Makoto MURANAKA
Development of Physical and Chemical Model for Concrete Expansion due to ASR based on Reaction Mechanism
Takumi SHIMOMURA
As present, chemical method and mortar-bar method are used as the evaluation test of alkali-silica reactivity of aggregate. On the other hand, the number of cases that alkali-silica reactivity has not beenĦĦevaluated according to existing standard is increasing recently. Existing standard can evaluate the reactivity under the limited conditions. To solve this problem, we tried to establish the evaluation method for ASR expansion. First objective of this study is to develop the prediction model that can evaluate alkali-silica reactivity quantitatively in a short time.
ASR often continues to react during several decades in real structures. Because expansion of concrete due to ASR is restrained by reinforcement and external force in real structures, the expansion behavior under the restraint condition should be studied. Second objective of this study is to develop the analytical model that can predict the ASR expansion under the restraint condition.
As first step of this study, the Modified U.F.O. model, which was developed mainly for mortar, were applied to concrete material. As a result, it is cleared that this model was not applicable to concrete, and three issues to be solved were derived.
As second step, experimental and analytical investigations were carried out as to these issues. Through these investigations, we developed numerical model for the reaction rate of reactive aggregate under alkaline condition. We also developed the numerical model for initial alkali consumption by reactive aggregate. Through the numerical study, we found that the diffusion of alkaline ion in mortar layer influences on reaction rate on the surface of reactive gravel. We modified our numerical model reflecting on these analytical and numerical results. Then, we verified modified model with several test results.
As final step of this study, we developed unique ASR expansion model which takes into account the influence of reinforcement ratio. The higher the reinforcement ratio is, the smaller the ASR expansion is. We assumed that part of alkali silica gel leaks into micro pores under restraint condition. Reflecting on this assumption, we developed the expansion model with pore volume distribution density function. By comparing with experimental results, our new model was verified to predict the expansion of reinforced concrete due to ASR.
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