(Received 27 September 1998; accepted 9 July 1999)
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This paper presents data from laboratory studies to assess the suitability of the accelerated mortar bar test (CSA A23.2-25A and ASTM C 1260) as a method for evaluating the effect of mineral admixtures on expansion due to alkali-silica reaction (ASR). A wide range of materials such as fly ash, slag, silica fume and natural pozzolans have been tested at different replacement levels in combination with various reactive aggregates including siliceous limestone, greywacke, granite and sandstone. Results are presented for 70 different material combinations tested by both the accelerated test and the Canadian Standards Association concrete prism test (CSA A23.2-14A and ASTM C 1293).
For aggregates that were shown to be deleteriously reactive by both test methods there was a generally good agreement between the test results when the failure criteria used were expansion of mortar bars at 14 days > 0.10% and expansion of concrete prisms at 2 years > 0.040%. Only 5 out of 70 mixtures passed the mortar bar test and failed the concrete prism test and in two these 5 cases the extent of failure was insignificant (that is, 0.042% expansion at 2 years in both cases). It is concluded that combinations of pozzolans and reactive aggregates that pass the accelerated mortar bar test can be used in the field with a very low (and acceptable) risk of deleterious expansion due to ASR.
A large number of the mortar bars were subjected to pore solution expression and analysis after 14 days in 1 M NaOH at 80°C. There is a broad correlation between the pore solution alkalinity and expansion at the end of the test. This suggests that the mineral admixtures suppress expansion in this test by reducing both the alkalinity of the pore solution in the bar and the penetration (diffusion) of alkalis into the bar from the host solution.
Vice-president, Marketing and Technical Sales, LaFarge Corporation, Southfield, MI
Associate professor, Toronto University, Toronto, Ont.
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