One of the major barriers to scale up of antibiotic stewardship interventions is the difficulty of engaging already overtaxed personnel. As part of a multisite antibiotic stewardship project to decrease antibiotics treatment of asymptomatic bacteriuria, we explored how to measure local implementation efforts, and what dose of the intervention was necessary to improve clinical outcomes.The intervention was implemented in 4 different sites from February 2019 through May 2020. We chose 3 measures of implementation: the number of intervention delivery sessions (adoption), total number of health care professionals reached (penetration), and minutes spent in delivery of the intervention (adoption). Local site champions kept activity logs. Antibiotic prescriptions were included if ordered within one calendar day prior or two days after a urine culture was ordered on the same patient. Correlation between implementation measures and clinical outcomes , and length of antibiotic treatment (LOT)) was calculated using the mixed linear models method.Overall, the minutes spent in delivery ranged from 2567 minutes at the most engaged site to 679 in the least engaged site . The number of healthcare professionals reached ranged from 798 to 433, and the number of sessions delivered ranged from 240 to 45. Minutes spent in delivery was inversely correlated with two of our three clinical metrics, DOT  and LOT ; minutes spent and urine cultures were not significantly correlated (Table 1). We did not find a significant relationship between the number of intervention delivery sessions or total number of health care professionals reached and any of the clinical outcomes.We found a significant inverse correlation between the number of minutes a local site champion spent delivering the antibiotic stewardship intervention and antibiotic use, both DOT and LOT. In other words, more time spent delivering the intervention locally was associated with a decrease in antibiotics ordered. Our implementation metric (adoption) is scalable and readily adaptable to large antibiotic stewardship dissemination projects.Larissa Grigoryan, MD, PhD, Rebiotix Inc: Grant/Research Support Barbara Trautner, MD, PhD, Genetech: Advisor/Consultant.


Remote Infectious Disease (ID) physicians can provide stewardship support through telehealth. Using the RE-AIM framework, we assessed the implementation of telehealth-supported prospective-audit-and-feedback (tele-PAF) across 3 rural Veterans Administration medical centers (VAMC).All 3 invited sites agreed to participate and lacked ID support for stewardship at baseline. During 2021, an ID physician met virtually 3 times/week with the stewardship pharmacist champion at each participating VAMC to review patients on antibiotics in acute-care (mean daily census 3/site) and nursing-homes ; real-time feedback on antibiotic use was given to clinicians. The primary outcome of effectiveness was monthly antibiotic days of therapy (DOT) per 1,000 days-present aggregated across all sites; the secondary outcome was days of antibiotic spectrum coverage (DASC) per 1,000 days-present. An interrupted time-series analysis was performed to asses these outcomes during the 1-year intervention period vs. the 2-year prior baseline. Semi-structured interviews with 20 clinicians and pharmacists were conducted to assess implementation.RE-AIM elements are summarized in Table 1. Tele-PAF reviewed 502 unique patients and made 681 recommendations to 23 clinicians; 77% of recommendations were accepted. The most common recommendations were to stop antibiotics (28%) and change duration (20%). After the start of tele-PAF, antibiotic DOT and DASC immediately decreased in acute-care  and NHs . Both metrics began to rise again in acute-care  but were stable in NHs . Clinicians generally appreciated feedback, found it compatible with their workflow and responded favorably to collaborative discussions. Barriers included difficulty establishing rapport with some providers.The implementation of tele-PAF was associated with sustained reductions in antibiotic use across 3 NHs but not in the studied small acute-care units. Overall, clinicians perceived the intervention as acceptable and appropriate. Wider implementation of telehealth-supported stewardship activities may achieve reductions in antibiotic use.Daniel J. Livorsi, MD, Merck & Co.: Grant/Research Support.


Pseudomonas aeruginosa bacterium is a common pathogen of cystic fibrosis (CF) patients due to its ability to evolve resistance to antibiotics during treatments. While P. aeruginosa resistance evolution is well-characterized in monocultures, it is less well-understood in polymicrobial CF infections. Here, we investigated how exposure to ciprofloxacin, colistin, or tobramycin antibiotics, administered at sub-minimum inhibitory concentration (MIC) doses, both alone and in combination, shaped the tolerance evolution of P. aeruginosa  in the absence and presence of a commonly co-occurring species, Stenotrophomonas maltophilia. The increases in antibiotic tolerances were primarily driven by the presence of that antibiotic in the treatment. We observed a reciprocal cross-tolerance between ciprofloxacin and tobramycin, and, when combined, the selected antibiotics increased the MICs for all of the antibiotics. Though the presence of S. maltophilia did not affect the tolerance or the MIC evolution, it drove P. aeruginosa into extinction more frequently in the presence of tobramycin due to its relatively greater innate tobramycin tolerance. In contrast, P. aeruginosa dominated and drove S. maltophilia extinct in most other treatments. Together, our findings suggest that besides driving high-level antibiotic tolerance evolution, sub-MIC antibiotic exposure can alter competitive bacterial interactions, leading to target pathogen extinctions in multispecies communities.The IMPORTANCE Cystic fibrosis (CF) is a genetic condition that results in thick mucus secretions in the lungs that are susceptible to chronic bacterial infections. The bacterial pathogen Pseudomonas aeruginosa is often associated with morbidity in CF and is difficult to treat due to its high resistance to antibiotics. The resistance evolution of Pseudomonas aeruginosa is poorly understood in polymicrobial infections that are typical of CF. To study this, we exposed P. aeruginosa to sublethal concentrations of ciprofloxacin, colistin, or tobramycin antibiotics in the absence and presence of a commonly co-occurring CF species, Stenotrophomonas maltophilia. We found that low-level antibiotic concentrations selected for high-level antibiotic resistance. While P. aeruginosa dominated in most antibiotic treatments, S. maltophilia drove it into extinction in the presence of tobramycin due to an innately higher tobramycin resistance. Our findings suggest that, besides driving high-level antibiotic tolerance evolution, sublethal antibiotic exposure can magnify competition in bacterial communities, which can lead to target pathogen extinctions in multispecies communities. Pseudomonas aeruginosa is the most prevalent pathogen associated with morbidity  is a genetic condition that is characterized by impaired chloride ion channel function, which results in thick mucus secretions in the lungs that are susceptible to chronic bacterial infection . Of the orbidity , 3, and orbidity , 5. ThouCF lungs –10.P. aeruginosa or to help resolve pulmonary exacerbations    of the antipseudomonal antibiotics ciprofloxacin, colistin, and tobramycin. These antibiotics were selected because of their use either in P. aeruginosa eradication therapy or in the treatment of pulmonary exacerbations   either aophilia) . Two strrbations , 43, 44 rbations –47. EachP. aeruginosa and S. maltophilia for any extinctions and monitored the changes in the total population densities across the 192 selection lines. Following the experiment, we measured the ability of the evolved focal P. aeruginosa isolates to grow in the treatment concentrations of the individual antibiotics, relative to ancestral stock strains. Moreover, the MICs of each antibiotic were determined for all of the evolved P. aeruginosa isolates. We hypothesized that: (i) antibiotic tolerance evolution could be constrained in the presence of a competitor but promoted in the presence of multiple antibiotics if cross-tolerance evolution is common and (ii) antibiotic exposure could change the community composition due to differences between the species’ innate susceptibilities to the antibiotics or due to the evolution of tolerance-growth trade-offs.During the serial transfer experiment, which took place over 21 days, we tracked the presence of S. maltophilia did not affect the evolution of antibiotic tolerance or the MIC with either of the P. aeruginosa strains, likely due to the frequent extinctions during the early phase of the selection experiment. However, while both of the P. aeruginosa strains were able to dominate the “No Antibiotic” control and many of the antibiotic-containing coculture treatments, the tobramycin-containing antibiotic treatments triggered P. aeruginosa extinctions in 15% of the coculture populations. Such extinctions were more common when S. maltophilia was cultured with PAO1 than with LESB58. Together, these results suggest that the effects of sub-MIC antibiotic concentrations could be magnified in polymicrobial communities due to competition, an asymmetry in innate antibiotic tolerances, and the differential evolution of antibiotic tolerances and their associated costs.We found that increases in antibiotic tolerance or the MIC were not generally enhanced by antibiotic combinations. Rather, increases in the tolerance or the MIC to a given antibiotic were driven by the presence of that antibiotic in the treatment combination, which occasionally led to cross-tolerance. Similarly, the presence of P. aeruginosa populations’ abilities to grow  in the presence of the treatment concentration of each of the antibiotics and compared this to the measured growth without the antibiotic . Some P. aeruginosa monoculture replicates were removed from the analyses due to contamination with S. maltophilia . Moreover, as P. aeruginosa went extinct in some of the tobramycin-containing treatments (24/143 selection lines), the evolution of tolerance was compared using only the surviving treatment replicates.To test potential tolerance evolution, we measured the evolved S. maltophilia (P > 0.05)  .post hoc pairwise comparisons, PAO1: t[48] = 11.78 [CIP]; 13.76 [CIP+CST]; 11.42 [CIP+TOB], P < 0.001; LESB58: t[66] = 4.73 [CIP]; 4.82 [CIP+CST], P < 0.001; t[66] = 4.42, P = 0.001 [CIP+TOB]; t[66] = 3.46, P = 0.026 [CIP+CST+TOB])     mono-, CIP+colistin (CST), and CIP+tobramycin TOB) treatments, compared to the “No Antibiotic” control treatment, as well as with the CIP+CST+TOB treatment in LESB58 (ST+TOB])  and B. S treatmen< 0.001) , whereas< 0.001) . In contST+TOB])  and D.vice versa)       . In PAO1< 0.001) . Additio= 0.093) . A simil= 0.011) . Further= 0.006) . Additio= 0.002)  and F. TP. aeruginosa genotype replicates evolved to grow better in the growth media, relative