Creep affects the long-term deformation of concrete structures. Nonlinear creep further overestimates the safety factor of structures and affects the safety service performance. The coupling of creep and a damage model considering the rate effect is conducive to accurate prediction of nonlinear creep, but the iterative process of strain makes the calculation method more complex. The purpose of this study is to propose a nonlinear creep explicit method that considers the damage evolution of concrete under compression. Two groups of axial compression members with compressive stresses of 0.2 fc and 0.4 fc were made. Considering the law of concrete damage evolution under uniaxial compression, coupled with elastic creep and damage incremental strain, the lower limit of the medium stress level that gives rise to nonlinear creep is analyzed. The concrete nonlinear creep amplification coefficient with a loading age of 28 days and loading duration of 360 days is studied with consideration for the uncertainty of relative humidity and the theoretical thickness of the component. On this basis, the explicit calculation formula of the nonlinear creep amplification coefficient related to the concrete axial compressive strength and stress level is given. The results indicate that the nonlinear creep amplification coefficient increases nonlinearly with an increase in the stress level, and, when the compressive stress level ratio is higher than 0.6, the nonlinear creep amplification coefficient increases significantly; when the stress level is determined, the creep amplification coefficient decreases gradually with an increase in the compressive strength of the concrete. It is suggested that a stress level range of 0.35~0.75 should be used for the study of a nonlinear creep amplification factor under the medium stress state. Creep has an important influence on the long-term behavior of concrete structures. Creep refers to the phenomenon in which a concrete structure is continuously compressed, and the strain deformation increases over time. Generally, creep refers to linear creep. A nonlinear creep phenomenon is mainly caused by micro-cracks appearing at the interface between the aggregate, solidified cement slurry and internal mortar ,2. NonliIt is well known that creep is potentially harmful to the safety, durability and service properties of concrete structures. The appearance of nonlinear creep further overestimates the structural safety factor, which seriously affects the overall performance and public safety of the structure. The creep coefficient is used to describe the concrete creep response, considering the environmental temperature, relative humidity, concrete age and other factors related to concrete ,13,14,15η = 0.4 ~ 0.8), the concrete interface cracks grow rapidly, and the creep is nonlinear. In the third stage, the concrete internal mortar cracks and interface cracks develop rapidly until the concrete structure fails. A group of circular concrete structures was tested by Mazzotti et al. equation ,37:(3)ε is the effective modulus, φ is the creep coefficient and χ is the aging coefficient:Equation (3) is the stress–strain relationship based on the elastic creep theory, but the above equation contains the integral of the entire stress history, which is inconvenient for the practical application of engineering calculations. Apply the median integral theorem to the creep constitutive equation of concrete under compression :(4)ε(t)=R = 0.91eφ−0.686 for the elastic continuation and plastic flow theory and as R = eφ− for the aging theory . For the sake of simplicity, this paper uses a = 2. Under a constant stress level, the stress level η is a fixed value. Therefore, the damage of the concrete is expressed as:Since the descending section of the concrete compressive stress–strain curve represents the residual strength of the concrete, this article analyzes the rising section of the compressive stress–strain curve, and the curve equation of the rising section is ,41:(15)ηd(τ) = de of the concrete has completed damage accumulation, the incremental creep strain is:τ is the cumulative completion time of the concrete damage, and Δt is the incremental damage evolution time. Substituting the above formula into Equation (4), which considers the creep calculation method for the damage evolution of concrete during compression yielding:When the damage evolution parameter Define the creep amplification factor as the ratio of the incremental strain to the elastic creep strain of the damage evolution of concrete:Therefore, the creep strain calculations in Equations (8) and (18) under a medium stress level can be simplified as follows:Based on the elastic creep theory, the above formula considers the damage evolution of concrete, and the creep coefficient in the code can still be used. Compared with the incremental representation method of the rheological model, Equation (18) simplifies the calculation of nonlinear creep.fc = 20 MPa~60 MPa, and the calculation results of the creep amplification coefficient variation interval obtained by the calculation method in In order to study the variation of the concrete creep magnification factor, the relative humidity of the concrete is from 40% to 70%, the theoretical thickness of the component is from 35 mm to 75 mm, the duration of compression load is 360 days, and the concrete age at loading is 28 days. The standard value of the concrete strength is η = 0.75, and the creep deformation of the concrete component with a compressive strength of 20 MPa is 2.18 times higher than that of the linear calculation method, and considering the influence of the relative humidity and theoretical thickness of the component, the 95% confidence interval of the amplification coefficient is , and the influence of nonlinear creep cannot be ignored. Under the same conditions, for the concrete members with strengths of 30 MPa~60 MPa, the range of the nonlinear amplification coefficient is , ,  and , respectively. It can be seen that the amplification coefficient of nonlinear creep decreases with an increase in the concrete strength, mainly due to the decrease in the concrete damage. For the amplification coefficient under the stress level η = 0.4, it has a great influence on the concrete with 20 MPa, and the maximum creep strain increases by 18%, but it has little influence on the concrete with 30 MPa~60 MPa, and the maximum creep strain decreases from 8% to 3%, which is consistent with the existing research conclusions that the lower limit of the nonlinear creep stress level is calculated from 0.4, which is mainly related to the concrete strength.When the upper limit of the stress level interval is fc to 0.6fc, the nonlinear increasing trend of the amplification coefficient is small, and, when the stress level is higher than 0.6fc, the nonlinear creep increases obviously, which is consistent with the research results by Mazzotti and Savoia [For the concrete with the same strength, the creep amplification coefficient increases with the increase in the stress level, and the creep amplification coefficient changes nonlinearly. By comparing the nonlinear creep amplification factor of concrete with a compressive strength of 20 Mpa~60 Mpa, when the stress level rises from 0.4d Savoia . The avey = bax, as shown in Nonlinear fitting is performed using the mean value of the creep magnification coefficient as a representative value, and the fitting function is in the form of a power function fc are shown in a and b of the power function are related to the concrete axial strength when considering the concrete damage evolution. The coefficient a gradually decreases with the increase in the concrete axial strength. The coefficient b increases gradually with the increase in the concrete axial strength. Fit the correlation coefficients a and b with the strength values. From a = 3.6 − 0.02fc and b = 2.8 + 0.05fc.The values of the power function coefficients of various concrete cylinder strengths Therefore, considering the effects of the nonlinear creep of the concrete compression damage evolution, when the stress level ranges from 0.35 to 0.75, the creep amplification factor of the concrete damage evolution is:The development curve of the nonlinear creep amplification coefficient under varying concrete strengths is compared with the theoretical amplification coefficient provided in the literature ,42, and The nonlinear amplification coefficient is applied to the calculation of the concrete creep strain and compared with the strain value of the nonlinear creep test of the cylinder. Hamed  designedFu  comparedIt can be seen from (1)fc to 0.75fc.Considering the multi-level effects of concrete creep, it is recommended that the study of the nonlinear creep magnification factor in the medium stress state should take a stress level range from 0.35(2)The nonlinear creep model of concrete under different strengths is constructed by coupling the concrete damage evolution with elastic creep, which can better reflect the nonlinear creep of the concrete under a medium stress state and simplify the calculation process.(3)Concrete nonlinear creep is related to stress level and concrete strength. The nonlinear creep amplification coefficient of concrete with the same strengths increases nonlinearly with an increase in the compressive stress level; when the concrete compressive stress level is determined, the nonlinear creep magnification factor gradually decreases significantly with an increase in the concrete strength. The nonlinear creep amplification coefficient is positively related to the stress level and negatively related to the concrete compressive strength.It is believed that the creep strain calculated from the elastic stress–strain relationship of concrete is lower than concrete creep under higher compressive stress, mainly because the damage caused by concrete compression is ignored, including the development of interface cracking and internal mortar cracking. The following conclusions can be drawn:


Carbon-fiber-reinforced polymer (CFRP) is a composite material used to mend and strengthen concrete structural elements in civil engineering. The prime aim of this experimental study is to investigate the comportment of confined concrete cylinders (CCC) under uniaxial loads by altering the concrete strength, the CFRP angle orientation, and the volumetric ratio, following the externally bonded reinforcement technique (EBR). We present the results of the confinement effect and failure mechanisms issue of more than 150 specimens of CFRP confined concrete cylinders that have been undertaken and in which several parameters were altered. Totally and partially confined concrete cylinders were tested for failure under axial compressive loads and indirect tensile tests. Four different ratios of water/cement  were investigated. In addition, three sand–resin ratios were prepared to improve the mechanical properties and the adhesion of the CFRP and the concrete. The obtained results revealed a clear improvement in the compressive strength of the specimens made with low strength concrete (from 38% to 66%) compared to those made of high strength concrete (from 11% to 31%), where the improvements are relatively low. Furthermore, the transversally confined concrete cylinders presented significant gains in strength over those confined longitudinally. Lastly, adding sand to the resin increases the compressive strength of confined concrete cylinders (1.19% to 54.62%) and reduces the cost of the resin used for fixing CFRP materials. Concrete is the most used material in the world of construction. This material can be affected by internal and external actions . These actions can decrease the carrying capacity of the concrete structural elements. Over the last four decades, the strengthening of reinforced concrete has significantly developed. The benefits of reinforcement are essentially focused on conserving the environment. The reinforcement of concrete structures postpones their demolition. Waste debris is noisy and dusty and may produce hazardous materials for adjacent buildings that require removal. Furthermore, to preserve the archaeological heritage for future generations, there is a need to increase the performance of the load-bearing elements of old structures.Carbon-fiber-reinforced polymer (CFRP) is a composite material to strengthen concrete structures. Several reinforcement techniques based on various materials have been reported in the literature, using carbon- or glass-fiber-reinforced polymer (CFRP or GFRP) and steel plates. Structural elements, such as the beams ,2,3, colAs the concrete weakens in sustaining tensile loads, it starts to crack and eventually crumbles and disintegrates at even weaker stresses. Structural element confinement is the best-suited