M. B Mgangira, S XUNGU and J GIANI AN INVESTIGATION OF AGGREGATE DEGRADATION IN A HIGH STRESS FIELD M. B Mgangira, S XUNGU and J GIANI Southern Africa Transport Conference 2018 CSIR International Conference Centre 10 July 2018

DEMONSTRATION RESULTS PRESENTATION INTRODUCTION CONTEXT CONCEPT DEMONSTRATION RESULTS CONCLUDING REMARKS Thank you

Thank you INTRODUCTION Background Ultimate goal Research initiatives on aggregate characterisation Ultimate goal Quantify aggregate abrasion resistance and therefore durability solely dominated by particle-to-particle interaction mechanism Thank you

Optimisation in the use of aggregates CONTEXT Optimisation in the use of aggregates Impact on long-term stability of pavements Introduction

CONTEXT Test methods to evaluate the durability or quality of aggregates, resistance to abrasion, involving some form of particle to particle interaction under, for example: L.A abrasion (LAA) Aggregate Crushing Value (ACV), Aggregate Impact Value (AIV), Durability Mill Index (DMI) Aggregate Durability Index (ADI) Micro-Deval (MDE). Thank you

CONTEXT A charge of steel balls is used to induce aggregate wear The interior of the drum is mounted with a shelf which picks up and drops the aggregates and the steel balls as the drum rotates Thank you

CONTEXT To provide coherent body of knowledge on aggregate degradation solely dominated by particle-to-particle interaction mechanism Quantify the influence of stress levels on rate of aggregate degradation Establish an experimental system Thank you

Thank you CONTEXT Concept An experimental system, to assist in the evaluation of aggregate quality, using a customised rolling model drum, in which the aggregate assemblage is subjected to different stress levels Thank you

Thank you CONTEXT Concept Numerical simulations are restricted to spherical particles, mainly because of the high computational costs Solution available in physical modelling: Increase the self weight of the aggregates Thank you

Use of Geotechnical centrifuge to increase self weight of aggregates CONCEPT Use of Geotechnical centrifuge to increase self weight of aggregates Introduction

Thank you CONCEPT Concept F = M.a The magnitude of the induced, normal contact and tangential forces, between the particles are a result of the g-level during the testing Thank you Ng

Thank you CONCEPT Granular flow This will be possible if the behaviour of the mass of the particles in the model drum is further dominated by cascading and cataracting behaviour Thank you Cascading Cataracting

Thank you CONCEPTS Granular flow Cascading and Cataracting behaviour Centrifuging

CONCEPT Concept Thank you

Longitudinal Cracking TESTING SYSTEM Testing 10g 20g 100rev/min 5 minutes Longitudinal Cracking

DEMONSTRATION RESULTS Sieve analysis Particle shape analysis Particle volume (V) Particle surface area (SA) Longitudinal Cracking

DEMONSTRATION RESULTS Longitudinal Cracking

DEMONSTRATION RESULTS Longitudinal Cracking

DEMONSTRATION RESULTS Longitudinal Cracking

RESULTS

CONCLUDING REMARKS Experimental platform has demonstrated the possibility of quantifying aggregate degradation solely due to particle-to-particle interaction mechanism

CONCLUDING REMARKS Future work: Flow of particles involves complex particle–particle and particle–wall interactions and, depending on the particle physical characteristics and drum operating conditions, can display different flow regimes

CONCLUDING REMARKS Future work: Effect of the pay-load (filling ratio) in the model drum during the testing. The testing of mixtures of various particle sizes influence of wet and dry test conditions Different types of rock samples.

Thank you