Repair and Treatment of Alkali–Silica Reaction (ASR)-Affected Transportation Infrastructures: Review and Interview

Abstract

Alkali–silica reaction (ASR) can create significant cracking, compromising the durability and structural integrity of concrete elements. Currently, there is no known way to halt or reverse ASR damage, and the expansion will continue until it impairs ride quality or structural capacity, requiring the replacement of the affected elements. For certain existing structures or structural elements, the progression of an alkali–silica reaction may slow down depending on the type, dimensions of the affected element, service conditions, and environmental factors. Early intervention with repairs, however, may delay the need for replacement and extend the service life of the structure. Repair methods, such as crack filling, sealing, and breathable coatings, help reduce moisture intake and slow expansion. These repairs can also be combined with strengthening techniques to counteract the expansive forces caused by ASRs. The primary goal of these repairs is to extend the life of the structure until replacement or abandonment is necessary. There is a lack of information regarding the long-term performance of repairs and the most widely accepted repair methods. However, the literature and knowledge from the field shows that the time gained through these repairs varies significantly depending on location and exposure conditions, indicating that replacement remains the only reliable solution. Still, given that repairs can cost only 10–20% of full replacement, they remain a viable option for agencies managing limited budgets for immediate replacement.

1. Introduction

The alkali–silica reaction (ASR) is a chemical reaction that begins with the dissolution of reactive silica existing in the aggregate at high pH due to the presence of alkalis in concrete pore solution, resulting in the creation of alkali–silica gels [1,2]. The ASR gels that have high water absorption tendency cause localized stresses resulting from expansion. Some ASR gels have high water absorption and, consequently, high swelling capability, which can cause concrete cracking, spalling, pop-outs, and overall durability reduction, resulting in significant maintenance and reconstruction costs to concrete infrastructure [1,3,4]. As a result of the observed deterioration of numerous concrete structures such as dams, pavements, bridges, walls, barriers, and nuclear/power plants, the ASR is known to cause a major infrastructure durability issue worldwide [1,2].

Presently, there are well-established methodologies for identifying aggregates that may potentially react and effective measures to mitigate the risk of detrimental reactions in new concrete construction [5]. However, many older concrete structures worldwide are affected by ASRs to varying degrees, largely due to the absence of effective testing methods or guidelines at the time of their construction. Since the ASR compromises the strength and durability of concrete structures, it is advisable to explore the application of suitable technologies to delay the progress of ASRs or to address the resulting symptoms, thereby extending the structure’s service life until a full replacement of the distressed element is made.

For an ASR to occur, the following conditions must be present: (1) concrete must contain a sufficient amount of alkalis; (2) the aggregates in the concrete must possess enough reactive silica; and (3) there must be adequate moisture in the concrete to sustain the reactions [1,2,3,4,5,6]. Therefore, when seeking to mitigate or retard an active ASR by addressing its root causes, efforts should be directed toward minimizing or eliminating the factors mentioned above [6].

Stopping an ASR in existing structures is difficult, sometimes impossible, and may require waterproofing with coatings and/or slot cutting to release stresses caused by the expansion of ASR gels or subjecting the element to compression if possible [1,6]. On the other hand, the stages and mechanisms through which ASR expansion occurs are still unknown [7]. The complexity of an ASR and the wide range of factors influencing its manifestation and progression in various applications contribute to the lack of a standardized solution. For this reason, there is still no unanimous approach for the repair and treatment of ASR-affected structures. Some technologies may be in practice internationally but may not be widely known or accessible in other regions due to differences in environmental conditions, stress levels, technology availability, and expertise. Therefore, understanding the diverse approaches and technologies used internationally becomes essential to develop effective repair and treatment methodologies for different parts of the structure.

This study aims to complete an extensive literature review to investigate the repair and treatment strategies employed globally for structures affected by an ASR. Additionally, this study seeks to conduct a comprehensive survey of US state Departments of Transportation (DOTs) to provide insights, into both successful and unsuccessful ASR repair and rehabilitation strategies employed in each state. The goal is to gain valuable insights into the long-term effectiveness and feasibility of ASR repair and rehabilitation strategies for managing ASR-affected structures. This effort aims to assist transportation agencies in developing their own ASR mitigation and repair or replacement practices, drawing from the experiences of other agencies. The specific objectives of this study were to achieve the following:

• Review the current practices employed by US state DOTs and international sources for addressing ASR-affected structures;
• Identify commonly used repair and treatment techniques;
• Evaluate the success rates and challenges faced in implementing these strategies;
• Determine the mitigation strategies in new construction.

2. Methodology

2.1. Literature Review

A systematic literature review was conducted to synthesize current research on ASR-affected structures. The objective of this search was to achieve the following:

• Locate peer-reviewed and the other published literature or credible research, best practices, and documentation related to the repair and treatment of structures affected by ASR;
• Analyze the various approaches, technologies, and materials used to repair ASR-affected structures;
• Evaluate the performance, advantages, and limitations of different repair and rehabilitation strategies;
• Identify emerging technologies and innovative solutions that show promise for ASR mitigation in new construction;
• Provide insights on best practices and recommendations based on the findings.

The literature search was not limited to transportation infrastructure; research related to dams, nuclear power facilities, viaducts, and maritime structures was also considered.

The literature search was conducted using academic databases including TRID, RIP, ASCE Library, Google Scholar, ScienceDirect, ROSA-P, etc. Search terms included all forms of the following: alkali-silica reaction, alkali-silica reaction, ASR, alkali-aggregate reaction, AAR, mitigation, inhibition, repair, control, rehabilitation, remediation, suppression, management, assessment, service life, arrest, effective, successful, strategies, treatment, department of transportation, prevention, challenge, lessons learned, structure, bridge, infrastructure, and influence. Since ASRs develop over a long period and considerable efforts have been made to mitigate ASRs in newly constructed structures since the 1990s—resulting in fewer ASR cases today compared to the past—no specific limitation was imposed on the publication date for the reviewed studies.

2.2. Survey of State DOTs

After reviewing the literature on ASR repair strategies, this research employed semi-structured interviews to explore the practical experiences and challenges faced by state DOTs in addressing ASR issues across different states. The main objectives of this phase were to achieve the following:

• Identify and contact all state DOTs across the country;
• Gather information on their practices, policies, and experiences regarding ASR-affected structures;
• Obtain data on the methods, materials, and techniques used for repair and treatment;
• Analyze the success rates, challenges faced, and lessons learned from their experiences;
• Assess the effectiveness and durability of the implemented strategies;
• Determine the mitigation strategies in new construction.

Semi-structured interviews featuring a set of prepared questions (see Supplementary File S1) but allowing room for open discussion were used as the primary method. This approach provided a balance between structured questioning and flexibility, enabling participants to elaborate on their experiences while ensuring comparability across interviews.

Participants were selected by contacting material divisions in each state DOT, along with representatives from bridge divisions where relevant, targeting professionals directly involved in managing the ASR-affected structure. Interviews were conducted via video conferencing to accommodate the geographic spread of participants. In total, 29 interviews were completed, each lasting approximately 60 to 90 min. Figure 1 displays the states involved in this study: green represents states with no ASR issues, red indicates states with ASR issues that were interviewed, and gray denotes states that did not participate in this study.

Figure 1. Interviewed state DOTs: States with reported and confirmed ASR issues are shown in red, and states without reported ASR issues are shown in green. States shown in gray are those not participating in this study.

No bias was introduced in the selection process, as all DOTs were contacted; however, not all responded or chose to participate. Therefore, a limitation of this methodology is the potential unwanted bias resulting from the limited participation, which may not fully capture the diversity of experiences across all DOTs.

3. Findings

3.1. Literature Review

The following section presents examples of structures that have experienced ASR deterioration from various countries, along with the methods used for repairing or replacing the elements affected by ASR distress. The elements include pavements, bridge abutments, bridge decks, beams, and bridge substructures. Also included are the laboratory evaluation and the exposure sites to determine the effectiveness of different repair techniques. The literature review is summarized in Table 1, Table 2, Table 3, Table 4, Table 5, Table 6 and Table 7. Supplementary File S2 provides a detailed write-up on each case, offering further insights into each repair.

Table 1. Repair strategies for hydraulic, marine, and wastewater structures affected by ASR.

