Abstract
The negative environmental impact of cement production emphasizes the need to use alternative binders for construction materials. Alkali-activated slag is a more environmentally friendly candidate which can be utilized in the design of mortars with favorable material properties. However, the electrical properties of such materials are generally poor and need to be optimized by various metallic or carbon-based admixtures to gain new sophisticated material functions, such as self-sensing, self-heating, or energy harvesting. This paper investigates the influence of waste metal powder originating from the 3D printing process on the material properties of alkali-activated slag mortars. The untreated metal powder was characterized by means of XRD and SEM/EDS analyses revealing high nickel content, which was promising in terms of gaining self-heating function due to the high electrical conductivity and stability of nickel in a highly alkaline environment. The designed mortars with the waste metal admixture in the amount up to 250 wt.% to the slag and aggregates were then characterized in terms of basic physical, thermal, and electrical properties. Compared to the reference mortar, the designed mortars were of increased porosity of 17–32%. The thermal conductivity of ~1–1.1 W/m·K was at a favorable level for self-heating. However, the electrical conductivity of ~10−6 S/m was insufficient to allow the generation of the Joule heat. Even though a high amount of 3D printing waste could be used due to the good workability of mixtures, its additional treatment will be necessary to achieve reasonable, effective electrical conductivity of mortars resulting in self-heating function.
Highlights
Alkali-activated slag mortars (AASMs) are composites based on ground-granulated blast-furnace slag (GGBFS), the precursor rich in CaO content (~35–40%) with latent hydraulicity
The influence of various electrically conductive admixtures (ECAs) on the effective electrical conductivity of the designed materials have been investigated in the past, mainly studied for cementitious materials, e.g., El-Dieb et al [10] focused on steel shavings, carbon powder, and graphite powder that were used as a partial replacement of fine aggregates to reach favorable electrical properties
The designed AASMs were based on ground-granulated GGBFS, three fractions of fine aggregates, sodium silicate activator-water glass (WG), and M3DPWP (Figure 1)
Summary
Alkali-activated slag mortars (AASMs) are composites based on ground-granulated blast-furnace slag (GGBFS), the precursor rich in CaO content (~35–40%) with latent hydraulicity. The electrical conductivity of such materials ranges between ~10−9 –10−4 S/m [6,7,8,9], which is typical for electrical insulators. This shortcoming can be overcome by admixing electrically conductive admixtures (ECAs), which in certain dosages ensure significant improvement in electrical properties of the doped composites. The influence of various ECAs on the effective electrical conductivity of the designed materials have been investigated in the past, mainly studied for cementitious materials, e.g., El-Dieb et al [10] focused on steel shavings, carbon powder, and graphite powder that were used as a partial replacement of fine aggregates to reach favorable electrical properties. Belli et al [11] focused on the optimization of high-conductive multifunctional fiber-reinforced cement mortars by using virgin carbon fibers, recycled carbon fibers, and brass-plated steel fibers, Berrocal et al [12]
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