Effects of Hygrothermal Aging and Cyclic Compressive Loading on the Mechanical and Electrical Properties of Conductive Composites

Conductive polymers and their composites have been widely applied in different applications, including sensing applications. Herein, we constructed a conductive composite of polypropylene, carbon black, and multi-walled carbon nanotubes (PP/CB/MWCNTs) to experimentally study its sensing behaviors in a humid thermal environment. The as-synthesized PP/CB/MWCNT composite polymer was immersed in simulated sweat in deionized water at 67 °C. Regarding their electrical and mechanical properties, different experimental parameters, such as cyclic loading and hygrothermal aging, were investigated by recording the mass changes, carrying out strain sensing experiments, and performing dynamic mechanical analyses before and after the immersion test. The results reveal that the filler content improved the rate of water absorption but decreased at higher concentrations of the solution. The sensitivity of the material decreased by up to 53% after the hygrothermal ageing and cyclic loading. Moreover, the sensitivity under cyclic compression loading decreased with an increasing immersion time, qualitatively illustrated by an effective quantum tunneling effect and conducting path model. Finally, hygrothermal aging reduced the composite's glass transition temperature. This reduction was the most significant for specimens immersed in deionized water, ascribed to the moisture absorption, reducing the molecular chain activity.

Mechanical and Durability Evaluation of Metakaolin as Cement Replacement Material in Concrete

Due to the increasing prices of cement and its harmful effect on the environment, the use of cement has become highly unsustainable in concrete. There is a considerable need for promoting the use of cement replacement materials. This study investigates the effect of variable percentages of metakaolin (MK) on the mechanical and durability performance of concrete. Kaolin clay (KC) was used in the current research to prepare the MK by the calcination process; it was ground in a ball mill to its maximum achievable fineness value of 2550 m²/Kg. Four replacement levels of MK, i.e., 5%, 10%, 15%, and 20% by weight of cement, in addition to control samples, at a constant water-to-cement (w/c) ratio of 0.55 were used. For evaluating the mechanical and durability performance, 27 cubes (6 in. × 6 in. × 6 in.) and 6 cylinders (3.875 in. diameter, 2 in. height) were cast for each mix. These samples were tested for compressive strength under standard conditions and in an acidic environment, in addition to being subjected to water permeability, sorptivity, and water absorption tests. Chemical analysis revealed that MK could be used as pozzolana as per the American Society for Testing and Materials (ASTM C 618:2003). The results demonstrated an increased compressive strength of concrete owing to an increased percentage of MK in the mix with aging. In particular, the concrete having 20% MK after curing under standard conditions exhibited 33.43% higher compressive strength at 90 days as compared to similarly aged control concrete. However, with increasing MK, the workability of concrete decreased drastically. After being subjected to an acid attack (immersing concrete cubes in 2% sulfuric acid solution), the samples exhibited a significant decrease in compressive strength at 90 days in comparison to those without acid attack at the same age. The density of acid attack increased with increasing MK with a maximum corresponding to 5% MK concrete. The current findings suggest that the local MK has the potential to produce good-quality concrete in a normal environment.

A Comparative Study on Hygric Properties and Compressive Strength of Ceramic Bricks

This article analyzes the results of capillary rise, compressive strength and water absorption tests on solid ceramic bricks from existing structures and demolition materials taken from 11 different structures. In addition (for more extensive interpretation and evaluation of porosity), tests were performed for the selected series of bricks using a mercury porosimeter (MIP) and a micro computed tomography (micro-CT). Contemporary bricks (2 series) were also evaluated for comparison purposes. The conducted tests indicate that bricks obtained from different sources are characterized by "individual" relation of compressive strength and porosity, and "individual" relation of water absorption coefficient and porosity. In addition, on the basis of the results obtained in the study, compared with the literature data, it can be deduced that ceramic bricks with a water absorption coefficient of less than 50 g/m²s^0.5 are characterized by a compressive strength of more than 80 MPa. As the research shows, the properties of bricks even from a single building can differ one from another, which can result in varying durability even within a single building. When choosing a material during the renovation or restoration of facilities, it is important to perform tests on the physical and mechanical properties of the original material, which will be reused.

