The sulphur amino acids methionine (Met) and cysteine (Cys) and their derivative taurine (Tau) are metabolically active molecules with interlinked roles in nutritional requirements. Deficiencies in these nutrients are linked to poor growth and health; however, the impacts of these deficiencies on organ structure and function are largely unknown. This study examined the effects of dietary Met, Cys and Tau fed at different levels on yellowtail kingfish (YTK) liver histology and surface colour, plasma biochemistry and posterior intestine histology. Samples were collected from two dose–response feeding trials that quantified (1) the Tau requirement and sparing effect of Met by feeding YTK diets containing one of seven levels of Tau at one of two levels of Met and (2) the Met requirement and sparing effect of Cys by feeding YTK diets containing one of five levels of Met at one of two levels of Cys. YTK fed inadequate levels of dietary Met, Cys and Tau exhibited thicker bile ducts, less red livers, more intestinal acidic goblet cell mucus and supranuclear vacuoles and less posterior intestinal absorptive surface area. Further, thicker bile ducts correlated with less red livers , whereas increased hepatic fat correlated with a liver yellowing (b*). Our results indicate a shift towards histological properties and functions indicative of improved intrahepatic biliary condition, posterior intestinal nutrient absorption and homoeostasis of YTK fed adequate amounts of Met, Cys and Tau. These findings may assist in formulating aquafeed for optimised gastrointestinal and liver functions and maintaining good health in YTK. Fishmeal in aquafeed formulations for carnivorous fish can be progressively replaced using a nutrient-based approach in which dietary proteins that may lack essential nutrients are balanced with crystalline and synthetic nutrients to meet the dietary requirements of the species. Although these proteins are more sustainable and economically viable, the efficient production of healthy fish requires the quantification of the obligatory dietary requirements and measurements on the capacity for metabolic bioconversions in target species. Further, nutrient-based formulations carry the risk of over- or undersupplying essential dietary nutrients, especially when the species-specific nutrient requirements are unknown.Seriola lalandi; hereafter referred to as YTK) is a carnivorous fish farmed for its high-quality white meat and increased demands, in tandem with the limited supply of marketable quantities, have led to an increased interest in YTK feeds. Previous research has demonstrated inferior growth, feed efficiency and pathological conditions in YTK fed sub- and supra-optimal levels of the sulphur amino acids (SAA’s) methionine (Met), cysteine (Cys) and also taurine (Tau) in low-fishmeal diets. Such conditions included small white spots and green patches on the liver, cataracts and enteritis–4.Yellowtail kingfish  requirement for the transsulphuration of Met to Cys in various fish species,9–11. Although Cys is a semi-essential amino acid in aquafeeds, the intracellular availability of Cys remains critical for the fitness of animals, forming substrate for the de novo synthesis of glutathione, pyruvate, inorganic sulphur, CoA and Tau–14. However, excess dietary Cys impairs growth, while excess injected Cys in fish causes mortality in a manner that is similar to excess in Met,16. A high level of Cys has also been shown to induce pathological liver conditions in rats,18.In fish, Met deficiencies are associated with an increase in retinal degeneration, bilateral cataract, non-infectious enteritis, inflammatory cell invasion, widening of the lamina propria and hepatocyte necrosis and atrophy,20. In fish, Tau contributes to the maintenance of physiological homoeostasis by (1) conjugating with bile acid, emulsifying ingested lipids in the intestine; (2) conjugating with bilirubin to form ditaurobilirubin, eliminating the toxic by-products of heme breakdown through bile,23; (3) regulating glucose metabolism and (4) osmoregulating and stabilising the membranes of erythrocytes. Tau supplementation to a plant protein-based diet ameliorated gut inflammatory markers and apoptosis in the European seabass intestine and reduced the signs of green liver syndrome in Japanese yellowtail (S. quinqueradiata) fed a zero-fishmeal diet. Both studies indicated beneficial effects of Tau in fish; however, information on single and interactive effects of dietary Met, Cys and Tau on fish intestinal and hepatic health is still limited,28,29.In animals, the hepatic transsulphuration and decarboxylation of Met and Cys produce Tau, an amino sulphonic acid, which is considered semi-essential in fishet al. established that the Tau requirement in YTK can be satisfied by sufficient dietary Met, inferring that Tau is conditionally dispensable. Follow-up experimentation further quantified the minimum obligatory Met requirement, the TSAA requirement and Cys sparing capacity for Met to meet the TSAA requirement in juvenile YTK. YTK fed sub- and supra-optimal levels of SAA exhibited poor feed conversion ratios and specific growth rates, but it was only at sub-optimal levels of SAA that YTK developed clinical signs of cataracts. The dietary Met, Cys and Tau appear to play critical roles in the metabolic pathways of carnivorous fish to maintain good health, sustained growth and resistance to environmental stressors, including pathogens. Nevertheless, knowledge of the effects of dietary Met, Cys and Tau on clinical pathology and adverse posterior intestinal and hepatic changes are, to our knowledge, limited in YTK.Candebat ,30,31. A comprehensive quantitative histological and biochemical dataset will provide reference values for fish and would serve not only as a diagnostic tool for clinical symptoms but also as a biomarker to identify adequate dietary level of SAA that may optimise physiological and histological conditions.Overall, deficiencies in essential amino acids are recognised to impair growth in fish, yet knowledge on the extensiveness of their physiological functions and metabolic interrelatedness are still being investigated. Histomorphometric and histochemical measurements of fish organs and tissues can elucidate the modifying effects of dietary amino acids on inflammatory, immune, digestive, homoeostatic stability, compositional and metabolic functionset al.,19, and determine the extent to which replete, deficient or in excess combinations of dietary Met, Cys and Tau may alter function.The aim of this study is to observe the homoeostatic, metabolic, protective, digestive and absorptive properties of the systems to evaluate the health status of YTK, derived from the requirement studies published by Candebat , and were conducted at the Port Stephens Fisheries Institute, NSW, Australia.All experiments were performed under the NSW DPI Fisheries Animal Care and Ethics Research Authority, known as ‘Aquaculture Nutrition ACEC 93/5–Port Stephens’,19 were collected to investigate the effects of different dietary Met, Cys and Tau levels on liver histology, posterior intestine histology, blood plasma biochemistry and liver surface colour in juvenile YTK. Detailed descriptions of experimental design, diet formulation and manufacture, experimental facilities and procedures are presented in Candebat et al. and Candebat et al..Samples from two separately conducted feeding trialset al. will be referred to as TauMet study and diets annotated with T + M. Briefly, the objective of the TauMet study was to quantify the Tau requirement in juvenile YTK at a Met content that either met or exceeded current industry practice (11 g Met/kg diet). For that purpose, a factorial dose–response approach was applied, using seven incremental levels of Tau, ranging from 1·6 to 20·4 g/kg diet, crossed with either one of two levels of dietary Met (10·9 g/kg diet or 17·2 g/kg diet) at one constant Cys level (mean: 5·9 (sem 0·2) g/kg diet; sem 0·4) g/fish). After 7 weeks, tissue samples from fish (n ≥ 6) from all fourteen feeding treatments were collected, all of which were analysed for liver surface colour and plasma biochemical analysis, and of which selected dietary treatments of YTK were analysed for liver and posterior intestine histology. Please refer to Throughout the present study, the first feeding trial by Candebat et al. is referred to as the MetCys study, and the diets are annotated with M + C, whereas the commercial diet is annotated as Com. The objective of the MetCys study was to quantify the dietary Met requirements at Cys levels that met or exceeded industry practice. Again, a factorial dose–response approach was applied, using five levels of Met, ranging from 7·9 to 25·2 g/kg, combined with either one of two levels of dietary Cys (5·6 or 13·9 g/kg) at one constant Tau level (7·0 (sem 0·03) g/kg; sem 1·0) g/fish). After 8 weeks, the posterior intestines of six individual fish fed one of four diets, which contained the lowest or highest amount of Met and/or Cys, were collected . In addition, posterior intestines from six individual fish fed a commercial diet were collected for histological analysis °C), salinity (33·3 (se 4·6) %), dissolved oxygen (7·0 (se 1·0) mg/l), pH (8·3 (se 0·5) and TAN (0·7 (se 0·4) mg/l). For the MetCys investigation, the parameters were temperature (21·2 (se 0·6)°C), salinity (32·9 (se 3·2) %), dissolved oxygen (12·1 (se 3·0) mg/l), pH (7·4 (se 0·4)) and TAN (≤ 0·25 mg/l).Fish used in this study were the progeny of wild-caught YTK brood stock held at the Port Stephens Fisheries Institute hatchery. Juvenile YTK were fed a commercial floating pellet  and maintained at 15–19°C before experiment stocking. Throughout the feeding trials, fixed photoperiods of 12 light: 12 dark (TauMet study) and 11 light: 13 dark (MetCys study) were maintained, using dimmable, overhead LED lamps and simulating natural photoperiods of the season. Water quality parameters were monitored daily (mean) for the TauMet study: temperature  and centrifuged (LabCo®Mini Centrifuge) at 113 × 100 rpm for 14 min. Following centrifugation, the blood plasma was collected and pooled per experiment tank and frozen at −20°C until further biochemical analysis. The livers from the same six fish were removed and photographed under standardised light conditions for the digital liver surface colour analysis . Additionally, liver and posterior intestinal samples were collected from an additional six to eight fish fed diets T + M 1, 3, 4, 7, 8, 10, 11 and 14, after euthanising with the recommended dose of Aqui-S®  and transferred to 10 % buffered formalin for histological analysis.After the TauMet feeding trial, YTK were fasted for 24 h, and all fourteen YTK of each tank were individually measured for total length, whole body, fillet, viscera, liver and intraperitoneal fat weight. Six randomly selected fish per feeding treatment were euthanised by a spike to the brain, followed by immediate blood sampling. Approximately 1 ml of blood was collected from the caudal vein, using a 5 ml syringe and a 19 g × 38 mm gauge needle (Terumo). Collected blood was then rapidly transferred into lithium heparin-coated tubes (MiniCollectn 30) were sampled for posterior intestines and transferred in 10 % buffered formalin for histological analysis.After the MetCys feeding trial, YTK were fasted for 24 h and euthanised as above. Four initial fish, subsampled at the commencement of the trial, and twelve YTK from each replicate tank at the conclusion of the trial were individually measured for total length, whole body, viscera and liver weight. The posterior intestines of the four initial fish and six of the twelve measured fish fed the diets M + C 1, 2, 3, 4 and Com  and embedded in paraffin (HistoCore Arcadia C & H Embedding Center Leica Microsystems Pty Ltd) according to the standard histological procedure. Subsequently, samples were cut into ∼4 µM sections with a rotary microtome  and mounted onto glass slides for histological staining.. Prior to the data collection, histology slides of the posterior intestine and liver were scanned at 40× magnification using an automated slide-scanning system . Aperio ImageScope