Recent studies have examined hypertrophic pachymeningitis as an IgG4-RD. However, there are no reports of immunoglobulin G4 (IgG4)-related hypertrophic pachymeningitis with polycystic subdural hygroma.A 56-year-old man presented to the hospital with complaints of a persistent, pulsatile, occipital headache and general malaise. Magnetic resonance imaging of the brain revealed hypertrophic pachymeningitis with polycystic subdural hygroma and hematoma. Based on the dural biopsy findings and exclusion of other diseases, the patient was diagnosed with immunoglobulin G4 (IgG4)-related hypertrophic pachymeningitis. IgG4-related diseases may cause subdural hygroma more commonly than other diseases that cause hypertrophic pachymeningitis.This is the first case report discussing polycystic subdural hygroma and hematoma with IgG4-related hypertrophic pachymeningitis. Immunoglobulin G4-related disease (IgG4-RD) was first reported as hyper-IgG4emia in autoimmune pancreatitis . In receA 56-year-old man with a history of asthma, sinusitis, serous otitis media, idiopathic eosinophilia, recurrent idiopathic myocarditis, and idiopathic interstitial pneumonia was treated with prednisolone (PSL) at a dose of 27.5 mg/day. He had no symptom with steroid therapy. He complained of a persistent, pulsatile, occipital headache, and general malaise 2 weeks before admission, when the dose of PSL was reduced from 27.5 mg/day to 22.5 mg/day. However, he did not exhibit symptoms such as fever, weight loss, joint pain, rash, or diarrhea. A neurological examination revealed paralysis of the left abducens nerve. Magnetic resonance imaging (MRI) of the brain showed polycystic subdural hygroma and hematoma. In addition, with contrast enhancement, a diffuse thickening of the dura mater was observed Fig. . Whole-bIntracranial hypertrophic pachymeningitis rarely accompanies subdural hygroma or hematoma. Only three cases have been reported in the literature , 8, incl


Antimicrobial resistance (AMR), recognised as a serious and growing threat to global health, is promoted by multiple drivers, including antibiotic use in the livestock sector. Thus, understanding factors influencing antibiotic use in livestock production is essential to the design and implementation of effective interventions to reduce AMR. This qualitative study aimed to explore the experiences and views of the key actors associated with the use of antibiotics for pig farming in Thailand, from local farmers to officers in central government institutions.A total of 31 in-depth interviews were conducted with different categories of actors: pig farmers (n = 13), drug retailers (n = 5), veterinarians (n = 7), government officers (n = 3) and representatives of animal and human health associations (n = 2). Themes emerging from the interviews were identified and explored using thematic analysis. In addition, direct observations were conducted in the pig farms.The findings highlight the multi-faceted nature of the views and practices that may contribute to misuse or overuse of antibiotics in the study locations, including misconceptions about the nature of antibiotics and AMR , lack of facilities and financial means to establish an antibiotic-free farm, lack of sufficient training on AMR and antibiotic prescribing for veterinarians, the profit motive of pharmaceutical companies and their ties to farm consultants, and lack of sufficient regulatory oversight.Our study indicates a clear need to improve antibiotic use for pig production in Thailand. Farmers need better access to veterinary services and reliable information about animal health needs and antibiotics. Innovative investments in biosecurity could improve farm management and decrease reliance on antibiotics, although the cost of these interventions should be low to ensure wide uptake in the livestock sector. Lastly, further development of professional training and clinical guidelines, and the establishment of a code of conduct, would help improve antibiotic dispensing practices. Antimicrobial resistance (AMR), recognised as a serious and growing threat to global health, is driven by many factors including antibiotic use not only in humans but also in animals. In many countries, antibiotics are widely applied to promote growth in livestock in addition to preventing and treating infections . This prIn the pig sector, intensive use of antibiotics has promoted resistance of both commensal and pathogenic bacteria , 7, partactors associated with the use of antibiotics for pig farming in Thailand, from local farmers to officers in central government institutions. After a description of the study context, methods, and the presentation of findings, implications of the study for the design and implementation of action plans on AMR are discussed.Despite these studies, our knowledge of practices influencing the agricultural use of antibiotics is still scarce, especially in countries where resources to conduct research and evaluation are more limited. Considering this gap in knowledge, this article reports findings from a study which aimed to explore the experiences and views of key The Thai agricultural sector accounts for approximately 10% of GDP (USD 42 billion in 2018) with livestock production, including pigs, contributing around USD 400 million . In 2017This qualitative study was conducted between March 2018 and January 2019 in a province in the central region of Thailand, which accounts for about 20% of annual domestic pig production and hosts different production systems, from smallholders to large industrial farms. The study was part of a larger project which included a cross-sectional survey of antibiotic use among pig farmers in six sub-districts with the highest number of pig farms in the same province . The resParticipants in this study were recruited from the larger sample of 84 farmers included in the cross-sectional survey . In totaDrawing from previous studies , 24, theThe interview audio recordings were transcribed verbatim and anonymised by the researcher (AL). Data were imported into the software NVivo 12 for qualitative analysis. The researcher (AL) generated initial codes after iterative reading of the transcripts. The field notes were reviewed in parallel with the transcripts. Then two researchers (AL and VT) identified and organised themes and sub-themes. To reduce subjective bias, the researchers  discussed emerging findings and their interpretation throughout the process of analysis. In qualitative data analysis, themes are considered robust when they are cohesive and meaningful within the entire data set . Thus, cTable The analysis of the interviews revealed diverse and at times competing views of different actors in the agricultural sector about antibiotic use – the pig farmers, health professionals, and the pharmaceutical industry, considered in turn in the sections below.Medicines are really important in my farm. Without medicines, my pigs would be very ill. Antibiotics protect my pigs from becoming worse. At the suckling and nursery stages, the piglets are so vulnerable. I usually apply antibiotics to 100% of them. Whether or not they are sick, I must use antibiotics for prevention… All the pig farmers interviewed believed that some form of medication, including antibiotics, was necessary to maintain animal health, and control and prevent disease.I think that antibiotic use is a cheap solution…and affordable… The cost of production is not really different whether we add medicine [antibiotics] or not. For example, now the cheapest medicine is chlortetracycline. For nursery pigs, the feed mixed with chlortetracycline is baht 22.60 compared with baht 22 per kilogram of regular feed [without antibiotics]. It doesn't add much to my budget. Many farmers explained that antibiotics are an affordable approach to reduce pig mortality. One farmer estimated that medicated feed cost only 2.7% more than non-medicated feed and administering antibiotics to the whole herd via medicated feed was less labour intensive than individual treatment.(yaa-pati-cheewana) while commercial farmers could generally differentiate between antibiotics and other medicines. Most farmers who understood the meaning of antibiotics said they used them according to the indications on the package labels or following the recommendations of pharmacists. However, some farmers routinely used high potency antibiotics without clinical justification:For the treatment of common diseases, I apply a broad-spectrum antibiotic such as amoxycillin. If there is no improvement, I will change to cepha(losporin), cefo(xamine) or enrofloxacin…I believe in higher potency antibiotics. If there is no price difference, I always select higher potency antibiotics Knowledge of antibiotics differed greatly amongst pig farmers. None of the three smallholder farmers understood the word “antibiotics” Our pigs are good, clean. I know resistant pathogens, but I don’t think that we (farmers) are involved in it. Commercial farmers also understood the concept of antibiotic resistance but they were elusive when the researcher raised the issue that excessive antibiotic use in the farm was an important contributing factor:I give more attention to prevention than treatment. Water quality, low pig density and good air ventilation are essential for healthy pigs…. When the pigs are healthy, I don’t need to use antibiotics. All interviewed farmers agreed that sound farm management was key to animal health and consequently to reducing the need for antibiotics.2 costs more than 1 million THB  …the closed system would improve the health of my pigs and minimise the introduction of pathogens in the farm… so it would reduce the need for antibiotics. But this adds to the production cost. I can't afford it. A closed system housing of 300 mThe government officers in this study also believed that GAP certification contributes to the optimised use of antibiotics. Indeed, the antibiotic-free farms in our study were GAP-certified farms with bio-security measures such as change of clothing and boots and disinfection of all vehicles before entering the farm Fig. . HoweverThe GAP criteria are quite strict. They require a farm veterinarian to monitor antibiotic use in the farm. If antibiotic residue is found in pork products, the farm veterinarian must take responsibility. When the farm veterinarian is not available, farmers often give antibiotics to their animals without prescription. .With the GAP certification, the farmer must report on administrative records all medicines used in the farm and declare they were prescribed by the farm veterinarian. However, farmers may choose to not follow