english M. TORRES-CARRASCO, F. PUERTAS
Rezumat
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.
Cuvinte cheie
activare alcalină, geopolimeri, zguri, durabilitate
LAURA BĂRBULESCU, ALINA BĂDĂNOIU, ADRIAN NICOARĂ, CRISTIAN PÎRVU
Rezumat
În lucrare se prezintă o serie de proprietăţi fizice şi mecanice ale unor mortare pe bază de ciment portland în care agregatul (nisip cuarţos) a fost înlocuit cu două tipuri de deşeuri. Aceste deşeuri provin din procesul de prelucrare a lingourilor de aliaje de titan, prin sablare cu alice de oţel (DS) sau prin abraziune/polizare (DSIC).
Înlocuirea totală a nisipului cu deşeul DSIC în mortare, a determinat o creştere a valorilor rezistenţei la încovoiere şi compresiune în comparaţie cu cele înregistrate pentru mortarul preparat cu agregat convenţional (nisip). Acest lucru se poate datora conţinutului mare de titan (metalic sau sub formă de oxid), specific pentru acest tip de deşeu.
Înlocuirea parțială a agregatului natural (nisip cuarţos) sau a celui neconvenţional - deşeu DSIC, cu deşeul DS a determinat o scădere a rezistenţelor la încovoiere şi compresiune ale probelor de mortar, atât la perioade scurte de întărire (3 zile), cât şi la perioade mai îndelungate de timp (28 zile).
Cuvinte cheie
deșeu de titan, agregate alternative, ciment portland, mortar
I.DIAZ-PEÑA, J. G. RANGEL-PERAZA, A.M. GUZMAN, R. GONZÁLEZ-LOPEZ , A.A. ZALDIVAR-CADENA , J. HERNÁNDEZ-SANDOVAL
Rezumat
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.
Cuvinte cheie
protecție electrochimică, nanosilice, pasta ciment portland
DANUTĖ VAIČIUKYNIENĖ, ARAS KANTAUTAS, ŽYMANTAS RUDŽIONIS, VITOLDAS VAITKEVIČIUS, MINDAUGAS ŠUKUTIS
Rezumat
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.
Cuvinte cheie
deseuri de sticlă reciclată, pudră de sticlă zeolitica, ciment, zeolit
YANG ZENGKE, HUANG WEI, ZHANG MIN
Rezumat
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.
Cuvinte cheie
fibre de oțel, fibre de polipropilenă, cărămidă reciclată, șlam, ceramsit, experiment ortogonal
XIAO-WEI CUI, CHANG-LONG WANG, WEN NI, YAN-QING DI, HAN-LONG CUI, LIE CHEN
Rezumat
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.
Cuvinte cheie
deșeuri cu minereu de fier, beton celular autoclavizat, etringit, tobermorit
UMUT NACI BAYKAN, MURSEL ERDAL, LATIF ONUR UGUR
Rezumat
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.
Cuvinte cheie
încercare nedistructivă, beton, model Fuzzy, modelare statistică
LAMIA BOUCHHIMA, MOHAMED JAMEL ROUIS, MOHAMED CHOURA
Rezumat
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.
Cuvinte cheie
fosfogips, caramizi, durabilitate
CORNELIA - FLORENTINA DOBRESCU
Rezumat
Evaluarea comportării pământurilor naturale și stabilizate cu lianţi cu beneficii ecologice de tipul varului s-a bazat pe modelarea caracteristicilor de performanţă legate de creşterea portanţei lucrărilor de infrastructură prin dezvoltarea de corelaţii parametrice. Valoarea indicelui CBR constituie unul dintre parametrii frecvent utilizaţi, atât în etapa de proiectare, execuţie cât și în cea de controlul calităţii structurilor rutiere. Luând în considerare necesitatea numărului mare de încercări şi probe, precum şi perioada lungă asociată cu executarea acestora, se utilizează frecvent varianta alternativă bazată pe corelaţii empirice ale indicelui CBR cu caracteristicile terenului datorită atât timpului redus pentru execuţie, cât şi a verificării independente şi controlul calităţii rezultatelor. Caracteristicile de portanţă ale structurilor simulate în laborator au evidenţiat creşteri semnificative ale CBR ca rezultat al stabilizării cu var în condiţii naturale şi de inundare. Influenţa caracteristicilor de compactare asupra valorii CBR, în funcţie de indicatorii obtinuţi din încercări şi indicatori derivaţi exprimaţi prin coeficienţi de corelaţie, s-a reflectat prin corelaţii foarte bune între variabilele statistice analizate. Analizele comparative între parametrii obţinuţi experimental şi cei prognozaţi prin relaţii empirice au condus la calibrarea modelelor de regresie liniară simplă dedicate tipului de pământ studiat.