technique against future hazardous actions to overcome this behavior. Columns’ reinforcement using composite materials is carried out by wrapping them with FRP composite. The lateral expansion of concrete under compressive stress leads the tensile on the reinforcement in the fibers’ way. As a result, the confinement pressure increases proportionally with the lateral expansion until the composite material fails.The main aim of the present experimental work is to study the behavior of the confined concrete cylinders (CCC) by using the CFRP composite under uniaxial load using the following parameters: the concrete strength (from 25 MPa up to 47 MPa), the CFRP angle orientation (0° and 90°), and the volumetric ratio (from 0.46% to 2.5%). In addition, the aim is also to check the obtained results by Abdulla et al.  when addAccording to this literature review, the most researched parameters were the volumetric ratio, the CFRP layer number, the slenderness ratio, the spacing between the band fibers, the concrete strength, and the CFRP orientation angle. As such, several issues need to be clarified: (1) the behavior of partially confined cylinders with an orientation angle of 90°; (2) the confinement ratio effect on the tensile strength; and (3) the failure mode of partially confined cylinders having an orientation angle of 90°.It is worth mentioning the work of Abdulla et al. , where t2 (diameter × length), in order to obtain a desirable model of failure [A total of 150 concrete specimens were examined in this study. Calcareous crushed aggregates from the quarry of Ain Roua region of Sétif, Algeria, were used. They are of three granular classes: sand 0/5 mm, gravel 5/15 mm, and gravel 15/25 mm . Ordinar failure , were fi failure . More deFurthermore, a superplasticizer (SP) was added depending on the cement weight see  to improhttps://dza.sika.com/, accessed on 8 June 2021). The epoxy adhesive used in this study was (Sikadur®-330), composed of two components: resin and hardener, which were mixed in a ratio of 1/4. The main features of epoxy and CFRP wraps are summarized in The carbon-fiber-reinforced polymer (CFRP) used in this experimental study was a 230C/45 type Sika Wrap. The used CFRP type was unidirectional, manufactured by SIKA Company (®-330). To ensure a maximal bond between CFRP and concrete, the contact surfaces of the cylindrical concrete specimens were raised and brushed using a stainless-steel brush. Then, a compressed air (air gun) was used to remove any impurities and ensure perfect adhesion between the epoxy–concrete and the epoxy–CFRP. Next, the CFRP sheets were cut in bands of different lengths and widths to cover the required surface on the concrete specimens. For strengthening the cylindrical concrete specimens, an epoxy layer at about 1 mm of thickness was applied on the surface of the concrete and the carbon sheets. Then, a slight pressure was applied by a roller to wipe out voids. Moreover, another layer of epoxy was applied to the CFRP sheets. Finally, the concrete specimens were placed in the open air at an ambient temperature of 25 °C inside the workshop of the laboratory until the testing day.The carbon-fiber-reinforced polymers (CFRP) sheets were fixed on the specimens using an epoxy adhesive  of the total outer surface of concrete specimens , while iTo easily distinguish between the various cylinders, the configurations were designated by the confinement rate, the orientation of the CFRP, and the concrete type. The first letter, T, H, or Q, indicates that the confinement was conducted totally (fully), half, or quarter. The second letter, C, indicates that the type of reinforcement is CFRP confinement. The third letter, L or T, means that the reinforcement orientation is longitudinal or transverse. Finally, the last letter, A, B, C, or D, signifies the ratio of water added to the concrete W/C being 0.33, 0.36, 0.401, or 0.522, respectively.Prior to the compressive strength tests at 28 days under axial load, all concrete specimens were capped with sulfur mortar for accurate tests. After that, the specimens were tested under compressive and tensile strength (indirect tensile) tests to measure each type of reinforcement’s different strengths and behaviors. All tests were carried out using the MCC8 machine with 3000 kN capacity with an accuracy of ±1% . The specimens were subjected to a stress rate of 0.5 MPa/sec until failure. Three Linear Variable Differential Transducers carried out strain acquisition (LVDT) placed at the mid-height of the specimens, as shown in All the reinforced concrete cylinders (RCC) with CFRP had a typical behavior. Two phases were observed in In the first phase, the load is essentially supported by the concrete. This is confirmed by the noise caused by the micro-cracks propagating towards the concrete core. Since the shrinking of the concrete during this phase is small, the lateral expansion of the cylinder must be too small, which can be explained by the fact that the fibers do not have a significant contribution in this stage.-fρ is CFRP reinforcement ratio;-fA is the CFRP area;-D is the cylinder diameter.In the second phase, the curves tend to flatten. Consequently, most of the deformations were supported by the fibers. As a result, the stresses slowly evolved until the configuration failed; the results obtained are depicted in The first is the cohesion brought by the fiber when added to the surface of the cylinder through the resin, thus forming the composite material of concrete and fiber that adhere to resist the compressive force.The second reason is that during the lateral expansion of concrete, a mechanism of stress transfer to the lateral direction of the fiber is created, and consequently, part of the load is taken by the latter.The obtained results of the reinforced concrete cylinders by CFRP according to the orientation of the reinforcements are presented in From Furthermore, longitudinally reinforced concrete cylinders have a high ductility compared to transversely reinforced cylinders. This behavior can be useful during seismic loading because the plastic bearing can dissipate energy. The half and quarter transversely (HCT and QCT) confined specimens underwent an increase in the ultimate compressive stress from 3% to 15% and from 9% to 16%, respectively, compared to the half and quarter longitudinally confined cylinders (HCL and QCL). Nevertheless, a remarkable decrease in the ultimate compressive strain was recorded.The confinement efficiency for the configurations made with W/C ratios 0.33 and 0.36 was lower than that of ratios 0.401 and 0.522. When the stress reaches the ultimate elasticity, the cracks start propagating rapidly in the cylinders’ core, and the specimen’s failure occurs suddenly. The fully confined concrete specimens showed an increase in the ultimate compressive stress compared to the control specimens . The ultimate compressive stress was observed in the case of the half-confined specimens (HCT), i.e., 19%, 11%, 38%, and 52% for W/C ratios of 0.33, 0.36, 0.401, and 0.522, respectively. Meanwhile, the half confined longitudinally (HCL) of concrete specimens, an improvement in ultimate compressive stress of 24%, 23%, 58%, and 57% for W/C ratios of 0.33, 0.36, 0.401, and 0.522, respectively, were noted. The other two types of configurations (QCL and QCT) also showed an increase in the ultimate compressive stress .An increase in ultimate compressive stress compared to control specimens from 3% to 66% was induced for W/C ratios ranging from 0.33 to 0.522 with a change in a volumetric ratio of 0.025, 0.01, and 0.0046. It is noticed that the strength gain of the confined concrete specimens improved inversely with the concrete compressive strengths. Gains in ultimate compressive stresses ranging from 11% to 57% were recorded for the half confined and quarter confined specimens for W/C ratios ranging from 0.33 to 0.522, through 0.36 and 0.401.2) according to the standard NF P18-408 [ P18-408  for the A clear improvement in the tensile strength of the partially transversely confined (HCT and QCT) specimens was observed compared to the tensile strength of the control concrete specimen and the partially longitudinally confined specimens. However, this improvement becomes insignificant when comparing the tensile strength of specimens with different CFRP volumetric ratios. As it can be seen, there is an improvement of the tensile strength following the increase of the compressive strength, but it is not with the same magnitude.All longitudinally reinforced specimens failed by splitting a. LongitTransversely reinforced specimens made from concrete with different W/C ratios of 0.36, 0.401, and 0.522 underwent a biconical fracture plane b, and miThe summary of the measured compressive strength for both confinement modes, transversal ‘T’ or longitudinal ‘L’, at each experimental point is presented in The correlations between the predicted and observed values for both longitudinal confinement (LC) and transversal confinement (TC) are shown in The iso-response curves and the response surfaces  were useAccording to The mathematical relationship of the compressive strength for specimens with longitudinal confinement is given by:It is worth mentioning from the surface response that the increase in the transversal confinement percentage has increased the compressive strength, while the increase in the W/C ratio has led to its decrease.In the context of confirming or refuting the obtained results reported by Abdulla et al. , in whicThe three obtained curves reveal the same behavior. Adding sand to the resin has increased the stiffness, the ultimate compressive stress, and the ductility of the reinforced concrete (RC) cylinders. The combination of sand and resin has created silanol bonds which are very strong and require high energy to break. Furthermore, by increasing the sand content in the sealing material, Young’s modulus of the mixture (sand/resin) increases, and the resin becomes increasingly rough. This increases tangential forces between the two surfaces, resin–concrete and resin–CFRP, and the adhesion between the surfaces becomes greater.The specimens, which were sealed using the resin having S/R ratios of 0.50, 0.65, and 0.85, exhibited an increase in their ultimate stresses from 1.19% to 54.62%, while an improvement from 2.70% to 15.19% was observed in the ultimate strains. These will increase the absorption energy, making the element more ductile and reducing the cost of the resin used for fixing CFRP materials. Our results are in accordance with those of Abdulla et al. [In conclusion, an experimental investigation of the compressive behavior of concrete cylinders externally confined by CFRP wrapping has been presented in this paper. Reinforcements (confinement) were performed using longitudinal, lateral, and radially spaced sheets. The effects of the principal variables, such as the concrete strength, the angle orientation, the volumetric ratio of CFRP, and the addition of sand to resin, were investigated. We made the following conclusions:The transversely confined concrete cylinders led the CFRP to develop their capacity (strength) better than the longitudinal ones. However, all confined concrete specimens with a longitudinal orientation showed a larger flat region as a plastic region prior to failure than those with a transversal orientation. Such behavior may be very helpful for cyclic loading.The configuration cylinders made with a low concrete strength showed a higher effect of CFRP confinement than those made with high concrete strength. Hence, the effect of CFRP confinement decreases with increasing the concrete strength.Increasing the volumetric ratio of CFRP produced an increase in the compressive strength of the confined column from 3% to 56% compared to the control cylinder. Nevertheless, a decrease in the deformation was noticed.The improvement in tensile strength was only recorded in the transversely confined specimens.The results of the factorial plan showed a good correlation between the experimental and expected results.The addition of sand to the resin increased the stress and the ultimate compressive strain, which confirms the results of Abdulla et al. . Hence, It would be desirable to complete this study through further investigations on the problem associated with: (1) the durability of structural elements reinforced by CFRP in aggressive environments, and (2) the CFRPs compatibility issues encountered in historic masonry structures. It would also be useful to complete a comparative study between the reinforcement by CFRP and the FRCMs in order to present the advantages and disadvantages of FRCMs. The future works are also to calibrate with numerical modelling the obtained experimental results by using the Ansys software package.


