Cube Samples Research Articles

Performance of Pozzolan-Based Reactive Magnesia Cement Mixes against Sulphate Attack

Reactive magnesia cement (RMC) has gained interest due to its lower production temperatures when compared to Portland cement. In this study, the performance of pozzolan-based RMC concrete samples against sulphate attack was examined. Cube samples, after being removed from their moulds, were stored in a CO2-rich environment to gain compressive strength. Information obtained from XRD showed the formation of Mg carbonates in different forms. The use of fly ash and slag in large volumes reduces the environmental impact of concrete, but the use of these components have been found to greatly affect the formation of Mg carbonates in RMC mixes. This is mainly due to their filler effects. The coexistence of Ca- and Mg-based products was found in the slag-RMC mixes. The concrete samples based on RMC underwent mass and strength losses when stored in a MgSO4 solution for up to 12 weeks. The removal of Mg from the microstructure of these samples was confirmed using SEM analysis. The use of the most widely used pozzolans at 50% by weight of the binder greatly affected the carbonation mechanism of the RMC mixes. This finding suggests that they should be limited in the design of Mg-based products that harden under CO2-rich conditions.

Mathematical modeling and regression analysis using MATLAB for optimization of microwave drying efficiency of banana

This study examined the influence of microwave (MW) power (300–800 W) and standard geometries (slab, cube, disc, sphere) on banana drying kinetics. Nine thin-layer models were explored. Model validation employed the coefficient of determination and root mean square errors, further checked using residual sum of squares and zero mean of errors. The Henderson and Pabis model emerged as optimal for thin-layer drying. As MW power ranged from 300 to 800 W, drying times reduced: slabs (700–220 sec), cubes (800–300 sec), discs (560–160 sec), and spheres (620–200 sec). Moisture diffusivities spanned 9.12×10−9 to 7.2×10−6 m2/s, revealing reduced moisture diffusion at lower MW power. Activation energies were tabulated for discs (25.54 W/g), spheres (108.96 W/g), cubes (88.41 W/g), and slabs (107.56 W/g). Sample mass uncertainty was approximated at 0.03 g (∼1% error). Specific energy varied between 140 and 244 kJ, while microwave energy values ranged from 44.58 to 112.8 MJ/kg, declining with increased power. Cube samples showed maximum energy consumption, whereas disc samples typically consumed the least. Notably, disc-shaped bananas demonstrated peak drying energy efficiencies (41.75–51.3 %) across all MW power levels. Average drying efficiencies were observed between 19.97 and 51.3 % for the studied power range.

Multifractal analysis on CT soil images: Fluctuation analysis versus mass distribution

The combined action of physical, chemical and biological processes at different scales creates a highly complex soil architecture. At the same time, this soil pores' complexity is crucial in maintaining soil biogeochemical and biophysical processes. The development of digital image processing and a multiscaling analysis allow a better study to quantify pore complexity and evaluate pore spatial variability. This study took saline soils from coastal reclamation areas as an example and aimed to compare the multifractality of porosity series using different methods on sample cubes of 512 pixels in length extracted at different soil depths. Two measures were selected to represent the porosity series: the average grey values (AVG) of each slice and the CT-porosity (CTP) of binarized slices. The mass distribution (MD), detrended fluctuation analysis (DFA), and the moments function (K) were the methods applied in the multiscaling study. Shuffled and surrogated series were used to analyze the two possible multifractality sources, the probability distribution density function (PDF) and long-range correlations, respectively.The results showed that MD gave the minimum multifractal spectrum, which appeared as a point in AGV and a narrow concave parabola in CTP. On the other hand, both AGV and CTP showed a higher complexity, a clear and significant multifractal behaviour when DFA and K were used. The shuffled and surrogated series pointed out that the long-range correlations were the main factor of the multifractal sources of the porosity series. Both long-range correlations and PDF influenced more heavily on the multifractality of porosity in topsoil (0– 20 cm) than in the deeper soil (20– 60 cm), implying that the porosity series in topsoil had stronger multifractality. In addition, the DFA and K, combined with shuffled and surrogated series analysis, can distinguish between different factors in the multiscaling behaviour of different soil textures and time reclamation.

