Performance of Bitumen stabilised materials using Recycled concrete aggregate:

Nokuthula Mazibuko

Stellenbosch University

Outline

1. Introduction and Background

2. Study Method

3. Results and Discussion

4. Conclusions

Introduction and Background

• Sustainability = reuse of materials, reduction of waste, carbon emissions and energy usage

• In road construction = Use of CDW reduce waste and BSMs enhance existing materials for reuse.

(Barnes, 2016) (Jenkins, 2016)

Introduction and Background: RCA viable alternative

(Barisanga, 2014) (SAPEM, 2014)

Introduction and Background: RCA viable alternative

(Rudman & Jenkins, 2015)

Introduction and Background: Benefits of BSMs

(Bredenhann and Jenkins, 2015) (Jenkins and Collins, 2011)

Project study: RCA Preliminary aggregate properties

Aggregate PropertySpecifications 

UsedGrading modulus (GM) SAPEM chapter 3

Plasticity index (PI) SANS 3001‐GR10

Maximum dry density (MDD)

SANS 3001‐GR30

Optimum moisture content (OMC)

SANS 3001‐GR30

4 day soaked CBR SANS 3001‐GR40

pH SANS 3001‐GR57

Hygroscopic moisture content

SANS 3001‐GR20

Project study: BSM Production guided by TG2 (2009)

Mixing 3‐day curingVibratory compaction

Project study: BSM Testing ITS, Monotonic and Dynamic triaxialtesting

Results and Discussion: RCA Physical properties

Aggregate Property Result BSM Classification

Grading modulus (GM) 2.56 BSM1

Plasticity index (PI) Non plastic BSM1

Maximum dry density (MDD) 1903 kg/m3 ‐

Optimum moisture content (OMC) 13% ‐

4 day soaked CBR 50% BSM2

pH 12.32 ‐

Hygroscopic moisture content 2.3 – 2.96% ‐

Results and Discussion: ITS Optimum binder

Results and Discussion: Active filler wet and dry ITS

Results and Discussion: Shear Parameters

Shear parameters/Binder Foamed Bitumen

BSM Class

Bitumen emulsion

BSM Class

Cohesion (kPa) 177 kPa BSM2 174 kPa BSM2

Internal angle of friction 50.4o BSM1 47.9o BSM1

Retained Cohesion 90% BSM1 88.2% BSM1

Results and Discussion: Shear Parameters Comparision

BSM 2 Cohesion (100kPa to 250kPa)

BSM 1 internal angle of friction 40o

Results and Discussion: Resilient Modulus Mr vs Bulk Stress

Results and Discussion: Mr range

Foamed RCA (376 to 660MPa)Bitumen Emulsion RCA (360 to 575 MPa)

(SAPEM, 2014)

Conclusions and Practical considerations

• Based on the preliminary properties of RCA based on the TG2, RCA is a suitable aggregate for BSM.

• The latent cement and mortar of RCA provides the dispersion of the binder in the mix therefore, no active filler was required.

• Shear parameters indicate a BSM1 can be produced with 2.2% bitumen content.

• Slight difference in response for foamed and bitumen emulsion due to coating of aggregates.

• Pre‐soaking of the aggregate is important to reduce the absorption of the binder by the mortar during mixing.

Barisanga, F. 2014. Material Characterisation and Response Modelling of Recycled Concrete

and Masonry in Pavements. Stellenbosch University.

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Bredenhann, S.J. & Jenkins, K.J. 2015. Bitumen Stabilised Materials : Real Performance

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(BSMs). In 10th Conference on Asphalt Pavements for Southern Africa. 1–14.

Jenkins, K. 2016. Pavement Materials Behaviour What is a BSM ? Stellenbosch.

Rudman, C.E. & Jenkins, K.. 2015. Self-Cementing Mechanisms of Recycled Concrete and

Masonry Aggregate. In Durban Conference on Asphalt Pavements for Southern Africa.

SAPEM, C. 2014. South Afican Pavement Engineering Manaul - Chapter 10.