AHRU accounts for a substantial portion (18.6%) of LGIB in our area, where the aging rate is the highest in Japan. Since AHRU is a potentially life-threatening disease that requires urgent identification and management, further studies to identify robust risk factors associated with serious clinical outcomes are required.Acute hemorrhagic rectal ulcer (AHRU) is a relatively rare disease that can lead to massive hematochezia. Although AHRU is a potentially life-threatening disease, its characteristics and clinical course are not fully understood. In this study, the clinical features were compared between AHRU and lower gastrointestinal bleeding (LGIB) from other causes (non-AHRU). Then, risk factors for all-cause in-hospital mortality in patients with AHRU were identified. A total of 387 consecutive adult patients with LGIB who were managed at two tertiary academic hospitals in Akita prefecture in Japan were retrospectively enrolled. Subjects were divided into AHRU and non-AHRU groups according to the source of bleeding. Regression analyses were used to investigate significant associations, and the results were expressed as odds ratios (ORs) and 95% confidence intervals (CIs). AHRU was found as the bleeding source in 72 (18.6%) of the patients. In comparison to non-AHRU, having AHRU was significantly associated with in-hospital onset, age > 65 years, and systolic blood pressure < 90 mmHg. The AHRU group had a significantly higher in-hospital mortality rate in comparison to the non-AHRU group (18.0% vs. 8.3,  Acute hemorrhagic rectal ulcer (AHRU) is a relatively rare disease that is responsible for massive hematochezia. Soeno et al. first described the term “AHRU” in a report from our institute  in Japan in 1981 ,11,12,13With an aging population, the incidence of AHRU seems to be increasing in Japan. Although previous studies from other areas reported that AHRU accounted for 2.8–8% of the causes of lower gastrointestinal bleeding (LGIB) ,15, we hPreviously, the clinical course of AHRU was considered to be favorable once hemostasis was achieved ,14. SubsWe recently collected clinical data on LGIB in our area and reported the usefulness of various scoring systems to predict serious clinical outcomes, such as in-hospital mortality . Using tIn our original study , we retrA colonoscopy was performed emergently or electively with or without computed tomography (CT) in all patients with LGIB in order to identify the bleeding source. Then, depending on the source of bleeding, the entire LGIB cohort was divided into two groups: the AHRU group and the (non-AHRU) group. Both definite and presumptive sources of LGIB were included. Definite sources of bleeding were defined as lesions with documented visualization of active bleeding, a visible vessel, or adherent clot (stigmata of recent hemorrhage). Presumptive diagnoses were defined as cases of diverticula, hemorrhoids, or angiodysplasia without stigmata of recent bleeding.This study protocol was reviewed and approved by the ethics committees of the two participating institutes (2676).The following patient’s medical information and data were collected from electronic medical records: patient demographics (age and sex); in-hospital or out-of-hospital onset; altered mental status; vital signs (systolic blood pressure and pulse); physical condition (Eastern Cooperative Oncology Group Performance Status: ECOG-PS); comorbid conditions (Charlson Comorbidity Index: CCI); blood test results ; and blood urea nitrogen (BUN)); and medication  at the onset of LGIB. In addition, additional data required to determine the scores of 3 scoring systems  ,21,22,23LGIB was defined as the presentation of hematochezia, including red blood or clots per rectum, maroon-colored stool, or blood mixed in with stool, without any findings indicative of upper gastrointestinal bleeding at esophagogastroduodenoscopy. AHRU was defined as acute and painless hematochezia with endoscopic documentation of rectal ulcer(s) . In-hospContinuous variables were expressed as the median and interquartile range and were compared using the Mann–Whitney U test. Categorical valuables were expressed as the number and proportion, and were compared using Fisher’s exact test or the chi-square test, as appropriate.p value of <0.20 in univariate analysis were included in multivariate analysis, and the results were expressed as odds ratios (ORs) and 95% confidence intervals (CIs).Initially, clinical features and treatment outcomes were compared between AHRU and non-AHRU, and factors associated with having AHRU (relative to non-AHRU) were identified. Then, we attempted to identify factors associated with rebleeding and in-hospital mortality in AHRU patients. In these regression analyses, factors that showed a p value of <0.05 were considered statistically significant.The diagnostic performance of 3 scoring systems for predicting rebleeding and in-hospital mortality among patients with AHRU was assessed by a receiver operating characteristic curve analysis, and the area under the receiver operating characteristic curve (AUC) was calculated. All analyses were conducted using the EZR software program  . p valuen = 132; ischemic colitis, n = 54; delayed post-polypectomy-induced bleeding, n = 23; hemorrhoid bleeding, n = 21; bleeding colonic cancer, n = 18; bleeding colitis, n = 13; telangiectasia, n = 8; and unknown/others, n = 32) constituted the non-AHRU group. Representative endoscopic images of AHRU are shown in Based on colonoscopy and CT examination, among 387 enrolled patients with major LGIB, AHRU was found as the bleeding source in 72 18.6%) cases, as was reported in our recent study [.6% casesAHRU mainly occurs in elderly individuals (median age: 79 years) with several comorbidities (median CCI: of 3), and 50% 36 of 72) of cases involve bedridden patients (ECOG-PS = 3 or 4) as previously reported  of 72 of. Table 1p < 0.0001) in comparison to the non-AHRU group  vs. 1 ; NOBLADS: 4  vs. 3 ; ABC: 3.5  vs. 2 ), suggesting that AHRU was potentially associated with worse clinical outcomes.In particular, in comparison to the non-AHRU group, the AHRU group showed higher age, a poorer general condition indicated by a higher ECOG-PS score, higher CCI score, and higher proportion of in-hospital onset, more massive bleeding indicated by lower blood pressure and lower hemoglobin, and a poorer nutritional status indicated by a lower serum albumin level. On the other hand, there were no significant differences in sex or medication between the two groups. Consequently, the AHRU group showed higher scores in all three scoring systems, with a highly significant difference , followed by age >65 years , and systolic blood pressure <90 mmHg .Comparisons of the treatment outcomes between the AHRU and non-AHRU groups are shown in p < 0.0001 for hemostasis; 41.6% vs. 23.2%, p = 0.003 for blood transfusion), which reflected the observation that the AHRU group had more massive bleeding in comparison to the non-AHRU group (p = 0.027). The causes of 13 deaths in the AHRU group were malignancy (n = 5), pneumonia (n = 2), sepsis (n = 2), heart failure (n = 1), renal failure (n = 1), respiratory failure (n = 1), and senility (n = 1); thus, no one died directly from uncontrolled bleeding.The AHRU group more frequently received both endoscopic hemostasis and blood transfusion in comparison to the non-AHRU group  to predict rebleeding and in-hospital mortality among patients with AHRUs is shown in Overall, the performance of these scoring systems is largely suboptimal, especially for the prediction of in-hospital mortality. For instance, although we recently developed the CHAMPS score and demonstrated good performance of the score to predict in-hospital mortality in the entire LGIB cohort with an AUC (95%CI) of 0.80 (0.73–0.87) , the perAfter demonstrating the poor performance of the three existing scoring systems in the prediction of serious clinical outcomes within the AHRU group, we investigated the associations of individual clinical factors with rebleeding or in-hospital mortality in this group .p = 0.04) and the statistical significance remained in multivariate analysis .Although some factors were significantly associated with rebleeding in univariate analysis , the statistical significance of these factors was lost in multivariate analysis. On the other hand, serum albumin level of <2.5 g/dL was a single, statistically significant factor associated with in-hospital mortality in univariate analysis , severe comorbidity, and hypoalbuminemia were significantly associated with the onset of AHRU ,9,10,12.Previous studies demonstrated high rates of mortality in AHRU, ranging from approximately 15% to 25% ,11,15,16Several scoring systems have been developed to predict serious clinical outcomes following gastrointestinal bleeding, and previous studies have successfully demonstrated the usefulness of some scoring systems not only for upper gastrointestinal bleeding but also for LGIB ,22,23. NAccordingly, we attempted to identify factors associated with rebleeding and mortality in AHRU. Thus far, three studies have investigated factors associated with rebleeding in AHRU ,8,11. Thp = 0.49; percentage of thrombocytopenia defined as <100,000/µL: 23% vs. 10.2%, p = 0.35). Interestingly, although all three scoring systems investigated in this study  included hypoalbuminemia as a variable [On the other hand, a single previous study investigated factors associated with mortality among 36 patients with AHRU occurring after ICU admission, and found that thrombocytopenia was a risk factor for 4-week mortality . In the variable ,21,22,23Regarding the etiology of AHRU, Nakamura et al. reported that rectal mucosal blood flow was reduced in the supine position during bed rest and that the reduction in blood flow could be responsible for the development of AHRU, which frequently occurs in bedridden patients . Howevern = 72), which precluded solid analyses to identify factors associated with the clinical outcomes. However, AHRU is still a rare disease, and we enrolled a relatively large number of patients with AHRU in comparison to most previous studies [One limitation of this study was the relatively small number of AHRU patients n = 7, which p studies ,15,16,17In conclusion, AHRU accounts for a substantial portion (18.6%) of major LGIB in Akita prefecture, where the aging rate is the highest in Japan, and this phenomenon can be expected to be observed in other areas in Japan and other countries with an aging population. Since AHRU is a potentially life-threatening disease that requires urgent identification and management, further studies are required to identify robust risk factors associated with clinical outcomes.


