Performance evaluation and multi-objective optimization for alkali-activated slag concrete with recycled aggregate

Abstract

This study aims to investigate the effect of combined alkali-activators and alkali contents on the engineering and sustainability performance of the alkali-activated slag recycled concretes (AASRCs). The optimal activator type and its alkali content were identified using a combined analytic hierarchy process and integrated performance degree (IPD) model from a decision-making perspective. Three activators were selected, i.e., water glass (WG), combined WG and sodium carbonate (WN), and combined calcium oxide and sodium carbonate (CN). The alkali contents of activators were determined as 4%, 5%, and 6% in terms of the mass ratio of Na2O to binder. The results showed that WG-activated concrete (WGC) obtained the highest slump and compressive strength, and followed by WN-activated concrete (WNC) and CN-activated concrete (CNC). The autogenous shrinkage of CNCs drastically reduced compared to those of WGCs and WNCs. Moreover, CNCs exhibited obvious advantages over WGCs and WNCs in energy consumption, environmental impacts, and life-cycle cost. The AASRCs with higher alkali content generated greater environmental and economic impacts. The CNC with an alkali content of 4% showed the highest IPD value of 0.727 and obtained the optimum overall performance. This study extends the knowledge of the effect of combined activators on AASRC performance, and proposes a framework incorporating engineering, environmental, and economic aspects to optimize the activator type and its alkali content.