english A.UĞUR OZTURK, R. TUĞRUL ERDEM
Rezumat
Compatibility of different based superplasticizers with air-entraining admixture has been investigated. Physical and mechanical properties such as flow, setting time and compressive strength of cement mortars incorporating an air-entraining admixture (HS) with naphthalene sulfonate (SPNS) and modified polymer (SPMP) based admixtures have been determined. Also, the effects of their combinations on the freeze-thaw resistance of cement mortars have been determined. All admixtures are used with three different ratios and one of them is for overdosage effect. Results indicate that cement mortars having lowest early strength values are mortars incorporating 1.5% SPMP and 2.0% SPNS by mass of cement. The most effective series for the ultimate highest strength values were series with 0.05 % HS and 0.8 % SPMP. The freeze-thaw resistances of cement mortars were investigated for 50, 100, 150 and 200 freeze-thaw cycles. Indeed, the most effective series for freeze-thaw resistance were series with 0.05 % HS and 0.8 % SPMP.
Cuvinte cheie
aditivi, superplastifianți, compatibilitate, îngheț/dezgheț
JANNE PESONEN, JUHO YLINIEMI, TOIVO KUOKKANEN, KATJA OHENOJA, MIRJA ILLIKAINEN
Rezumat
Combustion affects the physical and chemical characteristics of fly ash. Peat and biomass are typically combusted using fluidized-bed combustion (FBC) technique, which causes the fly ash to have a low chemical reactivity. Especially low-Ca FBC ashes have very weak hardening properties, which reduce their utilization potential in many applications. This study examined the effect of adding alkaline activator and Portland cement on the hardening of two peat-wood fluidized bed combustion fly ash samples—one of high-calcium fly ash (24.9 % Ca) and the other low-calcium fly ash (9.7 % Ca). The reactive components of the raw materials, the mineralogical compositions, and compressive strengths of the resulting mortars were studied. Significant improvement to strength development was achieved. The addition of Portland cement proved necessary for low-Ca ash to harden at all. The ash cannot be considered solely as a filler material, since the reactive component (Ca, Si, Al, and S) contents of the ash, especially the Ca content, affect the strength development. Strength development of the mortars can be partly explained by the Ca/(Si + Al + S) ratio and the sum of the reactive components.
Cuvinte cheie
cenușă zburătoare, biomasă, turbă, ciment portland, activare alcalină, pat fluidizat
BORDJIBA ABDELHAK, HACEN-CHAOUCH ABDELMADJID, GUENFOUD HAMZA, GUENFOUD MOHAMED
Rezumat
The design of a safe and respectful roadway to the environment must meet the users’ requirements in the present without compromising those of future generations. Under the traffic action, always more constraint and the climatic blitzes, the pavements crumbling occurs rapidly, which leads to severe impairments that are reflected on the surface layers: rutting, cracking, substances rejection, polishing and pulling out the aggregates on surface. This situation often involves the renovation of the surface’s layers. It is, therefore urgent to appeal to a new vision of pavement design based on optimizing the use of local materials, non-renewable, and respect for the environment. The recycling of bituminous substances are one of the relevant solutions. It has the advantage of reusing building materials by mixing them with a proportion of refined ones to achieve the required performance. This assignment researches for different rates of coated aggregates, the effects of manufacturing temperature and blending time in the mixing of the constituents during production as well as the additive plastomers of polyolefins on the improvement of the recycled asphalt rutting. Rutting is one of the most encountered degradation phenomena in the Algerian roads. The formulated hypothesis used here assumes that the elastomer polyolefins additive have an influence on the mechanical performance (rutting) of the recycled asphalt and also on the rate of the used asphalt aggregates. To justify this hypothesis it is mandatory to go through the manufacture of the asphalt with different rate of asphalt aggregates. To reduce the number of experimental tests necessary for this study, we used the experimental approaches method.
Cuvinte cheie
beton asfaltic, reciclare, mediu, liant
ZHOU LINA , WANG ZHENG, LU SHUANG
Rezumat
The leaching behaviour of hydraulic concrete can’t be ignored for its long-term exposure to surrounding water resulting in irreversible damage of durability, such as strength loss and porosity increase. The coupled effect of leaching and freeze-thaw cycles on the durability of hydraulic concrete in severe cold regions is a bigger challenge. For the quite slow process of natural leaching, electrochemical accelerated leaching method (EALM) was proposed to investigate the damage evolution under two test schemes (scheme one is only leaching for 50 days and scheme two is first 100 rapid freeze-thaw cycles and then leaching for 50 days) designed in this work. The electrical resistivity and calcium oxide dissolved mass were measured through electrode impedance spectroscopy (EIS) and EDTA titration method, respectively. Based on electrical resistivity measurement, the measurable damage can be discussed during above-mentioned single and coupled tests. The results indicate that compared with single leaching the coupled leaching with the freeze-thaw cycling leads to over 50% electrical resistance loss, the largest difference of both calcium oxide dissolved mass and pH in cathode room on the 21st day.
Cuvinte cheie
lixiviere, beton hidraulic, efect cuplat EALM, EIS
ELENA DUMITRESCU, ECATERINA ANDRONESCU
Rezumat
Lucrarea prezintă rezultatele experimentale pentru inertizarea deşeurilor solide (cu conţinut de metale grele) în lianţi magneziano-fosfatici (CBPC). Prin acest proces deşeurile periculoase se transformă în deşeuri nepericuloase.
S-a studiat inertizarea deşeului de sol contaminat cu 2000 mg/kg metale grele (Cu, Ni, Pb şi Zn) în CBPC comparativ cu inertizarea în pasta de ciment portland. Încărcarea în deşeu a fost de 50%, 70% şi 80 %. Deoarece sistemul CBPC este unul cu întărire rapidă, s-au utilizat întârzietori de priză (acid boric şi lignosulfonat de calciu) în concentraţie de 1% (raportat la cantitatea de oxid de magneziu şi fosfat diacid de potasiu). Pentru determinarea eficienţei procesului de inertizare a deşeurilor s-au realizat teste de levigare în apă şi în soluţie acidă, valorile obţinute comparându-se cu cele reglementate.