For both scenarios, the optimal ratio for the web height and total span (eL) lies between eL/20 and eL/16. The web height, the concrete strength, and the slab thickness were the design variables with more influence on the value of the vertical acceleration. The Pareto-optimal solutions were considerably sensitive to the parameters varied in each scenario, changing concrete consumption and dimensions of the welded steel I-beam, evidencing the importance of carrying out a sensitivity analysis in optimization problems.The demand for more sustainable structures has been shown as a growing tendency, and engineers can use optimization techniques to aid in the design and sizing stage, achieving solutions that minimize its cost and environmental and social impacts. In pedestrian bridges, which are subjected to human-induced vibrations, it is also important to ensure the users’ comfort, besides the security verifications. In this context, the objective of this paper is to perform a multi-objective optimization of a steel-concrete composite pedestrian bridge, minimizing cost, carbon dioxide emissions, and vertical acceleration caused by human walking. For this, the Multi-Objective Harmony Search (MOHS) was applied to obtain non-dominated solutions and compose a Pareto Front. Two scenarios were considered with different unit emissions obtained from a life cycle assessment in the literature. Results show that by increasing 15% the structure cost, the vertical acceleration is reduced from 2.5 to 1.0 m/s The civil construction industry plays an important role in the economic and social development of countries, while at the same time resulting in major environmental impacts. The sector was responsible for 34% of energy consumption and 37% of total carbon dioxide emissions worldwide in 2021 [For bridges, the sustainable performance of the structure is directly related to the initial stages of the design, starting from the choice of which material will be used . In the In the case of pedestrian bridges, besides considering the cost and environmental impacts, pedestrian comfort can be one of the objectives of the optimization problem. With the growth in the slenderness of this type of structure, they became more susceptible to human-induced vibrations ,12,13. TAmong the optimization techniques applied to structural engineering, the Harmony Search is a metaheuristic inspired by jazz musical improvisation, and its algorithm is based on memorization and improvisation. Although the original method was designed for mono-objective optimization, some publications successfully implement a multiobjective harmony search (MOHS). As examples, the research of Kougias and Theodossiou , Jeddi a2 emissions. The optimization considering tuned mass dampers in pedestrian bridges is a topic of interest in different publications [Researchers have applied optimization techniques in the design of pedestrian bridges with distinct objectives. Ferenc and Mikulski  performeications ,25,26. Aications .2 unit emission of the concrete slab are studied, with different values obtained from a life cycle assessment presented by Santoro and Kripka [In this research, in addition to focusing on the sustainable design of pedestrian bridges, pedestrian comfort is jointly evaluated in terms of vertical accelerations caused by human-induced vibrations. The objective of this paper is to provide subsidies for decision-making in the sustainable design of a pedestrian bridge with a steel-concrete composite structure, aiming to minimize the vertical accelerations, as well as the cost and the emission of carbon dioxide. For that, a Python program is developed, implementing an algorithm of the multiobjective harmony search and verification routines regarding the structure’s ultimate and serviceability limit states. Two scenarios for the COd Kripka . This seAmong the various optimization methods applied to structural engineering, the Harmony Search (HS) is an algorithm that has been showing competitive results. Proposed originally in 2001 by Geem, Kim and Loganathan , the HS Although the HS was designed to solve mono-objective optimization problems ,30,31, tFrom MOHS2, Sivasubramani and Swarup  publisheThe algorithm of the MOHS used in this study can be described by the following 5 main steps, which are also illustrated in min and PARmax), maximum and minimum bandwidth (bwmin and bwmax) and the maximum improvisation number (MI).Step 1. Initialize the objective functions, constraints, and parameters of the method: harmony memory size (HMS), harmony memory considering rate (HMCR), maximum and minimum pitch adjustment rate (PARStep 2. Harmony memory (HM) initialization with random starting solutions generated within the discrete search space.2) with the same number of harmonies as the HMS value. Each harmony can be generated in three different ways: random selection, memory consideration, or pitch adjustment. If a random number 1rand is equal to or bigger than HMCR, the value of the variable is obtained by random generation; otherwise, it is obtained by memory consideration. In this case, a new random number 2rand is compared to PAR, and if the 2rand value is equal or bigger, the value of the variable is randomly selected from harmony in the HM. If 2rand is smaller than PAR, then the new value is submitted to pitch adjustment, considering a value of the variable stored in HM and performing a step based on the bw parameter.Step 3. Improvise a new harmony memory  are the characteristic strength of concrete (ckf), the concrete slab thickness, the steel beam dimensions, and the interaction degree (α) of the composite beam, as shown in wh is the web height, wt, fs,t and fit are, respectively, the thickness of the web, of the superior and inferior flanges, and fsb and fib are the width of the superior and inferior flanges. In total, 9 design variables are considered, and their values are discrete to ensure that the solutions are feasible and represent a real design. The possible intervals for each variable are shown in the following equations, which form the lateral constraints of the optimization problem. These discrete intervals also limit the minimum and maximum dimensions of the structural elements, as well as consider the manufacturing standard of Brazilian metallurgists.The optimization problem variables (2 emissions associated with the construction phase of the pedestrian bridge. Equation (7) is used to evaluate the monetary cost of the structure (C), in the function of the unit costs (ic) and the respective quantity of material consumed (iq), the elements  and evaluated similarly to the cost, as can be seen in Equation (8). The elements (ee) are the same as in the cost evaluation but consider a unit emission of CO2 (ie). For the steel I-beam, the value of unit emission adopted was provided by Worldsteel [The environmental impact of the structure construction is measured in terms of COrldsteel . On the rldsteel  and are 2 emissions, considering the acquisition of raw materials, transport to the concrete plant, production in the concrete batch, and the concrete transport to the building site. More details are presented in the original publication.This paper proposes two optimization scenarios, which consider different unit emission values for the concrete and its reinforcement, based on results obtained by Santoro and Kripka . In the Scenario (A)—unit emissions obtained from the on-site survey for the study region. In Scenario (B)—unit emissions calculated using the SimaPro software, with Ecoinvent 3.5 database and ReCiPe 2016 method, with adjustments in the processes and quantities to make the values compatible with the same region. These values are displayed as emission B in The scenarios studied in this research are:a,K%95, C, K1, K2 e fK are tabled constant values from the same code, d is the pedestrian density , L is the structure length, b is the width of the pedestrian bridge, and iM is the modal mass, associated to mode i.Finally, the third objective function is to minimize the vertical accelerations generated by human-induced vibrations, according to Equation (9). With this objective, it is sought to increase the comfort of the pedestrians using the structure. The formulation is provided by the Brazilian code ABNT NBR 7187 , where K2), and railing (1 kN/m). As variable actions, there is the constructive live load (1 kN/m2), the pedestrian live load (5 kN/m2) [The stresses, displacements, and dynamic parameters of the structural model are analytically calculated through the implementation of the formulas in the Python program developed in this study. The analysis considered a linear behavior of the steel I-beams and concrete slab. As permanent loads, it was taken into account the self-weight of the structure and shear connectors , a concrete regularization (0.3 kN/m5 kN/m2) , as well5 kN/m2)  and a 102 [The verifications of the ultimate limit state refer to the shear stress and the bending moment acting on the composite beam , as well2 . 