Nowadays, the construction industry is challenged not only by increasingly strict environmental regulations, but also by a shortage of raw materials and additives. It is critical to find new sources with which the circular economy and zero waste approach can be achieved. Promising candidates are alkali activated cements (AAC), which offer the potential to convert industrial wastes into higher added value products. The aim of the present research is to develop waste-based AAC foams with thermal insulation properties. During the experiments, pozzolanic materials  and waste concrete powder were used to produce first dense and then foamed structural materials. The effects of the concrete fractions, the relative proportions of each fraction, the liquid/solid ratio, and the amount of foaming agents on the physical properties were investigated. A correlation between macroscopic properties  and micro/macro structure was examined. It was found that concrete waste itself is suitable for the production of AACs, but when combined with other aluminosilicate source, the strength can be increased from 10 MPa up to 47 MPa. The thermal conductivity (0.049 W/mK) of the produced non-flammable foams is comparable to commercially available insulating materials. With the continuous growth of the population, as well as the development of industry and technology, the environment is being increasingly transformed; the size of untouched natural areas is decreasing. According to forecasts, more than 230 billion square meters of new buildings will be added to the built environment over the next 40 years. To put it in perspective, this is equivalent to adding Japan’s current floor area to the planet every year, the whole of New York City every 34 days, or Paris’s entire building stock every week ,2. Such The demand for cheaper and more widely available raw materials and a full life-cycle assessment has long been the primary motivation for sustainability and greener structures in the construction and building materials industry. In our dynamic world, the appearance of a new material often equals the absence of another material, so it is important that construction projects are carried out in the spirit of the green economy and a zero-waste approach. A significant part of the research is dealing with the possibilities of using alternative materials, mainly industrial wastes and by-products ,11,12,13Alkali-activated cements (AAC), as prominent representatives of waste utilization, are becoming increasingly known material systems. One of the great advantages is that these systems can use wastes  not only as an aggregate ,15,16,17The combination of industrial by-products and wastes from construction and demolition activities allows the production of higher value-added AACs with a solid fraction consisting exclusively of wastes. Much of the research is focused on traditional building applications ,32,33,34The present study investigates “dense” and foamed AACs produced with the combination of concrete waste with more active raw materials . This paper extends to the exploration of the relationships between macroscopic properties  and micro/macro structure, the applicability of concrete waste as a raw material, as well as the potential to create larger foam building elements. This work can provide preliminary evidence that, by carefully choosing the experimental parameters, waste concrete can be used to produce higher value-added AACs that can contribute to the achievement of a green economy and zero-waste approaches. Based on the experiments performed in the scope of the present research, the foamed AAC produced from waste concrete can be deemed a promising thermal insulating material.The raw material for the experiments was ground granulated blast furnace slag (GGBFS), which was provided by ISD DUNAFERR Zrt. . For the purpose of comparison with other aluminosilicate sources, test specimens were prepared using Metaver R type metakaolin (MK)  and fly ash (FA) . The chemical composition of the starting materials  was deteBased on the XRD analysis of the raw materials see , it can For the preparation of AAC mortars, in the case of control samples, standard quartz sand  required for the preparation of AACs was provided by a mixture of analytical grade NaOH pellets  and a commercially available sodium silicate solution . The chemical composition of the latter was as follows: 6.8 wt% Na2O2  diluted to 4.5 wt% as a foaming agent  was used as a stabilizing agent, and a solution of 30 wt% of Hs et al. ).2SiO3 solution (and in distilled water). For the reason of reproducibility, all mixtures were prepared using an activating solution cooled to room temperature.In experimental work, “dense” and foamed AACs were prepared. In both cases, the activating solution was prepared in the same way: solid NaOH was dissolved directly in NaFor the production of the AAC mortars (“dense”), the required amount of raw material  was first measured, then the appropriately cooled activating solution was added. Identical conditions were ensured during the mixing, i.e., the slurry of raw material–alkaline solution was homogenized for 1 min at 900 rpm, then the aggregate (standard quartz sand or waste concrete) was added . The resulting mortar was further mixed for 1 min at 900 rpm.2O2 solution was added and homogenized for 1 min at 600 rpm.The steps for the preparation of AAC foams up to the addition of the foaming components were the same as for “dense” specimens . After homogenization of the waste concrete in the AAC slurry, sodium oleate was added. The resulting mixture was further stirred for 1 min at 1200 rpm, and finally, the HThe prepared fresh mixture was cast into ø30 mm × 30 mm cylindrical PVC molds for both “dense” and foamed AACs and was stored under ambient conditions (21–23 °C and RH = 50 ± 10%). Samples were demolded at 1 day of age, and the qualification tests were performed at 7 and 28 days of age. In this study, the 28-day average test results were reported.2/Al2O3 = 6.6, Na2O/Al2O3 = 1.1, the mass ratio of Na2SiO3 to NaOH in the activating solution was 6.6, and that of the activating solution and blast furnace slag powder was 0.6. First, control samples containing standard quartz sand were prepared, then the total amount of the aggregate was replaced with waste concrete. Different liquid/solid (L/S) ratios  were used to determine the appropriate mixing consistency  by varying the L/S ratio (0.315–0.42). The molar ratios used were as follows: SiO2/Al2O3 molar ratio in the fly ash-based mixture was 8.8, the Na2O/Al2O3 molar ratio was 1.9, the mass ratio of sodium silicate and sodium hydroxide in the activating solution was 14.3, and that of the activating solution and fly ash powder was 1.8. The following molar ratios were used in the metakaolin-based mixture: SiO2/Al2O3 = 7.6, Na2O/Al2O3 = 1.25, the mass ratio of Na2SiO3 to NaOH in the activating solution was 8.0, while the mass ratio of the activating solution to metakaolin powder was 1.2. The relative proportions of the components of the AAC samples prepared by combining the three different aluminosilicate sources and waste concrete are shown in In the final phase of the mortar specimens test, AACs were produced by combining waste concrete with a particle size equal to the standard quartz sand and other more active raw materials . The SiO2O2 solution (10 wt%) was fixed, and the stabilizer content ) was varied. The second time, taking into account the relevant physical properties, the sodium oleate content was fixed (0.1 wt%) and the amount of foaming agent was varied .In the second phase of the experimental work, foamed AAC specimens were prepared from the optimal mixtures of “dense” samples. The required amount of the foaming components (stabilizing agent and foaming agent) was determined in the case of GGBFS-waste concrete-based AAC. First, the amount of H2O2 solution.In the case of the foamed products, as with the “dense” specimens, the effect of the combination of more active raw materials and waste concrete on the physical properties was investigated. Accordingly, in parallel to the slag-based mixtures, fly ash and metakaolin-based foamed AAC specimens were produced using 0.1 wt% sodium-oleate and 7.5 wt% HFinally, the potential to create GGBFS—waste concrete-based foamed products on a larger size was investigated, with the green economy and zero-waste approach in mind. On the one hand, samples of dimensions 200 mm × 200 mm × 15 mm were prepared , and on the other hand, test specimens of dimensions 40 mm × 40 mm × 160 mm were prepared in accordance with the standard specifications used for cements (EN 196-1). The experiments for the foamed AACs, as in the case of the “dense” samples, consisted of several series, the details of which are shown in Qualitative and quantitative phase analyses of the aluminosilicate sources and waste concrete powder were carried out using a Philips PW 3710 type X-ray diffractometer with CuKα radiation , graphite monochromator, and 0.02° 2Θ/s speed . The X’Pert Data Collector software (version 2.2) was used to control the device and collect data. An internal standard method was used to determine the amounts of crystalline phases and the amorphous fraction. In the process, 0.1000 g of ZnO was added to 0.9000 g of powdered sample (maximum particle size < 63 μm). In order to avoid orientation, back-loaded samples were used in the tests. The evaluation of X-ray diffractograms and the implementation of Rietveld analysis were carried out with the help of X’Pert Highscore Plus and the ICDD PDF-2 reference database.2B4O7 + LiBO2) according to the EN 196-2:2013 standard.The chemical composition of the starting materials  was determined using a Philips Axios PW 4400/24 type wavelength-dispersive X-ray fluorescence analyzer with melt sample preparation  were determined using a Fritsch Laser Particle Sizer “Analysette 22”-type laser granulometer. The measuring range of the device is 0.1–1160 μm, the total measurement time is two minutes, and the red He-Ne laser beam used has a wavelength of 632.8 nm and a power of <3 mW. The required sample amount (0.5–1.0 g) was loaded manually, taking into account the appropriate feedback from the instrument . In order to achieve appropriate dispersion and prevent intergranular aggregation prior to the start of the measurements, the samples were treated in a water bath equipped with an ultrasonic stirrer and pump for 60 s.The compressive strength of all AAC samples and the flexural strength of the standard-size foamed specimens were determined with the help of a CONTROLS Automax5 automatic double chamber device with an upper measuring limit of 15/300 kN in terms of load. The measurements were performed according to the relevant cement standard (EN196-1), using a loading rate of 2400 N/s for compressive strength and 50 N/s for flexural strength tests. In the case of compressive strength tests, however, the sample sizes differed from the standard . Prior to the start of the test, the surfaces of cylindrical specimens were filed down perpendicular to the side. With respect to each mixture, three parallel measurements were performed, and the average strength values were reported.3. With respect to each mixture, three parallel measurements were performed, and the average bulk density and open porosity values with standard deviation were reported.The bulk density and open porosity of the foamed AAC samples were determined using the Archimedes method. The specimens were placed in distilled water and boiled for 2 h. After boiling, the test specimens were cooled, and then their water-saturated weight was measured with the help of a hydrostatic balance in air and through immersion in distilled water. The density of the liquid medium was 1000 kg/mThe thermal conductivity of the AAC foams was determined using a non-equilibrium method, namely, the modified transient plane source method (MTPS), according to the requirements of the ASTM D7984 standard. To carry out the measurements, C-Therm TCi equipment was used, with a measurement range of 0.002–220 W/mK. Prior to the start of the test, the surfaces of the specimens were filed down flat, and the dust in the exposed pores was removed. The thermal conductivity of the larger (200 mm × 200 mm × 15 mm) samples made from the optimal mixture was determined using an equilibrium method, namely, the longitudinal heat flow meter method (ASTM C518), with the help of a NETZSCH HFM 436/3/1 Lambda device . Before starting the measurements, the samples’ surfaces were filed down perpendicular to the side.Computed tomography (CT) images of the foamed specimens were made with the help of a Nikon XT H 225 ST type X-ray tomography and the associated VG Studio 3.4 software. During the measurements, a cathode current of 85 μA and an accelerating voltage of 160 kV were used .In the first stage of the experiments, GGBFS-based AAC mortar samples were prepared using standard quartz sand as a filler and waste concrete generated during construction and demolition activities.As a first step, the control samples were prepared using standard quartz sand with a coarser particle size than waste concrete. Then, the total amount of inert aggregate was replaced by WC. While a liquid/solid ratio of 0.21 was sufficient for the workability of the sand-containing samples, this proved to be insufficient when using fine-grained waste concrete. In order to ensure the proper consistency of fresh mortar, mixtures with different L/S ratios were prepared. 