A direct current (DC) streetcar project with rails embedded in the street is under development south of Lake Union in Seattle, Washington. DC trains can produce stray currents which can accelerate the corrosion of buried utilities. As a first line of defense this project employs an insulated formed rubber rail boot encased in the concrete track slab. A rubber boot encasing the rails provides a high resistance to earth and is an effective barrier providing a reduction of stray current discharges. Traditionally, Seattle Public Utilities (SPU) would have replaced any watermains within 10 feet parallel to the rail and crossings. The pipe was evaluated and found to have at least 100 years of useful life left if the pipe environment were to remain the same. If the pipe were replaced, SPU would coat the replacement pipe as a secondary barrier against stray current. If the pipe was to remain in the ground, a secondary protection measure would need to be evaluated. In an effort to augment traditional stray current control methods and significantly increase rail to earth resistance values at boot defects, it was decided to investigate the benefits of increased resistivity of the concrete track slab. Multiple track slab concrete mixes were tested to evaluate the impacts on resistivity of water reducers, a waterproofing agent and mineral admixtures including slag, fly ash, and condensed silica. To provide a comparative baseline, samples from routine City of Seattle concretes were also tested. Surface resistivity measurements of the several concretes were obtained over time using the State of Florida Test Method FM 5-578. Resistivity was also obtained using the Wenner four-pin test method. In addition, correlative testing was conducted using ASTM C 1212 Standard Test Method for the Electrical Indication of Concrete’s Ability to Resist Chloride Penetration – what is also known as the “Coulomb Test”. After initial screening, final mix designs were again evaluated for electrical resistance and also for resistance to drying and autogenous shrinkage. This paper discusses the several test methods employed in addition to the effects of trial mix composition.

Subject
Silica fumes, Footwear, Test methods, Water, Piping, Rails, Pores, Electrical resistivity, Cement, Stray current, Construction, Immersion, Concrete
Keywords:
concrete, resistivity, stray current
© 2007 Association for Materials Protection and Performance (AMPP). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of AMPP. Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
2007
Association for Materials Protection and Performance (AMPP)
You do not currently have access to this content.