Structure	Time to Distress	Cause and Damage	Repair Strategies	Repair Effectiveness	Ref.
Val De La Mare Dam, Jersey, UK   Construction: 1958–1962	9 years (1971)	Cause: -Aggregates with reactive silica and cement alkali content of up to 0.95% Na2Oeq.   Damage -Cracking and differential displacement in mass concrete blocks.	In 1974: -Anchoring into underlaying rock with post-tensioned steel bars. Pressure relief drainage holes were also drilled. -Polymer grout was used to seal cracks.   In 2011: -Lining with polyvinyl chloride (PVC) geomembrane and geotextile. The liner was bonded with epoxy resin and stainless-steel strips.	1975 to 2010: -Expansion continued; -One anchor failed; -Grout ineffective in sealing cracks; -Service life extended;   2011 to date: -No further updates are available.	[8,9,10]
Maentwrog Dam, UK   Construction: 1926–1928	N/S *	Cause: -Use of greywacke reactive aggregates.   Damage -Cracking and seepage.	In 1944: -After minimal success in reducing leakage, the upstream face was reinforced using the gunite method.   In 1958–1978: -The gunite layer was removed, and the upstream face was covered with glass fiber-reinforced bitumen; -Several grouting attempts were made.   In 1983: -Cracks on the upstream face were sealed using an underwater elastomeric sealant.	In 1992: The dam had to be replaced due to severe ASR damage.	[11]
Gravity Dam, India   Construction: 1962	25 years	Damage -Cracks on the upstream face; -The structural stability of the dam was not compromised, but its serviceability was affected.	In late 1980s: -Cracks on the upstream face were sealed with epoxy grout and then painted with epoxy.   In late 1990s: -Various repair products were employed; -A specialized repair mortar was applied as a cementitious slurry to the pre-saturated surfaces of the existing structures.	Late 1990s to date: -No further updates are available.	[12]
Wastewater Treatment Plant, OK, USA	N/S	Damage -Widespread map cracking; -Large cracks; -Out-of-plane displacements.	-A structural retrofit was implemented; -Large ring beams were designed and dowelled into the existing basin walls; -Existing cracks were sealed by applying a robust epoxy-based coating; -Large cracks were sealed with epoxy injection.	-The coating is expected to last around 20 years, and, with one additional reapplication, the overall service life of the structure is expected to extend over 35 years; -The overall repair cost was 22.8% of the replacement cost; -No further updates are available.	[13]
Marine Structure, Western Australia   Construction: 1962	39 years (1992)	Damage -Cracks measuring 0.4 to 0.6 mm in width; -The cracks varied in depth from 50 to 150 mm and were most severe at the ends of the beams; -About 50% of the transverse beams and 20% of the longitudinal beams exhibited these cracks.	-A trial silane coating was applied to one of the transverse beams.	-The silane coating effectively reduced the rate of expansion; -The silane coating was not sufficient to resolve the problem entirely; -Replacing the affected components was determined to be the most effective solution.	[14]

* N/S: Not specified.

Table 2. Repair strategies for bridge structures affected by ASR.

Structure	Time to Distress	Cause and Damage	Repair Strategies	Repair Effectiveness	Ref.
7 pre-stressed post-tensioned single-span UK Bridge   Construction: 1974/75	7 years	-ASR cracking in precast prestressed concrete beams; -The strength of the beams had not been compromised.	-Cracks treated with epoxy (1984/85); -One bridge was painted with a protective coating (1987).	-Crack repair ineffective; -Structure remained in service; -No further updates are available.	[15]
Long Bridge, Australia   Construction: 1979	13 years	Cause: -Marine environment contributed to ASR. Damage -Severe ASR cracking in piles; -Crack widths ranged from 0.1 mm to a maximum of 8 mm; -Crack orientation being vertical, aligned with the axis of the pile.	-Piles with individual crack widths in the range of 2–3 mm where ASR expansion had nearly ceased were selected for repair; -Circular reinforced concrete jackets were used.	-No further updates are available.	[16]
Great River Bridge, IA, USA   Construction: 1992	<1 year	Damage -ASR in reinforced concrete pylons; -Crack widths ranged from 0.5 mm to 0.8 mm; -In 2003, the maximum measured centerline crack widths reached approximately 7.6 mm.	-Breathable coating was applied.	-The cost of the repair was approximately 7% of the bridge’s replacement cost; -No further updates are available.	[17]
Bibb Graves Bridge, AL, USA   Construction: 1931	25 years (1956)	Cause: -Use of siliceous gravel coarse aggregate and predominantly siliceous natural sand fine aggregate.   Damage -ASR in the reinforced concrete arch.	-Water blasting and silane sealer application; -A hydrophobic penetrating sealer was applied (2010); -Cracks were filled with flexible sealant (2010); -Epoxy flood coat applied at the top of the arches (2010).	-Not effective, expansion and cracking continued.	[18]
Montrose New Bridge, Montrose, Scotland   Construction: 1931	29 years (1960)	Damage -ASR cracks in superstructure.	-Cracks injected with epoxy resin and repair areas sealed with epoxy mortar (1979); -Reinforcing the bridge with straps, plates, and tensioned through-bolts to provide full containment (1994).	-Not effective, expansion and cracking continued; -Bridge was removed from service in 2004.	[19,20]
Elgeseter Bridge, Norway   Construction: 1951	40 years (1990s)	Damage -Vertical cracks in the columns; -Horizontal displacement of columns; -Closure of the expansion joint.	-Expansion joint, which had closed, was repaired with epoxy concrete (1995); -Columns were treated using different silanes (1999); -One row of columns was repaired using CFRP ** (2003); -The most critical beams were rehabilitated using CFRP (2013); -New membranes were applied to the driving lanes and pedestrian sections (2014 & 2015).	-The repairs completed before 2000 were not effective; -ASR remains a significant concern for this infrastructure.	[21,22,23,24]
Highway Bridge Columns, TX, USA   Construction: 1990s	5–7 years	Damage -ASR cracks in substructure.	-Different repair techniques as field testing: ➢ Sodium silicate applied over a blasted surface; ➢ Topical silane applied over the original painted surface; ➢ Topical silane applied over a blasted surface; ➢ Lithium vacuum impregnation; ➢ Electrochemical lithium impregnation.	-Lithium impregnation exacerbated ASR expansion; -Topical silane applied over a blasted surface did not reduce expansion; -Sodium silicate applied over a blasted surface, topical silane applied over the original painted surface, and lithium vacuum impregnation effectively controlled expansion.	[25]
Series of bridges, ME, USA   Construction: N/S	N/S *	Damage -ASR cracks in the substructure.	-ASR was treated using various surface treatment products, including 100% silane, 40% water-based silane, elastomeric coating, and electrochemical lithium (2010); -One severely deteriorated column was reinforced with four layers of CFRP.	-The lithium treatment appeared to increase expansion in the treated elements; -Silane treatment was not effective in reducing RH ***; -Silane treatment on a slender circular column may have reduced expansion; -It was too early to draw definitive conclusions.	[26]
4-span continuous reinforced concrete slab bridge structure, France   Construction: 1976	10 years (1986)	Damage -ASR damage in both superstructure and substructure.	-Cracks were repaired with an epoxy resin mortar (1990); -A coating system was applied (e.g., cold impregnation, a bituminous membrane, asphalt, and a gravel-coated wearing course) (1990); -The underside of the deck, piers, and abutments were coated with a polymer-modified cement mortar (1990).	-The waterproofing effort was unsuccessful.	[27]
Four railway bridges, Victoria, Australia   Construction: 1957–1958	N/S	Damage -ASR and Delayed Ettringite Formation (DEF) in the piers; The cracks varied in width and length, ranging from 0.1 mm to 10 mm.	-CFRP was used for severely affected piers; -Cracks were filled with epoxy injection; -Following the application of CFRP, a protective and waterproofing coating was added.	2019 to date:   -Repair remains fully functional and has not encountered any issues.	[28,29]
Railway Bridge, Montreal, Canada   Construction: N/S	N/S	Damage -Piers showed significant damage due to ASR.	-Holes were drilled into the piers to insert steel columns to transfer the bridge loads to deeper, undamaged concrete.	-The repair cost was only 10% of the cost of replacing the bridge with a new structure; -No further updates are available.	[30]
Hanshin Expressway, Japan   Construction: 1979	4 years (1982)	Damage -ASR damage was identified in the concrete piers.	-Piers were dried to a moisture level below 80%; -Cracks were filled with epoxy resin injected under pressure. Two surface repair methods were used (one involved epoxy resin coating, and the other, silane impregnation, was followed by polymer cement for protection).	-Repair was effective in controlling ASR.	[31]
Toyokawa Highway Bridge, Japan   Construction: 1979	21 years (1990)	Damage -ASR damage was identified in the concrete columns and beams; -Cracks widened progressively over time.	-Prestressing steel wire known as the PC confined method was applied.	-A significant reduction in the expansion rate was observed.	[32]
Bridge at the interchange of I-10 and I-45 in Houston, TX, USA   Construction: Late 1990s	7 years (2006)	Damage -The columns of the bridge were identified as suffering from ASR.	-The treatment methods evaluated included lithium nitrate applications (via vacuum and electrochemical processes) and various coatings/sealers such as sodium silicate and a silane/siloxane blend.	-Lithium treatments were not effective; -The effectiveness of silane depended on the surface preparation; -For other repair techniques, the results were inconclusive as the degree of the ASR and the state of the ASR in the treated elements had an impact on the treatment performance.	[26]
Curved prestressed reinforced concrete bridge, Portugal   Construction: 1998	11 years (2009)	Damage -Severe cracking was observed in certain piers due to ASR and DEF.	-A coating system applied consisted of a polymer-modified cementitious layer and a water-based acrylic layer (2021).	-Coating was not effective in areas exposed to moisture.	[33]
Barron River Bridge, Queensland, Australia   Construction: 1977	23 years (2000)	Damage -Severe cracking was observed in certain piers.	-A special wrapping system consisting of laminates of carbon or glass fabric that were saturated with resin was applied;	-The repair is still functional; -The repair cost 37.5% of the reinforced concrete encasement.	[34]

* N/S: Not specified. ** CFRP: Carbon Fiber-Reinforced Polymer. *** RH: Relative humidity.

