Influence of Two-Stage Mixing Approach on Thixotropic Behavior of Self-Compacting Recycled Aggregate Concrete

Abstract

Thixotropy is a rheological parameter that can control the formwork pressure, multilayer casting, and stability of self-compacting concrete (SCC). The use of recycled coarse aggregate (RCA) increases the friction between the particles, thereby increasing the rheological parameters, including thixotropy, which is not always desirable. However, adoption of the two-stage mixing approach (TSMA) reduces this frictional force, and self-compacting recycled aggregate concrete (SCRAC) may have versatile use like natural aggregate-based SCC. In this research, the thixotropic characteristic of SCRAC prepared by a TSMA is investigated by evaluating the structural breakdown area (Ab) and the relative drop in apparent viscosity (Δηr-app) through a stress growth protocol using a vane-geometry rheometer. Several conventional fresh properties along with rheological properties, compressive strength, X-ray diffraction, Fourier-transform infrared spectroscopy, differential scanning calorimetry, and field emission scanning electron microscopy analyses are also conducted. The degree of thixotropy in terms of Ab and Δηr-app is noted to be increased with the increase in RCA% in the normal mixing approach (NMA). However, after adopting the TSMA, the influence is observed to be comparatively less. Moreover, the proposed TSMA exhibits better other fresh and hardened properties than NMA. The improved performance is attributed to the adoption of the right kind of treatment in the initial stage of mixing of TSMA. This treatment results in the smoothing of the rough surface of the RCAs along with the formation of more hydrated products in the new interfacial transition zone regions.