română M. TORRES-CARRASCO, F. PUERTAS
Abstract
The study and development of new binders as alternatives to portland cement is a priority line of research the world over that aims to minimise the pollutant gas emissions and substantially reduce the energy consumption inherent in cement manufacture.
Cement manufacture has a heavy environmental footprint, for it exploits natural resources (quarries) and emits large quantities of polluting gas (CO2, SO2, NOx) into the air. World-wide, around 5 % to 7 % of CO2 emissions can be attributed to the cement industry. In addition, given the power consumed to heat kilns to the necessary temperatures and drive the mills that grind the clinker, cement manufacture has a high energy price tag.
This review traces the history and development of alkaline activation, explaining the most characteristic features of the chemistry involved and drawing a comparison between the economic and environmental data for these alternative materials and for portland cement. The findings show that alkaline-activated cements and concretes perform better in both respects. Nonetheless, alkaline cement chemistry cannot yet be said to be wholly eco-friendly, for large amounts of CO2 are emitted in the production of alkaline solutions such as sodium silicates, which is, moreover, a costly process. For those reasons research should be ongoing on the valorisation of alternative materials with characteristics and properties similar to those of the commercial solutions used to date to prepare these systems.
Keywords
alkali activation, geopoymers, slags, fly ash, durability
LAURA BĂRBULESCU, ALINA BĂDĂNOIU, ADRIAN NICOARĂ, CRISTIAN PÎRVU
Abstract
This paper presents some physical and mechanical properties of Portland cement mortars prepared with two types of waste as alternative aggregates. These wastes result during the mechanical processing of titanium alloy ingots by shot blasting with steel beads (DS) or by surface abrasion/polishing process with abrasive discs (DSIC).
The total replacement of natural aggregate (sand) with DSIC waste determines an increase of flexural and compressive strengths (with respect to the mortar prepared with sand) most probably due to its high content in Ti (metal and oxide).
The partial replacement of sand or DSIC with DS waste determines a decrease of flexural and compressive strengths both at early ages (3 days) and longer hardening times (28 days).
Keywords
Waste, Ti processing, alternative aggregate, Portland cement, mortar.
I.DIAZ-PEÑA, J. G. RANGEL-PERAZA, A.M. GUZMAN, R. GONZÁLEZ-LOPEZ , A.A. ZALDIVAR-CADENA , J. HERNÁNDEZ-SANDOVAL
Abstract
The aim of this work was to study the effect of the interaction of colloidal nano SiO2 (NS) with a hardened Portland cement paste (PCP). An electric circuit arrangement with two electrodes was used to create an electric field around a PCP sample. NS was used as catholyte and water as anolyte to assure electric conductivity. Results obtained using an optical Microscopy and Scanning Electron Microscopy showed that NS particles reached a distance up to 1.5 mm from the surface in contact with the PCP sample to the interior of the sample. Energy dispersive X-ray Spectroscopy showed an enrichment of Si in the zone where NS migrated. An alteration of the Ca/Si ratios was also observed, with values below of both conventional anhydrous and hydrated phases. Thermo-gravimetric analysis (TG) showed that NS affected the content balance between CSH gel and Ca(OH)2 in a migrated NS sample compared with a reference sample; this could represent an evidence that NS affected the cement matrix with a possible pozzolanic reaction even after the hardened stage of the PCP.
Keywords
Electrochemical migration, nano SiO2, Portland cement paste
DANUTĖ VAIČIUKYNIENĖ, ARAS KANTAUTAS, ŽYMANTAS RUDŽIONIS, VITOLDAS VAITKEVIČIUS, MINDAUGAS ŠUKUTIS
Abstract
There is a lot of industrial and household waste in the world. Rational use of the waste by applying new technological solutions can significantly reduce energy consumption and emissions into the environment. Waste glass is one of such waste that, if non-utilized, fully decomposes in nature within a few thousand years. This paper presents the research of colourless ground waste glass used as a substitute for Portland cement. Glass powders were zeolitized to improve the pozzolanic properties of the material. The research results showed that hydration temperature and compressive strength of the specimens with 5% and 10% of the cement replaced by zeolitized admixture is similar or higher compared with the specimens where non-zeolitized glass powder is used. In summary it can be concluded that zeolitization of ground glass powder is feasible only in the production of specialized concrete products.
Keywords
recycled waste glass, zeolitized glass powders, cement suplementary materials, zeolite
YANG ZENGKE, HUANG WEI, ZHANG MIN
Abstract
In this paper, orthogonal tests are designed to investigate the effects of three factors, including water-cement ratio, aggregate replacement rate and fiber content, on the performance of these kinds of fiber reinforced concrete through the range analysis and variance analysis. The results show that: water-cement ratio has significant effects on the strength of all four kinds of fiber reinforced concrete; aggregate replacement rate has little influence on the strength of polypropylene (steel) fiber recycled brick concrete but significantly affects the strength of polypropylene (steel) fiber sludge ceramsite concrete; the variation of fiber content has no significant influence on the cube compressive strength of all four kinds of fiber concrete but obviously affects their cube splitting tensile strength.
Keywords
Steel fiber; Polypropylene fiber; Recycled brick; Sludge ceramsite; Orthogonal experiment
XIAO-WEI CUI, CHANG-LONG WANG, WEN NI, YAN-QING DI, HAN-LONG CUI, LIE CHEN
Abstract
To comprehensively utilize iron ore tailings (IOT), it was used as main siliceous materials in autoclaved aerated concrete (ACC) with excellent mechanical properties in this study. The physical and mechanical properties of AAC were analyzed by using X-ray diffraction analysis (XRD), fourier transform-infrared spectroscopy (FT-IR), thermogravimetric/differential scanning calorimeter (TG-DSC) and scanning electron microscope (SEM). The hydration products and microstructure with different stages of AAC were detected. The results show that that the main hydration products including ettringite (AFt), low crystallinity of C-S-H gels and Ca(OH)2 were generated before the autoclaving. After the autoclaving, the major hydration products were tobermorite, C-S-H gels and hibschite in the final AAC, AFt was decomposed. XRD diffraction peaks of the original mineral composition in IOT were reduced, which indicated that the mineral composition of IOT were decomposed, and the reaction between active components of SiO2, Al2O3 and Ca(OH)2 caused the formation of tobermorite under conditions of high temperature and pressure and hot alkaline activation.
Keywords
iron ore tailings; autoclaved aerated concrete; ettringite; tobermorite; C-S-H
UMUT NACI BAYKAN, MURSEL ERDAL, LATIF ONUR UGUR
Abstract
In this study, a fuzzy logic prediction model for compressive strength of concrete was developed based on various non-destructive tests, such as Windsor Probe Penetration Test, Ultrasonic Pulse Velocity and Schmidt Hammer. Experimental results of non-destructive tests were used to construct the fuzzy logic model. The obtained results with fuzzy logic were compared with the multiple linear regression model and experimental values. It was observed that, non-destructive tests’ determination abilities were increased by using fuzzy logic. Results have shown that, fuzzy logic systems have strong potential for predicting 28 days compressive strength using Windsor Probe Penetration value, Ultrasonic Pulse Velocity and Schmidt Hammer rebound as inputs variables.
Keywords
Non-destructive testing, Concrete, Fuzzy logic, Compressive strength, Statistical Modelling
C.R. IORDĂNESCU (ȘTEFAN), M. ELIȘA, G. EPURESCU, M. FILIPESCU, M. ENCULESCU, R.C.C. MONTEIRO, L. CONSTANTIN
Abstract
In the present work we study the optical, structural and morphological properties of CdS-doped glass films, deposited by Pulsed Laser Deposition (PLD) method. The glass target used for ablation was prepared by conventional melt-quenching technique and the semiconductor dopant, CdS powder, was embedded in the borosilicate melt glass host by continuous stirring. In order to improve the properties of the films, the laser wavelength was modified. Photoluminescence emission (PL) of CdS-doped glass films revealed a broad band located in the visible range. The structural analysis was carried out by micro-Raman spectroscopy, pointing out specific vibration modes for Si-O-Si bonds as well as for CdS dopant. The morphology and the chemical characterization of the films were investigated by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX) and Atomic Force Microscopy (AFM).
Keywords
borosilicate glass, thin film, pulsed laser deposition, luminescence, CdS-doped glass
HAN XUECAI, TONG YILIN
Abstract
Chalcogenide glasses have many potential applications as a result of their particular optical and electrical properties, which are considered to be strongly determined by the elementary network-forming structural units and their mutual interconnection. The aim of our work is the investigation and modeling of As-rich chalcogenide glasses with possible basic structure units. Ab initio quantum chemical calculation with DFT/B3LYP method is performed to investigate the cage-like AsxSySez. The calculated total energy reveals that the total energy at the stationary point with the As4SnSe3-n (n=0,1,2,3) and As4SnSe4-n n(n=0,1,2,3,4)clusters decrease corresponding to the fall of S and Se content in the As4SnSe3-n and As4SnSe4-n clusters, respectively. The calculated fundamental frequencies were utilized to predict the assignment of unknown peaks in As-S-Se Raman spectra, which is considered to have good accordance between experimental and calculated data, it is concluded that the cage-like AsxSySez clusters play an important role in the structure of As-S-Se amorphous system.
Keywords
ab initio, DFT, chalcogenide glass, vibration analysis
A. EL HAT, A. HADRI, F.Z. CHAFI, B. FARES, N. HASSANAIN , A. MZERD
Abstract
Zn1-xCuxO thin films with different Cu concentration x= (0; 2; 5; 7 at %) are deposited by spray pyrolysis technique on heated glass substrate at 350°C. The physical properties of the films are characterized by several techniques in order to study their structural, surface roughness, optical and electrical properties. It is observed from X-ray diffraction (XRD) analysis that the Cu doped ZnO films are polycrystalline and exhibit a preferential orientation along (002) plane. The Atomic force microscopy (AFM) measurements revealed that the surface roughness of the films is decreased from 0 to 5 at % Cu then increased strongly for 7 at % Cu. From optical measurements, a significant decrease in average optical transmission is observed for all doped samples and the band gap value is decreased from 3.3 to 3.07 eV with increase in Cu concentration. The Hall Effect electrical measurements show that all samples are n-type and the best value of the electrical resistivity 1.35x10-1(Ω.cm) is obtained for 5 at % Cu.
