Plastering is the process of covering the walls with plaster. The main purpose of doing plastering is to provide a smooth finishing surface and for avoiding deterioration of the walls.
Plaster is a plastic material that is a mixture of cement, sand with water. A good plaster should not show any volume change after drying and should not develop cracks. It also helps in making the structure weather resistant and durable. Plastering can be done on external as well as internal walls.
The choice of ratio of cement mortar for plastering can be chosen on the basis of requirement. In this article, we will discuss the various types of plastering in a building.
Types of Plastering
There are different types of plastering used in construction:
Cement plastering
Lime plastering
Mud plastering
Stucco plastering
Gypsum plastering
1. Cement plastering
Cement plastering is a type of plastering consisting of a mixture of portland cement, sand and water in appropriate proportion. The minimum thickness of cement plaster should be 10 mm. For brick walls, thickness plastering is between 15 mm to 20 mm.
Also, Plastering is applicable for both internal and external walls. Cement plastering is mostly suitable for damp conditions. It acts as a protective layer and avoids corrosion. For RCC surfaces, 1:3 or 1:4 cement plaster is applicable. For external walls 1:5 or 1:8 cement plaster is applicable. After plastering, to avoid the developing of cracks, curing is done.
2. Lime plastering
Lime plaster consists of lime, sand and water. Since it consists of lime it is called lime plaster. Non-hydraulic hydrated lime is used in Lime plastering. It is one of the oldest plastering methods. When comparing with cement plaster, lime plaster has low binding capacity and delay in setting. The ratio of lime and sand for this plaster is 1:3 to 1:4.
3. Mud plastering
Mud plastering is one of the cheapest types of plastering. Another name of mud plaster is earthen plaster. Before plastering, eliminate dust and scrap the surface for making it rough. Generally, mud plastering is done in two coats. The thickness of the first coat is 18 mm and that of the second coat should be 6 to 7 mm. This plastering is less toxic and eco-friendly.
4. Stucco plastering
Stucco plastering is a type of plastering that gives an aesthetic appearance. It consists of aggregates, binders and water. It is applicable for both internal and external walls. There are two types of stucco plaster, Modern and traditional plaster. Usually, three coats of stucco plastering are applied they are scratch coat, fine coat and finishing coat. The thickness of stucco plaster should be 25 mm.
5. Gypsum plastering
Gypsum plastering is a type of plastering where gypsum replaces with cement. This plastering provides good finishing for the surface. Gypsum is a binding material. The thickness of gypsum plastering can be 6 to 20 mm. An important characteristic of gypsum is they do not shrink during drying. Hence we can avoid the development of cracks. Gypsum plaster does not need curing. Also, it is white in colour, So it gives a good aesthetic appearance.
What are Deep Foundation? The Common Types of Deep Foundation
1. What are Deep Foundations?
A deep foundation is needed to carry loads at depth or for functional reasons from a structure through weak compressible soils or fills on to stronger and less compressible soils or rocks.
Deep foundations under the finished ground surface are founded too deeply for their base bearing ability to be affected by surface conditions, generally at depths > 3 m below the finished ground level.
When unsuitable soils are present near the surface, the deep foundation may be used to transfer the load to a deeper, more capable strata at depth.
2. Types of Deep Foundation
The types of deep foundations in general use are as follows:
Basements
Buoyancy rafts (hollow box foundations)
Caissons
Cylinders
Shaft foundations
Pile foundations
a. Basement foundation
They are hollow substructures built to provide space below ground level for the work or storage. The structural design is driven by its practical needs rather than by considerations of the most effective method of resisting external earth and hydrostatic pressures. In open excavations, they are set up in place.
b.Buoyancy Rafts (Hollow Box Foundations)
Buoyancy rafts or hollow box foundations also known as the floating foundations is a type of deep foundation is used in building construction on soft and weak soils.
They are designed to provide a buoyant or semi-buoyant substructure underneath which reduces net loading to the desired low intensity on the soil. Buoyancy rafts can be constructed to be sunk as caissons, and can also be installed in open excavations.
Buoyancy rafts are more expensive than traditional forms of foundations. For that reason, their use is usually restricted to sites that are on silts, soft sands and other alluvial deposits that are very deep, or where loads can be kept concentric. Schemes requiring underground tanks or where it’s economical to incorporate deep basements into the design are common.
c. Caissons Foundations
A caisson is a sort of foundation of the state of the hollow prismatic box, which is worked over the ground level and afterward sunk to the necessary depth as a solitary unit. It is a watertight chamber utilized for establishing foundations submerged as in rivers, lakes, harbors, etc. The caissons are of three types:
Open Caissons: Open caissons are of hollow chambers, open both at the top and the bottom. The lower part of the caisson has a bleeding edge. The caisson is sunk into place by eliminating the soil from within the shaft until the bearing layer is reached. Well foundations are special type of open caissons used in India.
