Investigation On The Interaction Between Aluminosilicate Dehydrated Phases And Pozzolanic Material

Reutilizing construction wastes to realize its resource recovery is one of the effective measures to conserve energy and resources and reduce environmental problems. It has been widely validated that dehydrated cement paste (DCP) exhibit rehydration reactivity. However, it exerts adverse effects on the workability of hardened paste due to the generation of massive f-CaO. Therefore, the present paper aims at taking advantage of its adverse effects.Fly ash was added as a partial replacement of dehydrated cement paste and dehydrated aerated concrete respectively at levels of 10%,20%and 30% by weight of the total cementitious material. And they were marked as DF and AF respectively. The effects of different fly ash content on the two different composite cementitious materials were studied in this project. A lot of experimental methods, such as heat of hydration, content of non-evaporable water, compressive strength and microstructure, were employed to investigate the interaction mechanism and structural formation process between different dehydrated phases and fly ash. The main results are as follows:(1) Heat treatment temperature is the main factor that impacting the reactivity of dehydrated aerated concrete (DAC). The experimental results of mineral composition analysis and mechanical properties indicate that the dehydrated phase obtained under 700℃shows relative high reactivity since lower temperatures result in incomplete dehydroxylation while higher temperatures lead to higher degree of crystallization accompanying lower reactivity. And the corresponding dehydrated products are mainly composed of P-C2S and CaO.(2) Compared with DAC, Dehydrated cement paste is more effective in exciting pozzolanic activity of fly ash. It exhibits obvious advantages in terms of mechanical performance, hydration properties and microstructure in DF system. Especially in the later hydration process, it presents potential strength development and the distinct etching mark on the surface of fly ash at 28d shows the higher degree of pozzolanic reaction. In AF system the pozzolanic is slow to start and it does not progress to any significant degree since fly ash plays a role of inert filling effect. This may be attributed to higher f-CaO content in DF system activating the pozzolanic reaction of fly ash effectively.(3) There is higher growth rate of non-evaporable water content at early age in DF system, and the amount of non-evaporable water content at 3d has reached 70% of that at 60d. Nevertheless, it goes upwards steadily in AF system. The development trends of non-evaporable water content approximately coincide with the strength development in each experimental group.