Toate deşeurile stabilizate atât cu ciment portland cât şi cu CBPC îndeplinesc criteriul stabilit pentru rezistenţa la compresiune pentru acceptarea deşeurilor în depozite de deşeuri, dar stabilizarea în CBPC este mai eficientă faţă de stabilizarea în ciment.
Din punct de vedere al levigabilităţii nichelului în apă,, stabilizarea cu CBPC permite încărcări în deşeu de 80%, faţă de stabilizarea în ciment care permite o încărcare de 50%.
Cuvinte cheie
inertizare deșeuri, sol contaminat, metale grele, lianți maneziano-fosfatici
CLAUDIU ACIU, CECILIA ROMAN, DANA - ADRIANA ILUŢIU - VARVARA, CARMEN PUIA, OANA CADAR
Rezumat
Acest studiu s-a axat pe realizarea de mortare de tencuială cu bune proprietăţi antibacteriene şi antifungice şi caracteristici fizice şi mecanice adecvate privind rezistenţele mecanice (CS IV), o bună aderenţă la substrat şi absorbţie redusă de apă prin capilaritate (W2). Au fost folosite suspensii (densitate 106 celule/ml) de patru specii de bacterii (Escherichia coli, Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa) şi două specii de fungi (Aspergillus niger and Penicillium chrysogenum). Pentru efect antibacterian şi antifungic la suprafaţa mortarelor sunt necesare concentraţii mai mari de 5% nanopulberi de Ag/ZnO (0.05 % gr.). Ca urmare, mortarele de tencuială obţinute pot fi folosite pentru inhibarea creşterii agenților patogeni de interes pentru mediu şi igienă.
Cuvinte cheie
mortar, ZnO, argint, proprietăți antibacteriene și antifungicide
BOJAN MILOŠEVIĆ, ŽARKO PETROVIĆ, MARINA MIJALKOVIĆ, SLOBODAN RANKOVIĆ
Rezumat
Self-compacting concrete (SCC) is intensively used in civil engineering due to its excellent characteristics both in fresh and in hardened state. In the several recent years, there is a growing need for testing of recycled aggregate use for making of concrete, which protects the environment and solves the problem of construction rubble disposal sites. The goal of this paper is to test the potential of usage of coarse recycled aggregate, obtained by crushing of concrete elements mechanically damaged in the production process of prefabrication elements, for making of SCC. Three concrete mixes were prepared for the experiment: the mixture made with the river aggregate as a reference mixture, the mixture where the coarsest fraction of the river aggregate was replaced by the recycled aggregate and the mixture in which both coarse fractions of the river aggregate were replaced by the recycled aggregate. In making of these concrete mixes, the principle of equal consistency of mixtures was followed. The mechanical characteristics determined for all the mixtures were: compressive strength, splitting tensile strength and modulus of elasticity. The obtained results indicate that the properties of these concretes exhibit minimal differences, and the application of the recycled aggregate obtained by crushing of prefabricated elements mechanically damaged in production process is justifiable for making of SCC.
Cuvinte cheie
beton autocompactant, reciclare agregate
ELENA DUMITRESCU, ECATERINA ANDRONESCU
Rezumat
Lucrarea prezintă rezultatele experimentale pentru inertizarea deșeurilor lichide în lianți magneziano-fosfatici (CBPC). Prin acest proces deșeurile periculoase se transformă în deșeuri nepericuloase.
S-a studiat inertizarea deșeurilor lichide cu conținut de metale grele (Ba, Cd, Cu, Ni, Pb) cuprins între 3000 mg/l și 30000 mg/l, în CBPC comparativ cu inertizarea în pastă de ciment portland. Deoarece sistemul CBPC este unul cu întărire rapidă, s-a utilizat ca întârzietor de priză acidul boric în concentrație de 3% (raportat la cantitatea de oxid de magneziu și fosfat diacid de potasiu). Pentru a mări eficiența inertizării cadmiului s-a adăugat acid fosforic. De asemenea, s-a studiat influența adăugării dimetilditiocarbamatului de sodiu. S-a determinat temperatura maximă a sistemelor obținute, timpul de început de priză și rezistența la compresiune. Pentru determinarea eficienței procesului de inertizare a deșeurilor s-au realizat teste de levigare în apă și în soluție acidă, valorile obținute comparându-se cu cele reglementate.
Cuvinte cheie
inertizare deșeu, metale grele, lianți magneziano - fosfatici, lixiviere
VASILE RUS, HORAŢIU VERMEŞAN, ANDREEA HEGYI, ANCUŢA ELENA TIUC
Rezumat
Acestă lucrare are drept scop stabilirea unui model de evoluţie a grosimii şi a densităţii stratului de produşi de coroziune formaţi pe armătura zincată termic introdusă în betonul proaspăt. Pentru acest studiu s-au folosit atât armături zincate termic nepasivate, cât şi pasivate, folosind diverse soluţii de pasivare pe bază de crom. Pentru efectuarea testelor experimentale s-a folosit spectroscopia de impedanţă electrochimică (EIS). Evoluţia stratului de produşi de coroziune s-a studiat luând în considerare parametri circuitului echivalent obţinut prin fitarea curbelor de spectroscopie de impedanţă electrochimică obţinute experimental. Modelul de evoluţie a stratului s-a construit studiind evoluţia în timp a grosimii stratului raportată la rezistenţa lui la polarizare.
Cuvinte cheie
spectroscopie de impedanță electrocimică, armătură zincată, coroziune, interfață beton proaspăt
QINGFENG WANG
Rezumat
The calcium magnesium aluminate cement often presents a longer setting time than the conventional calcium aluminate cement containing 70wt. % Al2O3, owing to the presence of the MgAl2O4 spinel in the cement clinker. In this paper, calcium chloride was used to control the hydration rate of the cement containing MgAl2O4 spinel. The temperature development of cement pastes was employed to characterize the hydration and setting behavior of the cement. The electrical conductivity measurement was utilized to evaluate the dissolution-precipitation rate of the cement. X-ray diffraction was conducted to identify the hydrates after halting cement hydration by vacuum freeze drying at a certain curing time. And scanning electron microscopy was used to observe the microstructure development during the cement hydration. These results reveal that calcium chloride addition intensifies the hydration of the calcium magnesium aluminate cement.
