In the third year of a research project on roller-compacted concrete pavements, a test section was cast during the summer of 1989, using 13 different mixtures. Five types of binder (ASTM Types I, I + slag, I + fly ash, a blended silica fume cement, and a blended silica fume cement + fly ash) were used to prepare these mixtures. To verify whether a proper air bubble network could be obtained, two different air-entraining admixtures were utilized. Approximately half of the mixtures were air-entrained. Half of the test section was moist-cured for 14 days and a white curing compound was sprayed on the remaining portion. Samples representative of all mixtures and all curing conditions were taken from the pavement after 28 days. The air-void characteristics of all concretes were determined in accordance with ASTM C 457, and the salt scaling resistance of all combinations (of the type of mixture and the type of curing) was evaluated using ASTM C 672 on both rolled and sawn surfaces. Results indicate that it is extremely difficult to entrain air in this type of concrete. In accordance with previous results, good scaling resistances were obtained with the silica fume concretes cured with a membrane.

Results of an investigation of cement paste structure, and strength, permeability, and frost resistance of concrete with admixtures of silica fume type are given. The admixtures are waste materials from metallic silicon, low-grade ferrosilicon, ferrosilicon chrome production, containing SiO2 in the amount of 92, 70, and 66 percent, and surface area of 25.0, 44.9, and 18.5 mý/g, respectively. The influence of the admixtures on the cement paste microstructure results in an increase of gel porosity volume, decrease of capillarity porosity, and in an increase of strength. Thus, concrete strength increases and its permeability decreases. Physical and chemical properties of the silica fume-type admixtures insignificantly affect gel pore volume, whereas they have significant influence on capillary porosity. An increased dosage of high-range water-reducing admixture (HRWR) is a beneficent factor in increasing hydration degree and gel porosity, decreasing capillary porosity volume, and, consequently, increasing strength. Concrete frost resistance with silica fume dosages up to 10 percent of cement mass is not lower than the reference concrete with the same amount of binder.

The behavior of mortars containing fly ashes and slag in seawater has been studied under two different exposure conditions. Examined first was whether the achievement of strengths at 28 days, either similar to or higher than those of reference mortars, would lead to mortars with a durability as high as in the case of reference mortars or even higher, due to the addition of superplasticizers and the substitution of fly ashes or slag for some cement quantities. Secondly, a cement portion issued from a reference mortar was replaced by corresponding fly ash and slag quantities, the E/C ratio and the workability being kept constant, and variations of the duration of humid curing were imposed to observe their influence on the behavior in seawater. Results obtained show that: a) the criterion of strength at 28 days does not allow a guarantee of the durability in seawater; b) the direct substitution, in the mortar, of fly ashes or slag, for a certain amount of cement (known in the French regulations as nonresistant to seawater) does not improve the long-term behavior; and c) the humid curing during 7 days is, by far, the best.

It is well known that curing concrete at elevated temperatures reduces the final compressive strength. The reduction depends on the temperature regime as well as the concrete composition. This program was based on recent data indicating that concrete containing condensed silica fume suffers less strength loss if a strength of about 10 MPa is reached at 20 C before heating. In this investigation, concrete characteristics were w/c + s = 0.30, 0.45, and 0.60 with and without 8 percent condensed silica fume. The temperature regime was to transfer specimens at 40 and 60 C, after delay times at 20 C. The delay times corresponded to strengths of about, 0, 3, 6, 9, 12, and 16 MPa. After 6 days, all specimens were cooled to 20 C and tested at 28d. The results show that the delay period had no significant influence on the final strength, except for the specimens with zero delay. The rest suffered some strength reduction compared to 20 C references, about 15 percent for w/c + s = 0.60, and less than 10 percent for the others. The reductions at 60 C were slightly greater than at 40 C. Concretes containing condensed silica fume generally suffered the smallest strength reductions.

After calcination at 650 to 850 C, kaolinitic clays show an interesting pozzolanic property. Thermal activation leads to metakaolin, an amorphous phase which is very reactive. In this study, different clays were tested with various granular sizes and calcination parameters. The pozzolanic properties were investigated using metakaolin-lime mixtures by the evaluation of both the mechanical strength and combined lime. The mineralogical composition, particle size distribution, and degree of amorphousness were the main factors affecting the pozzolanic activity of calcined clays. Influence of the pozzolanic activity on the mechanical and durability properties of concrete was established from test results on blended portland-metakaolin cements.