Abstract
The clinker production process used to make cement requires significant amounts of energy, which negatively impacts the environment by releasing large amounts of CO2 during the process. Researchers are constantly striving to reduce the significant carbon footprint that cement production creates. The use of suitable industrial by-products, so-called Supplementary Cementitious Materials (SCMs), is one of the successfully tested ways to reduce the clinker content in cement and thus its carbon footprint. The latter is achieved by replacing part of the cement with a certain amount of the SCM. This will help construction companies to produce and use more environmentally friendly products. The SCM of interest in this research study is granulated blast furnace slag (GBFS), which is referred to as slag in this dissertation and is an acceptable cementitious supplementary material (SCM) used and approved by cement standards and cement manufacturers.
The commonly used approaches in slag activation include mechanical activation (milling/grinding) and chemical activation. However, there are few studies on the synthesis of nanoparticles (NPs) from cementitious materials. Therefore, this study aimed to synthesise and characterize nanoslag from South African granulated blast furnace slag and use it as an activator in a slag cement by applying a hydrothermal process. This is performed to improve the pozzolanic reaction between slag and Portland cement without compromising performance and durability in slag cement. The use of NPs as additives in cement has become the focus of research in recent years. Literature has proved that adding NPs to cement can enhance the properties of the particular cement by one of, or a combination of the following: generating
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additional C-S-H gel, hydration acceleration, generating denser microstructure, and reduction in porosity (Paul, Van Rooyen, van Zijl, & Petrik, 2018).
Characterization techniques used include Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), heat of hydration (HOH), thermogravimetric analysis (TGA), and X-ray fluorescence (XRF).
Upon hydration, microscopic images revealed an agglomeration which proved NPs were successfully synthesized. The FTIR studies confirmed the formation of a new C-S-H gel. XRD studies showed the consumption of CH (Portlandite). HOH results clearly showed that incorporation of Nano Slag in Slag cement increases the early hydration reaction rate, which was supported by the improved early age compressive strength, which increased by about 3% for all curing ages. The latter was attributed to the large surface area which the synthesised Nano Slag possesses compared to that of the cementitious components in the slag cement blend.