Cofferdams-Types of Cofferdam and construction

Cofferdams are enclosures built inside bodies of water such as lakes and rivers to provide a dry working environment throughout the construction period. Cofferdams are temporary dykes that are built across a body of water. They allow the water to be pumped outside, ensuring a clean and dry construction site.

This article is about the significance and definition of Cofferdam and about the different types of cofferdams preferred in construction works.

  1. Significance of cofferdams
  2. What is a Cofferdam?
  3. Types of cofferdams
    1. Earthen cofferdam
    2. Rock-fill cofferdams
    3. Single walled cofferdams
    4. Double walled cofferdams

Significance of cofferdams

Construction in water is the most challenging task in civil engineering. A safe and dry working environment is necessary to preserve the project’s safety and construction quality. However, various strategies are used to construct structures in the water and maintain the area’s dryness. One of the most popular and widely utilised ways is the use of cofferdam.

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What is a Cofferdam?

Making cofferdam involves building watertight barriers all around the construction site, pumping the water out to expose the water, and then erecting the cofferdams. For bridge piers, marine jetties, ports, etc. cofferdams are preferred. Size, water depth, water flow velocity, and other factors affect the design and types of cofferdam. Let us have a look into the types of cofferdams popularly used in construction.

Types of cofferdams

Depending on the design requirements, water depth, soil conditions, type of material used, etc., coffer dams are classified into many types.

  • Earth cofferdam
  • Rock fill cofferdam
  • Single sheet pile cofferdam
  • Double-wall sheet piling cofferdam
  • Braced cofferdam
  • Cellular cofferdam

Earthen cofferdam

Earthen cofferdam is the most common and simplest type of cofferdam. They are appropriate for locations with minimal water depth and water current. Sand, soil, clay, and boulders that are readily available locally are used to construct earthen cofferdam. The earthen cofferdam must be at least one metre above the maximum water level.

When an area of excavation is quite extensive, earthen cofferdam is used and require a sizable base area. To withstand water pressure and seepage, impervious clay core or sheet piles are driven in the centre. In order to prevent scouring and possible dam failures, the upstream side is stone-pitched. These technologies do not, however, completely provide waterproof zones. Generally, to remove the water, pumps and waterproofing systems must be installed.

Earthen Cofferdams
Earthen Cofferdams

Rock-fill cofferdams

When compared to earthen cofferdams, rockfill cofferdams are superior. The choice of rockfill dams is influenced by the cost and availability of rocks in the area. Generally, the rockfill dam’s maximum height should be limited to under 10 feet. The rockfill area is pervious and will be lined with an impervious clay layer to prevent seepage and dam failure.

Rock filled Cofferdams
Rock filled cofferdam

Single walled cofferdams

When the depth of the water is less than 6 metres and the area of work is localised, such as on a bridge pier, single-walled cofferdams are preferred. Basically, single-walled coffer dams are primarily built by driving steel sheets into the inside as a support layer after driving timber sheets into the exterior as guide piles. In situations where the water is deep, guide piles may be steel sections.

After the guide piles have been driven, wales or runners made of wood logs are bolted to the guide piles at appropriate vertical intervals. Wales are used to position the inside sheets’ distance from the wooden planks at a specific distance as shown in the figure. Mostly, these wales are fastened to the sheets using bolts from both sides.

Single walled Cofferdams
Single walled cofferdam

The inside sheet piles have strong bracing. Sandbags are positioned on both sides of the walls to increase stability even more. For clay, the penetration depth should be approximately 1 metre, 0.5-0.75 metres for sand, and 0.25-0.5 metres for gravel, etc. Construction can begin when the interior water has been pumped out.

Also Read : Reservoirs vs Dams – Reservoir – types and functions

Double walled cofferdams

Double-walled cofferdams are preferred when the construction area is large, the water depth is higher than 6 metres, and single-walled cofferdams appear to be uneconomical. Double-walled cofferdams Consist of two straight, parallel vertical walls of sheet piling coupled together, with the space between them filled with soil. If the height is greater than 3 mtr, double wall sheet piles must be strutted as illustrated in the figure.