Cuvinte cheie
portanță, stabilizare, corelații parametrice, structuri de sol
I.GOMOIU, M. ENACHE, D. MOHANU, I. MOHANU, I. PETRE, R. COJOC
Rezumat
Rezistenţa la fungi a unui număr de 4 noi mortare a fost studiată în conformitate cu SREN 847:2000 (ISO 847: 1997). Suspensii de spori obţinute de la fungi filamentoşi aparţinând speciilor Aspergillus niger, Cladosporium herbarum, Ulocladium chartarum şi Penicilium sp. izolate de pe frescele contaminate de la biserica Amărăşti din judeţul Vâlcea au fost inoculate pe suprafaţa mortarelor în prezenţa şi în absenţa glucozei. După incubarea în camere umede (RH = 90-95%, temperatura = 22-260C), creşterea fungilor a fost evaluată la 1, 3, 6 şi 9 luni, prin analiza vizuală, la microscopul optic şi la cel cu baleiaj. Creşterea fungică pe suprafaţa mortarului în prezenţa şi în absenţa glucozei, efectul toxic al mortarelor şi rezistenţa acestora la biodeteriorare a fost exprimată valoric (0-5). Ca urmare a faptului că mortarele au fost sensibile la biodeteriorare s-a studiat sensibilitatea fungilor la următorii biocizi: Preventol RI 50 10%; Biotin R 8%; Biotin T 3%. Stabilirea eficienţei biocizilor în activitatea de decontaminare a permis elaborarea procedeului adecvat de obţinere a mortarelor precum şi a metodologiei de decontaminare in situ.
Cuvinte cheie
mortar, biodeteriorare, suspensii de spori, biocide, toxicitate mortar
XIAONIU YU, CHUNXIANG QIAN, LINZHU SUN, ZHIHAI HE, WEI LI, LINGJIE WU
Rezumat
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.
Cuvinte cheie
fosfați de magneziu, bionanoparticule, rezistență la compresiune, TEM
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Anul
2017
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Numărul
47 (2)
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Paginile
143-146
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Domenii de interes
BIOMATERIALE ȘI BIONANOMATERIALE; SUBSTANȚE, PROCEDURI ȘI DISPOZITIVE PENTRU MEDICINĂ
HUI WANG , XIAOJIAN GAO, ANASTASIIA GARIPOVA, HUALONG YANG
Rezumat
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.
Cuvinte cheie
nanofibre de carbon, pastă de ciment, tipuri de electrozi, rezistivitate, piezorezistivitate
SANDRA CUNHA, JOSÉ AGUIAR, VICTOR FERREIRA
Rezumat
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.
Cuvinte cheie
durabilitate, microstructură, mortare, rezistență îngheț - dezgheț, microcapsule cu schimbare de fază (PCM)
D.C. NĂSTAC, R. M. FECHET
Rezumat
Materialele alternative, cum ar fi deșeurile și subprodusele industriale pot fi cu ușurință și economic utilizate ca materie primă în fabricarea clincherului de ciment Portland. Aceste materiale sunt generate din abundență, ca urmare a creșterii industrializării la nivel mondial. Două tipuri de deșeuri provenite din industria minieră au fost utilizate ca materie primă secundară într-o concentrație care a variat între 1,4 și 3,5%. Din aceste clinchere au fost obținute cimenturi CEM I pentru care s-a determinat rezistența la compresiune. Diferite cantități de nămol generat în stațiile de tratare a efluenților de la câmpurile petroliere care au variat între 3 și 7% au fost adăugate la un amestec de bază de materii prime, fiind analizat efectul asupra procesului de clincherizare. Au fost determinate compozițiile chimice și mineralogice ale deșeurilor și amestecurilor de materii prime. A fost investigată aptitudinea la ardere a amestecurilor de materii prime care conțin concentrații diferite de deșeuri, în diverse etape de ardere într-un cuptor de laborator. S-a observat o aptitudine la ardere îmbunătățită, fără a afecta calitatea clincherului.
