Ultrasonic Water Research Articles

Green synthesis of MIL-100(Fe) metal-organic frameworks as a carrier for chloroquine delivery

The metal-organic framework MIL-100(Fe) was synthesized by the green process using the ultrasonic method and water. By using this approach, the energy consumption was reduced by 100 times compared to the hydrothermal method. The prepared MIL-100(Fe) was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and BET surface area measurements. The XRD pattern showed characteristic peaks of MIL-100 (Fe) with the main peaks at 6.3o, 10.3o, 11.1o, and 20.1o. The prepared MIL-100(Fe) was of particle size in a range of from 100 nm to 200 nm, and surface area of 950 m2/g with a pore volume of 0.52 cm3/g. The obtained MIL-100 (Fe) showed a high loading capacity for the chloroquine drug with a maximal capacity of 555 mg/g.

Influences of agro-wastes on the physico-mechanical and durability properties of unfired clay blocks

The increasing demand for construction materials along with the challenge of waste management has necessitated the development of sustainable materials utilising wastes properly. Therefore, this research examines the utilisation of various agricultural wastes, such as Eggshell Powder (ESP), Sawdust Powder (SDP) and Coconut Husk Powder (CHP), in the production of unfired clay blocks. Samples were made with various percentages of wastes: 10–50% of dry wt. of clay for ESP and 2.5–10% for SDP and CHP. In this study, the physico-mechanical and durability properties of unfired clay blocks were investigated by conducting density, linear shrinkage, capillary water absorption, flexural strength, compressive strength, ultrasonic pulse velocity test, drip test and water spray test. The tests were carried out in two phases, with the first phase including the individual integration of waste in the mixture and the second phase combining ESP (10–30%) with the optimum SDP (2.5%) and CHP (2.5%). The test results show that when the additives were used individually, the 40% ESP samples performed the best whereas for SDP and CHP 2.5% content showed better performance. Contrarily, the samples' overall characteristics deteriorated when ESP, SDP, and CHP were used together. Nevertheless, all the samples met the strength requirement of the standards and passed the durability tests. The results of this study might be useful in assessing the potential of ESP, SDP and CHP for the production of unfired clay blocks as well as finding a feasible solution to the waste management problem.

Determination of Prooxidant Activities of Several Fruit Juices and Herbs

Under oxidative stress conditions, which are defined as the deterioration of antioxidant and prooxidant balance in the organism in favor of prooxidants, ROS species that trigger the formation of various diseases occur. The fact that these harmful species cause oxidative damage to biological macromolecules is expressed as prooxidant activity. In this study, Cu(II)‒catalyzed prooxidant activities of pomegranate, apricot, peach, and pear juices and extracts of mint, white tea, and rosehip were measured by using gold nanoclusters synthesized via chicken egg white proteins. Fluorometric and spectrophotometric gold nanocluster biosensors and carbonyl assay were used. The fruit juices were used directly by diluting with pure water. Herbal plant samples were extracted in an ultrasonic water bath, filtered through microfilters, and stored in the refrigerator. Total prooxidant activities of fruit juices and herbal plants were calculated in terms of mM epicatechin equivalent, and the results obtained by applying all methods were compared with each other. It has been found that the applied methods can be used to accurately determine the total prooxidant activity of many food products.

Mechanical performance, water and chloride permeability of hybrid steel-polypropylene fiber-reinforced recycled aggregate concrete

Environmental impact and inherit brittleness of conventional concrete can be reduced simultaneously by utilising recycled aggregates instead of natural ones and fiber-reinforcements. In this research, the effect of incorporating single steel fiber (SF) and polypropylene fibers (PPF) and hybrid SF-PPF was studied on the performance of recycled aggregate concrete (RC). Both single fibers and hybrid fibers were used at the volume fraction of 1%. Examined properties included compressive strength-fcm, flexural strength-fbm, ultrasonic pulse velocity-UPV, water absorption-WA, and rapid chloride permeability-RCP. The results revealed the use of single SF and hybrid SF-PPF in incredibly advanced the flexural performance of RC. Single SF-reinforced-RC or hybrid SF-PPF-reinforced RC showed markedly higher flexural strength than that of the conventional plain NC. The optimum compressive and flexural strength were obtained when plain NC and RC were reinforced with 0.85%SF-0.15%PPF. Flexural strength of RC reinforced with 0.85%SF-0.15%PPF was 26% higher compared to that of the plain-NC. The use of hybrid SF-PPF also reduced the water permeability capacity of RC better than the use of single SF or PPF. Hybrid fiber-reinforced RC has implications for cheaper and eco-friendly concrete than single SF-reinforced concrete.

