This study investigates the durability of glass fiber-reinforced polymer (GFRP) reinforcing bars (rebars) and their bond in concrete. Accelerated aging tests were first conducted on bare rebars that were either subjected to direct immersion in an alkaline solution or previously embedded in concrete before immersion in the solution (indirect immersion). Accelerated aging was conducted at different temperatures of the solution  and for various periods up to 240 days. Residual tensile properties were determined for rebars subjected to direct immersion and served as input data of a predictive Arrhenius model. A large decrease in the residual tensile strength assigned to the alkali-attack of glass fibers was extrapolated in the long term, suggesting that direct immersion is very severe compared to actual service conditions. Short-beam tests were also performed on rebars conditioned under direct/indirect immersion conditions, but did not reveal any significant evolution of the interlaminar shear strength (ILSS). In a second part, bond tests were performed on pull-out specimens after immersion in the alkaline solution at different temperatures, in order to assess possible changes in the concrete/GFRP bond properties over aging. Results showed antagonistic effects, with an initial increase in bond strength assigned to a confinement effect of the rebar resulting from changes in the concrete properties over aging, followed by a decreasing trend possibly resulting from interfacial degradation. Complementary characterizations by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy were also carried out to evaluate the effects of aging on the physical/microstructural properties of GFRPs. The use of glass fiber-reinforced polymer (GFRP) reinforcing bars (rebars) as a replacement for traditional steel reinforcement is an attractive solution to prevent the corrosion of reinforced concrete (RC) structures, which is the main pathology encountered on civil infrastructures worldwide. Although GFRP rebars have been increasingly used since the 1990s, there is still a lack of knowledge regarding their long-term durability in the alkaline concrete environment.Humidity and hydroxyl ions coming from the concrete pore medium rich in alkalis, are indeed likely to diffuse through the GFRP rebar and degrade their component materials. In particular, glass fibers are prone to hydrolytic degradation according to the etching process reported in Equation 1) [ [1]. AlkSeveral studies are available in the literature regarding the durability of GFRP bars subjected to alkaline environments. Experimental programs are most often based on accelerated aging tests wherein GFRP rebars are exposed to different alkaline conditions  ,14,15,16In the previous studies, the direct immersion of the GFRP rebars in alkaline solutions generally resulted in the significant degradation of the tensile strength over relatively limited time. For instance, Chen et al. reported strength losses up to 80% in the case of GFRP rebars aged for 240 days in a solution of pH 12.7 at a temperature of 60 °C . HoweverAccelerated aging of GFRP rebars in moist cement mortar or in moist concrete has only been investigated by few authors ,6,11,13 Regarding the influence of accelerated aging on the bond behavior between GFRP rebars and concrete, fewer studies are available in the literature ,20,21,22In this context, the objective of the present study is to provide additional experimental data regarding the accelerated aging behaviour of GFRP rebars and GFRP/concrete interfaces under alkaline environments. Glass/vinylester rebars of nominal diameter 12.7 mm were exclusively considered in this work. An accelerated aging program was conducted on these rebars subjected to direct immersion in an alkaline solution and on the same type of rebars previously embedded in a concrete cylinder before immersion in the solution (this specific condition will subsequently be denoted indirect immersion). The objective of comparing these two conditions (direct/indirect immersion) is to check that the degradation kinetics is slowed down by reducing the mobility of hydroxyl ions thanks to the intermediate concrete coating. Pull-out specimens were also exposed to the alkaline solution in order to study the durability of the rebar/concrete interface. Exposures were carried-out at different temperatures  in order to vary the acceleration factor of the degradation kinetics and for different periods up to 240 days. A total of 130 samples was considered in this durability program. Mechanical characterization was performed at selected aging times  by tensile, short-beam and pull-out tests (depending on the type of sample) in order to evaluate the residual properties. An Arrhenius approach was proposed to predict the long-term evolution of the tensile strength in the case of rebars subjected to direct immersion. Besides, physico-chemical characterizations were also carried out by various techniques  to detect the possible microstructural/chemical degradations of the GFRP rebars over aging and compare the effects of direct/indirect immersion protocols.The rebars considered in this study were commercially available sand-coated glass/vinylester rods manufactured by Pultrall Inc. Company  under the brand V-ROD. All GFRP rebars had a nominal diameter of 12.7 mm. As previously mentioned, in the framework of the accelerated aging program, some rebars were directly immersed in an alkaline solution, while others were embedded in concrete before being immersed in the same alkaline solution (indirect immersion). One of the objectives of this study was to compare the effects of direct and indirect exposures.Additionally, pull-out specimens were also aged in the alkaline solution to evaluate the evolution of the bond properties at the rebar/concrete interface.In order to evaluate the impact of direct immersion on the longitudinal tensile strength and elastic modulus of the GRFP rebars, samples of length 1.20 m were immersed in the alkaline solution (the composition of the solution is specified in Shorter rebars (32 cm long) were also prepared according to the same protocol. After aging under direct immersion, these bars were cut into three sections of 10 cm, which were then tested by short-beam test in order to evaluate their residual interlaminar shear strength (ILSS). The remaining 2 cm were used for microstructural observations and physico-chemical analyses  after 28 days of cure out of water. These tests provided a mean compressive strength of 29.4 ± 0.4 MPa. More details regarding the concrete formulation and the compressive tests are available in .After 28 days of cure, a part of the embedded GFRP specimens was immersed in the alkaline solution at different temperatures . This configuration allows the studying of the effect of alkali diffusion from the solution to the core GFRP rebar through the porous structure of the surrounding concrete cylinder, while ensuring an ionic balance between the solution contained in the pores and the external solution. The mobility of alkali ions is expected to be significantly lower than in the case of direct immersion of GFRP rebars in the solution. Nevertheless, it was chosen to use a normal-strength concrete, which is generally more porous than high strength concrete. This choice was deliberately made to preserve a certain diffusion of the alkalis in the concrete pore, so that the conditions of the study remain sufficiently conservative.Another portion of the specimens was subjected to pure thermal aging at 40 °C and 60 °C in the air. Such conditioning out of the alkaline solution was considered for detecting specific effects possibly induced by the thermal solicitation .After aging, the GFRP rebars were carefully extracted from the concrete cylinders by splitting the concrete piece and then characterized by short-beam tests for evaluating their residual ILSS . The specimen’s geometry is illustrated in After concrete casting, pull-out specimens were stored for 28 days in the laboratory and then placed in the aging environments. A part of the specimens was immersed in the alkaline solution at the various temperatures . The other part was again subjected to pure thermal aging in the air at 40 °C and 60 °C to assess possible thermal effects on the bond properties.Five tanks were used for conditioning the samples in the different accelerated aging environments, as shown in The alkaline solution was composed of 0.1 mol/L (4 g/L) of sodium hydroxide (NaOH) and 0.5 mol/L (28.05 g/L) of potassium hydroxide (KOH). This solution is commonly used at Eiffel University in the framework of durability/corrosion studies ,37 becauThe two other tanks, in which the aging environments were denoted 40-T and 60-T, were filled with water and regulated at temperatures of 40 °C en 60 °C, respectively. These tanks were intended for applying pure thermal aging conditions, in order to study possible differential thermal effects between the rebars and concrete. Before being placed in these tanks, the specimens were first wrapped with hermetic plastic bags to avoid contact with water and keep them in a dry state b. Only eFinally, the specimens were conditioned for periods of 120 and 240 days in these various environments, and then removed from the tanks in order to be tested.When rebars are immersed in an alkaline solution, water absorption may occur, possibly leading to the swelling of the polymer matrix and changes in the diameter and mass of the GFRP rod. In order to monitor these possible changes over aging, three dedicated sand-coated GFRP rebars and one uncoated rebar (a rod with a smooth finish produced by the same manufacturer) were placed in each of the tanks containing the alkaline solution environments . The bar edges were also coated with an epoxy resin prior to immersion, to avoid moisture diffusion through the cut sections. These rebars were periodically removed from the baths and their mass was determined using a balance of precision 0.1 g, in order to assess the amount of absorbed water compared to the initial state.In addition, diameter measurements were performed with a caliper of precision 0.01 mm at fixed locations of the bars identified by marks (reticles) drawn at the surface (one mark per sand-coated rebar and 3 marks per smooth rebar). Such marked rebars are shown in Microstructural observations were made on polished cross-sections of the GFRP rebars using a Hitachi  S570 scanning electron microscope (SEM) operating in secondary electron mode. The objective was to detect the possible degradation of the fibers, polymer matrix or fiber/matrix interface after aging.In addition, analysis of the surface elemental composition was performed using a Quantax energy-dispersive X-ray (EDX) probe from Bruker Corporation . This technique enables the mapping of the spatial distribution of a given chemical element at the surface of the sample. It was used to detect possible concentrations of K or Na elements in the aged rebars that would clearly evidence the diffusion of alkali ions into the sample during aging.gT(1) and gT(2) respectively. The objective was to detect possible changes in these glass transition temperatures during aging that would reveal microstructural modification or chemical alteration of the vinylester network [Samples taken from the surface and the core of aged rebars were analyzed by differential scanning calorimetry (DSC), using a DSC Q100 apparatus from TA Instruments . Analyses were carried out according to the NF EN ISO 11357-2 standard . The sam network .