english CRISTINA STANCU
Rezumat
Lucrarea își propune sa prezinte importanța participării laboratoarelor la scheme de competenta interlaboratoare (ILC), folosind studiul de caz denumit Încercări Interlaboratorare pe adezivi pentru plăci ceramice. În prezent, schema ILC organizată de CEPROCIM este singura adresată laboratoarelor de încercări a adezivilor pentru plăci ceramice.
Lucrarea își propune să prezinte de asemenea, prin utilizarea mai multor studii de caz, influența participării continue la schema ILC asupra îmbunătățirii performanței participanților și a coeficientului de variație, precum și influența pe care noii participanți o aduc. Studiile de caz reprezintă atât laboratoare acreditate conform EN ISO/IEC 17025, cât și laboratoare neacreditate ale căror performanțe (scorul z) au fost evaluate în timpul participării lor la toate cele 12 ediții ale Încercărilor Interlaboratoare pe adeziv pentru plăci ceramice.
Cuvinte cheie
schemă comparativă inter-laboratoare, adeziv, plăci ceramice, rezistență inițială la adeziune, rezistența adeziunii la tracțiune după imersia în apă, timp deschis, scor - z
GHEORGHE DOBRA, SORIN ILIEV, LUCIAN COTEȚ, ALINA BOIANGIU, ILEANA MOHANU, NICOLETA FLORENTINA CÎRSTEA
Rezumat
În această lucrare a fost investigată posibilitatea obținerii ceramicii poroase prin utilizarea a două sortimente comerciale de hidroxid de aluminiu cu finețe diferită (de la Vimetco Alum SA Tulcea România). Metoda propusă pentru obținerea unei astfel de ceramici se bazează pe o presare foarte scăzută (30kN) a amestecurilor de pulberi, urmată de un tratament termic la 1550oC. A fost investigat efectul fineții hidroxidului de aluminiu asupra porozității și densității aparente, rezistenței la compresiune și coeficientului de dilatare termică ale ceramicii obținute. De asemenea, caracteristicile mineralogice și microstructurale au fost evaluate prin analize XRD și SEM. Rezultatele au arătat că ambele probe de hidroxid de aluminiu au condus la îmbunătățirea proprietăților de porozitate, densitate și rezistență mecanică în comparație cu ceramica standard preparată cu alumină calcinată. Utilizarea pulberii mai grosiere (sub 45µm) în proporție de 25% conduce la obținerea unor ceramici cu caracteristici fizico-mecanice apropiate de cele ale ceramicilor realizate cu pulbere mai fină (sub 10µm) în proporție de 25-50%, cu efect benefic asupra costurilor de producție. Proprietățile ceramicilor poroase au sugerat că pot fi utilizate în aplicații de filtrare.
Cuvinte cheie
hidroxid de aluminiu, ceramici poroase, microstructură, caracterizare fizică și mecanică
ANGELA SPOIALĂ, CORNELIA-IOANA ILIE, GEORGIANA DOLETE, ROXANA-DOINA TRUȘCĂ, LUDMILA MOTELICĂ, OVIDIU-CRISTIAN OPREA, DENISA FICAI, ANTON FICAI, ECATERINA ANDRONESCU, LIA-MARA DIȚU
Rezumat
Scopul acestui articol constă în sinteza membranelor compozite antimicrobiene utilizând chitosanul (CS) și nanoparticulele de oxid de zinc (ZnO) ca adsorbanți pentru îndepărtarea metalelor grele. Membranele compozite CS/ZnO au fost pregătite prin metoda electrofilării. Concentrația nanoparticulelor de ZnO din membranele compozite CS/ZnO a fost de 1%, respectiv 5%. Membranele sintetizate au fost caracterizate prin spectrosocopie în infraroșu cu transformata Fourier (FTIR), microscopie electronică cu baleiaj (SEM), analiza termică diferențială (ATD), capacitate de hidratare, activitate antimicrobiană, cât și retenția metalelor grele prin spectrometrie de masă cu plasmă cuplată inductiv (ICP-MS). Grosimea membranelor compozite CS/ZnO a fost de 20µm (CS/ZnO 1%) și 30µm (CS/ZnO 5%). Aspectul membranelor sintetizate prezintă morfologie netedă și uniformă, sugerând integrarea nanoparticulelor de ZnO în membrane. Măsurătorile FTIR denotă prezența grupărilor funcționale relevante atât ale chitosanului, cât și a ZnO din membranele compozite. Măsurătorile ICP-MS oferă informații cu privire la capacitatea de retenție a acestor membrane, indicând faptul că CS/ZnO 5% a avut cea mai înaltă rată de retenție. Se așteaptă ca membranele compozite CS/ZnO să fie utilizate ca materiale adsorbante pentru aplicații de purificare a apei.
Cuvinte cheie
ZnO, chitosan, membrane nanocompozite, antimicrobian, purificare apă
OUADAH NOUREDINE, ABDESSEMED MOULOUD, KECHOUANE FOUAD
Rezumat
The use of composites for the reinforcement of concrete structures, sometimes poses the problem of the detachment of the composite plates/fibers from the surface of the concrete support, especially in arid or dry climates. This phenomenon of disbonding, due to the poor performance of the matrix (adhesive glue), affects nearly 8% of the structures reinforced with FRP in Algeria and negatively influences the durability and bearing capacity of the reinforced structure over time. This article presents the results of a study on reinforced concrete structures. It concerns the insertion of carbon nanotubes (CNT) in epoxy resin, used as an adhesive for CFRP composites. The objective is to evaluate the improvement of the mechanical performances of the resin used and to contribute to reduce the phenomenon of disbonding. An experimental work carried out on a set of reinforced concrete beams, strengthened by CFRP plates, with the insertion of carbon nanotube powders (CNT) in the resin used, with percentages varying from 0 to 2%, has been performed. To validate the results obtained, a numerical work based on the finite element method was developed taking the case of a concrete bridge requiring repairs. The results showed that the nano-composites (CNTs) improve the mechanical performance of the epoxy resin and bring an appreciable gain of the order of 50 to 170% to the constraints. Moreover, this technique of moderation of composites by adding nanotubes (CNTs), gives an appreciable gain at vibration frequencies. This was confirmed by the results of the modal analysis of the bridge structure repaired with 2% addition of CNTs.
Cuvinte cheie
beton, armare, compozit, adeziv, nanotub, desfacere, frecvență, analiză, structură
A nondestructive testing technique for high strength concrete：explosive-loaded nail penetration test
CHAORAN DUAN , SUHANG YANG
Rezumat
The traditional nondestructive techniques (NDT) may be insufficient to estimate the compressive strength of high strength concrete used widely in modern architecture engineering. This paper adopts the penetration test for this purpose with some advantages. This method is more convenient and more efficient than the traditional ones. The explosive-loaded nail penetration test (ENPT) can widen the testing rage of NDTs which are used to estimate the compressive strength of high strength concrete. Experimental results shown a good relationship between the compressive strength of concrete specimen (30-80MPa) and the results obtained from the ENPT. Other NDT techniques like Schmidt rebound hammer (SRH) and ultrasonic pulse velocity (UPV) were also applied to concrete specimens as comparisons and the results shown that the ENPT is more reliable. Since the penetration depth is closely related to the large-scale compressive strength obtained from indoor and field tests, the new test method is considered to be effective.