to their ancestors . Moreover, the growth of evolved LESB58 populations treated with any tobramycin-containing antibiotic treatment were significantly below that of the “No Antibiotic” control treatment   . These rP. aeruginosa replicate populations as well as the MIC capable of inhibiting 50% of replicates (MIC50) for each treatment to quantify whether exposure to low antibiotic concentrations led to an increased MIC. For both of the P. aeruginosa strains across all three antibiotics, there was no effect of previous exposure to S. maltophilia on the MICs. However, the MICs of the evolved populations changed considerably with both P. aeruginosa strains in response to all antibiotics (Table S3).We measured changes in the MIC of each antibiotic for evolved (i) Changes in ciprofloxacin MIC. Both evolved P. aeruginosa strains showed large increases in MIC to ciprofloxacin    , further suggesting that there is some cross-tolerance provided by tobramycin, as is also seen in the growth measurements  ; (pairwi 0.0019) . Indeed, 0.0064) , such thurements . The MIC(ii) Changes in colistin MIC. As opposed to ciprofloxacin, the MICs of colistin did not increase as a result of prior colistin exposure during the selection experiment  (periment  and D. Iperiment . Slightl= 0.037) . Overall(iii) Changes in tobramycin MIC. The MIC changes for tobramycin were similar between both P. aeruginosa strains   . Both strains also had a significant increase in MIC as a result of the CIP mono-treatment, compared to the “No Antibiotic” control treatment . However, this increase did not reach the same values as did the tobramycin containing treatments; the MIC of the CIP mono-treated LESB58 isolates was significantly lower than those of the TOB, CST+TOB, and CIP+CST+TOB treatments , suggesting that the cross-tolerance provided by ciprofloxacin was weaker than that of tobramycin. Overall, both P. aeruginosa strains evolved increases in the tobramycin MIC, which was primarily driven by the previous exposure to tobramycin during the selection experiment. strains  and F. T strains , whereas strains . For bot< 0.001)  (pairwis 0.0053) . For LES600) of each bacterial population at the final time point of the selection experiment to determine the extent to which antibiotics inhibited bacterial growth (measurements were taken at the population level and did not differentiate species frequencies). For both Pseudomonas strains, there was a significant effect of antibiotic treatment on the total population density (P < 0.001) (Table S4), and with the exception of the CST mono-treatment, antibiotics generally decreased the total population density, relative to the “No Antibiotic” control treatment  (P > 0.05) (Table S4), and although there was a significant effect in LESB58 (P = 0.022) (Table S4), this was likely driven by the large difference in population density between the two CST-mono-treated cultures    and D. T= 0.034)  and D. TP. aeruginosa and S. maltophilia cocultures at the end of the experiment to examine the effects of antibiotics on the species coexistence. We found that P. aeruginosa survived in all monocultures across the different treatments (except for a single PAO1 replicate that went extinct under the CST+TOB treatment). This suggests that the low concentrations of the antibiotic were not sufficient to kill P. aeruginosa, even when applied in combination. However, extinctions of P. aeruginosa were more common in the presence of S. maltophilia . In contrast, the TOB mono-treatment allowed for a prolonged coexistence between the two bacteria, and S. maltophilia was able to survive with both P. aeruginosa genotypes in two of the six TOB mono-treatment replicates and to fully outcompete P. aeruginosa in a further three replicates . However, when S. maltophilia survived for longer, such as in the TOB mono-treatment or in the CST+TOB treatment for LESB58 , there remained no significant effect of competition on the tolerance or the MIC evolution, compared with monoculture growth. This suggests that the presence of S. maltophilia indeed had no effect on P. aeruginosa tolerance evolution. However, due to the nature of our experimental setup, wherein evolutionary dynamics are inherently linked with ecological dynamics, it is difficult to isolate the effect that S. maltophilia may have had on the evolution of tolerance in P. aeruginosa. An alternative experimental setup, such as introducing fresh populations of S. maltophilia at each time point, could isolate the evolutionary effect of a competitor. Alternatively, it is possible that the effect of S. maltophilia occurred at an earlier time point. Quinn et al. , as it compares the growth of the same replicate under different conditions, thereby accounting for any morphological changes that have arisen via adaptation to the growth medium. To fully compensate for this in the future, we could perform direct counts of viable cells, such as by counting colony-forming units (CFU).We predicted that the presence of multiple antibiotics could select for increased levels of antibiotic tolerance, potentially due to cross-tolerance or via selection for generalized resistance mechanisms, such as efflux pumps , 5. In sP. aeruginosa, namely, the upregulation of the MexXY-OprM efflux pump , which could have reduced the negative effects of the antibiotics in the CIP+TOB and triple antibiotic treatments, compared to PAO1. The initial differences in antibiotic susceptibility could reflect contrasting evolutionary histories between these two strains. PAO1 is highly lab-adapted due to repeated culturing in lab media, whereas LESB58, a transmissible strain isolated in 1988 from CF patients , and LESB58, a transmissible CF lung isolated strain , referred to here as “NB”, that allowed for the stable coexistence of both the focal pathogen (P. aeruginosa) and the competitor  species over a single 72 h growth period. All cultures, unless otherwise stated, were grown at 37°C with shaking at 180 rpm.Two strains of d strain . Stenotr patient , was useP. aeruginosa strain PAO1 or LESB58) was grown in a culture either alone (monoculture) or with S. maltophilia (coculture) and was treated with subinhibitory concentrations of ciprofloxacin (CIP), colistin (CST), and tobramycin (TOB) antibiotics in all one-, two-and three-way combinations . Each treatment was replicated 6 times for both focal pathogens in the absence and presence of S. maltophilia, resulting in a total of 192 selection lines. During the initial setup, overnight cultures from frozen stocks of PAO1, LESB58, and S. maltophilia were diluted down to the same optical density at 600 nm , corresponding to cell densities of 7.4 × 106, 2.2 × 107, and 4.6 × 106 CFU/mL, respectively. Monocultures consisted of 20 μL of the P. aeruginosa strain, whereas the cocultures mixed 10 μL of the P. aeruginosa strain with 10 μL of S. maltophilia, each in 200 μL of NB supplemented with 1 of the 8 antibiotic treatments for a total volume of 220 μL. The concentrations of the antibiotics  were chosen to be below the MIC of all three species (as determined below) (600 was measured (Tecan Infinite 200) as a proxy measure of the bacterial population densities. After measurement, each replicate was again mixed, and 20 μL of each culture were transferred to 200 μL of fresh medium with the same antibiotic treatment. These fresh plates were incubated for 72 h until the next serial transfer. The presence or absence of each species in each culture was determined following each transfer by growing subsamples of the 72-hour cultures on different selective agar; Pseudomonas selective agar , and S. maltophilia selective agar: LB agar  supplemented with 64 μg/mL tobramycin incubated at 30°C, rather than 37°C, as S. maltophilia is innately resistant toward tobramycin at 30°C , and these were excluded from the analyses. Whole population bacterial samples were picked from the agar plates for each replicate, grown overnight in NB, and cryopreserved in 20% glycerol to be frozen at −80°C. The selection experiment was carried out for 21 days, equating to 6 serial transfers. See During the selection experiment, a focal bacterium (either d below) ; Fig. S1 at 30°C . Some mo5 to 2−6) and grown in static conditions in triplicate. The OD600 was measured after 24 h (Tecan Sunrise). The MIC was defined as the lowest concentration of antibiotic at which there was no growth. We found no considerable difference between shaken and static conditions when determining the MIC in our preliminary experiments. For the evolved strains, the MIC50 of a bacterial population was defined as the MIC required to inhibit half of the replicates of that population. We also grew all bacteria  without antibiotic in NB for 24 h, using the same protocol as described above.Both prior to and following the selection experiment, the MIC of each of the three antibiotics, ciprofloxacin, colistin, and tobramycin, was determined via broth microdilution for the three bacteria strains. Briefly, overnight cultures from frozen samples were diluted 1:10 in phosphate buffered saline (PBS) and were further diluted 1:10 into NB with antibiotic concentrations ranging from 32 μg/mL to 0.015625 μg/mL . Such a measure is a proxy for the growth of the bacteria that accounts for the differences in medium adaptation when comparing antibiotic tolerance. Accordingly, we use this measure and its associated statistics in N ≤ 6 replicates, dependent on extinctions.To assess the difference in tolerance of the antibiotics for each individual evolved replicate and ancestral strain, at the treatment concentrations used during the selection experiments, we defined a growth proxy, 600 from the growth of the evolved strain after 24 h without antibiotic. The definition is analogous for the ancestral strain. We use this measure and its associated statistics in We used a similar growth proxy, tidyverse suite of packages .The population density and species presence and absence data from the transfer experiment, the ancestral and evolved strain growth with and without antibiotic, and the MIC data have been deposited in Dryad (


