română 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.
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Year
2024
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Issue
54 (2)
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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