Evaluating the eco-compatibility of mortars with feldspar-based fine aggregate

As cement manufacturing is associated with CO2 emissions that contribute to environmental problems, cement usage must be reduced and alternative aggregates must be developed. Thus, we developed and evaluated a mortar that uses feldspar as a fine aggregate, which does not require additional mineral admixtures. Feldspar and conventional plastering sand-based specimens were prepared with a fine aggregate proportion of 75%, 80%, or 85%. The compressive strength test results confirmed that the strength of the feldspar-based mortar was 1.1–4.5 times higher than conventional plastering sand-based mortar. Microstructure analysis after 3 and 7 d of curing revealed the existence of capillary micropores and gel pores, which improved water tightness. C-S-H and C-S-H gel hydration was also observed at the early stage, and the amount of C-S-H also increased. Further, an additional reaction may have occurred between feldspar compounds, SiO2 and Al2O3, and Ca(OH)2 that accelerated C-S-H production and contributed to the higher compressive strength. The relatively high-strength feldspar-based mortar is expected to reduce cement dependency, which can be achieved using a fine-aggregate feldspar mixing ratio according to project requirements. Thus, the proposed fine aggregate alternative can help alleviate the environmental problems associated with cement usage. It also has potential as an eco-friendly building material.