People from all over the world have been migrating in large numbers to metropolitan areas since the industrial revolution. As a result of the desire to fit as much as possible on as little space as feasible, land costs in desirable locations have increased to virtually prohibitive levels, and building heights have increased as well.

To discover a suitable and affordable material for high-rise multistory buildings, architects and engineers have increasingly turned to concrete. In Cincinnati, Ohio, the first skyscraper made of concrete was constructed in 1902. It was the 16-story, 210-foot- tall Ingalls Building, which has recently undergone cosmetic work and is still in operation.

“The Burj Khalifa in Dubai is the tallest reinforced concrete structure in the world right now”

Numerous factors contribute to the rise in high-rise building use of concrete. The structural interaction of a building frame is unmatched thanks to the continuity concrete offers. The shortest floor depths are available in concrete floor systems like flat slab and flat plate. Low material prices apply. Concrete is easily adaptable to unconventional layouts, such as the curvy and circular shapes that are currently very fashionable. Concrete's potential in this area is being increased by high strength reinforcing rods.

A more effective method of designing in concrete is provided by ultimate strength design, which is currently gaining popularity in India. Last but not least, concrete construction frames are inexpensive. Lower labor costs in India are an additional benefit that significantly reduces the cost of concrete frames. In this work, the challenge of generating homogeneous, high-quality concrete is mostly dependent on two fundamental factors: mix design and placement and curing techniques.

Designing a concrete mix with the qualities desired in high-rise buildings while utilizing the materials at hand is frequently a major problem. A number of trial mixes need be created for a project as large as a high-rise structure in order to find a concrete that will meet the necessary specifications. Keeping economy, pre venting segregation, reducing bleeding and laitance formation, and ensuring desired flow ability, uniformity, durability, and high strengths are the important challenges in this task.

The mix design must take into account the drastically different ambient conditions that will be experienced during construction because high-rise structures frequently take a year or longer to complete. Additionally, for a high-rise building, more than one basic mix design may be required. For instance, many structures now specify standard concrete for columns and sheer walls but lightweight aggregate concrete for the floor slabs. Due of their angular shapes, many lightweight aggregates are difficult to thoroughly coat, and extra measures must be taken to provide high workability and finishing attributes.

Even if standard concrete were to be utilized throughout the entire construction, the mix design for the foundations and exposed columns would most likely differ. Care must be taken to ensure that the maximum coarse aggregate size utilized does not inhibit appropriate consolidation of the concrete in narrow forms and around the bars in high- rise buildings where reinforcing concentration is frequently fairly heavy. According to the Indian Building Code, the aggregate's maximum size cannot be greater than one-fifth of the distance between the sides of the forms or greater than three- fourths of the minimum clear space between the bars.

The tendency of mixes to bleed and generate laitance is aggravated by the narrow, high forms frequently utilized for columns and shear walls. These issues arise frequently in the construction of tall buildings, but they can be avoided by paying particular attention to two areas of the mix design, specifically the consistency of the cement paste and the physical makeup and features of the aggregates.

Avoiding harsh or smooth non-absorbent aggregates and inadequate gradation are the main factors with regard to the latter in preventing Concrete for high-rise buildings from bleeding. Poor particle shape and harsh aggregates frequently necessitate the addition of additional placement water by employees at the working site. Watering concrete worsens bleeding and increases the likelihood of segregation, both of which lead to water gain.

Blood loss, the development of laitance, and segregation can all be significantly reduced with the use of air entrainment and little water content. As has been indicated, these issues are made particularly difficult by the height and narrowness of columns and shear wall forms. Water gain will naturally be minimized when the unit water content can be lowered by suitable mix proportioning and the application of an air-entraining water reduction agent.

Additionally, compared to a mix that isn't air entrained, concrete produced by air entrainment is fatter, more cohesive, and more resistant to segregation. Compounds that reduce water content and stop bleeding also produce stronger concrete and greater workability, two qualities that are highly desired when pouring concrete for tall constructions.

But without adequate putting techniques, even the best-designed concrete will segregate and bleed, leading to problems like crack formation and a weak link to steel. For the most part, tall building members can be concreted using the standard desired laying techniques. However, certain placing-related factors require extra caution. Due to the normal height of the column and wall forms and the frequently close spacing of the reinforcing bars, workers must exercise caution when pouring and vibrating concrete in this operation. When throwing concrete, there should always be less than four feet of free fall, and it should do so on a true vertical plane. For deep forms, concrete should be poured into a hopper that has a flexible drop chute attached to it that extends to within four feet of the form's bottom.

If this isn't done, the coarse aggregate will separate if it bounces off the forms' sides and through the network of bars. The bars and shapes will also be covered in mortar, which will dry before concrete is poured on top of it. Poor bond strength, dusting, and a mottled surface look are the results. If the type or concentration of reinforcement makes this placing method impracticable, a duct should be constructed at every third interval between studs.

