U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590

Skip to content
Facebook iconYouTube iconTwitter iconFlickr iconLinkedInInstagram

Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations

This fact sheet is an archived publication and may contain dated technical, contact, and link information
Back to Publication List        
Publication Number:  FHWA-HRT-20-042    Date:  June 2020
Publication Number: FHWA-HRT-20-042
Date: June 2020


Applying Raman Spectroscopy to Study Alkali - Silica Reaction Gels

PDF Version (2.8 MB)

PDF files can be viewed with the Acrobat® Reader®



Alkali—silica reaction (ASR) is one of the various degradation mechanisms affecting the serviceability of concrete transportation infrastructure in the United States. Despite awareness of this problem since 1940, lack of important information on the ASR gel structure has hampered developing effective early diagnosis or preventive and mitigation strategies. Essential aspects of the ASR mechanism, such as the roles of calcium and aluminum and how the composition of produced gel affects swelling properties in the concrete, can be better understood with an efficient technique to probe the structure of the amorphous ASR gel. The research presented in this report explores the possibility of using Raman spectroscopy as a tool to investigate the structure of ASR gels. Raman spectroscopy provides a simple, powerful method to gain important structural information on ASR gels that could benefit both fundamental research and forensic investigation of concrete. The results of this work may benefit those interested in improving their understanding of the ASR mechanism to develop better test methods or mitigation or repair strategies, including State transportation departments, researchers, and design consultants.

Cheryl Allen Richter, P.E., Ph.D.
Director, Office of Infrastructure
Research and Development


This document is disseminated under the sponsorship of the U.S. Department of Transportation (USDOT) in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers' names appear in this report only because they are considered essential to the objective of the document.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

Technical Report Documentation Page

1. Report No.


2. Government Accession No. 3 Recipient's Catalog No.
4. Title and Subtitle

Applying Raman Spectroscopy to Study Alkali—Silica Reaction Gels

5. Report Date

June 2020

6. Performing Organization Code
7. Author(s)

Chandni Balachandran (ORCID: 0000-0001-5198-7448), Jose F. Munoz (ORCID: 0000-0003-2946-9868), and Terence S. Arnold (HRDI-10; ORCID: 0000-0001-5707-6397)

8. Performing Organization Report No.


9. Performing Organization Name and Address

SES Group and Associates LLC
614 Biddle St.
Chesapeake City, MD 21915

10. Work Unit No. (TRAIS)
11. Contract or Grant No.

DTFH61-13-D-00007 and DTFH61-17-D-00017

12. Sponsoring Agency Name and Address

Office of Research, Development, and Technology Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101

13. Type of Report and Period Covered

Final Report; February 2010–December 2018

14. Sponsoring Agency Code


15. Supplementary Notes

The Contracting Officer's Representative was Dennis Sixbey (HRDI-10).

16. Abstract

Alkali—silica reaction (ASR) is a chemical distress mechanism that adversely affects the service life of concrete pavements. Key aspects of the reaction, such as the roles of calcium and aluminum on the structure of the gel and their correlation with swelling properties, have not yet been fully understood owing to the complex reaction mechanism. These problems emphasize the importance of developing analytical techniques, such as Raman spectroscopy, to effectively study ASR products. The research presented in this report explores the possibility of using Raman spectroscopy to provide valuable insight into the structure of ASR gels, both in synthetic systems as well as concrete and mortar samples. This information will aid in better understanding of the mechanism of the reaction and improve repair strategies for damaged structures. The research team used published literature to verify the structural information derived using Raman spectroscopic analysis, thus establishing the validity of the methodology. Increasing alkali content in synthetic ASR gels resulted in depolymerization of the silicate structure, and a strong correlation was observed between the peak position of the most intense band in the low frequency region and alkali/silica ratio for gels with a composition similar to field ASR gels. Further, an attempt was made to use Raman spectroscopy to characterize ASR gels within concrete and mortar samples, and limitations of applying this technique to probe products within a cementitious matrix were identified. Finally, the study touched on the possibility of using surface-enhanced Raman spectroscopy to improve sensitivity of the technique when applied to concrete samples.

17. Key Words

Raman spectroscopy, alkali—silica reaction gels, silica polymerization, surface-enhanced Raman scattering, silver nanoparticles, concrete

18. Distribution Statement

No restrictions. This document is available to the public through the National Technical Information Service, Springfield, VA 22161.

19. Security Classification
(of this report)


20. Security Classification
(of this page)


21. No. of Pages


22. Price


Form DOT F 1700.7 (8-72) Reproduction of completed page authorized



Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000
Turner-Fairbank Highway Research Center | 6300 Georgetown Pike | McLean, VA | 22101