3) can be kept at the same level at the lowest F/S ratio (0.315). Although the further increase in the liquid/solid ratio facilitated the workability of concrete-containing mixtures, it did not always have a positive effect on the strength values. This was because the alkaline activation reaction, in contrast to the hydration experienced in the case of classic Portland cements, did not require a large amount of water, so that the excess water content (only necessary for workability) evaporated during the setting and solidification mechanisms, leaving pores, which led to a reduction in strength. Based on the results, it can be said that with the proper amount of activating solution (L/S = 0.368), the samples containing waste concrete can achieve higher strength than their counterparts produced using sand; a strength increase of ~13% was observed compared to the value of the control samples (from 28.4 to 32.2 MPa). The different results obtained using the two aggregates can be explained on the one hand by the different particle size distribution of sand and concrete   that are not found in WC, only the fractions below 500 μm were used for further mixtures. Taking into account the finer fractions, the sand contains 42.5 wt% of particles between 250 and 500 μm, 57.0 wt% of particles between 63 and 250 μm, and 0.5 wt% of particles below 63 μm, and this particle size distribution was considered the relevant one for waste concrete. For both aggregates, three different liquid/solid ratios  were used in order to investigate the behavior of the aggregates during the alkaline activation reaction. For mixtures with the same activating solution content and particle size distribution, it was assumed that mixtures containing sand and concrete would have similar consistencies. However, contrary to expectations, the sand mixtures had lower viscosities than their counterparts containing waste concrete with the same activating solution content. For all three liquid/solid ratios, the waste concrete samples had the highest strength values. As in the previous stage of experiments, strength was maximized in this case using the 0.368 L/S ratio; a ~twofold strength increase compared to the value of the sand-containing samples  was observed. Since the sand and the waste concrete at this stage had the same particle size distribution, it can be concluded that the difference in the results obtained using the two aggregates was not due to the filler effect related to particle size.2/Al2O3 and Na2O/SiO2 ratios), L/S ratio, and heat treatment [Based on the results and experience of the first and second series of experiments, it is likely that the waste concrete particles, unlike the sand particles, are involved in the alkali activation reaction. To demonstrate this, unfractionated WC was used to prepare AAC test specimens (without the addition of blast furnace slag). In this case also, three different L/S ratios were used to ensure the appropriate workability. Based on the results of reatment ,28,29) aIn the final phase of the AAC mortar specimen test, the effect on strength and bulk density of the combination of waste concrete (with a defined particle size distribution) and other more active raw materials  was studied a.2 + CaO content  does not reach the value of the first strength class (32.5 MPa) according to the cement standard (EN 197-1), the relevant values of the other two more active material-based samples (36.1 and 47.0 MPa) are above it. Furthermore, using blast furnace slag, products can be developed with strengths exceeding the value of the second strength class (42.5 MPa). Therefore, it can be said that it has been proven possible to develop a waste-based AAC system whose physical properties are competitive with those of classical binders. Although all AACs were prepared using a 1:2 pozzolanic material:waste concrete mass ratio, it is important to note that there are differences in the waste content of the mixtures prepared using various aluminosilicate sources. 2O2.In the second stage of the experiments, our goal was to produce special products, namely, foamed elements. In the development of the porous samples, efforts were made to fix the technological parameters (amount of foaming and stabilizing agent) that can be used to tailor the relevant properties  as desired. First, the blast furnace slag and waste concrete-based mixtures (using a 1:2 GGBFS:WC mass ratio) were foamed. It was specified that the product strength should reach or exceed 1 MPa, as this value corresponds to the minimum strength class for aerated concrete building elements, in accordance with the requirements of standard GB11968-2006. The purpose of the experiments was to produce foams with the lowest possible thermal conductivity, which can practically be considered a thermal insulating material . The success of this effort lies in the controllability of the pore system of foams, which, based on the relevant literature, can be best achieved by the combined technique of saponification/peroxide decomposition/gel casting ,36,37,382O2 (5–15 wt%) was varied at a fixed sodium oleate content to improve the physical properties of the products. The results obtained from the measurements are summarized in As a first step in the optimization of the foaming parameters, a fixed foaming agent concentration (4.5 wt%) and amount ) were applied, while the content of sodium oleate was varied ). Taking into account the relevant physical properties ; thus, this sodium oleate content was used for the further part of the experiments.With the increase of the amount of foam stabilizer, the apparent porosity of the samples increased, and the bulk density, compressive strength, and thermal conductivity values decreased accordingly. The samples containing 0.1 wt% sodium oleate were an exception, for which the compressive strength and thermal conductivity did not change in line with the open porosity. This can be explained by the mechanism of action of the saponification reaction in an alkaline medium. An increase in the amount of stabilizing agent increases the amount of surfactant formed in the strongly alkaline medium, which facilitates gas bubble stabilization ,36,37,382O2 solution was varied to improve the physical properties. As a first step, 5 and 15 wt% were chosen in addition to the existing 10 wt% foaming agent content. Then, in order to optimize the strength–conductivity relationship, intermediate measuring points were used: 8.25, 7.5, and 6.25 wt% H2O2 contents  relevant for the application can be achieved with lower amounts. Based on the results, the mixture containing 7.5 wt% H2O2 is the most favorable choice for use as a thermal insulating material since it has the lowest thermal conductivity. The product, with a thermal conductivity of 0.049 W/mK, can be practically considered a thermal insulating material, which also has the proper strength (1.3 MPa) for the application. If the pore structure of specimens prepared with different amounts of stabilizing and foaming agents is compared (Excessive amounts (15 wt%) of Hcompared , signifiAs the amount of foaming agent was increased, the pore size distribution of the foams became much more inhomogeneous, resulting in unfavorably large pores (average pore diameter: 3860 ± 840 μm) both in terms of compressive strength and thermal insulation properties a. The CTSimilar to the “dense” AACs, the macroscopic properties of the foamed products were investigated using waste concrete in combination with other more active raw materials (metakaolin and fly ash) instead of blast furnace slag . While the strength of the products using slag and metakaolin met the 1 MPa requirement, the fly ash-based mixtures did not. In the latter case, a significant reduction in compressive strength was to be expected, as the fly ash-containing specimens also performed the worst among the “dense” AAC specimens. The pore structure of the AAC products prepared with the three different more active raw materials  consistsBoth slag and metakaolin-based mixtures can be used to produce a thermal insulating material. However, it is important to note that while slag is an industrial by-product, metakaolin is obtained by calcination, which significantly increases the cost of the raw material. Keeping this fact in mind, as well as green economy and zero-waste approaches, further experiments were carried out to determine the feasibility of using waste concrete-slag-based foamed products in larger sizes.In order to find out whether the foaming method used in this study can be used to produce larger building elements, scale-up experiments were carried out. Considering that the mixture containing blast furnace slag achieved the most favorable results in the case of small samples (ø30 mm × 30 mm cylinder), this mixture was used for the last part of the experimental work. On the one hand, in accordance with standard specifications used for cements (EN 196-1), specimens of dimensions 40 mm × 40 mm × 160 mm were produced for flexural and compressive strength tests. On the other hand, a sample of dimensions 200 mm × 200 mm × 15 mm was prepared for thermal conductivity measurements using the longitudinal heat flow meter method. The results of the scale-up experiments are summarized in If the physical properties of the blast furnace slag and waste concrete-based porous AAC sample developed are compared with those of other commercially available thermal insulating materials, it can be concluded that the product investigated in this study may be suitable for reducing energy loss in buildings. Although the thermal conductivity of the produced waste-based AAC is higher than that of extruded polystyrene, foamed glass, mineral wool, expanded perlite, and cork board ,41,42,43Waste concrete from construction and demolition activities is not an inert, non-reactive aggregate in the alkali activation reaction but an active component. WC can be used as a raw material for AACs, but the strength of the product obtained (10.5 MPa) is significantly lower than that of conventional binders.To increase the strength value of waste concrete-based AACs, controlled conditions  and the addition of a more active raw material  are required. The most significant strength improvement (from 10.5 up to 47.0 MPa) can be achieved with mixtures containing ⅓ part blast furnace slag and ⅔ part waste concrete.By combining waste concrete with various alumino-silicate sources, both AAC mortar specimens and foamed elements can be produced. The foaming process of waste concrete-based AACs can be carried out under favorable conditions, and the physical properties of the products  can be controlled by adjusting the amount of stabilizing and foaming agents.2O2 is the most favorable choice; the thermal conductivity of the waste concrete-based product obtained in this way is 0.049 W/mK, and its strength is 1.3 MPa.For use as a thermal insulating material, a mixture containing 0.1 wt% foam stabilizer and 7.5 wt% HBoth waste concrete-slag and waste concrete-metakaolin-based mixtures may be suitable for the production of thermal insulating building elements.With the foaming method used in this study, the waste concrete-slag-based AAC can be produced in larger sizes. Considering the physical properties of the specimens of dimensions 40 mm × 40 mm × 160 mm and 200 mm × 200 mm × 15 mm, the developed foams have remarkable potential for use in thermal insulating applications.This paper aimed to produce and test waste concrete-based AACs with remarkable potential for use in the scope of both traditional construction applications (“dense” specimens) and specific applications (lightweight/foamed elements). The primary goal of the research was to find the optimum for the experimental parameters that can be applied to develop AACs with controlled properties. The following conclusions can be drawn based on the experiments performed:On the whole, it can be concluded that, after a proper selection of the experimental parameters, waste concrete can be used to produce higher value-added AACs that contribute to the achievement of a green economy and zero-waste approaches. The physical properties of the developed waste concrete-based AACs are competitive with those of conventional binders in the case of “dense” elements and comparable with those of the most commonly used insulating materials in the case of foamed products.


