Pseudomonas aeruginosa is a bacterial pathogen associated with a wide range of infections and utilizes several strategies to establish and maintain infection including biofilm production, multidrug resistance, and antibiotic tolerance. Multidrug resistance in P. aeruginosa, as well as in all other bacterial pathogens, is a growing concern. Aminoglycoside resistance, in particular, is a major concern in P. aeruginosa infections and must be better understood in order to maintain effective clinical treatment. In this review, the various antibiotic resistance and tolerance mechanisms of Pseudomonas are explored including: classic mutation driven resistance, adaptive resistance, persister cells, small colony variants, phoenix colonies, and biofilms. It is important to further characterize each of these phenotypes and continue to evaluate antibiotic surviving isolates for novel driving mechanisms, so that we are better prepared to combat the rising number of recurrent and recalcitrant infections. P. aeruolerance . Along w concern . In addi develop . Aminoglruginosa  and is sP. aeruginosa has multiple antibiotic resistance and tolerance phenotypes which could allow survival of a bacterial population during antibiotic treatment of an infection. These phenotypes are highly diverse in not only their mechanisms of development but also in the extent to which they are able to survive in the presence of antibiotics. Antibiotic tolerance has also been found to allow for development of complete antibiotic resistance [sistance , further2Antibiotic resistance is characterized primarily by genetic alterations which allow cells to actively resist killing by antibiotics. This can be accomplished through antibiotic target site modification, enzymatic degradation of the antibiotic, or an increase in expression of efflux pump genes . Additio2.1P. aeruginosa is primarily accomplished using aminoglycosides such as gentamicin or tobramycin. Aminoglycoside resistance through modifying enzymes which inactivate the aminoglycoside has been known to exist since the 1960's and 1970's [P. aeruginosa clinical isolates found overexpression of MexXY-OprM in 53% of strains, indicating the importance of efflux pumps as well in a clinical setting [“Classical” antibiotic resistance is driven by either stable mutations or horizontal gene transfer of plasmids harboring resistance genes, both of which allow bacteria to survive in the presence of antibiotics at both high concentrations and over repeated exposures. Treatment of d 1970's . These ed 1970's . In addid 1970's ,28, and,d 1970's . Target d 1970's ,33. Antid 1970's ,35. Clind 1970's . Another setting .2.2In additional to classical antibiotic resistance, in which a complete population exhibits the phenotype, heteroresistance is a classification characterized by a small subset of genetically resistant bacteria hiding within a population which is overall susceptible to the antibiotic ,37. Duri2.3P. aeruginosa, termed adaptive resistance, is characterized by a transient resistance to antibiotics. Adaptive resistance in P. aeruginosa was first identified clinically in sputum samples from CF patients in 1996 [Another antibiotic survival mechanism of  in 1996 . While t in 1996 . Once th in 1996 . Current3In addition to antibiotic resistance, antibiotic tolerance is an area of increased concern, especially given the potential of tolerance leading to population resistance over time . Antibio3.1Staphylococcus aureus by Hobby et al., in 1942 [Staphylococcus pyogenes, adding that while persister cells were able to survive antibiotics (penicillin), they were not genetically different than wild-type [Escherichia coli which led to the development of the persister cell phenotype, the MqsR/MqsA system and the TisB/IstR-1 system [E. coli persister cells have been studied extensively, these TA systems do not have homologs in P. aeruginosa and little is known about the mechanisms behind P. aeruginosa persister cell development despite a high level of emergence specifically within CF patients [Persister cells are an antibiotic tolerant phenotype of bacteria which enter a metabolically inactive state of dormancy but return to a wild-type level of antibiotic susceptibility once antibiotic concentrations drop below the MIC leading to a population which is again susceptible to the antibiotic  5,51,52,5251,52. in 1942 . Two yeaild-type . Furtherild-type . TA systild-type . Overpro1 system ,59. With1 system . For the1 system . Althougpatients . Persistpatients ), howevepatients , althoug3.2P. aeruginosa, they were first described in CF associated P. aeruginosa respiratory tract infections [P. aeruginosa SCVs, it was found that 33 patient samples contained isolates from this phenotype. SCVs are typically characterized by their small size relative to wild-type. This small colony size is due to either a slower growth rate like that exhibited by Staphylococcus aureus SCVs [Pseudomonas' rugose SCVs (RSCVs), which also allow SCVs to be tolerant to a range of antibiotic classes [P. aeruginosa RSCVs could be induced by the addition of kanamycin to culturing media and were able to link the phenotype to the cyclic-di-GMP (cdG) phosphodiesterase gene, pvrR [P. aeruginosa PAO1, the WspR diguanylate cyclase (DGC) [Small colony variants (SCV) are phenotypic variants directly associated with antibiotic tolerance and persistent infections. In fections . After tfections . After teus SCVs ,69, or m classes ,69. SCVs classes . Drenkarne, pvrR . Additiose (DGC) . cdG is se (DGC) . cdG is se (DGC) . Within se (DGC) . These cse (DGC) .3.3P. aeruginosa which is driven by an alternative metabolism induced in anaerobic or microaerobic environments [Pseudomonas cells as an alternative electron acceptor due to the lack of available oxygen. Further research has shown that when glucose and pyruvate are converted into acetate by fermentation, phenazines are able to regenerate the oxidant NAD(P)H by acting as an extracellular electron shuttle and alleviating the redox constraints on the metabolic pathway [P. aeruginosa. Agmatine is a pre-poly-amine intermediate metabolite of the arginine decarboxylase pathway. After observing a correlation between agmatine concentration and CF disease severity, McCurtain et al. further explored the effects of this metabolite on antibiotic tolerance and virulence. It was found that cells harboring an increased amount of agmatine were tolerant to positively charged aminoglycosides and polymyxins but were still susceptible to antibiotics with a neutral charge. It is believed that this is due to membrane stabilization since agmatine is also positively charged [P. aeruginosa including the mechanisms conferring this type of antibiotic tolerance, particularly their role in a clinical setting.In addition to the aforementioned, well described, antibiotic tolerant phenotypes, other metabolic variants have been identified which are tolerant to antibiotics. In 2019, Schiessl et al. described an antibiotic tolerant phenotype of ronments . This pa pathway . While t pathway . An over charged . Further3.48 CFU/mL [9 CFU/mL) used to detect phoenix colonies provide a more sensitive system which may be able to further detect heteroresistance [In 2020, Sindeldecker et al. described a novel antibiotic tolerant phenotype which they have termed phoenix colonies . Phoenix8 CFU/mL . The higsistance . As phoe3.5P. aeruginosa specifically, the main components of the EPS are Pel, Psl, and alginate, three exopolysaccharides [In addition to phenotypes which occur in single cells of a population, antibiotic tolerance can also be conferred at the population level though mechanisms such as biofilm formation. Biofilms are populations of bacteria which conglomerate and encase themselves in an extracellular polymeric substance (EPS) . The EPScharides . cdG is charides . Quorum charides  and conscharides . One impcharides , the moscharides ,99. Thischarides ,100,101.charides ,102. As charides . Clinicacharides . Biofilm4P. aeruginosa, at both the single cell .The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Paul Stoodley reports financial support was provided by


