CONSTRUCTION TECHNIQUES

Module 3:
RMC Plant-
 Few things are more aggravating to produce on a worksite than concrete. Bags of cement,
sand, aggregate (gravel) and possibly other additives must be delivered to the
construction area. A supply of clean water is also necessary, along with a rented concrete
mixing hopper.
 Even after all the dusty and heavy ingredients have been loaded into the hopper, one
small error in the wet/dry ratio can render an entire batch of concrete unusable. One
common solution to this messy and time-consuming problem is “READY MIX
CONCRETE”.
 Ready-mix concrete (RMC) is a ready-to-use material, with predetermined mixture of
cement, sand, aggregates and water. RMC is a type of concrete manufactured in a factory
according to a set recipe or as per specifications of the customer, at a centrally located
batching plant.
 It is delivered to a worksite, often in truck mixers capable of mixing the ingredients of the
concrete en route or just before delivery of the batch.
 This results in a precise mixture, allowing specialty concrete mixtures to be developed
and implemented on construction sites.
 The second option available is to mix the concrete at the batching plant and deliver the
mixed concrete to the site in an agitator truck, which keeps the mixed concrete in correct
form. In the case of the centrally mixed type, the drum carrying the concrete revolves
slowly so as to prevent the mixed concrete from "segregation" and prevent its stiffening
due to initial set.
 The use of the RMC is facilitated through a truck-mounted boom placer' that can pump
the product for ready use at multi-storied construction sites. A boom placer can pump the
concrete up 80 meters.
 RMC is preferred to on-site concrete mixing because of the precision of the mixture and
reduced worksite confusion. It facilitates speedy construction through programmed
delivery at site and mechanized operation with consequent economy.
 It also decreases labour, site supervising cost and project time, resulting in savings.
Proper control and economy in use of raw material results in saving of natural resources.
It assures consistent quality through accurate computerized control of aggregates and
water as per mix designs. It minimizes cement wastage due to bulk handling and there is
no dust problem and therefore, pollution-free.
 Ready mix concrete is usually ordered in units of cubic yards or meters. It must remain in
motion until it is ready to be poured, or the cement may begin to solidify. The ready mix
concrete is generally released from the hopper in a relatively steady stream through a
trough system. Workers use shovels and hoes to push the concrete into place.
 Some projects may require more than one production run of ready mix concrete, so more
trucks may arrive as needed or additional batches may be produced offsite and delivered.
 However there are some disadvantages of RMC to, like double handling, which results in
additional cost and losses in weight, requirement of god owns for storage of cement and
large area at site for storage of raw materials.
 Aggregates get mixed and impurities creep in because of wind, weather and mishandling
at site. Improper mixing at site, as there is ineffective control and intangible cost
associated with unorganized preparation at site are other drawbacks of RMC.
 There are always possibilities of manipulation; manual error and mischief as concreting
are done at the mercy of gangs, who manipulate the concrete mixes and water cement
ratio.
 The first ready-mix factory, which was built in the 1930s, remained in a standstill position
till 1960s, but continued to grow since then.

History:
 Ready mix concrete was first patented in Germany in 1903, its commercial delivery was
not possible due to lack of transportation needs.
 The first commercial delivery was made in Baltimore USA in 1913.The first revolving
drum type transit mixer was developed in 1926. In 1931, a RMC plant was set up for the
construction of Heathrow airport, London.
 In the mid 90’s there were about 1100 RMC plants in UK consuming about 45% of
cement produced in that country. In Europe in 1997 there were 5850 companies
producing a total of 305 million cusecs of RMC. In USA by 1990, around 72% (more
than 2/3rd) of cement produced was being used by various RMC plants. In Japan first
RMC plant was set up in 1949. By 1992 Japan was the then largest producer of RMC,
producing 18196 million tons of concrete. in many other countries of the world including
some of the developing countries like Taiwan, Malaysia etc, RMC industry is well
developed.
Development in India:
 In India RMC was first initially was used in 1950 during the construction sites of Dams
like likeBhakraNangal, Koyna. At the construction the transportation of concrete is done
by either manually or mechanically using ropeways &buckets or conveyor systems. RMC
at Pune in the year 1991. However, due to various pit falls and problems this plant did not
survive for long and was closed. Within a couple of months in the year 1993, two RMC
plants were set up in Mumbai to commercially sell RMC to the projects where they were
installed. Unitech Construction set up one plant at Hiranandani Complex and Associated
Cement Companies set up another plant at Bharat Diamond Bourse Commercial
Complex.
 The first concrete mixed off site and delivered to a construction site was effectively done
in Baltimore, United States in 1913 just before the First World War.
 The increasing availability of special transport vehicles, supplied by the new and fast-
growing automobile industry, played a positive role in the development of RMC industry.
Layout of RMC Plant-