Iron tailings sand is a kind of mineral waste, and open-air storage is a common treatment method for iron tailings, which not only has a huge impact on the ecological environment but also occupies a lot of land resources. Therefore, the preparation of high-ductility fiber reinforced iron tailings concrete and its application in practical engineering structures have good application prospects. This paper is based on the deep learning research on the mechanical and carbonization properties of hybrid fiber iron tailings concrete. Therefore, tailings sands with different substitution rates, single-mixed steel fiber, and mixed steel-PVA fiber concrete were prepared in this paper. Its compressive strength, split tensile strength, axial compressive strength, elastic modulus, strain, and carbonization depth were tested. Through the existing concrete compressive stress-strain curve equations, the nonlinear calculation of each group of concrete compressive stress-strain curve equations in this paper is carried out, some parameters are determined, and the carbonation depth equation is established. The results show that, with the increase of tailings content, the properties of concrete increase first and then decrease and the addition of fibers can effectively improve the strength, elastic modulus, peak strain, and carbonization depth of concrete. However, with the increase of PVA fiber content, its performance enhancement effect decreased. In China, the comprehensive utilization of iron tailings sand began in the 1990s. After years of experimental research, a relatively mature conclusion has been achieved in the use of iron tailings sand for the preparation of iron tailings concrete. The preparation, mechanical properties, and durability of tailings concrete were further researched and developed. In the process of iron ore mining, a large amount of solid waste will be produced. Processing tailings waste into building materials is the most effective way to absorb mineral waste and has high ecological benefits and engineering value. Due to the high compressive strength, rough texture, and angular shape of iron tailings particles, iron tailings-made concrete has better ITZ properties and durability than ordinary concrete. By using mechanical activation to improve the pozzolanic activity and hydration performance of iron tailings, secondary hydration reaction occurs with cement to improve concrete strength. A large number of experimental studies have shown that, with the increase of iron tailings replacement rate, the workability of concrete decreases, which may be due to the high water absorption and specific surface area of iron tailings material, which leads to a decrease in workability. Although iron tailings as fine aggregates can improve the compressive strength of concrete, considering that it will reduce the workability of concrete, it is generally recommended to use iron tailings not exceeding 30% as fine aggregates. Lv conducted a comparative study by completely replacing ordinary aggregates with iron tailings in dam concrete with different grades.It can be seen from the above literature that scholars have little research on the carbonization properties of iron tailings and hybrid fibers. Therefore, this paper studies its mechanical properties such as compressive strength, axial compressive strength, elastic modulus, stress-strain, and carbonization depth and provides a basis for the carbonization performance of iron tailings hybrid fibers in a wider range of applications –10.The cementitious material used in this test consists of two parts, Qinling brand ordinary Portland cement and fly ash with a strength grade of P·O 42.5 R. The minerals and physical properties of the two materials are shown in Tables The aggregate is composed of natural crushed stone and fine aggregate, and the fine aggregate is river sand and natural sand. The physical properties of the tested aggregate are shown in The fibers used in the test are steel fibers and PVA fibers, and the performance indicators of the two fibers are shown in This test is divided into ordinary concrete (NC), iron tailings concrete (TAC), steel fiber concrete (TAC-S), and steel-polyvinyl alcohol fiber concrete (TAC-S-P) according to the iron tailings replacement rate and fiber content. . The replacement rate of iron tailings is 30%, 50%, and 100%. In most studies, the optimal dosage of steel fiber is roughly 1.5%. The effects of polyvinyl alcohol fiber content of 0, 0.3%, 0.6%, and 0.9% on the mechanical properties and carbonation durability of concrete were discussed .This article refers to the requirements of the “Ordinary Concrete Mix Proportion Design Regulations” (JGJ55-2011) and other specifications. After the previous trial and adjustment, the concrete mix design is shown in ∗1 is for number naming; take “T30-S1.5-P0.3 as an example;” T stands for iron tailings, S stands for steel fiber, P stands for PVA fiber, the number “30” means 30% iron tailings replacement rate, and the number “0.3″ means that the PVA fiber content is 0.3%.According to the mixing ratio of 5 in The carbonization experiment was carried out in a carbonization test chamber, the CO2 concentration was kept at (20 ± 3)%, the humidity was controlled at (70 ± 5)%, the temperature in the chamber was controlled at (20 ± 2)°C, and the carbonization ages were 7, 14, 28, and 56 days.With the increasing carbonation age, the compressive strength of concrete always maintains a stable growth trend. When the carbonation age reaches 7d, the increase of compressive strength is the largest, and the compressive strength increases by 5.5%, 3.5%, 8.2%, and 10.2%, respectively. With the increase of age, the growth of carbonation compressive strength gradually stabilized.2 to form water-insoluble calcium carbonate. Calcium carbonate fills the cemented pores and microcracks inside the concrete, weakens the subsequent diffusion of CO2, and increases the density and strength of the concrete [When the concrete carbonizes, the chemical composition and pore structure inside the matrix change. CO2 reacts with Ca (OH)concrete , 14.Carbonation has little effect on the strength of fiber reinforced concrete, because the addition of fibers improves the internal structure of the concrete, making it difficult for CO2 to penetrate into the concrete. After carbonization for 7d, the compressive strength of concrete increased by 5.5%, 1.9%, 4.7%, and 5.4%, respectively.The improvement of fiber reinforced concrete strength is mainly due to two aspects of crack resistance and toughening. The anticracking effect of fibers depends on the distribution of fibers in concrete. When only steel fibers are mixed into concrete, since the density of steel fibers is greater than that of the matrix, it will sink under the action of self-weight and vibration, resulting in steel fibers in the concrete. The uneven distribution in the concrete can easily cause local stress concentration during compression, resulting in premature failure of the specimen. The increase in toughness is due to the fiber bridging-debonding-slip failure mode, which generates more dissipated energy. There are hydroxyl groups in the molecular chain of PVA fiber, which can form a strong bond between the fiber and the concrete matrix. A large number of fine PVA fibers will increase the surface area in contact with the concrete matrix, which can better transmit stress through cracks. After adding PVA fiber, a complex three-dimensional fiber network is formed with the random distribution of steel fiber. The steel fiber can inhibit the large cracks in the concrete, and the PVA fiber inhibits the early plastic shrinkage and drying shrinkage microcracks. And as a steel fiber hybrid carrier, the steel fiber is evenly dispersed in the matrix, which produces a good synergy with the steel fiber, produces a positive hybrid effect, and improves the strength of the concrete.With the increase of PVA fiber content, it is relatively difficult to disperse too much PVA fiber, and there will be obvious agglomeration phenomenon, resulting in the formation of new weak areas where there are no fibers or less fibers in the concrete. The intervention of fibers causes the redistribution and transfer of concrete stress. If the distribution of this stress cannot achieve a true equilibrium, new stress concentrations may be formed, resulting in cracking in the area where fibers are lacking .Tensile strength is an important index to determine the crack resistance in concrete design, and it is also a key parameter to indirectly determine the bond strength of each component of concrete. In this experiment, 30% of iron tailings was the optimal replacement level, the concrete had the densest filling structure, and the bonding performance between the aggregate and the cement mortar was improved. As the content of iron tailings increases, the bonding properties between aggregates deteriorate, resulting in a decrease in tensile strength.Carbonization makes the splitting tensile strength value of concrete more complicated. With the increase of carbonization age, the carbonization strength value fluctuates greatly. The addition of iron tailings has a great influence on the strength value of the low carbonization period. When the carbonization cycle is long, the effect is relatively small. For example, when the dosage is 100%, the strength value increases by 6.9%, 3.2%, 1.25%, and 3.7%, respectively, at the carbonization age of 7d, 14d, 28d, and 56d. The reason is that as the carbonization time increases, the hydration products gradually fill the pores in the concrete after carbonization, so that there are fewer channels for CO2 to enter and leave the concrete, which reduces the impact of carbonization –20.It can be seen from The effect of single-doped steel fiber on the splitting tensile properties of iron tailings concrete can be explained as follows: due to the rough surface of iron tailings, the bonding performance between steel fibers and aggregates is enhanced, and when the concrete is loaded, the steel fibers are difficult to be pulled out or break, thereby increasing the tensile strength value. Second, steel fibers can inhibit the development of cracks. Third, the tensile force is transmitted to the steel fibers through the concrete matrix, and the bridging effect between the steel fibers and the concrete makes up for the defects of the concrete matrix. During the splitting and tensile failure of concrete, steel fibers absorb a lot of energy.Mixing fibers can significantly improve the tensile strength value of concrete, and the mixing effect is better than that of steel fibers alone. When steel fibers are mixed with PVA fibers, PVA fibers form a fiber grid, evenly dispersed in concrete. It has a good synergistic effect with steel fiber, and a positive hybrid effect occurs, which greatly improves the tensile strength value of concrete. With the increase of PVA fiber volume ratio, the tensile strength value of hybrid fiber reinforced concrete showed an increasing trend. This is because, with the increase of PVA fiber content, the fiber spacing is relatively low in concrete, which can effectively limit the development of primary cracks caused by factors such as segregation and shrinkage, thereby improving the tensile strength value. When the fiber content is more than 0.6%, the tensile strength value of concrete will be reduced. According to the analysis of the compressive test above, if too much PVA fiber is added, there will be obvious agglomeration, so that the fibers are not uniformly distributed in the concrete, and the fiber distribution is too sparse or too dense at the splitting interface, resulting in a larger concentrated stress reducing the tensile strength value.With the increase of carbonization age, the value of splitting tensile strength has been increasing. It may be because in the early stage of carbonization CO2 in the air penetrates into the internal pores of the concrete and dissolves the water in the pores. The carbonization reaction of the hydration product generates calcium carbonate, which fills part of the pores, and the