The Use of Marble Dust, Bagasse Ash, and Paddy Straw to Improve the Water Absorption and Linear Shrinkage of Unfired Soil Block for Structure Applications

Unfired admixed soil blocks are made up of soil plus stabilizers such as binders, fibers, or a combination of both. Soil is abundant on Earth, and it has been used to provide shelter to millions of people. The manufacturing and usage of cement and cement blocks raise several environmental and economic challenges. Due to disposal issues, agricultural and industrial waste is currently the biggest hazard to the environment and humanity in the world. Consequently, environmental degradation brought on by agricultural waste harms the ecology. As a result, researchers are attempting to develop an alternative to cement blocks, and various tests on unfired admixed soil blocks have been done. This investigation uses agricultural waste (i.e., paddy straw fiber and sugarcane bagasse ash) and industrial waste (i.e., marble dust) in manufacturing unfired admixed soil blocks. Under this investigation, the applicability of unfired soil blocks admixed with marble dust, paddy straw fiber, and bagasse ash was studied. The marble dust level ranged from 25% to 35%, bagasse ash content ranged from 7.5% to 12.5%, and the content of paddy straw fiber ranged from 0.8% to 1.2% by soil dry weight. Various tests were conducted on the 81 mix designs of the prepared unfired admixed soil blocks to find out the physical properties of the block followed by modeling and optimization. The findings demonstrate that the suggested method is a superior alternative to burned bricks for improving the physical properties of admixed soil blocks without firing.

Influences of Efficient Spraying of Cement-Based Slurries on Recycled Coarse Aggregate

The inferior property is usually one of the major problems of recycled coarse aggregate (RCA), and the utilization of the RCA is limited. Strengthening the RCA is being widely explored. Immersing the RCA in the cement-based slurry is an effective approach. However, lots of slurry and time are required, and it is difficult to integrate the immersing method into the production line of the RCA. In this paper, a circular spraying method was proposed to treat the RCA using cement-based slurry. The immersing method was also conducted to verify the feasibility of the spraying method. The crushing value (CV), 24 h water absorption (WA), apparent density (AD) and dynamic water absorption (DWA) were tested, and the micro-morphology was also observed to explore the strengthening mechanism. Results showed that the CV and the WA decreased by up to 30.0% and 14.3% when the spraying method was used. The AD was slightly influenced by the cement-based slurry regardless of the treatment method. Considering the CV, WA and AD, the comprehensive grade of the RCA could be enhanced from III to II by using the spraying method. It was worth noting that the effects of the spraying method and the immersing method were basically equivalent. When the spraying method was adopted, only about 1 min and a small amount of slurry (about 5% of the RCA mass) were required to treat the RCA.

Characterization of Self-Growing Biomaterials Made of Fungal Mycelium and Various Lignocellulose-Containing Ingredients

In this study, novel blends of mycelium biocomposites (MB) were developed. Various combinations of birch sawdust and hemp shives with birch bark (BB) and wheat bran (WB) additives were inoculated with basidiomycete Trametes versicolor to produce self-growing biomaterials. MB were characterized according to mycelial biomass increment in final samples, changes in chemical composition, elemental (C, H, N) analyses, granulometry of substrates, water-related and mechanical properties, as well as mold resistance and biodegradability. The mycelial biomass in manufactured MB increased by ~100% and ~50% in hemp and sawdust substrates, respectively. The lignocellulose ingredients during fungal growth were degraded as follows: cellulose up to 7% and 28% in sawdust and hemp substrates, respectively, and lignin in the range of 13% in both substrates. A larger granulometric fraction in hemp MB ensured higher strength property but weakened water absorption (600-880%) performance. Perspective MB combinations regarding strength performance were hemp/BB and pure hemp MB (σ10 0.19-0.20 MPa; E 2.9 MPa), as well as sawdust/WB combination (σ10 0.23 MPa; E 2.9 MPa). WB positively affected fungal biomass yield, but elevated water absorption ability. WB improved compressive strength in the sawdust samples but decreased it in the hemp samples. BB supplement reduced water absorption by more than 100% and increased the density of sawdust and hemp samples. All MB samples were susceptible to mold contamination after full water immersion, with identified fungal genera Rhizopus, Trichoderma and Achremonium. The MB exhibited high biodegradability after 12 weeks' exposure in compost, and are therefore competitive with non-biodegradable synthetic foam materials.