Double walled cofferdams
Double walled cofferdams

In order to give stability to the cofferdam, the filling materials must be carefully chosen while taking the coefficient of friction into account. The sheet piles are driven into the bed in the upstream area to a good depth to avoid leaking from the ground below.

Refractory Bricks – Properties and Types

Refractory bricks, also known as firebrick are ceramic materials used to line furnaces, kilns, fireboxes, and fireplaces. A refractory brick is designed to withstand high temperatures while still having poor thermal conductivity for increased energy efficiency. Refractory bricks are used in place of regular bricks, which always have a tendency to shatter at high temperatures. These bricks may also go by the titles ceramic bricks or fire bricks. Brick is one of the most popular construction materials used since ancient times. Regular bricks tend to crack at high temperatures and are not preferred for high-temperature areas. In such conditions, conventional bricks are often replaced by Refractory bricks.

This article is about refractory brick, their types, and their properties.

  1. What are refractory bricks?
  2. Properties of Refractory brick
  3. Types of Refractory bricks
    1. Acid refractory bricks
    2. Basic refractory bricks
    3. Neutral refractory bricks

What are refractory bricks?

Refractory brick is a type of brick that can resist high temperatures. It is also known as ceramic bricks or fire bricks. Generally, they are yellowish-white in colour. These bricks have good thermal resistance and good compressive strength. The chemical composition of fire bricks differs from regular bricks’ chemical composition. It mainly consists of 25 to 30% alumina, and 60 to 70% silica. Also, oxides of magnesium, calcium, potassium etc are present. The main application of fire bricks is in the construction of kilns, furnaces, etc. They are able to withstand temperatures above 2100 degrees Celsius. Thus the thermal capacity helps the structure to be stable at high temperatures. 

refractory-bricks
refractory-bricks

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Properties of Refractory brick

Following are the properties of Refractory brick.

  • Refractory brick should resist high temperatures.
  • They have good compressive strength. 
  • The weight of fire bricks is 150 lbs per cubic ft. 
  • The size of refractory brick is 9×4.5×2.5 inches or 9×2.7×2.25 inches. 
  • They also have good chemical resistance, Since they do not react with the furnace gases. 
  • The water absorption of refractory brick is 5 to 10%. 
  • They have a high fusion point. 
refractory-brick
refractory-brick

Types of Refractory bricks

Refractory bricks are available in various sizes and shapes. There mainly three types of refractory brick

  • Acid refractory bricks
  • Basic refractory Bricks
  • Neutral refractory Bricks

Acid refractory bricks

The acid refractory brick includes silica bricks and ganister bricks. Silica brick consists of 93% of Silicon dioxide. They possess good strength and fusion points. Also, they are hard and it is suitable for acid lining in furnaces. They can withstand temperatures up to 2000 degrees Celsius. Silica bricks are made from sandstone or quartzite. Ganister bricks consist of 85% of silica, 10% clay and 2% of lime. They are also hard and can withstand temperatures up to 2100 degrees Celsius. But acid bricks are not suitable to undergo rapid temperature. Since they tend to spall. 

Basic refractory bricks

Basic refractory bricks are basic in nature. They have good corrosion resistance and chemical resistance. They consist of Magnesite bricks, dolomite bricks and Bauxite bricks. Magnesite bricks contain 85% of magnesium oxide and 3 to 5% of iron oxide. They are suitable for the lining of the furnace. They can withstand temperatures up to 1800 to 2100 degrees Celsius. Dolomite bricks can withstand temperatures up to 1400 to 1600 degrees Celsius. It contains a high amount of dolomite. Bauxite bricks are a type of basic refractories that can withstand temperatures up to 1600 degrees Celsius and contains 85% of bauxite. 

Neutral refractory bricks

Neutral refractory bricks are suitable in places to separate the acid and basic lining in the furnace. They consist of chromite bricks, carborundum, spinal bricks and forsterite bricks. These bricks have a high percentage of chrome and magnesite. 