Cuvinte cheie
materii prime alternative, clincher de ciment portland, steril minier, nămol de petrol
E. RĂDULESCU, R. LISNIC, I. IORDACHE, S. NICULESCU, T. IOVU
Rezumat
Utilizarea combustibililor alternativi în industria cimentului a atins praguri semnificative, în prezent căutându-se soluţii pentru optimizarea amestecului de combustibili în vederea unei bune operări a cuptorului. Lucrarea prezintă determinarea necesarului de aer de combustie în cazul utilizării la ardere a unui amestec de combustibili (convenţionali şi alternativi) în diferite proporţii precum şi influenţa utilizării acestora asupra producţiei şi consumurilor în fabricile de ciment.
Cuvinte cheie
cuptor de clincher, combustibili alternativi, parametrii de proces, combustie
M.Z.BESSENOUCI, N.E.BIBI-TRIKI, M.HENAOUI, S.KHELLADI
Rezumat
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.
Cuvinte cheie
beton ușor, beton puzzolanic, materiale poroase, modelare, abordare termodinamică
G. MURALI, V. CHANDANA
Rezumat
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.
Cuvinte cheie
analiză Weibull, rezistență la impact, beton autocompactant
RAHMAT MADANDOUST , MOSTAFA KAZEMI, SEDIGHE YOUSEFI MOGHADAM
Rezumat
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.
Cuvinte cheie
rezistență la întindere beton, analiză FE, zonă de rupere
D. GEORGESCU, A. APOSTU, G. CROITORU
Rezumat
Articolul prezintă rezultatele unor cercetări experimentale efectuate pentru stabilirea nivelurilor de performanță a betoanelor preparate cu diferite tipuri de cimenturi și agregate care se utilizează pe teritoriul Republicii Moldova în vederea elaborării Anexei Naționale la standardul EN 206-2013. Determinarea caracteristicilor de rezistență și durabilitate s-a efectuat prin aplicarea unor standarde europene și naționale și a avut drept obiective principale stabilirea domeniilor de utilizare a betoanelor și analiza condițiilor de aplicare a metodelor bazate pe performanță a durabilității. În Anexa Națională s-au prezentat, din rațiuni legate de aplicarea practică a documentului, reguli de tip „deemed to satisfy” în ceea ce privește tipurile și calitatea materialelor, compoziția betonului și clasele minime de rezistență la compresiune, în funcție de o anumită utilizare a betonului.
Cuvinte cheie
ciment, beton, performanță durabilitate
E. RĂDULESCU, I. IORDACHE , R. LISNIC, S. NICULESCU, L. DRAGU
Rezumat
O soluţie la problema deşeurilor produse în cantităţi tot mai mari, a apărut în urmă cu peste 35 de ani când au început să fie utilizaţi pe plan internaţional combustibilii alternativi. Economisirea de cantităţi semnificative de combustibili fosili reprezintă un avantaj important al folosirii acestui tip de deşeu combustibil.
Deşeurile petroliere provin din activităţile curente ale industriei petroliere precum şi din activităţi de ecologizare a batalurilor istorice cu produse petroliere. Lucrarea îşi propune o evaluare a emisiilor de monoxid de carbon rezultate la arderea combustibilor solizi clasici şi alternativi (nămol petrolier și rumeguş) intr-o instalaţie de clincherizare. Natura şi proporţia combustibilului utilizat pot influenţa nivelul emisiilor de monoxid de carbon.
Cuvinte cheie
ardere, CO, combustibili alternativi, cuptor de clinker, nămol petrolier
A. SAMAOUALI, Y. EL RHAFFARI, M. HRAITA, L. LAANAB, H. OUDRHIRI, Y. GERAUD
Rezumat
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.
Cuvinte cheie
monumente istorice în Maroc, calcarenite, porozitate
D. RADU, Z. GHIZDĂVEȚ
Rezumat
Reacțiile care conduc la formarea clincherului din amestecul de materii prime au loc practic între oxizi și sunt de tipul acid-bază. Din acest motiv pare rațional să se considere că o caracteristica intrinsecă a amestecului de materii prime, precum diferența de bazicitate intre oxizii componenți, determina din punct de vedere chimic, aptitudinea la clincherizare. Influența acestei caracteristici, alături de modulul de saturare în calce Sk se manifestă atât asupra vitezei de reacție între oxizi cât și asupra randamentului de transformare a reactanților în produși de reacție. În lucrare se prezintă o serie de corelații între aptitudinea la clincherizare vs. diferența de bazicitate si Sk. Rezultatele sunt obținute pentru o serie de amestecuri brute străine si romanești. Ele atestă corectitudinea ipotezei de start.