Altered lower back muscle activity is proposed as a contributing factor to the reoccurrence and chronicity of low back pain (LBP). This study compared lumbar muscle activity during trunk extension in patients with continuous chronic LBP (CLBP), non-continuous CLBP, recurrent LBP (RLBP) and healthy subjects.In 75 subjects , surface electromyographic (EMG) activity of the lumbar erector spinae (ES), multifidus (MF), latissimus dorsi (LD) and gluteus maximus (GM) was recorded during the concentric, holding and eccentric phase of a modified Biering Sorenson exercise.p = 0.011; p = 0.009 respectively) and the holding phase . Higher EMG activity was observed in continuous CLBP compared to RLBP in the ES and MF muscles in the holding phase , and in the MF in the concentric phase (p = 0.046), but not in the ES (p = 0.062). No differences in muscle activity were established in either the concentric, holding, and eccentric phase for the LD and GM muscles. No differences were found between non-continuous CLBP and the other groups.Continuous CLBP patients showed higher EMG activity in the ES and MF muscles compared to healthy controls in the concentric (An enhanced muscle activity of the lumbar muscles during the concentric and holding phase was observed during trunk extension in patients with continuous CLBP compared to patients with RLBP and healthy subjects. No differences between groups are present in the GM and LD muscles during concentric and holding phases and for any muscle in the eccentric phase. Recurrence is common in people with low back pain (LBP) , but it Altered back muscle activity has been proposed as a factor contributing to LBP. Several lumbar muscles such as erector spinae (ES), multifidus (MF), latissimus dorsi (LD) and gluteus maximus (GM) play an important role in the stabilization and dynamic control of the lumbar spine , 3.Numerous studies have reported changes in the back muscle activity patterns in both patients with recurrent and chronic LBP. Enhanced activity of the superficial back muscles has been reported in people with chronic LBP (CLBP) compared to healthy controls –6 as a cCurrently, differences in lumbar muscle activity between patients with recurrent and chronic LBP are still unclear. It can be hypothesised that different mechanisms occur in both LBP populations. A recent study established enhanced metabolic activity in CLBP patients compared to RLBP patients . It is tFurthermore, heterogeneity amongst CLBP patients is known. Some authors suggest that the CLBP group consists of several subgroups, each marked by different characteristics  and diffHence, this study aims to compare lumbar muscle activity in the ES, MF, LD and GM during trunk extension in patients with different LBP persistence levels and healthy subjects.We hypothesized that LBP might represent itself as a spectrum in which electrical muscle activity is normal in healthy persons and alterations in muscle activity is directly proportional to the continuation of pain complaints.This comparative cross-sectional study was part of a larger study of which results of other endpoints have been published elsewhere , 14. SubIn this study, participants had to perform 10 repetitions of the modified Biering-Sorenson test on a variable angle table  Fig. . The EMGBefore the execution of the extension exercises, 3 maximal voluntary contraction (MVC) trials of 4 s duration, with 30 s of rest between each trial, were captured per muscle group. This procedure was conducted according to the Noraxon guidelines. All tests were performed with the patient in prone position. MVC’s for LD and GM were measured at both right and left side . To obtaThe raw EMG signals were submitted to electrocardiography and high pass filtering (20 Hz), rectification and smoothing using a root mean square algorithm with a 100 ms time constant. The highest activity of the MVC’s performed during 3 s was analysed. Two markers were placed for each contraction type of the exercise  and the interval between each pair of markers was considered for further analysis. To evaluate the intensity of the muscle activity during each phase of the exercise, Root Mean Square calculations and post hoc assembly of the average activation patterns were calculated. The average activity signals were normalized to MVC voltage. All EMG data-processing was performed using the MR3.10 software  , 18.All subjects were asked to indicate the site of the symptoms  as well as to rate their current pain intensity before, during and immediately after exercise performance by means of a Numerical Rating Scale . In addition, before the exercise, participants were asked to rate their expected pain from the exercise. After the exercise the rate of perceived exertion (RPE) on a BORG scale (ranging 6–20) was also registered. Disability on the day of assessment was assessed by the Roland-Morris disability questionnaire, representing the daily physical activities and functions affected by LBP complaints . Pain scStatistics were performed in SPSS . Normality of all demographical and movement parameters was checked visually and through the Shapiro-Wilk test. Since the data were not normally distributed, differences between groups for demographical parameters, pain measurements, perceived exertion rate, disability, and assisted weight were analysed by the Kruskall-Wallis test, whereas a Mann-Whitney U test was used for post-hoc pairwise comparison in case of significant differences between groups. The Pearson Chi-Square was used to assess differences between groups for sex distribution and symptom site. To counter multiple testing, significance was set at α < 0.01.A mixed model analysis was performed to compare EMG activity of the different muscles between subjects. Model selection and validation was based on statistical tests for parameter estimates, comparison of Akaike’s Information Criterion values and inspection of residual plots. These mixed models account for correlated measures by including a random intercept for “subject” and “side” (left and right) and were adjusted for “group”  and “phase” . Interaction effects between group and phase were investigated. Furthermore, age as a covariate appeared not influential on the outcome for EMG. No other relevant covariates were taken into account. Parameter estimation was performed by restricted maximum likelihood and estimated means were corrected by Bonferroni to adjust for multiple comparison. Significance was set at α < 0.05.p = 0.011). Post-hoc comparisons showed that patients with continuous CLBP were significantly older compared to patients with RLBP (p = 0.002) while there was no difference between the other groups. No differences between any groups were noted for BMI, sex and assisted weight.Seventy-five subjects participated in this study of which 16 had continuous CLBP, 15 non-continuous CLBP, 23 RLBP and 21 healthy controls. All patient characteristics can be found in Table p < 0.001), during (p < 0.001) and after (p < 0.001) exercise, as well as for expected pain (p < 0.001) (Table Significant differences between groups were found for pain before (1) Table . No diffp < 0.001; p < 0.001 respectively) and healthy controls . No significant differences in pain before exercise was seen between healthy controls and RLBP and between continuous and non-continuous CLBP.Before exercise, patients with continuous CLBP and non-continuous CLBP indicated higher pain intensity compared to RLBP (p = 0.001), non-continuous CLBP (p < 0.001) and continuous CLBP (p < 0.001). No differences in pain during exercise were seen between the LBP groups.During exercise, lower pain intensities were reported by healthy controls compared to RLBP (p = 0.001), non-continuous (p < 0.001) and continuous CLBP (p < 0.001). Furthermore, patients with RLBP had significant lower pain afterwards compared to continuous CLBP (p < 0.001). No differences were found between non-continuous CLBP and RLBP or between non-continuous CLBP and continuous CLBP.After exercise, healthy controls reported significant lower pain compared to RLBP  and in continuous CLBP compared to RLBP (p = 0.003). No differences were found between healthy controls and RLBP, non-continuous and RLBP and non-continuous and continuous CLBP.Pain expected after exercise was significantly higher in non-continuous and continuous CLBP compared to healthy controls (p < 0.001). Furthermore, patients with RLBP experienced higher levels of disability compared to healthy controls (p < 0.001). No difference in disability was found between patients with continuous and non-continuous CLBP.Patients with continuous and non-continuous CLBP were more disabled compared to healthy controls and patients with RLBP , but not for LD or GM (p > 0.05).A significant interaction effect for phase and group was found for the ES and MF muscles  and RLBP . Also in the concentric phase, significant higher EMG activity was seen in continuous CLBP compared to healthy controls in ES (p = 0.011) and in MF (p = 0.009). Furthermore, significant higher EMG activity is seen in the concentric phase in the continuous CLBP group compared to