Fig. 3.1: Layout of RMC Plant

The layout of RMC plant can vary depending on the available space, local regulations, and
production capacity. However, a typical layout includes:
1. Batching Area:
This area houses the batching system, including weigh hoppers, conveyors, and aggregate
storage bins.
2. Mixing Area:
The mixing unit is located here, and it can be a central mixer or a portable mixer truck
loading station.
3. Cement Silos:
Cement silos are often positioned near the mixing area for easy access.
4. Water and Admixture Storage:
Tanks or containers for water and admixtures are located near the mixing area for
convenience.
5. Control Room:
The control room oversees the entire plant's operation and is equipped with monitoring
and control systems.
6. Truck Loading Area:
Ready-mixed concrete is loaded onto transit mixer trucks for delivery to construction
sites. This area should be easily accessible for trucks.

Working of RMC Plant:

A Ready-Mix Concrete (RMC) plant is a specialized facility that produces concrete mixtures
in large quantities based on a predefined mix design. RMC is a type of concrete that is
manufactured at a central plant and then transported to construction sites in a ready-to-use
form. Here’s how an RMC plant typically works:
1. Aggregate Storage and Handling:
 The process begins with the storage of aggregates such as sand, gravel, and crushed
stone in separate bins or compartments. These aggregates are the primary components
of concrete.
 Each aggregate type is stored in designated bins and is typically organized by size and
type.
2. Cement Storage and Handling:
 Cement, the binding agent in concrete, is stored in silos or large storage containers.
These silos are often equipped with systems to control the flow and measure the
amount of cement being dispensed.
3. Water and Admixture Storage:
 Water and chemical admixtures are also stored in tanks or containers. Admixtures are
used to modify the properties of the concrete, such as setting time, workability, or
strength.
4. Weighing and Batching:
 To ensure the correct proportions of aggregates, cement, water, and admixtures, the
RMC plant uses sophisticated batching equipment. This equipment precisely
measures and weighs each component according to the mix design specified for a
particular order.
 The batchers discharge the measured materials into a mixing drum or mixer truck in
the predetermined order.
5. Mixing:
 The mixing process occurs in a rotating drum or mixing truck. The drum's blades or
agitators thoroughly blend the materials, ensuring uniformity and consistency.
 Mixing times may vary depending on the type of mixer and the specific mix design,
but they typically last for a few minutes.
6. Quality Control & Testing:
 RMC plants often have quality control measures in place to ensure that the produced
concrete meets the specified standards and mix design.
 Samples of the concrete are routinely taken for testing, including workability, slump,
compressive strength, and other properties.
7. Transportation:
 Once the concrete is thoroughly mixed and quality-checked, it is loaded into concrete
mixer trucks, also known as transit mixers.
 These mixer trucks are equipped with rotating drums to keep the concrete agitated
during transportation to prevent segregation or setting.
8. Delivery to the Construction Site:
 The mixer trucks transport the ready-mix concrete to construction sites. The concrete
is delivered directly to the location where it is needed, ensuring minimal waste and
efficient placement.
 Depending on the project, concrete may be discharged directly from the mixer truck
or pumped to the desired location.
9. Placement & Use:
 At the construction site, the concrete is placed into forms, molds, or directly into the
desired area.
 Construction workers work quickly to finish and shape the concrete before it sets.
10. Curing:
 After placement, the concrete requires proper curing to achieve its design strength and
durability. Curing can involve covering the concrete with wet burlap, plastic sheeting,
or applying curing compounds.
11. Cleanup:
 After the concrete has been placed and cured, the RMC plant and construction site are
cleaned and any excess materials are disposed of properly.
RMC plant provides several advantages, including consistent quality, reduced on-site labor
requirements, efficient material usage, and the ability to meet strict project specifications. It is
a valuable resource for large-scale construction projects where high-quality concrete is
required.

