"PREFACE The Canada Centre for Mineral and Energy Technology (CANMET) of Natural Resources Canada@ Ottawa@ has played a significant role in Canada for over 33 years in the area of durability of concrete. In August 1991@ CANMET in association with the American Concrete Institute@ Institute for Research in Construction/National Research Council@ Ottawa@ sponsored the second CANMET/ACI International Conference on Durability of Concrete. The conference was held August 4-9@ 1991@ in Montreal@ Canada@ and was a followup of the Katherine and Bryant Mather International Conference on Concrete Durability held in Atlanta@ Georgia@ April 27-May 1@ 1987. Unlike the first conference@ this second conference was not named after any individual or individuals@ and the future conferences in this series would follow this precedent. The refereed proceedings of the Atlanta and Montreal conferences were published as ACI SP-100 and ACI SP-126@ respectively. In 1994@ CANMET@ in association with the American Concrete Institute and several other organizations in Canada and France@ Sponsored the Third International Conference on the subject. The conference was held May 22-28@ 1994@ in Nice@ France. The proceedings of the of the conference consisting of 65 refereed papers were published as ACI SP-145. In 1997@ CANMET in association with the American Concrete Institute and several other organizations in Australia sponsored the Fourth International Conference on the subject. The conference was held in Sydney@ Australia. More than 120 papers from 30 countries were received and peer reviewed in accordance with the policies of the American Concrete Institute; 81 were accepted for publication. The accepted papers deal with all aspects of durability of concrete@ including chloride and sulphate attack@ freezing and thawing cycling@ alkali-aggregate reactions@ cathodic protection@ and the role of supplementary cementing materials to enhance durability of concrete. A number of papers dealt with the durability of fiber-reinforced concrete and performance of repaired concrete structures. To all those whose submission could not be included in the symposium volume@ the Institute and the Conference Organizing Committee extend their appreciation for their efforts and interest. In addition to the papers which have been published in the refereed proceedings@ more than 30 other papers were presented at the conference. A number of these were published as ""supplementary papers""@ and the authors of these papers are encouraged to publish these in technical journals of their choice. Thanks are extended to 20 members of the review panel which met in Casablanca@ Morocco in May 1996 to review the papers. Several other ACI and non-ACI members also assisted in the review process@ and their help is gratefully acknowledged Without the dedicated efforts of the reviewers it would not have been possible to have the proceedings ready for distribution at the conference. The cooperation of the authors in accepting reviewers' suggestions@ and in revising their manuscripts accordingly is greatly appreciated. The authors are also to be commended for their prompt return of the revised manuscripts. The help and assistance of A. Bilodeau (Chairman)@ B. Fournier@ and R. Chevrier (members) of the slide review panel are gratefully acknowledged. Thanks are also extended to Harry S. Wilson@ Maria Venturino@ and Gordon D. Brearly for their help in the processing of manuscripts@ both for the ACI proceedings and the supplementary volume. The contribution of Helayne Beavers@ Managing Editor@ ACI@ and her staff to publish the proceedings on time is recognized."