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A system of alkali-activated fly ash (FA)/slag (AAFS) mixtures as a clinkerless cement was investigated with different dosages of Na 2 CO 3 , as a sustainable activator. The effect of incorporating various proportions of reactive magnesia (MgO) was also examined. Mechanical, mineralogical, and microstructural characterisation of the cement pastes was carried out using the unconfined compressive strength, X-ray diffraction, thermogravimetric analysis, infrared spectroscopy and scanning electron microscopy. It was found that the strength of Na 2 CO 3 activated FA/slag mixtures generally increased with time and the Na 2 CO 3 dosage. The hydration products were mainly C-(N)-AS -H gel of low-crystallinity, which is rich in Al and may have included Na in its structure, and hydrotalcite-like phases. Adding reactive MgO in the mixes showed an accelerating effect on the hydration rate as suggested by the isothermal calorimetry data. Additionally, findings revealed variations on the strength of the pastes and the chemical compositions of the hydration products by introducing reactive MgO into the mixtures.

Various innovative research in the cement industry is looking into improving its environmental sustainability. Sodium carbonate-activated slag/fly ash (NC-SF) binders has recently evolved as a potentially more sustainable binding materials than both Portland cement and conventional alkali activated materials such as sodium silicate and sodium hydroxide activated materials. The reaction mechanism and some microstructural properties of NC-SF cements have been a major area of research recently. However, very few studies have scaled up the investigation of these binders into concrete specimens. This paper, therefore, provides new insight into the strength development and the durability performance of NC-SF concrete and MgO-modified NC-SF concrete. Concrete testing included measurements of compressive strength, split tensile strength, water absorption, depth of carbonation, sulphate exposure, acid exposure and elevated-temperature exposure. Microstructure studies were conducted using Powder X-Ray diffraction (PXRD), Thermogravimetric analysis (TGA) and Attenuated Total Reflectance Fourier Transform Infrared spectroscopy (ATR-FTIR). It is concluded that NC-SF concrete mixes develop acceptable mechanical strength and demonstrate high resistance to sulphate attack. They also showed higher resistance to acid attack than the control mix based on sodium silicate-activated slag concrete. Here, emphasis is placed on the potential of developing NC-SF concrete with excellent performance and less complicated production methods as well as a low carbon footprint. It is also found that the use of reactive MgO enhanced the strength development of NC-SF concrete as well as its resistance to acid and carbonation.

The utilization of fine powders as fillers in self-compacting concrete (SCC) application is widespread, particularly in Europe. The incorporation of these fillers to attain the self-compatibility properties of SCC seems to be cheaper than the use of chemical admixtures. Among the wide range of potential fillers, dolomitic powders, particularly generated as by-products from quarry’s processing, are locally available and can be used to produce SCC. Few studies have shown that dolomitic powders can be incorporated in the SCC’s mix design, resulting in acceptable fresh and hardened properties of SCC. The particle size distribution and fineness of the dolomitic powder as well as the level of addition are the key factors affecting those properties. The influence of the chemical nature of the dolomitic powder on the properties of SCC, particularly the durability (e.g. alkali-carbonate reaction), is yet to be investigated. Furthermore, more efforts are still required to investigate the use of dolomitic by-products in the production of SCC.

Presenting a promising option that could be used to encapsulate nuclear waste material for disposal, supersulfated cement (SSC) is, again, receiving wide attention among research community as a cementitious system that has noteworthy properties. It is also an environmentally friendly cement since it is mainly composed of ground granulated blast furnace slag (GGBS) that is activated by a sulphate source such as gypsum, hemihydrate or anhydrite. Although there is some research on SSC, little research work has focused on modelling the effects of the various parameters using a statistical approach which is the aim of this paper. The effect of dosages of GGBS, anhydrite (ANH) and water-to-binder ratio (W/B) on the fresh and rheological parameters, induced bleeding, permeability, compressibility, and compressive strength of supersulfated grouts was investigated. Then, statistical models and isoresponse curves were developed to capture the significant trends of the tested parameters using factorial design approach. The models suggested that that W/B had significantly higher influence on most of the parameters tested while the influence of GGBS and ANH and their interactions varied depending on the parameter in question. . The findings of this study show the importance of understanding the role of and optimising the relevant key factors in producing SSC fit-for-purpose. The statistical models developed in this paper can facilitate optimizing the mixture proportions of grouts for target performance by reducing the number of trial batches needed.