Pneumatic Caissons: Pneumatic caissons are closed at the top but open at the bottom. A pneumatic caisson has a working camber at its bottom in which compressed air is maintained at the required pressure to prevent entry of water into the chamber. So, these type of excavations are done in dry.
Floating Caissons: Floating caissons are open at the top but closed at the bottom. These caissons are developed ashore and afterward shipped to the site and floated to where these are to be finally installed. These are sunk at that spot by filling them with sand, ballast, water or concrete to an evened out bearing surface.
d. Cylinders
These foundations are placed when there is required to place only a single cylindrical unit.
e. Drilled Shaft foundations
These foundations are constructed by drilling a cylindrical hole within a deep excavation and subsequently placing concrete or another prefabricated load-bearing unit in it.
Their length and size can be easily tailored. Drilled shafts can be constructed near existing structures and under low overhead conditions, making them suitable for use in numerous seismic retrofit projects.
It may, however, be difficult to install them under certain conditions such as soils with boulders, soft soil, loose sand, and sand under water.
e. Pile foundations
Pile foundations are relatively long and slender members designed by driving preformed units to the desired foundation level, or by driving or drilling in tubes to the appropriate depth – tubes filled with concrete before or during withdrawal or by drilling unlined or wholly or partially lined boreholes filled with concrete after that.
What is Self-Leveling Concrete? Properties, Advantages and Disadvantages
1. Introduction
Self-leveling concrete is a polymer-modified high-performance concrete that has the ability to flow, compact, and provide a leveled surface when poured over an area. Self-leveling concrete does not require vibration as required for normal concrete.
It is poured in liquid form and goes down 1/4 to 1.5 inch thick in single pass. A gauging tool is used to spread it in place. Qualities include smoothness, flatness and a compressive strength over that of traditional concrete floors. After you apply it, you can add decorative overlays or concrete stains or dyes.
Self-leveling overlays are among the newest trends for architects and commercial property owners. It is quick to install and can be installed pre or post construction. It can cover plywood or tile floors as well, and is flood proof and hypoallergenic.
2. Properties of Self-Leveling Concrete (SLC)
Low Plastic Viscosity.
High Flow-ability.
Low segregation.
Low Bleeding.
Stability.
a- Low Plastic Viscosity
The low plastic property of SLC increases the flow ability properties which imparts the self-leveling property. The balance and proportion of the above-mentioned properties in mix design help to design the desired SLC concrete.
b- High Flow-ability
Providing low viscosity of the concrete mix can result in stability issues. This can result in high segregation and bleeding problems. This low viscosity or high flow-ability is introduced by the addition of super plasticizes or polymer agents that maintain stability without affecting the flow-ability characteristics.
c- Stability
High-homogeneity is received by self-leveling concrete with its self-leveling property. The flow-ability properties of SLC are greater as compared with (SCC) self-compacting concrete. This increase in flow-ability is one reason to obtain good finish in final hardened SLC
d- Low segregation / Low Bleeding
The viscosity agents added prevents the settling down of aggregates that cause segregation and keep the cohesiveness of the mix within the bond which in turn helps in avoiding bleeding. Maintain the viscosity throughout the layer without letting the aggregates to settle at the bottom.
3. Advantages of Self-Leveling Concrete (SLC)
Labor required less.
Leveled and smooth surface.
Water Resistant surface.
SLC concrete gives a flat and smooth surface.
The best choice of heavily reinforced concrete construction.
The hardening of concrete is taking place in a homogeneous way.
The best option where form-work is arranged in unusual geometry.
Compressive strength is higher as compared to traditional concrete.
Self-leveling concrete gives cohesive concrete that resits bleeding and segregation issues.
Easy to use. Self-leveling concrete also levels the playing field. Now subfloor leveling is a DIY project.
Two options to choose. Acrylic-based concrete is more giving, has a slight flex and sturdiness. Water-based concrete dries fast and is harder than standard concrete.
Radiant heat capable. Most self-leveling concrete brands and styles are rated for using over around or under radiant floor heating systems.
Quick acting. The formula that makes up the concrete compound is strong, durable and fast acting. It can set up in as little as 10 minutes and be ready for most flooring types in just a few hours.
Hypoallergenic. Unlike standard concrete which has been known to cause work-induced asthma, self-leveling concrete doesn’t contain those chemicals and minerals.
Mold and mildew resistant. Even when installed in wet areas, self-leveling concrete is more resistant to mold and mildew growth than standard concrete.