Production of Concrete Using Contaminated Water and Its Effects on Compressive Strength of Concrete

In saline environment and places where there is no access to clean water for concrete work, contaminated water is often used for mixing and preparation of concrete for different structural members of buildings and this practice is in complete violation of most approved standard codes for concrete production. This study is aimed at determining effects of the use of salt contaminated water on compressive strength of concrete with a view to providing mitigating measures. 150 mm cube samples were cast with these water samples. Compressive strength test was carried out on the cubes. Findings revealed that for potable water, the initial strength was retarded in the first 7 days, uniformly progresses through 14 days, 21 days until the 28 days. In the case of contamination of 1000 mg/litre, concrete strength follows the same trend as the control. As the quantity of contaminated salt increases after this stage, the compressive strength generally decreases. It was further observed that the contamination effects were not pronounced on the strength within the first 7 days. According to the 28 day compressive strength ranged from 23.26 to 15.78 N/mm2 as the concentration of contaminant (NaCl) in concrete mixing water ranged from 0 to 5000 mg/l. The study therefore concludes that the salt contaminated water have adverse effect on the properties of concrete. The use of salt contaminated water for concrete mixing is seen to favorable for strength development only at 4000 and 5000 mg dosages at early ages and reduction in long term strength.

Investigating the effect of Manufactured sand and Silica Fume on the properties of Concrete

In the present era, concrete is one of the most commonly used construction materials worldwide. Consequently, the demand for natural river sand is increasing. Since the mining of natural sand has already been outlawed by the government in many regions, now it is essential to look into sustainable materials to control natural sand extraction. Hence, manufactured sand (MS) has been shown in numerous studies to be a more practical and environmentally responsible alternative to river sand (RS), which is normally used in the production of concrete. At the same time, the cement industry produces tons of greenhouse gases into the atmosphere, affecting atmospheric conditions. Now, it’s time to look into a suitable replacement material for cement. To investigate the feasibility of using manufactured sand & silica fume in place of river sand and cement under normal climatic conditions fresh, mechanical and durability properties were conducted in the laboratory. Twelve samples of M30 grade cubes and cylinders at desired M sand percentages of 0, 20, 40, 60, 80, and 100 & 0% and 5% variation of silica fume with cement are included in this study as a comparison to the control mix. After 28 days of water curing, a random variation in the properties of concrete was observed in the samples. In this experimental study, SF represents Silica Fume, MS represents manufactured sand, RS represents river sand, FA represents Fine aggregates and CA represents Coarse aggregates.

Selective laser melting of glass with irregular shaped powder

Glass has unique physical characteristics, such as transparency, chemical durability, thermal stability, and electric resistivity, making it an attractive material for numerous industries. As a result, there is a growing interest in the additive manufacturing of glass powder. However, most of the selective laser melting (SLM) processes primarily rely on the utilization of spherical glass powder, and there are no reports of the use of non-spherical glass powders. This paper explores the benefits and possibilities of irregular shaped powder used in SLM of glass. Through a progression of experiments from single-track to single-layer and, ultimately, cube fabrication, the relative density of cube samples was as high as 95%. Feasibility examples were successfully demonstrated, indicating that the irregularly-shaped soda-lime silica glass powder can be successfully used in the SLM process and that process parameter changes can be optimized to yield builds with comparable porosity levels to builds using typical spherical powder.