Evaluation of the Nature and Concentration of the Surfactant on the Properties of Red Mud/Metakaolin Porous Geopolymers Foamed with Aluminium

The chemical foaming technique is possibly the most common method of producing porous geopolymers. Despite this, to date, the role of the content and type of surfactant on the pore size distribution of porous geopolymers is not fully perceived, as constant surfactant dosages are usually employed. In addition, the comparison of literature studies is challenging since a distinct mixture of designs is employed. This investigation intends to provide additional insights on the topic, focusing on synthesizing red mud/metakaolin geopolymer foams and envisioning their use in thermal insulating applications. Various mixtures were prepared using three commercially available surfactants, namely Hostapur OSB, sodium dodecyl sulfate (SDS), and Triton X114. The content of the surfactant (0.025, 0.05, and 0.075 wt.%) and the amount of the foaming agent (aluminum powder, Al; 0.05, 0.075, and 0.10 wt.%) was modified, keeping the binder composition constant and the physical properties of the produced geopolymers were characterized. Results show that the combination between sodium dodecyl sulfate (0.025 wt.%) and aluminum (0.10 wt.%) leads to the strongest reduction in the foam density, the lowest value here reported being -400 kg/m³. On the other hand, samples produced with Hostapur OSB have much higher open porosity (up to 47.7%) and water absorption (up to 80.4%) values, showing that this surfactant leads to a pore network with higher connectivity. In addition, the microstructure of the foams, particularly pore morphology (size and shape) and connectivity between the produced pores are highly dependent on the type of surfactant, sodium dodecyl sulfate generating coarser pore size distribution with round, but mostly closed pores, while a narrower pore size distribution coupled with smaller size pores is seen with the Hostapur. These results suggest the feasibility of tuning the foams' properties (porosity and mechanical performance) according to the application by the proper combination of the type of surfactant and their concentration, enabling their use as thermal and acoustic insulators or as filters/membranes in wastewater treatment systems.

Effect of Water-Resistant Properties of Kraft Paper (KP) Using Sulfur Hexafluoride (SF6) Plasma Coating

Sulfur hexafluoride (SF₆) plasma at different pressures, powers, and times was used to treat Kraft paper (KP) to enhance its water resistance. The KP was treated with SF₆ plasma from 20–300 mTorr of pressure at powers from 25–75 Watts and treatment times from 1–30 min at 13.56 MHz. The prepared papers were characterized by contact angle measurement and water absorption. The selected optimum condition for the plasma-treated KP was 200 mTorr at 50 Watts for 5 min. Advancement with the change in treatment times (3, 5, and 7 min) on the physical and mechanical properties, water resistance, and morphology of KP with SF₆ plasma at 200 mTorr and 50 Watts was evaluated. The changes in the chemical compositions of the plasma-treated papers were analyzed with an XPS analysis. The treatment times of 0, 3, 5, and 7 min revealed fluorine/carbon (F/C) atomic concentration percentages at 0.00/72.70, 40.48/40.97, 40.18/37.95, and 45.72/39.48, respectively. The XPS spectra showed three newly raised peaks at 289.7~289.8, 291.5~291.7, and 293.4~293.6 eV in the 3, 5, and 7 min plasma-treated KPs belonging to the CF, CF₂, and CF₃ moieties. The 5 min plasma-treated paper promoted a better interaction between the SF₆ plasma and the paper yielded by the F atoms. As the treatment time for the treated KPs increased, the contact angle, water absorption time, and Cobb test values increased. However, the thickness and tensile strength did not show remarkable changes. The SEM images revealed that, as the treatment time increased, the surface roughness of the plasma-treated KPs also increased, leading to improved water resistance properties. Overall, the SF₆ plasma treatment modified the surface at the nano-layer range, creating super-hydrophobicity surfaces.

Durability Properties of Lightweight Foamed Concrete Reinforced with Lignocellulosic Fibers

Worldwide concern and ascendancy of emissions and carbon footprints have propelled a substantial number of explorations into green concrete technology. Furthermore, construction material costs have increased along with their gradual impact on the environment, which has led researchers to recognize the importance of natural fibers in improving the durability and mechanical properties of concrete. Natural fibers are abundantly available making them relatively relevant as a reinforcing material in concrete. Presently, it should be recognized that most construction products are manufactured using resources that demand a high quantity of energy and are not sustainable, which may lead to a global crisis. Consequently, the use of plant fibers in lightweight foamed concrete (LFC) is deemed a practical possibility for making concrete a sustainable material that responds to this dilemma. The main objective of this study is to investigate the effect of the addition of lignocellulosic fibers on the performance of LFC. In this investigation, four different types of lignocellulosic plant fibers were considered which were kenaf, ramie, hemp and jute fibers. A total of ten mixes were made and tested in this study. LFC samples with a density of 700 kg/m³ and 1400 kg/m³ were fabricated. The weight fraction for the lignocellulosic plant fibers was kept at 0.45%. The durability parameters assessed were flowability, water absorption capability, porosity and ultrasonic pulse velocity (UPV). The results revealed that the presence of cellulosic plant fibers in LFC plays an important role in enhancing all the durability parameters considered in this study. For workability, the addition of ramie fiber led to the lowest slump while the inclusion of kenaf fiber provided optimum UPV. For porosity and water absorption, the addition of jute fiber led to the best results.

