Durability and performance characteristics of eco-friendly geopolymer binders based on electric-arc-furnace slag and dealuminated kaolin

Abstract

The pursuit of sustainable development is an essential aspect of modern society's progress, aiming to achieve goals without causing waste, pollution, harm, or environmental degradation. The study focused on developing environmentally friendly binders by utilizing two industrial solid wastes: electric arc furnace slag (EAFS) and dealuminated kaolin (DK). The investigation aimed to assess the physio-mechanical, chemical properties, and durability of the binders against elevated temperatures and exposure to seawater, thereby contributing to sustainable practices. The eco-friendly geopolymer binders, EAFS and DK were blended in various proportions and mixed with alkaline activators. The resulting binders were cured at 40°C and a relative humidity of 98±2% for 180 days. Some of the binders were subjected to temperature increments in the order of 200, 400, 600, 800, and 1000°C, while the other geopolymer binders were immersed in seawater for upto 180 days. Setting times, compressive strength tests, evaluation of free slag and combined water contents, and analysis of the effects of elevated temperatures and seawater exposure on the phase composition of the geopolymer binders were conducted using XRD, TGA/DTG, and SEM/EDX. The finding showed the replacement of 10–20% of EAFS with DK resulted in a reduction in both the initial and final setting times. Increasing the amount of alkali activation content of EAFS upto (1.00 mol/Kg Na2O) (ES3 mix) leads to an increase in the values of compressive strength. Further increase in the alkali content (1.50 mol/Kg Na2O) reduces the compressive strength. The incorporation of DK enhanced the compressive strength value upto 30% DK (ES-DK3 mix). The increase in DK content beyond 30% resulted in reduced compressive strength values. ES-DK3 mix improved the thermal stability of the geopolymer matrix as well as demonstrated higher relative compressive strength values, especially at 1000°C. In addition to the mix, ES-DK3 showed superior durability against the attack of seawater. The compressive strength showed a sharp increase for specimens submerged in seawater for upto 180-days, this is attributed to the high reactivity of DK which acts as a nucleating agent that fills the open matrix preventing the penetration of SO42- and Cl- ions to inhibit the formation of nonbinding material.