Although reinforced concrete (RC) columns subjected to combined axial compression and flexural loads  are the most common structural members used in practice, research on FRP-confined circular RC columns subjected to eccentric axial compression has been very limited. More specifically, the available eccentric-loading models were mainly based on existing concentric stress–strain models of FRP-confined unreinforced concrete columns of small scale. The strength and ductility of FRP-strengthened slender circular RC columns predicted using these models showed significant errors. In light of such demand to date, this paper presents a stress–strain model for FRP-confined circular reinforced concrete (RC) columns under eccentric axial compression. The model is mainly based on observations of tests and results reported in the technical literature, in which 207 results of FRP-confined circular unreinforced and reinforced concrete columns were carefully studied and analyzed. A model for the axial-flexural interaction of FRP-confined concrete is also provided. Based on a full parametric analysis, a simple formula of the slenderness limit for FRP-strengthened RC columns is further provided. The proposed model considers the effects of key parameters such as longitudinal and hoop steel reinforcement, level of FRP hoop confinement, slenderness ratio, presence of longitudinal FRP wraps, and varying eccentricity ratio. The accuracy of the proposed model is finally validated through comparisons made between the predictions and the compiled test results. The building industry plays a significant role in the development of human history. There are various building materials, such as structural materials, decorative materials, and some special materials, that have significantly contributed to the development of the building industry. Structural materials include metal, bamboo, wood, concrete, stone, cement, brick, plastics, ceramics, glass, and composite materials; decorative materials include various coatings, paints, glass with special effects, etc.; special materials refer to waterproof, fire-retardant, heat insulation, etc .With the development of material science and technology, polymer materials exhibit a potential role in the building industry due to their excellent properties compared with inorganic materials. Building polymers commonly used in the construction industry include polyethylene (PE), polyvinyl chloride (PVC), polymethyl methacrylate (PMMA), polyester resin (PR), polystyrene (PS), polypropylene (PP), phenolic resin (PF), and organic silicon resin (OSR). By adding these polymers into traditional building materials, such as concrete and mortar, polymer-based building materials have great benefits when used in construction engineering. Compared with cement concrete, it provides good mechanical strength, short curing period, high adhesion, wear resistance, weather resistance, waterproof, high insulation performance, etc .For fast construction, high-quality control, less waste, and construction interruption, the construction industry is transforming into prefabrication or modularization i.e., ,3). To r. To r3])Due to their high strength and light weight, corrosion resistance, dimensional stability, low thermal conductivity, no conductivity, electromagnetic transparency, impact resistance, and low lifecycle costs, the FRPs provide excellent weather resistance, high durability, adaptable aesthetic appeal, cost-effective manufacturing processes, and other potential benefits. FRPs have been used to replace the traditional construction materials . In modern buildings. FRPs also have the potential to strengthen and/or retrofit existing concrete structures and reduce the amount of reinforcement and cementitious materials in concrete i.e., ,5,6,7). ,6,7. 5,6In recent years, significant research has been carried out on the use of fiber-reinforced polymer (FRP) composite materials for enhancing the axial strength, bond strength between concrete and composite materials, shear, deformation, durability, and thermal resistance of concrete  up to 20.4. The tests revealed reductions in the effectiveness of confinement by increasing the eccentricity and slenderness levels. Further insight into the tests in ) in Ref. , in whichsλ) and the longitudinal reinforcing steel bars (vsλ) are provided as:yhf and ylf are the yield strengths of the hoop and longitudinal reinforcing steel bars (MPa), respectively; hsρ and vsρ are the ratios of the hoop and longitudinal steel bars, respectively; hsd is the diameter of the hoop bar (mm); cD is the diameter of the concrete core measured to the outside of the hoop bars (mm) . The final coefficient vk is used herein to quantify the effectiveness of hoop steel confinement in the vertical direction between the hoop reinforcing bars. For concrete columns confined with circular hoop bars, vk is given in Equation (6)  is the total cross sectional area of the column.Tests on FRP-confined RC columns have revealed a contribution made by the internal hoop reinforcement to the peak strength and strain enhancements  of about 93.7% and were based on the analysis of all 207 specimens summarized in l is column height (mm); e is loading eccentricity (mm); URCδ and CRCδ (dimensionless coefficients) are strength gains of unwrapped and FRP-wrapped RC columns, respectively. The resulting values of B1.1, B1.2, B1.3, B1.4 in Equation (8) are 31.53, 1.38, 14.97 and 0.54, respectively. In Equation (9), B2.1 = 5.264; B2.2 = 1.295; B2.3 = 0.643; B2.4 = −2.733; B2.5 = −0.614. The coefficients of Equation (10) are obtained as B3.1 = 1.083; B3.2 = −0.092; B3.3 = 4.330; B3.4 = −2.386.The peak strength, finement ,61. For finement  and Kaesfinement . The expAAE). Predictions given by the proposed expressions and those of the models [AAE = 29.3). Moreover, the direct use of these models leads to significant errors in predicting the tested peak strength of FRP-confined slender RC columns. In a range of higher slenderness ratios ranging from 23.7 to 32, the experimental results are overestimated by 45.6% . The ratio between the analytical results given by the new model and the results equal 101% with an AAE value of about 7.2, whereas the ratio between the analytical results from the existing models and the results is equal to 128.5% with an AAE value of about 38.7. Finally, it can be concluded that the present model agrees best with the test results.The proposed peak strength model is applicable for FRP-confined unreinforced columns, FRP-confined RC columns, and unwrapped RC columns. The accuracy of the proposed and existing expressions is assessed by the average absolute error , in which the correlation coefficients are 91.9 and 88.7% for the first and second parts of the expression, respectively:CZ indicates that the proposed expression can predict the maximum confined strain in the compression zone of the cross-section, whereas CZ and TZ refer to the ultimate strain in compression and tension section sides, respectively; coɛ is the compressive strain corresponding to the peak strength of unconfined concrete and is taken to be 0.002. In the present model, the (ccɛ/coɛ)con ratio was determined from the concentrically loaded model of Wang et al. [B4.1, B4.2, B4.3, B4.4, B4.5, B4.6, B4.7 in Equation (11) are obtained to be 12.23, 0.87, 19.83, 0.66, 3.77, −1.10, 0.11, respectively, whereas in its second part B5.1 = 0.68, B5.2 = 3.15, B5.3 = 7.84, B5.4 = 0.55, B5.5 = −0.98, B5.6 = 0.69, B5.7 = 0.34.Similar to the model given in Equation (9), an expression for the peak strain g et al. , as provflf and fls (MPa) are the lateral confinement pressures provided by the FRP wrap and internal steel reinforcement, respectively; feɛ is the actual rupture strain of the FRP wrap and is considered to be equal to 0.8 times the fuɛ value [The model proposed for the ultimate strain is also applicable for FRP-confined unreinforced columns, FRP-confined RC columns, and unwrapped RC columns. Predictions given by the proposed Equation (11) and those of the models ,41,47,48fu value .fn = 1,2, f,vn = 0,1,2,4), slenderness ratio , eccentricity ratio , and strength of unconfined concrete . For example, the symbol S8 in S8L2V4C60S12.1 and its number represent the specimen code of a particular category. The following letter L and its number refer to the number of layers of FRP hoop wraps, whereas V4 refers to the number of layers of FRP longitudinal wraps. The term C60 refers to the concrete type. Finally, the last symbol, S, and the number following it refer to the slenderness ratio. In To propose a slenderness limit for FRP-confined RC columns, a total of 32 specimens were designed and analyzed. The control specimen as provided in kl/r = 22). This is attributed to the fact that reductions in strengths of FRP-wrapped columns are higher than those of the unwrapped columns, and that the slenderness effects are more significant for FRP-wrapped columns with higher confinement levels . ,30. kl/r12.8 see , is typi12.8 see . The satδCRC (Equation (9)) is greater than one, the resulting threshold represents the sufficiently confined concrete. Based on an analytical paper by Pham and Hadi [A confined column needs a minimum amount of FRP wraps for sufficient confinement ,67,68,69and Hadi  on FRP-cf,vn = 0,1,2,4), slenderness ratio , eccentric loading ratio , and unconfined concrete strength .For columns under eccentric loads, five specimens with different geometry and loading characteristics were studied. The original specimen is similar to that