The present paper describes a research effort to quantify the internal stresses that develop in a coating system during curing and exposure. Several common overcoating systems (typically used for bridge structures) were investigated that included a poly silicone alkyd, an acrylic, a moisture-cured urethane, and an epoxy. The work reported in this paper constitutes part of an NCHRP-IDEA project1 the main objective of which was to design and demonstrate an innovative field device to assess the risk of overcoating failures. Work related to the design and development of the adhesion tester is the subject of another paper to be published later.

Two methods of measuring cure-induced stresses in coatings were examined: (a) Deflection measurements using a capacitive transducer and (b) Direct measurements using a miniature surface mounted fiber optic (FO) strain gage. The latter technique was chosen for conducting the experiments because of accuracy and ease of use. The results indicated that the ambient relative humidity (RH) has a significant effect on the type and magnitude of stresses developed by different types of coatings during curing and aging. The stresses measured during this program were found to be as high as 9 to 11 MPa (1305 to 1595 psi), similar to cure stresses reported in the literature.

Subject
Coatings, Curing, Overcoatings, Internal stress, Measurement, Stress, Fibers, Coating stress, Epoxies, Urethane, Alkyds, Coating systems, Acrylics
© 2003 Association for Materials Protection and Performance (AMPP). All rights reserved. This work is protected by both domestic and international copyright laws. 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).
2003
Association for Materials Protection and Performance (AMPP)
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