Porous electrospun microfibers for low flow-resistant solid phase extraction of fluoroquinolones in tap water, egg and milk samples

In this work, porous electrospun microfibers (PEMFs) were prepared using a polyimide/polyvinylpyrrolidone/polyethylene glycol (PI/PVP/PEG) solution mixture with coaxial ultrasonic water vapor spraying. After removing PVP and PEG by ultrasonic water washing, the PEMFs were successfully demonstrated as adsorbents for solid phase extraction (SPE). Most non-porous electrospun nanofibers are hundreds of nanometers in diameter, with a specific surface area of dozens of square meters per gram. In contrast, the diameter of the as-prepared PEMFs was tuned between 3 and 8μm, the specific surface area was 76 m2g-1 and the pore size was ca 25nm. Therefore, the flow resistance of the PEMF-SPE cartridges was similar to those of conventional commercial SPE cartridges, and much lower than those of SPE cartridges packed with electrospun nanofibers. Using the PEMF-SPE cartridges with ultra-performance liquid chromatography-fluorescence detector (UPLC-FLD), five fluoroquinolones (FQs) in tap water, egg and milk samples were extracted and quantified successfully. After optimizing the extraction conditions, FQs in water samples were extracted and eluted with high recoveries of 84.8-114.8%. The inter-batch and intra-batch relative standard deviation (RSD) values for the FQs were in the range of 1.9-9.5% (n=3), and the limits of detection were between 0.0024-0.014μg L-1. The method was linear in the concentration range of 0.005-10μg L-1. The reliability of the developed method was validated by analyzing tap water, egg and milk samples, and the recovery values were found to be in the range of 74.8-116.6% under the optimized conditions.

Durability and Safety Performance of Pavements with Added Photocatalysts

The use of photocatalysts to enhance the performance of construction materials with large surfaces exposed to sunlight has become an increasingly common practice in recent decades. Although construction material durability is of crucial importance and is extensively studied when incorporating new additions, very few studies have specifically addressed the effects when adding photocatalysts. This paper discusses the effect of TiO2-based photocatalysts on pavement durability (porosity, time of transmission of ultrasonic pulses, freeze-thaw resistance and capillary water absorption) and safety (slip resistance and roughness) by comparison of commercial photocatalytic materials of different families and twin materials without the photocatalyst added. The analysis covers concrete tile pavements and porous asphalt treated with photocatalysts in the form of sprayed emulsions, slurry admixtures or built-in during casting. The findings show that changes in the properties of a construction material induced by photocatalytic functionality depend primarily on the porous structure of the matrix and the properties of the resulting photocatalytic surface.

Sustainable utilization of waste slag aggregates as replacement of coarse aggregates in concrete

The current study mainly aims on the usage of waste coarse slag aggregates (CSA) to prepare coarse slag aggregate concrete (CSAC). The waste slag aggregates are the by-products mainly obtained from the iron and steel industries. These wastes are mostly disposed off into the landfills and the newer alternative method of disposing are being researched. Also, the increasing rate of construction has resulted into the diminishing of natural raw materials. The present paper focuses on incorporating CSA as the replacement of 20 mm natural coarse aggregates to prepare CSAC for various volumetric replacement of 20%, 40%, 60%, 80% and 100%. Cube and beam samples having different percentages of CSA were casted to undergo the experimental analysis. The fresh, mechanical and durability parameters has been studied by performing workability, density, compressive strength, split tensile strength, ultrasonic pulse velocity, water absorption and water permeability tests, for the in-depth analysis. The outcomes from the experiments has shown decrease in the strength and durability properties for increasing count of CSA. Decrease in compressive and split tensile strength of 39.08% and 37.50% respectively was observed for 100% CSA replacement. In case of durability properties, the penetration depth has increased up to 69.84% for the 100% CA replacement sample. However, a very marginal decrease in the values were observed for the replacement content up to 40%. The study concluded that the utilization of slag aggregate is a sustainable approach by preserving the naturally available raw materials and also construction can be made economical.

