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Case Study: Trump international hotel and tower, Chicago

The Trump International Hotel and Tower in downtown Chicago stands at a stunning 92 stories, made entirely out of reinforced concrete. A total of 194,000 cubic yards of concrete was used on the project. Architect and engineer Skidmore, Owings & Merrill specified high-performance concrete, and the concrete supplier designed the mixes. Columns and walls required 12,000 psi at 90 days up to level 51 with some lateral resisting elements up to 16,000 psi. SCC was specified for many of the structural elements because of reinforcement congestion. To reduce heat of hydration, high volumes of SCMs were specified for the mat foundation, which included a combination of slag cement, fly ash, and silica fume. At time of construction, the 5,000-cubic-yard mat foundation was the largest single SCC placement in North America.

The high-performance reinforced concrete system helped minimize floor thickness, creating higher ceilings. Residential floors also feature open spans up to 30 feet without requiring perimeter spandrel beams, permitting panoramic vistas of Chicago and Lake Michigan. Combining several innovative concrete technologies allowed for quick, efficient construction as well as new opportunities that are not available with conventional concrete.

Geopolymer Concrete

Although we are likely years away from widespread commercialization, one of the more interesting areas of research and development is on geopolymer concrete, which uses fly ash and/or slag and chemical activators as the binder in place of portland cement. Geopolymer concrete is made by using a source of silicon and aluminum, usually fly ash or slag, and combining it with an alkaline activating solution that polymerizes these materials into molecular chains to create a hardened binder. The more common activating solutions include sodium hydroxide or potassium hydroxide, which liberates the silicon and aluminum.

Compressive strength of geopolymer concrete is comparable to portland cement concrete or higher, and strength gain is generally faster with strengths of 3,500 psi or higher at 24 hours. Compressive strengths at 28 days have shown to be 8,000 to 10,000 psi. Research shows that geopolymer concrete has lower drying shrinkage, lower heat of hydration, improved chloride permeability, and is more resistant to acids. And its fire resistance is considerably better than portland cement concrete, which is already highly fire resistant, making geopolymer concretes ideal for special high-temperature applications.

To date, most of these products have not developed beyond the research and development stage. A company called Ceratech launched geopolymer concrete in in 2002 but later closed. A product called Pyrament was launched in the 1980s but was not successfully commercialized. Some of the drawbacks include the high cost and energy to produce the chemical activator, the difficulty and safety concerns in handling a highly alkaline solution, and the need to control temperature during the curing process. In addition, building code approvals are always a hurdle. Currently the most promising applications are in severe environments, such as precast concrete bridges, or other specialty applications, such as high-acid or high-temperature environments or for rapid repair.

The key to geopolymer concrete commercialization will be to develop low-cost, easy-to-use activators. One promising development is at Rice University, where engineers have developed a geopolymer concrete that requires only a small fraction of the sodium-based activation chemicals used in other geopolymer concretes. According to the researchers, they used sophisticated statistical methods to optimize the mixing strategies for ingredients. This resulted in an optimal balance of calcium-rich fly ash, nanosilica, and calcium oxide with less than 5 percent of the traditional sodium-based activator.

Photo: Greg Balfour Evans/Alamy Stock Photo

Case Study: 102 Rivonia, Johannesburg, South Africa

102 Rivonia Road consists of two main buildings with connected walkways in between to create a sense of connectedness and encourage collaboration between different areas of the office. It was designed with sustainability in mind, being 50 percent more sustainable than the average office building with a 4-star Green Star SA (South Africa) rating. Air-cooled chillers and a fire system that recycles used water also contributed to the project’s energy efficiency. Notably, the use of fly ash in the concrete reduced the overall material use of the project by 30 percent, which also heavily contributed to the project having a lower carbon footprint.

Case Study: Global Change Institute, Brisbane, Australia

As Australia’s first carbon neutral building, the Global Change Institute at the University of Queensland was designed to meet the highest level of sustainability. It is one of the first buildings to be registered for The Living Building Challenge. Some of the green building features include operable sun-shading, bio-retention basin, on-site greywater system, solar energy and thermal chimney. And it is the first building to include structural geopolymer precast concrete, significantly reducing the carbon footprint of construction materials.

Conclusion

More than 20 billion tons of concrete are produced around the world each year. As a result, concrete construction contributes about 5 percent of global CO₂ emissions primarily due to the cement manufacturing process. The demand for concrete will likely continue to grow as the population grows. In addition, the demands on strength, durability, and workability will continue to increase. A combination of traditional and advanced technologies will help meet these new demands. Technologies such as TiO₂ cements, SCC, SCMs, and fibers are being used now to varying degrees with outstanding results. Carbon capture and sequestration are in their infancy but show great promise. Fly ash beneficiation will help meet the demand for affordable, high performance concretes, and geopolymer concretes may one day help make concrete carbon neutral without sacrificing performance.

End Notes

¹TX Active. Lehigh Hanson. Web. 29 April 2021

²Ductal. Web. 29 April 2021

³First Graphene. Web. 29 April 2021

⁴CarbonCure. Web. 29 April 2021

⁵Solidia Technologies. Web. 29 April 2021

⁶Blue Planet. Web. 29 April 2021

⁷Greener Cement. Web. 29 April 2021