the RLBP for the MF muscle (p = 0.046), but not for the ES muscle (p = 0.062). No differences in ES or MF muscle activity were found between healthy controls and RLBP, between healthy controls and non-continuous CLBP, between RLBP and non-continuous CLBP and between non-continuous CLBP and continuous CLBP. Finally, no differences between groups were found for LD or GM in either the concentric, holding or eccentric phase. Moreover, no differences between groups were found for any muscle in the eccentric phase. Details on the EMG measurements can be found in Table Patients with continuous CLBP showed higher ES and MF EMG activity in the holding phase compared to healthy controls (p = 0.062). However, no differences between groups were found for GM and LD in any phase. Finally, no differences were detected between non-continuous and continuous CLBP nor between the RLBP patients and healthy persons, at any phase of the exercise.This study intended to establish differences in myoelectrical lumbar muscle activity between healthy subjects and patients with RLBP, continuous and non-continuous CLBP proportionally to the continuation of pain complaints. This study could partly confirm the initial hypothesis. Results show that muscle activity in the ES and MF in the concentric and holding phase was higher in continuous CLBP compared to healthy people. Similarly, enhanced muscle activity was established in the MF and ES in continuous CLBP compared to RLBP, except for ES in the concentric phase  and MF (in the concentric and holding phase) confirms the limited previous research establishing enhanced muscle activity in the lumbar muscles in continuous CLBP compared to RLBP. Goubert et al. (2017)  evaluateNo significant differences between groups could be found in the eccentric phase. Previous research established overall muscle activity in the concentric phase is higher compared to the eccentric phase , 23, 24,No differences between the LBP groups were found for the GM or LD muscle activity. This is in accordance with a previous study establishing only limited activation of the GM and LD during the modified Biering-Sorenson exercise .We could not find evidence for alterations in RLBP in remission compared to healthy controls. This is however in contrast with findings of previous research showing either lower muscle activity in the MF during pain-free episodes in RLBP , or enhaNo differences in lumbar muscle activity were found between the non-continuous CLBP and the RLBP or the continuous CLBP. Taken together with the above-mentioned results, this study might suggest that the LBP population represents itself as a spectrum, in which muscle activity in MF and ES in the holding and concentric phase is normal in healthy persons and increases gradually with the amount of pain days in LBP populations. These findings provide a potential pathophysiological mechanism for the increased likelihood of recurrence and maintenance of the LBP condition. The pain intensity before, during and after exercise, disability and rate of perceived exertion in this LBP population are also positioned along a continuum being the lowest in RLBP, increasing in non-continuous CLBP and the highest in continuous CLBP. Although the distributions represent a spectrum of LBP, it should be highlighted that a large heterogeneity exists in the individual pain and disability scores, indicating treatment strategies should always be individualized.In our study, both CLBP groups indicated higher expected pain due to exercise compared to asymptomatic participants and RLBP, although only a borderline higher expected pain was noted in the non-continuous CLBP group compared to the RLBP group. These results are in line with previous studies establishing the relationship between expectancy of pain and pain-related fear for movement . FurtherFrom a clinical point of view, this study offers additional knowledge that muscle activity is higher in patients with continuous CLBP compared to RLBP, and non-continuous CLBP seem to float in between. These findings highlight the importance of strategies in normalizing muscle activity in the three LBP groups during rehabilitation. However, there are some limitations that must be considered. The amount of physical activity of the participants was not registered in the current study. Since the positive influence of an active lifestyle on spinal control has already been demonstrated , particiIn summary, continuous CLBP patients present increased ES and MF muscle activity during the holding and concentric phase of an extension exercise compared to healthy controls and to a lesser extent compared to RLBP patients. No differences in muscle activity are found between RLBP and healthy persons and between non-continuous CLBP and all other groups. No differences in muscle activity are found for GM and LD.


TB is still one of the leading causes of death among HIV patients. This study evaluates the effect of TB on the mortality rate, survival time, and predictors of survival in patients with AIDS living in different areas in São Paulo State (SPS).Retrospective cohort of adolescents and adults with AIDS, diagnosed between 2003 and 2007 and followed-up until 2014. Data were obtained from the Brazilian Ministry of Health. Mortality rates were estimated by person-years. Survival analysis used the date of diagnosis as the reference for the construction of Kaplan–Meier curves. The Cox model was used for the investigation of survival-associated factors.3 at diagnosis of AIDS. The 12-year survival probabilities were 74.1% and 55.7% among patients without and with TB co-infection, respectively. After adjustment for sex, age and year of diagnosis, the following exposures were independently associated with lower survival: residing in municipalities of the Interior (Hazard ratio (HR) = 1.43) and Coastal Area (HR = 1.9); illiteracy (HR = 2.61); being co-infected with TB (HR = 1.70); CD4 count below 200 cells/mm3 at AIDS diagnosis (HR = 2.31); viral load above 500 copies/ml at AIDS diagnosis (HR = 1.99); HAART1 regimen (one non-nucleoside reverse transcriptase inhibitor or boosted old protease inhibitors) (HR = 1.94).A total of 35,515 patients were included, of whom 63.0% were male; 64.7% at the age group of 30 to 49 years, 64.4% were white, 12.9% co-infected with TB, and 37.6% had CD4 count above 200 cells/mmThe impact of TB on survival of AIDS was heterogeneous, and affected by age, years of formal education, early AIDS diagnosis, and proper ARV treatment. These factors may not fully explain the different survival outcomes in each of the four regions within the same state. These results may subsidize focused interventions and public health policies conveying specific needs in each of the areas. Until covid-19 pandemic, tuberculosis (TB) was the leading cause of death from a single infectious agent worldwide, accounting for one-third of all deaths among people living with HIV/AIDS. This disease is therefore an important factor associated with lower survival in this group of patients . The intIn Brazil, the Unified Health System (SUS in the Portuguese acronym) provides universal and free of charge health care and that includes diagnosis and treatment for TB and HIV/AIDS. In São Paulo state, TB diagnosis and treatment is provided by the primary health care, where HIV diagnosis is also offered, often with rapid tests. While HIV clinics are less numerous than primary health units, both are spread around cities and towns to provide access. The introduction of HAART in 1996 led to a substantial decline in mortality and an increase in the survival of patients living with HIV/AIDS –7. In BrThe burdens of AIDS and TB in São Paulo are high. In 2014, the last year of this study follow-up, new 7137 and 16,477 AIDS and TB cases were reported and represented 15 and 24% of all AIDS and TB new cases in Brazil . The preConsidering the high burden of AIDS and TB in São Paulo and the paucity of publications on the importance of TB–HIV co-infection in the state, we conducted this study to estimate mortality rates and the median survival time in AIDS patients diagnosed between 2003 and 2007, and followed-up until 2014 with and without TB. In addition, we investigated the importance of TB co-infection as a predictor of survival in a cohort of patients with AIDS living in the four different areas of the state, each one with different incidences of AIDS and TB.This is a retrospective cohort study that evaluated all patients with AIDS aged 13 years or older reported to the São Paulo epidemiological surveillance system, who were diagnosed with AIDS between 2003 and 2007 and