−1, with a resolution of 4 cm−1 and an accumulation of 32 spectra. The objective was to detect any changes in the chemical structure of the vinylester matrix after aging.Fourier transform infrared (FTIR) analyses were performed using a Nicolet 380 spectrometer from Thermo Fisher Scientific . This technique allows the detection of the characteristic vibrations of chemical bonds and therefore, to highlight the different functions/molecular groups that compose the chemical structure of a material. These analyses were carried out in attenuated total reflectance (ATR) mode on samples taken near the rebar surface. Spectra were collected in the wavelength range 4000–400 cmAfter aging by direct immersion in the alkaline solution at 20 °C, 40 °C and 60 °C, the 1.20-m-long rebars were characterized in tension according to the ASTM D7205 standard  in orderBefore testing, a specific anchoring device was sealed on each end of the rebars. This device consists of a steel tube filled with an expansive mortar, allowing a more uniform distribution of the radial stresses in the rebar at the time of testing and thus, avoiding premature failure in the anchoring areas of the press jaws. Tests were carried out using a 250 kN universal testing machine from Instron . Loading was controlled by the upper cross-beam displacement with a displacement rate of 10 mm/min. During the test, the rebar deformation was locally measured by a linear variable differential transformer (LVDT) type extensometer. More details on this experimental setup can be found in .After both aging by direct and indirect immersion, the samples intended for interlaminar shear characterization were tested by the short-beam method, according to ASTM D4475 standard .F by the relation ILSS = 0.849 F/Ø2 [Tests were carried out on 100 mm-long rebar samples. Three identical samples were tested for each aging condition and aging time. To perform these tests, a specific frame  was manu849 F/Ø2 .The specimens dedicated to bond characterizations were tested by the pull-out method according to the ACI 440.3R-04 guidelines , using abτ can be determined as the ratio of the maximum tensile force F exerted on the loaded end to the surface area of the rebar embedded in concrete. It is expressed in the following form:At the end of the test, the bond strength L is the embedment length in concrete. As a reminder, the frame is embedded over a length equal to six times its diameter . This result suggests that the substantial diffusion of alkalis may occur within GFRP rebars subjected to direct immersion, but it remains restricted to the outermost layer of the bar.To conclude, SEM images and EDX analyses provide evidence for the greater severity of the aging protocol based on the direct immersion of GFRP rebars in the alkaline solution compared to the indirect immersion involving an intermediate concrete cover. Note that rather similar conclusions were drawn by several authors when comparing direct immersion in an alkaline solution to indirect immersion in water (GFRP bars aged in moist concrete) ,6,11,12.gT) of the vinylester matrix determined from DSC thermograms are reported in DSC analyses were performed on small samples (a few mg) taken from the surface (just beneath the sand coating layer) of GFRP rebars aged for 240 days by direct immersion in the alkaline solution (AK-D) at 20 °C, 40 °C and 60 °C and on samples taken from the surface of unaged reference rebars as well (REF). Analyses were also carried out on samples taken from the core of GFRP rebars, in the case of reference and 60-AK-D specimens. The glass transition temperatures (gT (1)) and at the second run (gT (2)), regardless of the location of the sample (surface or core). The vinylester matrix of these GFRPs seems therefore little affected by direct immersion conditions and exhibits good chemical stability under alkaline environments.Very little variation of the glass transition temperature is observed over aging. This is true for both values determined at the first run (gT (1) and gT (2) for a given sample . This is verified for both the reference sample and the aged rebars. It shows that the vinylester matrix has not been fully cured during the manufacturing process and that some post-curing effect takes place during the first DSC run, leading to an increase in the glass transition temperature at the second run. Besides, one can notice a difference between the values of −1 is of great interest as it contains the vibration bands of hydroxyl groups (OH) [ups (OH) . In thisAll GFRP rebars showed brittle failure during a tensile test. The elastic modulus and tensile strength determined for the reference specimens and the aged GFRP rebars are reported in Experimental results reveal only small variations in the elastic modulus after aging (with a maximum loss of 7% after 240 days at 60 °C). Conversely, a substantial decrease in the tensile strength is observed after aging. In particular, one can notice (i) a gradual decrease in resistance over time and (ii), at a given time, a drop of resistance when raising the aging temperature (strength loss up to 42% after 240 days at 60 °C). These trends suggest that significant degradation of the material takes place over prolonged direct immersion of GFRP rebars in the alkaline solution, in accordance with previous SEM observations. They also corroborate observations made by other authors ,5,7, whoNevertheless, one must remind that this accelerated condition is much more severe than the actual exposition in concrete structures ,6,11,12.T, the reaction kinetics is characterized by the rate coefficient k, which can be expressed in the following form, according to Arrhenius law:k is the reaction rate coefficient related to the rate of degradation (homogeneous to the inverse of time); aE is the activation energy of the reaction (in J·mol−1); R is the ideal gas constant (in J·mol−1·K−1); T is the absolute temperature (in K), and A is a pre-exponential factor.In this paragraph, we propose to quantify the acceleration effect produced by temperature on the degradation kinetics of GFRP rebars exposed to direct immersion in the alkaline solution. This approach is based on the Arrhenius law, which has been widely used in the literature for predicting the degradation behavior of composite rebars ,23,24,25T0 and T1, during periods t0 and t1 and having led to degradation rates k0 and k1. For an equivalent level of degradation, the ratio between the time t0 necessary to achieve this degradation level in test 0 and the time t1 necessary in test 1 is called the time shift factor (TSF). It can be written in the following form:Let us consider two isothermal tests, test 0 and test 1, carried out respectively at temperatures R(t) the residual tensile strength of the rebars at any time t during the degradation process. We propose to describe the residual tensile strength evolution R(t), expressed as a percentage of the initial resistance value, in the following form:τ is the characteristic degradation time, which depends on the temperature.Let us now denote by τ coefficients for the three test temperatures considered in this study . The results of these identifications are displayed in From experimental data, it is possible to trace the evolution of the residual tensile strength of rebars (in %) as a function of time for each aging temperature see . AlthougR(t) at different temperatures, the natural logarithm of the reaction time necessary to reach residual tensile strength values of 90%, 80% and 70%, versus the inverse of the absolute temperature. Linear regressions of these data series, also called Arrhenius lines, make it possible to estimate the quantity aE/R, which is equal to the slope of the lines. Indeed, from Equation (3), we deduce:It is worth noting that the three Arrhenius lines displayed on aE/R = 3500 K. Considering a reference temperature of 20 °C, TSF can then be determined at 40 °C and 60 °C using Equation (4), and their values are reported in After the identification of the slopes of Arrhenius lines in Finally, knowledge of the temperature shift factors enable the construction of the master curve describing the long-term evolution of the residual tensile strength at the reference temperature of 20 °C, as shown in This master curve predicts a large degradation of the tensile strength of about 40% after 2.5 years of exposure. Similar predictions were reported by  on glassRobert et al. , who invThe notable divergence between tendencies resulting from the two accelerated aging methods  stress the need to carry out further comparative studies between real aging/accelerated aging, in order to be able to recommend a representative accelerated aging protocol in the future.Short-beam tests were performed on reference samples and on GFRP rebars exposed for 240 days to direct (AK-D) and indirect (AK-I) immersion in the alkaline solution at different temperatures and to pure thermal aging (T) as well. ILSS values determined on the various specimens are referenced in At first, the results show that accelerated aging does not induce a significant decrease in the ILSS of GFRP rebars, whatever the type of accelerated environment. With regard to rebars subjected to direct immersion in the alkaline solution (AK-D), it is even possible to note slight increases in ILSS (except for the 60-AK-D-240D samples). The trend observed here is therefore very different from that previously described for the tensile strength. Note that the failure mechanisms of these two tests are very different, because the ILSS value relates more to the properties of the matrix and fiber/matrix interface, while the longitudinal tensile strength is mainly governed by the tensile properties of glass fibers. The relative stability of the ILSS of aged bars would therefore confirm the good chemical resistance of the vinylester matrix that had already been demonstrated previously by DSC and FTIR analyses and also the good resistance of the fiber/matrix interface .In addition, for a given temperature and exposure time, rebars exposed to direct immersion (AK-D) exhibit slightly higher ILSS values compared to rebars exposed to indirect immersion (AK-I), and some values may even be greater than the initial ILSS (up to a 17% increase for 60-AK-D-120D rebars). Because this property (ILSS) related the chemical resistance of the matrix and the fiber/matrix interface, direct immersion in the alkaline solution does not therefore represent a particularly penalizing condition.The results also highlight higher ILSS values for the rebars subjected to the AK-I environment compared to pure thermal aging out of solution (T). This phenomenon could result from a possible confinement effect of the fibers in the AK-I condition, driven by the swelling of the polymer matrix due to the absorption of some interstitial solution. Such a confinement effect would be beneficial to the fiber/matrix load transfer and hence to the ILSS. Finally, the overall higher ILSS values obtained for rebars aged in direct immersion (AK-D) compared to those aged in the two other environments could result from a greater diffusion of the solution in these AK-D samples, hence a larger swelling phenomenon of the polymer matrix and a stronger confinement effect of the fibers. However, this hypothesis remains uncertain, as the monitoring of the mass and diameter of GFRP rebars did not reveal very significant evolution.The results presented in this section are quite remarkable, as in previous work by Chen et al. , focusedThe vinylester resin of GFRP rebars used in the present study therefore appears to be very stable in alkaline environments.Bond properties of GFRP rebars with concrete are closely related to the properties of the host concrete. To explain the possible evolution of the bond properties during aging, it is thus necessary to monitor the evolutions of the concrete properties in the same aging conditions as well. In this line, concrete cylinders  were stored in the various aging environments  in order to be tested in compression after 240 days of exposure. Results of the compression tests are reported in Pull-out tests were then carried out on specimens aged for 240 days in the different environments, and the typical failure modes are illustrated in Bond strength values determined on reference and aged pull-out specimens are reported in Globally, an initial increase in bond strength is observed over the first 120 days of exposure, regardless of the type of aging environment, followed by a decreasing trend between 120 days and 240 days. The bond strength values at 240 days of exposure still remain higher than that of the reference specimens. Note that experimental dispersion was rather large in the case of aged samples, which made comparisons difficult.The improvement in the concrete properties over aging (as shown previously on concrete cylinders) has certainly played a beneficial role on the rebar/concrete bond as well.In this context, the significant increase in bond strength over the first 120 days exposure may thus relate (i) to an increased shear strength of the concrete close to the concrete/rebar interface, (ii) to a confinement effect of the rebar driven by shrinkage of the post-cured concrete or (iii) to a synergy of the two phenomena. Nevertheless, this beneficial post-cure of concrete may have masked possible degradation mechanisms of the concrete/rebar interface after aging, at least in the first stage of exposure wherein the kinetics of the hydration reaction of concrete is still high. As this kinetics reaches a steady state, the interfacial degradation process may become predominant over the post-cure, which could explain the decreasing trend of the bond strength between 120 and 240 days of exposure. In order to validate this hypothesis and confirm the decreasing trend in the long term, further experimental programs are needed with extended periods of aging.Regarding the 60-AK-I-240D specimens, although compression tests on concrete cylinders have revealed a loss of compressive strength, the bond strength still remains higher than that of the reference specimens. If an internal swelling reaction of concrete has actually taken place in these specimens, this reaction may have produced additional confinement of the GFRP rebars and hence, increased the bond properties.Finally, it should be noted that with higher-performance concrete, one could also expect an initial increase in the bond strength related to the maturation of concrete. Differently, the subsequent decreasing trend might be less (or not) visible, due to the low porosity of high-performance concrete, which prevents the extensive diffusion of alkali ions.Overall, the findings of the present study regarding the bond behavior provide more optimistic trends than results presented by other authors ,20,21,22The objective of this study was to understand as rationally as possible the durability of GFRP rebars exposed to alkaline environments. In this study, GFRP rebars were aged in different aggressive conditions , and the main physical, mechanical and bond properties were monitored during aging. Complementary characterizations were also carried out by SEM, EDX, DSC, FTIR and mass/diameter monitoring, in order to relate the observed evolutions of macroscopic properties to possible microstructural changes or degradations. After the direct immersion of the GFRP rebars in the alkaline solution, a significant reduction in the longitudinal tensile strength was observed (of more than 40% after immersion at 60 °C for 240 days), which was correlated to the degradations of the glass fibers and the fiber/matrix interface in the outermost region/layer of the bars, as evidenced by SEM observations. A predictive model, based on the Arrhenius law, then made it possible to extrapolate the loss of tensile strength over a period of approximately 2.5 years at a reference temperature of 20 °C. However, this type of accelerated aging by direct immersion remains much more severe than exposition to the actual concrete environment where the mobility of hydroxyl ions is rather limited. SEM observations showed much less degradation on rebars exposed to indirect aging  compared to direct immersion. Subsequently, it could be interesting to investigate in a further study the evolution of the tensile properties of rebars subjected to indirect aging. This environment would thus allow a reasonable diffusion kinetics of alkalis from the solution to the rebar via the porosity of concrete.Globally, whatever the considered aging environment, no significant degradation of the vinylester matrix of GFRP rebars was detected . In addition, the monitoring of the mass/diameter of GFRP rebars did not reveal any notable variation during aging. These observations, together with EDX analyses, allow the conclusion that the absorption of the solution by the GFRP rebars remains very limited despite the great aggressiveness of the imposed accelerated aging conditions. Likewise, very little change in the interlaminar shear strength was observed after aging (an increase in ILSS was even highlighted for rebars subjected to direct immersion), indicating good chemical resistance of the vinylester matrix and the fiber/vinylester matrix interface in the core rebar.Finally, several conclusions were drawn regarding the evolution of the bond properties of GFRP rebars in concrete during aging. The initial increase in bond strength observed in the first stage of exposure (from 0 to 120 days), which differs from trends usually described in the literature, has been assigned to the evolution of the concrete properties  that produces additional confinement of the GFRP rebar. However, in a second stage (between 120 days and 240 days of exposure), the results of pull-out tests highlight a decreasing trend of the bond strength, suggesting that the degradation process at the concrete/rebar interface becomes predominant over the other beneficial effects. Further research is needed to validate this hypothesis, in particular durability studies conducted over longer exposure times. Nevertheless, the present results can be considered optimistic since the bond strengths of aged specimens (up to 240 days exposure) are above that of unaged reference specimens.


This work aimed to study the effect of a microfibrillated cellulose additive on strength, elastic modulus, heat release, and shrinkage of mortar and concrete. The dosage of the additive varies from 0.4 to 4.5% by weight of the cement. The change in strength with an increase in the dosage of the additive occurred in a wave-like manner. The uneven character of the change in the results also took place in the determination of heat release and shrinkage. In general, heat release and shrinkage decreased at increasing additive dosage. The additive showed the greatest decrease in the heat release of concrete at a content of 2%. The heat release of concrete practically differed little from the exotherm of the standard at an additive content of 1 and 1.5%. The addition of microfibrillated cellulose additive in small (0.5%) and large (1.5%) amounts reduced shrinkage compared to the reference, and at an intermediate content (1%), the shrinkage was higher than in the reference specimens. In this case, the water evaporation rate from concrete increased with an increase in the additive. With an increase in the additive dosage, the modulus of elasticity decreases. Thus, the microfibrillated cellulose additive provides concrete with lower values of the modulus of elasticity, heat release, and shrinkage, and the additive is recommended for use in concretes with increased crack resistance during the hardening period. The recommended additive content is 0.5% by weight of cement. At the specified dosage, it is possible to provide the class of concrete in terms of compressive strength C35/45. Much attention is paid to a direction in concrete technology associated with using nanostructures of carbon, oxides of silicon, titanium, iron, and others ,2,3,4,5.There is evidence  that SBPIt was established  that por3. Regulating the mixture’s rheological characteristics is carried out by changing the additive’s dosage, which, according to the manufacturer’s recommendation, varies from 0.5 to 2.5% of the cement mass and is introduced into the concrete mixture after adding water.The investigated additive Pro-Flowstab is a ready-to-use aqueous suspension of microfibrillated cellulose from beet pulp, with a pH of about four and a density of about 1 g/cmAccording to the manufacturer’s data, microfibrillar cellulose Pro-Flowstab, obtained from the primary wall of parenchymal cells, consists of microfibrils, including elementary nanofibrils with a 2–4 nm diameter, consisting of 18–24 strands of the cellulose polymer. According to the data of . In addiThere is no generally accepted classification of supramolecular structures in the literature. The terms used for nano- and micro-sized cellulosic materials are not fully established. The same material may have different names, or the same terms may be used for different materials. M. Ioelovich gives the following characteristics of the micro- and nanostructures of fibrillated cellulose. The units of cellulose macromolecules connected by hydrogen bonds of hydroxyl groups form the primary elements of the supramolecular structure, elementary nanofibrils with transverse dimensions of 3–10 nm, depending on the origin of cellulose. Due to the high specific surface area, primary nanofibrils tend to aggregate to form fibrillar bundles called microfibrils. In turn, elementary nanofibrils and their beams contain crystallites and amorphous domains.The authors of  considerThe authors of ,24 distiAt an early age (in the first 12 h), the addition of cellulose nanofiber reduces cement hydration, and then nanofibrils accelerate cement hydration. Furthermore, the hydration peaks increase with increasing nanofiber content. So, the general tendency is that cement hydration is enhanced by nanofibrils . A notabThe variety of structures and morphology of cellulose fibers does not allow transferring the test results of some materials to others. In each case, studies should be carried out on specific types of cellulose fibers. The Pro-Flowstab additive is poorly understood. Only its rheological properties and strength in the composition of cement stone are known . TherefoThis study uses the following materials.2/kg, a normal density of 25.1%, mineralogical composition: C3S = 61.1; C2S = 17.8; C3A = 5.7; C4AF = 13.4%.1. Portland cement without mineral additives CEM I 42.5 N produced by JSC "Mikhailovcement" , according to Russian State Standard GOST 31108-2016 “Common cements. Specifications” , with a 2. Grade 1 sand for construction works from the Sestrinsky open-pit mine, according to Russian State Standard GOST 8736-2014 “Sand for construction works. Specifications”  with a f3. Granite crushed stone, fraction 5–10 mm, "LSR-Basic Materials North-West"  according to Russian State Standard GOST 8267-93 “Crushed stone and gravel of solid rocks for construction works. Specifications” , the gra4. Superplasticizer: MC-Techniflow 178 (hereinafter SP) manufactured by MC-Bauchemie .3. The additive produced by “Bang & Bonsomer Group Oy” .5. Additive Pro-Flowstab based on nano/microfibrillated cellulose from beet pulp in the form of an aqueous suspension, with a density of about 1 g/cmThe experiments were carried out to evaluate the Pro-Flowstab additive to increase the ultimate tensile deformation of concrete, which is included in the formula for the criterion of concrete crack resistance. The dosage of the additive in the experiments with the mortar was from 0.4% to 4.5% by weight of cement, and it was 1%, 1.5%, and 2% in the experiments with concrete. In the first case, it was decided to expand the additive dosage limits in comparison with the manufacturer’s recommendations (0.5–2.5%). In the second case, the additive content was in accordance with the recommendations. The primary test in this work was to determine the elastic modulus. First, the mortar was tested on specimens with dimensions of 40 × 40 × 160 mm for bending and compression, according to Russian State Standard GOST 30744-2001 “Cements. Methods of testing with using polyfraction standard sand” , with beTo preliminarily assess the effect of the MFC additive on the deformative properties of the material, the deflection of bending specimens with dimensions of 40 × 40 × 160 mm was determined according to the scheme shown in We understand that this test scheme is not entirely correct for determining the modulus of deformation in bending, since the indicator readouts take into account the deflection of the beam and the deformation of the crushing of the material under the supports. However, this general deformation characterizes the material’s stiffness and allows the comparison of specimens in their deformation capacity.The specimens were subjected to stepwise loading, holding at each step for 4–5 min, after which the readout was taken on a dial indicator with a division value of 1 μm. The loading was stopped at each stage when a certain equal stress level was reached. Three samples of each composition were tested. From mortar mixtures of series A, three specimens (with dimensions of 40 × 40 × 160 mm) of each composition were made in special shapes, making it possible to lay metal inserts along the ends of the specimens, serving as benchmarks for measuring shrinkage. Specimens in molds were stored in a chamber for standard hardening at a temperature of (20 ± 2 °C) and relative humidity (95 ± 5%). The specimens were removed