Abstract
Alkali-silica reaction (ASR) can cause expansion and cracking of concrete. Despite significant progress over the past 80 years, the molecular structures of the ASR products remain poorly understood. These reaction products are present in very small amounts within concrete aggregates, which severely limit their chemical and physical characterizations. In this study, synthesis of an ASR product structurally identical to that formed in field concrete is achieved in large quantities at 40 °C. The temperature is found to affect the formation of different types of crystalline ASR products: 12.0 Å (<40 °C), 10.8 Å (around 40 °C), and 13.1 Å (60–80 °C for K-shlykovite), which all have layered silicate-sheet structures. Both 10.8 and 13.1 Å ASR products cannot swell at high relative humidity. This suggests that swelling of the studied crystalline ASR products by uptake of water cannot be the mechanism of ASR-induced expansion at 40 to 80 °C. These findings help to better understand ASR in concrete and pave the way for developing innovative solutions for limiting ASR.
Highlights
For the alkali-silica reaction (ASR) product formed in field concretes, the data obtained from synchrotron-based microXRD measurements for ASR products formed in an intact vein in a concrete aggregate is used (Mels_A), where no contaminations of the ASR product by other crystalline solids are expected [12]
This suggests that the ASR product formed in the vein of aggregate in the field concrete is structurally identical to the ASR product synthesized in the laboratory at 40 °C
Some differences in the relative intensities of the XRD peaks are observed between the lab-synthesized ASR product and the ASR product formed in field concrete
Summary
Understanding the reaction mechanism and expansion of concrete caused by ASR is challenging, since it is very difficult to isolate a sufficient quantity of phase pure ASR product due to the micro-scale size and tiny amount of these products formed in the veins of concrete aggregates. This difficulty prevented the characterizations of the ASR products with various conventional lab techniques [11]
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