Benefits of post-tensioning concrete slabs in building

Post-tensioned concrete slabs in buildings provide various benefits over reinforced concrete slabs & other structural systems toward both single and multi-level structures. Described below, some of the advantages of the slabs :-

Longer Spans: Longer spans are utilized to lessen the number of columns. It leads to bigger, column free floor areas which significantly enhance the adaptability of application for the structure as well as leads to greater rental returns.

Entire structural cost: The complete cost of materials, labor and formwork which are essential to build up a floor is decreased for spans higher than 7 meters and consequently leads to huge cost savings.

Minimized floor to floor height: Thinner slabs are utilized for the similar imposed loads. The decreased section depths facilitate least building height together with consequent savings in facade costs. As a substitute, toward bigger buildings, it facilitates more floors to be developed inside the original building envelope.

Deflection Free Slabs: Unwanted deflections under service loads are virtually removed.

Water-resistant slabs: Post-tensioned slabs are designed to remain free from cracks and as a result water-resistant slabs should be formed with proper design, detailing and construction. The selection of concrete mix and curing method together with standard workmanship are also very important.

Early formwork stripping: The earlier stripping of formwork and curtailed backpropping requirements facilitate rapid construction cycles as well as fast reprocessing of formwork.

Materials Handling: The decreased material quantities in concrete and reinforcement significantly offer benefit to on-site carnage requirements. The stability of post-tensioning strand is roughly 4 times that of traditional reinforcement. So, the whole weight of reinforcing material is considerably minimized.

Column and footing design: The decreased floor dead loads are applied to create cost-effective design of the reinforcement concrete columns and footings. In multi-storied buildings, decreased column sizes may raise the floor net rentable area.



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Some vital points to be remembered before purchasing ready mix concrete

The ready mix concrete is better as compared to the ordinary concrete mix since it needs less labour, time, efforts and cost. It facilitates to retain homogeneous quality during the work and provides the high speed of concrete construction.

With ready mix concrete, various types of issues like inferior workability, segregation, and bleeding, inappropriate water cement ratio, insufficient mixing time can be easily resolved in the construction site.

Prior to order ready mix concrete, the following points should be taken into consideration :-

01. Grade of Concrete or Mix Design

• Types of work where the concrete will be poured i.e. foundation slab, floor slab, pavements, etc.
• Grade of concrete necessary on site, i.e. M15, M20, M25, M30, etc.
• Slump of concrete both at the batching plant and at the job site.
• The quantity of concrete in cubic meter or cubic yard.
• Address or place of concrete pouring.
• Time of requirement of ready mix concrete on site.
• Time of interval among the two consecutive deliveries of RMC (in the case of higher quantity i.e. exceeding 6 cubic meter).

02. Fly Ash should not be used extra: It is essential to get the proper ratio of fly ash in the concrete. Some RMC producer includes extreme amount of fly ash in concrete which aren’t suggested also by the standards.

Generally, the fly ash is added in concrete at levels which vary from 15% to 25% by mass of the cementitious material component. Plant owner accomplishes this so that the cost is decreased and the profit is raised. So, the purchase should be careful for buying RMC at lower rates, and not get deceived with this lower rates.

It is also essential to get the source of every concrete ingredients (cement, aggregates, admixture, and water), the ratio and quantity of the concrete material per cubic meter, and the types of admixtures applied in RMC. So, prior to give order for ready mix concrete, obtain the above information. i.e. details of mix design from dealer.

03. Source of materials: The RMC dealers buy various concrete materials from diverse sources. The quality of materials may not be always good. So, all the sources should be assessed carefully. If their sources are recognized in the local market for the quality, then the ready-mix dealer can be selected, who will purchase the concrete materials from those renowned sources.

04. Time for Transportation: According to IS 4926:2003, it is recommended to pour the ready mix concrete within 2 hours from the time of loading at the central batching plant. However, a higher period is allowed if retarding admixture is utilized. But, determine the type of retarder used and all steps are followed as suggested by retarding manufacture.

05. Application of Admixture: Sometimes the extra dose of admixture is included at the project site to retrieve the workability of concrete. Some admixtures have chlorides, and if so, it is required to get the amount of chloride content in percentage of the total mass of admixture. If the amount of chloride is increased in ready mix concrete, it will lead to corrosion of the reinforcement steel and the service life of the house or building will be significantly affected. Hence, such admixtures should not be used.