Table 3. Repair strategies for highway barrier walls affected by ASR.

Location	Repair Strategies	Repair Effectiveness	Ref.
Canada	-Four different types of sealers: two silanes, one oligosiloxane, and one polysiloxane were applied on different sections of two highway median barriers (1991).	-Different performances were observed among different sealers; -The effectiveness of oligosiloxane- and polysiloxane-based sealers to control ASR expansion was limited to one or two years.	[35]
MA, USA	-A total of 30% lithium nitrate, applied both topically (in single, double, and quadruple applications) and by vacuum impregnation (single and double applications) (2005); -Lithium silicate and silane treatments (20% and 40% alcohol-based, and 40% water-based) were also applied (2005); -An elastomeric paint was applied over the existing silane (2010).	-Lithium treatment was ineffective; -Silane-based treatments were effective.	[26]
Interstate 49 in Northwest Arkansas, USA	-Three commercially available products including silane, elastomeric breathable vapor, and boiled linseed oil were applied to different sections (2013).	-Silane treatments effectively reduced expansion; -Linseed oil and elastomeric paint treatments yielded inconclusive results.	[26,36]
Interstate 89 in VT, USA	-Barrier walls were treated with three different sealers: 100% silane, 40% water-based silane, and 40% alcohol-based silane, as well as an elastomeric coating (2011).	-No definitive conclusions about the performance of each sealer could be drawn; -It was deemed too early to draw any meaningful conclusions; -No further updates are available.	[26]
GA, USA	-Different sealers, including 100% silane, water-based silane, alcohol-based silane, and three proprietary slurry products, were applied.	-No conclusions could be drawn about the effectiveness of the treatments; -No further updates are available.	[37]

Table 4. Repair strategies for pavements affected by ASR.

Location	Time to Distress	Repair Strategies	Repair Effectiveness	Ref.
South Africa   Construction: 1969	6 years	-Different approaches were tested: ➢ Removing the cracked concrete and replacing it with high-quality, low-shrinkage concrete; ➢ Undersealing involved filling the voids between the slab and subbase with various grout mixtures; ➢ Freezing the joints by injecting low-viscosity epoxy into the cracks and installing tie-bars; ➢ Applying geofabric-reinforced asphalt overlays.	-Replacing the pavement with high-quality concrete was the most effective repair strategy; -Undersealing had limited success in controlling vertical movement; -The freezing method was less successful than the concrete replacement method; -Geofabric-reinforced asphalt overlays showed limitations in handling environmental stresses and accelerated traffic loading.	[38]
Airport Runway Pavement, AR, USA   Construction: 1998	4 years (2002)	-Various surface sealants were tested including elastomeric coating, linseed oil, and silane coating (2008).	-RH * varied with ambient conditions; -Silane and linseed oil had minimal effect in ASR control; -Elastomeric paint was ineffective; -Ultimately, the runway was replaced (2012).	[39]
Air Service Apron Pavement, WY, USA   Construction: 1997	5 years	-Various chemical surface treatments and sealers including sodium tartrate, siloxane, silane, lithium nitrate, a combination of lithium nitrate with silane and siloxane, and boiled linseed oil were applied (2006).	-The repair was ineffective; -The apron was replaced (2008).	[40]
AR, USA	N/S **	-Two different silane-based sealers including 100% silane and 40% water-based silane were applied to the pavement.	-It was deemed too early to draw any meaningful conclusions; -No further updates are available.	[26]
DE, USA	N/S	-Pavement was treated by topical application of 30% lithium nitrate (2009).	-The repair was ineffective.	[26]

* RH: Relative humidity. ** N/S: Not specified.

Table 5. Repair strategies for other structures affected by ASR.

Structure	Time to Distress	Repair Strategies	Repair Effectiveness	Ref.
Generating Unit, Brazil   Construction: 1972–1997	<10 years	-Structural modifications were applied; -The accumulated stress was released by cutting some elements; -Turbine parts were repositioned.	-Repair was effective; -No further updates are available.	[41]

Table 6. Outdoor exposure testing (performed at UT Austin exposure site).

Specimen	Experimental Program	Repair Strategies	Repair Effectiveness	Ref.
Bridge decks	-A total of 60 bridge deck elements were constructed; -A total of 29 decks made with reactive fine aggregate, 29 decks made with reactive coarse aggregate, and two non-reactive slabs.	A series of treatment methods and materials were evaluated, including the following: ➢ Electrochemical impregnation with lithium nitrate (LiNO3); ➢ Vacuum impregnation with lithium nitrate (LiNO3); ➢ Silane treatments (40% water-based and 100% water-based); ➢ Topical lithium applications (both single and weekly); ➢ 50 mm thick asphalt overlay; ➢ 150 mm thick unbonded; ➢ Concrete overlay; ➢ Polymer overlay;	-Silane was effective; -Concrete overlays with a two-layer waterproofing membrane were effective; -Other treatments were not effective.	[42]
Concrete columns	-A total of 36 spirally reinforced concrete columns were constructed; -Half of the columns were made with reactive fine aggregate, while the other half used reactive coarse aggregate.	➢ Electrochemical impregnation with lithium nitrate (LiNO3); ➢ Silane treatments (40% water-based and 100% water-based); ➢ CFRP wraps (one, two, and four layers); ➢ Eliminator membrane.	-Electrochemical treatment with lithium nitrate did not yield any benefits; -Both types of silane were effective in reducing column expansion; -The outcomes for columns treated with CFRP wraps and the eliminator membrane were inconclusive.	[42]

Table 7. Experimental studies focused on repair strategies for concrete affected by ASR.

Specimen	Experimental Program	Repair Strategies	Repair Effectiveness	Ref.
Concrete beams	-A series of large beams (“large” is not defined) were fabricated; -One set of samples was tested in a mild climate with seasonal rain; -The other set was exposed to a climate having summer rainfall and dry cool winters.	-A total of 19 surface treatments were tested; - Treatments included acrylic PVA, magnesium fluosilicate, polyurethane, and silicone; -Silane and silicone were applied as pore liner penetrants.	-Surface treatments were not effective; -After four years of exposure, the silane retained its effectiveness, while the silicone lost its impact.	[43]
Concrete columns	-Two types of reinforced concrete (RC) columns, circular and square, were prepared for testing; -The specimens were kept in an environment at 8 °C and 100% RH for up to six months.	Two confinement approaches were applied to the damaged columns: ➢ Active Confinement: CFRP * wraps were applied after the columns had been exposed to environmental conditions for 1 and 2 months, while they still had the potential for further expansion. ➢ Passive Confinement: CFRP wraps were applied after 6 months of environmental exposure when the columns had reached their maximum expansion (which occurred after 3 months).	-CFRP was effective in maintaining the load capacity of these columns	[44,45]
Circular concrete columns	-A total of 26 columns, using reactive aggregates, were prepared; -The columns were wrapped with one or two layers of CFRP at different stages of expansion.	-CFRP was applied at various intervals after casting and monitored both radial and axial expansion.	-CFRP wrapping significantly reduces both radial and axial expansion; -The efficiency of reducing ASR expansion depended on both the timing of the CFRP wrapping and the number of layers applied to the column.	[46,47]
Concrete cylinders	-Concrete cylinders with reactive aggregates were cast; -Wrapping was applied at different stages of ASR expansion; -Key parameters such as expansion, stiffness damage index (SDI), and compressive strength were measured.	-CFRP and Basalt Fiber-Reinforced Polymer (BFRP) wraps were applied.	-Both wrapping systems were effective.	[48]

* CFRP: Carbon Fiber-Reinforced Polymer.

3.2. Lessons Learned from the Literature Review

Based on a review of 15 ASR-affected structures (presented in Table 1, Table 2, Table 3, Table 4, Table 5, Table 6 and Table 7), visible ASR distress on average appeared after 16 years with a standard deviation of ±11.5 years. The timeframe ranged from as early as 4 years to as long as 40 years, with a median of 13 years, indicating that, while some structures showed ASR signs earlier, most began to experience ASR distress between 13 and 16 years.

The same analysis of the three pavements indicated that ASR distress, on average, appeared after 5 years, which is shorter than the timeframe observed for bridges and hydraulic structures.