in δCRC is equal to 1, then the lf/fc’f ratio is about 0.22, and such a threshold is larger than that of FRP-confined circular columns under concentric loading due to the reduced effects caused by the eccentric loads. Refer to the discussions of The response between the effective confining pressure ratio and the confined axial load ratio is given in x = c/ɛcoɛ and c/fc’y = f; ɛc and cf are assumed levels of longitudinal axial strain and stress, respectively. The coefficient A, which can be determined from the boundary condition c/dɛcdσ = cE at cɛ = 0, is provided as follows:cE = 4736co = fc’/ɛcoE (MPa) is the secant modulus at the peak stress of unconfined concrete.X = cc/ɛcoɛ and Y = cc/fc’f.According to Ref. , A desigfc′(MPa)  is the er in Equation (17) is of significant importance because it controls the overall shape of the stress–strain curve. From two different methodologies of analysis conducted on 64 stress–strain test responses reported by two independent research groups [r is related to the lateral confinement provided by the internal steel confinement and external FRP wraps, as well as the contribution made by the longitudinal FRP sheets. Based on these observations, the following model B6.1, B6.2, B6.3, B6.4, B6.5, B6.6 in Equation (18) are proposed to be equal to −72.29, 74.16, 1.16, −0.24, 0.41, 2.34, respectively, whereas in its second part B7.1 = 1.10, B7.2 = −0.19, B7.3 = −2.88, B7.4 = 1.89, B7.5 = 1.41.The parameter h groups ,26, the ciɛ at the centroid of ith segment is determined using linear trigonometry and the stress cif is then calculated using the FRP-confined concrete stress–strain models in ciA is the ith concrete segment area; cif is the stress at the centroid of the ith concrete segment; sA1 to sA4 are section areas of a single reinforcing steel bar ; sf1 to sf4 are the corresponding stress results of the steel bars. The term ciS is the distance between the column centroid and the center of the segment I, and S1 to S4 are the distances between the column centroid and the steel reinforcement bars 1 to 4, respectively. The effect of using longitudinal FRP wraps on the column response is also introduced into the above two expressions, in which vA is the area of longitudinal FRP wraps and is calculated using the geometric properties of a circular segment, fFRP is the ultimate tensile strength of FRP wraps, and z is the distance between the column’s centroid and the centroid of FRP composites.Only limited research focusing on the axial load-bending moment response is available for FRP-confined columns e.g., ,27,28). ,28. 27,2uN = 0.85cc’f (gA − stA) + yAstf, where the column was considered as unconfined in the case of lower load levels (uN ≤ 0.1c’Agf), and its strength in pure flexure was obtained accordingly. The comparisons included analytical and test P–M responses with different wrapping systems. In B8.1, B8.2, B8.3, B8.4, B8.5, B8.6, B8.7, B8.8 in Equation (21) are 0.33, 9.37, 49.21, 0.93, −1.15, −0.31, 0.72, 1.38, respectively.The P–M interaction responses using the newly proposed expressions (Equations (21) and (22)) are shown in None of the existing design codes and models, among them the GB 50608  and ConcThe slenderness limit is proposed to be dependent on the FRP confinement level, and the averaged result from the presented model matches well with the averaged results by Jiang and Teng , De LoreA design-oriented stress–strain model was newly developed using a database of 207 FRP-confined plain and RC columns under different loading conditions. The model parameters included longitudinal and hoop steel reinforcement ratio, amount of FRP hoop wraps, presence of longitudinal FRP sheets, slenderness ratio, eccentric loading ratio, column section’s size, and compressive strength of unconfined concrete.Based on a parametric investigation by the model, the sufficiently confined concrete threshold under eccentric loads was proposed to be 0.22, which is larger than that of Pham and Hadi. , since tFor slender columns, significantly underestimated predictions of the P–M responses were obtained using both the existing concentric and eccentric stress–strain models of FRP-confined concrete cylinders. However, good agreement between the proposed predictions and tested responses was found, confirming that the model can simulate slender RC columns experiencing greater flexural resistance when strengthened with lateral and longitudinal FRP sheets.Based on analytical investigation of a comprehensive database of eccentrically loaded short and slender circular RC columns of varying slenderness ratios and FRP wrapping systems, the following conclusions are drawn as follows:


The application of concrete containing mineral admixtures was attempted in Northwest China in this study, where the environment has the characteristics of low humidity and large temperature variation. The harsh environment was simulated by using an environmental chamber in the laboratory and four types of concrete were prepared, including ordinary concrete and three kinds of mineral admixture concretes with different contents of fly ash and blast-furnace slag. These concretes were cured in the environmental chamber according to the real curing conditions during construction. The compression strength, fracture properties, SEM images, air-void characteristics, and X-ray diffraction features were researched at the early ages of curing before 28 d. The results showed that the addition of fly ash and slag can improve the compression strength and fracture properties of concrete in the environment of low humidity and large temperature variation. The optimal mixing of mineral admixture was 10% fly ash and 20% slag by replacing the cement in concrete, which can improve the compression strength, initial fracture toughness, unstable fracture toughness, and fracture energy by 23.9%, 25.2%, 45.3%, and 22.6%, respectively, compared to ordinary concrete. Through the analysis of the microstructure of concrete, the addition of fly ash and slag can weaken the negative effects of the harsh environment of low humidity and large temperature variation on concrete microstructure and cement hydration. In the past three decades, the economy of China developed rapidly. In 2019, China’s GDP reach USD 14.343 trillion, ranking second in the world. However, there is an imbalance between the east and the west of China, and the infrastructure construction is relatively weak in the Northwest China. According to the GDP data of 2019, the total GDP of western region is USD 2.983 trillion, accounting for 20.8% of the national GDP; while the eastern region is USD 7.444 trillion, accounting for 51.9%. In recent years, China has accelerated the pace of infrastructure construction in the Northwest. From 2015 to 2019, China’s road construction investment had increased by 32.6%. In 2019, China completed CNY 10,049.8 billion in road construction investment in the Northwest [Existing research has proven that the humidity and temperature in the curing environment have an impact on the mechanical characteristics and microstructure of concrete. When concrete is cured in a dry environment, the water inside the concrete will evaporate to the outside, resulting in the chaos of ion migration inside the concrete and weakening the hydration products in the interface transition zone (ITZ) . AM SoliIn recent years, an effective method of adding mineral admixtures was adopted by scholars to improve the performance of concrete ,10,11. AIn the process of infrastructure construction in Northwest China, the use of concrete with mineral admixtures may be able to withstand the harsh environment and bring considerable economic benefits. However, there were few studies that paid attention to the characteristics of concrete containing mineral admixtures in such a complex environment. Only Jiang et al.  investig2/kg in this study. The fine aggregate utilized was natural river sand with a fineness modulus of 2.85 and an apparent density of 2640 kg/m3. The coarse aggregate was natural crushed stone with a particle size of 5−20 mm and an apparent density of 2760 kg/m3. The used superplasticizer, working as a water reducing admixture, had a water-reducing rate of 25–30%. The water used in the tests was local tap water.The Portland cement of P.O. 42.5  was useTwo kinds of mineral admixtures were adopted in this research, including fly ash and blast-furnace slag. The fly ash is first level in Class F according to the Chinese national standard GB/T 1596-2017 , and theIn the laboratory trials, four groups of concrete with a strength grade of C 45 were manufactured according to the Chinese national standard JGJ 55-2011 , and theIn each group of concrete, six specimens were prepared, including three cube specimens with size of 100 mm × 100 mm × 100 mm for compression strength tests and three prism specimens with size of 100 mm × 100 mm × 515 mm for fracture tests. When the prisms were manufactured, a steel plate with a dimension of 100 mm × 40 mm × 3 mm was welded in the middle of the concrete mold to prefabricate a notch with a width of 3 mm and a depth of 40 mm in the specimens, as shown in An environmental chamber was utilized to simulate the environment of low humidity and large temperature variation in Northwest China. The meteorological data from 1990 to 2020 were analyzed, and the most adverse environmental state was implemented by the environmental chamber: The humidity was maintained at 35%, and the temperature changed periodically from −5 °C to 40 °C every day. From 