The degree of conversion ranged from 55.0 to 59.8% and was not affected by the addition of MA-POSS-8. Viscosity ranged from 60.0 to 422.3 mPa*s and was not affected by MA-POSS-8 except for one methacrylate-based resin with 60 wt.% BisGMA. Martens hardness and indentation modulus ranged from 161.3 to 138.1 N/mm2 and 4.2 to 3.9 kN/mm2 and were affected by MA-POSS-8 in only one resin . Water sorption was not affected by MA-POSS-8; sol fraction was below the detection limit. Formation of Ca/P precipitates was observed on all specimens of test and control groups. Material properties were not affected adversly by MA-POSS-8 except for slight differences in Martens Hardness, indentation modulus, viscosity, in some groups.The use of functionalized dental adhesives that might prevent degradation of the dentin hybrid layer has been proposed. The aim of the study was to characterize the physicochemical properties and the potential to induce mineral precipitation of methacrylate-based resins containing methacryl-functionalized polyhedral oligomeric silsesquioxane (MA-POSS-8). In total, six different compositions of resins based on bisphenol A glycerolate dimethacrylate , triethylene glycol dimethacrylate  and 2-hydroxyethyl methacrylate  were prepared and infiltrated with 5 wt.% MA-POSS-8. Unfilled resins served as control. Degree of conversion, viscosity, Martens hardness, indentation modulus, water sorption, and sol fraction were investigated. Polymerized specimens were examined by SEM/EDX for the presence of Ca/P precipitates after immersion in artificial saliva for 28 days at 37 °C. Statistical analysis was performed with two-way ANOVA and Tukey’s post-hoc test ( In order to prevent the hybrid layer between a tooth and composite filling from its typical degradation, several attempts have been made to develop bioactive adhesives that would help to restore the hybrid layer during the degradation process ,2. SeverPOSS were successfully used to improve the mechanical properties of dental composites ,8,9. Riz2C=C(CH3)CO2CH2CH(OH)CH2OC6H4]2C(CH3)2, CAS: 1565-94-2, Sigma–Aldrich Chemistry, St. Louis, MO, USA), TEGDMA (CH2=C(CH3)COO(CH2CH2O)3COC(CH3)=CH2, CAS-number 109-16-0, Sigma–Aldrich Chemistry), and HEMA (CH2=C(CH3)COOCH2CH2OH, CAS: 868-77-9, Sigma–Aldrich Chemistry, ®, Hattiesburg, MS, USA) was added to the experimental groups, while the control groups remained unchanged. All resins were then further mixed for 10 min in dark. The resin blends for measuring water sorption, sol fraction, mineral inducing capacity, Martens hardness, and indentation modulus were then removed with a pipette and placed in a Teflon mold. Subsequently, each specimen was light cured from each side for 60 s . To examine the degree of conversion the resin blends were immediately used. For viscosity measurements resins were prepared without an initiator.In total, six experimental methacrylate-based resins were prepared consisting of the monomers BisGMA  and the spectra were collected for the next 390 s.Fourier transformation infrared spectrometry equipped with an attenuated total reflectance accessory  was used to determine the degree of conversion (n = 5). Absorbance spectra were collected by 20 repeated scans in the range of 700 to 4000 cm−1) and the benzyl-groups (aromatic C=C 1608 cm−1) before and after curing was used to calculate the degree of conversion [The ratio between the peak heights of the vinyl- DegreThe oscillation tests (n = 3) were performed at 25 °C using a rheometer . A cone plate geometry with 40 mm diameter and 2° cone angle was used. The resin blends were prepared as described above but without an initiator to avoid polymerization during the experiment. Initially, the amplitude was varied  at a constant frequency to confirm the linear regime of the viscoelastic behavior of the samples. Subsequently, the shear test was performed at the constant amplitude of 15% and varying frequency (10 to 100 rad/s and 100 to 5 rad/s). The steady shear was studied in the range from 1 to 100 1/s and from 100 to 1/s. The two runs were used to check for the reproducibility and to prevent the influence of any sample history on the results. The results of the viscosity were fitted by cross-fit model (Newtonian).2, Bluephase, Ivoclar Vivadent GmbH, Schaan, Liechtenstein). After 24 h under dry conditions at room temperature, the samples were embedded in resin  and polished .Cylindrical specimens were prepared in standardized Teflon forms  and polymerized for 60 s from both sides (>1000 mW/cmHM) was derived from the applied force (F) and the impressed area sA calculated from a penetration depth (h) [Measurement of Martens hardness and indentation modulus was performed with a universal testing machine . The Martens hardness (epth (h) :(2)HM= FIT can be determined from the tangent for the calculation of indentation hardness.6 N/mm2); h/df is evaluated of the test force removal curve at maximum test force; ch is the depth of contact of the indenter with the specimen calculated.The indentation modulus EThe hardness measurement was performed three times per specimen and averaged.2, Bluephase, Ivoclar Vivadent GmbH, Schaan, Liechtenstein), the specimens were kept in a desiccator with silicate gel for drying. The mass was measured with a precision scale  every second day until the difference between two following measurements was below or equal to 0.1 mg (WS) and the sol fraction (SF):The specimens  were prepared, as described above. After curing . Then, the specimens were polished  and stored in artificial saliva [2*2H2O , 3.0 mmol/L NH4Cl , 17.0 mmol/l KCl , 2.0 mmol/L NaSCN , 2.4 mmol/l KH2PO4 , 3.3 mmol/L urea  and 2.4 mmol/L Na2HPO4 . Afterwards all specimens were carefully rinsed with distilled water and stored in a desiccator. One specimen of each group was sputtered by platinum-palladium and inspected by scanning electron microscopy at 10 kV for possible precipitates . To determine the elemental composition of the precipitates, energy-dispersive X-ray spectroscopy analyses at 15 kV was performed  at three characteristic points on carbon sputtered specimens (each group n = 1).Specimens  were prepared in a teflon form and light cured for 60 s from both sides . p < 0.101), but the presence of MA-POSS-8 significantly affected the results (p < 0.001). No interaction between the factors was observed (p < 0.450). Pairwise comparisons between resins with and without MA-POSS-8 revealed no significant differences in the different groups (The degree of conversion ranged from 55.0 to 59.8% . ANOVA rt groups .p < 0.001) and the presence of MA-POSS-8 (p < 0.001) significantly affected viscosity; the interaction was significant (p < 0.0001). Only in resin 3, the viscosity decreased from 422.3 to 333.9 mPa*s when MA-POSS-8 was added. A tendency to lower viscosity through the MA-POSS-8 can be seen in all studied groups except resin 4; however, the pairwise comparisons revealed no significant differences.Both parameters, the composition of experimental methacrylate-based resin (p < 0.001) and indentation modulus (p < 0.001). In addition, a significant effect of MA-POSS-8 could be shown for Martens hardness (p < 0.001) and indentation modulus (p < 0.001). For both Martens hardness (p < 0.001) and indentation modulus (p < 0.003) the interaction between both factors was significant. Martens hardness was reduced significantly only in resin 2 from 161.3 (without MA-POSS-8) to 138.1 N/mm2 (with MA-POSS-8). Similarly, the addition of MA-POSS-8 resulted in a significant difference in the indentation modulus in resin 2  and MA-POSS-8 (p < 0.002), but no significant interaction between the factors was observed (p < 0.540). Post-hoc tests showed no significant differences between the control and test groups. The lowest water sorption was found in the groups with the lowest amount of HEMA and the highest amount of BisGMA; and oppositely, the most hydrophilic behavior was detected in groups with the highest proportion of HEMA and lowest concentration of BisGMA. By keeping a constant proportion of BisGMA, water sorption increased with increasing HEMA concentration  can be estimated from the measured DC of the unfilled (AdhDC) and filled (AdhPOSSDC) adhesive system:VAdh and VAdhPOSS are the normalized molar fractions of C=C groups on the only monomers resp. MA-POSS-8 particles in the system. These were estimated based on each adhesive composition .In this study, the incorporation of MA-POSS-8 did not hinder the polymerization of all experimental resins. This is in line with a previous study by Rizk et al. . Due to position  and the POSSDC ranged from 3.1% up to 56.4%. In the groups with a higher concentration of HEMA (resins 4 to 6), a decreasing trend with an increase of BisGMA fraction and thus also viscosity of the adhesive was observed . This trend is not seen in the group with lower HEMA fraction . Interestingly, the largest difference was found in the groups with only a slight difference in the monomer composition and a very similar viscosity (resins 1 and 4). In this case, a higher HEMA proportion leads to a higher POSSDC, possibly due to a dilution effect and increase of mobility of radicals. Additionally, at both adhesives with the highest viscosity (3 and 6) a very low conversion of MA-POSS-8 was estimated. Overall, there are certainly several factors that influence the MA-POSS-8 conversion. Our data indicate the importance of viscosity and proportion of monomers with various functionality and size. Since in all groups a positive POSSDC was determined, the conversion of all reactive components and the network density could be stable or even improved through the addition of MA-POSS-8 even though such conclusion could not be taken based barely on the measured DC or ITE.The calculated In this study, the addition of MA-POSS-8 did not improve the properties of the experimental resins. Other studies investigating the effect of MA-POSS-8 in concentrations below 5% found significantly improved mechanical properties ,24, whil2+) from the medium, serving as nucleation points.After 28 days of storage in artificial saliva Ca/P-precipitation could be observed on the surface of the test and control groups, without differences. A similar observation was described by Engstrand et al. , who invSimilarly, EDX analysis of the precipitates was below the stochiometric molar ratio of hydroxyapatite (1.67) at any resin. This ratio is preferred since it defines the structure of the natural enamel. However, it should be noted that the structure of the Ca/P precipitates is highly depend on the composition, time of immersion and the pH of the medium used ,28.The addition of MA-POSS-8 to the methacrylate-based resins did not affect the material properties adversely. Depending on the monomer concentrations, MA-POSS-8 may slightly improve viscosity, or slightly affect other mechanical properties. To improve mineral precipitation and capacity, probably a concentration higher than 5 wt.% MA-POSS-8 is needed.