Suppressing ASRs in existing concrete is more challenging than preventing its formation in new concrete. Methods for mitigating ASRs in new concrete focus on reducing one of the essential constituents required for ASRs to occur: water, alkalis, or silica. However, there is no unanimous approach to suppressing ASRs in existing concrete, especially for certain structures, such as piers in the ocean or seawater, where it is impossible to eliminate both moisture and external alkalis. Studies have shown that exposure to sea water and deicing salts can significantly exacerbate ASRs, making it more challenging to control in these environments [49,50,51].

While replacing ASR-affected concrete members may represent the safest remedial measure, this may not be economically viable [52]. In many cases, controlling internal moisture through surface treatments is often the most accepted mitigation strategy, especially for thin cross-sections and high surface area-to-volume ratios, such as in pavements, bridge decks, and median barriers. However, the effectiveness of chemical surface sealers varies based on the material and product used, the severity of the ASR, the stage of ASR expansion, and the location and application of the treated element.

The most promising surface treatments are those that impede water entry into a concrete structure while allowing free water, either already present or periodically seeping in, to evaporate through the treatment’s pores. Ideally, the best treatment should function like human skin—impenetrable to external water but able to release moisture from within [43]. Among these, silane—despite not fully succeeding in reducing internal relative humidity—has proven to be the most effective for moisture protection in bridge elements and median barriers. This is in contrast to surface coatings, which may trap moisture already present in the concrete [25,43]. Different degrees of effectiveness have been observed with specific silane bases (i.e., alcohol base, water base, and 100 percent silane) [35,53]. However, it is important to note that, as the field implementation of different sealer products showed, not all surface treatment products are equally effective in reducing internal humidity and controlling ASR-induced expansion, so the performance of each product should be tested.

Various repair strategies have been employed to reduce moisture ingress through cracks. Flexible grouts or caulking are generally more effective at sealing cracks and preventing water entry. While rigid polymer- and cement-based grouts may initially stabilize cracks, their rigid nature can lead to adjacent cracks due to strong bonding with the substrate concrete [6].

Most studies on ASR-affected reinforced concrete structures indicate that, while large expansions, extensive cracking, and the degradation of strength and stiffness occur, the compressive strength is not compromised [54,55]. The literature agrees that ASRs reduce the static elastic modulus of concrete, even at low levels of expansion, raising concerns about concrete stiffness and the potential for reinforcement yield, which can affect deflections [32,56,57,58]. Consequently, many repairs have focused on restoring the strength of ASR-affected structures.

Field trials have shown that physical restraint or confinement—such as encapsulating affected members with non-reactive concrete, applying stress, or adding reinforcement—can significantly mitigate the harmful expansion associated with ASR. A detailed structural evaluation is essential, and care must be taken in selecting and implementing this type of mitigation. Repairs can have varying effects at both local and global scales, particularly for structural modifications. Post-tensioning, whether in one or two dimensions or through encasement in conventional reinforced concrete, is currently used to restore structural integrity. However, it should generally be limited to relatively small masses of structural concrete due to the significant forces that may result from the expansive process caused by ASRs [6]. While post-tensioned tendons or cables are effective for bridge and highway structures, they may be less appealing for larger concrete structures due to the need for periodic de-stressing [6]. It is important to highlight that, for many structural repairs in the literature, there have been no updates on their long-term performance. In cases where updates are available, replacement has ultimately been the final solution for ASR-affected structures.

For certain applications, such as pavements affected by ASR-induced expansion, removing sections of concrete near joints through saw cutting can help extend service life. This approach eliminates joint-related failures and minimizes ride quality issues; however, it should be noted that this method only relieves stresses without addressing the root cause of the expansion [6].

3.3. Interviews with State DOTs

A summary of the interviews with each DOT is presented in Table 8 and Table 9 and is presented in alphabetical order. This information outlines the extent of the ASR problem, particularly in older structures, as well as the repair techniques employed. It also includes details on how the ASR issue is addressed through testing and mitigation strategies in new construction. More information from each interview can be found in Supplementary File S3, which the authors encourage the readers to review, as it contains valuable and unique insights.

Table 8. ASR mitigation strategies adopted by different state DOTs.