Production capacity-
The production capacity of RMC plant can vary significantly based on its size and
equipment. Small plants may have a production capacity of 20 to 60 cubic meters per hour,
while larger plants can produce several hundred cubic meters per hour. The capacity is
determined by factors like the number of mixers, batching efficiency, and the number of
trucks available for delivery. Plant operators can adjust production capacity by controlling
batching times and mixer utilization.
Type of concrete mixers-
1. Batch Concrete Mixer:
Use: Batch mixers are commonly used in small to medium-sized construction projects.
They are versatile and suitable for mixing concrete, mortar and other materials in batches.
Operation: Batch mixers load the ingredients into a drum or pan and mix them until the
desired consistency is achieved.
2. Continuous Concrete Mixer:
Use: Continuous mixers are used for large-scale construction projects or projects with
high concrete demand. They are efficient and provide a continuous supply of concrete.
Operation: Continuous mixers continuously feed ingredients into a mixing drum,
ensuring a consistent flow of mixed concrete.

Fig. 3.2: Continuous Concrete Mixer

3. Tilting Drum Concrete Mixer:

Use: Tilting drum mixers are widely used in small to medium-sized construction sites.
They are portable and convenient for on-site mixing.
Operation: The drum of these mixers tilts to pour the concrete mix, making them
suitable for both mixing and pouring.

Fig. 3.3: Tilting Drum Concrete Mixer

4. Non-Tilting Drum Concrete Mixer:

Use: Non-tilting drum mixers are typically used for larger construction projects. They are
less portable but can handle larger batches.
 Operation: The drum of these mixers does not tilt. Instead, the ingredients are loaded and
discharged from the same end.

Fig. 3.4: Non-Tilting Drum Concrete Mixer

5. Pan Concrete Mixer:
Use: Pan Mixers are used for mixing small quantities of concrete or for specialized
applications like refractory and precast concrete.
Operation: A pan mixer has a stationary mixing pan and a set of rotating blades or
paddles that mix the ingredients within the pan.

Fig. 3.5: Pan Concrete Mixer

6. Twin-Shaft Concrete Mixer:

Use: Twin-shaft mixers are suitable for large-scale projects that require high-quality,
uniform concrete mixes. They are commonly used in precast and high-performance
concrete applications.
Operation: Twin-shaft mixers have two horizontal shafts with counter-rotating blades
that provide intense mixing action.

(a) (b)
Fig. 3.6: Twin-Shaft Concrete Mixer
7. Planetary Concrete Mixer:
Use: Planetary mixers are known for their thorough and efficient mixing. They are used
in applications that require precise and consistent mixing, such as in the production of
concrete blocks and precast products.
Operation: A planetary mixer has a vertically oriented mixing drum with a set of rotating
blades that move both vertically and horizontally.

(a) (b)
Fig. 3.7: Planetary Concrete Mixer

8. Volumetric Concrete Mixer:

Use: Volumetric mixers are versatile and suitable for remote or mobile construction sites
where ready-mix concrete delivery may not be readily available.
Operation: These mixers mix concrete on-site by proportioning and blending the raw
materials, such as cement, aggregates, and water, as needed.

Fig. 3.8: Volumetric Concrete Mixer

9. Reversing Drum Concrete Mixer:

Use: Reversing drum mixers are commonly used in small construction projects and for
mixing specialty concrete products.
Operation: These mixers have a rotating drum that can mix in both directions, allowing
for efficient and thorough mixing.
 Fig. 3.9: Reversing Drum Concrete Mixer
The choice of concrete mixer depends on the scale of the project, the required quality of the
concrete mix, the available space, and the mobility requirements. Different mixers excel in
various situations, from small-scale residential projects to large-scale commercial and
industrial construction.

