Chemical Abstracts (CAplus) (iki 2021 m.)

Due to sustainability goals, there is an increasing need to recycle waste. In this concrete study, waste from the concrete production industry – concrete slurry, and glass industry waste were used. The concrete slurry was obtained by washing equipment in the concrete industry. The glass processing waste was obtained from technical water. The wet concrete slurry was used to replace the amount of water, the dry concrete slurry was used to replace the amount of fine aggregate, and the glass processing waste was used to replace the amount of cement from 5 % to 30 %. Thus, cement, sand, gravel, a superplasticiser, a crystallising admixture, and an air-entraining admixture were used in the concrete composition. In all the compositions, the same w/c ratio was maintained. For the fresh concrete mix, the density, air content, and hydration heat release were determined. For the hardened specimens, the speed of the ultrasound pulse propagation, density, compressive strength, water absorption, microstructure, and porosity parameters were determined. The determined mechanical properties indicate that replacing up to 20 % of cement with glass processing waste improves the results.

The article analyses the effect of pozzolanic waste on the properties of cement mortar. Seven batches of specimens were made for the tests: control specimens without any pozzolanic waste, three batches of specimens where cement was replaced with 5%, 10%, and 15% of wood fly ash, and three batches of specimens where cement was replaced with 5%, 10%, and 15% of ground glass. The replacement of 5% of cement with pozzolanic waste in the mix increased the density, the ultrasonic pulse velocity, compressive and flexural strengths of the mortar. A further increase of pozzolanic waste content degraded the values of physical and mechanical properties, as the lower amount of cement did not ensure a strong bond between the aggregate and the cement matrix. The alkali-silica reaction tests revealed that the expansion of the specimens containing 5% of pozzolanic waste as cement replacement does not the permissible limit of 0.1%. With the increase of pozzolanic waste content up to 15%, the expansion of specimens modified with wood fly ash continues decreasing down to the limit of 0.01%, whereas the expansion of the specimens modified with ground glass starts increasing to the limit of 0.05%.

The article analyses the effect of cellulose fiber on the properties and structure of hardened cement paste. Nine batches of concrete were mixed: one batch for the control sample without cellulose fiber, and eight batches with cellulose fiber introduced at the rate from 0.25% to 2 %. The modification of hardened cement pastes with cellulose fiber showed that the addition of cellulose fiber at 2 % caused a 5.4% drop in the heat of hydration, which increases the workability of concrete mix and has a positive effect on concrete manufacturing. The cellulose fiber obtained from waste paper has a positive effect on the microstructure of hardened cement paste as it bonds well to the cement matrix in mortars containing 1 % of cellulose fiber. The flexural strength of hardened cement paste was found to increase with higher cellulose fiber content. The control sample without cellulose fiber had the flexural strength of 3.24 MPa and the sample modified with 2% of cellulose fiber had the flexural strength of 6.89 MPa, which is more than twice the value of the control sample. Thus, cellulose fiber can be added up to 1 % in the production of modified concrete products subjected to flexural force during operation.

This paper analyses the impact of rubber additive content on the properties of cement composite. It describes the materials and the test methods used to determine various parameters of the composite mix and the cured composite. The properties of the cured composite were tested and compared. The effect of the amount of rubber additive on the following properties of cement composite was tested and analysed: slump flow, density, ultrasonic pulse velocity, compressive and flexural strengths, thermal conductivity, water absorption, and resistance to freeze-thaw cycles. The cement composite was produced by using crushed waste tyre granules as fine aggregate, i.e. sand was replaced with crushed tyre granules from 0 % to 10 %. The tests showed that the rubber additive used as sand replacement had little impact on the properties of the cement composite: density, ultrasonic pulse velocity, flexural and compressive strengths of the modified composite decreased, but resistance to freeze-thaw cycles increased. According to the test results and their analysis, 10 % is the optimal rubber additive content to be used as sand replacement in cement composite, which would have higher frost resistance and a lower coefficient of thermal conductivity.

Lead is a heavy metal with strong toxic properties. This chemical element is found in wastewater and sometimes in drinking water. The article deals with the removal of lead(II) ions from polluted water using a sorption process to determine the most effective sorbent for the removal of lead(II) ions. Three sorbents were used in the research: clay, sapropel, and iron sludge. All three sorbents investigated reduce the concentration of lead(II) ions in water: clay efficiency was of 65.7-90 %, sapropel of 94.3-100 %, and iron sludge of 84.3-97 %, depending on sorbent type and contact duration. The research has shown that the most effective way to remove lead(II) ions from the test water is sapropel. Using different amounts of sapropel (1, 2, 3, 4, 5, 6 g/dm3 and 0.1, 0.2, 0.4, 0.5, 0.6, 0.8 g/dm3) and different duration of contact (30, 60, 90, 120 and 150 minutes), the concentration of lead(II) ions in the test water after purification did not exceed the permissible values for drinking water (10 µg/dm3), so that the lowest sapropel content of 0.1 g/dm3 can be used for sorption. Lead(II) ions are most effectively removed when contact time is 30 min.