Cuvinte cheie
rezistență la compresiune, încercare in-situ, beton de înaltă rezistență, încercare nedistructivă (NDT), încercare (ENPT)
SELÇUK MEMİŞ , ALİ ALSHAAB RAMROOM
Rezumat
In this study, the effects of silica fume (SF), fly ash (FA) and granulated blast furnace slag (GBFS) on the design and fire resistance properties of ultra-high performance concrete (UHPC) were analyzed using the Taguchi L16 method. Samples were exposed to temperatures of 300 °C, 450 °C and 600 °C. The composition of the UHPC was: sand/binder ratio = 1, water/binder ratio = 0.19, Polycarboxylate superplasticizer (PCE) /binder ratio = 3.5%, pozzolanic (SF, FA and GBFS)/binder ratio = (0, 10, 15, 20)% and steel fibers = 1% by volume, and a Taguchi L16 program was prepared that consisted of 240 samples (40x40x160mm). The high-temperature properties of the UHPC samples were evaluated. Because several mixtures could withstand a temperature of 450 °C, it was determined that the losses were more effective when the highest temperature reached was greater than or equal to 600 °C, and the twelve mixtures are damaged by breaking them up. When the actual values obtained in the verification test were examined, it was determined that the results were sufficient for the compressive and flexural strength and physical properties of the concrete under various heating conditions and the Taguchi optimization was successfully implemented.
Cuvinte cheie
beton ultra performant (UHPC), ciment, fibre de oțel, superplastifianți bazați pe eter policarboxilat (PCEs), rezistență la compresiune, metoda Taguchi, rezistența la foc
D. VAIČIUKYNIENĖ , A. KANTAUTAS, A. A. NAVICKAS, V. VAIČIUKYNAS, E. IVANAUSKAS, A. AUGONIS, THIYAGARAJU LOGANATHAN
Rezumat
Recently, supplementary cementitious materials are widely used in cements systems. One of these materials could be a zeolitic by-product. The present study carried out experiments with the aim to find out the impact of zeolitic by-product with incorporated CaCl2 on the main features of hardened cement paste. A zeolitic by-product is the cracking catalyst of a fluidized bed. It was treated with saturated CaCl2 solution. Specimens were produced from Portland cement paste with a zeolitic by-product as supplementary cementitious material. It was determined that according to the X-ray the modified zeolitic by-product resulted in the formation of substantial amounts of hydrocalumite (Ca4Al2O6Cl2∙10H2O). The results indicate that the addition of small amounts of this additive can increase the compressive strength of the early and late hydration ages as well. In Portland cement systems the zeolitic by-product with inserted CaCl2 behaved as a hydration accelerator, had the filler effect at early-ages, and acted as a pozzolanic material at later-ages.
Cuvinte cheie
deșeu zeolitic, pastă întărită de ciment, hidratare ciment portland, material suplimentar cimentos, accelerator CaCl2
CRISTIAN PETCU, VASILICA VASILE
Rezumat
Industria construcțiilor folosește o cantitate din ce în ce mai mare de materiale de izolare termică pentru a satisface cerințele tot mai mari de eficiență energetică din sectorul construcțiilor. Utilizarea exclusivă a izolației termice sintetice poate duce la un proces complicat de reintegrare a deșeurilor din demolări în economie și potențiale daune mediului în timp. Utilizarea materialelor naturale tradiționale este ecologică și printr-un design adecvat al clădirilor, oferă elemente de construcție eficiente. Această lucrare încearcă să sporească gradul de conștientizare al profesioniștilor asupra unor subproduse tipice din industrie (paie, rumeguș, celuloză), cu caracteristici termo-fizice interesante pentru sectorul construcțiilor. Pe lângă informațiile necesare pentru calcule inginerești obișnuite, cum ar fi coeficientul de conductivitate termică, am măsurat datele necesare pentru simularea dinamică a clădirii, cum ar fi difuzivitatea termică, capacitatea termică volumetrică și căldura specifică masică
Cuvinte cheie
termoizolație, deșeuri, sustenabilitate, materiale de construcții, clădiri sustenabile
ALI SABERI VARZANEH, MAHMOOD NADERI
Rezumat
Curing and compaction are two major factors in the interface bond strength of concrete and repair mortars. Ignoring these two factors would create fine holes in the concrete-mortar interface and reduce the adhesion. Hence, the present study has aimed to evaluate the effects of initial pressure and fiber on adhesion between mortars and concrete substrates using the twist-off and pull-off tests. The effects of fibers on the shrinkage of mortars are also discussed. The influences of pre-pressure and fibers on the adhesion of the two layers were demonstrated using the scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods. The results indicated that initial pressure had positive impacts on the interface shear and tensile bond strength in the twist-off and pull-off tests, and the effect of pre-pressure was greater on mortars with more aggregates. Moreover, fibers reduced the mortar shrinkage and increased the adhesion. Considering the high correlation between the twist-off and pull-off results, affordable and available twist-off apparatus can be employed instead of expensive pull-off apparatus to measure the concrete-mortar adhesion.
Cuvinte cheie
Twist-off, Pull-off, pre-presiune, legătură, fibră
MARINELA BARBUȚĂ, PETRU MIHAI , ALINA-MIHAELA NICUȚĂ PRECUL, LILIANA BEJAN, NICOLAE ȚĂRANU, OANA-MIHAELA BANU
Rezumat
Articolul prezintă rezultatele experimentale și numerice obținute pe blocuri din beton preparate folosind deșeuri ca înlocuitor pentru agregatele naturale. Au fost folosite două tipuri de deșeuri, recipiente din PET tocate și rumeguș pentru înlocuirea nisipului într-un dozaj de 40%. De asemenea, 10% din cantitatea de ciment aferentă rețetei betonului obișnuit a fost înlocuit cu cenușă zburătoare. Au fost determinate experimental densitatea, rezistența la compresiune, modulul de elasticitate și diagrama forță de compresiune-deformație. Blocurile din beton cu goluri construite au fost testate la compresiune fiind evidențiate sarcina limită ultimă la compresiune și modurile de cedare. S-a efectuat și o analiză numerică a comportării la compresiune a blocurilor din beton cu goluri, utilizând programul de modelare cu element finit ATENA. S-a remarcat faptul că cedarea blocurilor supuse la compresiune a fost una de tip progresiv, în trepte, distribuția fisurilor fiind aferentă zonelor în care tensiunile de întindere depășesc rezistențele materialelor analizate. Rezultatele studiilor efectuate au relevat o bună corelare a datelor numerice cu cele experimentale.
Cuvinte cheie
cenușă zburătoare, sticle de plastic tocate, deșeu de rumeguș, dezvoltare sustenabilă, rezistență la compresiune, analiza numerică
SUMATHI A, ELAVARASI D , SARAVANA RAJA MOHAN K
Rezumat
The current research was carried out on the effect of natural sand replaced by manufactured sand (M-sand) in fibrous concrete infiltrated with slurry under static and impact loading. The compressive strength, split tensile strength and impact strength of Slurry infiltrated fibrous concrete (SIFCON) with partial replacement of river sand by M-sand. Hooked end steel fibres of 10% by volume fraction and a constant slurry mix of 1:1 with water cement ratio of 0.4 were used. The low velocity impact response is conducted on 150 mm and 60 mm high cylindrical specimen diameters using the drop weight impact test device as per ACI Committee 544-89. By dropping a steel ball of 4.5 kg with a falling height of 457 mm with the use of a self-manufactured drop-hammer impact test setup, the replication of a low-velocity impact on the cylinder was achieved. The test results show that the strength and energy absorption capacity of SIFCON with 50% of natural sand substituted by M-sand significantly improved compared to all other replacement of M-sand. It was found that optimum replacement level of river sand by M-sand as 50%. Regression analysis has been developed from the experimental results to predict the first crack and ultimate energy absorption capacity of SIFCON. The analytical values from the regression model are well correlated with the experimental results.
