Simulation of the Attrition of Recycled Concrete Aggregates during Concrete Mixing

Abstract

Concrete mixing can lead to mechanical degradation of aggregates, particularly when dealing with recycled concrete aggregates. In this work, the attrition of such materials during mixing is studied by means of experiments and simulations. The effect of the presence of fines, water addition, flow configuration of the mixer (co- or counter-current) and impeller frequency is discussed. Experiments were performed in a laboratory Eirich mixer. Discrete element numerical simulations (DEM) were performed on the same geometry by mimicking the behaviour of the material and, in particular, the cohesion induced by water and the cement paste using either Hertz–Mindlin or Hertz–Mindlin with Johnson–Kendall–Roberts (JKR) contact laws. The combination of the collision energy spectra extracted from the DEM simulations and an attrition model allowed the prediction of the mass loss due to attrition in 1-min experiments. Semi-quantitative agreement was observed between experiments and simulations, with a mean relative error of 26.4%. These showed that higher mass losses resulted from operation at the highest impeller speeds, co-current operation, and also with the wet aggregate. Mixing of the agglomerate in the concrete mix resulted in a significant reduction in attrition when compared to mixing aggregates alone. With further validation, the proposed simulation approach can become a valuable tool in the optimization of mixing by allowing the effects of material, machine and process variables to be studied on the mass loss due to attrition.

Review and Further Validation of a Practical Single-Particle Breakage Model

“…Experimental results represent symbols and lines the model fit (Carvalho and Tavares, 2011). cessfully applied to both natural and recycled aggregates (Cunha et al, 2014;Moreno-Juez et al, 2021) and iron ore pellets (Boechat et al, 2018;. Unfortunately, it has only been validated for particles contained in a relatively limited (22-9 mm) range of sizes.…”

“…The full version of the breakage model has been used to predict degradation during handling of materials (Tavares and Carvalho, 2011). It has also been used, coupled to DEM, to model crushing in a vertical shaft impact crusher (Cunha et al, 2014), as well as of degradation of recycled aggregate in a high-shear mixer (Moreno-Juez et al, 2021). The modeling approach has also been used to predict degradation of iron ore pellets during handling using slightly customized mathematical expressions Tavares et al, 2018).…”

Effect of Concrete Micro-Mechanical Properties under the Coupled Corrosion of Sulfate and High Water Head

“…where dε p ij is the plastic strain increment. Referring to the research of Hu et al [22], the generation and development of microcracks are related to the macroscopic plastic strain of concrete. Relationship between mechanical damage variable and equivalent plastic strain:…”

Prediction Model for Compressive Strength of Porous Concrete with Low-Grade Recycled Aggregate

“…As we all know, compared with natural aggregates, there are weaker mechanical properties and greater attrition of recycled aggregates [ 30 ], which means that traditional material models are not necessarily suitable for recycled aggregate products [ 31 ]. At present, studies have shown that the mechanical properties of porous concrete with recycled aggregate (RPOC) are defective, but there are relatively few on strength prediction, and most of them are general mathematical relationships established by numerical fitting.…”