Improvement of the durability of concrete by substitution of raw ground colemanite

This study investigated the effects of raw ground colemanite (GC) mineral on concrete strength and durability. Concrete mixtures were prepared at six replacement levels of GC (0%, 1%, 2%, 3%, 4% and 5%, by weight of cement). Fresh state properties of concrete samples were measured. Schmidt Hammer, ultrasound pulse velocity, abrasion, flexural, and compressive strength tests were performed on the cube, cylinder and prismatic concrete samples on the 7th, 28th, and 90th days. As concrete durability has a negative impact on many physical and chemical factors, the durability properties of the samples after wet-dry, freeze-thaw, sulphate, and chloride exposure were investigated, resulting in the finding that GC substitution up to 5% yields the desired compressive strength for the C30/37 concrete class. The optimal GC substitution ratio was determined to be 3%, as this ratio increases the strength and durability probabilities. It was decided that raw GC mineral substitution with an average particle size of 12 µm and increasing adhesion force in concrete production is convenient, particularly in the context of improving material properties against environmental circumstances, saving cement, and utilizing boron minerals.

Factors controlling reaction pathways during fluid–rock interactions

Potential fluid pathways for fluid–rock interactions and the factors controlling these pathways have been investigated experimentally by simulating hydrothermal conditions, using sample cubes of Carrara Marble (calcite) and an anorthosite (plagioclase) rock in different solutions (pure water, sodium chloride, artificial seawater, sodium phosphate and sodium silicate) at 200 °C. Analytical techniques including SEM, Raman Spectroscopy, atomic force microscopy, and Electron Microprobe Analysis were used to characterize fluid-induced reactions. Results show aqueous fluids can penetrate grain boundaries within rocks and, dependent on fluid and solid compositions, coupled replacement reactions can occur. The available fluid volume for the reaction in a grain boundary versus the bulk fluid can influence replacement reaction pathways. When 0.1 M Na2HPO4 was used with Carrara Marble, or a Na-silicate solution was used with anorthosite, the replacement of calcite by hydroxylapatite or labradorite by albite, respectively, occurred along the grain boundaries of both rock types. In the experiments using seawater, the replacement of calcite by Mg-carbonates occurred predominantly from the sides of the cube samples and the grain boundaries were minimally affected within the timescale of the experiments (1–3 months). With 1 M Na2HPO4, hydroxylapatite precipitated both along the marble grain boundaries and the sample sides. Models based on experimental observations and PhreeqC simulations highlight the importance of grain boundaries and interconnected porosity in fluid-induced reactions. Such factors play an important role in the kinetics and relative solubilities of rock systems by changing the conditions at the interfacial fluid–mineral boundary layer that will determine initial dissolution or precipitation and whether the supersaturation of a product phase is reached.

Efficacy of high-volume fly ash and slag on the physicomechanical, durability, and analytical characteristics of high-strength mass concrete

In the last decade, the use of high-strength mass concrete has increased for the building of various high-impact infrastructure projects. Due to the larger size of sections and greater volume of Portland cement, the reduction of core strength and durability is often witnessed in these concrete sections. In this study, an attempt has been made to minimize the above issues by substituting ordinary Portland cement (OPC) with high-volume fly ash (FA) and ground granulated blast furnace slag (GGBFS). For this purpose, six types of samples viz. S1 (100% OPC), S2 (20% FA + 80% OPC), S3 (35% FA + 65% OPC), S4 (50% GGBFS + 50% OPC), S5 (70% GGBFS + 30% OPC), and S6 (33% FA + 33% GGBFS + 34% OPC) were prepared. The performances on the actual core concrete were evaluated by analyzing the peak temperature, compressive strength of cylindrical cores, rapid chloride migration test (RCMT), X-ray diffraction (XRD), thermogravimetry (TG), Fourier-transform infrared spectroscopy (FTIR), and field emission scanning electron microscopy (FESEM). Additionally, the bulk densities (wet and dry), water absorption, apparent porosity, and compressive strength of cube samples are also reported. Analyzing the results critically, it was observed that the use of high-volume FA and GGBFS (S5 and S6 samples) lowered the peak core temperature by 11–13 °C, increased the compressive strength of cores by 8–10 MPa, and lowered the RCMT values of cores by 12 × 10−12 - 13 × 10−12 m2/s as compared to the S1 (control) sample. Additionally, the increase in the ratio of the core-to-cube strength for the S5 and S6 samples is noted to be 24% and 29%, respectively, more than the control sample at 56 days of curing. The enhanced performance of the high-volume FA and GGBFS-based samples is due to the less core temperature rise due to less hydration reaction at the early ages and more secondary hydration reaction at the later ages, which has been justified by the XRD, FTIR, TG, and FESEM analyses. Finally, the sustainability and cost analysis revealed that the use of high-volume FA and GGBFS can significantly reduce embodied energy by 39–42%, embodied carbon by 53–58%, and production costs by 16–17%. The approach proposed in the article regarding the use of high-volume FA and GGBFS results in more green, durable, sustainable, and cost-effective high-strength mass concrete.