followed up until December 31, 2014. This study is part of a survey that covers all cases of AIDS reported in Brazil over the same period, which compose the BIAIDS-Brasil Cohort, a survival analysis of AIDS in Brazil .The study area was São Paulo state, with a population of 44 million inhabitants in 2014 . In thatNew cases of AIDS of both sexes, aged 13 or older, living in São Paulo state and reported to the AIDS surveillance system were included in the study population. Patients who died within 30 days of being diagnosed with AIDS were excluded. HIV infected individuals without AIDS and those registered with and monitored for less than 30 days by the Sistema de Controle de Exames Laboratoriais (SISCEL—Laboratory Test Control System) and/or by the Sistema de Controle Logístico de Medicamentos (SICLOM—Logistics Control System of Medicines) were also excluded.3, regardless other causes of immunodeficiency. Death from AIDS was defined as any case whose underlying cause of death was AIDS, reported as B20 to B24 of the 10th version of the International Classification of Diseases (ICD-10)  wΧ2) and continuous variables by the Student t-test or Mann–Whitney–Wilcoxon test. Data from each of the four regions were analyzed: (i) São Paulo City ; (ii) Greater São Paulo Region, excluding the capital (GSPR); (iii) São Paulo State Coastal Area (SPCA), and (iv) Interior São Paulo State (ISPS).The main characteristics of the study population were described. Categorical variables were compared by the Chi-squared test  as the denominator .The Kaplan–Meier method was applied to estimate the median survival time of patients with AIDS. The Peto log-rank test was used for the comparison of estimated survival curves. The data were censored in three situations: (i) patients who on December 31, 2014, the date of completion of the study, were alive and under follow-up (administrative censoring); (ii) patients who died from a cause other than AIDS; in this case, the data were censored on the day of death; (iii) patients who dropped out of follow-up, i.e., those who had no new records in SISCEL/SICLOM for a period of 1 year or longer; in this case, the data were censored on the day of this last record.In order to investigate the association between exposures of interest and time to death from AIDS, the Cox proportional hazards model was applied to estimate the unadjusted and adjusted hazard ratio (HR), with 95% confidence intervals (95% CI). Variables with p < 0.25 in bivariate analysis and/or that exhibited biological plausibility, adjusted for age, sex and year of diagnosis, were included in the final Cox model. The likelihood ratio test and Schoenfeld residuals were used to assess the goodness-of-fit of the final model.The protocol of this study was submitted to and approved by the Ethics Committee on Research Involving Humans of the STD/AIDS Referral and Training Center, São Paulo State Department of Health . Informed consent was not required and obtained as it is a retrospective study. All methods were performed in accordance with the relevant guidelines and regulations and ethics committee directions.Initially, 49,067 new AIDS cases reported to the epidemiological surveillance were identified. According to the inclusion and exclusion criteria of the study, 8278 16.9%) patients diagnosed with AIDS on the day of death, 4997 (10.2%) who were followed-up for less than 30 days, and 277 (0.6%) with inconsistent data were excluded. The study population consisted of 35,515 patients; of whom, 27,029 (69.1%) were followed-up during the study period, here included 2487 patients who died of other causes than AIDS, and 8486/35,515 (23.9%) who had AIDS as underlying cause of death, totaling 10,973 (30.9%) deaths  and excluded ones . However, the prevalence of TB co-infection was higher in the study group than among excluded patients, 12.9%  versus 7.3% (468/6427), p < 0.001. It should be noted that this information was not available for 7125/13,552 (52.6%) patients.3 at AIDS diagnosis  were male, 64.7%  belonged to the 30 to 49 years age group, while the mean and median age was 37.4, 95% CI (37.3–37.5) and 36 years, respectively; 64.4%  were white (self-reported), 97.2%  lived in the urban area, 52.7%  had more than 7 years of schooling, 12.9%  were co-infected with TB, and 37.6%  had CD4 count below 200 cells/mm3 at AIDS diagnosis , and patients who did not receive ARV  in the co-infected group  showed a higher proportion of men , individuals with up to 7 years of schooling , individuals with a higher mean and median age (38.1 and 37 years versus 37.3 and 36 years), blacks and mixed race/black , injection drug users (IDU) , patients with CD4 count below 200 cells/mm3 at diagnosis , and patients who did not receive ARV .When we compared the 24,542 patients who continued the follow-up until the end of 2014 with the 8486 patients who had died from AIDS as underlying cause, we found among the patients who died a higher proportion of TB co-infected patients , individuals with up to 7 years of schooling , individuals with CD4 count below 200 cells/mmThe AIDS-related mortality rate in the groups with and without TB co-infection was higher in the 1st year after diagnosis and declined progressively until the end of follow-up. However, these rates were not homogenous across the four regions of the state, being expressively higher in SPCA and lower in GSPR. Among non-coinfected patients, respectively comparing SPCA and GSPR residents, the relative risk (RR) was 1.74 (p < 0.001) in the first year of follow-up and 2.38 (p < 0.001) at the end of follow-up  Fig. ; howeverThe 12-year survival after AIDS diagnosis in patients without and with TB co-infection was different in the regions of the state, as follows: SPCA: 75.3% versus 60.5% ; capital: 76.3% versus 55.9% ; GSPR: 75.9% versus 53.2% ; ISPS: 71.6% versus 53.2% , with significantly lower survival in co-infected patients from all regions ; viral load above 500 copies/ml at diagnosis ; HAART1 ; pre-HAART , and no ARV use   was, in 2014, the lowest of the four regions, and AIDS incidence 30.9/100,000) was only above the one in ISPS, where it was estimated in 21.9. In this setting, mortality rate for TB coinfected patients 1 year after AIDS diagnosis (10.2) was lower than the 14.2 at the end of 12 years follow-up for the same group of patients living in SPCA, and would still reach a low 5.2 in the same period. Along the coast, TB incidence in 2014 was nearly four times that of GSPR, whereas AIDS incidence was 1.6 times higher [/100,000 A nationwide evaluation classified Brazilian municipalities in lower or higher socio-economic scenarios (LSS and HSS) defined by multiple variables including Gini index, HDI, illiteracy, poverty, among others. LSS municipalities had higher TB incidence and mortality. The whole SPCA was classified in the LSS, whereas part of GSPR, the capital and apart from small islets, ISPS were HSS . This daSuccessful prevention strategies and timely effective treatment strategies would probably impact both infections burden and related mortality. Understanding the differences in each of the regions and its specific needs is urgently needed.The interpretation of the present results must take into account some limitations of the study, including the use of secondary surveillance data that are prone to underreporting and lack of completeness. Data on the treatment regimens refer to the drugs distributed to patients and not necessarily to their effective use. Date of TB occurrence and its treatment outcomes were not included in the analysis and within this context, it is possible that TB timing and unfavorable outcomes, such as TB losses to follow up, may also be associated with mortality .The research shows that TB co-infection still has a high impact on mortality of patients living with AIDS, with the highest number of deaths occurring in the 1st year after AIDS diagnosis. Within the four São Paulo state regions, mortality rates were worse in the coastal area, where incidence of both infections and social economic indicators are worse. Whether one cause or consequence of the other, it seems that without addressing social disparities, HIV and TB control will not be achieved. The implications of factors associated with survival, with emphasis on age, education, early diagnosis and effective treatment regimens reaffirm this understanding. The richest state of a middle-income country with universal free of charge medical care has yet to find and implement interventions and intersectoral policies to promote health and living equity to patch the gap that still leaves out the most vulnerable.


