Use of recycled aggregates of concrete in total replacement of natural materials

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International HISER Conference on Advances in Recycling and Management of Construction and Demolition Waste

21-23 June 2017, Delft University of Technology, Delft, The Netherlands

188

Use of recycled aggregates of concrete in total replacement of natural materials: Influence on the determination of concrete formulation

parameters

Sandrine Braymand1, Sébastien Roux2, Kunwufine Deodonne3, Françoise Feugeas4, Christophe Fond5

1

ICube, Strasbourg Univ., CNRS, 72 Route du Rhin, Illkirch, France, Phone (+33) 368 85 85 08, E-Mail: s.braymand@unistra.fr, 2

IJL, Lorraine Univ., CNRS, Rue du Doyen Urion, Villers lès Nancy, France, E-Mail: sebastien.roux@univ-lorraine.fr

3

UNEVOC, Ministry of Secondary Education, Yaoundé, Cameroun 4

ICube, INSA Strasbourg, CNRS, 24 bd de la Victoire, Strasbourg, France, E-Mail: francoise.feugeas@insa-strasbourg.fr

5

ICube, Strasbourg Univ., CNRS, 72 Route du Rhin, Illkirch, France, E-Mail: christophe.fond@unistra.fr,

Abstract

The study presented here aims to develop the use of recycled aggregate issued of concrete in total replacement of natural materials (sand and gravel). In regard to natural aggregates, recycled concrete aggregates (RCA) contain mortar that influences theirs properties and those of concrete in which they are used (RCA). The objective of this work is to analyze the characteristics of concrete with 100 % of RCA. In this way, following an experimental analysis of physical, mechanical and mineralogical properties of recycled aggregates, these characteristics lead to suggesting adaptations on formulation parameters of concrete and mortar. Moreover, it was shown that the use of superplasticizers is necessary to reach satisfactory properties of concrete.

Keywords: recycled aggregate concrete, absorption, morphology, design concrete, admixture

Introduction

It becomes essential to limit environmental impact of building materials and to consider the life cycle of materials used. Recycling of materials from demolition has the dual objective of preserving natural resources and limiting the number of storage sites. The presence of primary mortar (Figure 1) in recycled concrete aggregate (RCA) is responsible for the different behavior of these aggregates and natural aggregates [BRA 15]. In order to understanding influences of these differences on the composition of concrete in which RCA could be introduced, a complete characterization of these recycled materials is necessary. Indeed, many properties at fresh and hardened state of concrete are modified by this mortar presence. The use of admixture is proposed in this study in order to balance these effects on concrete made with 100% of RCA. [MAR 11, SRI 87, DEJ 11, EVA 14, DUC 12, TAM 08, HAN 92, RAM 09].

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189 Experimental Methods and Results

Properties of recycled concrete aggregates collected from several sources (GR1 to GR6) are studied to identify and analyze their specificities; results are compared to natural ones (GNC, GNR). Due to mortar content included in RCA, they present higher water absorption (Figure 2), lower mechanical strength, a spreader granular distribution (Figure 3) and a different shape compared to natural aggregates. Finally, the absorption and morphology of recycled aggregates depend on the granular fraction. Correlation between morphological and mechanical properties with water absorption have been demonstrated (Figure 4).

Figure 2. Water absorption (WA24) of RCA compared to Natural aggregate NA

GR1-GR5: Recycled Concrete Aggregate, GNC: Natural Crushed Aggregate, GNR: Natural Rolled Aggregate

Figure 3. Granular Distribution of RCA compared to NA

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190

In order to balance the loss of workability and mechanical strength of concrete containing recycled aggregate, several superplasticizers and formulations are tested. Some polycarboxylates are identified as appropriate superplasticizers for RAC [BRA 15].

Thus, admixtures enhance the immediate workability (rheology measurement at 5 minutes) of fresh concrete made of natural or recycled aggregate but retention of this property over time is not obtained for concrete with RCA (Figure 5 and Figure 6). Moreover, some superplasticizers admixtures allow enhancing mechanical strength, due to a better manufacturing. These concrete (RAC and NAC) are composed with constant volumes proportions of constituents. In particular a constant cement content and an equal W/C ratio (Efficient water) are used.

Conclusion

Analysis of properties of RCA allowed the optimization of concrete formulation methods with use of superplasticizers. Moreover, the complexity of absorption and desorption kinetics lead to a discussion around effective water definition. The difference between the morphology of recycled aggregates and natural ones involves a correction of the granular skeleton, particularly when determining of the specific surface area of aggregates. Finally, their weakness during mechanical test modifies the granular skeleton and need to be taken into consideration.

Figure 5. Initial and final slump of Recycled Aggregate Concrete (BGR) and Natural Aggregate

Concrete (BGNC) Acknowledgement

The authors wish to express their gratitude to the European community for their contribution to this research project, in part through the program Interreg IV (Cross Boarder Areas of the Rhin Program) entitled “To increase the knowledge transfer in sustainable civil engineering”. They also thank CHRYSO company for its financial contribution and the availability of the admixtures.

References

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[DEJ 11] DE JUAN M.S., GUTIÉRREZ P.A., Study on the influence of attached mortar content on the properties of recycled concrete aggregate, Constr. Build. Mater., vol 23,n°2, 2011, p. 872-877.

[SRI 87] SRI RAVINDRARAJAH R., TAM C.T., Recycling concrete as fine aggregate in concrete, Int. J. Cem. Compos. Lightweight Concr, vol.9, n°4, 1987, p. 235-241.

[EVA 14] EVANGELISTA L., DE BRITO J., Concrete with fine recycled aggregates: a review, Eur. J. Environ. Civ. Eng, vol. 8, n°2, 2014, p. 129-172.

[DUC 12] DUC-TUNG D., (Multi-) recyclage du béton hydraulique, Thèse de Doctorat, Ecole centrale de Nantes, 2012.

[TAM 08] TAM V.W., WANG K., TAM C.M., Assessing relationships among properties of demolished concrete, recycled aggregate and recycled aggregate concrete using regression analysis, J. Hazard. Mater, vol. 152, n°2, 2008, p. 703–714.

[HAN 92] HANSEN T.C., Recycling of Demolished Concrete and Masonry, Editions Taylor & Francis, 1992.

[RAM 09] RAMAMURTHY K., PADMINI A.K., MATHEWS M.S., Influence of parent concrete on the properties of recycled aggregate concrete, Constr. Build. Mater. Vol. 23, n°2, p. 829–836.

[BRA 14] BRAYMAND S., ROUX S., DEODONNE K., MIHALCEA C.., FEUGEAS F., FOND C.: Les granulats recyclés de bétons: un matériau à fort potentiel de valorisation dans les bétons, Acte du congrès Matériaux 2014, 24-28 nov. 2014, Montpellier, France, (2014). [BRA 15] BRAYMAND S., FRANÇOIS P., FEUGEAS F., FOND C., Rheological properties of recycled aggregate concrete using superplasticizers, J. Civil E. and Arch., vol. 9, 2015, p. 591-597.