Some useful tips to work out the costs of concrete

While going to estimate the cost of new concrete, different types of variables should be taken into consideration which range from surface prep, formwork, reinforcing materials, and finish work, as well as the cost of the ready-mix concrete.

It will compute the total price of the job. Costs for certain items will differ from location to location or from site to site, but a rough estimate can be obtained with some averaged amounts.

Cost Per Yard of Ready-Mix Concrete: The most vital item should be the price of concrete, whether ready-mix concrete or other concrete material is applied. As soon as the project specifications and job location are defined, get quotes from local ready-mix concrete suppliers.

Concrete pricing is generally quoted per cubic yard or cubic meter (metre). For an average estimating number, it is recommended to apply $77 per cubic yard.

Cost of Concrete Sub-Grade Work: When the concrete is placed over soil, it is required to grade or arrange the surface for the concrete. Pricing for this can contain expenses associated with grading, compacting soil, excavating, trenching, and other components.

As a perfect average, one can apply $65 per hour of work to set up the surface, provided that the surface is in excess of 75 percent leveled and no special work is required to set up the site.

Costs for Extra Sub-Grade or Site Work: When the surface is not leveled, it is required to include expenses for more site work, like excavating and filling with proper material or eliminating a soft spot on the terrain to prepare it for bearing structural loads.

Based on the distance from where the sand or any other suitable fill material will be arranged, it could include over $10 per cubic yard or meter to your estimate. The cost might be incurred for setting up polyurethane plastic or vapor barrier prior to set the concrete.

Cost of Concrete Formwork: Building concrete forms generally demonstrate a vital part of the total cost of concrete work, as it is one of the most labor-intensive features of the job. It is necessary to recognize the type of formwork to be applied, method of installation, and whether you will purchase or rent the form materials. Other related costs may involve a crane or other equipment applied to move the form materials, form release product, re-using form materials, and the cost to repair forms after different applications.

Usually, the cost of the formwork is $1.10 per square foot of the concrete area. This estimate is prepared for a square or rectangular area. The cost of formwork is increased for rounded or contoured concrete.

Cost to Finish Concrete: Concrete prices mainly differ on the basis of the type of finishing provided in the design. Concrete gets finished in various ways like smooth surface, exposed aggregate surface, or stamped concrete finish. Some surfaces need only a strike-off and screed to suitable contour and elevation, while for others surfaces, a broomed, floated, or troweled finish should be provided. To work out finishing in your concrete pricing analysis, you can include $0.75 per square foot or perhaps more, based on the complication of the specified finish. The cost of any curing compound or testing services should also be taken into consideration.

Cost of Concrete Reinforcement: Most concrete comprises of some type of reinforcement, like rebar, wire mesh, plastic mesh, or fiber which should be added to the concrete mix to raise the strength and crack-resistance. Standard reinforcing materials can include roughly $0.18 cents per square foot. This number is higher for large-diameter rebar or other special reinforcement.



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Published By
Rajib Dey
www.constructioncost.co
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The Basic Requirements of Formwork

Formwork is a concrete construction that is used as either short or permanent molds into which fresh concrete or similar kind of materials are gushed to make it harden. The different types of concrete formwork construction depend on the material and the kind of structural element. They are given various names as per the type of structural member construction like slab framework, beam framework, column framework etc. to use in beams and columns.

The harden process requires time and includes an expenditure up to 20 to 25% of the cost of the structure or more than that; the temporary design structures are made of economic expenditure.

While the removing process of the framework is known as stripping that can also be used later; the unusable are called panel forms and the non-useable are called stationary forms. The most commonly used material for formwork is Timber.

This article is a short knowledge for people about formwork, the different types of formwork and the basic needs to complete a formwork properly. Formwork comes in several types such as:

1. Traditional timber framework
2. Engineering Formwork System
3. Re-usable plastic formwork
4. Permanent Insulated Formwork systems
5. Stay-In-Place structural formwork systems
6. Flexible formwork

Requirements of Formwork: It is stated above that framework varies as per material and material is the main ingredient for every framework, but for any kind of chosen material the three common principles of quality, safety and economy should be the same. While the quality of material ensures safety and also considerably helps to achieve the economy; any kind of failure in framework can cause of the loss of life and tragic financial loss. To avoid the loss the following guidelines should be followed from start to framing materials and for the associated components:

1. Strength: The strength of material must be sufficient to strong the forces expected and this is the important for both the structural design and safety aspect.
2. Stiffness: the structural movement under load should be small and sure; these deformities and separations are the necessary part of the whole deviations in the formed concrete surface. While planning the formwork system, a designer must take decisions upon the total acceptable variations and the extend workmanship errors and structural deformity. The material stiffness and the workmanship accuracy must be stable to ensure the stability of the total deviations to keep the tolerances.
3. Impact Resistance: The forms are made to make sure that the damaged form that is useless does not make falling debris and to make sure this important safety quality, materials displaying ductile failure are far above than those fail in a hasty and brittle manner.
4. Durability: The framework must be durable either it will affect the economy and the achievement quality concrete product at every reuse of the formwork; formwork is always pre made and used out in the open. When the matter of re-uses came the thing is dependable on its reaction of materials and components with weather and the framing, components and formface materials should be strong in any environment. Material durability is important for both the achievement of good quality concrete surface finishes and safe formwork structures.
5. Weight: While the assembling process in formwork, both the members and components are shifted into position by hand that will be applicable after the complete framework which are heavy and need a crane to do the shifting work. So the framing members, formwork components and formface materials must be keep in size so that they must be carried and lifted by the worker or the crane etc.
6. Accuracy: Every construction process is dependable on a lot of money so the work of lifting and cutting of materials must be done within a minimum amount of money and consistency of size of materials, plywood sheets and framing members is very important.
7. Compatibility: The framework materials should be fitted with either the fluid concrete or the strong concrete and at the formface, the elements of the form materials must not react with the wet cement or concrete.
8. Insulation: Some materials react with the environment if it’s become extra hot or cold, so the protection for the materials is must; if the mix becomes frozen and the chemical bondage damages then the concrete has to be placed at low temperatures, heat the mixing water etc. The placing of the fluid concrete for all forms can cause some damage with the crushed rock aggregate and the proper steps has to be taken to stop it.




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Published By
Rajib Dey
www.constructioncost.co
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The fundamentals of setting up Post-Tensioning Slabs

Construction of post-tensioned slabs on grade is equivalent to apply reinforcing steel, devoid of the tensioning step.

Cables are set up as per instructions of the engineer and placed to go over the center of the slab. For residential construction, tendons at 48 inches on center are generally accepted. Commercial foundations will contain much more steel. Tendons are routed around obstructions smoothly.

Generally, a residential post-tensioned concrete slab should have been 8 inches thick with 3000 psi concrete. As soon as the concrete achieves strength to 2000 psi, normally within the 3 to 10 days as suggested by PTI, the tendons are stressed.

Now-a-days, tendons are seven high-strength steel wires wound together and arranged inside a plastic duct. A PT anchor is situated at each end and these are found in pockets which are implanted into the slab edge. As soon as the strands are stressed, the wires are expanded —about 4 inches for a 50 foot strand—to employ 33,000 pounds of load.

The qualified workers should be appointed for doing stressing. Once the stressing is completed, the tendon is cut off and the pocket in which the anchors are situated is filled with grout to defend then against corrosion.

Bigger structural concrete members may also be post-tensioned, particularly in bridges and floors and beams in parking structures. The process is equivalent to that applied for slabs, with the exception of a bigger scale. The tendons will frequently be "draped" in order that they are low at the midpoint of a beam and high at the supports—this arranges the steel at the point of highest tension where it can retain the concrete to be remained together firmly.

With structural members the duct is frequently grouted full following stressing to tie the strand to the concrete along its entire length—these are known as bonded tendons. Unbonded tendons are mostly found in residential slabs and stay free to progress within the duct and are safeguarded from corrosion with grease.

The position of PT tendon and stressing is normally performed with companies with certified workers having expertise in this type of work.

For more information, read the following construction article concretenetwork.com



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Published By
Rajib Dey
www.constructioncost.co
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Details of design and construction process of Burj Khalifa

Excavation work began for Burj Khalifa is known as the tallest skyscraper in the world in and it’s excavation work was started in January 2004. It took 1325 days for the completion of the structure.

The superstructure is supported with over 165 stories. The final height of the building is 2,717 feet (828 meters). The 280,000 m2 (3,000,000 ft2) reinforced concrete is used for Dubai tower and employed for retail, a Giorgio Armani Hotel, residential and office.

Structural System Description: 3D Structural Analysis Model of Burj Dubai TowerBurj Khalifa contains "refuge floors" at 25 to 30 story intervals which have great fire resistance capacity as well as individual air supplies to cope up with any emergency situation. With the support of reinforced concrete structure, the building becomes stronger as compared to steel-frame skyscrapers.

Designers intentionally constructed the structural concrete in Burj Dubai as "Y" shaped in plan with the purpose of minimizing the effect of wind forces on the tower along with the intension to retain the structure simple and support constructability. The structural system is defined as a "buttressed" core.

Every section contains its own high performance concrete corridor walls and perimeter columns and supports the others through a six-sided central core, or hexagonal hub. So, a tower is built with enormously rigid lateral and torsion capacity. An inflexible geometry is utilized with the tower that organized all the common central core, wall, and column elements.

Each tier of the building sets back in a spiral stepping pattern up the building. The setbacks are arranged through the Tower's grid, so that the building stepping can be completed by positioning the columns over with walls beneath to set a smooth load path. It facilitates the construction to get rid of the issues resulting from column transfers.

The setbacks are arranged in such way that the Tower's width alters at each setback. The benefit of the stepping and shaping is to "confuse the wind'1. The wind vortices don’t get structured as at each new tier the wind experiences a dissimilar building shape.

Structural Analysis and Design Facts: The center hexagonal reinforced concrete core walls set the torsional resistance of the structure same as a closed tube or axle. The center hexagonal walls are supported with the wing walls and hammer head walls which operate as the webs and flanges of a beam to withstand the wind shears and moments.

Outriggers at the mechanical floors facilitate the columns to contribute to the lateral load resistance of the structure; so, all of the vertical concrete is applied to support both gravity and lateral loads. The wall concrete designated strengths vary from C80 to C60 cube strength and employ Portland cement and fly ash.

To get more information on construction details, go through the following article aboutcivil.org




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Published By
Rajib Dey
www.constructioncost.co
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