4. Disadvantages of Self-Leveling Concrete (SLC)
Fast acting. Yes, this is also a pro item, but it dries fast. You shouldn’t mix until you are ready to pour, and when you pour you shouldn’t stop. Finding the right balance can be difficult.
Doesn’t repair subfloors. If there is damage, cracks, joints or weak spots in your subfloor, self-leveling concrete will not fix or patch them. If the spot worsens, it will disrupt the self-leveling concrete and the floor above it, too.
Difficult to remove. If you splash, get it on your clothing, tools or other surfaces and it is allowed to dry, you will have a difficult time getting it off. Any spills or splashes need to be cleaned up quickly.
Mixing is hard. You need to be precise in your measurements and you don’t get to make mistakes. If you add too much water or not enough, it will affect how the concrete pours and how viscous it becomes.
A bridge’s railing depends on various factors such as location, material, and purpose. The railing adds safety for pedestrians, aesthetics, and a custom touch to bridge construction.
Guardrails for bridges are located prominently to make the public stay alert and safe during their drive through bridges. These railings not only keep the traffic within the boundaries but also improve the bridge aesthetics.
Types of Bridge Railings
The common types of railings used for bridges are:
Steel bridge railings
W-Beam railings
Thrie-Beam railings
Concrete beam railings
1. Steel Bridge Railings
Steel railings come in different cross-sections and designs. The most common type of steel bridge rail is a tubular rail system. These types of railings can be built alone or integrated into the concrete curb or on a low barrier wall.
For bridges with low-vehicular traffic and for pedestrians, architectural steel railings are commonly used. Architecturally important bridges do not have a bulky and heavy design. They incorporate decorative railings without compromising pedestrian safety.
2. W-Beam Bridge Railings
W-Beam railings are used for bridges with less traffic. As shown in the figure-2, W-Beam railings have a two-wave design and are attached to steel posts or truss girders.
W-Beam is a simple steel railing system that can be designed for higher strength.
3. Thrie Beam Bridge Railings
Thrie beams are high-strength guard rail systems designed for highways, especially on sharp curves and slopes.
Thrie-Beam features ‘three’ waves across its section versus ‘two’ on W-Beam and therefore provides greater rigidity, which in turn means lower deflections and higher containment that is more suitable for heavier vehicle protection.
Thrie beam rail systems can absorb the impact of out-of-control vehicles and guide them to a safer stop. These rail systems provide excellent performance and versatility.
It has an added corrugation that gives an advantage for use in transitions to bridges and along high volume, high speed roadways.
4. Concrete Bridge Railings
Concrete is the most common material used for bridge construction. Concrete railings are attached to the bridge’s deck slab to create a strong vehicle barrier.
A concrete railing attaches to the bridge’s deck slab and creates a powerful vehicular barrier. These sturdy railings are ideal for high traffic roadways or areas where run-off the road accidents are frequent.
The initial construction cost of concrete railings is high. Huge concrete railings in some situations can impede an open road view. In such situations, concrete railings with high strength can be combined with a tubular railing system.
The dimensions and construction of bridge railings are dependent on the construction budget, the bridge deck material, and the mandated state specifications.
The cement industry is one of the main producers of carbon dioxide, and growing consumer awareness of climate change and the environmental impact of construction have some clients looking for alternatives to materials that rely on cement.
There is a growing range of concrete alternatives. These materials provide similar benefits as concrete, like strength, durability, and longevity, but at a lower carbon cost, with less environmental impact, and often with an appealing and distinctive appearance.
Concrete Alternatives For Construction
1. Recycled Plastic
Plastic is the most concerned material that significantly impacts the environment as they are non-biodegradable. It is essential to know that only 9% of the total plastic produced can be recycled.
So innovations suggest using recyclable plastic in facades of buildings or other structures. Using recycled plastic in construction is a great way to achieve fewer greenhouse gases effect while unclogging the plastic-filled landfills.
The recycled plastic can substitute 20% of aggregate in concrete; concrete blocks filled with recycled plastic are much lighter when compared to conventional concrete blocks. Using these blocks in small-scale construction is recommended while not suitable in taller structures.
Some advantages of using recycled plastic as concrete alternatives include that recycled plastic is highly versatile and can be resistant to impact, water, and chemicals.
Concrete production using recycled plastic requires less cost, and it has excellent electrical insulation and thermal properties. While the disadvantage is that plastic has a Low melting point.
2. Ashcrete
The main component in ashcrete is Fly Ash, which is a by-product of coal combustion, which is used to be discarded in the ground. Still, innovations lead this material to have a significant role to play in the green concrete manufacturing process.
Ashcrete is a concrete alternative used in modern construction to reduce the greenhouse effect, and it is also said that 25% of cement can be replaced using high-volume fly ash.
