Durability and microstructural study of sustainable concrete containing lime, ground and non-ground granulated blast furnace slag and recycled coarse aggregate

This study investigates the durability and microstructural characteristics of concrete incorporating sustainable materials. Lime and ground granulated blast furnace slag (GGBFS) are used as partial replacements for cement, while granulated blast furnace slag (GBFS) and recycled coarse aggregate (RCA) are used to replace natural fine and coarse aggregates. Durability performance is evaluated by sulphate attack, rapid chloride permeability, water sorptivity, carbonation and fire resistance tests. Microstructural properties are examined using X-ray diffraction, scanning electron microscopy, Fourier transform infra-red spectroscopy and thermogravimetric analysis. A total of 11 concrete mixes were prepared, including a control mix without additives, one mix with 60% GGBFS and nine mixes containing different combinations of 50, 75 and 100% GBFS and RCA, along with 6% lime and 60% GGBFS. The use of GGBFS improves durability by reducing the amount of free calcium hydroxide and filling the concrete pores. However, increasing GBFS and RCA content tends to reduce durability due to their relatively weaker properties. Microstructural analyses support these trends. Three mixes among nine mixes exhibit superior or comparable durability as compared to the control concrete, highlighting their potential for promoting sustainable concrete production, reducing waste and supporting the circular economy in construction.