Multiscale investigation of the impact of recycled plastic aggregate as a fine aggregate replacement on one-part alkali-activated mortar performance

Due to the use of solid alkaline activators, one-part alkali-activated materials, often referred to as ‘just add water' materials, have garnered increased interest for commercialization. This study primarily aimed to evaluate the impact of recycled plastic aggregate (RPA) on the performance of one-part alkali-activated mortars (OPAAM). The OPAAM samples were prepared by replacing sand with RPA, up to 50 % by volume of fine aggregate. Various properties of the OPAAM samples were examined, including flowability, density, water absorption, porosity, compressive strength, flexural strength, splitting tensile strength, and microstructural features. Experimental investigations revealed that the mechanical properties of the OPAAM decreased with an increase in RPA in the mixture. At 28 days, both the control mixture and the mixture with 10 % plastic aggregate exhibited the highest compressive strength, approximately 46 MPa, compared to the other mixtures. All mixtures consistently showed improved strength performance after 28 days. The porosity and water absorption of the samples increased with a higher replacement of fine aggregate with plastic aggregate. Microstructural findings indicated a weaker interfacial transition zone (ITZ) between the RPA-paste compared to that of the sand-paste. The ITZ appeared weakened by microcracks dispersed in the interface between the paste and recycled plastic aggregate. Despite the decrease in mechanical properties, the inclusion of RPA in amounts ranging from 10 % to 50 % resulted in significant reductions in total equivalent CO2 emissions, ranging from 22.7 % to 113.5 %. However, the benefits of using this greener option will be offset by the higher cost, ranging from 5 % to 20 %.