The environment of an underground structure is much more complex than the above-ground environment. Erosion processes are underway in soil and groundwater; groundwater seepage and soil pressure are also typical for underground environments. Alternating layers of dry and wet soil have a strong effect on concrete, and they reduce its durability. Corrosion of cement concretes is caused by the diffusion of free calcium hydroxide, located in the pores of concrete, from the volume of the cement stone to its surface, bordering on an aggressive environment, and the further transition of the substance through the phase boundary solid (concrete)–soil-aggressive environment (liquid). Due to the fact that all minerals in cement stone exist only in saturated or close-to-saturated solutions of calcium hydroxide, a decrease in the content of which in the pores of concrete as a result of mass transfer processes causes a change in the phase and thermodynamic equilibrium in the body of concrete and leads to the decomposition of highly basic compounds of cement stone and, consequently, to the deterioration of the mechanical properties of concrete . A mathematical model of mass transfer in a two-layer plate imitating the “reinforced concrete structure—layer of the soil–coastal marine area” system is proposed as a system of nonstationary partial derivative differential equations of the parabolic type with Newmann’s boundary conditions inside the building and at the interface between the soil and the marine environment and with conjugating boundary conditions at the interface between the concrete and the soil. When the boundary problem of mass conductivity in the “concrete–soil” system is solved, expressions are obtained to determine the dynamics of the concentration profiles of the target component  in the volumes of the concrete and soil. As a result, one can select the optimum composition of concrete, having high anticorrosion properties, to extend the durability of the concrete constructions of offshore marine structures. Today, the construction industry is solving a high-priority task of developing effective recommendations to prevent the corrosion-induced failure of reinforced concrete structures, and the solution should be based on both classical and the most recent theoretical and experimental studies ,2,3,4,5.Corrosion of concrete is a complex physical and chemical process that eventually leads to the failure of reinforced concrete structures. Calcium hydroxide (CaOH) is the main component of concrete and is involved in the cement stone degradation process in the initial stage. Various mechanisms of transfer of aggressive substances to corrosive surfaces are triggered in the process of concrete corrosion ,4,5,6,7.Seawater is a highly aggressive medium containing large amounts of dissolved salts; it causes chemical corrosion of both concrete itself and reinforced concrete structures ,9,10.3 in seawater with a salt content of 33–35 kg/m3, which is explained by the dissolution of sulfate compounds of Ca, Na, K, and Mg, same as in fresh water, but in much larger amounts and with a predominance of sodium and magnesium salts. It is obvious that sulfate and chloride ions are the main components. Hence, we can conclude that the corrosion of concrete in structures is a complex physical and chemical process that becomes more complicated as a result of sulfate and chloride corrosion ; τ* is time in the range ; Here, x** is the coordinate in the ground in the range .Here, Now we address the problem of boundary conditions. A condition on the inner surface of a structure means that no transferable component travels from the structure to the inner space. Mathematically, this condition is written as follows:The proposed methodology for solving the mass transfer problems under study involves the use of the “microprocess method” in calculations ,39,40. TThe conjugating boundary condition in the place of contact between the solid phases (the structure and soil) is determined by the conditions of expressions (1) and (2), or (10) and (11).The boundary condition in the place of contact between the coastline soil and seawater is determined with expressions (6) and (7), provided that:qH(τ) is mass flux density as determined by Equation (7).Here, Initial values of concentrations.m” as the equilibrium in the “structure–soil” system.Values of Henry constants “mA” as the equilibrium in the “soil–water area” system.Values of Henry constants “β” that shows mass transfer from the soil to the water area.Value of coefficient “Experimental information is needed to initiate the use of the engineering calculation method:The calculation method is implemented in compliance with the following algorithm: First, we take into account that the calculation starts in the case of uniform initial concentration distributions, i.e., the following items are set:+2/kg of concrete)/(kg of Ca+2/kg of soil)].Well-known reference data are sourced for the values of the equilibrium constants in the “reinforced concrete–soil” system: m [ The concentration change in the structure is arbitrarily selected at the interface ∆Cx → ∆x1 is selected;(1b) The calculation step along coordinate (1c) The value of the concentration gradient is determined:(1d) The value of the substance flow density is determined:1 is selected, and the corresponding value of the Fourier number is determined:(1e) The value of the time interval ∆τε1 is unsatisfactory, the calculation process restarts from position (1a).(1f) The distribution of the concentrations over the thickness of the structure is calculated, and the value of If the condition is satisfied, the next stage of the calculation is initiated.In the second stage of the calculation:(2a) The boundary condition for the problem of concentration distribution in the soil layer is found using boundary condition (1d):β and the Henry coefficient in the “soil–liquid” system that equals Am.(2b) We know the coefficient of mass flow in the liquid phase that equals The task is to find the value of mass flow density for the external boundary condition (7);(2c) Below is the calculation of the concentration distribution in the soil layer for the moment 2 is not satisfied, a new value The obtained values of concentrations are compared:In the third step, when equilibrium is attained at the interface between the solid phases, the process of mass transfer continues. This process is mass transfer from the reinforced concrete structure through the soil layer into the sea area.Numerical experiments were conducted to evaluate the adequacy of the proposed mathematical model, which takes into account the extent of influence of soil and seawater salinity properties on free calcium hydroxide mass transfer processes that accompany corrosion-induced damage to concrete in the liquid medium.Let us transform Equations (20) and (22).2+) in the initial moment at the point having the coordinate x = 0.Let us write down the dimensionless concentration:Dimensionless constant: Hence, by transforming (20), we write down the following:Let us transform each term of the right-hand side of Equation (39) one by one.The first summand is as follows:Let us add a complex to the second summand: δ1 under the sign of the differential:The third summand (39) is easily transformed by introducing The fourth summand, like the second one, is transformed by its multiplying by the complex Thus, the general final solution (20) is as follows:We write down solution (22) and make the same transformations but omit the mathematical calculations:Uniform initial distribution;Constancy of Kirpichev criteria values.Next, we obtain solutions for the two important special cases:As for the first special case (a), solutions are easily obtained from expressions (45) and (46):As for the second case, the solution can be found using the transformation of expression (45):The integral in the final summand is calculated as follows:Similarly, the transformation of Equation (46) leads to the result:Hence, these are the solutions for the constant values of the Kirpichev criteria.Finally, for the case of the uniform initial distribution of concentrations and constant values of the Kirpichev criteria, we obtain:The final solutions to problems of nonstationary mass conductivity in dimensionless form, applied to the special case of uniform initial concentration distributions and constant values of the Kirpichev criteria, are as follows:Some of the results of the calculations made in (54) and (55) are shown in m.1 = 0). Obviously, the greater the value of the Kirpichev number at the boundary with the soil, the greater the value of the tangent angle of the lines at the “structure–soil” boundary.0, the transferred component is saturated in the material of the structure:2+ in the soil is close to zero:The data in The calculated dynamic profiles of concentrations and process kinetics make it possible to solve both direct and inverse problems of mass conductivity. The direct problem consists in calculating the dynamics of the concentration fields of a transferred component in the simulated system during the process time.k1 and k2, and the coefficient of mass transfer in liquid phase β.The objective of the inverse problem is to use experimental and numerical methods to determine the kinetic coefficients of the process: mass conductivity 0 to the working concentration (In a reinforced concrete structure, the change in the concentration of the transferred component occurs from the maximum content of Untration a; in thentration b.The above expressions facilitate the determination of the value of concentrations of the transferred component over the thickness of the concrete structure and soil at any time, and they also enable the calculation of the concentration of free calcium hydroxide in the liquid phase, calculating the process kinetics according to solid phases in concrete and soil, which ultimately enables the forecasting of the durability and reliability of building structures with a minimum error.In addition, the calculated values of the concentration profiles make it possible to find the maximum values of the concentration gradients and their location. Accordingly, the concentration gradients determine the stresses that can occur in the structure and which lead to the appearance of microcracks, which are the cause of a decrease in the strength of the concrete structure.


