Structure and nanomechanical characterization of synthetic calcium-silicate-hydrate with poly-methacrylic acid

Abstract

The principal phase of hardened Portland cement pastes is calcium silicate hydrate (C-S-H), which influences the physical and mechanical properties of construction materials. In this work, calcium silicate hydrate (C-S-H) was synthesized, with the addition of poly-methacrylic acid with sodium (PMA), for the development of C-S-H/ polymer nanocomposites. Among the polymers available, PMA is indicated in the literature as one of those viable for producing C-S-H/polymer complexes. However, no consensus exists regarding the type of interaction this produces. The resulting compounds were characterized by XRD, FT-IR, TGA, carbon content (CHN), TEM, SEM and elastic modulus and hardness were measured by instrumented indentation. A significant change was verified in the nanomechanical properties of C-S-H with PMA, resulting in reduction in the elastic modulus and hardness. The set of results presented do not confirm the intercalation of PMA in the interlayer space of C-S-H, but presented evidence of the potential for intercalation, since changes in the microstructure clearly occurred.

Characterization of Calcium Silicate Hydrate Gels with Different Calcium to Silica Ratios and Polymer Modifications

“…Figure 7 shows the wide-angle XRD pattern of the four CSH gels, which depict the formation of the crystalline structure of CH and tobermorite. It is known that the formation of tobermorite affects surface morphology [ 25 , 26 ]. The peaks that appeared at 29°, 32°, and 49° (2θ) were associated with the tobermorite, verifying the presence of a crystalline formation in the specimens.…”

“…The Raman bands characteristics of the CSH1 at 1 day, 3 days, 7 days and 14 days, and that of the CSH3 and CSH4 at 14 days, in the frequency range of 200–1800 cm −1 , are illustrated in Figure 9 . The highest peak intensity in the spectra of all specimens was observed at the peak located at about 668 cm −1 , which can be attributed to the vibrations of Si–O–Si symmetric bending (SB) Q 2 [ 26 ]. The increasing peak intensity over time indicates the formation of additional CSH gel in the sample of the CSH1.…”

“…Although variable stoichiometry makes it difficult to accurately characterize the exact nature of its nanostructure [ 18 ], it has been reported that CSH gels have a three-dimensional atomic structure similar to naturally occurring tobermorite [ 19 ] with a layered geometry that mainly consists of calcium silicate sheets [ 20 ] containing chain units of silicates connected by calcium ions. Manipulating the CSH structure at a micro and nano scale by utilizing innovative methods such as bioinspired approaches has been the goal of numerous research efforts [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ]. Among the bioinspired structural concepts, integration of CSH with organic components has been of great interest.…”

“…Among the bioinspired structural concepts, integration of CSH with organic components has been of great interest. Different studies have been performed to evaluate the possibility of modifying the structure of CSH with polymers [ 21 , 22 , 24 , 25 , 26 , 29 , 30 , 31 , 32 ]. Khoshnazar et al [ 29 , 30 ] investigated the characteristics of CSH modified with nitrobenzoic acid and found that, at a low concentration of nitrobenzoic acid (0.01 mol per mol of Ca), the creep modulus and hardness of CSH systems can be improved.…”

“…The type of polymer and Ca/Si molar ratio of CSH are responsible for the intercalation characteristics. Likewise, Pelisser et al [ 26 , 31 ] evaluated the addition of poly (diallyldimethylammonium chloride) during CSH synthesis using a direct precipitation method and observed intercalation of the polymer within the CSH lamellae with a decreased packing density, elastic modulus and indentation. In contrast, in an investigation of CSH modifications with neutral (PVA, PVME, PEO), cationic (PDC, PVBC) and anionic (PSS) polymers by Merlin et al [ 32 ], no intercalation of polymeric molecules within the layered structure of the CSH at a nanoscale was observed.…”