Internally cured bridges stand the test of time

by tanya_martins | January 17, 2025 8:12 am

By Darren Medeiros

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Early-age cracking in bridge decks and structural elements can significantly reduce the functional life of a bridge, necessitating frequent repairs and premature replacement. Cracked and otherwise more permeable concrete structures can represent a high cost to Departments of Transportation (DOTs), their constituents, and the environment. Project stakeholders can mitigate these economic and ecological costs by using less permeable, more durable and more resilient concrete materials to extend a bridge’s service life.

Internally cured concrete has been shown to reduce instances of both autogenous and dry shrinkage to decrease the potential for early-age cracking. This supports a concrete that is less permeable and, thereby, more resistant to chloride attack than traditionally cured mixes. Additionally, when internal curing is facilitated through pre-saturated lightweight aggregates, such as expanded shale, clay, and slate (ESCS), it can produce a denser cement microstructure,¹ supporting less permeable concrete. This is especially true for concretes with high fly ash or other cementitious materials, which can reduce chloride permeability by as much as 
50 percent.² Further, using prewetted ESCS to facilitate internal curing can benefit bridge repair and construction projects in hotter climates by reducing the thermal stresses concrete experiences during curing, thereby delaying and minimizing the risk of cracking.³

The discussion around more resilient infrastructure is timely as the construction industry nears 2030’s sustainability goals, considering the present state of the country’s highways, bridges, and roads. In the 2021 Infrastructure Report Card, the American Society of Civil Engineers (ASCE) stated that 42 percent of highway bridges are more than 50 years old, the expected end of the service life for most bridges in the United States. Hence, engineers, specifiers, and other project stakeholders are at a critical juncture in designing more resilient bridges. Internally cured concrete can be an essential step in realizing this goal. As less permeable concrete, it can contribute to longer-lasting bridges that need fewer repairs over their service life—especially in locations near saltwater or ones where salt-based deicers are used. This reduces the total cost of ownership of a structure and contributes to improved infrastructure.

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Internal curing and early-age 
cracking mitigation

Generally, internal curing is curing concrete from the inside out. Since 2013, the American Concrete Institute (ACI) has defined internal curing as “a process by which the hydration of cement continues because of the availability of internal water that is not part of the mixing water” and has outlined specific standards in ACI 308.1.

Prewetted ESCS fine aggregate supplies additional water throughout the concrete mix to continue hydration after the concrete is set. As the concrete cures, it draws the water out of the pores to keep the mix internally hydrated. The extra hydration reduces shrinkage until the concrete gains enough strength to minimize cracking, a common cause of chloride penetration. In a 2009 study, researchers stated using lightweight fine aggregates contributes to a 
67 percent reduction of autogenous shrinkage at 
28 days and a 37 percent reduction in drying shrinkage at 90 days.⁴ Given shrinkage can be a significant contributing factor to cracking, lowering the amount of shrinkage that occurs can be a practical step towards mitigating the number and size of cracks compared to conventionally cured concrete, which results in a less permeable material. Without cracking and microcracking, concrete has 
a smaller chance of corrosion due to chloride attack, which can prolong the lifespan and durability of 
the material.

In addition, ESCS can help concrete mixes overcome some limitations associated with using concretes with high fly ash content. According to the Federal Highway Association (FHA), this material, along with other supplementary cementitious materials (SCMs), can help concrete become less permeable and improve its resistance to chemical ingress. However, high fly ash content can make concrete more prone to shrinkage and cracking.⁵ Saturated lightweight aggregate contributes to slower hydration of concretes with high fly ash content, allowing pozzolanic reactions to occur, thereby improving the density of the cementitious mix and mitigating instances of autogenous shrinkage and early-age cracking. As such, ESCS lightweight aggregates can be instrumental in reducing factors that contribute to early-age cracking while supporting generally less permeable concrete mixes.

A less permeable concrete means lower risks of chloride attack

Concrete structures that experience less cracking during curing and are generally less permeable tend to have longer lifespans than average because they can protect steel reinforcements from corrosion caused by the ingress of chloride and other chemicals. It is estimated that chloride attack is responsible for 40 percent of concrete failures.⁶ As a result, producing concrete that guards against the penetration of corrosive chemicals is a vital first step toward creating longer-lasting, more resilient bridges.

This is especially true in locations near saltwater or where salt-based deicers are frequently used. In both circumstances, chlorides are diluted into water—a danger compounded in areas that experience rapid freeze-thaw cycles. If concrete structures in these locations are cracked, chloride-rich water can infiltrate, leading to rapid corrosion of the rebar. When the steel corrodes, the concrete structure experiences a reduction in tensile strength and load-bearing capacity. This, in turn, can make a bridge deck more prone to failure. While cracks represent a more substantial means for chloride attack, generally, more permeable concretes can also be vulnerable to chemical penetration.

Concrete with a lower risk of cracking and a denser cementitious mix can withstand the elements longer, reducing the need to repair, replace, or rebuild structures. In a 2013 study, the Indiana Department of Transportation (DOT) constructed four bridges with internally cured concrete and compared the performance of these bridges to traditionally cured ones.⁷ The results of this study indicate that internally cured concrete bridges have the potential to more than triple the service life of a typical bridge deck in Indiana due, in part, to the material’s ability to reduce early-age autogenous shrinkage by more than 80 percent. Likewise, the New York DOT used internally cured concrete in multiple bridges across the state to quantify the benefits of this curing technique. Experimental results show a 70 percent reduction in cracking, including several multi-span bridges that showed no cracking. The decrease in cracks supports improved resiliency in bridge construction.

