The widening of I-95 from four to six lanes, between SR 528 and SR 519, comprising of approximately 120,000 cubic yards of mainline paving, is drawing to a conclusion in the first quarter of 2009.  The one hundred and fifty million dollar project is being nominated for an Environmental and Innovative award by the Slag Cement Association.

The project was started in 2007 by Kiewit Southern Company as a design build project.  Even though slag cement was new to Kiewit’s Florida team, Hanson Slag Cement’s (HSC) CAMCEM™ was a logical choice for consideration as a cementitious material based on other successful projects.  In fact numerous mix designs were considered, but two slag cement mixes stood out as dramatically superior in performance to all others based on strength, slump retention and ease of slipforming. 

Whereas 50% replacement of portand cement with slag cement is a common slag dose in Florida concrete and paving, this 60% replacement was a first in a project of this size.  The mix was developed in conjunction with HSC as a hot weather mix that would continue to improve paving characteristics even in high temperatures experienced in the summer in Florida.  The mix proved so robust, that it has been used year round, even in cooler winter Florida temperatures, with superior results both from a maturity meter and physical concrete break perspective.

The Florida Department of Transportation (FDOT), has allowed slag cement in its’ specifications since the mid eighties and has conducted numerous strength, permeability and sulphate tests to qualify slag cements for use in Florida.  In fact, in an aggressive environment, a minimum of 50% slag is specified in the state.

Mike Bergin – FDOT - State Structural Materials Engineer, stated that “As a general statement one of the properties that the Florida Department of Transportation considers a plus for slag cement is a reduction in heat when slag cement is substituted for a percentage of the ordinary Portland cement. Our current specification (Section 346) allows for a 50 to 70 % replacement, providing a substantial heat reduction during the hydration process as concrete is curing. Even at the replacement rates indicated in our specifications, the concrete still gains adequate strength for early form removal and does not generate excessive heat, which generally initiates cracking.”

Although slag cement was specified for durability and strength other benefits were realized by its use.  This is illustrated by the second SCA award nomination.  The environmental award nomination is due to the nature of slag as a recycled product. Since it is a byproduct of manufacturing iron there is less environmental impact from mining and burning of fossil fuels in the production of slag cement.  Thus even though concrete is a “green product” in its own right it can be improved further by using slag cement.  In this case the use of slag further lowered the carbon footprint for the project by 33 million lbs of CO2. 

In summary, the higher strength and durability of the concrete paving will lead to a longer life cycle, helping maintain Florida infrastructure for many years to come.  In addition, the environmental gains achieved will reflect Floridians growing concern for the environment.