Salmonella in raised-without-antibiotics cattle, we tested the effect of removing antibiotic use from all beef cattle production. We found an average of 1.2 antibiotic-resistant nontyphoidal salmonellosis cases per 1 million beef meals made with beef initially contaminated with antibiotic-resistant nontyphoidal Salmonella at slaughter or retail and 0.031 cases per 1 million meals irrespective of beef contamination status. Neither outcome showed sustained change except for increases in 2003 and 2009 (>98% confidence) when larger or more outbreaks occurred. Switching all beef production to a raised-without-antibiotics system may not have a significant effect on antibiotic-resistant nontyphoidal salmonellosis (94.3% confidence).Restricting antibiotic use in food production animals is a target for reducing antimicrobial drug–resistant infections in humans. To estimate the probability of antibiotic-resistant nontyphoidal salmonellosis per meal made with beef during 2002–2010, we used US surveillance data. Applying data for nontyphoidal  Increased antimicrobial resistance (AMR), or antibiotic resistance, has resulted in initiatives to reduce the use of antibiotics in food production animals , which leads to >1 million foodborne illnesses and 20,000 hospitalizations per year  and the number of meals made with beef that year  (We used this model for 3 objectives: 1) estimate the risk for antibiotic-resistant nontyphoidal salmonellosis per meal made with beef, using the yearly cases of illnesses  ; 2) evalMealres) .https://www.cdc.gov/foodnet/index.html), an active foodborne disease surveillance system, after adjusting for the proportion of the US population included in FoodNet surveillance sites. To correct for underdiagnosis and restrict case estimates to domestically acquired foodborne cases, we also included adjustment factors constant for the study period. By using annual food attribution estimates derived from the National Outbreak Reporting System , cases of nontyphoidal salmonellosis were further restricted to foodborne cases attributed to ground beef and intact beef. To ensure that the resistance fraction is specific to nontyphoidal salmonellosis attributed to consumption of beef, we estimated the fraction of beef-attributed nontyphoidal salmonellosis cases with AMR by matching cases in the Centers for Disease Control and Prevention data collected from clinical patient samples as part of NARMS . By using resMeals, we assumed that the beef used to prepare a meal was initially contaminated (as measured at the slaughter plant or retail) with the pathogen. This assumption does not necessarily mean that the actual meal consumed was contaminated because safe cooking and handling practices would reduce or completely inactivate the bacterial load.We calculated the number of beef meals consumed annually in the United States by using beef disappearance data from the US Department of Agriculture (USDA) . Also, by using all meals in the denominator, we calculated the probability of antibiotic-resistant nontyphoidal salmonellosis per meal made with beef, regardless of contamination status   and as the mean of each for all years combined . We repeated the analyses for NTS with multidrug resistance (NTSMDR)  and for clinically relevant resistance (NTSCRR), also known as resistance of concern   . We repoTo identify the confidence of a consistent increase (or decrease) in each outcome over the study period, we used Mann-Kendall trend test bootstrapping  from the National Animal Health Monitoring System feedlot survey  its prevalence in meals prepared with beef and that RR has a direct linear effect on the change in resIll. This relationship is documented for food pathogens  for each year of the study and for all years combined.To relax this assumption, for scenario 2, we empirically estimated the relationship between antibiotic-resistant NTS prevalence in beef and https://www.R-project.org). We used Monte Carlo simulation to calculate the posterior uncertainty in all outcomes. Statistical significance was assessed at the 95% confidence level. We report mean and 95% credible interval (CrI) for all outcomes. We performed a sensitivity analysis of the key drivers of illP and ill,overallP by calculating the effect that extreme values of each input had on the output means . Approximately 93% of meals with beef initially contaminated with antibiotic-resistant NTS  were made with ground beef (resIll was 0.64 (0.0036–2.75)/100,000 persons.During 2002–2010, approximately 554 beef meals were consumed, 59% as ground beef. Of these meals, 4% came from beef at slaughter or retail with NTS, half of which were antibiotic-resistant /1 million beef meals; intact and ground beef contributed equally to the rate . The ris>1 antibiotic  showed ecreased . In contecreased .resIll, illP, and mealP but generally no yearly changes in meals made with beef initially contaminated with antibiotic-resistant NTS . For all beef and for ground beef and intact beef individually, defining resistance as resistance to >1 antibiotic, resIll, illP, and mealP were higher in 2003 and 2009 and a peak for ground beef also occurred in 2014. resMeals showed no significant year-to-year changes for all beef cuts combined. Intact beef resMeals had 1 peak in 2001 (100% confidence). When MDR and CRR were used as the resistance definition, only the peaks in 2003 and in 2014 remained significant. A peak in some intact beef risks and illnesses was also observed in 2000 (We found some year-to-year variations in  in 2000 .<94.3% confidence) in antibiotic-resistant salmonellosis for any year when switching from current antibiotic practices to hypothetical 100% raised-without-antibiotics production. The mean change in the number of antibiotic-resistant nontyphoidal salmonellosis cases across the study period was −5,218  in 2003 and 2 Salmonella Montevideo matched samples  had MDR. This increase remained after we adjusted for exposure to infection in the form of meals prepared with beef with NTS and the fraction of these with AMR, which were stable. The association between MDR and CRR and larger/more frequent outbreaks may suggest a link between multidrug resistance and pathogenicity or infectivity, as described by Guillard et al.  that found few AMR differences between raised-without-antibiotics and conventionally raised cattle production. Our findings also demonstrate that a direct relationship between prevalence of antibiotic-resistant NTS in beef and resulting AMR salmonellosis is not supported by current surveillance data.The scenarios with all raised-without-antibiotics beef cattle enabled us to model a hypothetical upper limit of the human health effect of antibiotic reduction and resulted in nonsignificant changes in resistant illnesses overall. This finding held true even under an unrealistic assumption of a direct decrease in resistant illnesses resulting from decreased pathogen prevalence and resistance after complete withdrawal of antibiotics. Being based solely on nationwide estimates—resistant illnesses based on surveillance data and the effect of antibiotic use on antibiotic-resistant NTS based on a nationwide survey (This analysis suggests that the risk of contracting antibiotic-resistant nontyphoidal salmonellosis from beef consumption is <1 time/32 million beef meals and remained stable during 2002–2010. Despite assessing salmonellosis only, our work highlights improvements needed to better quantify the effect that antibiotic use in livestock has on human health: monitoring of clinical outcomes in foodborne surveillance programs, better connection between surveillance for foodborne pathogen resistance and outbreak sourcing, and detailed studies exploring the effect of raised-without-antibiotics production practices on pathogen prevalence and resistance throughout the farm-to-fork production chain. Elucidating not only consumers’ exposure to resistant pathogens but also how exposure translates into resistant illnesses and, ultimately, treatment failures, is required for the development of optimal AMR reduction strategies.Supplemental methods and results for study of risk for antibiotic-resistant salmonellosis from beef, United States, 2002–2010.


Antibiotic-loaded bone cement, or antibiotic-impregnated polymethylmethacrylate (PMMA), were developed to prevent and treat bone and joint infections. Gentamicin is an antibiotic that is commonly used in combination with PMMA; however, gentamicin powder is hard to obtain in many countries. This study aimed to evaluate the elution characteristics of gentamicin-impregnated PMMA made with lyophilized liquid gentamicin, compared with PMMA; which is made from commercial gentamicin powder.3 and 110 cm2, respectively. Each spacer was immersed in phosphate-buffered saline, which was changed daily under sterile conditions. The solutions were collected to measure the level of gentamicin using the enzyme multiplied immunoassay technique (EMIT), at days 1, 2, 3, 4, 5, 6, 7, 14, 21, 28, 35 and 42.The experimental sample was divided into 2 groups: the gentamicin power group (PG-PMMA) and the lyophilized liquid gentamicin group (LG-PMMA). Ten cement spacers were prepared in each group. These were produced by mixing gentamicin powder, or lyophilized liquid gentamicin, with a powder polymer before adding the liquid monomer (2 g of gentamicin and 40 g of PMMA). The volume and surface area of the antibiotic-impregnated cement spacers were 50 cmP< 0.05).The collections from both groups had high concentrations of gentamicin on day 1 (113.63 ± 23.42 mg/dL in LG-PMMA and 61.7 ±8.37 mg/dL in PG-PMMA), but experienced a continuous decrease over time. The PMMA spacers from both groups could release gentamicin for up to 6 weeks (3.28 ± 1.17 mg/dL in LG-PMMA and 1.21 ± 0.28 mg/dL in PG-PMMA). However, there were significantly higher levels of gentamicin concentrations in the LG-PMMA group compared to the PG-PMMA group at all time points (Gentamicin-impregnated PMMA made with lyophilized liquid gentamicin had approximately a two times higher rate of antibiotic elution in preliminary in vitro studies, as compared with PMMA made with premixed gentamicin powder. Osteomyelitis and periprosthetic joint infections are serious conditions, which lead to significant morbidity, require prolonged treatment and are associated with high rates of recurrence , 2. AntiThe lyophilization technique, or freeze drying, is a process of dehydration via the lowering of temperature until water freezes; this enables water to change directly from its solid phase to its gas phase. This process is commonplace in procedures of pharmaceutical formulations . However3 and 110 cm3, respectively , 10 cement spacers were made by mixing 40 g of methylmethacrylate polymer  with 2 g of gentamicin powder  in a sterile bowl , consisting of 10 cement spacers prepared following the same steps as those for the gentamicin powder group; with the exception of using 2 g of lyophilized liquid gentamicin. These were produced by the freeze-drying process (this removes water from a product after it is frozen and placed under a vacuum) for a total of 25 vials of liquid gentamicin [Gentamicin 80 mg/2 ml  ].  