română ALEXANDRA GABRIELA PALADE, MIHAELA IVANCIA, DIANA FELICIA LOGHIN, ANCA MIHAELA MOCANU
Abstract
The paper aims to obtain prosthetic devices made of two different dental ceramics and characterized by infrared absorption spectroscopy (FITR), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX) and thermal analysis (TG- DTG-DTA). The two types of dental ceramics (VITA VM13 and IPS Style) were analyzed both in powder form, in the form before the firing process, and in the one resulting after this stage, sintered mass. The TG, DTG and DTA thermal analysis study identified the temperature range in which the ceramics are thermally stable and can be used in dental technique, with IPS Style ceramics showing a lower degree of decomposition.
Keywords
ceramic mass kits, layering technique, absorption spectroscopy, scanning electron microscopy, X-ray spectroscopy, thermal analysis.
MEDDOUR BELKACEM, BREK SAMIR, SAOUDI ABDELHAK, BAKHOUCHE HIBAT ERRAHMANE
Abstract
The choice of material for an implant is considered one of the best for successful arthroplasty. The prosthesis implants for knee joints are usually made of metallic biocompatible materials and polymers. However, this work proposes the replacement of stainless steel with zirconia. Zirconia is known for its weak cracking strength; therefore, this paper aims to predict the cracking of the femoral implant made of zirconia. To do so, a pre-crack was created while performing a numerical simulation to determine the stress intensity factor. This procedure is repeated for the incremented length of the pre-crack until the stress intensity factor reaches the fracture toughness value. To extend the investigation, three areas of the femoral implant where the stress concentration could be expected were considered. In all cases, the simulation results showed good zirconia behavior against cracking, and no crack propagation was expected.
Keywords
crack, toughness fracture; zirconia; knee
NOUR-DJIHANE MAZOUZI, KHALIDA BOUTEMAK, AHMAD HADDAD
Abstract
Films based on hydroxypropylmethylcellulose (HPMC) find applications in for various applications due to their environmental nature, low cost, flexibility and transparency. However, the mechanical properties and moisture content need to be improved. The point of this study was to examine the impact of the magnesium oxide (MgO) addition on the physicochemical, mechanical and rheological properties of hydroxymethylcellulose films. HPMC/MgO composite films showed a four-fold increase in mechanical properties compared to unreinforced HPMC films. In addition, the addition of MgO nanoparticles reduced the moisture content to 2%. The latter was influenced by the difference in water solubility of various composite films, the incorporation of MgO into HPMC films improved the water barrier properties despite the increased water resistance value. Steam wettability was obtained for the HPMC/MgO composite film.
Keywords
hydroxypropyl methylcellulose HPMC, magnesium oxide MgO, nanoparticles, rheological properties
HAO LI, WEI ZHOU, KSENIIA RUDENKO
Abstract
High-performance fiber-reinforced cement composites (HPFRCCs) are attractive in applied in life-cycle structures. Hybrid properties of HPFRCCs with various fibers was experimentally investigated in this study. Three fibers contains the long and short smooth steel fibers and PE fibers, were blended into paste and mortar reinforced with 1.5% vol. fibers, respectively. Enhancements in mechanical properties including compressive strength and flexural strength, and workability were various for different types of fibers. The results show that for FRCCs with available amount of PE and steel fiber was achieved satisfactory workability. The better compressive strength was obtained at 28 day is 100.5MPa and 95.0MPa for the paste and the mortar, respectively. Incorporation of PE fiber in cement paste led to improvement in flexural strength. Microstructure has indicated effectively dense cementitious composites strong bond between the fibers and the cement paste for both of the mixes.