software (Leica Biosystems) was used to visualise and measure the stained organs.Slides were stained with either haematoxylin–eosin, a combination of Alcian blue  and periodic acid-Schiff (PAS) or toluidine blue and followed a slightly adjusted staining protocols by the James Cook University Veterinary Pathology Department. The pH of the AB stain was 2·5 to stain most of the acid goblet cell mucus. Livers were stained with haematoxylin–eosin for semi-quantitative and quantitative morphometric and cytological evaluations. Posterior intestines were stained with AB-PAS for histomorphometric and histochemical evaluation of structures and the joint detection of neutral , acid  and mixed  goblet cell mucus. Additionally, sections of posterior intestines were stained with toluidine blue; however, mast cells were not detected2/area) per liver section (2/area), respectively  and R Studio v.4.0., using the R packages car, carData, ggplot2, ggpubr, multcompView, plyr and PMCMRplus. All dependent variables from the TauMet and MetCys study were subjected to two-way ANOVA to examine the effect of seven dietary Tau levels at each of two dietary Met levels (TauMet study) or five dietary Met levels at each of two dietary Cys levels (MetCys study). Prior to statistical analysis, dependent variables were validated for assumptions of (1) normality via Shapiro–Wilk test and (2) homogeneity of variance via Levene’s test. If assumptions were not met, dependent variables were log, sqrt, ln and inverse transformed. Further, dependent variables were assessed for the assumptions of (3) linearity with covariates including body weight and VA and (4) homogeneity of regression slopes between treatments. If assumptions 3 and 4 were met, dependent variables were subjected to two-way ANCOVA to control for the influence of the covariate . All dietary treatment means within the feeding trial were compared via Tukey honestly significant difference (HSD) post hoc test in the event of a significant interaction. Similarly, in the event of no significant interaction but significant main factor effects, the respective factor level means were compared using Tukey HSD post hoc testP < 0·05. Pearson’s correlation coefficients between liver colour values and TDW thickness, fattiness, plasma cholesterol and TAG were calculated using Excel.An abbreviation list on the measured responses can be found in et al.. Before image acquisition, livers were visually assessed for whole or partial green discolouration. Images of eighty-four ex vivo YTK liver (TauMet study) were taken under standardised light and object orientation conditions. All images were captured using a digital SLR camera (Sony ILCE-6300) with a 16 mm lens and fixed settings of ISO-250, 1/13 s shutter speed, a focal length of 20 mm and aperture ƒ/6·3. Livers were carefully patted dry with paper towels before being placed individually on an 18 % grey card background  inside a 290 × 450 mm closed photo box. The camera was placed in a slot at the top of the photo box, creating a perpendicular distance of 250 mm between the camera and liver samples. The photo box was made of white polypropylene, and the walls served as a diffuser to minimise the glare of lighting. The container was illuminated with 2 × 11 W white LED lights (Mirabella) placed 20 cm outside the longitudinal walls of the photo box. Additionally, the images were taken in a dark room, away from daylight, to standardise the lighting conditions. The colour assessment methodology applied to YTK liver was adapted from Weller & Westneat and van Belleghem et al..Image acquisition methods were adapted from Trampel .Average liver colour, liver colour composition and colour distance of individual YTK liver samples (TauMet study) were assessed. Image backgrounds, blood vessels on the liver and glare were removed to reduce bias from these artifacts. Liver images were compared via RStudio v.4.0. (colour distance package) by distinguishing colour intensity and relative proportion of red, green, blue (RGB) metrics, followed by colour distance calculations to quantify the degree of similarity or dissimilarity between two imagesColour distance values were plotted using a principal coordinate analysis (PCoA) graph, visualising dissimilarity by distance and similarity by clustering. This was achieved via RStudio v.4.0., using the R packages ggrepel, devtools, colordistance, ComplexHeatmap, splitstackshape, readxl, ggpubr and cowplot.. Three areas of each liver were selected (46·441 (se 897) pixels/area and 51·2 (se 0·8) colours/area) to provide information on RGB and distribution. The average colour of ex vivo livers was assessed via Adobe Photoshop 2021 by applying a blur filter on the extracted liver areas and calculating the average value in CIE Lab , RGB  and HSB . The average colour was then sampled with the Photoshop eyedropper tool.The colour composition of each liver was assessed using ImageJ software with the 3D Color Inspector/colour histogram pluginse 0·4) per 94 µm2) than YTK fed Met levels above current industry practice (5·05 (se 1·5) per 94 µm2). Cytoplasm eosinophilia in hepatocytes was most pronounced in YTK fed diet T + M 3 at 14·5 (se 1·3) per 94 µm2 and was on average higher in YTK fed dietary Met at 10·9 g/kg; however, dietary Met and Tau did interact. Various hepatocytes also exhibited marginated chromatin, which was most pronounced in YTK fed diet T + M 4 (13·6 (se 1·6) per 94 µm2); however, there were no significant differences among treatments.Overall, the histological appearance of the livers was normal relative to that of farmed fish, with fatty livers and irregularities being minor in all treatments. Dietary Tau and Met did not statistically affect the score of the semi-quantitative fattiness measurement; however, quantitative measurements of the BDW thickness, necrotic hepatocytes, cytoplasmic eosinophilia and large nuclei in hepatocytes were all modulated by diet . YTK fedPlasma from YTK in this study had in comparison a mild elevation to depression of plasma biochemical parameters . Further. Feeding dietary Met at 17·2 g/kg resulted in significantly higher red (R) and blue (B) values of liver surface colour compared with feeding Met levels at 10·9 Met/kg , r®® and brightness (B) values were dependent on dietary Tau and Met . The a* 9 Met/kg ; Table 4The average colour of the liver surface, as indicated by the hex code, of each T + M diet was distinct . HoweverThe colour distance between the individual liver surface colours ranged from 0 to 1 in a heatmap, and the conversion into a PCoA distribution indicates the colour distance between the T + M diets , identifWeak to strong relationships between liver surface colour and liver histology and plasma biochemistry were found . The BDW2) and lamina epithelial. Each 4 µm thick section of the intestine had between 68 and 137 villi  that ranged from 3·9 to 5·6 mm in length (VL). The villi were complex, branching into several villus tips.The posterior intestinal wall of YTK (250–327 g) ranged from 1 to 1·5 mm thick . The intHistomorphometric measurements were tested for possible effects of body weight and VA before being subjected to two-way ANOVA. However, relationships violated linearity and were not statistically significant; thus, data were not controlled. Exceptions were the measured lamina epithelial and LPA, which strongly correlated with the VA and met assumptions to adjust means for VA via two-way ANCOVA. YTK fed the diets T + M 8, 11 and 14 exhibited increased PIC, total villus height, VL, VA, lamina epithelial surface, TIW and MI thickness, whereas YTK fed less dietary Tau and Met (e.g. diet T + M 1) had less intestinal surface area, for example, PIC, total villus height, VL, TIW and MI. However, YTK fed less dietary Tau had more villi, in which number decreased when YTK were fed more dietary Tau. The intestinal mucosa did not exhibit necrosis or acute inflammation. Nevertheless, the VA-controlled LPA were responsive to dietary Met and Tau. Overall, YTK fed dietary Met at 17·2 g/kg exhibited greater LPA, which may indicate increased lymphocytes, macrophages and eosinophilic granule cell accumulations. The histochemical analysis of the posterior intestine revealed three types of mucus from goblet cells that stained: acidic, neutral and mixed . The posThe total goblet cell mucus production was most pronounced in fish fed the T + M 7 diet, exhibiting the greatest total goblet cell density TGC/VA; ; Table 7se 1·45) µm), there were also smaller bullet-shaped S-PAS+ bodies situated in the apical areas of the enterocytes with an average size of 18·36 (se 0·68) µm (se 0·007) per µm2). YTK had supranuclear vacuoles that were also situated in the apical cytoplasm of enterocytes in the lamina epithelial and were on average 21·4 (se 1·08) µm. The supranuclear vacuoles density in YTK fed the T + M diets was significantly affected by interacting dietary Tau and Met, where fish fed the T + M 1 diet exhibited an exceptionally higher supranuclear vacuole density (0·055 (se 0·004) per µm2) than other T + M diets.Besides larger goblet cells that stained PAS+ (41·4 (2). Each intestinal cross-section (4 µm) contained between 64 and 124 villi  that ranged from 4·1 to 4·9 mm in length (VL) and exhibited multiple tips, which contributes to a greater complexity and surface area.Overall, the posterior intestines appeared clinically inconspicuous. The posterior intestinal wall of YTK (140–230 g) was between 1 and 1·3 mm thick . The micHistomorphometric measurements from the MetCys study were tested for possible effects of body weight and VA before being subjected to two-way ANOVA to test for Met and Cys effects on the dependent variables. However, relationships mostly violated linearity and were not statistically significant; thus, data were not controlled. Exceptions were the lamina epithelial and LPA, which strongly correlated with the VA and met assumptions to adjust means for VA via two-way ANCOVA., had the longest villi, thickest MI, more villi in the posterior intestine and increased lamina epithelial area, indicating more complex villi and greater absorptive surface area. In comparison, YTK fed diet M + C 1, in which Met and Cys content were below that of the TSAA and MOM requirement, had the least villi in the posterior intestine, less lamina epithelial area and shorter villi, yet the thickest intestinal wall, whereas YTK that were fed the high dietary Cys series, M + C 3 and 4, had significantly shorter villi, decreased villi height, thinner intestinal walls, the least lamina epithelial surface and VA.YTK fed the M + C 2 diet, which was closest to meeting the average minimum obligatory methionine requirement (14·3 g/kg) and the TSAA (Met) requirement (26·2 g/kg) at 5·9 g Cys/kg in YTKse 654) µm), TIW (716 (se 13) µm), MI (261 (se 5) µm) and S (275 (se 5) µm). YTK fed the Com or M + C diets and sampled after 8 weeks had comparatively thicker PIC, TIW, MI, stratum granulosum and stratum compactum indicating histomorphometric changes in the posterior intestine that may have been induced substantially through growth and ontogenic changes.YTK sampled at the start of the MetCys feeding trial had substantially thinner PIC (28 551 (se 0·022) per µm2 and 0·264 (se 0·041) per µm2). Overall, YTK fed M + C and commercial diets exhibited considerably lower S-PAS+ and higher supranuclear vacuoles densities than YTK fed the T + M diets  . The his M diets .,19. However, information on the liver and posterior intestine condition of juvenile YTK fed sub-optimal, optimal and supra-optimal combinations of Met, Cys and Tau remains unknown. This study provides primary data on the Met, Cys and Tau altering effects on the plasma biochemistry and functional and structural properties of hepatic and intestinal tissues, demonstrating that adequate intakes of Met, Cys and Tau can improve nutrient assimilation capacity and help to maintain homoeostasis. Diets T + M 11 and M + C 2 came closest to the Met, Cys and Tau specifications to meet YTK requirements for optimised growth, feed efficiency and protein retention,19. As a reference, a level of 24·5 g Met+Cys/kg was recommended for YTK diets, provided that 7·7 g Tau/kg, at least 14·3 g