from the mold one day after fabrication. After that, the measurement of the specimen length was started using a device equipped with a mercer clock gauge with a scale division of 1 μm see . During 3; water-cement ratio W/C = 0.49, considering the water content in the MFC suspension; the proportion of sand in the mass of aggregates r = 0.40. The cone slump was selected by adjusting the dosage of the superplasticizer MC-TechniFlow 178 to maintain the uniformity of the mixtures. The dry matter content of the MFC suspension from the concrete volume was, respectively, 0.016; 0.024; and 0.032%.The concrete tests were designated as series C. To determine the effect of Pro-Flowstab additive on the properties of concrete, 4 compositions were prepared that differ in the content of the MFC additive, which was 0; 1.0; 1.5; and 2% by weight of cement. The following parameters characterized concrete compositions: cement consumption C = 465 kg/mThe ultimate compressive strength was determined on cube specimens 70 × 70 × 70 mm, according to Russian State Standard GOST 10180-2012 “Concretes. Methods for strength determination using reference specimens” . StrengtThe tensile elastic modulus of concrete was determined following the Russian Standard GOST 24452-80 , for det1 = Q2, the ratio of the heat release rates, as well as the corresponding times τ2 and τ1, remains constant throughout the entire process:The heat release of concrete Q was determined according to EN 196-9: 2010 , by the t was calculated by the formula:1 − t2 = ε, then ft = 2, that is, when the temperature rises by ε degrees, the heat release rate doubles. Two twin specimens of each concrete composition were tested. The readings of the temperature sensors were recorded by the Terem-4 multichannel meter recorder every 30 min.The temperature function fThe rules for holding the specimens and the test periods were adopted according to Russian State Standard GOST “Concretes. Methods for strength determination using reference specimens” 10180-2012 . The samThe compositions of mortar mixtures are divided into two series, A and B see . All comThe results of testing cement specimens with dimensions of 40 × 40 × 160 mm are given in From Tests show that strength does not change uniformly with increasing Pro-Flowstab additive content. However, in series A, there is a certain tendency in the change in strength, approximating a third degree polynomial . This teThe presence of extrema of the function usually indicates a change in the mechanism of influence, resulting from an oppositely acting competing factor, which in this case could be the reinforcing effect of the additive. However, testing the hypothesis by Fisher’s criterion did not confirm the adequacy of the model. In addition, an experimental verification was carried out by testing specimens with the same actual W/C, including the amount of water in the MFC dispersion (series B). At the same time, a decrease in the ultimate strength of the specimens in compression with an increase in the amount of additive was observed. Still, in the case of bending, a U-shaped curve was also observed, as in series A. Below, in experiments with concrete (series C), it is shown that the compressive strength clearly decreases with an increase in the additive content, but the flexural strength here also has a characteristic minimum at an intermediate dosage of MFC. It can also be assumed that at low dosages of the additive, the decrease in strength is caused by the negative effect of fatty acids contained in the membranes of parenchymal cells of microcellulose, and the insufficient reinforcing effect of the additive fibers. With an increase in dosage, the reinforcing effect is enhanced and surpasses the effect of organic compounds.To preliminarily assess the effect of the MFC additive on the deformative properties of the material, the deflection of bending specimens with dimensions of 40 × 40 × 160 mm was determined, according to the scheme shown in The testing results of specimen series A are shown in f with the coefficient of determination in the range R2 = 0.9905–0.9992. All curves lie in close proximity to each other and have close slope values, which indicates an insignificant discrepancy between the deformation properties of the compositions containing the Pro-Flowstab additive.The angular coefficient values ∆σ/∆f depending on the content of the Pro-Flowstab additive and the age of the series A specimens are shown in The ∆σ/∆f values of the specimens for 28 days of hardening are lower than those for 7 days, with the Pro-Flowstab additive content of 0 and 0.4% see , which dThe testing results of series B specimens are shown below.The angular coefficient values ∆σ/∆f depending on the content of the Pro-Flowstab additive and the age of the series B specimens are shown in f over series and ages.In contrast to the specimens of series A, there is a synchronous decrease in the angular coefficient, and, consequently, in the deformation modulus with an increase in the Pro-Flowstab content. To assess the effect of age and compare the data for series A and B, Taking into account that the water contained in the additive in the W/C value had practically no effect on the test results;The deformation capacity decreases insignificantly with the age of the specimens . This occurs as a result of an increase in the stiffness of the internal bonds.According to The test results of specimens for strength in compression and tensile are shown in As shown in The results of determining the tensile modulus of concrete are shown in 2 = 0.937−0.994, which is quite satisfactory. The graphs in The results of measuring the tensile strain of specimen series C, depending on the applied stress, are approximated by a linear dependence with the coefficient of determination RAs shown in The effect of Pro-Flowstab on the cumulative heat release per 1 kg of cement q = Q/C is shown in The total amount of heat a releaseThe results of testing the compositions for linear shrinkage are shown in Testing of cement-sand specimens of prisms showed that in most cases the control composition, which did not contain the Pro-Flowstab additive, had the greatest strength, both in bending and in compression. With an increase in the amount of additive, starting from 0.4% by weight of cement to 0.9−1.5%, a decrease in strength was observed. With a further increase in the dosage to 3−4.5%, the strength increased but remained below the strength of the reference. In the case of concrete tests, compressive strength decreases more significantly than tensile strength. So, at a dosage of Pro-Flowstab 1, 1.5, and 2%, and the age of the specimens being 28 days, the compressive strength decreased, respectively, by 3.1, 11.7, and 22.3%, and tensile strength by 6.4, 7.4, and 18.9%, compared to the strength of the reference. These results are consistent with several sources that indicated a slowdown in hydration and a decrease in the strength of cement-based mixtures in the presence of MFC ,14,15,162 = 0.9905−0.9992. All compositions have close values of the angular coefficients σ/f, which indicates an insignificant discrepancy in the deformation properties of mortar, containing and not containing the Pro-Flowstab additive. In the case of concrete, the additive affected the modulus of elasticity differently at the age of the specimens, 7 and 28 days. The concrete showed a slight increase in the modulus of elasticity at 7 days of age and a decrease at 28 days.There was a good linear correlation between the stress σ and the conditional deflection f with the coefficient of determination in the range RThe integral heat released by cement during hydration in concrete is reduced in the presence of Pro-Flowstab, starting from a period of about 2 days. At a low additive content of 1 and 1.5%, the heat release of concrete slightly differs from the exotherm of the reference. The most significant decrease in heat release to concrete that was aged 11 days was observed by adding Pro-Flowstab at a content of 2%. For the composition with a 2% content of the additive, the curve of the heat release rate dq/dτ shifted towards later periods, i.e., an increase in the duration of the induction period. The increase confirms the results of other authors on the retardation of cement hydration in the early stages of hardening. At the same time, a higher hydration peak value may mean that the Pro-Flowstab additive enhances hydration.With an additive content of 0.5%, the shrinkage of the specimens by the age of 100 days decreased in comparison with the reference by about 20%. At the same time, it is interesting that with a lower shrinkage, by this time this concrete had lost about 30% more of the amount to water evaporation than the reference composition. With an increase in the dosage of the additive, the amount of evaporated moisture increasesd. So, with an additive content of 1.5%, the difference in water loss was about 67%. This circumstance is probably explained by the fact that cellulose fibers restrain the convergence processes of tobermorite gel particles and their compaction. On the other hand, the gaps between the gel particles, while remaining enlarged, retain moisture with less energy and increase its evaporation rate.A feature of the tested additive is its non-monotonic wave-like effect on the properties of concrete, depending on the dosage. Perhaps this is a consequence of increased acidity (pH = 4), due to the presence of fatty acids. These fatty acids are found mainly in the parenchymal cells of plants, from the primary membrane of which this type of microcellulose is obtained. In any case, this is a matter for further research and improvement of the production technology.Pro-Flowstab additive appeared on the construction market relatively recently, and is poorly studied. In this work, experimental studies on the effect of the Pro-Flowstab additive on the strength, deformability, heat release, and air shrinkage of cement composites are carried out since these properties determine the crack resistance of concrete.For mortar with an increase in the content of additive Pro-Flowstab, a decrease in strength was observed, both in bending and in compression. Similar results were obtained in the case of concrete tests. Compression, tensile, and flexural tests of concrete showed a decrease in strength in the presence of Pro-Flowstab additive. Compressive strength decreases more significantly than tensile strength.The addition of Pro-Flowstab to cementitious composites requires reducing either the amount of superplasticizer or the water/cement ratio to obtain equal flow. Adjustment of the workability of the mixture in one and the other way did not show significant differences in strength and deformation properties.Adding Pro-Flowstab additive does not significantly affect the deformation properties of mortar. For concrete, the presence of Pro-Flowstab admixture significantly affects the modulus of elasticity. An increase in the dosage of the Pro-Flowstab additive by 0.5% of the cement mass reduces the elastic modulus of concrete by 1.75 GPa. From the point of view of the crack resistance of concrete, this circumstance is positive, provided that the strength remains unchanged.Pro-Flowstab additive reduces the integral heat released by cement during hydration, and, at the same time, delays this process. However, the higher hydration peak value may mean the general tendency is that the Pro-Flowstab enhances hydration.Pro-Flowstab additive has a positive effect on the air shrinkage of concrete. The higher the content of Pro-Flowstab, the higher the concrete shrinkage, with the same amount of lost water. On the other hand, the specimens with the additive must lose more water to achieve the same shrinkage value.Thus, the Pro-Flowstab additive, providing concrete with lower elastic modulus values, heat release, and shrinkage, can be recommended for use in concretes with increased crack resistance during the hardening period. The recommended additive content is 0.5% by weight of cement. There is an insignificant loss in strength with this content but a significant decrease in concrete shrinkage with moderate heat release. At the specified dosage, it is possible to provide the class of concrete in terms of compressive strength C35/45 following Russian State Standard GOST 57345-2016 /EN 206-1:2013 “Concrete. General specifications”.


A promising protection strategy is to incorporate polyhedral oligomeric silsesquioxane (POSS) molecules into the polymer backbone. In this study, the space durability of epoxy-POSS (EPOSS) nanocomposites was investigated. Two types of POSS molecules were incorporated separately—amine-based and epoxy-based. The outgassing properties of the EPOSS, in terms of total mass loss, collected volatile condensable material, and water vapor regain were measured as a function of POSS type and content. The AO durability was studied using a ground-based AO simulation system. Surface compositions of EPOSS were studied using high-resolution scanning electron microscopy and X-ray photoelectron spectroscopy. It was found that with respect to the outgassing properties, only some of the EPOSS compositions were suitable for the ultrahigh vacuum space environment, and that the POSS type and content had a strong effect on their outgassing properties. Regardless of the POSS type being used, the AO durability improved significantly. This improvement is attributed to the formation of a self-passivated AO durable SiO The0−9 Torr ,8,9,10. 0−9 Torr . Hence, 0−9 Torr  or ECSS-0−9 Torr  standardShape memory polymers (SMPs) are stimuli-responsive materials that, after deformation, can return to their pre-deformed shape by applying external stimuli ,16,17,184–109 O-atoms/cm3 [13–1015 O-atoms/(cm2·s) [The most destructive element for organic materials being used in LEO space application is AO ,35,36. A/(cm2·s) . Unprote/(cm2·s) . However/(cm2·s) .2) or indium tin oxide (ITO) coatings. However, these protective coatings can be damaged due to hypervelocity debris, as well as by on-ground handling during the spacecraft integration processes [1.5 POSS that leads to the formation of a passivated layer of SiO2 [Due to these extreme LEO environments, and especially due to the potential change in the thermo-optical properties of LEO-exposed materials, SMP-based epoxy resins are required to be protected against AO. Usually, this protection is provided to the spacecraft external materials by application of ~100 nm thick silicon dioxide  SMPs were investigated . The firIn the present work, we studied the effect of incorporation of these two types of POSS molecules on the LEO space environment durability, using ground-based outgassing and AO exposure simulation facilities. To validate and comprehend the morphological and chemical mechanisms of the interaction between the EPOSS and AO, the surfaces of the EPOSS samples were characterized using high-resolution scanning electron microscopy (HRSEM) and X-ray photoelectron spectroscopy (XPS). A model that connects the EPOSS structure to its space durability properties is suggested.®  [®  epoxy monomer  ), havingMS, USA) ), with aPlastics ), with aAM-POSS or EP-POSS reactants were used to substitute the Jeffamine D230 crosslinker or the epoxy EPON 826 resin, respectively. In both cases, a 1:1 molar ratio between the amine and the epoxide functional groups was maintained. The maximum concentration of POSS was reached by completely replacing the epoxy resin with EP-POSS, or by replacing the Jeffamine D230 crosslinker with AM-POSS. The various compositions of the EPOSS nanocomposites are given in ®, Ellijay, GA, USA) release agent. The cavity dimensions were 12 mm diameter and 1 mm depth. Finally, the adhesive was cured at 100 °C for 1.5 h and then post-cured at 130 °C for 3 h [The samples were prepared in the following manner: The epoxy resin, crosslinker, and POSS reactants were weighed and transferred into a glass vial. First, the vial was heated to 80 °C and shaken by a vortex shaker for 1 min at 3000 rpm, thus producing a precured adhesive. Second, the adhesive was degassed for 8 min at a pressure lower than 10 Torr and a temperature of 80 °C. Third, the precured adhesive was casted into a disk-shaped aluminum mold pretreated with a Watershield™  content from the sample is evaluated by the wt.% of the total mass loss (TML), before and after the experiment, out of the original sample mass. The sample mass was measured by a SE2 micro-balance  with a readability of 0.1 µg.The outgassing properties of various EPOSS samples under vacuum and heat were determined according to ASTM E595-15  and ECSSDuring the outgassing experiments, a collecting plate was kept at 25 °C to measure the wt.% of the collected volatile condensable material (CVCM) out of the original sample mass. After the outgassing process, the samples were transferred back to the humidity chamber for another 24 h. The volatile content, equivalent to water mass, was calculated by measuring the wt.% of water vapor regain (WVR) mass out of the original sample mass. The TML of the sample excluding the WVR was designated as the recovered mass loss . According to the ASTM E595-15 standard, the screening criteria require a TML of less than 1 wt.% and CVCM lower than 0.1 wt.% in order for a material to be considered for space applications. In comparison, according to the ECSS-Q-ST-70-02C standard, the screening criteria requires RML of less than 1 wt.% and CVCM lower than 0.1 wt.%.−3 Torr for 72 h. Following the outgassing stage, the samples were exposed to an environment simulating AO in a ground simulation system based on a LITMAS® RPS, LB-3001 RF-oxygen plasma source . During the exposure experiments, each sample was placed on a holder inside the vacuum chamber, down-stream from the plasma source. The pressure inside the chamber was maintained at 2 × 10−2 Torr. The uniformity of the AO plasma source was confirmed by placing a Kapton sample near each EP-POSS sample. The mass loss of the Kapton samples was used to determine the AO equivalent fluence and flux. The equivalent AO flux that the RF plasma produced was at the order of 1014–1015 O-atoms/(cm2·s). For mass loss measurements, the samples were removed periodically from the system. Weight measurements were carried out using the Sartorius SE2 micro-balance. The AO equivalent fluence has been determined using the Kapton erosion yield , Δm is the mass loss (g), A is the sample’s exposed area (cm2), ρ is the material density (g/cm3), and E is the erosion yield (cm3/O-atom). The erosion yield was calculated from the mass loss of the sample after exposure to the total AO fluence.The durability of the samples to AO erosion was studied in accordance with the ASTM E2089-00 standard . Initial3/O-atom ), densit-atom [3 ), and it-atom [3 . Then, aα monochromatic source (1486.6 eV), and the emitted photoelectrons were analyzed by a spherical analyzer with a slit aperture of 0.8 mm. The samples were characterized by depth profiling using 5 kV argon ions at a sputter rate of 47.6 Å/min, as measured on a SiO2/Si reference sample. Sample charging was compensated with a charge neutralizer, and the binding energies were calibrated according to the C 1s reference line at 285 eV. High-resolution XPS spectra were taken at pass energy of 11.75 eV. Spectra analysis of the different XPS lines was carried out using CasaXPS software  with a Gaussian–Lorentzian product function and a non-linear Shirley background subtraction [The change in the samples’ surface morphology as a function of AO flux was characterized using a Sigma 300 VP HRSEM from ZEISS . XPS measurements were performed using a PHI 5600 Multi-Technique System . The samples were irradiated with an Al Ktraction . The GauIn the case of EP-EPOSS, as the EP-POSS content is increased, the TML, RML, and WVR values increase as well. On the other hand, increasing the EP-POSS content doesn’t affect the CVCM values, which are maintained at ~0.005 wt.%. The 10EP sample is the only EP-EPOSS composition that complies with the ECSS-Q-ST-70-02C acceptance criteria, albeit not with the ASTM E595-15 standard.Tg values [The increase in the TML and RML values, as the EP-POSS content was increased, may be associated with the lower degree of curing of the EP-EPOSS samples compared to pristine epoxy . Under tg values ,60,61. Ag values . The lowAs shown in Tg values were similar to the Tg of pristine epoxy for most of the compositions, and even slightly higher in the case of 50AM [Tg, and decrease the chain mobility [In the case of the AM-EPOSS samples, the trend is opposite to that of the EP-EPOSS samples—as the AM-POSS content was increased, the TML, RML, and WVR values decreased, see  of 50AM . The reamobility ,64. The mobility . It is a19 O-atoms/cm2 but showed a much lower erosion rate pattern with the increase of the AO fluence. The lower erosion rate became more dominant as the amount of POSS was increased. This behavior indicates the formation of a SiO2 self-passivation layer on the EPOSS surfaces, which results in a decrease in the erosion rate [The mass loss (%) due to AO exposure of the AM-EPOSS and EP-EPOSS samples vs. AO equivalent fluence is shown in ion rate .2 [−24 cm3/O-atom in the case of epoxy, to 3 × 10−25 cm3/O-atom in the case of the 50AM sample. The addition of AM-POSS can therefore improve the epoxy durability to AO erosion by a factor of twenty. However, the erosion yield of the EP-EPOSS samples was only ~3 times smaller compared to the erosion yield of the epoxy and was less dependent on EP-POSS content. The reason for this difference lies in the different morphology of these two types of nanocomposites, as discussed below.The erosion yield of the EPOSS samples is presented in 2 . It is eIn general, ground simulation of the LEO hyperthermal AO environment by exposure to RF-plasma thermal AO has similar effects on organic materials . However2 passivation layer. Accordingly, the EP-EPOSS mass loss was higher than that of AM-EPOSS, until an effective passivation layer was formed on the surface. These results, combined with the outgassing tests results, lead to the conclusion that AM-EPOSS samples have superior properties compared to EP-EPOSS for space applications.19 O-atoms/cm2. 20 O-atoms/cm2. 20 O-atoms/cm2.HRSEM images of the surface morphology as a function of AO equivalent fluence are depicted in 19 O-atoms/cm2, in comparison to the surface morphology of epoxy (20 and 1.5 × 1020 O-atoms/cm2, the surface morphology of the epoxy did not change significantly (see The surface of the pristine samples is smooth and uniform, regardless of the POSS content a,e,i. Inof epoxy b,f,j. AtThe surface morphology of 20AM f–h and 220 O-atoms/cm2 are shown in High-resolution images of the surface morphology of the samples after exposure to AO equivalent fluence of 1.5 × 102 passivation layer on the sample surface [2 layer. surface . XPS meaThe oxidation of the POSS molecules and the formation of this passivation layer decreased the AO erosion rate of the POSS-containing samples. However, the presence of the Si-based contamination and its exposure to AO didn’t form a passivation layer, as indicated by the fast erosion rate of the epoxy see .2 passivation layer on the 20EP sample was thicker but less dense than that on the 20AM sample.AM-EPOSS and EP-EPOSS samples were prepared with various POSS contents. The effects of the POSS type and content on the outgassing properties and AO durability of the various compositions were studied. It was found that for EP-EPOSS samples, as the POSS content was increased, the TML and RML outgassing properties deteriorated. However, the EP-POSS content did not have any influence on the CVCM value, which was found to satisfy the outgassing criteria. It is suggested that, as the EP-POSS content was increased the increased presence of ether linkages leads to an increase in the chain mobility. Thus, uncured molecules and small molecular fragments can diffuse more easily to the surface and outgas.In contrast, in the case of the AM-EPOSS samples, the increase of AM-POSS content resulted in improved TML and RML outgassing properties, while the CVCM was almost constant and way below the outgassing acceptance criteria. The reason for this phenomenon is that as the AM-POSS content was increased the presence of phenyl rings increased too. This led to an increase in the backbone rigidity of the network and to a decrease of the chain mobility.The lower chain mobility reduced the rate of diffusion of small molecular fragments towards the surface, thus decreasing the amount of outgassing species. In addition, according to the CVCM results, the outgassing fragments are more condensable, and probably heavier, in AM-EPOSS than in EP-EPOSS.1.5 POSS into SiO2 layer. AM-EPOSS was found to have better AO durability compared to EP-EPOSS, and in that sense it is more suitable for LEO space applications. The EP-EPOSS exhibited lower AO durability, compared to AM-EPOSS, due to the higher chain mobility, which caused increased AO-induced damage deep below its surface. As a result, the SiO2 passivation layer on EP-EPOSS surface was thicker and more porous than that of AM-EPOSS.The EPOSS samples exhibited higher durability to AO erosion compared to pristine epoxy. The decreased erosion rate is attributed to the formation of a passivation layer due to AO oxidation of the SiOThe durability of AM-EPOSS to AO erosion improved with increasing AM-POSS content. However, in the case EP-EPOSS, no measurable change could be found in the erosion rate due to increase in EP-POSS content and exposure to AO for POSS contents of 10 wt.% and above.This work presents novel SMP nanocomposite materials with excellent outgassing properties for most of the measured compositions. It demonstrates the ability to incorporate POSS molecules into the backbone of EPOSS to increase their AO durability. The diversity of the POSS types and contents and the associated material properties enable to promote the development of these materials for future SMP-based deployable space applications.


The animals underwent withdrawal for 5 days and were readministered the drugs after 10 days. Serum and urine analytes were profiled using gas chromatography-mass spectrometry (GC-MS), and metabolic patterns were evaluated based on metabonomics data. Metabonomics data showed that heroin administration changed metabolic pattern, and heroin withdrawal did not quickly restore it to baseline levels. A relapse of heroin exposure changed metabolic pattern again. In contrast, although the administration of morphine changed metabolic pattern, whether from morphine withdrawal or relapse, metabolic pattern was similar to control levels. The analysis of metabolites showed that both heroin and morphine interfered with lipid metabolism, the tricarboxylic acid (TCA) cycle and amino acid metabolism. In addition, both heroin and morphine increased the levels of 3-hydroxybutyric acid and citric acid but decreased the serum levels of 2-ketoglutaric acid and tryptophan. Moreover, heroin and morphine reduced the levels of aconitic acid, cysteine, glycine, and oxalic acid in urine. The results show 3-Hydroxybutyric acid, tryptophan, citric acid and 2-ketoglutaric acid can be used as potential markers of opiate abuse in serum, while oxalic acid, aconitic acid, cysteine, and glycine can be used as potential markers in urine.Although heroin and morphine are structural analogues and morphine is a metabolite of heroin, it is not known how the effect of each substance on metabolites in vivo differs. Heroin and morphine were administered to C57BL/6J mice in increasing doses from 2 to 25 and 3 to 9 mg kg The abuse of opiates has had an extremely negative impact worldwide and has become an increasingly serious social problem. Morphine is a prescription opiate, most commonly used for pain management, and can provide significant relief to patients suffering from pain . HoweverDeath from a heroin overdose invariably results from respiratory depression, and an overdose of opiates, such as morphine and fentanyl, can also cause respiratory depression ,11. In aThe current study is designed to investigate the metabolic changes in the serum and urine after heroin or morphine exposure, withdrawal, and relapse, using an untargeted metabonomics method. Metabonomics, a global metabolic profiling method, offers insight into the mechanisms of opiate toxicity, and various biomarkers of opiate abuse can provide reliable forensic and clinical explanations . Li et aIn this study, we used a gas chromatography-mass spectrometry (GC-MS)-based metabonomics method coupled with multivariate statistical analysis to identify differentially expressed metabolites in the serum and urine of mice induced by repeated heroin or morphine exposure, withdrawal, and relapse. An important advantage of GC-MS is that it can identify a large number of substances in a single analysis of a very complex sample ,30. To fRepresentative GC-MS chromatograms of sera from the heroin-treated group and control group are shown in To obtain an overview of the data set, unsupervised principal component analysis (PCA) was applied. No outliers were found in the PCA model (data not shown). A partial-least-squares-discriminant-analysis (PLS-DA) loading plot is shown in The PLS-DA loading plot of morphine-treated samples is shown in Representative GC-MS chromatograms of urine from the heroin-treated group and control group are shown in The PLS-DA loading plot of heroin in urine showed a pattern like that of heroin in serum . In geneThe PLS-DA loading plot of morphine in urine also showed a pattern similar to that of morphine in serum  but was The differential metabolites (TOP 25) in serum of seven groups are shown in a heat map . The heaAs shown in Morphine resulted in marked elevations in 3-hydroxybutyric acid, citric acid and α-tocopherol levels and reduced the levels of alanine, pyruvic acid, 2-ketoglutaic acid, cysteine, tryptophan and valine . TherefoThe differential metabolites (TOP 25) in the urine samples of seven groups are shown in a heat map . SimilarMore concretely, the level of citric acid in urine gradually increased with the extension of heroin administration time A, and thMorphine significantly increased the levels of 3-hydroxybutyric acid, γ-aminobutyric acid, and ornithine and decreased the levels of citric acid, aconitic acid, cysteine, tryptophan, glycine, and oxalic acid . Hence, Although heroin and morphine have different effects on the body, some endogenous metabolites exhibited similar changes and can be used as potential markers of opiate abuse. Both heroin and morphine exposure increased the serum levels of 3-hydroxybutyric acid  and citrBoth heroin and morphine exposure reduced the urine levels of aconitic acid , cysteinThis study produced three main findings: (1) repeated heroin and morphine exposure caused significant metabolic changes in the serum and urine, and the differential metabolites mainly involved lipid metabolism, TCA cycle and amino acid metabolism; (2) after 5 days of morphine withdrawal intervention, most differential metabolites in the serum and urine were similar to control levels, but changes persisted in the serum and urine after heroin withdrawal; and (3) after 5 days of heroin relapse, the metabolites in serum and urine changed again, while some of the metabolites in serum and urine did not change significantly after 5 days of morphine relapse.Specifically, the influences of heroin on serum and urine are not all the same, so too for morphine. For example, the changes of metabolites, such as 3-hydroxybutyric acid and tryptophan, in serum are opposite to those in urine, which can be used as potential biomarkers of heroin abuse, while aconitic acid, ornithine, and γ-aminobutyric acid in serum represent morphine. Compared with heroin, morphine significantly increased 3-hydroxybutyric acid, the levels of γ-aminobutyric acid and ornithine decreased the levels of citric acid. Therefore, citric acid, 3-hydroxybutyric acid, γ-aminobutyric acid, and ornithine can be used as potential markers to distinguish heroin and morphine in urine. This is the advantage of urine samples.Lipids provide essential fatty acids for the body, and ketone bodies are intermediate products of the oxidative decomposition of fatty acids, including acetoacetic acid, β-hydroxybutyric acid , and acetone . Ketone In addition, some studies have shown that 72.7% of aging, male Mexican-American long-term injection drug users (IDUs) with long-term heroin injection suffered from different forms of liver injury  ,37, and This work not only focused on the long-term effects of opiates (heroin and morphine) but also explored the long-term effects after opiate withdrawal and relapse. Our data indicated that repeated heroin exposure induced a long-lasting metabolic effect in the serum and urine, whereas repeated morphine treatment induced a reversible effect in the serum and urine. This result may be due to the difference in resistance of mice to heroin and morphine. However, although the effect of withdrawal or relapse on metabolism is inconsistent between morphine and heroin, the serum tryptophan level of both morphine and heroin decreased further after withdrawal, while the level of tryptophan after relapse was similar to that before withdrawal. Tryptophan is the only precursor of serotonin, which is a key monoamine neurotransmitter involved in central nervous transmission and regulation of intestinal physiological function ,40. ThusIn summary, this study identified that the effect of heroin on the body was dissimilar to that of morphine. The endogenous metabolites with different changing trends can be used as potential markers to distinguish heroin use from morphine use, while the endogenous metabolites with the same changing trends can be used as potential markers of opiate abuse. However, both heroin and morphine exposure significantly interfered with the TCA cycle and lipid and amino acid metabolism. The change in tryptophan levels suggested that the brain serotonin system may mediate some behavioral effects of heroin and morphine withdrawal.13C2 acid (99 at.% 13C), alkane standard solution (C8–C40), methoxyamine hydrochloride (purity 98%), and pyridine (≥99.8% GC) were purchased from Sigma Aldrich. N-methyl-N-(trimethylsilyl)trifluoroacetamide with 1% trimethylchlorosilane were provided by Thermo Scientific . HPLC-grade methanol and n-heptane were obtained from Tedia Company  and Merck , respectively. Purified water was produced with a Milli-Q system .Reference standards of heroin and morphine were provided by the Jiangsu Institute for Food and Drug Control . The internal standard (IS) compound myristic-1,2-Chromatographic separation of the analytes was achieved using a Shimadzu GCMS-QP2010  equipped with an RTx-5MS column . A Sorvall Biofuge Stratos centrifuge  and an SPD2010-230 SpeedVac Concentrator  were used to centrifuge the samples and evaporate the supernatants to dryness, respectively.Male C57BL/6J mice  were housed individually in metabolic cages with access to a standard chow diet under standard laboratory conditions with a 12 h light/dark cycle (lights were on from 7 AM to 7 PM) and temperature of 22 ± 2 °C. All experimental procedures involving the use of animals complied with the Guidelines for Animal Experimentation of the China Pharmaceutical University , and the protocol was approved by the Animal Ethics Committee of that institution.−1 on the first day, increasing by 1.2 mg kg−1 d−1 to a final dose of 24.8 mg kg−1 and morphine administered at a dose of 3 mg kg−1 on the first day, increasing by 1 mg kg−1 every 3 days to a final dose of 9 mg kg−1. Heroin or morphine exposure was stopped for 5 days  after 10 days of administration, and then the mice were administered heroin or morphine again for another 5 days (the relapse period). Blood samples were collected on days 5, 10, 15 , and 20 (exposure and relapse) from the orbital venous plexus, and urine was collected 12 h before the blood samples were collected. The serum and urine samples were prepared and stored at 70 °C. All serum and urine samples were thawed at 37 °C for 20 min and mixed by vortexing before extraction.After adaptation to standard laboratory conditions for 2 weeks, the mice were randomly allocated to four groups: the continuous administration group (heroin and morphine), the withdrawal group (heroin and morphine), the relapse group (heroin and morphine) and the control group, and the continuous administration group was further divided into 5, 10, 15, and 20 days of continuous administration (n ≥ 6 in each group). The heroin- and morphine-treated groups were administered intraperitoneal heroin or morphine in 0.9% saline, and the control was given an equal volume of vehicle. The mice were given heroin or morphine (or vehicle) twice daily for 20 days, with heroin administered at a dose of 2 mg kg13C2 (5 μg mL−1) and vigorously vortexed. An aliquot of urine (30 μL) was first added to urinase to decompose any excess urea and then added to 250 μL of methanol and vigorously vortexed. The supernatants of the serum (100 μL) and urine (60 μL) were then dried, methoxylated, trimethylsilylated, and analyzed via GC-MS [The serum and urine samples were pretreated, extracted, and derivatized as previously reported ,43. Brieia GC-MS . To miniThe peaks were automatically detected, the mass spectra were deconvoluted, and the GC TOF/MS data were acquired as reported previously . Each ofp value < 0.05 were considered statistically significant. Heat maps were generated using MetaboAnalyst [The relative quantitative data for the peaks (peak areas) were first normalized against the IS and then subjected to multivariate statistical analysis using SIMCA-P 13 software  . To minioAnalyst .


Usually, C30/37 strength class concrete is used to construct concrete pavements on a rigid, semi-rigid or flexible base. Concrete with such a strength delivers essential design characteristics: flexural strength and tensile splitting strength are between 4.5–5.4 MPa and 2.8–3.7 MPa, respectively. Design characteristics can be significantly increased by densifying the concrete mixture, i.e., adding silica fume, steel or polypropylene macro fibers. As high-performance concrete characteristics are 20–60% higher than those for standard concrete (C30/37), new possibilities to reduce the thickness of concrete pavement slabs appear. The theoretical analysis of concrete pavement structures with high-performance concrete mixtures  showed that slab thickness could be reduced by 6–39% compared to a standard concrete pavement structure depending on the concrete properties and design method. From all those pavement structures, three concrete mixtures were determined as the most rational ones in terms of PCP thickness reduction and total pavement cost: (i) with 49.5 kg/m The operation and maintenance of a road network is a challenge, and it becomes even more complicated with the continuous growth of traffic. It is estimated that passenger transport will grow by up to 42% by 2050 and freight transport up to 60% . For sucTypically, a concrete mixture with a strength class of C30/37 is used to construct concrete pavements. In these cases, the pavement thickness varies from 175 to 400 mm depending on the traffic, environmental conditions, base type , slab dimensions and concrete mixture characteristics ,3,4,5. POne of the options to reduce the thickness of the slab is to improve the design characteristics of the concrete mixture. It is achieved by densifying the mixture, i.e., adding silica fume, steel or polypropylene macro fibers into the concrete mixture. Mostly, the purpose of these admixtures is to improve compressive strength due to hydraulic or pozzolanic (or even both) activity in high-strength concrete. Admixtures can be added as supplementary components or just as a replacement for cement. Compared to fly ash, natural zeolite or ground granulated blast, silica fume is exceptional ,9. Frequ3) constructed on the subsoil. The study showed that fibers significantly increase the total load capacity of the slab and that load capacity increases further with the increase in fiber content. Higher content of fibers also significantly influenced the total deformations, which are important for the serviceability limit state. In general, an improvement of concrete characteristics leads to a reduction in the thickness of concrete slabs [Cajka et al. (2020)  analyzedte slabs . Parker te slabs  found thte slabs  determinte slabs . All thete slabs . Rodden te slabs  have madTaken together, the effect of concrete mixture composition  on concrete performance is now well established. However, only a few studies have investigated how the improved design characteristics influence the pavement thickness and how it differs depending on the design method. The purpose of this paper is to identify the most rational pavement structures with high-performance concrete mixtures  in terms of PCP thickness and total pavement cost and to show the benefit of concrete mixtures with enhanced design characteristics compared to a standard concrete mixture. Since there exist a number of different pavement design methods and it is unclear which one should be used and how the results differ among them, the effect of different calculation methods on slab thickness was analyzed in this paper as well. All pavement structures were designed to withstand 76 million equivalent single axle loads for 30 years.Depending on the design methodology, different mechanical characteristics of concrete are used to calculate the required PCP thickness. Designing concrete pavement structures according to Richtlinien für die rechnerische Dimensionierung von Betondecken im Oberbau von Verkehrsflächen RDO Beton 09 , the twoIn contrast, when using design software such as StreetPave or FAARFIELD, the most important mechanical characteristic of concrete is flexural strength. Design software FAARFIELD and StreetPave use similar concrete mechanical characteristics of concrete in calculations. The main difference between these two design software is that FAARFIELD is fully adapted for airfield pavement calculations. FAARFIELD is using a different load spectrum, which is expressed by different types of aircraft. The FAARFIELD design process currently considers only one mode of failure for rigid pavement: bottom-up cracking of the PCP slab. Cracking is controlled by limiting the horizontal stress at the bottom of the PCP slab and does not consider the failure of subbase and subgrade layers. A three-dimensional finite element model is used to compute the edge stresses in PCP slabs. The model has the advantage of considering where the critical stresses for slab design occur. Critical stresses normally occur at slab edges but may be located at the center of the slab with certain aircraft gear configurations .Design program StreetPave calculations are based on the mechanistic–empirical pavement design method. The design methodology used in StreetPave was taken from the PCA’s Thickness Design for Concrete Highways and Streets manual . The proThe other known software for calculation PCP thickness is MnDOT’s RigidPave design software. This software is based on the 1981 AASHTO Interim Guide. Under this design method, MnDOT designs and constructs only jointed plain concrete pavement (JPCP). Slab thickness is determined using the cumulative 35-year design-lane concrete equivalent single axle loads (CESALs), which are based on the AASHTO load equivalency factors (LEFs). The equation was developed from the AASHTO road test and solves for the cumulative number of ESALs a pavement can withstand before it falls to a given serviceability level. The values used in RigidPave calculations are terminal serviceability, modulus of subgrade reaction, concrete modulus of rupture, concrete modulus of elasticity and number of ESALs to reach terminal serviceability .The method, detailed in mechanistic–empirical pavement design guide, in addition to flexural strength, also includes the modulus of elasticity and the coefficient of thermal expansion. It was observed that crack rate prediction is the least sensitive to changes in flexural strength but is most sensitive to changes in coefficient of thermal expansion . In thisOverall, major characteristics affecting PCP thickness are tensile splitting strength, tensile elastic modulus and flexural strength.Two methods with different methodological principles and required mechanical characteristics of the concrete were chosen to calculate the PCP thickness. Since mechanistic-empirical methods are more widely used for the design of pavement structures, the open-access software StreetPave , was selected, which complies with the principles of mechanistic-empirical design methods. Moreover, Rodden et al. (2019)  stated tPCP thickness was calculated for the service life of 30 years irrespective of the used method. In all cases, the number of equivalent single axle load (10 t) was 76 million. The required PCP thickness was calculated for structures with different base layers—unbound crushed aggregate base and hydraulically bound base layer. The reinforcement of the joints was also included as a variable—calculation was made assuming that the reinforcement was provided by dowels in transverse joints and reinforced anchors in longitudinal joints as well as without reinforcement at all.The mechanical characteristics of high-performance concrete mixtures used to calculate the PCP thickness according to both methods are presented in When using the method detailed in RDO Beton 09, the slab thickness was calculated corresponding to the boundary conditions of bearing capacity, serviceability and fatigue resistance . The loa2.The limit bending moment for each boundary condition is calculated according to Equation (1).EV caused by traffic load (Equation (2)) and design moment MET caused by temperature regime (Equation (3)).−6/K; 2; The design bending moment for each boundary condition is calculated as a sum of design moment MThe essential factor for the calculation of concrete pavement thickness is the characteristic tensile splitting strength of the concrete. In addition to the fact that the limit bending moment depends directly on the characteristic tensile splitting strength, this characteristic is also used to define the probability of failure. The material factor, which determines the probability of failure and its relationship to the road category, is defined by the Gaussian normal distribution of the tensile splitting strength. Concrete pavement is not dimensioned as a part of a package of layers. It is analyzed as a stand-alone component with the provision that concrete pavement works on its own, as a result of its different temperature dependencies in comparison with those of the base courses and the different material parameters such as the elasticity modulus, splitting tensile strength, thermal expansion coefficient as well as their necessary division into individual slabs through joints. The method does not directly include the load-bearing capacity and thickness of the subgrade and subbase layers but is related to the technical regulation requirements of the frost resistance of the structure and the load-bearing characteristics of the individual layers. Only the bearing capacity of the base layer is directly estimated in the calculation. However, it should be noted that the bedding modulus of the hydraulically bound base layer does not require verification, and the same fixed value is used in all cases. This means that the results are only valid if all the requirements of technical regulations for structural strength and resistance to adverse climate factors are met. The input parameters for calculation according to RDO Beton 09 are given in Using the method according to PCA design methodology, the slab thickness was calculated with the automated design software StreetPave. The design inputs are shown in The minimum PCP slab thickness calculated according to RDO Beton 09 is presented in The minimum PCP slab thickness calculated with the design program StreetPave is presented in Calculations using the RDO Beton 09 method showed that the thickness of the PCP varies from 192 to 366 mm depending on the type of the base layer and the joint reinforcement option . ResultsOverall, calculations made by the RDO Beton 09 method showed a more massive concrete pavement thickness required to withstand the same 76 million of equivalent 10 t weight of standard axle load than the design software StreetPave. Calculations made according to RDO Beton 09 showed that concrete pavement with crushed aggregate base and reinforced joints requires a 1.9–4.2% thicker concrete layer than concrete pavement with hydraulically bound base and reinforced joints, with unreinforced joints—from 2.7% to 5%. Calculations made with the design software StreetPave showed that concrete pavement with crushed aggregate base and reinforced joints requires a 1.4–1.6% thicker concrete layer than concrete pavement with hydraulically bound base and reinforced joints, with unreinforced joints—from 2% to 2.3%. Comparison of PCP slab thickness on hydraulically bound base and unreinforced joints with reinforced joints has shown from 15.8% to 19.3% thicker PCP slab according to RDO Beton 09 calculation method and from 16.6% to 17.6% thicker PCP slab according to the design software StreetPave calculation. The comparison of PCP slab thickness on a crushed aggregate base and unreinforced joints with reinforced joints has shown from 16.8% to 20.1% thicker PCP slab according to RDO Beton 09 calculation method and from 17.3% to 18.4% thicker PCP slab according to the design software StreetPave calculation. Looking at the obtained results, it is possible to see the interface of the RDO Beton 09 method with the catalog of Lithuanian standard pavement structures. First of all, the RDO Beton 09 method seems to be subject to the condition of equivalence between different base layers. The calculated pavement thickness when using a reference concrete mixture with silica fume (mixture code SF), the mechanical characteristics of which are essentially the same as the German-regulated concrete mixtures for road construction, does not differ significantly when a crushed aggregate base layer or a hydraulically bound base layer is used. In Lithuanian standard pavement structures, regardless of the type of base layer, the thickness of the concrete pavement is constant as the equivalence of different base layers is achieved through its different thicknesses. Furthermore, the PCP thickness calculated according to RDO Beton 09 differs from the Lithuanian standard structure for the same traffic conditions by 5.6–7.8%, which may primarily be related to the large number of variables in the RDO Beton 09 method. Considering this, it can be stated that the method correlates with the catalog of Lithuanian standard pavement structures.As seen in The comparison of the findings with those of other studies ,31,38 coComparing the correlation of concrete pavement thickness with the mechanical characteristics of concrete, it can be seen that the RDO Beton 09 method is significantly more sensitive to the change in the main characteristics of the concrete. As can be seen from Fiber and/or silica fume reinforced fresh concrete is relatively expensive , but cost-benefit analysis should reveal the potential benefits of PCP slabs made from concrete with improved characteristics. Each mixture type should be analyzed considering not only economic advantages in materials caused by improvement in the strength and reduced thickness of PCP slab due to the improvement of concrete characteristics but also construction and transportation expenses. For this purpose, the cost of fresh concrete in terms of compressive and flexural strengths, the cost of a square meter of pavement on crushed aggregate base and cost of a square meter of pavement on hydraulically bound base are presented in the following figures. All calculations are theoretical.The results of compressive strength indicated the tendency that compressive strength increases with a mixture cost. As expected, reinforced concrete mixtures have higher values than the reference mixture. The mixture with silica fume and steel fibers (S + SF) has the highest values and is even cheaper than mixtures with silica fume and both types of polypropylene fibers (PP_A + SF and PP_B + SF), which does not achieve even 60 MPa. Furthermore, the reference mixture with only silica fume (Ref + SF) showed a high compressive strength value and cost ratio because the mixture achieved 57.3 MPa with EUR 111.42 cost, while mixtures with polypropylene (PP_A and PP_B) did not achieve this compressive strength value and cost even more .The results of flexural strength and cost ratio indicate that the mixture reinforced with silica fume and steel fiber (S + SF) has the highest values of flexural strength (9.0 MPa), and the cost of this mixture is EUR 152.01. There is no reason to use concrete with silica fume and both types of polypropylenes (PP_A + SF and PP_B + SF) because the mixtures did not achieve as good results as mixtures with silica fume and steel fiber (S + SF), and average costs are even higher. The mixture with only steel fibers (S) also has a satisfying result because it reaches a flexural strength of 7.7 MPa, and the cost is EUR 130.59. Comparing the reference mixture with silica fume (Ref + SF) to the mixture reinforced with steel fibers (S), the reference mixture is an even better choice because it reaches the same flexural strength and cost EUR 111.42 .The idea of cost-benefit analysis is to evaluate the economic effect of the usage of a thinner PCP slab made from improved concrete instead of using a thicker slab with reference concrete. To evaluate the cost benefit of PCP slabs made from concrete mixtures with improved characteristics, the expenses of fresh concrete mixtures, dowels, slab manufacturing, storage and transportation and PCP pavement construction were considered. It is known that the manufacturing, transportation and installation of thicker slabs require many more expenses compared to thinner slabs. To evaluate the cost of slab manufacturing and installation, the fresh concrete cost was multiplied by a coefficient of 1.15 for the thickest slab and multiplied by a coefficient of 1.0 for the thinnest slab. To evaluate the cost of transportation, the cost of fresh concrete was multiplied by a coefficient of 1.3 for the thickest slab and multiplied by a coefficient of 1.0 for the thinnest slab. The coefficients for other mixtures slabs were interpolated considering the thickness of each PCP slab.As discussed in previous sections, the StreetPave method is not sensitive to concrete characteristics  compared to RDO Beton 09 . Even without cost-benefit analysis, it can be seen that the total price of PCP pavement, calculated using StreetPave, would mainly depend on the fresh concrete price. Considering these facts, the cost per square meter of pavement analyses was performed only on results received from RDO Beton 09. 2 respectively), while S + SF (R) has the lowest price (37.80 EUR/m2). This analysis confirms that the most important factor in cost-benefit analysis is the total cost of PCP construction, not only cost of fresh concrete.2, respectively) while S + SF (R) has the lowest price (36.40 EUR/m2).As can be seen from Cost to benefit analysis shows that the use of concrete with steel fiber or polypropylene A fiber w/ or w/o silica fume and the use of dowels for jointing slabs provides the highest economic effect. Moreover, the use of the reference mixture or SF mixture without fibers for PCP pavement is the most uneconomic.A minimum thickness of PCP slab depends not only on the pavement structure, joint type and materials characteristics but also on the applied design method. At the same conditions, the semi-probabilistic empirical pavement design method (RDO Beton 09 method) led to a 2–50% thicker PCP slab than the software StreetPave . The lowest difference was determined when a concrete mixture with polypropylene_A fiber and silica fume was used, while a reference mixture gave the highest difference irrespective of the presence or absence of silica fume. The main reason for that is the use of different concrete characteristics for PCP thickness calculation  and the different sensitivity to the change in those characteristics.The comparison of PCP slab thickness with concrete mechanical characteristics used to calculate the thickness showed that the RDO Beton 09 method is significantly more sensitive to the change in the characteristic values of the concrete than StreetPave software. In the case of the RDO Beton 09 method, the 54% increase in the tensile splitting strength of concrete reduced the thickness of the PCP slab by 36%, while the same percentage increase in flexural strength (StreetPave) reduced the thickness of PCP only by 9%.3 of silica fume and 49.5 kg/m3 of steel fibers in the concrete mixture.The replacement of standard (C30/37) concrete mixture with a high-performance one  reduces the thickness of PCP slab from 6% to 39% depending on the design method. With both design methods, the highest decrease in thickness of PCP slab (124 mm with RDO Beton 09 method and 24 mm with StreetPave) was determined when a concrete mixture with tensile splitting strength of 6 MPa, tensile elastic modulus of 91 GPa and flexural strength of 9 MPa was used. Those characteristics were achieved by adding 25.2 kg/mJoint type has a much larger effect on the PCP slab thickness than base type, irrespective of design method and the mechanical characteristics of the concrete mixture. The thickness of PCP slab with dowel reinforced joints was 14–17% lower than that with unreinforced joints, while hydraulically bound base course resulted in only 2–5% lower thickness than unbound base course (crushed aggregate).2) when comparing to the reference mixture (58.33 EUR/m2).The cost-benefit analysis showed that the use of a concrete mixture with either steel or polypropylene fibers, irrespective of the presence of silica fume, has a significant economic effect on the total cost per square meter of PCP. Comparing to reference concrete, the total cost per square meter of PCP with fibers decreased from 8.8% to 27.2% when the pavement is on a crushed aggregate base and from 11.2% to 29.0% when the pavement is on a hydraulically bound base. If dowel reinforced joints are used, the economic effect is even higher—the total cost per square meter of PCP decreases from 19.8% to 35.2% when the pavement is on a crushed aggregate base, and from 20.9% to 36.2% when the pavement is on a hydraulically bound base. Based on the theoretical calculations, the use of concrete with both steel fiber and silica fume and reinforced joints is the most economic ;Concrete mixture with 49.5 kg/m−3 of polypropylene fibers (type A) ;Concrete mixture with 10.0 kg/m−3 of steel fibers ;Concrete mixture with 49.5 kg/m−3 of polypropylene fibers (type A) and 25.2 kg/m3 of silica fume 49.5 kg/m3 .Concrete mixture with 10.0 kg/mFrom all analyzed pavement structures with different concrete mixtures, four concrete mixtures, which are listed below, can be assumed as the most rational ones in terms of PCP thickness reduction and total pavement cost:The concrete pavement thickness calculations using two different methods, two different base types, reinforced joints and unreinforced joints, as well as a cost-benefits analysis of high-performance concrete led to the following conclusions:2, including the expenses of fresh concrete mixture, dowels (if needed), slab manufacturing, storage and transportation, is achieved if PCP with reinforced joints is constructed either on a hydraulically bound base course or on unbound base course (crushed aggregate). These pavement structures operate without failure for 30 years and withstand 76 million ESALs.Based on the theoretical calculations, a lower cost than 40 EUR/m