The impact of antibiotic time-outs (ATOs) on antibiotic use relies heavily on prescriber interaction, which may be reduced due to workflow disruption or alert fatigue. In August 2022, Hartford HealthCare implemented a 72-hour ATO best practice alert. Herein, we evaluated prescriber behavior when interacting with the ATO alert to assess the impact on prescriber stewardship workflow.An ATO alert was designed to fire between 0700 and 1630. Upon firing, prescribers were prompted to assess for antibiotic modification – a composite including discontinuation, de-escalation, inclusion of stop-date, and transition to oral therapies. Additional responses were included to defer re-firing for patients deemed not to be a candidate for antibiotic modification. The primary endpoint was defined as the rate of ATO response aligning with antibiotic modification for the 10 most frequently utilized antibiotics and assessed from 10/1/22 – 12/31/22. A predefined subset of patients was evaluated for ATO appropriateness by prescriber specialty and role.A total of 15,383 ATO alerts were included for analysis, corresponding to 3,498 unique patients. The primary endpoint occurred in 21.4% of cases. The most commonly selected ATO response was a reminder in 10 minutes (48.2%). The median time viewing the ATO alert was 5 seconds (IQR 4 – 8s). In a subset of 400 patients, ATO selections were found to be appropriate in 56% of cases. When stratified by prescriber role, attending physicians were more likely to appropriately utilize the ATO compared to resident and advanced practice practitioners  and were more likely to select an ATO response aligning with antibiotic modification .ATO selection corresponding to antibiotic modification was low regardless of prescriber role. Further work optimizing the ATO design will be required to improve integration into stewardship workflow.Joseph L. Kuti, PharmD, bioMeriuex Inc.: Grant/Research Support|Entasis Therapeutics: Grant/Research Support|Merck & Co, Inc: Grant/Research Support|Shionogi Inc: Advisor/Consultant|Shionogi Inc: Grant/Research Support|Shionogi Inc: Honoraria


This paper is a review of studies on the use of the polyhedral oligomeric silsesquioxanes (POSS) of various structures in the synthesis of polyolefins and the modification of their properties, namely: (1) components of organometallic catalytic systems for the polymerization of olefins, (2) comonomers in the copolymerization with ethylene, and (3) fillers in composites based on polyolefins. In addition, studies on the use of new silicon compounds, i.e., siloxane–silsesquioxane resins, as fillers for composites based on polyolefins are presented. The authors dedicate this paper to Professor Bogdan Marciniec on the occasion of his jubilee. After a stagnation in 2020 due to the COVID-19 pandemic, global plastics production increased to 390.7 million tons in 2021. The largest part of the world’s production is made up of polyolefins. It is estimated that approximately 105 million tons of polyethylene (PE) and 75 million tons of polypropylene (PP) were produced worldwide in 2021 in total, covering 46.2% of global plastics production Ti(CH2Ph)2 (5a) and Cp’’[(c-C6H11)7Si7O10(O{SiMe2O}2)]Ti(CH2Ph)2 (5b) [B(C6F5)4] were used as cocatalysts. Moreover, it was shown that cationic titanium species formed by reacting 5a and 5b with B(C6F5)3 are stable for a long time, in contrast to active species formed in 4a/B(C6F5)3 based on the silsesquioxane with isolated silanol [c-C5H9)7Si8O13]TiCl2 (6a) and Cp”[(c-C5H9)7Si8O13]2TiCl (6b) 2) [6b with MAO raised questions about the stability of metallasilsesquioxanes in reaction with aluminum alkyls. Zirconocene complexes with silsesquioxane moiety [{(c-C5H9)7Si8O12O}2Zr(η5-C5H5)2] (7a) and [(c-C5H9)7Si7O9(OSiMe3)O2}- Zr(η5-C5H5)2] (7b) when combined with MAO were approximately as active as ZrCl2(η5-C5H5)2]  .i-Octyl)7Si7O9(OH)3, synthesized a series of group 4 metallasilsesquioxanes 8a–8g with additional X ligand  and evaluated them in ethylene polymerization n  precatalyst, which exists as a mixture of monomeric 11a and dimeric 11b form in the mole ratio of 3:1 [B(C6F5)4], B(C6F5)3, [PhNMeH][B(C6F5)4]) in combination with (iBu)3Al. Neither complex was active in this reaction when activated with a simple organoaluminum compound, and monomer conversion in the presence of other catalytic systems did not exceed 20.1%. Complexes 12c–12e, having tridentate ligands, and bimetallic complex 13a showed the highest activity in combination with MAO, while complexes 12a and 12b were not active in conjunction with this cocatalyst. Efficiency of the boron containing cocatalysts, regardless of the structure of the complex used, increased in series B(C6F5)3 < [PhNMeH][B(C6F5)4] < [Ph3C][B(C6F5)4]. The influence of the type of cocatalyst on the molecular weight of the polymers was opposite. The highest and the lowest molecular weight have polymers produced by complexes activated by B(C6F5)4 and [Ph3C][B(C6F5)4], respectively. For example 27,300 g/mol, 8200 g/mol, and 5800 g/mol had polymers produced in sequence by 12b/B(C6F5)4, 12b/[PhNMeH][B(C6F5)4] and 12b/[Ph3C][B(C6F5)4]. In addition, it was found that the increase in the number of donor atoms in the ligand structure increased the activity of the catalyst (12a < 12b < 12c) and also resulted in a decrease in molecular weight of poly(1-octene). Microstructure analysis revealed that produced poly(1-olefins) were moderately isotactic, with mmmm pentad ranging from 44 to 74%, and possessed various end-groups suggesting involvement of different chain terminations after the previous 1,2- or 2,1-insertion of a monomer molecule [B(C6F5)4]. They turned out to be highly active after activation with EtAlCl2 (up to 8610.0 kg/(molV·0.5 h)). In conjunction with other cocatalysts, their activity was lower and ranged from 58 kg/(molV·0.5 h) to 345.7 kg/(molV·0.5 h). Moreover, the efficiency of vanadium complexes activated by EtAlCl2 increased with increasing denticity of silsesquioxane ligand (17a < 17b < 17c), and bimetallic complex 17d was most active. It was also shown that synthesized polyethylenes have high to ultra-high molecular weights (wM = 370 × 103–4423 × 103 g/mol) depending on the cocatalyst used and the reaction conditions. Unlike the titanium counterparts, all vanadium complexes, regardless of the type of cocatalyst used, produced polymers with unimodal molecular weight distribution. The results of the copolymerization test, which was carried out for 17d/EtAlCl2, revealed considerable compositional heterogeneity of the produced copolymer and moderate incorporation of 1-octene comonomer (2.2 mol%).Our studies involved complexes 17a–17d . To our 17a–17c for the synthesis of poly(1-octene) [> [Ph3C][C(C6B5)4] > B(C6F5)3> [PhNMe2H][B(C6F5)4] > Et2AlCl. Produced poly(1-octenes) were in the form of sticky solid material or viscous oil and were moderately isotactic (mmmm = 51–64%). Further studies showed that the polymer with the highest isotactic pentad content, 75%, can be obtained with 17d/(iBu)3Al/[Ph3C][B(C6F5)4]  .18 and found that it polymerized ethylene at 1 atm pressure after addition of 1.5–10 equivalent of Me3Al and produced linear polyethylene with wM = 30.7 × 103 g/mol [19a–19d were obtained by reaction of Cr[CH(SiMe3)2]3 with functionalized POSS: R7Si7O9(OH)2(OSiMe2R’) where R = iBu, R’ = Me, Ph, C6H4(OMe-2), C6H4(PPh2–2). It was shown that catalyst activity and the molecular weight of polyethylene were sensitive to the coordination environment of the chromium center. The activity of chromium complexes towards ethylene polymerization in the presence of (iBu)3Al at 60 °C and at 0.5 MPa ranged from about 30 to about 60 kg/(molCr·h), and it was dependent on the modification of the POSS cage as follows: 19b < 19c < 19a < 19d. Complexes 19a and 19b at 50 °C gave polyethylene with a very high molecular weight (wM = 1.8·106 and 3.3·106 g/mol), with a rather wide molecular weight distribution (MWD) due to slight tailing on the low molecular side. At the same reaction condition, complexes 19c and 19d produced bimodal polyethylene with lower wM. The effect of the POSS cage structure and the chromium oxidation state on ethylene polymerization was presented in 3) and Cr(VI) (CrO3) compounds, respectively. Tri-n-octylaluminum and triisobutylaluminium modified with butylated hydroxytoluene (TIBA-BHT) were used as cocatalysts. It was revealed that all investigated complexes were less active than the appropriate chromium compounds supported on SiO2, and that the Cr oxidation state has an important effect on the behavior of the catalyst. Complexes containing Cr(VI) exhibited higher activities (up to 523 g/(gcat·h)) than trivalent ones (up to 64 g/(gcat·h)). Produced polyethylenes had bimodal molecular weight distributions.Chromium–silsesquioxane compounds  have bee03 g/mol . In much03 g/mol , chromiuented in . ComplexHybrid (co)polymers containing polyhedral oligomeric silsesquioxanes have attracted great interest in recent years. Literature data show that functionalized silsesquioxanes, both monofunctional and multifunctional, such as styryl-POSS, methacrylate-POSS, norbornyl-POSS, amine-POSS, hydroxyl-POSS, epoxy-POSS, phenolic-POSS, benzoxazine-POSS, and alkenyl-POSS have been used as monomers in homo- or copolymerization ,9,10,57.2ZrCl2, Me2Si(Ind)2ZrCl2, and Me2Si[(Me4Cp)(t-BuN)]TiCl2 (2Si[(Me4Cp)(t-BuN)]TiCl2 complex  in comparison with neat polyethylene and polypropylene.The first literature report related to homopolymerization of POSS and copolymerization of POSS with ethylene or propylene was published by Tsuhida et al. . The POSN)]TiCl2 b–d activ complex d. Additii-Bu-3 (rac-Et(Ind)2ZrCl2, activated with modified methylaluminoxane (MMAO) 2ZrCl2/MMAO catalytic system  in comparison with neat polypropylene.Zhang et al.  reportedi-Bu-3 a over rae (MMAO) e. The himonomers a were alc system e. CopolyIn this regard, there were no comprehensive studies on the influence of the structure of alkenylsilsesquioxane comonomers on the performance of copolymerization with olefins and physicochemical properties of copolymers, which limits the possibilities of planning and controlling the synthesis of copolymers with specific properties. Furthermore, there were no studies concerning the use of copolymerization of ethylene with multi-alkenylsilsesquioxanes. On the other hand, POSS units can improve thermal stability, what is a desirable effect in the case of polyolefins. Therefore, the purpose of our research was the comprehensive synthesis and the evaluation of composition and physicochemical properties of new hybrid ethylene copolymers with alkenylsilsesquioxanes, including different structure of the POSS cage. It was also important to select an active catalytic system in this process and to determine the optimal conditions for carrying out polymerization , enabling the most effective synthesis of polyolefins containing alkenylsilsesquioxane units.coordination copolymerization of ethylene with alkenylsilsesquioxanes was described in [3)2-). Moreover, monoalkenylsilsesquioxanes contained iso-butyl (iBu) or cyclohexyl (Cy) as the non-reactive functional group (iBu or phenyl (Ph) as non-reactive groups, were used for the first time in copolymerization with ethylene.Low pressure ribed in ,73,74,75al group a. Furtheal group b and incal group c,d, contA metallocene complex a and, foansa-metallocene catalysts  in comparison with crude copolymers [The incorporation degree of POSS units into the polymer chain affected the thermal stability of the obtained copolymers . The E/Ppolymers . Moreovepolymers . It was R2 and with a hydrogen atom, or the tert-butyl group as R1 substituents in phenoxy-imine ligands silsesquioxane , a result which has been associated with the different structural parameters of postmetallocene catalysts [ansa-metallocene catalyst [Our investigation also confirmed the efficiency of post-metallocene catalysts  in copolymerization of ethylene with selected POSS comonomers . Three b ligands b. Moreov ligands c was alsatalysts  in compacatalyst . Moreoverac-Et(Ind)2ZrCl2 zirconium complex was higher at the similar POSS content in the polymer chain than that of the products obtained using the d)2ZrCl2 a. This pep = 0.2 MPa), whereas higher ethylene pressure (ep = 0.5 MPa) resulted in synthesizing copolymers with linear structures. In turn, the tri-alkenylsilsesquioxanes  of ethylene copolymers with multi-alkenylsilsesquioxanes  produced by organometallic catalysts and the relation between the copolymer structure and its physicochemical properties ,78. It wIn addition, the thermal degradation of ethylene copolymers with di-, tri- and tetra-alkenylsilsesquioxanes was evaluated in detail under isothermal conditions (100 °C) based on structural changes in FT-IR spectrum . The kinansa-metallocene centers into precursors of the centers of active forms [ansa-metallocene; additionally, it competed with the cocatalyst for access to the catalyst, which is an unprecedented phenomenon in case of coordination polymerization [One of the most interesting results of the research on ethylene/POSS copolymerization was demonstrating that tri-alkenylsilsesquioxane containing an incompletely condensed POSS cage not only acted as a comonomer but also transformed the inactive forms of the ve forms ,74. Modirization .Moreover, the morphological, viscoelastic, and dynamic mechanical properties of ethylene/multi-alkenylsilsesquioxanes copolymers with different architecture (linear and cross-linked) were also investigated . The WAX3), talc, metal oxides , metal hydroxides (Mg(OH)2, Al(OH)3), layered silicates , and others [As already mentioned, significant growth in technology over the last few decades has created the need to design and fabricate new materials with improved, and sometimes new, properties. Recent trends in this area are related to the development of hybrid composite materials. Introduction of inorganic substances as fillers into polymer matrices improved selected properties of polymer materials, such as stiffness, breaking strength, hardness, thermal stability, flammability, etc., and sometimes reduced their costs . The mosd others ,83,84,85d others . This isd others . Unfortud others . For thid others ,84,88,89d others ,91,92,93d others ,95,96,97d others ,103,104 d others ,99,101.iPP), different grades of polyethylene ), and ultra-high molecular weight polyethylene have been used. Silsesquioxanes applied as fillers were structurally very diverse, with completely and incompletely condensed silicon cores, both monofunctional and multifunctional, including homo- and heterosubstituted compounds. POSS fillers were usually incorporated into the polyolefin matrix through convenient and simple melt blending. Nonreactive POSS molecules were mixed with polymer using an array of extruders and internal mixers. The amount of POSS fillers introduced into the polyolefin matrix usually does not exceed 10 wt%, and most often it is below 1 wt% and even parts per million [Over the past two decades, there has been a rapid increase in research interest in exploring POSS-containing polyolefin nanocomposites. As the polyolefin matrix, isotactic polypropylene . POSS particles were found to influence the crystallization process of iPP under both isothermal and nonisothermal conditions by acting as nucleating agents. Moreover, despite the significant share of the filler used, formation of its aggregates in the matrix was not observed. In turn, other researchers [i-octyl did not bring any apparent improvement of POSS dispersion. On the other hand, Chen et al. found [iPP and affect the thermal properties of iPP/POSS nanocomposites.The impact of POSS additive on the crystallization behavior of the polyolefin matrix inter alia was studied in the first paper describing the use of nanostructured POSS moiety as a filler of mposites . The choearchers  studyingl. found  that POSiPP composites covered mainly the properties of nanocomposites, which contained POSS with relatively short alkyl chain substituents (from methyl to i-octyl) [nH2n+1, and n = 8, 12 and 18. The selected POSS compounds were blended with low density polyethylene. They reported that the miscibility and dispersal of the POSS molecules was seen to increase with the increasing alkyl-chain length substituents, suggesting increased compatibility and interaction with host polymer chains.The influence of POSS substituent groups on morphological and thermal characteristics of melt-blended POSS/i-octyl) ,116,117.i-octyl) ,119 synt8 POSS with eight n-octyl and n-octadecyl substituents were melt blended in various contents (1–10 wt%) with commercially available polyolefins , and the influence of the structure and the content of POSS nanofiller into the matrix on the morphology and properties of the obtained nanocomposites were assessed. It was established that the properties of polyolefin/POSS nanocomposites depend mainly on the structure of the n-alkyl groups attached to the silicon–oxygen POSS core. Longer alkyl chains in the filler molecule improve its compatibility and dispersion in the material, which was confirmed based on the results of structural properties tests using scanning electron microscopy and X-ray energy dispersive spectroscopy (SEM/EDS), WAXS, SAXS, position annihilation lifetime spectroscopy (PALS), and decomposable entropic descriptor methods [n-octyl) hydrocarbon substituents in their structure proved to be more effective as agents which accelerate the polymer crystallization process [n-octyl to n-octadecyl in silicon filler molecules resulted in improved mechanical and processing properties, as well as in higher thermal stability and reduced flammability of polyolefin materials. Importantly, the presence of long hydrocarbon chains in the filler molecules had a key role in providing their high homogeneity in the polymer matrix, and thereby ensuring the appropriate reinforcement of such materials [Based on this assumption in our studies ,122,123, process ,122. Thei-butyl polyhedral oligomeric silsesquioxane (BuPOSS) nanocomposites were also prepared via melt blending. Dispersion of two fillers, C30PSS and BuPOSS, in the polymer matrix was analyzed by the SEM/EDS method. The properties of neat LLDPE, LLDPE/C30PSS, and LLDPE/BuPOSS composites were studied, and the obtained results showed that C30PSS could be used as an inexpensive filler providing good dispersion in the LLDPE matrix and improving the rheological and mechanical properties of the polymeric material.Not so long ago, Zhang et al. reported  that a ni-butyl silsesquioxanes [i-butylsilsesquioxanes with TiIV, VV and AlIII-metal centers as fillers in polypropylene nanocomposites [A special group of silsesquioxane fillers of polyolefin-based