Study on the corrosion behavior and mechanical response of weakly cemented sandstone in alkaline solutions.

This study examines the corrosion characteristics of weakly cemented sandstone under alkaline conditions, evaluating the effects of varying pH levels on its macroscopic degradation, micro-porosity, and mechanical properties, notably uniaxial compressive strength. Findings reveal that heightened alkalinity exacerbates rock damage, although a temporary alleviation in mass loss occurs between pH 9 and 11 due to pore clogging by complexes formed from cations like Ca2+ and Mg2+.Increased alkalinity induces marked changes in pore features, with an observed rise in pore numbers, transformation of pore shapes from elongated to more spherical, and adjustments in porosity, pore size, and roundness. Furthermore, the study confirms a decline in both the rock's compressive strength and elastic modulus as pH rises. These revelations shed light on the role of pH in the corrosion behavior of weakly cemented sandstone under alkaline conditions, providing a fresh perspective for understanding its corrosion mechanisms in such environments.

Rising Alkali-to-Acid Ratios in the Atmosphere May Correspond to Increased Aerosol Acidity.

Aerosol acidity (or pH) is one central parameter in determining the health, climate, and ecological effects of aerosols. While it is traditionally assumed that the long-term aerosol pH levels are determined by the relative abundances of atmospheric alkaline to acidic substances (referred to as RC/A hereinafter), we observed contrasting pH─RC/A trends at different sites globally, i.e., rising alkali-to-acid ratios in the atmosphere may unexpectedly lead to increased aerosol acidity. Here, we examined this apparently counterintuitive phenomenon using the multiphase buffer theory. We show that the aerosol water content (AWC) set a pH "baseline" as the peak buffer pH, while the RC/A and particle-phase chemical compositions determine the deviation of pH from this baseline within the buffer ranges. Therefore, contrasting long-term pH trends may emerge when RC/A increases while the AWC or nitrate fraction decreases, or vice versa. Our results provided a theoretical framework for a quantitative understanding of the response of aerosol pH to variations in SO2, NOx versus NH3, and dust emissions, offering broad applications in studies on aerosol pH and the associated environmental and health effects.

Hydrocyclone combines with alkali-thermal pretreatment to enhance short-chain fatty acids production from anaerobic fermentation of waste activated sludge.

The production of short-chain fatty acids (SCFAs) through anaerobic fermentation of waste activated sludge (WAS) is commonly constrained by limited substrate availability, particularly for WAS with low organic content. Combining the hydrocyclone (HC) selection with alkali-thermal (AT) pretreatment is a promising solution to address this limitation. The results indicated that HC selection modified the sludge properties by enhancing the ratio of mixed liquid volatile suspended solids (MLVSS)/mixed liquid suspended solids (MLSS) by 19.0% and decreasing the mean particle size by 17.4%, which were beneficial for the subsequent anaerobic fermentation process. Under the optimal HC + AT condition, the peak value of SCFAs production reached 4951.9 mg COD/L, representing a 23.2% increase compared to the raw sludge with only AT pretreatment. Mechanism investigations revealed such enhancement beyond mechanical separation. It involved an increase in bound extracellular polymeric substances (EPS) through HC selection and the disruption of sludge spatial structure by AT pretreatment. Consequently, this combination pretreatment accelerated the transfer of particulate organics (i.e., bound EPS and intracellular components) to the supernatant, thus increasing the accessibility of WAS substrate to hydrolytic and acidifying bacteria. Furthermore, the microbial structure was altered with the enrichment of key functional microorganisms, probably due to the facilitation of substrate biotransformation and product output. Meanwhile, the activity of hydrolases and SCFAs-forming enzymes increased, while that of methanogenic enzymes decreased. Overall, this strategy successfully enhanced SCFAs production from WAS while reducing the environmental risks of WAS disposal.

Estimating energy left in discarded alkaline batteries: Evaluating consumption and recovery opportunities.

