| ASR occurrs in the ITZ and ITZ is the weak link in concrete. The mechanism of lithium salts in suppressing ASR has been controversial, therefore, it is significant to study the mechanism of lithium salts in suppressing ASR from ITZ.In this paper, different contents of lithium salts were mixed in the concrete specimens containign different concentrations of KOH and NaCl. The specimens were cured in standard conditions for 28d. The changes of the morphology, pore structure and the elements distribution in ITZ were observed and analyzed by SEM and SEM-BSE. And the expansion of the corresponding mortar bar and changes of ions in pore solution were measured.The results showed that the morphology of ITZ in ASR concrete were complex and loose. Lots of CSH gel, CH crystal and AFt crystal occured in ITZ. The size of CH crystal was smaller, and Si, Al, Na, K elements accumulated in the ITZ. The ITZ in specimens added with lithium salt became dense, and the morphology was simple. The products in ITZ were mainly CH crystals and CSH gel. Closely connected CH crystals were larger and grew in the gel in form of tabular. The incoporation of lithium salt reduced the enrichment of Na, K elements in the ITZ, decreased the Ca/Si ratio of C-S-H gel which binded Na and K. At the same time the lithium salt reduced the porosity and average pore size in the ITZ. As the Li+/K+ molar ratio increased, the ITZ became dense, the size of CH crystal also tended to be larger, Ca/Si ratio of C-S-H decreased, the enrichment and content of Na and K decreased, the porosity and pore size of ITZ decreased.The analysis of the experiments revealed that the incorporation of lithium salts can improve the density of the ITZ of ASR concrete and the structure of the ITZ, forming low Ca/ Si ratio L-S-H which include less of Na and K. Lithium salts also reduce the porosity and average pore size in the ITZ, so that the ASR is inhibited, and with the increase of Li+/K+ molar ratio, the inhibitory effect improve appearently.
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