română DAN GEORGESCU, ADELINA APOSTU, RADU GAVRILESCU
Abstract
The article presents the analysis and practical application modalities of certain modern methods to assess the characteristic compressive strength of the concrete manufactured in plants, using the concrete family concept, in accordance with CP 012-1/2007 “Practice Code for the manufacturing of concrete”, and the CUSUM analyses type (cumulative sum) according to ACI 214 R-02 “Evaluation of Strength Test Results of Concrete”. The concrete family system offers effective control means for a high number of different concretes. The analyses CUSUM type are extremely useful in the continuous pursuit of the quality of concrete manufactured in plants, being able to identify the negative tendencies in the evolution of concrete resistant values and therefore, there can be identified, for the reference concrete level, the causes of these evolutions.
Keywords
concrete, evaluation, conformity, compressive strength, concrete’s family, cumulative sum
LIANA TEREC, HENRIETTE SZILAGYI
Abstract
In order to obtain self-compacting concrete (SCC) for the construction industry, an important experimental program for the evaluation of the properties of fresh and hardened concrete was conducted at INCERC Cluj-Napoca Branch. The principal objectives of the research program were: to design the mix proportions for SCC, to assess the properties of fresh and hardened SCC and to study the behavior of SCC elements subjected to different loads. The fresh SCC evaluated properties were: slump flow, passing ability, viscosity and segregation resistance.
Keywords
construction (D, d), special concretes (D, a), compacting (A), limestone (D, d), organic polymers (D, a)
KSENIJA JANKOVIC, SRBOLJUB J.STANKOVIC, DRAGAN NIKOLIC, DRAGAN BOJOVIC, LJILJANA LONCAR
Abstract
The evaluation of the dynamic modulus of elasticity of twelve different concrete mix proportions as a function of the density and degradations due to freeze/thaw cycles is presented in this paper. Pore system and saturation are the main factors for concrete freeze-thaw resistance. The frequency analysis of ultrasonic waves in concrete after every 25 cycles was done. Dynamic modulus of elasticity was determination by resonance frequency analysis. This parameter is 35-50% smaller for concrete with recycled bricks as aggregate than ordinary concrete. For all concrete mixes dynamic and static (measured by destructive testing) modules of elasticity were compared.
Keywords
dynamic modulus of elasticity, ultrasonic waves, freeze-thaw resistance, recycled aggregate concrete
IOANA PAPAYIANNI, MARIA STEFANIDOU
Abstract
Binders are one of the basic constituent of mortars that plays an important role to their mechanical behavior and their behavior in physico-chemical interactions with the environment. The type, the quantity and the fineness of the binders result in different properties in the setting and in the hardening stage of mortars.
In the present paper very fine materials in the scale of nano were added to conventional binders such as lime and natural pozzolan. Properties of workability of the fresh mixtures, compression strength and porosity of the harden specimens were recorded in combination with structural observations using Scanning Electron Microscopy (SEM). Also, pore size distribution properties were recorded using Mercury Intrusion Porosimetry (M.I.P.). Based on the results, structural changes have been observed in nano-modified structures and early-age strength has been achieved in pozzolan mixtures. Pores, larger than 10μm have been reduced in mixtures with nanoparticles. The research is a precursor for the influence of nanoparticles to macro-scale properties of repair, lime-based mortars.
Keywords
D. mortars, B. nanoheterogenous structure
CRISTINA CIOBANU, STELIAN ILUC, IOAN LAZĂU, CORNELIA PĂCURARIU
Abstract
The effects of some commercial cellulose ethers type MHEC on some physico-mechanical properties (consistency, setting time and mechanical strength) of some mortars based on portland cement (CEM I 42.5 R), limestone filler and quartz sand were studied. It was observed that cellulose ethers increase setting time and the amount of water needed to achieve standard consistency while mechanical strength significant decreases. The intensity of these effects depends on the substitution degree of cellulose ethers and on the proportion in which they are added in mortars and less on the viscosity declared by the manufacturer.
