Iron mineral admixtures improve the sulfuric acid resistance of low-calcium alkali-activated cements

We investigated the sulfuric acid resistance of low-calcium alkali-activated materials (i.e., geopolymers) supplemented with an iron mineral admixture (i.e., hematite). Geopolymers without and with 5% hematite were produced at two alkali contents (Na:Al = 0.86 and 1.39). Acid degradation reactions were comprehensibly studied through three replenishes of acid. Results demonstrate that hematite is chemically active upon acid exposure yielding a short-term increase in acid neutralization capacity. Prolonged acid resistance was enhanced in high alkali content formulations with hematite. Acid exposure revealed minimal changes to mineralogy, molecular structure, and micro-scale porosity in these samples, resulting in less dealumination and silicon leaching. Thus, results indicate that the acid buffering capacity of geopolymers, specifically at higher alkali content formulations, increases due to the addition of hematite. The increased buffering capacity leads to lower degrees of dealumination of the N-A-S-H cementitious binder. These results are important as they may help explain the increased acid durability of alkali-activated materials synthesized from industrial aluminosilicate precursors (e.g., slag, fly ash, lateritic clays) that may contain iron minerals

Atomic structure and phase assemblages in novel M-(N)-A-S-H materials

This paper investigates the atomic structure and phase assemblages in new sodium-stabilized magnesium aluminosilicate hydrate (M-(N)-A-S-H) cementitious binders. Results indicate that in the absence of Ca2+, Mg2+ promotes a binder atomic structure of Si-Al tetrahedral sheets and octahedral Mg sheets with hydrated Na+ cations likely in the interlayer sites similar to trioctahedral micas (phyllosilicates). NMR studies verify the incorporation of Al in tetrahedral silicate sheets. XRD demonstrates the ability of these regions to nucleate and form zeolites (i.e., sodalite) as well as the formation of Mg-Al layered double hydroxide (LDH) phases (i.e., meixnerite), which is expected due to high concentrations of Mg and Al. TGA results indicate that M-(N)-A-S-H possesses chemically bound water and hydroxyl units similar to other Mg binders. These results evince the critical role of Mg to form unique atomic structures and durability-linked phases in low-calcium alkali-activated materials

Silica-modifying chemical admixtures for directed zeolitization of metakaolin-based alkali-activated materials

The effect of using trimethyladamantyl-ammonium hydroxide (TMAAOH) as a silica-modifying admixture to induce early-age mineralization during alkali-activation of metakaolin was investigated and reported herein. In all material formulations, the use of TMAAOH induced early-age mineralization, increased mixture stiffening in the fresh state, and lowered total heat of reaction. In activating solutions with silica moduli above unity (Ms >1.0), mineralogy results demonstrate that TMAAOH induces the nucleation and growth of metastable zeolitic phases, which correlated with increased permeability and increased plastic shrinkage of the paste. When TMAAOH was added to activating solutions with silica moduli near unity (Ms ~1.0), the controlled formation of crystalline, silica-rich faujasite was observed, which correlated with reduced permeability and lower plastic shrinkage. Together, these results demonstrate for the first time that silica-templating agents such as TMAAOH can be exploited in the deisgn of new chemical admixtures that directly influence the dynamics of zeolitization in alkali-activated materials

A preliminary study on the development and characterisation of enzymatically grafted P(3HB)-ethyl cellulose based novel composites

In the present study, a novel enzyme-based grafting of poly(3-hydroxybutyrate) [P(3HB)] onto the ethyl cellulose (EC) as a backbone polymer was developed under a mild and ecofriendly environment and laccase was used as a grafting tool. The resulting composites were characterised using various instrumental and imaging techniques. The high intensity of the 3,358 cm−1 band in the FTIR spectra showed an increase of hydrogen–bonding interactions between P(3HB) and EC at that distinct wavelength region. The morphology was examined by scanning electron microscopy, which showed the well dispersed P(3HB) in the backbone polymer of EC. X-ray diffraction pattern for P(3HB) showed distinct peaks at 2-theta values of 28°, 32°, 34°, 39°, 46°, 57°, 64°, 78° and 84°. In comparison with those of neat P(3HB), the degree of crystallinity for P(3HB)-g-EC decreased. The tensile strength, elongations at break and Young’s modulus of P(3HB)-g-EC reached the highest levels in comparison to the film prepared with pure P(3HB) only, which was too brittle to measure any of the above said characteristics. Results obtained in the present study suggest P(3HB)-g-EC as a potential candidate for various biotechnological applications, such as tissue engineering and packaging