Machinery for vertical and horizontal transportation of concrete-

Concrete is often transported vertically and horizontally using various types of machinery and
equipment to ensure efficient and safe construction processes. Here are some common
machines used for vertical and horizontal transportation of concrete:
1. Vertical Transportation of Concrete:
A. Concrete Pump:
Use: Concrete pumps are widely used for vertical transportation, especially in high-
rise construction projects. They efficiently deliver concrete to elevated or hard-to-
reach locations, such as upper floors or the tops of tall buildings.
Operation: A concrete pump uses a hydraulic system to pump concrete through a
network of pipes and hoses. It can be either a truck-mounted pump or a stationary
pump.
B. Boom Truck or Concrete Placing Boom:
Use: Boom trucks or concrete placing booms are equipped with extendable arms or
booms that can reach over obstacles or into tight spaces to place concrete precisely.
Operation: The operator positions the boom to the desired location, and concrete is
poured directly from the end of the boom, allowing for accurate placement.
2. Horizontal Transportation of Concrete:
A. Concrete Mixer Truck:
Use: Concrete mixer trucks are commonly used for horizontal transportation of
freshly mixed concrete from the batching plant to the construction site. They are
essential for most construction projects.
Operation: These trucks have a rotating drum that keeps the concrete mixed and in a
liquid state during transport. The drum is rotated during transit to prevent the concrete
from settling.
B. Belt Conveyors:
Use: Belt conveyors are used for horizontal transportation over short to medium
distances. They are often employed to transfer concrete from a batching plant to a
specific location on the construction site.
 Operation: The conveyor belt moves continuously, carrying concrete from one point
to another. Belt conveyors are particularly useful when a consistent flow of concrete
is required.
C. Bucket and Crane:
Use: In situations where a short horizontal transfer of concrete is needed, a bucket
attached to a crane can be used to transport and pour concrete.
Operation: The crane operator lifts the bucket filled with concrete and maneuvers it
to the desired location for discharge.
D. Chute and Wheelbarrow:
Use: For relatively short distances and small quantities of concrete, a chute may be
attached to the discharge end of the concrete mixer truck. Workers can then use
wheelbarrows to move the concrete to the precise location.
Operation: Concrete flows through the chute into the wheelbarrows, which are
manually transported to the required location.
E. Concrete Conveyor Systems:
Use: Specialized conveyor systems, such as conveyor belts or slingers, are used for
horizontal transportation of concrete over long distances or across challenging
terrains.
Operation: These systems can be automated or operated manually to move large
quantities of concrete efficiently.
The choice of machinery for concrete transportation depends on factors like the distance to be
covered, accessibility of the construction site, the volume of concrete required, and the
specific requirements of the project. Proper planning and selection of the appropriate
equipment are crucial for ensuring the efficient and safe transportation of concrete during
construction.

Grouting-
Grouting is a construction technique used to fill voids, gaps, or spaces in the ground or
structures with a fluid material known as grout. Grout is typically a mixture of water, cement,
and sometimes additives, designed to fill and seal gaps improve structural integrity, or
stabilize the surrounding environment. Grouting is a versatile method employed in various
construction and engineering applications.

Uses of Grouting:
 Foundation Stabilization: Grouting is used to improve the load-bearing capacity and
stability of foundations by filling voids or weak soil layers beneath them.
 Tunnelling and Mining: In underground construction, grouting can be used to control
water ingress, stabilize the tunnel or mine walls, and enhance ground support.
 Soil and Rock Anchoring: Grouting is used to anchor structures or reinforcement
elements (such as rock bolts or soil nails) into the surrounding soil or rock, increasing
their stability.
 Sealing Leaks: Grouting is employed to seal leaks in structures such as dams, tunnels,
and underground pipelines to prevent water infiltration.
 Void Filling: Grout is used to fill voids or cavities left behind during excavation, mining,
or other construction activities.
 Underpinning: Grouting can be used as part of underpinning procedures to lift and
stabilize settled or sinking structures.
 Injection Grouting: This technique involves injecting grout into cracks, joints, or gaps in
concrete or masonry structures to improve their integrity and prevent water penetration.

Types of Grouting:
1. Cement Grouting:
This is the most common type of grouting and involves mixing Portland cement with
water to create a dense and durable grout. It is often used for soil stabilization and
foundation underpinning.