Each year, a significant number of single-use alkaline batteries with untapped energy are discarded. This study aims to analyze the usage patterns of alkaline batteries based on a dataset of 1021 used batteries, ranging from Size AA to 9V, collected from households in the State of New York. We measure the energy loss resulting from underutilized batteries and examine the corresponding environmental and economic impacts on a national scale. Discarded AA alkaline batteries maintain about 13 % of their initial energy, that results in an estimated annual energy loss of 660 MWh for all AA alkaline batteries in the U.S., and about 40 MWh in New York State. Annually in the U.S., consumers discard AA alkaline batteries with approximately $80 million worth of unused energy, including $4.8 million in New York State alone. We also show that the lifecycle impact of batteries should be multiplied by 1.25 to account for their underutilization. To address these issues, we propose actionable recommendations for improving battery consumption practices and facilitating End-of-Life/Use (EoL/U) recovery processes. The findings show the need for policy interventions to better manage battery usage and disposal toward reducing energy waste and mitigating environmental impacts.

Solidification and utilization of municipal solid waste incineration ashes: Advancements in alkali-activated materials and stabilization techniques, a review.

Researchers are actively investigating methodologies for the detoxification and utilization of Municipal Solid Waste Incineration Bottom Ash (MSWIBA) and Fly Ash (MSWIFA), given their potential as alkali-activated materials (AAMs) with low energy consumption. Recent studies highlight that AAMs from MSWIFA and MSWIBA demonstrate significant durability in both acidic and alkaline environments. This article provides a comprehensive overview of the processes for producing MSWIFA and MSWIBA, evaluating innovative engineering stabilization techniques such as graphene nano-platelets and lightweight artificial cold-bonded aggregates, along with their respective advantages and limitations. Additionally, this review meticulously incorporates relevant reactions. Recommendations are also presented to guide future research endeavors aimed at refining these methodologies.

Alkalinity control in sludge propels the conversion of concrete slurry waste into micro- and nano-sized biogenic CaCO3.

The utilization of Bacillus sp. for the production of bio-CaCO3 in concrete crack repair and strength enhancement has attracted considerable attention. However, microbial-induced calcium carbonate precipitation (MICP) has yet to be explored as a precedent with activated sludge. Here calcium sourced from concrete slurry waste (CSW) and carbon from sludge microbial ß-oxidation under alkaline were used to generate micro/nano CaCO3. The results indicate that the main crystalline form of the generated precipitated particles is calcite, with a particle size ranging from 0.7 to 10 µm. Minimal heavy metals were found in the supernatant following settling. And at the optimum pH of 8.5-9, carbon capture reached 743 mg L-1, and CaCO3 production reached 1,191 mg L-1, and dominant phylum were Proteobacteria and Bacteroidota, with Thauera being a prevalent genus adept in ß-oxidation. Mass balance analysis showed that alkali promotes microbial ß-oxidation of organisms to produce CO2 and facilitate storage. Thus, the alkaline regulation of metabolism between microbe and CSW provides a novel way of sludge to initiate MICP.

Pectic polysaccharides from Tartary buckwheat sprouts: Effects of ultrasound-assisted Fenton treatment and mild alkali treatment on their physicochemical characteristics and biological functions.

Buckwheat sprouts are rich in pectic polysaccharides, which possess numerous health-improving benefits. However, the precise structure-activity relationship of pectic polysaccharides from Tartary buckwheat sprouts (TP) is still scant, which ultimately restricts their applications in the food industry. Hence, both ultrasound-assisted Fenton treatment (UAFT) and mild alkali treatment (MATT) were utilized for the modification of TP, and then the effects of physicochemical characteristics of original and modified TPs on their bioactivities were assessed. Our findings reveled that the UAFT treatment could precisely reduce TP's molecular weight, with the levels decreased from 8.191 × 104 Da to 0.957 × 104 Da. Meanwhile, the MATT treatment could precisely reduce TP's esterification degree, with the values decreased from 28.04 % to 4.72 %. Nevertheless, both UAFT and MATT treatments had limited effects on the backbone and branched chain of TP. Moreover, our findings unveiled that the UAFT treatment could notably promote TP's antioxidant, antiglycation, and immunostimulatory effects, while remarkedly reduce TP's anti-hyperlipidemic effect, which were probably owing to that the UAFT treatment obviously reduced TP's molecular weight. Additionally, the MATT treatment could also promote TP's immunostimulatory effect, which was probably attributed to that the MATT treatment significantly decreased TP's esterification degree. Interestingly, the MATT treatment could regulate TP's antioxidant and antiglycation effects, which was probably attributed to that the MATT treatment simultaneously reduced its esterification degree and bound phenolics. Our findings are conducive to understanding TP's structure-activity relationship, and can afford a scientific theoretical basis for the development of functional or healthy products based on TPs. Besides, the UAFT treatment can be a promising approach for the modification of TP to improve its biological functions.

