建筑材料外文翻译--普通硅酸盐水泥中掺入硅灰和石膏对水化反应的影响.doc

普通硅酸盐水泥中掺入硅灰和石膏对水化反应的影响 在混凝土设计中掺加活性矿物替代是一个很重要的环节。但这样的使用并不是总是适合的，由于水化反应放出的热量偶尔会影响混凝土的质量，从而影响h混凝土结构的耐久性。在具有两种不同矿物成分的普通硅酸盐水泥中掺加高达20%的硅灰的对其的影响是显而易见的。添加过多的石膏，三氧化硫的含量就会达到7.0%。 在这个研究上最先进的技术是导热量热法和拉蒂尼测试，提供的方法是要设定时间和x射线衍射。结果表明，用硅灰取代水泥的百分数为20%的时会影响水泥浆体的流动性。根据标准稠度和时间来衡量需水量的多少。这些效果的发展取决于熟料的矿物组成。二氧化硅会直接和间接的影响水化反应：后者是因为在早期火山灰质活性的增加，前者是因为它的形态（微小的球体）和比表面积大。每克硅酸盐水泥在早期总的水化热释放量在显著地上升，硅灰被认为对热效应起一个协同作用，随之而来的风险是产生细小的裂缝。在石膏过量的情况下，水化反应的加快和衰减会使每克硅酸盐水泥产生更大的水化热，特别是在硅酸盐水泥的C3A的含量大时。关键字：石膏，水化热，波特兰水泥，硅灰 水泥的研究范围从个人分析到每个组件阶段,研究高度复杂的系统以及他们所有的变量，联合研究硅酸盐熟料组件与石膏(CaSO4.2H2O)的交互作用来测量凝结时间，例如，已经发现： 在硅酸盐水泥中C3A和C4A都会与石膏发生反应，但是由于C3A更容易与石膏反应，所以水泥中大量的C3A被很快反应掉。石膏的用量会受到所设置的凝结时间的限制，导致所形成的钙矾石会比预期的要少。 石膏也加快了钙硅酸盐的水化速率,同时在水花过程中争夺硫酸根离子，虑到大量的硫酸盐包含在CSH凝胶中。2至6%的石膏在加速水化硅酸三钙的形成，2%至4%在促进水泥石的水化。 石膏含量高有助于形成大量的钙矾石，然而这会阻止凝结时间和硬化，这些明显的变化是因为微观结构的膨胀和开裂。石膏含量低，反过来，会形成更多的硫酸盐，降低了水化反应的强度，从而阻碍了C3A的的分解。 研究矿物火山灰还补充开发了离散系统的分析，硅灰是一种高度火山灰，此外,人们已经发现： 三天后,在掺量为5%或10%时，C3A的水化反应是缓慢的。 掺量增加5 - 10%，28后C3A的水化反应会加快。 最后，在第一次的28天，也会加深C2A的水化反应。所有上述的结果是在早期产生更大的水化热,百分数增加从5%提高到到10%，这一效应会越来越强烈，那是因为硅灰的BET比表面大的原因。此外，因为在早期硅灰中的氢氧化钙的反应会间接地刺激整个效应，来促进物质的生成。一方面,硅灰的反应已甚至发生在最初的几天，主要是根据液相时消耗的Ca2+，但也吸收OH-和k+。在另一方面，每克掺杂了硅灰的硅酸盐水泥释放的热量比没掺杂硅灰的硅酸盐水泥要多。实验目的 鉴于要考虑石膏和硅灰这些物质，现在研究的目标是分析两种不同成分的硅酸盐水泥水化反应的整体效应，以限制他们在高性能混凝土中的使用。材料和方法 选择两种不同矿物组成的硅酸盐水泥为研究对象。一种C3A的含量高，称为PC1；另一种是C3A含量最低（1%）和C3A含量最大，称为PC2;其他成分是一个非常活跃的火山灰质矿物(硅灰)和丰富的地面天然石膏。蒸馏水用于砂浆中。表1中给出了波特兰水泥的化学成分、密度和BET比表面。从硅酸盐水泥的化学成分分析找到了其组成：pc1中的组成是 C3S（1%）、C2S（16%）、C3A（14%）、C4AF（5%）;PC2中的组成是 C3S（79%）,C2S(2%),C3A(0%)、C4AF(10%)。 不同的化学和矿物成分的两种硅酸盐水泥主要差别表现在密度不同。他们的细度,相反,是可比的。比例系数是：90%的Sio2,88.64%的Sio2是活性的，然而比石英（2.7）的密度要低得多，但是比表面积却非常大。图一是它的衍射图，揭示了方英石的存在。他指示性的物质的扩散模式主要是玻璃的性质。 由硅酸盐水泥混合的每个样品，混合比例大致在90/10 和80/20，石膏含量较少时，其SO3的含量大致在7%。表2给出了500g样本的凝结时间和需水量，按照欧洲标准 EN 196, 第三页执行。 水的多少对形态有很大的影响。硅酸盐水泥颗粒可以增加水泥水化的的反应面积。此外,鉴于其密度和比表面积，此外，硅灰的组成比硅酸盐水泥粒子数量更大，这也极大的增加了水的需求。 火山灰活性是由弗拉蒂尼化学测试来评定的。对于一个给定的一段时间，在40C温度下，通过比较氢氧化钙在水溶液中的溶解量（在这个实验中，规定时间是48h），氢氧化钙在碱性溶液在相同的温度下的溶解度等温线。这个火山灰活性的被定义为一个较低的氢氧化钙浓度的样品溶液要超过溶解度等温线，这是由于它在火山灰反应中被吸收（图二）。 热量的释放模式确定是通过热传导的方式。在25C进行了测量，记录在第一个48小时内的水化热和总的热释放量的数据，是通过计算面积不同下热量释放率的曲线。这种方法被广泛用于监控纯硅酸盐水泥中的水化以及含有矿物添加粘合剂。获得同样可行的样品,纯硅酸盐水泥水胶比为0.5； 硅灰掺量为10%时的混合物的水胶比为0.75，硅灰掺量为20%时的混合物的水胶比为0.65.结果与讨论 图二显示了OH-和CaO在48小时后的数量，注意，火山灰的活性是在48小时内。在PC1的实验中，代替的硅灰的掺量是10%，在PC2中代替的硅灰的掺量在15%以上。这些数据未能显示在那个时间段里火山灰的水化反应的速度是如此之高，以至于它无法反驳或补偿由固定的氢氧化钙产生的热量。 当石膏添加到样品中时，由于CaO部分溶解于水中，所以OH-下降，由于部分稀释的原因，在第一个48小时内火山灰质硅酸盐水泥活性并没有体现出来。 图三和图四分别显示PC1和PC2在48h的热量曲线。第一阶段为诱导期，图三显示了热量释放速率高是因为C3A的初始水化反应。两小时后第一个峰出现时，速率下降到0.91W/kg。紧随其后的是水化反应的加速与CSH凝胶的开始沉淀,由于C3S的存在，曲线出现第二个峰值时是在11：12，速率达到了2.97W/kg。当反应开始加速，PC1开始消耗。13小时以后，水化反应速度开始下降。这个阶段发生铝化反应，SO3/Al2O3 的比例小于3（这个实验是0.69）。但最突出的效应是反应放出巨大的热量。当速率上升到3.33W/kg时，热量释放曲线出现第三个峰值。最后，水化反应开始变慢，保持在一个较低的速率。 48小时候实验完成，把热量释放曲线的第三个峰值作为参考。 虽然在PC1中加10%和加20%的硅灰相对于纯PC1来说热量的本质是一样的，但是还是发现有些差异的。在第一个阶段，例如速率在0.83和0.88之间时，硅灰粒子的效果是稀释硅酸盐水泥。然而，与此同时，当它们混合时水化反应会增强，第一个峰出现的时间要比纯PC1要早。初步反应开始紧追其后的是水化反应的加速，在第二阶段反应时间在7:5410:12之间，C3S的凝胶形成了。