Abstract: With an objective of disclosing the effect of aggregate lithology on MgO mortar expansion, we investigated the expansive performances of cement mortar made from various fine aggregates under water curing at 20℃, 38℃ and 60℃ respectively, and probed into the microstructure and elements enrichment on the interfacial transition zone(ITZ) between cement matrix and fine aggregate by employing of EDS, Elements enrichment and BEIW. Results indicated that when curing temperature was elevated from 20℃ to 60℃, mortar expansion was increased, the greatest of which was mortar made from gabbro and natural sand, followed by mortar made from limestone sand and then basalt. Cured in water at 38℃, the enrichment of elements Ca and Mg in ITZ of gabbro and basalt mortar grew more obviously than that of limestone and natural sand mortar. Higher surface porosity and moisture content of natural sand was preferable for MgO migrating to ITZ for hydration, and favorable for the growth of brucite, an exterior expansive hydration products of larger size. Overall, the effect of fine aggregates on MgO mortar expansion was achieved by changing elements enrichment and patterns and morphology of hydration products on the ITZ. The artificial fine aggregate containing fine powder can change the expansion property of MgO mortar by changing the hydration level of MgO cement and the volume of total MgO.

Key words: fine aggregate, expansion rate, interfacial transition zone(ITZ), element enrichment