Further, internal curing is also achieved when concrete uses ESCS to meet structural lightweight concrete (SLC) parameters. In addition to reducing early-age cracking, SLC made with ESCS enhances the bond between the aggregate and the surrounding cementitious matrix. The stronger bond between the aggregate and binder further reduces cracking and other forms of permeability to support a more durable and resilient concrete. This, in turn, extends the material’s lifespan and reduces the environmental impact of structural maintenance over the building’s service life.

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Examples of internally cured bridges supporting resilience

The benefits of internally cured concrete bridges extend beyond Indiana and New York. DOTs from Utah to Louisiana have used this method of curing to support longer-lasting bridge decks and structures. Often, internal curing begins as a small field test that is studied. Once a DOT has data that quantifies how internal curing can support its bridge projects, it uses this type of concrete on a large scale.

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For example, in 2012, researchers at Brigham Young University evaluated bridge decks across multiple Utah locations. These decks used both traditional and internal curing techniques. They found that, on average, the conventionally cured bridge decks had between four and 21 times as much cracking as the internally cured decks at five and eight months. In addition, the cracks on the traditionally cured decks were located throughout the bridge, whereas those in the internally cured decks were mainly found on the deck ends.

Similar results were shown in Louisiana. The engineering department of the Lafayette Consolidated Government first used internal curing on a small five-span bridge on West Congress Street at the west end of the parish. Of the project, Tyson Rupnow, Ph.D., P.E., associate director of research at the Louisiana Transportation Research Center (LTRC), says, “Internal curing helps reduce concrete cracking, thus allowing us to increase the service life of our deck structures and reduce overall maintenance costs.”

As a result of this small project, the Lafayette Consolidated Government modified its bridge specifications to require internal curing on exposed concrete elements—diaphragms, deck surfaces, guard rail walls, and approach slabs—to improve the return on investment (ROI) of taxpayer dollars.

It is important to note internal curing also supports non-bridge pavements. In 2005, a paving project in Hutchins, Tex., used internal curing to minimize cracks. Due to the improvements this curing technique provides, lightweight aggregate was used in more paving projects throughout the Dallas Fort Worth area. A report on this project states internal curing resulted in the mitigation or elimination of plastic and drying shrinkage cracking and limiting the effects of self-desiccation—an important factor given the extreme heat of Texas summers. Contractors reported the concrete was also easier to work and consolidate, which reduced the total placing time. Similarly, the Kansas DOT used internally cured concrete to support pavement design in a 24-km 
(15-mile) paving project just south of the Kansas City metropolitan area. The project showed benefits similar to those of the Texas project.

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Internally cured concrete extends service life

These examples and experimental data demonstrate internally cured concrete can be a viable first step toward improving the nation’s infrastructure. This method of curing significantly reduces the potential for early-age cracking in multiple climates and conditions. It also enhances cracking resistance in concretes with high fly ash content. These benefits result in bridges that can outlast the service life of traditionally cured bridge decks and structures.

Longer-lasting bridges not only represent a way to stretch taxpayer dollars for needed infrastructure repair and replacement, but they also support a more ecologically conscious approach to construction as fewer materials, fuel, and waste will be generated throughout the service life of internally cured concrete bridges. Considering the data from infrastructure projects across the United States, the question becomes whether internal curing will improve a concrete bridge and to what degree internal curing will enhance concrete bridge decks and structures both in the present and future.

Notes

¹ See “Internal Curing Improves Concrete throughout its Life.” Concrete In Focus by Bentz, D., Castro, 
J., Henkensiefken, R., Haejin, K., Weiss, J.

² Review “Permeability of concrete containing large amounts of fly ash,” Cement and Concrete Research, 24(5), pages 913–922.

³ “Cracking Tendency of Lightweight Concrete,” Highway Research Center by Byard, B. 
and Schindler, A.

⁴ “Internal Curing of Engineered Cementitious Composites for Prevention of Early Age Autogenous Shrinkage Cracking.” Cement and Concrete Research, 39(10), pages 893–901.

⁵ “Application of Internal Curing for Mixtures Containing High Volumes of Fly Ash.” Cement and Concrete Composites, 34(9).

⁶ “Evaluating effect of chloride attack and concrete cover on the probability of corrosion.” Frontiers of Structural and Civil Engineering. Pages 379-390. 10.1007/s11709-013-0223-9.

⁷ Documentation of the INDOT experience and construction of the bridge decks containing internal curing in 2013 (Joint Transportation Research Program Publication No. FHWA/IN/JTRP-2015/10).

Author

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Darren Medeiros is a regional technical salesperson at Holcim Lightweight Aggregates—Utelite Plant. He has two decades of experience in the lightweight aggregate industry and is active in several Expanded Shale, Clay, and Slate Institute (ESCSI) committees involving the use of lightweight concrete. 

Key Takeaways

Internally cured concrete, achieved through pre-saturated lightweight aggregates such as expanded shale, clay, and slate (ESCS), offers a durable solution to early-age cracking in bridge decks. This technique reduces autogenous and drying shrinkage, producing less permeable concrete that withstands chloride penetration—a critical factor in concrete corrosion and failure. Studies show that internally cured concrete triples bridge deck longevity, with Department of Transportation (DOT) projects across states such as Indiana, New York, Utah, and Louisiana demonstrating significant crack reduction. 
This approach enhances structural resilience and reduces environmental impact by lowering maintenance needs and extending service life. As the U.S. infrastructure ages, internal curing presents an effective strategy to build longer-lasting, cost-effective, and environmentally sustainable bridges.

Source URL: https://www.constructionspecifier.com/internally-cured-concrete-enhances-bridge-durability-and-longevity/

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