Cuvinte cheie
SIFCON, nisip M, absorbție energie, index ductilitate, analiza regresiei
ALINA MELINESCU, ENIKÖ VOLCEANOV, MIHAI EFTIMIE, DAN BATALU, ADRIAN VOLCEANOV, LAVINIA GABRIELA POPESCU
Rezumat
Lucrarea are ca obiectiv îmbunătățirea vitezei de depunere, a omogenității și a durificării nanocompozitului Ni-P-TiO2 pe suprafețe din oțel cu conținut redus de carbon, comparativ cu acoperirea Ni-P. Au fost dezvoltate două compoziții pentru baia de depunere fără electroliză, și anume baia (A), compusă din soluții apoase de sulfat de nichel și hipofosfit de sodiu și diverse adaosuri pentru a stabiliza și accelera viteza de depunere în timpul placării, și baia (T): baia (A) la care au fost adăugate particule de TiO2 nanodimensionate într-o concentrație de 10 g/l. Vitezele de depunere, co-depunerea particulelor și rugozitatea au fost influențate de concentrația pulberii nanometrice, temperatură, viteza de agitare, pH și durata depunerii în baie. Aderența și uniformitatea straturilor compozite analizate metalografic si prin SEM sunt adecvate, astfel că interfața stratului compozit cu suportul din oțel este perfect continuă, fără discontinuități, iar stratul este uniform. După depunere, acoperirea a fost necristalină. Datorită tratamentului termic duritatea acoperirii fără electroliză de nanocompozit Ni-P este crescută în mod semnificativ. Performanța acoperirilor nanocompozite Ni-P-TiO2 este analizată din perspectiva morfologiei suprafeței, compoziției fazale, uzurii și durității pentru a evalua caracteristicile de uzură și este comparată cu acoperirile aliate din Ni-P. Variația durității cu tratamentul termic prezintă o tendință similară pentru aceste acoperiri, ceea ce sugerează același mecanism de întărire la tratamentul termic pentru acoperirile nanocompozite fără electroliză de Ni-P și Ni-P-TiO2.
Cuvinte cheie
depunere fără electroliză, acoperiri, strat nanocompozit de Ni-P-TiO2 , substrat de oțel
ALINA IULIA DUMITRU, GEORGETA VELCIU, DELIA PATROI JANA PINTEA, TUDOR-GABRIEL DUMITRU, ILDIKO PETER
Rezumat
A fost studiată influența dopanților, Y3+, Sm3+ și Bi3+ precum și condițiile de polarizare asupra proprietăților piezoelectrice ale compozițiilor (Pb0.91Me0.06)(Ti0.98Mn0.02)O3. Compoziţiile au fost obţinute prin metoda reacţiilor în stare solidă, la temperatură ridicată de sinterizare (1190°C şi 1240°C). În lucrarea de față a fost luat în considerare și investigat efectul temperaturii de sinterizare asupra unor proprietăți, în special asupra caracteristicilor fizice, asupra caracteristicilor structurale și microstructurale și asupra proprietăților dielectrice și piezo-electrice ale materialelor.
Din studiile efectuate, reiese că tipul de dopant are efect asupra structurii și microstructurii cât și asupra proprietăților dielectrice și piezoelectrice. Structura a fost identificată prin măsurători cu raze X, iar dimensiunea cristalitelor a fost determinată prin analize SEM. La temperatura camerei, toate probele sinterizate prezintă o structură perovskit tetragonală.
Determinările parametrilor piezoelectrici (kp) au fost efectuate folosind metoda de rezonanță - antirezonanță. Rezultatele obţinute indică faptul că compoziţiile sinterizate ( PT dopat) pot fi utilizate în obținerea de elemente active cât și ţinte pentru depunere.
Cuvinte cheie
PZT dopat, proprietăți dielectrice și piezo-electrice, proprietăți fero-electrice
LÜTFIYE DAHIL, KHALED NIMER MOHAMMED AL-NIMER
Rezumat
In the present study, crash simulations for thin-walled circular and square cross-section samples made of intra-layer glass-carbon/epoxy hybrid composite, and aluminum have been conducted; and energy absorption capacity and deformation modes are obtained. Results related to some post-collision parameters such as variation of displacement and force are presented for each combination of cross-sectional geometry and material, as well. Numerical method is validated by a previous experimental drop-weight study. Numerical calculations have shown that the hybrid composite sample of square cross-section exhibits the highest load resistance and maximum crash energy absorption, while aluminum samples have a low load resistance and energy absorption capacity the circular Al samples have smaller displacement than that of the square samples.
Cuvinte cheie
CUVINTE CHEIE (ROMÂNĂ)
I. REGINA MARY , T.BHAGAVATHI PUSHPA
Rezumat
This paper shows the study of a statistical approach for finding the optimum values of the dependent and independent factors in Geopolymer concrete (GPC) composites using 75:25 of fly ash and Ground Granulated Blast Furnace Slag (GGBS). The input parameters considered in this study were alkali/binder, binder content and water/solids ratio. These factors affect the fresh and hardened properties of Geopolymer concrete such as slump value, compressive strength and split tensile strength for 28 days ambient curing. Response Surface Methodology (RSM) technique was used to optimize the trial mixes using Box-Behnken Design (BBD) by considering three factors. Results show that the optimum compressive strength of 57.05 MPa, optimum tensile strength of 4.52 MPa and optimum slump value of 135.034 mm was achieved by using optimum alkali/binder ratio, binder content and water/solids ratio of 0.386,420 kg/m3 and 0.17 respectively. The desirability achieved for the optimum value is 0.9212 and the mean error was less than 5%. ANOVA results of the regression studies showed that each factor contribute significantly to the strength development of GPC.
Cuvinte cheie
metodologia suprafeței de răspuns, ANOVA, regresie, Box-Behnken, beton geopolimeric, valoare optimă
MARIAM FAROUK GHAZY, METWALLY ABD ALLAH ABD ELATY, MOHAMED FATTOUH ABD EL HAMEED
Rezumat
In this study a hybrid method including a response surface methodology, technique for order preference by similarity to ideal solution (TOPSIS), and a particle swarm optimization (PSO) algorithm were proposed to determine optimal parameter settings of the geopolymer (GP) mortar. Compressive strength, flexural strength, splitting tensile strength, and weight loss were used as the most important characteristics. Six factors (metakaolin, cement, sodium silicate solution, polypropylene fibers, curing temperature, and elevated temperature) each at three levels with 54 experiments was selected. TOPSIS method was used to convert the single-responses to an equivalent single-response known as a multi-performance characteristics index (MPCI). The significance of the process parameters was also evaluated using the analysis of variance. The PSO was used to predict optimal parameter settings of the GP-mortar process. The approach and the methodologies employed in this work can be utilized in solving the mixture proportions of the optimization problem.
Cuvinte cheie
mortar geopolimeric, metodologia suprafeței de răspuns, TOPSIS, optimizarea roiului de particule, proprietăți mecanice, temperaturi crescute
VIRGIL PENTA, CAMELIA UNGUREANU, ANDREI BOGDAN STOIAN, CRISTIAN PIRVU
Rezumat
Candida albicans este cel mai frecvent izolată drojdie patogenă și este prezentă în cavitatea bucală a aproape jumătate din populație. Deoarece au existat mai multe studii aparent contradictorii cu privire la efectul electricității asupra comportamentului Candida albicans, propunem o nouă metodă de măsurare: Spectroscopia de impedanță electrochimică (EIS) cuplată cu Rezonanța de Suprafață a Plasmonilor (SPR). Împreună cu alte metode electrochimice și cu imagini de înaltă rezoluție cu ajutorul Microscopiei de Forță Atomică (AFM) s-a investigat efectul potențialelor electrice măsurate între materialele metalice intraorale asupra Candida albicans.
