AVAILABLE ALKALIS FROM SUPPLEMENTARY CEMENTING MATERIALS

Different methods were investigated to determine the amount of alkalies released by various supplementary cementing materials (SCM) available for alkali-silica reactivity. These are the ASTM C 114 method (water-soluble alkalies); the ASTM C 311 method (available alkalies), performed however over different periods of time from 7 days to 1 year, a modified ASTM C 311 method performed up to 1 year on SCM-cement mixtures, and chemistry of pore solutions extracted from SCM-cement paste samples made with the same cement. SCM proportions and a 0.5 water/cement + SCM. The ASTM C 114 method gives only the amount of rapidly soluble alkali in the form of alkali salts (sulfates and chlorides). The ASTM C 311 standard and modified methods give values between 40 and 100 percent of total alkalies; in most cases, both methods clearly overestimate the percentage of alkalies available from supplementary cementing materials, probably because a large proportion of alkalies entrapped in secondary hydrates are released when the samples are thoroughly washed with water at the end of the tests. Indeed, for all good SCMs tested the results from pore solution chemistry suggest that more alkalies are entrapped in secondary hydrates than released from SCMs in the pore solution (negative contributions). These results are in good agreement with expansion tests on concretes made with the same SCMs and two very reactive aggregates. The pore solution extraction method appears to be the best method to evaluate the balance between the alkalies released by SCMs in the pore solution and those entrapped in reaction hydrates, i.e., the percentage of alkalies that are effectively available for ASR.