Keywords
spray pyrolysis, ZnO thin films, Cu-doped ZnO, Hall Effect, Band gap, AFM, Refractive index, extinction coefficient
ȘTEFANIA MARIN, MĂDĂLINA GEORGIANA ALBU KAYA, GEORGETA VOICU, GRAȚIELA TEODORA TIHAN
Abstract
In this work the attention was focused on the superior properties of polyvinylalcohol – collagen hydrogels.Burns leads to exposure of the deeper layers of skin proportional to the size and depth of the wound. The pH level in the wound bed is a key parameter for assessing indicative of wound healing problems and temperature the same. The lower temperatures can stop the activity of the cells involved in the healing process.The aim of this study was to characterize hydrogels previously obtained in terms of pH and temperature sensitivity in order to choose the most appropriate formulation that could be used for burn healing. Hydrogels were made from collagen gel with initial concentration of 2.85% and polyvinyl alcohol having a molecular weight of 60 000 Da. The hydrogels obtained were lyophilized in order to be analyzed by microstructural appearance (SEM images) and also from the point of view of their sensitivity to different values of pH and temperature. Based on result obtained it was demonstrated that the sample with equal proportions of collagen and polyvinyl alcohol shows that it has the required properties in order to be used as a dressing in healing burns. This hydrogel will be basic support for new smart dressings with included nanoparticles, with targeted applications in medicine.
Keywords
composite, collagen, polyvinyl alcohol, hydrogels, pH, temperature
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Year
2017
-
Issue
47 (1)
-
Pages
78-83
GHEORGHE ION POPESCU, OLIVERA LUPESCU , MIHAIL NAGEA, DAN CORNECI
Abstract
Fibrin-based sealants are mainly based on fibrinogen and thrombin; in the presence of even small amounts of Factor XIII and calcium, fibrinogen is polymerised by thrombin into insoluble fibrin, which organises as a network with multiple functions: it has a major role into the coagulation cascade and it also enhance wound healing, thus playing a key role in human body reaction to any type of aggression, including the surgical procedures. Due to their properties, fibrin-derived materials have been intensively studied and enhanced, so that they nowadays represent a group of great interest for many medical fields. One of the most frequently performed orthopaedic procedures, hip arthroplasty is, in the same time, considerably invasive upon homeostasis, especially due to bleeding, which can lead to dramatic outcome of the patients, as well as upon the soft tissues, with different healing properties. Intensive studies have been thus performed in order to find materials able to diminish these effects, fibrin-based sealants proving themselves as able to fulfil these requirements. This paper reflects the clinical experience of using a Fibrin-based sealant in major orthopaedic procedures, revealing the advantages of using this type of materials for the outcome of the patients.
Keywords
fibrin sealants, hip arthroplasty, haemostatic, fibrin glue
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Year
2017
-
Issue
47 (1)
-
Pages
84-90
M.A. IONESCU, I. CIUCĂ
Abstract
Surface roughness measurements by AFM and SEM were performed on thin films of Parylene-N and Parylene-C deposited via Chemical Vapour Deposition of polymers also known as Polymer Vapour Depostion (PVD) on Si(111). AFM revealed a smoother surface for Parylene–C, while the Parylene–N showed a dimpled surface with isolated valleys. SEM on Parylene–C showed a smooth surface, with debris, while the Parylene–N revealed a dimpled surface with fibrils bundled together. Angles measured on AFM profile lines are larger when compared to angles measured on SEM images because of the broadening effect in AFM due to tip size. Global features are kept similar. The Parylene-C coating appears with a convex shape, the edges being thicker with a gradient towards the center. Parylene – N appears uniform in thickness with the dimpled aspect observed on the smaller observed surface.
At least at this scale, by surface morphology, we could infer that Parylene – N was deposited homogeneous or that the Parylene – C coating was warped. If this is so we think that Parylene-N’s higher level molecular activity during deposition generates greater penetration into crevices than that observed in Parylene-C, making it superior for coating complex topographies specially for medical instrumentation.
Keywords
Atomic Force Microscopy, Scanning Electron Microscopy, Parylene-N, Parylene-C
S. RAJESH, G. B. BHASKAR, R.SUBASH, K. PAZHANIVEL, S. SURESH SAGADEVAN
Abstract
The advancement in fiber composite technology puts back many dense materials by high strength to density ratio. Many attempts have been made with glass/carbon fiber for suspension system; still, not much has been done in the direction of optimization of the design of the leaf spring. This paper reports the work in which a new glass/carbon fiber composite material was made and tested under Tsai–Wu failure stress criteria. The Response Surface Methodology (RSM) was applied to identify the optimal composite leaf spring’s design with less stress-strain and deflection. The mechanical properties of the optimal geometry glass/carbon fiber composite leaf spring were experimentally evaluated and compared with the conventional leaf spring.
Keywords
Optimization; leaf spring; Composite; Suspension; Fiber Reinforced Plastic (FRP)
LAMIA BOUCHHIMA, MOHAMED JAMEL ROUIS, MOHAMED CHOURA
Abstract
Housing is a great problem in today’s world. The most basic building material for construction of houses is the usual burnt clay brick. A significant quantity of fuel is utilized in making these bricks. Also, continuous removal of topsoil, in producing conventional bricks, creates environmental problems. A feasibility study was undertaken on the production of full bricks by using of crushing sand-natural hydraulic lime-cement-phosphogypsum (CS-NHL-C-PG) to solve the problems of housing shortage and at the same time to build houses economically by utilizing industrial wastes. The compressive strength, flexural strength water absorption, density and speed of sound of these bricks are investigated. It is observed that these bricks have sufficient strength for their use in low cost housing development. Tests were also conducted to study the relationship between ultrasound pulse velocity (UPV) with strength of bricks. The results suggest that compressive and flexural strength values may approximately be determined without a destructive testing by using the non-destructive UPV measurements.
Keywords
Phosphogypsum, Full brick, Strength, Durability
CORNELIA - FLORENTINA DOBRESCU
Abstract
The assessment of natural and stabilized soils behaviour, using binders with ecological benefits like lime, is based on modelling of the performance characteristics related to the bearing increase of infrastructure works by developing parametric correlations. The value of CBR index represents one of the most used parameters in design, execution and quality control of road structures. Taking into consideration the necessity of a large number of tests and specimens and the long period associated to their execution, a widely used an alternative method based on correlations of CBR value and soil characteristics due to time saving, as well as independent verification and quality control of results, is used. A significant increase of CBR values due to lime stabilization in both natural and soaked conditions has been noticed. The influence of the compaction characteristics on CBR value depending on the index obtained during tests and the derived index expressed by correlation coefficients, has been reflected by good correlations of the analyzed statistical variables. The calibration modelling of data for a simple linear regression has been put into evidence by using comparative analyzes of experimental and predictable parameters.
Keywords
bearing capacity, stabilization, parametric modelling, soil structures
S.CAVALU, C. RAŢIU
Abstract
PMMA (poly methyl methacrylate)- based biomaterials still have many shortcomings. Over the last two decades, additives have been developed to address these shortcomings. In our approach, acrylic bone cements were prepared by reinforcing commercial PMMA-based bone cements with 5% Mg3Al2(SiO4)3. Structural investigation performed by ATR FTIR (Atenuated Total Reflectance Fourier Transform Infrared Spectroscopy) spectroscopy and XRD (X-Rays Difraction) demonstrated the inclusion of the crystalline phase in polymeric matrix. The SEM (Scanning Electron Microscopy) images (surface and fracture) revealed that the addition of 5% Mg3Al2(SiO4)3 create a porous structure in PMMA matrix, and facilitate the hydroxyapatite formation in vitro. The biocompatibility tests using human fibroblasts and SEM micrographs revealed the cells attachment and spreading on the surface of both specimens (with and without magnesium aluminosilicate). The fibroblasts showed a wide variety of shapes after 24 hours incubation: spread multipolar or round, as well as spindle shaped or elongated cells. No significant cytotoxic effect was noticed by MTT assay (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) tetrazolium reduction); moreover, the proliferation rate seems to be favored by the presence of 5% Mg3Al2(SiO4)3.
Keywords
PMMA bone cement, magnesium aluminosilicate, FTIR, XRD, SEM, biocompatibility
MAHAMASUHAIMI MASAE, LEK SIKONG , WITTHAYA SRIRIKUN
Abstract
Nanocrystalline TiO2 powder with and without Se doping were successfully synthesized at low temperature by a microwave-assisted sol–gel method. The synthesized TiO2 powders were characterized by XRD, UV-vis, FT-IR and SEM. It was found that anatase and brookite phase was formed after refluxed at 80°C using a domestic microwave oven. The study also investigated the efficiency of this compound to inhibit the growth of Escherichia coli with various concentrations of 0, 0.5, 1.0 and 2.0 mole% doping Se. The antibacterial activity against Escherichia coli was investigated with a vitro test, from which the mixture of conidial suspension and the Se-doped TiO2 powder was added to Macconkey Agar plates under fluorescent light irradiation. It was found that Se-doped TiO2 nanoparticles enhance photocatalytic activity and bacterial inactivation efficiency. In addition, 1.0 mole %Se doped TiO2 nanoparticles can destroy the bacteria within 10 min. Furthermore, the disinfection efficiency of Se-doped TiO2 is good activity is mainly related to the high OH radicals on its surface. The absorption threshold of the Se-doped photocatalyst shifted to the visible region of the spectrum.
Keywords
Antibacterial activity, low temperature TiO2 preparation, sol-gel.
I.GOMOIU, M. ENACHE, D. MOHANU, I. MOHANU, I. PETRE, R. COJOC
Abstract
The fungal resistance of 4 new mortars was studied according to SREN 847:2000 (ISO 847:1997). Spore suspensions of filamentous fungi belonging to Aspergillus niger, Cladosporium herbarum, Ulocladium chartarum and Penicillium sp., isolated from the contaminated frescoes of Amărăşti and Ioneşti churches from Vâlcea County, were inoculated onto the surface of mortars with and without glucose and incubated in humid chambers (RH = 90-95%, temperature = 22-260C); fungal growth was analyzed at 1, 3, 6 and 9 months by visual inspection, optical microscope and Scanning Electron Microscope. The fungal growth on the surface of mortars with and without glucose, the toxic effect of mortars as well as mortars resistance to biodeterioration were marked with numbers 0-5. Due to the fact that all mortars had been sensitive to biodeterioration, chemical treatments with 10% Preventol RI 50, 8% Biotin R and 3% Biotin T had been performed. Assessment of the efficiency of biocides for decontamination allowed suggesting a procedure to be followed in order to obtain long term resistant mortars and to suggest the procedure of chemical treatment in case that new fungal growth will be detected.
Keywords
mortar, biodeterioration, spore suspensions, fungal growth, biocides, mortar toxicity
XIAONIU YU, CHUNXIANG QIAN, LINZHU SUN, ZHIHAI HE, WEI LI, LINGJIE WU
Abstract
Magnesium phosphates can be prepared by microbial induced deposition, and bio-grouting and stirring processes are used to bind loose sand particles. The result shows that loose sand particles can well be cemented by stirring method. However, loose particles are not bound by pumping method. The X-ray diffraction (XRD) of the precipitated slurry indicates that the main component is a mixture of hydrated magnesium phosphate. Energy dispersive spectrometer (EDS) displays that elements of sandstones are mainly C, Si, O, P, Mg, Na and Cl. The average compressive strength and porosity of sandstones are 0.99±0.3MPa and 26.3±0.5%, respectively. Scanning electron microscope (SEM) shows that the cementation material in sandstones is flake nano-clusters with the size in the range of 0.5-1.5µm. Transmission electron microscopy (TEM) further indicates that a single nanoparticle is like irregular sheet in morphology, and the size of the cementitious material is in the range of 200-500 nm.
Keywords
magnesium phosphates; pumping method; stirring method; sandstone; compressive strength; Transmission Electron Microscopy
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Year
2017
-
Issue
47 (2)
-
Pages
143-146
HUI WANG , XIAOJIAN GAO, ANASTASIIA GARIPOVA, HUALONG YANG
Abstract
This paper investigated the influence of embedded electrode and pasted electrode on the resistivity behavior of carbon nanofibers (CNFs) cement paste by using the alternating current (AC) method. The dosage of CNFs ranged from 0.75% to 3.125 % by volume of cement and the samples were measured after four treatment conditions including oven dried for 3 days, being sealed for 30 days, immersed in tap water or 3.5% NaCl solution for 30 days respectively. The piezoresistive performances of carbon nanofibers cement pastes (CNFP) with two types of electrodes under oven dry state were also studied. Results indicated that the average value and variability coefficient (Cv) of electrical resistivity were reduced by the increase of AC frequency only if the CNFs content was less than 2.5 vol.%. The immersion of water and NaCl solution reduced the resistivity of CNFP when the CNFs dosage is below 2.5 vol.%. The CNFP with pasted electrodes presented higher resistivity than the specimen with embedded electrodes when the CNFs content was lower than 3.125 vol.%. However, as the CNF content exceeded 2.5vol.%, the resistivity of CNFP with two types of electrodes were almost the same. The CNFP with two electrode types presented different piezoresistive performances at various amount of CNFs. A computational model for the piezoresistivity of CNFs cement paste was obtained from this research. The results of this research also demonstrated the improving effects of CNFs on the ductility and axial compressive strength of CNFP.
Keywords
Carbon nanofibers; Cement paste; Electrode types; AC Frequency; Saturation degree; Resistivity; Piezoresistivity; Compressive strength
A. PASCU, E.M. STANCIU, I. C. ROATĂ, I. HULKA, D. UȚU, I. MAIOR
Abstract
The paper presents the influence of the deposition process parameters in order to obtain dense and no major defect biocompatible alloys based on Inconel 718 hard coatings deposited on AISI 5140 carbon steel substrate using laser cladding method. Moreover, the cladded coating properties under optimal manufacturing conditions in terms of microhardness and tribological behaviour were improved by surface solar energy irradiation. The microstructure of the Inconel 718 coating before and after solar heat treatment was investigated by scanning electron microscopy (SEM) and the sliding wear resistance was determined by pin-on-disk method (POD).
Keywords
biocompatible coatings, laser cladding, solar heat treatment, wear resistance
SANDRA CUNHA, JOSÉ AGUIAR, VICTOR FERREIRA
Abstract
The construction is responsible for high consumptions of energy and raw materials. It becomes imperative to develop new sustainable constructive solutions. The mortars with incorporation of phase change materials (PCM) have the ability to regulate the temperature inside buildings, using only the energy supplied by the sun. The main focus of this study was the microstructure and durability of mortars with PCM incorporation. The binders studied were aerial lime, hydraulic lime, gypsum and cement. The proportions of PCM studied were 0% and 40% of the mass of the sand. It can be concluded that the incorporation of phase change material in mortars causes significant changes in their properties, in fresh and hardened state, such as microstructure, water absorption by capillarity and immersion, and degradation by freeze-thaw. Consequently, the addition of this material affects the durability and microstructure of the mortars developed.
Keywords
Durability; Microstructure; Mortars; Phase Change Materials (PCM); Freeze-thaw resistance; Water absorption
D.C. NĂSTAC, R. M. FECHET
Abstract
Alternative materials such as industrial wastes and by-products can be easily and economically utilized as raw material in Portland cement clinker manufacture. These materials are generated in abundance as a result of growing worldwide industrialization. Two types of wastes from mining industry were used as secondary raw material in a concentration ranging from 1.4 to 3.5%. CEM I cements were obtained from these clinkers and compressive strength was determined. Different amounts varying between 3 and 7% of sludge generated in the effluent treatment plants of oil fields were added to a base raw mixture and the effect on the clinkering process was studied. The chemical and mineralogical compositions of the wastes and raw meals were determined. The raw mixes burnability containing different concentrations of wastes in various stages of burning in a laboratory furnace to form a Portland cement clinker was investigated. An improved burnability was noticed without affecting the clinker quality.
Keywords
alternative raw materials, Portland cement clinker, tailing waste, effluent treatment plants sludge
E. RĂDULESCU, R. LISNIC, I. IORDACHE, S. NICULESCU, T. IOVU
Abstract
The usage of fuels in cement industry has achieved significant thresholds, currently is seeking solutions for the optimization of fuel mix necessary for a good kiln operations. The study presents the combustion air needed for a fuel mix (conventional and alternative fuels) in different percentages as well as their influence on production and consumption in cement plants.
Keywords
clinker kiln, alternative fuels, fuel specific consumption, process parameters, combustion
M.Z.BESSENOUCI, N.E.BIBI-TRIKI, M.HENAOUI, S.KHELLADI
Abstract
The present work focuses mainly on the thermo mechanical experimentation of different samples of lightweight concrete with different compositions and cement dosages.
The use of pozzolan in the compositions of lightweight concrete in the form of aggregates constitutes the essence of granular skeleton of the concrete.
Keywords
Lightweight concrete, Pozzolan concrete, Porous materials, Compression strength, Thermal conductivity, Aggregates of pozzolan, Thermal insulation, Modeling, Building
G. MURALI, V. CHANDANA
Abstract
The variations in impact strength of self-compacting concrete reinforced with recycled Carbon Fibre Reinforced Polymer (CFRP) Pieces were examined using Weibull reliability analysis. For this purpose, the experimental results of an earlier research were investigated statistically using the two parameter Weibull distribution. The shape and scale parameter of Weibull distribution function was determined from five statistical methods namely Least-Squares (LS) regression of Y on X, Least-Squares (LS) regression of X on Y, Empirical Method (EM), Energy Factor Pattern Method (EPM) and Graphical Method (GM). The Weibull parameters were used to describe the impact strengths (number of blows required to cause first crack and failure) in terms of reliability. Further, regression equations were developed between the impact strength and reliability of self-compacting concrete reinforced with recycled CFRP Pieces. In order to validate the developed linear regression equations, six reliable statistical indicators namely Root Mean Square Error (RMSE), Mean Absolute Percentage Error (MAPE), Mean Absolute Deviation (MAD), Integral Absolute Error (IAE), Relative Root Mean Square Error (RRMSE) and Relative Percentage Error (RPE) have been used. Results suggested that the LS- X on Y, EM and EPM are more effective to estimate the Weibull parameters. The developed linear regressions equations which were validated by six statistical indicators show a good fit and higher accuracy.
Keywords
Weibull, Impact strength, Least-square, Reliability, Shape parameter, Scale parameter
RAHMAT MADANDOUST , MOSTAFA KAZEMI, SEDIGHE YOUSEFI MOGHADAM
Abstract
In the present numerical study, an attempt is made at a comparative analysis, in terms of tensile strength of concrete, among the modulus of rupture test, Brazilian splitting test and concrete direct tension test. In direct test method, two aligned steel bars were placed in a cylindrical specimen to transmit the uniaxial force to the concrete specimen. The tensile strength of concrete affects the behavior of concrete structure. Drawing on this, estimating true tensile strength, as one of the basic properties of concrete, is headed by researchers. The present study intends to analyze tensile strength tests of concrete by means of finite element (FE) method employing ABAQUS software. The accuracy of the FE models is confirmed using outputs of previous experimental studies. Results indicate that although all these tests are usually used to estimate the tensile strength of concrete, modulus of rupture and Brazilian splitting tests investigate better behavior of concrete in tension and the results of which are also more reliable than those of concrete direct tension test. Furthermore, it seems that the steel bars in direct tension test affect the stress distribution.
Keywords
tensile strength of concrete, FE analysis, fracture zone, tensile damage
D. GEORGESCU, A. APOSTU, G. CROITORU
Abstract
This article presents the results of some experimental researches carried out in order to establish the level of performance of the concretes prepared with different types of cements and aggregates that are used in the Republic of Moldova, with a view to develop the National Annex to the EN 206-2013 standard.
Establishing the characteristics of resistance and durability was done by applying some European and national standards and had as its main objectives to establish the domains of using the concretes and the analysis of the conditions of applying the methods based on the performance of durability. In the National Annex were presented (by means linked to practical applying of the document), ”deemed to satisfy” rules regarding the types and quality of materials, the composition of concrete and minimal classes of resistance at compression, depending on a certain use of the concrete.
Keywords
cement, concrete, performance, durability
E. RĂDULESCU, I. IORDACHE , R. LISNIC, S. NICULESCU, L. DRAGU
Abstract
A solution to waste generated in increasing amounts, appeared over 35 years ago when alternative fuels started to be used worldwide. Saving the significant amounts of fossil fuels represent an important advantage of using these fuels.
Petroleum wastes are generated from current activities of oil industry as well as from remediation activities of historical petroleum ponds. The study aims an assessment of carbon monoxide emissions generated from the combustion of classic and alternative (oil sludge and sawdust) solid fuels in a clinkering installation. The nature and ratio of fuel used can influence the level of carbon monoxide emissions.
Keywords
combustion, carbon monoxide, alternative fuels, clinker kiln, petroleum waste
A. SAMAOUALI, Y. EL RHAFFARI, M. HRAITA, L. LAANAB, H. OUDRHIRI, Y. GERAUD
Abstract
The aim of this work is to determine the physical and mineralogical characteristics of the building stones used in the archeological Roman site named Chellah in the Rabat city (Morocco). For that, many experimental measurements, based on the mercury intrusion porosimetry and Scanning Electron Microscopy were carried out on samples extracted from different areas of the building. The SEM analysis shows a net change in the internal structure of the altered stone according to the depth. The porosity is essentially localized between the primary particles and can be completely sealed by secondary precipitations. The mercury porosimetry measurements allow obtaining several parameters and show the presence of three types of porosity domains :i) a macroporosity domain in which the access ray is greater than 2 µm), ii) a microporosity domain in which the access ray is smaller than 0.2 µm and iii) no porosity variation (0.2 < access ray < 2 µm), which evolves to a class of mesoporosity during the alteration of the material. The increase in the microporosity and macroporosity is caused by a partial dissolution of cements. The analysis of altered and unaltered samples of various orientations shows a difference between the pore volumes for samples perpendicular and parallel to the bedding plane. This result confirms that Calcarenite stones are anisotropic materials in which the porous network connectivity is characteristic of the petrophysical properties anisotropy.
Keywords
Chellah monument, Calcarenites, mercury intrusion porosimetry, porous network, anisotropic connectivity
Z. VULUGA. J. PACEAGIU, M. IORGA, A. MOANȚĂ, H. POP
Abstract
In this paper, new composites based on polypropylene (PP) filled with 5 ÷15% natural siliceous material and 20% styrene-butadiene –styrene block copolymer (SBS) were prepared. The siliceous fillers used in this work were the volcanic tuff and kaolinite clay. PP composites filled with mineral filler and SBS were prepared using extrusion compounding and injection molding by dynamical melt processing.
The influence of the mineral filler and SBS on the thermal properties (thermal conductivity and thermal stability evaluated by TG/DTA analyses) and mechanical properties (elasticity modulus, yield strength, elongation at break and Izod impact strength) of the PP matrix composites were studied.
The results showed that the elasticity modulus of new composites is enhanced with increasing the filler content. A better behavior is noticed in case of volcanic tuff using. The Izod impact strength is more enhanced (of 2.5 times) by adding of 20% SBS in the PP/mineral filler composites. Also, the thermal behavior of PP matrix composites is improved.
Keywords
organo-mineral composites, volcanic tuff, clay, mechanical properties, thermal properties .
ALIM KAŞTAN, YILMAZ YALÇIN, HÜSEYIN ÜNAL
Abstract
This study investigates the wear behavior of the composites such as wear rate-load, coefficient of friction-load and coefficient of friction-direction relationships. For this purpose, polyamide 6 (PA 6), high density polyethylene (HDPE), montmorillonite as nanoclay (NC) and the compatibilizer maleic anhydride-grafted-polyethylene (PE-g-MA) are used in this study. The HDPE, nanoclay (montmorillonite) and the compatibilizer are added to a PA 6 matrix material and their effect on the wear property of the composite is investigated. The wear tests are performed in a pin-on disk machine to determine these properties. Optical microscope examination of the wear surfaces is conducted by a transmission electron microscope (TEM) in order to find out more about the material characterization. As a result of the experiments, it is observed that 1% nanoclay (montmorillonite) added to the material has a positive effect on the wear. However, the wear is observed to increase with an increase in the rate of the nanoclay.
Keywords
Polymer, Nanocomposites, Polyamide 6, High density polyethylene, Wear
M.ZİYA KARATAŞ, TAMER RIZAOĞLU
Abstract
The development of materials that provide thermal comfort in buildings have become popular in recent years.The investigation of the technical characteristics of these products and the development on these characteristics have been accelerated in line with this trend. In this context, as well as the specifications of the materials used, the sensitivity to environment and economical processing are also important. In this study, particularly due to the low thermal conductivity of muscovite, mica schists were used as one of the components of the composites together with well-known natural isolation materials such as perlite and pumice. On the other hand, for the first time, the arenitized granite was used for this purpose. The physical and mechanical tests were performed on blocks (40x40x160 mm in size) prepared from the combination of the materials mentioned above and final products (isolation panels) produced after the application of the mixtures on Expanded Polystyrene foam (EPS), Extruded Polystyrene foam XPS and Mineral wool. Both blocks and plates provide the expected technical satisfaction for the physical and mechanical characteristics, according to ASTM and Turkish standards.
Keywords
Natural materials, Isolation plates, XPS, EPS, Mineral Wool
I.HUDIȘTEANU, N. ȚĂRANU, D. N. ISOPESCU, L. BEJAN, A. AXINTE, D. UNGUREANU
Abstract
The paper presents a comparative analysis of six cases of symmetrically balanced composite laminates, having the same stacking sequences in terms of fibre orientation angles, but different composite laminas. The purpose of the paper is to investigate the influence of the selection of the composite materials and configurations of the laminas on the mechanical performances of laminated composites.
A finite element analysis in ANSYS Composite Pre/Post software is performed in order to study the mechanical characteristics under tensile loading of the composite laminates and to analyse the stresses and damage distributions on each layer with different fibre orientations.
The results are comparatively presented in terms of the in-plane and flexural engineering constants of the considered laminates, ultimate loads when first ply failure (FPF) and last ply failure (LPF) occur, and their corresponding equivalent stresses on the layers of the laminates.
The damage initiation and damage evolution on the layers of the composite elements are indicated for different loading steps.
Keywords
composite laminates, failure criteria, first ply failure, last ply failure, damage initiation and evolution
C. O. BURADA, M. M. STĂNESCU, C. M. MIRIŢOIU, A. BOLCU
Abstract
The research presented in this paper consists in obtaining some composite platbands from polyester resin with randomly disposed fiber glass fabric as reinforcement. For the obtained samples, tensile loading on an universal testing machine was made and their elasticity modulus has been determined. Then, the experimental results have been compared with the ones obtained from some analytical methods. In the second part of the paper, the platbands were clamped at one end and the other was left free. By placing an accelerometer at the free end, free vibrations were recorded. By analyzing the free vibrations, the damping factors per unit mass and length, the eigenfrequency, the dynamic Young modulus and the loss factor have been determined. Very close results have been obtained between the static and dynamic Young moduli and, in the end, an overall elasticity modulus for samples with different glass fiber volume fractions has been defined.
Keywords
elasticity modulus, static loading, damping factor, eigenfrequency, loss factor, free vibrations .
A. MOANȚĂ, I. MOHANU, J. PACEAGIU, D.C. NĂSTAC, I. PETRE, R.M. FECHET
Abstract
The paper presents the results of laboratory research concerning the possibility of replacement the pyrite cinder from the clinker’s raw mix, with other waste with high Fe2O3 content, like mill scale. An assessment of technological and qualitative aspects that involved this issue was taken into account. The influence of mill scale both on the raw mix burnability and clinker characteristics was investigated. The composition, mineralogical and structural – textural features of the resulted clinkers were characterised by wet chemistry, X-rays diffraction, and optical microscopy analysis. Also, theoretical consumption of heat at clinker formation was assessed. Cements CEM I were obtained from clinkers synthetised in the laboratory. These cements were characterized from physical-mechanical point of view, according to SR EN 197-1. The qualitative appreciations and the technological behavior were achieved in comparison with a raw mix, obtained from current raw materials, considered as reference. Presence of mill scale in raw mix did not modify qualitative characteristics of the clinker and cement, respectively. This finding sustains the possibility of replacement of the pyrite cinder with mill scale in clinker raw mix.
Keywords
clinker, steel mill scale waste, cement
D. RADU, Z. GHIZDĂVEȚ
Abstract
Reactions that conclude to clinker formation from raw materials can be, basically, considered as taking place between oxides, and are of an acid-base nature. A straightforward hypothesis can follow: the basicity gradient between oxides – which is an intrinsic attribute of the raw meal – determines from a chemical viewpoint the raw mixes burnability. This feature, along with the Lime Saturation Factor, LSF, influences both reactions’ kinetics and the degree of transformation of the reactants in reaction products. In this paper, a series of correlations between burnability and basicity gradient and LSF were extracted; in that purpose, there were used several series of foreign and indigenous raw meals. The analysis of the results confirmed the starting hypothesis.
Keywords
clinker, raw mix, burnability, acidity and basicity, correlations
ANDREI-DAN BUSUIOC, RAMONA ENUŢĂ, ŞTEFANIA STOLERIU, OVIDIU OPREA, TEODOR VIŞAN
Abstract
La3+ or V5+ doped SnO2 powders were synthesized by the precipitation method, the crystalline phases being obtained after a thermal treatment at 400 °C. The calcined samples were characterized in terms of crystalline structure, morphology and optical properties by employing X-ray diffraction, scanning electron microscopy and UV-Vis spectroscopy. The results indicate that both doping cations modify the average crystallite size and bandgap of SnO2 based materials, while their concentration permits a fine tuning of the functional features.
Keywords
Semiconductor Oxides; Precipitation Method; Dopants; Bandgap; Gas Sensors
ADRIAN VOLCEANOV, ENIKO VOLCEANOV, ALEXANDRU CONSTANTINESCU, AUGUSTIN SEMENESCU
Abstract
Hardness is an important mechanical property of materials. It is defined as the resistance of a material to localized deformation. The ionicity of chemical bond plays a significant role in mechanical properties such as hardness, bulk modulus. Recent studies have shown that hardness, a complex property, can be calculated using very simple approaches or even analytical formulae. In these models, the theoretical hardness is described as a function of the bond density and bond strength. The bond strength may be characterized by energy gap, reference potential, electron–holding energy or Gibbs free energy, and different expressions of bond strength may lead to different hardness models. The chemical bond parameters and hardness values of crystals had been calculated based on our own model of ionicity derived from the dielectric theory of the chemical bondings. Part 1 of the paper deals with the correlation between bond length, unit cell parameters, ionicity, and hardness for some homodesmic inorganic compounds. The results of computation and comparison with experimental data are performed.
Keywords
hardness, ionicity, homodesmic structures
OUIDETTE SLIMI, LAID HAMMICHE, DJAMEL DJOUADI, AZEDDINE CHELOUCHE, MALAAZ MEDDOURI
Abstract
Nanocomposite films formed by direct inclusion of ZnO aerogel nanoparticles in liquid state silica matrix and deposited by dip and spin-coating techniques on glass substrates were elaborated. The ZnO aerogel particles were synthesized in supercritical methanol using a modified sol-gel process. The elaborated particles and the coated composite films were characterized by XRD, FTIR spectroscopy and by optical absorption. XRD patterns show a broadening of diffraction peaks of ZnO crystallites and a significant reduction in the intensity after their dispersion in silica. A reduction in lattice parameters was observed after the introduction of ZnO aerogel particles in silica. The Zn-O vibration bond strongly shifts to lower wavenumbers in composite films compared to the aerogel due to the formation of silica layerand successfully grafted over the ZnO nanoparticles. A strong Zn-O-Zn vibration bond is observed only in the spin-coated film. The blue shift observed in the absorption spectra indicates an enhancement in the optical band gap due to quantum confinement effect of ZnO nanoparticles when they are dispersed in silica matrix.
Keywords
supercritical drying, ZnO aerogel, composite films, spin-coating, dip-coating
ANDRADA PASCU, ALIDA TIMAR-GABOR, AHMED KADARI, VIORICA SIMON
Abstract
Structural characteristics of undoped and gadolinium doped melt-derived samples of SiO2-B2O3 oxide system, as well as thermoluminescence (TL) properties and kinetic parameters of the sample with 40SiO2∙59.5B2O3∙0.5Gd2O3 composition were investigated in the present study. The gadolinium doped sample showed bright TL signal following irradiation with 6 Gy, good repeatability (under 10% deviation from the unit), linear dose dependence for the tested dose range (0.75 Gy – 9 Gy) and a minimum detectable dose of 34 mGy for instantaneous measurements. The kinetic parameters associated with the glow curves of 40SiO2∙59.5B2O3∙0.5Gd2O3 sample followed second order kinetics, while the value of the average activation energy was 0.88 eV. Both undoped and gadolinium doped samples were characterized by similar structural features.
Keywords
TGA, XRD, FTIR, thermoluminescence (TL), kinetic parameters, borosilicates
ALI UĞUR ÖZTÜRK, GÖKHAN KAPLAN
Abstract
Workability, strength and durability are among the most important properties when working with concrete. Increased compressive strength of concrete has favorable impact on durability along with on its several other features. To ensure a high degree of durability, it is essential that clean, sound materials and the lowest possible water content are used in the concrete, together with thorough mixing. Good consolidation during placement of the concrete is important, as are proper curing and protection of the concrete during the early hardening period, which assure favorable conditions of temperature and moisture. Cure concrete properly for a minimum of three days in order to develop good durability.
In this study mortars with white cement and Portland cement and different w/c ratios were produced and investigated. The mortars produced were then tested for the impacts of alkali silica reaction (ASR), high temperatures, abrasion and acid effect. Results show that less expansion was measured on the mortars using portland cement while the white cement gave the largest expansions (approximate 0.60%).However, there was no significant difference between cements in terms of their acid resistance. The impact of higher temperatures on mortars produced using white cement was less in comparison with normal Portland cement. Durability tests showed that w/c ratio plays an important role.
Keywords
White cement, alkali silica reaction, acid effect, high temperature, water/cement ratio
LIDIA RADU, NASTASIA SACA, MARIA GHEORGHE, CLAUDIU MAZILU, VIOREL FUGARU
Abstract
The article presents the influence of the heavy aggregates and the water/binder ratios on the engineering and gamma shielding properties of the concrete. The elements with great atomic number, Z as Pb (Z = 82) and Ba (Z = 56) contented in the used heavy aggregate, namely lead slag, cathode ray tube (CRT) glass waste and barite, showed a decisive contribution to the increase of the concrete gamma radiation shielding. Also, the high density of the concrete was significantly influenced by the steel shot aggregate as partially substitute of the siliceous sand.
The concrete with CRT glass waste recycled sand had 360 days compressive strength (88.3 MPa) higher than the river sand concrete (83.5 MPa), at the same aggregate volumes and the same water/cement, w/c, ratio (0.38).
The results showed that concrete with complex aggregate based on barite, steel shot and CRT waste glass have had the highest gamma linear attenuation coefficient of 0.192 cm-1 for Co-60, higher by 18.2 % than concrete with barite as total aggregate.
Keywords
Heavyweight concrete, density, linear attenuation coefficient, compressive strength
FARID BENMERIOUL, AHMED TAFRAOUI, ABDELKADIR MAKANI, SAID ZAOUAI
Abstract
Sustainability of the construction industry is a challenge to every concerned civili Engineering professional. Iron ore tailings is an industrial waste derived from the production process of iron ore. This study consider the possibility of using this waste for making concrete. The tailings was combined with sand in varying proportion as fine aggregate in concrete. One control sample with no tailings and four others incorporating tailings at varying percentage as partial replacement for sand were used for the experimental program. The physical and microscopic properties of the tailings were compared with those of sand. The mechanical properties and microstructure of the hardened concrete were also studied. The outcomes of experimental tests shows that the tailings increased the denseness of concrete matrix and improved the water resistance of the concrete.
Keywords
Fine aggregate; Concrete; Iron ore Tailings; Strength; Microstructure; Water sorptivity.
MIHAELA-ANDREEA MONCEA, FLORINA-DIANA DUMITRU, ANA-MARIA PANAIT
Abstract
Concrete corrosion represents a complex process, the mechanisms by which it occurs being particularized depending on the environment where it is exploited. Thus, for a concrete exploited in natural aggressive environments (alpine, marine), the corrosion processes will take place with lower speeds than for a concrete exploited in aggressive industrial environments.
In order to highlight the effects of marine environment on the concrete structure, at high periods of time, the ancient concrete constructions from the Romanian coastline, represented by casemates (built since 1942), in the present paper, these type of structures were visually assessed in situ. The effects of marine corrosion at microstructural level were also analyzed by sampling the concrete specimens, mainly from the concrete/reinforcement interface areas, from the body of casemates located in Tuzla, Costineşti, Olimp, Mangalia, 2 Mai and Vama Veche resorts. For this purpose, X-ray fluorescence (XRF) was used to determine the content of chemical species with corrosive potential from the concrete composition, and scanning electron microscopy analyses (SEM) coupled with energy dispersive X-ray spectroscopy (EDS) to identify the crystalline corrosion products formed at the concrete/reinforcement interface.
The visual assessment of the ancient concrete structures showed a precarious conservation state of these strategic military objectives, with significant historical value. The chemical analyses, performed through XRF on ground and sieved concrete specimens, highlighted the presence of high amounts of Fe2O3, extracted by metal corrosion from the reinforcement, as well as high amounts of Cl and alkali, originating from the natural marine environment. The SEM analyses revealed a porous microstructure with crystalline compounds belonging to the hardened cement structure - ettringite, calcium hydroxide and calcium silicates hydrates – and corrosion compounds such as magnetite (Fe2O3), akaganeite (β-FeOOH) and lepidocrocite (γ-FeOOH), formed by chemical interactions between the aggressive ions of the marine environment and iron from the reinforcement.
Keywords
concrete corrosion, marine environment, SEM, EDS, XRF analyses
DAN BABOR, LOREDANA JUDELE, DANIEL LEPĂDATU
Abstract
Constructions composed of mortars and cement concretes are exposed to advanced nitrate ion corrosion processes if they are used in aggressive mediums, specific to nitrogen fertilizer industry. The paper aims at tracking down the behavior of cement mortars with a high content of slag (75%) exposed to nitrate ion corrosion as well as carrying out a analysis that might reveal the time evolution of mechanical strength of the standard mortar samples or of those containing slag, when they are submerged in various aggressive solutions. Corrosive agents, acting on the above mentioned items are in particular nitrogen oxides and ammonia gas. These compounds are found in considerable amounts in the atmospheric feature of this type of industry and their effect is intensified by an accidental increase of humidity, temperature, or steam, or unexhausted corrosive gases accompanied, possibly, by inadequate ventilation. The analysis of complex chemical processes enables the highlighting of the influence of different corrosive agents on the strength of these special mortars.
Keywords
acid nitric corrosion, slag mortar, compressive and flexural strengths
SELIM KORKMAZ , FAHRI BIRINCI
Abstract
In this study, the effects of using fiber in self compacting concrete (SCC) on flow parameters, tensile and compressive strength of concrete were investigated. Unit weight, air content, slump flow, J-ring, V-funnel tests on fresh concrete and compressive, splitting tensile along with flexural strength tests on hardened concrete were performed, in addition fresh and hardened concrete properties were studied for to determine the relationship between them. A polypropylene fiber, an alkali-resistant glass fiber and two types steel fibers which have the different lengths and the different length/diameter ratio were used in the test specimens. It is observed that an increase in the amount, length and length/diameter ratio of steel fibers resulted in an increase of the tensile strength of concrete (more than 90% in flexural tensile strength according to non-fiber concrete series), while, properties of fresh concrete deteriorated and compressive strength of concrete decreased.
Keywords
self compacting concrete, SCC, fibers, fiber concrete, tensile strength.
RUBEN P. BORG, CHARLO BRIGUGLIO, VYTAUTAS BOCULLO, DANUTĖ VAIČIUKYNIENĖ
Abstract
Concrete produced from ordinary Portland cement (OPC), is a building material with wide applications, due to various factors, including strength and durability characteristics. Nevertheless, OPC concrete has a significant environmental impact due to resource consumption and energy intensive production of the cement as a result also of the high temperatures during manufacture. The main factors that affect the geopolymerisation process include the type and characteristics of the raw materials, the alkaline activators and the curing conditions. The optimum alkaline solution used and activator, to raw material mass ratio depend on the type and characteristics of the raw materials being used. Furthermore, the curing conditions adopted depends on the characteristics of the raw materials and activators. Industrial by-products and waste rich in SiO2 and Al2O3 can be utilized as raw material for geopolymer concrete. In this research, three different waste materials were considered: Polish coal burning fly ash (FA), Lithuanian biomass bottom ash (BMBA), AlF3 production waste (PW). Paste was produced to determine the influence of the Al2O3/Na2O ratio on the geopolymer paste properties. The material properties were determined for the curing conditions set with respect to X-Ray diffraction characterisation (XRD), Helium Pycnometry (HP) and Mercury Intrusion Porosimetry (MIP) and compressive strength.
This research shows that, the three waste materials analysed, all have great potential for use as a geopolymer concrete, to varying degrees. It was further determined that the mix ratios and the curing environment are critical for the performance of the material in cast in situ and precast concrete applications.
Keywords
geopolymer binder, industrial by-products, AlF3 production waste, type F fly ash, biomass bottom ashes, waste.
AURELIA BRADU, PETRU MIHAI, MIHAI BUDESCU, OANA-MIHAELA BANU, NICOLAE ŢĂRANU, NICOLAE FLOREA
Abstract
The self-compacting concrete (SCC) can be promoted in construction industry only after performing a wide range of studies upon its properties. The mechanical characteristics of this material have been less analysed, the up-to-date results from the scientific literature often being in contradiction. The study of the SCC behaviour in the post-elastic range, which is an important feature in the structural design of the constructions located in seismic areas, provides the possibility to evaluate the real energy dissipation capacity. Within this paper, a comparative study between the essential properties and the complete stress-strain curves of the (SCC) and vibrated concrete (VC) loaded in compression has been performed. The experimental program has been carried out using an innovative testing system conceived and patented at the Faculty of Civil Engineering and Building Services from the ”Gheorghe Asachi” Technical University of Iasi. The analysed concrete mixes have been prepared in three batches keeping constant the amount of cement, and the concrete flowability was achieved through variation of the limestone filler and concrete admixtures quantities. The mechanical characteristics of both self-compacting concrete and vibrated concrete are different. This difference becomes more obvious once the volumetric fractions of coarse and fine aggregates are modified. It can be also stated that the complete stress-strain curves of SCC and VC are different revealing the convenient capacity of SCC to absorb deformation energy.
Keywords
self-compacting concrete, workability, post-elastic domain, complete stress-strain curve, energy dissipation capacity
AMIN KHAZAEE, ALI KHAZAEE
Abstract
Because high performance concrete (HPC) is a complex composite material, model of its compressive strength is highly nonlinear. Common mathematical models cannot handle this nonlinearity and recent studies tried to propose predictive models based on advanced machine learning approaches. Support vector regression (SVR) by incorporating different linear and nonlinear kernels has proved its effectiveness to solve such problems. However, the problem of model selection in SVR, provided limitation for effective concrete compressive strength (CCS) prediction. We employed the search ability of evolutionary algorithms and proposed a hybrid SVR-artificial bee colony (SVR-ABC) algorithm for the problem of CCS prediction. The proposed method can estimate CCS of different composition concretes with a high accuracy.
Keywords
Concrete Compressive strength; Prediction; Support Vector Regression; Artificial Bee Colony
C.VIVEKANANDHAN, P.S.SAMPATH, SURESH SAGADEVAN
Abstract
Composite materials are being widely employed in numerous modern applications. Fabrication of new composite materials has been holding the consideration of scientists worldwide and attempts are being made to improve the applicability of these materials. In perspective of this advancement in the research field, the present work attempts to concentrate the impact of nanoclay content on the structural and morphological behavior of epoxy composites. Epoxy materials were reinforced with various particulate portions of chosen nanoclay and the specimens were investigated. The structural examination of the polymer composite with X-ray diffraction showed that the nanoclay was distributed as an intercalated structure in the polymer matrix, and the d-spacing of layers decreased with increasing nanoclay content. SEM images analysis revealed that 2% nanoclay reinforced samples exhibited less number of but more uniform pores compared with 10% nanoclay reinforced samples.
Keywords
Composite materials, Nanoclay, Scanning electron microscopy, X-ray diffraction.
C. RAMESH, C. MANICKAM, T. MARIDURAI, V.R. ARUN PRAKASH
Abstract
In this present work particulate epoxy composite was prepared with thermo assisted surface treated Fe2O3 fine particles. The principal aim of this work is to improve wear resistance of epoxy resin by reinforcing iron oxide particles. Particle size of 800nm and 200nm were used to fabricate particular composites. Particles were heat treated from 30º C to 900º C in a muffle furnace to relive induced stresses which are gained in pre processes and getting magnetite phase. The resultant phase change in iron oxide particles were confirmed by X-ray diffraction. The heat treated particles were again surface treated with a silane coupling agent 3-Aminopropyletriethoxysilane (APTMS). The composites were prepared with reinforcement of 1wt%, 3wt% and 5wt% of iron oxide filler into epoxy resin. All proportions of composites were cured by an aliphatic hardener triethylenetetramine (TETA). Wear characters of epoxy-iron(III)oxide system was studied with pin-on-disc setup. Wear resistance was improved significantly for particle loaded composite in which heat treated siliconized iron oxide-epoxy system gave better result. Scanning electron microscopic images revealed filler dispersion on epoxy matrix.
Keywords
Particulate composite; APTMS; SEM; Optical microscopy; Pin-on-disc
BOUZEROURA MANSOUR, BOUAFIA YOUCEF, MOUSSACEB KARIM, DJENADI ROCHEDDINE
Abstract
The present work were the efficiency and mechanism of stabilization/solidification of ultimate inorganic waste (hydroxides and metal fibers sludge), in cement matrix. This waste, characterized by the standard toxicity characteristic leaching procedure (TCLP) test, showed that the concentrations (mg/kg) of heavy metals were: Ni2+= 384.9, Cr3+ = 80.2 and Pb2+ = 165.6, the average concentrations of heavy metals in the raw waste far exceed those of standards required. Leaching of heavy metals from the mortar and concrete was evaluated by the Monolithic leaching test (MLT), under dynamic leaching conditions for 64 days with periodic leachate renewal in different mediums: neutral, basic, acid and sulfated, for two types of formulations selected: Mortar MD and Concrete B (25%). The mechanical strength, XRD, endogenous shrinkage and total withdrawal (with and without exchange with the surroundings) were analyzed. The amounts of heavy metals released into the sulfated medium are important compared with those observed in other mediums. The results showed that heavy metals could be effectively, immobilized in cement matrices. It was concluded that further research on the influence of the metal fibers in the retention of heavy metals is needed to improve the effectiveness of stabilization / solidification in cement matrices.
Keywords
Hydroxides sludge, metal fibers, cementitious matrix, leaching, stabilization / solidification
ANDREI-DAN BUSUIOC, RAMONA ENUŢĂ, ŞTEFANIA STOLERIU, TEODOR VIŞAN
Abstract
Pure and La3+ or V5+ doped SnO2 based ceramics were obtained by shaping and sintering of nanosized powders, previously synthesized by the precipitation method. The thermal treatment temperature was in the 1300 - 1500°C range. The resulted ceramic bodies were characterized through X-ray diffraction and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. The ceramic properties and sensitivity towards methane and isopropyl alcohol vapours were also determined. It was demonstrated that dopants use has a beneficial effect on the gas detection capability, especially at low concentrations.
Keywords
Tin Oxide; Semiconductor; Ceramics; Dopants; Gas Sensitivity.
ENIKÖ VOLCEANOV, ADRIAN VOLCEANOV, SIMONA MARIA SANDU
Abstract
The purpose of this work is to examine the possibility of developing a new way to use abundant ash waste from coal burning through a rapid thermal treatment of ceramic composite bodies. The formulation of ceramic bodies was realized with clay and 10-50% (by weight) fly ash (class F) originated from bituminous coal burning and followed by rapid sintering at 950°C, 1000°C and 1050°C in microwave field at varying intervals of time ranging from 5 to 20 minutes. The ceramic properties in conjunction with morphological-structural characteristics after microwave field roasting were investigated. The results show that the development of lightweight ceramic starting from clay and coal ash can be effective in appropriate heat treatment conditions in microwave field at 2.45 GHz frequency. The effectiveness of the sintering process was evaluated as a function of the sintering time and specimen composition. The mineralogical phase analysis of samples cured at 1050°C for 20 minute showed the major crystalline mineral compounds as: quartz, mullite and hematite. The ceramic properties recommend them as lightweight aggregates for application in building materials area.
Keywords
Coal ash, Lightweight ceramic, Microwaves
COSMIN VANCEA, MARIUS GHEJU, GIANNIN MOȘOARCĂ
Abstract
The present paper proposes an innovative way to harness the exhausted reactive mixtures resulted from the removal of Cr(VI) with Fe0 in continuous-flow system (column experiments), by vitrification using two types of common waste glasses: window panes and cathode ray tubes (CRT). The melting of the two types of wastes (glass and the reactive mixture containing chromium), conducted in economically advantageous conditions at 1000°C for 180 minutes generates very viscous melts that were difficult to process. Therefore it was considered necessary to use borax as a flux in order to improve the fluidity of the melted glasses. The RX diffraction was used to confirm the vitreous character of the samples, validating the purposed melting conditions. The hydrolytically stability, determined according to the ISO 719/1985, classify all the investigated glasses in the most stable class of glasses HGB1. The chemical stability and chromium and iron ions leachability were determined and American Extraction Procedure Toxicity Test respectively. The chemical stability of the glasses expressed by measuring their dissolution rate show two different behaviors: one for acidic and neutral mediums and another for alkaline medium, corresponding to two different attack mechanisms on the glass matrix. At pH = 5.5 and pH = 7.0 the glasses dissolution rates are very low, between 0.013-0.059 g/h, while at pH = 8.5 the values rise to 0.143-0.492 g/h. The amounts of chromium and iron ions leached from all the investigated glasses regardless the environment’s pH and the considered time are very low, between 0-0.0104 % of the total chromium and between 0-0.0042 % of the total iron brought by the exhausted reactive mixtures. The obtained results confirm the viability of the suggested solution for immobilizing the exhausted reactive mixtures containing chromium together with common waste glasses in order to obtain glasses having very high chemical stability with multiple economic advantages.
Keywords
wastes vitrification, waste glasses, glass recycling, chromium wastes.
A. DJERIDI, N. KAMEL, A. BENMOUNAH, D. MOUDIR, S. KAMARIZ, Y. MOUHEB
Abstract
An iron phosphate glass in the system 25 wt.% Fe2O3- 57 wt.% P2O5 - 8 wt.% B2O3 - 8 wt.% Na2O - 2 wt.% As2O3 was synthesized by a double melting /casting method at 1100°C. Fe/P is atomic weight ratio is fixed to 0.67. 20 wt.% of simulated nuclear wastes were successfully immobilized in the glass bulk. Both density and molar volume, measured for both pure and waste loaded glasses, are representative values of phosphate glasses. X-ray diffraction analysis confirmed the amorphous feature of both glasses, and scanning electron microscopy allows the microstructure observations. The glass transition temperature (Tg), the crystallization (Tc) and melting (Tm) temperatures are measured by DTA analysis. Tg = 623 and 580°C; Tc= 766 and 679 °C and Tm=933 and 929 °C; for the pure and RW loaded glasses, respectively. Hruby (KH =(Tc - Tg)/(Tm - Tc), Weinberg (KW =(Tc - Tg)/Tm) and Lu/Liu (KLL = Tc/(Tg + Tm)) criteria were used for the evaluation of glass stability of both pure and radioactive waste loaded glasses. Although the values are lower for the radioactive waste loaded glass compared to those for the pure glass, and thus, the no loaded glass is more stable than the radioactive waste loaded one. The calculated criteria remain in an acceptable interval between 0.11-0.86, suggesting that the glass stability is not altered by the addition of 20 wt.% of simulated radioactive waste. The glass forming ability (GFA) is assessed by ΔTxg =(Tx – Tg), ω2, α, β, γm, and ε criteria. The calculated criteria allow valuable conclusions on the good thermal behavior of the radioactive waste loaded phosphate glass.
Keywords
Iron phosphate glass, Thermal stability, Glass forming ability, Radioactive waste, DTA, XRD, SEM.
ALEMDAR ONGUN, AHMET AVCI, ALI ERIŞEN
Abstract
This study was conducted for the purpose of examining the mechanical relations of the multi-walled carbon nanotube (MWCNT) and the nanoclay (NC) with each other on the carbon fiber composite materials. Samples were prepared by reinforcing the MWCNT and the NC into the epoxy matrix at various rates to have them absorbed into the carbon fiber laminates via the vacuum infusion method. Carbon nanotube (CNT) was added into all the epoxy samples at a rate of 0.3 wt% of the epoxy weight, while the nanoclay was added at rates of 1 wt%, 3 wt% and 5 wt% of the epoxy weight. Additionally, the only CNT-reinforced samples (also, not reinforced with NC) were also readied in order to observe the difference. Tensile tests and three point bending tests were conducted to determine the mechanical properties. The NC and the CNT were observed to adhere to the carbon fiber filaments in the scanning electron microscope (SEM), and NC-based bridge cracks were noted.
Keywords
Multi Walled Carbon Nanotube, Nanoclay, Tensile Test, Three Point Bending Test
M. BALTAKYS , R. SIAUCIUNAS, A. EISINAS
Abstract
The influence of hardening conditions on the mineralogical composition and mechanical properties of AAC were examined. Samples with dimensions 100x100x100 mm from industrial cakes were cut and hardened at saturated steam pressure for 4–16 h at 170–200 °C temperatures. The biggest quantity of 1.13 nm tobermorite and C-S-H (I) was formed after 8 h of treatment at 180 °C temperature and AAC samples reached the highest compressive strength. The morphology of tobermorite depends on temperature: at 200 °C the surface of pores is covered with fibrous shape crystals and the mixture of plate shape crystals together with fibrous crystals and amorphous aggregates is formed in the structure material, while at 180 °C platy shape crystals are formed in all samples. It was estimated too, that thermal shrinkage of samples, hardened at 200 °C, decreased twice. The products were characterized by XRD, STA, SEM, MIP and dilatometric analysis.
Keywords
Aerated concrete, Compressive strength, Structural analysis, Tobermorite
ABIDENG HAWA , PREECHA SALAEMAE, WORAPHOT PRACHASAREE, DANUPON TONNAYOPAS
Abstract
This study assessed and investigated the compressive strength and microstructure of geopolymer mortars containing field Para rubber latex (FPRL). Fly ash based geopolymer mortar blends were prepared with FPRL to fly ash ratios 0.10:1, 0.20:1 and 0.30:1 by weight, and with varied heat curing times. The microstructure was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR), and additionally compressive strength and density were determined. The results show that geopolymers with FPRL had compressive strengths in the range 10-30 MPa at 28 days of age. Assessed SEM images showed that FPRL gave a highly porous microstructure and correspondingly low density. The geopolymer mortars incorporating FPRL could be used in building walls or in paving blocks.
Keywords
microstructure; geopolymer; mortar; field Para rubber latex; density
P. JAISHANKAR , K. SARAVANA RAJA MOHAN
Abstract
In the present scenario of emerging concepts of nano materials and micro technologies, researchers are investigating how and what nano materials can be used to improve different characteristics of conventional concrete. With increase in trend towards the wider use of concrete for prestressed concrete and high rise buildings there is a growing demand concrete with higher strength. In the present research, the effect of nano silica on high performance concrete has for been studied. Nano silica is an ultrafine airborne material with spherical particles less than 20 nm in diameter, the average being about 15 nm. Concrete mixes prepared by replacing portland cement with nano silica at 1%, 1.5%, 2%, 2.5%, 3% with curing age of 28 days. The mechanical tests like- compressive strength, flexural strength, modulus of elasticity, splitting tension test and rapid chloride permeability test of high performance concrete were studied. The micro analyses were studied using scanning electron microscope and energy dispersive spectroscopy to know the effect of nano silica on high performance concrete. The experiment result shows that, at 3% of nano silica has better mechanical properties, voids were also reduced because of that denser matrix was formed in the high performance concrete.
Keywords
Nano silica, Silica fume, Mechanical strength, SEM, EDS
LAMIA BOUCHHIMA , MOHAMED JAMEL ROUIS , MOHAMED CHOURA
Abstract
A feasibility study was undertaken on the production of phosphogypsum-crushing sand based bricks to build houses economically by utilizing of industrial wastes. All full bricks were made on a bench model, semiautomatic press having a capacity of 25 tons, as shown in appendix, to produce bricks of 51 mm×95 mm×203 mm in size under a static compaction of 15, 20 and 27MPa. The compressive strength, flexural strength water absorption, density and speed of sound for these bricks were investigated. It was observed that these bricks have sufficient mechanical strengths for their use in low cost housing development. Tests were also conducted to study the pressure influence on bricks properties. The results suggest that compressive and flexural strength increase with pressure. This increase is more important for pressure increase from 20 to 27 MPa. The concentrations of the selected metal species, i.e., Cd, Cu, Zn, Ni, Pb, and Cr, for all mixes-design, were well below the regulatory limits. Thus, this result indicates that phosphogypsum (PG) amended bricks specimens and can be considered as non-hazardous material.
Keywords
Phosphogypsum, full bricks, mechanical strengths, compaction pressure
NAILIA R. RAKHIMOVA, RAVIL Z. RAKHIMOV, ALBERT R. GAIFULLIN, VLADIMIR P. MOROZOV
Abstract
The increasing worldwide production of Portland cement and demand to reduce CO2 emissions has resulted in the need to increase the volume and varieties of supplementary cementitious materials. The most promising source of raw materials for the production of supplementary cementitious materials is ubiquitous and unlimited reserves of polymineral clays. In this article the effect of calcined loam clays depending on its concentration, calcination temperature (400-8000C), and specific surface area (250-800 m2/kg) on the properties of Portland cement is studied. It is found out the calcined loam clays increase the compressive strength of Portland cement hardened paste up to 35%, density up to 1.4%, water resistance from 0.92 to 0.93-0.97, and decrease the water adsorption from 1 to 0.9%. The reasonability of production and application of calcined loam clays, which aren’t lower in efficiency than high-priced metakaolin, is stated.
Keywords
metakaolin, light loam, calcination, Portland cement paste, pozzolana, compressive strength, density
RAMKUMAR V.R , CHINNARAJU K. , MURALI G.
Abstract
This study examines the low-energy impact response of Fibre Reinforced Concrete (FRC) made of binary and quaternary cementitious blends, comprising of Lime Sludge (LS), Fly Ash (FA) and Metakaolin (MT). Hooked end steel fibres of aspect ratio 50 were used at different volume fractions of 0.5%, 1.0%, and 1.5%. Altogether 34 concrete mixes were designed using binary and quaternary cementitious systems with water-to-cementitious ratios (w/c) of 0.32 and 0.4. The binary systems were designed with various LS proportions ranging from 5% to 15%, although the quaternary system consisted of various proportions of LS (5%, 10% and 15%), 15% of FA and 5% of MT as a partial substitute of cement. Impact test was conducted on FRC specimens using drop weight facility, recommended by American Concrete Institute (ACI) Committee 544. Based on the obtained experimental results, an analytical multiple linear regression analysis was executed to evaluate the impact energy at first crack and failure of FRC made with binary and quaternary cementitious blends. These result reveals that replacing cement by optimized proportions of 10% LS, 15% FA and 5% MT as a pozzolanic material along with steelfibres has significantly enhanced the impact energy absorption capacity of concrete.
Keywords
Impact load, Fibre, Lime sludge, fly ash, Metakaolin
SUMATHI ARUNACHALAM, VUPPALAPATTI MANISH KUMAR REDDY, SARAVANA RAJA MOHAN KALIYAPERUMAL
Abstract
The increased demand in energy consumption and the concern with the green house effect has driven the industry to replace conventional construction with alternate approaches, sources and structural systems. In this study, strength properties were investigated by incorporating various combinations of hybrid fibres. In the present experimental work, M40 grade of concrete has been designed with ACI standards with four different proportions of hybrid fibres that are added with concrete ingredients. The proportion of Glass and Nylon – 6 fibres are added by 60% and 40% respectively with different hybridization ratios i.e. 0%, 0.5%, 1.0 %, 1.5% and 2%. Experiments were conducted to study the effect of hybrid fibresunder compression, split tension and flexure in different proportions in hardened concrete specimens and the same were compared with the control concrete. The result shows that the percentage of fibres increases the strength of concrete than control concrete. Hybrid ratio 1.5 % gives maximum results and considered as optimum percentage for all the strength parameters.
Keywords
Hybrid fibre reinforced concrete (HFRC), Nylon – 6 fibre, Glass fibre, Compressive strength, Split tensile strength, Flexural strength, Stress- strain curve
F.J. VÁZQUEZ-RODRÍGUEZ, E.U. DE LOS SANTOS, J.M. MENDOZA-RANGEL, C. GÓMEZ-RODRÍGUEZ, A.ARATO, EDÉN A. RODRÍGUEZ
Abstract
Reinforced concrete structures exposed to aggressive industrial environments suffer different accelerated deterioration mechanisms. In chlor-alkali production plants, the industrial environment contains high concentrations of carbonates and chlorides, damaging the structures and causing constant stoppages and repair processes on the structure of reinforced concrete. In this study, the effect of using internal curing on high performance concrete with low water/binder ratios was studied, implementing pumicite as internal curing agent, chemical additives and replacing Portland cement with pulverized fly ash. Durability measurements conducted were permeability of chloride ions, and carbonation depth under industrial and laboratory conditions. Results showed that there is a reduction of the aggressive agents transport mechanisms when internal curing is applied. However, measurements at long ages must be done to evaluate the synergistic effect of the agents contained in the industrial environment on the metal reinforcement.
Keywords
Durability, Corrosion, Internal Curing, Composite, Structural Application.
SEDIGHE YOUSEFI MOGHADAM, RAHMAT MADANDOUST , MALEK MOHAMMAD RANJBAR, MOSTAFA KAZEMI
Abstract
The main objective of this study is to numerically investigate rehabilitation of corrosion-damaged reinforced concrete (RC) beams with carbon fiber reinforced polymer (CFRP). In this study, three dimensional (3D) finite element (FE) models for the RC beams, strengthened with FRP sheets, was created. The effect of repairing on corrosion damaged RC beams has been investigated using FRP on load carrying capacity, ultimate deflection and ductility. To achieve these objectives, a beam with average steel mass losses of 31.6% was strengthened with various procedures using CFRP sheet. In addition, a beam with average steel mass losses of approximately 14.2% was strengthened. Results indicate that strengthening of all procedures using FRP sheet increase load carrying capacity and reduce ultimate deflection of the beam. In addition, the effect of strengthening on ultimate load carrying capacity of the beam keeps on increasing with the increase in percentage of corrosion.
Keywords
Carbon fiber reinforced polymer (CFRP), Corrosion, Retrofit, Reinforced concrete (RC)
DRAGOȘ UNGUREANU, NICOLAE ȚĂRANU , DORINA NICOLINA ISOPESCU, VLAD LUPĂȘTEANU, PETRU MIHAI, IULIANA HUDIȘTEANU
Abstract
This paper presents the outcomes of a comparative study between two fibre reinforced polymer (FRP) composites adhesively bonded joints, namely the single lap joint (SLJ) and the thick adherents joint (TAJ). Thus, 18 distinct models have been conceived and analysed. The variable parameters which are considered in this study are: the bond length and the thickness of the adhesive.
The two general types of joints have been modelled in Ansys Workbench finite element analysis software. Each model has been loaded longitudinally with a tensile force of 1000 N. The parameters that characterise the surface of the FRP composite elements have been determined based on microscopic studies, through graphic and numerical processing of the images.
Based on the outcomes numerical analysis, the variation of the stresses along the bond length has been graphically illustrated. The results delivered by the numerical analysis have been compared with the ones obtained analytically, by applying the available theoretical models. It was concluded that the two methods, provide similar predictions regarding the distribution and the peak values of the shear stresses.
Keywords
adhesive joint, glass fibre reinforced polymer composite, finite element modelling, analytical models
A. DURÁN-HERRERA, R. DE-LEÓN, C. A. JUÁREZ, P. VALDEZ-TAMEZ
Abstract
Two viable technologies that may be used to reduce shrinkage at early ages in high-performance concrete, such as self-consolidating concrete, include internal curing and shrinkage- reducing admixtures. By combining an internal source of curing water and an admixture that decreases the surface tension of pore solution, an improved overall shrinkage reduction can be achieved. Based on the evidence resulting from this synergy, this investigation focuses on the effect of Opuntia Ficus Indica Mucilage (OFIM) as a reducer of the pore solution surface tension, to establish its effectiveness in shrinkage mitigation, in comparison with the effect of conventional internal curing with water and that of a commercial shrinkage-reducing admixture. Autogenous strain and drying shrinkage deformations were determined according to ASTM C 1698 and C 157 test methods, respectively. Result show that the incorporation of OFIM does not have a significant effect on mechanical and elastic properties of the concrete, and could lead to substantial benefits in terms of shrinkage mitigation, particularly at early ages.
Keywords
self-consolidating concrete, internal curing, autogenous shrinkage, drying shrinkage, shrinkage-reducing admixture, opuntia ficus indica mucilage.
DĂNUȚ TRAIAN BABOR, TUDOREL BĂLĂU MÎNDRU, MELINDA PRUNEANU, IULIA BĂLĂU MÎNDRU
Abstract
This paper presents the influence of some fractions obtained from alkaline hydrolysis of Chamois leather dust resulted from the buffing operation, on the physical and mechanical characteristics of a new type of cement-based lightweight building materials. The average molecular weight of the hydrolysis product and the changes in the characteristic peaks of IR spectral bands shows the obtaining of a polypeptide mixture after the chemical treatment. Hydrolysis products and solid residues were used in a series of mortar recipes; the obtained results indicate an improvement of the main physical and mechanical characteristics of mortar, such as water absorption, flexural and compressive strength, compared to the reference mix.
Keywords
Lightweight mortar, chamois powder, alkaline hydrolysis, polypeptide by-products, compressive strength, flexural strength
DANIELA FIAT
Abstract
The paper presents the results of the studies performed on the influence of redispersible powders and of the cellulose ethers in mineral plasters applied as the last layer in exterior thermal insulation composite systems. Starting from traditional recipes, using polymeric additives specific for ETICS, there were developed original products in which the polymer additive (redispersible powder) concentration was modified with impact on physical and mechanical characteristics.
The using of the cellulose ether led to obtaining some light compositions (smaller density) and good workability at application.
The using of the redispersible powders has contributed to obtaining some mortars with low water permeability, high water vapour permeability and good support adherence, significant advantages for the products durability.
There have been highlighted the chemical interactions between the redispersible powders and the Ca2+ ions released during the cement hydration process. The redispersible powders act as a second binder in the system, thus leading to improved performance.
Keywords
mortar plasters, polymeric additives, cellulose ether, redispersible powders
ANA-MARIA DRAGOMIR, RAZVAN LISNIC, TUDOR PRISECARU, MALINA MIHAELA PRISECARU, CRISTINA ANDREEA VÎJAN, DANIELA CRISTINA NĂSTAC
Abstract
Synthetic gypsum CaSO4.2H2O (also called flue gas desulpurization – FGD gypsum) is a co-product resulted from the wet process of flue gas desulphurisation in thermal power plants. The gases are desulphurised with an injection of a lime or limestone suspension. The product that is initially formed by gas desulphurization is calcium sulphite. This, by forced oxidation, turns into calcium sulfate dihydrate - CaSO4.2H2O, initially in the form of a suspension.
The article presents the main characteristics of synthetic gypsum obtained in the industrial environment comparative with natural gypsum. It also presents the opportunity to capitalize this co-product in the building materials industry.
Keywords
wet FGD, synthetic gypsum, clinker, cement