Cuvinte cheie
clorură de calciu, ciment aluminos, hidratare, microstructură
KSENIJA JANKOVIĆ , LJILJANA LONCAR, DRAGAN BOJOVIĆ, MARKO STOJANOVIĆ
Rezumat
Adequate measures must be taken during the determination of the concrete composition for ensuring the durability of concrete exposed to an aggressive environment. The influence of the cement type on the freeze/thaw resistance with and without de-icing salt of concrete was tested. Samples were made using five types of cement. All types of concrete made according to the recommendations of the Serbian and European norms had the required frost resistance. Besides the respected recommendations, concrete made using cement with 35% mineral additions of fly ash and lime was not freeze/thaw resistant with de-icing salt.
Weathering resistance for paving units is determined according to EN 1338 and EN 1339 for freeze/thaw resistance with de-icing salt or water absorption. Taking into account previous investigations, only samples which were made in accordance with the recommendations of the Serbian Building code requirements for concrete and reinforced concrete - BAB 87 and European norms EN 206-1 were tested. Regarding water absorption, it is expected that in the case of established production all types of concrete would be integrated into class 2 according to EN.
Also, for two representative types of concrete with different air content and degree of damage done by destructive test, non-destructive test by device RapidAir 457 was done (specific surface, spacing factor, void frequency and average chord length)
Cuvinte cheie
durabilitate beton, diferite tipuri de ciment, rezistență îngheț - dezgheț, rezistență la îmbătrânire
IONELA PETRE, MIRELA MENICU, ILEANA MOHANU, FLORIN BERNEA, CAMELIA ȘERBAN
Rezumat
In procesul de clincherizare o influenţă negativă asupra funcţionării instalaţiei de clincherizare şi calităţii clincherului o are prezenţa compuşilor volatili (alcalii, sulf, clor). Aceştia sunt aduşi în sistem de materiile prime şi combustibilii utilizaţi. La nivel internaţional pentru reducerea efectelor negative ale compuşilor volatili o metodă eficientă o reprezintă introducerea bypass-ului. In lucrare sunt prezentate rezultatele calculelor teoretice de bypass relevându-se influenţa gradului de bypass asupra reducerii continuţului de alcalii din clincher.
Cuvinte cheie
by-pass, volatilitate alcalii, clincher, instalație de clincherizare
DAN GEORGESCU , ADELINA APOSTU
Rezumat
Articolul prezintă o propunere de extindere a aplicării principiului / procedurii durabilităţii echivalente (PDE). Se propun şi aplică criterii pentru determinarea rezistenţei la îngheţ - dezgheţ a betonului în contextul extinderii aplicării procedurii de durabilitate echivalentă la construcţii existente. Metoda propusă reprezintă o extindere a aplicării procedurii PDE luând în considerare: reducerea incertitudinilor legate de punerea în operă a betonului, a finisării, tratării betonului şi de gradul de îmbunătăţire în timp a performanţelor betonului. Aplicarea metodelor de încercare standardizate la nivel european şi la evaluarea rezistenţei la îngheţ - dezgheţ a betonului din construcţii existente reprezintă un pas înainte în creşterea durabilităţii betonului şi a duratei de viaţă a construcţiilor. Metoda propusă este similară cu cea utilizată la evaluarea rezistenţelor betonului.
Cuvinte cheie
beton, durabilitate, evaluare, performanță
M. HRAITA, Y. EL RHAFFARI, G. FADILI, A. SAMAOUALI, Y. GÉRAUD, M. BOUKALOUCH
Rezumat
The importance of capillary imbibition and evaporation processes in the alteration of building stones under the action of salt crystallization can be estimated by various experimental techniques. The aim of this study is to understand the direct relationships between salt weathering, petrophysical and structural properties. We chose to work on calcarenite stone which was commonly used as building material in historical monuments in Morocco. Laboratory wetting-drying cycles were tested on calcarenite specimens with sodium chloride solutions of different concentrations. Results show that the permeability and specific mass of precipitated salt depend on the material porosity and solution concentration. Moreover, variations of thermal conductivity and permeability during applied cycles are less important for samples taken parallel to the sediment bedding than for those taken perpendicularly. The material anisotropy will also be discussed.
Cuvinte cheie
calcarenite, săruri, monumente istorice Marocane
MIHAI ROHAN
Rezumat
În Romania există mai multe industrii care deja aplică conceptul economiei circulare, printre care și industria cimentului/betonului care transformă deşeurile în resurse alternative de materii prime şi energie şi valorifică deja cantităţi semnificative de deşeuri provenind din alte industrii precum şi deşeuri menajere sortate. Co-procesarea deşeurilor în industria cimentului este o metodă de valorificare a deşeurilor, recunoscută drept una dintre cele mai bune practici de eficientizare a utilizării resurselor. Prin co-procesare are loc simultan atât reciclarea conţinutului mineral al deşeurilor, cât și recuperarea energiei acestora, ceea ce conduce la reducerea emisiilor indirecte de CO2.
De asemenea, produsul de larg consum al acestei industrii - betonul din ciment - poate fi reciclat 100% drept agregate alternative utilizate la construirea infrastructurii de transport sau pentru obţinerea unui nou beton.
Astfel industria cimentului/betonului contribuie la conservarea resurselor naturale prin înlocuirea lor cu resurse alternative provenite din deşeuri şi devine parte integrantă a economiei circulare - deziderat european pentru eficientizarea utilizării resurselor şi asigurarea securităţii energetice.
