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Just before 3 a.m. on Saturday, February 14, the mercury read 27\u00b0F in downtown Chicago with dropping temps and winds up to 40 mph expected as the morning progressed.<\/p>\nJust before 3 a.m. on Saturday, February 14, the mercury read 27\u00b0F in downtown Chicago with dropping temps and winds up to 40 mph expected as the morning progressed.<\/p>\n
Still, it was the best weather the city had seen in days \u2013 so workers from\u00a0Goebel Forming\u00a0<\/strong>readied themselves as VCNA Prairie trucks carrying\u00a0self-consolidating concrete\u00a0<\/a>(SCC) rolled up for the mat pour supporting a new, 54-story tower at\u00a0150 N. Riverside Drive\u00a0<\/a>.<\/p>\n Designed by\u00a0Goettsch Partners\u00a0<\/strong>for developer\u00a0John O\u2019Donnell<\/strong>, the structure sits on a slim site beside the Chicago River, made even more challenging by the railroad tracks that crisscross it.<\/p>\n Unlike the structure just north of it, the new tower will not span the tracks; instead, its narrow foundation fits neatly between the tracks and the river\u2019s edge.<\/p>\n But the location \u2013 just blocks from the ice-bound shores of Lake Michigan \u2013\u00a0made the bitter temperatures even more difficult to take on D-day, says\u00a0Trinidad Vega<\/strong>, Goebel VP and Job Superintendent.<\/p>\n \u201cNo question \u2013 it was incredibly cold out there!\u201d he says. \u201cBut since we were working with SCC, we had a much smaller crew. Our two pumps remained stationary, and without the need to vibrate the mix, the carpenters, ironworkers and laborers working down in the hole were kept to a minimum.\u201d<\/p>\n The building\u2019s foundation measures 10\u2019 thick, 162\u2019 long and just 47\u2019 wide, Vega notes. From this slender base, the tower will flare out to maximum width at the 7th floor and measure 742 feet tall when completed.<\/p>\n In all, the job will require 55,000 cubic yards with 12 unique mixes, says\u00a0Steve Fleming<\/strong>, Prairie\u2019s head of Technical Services and Support.<\/p>\n Working closely with Goebel crews were Prairie\u2019s QC experts, both on-site and at nearby Yard 32, where trucks loaded with specially formulated and heated mix were scheduled to support placement of more than 200 yards per hour.<\/p>\n \u201cWe had one QC technician stationed at each pump on the site, monitoring flow and sending feedback to supervisors at the yard,\u201d says Prairie Senior Technical Support Rep\u00a0Gary Hall.<\/strong><\/p>\n A full set of tests measuring air, mix temperature, compressive strength and spread (the SCC equivalent of slump) were taken every 200 cubic yards by Flood Testing Laboratories, Hall notes.<\/p>\n Testing before, during and after the pour<\/p>\n \u201cFlowability was critical for this job,\u201d Fleming says. \u201cWe did extensive tests ahead of the pour to pinpoint the right levels of polycarboxylate-based, high-range water reducer and high-volume cementitious supplements such as fly ash to assure the mix would pump well without segregating.\u201d<\/p>\n Follow-up tests to confirm the concrete reaches 8,000 psi at 56 days will be taken. The mat does not have a specific early-strength requirement.<\/p>\n Other high-strength mixes specified for the job must meet exacting requirements. \u201cAbove the foundation to level 9, the design calls for 12,000-psi concrete with 6,600 ksi modulus of elasticity,\u201d says Fleming. The mix for floors 10 through 22 must deliver 10,000 psi and 6,000 ksi Ec , with all successive levels at 8,000 psi and 5,400 ksi Ec.<\/p>\nEarly day at Yard 32<\/h2>\n
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