Cuvinte cheie
Candida albicans, biofilm, rezonanța de suprafață a plasmonilor, spectroscopia de impedanță electrochimică, microscopie de forță atomică
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Anul
2022
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Numărul
52 (2)
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Paginile
145-155
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Domenii de interes
BIOMATERIALE ȘI BIONANOMATERIALE; SUBSTANȚE, PROCEDURI ȘI DISPOZITIVE PENTRU MEDICINĂ
ZENO GHIZDĂVEȚ, OVIDIU DUMITRESCU, MIHAI EFTIMIE, ADRIANA MOANȚĂ, IONELA PETRE, NICOLETA CÎRSTEA
Rezumat
Două clase de deșeuri de sticlă, colorate (C) și transparente (A), vor fi utilizate pentru substituția parțială a amestecurilor brute, în special a nisipului, în obținerea clincherului de ciment. Metode statistice avansate vor ajuta la identificarea și extragerea corelațiilor compoziție–măcinare amestec brut–clincherizare–măcinare ciment–proprietăți. Se urmăreste dacă și cum înlocuirea parțială a materiilor prime cu sticlă ar putea influența unele proprietăți ale cimentului. Se investighează dacă diversele amestecuri de materii prime și deșeuri de sticlă vor prezenta un comportament diferit la măcinare. Substituția totală a nisipului cu sticlă implică un aport mai mare de alcalii, care poate influența compoziția și calitatea clincherului dar și funcționarea instalației de clincherizare. Aptitudinea la măcinare afectează direct costurile operaționale, deci va fi și ea evaluată și corelată; printre alți factori, aptitudinea la măcinare este legată de cantitatea de alcalii din clincher.
Cuvinte cheie
deșeuri de sticlă, clincher, substituție parțială, corelații
CORNELIA-FLORENTINA DOBRESCU, RAMONA PINȚOI
Rezumat
Lucrarea îşi propune analiza utilizării potenţiale a deşeurilor din sticlă pentru producerea materialelor de constructii şi îmbunătăţirea pământurilor argiloase. Aplicaţiile experimentale bazate pe integrarea produselor reciclate cu rol de lianţi au evidenţiat că deşeurile de sticlă contribuie în mod pozitiv la proprietăţile micro-structurale ale amestecului printr-o îmbunătăţire evidentă a performanţelor mecanice. În cadrul lucrării este structurat un program experimental care reprezintă o etapă premergătoare pentru modelările la scară redusă aplicate în proiectarea de structuri şi elemente eco-sustenabile utile în lucrările de construcţii. Rezultatele obținute au confirmat eficienţa utilizării sticlei reciclate ca material de construcţie în aplicaţiile inginereşti. Avantajele utilizării deşeurilor de sticlă în fabricarea elementelor de construcţii constau în durabilitatea materialului, rezistenţa la abraziune îmbunătăţiţă a betonului, îmbunătăţirea proprietăţilor reologice ale betonului proaspăt fără a utiliza superplastifianţi în amestecuri.
Cuvinte cheie
stabilitate, performanță, îmbunătățire, materiale alternative, soluri aegiloase, deșeuri de sticlă
VIOLETA TSAKIRIS, DORINEL TĂLPEANU , MAGDALENA VALENTINA LUNGU, DELIA PĂTROI, GABRIELA BEATRICE SBÂRCEA, VIRGIL EMANUEL MARINESCU
Rezumat
Pentru înlocuirea și regenerarea țesuturilor dure și deteriorate, se preferă utilizarea implanturilor ortopedice din biomateriale pe bază de Mg. Este de dorit ca implanturile ortopedice să aibă proprietăți mecanice similare cu cele ale osului natural pentru a evita efectul tensiunilor datorat diferenței de proprietăți dintre materiale, adică dintre os și implant. Numeroase studii au arătat că, dintre toate biomaterialele metalice, Mg folosit ca biomaterial ortopedic poate favoriza reconstrucția osoasă și poate accelera procesul de vindecare, având atât densitatea cât și modulul de elasticitate apropiate de al osului cortical.
În această lucrare, biomaterialele Mg-Zn-(Mn) cu 5%gr. Zn, cu/fără un adaos mic de Mn (0.3 %gr.), au fost sintetizate prin măcinarea mecanică de înaltă energie a amestecurilor de pulberi componente și consolidate prin tehnica Spark Plasma Sintering, la diferite temperaturi de sinterizare (350, 400 și 450°C), pentru a fi utilizate ca implanturi ortopedice. S-a investigat influența parametrilor mecanici de măcinare și sinterizare asupra caracteristicilor chimice, structurale și fizice. Proprietăți adecvate pentru aplicația vizată, în ceea ce privește proprietățile fizice, cum ar fi densitatea 1.77-1.78 g/cm3, duritatea (95-112 HV) și modulul Young (36-46 GPa) recomandă aliajele Mg-Zn-(Mn) obținute, ca potențiale biomateriale. Aceste biomateriale au rezultat din pulberea compozită măcinată mecanic timp de 5 ore şi sinterizată la cea mai mare temperatură de sinterizare (450°C).
Cuvinte cheie
magneziu dopat, biomaterial, tehnica SPS, implanturi osoase
-
Anul
2022
-
Numărul
52 (2)
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Paginile
168-176
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Domenii de interes
BIOMATERIALE ȘI BIONANOMATERIALE; SUBSTANȚE, PROCEDURI ȘI DISPOZITIVE PENTRU MEDICINĂ
LEONID DVORKIN, VADIM ZHITKOVSKY , VITALIY MARCHUK, YURI RIBAKOV
Rezumat
The research is focused on obtaining high-strength mortars from composite cements, containing up to 50% of fly ash and a polyfunctional modifying admixture. The polyfunctional modifier contains a superplasticizer and an intensifier for cement grinding. Using mathematical experiments planning, experimental-statistical models of mortars strength in bending and compression at 2 and 28 days were obtained. The models take into account the influence of the fly ash amount, superplasticizer content and type and cement grinding fineness. Analytical results based on the obtained models and the influence of the investigated factors are presented. The obtained mathematical models of mortar strength allowed optimization of the required technological solutions that provide the necessary mechanical characteristics of mortars at minimum cost.
Cuvinte cheie
mortar, cenușă zburătoare, cimenturi compozite, superplastifiant, măcinare, modele experimentale - statistice, optimizare
V. VOLCHUK, S. KROVIAKOV, V. KRYZHANOVSKYI
Rezumat
Macrostructure of the modified expanded clay concrete in the matrix-filler form system was considered. Statistical criteria of the macrostructure expanded clay concrete elements using a topological composition and fractal invariants were determined. The criteria describe metric discrepancy of length, diameter and area of macrostructure elements with their topological equivalents. It is shown that taking into account the indicators of metric discrepancy between length of the interphase and intraphase diameter boundaries, pore and coarse aggregate area leads to accuracy increase and is consistent with the theoretical prerequisites for influence of the investigated structural elements on strength. It has been established that the empirical model, taking into account the metric area deviation of expanded clay gravel fractions, has the highest accuracy in concrete strength predicting (R2=0.92), and the model for flexural strength assessing taking into account the diameter of its fractions has the lowest accuracy (R2=0.44). As the study results have shown, the statistical criteria for metric discrepancy of structural elements can be used as correction coefficients or constants in existing empirical models for strength assessing of lightweight concrete, taking into account the macrostructure effect.