Fig. 3.10: Cement Grouting

2. Chemical Grouting:
Chemical grouting uses specialty chemicals and resins instead of cement to create a grout
that can be injected into soil or structures. It is often used for soil improvement, sealing
leaks, and underpinning.
 Fig. 3.11: Chemical Grouting

3. Pressure Grouting:
In pressure grouting, grout is injected into the ground or structures under pressure to
ensure it penetrates voids and cracks effectively.

Fig. 3.12: Pressure Grouting

4. Compaction Grouting:
This technique involves injecting a low-slump, highly compacted grout to densify and
strengthen loose or unstable soil.

Fig. 3.13: Compaction Grouting (Compaction by displacement of soil grains by grouts)

5. Jet Grouting:
Jet grouting uses high-pressure jets to mix grout with the surrounding soil or rock,
creating a homogeneous mass. It is used for soil improvement and creating underground
barriers.

Fig. 3.14: Jet Grouting (Partial replacement/mixed in place)

6. Permeation Grouting:
Permeation grouting involves injecting a low-viscosity grout into the ground to fill and
stabilize fine fractures and pores.

Fig. 3.15: Permeation Grouting (Grouts flowing into void space)

7. Slurry Grouting:
Slurry grouting uses a mix of cement, water, and additives to create a flow able grout
suitable for filling large voids or annular spaces.

Advantages of Grouting:
 Strengthening: Grouting can improve the stability and load-bearing capacity of
foundations and soil.
 Waterproofing: It can seal cracks and prevent water infiltration in structures.
 Soil Improvement: Grouting can densify loose or granular soil, enhancing its
engineering properties.
 Versatility: Different types of grouting can be tailored to specific project requirements.
 Longevity: Well-executed grouting can provide long-lasting results.
Disadvantages of Grouting:
 Cost: Grouting can be expensive, depending on the project scope and materials used.
 Skilled Labour: Proper grouting requires skilled operators and careful execution.
 Environmental Concerns: The disposal of grouting materials and their environmental
impact should be considered.
 Material Selection: Choosing the wrong grout type or mix design can lead to ineffective
results.
Grouting operations require careful planning, proper material selection, and skilled execution
to achieve the desired results. The choice of grouting method depends on the specific project
requirements, the type of ground or structure being treated, and the desired outcomes, such as
stabilization, waterproofing, or sealing.

Shotcreting-
Shotcreting, also known as shotcrete, is a construction technique that involves spraying or
“shooting” a mixture of cement, aggregates, water, and sometimes additives onto a surface at
high velocity. This process creates a layer of concrete that adheres to the receiving surface
without the need for formwork, making it a versatile and widely used construction method.

Uses of Shotcreting:
 Tunnel Construction: Shotcrete is commonly used to line tunnels and underground
passages, providing structural support and preventing water ingress.
 Slope Stabilization: It is used to reinforce and stabilize slopes, especially in areas prone
to landslides and erosion.
 Swimming Pool Construction: Shotcrete is often used for constructing the shell of
swimming pools, providing a durable and watertight structure.
 Retaining Walls: Shotcrete can be applied to create retaining walls, especially in
challenging terrain where traditional wall construction methods are impractical.
 Repair and Rehabilitation: Shotcrete is employed for repairing and rehabilitating
deteriorating concrete structures, such as bridges and buildings.
 Mining and Underground Excavations: In mining operations, shotcrete is used for
ground support and for preventing rockfalls in underground excavations.
 Decorative Applications: It can be used for decorative finishes, such as artistic
sculptures and architectural details.

Types of Shotcreting:
1. Dry-Mix Shotcrete:
In this method, dry ingredients (cement and aggregates) are pre-mixed and fed into a
nozzle. Water is added at the nozzle, where it combines with the dry mix and is sprayed
onto the surface.
2. Wet-Mix Shotcrete:
In wet-mix shotcreting, all ingredients (cement, aggregates, water, and sometimes
additives) are mixed together in a concrete mixer before being pumped through a hose to
the nozzle, where it is sprayed onto the surface.
Advantages of Shotcreting:
 Rapid Application: Shotcreting is a fast construction method, allowing for quick project
completion.
 Adaptability: It can be applied to various surfaces, including irregular or vertical ones,
without the need for formwork.
 Enhanced Strength: Shotcrete typically has improved compressive strength compared to
traditional cast-in-place concrete.
 Reduced Formwork: Shotcreting eliminates the need for traditional formwork, saving
time and materials.
 Excellent Bonding: Shotcrete adheres well to existing surfaces, providing good bonding
and preventing delamination.