To make ashcrete similar to conventional cement, fly ash is mixed with water and lime to make it stronger and durable. Another advantage of using fly ash is that it makes concrete restraint to alkali-silica reactivity.
3. Green Concrete
Green concrete is a form of eco-friendly concrete that is manufactured using waste or residual materials from different industries, and requires less amount of energy for production. Compared to traditional concrete, it produces less carbon dioxide, and is considered cheap and more durable.
The manufacturing process of green concrete consumes Less amount of energy when compared to conventional. concrete.
The carbon emission from the production is comparatively less, and it is an economical. and durable concrete alternative.
4. Blast Furnace Slag
Blast furnace slag is a by-product produced and used as a concrete alternative in construction, and it is an environmentally friendly material that would impact less greenhouse gas effect.
This blast furnace slag comes in the form of glassy granular material produced by quenching molten iron slag from the blast furnace into steam or water.
This concrete alternative can replace 70-80% of cement and improve the durability and strength of concrete. During the blast furnace slag, the production process emits less hydration or heat.
5. Papercrete or Fibrous Concrete
Papercrete is a concrete alternative made by recycling the waste paper and used as an aggregate material in concrete. The cement is not entirely replaced by papercrete in the concrete mixture.
But some small quantities of papercrete are enough to combat some harmful effects during concrete production. Papercrete is considered to be one of the cheap or economic concrete alternatives.
The workability of this concrete alternative material is good enough; it can be molded into different shapes. The concrete blocks made from papercrete are lightweight.
Along with the advantages, there are some disadvantages of papercrete. The damp resistance of paper is low and has Less compressive strength than traditional concrete.
6. Bamboo
In many countries, Bamboo has replaced steel, has modern innovation comes with new ideas regarding concrete alternatives.
Bamboo is considered one of the best concrete alternatives as they possess characteristics like tensile strength, lightweight, and fast-growing renewable nature.
Bamboo is mainly used in framing buildings and shelters, as these are locally available building materials and cost very little compared to conventional materials.
In galsscrete, glass substitutes fine aggregates in the concrete mixture, and the glass is broken into small pieces. The concrete mix of glasscrete includes cement, coarse aggregate, and glass aggregate components.
Concrete with broken glass has better workability than concrete with natural. sand. Using glass can increase the durability and efficiency of the concrete.
Hempcrete, also known as hemplime, is a bio-composite material that can be used in construction as an alternative to materials such as concrete and traditional insulation.
Hempcrete is made by using the woody inner fiber of the hemp plant. The manufacturing process of hempcrete involves bounding hemp fibers with Lime to crate concrete-like shapes that are lighter and stronger.
Some advantages of hemperete are that they are super lightweight, and hemp is a renewable resource as they are grown continuously.
9. Micro Silica
Micro silica is the by-product of ferrosilicon alloy and silicon production and from the condensation of silicon dioxide, which comes as an ultra-fine powder. Micro silica is also known as Silica Fumes.
Micro silica has a great advantage; when added to the concrete mixture, they increase the durability of concrete by making concrete less porous and increasing its compressive strength.
Burj Khalifa is constructed using Micro Silica
This type of concrete alternative is most often used in structures that are exposed to harsh conditions like exposure to chemicals when compared to conventional. concrete, This type of concrete is less harmful to the environment, thus making it an eco-friendly material.
10. Rammed Earth
Rammed earth is made by compacting dampened subsoil between temporary formwork. The earth, once cured, is strong, durable, and resistant to the elements with the right treatment. It can be further strengthened with the use of construction techniques like rebar and steel frames.
Because the mixture of subsoil needed for rammed earth is readily available on many construction sites, it can sometimes be as easy to source as concrete — or even easier.
Construction crews require only minimal training on the material to build new structures using it. Building a rammed earth structure is a labour-intensive process, however, meaning that labour costs for a building may be higher when rammed earth is used. A crew will also need at least one skilled laborer to lead the construction process.
The material also has a unique visual appearance. It’s multi-colored, and with the layers of soil visible in the final product, it makes a good choice for clients who want a distinctive building facade or interior walls.
11. Timbercrete
Timbercrete is made from a mixture of waste sawdust and cement. It’s lighter than concrete, and because it reduces the amount of cement necessary for each brick or slab, it’s also less carbon-intensive. Depending on the ratio of sawdust to cement, it can be comparably strong and weather-resistant.
12. Ferrock
Ferrock is a carbon-negative concrete alternative. The material’s name comes from ferrous rock, but it is primarily composed of waste steel dust and ground silica glass.
The material generates significantly less carbon dioxide than concrete. It’s also very strong — around five times more sturdy than Portland cement. It’s also flexible, meaning it can bend without breaking due to compression or seismic action.
