Abstract:

MgO expansion agent, with its delayed micro-expansion properties, could enhance the mechanical properties and deformation performance of mass concrete. The pre-compressive stress could effectively improve its thermal crack resistance, yet researches on its micro mechanism are inadequate. The mechanical properties of concrete with different MgO dosages and different activity indexes are researched by macro and micro approaches, and the mechanism of MgO influencing on the concrete performance is researched by using SEM/EDS. Results indicated that MgO replacing some amount of cement in the concrete would reduce the concrete's strength; when the MgO dosage was between 4% and 5%, concrete with activity index of 100s exhibited larger expansion than that with activity index of 50s. The expansion of MgO-mixed concrete was specifically dependent on the uniformity degree of the distribution of element Ca, Si, Mg and Al. By adding MgO in the concrete, enrichment of elements Ca, Si, Mg and Al in the vicinity of interfacial transition zone was altered whereas elements Ca and Mg were intended to accumulate and hence decreased the strength of concrete. 

Key words: concrete, MgO, uniformity, element enrichment, expansive property