For complete utilization of construction and demolition (C&D) waste, an investigation of all size fractions of C&D waste generated during the recycling process should be conducted. In this work, the effects of three recycled concrete materials with different sizes (recycled coarse aggregate (RCA) with a size of 4.75–25 mm, recycled fine aggregate (RFA) of 0.15–4.75 mm, and recycled powder (RP) smaller than 0.15 mm) produced from concrete waste on the fresh and hardened mechanical properties of concrete were evaluated. The replacement ratios of natural coarse and fine aggregates by RCA and RFA were 30, 60, and 100%, and those of ordinary Portland cement for RP were 10, 20, and 30%. The results showed that the concrete properties deteriorated with increasing replacement ratio regardless of the type of recycled materials. The properties were reduced in the order of the use of RFA, RCA, and the simultaneous use of RCA and RFA. In addition, concrete with 30% RP showed lower mechanical strength than concrete with 100% RCA and 100% RFA. However, all concretes could be applicable for structural purposes under different environmental exposure conditions. In particular, concretes with 10% RP and 20% RP showed better cost-benefits compared to natural aggregate concrete with 100% ordinary Portland cement. These promising findings provide valuable initiatives for the effective and complete recycling of C&D waste. One of the areas of human activity involved in the increase of CO2 emission is the concrete industry. Despite the efforts of several researchers, such as carbon-friendly design and extending the lifecycle of structures to reduce CO2 emissions [2, is the production of cement, the key constituent of concrete. According to Andrew [2 emissions accompanying the cement production in 2016 were estimated at 1.45 ± 0.20 Gt CO2. However, other technological operations related to the production of concrete, from the extraction of natural resources , their transport, through mixing the components of the concrete mixture, its laying and compaction, including concrete care as well as the use and maintenance of buildings until the last stages of their life, also make a significant contribution to the anthropogenic CO2 emissions [The evidence for the loss of stability of the Earth’s natural climate system, especially in view of the increase in the frequency of extreme weather phenomena including global warming, despite the debate over their actual causes  is difficult to contest. However, the most probable main cause is the growing increase of carbon dioxide .2 emissions in the concrete industry. Accordingly, several studies have investigated the effectiveness of various supplementary cementitious materials, such as glass powder and fly ash, to decrease cement usage [RCA, which occupies the largest volume in concrete, has received the most attention from researchers as a substitute for natural coarse aggregates (NCA). In addition, technologies and methods for improving the performance of recycled aggregate concrete (RAC) have been developed mainly based on RCA. Therefore, the knowledge system on the effects of RCA on concrete is well-established ,14, and nt usage ,28. Howent usage . In the In this context, the transition to the ‘zero-waste’ pursued by today’s society in the construction sector cannot be achieved without a systematic discussion of the influence of recycled concrete materials of all size fractions generated from C&D waste. As described above, several studies have been conducted on the application of RCA, RFA, and RP as concrete materials, but these studies discuss the properties of concrete using materials obtained from different C&D waste sources or using two recycled concrete materials, mainly RCA and RP ,30,31. P2/g was used as a cementitious binder. The composition of RC is provided in The RCA, RFA, and RP used in this study were obtained by crushing intentionally produced NAC. This NAC serves both as a parent concrete for obtaining recycled concrete materials and as a reference concrete (RC) for property comparison. Natural granitic crushed aggregate with a nominal maximum aggregate size of 25 mm and siliceous river sand were used as NCA and NFA for the production of parent concrete. The specific gravity and water absorption of NCA were 2.68 and 0.88%, respectively, and those of NFA were 2.6 and 0.91%. Ordinary Portland cement (OPC) with a specific gravity of 3.14 and a specific surface area of 3550 cmAt 56 days of age, the RC specimens after the testing described in To investigate the influence of RCA, RFA, and RP on the mechanical performance of concrete, 12 different concrete mixtures were prepared based on the ACI mix design . AccordiRCAC-replacement ratio: concrete made from NCA, NFA, OPC, and RCA that replaces NCA in a certain ratio .RFAC-replacement ratio: concrete made from NCA, NFA, OPC, and RFA that replaces NFA in a certain ratio .RPC-replacement ratio: Concrete made with NCA, NFA, OPC, and RP that replaces OPC in a certain proportion . Test results for RPC were adopted from the previous study of the author .RCFAC-replacement ratio: Concrete made by replacing both NCA and NFA with RCA and RFA in a certain percentage . OPC was used as a binder.Therefore, in this study, the replacement ratios of 30%, 60%, and 100% were applied. The description and notation for each mixture are as follows:3 binder , and the water-to-cement (w/c) ratio was fixed at 0.45. Details of the mix proportions of concrete are shown in All concrete mixes had a constant quantity of 389 kg/mSince the moisture state of aggregates is one of the parameters influencing the properties of concrete, the moisture condition of each aggregate was considered before mixing. Due to the high water absorption of RCA, pre-wetting is required to obtain proper workability. However, RCA in the saturated surface dry (SSD) state did not produce a favorable effect in terms of mechanical properties of concrete ,35. On tA mechanical pan mixer with a capacity of 60 L was used for the mixing of concrete components. Coarse and fine aggregates were put in a mixer and mixed for 30 s, then OPC was added and mixed for 90 s to disperse the material. Water was then added and mixed for 2 min. After the mixing process, the fresh properties of the concrete were evaluated, and specimens for evaluating the mechanical properties of the concrete were made in 100 × 200 cylindrical molds as per ASTM C192 . The spe3) of each concrete was calculated based on the raw material price surveyed by the Construction Association of Korea as of November 2021  from the manufacture of concrete components are presented and the values have been taken from [Based on the mix proportions, the global warming potential (GWP) of each mix was assessed. In ken from ,45,46.The test results for the air content of the concrete mixes are shown in The 28- and 56-day compressive strengths for different types of concrete incorporating each recycled concrete material are shown in The experimental results have shown that the addition of recycled concrete materials reduces compressive strength regardless of the type of recycled material. This is in line with the general consensus of previous studies that the use of recycled concrete materials has a negative effect on the mechanical properties of concrete ,51,52,53For concrete incorporating RP, the difference in compressive strength between RPC-10 and RC was 0.5 and 1 MPa at 28 days and 56 days, which is only 1% and 3% lower than that of RC. This insignificant variation was attributed to the filling effect, whereby RP, which is finer than NFA, fills the micropores, where the concrete becomes more compact and dense, reducing internal stresses and early crack propagation . HoweverThe test results for splitting tensile strength at 28 days are presented in The addition of 10% RP did not seem to have a significant effect on the splitting tensile strength of concrete. However, when 20% RP was added, tensile strength dropped sharply and showed similar strength to that of RCFAC-100. The tensile strength loss of RPC observed in this study was 4–29%, which is in good agreement with the values reported in previous literature. Cantero et al.  reportedThe test results of the elastic modulus of concretes at 28 and 56 days are presented in Since the elastic modulus of concrete is closely related to the stiffness of the aggregate, porosity, and bonding of mortar, Evangelista and de Brito  noted thThe addition of 10 and 20% of RP caused only 2 and 6% of elastic modulus loss, showing superior modulus compared to other types of concrete, but a sharp loss of 23% was observed at 30% RP addition. Although this was not exactly consistent with the conclusion of a study by Xiao et al. , that re2) for all specimens was 0.50, which does not indicate a strong correlation. In particular, considering that RPC-30 mix has a very high density of about 2300 kg/m3 at the low strength of 26 MPa compared to other mixtures, regression analysis of concrete made with recycled aggregates  and RP was performed separately. As a result, strong correlations were found in both groups. Concrete with RP showed a R2 of 0.87, and concrete with aggregates had a R2 of 0.94.cuf) and splitting tensile strength (spf) at 28 days of age is shown in The relationship between compressive strength  of concrete mixtures at 28 and 56 days. In 2 value of 0.94 was observed between compressive strength and elastic modulus. In addition, a similar pattern of the relationship between compressive strength and splitting tensile strength found in the previous section was observed.A strong correlation with the RThe equations presented in each code overestimated the elastic modulus, while the prediction models based on concrete with recycled aggregates agreed well with the current experimental results. In this regard, Wang et al.  pointed In All the concrete mixes incorporating recycled concrete materials are about 2.6% to 20% more economical than RC made of NCA and NFA, in proportion to the material replacement ratio. It should be noted that the concretes with the lowest manufacturing cost are RPC-30 and RCFAC-100, but these two mixtures