In the procedure proposed by Bérubé et al. (2002) and described in the Appendix I, the current rate of ASR expansion in field concrete can be estimated in the laboratory, based on the "residual aggregate reactivity" and the "water-soluble alkali content" (see Appendix H) measured for the concrete under study, combined with estimates/measurements of the temperature, humidity and restraining (compressive stress) conditions prevailing in the field (see Appendix I).
The "residual aggregate reactivity" can be determined by testing cores in 1N NaOH solution at 38°C (100°F) or, better for coarse reactive aggregates, by conducting Concrete Prism Tests ASTM C 1293 on aggregates extracted from the cores. This extraction can be made using the procedure first proposed by Grattan-Bellew and Danay (1992) (also described in Grattan-Bellew 1995), which consists of rapid cycles of freezing in liquid nitrogen and thawing in a microwave oven. The procedure was revisited by Pedneault (1996) who established the standard procedure described hereafter. It must be mentioned that only the coarse aggregates can be isolated using this procedure, which is then not useful when the reactive aggregate material belong to the sand fraction.
The mass of concrete necessary to recover enough coarse aggregate particles to make three concrete prisms, in accordance with the Concrete Prism Test ASTM C 1293, varies with the nature of the coarse aggregates, their maximum size, and the pre-existing degree of concrete deterioration. For concretes containing coarse aggregates in the range of 5 to 20 mm (approximately 0.25 to 0.75 in), Pedneault (1996) obtained recoveries ranging from less than 20 percent (for highly friable reacted Potsdam sandstone particles of 5 to 10 mm (approximately 0.25 to 0.38 in) in size), to almost 100 percent (for unreacted limestone particles of 14 to 20 mm (approximately 0.50 to 0.75 in) in size).
The concrete sample is broken with a hammer in order to obtain individual fragments of less than 2 kg. After crushing, the sample is immersed in tap water at 23°C (73°F) for at least 36 hours.
The concrete sample (or a sub-sample) is placed in a stainless steel mesh basket and immersed in liquid nitrogen for 25 minutes, using a solid/liquid ratio of 0.40 or less. In order to minimize evaporation, it is recommended to put the liquid nitrogen in well insulated steel container. Despite this, it should be expected that about half of the volume of liquid nitrogen might evaporates by the end of the immersion period of 25 minutes.
The stainless steel mesh basket containing the concrete sample (or sub-sample) is pulled out of the liquid nitrogen, and the concrete sample (or sub-sample) placed in a microwave oven, set at maximum power for 35 minutes (maximum mass of 4 to 5 kg (9 to 11 lbs) of concrete per batch).
Freezing and thawing cycles are repeated until the sample (or sub-sample) is completely cracked. A minimum of four cycles is generally required for good quality concretes while only one cycle may be necessary in the case of severely deteriorated concretes.
The coarse aggregates are manually separated from the concrete fragments using a small hammer. Additional wetting/freezing/drying cycles (Sections G.2.1 and G.2.2) may be required at this stage if the coarse aggregate particles are still difficult to extract.
The extracted particles are cleaned of any residual adhering cement paste by immersion for 30 seconds in diluted hydrochloric acid (5 percent).
The Concrete Prism Test ASTM C 1293 can be conducted using the extracted aggregate particles as the coarse aggregate (see Notes 1 and 2).19, 20
American Standards for Testing and Materials (ASTM), "Standard Test Method for Determination of Length Change of Concrete Due to Alkali-Silica Reaction," ASTM International, ASTM C1293.
Bérubé, M.A., Frenette, J. and Rivest, M., "Laboratory Assessment of the Potential Rate of ASR Expansion of Field Concrete," Cement, Concrete, and Aggregates, 24 (1), 28-36, 2002.
Grattan-Bellew, P.E., "Laboratory Evaluation of Alkali-silica Reaction in Concrete from Saunders Generating Station," ACI Materials Journal, 92 (2) : 126-134, 1995.
Grattan-Bellew, P.E, and Danay, A., "Comparison of Laboratory and Field Evaluation of Alkali-silica Reaction in Large Dams," Proceedings of the International Conference on Concrete Alkali
Aggregate Reactions in Hydroelectric Plants and Dams, eds. Canadian Electrical Association & Canadian National Committee of the International Commission on Large Dams, Fredericton (Canada), 23 p., 1992.
Pedneault, J., "Development of Testing and Analytical Procedures for the Evaluation of the Residual Potential of Reaction, Expansion, and Deterioration of Concrete Affected by ASR," M.Sc. Memoir, Laval University, Québec City, Canada, 1996.
19Since the recovery of aggregate particles in the range of 5-10 mm (approximately 0.25 to 0.38 in) is more difficult, it may be necessary to crush the coarsest extracted particles to satisfy the requirements of the test method ASTM C 1293 for which equal masses of particles of sizes 5-10 (approximately 0.25 to 0.38 in), 10-14 (approximately 0.38 to 0.50 in),, and 14-20 mm (approximately 0.50 to 0.75 in) are required.
20It is recommended that the ASTM test be performed using the original fine aggregate, if still available, or a similar fine aggregate.