solution, at a pH of 7.4  for preparation of a standard elusion test. All cement spacers were fully immersed in PBS, after which the bottles were covered and then placed in an incubator at 37 °C. The PBS solution in each bottle was changed every day, with 100 mL sterile PBS solution for 6 weeks. On days 1, 2, 3, 4, 5, 6, 7, 14, 21, 28, 35, and 42 the solutions were sent to evaluate their elution of gentamicin. The Enzyme Multiplied Immunoassay Technique (EMIT) was used to evaluate the elution characteristics of gentamicin. A fluorescence polarization immunoassay (FPIA)  was used to determine the concentrations of gentamicin released. Both LG-PMMA and PG-PMMA spacers were analyzed with a scanning electron microscope [ver. Quanta 400 (SEM-Quanta)] for surface evaluation [p-value less than 0.05 was considered to indicate a statistically significant difference.R software version 3.1.0  was used for statistical analysis. The gentamicin concentration between time points in both groups was evaluated using Student t-test. The differences in gentamicin concentration between the groups, along the 6 weeks of study, were evaluated using Generalized Estimating Equations (GEE). A P< 0.05).The concentrations of gentamicin from the samples of both groups are shown in Table p< 0.05)  Fig.. Results.05) Fig.a were mo.05) Fig.b.Fig. 2The most important benefit of antibiotic-impregnated cement is its ability to provide a high concentration of antibiotics at the local site . AntibioThis study found that antibiotic-impregnated PMMA, using lyophilized liquid gentamicin, exhibited excellent elution characteristics compared to PMMA produced with gentamicin powder. The reason for this result can be found in previous studies; wherein, a previous report claimed that increasing the porosity of antibiotic-impregnated PMMA increases the antibiotic elution rate . FurtherStaphylococcus aureus ATCC 25923 (S. aureus) for Gram-positive bacteria (GPB) and Escherichia coli ATCC 25922 (E.coli) for Gram-negative bacteria (GNB). The results showed lyophilized gentamicin had an antimicrobial effect. The sterile filter paper discs (6 mm), containing 10 μl of lyophilized gentamicin solution (concentration 39.06 μg /ml), demonstrated a 15 mm inhibition zone for E.coli and an 18 mm inhibition zone for S aureus. This reached the sensitive level (≥ 15 mm) of standard laboratory testing, which used commercial antibiotic discs that contained Gentamicin 10 μg [This study has a number of limitations. First, this study used a hand mixing method that was a potential source of variability; hence, the resultant porosity may vary significantly. It would be more appropriate to use a standardized mixing approach with a device. Therefore, further research in clinical settings is needed to confirm these results before applying them in standard clinical practice. Second, the results from the scanning electron microscope (SEM) were obtained from direct inspection of the surface appearance of the cement spacers; instead of direct measurement of pore size. Finally, this study was only a quantitative study of gentamicin elution without microbiological study. However, the antimicrobial effectiveness of our in-house lyophilized gentamicin was confirmed via disk diffusion method (Agar diffusion test), for antibiotic susceptibility testing Fig. in 10 μg . So, we Gentamicin-impregnated PMMA made with lyophilized liquid gentamicin had approximately a two times higher rate of antibiotic elution in preliminary in vitro studies, comparing with PMMA made from premixed gentamicin powder. This regimen could be utilized in centers with limited availability of premixed gentamicin powder to treat bone and joint infections.


Our prospective study demonstrates a model of successful antimicrobial stewardship intervention that improves appropriateness on SAP.Surgical site infections (SSIs) are the most common healthcare-associated infections. The appropriate use of Surgical Antibiotic Prophylaxis (SAP) is a key component to reduce SSIs, while its inappropriate application is a major cause of some emerging infections and selects for antibiotic resistance. We describe an Antimicrobial Stewardship (AMS) intervention on SAP appropriateness. The prospective study was conducted in an Italian hospital, in 12 main surgical units, and was organized in three subsequent phases, as follows. Phase 0: Definition of hospital evidence-based guidelines and a new workflow to optimize the process of ordering, dispensing, administering and documenting the SAP. Phase 1: We analysed 2059 elective surgical cases from January to June 2018 for three SAP parameters of appropriateness: indication, choice and dose. Phase 2: In July 2018, an audit was performed to analyse the results; we reviewed 1781 elective surgical procedures from July to December 2018 looking for the same three SAP appropriateness parameters. The comparative analysis between phases 1 and 2 demonstrated that the correct indication, the correct dose and the overall compliance significantly improved ( Surgical site infections (SSIs) are now the most common 20%) and costly of all hospital-acquired infections. They represent a major clinical problem in terms of mortality, morbidity, length of stay and overall costs. SSIs are a global priority also because 20%–35% of them are caused by antibiotic-resistant strains ,2.0% and coThe burden of infections in Europe is similar to the combined burden of three major infectious diseases , and about 75% of the total burden of infections with antibiotic-resistant bacteria were associated with healthcare. Italy and Greece had a substantially higher estimated burden of antibiotic-resistant bacteria than other EU and EEA countries .The appropriate usage of Surgical Antibiotic Prophylaxis (SAP) significantly reduces the risk of SSI ,5, whileFor this reason, international and national guidelines have been developed to guide clinicians in the optimal use of SAP ,13,14.Italy is one of the largest consumers of Broad-Spectrum Agents (BSAs) in Europe . SAP conAntimicrobial Stewardship (AMS) is a systematic approach to improve the appropriateness of antimicrobial use in order to optimize the treatment of infections, to minimize the adverse effects associated with antibiotic use and to reduce antimicrobial resistance, toxicity and costs ,18.The 2016 definition by the Society for Healthcare Epidemiology of America (SHEA) describes AMS as a “set of coordinated strategies to improve the use of antimicrobial medications with the goal to enhance patient health outcomes, reduce antibiotic resistance, and decrease unnecessary costs”.There is no universally recognized intervention for improving SAP appropriateness: we describe, in our prospective study, a successful AMS intervention on SAP appropriateness with a significant improvement in overall compliance to guidelines.Our prospective study was conducted at “Santa Maria” hospital, which is a tertiary hospital in Terni, Umbria, Italy with 564 beds.The AMS program at “Santa Maria” Hospital began in February 2016 as a multilevel program with a comprehensive approach to improving the optimization of antibiotic use that is based on international and national guidelines, but tailored to our hospital’s reality.The AMS team has been in place from July 2018 and is a multidisciplinary team composed of pharmacists, experts in infection control, anaesthesiologists/intensivists, microbiologists, risk management specialists and surgeons, coordinated by infectivologists with expertise in antimicrobial stewardship.The study included elective surgical procedures performed in 2018 in our hospital in 12 main surgical units .https://www.dedalus.eu).In our hospital the patients’ data were reported using an electronic health chart while the information about the patients in the operating room were recorded using healthcare software  analysed 2059 elective surgical procedures in the 12 surgical wards from January to June 2018, looking for three SAP appropriateness parameters: indication, choice and dose. The data are reported in Successively, the same two authors analysed 1781 elective surgical procedures from July to December 2018 for the same three SAP appropriateness parameters: indication, choice and dose. The data are reported in To test the effectiveness of the AMS intervention’s educational audit, percentages of compliance with the recommendations in phase 1 and phase 2 were compared through the standard Pearson’s Chi-squared test (software R-basic package v. 3.3.2), with a significance threshold of α = 0.05.In phase 1, from January to June 2018, 2059 elective surgical, consecutive procedures were undertaken in 12 surgical wards.The indication of antibiotic administration was in most cases appropriate, with a rate of 73.6% (1516/2059).The indication was inappropriate in 26.4% (543/2059) of cases as patients (98%) received a prophylactic antibiotic, and it was also inappropriate if the American Society of Anaesthesiologists’ physical status classification (ASA score) was <3, because the indication to SAP required an ASA score ≥ 3.In 1516 elective surgical consecutive procedures the appropriate indication to SAP was evaluated. The choice of antibiotic was appropriate with a rate of 78.4% (1188/1516). The most frequent inappropriate choice of antibiotic was the utilization of cefazoline  instead of cefuroxime .In 1188 surgical procedures with an appropriate choice of antibiotic, the compliance to dose was evaluated. The dose was appropriate with a rate of 69.7% (828/1188). In all cases, the inappropriate dose of antibiotic was the administration of 1 g of cefazolin instead of 2 g.The overall compliance for the 3 appropriateness SAP parameters evaluated was 40.2% .In phase 2, after the audit, from July to December 2018, 1781 elective surgical consecutive procedures were evaluated for compliance to the same three parameters of SAP appropriateness: indication, choice and dose.The indication to SAP was appropriate with a rate of 77.8% (1386/1781). The compliance with appropriate choice of antibiotic was correct in 78.4% (1087/1386) of cases. In 911 of 1087 (83.8%) cases the compliance to dose was appropriate. The overall compliance for the three SAP appropriateness parameters was 911/1781 (a rate of 51.1%).In both phase 1 and phase 2, only antibiotics included in the guidelines were used. The most frequently used antibiotic was cefazolin (90% of cases).p-value 0.00128), moving from 73.6% (correct indication in 1516/2059 patients) in phase 1 to 77.8% (correct indication in 1386/1781 patients) in phase 2. The choice of antibiotic did not show any significant improvement , remaining almost the same: 78.4% (1188/1516) in phase 1 versus 78.4% (1087/1386) in phase 2. The correct dosage significantly improved , moving from 69.7% (828/1188) in phase 1 to 83.8% (911/1087) in phase 2. The overall compliance had a significant improvement  passing from 40.2% (828/2059) in phase 1 to 51.1% (911/1781) in phase 2  to increase compliance:One of the main actions of the ECDC, reported from Rodríguez-Caravaca et al. , was theAudits and feedback are the most common ECDC actions reported in the literature. In fact, modern healthcare systems always track performance outcomes to look for ways to improve quality of care.The educational program is usually performed through meeting with hospital surgeons and lectures about Surgical Antibiotic Prophylaxis .The implementation of standardized order forms has been reported only from Garcia et al. , suggestIn this study we performed all the five actions suggested by the ECDC to increase the compliance in SAP. At present, the prospective realization and the complete adherence to ECDC guidelines may be the most important results.This study was designed by our hospital AMS team. It attempted to overcome the obstacles preventing the implementation of adequate SAP by the definition of hospital guidelines on SAP with the involvement of surgeons as well as the creation of a protocol which has standardized the workflow and tried to overcome the organizational and logistical problems.The responsibility of SAP administration was shifted to the anaesthesiologists;Audits with feedback on appropriateness of prescription were performed every six months;Medical grand rounds were performed to promote the excellence and quality in Surgical Antibiotic Prophylaxis;The synergism with pharmacists permitted the organization of an operative block satellite pharmacy for antibiotic prophylaxis; andAll the actions were performed by a multidisciplinary team.In our protocol, we have programmed all the ECDC actions:p-value 0.00128), appropriate dosage  and overall compliance  between phases 1 and 2.In our study, the application of the five ECDC actions, the implementation of a model with a definition of the workflow and accountability and the systematic collection of data by a surveillance team granted a meaningful implementation of the compliance with a significant improvement of appropriate indication , therefore it will be necessary to organize more audits concerning the appropriateness of the utilization of first- and second-generation cephalosporins.The satellite pharmacy provided only eight types of antibiotics , all quoted in local hospital guidelines, without the possibility to prescribe other antibiotics, which led to a very high utilization of cefazolin (90%). However, there was no significant improvement in the choice of antibiotic (We believe that more studies should analyse the effectiveness of the intervention instead of evaluating only the compliance.Our study has a limitation: we could not analyse the timing and the possible redosing of SAP. Several studies have confirmed the relationship between the timing of SAP and SSI risk and the importance of maintaining adequate antibiotic serum concentrations throughout the operation ,25,26,27The appropriateness of SAP is a key component to reduce SSIs . Approxi