nanocomposites are metal-containing POSS, initially interesting for their potential catalytic activity and later also investigated as additives for modifying structural, morphological, and thermal properties of the polyolefin matrix. Fina et al. investigated dimeric and oligomeric Al and Zn-containing uioxanes ,126, andmposites ,128. ThePrevious studies of composites based on polyolefins with POSS fillers, differing in the structure of the silicon–oxygen cage, and, above all, in the type and number of substituents, have shown that the incorporation of heat-resistant POSS compounds into the polyolefin matrix affects the crystallization and melting characteristics of the polymer; modifies its thermal properties, providing greater thermal stability; improves mechanical properties, such as tensile or flexural modulus, tensile strength, heat deflection temperature, and rheological properties of materials ; and even reduces flammability of the obtained polymer material. It is believed that the observed effects result mainly from the POSS–polymer and POSS–POSS interactions, which depends on the structure of the substituents attached to the POSS cage.iPP nanocomposites. It was stated that incorporation of POSS–sorbitol into iPP could significantly increase the crystallinity and the mechanical properties of the polymer material. In turn, Mao et al. reported [β-nucleating agent on the surface of POSS not only improved the interfacial interaction between POSS and the polymer matrix using interfacial crystallization, but also promoted formation of β-crystals with a toughening effect, which is very important to prepare excellent-performance PP/POSS nanocomposites and to reduce the amount of expensive POSS compound used. Dintcheva et al. [POSS compounds were also introduced as an additional component to polymers already containing another functional additive to enhance its function. The synergistic effect of both additives allowed to enhance the improvement of the desired properties of the composites using a very small amount of POSS, which is important for practical use considering the high price of silsesquioxanes. Roy et al. ,130,131 reported  that an a et al.  synthesiIn addition to improving the mechanical performance and thermal properties of polyolefins, POSS molecules are introduced into these highly flammable polymers to also improve their flame retardancy. Zhang et al. recently reported  a flame-8- or Q8-type cages constitute network nodes, and these are connected with each other by siloxane bridges. An important advantage of this group of compounds is the possibility to vary their structure by changing the length of the siloxane bridge and its functionalization by the introduction of appropriate functional groups [As mentioned above, despite a number of beneficial properties of polyolefin/POSS composites, their commercial use is still limited due to the high cost of POSS fillers. This contributed to the development of siloxane–silsesquioxane resins as a less expensive alternative, which may retain the advantageous features of typical POSS compounds. The siloxane–silsesquioxane resins are characterized by a unique extended network structure, in which the silicon–oxygen Tl groups . Example8 nodes, for the preparation of polyurethane-based materials. In that case, siloxane–silsesquioxane resins were capable of bonding covalently with the polyurethane matrix. The resulting composite materials showed improved thermal stability or increased crystallization temperatures depending on the length of siloxane chains in their structure.Siloxane-silsesquioxane resins are relatively new materials, and, in the literature, there is a limited number of studies on synthesis, characterization, and possible applications of these compounds. In addition, only a few of them relate to composite materials with siloxane-silsesquioxane resins as fillers. Dobrzynska-Mizera et al. ,140 repon-alkyl-functionalized S4SQ-8 and S4SQ-18  siloxane–silsesquioxane resins were synthesized and applied as fillers for polypropylene and polyethylene nanocomposites [n-alkyl groups determined the achievement of homogeneous composite materials, which was confirmed with the use of SEM/EDS and WAXS methods [α-phase. The average parameters of lamellar stacks (evidenced by SAXS data) and the changes in PALS parameters confirmed that alkyl-functionalized siloxane–silsesquioxane resins are located mainly in the amorphous phase of the polymer due to their highly extensive network structure. In turn, particles of non-functionalized S4SQ-H resin could be located both in the crystalline and amorphous regions. DSC analysis revealed that siloxane–silsesquioxane resins enhanced the crystallization process of PE and PP neat polymer, which proved that they could be considered as nucleating agents. Thermal, mechanical, and processing properties, as well as thermal stability and flammability, of the polyolefin/siloxane–silsesquioxane resin composites varied depending on the structure of the filler used. Moreover the presence of long hydrocarbon chains in the filler molecules had a key role in providing their high homogeneity in the polymer matrix, and thereby ensured the appropriate reinforcement of such materials. Materials containing non-functionalized siloxane–silsesquioxane resins were, in principle, characterized by the least favorable properties, despite the fact that they were often better in comparison with the properties of neat polymers.In our studies, non-functionalized (containing hydrogen atoms as substituents in siloxane bridges) and mposites ,144,145. methods ,143. It Moreover, composites filled with siloxane–silsesquioxane resins showed a large similarity to materials containing alkyl-functionalized POSS. Silicon compounds containing shorter hydrocarbon substituents in their structures proved to be more effective as agents, which accelerated the polymer crystallization process. In turn, increasing the length of hydrocarbon chains in silicon filler molecules resulted in improved mechanical and processing properties, as well as in higher thermal stability and reduced flammability of polyolefin materials ,145.n-octyl and n-octadecyl functionalized polyhedral oligomeric silsesquioxanes and siloxane–silsesquioxane resins may be considered as promising nanofillers and also as UV stabilizers and/or antioxidants for polyolefin nanocomposites. However, it should be emphasized that resin particles turned out to be the more effective nucleants than POSS with the same substituents.It could be stated, on the basis of our studies, that n-alkyl substituents in these molecules, it is possible to design the properties of polyolefin composite materials for a given direction of their use.Finally, the results confirm that, through appropriate selection of the structure of silicon compounds, as well as the type and length of Application of organic–inorganic compounds such as polyhedral oligomeric silsesquioxanes and siloxane–silsesquioxane resins in the area of polyolefins opened up the door for preparation of materials with improved properties. Incorporation of these compounds to polymeric materials both as comonomers and as fillers has a beneficial effect on many properties of the obtained copolymers and composites, among which the most interesting are the crystallization behavior, higher thermal stability, and reduced flammability. Moreover, easy modification of silicon compounds by altering the structure of non-reactive and/or reactive substituents attached to the silicon–oxygen core enables not only to design polyolefin materials with a wide range of physico–chemical properties, but also makes silsesquioxanes applicable in the creation of new catalysts for olefin polymerization, including homogeneous analogs of supported catalysts. This allowed for a better understanding of the mechanism of ethylene polymerization with industrial Philips-type catalysts. On the other hand, this review showed the limitations of using silsesquioxanes in the synthesis of polyolefins. The limitations concern the activity of silsesquioxane complexes  and their low comonomer incorporation capacity. Furthermore, until today, there have been no known catalytic systems that would be able to incorporate POSS-comonomer into polyethylene macromolecules with high efficiency. Finally, although much attention has been paid to the influence of the silsesquioxane structure on compatibility between composite components and the properties of the materials, the correlation between the microscopic and macroscopic properties of polyolefin/POSS nanocomposites, which is of particular importance for the design of their properties, has not been fully resolved so far. Thus, further investigations regarding the application of silsesquioxanes in polyolefin synthesis and modification are expected. As has been shown, applications of silsesquioxanes in the field of polyolefin are very diverse, and their use in each area significantly expands our knowledge about polyolefins. However, from a practical point of view, the use of silsesquioxanes as fillers, especially additives used in small amounts (due to the high price of POSS), for the desired modification of polymer properties with other modifiers seems to be the most promising. The use of much cheaper and effective siloxane–silsesquioxane resins seems particularly interesting for this purpose.