Sulfate Freeze-Thaw Resistance of Magnesium Potassium Phosphate Cement Mortar according to Hydration Age

Concrete structures can be degraded by exposure to environmental stressors such as freeze–thaw cycling and salt corrosion. Magnesium potassium phosphate cement (MKPC) mortar is useful for the rapid repair of such structures but must acquire environmental resistance rapidly. In this study, the freeze–thaw resistance of MKPC mortar specimens of different hydration ages was tested in water and a 5% Na₂SO₄ solution. The strength, volume deformation, and water absorption rates were compared with those of full-age MKPC mortar specimens (28 d). The phase composition and microscopic morphology of the MKPC mortar specimens before and after corrosion were observed, and the corrosion-resistance mechanism was analyzed. After 225 freeze–thaw cycles in water and sulfate solution, the strength residual rates of the early-age specimen (1 d) were higher than those of the full-age specimen (28 d). The degree of strength attenuation in the 1 d specimen was lower in the sulfate environment than in the water environment. After 225 freeze–thaw cycles, the volume expansion rates of 1 d specimens in water or sulfate were 0.487% and 0.518%, respectively, while those of 28 d specimens were 0.963% and 1.308%. The comparison shows that the 1 d specimen had significantly better deformation resistance under freeze–thaw than the 28 d specimen. After 225 freeze–thaw cycles, the water absorption rates of 1 d specimens were 1.95% and 1.64% in water and sulfate solution, respectively, while those of 28 d specimens were 2.20% and 1.83%. This indicates that freeze–thaw cycling has a greater effect on the pore structure of fully aged mortar than on early-age mortar (1 d). Therefore, MKPC mortar is suitable for the rapid repair of concrete structures in harsh environments. The results form a theoretical basis for winter emergency repair projects. They also further the understanding of the application of MKPC-based materials in extreme environments.

Influence of Atmospheric Conditions on Mechanical Properties of Polyamide with Different Content of Recycled Material in Selective Laser Sintering

The price of material is an important factor when selecting the additive polymer procedure. In selective laser sintering (SLS), the price can be reduced by the recycling of material, i.e., with different shares of original and recycled material, as well as by the orientation of the product during manufacturing. Numerous tests warn that orientation in the direction of z axis should be as low as possible to reduce the total price of the product. The product also has to satisfy the influence of atmospheric conditions to which it is exposed during its lifetime, i.e., UV radiation and humid environment. UV light, with sun being its most common source, and average humidity in different parts of the world can be approximately from 20% to 90%, depending on time, day and geographic location. In this work, the test specimens have been made of original, mixed and 100% recycled material and then exposed to the influences of UV radiation and water absorption. After having been exposed to atmospheric conditions for a longer time, the mechanical properties of the polyamide products made by selective laser sintering were tested. The results show that exposure to UV radiation reduces tensile elongation at all ratios of recycled material and orientation of 70-90% except in the z direction, while in flexural deformation it is the other way around. The effect of water was observed only between the 7th-14th day of absorption with a decrease in strength until the deformation did not change.

An Investigation of the Ground Walnut Shells' Addition Effect on the Properties of the Fly Ash-Based Geopolymer

The development of geopolymers is in line with the requirements of sustainable development. Creating a new type of material from various industrial and bio-based wastes and by-products can lead to reduced energy consumption, reduced waste generation, reduced global CO₂ emissions, as well as reduced resource extraction of natural resources. In this study, geopolymer composites based on class F fly ash with the addition of fine quartz sand and ground walnut shells used as a substitute for sand were examined. The study focused on investigating the effects of different weight percentages of ground walnut shells and quartz sand on the density and strength properties, including compressive and flexural strength, thermal conductivity, efflorescence formation, and water absorption of the fly ash-based geopolymer composites. The microstructure of the studied geopolymers was also analyzed using a scanning electron microscope (SEM). It was observed that the addition of ground walnut shells contributes to the decrease in density and mechanical properties, increase in absorption properties, and decrease in porosity of fly ash-based geopolymers. Furthermore, the addition of ground walnut shells allows for a significant reduction in efflorescence on the surface of the tested geopolymer composites. Moreover, partial or complete replacement of sand by ground walnut shells in geopolymer composites based on fly ash allows for a significant reduction in their thermal conductivity, which makes it possible to use these composites as insulation materials.

