Researching Internal Curing in Indiana

By Jack Spaulding, Hydraulic Press Brick Company

The Indiana Department of Transportation issued four bridge contracts for 2013. The specified concrete mixtures will incorporate internal curing using ESCS lightweight aggregate as an integral part of the concrete deck and cast side rail designs. The four bridge decks are located with two in the north and two in the south-central section of the state.

Contract B-33379 is on Interstate I-69. The northbound lanes over Little Black Creek in Grant County are designed with internal curing while the southbound lanes are designed with conventional concrete. The project will give a direct, side-by-side comparison of internally cured and conventional concrete bridge decks exposed to the rigors of interstate travel.

The three remaining ESCS internally cured decks are smaller structures and located in traffic areas varying from light to moderate traffic patterns. All of the decks are in areas of moderate/high freeze thaw and experience repeated wintertime anti-icing liquid chloride and salt applications.

Purdue University is working with the Indiana Department of Transportation on a long range internal curing research program that will go on for “decades.” Purdue’s research team directed by Dr. Jason Weiss is present at each concrete placement. The team calculates internal and external moisture levels of the stockpiled lightweight fine aggregate, and coordinates with INDOT on mixture design water adjustment. Along with the INDOT testing personnel on the project, they determine slump, air entrainment and unit weights, as well as cast cylinders for compressive strength and chloride permeability. Additionally, Purdue is taking 10 to 20 barrel samples on each of the projects for long range observation of chloride transport.

INDOT’s internal curing test program represents one of the most diligent, meticulously coordinated concrete field investigations in the country. Nothing is left to chance as field and lab results are documented, compared and confirmed by multiple testing entities.

These internally cured concrete testing projects have attracted interest from several other various agencies and private concerns that have visited the projects. Some have even taken samples for their own testing. The concept of internal curing is very simple and has been known about and verified for over 60 years. Internal curing involves a minor change to the concrete mixture where a small amount of sand is replaced with prewetted lightweight aggregate. IC concrete looks and acts almost identical to conventional concrete.

INDOT’s is to be complemented, as their position is to give the concrete industry, the State of Indiana and the Federal Highway Administration accurately documented advantages for using internal curing in structural concrete.

INDOT’s efforts are already paying off as their Office of Material Management materials supervisor, Tony Zander, simplified the field testing of free water and absorbed water in lightweight aggregate fines by using a centrifuge extractor. Rather than undergo a time consuming, towel-dry method which can be problematic under field conditions, Zander has researched the extractor results to correlate with the towel-dry results when the centrifuge extractor is operated at 500 rpm for 20 minutes. Purdue University has done similar test comparisons using Zander’s method and found 3 minutes at 2000 rpm is equivalent to towel-dry results and to the centrifuge operated at 20 minutes at 500 rpm. Tim Barrett, field team leader for Purdue said, “This fast track method gives us the ability to actually test the absorbed and free water amount of the saturated lightweight aggregate fines used in every load of concrete.”

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