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Instruments / Technical Area	Publication Details	Published	Actions
I15-Extreme Conditions	Mechanical behavior and phase change of alkali-silica reaction products under hydrostatic compression Guoqing Geng , Zhenguo Shi , Andreas Leemann , Konstantin Glazyrin , Annette Kleppe , Dominik Daisenberger , Sergey Churakov , Barbara Lothenbach , Erich Wieland , Rainer Daehn Acta Crystallographica Section B Structural Science, Crystal Engineering And Materials 76, 674 - 682 DOI: 10.1107/S205252062000846X Diamond Proposal Number(s): [18643] Show Abstract ▼ Abstract: Alkali-silica reaction (ASR) causes severe degradation of concrete. The mechanical property of the ASR product is fundamental to the multiscale modeling of concrete behavior over the long term. Despite years of study, there is a lack of consensus regarding the structure and elastic modulus of the ASR product. Here, ASR products from both degraded field infrastructures and laboratory synthesis were investigated using high-pressure X-ray diffraction. The results unveiled the multiphase and metastable nature of ASR products from the field. The dominant phase undergoes permanent phase change via collapsing of the interlayer region and in-planar glide of the main layer, under pressure >2 GPa. The bulk moduli of the low- and high-pressure polymorphs are 27±3 and 46±3 GPa, respectively. The laboratory-synthesized sample and the minor phase in the field samples undergo no changes of phase during compression. Their bulk moduli are 35±2 and 76±4 GPa, respectively. The results provide the first atomistic-scale measurement of the mechanical property of crystalline ASR products.	Aug 2020
I15-Extreme Conditions	Influence of decalcification on structural and mechanical properties of synthetic calcium silicate hydrate (C-S-H) Lin Liu , Can Sun , Guoqing Geng , Pan Feng , Jiaqi Li Cement And Concrete Research 123 DOI: 10.1016/j.cemconres.2019.105793 Diamond Proposal Number(s): [18643] Show Abstract ▼ Abstract: Decalcification causes critical degradation of calcium silicate hydrate (C-S-H) – the principal binder in concrete. Contrary to structural change, the decalcification-induced change of C-S-H mechanical properties has not been sufficiently investigated. To fill this gap, here C-S-H was synthesized and decalcified using NH4NO3 solutions. It was then subjected to chemical analysis and high pressure X-ray diffraction study. Our results indicate that C-S-H decalcifies only in the interlayer which reduces its stiffness along the c-axis. The incompressibility and the transverse isotropy remain unchanged for the calcium silicate main layer, despite the vast change of silicate chain linkage. The intralayer Ca does not leach as long as C-S-H maintains the tobermorite-like structure. A ~30% reduction of bulk modulus is estimated for decalcified C-S-H. Our results add fundamental knowledge to the structure-property correlation of C-S-H subjected to decalcification.	Sep 2019

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