DOT	ASR Severity	Aggregates	ASR Mitigation Strategies	Effectiveness
Alabama	Not significant	-Limestone and sandstone in the north and river gravel in the south.	-Cement alkali content limit: ≤0.6% Na2Oeq. -Concrete alkali loading limit: ≤2.4 Kg/m3 (4.00 lb/yd3). -Aggregate reactivity tests: None. -SCMs: Fly ash is primarily used.	-Satisfied with their outcomes.
Arkansas	Moderate	-Reactive fine river gravel.	-Cement alkali content limit: ≤0.6% Na2Oeq. -Aggregate reactivity tests: ASTM C1260 and ASTM C1567. -SCMs (since the mid-90s): Primarily fly ash capped at 20%.	-Not satisfied with reactivity tests. -Aiming to increase fly ash content to 25% for better ASR mitigation.
California	Moderate to severe	-Moderately to highly reactive aggregates.	-Cement alkali content limit: ≤0.6% Na2Oeq. -Aggregate reactivity tests: ASTM C1293, ASTM C1260. -SCMs (since the mid-90s): Fly ash, metakaolin, silica fume, and Ground Granulated Blast-Furnace Slag (GGBFS), natural pozzolans and blended SCMs.	-Satisfied with their outcomes.
Colorado	Moderate	-Most aggregates are reactive. -Slightly reactive aggregates found around the Denver Metro area.	-Cement alkali content limit: No limits. Used to be ≤0.6% Na2Oeq. -Aggregate reactivity tests: ASTM C1260, ASTM C1567. -SCMs (since the mid-80s): Minimum of 20% Class F, natural pozzolans (e.g., volcanic ash).	-The experience with fly ash has been mixed, while earlier projects encountered air issues. -Newer mixes incorporating up to 50% pozzolans have been more successful.
Connecticut	Not significant	-No known reactive aggregates. -The typical aggregates used include trap rock, various broken and crushed stones, and some gravel.	-Cement alkali content limit: No limits. -Aggregate reactivity tests: petrographic analysis for new sources. -SCMs (since 1990s): Slag (20–30%) and recycled glass known as “Pozzotive”.	-Satisfied with their outcomes.
Delaware	Severe	-Limestone aggregates sourced from Maryland and Pennsylvania. -Reactive sands.	-Cement alkali content limit: ≤1.25% Na2Oeq. -Concrete alkali loading limit: ≤1.50 Kg/m3 (2.5 lb/yd3). -Aggregate reactivity tests: ASTM C1260 and ASTM C1567. -SCMs (since mid-1990s): 40% fly ash and 50% slag in standard mixes, 35–40% fly ash or 65% slag for higher alkali cements.	-Discrepancies have been observed between ASTM C1260 and ASTM C1293. -ASTM C1260 test producing false positives. -Incorporating SCMs helped the state to reduce the ASR issues.
Florida	Not significant	-Predominantly limestone.	-Cement alkali content limit: ≤0.6% Na2Oeq. -SCMs (since the mid-80s): Primarily fly ash Class F with typical replacement levels between 18% and 20%, though this can go up to 50%.	-Satisfied with their outcomes.
Idaho	Moderate to severe	-Fine and coarse reactive aggregates.	-Cement alkali content limit: ≤0.6% Na2Oeq. -Concrete alkali loading limit: ≤1.80 Kg/m3 (3 lb/yd3) (was removed since contractors could not meet that standard). -Aggregate reactivity tests: AASHTO T380 and CRD C662, which accounts for lithium. -SCMs: Fly ash, lithium, and slag in the northern regions.	-The state is satisfied with the aggregate reactivity testing methods. -The current test methods are unreliable for job mix evaluation. -Despite including 20–25% fly ash in the mixes, ASR issues persist.
Illinois	Moderate	-Reactive fine aggregates. -Coarse aggregates are crushed limestone or dolomitic limestone.	-Cement alkali content limit: ≤ 0.4% Na2Oeq for very reactive aggregates, 0.6% Na2Oeq for reactive aggregates, no limits for nonreactive aggregates. -Concrete alkali loading limit: Indirectly considered by limiting maximum cement content. -Aggregate reactivity tests: ASTM C1260. -SCMs (since mid-1980s): Class C and F fly ash and Grade 100 slag cement.	-The use of Class F fly ash is on the rise, as it is deemed effective in countering ASR.
Indiana	Not significant	-Limestone, dolomitic limestone, and natural sand. -Did not exhibit reactive tendencies.	-Adhering to AASHTO M240. -Aggregate reactivity tests: No standard tests. -SCMs: Fly ash (28%) and slag (30%).	-Satisfied with their outcomes.
Louisiana	ASR: Not significant ACR: Significant	-Chert river gravel as the main aggregates. -Limestone from Mexico, Kentucky, and Missouri.	-Cement alkali content limit: ≤0.6% Na2Oeq. -Producing low-permeability concrete. -Aggregate reactivity tests: switching to AASHTO T380, AASHTO TP 144 (T-FAST). -SCMs (since mid-1980s): Slag, fly ash, or a combination, ternary systems (slag, class F fly ash + class C fly ash). -The state mandates that nearly all mixes contain at least 50% SCMs.	-Since introducing these SCMs, the state has reported no ASR issues. -ASTM C1260 has produced many false positives.
Maine	Severe	-Gravel with non-reactive to moderately reactive.	-Cement alkali content limit: No limits. -Aggregate reactivity tests: ASTM C1567, looking at AASHTO TP 144 (T-FAST). -SCMs (since 2000s): primarily 50% slag.	-Inconsistent results from ASTM C1567.
Michigan	Severe	-Coarse aggregates are primarily limestone and carbonate types. -Fine aggregates are reactive.	-Cement alkali content limit: No limits. -Aggregate reactivity tests: ASTM C1567, C1260, and C1293. -SCMs (since 1980s, mandated in 2012): Slag is used more often than fly ash.	-N/A *
Minnesota	Mild	-Quartzite, granite, basalt, carbonate rocks and natural gravel. -Fine aggregates are reactive.	-Cement alkali content limit: No limits (used to be 0.60% Na2Oeq). -Concrete alkali loading limit: ≤1.80 Kg/m3 (3 lb/yd3) (removed). -Aggregate reactivity tests: Modified ASTM C1567 and modified ASTM C1260. -SCMs (since 1970s): 30% Class C fly ash, 20% Class F fly ash, or 35% slag.	-Satisfied with their outcomes.
Nevada	Not significant	-Northern region primarily composed of volcanic rock sources. -The southern regions are dominated by limestone and some basalt.	-Cement alkali content limit: ≤0.6% Na2Oeq. -Concrete alkali loading limit: Indirectly considered by limiting maximum cement content. -Aggregate reactivity tests: AASHTO T303. -SCMs (since early 2010s): Southern region primarily utilizes fly ash, while the northern region uses Class N pozzolans, such as calcined clay and metakaolin. -Applying epoxy or polymer overlays on newly constructed concrete bridge decks.	-Satisfied with their outcomes.
New York	Not significant	-Limestone, dolomite, sandstone, granite, trap rock, marble, and argillite. -Aggregate sources include some reactive materials from across the Northeast. -Reactivity classification of many sources remains unclear.	-Cement alkali content limit: ≤0.7% Na2Oeq for reactive aggregates. If cement alkali content exceeds 0.7% with reactive aggregates, SCMs must be used. -Begun to consider alkali loading. -Aggregate reactivity tests: In-house petrographic evaluation of aggregates. Third-party testing (AASHTO TP 144 (T-FAST)). -SCMs (Since mid-1990s): Fly ash, silica fume, and slag cement. -Moving towards PEM.	-ASTM C1260 gives false positives or negatives. -Satisfied with their outcomes.
North Carolina	Mild to Moderate	-Aggregates with different levels of reactivity.	-Cement alkali content limit: ≤1% Na2Oeq. If cement alkali content exceeds 0.6%, SCMs must be used. -Aggregate reactivity tests: AASHTO T380, AASHTO TP 144 (T-FAST), modified T-FAST. -SCMs: Began using SCMs in early 2000s.	-Satisfied with their outcomes.
North Dakota	Mild	-Glacially deposited aggregates and dolomite. -Non-reactive for the most part. -Reactive sand used in pavements.	-Cement alkali content limit: ≤0.6% Na2Oeq. -Aggregate reactivity tests: ASTM C1260 and ASTM C1567. They have considered AASHTO TP 144 (T-FAST). -SCMs (Since 1980s): Class F fly ash at 20–30% (25% typical).	-Satisfied with their outcomes.
Ohio	Not significant	-Gravels, limestone, dolomite, and lightweight aggregate (expanded shale). -Non-reactive aggregates for the most part.	-Cement alkali content limit: No limits. -Aggregate reactivity tests: ASTM C1293. -SCMs (Since 1990s): Fly ash (up to 25%), slag cement (up to 30%), and silica fume.	-Satisfied with their outcomes.
Oklahoma	Not significant	-Mostly limestone.	-Cement alkali content limit: ≤ 0.95%Na2Oeq. -Aggregate reactivity tests: ASTM C1260. -SCMs: Fly ash (up to 20%), slag cement (up to 50%), and silica fume (up to 10%).	-Satisfied with their outcomes.
Pennsylvania	Mild to Moderate	-Carbonate, sedimentary, and metamorphic rocks. -Significant amounts of gravel used. -ASR issues with sedimentary rocks and certain natural sands.	-Cement alkali content limit: ≤1.25%Na2Oeq. -Pay attention to alkali loading, yet no requirement. -Aggregate reactivity tests: AASHTO T303 and ASTM C1293. ASTM C1778 for job mix evaluation. Exploring AASHTO TP 144 (T-FAST). -SCMs (Since 1990s): Class F and C fly ash, slag cement, and silica fume. -Lithium admixtures were also used.	-False negatives with AASHTO T303. -Satisfied with their outcomes.
Rhode Island	Moderate	-Mostly mildly reactive granitic aggregates. -One highly reactive source exists.	-Cement alkali content limit: No limits. -Aggregate reactivity tests: ASTM C1567. -SCMs (since mid-1990s): Mainly silica fume and fly ash. In some cases, slag cement. SCMs used since the mid-1990s for strength (silica fume). SCMs for ASR mitigation since 2008.	-Too early to determine effectiveness.
South Carolina	Not significant	-Mostly granite.	-Cement alkali content limit: ≤0.6% Na2Oeq. -Aggregate reactivity tests: None. -SCMs (since 1990s): Fly ash (up to 20%).	-Satisfied with their outcomes.
South Dakota	Moderate to Severe	-Coarse aggregates are crushed ledge rock, limestone, granite, and natural round river rock. Fine aggregates are natural sand.	-Cement alkali content limit: ≤0.6%Na2Oeq. -Aggregate reactivity tests: ASTM C1260 and ASTM C1567. -SCMs (since 1990s): Class C and F fly ash with a 20 to 25% replacement for cement.	-Problems observed with Class C fly ash. -Positive experience with Class F fly ash.
Tennessee	Moderate	-Granite, limestone, and gravel. -For the most part, aggregates are not reactive.	-Cement alkali content limit: ≤0.6% Na2Oeq for pavements only. -Aggregate reactivity tests: None specified. Has explored ASTM C1293. Considering AASHTO TP 144. -SCMs (since 1990s): Not mandatory, however, about 60% of their concretes contain SCMs. Class F fly ash (25%) or slag cement (35%) is primarily used.	-False positives and negatives with ASTM C1260. -Exploring new alternatives.
Texas	Mild (less than 1% of structures)	-Limestone and silicious gravels and sands.	-Concrete alkali loading limit: ≤2.1 Kg/m3 (3.5 lb/yd3). -Aggregate reactivity tests: None. -SCMs: Used since the late 1990s.	-Satisfied with their outcomes.
Utah	Not significant	-Non-reactive for the most part.	-Cement alkali content limit: ≤0.8% Na2Oeq. -Aggregate reactivity tests: ASTM C1260 and ASTM C1567. Tests performed by concrete producers. -SCMs: Fly ash and natural pozzolan for the most part at dosages of 20–40%. Used since the late 1990s.	-Satisfied with their outcomes.
Wyoming	Severe	-Very reactive.	-Cement alkali content limit: ≤0.65% Na2Oeq (old). -Concrete alkali loading limit: ≤2.4 Kg/m3 (4.00 lb/yd3) (new). -Aggregate reactivity tests: ASTM C1567. -SCMs (since late 1980s): Mainly fly ash (20–25%). Plans to increase the maximum dosage to 30%. Slag cement and natural pozzolan are emerging. -Lithium nitrate admixture.	-Positive results for lithium nitrate in combination with fly ash. -Working on improvements.

* Not applicable.

Table 9. ASR repair strategies adopted by different state DOTs.