This study has examined the effect of a zeolite-based additive on cement hydration processes. This additive and samples of hardened cement pastes have been examined using X-ray diffraction, thermoanalytical methods (TG and DSC) and FTIR spectroscopy analysis. The results show that a modified zeolite additive increases the compressive strength of hardened cement paste specimens. The increase in compressive strength may be related to active SiO2 and Al2O3 present in the modified zeolite. The highest density was recorded in specimens containing 10% of the modified zeolite additive. Instrumental analysis has revealed that with the increase of this zeolite additive content the content of portlandite – Ca(OH)2 – in the mineral composition of hardened cement paste reduces from 11.9 to 5.3% after 3 days of setting and from 15.0 to 7.6% after 28 days of setting. The highest amounts of C-S-H gel are observed when the modified zeolite additive is used.

The purpose of this work was to develop a novel morphology of gas sensing layer based on porphyrin sheets and nanotubes and to investigate the physical-chemistry and sensing properties of the porphyrin layer. In the present work the porphyrins nanoparticles were synthesized by ionic selfassembly in aqueous solutions of two oppositely charged non-metal porphyrins, namely, the anionic Meso-tetra (4-sulfonatophenyl) porphine dihydrochloride (TPPS4) and cationic Meso-tetra (4-pyridyl) porphine (T4MPyP) and an ethanol was not added to the solution. We investigated in details the nanosheets and nanotubes formation and behaviors of aggregation induced by mixing an anionic TPPS4 and cationic T4MPyP acidic solutions by means of the UV-vis spectroscopy and aggregates structure and morphology by transmission electron microscopy (TEM), scanning electron microscopy (SEM). The sensing capabilities of the samples have been finally evaluated by exposing the films to the different concentration of ethanol atmospheres.

Chitosan-O-alginate comb copolymers with a different degree of chitosan substitution were synthesized using chitosan protected by phthaloylation and “activated” by tosylation, and reduced low-molecular-weight sodium alginate. The obtained chitosan derivatives were characterized by FT-IR and 1H NMR spectroscopy, functional group analysis, viscometry and potentiometric titration. The novel nature-friendly polyampholytes contained a 15–25-fold excess of carboxyl groups and were soluble in neutral and alkaline water. The intrinsic viscosity and molecular weight of these chitosan derivatives were relatively low, suggesting a significant breakdown of chitosan backbone under derivatization. The solution viscosity of the polyampholytes had a tendency to decrease by lowering the pH toward a supposed isoelectric point at pH 3.5–4.0. Comb-shaped copolymers in aqueous solutions are expected to form tight coils which are stabilized by intra- and intermolecular complexes between carboxyl and amine groups.

Many industrial pollutants, xenobiotics, and industry-important compounds are known to be oxidized by peroxidases. It has been shown that highly efficient peroxidase substrates are able to enhance the oxidation of low reactive substrate by acting as mediators. To explore this effect, the oxidation of two N-hydroxy derivatives, i.e., N-hydroxy-N-phenyl-acetamide (HPA) and N-hydroxy-N-phenyl-carbamic acid methyl ester (HPCM) catalyzed by recombinant Coprinus cinereus (rCiP) peroxidase has been studied in presence of efficient substrate 3-(4a,10a-dihydro- phenoxazin-10-yl)-propane-1-sulfonic acid (PPSA) at pH 8.5. The bimolecular constant of PPSA cation radical reaction with HPA was estimated to be (2.5 +/- 0.2)center dot 10(7) M-1 s(-1) and for HPCM was even higher. The kinetic measurements show that rCiP-catalyzed oxidation of HPA and HPCM can increase up to 33,000 times and 5,500 times in the presence of equivalent concentration of high reactive substrate PPSA. The mathematical model of synergistic rCiP-catalyzed HPA-PPSA and HPCM-PPSA oxidation was proposed. Experimentally obtained rate constants were in good agreement with those calculated from the model confirming the synergistic scheme of the substrate oxidation. In order to explain the different reactivity of substrates, the docking of substrates in the active site of the enzyme was calculated. Molecular dynamic calculations show that the enzyme-substrate complexes are structurally stable. The high reactive PPSA exhibited higher affinity to enzyme active site than HPA and HPCM. Furthermore, the orientation of HPA and HPCM was not favorable for proton transfer to the distal histidine, and different substrate reactivity was explained by these diversities.

Eight contemporary pottery samples were investigated by thermal analysis (TG-DTA) in order to define the effects of fabrication. The results of the measurements were shown to depend on firing conditions. In this article, the results of thermoanalytical characterization of two archaeological pottery samples from different regions of Lithuania are also presented. The samples of ancient pottery from Nikėlai and Jurgaičiai villages were investigated. The TG-DTA results for the historical pottery samples from different districts of Lithuania showed an analogous thermal behaviour, possibly due to similar fabrication conditions.