română NICOLAE ŢĂRANU, DRAGOŞ BANU, GABRIEL OPRIŞAN, MIHAI BUDESCU, LILIANA BEJAN
Abstract
Fibre reinforced polymer (FRP) composites have been successfully implemented to strengthening of reinforced concrete (RC) slabs improving their structural response to various loading schemes. The most utilized techniques are based on prefabricated FRP composite strips bonded to the tension side with adhesives or by bonding quasi-unidirectional fabrics made of carbon or glass fibres impregnated with polymeric resins.
An extensive research program has been carried out at The Faculty of Civil Engineering and Building Services Iaşi, by testing a number of thin reinforced concrete (RC) slabs strengthened with CFRP strips in different solutions, to characterize the structural response, identify the failure modes and evaluate the structural efficiency of this composite strengthening solution. The structural response has been evaluated through testing a number RC slabs under bending from transverse loading. The difference in structural behaviour of unstrengthened and strengthened slabs has been revealed on both loading bearing capacity and stiffness. The validity of experimental results has been checked by numerical modelling using ABAQUS software package.
Keywords
thin RC slabs, strengthening, composite strips, bonding, failure modes, numerical modelling
BAOMIN WANG, HONGMEI AI, KAI SONG, YU HAN, TINGTING ZHANG
Abstract
The previous studies show that the concretes containing scrap rubber powder with particle size of 180µm, 150µm and 120µm exhibit a excellent freezing resistance durability. The influence of rubber powder content, particle size and water-cement ratio on resistance to chloride ion penetration of concrete were studied. The experimental results illustrate that the resistance to chloride ion penetration of rubber concrete improved along with the increasing of rubber powder content, decreased with powder particle size and decreased with the water-cement ratio. Compared with the reference concrete, the permeability grade of concrete with rubber powder content of over 20kg/m3 and powder particle size of less than 150µm will change from “low” grade to “medium” grade.
Keywords
scrap rubber powder, concrete, chloride ion penetration, durability
ÁNGEL PALOMO, OLGA MALTSEVA, INÉS GARCÍA-LODEIRO, ANA FERNÁNDEZ-JIMÉNEZ
Abstract
The binders known as blended or hybrid alkaline cements are obtained by alkali-activating cementitious blends in the Na2O-CaO-SiO2-Al2O3-H2O system. The present paper discusses the results of alkali activating blends prepared were: binder BSLAG = 20 % OPC clinker + 80 % BFS; and binder BFA = 20 % OPC clinker + 80 % FA. The 2-day mechanical strength was over 15 MPa. The main reaction products were gels whose composition varied depending on the initial Ca content. In alkali-activated BSLAG cement they consisted of a mix of C S H/C A S H and in activated BFA cement of a mix of C A S H /(N,C) A S H.
Keywords
hybrid cement, alkaline activation, C-A-S-H gel N-A-S-H gel, geopolymer
MARIA GHEORGHE, LIDIA RADU, DANIELA NĂSTAC, NASTASIA SACA
Abstract
A major environmental risk factor, associated with the use of construction materials, is their potential emission of pollutants and their migration in the aqueous medium (groundwater, surface water and precipitation).
The paper aim is to evaluate the environmental properties of concrete with cement manufactured by using of the alternative fuel.
Concrete matrix ability of heavy metals immobilization was assessed experimentally by appropriate leaching tests. Dynamic surface leaching test on monolithic concrete samples simulates release of contaminants from concrete products during service life. The potential leaching characteristics of the concrete after demolition were estimated by the extraction test, with assessment of the leaching availability (or the maximum leaching fraction). Also, there carried out the extractions at different values of pH for establishment the pH influence on heavy metals leaching.
The emission values of heavy metals from monolithic concrete samples after 64 days were compared with the regulated, as according to Dutch Building Materials Decree (DMBD). The release values of the heavy metals from concrete were well below of the DMBD regulated criteria, referring to categoria I of construction materials.
The extraction test results showed that pH plays a crucial role on the heavy metals leachability. The cationic contaminants (Mn, Ni, Co, and Cu) were leached at pH values < 7. The cations solubility is much lower than that of the oxyanionic in the alkaline aqueous medium of concrete pore with pH ≥ 12.5. The higher alkalinity of leachate provided from alkaline character of cement matrix was favorable to leach of Cr (VI), As (V), Sb (V) and V (V) as oxyanions.
The experimental results obtained can be a contribution referring to assessing the environmentally friendly character of the concrete due cementitious matrix ability to heavy metals immobilization.