1:00 a.m. to 6:00 a.m., it was a constant of −5 °C. Then, the temperature gradually raised to 40 °C from 6:00 a.m. to 14:00 p.m. This high temperature remained until 20:00 p.m. and gradually dropped to −5 °C at 1:00 a.m. the next day. The detailed change process of humidity and temperature in one day was displayed in After cured for one day under indoor conditions, the concrete specimens were demolded and then placed into the environmental chamber. In order to simulate the real curing condition during construction, a layer of water-saturated geotextile (sprinkling water every day) was covered on the concrete specimens in the first 14 d. Then the geotextile was removed to expose the concrete to the environmental chamber with no sprinkling water from 14 to 28 d.fcc is the compression strength of the cube specimen (MPa), P is the peak load during the compression test (N), and A is the bearing area of the specimen (mm2).The compression strength tests were conducted according to the Chinese national standard GB/T 50081-2019 . When thDue to the harsh environment in the western region of China, concrete is prone to fine cracks during curing. These microcracks will develop, connect, and merge into one or more macrocracks, which can expand gradually and may lead to structural damage. Traditional strength measurements cannot study the effect of cracks on the structure, so the early-age fracture properties of the concretes were detected by a method of three-point bending test at the ages of 3 d, 7 d, 14 d, and 28 d. The tests were carried out by using an electro-hydraulic servo universal testing machine of type WAW-1000 , as shown in After facture tests, the double-K fracture mode  was usedTo research the influence of mineral admixture on the internal microstructure of concrete under the harsh environment. Scanning electron microscope (SEM) observation for concrete was conducted. After fracture tests, the concrete specimens were cut into cube samples with side length less than 10 mm. The cubes were dried in an oven for 24 h at a temperature of 60 °C and then placed into anhydrous ethanol to prevent further hydration . Before Cutting the concrete specimens to make an observation surface, which must be perpendicular to the casting surface. The observation surface was smoothened and washed several times until it was flat with only pores and void left. Drying the specimens at a temperature of 105 ± 5 °C before detection.Observing the smooth surface by using the hardened concrete pore structure analyzer. The observation area was divided into multiple sub-areas with the same size and each sub-area was taken photos. These photos were binarized for determining the number of air-voids and the chord length by the linear traverse method.According to the collected information, the hardened concrete pore structure analyzer calculated the air-void system parameters of concrete, including the air content, average air-void size, and spacing factor. The air content can be considered as the porosity of concrete. The spacing factor represents the average distance between any point in the concrete matrix and the air-void, and a lower value of spacing factor means more air-voids in the observation area.The internal pore structure of concrete can explain its mechanical properties, so the linear traverse method  was usedFor each group of concrete, three observation surfaces were prepared, and the air-void system parameters were the average values of the three specimens.To study the hydration degree of cement in concrete, crumb inside concrete was dried and grounded into power for X-ray diffraction test to detect the phase composition by using an X-ray diffractometer. During the test, the scanning speed was 0.15 s/step, the step length was 0.013 mm, and the scanning angle range is 5–70°.2 and Al2O3 in fly ash and slag can react with Ca(OH)2 in the presence of water and produced calcium silicate hydrate and calcium sulphoaluminate hydrate, resulting in the consumption of Ca(OH)2 and the promotion of the hydration reaction [The early-age compression strengths of the four types of concrete were displayed in reaction . After 1reaction . Moreovereaction , the earTo research the growth rule of the strength of concrete in the environment of low humidity and large temperature variation, the ratios of concrete compression strength to its 28-day strength of OC and F10S20 concrete were plotted in The load-CMOD (P-CMOD) curves of the four types of concrete at early ages were plotted in From In fracture tests, the initial fracture toughness and unstable fracture toughness represent the ability of concrete to resist cracking and resist crack propagation, respectively. The fracture toughness of concretes versus curing age was shown in Fracture energy represents the consumed energy by unit crack area in the process of expansion. The variation of fracture energy of the four types of concretes with curing age was shown in The interface transition zone is the weakest and most sensitive area inside the concrete, and the breakdown of concrete often starts here . In the From the experimental results of mechanical characteristics, F10S20 concrete revealed the best performance among the three types of concrete with mineral admixtures. One of the reasons for this was that F10S20 concrete had higher content of slag and lower content of fly ash. Slag with high contents of calcium oxide can participate in the hydration process of cement at the early age and improve the hydration products in concrete . The actFrom the SEM images of OC and F10S20 concrete, the influence of mineral admixture on the internal microstructure of concrete can be clearly observed, as shown in To investigate the influence of low humidity and large temperature variation on the concretes, three air-void parameters of OC and F10S20 concrete versus curing age were detected, including porosity, average air-void size, and spacing factor, as shown in The air-void size distribution of OC and F10S20 concrete at different ages was drawn in 4), calcium hydroxide (Ca(OH)2), silica (SiO2), calcium carbonate (CaCO3), and calcium silicate (CnS) in concrete, and SiO2 had the highest diffraction peak. This was because the test sample contained a certain amount of sand, which was mainly composed of silica. Ca(OH)2, as the hydration product, can reflect the hydration degree in concrete. From 2 in the four types of concrete was as follows: OC > F10S20 > F15S20 > F15S15. OC concrete had the highest cement content in the four kinds of concrete, resulting in the highest amount of Ca(OH)2 at the curing age of 28 d. Slag contained more CaO, which can generate Ca(OH)2 with water. Therefore, F10S20 and F15S20 concrete, which had higher slag content, had higher Ca(OH)2 content than F15S15. Moreover, the diffraction peaks of CaSO4 (2θ = 11.67°) in the concrete with mineral admixtures was higher than that in OC concrete, indicating that more CaSO4 was produced in concrete because of the addition of fly ash and slag. The produced CaSO4 and AFt can both fill in the pores and improve the compaction of concrete.X-ray diffraction can be used to analyze the phase composition in concrete, through which the hydration characteristics of concrete can be studied. This paper investigated the early-age mechanical characteristics and microstructures of concrete with mineral admixtures under the environment of low humidity and large temperature variation. Four types of concrete, including ordinary concrete and three kinds of mineral admixtures concrete, were prepared and cured in an environmental chamber, which was used to simulate the real curing condition during construction in Northwest China. The compression strength, fracture properties, SEM images, air-void characteristics, and X-ray diffraction features of concrete were researched. The following conclusions can be drawn.Under the simulative curing environment during construction, the compression strength of ordinary concrete was higher before the first 3 d but was surpassed by the concrete with mineral admixtures after exposure to the curing environment of low humidity and large temperature variation. The fracture properties of concrete increased in the first 14 d and decreased in the last 14 d during the curing period, and the fracture toughness of the mineral admixture concrete was higher than the ordinary concrete. Among the three kinds of concrete containing mineral admixtures, F10S20 concrete showed the best performance, whose compression strength, initial fracture toughness, unstable fracture toughness, and fracture energy were 23.9%, 25.2%, 45.3%, and 22.6% higher than OC concrete, respectively, at the curing age of 28 d.The addition of fly ash and slag can weaken the negative effects of the harsh environment of low humidity and large temperature variation on concrete microstructure and cement hydration. Firstly, the mineral admixture can reduce the pores in the concrete caused by drying shrinkage and temperature variation and can reduce the size of the pores. Secondly, fly ash and slag can improve the hydration degree in concrete, even under the condition of lacking water.Even though the experimental design in this research was specific, including adopting the environmental parameters of Northwest China and few kinds of concrete with mineral admixtures being prepared, the research results can still provide valuable theoretical guidance for the application of mineral admixtures concrete in the environment of low humidity and large temperature variation.