Non-Destructive Evaluation of Coating Thickness Using Water Immersion Ultrasonic Testing

The coating is applied to prevent corrosion on the surface of ships or marine structures, and the thickness of the coating affects its anti-corrosion effect. As a result, non-destructive testing (NDT) is required to measure coating thickness, and ultrasonic NDT is a convenient and quick way to measure the thickness of underwater coatings. However, the offshore coating’s energy attenuation and absorption rates are high, the ultrasonic pulse echo test is difficult, and the testing environment is harsh. Because of the coating’s high attenuation, the distance of the optimal water delay line designed based on the reflection coefficient of the vertically incident wave is used. To accurately measure the thickness of the coating material, TOF of the reflected echo on the time-domain waveform was evaluated. The experimental results show that, when compared to caliper measurements, the coating thickness measured by the proposed method has a lower error and can be used for accurate measurement. The use of ultrasonic water immersion measurement is almost limitless in terms of size, location, and material of the object to be measured, and it is expected to be used to measure the thickness of the surface coating of ships or marine structures in the water.

Effects of demineralization on the composition of microalgae pyrolysis volatiles in py-GC–MS

This study compared the volatiles distribution in analytical scale pyrolysis (py-GC–MS) of Nannochloropsis gaditana (marine microalgae) and Scenedesmus almeriensis (freshwater microalgae) and their demineralized counterparts. The role of inorganic elements and their removal via ultrasonic treatment, water washing and (in)organic acid leaching were elucidated. Principal component analysis (PCA) and grey relational analysis were applied to analyze the pyrolysis volatiles distribution and demonstrate the influence of inorganic elements in pyrolysis, respectively. Demineralization affects (breaks down) the chemical structure of carbohydrates, followed by (to a lesser extent) proteins and lipids. Acid leaching promoted hydrolysis and suppressed the catalytic effect associated to inorganic elements in subsequent pyrolysis, compared to ultrasonic treatment and water washing. Elements like K and Na had a larger catalytic influence on microalgae pyrolysis than Ca and Mg. The composition and pyrolytic formation mechanism of major product groups at 500 °C were studied, including anhydrosugars, phenolics, furans, carboxylic acids, alcohols, aliphatic hydrocarbons, aromatic hydrocarbons, N-heterocyclic compounds, nitriles and amides. The results indicate that demineralization shows positive effects on fast pyrolysis of microalgae: (1) by disrupting the cell wall and releasing the lipids and cellular contents. Based on the py-GC–MS peak area normalized to sample mass, the relative contribution of hydrocarbons in the pyrolysis vapors increased from 25.5 % (NG: Nannochloropsis gaditana) to 32.1 % (NG-HCl: Nannochloropsis gaditana, HCl treated), and from 16.1 % (SA: Scenedesmus almeriensis) to 22.4 % (SA-HCl: Scenedesmus almeriensis, HCl treated); (2) by decreasing the relative yields in O-containing compounds resulting from the suppressed catalytic effects of alkali and alkaline earth metals (53.3 % (NG) to 37.1 % (NG-HCl), 57.5 % (SA) to 47.8 % (SA-HCl)) that would otherwise have been present in non-demineralized microalgae feedstock. The effects of demineralization on the denitrogenation of pyrolysis vapors were not that obvious. Suggestions for potential full scale applications have been proposed.

