Characterization of the Bonds Developed between Calcium Silicate Hydrate and Polycarboxylate-Based Superplasticizers with Silyl Functionalities
KAUST DepartmentImaging and Characterization Core Lab
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AbstractMajor developments in concrete technology have been achieved with the use of polycarboxylate-based superplasticizers (PCEs) to improve the concrete rheology without increasing the mix water content. Currently, it is possible to control the fluidity of the fresh concrete and obtain stronger and more durable structures. Therefore, there is a strong incentive to understand the interactions between PCEs and cement hydrates at the atomic scale to design new customized functional PCEs according to the ever-increasing requirements of the concrete industry. Here, the bonding types generated between a PCE with silyl functionalities (PCE-Sil) and a synthetic calcium silicate hydrate (C-S-H) are analyzed using XRD, 29Si NMR spectroscopy, and synchrotron-based techniques, such as NEXAFS and EXAFS. The results indicated that the carboxylic groups present in PCE-Sil interact by a ligand-type bond with calcium, which modified not only the symmetry and coordination number of the calcium located at the surface of C-S-H but also the neighboring silicon atoms of the C-S-H. In addition, the silyl functionalities of the PCE-Sil generated covalent bonds through siloxane bridges between the silanol groups of PCE-Sil and the nonbonding oxygen located at the dimeric sites in C-S-H, forming new bridging silicon sites and subsequently increasing the silicate polymerization.
CitationOrozco CA, Chun BW, Geng G, Emwas AH, Monteiro PJM (2017) Characterization of the Bonds Developed between Calcium Silicate Hydrate and Polycarboxylate-Based Superplasticizers with Silyl Functionalities. Langmuir 33: 3404–3412. Available: http://dx.doi.org/10.1021/acs.langmuir.6b04368.
SponsorsResearch done at the Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. This research was funded by the Republic of Singapore’s National Research Foundation through a grant to the Berkeley Education Alliance for Research in Singapore (BEARS) for the Singapore-Berkeley Building Efficiency and Sustainability in the Tropics (SinBerBEST) Program. BEARS has been established by the University of California, Berkeley as a center for intellectual excellence in research and education in Singapore. We thank Erich D. Rodríguez (CNPq BJT Grant No. 406684/2013-8), Marlon Longhi (UFRGS), and Flavio C. Vicentin (Brazilian Synchrotron Light Laboratory, LNLS) for performing Ca k-edge XAS experiments at LNLS (Brazilian Synchrotron Light Laboratory) funded by Grant Nos. SXS-17805 and SXS-18902. C.A.O. thanks the Colciencias-Fulbright Fellowship for the financial support for graduate studies at UC Berkeley. Finally, we want to thank Dr. Lynne Batchelder of GRACE & Co. for the 1H NMR data analysis.
PublisherAmerican Chemical Society (ACS)