Keywords
high-performance fiber-reinforced cement composites (HPFRCCs), compressive strength, flexural strength, workability
GONZÁLEZ-FÉLIX JULIO CESAR, MENDOZA-RANGEL JOSÉ MANUEL, DIAZ-PEÑA ISMAEL, FÉLIX-MEDINA JENNIFER VIANEY
Abstract
The addition of Polypropylene Microfibers (PM) to an Ordinary Portland Cement (PC) based mortar with a substitution by weight of ground Fly Ash (FA) promotes a decrement of the angle of internal friction (Φ) in a cementitious matrix of the repair mortar and an increment of the cohesion (c) value in the interface between the substrate and the repair mortar zone. Mixtures samples were prepared by replacing cement by fly ash at 0% and 20% by weight, additions of polypropylene microfibers at 0% and 5% and compared with a reference mixture. The characterization of raw materials was carried out by Scanning Electron Microscopy (SEM) with Secondary Electrons (SE) for morphology, Backscattering Electrons (BE) for chemical composition and Energy Dispersive X-Ray Spectroscopy (EDS) for elemental analysis. Substrate and repair mortars were tested for compressive strength, indirect tensile strength, Young’s Modulus, Poisson Coefficient to study the mechanical behavior of the specimens. Electrical resistivity and carbonatation depth (concentration 4%, relative humidity 60 +/- 5%) were analyzed to study the durability of the samples. Samples with FA show a slightly decrement of the cohesion of the interface but samples with PM show an increment of this value, resulting in a higher cohesion with only PM. The use separately of FA and PM promote a lower angle of internal friction than reference samples. The results obtained under the experimental conditions used in this work, show that there is a synergistic effect between the use of polypropylene fibers and the pozzolanic material to reduce the carbonation depth caused using only the microfibers in the mixture.
Keywords
Fly Ash, Repair Mortar, Mechanical Properties, Polypropylene Microfibers, Durability, Cement Base Materials
SANG-SOON PARK
Abstract
Concrete sewer pipe line is one of the important civil infrastructures. Since the concrete sewer pipe is buried underground, the deterioration could be serious problem in maintenance and the repair and replacement cost is very high. The main aggressive factor affecting the durability of concrete sewer pipe is chemical attack by chloride and sulfate, so the sulfate resistant concrete should be used for the construction of sewer pipe line. In this study, the feasibility for the application of ferronickel slag powder (FSP) as a supplementary cementing material (SCM) used to improve the performance of concrete sewer pipe was investigated and the experimental tests were performed with different replacement ratio and fineness to determine the optimum level of replacement securing the improved chemical resistance and durability. The improvement of durability and chemical resistance of FSP contained mortar was verified through accelerated chloride ion penetration test, chemical resistance test and microstructural analysis. The optimum replacement rate of FSP can be considered as 40 % to assure the durability of concrete sewer pipe.
Keywords
concrete sewer pipe; ferronickel slag powder; durability; chemical resistance
SAFIA KHENGAOUI, MOULOUD ABDESSEMED, SAID KENAI, NOUREDDINE OUADAH
Abstract
In many countries, linear infrastructures (roads, railways or airports) are the most efficient and advantageous means of transport for citizens. Some of these infrastructures, such as roads or runways, are made of concrete, and as they are exposed to repeated loads and weather conditions, cracks are forming and spreading throughout the pavement. Several repair techniques have been applied to ensure their continued use under various types of traffic. The repair technique of adding lightweight welded mesh or geosynthetic layers seems to be a suitable solution, given their mechanical and aesthetic performance. This paper presents an experimental study on the effect of wire mesh and geogrids on the reinforcement of rigid concrete pavements. Twenty-four (24) specimens of concrete slabs, unreinforced and reinforced with a combination of geogrid sheets and wire mesh, were fabricated and tested in four-point bending. Validation of the experimental results was obtained by applying the finite element method, using a commercial software. Non-destructive in situ tests with a heavy deflectometer (HWD) were carried out on the central part of a rigid runway located in southern Algeria (arid zone), before and after its reinforcement with geogrids. It was found that geogrids are more effective than wire mesh in terms of tensile strength, stress and displacement reduction and downward crack propagation, with percentages ranging from 15 to 30%.
