Analysis and optimization of design parameters for recycled concrete modified with nano-CaCO3 considering environmental and economic and mechanical properties

To reduce carbon emissions, it is advisable to replace coarse aggregates with recycled concrete; however, the low strength of recycled concrete necessitates the addition of nanomaterials to enhance its mechanical properties. In this study, compressive tests, lifecycle assessment, and lifecycle costing methods were used to examine the environmental, economic, and mechanical properties of concrete, and the recycled-aggregate (RA) replacement rate, nano-CaCO 3 (NC) modification, and water–cement (W/C) ratio were examined as the main influencing factors. For multi-objective optimization considering the environment, economy, and compressive strength, the response surface method combined with a genetic algorithm was used. Subsequently, the TOPSIS and rank-sum ratio methods were employed to determine the optimal parameter design. The results indicated that the compressive strength of nano-modified recycled concrete decreases with an increase in the RA replacement rate and that NC can moderately increase the strength of concrete. The carbon emissions and cost of concrete decrease with increases in the RA replacement rate and W/C ratio, and they increase with the NC content. Among the factors considered, they are most significantly affected by the RA replacement rate. Using a multi-objective optimization approach together with a comprehensive evaluation, the optimal combination of parameters was determined to be 1.5% NC, 50% RA replacement, and a W/C ratio of 0.5.