The construction of the new I95 toll lanes for the Maryland Transportation Authority required a complete redesign and reconstruction of the I95N & I695 interchange. This project required 53,720 cubic yards of concrete in the substructure and superstructure. The interchange construction began in 2007, and should be completed near the end of 2009. The contractors for the project include Wagman, Corman, and McLean.

The design of the substructure was categorized as “mass” concrete by MdTA. This created concern for controlling the concrete temperatures to prevent thermal cracking. From past experience on Virginia’s Route 895, and the Woodrow Wilson Bridge, it was recommended to use a maximum of 75 % replacement of slag cement for Portland cement to control maximum temperature, and temperature differential (Temperture vs Time Graph). The specified mix for the substructure was SHA Mix 3, with a 3500 psi strength requirement, and minimum cementitious content of 580 lbs/cy.

The state of Maryland has specified slag cement replacements of 25% – 50% in their concrete mixes since the early 1980’s, but 75% raised some concerns from the contractor relative to early strength gain for stripping forms. Initial testing was conducted with the submitted mixes by Flood Laboratories, Chicago, Ill. (Tail Batch Data) to determine early strength, 28 day strength, and heat generated. The test data verified strength and temperature requirements. The concrete was supplied by S&G Concrete, and the slag cement (NewCem) was manufactured by Lafarge NA at their Sparrows Point plant.

The superstructure consisted of Mix 6 for the decks, and Mix 6 Slipform for the barrier walls. The Mix 6 and Mix 6 Slipform used replacement levels of 50 % which provided not only strength enhancement, but improved resistance to sulfates, reduced permeability, and reduced expansion due to alkali reactivity.

Joe Jachelski, Project Coordinator, from MdTA, and Gradon Tobery, Construction Manager, feel the project complies with Governor O’Malley’s initiative of “Green Build”. The use of slag cement impacts sustainable design. For every ton of slag cement used (7160), it reduces approximately 90% 6440 tons of CO2 that would be emitted into the environment. Also, the sustainable site requirement was achieved by constructing the new interchange within the footprint of the old, not requiring the purchase, or development of any additional right-of-way.

George Hastings, from Gannett Fleming Inc., materials testing and control, said the performance of the slag cement mixes was consistent, allowing the placements to be on schedule.

Additional pictures of the project can be seen at the Maryland Transportation Authority Website.

www.mdta.state.md.us , then click on I-95 Express Toll Lanes.