Keywords
Pavement, rigid, geogrid, wire mesh, reinforcement, experimentation, HWD, numerical
RASIM CEM SAKA, HALIT YAZICI
Abstract
In this study, LC30 structural lightweight concrete and LC60 high performance structural lightweight concrete were produced by using completely pumice aggregate. A total of 6 mixture designs were created by substituting 40% fly ash (FA) by weight into cement and adding 5.5 kg/m3 polypropylene fiber (PPF) to two different lightweight concrete designs. Flexural strength, compressive strength, total water absorption, electrical resistivity, rapid chloride ion penetrability tests were carried out on the produced concretes, and SEM-EDS analyzes were performed. As a result, lightweight structural concretes with a unit weight below 2000 kg/m3 could be produced by using 100% pumice aggregate, and LC60 high-performance lightweight concrete exhibited superior performance in all mechanical and physical tests compared to LC30 lightweight concrete. Since pumice has a porous structure, it has been confirmed by SEM images that there is a good interface between the aggregate and the matrix.
Keywords
Pumice, Fly ash, Synthetic fiber, Structural lightweight concrete, Lightweight aggregate
DAN PAUL GEORGESCU, CLAUDIU MAZILU, ADELINA APOSTU, ALIN BARBU
Abstract
The use of recycled aggregates is an efficient method and an important component for the sustainable development of the field of reinforced concrete constructions. Considering the particularities of concrete prepared with recycled aggregates, related to the origin of the aggregates but especially to the adherent mortar layer, in European regulations their use is restricted according to the exposure classes of the concrete. This limitation is due to the lower performance regarding the durability of concrete made with recycled aggregates, which in certain cases also requires a pretreatment operation. The research carried out, presented in this article, highlighted the particularities of the strength and durability characteristics of concrete prepared with recycled aggregates with and without the use of microsilica and nanosilica. By applying some experimental performance methods to evaluate the durability of concrete, it was possible to optimize the composition of concrete prepared with recycled aggregates. Also, in the case of the use of silica, the improvement of the performance of the concrete has been demonstrated, as well as the possibility of increasing the percentage of recycled aggregates used in its preparation, compared to that indicated in the current regulations.
Keywords
concretes, micro and nanosilica, recycled concrete aggregates, durability
IOANA GOMOIU, MĂDĂLIN ENACHE, SIMONA NEAGU, ROBERT RUGINESCU, MARIA DUMBRĂVICIAN, ILEANA MOHANU, ROXANA COJOC
Abstract
Mural biocleaning is an ecological method performed with bacterial cells or enzymes and polysaccharides of microbial origin. This process allows the removal of black scales, organic materials used in the previous restoration, and accidental or accumulated organic deposits over time. Lipases produced by the halotolerant bacterium Bacillus sp. BA N P3.3 (E) were used to remove some restoration materials (Paraloid® B72 acrylic resin and Transparent Casein Dispersion) as well as accidental organic deposits (beeswax, sunflower oil, soot) from the surface of the murals. A new bacterial gel (HG) was obtained using a halotolerant bacterial strain. Bacterial lipases were integrated into the bacterial gel (HGE) and then applied to the surface of the frescoes mock-ups for 5 hours and 10 hours. The results obtained in the case of biocleaning with lipases integrated in the bacterial gel were more efficient than those with esterases integrated in Agarart. In a single application step, more than 50% of the existing restoration materials or organic deposits on the frescoes mock-ups were removed. Biocleaning efficiency was evaluated by direct examination and microscopy (optical and scanning electron microscope). The biocleaning of murals with bacterial metabolites is safe, low cost, non-invasive, risk free and very competitive with chemical cleaning methods.
Keywords
halotolerant bacteria, biotechnologies for restoration, bacterial lipases, integrated lipases in halohydrogels, biocleaning with bacterial metabolites.