Cuvinte cheie
ciment, beton, deșeu, reciclare, economie circulară, valorificare
ANGEL PALOMO, OLGA MALTSEVA, ANA FERNANDEZ-JIMENEZ
Rezumat
Coal fly ash can be subject to large variations in characteristics as a function of the type of coal burned, the operation status of the coal power plant and the ash separation technology employed. Good quality fly ash is in demand in the cement industry (and in the concrete plants) due to its ability to partially substitute some Portland cement (typically between 10% and 25%). On the other hand, coal bottom ash, due to its coarser nature, is generally considered as a low value by-product that may at best be used as a partial replacement for aggregates in concretes or as geotechnical fill material. In this paper authors propose a procedure (mechanical-chemical combined procedure) by which to transform regular coal combustion products (fly ashes and/or bottom ashes) into Ultra-Reactive Ashes (URA).
URA is a product with very interesting cementitious characteristics which can become the most important component of a new family of extra-durable and cheap ecoconcretes.
Cuvinte cheie
cenușă zburătoare, activare chimică, activare mecanică, beton geopolimer
CARMEN MUNTEANU, MARIA GEORGESCU
Rezumat
Lucrarea aduce informaţii obţinute prin cercetări proprii, referitoare la prepararea şi caracterizarea unor betoane în care liantul a constat din ciment portland cu conţinut variabil de cenuşă de termocentrală, iar ca agregat, s-a utilizat beton vechi, concasat, care a substituit parţial sau integral, agregatul de balastieră, convenţional. Betoanele au fost aditivate cu 0,9% superplastifiant policarboxilic.
Pe baza datelor experimentale, se pot stabili corelaţii utile compoziţie – proprietăţi (rezistenţă mecanică, impermeabilitate, rezistenţă la îngheţ-dezgheţ). Pe baza acestora, se poate aprecia că este posibilă valorificarea simultană a cenuşii de termocentrală şi a betonului vechi (concasat), prin obţinerea unor betoane care, pentru anumite caracteristici compoziţionale, prezintă proprietăţi (rezistenţă mecanică, impermeabilitate, rezistenţă la îngheţ-dezgheţ) apropiate de ale unui beton de referinţă, preparat cu materiale convenţionale. O astfel de valorificare a deşeurilor menţionate are, desigur, implicaţii favorabile asupra mediului.
Cuvinte cheie
beton, reciclare agregate, cenușă termocentrală, proprietăți
GORDANA TOPLIČIĆ ĆURČIĆ, DUŠAN GRDIĆ, NENAD RISTIĆ, ZORAN GRDIĆ
Rezumat
The share of aggregate in concrete composition, in terms of volume is 70%-80%. The properties of fresh and hardened concrete depend on the aggregate properties, primarily on particle size distribution. The paper considered impact of particle size distribution of aggregates from two screening plants from the South Morava river on the properties of concrete. The intention was to make concrete mixtures with the aggregate which would have as identical particle size distribution, as similar consistency of fresh concrete as possible and same compressive strengths. For making of afore mentioned concrete mixes, the same sort of cement and same admixtures were used.
It was concluded that the difference in the particle size distribution of aggregate fractions had an impact on the composition of concrete mixes of the identical properties. Specifically, the quantities of cement, admixtures and water were different in the afore mentioned mixtures.
The technical specifications of the cement manufacturers include a recommended quantity of cement for specified concrete classes. It is concluded that these values are only rough guidelines. The same holds for the recommended quantities of admixtures. For that reason, every required concrete mixture must be verified in laboratory, i.e., previously tested.
Cuvinte cheie
agregate de râu, curbă granulometrică, ciment, aditivi, beton
R. TUĞRUL ERDEM , A. UĞUR OZTURK, ENGIN GÜCÜYEN
Rezumat
Due to several advantages of cementitious materials especially mortars, they are widely used in construction works. It is important to determine the mechanical properties of cementitious materials to understand their behavior under different effects. In this study, Artificial Neural Networks (ANN) analysis is used to predict the 7 and 28 days compression strength values of cement mortars. Physical-mechanical properties such as flow, setting time and compressive strength of cement mortars incorporating of different chemical admixtures such as air-entraining admixture (HS), naphthalene sulfonate based (SPNS) and modified polymer (SPMP) based admixtures have been determined. The aim of the usage of combinations of air-entraining admixture with two different based superplasticizers is to form different inner structure affecting on compressive strength. All admixtures are used with three different ratios by cement weight and one of them is for overdosage effect. ANN analysis has been performed to predict the compression strength values after 7 and 28 days, in correlation with experimental part of the study. According to this view, 28 sets have been prepared with different combination of admixtures. At early ages, HS015-SPNS2.0 series had the lowest strength whereas the highest compressive strength at 28 days were obtained for HS005-SPMP0.8 series. Obtained compression strength values after 7 and 28 days have also been predicted by ANN analysis. It is stated that the established ANN model indicates a great capacity to predict the compressive strength values in the end.
Cuvinte cheie
ANN, aditivi, superplastifiant, mortare de ciment
CONSTANTIN GAVRILOAIA, NICOLAE ȚĂRANU, RALUCA ONOFREI, MIHAI BUDESCU, PETRU MIHAI, IOANA-SORINA ENȚUC
Rezumat
Caracteristicile dinamice ale unui element de construcții sunt caracterizate prin frecvența proprie de vibrație, coeficientul de amortizare și rigiditatea acestuia. În lucrare se studiază variația frecvenţei proprii de vibraţie a unor elemente din beton armat în raport cu starea de degradare cauzată de fisurarea betonului şi curgerea armǎturii.
Un program experimental, efectuat la Facultatea de Construcţii şi Instalaţii din Iaşi, a evidențiat relaţia dintre frecvenţa proprie de vibraţie şi stadiul degradării unor console din beton armat solicitate la încovoiere. În cadrul programului au fost testate, până la diverse stadii de degradare, patru grinzi din beton armat cu aceeaşi clasă de beton dar cu armări diferite. Rezultatele experimentale au fost validate prin modelare numerică utilizând programul pe bază de element finit LUSAS.