Keywords
concrete, cement, alternative fuels, leaching test, heavy metals
DAN GEORGESCU, RADU GAVRILESCU
Abstract
The article presents novelty aspects for the modern approaches proposed in reviewing the European standard EN 206 „Concrete - Specification, performance, production and conformity” regarding concrete’s equivalent performance concept and the theoretic basis for the experimental determination of “k” coefficient in case of using additions in concretes in order to obtain performances equivalent to those of concretes without additions. In the article are presented theoretical application methods and/or experimental applications of such methods performed by the authors. The methods, suggested in the European standard, will be the basis for Romanian regulations’ review regarding the production of concrete.
Keywords
concrete, mechanical strengths, durability, equivalent performance
IONELA PETRE, MARCELA MUNTEAN, ADRIANA MOANŢĂ
Abstract
The paper presents investigations with regard to the influence of the surfactant additive HEA2 (triethanolamine acetate) on the specific power consumption at grinding, the particle size distribution and the mechanical properties of unitary cements and with addition of blast furnace slag with advanced fineness. The additive was dosed in three different ratios (0.03%, 0.05% and 0.1%), reported at the weight of cement subject to grinding. Grinding fineness of the cements, expressed through Blaine specific surface, was of 8000 cm2/g. It was found that even if grinding the blast furnace slag and the blast furnace slag cement were carried out without any surfactant, the power consumption was lower than when grinding the ordinary Portland cement. The effect of the surfactant on the specific power consumption at grinding is greater for the ordinary Portland cement than for the blast furnace slag cementIn terms of the surfactant effect on the particle size distribution, HEA2 was found to lead to a particle size distribution gliding towards finer fractions, namely, to a higher ratio of the fractions smaller than 3 and 16 microns, respectively, as compared to the reference cement (without additive).
Using of the additive HEA2 at grinding of the cements with addition of blast furnace slag lead to increasing of mechanical strengths at compression, at all hardening terms, in comparison with etalon cements.
Keywords
grindability, surfactants, advanced fineness cement, slag cement
GEORGE ŢĂRANU, IRINA LUNGU, NICOLAE ŢĂRANU, MIHAI BUDESCU
Abstract
Composite materials made of glass fibre reinforced mineral matrices are nowadays utilized in both new construction elements and in strengthening solutions of deteriorated civil engineering structures. The use of such materials requires a good knowledge of their strength and stiffness properties for the corresponding design works.
An extensive experimental program has been carried out at the Faculty of Civil Engineering and Building Services of the “Gheorghe Asachi” Technical University of Iasi to reveal the usage possibilities of mineral matrix composites, relating to regular construction elements and to specialized modules in emergency conditions. The research program has included theoretical and experimental studies regarding the utilization of ecological reinforced matrix, obtained by partial substitution of the ordinary Portland cement by a hydraulic binder manufactured from industrial wastes. The mechanical strengths and the elastic moduli from composites with various mixes and fibre volume fractions experimentally established confirm the suitability of these materials to structural members subjected mainly to axial loading.
Keywords
mineral matrix composites, glass fibre mesh, mechanical strength, elastic modulus, structural response
DANIELA FIAT, MIRELA LAZĂR, GHEORGHE HUBCA
Abstract
This paper highlights the influence of polymer additives on the durability of experimental dry-mix colored plasters compositions, that include them, after the exposure to urban-industrial environment (natural aging) and to UV radiation (accelerated aging).
Keywords
premixed dry mortar, polymer additive, redispersible powders, cellulose ethers
LU SHUANG, WANG ZHENG, DONGQING ZHANG
Abstract
The electrical conductivity of the cement based materials mainly depends on the properties of its pore solution, and its freeze-thaw cycling damage properties are related to the pore size and distribution definitely. This paper has studied on the relationship between the electrical resistivity variation and the freeze-thaw cycling damage behavior of the autoclaved fly ash brick. Test results show that, the hysteresis effect of the electrical conductivity of the autoclaved fly ash brick has been changed significantly, whereas its frost-resistance ability decrease in quantity with increasing amount of fly ash added. Bricks with more cement added give high frost-resistance ability, such that the remarkable descent stage of them change from -10~0 0C to -20~0 0C. The addition of air entraining agent has little or undesirable effect on the frost-resistance ability of the autoclaved fly ash bricks.
Keywords
Fly ash brick, electrical conductivity, frost-resistance, electrical resistance
ANA FERNÁNDEZ-JIMÉNEZ, ELENA FLORES, OLGA MALTSEVA, INÉS GARCÍA-LODEIRO, ÁNGEL PALOMO
Abstract
This part of the research explored the reaction of hybrid alkaline cements when they are exposed to acid (0.1-N HCl), sulphates and seawater. The hybrid cement used in the experiments comprised essentially metallurgical slag generated by the Fe and Zn industries. A standard Portland cement was used as the reference system. The findings showed that performance of these hybrid cements was similar to the results observed for the control. In a subsequent industrial trial, the concrete made with this experimental binder was successfully used in the manufacture of precast blocks and pavers.
Keywords
hybrid cement, alkali activation, geopolymer concrete, durability, blocks
ZENO GHIZDĂVEŢ, ROMAN GRĂDINARU, ADRIAN MUSTAŢĂ
Abstract
This paper presents a mathematical model for the heat transfer in the clinkering area of the rotary kiln. This problem can be solved in several ways. One simplistic approach would be to know the flame temperature in order to compute, among other secondary parameters, the temperature profile of the material. Another – much more practical – option is to know (to set) the temperature profile of the material over the length of the clinkering area of the rotary kiln, that further could be used to calculate the gas and kiln wall/shell temperature.
In this study it was consolidated this last alternative which requires the heating curve of the material (it is known/given the distribution of the material temperature in the rotary kiln, as necessary to obtain clinker quality). We then moved forward by implementing a broader approach, i.e. by assuming different amounts of fuel allocation over the length on the clinkering area; this distribution could be correlated with flame shape. Several coating width values were also included in simulation as an input parameter, thus contributing to broadening the options and to increase the realism level.
The model used a series of assumptions, limitations and simplifications. They are due to the complex nature of processes taking place in this area and are compulsory because the clinkering area could be considered independent and having a fixed length only under ideal conditions! In real life, complex interactions of material and energy with other parts of the clinkering plant can be easily identified.
Keywords
modeling, heat transfer, rotary kiln, clinker, flame simulation
IONELA PETRE, ADRIANA MOANŢĂ, ROXANA TRUŞCĂ, MARCELA MUNTEAN
Abstract
In present conditions of extension and perfection of the types of materials used at injection works, determined by diversifying of cases of which solving is indicated the injection, using of the cements with advanced fineness present numerous advantages and opportunities of technical, ecological and economic order.
The paper presents the results obtained as consequence of researches made in laboratory regarding obtaining of some mix cements with advanced grinding fineness. It were performed and characterized from physical-mechanical point of view with unique addition of 15% granulated blast furnace slag, fly ash respectively. Grinding fineness of cements, expressed as Blaine specific surface was of 8000 cm2/g. With obtained cements were performed fluids of injection with ratios water/cement varying between 0.4 and 0.8 and different proportions of superplasticizer SP430. Fluids of injection were
Keywords
Cement with advanced fineness, Granulated blast furnace slag, Fly ash, Fluids of injection, Rheology
MARIA STEFANIDOU
Abstract
Repair mortars based on lime known as “traditional” mortars have been applied the last decades in monuments and historic buildings as the best solution in terms of compatibility. However, problems of durability have been arising due to their weak structure and easy fracture pattern. In order to improve their durability, the new developed tools of nanotechnology are tested in order to strengthen the structure of repair mortars and restrict the durability problems. In the present work, nano-SiO2 of approximately 14nm in diameter is added in lime- natural pozzolana binders, which are the most common used binders of the “traditional” mortars, in different percentages in order to study the micro and nano structure of the produced pastes using Scanning and Transmission Electron Microscopy. Additionally, their mechanical and physical properties are tested from 3 up to the age of 28 days. From the study derives that nano-modified lime-pozzolana binders have a dense structure with reduced large pores and increased strength. Additionally, the catalytic role of nano-particles to crystal formation is confirmed.
Keywords
nano-SiO2; lime-pozzolana pastes; strength; SEM; TEM
DANIEL COVATARIU, IRINA LUNGU, NICOLAE ŢĂRANU, MIHAI BUDESCU, IONUŢ OVIDIU TOMA
Abstract
Low strength mortars have been widely utilized to masonry buildings representing historical heritage. These mortars use as binder lime, clay or mixes of those materials. The masonry failure very often occurs within the joints filled with weak mortars. Structural rehabilitation of masonry framing systems using weak mortars is mainly focused on the enhancing load bearing characteristics of their joints using durable materials, fibrous composites or mortar with various additives.
A research program has been carried out at the Faculty of Civil Engineering and Building Services of Iasi aiming to evaluate a number of strengthening solutions for the masonry joints, using reinforcing chords made of steel, carbon and glass fibres. In addition, strengthening measures have been taken by re-joining the masonry units with mortars including rubber powder and polypropylene fibres.
Mechanical tests have been performed to evaluate the structural response of the masonry components and of the masonry samples with strengthened joints. The experimental results have revealed significant increase in strength and stiffness depending on the used materials and solutions.
Keywords
structural rehabilitation, weak mortars, joints strengthening, structural response, fibre chords, improved mortars
IVANA JOVANOVIĆ, SANJA BUGARINOVIĆ, DANIELA UROŠEVIĆ, LJUBIŠA OBRADOVIĆ, SRĐANA MAGDALINOVIĆ
Abstract
This paper presents an overview of laboratory testing carried out to determine the influence of fly ash, as a component in cement mixture, on physical-mechanical properties of cement. Fly ash, used in this testing, was treated by different physical methods – grinding, very fine grinding and classification. The addition of fly ash varied from 10 to 50% by weight in the mixtures with cement. In the first instance, the results were evaluated by the most important criteria, the compressive strength of mortar containing prepared mixtures. In addition to that, the flexural strength of mortar, soundness of cement pastes, initial and final setting time, as well as the amount of water, required to produce the standard consistency of cement paste, were also investigated. The reported values have completly satisfied the appropriate standard.
Keywords
Portland cement, fly ash, grinding, classification
ANJA TERZIĆ, ZAGORKA RADOJEVIĆ, LILJANA MILIČIĆ, LJUBICA PAVLOVIĆ, JOVICA STOJANOVIĆ
Abstract
High-temperature concrete binders in which fly ash, as environmentally harmful secondary raw material, is combined with masonry and refractory cement is a new option for reapplication of this coal combustion by-product. In this study, the design of the bonding agents was based on the fly ash from lignite coal combustion process and two types of cement: Portland cement and aluminate cement. Fly ash was applied without any further mechanical or thermal treatment. Mechanical properties of the binders were investigated and subsequently correlated with changes which occurred in the phase composition and microstructure of the agents. Scanning electron microscopy was used in investigation of microstructural changes caused by temperature. X-ray diffraction method was used in monitoring of the mineral phase changes also induced by increasing temperature. The investigations conducted on the bonding agents highlighted presence of good refractory properties and temperature-resistance, and also showed high values of compressive strength. The investigated bonding agents, thus, can be applied in refractory concretes, but also in various types of thermo-insulations.
Keywords
Portland cement, refractory cement, fly ash, microstructure, compressive strength
M.MOHAMMADIAN, A.K.HAGHI
Abstract
Plastic waste management is one of the major environmental concerns in the world. Plastics can be separated into two types. The first type is thermoplastic, which can be melted for recycling in the plastic industry, such as polyethyleneterephthalate (PET). The second type is thermosetting plastic. This plastic cannot be melted by heating (such as melamine). At present, these plastic wastes are disposed by either burning or burying. Therefore, both the ways contributing to the environmental problems. This paper describes the use of thermosetting plastic waste as aggregate within lightweight concrete for building application and possibilities for re-use of thermosetting plastic waste in the concrete are described in detail.
Keywords
Recycled thermosetting plastic, composite, concrete
MYKOLA ZAICHENKO, SERHII LAKHTARYNA
Abstract
In order to optimize the grain size composition of Portland cement with the addition of silica fume and to activate the hardening process of composite cement the method for surface modification in high-voltage electric field is proposed. The electrical agglomeration setup to produce modified composite cement has been designed. An observation of a cross-section of a cement particle by scanning electron microscopy and an analysis of the element distribution on the surface of modified composite cement particles are shown. According to the test results, cement pastes based on the modified composite cement possess the 28-day compressive strength of up to 89.3MPa, a 37% increase over the reference.
Keywords
Portland-composite cements, silica fume, spherical cement, agglomeration
ZENO GHIZDĂVEŢ, ROMAN GRĂDINARU
Abstract
In this paper, heat balance calculations were performed on a clinkering plant based on the dry process, no calciner. Parameter values were iteratively averaged over different time periods. The purpose of this work is to determine the influence of the averaging time interval on the precision and accuracy of the calculations and to extract some useful information about the process itself.
Five parameters that were selected by a simple statistical correlation analysis were considered. For each parameter two series of data of the same length (256 hours) of uninterrupted processing were used. Ordinary variations for the process parameters’ evolution and for the particular plant were recorded.
Fractal dimension calculations were made on each parameter, for both hourly and averaged sequences of data and for the two series (this has been done for confirmation). Results clearly show that each parameter can be identified by a particular fractal dimension. This simple technique can be used, for instance, to detect abnormal trends that can escape visual analysis.
Keywords
clinkering plant, heat balance, fractal dimension
RADU COJOCARU, RADU ANDREI, MARIUS MUSCALU, NICOLAE ŢĂRANU, MIHAI BUDESCU, IRINA LUNGU
Abstract
The crushed cement concrete obtained as a result of rehabilitation of road and airport pavements is actually inefficiently used in road and airport construction. To integrate this recycled aggregate in the new pavement structure it was necessary to know its mechanical performance and to consider it in the structural design process.
In these respect, two types of cement concrete, namely plain cement concrete and roller compacted concrete, having in their composition different percentages of recycled aggregates have been used in the experimental program. Also disperse reinforcement with recycled steel fibres has been considered, in order to improve the pavement behaviour during exploitation.
This paper presents the results of an experimental program in which it has been found that the requirements of the present design standards concerning the strength characteristics of these new materials are fulfilled but with rigidity characteristics different than those found in the existing design diagrams.
Therefore implementation of these cement concretes made with recycled materials for airport pavements can be achieved only with the condition to adapt the actual structural design methods, such as to cover the extended range calculation parameters.
The paper deals with the laboratory research of these new materials and based on these results proposes to take into account a larger range of elasticity modulus values, in order to use them in the process of structural design of airport rigid pavements.
Keywords
plain cement concrete, recycled materials, mechanical performances, rigid airport pavements structures, structural design
SANJEEV KUMAR VERMA, SUDHIR SINGH BHADAURIA, SALEEM AKHTAR
Abstract
Chloride ingress in concrete structures has been defined and modeled using Fick’s law of diffusion by many researchers, and most of the researchers considered diffusion coefficient and surface chloride content as constants. Now, it has been recognized that diffusion coefficient (D) and surface chloride content (Cs) varies with the increase in age of the structure. This paper presents a methodology for evaluating the values of D and Cs for concrete structures of different age groups, and also investigated the variation of these parameters with respect to age of structure by using results of a field survey.
Keywords
Concrete, Chloride diffusion coefficient, Modeling transport
SLOBODAN RANKOVIĆ, RADOMIR FOLIĆ, MARINA MIJALKOVIĆ
Abstract
The paper presents the results of experimental and numerical investigations of the reinforced concrete (RC) beams strengthened with the near surface mounted (NSM) carbon and glass FRP bars. Three concrete beams were tested for bending during which the deformations of beams, pattern of cracks and the strains in steel, FRP and concrete were recorded until failure under monotonically increased loading. Additional glass (Ø10mm) and carbon (Ø8mm) FRP bars improved the bearing capacity over the control RC beams by increasing it by 73% and 89%, respectively. A nonlinear analysis model based on FEM is proposed to analyse the behaviour of the strengthened beams. The model was developed using ANSIS software package and the recommended constitutive models therein for concrete, steel and FRP reinforcement. The numerical results obtained using the developed model correlated very well with the experimental results and demonstrated not only significantly increased loading capacity and stiffness, but also considerable ductility of the strengthened beams.
Keywords
FRP reinforcement, NSM method, flexural strengthening, RC beams, testing, non-linear FEM analysis
IOSIF BUCHMAN, TAMAS DENCSAK
Abstract
Special industrial concrete (SIC) had the following composition: cement, silica fume, water, superplasticizer, aggregates, and steel fibers. Studies and researches have been carried out at the Civil, Industrial and Agricultural Buildings Department of “POLITEHNICA” University of Timisoara, for the introduction of this concrete in Romania. This work presents some of the technical and economic aspects of the studies and researches concerning the special industrial concrete.
Keywords
special industrial concrete, silica fume, superplasticizer, steel fibers, production cost
JENICA PACEAGIU, GHERGHINA CIORTAN
Abstract
Information about the evaluation of the behavior of Portland cement to chemical attack exerted by organic acid medium is still limited and there is no standardized method for evaluation of its chemical stability. Most studies assess the durability of cement without addition (type CEM I) or containing various proportions of granulated blast furnace slag (type CEM II /A-S, CEM III/B) in contact with organic media such as acetic or lactic acid, and most refer to the behavior of cement pastes and mortars.
This paper presents data on the acid corrosion resistance of common cements type CEM II/A-V, CEM II/B-M(S-V) and CEM V/A(S-V) (according to EN 197-1) compared with that of cement without additions (type CEM I). The evolution of the mechanical strengths and weight changes of the mortar specimens, immersed into 5% solution of lactic acid, acetic acid or lactic acid + acetic acid for periods of time up to 180 days, combined with evolution of the pH and concentration of species presented in solution have shown that the acid corrosion resistance of cements containing granulated blast furnace slag and fly ash is higher than that of fly ash cement and sole Portland cement.
Keywords
composite cements, chemical stability, organic acids, mechanical strength