-
Year
2024
-
Issue
54 (2)
-
Pages
101-107
ALEXANDRU VIȘAN, IULIANA CIURCAN, CRISTINA ILEANA COVALIU – MIERLĂ
Abstract
Benzyl dimethyl tetradecyl ammonium chloride (BAC-14) is a quaternary ammonium salt used in disinfection products prepared in hospitals and in the food processing industry. Its disinfection properties make it used in many industries, such as the textile industry, agriculture, the industry of care products, and for maintenance of the balance of microorganisms in wastewater treatment plants. Conventional wastewater treatment techniques are inadequate in managing BAC-C14 for the reason of its biological degradation resistance, toxicity to beneficial microorganisms, and propensity to generate detrimental by-products. The occurrence of BAC-C14 in wastewater could require more sophisticated treatment procedures, hence increasing complexity and cost. Moreover, antibiotic resistance and sludge contamination enhance its treatment complexities. Considering these reasons, it is necessary to research effective methods of treating wastewater containing BAC-C14 through photocatalysis. The photocatalysis used in the degradation of BAC-14 presents important advantages such as: high efficiency in the degradation of contaminants; the possibility of using renewable resources in the treatment; the adaptability of the process to different sources of wastewater; the minimization of residual substances in the treatment of wastewater; and low costs.
Keywords
CUVINTE CHEIE (ENGLEZĂ)
ALEXANDRU VIȘAN, IULIANA CIURCAN, GIGEL PARASCHIV, SORIN ȘTEFAN BIRIȘ, FLORINELA PÎRVU, CRISTINA ILEANA COVALIU – MIERLĂ
Abstract
Benzyldimethyldodecyl ammonium chloride (DDBAC) is extensively utilized in domestic and industrial applications. The amounts of DDBAC used in different applications are likely to lead to their release into wastewater treatment plants, following dispersing into numerous environments through wastewater discharge and sludge land application. DDBACs are considered aerobically biodegradable; however, their decomposition is affected by factors like their structure, level of dissolved oxygen, and interactions with anionic surfactants. The photocatalytic technology demonstrates a sustainable and environmentally favourable approach to resolving energy and environmental concerns. The successful development of a photocatalyst is contingent upon four critical components: the density of active sites, the rate of photoinduced electron-hole recombination, redox capacity and light absorption. In this paper, are presented the results obtained by applying the photocatalytic technology sustain by titanium dioxide (TiO2) semiconductor for removing DDBAC from wastewater.
Keywords
advanced photocatalytic oxidation, surfactants, wastewater treatment, photocatalysis
HIBA A. OLEIWI, TAHA H. ABOOD AL-SAADI, NASRI S. M. NAMER
Abstract
The composition, hydrolytic stability, and mechanical properties, as well as the microstructure of produced geopolymers (as paste and as mortar), were investigated. The manufacturing processes investigated in this study involved green glass powder as raw materials and two types of alkali activators (i.e., NaOH and KOH) solutions. For pastes, different molarity concentrations of alkali activator solutions (N3, N6, N9, K3, K6, and K9) were employed to assess the mechanical properties (compressive strength). N6 and K9 alkali activators were used for mortar preparation, and for comparison, they were considered ordinary Portland cement paste and mortar. Generally, the compressive strength values of paste specimens increase with NaOH and KOH concentrations increasing. It is worth mentioning that N6 and K9-based geopolymer formulas are the best mixtures due to their highest compressive strength as compared with cement paste at the same curing conditions of 7 and 28 days. In addition, for mortar specimens, the compressive strength of N6 mortar is higher than that of K9 specimens for curing times 7 and 28 days. The hydrolytic stability of pastes and mortars was assessed by measuring the compressive strength and weight changes for the specimens before and after immersion in distilled water. It is to be mentioned that for all studied pastes, the compressive strength losses are 30-70%, and for studied mortars, the compressive strength losses are 1-20% compared with cement under the same conditions. Moreover, weight loss is recorded for all geopolymer compositions.
Keywords
Geopolymers, glass waste, alkali activator, compressive strength, hydrolytic stability.