Waffle Slab or Ribbed slab details and Construction, Advantages

Waffle slabs are ribbed reinforced concrete slabs. A waffle slab often referred to as a ribbed slab, is a structural component that is plain on top and has a grid pattern on the bottom. A waffle slab also called a two-way joist slab got ribs running perpendicular to each other in two directions on the underside. This slab resembles pockets of waffles because of its grid pattern. Hence they are named Waffle slab systems.

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For spans longer than 40 feet (12 metres), waffle slabs are chosen because they are stronger than flat slabs, flat slabs with drop panels, two-way slabs, one-way slabs, and one-way joist slabs. These are more expensive than other slabs but in turn, are more rigid and stable. Waffle slabs are apt for both ceiling and floor slabs. Slabs are one of the important structural components of a building. They provide a flat surface and help in transferring load. This article is about what is waffle slabs, the Construction process, Advantages and Disadvantages. 

  1. What is a waffle slab – Details and construction
  2. Waffle slab construction details
    1. In situ construction
    2. Precast
    3. Prefabricated
  3. Advantages of Waffle slab 
  4. Disadvantages of Waffle slab

What is a waffle slab – Details and construction

A waffle slab is a type of slab that is appropriate for industrial and commercial buildings. Waffle slabs are also referred to as two-way joist slabs or ribbed slabs. They have a flat top and grids on the underside. It has greater strength than flat slabs and hence is suited for longer spans. It enables both distributed and point vertical actions. The bottom layer of concrete reinforcement in waffle slabs is replaced by concrete ribs running in two orthogonal directions. Additionally, the rib depth should range from 135mm to 235mm. Because the overall depth of the floor increases as the depth of the ribs does. The structure’s lateral loading is impacted by this.

Waffle slab - supports and pods

Waffle slab construction details

The waffle slabs need only 70% of concrete and 80% of steel from the concrete and steel used for the construction of the raft slab. The construction stages of the waffle slab include the following

  • The first step is to create the forms
  • Place the formwork components in place.
  • Position your waffle pods or moulds on the shuttering. Generally, the pods are typically constructed of plastic, and they come in a variety of sizes and shapes. The size of the pod is determined by the requirements and span length. A significant number of pods are necessary for greater spans. Accordingly, the same size pods should be used for the entire slab.
waffle pods and beam supports
  • Place the support components horizontally and vertically according to the connectors.
  • Lay out the waffle pods and spacer within the formwork in a grid pattern beginning at one corner, following the instructions in the design.
  • Fix the pod corners to the framework using cube joints.
  • Position reinforcement bars on the spacers between the waffle Pods.
  • Reinforcement is added in the two directions after the formwork has been fixed.
  • Lay the top mesh out according to the design specifications, then secure it where necessary.
  • Making sure connecting ribs are filled, pour the concrete and give it a good vibrating.
  • After the setting of the concrete, remove the frames into which the waffles are embedded. Then slowly remove the waffle forms. 

The construction of a waffle slab can be done in three ways

In situ construction

This process entails placing formwork and pouring concrete over it. A slab is cast on-site in the desired size and according to the design.

Precast

Using this technique, the casting of the slab panel is done elsewhere, and it is then placed, connected, and reinforced with concrete.

Prefabricated

In this procedure, reinforcement is built into the slab panels using prefabricated steel bars. Slabs are manufactured elsewhere and brought to the location to be erected.

Advantages of Waffle slab 

  • It is suitable for large-span structures and can be achieved with less concrete and rebar than similar conventional slabs
  • They require only a fewer number of columns.
  • It possesses a higher load-carrying capacity
  • It has higher structural stability
  • They have a good aesthetic appearance. 
  • Waffle slabs are suitable for roof slabs and floor slabs.
  • Waffle slabs have high vibration control capacity
  • The construction of this slab can be done faster and easier.
  • They are light weighted 
  • They require low construction costs, Hence they are economical when compared to other conventional slabs of the same span
  • It requires only less amount concrete and can be reinforced with mesh or rebars.

