Search Results (13)

Utilizing recycled aggregates (RAs) in concrete production represents a promising path toward sustainability; however, it often results in reduced physical and durability properties. The weak interfacial transition zone (ITZ) and the adhered mortar in recycled aggregate concrete (RAC) contribute to lower mechanical strength and limit its application in demanding environments. This study investigates an accelerated carbonation technique to enhance the mechanical and durability properties of RA and RAC. Recycled aggregates, with a particle size of 10–20 mm, were subjected to carbonation at 1 bar for 2 h in a controlled carbonation chamber. Results demonstrate substantial improvements in the compressive and split tensile strengths of the carbonated recycled aggregate concrete (CRAC), with increases of 30% and 42% compared to conventional RAC, respectively. The CRAC mix also exhibited a 1.5% increase in dry density and reduced water absorption (6%) compared to RAC (7.58%). After 90 days of acid exposure, compressive strength reductions of 48.85% and 37.9% were observed for RAC and CRAC mixes, respectively, from their 28-day strength, while weight loss in CRAC was limited to 5.4%, compared to 10.92% in RAC. In sulfate exposure tests over 150 days, RAC and CRAC showed compressive strength reductions of 31.4% and 19.7% and weight losses of 3.6% and 2.2%, respectively, indicating enhanced resistance of CRAC to harsh environments. However, CRAC blended with supplementary cementitious materials (SCMs) showed diminished mechanical properties, likely due to a reduced alkaline environment caused by rapid calcium hydroxide absorption in RA pores during carbonation. Overall, the findings highlight the practical potential of accelerated carbonation to improve the performance of RAC, offering a viable pathway for sustainable construction applications. Full article

In current times, the diminishing reserves of petroleum, increased energy consumption across various sectors, and their consequential environmental impact have become apparent. Consequently, it is necessary to develop sustainable and eco-friendly energy sources to meet growing demands. The article aimed to blend castor and neem oils (in a 50:50 ratio) to rectify the drawbacks present in castor biodiesel such as elevated kinematic viscosity and density. Response surface methodology was used to study the optimization of the two-step biodiesel production process through the use of a central composite design (CCD). For the esterification step, a methanol-to-oil molar ratio of 7.5:1, 1.75 wt.% of H₂SO₄, and a temperature of 55 °C were optimal. In the transesterification step, optimized conditions included a methanol-to-oil molar ratio of 9:1, 2.50 wt.% of calcium oxide, a temperature of 55 °C, and a stirring speed of 900 rpm, resulting in a 93% yield of methyl ester. Different properties of produced biodiesel were examined using the standard values provided by EN 14214 and ASTM D6751. The production of biodiesel from a mixture of castor and neem oils did not have any adverse impacts on food security. Full article

In recent years, the synthesis of ammonia (NH₃) has been developed by electrocatalytic technology that is a potential way to effectively replace the Haber–Bosch process, which is an industrial synthesis of NH₃. Industrial ammonia has caused a series of problems for the population and environment. In the face of sustainable green synthesis methods, the advantages of electrocatalytic nitrogen reduction for synthesis of NH₃ in aqueous media have attracted a great amount of attention from researchers. This review summarizes the recent progress on the highly efficient electrocatalysts based on 2D non-metallic nanomaterial and provides a brief overview of the synthesis principle of electrocatalysis and the performance measurement indicators of electrocatalysts. Moreover, the current development of N₂ reduction reaction (NRR) electrocatalyst is discussed and prospected. Full article