Experimental Study on the Mechanical Properties, Water Absorption, and Fiber Degradation of Naturally Aged Glass Fiber and Polypropylene Fiber-Reinforced Concrete

The main objective of this study is to better understand the performance changes of naturally aged glass fiber-reinforced concrete (GFRC) and polypropylene fiber-reinforced concrete (PPFRC), especially the degradation of fibers, which is of great significance for evaluating the durability of structures using these two types of composite materials. The mechanical properties, water absorption, and microstructures of GFRC and PPFRC at a curing age of three years, including their compressive strength, full curves of water absorption, fiber-matrix interaction, and fiber degradation, were systematically studied, and the related properties were compared with those at the curing age of 28 days. The degradation of fibers after freeze-thaw cycles was also studied. The results revealed the following. The water/binder ratio (w/b) affects the rate of increase of the long-term compressive strength of naturally aged concrete. In general, the water absorption of fiber-reinforced concrete (FRC) at the curing age of three years was found to be significantly reduced, but with the increases of w/b and the fiber content to the maximum values, the water absorption of the specimens cured for three years was higher than that of the specimens cured for 28 days. Moreover, with the increase of the curing age, the optimal glass fiber (GF) contents for reducing the water absorption decreased from 1.35% to 0.90% (w/b = 0.30), and from 0.90% to 0.45% (w/b = 0.35), respectively. The GF surface was degraded into continuous pits with diameters of about 200 to 600 nm, and the surface of the pits was attached with spherical granular C-S-H gel products with diameters of about 30 to 44 nm. The freeze-thaw cycles were found to have no significant effect on the pits on the GF surface and the granular C-S-H gel products attached to the pits, but caused a portion of the cement matrix covering the GF to fall off. The interfacial bonding between the polypropylene fiber (PPF) and the cement matrix exhibited almost no change in the PPFRC after three years of curing as compared with that after 28 days of curing. Furthermore, the cement hydration gel on the PPF surface was not significantly damaged by 150 freeze-thaw cycles.

Characterization and Performance Evaluation of Metakaolin-Based Geopolymer Foams Obtained by Adding Palm Olein as the Foam Stabilizer

Geopolymer foams with different pore structures can be used in construction, water treatment, and heavy metal adsorption. The preparation of high porosity geopolymer foams using vegetable oil as a foam stabilizer is a feasible and cost-effective route. In this study, metakaolin-based geopolymer foams with hierarchical pore structures were fabricated by adding H₂O₂ as the foaming agent with palm olein as the foam stabilizer. The effects of H₂O₂ and palm olein content on the chemical features and pore structure of geopolymer foams were evaluated. Water absorption, thermal conductivity, and mechanical behaviors of geopolymer foams were also investigated. The results indicate that fatty acid salt surfactants were generated in situ in the geopolymer matrix due to the addition of palm olein. Geopolymer foams with H₂O₂ and palm olein addition possess a homogeneously concentrated macropore distribution. Palm olein exhibits a refining effect on intrinsic pores formed by geopolymerization. In addition, using appropriate amounts of palm olein and H₂O₂, geopolymer foams can achieve higher open porosity and better pore connectivity, resulting in the improvement of water absorption and thermal insulation capacity.

Quantification of the Hardened Cement Paste Content in Fine Recycled Concrete Aggregates by Means of Salicylic Acid Dissolution

Adherent hardened cement paste attached to recycled concrete aggregates (RCA) generally presents a higher porosity than natural aggregates, which induces a lower porosity in the properties of RCA. The characterization of the adherent hardened cement paste content (HCPC) in the fine RCA would promote better applications of RCA in concrete, but the determination of HCPC in fine RCA is not well established. A simple method based on salicylic acid dissolution was specifically developed to quantify the HCPC in RCA, especially for RCA containing limestone aggregates. The results demonstrated that the soluble fraction in salicylic acid (SFSA) was equal to the HCPC for white cement and slightly lower for grey Portland cement, which was also confirmed by a theoretical approach using modelling the hydration of cement paste with the chemical equations and the stoichiometric ratios. The physical and mechanical properties of RCA (e.g., water absorption) were strongly correlated to the SFSA. For industrial RCA, SFSA did not give the exact value of HCPC, but it was sufficient to correlate HCPC with the other properties of RCA. The water absorption could be estimated with good accuracy for very fine RCA (laboratory-manufactured RCA or industrial RCA) by extrapolating the relationship between water absorption and HCPC, which is very important for concrete formulation.