06. Test of Concrete: It is indicated in standards that the ready mix concrete dealers should arrange test facilities at its premises to conduct routine tests, i.e. concrete slump test, concrete cube testing, etc. So, it is possible to double check the workability and strength of ordered concrete.

The workability of concrete can also be verified with slump test on site. Slump of concrete is primarily based on the condition of placement and the requirement of degree of workability. According to IS 456:2000, low reinforced sections like slabs, beams, walls, columns, etc. are casted with the slump of 25 to 75 mm. Heavily reinforced sections like slabs, beams, walls, columns, etc. are casted with the slump of 50 to 100 mm. From slip form work or pumped concrete, the appropriate slump of concrete is 75 to 100mm.

07. Information about Delivery Ticket of Ready Mix Concrete

The information given below, should be providedd in the ready mix concrete delivery ticket for each batch:

• Name and number of the ready-mixed concrete plant.
• Date and serial number of the ticket
• Truck Number
• Name of the purchaser and location of the site
• Grade of concrete
• Mix design details
• Type and size of concrete ingredients and their weight in table format.
• The quantity of concrete in the cubic meter
• Time of loading
• Slump results at the batching plant
• Signature of the concrete plant operator

The information given below, is required to be filled on ready mix concrete ticket on site.

• Time of arrival on site
• The time when discharge was completed
• Any water/admixture added on site
• Location of pouring of concrete
• Slump test result at the site
• Signature of RMC receiver



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How leftover concrete casting structures are used to reduce project cost

In high-rise building projects, the construction materials significantly contribute to find out the value of a project, the profit and loss of the project, even in the acceleration of the project's time.

Concrete is the prime material that is frequently utilized in multilevel projects as it is user-friendly, strong, and cost-effective.

The concrete that is utilized recurrently wasted in the process because of several errors in the execution of casting. The factors that influence the wasting of The ready mix concrete is wasted due to several factors like miscalculations / calculations in the job site, impaired equipment, awful weather, as well as inaccurate application processes.

Given below, some useful guidelines to utilize the remaining concrete casting structures so that the expenditure of a project is reduced significantly.

Utilized as a practical column or precast lintel beam.

In some big projects, practical columns or lintel beams on the wall installation work already apply precast methods. Generally, the concrete applied is instant concrete with K-225 or K-250. It is suggested that the residual structural casting concrete should be employed to minimize the waste of concrete and purchase instant concrete.

Utilized as Cansteen: Cansteen stands for edge of the pedestrian, the sidewalk, the separator, the edge of the road, the park, the boulevard, and so on. It acts as a booster for the road. Normally, cansteen is budgeted in BQ ordering finished products just by precast. The leftover structural casting concrete is utilized as a cansteen to reduce the budget.

Utilized as a Car Stoper: Car stopper belongs to the embankment in the safety parking area for providing to stop any car. Different types of materials like iron pipes, concrete and rubber are normally applied as car stopper.

Utilized as Paving Block: Paving blocks usually applied as outdoor parking areas, jogging tracks, parks, sidewalks, home yards and pedestrians are made precast with the rest of the concrete casting structure.

Some of the application of the remaining concrete casting structure which if employed can minimize project costs should be carefully examined and controlled effectively in the arrangement of the material as without that it will confine the project loading dock area that impacts the disruption of work execution.



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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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Uses and benefits of concrete pumping

Concrete pumping is the latest technology applied in the modern construction industry to set the concrete in all the structures ranging from high skyscrapers to the slightest convenience store. With concrete pumping, it is possible to arrange the concrete where it requires to fit.

Concrete pumping is the most convenient method for pouring concrete through a machine to transmit the liquid concrete. Normally, two basic types of pumps are utilized in concrete pumping i.e. boom pump and line pump.

Boom pump – It is self-contained unit that comprises of the frame and a truck. It is mostly applied to pour concrete in high up or difficult to arrive at the location.

Line pump – It is a portable unit that can pump structural concrete along with mortar, shotcrete, grout, wet screeds and foamed concrete.

Given below, some useful benefits of concrete pumping :-

Huge savings in time - Time is significantly reduced as the time is only required for mixing concrete and delivering to proper location.

Besides, the crew doesn’t have to make way for concrete trucks to pour the concrete to all the various locations.

Greater Productivity – The concrete pumping allows the crew members to deal with other aspects of the project since they don’t require to utilize shovels and wheelbarrows for the purpose of shifting concrete where it requires to fit.

Higher Precision – As the concrete pump expands from the truck right to the proper location the concrete is required, the entire process is error-less and precise.

