română ILEANA MOHANU, NICOLETA VLAD, GEORGE STANCIU, ROXANA FECHET
Abstract
Clinker is the basis component of Portland cement, which participate in forming of the strength structure of the binder matrix. Clinker storage in improper conditions may have as consequence modification of its characteristics and implicitly, of the cement preformaces. The work follows storage influence in uncover stockpiles of clinker and granulated furnace slag on their characteristics and on the performances of a cement type CEM II/A-S with 20% granulated furnace slag. In this way, at different periods, chemical and mineralogical investigations (X-ray diffraction, optical microscopy) are carried out. Also, hydraulic activity influence of the clinker and granulated furnace slag on physical-mechanical characteristics of the cement is presented.
Keywords
clinker, blast furnace slag, storage
MARIA GEORGESCU, GABRIELA NICULAE
Abstract
Waste derived from different industries co-processing represents a priority for cement industry in its efforts towards the sustainable development. In this respect, it becomes highly important identifying the impact of the alternative fuels use on the composition and structure of the clinker and on the cement properties.
The paper presents some investigations on some industrial clinkers produced by using a complex alternative fuel mix and a relatively high substitution rate of the traditional fuel with alternative fuels – 34 % - 60 %, in comparison with a reference clinker burnt using coal.
The investigations of the mineralogical composition by Rietveld method and of the structural and textural characteristics by electronic microscopy SEM, showed no significant difference in terms of main mineralogical compounds content and of the structure and textural appearance, between the clinker burnt with traditional fuels and the clinkers produced in the same installation, but using various types of alternative fuels and thermal substitution up to 60 %.
Keywords
waste-derived alternative fuels, clinker quality, Rietveld method, SEM
ION TEOREANU, NICOLETA DENEANU, MIRELA DULAMĂ
Abstract
There are a variety of matrix materials and commercially techniques available for conditioning organic radioactive wastes. This paper provides an overview of the application context and evolution of several important matrix materials and offers comments on the waste form requirements under disposal conditions. In this paper emphasis has been placed on the conditioning options available commercially and that have, to various degrees, been demonstrated to be viable. At the same time, it is recognized that other matrices are being researched as possible for future options. Included in these options are magnesium phosphates binding systems and mixed cement with Portland composite cement and Calcium
Keywords
composite cements, calcium aluminate cement, magnesium phosphate binding systems, organic radioactive wastes
DAN GEORGESCU, ADELINA APOSTU, GHIULGIAN MIRON
Abstract
The article presents the results of experimental researches conducted for the first time in Romania, in the Research and Testing Laboratory of Reinforced Concrete from Technical University of Civil Engineering Bucharest, Romania, in order to study the possibility to apply in Romania a new European evaluation criteria of concretes freeze-thaw resistance, concrete mixes with different cement types. Concrete freeze-thaw resistance was evaluated applying the standard methods on European level (CEN/TS 12390-9, CEN/TR 15177) depending on the calculation of the scaled material quantity and on determination of dynamic elastic modulus values of concrete samples tested on repeated standard freeze-thaw cycles. The mass reducing of the concrete samples and dynamic elastic modulus are compared with proposed limit values, depending on the situation in one of XF exposure class.
Keywords
durability, composite cement, concrete
CONSTANTIN BUDAN, DANIEL NICOLAE STOICA, ADRĂNEL MARIN COTESCU
Abstract
Reinforcement corrosion in principle is due by the slurry pH of concrete pores reduction and the presence of oxygen.
Time of occurrence of the phenomenon, as an effect on the strength characteristics, is in principle at least two years. If in the natural corrosion, the elements of monolithic concrete bear the blame is on the coverage with concrete for the reinforcement, at the precast concrete, corrosion may occur mainly due to chloride ions contained in concrete. Can be taken into account other possible causes, related to the concentration of static or dynamic external loads on the elements, the presence of lime in the concrete repair compositions or dispersion currents. Whatever the cause, the phenomena must be known and kept under control at least as concrete elements containing highly corroded reinforcement that are not apparent, can suffer significant degradation (up to collapse) in during exceptional applied loads. However, knowledge deployment of reinforcement corrosion processes contributes to improving the control of reinforced concrete, to prevent and reduce destruction.
Keywords
corrosion, reinforcement, concrete, influence factors, anticorrosive protection
ION NEAMŢU
Abstract
Compactness is a main feature of concrete tiles. Compactnessess increase influence positive mechanical resistance of tiles while reducing their permeability to water before and especially improves reaction time to gelivity processes.
To obtain greater compactness of tiles is used:
a) an aggregate (sand) with optimal characteristics;
b) the addition of ultra fine powders, hydraulic active, able to better fill the capillary and crazing pores of cement stone (fly ash);
c) the use of added superplasticising, whose complex action lead to increased growth workability concrete and concrete compactnessess.
