August 2018


Sixth Street Viaduct Concrete Stays Cool in a Cool Way


Starting in late July, the Sixth Street Viaduct construction team began using liquid nitrogen to control the temperature of the concrete and help keep it nice and cool. Check out the picture above— you can see the cloud of water vapour coming out of the mixer trucks, after the liquid nitrogen and concrete materials were combined.

Dealing with concrete in high summer temperatures can be especially tricky, because higher temperatures can lead to a weaker final product. Most people think of concrete hardening as a drying process, but it’s actually important to keep the concrete cool and wet so that it cures and hardens correctly.

A chemical reaction that solidifies the concrete happens when the cement and aggregate mixture comes into contact with water. This reaction is exothermic, which means that it produces heat. Excess heat can cause the reaction to happen too quickly, which can make the hardened concrete especially prone to cracks. The Sixth Street team is trying to stop the reaction from happening inside the mixing trucks!

Sometimes cool water or a mixture of cool water and ice are used to control concrete temperatures on construction sites, but liquid nitrogen is a much more efficient coolant. This is because liquid nitrogen is extremely cold, with a boiling point of -321 degrees Fahrenheit. It can also cool the concrete much more uniformly than ice water can.

So if you see some steam coming from the Sixth Street Viaduct construction site, it's not a heavy metal band performing, it's just a hot day at the viaduct!

About the Project

Stay Involved!

The Sixth Street Viaduct Replacement Project is a new, 3,500-foot long viaduct connecting Boyle Heights and the Arts District across the Los Angeles River. The original viaduct was built in 1932, but had significantly deteriorated due to "concrete cancer"; it was demolished in 2016. The new viaduct will have ten pairs of lit arches, bike lanes and wider sidewalks, along with stairway access and bike ramps connecting to 12 acres of recreational and open space under the bridge. The $482 million dollar project is the largest bridge project in the history of the city. The bridge is funded primarily through the Federal Highway Administration, with additional City support. The viaduct is expected to be completed by the end of 2020.

To stay involved, sign up for email or text updates at:

The Bureau of Engineering is the City's lead agency for the planning, design and construction management of the City's public buildings and its public infrastructure. Engineering is also responsible for managing permitting for all construction that takes place in the public right-of-way, as well as managing the City's state-of-the-art online mapping system, NavigateLA. Engineering is committed to designing and building environmentally-sustainable projects that include extensive community input. Engineering projects and services support the City's goals of creating a prosperous, livable and safe city for all residents and businesses.

Follow us on Facebook (@6thstviaduct), Twitter (@6thstviaduct) and Instagram (@6thstviaduct)

And check out our website at