Mitigation of Drying and Carbonation Shrinkage of Cement Paste using Magnesia

Abstract

In this work, the effect of magnesia (MgO) on the hydrated phase assemblage, microstructure, as well as drying and carbonation shrinkage of hardened Portland cement paste is studied. By means of X-ray diffraction, scanning electron microscopy (SEM/EDS), and thermodynamic simulation, it shows that MgO hydration does not substantially alter the phase assemblage and microstructure of hardened cement paste, except the formation of brucite. The 5% MgO addition reduces the drying shrinkage of cement by about half, which cannot be simply explained by the molar volumetric increase due to MgO to brucite conversion. The results suggest that besides generating early-age expansion offsetting subsequent drying shrinkage, the formed brucite at early stages can enhance the matrix stiffness probably due to crystal formation with reinforcing potentials. In addition, the MgO addition improves the carbonation resistance of hardened cement due to the formation of magnesium-containing calcium carbonates. However, the effectiveness of MgO in mitigating carbonation shrinkage depends on the drying and carbonation sequence.

Mechanical performance and autogenous and drying shrinkage of MgO-based recycled aggregate high-performance concrete

“…So far, the use of reactive MgO has been validated exclusively regarding the production of cement pastes and mortars. Recent studies have shown that reactive MgO as cement replacement in relatively high quantities (10-20%) can be successfully used to produce mortars with improved shrinkage behaviour [37], reducing both autogenous [38] and total shrinkage [39]. The decrease in total shrinkage obtained for a MgO content of only 10% was between 18 and 49%, depending on its fineness [40].…”

Influence of Magnesium Oxide on Carbonation of Cement Paste Containing Limestone and Metakaolin

“…The reactive magnesia (magnesium oxide, MgO) as an additive in concrete has demonstrated benefits in enhancing the carbonation resistance of conventional OPC [18,19] and alkali-activated concrete [20,21]. However, to the best of the authors' knowledge, no work regarding the influence of reactive MgO addition on the reaction and carbonation of LC 3 systems has been documented in the literature.…”