veterinarian’s prescription. We cannot really monitor this. Limited availability of farm veterinarians and gaps in the monitoring system were seen as further challenges to the implementation of GAP requirements.Textbox 1: antibiotic-free farm2. Eight barns were lined up in an east–west direction to minimize direct sunlight. Each barn had an indoor area of 400 m2, with access to an outdoor area of 800 m2 for two to three hours during the day, allowing the pigs to move in and out freely. There were no inside partitions, so all 400 pigs (per barn) could live together. The barn floors were made of concrete and cleaned daily by farm workers. Weaning pigs were sourced from another farm, located 17 kms away and owned by the same farmer. If sick pigs were found, they were isolated for treatment or culling.The antibiotic-free farm A was a 5000-fattener farm covering 8,000 mObservations found that all barns were clean. The researchers also observed pigs roaming around, digging up the ground in search for roots, and also eating fruits from trees that the farmer grew outside the barn. The owner said this farming concept was intended to raise “happy and healthy pigs” because the animals could express their natural behaviour and were not stressed. He said this was a feasible alternative to using antibiotics. The farm received many visitors, with walls lined with photos of international guests and actors.The owner of an antibiotic-free farm expressed concerns that market demand for antibiotic-free pork was still low. Another participant pointed out that antibiotic-free standards cannot be fully met in Thailand since most slaughterhouses do not have facilities to separate antibiotic-free pork and medicated pork, causing possible contamination. However, a farmer explained that large companies would not face this problem since they usually control the whole supply chain, including the farm, the slaughterhouse and the retail outlet.Antibiotics and other medicines used in the farms were provided by different categories of actors working in the agricultural sector, including veterinary practitioners, veterinarians in pharmacies, representatives of pharmaceutical companies and animal husbandry specialists. Most farmers in our sample relied on the advice of veterinarians regarding the selection and use of antibiotics. However, only one out of 13 farms hired a full-time licensed veterinarian, while the others hired “farm consultants” who were academics, reportedly tied to pharmaceutical companies. Smallholder farmers had limited access to veterinary services, due to lack of public veterinary health facilities and district veterinarians, while most animal clinics served companion animals only. All smallholder farmers received advice on antibiotic use from other farmers or the pharmacies where they purchased antibiotics.Interviews with key informants from the veterinary and pharmacy councils confirmed that courses on the prudent use of antibiotics were not included in the veterinary and animal husbandry curriculum, while the pharmacy curriculum did not cover use of antibiotics in animals. A key informant from a veterinary association mentioned that their association provided in-service training and clinical practice guidelines for disease management. However, veterinarians expressed concern over lack of clinical guidelines, lack of protocols for sample collection, difficulties in laboratory sample transportation, delays in receiving lab results and high cost of bacterial culture and drug sensitivity testing.Of course, we use a large amount of antibiotics in livestock, but I believe that other sectors such as doctors, pharmacists and orchards use more. Patients who don't take the full dose are the cause of the resistant bacteria … I don’t believe that people will die from AMR transmitted by animals. ]Most veterinarians were aware of government policy on reducing the use of antibiotics. However, some of them became defensive when the researcher raised the issue of AMR. They said antibiotics were used only when necessary, and not indiscriminately as perceived by the public.All pharmaceutical companies offer sales promotions. You can choose either 10% discount or international leisure travel awards. In previous years, I have travelled to the US, Iceland, Spain, Japan. I feel like I have to order more medicines to gain the award. Representatives of pharmaceutical companies offered me a dinner or presents such as a liquor… and they asked me to help them achieve their sales target… Commercial farmers explained they could buy antibiotics easily at pharmacies or from representatives of pharmaceutical companies who visited their farms. Respondents from the three commercial farms also reported that representatives of pharmaceutical companies encouraged the purchase of antibiotics and other medicines through discounts and gifts such as leisure travel.We have only a few inspectors. We cannot inspect all pharmacies in our catchment area, particularly the animal pharmacies. It is not our priority as the governor gives priority to the control of illegal drugs In addition, government officers noted that indiscriminate sales were difficult to control due to lack of sufficient human resources.Most lecturers are linked with pharmaceutical companies. They support lecturers by providing equipment to their university (…) When these lecturers come here and recommend to purchase the antibiotics from a company, it is difficult to deny their advice. Farmers who hired academic lecturers as farm consultants felt “obligated” to follow their recommendations on various aspects of farm mangement, including advice on the choice of antibiotics. Two farmers believed that academic consultants would receive gifts from the pharmaceutical companies they recommended, such as equipment for their faculty or honoraria.This qualitative study aimed to deepen understanding of the complex set of factors influencing the use of antibiotics for pig farming in a particular context of livestock production. As described above and summarised in Fig. aa-kha-chue (“drug that kills germs”), yaa-khae-akseab (“anti-inflammatory drug”) and yaa-pati-cheewana (“drug that fights microbes”). The term yaa-kha-chue is particularly confusing since it can also be used to indicate other types of drugs such as antifungal, anthelmintic, and antiprotozoal drugs. In addition, yaa-pati-cheewana is a technical term which is often used in AMR campaigns but is not commonly understood by lay people as we found in our study. That said, we should bear in mind that a good understanding of antibiotics does not necessarily translate into appropriate use. For example, a study in Lithuania found no correlation between knowledge of antibiotics and their use for self-medication [Our findings also showed that farmers, particularly smallholders, may have inadequate understanding of antibiotics and antibiotic resistance. As emerged in some interviews, this can partly be explained by the existence of different ways to refer to “antibiotics” in Thai, including ydication . The crodication .Further considering our findings, we can draw some lessons on policy and regulatory issues that need to be addressed to improve antibiotic use in the pig sector. In most countries, it is recognised that veterinarians and animal health authorities should play a key role in providing information about antibiotics and their appropriate use , 28. In Lastly, the role of pharmaceutical companies and market incentives to promote antibiotic use, including the provisions of gifts and other rewards, deserves particular attention –38. In sIn the future, rules on market access could help increase safety standards for the production, processing and sale of pig products , 44. In Yet tighter restrictions on the use of antibiotics may have a negative impact on the financial viability of smallholders. First, a large farm has higher capacity to replace antibiotic use with other preventive measures such as vaccination and improved infrastructure, while smallholders may not be able to afford these additional costs. Second, as we have seen, the pig production and supply chain in Thailand is structured in a way that limits access of smallholder farmers to the premium markets of antibiotic-free products. Large farm owners can produce antibiotic-free pork in their own farms, process the meat in their slaughterhouses and pack the final product in their retail shops, ensuring supply to premium markets from the farm to the fork. In contrast, interviews with farmers revealed that antibiotic-free pork and other pork are not processed and packed separately at external slaughterhouses. As a result, those who cannot afford the maintenance of a slaughterhouse may find it difficult to produce antibiotic-free meat.To our knowledge, this is the first qualitative investigation of factors influencing the use of antibiotics in pig production in a middle-income country. The study aimed to unpack the complexity of interactions among actors involved in antibiotic use, in the wider policy and regulatory context. However, limitations should be noted. Since AMR is a sensitive issue in Thailand, the number of farmers who agreed to participate in the study was rather small. In addition, findings cannot be generalised widely although we hope this study can provide useful insights to better understand antibiotic use in many other settings with similar livestock production systems, markets and regulatory environments.Our study highlights the need to improve antibiotic use for pig production in Thailand. Given that farmers had limited knowledge and awareness of antibiotics and AMR, access to veterinary services and reliable information about animal health needs to be improved, particularly for smallholder farmers. Innovative low-cost investment in biosecurity could result in better farm management leading to effective disease control, improved animal health and decreased reliance on antibiotics. Poor antibiotic prescribing could be addressed through continued professional development and training, stronger undergraduate curricula, and monitoring adherence to clinical guidelines. Controlling the commercial interests of the industry and health professionals in promoting antibiotics will also require the establishment, enforcement and monitoring of a code of conduct. Finally, the combination of private market access rules and control through regulations could be another effective instrument to govern the use of antibiotics where other approaches are ineffective.Additional file 1. Factors influencing the use of antibiotics for pig production in Thailand: Interview guide.


A sustainable solution for the global construction industry can be partial substitution of Ordinary Portland Cement (OPC) by use of supplementary cementitious materials (SCMs) sourced from industrial end-of-life (EOL) products that contain calcareous, siliceous and aluminous materials. Candidate EOL materials include fly ash (FA), silica fume (SF), natural pozzolanic materials like sugarcane bagasse ash (SBA), palm oil fuel ash (POFA), rice husk ash (RHA), mine tailings, marble dust, construction and demolition debris (CDD). Studies have revealed these materials to be cementitious and/or pozzolanic in nature. Their use as SCMs would decrease the amount of cement used in the production of concrete, decreasing carbon emissions associated with cement production. In addition to cement substitution, EOL products as SCMs have also served as coarse and also fine aggregates in the production of eco-friendly concretes. In the face of rapidly expanding urbanization, environmental sustainability represents a serious challenge for the construction industry, whose consumption of concrete requires a significant quantity of natural reserves worldwide and necessitates the development of alternative materials and sources. The fabrication of concrete consumes around 27 billion tonnes of feedstock, representing 4 tonnes of concrete for each person every year. By 2050, concrete production will be four times higher than in 1990. Aggregates and binder  represent around 60%–80% and 10%–15% of the total weight of concrete, respectively ..83].Sugarcane bagasse ash (SBA) is a by-product of producing juice from sugar cane by crushing the stalks of the plants see . The addUse of SBA as limited cement substitute reduces hydration heat, compared to that of the control reference. The decrease of semi-adiabatic temperature rise (°C) is proportional to the percentage of SBA replaced see . TherefoSBA incorporation improved concrete durability. A composite concrete with additions of different amounts of SBA was studied in the context of chloride attack see , as wellWastes of different sources have been investigated for their possibility in re-use, to reduce their environmental impact, in landfill volume and decomposition by-products . Sewage 2 (around 76%) content of POFA offers relatively high pozzolanic activity, when used as binder in concrete production. Even though a few performance parameters of concrete  are negatively influenced by POFA, several studies claimed that palm oil fuel ash may be appropriate in different applications [Palm oil fuel ash (POFA) is an important cash-crop in tropical countries, especially in Malaysia and Indonesia . For eveications ,92. It mications ,93,94. Mine tailings. The amount of mine tailings has grown excessively with an ever increasing demand for metal and mineral resources . Mining Therefore, depositories of tailings have lately gained global attention . However3) can form up to 99% of the total amount of this carbonated rock. Additional phases may also include SiO2, MgO, Fe2O3, Al2O3 and Na2O and, in minor ratio, MnO, K2O, P2O5, F, Cu, S, Pb and Zn [3, generating approximately 375,000 m3 of marble powder [Marble dust. Marble is a finely crystallized metamorphic rock originating from the low-intensity metamorphism of calcareous and dolomitic rocks. Calcium carbonate (CaCOb and Zn . For a le powder . Throughe powder . In the e powder .Construction and demolition debris (CDD) constitute one of the massive flows of solid waste generated from municipal and commercial activities of modern society . UsuallyA life-cycle assessment (LCA) is a method for assessing all the potential environmental impacts of a product, process, or activity over its entire life cycle . SeveralSustainability through re-use of accessible economic and social resources is a way to attain equilibrium with the environment, while ensuring long-term development and endurance . A benefWith regard to the LCA of concrete, 4 aspects should be considered: (1) design, (2) production/execution, (3) usage and (4) end-of-life disposal. Structural concrete has life expectancy differentiated by application, such as in pillars, beams and walls. While the durability over time for foundation or load-bearing structural elements is 50–300 years, the corresponding lifetime for cover walls is only 20–50 years . TherefoThe necessity for further LCA studies on the treatment and re-use of construction waste is clear. Instead of being released into the environment, it can be re-valorised in the life cycle of new designs of concrete. Use of waste like fly ash, blast furnace slag and other mineral admixtures as a binder for the production of concrete is becoming common in the construction industry. Replacing the principal factor responsible for the negative environmental effects of concrete is the key to generating an ecologically beneficial life cycle for concrete ,117,118.With regards to economic impact, regenerating alternative EOL materials for binder components in concrete would decrease the cost of construction without sacrificing performance. Other costs can also be considered, such as those concerning the source and transport of the alternative SCM materials, controlled combustion process and also savings as a result of diversion, such as disposal management. Consequently, the environmental advantages will reduce the enormous demand for Portland cement per unit volume of concrete, in addition to a concurrent and meaningful reduction in Greenhouse Gas (GHG) emissions ,119,120.2 through the calcination process, which contributes substantial adverse impact on global warming. Efforts are needed to design and develop more ecologically friendly concrete with improved performance in strength and durability.Concrete represents one of the most widely used construction materials worldwide by volume. Portland cement production is highly energy intensive, and emits significant amounts of CO2 and is present as spheres with average diameters about 100 times smaller than cement particles. The large specific surface of SF, ca. 20,000 m2/kg, is 10 to 20 times greater than that of other pozzolanic materials, imbuing it with high pozzolanic activity and fluidization properties.SCMs are frequently applied in concrete mixtures as a substitute for clinker in cement or cement in concrete. This approach yields concrete with reduced cost, decreased environmental impact, higher long-term strength and better long-term durability. Presently the two most common SCMs are silica fume and fly ash. As a by-product of the silicon and ferrosilicon alloy fabrication, SF contains more than 90% SiOFA has also been widely used in concrete mix design, due to its growing availability and substantial environmental complications appeared by release of fly ash. Physical characteristics of FA can differ on the nature of coal, rank, mineral matter chemistry and mineralogy, furnace design, furnace operation and method of particulate control, while chemical characteristics are relatively insensitive those factors. FA has been used in the manufacturing of bricks, concrete and cement-composites like columns, beams, slabs, columns, sheets, pipes, wall panels, etc. Typically, about 25% of FA is used as a substitute for cement to achieve effective final products. FA increases durability, workability, density and workability of concrete, while simultaneously decreasing water demand, porosity and permeability of concrete.In the present, the use of industrial EOL materials in concrete has been demonstrated. However, it is clear that more research is needed to assess the feasibility of long-term performance, develop more ecologically sound production, in addition to quality assessment of these materials. When ashes of high quality can be regularly obtained with reduced financial and most importantly environmental costs, their use in the engineering domain will become more widespread. Technical and economic performances of alternative SCM is evident, proving that along with the studying of the material’s mechanical and physico-chemical properties, the review of its life cycle is as well important and will mention whether it will be environmentally feasible to apply the SCM admixture at the total scale of the life cycle of concrete.


Recently, 3D concrete printing has progressed rapidly in the construction industry. However, this technique still contains several factors that influence the buildability and mechanical properties of the printed concrete. Therefore, this study investigated the effects of the nozzle speed, the interlayer interval time, the rotations per minute (RPMs) of the screw in the 3D printing device, and the presence of lateral supports on the buildability of 3D concrete printing. In addition, this paper presents the results of the mechanical properties, including the compressive, splitting tensile, and flexural tensile strengths of 3D printed concrete. The buildability of 3D printed structures was improved with an extended interlayer interval time of up to 300 s. The printing processes were interrupted because of tearing of concrete filaments, which was related to excessive RPMs of the mixing screw. The test results also showed that a lateral support with a wide contact surface could improve the resistance to buckling failure for 3D printed structures. The test results of the mechanical properties of the 3D printed concrete specimens indicated that the compressive, splitting tensile, and flexural tensile strengths significantly depended on the bonding behavior at the interlayers of the printed specimens. In addition, although metal laths were expected to improve the tensile strength of the printed specimens, they adversely affected the tensile performance due to weak bonding between the reinforcements and concrete filaments. The 3D printing technique has become promising for prefabricated structures because of its outstanding flexibility in both architectural and structural designs . WithoutAlthough the 3D printing method is considered a promising technique, some factors still influence the printing performance. For example, the printing performance is strongly dependent on the fresh properties of concrete, such as its rheology and green strength ,14,15, aPanda et al.  investigThe effect of the interlayer interval time (delay time) during 3D concrete printing also has a significant influence on the buildability as well as the interlayer bonding strength of filaments. According to Le et al.  and SanjMoreover, the printed structure may collapse suddenly by buckling during printing; the buckling behavior depends on the geometry and support conditions of the structure. Thus, lateral support or reinforcement is needed ,24. For In addition, the anisotropic strength of 3D printed concrete is a concern because the printing direction significantly affects the material properties of 3D printed concrete in the hardened state ,26,27,28Based on previous studies, the aim of this study was to investigate the buildability of 3D printed concrete during printing and the mechanical properties of the 3D printed concrete in a hardened state. The effects of the nozzle speed, interlayer interval time, and presence of lateral support on the buildability of the 3D concrete printing were investigated. To investigate the mechanical properties of 3D printed concrete, compressive, splitting tensile, and flexural tensile tests in three different loading directions were carried out. Finally, the mechanical properties of the monolithic specimens and printed specimens were compared.3, as shown in Currently, several printing techniques have been applied in building construction, such as contour crafting , Apis-CoTo investigate the buildability and mechanical properties of 3D printed concrete, ten concrete structures were printed, as listed in Three structures, namely, S1, S2, and S3 in Group 1, were printed to investigate the effect of the interlayer interval time and rotations per minute (RPMs) of the mixing screw on the buildability of the structures. Accordingly, the three structures in Group 1 had the same shapes and dimensions but different interlayer interval times or RPMs of the mixing screw.Three structures, namely, S4, S5, and S6 in Group 2, were printed to investigate the effect of lateral supports inside walls on the buildability of the structures. Accordingly, wall members of the three structures were supported laterally by members with zigzag shapes inside walls. Structures S4 and S5 had the same rectangular wall dimensions, but the details of the connected parts between the wall and lateral supports were different from each other. For structure S4, the wall and lateral supports were connected to the wall by point contact, as shown in Four structures, namely, S7 through S10 in Group 3, were printed to investigate the effect of the interlayer interval time on the buildability of the structures and mechanical properties in the hardened state of the 3D printed concrete. Among these four structures, structures S7 and S8 were duplicates, and structures S9 and S10 were also duplicates except for the interlayer reinforcement. The four structures were printed with the same printing process, as shown in 3 was used for the mixture. Additionally, two types of cementitious materials, namely, silica fume  and class C fly ash , were added to the mixture. To improve the extrusion and bonding properties, SF with a SiO2 content of 91.3% was used as a supplementary cementitious material. Class C FA used in the mixture had a density of 2.26 g/cm3 and a loss on ignition of 2.8%. Sand with a size range from 0.16–0.2 mm was selected to ensure good extrusion during the printing process. To increase the concrete filament extrusion under the low water-binder ratio of 0.29, a high-performance water-reducing agent  was added to the mixture. Finally, the mixture included a viscosity agent to prevent segregation of the materials and enhance the viscosity of the mixture.The mixture used for the 3D printing process is given in The repeatability of the process is a critical requirement for 3D printing technology. The width, height, and material characteristics of the printed structures should remain almost the same for each printing process. To achieve repeatable printing in this study, the nozzle height and speed, concrete pumping rate, and RPMs of the mixing screw were controlled by an accurate printing device. Moreover, the test structures were printed on a stable platform. A nozzle height of 10 mm from the existing printed layer was maintained during the printing process. In addition, to control the quality of the mixture, the properties of the materials in the fresh state were measured.The rheological properties of printing concrete primarily affect extrusion. Therefore, the fluidity and extrusion rate of concrete were measured before printing the structures. The fluidity of the concrete filament was estimated by a flow table test according to ASTM C 230 . The extThe measurement of early-age mechanical strength is one of the possible ways to find the stiffness of printing materials. Green strength measurement by a uniaxial unconfined compression test on cylindrical samples has been found to be useful in concrete printing applications. Voigt et al.  found thFor green strength measurement, the specimen preparation and testing process should be designed to minimize unintentional breakdown of the thixotropic behavior of the concrete . MoreoveThe critical criterion for fabricating concrete structures via 3D printing is the vertical deposition of filament layers. The buildability is a significant parameter to evaluate the printable performance of concrete filaments. The buildability refers to the resistance of the deposited fresh concrete to deformation during construction and the ability of the concrete to retain its extruded shape . The 3D The buildability of 3D printed concrete structures was investigated based on the layer deposition process. Among the six S1 through S6 structures, S1, S2, S4, and S6 collapsed suddenly, as shown in To investigate the influence of the interlayer interval time on the buildability of the 3D printed concrete, three different nozzle speeds of 50, 80, and 100 s and different structural shapes were applied to print the concrete structures, as shown in First, structures S1, S2, and S3 were printed with the same dimensions of 1500 mm × 300 mm along the centerline of the wall but with different nozzle speeds. Due to the different nozzle speeds, structure S1 was printed with an interlayer interval time of 36 s, while structures S2 and S3 were printed with an interlayer interval time of 45 s. The maximum number of printed layers in structures S1, S2, and S3 were 19, 49, and 29, respectively. The maximum number of printed layers upon the collapse of structure S1 was much lower than those of structures S2 and S3. Therefore, the test results showed that the buildability of the 3D concrete printed structures increased as the interlayer interval time increased. According to previous studies ,37,38,39Structures S2 and S3 were printed with the same interlayer interval time but with different RPM values of the screw in the storage bin during printing of the structures. The printing of structure S3 was stopped when tearing of the filaments in the structure in the top layer was observed, as shown in The buildability of structures S5 and S7, which had similar geometries, was also compared to investigate the buildability of 3D printed concrete at different interlayer interval times. Structure S7 with an interlayer interval time of 300 s was printed up to 52 layers, whereas structure S5 with an interval time of 57 s was printed up to 28 layers. The comparison also showed that an increased interlayer interval time favorably affected the buildability of the printed concrete.The different interlayer interval times in structures S6 and S9 were compared because the two structures had the same long wall length of 500 mm between lateral supports. Structure S6 was printed with an interval time of 30 s, while the interlayer interval time of structure S9 was extended to ten times that of structure S6. Structure S6 was stacked up to 33 layers and then collapsed by buckling along the long wall. Moreover, structure S9 was printed up to 52 layers, and then printing of the structure was stopped because it was to be used for investigating the mechanical properties of the concrete in the hardened state.Therefore, a comparison of printed structures with interlayer interval times ranging from 36 to 300 s showed that an increased interlayer interval time favorably affected the buildability of the concrete. The interlayer interval time of the printing process influenced the green strength of the 3D printed concrete. If the interlayer interval time was too short, the green strength of the 3D printed concrete was not high enough to support the upper layers, which might lead to early collapse of the structure, and vice versa.The 3D printed concrete structures in Group 1 in this study failed by buckling, so it was important for the 3D printed concrete structures to resist buckling. The lateral supports printed inside the structure could enhance the resistance to buckling failure along the long wall of the structures. Two types of zigzag lateral supports were printed inside structures S4 and S5, as presented in Structure S4 contained lateral supports that were printed inside the structure and connected to the long wall by a contacting point. Structure S5 contained lateral supports inside the structure, the arrangement of which was similar to that in structure S4, but they were connected to the long wall by a contact with a width of 100 mm.The test results showed that structure S4 was printed up to 22 layers and then collapsed by buckling failure along the long wall. Moreover, 28 layers were stacked in structure S5, and then the printing process was interrupted because of the tearing of the concrete in the top layer, as shown in Similarly, structure S6 was printed with lateral supports that were connected to the long wall by contact points with a width of 100 mm. Structure S6 was stacked up to 33 layers prior to collapse, although it was printed with a shorter interlayer interval time of 30 s than that of 55 s for structure S4. The number of printed layers in structure S6 was higher than that in structure S4.Structure S6 failed due to buckling because this structure was printed with a short interlayer interval time.Therefore, the zigzag-shaped lateral supports printed inside the structure, especially with long connecting widths, could increase the resistance to buckling failure in 3D printed concrete structures. The test results in this study are in good agreement with those of a previous study , where 3A numerical model was developed to predict different failure modes based on the material properties of the concrete in the fresh state and on the failure criterion by Wolfs et al. . AccordiThis study originally focused on the experimental program and discussion of the test results in terms of buildability. Prediction of the failure mode or numerical resistance for the structures printed in this study could not be performed because the heterogeneous strength and stiffness characteristics of the concrete used in this study, which are necessary to analyze the numerical resistance to failure, could not be estimated from the green strength test. Therefore, numerical predictions of failure modes based on the developed model should be investigated in a future study.In this study, after the printed structures were hardened, the walls of the 3D printed structure in the hardened state from Group 3, as shown in A typical representation of specimens cut from a 3D printed concrete wall is shown in In addition, the monolithic specimens were cast in dimensions of 50 mm × 50 mm × 50 mm for the cubic specimens and 40 mm × 40 mm × 160 mm for the prismatic specimens, as proposed in ASTM C109/C 109M-07 and C348-18 ,42. The Unlike the monolithic specimens, the printed specimens had anisotropic mechanical properties that depended on the different loading directions; this dependency was based on the layer stacking directions of the 3D printed concrete. Accordingly, the printed specimens were tested in three mutually perpendicular loading directions, as shown in l is the length (mm), b is the width of the specimen (mm), and P is the maximum load (N).The compressive strength test was performed on the cubic specimens. Before the compressive strength testing of the monolithic and printed specimens was performed, the lengths of all sides of the specimens were measured. The compressive strengths of the printed specimens were measured in three loading directions, namely, I, II, and III. However, loading directions II and III were actually the same, and thus, the compressive tests were performed in loading directions I and II. For each loading direction, five monolithic and printed specimens were tested for their compressive strengths in accordance with ASTM C109/C 109M-07 . The coml is the length of line contact of the load (mm), b is the nominal cross-sectional dimension (mm), and P is the maximum load (N).The splitting tensile strength test was also determined for the cubic specimens. For the printed specimens, splitting tensile tests were conducted in three loading directions, namely, I, II, and III. For each loading direction, five monolithic and printed cubic specimens were tested for their splitting tensile strengths in accordance with ASTM C 496/C 496M-04 . The spll is the distance between the supports (mm), b is the length of the squared section of the prism specimen (mm), and P is the maximum load (N).For the flexural tensile test, the test in loading direction III could not be performed because of problems encountered while cutting the specimens out of the 3D printed structures. Five prismatic specimens were used for the flexural tensile test in each loading direction (I and II) in accordance with ASTM C348-18 . The fleAfter five specimens were tested for each strength, the means and standard deviations of the test results were calculated to estimate the strength properties of the monolithic and printed specimens.Compressive strength tests were performed for both the monolithic and printed cube specimens. The printed specimens were categorized into those without metal lath reinforcement and those reinforced by metal lath reinforcement. The compressive test results are given in The compressive strength of the monolithic specimen was 72.8 MPa, while those of the printed specimens without metal lath reinforcement in loading directions I and II were 23.5 and 31.0 MPa, respectively. For the printed specimens reinforced by the metal lath, the compressive strengths in loading directions I and II were 24.6 and 24.0 MPa, respectively. The compressive strengths of the printed cubic specimens ranged from approximately 32.3 to 42.6% lower than those of the monolithic specimens.For loading direction I, the compressive strengths of the printed specimens with and without metal lath reinforcement showed similar values. The failure patterns were accompanied by the propagation of vertical cracks over the height of the specimens, as shown in For loading direction II (or III), the failure of the printed cubic specimens resulted from interface failures between the layers. The failure pattern also indicated that the compressive strengths were highly dependent on the bonding capacity at the interlayers of the printed specimens because the specimens in this loading direction were subjected to lateral deformation under vertical compressive loading.The compressive strength of the printed specimens without a metal lath was greater than that of the specimens reinforced by a metal lath. This implied that the bonding performance of the printed specimens without a metal lath at the interlayers was higher than that of the printed specimens reinforced by a metal lath at the interlayers. Metal lath reinforcements at the interlayers were expected to improve the bonding and tensile performance of the 3D printed concrete. In contrast, the metal lath reinforcement adversely affected the interlayer adhesion performance due to weak bonding between the reinforcement and concrete filaments. The failure of the printed specimen reinforced by the metal lath shown in Splitting tensile testing was performed on both the monolithic and printed specimens in different loading directions. A comparison of the splitting tensile strengths for the monolithic and printed specimens is shown in The splitting tensile strengths in loading directions I and II of the printed specimens with and without metal laths were not significantly different. Therefore, the interlayer reinforcement hardly affected the splitting tensile strength, although the metal lath reinforcement at the interlayers was expected to improve the splitting tensile strength of the printed specimens. The failure pattern of the printed specimens in loading direction II is shown in The effect of the imperfect adhesion between the concrete filaments and reinforcements on the tensile strength was also observed in the splitting tensile strength in loading direction III. The splitting tensile strength of the specimens reinforced by the metal laths was lower than that of the specimens without the metal laths. The test results were different from the expectation that the metal lath reinforcement at the interlayer would increase the splitting tensile strength of the printed specimens in this loading direction. The failure pattern of the printed specimens in loading direction III is shown in Finally, the test results in this study implied that the bonding conditions between the concrete filaments and reinforcements at the interlayers played a significant role in the splitting tensile behavior. Therefore, the adhesion between the concrete filaments and reinforcements should be confirmed to improve the tensile behavior of 3D printed concrete structures.The printed prismatic specimens with and without metal laths were tested in two different loading directions, namely, I and II. The flexural strength testing of specimens in loading direction III was not performed because of difficulties in preparing those specimens. A comparison of the flexural tensile strength results for the monolithic and printed specimens is shown in The flexural tensile strength of the monolithic specimen was 11.9 MPa, while those of the printed specimens without metal lath reinforcement were 6.5 and 6.1 MPa in loading directions I and II, respectively. The test results show that the flexural tensile strengths of the printed specimens without reinforcement were approximately half that of the monolithic cast specimens.In addition, the flexural tensile strengths of the printed specimens reinforced by metal laths were 18.5 and 11.0 MPa for loading directions I and II, respectively. The flexural tensile strength of the printed specimens without metal lath reinforcement was lower than that of printed specimens reinforced by metal laths. This was because metal lath reinforcement in the tensile zone acted as a tensile reinforcement. Accordingly, the metal lath reinforcement increased the flexural tensile behavior of the 3D printed specimens in both loading directions I and II.However, the flexural tensile behavior in loading direction II, as shown in The interlayer interval time significantly influenced the buildability of 3D printed concrete. The test results showed that an extended interlayer interval time of up to 300 s contributed to the green strength of the 3D printed concrete and thus increased the buildability of the 3D printed concrete.The 3D printed concrete structures with lateral supports could increase the resistance to collapse due to buckling failure. In particular, a wide connecting width between the lateral support and the structure wall improved the capacity of layer decomposition in the 3D printed concrete.The compressive strengths of the 3D printed cubic specimens were 32.3~42.6% lower than those of the monolithic specimens. In addition, the weak bonding performance between the reinforcement and concrete filaments caused the low compressive strength of the printed specimens in direction II.The splitting tensile strength of the 3D printed concrete specimens was 11.1~39.7% lower than that of the monolithic specimens, depending on the loading directions. The splitting tensile failure was accompanied by debonding between the printed layers, which implied that the bonding performance between the concrete filaments and reinforcements should be confirmed when interlayer reinforcements are included.The flexural tensile strengths of the 3D printed specimens without reinforcements at the interlayers were approximately half that of the monolithic cast specimens. The flexural tensile strength of the printed specimens was improved by the metal lath reinforcements. The failure pattern also revealed that the bonding between the interlayers and reinforcements might influence the flexural strength.The buildability and mechanical properties of 3D printed concrete were investigated in this study. Based on the extensive experimental results, the following conclusions can be drawn:


A detailed comparative analysis of mechanical and physical features of the concrete composite with the addition of recycled steel fibres (RSF) in relation to the steel fibre concrete commonly used for industrial floors was conducted. A study was carried out using micro-computed tomography and the scanning electron microscope to determine the fibres’ characteristics, incl. the EDS spectrum. In order to designate the full performance of the physical and mechanical features of the novel composite, a wide range of tests was performed with particular emphasis on the determination of the tensile strength of the composite. This parameter appointed by tensile strength testing for splitting, residual tensile strength test (3-point test), and a wedge splitting test (WST), demonstrated the increase of tensile strength (vs unmodified concrete) by 43%, 30%, and 70% relevantly to the method. The indication of the reinforced composite’s fracture characteristics using the digital image correlation (DIC) method allowed to illustrate the map of deformation of the samples during WST. The novel composite was tested in reference to the circular economy concept and showed 31.3% lower energy consumption and 30.8% lower CO Due to the increasing EU car production, the problem of end-of-life tyre utilisation in an eco-friendly way is still growing. It is estimated that around 3.3 million tons of used tyres per year in Europe require recycling. In EC countries, restrictive regulations have been introduced to support solutions for the recovery, recycling or reuse of tyres towards the reduction of their harmful impact on the environment. In accordance with the Landfill Directive (1999/31/EC), the disposal of end-of-life tyres to landfills is prohibited. The directive introduced a ban on the storage of all used tyres since 2003, and since 2006 this ban included additionally crumbled tyres. Another End-of-Life Vehicle Directive (2000/53/EC) ordered the removal of tyres from vehicles before scrapping, and the Waste Incineration directive obliged cement plants using tyres as fuel to achieve lower limits for the content of pollutants in waste gases.Used tyres (end-of-life tyres ELT) are recycled in two ways: towards obtaining energy or material. Novel solutions for raw materials or innovative products resulting from ELT are desired. However, still, up to 64% of used tyres are subject to energy recycling, i.e., they are burned mostly in cement kilns .Due to the growing awareness of the need for sustainable development in the construction sector, new research has been conducted on the use of raw materials derived from tyre recycling processes. Tyre shredding in an ambient method is the most commonly used mode of ELT recycling. Pre-cut tyres are shredded in special granulators and rolling mills. Pneumatic separation is used to remove the textile fibres, and the steel fibres are removed by means of an electromagnet. Tyres are 100% recyclable. All tyre components, i.e., rubber, metals, and textiles, can be recovered. However, only rubber is widely reused in various commercial products, as evidenced by numerous studies published in the literature ,13,14,15The use of steel fibres is much more difficult compared to the rubber raw material due to their heterogeneity, irregular shape, and frequent rubber contamination. In the majority of tyre recovery plants using the ambient grinding method, steel collected from separators is contaminated with rubber by up to 10%. Together with irregular geometric characteristics, these are the key features that determine the suitability of recycled fibres for their further high-quality applications. Fibres from various tyre recycling plants were considered for further research, but only those obtained from the recycling process invented by KAHL Holding GmbH showed the lowest degree of pollution. It was noticed that the latest KAHL technology focused on the high effectiveness of rubber recovery, allowing obtaining steel fibres with no greater than 2% impurity a.Research on the methods of the valuable ELT steel application in the construction sector was conducted at numerous institutes. The majority of the studies focused on fibre concrete as one of the possible areas for the use of steel fibres from recycled tyres. According to numerous publications ,17,18, tStrengthening the concrete matrix with heterogeneous RSF fibres made of high-quality steel can improve the concrete properties. However, in most cases, the researchers had encountered a problem of high rubber contamination and developed a pretreatment method to clean fibres before their use in concrete ,20,21. TThe main objective of the research was to develop the method of valuable steel tyre cord application in the construction sector. This paper demonstrates the results of studies conducted in order to prove the feasibility of replacing industrially produced fibres (ISF) with RSF fibres in the concrete composite commonly used for industrial floors.In order to determine the full characteristics of the designed composite with RSF fibres, 3 different concrete mixes were designed based on the components previously selected within preliminary tests and recommendations for the design of industrial concrete floors.2/g was used as the most commonly used cement in Poland for industrial floors. A PCE polymer superplasticiser  was used added at an amount of 1%.CEM II/B-S 42.5N-NA low-alkali slag Portland cement  with an average specific surface area of 4110 cmGlacial origin aggregates found in Pomerania  were used to make all concrete mixtures. Natural washed aggregates with fractions 0/2, 2/8, and 8/16 were used. A sand point equal to 43% was assumed. For gravel, the percentage advantage of natural aggregate fraction 2/8 (60%) over the 8/16 (40%) mm fraction was adopted, as it is a solution reducing the cost of fibre concrete and supporting environmental protection due to the prevalence of fine aggregates occurrence in northern Poland.The use of almost pure fibres RSF without any pretreatment was essential in research. RSF fibres a are chaThe structural and chemical analysis of RSF fibres was performed using a Field Emission Gun (FEG) scanning electron microscope , the operation of which is based on Energy Dispersive X-ray Spectroscopy (EDS) analysis. Use of a scanning microscope  combines the highest quality of imaging with chemical and structural analysis in the nanometer scale. EDS analysis allowed for the surface and volume identification of chemical elements included in the composition of tested RSF fibres.SEM images  taken byThe EDS analysis showed that the chemical composition of some RSF fibres contains percentages of copper and zinc . The prethe percentage distribution of the fibre length,percentage distribution of the diameters of the fibres,percentage distribution of fibre slenderness,percentage distribution of the fibre orientation.The 3D Skyscan 1173 X-ray microtomography  was used to perform a comprehensive analysis of the characteristics and distribution of fibres in the concrete. X-ray microtomography (μCT) is a 3D imaging technique that uses X-rays to create cross sections of a physical object to recreate a virtual model (3D model) without destroying the sample. The following parameters were determined as part of the research:The research was carried out on scans of 75 mm side samples made of RSFRC concrete. The maximum size of the test samples was narrowed down to a cube with a side of 70 mm to eliminate boundary disturbances. As part of the analysis of the characteristics of fibres, the following parameters were determined: relative frequency of the fibre length and relative frequency of the fibre diameter.efl of anchoring the fibres. At the same time, it was found that about 90% of RSF fibres have a diameter in the range of 0.1 to 0.4 mm  b with a Concerning the determination of the physical and mechanical characteristics of the designed composite, a wide range of tests was carried out on unreinforced concrete (NC), reinforced with ISF fibres (SFRC) and RSF fibres (RSFRC). The composition of the concrete mix was determined in accordance with the recommendations for the design of industrial concrete floors and based on the conclusions of preliminary tests.3 and the factor w/c = 0.5. The additional design assumptions were as follows; S3 consistency class of concrete mix, concrete class of min. C25/30; adoption of RSF fibres with a content of 50 kg/m3 and a comparatively ISF fibres with a content of 25 kg/m3. The application of double content of RSF fibres versus ISF fibres was conducted due to previous study on geometrical characteristics of the recycled fibres, where it was demonstrated that only about 60% of RSF fibres improve the parameters of the composite.The recipe of each mix  was initThe study was initiated by assigning the rheological properties of the concrete mix. The research was conducted on the determination of the consistency, the air content and density of concrete mixes which contained fibres (ISF and RSF) or were plain. The consistency of the concrete mix was tested by the Abrams cone slump method in accordance with the EN 12350-2 standard, the air content was determined using the pressure method based on the Boyle–Mariott law in accordance with the EN 12350-7 code and the concrete mix density was tested in accordance with the EN 12350-6 standard.The next stage of the research was concerned with the determination of the parameters of concrete composites. It contained the analysis of the distribution of ISF and RSF fibres in studied concrete mixes. The imagines of the distribution of ISF and RSF fibres in the samples of concrete composites were taken, and the orientation of their position in concrete was determined in relation to the Cartesian system. The research was carried out on 3D scans of 75 mm side samples made of RSFRC and SFRC concrete . The expIn order to designate the full characteristics of the physical and mechanical features of the proposed new composite, a wide range of tests was performed, starting with the compressive strength test. That test was carried out on 6 cubic samples with a side of 150 mm for each of the 3 series, in accordance with the EN 12390-3 standard, using CONTROLS testing machine  enabling electronic recording of the results.strength-CMOD for the tested samples.Assigning other mechanical properties, particular emphasis was put on the determination of the tensile strength of the composite. This parameter was appointed by three different methods: tensile strength testing for splitting (Brazilian method), residual tensile strength test (3-point test) and testing of tensile strength by a wedge splitting (WST method). The last two methods allowed us to determine the dependence of The Brazilian method of splitting a concrete sample during compression is the most commonly used method of testing concrete tensile strength. According to the EN 12390-6 standard, tests were performed on cubic samples with a side of 150 mm, 6 samples for each of the 3 series after 28 days of maturation, using CONTROLS testing machine.In the case of composites reinforced with steel fibres, the determination of the residual tensile strength is the key test used in the calculation of structural elements made of fibre concrete according to the recommendations of RILEM TC 162-TDF. The addition of steel fibres is intended to transfer stresses in the tension zone after the first crack has appeared. Tensile strength was measured in accordance with EN 14651 code. The method is performing a 3-point test  in ordermax.The wedge splitting test (WST) is an alternative method of determining the σ-CMOD relationship. The test was developed in 1986 by H.N. Linsbauer and E.K. Tschegga . Since t3 was fixed, according to the procedure described in EN 13892-3. Abrasion was determined by the loss of height and volume of the sample determined on the basis of the weight loss of the tested sample.Due to the intended use of the designed composites in industrial concrete floors, additional tests were performed on the impact of RSF fibre addition on adhesion and abrasion of concrete. The adhesion of concrete layers was determined by the pull-off test in accordance with EN 1542 code. The test was performed for 7 samples from each of the 3 series of concrete. The abrasion resistance was determined using a Boehme dial, over which a test specimen with dimensions 71 × 71 × 71 mmZ-axis , residual tensile strength test (3-point test) and testing of tensile strength by a wedge splitting (WST method). Results of these tests are presented in In the case of tensile strength at splitting, the average strength of ISF fibre modified concrete is 31% higher, and in the case of RSF fibre modified concrete, it is 43% higher than the average strength of reference concrete without fibres.F-deflection) and the tensile stresses on the opening width of crack (σ-CMOD) for composites without fibres and modified with ISF and RSF fibres with a crack width up to 4 mm. To better illustrate the behaviour of samples in the early deformation phase, F-deflection relationships for non-fibre (NC) and fibre (SFRC and RSFRC) composites obtained during residual strength testing at a deflection of 0.4 mm, which shows differences in the behaviour of the samples before scratching.The 3-point bending test allowed to determine the dependence of the applied force on the deflection  versus R1kf = 2.29 MPa for SFRC composites. A similar relationship applies to the residual strength R3kf corresponding to a crack opening equal to 3CMOD = 2.5. For RSFRC samples, the residual strength R3kf is 1.26 MPa, and for SFRC samples the residual strength R3kf is significantly lower, it is 0.91 MPa.The  diagram  illustra diagram , RSFRC cNTσ of NC concrete constituted about 60–70% of the tensile strength by splitting of concrete reinforced with steel fibres (SRFC and RSFCR). The values of the corresponding maximum tensile stress NTσ for concrete: NC, SRFC and RSFCR are shown in σ-CMOD relationship (The tensile strength test by splitting referring to the WST method showed the strength tionship  demonstrmax behind the vertex (85% after F) indicates much faster crack penetration in concrete without fibres. In addition, it was observed that the crack location zone was more curved in the case of concrete with ISF fibres than RSF fibres  was used to determine the map of sample deformation during stretching by wedge splitting test (WST). By analysing the places of deformation concentration, the sample cracking zone was located. Comparison of deformation propagation map images in the elastic zone , residual tensile strength test (3-point test) and a wedge splitting test (WST method) have confirmed the increase in tensile strength when modifying concrete with RSF fibres .F-deflection relationships at the bending test of fibre concrete elements  to 70% (tensile strength determined in the splitting test during the WST test) relative to NC concrete was observed for all measuring methods  was observed for the composite modified with RSF fibres. The test results confirm that the designed RSFRC concrete meets the requirement for industrial floors, where it is recommended that the value of the surface tensile strength tested by the pull-off test be above 1.5 MPa .The results of tests on concrete abrasion resistance showed a significant influence of steel fibres on composite abrasion resistance. The test carried out on the Boehme disk showed a volume loss for the SFRC samples smaller by 11%, and for the RSFRC samples smaller by 15% compared to those obtained for NC concrete .2 emission for the concrete recipe with RSF fibres  significantly affecting the natural environment. Replacing industrially produced steel fibres with waste fibres obtained in the recovery of rubber from used tyres may impact on the reduction of energy consumption and greenhouse gas emissions. Considering the extension of reused components in tyre recycling process, the proposed solution fully responds to the Circular Economy concept.Comparing the energy consumption and COF fibres  to ISF fF fibres  shows 31In this study, the possibility of replacing industrial fibres in concrete with RSF fibres treated as waste from tyre recycling processes was demonstrated. To estimate the efficiency of RSF fibre concrete, a wide range of strength tests was performed, emphasising the determination of the tensile strength of the composite. The research and analysis showed that RSF fibres have parameters comparable to those of industrial steel fibres used to reinforce concrete industrial floors.The following conclusions can be drawn from the research described in this paper.3) versus ISF fibres (25 kg/m3) in proposed concrete mix.The geometric examination of the fibres confirmed that the fibres from the recycling of tyres used for the tests are characterised by varying lengths, diameter, slenderness and shape. Such a mixture can be classified as hybrid fibres, which show higher efficiency in concrete than fibres of the equal length. However, considering the geometrical characteristics of the fibres, is was shown that only about 60% of the RSF fibres in concrete improve the parameters of the composite. This indicates the application of double content of RSF fibres , consistency (reduction by one class), air content in the mix, and strength parameters. The addition of steel fibres can enhance concrete performance, especially the compressive strength (by 13.5% for composite modified with ISF fibres and by 22% for concrete modified with RSF fibres). Tensile strength tests carried out by three methods: Brazilian splitting, bending (3-point test), and WST splitting confirmed the increase in tensile strength when modifying concrete with RSF fibres, respectively, by 43%, 30% and 70% in comparison to the average strength of reference concrete without fibres. Moreover, RSF fibres significantly improved the abrasion resistance of the composite (by 42%).The calculation of environmental parameters of concrete with RSF fibres showed significantly lower energy consumption (by 31.3%) and lower CO2 emission (by 30.8%) than concrete with ISF fibres due to the energy-consuming production processes of industrial fibres.The main limitation for the substitution of ISF fibres with fibres derived from the recycling of tyres in concrete was recognised in improper distribution of irregular RSF fibres and the threat of fibre clusters, i.e., “balls”. However, the 3D images of samples had demonstrated the lack of clusters of RSF fibres and therefore proved that no additional requirements are needed for mixing the components during the production of proposed fibre concrete.2 emissions and waste recycling have great potential for rapid commercialisation. Therefore, further investigations are recommended to explore the possibility of utilising RSF as an eco-friendly material to mitigate the challenges of the sustainable construction industry.The above-mentioned conclusions prove the possibility of replacing industrial fibres with RSF fibres without reducing fibre concrete’s strength parameters. In addition, due to the growing public awareness of the need to protect the environment and the climate consequences associated with excessive greenhouse gas emissions, all solutions to reduce CO


High-performance concrete has low tensile strength and brittle failure. In order to improve these properties of unreinforced concrete, the effects of adding recycled polypropylene fibers on the mechanical properties of concrete were investigated. The polypropylene fibers used were made from recycled plastic packaging for environmental reasons (long degradation time). The compressive, flexural and split tensile strengths after 1, 7, 14 and 28 days were tested. Moreover, the initial and final binding times were determined. This experimental work has included three different contents  for two types of recycled polypropylene fibers. The addition of fibers improves the properties of concrete. The highest values of mechanical properties were obtained for concrete with 1.0% of polypropylene fibers for each type of fiber. The obtained effect of an increase in mechanical properties with the addition of recycled fibers compared to unreinforced concrete is unexpected and unparalleled for polypropylene fiber-reinforced concrete (69.7% and 39.4% increase in compressive strength for green polypropylene fiber (PPG) and white polypropylene fiber (PPW) respectively, 276.0% and 162.4% increase in flexural strength for PPG and PPW respectively, and 269.4% and 254.2% increase in split tensile strength for PPG and PPW respectively). Due to high demand, the global production of fossil-based plastics has grown from 1.5 million tons in 1950 to 288 million tons in 2012 and 322 million tons in 2015. It can be assumed that the upwards trend will continue ,5. There2 [The wide application of plastics in most daily activities increases the volume of plastic waste . Approxi2 ) 13], s, s2 [13]2  and othe2 ,16,17,182 .An effective way to improve this condition is the management of polymer materials in various branches of the economy. Nowadays, large amounts of plastic waste are used in the construction industry. Concrete plays an important role in the process of recycling waste materials ,22, especf = 38.10 MPa). Tough fibers with 18 μm diameter, 9 mm length, and aspect ratio 500, of 0.91 g/cm3 and with low tensile strength  were used. Moreover, ordinary Portland cement of Grade 43 was used. A percentage increase in compressive strength ranging from 4 to 12% with the addition of 0 to 3% of fibers constructed of plastic waste was determined by Alsadey and Salem [Traditionally, fibers are used in concrete to improve its post-cracking performance by bridging cracks and preventing the initiation and propagation of shrinkage cracks ,28,29. T3 polypropylene fibers than unmodified samples. Similar results were obtained by Qin et al. [3) and the lower grain of aggregates: quartz powder (grain size 10–45 μm) and silica sand (grain size 150 ÷ 600 mm). The maximum value of compressive strength obtained by Li et al. [Li et al.  obtainedn et al.   and white polypropylene fiber (PPW)) were investigated. The fibers were made at the same process of recycling, but PPW were produced using an additional extruder applying a structure to their surface. Whereby, the findings of the study make an important contribution towards an effective and ecological solution of utilizing plastic waste (packaging waste) in concrete. The materials used in this study were Portland cement, water and a polycarboxylate deflocculant used as a hardening admixture. The industrial Portland cement was CEM I 42.5R, according to PN-EN 197-1:2011. Its chemical composition and physical properties, measured as per PN EN 196-6:2011, is given in UC = 4.8 and CC = 1.9).As a filler, quartz sand with fraction of 0.125–0.250 mm, 0.250–0.500 mm and 0.500–1.000 mm was used . The filIn order to increase the workability of the mix, chemical admixtures were added to fiber-reinforced concrete mixes. A chlorine-free, low-alkaline liquid chemical admixture based on an aqueous solution of modified polycarboxylic ethers (melamine and silanes/siloxanes) was used . The polTwo polypropylene fibers from waste materials were used . Both fiPolypropylene fibers of about 31 mm length (30.9 ± 0.5 mm for PPG and 31.2 ± 0.5 mm for PPW) and 1.000 microns in diameter were used. The tensile strength of fibers is about 520 MPa. Three different types of mortar mixes  were produced. The polypropylene fiber content was 0.5, 1.0 and 1.5 wt.% (by mass of the cement), marked in the article as 0.5PPG or 0.5PPW, 1.0PPG or 1.0PPW, and 1.5PPG or 1.5 PPW depending on the type of fiber (green—PPG or white—PPW). In total, seven different mixes were produced to investigate the effect of polypropylene fiber content on the properties of cementitious mix see . A constThe fibers were added to the cementitious mixture, after mixing other components for 2 min. The whole mixing time lasted for a maximum of 5 min. All samples were obtained in laboratory conditions (21 °C temperature and 50% humidity). The samples were stored in water according to PN-EN 12390-2:2019.The initial and final setting times and the drop cone test were determined. The initial and final setting times were measured with the Vicat apparatus .The workability of fresh concrete was determined using a slump cone according to PN-EN 12350-2:2019. The presented in article values are average values of five measured specimens for each mix.The mechanical properties of the mortar  were determined. The samples were tested using a Zwick machine . Compressive strength was measured on samples 100 mm × 100 mm × 100 mm, according to PN-EN 12390-3:2019 + AC:2012.Flexural strength was tested in a three-point bending set-up with beams 40 mm × 40 mm × 160 mm, according to PN-EN 12390-5:2019. The nominal distance between the supports was 100 mm. The rollers allowed for free horizontal movement. Split tensile strength was tested on a cylinder 0.15 m in diameter and 0.30 m in height, according to PN-EN 12390-6:2011.The above tests were carried out after 1, 7, 14 and 28 days of curing process to evaluate the behavior of the mix with two types of polypropylene fibers in time. The presented values are the average values of three samples for each mix.The distribution of the initial and final setting times for the mixes with different content of polypropylene fibers for two different types of fiber are presented in The influence of the fibers’ external structure is not apparent in tests. The surface of PPG is smooth, while the surface of PPW is irregular, which is due to the modification process of PPW . AdditioThe result of slump flow (SF) test were shown in The results of compressive strength for samples with the addition of 0.5, 1.0 and 1.5 wt.% of fibers (PPG or PPW) were shown in The highest values of compressive strength during the entire curing process were obtained for the samples containing 1.0 wt.% of polypropylene fibers. After one day of curing, the compressive strength for samples with 1.0% content of PPG was three times higher (55.0 MPa) than for the base sample (without fibers). After seven days, it was about 3.5 higher (75.0 MPa) than for the base sample. In the following days (14 and 28 days), the compressive strength of fiber-reinforced concrete was higher by approximately two times compared to unreinforced concrete, and was equal to 76.0 and 84.0 MPa respectively. For concrete with white polypropylene fibers (PPW), the values were about 5 to 10% lower than for samples with PPG and they were equal to 50.0 MPa after 1 day, 65.0 MPa after 7 days, 72.0 MPa after 14 days and 80.5 MPa after 28 days. It can be observed that with the addition of 0.5 wt.% of fiber, in 1, 7, 14 and 28 days compressive strength was increased compared to normal concrete by 134.3%, 136.4%, 59.1% and 46.5% for PPG, and 114.3%, 136.4%, 48.9% and 43.4% for PPW. With the addition of 1.0 wt.% of fibers, the increase in strength compared to unreinforced concrete is 214.3%, 240.9%, 72.7% and 69.7% for PPG, and 185.7%, 195.5%, 63.6% and 62.6% for PPW. With the addition of 1.5 wt.% of fibers, this increase is 191.4%, 204.6%, 56.8% and 43.4% for PPG, and 174.3%, 177.3%, 50.0% and 39.4% for PPW.Each time, higher values of compressive strength were observed for green polypropylene fibers (PPG), which were slightly longer and thinner  and withc,28f was achieved earlier than for unreinforced concrete (without fibers), between 1 and 7 days. R2 for Equations (1)–(6) were 0.9274, 0.985, 0.9931, 0.9252, 0.9754 and 0.9929, respectively. The relationship for plain concrete, marked as base, was the background in R2 = 0.9185.For all analyzed samples with different fiber content the required compressive strength It can be observed that the nature of the recycled fiber-reinforced concrete curing process is faster than for the reference concrete (without fibers). This allows it to be used in places where high strength is required fast. The faster stabilization in curing time with the addition of polymer was observed by Albano et al. . They recf = 84.00 MPa for PPG and 80.50 MPa for PPW) and/or an increase of compressive strength (69.7% for PPG and 63.6% for PPW) of fiber-reinforced concrete compared to normal concrete were lower. Bayasi and Zeng [and Zeng  obtainedand Zeng  observedand Zeng . Higher and Zeng .This effect of the addition of recycled fibers is unexpected and unparalleled in the results of other works. The properties of fiber-reinforced concrete depend on the type of fiber, its size and properties, aspect ratio, distribution of fibers and other features . The usetk,28 =f 15.6 MPa). In the following days, flexural strengths of all samples of fiber-reinforced concrete were higher than 28 days of flexural strengths of base concrete. The highest values of 7, 14 and 28 days of flexural strength were obtained for the samples with the addition of 1.0 wt.% PPG. They were equal to 26.9 MPa for 7 days, 48.4 MPa for 14 days and 58.8 for 28 days. These values are about 2.5, 3.5 and 3.8 times higher than for unreinforced concrete respectively and about 1.2, 1.5 and 1.4 times higher than for samples with the addition of 1.0 wt.% PPW. Mehta and Monteiro indicated that the inclusion of 1.25% steel fiber content caused flexural strength to increase by about two times [wo times . It can be observed that with the addition of 0.5 wt.% of fiber 1, 7, 14 and 28 days compressive strength was increased compared to normal concrete by 25.0%, 147.1%, 240.9% and 260.0% for PPG, and 56.3%, 88.2%, 111.4% and 140.0% for PPW. With the addition of 1.0 wt.% fibers, the increase in strength compared to the reference concrete is 31.3%, 152.9%, 252.3% and 276.0% for PPG, and 59.4%, 111.8%, 131.8% and 162.4% for PPW. With the addition of 1.5 wt.% fibers, this increase is 25.0%, 135.3%, 184.1% and 220.0% for PPG, and 50.0%, 85.9%, 113.6% and 148.0% for PPW. Mohammadi et al.  reportedFlexural strength increased with the increasing percentage of fibers for all samples of reinforced concrete up to a certain fiber content and then decreased. This trend is consistent with the observations of Singh  and DharThe results of split tensile strength for samples with the addition of 0.0%, 0.5%, 1.0% and 1.5 wt.% of fibers (PPG or PPW) are shown in It can be observed that with the addition of 0.5 wt.% of fibers, 1, 7, 14 and 28 days split flexure strength were increased compared to normal concrete by 284.8%, 237.2%, 241.6% and 222.7% for PPG, and 268.8%, 221.2%, 215.8% and 211.8% for PPW. With the addition of 1.0 wt.% of fibers, the increase in strength compared to the reference concrete is 315.2%, 276.3%, 246.5% and 269.4% for PPG, and 291.1%, 234.0%, 229.2% and 254.2% for PPW. With the addition of 1.5 wt.% of fibers this increase is 367.0%, 345.5%, 459.4% and 483.0% for PPG, and 347.3%, 305.1%, 351.0% and 412.7% for PPW. Split tensile strength increased with non-linear increasing percentage of fibers for all samples of reinforced concrete, regardless of the type of fiber .The obtained increase of split tensile strength is a novelty in research on polypropylene fiber-reinforced concrete. Dharan and Lal  obtained(1)The decrease in the slump flow with addition of PP fibers was observed, but all mixes were within slump flow class SF1;(2)The obtained 28 days compressive strengths of reinforced concrete were from 69.0 to 84.0 MPa for different content of fibers, what meet the requirements for high-strength concrete;(3)The increase in mechanical properties as an effect of the addition of recycled polypropylene fibers compared to unreinforced concrete is unexpected and unparalleled ;(4)The highest values of mechanical properties were obtained for concrete with 1.0 wt.% of polypropylene fibers for each type of fiber;(5)The higher values for all tested properties were determined for PPG fibers;(6)The nature of the recycled fiber-reinforced concrete curing process is faster than for the reference concrete (without fibers);(7)For all fiber-reinforced concrete samples the required compressive strength was achieved earlier than for normal concrete (between 1 and 7 days) which allows it to be used in places where high strength is required fast.The aim of the study was to assess the possibility of using fiber made from used (recycled) PP packaging as an alternative to traditional fibers used in reinforced concrete. This experimental work has included three different contents  for two types of macro-polymeric fibers (green polypropylene fiber PPG with smooth surface and white polypropylene fiber PPW with the surface structure applied). Based on the results of this experimental investigation, the following key conclusions can be drawn:The present work belongs to a wider research project aimed at developing environmentally friendly concrete according to sustainable development and the circular economy rules. Therefore, as part of further research, we plan to carry out tests for other types of cement, other types of plastic waste recycled fibers, and different contents and dimensions of those fibers, with particular emphasis on fatigue tests.


Antibiotic prescribing practices across the Veterans’ Health Administration (VA) experienced significant shifts during the coronavirus disease 2019 (COVID-19) pandemic. From 2015 to 2019, antibiotic use between January and May decreased from 638 to 602 days of therapy (DOT) per 1,000 days present (DP), while the corresponding months in 2020 saw antibiotic utilization rise to 628 DOT per 1,000 DP. Reports of increased antibiotic use during the COVID-19 pandemic have generally been from heavily impacted facilities or geographic regions and provide few details regarding patterns of antibiotic use.1–3 To provide a broader overview of changes in antibiotic use in a healthcare system with a long-standing enterprise-wide commitment to antibiotic stewardship, we compared patterns of antibiotic use throughout the VA health system from January through May 2020 with corresponding periods in prior years.Inpatient antimicrobial use has decreased in the Veterans’ Health Administration (VA) over the past decade.2 To reduce the impact of seasonal effects, only data from January 1 to May 31 for each year were included. Days of therapy (DOT) per 1, 000 days present (DP) were calculated and stratified by CDC-defined standardized antimicrobial administration ratio (SAAR) antibiotic classes.4Data on antibacterial use from 2015 through 2020 were extracted from the VA Corporate Data Warehouse for acute inpatient care units in all VA facilities excluding those that provide limited acute inpatient services using previously described methods.Because of changes in healthcare utilization that have accompanied the COVID-19 pandemic, we also examined changes in the total number of days of antibiotic therapy to provide insight into whether more days of therapy were being administered or whether the changes in therapy reflected the same amount of antibiotic use distributed across a smaller hospital population. To evaluate the impact of initial COVID-19 case burden, we conducted a subset analysis excluding facilities with the highest initial COVID-19 case loads . This study was approved by the VA Central Institutional Review Board.Data were available for 84 inpatient VA facilities. From 2015 through 2019, antibiotic use during January–May of each year decreased from 638 to 602 DOT per 1,000 DP  -defined SAAR classes , broad-spectrum agents used for community-onset infections , and broad-spectrum agents used for hospital-onset infections . Use of narrow-spectrum β-lactam agents decreased . Lesser changes were observed in the use of antibacterial agents predominantly used for resistant gram-positive infections . The greatest increases in the use of individual antibiotics  were for ceftriaxone , cefepime , doxycycline , and azithromycin .For the period of January–May in 2015 through 2019, the number of acute–care DP at all VA facilities was 1,245,309 ± 31,178 (mean ± SD), and the total antibiotic DOT were 770,799 ± 35,288 , but increases were also seen in the use of broad-spectrum antibiotics that are typically used to treat hospital-acquired pathogens.We have demonstrated a substantial increase in the density of antimicrobial utilization during the period of January–May of 2020 at 84 VA medical facilities, which largely negated the downward trend of antibiotic use achieved through antimicrobial stewardship efforts over the prior 5 years.In addition to considering the density of antibiotic use , we also evaluated total antibiotic use to partially account for decreases in healthcare utilization both for elective procedures and emergency conditions during the COVID-19 pandemic. The absolute number of antibiotic days decreased, albeit at a lesser rate than did the number of hospital days. However, although overall institutional use of antibiotics has decreased, the increased density of antibiotic use as measured by the use per patient day may still adversely impact patient-level outcomes and institutional antimicrobial resistance patterns.1 Another single-center study from Spain showed increased use of amoxicillin-clavulanate during the early phase of the pandemic, followed by later increased utilization of broad-spectrum antibiotics.2Our findings confirm and extend prior smaller-scale studies. A single-center study at an academic hospital in Virginia reported significantly increased use of ceftriaxone and azithromycin but not of other broad-spectrum antibiotics coincident with the onset of the pandemic.3 diversion of clinical resources from stewardship activities during a time of crisis, and an increased proportion of hospitalizations due to respiratory infections, which typically prompt antibiotic therapy. Our finding that increases in antibiotic use were generalized across the VA and not restricted to facilities in areas with the highest case burden of COVID-19 suggests that issues not directly related to the care of COVID-19 patients contribute to the increased density of antibiotic use.There are several potential explanations for the observed increases in antimicrobial use including concerns of bacterial coinfection in suspected or newly diagnosed COVID-19 patients, increased risk of nosocomial infection due to administration of immunomodulatory therapy, reluctance to obtain diagnostic respiratory specimens,6 In view of the similarities in the presentation of bacterial CAP and severe COVID-19, the co-chairs of the 2019 American Thoracic Society and Infectious Diseases Society of America CAP guidelines recommend empiric antibiotics for patients with CAP without confirmed COVID-19 while indicating that antibiotics are not required in all patients with confirmed COVID-19–related pneumonia.7The World Health Organization recommends prompt administration of empiric antimicrobials in persons with suspected or confirmed severe COVID-19.8–10However, the value of routine antibiotic therapy for patients with confirmed COVID-19 is questionable. While including publications with differing definitions of infection, and inconsistent timing and settings of sample collection, it is notable that recent meta-analyses found that the estimated rates of identified initial co-infection in COVID-19 cases average 3.5% while reports of secondary bacterial infection emerging during the course of hospitalization ranged from 0% to 45.5% with pooled rates of 7%–8%.This study has several limitations. First, although this was a multicenter study, the participating institutions were all VA facilities, which may limit generalizability. Additionally, we did not analyze patient-level data; thus, appropriateness, indication, or duration of antibiotics were not evaluated. We did not assess the degree to which each facility was affected by the pandemic, changes in the composition of the hospitalized patient populations, or other facility characteristics that may influence antimicrobial use. Future studies looking specifically at appropriateness of antibiotics administered to patients with COVID-19 should examine these issues.