The Study Of Aggregate Kinds On Expansive Performance Of MgO Concrete

Characterized by large volume and poor conductivity, mass concrete was vulnerable to thermal cracking stem from significant temperature gradient and tensile stress surpassing ultimate tensile strength. Conventional counter measures for thermal control was time-consuming, laborious and cost-increasing as well as unfavorable for fast construction. Practices justified that MgO concrete by use of expansion produced by MgO hydrating with water started another effective approach to address thermal cracking of mass concrete. So far, the majority of researches with regard to MgO concrete was focused on MgO expansive itself while rarely dabbled in aggregate,3/4in proportion of concrete volume. Considering big variety of aggregates used in different constructions, some common aggregates were selected to make MgO concrete with object of obtaining general law of aggregates on concrete performances to serve practice better.This paper had primarily investigated performances of MgO paste, mortar and concrete made from different powder, fine and coarse aggregates with employment of macro and micro techniques including TG-DSC and XRD, especially the deformation performance, and cracking sensitivity and phase composition and elements enrichment in interfacial transition zone was explored.The results showed that hydration degree of MgO in paste made from different powders varied with the highest in limestone paste, followed by diorite and basalt paste.Expansion rate of MgO mortar did vary with changes in temperature and time needed to stabilize was shortened with increase in temperature. With increase in curing temperature, mortar made from natural sand was featured by the most significant elevation in expansion rate, followed by diorite and limestone sand with the least in basalt mortar. Average diameter parameter of basalt and diorite exhibited little difference with age development while that of limestone mortar was notably reduced.Mechanical performances of MgO concrete was well correlated with its expansion and concrete made from limestone aggregate was observed to be most sensitive to expansion while slight expansion was observed in concrete made from basalt aggregate at later stage. Dry shrinkage of MgO concrete was related with water absorption of aggregate and little difference was observed in between due to micro expansion of MgO. Eary crack resistance of concrete indicated that MgO concrete made from artificial aggregates was similar to each other, of which basalt was ranked as the most significant. Worth noticing, made from the same aggregate though, expansion law of mortar and concrete was different from each other.Micro tests from EDS and SEM demonstrated that products of hydration in ITZ of MgO concrete were similar while different in type and crystallization degree. Elements Ca and Mg was apparently enriched in ITZ and their enrichment was in good relationship with macro expansion. With development of age, elements enrichment of Ca and Mg declined and displayed more uniform distribution and element Fe was also enriched especially in limestone concrete ITZ.