Met/kg and no more than 13·9 g Cys/kg were supplied,19.The TSAA, minimum obligatory Met and Tau requirements of juvenile YTK have recently been quantified based on indices such as optimised growth, feed efficiency and protein retention,42. Tau may have alleviated the symptoms of BDW thickening by conjugating with hydrophilic bile acids that are less cytotoxic and that stimulate secretin hydrocholeresis–46. Dietary Met supplementation may have increased the production of S-adenosyl Met, known to improve conditions of chronic liver diseases, and Tau,48.To our knowledge, this is the first study to observe that higher levels of dietary Tau led to significantly thinner TDW in fish. In mice and humans, intrahepatic TDW thickening and proliferation are a negative property that is linked to bile acid-induced inflammation, fibrosis and necrosis of cholangiocytes and hepatocytes with consequential reductions in biliary flow. Biochemical blood plasma parameters were dependent on diet-induced Tau and Met changes, which were slightly either increased or decreased when fed sub-optimal levels of dietary Met and Tau compared with the reference ranges of healthy YTK. Overall, blood plasma lipid concentrations were up to 4 times lower than the suggested reference ranges for YTK ,  and Japanese yellowtail  . However, the deviation from the latter communications may be due to differences in fat contents of fed diets, fish size or other factors. YTK fed dietary Met at 17·2 g/kg showed increases in plasma TAG contents, which is coherent with results reported for rats, where Met restrictions altered lipogenesis and decreased circulating lipid levels. Additionally, YTK fed diets containing Met levels at 17·2 g/kg exhibited higher AST and LD activity, which are pathological markers for cell damage when exceeding reference range thresholds and correlate with findings of increased necrotic hepatocytes. However, in the absence of reference ranges or indication of pathology, elevated levels of these enzymes may indicate their activity level in the plasma rather than liberation from cell lysis. This is consistent with Liu et al., who found elevated LD for the fastest growing YTK in their study, consistent with its role in energetics. Likewise, the elevated AST levels for fish fed higher levels of Met found in our study are likely due to altered amino acid metabolism rather than pathology. LD is a glycolytic enzyme critical for fish burst swimming capacity and directly linked to metabolic rate. Met is metabolised to cystathionine, which can form α-ketoglutarate, which is transaminated by AST to glutamate.Blood plasma biochemistry was compared with results from reference ranges on sick, subclinical and healthy YTK plasma biochemistry subjectively described the colour of ‘normal’ liver as red to light red and fatty liver as ‘coffee with cream’ in largemouth bass  and redbreast sunfish (Lepomis auritus). In contrast, Brusle and Anadon described the colour of ‘normal’ fish liver as red–brown and fatty liver as yellow. The liver surface colour of YTK fed the T + M diets was bluer, greener and 16 % lighter than the hex colour ‘dark red’ (#AB2328), which is subjectively classified as a ‘normal’ liver by Brusle and Anadon and Schmitt and Dethloff.Schmitt and Dethloff. The digital assessment of broiler liver surface colour linked lightness to a carbohydrate-rich diet, whereas a darkening was linked to feeding less fat, more Met or fasting animals for 12 h. YTK from this study had more cholesterol and TAG in blood plasma when fed the higher Met diets (17·2 g/kg) but interestingly not a higher fattiness score in their liver. The subjective and semi-quantitative hepatic fattiness scoring may not have been sensitive enough to capture dietary Met effects; however, hepatic fat positively correlated with the yellow–blue channel (b*), indicating that increased hepatic fat made the liver surface colour appear more yellow.Previously, the subjective assessment of zebrafish linked liver surface colour lightness to hepatic TAG accumulations,57. A thickening of the intrahepatic TDW may indicate a compromised export of breakdown and bile products and may consequently alter the liver surface colour. Further research is warranted, but to our knowledge, the present study is the first to establish a link between liver surface colour and Tau-dependent BDW thickness. The liver surface colours of YTK fed diets T + M 3 and T + M 4, which contained sufficient dietary Tau to meet the requirement at a Met content of 11 g/kg, were up to 21 % more red (a* = 34·2 and 34·0) than YTK fed any other T + M diet. YTK fed the T + M 11 diet, which was closest to meeting the TSAA requirement and met the Tau requirement, had the reddest yet brightest liver surface colour throughout all treatments. This suggests that YTK fed dietary Tau and Met close to the requirement had better liver conditions, assuming that redder livers are necessarily healthier livers. The accuracy of a subjective colour scoring system for fish liver remains questionable: firstly, because relationships between objective, quantitative histology and macroscopic colour scores have not been established, and secondly because the subjective judgement relies on the observer’s perception of colour. At this stage, subjective colour assessments may serve as a simple clinical tool when underlying health conditions present in strong colour variations. More subtle colour changes may not be visible to the naked eye, whereas standardised instruments may overcome this issue.Interestingly, the intrahepatic BDW thickness correlated with the liver surface colour, where thickness was significantly affected by dietary Tau. YTK fed T + M 7 and 14, which contained the maximum inclusion of dietary Tau (20·4 and 20·0 g/kg) and YTK fed T + M 1, which contained the least amount of dietary Tau, had the thinnest BDW. Yet only YTK fed T + M indicated the least red and bright livers (hex colour: B86948). Bile ducts are responsible for the transport of bile, which is comprised of water, bile salt, conjugated bilirubin (yellow), cholesterol, lecithin and inorganic substances from the hepatocytes into the intestine for digestion and waste removalet al. in YTK and Takagi et al. in red seabream. Japanese Yellowtail, red seabream (Pagrus major), and Totoaba  fed low-fishmeal diets deficient in Tau exhibited accumulated biliverdin and bilirubin in the liver due to increased haemolysis and insufficient conjugation with Tau for the excretion into the biliary system,27,59–61. However, YTK fed a Tau and Met deficient diet (T + M 1 diet) had no signs of green liver discolourations, indicating that Tau deficiencies may not cause green liver syndrome but might exacerbate previous conditions. This finding is similar to YTK that were fed soya protein concentrate based diets low in Tau, Met and lysine, yet had no green liver, whereas YTK fed a 100 % rapeseed oil-based diet and reared at 18°C had green livers. However, dietary Tau content in the experimental diets was not presented in that study. Interestingly, in the cases where low Tau correlated with green liver, the fish were often exposed to low temperatures (12·3–18·0°C) and/or fed alternative protein sources, indicating that low water temperature may contribute to green liver, including in Japanese yellowtail, red seabream and YTK. In poikilothermic frogs and salmon, hyperthermia increases haemolysis, increasing the biliverdin production, yet it reduces the biliverdin reductase, decreasing biliverdin (green) removal. This may lead to an accumulation of hepatic biliverdin and subsequently a green discolouration. YTK from this study were held at 23·3 (se 0·6)°C, which may be within the thermal tolerance to maintain a healthy balance between production and removal of haematogenous pigments. Japanese yellowtail held at 23·9 (se 2·0)°C and fed non-fishmeal diets had green liver due to mucosporozoa infestations that blocked the biliary system, indicating that the diet possibly made the fish susceptible to infestation. Overall, it appears that the green liver condition in fish may be induced by distinct physiological mechanisms that are triggered by a single factor or an interplay of factors such as imbalanced diet, toxicity, pathogens and water temperature.In our study, YTK livers did not exhibit segmental or diffuse green discolourations as previously described by Bowyer ,67,68, in this study the submucosa of YTK was not affected by either dietary Met or Tau. Adequate dietary Met can down-regulate pro-inflammatory and up-regulate anti-inflammatory cytokine mRNA levels. In Atlantic salmon, soya protein-based diets induced inflammatory responses and consequently increased stratum compactum/submucosal thickness. Interestingly, with an incremental increase in both dietary Met and Tau, the unaffected submucosa was reflected by a marked expansion rather than a reduction in the lamina propria. This observation is different from what one would expect. Expansion of the submucosa and lamina propria by immune cell infiltration usually coincides–73, but the expansion may also result from the lamina propria’s and stratum granulosum’s division by the stratum compactum, about which immune cell exchange is little known.Although it is widely recognised that dietary Tau and Met supplementation may be of benefit for fish health and growth. Overall, adequate dietary Tau and Met left the submucosa unaffected, yet simultaneously not the lamina propria. The reason behind this effect is unclear, and further research is warranted to understand the intestinal immune cell exchange and infiltration.Moreover, it is possible that the observed expansion of the lamina propria is not the product of an increased immune cell infiltration but may also be related to its additional role as circulatory system for nutrients and blood–77. The posterior intestine is often exposed to a higher bacterial load and has been shown to contain more acidic goblet cell mucus that is protective against pathogens,78. However, lipids and proteinogenic amino acids may be unavailable for absorption until reaching the posterior intestine and therefore, the posterior intestine may, to a certain extent, have goblet cell mucus that assists with the nutrient assimilation.Goblet cell mucus is divided into two pH types. Acidic mucus (AB+/blue) is suggested to form a barrier against pathogens, resisting degradation of bacterial glycosidase activity and limiting bacterial translocation by increasing viscoelasticity. Neutral mucus (PAS+/magenta) forms a physical barrier that promotes digestion and neutralises digestive juices, protecting the lamina epithelial from autodigestion. However, unlike our study, that study defined neutral and mixed goblet cells mucus as neutral. The anterior intestine of uninfected brown trout  had predominately neutral goblet cell mucus, whereas Cyathocephalus truncates-infected brown trout had 4 times more acid goblet cell mucus (43/villus) than neutral goblet cell mucus (10/villus), which is similar to the YTK from our study exhibiting 2–27 times more acid than neutral goblet cell mucus. This highlights the importance of acid goblet cell mucus as an immune response to pathogens in the posterior intestine of fish.YTK from our study had predominantly acidic and mixed posterior intestine goblet cell mucus and fewer neutral goblet cells, indicating that properties of the goblet cell mucus were protecting the system from pathogens. However, an increase of dietary Met, Cys or Tau decreased the secretion of acid goblet cell mucus and simultaneously stimulated the production of mixed and neutral goblet cell mucus, shifting the properties towards more digestive and absorptive functions. In a previous study, YTK had more neutral goblet cell mucus, in which composition was unaffected by soya protein inclusions and water temperature, acting as a lubricant and attacking pathogens–84. Yet, it has been suggested that less goblet cell mucus improves nutrient absorption capacity. YTK fed the T + M diets had 94–133 TGC per villus, which is similar to the TGC of the anterior intestine of Pomphorhynchus laevis infected brown trout (110 TGC per villus). YTK fed the T + M 11 and M + C 2 diet, which nearly met dietary Met, Cys and Tau requirements,19, had the least number of total goblet cells indicating that Met, Cys and Tau complete diets lessen the total goblet cell mucus production and improve absorption capacity. Overall, YTK indicated a shift towards absorptive properties when fed diets that contained adequate dietary Met, Cys and Tau levels.Apart from shifting the pH of the goblet cell mucus composition into the acidic range, the posterior intestine can also temporarily increase mucus secretion upon bacterial recognition. In YTK, amino acid retention was shown to depend on the water temperature and dissolved oxygen concentrations. Intestinal characteristics associated with increased absorptive area include enterocyte density, total villus height, VL, lamina epithelial area, villus density and intestinal circumference. YTK fed increasing dietary Met and Tau exhibited an increase in absorptive surface area. Further, YTK exhibited a decreasing absorptive surface area when fed Cys at 13·9 g/kg, marking an upper Cys threshold, which agrees with the suppressed growth and feed efficiency observed in YTK fed the same dietary Cys contents. Overall, YTK fed dietary Cys below 13·9 g/kg had more villi in the posterior intestine and an increased lamina epithelial area, thus larger surface areas for the absorption of nutrients.Enterocytes within the lamina epithelia are cells that absorb amino acids, simple peptides, lipids and monosaccharides via endocytosis, catabolise nutrients and release them into the circulation. Similar results have been attributed to lipid-rich diets, deficiencies of some fatty acids or diets rich in soyabean proteins,91. Since plasma TAG levels were particularly low for fish fed the low Met and low Tau diet, this result indicates that diets low in Tau and Met concurrently decrease the clearance of lipids from intestinal enterocytes and thereby decrease energy available for metabolism. YTK also had S-PAS+ bodies, indicative of glycogen or glycogen-rich accumulations such as lysosomes. YTK fed the T + M diets, which contained 23·8 % carbohydrate, had substantially more 185 S-PAS+ bodies per villus in comparison with YTK fed the M + C diets, which contained only 12·3 % carbohydrates and induced only half as many S-PAS+. Thus, increased dietary starch may increase dietary glycogen deposition.YTK had large, transparent supranuclear vacuoles in the cytoplasm of enterocytes. These vacuoles are presumed to have contained lipids that were washed out during histological processing as they did not stain positive for glycogen (PAS+) or protein (eosin). Deficiency in both Tau and Met (T + M 1) caused increased vacuolisation in the posterior intestine tissue and may be caused by increased lipid absorption or decreased clearance from enterocytes into blood circulationTo conclude, dietary Met, Cys and Tau-induced variations in the liver and posterior intestine suggest a shift in functional and structural properties. YTK fed insufficient dietary Met, Cys or Tau exhibited decreased red colouration in their livers, acidic goblet cell mucus with immune responsive properties, reduced absorptive surface area and increased accumulation of lipid supranuclear vacuoles. However, when YTK were fed diets containing Met, Cys and Tau close to their physiological requirements, TDW were relatively thinner, livers appeared redder and brighter, goblet cell mucus shifted towards absorptive properties, the intestinal absorptive surface area increased and YTK had less supranuclear vacuoles in villi enterocytes. These findings form a coherent, overarching picture with our previous findings of YTK fed dietary SAA and Tau at sub-optimal or supra-optimal levels, exhibiting inferior growth, feed efficiency, protein retention and eye health. This contrasts with YTK fed adequate levels and which subsequently exhibited a relatively superior response. Therefore, hepatic and intestinal histological responses that were statistically different to YTK fed adequate levels of Met, Cys and Tau may reflect nutritionally incomplete diets. With increasing commercial YTK aquaculture production, optimised gastrointestinal and liver function form critical components for good health and productivity. This study has shown that dietary SAA and Tau concentrations alter nutrient absorption and protective properties and provide insight into the macroscopy, histomorphology and histochemistry of the liver and posterior intestine. Further, this study provides useful information on methods for the collection of quantitative data from histological sections and liver surface colour rather than relying on subjective or qualitative evaluations and can be useful to implement deep learning algorithms that assist in automating this otherwise laborious process. Nevertheless, further research is needed to investigate the relationships between histology and organ function, particularly regarding intestinal goblet cell mucus, stratum granulosum and immune responses.


Urbanization processes in Asia are still ongoing; thus, aggregate demand is expected to increase in following years. Even though construction and demolition waste is a source for secondary building materials in industrialized countries, it is not yet an alternative construction material source in Vietnam as the urbanization process is still ongoing. Thus, there is a need for river sand and aggregates alternatives in concrete, namely manufactured sand (m-sand) from primary solid rock materials and secondary waste materials. The focus in the present study for Vietnam was on m-sand sand as alternative for river sand, and different ashes as alternatives for cement in concrete. The investigations comprised concrete lab tests according to the formulations of concrete strength class C 25/30 in accordance with DIN EN 206, followed by a lifecycle assessment study in order to identify the environmental impact of the alternatives. In total 84 samples were investigated, consisting of 3 reference samples, 18 samples with primary substitutes, 18 samples with secondary substitutes, and 45 samples with cement substitutes. This kind of holistic investigation approach comprising material alternatives and accompanying LCA was the first study for Vietnam, and even for Asia, and represents a substantial added value for future policy development in order to cope with resource scarcity. The results show that with the exception of metamorphic rocks, all m-sands meet the requirements for quality concrete. In terms of cement replacement, the mixes showed that a higher percentage of ash reduces the compressive strength. The compressive strength values of the mixes with up to 10% coal filter ash or rice husk ash were equivalent to the C25/30 standard concrete formulation. Higher ash contents up to 30% lead to the reduction of the concrete quality. The LCA study’s results highlighted the better environmental footprints across environmental impact categories in the 10% substitution material in comparison to the use of primary materials. The LCA analysis results showed that cement as a component in concrete holds the highest footprint. The use of secondary waste as alternative for cement provides significant environmental advantage. Natural resources such as water and river sand are extracted from freshwater environments to feed industrial applications around the world while water pollution, erosion, and destruction of habitats are related impacts. Sand river is a key material source for building sector including concrete industry in addition to gravel, cement, and water. However, unsound exploitation of such natural resources from river systems poses serious risks for ecosystems and nearby human settlements ,2 includ−1 [3/yr of sand (average) is extracted from Vietnamese Mekong Delta [The magnitude of river sand mining operations are underestimated by official statistics due to the unregulated markets and supply chains particularly in emerging economies . New ass−1 . Anotherng Delta . Remote ng Delta .Linear economy based on extraction of natural raw materials disregards the resource depletion risks and potential use of secondary materials in construction industry . DespitePrevious studies reveal waste foundry sand as alternative source to natural-based sand ,17. A reRapid urbanization process and development of construction sector release huge amounts of construction and demolition waste (CDW) that are disposed in municipal landfills or uncontrolled disposal sites polluting the natural environment under linear economy mechanisms . On the Sustainable construction mainly aims to reduce the negative environmental impacts generated by the construction industry . The utiThe production of concrete, the design and construction of concrete parts, the determination of properties and application rules in construction are regulated in the standard TCVN 7570:2006 “Aggregates for concrete and mortar—Specifications” . The maiLiterature and material availability research to find feasible substitutes;Two step concrete testing investigations to evaluate the possibilities of substituting sand with crushed sand or mineral wastes as well as cement with various ashes, comprising (a) manufacturing of concrete specimens and (b) uniaxial compression strengths (UCS) tests on them;Lifecycle assessment (LCA) of the investigated alternatives.The approach to the investigation was stepwise, comprising: Having in view the general material availability in Vietnam, being representative for other Asian countries as well, the focus was put on primary materials that are available as natural resources in Vietnam in order to produce m-sand  as well as fine particle aggregates that origin from secondary sources like agricultural or industrial wastes for replacing cement. Concrete cubes were manufactured with the alternative materials, followed by a subsequent uniaxial compression test in order to verify the unconfined compressive strengths. Following materials were investigated:Potential primary m-sand substitutes: Crushed solid rocks, particularly marble, amphibolite, granodiorite, basalt.Potential secondary m-sand substitutes: Crushed brick, crushed clinker:For m-sand comparison purposes was also used conventional crushed (broken) and river (round) concrete quartz sand , represeSecondary materials to substitute cement:Lignite filter ash, coarse ash, fly ash, and rice husk ash.Rice husk ash (RHA) was found in the literature research to be suitable for replacing  cement in concrete ,51,52,53DIN EN 12390-1: Testing hardened concrete—Part 1: Shape, dimensions, and other requirements for specimens and molds DIN EN 12390-2: Testing hardened concrete—Part 2: Making and curing specimens for strength tests DIN EN 12620: Aggregates for concrete DIN EN 206-1: Concrete—Part 1: Specification, performance, production, and conformity DIN EN ISO 17892-7: Uniaxial compression strengths (UCS) test .The following basic standards were considered when conducting the laboratory tests:The concrete test specimens were produced according to the concrete formulations of strength class C 25/30 in accordance with DIN EN 206 . For thePrimary aggregate substitutes: concrete sand, round (SR), concrete sand, broken (SB), marble (MA), amphibolite (AM), granodiorite (GD); basalt (BA);Secondary aggregate substitutes: crushed brick (CB), crushed clinker (CC);Secondary cement substitutes: lignite fly ash (LFA), coarse ash (CA), filter ash (FA) and rice husk ash (RHA).Test series 1: concrete of strength class C 25/30 with the potential primary m-sand substitutes SR, SB, MA, AM, GD, BA, as well as a reference sample for comparison;Test series 2: concrete of strength class C 25/30 with CB 10%, 30%, 50%;Test series 3: concrete of strength class C 25/30 with CC in 10%, 30%, 50% share;Test series 4: concrete of strength class C 25/30 with LFA, CA, FA, and RHA in 10%, 20%, 30% share.Following test settings and series were performed, each test in triple repetition:In total, 84 samples were investigated, consisting of 3 reference samples, 18 samples with primary substitutes, 18 samples with secondary substitutes, and 45 samples with cement substitutes. The base formulation C 25/30 concrete was replaced with different aggregates based on basalt, granite, marble, amphibolite, brick waste, and quartz .3 of cement and 1627 kg/m3 of aggregates (concrete sands or gravels) were mixed with 231 L/m3 of water. Prior to testing, through particle size distribution analysis, it was investigated whether the concrete sand meets the requirements according to DIN EN 12620  and DIN The second test series referred to the investigation of potential secondary m-sand substitutes, namely crushed brick and crushed clinker .The third test series referred to the investigation of secondary materials to substitute the cement though lignite filter ash, coarse ash, fly ash, and RHA . The C 2The specimens were stored at a temperature of approx. 20 °C. The specimens initially remained in the mold for 2 days. Subsequently, the already hardened specimens were removed from the mold and covered with a damp towel in a room at approx. 20 °C. The towels were wettened regularly to keep the relative humidity sufficiently constant. After 28 d curing time, the unconfined compressive strength of the specimens was determined according to DIN EN ISO 17892-7  using thThe specimens were firstly weighed, and the dimensions of the body were determined using a caliper gauge. The specimens were then subjected to stress under the ZD 100 tensile/compression testing machine, and the forces were noted until the respective specimen cube failed or cracked. The compressive strength was calculated from the parameters determined. The results are summarized in Goal and scope definition;Lifecycle inventory;Lifecycle impact assessment;Interpretation.The main objective was to estimate the environmental footprint of different sand and gravel alternatives utilized in selective construction applications replacing the conventional materials. In the present study was used lifecycle analysis (LCA) as a comparative sustainability performance tool. LCA is the most widely used holistic methodology, a multistage process, whose detailed definition is shown in the international standards of the series ISO 14040  and ISO TVCN ISO 14040:2009: Environmental management—Product lifecycle assessment, principles, and framework;TVCN ISO 14041:2011: Life Cycle Assessment of Products—Principles and Framework;TVCN ISO/TR 14047:2018: Environmental Management—Life Cycle Assessment;TVCN ISO/TR 14048:2012: Environmental Management—Life Cycle Assessment—Data Documentation Format.The LCA methodology is also recognized in Vietnam through the following norms:3 block of concrete at strength C25 using different aggregates.LCA was carried out using the Ecoinvent 3.6 database and the software Simapro 9.2. The software provided a user interface, the environmental information from the Ecoinvent database, and the options for the impact assessment method. The assessment methodology was ReCiPe 2016 Midpoint (H) V1.04/World (2010) H. The study involved the utilization of the LCA tool to calculate and analyze the environmental impacts of nonreinforced concrete of strength C25/30 using different aggregates with relevance to Vietnam. Using the LCA tool, the environmental footprints of the studied concrete were compared with each other. The system boundary considered was cradle to gate, where only material production and transportation to the site was considered. This study uses transport distances from cradle to gate as 30 km for traditional building materials based on information from Vietnamese experience. The functional unit for this study was the nonreinforced concrete sample of strength C25/30, where the materials were majorly produced outside of the construction area. The production of the materials comes with the product system. The functional unit for the study was a 1m2 eq. similar to the Vietnamese clinker and cement based on the environmental product declaration of the company INSEE Vietnam, Environmental Product Declaration (EPD) of Clinker and Cement VGD-ST-0014 [The selected unit processes for the LCI were modified for energy and water consumption, emissions for geographic relevance to the study. The cement unit process considered for this study was Portland cement global market-based because of Vietnamese relevant unit life cycle inventory process absence. The Ecoinvent Portland cement global unit process has a carbon footprint at a range of 0.44–0.96 kg CO-ST-0014 . In construction applications, the transportation of materials causes a substantial contribution to the environmental footprint ,67,68. CThe LCA was completed using an energy demand scenario analysis that was carried out through the method “cumulative energy demand (CED) V1.11” in Ecoinvent, representing the direct and indirect energy use in the MJ unit throughout the life cycle. The method is based on higher heating values (HHV) . The useAll lab results are documented in the The UCS results of the base formulation with primary m-sand substitutes are shown in Thus, the main result for aggregates replacement showed that except for amphibolite, brick, and clinker rubble, the C 25/30 standard formulations showed the required compressive strengths. The angular grains of the crushed materials do not have a substantial negative influence on the strength and the results are comparable to the concrete sand with round grain shape that represent the natural shape in contrast to the crushed materials. The substitutive material that resulted after the crushing process, showed visual differences in the grain form. Anyhow, all m-sand alternatives showed sand grains that have sharp edges and a rough surface. Moreover, all m-sand materials that originate from sedimentary and volcanic processes showed a compact material structure, in contrast to m-sand materials that originate from metamorphic formation processes. Those material have undergone a higher diagenetic pressure during the geological formation process leading to a platy to slatey structure and a higher tendency to break into plate-like particles. Consequently, the foliated grain shape of the metamorphic amphibolite leads to the significant reduction of the strength as was also reported by Małgorzata et al. (2016) . The rolThe results for the base formulations for concrete of strength class C 25/30 with various ash shares as cement substitute in form of ashes are shown in The substitution of cement with ash was carried out with five different ashes: coarse Vietnam ash (CA), filter ash (FA), lignite filter ash in two grades (LFA1/2), and rice husk ash (RHA). It should be noted that different types of ash have very different hydraulic properties, if considered to be used as hydraulic binder instead of cement. The mean σD results for CA correlated with the CA share in the specimens and covered a range between 13.69 (30% CA), 17.35 (20% CA), and 32.72 (10% CA) MPa and showed that CA might be a feasible substitute for replacing cement, however, only up to a share of 10%. Moreover, the mean σD results for LFA correlated with the LFA1/LFA2 share in the specimens and covered a range between 21.31/16.52 (30% LFA), 24.63/25.57 (20% LFA) and 30.33/26.90 (10% LFA) MPa and underlined the variety of the LFA properties. Even a share of up to 10% might be added as cement substitute, there might be available certain LFA ashes that’s properties allow for a share of 20%. The variability of the properties was also indicated in Terzić et al. (2013)  concludeThe addition of ash is only promising with 10% CA and LFA 1. Although the RHA and brick materials did not meet further expectations for use in concrete, these materials are well suited for landfill mineral seal layers in certain mix proportions .Thus, with the exception of Amphibolite, all manufactured sands meet the requirements for quality concrete and achieve the required compressive strength as the formulations with natural concrete sand. The flaky grain shape of metamorphic amphibolite, however, leads to a significant reduction in strength. With manufactured aggregates from different rock types (mostly igneous or metamorphic), the same concrete quality can be achieved for all building construction purposes with good availability and short transport distances compared to river or sea dredging. Replacing 50% concrete sand with relatively soft brick fragments did not produce acceptable results. The brick grains absorb a lot of water. Anyhow, the German standard only permits a maximum of 30% brick content.Magmatic and metamorphic rocks (with the exception of amphibolite) can be used as manufactured aggregates, replacing natural sand in concrete production. Selected ashes, especially coarse ash and lignite filter ash are suitable as cement substitutes, but only up to 10% proportion of concrete content. The ashes, but also brick dust, can also be used landfill mineral seal layers with up to 40% proportion of raw material content. Except for crushed amphibolite, brick rubble (crushed brick), and clinker rubble (crushed clinker), the modified C 25/30 concrete formulations show corresponding compressive strengths. The angular grains of the crushed materials obviously do not have a significant negative influence on the strength and the results are comparable to the concrete sand with round grain shape. The flaky grain shape of the metamorphic amphibolite leads to the significant reduction in strength. The brick and clinker rubble have negative effects on the strength in case they are substituted with higher percentages.For the LCA, amphibolite, clinker, and crushed brick were no longer considered, as those materials did not meet the concrete quality requirements. The LCA study results for the non-reinforced concrete of strength C25 involving conventional cement and alternative materials were compared and interpreted . Note th2 eq per m3 of concrete. The granite-based concrete has a 20% lower GWP impact than marble based concrete. The basalt concrete and crushed rounded quartz concrete has a 15% lower GWP impact than marble concrete. The cement contributes the highest share of GWP about 95%. The remaining contribution arises from aggregate about 1.4–2.18% and transportation processes contributing 2.68–3.54%. The variation in the GWP contribution from aggregates was directly related to their mass present within the concrete mixes. Among the aggregates, the marble concrete utilizing limestone-based unit process shoed higher mineral resource scarcity. This could be based on the characterization values associated with limestone and the absence of such factors for other raw materials quartz, basalt, and granite. In general, the granite aggregate concrete had a lower mineral resource scarcity footprint of 3.73 kg Cu eq. The land use impact footprint remains low for quartz-based aggregates concrete, which was about 50–55% lower than other aggregate concrete. The water consumption impact remains marginally nearby for all the concrete samples ranging 3.12–3.64 m3, with granite aggregate concrete having a higher value. The marble concrete tends to have a higher footprint in acidification, eutrophication, and fossil resource scarcity impacts.Among the different aggregate usage in the concrete, the granite-based concrete has the least impact with 346 kg COThe granite aggregate concrete has lower energy demand than other mixes across all the energy source categories . The eneThe study’s results highlighted the better environmental footprints across impact categories in utilizing granite aggregate concrete. Despite granite aggregate lower values, all the aggregates in general only had marginal differences among the impact footprint. The LCA analysis results showed that cement as a component in concrete holds the highest impact footprint. Therefore, it becomes necessary to consider alternative materials with lower environmental footprint to replace cement or technological improvements along the cement value chain to lower the product footprint, as it is a widely used construction material. The LCA study also indicates the need for shifting the energy sources from fossil-based in the construction value chain to low-carbon or emission-based renewable sources to attain the global net-zero targets.2 eq while the alternatives mixes had 362 kg CO2 eq —Green Database”  could be used as a starting point.