It seems that people’s quality of life can be positively influenced through bicycle tourism. Bicycle tourism can be an effective measure to enhance serious leisure, tourism satisfaction, and quality of life. To verify this empirically, a survey was conducted of bicycle tourists who visited Qinghai Lake in China during an international road bike race. The purpose of the present research is to prove the association between latent variables related to bicycle tourism through statistical analysis. For this, hypothetical relationships based on tourism motivation, serious leisure, tourism satisfaction, and quality of life were presented as research models. As a result of empirical analysis, it was analyzed that friends and nature had an effect on serious leisure among the motivation of bicycle tourism. In addition, it was found that the level of serious leisure for bicycle tourism exerted a positive influence on the satisfaction and quality of life. This suggests that bicycle tourism can improve the quality of life during travel to Qinghai lake by bicycle and revealed the crucial role in relationships is serious leisure. As a new type of tourism and one of the most personalized tourism activities, bicycle tourism is attracting more and more people. Compared to traditional mass tourism, bicycle tourism is recognized as a more free, flexible and in-depth tourism experience. In general, tourists can also satisfy their aesthetic desires and gain friendship and deviance enjoyment through tourism behaviors. From this point of view, bicycle tourism can be considered to be one of the various tourism actions that can sufficiently satisfy the needs of tourists and can satisfy a significant portion of the tourism demands of people in the modern society. In relation to bicycle tourism, an international road bike race has been held in Qinghai Lake, China, and this competition has generated various economic and social benefits to the host area through bicycle tourism. However, despite the contribution of such international road bike races, studies to understand the behavior of bicycle-related tourists through proper theories have not been conducted often. With the increasing desire of people for quality tourism activities, interest in bicycle tourism is gradually increasing, which can enhance quality of life via meaningful activity. Currently, the insufficient researches are either isolated qualitation ethnography or quantitation analysis which are primarily depictive and on the foundation of small and separated specimens ,2. For eSince the late 18th century, the invention and improvement of bicycles have gone evolved over 200 years. Simonsen, Jorensen, and Robbins  defined Motivation is an important variate in bicycle tour research and serves as the starting point in researching tourists’ behaviors and exploring tourists’ consumption. There are 3 commonly utilized theory structures to elucidate tourists’ motivations. Firstly, Maslow’s  hierarchStebbins  argues tHowever, for masses of people, leisure activities such as bike tours are vital, and encompass nature, friends and deviance. The normal definition of SL is that it’s the all-round seeking of amateur or voluntary activities that are adequate and intriguing for participants to discover a profession which acquires and expresses an integration of their specific abilities and experiences’ . The essNevertheless, it can be argued that the idea of SL has been almost neglected in researches pertaining to leisure , and praIn the past relevant leisure research, it is found that motivation and SL are related . Herman Hypothesis 1 (H1).The FRI is important sources of SL.Hypothesis 2 (H2).The DEV is important sources of SL.Hypothesis 3 (H3).The NAT is important sources of SL.In the majority of customer behavior models, satisfaction  serves as the center between the antecedents and descendants’ variates. A variety of customer behavior models have verified the roles of SAT in tourists’ loyal status ,29. The In the studies on sightseeing, massive past researches defined tourism SAT at the general level as a cumulative psychology status stemmed from the tour experiences ,36,37. SHypothesis 4 (H4).SL casts a positive influence on SAT.The concept of quality of life (hereafter QoL) is implicit in many researches on sightseeing influences. As per the OECD , QoL canHypothesis 5 (H5).SAT casts a positive influence on QoL.This research designed a self-reported questionnaire for exploring the association between motivation, SL, SAT, and QoL. The self-reported questionnaire comprised 5 parts: First, three dimensions  with 9 indicators to measure the motivation were adapted from studies of ,46,47,48In this study, five sites around Qinghai Lake were selected for investigation, including the Dayu tribe, Qibingying, the Erlang sword, the Heima River, and Birds Island. The peak season of Qinghai Tourism resulted in a large number of people who participated in bicycle tourism, and this makes the sampling more random and representative. Therefore, the target population of this study were bicycle tourists form China who traveled in the above 5 sites. By virtue of stochastic sample collection, the data were harvested from July 15th, 2018, to August 15th, 2018, before the COVID-19 pandemic outbreak. Finally, 400 questionnaires were used and overall 300 finished were utilized for further data analyses except ineligible ones .In this study, R-statistic was applied to perform descriptive statistics at first. On the foundation of Anderson and Gerbing’s recommendations, this research completed the SEM via a two-step method ,53. MoreThe result of 2 =289.396, df = 155, χ2/df = 1.867, p < 0.001, CFI = 0.960, NFI = 0.918, TLI = 0.951, and RMSEA = 0.054 [Firstly, the CFA was finished via R-studio with a MLE to identify the discriminant validity, and convergent validity of the indices. The fitting indexes reveal that the exterior model fitting was satisfactory with χ = 0.054 . Converg = 0.054 . To be s = 0.054  and Cron = 0.054 . Finally = 0.054 .2 = 373.301, df = 162, χ2/df = 2.304, p < 0.001, CFI = 0.937, NFI= 0.895, TLI = 0.926, RMSEA = 0.066. The modeling exhibited a sufficient fitting to the data. Of the five proposed hypotheses except H2 rejected all hypotheses were accepted. As shown in p < 0.001), H2: DVE has on significant influence on SL . H3: NAT casts a remarkable influence on SL , H4: SL casts a remarkable influence on SAT , H5: SAT casts a remarkable influence on QL . Indicating that greater scores on FRI and DEV meant higher scores on SL. Moreover, SL was found to positively correlate with SAT, SAT was found to positively correlate with QoL. Meaning that higher scores on SL meant higher scores on SAT, higher scores on SAT meant higher scores on QoL. However, the association between DEV to SL was not significant, p > 0.05 implying that there was lack of evidence for demonstrating a relationship between DEV to SL. The assumption test outcomes are presented by This section presents the results of structure modeling depicting bicycle tourism’ decision-making processes. The proposed theoretical model will be analyzed, and hypotheses will be tested in this section by employing R-studio . The strThis study used the research methodology of SEM to test the causality between the motivation factors of bicycle tourism, SL, bicycle tourism SAT, and QoL. As a result of empirical analysis, it was found that FRI and NAT were main motivating factors determining the level of SL, but DEV was not. The results of current study revealed that SL is closely related to the motivation of Qinghai lake bicycle tourists is consistent with the assertions of previous studies . The outThe present research has yielded certain theory-wise significance. This study supplemented the findings of previous studies related to QoL and SL by revealing that tourism satisfaction realizes the mediation of the association between SL and QoL. In the meantime, several researchers have argued that SL is an important predictor of QoL. According to previous studies, SL can positively predict QoL, and related indicators were found to be education level, self-development, self-expression, and self-satisfaction (pleasure) . In anotSome practical implications can be gained from this study. First, for practical insights, it is important to meet the recreational needs and life expectancy of bicycle tourists in Qinghai Lake. Specifically, by increasing social opportunities through bicycle tourism and providing many health-related, nature-friendly places, interest in bicycle tourism is raised, increasing SAT with bicycle tourism itself, and improving the QoL through bicycle tour. As such, it’s imperative to elevate the re-visit intention of bicycle tourists and to achieve the development of local tourism through bicycle tourism. In Qinghai Province, despite the continuous growth of bicycle tourism over the past decade, development plans for bicycle tourists have not materialized in relation to bicycle routes. To this end, Qinghai Province needs to actively build bicycle tourism infrastructure, such as developing bicycle routes to meet the current demand for bicycle tourists, increase bicycle tourism-related activities and promote economic development. Since bicycle tourists can spend more and stay longer in tourist destinations than regular visitors, the construction of bicycle tourism infrastructure will affect bicycle rental and repair shops, accommodation, food and beverage services, and development of key areas related to bicycle road development. In summary, this paper suggests that Qinghai should pursue bicycle tourism as a possible economic growth point and improve the prospects of regional development. Due to the diverse nature and motivating factors of friends, bicycle tourism can provide a differentiated tourism experience as a more environmentally friendly tourist transport and an opportunity to run a business in local development.Finding a means to revitalize the local economy has been recognized as a very important issue due to the changing economic and social conditions of the region, such as a decrease in local industrial activity, unemployment and an elevation in the quantity of workers moving to cities . TourismIn addition, this study focuses on the data and findings predate the pandemic outbreak, but COVID-19 has been a before and after in the tourism industry worldwide. Likewise, there are four limitations in this paper. Firstly, although friends, deviance and nature are main constrain factor for tourism motivation, there are still some crossed factors which may also affect tourism motivation and tourist’s satisfaction, such as health, values, and so on. Therefore, These crossed factors can be taken into consideration in future studies. Secondly, there is limitation of language bias as the questionnaire was only prepared into Chinese. As Mainland China are also main resource area of Qinghai Lake bicycle tourism, but Qinghai lake is also famous in Japan. However, Japanese who come to Qinghai lake cannot read Chinese very well. Therefore, in order to get generalized respondents, questionnaires in various languages should be made, which may also enhance the difficulty in conducting survey. Thirdly, the sample size in the current study is not balance, with more questionnaires were spread to Mainland Chinese tourists, which do not satisfy the requirements of multi-group test. In further studies, a variety of survey methods can be used to equalize the sample size of eastern and western tourists. It will be a good trial for future research to compare the difference between western tourists and eastern tourists in order to understand Relationships among Motivation, SL, SAT and QoL in bicycle tourism. Finally, the non-significance relationship between motivation and QoL differed from previous literature ,66,67. T


Coal gangue (CG) represents a huge amount of industrial solid waste in China, and usually is used as a coarse aggregate to produce low-strength coal-gangue-based concrete. In this paper, in order to prove the possibility to obtain a higher-strength concrete with a higher CG utilization rate, reactive powder concrete (RPC) with coal gangue as a sand replacement at different replacement ratios was studied. RPC samples were prepared by replacing natural river sand (RS) with CG sand at different CG/RS weight ratios from 0–100% at intervals of 25%. Mechanical tests were carried out, and the microstructure features of RPC samples at 28 days were characterized. The test results showed that strong back shrinkage of strength existed. On days 7 and 14, the flexural strengths of samples with CG/RS replacement ratios of 0–75% fluctuated around the mean value. Strengths of samples with a CG/RS replacement ratio of 100% dropped off. However, on day 28, the flexural strengths of samples with CG were all lower than the strengths of samples on days 7 and 14. The flexural strengths and compressive strengths of the RPC with a CG/RS replacement ratio of 100% on day 14 were 14.09 MPa and 37.03 MPa, respectively, which decreased to 6.42 MPa and 28.44 MPa, respectively, on day 28. Compared with natural river sand, CG sand reduced the working performance, compressive strength, and flexural strength of RPC. Microscopic analysis showed that on day 28, increasing the CG replacement ratio could inhibit cement hydration, weaken the interface transition zone, and lead to the degradation of the RPC’s performance. Modification of CG sand would be helpful to obtain higher-strength concrete. Coal gangue (CG) is the waste produced during coal mining and coal preparation plant operations, and is the largest source of industrial solid waste in China . Accumul2, and addition of steel microfibers [Reactive powder concrete (RPC) is a type of ultrahigh-performance concrete developed through microstructure reinforcement technology . It generofibers . Becauserofibers ,10.This study mainly investigated the potential reuse of CG sand in RPC. In order to prove the possibility to obtain a higher-strength concrete with a higher CG utilization rate, reactive powder concrete (RPC) with coal gangue as a sand replacement at different mix ratios was studied.The formability and indexes of RPC, including water absorption, porosity, flowability, and flexural and compressive strength, were tested. Furthermore, the rationality of the RPC ratio was evaluated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The phase composition and interfacial transition zone (ITZ) around the aggregate in the RPC were observed to reveal the mechanism underlying the change in the mechanical properties of RPC with the addition of CG. The results of this study are expected to contribute to the recycling of CG and to the improvement of the sustainability of coal resources.50) of the P•O 42.5, FA, SF, and LF as obtained by a laser particle size analyzer  were 10.3, 9.9, 0.2, and 12.0 μm, respectively. Further, straight copper-coated steel fibers that were 10 mm in length and 0.02 mm in diameter and with a density of 7850 kg/m3 and a tensile strength greater than 3000 MPa were added to the cement mixture to increase the flexural and tensile strengths. A polycarboxylic ether superplasticizer (SP) with 55% solid content was added to this mixture. The chemical composition of the mixture powder was tested by X-ray fluorescence .and is listed in Ordinary Portland Cement P•O 42.5, produced under the Chinese standard GB175-2007, was used in the RPC. Fly ash (FA), silica fume (SF), and limestone flour (LF) were added as supplementary cementitious materials. The mean particle sizes  and crushed CG were used as fine aggregates. The CG was collected from a waste disposal site in Budiertai, Inner Mongolia, for substituting parts of the RS as the aggregate. Both the RS and CG were crushed to a maximum particle size of 2 mm, and their size distribution results are shown in 2O3, so CG provides a certain amount of active component (Al2O3) for cement mortar, which can be hydrated with cement to produce ettringite.The XRD  test results for the RS and CG are shown in The microstructures of the CG and RS were characterized by SEM , and the results are shown in 3, and water and liquid admixtures were mixed at a ratio of 1:6.7. To utilize the CG as much as possible, the ratio of aggregate to binder material was 1.65.The mix proportions designed in this study are listed in The tensile strength of RPC is mainly determined by the added fibers, which also affect the compressive strength and fluidity of concrete to a certain extent. Hence, the role of steel fibers in the performance and strength of RPC with CG was experimentally evaluated. In this experiment, the steel fiber content in the proportioning scheme shown in Mixtures were prepared using a mortar mixer using a well-established procedure for RPC according to previous studies ,14. FirsFresh mixtures were poured into plastic molds with dimensions of 40 mm × 40 mm × 160 mm and then vibrated for 1 min to remove bubbles formed in the mixing process. Then, the molds were covered with plastic sheets to avoid surface moisture loss by the specimens, and were stored in natural conditions in a curing room at 20 ± 1 °C and 95% relative humidity (RH) for 48 h. After demolding, the specimens were stream-cured at 95 ± 1 °C and 95% RH for 24 h. Finally, the specimens continued to be naturally stored at 20 ± 1 °C and 95% RH until the testing times, namely 7, 14, and 28 days.D represents the particle size of raw materials with a unit of μm; P(D) is the accumulation fraction of particles finer than size D; minD and maxD are the minimum and maximum particle sizes in the mixtures, respectively; and q is the distribution modulus, which was set as 0.26 in this study.The modified Andreasen and Andersen model  was emplFluidity tests were conducted in accordance with the American Society for Testing and Materials (ASTM) C230/C230-14 to evaluate the workability of the fresh mixtures. Note that the fresh mixtures to be tested included a cement slurry containing different proportions of steel fibers.The flexural and compressive strengths on days 7, 14, and 28 were measured using a TYE-300 universal testing machine with a loading rate of 2 mm/min. The flexural strength was tested using a three-point method with a span distance of 100 mm. The mean value of the results of the three specimens was reported as the flexural strength for each mixture. Then, the compressive-strength test was conducted on the three broken specimens. The average of three results was considered the compressive strength for each mixture.The water absorption and porosity of the specimens on day 28 were measured in accordance with ASTM C 1585-2013. Three parallel samples with dimensions of 40 mm × 40 mm × 60 mm were cut after the mechanical tests, and their mean values were obtained as results.The concrete samples with different CG substitution rates were characterized through XRD at a scan rate of 5° (2θ)/min from 5° to 80°. The hydration reaction was studied on days 7 and 28 under RPC with different CG substitution rates. Scanning electron microscopy (SEM) was used to analyze the microstructures of the concrete specimens with different CG replacement rates. The morphology of hydration products and microstructure of the interfacial transition zone (ITZ) were analyzed by observing the microscopic images of the RPC surface and section and combining these results with XRD information.minD, was 0.0215 μm; and the maximum particle size of the RS and CG, maxD, was 2000 μm. The curves of the other five dry mixtures were obtained by sieving the dry mixtures to the required particle size. A high coefficient of determination (R2) was related to a high packing density of the dry mixtures. The coefficients of determination for CG0, CG25, CG50, CG75, and CG100 were 0.7584, 0.818, 0.8476, 0.8813, and 0.9237, respectively, and increased gradually with increasing replacement ratios of CG, achieving the maximum value at a 100% replacement ratio.The particle size distribution of dry mixtures with CG at different replacement ratios is shown in 2 values were shown for CG0 to CG100. However, because natural RS has a small particle size, particles with a large particle size lacked in the system, resulting in the maximum R2 for CG100.These results indicated that the inclusion of CG increased the packing density of the dry mixtures. According to the particle size distribution of the RS and CG shown in The fluidity of the RPC varied greatly with the change in CG replacement ratios. In this experiment, the fluidity of five specimens of RPC was uniformly controlled at 200 mm (±10 mm). The variation in w/b with the CG replacement ratio is shown in Compared with ordinary crushed stone, CG aggregate has a loose structure and comprises more flaky particles and pores; moreover, its properties can fluctuate considerably. Although CG has an apparent density similar to that of natural gravel, it is porous, and has a higher water-absorption ability. Owing to the large porosity of CG aggregate and a high number of microcracks in the crushing process, CG aggregate generally has a higher water absorption than natural gravel, and will absorb water in the fresh concrete during the mixing process, which seriously affects the working performance of concrete with CG aggregates ,17.The flexural and compressive strengths of the specimens with CG at different replacement ratios on days 7, 14, and 28 are shown in The flexural strength was mainly determined by the cementation strength of the concrete, the tensile strength of the steel fiber, the distribution of the steel fiber, and the wrapping tightness of the cementation material and steel fiber. As shown in With the increasing CG replacement ratio, the compressive strength of the concrete decreased gradually. The compressive strengths of CG0 to CG100 on day 14 were 67.23, 52.53, 47.23, 43.91, and 37.03 MPa, respectively. This was because the strength of the CG aggregate was low, and the hydration reaction of the concrete was degraded with the addition of CG, resulting in a low density, high porosity, and loose structure of the concrete due to the CG aggregate. The compressive strength of the specimens generally increased from day 7 to day 28, except with a CG replacement ratio of 100%. Back shrinkage of the compressive strength occurred when the CG replacement ratio was 100%.This was due to a crystal form change in the later stage of hydration, in which a low water-to-binder (w/b) ratio causes some microcracks in the hardened cement paste due to its volume expansion, resulting in a degradation in the properties of the RPC matrix ,19. In aWater absorption and porosity were directly related to the durability of the RPC. 2 hydration products were found in the cement matrix. However, as the CG replacement ratio increased, the amount of the substance in the white region decreased. In certain cases, the hydration reaction became less sufficient, and the cement matrix became looser with the increasing CG replacement ratio.3 and 0 kg/m3, respectively, for the above-mentioned CG replacement rates; then, the changes in fluidity and strength (on day 28) were compared.To explore the effects of steel fibers on the concrete’s performance and mechanical properties, and for the CG aggregate tests, the content of steel fibers was decreased from 160 to 80 kg/m3, the fluidity increased by 1.5–2.5 cm. This was mainly because the steel fibers served as a skeleton when they were mixed into the matrix, which prevented the flow of concrete. In addition, the steel fibers absorbed part of the water in the matrix, reducing the fluidity of the concrete.The content of steel fibers considerably affected the fluidity of the RPC. With the increase in fiber content, the fluidity of the concrete decreased significantly. As shown in 3, the flexural strength dropped to a range of 1.31–11.98 MPa. Specifically, with the increase in the CG replacement ratio, the effects of steel fibers on the flexural strength of the concrete decreased. This was because the factors of the steel fibers that contributed to the improvement in the flexural strength of the concrete were mainly determined by the strength of the steel fibers themselves and the degree of combination between the steel fibers and the concrete matrix. As the CG replacement ratio increased, the process of the hydration reaction was restrained or slowed down, leading to the reduction in hydration products and weakening of the combination degree between the steel fibers and the matrix. Therefore, the increase or decrease in the steel fiber content had little effect on the concrete with a high CG substitution rate.In terms of flexural strength, as shown in 3 to 0 kg/m3, the compressive strength decreased to a range of 2.88–36.54 MPa. This was because the addition of steel fibers increases the ductility of concrete, reduced the phenomenon of stress concentration in the concrete, and made the stress in the concrete more uniform in the test process. Moreover, the steel fibers serves as a skeleton in the matrix to compensate for the lack of aggregate strength [In terms of compressive strength, as shown in strength .2O3 and SiO2 in the CG with the cement easily generated gismondine. The hydration product of CG0 was mainly AFt. On day 28, the hydration products were more abundant, the number of different hydration products was greater, and the diffraction was more obvious, indicating that the hydration reaction occurred effectively.A comparative analysis of the XRD images indicated that diffraction products mainly fell into two categories. One was raw materials, including quartz, margarite, kaolinite, and calcite. Quartz and margarite were the main components of the river sand, and quartz and kaolinite were the main components of the CG sand. Calcite was the main component of the LF. The other was hydration products, including gismondine, AFt, and C-H-S. In the XRD patterns, with an increase in the CG ratio, the peak for margarite gradually weakened and the peak for kaolin was gradually enhanced, which was closely related to the phase compositions of the RS and CG, respectively. The XRD patterns for days 7 and 28 show similar variation trends. In terms of hydration products from day 7 to day 28, C-H-S existed mostly in the form of a gel in the concrete, and no crystallization peak was observed. With the increase in the CG replacement ratio, gismondine appeared increasingly frequently, because the reaction of active AlIn the CG100, hydration products on days 7 and 28 had hardly changed, because the hydration reaction in the early stage consumed a large amount of water, resulting in insufficient hydration reaction in the later stage. In terms of the microstructure of hydration products, as shown in 2 in the white area and the bubbles in the black area in the figure can be observed: with the increase in the CG replacement rate, the number of hydration products and bubbles in the CG100 could be obviously observed to decrease. This showed that the cement matrix was relatively loose, and the CG inhibited the hydration reaction, causing ring breakage in the interface structure to a certain extent [The ITZ was the weakest structural region in the concrete. n extent ,26.On days 7 and 14, the flexural strengths of samples with CG/RS weight ratios of 0–75% fluctuated around the mean value. Strengths of samples with CG/RS weight ratios of 100% dropped off. On day 28, the flexural strengths of samples containing CG were all lower than the strengths of samples on days 7 and 14. The flexural strengths of the RPC with a CG/RS replacement ratio of 100% on days 7 and day 14 were 11.18 MPa and 14.09 MPa, respectively, and decreased to 6.42 MPa on day 28.The compressive strength of the RPC with a CG/RS ratio of 100% on day 14 was 37.03 MPa, meeting the design requirements of C35 strength grade concrete, but on day 28, the compressive strength had decreased to 28.44 MPa.Strong back shrinkage of strength existed. A low water-to-binder (W/B) ratio caused some microcracks in the hardened cement paste due to its volume expansion, resulting in a degradation in the properties of the RPC matrix. More flexural strength loss than compressive strength loss occurred. Kaolinite participated in the hydration reaction to generate partially hydrated kaolin, which could have been the cause of the back shrinkage of strength.Steel fibers greatly improved the compressive strength and tensile strength of the RPC; however, they also decreased the fluidity. With the increasing CG replacement ratio, the main observed hydration products were transferred from AFt to AFt and gismondine. The CG inhibited the hydration reaction in the CG100 compared with that in the CG0.Compared with natural river sand, the CG sand reduced the working performance, compressive strength, and flexural strength of the RPC. A microscopic analysis showed that on day 28, increasing the CG ratio inhibited cement hydration, weakened the interface transition zone, and led to the degradation in RPC performance. Modification of the CG sand would be helpful to obtain higher-strength concrete.This study investigated the application of CG in RPC as a substitute for RS. The flow and mechanical properties of the RPC varied with the steel fiber content and CG substitution rate. The effects of the replacement ratio of CG on the hydration behavior and the structure in the interfacial transition zone were analyzed by XRD, SEM, and ESD. The main results were as follows:


The results have shown that under static load, as compared with PC, NC has both strength and elastic modulus increased obviously, while NS has strength decreased and elastic modulus increased, and under dynamic load, there is an obvious strain rate effect for the dynamic compressive strength, impact toughness, energy dissipation and impact failure mode of concrete. Under the same strain rate, the dynamic compressive strength, peak strain, impact toughness and energy dissipation of NC are significantly increased, while its dynamic elastic modulus is decreased. Compared with PC, NS has dynamic compressive strength, peak strain, impact toughness and energy dissipation decreased, and dynamic elastic modulus increased, NC has static and dynamic mechanical properties improved, NS has static and dynamic mechanical properties weakened, and NSC is between PC and NC in static and dynamic mechanical properties, but generally improved. Doped with nano-CaCO3, NC has compactness improved, weak areas reduced, and pore size distribution optimized, while doped with nano-SiO2, NS has obvious internal weak areas, with pore structure degraded.Three kinds of nano-concrete, i.e., 2.0% nano-SiO With the continuous expansion of concrete structure in scale and scope of use, its service environment and load are more and more complicated5. Therefore, considering the safety and reliability of concrete structure, it is necessary to adapt it to the increasingly harsh engineering conditions through relevant modifications8. Ultrafine powders, represented by nanomaterials, are a new material used for the modification of concrete10. The mechanical and deformation properties of concrete may be improved effectively after adding the nanomaterials into its matrix12.In the construction industry, concrete has become the most widely adopted building material with the maximum consumption in human history because it is convenient, economical, and practical, and it is irreplaceable in engineering2 modified concrete and nano-CaCO3 modified concrete15. Abreu G B D et al. found that nano-SiO2 added in high performance water-reducing agent of polycarboxylates was conductive to uniform dispersion of the agent in concrete. An appropriate amount of nano-SiO2 can improve the microstructure of concrete, thus increasing the compressive strength and elastic modulus of concrete16. Shaikh et al.17 studied the effect of nano-SiO2 on the mechanical properties of recycled coarse aggregate concrete, and found that nano-SiO2 can improve the compressive strength of recycled coarse aggregate concrete, in other words, if concrete contains 25% recycled coarse aggregate and 2.0% nano-SiO2, its compressive strength could reach 92% of the normal compressive strength of concrete. The study of Sivasankaran18 et al. concerning the influence of nano-SiO2 on the performance of concrete mixed with coal ash showed that after added with 1.0% nano-SiO2, the concrete containing 25% coal ash had a compressive strength increased by 23% and a tensile strength increased by 28%. Li et al.19 found that 2.0% nano-CaCO3 could enhance the compactness and mechanical properties of concrete, but excessive nano-CaCO3 led to local defects poor mechanical properties of concrete. Camiletti J et al. studied the influence of nano-CaCO3 on the early mechanical properties of ultra-high-performance concrete, and found that nano-CaCO3 promoted the early solidification and hardening of concrete. Specifically, 5–10% of nano-CaCO3could improve the mechanical properties of concrete effectively20. Most of above studies focused on static mechanical properties of nano-SiO2 modified concrete and nano-CaCO3 modified concrete22, that is, there are few studies concerning relevant dynamic mechanical properties. However, besides static load, many concrete structures will inevitably be threatened by dynamic loads24, e.g., impact, explosion and etc. during their service period27. Therefore, it is necessary to study the mechanical properties of nano-concrete under dynamic load28. In addition, the nano-SiO2 and nano-CaCO3 composite modified concrete is to be further explored, for there are few relevant reports.At present, the research on nano-concrete has been very fruitful, especially on nano-SiO2 and nano-CaCO3 are used as materials for modification and high-performance water-reducing agent of polycarboxylates as dispersant of nanomaterial and water reducing agent of concrete for preparing 3 kinds of nano-concrete , which were nano-SiO2 doped, nano-CaCO3 doped, and nano-SiO2/nano-CaCO3 co-doped respectively. HYY series hydraulic servo test system and Φ100 mm split Hopkinson pressure bar (SHPB) test system were utilized to study the static and dynamic properties of the three kinds of nano-concrete under different strain rates, and have a comparison with plain concrete (PC) based on indexes of static mechanical performance like stress–strain curve, compressive strength, flexural strength, splitting tensile strength, elastic modulus, and indexes of dynamic mechanical performance like compressive strength, peak strain, dynamic modulus of elasticity, impact toughness, impact energy dissipation, and impact failure mode. The effects of nano-SiO2 and nano-CaCO3 on the static and dynamic mechanical properties of the concretes were analyzed, and relevant microscopic mechanism was explored by scanning electron microscopy and mercury injection test.In this study, nano-SiO3, fineness modulus: 2.68, bulk density: 1450 kg/m3, and silt content: 1.0% of Ba river medium sand. The sand grading curve is shown in Fig. 3 of limestone gravel . Water-reducing agent: mother liquor of high-performance water-reducing agent of polycarboxylates of 40% solid content produced by Shaanxi Zhongyi Chemical Company, used as water-reducing agent for concrete and dispersant for nanoparticle. The main performance indexes are shown in Table 2 and nano-CaCO3 produced by Hangzhou Wanjing Company, as shown in Fig. Cement: Qinling PC32.5R cement, Yao County, Shaanxi. The main properties is shown in Table 2 doped concrete, NC, 2.0wt% nano-CaCO3 doped concrete, and NSC, 1.0wt% nano-SiO2-1.0wt% nano-CaCO3 co-doped concrete.Concrete specimens were prepared according to the mix ratios as shown in Table The concrete preparation process is as follows: (1) Mix the water-reducing agent with 3/4 water, stir until dissolution (30 s), and then, add nanoparticles into the solution. After high-speed mixing , perform ultrasonic dispersion (15 min) to make a mixture of nanoparticles. (2) Mix the coal ash and 1/2 cement until a uniform ash mixture is formed (30 s). (3) Add the mixture of nanoparticles to the ash mixture, and stir until a mortar is formed (30 s). (4) Add the sand and gravel successively into the mortar, and stir (60 s). (5) Add the remaining 1/4 of water and 1/2 of cement, and stir until a uniform mixture is formed (120 s), that is, fresh concrete.The fresh concrete is cast in a mold. After 24 h of curing in a standard curing box , the mold is removed. Then, the mold is further cured for 28 days. In the static mechanical test, the dimensions of specimen for concrete compression test and splitting tensile test of concrete are 100 mm × 100 mm × 100 mm, and for flexural test of concrete is 100 mm × 100 mm × 400 mm. The dimensions of specimen for dynamic mechanical test are Φ100 mm × 50 mm. The specimens are finely polished by double—end grindstone machine, and the final test specimen is a cylinder of diameter 99 mm ± 1 mm and length 49 mm ± 1 mm, with surface nonparallelism controlled within 0.02 mm. Some concrete specimens are as shown in Fig. In the static mechanical test, the HYY electro-hydraulic servo material test system was used for the compressive test, bending test, and splitting tensile test of concrete. The dynamic mechanical test was performed with Φ100 mm split Hopkinson pressure bar (SHPB) test system as shown in Fig. εI(t), the incident stress wave, part of which was reflected to form a reflected stress wave εR(t) as passing through interface A1, while another part formed transmitted stress wave εT(t) as passing from the specimen through interface A2 to the transmission bar. The incident stress wave and the reflected stress wave were measured by strain gage 1, and the transmitted stress wave is measured by strain gage 2.The propagation principle of stress wave for the SHPB test system was as shown in Fig. εs(t), σs(t)29.e represents the propagation velocity of stress wave in the bar, L, the thickness of specimen, τ, the propagation time of stress wave in the bar, Ee, Ae, elastic modulus and cross-sectional area of the bar respectively, As, the area of specimen end face.The "three-wave method" was used to process the test data and calculate the strain, strain rate and stress of specimen, i.e., εT(t) had good coincidence with εI(t) + εR(t) in waveform, indicating that the specimen was in a state of dynamic stress equilibrium during impact loading.Typical waveforms measured by the test were shown in Fig. For the SEM test, COXIEM-30 scanning electron microscope was used to observe the microstructure of concrete. The samples were fragments after the mechanical performance testing, and the samples were processed by a particle sputtering machine before testing. In the MIP test, the pore structure of concrete was analyzed by the PoreMaster Mercury Injection Apparatus. After normal curing, the samples underwent 1d of low-temperature drying at a temperature of 50 °C, and for the samples, the mass was accurately weighed before the mercury injection test.The stress–strain curve may comprehensively reflect the properties and indexes of material, and the changes of geometric features and feature points may directly reflect the strength and deformation characteristics of a specimen at different stress stages. The stress–strain curve of concrete under static compression load was shown in Fig. 2 had no obvious effect on the peak stress of concrete, while the addition of nano-CaCO3 had. As compared with PC, NS, NC and NSC were near the peak stress, and their curves were approximate a plateau, especially for NSC, indicating that NS, NC and NSC still maintain a certain strength in a large range with the increase of strain near the peak stress until the specimens lost their bearing capacity after failure, i.e., the addition of nano-SiO2 or nano-CaCO3 improved the deformation performance of concrete.The peak stress of NC and NSC was significantly higher than that of PC, and the peak stress of NC was the largest, while the peak stress values of NS and PC were not significantly different, indicating that the addition of nano-SiO3 significantly improved the strength of concrete, but nano-SiO2 was not so good, or even compromised the strength of concrete. The nano-CaCO3/nano-SiO2 co-doping also improved the strength, but to a limited extent. The strengthening effect of nano-CaCO3 was partly offset by nano-SiO2.The compressive strength, flexural strength, and splitting tensile strength of concrete are as shown in Fig. 2 or nano-CaCO3, the elastic modulus of concrete increased to greater than 18 GPa. The elastic modulus of NS was the largest, which was 21.22 GPa. As compared with NS and NC, the elastic modulus of NSC decreased, indicating that nano-SiO2 and nano-CaCO3 interacted in the concrete, thus inhibiting the strengthening effect mutually.The ability of concrete to resist elastic deformation can be expressed as elastic modulus. The commonly used expression modes for elastic modulus include initial elastic modulus, tangent modulus, secant modulus, mixed modulus, and etc., which have different meanings. Based on the stress–strain curve under the quasi-static compression load, the concrete samples mixed with different nanoparticles were different greatly in the ability to resist elastic deformation. In this study, the mixed elastic modulus was used for the expression as follows:The stress–strain curves of some concretes under dynamic load were as shown in Fig. 27. The relationship between concrete dynamic compressive strength and average strain rate was as shown in Fig. −1. For the four kinds of concrete, the dynamic compressive strength increased with the average strain rate. Under the same level of average strain rate, the dynamic compressive strength of NC was the largest, indicating that the addition of nano-CaCO3 increased the dynamic compressive strength of concrete significantly. As a whole, the fitting curve for dynamic compressive strength of NS was below that of PC, indicating that the addition of nano-SiO2 decreased the dynamic compressive strength of concrete. When the average strain rate was low, the dynamic compressive strength of NSC was smaller than that of PC, and when the average strain rate was high, the dynamic compressive strength of NSC was larger than that of PC, and the nano-CaCO3–nano-SiO2 co-doping improved the dynamic compressive strength of concrete at high strain rate. At the same average strain rate level, the dynamic compressive strength of NC was larger than that of NSC, and in improving the dynamic compressive strength of concrete, the effect of separate nano-CaCO3 doping was better than that of nano-CaCO3–nano-SiO2 co-doping.The dynamic compressive strength of concrete is the peak stress on the stress–strain curve of concrete under dynamic load, and the limit strength of concrete when it was damaged under dynamic load as well. It is an important parameter representing the bearing capacity of concrete under dynamic loadI represents the strength increase factor of concrete under dynamic load, which reflects the enhancement effect of dynamic load on the strength of concrete. Relevant formula is as follows:30. Therefore, peak strain is an important parameter representing the compressive deformability of concrete under dynamic load. The relationship between peak strain and average strain rate of concrete is as shown in Fig. −1, there were significant differences between the four kinds of concrete in the trend of peak strain. With the increase of the average strain rate, for PC, NC and NSC, the peak strain increased, while for NS, the peak strain decreased. Under the same average strain rate, as compared with PC, the peak strain of NC and NSC increased significantly, especially that of NC increased more obviously. The nano-CaCO3 can improve the deformability of concrete under dynamic load, while nano-CaCO3/nano-SiO2 co-doping may decrease the deformability of concrete under dynamic load. When the average strain rate was less than 70 s−1, the peak strain of NS was at maximum, and when the average strain rate was greater than 110 s−1, the mean strain rate of NS was at minimum. At a low strain rate level, the nano-SiO2 can improve the deformability of concrete, while at a high strain rate level, the nano-SiO2 will weaken the deformability of concrete.The peak strain refers to the strain corresponding to the peak stress of concrete under dynamic load. At this point, the concrete is at the critical value for unstable crack propagation, that is, any further loading will damage the concrete and make it unable to bear effective load any more3 can improve the dynamic elastic modulus of concrete at a low strain rate level, while nano-SiO2 can improve the dynamic elastic modulus of concrete at a high strain rate level. And the nano-CaCO3/nano-SiO2 co-doping may decrease the dynamic elastic modulus of concrete.The calculation method of dynamic elastic modulus of concrete is consistent with that of elastic modulus under static load, and the formula is as follows:31. Thus, the curve before the peak stress reflects the complete bearing process of concrete specimen before the destabilization. The physical significance of impact toughness The stress–strain curve represents the whole process of concrete specimen from loading to failure, and it may reflect the toughness of the specimen to a great extent. Figure −1, the impact toughness presented a certain strain rate effect and increased with f the average strain rate on the whole. Under the same level of average strain rate, the impact toughness of NC was the biggest, indicating that nano-CaCO3 can improve the impact toughness of concrete. As compared with PC, at a low strain rate level, the effect of nano-CaCO3 for improving the impact toughness of concrete was not good, while at a high strain rate level, the effect was enhanced obviously, and further advanced with the increase of the average strain rate. Under the same average strain rate level, NSC was between NS and PC for the impact toughness, indicating that nano-CaCO3/nano-SiO2 co-doping improved the impact toughness of concrete. With the increase of the average strain rate, the gap between NSC and PC continued to widen in impact toughness, and the effect of nano-CaCO3/nano-SiO2 co-doping for improvement of concrete impact toughness was more and more obvious. Under the same average strain rate, the impact toughness of NS was smaller than that of PC, but with the increase of the average strain rate, the difference between NS and PC in impact toughness became smaller and smaller. The impact toughness of concrete will be reduced by the addition of nano-SiO2, but at a high strain rate level, the nano-SiO2 had little effect on the impact toughness of concrete.The relationship between the impact toughness and average strain rate of concrete is as shown in Fig. 33. When the incident energy, transmitted energy, and reflected energy are expressed as Energy dissipation  Formula  can be o−1, the energy dissipation increased with the average strain rate on the whole, showing a strain rate effect. Generally, under the same average strain rate level, the energy dissipation of NC was the biggest, and when the average strain rate was 123.02 s−1, the energy dissipation of NC was up to 342.57 kJ. In energy dissipation, NSC was between NC and PC. At a low or medium strain rate (50–115 s−1), as compared with PC, the energy dissipation of NS was reduced, and at a high strain rate level (115–130 s−1), the energy dissipation of NS was greater than that of PC. Therefore, the nano-CaCO3 can improve the energy dissipation of concrete and enhance the capacity of concrete for absorbing energy. At a low or medium strain rate level, the nano-SiO2 can weaken the capacity of concrete for absorbing energy, and reduce its energy dissipation as well. At a high strain rate level, the nano-CaCO3 had the opposite effect. Although nano-CaCO3/nano-SiO2 co-doping can also increase the energy dissipation of concrete, the increase rate is smaller than that of nano-CaCO3, for the effect of nano-CaCO3 for improving the energy dissipation of concrete was partially offset by the nano-SiO2.The relationship between concrete energy dissipation and average strain rate is as shown in Fig. −1, even though the specimen remained intact without obvious fracture trace after the dynamic loading, a crack had been formed inside the specimen, and the specimen had been destroyed essentially. (2) Fragmentation. This type of failure modes is more serious than the edge failure, and the specimen does not break into several pieces after bearing dynamic load, e.g., the damage of PC at an average strain rate of 84.06 s−1. (3) Crushing destruction. There is almost no large fragment for this type of failure modes, and the specimen is generally broken into fragments. In general, the failure modes at a high strain rate are all of this type, e.g., the damage of NSC at an average strain rate of 123.02 s−1.In the SHPB test, the concrete specimens were damaged under a certain dynamic load, and the failure modes for each group of concrete specimens were as shown in Fig. The addition of nanoparticles can improve the structural composition of concrete at a microscopic level, thus affecting the static and dynamic mechanical properties of concrete. The micromorphology of concrete is as shown in Fig. 2 is of an amorphous vitreous structure with a large specific surface area and a large number of unsaturated bonds on the surface, for which large amounts of water may be adsorbed on the surface of the particles, showing a high chemical activity. In the early stage of cement hydration reaction, the hydration product Ca(OH)2 may react with nano-SiO2 to form a high strength C–S–H gel with flocculent structure, thus reducing the production of Ca(OH)2 and refining the crystal structure of Ca(OH)234. However, after a certain degree of hydration, the free water in contact with the cement particles in the concrete will decrease rapidly. Without enough water to react with the cement particles, the hydration reaction cannot be complete, thus forming an obvious weak area in the concrete, which leads to the degradation of static and dynamic mechanical properties of NS. The nano-CaCO3 particles in concrete may adsorb free CA2+ easily for its high surface energy, thus accelerating nucleation of Ca(OH)2 crystals around it, improving the enrichment and arrangement of Ca(OH)2 crystals, and promoting the crystals to fill the weak areas of concrete35. Furthermore, with nanometer CaCO3 as the core, the C–S–H gel is easy to form a new columnar network structure around the particles, which intersects with the original microstructure to fill the harmful voids, thus increasing the compactness of concrete, and strengthening the static and dynamic mechanical properties of NC. In nano-SiO2/nano-CaCO3 co-doping, the nano-SiO2 and the nano-CaCO3 may work together in concrete. Specifically, the nano-SiO2 leads to the formation of obvious weak areas in concrete, while the nano-CaCO3 promotes the filling of weak areas by Ca(OH)2 crystals. Under the combined action of the two, there may be still some weak areas in NSC, and so, NSC is between NS and PC for the mechanical properties.The nano-SiO3 can optimize the pore size distribution in concrete, refine the pore structure, and reduce large pores. The pore size distribution of NS was bimodal, similar to that of PC. Peak 1 of the pore size distribution curve shifted to large pore size, while for Peak 2, the range was expanded. The addition of nano-SiO2 degraded the pore structure of concrete, decreased the pore size, and increased the large pores36. NSC was between PC and NS in pore size distribution. Peak 1 on the pore size distribution curve was between Peak 1 of PC and Peak 1 of NS. As compared with PC, Peak 2 of NSC shifted towards large pore size, but the range was obviously reduced. The addition of nano-CaCO3 can optimize the pore structure of concrete, and so, the static and dynamic mechanical properties of NC were improved, while nano-SiO2 may degraded the pore structure of concrete, and thus, the static and dynamic mechanical properties of NS was compromised.The pore size distribution curve of concrete is as shown in Fig. 2 and nano-CaCO3 on the static and dynamic mechanical properties of concrete were explored as well. According to relevant analysis, single-doped nano-CaCO3 and co-doped nano-CaCO3/nano-SiO2 can improve the static and dynamic mechanical properties of concrete, while single-doped nano-SiO2 will weaken the static and dynamic mechanical properties of concrete. Overall, the findings are as follows:3 and co-doped nano-SiO2/nano-CaCO3 can improve the compressive strength, flexural strength, splitting tensile strength and elastic modulus of concrete. Single-doped nano-SiO2 may weaken the compressive strength, flexural strength and splitting tensile strength of concrete, but can increase the elastic modulus of concrete.Single-doped nano-CaCOThe dynamic compressive strength, impact toughness, energy dissipation and impact failure modes of concrete have an obvious strain rate effects. With the increase of strain rate, the dynamic compressive strength, impact toughness and energy dissipation of concrete increase gradually, and the damage degree becomes more significant.3 can improve the dynamic compressive strength, peak strain, impact toughness and energy dissipation of concrete, but may reduce the dynamic elastic modulus of concrete, while single-doped nano-SiO2 may decrease the compressive strength, peak strain, impact toughness and energy dissipation of concrete, but can increase the dynamic elastic modulus of concrete.Under the same strain rate level, single-doped nano-CaCO2/nano-CaCO3 can improve the static and dynamic mechanical properties of concrete, but the effect is weakened as compare with single -doped nano-CaCO3.For the static and dynamic mechanical properties, NSC is between PC and NC. On the whole, the co-doped nano-SiO3 can advance the compactness of concrete, improve the weak area of concrete, and optimize the pore size distribution of concrete; single-doped nano-SiO2 may cause obvious weak areas inside concrete, and degrade the pore structure deterioration; co-doped nano-SiO2/nano-CaCO3 can make the two nanomaterials work together in concrete.Single-doped nano-CaCOWith HYY series hydraulic servo test system and Φ100 mm split Hopkinson pressure bar (SHPB) test system, the static and dynamic mechanical tests under different strain rates were carried out, and the effects of nano-SiO


The breaking loads and the average pull-out strength of anchors in fibre-reinforced concrete substrates were determined. Fibre content ratios of 15, 30 and 50 kg/m3 were used. In addition, two different classes of concrete (C20/25 and C50/60) were tested. The addition of steel fibres caused a decrease in the pull-out strength by 5% for non-cracked concrete of C20/25 class and fibre content up to 30 kg/m3 and a further 7% for the remaining specified dosage. While for concrete of the C50/60 class, it a decrease in the pull-out strength of up to 20% was observed. For cracked concrete class C20/25 with crack initiation cw = 0.30 mm, the reduction was from 9% to 16% in relation to non-cracked concrete and a maximum of 18% for the fibre content of 50 kg/m3. The difference between the tensile load capacity of C50/60 class cracked and non-cracked concrete was lower than 5% and fell within the measurement error.The article presents the pull-out strength tests carried out on M10 expansion anchors in non-cracked and cracked concrete with a crack width c The rapid development of civilisation requires the involvement of new building materials and techniques to face the challenges of the century to come. In recent years, many studies concerning new generations of concretes have been published, including high-performance concrete (HPC), self-compacting concrete (SCC), eco-efficient concrete, and even self-healing concrete ,2,3. OneNowadays, due to energy efficiency and sustainability, an increase in the use of building insulation is observed . Moreove3 and 50 kg/m3 fibre content respectively. Gesoglu et al. [Anchoring in the fibre reinforced concrete was tested by Lee et al. , Bokor eu et al.  researchu et al.  and Eurou et al. . Fasteniu et al. ,36 and sThis study used M10 torque-controlled anchors LE-ZNA4 . The product has a valid European Technical Assessment. The geometry  and tensThe materials used in this study were Portland cement , steel fibres and tap water. The industrial Portland cement was CEM I 42.5R, according to PN-EN 197-1:2012 . Its cheSteelbet 50/0.8  steel fibres were used. The fibres are made of low carbon steel . The mea3 were used. So, steel fibre contents were 6.5, 13.0 and 21.5% of cement, respectively, for concrete C20/25 and 3.6, 7.2 and 11.5% of cement weight, respectively, for concrete C50/60.The concrete bases were prepared using the formula and aggregate grading curve prescribed in EADs  and Eurocutd as nominal.The fibres were dosed manually to the concrete mixture, after mixing other components for 15 min. The whole mixing time lasted for a maximum of 20 min. The mixture was poured in a rectangular mould of a concrete substrate with dimensions 4000 × 1000 × 400 mm dimensions. The concrete mixtures were compacted in the mould using a hand vibrator . All samples were obtained and stored in laboratory conditions (21 °C temperature and 50% humidity). Before the test itself, the anchors were installed in drill holes with While preparing the concrete substrates, a part of the mixture was poured into a 150 mm × 150 mm × 150 mm mould to determine the compressive strength. In this case, the concrete mixture was compacted using a compactor. All samples were obtained in laboratory conditions (21 °C temperature and 50% humidity). The samples for testing the properties of the substrate were stored in water according to PN-EN 12390-2:2019 .(1)Concrete substrates with different fibre content were prepared; the description was shown in (2)While preparing the concrete substrates, the samples are taken for compressive strength testing, see (3)The compressive strength tests of concrete samples with different fibre content were carried out after 28 days (to determine 28-days compressive strength) and 90 days (to compare compressive strength with results of pull-out tests) according to the procedure described in (4)The pull-out tests were carried out after 90 days, see (5)After the pull-out tests, the boreholes were drilled from the concrete substrate and the actual fibre content of the concrete was determined according to the procedure presented in In order to conduct the research, the experiments were carried out in the following stages:Compressive strength was measured on samples 150 mm × 150 mm × 150 mm, according to PN-EN 12390-3:2011 + AC:2012 , using aThe fibre content in concrete was determined on samples 109 mm × 109 mm, according to PN-EN 14721 + A1:2007 , using aThree samples per mix of fibre-reinforced concrete were tested.The tests consisted in determining the maximum pull-out force for steel expansion anchors in C20/25 and C50/60 concrete substrate (with and without fibre). Without accounting for spacing the distance of the anchors from the edge and the thickness of the base, pull-out strength determined based on tests of steel expansion anchors subjected to static or quasi-static load is described by the Formula (1).w =c 0.30 mm. The method of creating a crack is described in the guidelines for steel expansion fasteners.The tests were performed in a special test station enabling the initiation of cracks with the width of 0.30 mm , using aThe pull-out tests were carried out 90 days after forming the substrates. The tests should be carried out so that the pulling out was not affected by other external factors, such as temperature, humidity and distances from the edge and axis of the anchors.3, respectively. The decrease in compressive strength results from the reduced aggregate content in the concrete mixture.The results of the compressive strength tests of concrete samples for fibre-reinforced concrete of the C20/25 class are shown in In each case, the 90-days compressive strength was higher than after 28 days. After 90 days compressive strength for concrete without and with steel fibre addition increased by an average of 12% compared to 28 days compressive strength. However, the decrease in strength after 90 days was the same as for 28 days depending on the fibre content in the concrete mixture.The compressive strength of samples for C50/60 class concrete is shown in The maximum decrease in 28 and 90 days compressive strength were 12% and 17% respectively. Thus, these are definitely smaller decreases in strength compared to the C20/25 class concrete due to the amount of aggregate and the addition of steel fibres and its bulk density.3 and obtained maximum compressive strength for steel fibre of 55 kg/m3. The properties of reinforced concrete are influenced by the type of fibres, their properties, such as length, diameter proportions and, above all, their content [These observations of a decrease in compressive strength with steel fibre addition are in line with the results of other scientists. Lehner et al.  obtained content .3, 27.5 kg/m3 and 46.0 kg/m3, which corresponded to a 2% lower fibre content compared to the assumed content for 15.0 kg/m3 and 8% for other fibre content. While for concrete class C50/60, the real content of steel fibres was higher than assumed. The 8% increase in fibres content for the concrete with the addition of fibre above 30.0 kg/m3 was determined. Thus, the maximum changes in the fibre content within ±10% can be observed, which is a slight change and is not considered later in the manuscript. The changes in fibre content depend on the method of preparing the concrete substrates and the distribution of the fibres in the concrete mixture. In this study it is directly related to manual dosing, see For each case, the lack of fibre agglomeration in the concrete was observed, which is a major problem in fibre reinforced concrete mixtures.3 and 12% for the content of 50.0 kg/m3 was obtained  and were lower for steel fibre-reinforced concrete. For the concrete class of C20/25, a reduction of the load capacity by 5% for the fibre content of 15.0 and 30 kg/mobtained . While FIn the next step, the coefficient resulting from the compressive strength of the substrate has been included according to the procedure for determining load capacity in accordance with guidelines.These were the actual load capacities after the reduction with the coefficient resulting from concrete compression. For non-reduced load capacities, the initial decrease was 13% and 23% for the highest content of steel fibres. Such behaviour of the connectors characterised its structure. Along with the increased fibre content, the connector had the problem of opening the expansion cone when setting the installation torque. In all research cases, the image of destruction was observed as a pull of the connector with the cone. An example of the destruction image is shown in wc = 0.30 mm  substrate was determined. Based on the results of the experimental study, the following important conclusions can be drawn:(1)There were observed reductions in the compressive strength of C20/25 concrete substrates of the order of 15% for the lowest dose of steel fibres and 30% for the remaining ones, both after 28 days. After 90 days, the increase in strength was 10% compared to C20/25 concrete.(2)For concrete C50/60, there was an increase of 10% after 90 days, and the decreases resulting from the reinforcement were recorded at a maximum of 16%.(3)Steelbet 50/0.8 steel fibres affect the strength of anchors using M10 expansion anchors, reducing pull-out strength.(4)3 and a further 7% for the remaining specified dosage.The addition of fibres caused a decrease in the pull-out strength by 5% for non-cracked concrete of C20/25 class and fibre content up to 30 kg/m(5)wc = 0.30 mm, the reduction was from 9% to 16% in relation to non-cracked concrete and a maximum of 18% for the fibre content of 50 kg/m3.For cracked concrete with crack initiation (6)For concrete of the C50/60 class, a decrease in the pull-out strength of up to 20% was observedThe research aimed to assess the possibility of using M10 expansion fasteners installed in concrete substrates of class C20/25 and C50/60 with the addition of steel fibres of various contents. The fibre content of 15 kg/mThe difference between the tensile load capacity of C50/60 class cracked and non-cracked concrete was lower than 5% and fell within the measurement error.The article is part of a wider research project aimed at assessing the actual load capacity of expansion fasteners in steel fibre reinforced concrete substrates. Moreover, as part of further research, extensive tests of the properties of steel fibre reinforced concrete will be carried out in order to search for the relationship between these parameters and the load capacity of the fasteners. In addition, long-term studies will be conducted to evaluate the long-term effects on the analysed parameters.


Preeclampsia (PE), a placenta-associated pregnancy complication, is the leading cause of maternal and perinatal morbidity and mortality. Met/Erk signaling is inhibited in the placentas of patients with early-onset preeclampsia (E-PE), but the underlying mechanisms remain elusive. In this study, the expression modes of Met and endocytic vesicles in normal and preeclamptic placentas were compared. Biotinylation internalization/recycling assays were used to measure the endocytosis of Met under hypoxia and normoxia in HTR8/SVneo cells. In addition, the expression level of Cbl, a specific E3 ligase of Met, was measured under hypoxia and normoxia, and the endocytosis of Met was studied by using confocal microscopy.We found considerable intracellular accumulation of Met, which was colocalized with caveolin-1 (CAV-1), in trophoblasts from E-PE placentas. Prolonged hypoxic stimulation led to the remarkable augmentation of CAV-1-mediated Met endocytosis in HTR8/SVneo cells. In addition, the expression of Cbl was substantially repressed by sustained hypoxia, disrupting ubiquitin degradation and the subsequent intracellular accumulation of Met in HTR8/SVneo cells. The abnormal degradation of Met hampered the ability of hepatocyte growth factor (HGF) to promote trophoblast cell invasion. In E-PE placentas, aberrant upregulation of CAV-1 and downregulation of Cbl were observed in parallel to the intracellular accumulation of Met.These findings reveal that prolonged hypoxic stress induces the augmentation of endocytosis and repression of ubiquitin-mediated Met degradation, which leads to the impaired regulation of trophoblast invasion by HGF/Met signaling. These data provide novel evidence for elucidating the pathogenesis of preeclampsia, especially of the early-onset subtype.The online version contains supplementary material available at 10.1186/s12929-022-00791-5. Preeclampsia (PE), a leading cause of maternal and perinatal morbidity and mortality worldwide, is characterized by new-onset hypertension, proteinuria or dysfunction of multiple maternal organs after the 20th week of gestation –5. PlaceHepatocyte growth factor (HGF) is an essential regulator of placental development. Once Met binds to its ligand HGF, it is dimerized and phosphorylated, leading to its activation and stimulation of multiple downstream signaling pathways, including the MEK/Erk, phosphatidylinositol 3-kinase (PI-3K) and signal transduction and activators of transcription 3 (STAT3) pathways, which play important roles in the progression of trophoblast functions , 7. DefiLigand-induced signaling through the membrane receptor is tightly controlled. One mechanism involves the rapid internalization and subsequent degradation or recycling of the receptor in a process called receptor-mediated endocytosis, via which the cells can quickly switch off further signaling to maintain appropriate receptor activation , 16. EndThis evidence suggests that the impaired Met/Erk signaling in the E-PE placenta is due to abnormalities in the endocytosis and proteasomal degradation of Met in trophoblast cells. We tested this hypothesis by comparably analyzing the distributions and expression of Met, Clathrin, CAV-1 and Cbl in the placentas of PE patients and normal pregnant women. The CAV-1-mediated endocytosis and Cbl-coupled degradation of Met in human trophoblasts were examined under hypoxic stress. These findings reveal the mechanism by which sustained hypoxic stress induces the augmentation of endocytosis and repression of ubiquitin-mediated Met degradation and thereby hampers HGF/Met signaling to regulate trophoblast invasion. These data provide novel evidence for elucidating the pathogenesis of PE, especially the early-onset subtype.Human placental tissues were collected from the Department of Obstetrics and Gynecology, Peking University Third Hospital . The study protocol for tissue collection was approved by the Ethics Committee of Peking University Third Hospital and the Institute of Zoology, Chinese Academy of Sciences. Written informed consent was obtained from the enrolled pregnant women.In brief, placental tissues (chorionic villi and decidua) were obtained from patients who underwent therapeutic termination of pregnancy at gestational weeks 6–11. Placental specimens from PE patients and normal pregnant women were collected following cesarean section. According to the definition in Williams Obstetrics (23rd edition) and the American College of Obstetricians and Gynecologists (ACOG) guidelines , severe The immortalized human trophoblast cell line HTR8/SVneo was kindly provided by Dr. C.H. Graham at Queen’s University, Canada. The cells were cultured in Roswell Park Memorial Institute 1640 (RPMI 1640) medium  supplemented with 10% fetal bovine serum . HTR8/SVneo cells were starved for 24 h in media containing 0.5% FBS before treatment with HGF  at various concentrations. HEK293T cells were purchased from American Type Culture Collection  and cultured in Dulbecco’s modified Eagle’s medium (DMEM)  supplemented with 10% FBS.Transient transfection experiments were carried out by using Lipofectamine 2000 . The siRNA duplexes were synthesized by GenePharma Co., Ltd. , and the sequences were as follows: si-Met , si-CAV-1 , si-Cbl  and scramble negative control .WT expression plasmid. The Met mutant MetY1003F was constructed by using the QuickChange site-directed mutagenesis kit , with the tyrosine1003 residue being mutated to a phenylalanine residue. The primers for mutagenesis were 5′-GGAAAAGTAGCTCGGAAGTCTACAGATTCATTTGAAACCATTTCT-3′ (forward) and 5′-AGAAATGGTTTCAAATGAATCTGTAGACTTCCGAGCTACTTTTCC-3′ (reverse). The sequences were verified by DNA sequencing  and then ligated into the pcDNA3.1 vector.The full-length human Met coding sequence (cDNA) was amplified and inserted into the pcDNA3.1 vector  to generate the Met−ΔΔCT method and normalized to GAPDH or B2M .In vitro cell invasion was assayed by determining the ability of cells to invade a synthetic basement membrane, a growth factor-reduced Matrigel matrix . The experiment was carried out as described previously . All expAll statistical analyses were performed with the Statistical Program for Social Sciences (SPSS) 18.0 software package (IBM). Differences between groups were analyzed using the two-tailed Student’s t test or one-way analysis of variance (ANOVA) , followed by post hoc Tukey–Kramer multiple comparison analysis. Differences were considered significant at P < 0.05. Data are shown as the mean ± standard error of the mean (SEM) based on three independent experiments.Given that Met/Erk signaling was inhibited in E-PE placentas , we analThe endocytosis of membrane proteins in mammalian cells is mediated by mainly Clathrin and CAV-1-coupled caveolae –42. To c2 to mimic the pathological hypoxia observed in the PE placenta . The data are expressed as the mean ± SEM, and analysis was carried out by the two-tailed t test based on at least three independent experiments. Figure S6. MetY1003F overexpression attenuates Met activation in 293T cells. A, Typical results of Western blotting showing the levels of p-Met and Met in 293T cells upon transfection with wild-type MetWT or mutant MetY1003F (2 μg) and with or without HGF (20 ng/ml) exposure. B, Bar chart showing the relative density of p-Met/Met. The data are presented as the mean ± SEM, and comparisons between groups were made by one-way ANOVA followed by the Tukey–Kramer multiple comparisons post hoc test based on at least three independent experiments. *, compared with corresponding data in the control, p<0.05. Figure S7. The expression of Cbl and CAV-1 in CTRL and L-PE placentas. A-B, Results of real-time quantitative PCR showing the relative expression of Cbl and CAV-1 in the CTRL (n=14) and L-PE placentas (n=10). C, Typical results of Western blotting showing the protein levels of Cbl and CAV-1 in the CTRL (n=14) and L-PE placentas (n=10). D-E, Bar chart showing the relative density of Cbl and CAV-1. The data are expressed as the mean ± SEM, and analysis was carried out by the two-tailed t test based on at least three independent experiments.