Featured in Technology Today (Volume 38, Issue 3), a quarterly publication of the Louisiana Transportation Research Center.
Concrete is a crucial component in Louisiana’s transportation infrastructure, utilized in the construction and maintenance of many of the state’s roads, bridges, and other structures. One of concrete’s primary vulnerabilities is the alkali-silica reaction (ASR), which can cause “alligator cracking” (also known as “map cracking” or “pattern cracking”) over time, leading to costly repairs and potential safety concerns. For this reason, DOTD engineers are highly motivated to identify and implement the most efficient and effective test methods to evaluate ASR potential in its materials.
In response to this ongoing need, LTRC Concrete Research Manager Zhen Liu, Ph.D., P.E., recently completed a multi-year project assessing the suitability and potential adoption of an innovative test method called the Miniature Concrete Prism Test (MCPT). First published by the American Association of State Highway and Transportation Officials (AASHTO) in 2018, MCPT is advantageous for both its reliability and timeliness. Prior to the development of MCPT, the two tests most commonly used by industry researchers were the accelerated mortar bar test (AMBT), which is prone to produce false-positive or false-negative readings, and the concrete prism test (CPT), which yields much more reliable results but takes 1-2 years to produce. MCPT, by contrast, has been shown to yield accurate results in only 56 days, which significantly accelerates the evaluation process, leading to a more efficient completion of projects.
Dr. Liu, in partnership with fellow researchers Jose Milla, Ph.D., P.E., and William Saunders, E.I., designed and executed an extensive battery of laboratory tests over a one-year period, comparing and contrasting the results of the MCPT with those of the AMBT and CPT with the goal of evaluating its reliability in assessing ASR potential. A diverse array of 24 aggregates known to be potentially reactive were chosen, along with two control samples, ultimately producing a total of 96 unique mixtures for the research team’s evaluation. These samples were measured at 7, 28, and 56 days, as well as at 3, 6, 9, and 12 months, to assess their susceptibility to ASR. All tests were completed in accordance with the standards outlined by AASHTO and the American Society for Testing and Materials (ASTM).
The results from these tests yielded promising results overall. Drs. Liu and Milla, along with Saunders, found the MCPT and CPT methods produced an impressive 95.8% agreement rate for aggregate evaluation. Additionally, the team evaluated 33 of the mixtures for ASR mitigation strategies, revealing a 79% agreement rate between the MCPT and CPT methods. Based on these results, the researchers recommended that DOTD adopt the MCPT method to evaluate ASR reactivity for all coarse aggregates used in the state’s transportation system, as well as for fine aggregates that do not exceed a 0.30% expansion rate from the AMBT method.
Dr. Liu highlighted the significance and potential impact of these findings: “The Miniature Concrete Prism Test (MCPT) provides Louisiana’s engineers with a useful new tool to produce reliable results for the routine assessment of an aggregate’s alkali-silica reactivity over a much shorter period of time. By utilizing this test, suppliers no longer have to wait 12 months or more to receive the results they need.”
For more information on this project and its findings, please visit LTRC Final Report 700. You can also contact Zhen Liu, Ph.D., P.E., at (225) 767-9138 or zhen.liu@la.gov.