Disadvantages of Shotcreting:
 Skilled Labor: Shotcreting requires skilled operators to achieve proper thickness and
finish.
 Equipment Costs: The equipment needed for shotcreting can be costly, especially for
large projects.
 Material Waste: Overspray and rebound (material that does not adhere to the surface)
can lead to material wastage.
 Dust and Safety Concerns: Dry-mix shotcreting can generate dust, which may pose
health and safety risks to workers.
 Quality Control: Maintaining consistent quality can be challenging, especially with wet-
mix shotcreting, which relies on proper mixing and pumping.
Overall, shotcreting is a versatile construction technique with advantages in terms of speed,
adaptability, and strength. However, it requires skilled operators and proper equipment to
ensure successful and safe application.

Underwater concreting-
Underwater concreting is a construction technique that involves the placement, compaction,
and curing of concrete underwater. It is used in various civil engineering and marine
construction projects where structures need to be built or repaired beneath the water surface.

Uses of Underwater Concreting:

 Bridge Construction: Underwater concreting is used to construct bridge piers and
foundations in rivers, lakes, or coastal areas.
 Port and Harbour Development: It is employed for the construction and repair of quay
walls, breakwaters, and other maritime structures.
 Dam Construction: Underwater concreting is used to build and maintain dams,
spillways, and reservoir structures.
 Pipeline Installation: In offshore oil and gas projects, concrete is placed underwater to
secure and protect pipelines and risers.
 Subsea Tunnels: It is used for constructing subsea tunnels, such as underwater highway
tunnels or utility tunnels.
Types of Underwater Concreting:
1. Tremie Method:
The tremie method is the most common and widely used technique for underwater
concreting. It involves lowering a tremie pipe filled with concrete to the desired depth. As
the tremie pipe is gradually raised, concrete is released, displacing the water and filling
the forms.
2. Pumping Method:
In this method, a specialized underwater concrete pump is used to deliver concrete to the
placement location. The pump is positioned on a barge or platform, and the concrete is
pumped through a delivery hose or pipeline to the submerged area.

Methods of Underwater Concreting:

1. Drysuit Method:
In this method, divers wear drysuits equipped with umbilicals (hoses) that supply air and
communication. Divers place and compact the concrete manually.
2. Wet Method:
The wet method involves placing the concrete underwater without direct human contact.
It is commonly used with the tremie and pumping methods.

Advantages of Underwater Concreting:

 Structural Integrity: Underwater concreting allows for the construction of stable and
durable marine structures.
 Reduced Formwork: It eliminates the need for extensive formwork and falsework
typically required for above-water construction.
 Rapid Construction: Underwater concreting can expedite project schedules by allowing
continuous construction even in submerged conditions.
 Cost-Effective: In many cases, underwater concreting can be more cost-effective than
constructing cofferdams or dry construction methods.

Disadvantages of Underwater Concreting:

 Skilled Labor: Underwater concreting requires highly skilled and certified divers who
can work safely and effectively in challenging underwater conditions.
 Quality Control: Ensuring the quality of underwater concrete can be more challenging
due to limited visibility and accessibility.
 Environmental Considerations: Special attention must be given to environmental
impacts and the prevention of pollution during underwater concreting.
 Safety Risks: Working underwater poses unique safety risks, including decompression
sickness and limited visibility.
 Equipment Requirements: Specialized equipment, such as tremie pipes, underwater
pumps, and diving gear, is necessary, which can add to project costs.
Underwater concreting is a specialized construction technique that is crucial for various
marine and underwater projects. It offers advantages in terms of structural integrity and
project efficiency but requires careful planning, skilled labour, and adherence to safety and
environmental guidelines.

Type of formwork-
Formwork, also known as shuttering or moulds, is a temporary structure or framework used
in construction to support freshly poured concrete or other materials until they achieve
sufficient strength and stability. It defines the shape and structure of the final product and
plays a crucial role in ensuring the accuracy and quality of concrete structures.