did not achieve the target strength. Therefore, the unit price of concrete should not be considered as the only parameter in the economic analysis, and cost–benefit analysis should be performed based on the intended purpose. Since the slump of all concretes was within the tolerance range (100 ± 25 mm), a target strength of 30 MPa should be considered in this study. The same principle applies to eco-efficiency analysis. In view of that, the mixtures with values higher than RC  were RPC-10 and RPC-20. Since the unit cost of OPC is more than ten times higher than that of aggregate, replacing OPC by RP even at a low replacement ratio has a higher value over replacing natural aggregates with recycled aggregates.2 emissions from cement manufacturing were much higher than those from aggregate manufacturing. According to Flower and Sanjayan [2 emission coefficient related to cement production is 0.82 t CO2-eq./ton, while those of coarse granite aggregates and fine aggregates are 0.0459 and 0.0139 t CO2-eq./ton, respectively. Therefore, the replacement of OPC by RP can provide greater environmental benefits than the replacement of natural aggregates by recycled aggregates. For this reason, in the eco-efficiency defined as the ratio of the 28-day compressive strength to the GWP, concretes that showed higher values than RC were RPC-10 and RPC-20, and the remaining mixtures were in the range of 0.87–0.97, showing lower values than RC.A similar pattern was observed in environmental impact assessments. It is clear that concrete made from recycled materials has a lower GWP than RC, providing environmental benefits. When RCA and RFA were used separately at 100%, GWP could be reduced by about 3–4%, and when both materials were used simultaneously, about 7% of GWP could be reduced. Moreover, concrete with 10% replacement of OPC with RP reduced GWP by 7%, which is similar to that of concrete incorporating 100% RCA and 100% RFA simultaneously. The environmental impact was reduced by up to 20% as the RP content was increased up to 30%. This is because the COConsidering the above, the cost and environmental benefits of using recycled concrete materials are not sufficient to offset the unfavorable effect on the mechanical performance of concrete in some cases. Nevertheless, it should be noted that all concretes, except for RPC-30 and RCFAC-100, achieved their target strength and thus could be applied for structural purposes. In terms of cost value and eco-efficiency, the addition of 20% RP is recommended. In addition, although the cost value and eco-efficiency were lower than those of RC, the separate uses of 100% RCA and 100% RFA can be considered as a viable option because the unit cost and GWP of RCAC-100 and RFAC-100 were lower than those of RC while satisfying the required compressive strength. When RCA and RFA are used simultaneously, the replacement rate can be up to 60%.With the increased replacement ratios of natural materials by recycled materials, the slump of the concrete mixes was reduced (up to 19%) and the air content was increased (up to 0.6%) compared to the reference concrete, but the fresh properties were within the range required by the standard.As the replacement ratio increased, the mechanical properties of concrete decreased. The properties decreased in the order of RFAC, RCAC, and RCFAC at the same replacement ratio.The reduction of compressive strength and elastic modulus was only 1–4% for concrete with 10% RP and 6–8% for concrete with 20% RP. However, when 30% RP was added, the mechanical properties showed a rapid decrease of 23~29%, thus special attention is required for its use. Nevertheless, all mixtures could be applied as structural concretes under different environmental exposure conditions.The relationship between compressive strength, elastic modulus, and splitting tensile strength of concrete containing different size fractions of recycled concrete materials showed a strong correlation. However, for the relationship between compressive strength and density, RPC needs to be considered separately from RCAC, RFAC, and RCFAC.Replacing OPC with RP by up to 20%, cost value and eco-efficiency were superior to those of RC. Although the cost value and eco-efficiency of concrete incorporating RCA and RFA were lower, the production cost and GWP were lower than those of RC; thus, it can be considered economical and eco-friendly if the intended requirements are achieved.A study was conducted on the properties and the economic and environmental impact of concrete incorporating recycled concrete materials of different size fractions obtained from concrete waste. The following conclusions can be drawn:


In this study, the effect of internal pores formed by a superabsorbent polymer (SAP) was analyzed by evaluating the compressive strength, chloride penetration depth, drying shrinkage, and pore size distribution of SAP-containing concrete, while securing workability using a water-reducing agent (WRA). The experimental results showed that the amount of WRA necessary increased as the amount of SAP added increased, and that the compressive strength was the highest when the SAP content was 1.5% of the concrete mix. Drying shrinkage tended to decrease as the SAP content increased, and it decreased by approximately 31–41% when the SAP content was 2.0% compared to that of the reference mix. The SAP expanded by approximately three times inside concrete, and it was distributed within the internal pores of air-entrained concrete. The optimal SAP content in concrete mix was 1.5%, and an SAP content of 2.0% or higher adversely affected the workability and compressive strength. Concrete is undoubtedly an excellent civil and building material. Many researchers are working on various admixtures to improve the performance of concrete. Fly ash and blast furnace slag are widely known admixture materials to replace cement ,2,3, andSAPs decrease workability by absorbing mixing water, and workability rapidly decreases as the SAP content increases . In addiDrying shrinkage is a phenomenon that occurs when the moisture in concrete is released owing to low outside humidity. As moisture diffuses from the concrete surface to the outside after hardening, the capillary pressure, disjoining pressure, and surface tension change, which causes drying shrinkage. In general, drying shrinkage is significantly affected by the W/C ratio, and it tends to decrease as the W/C ratio decreases. It is well known that the addition of SAPs decreases autogenous shrinkage, and many studies have been conducted on this subject ,16,18,28The SAP that absorbs moisture inside the concrete mix expands, and its diameter increases by approximately three times according to a previous study . This voIn this study, a water-reducing agent (WRA) was used to prevent a decrease in workability caused by the addition of SAPs and to exclude the influence of adding mixing water to secure workability. In addition, the effect of internal pores formed by SAPs was investigated by evaluating the slump, air content, compressive strength, chloride penetration depth, drying shrinkage, and pore size distribution of concrete mixed with an SAP or an air-entraining (AE) agent. At this time, water-curing and sealed-curing experiments were separately conducted to evaluate the internal curing effect. In this study, the slump, air content, compressive strength, chloride penetration depth, drying shrinkage, and pore size distribution were measured on concrete that included an added SAP. The results were compared to the corresponding values in specimens without added SAP in order to evaluate changes in the properties of concrete. The SAP used in this study was atypical, the W/C ratio was set to 40% or 50%, and the amount of SAP added 0 (Ref.), 1.0%, 1.5%, and 2.0% of the cement mass. Additionally, a case in which an AE agent was added instead of an SAP was also studied.The concrete was cured under water or in sealed curing conditions to evaluate the internal curing effect of the SAP. Water curing was conducted by immersing the specimens in a constant-temperature water bath  after de-molding. Sealed curing was performed by sealing specimens with plastic material and storing them in a constant temperature and humidity chamber  after de-molding, so that moisture transfer to and from the outside could be restricted as much as possible. The SAP used in this study was an acrylic acid (AA)-based product, which is atypical. The shape of the SAP was determined by the manufacturing method. An atypical SAP product is manufactured in a large lump by gel polymerization and then crushed to the desired particle size. The SAP used in this study had particle sizes ranging from 38 to 100 μm. The cement used in this study was ordinary Portland cement (ASTM C 150) , and itsThe coarse aggregate used was a crushed stone with a maximum size of 19 mm, and the fine aggregate used was sand with a maximum size of 5 mm. The admixtures used in this study were an AE agent and a water-reducing agent (WRA). A polycarboxylic acid-based water-reducing agent was used.To evaluate the properties of fresh concrete mixed with the SAP, the slump and air content were measured in accordance with ASTM C 143  and ASTMIn most previous studies that used SAPs ,21,22,23In this study, the compressive strength of concrete was measured using Ø100 mm × 200 mm cylinder specimens in accordance with ASTM C 39 . The speA rapid chloride penetration test was conducted to evaluate the chloride penetration resistance with the addition of the SAP. The rapid chloride penetration test was performed according to the NT Build 492 standard. A concrete specimen with a size of Ø100 mm × 200 mm was cured for 28 days according to the curing method, and then cut into 50 ± 2 mm sections for testing. Subsequently each cut specimen was immersed in water for at least 24 h before a chloride penetration test, to prevent instantaneous absorption according to the internal moisture state. A 0.3 N sodium hydroxide (NaOH) aqueous solution was added to the positive electrode (+) of the test body, a 3% sodium chloride (NaCl) aqueous solution was added to the negative electrode (−), and