Frailty is a highly recognized geriatric syndrome resulting in decline in reserve across multiple physiological systems. Impaired physical function is one of the major indicators of frailty. The goal of this study was to evaluate an algorithm that discriminates between frailty groups (non-frail and pre-frail/frail) based on gait performance parameters derived from unsupervised daily physical activity (DPA).DPA was acquired for 48 h from older adults (≥65 years) using a tri-axial accelerometer motion-sensor. Continuous bouts of walking for 20s, 30s, 40s, 50s and 60s without pauses were identified from acceleration data. These were then used to extract qualitative measures  and quantitative measures  to characterize gait performance. Association between frailty and gait performance parameters was assessed using multinomial logistic models with frailty as the dependent variable, and gait performance parameters along with demographic parameters as independent variables.p < 0.05). Among the five different durations , gait performance parameters extracted from 60s continuous walks provided the best frailty assessment results. Using the 60s gait performance parameters in the logistic model, pre-frail/frail group (vs. non-frail) was identified with 76.8% sensitivity and 80% specificity.One hundred twenty-six older adults  were recruited. Step- and stride-times, frequency domain gait variability, and continuous walking quantitative measures were significantly different between non-frail and pre-frail/frail groups (Everyday walking characteristics were found to be associated with frailty. Along with quantitative measures of physical activity, qualitative measures are critical elements representing the early stages of frailty. In-home gait assessment offers an opportunity to screen for and monitor frailty.NCT01880229.The clinical trial was retrospectively registered on June 18th, 2013 with ClinicalTrials.gov, identifier  Among the population who are 60 years or older, frailty is a highly recognized syndrome that is associated with decline in function and reserve across multiple physiologic systems –5. FrailDPA data has been recently used to assess physical function, especially with the help of wearable sensor technology. Using wearable devices, it is possible to continuously measure DPA in the least intrusive manner and for longer durations of time in the participants’ natural environment. Among several DPA, motion analysis of the trunk during walking is known to provide insights regarding neuromuscular deficits associated with frailty and aging . In our In this study, we aimed to improve detection of frailty-related neuromuscular deficits based on gait performance parameters derived from unsupervised DPA. Previous studies have used trunk motion data from supervised in-lab gait tests to characterize sensorimotor gait performance among frail elders including gait variability, asymmetry, initiation, and irregularity , 18–22. This observational cross-sectional study was performed at Arizona Center on Aging, Tucson, AZ. Participants in this study were from primary, secondary, and tertiary health-care settings within our academic network and also from community providers and aging service organizations. DPA was recorded from eligible volunteers for 48 h and the walking data from the DPA was processed to study the gait performance parameters and associate these characteristics with frailty.Older adults (65 years or older), without severe mobility disorder and the ability to walk at least 10 m with or without an assistive device, were considered eligible for the study. Participants with cognitive-impairment   score ofThe recorded clinical measures included self-reported history of falls, use of assistive device and the number of prescriptions. Interviewer-administered questionnaires included the MMSE, Mobility-Tiredness Scale , Center Frailty was assessed using the five criteria proposed by Fried et al. , includiDPA was quantified for two consecutive days (48 h) using a tri-axial accelerometer sensor  fixed in a tee-shirt, with a device pocket located at the sternum. PAMSys is a small (5.1 × 3 × 1.6 cm), light (24 g) recording system containing inertial sensors. PAMSys is an ambulatory system designed and developed for human motion analysis using a kinematic sensor. It uses one kinematic sensor placed on the chest and is capable of accurately identifying and recording postural transitions (sit-to-stand and stand-to-sit), laying, walking, and standing –31. PAMSPrevious studies that explored the gait characteristics of non-disabled adults for 2 weeks to define walking duration, found that 81% of all walking bouts lasted about 60 s , 36. FurFor each continuous walking bout, the raw vertical acceleration signal extracted from the PAMSys sensor was filtered using a second order Butterworth filter (cut-off frequency of 2.5 Hz ), and thWe defined gait variability as the stride-to-stride fluctuation in gait cycles, which has been associated with high risk of fall and cognitive impairments in elders , 45–47. When gait becomes less automatic due to sarcopenia and cognitive aging, left-right step coordination may require more effort, especially among frail individuals , 37, 52.Ad1 and Ad2 are the prominence of the first and the second peaks respectively after the central (zero lag) peak  < r) and B as the number of matches of length m: (d < r)  < r) , 57–60.r = 0.2 times the standard deviation of the signal, which are commonly used to compute sample entropy of gait signal [The time-delay of the signal was calculated using mutual information method for all the continuous walks , and thet signal , 57–60.In addition to the above-mentioned features, we extracted the following parameters in each continuous walking event: maximum walking bout, maximum number of continuous steps, walking-bout variability , and total duration of continuous walks. Of note, the parameters extracted here were only obtained for continuous walking events with no pause of 1.7 s or longer, as described above. Duration of non-continuous walk  was obtained as a percentage of total duration of walking from the PAMsys sensor.p < 0.05.Separate analysis of variance (ANOVA) models were performed to compare sociodemographic parameters between the three Fried frailty groups. To explore differences in gait performance parameters among frailty categories, univariate ANOVA models were used with each gait performance parameter as the dependent variable, and the Fried frailty categories (non-frail and pre-frail/ frail) as the independent variable. Subsequently, gait performance parameters were used in a single multivariable nominal logistic model to assess the association between frailty categories and DPA gait performance parameters. In this model we combined pre-frail and frail groups, due to the limited number of frail participants. The model was developed following these steps: 1) univariate nominal logistic model analysis of the gait performance parameters as independent variables was performed. Gait performance parameters with significant association with frailty were considered for subsequent steps; 2) collinearity between the various gait performance parameters was tested using the variance inflation factor (VIF) index. VIF value greater than 10 represented the presence of collinearity ; and 3) p < 0.05) and lower performance scores in ADL (p < 0.05).The study involved a total of 126 participants, among whom 44 were non-frail, 60 were pre-frail and 22 were frail according to the Fried frailty criteria [p-values of one-way ANOVA test  older than the participants who had continuous walks (age: 77.94 ± 8.43). Frailty status was also significantly (p = 0.001) different between the participants who did not have any continuous walking bouts (87.5% pre-frail/frail) compared to those who had continuous walks (57.45% pre-frail/frail). However, the BMI and gender were not significantly different between these groups (p > 0.079).Of note, among the total 126 participants, 4 non-frail (9.09%), 17 pre-frail (28.33%), and 11 frail (50%) had no walking bout equal or longer than 60 s. These participants who did not have any 60s continuous walking bout (age: 81.59 ± 8.34) were significantly (p < 0.001). Further, among the frequency domain gait variability parameters, PSD amplitude, PSD slope, and the dominant frequency were significantly different between non-frail and pre-frail/frail groups (p < 0.05). However, step- and stride-time variabilities did not show statistical significance between the two groups (p > 0.1). Gait asymmetry, representing left and right step coordination, was not statistically significant between the two frailty groups (p > 0.1). Similarly, gait irregularity, measuring predictability of walking cycles, displayed an increasing trend towards pre-frailty/frailty; but the observed between-group differences were not significant (p > 0.1). All the continuous walk quantitative measures showed differences between the two groups, and most of these differences were statistically significant between the two groups (p < 0.05).Among the 60s continuous gait parameters, frequency domain gait variability parameters and quantitative measures including maximum number of continuous steps, maximum walking bout and total continuous walking duration best discriminated non-frail and pre-frail/frail individuals. Step- and stride-time were significantly different between non-frail vs pre-frail/frail (2), stride-time variability (%), dominant frequency (Hz), and maximum number of continuous steps were selected as independent variables , for which, age (years), BMI , when compared with continuous walks with shorter duration and walks that included pauses.The ability to walk longer distances is instrumental for humans to perform various activities of daily living and lead an independent life. Walking requires complex mechanisms within the human sensory motor system to provide the necessary timing, coordination, and balance such that the interplay between the center of mass and the base of support are regulated in a repetitive manner , 63. PreIn addition to previously reported quantitative gait parameters  , here weAdditionally, gait asymmetry and irregularity were also investigated here, as parameters that represent gait deficits independent of gait variability. Gait asymmetry, representing left-right step coordination, has been used as a metric to observe walking patterns in older individuals. Cognitive aging and sarcopenia render gait to be less automatic and left-right symmetry co-ordination is expected to require additional effort, especially in frail individuals . AlthougThere are limitations to consider in the interpretation of these findings. The first limitation is the lack of longitudinal validation of the DPA index for direct prediction of frailty-related health complications. Accordingly, due to a cross-sectional design of the current study, no conclusion can be made regarding the accuracy of the proposed index compared to the Fried test, or other types of frailty measures. Second limitation is adherence to the wearable sensor equipment. Though the participants did not express any obvious discomfort while wearing the sensors, it is possible that a few of the participants forgot to wear them immediately after a shower. Third, our sample was predominantly women. Although we did not observe a gender specific difference in gait performance, the model developed here may have limited generalizability to a population with a more balanced gender composition. Fourth, we consider a continuous walk as one with 20/30/40/50/60 s or longer duration with no pauses. However, it is possible that this walk was purposeful with the individual walking to a certain destination or that this walk was a random stroll with no specific purpose. These possibilities could potentially bias the quality of walking, but in our data we did not have the required information to categorize continuous walks as purposeful or random. Finally, not all participants, especially pre-frail and frail ones, had continuous walks during the 48 h of data collection, causing a reduced sample size for the pre-frail/frail group. To overcome this limitation, we combined pre-frail and frail participants and all the participants who did not exhibit continuous walking were automatically categorized as pre-frail/frail while developing the logistic model. Since detecting the onset of frailty at the pre-frail stage is most crucial in recovering health status , our finUsing gait performance parameters extracted from 60s continuous walks within 48 h of daily monitoring, pre-frailty/frailty was identified with a sensitivity of 76.8% and specificity of 80% among elders. Findings suggest that these DPA-based 60s continuous walking parameters, including gait variability and the amount of continuous walking, may noticeably improve gait deficit assessment compared to previous in-clinic gait assessment methods. The proposed gait performance characterization based on sensor-based daily physical activity provides potential for being integrated into clinical care for in-home screening of frailty (much as a holter monitor is used) to provide information pertaining to an individual’s condition before hospital admission, or when frailty is suspected. This method is advantageous over its in-clinic counterpart as it is objective rather than subjective self-reported measures of physical activity, and is measured in real-world walking activities rather than an artificial clinical setting. Although Fried’s frailty criteria  providesHealthcare research in wearable devices has been constantly growing in various areas like remote patient monitoring and healthcare –72, wearAdditional file 1: Supplementary Table 1(a-d). Gait performance parameters for 20s, 30s, 40s and 50s continuous walks, one-way ANOVA results, and Cohen's d effect sizes between non-frail(N) and pre-frail(P)/frail(F) groups; Supplementary Table 2. Logistic model performance comparison using gait performance parameters between different duration of continuous walks for 80% specificity.Additional file 2: Supplementary Figure 1. Logistic regression model receiver operating characteristic (ROC) curves for different continuous walk criteria . Results are presented for predictions using gait performance models .


Frost damage of concrete has significant effects on the safety and durability of concrete structures in cold regions, and the concrete structures after repair and reinforcement are still threatened by cyclic freezing and thawing. In this study, the new-to-old concrete interface was reinforced by steel bar. The shear strength of the new-to-old concrete interface was tested after the new-to-old combination was subjected to cyclic freeze–thaw. The effects of the diameter of the steel bar, the compressive strength of new concrete, the number of freeze–thaw cycles and the freezing temperatures on the shear properties of new-to-old concrete interface were studied. The results showed that, in a certain range, the shear strength of the interface was proportional to the diameter of the steel bar and the strength of the new concrete. Meanwhile, the shear strength of the reinforced interface decreased with the decreasing of the freezing temperature and the increasing of the number of freeze–thaw cycles. The bond strength of the new-to-old concrete interface is an important index to evaluate the repair-and-strengthen effect for concrete structures ,2. PatnaThe bearing performance of a concrete structure has a great relationship with the effect of environment ,17,18. IAfter reinforcement and maintenance, the structure in the cold area still faces the threat of freezing-and-thawing damage, which requires the research on the antifreeze performance of the old and new concrete interface. Naderi pointed out that 300 freeze–thaw cycles could reduce the shear bond strength of a resin mortar by up to about 80%, and 200 cycles of temperature changes could reduce the original shear bond strength of a cementations mortar by up to about 90% . The effThe reinforcement of new-to-old concrete interface by anchorage is also used in the repair of concrete structures . This stThe cubic compressive test was carried out by using an MTS universal testing machine. The test procedure followed the Chinese Standard . The comF is the largest shear force and A is the interface area.A shear fixture was developed for the interfacial shear test, which is shown in The shear strengths of interfaces are shown in A strength index, Another strength index, In order to study the effect of interface reinforcement by using the steel bar, strength index The values of Two strength levels of C30 and C35 were used as new concrete to study the effect of the compressive strength of new concrete on the shear strength of the new-to-old concrete interface. The old concrete had the same compressive strength, and all the specimens were reinforced by an 8 mm steel bar. The shear strengths of interfaces for using C30 and C35 as new concrete are illustrated in From Three different freezing temperatures, −6, −12 and −18 °C, were used to study the effect of minimum freezing temperatures on the shear strength of the new-to-old concrete interface. The thawing temperature was 5 °C, and the interface was reinforced by an 8 mm steel bar. These cases are grouped as XM, XK and XF in The residual shear strength rate of interface after specific FTCs is shown in The Qinling P.O. 42.5 ordinary Portland cement produced by Shaanxi Yaoxian Cement Co., Ltd, Tongchuan, China. was used. The physical properties of Portland cement and its chemical compositions were detailed in Natural river sand with diameters between 0.5 and 1.17 mm was used as fine aggregate. Natural crushed stones with diameters between 5 and 20 mm were used as coarse aggregates. Sand and aggregates were cleaned, screened and dried before being used.Steel bars made of HRB400  were used for reinforcement, as shown in A strength level of C30 was used for old concrete, and two strength levels of C30 and C35 were used for new concrete. The dimensions of the cubic concrete block were 100 mm × 100 mm × 100 mm. The dimensions of the new-to-old concrete combination were 100 mm × 100 mm × 200 mm. Some concrete specimens with dimensions of 100 mm × 100 mm × 200 mm were used to compare with the new-to-old concrete combination. The mix composition of concrete is shown in Five different numbers of freeze–thaw cycles, 0, 10, 15, 20 and 25, were chosen for analyzing the effect of FTCs on the new-to-old concrete interface. Three specimens were prepared for each number of FTCs, and the results were taken from the average of these three specimens. Three different steel reinforcement diameters, 8, 10 and 12 mm, were used for studying the effect of reinforcement on the shear strength of new-to-old concrete interface. In order to study the effect of freeze temperature on the interface, −6, −12 and −18 °C were considered as three different minimum freeze temperatures. Based on the abovementioned, all the experimental cases were grouped into 8 groups. The details of the experimental scheme are shown in (1) Mix composition of C30 was used for preparing 120 cubic concrete blocks. In total, 105 of them were prepared as old concrete for making new-to-old concrete combinations, and 15 of them were prepared for cyclic freeze-thaw tests.(2) In total, 105 of the cubic concrete blocks were pretreated by making the surfaces rough, as shown in Vsand is the volume of sand filled, and Soc is the surface area of the old concrete.The values of the roughness of the surfaces for old concrete are shown in (3) The old concrete blocks were drilled after roughness was measured. Then the steel bar was put into the hole and glued with concrete, by reinforcement adhesive. The reinforced old concrete blocks are shown in (4) The rough surfaces of the old concrete blocks were cleaned, presoaked and brushed with interface agent, for pouring new concrete. A mold with dimensions of 100 mm × 100 mm × 400 mm was used for making new-to-old concrete combinations. Each mold could fit two combinations. Two reinforced old concrete blocks were put into the mold first, and then new concrete was poured, as shown in (5) The new-to-old concrete combinations were put into water and soaked for 4 days, when their ages reached 24 days. The water surface was kept 20 mm higher than the specimens, as shown in Fifteen cubic concrete specimens, 15 concrete cuboids and 105 new-to-old concrete combinations were prepared for studying the effect of cyclic freeze–thaw on the shear strength of new-to-old concrete interfaces. All the specimens were subjected to 0, 10, 15, 20 and 25 FTCs, respectively. No interface, a rough interface without reinforcement and a rough interface reinforced by an 8, 10 and 12 mm steel bar were compared. Two different new concrete compressive strength levels, C30 and C35, were also considered. The influence of three different freezing temperatures, −6, −12 and −18 °C, on the shear strength of new-to-old concrete interfaces was studied. By the results of shear test of interface and analysis, the main conclusions could be drawn as follows:(1) With the increase of FTCs, the shear strengths of both the concrete body and the new-to-old concrete interfaces were decreasing monotonically. The effect of FTCs on the compressive strength of concrete cubic had a delay in respect to both the shear strength of the concrete cuboid and the shear strength of new-to-old concrete interface.(2) The shear strength of interface was clearly improved by using a steel bar. After the new-to-old concrete interface was subjected to freeze–thaw cycles, the reinforcement effect became more obvious. With the increase of the diameter of the steel bar, the shear strengths of interfaces were increasing. With the increase of FTCs, the improvement of the reinforcement was more effective, and the larger steel bar had a better effect.(3) The shear strength of interface could be increased by using new concrete with higher compressive strength. However, the effect was limited. The economic cost should be considered in practical engineering repairing.(4) Under the same FTCs, the lowest freezing temperature had the smallest residual shear strength rate. With the increase of FTCs, the lower freezing temperature had a more harmful effect on the shear strength of the new-to-old concrete interface.Overall, the use of a steel bar as anchorage for the repair of concrete structures could improve the bearing capacity and frost resistance of a new-to-old concrete interface. Only one steel bar was used in this research; however, different numbers of steel bars could be studied in the future for guiding practical usage.