Disadvantages of Waffle slab

  • Requires Expensive formwork
  • Requires skilled workmen and supervision for the construction of waffle slabs. 
  • Higher maintenance cost
  • The increase in the depth of ribs leads to an increase in the floor height.
  • This type of slab is not suitable for windy and slope areas.

Curing of Concrete – Concrete Curing Methods explained

Curing concrete is the process of preserving the requisite moisture and temperature in hardened concrete for continued hydration. Concrete’s curing is crucial for sustaining the material’s longevity and design strength. This article discusses the importance of curing and the various concrete curing methods prevailing on construction sites.

  1. Curing of concrete methods
  2. Why Curing of concrete is important?
  3. Concrete Curing time as per IS 456-2000
  4. Concrete curing methods
    1. Water Curing method
    2. Membrane Curing method
    3. Steam curing method
  5. Conclusion

Curing of concrete methods

Curing is the process of retaining moisture to allow fresh concrete to reach its intended strength in a predetermined manner through a hydration reaction. Concrete is a mixture of cementaggregates, and water in fixed designed proportions calculated based on specific strength requirements. The water to cement ratio is the most important factor in these proportions (Water cement ratio). In order to facilitate the hydration reaction, the water-cement ratio must be maintained. If the water evaporates quickly, there will not be enough water available for the hydration process. Because of this curing of concrete is required.

Curing assists in the retention of moisture until the hydration process is complete and it reaches the required strength. The American Concrete Institute (ACI) Committee 301 recommends a minimum cure duration equal to 70% of the required compressive strength. According to IS 456-2000 standards and construction norms, the curing period of 7 days/10 days is the time required to achieve at least 70% of the intended compressive strength. That is why concrete is cured for 7-10 days.

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Why Curing of concrete is important?

Perfect curing is necessary for the following reasons in order to achieve good strength and serviceability:

  • Curing prevents concrete from drying and maintains the acceptable temperature range by preventing moisture loss.
  • Curing increases the strength and decreases the permeability of hardened concrete.
  • Curing prevents the formation of cracks caused by thermal and plastic shrinkage.
  • Concrete curing maintains a strong link between the components and the reinforcement.
  • Curing can provide the desired strength and a durable concrete free of cracks.
  • Concrete curing assists in achieving high serviceability performance by improving abrasion resistance.

Also Read : Concrete Pumps Types – Application and advantages

Concrete Curing time as per IS 456-2000

According to the Indian Standard IS 456 – 2000, concrete should be allowed to cure for a minimum of seven days while using ordinary Portland cement and for a minimum of ten days while using blended cement or concrete with mineral admixtures. Additionally, it suggests that the curing time should not be less than 10 days for structures exposed to hot, dry weather and 14 days in case for or blended cement or cement with mineral admixtures.

OPC cement = 7 Days (Normal conditions) and 14 Days ( Hot and dry weather)

Concrete with mineral admixture or blended cement (PPC cement) = 7 Days (Normal conditions) and 14 Days ( Hot and dry weather)

Concrete curing methods

The curing method and time primarily depend on structure type, site conditions, and ingredient parameters. Some of the curing methods adopted in constructions sites are as follows.

  • Water curing
  • Membrane Curing
  • Steam curing

Water Curing method

Water curing is the most popular and common method adopted in construction sites. Basically, this method maintains or retains water on the concrete surface by various methods. This includes ponding, sprinkling and fogging, and saturated wet coverings or left-in-place forms.
Similarly, these methods prevent water loss from the concrete surface by continuous wetting of the exposed surface of the concrete.

Water curing
Water curing

Membrane Curing method

The basic concept of membrane curing is reducing the loss of water from the surface of the concrete. Generally, membrane curing methods uses curing compounds or impervious plastic sheets. Curing compounds are available in water-based and acrylic-based types. They form an impermeable membrane and reduces the loss of moisture.

