Title page for ETD etd-10122011-170158


Document Type Doctoral Thesis
Author Denneman, Erik
Email edenneman@csir.co.za
URN etd-10122011-170158
Document Title Fracture in high performance fibre reinforced concrete pavement materials
Degree PhD(Eng)
Department Civil Engineering
Supervisor
Advisor Name Title
Prof AT Visser Co-Supervisor
Prof E P Kearsley Supervisor
Keywords
  • high performance material
  • post crack stress capacity
  • fibre reinforced concrete
Date 2011-09-06
Availability unrestricted
Abstract
An innovative pavement system known as Ultra Thin Continuously Reinforced Concrete Pavement (UTCRCP) was recently developed in South Africa. The technology is currently being implemented on some major routes in the country. The system consists of a high performance fibre reinforced concrete pavement slab with a nominal thickness of approximately 50 mm. The material has a significant post crack stress capacity compared to plain concrete. Current design methods for UTCRCP are based on conventional linear elastic concrete pavement design methodology, which does not take into account post crack behaviour. Questions can be raised with regards to the suitability of conventional approaches for the design of this high performance material.

The hypothesis of the study is that the accuracy of design models for UTCRCP can benefit from the adoption of fracture mechanics concepts.

The experimental framework for this study includes fracture experiments under both monotonic and cyclic loading, on specimens of different sizes and geometries and produced from several mix designs. The aim is to quantify size effect in the high performance fibre reinforced concrete material, to determine fracture mechanics material parameters from monotonic tests, and to investigate the fatigue behaviour of the material.

As part of the study a method is developed to obtain the full work of fracture from three point bending tests by means of extrapolation of the load-displacement tail. This allows the specific fracture energy (G) of the material to be determined. An adjusted tensile splitting test method is developed to determine the tensile strength (&$964;) of the material.

The values of G and τ are used in the definition of a fracture mechanics based cohesive softening function. The final shape of the softening function combines a crack tip singularity with an exponential tail. The cohesive crack model is implemented in finite element methods to numerically simulate the fracture behaviour observed in the experiments. The numerical simulation provides reliable results for the different mixes, specimen sizes and geometries and predicts the size effect to occur.

Fracture mechanics based models for the prediction of the fatigue performance of the material are proposed. The predictive performance of the models is compared against a model representing the conventional design approach.

It is concluded that the findings of the study support the thesis that design methods for UTCRCP can benefit from the adoption of fracture mechanics concepts. This conclusion is mainly based on the following findings from the study:

  • The high performance fibre reinforced concrete material was found to be subject to significant size effect. As a consequence the MOR parameter will not yield reliable predictions of the flexural capacity of full size pavement structures,
  • In contrast to the MOR parameter, the fracture mechanics damage models developed as part of this study do provide reliable predictions of the flexural behaviour of the material,
  • The fatigue model developed based on fracture mechanics concepts, though not necessarily more precise, is more accurate.

2011 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria.

Please cite as follows:

Denneman, E 2011, Fracture in high performance fibre reinforced concrete pavement materials, PhD thesis, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-10122011-170158 / >

D11/9/63/ag

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