Opacified glazes for sanitary porcelain
Glazes for sanitary porcelain opacified with rutile, anatase and baddeleyte were synthesized. The standard glaze (raw materials: feldspar, kaolin, quartz, calcite, dolomite and zincite) has been obtained with different opacifiers content of 3, 5 and 10 mass %. Ten compositions have been prepared by classical ceramic technology and have been applied on the green sanitary ceramic substrate. Single firing was conducted in the laboratory electric kiln at maximum temperature of 1250oC, soaking time 15 minutes. By additive formulas, depending on composition, the following properties were calculated: density after Appen (2.564-2.720 g/cm3), surface tension at 1250oC after Dietzel (368-379 dyn/cm), thermal expansion coefficient (62-69).10-7 grd-1, elasticity module (7,440-8,100 kg/mm2), refractive index 1.525-1.627 and light dispersion 0.00896-0.02683 (both after Demkina). Experimentally, the working temperature of glazes by hot-stage microscopy and the surface texture of glazes by optical microscopy in the reflected light were determined. Depending on composition, solid solutions of feldspars, α-quartz and traces of α-cristobalite and opacifiers as rutile, anatase, Ti8O15, and baddeleyte were identified by XRD. Colour characteristics have been estimated in the HunterLab system (L* a* b* C* h*, remission spectra).
Within the framework of the paper it has been pursued the obtaining of decorative faience glazes, with firing temperatures around 1150°C and a PbO content as low as possible. With this view, there have been elaborated unfritted silicate-lead-alkaline glazes using a previously prepared lead silicate, feldspar, quartz, TiO2, ZnO, kaolin, wollastonite and pigment. The lead silicate proportion has been varied between 50% and 70% and there have been obtained glazes with firing temperatures between 1120°C and 1180°C. The main crystalline phase, which provides the decorative effect, is rutile. This has been identified by X-Ray diffraction and it is clearly visible in the optical microscopy images taken in transmitted light, as needle-like crystals arranged in radial-fibrous aggregates.
Unitary Portland cement, its derived blended binders, as well as other binding systems – based on lime, activated slag etc. – can represent efficient matrices for the immobilization of the wastes containing noxious substances (especially heavy metals).
Immobilization, by solidification / stabilization, of some noxious wastes in binding matrices has to be considered mainly from two points of view: their fixing and retention capacity and the changes brought by integrated wastes to the properties of the concretes containing such binding matrices. Based on these aspects, controlled disposal of toxic compounds can be assured, by their solidification / stabilisation in binding matrices, or concrete containing waste can be used for road infrastructure.
The present paper brings information regarding the immobilization of some complex wastes, containing Zn, Cr, Cu, Pb, in binding matrices and the influences of the waste on main properties of the binders. The considered binders – of Portland cement type, slag cement and alkaline activated slag binder, shown a good immobilization capacity of the considered wastes.
Chemical activation of fly ashes
The manifestation of the pozzolanic character of fly ashes can be improved by mechanical and/or chemical activation. The paper presents the positive effect of NaOH, single or together with CaSO4∙2H2O on the Ca(OH)2 linking of a fly ash from Mintia thermal station, grinded up to a specific surface area of 5530 cm2/g Blaine. The addition of small amounts of NaOH to the fly ash-lime-gypsum system determines the acceleration of the reaction processes with water, accompanied by the formation of hydrated compounds – calcium silicates and calcium aluminate hydrates and favours the formation of resistance hardening structures.
Cement designed for repairs to concrete elements by grouting
A distinct category of repair and consolidation works to meet the needs of civil, construction & environmental engineering as well as geotechnics & environmental geotechnics consists in strengthening and consolidation by grouting. The paper presents the results of laboratory investigations regarding the obtaining of cement for repairs to concrete elements by the grouting injection technique. Ordinary Portland cement sorts with varying fineness were obtained and characterised in terms of physical and mechanical properties. The obtained cement sorts were mixed with varying ratios of superplasticizers to obtain cement grouts. The rheological properties of the cement grouts were studied by carrying out determinations of flowability and settling.
CARPATCEMENT Holding SA, the national leader on the Romanian cement market operates three cement plants: Fieni (Dambovita county), Deva (Hunedoara county) and Bicaz (Neamt county) and belongs to the German group HeidelbergCement, the forth world cement producer and the biggest investor in building materials sector in Eastern Europe
Environmental protection is essential for Carpatcement Holding and the principles of sustainable development represent the basis of entire activity of the company. Consequently, a special attention is conferred to the responsible use of resources by co-processing of waste in all three plants.
During the co-incineration of waste complying with the legal requirement concerning emissions is vital and this is the reason why a mathematic modeling and also more series of tests were performed when different types of traditional and alternative fuels were used, monitoring the entire range of pollutants from dust, SO2, NOx until heavy metals and dioxins and furans.
The modeling and the monitoring tests proved that use of alternative fuels in the rotary clinker kilns of the type existing in Carpatcement Holding does not lead to increase of air emissions.
Relations between cement grindability and the specific power consumption in grinding in tube mills
The paper presents briefly the most frequently employed laboratory methods for determining the grindability of materials expressed mostly as specific power consumption in grinding depending on the fineness of the material to be ground. To convert the specific power consumption wx in grinding in the laboratory into specific power consumption w in grinding in industrial mills, this paper presents correlation parameters between the parameters of specific power consumption in grinding, a range of grinding plants, and a reference fineness in the case of the following grinding methods: CEPROCIM, Zeisel, and Bond.
Composition - basicity percentage implications for crystallizable oxide systems
Different types of structures can be obtained in the multi-component oxide systems function of chemical composition and the processing conditions. Thus, the basicity concept and the derived factor defined as “basicity percentage” can be used for structural characterization of some different multi-component oxide systems.
The paper underlines the relationship between the compositions of a significant number of glass ceramics precursor glasses and basicity percentage.
On assume that various precursor oxide systems with different corresponding values of basicity exhibit different crystallization parameters. A model of mathematical programming, for the optimal establishment of the chemical composition and of the basicity, which allows for example maximum rates of crystallization to be achieved, were established.
From this study, certain fields resulted, for the determined values of the basicity percentage, in various vitreous systems, as precursor for glass-ceramics, based on homogenous respectively heterogeneous nucleation.
Theoretical results derived from some literature data analysis, also in the case of a series of glass-ceramics experimentally achieved, were confirmed.
Way of reducing the environmental impact posed by a waste sand dump
To eliminate the impact on the environment generated by the existence of a sand waste dump resulting from the glass manufacturing process, the possibility of using this waste in the cement manufacturing process was analyzed.
The results obtained in laboratories are presented, namely by using the sand waste as a corrective addition, on the technological process and the quality of the cement.
Based on the results obtained, the required arrangements for transport, storing and batching of the sand waste in the raw mix were set.