Investigation of Color, Fastness, and Antimicrobial Properties of Wool Fabrics Dyed with Rosa Canina Leaf Extract

ABSTRACT Natural dyestuffs are innovative natural resources alternative to chemicals in the textile industry due to their antibacterial properties. The objective of this study was to reveal the color, fastness, and antibacterial efficiency of Rosa canina leaf extract in wool fabric dyeing. Aluminum potassium sulfate (KAl (SO4)2.12H2O), copper sulfate (CuSO4.5H2O), and iron sulfate (FeSO4.7H2O) metal salts were preferred in the pre-mordanting process. Two different natural dye concentrations (25% and 50%) were tested in mordant and non-mordant wool fabrics. The fastness values were ranked between medium and good grades with 2–6. One of the remarkable results was that the fastness values of the un-mordanted dyed samples were acceptable with 5. In disc diffusion analysis, ultrasonic water bath CH3OH extracts were found to be more effective against Staphylococcus aureus ATCC 25923 and Escherichia coli ATCC 25922 with 16.4 mm and 7.51 mm, respectively. Also, the dyed wool fabrics showed remarkable antimicrobial activity (reduction rates: w46e100) against two different bacteria according to AATCC 100 method.

Quantifiable method of polyunsaturated fatty acids in human plasma by optimized gas chromatography

To optimize the quantifiable method for determining polyunsaturated fatty acids in human plasma by gas chromatography(GC). Plasma was added with heptadecanoic acid methyl ester internal standard, and the total plasma lipids was extracted with methanol and n-hexane under the condition of ultrasonic water bath. The sulfuric acid methanol was used for methyl esterification. After centrifugation, the supernatant was filtered with a membrane and dried by nitrogen, and then re-dissolved by n-hexane. HP-88 GC column(30 m×0.25 mm, 0.2 μm) was used to separate linoleic acid(LA), α-linolenic acid(α-ALA), arachidonic acid(AA) and docosahexaenoic acid(DHA) with programmed temperature, and internal standard method was used to draw standard curve for quantitative analysis. Ultrasonic water bath at 40 ℃ for 20 min could realize a higher total lipid extraction rate in a shorter time. The experimental concentration of four fatty acids range showed a good linear relation with the peak area ratio, correlation coefficient(r>0.995). The rate of recovery of four fatty acids were between 84.05%-101.23% with relative standard deviation(RSD) of 1.21%-6.77%, and the RSD of precision, within-day stability and day to day stability were 0.01%-0.04% and 0.02%-0.07%, respectively. No significant differences in the concentration of α-ALA, AA and DHA were observed between plasma and serum. The concentration(M(P25, P75)) of LA was higher in serum [93.38(79.18, 116.41) μg/mL]compared with plasma [72.12(50.93, 101.13) μg/mL], and the difference were significant(P<0.05). This method has a higher rate of total plasma lipids with shorter time, and the internal standard-standard curve method could eliminate the influence of the sample amount on the result. The determination of four polyunsaturated fatty acids was accurate, which could be used for the determination of plasma polyunsaturated fatty acids content in large sample populations.

Experimental Investigation of Heat Transfer with Various Aqueous Mono/Hybrid Nanofluids in a Multi-Channel Heat Exchanger

The use of nanofluids for heat transfer has been examined in recent years as a potential method for augmentation of heat transfer in different systems. Often, the use of nanoparticles in a working fluid does not disrupt the system in significant ways. As a result of this general improvement of a system’s heat transfer capabilities with relatively few detrimental factors, nanofluids and hybrid nanofluids have become an area of considerable research interest. One subcategory of this research area that has been under consideration is the concentration of each of the nanoparticles, leading to either successful augmentation or hindrance. The focus of the current experimental investigation was to examine the resulting impact on heat transfer performance as a result of each nanofluid implemented in an identical three-channel heat exchanger. This work examined the experimental impacts of 0.5 wt% titania (TiO2), 1 wt% titania, a mixture of 0.5 wt% titania and 0.5% silica, and a 0.5 wt% hybrid nanofluid of titania synthetically modified with copper-based nanostructures (Cu + TiO2). The experimental work examined a range of heat flux densities from 3.85 W cm−2 to 7.51 W cm−2, and varying flow rates. Each of the nanoparticles were suspended in distilled water and then mixed using an ultrasonic water bath. The performances of each nanofluid were determined using the local Nusselt number to evaluate the possible thermal enhancement offered by each nanofluid mixture. While the 0.5 wt% Cu + TiO2 hybrid nanofluid did significantly increase performance, the use of a 0.5 wt% TiO2/SiO2 double nanofluid in a three-channel heat exchanger exhibited the greatest performance enhancement, with an average increase of 37.3% as compared to water.

