Effect of Chemico-Mechanical Treatment of Recycled Concrete Aggregate on Concrete Performance: A Review

Abstract

The rapid growth of construction and demolition waste, together with the steady depletion of natural aggregate sources, has made recycled concrete aggregate (RCA) an attractive option for new concrete. Its use is held back, however, by the layer of old mortar that clings to the aggregate surface, which raises water absorption and porosity and makes properties vary from one source to another. This paper reviews peer-reviewed work on concrete made with non-treated RCA and with RCA treated by chemical, mechanical, and other methods. Attention is given to how the origin of the aggregate, the type and severity of treatment, and the replacement level influence workability, density, water absorption, strength and durability. The studies reviewed agree that a suitable treatment improves aggregate quality and brings recycled aggregate concrete closer to the behaviour of natural aggregate concrete, but the extent of the gain depends on the quality of the parent concrete, the treatment conditions and the mix design. Acid soaking followed by abrasion, accelerated carbonation and nano-silica modification emerge as the most frequently studied routes. Gaps remain in standardised treatment protocols, long-term durability data, life-cycle and cost assessment, and treatment strategies matched to specific aggregate sources. The review also outlines the experimental programme planned by the authors, in which concrete with natural, non-treated and chemico-mechanically treated aggregate will be compared.

Introduction

Recycled concrete aggregate (RCA) offers a sustainable alternative to natural aggregates by reusing construction and demolition waste, reducing landfill disposal and conserving natural resources. However, RCA contains adhered old cement mortar, which is porous, micro-cracked and highly absorbent. These characteristics reduce the workability, strength and durability of recycled aggregate concrete (RAC). The presence of two interfacial transition zones (ITZs) also weakens the bond between the aggregate and the new cement paste.

RCA can be used without treatment after basic crushing, sieving, washing and drying, although its performance generally declines as the replacement percentage and water-cement ratio increase. Various pretreatment methods have been developed to improve its properties, including mechanical abrasion, acid treatment, accelerated carbonation and nano-silica modification. Among these, chemico-mechanical treatment, which combines chemical treatment with mechanical abrasion, is a promising approach because the chemical process loosens the adhered mortar while abrasion removes weakened material.

Recent studies indicate that treated RCA generally improves concrete density, workability, strength and durability compared with untreated RCA. For example, one study reported a 78% reduction in aggregate water absorption following hydrochloric acid immersion. Carbonation and combined carbonation–nano-silica treatments have also demonstrated promising results. Nevertheless, the effectiveness of these methods depends on the aggregate's source, parent concrete quality, treatment conditions, cost and environmental impact. Treated RCA concrete may still perform below conventional concrete made with natural aggregates.

The review examines recent literature on the characteristics and sources of RCA, the performance of untreated RAC, and the effectiveness of different aggregate treatment techniques. It also highlights the need for standardised treatment procedures, reliable quality control, long-term durability assessments and life-cycle cost analysis.

The proposed experimental programme will compare three concrete mixtures: natural aggregate concrete, concrete containing untreated RCA, and concrete containing RCA treated with 0.5 M hydrochloric acid for 48 hours followed by Los Angeles abrasion. The mixtures will be evaluated through slump, compressive strength and water absorption tests. The study aims to determine whether chemico-mechanical treatment can improve RCA quality and enhance the performance of recycled aggregate concrete.

Conclusion

Recycled concrete aggregate can replace natural aggregate in concrete, but the old mortar attached to it increases absorption and porosity and brings weak interfaces into the concrete. The work reviewed here shows that non-treated RCA is workable at moderate replacement levels yet limited in durability, and that mechanical, chemical, carbonation, nano-modification and combined treatments can improve both the aggregate and the concrete made from it. The improvement is not uniform. It depends on the source and quality of the aggregate, on how intensely it is treated and on the mix design, and treated RCA concrete in the studies discussed still did not always match natural aggregate concrete. From the study it is found evidential that soaking RCA in 0.5 M HCl for 48 hours, washing and drying it, and then abrading it in a Los Angeles machine with abrasion charges for specific rotation cycles, it will remove the adhered mortar considerably and we get cleaner RCA. Concrete made with this aggregate will be compared with natural aggregate concrete and non-treated RCA concrete using slump, compressive strength and water absorption tests, together with aggregate characterisation. The results will show how effective the treatment is and whether treated RCA is suitable for concrete production.

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Copyright

Copyright © 2026 Prof. Sagar R. Raut, Sukhada R. Lokhande, Nikita A. Hage, Manthan G. Darne. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.