Photoelectrochemical (PEC) hydrogen production from water splitting is a green technology that can solve the environmental and energy problems through converting solar energy into renewable hydrogen fuel. The construction of host/guest architecture in semiconductor photoanodes has proven to be an effective strategy to improve solar‐to‐fuel conversion efficiency dramatically. In host/guest photoanodes, the absorber layer is deposited onto a high‐surface‐area electron collector, resulting in a significant enhancements in light‐harvesting as well as charge collection and separation efficiency. The present review aims to summarize and highlight recent state‐of‐the‐art progresses in the architecture designing of host/guest photoanodes with integrated enhancement strategies, including i) light trapping effect; ii) optimization of conductive host scaffolds; iii) hierarchical structure engineering. The challenges and prospects for the future development of host/guest nanostructured photoanodes are also presented. Host/guest photoanodes consist of high‐surface‐area host scaffolds for quick electron transport and photoactive guest films for efficient visible‐light harvesting, resulting dramatically improved PEC performance. The present review aims to summarize and highlight recent state‐of‐the‐art progresses in the architecture designing of host/guest photoanodes with the integrated enhancement strategies. The challenges for the future development of host/guest photoanodes are also presented. Converting solar energy into renewable chemical fuels has been considered a promising solution to tackle both energy crises and environmental pollutions. Hydrogen fuel is a clean, renewable and carbon‐free fuel, which will play a vital role in a clean, secure, and affordable energy future. Photoelectrochemical (PEC) water splitting provides a green pathway for hydrogen fuel production through the direct conversion of solar energy. In 1972, Fujishima and Honda first conducted the pioneering work for PEC water splitting via TiO2 films as the photoanode. Following that, numerous research efforts have been made to realize a high solar‐to‐hydrogen (STH) conversion efficiency.The renewable solar energy received by the land per year (3.6 × 10rawatts).3, 4 Much effort has been made to develop advanced techniques for fabricating novel nanostructures as semiconductor photoanodes. Nanostructures can usually enhance solar energy harvesting, reduce diffusion length of the charge carriers, and increase the contact area with the electrolyte, thus improving the STH conversion efficiency of one PEC cell. Various nanostructures such as 1D nanorods (NRs) and nanowires (NWs), 2D nanosheets (NSs), 3D inverse opals (IOs) have been reported for efficient PEC applications. Although these single semiconductors demonstrate high PEC performance, it is difficult to satisfy these critical factors simultaneously on a single semiconductor photoanode. Constructing multicomponent heterostructure photoanodes is one of the most effective strategies to balance the harsh elements and achieve superior properties than individual components.The STH conversion efficiency of semiconductor photoanodes for practical application is primarily determined by several critical factors in the PEC process, including efficient visible light absorption, high separation and collection of charge carriers, and good long‐term chemical stability.18 Muc Metal oxides such as Fe2O3 and BiVO4 are usually used as guest materials to absorb visible solar light due to the narrow bandgap and good chemical stability at the highly oxidizing condition required for water oxidation. The wide bandgap materials such as SnO2, ZnO, and WO3 can act as host scaffolds to allow rapid electron extraction at the contact, owing to their excellent electron transport properties and suitable conduction band alignment to the guest absorber. Thus, the construction of host/guest architecture in photoanodes can simultaneously enhance visible light absorption as well as separation and collection of charge carriers, dramatically improving the solar‐to‐fuel conversion efficiency of PEC photoanodes. Typically, the configuration of PEC devices can be also divided into three types, namely nonintegrated/modular, fully integrated/wireless, and partially integrated/wired PEC devices. In the nonintegrated/modular PEC devices, water splitting and light absorption are achieved by electrodes and photovoltaic cells, respectively. Conversely, for fully integrated/wireless and partially integrated/wired PEC devices, water splitting and light absorption are combined into one electrode. The anode and cathode are in physical contact in fully integrated/wireless PEC devices, while they are connected through external wiring in partially integrated/wired PEC devices. Mostly host/guest photoanodes are designed as nonintegrated/modular PEC devices. After decades of development, numerous host/guest photoanodes have been reported for PEC applications. Therefore, it is essential to give a timely review on the architecture progress of host/guest nanostructured photoanodes.Inspired by the synergistic effects of a tree trunk for mass transport and leaves for light absorption in natural photosynthesis, host/guest multicomponent architectures are proposed for PEC water splitting, in which a highly dispersed light absorber acting as the guest material is deposited onto nanostructured host scaffolds.38 MetFigure The present review aims to summarize and highlight recent state‐of‐the‐art progresses in the architectural design of host/guest photoanodes with integrated enhancement strategies Figure 1, inclu2Figure ηabs) reflects the percentage of incident photons that are absorbed by the photoanode. Second, due to the band bending induced space‐charge field, the photogenerated electrons are transported toward the counter electrode through the external circuit and holes diffuse and migrate to the semiconductor/electrolyte interface simultaneously. Here, the separation efficiency (ηsep) describes the percentage of photogenerated carriers that are successfully transported to the electrode surface. Third, the electrons or holes that transferred to the metal/electrolyte or semiconductor/electrolyte junction take part in HER or OER, respectively. The charge transfer efficiency (ηtrans) indicates the percentage of surface‐reaching photogenerated carriers that finally participate in the desired reactions. Thermodynamically, water splitting is an uphill reaction with a minimum energy requirement of 1.23 eV. Thus, the energy of photons absorbed by a photoanode should be larger than 1.23 eV, corresponding to ≈1100 nm wavelength of light. However, the minimum practical energy required for PEC water splitting is around 1.8–2.0 eV, owing to the energy losses and the overpotential requirement for acceptable surface reaction kinetics.The configuration of one typical n‐type semiconductor‐based PEC cell is shown in Jpec) at 1.23 V versus RHE is frequently selected to compare the PEC performance of different photoanodes.Jpec is determined by the theoretical maximum current density (Jmax), ηabs, ηsep, and ηtrans, as shown in the following equationsThe measured photocurrent density Jpec at 1.e is the charge of a single electron, Eg is the bandgap energy of a semiconductor, and I(λ) represents the photon flux at a different wavelength. LHE is the light‐harvesting efficiency, which can be experimentally measured using a spectrometer equipped with an integrating sphere.Where Jmax describes the maximum photocurrent that can be achieved by a semiconductor under the assumption that all incident photons and photogenerated electrons are utilized for current formation. Bandgap energy determines the achievable Jmax, which is the upper limit of Jpec. The bandgap positions of typical semiconductors and the distribution of solar energy and Jmax over the wavelength are shown in Figure 3 , BiVO4 , and Fe2O3  can achieve larger Jmax than semiconductors with wider bandgaps, such as anatase TiO2 .Jpec is much lower than the theoretical Jmax due to poor ηabs, ηsep, and ηtrans. Surface coating of efficient OER catalysts is a well‐established technique to improve ηtrans. However, the enhancement of ηabs and ηsep still remains a challenge due to their complex interaction. For example, the direct increase of film thickness is beneficial to ηabs, but inevitably enlarges the carrier transfer path, resulting in low ηsep. Therefore, the overall photocurrent of a photoanode is mainly determined by the equilibrium of ηabs and ηsep. Developing rationally designed host/guest architectures with the targeted improvement strategies is a promising pathway to optimize ηabs and ηsep. The ηabs and ηsep can be experimentally measured by using a hole scavenge, such as Na2SO3, with a ηtrans of 100%.In the practical PEC process, the measured  Thus, Faradaic efficiency, incident photon‐to‐current efficiency (IPCE), and STH efficiency are frequently used as evaluation parameters. Faradaic efficiency can reveal the percentage of the charge carriers that are genuinely used for O2 or H2 production. It can be derived by dividing the electric charge calculated from the measured amount of evolved gas by the total electric charge. IPCE calculates the efficiency in the form of “electrons out per photons in” and takes the influences of spectral change of incident photons into consideration. IPCE describes the upper limit of efficiency to produce hydrogen or oxygen from water on the condition that all electrons and holes are used. STH efficiency, which is defined as the ratio of the generated chemical energy divided by the solar energy input, reports the efficiency of a PEC system under zero bias without any addition of sacrificial reagents. PEC system with a STH efficiency greater than 10% can be used for practical application, hence this parameter is commonly used in the ranking of a PEC device.When measuring photocurrent, side reactions or photocorrosion of semiconductors may also contribute to the total value of the photocurrent, resulting in the overestimation of PEC performance.69 Thu3Table 2, WO3, and ZnO are primary host scaffold materials, while narrow bandgap semiconductors, such as Fe2O3 and BiVO4 are typical guest materials. The architectures of nanostructured host/guest photoanodes can be divided into 1D core/shell nanostructures and hierarchical nanostructures, such as 1D/1D nanodendrite arrays, 1D/2D screw‐like nanostructures, and 3D/2D nanospheres/NSs. Although various architectures have been reported as host/guest photoanodes, their fabrication process can be divided into two independent parts: the growth of nanostructured host scaffolds and the following surface coating of guest semiconductor films. Thus, the benefits of one host scaffold can be applied to different guest materials. The host semiconductors usually exhibit little visible light absorption, owing to their wide bandgap. The bandgap energies of SnO2 and ZnO are 3.5 and 3.2 eV, respectively, making little contribution to visible light absorption in the host/guest photoanodes. WO3 has a bandgap of 2.7 eV that can harvest 12% of solar spectrum absorption. Compared to host scaffolds, guest semiconductors with narrow bandgaps have stronger visible light absorption. However, many guest semiconductors suffer from poor electron mobility. For example, Fe2O3 has low electron mobility (≈10−2 cm2 V−1 s−1) and a short hole diffusion length of 2–4 nm. Although BiVO4 has a moderate hole diffusion length of 100–200 nm, it is restricted by poor electron mobility (≈0.02–0.044 cm2 V−1 s−1). Under frontside light illumination, the photoexcited electrons are generated near the photoanode/electrolyte interface and have to cross the entire film thickness for chemical reaction. Thus, the low electron mobility inevitably restricts the transport of photogenerated electrons to the electron collector. On the contrary, host semiconductors exhibit a lower visible light absorption but much higher electrons mobility than guest materials, such as SnO2 (≈240 cm2 V−1 s−1), ZnO (≈200 cm2 V−1 s−1), WO3 (≈12 cm2 V−1 s−1). The improvement of host scaffolds on the charge collection of guest materials will be detailed in Section The host/guest photoanodes reported in recent years are summarized in e arrays,68 1D/ Lee et al. investigated the construction of heterojunction films consisting of guest BiVO4 with a series of host materials, such as Fe2O3, TiO2, SnO2, and WO3. As shown in Figure 2/BiVO4 and WO3/BiVO4 host/guest films can form a type‐II heterojunction due to the matched band alignment. Host/guest photoanodes showed an increased photocurrent at 1.23 V versus RHE compared to pristine BiVO4 films. However, the direct combination of Fe2O3/BiVO4 and TiO2/BiVO4 are not beneficial to the charge transfer in the heterojunction due to the unmatched band alignment, resulting in a decreased photocurrent. The band alignment between host materials and guest materials can be further judged with experimental techniques. The Mott–Schottky plots technique is frequently adopted to acquire the flat band potential, which is close to the CB edge. The VB edge can be calculated by the sum of the CB edge and the bandgap value. Hsu et al. measured the flat‐band potential of ZnO and Fe2O3  is more negative than that of Fe2O3 (−0.79 V vs Ag/AgCl). After contact, electrons in the Fermi level of ZnO migrate to Fe2O3 due to its more considerable work function. As the carrier concentration of Fe2O3 is lower than ZnO, the energy difference between CB and Fermi levels in ZnO is larger than that in Fe2O3. Thus, after the alignment of Fermi levels, the CB edge of ZnO becomes more positive than that of Fe2O3, achieving a ZnO/Fe2O3 heterojunction  of guest materials to the more conductive host materials and finally reach the counter electrode, while holes facilely move in the opposite direction, thus resulting in a spatial separation of electron–hole pairs and a depressed charge recombination.103 Le3 Figure .[82]n Figure . Bai et 4The emergence of host/guest architectures in photoanodes can enhance visible light absorption as well as the separation and collection of charge carriers, thus dramatically improving photocurrent and STH efficiency of photoanodes. Based on the construction feature of host/guest architectures in photoanodes, three targeted enhancement strategies including i) light trapping effect for enhanced light absorption; ii) optimization of conductive host scaffolds for improved charge separation; iii) hierarchical structure engineering for simultaneous enhancement of light absorption and charge separation were studied. This section aims to summarize and highlight recent state‐of‐the‐art progress in the architectural design of host/guest photoanodes with these enhancement strategies.4.1ηabs is determined by the light‐harvesting efficiency. Sufficient light‐harvesting is a prerequisite to enhancing PEC performance of host/guest photoanodes. The absorption of more incident photons generates more electron–hole pairs for the chemical reaction in a PEC cell. Light trapping induced by multiple light scattering or slow‐photon effect can prolong the optical path to increase the ηabs. Concurrently, the short hole diffusion path can be well maintained to avoid the adverse impact on ηsep. Light trapping effects are usually achieved in well‐designed porous or periodic host/guest nanostructured photoanodes.4 flat films and nanosphere arrays with relative film thickness   Figure . The UV–s Figure . 3D host IOs are usually fabricated by the template‐assisted method. In a typical synthesis process, the precursors of the host semiconductor are first infiltrated into self‐assembled 3D periodic opal templates. 3D host IOs can be obtained through the removal of the opals template by a postannealing or chemical corrosion. The photoactive guest semiconductors are then coated onto the 3D host IOs by spin‐coating or electrodeposition technique to create the host/guest photoanodes with periodic porous structures. Kim et al. reported the coating of guest BiVO4 thin layer on host 3D ZnO IOs to form typical periodic porous structures for improved PEC application. As shown in Figure 4 films. 3D ZnO IOs/BiVO4 films exhibited a 50% higher light‐harvesting efficiency than ZnO/BiVO4 bilayer films in the wavelength range of 450−500 nm  orientation of monoclinic WO3 can be observed by the high‐resolution transmission electron microscopy  (HRTEM), as shown in Figure 3 has inherently remarkable electron transport properties that greatly inhibited electron−hole recombination in Fe2O3 NPs. Yu‐Kuei et al. reported 1D ZnO/Fe2O3 core/shell nanostructures as the host/guest photoanode. Fe2O3 films with a thickness of a few nanometers were coated on 1D ZnO NWs that has a thickness of 80 nm  NRs as the host scaffold. Figure 18 cm−3) is threefold that of undoped ZnO NRs (2.42 × 1018 cm−3), suggesting an improvement in the charge collection in ZnO: N NRs. Similarly, 1D Sb: SnO2 nanotubes, and Sn: In2O3 NWs were reported as conductive host scaffolds to improve charge collection of the guest films. Sucheol et al. further investigated the direct contribution of conductive scaffolds on ηsep. The patterned F: SnO2 micropillar nanostructures were developed using printing and spray pyrolysis techniques. By adjusting the periods, two types of F: SnO2 micropillar nanostructures were obtained, denoted as MP1 and MP2. MP1 and MP2 have the same height of 1.9 µm and diameter of 500 nm, but different periods of 2 and 4 µm, respectively  and MP2/BiVO4 (74.2%) host/guest photoanodes at 1.23 V versus RHE are higher than that of flat BiVO4 films (49.2%)  Figure , suggest Zhou et al. prepared thin layers of guest BiVO4 coated onto host Sb: SnO2 nanorod arrays (NRA)  spectra is a contact‐free technique to investigate the carrier dynamics over nanometer length scales and the intrinsic conductivity within individual host scaffolds.127 Zha Figure , the elen Figure . This res Figure . Nyquist plots from the EIS test can be fitted with two resistance and capacitance (RC) circuit models. In the equivalent circuit, the series resistance (Rs), first RC circuit (R1 and CPE1), and charge transfer resistance (R2) can be acquired. R1 and CPE1 are determined by the charge transport process, and R2 is the charge transfer resistance across the semiconductor‐liquid junction interface, which corresponds to the biggest arc at the lower frequency. Xu et al. reported the in situ growth of photoactive guest ZnFe2O4 on host Al: ZnO NWs as the host/guest photoanode. Al: ZnO NWs/ZnFe2O4 films showed