Correlation mechanism between the law of ultrasonic propagation in coal samples and the migration of water

In order to reveal the correlation mechanism between the law of ultrasonic propagation and water migration. A simulation method for displaying the entire process of multi-field coupling ultrasonic excitation, propagation, and reception based on CT scanning reconstruction of the coal pore–fracture structure model is proposed. A porous medium water migration-ultrasonic wave propagation calculation model is constructed by introducing the water-injected coal porous medium water migration calculation model into the ultrasonic propagation calculation process. In the simulation analysis, the coal sample matrix and minerals reconstructed by CT scanning are regarded as homogeneous elastic materials, and the contribution of water migration to the elastic parameters is characterized in the form of equivalent parameters. The pore fracture is regarded as a pressure acoustic fluid, and the equivalent parameter method is used to characterize the water–gas distribution in the pore fracture. The electrostatic coupling solid mechanics and solid mechanics coupled pressure acoustics mode are used to simulate the propagation process of the ultrasonic wave excited by the ultrasonic transducer in the water-injected coal sample, thereby revealing the law of ultrasonic wave propagation in the water-injected porous medium. Research results show that the transmission rate of the ultrasonic wave decreases when the ultrasonic wave propagates to the location of the mineral, and the mineral transmits part of the displacement energy of the ultrasonic wave and partly reflects this energy. The first position reached during the ultrasonic propagation is the position where the fractures are slightly obstructed followed by after reflection, superposition, and finally full distribution. The water accelerates the propagation velocity of ultrasonic waves. However, the capability of ultrasonic waves to pass through the fractures slightly contributes to the presence of water inside the fractures and mainly depends on whether the migration of the coal matrix water covers the fracture area.

A Step to Smart Fishways: An Autonomous Obstruction Detection System Using Hydraulic Modeling and Sensor Networks.

Stepped fishways are structures that allow the free movement of fish in transversal obstacles in rivers. However, the lack of or incorrect maintenance may deviate them from this objective. To handle this problem, this research work presents a novel low-cost sensor network that combines fishway hydraulics with neural networks programmed in Python (Keras + TensorFlow), generating the first autonomous obstruction/malfunction detection system for stepped fishways. The system is based on a network of custom-made ultrasonic water level nodes that transmit data and alarms remotely and in real-time. Its performance was assessed in a field study case as well as offline, considering the influence of the number of sensing nodes and obstruction dimensions. Results show that the proposed system can detect malfunctions and that allows monitoring of the hydraulic performance of the fishway. Consequently, it optimizes the timing of maintenance on fishways and, thus, has the potential of automatizing and reducing the cost of these operations as well as augmenting the service of these structures. Therefore, this novel tool is a step forward to achieve smart fishway management and to increase their operability.

Ultrasonic Pulsating Water Jet Peening: Influence of Pressure and Pattern Strategy.

