Concrete Innovation: ODOT’s Strategic Approach to Internal Curing

A look at the Oregon DOT’s strategy for implementing internally cured concrete.

Concrete is commonly used in bridge deck construction, and while it offers many advantages, a long-standing problem is its susceptibility to cracks. Shrinkage cracks, a type of cracking that occurs as concrete loses moisture and shrinks during drying, provide a path for water and other ions to the concrete’s interior. Over time, this leads to unplanned maintenance to address the cracking and preserve the structural integrity of the bridge.

The Every Day Counts round seven (EDC-7) enhancing performance with internally cured concrete (EPIC²) initiative is advancing internal curing as a remedy for shrinkage cracking issues in higher-performance concretes. Internal curing uses materials such as lightweight fine aggregates (a type of sand) to provide a source of moisture from inside the concrete as it cures, unlike conventional curing where water is supplied on the concrete’s surface. The result is a more uniform cure that resists cracks and improves durability—extending bridge deck lifespans by 25 to 50 years.

The Oregon Department of Transportation (ODOT) began piloting internal curing technology in 2017 and completed 15 projects between 2017 and 2023. David Dobson, ODOT Statewide Structural Materials Engineer, described ODOT’s implementation strategy during an EDC-7 EPIC² webinar. He said research and initial results showed internal curing could extend the service life of bridge decks and reduce the resources the agency was spending on bridge maintenance. However, getting contractor support was a challenge due to their perceived risk in using a new material.

Pausing the Pilots

A 2021 project, the Bear Creek Bridge, was a turning point in ODOT’s internal curing implementation program as they saw inflated bid costs. ODOT had assumed a small premium for material, freight, and stockpiling, but on this project the contractor bid came in at four times the engineer’s estimate. Several factors including contractor uncertainty with internal curing contributed to the higher bid. Changes in the implementation plan were needed to both gain contractor buy-in and maintain internal agency support for the technology.

Concerns voiced by contractors included that they perceived internal curing as too risky, they thought ODOT should conduct a lifecycle cost-benefit analysis, and they struggled to see the value in the technology. Dobson said ODOT took a strategic pause in implementation to address these concerns.

Addressing Contractor Risk

One step ODOT took to reduce contractors’ perceived risk was to simplify agency specifications to make them more straightforward and user friendly. They simplified the specification for internal curing by pre-determining the amount of lightweight fine aggregate needed to reach the desired hydration level. This amount, specifically for ODOT mixtures, came to about 350 pounds per cubic yard. Moving from providing a formula to making the specification more prescriptive reduced uncertainty for contractors at the time of bid, which improved buy-in.

ODOT also modified the agency’s standard test method to enable better aggregate conditioning and quality control during concrete production. Dobson said the modifications simplified the conditioning process and streamlined moisture testing, which improved consistency for contractors.

During this pause in the program, ODOT added approved sources to its Qualified Products List that would be ready to go during bid and mixture design development, providing a quick reference for contractors. ODOT also performed additional educational activities on internal curing with both contractors and suppliers.

Quantifying the Benefits

ODOT surveyed 11 of its bridge decks to compare shrinkage cracking in internally cured and traditionally cured decks, and the results were significant.

“We knew the research showed internal curing reduces cracking,” said Dobson, “and after our first projects, we knew the bridge inspectors were saying, ‘Hey, these bridge decks look really good. They’re not cracking like we typically see.’ But we didn’t have a number, so we decided to do a crack survey on high-performance concrete and compare normally cured decks with internally cured decks, and we saw a 70-percent reduction in crack density.”

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Listen to David Dobson in a short webinar clip to learn more.

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ODOT also performed a cost-benefit analysis on internal versus traditional curing using service life and maintenance needs for comparison. They found internal curing was comparable at (up to three times) the bid price of traditional concrete.

“Internally cured bridge decks are still cost comparable even if you were paying three times the bid price of your normal deck mixture,” said Dobson. “We’re getting a good bargain out of adding 350 pounds of sand, absolutely.”

Improving the Value Proposition

Since ODOT resumed implementation of internal curing, as-installed prices have decreased and stabilized, and the agency is seeking to further improve the value for contractors. ODOT is pursuing a decrease in wet-cure duration for internally cured bridge decks, from 14 days down to 7 days, to provide contractors a time savings. They are also investigating additional material sources within the region.

Internal curing is now ODOT’s default standard concrete for bridge decks, and staff are looking into other ODOT use cases, including paving and overlays. They are also recommending the practice to other agencies within Oregon.

“The 70-percent reduction in cracking is going to directly increase the service life of our bridge decks and fundamentally change the maintenance strategy,” said Dobson. “When we have a bridge deck that doesn’t crack, we have a lot more options in maintenance, a lot more flexibility, and time is not nearly as critical, because chlorides aren’t getting right down to the reinforcement on day one.”