Circular Material Solutions in Building Mortars: Technical Performance, Environmental Impacts and Economic Implications—A Review

The growing demand for sustainable building materials has accelerated the implementation of circular economy principles in the construction sector. Among cement-based materials, mortars offer significant opportunities for utilizing secondary raw materials and industrial by-products due to their compositional flexibility and wide range of applications. This review discusses the application of circular economy material solutions in cement mortars, including recycled aggregates, complementary cementitious materials, alternative binders, and recycled mixing water. Their impact on fresh properties, mechanical properties, durability, and functional properties, as well as related environmental and economic aspects, is analyzed. The studies reviewed indicate that the performance of mortars containing circular materials depends on the material type, its properties, the level of exchange, and the mix composition. Partial cement substitution commonly results in GWP reductions of approximately 10–40%, whereas higher replacement levels, alternative binder systems, recycled fibres, and carbon-storing materials may provide greater reductions under favourable conditions. Many factors influence the environmental and economic benefits, including processing requirements, transportation distances, local availability of secondary resources, and life-cycle assumptions. Despite significant progress in recent years, challenges related to material variability, standardization, and long-term performance still limit the wider use of circular materials in mortar production. Further research should therefore focus on improving material characterization, harmonizing assessment methods, and supporting the practical implementation of circular solutions in the construction sector.