For the concrete to flow easily into the form, the hopper that feeds these ducts needs to be constructed with a pocket below the duct opening. Even with the usage of the duct system, separation will occur if the concrete is discharged at an angle to the sides of the form because it will bounce off the sides and up against the bars.

Concrete must have a different consistency in deep, narrow forms. The bottom of the form should have a mix of higher slump from 4 to 6 inches, and the top should have a mix of lower slumps. The overall quality of the concrete will be more evenly distributed thanks to water gain, and settlement shrinkage will be maintained to a minimum. High- rise building concreting can benefit greatly from vibration since it allows for the use of water with lower concentrations.

Vibration, though, can be employed improperly. It will separate if used with moist mixes or if used for an extended period of time. Additionally, the surface will be ripped and insufficiently compacted if vibration is utilized to move concrete horizontally rather than compact it. The vibrator head's penetration angle should be uniform in vibrating lifts, especially those that incorporate concretes with various slumps. In order to completely consolidate the two lifts, make sure the vibrator head extends a few inches into the concrete below. If there must be a delay between casting successive lifts, a retarder should be employed to ensure that the preceding lift is still plastic when casting the following layer.

The placing and finishing techniques used have a significant impact on the concrete flatwork's quality. Concrete should not be poured away from already-cast concrete; rather, it should be poured into its face. If placing concrete on a slope, always begin at the low point and work your way up; never do the opposite. A baffle should be placed at the end of the chute if one is being used to pour concrete onto a slope in order to slow the concrete's flow.

Lightweight concrete, which is presently so common for floor and roof slabs in tall buildings, will mainly adhere to these desirable proportioning and laying procedures. However, some variations exist as a result of the unit weight. More than 450,000 square feet of concrete curtain wall protected the reinforced concrete frame of the Denver- Hilton, another example of an all-concrete high-rise building.

Absorption qualities of lightweight materials. Extra-light aggregates, such vermiculites and expanded perlites, are often split into two classes: medium-light aggregates, and light aggregates (for example, expanded clays and shales). Only the latter can acquire the high compressive strengths required for high-rise building structural members. These medium-lightweight, high-strength aggregates can be further broken down into two types: coated aggregates, which are typically rounded in shape and have a hard, comparatively impervious coating over a porous core, and crushed aggregates, which are typically angular, irregular-shaped particles created by grinding to size large lumps of material that have, in a sense, exploded from the parent material. Coated aggregates, as one might anticipate, are preferred because they absorb less moisture and result in more workable concrete.

With lightweight aggregates, uniform workability of the mix is more difficult to maintain due to their general high absorption and the significant variance in absorption rates amongst particles. When placed incorrectly, coarse aggregates have a tendency to float to the surface because they are lighter than the concrete mass.

Agents that increase workability significantly and decrease the need for water are especially valuable in lightweight concrete. It is recommended to use air contents up to 7% higher than those typically prescribed for standard concrete.

It is crucial to apply the volumetric approach when determining the air content of lightweight concrete. The gravimetric test requires an extremely accurate determination of the specific gravity of lightweight aggregates, and the pressure method is inappropriate for highly porous aggregates.

Slump is a less trustworthy indicator of workability in regular weight concretes, and its dependability is further diminished in lightweight work. It should be kept in mind that lightweight aggregate concrete will have less slump for a given degree of workability than a typical sand and gravel mix if the slump test is employed to help quantify work ability.

Light weight concrete with a slump of two to three inches and an air content of three to seven percent will roughly have the same placement characteristics as heavy weight concrete with a slump of four to five inches. The Vee Bee Consistometer can be used to measure workability in lightweight concrete projects in a more trustworthy manner. A light weight plastic mixture that could be used would register between two and five V. B. degrees.

Lightweight mixtures should not be handled excessively. In comparison to heavier concretes, lighter mixes are more likely to trap air and honeycomb. Although vibration can be very useful in eliminating these flaws, it must be carefully monitored to prevent over-vibration, which would exacerbate water gain and segregation. Working with light weight concrete makes segregation easier to detect because the coarse particles, which are lighter than the mass rather than heavier, float to the surface when segregation occurs.

We at APEX Structures Pvt. Ltd. have experts, who can understand your requirement and can plan the best solution. Please contact us for the best solution. Apex Structure Private limited. (ASPL) is a leading infrastructure construction company based in central India Indore. The company has origin in 2000 as a proprietor concern. The company has been incorporated in Feb 2008 as Private Limited to take over the business of the proprietary. In a short span, we have worked in all major areas of Infrastructure development Projects like Residential Buildings, Commercial & Institutional Buildings, Malls and Clubhouses, Government Projects of Roads and Commercial buildings.

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