This precision helps with productivity, wasted concrete because of spillage and fewer times for cleaning up.

Curtailment in labor costs – Less workers are required to set up and utilize the concrete pump as compared to the standard method of executing things. As less workers are needed, the labor cost is also reduced considerably and a more gainful project is created for the builder.

Greater employee safety – The employees needed to drive the concrete pump remain safe as compared to the employees assigned to mix and move the concrete with the conventional method.

With concrete pumping, heavy lifting is not required and as concrete moves directly to the spot, it requires less possibility for mishaps that can lead to severe injury.

Applications of concrete pump:

Residential projects similar to walls, foundations and patios.
Agricultural projects similar to sheds, barns, silos and bunkers.
Civil projects like hydro stations, water treatment plants or bridges.
Commercial or industrial projects similar to high rise buildings, ice rinks, strip malls and factories.



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Different types of grades of concrete as per 456 : 2000 standard

This construction video tutorial from learning technology demonstrates the grades of concrete on the basis of IS 456 : 2000 standard. As per this standard the grades are categorized in three groups like ordinary concrete, standard concrete and high strength concrete. Here grades range from M10 to M80.

M10, M15 and M20 belong to Ordinary Concrete. M25, M30, M35, M40, M45, M50, M55 belong to Standard Concrete. M60, M65, M70, M75 and M80 belong to High Strength Concrete (HSC).

Here m denotes mix and number denotes characteristic compressive strength of 150 mm cube at 28 days in N/mm2 (Newton per millimeter square). It means if you take compressive test of a cube having dimensions 150 x 150 x 150 mm for 28 days, the value obtained is 10 N/mm2.

All these concrete grades are suitably for PCC work i.e. plain cement concrete work where rebar is not used.

Standard Concrete is generally used in 10 storied and higher buildings and super structures.

High strength concrete is mostly used for designing heavy structures.

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The role of water in concrete

Water Cement Ratio signifies the ratio among the weight of water to the weight of cement applied in concrete mix.

Generally, water cement ratio remains under 0.4 to 0.6 with adherence to IS Code 10262 (2009) for nominal mix (M10, M15 …. M25)

The strength of concrete is directly impacted by the water cement ratio. It enhances the strength if employed in perfect ratio and if the ratio is improper, the strength will be reduced.

The importance of Water in Concrete

Concrete refers to a macro content. It comprises of micro constituents like cement, sand, fine aggregate & Coarse aggregate. With the purpose of obtaining high strength concrete to resist the desired compressive strength, it is required to set exact ratio of admixture to unite these materials.

The role of water is important here to accelerate this chemical process by adding 23%-25% of the cement volume. It produces 15% of water cement paste also called gel to fill the voids in the concrete.

Impact of too much water in concrete: If additional water is added more than the permissible limit of 23%, the strength of concrete will be significantly affected.

If the task of adding water is continued to improve the workability then the concrete contains lots of fluid materials where the aggregates will settle down. As soon as the water is evaporated it puts down lots of voids in concrete which influences the concrete strength.

But if the guidelines are followed to retain the strength of the concrete then it will change the concrete workability and makes it difficult to manage and place them.

Workability signifies the capacity of concrete to manage, convey and place devoid of any segregation. The concrete becomes perfectly workable if it can be easily dealt with, placed and transported devoid of any segregation at the time of being placed in construction site.

For this purpose, plasticisers & superplasticizers are utilized to enhance the workability by keeping the W/C Ratio unchanged.

In order to know how to work out water cement ratio, go through the following construction article www.civilology.com

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Published By
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www.constructioncost.co
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Some useful construction tips on concrete mix design

This construction video tutorial focuses on concrete mix design. In this video grades are taken as M 7.5, M10, M15, M20 and mix ratios for cement, sand and aggregate are taken as 1:4:8, 1:3:6, 1:2:4, 1:1.5:3. The amount of water is required for amalgamating concrete in 50 kg cement.

Concrete mix design refers to the method of choosing the appropriate components (cement, sand and coarse aggregates) as well as their relevant proportions with the purpose of developing concrete by maintaining specific minimum strength & durability.

Objective of mix design
To make sure that the optimal ratios of the constituent materials is maintained to satisfy the need of the structure.
To obtain the preferred minimum strength in the hardened stage.

To obtain the needed minimum strength in the hardened stage.
To obtain the preferred strength in the specified environment conditions
To form concrete as inexpensively as possible.

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