DOT	ASR-Affected Elements	ASR Repair Strategies	Effectiveness
Alabama	N/A *	N/A	N/A
Arkansas	-Primarily concrete pavements and median barrier walls; -No significant damage to its bridge infrastructure.	-Epoxy patches; -Milling and overlaying with ultra-thin bonded wearing courses.	-Epoxy patches failed; -Milling + overlay gave positive results, especially for pavement repairs.
California	-Column and footpath.	-Full replacement rather than repairs.	-The best remediation action.
Colorado	-Pavements, bridge decks, piers, columns, and abutments.	-Rubblizing pavements and covering them with asphalt; -In the case of a bridge, complete replacement is considered.	-Satisfied with their outcomes.
Connecticut	N/A	N/A	N/A
Delaware	-Pavements, bridge decks, piers, columns, abutments, footings, and parapets.	-Applying ultra-thin overlays such as NovaChip.	-Satisfied with their outcomes by getting more than 20 years of extra service life.
Florida	N/A	N/A	N/A
Idaho	-Bridge decks, footings, parapets.	-Replacement is preferred; -Where replacement is impractical, try to keep moisture away from affected structures by applying polyester overlays and silane.	-The repairs prolong the life of structures until they reach a point of irreparable damage.
Illinois	-Pavements, bridge decks, parapets	-Moisture management employing sealing applications on bridge parapets; -Milling pavements for overlay with hot mix asphalt	-Limited extension of service life, typically lasting between five to ten years.
Indiana	N/A	N/A	N/A
Louisiana	-ACR issues: Pavements, bridge decks, footings.	-Rubblization and overlay; -Dewatering and CFRP wraps; -Hydro-blasting and applying dense concrete overlays, or fiber-reinforced materials.	-Repairs are temporary solutions; -Replacement is the ultimate decision.
Maine	-Pavements and median barrier walls.	-Applying 100% silane, 40% water-based silane, elastomeric coatings, and lithium nitrate; -Important traffic areas are prioritized for replacement.	-Strategies were unsuccessful; -Replacement is typically the best option.
Michigan	-Bridges and roadways.	-Silane waterproofing is applied especially on decks; -Epoxy overlays.	-Data on long-term effectiveness are limited; -Replacing components has become the most common solution.
Minnesota	-Pavements.	-Full-depth replacements of severely damaged concrete; -Penetrating sealers; -Diamond grinding; -Lithium treatment.	-Full-depth replacement seems to work. It is under long-term evaluation; -Penetration sealers and lithium were ineffective; -Diamond grinding exacerbated the ASR issue.
Nevada	N/S **	-Replacement of older structures, aged 50 to 70 years.	N/S
New York	N/A	N/A	N/A
North Carolina	-Areas experiencing wet–dry cycles such as bent caps; -Columns and piers.	-Deck overlay (latex-modified concrete, polymer concrete, or thin epoxy overlay) to limit water infiltration. -Wide cracks injected with epoxy, epoxy-coated jackets, and silane. -Decision depends on the severity, often leaning towards replacement.	-Too early to determine the effectiveness of epoxy-coated jackets.
North Dakota	-Primarily pavements (did not receive mitigation), footings, and parapets; -Typically observed at the end of service life, eliminating the need for repairs.	-Pavement rubblization; -Patching; -Replacement.	-Pavement rubblization is highly successful.
Ohio	N/A	N/A	N/A
Oklahoma	N/A	N/A	N/A
Pennsylvania	-Primarily pavements.	-Cost-based analysis to decide whether to repair or replace (moderately to severely affected structures); -If damage is too severe, then replacement; -For pavements, asphalt overlays are used to reduce water infiltration.	-Pavement overlay successful (20 to 25 years’ service life extension); -Challenges in determining the best repair strategies and scope of work.
Rhode Island	-Structural elements, particularly abutments.	-Penetrating sealers; -Remove affected concrete and replace it with higher-quality concrete.	-Penetrating sealers showed promise in slowing ASR progression; -Surface preparation and regular reapplication of sealers are challenges; -Effectiveness of strategies remains to be fully assessed.
South Carolina	N/A	N/A	N/A
South Dakota	-Bridge decks, barriers, and pavements.	-Topical lithium treatments; -Typically leaning towards replacement, especially for decks and pavements.	-Topical lithium: Minimal benefits and high cost.
Tennessee	-Bridge railings (ASR exacerbated by deicing salts)	-No formal repair strategies were implemented.	N/A
Texas	-Different structural elements like columns.	-Crack sealing; -Silane treatments; -CFRP wraps for columns; -Removal and replacement in rare cases; -Structural capacity of the affected element is assessed and managed until the end of service life.	-Success of these methods over time is difficult to determine (structures not actively monitored). -Repairs can help slow down ASR progression, but challenges remain with moisture retention in larger structures. -Applying sealers can be ideal if load capacity is intact. -Texas considers CFRP wraps the best solution for circular columns. On rectangular columns, full confinement was not achieved. -Wraps are effective in waterproofing and managing visible cracking. -Prevention is the most effective approach.
Utah	N/A	N/A	N/A
Wyoming	-Pavements and structural elements.	-Epoxy injection; -Silane/Siloxane sealers; -For small structures suffering from moderate to severe ASR, repair if moisture can be kept out, otherwise replace; -For larger structures, repairs should be re-applied until funds are available for replacement.	-Moderate success (5–10 years of service life extension).

* Not applicable. ** Not specified.

Figure 2 summarizes the states that employ mitigation strategies by limiting alkali loading or the alkali content of cement, compared to those without any such limitations.

Figure 2. Overview of state-level mitigation strategies based on alkali limits in cement or concrete mixtures: states with limitations on alkali loading and/or cement alkali content are shown in green; states without any limitations on alkali loading and/or alkali content are shown in red; and white shows the states not participating in this study.

3.4. Lessons Learned from Interviews

The prevalence of ASRs was not correlated with the average relative humidity of each state. This suggests that other factors, such as the source of aggregates and the application of concrete, play significant roles in ASR development. Even when using surface sealers as a potential solution to slow down ASRs, variable results and performances were observed, even within states that have similar humidity levels. This further confirms that there is no one-size-fits-all solution to the ASR issue. Consequently, different DOTs have adopted various prevention and repair strategies, as mentioned below.

3.4.1. Mitigation Strategies: Aggregate Testing

Despite experiencing ASR issues, some DOTs lack specific guidelines for ASR mitigation or aggregate testing. Most DOTs rely heavily on ASTM C1260 and ASTM C1567 to assess the reactivity of aggregates and evaluate the effectiveness of mitigation strategies, primarily due to their short testing durations. However, many agencies depend on aggregate producers to provide reactivity test results, with only a few DOTs conducting periodic tests themselves. The time gap between approval testing and actual placement can diminish the relevance of these tests by the time construction begins, as variations in aggregate chemistry can occur even within the same quarry due to differences in composition from various locations or geological layers.

In contrast, the New York DOT stands out as the only state that evaluates aggregates through petrographic analysis based on geological properties in-house, which is a more precise method. There is a general concern among DOTs that ASTM C1260 and ASTM C1567 do not accurately reflect the performance of aggregates in actual concrete mixtures. Aggregates that may pass current reactivity tests can still become reactive when combined with other aggregates, leading to potentially misleading test results. Some DOTs have encountered false negatives and false positives, particularly with ASTM C1260. As a result, there is a growing consensus that it is essential to test concrete samples with job-specific mix proportions to verify the potential for ASR and quantify its impact. This has led them to explore alternatives, such as the AASHTO-TP 144 method (known as T-FAST) developed by the Turner-Fairbank Highway Research Center (TFHRC), which shows promise for addressing the limitations of current practices.

As the demand for sustainable concrete solutions grows—especially with the use of new supplementary cementitious materials (SCMs), alternative cementitious materials (ACMs), and reactive aggregates to conserve natural resources—there is an increasing emphasis on developing simplified and efficient testing methods to assess ASR risks and evaluate the effectiveness of each system in mitigating ASRs.

Efforts are currently underway by Virginia’s DOT to modify AASHTO T380, allowing it to evaluate actual concrete mixtures and address these challenges comprehensively.

3.4.2. Mitigation Strategies: Cement and SCM Considerations

Nearly all interviewed DOTs agreed that, while ASR cannot be fully stopped, it can be prevented from the start. As a result, all states involved in this research have incorporated ASR-specific measures into their material specifications, although the level of emphasis varies. However, interviews revealed that relying solely on low-alkali types of cement without additional mitigation measures is not always effective in controlling ASRs. For this reason, several DOTs have transitioned from merely limiting the alkali content in cement to focusing on alkali loading within the concrete itself.

Some DOTs have gone further by placing restrictions on the maximum cementitious material content in each mix, aiming to better control alkali loading. In contrast, other DOTs require a minimum cementitious content for normal-weight concrete mixtures. The authors suggest that DOTs should shift away from the practice of simply limiting the alkali content in cement and instead adopt maximum limits on cementitious material content in each mixture to more effectively manage alkali loading.

The use of SCMs has been universally recognized as an effective ASR prevention strategy by nearly all DOTs. In fact, positive experiences with SCMs have been reported across the board, with only isolated cases of ASR occurring when inadequate dosages of Class C fly ash were used. Consequently, all DOTs agreed that the proper dosage of SCMs remains the most successful and reliable method for ASR prevention.

An interview with the Federal Highway Administration (FHWA) provided further insight into the challenges of ASR repair. The agency revealed that its ASR repair program had not been as effective as anticipated. As a result, since 2013, FHWA has shifted its focus away from the repair and rehabilitation of ASR-affected structures, emphasizing instead mitigation strategies in new concrete to avoid ASR-related issues altogether.

