Home health care (HHC) services are of vital importance for the health care system of many countries. Further increases in their demand must be expected and with it grows the need to sustain these services in times of disasters. Existing risk assessment tools and guides support HHC service providers to secure their services. However, they do not provide insights on interdependencies of complex systems like HHC. Causal-Loop-Diagrams (CLDs) are generated to visualize the impacts of epidemics, blackouts, heatwaves, and floods on the HHC system. CLDs help to understand the system design as well as cascading effects. Additionally, they simplify the process of identifying points of action in order to mitigate the impacts of disasters. In a case study, the course of the COVID-19 pandemic and its effects on HHC in Austria in spring 2020 are shown. A decision support system (DSS) to support the daily scheduling of HHC nurses is presented and applied to numerically analyze the impacts of the COVID-19 pandemic, using real-world data from a HHC service provider in Vienna. The DSS is based on a Tabu Search metaheuristic that specifically aims to deal with the peculiarities of urban regions. Various transport modes are considered, including time-dependent public transport. Many countries are experiencing a significant increase in demand for long-term care. The average share of the population aged 65old OECD . Many caold OECD , HHC serHHC service providers offer a wide range of services, ranging from assisting in daily life to qualified medical services. People with limited mobility or medical needs  require consistent services to avoid a deterioration of their health. But even seemingly less important tasks like assisting in daily life are of vital importance. These activities deal not only with personal hygiene or preparing meals, they are also used to monitor the health of the people. This information is crucial to adapt the services to the changing needs. Expecting an increase in demand and being a vital part of the health care system, HHC services must be sustained by all means in order to avoid health implications. To maintain business continuity, and thus continuity of care, HHC service providers must prepare for a variety of disaster situations.The aim of this paper is to analyze the effects of natural and technical disasters on HHC services in urban regions. Based on information from the Austrian Red Cross (ARC), one of the major HHC service providers in Austria, epidemics, heat waves, floods, and blackouts have been defined as most important. Initial analysis and results have been published in Rest et al.  and in tThe remainder of the paper is organized as follows: Sect. HHC provides unique capabilities to manage disaster situations, both before and during the event. The ability to deliver health services in non-structured environments makes them ideal as key responders in times of crisis NAHC . IdentifA manual for developing an all-hazards emergency preparedness plan is provided by the NAHC . It listunderstand the organization’s mission and mission-supporting systems.identify mission-threatening vulnerabilities of critical systems.understand system design and operation to determine failure modes.identify consequences of failures and cascading effects on other systems.Risk assessments are an important part of the risk management procedure and a precondition for the subsequent phases of the crisis management cycle . Knebel and Phillips  estimaterequired care) is thus offset by a reduced care potential (conducted care). The resulting gap creates a reinforcing feedback loop as unsatisfied demand decreases the human health of the care-dependent people. As a consequence, additional care is needed, which again increases the gap.The main challenge of epidemics can be summarized by a huge increase in the number of care-dependent people and service times, paired with a significant decrease of the availability of nurses and informal care. The efficiency of the conducted care services is also expected to decrease. A higher demand for HHC services  or of man-made- and technical failures. Alhelou et al.  publisheavailability of ICT) the available nurses are expected to decrease. Furthermore, the scheduling of the staff is less efficient, resulting in longer travel times and a reduced care efficiency. A blackout also directly affects the availability of transport. Electricity-based transport  will be inoperable and buses and cars suffer from lack of fuel and the failure of traffic management systems . A lack of availability of transport leads to longer travel times and to a reduction of available nurses and informal care.Blackouts affect nearly every aspect of daily life. Alhelou et al.  describeThe impacts on the health care sector are well documented by previous incidents. For example, the blackout that hit the northeast of the United States and the Canadian province of Ontario in August 2003 lasted for several days. Freese et al.  reveal thuman health in various ways, but most harm is done by the loss of electrically powered  equipment or by the occurrence of diseases. The availability of safe food/water decreases without electricity, which further reduces human health. Especially cities with many high-rise buildings are at risk and depending on the season, the lack of heating or air conditioning further aggravates these adverse health effects. The lower human health, the higher the number of care-dependent people and the higher the avg. care time. On the other hand, the informal care potential, the number of available nurses and the care efficiency are reduced. The top part of the CLD shows the same reinforcing feedback loop as during epidemics. Unsatisfied demand for care decreases the health of the care-dependent people, leading to an even higher demand.It can be concluded, that blackouts decrease availability of electricity. This variable corresponds to the previous blackout intensity.Heatwaves refer to continuous periods with high temperature that last for weeks. Because of climate change and global warming, the frequency and intensity of heatwaves is expected to increase. Chapman et al.  outline human health are well documented and several studies outline the causal relation of increased mortality and morbidity during heatwaves. Mayrhuber et al.  or (in)direct contact with an infected person. The infection mostly affects the respiratory tract, with symptoms ranging from those of a common cold to very severe respiratory infections. While most infected people show only mild symptoms, older people and those with pre-existing conditions are particularly at risk. As a result, more than half of all COVID-19-related deaths in most EU countries are attributable to elderly residents of long term care facilities and nursing homes ECDC . The WorIn spring 2020, there were no specific treatments or approved vaccines for COVID-19. The measures and recommended actions focused on the treatment of the symptoms as well as preventing the further spread of the disease. The first diagnosed infections in Europe (January 24) were associated with travels from or to areas in south-east Asia. At that time, the European countries relied on screening and isolating symptomatic people coming from such an area or who had direct contact with a confirmed case. The first major outbreak in Europe was in Lombardy, northern Italy and thus, in the immediate vicinity of Austria . For example, it allows HHC service providers to determine their operational limits and to adjust their processes and capacity planning, in order to enhance the resilience of their organization. Furthermore, a DSS can be used for the training of the dispatchers and nurses to prepare for various disaster events. During the response phase of a disaster, it guarantees that the available resources are used as efficiently as possible. By speeding up the planning process, a DSS also frees time of the dispatchers for other important activities.Applying operations research methods and techniques to support HHC received a lot of attention in the recent years. The organization and processes of HHC service providers differ even within a single country, resulting in a wide range of publications, addressing different aspects of HHC. The literature review of Hulshof et al.  lists vaingentus decision support KG, a spin-off of the Institute of Production and Logistics of the University of Natural Resources and Life Sciences Vienna. The DSS is used by a major HHC service provider in Vienna for their daily planning. In total this service provider has about 750 nurses and over 3000 clients. The HHC routing problem has a daily planning horizon and can be briefly described by the characteristics of the clients and nurses.The solution approach of the presented DSS and the underlying HHC routing problem are based on those published in Rest and Hirsch . They hamust be executed by a feasible and appropriately skilled nurse .has to start within its given (hard) time window.has a fixed duration that must not be shortened.should be assigned to the clients’ team of preferred nurses and all of his/her jobs should be assigned to the same nurse .should be planned so that the minimum and maximum time offsets between jobs are fulfilled .that is marked as ’multiclient job’ has to be carried out together with its counterpart .Nurses are required to...carry out jobs that correspond to their primary qualification or that require a qualification level that is included in their set of allowed qualifications .obey working time restrictions .hold breaks if the working time exceeds a certain time.work at most two shifts a day.use one of the available transport modes .start/end their shift either at a depot or directly at the location of their first/last job and return to a predefined location if working two shifts.not exceed the total overtime limit defined for all nurses.have a similar workload compared to the other nurses (relative to their target working time).A weighted objective function balances the opposing goals of minimizing the route lengths and maximizing the satisfaction of the clients and nurses. The client’s satisfaction is mainly determined by the consistency of care regarding the visiting times and nurses. For the nurses, overtime and over-qualification are crucial indicators for their satisfaction. A total of 11 soft constraints are used to configure the tradeoffs between the individual factors of the objective function. The actual weights have been set together with the dispatchers and the managerial decision makers of the the HHC service provider. In contrast to the algorithms published in Rest and Hirsch (Clients require one or more services (jobs) per day and each job...d Hirsch , the DSSThe presented HHC routing problem mainly distinguishes itself from other work by the fact that public transport is considered. Public transport operates on timetables that have different departure intervals and travel times during the day. Thus, their time-dependent travel times are modeled using a travel time matrix for each minute of the day. The DSS is able to process timetable data from public transport service providers in the General Transit Feed Specification (GTFS) format, developed by Google. Another unique feature are the mandatory breaks, which in contrast to previous work, can be split into smaller parts. To the best of our knowledge, there are still no other publications except for Rest and Hirsch  in the fTime and efficiency are crucial for practical applications. Due to the complexity of the routing problem, the DSS uses a Tabu Search metaheuristic. The algorithm is explained in detail in Rest and Hirsch . Its proThe presented algorithm is based on the same concepts used in Rest and Hirsch . HoweverFor easy integration in existing systems, the DSS has been developed as a web service using Java 8. This way, it is highly scalable to manage heavy workloads as well as highly customizable and expandable with regard to constraints and objective functions. It is able to solve real-world sized instances with about 250 jobs and 40 nurses within a few minutes. The DSS can be used to evaluate or improve the manual planning of the dispatchers or to compute schedules from scratch. The structure of the DSS is shown in Fig. Based on the findings in Sects. The DSS is applied to real-world data from a major HHC service provider in Vienna. A total of 16 instances . On the other hand, at high workloads, meeting the mandatory working time restrictions is more important. Furthermore, using the real-world setting allows for a good comparability of the results from before and during the pandemic. All computations have been carried out locally on a Lenovo ThinkPad T490 with an Intel Core i7-8565U processor, 16 GB of RAM and running Windows 10 Pro. The computation time limit has been set to 600 seconds per instance.The first scenario analyzes transport infrastructure impacts. As outlined in Sect. It can be seen that the restrictions on public transport result only in small increases in travel (incl. waiting) times and overtime, amounting to an average increase of the objective value of 6.6%. However, individual instances like The second scenario aims to analyze the operational limits of the different instances during the COVID-19 pandemic. In the CLD for epidemics in Sect. Table HHC services are rising in importance in the health care systems of many countries and with it grows the need to sustain these services in times of disasters. Risk assessment tools and guides support HHC service providers to secure their services. However, they do not provide insights on interdependencies of complex systems like HHC. CLDs have been used to visualize the impacts of epidemics, blackouts, heatwaves, and floods on the HHC system. They help to understand the system design as well as cascading effects. Additionally, SD simplifies the process of identifying points of action in order to mitigate the impacts of disasters. For example, during an epidemic, protective equipment is crucial as it prevents not only infection of HHC staff and transmission of the disease to clients, but increases their willingness to work. The CLDs also show the importance of informal care, provided by friends and relatives. This outlines the need for a close coordination with them. In case of their unavailability, HHC services need to step in immediately to prevent health issues. On the other hand, relatives might be able to reduce the pressure of HHC services if they are able to take over some tasks.In a case study, real-world data from a HHC service provider in Vienna was used to show the impacts of the COVID-19 pandemic on HHC in spring 2020. Furthermore, it shows the applicability of the presented DSS in times of disasters, which can be used for the daily scheduling of the nurses to ensure that the limited resources are used as efficient as possible. By speeding up the planning process, it frees time of the dispatchers for other important activities. It also allows HHC service providers to better prepare for disasters and helps to determine the operational limits of the nursing teams, operating in different areas with different characteristics . The DSS also shows the effects of using various transport modes. In urban regions, careful planning allows to cover many distances by foot or (electric) bicycles.While the DSS was used to analyze the impacts of the COVID-19 pandemic in Vienna, it can also be applied to analyze other disaster scenarios, such as those presented in Sect. However, the presented DSS has limitations. While supporting HHC service providers, it further increases their dependency on IT systems, which are especially vulnerable during disasters with limited availability of electricity. While it is designed to run on low-powered hardware like notebooks, continuous local backups of the relevant data are required. Furthermore, in its current stage of development, it is assumed that all jobs have to be carried out. At some point during major disasters the operational limits are reached. For these cases, a computer assisted triage system is needed to prioritize the most critical jobs and to carry out as many jobs as possible. Future work should also cover the dynamics of the HHC routing problem. The short computation times of the DSS allows for rapid re-scheduling, but the generated schedules might be entirely different each time. Especially with limited means of communications, it is usually preferable to adapt to the new situation with as few changes as possible.


The selection of material solutions is a basic decision-making problem that occurs in engineering issues. It affects the entire life cycle of a building structure, its safe use, maintenance costs, and a need to meet requirements for sustainable development, including recycling. This paper aims at selection of the optimum composition of HPC designed for monolithic girder structures of post-tension bridges. For the analysis, a set of 12 new-generation concretes (HPC) was designed, made, and tested. A full-scope set of evaluation criteria was created and then the optimal alternative was selected. For this purpose, an advanced hybrid algorithm combining EA FAHP  and FuzzyTOPSIS  methods was used. The obtained results indicate a possibility for the practical application of the proposed algorithm by decision-making engineering staff. It can also be the basis for further research on application compared to other material and design solutions and, depending on the issue, different combination of aggregated methods. Problems with selection of material and structural solutions are one of the fundamental decision-making issues in technical fields, including bridge construction. It is a complex issue, requiring experience and interdisciplinary knowledge. Its complexity increases along with the requirements imposed on modern cement-based materials. Bridges made of prestressed concrete are an excellent example, where the quality of the embedded material is of great importance for the durability of the structure. The production of concrete is nowadays a great design and execution challenge, and the choice of the optimum material solution is a fundamental decision-making problem in engineering terms. It is crucial and affects the entire service life of a bridge, from its design, through its use, up to its demolition, and recycling.Despite certain difficulties associated with erection, post-tensioned girder bridges have many advantages over classical reinforced concrete (RC) bridges, including the ability to transfer significant loads, achieve longer spans, reduce the height of cross-sections and span deflections, and have relatively high fatigue strength. These parameters showed a slight improvement due to the implementation of HPC with strength classes ranging from C50 to C100 and even C120 ,4,5.The first applications of HPC in prestressed bridges were recorded in the 1980s, e.g., the East Huntington Bridge over the Ohio River or the Tower Road Bridge in the state of Washington . The ter2 nano silicon dioxide used as a nanopowder is best known [The high-performance concrete, unlike the ordinary concrete, has a compact and tight microstructure and a low water-to-cement ratio (w/c ~ 0.2). Furthermore, it is a ecological material and thus not hazardous to human health ,10,11,12st known ,20,21,22The most numerous group of publications on the subject are research papers, combined with theoretical verification, e.g., ,24,25. TFollowing a survey of literature it was found that implementation of new solutions (formulas) of HPCs to be used for post-tensioned bridges is still a topical issue. The following trends can be observed: increasing durability of new bridges and associated reduction in maintenance costs, creating lighter, more cost-effective structures, increasing span limits, and reducing a number of girders.The character and complexity of the decision-making process in civil engineering is influenced by at least several factors. The first one is that design and execution conditions are never the same, which is characteristic for construction projects. The second one is the occurrence of many criteria, often contradictory, conditioned by factors that are difficult to measure, contractual, or which cannot be precisely defined. The need to take into account group ranks generated by appointed decision makers is also a difficulty. These problems are particularly evident with regard to issues undertaken by the authors in this paper and associated with the selection of concrete material solutions for advanced post-tensioned bridge span structures.Until now, the choice of structural materials has most often been determined by standard requirements together with cost minimization. Nowadays, despite the increased number of evaluation criteria and the importance of selection of optimal material solutions, this process, in most cases, is still solved only on the basis of knowledge and experience of the decision-making civil engineers. The reason for this state of affairs is the lack of a flexible, systematized assessment model that allows an unambiguous qualification of materials. The issue is also not solved by methods that have emerged in recent years, which are used to evaluate the environmental impact of materials and construction elements. They may be divided into two main groups: those which apply a qualitative approach with a system of criteria and scoring using a simple mathematical algorithm, and a quantitative approach based on LCA (Life Cycle Assessment) and guidelines set forth in ISO 14040. Methods that are better known are: BREEAM —Giudice et al.  and KeysIn the authors’ opinion, implementation of multi-criteria analysis methods referred to as MCDA , in particular the sub-group of FGDM (Fuzzy Group Decision Making) methods allowing for the application of fuzzy values, is far more promising. There are few publications only on the application of this type of MCDA methods in the material analysis. These are works on a variety of topics and with a different scope of analysis. Paper  comparesSimilar studies on the selection of material solutions for repairs of concrete structures can be found in ,46,47. TThe analysis of the literature indicates that the methods applied do not show flexibility, which would allow for a quick implementation of the algorithm to any decision-making problem in the selection of material and design solutions. In most cases, the application of only basic methods entails limitations associated with them in terms of analysis, e.g., the possibility for free shaping of the levels of the decision tree, a number of applied criteria/sub-criteria or analysed alternatives. The presented difficulties clearly indicate the necessity to apply computational methods, which at the same time allow to systematize the decision-making process, take into account the required set of evaluation criteria, and which have a relatively simple procedure algorithm.Being aware of the deficiency resulting from the literature review, this paper presents an original application of the MCDA methodology in the analysis of material solutions for HPC intended for spans of post-tensioned girder bridges.A procedure algorithm for the proposed analysis is presented in Despite the higher cost incurred during the erection of HPC post-tensioned bridges, the advantages indicated above may cause these structures to be more cost-effective than traditional ones made of reinforced concrete in the long-term operation. For that reason, a representative road viaduct over a main railway line, being a concept for a two-lane bypass of Bąków as a part of the DK-11 main road (Poland), was adopted for the analysis.A monolithic HPC structure was adapted for that purpose, with a cross-section in the form of a post-tensioned box girder with a total width of 15.00 m and a height of 2.2 m a. The stSupports are designed as reinforced concrete structures in the form of abutments and pillars supported on direct foundations  and on two rows of piles . Pillars have a deep beams structure, with a separate openwork upper part in the form of inclined, short columns. Pillar heights range from 6.4 m to 11.00 m.Properties of the concrete for the construction of monolithic post-tensioned bridges should be selected based on the following basic criteria: strength, tightness, and long-term deflections. Apart from the features mentioned, the actual execution conditions and possibilities as well as the economic criterion should also be taken into account.Requirements for the compressive strength of concrete depend primarily on the value of internal forces that occur in the structure. Application of higher strength concrete for prestressed concrete bridges than for RC bridges results from better utilization of concrete properties in prestressed structures, as compression occurring there is transferred by the entire cross-section of concrete. In addition, concretes with higher performance parameters are less prone to deformation and therefore losses of prestress force due to the elastic shortening of the concrete also being lower. Another argument to support the use of high-performance concrete in prestressed structures is the possible safe introduction of concentrated prestress forces and anchorage of tendons. Thus, in the case of post-tensioned bridges, the concrete must have as high of a compressive strength as possible when prestressed . For theA requirement for concrete tightness is an important parameter for any bridge structure as they are exposed to a direct impact of precipitation and large temperature fluctuations. Tight concrete can effectively protect, e.g., prestressing the steel against corrosion, which directly affects the durability and reliability of the bridge. Another important, but not the most important parameter of concrete in post-tensioned bridges, is a sufficiently high tensile strength of the concrete, as it ensures good adhesion to steel in case of elements where the post-tensioning force is transferred directly to the concrete (this applies to post-tensioned structures with adhesion). In concretes used for prestressed structures, it is also important to ensure the quality of technological processes following preparation of the concrete mix, which includes, among others, transport, pouring, compaction, and curing.Favourable technological properties of the concrete mix and a rapid increase in the concrete early strength;Favourable mechanical properties, in particular high compressive strength (after 28 days);High durability and resistance to environmental impacts.For the purposes of the analysed issue, 12 sets of concrete with different composition were designed and made. Design assumptions for concrete composition were focused to obtain:Such a material, in terms of its application in the building industry in the form of concrete products, should meet the requirements for its safe use in various environmental conditions, while ensuring occupational health and safety of users. These conditions are fulfilled when the concrete is designed and made of safe waste ingredients, i.e., that meet the acceptance criteria with regard to radioactivity and a content of heavy metals and hazardous compounds. These are requirements generally adopted for the raw materials used, guaranteed by manufacturers and included in their technical specifications. In addition, concrete as a product can already be tested for leachability of hazardous components. Such action is advisable and required when its production involves the content of unknown waste . However, in case of the tests performed in this study, the ingredients used for concrete come from known suppliers and have the manufacturers’ technical data sheets, which guarantee their safe use and influence on health and environment-related factors. Therefore, the paper focuses on the determination of physical and mechanical properties of the concretes tested, which, when used in structural products, will guarantee a long service life of the structure without any repairs, as well as high durability and safety for the environment (immobilisation of compounds coming from waste in the form of silica fumes).The economic aspect has been considered in two ways: directly, through the development of concrete sample composition, and indirectly, through evaluation of the bridge structures durability that has the impact on the environment through the extended life and reduction of maintenance and repair works.Tests were performed for concrete mixes and hardened concretes made of Portland cement CEM I 42.5R without and with an aqueous solution of hydrophilic nanosilica (HI) and hydrophobic nanosilica colloid (HF). Nanoadditives were used in an amount of 1.5% by weight to the weight of cement. Silica fume (D) was additionally added to concretes in the amount of 8% by mass. Whereas a 40% solution of polycarboxylic superplasticizer (SP) was used as a chemical admixture in the amount of 2% by mass of cement. Consistency of concrete mixes was adjusted by the amount of water (w/c ratio from 0.23 to 0.33).The composition of the designed concretes (S1–S12) is given in 3), according to PN-EN12350-6; air content by a water column method (with a measurement uncertainty of ±0.5%), according to PN-EN12350-7.Properties of fresh concrete mixes and hardened concrete were tested in the accredited Construction Material Laboratory of the Faculty of Civil Engineering and Architecture at the Opole University of Technology. A scope of tests performed was adequate to satisfy the requirements for the analysed post-tensioned bridge structure. Testing included the determination of concrete mix properties in terms of: a consistency class expressed by a slump test method (with a measurement uncertainty of ±1 cm), according to PN-EN 12350-2; density (with a measurement uncertainty of 10 kg/m3) according to PN-EN 12390-7, water penetration depth into concrete at a pressure of 0.5 atm (expanded uncertainty ±4 mm) according to PN-EN 12390-8, water absorption (expanded uncertainty ±0.36%) and freeze-thaw resistance in water (expanded uncertainty ±0.46%), both according to PN-B-06250. The repeatability of a given test, the quantity of concrete mix, as well as dimensions and a number of cubic specimens of hardened concrete were each time in accordance with the specified standards, and the analysis of the results took into account the extended uncertainty of measurement that the test results were subject to.The purpose of hardened concrete testing was to determine the early compressive strength (after 1 day of testing) and the final compressive strength (after 28 days of curing). Tests were performed according to the guidelines of PN-EN 12390-3 standard. The expanded uncertainty of measurements was ±2.9 MPa). Cubic specimens with dimensions of 100 × 100 × 100 mm were used for testing. In addition, after 28 days of concrete curing, the density was determined for cubes with the size 150 × 150 × 150 mm  and M2.2 ;-s4 for mixture M3.3 (1% by mass of polycarboxylate superplasticizer SP and 1.5% by mass of hydrophobic nanosilica HF);-s5 for mixes: M3.2 (1% by mass of polycarboxylate superplasticizer SP and 1.5% by mass of hydrophilic nanosilica HI), M4.2  and M4.3 .This caused a change in the consistency class from s1 determined for M1.1 reference mix and: M1.2, M2.1, M2.3, M3.1, and M4.1 mixes—modified by the nanoadditive content in an amount of 1.5% by mass to class:3 for mix M3.1, then by 100 kg/m3 for M3.2, and by 70 kg/m3 for M3.3 compared to M1.1. In addition, M4.1 mixes containing silica fume D and superplasticizer SP, as well as mixes with an additional 1.5% by mass of hydrophilic nanosilica HI (M4.2) or hydrophobic nanosilica HF (M4.3) showed an increased density compared to M1.1 reference mix.The addition of 1.5% by mass of hydrophilic nanosilica HI in M1.2, as well as hydrophobic nanosilica HF in M1.3 increased the density of mixes tested compared to density of M1.1 reference mix made of CEM I 42.5R cement. Whereas in mixes containing the addition of silica fume D (M2.1), as well as silica fume D and hydrophilic nanosilica HI (M2.2) or hydrophobic nanosilica HF (M2.3), a decrease in density was observed compared to the reference mix . On the The introduction of nanoadditives (HI and HF) to concrete mixes generally reduced the air content compared to the reference mix M1.1 made of CEM I 42.5R cement. Only M2.3 (with silica fume) and M3.3  mixes showed an increased air content compared to the M1.1 reference mix.3 was shown compared to the reference concrete (C1.1). A similar relation was also observed for the concretes: C2.1 (with 8% by mass of D) and concretes: C2.2 (with 8% by mass of D and 1.5% by mass of HI nanosilica) and C2.3 (with 8% by mass of D and 1.5% by mass of HF nanosilica). Concretes modified with superplasticizer SP (C3.1), as well as those containing 1% by mass of superplasticizer SP and 1.5% by mass of nanosilica HI (C3.2) and with 1% by mass of SP and 1.5% by mass of HF (C3.3) showed the increase in density compared to the C1.1 concrete by, respectively: 40 kg/m3 for C3.1, by 20 kg/m3 for C3.2 and by 40 kg/m3 for C3.3 concrete. Concretes C4.2 and C4.3, which apart from the superplasticizer and nanosilica also contained silica fume showed increased density compared to the reference concrete. On the other hand, C1.1 reference concrete and C4.1 concrete modified with 8% by mass of D fume and 1% by mass of superplasticizer SP had the same density value equal to 2390 kg/m3.It was found that the introduction of hydrophilic nanosilica HI to the concrete composition did not cause any changes in its density (in C1.2), other than under the influence of hydrophobic nanosilica HF in C1.3, where the decrease in density by about 20 kg/mSimultaneous application of both nanosilica HI and HF, silica fume D, and superplasticizer SP in concretes C4.2 and C4.3, allowed for proper reduction of the w/c ratio to 0.27, which had a beneficial effect on increasing their compressive strength compared to the reference concrete C1.1. However, application of nanosilica led to a slow increase in the early strength by 180% for C4.2 concrete with HI and by 169% for C4.3 concrete with HF, respectively.After 28 days of curing, the highest strength was demonstrated by C3.2 concrete containing polycarboxylate superplasticizer SP and hydrophilic nanosilica HI. The above indicates a compatible interaction of components used, both in terms of their quantity and type. This is also confirmed by test results of water absorption, which for C3.3 concretes (1% by mass of SP superplasticizer and 1.5% by mass of HI) was 3.9%, and for C4.2  was 3%, and for C4.3  was 2.6% and was considerably lower than water absorption of C1.1 reference concrete C1.1 made of cement CEM I 42.5R (5.4%). The introduction into the composition of concretes  of the polycarboxylate superplasticizer in C4.2 with HI and in C4.3 with HF resulted in the best tightness among the samples tested, which was confirmed by the lowest values of their water absorption and penetration depth of water supplied under the pressure of 0.5 atm. Those concretes also showed increased resistance to frost, determined by both the lowest reduction in weight and strength compared to the reference concrete (C1.1). The samples of those concretes subject to freezing did not show any cracks or visible wastage, and the average mass loss did not exceed 5% compared to the reference samples. Those concrete types reached a F100 frost resistance level. Only in the case of concrete containing 1.5% by mass of hydrophilic nanosilica (C4.2) was the strength reduction after 100 freeze/thaw cycles greater than for the reference concrete made of pure CEM I 42.5R cement .Samples of those concretes subject to freezing did not show any cracks or visible mass loss, and the average mass loss did not exceed 5% compared to reference samples. Those concrete types reached a F100 frost resistance level.The increased tightness of concretes was also confirmed by results of water absorption tests, which showed values below 5%, which, according to the requirements of the standard, allows the use of concretes with those additives in practical applications for the production of elements exposed to the direct impact of weather conditions.The structure of the hierarchical model includes the identification of a set of criteria that are components of the issue being analysed. The next step is to group them into thematically unified sets and to place them on appropriate levels of the hierarchical tree depending on the relations between them. A properly defined hierarchical model should enable a comprehensive assessment of the set of analysed alternatives leading to their ranking. The proposed set of criteria/sub-criteria is presented in -Structure safety is met a priori;-The aggregate type and particle size distribution are identical for all alternatives being analyzed;-Production of concrete and its transport are carried out by means of generally available equipment of concrete batching plants;-The mix is placed in the formwork while observing the technological regime (rheology of HPCs).The following assumptions were adopted during construction of the hierarchical tree:During evaluation of the destimulants, the highest ranks were assigned to alternatives with the lowest values of parameters analyzed.i+d and id−) and in finding values of the components of the ranking vector iS. By using the hybrid method, system evaluation measures can be obtained that take into account different aspects of the issue, allowing a more precise definition of the so-called utility function, leading to identification of conditions and the analysis of their intensity.In order to carry out the computational analysis of the issue, a hybrid algorithm consisting of two basic methods was proposed. The EA FAHP method  by entering them into the FuzzyTOPSIS calculation procedure. Calculations in the analysed issue based on results of the design and research part (Section 4) were carried out by means of the computational procedure developed according to the algorithm presented in Section 6. Both in the case of the pairwise comparison of criteria and sub-criteria in the EA FAHP method, as well as in the ranking of analyzed alternatives S1–S12 in terms of criteria/sub-criteria in the FuzzyTOPSIS method, the evaluation process was conducted by a team of DM (decision makers). The team consisted of persons with a long-term experience in civil engineering, as well as in the technology of building and cement-based materials. Based on the ranks obtained, differences were found only in nine cases , and the discrepancy was by 1 unit in each case. Discrepancies in the final ranks were determined by aggregation of individual judgements.When analysing the obtained pairwise comparison results for criteria/sub-criteria using the EA FAHP method, the value of the CR coefficient was within the range 0.0000–0.0616. Matrices of ranking obtained in the result of pairwise comparisons for main criteria A–D and sub-criteria A, C, and D in EA FAHP method using TFN  are shown in In the case of the C2 criterion, ranking of alternatives was estimated based on predicted parameters of the designed structure, i.e., its target technical condition. The mean values from the measurements were adopted as ranks of the alternatives determined by features tested with laboratory methods, and the standard deviation was approximated by fuzzy ranks.iE with (marked with *) obtained by means of EA FAHP method.Final ranking of alternatives (Si) of selected material solutions for concretes S1–S12 is presented in In result of the analysis performed, the highest rank was obtained by S11 sample, then concretes marked as S8 and S12, with ranks 0.865, 0.829, and 0.808, respectively . It can The highest rank obtained for S11 concrete is mainly due to its very good technical parameters, confirmed by tests. The use of additives in the form of silica fume, hydrophilic nanosilica, and a polycarboxylate superplasticizer resulted in high early and final strength, reduced water absorption, and increased freeze-thaw resistance compared to other samples. Simultaneous application of nano- and microsilica has proved to be a very beneficial solution, leading to densely packed spaces around cement grains and accelerated concrete curing . Such an effect is caused by an additional C-S-H phase, obtained in the pozzolanic reaction of silica fume and calcium hydroxide, in the form of a gel filling the micropores. Its presence causes better sealing of the cement matrix and a visible increase in the final strength of the concrete. The technical parameters obtained also indicate its increased durability.To make results (ranking) more clear in the context of HPC applications for post-tensioned girder bridges, three rating ranges (ranges I–III) were distinguished, i.e., 0–33%, 33–67%, and 67–100%, which can provide a convenient reference scale for designers and administrator . The higConcretes marked as S7, S10, S3, S2, and S5 in the ranking order are in range II and on the basis of analyses  it can bOn the basis of the performed tests and multi-criteria analysis, as well as previous experience in the use of HPCs for post-tensioned bridge structures, it can be assumed that this material also has ecological and economic potential for the projects implemented .It should also be noted that the rational detailed specification of criteria and the use of linguistic variables in the procedure  allow for a clear evaluation of the analysed samples, regardless of their design composition and mechanical properties. This is favoured by the establishment of interdisciplinary teams of DMs, recommended due to the complexity of the issue.The algorithm allows to consider various decision-making factors affecting the selection of the most favourable concrete and, ultimately, the quality of the execution and durability of post-tensioned girder bridges, taking into account economic and ecological factors;The results obtained confirmed the correctness of the algorithm and its application potential—it can be used as a tool supporting the development of new material solutions in bridge construction;The algorithm, unlike the methods used so far , allows for the mapping of real concrete quality assessment processes, taking into account uncertainty, incomplete information, as well as subjective and group ranks ;The practical aspect of the proposed model is the possibility of its relatively free adaptation to the specific character of the problem, without limiting a number of analysed alternatives (concrete samples) and the possibility for almost free shaping of the hierarchical tree;Modification of concrete composition by the simultaneous combination of silica fume and polycarboxylate superplasticizer added in the presence of hydrophilic or hydrophobic nanosilica proved to be a solution that allows for a significant reduction of the water-cement ratio, which has a beneficial effect on the improvement of physical parameters of concrete mixes and mechanical properties of hardened concretes. The above solution guarantees tight placing and compacting of mixes in moulds, their proper curing, as well as obtaining increased durability of hardened concretes demonstrated by a quick increase of early and final strength, high tightness, and very good resistance to weather conditions (temperatures below zero).Research on high-performance concretes for post-tensioned bridges, lasting for three decades, indicates the importance of the problem. At the same time, the presence of many criteria and almost unlimited design possibilities for the composition of concretes, cause the occurrence of considerable difficulties in obtaining an unambiguous solution in the selection of optimum material. Noting the lack of similar publications, this paper presents a computational and decision-making model for the evaluation and ranking of this type of concrete. The aggregated algorithm, which involves the EA FAHP and FuzzyTOPSIS methods, has been verified on a group of 12 samples of concretes designed for this purpose. On this basis, the following conclusions have been specified:It shall be also noted that the method has certain shortcomings, i.e., it is not possible to take into account a long-term dependence of the criteria ranks, e.g., associated with fluctuation of market conditions. Therefore, it seems necessary to improve the computational model by implementing the mathematical optimisation technique to support the analysis of multi-criteria decision-making problems, taking into account specific constraints and requirements. Other directions for further research should also consider the setting of precise ranges of final ranks depending on such factors as the technological, ecological, or economic aspects depending on the adopted criteria of sustainable development . Despite over 30-year experience in implementation of HPC, it should be noted that there is relatively little data on the durability and recycling of this material applied for bridge structures. In the current state of knowledge, these data can only be estimated.To sum up, the proposed hybrid MCDA method enables the identification of dominant criteria (sub-criteria) and selection of the most advantageous solution (concrete) for the application in question. The analysis is based on technical parameters of selected HPCs obtained in lab testing. The proper selection of structural material is particularly important in the case of post-tensioned bridges using HPC, as many parameters can have a decisive impact on the quality of execution, as well as the durability of the structure.The obtained results, as the outcome of a large spectrum of decision-making processes, indicate a possibility for popularization of the methodology proposed, provided that supplementary research is done . This may improve the technical level of the execution of post-tension girder bridges made of HPC.


In these tests, the 10% Na2SO4 solution and the 10% MgSO4 solution were used as the erosion medium, and the drying-wetting circle method was applied. It can be seen from the compressive tests and grey relational analysis that the MK admixture can improve the anti-Na2SO4-erosion capability of the concrete significantly, but weaken its anti-MgSO4-erosion capability; the UFA admixture can improve both the anti-Na2SO4-erosion and the anti-MgSO4-erosion capability of the concrete; and the composite admixture has superimposed effects and can enhance erosion resistance against these two erosion mediums. The phase composition and the changes of the macro morphology and the micro structure during the erosion process caused by mono sulfate ions and complex ions has been observed through X-ray diffraction (XRD), FTIR spectrum (FTIR), and scanning electron microscope (SEM), based on which it was determined that the erosion of single-added SO42− ions can produce erosive outputs of ettringite, gypsum, and mirabilite in the concrete, and cause corner scaling or deformation. Mg2+ and SO42− reacted in the concrete and produced brucite, M-S-H, ettringite, and gypsum, etc. The erosion of complex ions can cause scaling of the cement mortar and aggregate from the surface or the desquamation of corners.In order to study the degradation laws and mechanisms of admixture concretes with single-added SO The reaficantly . For magharacter . Generalharacter  have conAlthough a number of studies ,11,12,132 [2 exhausted in cement production accounts for 5–8% in all the greenhouse gases. Using a mineral admixture instead of cement can not only reduce the greenhouse gas exhaustion so as to protect the environment, but also improve the concrete durability [There are many ways to improve the concrete performance to resist sulfate attack, Both coating ,22 and a2 ,27. The rability ,29,30. Srability  show tharability  show tharability  uses two2SO4 solution and 10% MgSO4 solution were taken as the corrosive medium, the drying-wetting circle method was used as the study method, and the compressive strength and strength loss rate were used as the indicators to study the durability degradation law of admixture concrete in this study. The grey relational analysis was applied to analyze the durability of admixture concrete, which were respectively added with mono MK, mono UFA, and composite MK and UFA. Ten different kinds of concretes were used in this experiment, and the micro analysis has been carried out respectively on ordinary concrete [In these papers, the traditional mineral admixtures, like common fly ash or mineral slag powder admixture, are used, which would have a negative impact on the mechanical properties of the concrete in the early stage. Highly active mineral admixtures, such as MK and UFA, can improve not only the concrete compressive strength in the early stage, but also the durability after compounding. MK ,35 is acconcrete , MK concconcrete , and UFAconcrete . which eMetakaolin is made by mineral kaolin after being roasted at 500~900 °C. MK used in this study is made by Shanghai Lingdong Co., Ltd. , particle size: 1.8 μm. The particle size distribution is shown in UFA is made by Henan Zhengzhou Huifeng New Material Co., Ltd. , particle size: 5.95 μm. As shown in 3 and the specific surface area of 3320 cm2/g was applied in this study. The mixture proportion of admixture concrete is shown in The common PO42.5(a Chinese standard ordinary Portland cement) cement with density of 3.13 g/cmMedium sand from Huaihe river is used as the fine aggregate with a fineness modulus of 2.9. As for the coarse aggregates, gravels with continuous grading of 5~15 mm were used. The polycarboxylate superplasticizer made of Shanxi Qinfen Construction Materials Co., Ltd.  was applied in this study, achieving a 37% water reduction rate.The proportion of mineral admixture concrete is as shown in Non-standard 100 mm × 100 mm × 100 mm cubic specimens were taken in this experiment, for which the uniaxial compression test is carried out according to Standard of GB/T 50081—2002 . During According to GB/T 176—2008 , the opt2SO4 and a 10% solution of MgSO4 are used as the erosion medium. The experiment includes four periods, i.e., the dry-wet alternation for 20, 40, 80, and 120 cycles respectively. During the test, the PH value of the immersing solution was checked once every seven days, and the PH value was kept at 7.00 ± 0.50 with pure concentrated sulfuric acid. The solution was changed every 20 days.The dry state and wet state are as shown in After each period, tests were made to check the changes of compressive strength of each set of concrete. At the same time, the compressive strength of common concrete in water is tested for comparison. Finally, micro observation was performed with XRD and SEM.2SO4 solution is slightly lower than that in the MgSO4 solution. With the pores going deeper, the difference between sulfate ion content in the Na2SO4 solution and the MgSO4 solution was enlarged. It is mainly the magnesium ions that make the difference, since the magnesium ions react with calcium hydroxide earlier than sulfate ions and produces new layer of brucite, which accelerate the emerging of micro cracks. Furthermore, the concrete pH value decreases, which makes the C-H-S in the ettringite degrade and turn into M-S-H. The increase of M-S-H speeds up the forming of gypsum, thereby changing the concrete components and their proportions, degrading the physical property consequently, and enlarging the thickness loss. For concrete in the sodium sulfate solution, sodium ions react in the concrete and produce mirabilite in most cases. From the macro view, this product is the crystallized salt attached to the surface of the cracks of the concrete, having little impact to the concrete properties. In the sodium sulfate solution, the ettringite and gypsum produced by sulfate ions in the concrete play a very important role in the erosion.Although the erosion solutions in this study were all 10% sulfate solutions, they varied in molar concentration of sulfate ions. In order to determine the sulfate iron concentrations in different circulation periods from the surface to the internal part of all groups of concretes, the titration method was used. It can be seen from N times, and The strength loss formula is given as below in order to figure out the impacts of different proportions of admixture on concrete strength:2SO4 solution can be divided into four stages: ascending, flat, descending, and quick descending stages. In the early stage, due to the great activity and smaller particle size of MK compared to cement, the powerful pozzolanic effect and filling effect make the concrete with MK more dense than common concrete, and the reduction of pores makes migration of the erosion solution even more difficult, so the concrete with mono MK additive shows a rising strength tendency in both ascending and flat stages at 0–40 cycles compared to the reference concrete. At the 40th–120th cycles, the strength of all groups decreased. This is mainly because a large amount of ettringite and gypsum were produced, which induced expansion and crack of admixture concrete, causing its strength to decline.As shown in 4 solution. It can be divided into three stages: ascending, descending, and quick descending. Since MK contains a large amount of active Al2O3 and SiO2, it can react with CH in cement and produce C-S-H cementing material so as to improve the concrete porosity. However, Mg2+ can react with C-S-H and obtains hydration products, such as M-S-H and M-C-S-H, which will soften the cement basement and cause the degradation of the compressive strength of the concrete [4 erosion resistance of the concrete significantly. Compared to the reference concrete, the compressive strength of the MK admixture concrete is improved more slowly after 0–20 circulations, but decreased more rapidly after 20–120 circulations.concrete . The sid2SO4, the higher proportion of the MK admixture, the less loss of compressive strength. The maximum loss rate of compressive strength is only 1.45~30.02%. When the concrete is eroded by MgSO4, the higher proportions of MK admixture, the more loss of compressive strength. The maximum loss rate of compressive strength varies from 41.65~52.46%. The erosion effects of MgSO4 solution on MK admixture concrete is much greater than that of the Na2SO4 solution.2SO4, solution, the changes can be divided into four stages: ascending, flat, descending, and quick descending. In 10% MgSO4 solution, the changes can be divided into three stages: ascending, descending, and quick descending. After 0–20 cycles, the concrete compressive strength keeps rising in both solutions because, on one hand, the cementing materials like the cement are still in the hydration stage while, on the other hand, a small amount of SO42− ions get in and react with the hydration products in the slurry and produce a slightly corrosive medium, which works just like the filler. After 20–120 cycles, the concrete compressive strength degrades. Compared to the reference concrete, the compressive strength of the UFA admixture concrete degrades slowly in two types of solutions. The main reason is that UFA reacts with Ca(OH)2 in cement, which reduces the production of ettringite or gypsum, reducing the progress of the expansion and cracks caused by ettringite and gypsum.It can be seen from 2 and produce gypsum (CaSO4·2H2O). The expansion of gypsum causes the compressive strength degradation. Ettringite is another factor that causes the loss of compressive strength. Ettringite can be produced in the concrete curing process. Additionally, in the reaction process between gypsum (CaSO4·2H2O) and tricalcium aluminate (C3A), secondary ettringite can also be produced [3A + 3CSH2 + 26H→C6AS3H32. With the increase of the UFA proportion, the contents of Ca(OH)2 and gypsum can be consequently reduced. Since UFA replaces part of the cement, the content of C3A can be reduced due to the higher proportion of UFA. Therefore, the higher proportion of UFA, the better performance of the concrete in resisting sulfate attack. As shown in 2SO4 is 5.67~26.55%. In the 10% solution of MgSO4 it is 5.52~34.2%. Both are lower than that of reference concrete. Definitely UFA helps to improve the anti-Na2SO4 and -MgSO4 erosion performance of concrete.produced : C3A + 32SO4 erosion and 0–40 cycles, the compressive strength of the reference concrete changes from an ascending to a descending tendency. The composite admixture containing MK and UFA with continuous grading cement particles produces superimposed effects, and further reduces the pores in the cementing system, achieving better concrete durability. Therefore, the compressive strength of composite admixture concrete keeps rising at this time. After 40–80 cycles, the compressive strength of the composite admixture concrete degrades more slowly compared to that of the reference concrete. As shown in 4 solution, Mg2+ in MK plays a very important role in the erosion to the composite admixture concrete. The compressive strength changes of the composite admixture concrete is similar to that of the reference concrete. After 0–20 cycles, the compressive strength changes from an ascending to a descending tendency. As shown in 4 solution than in the 10% Na2SO4 solution. Therefore, the MgSO4 solution has stronger erosion effects on mineral admixture concrete than the Na2SO4 solution.In the MgSO2SO4 and MgSO4 erosion resistance, the Deng’s grey relational analysis method is used here [x0. The compressive strength of the reference concrete, MK admixture, UFA admixture, and composite admixture concretes eroded by Na2SO4 and MgSO4 solutions after each cycle period are set in the influence factor sequence, marked as x1~x9. The calculation is made as shown below.Grey relational degree is often used to analyze the relations among different factors in the grey system ,46. The sed here . The com1)xi′ (1) refers to the first original test data. The detailed original strength sequence and sequence after undimensionalization are listed in Calculate the original value of each sequence, and use the initial value method to undimensionalize the original test data and turn it into a sequence convenient for comparison:2)Set up the difference transformation matrix1 and ∆2.Calculate the absolute value of difference between the main sequence and the influence factor sequence and set up the difference transformation matrix  ∆1 and ∆3)Calculate the grey relational degree2SO4, solution and 4 solution. Comparing the correlation degrees of the test groups in the two erosion solutions, it can be seen that when concrete is eroded by the Na2SO4 solution, the correlation degree of each admixture concrete group is in this order: composite admixture concrete > MK admixture concrete > UFA admixture concrete > reference concrete. The composite admixture concrete has the best Na2SO4 corrosion resistance performance, then comes the MK admixture concrete, followed by the UFA admixture concrete, and the reference concrete is the worst. The higher proportion of mineral admixture, the higher correlation degree, which means the MK, UFA, and the composite of MK and UFA can slow the compressive strength degradation when the concrete is eroded by SO42− ions. When the proportion of MK is 10% and the proportion of UFA is 30%, the concrete has the best Na2SO4 erosion resistance performance. All these results are in line with the experiment conclusions above.Correlation index:4 solution, the erosion resistance performances of admixture concrete are in this order: UFA admixture concrete > composite admixture concrete > reference concrete > MK admixture concrete. The higher proportion of MK, the lower correlation degree, which shows that MK plays a negative role in the SO42− and Mg2+ erosion resistance performance of admixture concrete. When UFA is added to concrete, the higher proportion of UFA, the higher correlation degree. This shows that UFA can improve the SO42− and Mg2+ erosion resistance performance. The admixture concrete show the best MgSO4 erosion resistance when the proportion of UFA is 30%. All these results are in line with the experiment conclusions above.When the concrete is eroded by MgSO2SO4 solution. After 20 cycles, there are some small defects on the surface of concrete. After 40 cycles, concrete scaling and small cracks emerged because of the internal expansion caused by ettringite and gypsum. After 120 cycles, the concrete expansion and scaling appear, showing O-shaped deformation.4 solution. After 20 cycles, there are more pores on the surface and surface scaling can be seen. After 40 cycles, the cement aggregate peels off on many parts of surface. The internal cement aggregate can be observed by eyes. After 120 cycles, the internal cement mortar structure is damaged seriously. Large blocks fall off both on the cross-section and on the sides.2SO4 solution. It shows a significant diffraction peak of Ca(OH)2, and a small diffraction peak of ettringite at the time having no erosion. Since concrete has aggregates, the diffraction peaks of quartz and calcite are also significant. In addition, there is the diffraction peak of albite, which is mainly formed by N-A-S-H losing water at the late stage of hydration [2SO4 solution, the diffraction peak of Ca(OH)2 becomes weak while the diffraction peak of ettringite(Aft) gets intensified, because the SO42− ions get in by diffusion and convection, thus reacting with Ca(OH)2 in the concrete and produce ettringite. After some dry-wet alternations, the diffraction peaks of CaSO4 and Na2SO4 can be seen. Moreover, the diffraction peak of CaSO4 gets intensified more and more with the increase of cycles. After 80 cycles, the concrete has some cracks and more Na2SO4 solution gets in, and crystals separate. Now the diffraction peak of Na2SO4 becomes intense and that of mirabilite can been seen. After 120 cycles, the diffraction peak of mirabilite becomes intense. The cracks on the surface of admixture concrete get larger and large blocks of cement mortar and aggregate peel off. The compressive strength degrades significantly.Micro analysis is conducted on the M10F30 concrete by XRD and SEM. ydration . With th4 solution, which is quite different from that of Na2SO4. After 20 cycles, the diffraction peaks of brucite, MgSO4, gypsum, and CaSO4 appear and the diffraction peaks of gypsum and CaSO4 are comparatively low at this time because the number of cycles is not large enough. With the increase of cycle number, the diffraction peak of ettringite becomes weaker and those of gypsum and CaSO4 become more intense. That is because most of the Ca(OH)2 in the concrete has been consumed and the pH value declines. The production of CaSO4 is fastened and CaSO4 begins to change into gypsum at that time. After even more cycles, the diffraction peaks of gypsum and brucite become more intense. The ettringite and C-S-H undergo a decalcification reaction and the production of brucite and CaSO4 is fastened. After decalcification, C-S-H changes into M-S-H, which causes the concrete property degradation [radation . After 14 solution. Three characteristic absorption peaks of O-H can be seen at 3648.5, 3452.7, and 168.81 cm−1 in test samples. These absorption peaks are relatively small, indicating that most calcium hydroxide has been consumed after 120 cycles. The characteristic absorption vibration peaks of C–O can been seen at 881.5 and 779.2 cm−1, which correspond to the erosion products shown in the figure above. The characteristic absorption peaks come from quartz and calcite. There are stretching vibration absorption peaks of S–O at 1161.2 and 608 cm−1 and absorption peaks of AlO6 at 552.3 and 862.5 cm−1, therefore, it can be known that there must be the erosion product of ettringite in the concrete. The pH value in the concrete must have declined after 120 cycles. In this condition, C-S-H reacts with MgSO4 and produces M-S-H. when the pH value in the concrete is comparatively low, there are characteristic absorption peaks of M-S-H at 1000 and 1040 cm−1 [M-S-H needs to be confirmed through FTIR. 040 cm−1 , and the2SO4. After 20 cycles, the concrete obtains a comparatively denser internal structure. Due to the pozzolanic effect of MK, certain hydration products occur, like the cube-shaped (C-A-H) and (C-S-A-H). A small amount of ettringite crystals get between the pores in the concrete. After 40 cycles, most calcium hydroxide has been consumed and the pH value of the concrete declines. As shown in 2SO4 erosion to the concrete mainly causes the expansion of ettringite. After 120 cycles, as shown in 4 solution. 4 erosion and provides space for erosion outputs superimposing. Compared with the diffraction peak and the SEM photos of Na2SO4, MgSO4 would induce gypsum earlier during the process of corroding admixture concrete, and have a larger amount of small ettringite. This is mainly because M-S-H can soften and damage the cement, allowing SO42− to get into the concrete easier and cause the secondary destruction of the admixture concrete in the corrosive solution. Most ettringite crystals are produced after the secondary destruction. After 120 cycles, as shown in 2SO4 erosion resistance of concrete. On the other hand, due to the effects of Mg2+, the addition of MK can reduce the MgSO4 erosion resistance. UFA can improve the Na2SO4 and MgSO4 erosion resistance of the concrete significantly. UFA and MK composite admixture concrete has the best Na2SO4 erosion resistance performance, but the weaker MgSO4 erosion resistance than mono UFA admixture concrete.The addition of MK can improve the Na2SO4 erosion resistance performance when the proportion of MK is 10% and the proportion of UFA is 30%. UFA admixture concrete has the best MgSO4 erosion resistance performance, especially when the proportion of UFA is 30%.Through grey relational analysis, it can be determined that the concrete has the best NaThrough XDR and FTIR, it is known that the erosion products made when sulfate salt corrodes the admixture concrete include ettringite, gypsum, and mirabilite. The erosion products made when complex ions corrode the admixture concrete include ettringite, gypsum, brucite, and M-S-H.Through macro and SEM observation, it can be determined that the destruction of the concrete made by mono sulfate salt can be divided into three stages: production of ettringite, erosion of gypsum and ettringite, and growth of ettringite and gypsum crystals. The destruction made by complex ions can be divided into three stages: initial production of brucite and ettringite, co-destruction from M-S-H, ettringite, and gypsum, and growth of crystals of brucite, ettringite, and gypsum.In order to compare the erosion impacts of different dosages of two different active mineral admixtures on the concrete performance of sulfate erosion resistance, compressive strength tests were conducted on concretes with different cycle age; the titration method was applied to determine the sulfate ions clearly; and grey relational analysis was used to process the compressive strength data. In addition, M10F30 is selected as the research object because of the following reasons: (1) Though the quantities of main erosion products in each group of concrete blocks are different, they are of the same types; (2) though their micro structures change at different times, they have similar changing rules; (3) M10F30 has better performance than that of other groups of concrete blocks; and (4) M10F30 mixes two mineral admixtures of MK and UFA at the same time, which is representative in micro analysis. Meanwhile, XRD and FTIR spectrum are adopted to analyze and compare the macro and micro morphology changes of concretes in various cycles, from which conclusions are obtained as below:The highly active mineral admixture of MK and UFA can not only improve the sulfate resistance of concrete, but also reduce the concrete cost and protect the environment. Magnesium ions play a very important role in the MK concrete anti-erosion performance. If the magnesium ion content in the environment is comparatively high, the proportion of MK must be eliminated, or other highly active admixtures should be mixed with MK to further improve the sulfate resistance of concrete and reduce the harms brought by magnesium ion invasion.Admixture concrete eroded by either mono sulfate or complex ions would degrade in three stages. The experiments show that after the second stage, the concrete degrades rapidly, with much more erosion products. Some erosion resistance measures must be done in this stage so as to slow the concrete degradation.


Antibiotic resistance is a worldwide public health emergency. Nonprescription antibiotic use is a chief cause of antibiotic resistance. The Saudi Government, as a consequence, imposed in 2018 executive regulations to prevent the distribution of antibiotics without a prescription. Herein, we aimed to investigate the prevalence of and risk factors for nonprescription antibiotic use among individuals presenting to one hospital in Saudi Arabia after enacting these regulations. This cross-sectional study was conducted on people, aged ≥18 years, who presented to the primary healthcare clinics of King Khalid University Hospital in Riyadh during the period between 1/1/2019 and 28/2/2019. Participants were asked to fill out a self-administrated questionnaire assessing their nonprescription antibiotic use during the past year in addition to sociodemographic information. Then, logistic regression analyses were performed to calculate the odds ratios (ORs) and corresponding 95% confidence intervals (CIs) for age, sex, education, and nationality of any nonprescription antibiotic use compared with no use within the past year. Out of 463 participants, 62.9% were females, 67.4% were <40 years, and 93.7% were Saudi citizens. Overall, 30.5% of participants reported nonprescription antibiotic use during the past year (19.7% one to two times and 10.8% more than two times). Male and non-Saudi participants were more likely to report any nonprescription antibiotic use, with HRs (95% CIs) of 1.99  and 3.81 , respectively. The main reasons behind nonprescription antibiotic use were having previous experience with a health condition (69.2%), inaccessibility of healthcare (26.6%), and recommendation from a relative or a friend (16.1%). A major limitation of this study was that it included individuals attending one hospital. Individuals who seek medical consultation could be dissimilar to those who do not see doctors regarding nonprescription antibiotic use.  As early as 1945, Sir Alexander Fleming, best known for discovering penicillin, warned of antibiotic abuse due to the expected increase in public demand . Nonprescription antibiotic use, defined as the utilization of antibiotics to treat self-diagnosed health conditions without medical consultation and prescription, is considered a major form of antibiotic abuse that can lead to antibiotic resistance ,4,5. AntPrevious studies showed a high prevalence of nonprescription antibiotic use in developed ,7,8,9,10Saudi Arabia was among the first countries to raise alarm against nonprescription antibiotic use. An early study, by Saeed (1988), showed that more than half of the primary healthcare patients in one clinic in Riyadh attempted the use of nonprescription medication including antibiotics . Later, To curb self-medication and nonprescription antibiotic use in Saudi Arabia, the Saudi Ministry of Health imposed in 2018 provisions of the Executive Regulations of Health Practice Law, which prohibits pharmacists from dispensing drugs without a medical prescription issued by a licensed physician. According to the new regulations, no antibiotics are allowed to be sold as over-the-counter medications. The ministry warned that pharmacists who break the new provisions may face up to USD 26,600 in fines. These actions were accompanied by several activities to raise awareness among the public about the dangers of irrational use of antibiotics .Given the rising consensus that nonprescription antibiotic use is a serious public health challenge that needs novel strategies for prevention, in addition to the lack of studies covering this topic in Saudi Arabia after imposing the new regulations, we, therefore, conducted this cross-sectional study to assess the prevalence of nonprescription antibiotic use among people attending the primary healthcare clinics of King Khalid University Hospital in Riyadh and investigate the risk factors for this practice and the reasons behind it.The Saudi healthcare system has four healthcare levels. The first level is primary healthcare that provides essential curative, preventive, and promotive services. The second level consists of general and peripheral community hospitals that offer specialized diagnostic and curative services. The third level includes equipped hospitals to provide advanced diagnostic, curative, and rehabilitative services. The fourth level comprises medical sites where patients receive highly advanced health services such as stem cell transplantation and chemoimmunotherapy. Most second-, third-, and fourth-level healthcare settings provide primary healthcare services as well.In this cross-sectional study, our eligibility criteria included: (1) people who presented to the primary healthcare clinics of King Khalid University Hospital in Riyadh during the period between 1/1/2019 and 28/2/2019 and (2) aged ≥18 years. The primary healthcare clinics of King Khalid University Hospital receive 10 to 15 patients during the working days (five days per week) between 9 a.m. and 2 p.m. Healthcare services in these clinics are provided for free to Saudi and non-Saudi people. Eligible people, regardless of their health conditions, were asked to participate in this study after seeing their physicians and receiving their medical examinations. Those who agreed to participate were asked to sign informed consent forms and complete a questionnaire. No incentives were offered for participation.We calculated the minimum sample size using the Epi-Info version 7 Stat Calc (Center for Disease Control (CDC), World Health Organizations (WHO)) based on the following criteria: (1) population size of 999,999; (2) expected prevalence of nonprescription antibiotic use of 25%; (3) a confidence level of 95% and (4) a margin of error of 5%. However, we increased the minimum required sample size by almost 20% to enhance the statistical power of the study, avoid an unexpected low response rate, and allow us to further stratify nonprescription antibiotic users by frequency.during the past year, how many times have you used antibiotics without a prescription?” The responses were “never”, “one or two times”, and “more than two times”. Those who reported nonprescription antibiotic use were asked “why have you used antibiotic without prescription?” and respondents were allowed to select one or more of the following responses: “previous experience with the health condition”, “inaccessibility of healthcare”, “recommendation from a relative or a friend”, and “other unspecified reasons”. All individuals completed the questionnaires for themselves, except for five uneducated participants, who received assistance from their companions and the data collectors. All questionnaires were finally collected by the last five authors of this study.Participants were asked to fill out a paper-based self-administrated Arabic questionnaire composed of two sections. one or two times” and “more than two times” compared with “never”) during the past year and (2) frequent nonprescription antibiotic (“more than two times” compared with “never”) during the past year. Two models of regression analyses were conducted: unadjusted and adjusted for age, sex, and education. Because of the limited frequency of village residents, the residence variable was excluded from the regression models. As a sensitivity analysis, we repeated the analysis using the same categories used in our data collection questionnaire. p-values < 0.05 were considered statistically significant. The Statistical Package for Social Science (SPSS) was used for analysis.Descriptive data in the form of frequencies and percentages were used to present the sociodemographic characteristics of the participants and the reasons behind nonprescription antibiotic use. The logistic regression analyses were performed to calculate the odds ratios (ORs) and corresponding 95% confidence intervals (CIs) for age (<40 versus ≥40 years), sex , education (high school and lower education versus university and postgraduate), and nationality (Saudi versus non-Saudi) of (1) any nonprescription antibiotic  .In the unadjusted model, male and non-Saudi participants were more likely to report any nonprescription antibiotic use, with HRs (95% CIs) of 2.04  and 3.54 , respectively. Adjusting for other factors did not change the results, with HRs (95% CIs) of 1.99  and 3.81 , respectively . SimilarWhen we repeated the analysis, whether for any versus never or frequent versus never nonprescription antibiotic use, using the same categories as in , the resThe reasons behind nonprescription antibiotic use were having previous experience with the health condition (69.2%), inaccessibility of healthcare (26.6%), a recommendation from a relative or a friend (16.1%), and other unspecified reasons (4.9%) .This study indicated that the prevalence of nonprescription antibiotic use during the past year among people who presented to the primary healthcare clinics of King Khalid University Hospital in Riyadh between 1/1/2019 and 28/2/2019 was 30.5%. Male and non-Saudi participants reported more nonprescription antibiotic use than female and Saudi participants. Having previous experience with the health condition and inaccessibility of healthcare were the major reasons behind nonprescription antibiotic use.Our results differed from a previous study conducted on 519 people who presented to the same primary healthcare clinics in Riyadh in 2015 . AlthougIt is quite difficult to compare our results with those emerging from other international studies because of the wide variations in the sociodemographic characteristics across the studies, which may affect the prevalence, differences in the study designs, inconsistencies in defining nonprescription antibiotic use, and differences in the periods during which the prevalence of nonprescription antibiotic use was assessed ,17,18,19Of note, our results indicated that male participants tended to practice nonprescription antibiotic use more than female ones. This finding agreed with the previous study from Riyadh . CompareIn agreement with the previous Riyadh study and other studies conducted on Arab populations ,14,15,30It should be noted that this study posed several limitations that should be addressed. First, this is a unicentric study that was conducted on people presenting to the primary healthcare clinics of one university hospital. Perhaps individuals who do not go to healthcare centers are more likely to self-medicate than those who visit the doctor at some point. Second, although we investigated the primary healthcare clinics during the past year of data collection only, the possibility of recall bias cannot be entirely excluded. It could be speculated that patients with severe infections probably remember better that they had an infectious condition and that an antibiotic was prescribed, while those with milder conditions were probably more likely to forget that they had taken an antibiotic. Third, the cross-sectional design of this study did not allow us to assess the trends of nonprescription antibiotic use throughout the past years. Fourth, some sociodemographic characteristics that could be associated with nonprescription antibiotic use, such as annual income, occupation, medical condition, and the exact nationalities of non-Saudi participants, were not studied. Fifth, many sociodemographic questions and questions about the reasons behind nonprescription antibiotic use were somewhat restrictive. We believe that a qualitative study might have provided more comprehensive information. Sixth, it is not clear from the study whether participants used newly purchased or leftover antibiotics. However, since this study was conducted one year after implementing the law, it is highly probable that nonprescription antibiotic use in our study included mostly newly purchased antibiotics. Seventh, we had no data about the types of antibiotics that were used without prescription and for which conditions. In conclusion, this study showed that nonprescription antibiotic use was not uncommon among people in Saudi Arabia. Being male or non-Saudi was a predictor of nonprescription antibiotic use. People in Saudi Arabia resorted to nonprescription antibiotic use if they had previous experience with the health condition or in the case of the inaccessibility of healthcare. Compared to a previous similar study in Riyadh , a 10% dFuture research should correlate antibiotic resistance and risk factors for nonprescription antibiotic use in Saudi Arabia. Qualitative research to figure out the general population’s, doctors’, and pharmacists’ perceptions about nonprescription antibiotic use in Saudi Arabia and the newly imposed law should be considered. Moreover, studying the prevalence of and risk factors for nonprescription antibiotic use among non-Saudi residents should be considered. More awareness programs should be initiated to educate people about the importance of avoiding antibiotic abuse, especially nonprescription antibiotic use. These programs should be tailored to be suitable for the sociocultural characteristics of people living in Saudi Arabia.