An In-situ 3 D Micro-XRD Investigation of Water Uptake by Alkali-Silica-Reaction 1 ( ASR ) Product 2 3

21 The ASR products in concrete have various chemical compositions. It is yet unclear whether 22 and how these products develop micro-expansion upon moisture ingress. This paper presents a 23 3D in-situ observation of the crystallography and volume change of an ASR-product-filled vein, 24 under varying relative-humidity (R.H.). The vein was observed to contain two nano-crystalline 25 This document is the accepted manuscript version of the following article: Geng, G., Barbotin, S., Shakoorioskooie, M., Shi, Z., Leemann, A., Sanchez, D. F., ... Dähn, R. (2021). An in-situ 3D micro-XRD investigation of water uptake by alkali-silica-reaction (ASR) product. Cement and Concrete Research, 141, 106331 (8 pp.). https://doi.org/10.1016/j.cemconres.2020.106331 This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ 2 phases with distinct basal spacings, and distribute heterogeneously in space. When R.H. 26 changed from 10% to >38%, the basal spacing increased from 7.43Å to 8.89Å for one phase, 27 whereas remained constant (~10.9Å) for the other. This is the first time that an ASR product is 28 observed in-situ to exhibit crystal structural expansion during wetting process. However, the 29 product-filled vein exhibited no noticeable swelling when R.H. varied from 10% to 97%. Our 30 findings provide the first direct evidence that the moisturization-induced crystal structural 31 change of ASR product may not be a plausible explanation to the macroscale concrete 32 expansion. 33 34