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Recently, in Japan, application of the roller compacted dam concrete (RCD) method has increased in the construction of concrete gravity dams. The concrete for the RCD method (RCD concrete) features a very stiff consistency with low water content, which enables the use of a vibration roller for compaction. Most of the cement used so far for RCD concrete has used a combination of fly ash with moderate heat portland cement. However, the supply of high-quality fly ash for use in concrete has recently lessened in Japan. One admixture replacing fly ash is granulated blast furnace slag. In this study, properties of RCD concrete made with slag cement featuring blends of moderate heat portland cement and granulated blast furnace slag were examined. The effect of fineness of the individual slag cement components on compressive strength and adiabatic temperature rise were studied. The unit cement content in the concrete was 120 kg/m 3. The maximum size of the coarse aggregate was 150 mm. The results show that concrete with moderate low-heat slag cement can provide the same or better performance as fly ash cement concrete by employing a rational combination of fineness and slag content. Also, the advantages of slag cement at longer ages were confirmed. The results obtained in this study are now being applied to an actual dam construction.

Results of a laboratory test series are reported concerning the effect of cement type, class of fly ash, and fineness of fly ash on the strength development of mortars. Thirty percent by weight of portland cement was substituted by fly ash. The following materials were used in various combinations: Type I and Type III portland cements, Class F fly ash before and after grinding, Class C fly ash before and after grinding, a silica fume, a superplasticizer, and an accelerating admixture. More than 60 different compositions were tested in all. Standard flow, compressive strength, and pulse velocity measurements were performed in the standard manner at 1, 7, and 28 days. The obtained results show the effects of fineness of fly ash, along with other characteristics of mortar composition, on the flow and strength development, as well as the interactions between fineness and cement type. For instance, as expected, ground Class F fly ash with Type I cement produced lower strengths at 1 day than the same fly ash with its original fineness and Type III cement; however, at 7 and 28 days, the fly ash mortars with Type I cement showed higher strengths. The results of the pulse velocity tests showed the same trend as the strength results.

The customary criterion for establishing grades of structural concrete is the crushing strength measured in an arbitrary manner on a standardized specimen stored in a stipulated fashion for approximately a month after making. In some parts of the world, the specimen is a cube, and in other parts of the world, the specimen is a cylinder. There have been debates as to how the strength at 28 days can be predicted from procedures performed at early ages, especially 24 hr, on the grounds that a month is not soon enough. The intent of this paper is to suggest that the only time that really is "soon enough" to know that the grade of the concrete in any batch is correct is before the concrete is discharged from the concrete mixer into the forms. It is suggested, therefore, that effort would preferably be expended upon insuring that the materials used are those intended and the proportions in which they are used are those that were intended. If this is the case, the grade of concrete will be proper at all ages, and testing at any age is merely confirmation.

The three power centers in the world today must support the tremendous concrete construction and building investments that are needed in the developing regions where 90 percent of the world's population lives. Concurrently, renovations and renewals are required in industrial countries. Profound updating of conventional concrete technology is necessary, recognizing the differences between the behavior of test samples of concrete under laboratory conditions and of field concrete. For example, the historic development of curing concrete is reviewed with emphasis on the methods for monitoring heat development during curing of modern concrete. Proposals for wider transfer of this technology are also presented.

In-place testing is used to estimate the compressive strength of concrete in a structure by measuring another related property. A strength relationship is used to convert the in-place test results to an estimate of the compressive strength. Statistical methods are needed for reliable estimates of in-place strength. Such methods should account for the uncertainties in the measured property, the uncertainty of the strength relationship, and the variability of the in-place concrete. Standard statistical procedures for dealing with these uncertainties have not yet been adopted in North American practice. Recommendations are provided for developing the strength relationship, and a reliable, easy-to-use approach is presented to estimate in-place characteristic strength.