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Concrete is the most consumed material in the construction industry. Using recycled aggregates (RA) and silica fume (SF) in concrete and mortar could preserve natural aggregates (NA) and reduce CO 2 emissions and construction and demolition waste (C&DW) generation. Optimizing the mixture design based on both fresh and hardened properties of recycled self-consolidating mortar (RSCM) has not been performed. In this study, multi-objective optimization of mechanical properties and workability of RSCM containing SF was performed via Taguchi Design Method (TDM) with four main variables including cement content, W/C ratio, SF content and superplasticizer content at three different levels. SF was used to decrease the environmental pollution caused by cement production as well as compensating the negative effect of RA on the mechanical properties of RSCM. The results revealed that TDM could appropriately predict the workability and compressive strength of RSCM. Also, mixture design containing W/C = 0.39, SF = 6%, cement = 750 kg/m 3 and SP = 0.33% was found as the optimum mixture having the highest compressive strength and acceptable workability as well as low cost and environmental concerns., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper, (© 2023 Published by Elsevier Ltd.)

Reusing industrial by-products and agricultural waste as supplementary cementitious materials for producing sustainable concrete is one of the most promising ways to reduce cement production and the detrimental effects of concrete constructions on the environment. However, when it comes to preparing self-consolidating concrete (SCC) and mortar (SCMO) containing such materials in high volume, bleeding, and segregation of their fresh mixture are the crucial factors hindering their large-scale application. In this regard, the main aim of this study is to address such issues by designing sustainable SCMO using ground granulated blast furnace slag (GGBS) in high volume and rice husk ash (RHA) with comparatively lower environmental impact and high quality. To achieve this goal, the workability of fresh mixture and all its three main characteristics, including segregation resistance, passing ability, and filling ability, were evaluated with recently developed empirical apparatuses. For this purpose, 12 mixtures with different compositions were prepared to investigate the fresh properties, compressive strength, setting time, and environmental impact index. The results indicate that there are inextricable links between mixing proportions, strength, and carbon emissions of the mixture. Sustainable SCMO with an embodied-CO 2 index lower than 4.5 kg/MPa.m 3 , good workability, and compressive strength of 49.7 MPa was designed by optimizing cementitious content, while the e-CO 2 index of the control mixture was around 8 kg/MPa.m 3 . The addition of GGBFS and RHA not only decreased the e-CO 2 index but also increased the unit cement strength contribution index. The results also indicated that by increasing GGBFS, the fluidity and segregation of the mixture increased while adding RHA increased viscosity and modified bleeding and the segregation index. Moreover, the growth rate of the compressive strength in mixtures containing GGBFS was much higher than that of the control mix at the same age. The promising results of this experimental study indicate that utilization of GGBFS and RHA in SCMO mixture can provide a practical way to reduce the environmental effects of cement production and pave the way for friendly disposal of slag and waste products., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)