Proposed Method for Determining the Residual Mortar Content of Recycled Concrete Aggregates

TLDR

Recycling demolition concrete into recycled concrete aggregates offers economic and environmental benefits, yet its limited use in structural concrete stems from uncertainty about material properties, particularly the residual mortar attached to aggregates. This study aims to establish an accurate, standardized procedure for determining residual mortar content in RCAs, which is currently lacking. The proposed method combines freeze‑and‑thaw mechanical stresses with sodium sulfate chemical degradation to disintegrate residual mortar and sever its bond to natural aggregates, and its effectiveness is validated through comprehensive image analysis. Results show that the approach effectively removes attached residual mortar and enables precise measurement of residual mortar content.

Abstract

Abstract Recycling concrete from demolition of existing structures and using it as recycled concrete aggregates (RCAs) in structural-grade concrete have significant economic and environmental benefits. Currently, only a small portion of the concrete waste is reused in building construction, while most of it is used as either pavement base course or sent to landfills for disposal. The lack of confidence in the material properties of the concrete produced with RCAs is generally the main reason for its under-utilization in structural concrete. It has been demonstrated in the literature that the amount of residual mortar attached to the original (or “virgin”) aggregate particles is one of the factors affecting the material properties of RCAs. Therefore, before using RCAs in new concrete, it is crucial that the residual mortar content (RMC) is determined accurately; however, currently there is no standard procedure to determine this quantity. In this paper, an experimental method is proposed to determine the RMC of RCAs. The method comprises a combination of mechanical and chemical stresses that disintegrate the residual mortar and destroy the bond between the mortar and the natural aggregates. The mechanical stresses are created through subjecting RCA to freeze-and-thaw action, while the chemical degradation is achieved through exposure of the RCA to a sodium sulphate solution. The results of the proposed test procedure are validated by means of comprehensive image analysis. With the proposed approach, the attached residual mortar can be adequately removed, and the residual mortar content can be determined.