M.D.A. Thomas

Use of the Accelerated Mortar Bar Test to Evaluate the Effectiveness of LiNO 3 Against Alkali-Silica Reaction—Part 1: Pore Solution Chemistry and Influence of Various Parameters

For the time being, the only reliable test method to evaluate the effectiveness of lithium nitrate against alkali-silica reaction (ASR) in concrete is the concrete prism test (CPT) CSA A23.2-14A or ASTM C1293, extended to two years. In its actual form, the more commonly used accelerated mortar bar test (AMBT) CSA A23.2-25A or ASTM C1260 is not able to predict this effectiveness and needs to be modified to improve it’s reliability. Part I of this study, which involves a large variety of reactive aggregates from Canada and the United States, aims to evaluate the partition of various ions (OH−, Na+, K+, Li+, and silica species) between the mortar pore solution and the soak solution in the AMBT, and the effect of a number of experimental parameters on the expansion of mortar bars with/without lithium nitrate, e.g., the presence of lithium in the original mortar bars, the Li concentration in the soak solution, the concentration and the composition (NaOH versus KOH) of the soak solution, the cement alkali content, the water-to-cement ratio, and the initial 24-h soaking in pure water. The second part of this study (Part II) compares the above AMBT results with the CPT results for the same aggregates and aims to propose modifications to the AMBT when testing lithium nitrate against ASR to better correlate with the most realistic CPT results.

Use of the Accelerated Mortar Bar Test to Evaluate the Effectiveness of LiNO 3 Against Alkali-Silica Reaction—Part 2: Comparison with Results from the Concrete Prism Test

For the time being, the concrete prism test (CPT) CSA A23.2-14A or ASTM C1293 remains the most reliable test method to evaluate the effectiveness of lithium nitrate against alkali-silica reaction (ASR) in concrete; however, the extended testing period of two years has often limited its acceptance by practitioners. In its actual form, the popular accelerated mortar bar test (AMBT) CSA A23.2-25A or ASTM C1260 cannot be used to predict this effectiveness, thus it needs to be modified accordingly. Part I of this study looked at the influence of a number of parameters on the effectiveness of lithium to control expansion of mortar bars incorporating a variety of reactive aggregates from Canada and the United States. The second part of this study (Part II) compares the results obtained in modified versions of the AMBT with those from the CPT performed on the same aggregates, with the objective of proposing the best accelerated test procedure for determining the minimum amount of lithium nitrate necessary to counteract ASR expansion in concrete. The results obtained in this study have shown that the effectiveness of lithium nitrate greatly varies from one reactive aggregate to another while not being correlated with the degree of reactivity or the petrographic nature of the reactive aggregates to counteract. A safe method of predicting the effective [Li]/[Na+K] to used in concrete is proposed which uses two AMBTs, one of which involves adding lithium to both the mortar bar and the soak solution. It allows the prediction of an effective [Li]/[Na+K] for aggregates that respond relatively well to lithium. The method allows the identification of aggregates that respond particularly badly to the lithium, for which the concrete prism test is recommended for evaluating the minimum lithium dosage to use for ASR control.