也就是说,两个最小值出现的时间要早于纯PC1第一个波谷和第二个波谷之间的间隔也要比10%和20%硅灰含量要窄。这证明了硅灰的掺入促进了水化反应的进行，这个效应进一步证实了混合了硅灰的PC1比普通的PC1的有更高的热释放速率。随后，两种不同的混合物中SO3/Al2O3比例的下降促进了铝酸盐的形成。结果在11：3414：24之间第三个峰值出现，10%和20%掺量的混合物还是要高于纯PC1。此外，它们第三个峰的率值分别为4.77w/kg和8.20w/kg，同样要高于纯的PC1。结果再次证明要刺激水化反应要在PC1中加入硅灰。 简而言之，在PC1和所有的混合物中第一个峰值出现的比较早，时间相当。所有的混合物中第二个和第三个峰值的出现比纯PC1要出早而且反应强度要比纯PC1高。当把石膏加入到PC1中时，热量释放曲线会大幅度衰减，伴随着的是第三个峰的消失。当石膏掺入到硅灰或者硅灰和PC1的混合物中时，曲线中波峰的出现会推迟而且峰值会减少。对于纯PC1第三个峰则会完全消失。 图二为PC2的第一阶段或者称为诱导期，由于水化反应的初始阶段，有很高的的热量释放速率。1.37小时以后，速率降低到0.651w/kg之间。紧随其后的是水化反应的加速，开始形成CSH凝胶沉淀,直到7.39h时第二个波峰出现，峰值为3.25w/kg。PC2在设置的时间内放热速率开始加速（表二）。之后的反应，水化反应速率开始降低，速率值开始下降。实验的时间实在48h内完成，当热量释放曲线出现第二个波峰时读取数据。当PC2中C3A的含量为零时，在这种情况下就没有铝酸盐的形成了 。 虽然在PC2中加10%和加20%的硅灰相对于纯PC1来说热量的本质是一样的，但是还是发现有些差异的。在第一个阶段，例如速率在0.27和0.26之间时，硅灰粒子的效果是稀释硅酸盐水泥。然而，与此同时，当它们混合时水化反应开始减弱，观察到在1:152:27h之间出现低谷。在第一个峰和第二个峰之间水化反应持续的时间较长。第二个峰出现在8:559:24之间。对于用10%和20%替代用那个平来说，比PC2持续的时间要短，但是第一个波峰和第二个波峰之间的间隔时间要比PC2长。设置的开始时间和结束时间也要设置的更长。然而，在这个阶段，硅灰会刺激硅酸盐水泥的水化反应，混合物的第二个峰值的速率值等于或大于PC2的速率值。同理，第三个阶段中PC2没有铝酸盐生成的阶段。 总之，混合物中无论是第一个波峰和第二个波峰被推迟还是被率值降低，但是观察到PC1混合物的水化强度明显要高。明确的迹象表明，C3A的含量决定了水化反应的强度。 在PC2中添加石膏明显会影响硅酸盐水泥热量释放曲线的第一个波峰和第二个波峰，同事也会增大第一个波峰和第二个波峰之间的间隔时间。 每克硅酸盐水泥在48小时内释放的水化热的比例在图五中显示出来。人们会注意到在硅酸盐水泥中添加两种不同的矿物对水化热的影响。 在生产混合中同样添加20%的硅灰，PC1的产生的水化热要大于PC2。这种现象可以应用在硅酸盐水泥的生产中成分的使用中去。PC1C3A的含量高时，早期会产生大量的水化热。在实验研究的48h内，掺杂了硅灰或掺杂了大量硅灰的硅酸盐水泥相比普通的硅酸盐水泥产生的水化人要多。 混合物中掺入石膏，总热量在48h后会降低（图三和图四显示），尽管如此，在生产中我们还是要掺入石膏。结论 这些实验结论通过比较两种不同矿物组成的硅酸盐水泥，矿物是混合硅灰和石膏。结论如下： 硅灰在48h内的，它具有的火山灰活性会刺激硅酸盐水泥的水化反应，其中有： 直接影响：因为硅灰的球体较少，所以比表面积较大。因此，反应需要大量的水，刺激了水化反应的进行。 间接影响：它的化学性质火山灰活性在有利于早期反应的进行。 这种效果是如此的激烈,在某些情况下,相比热效应，它可能是一个协同作用的。因为这个原因,硅灰添加到水泥是用于制造高性能的散装水泥,生产中必须采取的直接和间接的方法减少其对水化热的影响,减少不良后果的造成开裂的风险等。 在所有情况下，添加石膏会减弱水化反应的强度。相对于没有添加石膏的硅酸盐水泥也会产生更多的水化热。 这些差异主要来自混合硅酸盐水泥中C3A较高，而C3S含量较低。相比普通硅酸盐水泥中C3A较低，而C3S含量较高。 致谢 我们要感谢扶轮基金会，布宜诺斯艾利斯省立大学，为我们提供的经济支持。同时感谢西班牙的爱德华多科研机构为我们提供了实验原材料实验仪器和实验技术。 参考文献1. S. Mindess and J. Young，混凝土，上海译文出版社，英格伍德克里夫19812.H. Ushiyama, Y. Shigetomi and Y. Inoue，石膏中水化硅酸三钙石和斜硅钙石的效应，“第十届水泥和化学国际大会论文集”，Goteborg二世,挪威1997,p.4.3.A. A. Amer, J. Thermal Anal., 54 (1998) 837.4. Z. Giergiczny, J. Therm. Anal. Cal., 76 (2004) 747.5.E. El-Shimy, S. A. Abo-El-Enein, H. El-Didamony andT. A. Osman, J. Therm. Anal. Cal., 60 (2000) 549.CALORIMETRY OF PORTLAND CEMENT WITH SILICA FUME AND GYPSUM ADDITIONS The use of active mineral additions is an important alternative in concrete design. Such use is not always appropriate, however, because the heat released during hydration reactions may on occasion affect the quality of the resulting concrete and, ultimately, structural durability. The effect of adding up to 20% silica fume on two ordinary Portland cements with very different mineralogical compositions is analyzed in the present paper. Excess gypsum was added in amounts such that its percentage by mass of SO3 came to 7.0%. The chief techniques used in this study were heat conduction calorimetry and the Frattini test, supplemented with the determination of setting