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Portland Water Bureau

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June 2019 Update: Washington Park Reservoir Improvement Project

As the weather warms and the Washington Park gardens wake up, crews have been busy making significant headway at the Washington Park Reservoir Improvement Project work site. Accomplishments include:

  • Pouring the first wall sections
  • Setting up stations to infuse concrete with liquid nitrogen which help regulate concrete cooling temperatures
  • Removing of two dead trees outside of the construction work area by Portland Parks & Recreation.
  • Installing the second tower crane

Cooling Concrete with Liquid Nitrogen

Managing the placement and curing of concrete at the Washington Park Reservoir Improvement Project is a delicate act, particularly during the warmer months. As concrete is “batched at the plant” and then is placed and cures, its temperature heats up. During warm weather, it can heat to temperatures that cause thermal stresses and potential concrete damage. To reach the needed strength for the finished concrete, the heat levels need to be controlled to maintain the tolerances required in the reservoir design.

Watch an example video of liquid nitrogen
being injected into concrete.

To ensure the concrete does not overheat during the warmer months, the contractor will cool the concrete with liquid nitrogen. In the Reservoir 4 area, a liquid nitrogen tank and four bays are being temporarily installed. As concrete trucks enter the project site, they will pull into one of the bays where the load will be injected and mixed with liquid nitrogen. Then the truck will move to the construction zone in Reservoir 3 and the concrete will be pumped into the waiting forms.

Things to know about liquid nitrogen:

  • There is the possible presence of fog at the work site. The boiling point of liquid nitrogen is -321 degrees Fahrenheit. When it hits air, it boils and chills the surrounding air, causing the humidity in the air to condense into fog. When this process is in operation, neighbors may notice a fog in the area of Reservoir 4.
  • Liquid nitrogen is cold enough to cause severe frostbite upon contact with living tissue. Workers will be wearing proper safety gear when injecting the nitrogen into the concrete trucks to help prevent contact or inhalation of the extremely cold vapor.
  • A common use of liquid nitrogen is in the freezing and transport of food products.

About this Project

The new 12.4-million gallon, seismically reinforced underground reservoir is being built inside the footprint of the former Reservoir 3. (upper) A new reflection pool on top of the reservoir will retain the historic look and feel of the original. The new reservoir has been engineered to withstand ongoing landside encroachment and potentially catastrophic effects of a major earthquake.

The new reservoir will supply water to Portland’s west side, serving approximately 360,000 people, including all downtown businesses and residents, 20 schools, five hospital complexes, and more than 60 parks.

This system of water conveyance and storage makes Portland a livable and thriving community, ensuring public health and economic viability.

Learn more about this project and the benefits it will provide to our region at