A sequential approach of alkali enzymatic extraction of dietary fiber from rice bran: Effects on structural, thermal, crystalline properties, and food application.

Rice bran is abundant in dietary fiber and is often referred to as the seventh nutrient, recognized for its numerous health benefits. The objective of the current study is to investigate the extraction of both soluble and insoluble dietary fiber from defatted rice bran (DRB) using an alkali-enzymatic treatment through response surface methodology. The independent variables like substrate percentage (5-30 %), enzyme concentration (1-50 µL/g), and treatment time (2-12 h) and dependent variables were the yield of soluble and insoluble DF. The highest extraction yield was observed with alkali enzyme concentration (50 µL/g) treatment, resulting in 2 % SDF and 59.5 % IDF at 24 h of extraction. The results indicate that cellulase-AC enzyme aids in the hydrolysis of higher polysaccharides, leading to structural alterations in DRB and an increase in DF yield. Furthermore, the disruption of intra-molecular hydrogen bonding between oligosaccharides and the starch matrix helps to increase in DF yield, was also confirmed through FTIR and SEM. The extracted DF soluble and insoluble was then used to develop rice porridge. Sensory evaluation using fuzzy logic analysis reported the highest scores for samples containing 0.5 % insoluble DF and 1.25 % soluble DF.

Effect of environmental factors on adsorption of ciprofloxacin from wastewater by microwave alkali modified fly ash.

Antibiotics, as emerging persistent pollutants, pose significant threats to human health. The effective and low-cost removal of ciprofloxacin (CIP) from wastewater has become an important research focus. In this study, fly ash (FA) was used as the raw material, and modified fly ash (MFA) was prepared by varying microwave power, alkali concentration, and immersion time to investigate its adsorption characteristics for CIP. Results showed that the optimal preparation conditions for MFA with the most effective adsorption of CIP, using the Box-Behnken response surface methodology, were a microwave power of 480 W, an alkali concentration of 1.5 mol/L, and a modification time of 3 h. Scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction analyses revealed that after modification, the glassy structure of FA is destroyed, the specific surface area is increased, and obvious hydroxyl O-H absorption peaks appear. Both FA and MFA exhibited adsorption processes for CIP that conformed to pseudo-second-order kinetics and the Langmuir equation. Maximum adsorption of CIP (9.61 and 12.67 mg/g) was achieved at pH = 6. With increasing temperature, the adsorption capacity of both FA and MFA for CIP decreased, indicating an exothermic process. The adsorption capacity of CIP decreased with increasing ion concentration, with the impact order of ions being Al3+ > Ca2+ > Na+. The results show that pore filling, electrostatic interaction, ion exchange and complexation are the main ways of CIP adsorption by FA. Microwave alkali modified fly ash is an economical and efficient adsorbent for CIP removal in water, realizing the purpose of "treating waste with waste". This study provides a scientific basis for controlling CIP treatment in wastewater.

Efficient fabrication of cellulose polymer networks via alkaline swelling strategy for wood bonding.

