Lubica Gáliková

Changes of thermal events of macrodefect-free (MDF) cements due to the deterioration in the moist atmosphere ☆

Sulfoaluminate ferrite belite (SAFB) clinker premixed with Portland cement in mass ratio 85:15 was combined with hydroxypropylmethyl cellulose (HPMC) or sodium poly-phosphate (poly-P) for the macrodefect-free (MDF) process and subsequent moisture treatment. Mass changes as the measure of the moisture resistance and thermoanalytical traces of MDF cements gave useful information. The mass change depends more on the humidity than on the composition (polymer and inorganic constituents) of the MDF cement or duration of the original MDF cement synthesis. The values of mass changes at 100% relative humidity (RH) and at ambient conditions are affected by the nature of the polymer, poly-P being highly advantageous. Attack by environmental water and carbon dioxide increases the contents of C4(A,F)SH12(AFm) and CaCO3, represented by thermogravimetry (TG) effects at 250°C and differential thermal analysis (DTA) peaks at 600–700°, respectively. In contrast, the quantity of cross-linking, where the decomposition of Al(Fe)–O–C(P) bonds typically produces TG–DTA effects at 250–550°C, remains intact during the moisture attack.

Attack by Moisture on Advanced Cement-Based Macroscopic Defect-free Materials A Thermoanalytical Study

When exposed to attack by moisture, macroscopic defect-free materials (MDFs) undergo mass and phase changes. The nature of such changes was studied thermoanalytically. Attacked samples differ from non-attacked samples in the degradation of classical cement hydrates (TG, below 200°C) and calcium carbonate (TG, DTA, 550-650°C). Quantitative assessment favours the hypothesis of the impregnation/barrier effect due to the incorporation of polyphosphate glass into the structure of the MDFs. The identity of the thermal decomposition of attacked and non-attacked samples in the range 250-400°C demonstrates the resistance of cross-linked sections of polymer and clinker constituents to the effects of moisture.

Model MDFs related to sulfobelitic systems: Studies by 57Fe Mössbauer and electrical impedance techniques

New studies of the MDF-processibility of particular components of potential sulfobelitic clinkers in combination with hydroxypropylmethyl cellulose (hpmc) and/or polyphosphates (poly-P) are presented. The involvement of AlFe, P and C atoms in chemical cross-links within amorphous AFm -like reaction products in several subsystems of a complex sulfobelitic clinker/polymer system is examined by (i) 57Fe Mossbauer spectroscopy (to investigate Fe-atom local environments) and (ii) electrochemical impedance measurements (to characterize conductivity variations). FeIII atoms are octahedrally coordinated by oxygens in their first coordination sphere, with some replacement of H atoms by C or P atoms in the second coordination sphere, forming cross-links of the type AlFe — O — CP in hydrated products. Impedance spectra were typical of electronically- insulating materials functioning as solid electrolytes, with conductivity values depending on polymer/gel composition as well as on temperature.

Studies of model macroscopic-defect-free materials. Part 1.—Investigations of the system 4CaO · Al2O3· Fe2O3–4CaO · 3Al2O3· SO3–hpmc–H2O by X-ray, thermoanalytical and NMR techniques

Model macroscopic-defect-free (MDF) materials representing selected compositions in the system 4CaO · Al2O3· Fe2O3–4CaO · 3Al2O3· SO3–hpmc–H2O have been prepared, with a variety of water-to-solid ratios and reactions quenched at varying times. Product mixtures were examined by analytical X-ray powder diffraction, thermal analyses and 27Al MAS NMR spectroscopy. Inhibition of crystallisation of hydrated products and elevated temperatures for thermal transformations of those products occur in materials prepared under MDF processing conditions, which incorporate organopolymer (hpmc, hydroxypropylmethylcellulose) into an amorphous hydrated product. Al–O–C crosslinks can be invoked to explain the 27Al spectra, and also the elevation in temperatures of thermal events.