Cuvinte cheie
grinzi de beton armat, frecvență vibrație, stadii de degradare, modelare numerică
MICHAL HORA, PAVEL REITERMAN
Rezumat
This research is focused on concrete with rubber powder content exposed to low (freezing) temperatures. Rubber powder serves as air-entraining agent and should provide better freeze-thaw protection. On the other hand, rubber powder limits maximum compressive strength of concrete. The main purpose of this research is to find an optimal rubber powder content in order to satisfy needs for the minimal loss in strength of concrete as well as high freezing-thawing resistance. A freeze-thaw test was carried out on five concrete mixes with different contain of several rubber fractions to determine the optimal rubber grading. Specimens with rubber powder were tested on compressive strength, splitting tensile strength, tensile strength and moduli of elasticity. The specimens with rubber content were tested at laboratory temperature as well as at freezing temperatures. Influence of rubber addition was assessed on the base of original and residual values of studied properties after freeze-thaw loading. Resistance to frost damaged was determined by splitting tensile strength test and tensile strength test. Non-destructive methodology was predominantly used to monitor gradual deterioration during freeze-thaw cycling.
Cuvinte cheie
îngheț, dezgheț, pudră de cauciuc, antrenor de aer
GENG LIN, CHANG-LONG WANG , CHUN-YU QIAO, HAN-LONG CUI, LIE CHEN, SHUO YU
Rezumat
To comprehensively utilize lead-zinc tailings (LZT), it was used as main siliceous materials in autoclaved aerated concrete (ACC) in this study. The effects of fineness and content of LZT on the properties, hydration products and microstructures of AAC were investigated by the mechanical test, X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric/differential scanning calorimeter (TG-DSC) and scanning electron microscope (SEM). And the composition and morphology of the hydration products in AAC at varying stages were detected. The results show that the ACC containing 62% LZT (in mass percentage) with a specific surface area of 325 m2 kg-1 can achieve a bulk density of 587 kg m-3 and compressive strength of 4.94 MPa, which qualifies the requirements of A3.5, B06 level of AAC sample regulated by the composition and morphology GB/T 11969-2008. The mobility of slurry and hydration activity both increase as the fineness of LZT decreases. However, the small size of LZT particles and the high thickness of the slurry are harmful to form a good pore structure, which would influence the properties of AAC. When the blending percentage of LTZ is too high, the unreacted LTZ particles increase and accumulate within the system, which reduces the space among them and thus influences the growth and crystallization of hydration products. The main hydration products before curing are AFt and C-S-H gels. And then AFt decomposes and some amount of C-S-H transitions to tobermorite after curing and autoclaved.
Cuvinte cheie
steril plumb - zinc, beton celular autoclavizat, tobermorit
FAEZEHOSSADAT KHADEMI, MAHMOOD AKBARI, SAYED MOHAMMADMEHDI JAMAL
Rezumat
Ultrasonic pulse velocity (UPV) test method is used in this study for evaluating the compressive strength of concrete. A series of UPV tests were performed to evaluate the 28-day compressive strength of concrete and examine the effect of concrete mixture parameters on the UPV of concrete. It was found that concrete with higher 28-day compressive strength gives higher UPV and that an exponential relationship exists between the UPV and 28-day compressive strength of concrete. The results showed that the aggregate size has a significant effect on the strength of concrete. Concrete with larger aggregate size was found to give lower UPV and compressive strength. UPV results also indicated that the UPV and compressive strength of concrete consistently decrease with increase in water-cement ratio of concrete. The effect of using microsilica (Silica fume) in concrete is also studied. It was found that as the microsilica to cement ratio increases in concrete, the UPV and compressive strength of concrete increase. The effects of the ingredient materials on UPV were analyzed and potential mechanisms were proposed. To make the results applicable, the artificial neural network (ANN) method was used to predict the compressive strength of concrete based on the evaluated concrete mix parameters and ultrasonic pulse velocity. The ANN analysis demonstrated high reliability in predicting the compressive strength values of concrete.
Cuvinte cheie
beton, rezistență mecanică, încercare UPV, modelare rețele neuronale artificiale
AYED KADA, KERDAL DJAMEL EDDINE, SOLTANI RABAH
Rezumat
The study carried out herein aims at investigating the instantaneous and deferred mechanical behaviours of self compacting concrete (SCC). The survey was carried out in three steps. In the first step, local industrial waste fines, such as limestone (L), siliceous (S) and natural pozzolanic (PZ) fillers, were used in the preparation of the self compacting concrete; in the second, a study was performed to optimize the SCC formulation by varying the volume of paste; and finally, the effect of varying the volume of paste on the mechanical strength and shrinkage of the SCC was examined in the third part. Results showed that the addition of local fillers, according to international recommendations, in the preparation of SCC mixes gives better compressive strength and shrinkage behaviour than that of vibrated concretes.
Cuvinte cheie
beton autocompactant, filer calcar, filer silicios, puzzolană naturală, contracție
NALAN KALKAN, RECEP KANIT
Rezumat
The importance of capillary imbibition and evaporation processes in the alteration of building stones under the action of salt crystallization can be estimated by various experimental techniques. The aim of this study is to understand the direct relationships between salt weathering, petrophysical and structural properties. We chose to work on calcarenite stone which was commonly used as building material in historical monuments in Morocco. Laboratory wetting-drying cycles were tested on calcarenite specimens with sodium chloride solutions of different concentrations. Results show that the permeability and specific mass of precipitated salt depend on the material porosity and solution concentration. Moreover, variations of thermal conductivity and permeability during applied cycles are less important for samples taken parallel to the sediment bedding than for those taken perpendicularly. The material anisotropy will also be discussed.
Cuvinte cheie
structuri de zudărie, beton torcretat armat, încercări ciclice
LAVINIA GABRIELA POPESCU, ENIKÖ VOLCEANOV, ILDIKO ANGER, ALEXANDRA GEORGIANA MOISE, ADRIAN VOLCEANOV, ECATERINA MATEI
Rezumat
Lucrarea prezintă o evaluare comparativă a factorilor de mediu la utilizarea unui deşeu industrial – zgura albă provenită din metalurgia secundară. Au fost investigate zguri LF din două surse sub formă de pulbere, prelucrate ulterior sub formă de pelete.
Compoziţia chimică a zgurilor evaluate a fost determinată prin spectrometrie de fluorescenţă cu raze X (XRF).
Au fost efectuate teste de levigabilitate şi analize ale compoziţiei chimice prin diverse metode. Astfel, compoziţia chimică a levigatului rezultat pentru diferite fracţii granulometrice ale deşeului de zgură LF a fost determinată cu ajutorul spectrometriei de absorbţie atomică în flacără (FAAS) și prin spectrometrie de emisie optică în plasmă cuplată inductiv (ICP-OES), în special pentru determinarea conţinutului de metale grele, antrenate din zgură.
De asemenea, a fost investigată evoluţia pH-ului şi conductibilităţii electrice pe probele de levigat, preparate la raportul solid / lichid de 1:2 și 1:10.
Avantajul folosirii zgurilor LF sub formă de pelete constă în reducerea instabilităţii zgurii LF, spre deosebire de zgura iniţială care are caracter prăfos, fapt ce duce la dispersia prafului în mediul înconjurător. Acest lucru este posibil prin prelucrarea zgurii la o granulaţie optimă, care conduce la obţinerea unui produs mai omogen şi din punct de vedere al caracteristicilor fizico-chimice. Acest lucru permite utilizarea efectivă ca amendament al solurilor acide în agricultură.
Cuvinte cheie
peleți, zguri metalurgice, lixiviere, sol acid, agricultura sustenabilă
RODICA-MARIANA ION, MIHAELA-LUCIA ION, ADRIAN RADU, RALUCA-IOANA ŞUICĂ-BUNGHEZ, RADU-CLAUDIU FIERĂSCU, IRINA FIERĂSCU, SOFIA TEODORESCU
Rezumat
În domeniul restaurării arhitecturale, prin intermediul unor studii de caz sunt analizate materialele vechi, precum şi dezintegrarea lor în medii agresive. Unele proprietăţi (capilaritate, porozitate) sunt testate pe diferite suprafeţe de faţadă, în scopul identificării materialelor constituente şi selecţiei materialelor utile în restaurare. Studiile de microscopie (MO, AFM) realizate permit observarea principalelor semne de alterare şi a rezultatelor consolidării cu diverse materiale. Tehnici precum EDXRF și ICP-AES oferă informaţii asupra compoziţiei elementale a probei, în timp ce GC-MS permite identificarea răşinilor de conifere din adezivii utilizaţi anterior pentru restaurare. Identificarea terpenelor şi a derivaţilor acestora evidenţiază prezenţa uleiurilor vegetale şi a răşinilor de conifere. De asemenea, parametrii de culoare CIELAB reprezintă o dovadă a eficacităţii procesului de conservare. În plus, în această lucrare este investigată comparaţia dintre mortarele tradiţionale (pe bază de ciment) cu cele bazate pe nanomateriale (hidroxid de calciu, hidroxiapatită şi amestecul lor controlat) utilizate în restaurare.
Cuvinte cheie
nanomateriale, caracterizare, restaurare fațade
PAVEL KRIVENKO, OLEG PETROPAVLOVSKII, HRYHORII VOZNIUK
Rezumat
At present, a tendency to substitute hazardous organic adhesives in the majority of building materials is clearly observed. This is connected with the more strict than before requirements for health safety, fire safety and durability. The most important task is substitution of organic binders, traditionally used as adhesives for gluing concrete, brick and ceramics with non-hazardous inorganic binders. To solve this problem an adhesive for concrete, brick and ceramics based on ecologically friendly alkaline aluminosilicate binder (geocement) has been developed. This binder is itself an inorganic polymer, which combines properties of inorganic substances (high strength and frost resistance) and those of organic substances (elasticity, adhesion to various materials etc.) and is analogue to alkaline aluminosilicate materials occurring in nature: zeolites, feldspathoids, etc. Bonding strength of the geocement-based adhesives to various surfaces is higher than 1 MPa. With taking into account high pH of the geocement stone a proper choice of fillera and additives is important. The purpose of the study was to reveal influence of the geocement-based adhesive composition on properties and, accordingly, on structure of the interfacial transition zones: "concrete−concrete", "concrete−ceramics", "ceramics−ceramics".
Cuvinte cheie
structuri alumino - silicatice, adezivi pe bază de geociment, metacaolin, mică felspat
IOANA GOMOIU, MADALIN ENACHE, ILEANA MOHANU, ROXANA COJOC, SIMONA NEAGU, DAN MOHANU
Rezumat
Colonizarea microbiană şi biodeteriorarea picturilor murale din monumete istorice au ca efect deteriorări estetice şi structurale datorită degradării lianţilor organici, biomineralizării, biofilmelor colorate şi a modificărilor de culoare. Mortarul original şi cel de reparaţie din trapeza Complexului Monastic Hurezi-România au fost analizate din punct de vedere structural şi microbiologic. Analiza directă efectuată in situ pe peretele de nord şi vest a pus în evidenţă: fisuri, zone de culoare roz de dimensiuni reduse şi mari la nivelul picturii murale, a mortarului original şi de reparaţie; zone mici, de culoare neagră pe mortarul de reparaţie; eflorescenţe de culoare roz sau alb în principal pe mortarul de reparaţie. Observaţiile microscopice efectuate atât in situ cât şi în laborator (microscopie optică şi microscopie electronică de baleiaj) au identificat biofilmul de culoare roz şi colonii mici de culoare neagră. Caracteristicile mortarelor sunt favorabile pentru aderarea şi multiplicarea bacteriilor şi fungilor.
Cuvinte cheie
colonizare microbiană, biofilm roz, biopigment negru, mortar strat de pictură
ILEANA MOHANU, DAN MOHANU, IOANA GOMOIU, ADRIANA MOANŢĂ, LILIANA RADU, CRISTINA SERENDAN
Rezumat
Bisericile de lemn pictate în frescă, prezente exclusiv în zona de sud a României, reprezintă o categorie restrânsă, prea puţin explorată şi, în plus, ameninţată cu dispariţia. Principala problemă de conservare o reprezintă refacerea aderenţei frescei la suportul de lemn.