On the construction site, the material sets faster than concrete, making it practical for jobs where speed is necessary. The material can be hard to source due to its novelty, but in areas where it is available, it makes an excellent alternative to concrete.
Grasscrete is manufactured by a simple process by pouring concrete over styrene void formers. It is thus a cast on site cellular reinforced concrete system with void created by formers.
Former is fundamentally equipment or a mould that forms voids in the concrete, which can be filled later with a variety of porous materials such as stone, gravel or vegetation.
Grasscrete is one of the pavements methods where instead of the plain paving surface, vegetation or grass is grown on the surface, which gives an appealing look to pavements or driveways.
Grasscrete consists of a reinforced cellular cast on-site concrete on that one can grow natural grass by filling those voids with either soil or stones. These voids are created with the help of plastic formers (generally called moulds).
This type of pavement is widely adopted in major cities and modern designs because of its aesthetically appealing and environmentally favorable.
Types Of Grasscrete
Stone Filled Grasscrete
Partially Concealed Grasscrete
Concealed Grasscrete
1. Stone Filled Grasscrete
As the name suggests, in stone-filled grasscrete instead of soil, crushed stones are filled between the concrete. These crushed stones’ size comes in a range of 1/2 inches to 3/4 inches.
Generally, the draining capacity of stone-filled grasscrete rates up to 480 inches per hour with 100% water retention. The main reason to consider this one is that it is considered a low-maintenance design, and it is best suited for traffic sustained areas and provides max percolation rates.
This type of Grasscrete is ideal if you are looking for considerably a low maintenance design. Stone filled Grasscrete is perfect for sustained traffic areas. Furthermore, it provides maximum percolation rates. It is both functional and environment friendly.
This grasscrete type is used for:
Military Installations
Access Roads
Vehicle Parking
Fire and Emergency Access
2. Partially Concealed Grasscrete
In this type of grasscrete, the vegetation or the grass is placed parallel to the concrete. Usually, concrete with a thickness of 51/2″ is provided along with a half-inch space to protect the root alongside the vegetation.
Partially concealed grasscrete is eco-friendly and pleasing in appearance. It is most suited for sustained traffic areas.
This grasscrete type is used for:
Road Shoulders
Access Roads
Driveways
Fire and Emergency Access
Vehicle Parking
3. Concealed Grasscrete
In concealed grasscrete, a layer of soil with linch thickness is laid on the concrete. While the concert below has a depth of five and a half inches.
The vegetation or the grass laid on the soil surface. These types of grasscrete are best suited for low-traffic areas.
This grasscrete type is used for:
Medians
Low traffic access roads
Overflow vehicle parking
Fire and emergency access
Advantages Of Grasscrete
There are various advantages, including Economical, Structural, and Environmental benefits.
1. Economical Advantages
Longer Lifecycle:
Grasscrete has a longer lifecycle in comparison to the other conventional impervious paving systems. In fact, Grasscrete has installations that go back in time as far as 1974 that is still in place today.
Reduces Costly Infrastructure;
One of the unique properties of Grasscrete is that, it allows natural water infiltration. And it is also established that treating stormwater is not a practical solution but is also regulated by a number of agencies. Thus, the need for expensive stormwater infrastructure such as curbs, gutters and underground piping can be reduced or even eliminated in some cases.
Low Maintenance Costs:
The most viable option associated with low maintenance cost is the stone filled Grasscrete. It is also the most widely used Grasscrete. Clogging of the voids in areas having slope less than 1% is not typical although, these voids can be cleaned out easily.
2. Environmental Benefits of Grasscrete:
Increases Green Space and Reduces Heat Island Effect:
Heat islands are nothing but the built up areas that are hotter than the nearby rural areas. The visually appealing green space/vegetation reduces the heat Island effect, thereby creating a comfortable, attractive and a calming parking area for the use of vehicles. This is how Grasscrete allows a barren vehicular area transform into a green urban oasis.
Uses Recycled Materials:
The use of recycled material is encouraged in Grasscrete right from the manufacturing process of the concrete mix to fill the voids and the sub base layers. Grasscrete maintains its environmental focus by utilizing the recycled materials to its 100% capacity.
Infiltration of Storm Water:
Grasscrete not only maintains the natural equilibrium of the groundwater recharge but also significantly reduces the runoff. Infiltration of the stormwater in Grasscrete is at about the same rate as any other ordinary lawn located in the same area.
What Is Vibrator? Types Of Vibrators Used In Construction
Introduction
Vibrators are used to compact concrete on the construction site. They are available in a wide range of shapes and sizes. Some Concrete Vibrators are smaller, more efficient, and run on battery power, while others are much larger and rely on electric power.
