Influence of NaOH molarity and Portland cement addition on performance of alkali activated cements based in silicomanganese slags

Abstract

The aim of this research is to explore the potential of recycling the waste of silicomanganese slag (SiMnS) from the ferroalloy industry in the synthesis of alkali-activated cements. The influence of the concentration of the activator NaOH (4, 6, 8, and 10 M) and the partial substitution of the waste with Portland cement (PC) (10–30 wt%) on the technological properties and microstructure of binders cured at room temperature has been studied. The SiMnS binders and the hybrid cements incorporating PC have been characterized using X-ray diffraction analysis (XRD), infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) combined with energy-dispersive spectroscopy (EDS). The results indicate that compressive strength improve with an increase in molarity from 4 to 6 M from 7.8 up to 14.0 MPa, respectively, at 28 curing days. Similar mechanical properties are observed for higher molarity increments (8 M and 10 M) (12.9 and 13.6 MPa, respectively). The main reaction product formed is a (C,N)-A-S-H gel with different morphologies. Partial substitution of SiMn slag with PC led to hybrid cements with a denser structure due to a greater amount of C-S-H gel, coexisting with C,N-A-S-H gel. Therefore, the optimal combination of SiMn slag (70 wt%) and PC (30 wt%) significantly enhances the technological properties of the SiMn slag binders obtaining optimum compressive strengths of 24.7 MPa. The results of this study demonstrate that silicomanganese slag can be utilized as an environmentally friendly solution in the production of binders and hybrid cements that meet the required technical specifications and standards for use and application in the construction sector in the line of current circular economy policies and Sustainable Development Goals.