4 in this research.All the verifications above must be met for the solution to be considered feasible. In the optimization problem, this is handled by constraints in the form of normalized inequations created from the verifications. Solutions that fail any of the constraints are penalized by an increase in the objective function (in the case of minimization), turning the solution less efficient for the optimization algorithm. In this paper, the penalization is obtained by the sum of the products of the constraint by a penalty factor. This value was determined based on a series of previous tests, where the lowest penalty factor that resulted in feasible solutions after the optimization end was adopted, with a value of 102, it is necessary to invest R$ 200.00 ($ 38.40) per meter of the structure, which corresponds to an increase of 15% in the cost. To reduce the acceleration from 2.5 to 1.5 m/s2, it is necessary an increase of only 7% in the structure cost.The Pareto-optimal solutions for each scenario are presented in 2 emissions due to the unit emissions being considerably lower in comparison to Scenario (B). It is also possible to notice that for Scenario (A), solutions are distributed almost linearly, with the emissions growing as the cost increases. On the other hand, in Scenario (B), the solutions are more dispersed, without a clear tendency between the two objectives. However, the cost and the CO2 emissions of the pedestrian bridge are not conflicting objectives, with solutions that are at the same time efficient in terms of costs and environmental impacts.Optimization results for emission and cost are shown in 2 emissions. In contrast, other solutions adopted smaller web heights, bigger slab thickness, and higher concrete strengths, reducing the costs but trading off a poorer performance in terms of environmental impacts.This behavior for Scenario (B) can be mainly explained by a difference in the Pareto-optimal cross-section configuration. Some solutions showed a preference for bigger web heights and smaller slab thickness and concrete strength, being the ones with the best performance in terms of pedestrian comfort and CO2 emissions. A possible explanation for this is that to minimize costs, the optimization algorithm favors solutions that reduce material consumption, which also reduces the environmental impact of the structure. Therefore, minimizing costs and emissions are not conflicting objectives, as the literature also points out [Still, this can be evidence that the reduction in the cost of the structure is also an effective way to achieve environmentally cleaner designs in terms of COints out ,46,47, fwh) is a design variable that notoriously influences the cost, the environmental impact, and the vertical acceleration generated by human-induced vibrations. This occurs due to the influence of the variable in the structure’s resistance and stiffness. For Scenario (A), Pareto-optimal solutions with smaller wh have lower cost and environmental impact but perform poorer in comfort for the pedestrians, as wh, for Scenario (A) are in the range of 900 mm and 1100 mm. The figure also shows that increasing this variable is an effective way to reduce the vertical accelerations from 2.5 m/s2 to 1.0 m/s2. However, to reduce accelerations further, other variables should be considered, such as the superior and inferior flange width, slab thickness, and concrete strength. The change in the behavior occurs as an attempt to satisfy the constraints regarding slenderness and the bending moment about the weak axis of the I-beam.The web height  lies between eL/20 and eL/16.Again, Scenario (B) presented a quite different behavior, although the interval of optimal values for wh that complies with the maximum slenderness, given that this is an effective way to increase the beam’s stiffness. However, solutions that increase only the slenderness ratio can have a lower resisting capacity in the weak axis of the I-beam profile, and because of that, the constraint related to the verification of horizontal loads is also important in the sizing of the beam. For this restriction to be satisfied, solutions must also increase the flanges width and thickness of the I beam cross-section.Regarding the constraints of the optimization problem, the ones that govern the structure sizing are, in the vast majority, the displacement, the I-beam slenderness, and the horizontal bending moment that acts in the weak axis of the steel beam. As displacement is the active restriction in almost every solution, the algorithm shows a preference for adopting the biggest 2 released in its construction is due to the structural element. In Scenario (B), the concrete slab contribution of emissions increases to almost 46%. For this reason, the results show a certain preference for solutions with the minimum slab thickness, reducing the volume of concrete consumed.In cost terms, the welded I-beam is the element with the vast majority contribution to the value, as shown in Varying the unit emissions of the concrete and its reinforcement caused changes in the optimal values for the design variables. The average value of each variable is presented in As can be noticed from the above, the values adopted for unit emissions can significantly change the results, both in terms of quantifying the environmental impact and in the optimal configuration of the solutions. This shows the importance of ensuring the reliability of the LCA study so that its practical applications are valid and represent reality as faithfully as possible. Regarding the impacts on the optimization results, it becomes clear the need to carry out sensitivity analyses to better understand the behavior of the results under possible changes in the parameters of the problem. It is also important to emphasize that the optimal solutions are intrinsically linked to the problem modeling and its limitations, and special care must be taken when extrapolating such results to different situations and applications. Finally, the program developed in this research proved to be capable of obtaining a Pareto front of non-dominated solutions, which can aid in the decision-making process during the design of a steel-concrete composite pedestrian bridge. In addition, the MOHS algorithm proved to be applicable in the optimization of three distinct objectives for the structural engineering problem studied. It is worth mentioning that both the methodology of this work and the developed program are adaptable for different types of structures, given that certain changes in the code are made, such as in the structural analysis and the pertinent verifications. This allows the study of other structural problems focused on their sustainability, and the efficiency of the optimization algorithm in different situations.2 emission of the concrete. The first (A) uses unit emissions of a cradle-to-gate LCA from the on-site survey for the study region, while the second (B) are values obtained from the SimaPro software. The program developed was able to successfully obtain a Pareto front of non-dominated and feasible solutions, considering the three distinct objectives. With the analysis of the results, several conclusions are drawn which can be of aid during the decision-making in the design of sustainable pedestrian bridges of composite structure, taking into account the user’s comfort.This paper presented a multiobjective optimization of a pedestrian bridge of steel-concrete composite structure, considering the cost, the emissions of carbon dioxide, and the comfort of the pedestrians. The set of Pareto-optimal solutions was obtained through the implementation in Python of a multiobjective Harmony Search algorithm, which uses non-dominated ranking and crowding distance metrics to classify the solutions. The program developed also performs the structural analysis of the structure and verifies the ultimate and serviceability limit states of the composite beam and concrete slab, according to the respective Brazilian codes. Two scenarios were studied, considering different values for the unit CO2 to 1.5 m/s2 by an increase of 7% in its cost and to 1.0 m/s2 by an increase of 15%. For Scenario (A), an efficient way to reduce the vertical acceleration down to 1.0 m/s2 is to increase the web height of the I-beam, although further minimization must also increase superior and inferior flange width, slab thickness, and concrete strength. Scenario (B) showed a preference for changing the slab thickness, concrete strength, and flanges width, with solutions maintaining similar web heights while the acceleration is still reduced. For both cases, the optimal ratio for the web height and the total span (eL) is from eL/20 and eL/16. For Scenario (A), the web height grows from 850 mm while the vertical acceleration decreases until 1.0 m/s2, and from then on, the values stabilize at around 1050 mm. The optimal web heights for Scenario (B) are concentrated in both extremes in an almost constant behavior along vertical acceleration, with no values in the middle of the range.The results show that, for both scenarios, it is possible to significantly increase the comfort of pedestrians by a slight increase in the structure cost and emission. A structure can have its vertical acceleration reduced from 2.5 m/s2 emissions and vertical acceleration but with higher monetary costs. The web height is also important for the structure sizing since it is directly related to the displacements, the active constraint in most solutions. Nevertheless, the width of superior and inferior flanges is crucial to satisfy restrictions regarding the slenderness ratio and moments acting in the weak axis of the I-beam section. These results indicate that other design variables other than web height can play an important role in the vertical acceleration and sizing of the structure, evidencing the importance of them being considered in the decision-making process by engineers.In terms of costs, the steel I-beam is the main contributor to the total budget in both scenarios, with a 95% share of the value. On the other hand, the contribution of the concrete slab in the total emissions was raised from 26.42% to 45.57% in scenarios (A) to (B), given the bigger concrete unit emissions considered in the last scenario. In the first scenario, the costs and emissions grow together with the increase of the web height, trading off for lower vertical accelerations. However, in scenario (B), solutions with bigger web heights, minimum concrete strength, and slab thickness perform better in terms of CO2 emissions and the cost of the pedestrian bridge. For the first scenario, the solutions presented a clear tendency of linear growth between the cost and emission, while in the second, the Pareto-optimal solutions were more dispersed. The optimal values of the design variables were also affected, with scenario (B) presenting a bigger consumption of concrete when compared to scenario (A). Therefore, two broader conclusions can be drawn from the variations in the results of the sensitivity analysis. First, the importance of considering different scenarios in optimization problems, as the results can be highly sensitive to changes in certain parameters. Second, the necessity of guaranteeing the reliability of the life cycle assessment is to make sure the results will be representative and applicable in practical ways, especially when raising sizing parameters for project development.The behavior of the Pareto-optimal solutions suffered a considerable change for each scenario when analyzing the COIn spite of the fact that Brazilian Standards were considered in the computational implementation of the formulation and subsequent optimization, this aspect does not influence the results or the conclusions obtained once the same considerations and hypostasis were adopted in all the structures analyzed.


