Performance of C&DW materials for road applications validated by field monitoring

(1)

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

201

Performance of C&DW materials for road applications validated by field monitoring

J. Neves1, A. C. Freire2, A. J. Roque2, I. M. Martins2 and M. L. Antunes2

1

CERIS/CESUR, Instituto Superior Técnico, Universidade de Lisboa, Portugal; E-mail: jose.manuel.neves@tecnico.ulisboa.pt

2

Laboratório Nacional de Engenharia Civil, Lisboa, Portugal;

E-mail: acfreire@lnec.pt; aroque@lnec.pt; imartins@lnec.pt; mlantunes@lnec.pt

Abstract

SUPREMA – Sustainable Application of Construction and Demolition Recycled Materials in Road Infrastructures was a research project developed by the Laboratório Nacional de Engenharia Civil (LNEC), in cooperation with the University of Lisbon (IST). The use of recycled materials has major environmental and economic benefits. Its recycling contributes for a more sustainable construction and rehabilitation of road pavements. The main goals of this project were to achieve a deeper knowledge on recycled materials and correspondent technologies and to increase the confidence of road agencies and construction companies for its application in road pavements.

The objective of the paper is to analyse the mechanical performance of recycled aggregates, from construction and demolition waste (C&DW), used in unbound granular layers and evaluated on experimental sections of asphalt pavements. Four sections were instrumented with strain gauges and load cells. The recycled aggregates used in these sections were: crushed concrete, crushed mixed concrete and crushed and milled reclaimed asphalt pavement (RAP). A crushed natural limestone aggregate was used in one section as a reference material. The sections were submitted to in situ load tests performed by the Falling Weight Deflectometer (FWD). In addition, an extensive program of laboratory tests was also performed related to geometrical, physical, mechanical, chemical and environmental characteristics.

This paper presents the mechanical behaviour of aggregate layers obtained from the back-analysis of FWD tests results and from the instrumentation measurements. In general, it was concluded that stiffness of unbound granular layers with recycled aggregates could be considered equivalent to the stiffness of layers constructed by natural aggregates. Results of resilient modulus obtained for the studied recycled aggregates could be useful for pavement design purposes.

Keywords: road, pavement, C&DW, recycling, performance. Introduction

Experimental investigation involving laboratory (e.g. large-scale triaxial tests) and in situ tests (e.g. plate load tests, falling weight deflectometer tests) are essential in order to validate an adequate mechanical behaviour of the recycled materials (Aurstad et al. 2009). Considering the enormous variety of origins and conditions of the application, it is advisable a thorough research based on real sections, monitored along the life cycle of the recycled materials.

LNEC in cooperation with IST, Portugal, carried out the research project SUPREMA – Sustainable Application of Construction and Demolition Recycled Materials (C&DRM) in Road Infrastructures. The project has included an extensive experimental programme

(2)

202

comprising laboratory and in situ tests performed on natural and selected recycled aggregates (Freire et al. 2011). Based on the experimental sections monitoring, this paper presents the mechanical performance of unbound granular layers composed by recycled aggregates from C&DW, in terms of resilient modulus. These results were obtained from back-analysis of FWD tests, performed after the pavements construction, and the validation of instrumentation measurements.

Methodology

Four different aggregates were selected to the construction of the experimental sections in order to evaluate the mechanical performance: crushed mixed concrete (CMC), composed by a mixture of concrete and clay masonry units; crushed reclaimed asphalt pavement (CRAP); milled reclaimed asphalt pavement (MRAP); and natural aggregate from crushed limestone rock (ABGE), as a reference material. In the case of MRAP, a mixture of RAP (30%) and ABGE (70%) was used. Table 1 presents the proportion of the constituents in the case of the recycled aggregates obtained in accordance to the procedure of the EN 933-11. Other laboratory tests were performed on the materials, aiming at the geometric, physical, mechanical, and chemical and environmental characterization (Freire et al. 2011, Roque et al. 2016).

The pavements of the experimental sections consisted of unbound granular layers (UGM), composed by recycled and natural aggregates, and wearing course, composed by asphalt concrete (AC). A total of four sections were constructed with the geometry presented in the Figure 1a. Each section was divided in two sub-sections where strain gauges and load cells were placed, as represented in Figure 1b. The structural behaviour of the pavements was evaluated by FWD tests, associated with strain gauges and load cells measurements. Temperature was also controlled by thermocouples. Freire et al. (2013) present more details on the construction and in situ monitoring of the experimental sections.

Results and Discussion

The Figure 2 presents the resilient modulus from back-analysis of FWD tests carried out after sections construction, validated by strain gauge measurements. The results confirmed that recycled aggregates showed a different behaviour from natural aggregate. However and besides a certain scattering, all recycled aggregates demonstrated an acceptable performance, even in the case of CRAP where higher deformability was observed and so further research is recommended.

Table 1. Proportion of the constituents in the recycled aggregates.

Constituents CMC CRAP MRAP

Rc (%) Concrete, concrete products, mortar,

concrete masonry units 67 19 0.1

Ru (%) Unbound aggregate, natural stone,

hydraulically bound aggregate 17 10 17

Ra (%)

Clay masonry units (i.e. bricks and tiles), calcium silicate masonry units, aerated non-floating concrete

1.9 69 83

Rb (%) Bituminous materials 13 1.8 0.0

Rs (%) Soils 0.0 0.0 0.0

Rg (%) Glass 0.3 0.0 0.0

X (%) Other: cohesive (i.e. clay and soil),

(3)

203 nonferrous), non-floating wood, plastic and rubber, gypsum plaster

FL (cm3/g) Floating particles 0.6 0.0 0.0

(a) Sections

(b) Sub-sections

Figure 1. Geometry of the experimental sections.

Figure 2. Resilient modulus.

Conclusion

This paper describes a research study related to the mechanical performance of recycled aggregates, applied in unbound granular layers. This evaluation was based on FWD tests and instrumentation measurements performed in experimental sections. Results confirmed that in general recycled materials form C&DW, have demonstrated an acceptable behaviour in terms of resilient modulus. These findings encourage with confidence the reuse of recycled

aggregates, provided best practices of construction and quality control are always implemented. 100 150 200 250 300 350 400

ABGE CMC MRAP CRAP

R e si li e n t m o d u lu s (M P a )

(4)

204

Acknowledgements

The authors acknowledge FCT (PTDC/ECM/100931/2008), by the financial support, and AMBIGROUP for providing the conditions to the implementation of the experimental sections.

References

- Aurstad, J., Dahlhaug, J.E., Berntsen, G. (2009). Unbound crushed concrete in high volume roads — evaluation of field behavior and structural performance. Proceedings of the 8th International Conference on the Bearing Capacity of Roads, Railways, and Airfields, Illinois, USA.

- Freire, A., Neves, J., Roque, A.J., Martins, I.M., Antunes, M.L., Faria, G. (2011). Sustainable application of construction and demolition recycled materials (C&DRM) in road infrastructures. Proceedings of the 1st International Conference WASTES, Guimarães, Portugal.

- Freire, A., Neves, J., Roque, A.J., Martins, I.M., Antunes, M.L., Faria, G. (2013). Use of construction and demolition recycled materials (C&DRM) in road pavements validated on experimental test sections. Proceedings of the 2nd International Conference WASTES, Guimarães, Portugal.

- Roque, A.J., Martins, I.M., Freire, A.C, Neves, J., Antunes, M.L. (2016). Assessment of environmental hazardous of construction and demolition recycled materials (C&DRM) from laboratory and field leaching tests application in road pavement layers. Procedia Engineering, Volume 143, 204-211.