The results clearly show that the use of sand or cement mixtures are substituted with ash from thermo present consisting advantages in better mechanical resistance, more uniform texture, better reaction to gelivity, lower cost price, and not least solveing environmental problems by using the waste ash resulting from coal combustion.
Keywords
porosity, gelivity, compactnessess, permeability, additives
DOREL RADU, ANDREEA DAVID, ZENO GHIZDĂVEŢ
Abstract
The more emphasized tendency to use alternative fuels along with the traditional ones in clinkering plants raises a series of problems regarding technological, thermo-technical, economical and environmental issues. Whereas technological and economical aspects are mostly established, from the thermo-technical point of view, not all changes that occur in a clinkering plant when one fuel is replaced by another one have been studied yet.
In present article, the second from a series of four, it is emphasized the way that certain thermo-technical parameters influence the flow and chemical composition of the hot gases exhausted into the atmosphere. The thermo-technical parameters that were taken into account were: absolute productivity, theoretical temperature, dissociation degree of some components of the hot gases and coefficient of air in excess used for the combustion.
Keywords
kilns, hot gases, dissociation, productivity, emissions
NICOLAE ANGELESCU, MARCELA MUNTEAN, CRISTINA IONIŢĂ
Abstract
The aluminous cement is the compound, which by its hydration-hydrolysis, is involved in the hardening process of the refractory concretes, under normal condition, like the consequence of hydraulic binding. A high value of aluminous cement dosage in concrete is followed by the decrease of the maximum use temperature and the depreciation of the mechanical and structural characteristics for this refractory material. The refractory concretes are widely manufactured mainly by using a common values of aluminous cement dosage (~20%). Also, there is the trend to decrease the cement dosage, at to very low limits, even up to its remove in order to improve the quality and use properties for these products. This is possible with by substitution of the aluminous cement with admixtures which are capable to develop other binding forms, next to hydraulic one. The aim of the present paper is to present the utilization possibilities of the aluminous and siliceous powders like substituents of the aluminous cement which are able to develop other binding forms, different from the hydraulic one.
Keywords
Refractory concrete, coagulation, hydraulic binding, complex binding system, admixtures, reaction activator
MARIN AMĂREANU
Abstract
The paper presents a study focused on behavior in cement concrete of the macromolecular compounds and of macromolecular compounds associated with various mineral addition materials, and their influence on hydration-hydrolysis processes, emphasizing the mechanisms related to setting and hardening of these complex binding systems. The studies are concerning the complex hardening processes of complex binding systems: Portland cement - epoxy resin - water, Portland cement - epoxy resin + hardening agent - water, Portland cement - polyvinyl acetate – water. To these binding systems, different additions (of ultrafine particles): silica fume (SF), diatomite (D), and fly ash (FA) were added.
Keywords
Polymer concrete, mechanical properties, epoxy resin, vinyl polyacetate, mineral addition materials
LIANA TEREC, TUDOR BUGNARIU, MIRCEA PĂSTRAV
Abstract
An important theoretic research program was conducted in INCERC Cluj, in order to study the strengthening technique of the low or moderate damaged reinforced concrete frame structures, one of the existing construction types susceptible to damage.
The principal objectives of the analytical studies were to analyze the behavior under seismic loads of infill walls connected to the reinforced concrete frame with bonded anchors and to evaluate the influence of several parameters, like the thickness of infill walls, the thickness of the jackets, respectively the longitudinal reinforcement ratio in the jacket of the columns.
Keywords
construction (D, d), composites (B), concrete (D, a), reinforcement (D, a), modeling (B)
KSENIJA JANKOVIC, DRAGAN BOJOVIC, DRAGAN NICOLIC
Abstract
By using crushed brick as aggregate, the structure of concrete can be effectively modeled and materials with very different physical-mechanical characteristics can be obtained. Determination of the influence of polymer admixture on some modified concrete properties is shown in this paper. Experimental work included several types of concrete made with different cement content (250 or 350 kg/m3), and same consistency (slump about 5 cm). Few types of concrete made with 4% admixture of polymer (dry material) by weight of cement. Recycled brick or combination of river sand and recycled brick were used as aggregates. Results of determination of concrete compressive and bending strength, modulus of elasticity, coefficient of thermal conductivity, resistance to freezing-thawing, water permeability, shrinkage and creep, and stress - strain diagram were observed.
Keywords
lightweight concrete, recycled bricks, polymer, mechanical-rheological properties
MARIA GEORGESCU, NASTASIA SACA, GEORGETA VOICU
Abstract
The behaviour of the blended cements containing limestone filler exposed to corosive environment is important for the durability of the concretes made with such of binders. The paper brings information regarding the behaviour of some blended cements containing Portland cement with 10-40% limestone filler additions in contact with a 5% MgCl2 solution.