Evaluation of Mechanical and Microstructural Properties and Global Warming Potential of Green Concrete with Wheat Straw Ash and Silica Fume

Cement and concrete are among the major contributors to CO₂ emissions in modern society. Researchers have been investigating the possibility of replacing cement with industrial waste in concrete production to reduce its environmental impact. Therefore, the focus of this paper is on the effective use of wheat straw ash (WSA) together with silica fume (SF) as a cement substitute to produce high-performance and sustainable concrete. Different binary and ternary mixes containing WSA and SF were investigated for their mechanical and microstructural properties and global warming potential (GWP). The current results indicated that the binary and ternary mixes containing, respectively, 20% WSA (WSA20) and 33% WSA together with 7% SF (WSA33SF7) exhibited higher strengths than that of control mix and other binary and ternary mixes. The comparative lower apparent porosity and water absorption values of WSA20 and WSA33SF7 among all mixes also validated the findings of their higher strength results. Moreover, SEM-EDS and FTIR analyses has revealed the presence of dense and compact microstructure, which are mostly caused by formation of high-density calcium silicate hydrate (C-S-H) and calcium hydroxide (C-H) phases in both blends. FTIR and TGA analyses also revealed a reduction in the portlandite phase in these mixes, causing densification of microstructures and pores. Additionally, N₂ adsorption isotherm analysis demonstrates that the pore structure of these mixes has been densified as evidenced by a reduction in intruded volume and a rise in BET surface area. Furthermore, both mixes had lower CO₂-eq intensity per MPa as compared to control, which indicates their significant impact on producing green concretes through their reduced GWPs. Thus, this research shows that WSA alone or its blend with SF can be considered as a source of revenue for the concrete industry for developing high-performance and sustainable concretes.

Suspended Multifunctional Nanocellulose as Additive for Mortars

Cellulose derivatives have found significant applications in composite materials, mainly because of the increased mechanical performance they ensure. When added to cement-based materials, either in the form of nanocrystals, nanofibrils or micro/nanofibers, cellulose acts on the mixture with fresh and hardened properties, affecting rheology, shrinkage, hydration, and the resulting mechanical properties, microstructure, and durability. Commercial cotton wool was selected as starting material to produce multifunctional nanocelluloses to test as additives for mortars. Cotton wool was oxidized to oxidized nanocellulose (ONC), a charged nanocellulose capable of electrostatic interaction, merging cellulose and nanoparticles properties. Oxidized nanocellulose (ONC) was further functionalized by a radical-based mechanism with glycidyl methacrylate (GMA) and with a mixture of GMA and the crosslinking agent ethylene glycol dimethacrylate (EGDMA) affording ONC-GMA and ONC-GMA-EGDMA, both multifunctional-charged nanocellulose merging cellulose and bound acrylates properties. In this work, only ONC was found to be properly suitable for suspension and addition to a commercial mortar to assess the variation in mechanical properties and water-mortar interactions as a consequence of the modified microstructure obtained. The addition of oxidized nanocellulose caused an alteration of mortar porosity, with a decreased percentage of porosity and pore size distribution shifted towards smaller pores, with a consequent increase in compressive resistance, decrease in water absorption coefficient, and increased percentage of micropores present in the material, indicating a potential improvement in mortar durability.

Experimental Study on High-Temperature Damage Repair of Concrete by Soybean Urease Induced Carbonate Precipitation

In this study, the effects of soybean-urease-induced carbonate precipitation on a high-temperature damage repair of concrete were explored. C50 concrete specimens were exposed to high temperatures from 300 to 600 °C, then cooled to an ambient temperature and repaired by two different methods. The influences of the damage temperature and repair methods on surface film thickness, average infrared temperature increase, water absorption, and compressive strength were investigated. Scanning electron microscopy (SEM) images were carried out to further study the mechanism involved. The results revealed that the white sediments on the surface of the repaired specimens were calcium carbonate (CaCO₃) and calcium oxalate (CaC₂O₄). The surface film thickness reached up to 1.94 mm after repair. The average infrared temperature increase in the repaired specimens at different damage temperatures was averagely reduced by about 80% compared with that before the repair. It showed more obvious repair effects at higher temperatures in water absorption and compressive strength tests; the compressive strength of repaired specimens was 194% higher than that before repairs at 600 °C. A negative pressure method was found to be more effective than an immersion method. This study revealed the utilization of SICP on repairing high-temperature damage of concrete is feasible theoretically.