The cracking of the negative moment area of steel–normal concrete (NC) composite bridges is common owning to the low tensile strength of concrete. In order to solve the problem, Ultra High Performance Concrete (UHPC) is used to enhance the tensile performance of the negative moment area. This paper conducted interface experiments to study the bonding behaviour of the UHPC–NC interface. The design parametric analysis of steel–NC–UHPC composite bridges was carried out based on the interface experimental results. Firstly, slant shear tests and flexural shear tests were carried out to study the rationality of the interface handling methods. Then, the finite element model was used to analyze the state of every component in the composite beams based on experimental results, such as the stress of UHPC, concrete and steel plate. Finally, the calculation results of finite analysis were compared and summarized. It is concluded that (1) the chiseling interface can meet the utilization requirements of physical bridges. The average shear stress and flexural tensile strength of the chiseling interface are 10.29 MPa and 1.93 MPa, respectively. In the failure state, a slight interface damage occurs for specimens with a chiseling interface. (2) The influence on overall performance is different for changes in different design parameters. The thickness of concrete has a significant influence on the stress distribution of composite slabs. (3) Reliable interface simulation is conducted in the finite element models based on interface test results. The stress variation patterns are reflected in the change of design parameters. Steel concrete composite beams achieve higher strength and stiffness than concrete beams. The tensile strength of steel and compressive strength of concrete are fully utilized in steel–concrete composite bridges . HoweverUHPC is a material with higher tensile strength and good ductility ,4. UHPC The development process of UHPC involves industrial by-products, such as slag and silica fume instead of Portland cement , adding Besides, reliable interface between UHPC and concrete is crucial to achieve the shared force. The interface bond strength is influenced by various factors, such as surface treatment ,17, curiThis paper studies the bonding behaviour of UHPC-NC interface, and conducts a parametric analysis of the design parameters of steel–NC–UHPC composite beams. Firstly, slant shear tests and flexural tensile tests were carried out to study the interface performance with different handling methods. Then, a finite model was used to analyze the state of every component in steel–NC–UHPC composite beams. Finally, the calculation results of finite analysis were compared and summarized. This study provides support and reference for the design and construction of steel–NC–UHPC composite slabs.The concrete used in the present research was obtained from an original concrete, produced and delivered by a ready-mix concrete company. After 28 days of curing conditions, an average compressive strength of 43.27 MPa was obtained for concrete. The Ultra High-Performance Concrete (UHPC) was cast in place and cured according to the construction environment. After 28 days, an average compressive strength of 122.84 MPa was obtained for UHPC. The constituents of concrete are listed in UHPC was designed according to the requirements of tensile strength and shrinkage creep deformation. The components of UHPC are listed in The characteristics of steel fibers in the UHPC can be seen in 3, grouped in 2 sets of 3 specimens, were produced, with the interface surface at 30° with the vertical. Each of these was composed of half in NC and half in UHPC, 2 sets corresponding to the 2 types of surface handling methods considered, respectively. The interface processing methods included chiseling and smooth interface. In addition, the interface was always dried before casting the UHPC overlay. The slant shear specimens are shown in Six prismatic specimens with 100 × 100 × 300 mmTwo types of surface processing methods were considered: smooth surface and chiseling surface. Surface laitance is only cleaned in the smooth surface. The chiseling surface shows the coarse aggregate, and the valley peak is about 15 mm.The slant shear tests were conducted in the universal testing machine. The load was recorded via a force transducer. Before loading, the loading area should be cleaned and kept level, which ensures uniform loading. The loading diagram of slant shear tests is shown in The phenomenon of slant specimens with different interfaces is diverse. From As for slant shear tests, there are three failure types of interface in total.(1)A: interface of concrete and UHPC is invalid, concrete is intact;(2)B: interface of concrete and UHPC is invalid, there is a slight damage to concrete;(3)C: interface of concrete and UHPC has slight damage, concrete is crushed.The normal shear stress of interface can be given according to the requirements of ACI 546 . The diaNormal stress of interface can be calculated with Equation (2).Shear stress of interface can be calculated with Equation (3).The slant shear strength of interface should be calculated according to the bonding area. The interface shear strength is shown in From 3, grouped in 2 sets of 3 specimens, were produced with the interface surface at 90° with the vertical. Each of these was composed of half in NC and half in UHPC, 2 sets corresponding to the 2 types of surface handling methods considered. The specimen before pouring UHPC is shown in Six prismatic specimens with 150 × 150 × 600 mmThe flexural tensile tests were conducted according to the Standard for test methods of concrete physical and mechanical properties (GB/T 50081—2019) . The loaNumberFailure typeIflexural tensile failure of UHPC sideIIflexural tensile failure of interfaceIIIflexural tensile failure of concrete sideThe failure of flexural tensile tests can be divided into three types according to the test phenomenon.The failure types of flexural tensile specimens can be seen in The flexural tensile strength can be calculated by Equations (4)–(6).σ is the flexural tensile stress of the interface; M is the bending moment in the interface; W is the resistance moments of the section; F is the concentrated load; L is the effective span of flexural tensile specimens; b is the width of the section; h is the height of specimens.Thus,From The bridge is a three-span continuous steel–concrete composite girder bridge. The span is 40 + 60 + 40 = 140 m, and the width is 16.5 m. The layout of the bridge slab is: 0.5 m (anti-collision guardrail) +7.5 m (motor vehicle lane) +0.5 m  +7.5 m (motor vehicle lane) + 0.5 m (anti-collision guardrail). The bridge pavement is made with a 2 mm waterproof layer and 100 mm asphalt mix.The bridge deck is a composite bridge slab, in which the inner thickness is 270 mm, and the thickness of the root of the cantilever slab is 370 mm. The thickness of the bottom steel plate is 8 mm. The steel plate and concrete are connected with T-type steel ribs and studs. The cross section of steel–NC–UHPC composite beam is shown in Shell181 element is used to simulate the steel beam, and the solid185 element is used to simulate concrete and UHPC using the Ansys software 2022 R1 . ReinforThe finite model contains a total of 35,586 nodes and 32,220 elements. The model is constrained, with one fixed end and one simply supported end, and the loads are arranged according to lanes for vehicle loads. The finite model is shown in The proprieties of concrete and UHPC are the same as these of the interface tests. Elastic modulus of concrete and UHPC are 30,041 MPa and 41,617 MPa, respectively. Poisson’s Ratio is 0.2. The yield strength and tensile strength of steel bars, steel ribs and steel plate are adopted according to the related guidelines. All the reinforcements had the same elastic modulus of 200 GPa and Poisson’s Ratio of 0.3. The elastic modulus and Poisson’s Ratio of studs and steel ribs were the same as those of reinforcements. All components are in the elastic state in the finite analysis.The common nodes are used to simulate the behaviour of steel plate and concrete, because studs and steel ribs provide enough interface shear capacity. From the results of the interface tests of UHPC and concrete, it is indicated that the shear capacity of the chiseling interface meets the requirements of related guidelines. Thus, the interface slip is neglected in the current finite model. The steel bars and steel ribs are coupled with the concrete and UHPC layer.In order to ensure that the design of the composite bridge deck meets the requirements of codes under vehicle loading, a local finite model is established for finite element calculation and analysis. In accordance with the existing design of composite slabs, the spacing of horizontal partitions is 3.5 m and three sections are selected to analyze the behaviour. The vehicle loading adopts axial loading with a load of 140 kN. The elevation arrangement of vehicle loading is shown in Variable analysis is carried out to understand the sensitivity and distribution of the stresses of different parts with change in the design parameters of composite beams. This provides a reference for the analysis of the main factors in the design of composite beams. In the parametric analysis, the thickness of concrete changes from 0.08 m to 0.3 m with a 0.05 m-thick UHPC layer. The parameter can be seen in As we all know, thickness has a great effect on the bearing capacity of bridge slabs. In the meantime, increase in thickness of slabs will enhance mechanical performance in the service state. In order to reveal the influence on normal stress of every component with the change in thickness of a concrete layer, a series of finite models are modelled and calculated. The normal stress of concrete, UHPC, steel plate and steel ribs is extracted from the results, as in As can be seen from For composite slabs with a large cantilever span, bottom steel plate not only provides construction templates, but also improves the mechanical performance of bridge slabs, with higher compressive and tensile strength than that of concrete. In order to show the influence on normal stress of every component with change in the thickness of steel plate, a series of finite models is modelled and calculated. The normal stress of concrete, UHPC, steel plate and steel ribs is extracted from the results, as seen in It is shown in In conjunction with the actual construction process of the bridge, the steel plates initially function as a formwork to carry the self-weight of the concrete and UHPC. For this state of construction, the analysis of the stresses on the steel plates and steel ribs is carried out to determine a reasonable spacing for the steel ribs.According to the calculation results in (1)Chiseling interface prohibits the occurrence of interface failure and can be applied in the engineering. There is only slight interface damage to the chiseling surface based on the results of slant shear tests and flexural shear tests, which meets the needs of physical engineering.(2)The phenomenon in the slant shear tests and flexural tensile tests is similar, which can reflect the interface bonding performance. Compared with direct shear tests and pull-out tests, it is easy to conduct slant shear tests and flexural tensile tests.(3)The thickness of concrete, steel plate has a huge influence on the normal use of composite slabs. The normal stress of UHPC, concrete and steel plate will decrease with the increase in the thickness of concrete and steel plate. Besides, reducing the interval of steel ribs can effectively improve the flexural performance and decrease the stress of UHPC, concrete and steel plate.In the paper, interface tests and finite analysis are used to study the interface shear behaviour and the flexural performance of steel–NC–UHPC composite slabs. The study reveals the mechanical performance of interface and composite slabs. The following conclusions are drawn:There is a trend for UHPC to be used in bridge engineering in the future. The study of interface performance and parametric analysis of steel–NC–UHPC composite slabs provides reference and support for the design of composite bridges.