a lower R1 (158.5 Ω) than pristine ZnO NWs/ZnFe2O4 (309.4 Ω), indicating a higher conductivity of Al: ZnO scaffolds for the transport of photogenerated electrons  by EIS measurements could be partly attributed to the conductive Sn: In2O3 NWs, compared to pristine In2O3 NWs/BiVO4 (243.3 Ω).The charge transport capability of the host scaffolds in host/guest photoanodes is also frequently investigated with the photoassisted electrical impedance spectroscopy (EIS), which can reveal the charge transfer at the photoanode surface and in the bulk semiconductor.128 Ny4 films, and it showed enhanced light‐harvesting and electron transport from BiVO4 to Al: ZnO IOs. The optimization of dopant concentration in host metal oxides is also a critical factor for efficient PEC performance of host/guest photoanodes. Xu et al. investigated the effect of dopant concentration of Sb element in SnO2 macropores as the host scaffolds  direct growth of 1D guest nanostructures on 1D, 2D, or 3D host scaffolds; ii) coating of guest films on the fabricated hierarchical host scaffolds.Hierarchical nanostructures are constructed by the secondary growth of nanostructures on preacquired nanostructures, which would inherently increase the surface areas for mass transfer.131 Th4 thin films. Hierarchical ZnO nanodendrite host scaffolds were fabricated by the secondary growth of 1D ZnO branches on 1D ZnO NRs  light trapping effect; ii) optimization of conductive host scaffolds; and iii) hierarchical structure engineering are summarized and highlighted. and Ni‐Fe‐OH NSs, is one of the common strategies to accelerate OER kinetics and reduce surface trap states. The detailed contribution of OER catalysts in PEC application can be found in many other reviews, which is not summarized in the scope of this review. Another challenge is in obtaining the uniform coating of photoactive thin films on the host scaffolds, especially for the hierarchical host scaffolds with a high aspect ratio. Traditional coating techniques such as spin‐coating, dip‐coating, and chemical vapor deposition may not fully infiltrate precursors into the bottom areas of the host scaffolds. Pressure tuned atomic layer deposition (ALD) has been reported for the uniform coating of photoactive films on porous structures. However, only certain photoactive semiconductors, such as TiO2 and Fe2O3, can be prepared by the ALD technique. Besides, the precursors for ALD applications are usually expensive. Thus, it is necessary to explore other methods for the uniform coating of photoactive thin films on the host scaffolds at a low cost.However, photoactive guest materials may still suffer from slow OER kinetics, and the mere introduction of host scaffolds cannot overcome this problem. Surface modification of photoanodes with active OER catalysts such as Co‐Pi NPs83 and solar cell, and ion battery. Based on the review of various nanostructured host scaffolds, an ideal host scaffold should fulfill the following requirements: low cost, high chemical stability, superior electrical conductivity, and periodic architectures. With the help of host scaffolds, the optical and electrical properties of various guest materials can be improved simply in constructing host/guest structures. However, to date, none of the reported host scaffolds can be scaled up for practical and commercial applications yet. Compared to ZnO, WO3, and pristine SnO2, F: SnO2 shows greatest potential as the candidate material for ideal host scaffolds. Although patterned F: SnO2 micropillar nanostructures and periodic F: SnO2 IOs have been reported as the host scaffolds, they still suffer from high cost and complicated fabrication processes. Research into alternative patterned F: SnO2 host scaffolds, with potential for mass production to replace flat F: SnO2 glass substrates, could generate substantial technological advances and commercial value in various fields. Moreover, the designing of fully integrated/wireless and partially integrated/wired PEC devices with host/guest structures should be developed for practical application.Host/guest architectures are not only applicable for PEC water splitting, but also for electrocatalyst,138 soThe authors declare no conflict of interest.


Antibiotic overuse in urgent cares is common. Despite institutional guidance that recommends ≤ 5 days of therapy for most infections, a prior review found prescribed durations were often longer. This study evaluates the impact of an intervention on guideline-concordant durations of therapy.This quasi-experimental study involved two urgent care centers (UC1 and UC2) in an integrated health care system. Prescriptions were included from January 2017 to May 2021 for patients ≥ 18 years of age for one of the following infections identified by ICD10 code: acute bacterial sinusitis, acute otitis media, cellulitis or skin abscess, COPD exacerbation, lower urinary tract infection, or pneumonia. The intervention was implemented in both urgent cares in January 2020 and included sharing baseline duration of therapy data with site directors and staff, providing in-person education on recommended durations of therapy, engaging peer champions, and posting educational flyers. An institutional smart phone application (app) with treatment recommendations for common infections was in place for the entirety of the study. The primary outcome was the proportion of antibiotic durations that were guideline-concordant during the app only and intervention periods in aggregate and by interrupted time-series analysis.On average, 1583 and 3850 antibiotic prescriptions were prescribed per year in UC1 and UC2, respectively. There was a significant increase in the proportion of guideline-concordant antibiotic prescriptions at the two sites by an absolute value of 20% (p< 0.0001) (Table). By interrupted time-series, the change in slope after the intervention was not statistically significant for UC1 (p= 0.11), UC2 (p= 0.73), or combined (p= 0.61); however, there was a significant increase in prescriptions for ≤ 5 days immediately after the intervention in UC1 (p= < 0.001) .This intervention to promote institutional guideline-concordant durations of therapy resulted in a significant increase in the proportion of antibiotic prescriptions for ≤ 5 days. Preventing prolonged durations of therapy is a potentially effective strategy to reduce antibiotic overuse in urgent cares.All Authors: No reported disclosures


Flowability measurements and mechanical measurements including compressive strength, flexural strength, splitting strength, elastic modulus, and California bearing ratio were conducted. The results show that the foamed concretes have excellent workability and stability with flowability within 170 and 190 mm. The high alkalinity of LM accelerated the hydration of FA, thereby increasing the early strength. The significant power functions were fitted for the relationships between flexural/splitting and compressive strength with all correlation coefficients (R2) larger with 0.95. The mechanical properties of the foamed concrete increased with the density increasing or LM–FA dosage decreasing. The compressive strength, tensile strength, CBR of all prepared foamed concretes were higher than the minimum requirements of 0.8 and 0.15 MPa and 8%, respectively in the standard.This paper aims to study the feasibility of low cement content foamed concrete using waste lime mud (LM) and fly ash (FA) as mineral additives. The LM/FA ratio was first optimized based on the compressive strength. Isothermal calorimetry test, ESEM, and XRD were used to investigate the role of LM during hydration. Afterward, the optimized LM/FA ratio (1/5) was used to design foamed concrete with various wet densities (600, 700, 800 and 900 kg/m It has been reported that decreasing the additional stress on the subgrade is an efficient solution to control uneven embankment settlement ,2. Foameparation ,5,6,7. Aparation ,9.3 could meet the requirements of both the static and dynamic conditions. The concrete was still integral after 2 million cyclic loading times, and the cumulative settlement at the top surface of the subgrade was 0.68 mm. She et al. [The applications of foamed concrete in road engineering have been extensively studied. Huang et al.  establise et al.  used foaHowever, the most used binding material in foamed concrete is ordinary Portland cement (OPC), which consumes many natural resources and energy, and meanwhile emits roughly 5–7% of the global carbon dioxide, leading to severe environmental and economic problems ,14,15,16The replacement of cement with FA is generally less than 50%. For the foamed concrete containing high volume FA, a series of problems such as low early strength and easy cracking due to low reactivity of FA have been reported ,27,28,29Lime mud (LM), a byproduct of the alkali recycling process in the paper industry  is diffiTherefore, the feasibility of using high volume LM–FA into foamed concrete as a low-cost and sustainable solution for road embankment was studied in this paper. The effect of the FA/LM ratio was first investigated based on the strength of the foamed concrete with 60 wt% LM–FA. Afterward, a total of seventeen sets of foamed concrete mixtures were prepared to study the effect of the mineral additives dosage and density on