In the event of vibration, compacting is caused by a reduction in internal friction between various concrete particles due to particle oscillation, resulting in a dense and compact concrete mass.
It is primarily utilized in the construction of roads, trains, and buildings for concrete compaction. It compacts newly poured concrete by removing trapped air and excess moisture. Its purpose is to secure the concrete in the formwork.
This is done to ensure correct concrete consolidation and prevent product faults. These vibrators can have vibration frequencies ranging from 2800 to 15000 rpm.
Types Of Vibrators Used In Construction
1. Internal Vibrators
Internal. vibrators, also known as immersion or concrete needle vibrators are the most common types of vibrators used on construction sites.
It comprises a steel tube with an eccentric vibrating element within (one end closed and rounded). The poker vibrator machine comprises a steel tube connected to an electric motor, a diesel engine, or a gasoline engine via a flexible tube.
The size of poker ranges from 40 to 100 mm in diameter. The poker diameter is determined by taking into account the distance between the reinforcing bars in the formwork.
Internal vibrator machine’s needle sizes range from 25 mm to 90 mm, with a minimum of 25 mm and a maximum of 35 mm used for roof slab casting.
For the compaction of concrete mass in column and beam structures, we should utilize a vibrator machine with 40 mm and 60 mm needles.
When proposing a strong footing and various bridge structures, we should use a vibrator machine with a 75 mm and 90 mm needle to compact the concrete mass by capturing air gaps and preventing honeycomb.
Vibrations from vibrator machines have a frequency of up to 15000 rpm. However, with an accel, a range of 3000 to 6000 rpm is advised as a preferable minimum.
2. External Vibrator
These vibrators are clamped rigidly to the form work at the pre-determined points so that the form and concrete are vibrated. They consume more power for a given compaction effect than internal vibrators.
The external vibrator is also known as shutter shape vibrator. It includes a base plate. It is used to compact the surface of precast concrete as well as the freshly poured concrete. A three-phase induction motor powers it.
Its construction is completely dosed. It’s also trustworthy and easy to maintain, with a power cord made up of four rubber-coated cables. The casing is usually built of an aluminum alloy casting. It has a highly efficient lightweight motor structure.
According to the building pattern, the machine is secured to the formwork horizontally or vertically at acceptable spacing but not exceeding 90 cm in both directions.
3. Surface Vibrator
Surface vibrators are permanently affixed to the concrete mass. During the screening process, they vibrate the concrete away from the surface.
When used in conjunction with concrete with low water to cement ratio, it is an excellent choice for the compaction of shallow elements.
For greater depth than 250 mm of the concrete, we should not use it. With the help of this machine, even dry mixes can be compacted successfully. Surface vibrators include things like pan vibrators and vibrating screeds.
It is commonly used for compacting small slabs, mending, and fixing horizontal. surfaces such as pavement stabs. It spins at a frequency of around 4000 rpm.
4. Vibrating Table
Although the formwork is clamped to the vibrator, the principle of vibrating the concrete and formwork remains unchanged. The vibration flavor is also comparable.
A fast-spinning eccentric weight, in general, produces In a circular motion, the table vibrates. The system is made up of two shafts that rotate in opposite directions.
The table can be subjected to a horizontal component of vibration that can be neutralized. Only in the vertical direction is there a simple harmonic motion.
There are also some minor positives. Vibrating tables of high quality powered by an electromagnet powered by alternating current. The frequency range reached is between 1,500 and 7000 rpm.
A table with variable amplitude should be utilized for vibrating concrete sections of various diameters or laboratory purposes. Vibrations with varying frequencies are a bonus. A vibrating table is a safe and effective way of compacting precast concrete.
The benefit of providing consistent treatment electrically or pneumatically controlled vibrating tables is particularly beneficial for precasting work.
The vibrating tables are very efficient in compacting stiff and harsh concrete mixes required for manufacture of precast elements in the factories and test specimens in laboratories.
What Is Cantilever Bridge? Types Of Cantilever Bridges. Advantages and Disadvantages
Introduction
A cantilever bridge is a bridge whose main structures are cantilevers, which are used to build girder bridges and truss bridges. A cantilever bridge has advantages in both simply supported and continuous bridges, like they are suitable for foundation with uneven settlement; they can be built
without false-works but has larger span capacity.
For cantilever bridges with balanced construction, hinges are usually provided at contra-flexure points of a continuous span, and an intermediate simply supported span can be suspended between two hinges. Cantilever bridges were not only built as girder bridges but also widely used in truss bridges.
Cantilever bridges are widely seen in major cities and movies. Though you have seen them but might not know the name it is called.
A cantilever is a structure with one of its ends fixed and free at other ends. The other end projects horizontally into space, and it is this end that helps support the bridge.
