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

• The alkali content of fly ash is originally non-water-soluble.
• The alkali content of fly ash gradually becomes water-soluble during the cement hydration process.
• Lithium compounds could increase the water-soluble alkali concentration in cement specimen.
• ASR inhibition performance of LiNO3 is than that of LiOH addition.

This study uses fly ash to replace partial cement. NaOH is used to increase alkali content of cement to 1.0% Na2Oeq. LiOH and LiNO3 are added separately to obtain several Li/(Na + K) molar ratios to fabricate cement specimens cured at 38 °C 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, LiNO3 addition exhibits better performance in increasing water-soluble Li/(Na + K) molar ratio compared with LiOH addition.