Components of Formwork:
1. Forms:
Forms are the primary elements of formwork and are typically made from materials like
timber, plywood, steel, aluminum, or even plastic. They define the shape and dimensions
of the concrete element being cast.
2. Shores and Props:
Shores and props are vertical supports that provide the necessary stability to the
formwork, ensuring that it can withstand the weight of the concrete and other loads.
3. Braces:
Braces are diagonal or horizontal supports that help maintain the structural integrity of the
formwork by preventing it from shifting or collapsing during the concrete pour.
4. Ties and Fasteners:
Ties and fasteners are used to secure the forms in place and hold them tightly against the
lateral pressure exerted by the wet concrete. They can be removable or integral to the
forms.

Types of Formwork:
1. Traditional Timber Formwork:
This type of formwork uses timber as the primary material for both forms and supports. It
is commonly used in smaller construction projects and for simple concrete structures.
2. Engineered Formwork System:
Engineered formwork systems use prefabricated components made of steel, aluminum, or
engineered wood. They are designed for efficiency, reusability, and ease of assembly.
Examples include system formwork and table formwork.
3. Plastic Formwork:
Plastic formwork is made of lightweight, durable plastic materials. It is known for its ease
of handling, low maintenance, and reusability, making it suitable for various construction
applications.
4. Insulating Concrete Forms (ICFs):
ICFs consist of foam blocks or panels that are assembled to create formwork for casting
insulated concrete walls. They provide both structure and insulation.
5. Slip Formwork:
Slip formwork, or sliding formwork, is a continuous formwork system that is used for
casting tall vertical concrete structures, such as towers and chimneys. The formwork
 moves gradually upward as concrete is poured, creating a continuous and uninterrupted
structure.

Uses of Formwork:
Formwork is used in various construction applications to shape and support concrete or other
materials. Some common uses include:
 Slabs and Beams: Formwork is used to create horizontal surfaces, such as slabs and
beams, in buildings and bridges.
 Columns: Formwork is employed to shape and support the vertical columns that provide
structural support to a building or structure.
 Walls: Formwork is used to create both exterior and interior walls of buildings and other
concrete structures.
 Foundations: Formwork is essential for casting concrete foundations, including footing
and foundation walls.
 Stairs: Formwork is used to construct concrete staircases and landings.
 Bridges: In bridge construction, formwork is used to shape the components like piers,
abutments, and bridge decks.
 Tunnels: Formwork is employed in tunnel construction to create the lining of the tunnel.
 Retaining Walls: Formwork is used to construct retaining walls that provide structural
support and retain soil.
 Specialized Structures: Formwork is used in the construction of specialized structures,
such as water tanks, silos, and reservoirs.
Properly designed and installed formwork is essential for ensuring that concrete structures are
built with precision and accuracy. It helps achieve the desired architectural and structural
specifications and ensures the safety and integrity of the construction process.

Slip formwork-
Slip formwork, also known as sliding formwork or continuous formwork, is a construction
technique used to cast tall vertical concrete structures, such as towers, chimneys, silos, and
cores of high-rise buildings, in a continuous, uninterrupted process. Unlike traditional
formwork systems, where forms are fixed and removed after the concrete has set, slip
formwork involves a continuously moving formwork system that gradually rises as the
concrete is poured and sets.

Components of Slip Formwork:

1. Formwork:
The formwork in slip formwork consists of a vertically adjustable mold or shuttering
system that shapes the concrete structure.
2. Platform:
A working platform is built at the top of the slip form to provide a safe and stable
workspace for workers to place and finish the concrete.
3. Hydraulic Jacks:
Hydraulic jacks or other lifting mechanisms are used to raise and lower the formwork.
Process of Slip Formwork:
The slip formwork process typically involves the following steps:
1. Initial Setup: The formwork is initially set at the base of the structure, and the concrete
pouring begins.
2. Continuous Pouring: Concrete is continuously poured into the formwork as it gradually
rises.
3. Vibration and Consolidation: Vibrators are often used to ensure that the freshly poured
concrete is properly consolidated and free of air voids.
4. Curing: As the formwork moves upward, the concrete is allowed to cure, gaining
sufficient strength to support its weight.
5. Vertical Movement: Hydraulic jacks or other lifting mechanisms raise the formwork at a
controlled rate, typically a few centimeters per hour.
6. Reinforcement Installation: In some cases, reinforcing steel or other structural elements
are incorporated into the formwork as it moves upward.
7. Finishing: Workers at the top of the formwork platform finish the concrete surface as it
emerges from the form.
8. Completion: The process continues until the desired height of the structure is achieved or
until it reaches the top of the slip form.

