Mechanism of expansion of mortars immersed in sodium sulfate solutions
Mechanism of expansion of mortars immersed in sodium sulfate solutions
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DOI：
10.1016/j.cemconres.2012.10.001
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发表时间：
2013-01-01
影响因子：
11.4
通讯作者：
Scrivener, Karen
中科院分区：
文献类型：
--
作者：
Yu, Cheng;Sun, Wei;Scrivener, Karen
浸没在含有硫酸盐离子的溶液中的样品膨胀背后的机制一直存在争议。膨胀被认为起源于钙矾石的形成，但不可能在这两个过程之间找到任何直接的联系，也不可能将膨胀纯粹与固体体积的增加联系起来。结晶压力被认为是最可能的机制。该机制的一个关键方面是溶液中存在与生长晶体相关的过饱和，并且不可能直接测量试样内不同点孔溶液的组成。在本文中，我们提出了一个改进的结晶压力假设来解释硫酸盐相关膨胀。我们提供的证据表明，膨胀与嵌套在C-S-H中的单硫酸盐晶体向钙矾石的转变有关。最初，进入的硫酸盐在大孔隙中与含水合物的铝酸盐反应，生成不膨胀的钙矾石。在此过程中，溶液的组成被固体的沉淀所缓冲，因此进入的速率不强烈地依赖于溶液的组成。在所有这些“自由获取”的铝酸盐发生反应后，孔隙溶液中硫酸盐离子的浓度增加，正如C-S-H吸收的硫酸盐的增加所表明的那样。当溶液浓度达到临界水平时，它为钙矾石晶体在C-S-H内的小孔隙中析出提供了动力。由于约束和溶液的过饱和，钙矾石的形成导致膏体膨胀。(C) 2012 Elsevier Ltd.版权所有。
The mechanisms behind the expansion of samples immersed in solutions containing sulfate ions have been controversial. Expansion is believed to originate in the formation of ettringite, but it is not possible to find any direct correlation between these two processes or to relate expansion purely to the increase in solid volume. Crystallization pressure is considered to be the most likely mechanism. A key aspect of this mechanism is the existence of supersaturation in the solution with respect to the growing crystal and it is not possible to directly measure the composition of the pore solution at different points within the specimen.In this paper we present a refinement of the crystallization pressure hypothesis to explain sulfate related expansion. We provide evidence that expansion is related to the transformation of monosulfate crystals embedded in the C-S-H to ettringite. Initially incoming sulfate reacts with aluminate containing hydrates in large pores to give ettringite without expansion. During this process the composition of the solution is buffered by the precipitation of solids so the rate of ingress does not depend strongly on the solution composition. After all this "freely available" aluminate has reacted, the concentration of sulfate ions in the pore solution increases, as indicated by the rise of sulfate absorbed on C-S-H. When the solution concentration reaches a critical level it provides the driving force for the precipitation of ettringite crystals in small pores within the C-S-H. Due to the confinement and the supersaturation of the solution this formation of ettringite leads to expansion of the paste. (C) 2012 Elsevier Ltd. All rights reserved.