The Influence Of Alkali On The Interfacial Transition Zone Of Concrete

Concrete durability has been a major research topic of concrete materials science, and also a major scientific and technological problem to the engineering. Besides, it is closely related to national economy, social stability, environmental protection and sustainable development. However, interface problems and alkali - aggregate reaction (AAR) are two major factors affecting concrete durability, thus studying these two factors and identifying intrinsic links between the two factors have a great significance on the solution of concrete durability from the nature.In this paper, through the use of highly active zeolitezation perlite aggregate mixed with a different proportion of alkali, a research on the characteristics of interfacial transition zone (ITZ) in the potential alkali-silica environment has been studied, and the paper has summed up the influence of alkali on different water-cement ratio, active aggregate concrete ITZ. Meanwhile, as a kind of reference, it studys the influence of alkali on different water-cement ratio and non- active aggregate concrete ITZ composition and microstructure.The experimental results show that the ordinary concrete has those regulations as follows: In the ITZ, with the increase of alkali content, the size of CH crystal decreases, the number of AFt reduces, CH crystal orientation index decreases, and the microhardness of aggregate, ITZ and cement matrix become smaller. While with the increase of surfacial distance away from aggregate, both the size of CH crystal and CH crystal orientation index decrease. And in ITZ, the concentration phenomenon of the chemical elements as K, Si, Al does exist. With using the same alkali content, as the water-cement ratio increases, the width of ITZ increases, the number as well as the size of CH crystals increase, and CH crystal orientation index increases. And, high-alkaline with low water-cement ratio do harm to concrete, easy producing cracks in the interface and reducing bonding properties of the interface. However, as for potential alkali-silica reaction(ASR) concrete in ITZ, with the increase of alkali content, the width of ITZ becomes narrower, both the size of CH crystal and CH crystal orientation index decrease, the microhardness value of ITZ increases, the interfacial properties is improved, but the microhardness of cement matrix affected by alkali reduces. With the increase of surfacial distance away from the aggregate, both the size and orientation index of CH crystal do decrease, but Ca / Si increases. Elements as Si, Al, Na, K concentrate in one side of active aggregate, thus forming the phenomenon of "duplex interface". Meanwhile, with using the same alkali content, as the increase of water-cement ratio, the width of ITZ,the size of CH crystal and CH crystal orientation index increase, while the microhardness of ITZ and cement matrix becomes smaller. Finally, the following results have been found in ITZ through the comparison between the potential ASR concrete and ordinary concrete: under the conditions of high-alkali, the level of non-activity aggregate concrete reaction is lower than the activity aggregate concrete, while under the same conditions, the size of CH crystal and CH crystal orientation index are both smaller than those of ordinary concrete in the potential ASR concrete ITZ.The results show that: the potential ASR concrete ITZ not only has the characteristics of ordinary concrete ITZ, but also has its own properties. In this paper, through the use of high alkali and high activity zeolitezation perlite aggregate creating the interfacial environment of high alkali and rich silica, the intrinsic links between the interface problems and AAR has been studied, thus providing a new perspective and theoretical basis for the research on ASR and the deep analysis of mechanism and inhibiting mechanism of ASR with using the theory of interfacial physical chemistry.