Escherichia coli isolates were collected from each stool sample  and were subjected to breakpoint assays for ten antibiotics. Mixed-effects logistic models were used to identify potential factors influencing the likelihood of harboring antibiotic-resistant bacteria. For nine out of ten antibiotics, the odds of detecting resistant bacteria decreased by ~ 32%  for every unit of improvement of a hygiene scale. Hygiene differences between households had a greater impact on prevalence compared to antibiotic use differences. The likelihood of detecting resistant isolates was lower for five antibiotics among households that boiled raw milk before consumption (OR 0.31–0.69), and higher for nine antibiotics in urban households (OR > 1.89–9.6). Poor hygiene conditions likely obscure effects of individual antibiotic use, presumably due to enhanced microbial transmission. Consequently, efforts to improve antibiotic stewardship should be coupled with improving hygiene conditions.To examine the effects of poor sanitation and hygiene on the prevalence of antimicrobial-resistant bacteria, we surveyed households in two rural and two urban communities in Guatemala (N = 196 randomly selected households). One adult (≥ 18-years old) and, when available, one child (≤ 5 years-old) provided a stool sample. Up to 48 presumptive  To address this threat, public and private organizations are engaged in programs to improve surveillance for antimicrobial-resistant organisms, to improve antibiotic stewardship, and to identify novel therapeutics, all of which are considered priority actions for combating antimicrobial resistance (AMR)4. The strategies adopted to limit AMR will vary globally, particularly across countries with different degrees of wealth and development. The most effective intervention will likely depend on prevailing conditions. For example, high-income countries and low-income countries can differ in antimicrobial resistance patterns, antimicrobial use practices, access to healthcare services , sanitation and regulation infrastructures9.Antimicrobial-resistant infections contribute to hundreds-of-thousands of deaths worldwide12 and the agricultural sector15, have associated reductions in antimicrobial use and improved stewardship with decreases in the prevalence of antimicrobial resistance. In contrast, studies examining global patterns of AMR find that antibiotic use is not positively correlated with resistance in all cases and may instead be correlated with indicators of transmission, including access to clean water5 and open defecation6. This lack of association between antibiotic use and AMR in some settings may result from conditions in less-wealthy countries where the prevalence of antimicrobial resistance is more closely correlated with general transmission of bacteria16. Collignon et al. recently demonstrated that at a country-scale, several factors including poor infrastructure likely contribute to the overall prevalence of antibiotic-resistant pathogenic Escherichia coli in a country5. At a local scale, it has been postulated that if the frequency of transmission is high, the specific effect of antibiotic use on the prevalence of resistant bacteria can be overshadowed17, possibly due to transmission decoupling antibiotic selection events from the distribution of antimicrobial-resistant bacteria. If correct, we should observe a stronger correlation between antibiotic use practices and the prevalence of antibiotic resistant bacteria when transmission is limited.Studies conducted within high-income countries, particularly those concerning healthcare facilitiesEscherichia coli in four communities from the western highlands and lowlands of Guatemala. Study communities were identified to represent presumed variance in transmission rates between urban and rural areas determined by differences in sanitation, hygiene and population density. Highland and lowland communities were selected to maximize variation in the presumed prevalence of illnesses that drive antibiotic consumption and associated healthcare practices when experiencing vector-borne febrile illness, diarrhea, and respiratory illness. If there is a significant interaction between antibiotic use and transmission factors, this has important implications for how public health policies should direct resources to limit the prevalence of antibiotic-resistant bacteria in these communities.To test how antibiotic use and transmission factors interact to influence the distribution of antimicrobial-resistant bacteria in communities where these factors vary, we studied the distribution of antibiotic-resistant 18. We selected two communities in the lowland municipality of Coatepeque (average elevation 149 m): the urban community of El Jardin and the peri-urban  community of La Unión. In both lowland communities, predominant inhabitants include the Spanish-speaking Mestizo. Both the lowland and highland municipalities have high rates of poverty, although markedly higher in the highlands community .We executed a repeated-measures study that included a cross-sectional questionnaire and stool sample collection in October/November of 2017 (phase 1) and March/April of 2018 (phase 2). Within the department of Quetzaltenango , two municipalities were selected by convenience  to represent differences in climate, altitude, and ethnic cultural practices; all presumed to result in differences in the transmission and incidence of infection and resulting antibiotic use  were randomly selected (“participants”) from the list of household residents. The study protocol was approved by Washington State University in Pullman Institutional Review Board (15895-001), the Universidad del Valle de Guatemala-Center for Health Studies Ethics committee (159-01-2017), and the Guatemalan Ministry of Health Ethics Committee (10-2017). All research was performed in accordance with the relevant guidelines and regulations of these institutions.We consulted several data sets to generate lists for random selection of households. In 2016, the Ministry of Health and Social Assistance (MSPAS) in collaboration with the Universidad del Valle de Guatemala, carried out a census of households in both lowland communities. 2017 MSPAS census information was available for Monrovia. Census information was not available for San Juan Ostuncalco. Instead, we used Google Earth satellite imagery22 and included components from water sanitation and health (“WASH”) defining poor sanitation as meeting one of the following conditions set out by the Joint Monitoring Programme for Water Supply, Sanitation and Hygiene (JMP) of WHO and UNICEF: unimproved JMP toilet (pit latrine without slab/open/blind well), shared toilet, toilet not cleaned within the last four weeks, or the last time a child passed stool it was not disposed of in toilet23. See Supplement pgs. 2–4 for more information on selection criteria and questionnaire development.Survey instruments were based on similar studiesE. coli were obtained. Isolates were then tested for their susceptibility to ten antibiotics by using breakpoint assays24. For these assays, bacteria are grown on agar plates with fixed concentrations of antibiotic and they are considered “resistant” when growth occurs, or susceptible when growth does not occur. See Supplement pgs. 3–5 for information on isolation of E. coli, breakpoint assays, and validation of assays relative to classic agar diffusion assays.Stool collection kits and explicit instructions for stool collection were given to study participants enrolled in phase 1, the same participants were approached for a second stool sample collection in phase 2. Participants were instructed to pass stool into any clean and dry container, directly into the study-kit stool collection container, or onto the Kraft paper provided in the study kit . Households were contacted by study personnel within 24 h of initial study contact to collect stool samples. These were then transported in cooler boxes with ice packs and stored under refrigeration for a maximum of 5 days until they were shipped to a reference laboratory at the regional hospital in Quetzaltenango where isolates of presumptive 25) and from our own ethnographic work . Included variables represent the general categories of antibiotic use and access, hygiene and sanitation, sickness, and demographics  with resistance to ≥ 3 antimicrobial resistance phenotypes. Model fit was good to adequate and tests of model fit are provided in Supplement pg 6 and Table Model specification proceeded by entering independent variables into a mixed-effects logistic regression model that was clustered at the individual level. We specified models for all resistance phenotypes and a multidrug resistance phenotype (MDR), which we defined as resistance to three or more antibiotic classes. Results were summarized as odds ratios (OR), which we converted to percentage change in odds to facilitate interpretation . When specifying interactions between antibiotic use and hygiene/sanitation, continuous variables entered into interactions were first mean-centered to limit multicollinearityA total of 196 households across all four communities Table  participThe majority of enrolled households in these communities were characterized as having poor sanitation , including 16% of households having an JMP unimproved toilet and about half of households sharing a toilet that was not located on the premises (55%). Unimproved toilets were more common in rural areas (29%) versus urban areas (2%). More toilets were reported as shared and located outside the household in rural areas 73% compared with 33% in urban households. Thirty-seven percent of households were defined as “overcrowded” (> 3 people per sleeping room). Lowland regions had higher overall report of antibiotic use (see Table E. coli) were isolated from 273 individuals sampled. The prevalence of resistance to ampicillin, amoxicillin, streptomycin, sulfamethoxazole, trimethoprim, tetracycline, and the MDR resistance phenotype was about four times higher (> 30%) compared to ceftazidime, chloramphenicol, ciprofloxacin and kanamycin (< 8%). Breakpoint and disc diffusion assay results indicated the two methods provided a consistent estimate for the proportion of resistant strains across ten different antibiotics  was associated with a ≈30–50% decrease in odds of detecting resistance to all antibiotics Table . The solAdults had ≈ 60% reduced odds of harboring bacteria exhibiting resistance to most antibiotics compared to children. This significant difference did not hold for the less frequently encountered resistance phenotypes including ceftazidime, chloramphenicol and kanamycin. Adults had significantly higher odds of (125%) of exhibiting resistance to ciprofloxacin. For participants residing in urban areas, there was a significantly increased odds of detecting bacteria resistant to ampicillin (110%), ceftazidime (178%), chloramphenicol (231%), ciprofloxacin 496%) and the MDR phenotype (121%) (Table 96% and tP < 0.05) between antibiotic use and hygiene/sanitation were found for all antibiotics except for chloramphenicol and trimethoprim. To facilitate interpretation, we plotted the relationship between hygiene and antibiotic resistance separately for individuals that reported using antibiotics  and for those who reported not using antibiotics   are used. The higher prevalence of resistance in households reporting no milk consumption is more challenging to explain. It may be that households reporting no milk consumption are consuming other higher risk alternatives which could also be related to the ability to purchase milk. To examine this further, we generated a correlation matrix and found a weak positive correlation between milk consumption and wealth (r = 0.13) and between milk consumption and household hygiene (r = 0.13) . Medications in Guatemala are subsidized by the government through the Ministry of Health system and the National Social Security health care system, yet frequent stock-outs force most Guatemalans to purchase medications out-of-pocket at private pharmacies29. In these establishments, medications can be up to 20 times the international listed price . In contrast, amoxicillin and tetracycline are considerably more affordable and widely available in tiendas, perhaps reflecting antibiotic use in these communities where the average prevalence of resistance to amoxicillin and tetracycline was approximately 40%.Antibiotic use had little measurable impact in sub-optimal hygiene conditions. The overall prevalence of antibiotic-resistance phenotypes is consistent with the relative availability and cost of antibiotics sold without a prescription in these communities  likely does not reflect the same impact on the prevalence of antimicrobial resistance as another . Nevertheless, we argue our composite measure represents a measure of of household hygiene and sanitation with changes in the scale reflective of general increases and decreases in household hygiene and sanitation.As with any epidemiological study, we are limited to identifying correlated variables for largely uncontrolled systems, making clear cause-and-effect relationships difficult to identify due to confounded variables. An example of this is the apparent higher prevalence of resistance in rural households shown in the univariate comparison Fig.  vs. the The robust relationship between hygiene and resistance in the sampled Guatemalan communities, along with the interaction between hygiene and antibiotic use, provides important implications for the efficacy of stewardship efforts globally when aggregate hygiene levels are compromised. In such cases, investment in infrastructure to improve hygiene can be easily justified as a tool to limit the proliferation of antimicrobial resistance in communities across the globe. As this study highlights, assigning priorities and subsequent development of targeted strategies will require analysis of a greater spectrum of living conditions, using cross-cultural investigations developed and implemented by interdisciplinary teams from the natural and social sciences.The study protocol was approved by Washington State University in Pullman Institutional Review Board (15895-001), the Universidad del Valle de Guatemala-Center for Health Studies Ethics committee (159-01-2017), and the Guatemalan Ministry of Health Ethics Committee (10-2017).Supplementary file 1.Supplementary file 2.Supplementary file 3.Supplementary file 4.Supplementary file 5.