Cuvinte cheie
beton, structură, rezistență, dimensiune fractal, discrepanță metrică, echivalent topologic, model
ANIL NIŞ, TAHA SALAH WAHHAB AL-ANTAKI
Rezumat
In this study, volcanic pumice aggregate incorporated different lightweight concretes (LWC) were investigated under a 5% sulfuric acid environment. For this purpose; OPC, OPC-FA, OPC-S, OPC-FA+S with 0%, 50%, and 100% pumice incorporations were manufactured considering cement efficiency factors for fly ash (FA) and slag (S) given in the TS13515 and EN 206-1 to evaluate the applicability of cement efficiency factors in the water and sulfuric acid environments. The visual appearance, weight change, and compressive strength tests were executed, and strength gain index and strength loss index parameters were utilized for the evaluation. The results indicated that the cement efficiency factors for the fly ash and slag were found appropriate for the pumice aggregate replacements up to 100% for the LWC incorporating only fly ash or slag. However, when the fly ash and slag were used together, the cement efficiency factors should be reduced from 0.4 to 0.35 for FA and from 0.8 to 0.75 for slag materials.
Cuvinte cheie
agregat de piatră ponce vulcanică, beton ușor, factorul de eficiență al cimentului, durabilitate, rezistență la acid sulfuric
DENG CHEN, LI-WU MO, KAI-WEI LIU, AI-GUO WANG, SHI-PING ZHANG, QIN-FENG DI, JUN YAN
Rezumat
In order to investigate the hydration and pore structure evolution of wet white cement paste at early age, the transverse relaxation time (T2) spectrum signals of wet white cement paste were tested by 1H low-field nuclear magnetic resonance (NMR). The effects of water to cement (W/C) ratio on the T2 spectrum, T2 geometric average values, hydration degree and pore structure of the cement paste samples hydrated within 168 h were studied. The results show that the T2 can characterize the hydration process and pore structure of wet white cement paste. With the increase of hydration time, the T2 peak area and T2 geometric average values decrease gradually. The hydration degree of cement increases rapidly within the first 24 h, and then slows down gradually after 24 h. For the cement pastes hydrated from 0 h to 7 h, most of the evaporable water is filled in the capillary pores in the range of 10 nm ~1000 nm. With the continuous hydration of cement, the water in these pores is consumed and the peak pore radius decreases constantly. The increase of W/C ratio can improve the hydration degree, but results an increase in the porosity and the proportions of larger pores.
Cuvinte cheie
1H câmp jos de rezonanță magnetică nucleară, hidratare, structura porilor, ciment alb
NAZMI EKREN, CEYLIN EDA KARACAN
Rezumat
Electrospun patches have attracted interest in different biomedical fields, including tissue engineering and drug delivery. Portable electrospinning guns promise faster and more practical interventions in these areas. In this article, the design, construction and testing of a portable electrospinning gun are described to produce fiber and particle products. Results were discussed depending on the electrospinning gun’s working system and properties of the products. The electrospinning gun system could have a high voltage of up to 30 kV. Also, no heating problems were encountered during high voltage values. Due to the uniformity, reproducibility and tunability of the produced PCL and PMSQ fibers, it can be said that electrospinning gun can be used in nanotechnology, drug delivery systems and wound dressing applications.
Cuvinte cheie
CUVINTE CHEIE (ROMÂNĂ)
-
Anul
2022
-
Numărul
52 (3)
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Paginile
213-219
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Domenii de interes
BIOMATERIALE ȘI BIONANOMATERIALE; SUBSTANȚE, PROCEDURI ȘI DISPOZITIVE PENTRU MEDICINĂ
LÜTFIYE DAHIL, KENAN KAYA, ÖMER FARUK ERKENDIRCI, CIHAN SEZER
Rezumat
The present study experimentally investigates tensile strength and impact toughness of plain composites made of carbon, glass, Kevlar, and steel wire mesh fabric; and hybrid composites of carbon-Kevlar reinforcement with polyethylene matrix. Composites are prepared by employing a hot press technique, where reinforcement fabrics, as well as polyethylene film are stacked in varying number of layers. Samples were cut from the composite plates for uniaxial tensile loading and low-velocity Charpy impact tests, as well as for resin burn-off process. It is shown that number of layers affects tensile and impact characteristics, as in general, tensile strength of composites increases with number of layers. Also, impact energy absorbed by the specimens is also proportional to number of layers.
Cuvinte cheie
CUVINTE CHEIE (ROMÂNĂ)
ANDRADA-ELENA ALECU, ȘTEFANIA-ANDREEA GIRJOABA, MIHAELA BEREGOI, SORIN-ION JINGA, CRISTINA BUSUIOC
Rezumat
În această lucrare, fluorura de poliviniliden a fost obţinută sub formă de structuri unidimensionale cu ajutorul tehnicii electrofilării. Au fost testate mai multe tipuri de soluții precursoare pentru a găsi condițiile experimentale optime pentru a produce fibre netede, continue și fără „mărgele”, potrivite din punct de vedere morfologic pentru dezvoltarea de scaffolduri piezoelectrice dedicate aplicațiilor de inginerie tisulară. Astfel, a fost evaluată influența tipului de solvent, a concentrației de polimer, precum și a parametrilor de electrofilare (debit de alimentare, distanță spinaretă-colector și tensiune aplicată) și cea mai bună situație a fost aceea cu un raport de 2:3 între dimetilformamidă și acetonă, 20 % concentrație de polimer, 1 mL/h debit, 20 cm distanță și 18 kV tensiune. În final, fibrele au fost încărcate cu particule comerciale de titanat de bariu, ca primă încercare de a produce un compozit piezoelectric cu potențial în domeniul medical.
Cuvinte cheie
CUVINTE CHEIE (ROMÂNĂ)
I. GOMOIU , M. ENACHE, S. NEAGU , R. RUGINESCU, M. DUMBRĂVICIAN, R. RADVAN, L. GHERVASE, I. MOHANU, R. COJOC
Rezumat
Biocurățarea operelor de artă restaurate este o metodologie ecologică care evită folosirea solvenților toxici caracteristici pentru curățarea uscată, protejând astfel atât restauratorii cât și mediul înconjurător. Biocurățarea bazată pe culturi bacteriene viabile s-a dovedit a fi mai eficientă decât cea chimică deoarece a contribuit prin metaboliți specifici la îndepărtarea crustelor negre, depunerilor de săruri și a materialelor organice. Biocurățarea se aplică cu succes atât pentru îndepărtarea unor materiale folosite la restaurarea anterioară cât și a unor depuneri organice accidentale. Gelurile au atras interesul restauratorilor iar aplicarea acestora s-a extins la pictura murală, obiecte litice, documente și chiar la obiecte metalice. Hidrogelul Agarart este recomandat atât pentru curățarea operelor de artă cât și ca suport de imobilizare. Prezenta lucrare are ca scop atât îndepărtarea consolidanților (rășina acrilică Paraloid B72 și Dispersia Transparentă de Cazeină) cât și a depunerilor organice accidentale (ceara de albine, uleiul de floarea soarelui, gudroanele de cărbune) de pe suprafața picturii murale folosind enzime esterolitice produse de bacteria halotolerantă Bacillus sp. BA N P3.3, aplicate direct sau incluzionate în gelul Agarart. Experimentele s-au efectuat pe modele de laborator executate în tehnica al fresco, îmbătrânite prin expunere la variații de temperatură și umiditate, respectiv la radiații UV-A/UV-B. Deși biocurățarea s-a obținut atât prin aplicarea soluției enzimatice integrate (E-Agarart) cât și prin aplicarea preparatului enzimatic direct pe suprafața modelului experimental urmată de acoperirea cu gelul Agarart (E+Agarart), pentru evitarea formării eflorescențelor, recomandăm tratamentul cu enzime esterolitice integrate în gelul Agarart.
Cuvinte cheie
CUVINTE CHEIE (ROMÂNĂ)
-
Anul
2022
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Numărul
52 (3)
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Paginile
238-251
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Domenii de interes
BIOMATERIALE ȘI BIONANOMATERIALE; SUBSTANȚE, PROCEDURI ȘI DISPOZITIVE PENTRU MEDICINĂ
CONSTANTIN DORINEL VOINIȚCHI , DAN CARAGHEORGHEOPOL, FĂNICA CĂPĂȚÂNĂ, ANDREEA MATEI
Rezumat
Obiectivul acestei lucrări este o estimare a numă rului de fibre care traversează o secțiune.
Au fost utilizate două metode, considerînd o distribuție uniformă numărul mediu de fibre dintr-o secțiune oarecare a unei prisme cu lățime și grosime considerate infinite.
Metoda probabilistică a fost utilizată pentru zona centrală a prismei, în care nu se ține cont de efectul de perete.
A doua metodă a implicat o simulare Monte Carlo; rezultatele obținute prin cele două metode au fost apropiate.
Validarea experimentală a implicat utilizarea a două dozaje diferite, unul uzual (25kg/m3) și unul mult mai mare (125kg/m3), încercându-se evidențierea unui posibil efect de interinfluențare a fibrelor.
A fost studiat de asemenea și efectul granulelor mari care ar putea modifica distribuția fibrelor, prin realizarea unor probe de beton doar cu agregat mic 0/4mm și a unuia cu agregate mai mari 0/16mm. Rezultatele experimentale, apropiate de cele prevăzute prin cele două metode, au arătat o influență minoră a dozajului de fibre precum și a dimensiunii granulelor de agregat.
Cuvinte cheie
simulare Monte Carlo, fibra, distribuție, beton
CICI JENNIFER RAJ J , VINOD KUMAR M , SHABARISH S
Rezumat
The earthquake related destructions in buildings is alleviated by uncomplicated methods with the implementation of sand-tire mix as the base isolation material below the footing. Rubber which is the major raw material for the elastomeric bearings shall be replaced with sand-rubber mix. The mix is placed below the footing to determine the deflections of the footing for trials such as 0%, 10%, 20%, 30 % and 50% crumb rubber (CR). Furthermore, the behaviour of the footing is studied with these trials under static and cyclic loading. The research is exclusively dealt to determine the energy dissipation capacity and stiffness degradation of the footing with and without base isolation material (sand-rubber mix). From the investigation it was evident that 30% crumb rubber combination have better seismic energy mitigating capacity.
Cuvinte cheie
CUVINTE CHEIE (ROMÂNĂ)
KRISHNA KUMAR P , CHINNARAJU K
Rezumat
This paper demonstrates the comparative study of properties of foam concrete with polypropylene fiber and carbon fiber. The experimental investigations were done between foam concrete with 10% and 20% foam volume. As well as cuttle bone powder was partially replaced with cement as bio-filler in the aspect of cost cutting in foam concrete production and reducing environmental hazard. Both polypropylene and carbon fibers were added in the foam concrete in the percentage of 0.5%, 1%, 1.5%, 2%, 2.5%, 3% by mix volume fraction. The physical, mechanical, thermal and durability properties of foam concrete were investigated. The result showed inclusion of fibers in foam concrete increases the compressive strength with minimal reduction in densities. The hydrophobic properties of foam concrete were improved with polypropylene fiber addition, which decreases the adsorption and sorptivity characteristics. Irrespective of the type of fiber added the thermal conductivity of foam concrete also decreases when compared to conventional foam concrete. Polypropylene fiber in foam concrete showed the highest reduction in thermal conductivity. With the gainful impact saw on the density and strength performance and from the cost investigation, 2% Polypropylene fiber with 25% cuttlebone powder as cement replacement in foam concrete is recommended for the production of low cost and sustainable foamed concrete.
Cuvinte cheie
CUVINTE CHEIE (ROMÂNĂ)
QUN GUO, XIAOZHEN LI, JUNZHE LIU
Rezumat
The effect of rust inhibitor on the composition and microstructure of the passive film on the surface of the rebar in carbonated concrete was studied through XPS and other microstructure testing techniques.The mechanism of the rebar passive film formation under the action of rust inhibitor was clarified. The results show that the main components of the passive film are FeOOH, Fe3O4,FeO, and Fe2O3. The reaction of sodium molybdate (Na2MoO4) with Fe2+ resulted in the formation of the FeMoO4 protective layer.Benzotriazole (BTA) and Fe combined to form N-Fe bonds, which adhered to the surface of rebar and prevented corrosion. According to the composition and compactness of the passive film, Na2MoO4 + BTA has the best corrosion resistance effect.
Cuvinte cheie
CUVINTE CHEIE (ROMÂNĂ)
MURAT OZOCAK, CAN BURAK SİSMAN
Rezumat
The depletion of traditional energy sources and environmental problems have increased the orientation to new and renewable energy sources. In this context, studies have intensified on the use of wastes generated in different sectors for energy production. As a result of these studies, fuel briquettes were produced from hazelnut shells and put into use for heating purposes in different structures. In this study, it was aimed to prevent environmental problems caused by the ash formed as a result of burning the briquettes produced from hazelnut shells and to investigate its usability as a pozzolan in the production of economical and durable concrete with high insulation properties in the construction sector. In this way, it will be possible to convert ash, which is the waste of a useful product produced from an agricultural waste, into a product with high added value in the construction sector. For this purpose, the effects were investigated on the physical, mechanical and thermal properties of concrete of using briquette ash in different proportions (0, 5, 10, 15 and 20%) as a substitute for cement in concrete production. As a result of the research, it is recommended to use briquette ash up to 5% in order to produce concrete with sufficient strength and good insulation, as it is possible to use briquette ash as a pozzolan in concrete production.
Cuvinte cheie
CUVINTE CHEIE (ROMÂNĂ)
Cuvinte cheie
CUVINTE CHEIE (ROMÂNĂ)
SEYED VAHID RAZAVI TOSEE , IMAN FARIDMEHR
Rezumat
In this research, from zero to 100% every 10%, normal aggregates were replaced with heavy aggregate (a mixture of iron ore and barite) in the concrete. A total of 110 cylindrical specimens (15x30cm) and cubic specimens (15x15cm) were used to examine the specific gravity, compressive strength, and tensile strength of Heavyweight Concrete (HWC). The test results confirmed that by substituting Heavyweight Aggregate (HWA) iron ore and barite mixture for 10% (or higher) of regular aggregates, a specific weight greater than 2600 kg/m3 might achieve, and the resulting product classified as HWC. In the second phase of the research, to develop the Generalized Regression Neural Network (GRNN) for estimating compressive and tensile strength, 48 data records from the specimen tests were selected randomly to find the best network with minimum mean square error (MSE) and correlation coefficient. The results confirmed that the proposed informational model could adequately estimate the mechanical properties and simplify the design processes in computational intelligence structural design platforms in the future.
Cuvinte cheie
CUVINTE CHEIE (ROMÂNĂ)
B.RANJITH BABU, R.THENMOZHI
Rezumat
In this study, a high strength-lightweight concrete of 50 MPa compressive strength was developed using an artificial neural network through MatLab programming. For the structural application of lightweight concrete, density and strength are more crucial. According to IS 456-2000, the concrete used for structural elements such as beams, columns, and slabs must have a minimum compressive strength of 20 MPa. Historically, additional materials like silica fume and fly ash were utilized to partially substitute cement. Nowadays, fly ash is processed systematically into pelletized aggregates and heated to temperatures up to 1500 degrees Celsius and is used as aggregates in lightweight concrete adding to sustainability. A high-strength lightweight concrete was modeled using neural networks, and its compressive strength was validated using laboratory measurements. A total of 57 data sets were used to construct this mix, which was based on earlier research.