Keywords
cellulose ethers, hydration, thermal analyse, setting time, mechanical properties
CORINA MITU, DOREL RADU
Abstract
In the flow technology of manufacturing Portland cement, operation of grinding the mixture of raw materials is decisive to obtain a certain particle size distribution with a prescribed degree of uniformity for providing good clinkerization reaction of the mixture of raw materials.
Uniformity degree can be considered an important technological parameter which can measure the change of the particles size of the raw materials mixtures during grinding.
This paper presents some correlation between the uniformity degree and a number of granulometric characteristics of some mixtures of raw materials from cement industry which is changing during the grinding.
Keywords
grinding, mixture of raw materials, particle size distribution, uniformity degree
ZORAN GRDIĆ, GORDANA TOPLIČIĆ ĆURČIĆ, NENAD RISTIĆ, IVA DESPOTOVIĆ
Abstract
The mechanical and rheological properties of concrete depend to a great extent upon the type of realized structure which can be viewed from the aspect of the relationship of the space between the grains in the aggregate and the quantity of the the cement paste in the concrete. The influence of the degree of filling of the cavities in the aggregate with the paste (ke) on the consistency type has to view in the light of the realized structure of concrete taking into consideration the particle size distribution and water-cement ratio. Generally, with the increase of the degree of filling of the cavities in the aggregate with the cement paste from 0.9 to 2.5 the consistency of concrete changes from stiff to very fluid. The maximum values of compressive strength are realized when the degree of filling of the cavities in the aggregate that can be considered as optimal is within the relatively narrow limits, and then the value of the parameter ranges between 1.2 to 1.4.
Keywords
cement paste, aggregate, concrete, rheologic properties, mechanical properties
ZENO GHIZDĂVEŢ, DOREL RADU, ANDREEA DAVID
Abstract
A mathematical model used to design clinkering plants is used here to explore the influence of the cooling air temperature and of the fuel selection on both heat and raw materials requirements and even on the required kiln length. The interest is not purely theoretical as cumulated differences over a long range, could reach important values.
Keywords
clinkering plants, combustion, mathematical model, design
IOAN ROBU, GABRIELA ILIE, IOAN PORDEA
Abstract
The utilization of thermo-power station ashes in construction is of major importance from a technical, economic and environmental viewpoint nationally and internationally.
Their limited utilization could be triggered also by their radioactivity. This paper researches the determination of radioactivity index for ashes originality from the main Romanian thermo-power stations for pastes, mortars and concretes made of cement with an ash component.
Keywords
thermo-power plant ash, puzzolanic activity, radioactivity index, radiologic risk
ALICE RĂDUCANU, ANGELA STANCA, AURELIA MEGHEA, CONSTANTIN GRIGORIU, CRISTIAN VIESPE
Abstract
The paper addresses the topic on morphostructural characterization of ultrafine particles generated in coal-based power plants, with special reference to Mintia-Deva power plant, Romania. The particles oxidic composition, concentration and size distribution were investigated. The concentration measurements have been performed based on light scattering for micro-sized particles and differential mobility analysis for nanometric scale. The highest values of oxide component concentration have been registered in the coal powders sampled from the work places at breaking room and on conveying belts. The dust composition mainly consisted of silica, and also iron, aluminum, calcium and magnesium oxides, with more than 25% SiO2, 10% Al2O3, 4%Fe2O3.
Keywords
ultrafine particles, dust, silica nanoparticles, power plant emissions
MARIA GEORGESCU, IRINA CĂTĂNESCU, GEORGETA VOICU
Abstract
The geopolymer binders are relative new materials with three-dimensional polymer structures having a preponderant amorphous character compositional similar, natural feldspar. These materials are synthesised by the processing of silico-aluminates materials like fly ashes, granulated blast furnace slag, metakaolinite, with alkaline solutions like hydroxides or silicates. The compositional characteristics and processing peculiarities influence the geopolymers synthesis and microstructure. These factors influence the development of mechanical strengths.
The present paper brings information concerning the microstructural and compositional characteristics of some geopolymers synthesized from fly ash and NaOH solution in different conditions of curing.