a voltage of 30 V was applied for 8 h. The specimens for which the rapid chloride penetration test was completed were split, and the chloride penetration depth was measured by the silver nitrate discoloration method. The average value of three specimens was used. In this study, a mold gauge was used to measure the drying shrinkage according to the SAP content. The mold gauge is suitable for measuring the internal strain as it is embedded in concrete, and a PMF type was used. Prismatic specimens of size 100 mm × 100 mm × 400 mm were prepared in accordance with ASTM C 157  for use In this study, the entrained air and pore sizes in concrete were measured using image analysis and applying the traverse method in accordance with ASTM C 457 . The meaThe results of measuring the slump of concrete mixed with the SAP according to the W/C ratio and SAP content are shown in The results of measuring the air content of concrete mixed with SAPs according to the W/C ratio and SAP ratio are shown in The air content of hardened concrete mixed with SAPs may increase . In fresThe results of measuring the compressive strength of concrete mixed with SAPs according to the W/C ratio are shown in When the W/C ratio was 50% , the refWhen the AE agent was used, the lowest compressive strength was observed regardless of the W/C ratio. The use of the AE agent may improve workability owing to the entrained air, but it may decrease the compressive strength owing to the increase in air content. Therefore, it appears that the addition of an AE agent decreases the compressive strength.The results of the chloride penetration depth measurement by the rapid chloride penetration resistance test are shown in In the case of a W/C ratio of 50% b, the miThe results of measuring the drying shrinkage of concrete mixed with the SAP according to the W/C ratio are shown in In this study, mixing water was not added according to the SAP content. Therefore, the same unit water content was used in all concrete mixes under the same W/C ratio. Drying shrinkage occurs when the moisture in concrete is released to the outside. Therefore, a similar drying shrinkage should occur for concrete mixes with the same unit water content if the same materials are used. However, as the SAP content increased, the drying shrinkage decreased significantly. This appears to be due to the influence of the SAP which can be mainly divided into three categories.The first category is the influence of the reduced effective W/C ratio. As the SAP content increased, the effective W/C ratio decreased owing to the water absorption of the SAP, and thus, the drying shrinkage decreased. The second category is the influence of the reduced autogenous shrinkage. The drying shrinkage measured in this study includes autogenous shrinkage. The addition of the SAP significantly decreased autogenous shrinkage because of the internal curing effect in concrete, and the rate of decrease increased as the SAP content increased. Therefore, the reduced autogenous shrinkage by the SAP appears to have affected the decrease in drying shrinkage. The third category is the influence of relative humidity inside the concrete. The SAP added to the concrete expanded by absorbing water and maintained its saturation state during the water-curing period. When drying-shrinkage measurements were conducted under constant temperature and humidity conditions  upon the completion of water curing, shrinkage occurred as moisture evaporated from the concrete surface. Inside our sample concrete, however, a high relative humidity was maintained by the SAP in the saturation state, and the relatively high humidity could be maintained for longer with higher SAP content. The internal humidity appeared to decrease the drying shrinkage by interfering with the drying of concrete and the rapid evaporation of moisture.In some studies ,26, the The macroscopic pore size distributions of concrete mixed with SAP according to the W/C ratio are shown in In general, entrained air pockets are known to have a size between 50 and 300 μm. In a previous study , it was The reference mix (Ref.) exhibited a relatively higher proportion of pores larger than 300 μm than those in other concrete mixes. This appears to be because a large number of relatively large pores (500 μm or larger) and entrapped air were distributed with the general pore size distribution of concrete. It is expected that the addition of the AE agent and an SAP can improve the durability of concrete by decreasing the proportion of large pores (300 μm or larger), which may have an adverse effect on the durability of concrete.As SAP content increased, the WRA content required to secure workability increased. The maximum SAP content to secure workability was determined to be 1.5% or less.For the compressive strength of concrete mixed with SAP, the highest compressive strength was observed when the SAP content was 1.5% regardless of the curing method. When the SAP content was 1.5% or higher, sealed-cured specimens exhibited a higher compressive strength than water-cured specimens. This indicates that the compressive strength was affected by a reduction in the effective W/C ratio and the internal curing effect.The chloride penetration depth decreased when SAP was added, compared to that of the reference mix. The chloride penetration resistance was judged to improve owing to a decrease in the effective W/C ratio and the internal curing effect of SAP.As the SAP content increased, drying shrinkage showed a tendency to decrease. When the SAP content was 2.0%, the drying shrinkage decreased by approximately 31~41% compared to that of the reference mix depending on the W/C ratio. It appears that the drying shrinkage decreased owing to the combined effect of the reduction in the effective W/C ratio, the reduction in autogenous shrinkage, and the influence of the humidity inside the concrete.The addition of SAP increased the number of pores smaller than 300 μm compared to those in the reference mix. It is expected that desired pore sizes can be obtained inside concrete by adjusting the size of the dry SAP.In this study, the effect of internal pores formed by an SAP on the mechanical properties and drying shrinkage of concrete was evaluated, and the results are summarized as follows:


Manufacturing processes for monofunctional and multifunctional materials vary depending on the design optimization. Multifunctional continuous carbon fiber composites provide great potential in achieving coupled structural and electrical properties for their applications in aircraft, unmanned aircraft systems, and spacecraft. Proper optimization of tensile and electrical properties offers benefits early in the design and continuous operational safety phases to obtain coupled multifunctional properties. In this paper, fused filament fabrication additive manufacturing (AM) technique was used to fabricate continuous carbon fiber solid laminated composites test coupons. The proposed new method characterizes the electrical conductivity’s coupled effects on the tensile properties, including the failure loads and modes. This paper addresses a novel way of integrating electrical function into the composites that significantly reduce weight, potentially replacing the bulky electrical wires. Tensile and electrical conductivity tests were concurrently conducted on coupons, and the results were plotted and tabulated. The results showed the multifunctional properties of the maximum ultimate tensile strength of 392 MPa with the maximum tensile load of 8907 N, and resistance of 37.5 G·Ω. The average values for ultimate tensile strength and maximum load were 371 MPa and 8459 N, respectively. Additive manufacturing (AM) offers several advantages over traditional manufacturing techniques. Different AM techniques are available and the most commonly used AM technique is the fused filament fabrication (FFF) method. While the tensile strength of the 3D printed coupons was addressed, the experimental investigation of additive manufacturing of continuous carbon fiber composites as well as the electro-tensile multifunctional properties was not included . An openContinuous carbon fiber-reinforced polymer is manufactured using the FDM AM technique . FlexuraProcess-dependent factors on the damage and deformations of additively manufactured test coupons are evaluated for uniaxial tensile strength and inverse identification analyses . The effThus, in this investigation, the FFF 3D printing technique was used to fabricate continuous carbon fiber solid laminate composites test coupons. Multifunctional and coupled aspects of both tensile and electrical parameters of the 3D printed multifunctional continuous carbon fiber solid laminate composites are investigated concurrently. This will help evaluate multifunctional carbon fiber composites’ uses in the aircraft’s primary and secondary structures.The test specimens were digitally created as solid models using a CAD tool. The test specimens were manufactured using Markforged’s Continuous Carbon Fiber embedded into Onyx from Markforged Company . Since the continuous carbon fiber provides the best strength in the longitudinal direction, it was selected as the raw material. Continuous carbon fiber is also a commonly used composites raw material in aerospace applications due to its high strength-to-weight ratio. The raw materials, design parameters, and process parameters used in this investigation are listed in The temperature of the Onyx printing nozzle was 275 °C, and that of fiber laying nozzle was 250 °C. A special type of the FFF called as Markforged continuous filament fabrication (CFF) was used. The diameter of the extruded Onyx material was 0.40 mm wall thickness, and the diameter of the extruded fiber material was 0.9 mm wall thickness.3 (length × width × thickness). An isometric view of the test coupon is shown in The FFF AM technique was used to fabricate specimens at the RE3DTECH company . Markforged X7 printer was used for the manufacturing of the specimens. A raster angle chosen on the test coupons was 0 degree. Onyx FR and a spool of continuous carbon fiber, both fabricated by Markforged , were usThe