Concrete is the most widely used construction material. However, it cannot sustain the harsh environment and can easily deteriorate. It results in repair and reworks that amount to a considerable loss of money and time. The life span of concrete reduces if exposed to external attacks, for instance, sulfate attacks, alkali-silica reactions, corrosion, and drying shrinkage. These ubiquitous attacks cause a reduction in service life and raise the need for early repair and maintenance, resulting in higher life cycle costs and structural failures. To resolve these issues, the potential of styrene-butadiene-rubber (SBR) ultrafine powder as cement replacement polymeric admixture at 0%, 3%, 5%, 7%, and 10% have been evaluated. The effect of SBR-powder on concrete is investigated by conducting an alkali-silica reactivity test (ASR), rapid-chloride-permeability test (RCPT), drying shrinkage, and sulfate resistivity tests. Workability, compressive and flexural strength tests are also conducted. For ASR and drying shrinkage, mortar bar samples were cast, exposed to respective environments, and the percentage change in length was measured. For mechanical tests and RCPT, prisms, cylinders and cubes were cast and tested at 28 days. The SBR-powder modification reduces concrete’s permeability, drying shrinkage, and expansions due to ASR and sulfate attacks. SBR powder increased workability by 90%, compressive strength by 23%, and flexural strength by 9.4% in concrete when used at 10% cement replacement by weight. The SBR-powder (10%) modification reduced the RCPT value by up to one-third (67%), drying shrinkage by 53%, ASR by 57%, and sulfate reaction by 73%. Consequently, SBR powder usage can adequately improve the workability, mechanical properties, and durability of the concrete and lead to advanced sustainable concrete with low repair requirements. Full article

In recent times, the applications of fiber-reinforced recycled aggregate concrete (FRAC) in practical engineering have gained greater popularity due to its superior mechanical strength and fracture properties. To apply FRAC in buildings and other infrastructures, a thorough understanding of its residual mechanical properties and durability after exposure to fire is highly important. According to the established research, the properties and volume fractions of reinforcing fiber materials, replacement levels of recycled concrete aggregate (RCA), and heating condition would affect the thermal–mechanical properties of FRAC. This review paper aims to present a thorough and updated review of the mechanical performance at an elevated temperature and post-fire durability of FRAC reinforced with various types of fiber material, specifically steel fiber (SF), polypropylene (PP) fiber, and basalt fiber (BF). More explicitly, in this review article the residual mechanical properties of FRAC, such as compressive strength, splitting tensile capacity, modulus of elasticity, mass loss, spalling, and durability after exposure to elevated temperatures, are discussed. Furthermore, this study also encompasses the relationship among the dosages of fibers, replacement levels of recycled aggregate, and the relative residual mechanical properties of FRAC that would help in the optimum selection of the fiber content. Conclusively, this study elaborately reviews and summarizes the relevant and recent literature on recycled aggregate concrete containing SF, PP fiber, and BF. The study further provides a realistic comparison of these fibers in terms of the residual mechanical performance and durability of FRAC that would help in their future enhancements and applications in practical engineering. Full article

Flexural strength of concrete is an important property, especially for pavements. Concrete with higher flexural strength has fewer cracking and durability issues. Researchers use different materials, including fibers, polymers, and admixtures, to increase the flexural strength of concrete. Silicon carbide and tungsten carbide are some of the hardest materials on earth. In this research, the mechanical properties of carbide concrete composites were investigated. The silicon carbide and tungsten carbide at different percentages (1%, 2%, 3%, and 4%) by weight of cement along with hybrid silicon carbide and tungsten carbide (2% and 4%) were used to produce eleven mixes of concrete composites. The mechanical tests, including a compressive strength test and flexural strength test, along with the rapid chloride permeability test (RCPT), were conducted. It was concluded that mechanical properties were enhanced by increasing the percentages of both individual and hybrid carbides. The compressive strength was increased by 17% using 4% tungsten carbide, while flexural strength was increased by 39% at 4% tungsten carbide. The significant effect of carbides on flexural strength was also corroborated by ANOVA analysis. The improvement in flexural strength makes both carbides desirable for use in concrete pavement. Additionally, the permeability, the leading cause of durability issues, was reduced considerably by using tungsten carbide. It was concluded that both carbides provide promising results by enhancing the mechanical properties of concrete and are compatible with concrete to produce composites. Full article