Existing issues with bio-based adhesives, such as complex preparation processes, high energy consumption, and production costs, still need to be addressed. In our study, APTES was grafted onto microcrystalline cellulose (MCC) to generate active aminated cellulose, and then reacted with the epoxide group in glycerol triglycidyl ether (GTE) through a swelling strategy under alkaline solvent, forming a network structure via covalent cross-linking. The adhesive exhibits superior bonding performance and water-resistant property in the bonding strength test of poplar plywood, with a dry shear strength of 2.40 MPa, a wet shear strength of 2.16 MPa after soaking in 63 °C hot water, and a wet shear strength of 1.79 MPa after soaking in boiling water. In terms of cost calculation, the theoretical production cost of AC-GTE adhesive is calculated to be 5303.7 RMB per ton, which is comparable to that of phenol-formaldehyde (PF) resin and other petrochemical-based adhesives, and significantly lower than that of isocyanate-based adhesives. These research results can provide a practical example for producing high-efficiency, aldehyde-free, and low-cost bio-based adhesives.

Crucial effect of ovomucin on alkali-induced egg white gel formation: Properties, structure and facilitation mechanism.

Alkali-induced preserved egg gel formation is a dynamic process that involves complex protein changes. Ovomucin (OVM) is closely associated with the gel properties of egg white. In this study, the effect of OVM in alkali-induced egg white gel (AEWG) formation was investigated. The results suggested that OVM reduced the gel formation time by 15 %. The mechanical properties of the fully formed gel were also improved by OVM. Specifically, OVM increased the storage modulus (G') of the gel by 1.5-fold, while the hardness significantly increased from 78.90 ± 4.24 g to 99.80 ± 9.23 g. Low-field nuclear magnetic resonance (LF-NMR) demonstrated that OVM significantly shortened T23 relaxation time and reduced the water mobility, thus increasing the water holding capacity (WHC). Meanwhile, the presence of OVM resulted in a more homogeneous and denser microscopic morphology of the gel. Selective solubility experiments revealed that disulfide bonds are the primary force in gel formation. OVM promoted the formation of more disulfide bonds, which increased the strength and stability of the gel network. Overall, this research proved OVM plays a critical role in the performance improvement of AEWG, which provides a new insight into the quality control of preserved egg and protein gel foods.

Vermicompost and flue gas desulfurization gypsum addition to saline-alkali soil decreases nitrogen losses and enhances nitrogen storage capacity by lowering sodium concentration and alkalinity.

Saline-alkali soils have poor N storage capacity, high N loss and inadequate nutrient supply potential, which are the main limiting factors for crop yields. Vermicompost can increase organic nutrient content, improve soil structure, and enhance microbial activity and function, and the Ca2+ in flue gas desulfurization (FGD) gypsum can replace Na+ and neutralize alkalinity in saline-alkali soils though chemical improvement. This study aimed to determine if vermicompost and FGD gypsum addition could improve the N storage capacity through decreasing NH3 volatilization and 15N/NO3- leaching from saline-alkali soils. The results indicate that the combined application of vermicompost and FGD gypsum led to the displacement and leaching Na+ in the upper soil layer (0-10 cm), as well as the neutralization of HCO3- by the reaction with Ca2+. This treatment also improved soil organic matter content and macroaggregate structure. Also, these amendments significantly increased the abundance of nifH and amoA genes, while concurrently decreasing the abundance of nirK gene. The structural improvements and the lowering of Na + concentration in and alkalinity decreased cumulative NH3 volatilization, and leaching of 15N and NO3- to the deep soil layer (20-30 cm). FGD gypsum increased the 15N stocks and inorganic N stocks of saline-alkali soil, whereas vermicompost not only increased the 15N and inorganic N stocks, but also increased the total N stocks, the combination of vermicompost and FGD gypsum can not only increase the available N storage capacity, but also enhance the potential for N supply. Therefore, vermicompost and FGD gypsum decrease N loss and increase N storage capacity through structural improvement, and lowering of Na+ concentration and alkalinity, which is crucial for improving the productivity of saline-alkali soil.

Saline-alkali soil amended with biochar derived from maricultural-solid-waste: Ameliorative effect and mechanism.