T recovery ratio from HCD. This over-repair phenomenon of HCD by UFM GIDL is deeply discussed through oxide trap behaviors. When the applied gate-to-drain GIDL bias reaches 4 V, a significant electron trapping and interface trap generation of the fresh device with GIDL repair is observed, which greatly contributes to the approximate 114.7% over-repair VT ratio of the device under worst HCD stress . Based on the TCAD simulation results, the increase in the vertical electric field on the surface of the channel oxide layer is the direct cause of an extraordinary electron trapping effect accompanied by the over-repair phenomenon. Under a high positive electric field, a part of channel electrons is captured by oxide traps in the gate dielectric, leading to further VT recovery. Through the discharge-based multi-pulse (DMP) technique, the energy distribution of oxide traps after GIDL recovery is obtained. It is found that over-repair results in a 34% increment in oxide traps around the conduction energy band (Ec) of silicon, which corresponds to a higher stabilized VT shift under multi-cycle HCD-GIDL tests. The results provide a trap-based understanding of the transistor repairing technique, which could provide guidance for the reliable long-term operation of ICs.In this article, an experimental study on the gate-induced drain leakage (GIDL) current repairing worst hot carrier degradation (HCD) in Si p-FinFETs is investigated with the aid of an ultra-fast measurement (UFM) technique (~30 μs). It is found that increasing GIDL bias from 3 V to 4 V achieves a 114.7% V DRAM (dynamic random access memory) is one of the core components of electronic equipment, and it has become increasingly important in terms of the development of the information society . For higWith continuous channel length scaling, hot carrier degradation (HCD) has emerged as a major reliability issue in FinFETs . From thIT) [To ensure the reliable long-term operation of the transistor in ICs, controlling gate oxide quality is one of the most critical challenges. Several methods have been developed to recover the hot-carrier-induced damage. From the wafer-level view, the forming gas annealing (FGA) process utilizes high-pressure hydrogen or deuterium to passivate the dangling bonds at the interface and thus suppress the interface trap generation (ΔNIT) ,12. The IT) ,14. FromIT) . AnotherIT) ,17. The IT) . This acIT) . HoweverIT) .T over-recovery phenomenon. With the development of the ultra-fast measurement technique (UFM), the recovery effect during ID-VG measurement is effectively suppressed, further improving the accuracy in HCD characterization [However, the trap behaviors during the GIDL repairing process for HCD still remain to be discussed. Another issue that needs to be discussed is the underlying mechanism of the observed Vrization ,22. In trization ,24. WithThe remainder of this manuscript is organized as follows. 2 gate removal; (2) the growth of the 0.8 nm interface layer (IL) of SiO2 through chemical oxidation of O3; (3) the atom layer deposition (ALD) of 1.7 nm HfO2 as a high-k layer; (4) 450 °C post-deposition annealing (PDA); and (5) the deposition of a multi-layer gate stack including ALD Titanium Nitride (TiN)/ ALD Tantalum Nitride (TaN) /CVD Titanium Nitride (TiN)/ ALD Tungsten (W). The replacement metal gate (RMG) Si bulk p-FinFETs are fabricated using a fully-gate-last process. The equivalent oxide thickness (EOT) is 0.92 nm. The major steps for gate stack formation are shown in G,STR = VD,STR) [G,GIDL) and drain GIDL biases . In this article, the Keysight B1530 semiconductor analyzer is utilized to perform UFM of ID-VG characteristics using pulse-IV measurements with a duration of 30 μs [T) are obtained in measure-stress-measure (MSM) mode [T is extracted through the constant current method with the target linear drain current  of 100 nA × W/L [Devices are stressed under the worst HCD condition  ; then, aof 30 μs . Time evSM) mode . VT is enA × W/L ; here, WG is sequentially decreased to multiple gate discharge voltage  levels, while VD remains at the stress bias. Each discharge period lasts for only 1 s; then, a pulse-IV is performed to extract ΔVT. The overdrive voltage (VOV) is calculated by VOV = VG,DIS—VT; then, the ΔVT ~ VOV relationship is obtained to extract the energy distribution of oxide traps. All of the test results are averaged by a group of three devices at 125 °C.The DMP experiments are performed to investigate the energy distribution of generated oxide traps during GIDL repair. D-VG curve with GIDL is in good agreement with measured data within 1 m VT. The key simulation parameters, such as work function, stress, and the S/D distribution resistance, are concluded in To bring a further physical explanation, Sentaurus TCAD tools are employed to solve the electric field distribution of p-FinFETs under GIDL repair. The 3-D simulation structure of p-FinFETs with the same Fin shape in TEM is shown in T degradation of approximately 170 mV and a shift of 8 mV/dec in subthreshold swing (SS). Subsequently, the UFM GIDL repairing process is implemented for 1 ks with different repairing biases. Under moderate GIDL bias of VGD = 3 V , the VT shift is reduced to 60 mV, and the SS shift is negligible, corresponding to a 62.7% recovery ratio, as shown in GD = 4 V , the VT recovery ratio is increased to 114.7%, which indicates that the degraded device is over-repaired by GIDL repair. However, this improvement comes at the cost of degradation in SS of 9 mV/dec. Considering that SS degradation reflects the generation rate of interface traps [ce traps , excessice traps .G,GIDL = 0.5 V, VD,GIDL = −2.5 V) is applied, the recovery of VT is relatively low, measuring approximately 27 mV. However, under high GIDL biases , the recovery of VT exceeds 100 mV. It can be seen that at high gate-to-drain electric fields, a large number of electrons are injected into the gate oxide, which greatly contributes to VT recovery [To explain the over-repair phenomenon that occurs at high GIDL biases, a group of fresh devices is subjected to 1 ks GIDL biases, as shown in recovery . MoreoveGD increases from 3 V to 4 V, the channel electric field changes significantly at two positions: one near the drain region, and the other along the channel surface. The 1-D electric field, cut along the surface of oxide layer in 2-D view in x = 50 and Ex = 0 according to their positional coordinates. Furthermore, a physical explanation is given with the aid of TCAD simulation. The electric field distributions of the device under different GIDL biases are simulated. Cutting vertically the center of gate along the channel direction, the 2-D view of the electric field distributions is shown in GD increases from 3 V to 4 V, Ex = 50 and Ex = 0 increase by 1.26 and 6.89 times, respectively. As shown in T degradation. When a GIDL bias is applied, the strong positive electric field near the drain region promotes the trapped holes to be released, which results in VT recovery [x = 50 at VGD = 4 V corresponds to the higher VT recovery ratio (114.7%) in GD is also like applying a PBTI stress to the device, part of electrons in the channel are captured by the HfO2 traps, which also results in the recovery in VT [x = 0 at VGD = 4 V is the main cause of over 100 mV VT recovery in As Vrecovery . The higry in VT . The higT ~ VOV relationships under different GIDL biases are obtained in T is converted into the effective trap density (ΔNT) following the equation ΔNT = |ΔVT| × Cox / q [OV is converted into the corresponding energy level Ef relative to Ev, i.e., Ef—Ev. Additionally, the ΔNT ~ (Ef—Ev) relationships under different GIDL biases are obtained in T (ΔDT) is obtained by differentiating ΔNT against Ef—Ev, and the results are shown in HT) is extracted through the multi-DMP method separately, which is represented by a black curve [To further analyze the trap behaviors during the GIDL repairing process, DMP experiments are carried out. A group of fresh p-FinFETs is subjected to −2 V HCD stress for 200 s, followed by a 1 ks GIDL repairing process at different GIDL biases. The repaired devices are again applied with the same HCD stress and then discharged following the waveform in  Cox / q . VOV is ck curve .v, and two types of generated oxide traps in the bandgap. Generated trap 1 is at 0.2 eV below the mid-gap of silicon, and trap 2 is located around Ec of silicon. The pre-existing traps are mainly induced by the fabrication process and cannot be repaired by GIDL bias. While generated traps show clear dependence with applied GIDL biases. At a moderate GIDL bias of VGD = 3 V, when a new round of HCD stress is applied, the ΔDT of both trap 1 and trap 2 are reduced by 48% and 9% compared to that under HCD, respectively. While at a high GIDL bias of VGD = 4 V, the ΔDT of trap 2 is 34% higher than that under HCD. In addition, the energy position of trap 1 tends to approach Ec after repair, while the position of trap 2 remains unchanged. To make a clear comparison, ΔDT was integrated between Ev and Ec to extract ΔNT, as shown in GD increases from 3 V to 4 V, ΔNT is increased by 46%. It can be seen that, after applying a moderate GIDL bias, the oxide trap density is effectively reduced in the next round of HCD stress. However, at high GIDL biases, although more generated oxide traps are discharged after repair, they are re-charged in the next round of HCD stress, which results in the further generation of oxide trap 2.As can be seen from GD = 4 V, the repaired device exhibits a lower VT  but shows more severe degradation in the next round of HCD stress. As the HCD/GIDL cycle progressed, the degraded ΔVT and recovered ΔVT in each cycle gradually tended to be the same. As can be seen from T at high GIDL bias is almost 99.4% higher than that at moderate GIDL bias, which corresponds to the higher ΔNT at high GIDL bias in T and ΔVT illustrate that the cyclic charge–discharge behavior of oxide traps results in the dynamic equilibrium between VT degradation and recovery. To ensure the reliable operation of p-FinFETs under long-term HCD stress, moderate GIDL bias is recommended to ensure the minimum ΔVT under cyclic stress.To verify the effectiveness of different GIDL biases on long-term HCD recovery, multiple cycles of HCD and GIDL are applied, and the results are shown in c. Due to the shallow energy level of trap 2, it will be charged first during the second round of HCD stress, which corresponds to the higher ΔDT peak observed in c after capturing a hole. Trap 1 is located at a relatively deep level (0.2 eV below mid-gap of silicon), which will be fully charged only after a complete discharge. Therefore, under a moderate GIDL bias of VGD = 3 V, the ΔDT of trap 1 shows a 48% decrease compared to HCD. For the convenience of reading, all abbreviations and notations frequently used in this article can be seen in Finally, the energy level diagrams of the two generated traps are given in GD = 4 V, the VT recovery ratio reaches 114.7%. With a 6.89 times increase in the channel electric field, more PBTI components are introduced at high VGD, which are responsible for additional electron trapping and interface trap generation. At a moderate GIDL bias of VGD = 3 V, the effective density of generated oxide trap 1 (at 0.2 eV below mid-gap of silicon) and trap 2 (around Ec of silicon) are reduced by 48% and 9% in the next round of HCD stress. However, a high GIDL bias will lead to 34% further generation of trap 2. Furthermore, two generated traps show different charge–discharge properties, which corresponds to two types of oxide traps described in AG model. After multiple cycles of HCD/GIDL tests, the degraded and recovered VT reaches the same. The dynamic equilibrium between VT degradation and recovery can be attributed to the cyclic charge–discharge behaviors of oxide traps. To ensure long-term HCD reliability, a moderate GIDL bias is recommended.In this article, the GIDL repairing process is carried out with the UFM technique, and trap generations during GIDL repair are experimentally investigated. At a high GIDL bias of V


This study aims to achieve the sustainable utilization of waste glass resources through an investigation into the influence of three types of admixtures, namely waste glass powder (WGP) (G), waste glass powder–slag (G-S), and waste glass powder–fly ash (G-F), on the mechanical properties and durability performance of waste glass concrete. The experimental results demonstrate that the exclusive use of WGP as an admixture led to the relatively poor early compressive strength of the concrete, which decreased with an increase in dosage. However, at medium to long curing ages, the strength of the waste glass concrete could equal or even surpass that of ordinary concrete. When dual admixtures were employed, the G-S group exhibited higher compressive strength compared to the G-F group. Specifically, within the G-S group, a glass powder dosage of 15% yielded higher compressive strength, and after 180 days, the dual admixture groups exhibited greater strength than ordinary concrete (G0); the compressive strength of the tG1S1 group was 44.57 MPa, and that of the G0 group was 40.07 MPa. The chloride ion diffusion coefficient showed a varying trend with an increase in WGP dosage, initially decreasing and then increasing. The concrete’s resistance to erosion was maximized when the glass powder dosage reached 30%. As the WGP dosage increased, the overall frost resistance decreased. For a total dosage of 30%, the optimal glass powder dosage in both G-S and G-F groups was found to be 15%. Consequently, the cement industry has been recognized as one of the foremost and least ignorable causes of global warming [Concrete, one of the most extensively utilized construction materials on a global scale, requires the use of ordinary Portland cement (OPC) in its production process, which emits a significant amount of carbon dioxide , the deterioration rule under freeze–thaw action, and the ability to resist chlorine salt erosion. Because of this, this paper considers the influence of environmental factors in the northern coastal area of China and investigates the anti-chlorine erosion performance of glass powder (G) single-mixed as well as glass powder-mineral double-mixed (G-F/G-S) concrete, the mass loss after freeze–thaw cycle, the relative modulus of elasticity, and the compressive strength of different compounding ratios at different ages, to reveal the long-term mechanical properties and durability of glass powder concrete, and provide a theoretical basis and a basis for the popularization and application of glass powder concrete. The study reveals the long-term mechanical properties and durability of glass powder concrete and provides a theoretical basis and data support for the popularization and application of glass powder concrete.The experiment used ordinary Portland cement (PO42.5R) produced by Xiaoyetian Cement Factory in Dalian City, Liaoning Province, China, with a compressive strength of 53 MPa and a flexural strength of 9.1 MPa at 28 days. The waste glass used was ordinary transparent plate glass recycled from domestic use by Hangzhou Gaoke Composite Materials Co., Ltd. in Hangzhou, Zhejiang Province, China, with a particle size of 40 μm. It was ground into powder as shown in The slag powder and fly ash were both obtained from Ruian Longze Materials Co., Ltd. in Ruian, Zhejiang Province, China, with grade 1 fly ash and S95 grade slag powder. The details of their basic properties and chemical compositions can be found in The fine aggregate used was local river sand in Dalian, and the coarse aggregate was crushed stone with a particle size of 5–25 mm. Water was ordinary tap water from Dalian, and a standard high-performance polycarboxylate superplasticizer was used as the water-reducing agent.The present experiment focused on the study of single-admixture and dual-admixture concrete, with waste glass powder, fly ash, and slag powder as the research parameters. For single admixture concrete, WGP was substituted for cement in volume ratios of 10%, 20%, 30%, 40%, and 50%. For dual admixture concrete, the total admixture content was kept at 30%, with a water-to-binder ratio of 0.46. The basic mix proportions were determined based on the experimental methods specified in JCJ55-2011 “Standard for Mix Proportion Design of Ordinary Concrete” , and adjAccording to the specifications provided in JTG E30-2005 “Test Regulations for Cement and Concrete in Highway Engineering”  regardinThis article conducted a total of one mechanical performance test and two durability tests, including compressive strength test, electrical flux test, and freeze-thaw cycling test.The compressive strength test of the specimens was conducted using a DYE3000 pressure testing machine of Shengke Test Instrument Co., Ltd., Dalian, Liaoning Province, China, with the loading rate of 0.5–0.8 MPa/s. The test was stopped when the peak stress decreased to 40%. The electrical flux test was carried out using a DTL-6T chloride ion flux measuring instrument and a concrete vacuum saturation device of Dalian Shengke Test Instrument Co., Ltd. The chloride ion permeability of the tested specimens was calculated based on the flux measurement, and the chloride ion diffusion coefficient was also determined. The freeze–thaw cycling test was performed using a KD13–28V concrete rapid freeze–thaw testing machine of Shengke Test Instrument Co., Ltd. Dalian, Liaoning Province, China. During the cycling process, the lowest temperature at the center of the specimen was −18 °C, while the highest temperature was 5 °C. The solution used was pure water.The study incorporated various curing ages for conducting mechanical performance tests. Compressive strength tests were carried out on concrete specimens with different mix proportions at different curing ages. The experimental results revealed that when the applied load reached 85% of the ultimate load, cracks appeared on the surface of the specimen. As the load continued to increase, the specimen appeared transversely uplifted, the surface fell off, and finally collapsed, which is considered ductile destruction. Failure patterns of specimens with different admixtures and different dosage are basically the same, as illustrated in It can be observed that the compressive strength of the single-admixture WGP concrete shows a positive correlation with the curing age. At the same curing age, as the replacement ratio of WGP increases, the compressive strength generally exhibits a downward trend. Further investigation reveals that with the increase in curing age, the difference in strength between the GX group and the G0 group becomes smaller. Compared to the G0 group, the G3 group experienced a strength reduction of 25.4% at 3 days and 8.01% at 180 days. This phenomenon is attributed to the pozzolanic effect of the waste glass powder, which becomes prominent in long-term curing, promoting the formation of C-S-H gel and enhancing the rate of strength development in the WGP concrete. Among all of the groups, G1 exhibited the highest growth rate, surpassing the strength of the G0 group by 4.1% at 180 days.The influence of different glass powder dosages on the compressive strength of dual-admixture concrete at various curing ages is illustrated in 2, resulting in the formation of C-S-H gel and further enhancing the compressive strength of the concrete in the later stages [During the early curing ages (3–14 d), the compressive strength of the glass powder concrete is relatively slow. The G0 group increased by 9.44 MPa, the G-F group exhibited an average compressive strength growth of 8.85 MPa, and the G-S group had an average compressive strength growth of 10.04 MPa. In the medium- to long-term curing ages (28–180 d), the increase in compressive strength of the dual-admixture concrete becomes more significant. The G-F group showed an average increase in compressive strength of 8.12 MPa, the G-S group had an average increase of 8.07 MPa, and the G0 group experienced a growth of 6.68 MPa. It is worth noting that the compressive strength of both the G1F1 and G1S1 groups exceeded that of the other groups after 56 days. On the whole, the G-S concrete exhibited higher final strength than the G-F concrete. This indicates that the pozzolanic effect brought about by glass powder and slag powder has greater advantages in the long-term curing period compared to fly ash. This phenomenon may be attributed to the inert characteristics of glass powder, and the slag powder can better enhance the activity of glass powder by dissolving a large amount of silica. This promotes the reaction between glass powder and the hydration product Ca(OH)r stages ,33,39,40Compressive strength, as one of the important indicators in concrete design, is a key parameter that characterizes its mechanical performance. Based on the observed mechanism of the variation in compressive strength with the curing age, it is evident that the compressive strength of concrete varies at different curing ages. For predicting strength after 28 days, a time-dependent model can be employed for fitting and prediction purposes:Transforming Equation (1) leads to Equation (2):Utilizing Equation (2), the compressive strength of the blended concrete cubes with the admixture was fitted against the curing age, resulting in The horizontal y-axis represents a function variable with the curing age t (A).−2 cm2/s); The treatment of specimen electrical flux was conducted based on Equation (3), and the electrical flux values were converted according to Equation (4) depending on the size of the specimens. The conversion of concrete electrical flux values to chloride ion diffusion coefficient was carried out using an empirical Formula (5) proposed by Feng et al. ,42,43 fr−9 cm2/s). When glass powder is solely added, the overall trend of concrete resistance against chloride ion penetration shows an initial increase followed by a decrease. The electrical flux is minimum when the glass powder dosage is 30%, indicating the highest resistance against chloride ion erosion and the lowest chloride ion diffusion coefficient of 7 × 10−9 cm2/s. In the case of the simultaneous addition of glass powder and mineral admixture, the higher the proportion of glass powder, the lower the electrical flux. When the glass powder proportion is at 20% and 15%, the concrete exhibits even stronger resistance against chloride ion penetration. In conclusion, glass powder has the most significant impact on the resistance of concrete against chloride ion penetration, with an optimal dosage of 30% in sole addition, and 20% glass powder proportion in simultaneous addition.Based on the above data, it is evident that the concrete exhibits the strongest resistance against chloride ion penetration when the chloride ion diffusion coefficient is within the range of 3.07–7.50  for the regression equation of the time-dependent model was 0.92, indicating that the model can be used to predict compressive strength values at different ages.Predictions of compressive strength variation with age were conducted using a time-dependent model. It was found that as age increases, compressive strength shows an overall increasing trend. The greater the dosage of glass powder, the larger the slope, and the faster the rate of strength growth. The average coefficient of determination (RBoth sole and dual admixture concrete showed improved resistance to chloride ion erosion when the total dosage was 30%. When the glass powder was solely added at a dosage of 30%, the chloride ion diffusion coefficient was the lowest. In the case of dual admixture, the higher the dosage of glass powder, the stronger the resistance to chloride ion erosion, showing an overall positive correlation.In both sole and dual admixture concrete, the overall frost resistance tended to decrease with an increase in the dosage of glass powder. When the total dosage was 30%, both the G−F and G−S groups exhibited improved frost-resistance characteristics. The optimal frost resistance was achieved when the glass powder and mineral admixture each accounted for 15%.Based on the comparative analysis of compressive strength, resistance to chloride ion erosion, and frost resistance at different ages of WGP concrete, waste glass powder–fly ash concrete, and waste glass powder–slag powder concrete, the following main conclusions can be drawn:


The seismic behaviors of exterior polyvinyl chloride–carbon-fiber-reinforced polymer (PVC–CFRP) confined concrete (PCCC) column-ring-beam joints (hereafter referred to as exterior PCRB joints) under low cyclic loading were investigated. A total of 11 specimens were tested to analyze the effects of the structural parameters  on the failure modes and hysteretic behavior. Three different failure modes, including the failure of the frame beam, the failure of the junction between the frame beam and the ring beam, and the shear failure of the ring-beam joint, were observed. The experimental results showed that the pinching effects of the hysteresis curves decreased and that the slope of the descending stage of the skeleton curves gradually decreased with the enhancement of the reinforcement ratio of the ring beam, axial compression ratio, and ring-beam width. The effects of the CFRP-strip spacing and the reinforcement ratio of the frame beam on the hysteresis loops and skeleton curves were marginal, while the reinforcement ratio of the frame beam exerted significant effects on the failure modes. Therefore, a model for predicting the skeleton curves of exterior PCRB joints and hysteresis rules was proposed, based on the softening constitutive relation of the concrete and a regression analysis of the test data. Ultimately, a load–displacement hysteresis model of the exterior PCRB joints was established and validated by the test data, with good agreement. Reinforced concrete (RC) column–beam-joint core areas are prone to brittle shear failure when subjected to axial force, bending moment, and shear force, which may induce the collapse of entire frame structures ,2,3. TheTraditional RC columns are usually connected to RC beams to form frame systems, while CFST columns can be connected to both RC beams and steel beams. Hence, many emerging joint connections between CFST columns and beams have been proposed and studied. Han and Li systematically investigated the seismic behaviors of CFST columns attached to steel-beam joints with RC slabs ,15,16,17However, unlike connections to steel beams, connections between CFST columns and RC beams usually require the disconnection of the outer steel tube at the joint position to ensure that the RC beam’s longitudinal reinforcement passes through the joint-core area. This disconnection mode is conducive to the transfer of shear force and bending moment, improves the bonding performance of the longitudinal reinforcement and concrete in the joint core, and reduces the axial bearing capacity and stiffness of the joint core. To solve this problem, Fang et al. attempted to improve the bearing capacity of the joint core by increasing the cross-sectional area of the concrete in the joint-core area and allocating horizontal-ring reinforcement simultaneously; they demonstrated that this new ring-beam joint showed high axial bearing capacity . SubsequSimilarly to CFST structures, as another novel composite structure, PVC–CFRP confined concrete (PCCC) columns have received increasing attention in research in the past two decades, owing to their high bearing capacity, light weight, strong corrosion resistance, and convenient construction ,26,27,28To the best of our knowledge, few studies focus on the seismic behaviors of PCRB joints. However, as described above, the brittle shear failure of the joint-core area may induce the collapse of entire frame structures. Therefore, studies cannot be limited to static experiments if PCRB joints are to be applied in practical engineering. In this study, 11 exterior PCRB joints were tested to investigate the effects of the structural parameters on the seismic behaviors. Additionally, a n , and ring-beam width b were considered. The details of structural designs and the specific definitions of these different structural parameters are listed in To systematically and comprehensively investigate the failure modes and seismic behaviors of the exterior PCRB joints, a total of 11 one-third-scale specimens were tested under low cyclic loading considering the general sizes of the specimens for engineering and the feasibility of the tests, in accordance with the provisions of Chinese code JGJ/T 101-2015 . A exterThe thickness and outer diameter of all PVC tubes were 7.8 mm and 200 mm, respectively. The width of CFRP strips was 20 mm. The 20-mm-wide CFRP strips with 2 layers were wrapped around the PVC tubes, and the thickness of each layer was 0.111 mm. Furthermore, 3 layers of CFRP strip were adopted in the junction between the columns and ring-beam joint to prevent the early destruction of columns end. Additionally, the strength grade of all concretes was C30. The ultimate strength and elastic modulus of concrete were obtained from the standard test of concrete cubes (150 mm × 150 mm × 150 mm). The measured properties of the all the materials  used in the tests are summarized in The failure process of all the specimens can be summarized as three typical stages . Initially, the deformation of all the components of the specimens was not obvious, and the specimens showed elastic responses. As the displacement of the frame-beam end increased, the concrete in the junction between the ring beam and the frame beam began to crack, and the specimens entered the crack-development stage. Subsequently, several staggered diagonal cracks appeared on the surface of the ring-beam joint and the frame beam close to the ring beam. However, when the load reached 85–90% of the peak bearing capacity, specimens S9 and S6 showed different failure trends from the other specimens. For specimens S9 and S6, the cracks in the joint area almost did not develop any further, while the cracks in the frame beam and at the junction between the frame beam and the ring beam developed rapidly with the crushing of the frame-beam concrete, as shown in P–Δ hysteresis curves of all the specimens, in which P represents the vertical load applied to the end of the RC-frame beam and Δ denotes the corresponding vertical displacement. Initially, all the specimens showed elastic responses, the load and displacements increased linearly in general, and the stiffness and strength were not degraded. Subsequently, diagonal cracks appeared on the ring-beam surface, and the reinforcements in the joints yielded. The P–Δ curves gradually deviated from linearity as the displacements increased, and the specimens entered the elastic–plastic stage. At this stage, a certain amount of residual deformation occurred. Subsequently, the concrete cracks in the joint area developed further, and slippage between the reinforcement and the concrete occurred, which may be the reason for the pinching effects of the hysteresis curves. After the specimens reached the peak bearing capacity, the stiffness and strength degraded significantly. The load reduced slowly with the rapid increase in the displacement, which indicated that the specimens exhibited good ductility and energy-dissipation ability. In other words, the specimens allowed the dissipation of a significant amount of mechanical energy into internal energy [l energy .P–Δ skeleton curves of the specimens. They were obtained by connecting the peak points on the hysteresis curves. It can be seen that all the skeleton curves exhibited similar S shapes. Initially, the stress of all the specimens was small, and the skeleton curves increased approximately linearly. As the frame-beam-end displacement increased, the slopes of the skeleton curves gradually decreased. This phenomenon can be attributed to the cracking of the ring-beam concrete and the yield of the ring reinforcements in the ring-beam-joint area. Subsequently, most of the ring reinforcements and the ring-beam stirrups yielded, and significant slippage between the reinforcements and the concrete occurred in the joint area and at the junction of the ring beam and the frame beam. Ultimately, a gentle descending section can be observed in the skeleton curves.P–Δ skeleton curves were not obvious in the elastic stage, as shown in The effects of the P–Δ skeleton curves. Several previous studies proved that the decreases in CFRP-strip spacing can significantly improve the bearing capacity of PCCC columns under axial, eccentric, and lower cyclic loading [As shown in  loading ,29,32. HP–Δ skeleton curves in the elastic stage. Subsequently, the slopes of the skeleton curves increased as the P–Δ skeleton curves were similar to those of the aforementioned parameters on the P–Δ skeleton curves in the elastic stage, as demonstrated in The effects of P–Δ skeleton curves are shown in The effects of the b, n and In this section, on the basis of the softening constitutive relation of the concrete, the (1)The frame-beam section conforms to the plane-section hypothesis.(2)The tensile action of the concrete is ignored.(3)The effects of ring-beam-core-concrete shrinkage and creep are neglected.(4)The constitutive relation of the reinforcement is a bi-linear model.(5)The constitutive relation of the concrete proposed by Zhang and Hsu  is adoptn 42 MPa . The ε0 tion (3) .(3)ε0=−P–Δ skeleton curves of the exterior PCRB joints exhibited S shapes. To simplify the analysis, the yield point and peak point were selected as the turning points and the P–Δ skeleton curves were approximately simplified as three stages, namely the ascending stage (OA), the hardening stage (AB), and the descending stage (BC), as shown in P–Δ skeleton curves of the PCRB exterior joints.Clearly, the In this analysis, the frame-beam-end yield displacement t yields . The LfbBased on the equilibrium condition of the force, the yield-bearing capacity specimen . The Ec  with Li . SubsequUltimately, the yield-bearing capacity and yield displacement can be calculated by Equations (4) and (11), as listed in However, according to Equation (11), the frame beam’s longitudinal reinforcement is considered to yield completely, which leads to larger calculated values. Therefore, based on the characteristic value of the longitudinal reinforcement ratio of the frame beam  and (18) are listed in n. Regarding the regression analysis of the test data in this paper, The displacement ed by Li . AdditioAs illustrated in The test results and the calculated values of the important turning points of the skeleton curves are summarized in The model of the pecimens ,40,41. Tpecimens , considea and c are the calculated coefficients. The specific expressions are as follows:As shown in (a)Before the specimens yielded, the (b)After the specimens yielded, the (c)When the reverse loading reached the yield load, the The unloading stiffness at various displacement amplitudes was calculated according to Equations (25)–(27), and the calculation results are summarized in P–Δ hysteresis model of the exterior PCRB joints was established. The comparisons between the experimental hysteresis curves and the theoretical hysteresis curves are demonstrated in Using the skeleton-curve-prediction model and the hysteresis rules proposed above, the (1)Three failure modes of the exterior PCRB joints  were observed during the tests. The reinforcement ratio of the frame beam obviously affected the failure modes of the exterior PCRB joints.(2)With the increase in the ring-beam-reinforcement ratio, the axial compression ratio, and the ring-beam width, the pinching effect of the (3)Based on the softening constitutive relation of the concrete, a simplified tri-linear-relation model for predicting the (4)On the basis of the Clough bi-linear degradation model, the loading and unloading rules of the exterior PCRB joints under low cyclic loading were determined by the analysis of the (5)Although further research is needed, the proposed force–displacement hysteresis model is considered by the authors to be a useful tool for evaluating the hysteresis behavior of exterior PCRB joints under low cyclic loading.Experimental investigations on 11 exterior PCRB joints under low cyclic loading were carried out. The effects of several structural variables on the seismic behaviors were analyzed. The conclusions can be summarized within the scope of the aforementioned parameters, as follows: