Downtown’s next office tower can begin its 54-story climb along the banks of the Chicago River following a carefully choreographed concrete pour early Saturday morning.

Starting before sunrise, crews from Clark Construction directed 3,300 cubic yards (more than 300 truckloads) of the gray stuff through the spindly arms of three mobile pumps to form the reenforced foundation mat of the building known as 110 N. Wacker.

The weekend pour was accomplished in roughly eight hours with minimal impact to traffic. The construction site also welcomed the arrival of a red barge-mounted crane that same morning. The impressive machine can be seen floating up in a recently shared time-lapse video from Clark.

Over the weekend, the 110 N Wacker project team placed approximately 3,300 cubic yards mat foundation in just over eight hours! Once complete, this state-of-the-art skyscraper will further shape Chicago's iconic skyline. pic.twitter.com/14Z9omKSTu — Clark Construction (@ClarkBuilds) September 19, 2018

Under construction since spring, 110 N. Wacker replaces the 1950s-era former General Growth Building and will eventually climb to a height of 800 feet. It will be Chicago’s tallest purely commercial building since Two Prudential Plaza was built in 1990.

The Goettsch-designed tower will feature a glassy facade and a publicly accessible riverwalk set behind angled columns along the building’s western side. The plan also calls for a small pocket park along Randolph, ground floor retail, a soaring 45-foot-tall lobby, and 110 parking spaces concealed below Upper Wacker Drive.

Codeveloped by the Howard Hughes Corp. and Riverside Investment and Development, 110 N. Wacker will be anchored by Bank of America, which committed to 500,000 square feet in the waterfront building. Although the new office tower isn’t expected to open until 2020, construction fans can follow the action on the contractor’s overhead webcam.