At present, it is estimated that approximately 800 million hectares of arable land worldwide is saline-alkali soil, which has become one of the major limiting factors restricting global agricultural productivity. Meanwhile, the residual food and excreta of mariculture animals, accompanied by potential eutrophication pollution, remain an unresolved issue due to salinity. In this study, the ameliorative effects of biochar (BC700) prepared from maricultural-solid-waste on the biological properties and physicochemical of saline-alkali soil and Salicornia europaea L growth were investigated. Supplements of 1, 3 and 5% BC700 significantly increased the total nitrogen, available phosphorus, available potassium and organic carbon in soil by 2.00-68.30%, 26.74-64.96%, 7.74-52.53% and 3.43-64.96%, respectively. And BC700 significantly reduced soil pH. This occurred with enhanced soil urease, sucrase and alkaline phosphatase activities and alterations to the bacterial community structure, thus improving P and N cycling and the soil physicochemical properties. In addition, BC700 has weakened the competition between saline soil microorganisms and also changed the key species of microbial networks. Co-utilization of BC700 and S. europaea cultivation could increase the stability of the soil microbial community while the growth of the plant was significantly promoted by 19.8-25.4%. Supplements of 3% BC700 are recommended as an eco-friendly and effective treatment for the recycling of mariculture wastes for the improvement of saline-alkali soils.

Environmental assessment of alkali-activated materials based on agro-industrial waste as alkaline activators through leaching tests.

Global circular economy drives the development of sustainable alkali activated materials (AAM) for use as construction material from industrial by-products and wastes. The assessment of the potentially hazardous substances release of these new material combinations into the soil and groundwater over time is essential. In this study, the aim is the environmental assessment of three AAMs based on blast furnace slag (BFS), activated with almond shell biomass ash (ABA) as potassium source and three solid sources of silica from the agricultural industry, rice husk ash (RHA), spent diatomaceous earth (SDE) and bamboo leaf ash (BLA), using European horizontal leaching tests proposed for construction materials, for monolithic form, Dynamic Surface Leaching Test (DSLT) and for granular form, Up-flow Percolation Test and the Compliance leaching test, by simulating different scenarios of their entire life cycle. The leaching results of the AAM showed the effectiveness of the inertization of all the recycled materials studied, which exceeded some inert materials limits, by means of the activation process. Despite the absence of significant differences in the leaching mechanisms of the oxyanions As, Cr, Mo, Sb, Se and V between the three AAMs developed, they presented different long-term leaching behavior depending on their form, monolithic, or granular, and therefore in their different life cycle stages. Therefore, it is concluded that although the incorporation of agro-industrial waste as alternative activators in BFS based AAM according to the Dutch Soil Quality Decree (for unrestricted use of monolithic and granular materials) is an environmentally acceptable option, the design of waste derived AAMs should be assessed by means of a combination of leaching tests that cover their expected life cycle.

Combined alkali-photocatalytic stimulation enables click microbial domestication for boosted ammonia nitrogen removal.

Microbe-driven ammonia nitrogen removal plays a crucial role in the nitrogen cycle and wastewater treatment. However, the rational methods and mechanisms for boosting nitrogen conversion through microbial domestication are still limited. Herein, a combined alkali-photocatalytic stimulation strategy was developed to activate the Halomonas shizuishanensis DWK9 for efficient ammonia nitrogen removal. The strain DWK9 selected from saline-alkaline soil in Northwestern China possessed strong resistance to stress of saline-alkaline environment and free radicals, and was abundant in nitrogen conversion genes, thus is an ideal model for advanced microbial domestication. Bacterial in the combined alkali-photocatalytic stimulation group achieved a high ammonia nitrogen conversion rate of 67.5 %, 10 times outperforming the non-stimulated and single alkali/photocatalytic stimulation control groups. Morphology analysis revealed that the bacteria in the alkali-photocatalytic stimulated group formed a favorable structure for bioelectric transfer. Remarkably, the domesticated bacteria demonstrated improved electrochemical properties, including increased current capacity and lower overpotentials and impedance. Prokaryotic transcription genetic analysis together with qPCR analysis showed upregulation of denitrification-related metabolic pathway genes. A novel FAD dependent and NAD(P)H independent energy mode has been proposed. The universality and effectiveness of the as-developed combined alkali-photocatalytic microbial domestication strategy were further validated through indicator fish survival experiments. This work provides unprecedented degrees of freedom for the exploration of rational microbial engineering for optimized and controllable biogeochemical conversion.

