Rheology, mechanical properties and microstructure characterization of limestone calcined clay cement (LC3) incorporated sustainable lightweight self-compacting concrete

Abstract

In recent years, there has been growing interest in the possibility of achieving zero-emission goals using environmentally friendly building materials. Significantly, the concrete industry utilizes numerous alternatives as supplementary cementitious materials (SCMs) for development in construction sector. The integrity of these materials has the potential to alter the rheological properties of fresh concrete with ease of their chemical reactivity over time. The physico-chemical behavior of limestone calcined clay cement (LC³) and lightweight expanded clay aggregate (LECA) provides significant information about the intrinsic material characteristics including rheological attributes, of novel lightweight self-compacting concrete (LWSCC) of a target strength of 25 MPa. Primarily, the ease of flow in concrete is governed by the thixotropy and rheological parameters under dynamic motion. Secondarily, the perfect flow model is essential for determining the change in non-linearity in the mixes, leading to shear thickening. Therefore, the overall rheological behavior was determined through slump flow, L-box, U-box, V funnel, and shear flow curve tests using a coaxial vane rheometer with the help of Reiner-Riwlin (R-R) equations. Herschel-Bulkley (H-B) and Modified Bingham (M − B) equations numerically validates non-linearity with flow index (n) ranging between 1.52 and 1.79 with c/μ >0. For optimized LWSCC mix; the dynamic yield stresses varied by 20% owing to hydration acceleration and surface charge of metakaolin with an increase in plastic viscosity by 25% under low shear rate. It was found that the extent of flocculation and particle mitigation governs particle interactions in binders at low shear rates. Moreover, the significant reduction in fresh density by 35% (as compared to control mix) and the measurement of thermal conductivity through transient-state method explain the anisotropic structure effect of silicate layers in the heterogeneous LC³ system. A Microstructure study was employed to understand the contribution of secondary calcium silicate hydrate (C-S-H), chemical interaction of metakaolin, and interfacial transition zone (ITZ) through scanning electron microscopy (SEM). Finally, embodied energy assessment and cost analysis showed reduction in carbon dioxide (CO₂) emission and cost by nearly 16% and 13%, respectively, leading to a step toward global net zero emission with sustainability.