Această lucrare prezintă rezultatele primelor cercetări privind obţinerea unor materiale care să servească în procesul de consolidare a picturilor murale pe suport de lemn. În acest scop au fost realizate o serie de mortare pe bază de var hidratat, nisip de râu şi fibre de cânepă. Pentru îmbunătăţirea aderenţei a fost adăugat un aditiv acrilic. Au fost evaluate diferite caracteristici ale mortarelor în stare întărită, cum ar fi: densitate aparentă, absorbţie de apă, permeabilitate la vapori de apă, rezistenţă la încovoiere şi compresiune, rezistenţa la fenomenul de biodegradare. Utilizarea fibrelor în compoziţia mortarelor a condus la imbunătăţirea rezistenţelor mecanice la încovoiere şi compresiune.
Cuvinte cheie
frescă, mortar de var, fibră, rezistență mecanică, biodegradare
ZENO GHIZDĂVEȚ, DANIELA NĂSTAC, MIHAI EFTIMIE, B. ȘTEFAN, IONELA STANCIU, ADRIAN VOLCEANOV
Rezumat
Analiza multivariată a unei baze de date complexe a evidențiat corelații compoziție-condiții de procesare-microstructură pentru anumite clinchere. Baza de date a fost constituită din rezultatele de analiză chimică ale unor clinchere de ciment, informații extrase din analiza imaginilor de microscopie optică a clincherelor și o serie de parametri de proces pentru instalația de clincherizare. Clincherele au fost arse în condiții diferite în industrie (19) sau în laborator (14 clinchere). Analiza imaginilor pentru fiecare clincher a constat în calculul parametrilor de formă, dimensiunii fractale și a unui parametru derivat din entropia Shannon, denumit Grad de Uniformitate. Au fost izolate și analizate în imaginile de microscopie optică fazele C3A și C4AF care constituie faza interstițială. Rezultatele finale ale analizei au identificat în mod clar cei mai importanți parametri din baza de date disponibilă. S-a constatat, de asemenea, că există un element-pivot – conținutul de CaO liber – între verigile compoziție, procesare și microstructură. Concluzia imediată este că oxidul de calciu liber poate fi un element de legatură între analizele de laborator și parametrii industriali în înțelegerea unor astfel de corelații complexe.
Cuvinte cheie
analiză multi - variată, clincher, microscopie optică, entropia Shannon, dimensiune fractală, fază interstițială
YU HAN, BAO-MIN WANG , SHUAI LIU
Rezumat
Mechanical performances of carbon nanotubes reinforced cement-based composites have been studied separately. The autogenous shrinkage of cement-based composites doped with multi-walled carbon nanotubes (MWNTs) were investigated with low MWNTs concentration of 0, 0.05%, 0.1% and 0.15% by weight(wt%) of cement in the early age in this paper. Ultrasonic processing and a commercially surfactant were utilized to achieve homogenous MWNTs suspensions. The addition of MWNTs decreased the autogenous shrinkage of cement composites compared to the reference sample. When the MWNTs dosage was 0.15 wt%, the autogenous shrinkage of specimen was the minimum, which was 28% lower than the reference sample. The water-cement ratio affects the early-age autogenous shrinkage more obviously. The results indicated that MWNTs can also have a beneficial effect on the early strain capacity, the early-age and long term durability of the cement-based composites.
Cuvinte cheie
nanotuburi de carbon, compozite bazate pe ciment, durabilitate autocontracție la perioade scurte de întărire
J.S. POZO-ANTONIO, J. FEIJOO
Rezumat
Concrete lime- and NHL-based mortars were prepared with river sand and a standard ASTM sand as aggregate. The mortar samples were subjected to different curing conditions for 28 days in order to achieve the acceptable mortar strength in a shorter period of time, with the aim to move the repaired artworks from the restoration departments of museums while avoiding possible contamination or damages. The results are provided under the study of the influence of the curing conditions, the binder nature, the binder/aggregate ratio relation and the aggregate nature. The test results showed that ASTM sand was a good alternative to river sand; it even improved the mechanical characteristics and drying shrinkage of the NHL-based mortars and lime cement-based mortars. NHL5, with a lower amount of aggregates, achieved higher values of flexural tensile and compressive strength and performed mortars with lower shrinkage values, being the ASTM sand the aggregate that provided better properties. Synthetically, the lime based mortar NHL5 (1:1.75) with ASTM sand under 14 days at a RH of 90 ± 5% and 14 days at a RH of 60 ± 5% seemed to be a satisfactory solution to be used as repair mortar in order to achieve good mechanical and physical properties without long periods in restoration departments.
Cuvinte cheie
ciment portland, var, mortar, agregat de râu, mortare pentru reparații, proprietăți mecanice
CAI JUN, LI GENGYING
Rezumat
Self-compacting concrete (SCC), also known as self-consolidating concrete, can be classified as an advanced construction material. SCC is a highly flowable concrete that can achieve full compaction without the need of vibration. In this study, the influence of fly ash on workability, mechanical properties and drying shrinkage of SCC specimens were investigated. The amount of fly ash was varied from 0% to 60% by mass of the binder material. Workability of SCC was characterized by the slump flow and the V-funnel tests. Test results showed that the workability of fresh SCC is improved by increasing the amount of fly ash. Compressive strength, splitting tensile strength and flexural strength decrease with the increase of fly ash. Fly ash can obviously reduce the drying shrinkage of SCC.
Cuvinte cheie
beton autocompactant, proprietăți mecanice, contracție la uscare
RADU VOINIȚCHI, CONSTANTIN DORINEL VOINIȚCHI, VIOREL CRĂCIUN, ALINA BĂDĂNOIU
Rezumat
În această lucrare se prezintă influența dozajului și a formei granulelor de agregat asupra principalelor proprietăți ale unor betoane cu porozitate ridicată (BPR). Rezultatele prezentate în această lucrare permit stabilirea unei corelații între valoarea coeficientului de permeabilitate a amestecului de agregate și a BPR corespunzatoare, preparate cu diferite dozaje de ciment. Această corelație poate fi folosită pentru proiectarea compoziției unui BPR, cu o anumită valoare a permeabilității, folosind ca date inițiale rezultatele obținute la testarea permeabilității amestecului de agregate, cu aplicarea unui coeficient de corecție care depinde de dozajul de ciment.
