Alkali Silica Reaction (ASR) is one of the most prevalent deterioration mechanisms affecting concrete and reinforced concrete infrastructure and, therefore, is a major concern for owners and operators of infrastructure, including the NC Department of Transportation (NCDOT). Despite the significant amount of research on ASR and significant advances made in understanding the chemical and physical processes that occur within concrete, early detection in concrete and identification of reactive aggregates remains a major challenge.
This challenge remains mainly because accelerated tests are seldom reliable, showing a significant number of false positives or false negatives. An example of such tests is ASTM C 1260 (Standard Test Method for Potential Alkali Reactivity of Aggregates, Mortar-Bar Method). On the other hand, more reliable tests are very slow. A well known example is the ASTM C1293 (Standard Test Method for Determination of Length Change of Concrete Due to Alkali-Silica Reaction). Although accurate, the C1293 test can take up to two years to complete. Furthermore, it should be noted that existing standardized tests were designed to classify aggregate reactivity, not to assess a specific concrete mixture.
The main objective of the proposed research is to evaluate a modified version of the T-FAST test recently proposed by Mr. Lichtenwalner of the NCDOT. We will evaluate this test for a wide range of concrete mixtures containing aggregates with a known history and level of ASR reactivity. We will also examine the correlation of the Modified T-FAST test results with those from other test methods for aggregates that have known ASR activity in the field or at an exposure site. This correlation will be used to determine whether the Modified T-FAST test can be used to accurately predict reactivity and the long-term expansion of concrete.
As a part of the proposed research, we will also evaluate different parameters of the test method including exposure temperature, crushed vs. uncrushed concrete, minimum duration required, use of pore solution vs. NaOH solution, and whether concentration of calcium in the pore solution is a dependent parameter on the concentration of silicon. In all tests and evaluations, the intent is to work with Mr. Lichtenwalner to ensure that the tests performed by the research team are complementary to tests he has already completed.
Objectives of the proposed research include: (i) perform a comprehensive literature review of existing ASR test methods, (ii) develop a database for aggregates with known levels of reactivity and field or exposure site data available, (iii) secure aggregates with a range of ASR reactivity including no, low, moderate, and high reactivity, (iv) develop a test matrix using aggregates and concretes made with supplementary cementitious materials (SCM) and identify the parallel tests to be performed, (v) perform tests and use the data to optimize the Modified T-FAST test.
The final product of this research will be a refined version of the Modified T-FAST test method with optimized parameters and procedures. In addition, the products of research will include experimental data obtained in a series of ASR tests and the correlation between these test methods. We envision that the results of the research will be published in peer-reviewed journals and will be presented at TRB meetings and sessions.
The final report will include all the data and information collected during the project including the literature review, experimental design, test matrix, results, and the draft of the Modified T-FAST test method will be written in the format of an ASTM test method. The Modified T-FAST test can be used to update NCDOT concrete mix design specifications to allow a greater variety of material sources and optimization of concrete mix designs
