Nominee
RBC Gateway
Category
Innovative Project
Description
RBC Gateway is a 37 story multi use skyscraper totaling 1.2 million square feet. It is one of the ten tallest buildings in downtown Minneapolis, and includes: 531,000 square feet of office space, a five-star luxury hotel, 34 private condos, street level retail, 455-stall underground parking, and 17,000 square feet of public plaza.
Cemstone Products Company is the NRMCA member company that supplied 61,000 yards of highly technical concrete for this project. Concrete placements occurred from July of 2019 to May of 2022. Over 50 different concrete mixtures were supplied on this project, which included: mass concrete, up to 12,000 psi strength concrete, pumpable concrete that could go up 37 stories, air-entrained 5,000 psi lightweight concrete, exposed aggregate concrete, colored concrete, high-early strength concrete for post-tensioned decks, and many others.
Additionally, Cemstone provided Quality Control throughout the entirety of the project.
Evidence
Concrete used for the post-tensioned decks was the most significant amount used on the RBC Gateway Project. This mixture had a required compressive strength of 3,000 psi in 18-hours. Cemstone was able to reliably meet this compressive strength, which allowed the contractor to stay on schedule. This prevented extra labor hours and significant late penalties that could have occurred.
The typical method for obtaining this high early strength is to increase the cement content. Cemstone focused on obtaining this strength while limiting the increase in the cement content. Using data from the “NRMCA Member Industry-Average EPD for Ready Mix Concrete” document, it is estimated that the Global Warming Potential (GWP) was lowered by 73 kgCO2e/yd due to using this mix in comparison to the typical mix used for this application.
In January of 2022 Cemstone was able to switch the cement for this project from an ASTM C150 Type I/II cement to an ASTM C595 Type 1L cement. This change took the cement from containing approximately 4% limestone fines to containing approximately 10% limestone fines. It is estimated that this change lowered the GWP by an additional 29 kgCO2e/yd.
During placement of the concrete, the contractor required strict slump, air content, and temperature properties. Cemstone’s field technicians were always present at the ready-mix concrete plant and at the project during this time to ensure these plastic properties were met. For the 61,000 yards of concrete that was placed, no concrete was lost due to a failure to meet the requirements.
Reliably pumping concrete up multiple levels is much more cost effective than bucketing the concrete for placement. As deck levels get higher, pumping pressures increase and the risk of plugging the additional line increases. Cemstone was able to provide a concrete mix that pumped reliably without increasing the placement time.
With the RBC Gateway building located in downtown Minneapolis, the construction site was the size of the footprint of the building. The large amount of construction work going on in this small of a site, meant the project could be more hazardous. Cemstone had no injuries or safety issues on this project.
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