Chemistry for the design and better understanding of cement-based materials and composites

Macrodefect-free (MDF) materials are one example of “hot topics” in the field of cement-based materials and composites exerting new possibilities of the exploitation of added value. These are formed through cross-linking reactions of atoms at the interfaces of cement grains and functional polymers, when medium pressure and twin-rolling procedure are applied. The MDF-relevance of the system of Portland cement + polyphosphate is reported, together with optimal synthesis conditions and limiting rules. The chemistry knowledge about MDF materials has been shown critical for both procedure design and exploitation. Chemical shifts in both 27Al and 31P MAS NMR spectra confirm Al(6)—O—P(4) cross-linking in virgin probes and indicate secondary hydrolysis during moisture uptake in domains free of cross-links. Thermogravimetric identification of the contents of hydrated and cross-linked phases in virgin and in moisture-attacked MDF probes displays that moisture uptake is accompanied by an increase in content of cementitious hydrates and CaCO3. The key phenomena governing the moisture sensitivity/resistance are the density and compactness of interfacial Al(6)—O—P(4) cross-links vs. the access of the moist environment to the unreacted cement residue.

Cross-linking of atoms and thermal stability of new MDF compositions

We have summarized Al, Fe, C and P atoms incorporations within cross-linking interaction and location of those after MDF procedure of sulphobelitic clinker — hydroxypropylmethyl cellulose (hpmc) — sodium salt of polyphosphates (poly-P) compositions. Design of Al/Fe-O-C/P cross links is given and discussed. Thermoanalytical patterns (i) give the evidence of the presence of polymers in the reaction products and (ii) confirm the linkages of solidified polymers throughX=C or P of Al/Fe-O-X cross links in interphase regions with decomposition temperature interval higher than this in classical hydraulic materials. Designed local structure of interphase regions gives atomic level explanation of the densification of a bulk, its microstructure and exceptional technological properties. Similar phenomenon has been reported for the high aluminium — polyvinylalcohol/acetate MDF compositions. Moreover, variant clinker as well as polymers employed in syntheses represent one of the proposals aimed to the increase of the moisture resistence; our results are in the power of the above alternative for phases of sulphobelitic clinker.

Studies of model macroscopic-defect-free materials. Part 2.—Microstructure and open porosity in the system 4CaO·Al2O3· Fe2O3–4CaO·3Al2O3· SO3–hpmc–H2O

Model macroscopic-defect-free materials (MDFs) representing selected compositions in the system 4CaO · Al2O3· Fe2O3–4CaO · 3Al2O3· SO3–hmpc–H2O have been investigated by means of electron microscopy and mercury intrusion porosimetry. ‘Smooth spatial flow’ of unreacted grains into an intergranular hydrated-aluminium-monosulfate-related (AFm-like) phase and rigid linkage of clinker phase–intergranular mass–solidified polymer are demonstrated. Solidification of an intergranular Afm–like phase in the presence of hpmc and pressure during syntheses causes partial elimination of pores; electron microscopy shows the remaining pores to be isolated at the micrometre level. Pore size distributions reveal the role of pressure in packing the pores with diameter r > 100 nm. Careful control of the mixing and pressing of reaction mixtures results in porosities in the range typical of MDFs. A scheme interrelating the atomic- and particle-level phenomena is outlined, and includes formation of Al(Fe)–O–C crosslinks between cement clinker and polymer.

Macro-defect-free materials with controlled moisture resistance

The latest research on the reactivity toward cross-linking of inorganic matrixes formed by cement-based materials, and the associated grafting at the nanoscopic and atomic levels, is highly promising. Macro-defect-free (MDF) materials and technologies were originally comprised of high-alumina cements cross-linked to poly(vinyl alcohol/acetate) or of portland cement with poly(acrylamide). Although the high-alumina system has shown promising results and is the more efficient system, it suffers from economic disadvantages; modern efforts to identify MDF systems focus on portland cement and a variety of polymer additives. We report recent findings regarding the potential and limitations of portland cement-based MDF materials, considering aspects of the associated chemistry (at the nanoscopic and atomic levels), of the mechanism linking polymer to the surface of cement grains, and of technologically relevant attributes such as moisture resistance of the formed MDF material.