Cuvinte cheie
beton ușor
SREENATH SREEKUMARAN , SARAVANA RAJA MOHAN KALIYAPERUMAL
Rezumat
Reactive Powder Concrete (RPC) mixes consume a very high volume of cement in which a part only can undergo hydration due to the adoption of a very low water to binder (W/B) ratios. The unhydrated part of cement can act as a filler in the mixes. In this study, for the sustainable development of RPC mixes, the filler part of cement was replaced with Ground Granulated Blast furnace Slag (GGBS). Further reactive Rice Husk Ash (RHA) was introduced to the mix as a replacement for inert Quartz Powder (QP) filler to bring in a better pozzolanic activity. Flow characteristics of the mixes were evaluated. Compressive strength of the mixes was also evaluated. For the optimization of results, regression models were established based on Box-Behnken method of Experiment Design. Sustainability Indicators such as Embodied Energy (EE) and Embodied Carbon (EC) of the mixes were also evaluated. It was observed that flow of the mixes was improved considerably due to the addition of GGBS and got reduced due to the incorporation of RHA. Improved strength was observed up to 30% replacement of cement with GGBS. For all the cases, 100% replacement of QP with RHA lead to better strength results. Further, EE and EC of mixes were considerably reduced due to the incorporation of GGBS and RHA.
Cuvinte cheie
CUVINTE CHEIE (ROMÂNĂ)
HARIDASA ANAYAK, N KRISHNAMURTHY, SHAILESH RAO A
Rezumat
In recent years, the coating of different materials inside the cylinder liner has emerged as a prime focus of research among the scientists as it improves the efficiency of the engine. In this paper, the coating material, YSZ + Al2O3 with equal proportion were coated on the cast iron substrate using two bonding materials (Iron Nickel Aluminium composite powder (Metco 452) and Nickel Aluminium cermet (Metco 410 NS)) with the three-coating thickness of 100µm, 200µm and 300µm. Initially, the wear characteristics were carried out and properties like the coefficient of friction (CoF), wear rate for different load conditions were determined. The analyses of the worn sample were studied in details with the aid of SEM images. Further, the scratch studies for the worn samples were also carried out.
Cuvinte cheie
suflare plasmă, purtare, microduritate, grosimea stratului, coeficientul de frecare
MD INSIAT ISLAM RABBY , SITI UJILA MASURI, N.M.S. HASSAN, SK MAHAFUJUR RAHMAN, TAZEEN AFRIN MUMU, MAHFUZ ALAM
Rezumat
A triangular corrugated pipe was studied numerically along with Al2O3-water, CuO-water, and SiC-water nanofluids, to identify the thermal capacity for laminar flow. Ansys fluent software and steady-state control volume method were applied for simulation purposes. Hence, different volume fractions (1% - 5%) of CuO, Al2O3, and SiC nanoparticles were considered to mix with water to suspend nanofluids. 400 to 1200 Reynolds number with a constant wall heat flux of 1000 W/m2 were considered to calculate the heat transfer rate. In addition, the required pumping power for such enhancements was determined as well. The simulation results highlighted that corrugated pipe provided highest improvement in heat transfer with increase in Reynolds number compared to straight pipe. Consequently, the mixing of nanoparticles in the working fluid showed more enhancement. For the corrugated pipe, at Re =1200, CuO-water, Al2O3-water, and SiC-water nanofluids showed a maximum 11.94%, 8.96%, and 9.15% enhancement respectively of Nusselt number compared to water. Furthermore, CuO-water, Al2O3-water, and SiC-water nanofluids showed enhancement in pumping power compared to water. Additionally, a correlation to predict the Nusselt number for nanofluid and triangular corrugated pipe was also developed by using Buckingham π Theorem, which showed good agreement with numerical results. However, it can be concluded that corrugated pipe, along with nanofluids, provide enhancement in heat transfer for the laminar developed region of a pipe.
Cuvinte cheie
număr Nusselt, nanofluide, concentrația volumului, Teorema Buckingham π, forța de pompare
CORINA ANCA SIMION , IULIANA MĂDĂLINA STANCIU, TIBERIU BOGDAN SAVA, DORU GHEORGHE PACESILA
Rezumat
Acest articol prezintǎ rezultatele datǎrii cu radiocarbon prin metoda AMS pentru un eşantion de mortar hidraulic prelevat din fundaţiile vǎmii romane Porolissum - Moigrad, România. Datarea cu radiocarbon dă încredere în eșantionul care urmează a fi prelevat, și anume că acesta aparține perioadei istorice în cauză, și nu ca urmare a unor intervenții tardive sau recente. Studiul de caz oferă o descriere detaliată a metodei de pretratare a probei, stadiului de obținere a fracției de calcit provenit din momentul întăririi mortarului în zidărie, stadiului de separare și purificare a dioxidului de carbon rezultat în urma digestiei chimice a analitului final. Unele aspecte originale au fost dezvoltate la Laboratorul RoAMS, Mǎgurele. Reducerea dioxidului de carbon la carbon depus intim pe catalizatorul de fier (grafitizare), precum și etapa de măsurare AMS, calcule și calibrare sunt de asemenea descrise pe scurt. Rezultatul calibrat și interpretarea acestuia în context istoric și arheologic recomandă utilizarea acestui eșantion de mortar în viitoare analize multidisciplinare privind rețeta originală și posibilele surse de materii prime implicate.
Cuvinte cheie
CUVINTE CHEIE (ROMÂNĂ)
ANA J. MOMČILOVIĆ-PETRONIJEVIĆ , GORDANA A.TOPLIČIĆ-ĆURČIĆ, DUŠAN Z. GRDIĆ, DRAGAN M. ĐORĐEVIĆ, NENAD S. RISTIĆ ,ZORAN J. GRDIĆ
Rezumat
Caričin Grad is an archeological site dating back to VI century, located in the vicinity of present day Leskovac, Serbia. The city is the legacy of the famous early Byzantine Emperor Justinian I. The city, in the town planning terms, is divided into three large units. Acropolis, Middle town and Lower town, connected by the suburban area. The grandeur and importance of the city are witnessed by the remenants of several lines of city walls, planned street network, cisterns, thermae, aqueduct and sewage, numerous sacral buildings, administrative structures and housing architecture. Considering the complexity of the city, in town planning and architectonic terms, and diversity of building types in it, the mortars taken for analyses were collected from various types of buildings: from housing, public buildings, fortifications and from the aqueduct structure. In the paper, basic physical properties, as well as mineralogic, morphologic and chemical features of the sampled mortars were examined. The testing was performed using optical and scanning electron microscopy, XRF semi-quantitative analysis and XRD (x-ray diffraction). Based on the mentioned analyses, it was concluded that the main binder in the mortar was pulverized brick, which activated its pozzolanic activity. In addition, as an auxiliary binder, there was limestone powder, considering that the mortar contained the crushed limestone aggregates as well. The detected aggregate grains are the river aggregate, pieces of bricks and fine crushed limestone aggregate. These results would be further used for making the mix designs of repair mortars.
