Articles and issues

Background. Recycled concrete aggregate (RCA) from demolition waste could reduce landfilling and natural aggregate extraction in Chile, but its structural adequacy and environmental benefits for housing construction remain uncertain. This study evaluated the mechanical performance and life-cycle environmental impacts of recycled aggregate concrete for low-rise social housing in central Chile. Methods. Four grade G25 mixes were prepared with 0%, 30%, 50% and 100% replacement of natural coarse aggregate by RCA from a commercial recycling plant in the Santiago Metropolitan Region, at constant cement content and effective water-to-cement ratio. Compressive and splitting tensile strength, modulus of elasticity, water absorption and accelerated carbonation were measured. A cradle-to-site life-cycle assessment (modules A1–A4) used local supply-chain data, with sensitivity analyses of transport distance and cement content. Results. Compressive strength at 28 days decreased by 3.2%, 8.2% and 19.3% for 30%, 50% and 100% replacement, respectively, and only mixes with up to 50% RCA reached the target mean strength of 31 MPa. Cement accounted for 77–79% of global warming potential, which fell only from 318 to 312 kg CO₂-eq/m³ with full replacement; normalized by strength, full replacement increased global warming potential by about 22%. The 50% mix reduced natural aggregate use by 28% without additional cement. Conclusions. Replacing up to 50% of coarse aggregate with RCA is technically suitable for low-rise housing in central Chile. Its environmental value lies mainly in resource conservation and waste diversion, and substantial carbon savings will require lower-clinker binders.

Rapid urbanization and intensifying rainfall are overwhelming drainage systems in tropical cities, where conventional gray infrastructure is costly to expand and often poorly maintained. Nature-based solutions such as bioretention systems, green roofs, constructed wetlands, permeable pavements and restored urban streams are promoted as complements to pipes and channels, but most design guidance and performance data come from temperate climates. This review synthesizes evidence on the hydrological and water quality performance of nature-based stormwater solutions in tropical and subtropical cities, identifies the design adaptations that tropical conditions require and examines the barriers to their wider adoption. Field studies show that well-designed systems can substantially reduce runoff volumes and peak flows for frequent storms and remove most suspended solids, but their effect diminishes during the intense, long-duration events that cause the most damage. High rainfall intensity, year-round biological activity, deeply weathered soils, mosquito control requirements and dense informal settlement call for larger storage volumes, robust vegetation, rapid drawdown and integration with community-scale drainage. Implementation is constrained less by technical feasibility than by fragmented institutional responsibilities, limited maintenance funding, land scarcity and a lack of locally calibrated design standards. We propose priorities for long-term monitoring, design guidance and financing, and argue that tropical cities should plan nature-based solutions as part of hybrid green–gray systems sized for local rainfall regimes.