Cuvinte cheie
clincher, amestec brut, ardere, aciditate și bazicitate, corelare
ALI UĞUR ÖZTÜRK, GÖKHAN KAPLAN
Rezumat
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.
Cuvinte cheie
ciment alb, reacție silice - alcalii, temperatură înaltă, raport apă ciment
LIDIA RADU, NASTASIA SACA, MARIA GHEORGHE, CLAUDIU MAZILU, VIOREL FUGARU
Rezumat
Articolul prezintă influența agregatelor speciale, de densitate ridicată şi a raportului apă/liant asupra proprietăților caracteristice şi de ecranare a radiațiilor gama ale betonului. Elementele cu număr atomic, Z, mare cum sunt Pb (Z = 82) şi Ba (Z = 56) conținute în agregatele grele utilizate – zgură plumbică, deşeuri de sticlă de la tuburile catodice (CRT) şi barită de haldă – au prezentat o contribuție decisivă la creşterea coeficientului liniar de atenuare a radiației gama. De asemenea, substituirea nisipului silicios cu alice de oțel a condus la creşterea densității betonului şi, implicit, a capacității de ecranare.
Betonul cu nisip din deşeu de sticlă CRT a avut rezistența la compresiune la 360 de zile (88,3 MPa) mai mare decât cea a betonului cu nisip de râu (83,5 MPa), pentru acelaşi volum de agregat şi acelaşi raport apă/ciment (0,38).
Rezultatele au arătat că betonul cu agregat complex pe bază de barită, alice de oțel şi deşeu de sticlă CRT are cea mai bună capacitate de ecranare a radiației gama, concretizată de o creştere a coeficientului de atenuare liniară, de 0,192 cm-1 pentru Co-60, cu 18,2 % mai mare decât betonul cu agregat total de barită.
Cuvinte cheie
betoane cu capacitate de ecranare a radiațiilor gama, coeficient de atenuare liniară, densitate, rezistență la compresiune
FARID BENMERIOUL, AHMED TAFRAOUI, ABDELKADIR MAKANI, SAID ZAOUAI
Rezumat
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.
Cuvinte cheie
beton autocompactant, nisip de dună, proprietăți mecanice
MIHAELA-ANDREEA MONCEA, FLORINA-DIANA DUMITRU, ANA-MARIA PANAIT
Rezumat
Coroziunea betonului reprezintă un proces complex, mecanismele prin care se desfășoară fiind particularizate în funcție de mediul în care este exploatat betonul. Astfel, în cazul betonului exploatat în medii agresive naturale (alpin, marin), procesele de coroziune se vor desfășura cu viteze mai mici decât în cazul betonului exploatat în mediu agresiv industrial.
Pentru a evidenția efectele mediului marin asupra structurii betonului, la perioade mari de timp, vechile construcții de beton din zona de coastă a României, reprezentate de cazemate (construite începând cu anul 1942), în cadrul lucrării prezente, au fost evaluate vizual în situ astfel de structuri. De asemenea, s-au analizat efectele coroziunii marine la nivel microstructural, fiind prelevate probe de beton, cu preponderență din zonele de interfață beton/armătură, din corpul cazematelor situate în stațiunile Tuzla, Costinești, Olimp, Mangalia, 2 Mai și Vama Veche. S-au utilizat, în acest scop, fluorescența de raze X (XRF), în vederea stabilirii conținutului de specii chimice cu potențial coroziv din compoziția betonului și analize de microscopie electronică de baleiaj (SEM) cuplate cu spectroscopie de raze X cu energie dispersivă (EDS), în vederea identificării produșilor de coroziune cristalini, formați la interfața beton/armătură.
Evaluarea vizuală a vechilor structuri de beton a arătat starea precară de conservare a acestor obiective strategice militare cu valoare istorică semnificativă. Analizele chimice, prin XRF, realizate pe probe de beton măcinate și sitate, au evidențiat prezența în beton a unor proporții semnificative de Fe2O3, extras prin coroziune metalică din armătură, dar și proporții semnificative de Cl și alcalii, provenite din mediul natural marin. Analizele SEM au indicat o microstructură poroasă, în care sunt evidentiați compuși cristalini proprii pietrei de ciment - etringit, hidroxid de calciu și hidrosilicați de calciu - și compuși de coroziune de tipul magnetitei (Fe2O3), akaganeitului (β-FeOOH) sau lepidocrocitului (γ-FeOOH), formați prin interacții chimice între ionii agresivi ai mediului marin și fierul din armătură.
Cuvinte cheie
coroziune beton, mediu marin, analize SEM, EDS, XRF
DAN BABOR, LOREDANA JUDELE, DANIEL LEPĂDATU
Rezumat
Construcțiile alcătuite din mortare și betoane de ciment sunt expuse unor procese avansate de coroziune cu ionul azotat, fiind procese specifice industriei îngrășămintelor cu azot. Scopul lucrării este de a urmări comportarea mortarelor de ciment cu un conținut ridicat de zgură (75%), expus la coroziune cu ioni azotați și analiza evoluției în timp a rezistenței mecanice a probelor de mortar standard sau cu un anumit conținut de zgură, scufundate în diverse soluții agresive. Agenții corozivi, care acționează asupra elementelor enumerate sunt în special oxizi de azot și amoniac gazos, compuși care se găsesc în cantități apreciabile în atmosfera caracteristică a acestui tip de industrie. Efectul lor este potențat de creșterea accidentală a umidității, temperaturii sau de aburul și gazele corozive neevacuate eventual prin folosirea unor instalații de ventilație neadecvate. Analiza proceselor chimice complexe care au loc permite evidențierea influenței diferiților agenți corozivi asupra rezistenței acestor mortare speciale.
Cuvinte cheie
coroziune nitrică, mortar cu zgură, rezistențe mecanice
SELIM KORKMAZ , FAHRI BIRINCI
Rezumat
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.
Cuvinte cheie
beton autocompactant, fibre, orientare, proprietăți mecanice
RUBEN P. BORG, CHARLO BRIGUGLIO, VYTAUTAS BOCULLO, DANUTĖ VAIČIUKYNIENĖ
Rezumat
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.
Cuvinte cheie
liant de tip geopolimer, deșeuri, cenușă zburătoare, biomase
AURELIA BRADU, PETRU MIHAI, MIHAI BUDESCU, OANA-MIHAELA BANU, NICOLAE ŢĂRANU, NICOLAE FLOREA
Rezumat
Promovarea betonului autocompactant (BAC) în industria construcțiilor, poate fi realizată doar după efectuarea unor studii cuprinzătoare ale proprietăților acestuia. Caracteristicile mecanice ale acestui material au fost mai puțin analizate, rezultatele comunicate până în prezent în literatura de specialitate fiind deseori contradictorii. Studiul comportării BAC în domeniul postelastic, caracteristică importantă pentru proiectarea structurilor de construcții amplasate în zone seismice, asigură posibilitatea de a evalua capacitatea reală de disipare a energiei de deformare. În cadrul acestei lucrări a fost efectuat un studiu comparativ privind proprietățile principale și curbele caracteristice complete ale betonului autocompactant (BAC) și betonului vibrat (BV) la solicitarea de compresiune centrică. Programul experimental s-a efectuat utilizând un sistem de testare conceput și brevetat la Facultatea de Construcții și Instalații din cadrul Universității Tehnice ”Gheorghe Asachi” din Iași. Rețetele de beton analizate au fost realizate în trei serii, cu menținerea constantă a cantității de ciment, iar fluiditatea BAC fiind ajustată din variația adaosurilor de filer de calcar și a aditivilor superplastifianți. Proprietățile mecanice ale BAC diferă de cele ale BV mai ales în situația în care se modifică fracțiunile volumetrice ale agregatelor. De asemenea, curbele caracteristice complete ale celor două tipuri de beton diferă reliefând capacitatea de absorbție convenabilă a energiei de deformare de către BAC.
Cuvinte cheie
beton autocompactant, lucrabilitate, domeniu postelastic, curbă caracteristică completă, capacitate de dispersie energie
AMIN KHAZAEE, ALI KHAZAEE
Rezumat
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.