Advantages of Slip Formwork:

 Efficiency: Slip formwork allows for continuous construction, which can be faster than
traditional formwork systems.
 Consistency: The process results in a uniform and consistent concrete structure.
 Cost-Effective: It can reduce labour and material costs compared to other methods,
especially for tall structures.
 Safety: Workers are often confined to a protected platform, reducing the risk of falls and
other on-site accidents.

Disadvantages of Slip Formwork:

 Limited Versatility: Slip formwork is primarily suitable for vertical structures and may
not be practical for more complex shapes.
 Equipment and Expertise: Specialized equipment and skilled operators are required,
which may not be readily available in all locations.
 Initial Setup: The initial setup can be time-consuming, and the method may not be cost-
effective for smaller projects.
 Limited Access: The continuous nature of the process makes it challenging to access
specific areas for inspections or repairs.
Slip formwork is particularly valuable for constructing tall and straight concrete structures
efficiently. It is commonly used in the construction of high-rise buildings, chimneys, silos,
and other vertical elements where speed and precision are essential.
Placing concrete in normal and difficult situations requires a range of equipment to ensure
that the concrete is properly deposited, spread, and compacted. The choice of equipment
depends on factors such as the type of project, the accessibility of the construction site, the
volume of concrete to be placed, and the specific challenges posed by the site conditions.
Here is a list of equipment commonly used for placing concrete in various situations:

Equipment for placing of concrete in normal situations-

 Concrete Mixer Truck:
Used for transporting and delivering freshly mixed concrete from the batching plant to the
construction site. It has a rotating drum to keep the concrete in a liquid state during
transit.
 Concrete Pump:
Concrete pumps are used to deliver concrete to elevated or hard-to-reach areas. They
come in two main types: boom pumps and line pumps.
 Vibrators:
Internal and external vibrators are used to consolidate and remove air voids from freshly
poured concrete, ensuring proper compaction.
 Buckets and Wheelbarrows:
These manual tools are used for transporting small quantities of concrete within the
construction site.
 Concrete Chute:
A concrete chute is a long, sloping trough or pipe used to direct the flow of concrete from
the delivery point to the desired location within the forms.
 Straightedges and Screeds:
These tools are used to level and strike off the surface of the concrete to the desired grade
and elevation.
 Bull Float:
A bull float is a large, flat tool with a long handle used to smooth and finish the surface of
the concrete.

Equipment for placing of concrete in difficult situations-

 Concrete Pump with Boom Extension:
When faced with obstacles or hard-to-reach areas, a concrete pump with a boom
extension can provide additional reach and flexibility.
 Tremie Pipe:
Tremie pipes are used for placing concrete underwater or in situations where free fall of
concrete would cause segregation or contamination.
 Chutes with Hoppers:
For precise placement in vertical forms, chutes with hoppers are used to control the flow
of concrete.
 Concrete Buckets with Gates:
These buckets have gates or chutes that can be opened and closed to control the flow of
concrete during placement.
 Skip Hoists and Belt Conveyors:
These systems are used to transport concrete vertically in situations where it needs to be
lifted to higher levels.
 Placing Booms:
Placing booms are often used in high-rise construction projects to distribute concrete to
different floors and areas of the building.
 Pneumatic Concrete Conveyors:
These systems use air pressure to transport concrete over long distances or to difficult-to-
reach locations.
 High-Pressure Air or Water Injection:
In soil improvement projects, high-pressure injection systems can be used to place grout
or concrete in the ground.
 Specialized Forms:
In some cases, specialized formwork systems are used to shape and direct the flow of
concrete in complex or intricate structures.
 Shotcrete Equipment:
For applications like slope stabilization or tunnel construction, shotcrete equipment is
used to spray concrete onto surfaces in a controlled manner.
The selection of equipment for placing concrete in difficult situations depends on the specific
challenges posed by the project. Safety and proper planning are crucial when dealing with
challenging placements to ensure that the concrete is placed correctly and efficiently.