Amid the COVID-19 pandemic, a sudden surge in the production and utilization of disposable, single-use facial masks has been observed. Delinquency in proper disposal of used facial masks endangers the environment with a new form of non-biodegradable plastic waste that will take hundreds of years to break down. Therefore, there is an urgent need for the resourceful recycling of such waste in an environmentally friendly way. This study presents an efficient solution by using waste masks in fibered or crushed form to produce environmentally friendly and affordable green concrete. This investigation assessed the mechanical and durability properties of waste masks-incorporated concrete. A total of six mixes were prepared for standardized tests to determine compressive strength, split cylinder tensile strength and rapid chloride penetration test (RCPT), and freeze-thaw resistance. The percentage of mask fibers used were 0.5, 1, 1.5, and 2% of concrete by volume, while crushed masks were used at 0.5% only. The mask waste in both forms was found suitable to be used in concrete. One percent of waste mask fibers was found as an optimum value to increase compressive and tensile strength, reduce chloride permeability, and increase freeze-thaw resistance. Besides this, 0.5% crushed mask fiber also performed well, especially for producing less permeable and highly durable concrete. It is thus corroborated that waste masks that increase pollution worldwide can be utilized sustainably to help build green buildings. By reutilizing waste masks to produce improved concrete with better strengths and higher durability, circular economy and sustainability are achieved, along with efficient waste management. Full article

The omnipresence of risk prevails in almost every aspect of human life. Individuals and societal factors are pivotal in the decision-making process to judge acceptability and tolerability of risk. Tolerability of risk (ToR) is characterized by dynamism pinned in the process of decision making that helps to gauge the society and individual’s risk. The energy transition implies switching the energy system from fossil fuels or any traditional mechanism to modern renewable sources that are sustainable. The energy transition is paramount important in the current global energy system to attain sustainable goals for organizations. This study used the positivism research paradigm to address the research questions. The quantitative approach helps to examine the cause-and-effect relationship. It also helps to collect systematic information to meet the objectives of the research. A total sample of 300 was selected for the data collection from renewable energy companies. The study used positivism research philosophy applied deductive approach. The data is analyzed through PLS-SEM. It is summarized that the scale of risk acceptability and tolerability in Pakistan is moderate which encourages companies to work progressively and increases sociocultural activities to make society a partner of this new shift in energy transition that will ultimately increase the level of risk acceptability. Nevertheless, as a society, people are neither high-risk takers nor risk avoiders due to income constraints, macroeconomic uncertainty, and political instability. Full article

For the production of geopolymer concrete (GPC), fly-ash (FA) like waste material has been effectively utilized by various researchers. In this paper, the soft computing techniques known as gene expression programming (GEP) are executed to deliver an empirical equation to estimate the compressive strength $f_c^{\prime }$ of GPC made by employing FA. To build a model, a consistent, extensive and reliable data base is compiled through a detailed review of the published research. The compiled data set is comprised of 298 $f_c^{\prime }$ experimental results. The utmost dominant parameters are counted as explanatory variables, in other words, the extra water added as percent FA ($\%E_W$), the percentage of plasticizer ($\%P$), the initial curing temperature ($T$), the age of the specimen ($A$), the curing duration ($t$), the fine aggregate to total aggregate ratio ($F/A_G$), the percentage of total aggregate by volume ($\%A_G$), the percent SiO₂ solids to water ratio ($\% S/W$) in sodium silicate (Na₂SiO₃) solution, the NaOH solution molarity ($M$), the activator or alkali to FA ratio ($A_L/F_A$), the sodium oxide (Na₂O) to water ratio ($N/W$) for preparing Na₂SiO₃ solution, and the Na₂SiO₃ to NaOH ratio ($N_s/N_o$). A GEP empirical equation is proposed to estimate the $f_c^{\prime }$ of GPC made with FA. The accuracy, generalization, and prediction capability of the proposed model was evaluated by performing parametric analysis, applying statistical checks, and then compared with non-linear and linear regression equations. Full article