Cuvinte cheie
Caričin Grad, microscopie electronică B, mortare antice, microscopie optică B, mortare de reparație, metode de raze X
SATISHKUMAR SENGOTTAIYAN, SURESH PARAMASIVAM
Rezumat
The health risks connected with the use of asbestos-based brake linings have sparked research into the use of environmentally benign agro-based biomaterials as reinforcing agents in composite materials used in the manufacturing of brake pad linings. The purpose of this research is to determine the feasibility of employing coconut shell (CS) powder in the manufacturing of asbestos-free brake lining materials. The powders, in conjunction with the appropriate fillers, were utilised in the manufacture of the brake lining. The compositions of the reinforcing powders were varied between 20% and 35%, those of the resin binder were varied between 58 and 43%, and those of the filler metal and curing agents were maintained constant. Weighed, prepared, mixed, cured, and moulded these materials. Water and oil absorption, compressive strength, hardness, and wear tests were performed on the created composite materials. The research indicated that increasing the amount of reinforcing elements leads in an increase in the samples water and oil absorption. Compressive strength of the composite rose proportionately with the addition of up to 35% composition. The coefficient of friction tested was determined to be within an acceptable range. Additionally, when combined with other fillers and confined, CS powder shown great potential for brake lining manufacturing.
Cuvinte cheie
coji de nucă de cocos, garnituri de frână, rezistență la compresiune, duritate, uzură
-
Anul
2022
-
Numărul
52 (4)
-
Paginile
368-373
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Domenii de interes
BIOMATERIALE ȘI BIONANOMATERIALE; SUBSTANȚE, PROCEDURI ȘI DISPOZITIVE PENTRU MEDICINĂ
SASIKUMAR P, MANJU R
Rezumat
This research investigated the axial compression behaviour of high strength concrete Encased Steel Composite (ESC) columns. Six high strength concrete ESC columns were made with M70 grade concrete, including with and without Alkaline Resistant Glass Fibre (AR-GF), all the specimens were tested after curing periods. A study of structural performance was conducted, which included axial load-deformation, ultimate load-carrying capacity, failure mode, ductility, and stiffness. As a result of the experiments, the failure mode of ESC columns without AR-GF are sudden failures once the peak load is reached, and with AR-GF at 1.20% volume prevented concrete covers from spalling and increased the load-carrying capacity. In the whole experimental study, the reinforcement ratio was maintained at a constant. In conclusion, the results of the experimental study were compared with the Finite Element (FE) model results, the FE model is help to prediction of axial compression behaviour of ESC columns.
Cuvinte cheie
coloană din oțel compozit, deformare axială, încărcare axială, ductilitate, beton de inaltă performanță, rigiditate
KARTHICK PALANISAMY , REVATHI VAIYAPURI
Rezumat
Professor Davidovits fathered the idea that geopolymer binder is a viable alternative to Portland cement. Geopolymer can be synthesized by alkali activation of alumina silica rich inorganic materials of industrial by products and natural materials. An exhaustive study carried out on geopolymer concrete by the researchers establishes a strong pathway in the construction field. Furthermore, Self-Compacting Geopolymer Concrete (SCGPC) has been promoted using fly ash, GGBS, rice husk ash, silica fume, etc. In this respect, the present study proposes to carry out experimental studies on self-compacting geopolymer concrete, incorporating bottom ash and GGBS, under ambient curing condition. Bottom ash and GGBS were added in the proportion of 100:0, 75:25, 50:50, 25:75, 0:100. The fresh and hardened properties of the SCGPC were analysed for all the mixes. The test result of fresh concrete properties indicates that it satisfies the limits specified by EFNARC standards. The maximum compressive strength of self-compacting geopolymer concrete was ascribed as 38.5MPa and 54.8 MPa at 3 and 28 days by the mix containing only GGBS. An excellent strength achieved at early age is observed in the GGBS mix. Also, the strength results reveal that increase in the content of GGBS achieved greater strength.
Cuvinte cheie
silice de alumină, cenușă, GGBS, beton geopolimer auto compactant, EFNARC
BENGİ AYKAÇ , ALTAN YAVUZCAN
Rezumat
The presented study investigates the efficiency of repairing damaged reinforced concrete beams by a novel technique, which is the injection of epoxy resin to the cracks. The two main test parameters were the amount of flexural reinforcement (low, medium, and high) and the level of seismic damage before repair (light, moderate, and heavy). Nine cantilever beams were tested under reversed cyclic transverse loading in the undamaged (original) and repaired (after damaging) states. The test results were examined and discussed in terms of the initial flexural rigidity and ultimate load capacity. The technique was shown to be the most effective in damaged beams with mid-sized cracks. The minor cracks particularly in lightly-reinforced beams were not suitable for proper injection of resin, while the major cracks resulted in the epoxy to govern the flexural behavior of the beam after repair. The experimental load capacities were shown to be in close agreement with the analytical flexural capacities of the respective beams. The sizes of the cracks before repair and the longitudinal reinforcement did not affect the repaired beam to reach the load capacity of the original counterpart but affected the extent of deformations before reaching this load level.
Cuvinte cheie
reparație, lățime fisurare, armare la încovoiere, modernizare seismică, structuri beton
GANESH NAIDU GOPU, A. SOFI
Rezumat
The chloride attack on the reinforced concrete structure resulted in a substantial loss of bond strength due to reinforcing bar corrosion. E-glass, Steel and E-waste copper fibers were used in concrete to investigate corrosion-induced bonding behaviour. It was determined to perform pull-out tests in order to evaluate the bond behavior in relation to test variables such as the ratio of concrete cube clear cover (C) to rebar diameter (Ø) and the type of fiber. The bond stress-slip curves produced in this work adequately represented the bond behavior of corroded and uncorroded concrete specimens (with and without fibers). According to the findings, adding fibers to concrete appears to strengthen the connection and reduce corrosion. The bond strength of steel fiber reinforced concrete was found to be higher than that of concrete mixes including E-glass and E-copper wire fibers.
Cuvinte cheie
atac clorurat, forța de legătură, coroziune indusă, testul de extragere, viteza de coroziune
SASIKUMAR P, MANJU R
Rezumat
The present study carried out the axial compressive behaviour of High Strength Concrete (HSC) columns reinforced with GFRP bars under axial compression. Only a limited number of research works only done with GFRP Reinforced (RC) Concrete Columns. Twelve columns of 150x150mm cross-section and 1000mm height made with M70 grade of HSC, including 1.20% of Alkaline Resistant Glass Fibre (AR-GF), were tested under axial loading. The main parameters were studied in this research, including the Axial Load (AL) carrying capacity, axial deformation, failure pattern, ductility, and stiffness. GRFP RC columns are 90% axial load only carried compared to steel RC columns. The analytical study helped to predict the ultimate AL carrying capacity of HSC columns.
Cuvinte cheie
beton de înaltă performanță, încărcare axială, deformare axială, rigiditate, ductilitate bare GFRP
KHAWAJA ADEEL TARIQ, HADHI HASSAN KHAN, FARHAN ASIF, NOMAN JABBAR
Rezumat
The efficient pavement performance depends on the stability of the supporting layers. Road failures mostly occur due to poor selection of material and insufficient drainage arrangements. Subbase layer is an essential component of the pavement along with base, subgrade and surface wearing course. This research work is related to investigating the effect of Lime, Fly ash and Mat fiber on the strength and permeability characteristics of Subbase material. Results show that the maximum dry density and soaked California bearing ratios (CBR) values are increasing with the increase of lime and fly ash ratio in subbase. Whereas, maximum dry density and soaked California bearing ratios (CBR) values are decreasing with the increase of Mat fiber in the subbase. The increase in content of Mat fibers also resulted in increase in permeability of subbase material. It is also observed that higher content of fly ash results in swelling of the subbase material as compared with lime content.
Cuvinte cheie
sub-bază, var, cenușă zburătoare, valori CBR, covor din fibră