Innovative Geopolymer-Based Stabilization of Clayey Soil Using Alkali-Activated Construction and Demolition Wastes: Insights from Large-Scale-Model Tests

In developing and currently developed countries, dealing with solid wastes comprises one of the ultimate social, economical and environmental problems. Thus, geotechnical engineers have recently been in search of alternative waste materials in regard to the utilization of wastes in soil stabilization procedures. Construction demolition wastes, which constitute a significant part in the mentioned solid waste materials, have come to mind as an alternative to be implemented in such applications. By means of considering the utilization of these wastes, one aim has been to reduce both the amount of accumulated waste to the environment and related costs of stabilizing problematic soil conditions. Within the context of this study, improvability of fine-grained soils was questioned by means of utilizing alkaline activators to geopolymerize construction demolition wastes in order to procure an alternative material to cement. Eventually, optimum values for the considered NaOH, KOH and CaO alkaline activators were determined to be 8, 8 and 6 molal, respectively. The use of KOH, NaOH, and CaO activators during the geopolymerization process resulted in a significant improvement in bearing capacity compared with the untreated waste–soil mixtures. This finding indicates that these activators can be effective in enhancing the engineering performance of waste–soil mixtures. Among the activators investigated, NaOH exhibited the highest effectiveness in improving bearing capacity, yielding superior results compared with KOH and CaO. The superior performance of NaOH is considered to be potentially associated with its ability to promote the formation of a binding structure and facilitate interactions among the mixture constituents more effectively during geopolymerization. The resulting binding structure may strengthen the interparticle bonds between the soil and waste particles, thereby contributing to an improvement in the load-bearing capacity of the mixture. Therefore, based on the findings obtained, NaOH was concluded to be the most effective activator for enhancing bearing capacity under the conditions investigated. Additionally, temperature increments resulted in enhancements in the bearing capacities, and the maximum value was reached at the completion of day 28. Moreover, time-dependent settlements reduced by approximately up to 5.76–5.78 times. Consequently, it was observed that the geopolymerization method can be considered as a decent enough and novel alternative to cement for the improvement of engineering properties of fine-grained soils at significant ratios.