A New Approach to Preventing ASR

Alkali-silica reaction continues to be a challenging durability issue for portland cement-based concrete. In general, the research community has supported industry with practical solutions based on empirically derived relationships, mostly from accelerated test methods and to a lesser extent realistic exposure/field structures. The latest research shows that both the accelerated mortar bar test and the concrete prism test, with their current limits, do not match well to high alkali loading field exposed concrete blocks. The research questions driving the development of a new approach include: 1) Are these high alkali loading blocks (e.g., 3.78 to 5.25 kg/m3 Na2Oeq) too aggressive?; 2) Would low and moderate alkali loading blocks that are representative of a broader range of concretes (e.g., pavements, bridge decks, dams, foundations) show a better correlation?; and 3) Can we develop a better approach to ASR prevention that relies more on science and our current understanding of ASR rather than pure empiricism? The research team represented in this paper is investigating a new methodology that combines the alkali availability needed to initiate ASR (aggregate specific) with the available alkali from the total cementitious blend. The alkali sensitivity of aggregates is explored using a modification to the miniature concrete prism test (MCPT), the accelerated mortar bar test (AMBT), the University of New Brunswick concrete cylinder test (UNBCCT) and the T-FAST alkali threshold test (ATT). These methods are compared, and the most efficacious method (s) will be highlighted. A newly developed alkali leaching test (ALT) will be demonstrated to assess the available alkali from the entire cementitious blend (SCM + cement or portland limestone cement). The relationship between reactivity of a supplementary cementitious material and ASR expansion is also explored. Chemical admixtures capable of reducing alkali silica reaction will also be included in this new approach.