Polymer concrete (PC) has been used to replace cement concrete when harsh service conditions exist. Polymers have a high carbon footprint when considering their life cycle analysis, and with increased climate change concerns and the need to reduce greenhouse gas emission, bio-based polymers could be used as a sustainable alternative binder to produce PC. This paper examines the development and characterization of a novel bio-polymer concrete (BPC) using bio-based polyurethane used as the binder in lieu of cement, modified with benzoic acid and carboxyl-functionalized multi-walled carbon nanotubes (MWCNTs). The mechanical performance, durability, microstructure, and chemical properties of BPC are investigated. Moreover, the effect of the addition of benzoic acid and MWCNTs on the properties of BPC is studied. The new BPC shows relatively low density, appreciable compressive strength between 20–30 MPa, good tensile strength of 4 MPa, and excellent durability resistance against aggressive environments. The new BPC has a low carbon footprint, 50% lower than ordinary Portland cement concrete, and can provide a sustainable concrete alternative in infrastructural applications. Polyurethane (PU) is a class of polymer that has a wide range of physico-chemical properties. These properties are useful in different fields such as foams, coatings and adhesives, bio-medical sciences, plastic, thermoplastic, elastomers, and recently, the construction industry . PU consPolymer concrete (PC) has appeared as a widely attractive construction material for the last few decades. PC is developed by mixing well-graded aggregate/fillers and a polymer resin that partially or fully substitutes the cement binder. Due to its advantages, PC is usually used in applications that require excellent resistance to aggressive environmental conditions , and higIn 1970, URTEK (Finland) developed for the first time commercial PU concrete . PU concFor its valuable properties, the applications of PU concrete in numerous bridge engineering  are gaining considerable significance. PU concrete has been applied in several bridge engineering projects ,26,27. XDespite the benefits of PU concrete in the construction industry, PU polymer is well-known to have a very short setting time . As repoRecently, studies were directed toward investigating the potential of using bio-based polyurethane aggregate in concrete. Sari et al.  studied BPC is developed herein using polyol, isocyanate, and medium-graded aggregate. The polyol was Sovermol 750 . No cement was used in making the BPC. Sovermol 750 is a bio-based derived polyol with 65–80% renewable natural oil content. Natural-oil polyols are polyfunctional alcohols based on renewable raw materials like rapeseed oil, castor oil, soybean oil and palm kernel oil. Sovermol 750 has the hydroxyl number in the range of 300–330 mgKOH/g, moisture content of less than 0.1%, and acid number of less than 2.0. The isocyanate used was solvent-free, medium-viscosity polymethylene polyphenyl polyisocyanate, Lupranate M70L  with NCO content of 31.0 wt.%. Several trial mixes were designed and tested to identify, examine and overcome the challenges of producing BPC, including excessive foaming, fast setting, and zero flowability, as depicted in apK in the range of 2.8–4.5 will retard rather than prohibiting the polymerization of PU [apK equal to 4.2 was selected as the retarder for the BPC. The polyol was nano-modified utilizing COOH-functionalized MWCNTs . Introducing COOH-functionalized MWCNTs to the polymer matrix is expected to improve the rheology of the polymer, compensate the possible strength deterioration due to the use of acid, and enhance the thermal stability of BPC [It was suggested that when the mix acidity is increased, foam formation can be stopped due to the blockage of the active –NCO sites of polyisocyanate . It was on of PU . Therefoy of BPC ,35. Tabl3 of BPC. The design criteria was that the BPC would reach a setting time of at least 30 minutes and have a 7-day compressive strength of 20.7 MPa (3000 psi). Both criteria are driven by the need to improve the constructability of BPC. Twenty trial mixes with different PU contents  and benzoic acid dosages  were carried out. Adding PU at 16 vol.% of the total concrete volume and 4.0 wt.% of the total binder content resulted in the best performance for BPC at both fresh and hardened states. Hence, for the rest of the experiments, the 16 vol.% PU and 4.0 wt.% benzoic acid were selected as the reference mix to investigate the impact of benzoic acid and COOH-functionalized MWCNTs on the behavior of the BPC.. After 2 h, BPC’s ingredients were mixed as follows: the aggregate and nano-modified polyol were added to the mixer and mixed at room temperature at a rate of 1500 rpm for 1 min to ensure that the aggregate and polyol were fully and evenly mixed. For safety, the isocyanate and benzoic acid were slowly added and continued for three minutes. The materials and mixing procedure are shown in Before mixing, the polyol was nano-modified utilizing COOH-functionalized MWCNTs at an optimum dosage of 0.5 wt.% of binder; the optimum dosage was chosen based on previous work . The dis1–D4) and expressed as a percentage of the original base diameter (D0). A schematic representation of the flow table test is shown in Immediately after mixing, flowability and initial setting time of the BPC were evaluated. The flow table test at time zero was measured as per ASTM C230-14 . The flo. The compressive and splitting tensile strength tests were conducted following ASTM C39 [tf is the split tensile strength, P is the applied load, D is the diameter of the specimen, and L is the length of the specimen.The mechanical performance of BPC, including the modulus of elasticity, Poisson’s ratio, compressive, and splitting tensile strength, was evaluated. All mechanical testing was carried out at 7 days of age on cylindrical specimens of 8-inch (203 mm) height and 4-inch (101 mm) diameter. For each curing method, four specimens were tested. The static modulus of elasticity and Poisson’s ratio tests were performed as per ASTM C469-14 . A ForneASTM C39 . Both teThe durability of the BPC was assessed by examining weight loss after exposure to different mediums as per ASTM D543-14 . The 4 wMicrostructure characterization of BPC using a SEM was used to examine the microstructural features of air and heat-cured BPC. Fractured BPC specimens were examined using a VEGA3 thermionic emission SEM system by TESCAN . To improve conductivity, the specimens were sputter-coated with gold/palladium (Au/Pd). The electron beam energy used for all readings was 20 keV. The magnification varied from 400× to 1150× depending on the features to be detected.2 equivalent using CCalC2 toolbox developed at the University of Manchester [The carbon footprint analysis was performed to assess the greenhouse gas (GHG) emissions associated with manufactured BPC. The carbon footprint was evaluated by multiplying the quantity of each material in the mix design by its COnchester . The resFinally, chemical characterization of biopolymer PU on different polymer specimens was conducted, including pristine PU, PU polymer with 4 wt.% of benzoic acid, and PU nanocomposite containing 4 wt.% of benzoic acid and 0.5 wt.% of COOH-functionalized MWCNTs. We point out that chemical characterization tests used here are those typically used with polymers rather than those used with cement as the new BPC concrete has no cement. The goal of the chemical characterization was to (i) determine the role of benzoic acid in eliminating the foaming and short setting time of pristine PU polymer, (ii) elaborate on the role of reduced/delayed crosslinking density on the thermal properties of the polymer specimens, and (iii) investigate the role of addition of COOH-functionalized MWCNTs on the crosslinking density and thermal stability of the polymer specimens.SXX, using Equation (2) [SxH is the crosslinking reaction enthalpy of each test sample, and ΔSH0 is the reaction enthalpy of the reference uncured PU sample. The degree of crosslinking in the PU specimens was investigated qualitatively using the swelling index test. Three-disc specimens (~5 g each) were placed in 30 mL of toluene  and kept at ambient temperature for 2 h. The solvent was then decanted, and the specimens were surface dried by short contact with the filter paper to remove the liquid solvent adhering to the surface of the specimen. Promptly, the weight of the swollen polymer was determined using Equation (3).M1 is PU weight before placement in the solvent, and M2 is PU weight after placement in the solvent.To examine the thermal transitions of PU specimens, as well as measure the degree of crosslinking in the polymer specimens quantitatively, differential scanning calorimetry (DSC) measurements were carried out using a Discovery DSC 25 instrument from TA Instruments  operated under a nitrogen environment. Cured and uncured PU samples (5–10 mg) were heated up from 50 °C to 300 °C at a constant heating rate of 10 °C/min, held at 300 °C for 10 min and then cooled down to 50 °C following the same rate. The remaining crosslinking capability in the PU samples was determined by the degree of crosslinking, tion (2) .