Thermal loading, especially in fire scenarios, challenges the safety and long-term durability of concrete structures. The resulting heat propagation within the structure is governed by the heat conduction equation, which can be difficult to solve analytically because of the nonlinearity related to the thermophysical properties of concrete. A semi-analytical approach for the transient nonlinear heat conduction problem in concrete structures was established in the present work. The nonlinearity related to the temperature-dependent thermal conductivity, mass density, and specific heat capacity of heated concrete was taken into consideration. A Taylor series approximate solution was first established within a small neighborhood, employing the Boltzmann transformation in combination with the mean value theorem. Thereafter, it was extended to the whole domain by utilizing the Bernstein polynomial. The semi-analytical approach was validated by comparing it with the numerical results of two independent Finite Element simulations of nonlinear heat conduction along concrete plates, subjected to either moderate or fierce thermal loading. Absolute values of the relative errors are smaller than  Concrete structures are frequently subjected to daily temperature cycles ,2, sometIdentification of the temperature field is the prerequisite for performing a thermomechanical analysis of the behavior of thermally-loaded concrete structures. For example, following the simplified “rocode 2 , concretaterials ,10 and taterials ,12, as aaterials ,14, as aaterials ,16, as aaterials , which iDriven by the temperature difference, heat conducts within concrete, following 1)ρTCT∂mplicity . The theρTCT∂mplimplicity . This ismplicity  as a resmplicity  when heamplicity ,20. TherW/(m·∘C) , which dW/(m·∘C) . Review o 500 °C ,22. The /(kg·∘C) , which i/(kg·∘C) . TherefoK domain, see [The nonlinear heat conduction problem can be solved either numerically or analytically. An extensive amount of work has been found on the application of Finite Element method in solving the heat conduction problem in concrete structures ,24, suchain, see  for detaain, see , the homain, see , the tanain, see , and so ain, see , and of ain, see ,39, are The present study employed the Boltzmann transformation, in conjunction with the mean value theorem and Bernstein polynomial, for solving transient nonlinear heat conduction of concrete. The nonlinearity related to the temperature-dependent thermophysical properties, i.e., the mass density, specific heat capacity, and thermal conductivity, of concrete and the time-dependent boundary conditions was considered. For establishment of the analytical solution, the Boltzmann variable was first introduced in order to transfer the nonlinear partial differential equation of the heat conduction problem into a nonlinear ordinary differential equation. By utilizing the mean value theorem, an approximate integral form of the governing equation was derived, which was solved by linearization of the nonlinear equation and the first-order Taylor series approximation in a small neighborhood. Finally, the semi-analytical solution for the whole domain was established from the basic solution within the aforementioned neighborhood, by recalling the Bernstein polynomial. The solution was validated by numerical simulations and further applied to a scaled fire test, inspired by a three-span subway station . The theThe present study is structured as follows. x-coordinate, the governing Equation   U, is inerature,U=U(T)=∫Tt and the x-coordinate, i.e.,x-coordinate read asT and the Boltzmann variable Following the Boltzmann transformation ,39,42, tEquation  and reca read as∂ϕ∂t=−ϕ2tEquation  gives acquation imation: T˜=T+∆T≈Tquation (12ϕ(T˜−2∆quation (12ϕ(T−∆T)c standing for the higher order infinitesimal function, reading asa and b, are introduced: v as a parameter to be determined. At this point, an analytical solution of the nonlinear ordinary differential Equation (T.The approximate governing equation is solved by referring to the first-order Taylor series approximation. Equation  can be creads as:ϕ(T−2∆T)=Equation  results roduced: a=∫T−∆TThquation (ϕ(T)∫T−∆TEquation  is estabolved asϕ=v∫TThotn-th order Bernstein polynomial of w to be determined.The approximate solution within the whole domain is established by recalling the Bernstein polynomial . For theEquation , i.e., ϕEquation , the ϕ≈Bn=ϕ≈Bn(ϕEquation  into Equuations (ϕ(ξ)≈Bnx=tvessed asx=ϕt,whi4b.c.:Tx=0x-coordinate, i.e., Equation ρAs for the numerical simulation, the length and the width of the plate in The numerically quantified temperature field of the concrete plate at the time instant of 10 min, 60 min, and 180 min after the sudden temperature increase is illustrated in w are identified by solving Equation 48) into Equation , settingExample I. All the three related thermophysical parameters were assumed to be temperature-dependent. For distinguishing with Example I, the self-consolidating concrete (SCC) is considered, with its thermal conductivity follows [T standing for temperature in the physical unit of Celsius degree.In the following exemplary study, the initial temperature was still set equal to  follows ,(51)KT= follows ,(52)ρTCExample I. The numerical simulated distribution of the temperature, at the time instant of 10 min, 60 min, and 180 min after the sudden temperature increase is illustrated in As for the numerical simulation, the geometrical dimensions of the plate and the Finite Element mesh are the same as those of w, are identified by solving Equation 51) into Equation , settingThe validated semi-analytical approach of the transient nonlinear heat conduction problem was further utilized for prediction of the temperature evolution of a scaled model of a subway station. The tested model was subjected to a real fire loading scenario, resulting in a time-dependent surface temperature. The setup and the experimental measurements of the fire test will be presented first, followed by comparison with the prediction from the semi-analytical approach.The tested structure was stimulated by the station hall layer of a typical subway station in China, in the form of a closed-cell reinforced concrete frame. The tested model represents the substructure at a reduced geometric scale of 1:4, see nce with .As for the test setup, the structural model was placed sidelong on the top of a furnace and closed with a fire-resistant cover. Vertical and horizontal earth pressure were simulated by hydraulic jacks acting on the top slab and the right wall, as three sets of concentrated loads. The bottom slab and on the left wall were supported by hinge supports, see ion, see  for detaThermocouples were placed at midspan of the three cells of top slab, and at the geometric centers of the bottom slab, of the right column, as well as of the right wall. Six thermocouples were placed equidistantly along the thickness of the right cell of top slab, see the elliptic marker in t standing for time in physical units of seconds. It is very similar to the readings of the thermocouple, see the solid graph The tested model of the subway station was stored inside the laboratory before the fire test, leading to an isothermal initial configuration. The initial reference temperature was set equal to The thermophysical properties of the normal concrete, consisting the scaled model of the subway station, were considered to follow the Eurocode . The the process ,52,53, tw are identified by solving Equation 55) into Equation  for two From the point of view of practical engineering, the analytical solution of linear heat conduction is frequently used ,54. SorgThe temperature fields of the top slab, obtained from the engineering mechanics analysis  and the Example II, that is The influence of the nonlinearity related to the thermophysical properties of concrete on the heat conduction process is discussed in the following. Both the initial and boundary conditions follow those of Example II, i.e., Equations Example IS-II: The thermal conductivity was considered to be temperature-dependent, following Equation , whereasS-III: All three thermophysical properties were considered to be temperature-independent, reading as the values of Equations  and 52)52) by seThe semi-analytical solution of the heat conduction, considering thermophysical properties of S-II and S-III, was established, following the aforementioned strategy. Generally, heat propagates similarly along the length of the plate, whereas the speed of the conduction process differs. Temperature distributions along the length of the plate at the time instant of Equation . Howeverx-coordinate, as a result of the temperature-independent mass density, specific heat capacity, and thermal conductivity of concrete. However, it varies significantly in the case of S-I and S-II, reading as For clarification of the nonlinearity related to the thermophysical parameters, the corresponding profile of thermal diffusivity The nonlinearity, related to the temperature-dependent mass density, specific heat capacity, and thermal conductivity of concrete, was taken into consideration. The semi-analytical approach was validated by comparison with two independent Finite Element simulations of heated plates, consisting of normal and self-consolidating concrete, respectively. Absolute values of the difference of the semi-analytical solution, with respect to the numerical results, are smaller than By referring to the definition of the Boltzmann variable, the semi-analytical solution was further extended to consideration of a time-dependent thermal boundary condition, which is commonly encountered during the service life of concrete structures. The extended solution was compared with the experimental measurements of a fire test of a scaled concrete subway station. Satisfactory agreement was achieved.In the present paper, a semi-analytical approach to transient nonlinear heat conduction in a concrete structure, subjected to a time-dependent/independent thermal boundary condition, was established. Following the Boltzmann transformation of the partial differential equation to ordinary differential equation, the mean value theorem and Taylor series approximation were used for the solution in a small neighborhood, which was extended to the whole domain by utilizing the Bernstein polynomial. The established semi-analytical approach was first validated by comparing the numerical results with Finite Element simulations and then applied to a fire test. In this respect, the following conclusions are drawn:semi-infinite plate can still be widely used in real scenarios, such as the presented examples of the concrete plates and slabs in a subway station, subjected to either moderate or fierce fire loading.Because of the rather small thermal conductivity, concrete generally exhibits good thermal insulation performance. Therefore, the established semi-analytical approach of the nonlinear heat conduction for a The thermal insulation property also leads to significant temperature gradients in the vicinity of the heated surface and, therefore, strong nonlinearity of the thermal eigenstrain, as a product of the temperature difference and the thermal expansion coefficient of concrete. This nonlinearity governs the resulting thermal stresses of concrete structures ,30. In tTherefore, the established approach demonstrates its accuracy and stability in solving the transient nonlinear heat conduction problem in concrete structures. From the quantified temperature fields of the investigated scenarios, the following conclusions were drawn:It is recommended to position enough thermocouples close to the fire-exposed surface. With the knowledge of the temperature evolution of the heated surface, the established semi-analytical approach provides access to the evolution of the temperature fields within concrete structures, serving as the basis for the following thermomechanical analysis and damage evaluation.It is recommended to carry out careful inspection of the thermally-loaded concrete structures. The strong nonlinearity of the temperature field is very likely to result in significant thermal stresses and potential thermal cracking.As for the maintenance of concrete structures exposed to potential fire loading, the following recommendations can be made from the present study:Finally, it is worth mentioning that the presented semi-analytical approach was established by assuming semi-infinite boundary conditions, which is applicable to some heating scenarios because of the thermal inertia of concrete; for example, the presented fire test with a heating duration of 2 h and a maximum air temperature of around o 700 °C , extensi