Optimal design of ferronickel slag alkali-activated mortar for repair exposed to high thermal load

Abstract

In this work, the optimal design of a mortar based on alkali-activated material technology is presented. Ferronickel slag, a byproduct of the ferronickel alloy industry, was used both as a binder component (in a finely ground form) and as fine aggregate in alignment with a circular economy approach. The proportions of binder, fine aggregate, and water were optimized using Design of Experiment Design of Mixtures. The performance indicators evaluated were flow, flexural and compressive strength both before and after high-temperature exposure, mass loss, and thermal shrinkage. Life cycle assessment was used to calculate the relative environmental cost of the studied mixes in comparison to a counterpart traditional Ordinary Portland Cement mortar. The optimal mix design exhibited high flexural strength (8.5 and 10.5 MPa, before and after high-temperature exposure, respectively), an unheated compressive strength equal to 69.5 MPa, and a post-heating residual one of 33.9 MPa, 7.7% mass loss and 3.4% thermal shrinkage. Mercury Intrusion Porosimetry along with Scanning Electron Microscopy with Energy Dispersive X-Ray Analysis were also performed on optimal mortar samples in order to link micro-structural heat-induced changes to residual (post-heating) macro-mechanical performances. Finally, when compared to OPC-based products, the optimized mortar mix resulted in 70% lower CO2 emissions indicating great potential for the construction sector where concern about environmental impact keeps growing.

Diagonal Compression Tests on Unfired and Fired Masonry Wallettes Retrofitted with Textile-Reinforced Alkali-Activated Mortar

“…Previous characterization tests executed by Kapsalis et al [13] (individual results not included in this study) allowed for measuring the textile average peak stress, strain at peak stress and modulus of elasticity, which corresponded to 2231 MPa, 0.0105 and 212.5 GPa, respectively. The alkali-activated mortar recipe was the product of a mortar mix optimization effort based on the experiment and mixture designs [41]. The original recipe was modified to increase the workability by increasing the activator solution content (sum of water, KS and KOH).…”