the workability, compressive strength, flexural strength, splitting strength, elasticity modulus, and California bearing ratio. Besides, the isothermal calorimetry test, ESEM, and XRD were used to investigate the role of LM in hydration. The study provided a guidance for foamed concrete containing high volume of LM–FA in road embankment.3, a specific surface of 358 m2/kg, and a standard consistency of 27.9% was used. The specific gravity of FA was 2.4 g/cm3. LM was taken from a paper mill  with a pH value of 13.7. It was dried and ground to an average particle size of 45 μm. The primary chemical compositions of the cementitious materials used are shown in The raw materials of foamed concrete include P.O 42.5 cement, FA, LM, and foaming agent. Cement with a density of 3100 kg/m3. A protein-based foaming agent with a dilution ratio of 40–50 and a foaming ratio of about 1000–1200 was used. The standard foam density was 40–60 kg/m3. Polycarboxylate superplasticizer (PS) was utilized to increase the workability of fresh mixtures with a dosage of 0.35% by the mass of LM.As shown in 3 were designed. Moreover, the LM–FA dosage of 0%, 50%, 60%, 70%, 80% were used for the mixtures with the wet density of 800 and 900 kg/m3. The LM–FA dosages were 0%, 50%, 60% and 70% for the foamed concretes with 700 kg/m3 wet density, and 0%, 50%, and 60% for those with 600 kg/m3.Based on the compressive strength results from Series I, the optimum LM/FA ratio of 1/5 was used to prepare the mixtures in Series II. Foamed concretes with wet densities of 600, 700, 800, and 900 kg/m3 was produced through a foam generator in which compressed air and foaming agent were mixed. The mass ratio of the foaming agent to water was 1/49, and the compressed air pressure was 0.4 MPa. Then, the foam was added to the slurry and mixed for 30 s at the low speed. After that, the fresh properties including wet density and flowability were measured before casting. Finally, the mixtures were poured into the mold and covered with a plastic sheet to prevent water evaporation. After 24 h, the samples were stored in a standard curing room  until testing.A pre-foaming method was used to prepare foamed concrete following the Chinese CJJ/T177−2012 standard . Water wThe flowability of foamed concrete was measured following the Chinese CJJ/T177-2012 standard . This teWet density was calculated according to the fresh foamed concrete weight and the given volume of the standard vessels. The dry density of the specimen (100 mm × 100 mm × 100 mm) was measured after curing under standard conditions for 28 days. Before testing, each specimen was dried in an oven at 60 °C till constant weight.Compressive strength, flexural strength, tensile strength, and modulus of elasticity were measured following the Chinese GB/T 11969-2008 standard . CaliforAn eight-channel isothermal calorimeter model I-Cal 8000HPC was used to measure the heat evolution. Seven types of binder mixtures were prepared for the test. The LM–FA dosages of 0%, 60%, and 70% were used with the LM/FA ratios of 0/1, 1/5, and 1/1. A water-to-binder ratio of 0.55 was used for all mixtures. After mixing, the fresh mixture was cast into a glass thermos and then placed in the calorimeter chamber. The heat evolution rate was recorded continually up to 168 h (7 days) for the analysis.The pore structure and morphology of hydration products of foamed concretes were observed by environmental scanning electron microscopy (ESEM). Specimen of 10 × 10 × 5 mm from the center of foamed concrete was polished and dried. In total, 25.0 kV accelerating voltage was used during the scan, and 30×, 500×, and 2500× ESEM images were taken using an ESEM.X-ray diffractometer (XRD) was used to measure mineral composition phases of the foamed concrete with the LM–FA dosages of 0% and 70% at 28 days. Cu-Ka radiation at 40 kV and 30 mA with a scanning speed of 0.02°/s over a range of 10–90° were used during the measurement.In addition, the mixtures in Series Ⅰ had relatively consistent densities, indicating that the ratio of LM/FA had a negligible effect on the stability of the foamed concrete. In Series II, as expected, the dry density was positively correlated with the wet density. However, for the mixtures with the same wet density, the higher LM–FA dosage came the lower dry density due to less requirement of water for FA hydration. Specifically, the bound water in hydration products decreased, and more free water remained in the pores of the specimen. Therefore, the free water evaporated during the drying process, leading to a lower dry density.The compressive strength results of foamed concrete in Series I at different curing ages are shown in 3 wet density, as the LM–FA dosage increased from 0% to 70%, the 28-day compressive strength decreased by 1.1 MPa. However, the 28-day compressive strength of all mixtures was higher than 0.8 MPa which met the technical specification (JTG D30−2015) [The compressive strength results of the foamed concretes in Series Ⅱ are shown in 30−2015)  for highR2) higher than 0.95. Similar trends have been reported in previous research [In addition, density had a significant effect on compressive strength, i.e., a higher density considerably increased compressive strength. It can be attributed to the following two reasons: (1) The foamed concrete with a high wet density had a minor porosity and a thicker pore wall; (2) The internal pore structure was more integrated, resulting in the densification of the cell wall paste structure. research ,45.3 decreased by 0.21 MPa and 0.18 MPa, respectively. As shown in Although the tensile strength  of foamed concrete is much lower than that of ordinary concrete, this does not apply to the ratio of tensile/compressive strength . The rat2) of the fits were all above 0.97. As shown in 3 and 60% LM–FA (WD600MA60) has the lowest elastic modulus of about 1.1 GPa. The measured results show that all the mixtures in Series II met the requirement of technical specification (JTG D30−2015) [2) was above 0.99. Moreover, the elastic modulus of the foamed concrete with a higher density was more sensitive to LM–FA dosage.Additionally, the elastic modulus decreased gradually with the LM–FA dosage increasing. Foamed concrete with a wet density of 600 kg/m30−2015)  for elas2 greater than 0.95 [han 0.95 .3 wet density, compared to the specimen without LM–FA, the CBR decreased by 38.5%, 54.3%, and 68.0% for the 50%, 60%, and 70% LM–FA dosage, respectively. Foamed concrete with a wet density of 600 kg/m3 and 60% LM–FA (WD600MA60) had the smallest CBR of 13.5%. It met the requirement of the Chinese JTG D30-2015 [California load ratio is a measurement of the resistance of road materials to local load. It is commonly used to evaluate the bearing capacity of subgrade materials. D30-2015  standard2 and accelerating the hydration process [ process . On the other hand, for a given dosage of LM–FA, the cumulative heat of binder in the early hydration stage increased with LM/FA ratio increasing. However, as the hydration time increased, the binder with 1/5 LM/FA ratio possessed a lower accumulated heat of hydration. It explains that the long-term strength decreased of foamed concrete with a higher LM/FA ratio.2) after 28-day curing. Besides, calcium silicate hydrates (C-S-H), calcite (CaCO3), unreacted dicalcium silicate (C2S), and tricalcium silicate (C3S) were also found in the samples. Replaced cement with 70% LM–FA, the diffraction intensity of calcite significantly increased, and that of portlandite was reduced. Mullite, one of the mineral phases of FA, was also found. The hydration of FA consumed a large amount of Ca(OH)2 from cement hydration products and LM, thus resulting in an enhancement on the pozzolanic reaction of FA.The XRD patterns of foamed concrete with different LM–FA dosages are shown in (1)The high alkalinity of LM stimulated the activity of FA, thereby enhancing the mechanical properties of the foamed concretes with high LM–FA dosages at an early age. The contribution of LM to the long-term strength is mainly due to its filling effect. The optimal LM/FA ratio was 1/5.(2)2) of all equations were above 0.95.An exponential equation could describe the relationship between compressive strength and wet density. Both the splitting strength and flexural strength have a significant power function relationship with the compressive strength. The determination coefficients (R(3)Both the elasticity modulus and CBR grow exponentially with the wet density increasing. A higher LM–FA dosage led to a larger increased rate of elasticity modulus and CBR.(4)The mechanical properties of foamed concrete increased with the wet density increasing or LM–FA dosage decreasing. The compressive strength, tensile strength, CBR of all mixtures were higher than the minimum requirement of 0.8 MPa, 0.15 MPa, and 8%, respectively.In this paper, the feasibility of utilizing high volume of LM–FA foamed concrete as a lightweight filling material for embankment was investigated. The mixtures with various wet densities and LM–FA dosages were prepared and tested. Based on the experimental analysis, the following conclusions can be drawn:The effects of LM–FA dosage and wet density on the shrinkage, durability, and microstructure of foamed concrete will be studied in the future.