Peening techniques are nowadays attracting more research attention due to their association with the extending of the service life and improving surface texture of engineering components. Ultrasonic pulsating water jet peening represents a new way of mechanical surface treatment. Accelerated water droplets via hammer effect cause small elastic-plastic deformations on the surface. This work deals with peening of aluminum alloy using an ultrasonic pulsating water jet, where periodically acting water droplets were used as the peening medium. The aim of the work was the feasibility study of the peening process and to observe the effects of pressure (p = 10, 20 and 30 MPa) and pattern trajectory (linear hatch and cross hatch). The peened surfaces were analyzed by the surface roughness profile parameters Ra and Rz and the microhardness along the peening axis into the material. Graphically processed results show a clear increase of measured values with increasing pressure (p = 10, 20 and 30 MPa), where the roughness values ranged from 1.89 µm to 4.11 µm, and the microhardness values ranged from 43.3 HV0.005 to 47 HV0.005, as compared to 40.3 HV0.005 obtained for the untreated sample. The achieved results indicate potential using of an ultrasonic pulsating water jet as a new method of surface treatment of metals. By controlled distribution of water droplets, it is possible to achieve a local distribution of surface roughness, and at the same time, strengthening of the subsurface layers in the material without thermal influence on the material.

Effects of liquid droplet volume and impact frequency on the integrity of Al alloy AW2014 exposed to subsonic speeds of pulsating water jets

This study focuses on the analysis of the surface material integrity of the polished, rigid, solid surface of an aluminium alloy after periodical impingement of liquid droplets with variable volume and impact frequency distributions normal to the solid surface. The volume of water droplets was determined for the pressures of 20 and 40 MPa. By increasing the traverse speed of the ultrasonic pulsating water jet head with respect to the stationary tested specimen, the number of water droplet impacts on one area was controlled in order to reach the early erosion stages. Also, for the comparative study, aluminum alloy was exposed to continuous water jet for both supply pressure 20 and 40 MPa with traverse speed of 1 mm/s over the material surface. Systematic testing focused on material integrity in the early erosion stages in the interval between the elastically deformed surface and material disintegration was conducted with the aid of microhardness measurements, X-ray analysis of stress state, and microstructural analysis by SEM. The motivation for carrying out this experiment was to verify the effects of periodic drops on the integrity of the material and to identify the parameters leading to surface strengthening without erosion as compared to continuous jet. Such surface treatments can improve fatigue life, similarly to shot peening.

Experimental studies on the development of a self-healing cementitious matrix for repair and retrofitting of concrete structures

PurposeSelf-healing concrete is a revolutionary building material that will generally reduce the maintenance cost of concrete constructions. Self-healing of cracks in concrete structure would contribute to a longer service life of the concrete and would make the material more durable and more sustainable. The cementitious mortar with/without incorporating encapsulates at different percentages of slag replacement with the cement mix improves autogenous healing at different ages. Therefore, this study’s aim is to develop a self-healing cementitious matrix for repair and retrofitting of concrete structures.Design/methodology/approachIn the present work, waste straw pipes are used as a capsule, filled with the solution of sodium hydroxide (NaOH), sodium silicate (Na2SiO3) and colloidal nano-silica as self-healing activators. An artificial micro-crack on the control and blended mortar specimens at different percentages of slag replacement with cement (with/without encapsulation) is developed by applying a compressive load of 50% of its ultimate load-carrying capacity. The mechanical strength and ultrasonic pulse velocity, water absorption and chloride ion penetration test are conducted on the concrete specimen before and after the healing period. Finally, the self-healing activity of mortar mixes with/without encapsulation is analysed at different ages.FindingsThe encapsulated mortar mix with 10% of slag content has better self-healing potential than all other mixes considering mechanical strength and durability. The enhancement of the self-healing potential of such mortar mix is mainly due to hydration of anhydrous slag on the crack surface and transformation of amorphous slag to the crystalline phase in presence of encapsulated fluid.Research limitations/implicationsThe self-healing activities of the slag-based cementitious composite are studied for a healing period of 90 days only. The strength and durability performance of the cracked specimen may be increased after a long healing period.Practical implicationsThe outcome of the work will help repair the cracks in the concrete structure and enhances the service life.Originality/valueThis study identifies the addition encapsulates with a self-healing activator fluid that can recover its strength after minor damage.