The article presents a new functional method of designing self-compacting concrete (SCC). The assumptions of the functional method of designing self-compacting concrete were based on the double coating assumption . The proposed method is composed of four stages, each of which is responsible for the selection of a different component of the concrete mix. The proposed designing procedure takes into consideration such a selection of the mineral skeleton in terms of the volumetric saturation of the mineral skeleton, which prevents the blocking of aggregate grains, and the designed liquid phase demonstrated high structural viscosity and low yield stress. The performed experimental studies, the simulation of the elaborated mathematical model fully allowed for the verification of the theoretical assumptions that are the basis for the development of the method of designing self-compacting concrete. High architectonic and endurance requirements that are currently placed before the constructed engineering facilities force the constant progress and development of the technology of the basic construction material, which is (and will remain for a long time) cement concrete.Currently, an element that has become a big technological impediment is the necessity of ensuring the required compacting of cement concrete in reinforced concrete buildings, demonstrating very dense construction reinforcement. This refers above all to the construction of large sized facilities with a dense system of construction reinforcement, which may cause a lack of homogeneity of the structure, resulting from the insufficient vibration of the fresh concrete mix. The expected durability and ensuring the appropriately smooth external structure of the buildings have caused the dynamic development of concretes demonstrating high liquidity, which do not require the process of mechanical compacting.The effect of a range of design works was the creation  of a SCC concrete composite called self-compacting concrete, which, thanks to its specific properties, easily fills the formwork, self-compacts, and deaerates under the impact of its own weight. Its high liquidity results in the fact that it reaches locations that are hard to access (densely reinforced ones) and surrounds the construction reinforcement very well. Thanks to the increased viscosity of the cement paste, all the components of this concrete flow simultaneously, suspended in a dense stable structure without causing segregation and sedimentation. This is possible thanks to the increase in the share of the dust fraction below 0.125 mm and the application of a new generation of superplasticizers that increase the viscosity of make-up water and limit the phenomenon of segregation of coarse and very fine components of the concrete mix mineral skeleton.Since the elaboration of this concrete by Okamura and Ozawa ,2,3, numInitially, the elements considered the basic properties of a self-compacting concrete mix were the flow and the deaeration as well as compacting under the influence of its own mass. The above-mentioned properties did not characterize SCC in a full way, therefore observations of additional properties began such as flow through dense reinforcement, the dynamics of the flow, tightness and the ease of filling in forms, maintaining consistency in time, and the surface aesthetics. The development of a new technological field, which self-compacting concrete undoubtedly is, has resulted in the creation of a range of design works, the aim of which was obtaining concrete that meets the high technological and utilization requirements with very high liquidity.In Europe, one of the first applications of SCC was conducted in Sweden  where inThe aim of the work was to propose a design procedure that takes into consideration such a selection of the mineral skeleton in terms of the volumetric saturation of the mineral skeleton, which prevents the blocking of aggregate grains, and the designed liquid phase demonstrated high structural viscosity and low yield stress.two types of cement complying with PN-EN 197-1 , the cem3;in order to increase the viscosity of the concrete mix and reduce the amount of cement, a mineral additive was used in the form of limestone dust complying with the PN-EN 13043  with the3 and water absorption of 1.60%, and crushed-stone aggregate-basalt 2/8 and 8/16 with a density of 2.95 g/cm3 and water absorption of 0.50%, and natural sand-fraction 0/2 with a density of 2.64 g/cm3;two types of aggregate were used in the studies, natural aggregate-gravel-fraction 2/8 and 8/16 mm of a density of 2.65 g/cm3);A third-generation high-range/strong water-reducing admixture CP and VMA viscosity regulators complying with PN EN 934-1  and PN-Etap water complying with PN-EN.The research work included the use of:While performing an analysis of the mechanism of operation of the self-compacting of concrete, one can assume—in accordance with the assumptions of the physicochemical mechanics of dispersion systems—that it is a dispersion system composed of the dispersed phase  and of the liquid phase  ,18,36. TThe first stage of design was based on designing a cement paste that would demonstrate appropriate viscosity, viscosity hysteresis loop, and flow greater than 18 cm measured using the Southard viscometer. The first part of the laboratory experiment was based on rheological studies performed with the use of a rotary viscometer with coaxial cylinders, Rheotest 2, for the designed pastes with various water–cement ratios w/c  for two different cements (CEM I and CEM II), which allow for the assessment of the behavior of these pastes with a decreasing amount of water and a constant amount of cement. This device was used for determining the viscosity of the paste and the flow curves in the shear stress-shear rate system. The flow curves describing the mechanism of behavior of the continuous phase by creating the hysteresis loop were formed as a result of the increase and decrease of the shear rate. Additionally, examinations with a Southard viscometer were performed in order to determine the standard flow of the paste. Subsequently, in a further part of the experiment, the paste with the determined water–cement ratio (w/c) was subjected to modification performed using very strongly liquidating superplasticizers in the following doses of 0.5, 1.0, 1.5, and 2.0% in reference to the mass of the cement. The scheme of analyzing the pastes in the Rheotest 2 is presented in τ and of the shear rate gradient γ are associated with the radius of the coaxial cylinder system. Shear stress is expressed using Formula (1):2, Pa−1; 2; and α is the value read from the indicating instrument.The values of the shear stress 2, Pa−1; and −1.For the determined values of shear stress The next step of stage one is to calculate the minimum amount of the cement paste The graphical representation of the amount of paste described with Formula (3) is presented in b is calculated according to Formula (5) and is marked as z/gk; 3; and 3.z/gk; 2/g; and The minimum amount of paste filling the free space between the grains of aggregate Finally, the demand for the minimum amount of cement paste allowing for the flow of concrete is determined according to Formula (6):3; and 3.According to the assumptions of this method, the determined minimum amount of the cement paste 3.According to the formula for absolute volume:The final amount of aggregate ,71,72,733; 3; 3; 3; 3; 3; 3; 3; 3; 3; 3; and 3.In order to verify the correctness of the calculations of all the components of the concrete mix, it is necessary to use the formula for the so-called absolute volume (or the tightness condition), which has the following form:3.The second stage of the functional design of the self-compacting concrete mix is the selection of the grading of the mineral mix by determining the tightness of the aggregate skeleton and the maximum bulk density. This stage consisted of the optimum selection of the particular fractions of aggregate in such a way as to obtain the maximum degree of saturation . The methodology for performing this was based on the formerly  applied Determining the maximum density of the mineral skeleton should start from the coarsest fraction of the rock material . This activity should be repeated until the moment when the maximum bulk density is obtained and the subsequent attempt to add 2/8 material causes a decrease in the density of the mix. The mix of 8/16 and 2/8 gravel for which maximum bulk density is obtained is the desired starting material for subsequent attempts; the difference is that now finer materials are added .3.Finer material should be subsequently added in this way until, in the final part of this study, the mineral filler in the form of inert limestone dust is added and the mineral mix obtained in this experiment demonstrates maximum tightness and a minimum amount of free spaces. The effect of this part of the design is obtaining a mineral mix of maximum tightness resulting from appropriate proportions of particular mineral components. Subsequently, the specific density (without air voids) of the mineral components should be determined using the Le Chatelier Flask. Specific density should be calculated using Formula (12):3; and 3.On the basis of the experimentally determined maximum bulk density of the aggregate skeleton and the density of the mineral mix determined using the Le Chatelier Flask, it is possible to determine the amount of free spaces in the designed mineral mix. The free space in the designed mineral mix is calculated according to Formula (13):Stage III of design is determining the grading and, on its basis, calculating the specific surface area  of the designed aggregate skeleton. This stage is based on the assumption  that theThe reason for the occurrence of the blockade is the too close contact between the most coarse grains, resulting in the drastic increase of the yield stress, which hinders the flow and causes the blocking of the mineral skeleton .2/g, 2/g.The aggregate skeleton designed this way should demonstrate the smallest possible specific surface area, which may be calculated according to Formula (14):3.The specific surface area constitutes the area of the unfolded surface of all the grains of aggregate included in a given unit of volume. The higher the value of the specific surface area, the higher the demand for the content of the liquid phase. Knowing the grading and the designed grain size distribution curve, on the basis of b membrane coating the aggregate grains, it is possible to, with high accuracy, calculate the minimum amount of cement paste necessary for ensuring the proper flow of the self-compacting concrete mix.On the basis of the calculated specific surface area and the thickness of the The fourth stage of designing self-compacting concrete is based on the verification of the parameters of the concrete mix and of the hardened concrete through the creation of trial batches. Determining the parameters obtained by the self-compacting concrete mix may take place through a 4-grade assessment based on the L-box, the V-funnel, and the Abrams inverted cone. This stage of analysis is relatively simple, but very important because only here is it possible to observe the actual behavior of the mix and introduce necessary corrections to its composition.Additionally, for particular batches, the properties of hardened concrete were determined such as compressive strength after seven, 28, and 90 days, water absorption, resistance to the effect of freeze, and the density.This method was used to design the grading of the mineral skeleton of mastic asphalt, because it allowed for the design of a tight aggregate skeleton in an easy and accurate way, based on the mineral materials applied in the local construction market.At this stage of design, the main aim is to design a