New materials and methods available to concrete construction crews in the past decade present a financial dilemma:
A flashy material may offer advantages despite its upfront cost, but how do you know you aren’t sending your overall project into the red?
A research team took a stab at this problem and released their findings this morning to the Construction Industry Institute’s annual conference in Chicago. In some cases, the team found overall cost savings. For other scenarios, builders had to open their wallets.
As part of an ongoing CII craft productivity research program, the team studied three recent innovations in concrete—modular formwork, self-consolidating concrete and high-strength rebar—comparing them to their traditional counterparts.
Limited benchmarks make this type of study valuable.
“There’s not a whole lot of data out there,” remarked David MacNeel, operations manager at Baker Concrete Construction, a member of the CII team who spoke to ENR on the sidelines of this week’s conference.
Steeling the Show
High-strength rebar generally wins out over traditional steel reinforcement, the study shows.
Compared to traditional, 60-ksi rebar, the high-strength variety, rated at 100 ksi, costs twice as much to buy upfront. But it reduces overall reinforcing steel mass by 14% to 49%, translating into a net cost reduction of 12% to 33%. This assumes a 100-ksi rebar cost of $1,200 per ton versus 60-ksi rebar’s $600 per ton, with a labor cost of $710 per ton.
“The high strength steel definitely seemed to be on the winning end,” said MacNeel, with the caveat that only one supplier, MMFX Technologies Corp., Irvine, Calif., currently offers it
“You got to plan for it,” MacNeel added. “You can’t automatically think that you are going to be able to run down to the Home Depot to get some high-strength steel. It isn’t going to happen.”
The big advantages of high-strength steel are reduced rebar congestion (so concrete can flow evenly around it), reduced weight and increased design strength. Its detractors are higher cost, more brittleness, more complex structural analysis and its limited availability, researchers say.