Exploring alkali-treated corn cob for high-rate removal of NOX and SO2 from flue gas: Focus on carbon release capacity, removal performance, and comparison with conventional carbon sources.

This investigation explored the potential of utilizing alkali-treated corn cob (CC) as a solid carbon source to improve NOX and SO2 removal from flue gas. Leaching experiments unveiled a hierarchy of chemical oxygen demand release capacity: 0.03 mol/L alkali-treated CC > 0.02 mol/L > 0.01 mol/L > 0.005 mol/L > control. In NOX and SO2 removal experiments, as the inlet NOX concentration rose from 300 to 1000 mg/m3, the average NOX removal efficiency increased from 58.56 % to 80.00 %. Conversely, SO2 removal efficiency decreased from 99.96 % to 91.05 %, but swiftly rebounded to 98.56 % by day 18. The accumulation of N intermediates (NH4+, NO3-, NO2-) increased with escalating inlet NOX concentration, while the accumulation of S intermediates (SO42-, SO32-, S0) varied based on shifts in the population of functional bacteria. The elevation in inlet NOX concentration stimulated the growth of denitrifying bacteria, enhancing NOX removal efficiency. Concurrently, the population of nitrate-reducing sulfur-oxidizing bacteria and sulfate-reducing bacteria expanded, aiding in the accumulation of S0 and the removal of SO2. The comparison experiments on carbon sources confirmed the comparable NOX and SO2 removal efficiencies of alkali-treated CC and glucose, yet underscored differences in intermediates accumulation due to distinct genus structures.

Enhanced anaerobic digestion of waste-activated sludge by thermal-alkali pretreatment: a pilot-scale study.

The composition of waste-activated sludge (WAS) is complex, containing a large amount of harmful substances, which pose a threat to the environment and human health. The reduction and resource utilization of sludge has become a development demand in sludge treatment and disposal. Based on the technical bottlenecks in the practical application of direct anaerobic digestion technology, this study adopted two different thermal and thermal-alkali hydrolysis technologies to pretreat sludge. A pilot-scale experiment was conducted to investigate the experimental conditions, parameters, and effects of two hydrolysis technologies. This study showed that the optimal hydrolysis temperature was 70 °C, the hydrolysis effect and pH can reach equilibrium with the hydrolysis retention time was 4-8 h, and the optimal alkali concentration range was 0.0125-0.015 kg NaOH/kg dry-sludge. Thermal-alkali combination treatment greatly improved the performance of methane production, the addition of NaOH increased methane yield by 31.2% than that of 70 °C thermal hydrolysis. The average energy consumption is 75 kWh/m3 80% water-content sludge during the experiment. This study provides a better pretreatment strategy for exploring efficient anaerobic digestion treatment technologies suitable for southern characteristic sewage sludge.

Facilely Fabricated Single-Site Ptδ+-O(OH)x- Species Associated with Alkali on Zirconia Exhibiting Superior Catalytic Oxidation Reactivity.

