Vízügyi Közlemények, 1936 (18. évfolyam)

Kivonatok, mellékletek - Kivonat a 4. számhoz

22 sufficiently practicable, because some important properties of soils altering within a certain type cannot be depicted. In order, therefore, to illustrate certain properties which are important to agriculture, we have to use other charts, such as those employed by Kreybig (see references). III. RECENT FEATURES OF CONERETE MANUFACTURE. By A. SCHWERTNER. (Pages 541—557.) 1. The strength of concrete is primarily influenced by the water-cement ratio (fig. 1). In the diagram of experimental results curves of different equations may be drawn, such as the curves of Abrams and Bolomey. Fig. 2 and 3 show the methods of representing these curves by straight lines and the process of determining by experiment the constants of the equations. The strength of concrete is increased by lowering the cement-water ratio, but this has to be obtained without an essential change of the workability. In making a concrete of a certain plasticity, the smaller water-cement ratio may be chosen, the larger is the quantity of cement and the smaller the surface area of the aggregates to be moistened, i. e. the coarser the grains of the aggregates are. Table I shows the changes in the consistency of the concrete with regard to the composition of the aggregates. For estimating the composition of the aggregates, different limiting curves may be used, such as Fuller's curve (figs. 4 and 5), or that of the German specifications for reinforced concrete (fig. 6). The quality of the aggregates can be characterised by Abrams' fineness modulus (m) ; the method of determining this modulus is given in figures 7 and 8. Devices proposed for measuring the liquidity of the concrete (figs. 9 and 10) are of limited applicability. The object of rational concrete manufacture is to find the best relation between the strength, the water-cement ratio and the workability, by properly choosing or grading the aggregates. 2. The influence of temperature upon the setting of concrete is well known. Figure 11 shows, from Giïin's data, the changes in the strength of concrete set at different temperatures. At high temperatures a quick setting can be obtained ; recently use has been made of this advantage in manufacturing concrete wares and performing special works. (Railway station at the harbour of Havre). 3. Properties of concrete deposited during setting. Fig. 12 contains experimental results concerning the change in strength of concrete when the mix has been deposited after a few hours. The immediate placing and working of the mix does not seem to be absolutely necessary ; moreover, placing during the time of setting may increase the strength. The author explaines this fact by the warming curve of the Portland cement paste (fig. 13). Vicat's experiments show that the setting is completed in the sixth hour, while the warming curve shows that an intense chemical process begins only in the seventh or eigth hour. 4. Natural cements as complementary materials. Table II contains data of experiments carried out with concrete made by proportioning cement and