A cantilever bridge works in such a way that the bottom part of each cantilever is fixed or anchored into the ground, while the upper end of the cantilever supports the bridge itself.
The Cantilever bridge is a widely constructed bridge all over the world. These bridges are widely adopted mainly because They do not need any support. Usually, cantilever bridges are built when providing many supports is not possible.
Type Of Cantilever Bridges
The cantilever bridges are mainly divided into two types:
Balance Cantilever Bridges
Continuous Cantilever Bridges
1.Balanced Cantilever Bridges
The Balanced Cantilever Bridge does not require any falsework. Usually, this type of bridge is opted for constructing a long-span bridge.
If the bridge construction requirement is not suitable for simply supported or continuous frame type structures, then balanced cantilever bridges can be used.
We know that constructing a long-span continuous or simply supported bridge requires a solid foundation, which would be more expensive to construct.
Generally, balanced cantilever bridges are the combination of both simply supported structure and continuous structure.
The cantilever structure, which is constructed with only one cantilever length, must be small; otherwise, there may be chances of uplift at another end.
Cantilever balance Bridge has advantages of both continuous and simply supported structures. Like continuous bridges, The cantilever balance Bridge needs one line of bearings over the piers.
2.Continuous Cantilever Bridges
The continuous cantilever bridge is a truss bridge that extends across three or more supports without hinges or joints. Cantilever bridges are highly simplified, but they will explain the basic concepts of a conventional beam.
The abutments should be made heavy to compensate for the absence of a balanced cantilever. These types of Cantilever bridges work as continuous beam feet span between two support by maintaining their bending moment and Shear Strength throughout the beam.
Cantilever Bridge Advantages and Disadvantages
Advantages Cantilever Bridges
Generally, the requirement of falsework is not much, other than the requirement for the pier.
The suspended bridges sections are assembled that can only be elevated and attached between two cantilever spans.
Only one side of each cantilever requires support.
The floor of the bridge is simply formed into sections to preserve uniformity and ensure high quality.
It is less time-consuming, As multiple cantilever spans construction can be started simultaneously from all its columns.
Navigation or passage under the bridge is not disturbed during the construction process.
There is no need for synthetic support if the area has a strong rock structure and anchor arms are connected to the surrounding rock.
The span of cantilever bridges is usually longer than conventional beams since the cantilever is attached at the ends of the bridge.
Cantilever bridges can withstand the effects of thermal expansion and floor speed than other types of bridges.
In cantilever bridges, the lack of supporting piers provides extra flexibility to the styles and geometry of the highway supported by this bridge.
These bridges are most suitable for flood-prone areas and deep rocky valleys, where falsework might be dangerous or difficult.
Disadvantages Of Cantilever Bridges
Cantilever bridges cannot be constructed in extreme climate conditions due to the lack of multiple seasons.
Cantilever bridges require advanced analysis to prevent future fatigue failure of elements and welds.
Disability of the RC floor as part of a composite section.
It is challenging to construct and maintain these bridges, as they are largescale structures.
Requires bigger and stronger support columns to withstand the bridge load.
Generally, Long span bridges have truss bridges between the two cantilevers to reduce their weight.
Cantilever beams are not suitable for earthquake-prone areas or areas with low-rock stability.
A cantilever bridge requires a heavier structure to take care of its own stability by creating stability between compressive and tensile forces.
During the construction of Cantilever bridges, they experience a high level of tension which is known as negative moments.
Soil-cement is a mixture of soil and measured amount of cement, and water compacted at high density. They all together form a hardened mixture like concrete, under the hydration action of cement.
Soil cement is used to strengthen underlying soil conditions to support traffic loading. Cement stabilized base is also a common application to strengthen the base section directly underneath rigid or flexible pavements. Soil-cement can be used when paving roads, parking lots, airports, residential streets, and more. It’s a cost-effective pavement base known for its strength and durability.
Soil-cement is also called the cement-stabilized base, or cement-treated aggregate base.
Soil-cement Applications
It is primarily used as a base course for-
Roads
Airports
Shoulders
Parking Areas
It is also used for:
Sub-base for rigid pavements
Slope protection for earth embankments and dams.
Foundation Stabilization
Channel and Reservoir lining
How is soil-cement created?
First, rigorous laboratory tests are conducted to determine the cement and moisture content required to achieve the design compressive strength at a specific compactive effort. This analysis is then frequently referred to throughout the construction process to ensure that the soil-cement is of the highest quality.
Once the specific components of the mixture are decided, the material is mixed either in a central mixing plant or in-place. With central mixing plants, the soil-cement is first mixed and then brought to the job site. With in-place soil-cement construction, the mixing is done on-site. This involves first spreading the cement on the in-place soil. The cement, soil, and water are then mixed to a uniform consistency. During the final stages, the mixture goes through processes of compaction within a specified time limit and is cured. The curing process ensures that the soil-cement created is at its maximum strength.
