Life-cycle assessment and microstructural performance of andesite dust-modified alkali-activated hybrid mortars at...

In this study, seven alkali-activated mortar mixtures were produced using waste andesite dust (WAD), fly ash (FA), and calcium aluminate cement (CAC). All mortar specimens were stored under ambient conditions of 20 ± 2 °C and 50 ± 10% relative humidity until testing. Flexural and compressive strengths were evaluated at curing ages of 7, 28, and 56 days. A comprehensive microstructural characterization of selected mortars was performed through phase analysis (XRD), morphological and chemical investigations (SEM/EDX/mapping), and examination of the three-dimensional pore structure (micro-CT). Additionally, a Life Cycle Assessment (LCA) was conducted for all mortar scenarios using 1 m³ of mortar as the functional unit. The mixture containing 66.6% WAD and 33.3% CAC exhibited the highest compressive strength among all formulations, reaching 35.5 MPa after 56 days of ambient curing. Micro-CT analyses revealed that this mixture also possessed the lowest porosity. The incorporation of CAC led to the formation of additional crystalline phases, such as sodium anorthite. Due to its low Ca content, WAD primarily produced an N-A-S-H gel-dominated matrix, whereas hybrid mixtures also developed C-A-S-H gel. Furthermore, FESEM and EDX mapping confirmed that the addition of CAC resulted in a denser and more compact microstructure, attributable to the increased concentration of Ca ions, which directly contributed to enhanced mechanical performance. Although CAC-containing mixtures showed improved strength and microstructural density under ambient curing, their environmental impacts were higher; in contrast, the WAD-based mixture exhibited the lowest environmental footprint.