Machine learning techniques are widely used algorithms for predicting the mechanical properties of concrete. This study is based on the comparison of algorithms between individuals and ensemble approaches, such as bagging. Optimization for bagging is done by making 20 sub-models to depict the accurate one. Variables like cement content, fine and coarse aggregate, water, binder-to-water ratio, fly-ash, and superplasticizer are used for modeling. Model performance is evaluated by various statistical indicators like mean absolute error (MAE), mean square error (MSE), and root mean square error (RMSE). Individual algorithms show a moderate bias result. However, the ensemble model gives a better result with R² = 0.911 compared to the decision tree (DT) and gene expression programming (GEP). K-fold cross-validation confirms the model’s accuracy and is done by R², MAE, MSE, and RMSE. Statistical checks reveal that the decision tree with ensemble provides 25%, 121%, and 49% enhancement for errors like MAE, MSE, and RMSE between the target and outcome response. Full article

The complication linked with the prediction of the ultimate capacity of concrete-filled steel tubes (CFST) short circular columns reveals a need for conducting an in-depth structural behavioral analyses of this member subjected to axial-load only. The distinguishing feature of gene expression programming (GEP) has been utilized for establishing a prediction model for the axial behavior of long CFST. The proposed equation correlates the ultimate axial capacity of long circular CFST with depth, thickness, yield strength of steel, the compressive strength of concrete and the length of the CFST, without need for conducting any expensive and laborious experiments. A comprehensive CFST short circular column under an axial load was obtained from extensive literature to build the proposed models, and subsequently implemented for verification purposes. This model consists of extensive database literature and is comprised of 227 data samples. External validations were carried out using several statistical criteria recommended by researchers. The developed GEP model demonstrated superior performance to the available design methods for AS5100.6, EC4, AISC, BS, DBJ and AIJ design codes. The proposed design equations can be reliably used for pre-design purposes—or may be used as a fast check for deterministic solutions. Full article

Carbon nanotubes (CNTs) and graphite nanoplatelets (GNPs) belong to the family of graphite nanomaterials (GNMs) and are promising candidates for enhancing properties of cementitious matrix. However, the problem lies with their improper dispersion. In this paper graphite nanoplatelets are used with carbon nanotubes for dispersion facilitation of CNTs in cement mortar. The intended role is to use the GNPs particles for dispersion of CNTs and to investigate the synergistic effect of resulting nano-intruded mortar. Mechanical properties such as flexure and compressive strength have been studied along with volumetric stability, rheology, and workability. Varying dosages of CNTs to GNPs have been formulated and were analyzed. The hybrid use of CNTs-GNPs shows promise. Scanning electron microscopy reveals that hybrid CNTs/GNPs are well-suited for use in cement mortar composite performing a dual function. Full article

To find an effective alternative to scarce, high-cost noble platinum (Pt) electrocatalyst for hydrogen evolution reaction (HER), researchers are pursuing inexpensive and highly efficient materials as an electrocatalyst for large scale practical application. Layered transition metal dichalcogenides (TMDCs) are promising candidates for durable HER catalysts due to their cost-effective, highly active edges and Earth-abundant elements to replace Pt electrocatalysts. Herein, we design an active, stable earth-abundant TMDCs based catalyst, WS_(1−x)Se_x nanoparticles-decorated onto a 3D porous graphene/Ni foam. The WS_(1−x)Se_x/graphene/NF catalyst exhibits fast hydrogen evolution kinetics with a moderate overpotential of ~−93 mV to drive a current density of 10 mA cm⁻², a small Tafel slope of ~51 mV dec⁻¹, and a long cycling lifespan more than 20 h in 0.5 M sulfuric acid, which is much better than WS₂/NF and WS₂/graphene/NF catalysts. Our outcomes enabled a way to utilize the TMDCs decorated graphene and precious-metal-free electrocatalyst as mechanically robust and electrically conductive catalyst materials. Full article