Keywords
Fly ash; Geopolymer; Microstructure; Mechanical properties
MIRELA MENICU, ADRIANA MOANŢĂ, DANIELA NĂSTAC, ADRIAN MOTOC, RADU PITICESCU
Abstract
In accordance with the requirements imposed to binder materials for performing of modern constructions, a multitude of new materials with added value are researched and introduced in practice. The article presents both the obtaining method of photo-catalytic component (TiO2 nano-structured), methods of photo-catalyst characterization and also the obtaining of photo-catalytic binder materials. In order to obtain photo-catalyst material, the hydrothermal synthesis was used, and this material was characterized by X-rays diffraction in order to establish the composition and crystallites dimensions and by optical microscopy in order to see powders morphology.
Photo-catalytic binder materials with TiO2 nano-structured were obtained. The own results obtained as consequence of characterization from physical-mechanical point of view (water for the slurry of normal consistency, setting time, stability, and also mechanical strengths at bending and compression) of these materials.
Keywords
photo-catalytic binder materials, nano-structured TiO2, binder materials with self-cleaning, anti-bacteriological, pollution decreasing
MARIA GHEORGHE, NASTASIA SACA, CĂTĂLINA GHECEF, RAMONA PINTOI, LIDIA RADU
Abstract
This paper presents experimental obtained data regarding the properties of self compacted concrete (SCC) with fly ash content, such as workability, compressive strength evolution over time in comparison with the reference (concrete without fly ash or concrete with limestone filler content). In this way, were realized two series of mixes: SCC with CEM I 52.5R and SCC with CEM II/B-M (S-LL) 42.5N.
Research realized showed that the addition of 20-34% fly ash of total powder amount is beneficial for the consistency and resistance to segregation of concrete in fresh state. SCC compressive strengths at early age were significantly diminished by fly ash addition, but these are increasing until 360 days.
Keywords
self compacting concrete, fly ash, workability, compressive strength.
KSENIJA JANKOVIČ, GORAN CIROVIČ, DRAGAN NIKOLIČ, DRAGAN BOJOVIČ
Abstract
Preparation and microstructure of ultra high performance concrete (UHPC) have been intensively analyzed in the last few years. The mechanical properties (compressive strength and flexural strength) were investigated under different curing conditions (standard and steam curing). Silica fumes have characteristics that make them necessary in cement composites with ultra strength properties. The search for substitute products thus appears important if the use of UHPC is to become more widespread in the concrete industry. Possibilities of making ultra high performance self compacting concrete (UHPSCC) with materials available in Serbia, based on experimental work are discussed in this paper. Three series of samples were made with different types of fine reactive additives (silica fume was replaced with metakaolin at 20% and 40% and with fine fly ash at 20%). The produced mixes had self compacted consistency. The 28th day compressive strength varied between 165 and 195 MPa for the heat treated specimens and between 135 and 150 MPa for the ones that had not been heat treated. Furthermore, this paper presents SEM micrographs of C-S-H phase formed after steam curing and super-heated steam under preassure.
Keywords
UHPSCC, Fine reactive additive, Steam curing regime, Super-heated steam under preassure
DAN GEORGESCU, ADELINA APOSTU, RADU GAVRILESCU
Abstract
The design of the service life of reinforced concrete structures can be performed using design approaches with different levels of complexity (full probabilistic, based on partial factor or deemed to satisfy). No matter the complexity, the results of the experimental researches in-situ and in the laboratory must provide the necessary data for such approaches, for different types of degradation mechanism of reinforced concrete.
The article presents the results of experimental researches performed on concretes prepared with cement type CEM III/A Carpatcement, as an example for obtaining the necessary data in order to establish the service life of constructions performed with a certain type of cement.
Keywords
concrete, service life design, chlorides, carbonation
DAN GEORGESCU, ADELINA APOSTU, RADU GAVRILESCU
Abstract
The environmental actions can cause deteriorations of concrete having as consequence an intensified reduction of the elements/construction structures’ performance. The design of the service life of certain structures is performed considering methods with different complexities which must consider a rigorous selection of materials as well as important execution, execution inspection, maintenance factors and status assessment during service life. No matter the complexity of the method used, the design process of the service life must be based on the results obtained from certain experimental researches, necessary for the assessment of the evolution of materials’ characteristics, depending on different environmental conditions. The freeze/thaw attack with /and without de-icing agents represents one of the actions with frequent occurrence, causing important deteriorations of concrete.
The paper presents an analysis of the main experimental methods related to the freeze/thaw action (Part 1) and the results of certain experimental researches performed by authors in order to determine the freeze/thaw resistance of concretes manufactured with different types of cement produced by CARPATCEMENT HOLDING S.A. – HEIDELBERGCEMENT GROUP which will be presented in Part II.
Keywords
concrete, freeze /thaw attack, service life, experimental methods
GABRIEL OPRIŞAN, NICOLAE ŢĂRANU, VLAD MUNTEANU, MIHAI BUDESCU, CIPRIAN COZMANCIUC, RUXANDRA OLTEAN
Abstract
Structural rehabilitation of concrete columns using confining with composite membranes has become a largely accepted technique. An extensive experimental program has been carried-out at the Faculty of Civil Engineering and Building Services, Iasi, aiming to evaluate the efficiency of the confining effect on concrete columns using fiber reinforced polymer (FRP) composite membranes. The results have established the effectiveness of wrapping solution, based on glass fiber reinforced polymer (GFRP) and carbon fiber reinforced polymer (CFRP) composites, in increasing both strength and ductility. A predictive equation has been proposed by the authors, based on experimental results, in good agreement with existing models.
Keywords
hybrid confined columns, composite membranes, confinement pressure, wrapping, stress-strain curves, strength improvement
XIAOJIAN GAO, YINGZI YANG, HONGWEI DENG
Abstract
Shrinkage strains of high strength concretes with and without silica fume were measured at various depths from the drying surface by using linear variable differential transformer (LVDT) displacement sensors, and only one surface of the prism specimen was exposed to drying conditions (RH=75%, 54% and 33%) during the experiment. The results show that the internal shrinkage strain becomes lower with the increasing depth from drying surface. Such shrinkage difference gets severer with the longer drying time and the lower relative humidity of drying condition. There is a linear relationship between the reduction of internal relative humidity and shrinkage strain at every depth of specimen. However, the increased shrinkage at inner position is higher than that at outer position of each specimen when the same reduction of relative humidity happens.
Keywords
concrete, drying shrinkage, relative humidity, differential strain distribution
DANIELA LOREDANA BELEŞ, VLAD CODREA
Abstract
SO2 and VOC emissions belong to the first air pollutants which caused challenging experiences for cement industry. The reduction methods are particular for each cement plant, and are concerning the management of raw materials, combustibles or supplementary equipments and processes. The main raw material components responsible for SO2 and VOC emissions are the pyritic sulfur as well as the kerogen. Current paper describes the complete replacement of an organic and pyritic rich clay source with a non-contaminated new one and the corresponding impact on the emission level. Compared with the old clay deposit, the new clay type with very low pyrite and TOC content has determined a strong reduction of SO2 and VOC emissions.
Keywords
stack emissions, clayish materials, pyritic sulphur, sedimentary organic compounds
ILEANA MOHANU, MARIA GEORGESCU, DAN MOHANU, LIANA MANOLACHE, COSMIN DRĂGĂNOAIE
Abstract
The paper have information regarding the characteristics of some colored mortars based on lime –limestone-volcanic tuff-river sand, owned to some preservation-restoration works of the historical monuments plasters. Investigation was made regarding chemical, physical and chromatic properties of the raw materials. Different compositions of mortars were performed, being characterized from physical-mechanical point of view at terms of 28 and 56 days, and also aesthetic. Correlations were made between raw materials characteristics and those of mortars. It was stated that the type and limestone proportion modify in restricted limits physical-mechanical characteristics, imprinting to mortars, in the same time, different luminous, pastel tones.
Keywords
lime mortar, limestone, pozzolana, mechanical properties, colour