Strength and drying shrinkage of reactive MgO modified alkali-activated slag paste

Conventional alkali-activated slag (AAS) cements suffer from significant drying shrinkage which hinders their widespread application. This paper investigates the potential of using commercial reactive MgO to reduce the drying shrinkage of AAS. Two different reactive MgOs were added at a content of 2.5-7.5 wt% of the slag, which was activated by sodium hydroxide and water-glass. The strength and the drying shrinkage of those reactive MgO modified AAS (MAAS) pastes were measured up to 90 days. It is found that MgO with high reactivity accelerated the early hydration of AAS, while MgO with medium reactivity had little effect. The drying shrinkage was significantly reduced by highly reactive MgO but it also generated severe cracking under the dry condition. On the other hand, medium-reactive MgO only showed observable shrinkage-reducing effect after one month, but the cement soundness was improved. The hydration products, analysed by X-ray diffraction, thermogravimetric analysis and scanning electron microscopy techniques, showed that Mg was mainly incorporated in the hydrotalcite-like phases. It is concluded that the curing conditions and the time of hydrotalcite-like phases formation and their quantity are crucial to the developed strength and shrinkage reduction properties of MAAS, which are highly dependent on the reactivity and content of reactive MgO. Crown Copyright © 2013 Published by Elsevier Ltd. All rights reserved.

Properties of two model soils stabilized with different blends and contents of GGBS, MgO, lime, and PC

This paper addresses the use of ground granulated blast furnace slag (GGBS) and reactive magnesia (MgO) blends for soil stabilization, comparing them with GGBS-lime blends and Portland cement (PC) for enhanced technical performance. A range of tests were conducted to investigate the properties of stabilized soils, including unconfined compressive strength (UCS), permeability, and microstructural analyses by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The influence of GGBS:MgO ratio, binder content, soil type, and curing period were addressed. The UCS results revealed that GGBS-MgO was more efficient than GGBS-lime as a binder for soil stabilization, with an optimum MgO content in the range of 5-20% of the blends content, varying with binder content and curing age. The 28-day UCS values of the optimum GGBS-MgO mixes were up to almost four times higher than that of corresponding PC mixes. The microstructural analyses showed the hydrotalcite was produced during the GGBS hydration activated by MgO, although the main hydration products of the GGBS-MgO stabilized soils were similar to those of PC. © 2014 American Society of Civil Engineers.

Characterisation of different commercial reactive magnesia

Reactive magnesia (MgO) has emerged as an essential component in a new family of cements with significantly superior technical and environmental performance over Portland cement. The physical characteristics of different reactive magnesia, which are likely to affect their engineering performance, vary considerably depending on their origin and manufacturing processes. To appropriately utilise such a material, it is essential to develop a better understanding of the characteristics of different magnesia from various sources. In this study, the detailed characterisation of 14 commercial magnesia in terms of reactivity, textural properties, X-ray diffraction pattern, pH value and hydration behaviour and morphology is presented and correlation between them is developed. Relationships were developed between the reactivity, specific surface area, agglomeration ratio and hydration rate based on the experimental observations. As a result, the reactive magnesia used in this study were grouped into three categories and their characteristics and anticipated performances in different applications were discussed.

Properties and microstructure of GGBS-magnesia pastes

Reactive magnesia (MgO) was used as an alkali activator for ground granulated blast-furnace slag (GGBS) and its activating efficiency was investigated compared with hydrated lime. GGBS-MgO and GGBS-hydrated lime paste samples with different compositions and different water to solid ratios were prepared and cured for different periods. A range of tests was conducted to investigate the properties and microstructure of the pastes, including compressive strength, X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, energy dispersive X-ray and thermogravimetric analysis. The results showed that the reactive MgO acts as an effective alkali activator of GGBS, achieving higher 28-day compressive strength than that of the corresponding GGBS-hydrated lime system. The extensive microstructural investigation indicated that the main hydration product of reactive MgO-activated GGBS and hydrated lime-activated GGBS systems was hydrated calcium silicate, but there was much more hydrotalcite present in the former, which contributed to its superior 28-day compressive strength.