The Burj Khalifa, the world’s tallest building, has a laundry list of superlatives. Greatest number of stories, highest occupied floor, longest travel distance elevator, world’s highest swimming pool. Perhaps none of these would have been achievable without the great advances that have been made in concrete technology over the past 20 to 30 years.
Until the 1990s, concrete wasn’t a cost-effective solution for the construction of tall buildings – it had limited strength, it was heavy, and fabrication was longer than for steel construction. Generally steel was looked at as the solution for super-tall buildings.
However, there have been significant advances in many aspects of concrete technology with great increases in strength, modulus and durability. High-performance concrete (HPC) mixtures provide a wide range of mechanical and durability properties to meet the design requirements of a structure. Even so, the challenges facing the structural and construction engineers on the Burj Khalifa project have been huge. Most of the Burj Khalifa is a reinforced concrete structure, except for the top, which consists of a structural steel spire with a diagonally braced lateral system. 330,000 m3 (431,600 yd3) of high-performance concrete is used throughout the building.
One of the major requirements for the successful completion of this project was the ability to pump the concrete slurry up to a height of 600 meters (1968 feet) in a short enough time span (around 30 minutes) to ensure the concrete remained workable and retained its high performance properties. Three high-pressure pumps were used at the construction site to lift concrete up to crews working at unprecedented heights.
To decrease construction time, the concrete was designed to be self-consolidating (SCC), meaning a concrete mix that leveled itself solely due to its own weight, with little or no vibration. It spread into place, filled formwork, and packed tightly into even the most congested reinforcement, all without any mechanical vibration.
Great care was necessary to achieve and maintain the desired performance of concrete in this region. The Middle East is not a benign environment for concrete due to the extremely wide range of temperatures experienced throughout the year. The ability to pump and place concrete at high ambient temperature to significant heights while preventing excessive cracking and possible service life issues in the strong drying conditions was vital for the efficient and economic use of HPC. During the summer months, when shade temperatures can exceed 50°C (122°F), the concrete’s water content was almost completely composed of flake ice to achieve the common limit of 32°C (90°F). Whenever possible, and in particular during the hottest months, all pumping of concrete took place at night.
The importance of extensive testing of the concrete could not be overstated. Prior to the construction of the tower, extensive concrete testing and quality control programs were put in place to ensure that all concrete works were done in agreement with all parties involved. These programs started from the early development of the concrete mix design until the completion of all test and verification programs. Five different concrete mixture designs were tested. The testing regimes included, but were not limited to the following:
• Test the mechanical properties of each mixture, including compressive strength, modulus of elasticity, and split tensile strength
• Test and measure the concrete properties (fresh and hardened) before and after pumping
• Test for creep and shrinkage for all mixtures
• Test for water penetration and rapid chloride permeability
• Test the shrinkage of the concrete mixtures
• Pump simulation testing for all concrete mixtures grades up to at least 600 meters (1968 feet)
The Burj Khalifa is the current state-of-the-art in super-tall buildings, exploiting the latest advances in construction materials and methods. The result is a structure that surpasses anything that has been achieved before.
Until the 1990s, concrete wasn’t a cost-effective solution for the construction of tall buildings – it had limited strength, it was heavy, and fabrication was longer than for steel construction. Generally steel was looked at as the solution for super-tall buildings.
However, there have been significant advances in many aspects of concrete technology with great increases in strength, modulus and durability. High-performance concrete (HPC) mixtures provide a wide range of mechanical and durability properties to meet the design requirements of a structure. Even so, the challenges facing the structural and construction engineers on the Burj Khalifa project have been huge. Most of the Burj Khalifa is a reinforced concrete structure, except for the top, which consists of a structural steel spire with a diagonally braced lateral system. 330,000 m3 (431,600 yd3) of high-performance concrete is used throughout the building.
One of the major requirements for the successful completion of this project was the ability to pump the concrete slurry up to a height of 600 meters (1968 feet) in a short enough time span (around 30 minutes) to ensure the concrete remained workable and retained its high performance properties. Three high-pressure pumps were used at the construction site to lift concrete up to crews working at unprecedented heights.To decrease construction time, the concrete was designed to be self-consolidating (SCC), meaning a concrete mix that leveled itself solely due to its own weight, with little or no vibration. It spread into place, filled formwork, and packed tightly into even the most congested reinforcement, all without any mechanical vibration.
Great care was necessary to achieve and maintain the desired performance of concrete in this region. The Middle East is not a benign environment for concrete due to the extremely wide range of temperatures experienced throughout the year. The ability to pump and place concrete at high ambient temperature to significant heights while preventing excessive cracking and possible service life issues in the strong drying conditions was vital for the efficient and economic use of HPC. During the summer months, when shade temperatures can exceed 50°C (122°F), the concrete’s water content was almost completely composed of flake ice to achieve the common limit of 32°C (90°F). Whenever possible, and in particular during the hottest months, all pumping of concrete took place at night.
The importance of extensive testing of the concrete could not be overstated. Prior to the construction of the tower, extensive concrete testing and quality control programs were put in place to ensure that all concrete works were done in agreement with all parties involved. These programs started from the early development of the concrete mix design until the completion of all test and verification programs. Five different concrete mixture designs were tested. The testing regimes included, but were not limited to the following:
• Test the mechanical properties of each mixture, including compressive strength, modulus of elasticity, and split tensile strength
• Test and measure the concrete properties (fresh and hardened) before and after pumping
• Test for creep and shrinkage for all mixtures
• Test for water penetration and rapid chloride permeability
• Test the shrinkage of the concrete mixtures
• Pump simulation testing for all concrete mixtures grades up to at least 600 meters (1968 feet)
The Burj Khalifa is the current state-of-the-art in super-tall buildings, exploiting the latest advances in construction materials and methods. The result is a structure that surpasses anything that has been achieved before.
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