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Concrete cylinders, 255 mm in diameter, were made with high- and low-alkali cements, a highly alkali–silica-reactive coarse aggregate, and subjected to various conditions at 38 � C: (1) immersion in 3% NaCl solution; (2) immersion in 6% NaCl solution; (3) humid air at 100% RH, and (4) 14-day cycles including 12 days in humid air, 2 days of drying, and 3 h in 6% NaCl solution. After 1 year, a number of cylinders were drilled to obtain dry powder samples from different depths, which were analyzed for total and soluble chloride and for soluble sodium and potassium. Concrete cores were also taken in a number of parapets and abutments, either exposed to deicing salts or not, on which chemical analyses were also performed on slices taken at different depths from the exposed surface. The results obtained suggest that making concrete with a low-alkali content is an effective way to prevent expansion due to alkali–silica reaction even for concretes exposed to

This study follows another experimental study where different types of sealers were applied on plain and air-entrained large concrete cylinders made with high-alkali contents and highly alkali–silica reactive limestone aggregates. The main objective was to determine the effectiveness of these sealers in counteracting concrete expansion and surface deterioration due to alkali–silica reaction under various exposure conditions. This study indicated that all three sealers tested, the silane-, oligosiloxane-, and polysiloxane-based sealers, could stop concrete expansion due to ASR and even produced contraction, even for concrete cylinders subjected to wetting and drying, freezing and thawing, and sodium chloride solutions. In 1991, the same silane, oligosiloxane, and polysiloxane were applied on sections of median barriers showing various degrees of deterioration due to ASR. These sections were subjected to wetting and drying, freezing and thawing, and, during winter, to deicing salt. The silane was also applied on other sections of the same barriers in 1994. Observations and measurements over 10 years indicate that the aesthetic appearance of these median barriers, particularly those sealed with the silane, was greatly improved, while internal humidity was significantly reduced, and concrete expansion as well, when not arrested. The period of time during which the above three sealers were capable to stop ASR expansion varies with the sealer used and the degree of concrete deterioration at the time of sealing. For instance, the silane, which was the best among all products tested, caused concrete contraction for at least 6 years in median barriers that were severely affected by ASR, and likely for more than 10 years in moderately affected barriers. The overall results confirm the conclusions obtained previously in the laboratory: a good sealer such as the silane tested may greatly improve the aesthetic appearance and stop the expansion of non-massive ASR-affected concrete members, at least up to about 300 mm in thickness, and subjected to wetting and drying, freezing and thawing, and salt water. However, the poor result obtained in the field with another silane-based sealer indicates that a sealer cannot be selected based on its composition only.Key words: alkali–silica reaction, concrete; cracking, expansion, internal humidity, median barrier, sealer, silane, siloxane.

In the province of Québec, due to the particular geology and the historic use of high-alkali cements, a large number of concrete structures are affected by alkali-silica reactivity (ASR). Consequently, tremendous effort was made in this province during the last 20 years on (1) the determination in the laboratory (testing methods) as well as in the field (inspection of structures) of the potential alkali-aggregate reactivity (AAR) of concrete aggregates, (2) the prevention of AAR in new structures, and (3) the management of existing structures affected by this problem. For new structures, the most popular measure used in Québec in the presence of potentially reactive aggregates consists of limiting the alkali contribution by the cement to 3 kg/m3 of concrete (Na2Oeq). Also, blended silica fume cements were used on many occasions against ASR; ternary cements containing fly ash and silica fume, which proved in the laboratory to be effective against ASR, are presently available. As concerns the existing structures affected by ASR, many of them were repaired using various techniques ranging from the simple application of a penetrating sealer to the application of post-constraints or slot cutting.Key words: aggregate, alkali-aggregate reaction, cement, concrete, diagnosis, management, preventive measures, prognosis, Québec, testing.

Since 1993, the Quebec Department of Transportation requires all its concrete suppliers to demonstrate that their concrete satisfies the requirements of the CSA A23.1 standard as regards the maximum spacing factor of the air void system. This new requirement raises questions about the reproducibility of the ASTM C 457 test method. An interlaboratory study was carried out to verify if the variability of the test method is sufficiently low to allow reliable decisions on the acceptance or rejection of in-place hardened concrete. A total of 18 operators from 13 different laboratories microscopically examined the six concrete slabs used for the study. It is concluded that the average reproducibility coefficient of variation is 14.4% for the total air content measurement and 14.2% for the spacing factor measurement. Considering these results, the probability that the measured value of the spacing factor exceeds the mandatory limit of 230 μm on a concrete production containing an air void system with a spacing factor of 170 μm (the target value proposed in the CSA A23.1 M-94 standard) is less than 0.7% (a probability of error of about 1%, 5%, or 10% is typical of most quality control test methods). Key words: concrete, air content, air void measurement, spacing factor, ASTM C 457 standard, interlaboratory study, freeze–thaw durability.

This paper outlines the findings of laboratory tests to check the influence of curing and type of mould on scaling resistance of three types of concrete exposed to frost and deicing chemicals: a plain concrete and concretes with 5 and 10% silica fume (relative to total binding mass). Sodium chloride was the deicer used for the tests, which were performed according to standard ASTM C672 (Standard test method for scaling resistance of concrete surfaces exposed to deicing chemicals). The tests showed that type of mould (steel or wood) and curing (12 or 48 h) have relatively little influence on scaling resistance of concrete but that silica fume in the concrete can cause a significant drop in scaling resistance. Key words: concrete, silica fume, demolding age, formwork type, scaling resistance, freezing, deicing salt, sodium chloride. [Journal translation]

The comparison of certain genera representative of the ichthyofauna of the Escuminac Formation (Quebec, Canada) with those coming from contemporaneous deposits (Upper Devonian, Frasnian) located in the Baltic countries (U.S.S.R.), Western Australia, Nevada (U.S.A.), and Germany provides new evidence against a lacustrine origin of the Escuminac Formation. It is suggested that the Escuminac Formation was deposited in a coastal marine environment. This hypothesis is supported by results of a geochemical study.

The study of Plourdosteus canadensis (Brachythoraci, Placodermi) from the Escuminac Formation (Frasnian) led us to erect a new family: the Plourdosteidae. Firstly, we discuss all the characteristics that allowed Ørvig to differentiate the genus Plourdosteus from Coccosteus. It is proposed to consider Plourdosteus mironovi as a synonym of Plourdosteus trautscholdi, found in the Baltic region of the USSR. The characteristics that support the monophyly of the Plourdosteidae are listed and are represented on a phylogenetic diagram. In the conclusion, the Dunkleosteidea sup. fam. nov., the Plourdosteidae fam. nov., and the type species Plourdosteus canadensis are defined. The different species of Plourdosteus are also listed.