Cuvinte cheie
beton, predictie, rezistență la compresiune, model roi de albine
Stabilizarea / solidificarea hidroxizilor din nămolurile reziduale industriale în mortare și betoane
BOUZEROURA MANSOUR, BOUAFIA YOUCEF, MOUSSACEB KARIM, DJENADI ROCHEDDINE
Rezumat
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.
Cuvinte cheie
hidroxizi din nămoluri reziduale, matrici cimentitice, lixiviere, stabilizare/solidificare
M. BALTAKYS , R. SIAUCIUNAS, A. EISINAS
Rezumat
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.
Cuvinte cheie
beton aerat, rezistența la compresiune, analiza structurală, tobermorit
ABIDENG HAWA , PREECHA SALAEMAE, WORAPHOT PRACHASAREE, DANUPON TONNAYOPAS
Rezumat
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.
Cuvinte cheie
microstructură, geopolimer, mortar, cauciuc natural, densitate
P. JAISHANKAR , K. SARAVANA RAJA MOHAN
Rezumat
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.
Cuvinte cheie
nanosilice, silice ultrafină, rezistență mecanică, SEM, EDS
LAMIA BOUCHHIMA , MOHAMED JAMEL ROUIS , MOHAMED CHOURA
Rezumat
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.
Cuvinte cheie
Fosfogips, cărămizi, rezistențe mecanice, presiune de compactare
NAILIA R. RAKHIMOVA, RAVIL Z. RAKHIMOV, ALBERT R. GAIFULLIN, VLADIMIR P. MOROZOV
Rezumat
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.
Cuvinte cheie
metacaolin, argilă ușoară, calcinare, pastă de ciment portland, puzzolană, rezistență la compresiune, densitate
RAMKUMAR V.R , CHINNARAJU K. , MURALI G.
Rezumat
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.
Cuvinte cheie
sarcină la impact, fibră de barbotină calcaroasă, cenușă de termocentrală, metacaolin
SUMATHI ARUNACHALAM, VUPPALAPATTI MANISH KUMAR REDDY, SARAVANA RAJA MOHAN KALIYAPERUMAL
Rezumat
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.
Cuvinte cheie
beton armat cu fibre hibride (HFRC), Nylon - 6 fibre, fibre de sticlă, rezistență la compresiune, rezistență la întindere
F.J. VÁZQUEZ-RODRÍGUEZ, E.U. DE LOS SANTOS, J.M. MENDOZA-RANGEL, C. GÓMEZ-RODRÍGUEZ, A.ARATO, EDÉN A. RODRÍGUEZ
Rezumat
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.
Cuvinte cheie
durabilitate, coroziune, întărire internă, compozite, aplicație structurală
SEDIGHE YOUSEFI MOGHADAM, RAHMAT MADANDOUST , MALEK MOHAMMAD RANJBAR, MOSTAFA KAZEMI
Rezumat
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.
Cuvinte cheie
polimer armat cu fibre de carbon (CFRP), coroziune, RETROFIT, beton armat
DRAGOȘ UNGUREANU, NICOLAE ȚĂRANU , DORINA NICOLINA ISOPESCU, VLAD LUPĂȘTEANU, PETRU MIHAI, IULIANA HUDIȘTEANU
Rezumat
Această lucrare prezintă rezultatele unui studiu comparativ între două tipuri de îmbinări adezive utilizate la asamblarea elementelor compozite polimerice armate cu fibre (CPAF), și anume, îmbinarea realizată prin suprapunere simplă și îmbinarea cu aderenți rigizi. În acest sens, au fost concepute și analizate 18 modele geometrice. Parametrii variabili care au fost considerați în acest studiu sunt lungimea de conlucrare și grosimea stratului de adeziv.
Cele două tipologii de îmbinări au fost modelate cu ajutorul programului bazat pe calcul cu element finit Ansys Workbench. Fiecare model a fost încărcat cu o forță longitudinală de tracțiune, cu valoarea de 1000N. Parametrii care caracterizează suprafața elementelor CPAF au fost determinați în urma studiului microscopic, prin procesarea grafică și numerică a imaginilor captate.
Pe baza modelărilor numerice s-a trasat grafic variația tensiunilor în lungul zonei de îmbinare. Rezultatele analizelor numerice au fost comparate cu cele obținute pe cale analitică, pe baza modelelor teoretice existente. În urma studiului s-a concluzionat că ambele metode de analiză, atât numerică cât și analitică, oferă predicții similare privind distribuția și valorile ultime ale tensiunilor tangențiale.