bridging effect of the PVA fiber and the matrix makes the expansion stress distribution of the concrete pores more uniform. In the later stage of carbonization, the generated calcium carbonate fills the internal pores of the concrete, and the addition of fibers also reduces the cracks of the concrete, and it is difficult for CO2 to enter the concrete again, so the effect of increasing the tensile strength value in the later stage of carbonization is not obvious.When the steel fiber is used alone, due to the high density and thick diameter of the steel fiber, the volume ratio of the steel fiber contained in the same volume of concrete is larger, the fiber spacing of the steel fiber is significantly higher than that of other fibers, and CO2 easily enters the concrete. After adding PVA fiber, steel fiber and PVA fiber have a good synergistic effect, reducing the fiber spacing between fibers, and its effect on capillary thinning and blocking is more obvious, thereby reducing the pore channel of CO2 in the concrete, so the mixing effect is due to the single mixing of steel fibers , 22.The strength, deformation, and failure of concrete are related to the propagation of cracks. The essence of concrete failure is the expansion and penetration of original microcracks until macroscopic cracks are produced, which eventually lead to concrete instability and failure. Fiber can effectively prevent the generation and development of cracks and improve the crack resistance of concrete. The main reason is that when fibers are added to the concrete, they are evenly distributed in the concrete. As a result of fiber and concrete, there is a very strong grasp force; when the crack is further expanded, it can be timely blocked by adjacent fiber, in order to prevent crack expansion and improve the resistance of concrete cracking. The fiber forms a uniform three-dimensional chaotic support system in concrete, which can weaken the plastic shrinkage of mortar and disperse the shrinkage energy to the fiber filaments, thus effectively enhancing the toughness of concrete and reducing the cracks caused by the shrinkage of mortar. At the same time, the formation of uniform chaotic support system can effectively prevent aggregate segregation and ensure the uniform seepage of mortar in the early stage, so as to prevent the formation of settlement cracks. When the concrete bears the larger compression load and crack, the crack tip will produce stress concentration, and the crack will continue to expand under the continuous action of load. When the crack tip intersects with the fiber, the fiber can offset part of the stress and effectively prevent the crack from developing into a penetrating crack. With the decrease of fiber spacing, the stress concentration at the crack tip is gradually relieved or even disappears.The stress-strain relationship is a key parameter to measure the mechanical properties of concrete, and it is the main basis for analyzing the bearing capacity and deformation of concrete structures. The stress-strain curve of concrete includes an ascending segment and a descending segment, which is a comprehensive macroscopic response of the basic characteristics such as the appearance and development of plastic strain, the generation of microcracks, internal defects and damage, ultimate strength, residual strength, and deformation. In this paper, the stress-strain curves of concrete in carbonation 0d  and 56d are studied by adding different performance reinforcing materials, as shown in Figures From It can be seen from The axial compressive strength of each mix ratio is shown in Figures (1) Elastic Modulus of Iron Tailings Concrete before and after Carbonization. (2) Elastic Modulus of Fiber Reinforced Concrete before and after Carbonization. (1) Peak Strain of Iron Tailings Concrete before and after Carbonization. (2) Peak Strain before and after Carbonization of Fiber Reinforced Concrete. It can be seen from Based on the test results of deep learning, relevant discussions are mainly made from the carbonation depth of iron tailings concrete and the carbonation depth of fiber reinforced concrete. The main point of view is that, with the increase of carbonization age, the carbonation depth of concrete increases. Moreover, the carbonation depth of concrete also showed a state of first increase and then decrease, but with the increase of PVA fiber content the carbonation depth of concrete increased, showing a decreasing and then increasing trend.As shown in 2, the main hydration product of cement, to generate hydrated silicic acid. Calcium and calcium aluminate hydrate improve the internal pore structure of concrete, thereby improving the compactness of concrete. Another reason may be that iron tailings have higher water absorption than river sand and adding an appropriate proportion of iron tailings reduces the relative humidity inside the concrete, which is not conducive to the entry of CO2. With the increase of the replacement rate of iron tailings, the secondary hydration reaction of iron tailings leads to a large consumption of Ca(OH)2, the hydration product of cement, which reduces the alkalinity of the hydration solution and causes the carbonization and neutralization of the concrete to be shortened, thus making the concrete carbonization and neutralization shorter. The anticarbonation performance decreased.Iron tailings are low-activity mineral admixtures with small particle size, which can exert the microaggregate effect, fill the pores between the matrix particles, make the concrete more compact, and be beneficial to the carbonization resistance of the concrete. And iron tailings have potential hydraulic and pozzolanic activity. With the increase of carbonization age, the activity of iron tailings will undergo secondary hydration reaction with Ca(OH)As shown in The anticarbonation performance of fiber reinforced concrete is mainly reflected in two aspects: filling internal pores and reducing cracks. After a certain amount of steel fibers are mixed into the concrete, a complex three-dimensional chaotic support system is formed inside the matrix, which inhibits the subsidence of the aggregate and makes the mortar distribution more uniform, thereby improving the compactness of the concrete; at the same time, the steel is distributed in the concrete. The fibers make the capillary pores in the mortar smaller, and the capillaries are thinned or even blocked. In addition, when the concrete shrinks, the steel fiber can bear more shrinkage stress, which enhances the bonding force between the aggregate and the mortar and inhibits the formation of microcracks and the expansion of macrocracks. However, as CO2 continues to diffuse, it may lead to corrosion of steel fibers, and the formation of rust will destroy the bond between fibers and mortar, thus providing conditions for the penetration and diffusion of CO2.Mixing steel-PVA fibers in concrete will further improve the carbonization resistance of concrete. Due to the high density and thick diameter of steel fibers, the spacing of steel fibers in concrete is too large, and the grid effect formed by steel fibers in concrete is weakened. After adding PVA fibers, the fiber spacing becomes smaller, and the fiber network formed by fiber bridging can better hinder the expansion of pores and cracks in the concrete. On the other hand, PVA fiber is a relatively hydrophilic fiber, and a large amount of water will accumulate on the surface of the fiber, which creates conditions for cement hydration, inhibits early plastic shrinkage and drying shrinkage cracks, reduces its cracking temperature, and improves concrete crack resistance.2.With the increase of PVA fiber content, a large number of disordered distribution of PVA fibers in concrete will hinder the cement mortar from filling the pores of coarse aggregate, resulting in the increase of pores in the concrete. When the amount of PVA fiber increases, the mortar required to wrap the fiber is relatively reduced, which will cause concrete agglomeration during the mixing process and reduce the density of the concrete. Microscopically, there are weak interfaces intertwined between fibers and concrete. With the increase of fiber content, the number of weak interfaces in concrete increases, which provides conditions for the penetration of COAfter adding iron tailings, its compressive strength, splitting tensile strength, axial compressive strength, elastic modulus, and peak strain are enhanced in varying degrees, and the carbonation depth is reduced. With the increase of substitution rate, the performance enhancement effect shows a downward trend, but after the addition of fiber the failure form of concrete presents ductile failure, and its performance has been improved in all aspects.Through the existing concrete compressive stress-strain curve equation, the nonlinear calculation of each group of concrete compressive stress-strain curve in this paper is carried out, and some parameters are determined. The calculated results are in good agreement with the experimental results.With the increase of carbonation age, its compressive strength, splitting tensile strength, axial compressive strength, elastic modulus, and carbonation depth increase, the peak strain decreases, and the brittleness of concrete increases.Based on in-depth learning, this paper studies the mechanical and carbonation properties of concrete with different iron tailings replacement rates, single steel fiber, and mixed steel-PVA fiber concrete. Through the analysis of the test structure, the following conclusions are drawn:


The study was based on the Life Cycle Assessment methodology established by ISO 14040 and ISO 14044, and the 2006 Intergovernmental Panel of Experts on Climate Change (IPCC) Guidelines for National Greenhouse Gas Inventories. The production of ready-mixed concrete was considered for one year, with a “gate to gate” approach including the “transport of raw material” to the concrete plant and the subsequent “transport of final product” to the construction site. The results revealed that to produce 1 m3 of ready-mixed concrete, its production required 568.69 MJ of energy, accompanied by 42.83 kg CO2. Indirect transport generates the greatest environmental impact, especially the “transport of raw materials”, which represents approximately 80% of the embodied energy and 79% of CO2 emission.Concrete is the most commonly construction material used worldwide. In contrast to other countries, Ecuador lacks studies that determine the environmental impact of the production of construction materials. This research presents a quantification of embodied energy and CO It missions ,5. This missions . Hence, missions ,8.2 emissions and consumes large amounts of natural resources [2 emissions worldwide [Concrete is the most used construction material in the world ,10, withesources . Concretesources ,15. Althesources . Also a esources . That isesources . Consequorldwide , due to orldwide .According to the study by , it was In Ecuador, according to the 2015 Annual Survey of Buildings (Construction Permits) of the National Institute of Statistics and Censuses , it is e2 emissions to the environment of each stage of ready-mixed concrete production. It will allow decision makers to seek better ways to minimize their associated impacts. It is also expected that this document will strengthen current sustainable initiatives and encourage the development of new ones. It is important to point out that the novelty of the study consists in the field application Life Cycle Assessment in a specific locality, corresponding to a region that lacks databases for the Life Cycle Inventory, such as South America. Therefore, in addition to the above, this research will serve as a reference for other studies in the region.In this context, with the objective of providing local information that contributes to the generation of a national database of construction materials, which currently does not exist , the preConcrete is used due to its excellent characteristics, which include the following: good compression resistance, good fatigue behavior, excellent water resistance, good fire behavior and low maintenance cost . Ready-m2 emissions) and consumption of energy resources. Additionally, it is common to find studies about the use of raw materials [Concrete is a material that has grown in popularity due to its wide application and its large impact on the environment . The potaterials .2 in addition to being emitted during the concrete manufacture, also comes largely from the production of cement (as one of its main components) and from the acquisition of aggregates and raw materials [In terms of global warming, COaterials ,28,29.3 of simple concrete and reinforced concrete, respectively. While for the production of 1 m3 of concrete with natural aggregates, 1570.42 MJ are required in Serbia [In relation to the consumption of energy resources, according to  2600 MJ n Serbia . A studyn Serbia .2 emissions are considerable, its main limitation is that the raw material cost is significantly higher than that of OPC [Regarding the consumption of raw materials, it has been identified in the literature that the aim is to reduce the amount of clinker used in the manufacturing of cement and the replacement of part of the raw material by adding recycled materials ,34 or wat of OPC . Other ot of OPC . Even stt of OPC  addresset of OPC ,40 have t of OPC ,40. Othet of OPC .Since the aggregates come from the soil, novel methods such as the one proposed by  could beOther measures that are considered to improve the environmental performance of concrete are related to increasing the efficiency of the process and significantly reducing the use of non-renewable energy . It is a(1)From “cradle to grave” when it includes all the inputs/outputs of the processes that participate throughout its lifecycle, extraction of raw material, processing of materials for the manufacture of components, use of the product, and recycling or final management;(2)From “cradle to gate” when the scope of the system boundary is limited to inputs/outputs from the extraction of raw materials until the product is placed on the market (leaving the concrete plant);(3)From “gate to gate” when considering only the inputs/outputs of the manufacturing process of the product . In the The Life Cycle Assessment consists of four phases: Definition of goal and scope, Life Cycle Inventory Analysis (LCI), Life Cycle Impact Assessment (LCIA) and Life Cycle Interpretation . In the Of the LCA phases, with the exception of European countries and the United States, the greatest difficulties are found in the LCI phase due to lengthy data collection processes, since complete inventories are generally not available or are not reliable. Furthermore, using foreign databases can lead to errors due to the technology and power source used, if not used properly.This methodology is widely used to determine the environmental impacts of construction materials and several current studies on concrete use it ,46,47,48The energy demand in Ecuador has increased considerably in a decade (2009–2019), going from 69 million BOE  to 94 million BOE . Accordi2 emissions and virgin aggregates.The concrete industry has an impact on the indicated sectors since, for example, cement  presented a per capita consumption of 347 kg/hab (year 2019) , with Ec2 emissions). The research considers as a case study a plant located in the city of Cuenca, Ecuador under a “confidentiality agreement”.This study presents a quantitative, non-experimental, longitudinal approach carried out during a calendar year (2015). The main objective is to provide local data on environmental performance in the production of the ready-mixed concrete in two impact categories, corresponding to the consumption of energy resources and global warming  was applied [The quantification of the data followed the Life Cycle Assessment methodology according to the principles established in the standards ISO 14040 and ISO 14044 ,26. Addi applied .Following the LCA framework, three phases were developed: Definition of the goal and scope, LCI and LCIA. The fourth phase (Interpretation) was considered in the 2 emissions). The system boundary considered was “gate-to-gate”, including the previous stage corresponding to the “transport of raw material”, as well as the subsequent stage “transport of final product”. At the system boundary, only the elementary flows of the production chain of manufacturing were considered, leaving aside the energy consumptions from the administration.The objective was to quantify the impacts on the most relevant categories of the ready-mixed concrete production: consumption of energy resources, and global warming Receiving of raw materials: Mainly aggregates, cement and additives. Aggregates: Crushed stone with diameters of 38 and 19 mm and river sand. The product is weighed and stored in reinforced concrete compartments. Cement: It is transported in bulk from the main plant located in the city of Guayaquil. The trucks are weighed upon arrival and unload their product into cement storage silos. Additives: They are supplied wholesale by their supplier and arrive at the plant by means of cargo trucks. The most used additives are plasticizers, retardants, and accelerators.(2)Dosing of raw materials: By means of a front-wheel loader, the different types of aggregates are taken to the reception hopper, the aggregates are supplied by means of a conveyor belt and placed in the compartments proper to each type. In the dosing hopper, there is a scale to dose by weight the mixture of aggregates for each batch of concrete to be manufactured. Once the cement is weighed, it is transported to the pre-mixer drum. The aggregate mix, still dry, is transported to the pre-mixer drum, where it will be mixed with the cement, water, and additives. The water that will be used is stored in a tank; it is pumped, and its dosage depends directly on the automatic dosage system. The additives are dosed and then, they are pumped to the premix tank. When all the dosing has been completed, mixing is carried out until the characteristics of the desired concrete are obtained.(3)Concrete mixing: It is performed in the pre-mixing drum.(4)Concrete load in ready-mix truck: Once mixed and homogenized, it is passed to the mixer through an automatic system from the dispatch area.The four processes involved in the production of ready mixed concrete within the plant are briefly described below:Once the final product has been delivered, the mixer truck returns to the plant for washing. This consists of sediment separation and water recycling. The aggregates return to the aggregate stock and the water to the raw-material-dosing system by means of a pump.3 of ready-mixed concrete. In the impact category “consumption of energy resources”, the annual embodied energy was quantified in MJ/m3, and in the gases emitted to the atmosphere were expressed in kg CO2/m3 of the material manufactured [The functional unit chosen consisted in 1 mfactured ,58,59.The inputs and outputs of each unit processes specified in the flow chart of the ready mixed concrete production of the case studied were considered. The information was obtained from an analysis of the monthly and annual production databases of the plant.For the quantification of fuel for transport of raw material, data provided by the suppliers through a survey of information gathering in the field was used.Raw materials: Each raw material supplied to the plant during a year was quantified. Coarse aggregate , fine aggregate (sand), cement and chemical additives.Fuels: To quantify the fuel consumed in the first stage “transport of raw material”, information about the distance from the suppliers to the gate of the concrete plant, truck performance and return conditions (empty or loaded), was required. This study considered empty return trips. In the second stage “Manufacturing”, the fuel required in the operation of the front loader to transfer the aggregates to the receiving hopper, from which the dosing process start, was quantified. In addition, fuel was necessary in the ready mix-truck during the concrete loading. In the final stage “transport of final product”, the fuel consumed in the operation of the ready-mix truck to transport the concrete to the construction site was quantified. The trip back to the plant was also considered because the truck returns empty. To determine the embodied energy by transport, the conversion factor established by the SEAP Guidelines Part II was applied. The case study consumed, “diesel fuel”; therefore, the corresponding factor is 10 kWh/lt .Electricity: It was only required in the second stage (manufacturing), during the dosing, mixing and concrete load processes.3) by the premix plant over one year was considered as a single type of concrete.Final product: The total volume produced (m2 emissions (fuel and EE): To determine CO2 emissions derived from the use of fuel (diesel), Tier I established by 2006 IPCC Guidelines-Energy (Stationary Combustion) was applied, using Equation (1) [Emissions GHG, Fuel: Emissions of a given GHG by type of fuel;Fuel Consumption Fuel: Amount of fuel combusted;Emission Factor GHG, Fuel: Default emission factor of a given GHG by type of fuel.COtion (1) . The unition (1) .Emissio2, it includes the carbon oxidation factor, assumed to be 1. The CO2 emission factor applied is 267 g CO2/kWh for diesel fuel [For COsel fuel .2 emissions from annual electricity consumption, the basic equation established in the 2006 IPCC Guidelines—General Guidance and Reporting [AD: Activity dataEF: Emission FactorTo calculate the COeporting  was appl2/MWh eq obtained from the National Interconnected System of Ecuador was applied [AD, it was considered the total electricity consumed during one year in the ready mixed concrete production. Additionally, for EF, the value of 0.6760 t CO applied .2 emissions for being a representative GHG within the concrete production). The LCIA is developed in the This phase consists of transforming the data collected in the LCI into potential indicators of environmental impact. Two categories were considered: “Consumption of energy resources” and “Global