cement paste that would demonstrate appropriate viscosity, viscosity hysteresis loop, and flow greater than 18 cm as determined using the Southard viscometer.In this part, the research experiment was based on rheological analyses (performed with the use of the Rheotest 2 rotary viscometer and the Southard viscometer) of pastes demonstrating various water–cement ratios (w/c), starting from 0.6, 0.55, 0.50, 0.45, and ending with 0.40. All of the analyzed pastes were made of two cements (CEM I 32.5 R and CEM II/B-S 32.5 manufacturer—Lafarge).The measured values of the paste viscosity and the flow curves that formed as a result of the increase and decrease of the shear rate are demonstrated in the graph presenting the flow curves for the paste on the basis of CEM II with the water–cement ratio (w/c) = 0.5.The mathematical nature of the flow curves in Curve 1 (upper):Curve 2 (lower):In this way, the following was obtained:In the integral function, the expression had the following form:In accordance with the principles of the integral calculus of the polynomial function in determined limits of integration, the surface area of the viscosity hysteresis loop obtained for the given set was 407.887. The results of the performed studies for two types of cement and for various water–cement ratios (w/c) in the scope of the dependence of the viscosity of the cement paste on the type of cement and the water–cement ratio (w/c) are presented in Moreover, in order to verify Stage I, analysis of the pastes was performed using the Southard viscometer in which the flow of the paste was measured in cm and is presented in On the basis of the conducted research, the paste from the CEM II/B-S cement with the water–cement ratio (w/c) = 0.5 was selected.Next, for the selected water–cement ratio (w/c) = 0.5 and the CEM II/B-S 32.5 cement, the second part of the experiment was started, which consisted in the modification of the selected suspension with a third-generation high-range/strong water-reducing admixture CP and VMA viscosity regulators complying—CP1, CP2, CP3—in the following doses of 0.5, 1.0, 1.5, and 2.0% in reference to the mass of the cement, checking the compatibility of the admixture with the cement. The obtained study results related to the viscosity area of the hysteresis loop are presented in During the determining of both, the viscosity of the paste as well as of the viscosity area of the hysteresis loop, the best results were achieved for the a modified polycarboxylic high-range water-reducing admixture CP1 in the amount of 1.0% in reference to the mass of the cement. For the purpose of confirmation, the standard consistency test was performed using the Southard viscometer according to PN-86/B-04360 .The obtained results confirmed the rightness of both the selection of the CP1 superplasticizer as well as of the liquidating dose in the amount of 1.0%.The experimental verification of the theoretical assumptions of the selection of the dispersed phase was begun from the selection of the grading of the mineral mix by determining the tightness of the aggregate skeleton and determining the maximum bulk density according to the mastic asphalt design method adopted for this purpose. For this purpose, the maximum bulk density and the minimum amount of free spaces were determined for two different types of aggregate  and for 0/2 mm natural sand as well as for a mineral filler.3 of the mineral mix was obtained for 73% of 2/8 gravel in reference to the 8/16 fraction. Finer material was added to the constant amount of 8/16 mm (200 g) and 2/8 mm (146 g) gravel determined in this way in order to fill the free spaces in the mineral mix. This material was 0/2 mm sand in equal portions, per 30 g. The maximum bulk density equal to 2.208 g/cm3 of the mineral mix was obtained for 61% of sand in reference to the sum of the 8/16 and 2/8 fraction. The finest material in the form of the limestone filler in the amount of per 15 g was added to the constant amount of 8/16 mm (150 g) and 2/8 mm (109.5 g) gravel and of 0/2 mm sand (158 g) determined in this way. The tabular and graphical juxtapositions of the actions are presented below in For this purpose, the action started from the 8/16 fraction in a constant amount of 250 g and consecutively, finer 2/8 gravel was added in equal amounts of 30 g until obtaining the maximum density of the mix. These activities were repeated 10 times in order for the achieved result to be statistically reliable. The maximum bulk density equal 1.682 g/cm3 of the mineral mix was obtained for 10.77% of limestone dust in reference to the sum of the fractions of 8/16 mm and 2/8 mm gravel and 0/2 mm sand.The maximum bulk density equal of 2.236 g/cmOn the basis of the conducted studies related to determining the maximum bulk density, compositions of mineral mixes based on natural and crushed-stone aggregate were obtained. These compositions demonstrate the minimum amount of free spaces that have been juxtaposed in Subsequently, the Le Chatelier Flask was used to experimentally determine the specific density (without air voids) of the used materials, and the results are presented in On the basis of the determined maximum density of the mineral mix and of the density of particular materials determined using the Le Chatelier Flask, the amount of free spaces in the designed mineral mix was calculated according to the formula:The minimum amount of free spaces determined experimentally for the crushed-stone aggregate  has the following value:Such a tight structure of the mineral skeleton, obtained during designing Stage I cannot guarantee the flow of the concrete mix. Therefore, out of the designed tight aggregate skeleton, it is necessary to create a mineral skeleton of a dispersive structure allowing for free flow of the self-compacting concrete mix.At Stage III of the research experiment, the grading (size distribution) of particular components was determined and is included in Calculating the specific surface area  of the aggregate skeleton in order to separate the tightly positioned grains of the aggregate to the distance of the assumed membrane of the thickness “b” was performed on the basis of the designed compositions of mineral mixes for natural and crushed-stone aggregates .Z2 paste is the product of the specific surface area wP, the coating radius b  and the density of cement paste 3 with a determined water–cement ratio (w/c) = 0.5.The minimum amount of the Z2 = 0.1217 gz/gk, and for basalt aggregates Z2 = 0.1076 gz/gk.For a mineral skeleton designed this way, the minimum amount of paste for gravels is The third stage of design ends with determining the minimum amount of cement paste according to Formula (5). For gravel aggregate and paste with the water–cement ratio (w/c) = 0.5 with the dosage of 1.0% of CP1 in reference to the cement mass, it is:The final amount of gravel aggregate in the concrete mix calculated using Formula (9) for the gravel aggregate is:In accordance with earlier assumptions, the final amount of cement paste (the liquid phase) according to Formula (6) is:The minimum amount of cement paste according to Formula (5) for basalt aggregate and paste with the water–cement ratio (w/c) = 0.5, with the dosage of 1.0% of CP1 in reference to the cement mass is:The final amount of basalt aggregate in the concrete mix calculated using Formula (9) for gravel aggregate is:In accordance with earlier assumptions, the final amount of cement paste (the liquid phase) according to Formula (6) is:The final stage of design according to the new volumetric method was juxtaposing the recipes for the concrete mix, which is supposed to meet the features of self-compacting in At this stage of design, the decision was made that full analyses verifying the rheological and mechanical characteristics were to be conducted for all recipe compositions that differed from one another in terms of the amount of the filler. This aimed at verifying the decision made during design, which referred to the amount of the applied filler and the influence of the amount of the filler on the self-compacting properties of the concrete mixes.The juxtaposition of the compositions of all the recipes that were subjected to full verification of the rheological characteristics during analyses performed on concrete mixes in fresh and hardened condition is presented in Recipe numbers SCC 4-G and SCC 11-B were designed using the new method. The remaining ones were rejected during subsequent stages of design.Modeling phenomena and processes that occur in nature, with the use of a specialized mathematical and statistical apparatus, comes down to several significant elements ,75,76. Tsensu stricto nonlinear models, referred to as proper nonlinear models. While in the case of models that may undergo linearization, it is possible to use the least squares method estimators, however, in the process of the estimation of proper nonlinear models, this is not always possible. In such situations, methods of estimation of structural parameters of nonlinear models are applied, which are based on iterative algorithms that minimize the loss function proposed by A. Wald in 1939. The loss function defined as the sum of the squares of deviations of the observed values in reference to the theoretical values is most frequently applied and can be recorded in the following way:n is the number of observations.The matter which becomes crucial is the selection of an appropriate analytical form of the model in conditions of nonlinearity of the connection between the density and the total mass of the mineral mix . NonlineIf the loss function (15) achieves the minimum in the estimation process, then the estimators may be referred to as least squares estimators. The most frequently applied nonlinear estimation algorithms with dedicated computer software are: the quasi-Newton algorithm, the simplex algorithm, the Hooke and Jeeves pattern search method, and the Rosenbrock method of rotating coordinates .The quasi-Newton method is based on the following: in every step of the iteration, a function is estimated in various points for the purpose of the estimation of first and second order derivatives. This information is subsequently used in order to follow the path heading toward the minimum of the loss function. The quasi-Newton method is the most effective of the discussed methods . The simplest procedure is based on the estimation of the loss function derivatives. In every iteration, the function is estimated in m + 1 points in an m-dimensional space of parameters. In a two-dimensional space, the points form a triangle that “moves” toward the bottom of the loss function, until this function reaches a minimum. This method is less sensitive to local extrema than the quasi-Newton algorithm because the triangle is made bigger or smaller in the case of need in subsequent steps. In case of an m-dimensional space, the name of the figure is simplex. The Hooke–Jeeves method is based on relocating a whole set of points in an m-dimensional space by the distance of a step that is constantly changed and adjusted to minimize the loss function. In the Rosenbrock method of rotating coordinates, the space of parameters is rotated and one axis is aligned to the ridge. All the other axes remain orthogonal to this axis. If the loss function is unimodal and has detectable ridges pointing toward the function minimum, then the method will head precisely toward the function minimum. The search algorithm may be interrupted earlier if there are several limitations  that intersect, which leads to the discontinuity of the ridges. Sometimes the selection of a combination of methods delivers the best results of the estimation. The simplex, Hooke and Jeeves, and Rosenbrock methods are generally less sensitive to local minimums, so one can apply these methods together with the quasi-Newton