The interaction processes between the binding matrices and MgCl2 solution were assessed by XRD analysis and scanning electron microscopy (SEM). New types of hydrates are formed as a result of these processes.
The interaction processes take place gradually from the surface of the samples to their inside, and determines compositional and structural differences between the two zones.
The changes determined by the chemical processes in the composition of the mortar samples in contact with MgCl2 solution have negative consequences on their mechanical strengths, more important after longer periods of time. The behaviour of the blended cement containing 10% limestone filler exposed to MgCl2 solution is similarly to those of Portland cement.
Keywords
limestone filler cements, chemical stability, electronic microscopy analysis, mechanical strength
ALINA BĂDĂNOIU, GEORGETA VOICU
Abstract
The paper presents data regarding the freeze-thaw resistance of mortar specimens based on binary and ternary blended cements with limestone filler, slag or volcanic tuff additions in the presence/absence of de-icing salt (NaCl). Mortar’s degradation process was assessed visually and by compressive strength tests. The nature and microstructure of the hydrates present in mortar specimens subjected to freezing-thawing cycles were assessed by SEM microscopy. Mortars based on binary blended cements with slag or fly ash had a better frost resistance, in presence of de-icing salt, as compared with the mortar specimens with limestone filler content. The use of ternary blended cements (with limestone filler and slag or volcanic tuff) combined with a complex admixture (fluidizer and air-entrained) for mortars preparation, improves freeze-thaw resistance, as compared with mortars based on blended cement with limestone filler and, in some cases, on normal Portland cement.
Keywords
freeze-thaw resistance, portland cement, slag, volcanic tuff, limestone filler
ADRIANA MOANŢĂ, CARMEN CIONOIU, VICTOR FARAON, GEORGETA BĂLEANU, VASILICA DIMA
Abstract
The article presents the results of laboratory investigations regarding the performing of some reducing agents of Cr6+ for cement, which allow the manufacture of some ecological binders of high quality, according both for conditions imposed by the legislation in force and for elimination of inconveniences brought by ferrous sulphate used as a reducing agent of Cr6+.
Testing of reducing agents, for their characterization, was performed on unitary cements type CEM I and cements with additions type CEM II / A – S.
The obtained results allowed establishing of an optimal prescription of reducing agent, both from composition and its dosage point of view and of efficiency for reducing in time of Cr6+ from cement.
Keywords
reducing agent, hexavalent chromium, cement, ferrous sulphate, zeolite
JENICA PACEAGIU, ELENA RĂDULESCU, ANA MARIA DRAGOMIR, RAMONA HOTNOG
Abstract
This paper presents results of laboratory investigations on the technological behavior of the raw mix containing slag steel (a non-carbonated waste) as a partial substitute of clay, compared with typical raw mix (containing limestone, clay and pyrite cinder). It followed the influence on the grindability and burnability of the two raw mixtures and the characteristics of obtained clinkers. Also, were estimated theoretical heat consumption and CO2 emissions generated by the formation of the two clinkers. Finally, it assessed the influence of steel slag on physical and mechanical properties (water demand, setting time, soundness, compressive strength) of cement obtained by grinding clinker with gypsum up to o fineness of approx. 3500 cm2/g as compared with reference cement. The presence of steel slag introduced in the raw meal promoted better raw mix burnability. Being a non-carbonated source of lime (it contains calcium oxide bonded as silicates and alumino-silicates forms), it allows a reduction of both thermal requirement and emission of CO2 at clinker manufacture.
Keywords
steel slag, sintering, clinker, microstructure, cement properties
ROXANA FECHET, MARIUS ZLĂGNEAN, ADRIANA MOANŢĂ, ILEANA MOHANU
Abstract
The paper presents aspects concerning the obtaining of clinckers and Portland by using minerals from tailings ponds from Romania. Processing of solid minerals sterile and obtaining of subproducts which are economically usable has major importance, both from economical and ecological point of view, through environment protection.
The laboratory researches had followed elaboration of ecological technologies of processing the waste as mineral sterile, in order to obtain recovered products. Mainly, elaborated technological flows contain a first stage of hydro-gravitational concentration followed by a magnetic and electric separation of obtained concentrates. Thus, obtained sterile may be also used as raw material in order to obtain building materials. the use of the wastes as mineral sterile from settling ponds as a corrective addition to the raw mix in cement manufacturing have led to obtaining of clinkers with ordinary modular composition. From structural - mineralogical point of view, the quality of the obtained clinkers is good, being typical alite Portland clinkers. Cements of type CEM I, obtained through grinding of the clinkers with gypsum, at a fineness of about 3500cm2/g have presented physical mechanical characteristics in accordance with quality requirements imposed by SR-EN 197-1:2002 norm.
Keywords
mineral steriles, tailing ponds, ecological technologies, cement Portland