warming” . The most consumed raw material was the sand (fine aggregate) represented by 40.82% and the least consumed was the chemical additive with 0.22%. During the study year, a total of 1,354,236.24 L of diesel was consumed in the “transport of raw material” stage, 60,453.32 L of diesel in the direct transportation stage, and 264,539.19 L of diesel in the “transport of final product” stage to the construction site. The amount of fuel used within each stage in relation to the total is shown in In the first stage, the highest fuel consumption was consumed in the sand and cement transport with 34.59% and 33.07%, respectively. Even though cement represents around 1800 dispatches in the year compared to 7300 dispatches of aggregates in general, cement consumes a representative amount of fuel. This is because the cement plant is in a different city (259 km) than the location of the ready-mixed concrete plant, which increases fuel consumption. It has been identified that in other countries the distances between the concrete plant and the cement plant are much shorter. For example, in the United States and Portugal, the distances are 112 km  and 60 kIn the second stage, the front loader that transports the aggregates during the dosing process consumed 33.12% of fuel (diesel). The difference, 66.88% was used in the ready-mix trucks during concrete loading.In the third stage, fuel consumed in the “transport of final product” represented a total route (round trip) of 308,826 km, .Finally, the electricity consumption corresponding to the manufacture of ready mixed concrete reached 617,577 MJ. It represented 67.15% of the total electricity consumption of the plant (the difference corresponds to administrative activities).3. Its production maintained a monthly fluctuation between 5.06% and 12.12% of the total volume produced in the year.The annual production volume of ready-mixed concrete was quantified at 107,387 m2 emissions in the ready-mixed concrete production within the established boundaries was considered. The values obtained were 61,069,813 MJ and 4,599,508 kg CO2, respectively. This value in the functional unit corresponds to 568.69 MJ/m3 and 42.83 kg CO2/m3  are those that represents the highest incidence in the impact categories analyzed. Energy consumption and CO3 (4.57%) and total CO2 emissions was 2.58 kg CO2/m3 (6.03%). There is a greater participation in energy consumption and CO2 emissions from transport compared to the electricity used , which represents 6.58 kg CO2/m3 (15.36%).In relation to the last stage considered in the study, energy consumption for the “transport of final product” was 88.68 MJ/m2 emissions. The next significant stage corresponds to the “transport of final product” and reaches 15.59% in energy consumption and 15.36% in CO2 emissions.Among the three stages, the first one corresponding to the “transport of raw material” presents the highest consumption of energy resources, with a percentage of 79.83% of the total energy consumption. This represents 78.61% of COThis study in Ecuador shows that transport of raw materials has the greatest contribution to the environmental impacts of concrete, without considering cement. However, aggregates are also relevant in the overall environmental performance of concrete to avoid the scarcity of natural resources. In the analyzed ready-mixed concrete plant, it was found that the aggregates occupy 83.83% of the concrete components; however, alternative materials are not used to replace them. This is not uncommon since the research by  has iden2 emissions. The first stage has the highest incidence in the defined categories of impact due to the following factors: distant suppliers, return conditions of transport units and high frequency. In the first and second cases, materials such as aggregates have distances that mostly exceed 50 km and cement that exceeds 285 km. However, considering the complete cycle of each trip (round trip), since the units return empty to their place of origin, the distances traveled and fuel consumption are double. In the third case, the high frequency of transfers of the materials required is due to the high demand for concrete production, which for the year of study reached 107,387 m3.The ready-mixed concrete production flow diagram presented in this study consists of three stages. The first corresponds to the “transport of raw material” and represents 79.83% of the embodied energy and a carbon footprint of 78.61%. The second stage corresponding to manufacturing contributes 4.57% (diesel + electricity) in the embodied energy and corresponds to 6.03% of the carbon footprint. Finally, in the last stage of transporting the ready-mixed concrete to the work site, the embodied energy is 16.59% and represents 15.36% of the COA study  carried 2 emissions of different types of concrete are determined; among them, typical concretes, natural aggregates concrete (NAC), recycled aggregates concrete (RAC) and geopolymer concrete (GPC) are represented. Studies were also identified that quantify environmental impacts based on the compressive strength of concrete (between 18 MPa and 40 MPa) or simply refer to concrete in general [2. Regarding the system boundary of the analyzed studies, it was identified that mostly “cradle to gate” is used. However, there are also studies that use the “gate-to-gate” limit, such as the one presented in this study. In the first system boundary mentioned, it is possible to consider the stage corresponding to the transport of the final product to the construction site, while the second limit found can consider the stage corresponding to the transport of both the raw material and the construction site. From the information collected, it is indicated that the embodied energy values for the studies with a “cradle to gate” system boundary are between 1570.42 MJ/m3 and 5401 MJ/m3, while the CO2 values are between 225.84 kg CO2-Eq/m3 and 319.63 KgCO2-Eq/m3. It can be seen that there is not much variation between the studies that consider transportation to the construction site and those that do not, because this stage of transportation is not very representative in relation to the total [3 and 568.69 MJ/m3. Showing much larger differences than the previous limit. Likewise, it is identified that CO2 emissions are between 25.9 kg CO2-Eq/m3 and 256.78 KgCO2-Eq/m3. In this case, the difference in results is also significant. Some studies [ general . Regardi studies ,45,65 alIn order to achieve a correct comparison between studies, it is necessary to delimit parts of the unitary processes to find similarity and reduce the asymmetry of the study cases. However, not all studies provide sufficient information. In this paper, three studies were compared. The first one in Latin America (Chile) and two with international databases: ECOINVENT and ICE. The first is a globally recognized database for its wide variety of life cycle inventory data for materials and production processes, while the second, ICE created at the University of Bath has data on concrete in general and on different pre-mixed concretes in relation to their mechanical resistance.The research by , delimitCase 1: Comparison between two Latin American countries. To compare the case of Ecuador with the results of the research from Chile , “transpCase 2: To compare with ECOINVENT data (SimaPro 7.3), the indirect transport was not considered. Stage: manufacturing.Case 3: To compare with ICE version 2.0 data (January 2011), “transport of final product” was not considered. Stages: transport of raw materials + manufacturing.In relation to the results presented in 2 emissions, the results differ similarly in cases 2 and 3: the values corresponding to the case study of Ecuador are lower than baseline data from ECOINVENT and ICE in a percentage equivalent to 98.99% and 51.60%, respectively. While, in case 1, the annual value of CO2 emissions in the case study of Ecuador is 39.98% higher than the case study of Chile.In terms of COThe high disparity in the results obtained in the comparison cases studies, in addition to what has already been mentioned, may be due to the diversity of fuels consumed in each process, since the energy matrices of each country are different. It also influences other aspects such as emissions factors, technologies and equipment used, therefore, the emissions associated with its energy production would also be different . When coAdditionally, most studies (70%) are based on secondary data and a small percentage use data specific to one location. The study of  showed tFinally, there is a greater variation in the data when the system boundary is gate-to-gate than when it is cradle-to-gate. This is because the percentage of representation of cement production is really high. In the study of , it was 2. The system boundary considered is “gate to gate” including transportation .Applying the LCA methodology according to ISO 14040, ISO 14044 and the 2006 IPCC Guidelines for National Greenhouse Gas Inventories, it was determined that in order to produce one cubic meter of ready-mixed concrete, 568.69 MJ of energy was required with an emission of 42.83 kg CO2 emissions. However, the consumption of energy resources was mainly due to the transport of raw materials, since it represents 79.83%. In this same stage, the annual contributions of CO2 emissions to the environment represented 78.61%. Therefore, it is essential to consider alternatives to reduce these impacts. Perhaps, this can happen through the implantation of actions focused on reducing the number of dispatches of raw material, as well as looking for alternative sources of material exploitation to reduce the distances between the production plant and raw material suppliers.The study determined that indirect transport, which corresponds to the transport used outside the system boundary , represented 95.42% of the embodied energy and 93.97% of the CO2 emissions of each stage of the life cycle in detail. For example, there is information on the transport of raw materials, quantification of raw materials, fuels used, and transportation of the final product to the construction site. Therefore, the results of this study can be easily used by other investigations.Unlike previous studies, this research separately obtained the energy consumed and CO2 emissions. This is due to the fact that alternatives have not been sufficiently exploited to produce sustainable concrete and, thereby, also reduce the consumption of natural raw materials.On the other hand, it has been identified that the industry in Ecuador has great potential to reduce the embodied energy of its construction materials and, therefore, CO2 emissions of concrete makes it difficult to make comparisons between case studies, due to the difference in system limits and the particular conditions established for each case study.The high disparity between the results of studies that determine the embodied energy and CO2 emissions of construction materials, it is important to highlight the significant contribution of this research. Data on contained energy and CO2 emissions were provided for a specific case of ready-mixed concrete. A simple methodology was used to calculate these environmental impact categories, which can be replicated for the preparation of new studies that provide data on other construction materials. and thus have a national or regional database, the knowledge and application of which help to improve the manufacturing processes of construction materials with a focus on reducing environmental impact.Due to the fact that in the country and particularly in the city of Cuenca, there are no databases of contained energy and CO