Material properties of selective laser melting additive-manufactured Ti6Al4V alloys with different porosities

In this study, Ti6Al4V specimens with a variety of porosities were prepared using selective laser melting (SLM) by changing its laser hatch spacing. The pores on the surfaces perpendicular (SPER) to the stacking direction (SD) and surfaces parallel (SPAR) to SD of the cube samples were totally different from each other. The topography of SPER was dominated by the laser hatch spacing, whereas SPAR was almost entirely covered with non-molten powder particles having different looseness values. Thus, an optimal modeling direction exists for the real-time application of the alloys. The SLM-manufactured samples were scanned by computed tomography (CT) and then analyzed using the binarization method to investigate their internal porosity, which ranged from 20% to 45%. Tensile tests were conducted to describe their tensile behavior and evaluate their elastic moduli. These analyses revealed an inverse relationship between the porosity and elastic modulus as laser hatch spacing increased. An elastic modulus less than 2000 MPa was obtained using the SLM process, which is sufficient for applications requiring a low elastic modulus. Furthermore, their grain details were observed using electron backscattered diffraction (EBSD). The samples had typical fine acicular grains but with smaller average diameters as the laser hatch spacing increased. Furthermore, the average fraction of misorientation decreased because of the increasing small-angle grains and decreasing large-angle grains, indicating a significant influence of the laser hatch spacing on the grain orientation. Additionally, surface qualities were quantitatively assessed to reveal how laser hatch spacing affected the morphology. By comprehensively analyzing the surface morphology and quality, porosity and tensile properties, and grains details, a vivid material forming theory of the SLM process was concluded.

Introducing Hatch Spacing into Deposited Energy Density toward Efficient Optimization of Laser Powder Bed Fusion Process Parameters

The optimization of processing parameters is indispensable for the laser powder bed fusion (L-PBF) process. The deposited energy density (DED) is one of the process indexes for the L-PBF process and has a simplified formula of P·v−0.5, where P is the laser power, and v is the scan speed. This parameter describes the change in the relative density and the melt pool morphology with laser power and scan speed well, whereas it does not include the effect of other processing parameters, e.g., hatch spacing (S). In the present study, an attempt was made to incorporate the effect of S into DED. Al–12Si (mass%) alloy cube samples were fabricated by L-PBF under various P, v, and S, for evaluating the relative density and the melt pool morphology. The melt pool depth and width of L-PBF-manufactured Al–12Si alloy increased linearly with P·v−0.5 and did not exhibit a clear correlation with S. Based on the experimental observation, the effect of hatch spacing on DED was estimated to be S−0.5, and a new index of P·v−0.5·S−0.5 was proposed. This index described the change in the relative density of the L-PBF-manufactured Al–12Si alloy with laser conditions (P, v, and S) well when the thermal conduction mode melting was dominant. This study also indicated the limitation of the applicability of P·v−0.5·S−0.5 under the keyhole or transition mode melting.

The influence of viscosity-modifying agent and calcium carbonate on 3D printing mortar characteristics

3D printing or additive manufacturing is an example of technology development in the construction sector. In 3D printing mortar, many things need to be considered regarding the characteristics of the mortar, such as workability, initial setting time, compressive strength, extrudability, and buildability. In previous studies, there were problems in the printing process, such as a lousy extrusion process and cracks in the 3D printing mortar sample. This study used calcium carbonate and a viscosity-modifying agent (VMA) to modify the mixture to achieve the desired characteristics. The extrudability and buildability were tested by observing the extrusion process and measuring the thickness and width of each layer printed. Based on the research, adding calcium carbonate and VMA can reduce workability and accelerate the initial setting time of the mixture. The use of VMA can reduce the compressive strength of the mixture. Using calcium carbonate and VMA can also increase the buildability of the mixture. From the compressive strength test, there was a decrease of 39.26% in the 3D printing mortar sample compared to the mortar cube sample. In addition, it was found that the 3D printing mortar is anisotropic, so the compressive force’s direction affects the compressive strength produced.

Strength characteristics of lightweight concrete based on granular foam glass ceramics

Introduction. Over the past 20–30 years, a wide range of effective porous aggregates with a high content of glass phase of various types and low-heat-conducting lightweight concretes of various structures based on them has been developed.In recent years, JSC Research Center of Construction has developed a new highly efficient single-stage technology for the production of porous granular foam glass ceramics (UCS). It is based on the production of raw granules by mixing and granulating a highly porous powder of opal-cristobalite rock with a sodium-containing solution. This ensures the maximum area of the interfacial boundary, the most uniform distribution of all components at the micro level and, as a result, ensures glass formation at a temperature that does not exceed the foaming interval of the finished glass phase.The aim of the publication is to study the problems of the features of the strength characteristics of lightweight concrete on granular foam glass ceramics.Materials and methods. The strength of cubes made of light concrete on the UCS under compression (R) was determined on samples with a size of 10 × 10 × 10 cm and 7 × 7 × 7 cm according to State Standard 10180-2012 with an assessment of strength according to State Standard 18105-2018.The prismatic strength coefficient (Kpp) was determined by the results of compression tests of samples-prisms with dimensions of 10 × 10 × 40 cm and 7 × 7 × 28 cm and samples made from the same batch-cubes with dimensions of 10 × 10 × 10 cm and 7 × 7 × 7 cm.Bending tensile strength (Rtb) (Figure 2) and splitting strength (Rtt) were determined, respectively, on 10 × 10 × 40 cm prism samples and 10 × 10 × 10 cm cube samples according to State Standard 10180-2012 with an assessment of strength values according to State Standard 18105-2018.Axial tensile strength (Rtb) and splitting strength (Rtt) were determined, respectively, on prism samples measuring 7 × 7 × 28 cm according to State Standard 10180-2012. The strength of the prisms (prismatic strength, Rb) was determined on samples of prisms 10 × 10 × 40 cm according to State Standard 24452-80.Results. The article presents the results of experimental and theoretical studies of the basic strength properties of thermal insulation and structural-thermal insulation lightweight concrete on granulated foam ceramic (UCS) with a density of 500 to 800 kg/m3, as well as structural lightweight concrete with a density of up to 1700 kg/m3 of optimal compositions (prismatic compressive strength, prismatic strength coefficient, axial tensile strength, tensile strength during bending and splitting).Various dependencies on the evaluation of the experimental data obtained are analyzed and recommendations are given for inclusion in regulatory documents, in particular, in SP 351.1325800.2017 "Concrete and reinforced concrete structures made of light concrete. Design rules".Conclusions. Experimental data have been obtained on a higher prismatic strength coefficient for lightweight concrete at the UCS, which in the future may be the basis for increasing the standard design strength resistance under axial compression for this type of lightweight concrete.The values and formulas for determining the prismatic strength and the prismatic strength coefficient of light concrete of the tested compositions at the UCS can be used in the calculation and design of large-format wall panels of a new type.Experimental and calculated data on the tensile strength of the tested compositions of lightweight concrete of a porous structure at the UCS have been obtained, which can be taken into account when adjusting regulatory documents.When using lightweight concrete of a porous structure on the UCS to increase the shrinkage crack resistance of such concrete for enclosing structures, it is advisable to use dispersed reinforcement with polymer fiber, which also increases the heat-protective properties of such structures. The article presents the results of studies of the main strength properties of thermal insulation and structural-thermal insulation lightweight concretes on the UCS with a density of 500 to 800 kg/m3, as well as structural lightweight concretes with a density of up to 1700 kg/m3 of optimal compositions.Various dependencies on the evaluation of the experimental data obtained are analyzed and recommendations are given for inclusion in regulatory documents, in particular, in SP 351. 1325800.2017 "Concrete and reinforced concrete structures made of light concrete. Design rules".

Effects of cell morphology on the textural attributes of fruit cubes in freeze-drying: Apples, strawberries, and mangoes as examples.

The influence of cell morphology on the textural characteristic of freeze-dried apple, strawberry, and mango cubes was evaluated. Corresponding restructured cube samples without intact cell morphology were prepared as controls. Results indicated that the presence of cell morphology strengthened the shrinkage and collapse of samples during freeze-drying, especially in mangoes due to the high content of sugar. Intact cell morphology was found in natural fruit cubes after freeze-drying by scanning electron microscopy (SEM) observation, making them exhibit a more regular microporous structure, further resulting in higher hardness than the restructured cubes. However, the intact cell morphology negatively affected the crispness of freeze-dried cubes since it enhanced structural collapse. The freeze-dried samples without cell morphology would destroy the cellulose structure and form a continuous open-pore structure under the concentration effect of ice crystals during freezing, which accelerates the escape of water molecules, increases the drying rate, and avoid collapse. Sensory experiments found that restructured cubes without intact cell morphology exhibited greater comprehensive acceptance, suggesting the potential application of cell morphology disruption in the future freeze-drying industry.

ANALISIS PERBANDINGAN KUAT TEKAN MORTAR BERDASARKAN MODULUS HALUS BUTIR (MHB) PASIR SUNGAI DENGAN PASIR GUNUNG

Mortar is a cementation material composed of sand and cement with added water. River and mountain sand are types of sand that are available in large quantities in Bengkulu City. This study aimed to determine the effect of grain fine modulus from river sand on the compressive strength of mortar compared to Curup Mountain Sand. The sand river used was Kembang Sri River Sand (MHB 2,91), Penanding (MHB 2,204), Lubuk Kebur (MHB 3,452), Talang Rasau (MHB 2,257) and Curup Mountain Sand (MHB 1,29). The ratio variation between cement and sand used was 1Pc : 4Ps, 1Pc : 5Ps and 1Pc : 6Ps. Each variation was made 6 cube samples with a side dimension of 50 mm. The test was done at the age of the sample 28 days. The initial flow of the mixture plan is 105-115%. The results obtained of the highest value of mortar compressive strength for the mixture of 1Pc : 4Ps and 1Pc : 6Ps was found in Curup Mountain Sand, which was 14,08 MPa and 7,77 MPa. The highest value of mortar compressive strength for 1Pc : 5Ps mixture was found in Talang Rasau River Sand, which was 11.43 MPa (120,44% compared to Mountain Sand). The 1Pc:4Ps and 1Pc:6Ps mixture of Talang Rasau River Sand has a strength of 87.64% and 93.17% compared to Mountain Sand. Kembang Sri River sand has the lowest mortar compressive strength value for each mixture of 1Pc : 4Ps, 1Pc : 5Ps and 1Pc : 6Ps, compared to the strength of mountain sand was 34,80%, 27,40% and 28,57%. On the average, river sand with the gradation in zone III can be used for mortar mixture, although its strength is still below that of mountain sand.
 Keyword : river sand, mountain sand, mortar, fine modulus compressive strength.

Comparison between the Compressive Strength of Binary and Ternary Alkaline-activated Pozzolanic Concrete

This research compared the compressive strength of binary and ternary alkaline-activated pozzolanic concrete. Rice husk ash (RHA) and Metakaolin (MK) combined partially with Ordinary Portland Cement (OPC) each are the binary concrete while the combination of rice husk ash and metakaolin (RHA/MK) combined partially with OPC is the ternary concrete. The OPC was replaced at 15% each with RHA, MK and RHA/MK in ratios 0.33 (X), 0.5 (Y) and 1.0 (Z) of sodium silicate (NS) to sodium hydroxide (NH) as activator. A mix design ratio of 1:2:4 and water-cement ratio of 0.65 with alkaline liquid to pozzolan of 0.30 was used in the process of the study. Physical properties of the constituent materials as well chemical analysis of pozzolans were determined. Slump and compacting factor tests were done on the freshly mixed concrete to determine their workability while compression test was performed on the hardened concrete cube samples of side 150mm to obtain the compressive strength. Curing was done for 7 and 28 days inside water tank. The result of the compression test showed that the compressive strength of the ternary concrete continuously increased as the sodium silicate to sodium hydroxide ratio increased. At the maturity age of 28days, the values of the compressive strength were 14.2 MPa, 17.5 MPa and 20.3 MPa for sodium silicate (NS) to sodium hydroxide (NH) ratios of 0.33, 0.5 and 1.0 respectively. These values are higher than the compressive strength for the binary concrete of RHA and MK taken separately for the same NS to NH ratios which at 28days curing age were 10.9 MPa, 14.8 MPa, 16.2 MPa for RHA and 14.0 MPa, 15.3 MPa, 18.2 MPa for MK. The result of the research can be used in the construction industry for normal concrete work as well as serve for effective waste disposal of agricultural waste products such as RHA and MK to reduce environmental pollution.

REINFORCEMENT OF LONG CYLINDRICAL SHELL WITH STEEL FIBER

A technique for experimental study of long cylindrical shells is proposed in order to determine their stress-strain state, load-bearing capacity and crack resistance. To implement the task, the authors developed a special stand. For testing, eight models of a cylindrical shell were made ― 4 made of reinforced concrete and 4 made of fiber-reinforced concrete. Fiber-reinforced concrete shell specimens have additional dispersed reinforcement with steel fiber with bent ends in the amount of 1% by volume of concrete. Simultaneously with the shell samples, control samples of prisms and cubes were made to determine the physical and mechanical characteristics of concrete. Experimental and control samples were kept in the same temperature and humidity conditions for 28 days at a temperature of 16 ... 20º. To determine the physical and mechanical characteristics of concrete in each series, six control cubes 100x100x100 mm in size and three prisms 100x100x400 mm in size were tested. Tests of control samples were carried out according to DSTU B V.2.7-214:2009. Based on the results of these tests, it was established that the concrete of the shell specimens is represented by the C20/25 class in terms of compressive strength. The paper presents the results of testing a fiber-reinforced concrete cylindrical shell, the thickness of which is 45 mm. The shell was hinged at four points and loaded with a vertical distributed load applied in four strips, each 13 cm wide, and only along the body of the shell. Tests showed that the bearing capacity of the shell was 128.6 kN, and the first crack was formed at a load of 64.3 kN, which is 50.0% of the bearing capacity. Until the moment of loss of bearing capacity, 10 cracks were formed in the shell with the same initial opening width of 0.05 mm and a maximum final opening width of 0.7 mm. Computer simulation of the shell and calculations were performed using licensed software ANSYS 17.1. The bearing capacity determined in ANSYS was 120.2 kN, which is 6.5% less than in the experiment. The test methodology and the developed stand are universal in nature and will be used for further research.

Experimental studies for thin layer model validation and microwave drying characteristics of beetroot considering energy optimization

The drying kinetics of Beetroot was studied experimentally, followed by mathematical modeling. This work reveals the effect of input electrical power at 300, 600, and 800 W on the drying kinetics of Beetroot. The thin layer drying behavior of beetroot specimens was studied by employing seven distinct mathematical models. The models studied were contrasted between experimental and simulated moisture ratios based on their correlation coefficient and root mean square error values. The results indicate the page model as the best-suited model with values of correlation coefficient from 0.9881 to 0.9944 and root mean square error values from 0.0213 to 0.043 to define the thin layer beetroot drying behavior. The drying time was significantly reduced by about 400 s by raising the microwave output power by 500 W, i.e., from 300 W to 800 W. The drying process was noted to occur mainly during the falling rate period. The average moisture diffusivity varied between 1.78 × 10−8 and 4.38 × 10−7 m2/sec, whereas the values of activation energies determined were 69.99, 90.87, and 50.82 W/g for the cube, slab, and disc samples, respectively. The energy consumption and specific energies decreased with an increase in microwave power during drying. It was estimated that their values were in the range of 108–324 kJ and 16.57–49.54 MJ/kg water, respectively. Further, moisture diffusivities decreased with decreasing microwave power.

Crushed-stone sand for use in the development of self-compacting concrete (SCC)

SCCs, usually known as self-compacting concrete, are a kind of very fluid concrete having the capacity to flow without suffering any vibration. In order to reduce the possibility of bleeding and segregation, their makeup requires the inclusion of a significant number of fines. The usage of crushed sand, which is plentiful in limestone fines, may be shown to be a successful solution in terms of economics and ecology. This research examines the rheological, mechanical, and durability properties of self-consolidating concrete after adding quarry limestone fines to manufactured crushed sand (SCC). Five distinct SCC mixes were made with a consistent water-to-cement ratio of 0.40 and a cement content of 490 kg/m3 in order to accomplish this objective. The combinations substituted crushed limestone fines for crushed sand in varying proportions. The slump flow test, the V-funnel flow time test, the L-box height ratio test, the segregation resistance test, and the rheological test were all performed on the fresh SCC mixes using a rheometer. The compressive, tensile, and flexural strengths of SCC mixtures were assessed at the conclusion of the 28-day curing period. It was shown that raising the replacement amount of limestone fines in SCC mixes resulted in a decrease in both the slump flow and the yield stress when employing the two separate test modes in the fresh condition Samples of 7th and 28th day cubes were collected from the optimized mix proportion and subjected to Scanning Electron Microscope (SEM), X- Ray Diffraction (XRD). The images were interpreted and the result from micro-structural analysis were compared with their compressive strength. All of the SCC combinations examined had acceptable filling and passing capabilities, and no segregation was discovered in any of them. Using limestone fines instead of crushed sand also reduces the amount of water that is absorbed by capillaries, stops chloride ions from moving, and improves performance.

The experimental performance of durability and strength to repair for micro cracks in a self-healing bacterial concrete

Carbonate-producing bacteria have sparked a lot of attention as a promising, natural, and environmentally friendly new method for improving concrete properties. Using microbial-induced carbonate precipitation to ameliorate many concrete difficulties, such as fissure repair, reduction and change of porosity and permeability, has received a lot of attention. Furthermore, bacterial carbonate precipitation (bio deposition) has been proven to improve concrete's compressive strength. Meanwhile, it appears that the study of the appropriate dosage of bacterial solution and its influence on concrete durability has been thoroughly examined. As a result, it was determined to conduct research into finding the ideal doses of bacterial solution necessary for concrete by making several concrete cube samples with different bacterial solution concentrations, such as 20 ml, 40 ml, 60 ml, 80 ml and 100 ml. Furthermore, these varied samples are examined using a variety of laboratory procedures, including the slump cone test, compressive strength test, Ultrasonic pulse velocity, platelets, Acid attack test. To determine the best dose. Bacterial concrete has been found to be superior to conventional concrete in every facet of durability. Among the several specimens used, it was discovered that bacterial concrete containing 60 ml solution is the best dosage, with the strength being stable or decreasing after that.