An overview on the rheology of recycled aggregate concrete with the influence of chemical admixtures

Abstract

: Concrete is one of the most widely used construction material because of its property to be moulded into any kind of structure and shape due to its fluidity at early stages. The fresh properties of concrete can be characterized by its flow behaviour. Rheology is the scientific description of flow properties. Super-plasticizers and air-entrainers are some of the most used chemical admixtures that affect the rheological parameters of fresh cement-based material. Fresh concrete can be observed as a intense suspension of solid particles (aggregates) in a viscous medium, i.e. cement paste (Neophytou et al., 2010). The behaviour of a specimen of fresh composite material is defined in terms of its workability and is measured by numerous consistency methods. Establishing the model to predict plastic viscosity of concrete based on composition will be very much useful in the modern day concrete production. Traditionally rheological properties of concrete are conducted using rheometers.
In this study an attempt is made to use slump test, compaction factor test and concrete shear box test to obtain slump value, yield stress and plastic viscosity of Normal and Recycled aggregate concrete. In this limited study comparison is made between normal concrete and recycled aggregate concrete based on its rheological and strength properties by varying replacement percentages of recycled aggregate from 0% to 100% with addition of mineral and chemical admixtures. Based on the results of slump test, it can be predicted that the effect of SP increases for soaked conditions. Also, it was observed that the optimum percentage of replacement of natural coarse aggregates by recycled coarse aggregates was about 45%. The rheological properties were also studied using direct shear box test to obtain corresponding relative yield stress and plastic viscosity and a comparison was made between normal and recycled aggregate concrete.