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Characterization of recycled concrete aggregates

Abstract : Recycled (concrete) Aggregates (RA) are mainly composed of an intimate mix between Natural Aggregates (NA) and adherent cement paste (ACP). Properties of RA strongly depend on the properties of each of these two phases and on their proportions. ACP possesses in particular a much larger porosity than NA which changes significantly RA characteristics in comparison to those of NA. RA exhibit larger water absorption and lower particle density than NA. Moreover, their chemical composition is also affected by that of ACP and NA which might play a role in some pathology like alkali silica reaction. Main physical and chemical characteristics of RA have been measured in the RECYBÉTON project on coarse and fine recycled aggregates using experimental methods devoted to NA. Results show that traditional characterization procedures used for NA can be applied very satisfactorily to coarse RA. On the contrary, the measurement of properties of fines RA is more difficult. Indeed, crushing of old concrete concentrates ACP in the finer granular fraction, resulting in important heterogeneities in the composition of recycled sand comparatively to coarse RA. Fine RA contain more ACP than coarse RA leading to larger absorption and lower particle density for the smaller fraction. In order to improve the characterization methods of fine RA, chemical and thermal methods have been developed in order to assess the ACP content of recycled sand. From theoretical relations between ACP content and physical properties of RA, important properties like water absorption coefficient can be measured more accurately. Moreover, because of their characteristics, it is difficult to replace completely fine NA by fine RA in concrete. One solution is to mix fine RA with fine NA. Thus, methods have been developed to precisely control the proportion of the two constituents in mixtures containing a low proportion of RA (less than 10%). Mechanical properties of RA like resistance to shocks and abrasion and application of models allowing the prediction of compressive strengths of mortars and concretes made with RA have also been investigated. The results show that RA exhibit a larger “ceiling effect” than traditional NA, however, they lead to good bond properties between RA and new cement paste.
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https://hal.mines-ales.fr/hal-02442668
Contributor : Administrateur Imt - Mines Alès <>
Submitted on : Thursday, January 16, 2020 - 4:04:09 PM
Last modification on : Sunday, February 16, 2020 - 1:04:39 AM

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S. Remond, J.M. Mechling, R. Trauchessec, Eric Garcia-Diaz, R. Lavaud, et al.. Characterization of recycled concrete aggregates. Concrete Recycling : Research and Practice, CRC Press, 33-60 (Chap. 3), 2019, 9781351052825. ⟨10.1201/9781351052825-5⟩. ⟨hal-02442668⟩

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