【導(dǎo)讀】在混凝土設(shè)計中摻加活性礦物替代是一個很重要的環(huán)節(jié)。但這樣的使用并不?；炷两Y(jié)構(gòu)的耐久性。在具有兩種不同礦物成分的普通硅酸鹽水泥中摻加高達。20%的硅灰的對其的影響是顯而易見的。添加過多的石膏，三氧化硫的含量就會。定時間和x射線衍射。結(jié)果表明，用硅灰取代水泥的百分?jǐn)?shù)為20%的時會影響水。泥漿體的流動性。根據(jù)標(biāo)準(zhǔn)稠度和時間來衡量需水量的多少。決于熟料的礦物組成。二氧化硅會直接和間接的影響水化反應(yīng)：后者是因為在早。期火山灰質(zhì)活性的增加，前者是因為它的形態(tài)和比表面積大。在石膏過量的情況下，水化反。2至6%的石膏在加速水化硅酸三鈣的形成，2%至4%在促進水泥石的水化。硫酸鹽，降低了水化反應(yīng)的強度，從而阻礙了C3A的的分解。三天后,在摻量為5%或10%時，C3A的水化反應(yīng)是緩慢的。獲得同樣可行的樣品,純硅酸鹽水泥水膠比為；硅灰摻量為10%時的混合。13小時以后，水化反應(yīng)速度開始下降。初步反應(yīng)開始緊追其后的是水化反應(yīng)的加

　　

【正文】 spectively, for 10 and 20% replacement: ., not only later than in the case of PC2, but with a longer interval between the first trough and the second peak. The time lapsing between initial and end setting times was also longer and final setting was retarded in all these pastes. And yet, in this stage also, SF was observed to stimulate the hydration reactions in the fraction of the Portland cement with which it was mixed, with rates of release at the second peak equal to and greater than ( and W kg–1), respectively, the proportional rate for PC2 ( and –1). For the same reason as in the case of plain PC2, the third stage (transformation of the aluminous phase) was absent. In short, both the first trough and the second peak were retarded and attenuated in all the mixes, and although stimulation was observed, it was much less pronounced than for mixed cements containing PC1. This is an unequivocal sign that the higher C3A content in the latter is a determining factor in the enhanced stimulation of the hydration reaction Adding gypsum to PC2 significantly attenuated and retarded the first trough and second peak with respect to plain Portland cement. Similarly, adding gypsum to the mixes retarded the first trough and the second peak and widened the interval between the two. The percentage of total heat of hydration released per gram of Portland cement after 48 h is shown in Fig. 5. It will be noted that both the nature of the additions and the position of the cements affected mix behaviour, as did the presence or absence of gypsum up to an SO3 content of %. Fig. 5 Changes of hydration heat per gram of Portland cement for PC/SF mixes Silica fume, at percentages of both 10 and 20%, produced mixes that generated greater heat of hydration with PC1 than with PC2. This behaviour can be explained by the position of the Portland cements used. The high C3A content in PC1 naturally produced more heat of hydration at the early ages. After 48 h of hydration, SF indirectly prompted the respective fraction of the PC with which it was mixed to generate a larger amount of heat of hydration than the plain PC. (This involved direct stimulation of hydration via the internal and external humidification of each particle from the time the mixing water was initially added and/or indirect stimulation, due to the substantial pozzolanic activity of the silica fume in the early ages.) When gypsum was added to the mix, the total heatafter 48 h declined in all cases (calorimetric curves in Figs 3 and 4). Noheless, more heat per gram of Portland cement was released by the samples with gypsum. Conclusions The conclusions that may be drawn from the experiments conducted with two types of Portland cement with very different mineralogical positions, mixed with silica fume and gypsum, are as follows: ? Silica fume, which exhibited pozzolanic activity at 48 h, stimulated the hydration reactions in the PC fractions with which it was mixed, both: – directly: because of its size and shape (very small spheres, high specific surface), it demands greater amounts of mixing water, which would ultimately be the actual cause of this direct stimulation, and _ indirectly: its chemical properties favour very significant pozzolanic activity at early stages. This effect was so intense that in some cases it could be pared to a synergistic calorific effect. For this reason, when SF is added to cement to be used to make high performance bulk concrete, account must be taken of its direct and indirect effect on the generation of heat of hydration to minimize undesirable consequences, the risk of cracking, among others. ? Whilst the addition of gypsum retarded and attenuated the hydration reactions in all cases (with a smaller amount of total heat after 48 h), it also generated greater heat of hydration per gram of Portland cement than when no gypsum was added. ? The differences in the amount of heat produced per gram of Portland cement were more significant in mixes with Portland cement with a high C3A and low C3S content than in Portland cement with a low C3A and high C3S content. Acknowledgements We would like to thank the Fundaci243。n Rotaria and the Universidad Nacional de la Provincia de Buenos Aires, for financial support, and the Instituto de . ‘Eduardo Torroja’CSIC from Spain, as well, for providing the authors with necessary cementing materials and analytical and experimental techniques References 1 S. Mindess and J. Young, ‘Concrete’, PrenticeHall, Inc., Englewood Cliffs, New Yersey 1981. 2 H. Ushiyama, Y. Shigetomi and Y. Inoue‘Effect of gypsum on the hydration of alite and belite’, Proceedings of 10th International Congress on Chemistry of Cement, Vol. II, G246。teborg, Norway 1997, p. 4. 3 A. A. Amer, J. Thermal Anal., 54 (1998) 837. 4 Z. Giergiczny, J. Therm. Anal. Cal., 76 (2020) 747. 5 E. ElShimy, S. A. AboElEnein, H. ElDidamony andT. A. Osman, J. Therm. Anal. Cal., 60 (2020) 549.