Super-Adsorptive Biodegradable Hydrogel from Simply Treated Sugarcane Bagasse

There is a great demand for biodegradable hydrogel, and cellulose enriched wastes materials are widely used to serve this purpose for various advance applications (e.g., biomedical and environmental). Sugarcane bagasse is cellulose-enriched agro-waste, abundantly grown in Bangladesh. This study aimed to treat sugarcane bagasse-based agro-waste using a sustainable and ecofriendly approach to produce hydrogel with super-swelling capacity for adsorption of copper, chromium, iron ions, methylene blue and drimaren red dyes. To increase the swelling property of hydrogels, copolymerization of hydrophilic monomers is an effective technique. Therefore, this study aimed to prepare hydrogel via free radical graft-copolymerization reaction among acrylamide, methyl methacrylate and treated bagasse in the presence of N,N-methylene-bis-acrylamide as a crosslinker and potassium persulphate as an initiator. To obtain maximum yield, reaction conditions were optimized. It was found that hydrogel obtained from chemically treated sugarcane bagasse showed maximum water absorption capacity of 228.0 g/g, whereas untreated bagassebased hydrogel could absorb ~50 g/g of water. Maximum adsorption capacity of 247.0 mg/g was found for copper ion. In addition, organic pollutant removal from industrial effluent also showed good performance, removing >90% of methylene blue and 62% of drimaren red dye, with shorter kinetics. The biodegradability study showed that after 90 days of exposure, the hydrogels degraded to about 43% of their own mass. Therefore, the produced hydrogel could be an alternative adsorbent to remove pollutants and also for other potential applications.

Impact of Recycled Aggregate on the Mechanical and Environmental Properties of Concrete: A Review

This review aims to present and discuss the mechanical and environmental properties of two different type of recycled aggregates obtain from construction and demolition waste (CDW): (1) Recycled Concrete Aggregates (RCA) and (2) Mixed Recycled Aggregates (MRA). In addition, the properties of the concrete in the fresh (workability, water/cement ratio) and hardened state (mechanical and durability properties), as well as the environmental impact of the concrete produced with the two types of recycled aggregates, are presented and discussed. Due to the heterogeneous composition of recycled aggregates, the concrete properties can be significantly variable. The systematic review concerns scientific papers published from 2010 to 2020 and it shows the importance of the selection process in order to obtain high quality CDW as well as of the type of recycled aggregates on concrete properties. In particular, recycled concrete aggregates show a better quality and homogeneity than mixed recycled aggregates that make them more suitable for concrete. This work presents an overview on the influence of recycled aggregate quality on the physical, mechanical and environmental properties of concrete.

Improving Water-Absorption and Mechanical Strength: Lyotropic Liquid Crystalline-Based Spray Dressings as a Candidate Wound Management System

A spray dressing based on lyotropic liquid crystalline (LLC) with adjustable crystalline lattices was investigated in this study. It possesses water-triggering phase transition property and ease of spraying on wound, as well as stable drug encapsulation and controllable drug release. When it comes to wound with exudate, adequate water absorption and sustainable mechanical strength after water absorption was important for a good dressing, while most of the normal LLC dressings were still unable to meet such standards. Herein, a type of hyaluronic acid (HA)-incorporated LLC-based spray dressing (HLCSD) was developed to overcome the above limitations. After comparing HAs with different molecular weights (MWs) and concentrations, 3% HA with MW of 800~1000 kD was chosen as an ideal amount of excipients to add into the HLCSD. The water absorption of HLCSD precursor increased by 150% with the appearance of enlarged water channels. The complex modulus of HLCSD gel also increased from 1 to 100 kPa, which suggested lasting wound coverage and good patient compliance when used clinically. The spraying and phase transition properties of HLCSD was studied and showed acceptable changes. Moreover, good safety comparable with the commercial product Purilon® was also demonstrated in an in vivo acute skin irritation test. Thus, the improved HLCSD was a promising dressing for exudation wound treatment.

Technical Note: The impact of storage humidity on the response of reference-class ionization chambers

PURPOSE

A number of Farmer-type ionization chambers were tested against storage humidity to confirm whether they satisfied the criteria for the long-term stability of reference-class ionization chambers.

METHODS

The ionization chambers were stored for several months in an environment with relative humidity adjustable from 20 % to 80 %. The ionization chambers were removed from the storage environment at variable intervals ranging from 1 d to 70 d and irradiated in a Co-60 radiation beam. The responses for each ionization chamber were evaluated from the measured currents corrected for the atmospheric air density, and were compared with those predicted by the Co-60 half-life.

RESULTS

Certain ionization chambers gave a constant relative response regardless of the storage humidity, while the relative responses of two types of ionization chambers changed as a function of the storage humidity. The difference between the relative responses for the low (20 %∼30 %) and high (70 %∼80 %) storage relative humidity was ∼0.7 %. The response was larger for the high relative humidity storage. Immediately after the storage humidity changed, the relative response started to change by the day, and it took approximately 2 weeks to 2 months for the relative response to converge. For one type of the ionization chamber, the plastic outer wall and the outer electrode were replaced with those made of solid graphite, and it was confirmed that the remodeled ionization chamber did not exhibit the response change.

CONCLUSIONS

The present results and previous reports by other authors indicate that the magnitude of the change depends on the magnitude of the water absorption of the plastic used for the outer wall and/or the electrode of the ionization chamber. Thus, it is important in the selection of the reference-class ionization chamber to note the material and structure of the outer wall and electrode of the ionization chamber. If the ionization chamber has a hygroscopic wall and electrode and it is used as a reference ionization chamber, it is necessary to pay additional attention to the humidity difference for the storage, daily irradiation, and yearly calibration especially in regions with large seasonal humidity fluctuations. This article is protected by copyright. All rights reserved.

Experimental Investigation on the Influencing Factors of Compressive Strength of Foamed Lightweight Material Utilizing Completely Decomposed Granite

The utilization of construction waste soil to produce foamed concrete together with cement and a foaming agent is a promising method for waste recycling. Completely decomposed granite (CDG), which is widely available in southern China, was selected as a typical construction waste soil in foamed material production. The Taguchi method was applied to study the influence of various parameters on compressive strength, including cement dosage, CDG dosage, water to solid materials ratio (W/M), fine particles content, and gravel particles content. Analysis of variance (ANOVA) on a CDG-based sample showed that all factors have significant effects on compressive strength and the most effective parameter was cement dosage, followed in sequence by CDG dosage, W/M, gravel particles content, and fine particles content. However, only cement dosage and W/M influence the internal structure significantly during water/vacuum-immersion tests. The relationship between micro-pore structure and compressive strength suggested that with the decrease of open porosity, the compressive strength showed an increasing trend. This study reveals the possibility of CDG as a raw material for foamed lightweight soil and provides a technical reference of production procedure.

Comparative Reinforcement Effect of Achatina fulica Snail Shell Nanoparticles, Montmorillonite, and Kaolinite Nanoclay on the Mechanical and Physical Properties of Greenpoxy Biocomposite

This study investigated the comparative reinforcement effect of Achatina fulica snail shell nanoparticles, montmorillonite, and kaolinite nanoclay on greenpoxy. Greenpoxy nanocomposites of snail shell nanoparticles, montmorillonite, and kaolinite nanoclay were developed separately, with the nanofiller content ranging from 1 to 3% by weight. Specimens of the nanocomposites with different percentage weights of the nanoparticles were prepared using the resin casting method. Mechanical properties, such as the tensile strength, stiffness, hardness, and impact strength, and water absorption properties of the specimens were evaluated experimentally. It was observed that the incorporation of nanoparticles improved the mechanical properties of pure greenpoxy irrespective of the percentage weight, source, and type of reinforcement. Significantly, the loading of 1 wt.% of snail shell nanoparticles offered superior properties in most cases. Protein fibers and high-concentration calcium carbonate in snail shell nanoparticles, uniform dispersion, and excellent matrix/snail shell nanoparticle adhesion provided a strong structure, resulting in the high strength, stiffness, and decreased water uptake of the composites. The superior properties observed in snail shell nanoparticle composites suggest that this naturally sourced nanofiller can be used as a potential substitute for montmorillonite and kaolinite clays.

Cryodevices developed for minimum volume cooling vitrification of bovine oocytes

Unfertilized bovine oocytes can be efficiently cryopreserved only when an extremely rapid cooling rate (>20,000°C/min) is applied to oocytes with a very limited amount of surrounding vitrification solution. This protocol is defined as minimum volume cooling (MVC) vitrification. Various types of cryodevices, such as open pulled straw, Cryoloop, and Cryotop, have been developed to accelerate the cooling efficacy. Furthermore, hollow fibers with nano-scale pores, triangle nylon mesh sheets, and multilayer silk fibroin sheets have been optimized for the loading of large quantities of oocytes and/or the subsequent removal of excess vitrification solution, without requiring skillful operation to transfer individual oocytes using fine capillaries. This article provides an up-to-date review of cryodevices suitable for the MVC vitrification of bovine oocytes at the immature (germinal vesicle-) and mature (metaphase II-) stages.