Membrane curing /Curing compound
Membrane curing /Curing compound

Steam curing method

The steam curing process accelerates the process of strength gaining by using heat and providing additional moisture. Generally, this speeds up the early hardening process. Basically, these methods are familiar in prefabricated structures and factory-made precast components for the speedy recovery of form works.
Accordingly, Steam curing keeps the surface moist and raises the concrete temperature to speed up the strength achievement rate.

Steam curing - Precast factory
Precast factory

Conclusion

Now a days curing activity is not taken seriously and this hampers the strength and quality. Likewise, this is an activity to be done with utmost care to ensure design strength and serviceability of structures.

Intelligent transportation system – Components of Intelligent transportation system

Intelligent transportation system is a hot topic among all civil engineering subjects that has gained popularity and many countries are successfully implementing it. With the rapidly exploding population, ITS has even become a mandatory technique in all countries. Here, we are going to read through the main components of the intelligent transportation system. We will swim through the benefits of intelligent transportation system in the middle, then to uses and challenges of ITS.

  1. What is intelligent transportation system?
  2. Components of intelligent transportation system
  3. Benefits of intelligent transportation system
  4. Uses and challenges of intelligent transportation system
    1. 1. Use of cameras equipped with automatic number plate recognition(ANPR)
      1. Advantages
      2. Challenges
    2. 2. Speed violation recording cameras
      1.  Advantage
      2. Challenges
    3. 3. Cameras for recording violations of passing through red-lights at intersections
      1. Advantages
      2. Challenges
    4. 4. Equipping the transportation system with GPS
      1. Advantages
      2. Challenges
    5. 5. Use of intelligent routing systems for public transportation passengers
      1. Advantages
    6. 6.  Modern informative systems for offenders
      1. Advantages
      2. Challenges

What is intelligent transportation system?

What is Intelligent Transport System is the first step to dive in the topic. They are advanced applications which, aim to provide innovative services relating to different modes of transport and traffic management and enable various users to be better informed and make safer, more coordinated, and ‘smarter’ use of transport networks. In ITS the information and communication technologies are applied in the field of road transport, including infrastructure, vehicles and users, and in traffic management and mobility management, as well as for interfaces with other modes of transport.

Another answer to the question of what is Intelligent transportation system (ITS) is that, it is the application of sensing, analysis, control and communications technologies to ground transportation in order to improve safety, mobility and efficiency. ITS includes a wide range of applications that process and share information to ease congestion, improve traffic management, minimize environmental impact and increase the benefits of transportation to commercial users and the public in general.

Now, let me walk you through the main components of intelligent transportation system.

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Components of intelligent transportation system

Components of intelligent transportation systems

The main components of intelligent transportation system are,

1. Accurate tracking system
GPS enabled vehicles along with smartphone apps will help citizens to track buses and other vehicles.

2. Electronic timetables
Schedules of bus service should be updated in standard format which can be easily read by people and utilised by softwares.

3. Smart model to predict time of arrival
Transportation studies like that be conducted in IIT Madras, funded by Ministry of Urban Development. should be encouraged to obtain a robust algorithm to predict the arrival time of buses, which is what a citizen needs.

4. Standardisation by regulating authority

This is very important among all the components of intelligent transportation system. An authority should be set up which can standardise various components of the public transport and encourage the use of better and smart IT services in transport sector

5.Smart commuting

Latest information on traffic jams, accidents and ways for navigation

6. Mobile technology

App based technology, incentives for young technical entrepreneurs

7. Smart traffic control

Dynamic controls of traffic signals instead of current static control, automated system.

8. Scalability

The ITS should be easily applicable to 2nd tier cities so that problem of congestion doesn’t arise in the first place

9. Improved and better BRT system enacted with public participation

10. Installing CCTVs on traffic routes and in buses.

11. Creation of flyover and overbridges to eliminate need of traffic lights

12. Electronic payment of fare

13 Traveller’s advisory system like the use of advisory radio, SMS services, internet etc

14. Highway Management Systems: Use ramp metering techniques to measure and regulate by knowing the traffic entering or leaving the highway

15. Emergency Management Systems: To manage any unforeseen emergencies

16. Railroad Crossing: Gives signals about approaching rail junctions

17 Wireless communication System

18. Safe driving Support System

This includes,

a) Right turn collision prevention system

b) vehicle detection system
c) Pedestrian detection system

d) voice guidance

e) display warning

18. Electronic toll payment System

19. Computational technologie

20. Inductive loop detection and sensing technology

21.Freeway management.