method. This is especially convenient when there is no certainty regarding the appropriate initial values for the estimation. In such a case, the first method may generate the initial parameter estimators that will then be used in subsequent quasi-Newton method iterations. A significant problem of the construction of a non-linear model is the selection of the appropriate analytical form of the relationship. There is no universal method allowing for the determination of the analytical form of the function in every situation.On the basis of the existing theory explaining the mechanism of the analyzed phenomenon, the a priori knowledge about the analyzed phenomenon is used, constructing characteristic equations , the solution to which are appropriate function classes. In the case of a lack of theoretical solutions, empirical material is used. Graphs of the empirical dispersion of points (sets of points) are designated in the coordinate system and on the basis of the shape of those graphs, the adequate analytical function form is selected. Such an approach may be used in the case of a model only with one explanatory variable. Mixed method if the theory referring to the considered phenomenon indicates, for example, that the explained variable should have a saturation level, then it is necessary to adjust the curves that have a horizontal asymptote to empirical data.Due to a lack of theoretical solutions, the second method of procedure was adopted in the modeling. The best approximation results  were obtained for the segment nonlinear regression model in which, for each of the fractions of concrete, the analytical form of a perfect square trinomial was adopted.iρ is the density of the mineral skeleton in the ith step of the analysis; im is the total mass of the mineral skeleton in the ith step of the analysis; α11, α12, α13 are the parameters of the perfect square trinomial of the 1st fraction; α21, α22, α23 are the parameters of the perfect square trinomial of the 2nd fraction; and α31, α32, α33 are the parameters of the perfect square trinomial of the 3rd fraction.The model of segment nonlinear regression may be recorded in the following way :(16)ρi=(jI(p) is the logic value of sentence p for the jth fraction:ρ1, ρ2, ρ3 are the threshold values which are the maximum densities of the mineral skeleton for each fraction and iξ is the model’s disturbance term.An element that requires explanation is the emergence of a disturbance term in the general record of the model. The disturbance term is a random variable that is expressed in the form of differences between the actual values of density and the model ones . It is an immanent part of the model and may occur in the model due to three reasons.First, due to the fact that in the process of analyses in laboratory conditions other factors (of negligible significance) affecting density  have not been taken into account. Second, the wrong analytical form of the model was adopted, and third, the measurement of variables was performed with errors, .In the process of estimation of the parameters of the segment nonlinear regression model, the statistical data that were used constituted arithmetic averages calculated for the fractions on the basis of the results of 10 research series. Such a procedure results in annulling a high number of cases of non-systematic errors of measurements of a random nature.This information is subsequently used in order to follow the path heading toward the minimum of the loss function. The process of estimating parameters achieved convergence after 28 iterations (loss function minimum). The results of the estimation are juxtaposed in The following model was obtained:3. The high degree of the model’s adjustment to the empirical data is also visible in The degree of explanation of the variance of the sought maximum density of the mineral mix by the model was very high and was equal to 99.75%. The theoretical values deviated from the empirical values on average only by 4.78 mg/cma = 1 and b = 0.The comparison between empirical values and the theoretical ones indicates very good properties of the phenomenon description by the obtained model. In the case of function dependences, the points are arranged along a line The knowledge of the regression model of the mineral skeleton density in reference to its mass may be used in determining the tight structure of the concrete mineral skeleton. It is enough to—for each fraction—calculate the first order derivative in reference to mass and determine its zeros. Then, for the determined values of arguments (mass), the explained variable (density) will have the highest value. The density for the jth fraction may be calculated according to the following dependence:Then, the first derivative has the following form:Thus, the density maximum is obtained for:Formula (21) allows for determining such proportions of concrete components for which maximum density is obtained in particular stages of the analysis.Stage IV of designing self-compacting concrete consists of creating trial batches of the designed concrete mixes and in determining the self-compacting properties with the help of a three grade assessment based on the L-box, the V-funnel, and the Abrams inverted cone and in determining the mechanical properties after 90 days of concrete hardening.Analyses of the concrete mix were performed in accordance with the applicable standards and the results are juxtaposed in Subsequently, after performing the analyses of the features of the fresh concrete mix, cubic specimens were created for the purpose of verifying the mechanical properties of these mixes after 90 days of hardening. The results obtained during the analyses are presented in The concrete mix prepared according to the SCC 4-G recipe met all the rheological properties required for the SCC mix. It demonstrated the flow of 72 cm and the time of outflow from the measurement funnel was equal to 6.5 s. The concrete mix prepared according to recipe no. 11 also met all the rheological properties required for the SCC mix and it demonstrated the flow of 70 cm and the time of outflow from the measurement funnel equal to 7.7 s.t500 time), the yield stress was determined according to Formula (22):As a result of the studies carried out by the authors of the French method, Sedran and de Larrard , there it500 time), the plastic viscosity was determined according to Formula (23):On the basis of my own studies  with the help of the diameter and the dynamics of the flow obtained thanks to the Abrams inverted cone, a graphic verification of the Bingham model was performed .The article presents the functional method of designing self-compacting concrete. The proposed procedure takes into consideration such a selection of the mineral skeleton in terms of the volumetric saturation of the mineral skeleton, which prevents the blocking of aggregate grains, and the designed liquid phase demonstrated high structural viscosity and low yield stress. The performed experimental studies, the simulation of the elaborated mathematical model fully allowed for the verification of the theoretical assumptions that are the basis for the development of the method of designing self-compacting concrete.The designed cement paste demonstrated lowered yield stress and structural viscosity, which prevented the segregation and sedimentation of the components of the mineral mix during flow and gravity compacting. On the basis of the conducted studies of the flow curves of specimens made from pastes (the continuous phase) in the rotary viscometer, clear deviations were noticed in reference to the Bingham liquid model declared in the literature. These deviations in reference to the model adopted in the literature were observed in case of two main phenomena. First, after exceeding the yield strength The size of the area of the viscosity hysteresis loop of the analyzed cement pastes achieved higher values for the CEM II cement. This cement included a 20% addition of blast-furnace slag and, therefore, is a binder of a greater thixotropic nature, whereas the selection of the BV 10 superplasticizer guaranteed certain thixotropic properties with the lowest dosage in reference to the mass of the cement (only 1%). This was possible thanks to applying a new generation of a very strongly liquidating polymer CP, composed of various kinds of oligomers that increase the viscosity of make-up water and limit the segregation of the components of the concrete mix mineral skeleton.The selection of the CP1 polymer for the designed cement paste allowed for obtaining certain thixotropic properties with its minimum amount (the lowest dosage) in reference to the mass of the cement (only 1%). The decisive factors here were, above all, economical concerns and the informed avoidance of the problem of the repeated dosing of the superplasticizer at the construction site, which is typical for mixes with a high dose of the superplasticizer.u, which, by surrounding particular grains with a thin layer of the paste, allowed the concrete mix to free slide and flow without causing the phenomenon of coarse aggregate blocking. The grain size distribution curves of the designed mineral mixes were not located in the area of good grading applied during the design of the grading of ordinary concrete. The analysis of the graphic character of the grain size distribution curve allows for qualifying this type of mineral mix to the SMA  asphalt mix, which is known and widely used worldwide and has a macadam-concrete structure with clear flattening (deficiency) of the sand fraction from 0.5 to 4.0 mm.The designed mineral skeleton on the basis of coarse aggregate, fine aggregate (sand), and the inert filler demonstrated minimum free space. The tightly packed aggregate skeleton impacted the lowering of the demand for cement paste , resulting in the increase of strength and resistance to the effect of freeze. The creation of a dispersive structure was achieved through the introduction of the dispersion rate The experimental verification of the designed compositions of self-compacting concrete was performed with the use of the Abrams inverted cone, the L-box, and the V-Funnel, and the findings were that the best plastic properties as well as the best properties referring to strength and durability were demonstrated by the mix of the following composition: SCC 4-G and SCC 11-B.A properly designed mineral skeleton demonstrating minimum free space causes a reduction of the demand for cement and results in an increase in compressive strength and an increase in the concrete durability.Z2 paste allowed for the separation of the grains of the aggregate to the distance of layer b and resulted in free slide and flow of the mix, without the clear blocking of the aggregate.The introduction of a dispersive structure through the increase in the amount of the The cement paste based on the CEM II BV cement and the water–cement ratio (w/c) = 0.5 with 1% content of CP1 demonstrated reduced yield stress and viscosity typical for self-compacting concretes.On the basis of the analyses of the flow curves of the analyzed pastes, deviations were noticed in reference to the Bingham model declared in the literature, demonstrating pseudoplastic course.The concrete mixes prepared according to the SCC 4-G and SCC 11-B recipe met all the rheological properties required for the SCC mix. They demonstrated flow from 70 to 72 cm and the time of outflow from the measurement funnel from 6.5 to 7.7 s.The obtained results of the studies of hardened concrete met the designed concrete class C30/37 with much reserve and demonstrated resistance to the effect of freeze.The performed experimental studies, the simulation of the elaborated mathematical model, and the verification of the theoretical assumptions supported with the experimental part allow for the following conclusions: