Effects of fly ash and lithium compounds on the water-soluble alkali and lithium content of cement specimens

摘要

This study uses fly ash to replace partial cement. NaOH is used to increase alkali content of cement to 1.0% Na_2O_(eq). LiOH and LiNO_3 are added separately to obtain several Li/(Na + K) molar ratios to fabricate cement specimens cured at 38 ℃ in a 100% relative humidity environment. This study aims to observe the diachronic changes of water-soluble alkali and lithium content in specimens to understand the potential damaging effect of alkali-silica reaction by adding fly ash and lithium compounds simultaneously. Results indicate that the alkali content of fly ash is originally non-water-soluble, but it gradually becomes water-soluble during the hydration process. When lithium compounds are not added, an increase in cement alkali content increases both the amount and the ratio of water-soluble alkali in the specimens. Given the same curing time, when lithium compounds are added to cement, the ratio of water-soluble lithium content is higher than that of water-soluble alkali content. Therefore, water-soluble Li/(Na + K) molar ratio becomes higher than the original value. Furthermore, LiNO_3 addition exhibits better performance in increasing water-soluble Li/(Na + K) molar ratio compared with LiOH addition.