times and X-ray diffraction. The results obtained showed that replacing up to 20% of Portland cement with silica fume affected the rheology of the cement paste, measured in terms of water demand for normal consistency and setting times; the magnitude and direction of these effects depended on the mineralogical composition of the clinker. Hydration reactions were also observed be stimulated by silica fume, both directly and indirectly the latter as a result of the early and very substantial pozzolanic activity of the addition and the former because of its morphology (tiny spheres) and large BET specific surface. This translated into such a significant rise in the amounts of total heat of hydration released per gram of Portland cement at early ages, that silica fume may be regarded in some cases to cause a synergistic calorific effect with the concomitant risk of hairline cracking. The addition of excess gypsum, in turn, while prompting and attenuation of the calorimetric pattern of the resulting pastes in all cases, caused the Portland cement to generate greater heat of hydration per gram, particularly in the case of Portland cement with a high C3A content.Keywords: gypsum, heat of hydration, Portland cements, silica fume Cement studies range from the individual analysis of each of the component phases, to research into highly complex systems with all their variables. Joint studies of Portland clinker components and their interaction with the gypsum (CaSO4_2H2O) added to regulate setting time, for instance, have found that: The C3A and C4AF in ordinary Portland cement compete for gypsum, but as it is more reactive, C3A consumes higher quantities of the addition more rapidly.This, in conjunction with constraints on theamount of gypsum used to ensure that only the setting time is regulated, leads to the formation of less ettringite than might otherwise be expected . Gypsum also accelerates the hydration rate of calcium silicates, which likewise compete for sulphate ions during hydration, given the significant amount of sulphates included in the CSH gel. The inclusion of 2 to 6% of gypsum has been found to accelerate alite hydration, and from 2 to 4%, belite hydration . A high gypsum content contributes to the formation of large amounts of ettringite, however, which retards paste setting and hardening and prompts substantial changes in volume as a result of micro structural expansion and cracking; a low gypsum content, in turn, favours the formation of monosulphoaluminate solid solutions before the end of the latent period of C3S hydration, thereby retarding the acceleration period of this compound . The study of mineral pozzolanic additions has also developed from the analysis of discrete systems . In the case of silica fume, which is a highly pozzolanic addition, it has been found that: After three days, at addition rates of 5 and 10%, C3A hydration is retarded . Additions of 510% accelerate alite hydration up to the age of 28 days Lastly, including the addition also heightens the hydration rate of _C2S during the first 28 days . The outcome of all the foregoing is to produce greater heat of hydration at early ages , an effect that grows more intense as the percentage of the addition is raised from 5 to 10% . The high BET specific surface of silica fume has been identified as the cause of its over-stimulation of Portland cement hydration reactions 11. In addition, however, an indirect stimulatory effect on such reactions has been attributed to the substance, due to the fixation of calcium hydroxide in the pozzolanic reaction from the earliest ages 12. On the one hand, the pozzolanic reaction has been confirmed to take place even in the first few days, chiefly on the grounds of the consumption of Ca2+ ions in the liquid phase, but also of the uptake in descending order of OH and K+ ions 1317. And on the other, the amount of heat released per gram of Portland cement in pastes with silica fume has been found to amply exceed the amount of heat released by the respective plain pastes 18.-ExperimentalObjective In light of these considerations on substances such as gypsum and silica fume; the objective or purpose of the present study is, to analyze their overall effect on the hydration of two Portland cements with widely varying compositions, with a view to limiting their use in high performance concrete.Materials and methods Two Portland cements with widely differing mineralogical compositions were chosen for this study. One, with a very high C3A content, called PC1, and the other, with a minimum C3A content (1%) and a maximum C3S content, called PC2; the other constituents were a very active pozzolanic mineral addition (silica fume, SF) and rich ground natural gypsum. Distilled water was used in the mortar in all cases.The chemical composition, density and BET specific surface of the Portland cements and the addition are given in Table 1. The potential composition of thePortland cements found from their chemical composition and the Bogue equations was as follows: 51% C3S,16% C2S, 14% C3A and 5% C4AF for PC1 and 79% C3S, 2% C2S, 0% C3A and 10% C4AF for PC2. The different chemical and mineralogical compositions of the two cements Portland are partly reflected in the difference in their densities; their fineness, on the contrary, is comparable. SF contains: over 90% SiO2, 88.46% SiO2 r (reactive silica) 19, 20 and yet has a much lower density than quartz (2.70) and a very high specific surface. Its diffractogram, shown in Fig. 1, reveals the presence of cristobalite (C); the diffuse pattern is indicative of the substances primarily vitreous nature 21. The pastes for the study were made by mixing each Portland cement separately with SF, in percentages by mass of 90/10 and 80/20, in the absence of gypsum or with sufficient amounts to bring the total SO3 content to 7.0%. Table 2 gives the setting times and water demand for 500-g samples. These two physical parameters were determined as laid down in European standard EN 196, part 3 22. morphology had a significant effect on water demand. The SF spheres separated the Portland cement particles, making a greater surface area available for hydration. Moreover, given its density and specific surface, the silica fume comprised a larger number of particles than the Portland cement replaced, significantly increasing the water demand. Pozzolanic activity was evaluated chemically by Frattinis test 23, by comparing the amount of calcium hydroxide in an aqueous solution covering the hydrated sample at 40C for a given period of time (in this case, 48 h), with the solubility isotherm for calcium hydroxide in an alkaline solution at the same temperature. The indication of pozzolanic activity was defined to a lower calcium hydroxide concentration in the sample solution than on the solubility isotherm, due to its uptake in the pozzolanic reaction (=+result) (Fig. 2). The heat release pattern was ascertained by heat conduction calorimetry for pastes. Measurements were taken at a temperature of 25C. Data were recorded during the first 48 h of hydration and the total heat released was computed by integrating the area under the rate of release-age curve. This methodology is widely used to monitor hydration in pure Portland cement 1 as well as for cements containing mineral additions 24. To obtain equally workable pastes, the water:cementitious material ratios used were 0.5 for pure Portland cements, 0.625 for mixes with 10% SF and 0.75 for mixes with 20% silica fume.Results and discussion Figure 2 shows OH and CaO determined at 48 h. Note that the pastes with SF showed pozzolanic activity at 48 h (i.e., 6 days before its first specified age, 8 days 25), in the case of PC1 at (addition-cement) replacement rates of 10%, and in PC2 at rates of 15% or higher. Some of these mixes failed to show pozzolanicity at that age because the rate of the hydration reaction was so high that it could not be countered or compensated for by the fixation of the calcium hydroxide resulting from the pozzolanic reaction.Fig. 2 Pozzolanicity (Frattini test) at 48 h: results When gypsum was added to the samples, the CaO increased due to its partial dissolution in water, whereas OH declined, partially because of the effect dilution of the Portland cement, although no pozzolanic activity was detected in any of the samples within the first 48 h. Figures 3 and 4 show the first 48-h calorimetric curves for the samples containing PC1 and PC2, respectively. The first stage or induction period for plain PC1, visible in Fig. 3, shows a high rate of heat release due to initial hydrolysis and the hydration of the aluminous phase (primarily C3A); the rate dropped to 0.91 W kg1 after 2 h, accounting for the first trough on the calorimetric curve. This was followed by the acceleration of hydration reactions with the initial precipitation of the CSH gel, primarily from C3S , until the rate of heat release peaked for a second time at 2.97 W kg1 at reaction time 11:12. During acceleration, PC1 began to set (Table 2). Thereafter the rate of the hydration reactions declined through the 13th hour, overlapping in this stage with the aluminous phase transformation reactions, which take place when the SO3/Al2O3 molar ratio falls to under 3 (in this case, 0.69). But the most prominent effect of the reaction was the enormous amount of heat released, which rose to 3.33 W kg1, forming the third peak on the calorimetric curve, 17 h and 24 min into the reaction. Finally, the hydration reactions slowed to and remained at a low rate.Fig. 3 Calorimetric curves for mixes with PC1 The test was considered completed after 48 h, taking the reading at that time as the third trough on the calorimetric curve. Although when 10 and 20% SF was added to the PC1 the calorimetric phases or stages observed were essentially the same as for the plain PC1, certain differences were noted. During the first stage, for instance (from t=0 to the first trough), the effect of the SF particles was to dilute the Portland cement, with rates of 0.83 and 0.88 W kg1, respectively. At the same time, however, the hydration reactions were enhanced in the fraction of the PC1 with which they were mixed, given that the first trough appeared earlier than in plain PC1 (1:36 and 1:42 h, respectively). This was followed by the acceleration of the hydration reactions with the initial formation, in this case, of gels of chiefly C3S and SF origin and silanol groups of SF origin with the second trough recorded at reaction times of 10:12 and 7:54, respectively. That is to say, both minima appeared earlier than in plain PC1, and the interval between the first and second troughs was narrower with both 10 and 20% replacement rates. This confirmed that the hydration reaction was stimulated by the SF, an effect that was further corroborated by the higher rate of heat release values (3.92 and 4.11 W kg1) found for the mixes than for plain PC1. Subsequently, the low SO3/Al2O3 molar ratios in the two cement mixes (0.68 and 0.67, respectively) prompted aluminous phase transformation. The outcome was third peak reaction times of 14:24 and 11:34, respectively, for 10 and 20% replacement, both higher than for plain PC1. Moreover, the rate values at these third peaks were 4.77 and 8.20 W kg1 higher than for plain PC1 , again providing dual confirmation (troughs appearing in shorter times and higher heat of hydration release values) of hydration stimulation as a result of replacing PC1 with SF. In short, the first troughs on the heat release curves for the samples containing PC1 appeared earlier and were attenuated for all mixes, and the second and third peaks appeare