Durability characteristics of fly ash concrete containing lightly-burnt MgO

Hydration of Reactive MgO as Partial Cement Replacement and Its Influence on the Macroperformance of Cementitious Mortars

“…e results show greater carbonation depths with increasing MgO content, and there is no significant difference between MA and MG specimens. Even though less porous microstructures incorporating MgO have been observed elsewhere [25,62] suggesting reduced carbonation, the opposite trend was observed in the present study, and in others [62,63], they were substantiated by the results in Figure 8. e higher porosity in mixes containing increasing MgO content may have led to a greater surface area within the cementitious microstructure available to carbonate in the presence of CO 2 .…”

“…In the latter, the addition of MgO as cement replacement, in spite of the formation of Mg(OH) 2 , leads to a decreasing quantity of available C 2 S and C 3 S and consequently of C-S-H phases [35,58,59]. Nevertheless, if in the presence of an addition with amorphous SiO 2 , a greater rate of strength development could be observed as a result of pozzolanic reactions with Mg(OH) 2 [25]. Although the formation of Mg(OH) 2 is vital for strength gain at early curing ages, the ensuing formation of M-S-H will be the main contributing factor of the improvement of cementitious materials incorporating MgO [23].…”

“…e compatible chemical nature of MgO with that of cement may produce beneficial expansive components capable of reducing the number of microcracks and contribute to strength gain under certain circumstances [22]. Similar to that observed in the hydration of cement, after the formation of Mg(OH) 2 , ensuing pozzolanic reactions can lead to the formation of magnesium silicate hydrates (i.e., MgO-SiO 2 -H 2 O or M-S-H) [23] capable of presenting considerable strength gain [24], if in the presence of amorphous silica-bearing mineral additions, such as fly ash [25,26] or silica fume [27,28]. Another practical feature of using reactive MgO-based cementitious composites is their ability to capture a considerable amount of CO 2 thereby further decreasing the material's environmental impact throughout its life cycle.…”

Recent durability studies on concrete structure

“…5) Lightweight aggregates and viscosity modifier: Bentz et al explored two new approaches for increasing a mortar's resistance to sulfate attack: on one hand, fine lightweight aggregates were pre-wetted to enhance the microstructure of the interfacial transition zone, on the other hand, the isolated pores in the lightweight aggregates might help to accommodate the formation of expansive degradation products, such as ettringite, without creating substantial stresses and subsequent cracking; a viscosity modifier was added to the concrete mixture to increase the viscosity of the pore solution and thus slowed down the ingress of sulfates from the external environment [57]. 6) Magnesium oxide: The addition of magnesium oxide can improve the resistance of concrete to carbonation, chloride attack, and sulfate attack in the long-term [58]. 7) Superplasticizer: Proper amount of superplasticizer in concrete mix can cause high water reduction, thus reducing sulfate attack on the concrete and producing a more robust matrix [45].…”

The Evaluation of Damage Effects on MgO Added Concrete with Slag Cement Exposed to Calcium Chloride Deicing Salt

“…This enables the design and control of hydration reactivity and expansion properties by adjusting the calcining conditions [ 22 , 23 ]. Adding to that, the durability characteristics of concrete with FA and reactive MgO have showed improved resistance to carbonation, chloride attack, and sulfate attack in the long term by decreasing 0.03–0.3 μm pores associated with strength and ion diffusion [ 24 ].…”