(2)XSx=. Nicollet IS50 spectrometer  was utilized to perform the attenuated total reflectance infrared (ATR-FTIR) spectroscopy. The test was conducted using a scanning range of 4000–500 cm−1, a resolution of 4 cm−1, and a number of sample scans equal to 32. TGA was conducted on a TA550 thermogravimetric analyzer from TA Instruments operated under a nitrogen environment. The specimens were heated up from 50 °C to 450 °C at a constant heating rate of 10 °C/min, and the relative mass loss of the samples was recorded.Fourier transform infrared spectroscopy (FTIR) analysis and thermogravimetric analysis (TGA) were conducted to identify the differences between the functional groups of PU specimens and the mechanism of material decomposition, respectively2 [BPC maintained the shape of the mold, showing a high stiffness, thus, resulting in a 0% flowability as presented in 2 ,45. Figu2 . However2  reportedt-test (t-test) was applied to examine the statistical significance between the means. A 95% confidence interval was used (α = 0.05) for all the t-tests. All mechanical testing was performed on four different specimens for each curing condition (air and heat curing). The Student’s 3 ± 45 kg/m3 and 1858 kg/m3 ± 36 kg/m3, respectively. Therefore, thermal curing did not affect the density of BPC. Results were in agreement with PU concrete densities reported in the literature [BPC-A and BPC-H showed similar densities with a mean value of 1830 kg/mterature ,46. It iterature ,48, and terature , which it-test, α = 0.05). Both curing methods showed modulus of elasticity values similar to those reported in other PCs and lower than normal-strength concrete [The modulus of elasticity and Poisson’s ratio of air-cured BPC were 9.3 GPa ± 0.9 GPa, and 0.24, respectively, while for heat-cured BPC, the elasticity modulus slightly increased to have an elasticity modulus of 9.9 GPa ± 0.9 GPa and a Poisson’s ratio of 0.26. The effect of thermal curing on the modulus of elasticity was not statistically significant .SEM images of fractured BPC specimens are presented in SH0). For the cured pristine PU and PU containing 4 wt.% benzoic acid and 0.50 wt% COOH-functionalized MWCNTs, this peak almost disappeared, showing the roughly fully polymerized/crosslinked specimen (~100%). However, for the PU specimen containing 4.0 wt.% benzoic acid, a small exothermic peak in the range of 125–160 °C can be observed, which corresponds to the crosslinking enthalpy of 6 J/g (ΔSxH). Thus, the degree of crosslinking for the PU containing 4 wt.% benzoic acid is equal to 97%, meaning less polymerization/crosslinking degree due to the presence of the acid. However, the difference between the DSC thermograms of pristine PU and PU containing 4.0 wt.% benzoic acid was marginal, indicating the complete reaction of acid moieties with the PU system. An endothermic peak appeared at around 130 °C for the PU nanocomposite compared to other specimens. The appearance of such an endothermic peak indicates that some fractions of the hard segments present in the PU matrix participate in the regular crystalline arrangements due to the presence of chemically treated MWCNTs, which was not observed for the pristine PU and PU containing 4.0 wt.% benzoic acid. The findings align with other researchers’ findings reported in the literature [The chemical characterizations of the bio-based PU provide significant insight into the behavior of BPC. The DCS thermograms of PU specimens are depicted in The results of solvent swelling tests of PU specimens are shown in Data obtained here are in agreement with the findings of other researchers ,55 that Notwithstanding, the addition of COOH-functionalized MWCNTs not only promoted the crosslinking density of the PU specimen containing acid but also led to more crystallinity in the sample. The most probable mechanism by which the COOH-functionalized MWCNTs enhanced the degree of crosslinking is shown in −1 to approximately 2600 cm−1 indicating the acidic –OH stretch. The peak related to the C=O stretch was located at 1670 cm−1. Other bands are characteristic of this aromatic carboxylic acid compound [−1, and the stretching vibration peak for the –NCO (isocyanate groups) showed up at 2250 cm−1. The stretching modes at about 1550 and 1725 cm−1 are attributed to the hydrogen-bonded and free C=O groups present in urethane linkage (–HN–COO–) of the PU matrix, respectively [compound . For theectively .2 and –NCO to form a urea bond structure, further polymerization/crosslinking, and formation of a network structure. Bonds formed within the PU matrix due to the addition of surface functionalized MWCNTs confirmed observations through the SEM images . However, BPC outperformed ordinary concrete’s durability against aggressive environments and showed minimum weight loss while serving in highly aggressive acid environment.The low elastic modulus shall allow low tensile stress buildup from restrained shrinkage, which in turn, suppresses the reflective cracking.Chemical and microstructural analysis of bio-based PUs and PU concrete revealed that employment of MWCNTs in the polymer matrix compensated the lower crosslinking density due to the addition of benzoic acid to the PU, promoting the formation of urea bond structure, leading to further polymerization/crosslinking, and generated a percolated network structure within the polymer matrix.MWCNTs addition led to superior mechanical, thermal, and durability properties for the PU specimen containing benzoic acid and chemically treated MWCNTs.The carbon footprint for BPC was 50% lower than the reference cement concrete, which suggests BPC can provide a sustainable concrete alternative in infrastructural applications.This paper described the development and characterization of a low-carbon footprint BPC, where bio-based PU is used as the binder in lieu of cement, modified with benzoic acid and carboxyl-functionalized multi-walled carbon nanotubes (MWCNTs). The mechanical performance, durability, and the microstructure of BPC were characterized. Chemical characterization of the bio-based PU was also performed to understand the roles of the additives in enabling a bio-based polymer that can be used to produce concrete. The following conclusions can be drawn:The produced BPC with good physical and mechanical properties, including high thermal stability and excellent durability characteristics, suggest BPC be an excellent repair material for rapid repair applications in aggressive environments or applications where a fast-curing material is required. Limitations associated with bio-polymer concrete include the low flowability of the final concrete and the limited commercial availability of bio-based polyurethane.


This work represents a general strategy to design the hydrogels with customized networks and biomimetic mechanics, and illustrates underlying osteogenic mechanisms that will extend the design rationales for high‐functional biomaterials in tissue engineering.Development of artificial biomaterials by mimicking extracellular matrix of bone tissue is a promising strategy for bone regeneration. Hydrogel has emerged as a type of viable substitute, but its inhomogeneous networks and weak mechanics greatly impede clinical applications. Here, a dual crosslinked gelling system is developed with tunable architectures and mechanics to promote osteogenic capacity. Polyhedral oligomeric silsesquioxane (POSS) is designated as a rigid core surrounded by six disulfide‐linked PEG shells and two 2‐ureido‐4[1H]‐pyrimidinone (UPy) groups. Thiol‐disulfide exchange is employed to fabricate chemical network because of the pH‐responsive “on/off” function. While self‐complementary UPy motif is capable of optimizing local microstructure to enhance mechanical properties. Taking the merits of biocompatibility and high‐mechanics in periodontal ligament stem cells (PDLSCs) proliferation, attachment, and osteogenesis, hybrid hydrogel exhibits outstanding osteogenic potential both in vitro and in vivo. Importantly, it is the first time that a key epigenetic regulator of ten‐eleven translocation 2 (Tet2) is discovered to significantly elevate the continuously active the WNT/ β‐catenin through translocation 2 epigenetic regulation.A dual‐crosslinked gelling system with tunable architectures and mechanical properties can promote periodontal ligament stem cell‐mediated bone regeneration by activating WNT/ Current clinical strategies for bone tissue transplantation typically involve the use of autogenous, allogeneic, and/or prosthetic materials, which are used in more than 90% of graft surgeries.1 Howe These methods, however, are prone to rely on the preset crosslinker content and involve the issues of non‐immediate in situ regulation and tedious operations, making it difficult to precisely control the cross‐linking evolution once the gel formation is initiated. In addition, these chemical crosslinked hydrogels are extremely brittle and fragile due to the compact accumulation of hydrophobic cores and insufficient flexible chains for energy dissipation. To avoid these problems, major efforts have been devoted to optimizing the cross‐linking process to increase mechanical performances by implementing energy dissipation mechanisms and distinctive structures via the formation of multiple‐network. For example, the hydrogels can be directly incorporated with the reinforcing nanoparticles  or durable networks as the main constituent of noncovalent interactions via physical blending or chemical attachment. Under this circumstance, hierarchical hydrogen‐bonding interactions can endow the composite hydrogels with excellent self‐adaptive capacity and high energy dissipation upon exposure to external stress.Hydrogels have been extensively explored in the tissue engineering field owing to their good biocompatibility, biodegradation, and tunable physicochemical properties for bone regeneration. However, their inhomogeneous networks and weak mechanical properties greatly impede their clinical application for hard tissue regeneration. Current methodologies for tailoring hydrogels typically involve manipulating multiple external stimuli, such as pH, temperature, redox, and light.2 Thes Thanks to its excellent thermal and mechanical stabilities as well as simplicity in processing, POSS has been an important building block to generating a myriad of POSS‐incorporated hydrogels, which present a homogeneous system for developing high‐performance materials in diverse applications. However, these hydrogels are extremely brittle and fragile because of the compact accumulation of hydrophobic cores and insufficient flexible chains for energy dissipation, which relatively hampered their potential applications. Therefore, it is a prerequisite to have reversible interactions to construct strong and tough materials to maintain structural stability when such hybrid hydrogels are exposed to external stress. In views of the biomimicking modular design of skeletal muscle protein titin that possesses a remarkable combination of strength, toughness, and elasticity by reversible rupture of intramolecular secondary interactions, quadruple hydrogen bonding 2‐ureido‐4[1H]‐pyrimidinone (UPy) motifs have been widely pioneered and developed as an effective noncovalent interaction in