Cool! Now how are these components of the intelligent transportation system benefiting transportation? Let’s see below.

Benefits of intelligent transportation system

traffic at night - Components of intelligent transportation systems

The main benefits of intelligent transportation are as follows.

  • Develop (and subsequently renew), a secure and effective revenue collection system – this has formed the backbone of the ITS
  • Develop enhanced operations management capabilities to provide reliable services and deal with disruptions
  • Provide communications for staff security
  • Provide improved passenger information
  • Obtain data for planning, resource optimisation and performance monitoring
  • To assist the achievement of the quantity and quality of the service required in the service contract with the province of Florence

• To generate the trip logs, analysis and reporting required by the province of Florence under the service contract

• To manage the daily operations, on both normal and disrupted state

• To manage the driver vehicle handovers and shift-changes

• To provide the platform for real-time and other information to passengers

• To provide the platform for e-ticketing

• To identify vehicle faults and assist rapid response

• To support demand responsive transport and other non-standard mobility services

• To generate and manage data for post-event analysis, including running time analysis, scheduling, resource optimization, and incident investigation

So, I walked you through the important benefits of intelligent transportation system.

Its time to see the results now.

Uses and challenges of intelligent transportation system

Components of intelligent transportation systems

1. Use of cameras equipped with automatic number plate recognition(ANPR)

Equip the intersections with traffic light crossing violations recording system and video surveillance cameras monitoring traffic flow

Advantages

Cameras are capable of fining any number of offending vehicles simultaneously

Challenges

  • Drivers cover the number plate of their cars daily in order to not to be fined
  • Some drivers who repeatedly pass specific passages try to destroy or damage the cameras and their equipment.

2. Speed violation recording cameras

Fixed cameras equipped with radar technology are assembled to identify and record speed violations

 Advantage

Assured of getting fined through being caught on camera, drivers rarely attempt to drive over the speed limit

Challenges

  • After identifying the locations where the cameras are installed, drivers may attempt to increase their speed in the distances between cameras, and this may cause many disturbances in traffic flow.
  • Due to the weakness of technology, identifying motorcycles is not possible in this system

3. Cameras for recording violations of passing through red-lights at intersections

Cameras are assembled at intersections  to record the red light running violations.

Advantages

A decrease in this kind of violation will have a direct effect in reducing car crashes and capital loss.

Challenges

  • In many intersections, due to the low quality of crosswalks and zebra crossings, it is really hard to determine a threshold running from which enables the driver to be known as an offender
  • As in many intersections, turning left or right is not legally forbidden, it is really a hard job to distinguish the vehicles doing so from the violators.

4. Equipping the transportation system with GPS

Position of the buses and the approximate arrival time of buses to stations can be calculated those who are speeding or using unauthorized routes can be identified

Advantages

  • Reduction of dangerous high speed of buses
  • Decreasing of delay time of journey

Challenges

  • Some drivers try to deactivate the GPS before attempting violation. They cover the GPS with aluminum foil to make it disconnected from the center.
  • Due to the need for a GPRS platform for sending the information to the center, using this system in Tehran is very expensive.
  • Due to the low average educational level of drivers and users of public transportation services, the relevant systematic training for using this system will be needed.

5. Use of intelligent routing systems for public transportation passengers

Passenger can receive information about the journey duration and the best manner of navigation after determining the origin and destination and also specifying the desired transportation mode such as metro, taxi, bus or walking

Advantages

 Decrease in delay of journeys and an increase in productivity.

6.  Modern informative systems for offenders

All fine notifications and notices for a technical test will be informed to the offenders via SMS

Advantages

  • Deliver the fine notifications to the offenders, omitting the process of printing and stuffing envelopes with fine notification
  •  Informing all offenders of their violations in an online manner, and creating a cohesive database of the offenders.

