O&G has undertaken numerous concrete-heavy construction projects but the new Waterbury Bus Project ranks among the largest in site preparation and materials used, including 18,000 cubic yards of concrete furnished by the company’s own batch plants by the time the project ends in mid-2017. In a single week in mid-December, more than 700CY of high-performance concrete were poured here, with 50 mixer loads from Southbury and Torrington plants in one day.
The floors here will carry the city’s 98-piece fleet of transit vehicles, the largest of which tips the scales at 20 tons. The concrete mix engineered for the floors is rated at 5,000 pounds per square inch (psi). Bolstered by post-tensioning cables running through them, the floors will be more than able to bear the weight of the vehicles and the administrative floors above.
Post-tensioning is integral to the design of high-strength concrete floors. It compresses the concrete member, providing big benefits: it reduces cracking and the need for expansion joints, holds any minor cracks that develop tightly together, allows structural members to be thinner, and permits longer spans in elevated members like floors, which makes for fewer pillars and more open, usable space. Concrete sets up quickly here. Says General Superintendent Corey Morin, “Thirty feet behind where we are pouring we’re already walking on the new deck. When we do a test break 24 hours after the pour it’s almost full strength – 4,000 to 5,000psi. It’s impressive.” The low-shrinkage, quick-curing concrete used here also carries an additive to inhibit corrosion where concrete contacts metal.
As floors are prepared for post-tensioning, a design-specific number of tubular plastic sleeves, each containing a twisted steel cable (called a tendon), thread their way through the form in a sinuous, up-and-down path that gives the slab upward arch, helping to distribute the load between columns and prevent sagging when dozens of buses are on the floor. After the concrete has been poured and has set to at least 3,750psi, the cables inside the sleeves are hooked to tensioning equipment. They are stretched with as many as 280kips (1,000 pounds-force) to a predetermined length to reach the proper engineered compression.
What tricks do you use when the winter temperature dips below freezing and you’re needing water-based concrete to pour normally and cure properly, so that you can keep pushing the job ahead? Morin weighs in again: “They can use hot water at the plant. Add accelerator if needed. We can heat the ground. We use insulated blankets with radiant tubing. From below in the open space we have heaters.” The heaters are three diesel-powered units pushing two million BTUs to keep the space under the floor at 45 to 50 degrees.
SETTING A SUCCESSFUL COURSE
Pre-construction activities pay big dividends, Morin and Sitework Superintendent Kevin Mierzejewski know, so they settled into that process last winter and spring, long before any field work began. “The success we’re having here is very much related to our pre-con time in the office, as a team, sitting down and reading through the documents before we came to the site,” says Morin. “It helps to understand everything inside out and to hit the ground running. You want to come out here and get working on day one,” Mierzejewski adds.
For project lead Morin, spending time in the Main Office where the Building Division Estimating Department is gave the project a leg up. “Not only were we planning the work but we were helping Ernie [Torizzo] and Rob [Hall] price the way we proposed to build it. It made for a tighter bid,” says Morin.
The likelihood of getting the productive subcontractors you want correlates to time invested with them pre-bid. “Typically when you bring a contractor you know and trust in early,” Morin says, “you’re asking for their expertise on how they’d attack the job, and at the same time they’re being educated on the documents in a way they wouldn’t in a simple pricing review. When they understand the flow of the job, they are able to be more competitive.”
Project Manager Mike Skapczynski runs the job. He has managed challenging ConnDOT projects for O&G before and brings a mindset more general contractor than construction manager, an asset here where O&G is self- performing a sizable portion of the work. To Skapczynski’s thinking the key to success is also in the planning: “On any job, particularly a large one like this, you’re unfortunately going to encounter unforeseen conditions and changes. But when you plan early and strategically, it gives you the capability to react to that kind of adversity more effectively, which enables you to keep the project on track and keep the subcontractors motivated.”
Initially the team pushed itself into a great position, two months out ahead of the schedule. When design issues began cropping up (to-date there have been 400 requests for information by the team where discrepancies between the plans and site conditions were found, and 100 design changes from the client) Mierzejewski was able to redirect sitework to fallback tasks while waiting for answers. As fallbacks were checked off theproject slowed back to the original schedule.
Because this is a large, one-off building with some exotic construction and lots of coordination, the stack of plan books is intimidating. Keeping the documents updated and accurate is the shared responsibility of Document Control Specialist Hristo Miljovski and Project Engineers Meghan Semenetz, Zach Mordenti and Brendan Behm.
BIM 3-D modeling is helping maintain productivity here. A comprehensive, architect-supplied three-dimensional model heads off “clashes” – pipes and ductwork both needing to run in the same space, for example – that could happen in the field. O&G’s Virtual Design and Construction Manager, Nick Castler, is the model’s gatekeeper, reviewing weekly input from the trades, updating the model and walking through areas of congestion on a big screen at weekly coordination meetings with the team.
Jim Perault is the Concrete Superintendent. He was hired by O&G for this project, the largest concrete project he has been in charge of in his 38-year construction career. “It’s going great. It’s easy to work for a large company with the resources O&G has. To have the support I’ve got here from Corey, Kevin and Zach makes it a lot easier to put my focus on the work. It’s nice knowing I’ve got smart guys to bounce ideas off of.” He points to a one-two punch giving this project another advantage. “Having a smooth relationship between excavation and concrete work is essential to getting this kind of job done efficiently, and with the company performing both it’s been a real plus. On top of that, self-supplying the concrete – I’m getting tremendous service. With a simple shout I get what I need. The plants are close to the job, too. It all works together.” The biggest challenge Perault has faced has been keeping pace with the design changes. “We’ve gotten through them and have kept the job on track,” he says.
Erecting structural steel has just started, masonry and block work is slated for April weather permitting, and as soon as the steel is ready a rubber membrane roof will go up while under-slab utilities installation and fine grading will go on in preparation for pouring slabs on grade. “Then it’s all hands on deck for mechanical and finish work and our final
push here,” says Morin.