Înlocuirea fracțiunii 8/16 mm a agregatului (format din particule poliedrale) cu particule plate (caracterizate printr-un raport lungime/grosime mai mare ca 3) nu exercită o influență majoră asupra valorilor coeficientului de permeabilitate a amestecului de agregate și a BPR derivate. Totuși, s-a inregistrat o importantă scădere a rezistenței la compresiune a BPR atunci când particulele poliedrale de agregat (fracțiunea 8/16 mm) au fost înlocuite de cele plate.
Cuvinte cheie
beton cu permeabilitate ridicată, formă granule de agregat, permeabilitate la apă, rezistența la compresiune
G. MURALI, A.S. SANTHI , G. MOHAN GANESH
Rezumat
The aim of the study is to investigate the loss of mechanical properties such as compressive and splitting tensile strength of fiber-reinforced concrete (FRC) when exposed to impact load. Two different steel fibers i.e. hooked end and crimped end having the length of 50 mm and an aspect ratio of 50 were used as reinforcing materials in 0.5%, 1.0% and 1.5% volumes with a water-binder ratio of 0.42. The American concrete institute (ACI) committee 544 drop weight test was performed on 28 days cured cylinders, in order to determine the impact failure energy. In order to identify the loss of compressive and splitting tensile strength due to the effect of impact, another set of samples were prepared from the same concrete mixtures and exposed to impact loads of 25%, 40%, and 55% of their impact failure energy. Based on the results obtained from the experimental work, multivariate linear regression (MLR) models were developed using SPSS software to predict the percentage loss of compressive and splitting tensile strength due to the effect of impact load and the validity of the proposed model were verified with the test data of an earlier research. The results showed that the loss of compressive and splitting tensile strength in FRC significantly decreased compared with concrete without fiber, when exposed to impact loads. The results of the proposed model provided good agreement with the experimental results.
Cuvinte cheie
beton armat dispers, proprietăți mecanice
Evaluarea conformității structurale a betonului prin combinarea metodelor vizuale, fizice si chimice
ASLAM HUSSAIN , SALEEM AKHTAR
Rezumat
Structural Health Monitoring (SHM) plays an important role in retrofitting of concrete structures. In this paper, soundness of concrete material in three domes of a structure was evaluated by the use of Schmidt Rebound Hammer test and X-ray Diffraction (XRD) test after initially investigating the whole structure visually. It has been realized that value addition in the field of NonDestructive Testing (NDT) of Civil Engineering Structures is possible only through combination of various testing techniques. By successfully combining the results of visual inspection, strength based physical test and chemical test, authors have succeeded in introducing a novel idea for further research. XRD test, which has generally not been categorized as an NDT tool for structural evaluation, gives satisfactory results when combined with a strength based NDT tool.
Cuvinte cheie
evaluare conformitate structurală, beton, metode vizuale, fizice, chimice
AREF MOHAMAD AL-SWAIDANI
Rezumat
The objective of the present work is to predict the compressive strength, water permeability, chloride penetrability and porosity of concretes containing volcanic scoria as cement replacement after 2, 7, 28, 90 and 180 days curing. Concrete specimens have been produced with three different water-binder ratios of 0.5, 0.6 & 0.7 and replacement levels ranging from 10 to 35%. Test results revealed that curing time, the scoria content and the water-binder ratio had a large influence on all the examined properties of scoria-based concrete. An estimation equation has been developed by the authors to predict the studied properties depending on the water-binder ratio, the curing time and the replacement level of volcanic scoria. SEM/EDX analysis has been reported, as well.
Cuvinte cheie
beton cu rocă vulcanică, predicție, proprietăți
EMILIA MOSONYI, NICOLETA COBÂRZAN
Rezumat
Lucrarea reprezintă un studiu cu caracter interdisciplinar asupra zidurilor de fortificaţie din tuf vulcanic ale unui monument istoric, bazându-se pe: observaţii in situ, cercetări petrografice şi mineralogice (metoda colorării diferenţiate, microscopie în lumină polarizată prin transmisie, analize DRX) şi testări de absorbție a apei asupra unor probe extrase din elemente de construcţie înlocuite (plăci şi blocuri), mortare pe bază de ciment Portland alterate şi nealterate, plăci de tufuri vulcanice. Principalele procese de alterare evidenţiate au fost: fisurare intensă (fisuri de uscare, reacţii alcalii-agregate, carbonatare, cristalizare săruri, îngheţ-dezgheţ şi levigări asociate carbonatării secundare şi fenomene expansive induse de atacul sulfaţilor
Cuvinte cheie
clădiri istorice, tuf vulcanic, microscopie petrografică, atac sulfatic, compatibilitate
FLORENTINA ALINA BURLACU, CARMEN RĂCĂNEL, ADRIAN BURLACU
Rezumat
Siguranța rutieră are o importanță crescută, mai ales după ce ONU a proclamat perioada 2011-2020 Deceniul unei Acțiuni în Siguranța Circulației. Așa cum mulți factori contribuie la producerea accidentelor din trafic, infrastructura are propriul aport. Studiile referitoare la suprafața de rulare sunt foarte importante, în special datorită faptului că producerea accidentelor rutiere poate fi influențată de calitatea contactului pneu-carosabil. Aspecte precum rugozitate, permeabilitate și uniformitate sunt principalele proprietăți de care ar trebui să se țină cont pentru o suprafață de rulare. Lucrarea de cercetare prezentă are scopul de a corela caracteristicile materialelor folosite în stratul de uzură cu riscul de producere a accidentelor din trafic, prin calculul distanței de frânare, o subcomponentă a distanței de oprire. Rezultatele încercărilor de laborator realizate pe agregate vor arăta că varierea sursei materialelor, distanța de oprire poate să difere cu până la 20 de metri.
Cuvinte cheie
materiale rutiere, siguranță rutieră încercări de laborator