Cuvinte cheie
îmbinări adezive, compozite polimerice armate cu fibră de sticlă, modelare element finit, modele analitice
A. DURÁN-HERRERA, R. DE-LEÓN, C. A. JUÁREZ, P. VALDEZ-TAMEZ
Rezumat
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.
Cuvinte cheie
beton autoconsolidant, întărire internă, contracție autogenă, contracție la uscare, amestec de reducere a contracției, Opunia Ficus mucilage
DĂNUȚ TRAIAN BABOR, TUDOREL BĂLĂU MÎNDRU, MELINDA PRUNEANU, IULIA BĂLĂU MÎNDRU
Rezumat
Lucrarea de față prezintă influența unor componente de reacție rezultate ca urmare a hidrolizei alcaline a deșeurilor din pulberi de piei Chamois provenite de la operația de șlefuire, asupra caracteristicilor fizico-mecanice ale unui nou tip de material de construcții ușoare pe bază de ciment. Masa moleculară medie a produsului de hidroliză şi modificările survenite în picurile caracteristice ale benzilor spectrale IR, indică obținerea unui amestec polipeptidic după tratamentul chimic realizat. Produsele de hidroliză și reziduurile solide au fost folosite într-o serie de rețete de mortar; rezultatele obținute indică o îmbunătățire a principalelor caracteristici fizico-mecanice ale mortarului, cum ar fi absorbția de apă, rezistența la încovoiere și compresiune, în comparație cu rețeta convențională de mortar.
Cuvinte cheie
mortar ușor, pulberi chamois, hidroliză alcalină, reziduuri polipeptide, rezistență la compresiune, rezistență la incovoiere
DANIELA FIAT
Rezumat
În prezenta lucrare a fost studiată influenţa pulberilor redispersabile şi a eterilor de celuloză în tencuielile minerale aplicate ca ultim strat în sisteme de izolare termică la exterior. Pornind de la reţete tradiţionale, utilizând aditivi polimerici specifici pentru sistemele ETICS au fost concepute produse originale în care s-a modificat concentraţia de aditiv polimeric (pulbere redispersabilă) cu impact asupra caracteristicilor fizico-mecanice.
Utilizarea eterului de celuloză a condus la obţinerea unor compoziţii uşoare (densitate mai mică) şi lucrabilitate bună la aplicare.
Utilizarea pulberilor redispersabile a contibuit la obţinerea unor mortare cu permeabilitate la apă scăzută, permeabiltate mare la vapori şi aderenţă bună la suport, avantaje semnificative pentru durabilitatea produselor.
Au fost puse în evidenţă interacţiuni chimice între pulberile redispersabile şi ionii de Ca2+ eliberaţi la procesul de hidratare a cimentului. Pulberile redispersabile acţionează ca un al 2-lea liant în sistem conducând astfel la performanţe îmbunătăţite.
Cuvinte cheie
mortar de tencuială, aditivi polimerici, eter de celuloză, pulberi redisipabile
Studiu privind gipsul sintetic obținut prin desulfurarea umedă a gazelor de ardere din termocentrale
ANA-MARIA DRAGOMIR, RAZVAN LISNIC, TUDOR PRISECARU, MALINA MIHAELA PRISECARU, CRISTINA ANDREEA VÎJAN, DANIELA CRISTINA NĂSTAC
Rezumat
În procesul umed de desulfurare a gazelor din centralele termice rezultă CaSO4.2H2O, denumit gips de desulfurare sau gips sintetic. Gazele arse sunt desulfurate prin injectarea unei suspensii de filer de calcar sau var nestins. Produsul care se formează iniţial în urma desulfurării gazelor este sulfitul de calciu. Acesta, prin oxidare forţată, se transformă în sulfat de calciu dihidrat - CaSO4.2H2O, iniţial sub formă de suspensie, a cărui umiditate este redusă prin filtrare sau centrifugare.
În acest articol se prezinta caracteristicile principale ale gipsului sintetic obţinut la scară industrială comparativ cu cele ale gipsului natural. De asemenea, se prezintă posibilitatea de valorificare a acestui produs secundar în industria materialelor de construcţii.
Cuvinte cheie
FGD umed, gips sintetic, clincher, ciment