3.4.3. Mitigation Strategies: Repair Strategies

DOTs agreed that performing the repair is not the ultimate solution because the final decision is the replacement of the structure if it is severely damaged, but they preferred to follow a structural repair rather than replacement only due to funding issues. Performing ASR repair is expected to extend the service life for another 10–15 years (while many DOTs could reach only 5 to 10 years), allowing for programming the replacement over the next few years. In addition, repair would cost significantly less than abandonment and rebuild (10% to 20% of replacement cost). Moreover, repairing would not require any significant shutdown for a long time, and, therefore, no significant planning is required for managing the traffic.

The repair of ASR-affected structures is challenging because it involves two objectives: to repair the existing cracks and control further expansion in the concrete. Repairing existing cracks may fail due to more crack propagations or further expansion due to more ASRs. Moreover, when the repair of the cracks starts, there is no stopping point that extends the scope of the repair. To control the further expansion, the extent of future expansion can be estimated but cannot be determined precisely, which puts the performance of the repairs in question.

Since deleterious ASR expansion requires moisture, lowering internal relative humidity (RH) in the concrete can be highly effective in reducing further expansion. Methods of reducing internal concrete RH include the following: 1. Removal of external moisture sources through improved drainage and sealed joints. 2. Sealing existing cracks. 3. Application of surface sealers (silane is the most common). Improving drainage and the use of sealers has been shown to be highly effective in some cases. Sealers must be re-applied at regular intervals to remain effective. One DOT could manage the deleterious ASR expansion in field trials through the application of jackets. The encasement is especially effective for columns and piers and can be achieved by adding extra concrete or using methods like jacketing, which includes applying an external concrete collar, wrapping with a fiber-reinforced polymer (FRP), or using steel strapping. This approach aims to control an ASR rather than completely stop it. However, this strategy is not suitable for some structures, and the structural response to any added external restraint must be carefully evaluated prior to its application. Moreover, external jacketing and encapsulations prevent further inspection of the ASR-affected elements.

Challenges in managing ASR issues include a lack of standardized guidance for repairing structures and addressing moisture infiltration. At higher temperatures, the viscosity of the gel decreases, which enhances its mobility. This increase in mobility appears to outweigh the greater tendency to crack that results from the faster reaction rate [15]. Attributing damage specifically to ASRs can be challenging, given that other factors may also contribute to structural distress. Other issues like corrosion dictate the earlier repairs rather than the ASR. Therefore, in most cases, a combination of durability issues are involved, and many repairs that have been completed were not to solely address the ASR. Many of the DOTs agreed that applying sealers on newly constructed concrete structures will help to mitigate many issues including corrosion, ASRs, and the freeze–thaw of marginal concretes or reinforcement subject to corrosion.

3.5. Challenges of Each Repair Strategy

There is currently no definitive method for managing the effects of ASRs to ensure the long-term performance of affected structures. Preventative measures aimed at reducing ASR expansion or damage have unpredictable effectiveness, as the extent of future damage from the existing moisture in the concrete cannot be accurately assessed. This uncertainty stems from the difficulty in gauging the degree of the ASR and estimating future expansion based on current moisture levels.

To effectively manage ASRs in structural concrete, it is essential to evaluate the structure integrity, as both ASR and general cracking can significantly diminish its load-bearing capacity. A number of other considerations must be taken into account before initiating the repair of ASR-affected structures, such as the condition of the concrete and the repair material. The assessment of the concrete includes the stage of expansion, the moisture level in the concrete, and the area of repair coverage [59]. The lack of reliable methods for assessing these characteristics presents a critical gap in developing a comprehensive aging management plan. Furthermore, without tools or tests to predict the rate of degradation, more frequent inspections will be necessary compared to structures that are not experiencing degradation [60].

Despite efforts to control ASRs, some repair methods have proven less effective, and the long-term performance of others remains uncertain. Also, a method that was found successful in one location has been found to be unsuccessful or less than desired in another location, indicating the presence of many other factors that are difficult to control. Each repair method implemented in the field has encountered various issues and challenges, which are summarized below. The following explanations are based on insights from both the literature and interviews with various DOTs.

3.5.1. Impermeable Surface Coatings

Waterproofing concrete is an effective remediation method, but achieving a fully watertight structure is often impractical [15]. One preventive approach is using a polymer-based surface protection material to minimize moisture absorption and slow down further deterioration. However, not all coating materials are successful in preventing moisture penetration, and some fail to reduce ASR expansion [27]. Increasing the use of waterproof coatings can also limit the concrete’s ability to breathe, leading to increased vapor pressure beneath the coating, which may cause sections of the coating or surface layers to be blown off [15]. Additionally, the effectiveness of sealers can be compromised after cracks form, depending on the crack width [61]. Debonding at the concrete–sealer interface is another potential issue [62]. Coatings can also prevent concrete inspection unless they are transparent, making their use less favorable in some cases [15]. If coatings are necessary, factors like color, texture, and resistance to UV degradation should be carefully considered.

3.5.2. Vapor-Permeable Surface Sealers

Efforts to dry one side of a structure can unintentionally accelerate an ASR near the drying surface by concentrating alkalis, which increases reaction rates [63]. On the other hand, drying the internal surfaces of concrete can create issues if the external surface remains moist. Therefore, it is advisable to reduce the overall RH of the concrete evenly. Silanes and siloxanes, common components in many penetrating sealants, are well suited for this purpose [64]. Silanes can penetrate concrete, forming a hydrophobic barrier within the substrate that allows internal moisture to evaporate. However, while they are effective water repellents, silanes are not waterproofing agents, and their use is limited to structures with accessible external surfaces.

The development of silane formulations has kept pace with stricter regulations on volatile organic compounds (VOCs). Modern options include water-based or solvent-based silanes with higher concentrations to minimize VOC content [20]. Despite their benefits, silanes typically only penetrate about 2.5–3 mm into the concrete, meaning that their effect is mostly limited to shallow depths [63,65]. The performance of silane depends on several factors, including penetration depth, surface preparation, application methods, environmental conditions like RH and temperature, and the chemical properties of the silane itself [65,66]. Active cracking can compromise silane coating performance, and silane has been found to be less effective in extensively cracked areas [6,65].

A single application of a silane-based product is not a permanent solution, as its effectiveness decreases over time due to factors like the alkali pore solution in concrete, abrasion, and UV exposure. Therefore, reapplying silanes every five years is generally recommended [6,53]. The over-application of silane or other sealers can trap moisture beneath the sealer, reducing its effectiveness in lowering internal RH [66].

The benefits of sealers may not be evident when elements are continuously exposed to moisture, fully submerged, or not allowed to dry, as sealers require wet/dry cycles to effectively reduce internal RH [6]. Silane has proven ineffective at reducing internal RH in concrete pavements, slabs on grade, wing walls, or other applications where moisture is available from subgrade or from below (or beneath) [63].

Safety concerns also exist regarding silane products. One admixture manufacturer, for example, warns that direct contact with or the inhalation of silane can cause skin, eye, or respiratory irritation and may lead to dermatitis or allergic reactions [67]. With positive reports on the performance of concrete surface coatings, the market now offers a wide range of these products. This variety, however, makes selecting the right coating more difficult, particularly when performance data are lacking [68].

3.5.3. Lithium Impregnation

Several publications have reported that the penetration of lithium into hardened concrete was not sufficient to provide a beneficial reduction in expansion [6,69,70,71]. Vacuum impregnation was not found to be effective, which draws into question whether such an elaborative and expensive vacuuming technique is justified [6]. In addition, by electrochemical impregnation, lithium ions were clearly driven to the reinforcing steel, as was the intention, but, because the steel serves as a cathode in the electrochemical process, hydroxyl ions are produced at the surface of the reinforcing steel. To maintain charge neutrality and to offset the production of hydroxyl ions at the reinforcing steel surface, sodium and potassium ions from within the concrete migrated toward the steel surface. This creates an increase in the hydroxyl ion concentration, and a subsequent increase in alkali (sodium and potassium) concentration near the surface of the reinforcing steel may exacerbate ASR-induced expansion and cracking in this region [6].

3.5.4. Crack Repairs

The repair of cracks in ASR-affected concrete elements is complicated by the ongoing expansion process, which can proceed at varying rates and to different extents (residual expansion), depending on the reactivity of the aggregate, concrete alkali content, moisture availability, etc.