the construction of self‐adaptive materials. Hence, UPy is the potential candidate to fabricate toughened hydrogels with controlled properties. Interestingly, incorporation of UPy motifs to enhance the self‐healing POSS‐based materials is only an emerging field in aerospace coating materials, and their application in bone repair and regeneration has to the best of our knowledge not been proposed, especially in repairing connective tissue bone defects in vivo.Polyhedral oligomeric silsesquioxane (POSS) nanocages offer a striking alternative as it possesses a rigid cage‐like core surrounded by eight organic corner groups that can be functionalized for modification.5 Than but the osteogenic mechanism is relatively obscure, which is simply ascribed to its uniform structure, good biocompatibility, and the ability to initiate the cellular response to form apatite, the major inorganic component of bone. These mainstream views always lack sufficient conviction to clarify the causes and mechanism of bone formation. Mechanical cues sensed by the cells are propagated and transduced into signaling cascades, which lead to transient or sustained cellular responses. Besides, matrix stiffness is recognized as a potent regulator to alter the epigenetic status of cells during bone regeneration. A recent study uncovered the role of translocation 2 (Tet2) in response to matrix stiffness, and Tet2‐induced DNA demethylation can be promoted with mechanical cues from stiff matrix. Understanding the cellular response to matrix stiffness would help us to realize hydrogels with optimal combinations of structure manipulability, bioactivity, and clinical efficacy. Thus, developing and mechanistically investigating a gelling system with structural controllability and excellent mechanical properties is particularly appealing.In recent years, POSS units possessed excellent osteogenic effects,9 but Figure6‐U2, features a disulfide‐linked core/shell structure in which POSS acts as a rigid core surrounded by six disulfide‐linked flexible hydrophilic polyethylene glycol (PEG) chains that form the shell and two UPy groups. The thiol‐disulfide exchange reaction was employed to fabricate a “living” in situ chemical network because of its pH‐responsive “on/off” functionality, while the self‐complementary UPy motif reinforces the local microstructure to enhance mechanical properties. More importantly, this multifunctional POSS unit anchoring into the network possessed favorable cytocompatibility and osteogenic bioactivity that could support cell attachment, spreading, and proliferation. In this work, we demonstrated that the osteogenic differentiation potential of seeded periodontal ligament stem cells (PDLSCs) increased with suitable matrix stiffness. PDLSCs are one type of dental‐derived mesenchymal stem cells, attractive for craniofacial regeneration applications as they might be more committed to differentiating into craniofacial tissues compared with none dental‐derived stem cells under certain extracellular stimuli. Mechanistically, we have shown that the key epigenetic regulator TET2, which is associated with HDAC1, is upregulated in PDLSCs seeded on a stiff substrate, leading to suppression of E‐cadherin transcription and WNT/β‐catenin activation, thus promoting osteogenesis in the PDLSCs. Our findings demonstrate the potential clinical application of the POSS‐UPy hybrid hydrogel and have identified matrix stiffness as a key epigenetic regulator of PDLSCs‐mediated bone regeneration.Herein, we developed a class of dual crosslinked gelling systems with tunable architecture and mechanical properties to promote stem cells’ osteogenic capacity Figure1. The 26‐U2 polymer as the precursor molecule for the construction of tailored hybrid hydrogel through facile two‐step reactions , and 13C NMR spectrum also provided the evidence to verify the successful preparation of targeted POSS‐P6‐U2 polymer. It is mentioned that since the gel precursor of POSS‐P6‐U2 may not be a precise macromolecule and has three isomer structures, but actually, their differential components and various stereoisomers have little influence on the controlled network once the gel formation is initiated, because a variety of interchangeable PEG chain conformations can curl and entangle with each other to facilitate the hydrophobic areas, forming a series of random heterogeneous aggregates in solutions, let alone the more complex sol‐gel transition and full‐scale crosslinking evolution process.In view of the high hydrophobicity of POSS unit and UPy moiety, we employed the POSS‐Pns Figure2A. POSSs Figure  showed t6‐U2‐0.5 h) was formed around 0.5 h later and further shrank into a compact hydrogel (POSS‐P6‐U2‐12 h) after 0.5 day of aging , DC hydrogel from POSS‐P6‐U2‐0.5 h exhibited a higher mechanical strength originating from the robustly physical networks, which enabled hydrogels to dissociate to dissipate energy upon the applied strain. With the increase in crosslinking time, the microstructure of hybrid hydrogels became more compact and the swelling rate was lower due to the reduction of hydrophilicity by dissociation of hydrophilic PEG shells and optimization of the hydrogel network by self‐complementary UPy components. During this gelation process, a multistage abrupt increase of the storage modulus G΄ implied the formation of the stable hydrogel with high strength  and loss modulus (G″). The introduction of POSS units provided high strength for the hydrogels and the higher G΄ than G″ implied the typical formation of stable hydrogels Figure . Compareh Figure , however  analyses were also carried out to investigate the cell proliferation rate on hydrogels  or tumor necrosis factor‐α (TNF‐α) positive inflammatory cells at 8 weeks compared with 2 weeks  assay. Live/Dead staining confirmed that most of the PDLSCs cultivated in the hydrogels were alive (close to 100%) Figure3A, and s Figure . After i6‐U2‐12 h with high mechanical strength exhibited a better support for cell attachment, validated by vinculin for focal adhesion points (FAPs) staining and F‐actin for cytoskeleton labeling , alkaline phosphatase (ALP), and osteocalcin (OCN) were used as osteogenesis markers and analyzed with qPCR assay  images  . Moderately increased new bone area, BV/TV, and BMD were revealed in POSS‐P8‐0.5 h hydrogel group. While the least bone regeneration was shown in the tetra‐PEG group, POSS‐P6‐U2‐0.5 h, and control group. In accordance with µCT analysis, histological analysis with H&E  Figure  and bone) Figure  in the P6‐U2‐12 h exhibited superior osteogenesis, POSS‐P8‐0.5 h showed a more pronounced osteogenesis activity than that of POSS‐P6‐U2‐0.5 h. Based on Figure 8‐0.5 h, we previously found a dynamic and tunable manipulation of sequential morphology and size transformation in situ via a hierarchical assembly strategy based on a living thiol‐disulfide exchange reaction. By tailoring the external stimuli in an alkaline environment, the reactive points can be generated at the ends of initially unimolecular micelles, which subsequently drive the pre‐assemblies to periodically proceed into the hierarchically micellar connection, axial growth, bending, and cyclization processes from nanoscopic solution aggregate to macroscopic particles. This axially oriented structure facilitates cell differentiation and growth, but does not have enough flexible chains for energy dissipation, exhibiting brittle and fragile behaviors. In contrast, on the account of the weak self‐complementary effect of the UPy motif within a short time, POSS‐P6‐U2‐0.5 h exhibits a little higher modulus but spoils the ordered arrangement of structures at the same time, which may lead to the inferior osteogenesis activity than that of POSS‐P8‐0.5 h. However, extending the crosslinking time to 12 h, sufficient self‐adaptive behaviors endow the hydrogel with a newly well‐ordered network and excellent mechanics and bioactivity for osteogenesis.It was mentioned that although POSS‐Preaction.4 By t It has been reported that mechanical stress can inhibit cadherin, allowing the β‐catenin translocated into the nucleus and initiating osteogenesis‐related gene transcription. Activation of WNT/β‐catenin signaling pathway is essential for bone tissue regeneration and cell adhesion. By using western blot analysis, we found that PDLSCs cultured with high strength POSS‐P6‐U2‐12 h hydrogel expressed a lower level of E‐cadherin, accompanied by promoted expression levels of active‐β‐catenin and β‐catenin , enabling them to regulate gene expression independent of DNA demethylation process.25 To t Figure  and immuy Figure . The semS Figure  and ALP e Figure . More ex36‐U2 polymer with customized microstructures and optimal mechanical properties to control PDLSCs osteogenic capacity in vitro and in vivo. Depending on synergistic regulation of pH‐responsive chemical networks with an “on/off” function and physical networks with the dynamic self‐optimized arrangement, thiol‐disulfide exchange reaction endowed hydrogels with controlled architectures while UPy moieties contributed to a prominent increase in mechanical strengths. More intriguingly, the controllable POSS‐P6‐U2‐12 h hydrogel with a higher matrix stiffness displayed a significant increment of osteo‐induction ability toward PDLSCs. Mechanistically, we first found that the key epigenetic regulator TET2 was elevated after PDLSCs seeding on the stiffer substrates, associated with HDAC1, leading to the suppression of E‐cadherin transcription and promoting Wnt/β‐catenin sustained activation, which resulted in the elevated osteogenesis capacity of PDLSCs. Therefore, our findings demonstrated the potential clinical application of the PEG‐POSS‐UPy hybrid hydrogel, and uncovered the matrix stiffness as a key epigenetic regulator of PDLSCs mediated bone regeneration, which will hold great potential in the rational design of controlled gelling systems and motivate scientists to fabricate more advanced materials for various high‐tech applications.In conclusion, we have demonstrated a dual crosslinked gelling system from a precursor of POSS‐P4Detailed experimental section can be found in the Supporting InformationThe authors declare no conflict of interest.Supporting InformationClick here for additional data file.