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This study evaluates the progressive deterioration of concrete specimens made with ordinary portland cement containing high volume of fly ash (40%), natural pozzolan (40%) and ground-granulated blast-furnace slag (80%) exposed to sulfate soil. The sulfate performance of these specimens was compared with those made with ordinary portland cement (OPC) and sulfate-resisting portland cement (SRPC).Concrete mixtures were formulated with a w/cm of 0.52 and total cementitious content of 350 kg/m3. Concrete specimens were partially (150 x 300 mm cylinders and 900 x 150 x 150 mm beams) and totally buried in sulfate permeable soil for fifteen years and the mechanical properties were monitored by nondestructive testing (dynamic modulus and ultrasonic pulse velocity) and by destructive testing (compressive strength). The microstructure of concrete was evaluated using XRD analysis and optical microscope observation. The results demonstrate that sulfate resistance of concretes containing a high volume of mineral admixtures is equivalent to concrete made with SRPC cement when they were buried in sulfate soil. Concrete specimens presented a good visual appearance, without cracking at the edges, and they retained the strength and the elastic modulus. Microstructural analysis revels that this behavior can be attributed to the removal of CH, decreasing the gypsum and ettringite formation and the enhancement of paste-aggregate interface of concrete. However, they presented an extent of deterioration aboveground, characterized by the progressive surface scaling due to salt crystallization cycles which is a physical nature damage. This observation confirms the poor performance of concrete containing high volume of mineral admixtures exposed to drying and soaking test.

Researchers at the Building Research Establishment in the UK have recently excavated buried concrete specimens from a field trial site in central England. The specimens had been exposed to sulfate-bearing groundwater for a period of three years and as a consequence, many had undergone the thaumasite form of sulfate attack (TSA). Conventional sulfate attack, leading to the formation of ettringite and/or gypsum did not play a role in the deterioration process. TSA requires a source of carbonate ions, which is usually supplied through the use of a carbonate aggregate but, in this study, it has occurred in portland cement concretes containing an all-in siliceous aggregate. Evidence therefore points to carbonate ions dissolved in the groundwater as being an additional source. A selection of the concretes were examined using X-ray diffraction, chemical analysis and microscopy studies and this paper discusses the results obtained. A variety of binder/aggregate combinations were investigated and a clear distinction could be made after three years between TSA-susceptible and TSA-resistant mixtures. An approximate ‘depth of attack’ measurement has been determined for each of the susceptible mixtures. It was noticed however, that several of the unattacked concretes showed high total sulfate values (in excess of 6% by weight of binder) in their outer surfaces. This was a surprising result, the further investigation of which is reported in this paper.

Deterioration processes on concrete structures are a result of an interaction between the concrete and its environment. In this project the mechanisms of deterioration due to chemical interaction of sulfate containing aqueous solutions are being investigated by a non destructive test method. It uses ultrasonic surface waves to investigate the topmost layer of mortar samples. A pitch and catch arrangement in immersion technique is used to generate the so-called leaky Rayleigh wave. A reduction of the measured sound velocity is proposed to be an indicator of the degradation of the surface region of the mortar sample. First measurements have been performed for reference mortar and for mortar samples exposed to aggressive conditions. A reduction of the velocity of the leaky Rayleigh wave of more than 5% could be detected. This physical alteration was compared and correlated with microscopical findings of the surface layer.

The degradation of concrete exposed to environments containing sulfate ions is a complex phenomenon. The increasing complexity of cementitious materials through the incorporation of supplementary cementing materials coupled with the demand for structures with longer service life, require a better understanding of the process of sulfate attack. This paper discusses the issues involved and presents the approach of the NANOCEM consortium to the research needs.

SP-234 The Canada Centre for Mineral and Energy Technology (CANMET) of Natural Resources, Ottawa, Canada, has played a significant role in Canada for over 40 years in the area of durability of concrete. CANMET, in association with the American Concrete Institute and the Institute for Research in Construction/National Research Council, Ottawa, sponsored the First CANMET/ACI International Conference on Concrete Durability held in Atlanta, Georgia, April 27-May 1, 1987. The refereed proceedings of the Atlanta conference and Montreal conference (the Second CANMET/ACI International Conference on Concrete Durability, held August 4-9, 1991) were published as ACI SP-100 and ACI SP-126, respectively. Unlike the first conference, this second conference was not named after any individual(s), and the future conferences in this series would follow this precedent. In 2006, CANMET, in association with several other organizations in Canada and the U.S., sponsored the Seventh CANMET/ACI International Conference on Durability of Concrete. The conference was held in Montreal, Canada, on May 28-June 3, 2006. More than 75 papers were peer reviewed in accordance with the policies of the American Concrete Institute. The proceedings of the conference, consisting of 50 refereed papers, were published by the American Concrete Institute as ACI SP-234. In addition to the papers that have been published in the refereed proceedings, more than 50 other papers were presented at the conference. A number of these were published as supplementary papers in a special volume. During the conference, special sessions were held on subjects with sulfate attack on concrete and high-performance lightweight concrete. Some of the papers related to these subjects were published in the supplementary volume. Thanks are extended to more than 15 review panel members who met in Budapest, Hungary, in 2002 to review the papers. 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 their finalized manuscripts. The assistance of A. Bilodeau, Chair of the audio-visual review panel, is gratefully acknowledged. Thanks are also extended to P. Gupta and C. Mansfield-Joiner for their help in processing the manuscripts. The contributions of the ACI staff for their help in publishing the proceedings on time is also recognized. As an integral part of the conference, a special symposium was held to honor Professor K. Sakata of Japan for his outstanding contributions in the broad area of concrete design and technology over the past 20 years. The proceedings of the symposium were published as a separate volume.