Fabrication of robust isolated atom catalysts has been a research hotspot in the environment catalysis field for the removal of various contaminants, but there are still challenges in improving the reactivity and stability. Herein, through facile doping alkali metals in Pt catalyst on zirconia (Pt-Na/ZrO2), the atomically dispersed Ptδ+-O(OH)x- associated with alkali metal via oxygen bridge was successfully fabricated. This novel catalyst presented remarkably higher CO and hydrocarbon (HCs: C3H8, C7H8, C3H6, and CH4) oxidation activity than its counterpart (Pt/ZrO2). Systematically direct and solid evidence from experiments and density functional theory calculations demonstrated that the fabricated electron-rich Ptδ+-O(OH)x- related to Na species rather than the original Ptδ+-O(OH)x-, serving as the catalytically active species, can readily react with CO adsorbed on Ptδ+ to produce CO2 with significantly decreasing energy barrier in the rate-determining step from 1.97 to 0.93 eV. Additionally, owing to the strongly adsorbed and activated water by Na species, those fabricated single-site Ptδ+-O(OH)x- linked by Na species could be easily regenerated during the oxidation reaction, thus considerably boosting its oxidation reactivity and durability. Such facile construction of the alkali ion-linked active hydroxyl group was also realized by Li and K modification which could guide to the design of efficient catalysts for the removal of CO and HCs from industrial exhaust.

Alkali-activated geopolymers based on calcined phosphate sludges and metakaolin.

The extraction of phosphorite ore in Tunisia has resulted in the discharge of substantial amounts of phosphatic sludge into the region's water system. To mitigate this environmental issue and prevent heavy metal leaching, a geopolymerization process was employed using two types of Tunisian calcined phosphate sludges (Cal-PS1 and Cal-PS2) as substitutes for alkali-activated metakaolin. This study aimed to investigate and compare the physical and mechanical properties of the resulting geopolymers. The optimal substitution ratio of metakaolin with calcined phosphate sludge was determined to be 1.5, equivalent to 20 wt.% of calcined phosphate sludge. Compressive strength tests conducted after 28 days of curing revealed values of 37 MPa for Cal-PS1 specimens and 28 MPa for Cal-PS2 geopolymers while compressive strength of geopolymers soaked in water for 28 days showed a decrease with the addition of phosphate sludges. The specific surface areas of Cal-PS1 geopolymers ranged from 16.3 to 16.9 m2/g and from 17.62 to 18.73 m2/g for Cal-PS2 specimens exhibiting a mesoporous structure. The elasticity modulus of the geopolymers was found to increase with the increase of the apparent density of geopolymers and with the sludges content but it tended to be lower than the Portland cement elasticity modulus. Leaching test was conducted to evaluate the potential environmental applications of the geopolymers. This test demonstrated effective containment of heavy metals within the geopolymers' network, except for low levels of arsenic.

Development of innovative alkali activated paste reinforced with polyethylene fibers for concrete crack repair.

Concrete structures are susceptible to cracking, which can compromise their integrity and durability. Repairing them with ordinary Portland cement (OPC) paste causes shrinkage cracks to appear in the repaired surface. Alkali-activated binders offer a promising solution for repairing such cracks. This study aims to develop an alkali-activated paste (AAP) and investigate its effectiveness in repairing concrete cracks. AAPs, featuring varying percentages (0.5%, 0.75%, 1%, 1.25%, 1.5%, and 1.75%) of polyethylene (PE) fibers, are found to exhibit characteristics such as strain hardening, multiple plane cracking in tension and flexure tests, and stress-strain softening in compression tests. AAP without PE fibers experienced catastrophic failure in tension and flexure, preventing the determination of its stress-strain relationship. Notably, AAPs with 1.25% PE fibers demonstrated the highest tensile and flexural strength, exceeding that of 0.5% PE fiber reinforced AAP by 100% in tension and 70% in flexure. While 1% PE fibers resulted in the highest compressive strength, surpassing AAP without fibers by 17%. To evaluate the repair performance of AAP, OPC cubes were cast with pre-formed cracks. These cracks were induced by placing steel plates during casting and were designed to be full and half-length with widths of 1.5 mm and 3 mm. AAP both with and without PE fibers led to a substantial improvement in compressive strength, reducing the initial strength loss of 30%-50% before repair to a diminished range of 2%-20% post-repair. The impact of PE fiber content on the compressive strength of repaired OPC cube is marginal, providing more flexibility in using AAP with any fiber percentage while still achieving effective concrete crack repair. Considering economic and environmental factors, along with observed mechanical enhancements, AAPs show promising potential for widespread use in concrete repair and related applications, contributing valuable insights to the field of sustainable construction materials.