Assessment of electrophoresis and electroosmosis in construction materials: effect of enhancing electrolytes and heavy metals contamination

Electrokinetic effects are those that take place by application of an electric field to porous materials, with the zeta potential as the key parameter. Specifically, in the case of contaminated construction materials, the generation of an electroosmotic flux, with the corresponding dragging due to water transport, is a crucial mechanism to succeed in the treatment of decontamination. Therefore, it is of great interest trying to optimize the treatment by the addition of specific electrolytes enhancing the electrokinetic phenomena. Most of the data of zeta potential found in literature for construction materials are based in micro-electrophoresis measurements, which are quite far of the real conditions of application of the remediation treatments. In this paper, electrophoretic and electroosmotic experiments, with monolithic and powdered material respectively, have been carried out for mortar, brick and granite clean and contaminated with Cs, Sr, Co, Cd, Cu and Pb. The electrolytes tested have been distilled water (DW), Na2–EDTA, oxalic acid, acetic acid and citric acid. The zeta potential values have been determined through the two different techniques and the results compared and critically analysed

Phase evolution of C-(N)-A-S-H/N-A-S-H gel blends investigated via alkali-activation of synthetic calcium aluminosilicate precursors

Stoichiometrically-controlled alkali-activated pastes containing calcium-(sodium) aluminosilicate hydrate (C-(N)-A-S-H) and sodium aluminosilicate hydrate (N-A-S-H) gels are produced by alkali-activation of high-purity synthetic calcium aluminosilicate powders. These powders are chemically comparable to the glass in granulated blast furnace slag, but without interference from minor constituents. The physiochemical characteristics of these gels depend on precursor chemical composition. Increased Ca content of the precursor promotes formation of low-Al, high-Ca C-(N)-A-S-H with lower mean chain length as determined by quantification of solid state nuclear magnetic resonance spectra, and less formation of calcium carboaluminate ‘Alumino-ferrite mono’ (AFm) phases. Increased Al content promotes Al inclusion and reduced crosslinking within C-(N)-A-S-H, increased formation of calcium carboaluminate AFm phases, and formation of an additional N-A-S-H gel. Small changes in precursor composition can induce significant changes in phase evolution, nanostructure and physical properties, providing a novel route to understand microstructural development in alkali-activated binders and address key related durability issues

Composition-solubility-structure relationships in calcium (alkali) aluminosilicate hydrate (C-(N,K-)A-S-H)

The interplay between the solubility, structure and chemical composition of calcium (alkali) aluminosilicate hydrate (C-(N,K-)A-S-H) equilibrated at 50 °C is investigated in this paper. The tobermorite-like C-(N,K-)A-S-H products are more crystalline in the presence of alkalis, and generally have larger basal spacings at lower Ca/Si ratios. Both Na and K are incorporated into the interlayer space of the C-(N,K-)A-S-H phases, with more alkali uptake observed at higher alkali and lower Ca content. No relationship between Al and alkali uptake is identified at the Al concentrations investigated (Al/Si ≤ 0.1). More stable C-(N,K-)A-S-H is formed at higher alkali content, but this factor is only significant in some samples with Ca/Si ratios ≤1. Shorter chain lengths are formed at higher alkali and Ca content, and cross-linking between (alumino)silicate chains in the tobermorite-like structure is greatly promoted by increasing alkali and Al concentrations. The calculated solubility products do not depend greatly on the mean chain length in C-(N,K-)A-S-H at a constant Ca/(Al + Si) ratio, or the Al/Si ratio in C-(N,K-)A-S-H. These results are important for understanding the chemical stability of C-(N,K-)A-S-H, which is a key phase formed in the majority of cements and concretes used worldwide

Examination of alkali-activated material nanostructure during thermal treatment

The key nanostructural changes occurring in a series of alkali-activated materials (AAM) based on blends of slag and fly ash precursors during exposure to temperatures up to 1000 °C are investigated. The main reaction product in each AAM is a crosslinked sodium- and aluminium-substituted calcium silicate hydrate (C-(N)-A-S-H)-type gel. Increased alkali content promotes the formation of an additional sodium aluminosilicate hydrate (N-A-S-(H)) gel reaction product due to the structural limitations on Al substitution within the C-(N)-A-S-H gel. Heating each AAM to 1000 °C results in the crystallisation of the disordered gels and formation of sodalite, nepheline and wollastonite. Increased formation of N-A-S-(H) reduces binder structural water content after thermal treatment and correlates closely with previous observations of improved strength retention and reduced microcracking in these AAM after heating to 1000 °C. This provides new insight into thermally induced changes to gel atomic structure and thermal durability of C-(N)-A-S-H/N-A-S-H gel blends which are fundamental for the development of new fire-resistant construction materials

Solid-state nuclear magnetic resonance spectroscopy of cements

Cement is the ubiquitous material upon which modern civilisation is built, providing long-term strength, impermeability and durability for housing and infrastructure. The fundamental chemical interactions which control the structure and performance of cements have been the subject of intense research for decades, but the complex, crystallographically disordered nature of the key phases which form in hardened cements has raised difficulty in obtaining detailed information about local structure, reaction mechanisms and kinetics. Solid-state nuclear magnetic resonance (SS NMR)spectroscopy can resolve key atomic structural details within these materials and has emerged as a crucial tool in characterising cement structure and properties. This review provides a comprehensive overview of the application of multinuclear SS NMR spectroscopy to understand composition–structure–property relationships in cements. This includes anhydrous and hydrated phases in Portland cement, calcium aluminate cements, calcium sulfoaluminate cements, magnesia-based cements, alkali-activated and geopolymer cements and synthetic model systems. Advanced and multidimensional experiments probe 1 H, 13 C, 17 O, 19 F, 23 Na, 25 Mg, 27 Al, 29 Si, 31 P, 33 S, 35 Cl, 39 K and 43 Ca nuclei, to study atomic structure, phase evolution, nanostructural development, reaction mechanisms and kinetics. Thus, the mechanisms controlling the physical properties of cements can now be resolved and understood at an unprecedented and essential level of detail

INTERACTION DES SILICATES DE CALCIUM HYDRATES (C-S-H), PRINCIPAUX CONSTITUANTS DU CIMENT, AVEC LES CHLORURES D'ALCALINS. ANALOGIE AVEC LES ARGILES

CE TRAVAIL, S'INSCRIVANT DANS LE CADRE D'UNE ETUDE PLUS GENERALE SUR LA STRUCTURE ET LA REACTIVITE DU CIMENT, EST CONSACRE A L'ANALYSE EXPERIMENTALE ET THEORIQUE DE L'INTERACTION DES CHLORURES D'ALCALINS AVEC LES SILICATES DE CALCIUM HYDRATES (C-S-H), PRINCIPAUX CONSTITUANTS DE LA PATE DE CIMENT. L'INTERACTION DES ALCALINS AVEC LES C-S-H EST DE TYPE INTERFACIAL, METTANT EN JEU DES MECANISMES ELECTROSTATIQUES ET DE COMPLEXATION DE SURFACE. LA SURFACE DES C-S-H EST CONSTITUEE DES SITES SILANOL, PARTIELLEMENT DISSOCIES EN RAISON DU PH FORTEMENT BASIQUE DE LA SOLUTION INTERSTITIELLE. LES IONS CALCIUM, PRESENTS EN GRANDE QUANTITE DANS LA SOLUTION D'EQUILIBRE DES C-S-H, CONSTITUENT DES IONS DETERMINANT LE POTENTIEL POUR LA SURFACE DES C-S-H. LES IONS ALCALINS SEMBLENT ENTRER EN COMPETITION AVEC LE CALCIUM POUR CES MEMES SITES DE SURFACE. LES ISOTHERMES D'ADSORPTION MONTRENT QUE LE CESIUM PRESENTE UNE MEILLEURE AFFINITE QUE LE SODIUM ET LE LITHIUM POUR LA SURFACE DES C-S-H. PAR AILLEURS, LA RMN DU SOLIDE SUGGERE QUE LE CESIUM FORME AVEC LES SITES DE SURFACE DES COMPLEXES DE SPHERE INTERNE, ALORS QUE LE SODIUM SEMBLE CONSERVER SA SPHERE D'HYDRATATION. CES RESULTATS SE CORRELENT AVEC DES MESURES DE POTENTIEL ZETA, QUI LAISSENT SUPPOSER UNE ADSORPTION SPECIFIQUE DES IONS CESIUM, ET UN COMPORTEMENT INDIFFERENT DES DEUX AUTRES ALCALINS. UNE MODELISATION DE LA SURFACE DES C-S-H A ETE POSSIBLE A L'AIDE D'UN MODELE DE DOUBLE COUCHE ELECTRIQUE, AINSI QUE DE LOIS D'ACTION DE MASSE TRADUISANT LA COMPLEXATION DES DIFFERENTS IONS AVEC LES SITES SILANOL. L'ETUDE DANS SA GLOBALITE REPOSE SUR UNE ANALOGIE STRUCTURALE AVEC LES SMECTITES, ARGILES PRESENTANT DES PROPRIETES RECONNUES D'ADSORPTION DE CATIONS. LA SIMILITUDE STRUCTURALE ENTRE LES DEUX MINERAUX S'ACCOMPAGNE DE CERTAINES SIMILITUDES DE REACTIVITE, BIEN QUE DES DIFFERENCES SIGNIFICATIVES DE COMPORTEMENT PUISSENT EGALEMENT ETRE NOTEES.DIJON-BU Sciences Economie (212312102) / SudocSudocFranceF