One repair method involves sealing existing cracks with epoxy. While this approach aims to block additional water ingress by filling the cracks with an impermeable material, its success is challenging to quantify. If the concrete is already saturated, the epoxy may not displace the existing water, allowing the reaction to persist. Moreover, new cracks formed from continued moisture exposure could provide additional pathways for water infiltration. Therefore, this type of repair is not effective in active cracking [12]. Nearly all crack repairs using epoxy failed in the field in one project [27]. Traditional crack repair techniques for damaged elements subjected to significant on-going expansion could be a waste of money, as cracks would reappear [72]. The epoxy may fill some cracks, but it does not sufficiently bond to the crack wall to prevent the cracking restarting [19]. Injection pressure should be sufficient for a successful penetration; otherwise, the pores remain unpenetrated, or even higher pressure may induce more micro-cracks in the concrete and around the injection port. Cracks generated by an ASR can be expected to contain powdery or gel-like reaction products. The resin should have excellent wetting properties so that it can penetrate these products and wet the intact concrete forming the crack sides [43]. Injecting epoxy resin will restrict the mobility of ASR gel, which may increase the gel pressure that can only dissipate once a new crack forms, or the old crack reforms alongside the resin injection. Ideally, the end few millimeters of cracks should be sealed with a flexible product, allowing a void behind, into which the gel can grow [15]. Cured resins generally have coefficients of thermal expansion that are as much as 50 times that of concrete. In the exposed field situation, cyclic thermal stresses will therefore be set up at the resin-concrete interface. The resin must be able to accommodate this movement by creep, otherwise it will debond from the concrete [43,73]. The epoxy by itself cannot restore the strength of the concrete damaged by an ASR [19].

3.5.5. CFRP Wraps

The effectiveness of CFRP wrapping repair systems has not been adequately demonstrated for controlling the expansion of concrete elements with ongoing expansion. CFRP with a sufficient number of layers can reduce the expansion but does not eliminate it because the deleterious reaction continues. The degree of ASR expansion at the strengthening time is critical [48]. Repair would be more effective when the reaction is largely dissipated, and the residual expansion is small [72].

In addition, the modulus of elasticity of the CFRP has an influence on the appropriate number of layers and the effectiveness of the repair. Volume and properties of epoxy resin (e.g., creep) present in the wrapping are important factors in the performance of this type of repair [72,74,75]. The element shape (rectangular vs. circular) impacts the performance of CFRP, and it is difficult to confine many structural elements (e.g., square columns) [6,76]. A qualified structural engineer must design and implement the selected technique, and they must monitor subsequent strains to ensure that mitigation is effective and safe [6]. FRP can hide underneath defects and crack propagation. There is no non-destructive testing (NDT) technique to investigate the bond between concrete and FRP over time. The production of FRP involves chemicals that can lead to environmental degradation [77].

4. Translating Laboratory Findings to Field Applications in ASR Mitigation

A persistent challenge in ASR management is the discrepancy between laboratory findings and field performance. While laboratory testing provides valuable insights into reaction mechanisms and contributing factors, it is impractical to incorporate all influencing variables in a controlled setting. As a result, successful outcomes from laboratory tests or exposure site evaluations do not always guarantee success in the field. These testing programs often fail to account for the true scale of the structure, real alkali loading, the actual state of ASRs, load combinations, stress and strain conditions, multi-distress conditions (i.e., ASR combined with other deterioration mechanisms like corrosion, sulfate attack, or freeze–thaw), and ambient site conditions. In contrast, laboratory studies typically use small, uniform specimens with consistent moisture, alkali content, and stress conditions—variables that are highly changing in actual structures. This disconnect has led to overestimations of the field effectiveness of several treatments. For instance, although lithium compounds have shown effectiveness in laboratory studies on small specimens, there is little documentation supporting their efficacy in reducing ASR-induced expansion in actual structures [6]. Similarly, while surface sealers like silanes are shown to reduce internal RH in lab trials, their performance in the field depends heavily on application technique, product formulation, substrate condition, and environmental exposure, which are difficult to standardize across projects. Conversely, vacuum impregnation has proven ineffective in both laboratory and field settings [6]. Interviews with DOTs reinforce this gap, as many expressed frustrations with treatments that performed well in tests but failed to yield consistent results in the field. For this reason, a combination of laboratory testing and long-term field testing is recommended before concluding the effectiveness of each repair strategy.

5. Field Implementation

Repairing structures subjected to an ASR through sealing or strengthening at a reduced cost, 10 to 20%, of the total replacement cost would gain time, expected to be 5 to 20 years depending on the element, the exposure conditions, and the rate of reactions, until funds are acquired for replacement or abandonment.

It is expected that an additional 5 to 10 years will be added to the service life of the pavements if moisture intake on the surface is reduced. This saves money for transportation agencies by preventing pavement replacement and preventing regular repair and maintenance of the ASR-affected pavements. Moreover, one-time repairs reduce the need for road closures or shutdowns and therefore have a reduced impact on traffic. For the field implementation of repair strategies, the authors recommend the following:

• For an ASR to occur, sufficient moisture must be present in the concrete. Therefore, a practical repair approach is to minimize moisture within the concrete. Based on the lessons learned from the literature and interviews with the state DOTs, for ASR-affected structural elements, moisture control (e.g., using appropriate vapor-permeable surface sealants) and strengthening (e.g., using FRP wrapping) should be considered, if practical and economical, to gain time until funds are available for replacement.
• ASR gel is expansive, and insights from the literature review and interviews with state DOTs indicate that stopping an ASR is challenging. In some cases, reducing moisture in affected elements (e.g., pavements) is difficult. As a result, some DOTs have successfully used rubblization to create space for expansion and prevent crack reflection on the surface. For this reason, the authors recommend rubblizing ASR-affected pavements and repurposing the deteriorated concrete as a new base course.
• One state DOT successfully repaired ASR-affected pavement by minimizing moisture in areas with good drainage. This was achieved by placing an ultra-thin impermeable layer on the pavement surface to reduce moisture infiltration. Transportation agencies may benefit from considering this ultra-thin, gap-graded hot mix asphalt wearing course over a polymer-rich asphalt emulsion overlay on ASR-affected pavement (with good drainage), followed by a 76.2 mm (3-inch) wearing surface.

6. Recommendations

To enhance the effectiveness of ASR prevention and repair practices, the following recommendations are proposed:

• While several states already rely on SCMs such as fly ash and slag cement, promoting their use through updated guidelines or incentives can help ensure uniform ASR mitigation, especially where alkali limitations are not enforced.
• States should consider transitioning to newer, more reliable test methods for assessing aggregate reactivity. In addition, there is a need for clear guidance on how frequently aggregates from an active quarry should be tested to capture any variability over time.
• Relying solely on aggregate reactivity testing is not sufficient. Testing the job-specific mix design is essential to ensure that the combined effect of cement chemistry, SCMs, and admixtures results in an ASR-resistant concrete under field conditions.
• Facilitating regular knowledge-sharing forums among DOTs can help disseminate best practices and innovations in ASR mitigation, particularly where field performance has been successful.
• A closer connection between research institutions and state transportation agencies is critical. Understanding the practical challenges faced by DOTs can help shape research that is not only scientifically sound but also tailored for successful field implementation. This includes developing solutions that are constructible, cost-effective, and compatible with existing specifications.

7. Conclusions

The conclusions presented in this section are drawn from both the literature review and the interviews conducted with state Departments of Transportation (DOTs), providing a comprehensive overview of the findings. The conclusions from this research are as follows:

• The prevention of ASRs is easier and more effective than the repair and rehabilitation of ASR-affected structures. Strategies like aggregate prescreening and using SCMs at appropriate dosages have proven to be successful and cost-effective methods for preventing ASR distress in structures.
• The ultimate solution for any severely ASR-affected structure is replacement. Repairs are completed to extend the service life until the funding becomes available and replacement is programmed.
• The major objective in controlling ASRs in existing field structures is to minimize the amount of water available to the system. Applying silanes in some cases reduces the internal RH and the potential for future expansions. Silane was not effective in pavements and elements that are in contact with moisture continuously without enough time for drying. However, this observation does not automatically translate to all applications of silanes. Moreover, the efficacy of silane treatment on ASRs is difficult to determine especially considering the medium-to-long-term abrasion resistance of such surface treatment.
• The lithium nitrate applied by either vacuum treatment or topically to existing ASRs distressed structures showed no tangible benefit in terms of reducing cracking or expansions.
• The Minnesota DOT reported that the diamond grinding of ASR-affected pavements accelerated the reaction in areas with less ASR distress. Therefore, diamond grinding should be avoided.
• Three states with ASR issues in pavements achieved an extra 5 to 10 years of service life by controlling the moisture ingress with overlays. Therefore, this repair strategy can be considered for the repair and rehabilitation of ASR-affected pavements. For example, the Delaware DOT has used an ultra-thin, gap-graded hot mix asphalt wearing course over a polymer-rich asphalt emulsion overlay on an ASR-affected pavement (with good drainage), followed by a 76.2 mm (3-inch) wearing surface. This approach provided an additional 15 years of service life until now, and the repair has not yet reached the end of its lifespan. Given its promising outcomes, this repair strategy can be considered for the repair and rehabilitation of ASR-affected pavements.
• ASR-affected pavements can be rubblized and used as a base material, thus eliminating expensive removal and disposal costs.
• Any repair strategies like surface sealing or crack sealing are effective in non-active cracks. Crack growth or development compromises many repairs.