EFFECT OF REACTIVE MAGNESIUM OXIDE ON THE PHYSICO-MECHANICAL PROPERTIES AND DURABILITY OF CEMENT MORTAR

Abstract

The present work aims at studying the effect of MgO with different reactivities on physico-mechanical properties of cement mortar. In this study, the reactive MgO was prepared from calcination of hydro-magnesite at 550 and 1250°C,namely MgO550 andMgO1250. The reactivity of MgO was determined using acetic acid neutralization test. 2.5, 5, 10 and 15 % MgO550 and MgO1250 were added to cement mortar. Also, the cement mortar was replaced by MgO550 and MgO1250 at the same content. Different experimental methods such as compressive strength, water absorption and linear expansion were applied to study the performance of CM containing reactive MgOs as addition and replacement. In addition, the resistivity of CM containing reactive MgO550 and MgO1250 against 5% MgSO4 up to 6 M was implemented. The carbonation of firing resistivity of CM with or without MgO550 and MgO1250 was carried out. In this work, two different carbonation systems (normal carbonation and accelerated carbonation) were applied. The firing resistivity of CM having MgO550 and MgO1250 cured in Tw or exposed to CO2 gas was studied. Several findings can be summarized as follows: 1- The acetic acid neutralization test proved that, the MgO550 was more reactive than that of MgO1250. Also, the XRD-patterns showed that, the crystallinity of MgO1250 is higher than that of MgO550. 2- The water absorption of CM containing 2.5 and 5 wt., % MgO550 (as addition) was lower than that of CM. further addition of MgO550 up to 15 wt., % leads to the increase of water absorption. In contrast, the water absorption increased with increase of replacement level of CM by MgO550 up to 15 wt., %. A significant decrease in water absorption was observed in case of CM containing 2.5 and 5 wt., %MgO1250 as addition or replacement. The CM having 15 wt., % MgO1250 showed the highest water absorption compared to other mixes. 3- The compressive strength of CM having 2.5 and 5 wt., % MgO550 or MgO1250 (as addition) showed the