multifunctional and coupled tensile and electrical properties of additively manufactured continuous carbon fiber composites were simultaneously investigated using an MTS machine   per ASTMAGATE-WP3.3-033051-102 was used as a reference  and a roThe test coupons were additively manufactured using continuous carbon fiber composites and Onyx FR as raw materials and a Markforged additive manufacturing machine. Electro-tensile properties of additively manufactured continuous carbon fiber solid laminate composites in room temperature dry were investigated using load frame and Keysight B2987A Electrometer (Keysight Technologies). The coupling effects of tensile properties on the electrical properties were assessed. The failure modes of the tested specimens from this multifunctional testing are shown in The experimental results showed that the test coupons exerted a maximum ultimate tensile strength of 392 MPa with an associated maximum load of 8907 N. The electro-tensile response of additively manufactured multifunctional and continuous carbon fiber solid laminate composites is shown in The multifunctionality of 3D printed continuous carbon fiber composites is not well investigated due to their relative infancy. While the advanced carbon composites are not new to the research community, the multifunctionality characterization for electro-tensile properties of the multifunctional 3D printed continuous fiber composites is new and was explored in this research. This research designed, developed, tested, and analyzed the electrical conductivity effect on the 3D printed multifunctional continuous carbon fiber composites’ tensile properties. The proposed method addressed the integrated characterization of the multifunctional carbon fiber composite structures’ electrical and tension properties. The experimental results showed that the coupons exerted a maximum ultimate tensile strength of 392 MPa and associated maximum load of 8907 N. The average ultimate tensile strength of 371 MPa, average maximum load of 8459 N, and the maximum electrical resistance of 37.5 G·Ω, was observed as the multifunctional property. The electrical resistance of the coupons was considerably stable and consistent with the structural deformation of the 3D printed continuous carbon fiber test coupons. Slight fluctuation in the resistance versus strain plots may be attributed to the breaking of the external onyx coating from the solid continuous carbon fiber strand in the test coupons. The contacts amongst the onyx coatings and the inner continuous carbon fiber strands touched amongst themselves during the tensile testing of the coupons. This phenomenon resulted in a slight fluctuation in the electrical resistance versus strain and also initiated the onset and propagation of the microcracks. This unique behavior, called multifunctional behavior, highlights a small rise and decrease in resistance along with the strain levels due to simultaneous multifunctional electro-tensile testing. A small fluctuation in electrical resistance values along the strain levels signified the void contents and delamination defects of the coupons are negligible compared to the traditionally manufactured solid laminate composites. Thus, the lack of delamination and voids on the 3D printed coupons compared with the traditionally manufactured composites is an enhancing factor for the multifunctional properties of the continuous carbon fiber composites for aerospace applications. The consistent failure modes and their mechanisms of the specimens implied the electro-tensile multifunctional performance is similar to the traditional composites. There are still not enough publications addressing information and knowledge on multifunctional continuous carbon fiber composites production by the FFF and on their mechanical, physical and electrical characterizations. There are a lot of literature on the monofunctional investigation of the monofunctional composites. While there appears to be some good research works on the additive manufacturing of the monofunctional composites and plastics and their monofunctional properties characterization, the experimental investigation of additively manufactured continuous carbon fiber composites for the multifunctional electro-tensile properties is not addressed. Thus, this highlights the novelty of this study.The experimental electro-tensile properties of the additively manufactured continuous fiber composites at room temperature dry investigated in this study show promising application towards aerospace utilization due to their inherent multifunctional properties. In addition, the observed failure modes and mechanisms were found to be consistent when compared to their traditional monofunctional composites counterparts. Future direction of this research work can include validation of this study with analysis. The generated tenso-electric multifunctional properties from the multifunctional testing of the multifunctional continuous carbon fiber composites from this study can be employed on analysis in future research investigation.


With the recent and rapid development of concrete technologies and the ever-increasing use of concrete, adapting concrete to the specific needs and applications of civil engineering is necessary. Due to economic considerations and care for the natural environment, improving the methods currently used in concrete design is also necessary. In this study, the author used principal component analysis as a statistical tool in the concrete mix design process. Using a combination of PCA variables and 2D and 3D factors has made it possible to refine concrete recipes. Thirty-eight concrete mixes of different aggregate grades were analyzed using this method. The applied statistical analysis showed many interesting relationships between the properties of concrete and the content of its components such as the clustering of certain properties, showing dependence between the properties and the quantities of certain ingredients in concrete, and reducing noise in the data, which most importantly simplifies interpretation. This method of analysis can be used as an aid for concrete mix design. With the progression of civilization, a primary concern in civil engineering is building modern infrastructures for the industry and human housing needs. Concrete is still a commonly used material in construction all over the world ,2,3,4, wPrincipal component analysis (PCA) is a powerful tool that finds internal correlations within a set of data and develops a statistical representation of these datasets . MoreoveThe data used for the analysis are based on the author’s previous test results . The conThe aggregate fractions 0–0.5 mm and 0.5–2 mm were assessed within a scale from 0 to 100%, with steps equal to 10%, and the fraction 2–4 mm was assessed within a scale from 0 to 30%, with the same steps see . The watThe research program was divided into two stages. During the first stage, the properties of fresh mixes, such as consistency, apparent density, and air content, were tested. During the second stage, the properties of the hardened concrete, namely density, compressive strength, and splitting tensile strength, were examined. The test procedures were based on European standards see .3, and the air content ranged from 2.5 to 9.0%.The test results of the fresh concrete mix see  showed t3, that the compressive strength ranged from 15.30 to 25.60 MPa, and that the splitting tensile strength ranged from 1.9 to 2.7 MPa  are strongly correlated with each other because their projections lie close to each other. These variables are also strongly correlated with variable 3 (aggregate 2–4 mm), which indicates that a high content of this aggregate is correlated with high densities of the fresh mix and the hardened concrete and high compressive strengths. Variable 7 (air content in the fresh mix) is almost directly located on the side opposite to variable 3, which means that a high content of the coarsest fraction (aggregate 2–4 mm) is correlated with low values of air content in the fresh concrete mix.PCA with object grouping in a two-dimensional space shows that most cases characterized by a compressive strength of 22 MPa or above see  and a spMost cases characterized by a compressive strength of 16 MPa or below see  and a spVariables 8, 9, and 10—mix density, compressive strength, and concrete density in the hardened state, respectively see —are locaTaking into account the third factor and adding the third dimension to the 2D chart compare  resultedThe PCA provided in the experiment described above showed a strong tendency to group cases with similar properties. The positions of cases characterized by desirable properties, i.e., high compressive strength see , splittiClustered cases of certain properties were grouped together; i.e., cases characterized by high compressive and splitting tensile strength were plotted together.A dependence between the properties and quantities of certain ingredients in concrete was observed; for instance, a high compressive strength corresponded to a high content of coarse aggregate fractions, and a low compressive strength corresponded to a high content of fine aggregate fractions.Noise was reduced in the data, which simplified the interpretation of most of the important factors influencing the model: due to the water/cement ratio being constant in the experiment, these variables were plotted together on the chart; other correlated variables such as mix density and concrete density were plotted close to one another.Elements that influenced the model to a large extent were recognized; in factor 1, they were water and cement content and concrete density.PCA was found to be useful as an aid for concrete mix design.It is also an excellent aid in refining the composition of a concrete mixture with certain properties using a combination of PCA variables and 2D and 3D factors to refine the concrete design process.It could also be useful for designing other types of concretes by relying on the test results of these concretes.The principal component analysis method was used as a concrete mix design tool to obtain the following conclusions: