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水泥混凝土
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12.1.5 Composite cements and other topics Partial replacement of cement by silica fume increases the strength in concrete, but not in pastes (B169). This supports the view that the effect is due to a strengthening of the paste-aggregate bond (B169,R81,S128). Studies of concretes by backscattered electron imaging showed that the increase in porosity in the ITZ is much less marked if silica fume is present (B169,B170,R82,S133). Scrivener and Gartner (S128) found some increase in porosity, but attributed it almost entirely to the presence of hollow-shell grains. With pastes vibrated against a single piece of aggregate, in contrast, the replacement had no significant effect on the distribution of porosity within the ITZ, and some clumping of the silica fume was observed. Clumping was found to occur in pastes even when a superplasticizer was used (S133), suggesting that the coarse aggregate breaks up the clumps by crushing or shearing during mixing. Computer modelling of the ITZ (B171) confirmed that silica fume would be expected to decrease the gradient of capillary porosity in the ITZ but indicated that it would not eliminate it completely. The model also predicted that the effectiveness of mineral additions in increasing the integrity of the ITZ would depend on both their particle size and their reactivity. Inert additions would, with some reservations, have little effect, and flyash would be less effective than silica fume, because of its larger particle size and lower reactivity. The porosity in the ITZ may also be increased by dissolution of CH (B170). An experimental study showed that partial replacement of cement by flyash can either increase or decrease the width of the ITZ, depending on the characteristics of the flyash, but that slag had relatively little effect (C74). Interfaces of calcium aluminate cements with aggregates are discussed in Chapter 10. The ITZ between Portland cement paste and steel has been studied by SEM, using various techniques of specimen preparation (e.g. A38,B172). The major features observed have been substantial deposits of CH and, further away from the interface, a relatively weak, porous zone. Bentur et al. (B172) also reported the occurrence of a duplex film. Interfaces of cement or C3S pastes with zinc (A39,T64) or copper (T64) have been studied. |
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yzhang1986
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2楼2009-10-26 13:45:49
哇，太长了，终于翻完了……根据专业知识再仔细斟酌一下，供参考
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12.1.5 组成元素及其它 用硅粉取代部分水泥可以增加混凝度而不能增加粘度。这支持了是浆集键增强发挥作用的观点。通过背散射电子显像对混凝土的研究显示若硅粉存在则ITZ 的孔隙增幅明显降低。 Scrivener 和 Gartner (S128)发现一些孔隙增加，但都将之归于空心壳粒。 相反，随着坯泥撞击混凝土的单层，这种取代对ITZ的孔隙分布便没有明显效果，且可以观察到硅粉的结块。这种结块即使在使用了超增塑剂也会出现。ITZ (B171)的计算机模型证实硅粉可能降低了ITZ的毛细管多孔性但却不能完全将之消除。这一模型还预测矿物增加对ITZ完整性的提高效果依赖于其粒子的大小及反应性。保守地讲，惰性物质的增加几乎不会起作用，烟灰也不及硅粉，因为烟灰粒子大而反应性低。通过分解CH (B170)也将增加ITZ的孔隙度。一项实验研究显示用烟灰取代部分水泥，根据烟灰的不同特性可以提高或降低ITZ的宽度，但加入矿渣却几乎没什么效果。第十章讨论了聚合的铝酸钙水泥和混凝土之间的接触面问题。SEM利用不同的样本准备技术研究了普通水泥与钢之间的ITZ，他们观察到的主要特点是CH的大量存在，并可以看到非常不同于接触面的一个相对弱的多孔区。Bentur等也报道了双重膜的发现。水泥的接触面或含有锌(A39,T64)或铜的C3S(T64)糊剂也已被研究。 |
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