Foam concrete is widely used for its excellent properties, such as light weight, heat insulation, fire resistance, and sound insulation. The stability of foam is the main factor that affects the mechanical performance of foam concrete. The experiments are designed from two perspectives: the foam’s stability performance and the foam concrete’s modification effect. The effects on foam volume, foam half-life, foam bleeding rate, and foam pore size were investigated based on different concentrations of foam stabilizer CMC . A combination of macroscopic testing and microscopic analysis, a comparative study of dry density, water absorption test, mechanical property test, and pore structure analysis were conducted after using the modified foam for foam concrete. It is shown that the addition of CMC has an enhanced effect on foam stability. Foaming volume, water secretion rate, and average pore size showed a decreasing trend with the increase of CMC admixture, while the foam half-life displayed an increasing trend. In addition, adding CMC reduces the dry density and improves water absorption and compressive strength. The pore structure development of foam concrete has a noticeable improvement effect, and the optimal amount of admixture is 0.4%. Research results provide a reference for applying thickening foam stabilizer CMC in foam concrete. Foam concrete (FC) is material prepared by physical means, such as rapid mixing or compressed air. The slurry of foam and cement-based materials are then mixed and stirred. The lightweight foam concrete of different densities can be prepared by controlling the foam preparation ,2,3. In Foam is easy to combine and break in the preparation process, so it is crucial to improve its foam stability . TherefoCellulose ether is common to water retention and thickening agent for cementitious materials. It includes hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxymethyl cellulose, and carboxymethyl cellulose. CMC belongs to anionic cellulose ethers, cellulose-like substances with carboxymethyl substituents that are easily dispersed in water to form transparent colloidal solutions and have a high thickening efficiency due to the abundance of hydroxyl groups as well as hydrophobic chain segments . Acting Researchers have studied the application of CMC in cement-based materials. Farooque, K. N.  added CM3 was prepared in this study. Sodium dodecyl sulfate (SDS) is used as the foaming agent and sodium carboxymethyl cellulose (CMC) as a foam stabilizer. (i). The concentrations of foam stabilizing agent CMC  were compared in groups to explore the influence of CMC on foam performance under different concentrations. (ii). The foam with CMC was applied to the foam concrete. (iii). Through the macroscopic test of the dry density, water absorption, and compressive strength of the foamed concrete, the pore structure analysis, and the microscopic analysis, the foam stabilization effect of CMC and its influence on the performance of foamed concrete was studied.The above research mainly focuses on the macro performance of cement-based materials. However, the research on foam concrete needs to be more comprehensive, and the microanalysis of foam liquid after adding foam stabilizer CMC is less. Therefore, foam concrete with a dry density of 800 kg/mThe foaming volume and the half-life of foam measure the stability of foam and the foaming capacity of the foam solution. The longer the half-life, the better the stability of the foam . The infDue to the internal and external pressure difference and gravity effect of foam liquid film, foam always tends to drain, which will reduce the thickness of the foam liquid film. With liquid discharge, foam continues to merge, become more prominent, and finally breaks when the liquid film strength is insufficient . TherefoThe analysis shows that the foam bleeding rate increases with time; the foam bleeding rate is most intense at 60 min, and the stability is the lowest. However, adding CMC dramatical reduces the foam bleeding rate simultaneously, which can effectively slow down the rate of a foam burst. The effect is best when less than 0.4% is present in the admixture.The influence of CMC concentration on foam size is studied and the microscopic changes of each group at 60 min is studied. Microscopic pictures of each group at 60 min are shown in The reduction of the average-size bubbles is due to the addition of CMC to the foaming solution, which improves the solution viscosity , so impr3 and a minimum water absorption rate of 10% at a concentration of CMC 0%. The dry density of the foam concrete was 788 kg/m3 with a stabilizer concentration of 0.5%, which is a reduction of 115 kg/m3 with a higher water absorption rate of 19.6%, which is an increase of 9.6% compared to C0.In order to further analyze the correlation between dry density and water absorption in foam concrete, the measured dry density and water absorption test data of foam concrete are fitted. In order to better confirm the correlation between the CMC concentration of foam concrete and the compressive strength, the test data of the compressive strength of foam concrete were fitted. As shown in Generally, the indexes to evaluate the pore structure of foam concrete in experiments are pore-size distribution, average pore size, porosity, and roundness .In this experiment, sodium dodecyl sulfate (SDS) ) is used as a foaming agent, sodium carboxymethyl cellulose (CMC) ) is used as foaming stabilizer, and water  is used to prepare foam. The foam concrete specimens were prepared by adding ordinary Portland cement ), natural river sand ) and polycarboxylic acid superplasticizer (P.C.) ). The performance indexes of ordinary Portland cement are shown in This experiment uses the mix ratio of two materials (foaming liquid and foam concrete). The mix ratio of foaming liquid is designed according to the reference , as showIn this test, the foaming agent and concrete foam samples are prepared according to the method specified in JC/T 2199-2013 for foaming agents for foam concrete .The foaming agent preparation process is as follows: according to the set ratio , the foaming agent and foam stabilizing agent are slowly mixed into the water and mixed evenly with a glass rod; the foam solution, evenly mixed, is poured into the power-boosting electric stirrer at a speed of 2500 rpm for foaming, and after stirring for 3 min, the foam preparation is completed. (1)Weighing raw materials: According to the above ratio, the corresponding amount of cement, river sand, water-reducing agent, foaming agent, foam stabilizer, and water are weighed accurately with an electronic balance.(2)Preparation of cement slurry: The materials are mixed with a cement mortar mixer , and the weighed materials are mixed for 1 min to get the mixed dry mixture. Then the prepared water is added and mixed for 3 min to get the slurry.(3)Prefabricated foam: Power boosting electric agitator  is used for physical foaming of foaming agent solution, with a maximum power of 2500 rpm and mixing time of 5 min. The mixing and foaming process of the slurry is carried out at the same time.(4)Foam and slurry mixing: The foam is added to the mixture and stirred until completely uniform. Finally, it is poured into the model of 100 mm × 100 mm × 100 mm brushed with lubricating oil. According to experience, when pouring foamed concrete, it needs to be 2 cm higher than the model due to foam merging and breaking.(5)Scrap, demold, and sample cure: After curing for 24 h, scrape off the excess hardened foam concrete on the surface of the mold with a scraper, demold, and put the test block in the standard curing room  for curing until 28 d.The preparation process of the foam concrete sample is as follows: 1/2 of the foaming agent as a measure of foam stability. The stirring speed is 2500 RPM, and the mixing time is 5 min.The Waring Blender method  is used Following the Chinese standard Technical Code for Design and Construction of Cast in situ foam Light Soil Subgrade (TJG F10 01-2011) , the foaGAOSUO digital microscope specifications are as follows:Magnification: 1×~500×Imaging distance: manual adjustment 0~infinityImage resolution: standard 640 × 480Di is the ith bubble size and k is the number of bubbles. smD was determined by measuring at least 300 bubbles in each photograph.Fixed base: universal metal base ρ0 is the dry density of sample (kg/m3); m0 is the drying mass of the sample (g); V is the volume of the sample (mm3).RW is water absorption rate (%); m0 is the mass of dried sample (g); gm is the mass of the sample after water absorption (g).f is the compressive strength of the sample (MPa); F is the maximum damage load (KN); A is the compressed area of the sample (mm2).The dry density, water absorption, and compressive strength of foam concrete are tested according to the methods specified in the specification  of foam The image analysis method  analyzes(1)In terms of foam performance, increasing the concentration of CMC in the foaming solution will reduce the foaming volume and affect the foaming ability of the foaming solution. However, the half-life of foam has been significantly improved, and the turning point of slowing down the growth rate of foam half-life is the CMC concentration of 0.4%.(2)The use of CMC can effectively slow the speed of foam merging and bursting, improve the strength of the liquid film, and significantly reduce the amount of foam bleeding. The average pore size of foam changes to become more stable, which is of great significance in improving the stability of the foam.(3)In terms of foam concrete performance, the dry density, water absorption, and compressive strength will change with the increase of CMC concentration, but CMC concentrations that are too high will limit the growth of compressive strength within a specific range. The water absorption of the sample did not increase linearly with the decrease in dry density.(4)With the increase of CMC concentration, the pore size of foamed concrete is reduced, the pore distribution is uniform, and the pore shape is closer to the regular spherical shape, which can effectively improve the pore structure of foamed concrete.By adding CMC, a foam stabilizing agent, at different concentrations, the changes in foam properties and foam concrete properties were analyzed. According to the research results, the following conclusions can be drawn:


The electrochemical sensor was successfully applied for the determination of BLM in wastewater and reference material of human urine samples.In this paper, we report a highly sensitive voltammetric sensor for the determination of the anti-cancer antibiotic bleomycin (BLM) based on a screen-printed carbon sensor that is electrochemically pretreated and decorated with lead nanoparticles in the sample solution (pSPCE/PbNPs). These sensor surface manipulations contribute to significant amplification of the analytical signal and improvement of its shape and repeatability. The effect of the electrochemical behavior of BLM on the pSPCE/PbNPs was examined by electrochemical strategies. CV, EIS, and XPS were used to compare the sensor surface modifications. The effects of the type and pH of the supporting electrolyte and the procedure parameters were optimized. The features of the proposed procedure include: (a) very low limits of detection and quantification (2.8 × 10 Streptomyces verticillus. Clinically used bleomycin contains mainly bleomycin A2 and B2 and small amounts of other subfractions , and the Randles-Sevcik equation was used here [s) significantly increases with modification with PbNPs . However, electrochemical pretreatment does not contribute to an increase in As. Similarly, in the case of the value of the charge transfer resistance (Rct), only the modification with PbNPs causes a slight decrease in the resistance in relation to the unmodified electrode . The XPS analysis shows that the percentage atomic concentration of Pb is as follows: 0.3% for the SPCE/PbNPs and 0.9% for the pSPCE/PbNPs. The higher content of lead is associated with its additional deposition during the electrochemical pretreatment of the sensor. However, this increase does not translate into an increase in As. A very interesting conclusion can be drawn after a careful analysis of the deconvoluted Pb4f signal. The metallic form of lead (55.6%) prevails over lead oxides  at the electrochemically pretreated SPCE/PbNPs. In the case of the non-pretreated electrode, an opposite situation is observed since the metallic form of lead accounts for 40.3% of the total deposited lead film. Most probably, the increased proportion of metallic lead affects the repeatability of the deposited lead film before each measurement, thus contributing to the improvement in the shape of the BLM signal and its repeatability. The pSPCE/PbNPs and the bare SPCE had been characterized using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning and transmission electron microscopy (SEM and TEM), and energy-dispersive X-ray spectroscopy (EDS) in our previous research . In papesed here . It can The first step in optimizing the procedure was to select the appropriate type and pH of the supporting electrolyte. For this purpose, the influence of the pH value on the reduction signal of 2 nM BLM in the environment of acetic acid and NaAc—HAc solutions with different pH were evaluated. An increase in the BLM peak current was observed with an increase in pH to 4.5, and then a decrease in the BLM signal above this value until it disappeared completely at a pH value of 5.9 A. In viep) on the square root of the scan rate (υ1/2) (The voltammetric behavior of BLM at the pSPCE/PbNPs in the supporting electrolyte solution (0.05 M NaAc—HAc buffer of pH 4.5 and 0.05 mM Pb(II)) containing 0.1 µM BLM was examined using cyclic voltammetry. e (υ1/2) B suggeste (υ1/2) C shows tThe information on the electrochemical response of BLM was also obtained from the analysis of differential capacity curves of the double-layer interface pSPCE/PbNPs/NaAc—HAc buffer (pH 4.5) (frequency of 200 Hz). As shown in acc.) as well as time (tacc.), frequency (f), square-wave amplitude (ESW), and step potential (ΔE). BLM at a fixed concentration (2 nM) was added to the supporting electrolyte solution, and then the effect of the potential (Eacc.) on the reduction peak ranging from −0.8 to −1.3 V was examined. The highest peak current intensity was obtained at −1.0 V, and therefore this value was considered optimal (acc.) of 120 s was chosen; however, since the signal continues to increase with accumulation up to 600 s , Ca(II), glucose, dopamine, ascorbic acid, and uric acid do not significantly alter the peak current of BLM (they do not cause changes greater than 10%). Moreover, a 500-fold excess of V(V), a 200-fold excess of Ni(II), and a 100-fold excess of Fe(III), Cd(II), Cu(II), adenine, and testosterone had negligible effects on the BLM analytical signal. Since natural waters contain surfactants with a surface-active effect corresponding to 0.2–2.0 ppm of Triton X-100 , the infn = 9) confirms the acceptable reproducibility of the pSPCE/PbNPs sensor.Furthermore, three sensors were prepared independently and employed in the SWAdSV analysis of 2 nM BLM. The RSD value equal to 7.5% ; b—slope of calibration curve) [The determination of the effect of increasing BLM concentrations on the electrode was performed under optimized conditions using square-wave adsorptive stripping voltammetry (SWAdSV) A. It was× 10−8 M B. The lin curve) . The ana−1, and 50–70% of BLM is excreted within 24 h after administration in the urine in the unchanged form [−5 M, and therefore, when analyzing human urine samples, multiple sample dilutions  could be used. The wastewater samples, on the other hand, were diluted 10× and analyzed with an additional 1 × 10−5 mol L−1 DTPA in order to minimize the possible influence of metal ions present in the sample. Spiked samples were analyzed using the standard addition method. The small values of the coefficient of variation (1.16–2.5%) and the values of recoveries (96.0–103.5%) prove the good repeatability of the analytical signal and the good accuracy of the applied method, respectively  controlled by GPES 4.9 software (voltammetric measurements) and FRA 4.9 software  studies). The standard quartz electrochemical cell with a volume of 10 mL and a commercially available screen-printed carbon sensor  were applied for the experiments. The SPCE sensor consisted of a screen-printed carbon working electrode with a diameter of 4 mm, a silver screen-printed pseudo-reference electrode, and a platinum screen-printed auxiliary electrode.X-ray photoelectron spectroscopy (XPS) spectra were obtained using a Multi-Chamber Analytical System  with monochromated Kα-Al radiation (1486.6 eV)  and an X-ray power of 450 W.A 1 mM standard BLM solution was prepared by dissolving an appropriate amount of bleomycin sulfate  in a 0.9% NaCl  solution. This BLM solution was further diluted with saline to obtain BLM solution with a concentration of 10 µM. Sodium acetate and acetic acid used to make an acetate buffer (NaAc—HAc) of pH 4.5, which acted as the supporting electrolyte, were purchased from Merck. There were 1 mM stock solutions of Ni(II), Cd(II), Ca(II), V(V), Fe(III), Mg(II), Cu(II), glucose, ascorbic acid, dopamine, adenine, epinephrine, uric acid and testosterone that were prepared from Merck reagents in deionized water or ethanol (testosterone) and stored at 4 °C in the dark until the influence of interferents was examined. Diethylenetriaminepentaacetic acid (DTPA) was purchased from Merck. Ultra-purified water from a Milli-Q system  was used to prepare the solutions.clean.) for 10 s (tclean.) and then deposition of PbNPs on the electrode surface at a potential of −1.0 V during 120 s. SWV curves were recorded in the range from −1.0 to −1.7 V using a frequency (f) of 50 Hz, a square-wave amplitude (ESW) of 50 mV, and a step potential (ΔE) of 10 mV. After the presented sequence of measurements was performed, the electrode was rinsed with water and allowed to dry in the air. The pretreatment of the electrode was conducted only once before it was used in a series of measurements.For electrochemical pretreatment and simultaneous decoration of the electrode with nanoparticles of lead (PbNPs), a fresh electrode was placed in a 0.05 M NaAc—HAc solution (pH 4.5) containing 50 µM Pb(II), and subsequently, ten consecutive scans were performed using square-wave voltammetry (SWV). Apart from recording the voltammetric curve, each measurement consisted of electrochemical cleaning at a potential of 0.5 V (Eacc.) of −1.0 V for a time (tacc.) of 120 s, followed by electrochemical cleaning of the electrode surface at a potential of 0.5 V (Eclean.) for 10 s (tclean.). SWV curves were recorded from −1.0 to −1.7 V with f of 50 Hz, ESW of 50 mV, and ΔE of 10 mV.The BLM determination on the pSPCE/PbNPs was performed in the same solution that had been used for the pretreatment of the electrode. Only appropriate amounts of the sample or BLM standard were added to the solution. The square-wave adsorptive stripping voltammetric (SWAdSV) procedure also consisted of the same steps as outlined above, i.e., simultaneous electrodeposition of PbNPs and BLM accumulation at a potential , as well as samples of reference material (human urine) (Medidrug Basis-line U), were used for BLM determination at the pSPCE/PbNPs. The samples were spiked with a specific concentration of BLM and analyzed without any preparation.In summary, we proposed the application of electrochemical pretreatment (p) of the screen-printed carbon electrode (SPCE) surface and its modification with nanoparticles of lead (PbNPs) in the sample solution as an easy-to-employ method to prepare sensors and further use them for voltammetric determination of the anti-cancer antibiotic bleomycin (BLM). The modification of the electrode with PbNPs is necessary to obtain the BLM signal . Moreover, electrochemical pretreatment does not significantly affect the BLM peak current intensity but causes a slight shift of the peak potential towards less negative potential values and improves the shape of the BLM peak. Furthermore, pretreatment of the sensor before its use in a series of BLM measurements significantly improves the repeatability of the signal.s) increases, and the charge transfer resistance (Rct) decreases with PbNPs modification. However, electrochemical pretreatment does not contribute to a change in As and Rct compared to the SPCE/PbNPs. Most probably, the increased proportion of metallic lead  affects the repeatability of the deposited lead film before each measurement, thus contributing to the improvement of the shape of the BLM signal and its repeatability.The results obtained using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS) were used to characterize the sensors . The active surface area (A−10–2.0 × 10−9 M and 2.0 × 10−9–2.0 × 10−8 M), very low limits of detection and quantification , and a high sensitivity of 0.32 µA/nM. The pSPCE/PbNPs sensor and the SWAdSV procedure were effectively applied for direct analysis of human urine and wastewater samples towards the determination of BLM. The results show the potential of the pSPCE/PbNPs in using it as an electrochemical sensor for direct BLM analysis in real samples with a good recovery rate.It was confirmed based on the CV results that the process of BLM reduction on the pSPCE/PbNPs is not purely diffusion- or adsorption-controlled. The developed sensor was validated for selectivity, repeatability, and reproducibility toward BLM. The specific features of the proposed sensor include wide linear ranges (1.0 × 10