Toward industrial revolution 4.0: Development, validation, and application of 3D-printed IoT-based water quality monitoring system

Recent technological advances and developments have evolved the application of the Internet of Things (IoT), low-cost sensors, and three-dimensional (3D) printing for near-real-time water quality monitoring; however, these technologies have not yet been widely implemented in field operations. In this study, a solar-powered 3D-printed IoT-based water quality monitoring system (WQMS) that measures turbidity and water level every 2 h was developed and utilized in a palm oil plantation on Carey Island, Malaysia, for two months (November 28, 2019–January 21, 2020). The WQMS consists of four modules: energy, time, monitoring, and communication. The electrical consumption values of the WQMS in the standby, operating, and data transmission modes were calculated to determine the optimal monitoring frequency. The monitored data were uploaded to Ambient (an open cloud platform) for visualization and anomaly detection. The turbidity and ultrasonic water level sensors were calibrated and validated, and high linearities (R2 > 0.97) were obtained between the signal received and the actual measurements. The turbidity sensor provided an accurate measurement of turbidity within a range of 10–1000 FNU, whereas the optimum measurement range of the water level sensor was determined to be 2–400 cm. From the field study results, it can be observed that the contact-type sensor (for turbidity) requires monthly maintenance to prevent the deposition of mud/silt and biofouling problems, whereas the non-contact sensor (for water level) can consistently provide accurate measurements throughout a period of at least two months. The proposed WQMS implemented demonstrates the effective integration of IoT with 3D printing, microcomputers, and low-cost sensors, paving a new path for the development of cost-effective and reliable systems for water quality monitoring.

Durability and Mechanical Properties of Roller Compacted Concrete Containing Coarse Reclaimed Asphalt Pavement

The feasibility of utilizing Reclaimed Asphalt Pavement (RAP) as a replacement for coarse aggregates in Roller Compacted Concretes (RCCs) was assessed. This replacement was performed in different volumetric percentages (25%, 50%, 75%, and 100%). During this process, RAP materials were subject to abrasion and impact in the Los Angeles drum and mixer before being added to the mixture. Compressive strength, splitting tensile strength, flexural strength, crack propagation, Ultrasonic Pulse Velocity (UPV), electrical resistivity, density, and water absorption (in 7, 28, and 90 days of age) tests were done on all mixtures. Results show that utilizing RAP in RCC can cause a drop in the mechanical properties, but it has positive effects on crack propagation of the specimens due to their increased toughness. Increasing the amount of RAP in the mixtures has increased their electrical resistivity, likely owing to the hydrophobic properties of RAP, which causes prevention from connecting pores to each other. The relationship between the mechanical properties and UPV of the mixtures was analysed using regression models. Moreover, one- and two-way ANOVA (analysis of variance) tests were performed on the results at a 95% confidence level. Finally, replacing the coarse aggregates with RAP only up to 75% is suggested if pre-processing is performed.

Experimental investigation on the strength and durability properties of bacterial self-healing recycled aggregate concrete with mineral admixtures

Microcracks are the inherent feature of concrete and this feature also persists in recycled aggregate concrete (RAC) just like a conventional concrete. Due to external loading and chemical reactions, microcrack spreads, causing harmful species to enter the concrete causing durability of the concrete to deteriorate. In this study, the precipitations of bacterially induced CaCO3 were introduced in RAC as a strategy to repair cracks on their own. Recycled coarse aggregate (RCA) was used at the 50% and 100% levels by replacing natural coarse aggregate (NCA). In addition, 10% weight of cement was replaced in bacterial recycled aggregate concrete (BRAC) mixes with microsilica (MS) and metakaolin (MK). The competency of self-healing was assessed through compressive strength, ultrasonic pulse velocity (UPV) measurements, water permeability and microscopic inspection of crack healing. The maximum crack width of 0.63 mm was fully healed after 56 days of healing incubation. Depending on the cracking age regain in compressive strength was found to be in the range of 57% to 93% and the variation ratio (Rk) of the permeability coefficient was observed in the range of 143% to 181% in different BRAC mixes. The microstructure investigations were conducted using SEM with EDS and XRD techniques from which the morphology of bacterial precipitations and their composition were explored. Based on the results of the study, it is suggested that cracks in RAC can be self-repaired by bacterially attained self-healing phenomena and hence, its durability can be improved.