single-function tall building is defined as one where 85 percent or more of its total floor area is dedicated to a single use. A mixed-use tall building contains two or more functions (or uses), where each of the functions occupies a significant proportion7 of the tower’s total space. Support areas, such as car parks and mechanical plant space, do not constitute mixed-use functions. Functions are denoted on CTBUH “Tallest” lists in descending order (e.g., “hotel/office” indicates hotel function above office function).		To enlarge, click here
Footnote: 7This “significant proportion” can be judged as 15 percent or greater of either: (1) the total floor area, or (2) the total building height, in terms of number of floors occupied for the function. However, care should be taken in the case of supertall towers. For example a 20-story hotel function as part of a 150-story tower does not comply with the 15 percent rule, though this would clearly constitute mixed-use.
Building Status
Complete (Completion) A building is considered to be "Complete" (and officially added to the CTBUH Tallest Buildings lists) if it fulfills all of the following three criteria: 1) Topped out structurally and architecturally8 2) Fully-clad9 3) Open for business, or at least partially occupiable  Footnotes: 8The topping out architecturally of a building implies that ALL structural and finished architectural elements are in place. 9The omission of a small number of cladding panels to allow fixing of a construction hoist while interior fit-out of some building areas is continuing does not affect the status of “fully clad.” Under Construction (Start of Construction) A building is considered to be "Under Construction" once site clearing has been completed and foundation/piling work has begun. Structurally Topped Out A building is considered to be "Structurally Topped Out" when it is under construction, and the highest primary structural element is in place. Architecturally Topped Out A building is considered to be "Architecturally Topped Out" when it is under construction, and has reached its full height both structurally and architecturally (e.g., including its spires, parapets, etc.). On Hold A building is considered to be "On Hold" when construction works had begun, but work on-site has been halted  indefinitely, however there is still an intent to complete the construction to the original design at a future date. Never Completed A building is considered to be “Never Completed” when construction works had begun, but work on-site was halted and never resumed. The site may go on to accommodate a new building, different to the original design, that may or may not retain the original construction. Proposed A building is considered to be "Proposed" (i.e., a real proposal) when it fulfills all of the following criteria: 1) Has a specific site with ownership interests within the building development team 2) Has a full professional design team progressing the design beyond the conceptual stage 3) Has obtained, or is in the process of obtaining, formal planning consent/legal permission for construction 4) Has a full intention to progress the building to construction and completion Only buildings that have been announced publicly by the client and fulfill all the above criteria are included in the CTBUH "proposed" building listings. The source of the announcement must also be credible. Due to the changing nature of early stage designs and client information restrictions, some height data for proposals may be unconfirmed. Vision A building is considered to be a "Vision" when it either: 1) Is in the early stages of inception and does not yet fulfill the criteria under the “proposal” category, or 2) Was a proposal that never advanced to the construction stages, or 3) Was a theoretical proposition Demolished A building is considered to be "Demolished" after it has been destroyed by controlled end-of-life demolition, fire, natural catastrophe, war, terrorist attack, or through other means intended or unintended.
Structural Material
A steel tall building is defined as one where the main vertical and lateral structural elements and floor systems are constructed from steel. A concrete tall building is defined as one where the main vertical and lateral structural elements and floor systems are constructed from concrete. A composite tall building utilizes a combination of both steel and concrete acting compositely in the main structural elements, thus including a steel building with a concrete core. A mixed-structure tall building is any building that utilizes distinct steel and concrete systems above or below each other. There are two main types of mixed structural systems: a steel/concrete tall building indicates a steel structural system located above a concrete structural system, with the opposite true of a concrete/steel building. Additional Notes: 1) If a tall building is of steel construction with a floor system of concrete planks on steel beams, it is considered a steel tall building. 2) If a tall building is of steel construction with a floor system of a concrete slab on steel beams, it is considered a steel tall building. 3) If a tall building has steel columns plus a floor system of concrete beams, it is considered a composite tall building. This post originally appeared on CTBUH.

BASIC RCC SLAB DESIGN GUIDELINES

a) Effective span of slab:

Effective span of slab shall be lesser of the two
1.  L = clear span + d (effective depth )
2.  L = Center to center distance between the support


b) Depth of slab:

The depth of slab depends on bending moment  and deflection  criterion.  the trail depth can be obtained using:

• Effective depth d= Span /((L/d)_Basic x modification factor)
• For obtaining modification factor, the percentage of steel for slab can be assumed from 0.2 to 0.5%.
• The effective depth d of two way slabs can also be  assumed using cl.24.1,IS 456 provided short span is ?3.5m and loading class is <3.5KN/m²

Type of support	Fe-250	Fe-415
Simply supported	L/35	L/28
Continuous support	L/40	L/32

Or, the following thumb rules can be used:

• One way slab d=(L/22) to (L/28).
• Two way simply supported slab d=(L/20) to (L/30)
• Two way restrained slab d=(L/30) to (L/32)

c) Load on slab:

The load on slab comprises of Dead load, floor finish and live load. The loads are calculated per unit area (load/m²).
Dead load = D x 25 kN/m² ( Where D is thickness of slab in m)
Floor finish (Assumed as)= 1 to 2 kN/m²
Live load (Assumed as) = 3 to 5 kN/m² (depending on the occupancy of the building)

Detailing Requirements of RCC Slab as per (IS456: 2000) :

a) Nominal Cover:

For Mild exposure – 20 mm
For Moderate exposure – 30 mm
However, if the diameter of bar do not exceed 12 mm, or cover may be reduced by 5 mm. Thus for main reinforcement up to 12 mm diameter bar and for mild exposure, the nominal cover is 15 mm.


b) Minimum reinforcement:

The reinforcement in either direction in slab shall not be less than

• 0.15% of the total cross sectional area for Fe-250 steel
• 0.12% of the total cross-sectional area for Fe-415 & Fe-500 steel.

c) Spacing of bars:

The maximum spacing of bars shall not exceed :

• Main Steel – 3d or 300 mm whichever is smaller
• Distribution steel –5d or 450 mm whichever is smaller Where, ‘d’ is the effective depth of slab. Note: The minimum clear spacing of bars is not kept less than 75 mm (Preferably 100 mm) though code do not recommend any value.

d) Maximum diameter of bar:

The maximum diameter of bar in slab, shall not exceed D/8, where D is the total thickness of slab.


Steps to be followed in the design of slab :

1. Assuming suitable bearings (not less than 10cm), find the span of the slab between the centers of bearings.
2. Assume the thickness of slab (take 4 cm per metre run of the span).
3. Find the effective span which is lesser of (i) distance between centres of bearings, and (ii) clear span and effective depth.
4. Find the dead load and the live load per square meter of the slab.
5. Determine the maximum bending moment for a one meter wide strip of the slab.

The maximum bending moment per meter width of slab,

Where, w = total load intensity per square meter of the slab.

1. Equate the balanced moment of resistance to the maximum bending moment

Find the effective depth ‘d’ from the above equation.

1. Calculate the main reinforcement per metre width

For M15 concrete, lever arm = 0.87 d

Spacing of bar =

CONTINUOUS SLAB :

Suppose a slab is supported at the ends and also at intermediate points on beams, the maximum sagging and hogging moments to which the slab is subjected to due to uniformly distributed load, can be computed as follows:
Let

= intensity of dead load per square metre

= intensity of live load per square metre.


Bending moment due to dead load and live load may be taken as follows (IS: 456 – 2000)
 

	At middle of end span	Over support	At middle of interior support	Over interior support
BM due to dead load
Bending moment due to live load

TOP TEN INNOVATIONS IN CONSTRUCTION INDUSTRY

New materials and energy, design approaches, as well as advances in digital technology and big data, are creating a wave of innovation within the construction industry. Here are ten of the most exciting developments:

 

1. SELF-HEALING CONCRETE :

Cement is one of the most widely used materials in construction, but also one of the largest contributors to harmful carbon emissions, said to be responsible for around 7 per cent of annual global emissions. Cracking is a major problem in construction, usually caused by exposure to water and chemicals. Researchers at Bath University are looking to develop a self-healing concrete, using a mix containing bacteria within microcapsules, which will germinate when water enters a crack in the concrete to produce limestone, plugging the crack before water and oxygen has a chance to corrode the steel reinforcement.

 2. THERMAL BRIDGING :

Efficient insulation material is becoming increasingly important throughout the construction industry. Heat transmission through walls tends to be passed directly through the building envelope, be it masonry, block or stud frame, to the internal fascia such as drywall. This process is known as “thermal bridging”. Aerogel, a technology developed by Nasa for cryogenic insulation, is considered one of the most effective thermal insulation materials and US spin-off Thermablok has adapted it using a proprietary aerogel in a fibreglass matrix.  This can be used to insulate studs, which can reportedly increase overall wall R-value (an industry measure of thermal resistance) by more than 40 per cent.

3. PHOTOVOLTAIC GLAZING :

Building integrated photovoltaic (BIPV) glazing can help buildings generate their own electricity, by turning the whole building envelope into a solar panel. Companies such as Polysolar provide transparent photovoltaic glass as a structural building material, forming windows, façades and roofs. Polysolar’s technology is efficient at producing energy even on north-facing, vertical walls and its high performance at raised temperatures means it can be double glazed or insulated directly. As well as saving on energy bills and earning feed-in tariff revenues, its cost is only marginal over traditional glass, since construction and framework costs remain, while cladding and shading system costs are replaced.

4. KINETIC FOOTFALL :

Kinetic energy is another technology under development. Pavegen provides a technology that enables flooring to harness the energy of footsteps. It can be used indoors or outdoors in high traffic areas, and generates electricity from pedestrian footfall using an electromagnetic induction process and flywheel energy storage. The technology is best suited to transport hubs where a large flow of people will pass over it. The largest deployment the company has done so far is in a football pitch in Rio de Janeiro to help power the floodlights around the pitch. It also currently has a temporary installation outside London’s Canary Wharf station powering street lights.

5. KINETIC ROADS :

Italian startup Underground Power is exploring the potential of kinetic energy in roadways. It has developed a technology called Lybra, a tyre-like rubber paving that converts the kinetic energy produced by moving vehicles into electrical energy. Developed in co-operation with the Polytechnic University of Milan, Lybra operates on the principle that a braking car dissipates kinetic energy. The cutting-edge technology is able to collect, convert this energy into electricity and pass it on to the electricity grid. In addition to improving road safety, the device upgrades and promotes sustainability of road traffic.

6. PREDICTIVE SOFTWARE :

The structural integrity of any building is only as good as its individual parts. The way those parts fit together, along with the choice of materials and its specific site, all contribute to how the building will perform under normal, or extreme, conditions. Civil engineers need to integrate a vast number of pieces into building designs, while complying with increasingly demanding safety and government regulations. An example of this was work on the structural integrity of the arch rotation brackets at Wembley Stadium, undertaken by Bennett Associates, using ANSYS software, which simulated the stresses on the brackets that hold and move the distinctive arches above the stadium.

7. 3D MODELLING :

Planning innovation has been driven by the growth of smart cities. CyberCity3D (CC3D) is a geospatial-modelling innovator specialising in the production of smart 3D building models. It creates smart digital 3D buildings to help the architectural, engineering and construction sector visualise and communicate design and data with CC3D proprietary software. The models integrate with 3D geographic information system platforms, such as Autodesk and ESRI, and can stream 3D urban building data to Cesium’s open architecture virtual 3D globe. It provides data for urban, energy, sustainability and design planning, and works in conjunction with many smart city SaaS platforms such as Cityzenith.

 

8. MODULAR CONSTRUCTION :

Modular construction is increasingly popular where a building is constructed off-site using the same materials and designed to the same standards as conventional on-site construction. It limits environmental disruption, delivering components as and when needed, and turning construction into a logistics exercise. It also has strong sustainability benefits, from fewer vehicle movements to less waste. With up to 70 per cent of a building produced as components, it allows a move towards “just in time” manufacturing and delivery. In use in the United States and UK, Chinese developer Broad Sustainable Building recently completed a 57-storey skyscraper in 19 working days using this method.

9. CLOUD COLLABORATION :

basestone is a system allowing the remote sharing of data on a construction site in real time. It is predominantly a review tool for engineers and architects which digitises the drawing review process on construction projects, and allows for better collaboration. The cloud-based collaboration tool is focused on the installation of everything from steel beams to light fittings. The system is used to add “snags”, issues that happen during construction, on to pdfs, then users can mark or add notes through basestone. Trials have revealed possible cost-savings of around 60 per cent compared with traditional paper-based review methods.

10. ASSET MAPPING :

Asset mapping focuses on operational equipment, including heating and air conditioning, lighting and security systems, collecting data from serial numbers, firmware, engineering notes of when it was installed and by whom, and combines the data in one place. The system can show engineers in real time on a map where the equipment needs to be installed and, once the assets are connected to the real-time system using the internet of things, these can be monitored via the web, app, and other remote devices and systems. It helps customers build databases of asset performance, which can assist in proactive building maintenance, and also reduce building procurement and insurance costs.

 

PROPERTIES OF CONCRETE

Properties of concrete are influenced by many factors mainly due to mix proportion of cement, sand, aggregates and water. Ratio of these materials control the various concrete properties which are discussed below.

Different Properties of Concrete are as follows:

• Grades (M20, M25, M30 etc.)
• Compressive strength
• Characteristic Strength
• Tensile strength
• Durability
• Creep
• Shrinkage
• Unit weight
• Modular Ratio
• Poisson’s ratio

 

Grades of concrete :

Concrete is known by its grade which is designated as M15, M20 etc. in which letter M refers to concrete mix and number 15, 20 denotes the specified compressive strength (fck) of 150mm cube at 28 days, expressed in N/mm2. Thus, concrete is known by its compressive strength. M20 and M25 are the most common grades of concrete, and higher grades of concrete should be used for severe, very severe and extreme environments.

Compressive strength of concrete :

Like load, the strength of the concrete is also a quality which varies considerably for the same concrete mix. Therefore, a single representative value, known as characteristic strength is used.

 

Characteristic strength of concrete :

It is defined as the value of the strength below which not more then 5% of the test results are expected to fall (i.e. there is 95% probability of achieving this value only 5% of not achieving the same)

 

Characteristic strength of concrete in flexural member :

The characteristic strength of concrete in flexural member is taken as 0.67 times the strength of concrete cube.

 

Design strength (fd) and partial safety factor for material strength :

The strength to be taken for the purpose of design is known is known as design strength and is given by
Design strength (fd) = characteristic strength/ partial safety factor for material strength
The value of partial safety factor depends upon the type of material and upon the type of limit state. According to IS code, partial safety factor is taken as 1.5 for concrete and 1.15 for steel.
Design strength of concrete in member = 0.45fck

 

Tensile strength of concrete :

The estimate of flexural tensile strength or the modulus of rupture or the cracking strength of concrete from cube compressive strength is obtained by the relations
fcr = 0.7 fck N/mm²
The tensile strength of concrete in direct tension is obtained experimentally by split cylinder. It varies between 1/8 to 1/12 of cube compressive strength.

 

Creep in concrete :

Creep is defined as the plastic deformation under sustain load. Creep strain depends primarily on the duration of sustained loading. According to the code, the value of the ultimate creep coefficient is taken as 1.6 at 28 days of loading.

 

Shrinkage of Concrete :

The property of diminishing in volume during the process of drying and hardening is termed Shrinkage. It depends mainly on the duration of exposure. If this strain is prevented, it produces tensile stress in the concrete and hence concrete develops cracks.

 

Modular ratio :

Short term modular ratio is the modulus of elasticity of steel to the modulus of elasticity of concrete.

Short term modular ratio = Es / Ec

where,
Es = modulus of elasticity of steel (2×10^5  N/mm²)

Ec = modulus of elasticity of concrete (5000x√fck  N/mm²)

As the modulus of elasticity of concrete changes with time, age at loading etc the modular ratio also changes accordingly. Taking into account the effects of creep and shrinkage partially IS code gives the following expression for the long term modular ratio.

Long term modular ratio (m) = 280/ (3σ_cbc)

Where,  
σ_cbc = permissible compressive stress due to bending in concrete in N/mm².

Poisson’s ratio :

Poisson’s ratio varies between 0.1 for high strength concrete and 0.2 for weak mixes. It is normally taken as 0.15 for strength design and 0.2 for serviceability criteria.

 

Durability of concrete :

Durability of concrete is its ability to resist its disintegration and decay. One of the chief characteristics influencing durability of concrete is its permeability to increase of water and other potentially deleterious materials.
The desired low permeability in concrete is achieved by having adequate cement, sufficient low water/cement ratio, by ensuring full compaction of concrete and by adequate curing.

 

Unit weight of concrete :

The unit weight of concrete depends on percentage of reinforcement, type of aggregate, amount of voids and varies from 23 to 26KN/m². The unit weight of plain and reinforced concrete as specified by IS:456 are 24 and 25KN/m³ respectively.

TYPES OF CONCRETE AND ITS APPLICATIONS

 

High-strength concrete

High-strength concrete has a compressive strength greater than 40 MPa (5800 psi). High strength concrete is defined as concrete with a compressive strength class higher than C50/60. High-strength concrete is made by lowering the water-cement (W/C) ratio to 0.35 or lower. Often silica fume is added to prevent the formation of free calcium hydroxide crystals in the cement matrix, which might reduce the strength at the cement-aggregate bond.
Low W/C ratios and the use of silica fume make concrete mixes significantly less workable, which is particularly likely to be a problem in high-strength concrete applications where dense rebar cages are likely to be used. To compensate for the reduced workability, superplasticizers are commonly added to high-strength mixtures. Aggregate must be selected carefully for high-strength mixes, as weaker aggregates may not be strong enough to resist the loads imposed on the concrete and cause failure to start in the aggregate rather than in the matrix or at a void, as normally occurs in regular concrete.
In some applications of high-strength concrete the design criterion is the elastic modulus rather than the ultimate compressive strength.

Stamped concrete

Stamped concrete is an architectural concrete which has a superior surface finish. After a concrete floor has been laid, floor hardeners (can be pigmented) are impregnated on the surface and a mold which may be textured to replicate a stone / brick or even wood is stamped on to give an attractive textured surface finish. After sufficient hardening the surface is cleaned and generally sealed to give a protection. The wear resistance of stamped concrete is generally excellent and hence found in applications like parking lots, pavements, walkways etc.

High-performance concrete

High-performance concrete (HPC) is a relatively new term for concrete that conforms to a set of standards above those of the most common applications, but not limited to strength. While all high-strength concrete is also high-performance, not all high-performance concrete is high-strength. Some examples of such standards currently used in relation to HPC are:

• Ease of placement
• Compaction without segregation
• Early age strength
• Long-term mechanical properties
• Permeability
• Density
• Heat of hydration
• Toughness
• Volume stability
• Long life in severe environments
• Depending on its implementation, environmental

Ultra-high-performance concrete

Ultra-high-performance concrete is a new type of concrete that is being developed by agencies concerned with infrastructure protection. UHPC is characterized by being a steel fibre-reinforced cement composite material with compressive strengths in excess of 150 MPa, up to and possibly exceeding 250 MPa . UHPC is also characterized by its constituent material make-up: typically fine-grained sand, silica fume, small steel fibers, and special blends of high-strength Portland cement. Note that there is no large aggregate. The current types in production (Ductal, Taktl, etc.) differ from normal concrete in compression by their strain hardening, followed by sudden brittle failure. Ongoing research into UHPC failure via tensile and shear failure is being conducted by multiple government agencies and universities around the world.

Micro-reinforced ultra-high-performance concrete

Micro-reinforced ultra-high-performance concrete is the next generation of UHPC. In addition to high compressive strength, durability and abrasion resistance of UHPC, micro-reinforced UHPC is characterized by extreme ductility, energy absorption and resistance to chemicals, water and temperature. The continuous, multi-layered, three dimensional micro-steel mesh exceeds UHPC in durability, ductility and strength. The performance of the discontinuous and scattered fibers in UHPC is relatively unpredictable. Micro-reinforced UHPC is used in blast, ballistic and earthquake resistant construction, structural and architectural overlays, and complex facades.
Ducon was the early developer of micro-reinforced UHPC, which has been used in the construction of new World Trade Center in New York.

Self-consolidating concrete

The defects in concrete in Japan were found to be mainly due to high water-cement ratio to increase workability. Poor compaction occurred mostly because of the need for speedy construction in the 1960s and 1970s. Hajime Okamura envisioned the need for concrete which is highly workable and does not rely on the mechanical force for compaction. During the 1980s, Okamura and his Ph.D. student Kazamasa Ozawa at the University of Tokyo developed self-compacting concrete (SCC) which was cohesive, but flowable and took the shape of the formwork without use of any mechanical compaction. SCC is known as self-consolidating concrete in the United States.
SCC is characterized by the following:

• extreme fluidity as measured by flow, typically between 650–750 mm on a flow table, rather than slump (height)
• no need for vibrators to compact the concrete
• easier placement
• no bleeding, or aggregate segregation
• increased liquid head pressure, which can be detrimental to safety and workmanship

SCC can save up to 50% in labor costs due to 80% faster pouring and reduced wear and tear on formwork.
In 2005, self-consolidating concretes accounted for 10–15% of concrete sales in some European countries. In the precast concrete industry in the U.S., SCC represents over 75% of concrete production. 38 departments of transportation in the US accept the use of SCC for road and bridge projects.
This emerging technology is made possible by the use of polycarboxylates plasticizer instead of older naphthalene-based polymers, and viscosity modifiers to address aggregate segregation.
It is widely used in many countries around the world due to its various properties.

Shotcrete

Shotcrete (also known by the trade name Gunite) uses compressed air to shoot concrete onto (or into) a frame or structure. The greatest advantage of the process is that shotcrete can be applied overhead or on vertical surfaces without formwork. It is often used for concrete repairs or placement on bridges, dams, pools, and on other applications where forming is costly or material handling and installation is difficult.

There are two application methods for shotcrete.

• dry-mix – the dry mixture of cement and aggregates is filled into the machine and conveyed with compressed air through the hoses. The water needed for the hydration is added at the nozzle.
• wet-mix – the mixes are prepared with all necessary water for hydration. The mixes are pumped through the hoses. At the nozzle compressed air is added for spraying.

For both methods additives such as accelerators and fiber reinforcement may be used.

Limecrete

Limecrete or lime concrete is concrete where cement is replaced by lime.We know that lime has been used since Roman Times either as mass foundation concretes or as lightweight concretes using a variety of aggregates combined with a wide range of pozzolans (fired materials) that help to achieve increased strength and speed of set. This meant that lime could be used in a much wider variety of applications than previously such as floors, vaults or domes. Over the last decade, there has been a renewed interest in using lime for these applications again. This is because of environmental benefits and potential health benefits, when used with other lime products.

Environmental Benefits :

• Lime is burnt at a lower temperature than cement and so has an immediate energy saving of 20% (although kilns etc. are improving so figures do change). A standard lime mortar has about 60-70% of the embodied energy of a cement mortar. It is also considered to be more environmentally friendly because of its ability, through carbonation, to re-absorb its own weight in Carbon Dioxide (compensating for that given off during burning).
• Lime mortars allow other building components such as stone, wood and bricks to be reused and recycled because they can be easily cleaned of mortar/limewash.
• Lime enables other natural and sustainable products such as wood (including woodfibre, wood wool boards), hemp, straw etc. to be used because of its ability to control moisture (if cement were used, these buildings would compost!).

Health Benefits :

• Lime plaster is hygroscopic (literally means 'water seeking') which draws the moisture from the internal to the external environment, this helps to regulate humidity creating a more comfortable living environment as well as helping to control condensation and mould growth which have been shown to have links to allergies and asthmas.
• Lime plasters and limewash are non-toxic, therefore they do not contribute to indoor air pollution unlike some modern paints.

 

Pervious concrete

Pervious concrete, used in permeable paving, contains a network of holes or voids, to allow air or water to move through the concrete
This allows water to drain naturally through it, and can both remove the normal surface-water drainage infrastructure, and allow replenishment of groundwater when conventional concrete does not.
It is formed by leaving out some or all of the fine aggregate (fines). The remaining large aggregate then is bound by a relatively small amount of Portland cement. When set, typically between 15% and 25% of the concrete volume is voids, allowing water to drain at around 5 gal/ft²/ min (70 L/m²/min) through the concrete.

Installation :

Pervious concrete is installed by being poured into forms, then screeded off, to level (not smooth) the surface, then packed or tamped into place. Due to the low water content and air permeability, within 5–15 minutes of tamping, the concrete must be covered with a 6-mil poly plastic, or it will dry out prematurely and not properly hydrate and cure.

Characteristics :

Pervious concrete can significantly reduce noise, by allowing air to be squeezed between vehicle tires and the roadway to escape. Pervious concrete has been tested up to 4500 psi so far.

Roller-compacted concrete

Roller-compacted concrete, sometimes called rollcrete, is a low-cement-content stiff concrete placed using techniques borrowed from earthmoving and paving work. The concrete is placed on the surface to be covered, and is compacted in place using large heavy rollers typically used in earthwork. The concrete mix achieves a high density and cures over time into a strong monolithic block. Roller-compacted concrete is typically used for concrete pavement, but has also been used to build concrete dams, as the low cement content causes less heat to be generated while curing than typical for conventionally placed massive concrete pours.

 

Glass concrete

The use of recycled glass as aggregate in concrete has become popular in modern times, with large scale research being carried out at Columbia University in New York. This greatly enhances the aesthetic appeal of the concrete. Recent research findings have shown that concrete made with recycled glass aggregates have shown better long-term strength and better thermal insulation due to its better thermal properties of the glass aggregates.

 

Asphalt concrete

Strictly speaking, asphalt is a form of concrete as well, with bituminous materials replacing cement as the binder.

 

Rapid strength concrete

This type of concrete is able to develop high resistance within few hours after being manufactured. This feature has advantages such as removing the formwork early and to move forward in the building process at
record time, repair road surfaces that become fully operational in just a few hours.

 

Rubberized concrete

While "rubberized asphalt concrete" is common, rubberized Portland cement concrete ("rubberized PCC") is still undergoing experimental tests, as of 2009.

 

Polymer concrete

Polymer concrete is concrete which uses polymers to bind the aggregate. Polymer concrete can gain a lot of strength in a short amount of time. For example, a polymer mix may reach 5000 psi in only four hours. Polymer concrete is generally more expensive than conventional concretes.

Geopolymer concrete

Geopolymer cement is an alternative to ordinary Portland cement and is used to produce Geopolymer concrete by adding regular aggregates to a geopolymer cement slurry. It is made from inorganic aluminosilicate (Al-Si) polymer compounds that can utilise 100% recycled industrial waste (e.g. fly ash, copper slag) as the manufacturing inputs resulting in up to 80% lower carbon dioxide emissions. Greater chemical and thermal resistance, and better mechanical properties, are said to be achieved for geopolymer concrete at both atmospheric and extreme conditions.
Similar concretes have not only been used in Ancient Rome (see Roman cement), but also in the former Soviet Union in the 1950s and 1960s. Buildings in Ukraine are still standing after 45 years, so this kind of formulation has a sound track record.

 

Gypsum concrete

Gypsum concrete is a building material used as a floor underlayment used in wood-frame and concrete construction for fire ratings, sound reduction,radiant heating, and floor leveling. It is a mixture of gypsum, Portland cement, and sand.

Engineered cementitious composite

Engineered Cementitious Composite (ECC), also called bendable concrete, is an easily molded mortar-based composite reinforced with specially selected short random fibers, usually polymer fibers.Unlike regular concrete, ECC has a strain capacity in the range of 3–7%,compared to 0.1% for ordinary portland cement (OPC). ECC therefore acts more like a ductile metal than a brittle glass (as does OPC concrete), leading to a wide variety of applications.

Properties :

ECC has a variety of unique properties, including tensile properties superior to other fiber-reinforced composites, ease of processing on par with conventional cement, the use of only a small volume fraction of fibers (~ 2%), tight crack width, and a lack of anisotropically weak planes.These properties are due largely to the interaction between the fibers and cementing matrix, which can be custom-tailored through micromechanics design. Essentially, the fibers create many microcracks with a very specific width, rather than a few very large cracks (as in conventional concrete.) This allows ECC to deform without catastrophic failure.
This microcracking behavior leads to superior corrosion resistance (the cracks are so small and numerous that it is difficult for aggressive media to penetrate and attack the reinforcing steel) as well as to self-healing. In the presence of water (during a rainstorm, for instance) unreacted cement particles recently exposed due to cracking hydrate and form a number of products (Calcium Silicate Hydrate, calcite, etc.) that expand and fill in the crack. These products appear as a white ‘scar’ material filling in the crack. This self-healing behavior not only seals the crack to prevent transport of fluids, but mechanical properties are regained. This self-healing has been observed in a variety of conventional cement and concretes; however, above a certain crack width self healing becomes less effective. It is the tightly controlled crack widths seen in ECC that ensure all cracks thoroughly heal when exposed to the natural environment.
When combined with a more conductive material, all cement materials can increase and be used for damage-sensing. This is essentially based on the fact that conductivity will change as damage occurs; the addition of conductive material is meant to raise the conductivity to a level where such changes will be easily identified. Though not a material property of ECC itself, semi-conductive ECC for damage-sensing are being developed.

Types :

There are a number of different varieties of ECC, including:

• Lightweight (i.e. low density) ECC have been developed through the addition of air voids, glass bubbles, polymer spheres, and/or lightweight aggregate. Compared to other lightweight concretes, lightweight ECC has superior ductility. Applications include floating homes, barges, and canoes.
• ‘Self compacting concrete’ refers to a concrete that can flow under its own weight. For instance, a self-compacting material would be able to fill a mold containing elaborate pre-positioned steel reinforcement without the need of vibration or shaking to ensure even distribution. Self-compacting ECC was developed through the use of chemical admixtures to decrease viscosity and through controlling particle interactions with mix proportioning.
• Sprayable ECC, which can be pneumatically sprayed from a hose, have been developed by using various superplasticizing agents and viscosity-reducing admixtures. Compared to other sprayable fiber-reinforced composites, sprayable ECC has enhanced pumpability in addition to its unique mechanical properties. Sprayable ECC has been used for retrofitting/repair work and tunnel/sewer linings.
• An extrudable ECC for use in the extrusion of pipes was first developed in 1998. Extruded ECC pipes have both higher load capacity and higher deformability than any other extruded fiber-reinforced composite pipes.

Field Applications :

ECC have found use in a number of large-scale applications in Japan, Korea, Switzerland, Australia and the U.S. These include:

• The Mitaka Dam near Hiroshima was repaired using ECC in 2003. The surface of the then 60-year-old dam was severely damaged, showing evidence of cracks, spalling, and some water leakage. A 20 mm-thick layer of ECC was applied by spraying over the 600 m² surface.
• Also in 2003, an earth retaining wall in Gifu, Japan, was repaired using ECC.Ordinary portland cement could not be used due to the severity of the cracking in the original structure, which would have caused reflective cracking. ECC was intended to minimize this danger; after one year only microcracks of tolerable width were observed.
• The 95 m (312 ft.) Glorio Roppongi high-rise apartment building in Tokyo contains a total of 54 ECC coupling beams (two per story) intended to mitigate earthquake damage.The properties of ECC (high damage tolerance, high energy absorption, and ability to deform under shear) give it superior properties in seismic resistance applications when compared to ordinary portland cement. Similar structures include the 41-story Nabeaure Yokohama Tower (four coupling beams per floor.)
• The 1 km (0.62 mi) long Mihara Bridge in Hokkaido, Japan was opened to traffic in 2005. The steel-reinforced road bed contains nearly 800 m3 of ECC material. The tensile ductility and tight crack control behavior of ECC led to a 40% reduction in material used during construction.
• Similarly, a 225-mm thick ECC bridge deck on interstate 94 in Michigan was completed in 2005. 30 m³ of material was used, delivered on-site in standard mixing trucks. Due to the unique mechanical properties of ECC, this deck also used less material than a proposed deck made of ordinary portland cement. Both the University of Michigan and the Michigan Department of Transportation are monitoring the bridge in an attempt to verify the theoretical superior durability of ECC; after four years of monitoring, performance remained undiminished.
• The first self-consolidating and high-early-strength ECC patch repair was placed on Ellsworth Road Bridge over US-23 in November 2006. The high-early-strength ECC can achieve a compressive strength of 23.59 ± 1.40 MPa (3422.16 ± 203.33 psi) in four hours and 55.59 ± 2.17 MPa (8062.90 ± 315.03 psi) in 28 days, allowing for fast repair and re-opening the session to traffic. The high-early-strength ECC repair has shown superior long-term durability in field conditions compared to typical concrete repair materials.