Necrotizing soft tissue infections (NSTIs) are rare life-threatening bacterial infections characterized by an extensive necrosis of skin and subcutaneous tissues. Initial urgent management of NSTIs relies on broad-spectrum antibiotic therapy, rapid surgical debridement of all infected tissues and, when present, treatment of associated organ failures in the intensive care unit. Antibiotic therapy for NSTI patients faces several challenges and should (1) carry broad-spectrum activity against gram-positive and gram-negative pathogens because of frequent polymicrobial infections, considering extended coverage for multidrug resistance in selected cases. In practice, a broad-spectrum beta-lactam antibiotic  is the mainstay of empirical therapy; (2) decrease toxin production, typically using a clindamycin combination, mainly in proven or suspected group A streptococcus infections; and (3) achieve the best possible tissue diffusion with regards to impaired regional perfusion, tissue necrosis, and pharmacokinetic and pharmacodynamic alterations. The best duration of antibiotic treatment has not been well established and is generally comprised between 7 and 15 days. This article reviews the currently available knowledge regarding antibiotic use in NSTIs. Necrotizing soft tissue infections (NSTIs) are rare life-threatening bacterial infections characterized by an extensive necrosis of skin and subcutaneous tissues. NSTIs can affect any part of the body but the extremities—particularly the lower limbs—are most frequently involved ,2,3,4. MAs a consequence of their rarity, data on optimal antibiotic treatment in NSTI are scarce  and currThe aim of this article is to review the currently available knowledge regarding antibiotic use in NSTIs and provide clinicians with a practical tool to use at bedside.Enterobacteriaceae, nonfermenting bacilli and anaerobic bacteria. Anaerobic, aerobic, and facultative anaerobic bacteria act synergistically and fuel a cycle of bacterial colonization and inflammatory tissue necrosis [Staphylococcus aureus [S. aureus was reported to be more prevalent than GAS in monomicrobial NSTIs [S. aureus carrying the Panton-Valentine leucocidin was reported in the United States [Causative organisms vary widely according to infection site, underlying conditions, but also from one region of the world to the other ,16,17,18necrosis . Howevers aureus ,7,19,20.s aureus . A recend States ,23. Clasd States ,24. The Staphylococcus aureus (MRSA), can have an immediate impact on antimicrobial treatment. As recommended by the European Society of Clinical Microbiology and Infectious Diseases (ESCMID) [Because of their uncertain contribution to the microbiological diagnosis, superficial samples should be avoided . Contrar(ESCMID) , samples(ESCMID) ,30.The emergence of next-generation sequencing (NGS) methods is transforming medical diagnosis, including in infectious diseases. These methods include targeted metagenomics in which a PCR step (aiming to restrict the panel of microorganisms searched similarly to the 16S metagenomics for bacteria) precedes the sequencing, and shotgun metagenomics, a method consisting in sequencing the whole extracted nucleic acids (DNA and/or RNA). In the latter case, after subtraction of human sequences, analysis of the remaining reads leads to the identification of all the microorganisms present, including bacteria, viruses, yeasts, or parasites. Like in many other situations ,32,33, sAs discussed above, prospective or controlled data regarding antibiotic treatment specifically for NSTIs is scarce, with recommended antibiotic regimens mainly based on expert consensus. Some knowledge can however be derived from infections sharing similar characteristics, including non-necrotic skin and soft tissue infections, acute pancreatitis necrosis infection, or conditions with impaired regional perfusion such as diabetic foot or limb ischemia infection.We will present available data on the choice of molecules and modalities of treatment, before proposing a pragmatic antibiotic treatment scheme for suspected NSTI.versus amoxicillin-clavulanate in 804 patients with complicated skin infections, which included 54 NSTIs [As reported in a meta-analysis of randomized trials on antibiotics in complicated skin and soft-tissue infections , there i54 NSTIs . There w54 NSTIs . TigecycThe only molecule evaluated in higher numbers of NSTI patients is clindamycin, although the available literature, which is discussed below, mostly included invasive GAS infections overall.Pathogenicity of GAS NSTI seems to largely rely on the bacterial toxins that induce a strong immune response, including polyclonal T-cell activation and cytokine release. Although GAS infections remain highly susceptible to beta-lactams, particularly penicillin, association with clindamycin is strongly recommended in the case of NSTI . ClindamStreptococcus pyogenes isolates (n = 1893), clindamycin resistance was found in only 4.3% of cases [Interestingly, the anti-toxinic benefits of clindamycin were reported regardless of strain susceptibility . Moreoveof cases , but up of cases , and cliObservational studies have suggested a benefit of clindamycin as an adjunctive treatment in patients with invasive GAS (iGAS) infections, including NSTIs, supporting current recommendations by professional societies . CarapetAlthough less documented, linezolid, a member of the oxazolidinone class which also binds the 50S ribosomal subunit, might have comparable in vitro consequences on the toxin release by GAS .S. aureus and GAS [Recent studies, extensively by the INFECT study group , have hi and GAS . The cliNo study has evaluated the impact of treatment duration on NSTI outcome, resulting in heterogenous practices . GuideliThe mainstem of urgent empirical antibiotic treatment for NSTI is a broad spectrum ß-lactam. These antibiotics display time-dependent activity, where bacterial killing and treatment efficacy correlate with the duration of time that free (unbound) plasma drug concentrations remain above the minimum inhibitory concentration (MIC) of the offending pathogen (fT > MIC) . One majIn addition, hypoalbuminaemia is a common but frequently neglected condition in septic patients. With decreasing albumin concentrations, an increase in the unbound fraction of drugs can occur. The unbound fraction of antibiotics is not only available for elimination, but also for distribution. The Vd for moderate to highly protein-bound antibiotics can thus increase by up to 100% in critically ill patients with hypoalbuminaemia ,57. OverLastly, severe infections can cause vascular dysfunction, including microvascular failure, which can impair drug delivery into body tissues, particularly in patients with sepsis being treated with vasopressors. In this context, plasma concentrations may profoundly underestimate tissue concentrations .p = 0.045) and clinical cure significantly higher  in the continuous infusion group than in the intermittent infusion group in severe patients [There is evidence defining the impact of early and appropriate antibiotic administration on decreased mortality ,62. In spatients . In a mepatients , a findipatients . Howeverpatients . Despitepatients . Thus, gpatients .Other features of NSTIs raise the interest of optimizing antibiotic tissue delivery, as despite urgent and extensive removal of necrotic tissues as a mainstem of management ,11,12, a90) of S. aureus and S. pyogenes in blisters for meropenem, imipenem and piperacillin-tazobactam [S. aureus SSTIs [Soft tissue distribution is reportedly high for lipophilic molecules, such as oxazolidinones, quinolones, macrolides, metronidazole, daptomycin and tigecycline ,83,84,85zobactam ,90, and zobactam . One reczobactam . Takesueus SSTIs . Overallus SSTIs  Table 290 of S. These are derived from infection of necrosis in acute pancreatitis ,108. AltBacteroidetes genre, in this study. Others found no impact of ischemia on diffusion of metronidazole [Data is scarce regarding this issue, mainly derived from acute limb ischemia and diabetic foot infection. Interestingly, skin exudate antibiotic concentrations after intravenous administration were proposed as a means to evaluate local circulatory conditions, highlighting the link between tissue perfusion and drug delivery . Experimnidazole . In diabnidazole ,96,97,98nidazole . While cnidazole , and empnidazole . Maximalnidazole ,115. Intnidazole .Overall, data on antibiotic skin and soft tissue penetration in the setting of necrosis and altered perfusion abounds for improving PK/PD for hydrophilic molecules such as beta-lactams. Administration modalities should definitely be optimized with high-loading doses initially, continuous perfusion and therapeutic drug monitoring when available, as this has shown improved tissular penetration in other settings ,117,118,There are only anecdotical reports on the use of topical antibiotics in NSTIs , as was The treatment of NSTIs relies on antibiotics and early surgical debridement, which is one of the most important modifiable prognostic factors . With moTogether with urgent surgical removal of necrotic tissues, antibiotics are the cornerstone of NSTI management, its mainstem being urgent bactericidal intravenous administration of a broad-spectrum beta-lactam such as piperacillin-tazobactam. Though no literature specifically focusing on NSTI exists, clinicians face the association of the profound PK/PD alterations associated with sepsis  hindering drug diffusion. Administration modalities should definitely be optimized with high initial loading doses, continuous antibiotic perfusions and therapeutic drug monitoring when available. Future research focusing on antibiotic strategies in NSTI patients should assess the use of drugs with higher reported tissue diffusion, broader use of anti-toxinic, biofilm, or intracellular penetrating molecules as well as the effect of different/personalized treatment durations.