Some soil-cement applications also require a process called “micro-cracking”. Micro-cracking of the soil-cement layer reduces the rigidity of the layer and the potential for cracking to reflect from the layer to the pavement.
Main processes involved in the construction of soil-cement are:
Mixing
Compacting
Curing
Mixing
At the central mixing plant, mixing of the soil-cement mixture is done. The final mixture is then moved to the job site and laid over the already prepared sub-grade level.
Initially, a proper quantity of cement is being spread over the soil and mixed homogeneously. Then a measured amount of water is added and mixed thoroughly. The mixing can be done by hands or with mixing equipment or machines.
Compaction
Now the compaction of the whole mixture is done by normally used compaction equipment. The compaction is done with high precision to achieve the maximum advantage of the cement used.
Once it is done, the whole mixture layer is cemented permanently at a very high density. After compaction, it won’t let the soil to undergo further consolidation or settlement under huge traffic.
Curing
The last step is curing. It is performed to prevent evaporation of water to the atmosphere. Proper cement hydration will be enabled only with an adequate amount of water. For this, a bituminous coating is laid over the layer and would act as a bituminous surface. The thickness of the layer can be increased if the pavement is constructed in an area with huge traffic.
Performance of Soil-cement
Soil-cement thicknesses are less in comparison of that required for granular bases carrying the same traffic over the same subgrade. It is because the soil-cement is a cemented, rigid material that distributes loads over broad areas. The slab-like characteristics and strength like beam are unmatched by granular bases. Hard and rigid soil-cement resists cyclic cold, rain, and spring-thaw damage.
The maintenance reports of already constructed soil-cement pavement show that they are having good service at low maintenance costs.
Samples must be taken at the installation and after a certain period. The analysis showed that the strength and other performance factors increased with age. It was found to be four times greater than the initial values. The analysis shows that they possess a high reserve strength capacity.
Advantage of Soil-cement
It requires less maintenance cost
It is Cheap and highly economical
Soil swelling can be reduced
It is Widely available resources.
Better weather-resistance and strength
It can be employed for small works
Disadvantages of Soil-cement
Formation of cracks
An always requirement to check the quantity of water
Pervious Concrete – Advantages, Disadvantages and Application
What is Pervious Concrete?
Pervious concrete has large voids that allow water or air to pass through it. The pores size varies from 2 to 8 mm, has a void content of 18 to 35 percent.
Further, pervious concrete has a compressive strength of 2.8-28.0 Moa (ACI 522,2010). Pervious concrete is also known as porous concrete or water-permeable concrete.
Like conventional concrete, its made from a mixture of cement, coarse aggregates, and water. However, it contains little or no sand, which results in a porous open-cell structure that water passes through readily.
Pervious concrete is often used in pavements. It is useful to recharge groundwater, minimizing stormwater run-off by enabling it to seep into the ground.
Consequently, it offers and advantage in resolving critical environmental challenges. Hence, a better effort towards sustainable development.
While the first use of pervious concrete dates back to the 1800s in Europe as pavement surface, it gained popularity in the US in the 1970s. Later, the demand for porous concrete increased after WWII as the cement supplies were badly affected. However, India realized the benefits of it in the 2000s.
Advantages Of Pervious Concrete
The primary advantage of pervious concrete is that it absorbs the stormwater. However, it serves multiple direct and indirect benefits as well.
1.Groundwater Recharge
The stormwater seeps through the pervious concrete and infiltrates through the ground. It ultimately adds up to the groundwater increasing groundwater level.
2.Reduction In Surface Run-off
The stormwater run-off reduces as the pervious concrete surface lets the water seep through it to the ground. Hence, the surface run-off reduces.
3.Reduction Of Sewers
Due to the reduced stormwater surface run-off, the size and need of the stormwater sewers reduce. Therefore, offering savings in drainage system costs.
4.Development of Trees
The stormwater infiltration through the ground provides higher moisture content. Moreover, the voids of the pervious concrete allow the necessary air for roots to breathe. Consequently, offering a healthier environment for roots to grow into trees and plants.
5.Filtering Of Stormwater
The pervious concrete acts as a filter for the stormwater. The dirt gets trapped into voids, and hence only clear water reaches the stream, pond or lake.
Disadvantages Of Pervious Concrete
Can not be used in pavements with heavy traffic flow.
Requires longer curing time.
Difficult to find out water content in fresh concrete.
Conventional concrete tests like slump test, compaction factor test are not applicable.
Requires specialized construction practice.
Special design considerations need to be implemented.
Requires regular cleaning to maintain its permeability