TEODORA RADU, ALEXANDRINA NAN, IOLANDA GANEA, ALEXANDER BUNGE, CRISTINA DIMA, MARINELA GHIȚĂ
Abstract
This study aimed to obtain a modified bituminous mastic with industrial waste (residual household oil, stone dust), intended for use in the construction industry and to characterize it from a physical-mechanical point of view. The effects of substituting the filler from the bituminous mastic (50…100% gravimetric percentage) with a composite based on stone dust were studied using dynamic mechanical analyser (DMA) and standard methods specific to this type of material.
The performances determined by DMA analysis (loss and storage module, damping factor) has registered minimal variations with chemical composition. By comparing the properties obtained in the temperature range of 25…75°C, of the modified bituminous mastic with the addition of waste with those of a bituminous mastic currently available on the market, it shows that the addition of composite improves the physical-mechanical properties, while bringing economic and ecological advantages.
The determination of the main characteristics by standard methods specific to this type of material, such as softening point, density and needle penetration, has shown that the requirements for use in the construction materials industry for hot clogging of joints in road coatings are met.
Keywords
industrial waste, filler, stone dust, DMA analysis, bituminous mastic
Machine learning based prediction of compressive strength in concrete incorporating synthetic fibers
R. TUĞRUL ERDEM, AYBİKE ÖZYÜKSEL ÇİFTÇİOĞLU, ENGİN GÜCÜYEN, ERKAN KANTAR
Abstract
Different types of fibers are added to the concrete mixture to improve its behavior under different loading cases. This study intends to investigate the compressive strength of concrete cubic samples in which synthetic macro fibers are added in different amounts. For this purpose, a total of 72 cubic samples are produced in the experimental program. Axial pressure test is applied to cubic samples and 7 and 28 days compressive strength values are obtained in the end. However, a lot of effort has been spent to complete the time-consuming laboratory tests. To overcome this situation, four machine learning methods—Xgboost, Random Forest, Decision Tree, and Multiple Linear Regression—are adapted for efficient compressive strength forecasting. Moreover, four metrics are employed for a more meaningful evaluation of models: R2, RMSE, MAE, and MAPE. Remarkably, all models achieved R2 values exceeding 90%, with Xgboost notably reaching an impressive R2 value of 97%. This highlights the effectiveness of integrating machine learning in predicting compressive strength, offering a viable alternative to traditional laboratory tests. Incorporating the Shapley Additive exPlanation (SHAP) method, the study provides a detailed analysis of the models interpretability. SHAP analysis revealed that "Day" and "Fiber" have been identified as crucial features influencing compressive strength predictions. Localized SHAP analyses for specific samples further enhanced the understanding of individual predictions, emphasizing the practicality and transparency of machine learning in structural engineering. The promising results of this study indicate the potential for further advancements in enhancing performance, utilizing machine learning insights.
Keywords
Concrete; synthetic fibers; compressive strength; machine learning; Xgboost
TAIZHI XIANG, PENG ZHAO, WEIXING HOU, HAIYOU SHEN, ZIQUAN ZHAI, JINYUAN WANG, XINCHAO YE
Abstract
The development of Sea Water Sea Sand Concrete (SWSSC) holds critical importance for maritime engineering, especially given China s extensive marine resources and the potential they represent. Despite its promise, the utilization of SWSSC has been impeded by the corrosive nature of certain ions present within its constituents. The depletion of freshwater river sand coupled with advancements in construction material technology has reignited interest in SWSSC, prompting a reassessment of its viability. This review delineates the achievements in developing SWSSC, examining both the microstructural and macroscopic properties of key Supplementary Cementitious Materials (SCMs) such as seawater, sea sand, cement, fibers, and mineral admixtures. Each material s benefits and drawbacks are critically analyzed, with a focus on how they influence the concrete s durability and structural integrity. Furthermore, the review identifies existing gaps in research and offers direction for future investigations aimed at overcoming the challenges posed by corrosive elements and optimizing material properties for enhanced performance. The integration of innovative materials and techniques is proposed as a means to advance the practical application of SWSSC in building resilient marine infrastructure.
Keywords
Sea Water Sea Sand Concrete (SWSSC); Cement; Supplementary Cementitious Materials (SCMs); Fibers