Concrete condition-assessing penetrometers need to be able to distinguish between making contact with a hard (concrete) surface as opposed to a semi-solid (corroded concrete) surface. We investigated whether different shaped tips of a cylindrical penetrometer were better than others at maintaining contact with concrete and not slipping. We designed a range of simple symmetric tip shapes, controlled by a single superellipse parameter. We performed a finite element analysis of these parametric models in SolidWorks before machining in stainless steel. We tested our penetrometer tips on a concrete paver cut to four angles at 20 The worldwide costs for managing millions of kilometres of corroding and deteriorating concrete sewers are tremendous. For example, In 2002, in the United States, the estimated asset loss was USD 14 billion per year .Acidithiobacillus thiooxidans sulphide-oxidising micro-organisms [The concrete corrosion in these sewer assets is caused by biogenic hydrogen sulphide produced by the rganisms ,5. The rrganisms . The crorganisms ,7.Given the potential degraded pipe structural integrity and the high cost of replacement, accurate condition assessment becomes a high priority for water authorities. Traditional condition assessment approaches have included: visual (CCTV) acoustic, electrical and electromagnetic ,9. AlthoIf a hard surface is mistaken for a soft surface, concrete corrosion may be over-estimated, with the potential for triggering unnecessary remediation works. Unfortunately, the variably-angled surface of a concrete pipe can cause the tip of a force-sensing tactile penetrometer to slip and thus to make this mistake.Previously, we introduced a novel approach to sewer concrete pipe condition assessment using semi-automated penetration testing ,16, whicThe primary advantage of assessing the condition of a concrete surface by touch is that looks can sometimes be deceiving, particularly under variable lighting . On the For our previous penetrometer , we chosThis paper is structured as follows. In In this paper, we define tip shape in terms of the superellipse , a genern), as shown below in Special cases of Equation  yield diBefore milling the tips, we performed a Finite Element Analysis (FEA) because we did not want to create tips that were easily destroyed. We modelled using a 250 N load using SolidWorks, which is the max load force to be applied in our experimental analysis. We investigated the ability of our stainless steel penetrometer tips to maintain contact with concrete at different incident angles using an Instron 5980 Test Machine. Quasi-static indentation tests on the surface of each concrete paver were performed using the mechanical testing machine equipped with a 10 kN load cell. Each indenter type was mounted on the cross-head of the instrument and the concrete paver was placed on a stainless steel compression plate. The test configuration used is shown in Before milling the tips we performed a Finite Element Analysis (FEA) because we did not want to create tips that were easily destroyed. We modelled a 250 N load and 40x axis) against the force required (y axis) to maintain the displacement rate. An example of the ideal behaviour is shown in We recorded the depth at which the Instron drives the specially-shaped stainless steel tip into the surface of the cut concrete paver before stopping  starts with the steepest gradient both at the start and particularly around an extension of 3 mm. However, the middle section from approximately 0.1 to 2.8 mm has a lower gradient, which is also bumpier than the three other curves. The extruded squircle tip has the second steepest early gradient (dark blue), which rises above 50N at a 1 mm extension but then slips below 50 N at 3 mm, behaving similarly and better than the extruded round tip (light green). The squircle tip (light blue) exceeds 50 N second and climbs with minor slips until it crosses the extruded concave (black) tip around 3 mm but slips above 200 N.squircle, concave, and round tips. The extruded squircle and extruded convex tips then have the next best performance, with reasonably similar paths. The data are similar to the 80squircle grips better than the extruded squircle.In contrast to traditional condition assessment techniques  the penetrometer approach gives a clear indication of layer hardness due to corrosion . In contA simple parameterised representation of penetrometer tip shape was introduced, and the ability of our shaped-as-X steel tips to maintain indentation contact with concrete at different incident angles was investigated.While our modelling of the concave tip suggested that it would be fragile, in the laboratory setting it did not break against the concrete at any angle, and performed quite competitively against the higher angles. However, in deploying in a field environment, we would prefer not to use this tip for two reasons: we believe that it is more likely to break, and a sharp tip potentially creates a safety hazard.a = 1, b = 1, n = 4) as the best performer at maintaining surface contact through its changing curvature. In terms of selecting a force sensor to detect a solid surface, we chose a force sensor rated at 50 N, which gives us a maximum overextension of up to 2 mm. We plan to investigate other parameters such as material and shape complexity to further improve our penetrometer design.Consequently, we selected the basic squircle . Using a cluster of measurements over a small area, we expect that a better characterisation of the concrete condition will be possible.


Furthermore, this high efficiency can be achieved at a moderate temperature level, thus suiting concentrating solar power (CSP) applications, which are seen as a core business within supercritical technologies. In this context, numerous studies have been published, creating the need for a thorough analysis to identify research areas of interest and the main researchers in the field. In this work, a bibliometric analysis of supercritical CO2 for CSP applications was undertaken considering all indexed publications within the Web of Science between 1990 and 2020. The main researchers and areas of interest were identified through network mapping and text mining techniques, thus providing the reader with an unbiased overview of sCO2 research activities. The results of the review were compared with the most recent research projects and programs on sCO2 for CSP applications. It was found that popular research areas in this topic are related to optimization and thermodynamics analysis, which reflects the significance of power cycle configuration and working conditions. Growing interest in medium temperature applications and the design of sCO2 heat exchangers was also identified through density visualization maps and confirmed by a review of research projects.In recent years, supercritical CO In the case of CSP, sCO2 can perform as the working fluid in the power block, the heat transfer fluid (HTF) in the solar field, and/or in the thermal storage system. Thus, this introduction analyzes these possibilities, in addition to their integration in different schemes of solar thermal power plants (STPPs).The use of supercritical carbon dioxide  [2 is a key driver.According to IRENA, the amount of globally installed CSP power has significantly increased since 2010, translating into a reduction in the levelized cost of electricity (LCoE) from 0.346 USD/kWhgy (DOE) . In addigy (DOE) , in whic2 are reviewed. First, sCO2 power cycle layouts that are best integrated into CSP are described, second, sCO2 solar receivers are reviewed, and finally, integration schemes and thermal energy storage systems are proposed.In the following sections, the current state of STPP subsystems employing sCO2 power cycles based on a closed recompression layout present higher thermal efficiency than those of superheated or supercritical steam Rankine cycles at the temperature range of STPPs. This high efficiency is based on the peculiar thermophysical properties of CO2 in the region near the critical point . The sCO2 density close to and above the critical pressure is extremely high, so the compressor power is reduced [Supercritical CO reduced ,10.2 cycles exhibit other technological advantages compared to conventional steam Rankine cycles. For example, the turbomachinery size is smaller when operating near to the critical point, which implies good operational flexibility and the possibility of a lower LCoE; in addition, the sCO2 is less corrosive than steam at high temperature. Significant technological challenges also apply, including development of components capable of withstanding the demanding supercritical working conditions, such as the design of the primary heat exchanger needed when coupling the solar field and the power block for indirect configurations. Another challenge is the impact of the compressor inlet temperature on the power cycle efficiency [2 power cycles into the STPPs, particularly for dry configurations [2 is blended with certain additives to enable condensation at higher ambient temperatures, enabling required peak temperatures to be withstood without penalizing the power cycle efficiency, thus resulting in large reductions in LCoE [In addition, sCOficiency . When thurations ,13. To a in LCoE .2 cycles were mainly developed for nuclear applications, a growing interest in the integration of sCO2 into STPPs has recently arisen. Turchi et al. [2 turbine efficiency at the scale of operational CSP projects was assessed to promote this technology at commercial levels.Although sCOi et al.  presentei et al.  undertooi et al. , sCO2 tu2 cycles for power generation was presented. Wang et al. [2 in the primary heat exchanger which, as seen above, determines the molten salt temperatures and can result in lower investment in the coupled solar subsystem. This study concludes that no one layout is better than the others. The final choice depends on the specific operating and ambient conditions, and should account for the annual performance of the STPP.Subsequently, two important review works were published. In , a generg et al.  identifi2 cycles—the recompression and partial-cooling cycles—based on the global STPP performance. The authors concluded that the partial-cooling cycle has lower investment costs and generates more net electricity based on the larger temperature difference in the primary heat exchanger.A later work of NREL  analyzed2 layout. Several designs have been proposed in the literature for molten salt-to-CO2 heat exchangers, for both nuclear and CSP applications [2-to-liquid sodium compact heat exchangers for sodium-cooled fast reactors [2 circulates through the tubes. For this type of heat exchanger, a new sCO2 layout is proposed in [2 heat exchangers include using a moving packed-bed [Finally, it is important to note that one of the key elements for the feasibility of this technology is that the design of the primary heat exchanger connects the solar field and the power block because, in general, the fluids are not the same (indirect integration schemes). This is the case of a molten salt central receiver coupled to an sCOications ,21,22,23reactors . The simposed in , in whiccked-bed , fluidizcked-bed ,28, or scked-bed ,30.2 cycles for CSP, the research on sCO2 solar receivers is relatively new, although there now appears to be a growing interest. The review presented in this section is focused on sCO2 solar central receivers (CRs). As noted in [2, its application to parabolic trough (PT) fields is difficult, although theoretical studies have been conducted [As in the case of the supercritical COnoted in , due to onducted .A previous study reviewed compact heat exchanger (CHE) structures and the possibility of integrating them in pressurized solar receivers . Althoug2 central receivers proposed was based on the external tubular receiver concept [2 power cycle working at 200 bar and 700 °C has also been considered. In this case, additional requirements would be necessary to withstand the high pressure and temperature, and to enhance the heat transfer to the supercritical phase.One of the first supercritical CO concept ,34. Thisth cavity receiver for sCO2. This receiver consists of several plates joined by diffusion, with rectangular fins between them, in such a manner that square-shaped channels are formed. The optimal geometry of this CHE structure was selected through an optimization process, as explained in the same work.In the study presented in , the CHE2 that circulates through ducts embedded in the porous matrix itself.Another interesting configuration was proposed in . In this2 central receiver designs [e power cycle, and the second is a surround external receiver for a 10 MWe cycle. In both designs, the sCO2 circulates through a compact structure consisting of two attached plates with a wavy fin structure between them, which acts as the absorber surface for the concentrated solar radiation. The main difference is that the absorber plates are arranged to form a cavity in the first case, whereas they are arranged to form an external cylindrical receiver in the second. Because radiation losses would be very high in this last case, a radiation trap was designed, consisting of small quartz cylinders perpendicular to the wall, which reduce radiation and convection losses. In this manner, the receiver thermal efficiency remains high (80%) when working at temperatures of approximately 750 °C. In both designs, the objective of 0.06 USD/kWhe established by the SunShot Initiative is attained.Finally, a recent work by the National Renewable Energy Laboratory (NREL) presented two concepts for sCO designs . The fir2 cycle, and different schemes are defined depending on the HTF in the central receiver: liquid sodium [2 and molten salt-to-sCO2 [Most supercritical STPP layouts use indirect coupling because the HTF in the solar field and the working fluid in the power cycle are different. This is the configuration selected by the above-mentioned Gen3 CSP Roadmap  and ASTRd sodium  or molte-to-sCO2 ,23,39. A2 cycle is the most conventional approach, and there are several works in the literature about this configuration. In this scheme, the molten salts also perform as the thermal storage fluid, and the proposed configuration is usually a direct two-tank TES, although a thermocline can also be used [The molten salt receiver scheme coupled to a sCO be used ,23,40. T be used .2 cycle is analyzed in [2 power block are considered.An integration scheme in which a liquid metal solar receiver is coupled to a sCOlyzed in , where a2 cycle is represented in few works in the technical literature, although a global integration scheme is presented in [The STPP based on a particle receiver coupled to a sCOented in ,34, and ented in , the blaented in , the theented in , and theented in .2 cycle, the works of Li et al. [Regarding the pressurized air receiver coupled to a sCOi et al.  and Trevi et al.  can be h2 is used both as the HTF and working fluid. Turchi et al. [2 power block, and, because of the turbine/compressor compactness, it is possible to allocate them in the tower. As a result, the piping is reduced, thus also decreasing the pressure and heat loss, and improving the transient response.All the schemes described above match the indirect coupling. To conclude this section, we discuss the direct integration schemes between the solar field and the power block where sCOi et al.  presente2 cycles. Other studies proposed a direct coupling using a thermocline system. In this manner, Kelly et al. [Although most of these direct integration schemes are intended to be coupled to indirect thermal storage in molten salts , it shouy et al.  presentey et al. .2 in CSP is a recent but promising topic of investigation that is currently supported by several research programs. The number of research areas and new proposals has grown rapidly in recent years, aimed at developing more efficient and competitive STPPs. As a result, it is a challenge to undertake a review of the existing literature on supercritical CO2 power cycles for CSP applications. Bibliometrics tools can provide insights into the main researchers and institutions engaged in the topic, and the manner in which they are connected. This approach can also identify the main research trends and popular research topics that provided the motivation for this review article [To summarize this introduction, the use of sCO article .2 power cycles [r cycles ,53. Howe2 for power generation, to the best of the authors’ knowledge, there are no specifical bibliometric studies regarding CSP applications from a global approach, which represents the novelty of this work. The objective of this study was to evaluate sCO2-CSP global research trends quantitatively and qualitatively through bibliometric techniques. The study’s conclusions will not only provide a better understanding of popular sCO2-CSP research areas, but may also influence scholars’ and scientists’ future research. To succeed in this ambitious enterprise, this paper is organized as follows: in the next section, the working methodology is presented; 2 in CSP.Despite recent interest in supercritical CO2 related publications that were retrieved based on different question queries and consulted databases. Both Web of Science (WOS) and Scopus databases were consulted and publications including each query  were retrieved. To account for most publications within the field, different expressions and search combinations were considered and the logical operator “or” was introduced to combine all of them, thus resulting in the total corpus data of the study. It can be seen that the number of indexed publications relating to sCO2 power cycles that also included the keyword “solar” was similar among Web of Science (441 publications) and Scopus (468) databases. In both cases, those publications accounted for one-third of total sCO2 power cycle publications, which indicates the relevance of CSP applications within sCO2 technologies.2 power cycles using this database [The data set retrieved from the Web of Science (WOS) was preferred because it is claimed to contain journals with higher impact  and no pdatabase ,53. Undedatabase ,65.2 research with a focus on CSP applications, and to provide insights into technology trends.In this section, several bibliometric indicators are presented and discussed to analyze the main researchers in sCO2 power cycle publications (sCO2) between 1990 and 2020 according to the WOS. As shown, the first WOS sCO2 power cycle publication was indexed in 1993, but the first publication related to CSP applications appeared in 2005. Subsequently, the relevance of sCO2 solar-related publications has continued to grow and now accounts for one-third of the annual sCO2 publications. Furthermore, 70% of the total number of publications were published after 2015. It can also be noted that the contribution of solar-related publications to the existing sCO2 literature is around 30%. During 2020, the number of sCO2 publications reached its maximum despite the slight decrease in solar-related publications compared to previous years.2-CSP-related publications is slightly higher compared to the publication ratio shown in 2 technologies. It can also be observed in 2 power cycle citations were received after 2016.In terms of the number of citations, the contribution of sCO2-CSP documents.As shown in 2-CSP account for 82.6% of publications in cumulative terms. A closer look at the scientific production during 2020 indicates a clear growth in Chinese and Spanish publications, and the cumulative production of the 10 most productive countries increased slightly, to 86.5% of the annual publications.2 power cycles for concentrating solar power applications. Research institutions are ranked according to the number of publications. The number of authors that have published in the sCO2-CSP topic under the organization affiliation is reported, in addition to the accumulated number of citations (including self-citations). The publishing ratio (PC ratio) is determined as the ratio between the number of citations and publications for a given organization. The h-index of the institution is also provided considering only the number of publications and citations for the analyzed topic [ed topic . As show2-CSP topics in terms of the number of publications. It also shows the number of citations received in this topic, the PC ratio, and the equivalent h-index considering only sCO2-CSP publications. The authors with the most common affiliations of those publications are also shown. As shown, most of the relevant authors belong to the most productive organizations  followed by proceedings papers (31%), with the two categories combined accounting for 94% of corpus data.Regarding the document type distribution, 2-CSP are Energy Conversion and Management and Energy journals, with 40 publications each, followed by Applied Thermal Engineering with 30, as shown in 2-CSP publications, it can be seen that dedicated solar-related sources, such as Solar Energy and the Journal of Solar Energy Engineering Transactions of the ASME. The figure also shows the sources for proceedings papers, such as those of the SolarPaces conference, which were published in Energy Procedia until 2014 and have been collected under AIP Conference Proceedings since the 2015 edition.Within article publications, the most relevant publishing sources for sCO2-CSP literature. As indicated by the cumulative values, both sources followed the same trend in terms of publication records. This translated into an average contribution of open-access sources of around 20% in recent years, where the spike in 2005 corresponds to one open-source publication of the two publications that year.2-CSP topic. As can be observed, 1006 authors have published at least once on this topic, regardless of the number of citations received. This number falls significantly to 208 authors who have two sCO2-CSP-related publications and 10 citations.2-CSP publications and 25 citations requirement. This criterion resulted in 152 authors; however, only 66 were connected in terms of collaborative publications that also met the minimum number of publications and citations criteria. For representation purposes, only connected authors are represented to explore their collaborations. A thesaurus was used to avoid duplications in authors’ names.As can be noted in the map, authors are grouped under different clusters that indicate common collaboration. Furthermore, a repulsion representation scheme was chosen, which implies authors appearing closer to each other in the map have a closer relationship (in terms of collaborative publications) compared to those who appear more distant in the map. In addition, the size of the nodes is directly related to the number of authors’ publications. 2-CSP-related publications.2-CSP-related publications have been published in 105 different sources, but only 11 sources gather 10 or more publications on this topic, as also shown in Regarding publishing sources and their connections, 2-CSP documents did not cite the other journal documents. A thesaurus was used to avoid duplications among different publishing sources, particularly for those from conference proceedings, which are grouped regardless of the year and edition. For representation purposes, 2 power cycles within concentrating solar power (CSP) applications are addressed, both from a semantic perspective (relating to the most common keywords extracted from publications) and the manner in which they are connected to the most recent research projects, both in Europe and in the United States.In this section, technology trends for supercritical CO2-CSP publications. Text mining analysis was applied by extracting documents’ keywords from publication titles and abstracts, and those provided by authors from the retrieved sCO2-CSP publications relate to each other. A similar repulsion and clustering scheme was followed in keywords representation, and can be summarized as follows:2”, “concentrating solar power”, “performance” and “system”).Keywords located in the center of the map are the most relevant and general within the retrieved publications because they are highly connected to other topics in the network .The size of nodes indicates the keyword relevance in terms of the number of occurrences; in this case, the most common are presented in 2”, “concentrating solar power”, “system”, “Brayton cycle”, “generation”, “optimization” and “designs” keywords.Keywords are grouped into clusters to indicate the frequency of their joint appearance in publications, denoting that they refer to similar research areas. In this study, keywords are organized in seven clusters dominated by “supercritical CO2-CSP applications. However, most of those analyses relate to “performance analysis” and “multi objective optimization” according to the central areas of the map, whereas “off-design performance” studies remain in the periphery, indicating its lower relevance in terms of the number of publications. The incipient relevance of medium low-temperature applications within sCO2-CSP can also be observed as mild colored areas, including keywords such as “Rankine cycle”, “transcritical cycle”, “organic Rankine cycle”, “parabolic trough collector” and “waste heat recovery”. In addition, the growing relevance of “energy storage” can also be seen through common keywords of “thermal energy storage” and “phase-change materials”. Finally, “heat transfer” analysis and “heat exchanger” designs have gained relevance and are approaching the central area of the map.2 systems in their objectives, in the EU and the USA, respectively. The tables present the name of the project, its general objective, and the project coordinator and participants, in addition to its duration, funding received, and funding agency. As of 2021, ongoing projects combining CSP and sCO2 can be divided into two groups: one focused on the system integration of sCO2 cycles with state-of-the-art CSP technologies; and the other focused on new systems, components, and materials at higher temperatures with lower maturity. Among the demonstration group of projects, SOLARSCO2OL and TESTBED can be highlighted, in EU and USA, respectively, which both aim at a MW-scale pilot to show the technical and economic viability of integrating a conventional CSP molten salt system with a novel sCO2 cycle, and are therefore limited to a turbine inlet temperature of approximately 565 °C. This is also the case of the pilot plant being developed by EDF in China, which involves the retrofitting of Shouhang’s 10 MWe concentrated solar power plant that is operating at a maximum temperature of molten salt of 530 °C with a supercritical CO2 power cycle [er cycle .2, are the STEP project and Phase 3 of the US DOE Gen3 CSP program. The STEP project aims at demonstrating the technical viability of a 10 MW sCO2 cycle operating at 700 °C, at different configurations, with heat provided by natural gas. Phase 3 of the US DOE Gen3 CSP program, by comparison, focuses on demonstrating a new particle-based CSP system able to collect useful heat up to 900 °C, which can potentially enable high-temperature CSP-sCO2 systems in the future. In both the EU and the USA, particle-based systems appear to be the preferred path for future high-temperature CSP applications, at 700 °C or above. Considering that the maturity and commercial viability of such particle-based systems is yet to be proven, it can be estimated that, if sCO2 systems enter the CSP sector, then projects in the near term  will focus on using proven molten salt technology, thus indicating that most of the risk will relate to the sCO2 system itself.Other demonstration projects not included in the tables below, but of high relevance for CSP and sCO2-CSP applications. It can also be observed that some recent research projects (CARBOSOLA and DESOLINATION) focus on the medium temperature applications of sCO2-CSP, as also shown in the text mining analysis in 2 power cycle; this corresponds to the identification in As shown in the tables, most research projects involve significant optimization and system analysis activities, which reflects the significance of thermodynamic analysis for sCO2 (sCO2) for concentrating solar power (CSP) applications have gained significant attention in recent few years. This recent interest is based on high conversion efficiency predictions, which exceed 50% for the moderate temperature range, and the technology’s suitability for solar energy integration. This interest is also reflected in the large scientific bibliography (441 WOS indexed publications since 1993) and publicly funded research projects (24 projects in Europe and the United States since 2019). The main conclusions derived from the bibliometrics analysis conducted in this study are as follows:2 literature relates to solar energy applications;One-third of the existing sCO2 scientific publications has been observed, as 70% of the total number of documents were published after 2015 and 80% of citations were received after 2016;Rapid growth in sCOThe most productive publishing countries during 2020 were China and Spain, which combined accounted for almost 50% of the total publications, and the top 10 most productive countries contributed a combined 86.5% of the totalConsidering the whole publishing timeframe, institutions from the United States, China, and Australia still dominate in terms of publishing and citations; this was confirmed by the high number of interactions among authors and institutions from these countries;Despite the large number of publishing sources (105), most documents were retrieved from 10 general energy-related sources, which are also the most connected in terms of citations;Regarding text-mining techniques applied to the indexed publications, the most common keywords referred to cycle optimization, system analysis, and performance studies; growing interest was observed for medium-low temperature applications through related keywords, such as Rankine cycle, organic Rankine cycle, and waste heat recovery;Areas of research related to heat exchanger design and energy storage solutions were detected through a density visualization map, which is consistent with the objectives of ongoing projects in Europe and the United States.Research activities on supercritical CO


To explore the basic mechanical properties and size effects of recycled aggregate concrete (RAC) with different substitution ratios of coarse recycled concrete aggregates (CRCAs) to replace natural coarse aggregates (NCA), the failure modes and mechanical parameters of RAC under different loading conditions including compression, splitting tensile resistance and direct shear were compared and analyzed. The conclusions drawn are as follows: the failure mechanisms of concrete with different substitution ratios of CRCAs are similar; with the increase in substitution ratio, the peak compressive stress and peak tensile stress of RAC decrease gradually, the splitting limit displacement decreases, and the splitting tensile modulus slightly increases; with the increase in the concrete cube’s side length, the peak compressive stress of RAC declines gradually, but the integrity after compression is gradually improved; and the increase in the substitution ratio of the recycled aggregate reduces the impact of the size effect on the peak compressive stress of RAC. Furthermore, an influence equation of the coupling effect of the substitution ratio and size effect on the peak compressive stress of RAC was quantitatively established. The research results are of great significance for the engineering application of RAC and the strength selection of RAC structure design. The continuous development of urbanization and the alternation of old and new buildings have given rise to the problem of considerable construction and demolition (C&D) waste. How to dispose and reuse the C&D waste in an environmentally friendly way has attracted significant attention. In response to this issue, experts in related fields have proposed a kind of recycled aggregate concrete (RAC) which is formed by partly or completely replacing the natural coarse aggregates (NCAs) in ordinary concrete with the recycled concrete aggregates (RCAs) obtained by crushing and screening the concrete C&D waste. During the last 20 years, the recycling of C&D waste has emerged as a socioeconomic priority, mainly in developed countries, and in the present decade, developing countries are also gradually adopting this priority. Technologies for the separation and recovery of C&D waste are well established, readily accessible and generally inexpensive . AdditioWith regard to research on the basic mechanical properties of RAC, Katz  and AchtThe size effect of concrete defines the mechanical property of concrete as a variable that varies according to the geometric size of concrete, and studies on the size effect of concrete are conducive to further understanding the impact of small-size structure tests on actual structure research ,20. By aIn this paper, the basic mechanical properties and compression size effects of RAC with different aggregate substitution ratios were experimentally studied. Considering the impacts of factors such as five substitution ratios of recycled aggregate , three loading modes  and three side lengths , with the failure modes and mechanical parameters of RAC obtained by hydraulic servo-motor and direct shear apparatus under different loading modes, the basic mechanical properties and compression size effect of RAC were systematically analyzed from qualitative and quantitative perspectives, respectively.3.In this paper, an experimental study on the basic mechanical properties and compression size effect of RAC with different substitution ratios is presented. The aggregate substitution ratios of RAC employed in this study were 0%, 25%, 50%, 75%, and 100%, among which the concrete with a substitution ratio of 0% refers to ordinary concrete. The raw materials of these RAC specimens included cement, fine aggregate, coarse aggregate, and tap water; the additives in the raw material were not taken into account. The cement was ordinary Portland cement P·O 42.5 from China United Cement Corporation in Jiangsu province; the fine aggregates were natural river sand produced locally whose fineness modulus is 2.5 and apparent density is 2650 kg/mMany previous studies have presented that the compressive strength of recycled concrete mixed with a certain proportion of fine recycled concrete aggregates (FRCAs) is greatly reduced due to the large water absorption rate of FRCAs ,28,29. AWhen the substitution ratio of CRCA is 0%, this means that the concrete is ordinary concrete. In the present study, the design strength of ordinary concrete was 30 MPa. The design and calculation of the mix proportion were conducted according to the Specification for Mix Proportion Design of Ordinary Concrete (Chinese Standard JGJ 55-2011) . Before According to the calculation results of the mix proportion of RAC with different aggregate substitution ratios presented in In this paper, the basic mechanical properties and size effect of five kinds of RAC with different substitution ratios were studied. The loading modes employed for analyzing the basic mechanical properties included uniaxial compression, uniaxial tension, and shear, among which uniaxial tension was completed by splitting tensile loading. For investigating the size effect of concrete, considering the stress state of concrete in practical engineering, this research only conducted an experimental study on the compression size effect of RAC.According to the Standard for Test Method of Mechanical Properties on Ordinary Concrete (Chinese Standard GB/T 50081-2019) , the dimIn this paper, the compression loading of RAC was completed by the hydraulic servo-motor; the tension loading was realized by the combination of a hydraulic servo-motor and splitting tensile mold; and the shear loading was completed with the direct shear apparatus. The independent load transducers of the hydraulic servo-motor and the direct shear apparatus were able to meet the requirements of load measurement. The deformation was measured by the strain acquisition instrument and the independent deformation acquisition system. The load and deformation measurements were also able to meet the test requirements.The loading of RAC with different aggregate substitution ratios was realized by a load–displacement hybrid control. First, by means of the load control, with a 20% maximum strength as the preloading value, the loading and unloading processes were repeated three times to control the influence of the gap between the loading end of the equipment and the loading surface of the specimen on the test results. Then, the loading was started by displacement control at a speed of 1 mm/min. The load and deformation data were collected at the same time, and the loading was terminated when the specimen was damaged. In order to control the friction between the loading end of the equipment and the loading surface of the specimen, this study used the combination of three layers of polyethylene plastic film and mineral butter mentioned in Reference , so thatAccording to the experimental scheme of the basic mechanical properties of RAC with different aggregate substitution ratios, the failure modes of the concrete under compression, tension, and shear loading were obtained. Based on the study of the failure modes of RAC, the influence of the substitution ratio of recycled aggregate on the basic mechanical properties of RAC could be analyzed from a macroscopic perspective. In view of the length of the paper, the failure modes of RAC were analyzed at the aggregate substitution ratios of 0%, 50%, and 100%, as shown in As can be observed from In order to further study the shear failure mode of RAC, a substitution ratio of recycled aggregate of 50% was used for the analysis, as shown in It can be observed in The stress–strain curves of RAC under compression, tension, and shear loading were obtained based on the experimental scheme of the basic mechanical properties of RAC with different substitution ratios, as shown in It can be seen from With the peak stresses that were obtained from the stress–deformation curves of RAC with different substitution ratios under compression, tension, and shear loading modes, the impact of substitution ratios of recycled aggregate on the peak stress of RAC, as well as the relationship between the substitution ratio and the variation of peak stress, was studied. The results are given in To better analyze the influence of the substitution ratio of recycled aggregate on the peak compressive, tensile, and shear stresses of RAC, the correlation between the substitution ratio and peak stress of RAC was obtained from For different loading conditions, the strength of recycled concrete is expressed in the form of error bar. According to the analysis, the error range of the recycled concrete strength test value is controlled within 10%, which meets the research requirements. The analysis of Researchers’ opinions ,39 are dft is the peak tensile stress of concrete, fcu is the peak compressive stress of concrete, and τ is the peak shear stress of concrete.The literature  has propBased on the peak compressive stress, peak tensile stress, and peak shear stress of RAC with different substitution ratios, as well as Equations (1) and (2), the relationships among the compressive, tensile, and shear stresses of RAC were obtained, as shown in It can be observed from Based on the experimental scheme for five substitution ratios of recycled aggregate and three kinds of concrete cubes, the failure modes of RAC under different loading modes were obtained. Considering the length of the paper, the failure modes of specimens with different sizes at the substitution ratios of recycled aggregate of 0%, 50%, and 100% were analyzed, as shown in Analysis of Based on the loading scheme for the compression size effect of RAC with different substitution ratios, the peak compressive stresses of RAC under five substitution ratios of recycled aggregate  and three side lengths (70 mm/100 mm/150 mm) cubes were obtained, as shown in It can be understood from fcu,70, fcu,100, and fcu,150 are the peak compressive stresses of concrete cube specimens whose sizes are 70 mm/100 mm/150 mm, respectively; the unit is MPa, and γ100 and γ150 are the size effects of 100 mm/150 mm concrete cubes, respectively.In order to further quantitatively analyze the size effect law of RAC with different substitution ratios, this paper refers to the quantitative expression of the size effect presented in the relevant literature , and intAccording to Equations (3) and (4), as well as the test values of the peak compressive stress of RAC listed in It can be observed from With a decrease in the substitution ratio of recycled aggregate, the size effect of the peak compressive stress of concrete is gradually enhanced. The principal reason for this is that the initial injuries inside the RAC progressively increase with the rising substitution ratio. Compared with ordinary concrete, RAC exhibits a strong brittleness, which leads to an increase in the substitution ratio of recycled aggregate, thereby further reducing the impact of the size effect on the peak compressive stress of RAC. Our research conclusion is in line with the findings regarding the change law of the size effect on the peak compressive stress of ordinary concrete proposed in references ,43; thatN is the peak compressive stress of concrete, unit: MPa; σ∞ is the nominal peak compressive stress of concrete, unit: MPa; D is the side length of the concrete specimen, unit: mm; and Db is the corresponding characteristic dimension of the structure, unit: mm. In Equation (5), σ∞ and Db are the undetermined parameters of the equation.According to the basic theory of the size effect established based on the energy release criterion, the size effect of quasi-brittle materials is mainly caused by the strain energy consumed by the generation and expansion of macroscopic cracks inside the materials under external loads. Based on the two conditions of energy balance and deformation coordination, Bazant  proposed∞ are 19.78, 20.77, 18.61, 18.49, and 18.01, respectively, and the values of Db are 39.02, 21.34, 26.04, 18.54, and 13.76, respectively. The size effect law of RAC with different substitution ratios of recycled aggregate are shown in Equations (6)–(10) and With the peak compressive stresses of different concrete cubes, mathematical regression analysis was carried out through Equation (5). The results show that when the substitution ratios of recycled aggregate are 0%, 25%, 50%, 75%, and 100%, the corresponding values of parameter σ∞ and Db was studied first. Equations (11) and (12) and the expressions shown in Based on the size effect law, this paper proposes a formula for calculating the size effect on the compressive peak stress of RAC with different substitution ratios, which has good applicability and can better describe the size effect law of the compressive peak stress of RAC with different substitution ratios. To investigate the impact of the coupling effect of the substitution ratio of recycled aggregate and the side length of the specimen on the peak compressive stress of RAC, the influence law of the substitution ratio for parameters σ∞ and Db by the substitution ratio of recycled aggregate can explain the relationship between the parameters well. The following expression is obtained by substituting Equations (11) and (12) into Equation (5):It can be observed from Equations (11) and (12) and Equation (13) is the calculation equation for the peak compressive stress of RAC under the coupling effect of the substitution ratio of recycled aggregate and the side length of the concrete cube. According to the application range of the size effect of practical engineering concrete, when the impact of the size effect on the peak stress of concrete varies within 3%, the critical point for the stress state is called critical stress. The side length of the concrete cube corresponding to the critical stress is the critical dimension. Through Equation (13), the critical dimensions and critical stresses of RAC with different substitution ratios were obtained. The results show that when the substitution ratios are 0%, 25%, 50%, 75%, and 100%, the corresponding critical dimensions of concrete are 1026 mm, 882 mm, 732 mm, 578 mm, and 418 mm, and the critical stresses are 20.98 MPa, 20.36 MPa, 19.75 MPa, 19.14 MPa, and 18.53 MPa, respectively. Therefore, the conclusion that the critical dimension and critical stress of RAC both reduce gradually with the rising substitution ratio of recycled aggregate can be drawn.L and critical stress σL impacted by the substitution ratio of the recycled aggregate ξ, Equationss (14) and (15) and the quantitative expressions shown in By qualitatively analyzing the critical dimension DIt can be known from the above formulae and figure that the critical dimension and critical stress of RAC decrease almost linearly with an increase in the substitution ratio of recycled aggregate. The proposed formulae have a good applicability to the quantitative description of the critical dimension and critical stress of RAC affected by the substitution ratio of recycled aggregate.In this study, the basic mechanical properties of RAC with different substitution ratios under compression, tension, and shear actions, as well its compression size effects, were experimentally studied. By comparing and analyzing the failure modes and mechanical characteristic parameters of RAC under different loading conditions, the following conclusions can be drawn:1. With an increase in the substitution ratio of CRCA, the cracks formed on the non-loaded surface of concrete under compression failure mode gradually decline, whereas the tensile and shear failure sections of concrete are relatively unsmooth, accompanied by many concrete fragments, and their failure mechanisms are not affected by the substitution ratio of CRCA. As the specimen’s size increases, the integrity of concrete after the compression failure is progressively enhanced. The substitution ratio of CRCA has the smallest impact on the concrete’s compression failure when the side length of the concrete cube is 150 mm;2. The load–deformation curves of RAC with different substitution ratios of CRCA were basically the same in compression, splitting tensile, and shear. Additionally, the splitting and shear loading modes showed relatively obvious brittleness characteristics. With the increase in substitution ratio, the peak compressive stress and peak tensile stress of RAC decrease gradually, and the splitting limit displacement decrease, and the splitting tensile modulus increase slightly. Based on the relationship equation of the peak compressive stress, peak tensile stress, and peak shear stress of ordinary concrete, the compressive parameters of RAC with different substitution ratios were compared and the compressive performance of RAC was analyzed from a mechanism perspective;3. The size effect of RAC under compression was analyzed based on size effect degree. With the same substitution ratio of CRCA, the peak compressive stress of concrete decreases gradually with an increase in the side length of the concrete specimen. As the substitution ratio of CRCA increases, the impact of the size effect on the peak compressive stress of concrete declines gradually. The influence of size effect on the compressive strength of RAC is higher than that of ordinary concrete. Specifically, when the substitution ratios were 0% and 100%, the peak compressive stresses of RAC reduced by the influence of the size effect were up to 18.97% and 8.53%, respectively;4. Based on the law of the size effect, this paper proposes a calculation equation for the coupling effect of the substitution ratio of RAC and the size effect on the peak compressive stress of RAC. The proposed equation has good applicability. The analysis of the equation revealed that the critical dimension and critical stress of RAC both decline gradually with a rising substitution ratio of CRCA. The research results are of great significance to the application of RAC in engineering projects.


Fibrous sclerosing tumours and hypertrophic lesions in IgG4-related disease (IgG4-RD) are formed in various organs throughout the body, but disease in the oral region is not included among individual organ manifestations. We report a case of ossifying fibrous epulis that developed from the gingiva, as an instance of IgG4-RD.A 60-year-old Japanese man visited the Department of Oral and Maxillofacial Surgery, Gunma University Hospital, with a chief complaint of swelling of the left mandibular gingiva. A 65 mm × 45 mm pedunculated tumour was observed. The bilateral submandibular lymph nodes were enlarged. The intraoperative pathological diagnosis of the enlarged cervical lymph nodes was inflammation. Based on this diagnosis, surgical excision was limited to the intraoral tumour, which was subsequently pathologically diagnosed as ossifying fibrous epulis. Histopathologically, the ossifying fibrous epulis exhibited increased levels of fibroblasts and collagen fibres, as well as infiltration by numerous plasma cells. The IgG4/IgG cell ratio was > 40%. Serologic analysis revealed hyper-IgG4-emia (> 135 mg/dL). The patient met the comprehensive clinical diagnosis criteria and the American College of Rheumatology and European League Against Rheumatism classification criteria for IgG4-RD. Based on these criteria, we diagnosed the ossifying fibrous epulis in our patient as an IgG4-related disease. A pathological diagnosis of IgG4-related lymphadenopathy was established for the cervical lymph nodes. Concomitant clinical findings were consistent with type II IgG4-related lymphadenopathy.A routine serological test may be needed in cases with marked fibrous changes (such as epulis) in the oral cavity and plasma cells, accompanied by tumour formation, to determine the possibility of individual-organ manifestations of IgG4-related disease. IgG4-related disease (IgG4-RD) is a chronic inflammatory disorder characterised by high serum IgG4 levels and infiltration by IgG4(+) plasma cells. It was originally reported from Japan, although its exact epidemiology and pathology have not yet been fully elucidated. Despite the recent confirmation of an association of type 2 helper T (Th2) cells and regulatory T (Treg) cells with the pathophysiology of IgG4-RD, it is still ambiguous whether IgG4-RD is an autoimmune or allergic disease –3.The comprehensive clinical diagnosis (CCD) criteria , 2 develFibrous sclerosing tumours and hypertrophic lesions are formed in organs throughout the body, but disease in the oral region is not included among the individual organ manifestations of IgG4-RD. Only six studies have associated oral sclerosing disease with IgG4-RD upon searching PubMed from 2000 until 2020 –10.We encountered a patient with an oral sclerosing lesion and IgG4-related lymphadenopathy in the regional lymph nodes (submandibular lymph nodes) that diagnostically met both the CCD criteria and ACR/EULAR criteria.A 60-year-old Japanese man with painful and enlarged intraoral tumour on the left side visited the Department of Oral and Maxillofacial Surgery, Gunma University Hospital. An unusually large pedunculated tumour of approximately 65 mm × 45 mm was localised in the left lower alveolar region. The tumour surface was granulomatous, elastic-hard, partially ulcerated, and haemorrhagic. The tongue was displaced rightward by the tumour Fig. A. There Panoramic radiography and computed tomography (CT) scans both showed compressive bone resorption in the left mandible, but the cortical bone was retained Fig. B. It wasThe clinical diagnosis was a suspected malignant left lower gingival tumour with submandibular lymph node metastasis. The pathology of incisional biopsy indicated the possibility of a mesenchymal tumour, but no definite diagnosis could be made, because there was a strong inflammatory reaction. Thus, excision of the oral tumour , and excisional biopsy of the left submandibular lymph node, were planned. Radical neck dissection was also planned in the event of detecting a malignancy in the submandibular lymph node during intraoperative rapid pathological diagnosis. Rapid pathological diagnosis of the submandibular lymph node during surgery revealed only inflammation but no sign of malignancy. The oral tumour was dissected by subperiosteal detachment with a 10 mm safety margin Fig. A. The coThe cut surface of the excised tumour was solid and whitish. Haematoxylin and eosin (HE) staining revealed the surface to be covered with stratified squamous epithelium and outgrowths of fibroblasts and collagen fibres, showing marked storiform fibrosis. No capsule was present, and lamellar bone formation was observed in the outgrowing fibres. Reactive hyperplasia of blood vessels and inflammatory cell infiltration, such as neutrophils and plasma cells, were also detected Fig. Ba–c. ImmThe excised submandibular lymph node was soft, and the cut surface was solid and milky white. HE staining showed hyperplasia of the lymphoid follicles of irregular sizes accompanied by germinal centres. Blood vessels had grown between the lymphoid follicles and many plasma cells, and fewer eosinophils were mixed, showing a morphology similar to that of reactive lymphadenitis Fig. A, B. ImmBased on this information, a whole-body examination was performed by the Department of Nephrology and Rheumatology, but no finding suggesting the presence of IgG4-RD was observed in any other organ. Since the lesion was localised and the residual right submandibular lymph node was not enlarged, the patient was subjected to course observation. Approximately seven years after surgery, the course has been favourable, without enlargement of the submandibular lymph nodes, or appearance of a new lesion, and without recurrence of ossifying fibrous epulis.The oral tumour (ossifying fibrous epulis) and submandibular lymph nodes in our patient met all three CCD criteria for IgG4-RD: (1) clinical examination revealing characteristic diffuse/localised swellings or masses in single or multiple organs; (2) haematological examination revealing elevated serum IgG4 levels (> 135 mg/dL); and (3) pathological examination revealing (a) marked lymphocyte and plasmacyte infiltration and fibrosis, and (b) infiltration by IgG4(+) plasma cells, with a ratio of IgG4(+)/IgG(+) plasma cells > 40%, and > 10 IgG4(+) plasma cells per HPF. Thus, both oral and cervical lesions in the present case were included in the definitive diagnosis.Storiform fibrosis and obliterative phlebitis have been reported as other pathological characteristics of IgG4-RD, but their development often depends on the specific organ from which the disease develops . We obseStrehl et al.  and ŠteiImmunohistopathological testing revealed that TGF-β was expressed in many plasma cells in our patient Fig. Be. In IgThe disease-forming lesions in the lymph nodes observed in IgG4-RD are characteristic of a condition known as IgG4-related lymphadenopathy. IgG4-related lymphadenopathy is classified into five types based on clinical and pathological findings, and the type localised in the regional lymph nodes in IgG4-RD corresponds to type II. Since the epulis in the present cse was diagnosed as IgG4-RD of the oral cavity, and characteristic follicular hyperplasia and IgG4(+) plasma cell infiltration between follicles were detected, the present case was appropriately diagnosed with type II lymphadenopathy , 25.In conclusion, in the present case, we diagnosed epulis that developed from the gingiva as IgG4-RD. A routine serological test may be required in cases with marked fibrous changes, such as epulis, in the oral cavity and plasma cells accompanied by tumour formation to evaluate possible individual organ manifestations of IgG4-RD.


Metformin is among the most frequently prescribed drugs worldwide for a variety of indications. Although metformin has several important advantages, for example being easy to store and administer, it is associated with a high incidence of gastrointestinal side effects. Slower-release formulations of metformin may reduce the incidence of side effects while maintaining efficacy; however, there is a lack of systematic evidence available to guide head-to-head comparisons between different metformin formulations.PubMed, Web of Science, OVID EMBASE, MEDLINE, The Cochrane database and Clinicaltrials.gov were systematically searched (from inception to 25 January 2021). Trials that randomized adult participants to extended-release formulation of metformin (met-XR), delayed-release (met-DR) or immediate-release metformin (met-IR) were included. Two reviewers independently assessed articles for eligibility and risk-of-bias, with conflicts resolved by a third reviewer. Outcome measures were change in fasting plasma glucose (FPG), glycated haemoglobin (HbA1c), body weight, BMI, lipid profile and side effects. Meta-analyses were conducted using random-effects models.n = 3765) met eligibility criteria. There was no significant difference between the efficacy of met-IR, met-XR or met-DR in changing FPG (p = 0.93). A non-significant reduction in mean body weight was observed in individuals randomized to met-XR vs. met-IR . Individuals randomized to met-XR vs. met-IR had lower low-density lipoprotein (LDL) cholesterol levels . Gastrointestinal (GI) side effects were markedly reduced in patients randomised to met-DR vs. met-IR .Fifteen studies  versus immediate-release metformin formulations in terms of glycaemic control. There were insufficient studies available to compare the efficacy of different metformin formulations outside of diabetes care. However met-XR was associated with reduced serum LDL cholesterol concentrations, while met-DR was strongly associated with reduced GI side effects, which could improve drug compliance.The online version contains supplementary material available at 10.1007/s13300-021-01058-2. To view digital features for this article go to N,N-dimethylbiguanide) is increasingly prescribed worldwide for a widening variety of indications. In 2018, metformin was prescribed over 80 million times, making it the fourth most commonly prescribed drug in the USA [Metformin . Metformin is efficacious in controlling hyperglycaemia and thus minimising the long-term consequences of diabetes . MetformA significant barrier to the use of metformin is the high incidence of side effects, particularly gastrointestinal (GI) symptoms. Of all patients who take metformin, 20–30% report GI side effects; and approximately 5% of all patients discontinue treatment because of severe GI symptoms . The conWe systematically compared the efficacy and side effect profiles of met-IR, met-XR and met-DR. Despite the increased costs of longer-acting preparations of metformin, if there are significant gains in tolerability then increased use of these formulations may ultimately improve concordance, increase achievement of treatment goals and thus ultimately reduce spending within healthcare services.This systematic review and meta-analysis was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines . The sys2), mean body weight (kg), lipid profiles . Any side effects, including GI effects, reported by individual studies were recorded. Data reported only in meeting abstracts was included if the abstract contained sufficient information for assessment. One meeting abstract [Systematic literature searches using pre-specified terms (Supplementary Text S2) were performed on PubMed, Ovid EMBASE, Ovid Medline, Cochrane library, Clinicaltrials.gov and Web of Science from database inception to 25 January 2021. No language or location restrictions were applied. Studies that randomised adults to any ‘extended-release’ formulation of metformin  versus immediate-release metformin (met-IR) were included (Supplementary Table S1). Studies were included if they randomised patients for any indication. All treatment indications were screened for and diagnosed according to local criteria in each study, and we did not apply exclusions with respect to this. No restrictions were applied with respect to the length of follow-up period. Efficacy outcomes were change in fasting plasma glucose , change in glycated haemoglobin , body mass index  independently assessed each study using pre-determined inclusion/exclusion criteria (Supplementary Table 1). A third reviewer (CEA) was available to resolve cases where eligibility was unclear. An initial screen of titles and abstracts was performed, followed by a detailed full paper screen . Data extraction from eligible studies was conducted independently using a standardized pro forma by two authors (JLT-A and IDG) with a third author (CEA) available if required.Each study was independently assessed by two authors (JLT-A and IDG) for quality and validity using the Cochrane Collaboration tool for assessing risk of bias. A third reviewer (CEA) was available to resolve cases where risk of bias was unclear. Seven risk of bias domains were systematically assessed for each study and each domain was given a rating of low risk, unknown risk or high risk of bias (Supplementary Table S2). All risk of bias analysis was conducted at the study level.I2 statistic. We implemented random-effects meta-analyses using restricted maximum-likelihood (REML) estimator. Meta-regression was performed with fasting plasma glucose as the dependent variable and metformin dose as the predictor variable. Sensitivity analyses were performed using ‘leave-one-out’ (LOO) analysis for individual studies. All studies were analysed according to intention-to-treat. All outcomes were subjected to Grading of Recommendations, Assessment, Development and Evaluation (GRADE) analysis . Where p values are reported, an alpha level < 0.05 was considered statistically significant.The principal summary measures were unadjusted odds ratios (OR) (for dichotomous data) or mean difference (MD) (for continuous data). Meta-analysis and meta-regression were performed using Review Manager  and the metafor package in R version 3.5.1 . Funnel plots were constructed to assess publication bias. Meta-analyses with five or more studies included were also subjected to Egger’s test. Heterogeneity between studies was assessed using the n = 3765 participants). The majority of these studies  compared met-XR v. met-IR [n = 571) compared met-DR v. met-IR [n = 260) compared met-DR, met-XR and met-IR [The PRISMA flow chart  demonstrates the screening procedure involved to include 15 eligible studies . One study (n = 571) enrolled people with T2D and chronic kidney disease (CKD I/II) [n = 75) [The majority of studies enrolled people with type 2 diabetes   and one [n = 75) .For all indications and comparisons, the studies varied with respect to quality and design (Supplementary Table S3). The included studies demonstrated heterogeneity with respect to the dosage of metformin (600–2500 mg) and the study duration (Supplementary Table S3). The included studies came from a variety of geographical locations: Europe , Africa/Middle East , Asia (China and Taiwan) and North America /Latin America (USA and Brazil).The risk of bias was moderate-to-low in the majority of included studies; however two studies were open-label , 29. RemThe majority of outcomes were classified as having a moderate certainty of evidence , with one outcome having a high certainty of evidence (LDL cholesterol). The moderate certainty of evidence was due to from five outcomes having high heterogeneity between studies and four outcomes having high degrees of imprecision in the derived estimates. No publication bias  was detected. All studies reported direct evidence .n = 2855) reported either change in FPG or start-and-finish FPG concentrations over 33 separate groups. Of these, two groups were intermediate measurements of the same participants, so 31 groups (n = 2499) were included in meta-analysis . When summary measures were calculated using comparable dosages (1000–1500 mg), there was no significant difference between the efficacy of met-IR, met-XR or met-DR in changing FPG . Met-IR was only reported at two doses, so meta-regression could not reasonably be performed. There was significant dose-dependency of change in FPG for both met-DR and met-XR. For every 1000 mg dose, FPG decreased by 0.90 ± 0.40 mmol/l  with met-XR and 1.00 ± 0.40 mmol/l  with met-XR  reported HbA1c change or start and finish HbA1c concentrations over 29 separate groups . When summary measures were calculated using comparable dosages (1000–1500 mg), there was no significant difference between the efficacy of met-IR, met-XR or met-DR in reducing HbA1c    reported post-treatment BMI for met-IR vs. met-XR. There was no significant difference in post-treatment BMI between participants randomised to met-XR v. met-IR  Fig. a. Three Fig. n = 30 reportThere were no significant differences in the concentrations of total cholesterol, HDL cholesterol or triglycerides observed in participants randomised to met-XR versus met-IR Table . IndividI2 = 71%, p = 0.10), based on nine studies including 2164 participants , based on one study including 472 participants , in one study including 159 participants , based on change in FPG and in HbA1c after treatment. In addition, our analyses showed very similar reductions in FPG with randomisation to met-XR versus met-DR across a range of clinically relevant doses. There was no significant difference in the magnitude of weight loss experienced by patients randomised to different metformin formulations or in the change in their BMI during treatment. However, patients randomised to met-XR had significantly reduced LDL cholesterol levels compared to those randomised to met-IR. GI side effects were markedly reduced in patients randomised to longer-acting metformin preparations compared to met-IR, particularly with met-DR.Our analyses provides the first systematic comparison of the three formulations of metformin that have currently been trialled in head-to-head trials. Meta-regression and extensive sensitivity analyses have been performed to optimise comparisons between available studies and to leverage all existing data, despite methodological differences between the original studies, for example in dosing and study length. There are few previous syntheses of data directly comparing preparations of metformin. A previous comprehensive review concluded that side effects were reduced with met-XR compared to IR, but predated the availability of the new met-DR formulation .n = 571) [n = 260) [The drawing of definitive conclusions from our meta-analysis was limited by both the quantity and quality of the studies available. In particular, there was a lack of studies involving comparisons of individuals randomised to met-DR vs. met-IR   or met-Dn = 260) , 34. We Despite the frequent and widespread prescription of metformin worldwide, there is a relative lack of head-to-head comparison data regarding optimal formulations. This information is important to help guide decision-making about the cost–benefit ratio of prescribing long-acting metformin preparations; in some circumstances the relatively high upfront cost of these preparations may make their use prohibitive, despite potential clinical advantages . The equIn our analysis, mean body weight was reduced following treatment with metformin, regardless of formulation. The underlying mechanism of metformin-associated weight loss remains poorly understood and is likely multifactorial, with several possible contributing mechanisms. Metformin-associated weight loss may be centrally mediated via suppression of orexigenic hypothalamic neurons potentially via GDF-15 , by decrMetformin improves lipid profiles by decreasing the activity and expression of several products involved in lipid synthesis, including acetyl CoA carboxylase (ACCase), sterol regulatory element-binding protein 1 (SREBP-1), fatty acid synthase (FAS) and HMG CoA reductase (HMGCR) . We founOur results demonstrate equal efficacy of longer-acting  versus IR metformin formulations in terms of glycaemic control, but significant additional advantages with the longer-acting formulations. Metformin XR was associated with reduced serum LDL cholesterol concentrations, while metformin DR was strongly associated with reduced GI side effects, which could improve drug compliance. Further research is required to refine the optimal cost–benefit ratio of the different available preparations of metformin in various clinical circumstances.Supplementary file1 (XLSX 51 kb)Supplementary file2 (PDF 3077 kb)Below is the link to the electronic supplementary material.


The numbers of cycles to failure, the developments of strain, stiffness, dissipated energy and acoustic emission hits are focused on in the analyses. The results clearly show that coarse aggregates can influence the fatigue behaviour of concretes in a negative way at higher stress levels and in a positive way at lower stress levels compared to mortars. The granite coarse aggregate decreases the adverse effect at higher stress levels due to its lower modulus of elasticity compared to that of the basalt aggregate. Silica fume improves the fatigue behaviour of concrete and mortar strongly. The increase of the w/c ratio and, thus, the increase in porosity reduces the fatigue resistance of concrete and mortar significantly, due to the weakening of the mortar matrix and of the interfacial transition zone. The results demonstrate the interaction of the coarse aggregates and the mortar matrix with their specific properties, which leads to a certain fatigue behaviour. The acoustic emission gives additional valuable strain-independent information of the damage processes occurring, possibly also on micro- and nanoscales.The results of compressive fatigue investigations on four high-strength concretes and their corresponding mortars are presented. The influences of coarse aggregates generally, the substitution of basalt coarse aggregate by granite, the addition of silica fume and the variation of the water to cement ( Concrete compositions with ever-higher compressive strengths enable the realisation of more filigree concrete structures. These structures are exposed to fatigue-relevant loads to a higher extent because of their lower ratio of deadweight to non-static loads. Moreover, special structures, such as wind energy turbines or machine foundations, are generally exposed to fatigue loading with huge numbers of load cycles. The development of concrete types with ever-higher compressive strengths and the expanded construction of wind energy turbines have led to increased research activities in the field of fatigue resistance of concrete in the last few decades. After focusing mainly on the numbers of cycles to failure, the focus has been more on the damage process in concrete in the last years e.g. –3), usin, usin3])It is well-known that high-strength concrete has a denser binder matrix with increased compressive strength and improved interfacial transition zones (ITZ) compared to normal-strength concrete. This also leads to an increased modulus of elasticity. However, the influence of the improved microstructure on the compressive fatigue resistance has not yet been clarified. Contradictory results are documented in literature. Some investigators found that high-strength concrete has a lower fatigue resistance compared to normal-strength concrete (e.g. ). No or Only a few investigations were focused on the influence of the concrete composition and the porosity of the mortar matrix on the compressive fatigue behaviour. Mehmel and Kern  investigRegarding the influence of the type of coarse aggregate, Breitenbücher et al.  and IbukMehmel and Kern  and Luscw/c) ratios on the bending fatigue resistance for a normal-strength concrete )Indications are available that fatigue damage might be traced back to the formation and development of cracks in the mortar matrix and in the ITZ –15, 26. Overall, the measuring and analysing of (macroscopic) damage indicators is of great importance for the fatigue research of concrete, due to the existing limitations of the imaging techniques. In addition to strain, stiffness and dissipated energy development, the acoustic emission is a continuously measurable damage indicator, which allows for additional and strain-independent information about the damage process in concrete’s microstructure , 30–33. w/c ratio, respectively, higher porosity of microstructure are analysed. The fatigue behaviour of their corresponding hardened mortar matrix, called ‘mortar’, is analysed comparatively, investigating the influence of coarse aggregates. The numbers of cycles to failure, the developments of strain, stiffness, dissipated energy and AE-hits are focused on in the analyses. The results presented were determined within a conjoint research project together with Prof. Löhnert, TU Dresden, which is part of the DFG Priority Programme SPP 2020.In this paper, the results of compressive fatigue tests on four different, systematically modified concrete compositions and their corresponding mortars are presented. Two types of high-strength concrete with basalt, respectively, granite coarse aggregate, one high-strength concrete with added silica fume and one high-strength concrete with a higher w/c ratio of 0.35, basalt aggregate and without silica fume. Concrete RH1-B-Si has the same composition as RH1-B but the cement was partially replaced by silica fume, following the approach of the same paste film thickness of [w/c ratio of 0.5 and a lower compressive strength was considered. This composition is slightly further adjusted in order to ensure similar fresh concrete properties. Based on the reference composition, the basalt aggregate was substituted by granite aggregate with the same mass content and the same grain size distribution in concrete RH1-G. The densities of the aggregates were experimentally determined as 2.9 kg/dm3 for the basalt and as 2.7 kg/dm3 for the granite. Thus, the volume of the granite aggregate in RH1-G is with 105% slightly larger than the volume of the basalt aggregate in RH1-B.Four high-strength concretes were investigated Table . Concretkness of . In addiIn addition, corresponding mortars were investigated Table . The morh = 180 mm and a diameter of d = 60 mm. The test velocity was 0.5 MPa/s. The modulus of elasticity was determined according to DIN EN 12390-13 [h = 300 mm and d = 150 mm. The basalt has a mean compressive strength of fcm,b = 326 MPa and a mean modulus of elasticity of Em,b = 99,800 MPa. The values are fcm,g = 203 MPa and Em,g = 56,200 MPa for the granite. Thus, a high difference in the compressive strength and, especially, in the modulus of elasticity exists, as it was intended by the selection of the aggregate types investigated. The mean values of the 28-day compressive strength fcm,cube determined according to DIN EN 12390-3 [Ecm according to DIN EN 12390-13 [The compressive strengths of the aggregates were tested using drill cores with a height of 12390-13  using dr 12390-3  and the 12390-13  of the ffcm,cube and an increase of the modulus of elasticity Ecm (M-B-Si). Due to the higher w/c ratio of 0.5, the mortar M-B-w has a significantly lower 28-day compressive strength and a significantly lower modulus of elasticity compared to the reference mortar M-B. These changes in properties can be traced back to the higher porosity of M-B-w.With regard to the mortars, silica fume leads to a slight increase of the 28-day compressive strength fcm,cube only slightly compared to the mortar M-B. However, it increases the modulus of elasticity compared to that of the mortar. The silica fume leads to an increase of the compressive strength and modulus of elasticity of RH1-B-Si compared to RH1-B. Whereby the silica fume has an enhanced positive effect on the compressive strength of the concrete compared to that of the mortar, revealing its strengthening effect in the ITZ of the coarse aggregates and in highly stressed areas of the mortar matrix. The compressive strength fcm,cube of RH1-B-w is 63% and the modulus of elasticity Ecm 84% of that of the reference concrete RH1-B due to the higher w/c ratio. The basalt coarse aggregate in RH1-B-w leads to an increased modulus of elasticity but the compressive strength slightly decreases compared to the mortar. The substitution of basalt aggregate by granite aggregate has a negligible effect on the compressive strength but the modulus of elasticity is 89% of that of RH1-B due to the lower modulus of elasticity of the granite aggregate. The properties displayed in Table Regarding the concretes, the basalt aggregate in RH1-B increases the compressive strength fcm,ref were determined just before conducting the fatigue tests, using five specimens from the same batch and with the same geometry as the specimens used in the fatigue tests. These tests were conducted force-controlled with a test velocity of 0.5 MPa/s. The compressive fatigue reference strength fcm,ref was calculated for each concrete and mortar as the mean value of its compressive strengths. The compressive fatigue reference strength is required to determine the axial test stresses based on the chosen fatigues stress levels.The compressive fatigue reference strengths of the concretes and mortars h = 180 mm and diameter of d = 60 mm. PVC formwork was used for casting. The concrete was filled into the formworks in two equal layers and each layer was mechanically compacted using a vibrating table. The formwork of the concrete specimens was removed 7 days after concreting and the cylinders were stored in standard climate (20 °C/65% R.H.) until testing. The treatment of the mortar specimens was different compared to that of the concrete specimens in order to avoid increased microcracking due to shrinkage: the mortar specimens were also stored in standard climate until testing but the formwork was removed 14 days after concreting. Subsequently, these specimens were stored wrapped in plastic foil for 14 days and then without foil until testing for at least further 28 days in standard climate (gentle drying). The test surfaces of all specimens were plane-parallel ground and polished to achieve a uniform stress distribution. Due to the corona virus shutdown of the laboratory, the specimens of batch 1 (B1) of the concrete with silica fume had to be tested later than originally planned with an age of specimens between 126 and 147 days. Therefore, batch 2 (B2) was produced and additional fatigue tests were conducted. The age of all specimens at testing, except of those from batch 1, was between 56 and 87 days.The investigations were conducted using cylindrical specimens with a height of Smax = 0.85 or Smax = 0.70. The minimum stress level was kept constant at Smin = 0.05 in all tests. The test frequency applied was ft = 1.0 Hz in all fatigue tests. This test frequency was chosen in order to prevent specimens heating due to mechanical loading. The full amplitude was applied in the first load cycle. Three specimens of each concrete and mortar type were loaded at each stress level until fatigue failure occurred. Exception was made for the concrete with silica fume of batch 2 at Smax = 0.70 where two run-outs occurred. Overall, 47 specimens were tested in the fatigue investigations presented in this paper. An overview of the fatigue tests is available from Table The maximum stress level in the fatigue tests was either The fatigue tests were carried out force-controlled using a class 0.5 servo-hydraulic testing machine with a 500 kN actuator (according to ISO 7500-1 ). The axSmax = 0.85. However, flatter developments were determined for the specimens of batch 2 at Smax = 0.70 leading to higher numbers of cycles and test break-offs (run-out specimens). Additionally considering the similar values of compressive strengths of both batches  and due to the high-grade instable state of the microstructure, which is reached in the last cycle . For ths papers , 38).The peak strains were obtained by peak analyses of the sinusoidal strain curves determined by the three laser distance sensors and subsequently averaged in order to obtaining the mean strain development for each specimen. The gradient of the strain development in phase II (i.e. strain increase per load cycle) and the total growth of strain within the degradation process are focused on as parameters. The development of stiffness was determined for each specimen based on the secant modulus in the decreasing branch of the hysteresis loop, according to Eq. , using tRegarding the development of stiffness, the gradient of stiffness development in phase II (i.e. reduction of stiffness per load cycle) and the percentile reduction of stiffness from the first to the last load cycle (cf. Eq. ), with tThe dissipated energy was calculated for each load cycle as the area enclosed by the hysteresis loop. The development of dissipated energy describes the visco-elastic material behaviour within the fatigue process and, thus, the deformation capability. Here, the gradient of dissipated energy in phase II (i.e. dissipated energy per load cycle), the average dissipated energy per load cycle in phase II and the sum of dissipated energy within the complete fatigue process are analysed as parameters. The average dissipated energy per load cycle in phase II gives information about the range of deformation capability within the fatigue process for the purpose of comparison between different concretes and mortars. It is calculated as follows:The AE-hits are summarised from cycle to cycle and displayed as developments of cumulated AE-hits. The gradient of cumulated AE-hits in phase II (i.e. increase in AE-hits per load cycle) and the total number of AE-hits in the complete fatigue process are used as parameters.N/Nf and, subsequently, multiplying this averaged curve by the mean value of the number of cycles to failure Nf. Please note that the gradients of the curves are distorted due to this approach. Thus, the developments in Figs. In view of the multitude of single curves, averaged curves of the damage indicators were determined for each concrete and mortar for the purpose of graphical presentation. They were calculated for identical tests by averaging the developments of each damage indicator with regard to the related numbers of load cycles Nf). The numbers of cycles applied of the two run-out specimens of RH1-B-Si are not included in the appropriate mean value. All single and mean values are included in Table The mean numbers of cycles to failure of the concretes and mortars are presented in Fig. w/c ratio has a negative effect. However, the increase in mean number of cycles to failure of the mortar with silica fume is accompanied by a higher scatter of single values  or lower (RH1-B-Si and RH1-B-w) than those of the corresponding mortars. By contrast, at Smax = 0.70, all concretes reached significantly higher mean numbers of cycles to failure compared to their corresponding mortars. Regarding the concrete with silica fume, the difference in mean numbers of cycles to failure is higher than displayed in Fig. However, the numbers of cycles to failure of the concretes at Smax = 0.85 and Smax = 0.70 are shown in Fig. Smax = 0.85 (a) and Smax = 0.70 (b) are displayed. It is obvious that the mortar with the higher w/c ratio M-B-w shows the steepest gradients of strain in phase II, followed by the reference mortar M-B and the mortar with silica fume M-B-Si with the flattest gradient in phase II at both stress levels  compared to that of the mortar (M-B → M-B-w). Therefore, the relation of gradients in phase II of the mortar and the concrete is also reversed compared to the relation of RH1-B and M-B. All mortars have higher magnitudes of maximum strain compared to their corresponding concretes, whereby the differences depend on the type of mortar. However, these findings reveal the interaction of the coarse aggregates and the mortar with their specific properties, which leads to a certain strain development.However, in the case of the mortar and concrete with silica fume, the mortar specimens are strengthened to a higher degree. The gradient of strain is more decreased (M-B → M-B-Si) in comparison to the corresponding concrete (RH1-B → RH1-B-Si). Thus, the relation of gradients in phase II of the mortar and the concrete is reversed compared to that of RH1-B and M-B (without silica fume). In the case of the higher Smax = 0.85 and Smax = 0.70 and those for the concretes in Fig. w/c ratio. It is obvious from Fig. The developments of stiffness of the mortars are shown in Fig. w/c ratio shows the steepest gradients of stiffness in phase II, followed by the reference concrete RH1-B and the concrete with silica fume RH1-B-Si at both stress levels, thus, the same as for the mortars. However, at Smax = 0.70, the difference between the reference concrete and the concrete with silica fume and, thus, the effect of silica fume is small  and the highest for the concrete with the weakened mortar and ITZ (higher w/c ratio).Comparing the stiffness developments of the concretes with those of the corresponding mortars, all concretes show steeper gradients of stiffness in phase II at The developments of the dissipated energy within the fatigue process are shown for the mortars in Fig. Smax = 0.85 and, thus, the same order as for the mortars exists. Regarding Smax = 0.70, the highest value of the gradient is also reached by RH1-B-w, followed by RH1-B and RH1-B-Si with similar values (the latter would be further reduced by the run-out specimens). Compared to the basalt concrete RH1-B, the granite concrete RH1-G shows a flatter gradient in phase II at Smax = 0.85, but the relation is reversed at Smax = 0.70, same as detected for the gradient of strain  with their corresponding mortars . It should be noted that own fatigue tests with comparable loads conducted on the basalt stone showed no indications of damage occurring.w/c ratio RH1-B-w also have higher values compared to their corresponding mortars. They also reached lower numbers of cycles to failure compared to their corresponding mortars. These findings are also an indication of a negative effect of the basalt coarse aggregate at higher stress levels due to the induced inhomogeneous stress distribution, described previously in [At the lower stress level, the basalt coarse aggregate in concrete leads to an improved fatigue behaviour observable by the flatter gradients of strain, stiffness and dissipated energy in phase II and by the higher numbers of cycles to failure of all concretes. At the higher stress level, the gradients of stiffness are steeper for all concretes and, thus, more stiffness reduction per load cycle occurs in the concretes, indicating a negative effect. Regarding the gradient of strain in phase II, the concrete with silica fume RH1-B-Si and that with the higher ously in , 12.Smax = 0.85. Considering the overall view of the results obtained for the other concretes and mortars and considering that the gradients of stiffness show the same relation for RH1-B/M-B as for the other concretes/mortars, the following explanation is assumed: the concrete specimens of RH1-B, of course, contain a smaller volume of mortar matrix compared to the mortar specimens M-B. If a comparable stress distribution was present, then quantitatively less fatigue-induced damage would develop in the mortar matrix of the concrete. But concurrently a more inhomogeneous stress distribution compared to the (pure) mortar specimens is present at Smax = 0.85 due to the basalt coarse aggregate. This might lead to the development of more damage, especially, in highly stressed areas of the mortar matrix. Both effects superimpose and lead to the macroscopically detectable fatigue behaviour of the concrete.By contrast, the reference concrete RH1-B has a flatter gradient of strain compared to the corresponding mortar M-B and, furthermore, reached almost the same mean number of cycles to failure at w/c ratio (RH1-B-w/M-B-w). As a result, the relation of the gradients of strain and of the numbers of cycle to failure are different for these concretes/mortars compared to the reference concrete/mortar. Altogether, it is assumed that the similarity of the numbers of cycles to failure of RH1-B and M-B at Smax = 0.85 is a rather random result.Both effects are generally present for all concretes but the damage sensitivity of the mortars differs, due to the addition of silica fume (RH1-B-Si/M-B-Si), respectively, the increased The comparison of the average dissipated energy and the gradient of dissipated energy in phase II between the concretes and their mortars demonstrates, that the deformation capability and its increase due to the induced damage is reduced by the basalt coarse aggregate. The first aspect is connected to the higher stiffness of the coarse aggregate compared to the mortar matrix. The latter aspect must be connected to the smaller volume of the mortar matrix in the concrete, which is damaged. Exception was found for the gradient of dissipated energy of RH1-B-w and M-B-w at the higher stress level, which is steeper for the concrete. This might be related to a relatively strong damage development in the weakened mortar matrix due to the presence of coarse aggregate. Nevertheless, an increase of deformation capability due to the presence of basalt coarse aggregate seems to be conceivable in general, considering additional displacements between the coarse aggregates and the surrounding mortar matrix. Unfortunately, this cannot be differentiated based on the investigation conducted.Overall, the developments of strain and dissipated energy of concrete seem to be strongly influenced by the volume of and the damage development in the mortar matrix. The gradient of stiffness in phase II might be more influenced by the interaction of the basalt coarse aggregates and the surrounding mortar matrix. The effect of coarse aggregate could be predominated by the generation of an inhomogeneous stress distribution with highly stressed areas, especially at higher stress levels, which accelerate the damage processes in the mortar matrix and in the ITZ. At lower stress levels, smaller numbers of highly stressed areas and/or lower stresses in such areas can be assumed. Here, a predominantly beneficial effect exists due to the higher fatigue resistance and stiffness of the coarse aggregate compared to the surrounding mortar matrix, both leading to an attraction of stresses. An effect of the differing quantities of (weaker) ITZ in the concretes in comparison to the mortars, cannot be distinguished due to the superimposition of effects previously described.The substitution of basalt aggregate by granite aggregate with a considerably lower modulus of elasticity benefits the concrete’s fatigue behaviour at higher stress levels and impairs the behaviour at lower stress levels. This results in flatter gradients of strain, stiffness and dissipated energy in phase II of concrete RH1-G compared to the reference concrete RH1-B at the higher stress level and in a reversed relation at the lower stress level. The volume of both coarse aggregates used is slightly different  monotonically increasing loading. At the similar stress level of Smax = 0.70, a reversed influence is found here. However, in contrast to the investigation presented here, normal-strength concretes were under investigation in [For the higher stress level tated in , 16. In tated in , 16 at aation in , 16.The ‘crackling’ of the granite concrete RH1-G at the lower stress level, found by analyses of the characteristics of the AE-signals and previously reported in , might iThe results obtained clearly demonstrate that the addition of the silica fume leads to a better fatigue resistance of the concrete and mortar at high and low stress levels. This can be traced back to its strengthening effect in the mortar matrix and in the ITZ. Based on the comparison of the mortars (M-B → M-B-Si), respectively, concretes (RH1-B → RH1-B-Si), it becomes clear that the gradients of strain and stiffness in phase II are flatter due to the silica fume. The basalt coarse aggregate in the concrete leads to slightly steeper gradients of strain and stiffness at the higher stress level (M-B-Si → RH1-B-Si). Concurrently, the strengthening effect on the gradient of stiffness of the concrete and mortar is more pronounced at the higher stress level (stress level dependency). Thus, the effect of the silica fume seems to be related to the magnitude of stresses occurring in the microstructure and, therefore, also to the stress distribution in the concrete caused by the coarse aggregates.Based on the average dissipated energy and on the gradient of dissipated energy in phase II, it is observable that the silica fume additionally reduces the deformation capability and the increase in deformation capability due to fatigue damage of the concrete and mortar. These effects are more pronounced for the mortar specimens. The development of the dissipated energy of the concrete with silica fume at the higher stress level, representing shifts between the increase and decrease of the area of the hysteresis loop, is an indication of the occurrence of macroscopically measurable temporal equilibrium states. The fact that this kind of development was not detected for the corresponding mortar indicates a connection to the presence of coarse aggregates.The stepwise development of cumulated AE-hits at the lower stress level might represent damage processes on a very small scale , which are not macroscopically measurable. It is more pronounced for the concrete and mortar with silica fume compared to the other concretes and mortars investigated. Thus, the strengthening of the mortar, and perhaps also of the ITZ, due to the silica fume seems to improve the capability to reach equilibrium states of that damage processes on a very small scale. Overall, the results reveal that a strong positive influence of the silica fume exists on the concrete’s and mortar’s fatigue behaviour. It has to be assumed that the silica fume also improves the fatigue resistance of the ITZ, although this effect could not be distinguished within the investigations conducted.w/c ratio and, thus, the higher porosity in the mortar matrix and the concurrently weaker ITZ clearly lead to a worse fatigue behaviour of the concrete and mortar. Here, the difference in modulus of elasticity between the mortar and the basalt aggregate is the highest . This results in steeper gradients of strain, stiffness and dissipated energy. In contrast, at the lower stress level, the gradients of the concrete are flatter. Both effects (positive and negative) of the coarse aggregate previously described in Section w/c ratio, i.e. the porosity of the microstructure. Two maximum stress levels of Smax = 0.85 and Smax = 0.70 with the same minimum stress level of Smin = 0.05 and a test frequency of ft = 1.0 Hz were investigated. The developments of strain, stiffness, dissipated energy and cumulated AE-hits were analysed comparatively as damage indicators. Each influence was investigated separately in order to pinpoint each effect on the fatigue behaviour. The results of the influence of the composition of high-strength concrete and mortar can be summarised as follows:Basalt coarse aggregate impairs the fatigue behaviour of high-strength concrete at higher stress levels compared to that of the mortar due to the inhomogeneous stress distribution with more highly stressed areas in the microstructure, which accelerate the damage processes in the mortar matrix and in the ITZ. Basalt coarse aggregate improves the fatigue behaviour of high-strength concrete at lower stress levels compared to that of the mortar, due to its higher fatigue resistance and/or higher stiffness compared to the mortar matrix. Here, the attraction of stresses, which relieves stresses in the mortar matrix, might be of importance. However, the effect of coarse aggregate on the concrete’s fatigue behaviour depends on the difference in fatigue resistance and stiffness between the coarse aggregate and the surrounding mortar matrix.Granite aggregate, with its lower modulus of elasticity compared to basalt aggregate, might reduce the inhomogeneous stress distribution, especially at higher stress levels, and, thus, influences the fatigue behaviour of high-strength concrete in a positive way. This effect is reduced with decreasing stress levels. Furthermore, granite aggregate might increase the deformation capability of high-strength concrete compared to basalt aggregate.The silica fume can improve the fatigue behaviour of high-strength concrete and mortar to a high extent. The influence of added silica fume depends on the original properties of the mortar matrix and ITZ and on the internal stress distribution due to the interaction of the coarse aggregate and the mortar matrix.w/c ratio or, rather, higher porosity of the microstructure impairs the fatigue behaviour of high-strength concrete and mortar to a high extent. This must be traced back to the weakening of the mortar matrix and the ITZ.A higher The worse fatigue behaviour of the mortars at lower stress levels can be traced back to the smaller relative volume of basalt aggregate with its higher fatigue resistance and higher stiffness.Regarding high-strength concretes, the damage indicator gradient of strain in phase II is predominated by the damage processes in the mortar matrix and the volume of the mortar matrix. The gradients of stiffness and dissipated energy in phase II are more influenced by the interaction of coarse aggregate and mortar matrix.The number of AE-hits is a good parameter for the comparative evaluation of the damage activity of concretes and their corresponding mortar. Regarding the comparison of concretes with different mortar matrix, the characteristics of the AE-signals should be considered in addition to their number.The results of compressive fatigue investigations on four different compositions of high-strength concrete and their corresponding mortars were presented and discussed comparatively in this paper. For this purpose, the concrete compositions were systematically adjusted in order to analyse the influence of coarse aggregate in general, of two types of coarse aggregate , the addition of silica fume and the increase of the The investigations presented lead to new knowledge about the fatigue behaviour of concretes and mortars with respect to their compositions. By the analysis of acoustic emissions, additional strain-independent knowledge can be generated, whereby the characteristics of AE-signals should be considered more detailed in future analyses. The clustering of AE-hits  seems to