Challenges

  • As the telecommunications system and necessary infrastructure have not been completely developed, some problems in sending the SMS to offenders have been occasionally observed.
  •  Informative limitations such as length of words in SMS.

That’s it about ITS.

Continue learning!

MUST READ: Basic of civil engineering; Simple and in-depth guide

Construction Joints in concrete – Construction joint types in slabs

Construction joints in concrete are a crucial and fundamental component of civil engineering and construction. Changes in temperature and moisture can cause concrete to expand and contract. Because concrete is weak in tension, shrinkage and volume change in concrete cause cracks. The construction joints installed at strategic locations prevent the formation of cracks in concrete and the development of tensile stresses. A construction joint is a type of concrete joint used when a new section of concrete is poured next to an already set section of concrete. The purpose of a construction joint is to allow for some horizontal movement while remaining rigid against rotational and vertical movement. This article discusses the significance of construction joint types in concrete structures like slabs and pavements etc and their applications and features

  1. Construction joints in concrete – Significance
  2. Construction joints types
  3. Construction joints
  4. Expansion joints
  5. Contraction joints

Construction joints in concrete – Significance

In general, joints in concrete are strategically placed between slab and beam, wall and column, concrete floors, pavements and so on. Improper use of joints can result in defects, cracks, and the development of stresses. Construction joints can be filled or left empty. The space between joints is occasionally filled with materials like elastomers, bitumen asphalt mix, polysulphide sealents etc. Construction Joints also divide a larger span into smaller units, making construction easier. As a result, it also aids in preventing the total collapse of the structure. Depending on the type of joint, joints are installed either before or after the laying of concrete.

Construction joints types

On the basis of the functions, Joints in construction are classified into three types

  1. Construction joints
  2. Expansion joints
  3. Contraction joints

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Construction joints

Generally, construction is a time-consuming process. Construction joints separate the large concrete work into small units. This type of joint is apt for locations where the construction is stopped at the end of the day’s work. A construction joint is a type of concrete joint used when a new section of concrete is poured next to an already set section of concrete. The purpose of a construction joint is to allow for some horizontal movement while remaining rigid against rotational and vertical movement.Construction joints can be further classified into four types on the basis of the joint end. They are

  • Butt-type construction joint
  • Tong and groove type construction joint
  • Butt-type construction joint with dowels
  • Butt-type construction joints with tie bars
Concrete construction joints in concrete

On the basis of the structure, the construction joint can be vertical, horizontal and inclined. It is suitable for the construction of large slabs, irrigation channels, etc. These joints consist of keys at definite intervals. These keys help in resuming the work the next day. It also helps in uniform load distribution.

Expansion joints

Concrete tends to expand due to changes in temperature and moisture. This causes the development of cracks and leads to failure. To avoid this problem expansion joints are used. Another name for the expansion joint is the control joint. This joint allows the expansion of concrete without the development of stresses. Thus we can prevent cracks. Buildings longer than 45m typically have one or more expansion joints. The recommended c/c spacing in India is 30m. The joints are formed by leaving a space between the building components. Generally, the depth of the expansion joint is one-fourth of the slab thickness. Installation of expansion joints can be done before or after the laying of concrete. Before installing make sure to cut the joints deeply. It is apt between the bridge section, pavements, railway tracks etc. 

Concrete construction joints in concret

Contraction joints

Concrete is weak in tension, therefore contraction of the concrete induces stress leading to cracks. This occurs during the hardening of concrete. Contraction joints prevent the unnecessary development of cracks. This type of joint in construction is installed before the laying of concrete. It is apt during the construction of roads, retaining walls, floors, tunnels, canals, etc. Generally, the interval of contraction joints is between 5m to 10m. Jointing tools are used for the installation of contraction joints. If the concrete is reinforced, then contraction joints can be avoided. But in un-reinforced or lightly reinforced slabs this joint is necessary to minimise the formation of cracks. 

Construction joints in concrete

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