Abstract
This work aims at providing a better understanding of the mechanical properties of the reaction rim in the alkali-silica reaction. The elastic modulus of the calcium alkali silicate constituting the reaction rim, which is formed at the interface between alkali silicate and Ca(OH)2 in a chemically-idealized system of the alkali-silica reaction, was studied using nano-indentation. In addition, the corresponding calcium to silica mole ratio of the calcium alkali silicate was investigated. The results show that the elastic modulus of the calcium alkali silicate formed at the interface increased with the increase of the calcium to silica mole ratio and vice versa. Furthermore, the more calcium that was available for interaction with alkali silicate to form calcium alkali silicate, the higher the calcium to silica mole ratio and, consequently, the higher the elastic modulus of the formed calcium alkali silicate. This work provides illustrative evidence from a mechanical point of view on how the occurrence of cracks due to the alkali-silica reaction (ASR) is linked to the formation of the reaction rim. It has to be highlighted, however, that the simplified calcium-alkali-silicate system in this study is far from the real condition in concrete.
Highlights
The alkali-silica reaction (ASR) is a common durability problem affecting concrete structures.It contains a series of chemical and physical interactions between the reactive silica in the aggregates and the pore solution of the cement paste resulting in a slow, but severe expansive deterioration of the concrete
The most recent one is the reaction rim theory from Ichikawa et al in 2007 [6], linking the uncommon occurrence of the reaction rim in the ASR-affected concrete with the generation and accumulation of the interior expansive force. According to this model [6,7], which is schematically shown in Figure 1, the reaction rim develops by the formation and accumulation of calcium alkali silicate, which forms due to the interaction between alkali silicate and Ca2+ at the interface between the aggregate and the cement paste
Ca(OH)2 in a chemical model in our prior work, the elastic modulus of the calcium alkali silicate constituting this idealized reaction rim was investigated in this study
Summary
The alkali-silica reaction (ASR) is a common durability problem affecting concrete structures.It contains a series of chemical and physical interactions between the reactive silica in the aggregates and the pore solution of the cement paste resulting in a slow, but severe expansive deterioration of the concrete. ASR has been studied for several decades since it was firstly spotted in the 1940s, the mechanism of the generation and accumulation of the interior force at the micro scale causing the expansion and cracking of a concrete structure at the macro scale is still unclear Regarding this issue, many theories and models have been proposed [1,2,3,4,5]. The most recent one is the reaction rim theory from Ichikawa et al in 2007 [6], linking the uncommon occurrence of the reaction rim in the ASR-affected concrete with the generation and accumulation of the interior expansive force According to this model [6,7], which is schematically shown, the reaction rim develops by the formation and accumulation of calcium alkali silicate, which forms due to the interaction between alkali silicate and Ca2+ at the interface between the aggregate and the cement paste. Once the reactive silica particle is completely covered by the reaction rim, the reaction rim is able to behave as a semi-permeable membrane to prevent the extrusion of alkali silicate out of the reaction site while allowing the penetration of alkaline solution to attack the reactive silica and Materials 2016, 9, 787; doi:10.3390/ma9090787 www.mdpi.com/journal/materials generate alkali alkali silicate silicate continuously; continuously; see see Figure
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